WorldWideScience

Sample records for carbon cluster formation

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

    KAUST Repository

    Kalinina, Irina V.

    2014-01-01

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

  2. Support- dependent evolution of oxidation state and nanoassembly formation of subnanometer copper clusters under carbon dioxide conversion conditions

    Science.gov (United States)

    Halder, Avik; Yang, Bing; Kolipaka, Karthika L.; Pellin, Michael; Seifert, Soenke; Vajda, Stefan; Materials Science Division Team

    Size- and support- dependence of the properties of copper clusters have been investigated during carbon dioxide conversion with hydrogen at high reactant concentrations and atmospheric pressure. The model catalyst systems were prepared by depositing size-selected Cun clusters (n = 3, 4, 12 and 20) on various amorphous metal oxide (Al2O3, ZnO, and ZrO2) , and carbon-based (UNCD = ultrananocrystaline diamond) supports. During the temperature ramp, the evolution of the chemical state and size of the particles were characterized by in situ grazing incidence X-ray absorption near edge structure (GIXANES), and grazing incidence small angle X-ray scattering (GISAXS) respectively. Under reaction conditions the initially oxidized Cu clusters reduced at various temperatures depending on cluster size and support. Clusters supported on ZnO and UNCD were found to be sinter-resistant under reactive gases at elevated temperatures and atmospheric pressures, whereas on ZrO2 support the clusters formed stable aggregates. Clusters on Al2O3 support demonstrated unique properties, where a formation of a nanostructure was observed during heating, which then disintegrated during the cool down. Under applied conditions, Cu4 clusters on Al2O3 were found to be the most efficient in methanol formation.

  3. Isolated crater formation by gas cluster ion impact and their use as templates for carbon nanotube growth

    Energy Technology Data Exchange (ETDEWEB)

    Toyoda, Noriaki, E-mail: ntoyoda@incub.u-hyogo.ac.jp; Kimura, Asahi; Yamada, Isao

    2016-03-15

    Crater-like defects formations with gas cluster ion beams (GCIB) were used as templates for carbon nanotube (CNT) growth. Upon a gas cluster ion impact, dense energy is deposited on a target surface while energy/atom of gas cluster ion is low, which creates crater-like defects. Si and SiO{sub 2} were irradiated with Ar-GCIB, subsequently CNTs were grown with an alcohol catalytic CVD using Co and ethanol as catalyst and precursor, respectively. From SEM, AFM and Raman spectroscopy, it was shown that growth of CNT with small diameter was observed on SiO{sub 2} with Ar-GCIB irradiation. On Si targets, formation of craters with bottom oxide prevented Co diffusion during CNT growth, as a result, CNT growth was observed only on Si irradiated with high-energy Ar-GCIB. These results showed that isolated defects created by GCIB can be used as templates for nanotube growth.

  4. Formation and properties of astrophysical carbonaceous dust. I: ab-initio calculations of the configuration and binding energies of small carbon clusters

    CERN Document Server

    Mauney, Christopher; Lazzati, Davide

    2014-01-01

    The binding energies of n < 100 carbon clusters are calculated using the ab-initio density functional theory code Quantum Espresso. Carbon cluster geometries are determined using several levels of classical techniques and further refined using density functional theory. The resulting energies are used to compute the work of cluster formation and the nucleation rate in a saturated, hydrogen-poor carbon gas. Compared to classical calculations that adopt the capillary approximation, we find that nucleation of carbon clusters is enhanced at low temperatures and depressed at high temperatures. This difference is ascribed to the different behavior of the critical cluster size. We find that the critical cluster size is at n = 27 or n = 8 for a broad range of temperatures and saturations, instead of being a smooth function of such parameters. The results of our calculations can be used to follow carbonaceous cluster/grain formation, stability, and growth in hydrogen poor environments, such as the inner layers of c...

  5. Dust formation in carbon-rich Wolf-Rayet stars I. Chemistry of small carbon clusters and silicon species

    NARCIS (Netherlands)

    Cherchneff, [No Value; Le Teuff, YH; Williams, PM; Tielens, AGGM

    2000-01-01

    The formation of small carbon chains and molecular precursors to silicon carbide grains is investigated in the hot, hostile environment of carbon-rich Wolf-Rayet (WC) winds. We consider only WC stars which produce dust on a continuous basis and develop for the first time non-equilibrium, chemical ki

  6. Study on Cluster Formation of Poly 2-HYDROXYETHYL Methacrylate Functionalized Single-Walled Carbon Nanotubes

    Science.gov (United States)

    Ashok Kumar, Nanjundan; Kim, Sung Hun; Kim, Jong Tae; Lim, Kwon Taek; Jeong, Yeon Tae

    Cluster-like network structures of single-walled carbon nanotubes (SWNTs) were synthesized by chemical grafting poly 2-hydroxyethyl methacrylate (polyHEMA) to the sidewalls of SWNTs. Acid chloride-functionalized tubes were coupled with commercially available HEMA monomer, which was in turn polymerized using a radical initiator. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to identify the surface changes on the nanocomposites. Microscopic observations of the nanotube complexes by field emission scanning electron microscopy (FE-SEM) show that the tubes were dispersed and formed cluster-like network, branched structures with less bundling, thus, strongly suggesting a firm coating of the polymer on nanotube walls. The coating was further confirmed by transmission electron microscopy. The thermal properties of the nanotube complex as studied by thermal gravimetric analysis (TGA) revealed that coating enhanced stability of the complex, when compared to that of bulk polyHEMA and pristine SWNTs. The nanotube complexes showed excellent suspension stability when dispersed in organic solvent.

  7. When efficient star formation drives cluster formation

    CERN Document Server

    Parmentier, G

    2008-01-01

    We investigate the impact of the star formation efficiency in cluster forming cores on the evolution of the mass in star clusters over the age range 1-100Myr, when star clusters undergo their infant weight-loss/mortality phase. Assuming a constant formation rate of gas-embedded clusters and a weak tidal field, we show that the ratio between the total mass in stars bound to the clusters over that age range and the total mass in stars initially formed in gas-embedded clusters is a strongly increasing function of the averaged local SFE, with little influence from any assumed core mass-radius relation. Our results suggest that, for young starbursts with estimated tidal field strength and known recent star formation history, observed cluster-to-star mass ratios, once corrected for the undetected clusters, constitute promising probes of the local SFE, without the need of resorting to gas mass estimates. Similarly, the mass ratio of stars which remain in bound clusters at the end of the infant mortality/weight-loss ...

  8. Star Cluster Formation and Feedback

    CERN Document Server

    Krumholz, Mark R; Arce, Hector G; Dale, James E; Gutermuth, Robert; Klein, Richard I; Li, Zhi-Yun; Nakamura, Fumitaka; Zhang, Qizhou

    2014-01-01

    Stars do not generally form in isolation. Instead, they form in clusters, and in these clustered environments newborn stars can have profound effects on one another and on their parent gas clouds. Feedback from clustered stars is almost certainly responsible for a number of otherwise puzzling facts about star formation: that it is an inefficient process that proceeds slowly when averaged over galactic scales; that most stars disperse from their birth sites and dissolve into the galactic field over timescales $\\ll 1$ Gyr; and that newborn stars follow an initial mass function (IMF) with a distinct peak in the range $0.1 - 1$ $M_\\odot$, rather than an IMF dominated by brown dwarfs. In this review we summarize current observational constraints and theoretical models for the complex interplay between clustered star formation and feedback.

  9. Galaxy formation through hierarchical clustering

    Science.gov (United States)

    White, Simon D. M.; Frenk, Carlos S.

    1991-01-01

    Analytic methods for studying the formation of galaxies by gas condensation within massive dark halos are presented. The present scheme applies to cosmogonies where structure grows through hierarchical clustering of a mixture of gas and dissipationless dark matter. The simplest models consistent with the current understanding of N-body work on dissipationless clustering, and that of numerical and analytic work on gas evolution and cooling are adopted. Standard models for the evolution of the stellar population are also employed, and new models for the way star formation heats and enriches the surrounding gas are constructed. Detailed results are presented for a cold dark matter universe with Omega = 1 and H(0) = 50 km/s/Mpc, but the present methods are applicable to other models. The present luminosity functions contain significantly more faint galaxies than are observed.

  10. Formation of innovative clusters in tourism

    Directory of Open Access Journals (Sweden)

    Stanislav V. Koshcheev

    2011-06-01

    Full Text Available Modern preconditions of development innovative clusters in Russian economy are analyzed. The importance of application of cluster approach to management of innovations in tourism is shown. Necessity formation of innovative clusters in region of tourist specialization for increase of competitiveness of territory is reflected. The model of formation of innovative clusters in tourism is offered.

  11. Doping and cluster formation in diamond

    KAUST Repository

    Schwingenschlögl, Udo

    2011-09-09

    Introducing a cluster formation model, we provide a rational fundamental viewpoint for the difficulty to achieve n-type dopeddiamond. We argue that codoping is the way forward to form appropriately doped shallow regions in diamond and other forms of carbon such as graphene. The electronegativities of the codopants are an important design criterion for the donor atom to efficiently donate its electron. We propose that the nearest neighbour codopants should be of a considerably higher electronegativity compared to the donor atom. Codoping strategies should focus on phosphorous for which there are a number of appropriate codopants.

  12. Modeling Formation of Globular Clusters: Beacons of Galactic Star Formation

    CERN Document Server

    Gnedin, Oleg Y

    2010-01-01

    Modern hydrodynamic simulations of galaxy formation are able to predict accurately the rates and locations of the assembly of giant molecular clouds in early galaxies. These clouds could host star clusters with the masses and sizes of real globular clusters. I describe current state-of-the-art simulations aimed at understanding the origin of the cluster mass function and metallicity distribution. Metallicity bimodality of globular cluster systems appears to be a natural outcome of hierarchical formation and gradually declining fraction of cold gas in galaxies. Globular cluster formation was most prominent at redshifts z>3, when massive star clusters may have contributed as much as 20% of all galactic star formation.

  13. Star formation in dense clusters

    CERN Document Server

    Myers, Philip C

    2011-01-01

    A model of core-clump accretion with equally likely stopping describes star formation in the dense parts of clusters, where models of isolated collapsing cores may not apply. Each core accretes at a constant rate onto its protostar, while the surrounding clump gas accretes as a power of protostar mass. Short accretion flows resemble Shu accretion, and make low-mass stars. Long flows resemble reduced Bondi accretion and make massive stars. Accretion stops due to environmental processes of dynamical ejection, gravitational competition, and gas dispersal by stellar feedback, independent of initial core structure. The model matches the field star IMF from 0.01 to more than 10 solar masses. The core accretion rate and the mean accretion duration set the peak of the IMF, independent of the local Jeans mass. Massive protostars require the longest accretion durations, up to 0.5 Myr. The maximum protostar luminosity in a cluster indicates the mass and age of its oldest protostar. The distribution of protostar luminosi...

  14. Hierarchical Formation of Galactic Clusters

    CERN Document Server

    Elmegreen, B G

    2006-01-01

    Young stellar groupings and clusters have hierarchical patterns ranging from flocculent spiral arms and star complexes on the largest scale to OB associations, OB subgroups, small loose groups, clusters and cluster subclumps on the smallest scales. There is no obvious transition in morphology at the cluster boundary, suggesting that clusters are only the inner parts of the hierarchy where stars have had enough time to mix. The power-law cluster mass function follows from this hierarchical structure: n(M_cl) M_cl^-b for b~2. This value of b is independently required by the observation that the summed IMFs from many clusters in a galaxy equals approximately the IMF of each cluster.

  15. Quenching star formation in cluster galaxies

    CERN Document Server

    Taranu, Dan S; Balogh, Michael L; Smith, Russell J; Power, Chris; Krane, Brad

    2012-01-01

    In order to understand the processes that quench star formation within rich clusters, we construct a library of subhalo orbits drawn from lambdaCDM cosmological N-body simulations of four rich clusters. The orbits are combined with models of star formation followed by quenching in the cluster environment to predict colours and spectroscopic line indices of satellite galaxies. Simple models with only halo mass-dependent quenching and without environmental (i.e. cluster-dependent) quenching fail to reproduce the observed cluster-centric colour and absorption linestrength gradients. Models in which star formation is instantly quenched at the virial radius also fail to match the observations. Better matches to the data are achieved by more complicated bulge-disc models in which the bulge stellar populations depend only on the galaxy subhalo mass while the disc quenching depends on the cluster environment. In the most successful models quenching begins at pericentre, operating on an exponential timescale of 2 -- 3...

  16. Formation of cluster policy in Russian regions

    Directory of Open Access Journals (Sweden)

    Svetlana Nikolaevna Kotlyarova

    2012-06-01

    Full Text Available This paper deals with the problems of legal regulation of cluster development in the Russian Federation at the regional level. Basic regulations governing the formation and development of clusters were put in a system. It is concluded that own regulatory regions, and regions using mainly general federal approach to the formation of cluster policy are poorly developed. The practice of clustering of the Russian Federation was generalized. Prerequisites for the formation of clusters in the regions and their subsequent development were identified. A comparison of approaches to the formation of cluster policy in the Russian Federation was made, particularities in the areas of the clusters were highlighted and the types of state support for their formation were determined. The basic reasons for the development of regional clusters are: construction of the type of dominant firms, mutual cooperation of cluster members, active support from government and regional authorities (public-private partnerships and personal involvement of management in the region and bottom-up approach.

  17. Formation and dissolution of leaky clusters

    CERN Document Server

    Pfalzner, S

    2011-01-01

    Massive Galactic clusters (> 1000 Msun) exhibit a clear correlation between cluster density, size and age and can be sorted in two categories, i.e. starburst and leaky clusters. The reason for the existance of two types of massive clusters is an open question. However, the answer is probably connected to a different formation histories of the two types. In this study we concentrate onleaky clusters only and investigate possible formation scenarios and gas expulsion phase. This is done by using existing observational data and numerical results of embedded cluster properties. Assuming that a clear correlation between cluster density, size and age exists, it is shown that the density-radius development over time forembedded clusters can be approximated by rho \\approx 100*r ^{-1.3} Msun pc^{-3}. The consequences for the star formation process in leaky clusters are discussed and found to favour an inside-out star formation scenario with an initially low but later accelerated star formation rate. It is shown how th...

  18. Formation and Assembly of Massive Star Clusters

    Science.gov (United States)

    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

  19. FEATURES OF FORMATION OF REGIONAL CLUSTER STRUCTURES

    Directory of Open Access Journals (Sweden)

    Ekaterina V. Andreyeva

    2016-01-01

    Full Text Available In article is considered features of formation of cluster structures for increase of efficiency of economic entities and growth of investment and innovative appeal of the region. Cluster structures are described as a specialized product oriented commands, which were created for common decision making about production, nancial and organizational questions.

  20. Concept of the Ural pharmaceutical cluster formation

    Directory of Open Access Journals (Sweden)

    Aleksandr Petrovich Petrov

    2011-06-01

    Full Text Available This paper substantiates the necessity of cluster organization of the pharmaceutical industry in the region. The estimation of the state and prospects of development of such structures in the domestic economy is given. Sverdlovsk region was chosen as the object of study on the possibility of forming a pharmaceutical cluster. Objective prerequisites for the organization of a cluster of pharmaceutical production in Sverdlovsk region are considered, among these were distinguished: capacious and fast-growing market for pharmaceutical products, availability of potential development of the pharmaceutical industry in the territory and the key success factors for enterprises - potential participants of the cluster. Indicated key success factors are: presence of a creative team and close interaction between business and government, high level of cooperation among the enterprises of the cluster and commercialization of products, implementation of research and development expenditures etc. Thus, it was substantiated that in there all references and resources for the formation of a pharmaceutical cluster. The concept of formation and development of the Ural pharmaceutical cluster was elaborated. Inside the concept, the goals, objectives, processing, product and organizational priorities for cluster formation are identified. Architecture of this structure with a justification of its members and certain forms of interaction between them is proposed. The stages of formation and development of the Ural pharmaceutical cluster on the basis of a ten-year settlement period for the full range of activities for this project are substantiated. At each stage, a set of key objectives and results of the cluster was defined. The choice of phases was carried out on the basis of investment programs of cluster's enterprises strategic position on the mastering of markets and infrastructure development. An assessment of socio-economic efficiency of the Ural pharmaceutical

  1. Photodissociation and stability of carbon clusters; Photodissociation et stabilite d`agregats de carbone

    Energy Technology Data Exchange (ETDEWEB)

    Bouyer, R.

    1995-04-01

    This work is devoted to the study of the dissociation of ionised carbon clusters (containing 16 to 36 atoms) after photoexcitation by a UV-visible laser pulse. It contributes to experimental studies on formation mechanisms of carbon clusters, and particularly fullerenes. Its first aim is the knowledge of the internal energy of the clusters before dissociation. In the first part, a general overview summarizes the theoretical and experimental studies devoted to energetics (structure, stability, dissociation) of carbon clusters containing less than 60 atoms. In the second part, two techniques for producing mass-selected carbon clusters are described. The particular characteristics for such a production in a direct vaporization source are compared to those in a collisional-cooled source. The question of stability of intermediate-size clusters is asked. We study the photoabsorption spectroscopy of carbon clusters in the third part. A model for sequential absorption of several photons is developed, and used to analyze cluster dissociation versus the photoexcitation laser fluence. The absolute photoabsorption cross sections, and the number of absorbed photons are deduced. For some cluster sizes, laser wavelength scanning leads to evidence for existence of several clusters structures (or so-called isomers). The last part deals with photo dissociation mechanisms. Dissociation is found to occur after single-photon absorption, or after vibrational heating of the clusters. In that latter case, a statistical model including restricted intramolecular vibrational energy redistribution is used to calculate dissociation energies from measured fragmentation times of well-defined internal energy states. These energies, which are characteristic of cyclic structures, are then used to a better understanding of carbon cluster formation in a direct vaporization source. (Author). 76 refs., 63 figs., 23 tabs.

  2. Carbon-cluster mass calibration at SHIPTRAP

    Energy Technology Data Exchange (ETDEWEB)

    Chaudhuri, A.; Marx, G.; Schweikhard, L. [Ernst-Moritz-Arndt-Univ., Institut fur Physik, Greifswald (Germany); Block, M.; Eliseev, S.; Herfurth, F.; Martin, A.; Mukherjee, M.; Rauth, C.; Vorobjev, G. [GSI, Darmstadt (Germany); Eliseev, S.; Vorobjev, G. [Saint Petersburg Nuclear Physics Institute, Gatchina (Russian Federation); Ferrer, R. [Johannes Gutenberg-Univ., Institut fur Physik, Mainz (Germany)

    2007-10-15

    A carbon-cluster ion source has been installed and tested at SHIPTRAP, the Penning-trap mass spectrometer for precision mass measurements of heavy elements at GSI (Darmstadt, Germany). Carbon-cluster ions {sup 12}C{sub n}{sup +}, 5 {<=} n {<=} 23, were produced by laser-induced desorption and ionization from a carbon sample. They were tested for the first time as reference ions in an on-line mass measurement of the radionuclides {sup 144}Dy, {sup 146}Dy and {sup 147}Ho. In addition, carbon clusters of various sizes were used for an investigation of the systematic uncertainty of SHIPTRAP covering a mass range from 84 u to 240 u. The mass-dependent uncertainty was found to be negligible for the case of (m - m(ref)) < 100 u. However, a systematic uncertainty of 4.5*10{sup -8} was revealed. (authors)

  3. Cluster formation probability in the trans-tin and trans-lead nuclei

    Energy Technology Data Exchange (ETDEWEB)

    Santhosh, K.P. [School of Pure and Applied Physics, Kannur University, Payyanur Campus, Payyanur 670 327 (India)], E-mail: drkpsanthosh@gmail.com; Biju, R.K.; Sahadevan, Sabina [P.G. Department of Physics and Research Centre, Payyanur College, Payyanur 670 327 (India)

    2010-07-01

    Within our fission model, the Coulomb and proximity potential model (CPPM) cluster formation probabilities are calculated for different clusters ranging from carbon to silicon for the parents in the trans-tin and trans-lead regions. It is found that in trans-tin region the {sup 12}C, {sup 16}O, {sup 20}Ne and {sup 24}Mg clusters have maximum cluster formation probability and lowest half lives as compared to other clusters. In trans-lead region the {sup 14}C, {sup 18,20}O, {sup 23}F, {sup 24,26}Ne, {sup 28,30}Mg and {sup 34}Si clusters have the maximum cluster formation probability and minimum half life, which show that alpha like clusters are most probable for emission from trans-tin region while non-alpha clusters are probable from trans-lead region. These results stress the role of neutron proton symmetry and asymmetry of daughter nuclei in these two cases.

  4. Cluster formation probability in the trans-tin and trans-lead nuclei

    CERN Document Server

    Santhosh, K P; Sahadevan, Sabina; 10.1016/j.nuclphysa.2010.03.004

    2010-01-01

    Within our fission model, the Coulomb and proximity potential model (CPPM) cluster formation probabilities are calculated for different clusters ranging from carbon to silicon for the parents in the trans-tin and trans- lead regions. It is found that in trans-tin region the 12^C, 16^O, 20^Ne and 24^Mg clusters have maximum cluster formation probability and lowest half lives as compared to other clusters. In trans-lead region the 14^C, 18, 20^O, 23^F, 24,26^Ne, 28,30^Mg and 34^Si clusters have the maximum cluster formation probability and minimum half life, which show that alpha like clusters are most probable for emission from trans-tin region while non-alpha clusters are probable from trans-lead region. These results stress the role of neutron proton symmetry and asymmetry of daughter nuclei in these two cases.

  5. Isomer Spectrum of Small Carbon Clusters

    Institute of Scientific and Technical Information of China (English)

    SHENG Yang; LI Peng; NING Xi-Jing

    2004-01-01

    A theoretical method is developed to find isomers of cluster particles, and the isomer spectrum of carbon clusters Cn (n = 3-44) is obtained. It is found that the isomers of 3-11 atoms are in either mono-ring or line shapes,while the isomers of 12-18 atoms show flat sheet shapes. As cluster size increases, bowl isomers become more (n > 19) until cage isomers dominate the structures (n > 27). Based on the isomer spectrum, results of a previous experiment are interpreted.

  6. Formation Mechanisms of IMBH in Globular Clusters

    CERN Document Server

    Giersz, Mirek; Hypki, Arkadiusz; Askar, Abbas; Lützgendorf, Nora

    2016-01-01

    We very briefly discuss proposed in the literature possible scenarios for intermediate mass black holes (IMBH) formation in globular clusters. We also discuss the results of the MOCCA simulations of about 2000 models (BigSurvey) regarding the distribution of events connected with electromagnetic and gravitational radiations, namely: mass transfer on IMBH, collisions and mergers with IMBH and mergers with IMBH due to gravitational radiation. The rates of these events are very small, so their observation is very improbable.

  7. The effects of cluster carbon implantation at low temperature on damage recovery after annealing

    Science.gov (United States)

    Onoda, Hiroshi; Nakashima, Yoshiki; Hamamoto, Nariaki; Nagayama, Tsutomu; Koga, Yuji; Umisedo, Sei; Kawamura, Yasunori; Hashimoto, Masahiro

    2012-11-01

    Amorphous Si layer formation with cluster carbon ion implantations at low substrate temperature and its effects on damage recovery and diffusion suppression have been discussed. Cluster carbon molecule species (C3Hx˜C7Hx), implantation temperature (RT ˜ -60°C), implantation dose and energy were used as parameters. Amorphous Si formation by cluster carbon implantation is more effective compared with monomer carbon implantation. Low temperature cluster carbon implantations increase amorphous Si thickness far beyond monomer carbon implantation even at very low temperature. Amorphous-crystal interface smoothness was characterized by Rutherford Backscattering Spectroscopy, and is improved by lower temperature implantations. The smoothness improvement affects the residual damage, End of Range Defects, after annealing. Thicker amorphous Si over 100 nm depth can be formed with light Cn+ molecule implantations. That makes it possible to suppress wide distributed phosphorus diffusion.

  8. Carbon-cluster mass calibration at SHIPTRAP

    Energy Technology Data Exchange (ETDEWEB)

    Chaudhuri, Ankur

    2007-12-10

    A carbon-cluster ion source has been installed and tested at SHIPTRAP, the Penning-trap mass spectrometer for mass measurements of heavy elements at GSI/Darmstadt, Germany. A precision mass determination is carried out by measuring the ion cyclotron frequency {omega}{sub c}=qB=m, where q/m is the charge-to-mass ratio of the ion and B is the magnetic field. The mass of the ion of interest is obtained from the comparison of its cyclotron frequency {omega}{sub c} with that of a well-known reference ion. Carbon clusters are the mass reference of choice since the unified atomic mass unit is defined as 1/12 of the mass of the {sup 12}C atom. Thus the masses of carbon clusters {sup 12}C{sub n}, n=1,2,3,.. are multiples of the unified atomic mass unit. Carbon-cluster ions {sup 12}C{sub n}{sup +}, 5{<=}n{<=}23, were produced by laser-induced desorption and ionization from a carbon sample. Carbon clusters of various sizes ({sup 12}C{sub 7}{sup +}, {sup 12}C{sub 9}{sup +}, {sup 12}C{sub 10}{sup +}, {sup 12}C{sub 11}{sup +}, {sup 12}C{sub 12}{sup +}, {sup 12}C{sub 15}{sup +}, {sup 12}C{sub 18}{sup +}, {sup 12}C{sub 19}{sup +}, {sup 12}C{sub 20}{sup +}) were used for an investigation of the accuracy of SHIPTRAP covering a mass range from 84 u to 240 u. To this end the clusters were used both as ions of interest and reference ions. Hence the true values of the frequency ratios are exactly known. The mass-dependent uncertainty was found to be negligible for the case of (m-m{sub ref})<100 u. However, a systematic uncertainty of 4.5 x 10{sup -8} was revealed. In addition, carbon clusters were employed for the first time as reference ions in an on-line studies of short-lived nuclei. Absolute mass measurements of the radionuclides {sup 144}Dy, {sup 146}Dy and {sup 147}Ho were performed using {sup 12}C{sub 11}{sup +} as reference ion. The results agree with measurements during the same run using {sup 85}Rb{sup +} as reference ion. The investigated radionuclides were produced in the

  9. A free energy study of carbon clusters on Ir(111): Precursors to graphene growth

    Science.gov (United States)

    Tetlow, H.; Ford, I. J.; Kantorovich, L.

    2017-01-01

    It is widely accepted that the nucleation of graphene on transition metals is related to the formation of carbon clusters of various sizes and shapes on the surface. Assuming a low concentration of carbon atoms on a crystal surface, we derive a thermodynamic expression for the grand potential of the cluster of N carbon atoms, relative to a single carbon atom on the surface (the cluster work of formation). This is derived taking into account both the energetic and entropic contributions, including structural and rotational components, and is explicitly dependent on the temperature. Then, using ab initio density functional theory, we calculate the work of formation of carbon clusters CN on the Ir(111) surface as a function of temperature considering clusters with up to N = 16 C atoms. We consider five types of clusters (chains, rings, arches, top-hollow, and domes), and find, in agreement with previous zero temperature studies, that at elevated temperatures the structure most favoured depends on N, with chains and arches being the most likely at N 10 . Our calculations reveal the work of formation to have a much more complex character as a function of the cluster size than one would expect from classical nucleation theory: for typical conditions, the work of formation displays not one but two nucleation barriers, at around N = 4-5 and N = 9-11. This suggests, in agreement with existing LEEM data, that five atom carbon clusters, along with C monomers, must play a pivotal role in the nucleation and growth of graphene sheets, whereby the formation of large clusters is achieved from the coalescence of smaller clusters (Smoluchowski ripening). Although the main emphasis of our study is on thermodynamic aspects of nucleation, the pivotal role of kinetics of transitions between different cluster types during the nucleation process is also discussed for a few cases as illustrative examples.

  10. CONTROLLING THE FORMATION AND FUNCTIONING OF THE CLUSTER

    Directory of Open Access Journals (Sweden)

    A. S. Barzenkova

    2013-01-01

    Full Text Available The article presents the author's concept of the technique of controlling the formation and functioning of the cluster, which allows to objectively estimate the process of the formation of cluster, trace the dynamics of its life and assess the main areas and indi-cators cluster operation.

  11. Sarcomeric pattern formation by actin cluster coalescence.

    Directory of Open Access Journals (Sweden)

    Benjamin M Friedrich

    Full Text Available Contractile function of striated muscle cells depends crucially on the almost crystalline order of actin and myosin filaments in myofibrils, but the physical mechanisms that lead to myofibril assembly remains ill-defined. Passive diffusive sorting of actin filaments into sarcomeric order is kinetically impossible, suggesting a pivotal role of active processes in sarcomeric pattern formation. Using a one-dimensional computational model of an initially unstriated actin bundle, we show that actin filament treadmilling in the presence of processive plus-end crosslinking provides a simple and robust mechanism for the polarity sorting of actin filaments as well as for the correct localization of myosin filaments. We propose that the coalescence of crosslinked actin clusters could be key for sarcomeric pattern formation. In our simulations, sarcomere spacing is set by filament length prompting tight length control already at early stages of pattern formation. The proposed mechanism could be generic and apply both to premyofibrils and nascent myofibrils in developing muscle cells as well as possibly to striated stress-fibers in non-muscle cells.

  12. Sarcomeric Pattern Formation by Actin Cluster Coalescence

    Science.gov (United States)

    Friedrich, Benjamin M.; Fischer-Friedrich, Elisabeth; Gov, Nir S.; Safran, Samuel A.

    2012-01-01

    Contractile function of striated muscle cells depends crucially on the almost crystalline order of actin and myosin filaments in myofibrils, but the physical mechanisms that lead to myofibril assembly remains ill-defined. Passive diffusive sorting of actin filaments into sarcomeric order is kinetically impossible, suggesting a pivotal role of active processes in sarcomeric pattern formation. Using a one-dimensional computational model of an initially unstriated actin bundle, we show that actin filament treadmilling in the presence of processive plus-end crosslinking provides a simple and robust mechanism for the polarity sorting of actin filaments as well as for the correct localization of myosin filaments. We propose that the coalescence of crosslinked actin clusters could be key for sarcomeric pattern formation. In our simulations, sarcomere spacing is set by filament length prompting tight length control already at early stages of pattern formation. The proposed mechanism could be generic and apply both to premyofibrils and nascent myofibrils in developing muscle cells as well as possibly to striated stress-fibers in non-muscle cells. PMID:22685394

  13. On the formation of massive stellar clusters

    CERN Document Server

    Tenorio-Tagle, G; Silich, S A; Medina-Tanco, G A; Muñoz-Tunón, C; Tenorio-Tagle, Guillermo; Palous, Jan; Silich, Sergiy; Medina-Tanco, Gustavo A.; Munoz-Tunon, Casiana

    2003-01-01

    Here we model a star forming factory in which the continuous creation of stars results in a highly concentrated, massive (globular cluster-like) stellar system. We show that under very general conditions a large-scale gravitational instability in the ISM, which triggers the collapse of a massive cloud, leads with the aid of a spontaneous first generation of massive stars, to a standing, small-radius, cold and dense shell. Eventually, as more of the collapsing matter is processed and incorporated, the shell becomes gravitationally unstable and begins to fragment, allowing the formation of new stars, while keeping its location. This is due to a detailed balance established between the ram pressure from the collapsing cloud which, together with the gravitational force exerted on the shell by the forming cluster, acts against the mechanical energy deposited by the collection of new stars. We analyze the mass spectrum of fragments that result from the continuous fragmentation of the standing shell and show that it...

  14. FORMATION OF A INNOVATION REGIONAL CLUSTER MODEL

    Directory of Open Access Journals (Sweden)

    G. S. Merzlikina

    2015-01-01

    Full Text Available Summary. As a result of investigation of science and methodical approaches related problems of building and development of innovation clusters there were some issues in functional assignments of innovation and production clusters. Because of those issues, article’s authors differ conceptions of innovation cluster and production cluster, as they explain notion of innovation-production cluster. The main goal of this article is to reveal existing organizational issues in cluster building and its successful development. Based on regional clusters building analysis carried out there was typical practical structure of cluster members interaction revealed. This structure also have its cons, as following: absence cluster orientation to marketing environment, lack of members’ prolonged relations’ building and development system, along with ineffective management of information, financial and material streams within cluster, narrow competence difference and responsibility zones between cluster members, lack of transparence of cluster’s action, low environment changes adaptivity, hard to use cluster members’ intellectual property, and commercialization of hi-tech products. When all those issues listed above come together, it reduces life activity of existing models of innovative cluster-building along with practical opportunity of cluster realization. Because of that, authors offer an upgraded innovative-productive cluster building model with more efficient business processes management system, which includes advanced innovative cluster structure, competence matrix and subcluster responsibility zone. Suggested model differs from other ones by using unified innovative product development control center, which also controls production and marketing realization.

  15. THEORETICAL FOUNDATIONS OF FORMATION OF ENTREPRENEURIAL CLUSTER

    Directory of Open Access Journals (Sweden)

    Rizhikova A. M.

    2015-06-01

    Full Text Available This article investigates the development of entrepreneurial cluster set direction to support the creation of innovation clusters in Russia. In the face of increasing international competition, one of the most effective ways of development of small and medium-sized enterprises in the field of innovation is their clustering. We have discussed foreign experience of studying cluster initiatives and events on social development of the regions in the context of sociological knowledge about clusters. We have revealed the meaning of an innovation cluster and the difference between business and innovation clusters. The analysis has shown that a key advantage of the business cluster in relation to the network is the participation of state authorities, as well as functional and territorial factor. On the basis of the author's research we have highlighted a number of problems which solution has been carried out through the creation of business clusters

  16. Phosphorous transient enhanced diffusion suppression and activation enhancement with cluster carbon co-implantation

    Energy Technology Data Exchange (ETDEWEB)

    Nakashima, Yoshiki; Hamamoto, Nariaki; Nagayama, Tsutomu; Koga, Yuji; Umisedo, Sei; Kawamura, Yasunori; Hashimoto, Masahiro; Onoda, Hiroshi [Nissin Ion Equipment Co., Ltd., 575 Kuze Tonoshiro-cho, Minami-ku, Kyoto, 601-8205 (Japan)

    2012-11-06

    Carbon co-implantation is well known as an effective method for suppressing boron/phosphorous transient enhanced diffusion (TED). Germanium pre-amorphization implantation (PAI) is usually applied prior to carbon co-implantation for suppressing channeling tail of dopants. In this study, cluster carbon was applied instead of the combination of germanium PAI and monomer carbon co-implantation prior to phosphorous implantation. Dependence of phosphorous activation and TED on amorphous layer thickness, carbon dose, carbon distribution and substrate temperature have been investigated. Cluster carbon implantation enables thick amorphous layer formation and TED suppression at the same time and low temperature implantation enhances the ability of amorphous layer formation so that shallow junction and low Rs can be achieved without Ge implantation.

  17. Globular cluster system erosion and nucleus formation in elliptical galaxies

    CERN Document Server

    Capuzzo-Dolcetta, R

    1998-01-01

    The radial distribution of globular clusters in galaxies is always less peaked to the centre than the halo stars'. Extending previous work to a sample of HST globular cluster systems in ellipticals, we evaluate the number of clusters lost to the galactic centre as the integrals of the difference between the observed globular cluster system distribution and the underlying halo light profile. It results that the initial populations of globular clusters were from 25% to 50% richer than now. This significant number of missing globular clusters supports the hypothesis that a large quantity of globular cluster mass in form of globular clusters decayed and destroyed has been lost to the galactic centres, where plausibly contributed to formation and feeding of a mas sive object therein. It is relevant noting that the observed correlation between the core radius of the globular cluster system and the parent galaxy luminosity can be interpreted as a result of evolution.

  18. Computational Approaches for Probing the Formation of Atmospheric Molecular Clusters

    DEFF Research Database (Denmark)

    Elm, Jonas

    This thesis presents the investigation of atmospheric molecular clusters using computational methods. Previous investigations have focused on solving problems related to atmospheric nucleation, and have not been targeted at the performance of the applied methods. This thesis focuses on assessing...... the performance of computational strategies in order to identify a sturdy methodology, which should be applicable for handling various issues related to atmospheric cluster formation. Density functional theory (DFT) is applied to study individual cluster formation steps. Utilizing large test sets of numerous...... and pinic acid) for atmospheric cluster formation. Glycine is found to have a similar potential as ammonia in enhancing atmospheric nucleation. Pinic acid molecules form favourable clusters with sulfuric acid, but with formation free energies which are too low to explain observed nucleation rates. Pinic...

  19. The era of star formation in galaxy clusters

    Energy Technology Data Exchange (ETDEWEB)

    Brodwin, M. [Department of Physics and Astronomy, University of Missouri, 5110 Rockhill Road, Kansas City, MO 64110 (United States); Stanford, S. A. [University of California, Davis, CA 95616 (United States); Gonzalez, Anthony H.; Mancone, C. L.; Gettings, D. P. [Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States); Zeimann, G. R. [Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802 (United States); Snyder, G. F.; Ashby, M. L. N. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Pope, A.; Alberts, S. [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Eisenhardt, P. R.; Stern, D.; Moustakas, L. A. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Brown, M. J. I. [School of Physics, Monash University, Clayton, Victoria 3800 (Australia); Chary, R.-R. [Spitzer Science Center, MC 220-6, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Dey, Arjun [National Optical Astronomy Observatory, 950 N. Cherry Avenue, Tucson, AZ 85719 (United States); Galametz, A. [INAF—Osservatorio di Roma, Via Frascati 33, I-00040 Monteporzio (Italy); Jannuzi, B. T. [Steward Observatory, University of Arizona, 933 N. Cherry Avenue, Tucson, AZ 85121 (United States); Miller, E. D. [Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Moustakas, J. [Department of Physics and Astronomy, Siena College, 515 Loudon Road, Loudonville, NY 12211 (United States)

    2013-12-20

    We analyze the star formation properties of 16 infrared-selected, spectroscopically confirmed galaxy clusters at 1 < z < 1.5 from the Spitzer/IRAC Shallow Cluster Survey (ISCS). We present new spectroscopic confirmation for six of these high-redshift clusters, five of which are at z > 1.35. Using infrared luminosities measured with deep Spitzer/Multiband Imaging Photometer for Spitzer observations at 24 μm, along with robust optical + IRAC photometric redshifts and spectral-energy-distribution-fitted stellar masses, we present the dust-obscured star-forming fractions, star formation rates, and specific star formation rates in these clusters as functions of redshift and projected clustercentric radius. We find that z ∼ 1.4 represents a transition redshift for the ISCS sample, with clear evidence of an unquenched era of cluster star formation at earlier times. Beyond this redshift, the fraction of star-forming cluster members increases monotonically toward the cluster centers. Indeed, the specific star formation rate in the cores of these distant clusters is consistent with field values at similar redshifts, indicating that at z > 1.4 environment-dependent quenching had not yet been established in ISCS clusters. By combining these observations with complementary studies showing a rapid increase in the active galactic nucleus (AGN) fraction, a stochastic star formation history, and a major merging episode at the same epoch in this cluster sample, we suggest that the starburst activity is likely merger-driven and that the subsequent quenching is due to feedback from merger-fueled AGNs. The totality of the evidence suggests we are witnessing the final quenching period that brings an end to the era of star formation in galaxy clusters and initiates the era of passive evolution.

  20. Globular cluster formation with multiple stellar populations from hierarchical star cluster complexes

    Science.gov (United States)

    Bekki, Kenji

    2017-01-01

    Most old globular clusters (GCs) in the Galaxy are observed to have internal chemical abundance spreads in light elements. We discuss a new GC formation scenario based on hierarchical star formation within fractal molecular clouds. In the new scenario, a cluster of bound and unbound star clusters (`star cluster complex', SCC) that have a power-law cluster mass function with a slope (β) of 2 is first formed from a massive gas clump developed in a dwarf galaxy. Such cluster complexes and β = 2 are observed and expected from hierarchical star formation. The most massive star cluster (`main cluster'), which is the progenitor of a GC, can accrete gas ejected from asymptotic giant branch (AGB) stars initially in the cluster and other low-mass clusters before the clusters are tidally stripped or destroyed to become field stars in the dwarf. The SCC is initially embedded in a giant gas hole created by numerous supernovae of the SCC so that cold gas outside the hole can be accreted onto the main cluster later. New stars formed from the accreted gas have chemical abundances that are different from those of the original SCC. Using hydrodynamical simulations of GC formation based on this scenario, we show that the main cluster with the initial mass as large as [2 - 5] × 105M⊙ can accrete more than 105M⊙ gas from AGB stars of the SCC. We suggest that merging of hierarchical star cluster complexes can play key roles in stellar halo formation around GCs and self-enrichment processes in the early phase of GC formation.

  1. An Effective Method of Producing Small Neutral Carbon Clusters

    Institute of Scientific and Technical Information of China (English)

    XIA Zhu-Hong; CHEN Cheng-Chu; HSU Yen-Chu

    2007-01-01

    An effective method of producing small neutral carbon clusters Cn (n = 1-6) is described. The small carbon clusters (positive or negative charge or neutral) are formed by plasma which are produced by a high power 532nm pulse laser ablating the surface of the metal Mn rod to react with small hydrocarbons supplied by a pulse valve, then the neutral carbon clusters are extracted and photo-ionized by another laser (266nm or 355nm) in the ionization region of a linear time-of-flight mass spectrometer. The distributions of the initial neutral carbon clusters are analysed with the ionic species appeared in mass spectra. It is observed that the yield of small carbon clusters with the present method is about 10 times than that of the traditional widely used technology of laser vaporization of graphite.

  2. Panchromatic Hubble Andromeda Treasury XVI. Star Cluster Formation Efficiency and the Clustered Fraction of Young Stars

    CERN Document Server

    Johnson, L Clifton; Dalcanton, Julianne J; Beerman, Lori C; Fouesneau, Morgan; Lewis, Alexia R; Weisz, Daniel R; Williams, Benjamin F; Bell, Eric F; Dolphin, Andrew E; Larsen, Søren S; Sandstrom, Karin; Skillman, Evan D

    2016-01-01

    We use the Panchromatic Hubble Andromeda Treasury (PHAT) survey dataset to perform spatially resolved measurements of star cluster formation efficiency ($\\Gamma$), the fraction of stellar mass formed in long-lived star clusters. We use robust star formation history and cluster parameter constraints, obtained through color-magnitude diagram analysis of resolved stellar populations, to study Andromeda's cluster and field populations over the last $\\sim$300 Myr. We measure $\\Gamma$ of 4-8% for young, 10-100 Myr old populations in M31. We find that cluster formation efficiency varies systematically across the M31 disk, consistent with variations in mid-plane pressure. These $\\Gamma$ measurements expand the range of well-studied galactic environments, providing precise constraints in an HI-dominated, low intensity star formation environment. Spatially resolved results from M31 are broadly consistent with previous trends observed on galaxy-integrated scales, where $\\Gamma$ increases with increasing star formation r...

  3. Star Cluster Formation in Cosmological Simulations. I. Properties of Young Clusters

    Science.gov (United States)

    Li, Hui; Gnedin, Oleg Y.; Gnedin, Nickolay Y.; Meng, Xi; Semenov, Vadim A.; Kravtsov, Andrey V.

    2017-01-01

    We present a new implementation of star formation in cosmological simulations by considering star clusters as a unit of star formation. Cluster particles grow in mass over several million years at the rate determined by local gas properties, with high time resolution. The particle growth is terminated by its own energy and momentum feedback on the interstellar medium. We test this implementation for Milky Way-sized galaxies at high redshift by comparing the properties of model clusters with observations of young star clusters. We find that the cluster initial mass function is best described by a Schechter function rather than a single power law. In agreement with observations, at low masses the logarithmic slope is α ≈ 1.8{--}2, while the cutoff at high mass scales with the star formation rate (SFR). A related trend is a positive correlation between the surface density of the SFR and fraction of stars contained in massive clusters. Both trends indicate that the formation of massive star clusters is preferred during bursts of star formation. These bursts are often associated with major-merger events. We also find that the median timescale for cluster formation ranges from 0.5 to 4 Myr and decreases systematically with increasing star formation efficiency. Local variations in the gas density and cluster accretion rate naturally lead to the scatter of the overall formation efficiency by an order of magnitude, even when the instantaneous efficiency is kept constant. Comparison of the formation timescale with the observed age spread of young star clusters provides an additional important constraint on the modeling of star formation and feedback schemes.

  4. Detection of the linear carbon cluster C10: rotationally resolved diode-laser spectroscopy.

    Science.gov (United States)

    Giesen, T F; Berndt, U; Yamada, K M; Fuchs, G; Schieder, R; Winnewisser, G; Provencal, R A; Keutsch, F N; Van Orden, A; Saykally, R J

    2001-04-17

    Detected in interstellar space and as intermediates in soot formation, molecules of pure carbon in the form of linear chains or ring structures have interested researchers for several decades, who attempt to elucidate their physical properties and the processes govering their formation. A high-resolution infrared spectrometer housing a tunable diode laser and combined with an effective laser ablation source for the cluster production has been used to study the molecular properties of small carbon clusters; reported herein is the first gas-phase spectrum of linear C10.

  5. Clustering algorithms for Stokes space modulation format recognition

    DEFF Research Database (Denmark)

    Boada, Ricard; Borkowski, Robert; Tafur Monroy, Idelfonso

    2015-01-01

    Stokes space modulation format recognition (Stokes MFR) is a blind method enabling digital coherent receivers to infer modulation format information directly from a received polarization-division-multiplexed signal. A crucial part of the Stokes MFR is a clustering algorithm, which largely...... influences the performance of the detection process, particularly at low signal-to-noise ratios. This paper reports on an extensive study of six different clustering algorithms: k-means, expectation maximization, density-based DBSCAN and OPTICS, spectral clustering and maximum likelihood clustering, used...... for discriminating between dual polarization: BPSK, QPSK, 8-PSK, 8-QAM, and 16-QAM. We determine essential performance metrics for each clustering algorithm and modulation format under test: minimum required signal-to-noise ratio, detection accuracy and algorithm complexity....

  6. Quantum fluctuation effects on nuclear fragment and atomic cluster formation

    Energy Technology Data Exchange (ETDEWEB)

    Ohnishi, Akira [Hokkaido Univ., Sapporo (Japan). Dept. of Physics; Randrup, J.

    1997-05-01

    We investigate the nuclear fragmentation and atomic cluster formation by means of the recently proposed quantal Langevin treatment. It is shown that the effect of the quantal fluctuation is in the opposite direction in nuclear fragment and atomic cluster size distribution. This tendency is understood through the effective classical temperature for the observables. (author)

  7. Structure and cluster formation in granular media

    Indian Academy of Sciences (India)

    S Luding

    2005-06-01

    The two most important phenomena at the basis of granular media are excluded volume and dissipation. The former is captured by the hard sphere model and is responsible for, e.g., crystallization, the latter leads to interesting structures like clusters in non-equilibrium dynamical, freely cooling states. The freely cooling system is examined concerning the energy decay and the cluster evolution in time. Corrections for crystallization and multi-particle contacts are provided, which become more and more important with increasing density.

  8. The Era of Star Formation in Galaxy Clusters

    CERN Document Server

    Brodwin, M; Gonzalez, Anthony H; Zeimann, G R; Snyder, G F; Mancone, C L; Pope, A; Eisenhardt, P R; Stern, D; Alberts, S; Ashby, M L N; Brown, M J I; Chary, R -R; Dey, Arjun; Galametz, A; Gettings, D P; Jannuzi, B T; Miller, E D; Moustakas, J; Moustakas, L A

    2013-01-01

    We analyze the star formation properties of 16 infrared-selected, spectroscopically confirmed galaxy clusters at $1 1.35$. Using infrared luminosities measured with deep Spitzer/MIPS observations at 24 $\\mu$m, along with robust optical+IRAC photometric redshifts and SED-fitted stellar masses, we present the dust-obscured star-forming fractions, star formation rates and specific star formation rates in these clusters as functions of redshift and projected clustercentric radius. We find that $z\\sim 1.4$ represents a transition redshift for the ISCS sample, with clear evidence of an unquenched era of cluster star formation at earlier times. Beyond this redshift the fraction of star-forming cluster members increases monotonically toward the cluster centers. Indeed, the specific star formation rate in the cores of these distant clusters is consistent with field values at similar redshifts, indicating that at $z>1.4$ environment-dependent quenching had not yet been established in ISCS clusters. Combining these obse...

  9. STAR FORMATION IN HIGH-REDSHIFT CLUSTER ELLIPTICALS

    Energy Technology Data Exchange (ETDEWEB)

    Wagner, Cory R.; Brodwin, Mark [Department of Physics and Astronomy, University of Missouri, 5110 Rockhill Road, Kansas City, MO 64110 (United States); Snyder, Gregory F. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Gonzalez, Anthony H.; Mancone, Conor L. [Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States); Stanford, S. A. [University of California, Davis, CA 95616 (United States); Alberts, Stacey; Pope, Alexandra [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Stern, Daniel; Eisenhardt, Peter R. M. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Zeimann, Gregory R. [Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802 (United States); Chary, Ranga-Ram [Spitzer Science Center, MC 220-6, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91109 (United States); Dey, Arjun [NOAO, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Moustakas, John, E-mail: cwagner@astro.queensu.ca [Department of Physics and Astronomy, Siena College, 515 Loudon Road, Loudonville, NY 12211 (United States)

    2015-02-20

    We measure the star formation rates (SFRs) of massive (M {sub *} > 10{sup 10.1} M {sub ☉}) early-type galaxies (ETGs) in a sample of 11 high-redshift (1.0 < z < 1.5) galaxy clusters drawn from the IRAC Shallow Cluster Survey (ISCS). We identify ETGs visually from Hubble Space Telescope imaging and select likely cluster members as having either an appropriate spectroscopic redshift or red-sequence color. Mid-infrared SFRs are measured using Spitzer 24 μm data for isolated cluster galaxies for which contamination by neighbors, and active galactic nuclei, can be ruled out. Cluster ETGs show enhanced specific star formation rates (sSFRs) compared to cluster galaxies in the local universe, but have sSFRs more than four times lower than that of field ETGs at 1 < z < 1.5. Relative to the late-type cluster population, isolated ETGs show substantially quenched mean SFRs, yet still contribute 12% of the overall star formation activity measured in 1 < z < 1.5 clusters. We find that new ETGs are likely being formed in ISCS clusters; the fraction of cluster galaxies identified as ETGs increases from 34% to 56% from z ∼ 1.5 → 1.25. While the fraction of cluster ETGs that are highly star-forming (SFR ≥ 26 M {sub ☉} yr{sup –1}) drops from 27% to 10% over the same period, their sSFRs are roughly constant. All these factors taken together suggest that, particularly at z ≳ 1.25, the events that created these distant cluster ETGs—likely mergers, at least among the most massive—were both recent and gas-rich.

  10. Star formation properties of galaxy cluster A1767

    CERN Document Server

    Yan, Peng-Fei; Yuan, Qi-Rong

    2015-01-01

    Abell 1767 is a dynamically relaxed, cD cluster of galaxies with a redshift of 0.0703. Among 250 spectroscopically confirmed member galaxies within a projected radius of 2.5r_{200}, 243 galaxies (~ 97%) are spectroscopically covered by the Sloan Digital Sky Survey (SDSS). Based on this homogeneous spectral sample, the stellar evolutionary synthesis code, STARLIGHT, is applied to investigate the stellar populations and star formation histories (SFHs) of cluster galaxies. The star formation properties of galaxies, such as mean stellar ages, metallicities, stellar masses, and star formation rates (SFRs), are presented as the functions of local galaxy density. Strong environmental effect is found in the manner that massive galaxies in the high-density core region of cluster tend to have higher metallicities, longer mean stellar ages, and lower specific star formation rates (SSFRs), and their recent star formation activities have been remarkably suppressed. In addition, the correlations of the metallicity and SSFR...

  11. Star Formation in High-Redshift Cluster Ellipticals

    CERN Document Server

    Wagner, Cory R; Snyder, Gregory F; Gonzalez, Anthony H; Stanford, S A; Alberts, Stacey; Pope, Alexandra; Stern, Daniel; Zeimann, Gregory R; Chary, Ranga-Ram; Dey, Arjun; Eisenhardt, Peter R M; Mancone, Conor L; Moustakas, John

    2014-01-01

    We measure the star formation rates (SFRs) of massive ($M_{\\star}>10^{10.1}M_{\\odot}$) early-type galaxies (ETGs) in a sample of 11 high-redshift ($1.0 < z < 1.5$) galaxy clusters drawn from the IRAC Shallow Cluster Survey (ISCS). We identify ETGs visually from Hubble Space Telescope imaging and select likely cluster members as having either an appropriate spectroscopic redshift or red sequence color. Mid-infrared SFRs are measured using Spitzer 24 $\\mu$m data for isolated cluster galaxies for which contamination by neighbors, and active galactic nuclei, can be ruled out. Cluster ETGs show enhanced specific star formation rates (sSFRs) compared to cluster galaxies in the local Universe, but have sSFRs more than four times lower than that of field ETGs at $1 < z < 1.5$. Relative to the late-type cluster population, isolated ETGs show substantially quenched mean SFRs, yet still contribute 12% of the overall star formation activity measured in $1 < z < 1.5$ clusters. We find that new ETGs are l...

  12. Star Cluster Luminosity Functions and Cluster Formation Efficiencies in LEGUS Dwarf Galaxies

    Science.gov (United States)

    Cook, David O.; Lee, Janice C.; Adamo, Angela; Kim, Hwiyun; Ryon, Jenna E.; LEGUS Team

    2017-01-01

    We present preliminary results of star cluster luminosity functions (LFs) and cluster formation efficiencies (Γ) in the LEGUS dwarf galaxy sub-sample. We have used a combination of automated and visual identification techniques to allow us to construct a more complete sample of clusters in these low-mass, low-SFR environments compared to previous studies of dwarf galaxies. Cluster properties are derived from fitting UV and optical (NUV-I) HST photometry to both deterministic and stochastic single-aged stellar populations models. We compare the cluster formation efficiencies and LF slopes to those of previous studies in both dwarf and massive spiral galaxy environments. Recent studies have found that both the LF slope and Γ form trends with galaxy environment. Our LF slope and Γ measurements in the LEGUS dwarfs will allow us to test these trends in the extreme, low-SFR regime and provide a better understanding of the star formation process.

  13. The formation and dynamical evolution of young star clusters

    CERN Document Server

    Fujii, Michiko

    2015-01-01

    Recent observations have revealed a variety of young star clusters, including embedded systems, young massive clusters, and associations. We study the formation and dynamical evolution of these clusters using a combination of simulations and theoretical models. Our simulations start with a turbulent molecular cloud that collapses under its own gravity. The stars are assumed to form in the densest regions in the collapsing cloud after an initial free-fall times of the molecular cloud. The dynamical evolution of these stellar distributions are continued by means of direct $N$-body simulations. The molecular clouds typical for the Milky Way Galaxy tend to form embedded clusters which evolve to resemble open clusters. The associations were initially considerably more clumpy, but lost their irregularity in about a dynamical time scale due to the relaxation process. The densest molecular clouds, which are absent in the Milky Way but are typical in starburst galaxies, form massive young star clusters. They indeed ar...

  14. Carbon monoxide formation in tomatoes

    Energy Technology Data Exchange (ETDEWEB)

    Gladon, R.J.; Staby, G.L.

    1979-01-01

    Carbon monoxide (CO) is not emanated to any large extent from tomato fruits (Lycopersicon esculentum, Mill. cvs. Rutgers and Ohio MR-13), but is retained within the internal atmosphere. CO is found during all stages of fruit development, but no set pattern of CO concentration is evident.

  15. Photoelectron spectroscopic study of carbon aluminum hydride cluster anions

    Science.gov (United States)

    Zhang, Xinxing; Wang, Haopeng; Ganteför, Gerd; Eichhorn, Bryan W.; Kiran, Boggavarapu; Bowen, Kit H.

    2016-10-01

    Numerous previously unknown carbon aluminum hydride cluster anions were generated in the gas phase, identified by time-of-flight mass spectrometry and characterized by anion photoelectron spectroscopy, revealing their electronic structure. Density functional theory calculations on the CAl5-9H- and CAl5-7H2- found that several of them possess unusually high carbon atom coordination numbers. These cluster compositions have potential as the basis for new energetic materials.

  16. Hα star formation rates of z > 1 galaxy clusters in the IRAC shallow cluster survey

    Energy Technology Data Exchange (ETDEWEB)

    Zeimann, Gregory R.; Stanford, S. A. [Department of Physics, University of California, One Shields Avenue, Davis, CA 95616 (United States); Brodwin, Mark [University of Missouri-Kansas City, Kansas City, MO 64110 (United States); Gonzalez, Anthony H.; Mancone, Conor [Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States); Snyder, Gregory F. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Stern, Daniel; Eisenhardt, Peter [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Dey, Arjun [NOAO, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Moustakas, John [Department of Physics and Astronomy, Siena College, 515 Loudon Road, Loudonville, NY 12211 (United States)

    2013-12-20

    We present Hubble Space Telescope near-IR spectroscopy for 18 galaxy clusters at 1.0 Cluster Survey. We use Wide Field Camera 3 grism data to spectroscopically identify Hα emitters in both the cores of galaxy clusters as well as in field galaxies. We find a large cluster-to-cluster scatter in the star formation rates within a projected radius of 500 kpc, and many of our clusters (∼60%) have significant levels of star formation within a projected radius of 200 kpc. A stacking analysis reveals that dust reddening in these star-forming galaxies is positively correlated with stellar mass and may be higher in the field than the cluster at a fixed stellar mass. This may indicate a lower amount of gas in star-forming cluster galaxies than in the field population. Also, Hα equivalent widths of star-forming galaxies in the cluster environment are still suppressed below the level of the field. This suppression is most significant for lower mass galaxies (log M {sub *} < 10.0 M {sub ☉}). We therefore conclude that environmental effects are still important at 1.0 clusters with log M {sub *} ≲ 10.0 M {sub ☉}.

  17. Simulation of swift boron clusters traversing amorphous carbon foils

    OpenAIRE

    Heredia Ávalos, Santiago; Abril Sánchez, Isabel; Denton Zanello, Cristian D.; García Molina, Rafael

    2007-01-01

    We use a simulation code to study the interaction of swift boron clusters (Bn+, n=2–6, 14) with amorphous carbon foils. We analyze different aspects of this interaction, such as the evolution of the cluster structure inside the target, the energy and angle distributions at the detector or the stopping power ratio. Our simulation code follows in detail the motion of the cluster fragments through the target and in the vacuum until reaching a detector, taking into account the following interacti...

  18. Constraining Galaxy Formation Models with Dwarf Ellipticals in Clusters

    CERN Document Server

    Conselice, C J

    2005-01-01

    Recent observations demonstrate that dwarf elliptical (dE) galaxies in clusters, despite their faintness, are likely a critical galaxy type for understanding the processes behind galaxy formation. Dwarf ellipticals are the most common galaxy type, and are particularly abundant in rich galaxy clusters. The dwarf to giant ratio is in fact highest in rich clusters of galaxies, suggesting that cluster dEs do not form in groups that later merge to form clusters. Dwarf ellipticals are potentially the only galaxy type whose formation is sensitive to global, rather than local, environment. The dominant idea for explaining the formation of these systems, through Cold Dark Matter models, is that dEs form early and within their present environments. Recent results suggest that some dwarfs appear in clusters after the bulk of massive galaxies form, a scenario not predicted in standard hierarchical structure formation models. Many dEs have younger and more metal rich stellar populations than dwarfs in lower density enviro...

  19. SIGNATURES OF STAR CLUSTER FORMATION BY COLD COLLAPSE

    Energy Technology Data Exchange (ETDEWEB)

    Kuznetsova, Aleksandra; Hartmann, Lee [Department of Astronomy, University of Michigan, 1085 S. University Ave., Ann Arbor, MI 48109 (United States); Ballesteros-Paredes, Javier, E-mail: kuza@umich.edu [Centro de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Apdo. Postal 72-3 (Xangari), Morelia, Michocán 58089, México (Mexico)

    2015-12-10

    Subvirial gravitational collapse is one mechanism by which star clusters may form. Here we investigate whether this mechanism can be inferred from observations of young clusters. To address this question, we have computed smoothed particle hydrodynamics simulations of the initial formation and evolution of a dynamically young star cluster through cold (subvirial) collapse, starting with an ellipsoidal, turbulently seeded distribution of gas, and forming sink particles representing (proto)stars. While the initial density distributions of the clouds do not have large initial mass concentrations, gravitational focusing due to the global morphology leads to cluster formation. We use the resulting structures to extract observable morphological and kinematic signatures for the case of subvirial collapse. We find that the signatures of the initial conditions can be erased rapidly as the gas and stars collapse, suggesting that kinematic observations need to be made early in cluster formation and/or at larger scales, away from the growing cluster core. Our results emphasize that a dynamically young system is inherently evolving on short timescales, so that it can be highly misleading to use current-epoch conditions to study aspects such as star formation rates as a function of local density. Our simulations serve as a starting point for further studies of collapse including other factors such as magnetic fields and stellar feedback.

  20. Evolutionary formation of gene clusters by reorganization: the meleagrin/roquefortine paradigm in different fungi.

    Science.gov (United States)

    Martín, Juan F; Liras, Paloma

    2016-02-01

    The biosynthesis of secondary metabolites in fungi is catalyzed by enzymes encoded by genes linked in clusters that are frequently co-regulated at the transcriptional level. Formation of gene clusters may take place by de novo assembly of genes recruited from other cellular functions, but also novel gene clusters are formed by reorganization of progenitor clusters and are distributed by horizontal gene transfer. This article reviews (i) the published information on the roquefortine/meleagrin/neoxaline gene clusters of Penicillium chrysogenum (Penicillium rubens) and the short roquefortine cluster of Penicillium roqueforti, and (ii) the correlation of the genes present in those clusters with the enzymes and metabolites derived from these pathways. The P. chrysogenum roq/mel cluster consists of seven genes and includes a gene (roqT) encoding a 12-TMS transporter protein of the MFS family. Interestingly, the orthologous P. roquefortine gene cluster has only four genes and the roqT gene is present as a residual pseudogene that encodes only small peptides. Two of the genes present in the central region of the P. chrysogenum roq/mel cluster have been lost during the evolutionary formation of the short cluster and the order of the structural genes in the cluster has been rearranged. The two lost genes encode a N1 atom hydroxylase (nox) and a roquefortine scaffold-reorganizing oxygenase (sro). As a consequence P. roqueforti has lost the ability to convert the roquefortine-type carbon skeleton to the glandicoline/meleagrin-type scaffold and is unable to produce glandicoline B, meleagrin and neoxaline. The loss of this genetic information is not recent and occurred probably millions of years ago when a progenitor Penicillium strain got adapted to life in a few rich habitats such as cheese, fermented cereal grains or silage. P. roqueforti may be considered as a "domesticated" variant of a progenitor common to contemporary P. chrysogenum and related Penicillia.

  1. GAMMA RAYS FROM STAR FORMATION IN CLUSTERS OF GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Storm, Emma M.; Jeltema, Tesla E.; Profumo, Stefano [Department of Physics, University of California, 1156 High Street, Santa Cruz, CA 95064 (United States)

    2012-08-20

    Star formation in galaxies is observed to be associated with gamma-ray emission, presumably from non-thermal processes connected to the acceleration of cosmic-ray nuclei and electrons. The detection of gamma rays from starburst galaxies by the Fermi Large Area Telescope (LAT) has allowed the determination of a functional relationship between star formation rate and gamma-ray luminosity. Since star formation is known to scale with total infrared (8-1000 {mu}m) and radio (1.4 GHz) luminosity, the observed infrared and radio emission from a star-forming galaxy can be used to quantitatively infer the galaxy's gamma-ray luminosity. Similarly, star-forming galaxies within galaxy clusters allow us to derive lower limits on the gamma-ray emission from clusters, which have not yet been conclusively detected in gamma rays. In this study, we apply the functional relationships between gamma-ray luminosity and radio and IR luminosities of galaxies derived by the Fermi Collaboration to a sample of the best candidate galaxy clusters for detection in gamma rays in order to place lower limits on the gamma-ray emission associated with star formation in galaxy clusters. We find that several clusters have predicted gamma-ray emission from star formation that are within an order of magnitude of the upper limits derived in Ackermann et al. based on non-detection by Fermi-LAT. Given the current gamma-ray limits, star formation likely plays a significant role in the gamma-ray emission in some clusters, especially those with cool cores. We predict that both Fermi-LAT over the course of its lifetime and the future Cerenkov Telescope Array will be able to detect gamma-ray emission from star-forming galaxies in clusters.

  2. New insights on the formation of nuclear star clusters

    Science.gov (United States)

    Guillard, Nicolas; Emsellem, Eric; Renaud, Florent

    2016-10-01

    Nuclear clusters (NCs) are common stellar systems in the centres of galaxies. Yet, the physical mechanisms involved in their formation are still debated. Using a parsec-resolution hydrodynamical simulation of a dwarf galaxy, we propose an updated formation scenario for NCs. In this `wet migration scenario', a massive star cluster forms in the gas-rich disc, keeping a gas reservoir, and growing further while it migrates to the centre via a combination of interactions with other substructures and dynamical friction. A wet merger with another dense cluster and its own gas reservoir can occur, although this is not a prerequisite for the actual formation of the NC. The merging process does significantly alter the properties of the NC (mass, morphology, star formation history), also quenching the ongoing local star formation activity, thus leading to interesting observational diagnostics for the physical origin of NCs. A population of lower mass clusters co-exist during the simulation, but these are either destroyed via tidal forces, or have high angular momentum preventing them to interact with the NC and contribute to its growth. The proposed updated scenario emphasizes the role of gas reservoirs associated with the densest star clusters formed in a gas-rich low-mass galaxy.

  3. Spatial Clustering from GALEX-SDSS samples: Star Formation History and large-scale clustering

    CERN Document Server

    Heinis, Sebastien; Szalay, A S; Arnouts, Stephane; Aragon-Calvo, Miguel A; Wyder, Ted K; Barlow, Tom A; Foster, Karl; Friedman, Peter G; Martin, D Christopher; Morrissey, Patrick; Neff, Susan G; Schiminovich, David; Seibert, Mark; Bianchi, Luciana; Donas, Jose; Heckman, Timothy M; Lee, Young-Wook; Madore, Barry F; Milliard, Bruno; Rich, R Michael; Yi, Sukyoung K

    2009-01-01

    We measure the projected spatial correlation function w_p(r_p) from a large sample combining GALEX ultraviolet imaging with the SDSS spectroscopic sample. We study the dependence of the clustering strength for samples selected on (NUV - r)_abs color, specific star formation rate (SSFR), and stellar mass. We find that there is a smooth transition in the clustering of galaxies as a function of this color from weak clustering among blue galaxies to stronger clustering for red galaxies. The clustering of galaxies within the "green valley" has an intermediate strength, and is consistent with that expected from galaxy groups. The results are robust to the correction for dust extinction. The comparison with simple analytical modeling suggests that the halo occupation number increases with older star formation epochs. When splitting according to SSFR, we find that the SSFR is a more sensitive tracer of environment than stellar mass.

  4. More Magic Numbers in Anionic Titanium-carbon Mixed Clusters

    Institute of Scientific and Technical Information of China (English)

    ZHAU Huajin; LIU Bingchen; ZHOU Rufang; NI Guoquan

    2000-01-01

    @@ Met-Cars[1] and related transition metal-carbon clusters represent a latest breakthrough in gas phase cluster research following the discovery and macroscopic synthesis of fullerenes. Different kinds of structural growth patterns (SGPs) have been proposed to analyze the observed magic numbers of these transition metal-carbon mixed clusters, including the multicage SGP[2], the nanocrystal SGP[3], and the recent layered SGP[4]. Recording larger magic numbers will be of great help to test and distinguish between the various SGPs.

  5. STAR FORMATION AND RELAXATION IN 379 NEARBY GALAXY CLUSTERS

    Energy Technology Data Exchange (ETDEWEB)

    Cohen, Seth A.; Hickox, Ryan C.; Wegner, Gary A. [Department of Physics and Astronomy, Dartmouth College, 6127 Wilder Laboratory, Hanover, NH 03755 (United States)

    2015-06-10

    We investigate the relationship between star formation (SF) and level of relaxation in a sample of 379 galaxy clusters at z < 0.2. We use data from the Sloan Digital Sky Survey to measure cluster membership and level of relaxation, and to select star-forming galaxies based on mid-infrared emission detected with the Wide-Field Infrared Survey Explorer. For galaxies with absolute magnitudes M{sub r} < −19.5, we find an inverse correlation between SF fraction and cluster relaxation: as a cluster becomes less relaxed, its SF fraction increases. Furthermore, in general, the subtracted SF fraction in all unrelaxed clusters (0.117 ± 0.003) is higher than that in all relaxed clusters (0.097 ± 0.005). We verify the validity of our SF calculation methods and membership criteria through analysis of previous work. Our results agree with previous findings that a weak correlation exists between cluster SF and dynamical state, possibly because unrelaxed clusters are less evolved relative to relaxed clusters.

  6. Star formation in shocked cluster spirals and their tails

    CERN Document Server

    Roediger, E; Owers, M S; Ebeling, H; Sun, M

    2014-01-01

    Recent observations of ram pressure stripped spiral galaxies in clusters revealed details of the stripping process, i.e., the truncation of all interstellar medium (ISM) phases and of star formation (SF) in the disk, and multiphase star-forming tails. Some stripped galaxies, in particular in merging clusters, develop spectacular star-forming tails, giving them a jellyfish-like appearance. In merging clusters, merger shocks in the intra-cluster medium (ICM) are thought to have overrun these galaxies, enhancing the ambient ICM pressure and thus triggering SF, gas stripping and tail formation. We present idealised hydrodynamical simulations of this scenario, including standard descriptions for SF and stellar feedback. To aid the interpretation of recent and upcoming observations, we focus on particular structures and dynamics in SF patterns in the remaining gas disk and in the near tails, which are easiest to observe. The observed jellyfish morphology is qualitatively reproduced for, both, face-on and edge-on st...

  7. Star cluster formation in cosmological simulations. I. properties of young clusters

    CERN Document Server

    Li, Hui; Gnedin, Nickolay Y; Meng, Xi; Semenov, Vadim A; Kravtsov, Andrey V

    2016-01-01

    We present a new implementation of star formation in cosmological simulations, by considering star clusters as a unit of star formation. Cluster particles grow in mass over several million years at the rate determined by local gas properties, with high time resolution. The particle growth is terminated by its own energy and momentum feedback on the interstellar medium. We test this implementation for Milky Way-sized galaxies at high redshift, by comparing the properties of model clusters with observations of young star clusters. We find that the cluster initial mass function is best described by a Schechter function rather than a single power law. In agreement with observations, at low masses the logarithmic slope is $\\alpha\\approx 1.8-2$, while the cutoff at high mass scales with the star formation rate. A related trend is a positive correlation between the surface density of star formation rate and fraction of stars contained in massive clusters. Both trends indicate that the formation of massive star clust...

  8. Formation and evolution of black holes in dense star clusters

    Science.gov (United States)

    Goswami, Sanghamitra

    Using supercomputer simulations combining stellar dynamics and stellar evolution, we have studied various problems related to the existence of black holes in dense star clusters. We consider both stellar and intermediate-mass black holes, and we focus on massive, dense star clusters, such as old globular clusters and young, so called "super star clusters." The first problem concerns the formation of intermediate-mass black holes in young clusters through the runaway collision instability. A promising mechanism to form intermediate-mass black holes (IMBHs) is runaway mergers in dense star clusters, where main-sequence stars collide re- peatedly and form a very massive star (VMS), which then collapses to a black hole (BH). Here we study the effects of primordial mass segregation and the importance of the stellar initial mass function (IMF) on the runaway growth of VMSs using a dynamical Monte Carlo code to model systems with N as high as 10^6 stars. Our Monte Carlo code includes an explicittreatment of all stellar collisions. We place special emphasis on the possibility of top-heavy IMFs, as observed in some very young massive clusters. We find that both primordial mass segregation and the shape of the IMF affect the rate of core collapse of star clusters and thus the time of the runaway. When we include primordial mass segregation we generally see a decrease in core collapse time (tcc). Although for smaller degrees of primordial mass segregation this decrease in tcc is mostly due to the change in the density profile of the cluster, for highly mass-segregated (primordial) clusters, it is the increase in the average mass in the core which reduces the central relaxation time, decreasing tcc. Finally, flatter IMFs generally increase the average mass in the whole cluster, which increases tcc. For the range of IMFs investigated in this thesis, this increase in tcc is to some degree balanced by stellar collisions, which accelerate core collapse. Thus there is no

  9. SMBH Formation via Gas Accretion in Nuclear Stellar Clusters

    CERN Document Server

    Davies, Melvyn B; Bellovary, Jillian M

    2011-01-01

    Black holes exceeding a billion solar masses have been detected at redshifts greater than six. The rapid formation of these objects may suggest a massive early seed or a period of growth faster than Eddington. Here we suggest a new mechanism along these lines. We propose that in the process of hierarchical structure assembly, dense star clusters can be contracted on dynamical time scales due to the nearly free-fall inflow of self-gravitating gas with a mass comparable to or larger than that of the clusters. This increases the velocity dispersion to the point that the few remaining hard binaries can no longer effectively heat the cluster, and the cluster goes into a period of homologous core collapse. The cluster core can then reach a central density high enough for fast mergers of stellar-mass black holes and hence the rapid production of a black hole seed that could be $10^5 M_\\odot$ or larger.

  10. Growth of chiral single-walled carbon nanotube caps in the presence of a cobalt cluster

    Energy Technology Data Exchange (ETDEWEB)

    Gomez-Gualdron, Diego A; Balbuena, Perla B [Department of Chemical Engineering, Texas A and M University, College Station, TX 77843 (United States)], E-mail: balbuena@tamu.edu

    2009-05-27

    Density functional theory is used to simulate nanotube growth by addition of a pair of carbon atoms to a composite chiral nanotube cap/cobalt cluster system, with caps corresponding to near-armchair (6, 5), (7, 5) and near-zigzag (9, 1) nanotubes. Two different carbon addition processes are evaluated: in the first, the new carbon atoms are located in the vicinity of the armchair site of the cap rim, and thus this process provides insight into the root-growth mechanism; in the second the carbon atoms are initially located under the cobalt cluster, and thus this process helps one to evaluate the dissolution of carbon inside the metal cluster. The geometric evolution and energetics of the system are used to explain features of the mechanism of nanotube growth. The root-growth reaction is shown to occur by displacement of a cobalt atom initially interacting with the armchair site while the added carbon atoms bond to each other forming a new hexagonal ring, whereas the carbon dissolution process shows formation of dimers inside the cluster only for the (6, 5) system. The energetics for both steps reveals that the dissolution stage is probably controlling the overall nanotube growth rate.

  11. Growth of chiral single-walled carbon nanotube caps in the presence of a cobalt cluster.

    Science.gov (United States)

    Gómez-Gualdrón, Diego A; Balbuena, Perla B

    2009-05-27

    Density functional theory is used to simulate nanotube growth by addition of a pair of carbon atoms to a composite chiral nanotube cap/cobalt cluster system, with caps corresponding to near-armchair (6, 5), (7, 5) and near-zigzag (9, 1) nanotubes. Two different carbon addition processes are evaluated: in the first, the new carbon atoms are located in the vicinity of the armchair site of the cap rim, and thus this process provides insight into the root-growth mechanism; in the second the carbon atoms are initially located under the cobalt cluster, and thus this process helps one to evaluate the dissolution of carbon inside the metal cluster. The geometric evolution and energetics of the system are used to explain features of the mechanism of nanotube growth. The root-growth reaction is shown to occur by displacement of a cobalt atom initially interacting with the armchair site while the added carbon atoms bond to each other forming a new hexagonal ring, whereas the carbon dissolution process shows formation of dimers inside the cluster only for the (6, 5) system. The energetics for both steps reveals that the dissolution stage is probably controlling the overall nanotube growth rate.

  12. The Peculiarities of Cluster Formation in the Russian Nanotechnology Industry

    Directory of Open Access Journals (Sweden)

    Kurchenkov Vladimir Viktorovich

    2015-05-01

    Full Text Available The innovative development of the Russian economy in modern conditions should be based on the development of advanced nanotechnology. The formation of the nanotechnology industry in Russia requires optimal organization, the development of networking, the search for new forms of integrating the primary and secondary productions. The cluster organization in nanotech industry is based on high-tech production and has a number of advantages: uncertainty elimination, restriction of the competition by monopolization of supply with raw materials and semi-finished products, improvement of quality and decrease in expenses. The main forms of interaction of the enterprises and organizations which are a part of a nanoindustrial cluster are allocated. The article describes the peculiarities of the Russian nanoidustry formation, determines the significance of the cluster policy in this sphere. The author develops the criteria for identifying the nanoclusters on the basis of the basic nanotechnology and the nomenclature of final product. The author also proposes the approach to the analysis of cluster interaction and determines the boundaries of the cluster based on the difference between system and quasisystem cluster interaction. In this regard it is necessary to consider possibilities of the analysis of both system, and quasisystem interaction of the main participants of a nanoindustrial cluster.

  13. Panchromatic Hubble Andromeda Treasury. XVI. Star Cluster Formation Efficiency and the Clustered Fraction of Young Stars

    Science.gov (United States)

    Johnson, L. Clifton; Seth, Anil C.; Dalcanton, Julianne J.; Beerman, Lori C.; Fouesneau, Morgan; Lewis, Alexia R.; Weisz, Daniel R.; Williams, Benjamin F.; Bell, Eric F.; Dolphin, Andrew E.; Larsen, Søren S.; Sandstrom, Karin; Skillman, Evan D.

    2016-08-01

    We use the Panchromatic Hubble Andromeda Treasury survey data set to perform spatially resolved measurements of star cluster formation efficiency (Γ), the fraction of stellar mass formed in long-lived star clusters. We use robust star formation history and cluster parameter constraints, obtained through color-magnitude diagram analysis of resolved stellar populations, to study Andromeda’s cluster and field populations over the last ˜300 Myr. We measure Γ of 4%-8% for young, 10-100 Myr-old populations in M31. We find that cluster formation efficiency varies systematically across the M31 disk, consistent with variations in mid-plane pressure. These Γ measurements expand the range of well-studied galactic environments, providing precise constraints in an H i-dominated, low-intensity star formation environment. Spatially resolved results from M31 are broadly consistent with previous trends observed on galaxy-integrated scales, where Γ increases with increasing star formation rate surface density (ΣSFR). However, we can explain observed scatter in the relation and attain better agreement between observations and theoretical models if we account for environmental variations in gas depletion time (τ dep) when modeling Γ, accounting for the qualitative shift in star formation behavior when transitioning from a H2-dominated to a H i-dominated interstellar medium. We also demonstrate that Γ measurements in high ΣSFR starburst systems are well-explained by τ dep-dependent fiducial Γ models.

  14. Is acetylene essential for carbon dust formation?

    CERN Document Server

    Dhanoa, Harpreet

    2013-01-01

    We have carried out an investigation of the chemical evolution of gas in different carbon-rich circumstellar environments. Previous studies have tended to invoke terrestrial flame chemistries, based on acetylene (C2H2) combustion to model the formation of carbon dust, via Polycyclic Aromatic Hydrocarbons (PAHs). In this work we pay careful attention to the accurate calculation of the molecular photoreaction rate coefficients to ascertain whether there is a universal formation mechanism for carbon dust in strongly irradiated astrophysical environments. A large number of possible chemical channels may exist for the formation of PAHs, so we have concentrated on the viability of the formation of the smallest building block species, C2H2, in a variety of carbon-rich stellar outflows. C2H2 is very sensitive to dissociation by UV radiation. This sensitivity is tested, using models of the time-dependent chemistry. We find that C2H2 formation is sensitive to some of the physical parameters and that in some known sourc...

  15. Detecting Star Formation in Brightest Cluster Galaxies with GALEX

    CERN Document Server

    Hicks, Amalia; Donahue, Megan

    2010-01-01

    We present the results of GALEX observations of 17 cool core (CC) clusters of galaxies. We show that GALEX is easily capable of detecting star formation in brightest cluster galaxies (BCGs) out to $z\\ge 0.45$ and 50-100 kpc. In most of the CC clusters studied, we find significant UV luminosity excesses and colors that strongly suggest recent and/or current star formation. The BCGs are found to have blue UV colors in the center that become increasingly redder with radius, indicating that the UV signature of star formation is most easily detected in the central regions. Our findings show good agreement between UV star formation rates and estimates based on H$\\alpha$ observations. IR observations coupled with our data indicate moderate-to-high dust attenuation. Comparisons between our UV results and the X-ray properties of our sample suggest clear correlations between UV excess, cluster entropy, and central cooling time, confirming that the star formation is directly and incontrovertibly related to the cooling g...

  16. New insights on the formation of nuclear star clusters

    CERN Document Server

    Guillard, Nicolas; Renaud, Florent

    2016-01-01

    Nuclear Clusters (NCs) are common stellar systems in the centres of galaxies. Yet, the physical mechanisms involved in their formation are still debated. Using a parsec-resolution hydrodynamical simulation of a dwarf galaxy, we propose an updated formation scenario for NCs. In this 'wet migration scenario', a massive star cluster forms in the gas-rich disc, keeping a gas reservoir, and growing further while it migrates to the centre via a combination of interactions with other substructures and dynamical friction. A wet merger with another dense cluster and its own gas reservoir can occur, although this is not a pre-requisite for the actual formation of the NC. The merging process does significantly alter the properties of the NC (mass, morphology, star formation history), also quenching the on-going local star formation activity, thus leading to interesting observational diagnostics for the physical origin of NCs. A population of lower mass clusters co-exist during the simulation, but these are either destro...

  17. Sulfur(IV)-mediated carbon-carbon bond formation

    OpenAIRE

    Dean, William Michael

    2016-01-01

    This thesis details the development of methods for and application of the synthesis of carbon carbon bonds using organic sulfur(IV) chemistry. More specifically, the formation of C(sp2) C(sp3) and C(sp3) C(sp3) bonds is explored in detail. The necessity for this research stems from a correlation between a high proportion of sp3 centres in drug candidates, and their success in clinical trials. By facilitating the synthesis of drug candidates with higher fractions of sp3 hybridised carbon atoms...

  18. He cluster dynamics in W in the presence of cluster induced formation of He traps

    Science.gov (United States)

    Krasheninnikov, S. I.; Smirnov, R. D.

    2016-02-01

    The theoretical model describing spatiotemporal dynamics of He clusters in tungsten, which takes into account He trap generation associated with the growth of He clusters, is presented. Application of this model to the formation of the layer of nano-bubbles underneath of the surface of thick He irradiated sample, before surface morphology starts to change, gives very good agreement with currently available experimental data. The role of thermophoresis in a long-term evolution of nano-bubble containing structures is discussed.

  19. Star Formation and Supercluster Environment of 107 nearby Galaxy Clusters

    Science.gov (United States)

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

    2017-01-01

    We analyze the relationship between star formation (SF), substructure, and supercluster environment in a sample of 107 nearby galaxy clusters using data from the Sloan Digital Sky Survey. Previous works have investigated the relationships between SF and cluster substructure, and cluster substructure and supercluster environment, but definitive conclusions relating all three of these variables has remained elusive. We find an inverse relationship between cluster SF fraction (fSF) and supercluster environment density, calculated using the Galaxy luminosity density field at a smoothing length of 8 h‑1 Mpc (D8). The slope of fSF versus D8 is ‑0.008 ± 0.002. The fSF of clusters located in low-density large-scale environments, 0.244 ± 0.011, is higher than for clusters located in high-density supercluster cores, 0.202 ± 0.014. We also divide superclusters, according to their morphology, into filament- and spider-type systems. The inverse relationship between cluster fSF and large-scale density is dominated by filament- rather than spider-type superclusters. In high-density cores of superclusters, we find a higher fSF in spider-type superclusters, 0.229 ± 0.016, than in filament-type superclusters, 0.166 ± 0.019. Using principal component analysis, we confirm these results and the direct correlation between cluster substructure and SF. These results indicate that cluster SF is affected by both the dynamical age of the cluster (younger systems exhibit higher amounts of SF); the large-scale density of the supercluster environment (high-density core regions exhibit lower amounts of SF); and supercluster morphology (spider-type superclusters exhibit higher amounts of SF at high densities).

  20. Fragmentation energetics of clusters relevant to atmospheric new particle formation.

    Science.gov (United States)

    Bzdek, Bryan R; DePalma, Joseph W; Ridge, Douglas P; Laskin, Julia; Johnston, Murray V

    2013-02-27

    The exact mechanisms by which small clusters form and grow in the atmosphere are poorly understood, but this process may significantly impact cloud condensation nuclei number concentrations and global climate. Sulfuric acid is the key chemical component to new particle formation (NPF), but basic species such as ammonia are also important. Few laboratory experiments address the kinetics or thermodynamics of acid and base incorporation into small clusters. This work utilizes a Fourier transform ion cyclotron resonance mass spectrometer equipped with surface-induced dissociation to investigate time- and collision-energy-resolved fragmentation of positively charged ammonium bisulfate clusters. Critical energies for dissociation are obtained from Rice-Ramsperger-Kassel-Marcus/quasi-equilibrium theory modeling of the experimental data and are compared to quantum chemical calculations of the thermodynamics of cluster dissociation. Fragmentation of ammonium bisulfate clusters occurs by two pathways: (1) a two-step pathway whereby the cluster sequentially loses ammonia followed by sulfuric acid and (2) a one-step pathway whereby the cluster loses an ammonium bisulfate molecule. Experimental critical energies for loss of an ammonia molecule and loss of an ammonium bisulfate molecule are higher than the thermodynamic values. If cluster growth is considered the reverse of cluster fragmentation, these results require the presence of an activation barrier to describe the incorporation of ammonia into small acidic clusters and suggest that kinetically (i.e., diffusion) limited growth should not be assumed. An important corollary is that models of atmospheric NPF should be revised to consider activation barriers to individual chemical steps along the growth pathway.

  1. Fragmentation Energetics of Clusters Relevant to Atmospheric New Particle Formation

    Energy Technology Data Exchange (ETDEWEB)

    Bzdek, Bryan R.; Depalma, Joseph W.; Ridge, Douglas P.; Laskin, Julia; Johnston, Murray V.

    2013-02-27

    The exact mechanisms by which small clusters form and grow in the atmosphere are poorly understood, but this process may significantly impact cloud condensation nuclei number concentrations and global climate. Sulfuric acid is the key chemical component to new particle formation, but basic species such as ammonia are also important. However, few laboratory experiments address the kinetics or thermodynamics of acid and base incorporation into small clusters. This work utilizes a Fourier transform ion cyclotron resonance mass spectrometer equipped with surface-induced dissociation (FTICR-SID) to investigate time- and collision energy-resolved fragmentation of positively charged ammonium bisulfate clusters. Critical energies for dissociation are obtained from Rice-Ramsperger-Kassel-Marcus/Quasi-Equilibrium Theory (RRKM/QET) modeling of the experimental data and are compared to quantum chemical calculations of the thermodynamics of cluster dissociation. Fragmentation of ammonium bisulfate clusters occurs by two pathways: 1) a two-step pathway whereby the cluster sequentially loses ammonia followed by sulfuric acid and 2) a one-step pathway whereby the cluster loses an ammonium bisulfate molecule. Experimental critical energies for loss of an ammonia molecule and loss of an ammonium bisulfate molecule are higher than the thermodynamic values. If cluster growth is considered the reverse of cluster fragmentation, these results require the presence of an activation barrier to describe the incorporation of ammonia into small acidic clusters and suggest that kinetically (i.e. diffusion) limited growth should not be assumed. An important corollary is that models of atmospheric NPF should be revised to consider activation barriers to individual chemical steps along the growth pathway.

  2. Turbulence and Vorticity in Galaxy Clusters Generated by Structure Formation

    CERN Document Server

    Vazza, F; Brüggen, M; Brunetti, G; Gheller, C; Porter, D; Ryu, D

    2016-01-01

    Turbulence is a key ingredient for the evolution of the intracluster medium, whose properties can be predicted with high resolution numerical simulations. We present initial results on the generation of solenoidal and compressive turbulence in the intracluster medium during the formation of a small-size cluster using highly resolved, non-radiative cosmological simulations, with a refined monitoring in time. In this first of a series of papers, we closely look at one simulated cluster whose formation was distinguished by a merger around $z \\sim 0.3$. We separate laminar gas motions, turbulence and shocks with dedicated filtering strategies and distinguish the solenoidal and compressive components of the gas flows using Hodge-Helmholtz decomposition. Solenoidal turbulence dominates the dissipation of turbulent motions ($\\sim 95\\%$) in the central cluster volume at all epochs. The dissipation via compressive modes is found to be more important ($\\sim 30 \\%$ of the total) only at large radii ($\\geq 0.5 ~r_{\\rm vi...

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

    Directory of Open Access Journals (Sweden)

    Lorenzo Lovisari

    2013-12-01

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

  4. Formation and Stability of High-Spin Alkali Clusters

    Science.gov (United States)

    Schulz, C. P.; Claas, P.; Schumacher, D.; Stienkemeier, F.

    2004-01-01

    Helium nanodroplet isolation has been applied to agglomerate alkali clusters at temperatures of 380mK. The very weak binding to the surface of the droplets allows a selection of only weakly bound, high-spin states. Here we show that larger clusters of alkali atoms in high-spin states can be formed. The lack of strong bonds from pairing electrons makes these systems nonmetallic, vanderWaals like complexes of metal atoms. We find that sodium and potassium readily form such clusters containing up to 25atoms. In contrast, this process is suppressed for rubidium and cesium. Apparently, for these heavy alkalis, larger high-spin aggregates are not stable and depolarize spontaneously upon cluster formation.

  5. Linked supramolecular building blocks for enhanced cluster formation

    DEFF Research Database (Denmark)

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

    2015-01-01

    (Figure Presented). Methylene-bridged calix[4]arenes have emerged as extremely versatile ligand supports in the formation of new polymetallic clusters possessing fascinating magnetic properties. Metal ion binding rules established for this building block allow one to partially rationalise the com...

  6. The formation of acetylcholine receptor clusters visualized with quantum dots

    Directory of Open Access Journals (Sweden)

    Peng H Benjamin

    2009-07-01

    Full Text Available Abstract Background Motor innervation of skeletal muscle leads to the assembly of acetylcholine receptor (AChR clusters in the postsynaptic membrane at the vertebrate neuromuscular junction (NMJ. Synaptic AChR aggregation, according to the diffusion-mediated trapping hypothesis, involves the establishment of a postsynaptic scaffold that "traps" freely diffusing receptors into forming high-density clusters. Although this hypothesis is widely cited to explain the formation of postsynaptic AChR clusters, direct evidence at molecular level is lacking. Results Using quantum dots (QDs and live cell imaging, we provide new measurements supporting the diffusion-trap hypothesis as applied to AChR cluster formation. Consistent with published works, experiments on cultured Xenopus myotomal muscle cells revealed that AChRs at clusters that formed spontaneously (pre-patterned clusters, also called hot spots and at those induced by nerve-innervation or by growth factor-coated latex beads were very stable whereas diffuse receptors outside these regions were mobile. Moreover, despite the restriction of AChR movement at sites of synaptogenic stimulation, individual receptors away from these domains continued to exhibit free diffusion, indicating that AChR clustering at NMJ does not involve an active attraction of receptors but is passive and diffusion-driven. Conclusion Single-molecular tracking using QDs has provided direct evidence that the clustering of AChRs in muscle cells in response to synaptogenic stimuli is achieved by two distinct cellular processes: the Brownian motion of receptors in the membrane and their trapping and immobilization at the synaptic specialization. This study also provides a clearer picture of the "trap" that it is not a uniformly sticky area but consists of discrete foci at which AChRs are immobilized.

  7. Theory of cluster radioactive decay and of cluster formation in nuclei

    Science.gov (United States)

    Malik, S. S.; Gupta, Raj K.

    1989-05-01

    A new model is proposed for the mechanism of cluster formation and then penetration of the confining nuclear interaction barrier in radioactive nuclei. The cluster formation is treated as a quantum-mechanical fragmentation process and the WKB penetrability is found analytically. Applications of the model are made to 14C decay of 222-224Ra and 24Ne decay of 232U. The branching ratio for 14C decay of 232U is also calculated and is found to be incredibly small as compared to that for its 24Ne decay.

  8. Formation of Very Young Massive Clusters and implications for globular clusters

    CERN Document Server

    Banerjee, Sambaran

    2015-01-01

    How Very Young Massive star Clusters (VYMCs; also known as "starburst" clusters), which typically are of $\\gtrsim 10^4M_\\odot$ and are a few Myr old, form out of Giant Molecular Clouds is still largely an open question. Increasingly detailed observations of young star clusters and star-forming molecular clouds and computational studies provide clues about their formation scenarios and the underlying physical processes involved. This chapter is focused on reviewing the decade-long studies that attempt to computationally reproduce the well-observed nearby VYMCs, such as the Orion Nebula Cluster, R136 and NGC 3603 young cluster, thereby shedding light on birth conditions of massive star clusters, in general. On this regard, focus is given on direct N-body modeling of real-sized massive star clusters, with a monolithic structure and undergoing residual gas expulsion, which have consistently reproduced the observed characteristics of several VYMCs and also of young star clusters, in general. The connection of thes...

  9. Numerical simulation of primary cluster formation in silane plasmas

    CERN Document Server

    Gupta, N; Kroesen, G

    2003-01-01

    The usage of low-cost silicon-based solar cells is limited by their tendency to degrade on prolonged exposure to sunlight. Current research has indicated that the inclusion of nano-particles in the plasma-deposited film enhances its efficiency considerably. It is therefore essential to identify the plasma operating conditions such that nano-particles are formed and deposited in the film. The early stages of cluster formation, nucleation and coagulation are still open to experimental and theoretical investigation. In this paper, a simulation of the first stage of particle formation in capacitively coupled radio-frequency discharges in SiH sub 4 is attempted. A molecular dynamics based model has been set up to simulate one of the principal reaction pathways in cluster formation. This simulation model appears to produce valid and meaningful trends. Further studies are planned to explore the effect of other parameters and alternate pathways.

  10. Numerical simulation of primary cluster formation in silane plasmas

    Science.gov (United States)

    Gupta, Nandini; Stoffels, W. W.; Kroesen, G. M. W.

    2003-04-01

    The usage of low-cost silicon-based solar cells is limited by their tendency to degrade on prolonged exposure to sunlight. Current research has indicated that the inclusion of nano-particles in the plasma-deposited film enhances its efficiency considerably. It is therefore essential to identify the plasma operating conditions such that nano-particles are formed and deposited in the film. The early stages of cluster formation, nucleation and coagulation are still open to experimental and theoretical investigation. In this paper, a simulation of the first stage of particle formation in capacitively coupled radio-frequency discharges in SiH4 is attempted. A molecular dynamics based model has been set up to simulate one of the principal reaction pathways in cluster formation. This simulation model appears to produce valid and meaningful trends. Further studies are planned to explore the effect of other parameters and alternate pathways.

  11. Star formation in the massive cluster merger Abell 2744

    CERN Document Server

    Rawle, T D; Egami, E; Perez-Gonzalez, P G; Richard, J; Santos, J S; Valtchanov, I; Walth, G; Bouy, H; Haines, C P; Okabe, N

    2014-01-01

    We present a comprehensive study of star-forming (SF) galaxies in the HST Frontier Field recent cluster merger A2744 (z=0.308). Wide-field, ultraviolet-infrared (UV-IR) imaging enables a direct constraint of the total star formation rate (SFR) for 53 cluster galaxies, with SFR{UV+IR}=343+/-10 Msun/yr. Within the central 4 arcmin (1.1 Mpc) radius, the integrated SFR is complete, yielding a total SFR{UV+IR}=201+/-9 Msun/yr. Focussing on obscured star formation, this core region exhibits a total SFR{IR}=138+/-8 Msun/yr, a mass-normalised SFR{IR} of Sigma{SFR}=11.2+/-0.7 Msun/yr per 10^14 Msun and a fraction of IR-detected SF galaxies f{SF}=0.080(+0.010,-0.037). Overall, the cluster population at z~0.3 exhibits significant intrinsic scatter in IR properties (total SFR{IR}, Tdust distribution) apparently unrelated to the dynamical state: A2744 is noticeably different to the merging Bullet cluster, but similar to several relaxed clusters. However, in A2744 we identify a trail of SF sources including jellyfish galax...

  12. Implications for the formation of star clusters from extra-galactic star-formation rates

    CERN Document Server

    Weidner, C; Larsen, S S

    2004-01-01

    Observations indicate that young massive star clusters in spiral and dwarf galaxies follow a relation between luminosity of the brightest young cluster and the star-formation rate (SFR) of the host galaxy, in the sense that higher SFRs lead to the formation of brighter clusters. Assuming that the empirical relation between maximum cluster luminosity and SFR reflects an underlying similar relation between maximum cluster mass (M_ecl,max) and SFR, we compare the resulting SFR(M_ecl,max) relation with different theoretical models. The empirical correlation is found to suggest that individual star clusters form on a free-fall time-scale with their pre-cluster molecular-cloud-core radii typically being a few pc independent of mass. The cloud cores contract by factors of 5 to 10 while building-up the embedded cluster. A theoretical SFR(M_ecl,max) relation in very good agreement with the empirical correlation is obtained if the cluster mass function of a young population has a Salpeter exponent beta approx. 2.35 and...

  13. Formation of Carbonic Acid in Impact of CO2 on Ice and Water.

    Science.gov (United States)

    Hirshberg, Barak; Gerber, R Benny

    2016-08-01

    A new mode of formation is proposed for carbonic acid in the atmosphere. It involves impact of vibrationally excited gas-phase CO2 molecules on water or ice particles. This is a first mechanism that supports formation on ice as well as on liquid water surfaces. Results of ab initio molecular dynamics simulations are presented on collisions of CO2 with (H2O)n clusters (n = 1, 4, 8, 12). Efficient formation of carbonic acid is seen with product lifetimes exceeding 100 ps. The reaction is feasible even for collision of CO2 with a single water molecule but in a different mechanism than for larger clusters. For clusters, the transition state shows charge separation into H3O(+)···HCO3(-), which transforms into neutral carbonic acid as the product, hydrated by the remaining waters. Possible atmospheric implications of the results are discussed.

  14. The formation and evolution of star clusters in interacting galaxies

    CERN Document Server

    Maji, Moupiya; Li, Yuexing; Charlton, Jane; Hernquist, Lars; Knebe, Alexander

    2016-01-01

    Observations of globular clusters show that they have universal lognormal mass functions with a characteristic peak at $\\sim 2\\times 10^{5}\\, {\\rm{M_{\\odot}}}$, but the origin of this peaked distribution is highly debated. Here we investigate the formation and evolution of star clusters in interacting galaxies using high-resolution hydrodynamical simulations performed with two different codes in order to mitigate numerical artifacts. We find that massive star clusters in the range of $\\sim 10^{5.5} - 10^{7.5}\\, {\\rm{M_{\\odot}}}$ form preferentially in the highly-shocked regions produced by galaxy interactions. The nascent cluster-forming clouds have high gas pressures in the range of $P/k \\sim 10^8 - 10^{12}\\, \\rm{K}\\,\\rm{cm^{-3}}$, which is $\\sim 10^4 - 10^8$ times higher than the typical pressure of the interstellar medium but consistent with recent observations of a pre-super star cluster cloud in the Antennae Galaxies. Furthermore, these massive star clusters have quasi-lognormal initial mass functions wi...

  15. Formation and characterization of thioglycolic acid-silver cluster complexes.

    Science.gov (United States)

    Bellina, Bruno; Antoine, Rodolphe; Broyer, Michel; Gell, Lars; Sanader, Željka; Mitrić, Roland; Bonačić-Koutecký, Vlasta; Dugourd, Philippe

    2013-06-21

    Gas phase reactivity observed in an ion trap was used to produce silver clusters protected with thioglycolic acid. Fragmentation pathways as well as optical properties were explored experimentally and theoretically. Sequential losses of SCH2 and CO2 in the ion trap lead to redox reactions with charge transfers between the metal part and the carboxylate and thiolate groups. This allows us to control the number of electrons in the metallic subunit and thus optical properties of the complexes. The presented formation process can be used as a prototype for tuning optical and chemical properties of ligated metal clusters by varying the number of confined electrons within the metallic subunit.

  16. Star Formation and Chemical Enrichment for Globular Clusters

    Institute of Scientific and Technical Information of China (English)

    林清; 束成钢; 常瑞香; 赵君亮

    2001-01-01

    A model considering gas outflows due to supernova explosions is developed for the star formation and chemical enrichment for the globular clusters (GCs) in the Milky Way galaxy. Through Monte Carlo simulations, the observed global properties of GCs can be well reproduced, including the metallicity distribution, no-correlation between cluster masses and galactocentric distances, etc. The predicted mass function of the parent clouds for the observed GCs at present day can be well described as a power law with the index of-1.8, which is consistent with the current observations for the molecular clouds.

  17. STAR FORMATION ACTIVITY IN CLASH BRIGHTEST CLUSTER GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Fogarty, Kevin [Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); Postman, Marc [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Connor, Thomas; Donahue, Megan [Physics and Astronomy Dept., Michigan State University, East Lansing, MI 48824 (United States); Moustakas, John [Department of Physics and Astronomy, Siena College, 515 Loudon Road, Loudonville, NY 12211 (United States)

    2015-11-10

    The CLASH X-ray selected sample of 20 galaxy clusters contains 10 brightest cluster galaxies (BCGs) that exhibit significant (>5σ) extinction-corrected star formation rates (SFRs). Star formation activity is inferred from photometric estimates of UV and Hα+[N ii] emission in knots and filaments detected in CLASH Hubble Space Telescope ACS and WFC3 observations. UV-derived SFRs in these BCGs span two orders of magnitude, including two with a SFR ≳ 100 M{sub ⊙} yr{sup −1}. These measurements are supplemented with [O ii], [O iii], and Hβ fluxes measured from spectra obtained with the SOAR telescope. We confirm that photoionization from ongoing star formation powers the line emission nebulae in these BCGs, although in many BCGs there is also evidence of a LINER-like contribution to the line emission. Coupling these data with Chandra X-ray measurements, we infer that the star formation occurs exclusively in low-entropy cluster cores and exhibits a correlation with gas properties related to cooling. We also perform an in-depth study of the starburst history of the BCG in the cluster RXJ1532.9+3021, and create 2D maps of stellar properties on scales down to ∼350 pc. These maps reveal evidence for an ongoing burst occurring in elongated filaments, generally on ∼0.5–1.0 Gyr timescales, although some filaments are consistent with much younger (≲100 Myr) burst timescales and may be correlated with recent activity from the active galactic nucleus. The relationship between BCG SFRs and the surrounding intracluster medium gas properties provide new support for the process of feedback-regulated cooling in galaxy clusters and is consistent with recent theoretical predictions.

  18. Starbursts versus Truncated Star Formation in Nearby Clusters of Galaxies

    CERN Document Server

    Rose, J A; Caldwell, N; Chaboyer, B; Rose, James A.; Gaba, Alejandro E.; Caldwell, Nelson; Chaboyer, Brian

    2001-01-01

    We present long-slit spectroscopy, B and R bandpass imaging, and 21 cm observations of a sample of early-type galaxies in nearby clusters which are known to be either in a star-forming phase or to have had star formation which recently terminated. From the long-slit spectra, obtained with the Blanco 4-m telescope, we find that emission lines in the star-forming cluster galaxies are significantly more centrally concentrated than in a sample of field galaxies. The broadband imaging reveals that two currently star-forming early-type galaxies in the Pegasus I cluster have blue nuclei, again indicating that recent star formation has been concentrated. In contrast, the two galaxies for which star formation has already ended show no central color gradient. The Pegasus I galaxy with the most evident signs of ongoing star formation (NGC7648), exhibits signatures of a tidal encounter. Neutral hydrogen observations of that galaxy with the Arecibo radiotelescope reveal the presence of ~4 x 10^8 solar masses of HI. Arecib...

  19. Formation of globular clusters induced by external ultraviolet radiation

    CERN Document Server

    Hasegawa, Kenji; Kitayama, Tetsu

    2009-01-01

    We present a novel scenario for globular cluster (GC) formation, where the ultraviolet (UV) background radiation effectively works so as to produce compact star clusters. Here, we explore the formation of GCs in UV radiation fields. For this purpose, we calculate baryon and dark matter (DM) dynamics in spherical symmetry, incorporating the self-shielding effects by solving the radiative transfer of UV radiation. In addition, we prescribe the star formation in cooled gas components and pursue the dynamics of formed stars. As a result, we find that the evolution of subgalactic objects in UV background radiation are separated into three types, that is, (1) prompt star formation, where less massive clouds ~10^{5-8} M_sun are promptly self-shielded and undergo star formation, (2) delayed star formation, where photoionized massive clouds >10^8 M_sun collapse despite high thermal pressure and are eventually self-shielded to form stars in a delayed fashion, and (3) supersonic infall, where photoionized less massive c...

  20. Formation of stars and clusters over cosmological time

    CERN Document Server

    Elmegreen, Bruce G

    2014-01-01

    The concept that stars form in the modern era began some 60 years ago with the key observation of expanding OB associations. Now we see that these associations are an intermediate scale in a cascade of hierarchical structures that begins on the ambient Jeans length close to a kiloparsec in size and continues down to the interiors of clusters, perhaps even to binary and multiple stellar systems. The origin of this structure lies with the dynamical nature of cloud and star formation, driven by supersonic turbulence and interstellar gravity. Dynamical star formation is relatively fast compared to the timescale for cosmic accretion, and then the star formation rate keeps up with the accretion rate, leading to a sequence of near-equilibrium states during galaxy formation and evolution. Dynamical star formation also helps to explain the formation of bound clusters, which require a local efficiency that exceeds the average by more than an order of magnitude. Efficiency increases with density in a hierarchically stru...

  1. Galaxy and cluster formation in a neutrino universe

    Energy Technology Data Exchange (ETDEWEB)

    Doroshkevich, A.G.

    1984-07-01

    Analysis of 27 clusters of galaxies indicates that about 90% of the mass is hidden in neutrinos; the member galaxies account for (5--7)%, and (3--5)% comprises hot gas of very high entropy. Comparison of the cluster parameters against those of the primordial neutrino--gaseous ''pancakes'' yields an estimate for the redshift when the pancakes originally formed. A model is proposed for the ensuing pancake evolution: early supernovae would explode and further heat the pancake gas that has not yet cooled, raising its entropy to the values observed. The strong flows induced in the gas by the explosions would dictate the subsequent, galaxy-formation process and the observed supercluster structure: the mass distribution of the member galaxies and their correlation function. Only large-scale objects (superclusters, clusters) preserve information on the spectrum of the initial fluctuations.

  2. Cosmological MHD simulations of cluster formation with anisotropic thermal conduction

    CERN Document Server

    Ruszkowski, M; Bruggen, M; Parrish, I; Oh, S Peng

    2010-01-01

    (abridged) The ICM has been suggested to be buoyantly unstable in the presence of magnetic field and anisotropic thermal conduction. We perform first cosmological simulations of galaxy cluster formation that simultaneously include magnetic fields, radiative cooling and anisotropic thermal conduction. In isolated and idealized cluster models, the magnetothermal instability (MTI) tends to reorient the magnetic fields radially. Using cosmological simulations of the Santa Barbara cluster we detect radial bias in the velocity and magnetic fields. Such radial bias is consistent with either the inhomogeneous radial gas flows due to substructures or residual MTI-driven field rearangements that are expected even in the presence of turbulence. Although disentangling the two scenarios is challenging, we do not detect excess bias in the runs that include anisotropic thermal conduction. The anisotropy effect is potentially detectable via radio polarization measurements with LOFAR and SKA and future X-ray spectroscopic stu...

  3. Quenching of the star formation activity in cluster galaxies

    Science.gov (United States)

    Boselli, A.; Roehlly, Y.; Fossati, M.; Buat, V.; Boissier, S.; Boquien, M.; Burgarella, D.; Ciesla, L.; Gavazzi, G.; Serra, P.

    2016-11-01

    We study the star formation quenching mechanism in cluster galaxies by fitting the spectral energy distribution (SED) of the Herschel Reference Survey, a complete volume-limited K-band-selected sample of nearby galaxies including objects in different density regions, from the core of the Virgo cluster to the general field. The SEDs of the target galaxies were fitted using the CIGALE SED modelling code. The truncated activity of cluster galaxies was parametrised using a specific star formation history with two free parameters, the quenching age QA and the quenching factor QF. These two parameters are crucial for the identification of the quenching mechanism, which acts on long timescales when starvation processes are at work, but is rapid and efficient when ram pressure occurs. To be sensitive to an abrupt and recent variation of the star formation activity, we combined twenty photometric bands in the UV to far-infrared in a new way with three age-sensitive Balmer line absorption indices extracted from available medium-resolution (R 1000) integrated spectroscopy and with Hα narrow-band imaging data. The use of a truncated star formation history significantly increases the quality of the fit in HI-deficient galaxies of the sample, that is to say, in those objects whose atomic gas content has been removed during the interaction with the hostile cluster environment. The typical quenching age of the perturbed late-type galaxies is QA ≲ 300 Myr whenever the activity of star formation is reduced by 50% 80%, while that of the quiescent early-type objects is QA ≃ 1-3 Gyr. The fraction of late-type galaxies with a star formation activity reduced by QF > 80% and with an HI-deficiency parameter HI-def > 0.4 drops by a factor of 5 from the inner half virial radius of the Virgo cluster (R/Rvir 4). The efficient quenching of the star formation activity observed in Virgo suggests that the dominant stripping process is ram pressure. We discuss the implication of this result in

  4. Star Cluster Formation from Turbulent Clumps. I. The Fast Formation Limit

    Science.gov (United States)

    Farias, Juan P.; Tan, Jonathan C.; Chatterjee, Sourav

    2017-04-01

    We investigate the formation and early evolution of star clusters, assuming that they form from a turbulent starless clump of a given mass bounded inside a parent self-gravitating molecular cloud characterized by a particular mass surface density. As a first step, we assume instantaneous star cluster formation and gas expulsion. We draw our initial conditions from observed properties of starless clumps. We follow the early evolution of the clusters up to 20 Myr, investigating the effects of different star formation efficiencies, primordial binary fractions and eccentricities, and primordial mass segregation levels. We investigate clumps with initial masses of {M}{cl}=3000 {M}ȯ embedded in ambient cloud environments with mass surface densities {{{Σ }}}{cloud}=0.1 and 1 {{g}} {{cm}}-2. We show that these models of fast star cluster formation result, in the fiducial case, in clusters that expand rapidly, even considering only the bound members. Clusters formed from higher {{{Σ }}}{cloud} environments tend to expand more quickly and thus are soon larger than clusters born from lower {{{Σ }}}{cloud} conditions. To form a young cluster of a given age, stellar mass, and mass surface density, these models need to assume a parent molecular clump that is many times denser, which is unrealistic compared to observed systems. We also show that, in these models, the initial binary properties are only slightly modified by interactions, meaning that the binary properties, e.g., at 20 Myr, are very similar to those at birth. With this study, we set up the foundation for future work, where we will investigate more realistic models of star formation compared to this instantaneous, baseline case.

  5. DILUTE SURFACTANT METHODS FOR CARBONATE FORMATIONS

    Energy Technology Data Exchange (ETDEWEB)

    Kishore K. Mohanty

    2005-01-01

    There are many carbonate reservoirs in US (and the world) with light oil and fracture pressure below its minimum miscibility pressure (or reservoir may be naturally fractured). Many carbonate reservoirs are naturally fractured. Waterflooding is effective in fractured reservoirs, if the formation is water-wet. Many fractured carbonate reservoirs, however, are mixed-wet and recoveries with conventional methods are low (less than 10%). Thermal and miscible tertiary recovery techniques are not effective in these reservoirs. Surfactant flooding (or huff-n-puff) is the only hope, yet it was developed for sandstone reservoirs in the past. The goal of this research is to evaluate dilute (hence relatively inexpensive) surfactant methods for carbonate formations and identify conditions under which they can be effective. Imbibition in an originally oil-wet 2D capillary is the fastest in the case of Alf-38 and slowest in the case of DTAB (among the surfactants studied). Force of adhesion studies and contact angle measurements show that greater wettability alteration is possible with these anionic surfactants than the cationic surfactant studied. The water imbibition rate does not increase monotonically with an increase in the surfactant concentration. A numerical model has been developed that fits the rate of imbibition. Plans for the next quarter include conducting simulation and imbibition studies.

  6. Observations of Protostellar Outflow Feedback in Clustered Star Formation

    CERN Document Server

    Nakamura, Fumitaka

    2015-01-01

    We discuss the role of protostellar outflow feedback in clustered star formation using the observational data of recent molecular outflow surveys toward nearby cluster-forming clumps. We found that for almost all clumps, the outflow momentum injection rate is significantly larger than the turbulence dissipation rate. Therefore, the outflow feedback is likely to maintain supersonic turbulence in the clumps. For less massive clumps such as B59, L1551, and L1641N, the outflow kinetic energy is comparable to the clump gravitational energy. In such clumps, the outflow feedback probably affects significantly the clump dynamics. On the other hand, for clumps with masses larger than about 200 M$_\\odot$, the outflow kinetic energy is significantly smaller than the clump gravitational energy. Since the majority of stars form in such clumps, we conclude that outflow feedback cannot destroy the whole parent clump. These characteristics of the outflow feedback support the scenario of slow star formation.

  7. Star Formation in Undergraduate ALFALFA Team Galaxy Groups and Clusters

    Science.gov (United States)

    Koopmann, Rebecca A.; Durbala, Adriana; Finn, Rose; Haynes, Martha P.; Coble, Kimberly A.; Craig, David W.; Hoffman, G. Lyle; Miller, Brendan P.; Crone-Odekon, Mary; O'Donoghue, Aileen A.; Troischt, Parker; Undergraduate ALFALFA Team; ALFALFA Team

    2017-01-01

    The Undergraduate ALFALFA Team (UAT) Groups project is a coordinated study of gas and star formation properties of galaxies in and around 36 nearby (zwork undertaken by faculty and students at different institutions within the UAT. Here we present results from our wide area Hα and broadband R imaging project carried out with the WIYN 0.9m+MOSAIC/HDI at KPNO, including an analysis of radial star formation rates and extents of galaxies in the NGC 5846, Abell 779, NRGb331, and HCG 69 groups/clusters. This work has been supported by NSF grant AST-1211005 and AST-1637339.

  8. The Formation and Early Evolution of Young Massive Clusters

    CERN Document Server

    Longmore, Steven N; Bastian, Nate; Bally, John; Rathborne, Jill; Testi, Leonardo; Stolte, Andrea; Dale, James; Bressert, Eli; Alves, Joao

    2014-01-01

    We review the formation and early evolution of the most massive and dense young stellar clusters, focusing on the role they can play in our understanding of star and planet formation as a whole. Young massive cluster (YMC) progenitor clouds in the Galactic Center can accumulate to a high enough density without forming stars that the initial protostellar densities are close to the final stellar density. For this to hold in the disk, the time scale to accumulate the gas to such high densities must be much shorter than the star formation timescale. Otherwise the gas begins forming stars while it is being accumulated to high density. The distinction between the formation regimes in the two environments is consistent with the predictions of environmentally-dependent density thresholds for star formation. This implies that stars in YMCs of similar total mass and radius can have formed at widely different initial protostellar densities. The fact that no systematic variations in fundamental properties are observed be...

  9. Gamma Rays from Star Formation in Clusters of Galaxies

    CERN Document Server

    Storm, Emma; Profumo, Stefano

    2012-01-01

    Star formation in galaxies is observed to be associated with gamma-ray emission. The detection of gamma rays from star-forming galaxies by the Fermi Large Area Telescope (LAT) has allowed the determination of a functional relationship between star formation rate and gamma-ray luminosity (Ackermann et. al. 2012). Since star formation is known to scale with total infrared (8-1000 micrometers) and radio (1.4 GHz) luminosity, the observed infrared and radio emission from a star-forming galaxy can be used to quantitatively infer the galaxy's gamma-ray luminosity. Similarly, star forming galaxies within galaxy clusters allow us to derive lower limits on the gamma-ray emission from clusters, which have not yet been conclusively detected in gamma rays. In this study we apply the relationships between gamma-ray luminosity and radio and IR luminosities derived in Ackermann et. al. 2012 to a sample of galaxy clusters from Ackermann et. al. 2010 in order to place lower limits on the gamma-ray emission associated with sta...

  10. Dynamical formation of cataclysmic variables in globular clusters

    Science.gov (United States)

    Hong, Jongsuk; Vesperini, Enrico; Belloni, Diogo; Giersz, Mirek

    2017-01-01

    The formation and evolution of X-ray sources in globular clusters is likely to be affected by the cluster internal dynamics and the stellar interactions in the cluster dense environment. Several observational studies have revealed a correlation between the number of X-ray sources and the stellar encounter rate, and provided evidence of the role of dynamics in the formation of X-ray binaries. We have performed a survey of Monte Carlo simulations aimed at exploring the connection between the dynamics and formation of cataclysmic variables (CVs) and the origin of the observed correlation between the number of these objects, Ncv, and the stellar encounter rate, Γ. The results of our simulations show a correlation between Ncv and Γ, as found in observational data, illustrate the essential role played by the dynamics, and shed light on the dynamical history behind this correlation. CVs in our simulations are more centrally concentrated than single stars with masses close to those of turn-off stars, although this trend is stronger for CVs formed from primordial binaries undergoing exchange encounters, which include a population of more massive CVs absent in the group of CVs formed from binaries not suffering any component exchange.

  11. Dynamical Formation of Cataclysmic Variables in Globular Clusters

    CERN Document Server

    Hong, Jongsuk; Belloni, Diogo; Giersz, Mirek

    2016-01-01

    The formation and evolution of X-ray sources in globular clusters is likely to be affected by the cluster internal dynamics and the stellar interactions in the cluster dense environment.Several observational studies have revealed a correlation between the number of X-ray sources and the stellar encounter rate and provided evidence of the role of dynamics in the formation of X-ray binaries. We have performed a survey of Monte-Carlo simulations aimed at exploring the connection between the dynamics and formation of cataclysmic variables (CVs) and the origin of the observed correlation between the number of these objects, $N_{\\rm cv}$, and the stellar encounter rate, $\\Gamma$.The results of our simulations show a correlation between $N_{\\rm cv}$ and $\\Gamma$ as found in observational data, illustrate the essential role played by dynamics, and shed light on the dynamical history behind this correlation. CVs in our simulations are more centrally concentrated than single stars with masses close to those of turn-off...

  12. The life-cycle of star formation in distant clusters

    CERN Document Server

    Barger, A J; Ellis, Richard S; Couch, W J; Smail, I; Sharples, R M

    1995-01-01

    We analyse the detailed distribution of star-forming and post-starburst members in three distant (z = 0.31) galaxy clusters in terms of evolutionary sequences that incorporate secondary bursts of star formation on pre-existing stellar populations. Using the number density of spectroscopically-confirmed members on the EW(H\\delta) versus B-R plane from existing data, and for a larger K'-limited sample on the U-I versus I-K' plane from newly-acquired infrared images, we demonstrate that the proportion of cluster members undergoing secondary bursts of star formation during the last ~2 Gyr prior to the epoch of observation is probably as high as 30 per cent of the member galaxies. A key observation leading to this conclusion is the high proportion of H\\delta strong galaxies in all three clusters. The evolutionary modelling, whilst necessarily approximate, returns the correct proportions of galaxies in various stages of the star formation cycle both in terms of spectral and colour properties. HST images for the thr...

  13. The star cluster mass--galactocentric radius relation: Implications for cluster formation

    CERN Document Server

    Sun, Weijia; Fan, Zhou; Cameron, Ewan

    2015-01-01

    Whether or not the initial star cluster mass function is established through a universal, galactocentric-distance-independent stochastic process, on the scales of individual galaxies, remains an unsolved problem. This debate has recently gained new impetus through the publication of a study that concluded that the maximum cluster mass in a given population is not solely determined by size-of-sample effects. Here, we revisit the evidence in favor and against stochastic cluster formation by examining the young ($\\lesssim$ a few $\\times 10^8$ yr-old) star cluster mass--galactocentric radius relation in M33, M51, M83, and the Large Magellanic Cloud. To eliminate size-of-sample effects, we first adopt radial bin sizes containing constant numbers of clusters, which we use to quantify the radial distribution of the first- to fifth-ranked most massive clusters using ordinary least-squares fitting. We supplement this analysis with an application of quantile regression, a binless approach to rank-based regression takin...

  14. The orbital motion of the Arches cluster - clues on cluster formation near the galactic center

    Energy Technology Data Exchange (ETDEWEB)

    Stolte, Andrea; Ghez, Andrea M; Morris, Mark R; Lu, Jessica R [UCLA, 430 Portola Plaza, Los Angeles, CA 90095-1547 (United States); Brandner, Wolfgang [MPIA, Koenigstuhl 17, 69117 Heidelberg (Germany); Matthews, Keith [Caltech Optical Observatories, California Institute of Technology, MS 320-47, Pasadena, CA 91225 (United States)], E-mail: astolte@astro.ucla.edu, E-mail: kym@caltech.edu

    2008-10-15

    The Arches cluster is one of the most massive, young clusters in the Milky Way. Located inside the central molecular zone in the inner 200 pc of the Galactic center, it formed in one of the most extreme star-forming environments in the present-day Galaxy. Its young age of only 2.5 Myr allows us to observe the cluster despite the strong tidal shear forces in the inner Galaxy. The orbit of the cluster determines its dynamical evolution, tidal stripping, and hence its fate. We have measured the proper motion of the Arches cluster relative to the ambient field from Keck/NIRC2 LGS-AO and VLT/NAOS-CONICA NGS-AO observations taken 4.3 years earlier. When combined with the radial velocity, we derive a 3D space motion of 232 {+-} 30 km/s for the Arches. This motion is exceptionally large when compared to molecular cloud orbits in the GC, and places stringent constraints on the formation scenarios for starburst clusters in dense, nuclear environments.

  15. THE RELATION BETWEEN COOL CLUSTER CORES AND HERSCHEL-DETECTED STAR FORMATION IN BRIGHTEST CLUSTER GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    Rawle, T. D.; Egami, E.; Rex, M.; Fiedler, A.; Haines, C. P.; Pereira, M. J.; Portouw, J.; Walth, G. [Steward Observatory, University of Arizona, 933 N. Cherry Ave., Tucson, AZ 85721 (United States); Edge, A. C. [Institute for Computational Cosmology, Durham University, South Road, Durham DH1 3LE (United Kingdom); Smith, G. P. [School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT (United Kingdom); Altieri, B.; Valtchanov, I. [Herschel Science Centre, ESAC, ESA, P.O. Box 78, Villanueva de la Canada, 28691 Madrid (Spain); Perez-Gonzalez, P. G. [Departamento de Astrofisica, Facultad de CC. Fisicas, Universidad Complutense de Madrid, E-28040 Madrid (Spain); Van der Werf, P. P. [Sterrewacht Leiden, Leiden University, P.O. Box 9513, 2300 RA, Leiden (Netherlands); Zemcov, M., E-mail: trawle@as.arizona.edu [Department of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States)

    2012-03-01

    We present far-infrared (FIR) analysis of 68 brightest cluster galaxies (BCGs) at 0.08 < z < 1.0. Deriving total infrared luminosities directly from Spitzer and Herschel photometry spanning the peak of the dust component (24-500 {mu}m), we calculate the obscured star formation rate (SFR). 22{sup +6.2}{sub -5.3}% of the BCGs are detected in the far-infrared, with SFR = 1-150 M{sub Sun} yr{sup -1}. The infrared luminosity is highly correlated with cluster X-ray gas cooling times for cool-core clusters (gas cooling time <1 Gyr), strongly suggesting that the star formation in these BCGs is influenced by the cluster-scale cooling process. The occurrence of the molecular gas tracing H{alpha} emission is also correlated with obscured star formation. For all but the most luminous BCGs (L{sub TIR} > 2 Multiplication-Sign 10{sup 11} L{sub Sun }), only a small ({approx}<0.4 mag) reddening correction is required for SFR(H{alpha}) to agree with SFR{sub FIR}. The relatively low H{alpha} extinction (dust obscuration), compared to values reported for the general star-forming population, lends further weight to an alternate (external) origin for the cold gas. Finally, we use a stacking analysis of non-cool-core clusters to show that the majority of the fuel for star formation in the FIR-bright BCGs is unlikely to originate from normal stellar mass loss.

  16. Sequential clustering of star formations in IC 1396

    Institute of Scientific and Technical Information of China (English)

    Ya-Fang Huang; Jin-Zeng Li

    2013-01-01

    We present a comprehensive study of the H Ⅱ region IC 1396 and its star forming activity,in which multi-wavelength data ranging from the optical to the nearand far-infrared were employed.The surface density distribution of all the 2MASS sources with a certain detection toward IC 1396 indicates the existence of a compact cluster spatially consistent with the position of the exciting source of the H Ⅱ region,HD 206267.The spatial distribution of the sources with excessive infrared emission,selected based on archived 2MASS data,reveals the existence of four sub-clusters in this region.One is associated with the open cluster Trumpler 37.The other three are found to be spatially coincident with the bright rims of the H Ⅱ region.All the sources with excessive emission in the near infrared are cross-identified with AKARI IRC data.An analysis of the spectral energy distributions (SEDs) of the resultant sample leads to the identification of eight CLASS I,15 CLASS Ⅱ and 15 CLASS Ⅲ sources in IC 1396.Optical identification of the sample sources with R magnitudes brighter than 17 mag corroborates the results from the SED analysis.Based on the spatial distribution of the infrared young stellar objects at different evolutionary stages,the surrounding sub-clusters located in the bright rims are believed to be younger than the central one.This is consistent with a scenario of sequential star formation in this region.Imaging data of a dark patch in IC 1396 by Herschel SPIRE,on the other hand,indicate the presence of two far-infrared cores in LDN 1111,which are likely to be a new generation of protostellar objects in formation.So we infer that the star formation process in this H Ⅱ region was not continuous but rather episodic.

  17. On the Assembly of Dwarf Galaxies in Clusters and their Efficient Formation of Globular Clusters

    CERN Document Server

    Mistani, Pouria A; Pillepich, Annalisa; Sanchez-Janssen, Ruben; Vogelsberger, Mark; Nelson, Dylan; Rodriguez-Gomez, Vicente; Torrey, Paul; Hernquist, Lars

    2015-01-01

    Galaxy clusters contain a large population of low mass dwarf elliptical galaxies whose exact origin is unclear: their colors, structural properties and kinematics differ substantially from those of dwarf irregulars in the field. We use the Illustris cosmological simulation to study differences in the assembly paths of dwarf galaxies (3e8 < M_*/M_sun < 1e10) according to their environment. We find that cluster dwarfs achieve their maximum total and stellar mass on average ~ 8 and ~ 4.5 Gyr ago, respectively, around the time of infall into the clusters. In contrast, field dwarfs not subjected to environmental stripping, reach their maximum mass at redshift z = 0. This different assembly history naturally produces a color bimodality, with blue isolated dwarfs and redder cluster dwarfs exhibiting negligible star-formation today. The cessation of star formation happens over median times 3.5-5 Gyr depending on stellar mass, and shows a large scatter (~ 1-8 Gyr), with the lower values associated with starburst...

  18. Star Formation Activity in CLASH Brightest Cluster Galaxies

    Science.gov (United States)

    Fogarty, Kevin; Postman, Marc; Connor, Thomas; Donahue, Megan; Moustakas, John

    2015-11-01

    The CLASH X-ray selected sample of 20 galaxy clusters contains 10 brightest cluster galaxies (BCGs) that exhibit significant (>5σ) extinction-corrected star formation rates (SFRs). Star formation activity is inferred from photometric estimates of UV and Hα+[N ii] emission in knots and filaments detected in CLASH Hubble Space Telescope ACS and WFC3 observations. UV-derived SFRs in these BCGs span two orders of magnitude, including two with a SFR ≳ 100 M⊙ yr-1. These measurements are supplemented with [O ii], [O iii], and Hβ fluxes measured from spectra obtained with the SOAR telescope. We confirm that photoionization from ongoing star formation powers the line emission nebulae in these BCGs, although in many BCGs there is also evidence of a LINER-like contribution to the line emission. Coupling these data with Chandra X-ray measurements, we infer that the star formation occurs exclusively in low-entropy cluster cores and exhibits a correlation with gas properties related to cooling. We also perform an in-depth study of the starburst history of the BCG in the cluster RXJ1532.9+3021, and create 2D maps of stellar properties on scales down to ˜350 pc. These maps reveal evidence for an ongoing burst occurring in elongated filaments, generally on ˜0.5-1.0 Gyr timescales, although some filaments are consistent with much younger (≲100 Myr) burst timescales and may be correlated with recent activity from the active galactic nucleus. The relationship between BCG SFRs and the surrounding intracluster medium gas properties provide new support for the process of feedback-regulated cooling in galaxy clusters and is consistent with recent theoretical predictions. Based on observations obtained at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministério da Ciência, Tecnologia, e Inovação (MCTI) da República Federativa do Brasil, the U.S. National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel

  19. The formation of globular clusters through minihalo-minihalo mergers

    CERN Document Server

    Trenti, Michele; Jimenez, Raul

    2015-01-01

    We propose a novel scenario for the formation of Globular Clusters (GCs) based on the merger of two or more atomic cooling halos at high-redshift (z>6). The model naturally fulfills several key observational constraints on GCs that have emerged in the last decade. Specifically, absolute and relative ages, widespread presence of multiple stellar populations, spatial distribution around host galaxies, and correlations between galactocentric radius and metallicity. In our framework, the oldest globular clusters form the first generation stars as an intense burst in the center of a minihalo that grows above the threshold for hydrogen cooling (halo mass M_h~1e8 Msun) and undergoes a major merger within the cooling timescale (~150 Myr). Subsequent minor mergers and sustained gas infall bring new supply of pristine gas at the halo center, diluting AGB ejecta, and triggering additional bursts of star formation which form multiple generation of stars in the majority of the clusters. The DM halo around the GC is then s...

  20. The quenching of the star formation activity in cluster galaxies

    CERN Document Server

    Boselli, A; Fossati, M; Buat, V; Boissier, S; Boquien, M; Burgarella, D; Ciesla, L; Gavazzi, G; Serra, P

    2016-01-01

    We study the star formation quenching mechanism in cluster galaxies by fitting the SED of the Herschel Reference Survey, a complete volume-limited K-band-selected sample of nearby galaxies including objects in different density regions, from the core of the Virgo cluster to the general field. The SED are fitted using the CIGALE SED modelling code. The truncated activity of cluster galaxies is parametrised using a specific SFH with 2 free parameters, the quenching age QA and the quenching factor QF. These 2 parameters are crucial for the identification of the quenching mechanism which acts on long timescales if starvation while rapid and efficient if ram pressure. To be sensitive to an abrupt and recent variation of the star formation activity, we combine in a new way 20 UV to FIR photometric bands with 3 age-sensitive Balmer line absorption indices extracted from available medium-resolution integrated spectroscopy and with Halpha narrow band imaging data. The use of a truncated SFH significantly increases the...

  1. CELL FORMATION IN GROUP TECHNOLOGY: A SIMILARITY ORDER CLUSTERING APPROACH

    Directory of Open Access Journals (Sweden)

    Godfrey C. Onwubolu

    2012-01-01

    Full Text Available Grouping parts into families which can be produced by a cluster of machine cells is the cornerstone of cellular manufacturing, which in turn is the building block for flexible manufacturing systems. Cellular manufacturing is a group technology (GT concept that has recently attracted the attention of manufacturing firms operating under jobshop environment to consider redesigning their manufacturing systems so as to take advantage of increased throughput, reduction in work-in-progress, set-up time, and lead times; leading to product quality and customer satisfaction. The paper presents a generalised approach for machine cell formation from a jobshop using similarity order clustering technique for preliminary cell grouping and considering machine utilisation for the design of nonintergrouping material handling using the single-pass heuristic. The work addresses the shortcomings of cellular manufacturing systems design and implementations which ignore machine utilisations, group sizes and intergroup moves.

  2. The Formation of Cosmic Fullerenes from Arophatic Clusters

    Science.gov (United States)

    Micelotta, Elisabetta R.; Jones, Anthony P.; Cami, Jan; Peeters, Els; Bernard-Salas, Jeronimo; Fanchini, Giovanni

    2012-12-01

    Fullerenes have recently been identified in space and they may play a significant role in the gas and dust budget of various astrophysical objects including planetary nebulae (PNe), reflection nebulae, and H II regions. The tenuous nature of the gas in these environments precludes the formation of fullerene materials following known vaporization or combustion synthesis routes even on astronomical timescales. We have studied the processing of hydrogenated amorphous carbon (a-C:H or HAC) nanoparticles and their specific derivative structures, which we name "arophatics," in the circumstellar environments of young, carbon-rich PNe. We find that UV-irradiation of such particles can result in the formation of fullerenes, consistent with the known physical conditions in PNe and with available timescales.

  3. The formation of cosmic fullerenes from arophatic clusters

    CERN Document Server

    Micelotta, Elisabetta R; Cami, Jan; Peeters, Els; Bernard-Salas, Jeronimo; Fanchini, Giovanni

    2012-01-01

    Fullerenes have recently been identified in space and they may play a significant role in the gas and dust budget of various astrophysical objects including planetary nebulae (PNe), reflection nebulae (RNe) and H II regions. The tenuous nature of the gas in these environments precludes the formation of fullerene materials following known vaporization or combustion synthesis routes even on astronomical timescales. We have studied the processing of hydrogenated amorphous carbon (a-C:H or HAC) nano-particles and their specific derivative structures, which we name "arophatics", in the circumstellar environments of young, carbon-rich PNe. We find that UV-irradiation of such particles can result in the formation of fullerenes, consistent with the known physical conditions in PNe and with available timescales.

  4. The Orion Nebula Cluster as a Paradigm of Star Formation

    Science.gov (United States)

    Robberto, Massimo

    2014-10-01

    We propose a 52-orbit Treasury Program to investigate two fundamental questions of star formation: a) the low-mass tail of the IMF, down to a few Jupiter masses; b) the dynamical evolution of clusters, as revealed by stellar proper motions. We target the Orion Nebula Cluster (ONC) using WFC3 and ACS in coordinated parallel mode to perform a synoptic survey in the 1.345micron H2O feature and Ic broad-band. Our main objectives are: 1) to discover and classify ~500 brown dwarfs and planetary-mass objects in the field, extending the IMF down to lowest masses formed by gravitational collapse. Using the latest generation of high contrast image processing we will also search for faint companions, reaching down to sub-arcsecond separations and 1E-4 flux ratios. 2) to derive high precision (~0.2km/s) relative proper motions of low-mass stars and substellar objects (about 1000 sources total), leveraging on first epoch data obtained by our previous HST Treasury Program about 10 years ago. These data will unveil the cluster dynamics: velocity dispersion vs. mass, substructures, and the fraction of escaping sources. Only HST can access the IR H2O absorption feature sensitive to the effective temperature of substellar objects, while providing the exceptionally stable PSF needed for the detection of faint companions, and the identical ACS platform for our second epoch proper-motion survey. This program will provide the definitive HST legacy dataset on the ONC. Our High-Level Science Products will be mined by the community, both statistically to constrain competing theories of star formation, and to study in depth the multitude of exotic sources harboured by the cluster.

  5. The formation of S0 galaxies: evidence from globular clusters

    CERN Document Server

    Barr, J M; Bamford, S P; Bedregal, A G; Merrifield, M R

    2007-01-01

    We test the theory that lenticular (S0) galaxies form from spirals whose star formation has been shut down. We use the globular cluster specific frequency S_N, defined as the number of globular clusters normalised by the galaxy luminosity as a diagnostic. NTT/EMMI long-slit spectroscopic observations of 11 S0 galaxies at z < 0.006 are used to measure the absorption-line indices, Hdelta, Hgamma, Mgb, Fe5270 and Fe5335 within the central r_e/8. By inverting single-stellar population models, luminosity-weighted mean ages, metallicities and alpha-element abundance ratios are derived. We estimate the amount of fading a galaxy has undergone by comparing each galaxy's S_N with its deviation from the mean spiral S_N. Galaxies with higher S_N have older stellar populations. Moreover, we find that the zero-point and amount of fading is consistent with a scenario where lenticulars are formed by the quenching of star formation in spiral galaxies. Our data also rule out any formation method for S0s which creates a larg...

  6. Galaxy Formation at z~3 Constraints from Spatial Clustering

    CERN Document Server

    Wechsler, R H; Bullock, J S; Kolatt, T S; Primack, Joel R; Blumenthal, G R; Dekel, A; Wechsler, Risa H.; Somerville, Rachel S.; Bullock, James S.; Kolatt, Tsafrir S.; Primack, Joel R.; Blumenthal, George R.; Dekel, Avishai

    2001-01-01

    We use N-body simulations combined with semi-analytic models to compute the clustering properties of modeled galaxies at z~3, and confront these predictions with the clustering properties of the observed population of Lyman-break galaxies (LBGs). Several scenarios for the nature of LBGs are explored, which may be broadly categorized into models in which high-redshift star formation is driven by collisional starbursts and those in which quiescent star formation dominates. For each model, we make predictions for the LBG overdensity distribution, the variance of counts-in-cells, the correlation length, and close pair statistics. Models which assume a one-to-one relationship between massive dark-matter halos and galaxies are disfavored by close pair statistics, as are models in which colliding halos are associated with galaxies in a simplified way. However, when modeling of gas consumption and star formation is included using a semi-analytic treatment, the quiescent and collisional starburst models predict simila...

  7. On the electronic structure of small cyclic carbon clusters

    Energy Technology Data Exchange (ETDEWEB)

    Yousaf, Kazim E. [Department of Chemistry and Centre for Scientific Computing, University of Warwick, Coventry CV4 7AL (United Kingdom); Taylor, Peter R. [Department of Chemistry and Centre for Scientific Computing, University of Warwick, Coventry CV4 7AL (United Kingdom)], E-mail: p.r.taylor@warwick.ac.uk

    2008-06-16

    We present the results of correlated calculations on a variety of small carbon rings. Equilibrium structures and vibrational frequencies are calculated and transition states connecting symmetry-equivalent minima are considered in detail. We show that neither single-reference coupled-cluster nor multiconfigurational self-consistent field methods (even after perturbational inclusion of dynamical correlation effects) give qualitatively correct potential surfaces in the vicinity of the minima, suggesting that there is little recourse for these systems other than a multireference coupled-cluster treatment. Density-functional theory using the B3LYP functional produces results broadly in agreement with single-reference coupled-cluster methods and is thus no more reliable, but considerably more economical.

  8. Feedback Regulated Star Formation in Cool Core Clusters of Galaxies

    Science.gov (United States)

    Tremblay, Grant Russell

    2011-07-01

    /ISM heating by AGN feedback is directly observed. The ˜15 kpc soft excess filament, part of which is cospatial with extended 1.3 GHz radio emission, may be associated with dredge-up of low entropy gas by the propagating radio source. Results from our study of the hot X-ray gas are framed in the context of inferred young stellar component ages associated with the central emission line nebula in the BCG. We find that inferred ages of the young stellar component are both younger and older than the inferred ages of the X-ray cavities, suggesting that low levels of star formation have managed to persist amid the AGN feedback-driven excavation of the X-ray cavity network. In Chapter 3 we present Hubble Space Telescope far-ultraviolet imaging of seven BCGs in cool core clusters selected on the basis of elevated star formation rates. We find that even at low levels, star formation provides a dominant contribution to the ionizing photon reservoir required to power the observed luminosities of the emission line nebula. Weak, compact radio sources are observed in each of these seven BCGs. The combination of higher SFR and lower radio power is consistent with a scenario wherein a low state of AGN feedback allows for increased residual condensation from the ambient X-ray atmosphere, accounting for the elevated star formation rates. In Chapter 4 we present a comparison study of episodic star formation and AGN activity in the giant radio galaxy 3C 236, which is not associated with a cluster. We find that an episodic AGN/starburst connection can be fostered by a non-steady transport of gas to the nucleus. These results are then compared with Abell 2597, enabling a better understanding of the roles that may be played by cooling flows vs. mergers and hot vs. cold accretion modes in depositing the gaseous reservoirs that fuel both star formation and AGN activity. In Chapter 5 we broaden the context of the thesis with a search for high redshift Fanaroff-Riley class I radio galaxies, which may

  9. Ionization Thresholds of Small Carbon Clusters: Tunable VUVExperiments and Theory

    Energy Technology Data Exchange (ETDEWEB)

    Belau, Leonid; Wheeler, Steven E.; Ticknor, Brian W.; Ahmed,Musahid; Leone, Stephen R.; Allen, Wesley D.; Schaefer III, Henry F.; Duncan, Michael A.

    2007-07-31

    Small carbon clusters (Cn, n = 2-15) are produced in amolecular beam by pulsed laser vaporization and studied with vacuumultraviolet (VUV) photoionization mass spectrometry. The required VUVradiation in the 8-12 eV range is provided by the Advanced Light Source(ALS) at the Lawrence Berkeley National Laboratory. Mass spectra atvarious ionization energies reveal the qualitative relative abundances ofthe neutral carbon clusters produced. By far the most abundant species isC3. Using the tunability of the ALS, ionization threshold spectra arerecorded for the clusters up to 15 atoms in size. The ionizationthresholds are compared to those measured previously with charge-transferbracketing methods. To interpret the ionization thresholds for differentcluster sizes, new ab initio calculations are carried out on the clustersfor n = 4-10. Geometric structures are optimized at the CCSD(T) levelwith cc-pVTZ (or cc-pVDZ) basis sets, and focal point extrapolations areapplied to both neutral and cation species to determine adiabatic andvertical ionization potentials. The comparison of computed and measuredionization potentials makes it possible to investigate the isomericstructures of the neutral clusters produced in this experiment. Themeasurements are inconclusive for the n = 4-6 species because ofunquenched excited electronic states. However, the data provide evidencefor the prominence of linear structures for the n = 7, 9, 11, 13 speciesand the presence of cyclic C10.

  10. Formation of Few-Body Clusters in Nuclear Matter

    CERN Document Server

    Beyer, M

    2000-01-01

    Starting from a suitably modified three-body equation to include dominant medium effects such as self energy corrections and Pauli blocking I present results on several observables relevant for the formation of light clusters in a heavy ion collision at moderate energies. Properly taking into account the medium leads to the Mott effect, larger reaction rates, in turn, faster time scales for the deuteron life time and chemical relaxation time. Within a Boltzmann-Uehling-Uhlenbeck approach to simulate the heavy ion reactions, also the total number of deuterons and the energy spectrum are significantly changed due to medium effects in the elementary cross sections entering into the collision integrals.

  11. Mechanisms contributing to cluster formation in the inferior olivary nucleus in brainstem slices from postnatal mice

    DEFF Research Database (Denmark)

    Kølvraa, Mathias; Müller, Felix C; Jahnsen, Henrik

    2014-01-01

    with glutamate. Induced clusters were inhibited by tetrodotoxin, carbenoxelone and 18β-glycyrrhetinic acid, suggesting that sodium action potentials and electrical coupling are involved in glutamate-induced cluster formation, which could also be induced by activation of N-methyl-d-aspartate and α-amino-3-hydroxy......-5-methyl-4-isoxazolepropionic acid receptors. Spikelets and a small transient depolarizing response were observed during glutamate-induced cluster formation. Calcium transients spread with decreasing velocity during cluster formation, and somatic action potentials and cluster formation...... are accompanied by large dendritic calcium transients. In conclusion, cluster formation depends on gap junctions, sodium action potentials and spontaneous clusters occur randomly throughout the IO. The relative slow signal spread during cluster formation, combined with a strong dendritic influx of calcium, may...

  12. Environments and Morphologies of Red Sequence Galaxies with Residual Star Formation in Massive Clusters

    OpenAIRE

    Crossett, Jacob P.; Pimbblet, Kevin A.; Stott, John P; Jones, D. Heath

    2013-01-01

    We present a photometric investigation into recent star formation in galaxy clusters at z ~ 0.1. We use spectral energy distribution templates to quantify recent star formation in large X-ray selected clusters from the LARCS survey using matched GALEX NUV photometry. These clusters all have signs of red sequence galaxy recent star formation (as indicated by blue NUV-R colour), regardless of cluster morphology and size. A trend in environment is found for these galaxies, such that they prefer ...

  13. Simulation of swift boron clusters traversing amorphous carbon foils

    Science.gov (United States)

    Heredia-Avalos, Santiago; Abril, Isabel; Denton, Cristian D.; Garcia-Molina, Rafael

    2007-01-01

    We use a simulation code to study the interaction of swift boron clusters ( Bn+ , n=2-6 , 14) with amorphous carbon foils. We analyze different aspects of this interaction, such as the evolution of the cluster structure inside the target, the energy and angle distributions at the detector or the stopping power ratio. Our simulation code follows in detail the motion of the cluster fragments through the target and in the vacuum until reaching a detector, taking into account the following interactions: (i) wake force, (ii) Coulomb repulsion among cluster fragments, (iii) stopping force, and (iv) elastic scattering with the target nuclei. Electron capture and loss by each fragment is also included in the code, affecting the above-mentioned interactions. The clusters size grows inside the foil due mainly to the Coulomb explosion but this increase is less pronounced in the plane transversal to the beam direction because of the alignment effect of the wake forces. We obtain an enhancement of the stopping power ratio that increases with the projectile energy and with the number of molecular constituents. Our results agree very well with the available experimental data for the thicker foils (≳10μg/cm2) and are compatible (within the experimental error bars) for the thinner foils.

  14. Star Formation Efficiency in the Cool Cores of Galaxy Clusters

    Science.gov (United States)

    McDonald, Michael; Veilleux, Sylvain; Rupke, David S. N.; Mushotzky, Richard; Reynolds, Christopher

    2011-06-01

    We have assembled a sample of high spatial resolution far-UV (Hubble Space Telescope Advanced Camera for Surveys/Solar Blind Channel) and Hα (Maryland-Magellan Tunable Filter) imaging for 15 cool core galaxy clusters. These data provide a detailed view of the thin, extended filaments in the cores of these clusters. Based on the ratio of the far-UV to Hα luminosity, the UV spectral energy distribution, and the far-UV and Hα morphology, we conclude that the warm, ionized gas in the cluster cores is photoionized by massive, young stars in all but a few (A1991, A2052, A2580) systems. We show that the extended filaments, when considered separately, appear to be star forming in the majority of cases, while the nuclei tend to have slightly lower far-UV luminosity for a given Hα luminosity, suggesting a harder ionization source or higher extinction. We observe a slight offset in the UV/Hα ratio from the expected value for continuous star formation which can be modeled by assuming intrinsic extinction by modest amounts of dust (E(B - V) ~ 0.2) or a top-heavy initial mass function in the extended filaments. The measured star formation rates vary from ~0.05 M sun yr-1 in the nuclei of non-cooling systems, consistent with passive, red ellipticals, to ~5 M sun yr-1 in systems with complex, extended, optical filaments. Comparing the estimates of the star formation rate based on UV, Hα, and infrared luminosities to the spectroscopically determined X-ray cooling rate suggests a star formation efficiency of 14+18 - 8%. This value represents the time-averaged fraction, by mass, of gas cooling out of the intracluster medium, which turns into stars and agrees well with the global fraction of baryons in stars required by simulations to reproduce the stellar mass function for galaxies. This result provides a new constraint on the efficiency of star formation in accreting systems.

  15. Modeling the Formation of Globular Cluster Systems in the Virgo Cluster

    CERN Document Server

    Li, Hui

    2014-01-01

    Globular cluster (GC) systems are some of the oldest and most unique building blocks of galaxies. The mass and chemical composition of GCs preserve the fossil record of the early stages of formation of their host galaxies. The observed distribution of GC colors within massive early-type galaxies in the ACS Virgo Cluster Survey (ACSVCS) reveals a multi-modal shape, which likely corresponds to a multi-modal metallicity distribution. In this paper, we present a simple model for the formation and dynamical disruption of globular clusters that aims to match the ACSVCS data. We test the hypothesis that GCs are formed during major mergers of gas-rich galaxies and inherit the metallicity of their hosts. To trace merger events, we use halo merger trees extracted from a large cosmological N-body simulation. We select 20 halos in the mass range 2*10^{12}-7*10^{13} M_sun and match them to 18 Virgo galaxies with K-band luminosity between 3*10^{10} and 3*10^{11}L_sun. To set the Iron abundances, we use an empirical galaxy ...

  16. Stellar Collisions in Young Clusters: Formation of (Very) Massive Stars?

    CERN Document Server

    Freitag, Marc

    2007-01-01

    In young star clusters, the density can be high enough and the velocity dispersion low enough for stars to collide and merge with a significant probability. This has been suggested as a possible way to build up the high-mass portion of the stellar mass function and as a mechanism leading to the formation of one or two very massive stars (M > 150 Msun) through a collisional runaway. I quickly review the standard theory of stellar collisions, covering both the stellar dynamics of dense clusters and the hydrodynamics of encounters between stars. The conditions for collisions to take place at a significant rate are relatively well understood for idealised spherical cluster models without initial mass segregation, devoid of gas and composed of main-sequence (MS) stars. In this simplified situation, 2-body relaxation drives core collapse through mass segregation and a collisional phase ensues if the core collapse time is shorter than the MS lifetime of the most massive stars initially present. The outcome of this p...

  17. Star Formation Efficiency in the Cool Cores of Galaxy Clusters

    CERN Document Server

    McDonald, Michael; Rupke, David S N; Mushotzky, Richard; Reynolds, Christopher

    2011-01-01

    We have assembled a sample of high spatial resolution far-UV (Hubble Space Telescope Advanced Camera for Surveys Solar Blind Channel) and Halpha (Maryland-Magellan Tunable Filter) imaging for 15 cool core galaxy clusters. These data provide a detailed view of the thin, extended filaments in the cores of these clusters. Based on the ratio of the far-UV to Halpha luminosity, the UV spectral energy distribution, and the far-UV and Halpha morphology, we conclude that the warm, ionized gas in the cluster cores is photoionized by massive, young stars in all but a few (Abell 1991, Abell 2052, Abell 2580) systems. We show that the extended filaments, when considered separately, appear to be star-forming in the majority of cases, while the nuclei tend to have slightly lower far-UV luminosity for a given Halpha luminosity, suggesting a harder ionization source or higher extinction. We observe a slight offset in the UV/Halpha ratio from the expected value for continuous star formation which can be modeled by assuming in...

  18. The life-cycle of young star-clusters; the role of the galactic environment on cluster formation and evolution

    Science.gov (United States)

    Adamo, Angela

    2015-08-01

    Our understanding of star formation on galactic scales has been fairly grasped (e.g. the rate at which stars form scales proportionally to the molecular gas content) both in the local and high redshift universe. However, our knowledge on how star formation proceeds at small scales (e.g. the fraction of star formation happening in stellar clusters, the time-scales for star-forming regions to dissolve, the impact of the galactic environment on star and cluster formation) remains a challenge. Gravitationally bound young stellar clusters appear to be a commune product of star formation. There are tantalizing similarities between young star clusters and globular clusters, the latter formed by gravitationally bound ancient stellar populations. However, the young and globular cluster populations show statistical properties (mass functions, formation efficiencies, and survival times) that have been claimed incompatible, leaving the two populations being the results of distinct processes of formation. In my contribution, I will discuss the latest results produced with the analysis of the young cluster populations in several nearby galaxies. The use of new statistical methods, the link with dense gas fueling star formation, the access to homogenous datasets show, for the first time, clear evidence of the influence of the galactic environment in shaping the properties of young star cluster populations. After all, the differences between the two cluster populations may not be so pronounced, suggesting that the same physical formation process under different environmental conditions has been (and currently is) at work at high redshift (when globular clusters were formed) and in the local universe.

  19. Young Massive Clusters: Their Population Properties, Formation and Evolution, and Their Relation to the Ancient Globular Clusters

    Science.gov (United States)

    Bastian, N.

    2016-11-01

    This review summarises the main properties of Young Massive Clusters (YMCs), including their population properties, particularly focusing on extragalactic cluster samples. We discuss potential biases and caveats that can affect the construction of cluster samples and how incompleteness effects can result in erroneous conclusions regarding the long term survival of clusters. In addition to the luminosity, mass and age distributions of the clusters, we discuss the size distribution and profile evolution of the clusters. We also briefly discuss the stellar populations within YMCs. The final part of the review focusses on the connections between YMCs and the ancient globular clusters, whether or not they are related objects and how we can use what we know about YMC formation and evolution to understand how GCs formed in the early universe and how they relate to galaxy formation/evolution.

  20. Young Massive Clusters: Their Population Properties, Formation and Evolution, and Their Relation to the Ancient Globular Clusters

    CERN Document Server

    Bastian, Nate

    2016-01-01

    This review summarises the main properties of Young Massive Clusters (YMCs), including their population properties, particularly focusing on extragalactic cluster samples. We discuss potential biases and caveats that can affect the construction of cluster samples and how incompleteness effects can result in erroneous conclusions regarding the long term survival of clusters. In addition to the luminosity, mass and age distributions of the clusters, we discuss the size distribution and profile evolution of the clusters. We also briefly discuss the stellar populations within YMCs. The final part of the review focusses on the connections between YMCs and the ancient globular clusters, whether or not they are related objects and how we can use what we know about YMC formation and evolution to understand how GCs formed in the early universe and how they relate to galaxy formation/evolution.

  1. A CLUSTER IN THE MAKING: ALMA REVEALS THE INITIAL CONDITIONS FOR HIGH-MASS CLUSTER FORMATION

    Energy Technology Data Exchange (ETDEWEB)

    Rathborne, J. M.; Contreras, Y. [CSIRO Astronomy and Space Science, P.O. Box 76, Epping NSW, 1710 (Australia); Longmore, S. N.; Bastian, N. [Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF (United Kingdom); Jackson, J. M. [Institute for Astrophysical Research, Boston University, Boston, MA 02215 (United States); Alves, J. F. [University of Vienna, Türkenschanzstrasse 17, A-1180 Vienna (Austria); Bally, J. [Center for Astrophysics and Space Astronomy, University of Colorado, UCB 389, Boulder, CO 8030 (United States); Foster, J. B. [Department of Astronomy, Yale University, P.O. Box 208101 New Haven, CT 06520-8101 (United States); Garay, G. [Universidad de Chile, Camino El Observatorio1515, Las Condes, Santiago (Chile); Kruijssen, J. M. D. [Max-Planck Institut fur Astrophysik, Karl-Schwarzschild-Strasse 1, D-85748, Garching (Germany); Testi, L. [European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching bei Munchen (Germany); Walsh, A. J., E-mail: Jill.Rathborne@csiro.au [International Centre for Radio Astronomy Research, Curtin University, GPO Box U1987, Perth (Australia)

    2015-04-01

    G0.253+0.016 is a molecular clump that appears to be on the verge of forming a high-mass cluster: its extremely low dust temperature, high mass, and high density, combined with its lack of prevalent star formation, make it an excellent candidate for an Arches-like cluster in a very early stage of formation. Here we present new Atacama Large Millimeter/Sub-millimeter Array observations of its small-scale (∼0.07 pc) 3 mm dust continuum and molecular line emission from 17 different species that probe a range of distinct physical and chemical conditions. The data reveal a complex network of emission features with a complicated velocity structure: there is emission on all spatial scales, the morphology of which ranges from small, compact regions to extended, filamentary structures that are seen in both emission and absorption. The dust column density is well traced by molecules with higher excitation energies and critical densities, consistent with a clump that has a denser interior. A statistical analysis supports the idea that turbulence shapes the observed gas structure within G0.253+0.016. We find a clear break in the turbulent power spectrum derived from the optically thin dust continuum emission at a spatial scale of ∼0.1 pc, which may correspond to the spatial scale at which gravity has overcome the thermal pressure. We suggest that G0.253+0.016 is on the verge of forming a cluster from hierarchical, filamentary structures that arise from a highly turbulent medium. Although the stellar distribution within high-mass Arches-like clusters is compact, centrally condensed, and smooth, the observed gas distribution within G0.253+0.016 is extended, with no high-mass central concentration, and has a complex, hierarchical structure. If this clump gives rise to a high-mass cluster and its stars are formed from this initially hierarchical gas structure, then the resulting cluster must evolve into a centrally condensed structure via a dynamical process.

  2. The star cluster - field star connection in nearby spiral galaxies. II. Field star and cluster formation histories and their relation

    CERN Document Server

    Silva-Villa, Esteban

    2011-01-01

    Recent studies have started to cast doubt on the assumption that most stars are formed in clusters. Observational studies of field stars and star cluster systems in nearby galaxies can lead to better constraints on the fraction of stars forming in clusters. We aim to constrain the amount of star formation happening in long-lived clusters for four galaxies through the homogeneous study of field stars and star clusters. Using HST/ACS-WFPC2 images of the galaxies NGC45, NGC1313, NGC5236 and NGC7793, we estimate star formation histories by means of the synthetic CMD method. Masses and ages of star clusters are estimated using simple stellar population model fitting. Comparing observed and modeled luminosity functions we estimate cluster formation rates. By randomly sampling the stellar IMF, we construct artificial star clusters and quantify how stochastic effects influence cluster detection, integrated colors and age estimates. Star formation rates appear to be constant over the past 10-100 Myr. The number of clu...

  3. Lyman Alpha Emitters in the Hierarchically Clustering Galaxy Formation

    CERN Document Server

    Kobayashi, Masakazu A R; Nagashima, Masahiro

    2007-01-01

    We present a new theoretical model for the luminosity functions (LFs) of Lyman alpha (Lya) emitting galaxies in the framework of hierarchical galaxy formation. We extend a semi-analytic model of galaxy formation that reproduces a number of observations for local galaxies, without changing the original model parameters but introducing a physically-motivated modelling to describe the escape fraction of Lya photons from host galaxies (f_esc). Though a previous study using a hierarchical clustering model simply assumed a constant and universal value of f_esc, we incorporate two new effects on f_esc: extinction by interstellar dust and galaxy-scale outflow induced as a star formation feedback. It is found that the new model nicely reproduces all the observed Lya LFs of the Lya emitters (LAEs) at different redshifts in z ~ 3--6. Our model predicts that galaxies with strong outflows and f_esc ~ 1 are dominant in the observed LFs, which is consistent with available observations while the simple universal f_esc model ...

  4. Formation of thick dielectrophoretic carbon nanotube fibers

    Energy Technology Data Exchange (ETDEWEB)

    Plaado, Margo; Mononen, Robert Matias; Lohmus, Ruenno; Kink, Ilmar; Saal, Kristjan, E-mail: saal@fi.tartu.ee [Institute of Physics, University of Tartu, and Estonian Nanotechnology Competence Centre, 142 Riia Street, 51014 Tartu (Estonia)

    2011-07-29

    The aim of this work was to study the formation process of dielectrophoretic (DEP) carbon nanotube fibers (CNT-fibers) and characterize the fiber properties relevant to their technological applications. The fiber diameter was shown to increase when applied voltage was increased (up to 350 V{sub pp}) and when retraction speed was decreased (down from 400 {mu}m s{sup -1}) in accordance with theoretical expectations. This paper represents the first demonstration of the formation of thick DEP CNT-fibers (up to {approx} 0.4 mm). This is an intriguing result, as it expands the diversity of possible applications of the fibers and facilitates their characterization by analytical methods that require large quantities of the material. The performance of these thick fibers was as follows: a density of {approx} 0.35 g cm{sup -3}, a tensile strength of {approx} 15 MPa, a Young's modulus of {approx} 1 GPa, and an electrical resistivity of {approx} 70 m{Omega} cm.

  5. Catalytic carbide formation at aluminium-carbon interfaces

    Science.gov (United States)

    Maruyama, B.; Rabenberg, L.; Ohuchi, F. S.

    1990-01-01

    X-ray photoelectron spectroscopy investigations of the reaction of several monolayer-thick films of aluminum with glassy carbon substrates are presented. The influence of molecular oxygen and water vapor on the rate of reaction is examined. It is concluded that water vapor catalyzed the formation of aluminum carbide from aluminum and carbon by forming active sites which weakened carbon-carbon bonds at the glassy carbon surface, thus assisting their cleavage. The rate of carbide formation for undosed and molecular oxygen-dosed examples was less as neither metallic aluminum nor oxygen-formed alumina could bond to the carbon atom with sufficient strength to dissociate it quickly.

  6. The Role of Ram Pressure Stripping in the Quenching of Cluster Star Formation

    CERN Document Server

    Book, Laura G

    2010-01-01

    Recent observations of galaxy clusters have shown that environmental effects apparently associated with the cluster begin to lower the star formation rates of galaxies at distances as great as three times the cluster virial radius. These observations may indicate preprocessing of cluster galaxies in groups or in the cluster core for galaxies on highly elliptical orbits, but may also imply that the environmental effects due to the cluster are directly affecting galaxies on their first infall. To explore these issues, we investigate different models of ram pressure stripping as it acts on satellite galaxies in clusters, and compare to observations of the radial star formation gradient in clusters. We calculate the location of the accretion shock around model clusters, and use this as the radius of onset of ram pressure stripping in the Galform semi-analytic model of galaxy formation. Comparison of the results of our model, and previously considered, simpler ram pressure models, with recent observations indicate...

  7. M82, Starbursts, Star Clusters, and the Formation of Globular Clusters

    CERN Document Server

    Keto, E; Lo, K Y; Keto, Eric; Ho, Luis C.

    2005-01-01

    We observed the nearby starburst galaxy M82 in CO in the higher frequency (2--1) transition to achieve an angular resolution below 1 arc second or 17 pc at the target. We resolved the molecular gas into a large number of compact clouds, with masses ranging from about 2x10^3 to 2x10^6 solar masses. The mass spectrum scales as N(M) ~ M^-1.5, similar to the mass spectra of young massive star clusters suggesting that individual molecular clouds are transformed in the starburst into individual star clusters. The larger clouds are surrounded by supernovae and HII regions suggesting that star formation proceeds from the outside of the clouds and progresses inward consistent with triggering by a sudden increase in external pressure. The clouds with internal star formation have velocity gradients and inverse P-Cygni spectral line profiles indicating inward motions of 35 kms consistent with shock driven compression. Diffuse free-free radio emission and X-ray emission around the clouds provides evidence for superheated ...

  8. Revisiting the formation of cyclic clusters in liquid ethanol

    Science.gov (United States)

    Balanay, Mannix P.; Kim, Dong Hee; Fan, Haiyan

    2016-04-01

    The liquid phase of ethanol in pure and in non-polar solvents was studied at room temperature using Fourier transform infrared (FT-IR) and 1H nuclear magnetic resonance (NMR) spectroscopies together with theoretical approach. The FT-IR spectra for pure ethanol and solution in cyclohexane at different dilution stages are consistent with 1H NMR results. The results from both methods were best explained by the results of the density functional theory based on a multimeric model. It is suggested that cyclic trimers and tetramers are dominated in the solution of cyclohexane/hexane with the concentration greater than 0.5M at room temperature. In liquid ethanol, while the primary components at room temperature are cyclic trimers and tetramers, there is a certain amount (˜14%) of open hydroxide group representing the existence of chain like structures in the equilibria. The cyclic cluster model in the liquid and concentrated solution phase (>0.5M) can be used to explain the anomalously lower freezing point of ethanol (159 K) than that of water (273 K) at ambient conditions. In addition, 1H NMR at various dilution stages reveals the dynamics for the formation of cyclic clusters.

  9. Dynamical Formation of Close Binary Systems in Globular Clusters

    CERN Document Server

    Pooley, D; Anderson, S F; Baumgardt, H; Filippenko, A V; Gaensler, B M; Homer, L; Hut, P; Kaspi, V M; Margon, B; McMillan, S; Zwart, S P; Van der Klis, M; Verbunt, F

    2003-01-01

    We know from observations that globular clusters are very efficient catalysts in forming unusual short-period binary systems or their offspring, such as low-mass X-ray binaries (LMXBs; neutron stars accreting matter from low-mass stellar companions), cataclysmic variables (CVs; white dwarfs accreting matter from stellar companions), and millisecond pulsars (MSPs; rotating neutron stars with spin periods of a few ms). Although there has been little direct evidence, the overabundance of these objects in globular clusters has been attributed by numerous authors to the high densities in the cores, which leads to an increase in the formation rate of exotic binary systems through close stellar encounters. Many such close binary systems emit X-radiation at low luminosities (L_x < 10^{34} erg/s) and are being found in large numbers through observations with the Chandra X-ray Observatory. Here we present conclusive observational evidence for a link between the number of close binaries observed in X-rays in a globul...

  10. Formation of Compact Clusters from High Resolution Hybrid Cosmological Simulations

    CERN Document Server

    Richardson, Mark L A; Gray, William J

    2013-01-01

    The early Universe hosted a large population of small dark matter `minihalos' that were too small to cool and form stars on their own. These existed as static objects around larger galaxies until acted upon by some outside influence. Outflows, which have been observed around a variety of galaxies, can provide this influence in such a way as to collapse, rather than disperse the minihalo gas. Gray & Scannapieco performed an investigation in which idealized spherically-symmetric minihalos were struck by enriched outflows. Here we perform high-resolution cosmological simulations that form realistic minihalos, which we then extract to perform a large suite of simulations of outflow-minihalo interactions including non-equilibrium chemical reactions. In all models, the shocked minihalo forms molecules through non-equilibrium reactions, and then cools to form dense chemically homogenous clumps of star-forming gas. The formation of these high-redshift clusters will be observable with the next generation of telesc...

  11. Thermal recovery of bitumen from carbonate reservoirs: formation damage aspects

    Energy Technology Data Exchange (ETDEWEB)

    Thimm, H.F. [Thimm Petroleum Technologies Inc. (Canada)

    2011-07-01

    In Alberta, about a third of bitumen resources are located in carbonate reservoirs but none of it is considered as a reserve by the Alberta Energy Resources Conservation Board (ERCB). In fact no pilot has been successful in recovering bitumen from carbonate reservoirs due to formation damage problems. Carbonate rock is chemically active at the high temperatures reached in thermal recovery processes, carbon dioxide is generated and carbonate minerals are precipitated. The aim of this paper is to find methods to control the phenomenon. Kinetic and thermodynamic controls were used. Results showed that formation damage is due to aqueous carbon dioxide attacking the reservoir rock. They found that a reduction of the partial pressure of carbon dioxide could inhibit the initial dissolution of rock material by reducing the concentration of aqueous carbon dioxide. A method to overcome the formation damage problem was found and a co-injection of gas and steam process was developed to apply it.

  12. Open star cluster: formation, parameters, membership and importance

    CERN Document Server

    Joshi, Gireesh C

    2016-01-01

    We have been represented the collective information of estimation procedures of parameters of the open clusters and put them together for showing the importance of clusters to understand their role in stellar evolution phenomenon. Moreover, we have been discussed about analytic techniques to determine the structural and dynamical properties of galactic clusters. The members of clusters provide unique opportunity to determine their basic parameters such as: age, metallicity, distance, reddening etc. The membership probabilities of stars of clusters is assigned through the various approaches and each approach provides different number of probable members of the cluster. Here, we have been briefly discussed about various approaches to determine the stellar membership within clusters.

  13. Distances, Ages, and Epoch of Formation of Globular Clusters

    Science.gov (United States)

    Carretta, Eugenio; Gratton, Raffaele G.; Clementini, Gisella; Fusi Pecci, Flavio

    2000-04-01

    We review the results on distances and absolute ages of Galactic globular clusters (GCs) obtained after the release of the Hipparcos catalog. Several methods aimed at the definition of the Population II local distance scale are discussed, and their results compared, exploiting new results for RR Lyraes in the Large Magellanic Cloud (LMC). We find that the so-called short distance and long distance scales may be reconciled whether or not a consistent reddening scale is adopted for Cepheids and RR Lyrae variables in the LMC. Emphasis is given in the paper to the discussion of distances and ages of GCs derived using Hipparcos parallaxes of local subdwarfs. We find that the selection criteria adopted to choose the local subdwarfs, as well as the size of the corrections applied to existing systematic biases, are the main culprit for the differences found among the various independent studies that first used Hipparcos parallaxes and the subdwarf fitting technique. We also caution that the absolute age of M92 (usually considered one of the oldest clusters) still remains uncertain due to the lack of subdwarfs of comparable metallicity with accurate parallaxes. Distances and ages for the nine clusters discussed in a previous paper by Gratton et al. are rederived using an enlarged sample of local subdwarfs, which includes about 90% of the metal-poor dwarfs with accurate parallaxes (Δπ/πzero-age horizontal branch (ZAHB) absolute magnitude and metallicity for the nine program clusters turns out to be MV(ZAHB)=(0.18+/-0.09)([Fe/H]+1.5)+(0.53+/-0.12) Thanks to Hipparcos the major contribution to the total error budget associated with the subdwarf fitting technique has been moved from parallaxes to photometric calibrations, reddening, and metallicity scale. This total uncertainty still amounts to about +/-0.12 mag. We then compare the corresponding (true) LMC distance modulus μLMC=18.64+/-0.12 mag with other existing determinations. We conclude that at present the best

  14. In vivo cluster formation of nisin and lipid II is correlated with membrane depolarization.

    Science.gov (United States)

    Tol, Menno B; Morales Angeles, Danae; Scheffers, Dirk-Jan

    2015-01-01

    Nisin and related lantibiotics kill bacteria by pore formation or by sequestering lipid II. Some lantibiotics sequester lipid II into clusters, which were suggested to kill cells through delocalized peptidoglycan synthesis. Here, we show that cluster formation is always concomitant with (i) membrane pore formation and (ii) membrane depolarization. Nisin variants that cluster lipid II kill L-form bacteria with similar efficiency, suggesting that delocalization of peptidoglycan synthesis is not the primary killing mechanism of these lantibiotics.

  15. Formation and growth of molecular clusters containing sulfuric acid, water, ammonia, and dimethylamine.

    Science.gov (United States)

    DePalma, Joseph W; Doren, Douglas J; Johnston, Murray V

    2014-07-24

    The structures and thermochemistry of molecular clusters containing sulfuric acid, water, ammonia, and/or dimethylamine ((CH3)2NH or DMA) are explored using a combination of Monte Carlo configuration sampling, semiempirical calculations, and density functional theory (DFT) calculations. Clusters are of the general form [(BH(+))n(HSO4(-))n(H2O)y], where B = NH3 or DMA, 2 ≤ n ≤ 8, and 0 ≤ y ≤ 10. Cluster formulas are written based on the computed structures, which uniformly show proton transfer from each sulfuric acid molecule to a base molecule while the water molecules remain un-ionized. Cluster formation is energetically favorable, owing to strong electrostatic attraction among the ions. Water has a minor effect on the energetics of cluster formation, lowering the free energy of formation by ∼ 10% depending on the cluster size and number of water molecules. Cluster growth (addition of one base molecule and one sulfuric acid molecule to a pre-existing cluster) and base substitution (substituting DMA for ammonia) are also energetically favorable processes for both anhydrous and hydrated clusters. However, the effect of water is different for different bases. Hydrated ammonium bisulfate clusters have a more favorable free energy for growth (i.e., incrementing n with fixed y) than anhydrous clusters, while the reverse is observed for dimethylammonium bisulfate clusters, where the free energy for growth is more favorable for anhydrous clusters. The substitution of DMA for ammonia in bisulfate clusters is favorable but exhibits a complex water dependence. Base substitution in smaller bisulfate clusters is enhanced by the presence of water, while base substitution in larger bisulfate clusters is less favorable for hydrated clusters than that for anhydrous clusters. While DMA substitution can stabilize small clusters containing one or a few sulfuric acid molecules, the free energy advantage of forming amine clusters relative to ammonia clusters becomes less

  16. The effect of magnetic fields on star cluster formation

    CERN Document Server

    Price, Daniel

    2008-01-01

    We examine the effect of magnetic fields on star cluster formation by performing simulations following the self-gravitating collapse of a turbulent molecular cloud to form stars in ideal MHD. The collapse of the cloud is computed for global mass-to-flux ratios of infinity, 20, 10, 5 and 3, that is using both weak and strong magnetic fields. Whilst even at very low strengths the magnetic field is able to significantly influence the star formation process, for magnetic fields with plasma beta < 1 the results are substantially different to the hydrodynamic case. In these cases we find large-scale magnetically-supported voids imprinted in the cloud structure; anisotropic turbulent motions and column density structure aligned with the magnetic field lines, both of which have recently been observed in the Taurus molecular cloud. We also find strongly suppressed accretion in the magnetised runs, leading to up to a 75% reduction in the amount of mass converted into stars over the course of the calculations and a m...

  17. Fe-inserted and shell-shaped carbon nanoparticles by cluster-mediated laser pyrolysis

    Energy Technology Data Exchange (ETDEWEB)

    Fleaca, C.T., E-mail: claudiufleaca@yahoo.com [Laser Photochemistry Laboratory, National Institute for Lasers, Plasma and Radiation Physics (NILPRP), P.O. Box MG 36, R-077125 Bucharest-Magurele (Romania); Dumitrache, F.; Morjan, I.; Alexandrescu, R.; Sandu, I.; Luculescu, C.; Birjega, S. [Laser Photochemistry Laboratory, National Institute for Lasers, Plasma and Radiation Physics (NILPRP), P.O. Box MG 36, R-077125 Bucharest-Magurele (Romania); Prodan, G. [Ovidius University of Constanta, 124 Mamaia Bd., Constanta (Romania); Stamatin, I. [3 Nano-SAE Research Center, University of Bucharest, P.O. Box MG-38, R-077125 Bucharest-Magurele (Romania)

    2012-09-15

    Highlights: Black-Right-Pointing-Pointer Iron-inserted carbon nanoparticles were obtained by laser pyrolysis technique. Black-Right-Pointing-Pointer Two different structures (shell-shape and turbostratic) were found in the same experiment. Black-Right-Pointing-Pointer Increasing the pressure causes the increasing in carbon crystallinity/decreasing the Fe content. Black-Right-Pointing-Pointer Iron nanoinclusions are protected from oxidation by the carbon matrix. Black-Right-Pointing-Pointer Magnetism-related applications of these nanoparticles in life sciences are proposed. - Abstract: We report here the high-yield continuous synthesis of carbon nanoparticles with and without Fe content by laser pyrolysis technique. The laser beam decomposes (via C{sub 2}H{sub 4} sensitizer) the Fe(CO){sub 5} as Fe clusters which absorb themselves the laser radiation. They trigger the fast carbon particles formation by exothermic dehydrogenation/polymerization of the surrounded C{sub 2}H{sub 2} molecules. This combination between Fe clusters and C{sub 2}H{sub 2} generates nanoparticles with unusual structure. Depending on the gas pressure in the reaction chamber, two kinds of nanoparticles were obtained: at lower pressure, 30-40 nm diameter particles with a defective structure, part of them crowded with Fe clusters (3-6 nm) and two types of nanoparticles (around 50-60 nm) at the highest pressure. Some of them have a shell-shape structure, presenting a distinct envelope, other with a turbostratic arrangement, and few containing one or several smaller (3-20 nm) Fe nanoparticles trapped inside. We consider that these particular structures of our nanoparticles may be useful in applications such as MRI applications, drug delivery or catalysts.

  18. Self-organized formation of metal-carbon nanostructures by hyperthermal ion deposition

    Energy Technology Data Exchange (ETDEWEB)

    Hannstein, I.K.

    2006-04-26

    The quasi-simultaneous deposition of mass-selected hyperthermal carbon and metal ions results in a variety of interesting film morphologies, depending on the metal used and the deposition conditions. The observed features are of the order of a few nanometres and are therefore interesting for future potential applications in the various fields of nanotechnology. The present study focuses on the structural analysis of amorphous carbon films containing either copper, silver, gold, or iron using amongst others Rutherford Backscattering Spectroscopy, High Resolution Transmission Electron Microscopy, and Energy Dispersive X-Ray Spectroscopy. The film morphologies found are as follows: copper-containing films consist of copper nanoclusters with sizes ranging from about 3 to 9 nm uniformly distributed throughout the amorphous carbon matrix. The cluster size hereby rises with the copper content of the films. The silver containing films decompose into a pure amorphous carbon film with silver agglomerates at the surface. Both, the gold- and the iron-containing films show a multilayer structure of metal-rich layers with higher cluster density separated by metal-depleted amorphous carbon layers. The layer distances are of the order of up to 15 nm in the case of gold-carbon films and 7 nm in the case of iron-carbon films. The formation of theses different structures cannot be treated in the context of conventional self-organization mechanisms basing upon thermal diffusion and equilibrium thermodynamics. Instead, an ion-induced atomic transport, sputtering effects, and the stability of small metal clusters were taken into account in order to model the structure formation processes. A similar multilayer morphology was recently also reported in the literature for metal-carbon films grown by magnetron sputtering techniques. In order to investigate, whether the mechanisms are the same as in the case of the ion beam deposited films described above, first experiments were conducted

  19. Modelling clustering of vertically aligned carbon nanotube arrays

    Science.gov (United States)

    Schaber, Clemens F.; Filippov, Alexander E.; Heinlein, Thorsten; Schneider, Jörg J.; Gorb, Stanislav N.

    2015-01-01

    Previous research demonstrated that arrays of vertically aligned carbon nanotubes (VACNTs) exhibit strong frictional properties. Experiments indicated a strong decrease of the friction coefficient from the first to the second sliding cycle in repetitive measurements on the same VACNT spot, but stable values in consecutive cycles. VACNTs form clusters under shear applied during friction tests, and self-organization stabilizes the mechanical properties of the arrays. With increasing load in the range between 300 µN and 4 mN applied normally to the array surface during friction tests the size of the clusters increases, while the coefficient of friction decreases. To better understand the experimentally obtained results, we formulated and numerically studied a minimalistic model, which reproduces the main features of the system with a minimum of adjustable parameters. We calculate the van der Waals forces between the spherical friction probe and bunches of the arrays using the well-known Morse potential function to predict the number of clusters, their size, instantaneous and mean friction forces and the behaviour of the VACNTs during consecutive sliding cycles and at different normal loads. The data obtained by the model calculations coincide very well with the experimental data and can help in adapting VACNT arrays for biomimetic applications. PMID:26464787

  20. The formation of NGC 3603 young starburst cluster: "prompt" hierarchical assembly or monolithic starburst?

    CERN Document Server

    Banerjee, Sambaran

    2014-01-01

    The formation of very young massive clusters or "starburst" clusters is currently one of the most widely debated topic in astronomy. The classical notion dictates that a star cluster is formed in-situ in a dense molecular gas clump followed by a substantial residual gas expulsion. On the other hand, based on the observed morphologies of many young stellar associations, a hierarchical formation scenario is alternatively suggested. A very young (age $\\approx$ 1 Myr), massive ($>10^4M_\\odot$) star cluster like the Galactic NGC 3603 young cluster (HD 97950) is an appropriate testbed for distinguishing between such "monolithic" and "hierarchical" formation scenarios. A recent study by Banerjee and Kroupa (2014) demonstrates that the monolithic scenario remarkably reproduces the HD 97950 cluster. In the present work, we explore the possibility of the formation of the above cluster via hierarchical assembly of subclusters. These subclusters are initially distributed over a wide range of spatial volumes and have vari...

  1. Serine one-carbon catabolism with formate overflow

    Science.gov (United States)

    Meiser, Johannes; Tumanov, Sergey; Maddocks, Oliver; Labuschagne, Christiaan Fred; Athineos, Dimitris; Van Den Broek, Niels; Mackay, Gillian M.; Gottlieb, Eyal; Blyth, Karen; Vousden, Karen; Kamphorst, Jurre J.; Vazquez, Alexei

    2016-01-01

    Serine catabolism to glycine and a one-carbon unit has been linked to the anabolic requirements of proliferating mammalian cells. However, genome-scale modeling predicts a catabolic role with one-carbon release as formate. We experimentally prove that in cultured cancer cells and nontransformed fibroblasts, most of the serine-derived one-carbon units are released from cells as formate, and that formate release is dependent on mitochondrial reverse 10-CHO-THF synthetase activity. We also show that in cancer cells, formate release is coupled to mitochondrial complex I activity, whereas in nontransformed fibroblasts, it is partially insensitive to inhibition of complex I activity. We demonstrate that in mice, about 50% of plasma formate is derived from serine and that serine starvation or complex I inhibition reduces formate synthesis in vivo. These observations transform our understanding of one-carbon metabolism and have implications for the treatment of diabetes and cancer with complex I inhibitors.

  2. Fe-inserted and shell-shaped carbon nanoparticles by cluster-mediated laser pyrolysis

    Science.gov (United States)

    Fleaca, C. T.; Dumitrache, F.; Morjan, I.; Alexandrescu, R.; Sandu, I.; Luculescu, C.; Birjega, S.; Prodan, G.; Stamatin, I.

    2012-09-01

    We report here the high-yield continuous synthesis of carbon nanoparticles with and without Fe content by laser pyrolysis technique. The laser beam decomposes (via C2H4 sensitizer) the Fe(CO)5 as Fe clusters which absorb themselves the laser radiation. They trigger the fast carbon particles formation by exothermic dehydrogenation/polymerization of the surrounded C2H2 molecules. This combination between Fe clusters and C2H2 generates nanoparticles with unusual structure. Depending on the gas pressure in the reaction chamber, two kinds of nanoparticles were obtained: at lower pressure, 30-40 nm diameter particles with a defective structure, part of them crowded with Fe clusters (3-6 nm) and two types of nanoparticles (around 50-60 nm) at the highest pressure. Some of them have a shell-shape structure, presenting a distinct envelope, other with a turbostratic arrangement, and few containing one or several smaller (3-20 nm) Fe nanoparticles trapped inside. We consider that these particular structures of our nanoparticles may be useful in applications such as MRI applications, drug delivery or catalysts.

  3. Insights on Clusters Formation Mechanism by Time of Flight Mass Spectrometry. 2. The Case of Acetone-Water Clusters

    Science.gov (United States)

    Apicella, B.; Li, X.; Passaro, M.; Russo, C.

    2016-11-01

    This paper is the second of a series dealing with clusters formation mechanism. In part 1, water clusters with the addition of an electrophilic molecule such as ethanol were studied by Time Of Flight Mass Spectrometry (TOFMS). Mass distributions of molecular clusters of ethanol, water and ethanol-water mixed clusters, were obtained by means of two different ionization methods: Electron Ionization (EI) and picosecond laser Photo-Ionization (PI) at a wavelength of 355 nm. In part 2, the same experimental approach was employed to obtain mass spectra of clusters generated by acetone-water binary mixtures with a different composition. Strong dependence of the mass spectra of clusters with EI and PI on the acetone-water mixing ratio was observed. It was shown that the spectral pattern changes gradually and water-rich cluster signals become fainter while acetone-rich cluster signals become more intensive with increasing acetone concentrations from 0.3% to 40%. Owing to the hydrogen bond acceptor character of acetone, its self-association is discouraged with respect to ethanol. The autocorrelation function (AF) was used to analyze the variation of the water clusters composition with the increase of the acetone concentration in terms of fundamental periodicities. However, although acetone and ethanol present a very different hydrogen-bonding ability, similarly to ethanol-water system, in acetone-water system the formation of water-rich clusters and subsequent metastable fragmentation are the dominant process that determine the clusters distribution, irrespective of the ionization process, while the ionization process significantly affects the acetone-rich clusters distribution.

  4. Dilute Surfactant Methods for Carbonate Formations

    Energy Technology Data Exchange (ETDEWEB)

    Kishore K. Mohanty

    2006-02-01

    There are many fractured carbonate reservoirs in US (and the world) with light oil. Waterflooding is effective in fractured reservoirs, if the formation is water-wet. Many fractured carbonate reservoirs, however, are mixed-wet and recoveries with conventional methods are low (less than 10%). The process of using dilute anionic surfactants in alkaline solutions has been investigated in this work for oil recovery from fractured oil-wet carbonate reservoirs both experimentally and numerically. This process is a surfactant-aided gravity drainage where surfactant diffuses into the matrix, lowers IFT and contact angle, which decrease capillary pressure and increase oil relative permeability enabling gravity to drain the oil up. Anionic surfactants have been identified which at dilute concentration of 0.05 wt% and optimal salinity can lower the interfacial tension and change the wettability of the calcite surface to intermediate/water-wet condition as well or better than the cationic surfactant DTAB with a West Texas crude oil. The force of adhesion in AFM of oil-wet regions changes after anionic surfactant treatment to values similar to those of water-wet regions. The AFM topography images showed that the oil-wetting material was removed from the surface by the anionic surfactant treatment. Adsorption studies indicate that the extent of adsorption for anionic surfactants on calcite minerals decreases with increase in pH and with decrease in salinity. Surfactant adsorption can be minimized in the presence of Na{sub 2}CO{sub 3}. Laboratory-scale surfactant brine imbibition experiments give high oil recovery (20-42% OOIP in 50 days; up to 60% in 200 days) for initially oil-wet cores through wettability alteration and IFT reduction. Small (<10%) initial gas saturation does not affect significantly the rate of oil recovery in the imbibition process, but larger gas saturation decreases the oil recovery rate. As the core permeability decreases, the rate of oil recovery reduces

  5. Simulating the Formation of Carbon-rich Molecules on an idealised Graphitic Surface

    CERN Document Server

    Marshall, David W

    2015-01-01

    There is accumulating evidence for the presence of complex molecules, including carbon-bearing and organic molecules, in the interstellar medium. Much of this evidence comes to us from studies of chemical composition, photo- and mass-spectroscopy in cometary, meteoritic and asteroid samples, indicating a need to better understand the surface chemistry of astrophysical objects. There is also considerable interest in the origins of life-forming and life-sustaining molecules on Earth. Here, we perform reactive molecular dynamics simulations to probe the formation of carbon-rich molecules and clusters on carbonaceous surfaces resembling dust grains and meteoroids. Our results show that large chains form on graphitic surfaces at low temperatures (100K - 500K) and smaller fullerene-like molecules form at higher temperatures (2000K - 3000K). The formation is faster on the surface than in the gas at low temperatures but slower at high temperatures as surface interactions prevent small clusters from coagulation. We fi...

  6. On the Motion of Carbon Nanotube Clusters near Optical Fiber Tips: Thermophoresis, Radiative Pressure, and Convection Effects.

    Science.gov (United States)

    Vélez-Cordero, J Rodrigo; Hernández-Cordero, J

    2015-09-15

    We analyze the motion of multiwalled carbon nanotubes clusters in water or ethanol upon irradiation with a 975 and 1550 nm laser beam guided by an optical fiber. Upon measuring the velocities of the nanotube clusters in and out of the laser beam cone, we were able to identify thermophoresis, convection and radiation pressure as the main driving forces that determine the equilibrium position of the dispersion at low optical powers: while thermophoresis and convection pull the clusters toward the laser beam axis (negative Soret coefficient), radiation pressure pushes the clusters away from the fiber tip. A theoretical solution for the thermophoretic velocity, which considers interfacial motion and a repulsive potential interaction between the nanotubes and the solvent (hydrophobic interaction), shows that the main mechanism implicated in this type of thermophoresis is the thermal expansion of the fluid, and that the clusters migrate to hotter regions with a characteristic thermal diffusion coefficient D(T) of 9 × 10(-7) cm(2) K(-1) s(-1). We further show that the characteristic length associated with thermophoresis is not that of the nanotube clusters size, O(1) μm, but that corresponding to the microstructure of the clusters, O(1) nm. We finally discuss the role of the formation of gas-liquid interfaces (microbubbles) at high optical powers on the deposition of carbon nanotubes on the optical fiber end faces.

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

    Science.gov (United States)

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

    2008-07-01

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

  8. The star cluster - field star connection in nearby spiral galaxies. II. Field star and cluster formation histories and their relation

    Science.gov (United States)

    Silva-Villa, E.; Larsen, S. S.

    2011-05-01

    Context. Recent studies have started to cast doubt on the assumption that most stars are formed in clusters. Observational studies of field stars and star cluster systems in nearby galaxies can lead to better constraints on the fraction of stars forming in clusters. Ultimately this may lead to a better understanding of star formation in galaxies, and galaxy evolution in general. Aims: We aim to constrain the amount of star formation happening in long-lived clusters for four galaxies through the homogeneous, simultaneous study of field stars and star clusters. Methods: Using HST/ACS and HST/WFPC2 images of the galaxies NGC 45, NGC 1313, NGC 5236, and NGC 7793, we estimate star formation histories by means of the synthetic CMD method. Masses and ages of star clusters are estimated using simple stellar population model fitting. Comparing observed and modeled luminosity functions, we estimate cluster formation rates. By randomly sampling the stellar initial mass function (SIMF), we construct artificial star clusters and quantify how stochastic effects influence cluster detection, integrated colors, and age estimates. Results: Star formation rates appear to be constant over the past 107 - 108 years within the fields covered by our observations. The number of clusters identified per galaxy varies, with a few detected massive clusters (M ≥ 105 M⊙) and a few older than 1 Gyr. Among our sample of galaxies, NGC 5236 and NGC 1313 show high star and cluster formation rates, while NGC 7793 and NGC 45 show lower values. We find that stochastic sampling of the SIMF has a strong impact on the estimation of ages, colors, and completeness for clusters with masses ≤ 103 - 104 M⊙, while the effect is less pronounced for high masses. Stochasticity also makes size measurements highly uncertain at young ages (τ ≲ 108 yr), making it difficult to distinguish between clusters and stars based on sizes. Conclusions: The ratio of star formation happening in clusters (Γ) compared to

  9. Formation and properties of defects and small vacancy clusters in SiC: Ab initio calculations

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Fei; Weber, William J.; Xiao, H. Y.; Zu, Xiaotao T.

    2009-09-11

    Large-scale ab initio simulation methods have been employed to investigate the configurations and properties of defects in SiC. Atomic structures, formation energies and binding energies of small vacancy clusters have also been studied as a function of cluster size, and their relative stabilities are determined. The calculated formation energies of point defects are in good agreement with previously theoretical calculations. The results show that the most stable configuration of a di-vacancy cluster consists of two C vacancies located at second nearest neighbor sites, while a di-vacancy with two Si vacancies is not stable and may dissociate at room temperature. In general, the formation energies of small vacancy clusters increase with size, but the formation energies for clusters with a Si vacancy and n C vacancies (VSi-nVC) are much smaller than those with a C vacancy and n Si vacancies (VC-nVSi). These results demonstrate that the VSi-nVC clusters are more stable than the VC-nVSi clusters in SiC, and provide possible nucleation sites for larger vacancy clusters or voids to grow. For these small vacancy clusters, the binding energy decreases with increasing cluster size, and ranges from 2.5 to 4.6 eV. These results indicate that the small vacancy clusters in SiC are stable at temperatures up to 1900 K, which is consistent with experimental observations.

  10. Formation and properties of defects and small vacancy clusters in SiC: Ab initio calculations

    Science.gov (United States)

    Gao, F.; Weber, W. J.; Xiao, H. Y.; Zu, X. T.

    2009-09-01

    Large-scale ab initio simulation methods have been employed to investigate the configurations and properties of defects in SiC. Atomic structures, formation energies and binding energies of small vacancy clusters have also been studied as a function of cluster size, and their relative stabilities are determined. The calculated formation energies of point defects are in good agreement with previously theoretical calculations. The results show that the di-vacancy cluster consists of two C vacancies located at the second nearest neighbor sites is stable up to 1300 K, while a di-vacancy with two Si vacancies is not stable and may dissociate at room temperature. In general, the formation energies of small vacancy clusters increase with size, but the formation energies for clusters with a Si vacancy and nC vacancies (VSi-nVC) are much smaller than those with a C vacancy and nSi vacancies (VC-nVSi). These results demonstrate that the VSi-nVC clusters are more stable than the VC-nVSi clusters in SiC, and provide possible nucleation sites for larger vacancy clusters or voids to grow. For these small vacancy clusters, the binding energy decreases with increasing cluster size, and ranges from 2.5 to 4.6 eV. These results indicate that the small vacancy clusters in SiC are stable at temperatures up to 1900 K, which is consistent with experimental observations.

  11. Impact of diagenesis on carbonate mound formation

    NARCIS (Netherlands)

    van der Land, C.

    2011-01-01

    This thesis is devoted to define the parameters influencing cold-water coral growth and therefore carbonate mound development with a focus on the impact of diagenesis on mound sediments. The first part of this thesis (Chapters 2 to 4) discusses the distributionand growth history of carbonate mounds,

  12. Simulating radiative feedback and star cluster formation in GMCs: 1. Dependence on gravitational boundedness

    CERN Document Server

    Howard, Corey; Harris, William

    2016-01-01

    Radiative feedback is an important consequence of cluster formation in Giant Molecular Clouds (GMCs) in which newly formed clusters heat and ionize their surrounding gas. The process of cluster formation, and the role of radiative feedback, has not been fully explored in different GMC environments. We present a suite of simulations which explore how the initial gravitational boundedness, and radiative feedback, affect cluster formation. We model the early evolution (< 5 Myr) of turbulent, 10$^6$ M$_{\\odot}$ clouds with virial parameters ranging from 0.5 to 5. To model cluster formation, we use cluster sink particles, coupled to a raytracing scheme, and a custom subgrid model which populates a cluster via sampling an IMF with an efficiency of 20% per freefall time. We find that radiative feedback only decreases the cluster formation efficiency, measured via the total particle mass, by a few percent. The initial virial parameter plays a much stronger role in limiting cluster formation, with a spread of clust...

  13. FORMATION OF BRANCH TECHNOLOGY CLUSTERS IN INDUSTRIAL PRODUCTION

    Directory of Open Access Journals (Sweden)

    Sergei S. Kabanov

    2013-01-01

    Full Text Available A problem of cluster analysis as a universal method of interpreting the empirical research is considered in the article. Basic results of analysis of technological development of Russian industry are represented. Quantitative study of the existence of industrial clusters and practical recommendations to improve its internal economic characteristics are given.

  14. Environments and Morphologies of Red Sequence Galaxies with Residual Star Formation in Massive Clusters

    CERN Document Server

    Crossett, Jacob P; Stott, John P; Jones, D Heath

    2013-01-01

    We present a photometric investigation into recent star formation in galaxy clusters at z ~ 0.1. We use spectral energy distribution templates to quantify recent star formation in large X-ray selected clusters from the LARCS survey using matched GALEX NUV photometry. These clusters all have signs of red sequence galaxy recent star formation (as indicated by blue NUV-R colour), regardless of cluster morphology and size. A trend in environment is found for these galaxies, such that they prefer to occupy low density, high cluster radius environments. The morphology of these UV bright galaxies suggests that they are in fact red spirals, which we confirm with light curves and Galaxy Zoo voting percentages as morphological proxies. These UV bright galaxies are therefore seen to be either truncated spiral galaxies, caught by ram pressure in falling into the cluster, or high mass spirals, with the photometry dominated by the older stellar population.

  15. Effects of Cluster Size on Platinum-Oxygen Bonds Formation in Small Platinum Clusters

    Science.gov (United States)

    Oemry, Ferensa; Padama, Allan Abraham B.; Kishi, Hirofumi; Kunikata, Shinichi; Nakanishi, Hiroshi; Kasai, Hideaki; Maekawa, Hiroyoshi; Osumi, Kazuo; Sato, Kaoru

    2012-03-01

    We present the results of density functional theory calculation in oxygen dissociative adsorption process on two types of isolated platinum (Pt) clusters: Pt4 and Pt10, by taking into account the effect of cluster reconstruction. The strength of Pt-Pt bonds in the clusters is mainly defined by d-d hybridization and interstitial bonding orbitals (IBO). Oxygen that adsorbed on the clusters is weakening the IBO and thus inducing geometry reconstruction as occurred in Pt10 cluster. However, cluster that could undergo structural deformation is found to promote oxygen dissociation with no energy barrier. The details show that maintaining well-balanced of attractive and repulsive (Hellmann-Feynman) forces between atoms is considered to be the main key to avoid any considerable rise of energy barrier. Furthermore, a modest energy barrier that gained in Pt4 cluster is presumed to be originate from inequality of intramolecular forces between atoms.

  16. Knowledge Cluster Formation as a Science Policy in Malaysia: Lessons Learned

    Directory of Open Access Journals (Sweden)

    Hans-Dieter Evers

    2015-01-01

    Full Text Available Regional science policy aims to create productive knowledge clusters, which are central places within an epistemic landscape of knowledge production and dissemination. These so-called K-clusters are said to have the organisational capability to drive innovations and create new industries. Many governments have used cluster formation as one of their development strategies. This paper looks at Malaysia’s path towards a knowledge-based economy and offers some evidence on the current state of knowledge cluster formation in that country. If the formation of a knowledge cluster has been the government policy, what has been the result? Is there an epistemic landscape of knowledge clusters? Has the main knowledge cluster really materialised? Data collected from websites, directories, government publications and expert interviews have enabled us to construct the epistemic landscape of Peninsular Malaysia, and Penang in particular. We identify and describe several knowledge clusters with a high density of knowledge producing institutions and their knowledge workers. An analysis of the knowledge output, measured in terms of scientific publications, patents and trademarks, shows that knowledge clusters have indeed been productive – as predicted by cluster theory – although the internal working of clusters require further explanation.

  17. Carbon Diffusion and Kinetics During the Lath Martensite Formation

    OpenAIRE

    Hsu (xu Zuyao), T.Y.

    1995-01-01

    Calculations verify that carbon diffusion may occur during the lath martensite formation. Accordingly, the diffusion of interstitial atoms or ions must be taken into account when martensitic transformation is defined as a diffusionless transformation. In derivation of the kinetics equation of the athermal martensitic transfomation, regarding the carbon diffusion, i .e. the enrichment of the austenite during the lath martensite formation, and ΔG(γ→α) being function of the temperature and the c...

  18. Martensite Formation in Partially and Fully Austenitic Plain Carbon Steels

    NARCIS (Netherlands)

    Van Bohemen, S.M.C.; Sietsma, J.

    2009-01-01

    The progress of martensite formation in plain carbon steels Fe-0.46C, Fe-0.66C, and Fe-0.80C has been investigated by dilatometry. It is demonstrated that carbon enrichment of the remaining austenite due to intercritical annealing of Fe-0.46C and Fe-0.66C does not only depress the start temperature

  19. Formation of ordered CoAl alloy clusters by the plasma-gas condensation technique

    Science.gov (United States)

    Konno, Toyohiko J.; Yamamuro, Saeki; Sumiyama, Kenji

    2001-09-01

    CoxAl1-x alloy clusters were synthesized from a mixture of Co and Al metal vapors generated by the sputtering of pure metal targets. We observed that the produced alloy clusters were uniform in size, ranging from approximately 20 nm for Al-rich clusters to 10 nm for Co-rich clusters. For a wide average composition range (x≈0.4-0.7), the alloy clusters have the ordered B2 (CsCl-type) structure. In the Co-rich cluster aggregates (x=0.76), the clusters are composed of face-centered-cubic (fcc) Co and minor CoAl(B2) clusters. In the Al-rich aggregates (x=0.23), the clusters are mainly composed of the fcc-Al phase, although clusters occasionally possess a "core-shell structure" with the CoAl(B2) phase surrounded by an Al-rich amorphous phase. These observations are in general agreement with our prediction based on the equilibrium phase diagram. We also noticed that the average composition depends not only on the relative amount of Co and Al vapors, but also on their absolute amount, and even on the Ar gas flow rate, which promotes mixing and cooling the two vapors. These findings show that the formation of alloy clusters in vapor phase is strongly influenced by the kinetics of cluster formation, and is a competing process between the approach to equilibrium and the quenching of the whole system.

  20. Simulating the formation of carbon-rich molecules on an idealized graphitic surface

    Science.gov (United States)

    Marshall, David W.; Sadeghpour, H. R.

    2016-01-01

    There is accumulating evidence for the presence of complex molecules, including carbon-bearing and organic molecules, in the interstellar medium. Much of this evidence comes to us from studies of chemical composition, photo- and mass spectroscopy in cometary, meteoritic and asteroid samples, indicating a need to better understand the surface chemistry of astrophysical objects. There is also considerable interest in the origins of life-forming and life-sustaining molecules on the Earth. Here, we perform reactive molecular dynamics simulations to probe the formation of carbon-rich molecules and clusters on carbonaceous surfaces resembling dust grains and meteoroids. Our results show that large chains form on graphitic surfaces at low temperatures (100-500 K) and smaller fullerene-like molecules form at higher temperatures (2000-3000 K). The formation is faster on the surface than in the gas at low temperatures but slower at high temperatures as surface interactions prevent small clusters from coagulation. We find that for efficient formation of molecular complexity, mobility about the surface is important and helps to build larger carbon chains on the surface than in the gas phase at low temperatures. Finally, we show that the temperature of the surface strongly determines what kind of structures forms and that low turbulent environments are needed for efficient formation.

  1. Structural and scaling properties of galaxy clusters: probing the physics of structure formation

    CERN Document Server

    Arnaud, M; Pratt, G W

    2003-01-01

    We present XMM-Newton studies of the total mass, gas density, temperature and entropy profiles in nearby hot and cool clusters, together with follow-up observations of distant clusters from the SHARC Survey. The observed structural and scaling properties are compared with the predictions of the self-similar model of cluster formation. These data indicate that clusters do form a self-similar population down to low mass and up to high redshift, and give support to the standard picture of structure formation for the dark matter component. However, deviations from the standard scaling laws confirm that the specific physics of the gas component is still insufficiently understood.

  2. The star formation history of the Large Magellanic Cloud as seen by star clusters and stars

    OpenAIRE

    2010-01-01

    The aim of this work is to test to what extent the star cluster population of a galaxy can be utilised to constrain or estimate the star formation history, with the Large Magellanic Cloud as our testbed. We follow two methods to extract information about the star formation rate from star clusters, either using only the most massive clusters (Maschberger & Kroupa 2007) or using the whole cluster population, albeit this is only possible for a shorter age span. We compare these results with the ...

  3. Isolation and characterization of unusual multinuclear Schiff base complexes: rearrangements reactions and octanuclear cluster formation.

    Science.gov (United States)

    Martínez Belmonte, Marta; Escudero-Adán, Eduardo C; Martin, Eddy; Kleij, Arjan W

    2012-05-07

    The isolation and full characterization of multinuclear Schiff base complexes is reported, and their relevance as precursors for octanuclear Zn(8) salen cluster complex formation is discussed. Starting from simple precursors, three tetranuclear Zn(4) complexes were accessed that incorporate typical half-salen units and comprise of bridging acetates. The use of alternative reaction conditions or a step-wise approach smoothly leads to Zn(8) cluster formation. In addition, the tetranuclear Zn(4) complexes themselves may also serve as precursors toward Zn(8) cluster formation when treated under appropriate reaction conditions. The influence of the solvent medium in the latter Zn(4) → Zn(8) conversion was separately studied and revealed the formation of unusual pyridine-ligated multinuclear structures with fully condensed salen coordination pockets, providing a possible prelude to octanuclear cluster formation.

  4. Clues on galaxy and cluster formation from their scaling relations

    CERN Document Server

    Lanzoni, B; Cappi, A; Tormen, G; Zamorani, G

    2003-01-01

    By means of high-resolution N-body simulations in a LambdaCDM cosmology, we verify that scaling relations similar to those observed for nearby galaxy clusters are also defined by their dark matter hosts; the slopes, however, are not the same. We then show that the scaling relations of galaxy clusters can be explained as the result of the cosmological collapse of density fluctuations at the appropriate scales, plus a systematic trend of the M/L ratio with cluster mass. The empirical fact that the exponent of the Faber-Jackson relation of elliptical galaxies is significantly different (higher) than that of clusters, force us to conclude that the galaxy scaling laws might derive from the cosmological collapse of density fluctuations at the epoch when galactic scales became non-linear, plus modifications afterward due to early-time dissipative merging.

  5. The formation of filamentary structures in radiative cluster winds

    CERN Document Server

    Rodr'iguez-Gonz'alez, A; Raga, A C; Cant'o, J

    2008-01-01

    We explore the dynamics of a ``cluster wind'' flow in the regime in which the shocks resulting from the interaction of winds from nearby stars are radiative. We first show that for a cluster with T Tauri stars and/or Herbig Ae/Be stars, the wind interactions are indeed likely to be radiative. We then compute a set of four, three dimensional, radiative simulations of a cluster of 75 young stars, exploring the effects of varying the wind parameters and the density of the initial ISM that permeates the volume of the cluster. These simulations show that the ISM is compressed by the action of the winds into a structure of dense knots and filaments. The structures that are produced resemble in a qualitative way the observations of the IRAS 18511+0146 of Vig et al. (2007).

  6. Cluster Formation Using Kohonens Self-Organising Map

    Directory of Open Access Journals (Sweden)

    Vivekanand S Gogi

    2012-06-01

    Full Text Available An Artificial Neural Network (ANN is an information processing paradigm that is inspired by the way biological nervous systems, such as the brain, process information. The key element is the novel structure of the information processing system. It is composed of a large number of highly interconnected processing elements (neurons working in unison to solve specific problems. The objective of this research paper is to study the clustering of requests from the Flexible Manufacturing System machines to the Automated Storage/Retrieval system and to optimize the clustering of the requests. Artificial Neural Networks has been used for clustering the requests from the machines. Unsupervised Learning (training algorithm in Artificial Neural Networks is used and implemented using C++ programming language. The requests from the machines are successfully analyzed and optimization of clusters is done using Kohonens SelfOrganizing Map technique.

  7. Cluster formation as a measure of interpretability in multiple testing.

    Science.gov (United States)

    Shaffer, Juliet Popper

    2008-10-01

    Multiple test procedures are usually compared on various aspects of error control and power. Power is measured as some function of the number of false hypotheses correctly identified as false. However, given equal numbers of rejected false hypotheses, the pattern of rejections, i.e. the particular set of false hypotheses identified, may be crucial in interpreting the results for potential application.In an important area of application, comparisons among a set of treatments based on random samples from populations, two different approaches, cluster analysis and model selection, deal implicitly with such patterns, while traditional multiple testing procedures generally focus on the outcomes of subset and pairwise equality hypothesis tests, without considering the overall pattern of results in comparing methods. An important feature involving the pattern of rejections is their relevance for dividing the treatments into distinct subsets based on some parameter of interest, for example their means. This paper introduces some new measures relating to the potential of methods for achieving such divisions. Following Hartley (1955), sets of treatments with equal parameter values will be called clusters. Because it is necessary to distinguish between clusters in the populations and clustering in sample outcomes, the population clusters will be referred to as P -clusters; any related concepts defined in terms of the sample outcome will be referred to with the prefix outcome. Outcomes of multiple comparison procedures will be studied in terms of their probabilities of leading to separation of treatments into outcome clusters, with various measures relating to the number of such outcome clusters and the proportion of true vs. false outcome clusters. The definitions of true and false outcome clusters and related concepts, and the approach taken here, is in the tradition of hypothesis testing with attention to overall error control and power, but with added consideration of

  8. Formation of bcc and fcc during the coalescence of free and supported Fe and Ni clusters.

    Science.gov (United States)

    Li, Guojian; Wang, Qiang; Sui, Xudong; Wang, Kai; Wu, Chun; He, Jicheng

    2015-09-07

    The formation of bcc and fcc during the coalescence of free and supported Fe and Ni clusters has been studied by molecular dynamics simulation using an embedded atom method. Structural evolution of the clusters, coalesced under varying temperature, Ni content and substrate conditions, was explored by interatomic energy, snapshots, pair distribution functions and bond order parameters. The results show that the formation of bcc and fcc is strongly related to Ni content, substrate and coalescence temperature. Free clusters coalesced at 1200 K form bcc at lower Ni contents with fcc forming at higher Ni concentrations and no observable coexistence of bcc and fcc. Differences in coalescence at 1000 K result from the coexistence of bcc and fcc within the Ni range of 50-70%. Free clusters supported on disordered Ni substrates were shown to transform from spherical morphology to islands of supported clusters with preferred epitaxial orientation. The Ni content required to form bcc and fcc coexistence on supported clusters at 1000 K decreased to 30-50% Ni. Free clusters possessing bcc and fcc generally stacked along the bcc (110) and fcc (111) facets, whereas supported clusters stacked along the (111) bcc and (100) fcc planes. Structural transformation was induced by clusters containing greater numbers of atoms. Spread over the substrate enhanced interatomic energy, order substrates affect the epitaxial growth direction and increase the melting points of the supported clusters. This study can be used to predict the nature of fcc and bcc formation in Fe-Ni films.

  9. Pd clusters supported on amorphous, low-porosity carbon spheres for hydrogen production from formic acid.

    Science.gov (United States)

    Bulushev, Dmitri A; Bulusheva, Lyubov G; Beloshapkin, Sergey; O'Connor, Thomas; Okotrub, Alexander V; Ryan, Kevin M

    2015-04-29

    Amorphous, low-porosity carbon spheres on the order of a few micrometers in size were prepared by carbonization of squalane (C30H62) in supercritical CO2 at 823 K. The spheres were characterized and used as catalysts' supports for Pd. Near-edge X-ray absorption fine structure studies of the spheres revealed sp(2) and sp(3) hybridized carbon. To activate carbons for interaction with a metal precursor, often oxidative treatment of a support is needed. We showed that boiling of the obtained spheres in 28 wt % HNO3 did not affect the shape and bulk structure of the spheres, but led to creation of a considerable amount of surface oxygen-containing functional groups and increase of the content of sp(2) hybridized carbon on the surface. This carbon was seen by scanning transmission electron microscopy in the form of waving graphene flakes. The H/C atomic ratio in the spheres was relatively high (0.4) and did not change with the HNO3 treatment. Palladium was deposited by impregnation with Pd acetate followed by reduction in H2. This gave uniform Pd clusters with a size of 2-4 nm. The Pd supported on the original C spheres showed 2-3 times higher catalytic activity in vapor phase formic acid decomposition and higher selectivity for H2 formation (98-99%) than those for the catalyst based on the HNO3 treated spheres. Using of such low-porosity spheres as a catalyst support should prevent mass transfer limitations for fast catalytic reactions.

  10. Oxygen aggregation kinetics, thermal donors and carbon-oxygen defect formation in silicon containing carbon and tin

    Energy Technology Data Exchange (ETDEWEB)

    Angeletos, T.; Sgourou, E. N.; Andrianakis, A.; Diamantopoulou, A.; Londos, C. A. [Solid State Section, Physics Department, University of Athens, Panepistimiopolis, Zografos, 157 84 Athens (Greece); Chroneos, A. [Faculty of Engineering and Computing, Coventry University, Priory Street, Coventry CV1 5FB (United Kingdom); Department of Materials, Imperial College London, London SW7 2BP (United Kingdom)

    2015-07-07

    Localized vibrational mode spectroscopy measurements on Czochralski silicon (Cz-Si) samples subjected to isothermal annealing at 450 °C are reported. First, we studied the effect of carbon (C) and tin (Sn) isovalent dopants on the aggregation kinetics of oxygen. It is determined that the reduction rate of oxygen is described by the Johnson-Mehl-Avrami equation in accordance with previous reports. The activation energy related with the reaction rate constant of the process is calculated to increase from Cz-Si, to C-doped Cz-Si (CCz-Si), to Sn-doped Cz-Si contained C (SnCz-Si). This is attributed to the presence of the isovalent dopants that may impact both the kinetics of the oxygen atoms and also may lead to the formation of other oxygen-related clusters. Second, we studied the effect of Sn on the formation and evolution of carbon-oxygen (C-O) defects. It was determined that the presence of Sn suppresses the formation of the C-O defects as indicated by the reduction in the strength of the 683, 626, and 586 cm{sup −1} well-known bands of C{sub s}O{sub i} defect. The phenomenon is attributed to the association of Sn with C atoms that may prevent the pairing of O with C. Third, we investigated the effect of C and Sn on the formation of thermal donors (TDs). Regarding carbon our results verified previous reports that carbon suppresses the formation of TDs. Interestingly, when both C and Sn are present in Si, very weak bands of TDs were observed, although it is known that Sn alone suppress their formation. This may be attributed to the competing strains of C and Sn in the Si lattice.

  11. Formation of globular clusters induced by external ultraviolet radiation II: Three-dimensional radiation hydrodynamics simulations

    CERN Document Server

    Abe, Makito; Hasegawa, Kenji

    2016-01-01

    We explore the possibility of the formation of globular clusters under ultraviolet (UV) background radiation. One-dimensional spherical symmetric radiation hydrodynamics (RHD) simulations by Hasegawa et al. have demonstrated that the collapse of low-mass (10^6-10^7 solar masses) gas clouds exposed to intense UV radiation can lead to the formation of compact star clusters like globular clusters (GCs) if gas clouds contract with supersonic infall velocities. However, three-dimensional effects, such as the anisotropy of background radiation and the inhomogeneity in gas clouds, have not been studied so far. In this paper, we perform three-dimensional RHD simulations in a semi-cosmological context, and reconsider the formation of compact star clusters in strong UV radiation fields. As a result, we find that although anisotropic radiation fields bring an elongated shadow of neutral gas, almost spherical compact star clusters can be procreated from a "supersonic infall" cloud, since photo-dissociating radiation supp...

  12. Star formation in the first galaxies - III. Formation, evolution, and characteristics of the first stellar cluster

    CERN Document Server

    Safranek-Shrader, Chalence; Milosavljevic, Milos; Bromm, Volker

    2015-01-01

    We simulate the formation of a low metallicity (0.01 Zsun) stellar cluster in a dwarf galaxy at redshift z~14. Beginning with cosmological initial conditions, the simulation utilizes adaptive mesh refinement and sink particles to follow the collapse and evolution of gas past the opacity limit for fragmentation, thus resolving the formation of individual protostellar cores. A time- and location-dependent protostellar radiation field, which heats the gas by absorption on dust, is computed by integration of protostellar evolutionary tracks with the MESA code. The simulation also includes a robust non-equilibrium chemical network that self-consistently treats gas thermodynamics and dust-gas coupling. The system is evolved for 18 kyr after the first protostellar source has formed. In this time span, 30 sink particles representing protostellar cores form with a total mass of 81 Msun. Their masses range from ~0.1 Msun to 14.4 Msun with a median mass ~0.5-1 Msun. Massive protostars grow by competitive accretion while...

  13. The Turn Over of the Odd-even Pattern in Mass Spectra of Carbon Cluster Anions

    Institute of Scientific and Technical Information of China (English)

    NI Guoquan; LIU Bingchen; ZHAI Huajin

    2000-01-01

    @@ Although investigations by many authorsd on the properties of carbon cluster anions by mass spectrometry and photoelectron spectroscopy last more than a decade[1~3], a general conclusion concerning the various features of the carbon clusters generated most commonly in laser vaporization/molecular beam sources has not yet been reached. In this Letter we report that the turn-over of the odd-even patter in relative abundance in the mass spectra of carbon clusters and the "manipulation" of the pattern can be realized in a controlled way by altering the vaporizing laser intensity, the backing pressure and the conductance of carries gas.

  14. Hierarchically Clustered Star Formation in the Magellanic Clouds

    CERN Document Server

    Gouliermis, Dimitrios A; Ossenkopf, Volker; Klessen, Ralf S; Dolphin, Andrew E

    2012-01-01

    We present a cluster analysis of the bright main-sequence and faint pre--main-sequence stellar populations of a field ~ 90 x 90 pc centered on the HII region NGC 346/N66 in the Small Magellanic Cloud, from imaging with HST/ACS. We extend our earlier analysis on the stellar cluster population in the region to characterize the structuring behavior of young stars in the region as a whole with the use of stellar density maps interpreted through techniques designed for the study of the ISM structuring. In particular, we demonstrate with Cartwrigth & Whitworth's Q parameter, dendrograms, and the Delta-variance wavelet transform technique that the young stellar populations in the region NGC 346/N66 are hierarchically clustered, in agreement with other regions in the Magellanic Clouds observed with HST. The origin of this hierarchy is currently under investigation.

  15. Aging and memory improvement through semantic clustering: The role of list-presentation format.

    Science.gov (United States)

    Kuhlmann, Beatrice G; Touron, Dayna R

    2016-11-01

    The present study examined how the presentation format of the study list influences younger and older adults' semantic clustering. Spontaneous clustering did not differ between age groups or between an individual-words (presentation of individual study words in consecution) and a whole-list (presentation of the whole study list at once for the same total duration) presentation format in 132 younger (18-30 years, M = 19.7) and 120 older (60-84 years, M = 69.5) adults. However, after instructions to use semantic clustering (second list) age-related differences in recall magnified, indicating a utilization deficiency, and both age groups achieved higher recall in the whole-list than in the individual-words format. While this whole-list benefit was comparable across age groups, it is notable that older adults were only able to improve their average recall performance after clustering instructions in the whole-list but not in the individual-words format. In both formats, instructed clustering was correlated with processing resources (processing speed and, especially, working memory capacity), particularly in older adults. Spontaneous clustering, however, was not related to processing resources but to metacognitive beliefs about the efficacy and difficulty of semantic clustering, neither of which indicated awareness of the benefits of the whole-list presentation format in either age group. Taken together, the findings demonstrate that presentation format has a nontrivial influence on the utilization of semantic clustering in adults. The analyses further highlight important differences between output-based and list-based clustering measures. (PsycINFO Database Record

  16. Comparative Study of Formation and Stabilization of Gold and Silver Clusters and Nanoparticles in Mordenites

    NARCIS (Netherlands)

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

    2011-01-01

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

  17. The spatial distribution of star and cluster formation in M 51

    NARCIS (Netherlands)

    Scheepmaker, R.A.; Lamers, H.J.G.L.M.; Anders, P.; Larsen, S.S.

    2009-01-01

    Aims. We study the connection between spatially resolved star formation and young star clusters across the disc of M 51. Methods. We combine star cluster data based on B, V, and I-band Hubble Space Telescope ACS imaging, together with new WFPC2 U-band photometry to derive ages, masses, and extinctio

  18. Studies on the formation, evolution, and destruction of massive star clusters

    NARCIS (Netherlands)

    Bastian, Nathan John

    2005-01-01

    This thesis presents the results of mainly observational studies on the formation, evolution, and destruction of massive star clusters. We show, using a variety of observational techniques, that globular clusters which were once thought to only be able to form in the early universe are in fact still

  19. On the Formation of cD Galaxies and their Parent Clusters

    CERN Document Server

    Tovmassian, H M; 10.1111/j.1365-2966.2012.22044.x

    2012-01-01

    In order to study the mechanism of formation of cD galaxies we search for possible dependencies between the K-band luminosity of cDs and the parameters of their host clusters which we select to have a dominant cD galaxy, corresponding to a cluster morphology of Bautz-Morgan (BM) type I. As a comparison sample we use cD galaxies in clusters where they are not dominant, which we define here as non-BMI (NBMI) type clusters. We find that for 71 BMI clusters the absolute K-band luminosity of cDs depends on the cluster richness, but less strongly on the cluster velocity dispersion. Meanwhile, for 35 NBMI clusters the correlation between cD luminosity and cluster richness is weaker, and is absent between cD luminosity and velocity dispersion. In addition, we find that the luminosity of the cD galaxy hosted in BMI clusters tends to increase with the cD's peculiar velocity with respect to the cluster mean velocity. In contrast, for NBMI clusters the cD luminosity decreases with increasing peculiar velocity. Also, the ...

  20. Formation of proto-cluster: a virialized structure from gravo-turbulent collapse I. Simulation of cluster formation in collapsing molecular cloud

    CERN Document Server

    Lee, Yueh-Ning

    2016-01-01

    Stars are often observed to form in clusters. It is therefore important to understand how such a region of concentrated mass is assembled out of the diffuse medium and its properties eventually prescribe the important physical mechanisms and determine the characteristics of the stellar cluster. We study the formation of a gaseous proto-cluster inside a molecular cloud by performing high resolution MHD simulations and associate its internal properties to those of the parent cloud by varying the level of the initial turbulence of the cloud, with a view to better characterize the subsequent stellar cluster formation. The gaseous proto-cluster is formed out of global collapse of a molecular cloud, and has non-negligible rotation due to angular momentum conservation during the collapse of the object. Most of the star formation occurs in this region which occupies only a small volume fraction of the whole cloud. We identify such regions in simulations and compare the gas and sink particles to observations. The gase...

  1. Methodology of formation and development of the research-andproduction clusters in the region

    Directory of Open Access Journals (Sweden)

    E. L. Smolyanova

    2012-01-01

    Full Text Available In article the point of view of the author on set of means and the methods necessary for formation and development of research-and-production clusters is positioned. As the base doctrine of development of methodology of formation and development of research-andproduction clusters the indicative planning creating conditions for coordination of economic interests of business and the state is considered.

  2. Globular cluster ages and the formation of the galactic halo

    CERN Document Server

    Chaboyer, B; Sarajedini, A; Chaboyer, Brian; Sarajedini, Ata

    1995-01-01

    Main sequence turnoff magnitudes from the recent set of Yale isochrones (Chaboyer \\ea 1995) have been combined with a variety of relations for the absolute magnitude of RR Lyr stars (\\mvrr) to calibrate age as a function of the difference in magnitude between the main sequence turn-off and the horizontal branch (\\dv). A best estimate for the calibration of \\mvrr is derived from a survey of the current literature: \\mvrr = 0.20 \\feh + 0.98. This estimate, together with other calibrations (with slopes ranging from 0.15 to 0.30) has been used to derive \\dv ages for 43 Galactic globular clusters. Independent of the choice of \\mvrr, there is no strong evidence for an age-Galacto\\-centric distance relationship among the 43 globular clusters. However, an age-metallicity relation exists, with the metal-poor clusters being the oldest. A study of the age distribution reveals that an age range of 5 Gyr exists among the bulk of the globular clusters. In addition, about 10\\% of the sample are substantially younger, and inc...

  3. Fragmentation and Growth Energetics of Clusters Relevant to Atmospheric New Particle Formation

    Science.gov (United States)

    Bzdek, B. R.; DePalma, J. W.; Ridge, D. P.; Laskin, J.; Johnston, M. V.

    2013-12-01

    The exact mechanisms by which small clusters form and grow in the atmosphere are poorly understood, but this process may significantly impact cloud condensation nuclei number concentrations and global climate. Sulfuric acid is the key chemical component to new particle formation. However, basic species such as ammonia are also important. Few laboratory experiments address the kinetics or thermodynamics of acid and base incorporation into small clusters. This work utilizes a Fourier transform ion cyclotron resonance mass spectrometer equipped with surface-induced dissociation (FTICR-SID) to investigate time- and collision energy-resolved fragmentation of positively charged ammonium bisulfate clusters. The assumption underlying the experiment is that cluster growth can be considered the reverse of cluster fragmentation. Critical energies for fragmentation are obtained from Rice-Ramsperger-Kassel-Marcus/Quasi-Equilibrium Theory (RRKM/QET) modeling of the experimental data and are compared to quantum chemical calculations of the thermodynamics of cluster fragmentation. Fragmentation of ammonium bisulfate clusters occurs by two pathways: 1) a two-step pathway whereby the cluster sequentially loses ammonia followed by sulfuric acid and 2) a one-step pathway whereby the cluster loses an ammonium bisulfate molecule. Experimental critical energies for loss of an ammonia molecule and loss of an ammonium bisulfate molecule are higher than the thermodynamic values. If cluster growth is considered the reverse of cluster fragmentation, these results suggest that these clusters can grow by first adding sulfuric acid and then adding ammonia. Additionally, these results suggest the presence of an activation barrier to describe the incorporation of ammonia into small acidic clusters and therefore imply that kinetically (i.e. diffusion) limited growth should not be assumed. An important corollary is that models of atmospheric new particle formation should be revised to consider

  4. EXTENDED STAR FORMATION IN THE INTERMEDIATE-AGE LARGE MAGELLANIC CLOUD STAR CLUSTER NGC 2209

    Energy Technology Data Exchange (ETDEWEB)

    Keller, Stefan C.; Mackey, A. Dougal; Da Costa, Gary S. [Research School of Astronomy and Astrophysics, Australian National University, Canberra (Australia)

    2012-12-10

    We present observations of the 1 Gyr old star cluster NGC 2209 in the Large Magellanic Cloud made with the GMOS imager on the Gemini South Telescope. These observations show that the cluster exhibits a main-sequence turnoff that spans a broader range in luminosity than can be explained by a single-aged stellar population. This places NGC 2209 amongst a growing list of intermediate-age (1-3 Gyr) clusters that show evidence for extended or multiple epochs of star formation of between 50 and 460 Myr in extent. The extended main-sequence turnoff observed in NGC 2209 is a confirmation of the prediction in Keller et al. made on the basis of the cluster's large core radius. We propose that secondary star formation is a defining feature of the evolution of massive star clusters. Dissolution of lower mass clusters through evaporation results in only clusters that have experienced secondary star formation surviving for a Hubble time, thus providing a natural connection between the extended main-sequence turnoff phenomenon and the ubiquitous light-element abundance ranges seen in the ancient Galactic globular clusters.

  5. Massive Clusters in the Inner Regions of NGC 1365: Cluster Formation and Gas Dynamics in Galactic Bars

    CERN Document Server

    Elmegreen, Bruce G; Alloin, Danielle

    2009-01-01

    Cluster formation and gas dynamics in the central regions of barred galaxies are not well understood. This paper reviews the environment of three 10^7 Msun clusters near the inner Lindblad resonance of the barred spiral NGC 1365. The morphology, mass, and flow of HI and CO gas in the spiral and barred regions are examined for evidence of the location and mechanism of cluster formation. The accretion rate is compared with the star formation rate to infer the lifetime of the starburst. The gas appears to move from inside corotation in the spiral region to looping filaments in the interbar region at a rate of ~6 Msun/yr before impacting the bar dustlane somewhere along its length. The gas in this dustlane moves inward, growing in flux as a result of the accretion to ~40 Msun/yr near the ILR. This inner rate exceeds the current nuclear star formation rate by a factor of 4, suggesting continued buildup of nuclear mass for another ~0.5 Gyr. The bar may be only 1-2 Gyr old. Extrapolating the bar flow back in time, w...

  6. Mean-field instabilities and cluster formation in nuclear reactions

    CERN Document Server

    Colonna, M; Baran, V

    2016-01-01

    We review recent results on intermediate mass cluster production in heavy ion collisions at Fermi energy and in spallation reactions. Our studies are based on modern transport theories, employing effective interactions for the nuclear mean-field and incorporating two-body correlations and fluctuations. Namely we will consider the Stochastic Mean Field (SMF) approach and the recently developed Boltzmann-Langevin One Body (BLOB) model. We focus on cluster production emerging from the possible occurrence of low-density mean-field instabilities in heavy ion reactions. Within such a framework, the respective role of one and two-body effects, in the two models considered, will be carefully analysed. We will discuss, in particular, fragment production in central and semi-peripheral heavy ion collisions, which is the object of many recent experimental investigations. Moreover, in the context of spallation reactions, we will show how thermal expansion may trigger the development of mean-field instabilities, leading to...

  7. STAR CLUSTER FORMATION WITH STELLAR FEEDBACK AND LARGE-SCALE INFLOW

    Energy Technology Data Exchange (ETDEWEB)

    Matzner, Christopher D.; Jumper, Peter H., E-mail: matzner@astro.utoronto.ca [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, Ontario, M5S 3H4 (Canada)

    2015-12-10

    During star cluster formation, ongoing mass accretion is resisted by stellar feedback in the form of protostellar outflows from the low-mass stars and photo-ionization and radiation pressure feedback from the massive stars. We model the evolution of cluster-forming regions during a phase in which both accretion and feedback are present and use these models to investigate how star cluster formation might terminate. Protostellar outflows are the strongest form of feedback in low-mass regions, but these cannot stop cluster formation if matter continues to flow in. In more massive clusters, radiation pressure and photo-ionization rapidly clear the cluster-forming gas when its column density is too small. We assess the rates of dynamical mass ejection and of evaporation, while accounting for the important effect of dust opacity on photo-ionization. Our models are consistent with the census of protostellar outflows in NGC 1333 and Serpens South and with the dust temperatures observed in regions of massive star formation. Comparing observations of massive cluster-forming regions against our model parameter space, and against our expectations for accretion-driven evolution, we infer that massive-star feedback is a likely cause of gas disruption in regions with velocity dispersions less than a few kilometers per second, but that more massive and more turbulent regions are too strongly bound for stellar feedback to be disruptive.

  8. Acceleration of raindrops formation due to tangling-clustering instability in turbulent stratified atmosphere

    CERN Document Server

    Elperin, T; Krasovitov, B; Kulmala, M; Liberman, M; Rogachevskii, I; Zilitinkevich, S

    2013-01-01

    Condensation of water vapor on active cloud condensation nuclei produces micron-size water droplets. To form rain, they must grow rapidly into at least 50-100 micron-size droplets. Observations show that this process takes only 15-20 minutes. The unexplained physical mechanism of such fast growth, is crucial for understanding and modeling of rain, and known as "condensation-coalescence bottleneck in rain formation". We show that the recently discovered phenomenon of the tangling clustering instability of small droplets in temperature-stratified turbulence (Phys. Fluids 25, 085104, 2013) results in the formation of droplet clusters with drastically increased droplet number densities and strong five-orders-of-magnitude enhancement of the collision-coalescence rate inside the clusters. The mechanism of tangling clustering instability in the temperature-stratified turbulence is much more effective than the previously considered pure inertial clustering caused by the centrifugal effect of turbulent vortices. Our a...

  9. The Co-Formation of Spheroids and Quasars Traced in their Clustering

    CERN Document Server

    Hopkins, P F; Hernquist, L; Coil, A L; Myers, A D; Cox, T J; Spergel, D N; Hopkins, Philip F.; Lidz, Adam; Hernquist, Lars; Coil, Alison L.; Myers, Adam D.; Cox, Thomas J.; Spergel, David N.

    2006-01-01

    We compare observed clustering of quasars and galaxies as a function of redshift, mass, luminosity, & color/morphology, to constrain models of quasar fueling and spheroid-BH co-evolution. High redshift quasars are shown to be drawn from progenitors of local early-type galaxies, with the characteristic quasar luminosity L* reflecting a characteristic mass of 'active' BH/host populations at each redshift. Evolving observed high-z quasar clustering to z=0 predicts a trend of clustering in 'quasar remnants' as a function of stellar mass identical to that observed for early-types. However, quasar clustering does not simply reflect observed early (or late)-type populations; at each redshift, quasars cluster as an 'intermediate' population. Comparing with the age of elliptical stellar populations reveals that this 'intermediate' population represents those ellipticals undergoing or terminating their final significant star formation at each epoch. Assuming that quasar triggering is associated with the formation/t...

  10. Pseudopotential Density-Functional Calculations for Structures of Small Carbon Clusters CN (N = 2~8)

    Institute of Scientific and Technical Information of China (English)

    BAI Yu-Lin; CHEN Xiang-Rong; YANG Xiang-Dong; LU Peng-Fei

    2004-01-01

    We introduce a first-principles density-functional theory, i.e. the finite-difference pseudopotential densityfunctional theory in real space and the Langevin molecular dynamics annealing technique, to the descriptions of structures and some properties of small carbon clusters (CN, N = 2 ~ 8). It is shown that the odd-numbered clusters have linear structures and most of the even-numbered clusters prefer cyclic structures.

  11. Comparison of defect cluster accumulation and pattern formation in irradiated copper and nickel

    Energy Technology Data Exchange (ETDEWEB)

    Zinkle, S.J.; Snead, L.L. [Oak Ridge National Lab., TN (United States); Edwards, D.J. [Pacific Northwest Lab., Richland, WA (United States)] [and others

    1995-04-01

    The objective of this study is to compare the contrasting behavior of defect cluster formation in neutron-irradiated copper and nickel specimens. Transmission electron microscopy was used to examine the density and spatial distribution of defect clusters produced in copper and nickel as the result of fission neutron irradiation to damage levels of 0.01 to 0.25 displacements per atom (dpa) at irradiation temperature between 50 and 230{degrees}C. A comparison with published results in the literature indicates that defect cluster wall formation occurs in nickel irradiated at 0.2 to 0.4 T{sub M} in a wide variety of irradiation spectra. Defect cluster wall formation apparently only occurs in copper during low temperature irradiation with electrons and light ions. These results are discussed in terms of the thermal spike model for energetic displacement cascades.

  12. The Formation of Ethane from Carbon Dioxide under Cold Plasma

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Pulsed-corona plasma has been used as a new method for ethane dehydrogenation at low temperature and normal pressure using carbon dioxide as an oxidant in this paper. The effect of carbon dioxide content in the feed, power input, and flow rate of the reactants on the ethane dehydrogenation has been investigated. The experimental results show that the conversion of ethane increases with the increase in the amount of carbon dioxide in the feed. The yield of ethylene and acetylene decreases with the increase in the yield of carbon monoxide, indicating that the increased carbon dioxide leads to the part of ethylene and acetylene being oxidized to carbon monoxide. Power input is primarily an electrical parameter in pulsed-corona plasma, which plays an important role in reactant conversion and product formation. When the power input reaches 16 W, ethane conversion is 41.0% and carbon dioxide conversion is 26.3%. The total yield of ethylene and acetylene is 15.6%. The reduced flow rate of feed improves the conversion of ethane,carbon dioxide and the yield of acetylene, and induces carbon deposit as well.

  13. Formation of new stellar populations from gas accreted by massive young star clusters.

    Science.gov (United States)

    Li, Chengyuan; de Grijs, Richard; Deng, Licai; Geller, Aaron M; Xin, Yu; Hu, Yi; Faucher-Giguère, Claude-André

    2016-01-28

    Stars in clusters are thought to form in a single burst from a common progenitor cloud of molecular gas. However, massive, old 'globular' clusters--those with ages greater than ten billion years and masses several hundred thousand times that of the Sun--often harbour multiple stellar populations, indicating that more than one star-forming event occurred during their lifetimes. Colliding stellar winds from late-stage, asymptotic-giant-branch stars are often suggested to be triggers of second-generation star formation. For this to occur, the initial cluster masses need to be greater than a few million solar masses. Here we report observations of three massive relatively young star clusters (1-2 billion years old) in the Magellanic Clouds that show clear evidence of burst-like star formation that occurred a few hundred million years after their initial formation era. We show that such clusters could have accreted sufficient gas to form new stars if they had orbited in their host galaxies' gaseous disks throughout the period between their initial formation and the more recent bursts of star formation. This process may eventually give rise to the ubiquitous multiple stellar populations in globular clusters.

  14. Formation and microstructure of carbon encapsulated superparamagnetic Co nanoparticles

    Science.gov (United States)

    Sun, Xiang-Cheng; Reyes-Gasga, J.; Dong, X. L.

    Carbon encapsulated magnetic cobalt nanoparticles have been synthesized by the modified arc-discharge method. Both high resolution transmission electron microscopy (HREM) and powder X-ray diffraction (XRD) profiles reveal the presence of 8-15nm diameter crystallites coated with 1-3 carbon layers. In particular, HREM images indicate that the intimate and contiguous carbon fringe around those Co nanoparticles is good evidence for complete encapsulation by carbon shell layers. The encapsulated phases are identified as hcp α-Co, fcc β-Co and cobalt carbide (Co 3 C) nanocrystals using X-ray diffraction (XRD), nano-area electron diffraction (SAED) and energy dispersive X-ray analysis (EDX). However, some fcc β-Co particles with a significant fraction of stacking faults are observed by HREM and confirmed by means of numerical fast Fourier transform (FFT) of HREM lattice images. The carbon encapsulation formation and growth mechanism are also reviewed.

  15. Formation and local electronic structure of Ge clusters on Si(111)-7×7 surfaces

    Institute of Scientific and Technical Information of China (English)

    Ma Hai-Feng; Xu Ming-Chun; Yang Bing; Shi Dong-Xia; Guo Hai-Ming; Pang Shi-Jin; Gao Hong-Jun

    2007-01-01

    We report the formation and local electronic structure of Ge clusters on the Si(111)-7×7 surface studied by using variable temperature scanning tunnelling microscopy (VT-STM) and low-temperature scanning tunnelling spectroscopy (STS). Atom-resolved STM images reveal that the Ge atoms are prone to forming clusters with 1.0 nm in diameter for coverage up to 0.12 ML. Such Ge clusters preferentially nucleate at the centre of the faulted-half unit cells, leading to the 'dark sites' of Si centre adatoms from the surrounding three unfaulted-half unit cells in filled-state images. Biasdependent STM images show the charge transfer from the neighbouring Si adatoms to Ge clusters. Low-temperature STS of the Ge clusters reveals that there is a band gap on the Ge cluster and the large voltage threshold is about 0.9 V.

  16. Efficient star cluster formation in the core of a galaxy cluster: The dwarf irregular NGC 1427A in Fornax

    CERN Document Server

    Mora, Marcelo D; Puzia, Thomas H

    2014-01-01

    Gas-rich galaxies in dense environments such as galaxy clusters and massive groups are affected by a number of possible types of interactions with the cluster environment, which make their evolution radically different than that of field galaxies. The dIrr galaxy NGC 1427A, presently infalling towards the core of the Fornax galaxy cluster, offers a unique opportunity to study those processes in a level of detail not possible to achieve for galaxies at higher redshits. Using HST/ACS and auxiliary VLT/FORS ground-based observations, we study the properties of the most recent episodes of star formation in this gas-rich galaxy, the only one of its type near the core of the Fornax cluster. We study the structural and photometric properties of young star cluster complexes in NGC 1427A, identifying 12 bright such complexes with exceptionally blue colors. The comparison of our broadband near-UV/optical photometry with simple stellar population models yields ages below ~4x10^6 yr and stellar masses from a few thousand...

  17. Thick disk and pseudobulge formation in a clump cluster

    Directory of Open Access Journals (Sweden)

    Inoue S.

    2012-02-01

    Full Text Available Bulges in spiral galaxies have been supposed to be classified into two types: classical bulges or pseudobulges. Classical bulges are thought to form by galactic merger with bursty star formation, whereas pseudobulges are suggested to form by secular evolution. Noguchi (1998,199 suggested another bulge formation scenario, ‘clump-origin bulge’ [1,2]. He demonstrated using a numerical simulation that a galactic disc suffers dynamical instability to form clumpy structures in the early stage of disc formation, then the clumps are sucked into the galactic centre by dynamical friction and merge into a single bulge at the centre. Therefore, clump-origin bulges may have their own unique properties. I perform a high-resolution N-body/SPH simulation for the formation of the clump-origin bulge in an isolated galaxy model and study the formation of the clump-origin bulge. I find that the clump-origin bulge resembles pseudobulges in dynamical properties, a nearly exponential surface density profile, a barred boxy shape and a significant rotation. I also find that this bulge consists of old and metal-rich stars. These natures, old metal-rich population but pseudobulge-like structures, mean that the clump-origin bulge can not be simply classified into classical bulges nor pseudobulges. From these results, I discuss similarities of the clump-origin bulge to the Milky Way (MW bulge.

  18. Point-Defect Mediated Bonding of Pt Clusters on (5,5) Carbon Nanotubes

    DEFF Research Database (Denmark)

    Wang, J. G.; Lv, Y. A.; Li, X. N.;

    2009-01-01

    The adhesion of various sizes of Pt clusters on the metallic (5,5) carbon nanotubes (CNTs) with and without the point defect has been investigated by means of density functional theory (DFT). The calculations show that the binding energies of Pt-n (n = 1-6) clusters on the defect free CNTs are more......). The stronger orbital hybridization between the Pt atom and the carbon atom shows larger charge transfers on the defective CNTs than on the defect free CNTs, which allows the strong interaction between Pt clusters and CNTs. On the basis of DFT calculations, CNTs with point defect can be used as the catalyst...

  19. The regulation of star formation in cool-core clusters: imprints on the stellar populations of brightest cluster galaxies

    CERN Document Server

    Loubser, S I; Hoekstra, H; Mahdavi, A; Donahue, M; Bildfell, C; Voit, G M

    2015-01-01

    A fraction of brightest cluster galaxies (BCGs) shows bright emission in the UV and the blue part of the optical spectrum, which has been interpreted as evidence of recent star formation. Most of these results are based on the analysis of broadband photometric data. Here, we study the optical spectra of a sample of 19 BCGs hosted by X-ray luminous galaxy clusters at 0.15 < z < 0.3, a subset from the Canadian Cluster Comparison Project (CCCP) sample. We identify plausible star formation histories of the galaxies by fitting Simple Stellar Populations (SSPs) as well as composite populations, consisting of a young stellar component superimposed on an intermediate/old stellar component, to accurately constrain their star formation histories. We detect prominent young (~200 Myr) stellar populations in 4 of the 19 galaxies. Of the four, the BCG in Abell 1835 shows remarkable A-type stellar features indicating a relatively large population of young stars, which is extremely unusual even amongst star forming BCG...

  20. A Multi-Wavelength View of the Environments of Extreme Clustered Star Formation

    Science.gov (United States)

    De Buizer, James M.

    2017-01-01

    It is believed that the vast majority of, if not all, stars form within OB clusters. Most theories of star formation assume a star forms in isolation and ignore the fact that the cluster environment and, especially, the presence of extremely energetic and high mass young stellar objects nearby, may have a profound impact on the formation process of a typical cluster member. Giant HII (GHII) regions are Galactic analogs to starburst regions seen in external galaxies, hosting the most active areas of clustered star formation. As such, GHII regions represent a population of objects that can reveal a wealth of information on the environment of the earliest stages of clustered star formation and how it is affected by feedback from the most massive cluster members. This study employs new mid-infrared imaging data obtained from the airborne observatory, SOFIA, as well as archival imaging data from the near-infrared to cm radio wavelengths to create a rich multi-wavelength dataset of a dozen galactic GHII regions. These data allow quantification of the detailed physical conditions within GHII regions individually and as a population on both global and small scales.

  1. Formation of globular clusters induced by external ultraviolet radiation - II. Three-dimensional radiation hydrodynamics simulations

    Science.gov (United States)

    Abe, Makito; Umemura, Masayuki; Hasegawa, Kenji

    2016-12-01

    We explore the possibility of the formation of globular clusters (GCs) under ultraviolet (UV) background radiation. One-dimensional spherical symmetric radiation hydrodynamics (RHD) simulations by Hasegawa et al. have demonstrated that the collapse of low-mass (106-7 M⊙) gas clouds exposed to intense UV radiation can lead to the formation of compact star clusters like GCs if gas clouds contract with supersonic infall velocities. However, three-dimensional effects, such as the anisotropy of background radiation and the inhomogeneity in gas clouds, have not been studied so far. In this paper, we perform three-dimensional RHD simulations in a semicosmological context, and reconsider the formation of compact star clusters in strong UV radiation fields. As a result, we find that although anisotropic radiation fields bring an elongated shadow of neutral gas, almost spherical compact star clusters can be procreated from a `supersonic infall' cloud, since photodissociating radiation suppresses the formation of hydrogen molecules in the shadowed regions and the regions are compressed by UV heated ambient gas. The properties of resultant star clusters match those of GCs. On the other hand, in weak UV radiation fields, dark-matter-dominated star clusters with low stellar density form due to the self-shielding effect as well as the positive feedback by ionizing photons. Thus, we conclude that the `supersonic infall' under a strong UV background is a potential mechanism to form GCs.

  2. Formate oxidation driven calcium carbonate precipitation by Methylocystis parvus OBBP

    NARCIS (Netherlands)

    Ganendra, G; De Muynck, W; Ho, A.; Arvaniti, EC; Hosseinkhani, B; Ramos, JA; Rahier, H; Boon, N.

    2014-01-01

    Microbially Induced Carbonate Precipitation (MICP) applied in the construction industry poses several disadvantages such as ammonia release to the air and nitric acid production. An alternative MICP from calcium formate by Methylocystis parvus OBBP is presented in this study to overcome these disadv

  3. Formation rates, stability and reactivity of sulfuric acid - amine clusters predicted by computational chemistry

    Science.gov (United States)

    Kurtén, Theo; Ortega, Ismael; Kupiainen, Oona; Olenius, Tinja; Loukonen, Ville; Reiman, Heidi; McGrath, Matthew; Vehkamäki, Hanna

    2013-04-01

    Despite the importance of atmospheric particle formation for both climate and air quality, both experiments and non-empirical models using e.g. sulfuric acid, ammonia and water as condensing vapors have so far been unable to reproduce atmospheric observations using realistic trace gas concentrations. Recent experimental and theoretical evidence has shown that this mystery is likely resolved by amines. Combining first-principles evaporation rates for sulfuric acid - dimethylamine clusters with cluster kinetic modeling, we show that even sub-ppt concentrations of amines, together with atmospherically realistic concentrations of sulfuric acid, result in formation rates close to those observed in the atmosphere. Our simulated cluster formation rates are also close to, though somewhat larger than, those measured at the CLOUD experiment in CERN for both sulfuric acid - ammonia and sulfuric acid - dimethylamine systems. A sensitivity analysis indicates that the remaining discrepancy for the sulfuric acid - amine particle formation rates is likely caused by steric hindrances to cluster formation (due to alkyl groups of the amine molecules) rather than by significant errors in the evaporation rates. First-principles molecular dynamic and reaction kinetic modeling shed further light on the microscopic physics and chemistry of sulfuric acid - amine clusters. For example, while the number and type of hydrogen bonds in the clusters typically reach their equilibrium values on a picosecond timescale, and the overall bonding patterns predicted by traditional "static" quantum chemical calculations seem to be stable, the individual atoms participating in the hydrogen bonds continuously change at atmospherically realistic temperatures. From a chemical reactivity perspective, we have also discovered a surprising phenomenon: clustering with sulfuric acid molecules slightly increases the activation energy required for the abstraction of alkyl hydrogens from amine molecules. This implies

  4. Effect of secondary phase formation on the carbonation of olivine.

    Science.gov (United States)

    King, Helen E; Plümper, Oliver; Putnis, Andrew

    2010-08-15

    Large-scale olivine carbonation has been proposed as a potential method for sequestering CO(2) emissions. For in situ carbonation techniques, understanding the relationship between the formation of carbonate and other phases is important to predict the impact of possible passivating layers on the reaction. Therefore, we have conducted reactions of olivine with carbonated saline solutions in unstirred batch reactors. Altering the reaction conditions changed the Mg-carbonate morphology. We propose that this corresponded to changes in the ability of the system to precipitate hydromagnesite or magnesite. During high-temperature reactions (200 degrees C), an amorphous silica-enriched phase was precipitated that was transformed to lizardite as the reaction progressed. Hematite was also precipitated in the initial stages of these reactions but dissolved as the reaction proceeded. Comparison of the experimental observations with reaction models indicates that the reactions are governed by the interfacial fluid composition. The presence of a new Mg-silicate phase and the formation of secondary products at the olivine surface are likely to limit the extent of olivine to carbonate conversion.

  5. Stretching the threshold of reversible dynamics in silicon clusters: A case of carbon alloyed Si6

    Science.gov (United States)

    Nazrulla, Mohammed Azeezulla; Krishnamurty, Sailaja

    2016-09-01

    Silicon clusters with 3-50 atoms undergo isomerization/reversible dynamics or structural deformation at significantly lower temperatures of 350 K-500 K. Through Born Oppenheimer Molecular Dynamical (BOMD) simulations, the current study demonstrates that carbon alloying enhances the thermal stability of a silicon cluster. The study is carried out on a Si6 cluster which has been recently reported to undergo reversible dynamical movements using aberration-corrected transmission electron microscopy. Present BOMD simulations validate the experimentally observed reversible atomic displacements (reversible dynamical movements) at finite temperatures which are seen to persist nearly up to 2000 K. Carbon alloying of Si6 is seen to stretch the threshold of reversible dynamics from 200 K to 600 K depending upon the alloying concentration of carbon in the cluster.

  6. On the composition of ammonia-sulfuric acid clusters during aerosol particle formation

    Directory of Open Access Journals (Sweden)

    S. Schobesberger

    2014-05-01

    Full Text Available The formation of particles from precursor vapors is an important source of atmospheric aerosol. Research at the Cosmics Leaving OUtdoor Droplets (CLOUD facility at CERN tries to elucidate which vapors are responsible for this new particle formation, and how in detail it proceeds. Initial measurement campaigns at the CLOUD stainless-steel aerosol chamber focused on investigating particle formation from ammonia (NH3 and sulfuric acid (H2SO4. Experiments were conducted in the presence of water, ozone and sulfur dioxide. Contaminant trace gases were suppressed at the technological limit. For this study, we mapped out the compositions of small NH3-H2SO4 clusters over a wide range of atmospherically relevant environmental conditions. We covered [NH3] in the range from 2SO4] from 3.3 × 106 to 1.4 × 109 cm−3, and a temperature range from −25 to +20 °C. Negatively and positively charged clusters were directly measured by an atmospheric pressure interface time-of-flight (APi-TOF mass spectrometer, as they initially formed from gas-phase NH3 and H2SO4, and then grew to larger clusters containing more than 50 molecules of NH3 and H2SO4, corresponding to mobility-equivalent diameters greater than 2 nm. Water molecules evaporate from these clusters during sampling and are not observed. We found that the composition of the NH3-H2SO4 clusters is primarily determined by the ratio of gas-phase concentrations [NH3] / [H2SO4], as well as by temperature. Pure binary H2O-H2SO4 clusters (observed as clusters of only H2SO4 only form at [NH3] / [H2SO4]3] / [H2SO4], the composition of NH3-H2SO4 clusters was characterized by the number of NH3 molecules m added for each added H2SO4 molecule n (Δm / Δn, where n is in the range 4–18 (negatively charged clusters or 1–17 (positively charged clusters. For negatively charged clusters, Δm / Δn saturated between 1 and 1.4 for [NH3] / [H2SO4]>10. Positively charged clusters grew on average by Δm / Δn = 1.05 and

  7. Iron-carbide cluster thermal dynamics for catalyzed carbon nanotube growth

    Science.gov (United States)

    Ding, Feng; Bolton, Kim; Rosén, Arne

    2004-07-01

    Molecular dynamics simulations have been used to study the thermal behavior of FeN-mCm clusters where N, the total number of atoms, extends up to 2400. Comparison of the computed results with experimental data shows that the simulations yield the correct trends for the liquid-solid region of the iron-carbide phase diagram as well as the correct dependence of cluster melting point as a function of cluster size. The calculation indicates that, when carbon nanotubes (CNTs) are grown on large (>3-4 nm) catalyst particles at low temperatures (melting of the cluster. .

  8. Catalytic Formation of Propylene Carbonate from Supercritical Carbon Dioxide/Propylene Oxide Mixture

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Propylene carbonate was synthesized from supercritical carbon dioxide (SC-CO2)/ propylene oxide mixture with phthalocyaninatoaluminium chloride (ClAlPc)/ tetrabutylammon-ium bromide (n-Bu4NBr) as catalyst. The high rate of reaction was attributed to rapid diffusion and the high miscibility of propylene oxide in SC-CO2 under employed conditions. Various reaction periods present different formation rate of propylene carbonate, mainly due to the existence of phase change during the reaction. The experimental results demonstrate that SC-CO2 could be used as not only an environmentally benign solvent but also a carbon precursor in synthesis.

  9. Cluster Formation of Sulfuric Acid with Dimethylamine or Diamines and Detection with Chemical Ionization

    Science.gov (United States)

    Jen, C. N.; McMurry, P. H.; Hanson, D. R.

    2015-12-01

    Chemical ionization (CI) mass spectrometers are used to study atmospheric nucleation by detecting clusters produced by reactions of sulfuric acid and various basic gases. These instruments typically use nitrate to chemically ionize clusters for detection. In this study, we compare measured cluster concentrations formed by reacting sulfuric acid vapor with dimethylamine, ethylene diamine, tetramethylethylene diamine, or butanediamine (also known as putrescine) using nitrate and acetate ions. We show from flow reactor measurements that nitrate is unable to chemically ionize clusters with weak acidities. In addition, we vary the ion-molecule reaction time to probe the chemical ionization processes and lifetimes of ions composed of sulfuric acid and base molecules. We then model the neutral and ion cluster formation pathways, including chemical ionization, ion-induced clustering, and ion decomposition, to better identify which cluster types cannot be chemically ionized by nitrate. Our results show that sulfuric acid dimer with two diamines and sulfuric acid trimer with 2 or more base molecules cannot be chemical ionized by nitrate. We conclude that cluster concentrations measured with acetate CI gives a better representation of both cluster abundancies and their base content than nitrate CI.

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

    Institute of Scientific and Technical Information of China (English)

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

    2005-01-01

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

  11. A parsec-resolution simulation of the Antennae galaxies: Formation of star clusters during the merger

    CERN Document Server

    Renaud, Florent; Duc, Pierre-Alain

    2014-01-01

    We present a hydrodynamical simulation of an Antennae-like galaxy merger at parsec resolution, including a multi-component model for stellar feedback and reaching numerical convergence in the global star formation rate for the first time. We analyse the properties of the dense stellar objects formed during the different stages of the interaction. Each galactic encounter triggers a starburst activity, but the varying physical conditions change the triggering mechanism of each starburst. During the first two pericenter passages, the starburst is spatially extended and forms many star clusters. However, the starburst associated to the third, final passage is more centrally concentrated: stars form almost exclusively in the galactic nucleus and no new star cluster is formed. The maximum mass of stars clusters in this merger is more than 30 times higher than those in a simulation of an isolated Milky Way-like galaxy. Antennae-like mergers are therefore a formation channel of young massive clusters possibly leading...

  12. The Co-Formation of Spheroids and Quasars Traced in their Clustering

    Science.gov (United States)

    Hopkins, Philip F.; Lidz, Adam; Hernquist, Lars; Coil, Alison L.; Myers, Adam D.; Cox, Thomas J.; Spergel, David N.

    2007-06-01

    We compare observed clustering of quasars and galaxies as a function of redshift, mass, luminosity, and color/morphology, to constrain models of quasar fueling and the co-evolution of spheroids and supermassive black holes (BHs). High-redshift quasars are shown to be drawn from the progenitors of local early-type galaxies, with the characteristic quasar luminosity L* reflecting a characteristic mass of ``active'' BH/host populations at each epoch. Evolving observed high-z quasar clustering to z=0 predicts a trend of clustering in ``quasar remnants'' as a function of stellar mass identical to that observed for early types. However, quasar clustering does not simply reflect observed early (or late) type populations; at each redshift, quasars cluster as an ``intermediate'' population. Comparing with the age of elliptical stellar populations as a function of mass reveals that this ``intermediate'' population represents those ellipticals undergoing or terminating their final significant star formation activity at the given epoch. Assuming that quasar triggering is associated with the formation/termination epoch of ellipticals predicts quasar clustering at all observed redshifts without any model dependence or assumptions about quasar light curves, lifetimes, or accretion rates. This is not true for disks or quasar halos; i.e., quasars do not generically trace star formation or halo assembly. Quasar clustering at all redshifts is consistent with ~4×1012 h-1 Msolar, similar to group scales. This supports scenarios in which major mergers dominate the bright, high-redshift quasar populations. We show how improved clustering measurements can be used to constrain lower luminosity AGN fueling and whether or not accretion/star formation can ``shut down'' at z>3.

  13. Fragmentation and growth energetics of clusters relevant to new particle formation

    Science.gov (United States)

    Bzdek, Bryan R.; DePalma, Joseph W.; Ridge, Douglas P.; Laskin, Julia; Johnston, Murray V.

    2013-05-01

    The chemical mechanisms governing atmospheric new particle formation are not fully resolved, although this process may significantly impact cloud condensation nuclei levels. Whereas sulfuric acid is the key component, bases are also important in promoting nucleation and growth. This work utilizes a Fourier transform ion cyclotron resonance mass spectrometer (FTICR-MS) equipped with surface-induced dissociation (SID) to investigate time-and collision energy-resolved fragmentation of positively charged ammonium bisulfate clusters. Critical energies for dissociation are obtained from Rice-Ramsperger-Kassel-Marcus/Quasi-Equilibrium Theory (RRKM/QET) modeling of the experimental data and are compared to thermodynamic values. If cluster growth is considered the reverse of cluster dissociation, the results suggest that an activation barrier exists to the incorporation of ammonia into acidic clusters and that diffusion-limited cluster growth should not be assumed.

  14. Fragmentation and Growth Energetics of Ammonium Bisulfate Clusters Relevant to Atmospheric New Particle Formation

    Science.gov (United States)

    Bzdek, B. R.; DePalma, J.; Ridge, D. P.; Laskin, J.; Johnston, M. V.

    2012-12-01

    New particle formation (NPF) may significantly impact cloud albedo and global climate by influencing cloud condensation nuclei levels. The climate effects of NPF are governed by both the nucleation of new clusters and their growth to larger sizes. A firm understanding of the chemical mechanisms of small cluster growth to larger sizes is required to accurately model NPF. However, experimental measurements of the energetics of cluster growth are challenging. This presentation discusses results obtained using a new approach to studying cluster growth, by making measurements of cluster dissociation and inferring growth from the inverse process. In this work, the fragmentation energetics of positively charged ammonium bisulfate clusters of the form [(NH4)x(HSO4)x-1]+ were studied using a 6T Fourier transform ion cyclotron resonance mass spectrometer equipped with surface induced dissociation (SID), a method to fragment ions by impacting them on a surface at a precisely known collision energy. An ammonium bisulfate cluster was isolated and then fragmented by SID. Fragmentation efficiency curves were plotted as a function of collision energy and were fit to a Rice-Ramsperger-Kassel-Marcus/Quasi-Equilibrium Theory (RRKM/QET) model in order to extract threshold energies for dissociation. Two pathways exist for fragmentation of positively charged ammonium bisulfate clusters. The first is a one-step fragmentation pathway whereby the cluster loses an ammonium bisulfate molecule, [(NH4)(HSO4)]. The second fragmentation pathway is a two-step pathway, whereby the cluster first loses an ammonia molecule and next loses a sulfuric acid molecule. Assuming that cluster growth mechanisms are the reverse of cluster dissociation mechanisms, these observations suggest two potential growth pathways for ammonium bisulfate clusters: 1) growth by addition of an ammonium bisulfate molecule to a preexisting cluster and 2) stepwise growth by sequential addition of a sulfuric acid molecule

  15. Stresses and Cracking During Chromia-Spinel-NiO Cluster Formation in TBC Systems

    Science.gov (United States)

    Eriksson, Robert; Gupta, Mohit; Broitman, Esteban; Jonnalagadda, Krishna Praveen; Nylén, Per; Lin Peng, Ru

    2015-08-01

    Thermal barrier coatings (TBC) are used in gas turbines to reduce the temperatures in the underlying substrate. There are several mechanisms that may cause the TBC to fail; one of them is cracking in the coating interface due to extensive oxidation. In the present study, the role of so called chromia-spinel-NiO (CSN) clusters in TBC failure was studied. Such clusters have previously been found to be prone to cracking. Finite element modeling was performed on a CSN cluster to find out at which stage of its formation it cracks and what the driving mechanisms of cracking are. The geometry of a cluster was obtained from micrographs and modeled as close as possible. Nanoindentation was performed on the cluster to get the correct Young's moduli. The volumetric expansion associated with the formation of NiO was also included. It was found that the cracking of the CSN clusters is likely to occur during its last stage of formation as the last Ni-rich core oxidizes. Furthermore, it was shown that the volumetric expansion associated with the oxidation only plays a minor role and that the main reason for cracking is the high coefficient of thermal expansion of NiO.

  16. Formation of new stellar populations from gas accreted by massive young star clusters

    CERN Document Server

    Li, Chengyuan; Deng, Licai; Geller, Aaron M; Xin, Yu; Hu, Yi; Faucher-Giguere, Claude-Andre

    2016-01-01

    Stars in star clusters are thought to form in a single burst from a common progenitor cloud of molecular gas. However, massive, old globular clusters -- with ages greater than 10 billion years and masses of several hundred thousand solar masses -- often harbour multiple stellar populations, indicating that more than one star-forming event occurred during their lifetimes. Colliding stellar winds from late-stage, asymptotic-giant-branch stars are often invoked as second-generation star-formation trigger. The initial cluster masses should be at least 10 times more massive than they are today for this to work. However, large populations of clusters with masses greater than a few million solar masses are not found in the local Universe. Here we report on three 1-2 billion-year-old, massive star clusters in the Magellanic Clouds, which show clear evidence of burst-like star formation that occurred a few hundred million years after their initial formation era. We show that such clusters could accrete sufficient gas ...

  17. Stability of Galactic Gaseous Disks and the Formation of Massive Clusters

    CERN Document Server

    Escala, Andres

    2008-01-01

    We study gravitational instabilities in disks, with special attention to the most massive clumps that form because they are expected to be the progenitors of globular-type clusters. The maximum unstable mass is set by rotation and depends only on the surface density and orbital frequency of the disk. We propose that the formation of massive clusters is related to this largest scale in galaxies not stabilized by rotation. Using data from the literature, we predict that globular-like clusters can form in nuclear starburst disks and protogalactic disks but not in typical spiral galaxies, in agreement with observations.

  18. Stability of Galactic Gas Disks and the Formation of Massive Clusters

    CERN Document Server

    Escala, Andres

    2008-01-01

    We study gravitational instabilities in disks, with special attention to the most massive clumps that form because they are expected to be the progenitors of globular-type clusters. The maximum unstable mass is set by rotation and depends only on the surface density and orbital frequency of the disk. We propose that the formation of massive clusters is related to this largest scale in galaxies not stabilized by rotation. Using data from the literature, we predict that globular-like clusters can form in nuclear starburst disks and protogalactic disks but not in typical spiral galaxies, in agreement with observations.

  19. Dynamics of cluster formation in driven magnetic colloids dispersed on a monolayer.

    Science.gov (United States)

    Jäger, Sebastian; Stark, Holger; Klapp, Sabine H L

    2013-05-15

    We report computer simulation results on the cluster formation of dipolar colloidal particles driven by a rotating external field in a quasi-two-dimensional setup. We focus on the interplay between permanent dipolar and hydrodynamic interactions and its influence on the dynamic behavior of the particles. This includes their individual as well as their collective motion. To investigate these characteristics, we employ Brownian dynamics simulations of a finite system with and without hydrodynamic interactions. Our results indicate that hydrodynamic interactions have a profound impact on the dynamic behavior of the clusters and the dynamics of the clustering process.

  20. Problems of Formation and Funding of Tourist Clusters in the Regions of Russia

    Directory of Open Access Journals (Sweden)

    Igor Nikolaevich Molchanov

    2016-03-01

    Full Text Available The article deals with the urgent issues of the formation of clusters of tourism in the national economy of Russia. The attention is drawn to the need to develop domestic tourism at the regional level of governance in a rapidly changing geopolitical situation. The importance of tourism as one of the important areas of economic activity, affecting the pace of economic growth in the service industries is described. The advantages of the regional tourism clusters as a means of promoting the growth of productivity, efficiency and competitiveness of business entities of the tourism sector of the regional economy are revealed. The distinctive characteristics of regional tourism clusters are systematized; the definitions of tourist potential are structured; the cultural and historical heritage and tourist infrastructure are described. The author gives definition of the regional tourism cluster and explains its difference from the other definitions. The factors affecting the change in the situation in the sphere of tourism in Russia are described. The organizational prerequisites aimed at ensuring a coordinated interaction of all participants in the cluster and the establishment of the possible vectors of the coordinated development of economic and financial activity are formulated. There exist the possibility of organizational and economic measures aimed at development of the tourism sector of the regional economy. The potential sources of funding organizations participating in the cluster structures are investigated. The Russian experience in financing innovation clusters is described. The recommendations to improve the financial base of the emerging regional tourism clusters through the maximum use of budgetary and extra-budgetary resources are formulated. The use of public-private partnership is necessary. The attention is focused on the issues of financial security training, including specialists for newly established and functioning regional

  1. The extended star formation history of the star cluster NGC 2154 in the Large Magellanic Cloud

    CERN Document Server

    Baume, G; Costa, E; Méndez, R A; Girardi, L; Baume, Gustavo; Carraro, Giovanni; Costa, Edgardo; B., Rene' A. Mendez; Girardi, Leo

    2006-01-01

    The color-magnitude diagram (CMD) of the intermediate-age Large Magellanic Cloud (LMC) star cluster NGC 2154 and its adjacent field, has been analyzed using Padova stellar models to determine the cluster's fundamental parameters and its Star Formation History (SFH). Deep $BR$ CCD photometry, together with synthetic CMDs and Integrated Luminosity Functions (ILFs), has allowed us to infer that the cluster experienced an extended star formation period of about 1.2 Gyrs, which began approximately 2.3 Gyr and ended 1.1 Gyr ago. The physical reality of such a prolonged period of star formation is however questionable, and could be the result of inadequacies in the stellar evolutionary tracks themselves. A substantial fraction of binaries (70%) seems to exist in NGC 2154.

  2. Stellar contents and star formation in the young open cluster Stock 8

    CERN Document Server

    Jose, Jessy; Ojha, D K; Ogura, K; Chen, W P; Bhatt, B C; Ghosh, S K; Mito, H; Maheswar, G; Sharma, Saurabh

    2007-01-01

    We present $UBVI_c$ CCD photometry of the young open cluster Stock 8 with the aim to study the basic properties and star formation scenario in this region. The radius of the cluster is found to be $\\sim 6^{\\prime}$ ($\\sim 3.6$ pc) and the reddening within the cluster region varies from $E(B-V)=0.40$ to 0.60 mag. The cluster is located at a distance of $2.05 \\pm 0.10$ kpc. Using H$\\alpha$ slitless spectroscopy and 2MASS NIR data we identified H$\\alpha$ emission and NIR excess young stellar objects (YSOs), respectively. The colour-magnitude diagrams of these YSOs reveal that majority of these objects have ages between 1 to 5 Myr indicating a non-coeval star formation in the cluster. Massive stars in the cluster region reveal an average age of $\\le$ 2 Myr. In the cluster region ($r \\le 6^\\prime$) the slope of the mass function (MF), $\\Gamma$, in the mass range $\\sim 1.0 \\le M/M_\\odot < 13.4$ can be represented by a power law having a slope of $-1.38\\pm0.12$, which agrees well with Salpeter value (-1.35). In t...

  3. First nucleation theorem with cluster losses: sum rules and applications to new particle formation

    Science.gov (United States)

    McGraw, R. L.; Malila, J.; Laaksonen, A. J.; Lehtinen, K. E.

    2013-12-01

    Derivations of the first nucleation theorem for homogeneous nucleation invoke certain idealized conditions that would appear to render questionable any application the theorem to more complex systems such as atmospheric new particle formation (NPF). These include absence of cluster loss due to coagulation with background aerosol (or vessel walls in a laboratory experiment) and competing channels to NPF such as the potential conversion, hence loss, of pre-critical clusters by heterogeneous nucleation. To overcome these restrictions, we extend the kinetic derivation of the first nucleation theorem to include such cluster loss processes and discuss the implications of our findings for atmospheric NPF. The analysis yields a remarkable pair of sum rules that connect the formation and loss rates as a function of cluster size to the corresponding homogeneous nucleation rate. A third, equally remarkable, sum rule connects the observed, apparent critical size that results from naïve application of the first nucleation theorem without correcting for loss to the true critical cluster size from homogeneous nucleation theory, d*. We show that for clusters of true size d>d* (dclusters losses can be significant and multiple competing routes to stable NPF may be present at the same time.

  4. The relation between star formation, morphology and local density in high redshift clusters and groups

    CERN Document Server

    Poggianti, Bianca M; Finn, Rose; Bamford, Steven; De Lucia, Gabriella; Varela, Jesus; Aragon-Salamanca, Alfonso; Halliday, Claire; Noll, Stefan; Saglia, Roberto; Zaritsky, Dennis; Best, Philip; Clowe, Douglas; Milvang-Jensen, Bo; Jablonka, Pascale; Pello, Roser; Rudnick, Gregory; Simard, Luc; von der Linden, Anja; White, Simon

    2008-01-01

    We investigate how the [OII] properties and the morphologies of galaxies in clusters and groups at z=0.4-0.8 depend on projected local galaxy density, and compare with the field at similar redshifts and clusters at low-z. In both nearby and distant clusters, higher-density regions contain proportionally fewer star-forming galaxies, and the average [OII] equivalent width of star-forming galaxies is independent of local density. However, in distant clusters the average current star formation rate (SFR) in star-forming galaxies seems to peak at densities ~15-40 galaxies Mpc^{-2}. At odds with low-z results, at high-z the relation between star-forming fraction and local density varies from high- to low-mass clusters. Overall, our results suggest that at high-z the current star formation (SF) activity in star-forming galaxies does not depend strongly on global or local environment, though the possible SFR peak seems at odds with this conclusion. We find that the cluster SFR normalized by cluster mass anticorrelate...

  5. Carbon formation and metal dusting in advanced coal gasification processes

    Energy Technology Data Exchange (ETDEWEB)

    DeVan, J.H.; Tortorelli, P.F.; Judkins, R.R.; Wright, I.G.

    1997-02-01

    The product gases generated by coal gasification systems contain high concentrations of CO and, characteristically, have relatively high carbon activities. Accordingly, carbon deposition and metal dusting can potentially degrade the operation of such gasifier systems. Therefore, the product gas compositions of eight representative gasifier systems were examined with respect to the carbon activity of the gases at temperatures ranging from 480 to 1,090 C. Phase stability calculations indicated that Fe{sub 3}C is stable only under very limited thermodynamic conditions and with certain kinetic assumptions and that FeO and Fe{sub 0.877}S tend to form instead of the carbide. As formation of Fe{sub 3}C is a necessary step in the metal dusting of steels, there are numerous gasifier environments where this type of carbon-related degradation will not occur, particularly under conditions associated with higher oxygen and sulfur activities. These calculations also indicated that the removal of H{sub 2}S by a hot-gas cleanup system may have less effect on the formation of Fe{sub 3}C in air-blown gasifier environments, where the iron oxide phase can exist and is unaffected by the removal of sulfur, than in oxygen-blown systems, where iron sulfide provides the only potential barrier to Fe{sub 3}C formation. Use of carbon- and/or low-alloy steels dictates that the process gas composition be such that Fe{sub 3}C cannot form if the potential for metal dusting is to be eliminated. Alternatively, process modifications could include the reintroduction of hydrogen sulfide, cooling the gas to perhaps as low as 400 C and/or steam injection. If higher-alloy steels are used, a hydrogen sulfide-free gas may be processed without concern about carbon deposition and metal dusting.

  6. Star Formation In The Cluster Merger DLSCL J0916.2+2953

    CERN Document Server

    Mansheim, A S; Dawson, W A; Lubin, L M; Wittman, D; Schmidt, S

    2016-01-01

    We investigate star formation in DLSCL J0916.2+2953, a dissociative merger of two clusters at z=0.53 that has progressed $1.1^{+1.3}_{-0.4}$ Gyr since first pass-through. We attempt to reveal the effects a collision may have had on the evolution of the cluster galaxies by tracing their star formation history. We probe current and recent activity to identify a possible star formation event at the time of the merger using EW(Hd), EW([OII]), and D$_{n}$4000 measured from the composite spectra of 64 cluster and 153 coeval field galaxies. We supplement $Keck$ DEIMOS spectra with DLS and $HST$ imaging to determine the color, stellar mass, and morphology of each galaxy and conduct a comprehensive study of the populations in this complex structure. Spectral results indicate the average cluster and cluster red sequence galaxies experienced no enhanced star formation relative to the surrounding field during the merger, ruling out a predominantly merger-quenched population. We find that the average blue galaxy in the No...

  7. Modelling carbon overconsumption and the formation of extracellular particulate organic carbon

    Science.gov (United States)

    Schartau, M.; Engel, A.; Schröter, J.; Thoms, S.; Völker, C.; Wolf-Gladrow, D.

    2007-07-01

    During phytoplankton growth a fraction of dissolved inorganic carbon (DIC) assimilated by phytoplankton is exuded in the form of dissolved organic carbon (DOC), which can be transformed into extracellular particulate organic carbon (POC). A major fraction of extracellular POC is associated with carbon of transparent exopolymer particles (TEP; carbon content = TEPC) that form from dissolved polysaccharides (PCHO). The exudation of PCHO is linked to an excessive uptake of DIC that is not directly quantifiable from utilisation of dissolved inorganic nitrogen (DIN), called carbon overconsumption. Given these conditions, the concept of assuming a constant stoichiometric carbon-to-nitrogen (C:N) ratio for estimating new production of POC from DIN uptake becomes inappropriate. Here, a model of carbon overconsumption is analysed, combining phytoplankton growth with TEPC formation. The model describes two modes of carbon overconsumption. The first mode is associated with DOC exudation during phytoplankton biomass accumulation. The second mode is decoupled from algal growth, but leads to a continuous rise in POC while particulate organic nitrogen (PON) remains constant. While including PCHO coagulation, the model goes beyond a purely physiological explanation of building up carbon rich particulate organic matter (POM). The model is validated against observations from a mesocosm study. Maximum likelihood estimates of model parameters, such as nitrogen- and carbon loss rates of phytoplankton, are determined. The optimisation yields results with higher rates for carbon exudation than for the loss of organic nitrogen. It also suggests that the PCHO fraction of exuded DOC was 63±20% during the mesocosm experiment. Optimal estimates are obtained for coagulation kernels for PCHO transformation into TEPC. Model state estimates are consistent with observations, where 30% of the POC increase was attributed to TEPC formation. The proposed model is of low complexity and is applicable

  8. Modelling carbon overconsumption and the formation of extracellular particulate organic carbon

    Directory of Open Access Journals (Sweden)

    C. Völker

    2007-07-01

    Full Text Available During phytoplankton growth a fraction of dissolved inorganic carbon (DIC assimilated by phytoplankton is exuded in the form of dissolved organic carbon (DOC, which can be transformed into extracellular particulate organic carbon (POC. A major fraction of extracellular POC is associated with carbon of transparent exopolymer particles (TEP; carbon content = TEPC that form from dissolved polysaccharides (PCHO. The exudation of PCHO is linked to an excessive uptake of DIC that is not directly quantifiable from utilisation of dissolved inorganic nitrogen (DIN, called carbon overconsumption. Given these conditions, the concept of assuming a constant stoichiometric carbon-to-nitrogen (C:N ratio for estimating new production of POC from DIN uptake becomes inappropriate. Here, a model of carbon overconsumption is analysed, combining phytoplankton growth with TEPC formation. The model describes two modes of carbon overconsumption. The first mode is associated with DOC exudation during phytoplankton biomass accumulation. The second mode is decoupled from algal growth, but leads to a continuous rise in POC while particulate organic nitrogen (PON remains constant. While including PCHO coagulation, the model goes beyond a purely physiological explanation of building up carbon rich particulate organic matter (POM. The model is validated against observations from a mesocosm study. Maximum likelihood estimates of model parameters, such as nitrogen- and carbon loss rates of phytoplankton, are determined. The optimisation yields results with higher rates for carbon exudation than for the loss of organic nitrogen. It also suggests that the PCHO fraction of exuded DOC was 63±20% during the mesocosm experiment. Optimal estimates are obtained for coagulation kernels for PCHO transformation into TEPC. Model state estimates are consistent with observations, where 30% of the POC increase was attributed to TEPC formation. The proposed model is of low complexity and is

  9. Modelling carbon overconsumption and the formation of extracellular particulate organic carbon

    Directory of Open Access Journals (Sweden)

    M. Schartau

    2007-01-01

    Full Text Available During phytoplankton growth a fraction of dissolved inorganic carbon (DIC assimilated by phytoplankton is exuded in the form of dissolved organic carbon (DOC, which can be transformed into extracellular particulate organic carbon (POC. A major fraction of extracellular POC is associated with carbon of transparent exopolymer particles (TEP; carbon content = TEPC that form from dissolved polysaccharides (PCHO. The exudation of PCHO is linked to an excessive uptake of DIC that is not directly quantifiable from utilisation of dissolved inorganic nitrogen (DIN, called carbon overconsumption. Given these conditions, the concept of assuming a constant stoichiometric carbon-to-nitrogen (C:N ratio for estimating new production of POC from DIN uptake becomes inappropriate. Here, a model of carbon overconsumption is analysed, combining phytoplankton growth with TEPC formation. The model describes two modes of carbon overconsumption. The first mode is associated with DOC exudation during phytoplankton biomass accumulation. The second mode is decoupled from algal growth, but leads to a continuous rise in POC while particulate organic nitrogen (PON remains constant. While including PCHO coagulation, the model goes beyond a purely physiological explanation of building up carbon rich particulate organic matter (POM. The model is validated against observations from a mesocosm study. Maximum likelihood estimates of model parameters, such as nitrogen- and carbon loss rates of phytoplankton, are determined. The optimisation yields results with higher rates for carbon exudation than for the loss of organic nitrogen. It also suggests that the PCHO fraction of exuded DOC was 63±20% during the mesocosm experiment. Optimal estimates are obtained for coagulation kernels for PCHO transformation into TEPC. Model state estimates are consistent with observations, where 30% of the POC increase was attributed to TEPC formation. The proposed model is of low complexity and is

  10. Experimental study of carbonate formation in oceanic peridotite

    Science.gov (United States)

    Grozeva, Niya G.; Klein, Frieder; Seewald, Jeffrey S.; Sylva, Sean P.

    2017-02-01

    Interactions of CO2-rich aqueous fluids with mantle peridotite have major implications for geochemical budgets and microbial life in the shallow oceanic lithosphere through the formation of carbonate minerals and reduced carbon species. However, the underlying mechanisms controlling the transformation of CO2 to carbonates in ultramafic-hosted hydrothermal systems remain incompletely understood. A long-term laboratory experiment was conducted at 300 °C and 35 MPa to investigate serpentinization and carbonate formation pathways during hydrothermal alteration of peridotite. Powdered harzburgite was initially reacted with a Ca-rich aqueous fluid for 14,592 h (608 days) and changes in fluid composition were monitored with time. Once the system reached a steady state, a CO2(aq)-rich fluid was injected and allowed to react with the system for 5907 h (246 days). Fluid speciation and mineral analyses suggest that serpentinization of harzburgite in the CO2-poor system led to the precipitation of serpentine, brucite, magnetite, and minor calcite, in addition to other minor phases including chlorite and sulfur-poor Ni sulfides. The addition of the CO2(aq)-rich fluid caused dolomite, Ca-rich dolomite, and high-Mg calcite to form at the expense of olivine, calcite, and brucite, while serpentine remained unreactive. Replacement textures and mineral assemblages mimic those documented in carbonate-altered seafloor serpentinites, particularly those from the Mid-Atlantic Ridge and the Iberia Margin. In contrast to thermodynamic predictions, magnesite did not form in the experiment because the dissolution of clinopyroxene, in combination with the lack of serpentine reactivity, maintained low Mg/Ca ratios in solution. Clinopyroxene dissolution and unreactive serpentine may similarly maintain low Mg/Ca ratios in submarine serpentinization systems and limit magnesite formation in subseafloor environments. Results of this study suggest that the formation of Ca-Mg carbonates by mineral

  11. A Blind Equalizer Based on Unsupervised Gaussian Cluster Formation with an Adaptive Non—Linearity

    Institute of Scientific and Technical Information of China (English)

    LiuHanyu; TongWen; 等

    1997-01-01

    In this paper we present a blind equalizer algorithm based on an unsupervised Gaussian cluster formation technique with an optimized gradient adaptive step-size to update the equalizer coefficients.The novelty of this work lies in the optimization of the nonlinearity of the cluster formation used to achieve an optimal soft decision.The proposed iterative procedure combined with the variable step-size gradient-based adaptation,significantly accelerates the convergence speed of the blind equalization.The advantages of the proposed equalization techniques are illustrated by simulation.Simulation results obtained are compared with the Sato and Godard blind equalizers.

  12. FORMATION AND EVOLUTION OF NUCLEAR STAR CLUSTERS WITH IN SITU STAR FORMATION: NUCLEAR CORES AND AGE SEGREGATION

    Energy Technology Data Exchange (ETDEWEB)

    Aharon, Danor; Perets, Hagai B. [Physics Department, Technion—Israel Institute of Technology, Haifa 32000 (Israel)

    2015-02-01

    Nuclear stellar cluster (NSCs) are known to exist around massive black holes (MBHs) in galactic nuclei. Two formation scenarios were suggested for their origin: (1) buildup of NSCs from consecutive infall of stellar clusters and (2) continuous in situ star formation. Though the cluster infall scenario has been extensively studied, the in situ formation scenario has been hardly explored. Here we use Fokker-Planck (FP) calculations to study the effects of star formation on the buildup of NSCs and its implications for their long-term evolution and their resulting structure. We use the FP equation to describe the evolution of stellar populations and add appropriate source terms to account for the effects of newly formed stars. We show that continuous star formation even 1-2 pc away from the MBH can lead to the buildup of an NSC with properties similar to those of the Milky Way NSC. We find that the structure of the old stellar population in the NSC with in situ star formation could be very similar to the steady-state Bahcall-Wolf cuspy structure. However, its younger populations do not yet achieve a steady state. In particular, formed/evolved NSCs with in situ star formation contain differential age-segregated stellar populations that are not yet fully mixed. Younger stellar populations formed in the outer regions of the NSC have a cuspy structure toward the NSC outskirts, while showing a core-like distribution inward, with younger populations having larger core sizes. In principal, such a structure can give rise to an apparent core-like radial distribution of younger stars, as observed in the Galactic center.

  13. Molecular dynamics study of crater formation by core-shell structured cluster impact

    Science.gov (United States)

    Aoki, Takaaki; Seki, Toshio; Matsuo, Jiro

    2012-07-01

    Crater formation processes by the impacts of large clusters with binary atomic species were studied using molecular dynamics (MD) simulations. Argon and xenon atoms are artificially organized in core-shell cluster structures with various component ratios and irradiated on a Si(1 0 0) target surface. When the cluster has Xe1000 core covered with 1000 Ar atoms, and impacts at a total of 20 keV, the core Xe cluster penetrates into the deep area, and a crater with a conical shape is left on the target. On the other hand, in the case of a cluster with the opposite structure, Ar1000 core covered with 1000 Xe atoms, the cluster stops at a shallow area of the target. The incident cluster atoms are mixed and tend to spread in a lateral direction, which results in a square shaped crater with a shallower hole and wider opening. The MD simulations suggest that large cluster impacts cause different irradiation effects by changing the structure, even if the component ratio is the same.

  14. Assessment of the Cluster Formation Potential in the Regions of the Southern Federal District

    Directory of Open Access Journals (Sweden)

    Svetlana Anatolyevna Beloglazova

    2015-12-01

    Full Text Available Cluster policy implementation is an important factor of economic development of a country as a whole as well as of a particular region. The clustering approach to regional development attaches high importance to the microeconomic sphere, as well as territorial and social aspects of economic development. Clusterization provides effective tools for stimulating socio-political and economic development of area, multiplying growth of employment and investment, accelerating advanced technologies transfer; wages increasing, budget revenues growing, and enhancing competitiveness of regional production systems. Analysis of the prerequisites, conditions and resources for the formation and development of innovation clusters becomes the foundation for the scientific justifying regional economy modernization strategy and creating its points of growth and innovative mode of developing. The analysis carried out on the basis of the author’s methodology, and on subsequent grouping and ranking of 4 regions of the Southern Federal District, including the Volgograd region, by clustering processes intensity criterion, made it possible to shape a view of strengths and weaknesses of the regional economies, and give recommendations to improve the environment for innovative clusters forming and functioning. The carried-out analysis gave the chance to define regions with optimum conditions for introduction of cluster policy and regions with possibility of cluster development which are at lower level both on separate indicators, and on composite indexes of initial and resultant indicators.

  15. Star and Stellar Cluster Formation: ALMA-SKA Synergies

    CERN Document Server

    Fuller, G A; Rathborne, J M; Longmore, S; Molinari, S

    2015-01-01

    Over the next decade, observations conducted with ALMA and the SKA will reveal the process of mass assembly and accretion onto young stars and will be revolutionary for studies of star formation. Here we summarise the capabilities of ALMA and discuss recent results from its early science observations. We then review infrared and radio variability observations of both young low-mass and high-mass stars. A time domain SKA radio continuum survey of star forming regions is then outlined. This survey will produce radio light-curves for hundreds of young sources, providing for the first time a systematic survey of radio variability across the full range of stellar masses. These light-curves will probe the magnetospheric interactions of young binary systems, the origins of outflows, trace episodic accretion on the central sources and potentially constrain the rotation rates of embedded sources.

  16. Dwarf Detachment and Globular Cluster Formation in Arp 305

    CERN Document Server

    Hancock, M; Struck, C; Giroux, M L; Hurlock, S

    2009-01-01

    Tidal Dwarf Galaxies (TDG), concentrations of interstellar gas and stars in the tidal features of interacting galaxies, have been the subject of much scrutiny. The `smoking gun' that will prove the TDG hypothesis is the discovery of independent dwarf galaxies that are detached from other galaxies, but have clear tidal histories. As part of a search for TDGs we are using GALEX to conduct a large UV imaging survey of interacting galaxies selected from the Arp Atlas. As part of that study, we present a GALEX UV and SDSS and SARA optical study of the gas-rich interacting galaxy pair Arp 305. The GALEX UV data reveal much extended diffuse UV emission and star formation outside the disks including a candidate TDG between the two galaxies. We have used a smooth particle hydrodynamics code to model the interaction and determine the fate of the candidate TDG.

  17. Major contribution of neutral clusters to new particle formation in the free troposphere

    Directory of Open Access Journals (Sweden)

    C. Rose

    2014-07-01

    Full Text Available The formation of new aerosol particles in the atmosphere is a key process influencing the aerosol number concentration as well as the climate, in particular in the free troposphere (FT where the newly formed particles directly influence cloud formation. However, free tropospheric new particle formation (NPF is poorly documented due to logistic limitations and complex atmospheric dynamics around high altitude stations that make the observation of this day-time process challenging. Recent improvements in measurement techniques make now possible the detection of neutral clusters down to ~ 1 nm sizes, which opens new horizons in our understanding of the nucleation process. Indeed, only the charged fraction of clusters has been reported in the upper troposphere up to now. Here we report observations of charged and neutral clusters (1 to 2.5 nm mobility diameter during day-time free tropospheric conditions at the altitude site of Puy de Dôme (1465 m a.s.l., central France, between 10 and 29 February 2012. Our findings demonstrate that in the free troposphere, the formation of 1.5 nm neutral clusters is about 40 times higher than the one of ionic clusters during NPF events, indicating that they dominate in the nucleation process. We also observe that the total cluster concentration increases by a factor of 5.5 during NPF events compared to the other days, which was not clearly observed for the charged cluster population in the past. In the FT, the nucleation process does not seem to be sulphuric acid-limited, as previously suggested, and could be promoted by the transport of pollutants to the upper troposphere.

  18. On the composition of ammonia-sulfuric-acid ion clusters during aerosol particle formation

    Science.gov (United States)

    Schobesberger, S.; Franchin, A.; Bianchi, F.; Rondo, L.; Duplissy, J.; Kürten, A.; Ortega, I. K.; Metzger, A.; Schnitzhofer, R.; Almeida, J.; Amorim, A.; Dommen, J.; Dunne, E. M.; Ehn, M.; Gagné, S.; Ickes, L.; Junninen, H.; Hansel, A.; Kerminen, V.-M.; Kirkby, J.; Kupc, A.; Laaksonen, A.; Lehtipalo, K.; Mathot, S.; Onnela, A.; Petäjä, T.; Riccobono, F.; Santos, F. D.; Sipilä, M.; Tomé, A.; Tsagkogeorgas, G.; Viisanen, Y.; Wagner, P. E.; Wimmer, D.; Curtius, J.; Donahue, N. M.; Baltensperger, U.; Kulmala, M.; Worsnop, D. R.

    2015-01-01

    The formation of particles from precursor vapors is an important source of atmospheric aerosol. Research at the Cosmics Leaving OUtdoor Droplets (CLOUD) facility at CERN tries to elucidate which vapors are responsible for this new-particle formation, and how in detail it proceeds. Initial measurement campaigns at the CLOUD stainless-steel aerosol chamber focused on investigating particle formation from ammonia (NH3) and sulfuric acid (H2SO4). Experiments were conducted in the presence of water, ozone and sulfur dioxide. Contaminant trace gases were suppressed at the technological limit. For this study, we mapped out the compositions of small NH3-H2SO4 clusters over a wide range of atmospherically relevant environmental conditions. We covered [NH3] in the range from 10. Positively charged clusters grew on average by Δm/Δn = 1.05 and were only observed at sufficiently high [NH3] / [H2SO4]. The H2SO4 molecules of these clusters are partially neutralized by NH3, in close resemblance to the acid-base bindings of ammonium bisulfate. Supported by model simulations, we substantiate previous evidence for acid-base reactions being the essential mechanism behind the formation of these clusters under atmospheric conditions and up to sizes of at least 2 nm. Our results also suggest that electrically neutral NH3-H2SO4 clusters, unobservable in this study, have generally the same composition as ionic clusters for [NH3] / [H2SO4] > 10. We expect that NH3-H2SO4 clusters form and grow also mostly by Δm/Δn > 1 in the atmosphere's boundary layer, as [NH3] / [H2SO4] is mostly larger than 10. We compared our results from CLOUD with APi-TOF measurements of NH3-H2SO4 anion clusters during new-particle formation in the Finnish boreal forest. However, the exact role of NH3-H2SO4 clusters in boundary layer particle formation remains to be resolved.

  19. On the composition of ammonia-sulfuric acid clusters during aerosol particle formation

    Science.gov (United States)

    Schobesberger, S.; Franchin, A.; Bianchi, F.; Rondo, L.; Duplissy, J.; Kürten, A.; Ortega, I. K.; Metzger, A.; Schnitzhofer, R.; Almeida, J.; Amorim, A.; Dommen, J.; Dunne, E. M.; Ehn, M.; Gagné, S.; Ickes, L.; Junninen, H.; Hansel, A.; Kerminen, V.-M.; Kirkby, J.; Kupc, A.; Laaksonen, A.; Lehtipalo, K.; Mathot, S.; Onnela, A.; Petäjä, T.; Riccobono, F.; Santos, F. D.; Sipilä, M.; Tomé, A.; Tsagkogeorgas, G.; Viisanen, Y.; Wagner, P. E.; Wimmer, D.; Curtius, J.; Donahue, N. M.; Baltensperger, U.; Kulmala, M.; Worsnop, D. R.

    2014-05-01

    The formation of particles from precursor vapors is an important source of atmospheric aerosol. Research at the Cosmics Leaving OUtdoor Droplets (CLOUD) facility at CERN tries to elucidate which vapors are responsible for this new particle formation, and how in detail it proceeds. Initial measurement campaigns at the CLOUD stainless-steel aerosol chamber focused on investigating particle formation from ammonia (NH3) and sulfuric acid (H2SO4). Experiments were conducted in the presence of water, ozone and sulfur dioxide. Contaminant trace gases were suppressed at the technological limit. For this study, we mapped out the compositions of small NH3-H2SO4 clusters over a wide range of atmospherically relevant environmental conditions. We covered [NH3] in the range from 10. Positively charged clusters grew on average by Δm / Δn = 1.05 and were only observed at sufficiently high [NH3] / [H2SO4]. The H2SO4 molecules of these clusters are partially neutralized by NH3, in close resemblance to the acid-base bindings of ammonium bisulfate. Supported by model simulations, we substantiate previous evidence for acid-base reactions being the essential mechanism behind the formation of these clusters under atmospheric conditions and up to sizes of at least 2 nm. Our results also suggest that yet unobservable electrically neutral NH3-H2SO4 clusters grow by generally the same mechanism as ionic clusters, particularly for [NH3] / [H2SO4]>10. We expect that NH3-H2SO4 clusters form and grow also mostly by Δm / Δn>1 in the atmosphere's boundary layer, as [NH3] / [H2SO4] is mostly larger than 10. We compared our results from CLOUD with APi-TOF measurements of NH3-H2SO4 anion clusters during new particle formation in the Finnish boreal forest. However, the exact role of NH3-H2SO4 clusters in boundary layer particle formation remains to be resolved.

  20. Formation of carbon deposits from coal in an arc plasma

    Energy Technology Data Exchange (ETDEWEB)

    Wang, B.; Tian, Y.; Zhang, Y.; Zhu, S.; Lu, Y.; Zhang, Y.; Xie, K. [Taiyuan University of Technology, Taiyuan (China)

    2007-07-01

    The issue of deposited carbon (DC) on a reactor wall during the production of acetylene by the coal/arc plasma process is a potential obstacle for the industrialization process. The formation mechanism of DC is very difficult to reveal because the high complexity of coal and the volatile matter. Combining with quenching technique, the methane, liquid petroleum gas and benzene were employed as the model materials to roughly act as the light gas, chain and aromatic subcomponents of volatile matter, and then the reasonable formation mechanism of DC was subtly speculated accordingly.

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

    Science.gov (United States)

    Hartmann, H.; Popok, V. N.; Barke, I.; von Oeynhausen, V.; Meiwes-Broer, K.-H.

    2012-07-01

    The design and performance of an experimental setup utilizing a magnetron sputtering source for production of beams of ionized size-selected clusters for deposition in ultra-high vacuum is described. For the case of copper cluster formation the influence of different source parameters is studied and analyzed. Size-selected clusters are deposited on substrates and the efficiency of an electrostatic quadrupole mass selector is tested. Height analysis using atomic force microscopy (AFM) demonstrates relative standard size deviations of 7%-10% for the particles of various sizes between 6 nm and 19 nm. Combined analysis by AFM and transmission electron microscopy reveals that the clusters preserve almost spherical shape after the deposition on amorphous carbon substrates. Supported nanoparticles of a few nanometres in diameter have crystalline structure with a face-centered cubic (fcc) lattice.

  2. Investigation of the formation of Fe-filled carbon nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Reuther, H [Forschungszentrum Dresden-Rossendorf, PO Box 510119, D-01314 Dresden (Germany); Mueller, C; Leonhardt, A; Kutz, M C, E-mail: reuther@fzd.d [Leibniz-Institute of Solid State and Materials Research Dresden, PO Box 270116, D-01171 Dresden (Germany)

    2010-03-01

    The formation of Fe-filled carbon nanotubes by thermal decomposition of ferrocene combined with a Fe-catalyst-nanostructuring on an oxidized Si substrate is investigated in the temperature range of 1015 - 1200 K. The optimal growth conditions for aligned and homogeneous carbon nanotubes are found at 1103 K. Moessbauer spectroscopy (both in transmission geometry and CEMS) was used to analyze and quantify the different formed Fe-phases. In general, {alpha}-Fe, {gamma}-Fe and Fe{sub 3}C are found to form within the carbon nanotubes. Depending on the growth conditions their fractions vary strongly. Moreover, an alignment of the {alpha}-Fe in the tubes could be detected.

  3. Neutral molecular cluster formation of sulfuric acid–dimethylamine observed in real time under atmospheric conditions

    CERN Document Server

    Kürten, Andreas; Simon, Mario; Sipilä, Mikko; Sarnela, Nina; Junninen, Heikki; Adamov, Alexey; Almeida, João; Amorim, Antonio; Bianchi, Federico; Breitenlechner, Martin; Dommen, Josef; Donahue, Neil M; Duplissy, Jonathan; Ehrhart, Sebastian; Flagan, Richard C; Franchin, Alessandro; Hakala, Jani; Hansel, Armin; Heinritzi, Martin; Hutterli, Manuel; Kangasluoma, Juha; Kirkby, Jasper; Laaksonen, Ari; Lehtipalo, Katrianne; Leiminger, Markus; Makhmutov, Vladimir; Mathot, Serge; Onnela, Antti; Petäjä, Tuukka; Praplan, Arnaud P; Riccobono, Francesco; Rissanen, Matti P; Rondo, Linda; Schobesberger, Siegfried; Seinfeld, John H; Steiner, Gerhard; Tomé, António; Tröstl, Jasmin; Winkler, Paul M; Williamson, Christina; Wimmer, Daniela; Ye, Penglin; Baltensperger, Urs; Carslaw, Kenneth S; Kulmala, Markku; Worsnop, Douglas R; Curtius, Joachim

    2014-01-01

    For atmospheric sulfuric acid (SA) concentrations the presence of dimethylamine (DMA) at mixing ratios of several parts per trillion by volume can explain observed boundary layer new particle formation rates. However, the concentration and molecular composition of the neutral (uncharged) clusters have not been reported so far due to the lack of suitable instrumentation. Here we report on experiments from the Cosmics Leaving Outdoor Droplets chamber at the European Organization for Nuclear Research revealing the formation of neutral particles containing up to 14 SA and 16 DMA molecules, corresponding to a mobility diameter of about 2 nm, under atmospherically relevant conditions. These measurements bridge the gap between the molecular and particle perspectives of nucleation, revealing the fundamental processes involved in particle formation and growth. The neutral clusters are found to form at or close to the kinetic limit where particle formation is limited only by the collision rate of SA molecules. Even tho...

  4. Clustered star formation and outflows in AFGL 2591

    CERN Document Server

    Sanna, A; Carrasco-Gonzàlez, C; Menten, K M; Brunthaler, A; Moscadelli, L; Rygl, K L J

    2011-01-01

    We report on a detailed study of the water maser kinematics and radio continuum emission toward the most massive and young object in the star-forming region AFGL 2591. Our analysis shows at least two spatial scales of multiple star formation, one projected across 0.1 pc on the sky and another one at about 2000 AU from a ZAMS star of about 38 Solar masses. This young stellar object drives a powerful jet- and wind-driven outflow system with the water masers associated to the outflow walls, previously detected as a limb-brightened cavity in the NIR band. At about 1300 AU to the north of this object a younger protostar drives two bow shocks, outlined by arc-like water maser emission, at 200 AU either side of the source. We have traced the velocity profile of the gas that expands along these arc-like maser structures and compared it with the jet-driven outflow model. This analysis suggests that the ambient medium around the northern protostar is swept up by a jet-driven shock (>66 km/s) and perhaps a lower-velocit...

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

    CERN Document Server

    Safranek-Shrader, Chalence; Bromm, Volker

    2013-01-01

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

  6. The Red Sequence of High-Redshift Clusters: A Comparison with Cosmological Galaxy Formation Models

    Science.gov (United States)

    Menci, N.

    2008-10-01

    We compare the results from a state-of-the-art semi-analytic model of galaxy formation with spectroscopic observations of the distant galaxy clusters observed in the range 1≲ z≲ 1.5. In our model we find that i) a well-defined, narrow red sequence (RS) is obtained already by z≈ 1.2; this is more populated than the field RS analogously to what observed and predicted at z=0; ii) the predicted RS colors and width have average values of 1 and 0.15, respectively, with a cluster-to-cluster variance. The width of the RS of cluster galaxy is 5-10 times lower than the corresponding field value; iii) The predicted distribution of stellar ages of RS galaxies at z=1.2 are peaked at the value τ=3.7 Gyr for both cluster and field; however, for the latter the distribution is significantly skewed toward lower ages. When compared with observations, the above findings show an overall consistency, although the average value ≈ 0.07 of the observed cluster RS width at z≈1.2 is smaller than the corresponding model central value. We discuss the physical origin and the significance of the above results in the framework of cosmological galaxy formation.

  7. The formation history of massive cluster galaxies as revealed by CARLA

    CERN Document Server

    Cooke, E A; Rettura, A; Wylezalek, D; Galametz, A; Stern, D; Brodwin, M; Muldrew, S I; Almaini, O; Conselice, C J; Eisenhardt, P R; Hartley, W G; Jarvis, M; Seymour, N; Stanford, S A

    2015-01-01

    We use a sample of 37 of the densest clusters and protoclusters across $1.3 \\le z \\le 3.2$ from the Clusters Around Radio-Loud AGN (CARLA) survey to study the formation of massive cluster galaxies. We use optical $i'$-band and infrared 3.6$\\mu$m and 4.5$\\mu$m images to statistically select sources within these protoclusters and measure their median observed colours; $\\langle i'-[3.6] \\rangle$. We find the abundance of massive galaxies within the protoclusters increases with decreasing redshift, suggesting these objects may form an evolutionary sequence, with the lower redshift clusters in the sample having similar properties to the descendants of the high redshift protoclusters. We find that the protocluster galaxies have an approximately unevolving observed-frame $i'-[3.6]$ colour across the examined redshift range. We compare the evolution of the $\\langle i'-[3.6] \\rangle$ colour of massive cluster galaxies with simplistic galaxy formation models. Taking the full cluster population into account, we show tha...

  8. Star formation and black hole accretion activity in rich local clusters of galaxies

    CERN Document Server

    Bianconi, Matteo; Fadda, Dario

    2016-01-01

    We present a study of the star formation and central black hole accretion activity of the galaxies hosted in the two nearby (z$\\sim$0.2) rich galaxy clusters Abell 983 and 1731. Aims: We are able to quantify both the obscured and unobscured star formation rates, as well as the presence of active galactic nuclei (AGN) as a function of the environment in which the galaxy is located. Methods: We targeted the clusters with unprecedented deep infrared Spitzer observations (0.2 mJy @ 24 micron), near-IR Palomar imaging and optical WIYN spectroscopy. The extent of our observations ($\\sim$ 3 virial radii) covers the vast range of possible environments, from the very dense cluster centre to the very rarefied cluster outskirts and accretion regions. Results: The star forming members of the two clusters present star formation rates comparable with those measured in coeval field galaxies. The analysis of the spatial arrangement of the spectroscopically confirmed members reveals an elongated distribution for A1731 with re...

  9. Simulating galaxy Clusters -II: global star formation histories and galaxy populations

    CERN Document Server

    Romeo, A D; Sommer-Larsen, J

    2004-01-01

    Cosmological (LambdaCDM) TreeSPH simulations of the formation and evolution of galaxy groups and clusters have been performed. The simulations invoke star formation, chemical evolution with non-instantaneous recycling, metal dependent radiative cooling, strong star burst and (optionally) AGN driven galactic super winds, effects of a meta-galactic UV field and thermal conduction. The properties of the galaxy populations in two clusters, one Virgo-like (T~3 keV) and one (sub) Coma-like (T~6 keV), are discussed. The global star formation rates of the cluster galaxies are found to decrease very significantly with time from redshift z=2 to 0, in agreement with observations. The total K-band luminosity of the cluster galaxies correlates tightly with total cluster mass, and for models without additional AGN feedback, the zero point of the relation matches the observed one fairly well. The match to observed galaxy luminosity functions is reasonable, except for a deficiency of bright galaxies (M_B < -20), which bec...

  10. On Iron Enrichment, Star Formation, and Type Ia Supernovae in Galaxy Clusters

    Science.gov (United States)

    Loewenstein, Michael

    2006-01-01

    The nature of star formation and Type Ia supernovae (SNIa) in galaxies in the field and in rich galaxy clusters are contrasted by juxtaposing the buildup of heavy metals in the universe inferred from observed star formation and supernovae rate histories with data on the evolution of Fe abundances in the intracluster medium (ICM). Models for the chemical evolution of Fe in these environments are constructed, subject to observational constraints, for this purpose. While models with a mean delay for SNIa of 3 Gyr and standard initial mass function (IMF) are fully consistent with observations in the field, cluster Fe enrichment immediately tracked a rapid, top-heavy phase of star formation - although transport of Fe into the ICM may have been more prolonged and star formation likely continued beyond redshift 1. The means of this prompt enrichment consisted of SNII yielding greater than or equal to 0.1 solar mass per explosion (if the SNIa rate normalization is scaled down from its value in the field according to the relative number of candidate progenitor stars in the 3 - 8 solar mass range) and/or SNIa with short delay times originating during the rapid star formation epoch. Star formation is greater than 3 times more efficient in rich clusters than in the field, mitigating the overcooling problem in numerical cluster simulations. Both the fraction of baryons cycled through stars, and the fraction of the total present-day stellar mass in the form of stellar remnants, are substantially greater in clusters than in the field.

  11. Secondary brown carbon formation via the dicarbonyl imine pathway: nitrogen heterocycle formation and synergistic effects.

    Science.gov (United States)

    Kampf, C J; Filippi, A; Zuth, C; Hoffmann, T; Opatz, T

    2016-07-21

    Dicarbonyls are known to be important precursors of so-called atmospheric brown carbon, significantly affecting aerosol optical properties and radiative forcing. In this systematic study we report the formation of light-absorbing nitrogen containing compounds from simple 1,2-, 1,3-, 1,4-, and 1,5-dicarbonyl + amine reactions. A combination of spectrophotometric and mass spectrometric techniques was used to characterize reaction products in solutions mimicking atmospheric particulates. Experiments with individual dicarbonyls and dicarbonyl mixtures in ammonium sulfate and glycine solutions demonstrate that nitrogen heterocycles are common structural motifs of brown carbon chromophores formed in such reaction systems. 1,4- and 1,5-dicarbonyl reaction systems, which were used as surrogates for terpene ozonolysis products, showed rapid formation of light-absorbing material and products with absorbance maxima at ∼450 nm. Synergistic effects on absorbance properties were observed in mixed (di-)carbonyl experiments, as indicated by the formation of a strong absorber in ammonium sulfate solutions containing acetaldehyde and acetylacetone. This cross-reaction oligomer shows an absorbance maximum at 385 nm, relevant for the actinic flux region of the atmosphere. This study demonstrates the complexity of secondary brown carbon formation via the imine pathway and highlights that cross-reactions with synergistic effects have to be considered an important pathway for atmospheric BrC formation.

  12. Radical carbon-carbon bond formations enabled by visible light active photocatalysts.

    Science.gov (United States)

    Wallentin, Carl-Johan; Nguyen, John D; Stephenson, Corey R J

    2012-01-01

    This mini-review highlights the Stephenson group's contribution to the field of photoredox catalysis with emphasis on carbon-carbon bond formation. The realization of photoredox mediated reductive dehalogenation initiated investigations toward both intra- and intermolecular coupling reactions. These reactions commenced via visible light-mediated reduction of activated halogens to give carbon-centered radicals that were subsequently involved in carbon-carbon bond forming transformations. The developed protocols using Ru and Ir based polypyridyl complexes as photoredox catalysts were further tuned to efficiently catalyze overall redox neutral atom transfer radical addition reactions. Most recently, a simplistic flow reactor technique has been utilized to affect a broad scope of photocatalytic transformations with significant enhancement in reaction efficiency.

  13. Experimental comparison of impact of auction format on carbon allowance market

    DEFF Research Database (Denmark)

    Cong, Ronggang; Wei, Yi-Ming

    2012-01-01

    Carbon allowances auctions are a good way to achieve the carbon allowance allocations under international agreements to address global climate change. Based on an economic experiment, this paper compares three possible carbon allowance auction formats (uniform price auction, discriminatory price...

  14. Corrosion Products and Formation Mechanism During Initial Stage of Atmospheric Corrosion of Carbon Steel

    Institute of Scientific and Technical Information of China (English)

    XIAO Kui; DONG Chao-fang; LI Xiao-gang; WANG Fu-ming

    2008-01-01

    The formation and development of corrosion products on carbon steel surface during the initial stage of atmospheric corrosion in a laboratory simulated environment have been studied by scanning electron microscopy (SEM)and Raman spectroscopy.The results showed that two different shapes of corrosion products,that is,ring and chain,were formed in the initial stage of corrosion.MnS clusters were found in the nuclei of corrosion products at the active local corrosion sites.The ring-shaped products were composed of lepidocrocite (γ-FeOOH) and maghemite(γ-Fe2 O3) transformed from lepidocrocite.The chain-type products were goethite (α-FeOOH).A formation mechanism of the corrosion products is proposed.

  15. Progressive star formation in the young galactic super star cluster NGC 3603

    CERN Document Server

    Beccari, Giacomo; De Marchi, Guido; Paresce, Francesco; Young, Erick; Andersen, Morten; Panagia, Nino; Balick, Bruce; Bond, Howard; Calzetti, Daniela; Carollo, C Marcella; Disney, Michael J; Dopita, Michael A; Frogel, Jay A; Hall, Donald N B; Holtzman, Jon A; Kimble, Randy A; McCarthy, Patrick J; O'Connell, Robert W; Saha, Abhijit; Silk, Joseph I; Trauger, John T; Walker, Alistair R; Whitmore, Bradley C; Windhorst, Rogier A

    2010-01-01

    Early release science observations of the cluster NGC3603 with the WFC3 on the refurbished HST allow us to study its recent star formation history. Our analysis focuses on stars with Halpha excess emission, a robust indicator of their pre-main sequence (PMS) accreting status. The comparison with theoretical PMS isochrones shows that 2/3 of the objects with Halpha excess emission have ages from 1 to 10 Myr, with a median value of 3 Myr, while a surprising 1/3 of them are older than 10 Myr. The study of the spatial distribution of these PMS stars allows us to confirm their cluster membership and to statistically separate them from field stars. This result establishes unambiguously for the first time that star formation in and around the cluster has been ongoing for at least 10-20 Myr, at an apparently increasing rate.

  16. A new methodology to test galaxy formation models using the dependence of clustering on stellar mass

    CERN Document Server

    Campbell, David J R; Mitchell, Peter D; Helly, John C; Gonzalez-Perez, Violeta; Lacey, Cedric G; Lagos, Claudia del P; Simha, Vimal; Farrow, Daniel J

    2014-01-01

    We present predictions for the two-point correlation function of galaxy clustering as a function of stellar mass, computed using two new versions of the GALFORM semi-analytic galaxy formation model. These models make use of a new high resolution, large volume N-body simulation, set in the WMAP7 cosmology. One model uses a universal stellar initial mass function (IMF), while the other assumes different IMFs for quiescent star formation and bursts. Particular consideration is given to how the assumptions required to estimate the stellar masses of observed galaxies (such as the choice of IMF, stellar population synthesis model and dust extinction) influence the perceived dependence of galaxy clustering on stellar mass. Broad-band spectral energy distribution fitting is carried out to estimate stellar masses for the model galaxies in the same manner as in observational studies. We show clear differences between the clustering signals computed using the true and estimated model stellar masses. As such, we highligh...

  17. Dust-Obscured Star-Formation in Intermediate Redshift Galaxy Clusters

    CERN Document Server

    Finn, Rose A; Rudnick, Gregory; Poggianti, Bianca; Bell, Eric F; Hinz, Joannah; Jablonka, Pascale; Milvang-Jensen, Bo; Moustakas, John; Rines, Kenneth; Zaritsky, Dennis

    2010-01-01

    We present Spitzer MIPS 24-micron observations of 16 0.45A, and ~75% exhibit optical signatures of dusty starbursts. On average, the fraction of cluster LIRGs increases with projected cluster-centric radius but remains systematically lower than the field fraction over the area probed (< 1.5xR200). The amount of obscured star formation declines significantly over the 2.4 Gyr interval spanned by the EDisCS sample, and the rate of decline is the same for the cluster and field populations. Our results are consistent with an expo nentially declining LIRG fraction, with the decline in the field delayed by ~1 Gyr relative to the clusters.

  18. On Iron Enrichment, Star Formation, and Type Ia Supernovae in Galaxy Clusters

    CERN Document Server

    Loewenstein, M

    2006-01-01

    The nature of star formation and Type Ia supernovae (SNIa) in galaxies in the field and in rich galaxy clusters are contrasted by juxtaposing the build-up of heavy metals in the universe inferred from observed star formation and supernovae rate histories with data on the evolution of Fe abundances in the intracluster medium (ICM). Models for the chemical evolution of Fe in these environments are constructed, subject to observational constraints, for this purpose. While models with a mean delay for SNIa of 3 Gyr and standard initial mass function (IMF) are consistent with observations in the field, cluster Fe enrichment immediately tracks a rapid, top-heavy phase of star formation -- although transport of Fe into the ICM may be more prolonged and star formation likely continues to redshifts 3 times more efficient in rich clusters than in the field, mitigating the overcooling problem in numerical cluster simulations. Both the fraction of baryons cycled through stars, and the fraction of the total present-day st...

  19. Crossover model for the work of critical cluster formation in nucleation theory

    NARCIS (Netherlands)

    Kalikmanov, V.I.

    2004-01-01

    We propose a relation for the work of critical cluster formation in nucleation theory W for the systems with long-range interparticle interactions. The method of bridge functions is used to combine the system behavior at sufficiently small quenches, adequately predicted by the classical nucleation t

  20. THE MECHANISM OF FORMATION AND IMPLEMENTATION OF CLUSTER POLICY OF INDUSTRIAL ENTERPRISES AND BRANCHES

    Directory of Open Access Journals (Sweden)

    U. A. Salikov

    2013-01-01

    Full Text Available In article on the basis of analysis of scientific and practical prerequisites proposed the concept of managerial mechanism of formation and implementation of cluster policy of industrial enterprises, and also reviewed the conditions for the realization and func-tioning of this mechanism.

  1. Star Cluster Formation and Destruction in the Merging Galaxy NGC 3256

    CERN Document Server

    Mulia, Alexander J; Whitmore, Bradley C

    2016-01-01

    We use the Advanced Camera for Surveys on the Hubble Space Telescope to study the rich population of young massive star clusters in the main body of NGC 3256, a merging pair of galaxies with a high star formation rate (SFR) and SFR per unit area ($\\Sigma_{\\rm{SFR}}$). These clusters have luminosity and mass functions that follow power laws, $dN/dL \\propto L^{\\alpha}$ with $\\alpha = -2.23 \\pm 0.07$, and $dN/dM \\propto M^{\\beta}$ with $\\beta = -1.86 \\pm 0.34$ for $\\tau < 10$ Myr clusters, similar to those found in more quiescent galaxies. The age distribution can be described by $dN/d\\tau \\propto \\tau ^ \\gamma$, with $\\gamma \\approx -0.67 \\pm 0.08$ for clusters younger than about a few hundred million years, with no obvious dependence on cluster mass. This is consistent with a picture where $\\sim 80 \\%$ of the clusters are disrupted each decade in time. We investigate the claim that galaxies with high $\\Sigma_{\\rm{SFR}}$ form clusters more efficiently than quiescent systems by determining the fraction of sta...

  2. Nickel clusters embedded in carbon nanotubes as high performance magnets

    Science.gov (United States)

    Shiozawa, Hidetsugu; Briones-Leon, Antonio; Domanov, Oleg; Zechner, Georg; Sato, Yuta; Suenaga, Kazu; Saito, Takeshi; Eisterer, Michael; Weschke, Eugen; Lang, Wolfgang; Peterlik, Herwig; Pichler, Thomas

    2015-10-01

    Ensembles of fcc nickel nanowires have been synthesized with defined mean sizes in the interior of single-wall carbon nanotubes. The method allows the intrinsic nature of single-domain magnets to emerge with large coercivity as their size becomes as small as the exchange length of nickel. By means of X-ray magnetic circular dichroism we probe electronic interactions at nickel-carbon interfaces where nickel exhibit no hysteresis and size-dependent spin magnetic moment. A manifestation of the interacting two subsystems on a bulk scale is traced in the nanotube’s magnetoresistance as explained within the framework of weak localization.

  3. Clustered star formation as a natural explanation for the Halpha cut-off in disk galaxies.

    Science.gov (United States)

    Pflamm-Altenburg, Jan; Kroupa, Pavel

    2008-10-02

    The rate of star formation in a galaxy is often determined by the observation of emission in the Halpha line, which is related to the presence of short-lived massive stars. Disk galaxies show a strong cut-off in Halpha radiation at a certain galactocentric distance, which has led to the conclusion that star formation is suppressed in the outer regions of disk galaxies. This is seemingly in contradiction to recent observations in the ultraviolet which imply that disk galaxies have star formation beyond the Halpha cut-off, and that the star-formation-rate surface density is linearly related to the underlying gas surface density, which is a shallower relationship than that derived from Halpha luminosities. In a galaxy-wide formulation, the clustered nature of star formation has recently led to the insight that the total galactic Halpha luminosity is nonlinearly related to the galaxy-wide star formation rate. Here we show that a local formulation of the concept of clustered star formation naturally leads to a steeper radial decrease in the Halpha surface luminosity than in the star-formation-rate surface density, in quantitative agreement with the observations, and that the observed Halpha cut-off arises naturally.

  4. Star Formation in Intermediate Redshift 0.2 < Z < 0.7 Brightest Cluster Galaxies

    CERN Document Server

    Cooke, Kevin C; Baum, Stefi A; Tremblay, Grant R; Cox, Isabella G; Gladders, Michael D

    2016-01-01

    We present a multi-wavelength photometric and spectroscopic study of 42 Brightest Cluster Galaxies (BCGs) in two samples of clusters of galaxies chosen for the study of gravitational lensing. The study's initial sample combines 25 BCGs from the Cluster Lensing and Supernova Survey with Hubble (CLASH) sample and 37 BCGs from the Sloan Giant Arcs Survey (SGAS) with a total redshift range of 0.2 < Z < 0.7. Using archival GALEX, HST, WISE, Herschel, and VLA data we determine the BCGs' stellar mass, radio power, and star formation rates. The radio power is higher than expected if due to star formation, consistent with the BCGs being AGN-powered radio sources. This suggests that the AGN and star formation are both fueled by cold gas in the host galaxy. The specific star formation rate (sSFR) is low and constant with redshift. The mean sSFR is 9.42 * 10^-12 yr^-1 which corresponds to a mass doubling time of 105 billion years. These findings are consistent with models for hierarchical formation of BCGs which su...

  5. Cooling, AGN Feedback and Star Formation in Simulated Cool-Core Galaxy Clusters

    CERN Document Server

    Li, Yuan; Ruszkowski, Mateusz; Voit, G Mark; O'Shea, Brian W; Donahue, Megan

    2015-01-01

    Numerical simulations of active galactic nuclei (AGN) feedback in cool-core galaxy clusters have successfully avoided classical cooling flows, but often produce too much cold gas. We perform adaptive mesh simulations that include momentum-driven AGN feedback, self-gravity, star formation and stellar feedback, focusing on the interplay between cooling, AGN heating and star formation in an isolated cool-core cluster. Cold clumps triggered by AGN jets and turbulence form filamentary structures tens of kpc long. This cold gas feeds both star formation and the supermassive black hole (SMBH), triggering an AGN outburst that increases the entropy of the ICM and reduces its cooling rate. Within 1-2 Gyr, star formation completely consumes the cold gas, leading to a brief shutoff of the AGN. The ICM quickly cools and redevelops multiphase gas, followed by another cycle of star formation/AGN outburst. Within 6.5 Gyr, we observe three such cycles. There is good agreement between our simulated cluster and the observations...

  6. A unique model for the variety of multiple populations formation(s) in globular clusters: a temporal sequence

    CERN Document Server

    D'Antona, F; D'Ercole, A; Ventura, P; Milone, A P; Marino, A F; Tailo, M

    2016-01-01

    We explain the multiple populations recently found in the 'prototype' Globular Cluster (GC) NGC 2808 in the framework of the asymptotic giant branch (AGB) scenario. The chemistry of the five -or more- populations is approximately consistent with a sequence of star formation events, starting after the supernovae type II epoch, lasting approximately until the time when the third dredge up affects the AGB evolution (age ~90-120Myr), and ending when the type Ia supernovae begin exploding in the cluster, eventually clearing it from the gas. The formation of the different populations requires episodes of star formation in AGB gas diluted with different amounts of pristine gas. In the nitrogen-rich, helium-normal population identified in NGC 2808 by the UV Legacy Survey of GCs, the nitrogen increase is due to the third dredge up in the smallest mass AGB ejecta involved in the star formation of this population. The possibly-iron-rich small population in NGC 2808 may be a result of contamination by a single type Ia su...

  7. Effects of cooling and star formation on the baryon fractions in clusters

    CERN Document Server

    Kravtsov, A V; Vikhlinin, A A; Kravtsov, Andrey V.; Nagai, Daisuke; Vikhlinin, Alexey A.

    2005-01-01

    We study the effects of dissipation on the baryon fractions in clusters using high-resolution cosmological simulations of nine clusters that resolve formation of cluster galaxies. The simulations of each cluster are performed with the shock-capturing eulerian adaptive mesh refinement N-body+gasdynamics ART code with and without radiative cooling. We show that dissipation and associated galaxy formation increase the total baryon fractions within radii as large as the virial radius. The effect is the strongest within cluster cores, where the simulations with cooling have baryon fractions larger than the universal value, while the fraction of baryons in adiabatic simulations are smaller than universal. At larger radii (r >~ r_500) the cumulative baryon fractions in simulations with cooling are close to, while those in the adiabatic runs remain below than, the universal value. The gas fractions in simulations with dissipation are reduced by ~20-40% at r0.2, but differ systematically by up to 10% at small radii.

  8. The formation of very wide binaries during the star cluster dissolution phase

    CERN Document Server

    Kouwenhoven, M B N; Parker, Richard J; Davies, M B; Malmberg, D; Kroupa, P

    2010-01-01

    Over the past few decades, numerous wide (>1000 au) binaries in the Galactic field and halo have been discovered. Their existence cannot be explained by the process of star formation or by dynamical interactions in the field, and their origin has long been a mystery. We explain the origin of these wide binaries by formation during the dissolution phase of young star clusters: an initially unbound pair of stars may form a binary when their distance in phase-space is small. Using N-body simulations, we find that the resulting wide binary fraction in the semi-major axis range 1000 au - 0.1 pc for individual clusters is 1-30%, depending on the initial conditions. The existence of numerous wide binaries in the field is consistent with observational evidence that most clusters start out with a large degree of substructure. The wide binary fraction decreases strongly with increasing cluster mass, and the semi-major axis of the newly formed binaries is determined by the initial cluster size. The resulting eccentricit...

  9. The role of low-mass star clusters in massive star formation. The Orion Case

    CERN Document Server

    Rivilla, V M; Jimenez-Serra, I; Rodriguez-Franco, A

    2013-01-01

    To distinguish between the different theories proposed to explain massive star formation, it is crucial to establish the distribution, the extinction, and the density of low-mass stars in massive star-forming regions. We analyze deep X-ray observations of the Orion massive star-forming region using the Chandra Orion Ultradeep Project (COUP) catalog. We studied the stellar distribution as a function of extinction, with cells of 0.03 pc x 0.03 pc, the typical size of protostellar cores. We derived stellar density maps and calculated cluster stellar densities. We found that low-mass stars cluster toward the three massive star-forming regions: the Trapezium Cluster (TC), the Orion Hot Core (OHC), and OMC1-S. We derived low-mass stellar densities of 10^{5} stars pc^{-3} in the TC and OMC1-S, and of 10^{6} stars pc^{-3} in the OHC. The close association between the low-mass star clusters with massive star cradles supports the role of these clusters in the formation of massive stars. The X-ray observations show for ...

  10. A new methodology to test galaxy formation models using the dependence of clustering on stellar mass

    Science.gov (United States)

    Campbell, David J. R.; Baugh, Carlton M.; Mitchell, Peter D.; Helly, John C.; Gonzalez-Perez, Violeta; Lacey, Cedric G.; Lagos, Claudia del P.; Simha, Vimal; Farrow, Daniel J.

    2015-09-01

    We present predictions for the two-point correlation function of galaxy clustering as a function of stellar mass, computed using two new versions of the GALFORM semi-analytic galaxy formation model. These models make use of a high resolution, large volume N-body simulation, set in the 7-year Wilkinson Microwave Anisotropy Probe cosmology. One model uses a universal stellar initial mass function (IMF), while the other assumes different IMFs for quiescent star formation and bursts. Particular consideration is given to how the assumptions required to estimate the stellar masses of observed galaxies (such as the choice of IMF, stellar population synthesis model, and dust extinction) influence the perceived dependence of galaxy clustering on stellar mass. Broad-band spectral energy distribution fitting is carried out to estimate stellar masses for the model galaxies in the same manner as in observational studies. We show clear differences between the clustering signals computed using the true and estimated model stellar masses. As such, we highlight the importance of applying our methodology to compare theoretical models to observations. We introduce an alternative scheme for the calculation of the merger time-scales for satellite galaxies in GALFORM, which takes into account the dark matter subhalo information from the simulation. This reduces the amplitude of small-scale clustering. The new merger scheme offers improved or similar agreement with observational clustering measurements, over the redshift range 0 Public Extragalactic Redshift Survey, depending on the GALFORM model used.

  11. Study of Swarm Behavior in Modeling and Simulation of Cluster Formation in Nanofluids

    Directory of Open Access Journals (Sweden)

    Mohammad Pirani

    2013-01-01

    Full Text Available Modeling the multiagents cooperative systems inspired from biological self-organized systems in the context of swarm model has been under great considerations especially in the field of the cooperation of multi robots. These models are trying to optimize the behavior of artificial multiagent systems by introducing a consensus, which is a mathematical model between the agents as an intelligence property for each member of the swarm set. The application of this novel approach in the modeling of nonintelligent multi agents systems in the field of cohesion and cluster formation of nanoparticles in nanofluids has been investigated in this study. This goal can be obtained by applying the basic swarm model for agents that are more mechanistic by considering their physical properties such as their mass, diameter, as well as the physical properties of the flow. Clustering in nanofluids is one of the major issues in the study of its effects on heat transfer. Study of the cluster formation dynamics in nanofluids using the swarm model can be useful in controlling the size and formation time of the clusters as well as designing appropriate microchannels, which the nanoparticles are plunged into.

  12. Asymptotic Analysis of Coagulation–Fragmentation Equations of Carbon Nanotube Clusters

    Directory of Open Access Journals (Sweden)

    Castellano Gloria

    2007-01-01

    Full Text Available AbstractThe possibility of the existence of single-wall carbon nanotubes (SWNTs in organic solvents in the form of clusters is discussed. A theory is developed based on abundletmodel for clusters describing the distribution function of clusters by size. The phenomena have a unified explanation in the framework of the bundlet model of a cluster, in accordance with which the free energy of an SWNT involved in a cluster is combined from two components: a volume one, proportional to the number of moleculesnin a cluster, and a surface one, proportional ton1/2. During the latter stage of the fusion process, the dynamics were governed mainly by the displacement of the volume of liquid around the fusion site between the fused clusters. The same order of magnitude for the average cluster-fusion velocity is deduced if the fusion process starts with several fusion sites. Based on a simple kinetic model and starting from the initial state of pure monomers, micellization of rod-like aggregates at high critical micelle concentration occurs in three separated stages. A convenient relation is obtained for at transient stage. At equilibrium, another relation determines dimensionless binding energy α. A relation with surface dilatational viscosity is obtained.

  13. The Red Sequence of High-Redshift Clusters: a Comparison with Cosmological Galaxy Formation Models

    CERN Document Server

    Menci, N; Gobat, R; Strazzullo, V; Rettura, A; Mei, S; Demarco, R

    2008-01-01

    We compare the results from a semi-analytic model of galaxy formation with spectro-photometric observations of distant galaxy clusters observed in the range 0.8< z< 1.3. We investigate the properties of their red sequence (RS) galaxies and compare them with those of the field at the same redshift. In our model we find that i) a well-defined, narrow RS is obtained already by z= 1.2; this is found to be more populated than the field RS, analogously to what observed and predicted at z=0; ii) the predicted U-V rest-frame colors and scatter of the cluster RS at z=1.2 have average values of 1 and 0.15 respectively, with a cluster-to-cluster variance of 0.2 and 0.06, respectively. The scatter of the RS of cluster galaxies is around 5 times smaller than the corresponding field value; iii) when the RS galaxies are considered, the mass growth histories of field and cluster galaxies at z=1.2 are similar, with 90 % of the stellar mass of RS galaxies at z=1.2 already formed at cosmic times t=2.5 Gyr, and 50 % at t=1...

  14. Cluster formation in fluids with competing short-range and long-range interactions

    Energy Technology Data Exchange (ETDEWEB)

    Sweatman, Martin B., E-mail: martin.sweatman@ed.ac.uk; Fartaria, Rui [Institute of Materials and Processes, School of Engineering, University of Edinburgh, Edinburgh EH9 3JL (United Kingdom); Lue, Leo [Department of Chemical and Process Engineering, University of Strathclyde, Glasgow G1 1XJ (United Kingdom)

    2014-03-28

    We investigate the low density behaviour of fluids that interact through a short-ranged attraction together with a long-ranged repulsion (SALR potential) by developing a molecular thermodynamic model. The SALR potential is a model of effective solute interactions where the solvent degrees of freedom are integrated-out. For this system, we find that clusters form for a range of interaction parameters where attractive and repulsive interactions nearly balance, similar to micelle formation in aqueous surfactant solutions. We focus on systems for which equilibrium behaviour and liquid-like clusters (i.e., droplets) are expected, and find in addition a novel coexistence between a low density cluster phase and a high density cluster phase within a very narrow range of parameters. Moreover, a simple formula for the average cluster size is developed. Based on this formula, we propose a non-classical crystal nucleation pathway whereby macroscopic crystals are formed via crystal nucleation within microscopic precursor droplets. We also perform large-scale Monte Carlo simulations, which demonstrate that the cluster fluid phase is thermodynamically stable for this system.

  15. The IMF and Star Formation History of the Stellar Clusters in the Vela D Cloud

    CERN Document Server

    Massi, F; Vanzi, L; Massi, Fabrizio; Testi, Leonardo; Vanzi, Leonardo

    2005-01-01

    We present the results of a Near-Infrared deep photometric survey of a sample of six embedded star clusters in the Vela-D molecular cloud, all associated with luminous (~10^3 Lsun) IRAS sources. The clusters are unlikely to be older than a few 10^6 yrs, since all are still associated with molecular gas. We employed the fact that all clusters lie at the same distance and were observed with the same instrumental setting to derive their properties in a consistent way, being affected by the same instrumental and observational biases. We extracted the clusters' K Luminosity Functions (KLF) and developed a simple method to correct them for extinction, based on colour-magnitude diagrams. The reliability of the method has been tested by constructing synthetic clusters from theoretical tracks for pre-main sequence stars and a standard Initial Mass Function (IMF). The clusters' IMFs have been derived from the dereddened KLFs by adopting a set of pre-main sequence evolutionary tracks and assuming coeval star formation. ...

  16. Basic Tools for Studies on the Formation and Disruption of Star Clusters: the Luminosity Function

    CERN Document Server

    Gieles, M

    2009-01-01

    The luminosity function (LF) of young star clusters is often approximated by a power law function. For clusters in a wide range of galactic environments this has resulted in fit indices near -2, but on average slightly steeper. A fundamental property of the -2 power law function is that the luminosity of the brightest object (L_max) scales linearly with the total number of clusters, which is close to what is observed. This suggests that the formation of Young Massive Clusters (YMCs) is a result of the size of the sample, i.e. when the SFR is high it is statistically more likely to form YMCs, but no particular physical conditions are required. In this contribution we provide evidence that the LF of young clusters is not a -2 power law, but instead is curved, showing a systematic decrease of the (logarithmic) slope from roughly -1.8 at low luminosities to roughly -2.8 at high luminosities. The empirical LFs can be reproduced by model LFs using an underlying cluster IMF with a Schechter type truncation around M*...

  17. Cluster formation in fluids with competing short-range and long-range interactions.

    Science.gov (United States)

    Sweatman, Martin B; Fartaria, Rui; Lue, Leo

    2014-03-28

    We investigate the low density behaviour of fluids that interact through a short-ranged attraction together with a long-ranged repulsion (SALR potential) by developing a molecular thermodynamic model. The SALR potential is a model of effective solute interactions where the solvent degrees of freedom are integrated-out. For this system, we find that clusters form for a range of interaction parameters where attractive and repulsive interactions nearly balance, similar to micelle formation in aqueous surfactant solutions. We focus on systems for which equilibrium behaviour and liquid-like clusters (i.e., droplets) are expected, and find in addition a novel coexistence between a low density cluster phase and a high density cluster phase within a very narrow range of parameters. Moreover, a simple formula for the average cluster size is developed. Based on this formula, we propose a non-classical crystal nucleation pathway whereby macroscopic crystals are formed via crystal nucleation within microscopic precursor droplets. We also perform large-scale Monte Carlo simulations, which demonstrate that the cluster fluid phase is thermodynamically stable for this system.

  18. Evidence for a fundamental stellar upper mass limit from clustered star formation, and some implications therof

    CERN Document Server

    Kroupa, P; Kroupa, Pavel; Weidner, Carsten

    2005-01-01

    Theoretical considerations lead to the expectation that stars should not have masses larger than about m_{max*}=60-120Msun, while the observational evidence has been ambiguous. Only very recently has a physical stellar mass limit near 150Msun emerged thanks to modern high-resolution observations of local star-burst clusters. But this limit does not appear to depend on metallicity, in contradiction to theory. Important uncertainties remain though. It is now also emerging that star-clusters limit the masses of their constituent stars, such that a well-defined relation between the mass of the most massive star in a cluster and the cluster mass, m_{max}=F(M_ecl) \\le m_{max*}\\approx 150Msun, exists. One rather startling finding is that the observational data strongly favour clusters being built-up by consecutively forming more-massive stars until the most massive stars terminate further star-formation. The relation also implies that composite populations, which consist of many star clusters, most of which may be d...

  19. Pancakes of second generation and formation of fantomes of clusters of galaxies

    Energy Technology Data Exchange (ETDEWEB)

    Doroshkevich, A.G.

    1983-09-01

    The problem of formation of the second generation hot neutrino-gaseous ''pancakes'' is analyzed. These ''pancakes'' can evolve later into the gravitationally bounded hot neutrino-gaseous clouds-''fantomes'' of clusters. The temperature, mass and other parameters of ''fantomess'' are close to those of clusters of galaxies but ''fantomes'' do not (or nearly do not) contain ordinary galaxies. It is suggested that ''fantomes'' can be found in the X-ray surveys or by temperature fluctuations of relic radiation.

  20. The role of systematic innovation management in cluster formations based on ecologically oriented approach

    Directory of Open Access Journals (Sweden)

    L.H. Melnyk

    2014-09-01

    Full Text Available The aim of the article. The aim of the article is to study the role of the system of innovation management in cluster formations on the basis of ecologically oriented creative approach for sustainable development. The results of the analysis. The paper studies the problem of system management in the formation of cluster structures as еcopolis in the transition to environmentally sustainable development, addressed organizational and economic background applications eco-creative approach to the establishment and operation of еcopolis as self- reproduction socio-ecological-economic system. Perspective directions of solving the problems systems management in the context of sustainable development, in our view, next: the reproductive mechanism of the economic transformations directed on «green» development areas; dematerialization activation processes at various levels of management; ecologically oriented economic development (dynamic transformation of the economy, taking into account the principles of sustainable development based on innovation; clustering scientific production and educational specialization (ecopolis. Question the beneficial use of environmental conditions and initiatives arise when a key prerequisite for the formation of ecopolis. Conclusions and directions of further researches. It is shown that one of the best ways to achieve these goals, mechanisms that implement ecologically effective management at the regional level, is to create in the country such as forms of ecopolis. These studies need to continue to develop a system of tools and mechanisms to ensure the implementation of the concept of innovation management system such as cluster formations ecopolis in the context of sustainable development. Also it is required the development the organizational and economic development of system management tools cluster units.

  1. Multicolor Photometry of the Merging Galaxy Cluster A2319: Dynamics and Star Formation Properties

    Science.gov (United States)

    Yan, Peng-Fei; Yuan, Qi-Rong; Zhang, Li; Zhou, Xu

    2014-05-01

    Asymmetric X-ray emission and a powerful cluster-scale radio halo indicate that A2319 is a merging cluster of galaxies. This paper presents our multicolor photometry for A2319 with 15 optical intermediate filters in the Beijing-Arizona-Taiwan-Connecticut (BATC) system. There are 142 galaxies with known spectroscopic redshifts within the viewing field of 58' × 58' centered on this rich cluster, including 128 member galaxies (called sample I). A large velocity dispersion in the rest frame, 1622^{+91}_{-70} km s-1, suggests merger dynamics in A2319. The contour map of projected density and localized velocity structure confirm the so-called A2319B substructure, at ~10' northwest to the main concentration A2319A. The spectral energy distributions (SEDs) of more than 30,000 sources are obtained in our BATC photometry down to V ~ 20 mag. A u-band (~3551 Å) image with better seeing and spatial resolution, obtained with the Bok 2.3 m telescope at Kitt Peak, is taken to make star-galaxy separation and distinguish the overlapping contamination in the BATC aperture photometry. With color-color diagrams and photometric redshift technique, 233 galaxies brighter than h BATC = 19.0 are newly selected as member candidates after an exclusion of false candidates with contaminated BATC SEDs by eyeball-checking the u-band Bok image. The early-type galaxies are found to follow a tight color-magnitude correlation. Based on sample I and the enlarged sample of member galaxies (called sample II), subcluster A2319B is confirmed. The star formation properties of cluster galaxies are derived with the evolutionary synthesis model, PEGASE, assuming a Salpeter initial mass function and an exponentially decreasing star formation rate (SFR). A strong environmental effect on star formation histories is found in the manner that galaxies in the sparse regions have various star formation histories, while galaxies in the dense regions are found to have shorter SFR time scales, older stellar ages, and

  2. Large-Scale Structure Formation: from the first non-linear objects to massive galaxy clusters

    CERN Document Server

    Planelles, S; Bykov, A M

    2014-01-01

    The large-scale structure of the Universe formed from initially small perturbations in the cosmic density field, leading to galaxy clusters with up to 10^15 Msun at the present day. Here, we review the formation of structures in the Universe, considering the first primordial galaxies and the most massive galaxy clusters as extreme cases of structure formation where fundamental processes such as gravity, turbulence, cooling and feedback are particularly relevant. The first non-linear objects in the Universe formed in dark matter halos with 10^5-10^8 Msun at redshifts 10-30, leading to the first stars and massive black holes. At later stages, larger scales became non-linear, leading to the formation of galaxy clusters, the most massive objects in the Universe. We describe here their formation via gravitational processes, including the self-similar scaling relations, as well as the observed deviations from such self-similarity and the related non-gravitational physics (cooling, stellar feedback, AGN). While on i...

  3. The location, clustering, and propagation of massive star formation in giant molecular clouds

    CERN Document Server

    Ochsendorf, B B; Chastenet, J; Tielens, A G G M; Roman-Duval, J

    2016-01-01

    Massive stars are key players in the evolution of galaxies, yet their formation pathway remains unclear. In this work, we use data from several galaxy-wide surveys to build an unbiased dataset of ~700 massive young stellar objects (MYSOs), ~200 giant molecular clouds (GMCs), and ~100 young (<10 Myr) optical stellar clusters (SCs) in the Large Magellanic Cloud. We employ this data to quantitatively study the location and clustering of massive star formation and its relation to the internal structure of GMCs. We reveal that massive stars do not typically form at the highest column densities nor centers of their parent GMCs at the ~6 pc resolution of our observations. Massive star formation clusters over multiple generations and on size scales much smaller than the size of the parent GMC. We find that massive star formation is significantly boosted in clouds near SCs. Yet, whether a cloud is associated with a SC does not depend on either the cloud's mass or global surface density. These results reveal a conne...

  4. The general mechanisms of Cu cluster formation in the processes of condensation from the gas phase

    Indian Academy of Sciences (India)

    I V Chepkasov; Yu Ya Gafner; S L Gafner; S P Bardakhanov

    2015-06-01

    Technological applications of metallic clusters impose very strict requirements for particle size, shape, structure and defect density. Such geometrical characteristics of nanoparticles are mainly determined by the process of their growth. This work represents the basic mechanisms of cluster formation from the gas phase that has been studied on the example of copper. The process of Cu nanoclusters synthesis has been studied by the moleculardynamics method based on tight-binding potentials. It has been shown that depending on the size and temperature of the initial nanoclusters the process of nanoparticle formation can pass through different basic scenarios. The general conditions of different types of particles formation have been defined and clear dependence of the cluster shape from collision temperature of initial conglomerates has been shown. The simulation results demonstrate a very good agreement with the available experimental data. Thus, it has been shown that depending on the specific application of the synthesized particles or in electronics, where particles of a small size with a spherical shape are required, or in catalytic reactions, where the main factor of effectiveness is the maximum surface area with the help of temperature of the system it is possible to get the realization of a certain frequency of this or that scenario of the shape formation of nanocrystalline particles.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-02-15

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

  6. Carbon in Red Giants in Globular Clusters and Dwarf Spheroidal Galaxies

    CERN Document Server

    Kirby, Evan N; Zhang, Andrew J; Deng, Michelle; Cohen, Judith G; Guhathakurta, Puragra; Shetrone, Matthew D; Lee, Young Sun; Rizzi, Luca

    2015-01-01

    We present carbon abundances of red giants in Milky Way globular clusters and dwarf spheroidal galaxies (dSphs). Our sample includes measurements of carbon abundances for 154 giants in the clusters NGC 2419, M68, and M15 and 398 giants in the dSphs Sculptor, Fornax, Ursa Minor, and Draco. This sample doubles the number of dSph stars with measurements of [C/Fe]. The [C/Fe] ratio in the clusters decreases with increasing luminosity above log(L/L_sun) ~= 1.6, which can be explained by deep mixing in evolved giants. The same decrease is observed in dSphs, but the initial [C/Fe] of the dSph giants is not uniform. Stars in dSphs at lower metallicities have larger [C/Fe] ratios. We hypothesize that [C/Fe] (corrected to the initial carbon abundance) declines with increasing [Fe/H] due to the metallicity dependence of the carbon yield of asymptotic giant branch stars and due to the increasing importance of Type Ia supernovae at higher metallicities. We also identified 11 very carbon-rich giants (8 previously known) in...

  7. The influence of the cluster environment on the star formation efficiency of 12 Virgo spiral galaxies

    CERN Document Server

    Vollmer, B; Braine, J; Chung, A; Kenney, J D P

    2012-01-01

    The influence of the environment on gas surface density and star formation efficiency of cluster spiral galaxies is investigated. We extend previous work on radial profiles by a pixel-to pixel analysis looking for asymmetries due to environmental interactions. The star formation rate is derived from GALEX UV and Spitzer total infrared data. As in field galaxies, the star formation rate for most Virgo galaxies is approximately proportional to the molecular gas mass. Except for NGC 4438, the cluster environment does not affect the star formation efficiency with respect to the molecular gas. Gas truncation is not associated with major changes in the total gas surface density distribution of the inner disk of Virgo spiral galaxies. In three galaxies, possible increases in the molecular fraction and the star formation efficiency with respect to the total gas, of factors of 1.5 to 2, are observed on the windward side of the galactic disk. A significant increase of the star formation efficiency with respect to the m...

  8. The fate of spiral galaxies in clusters: the star formation history of the anemic Virgo cluster galaxy NGC 4569

    CERN Document Server

    Boselli, A; Cortese, L; De Paz, A G; Seibert, M; Madore, B F; Buat, V; Martin, D C

    2006-01-01

    We present a new method for studying the star formation history of late-type, cluster galaxies undergoing gas starvation or a ram-pressure stripping event by combining bidimensional multifrequency observations with multi-zones models of galactic chemical and spectrophotometricevolution. This method is applied to the Virgo cluster anemic galaxy NGC 4569. We extract radial profiles from recently obtained UV GALEX images at 1530 and 2310 A, from visible and near-IR narrow (Halpha) and broad band images at different wavelengths (u, B, g, V, r, i, z, J, H, K), from Spitzer IRAC and MIPS images and from atomic and molecular gas maps. The model in the absence of interaction (characterized by its rotation velocity and spin parameter) is constrained by the unperturbed H band light profile and by the Halpha rotation curve. We can reconstruct the observed total-gas radial-density profile and the light surface-brightness profiles at all wavelengths in a ram-pressure stripping scenario by making simple assumptions about t...

  9. Mapping the formation areas of giant molybdenum blue clusters: a spectroscopic study

    Energy Technology Data Exchange (ETDEWEB)

    Botar, Bogdan; Ellern, Arkady; Kogerler, Paul

    2012-05-18

    The self-assembly of soluble molybdenum blue species from simple molybdate solutions has primarily been associated with giant mixed-valent wheel-shaped cluster anions, derived from the {MoV/VI154/176} archetypes, and a {MoV/VI368} lemon-shaped cluster. The combined use of Raman spectroscopy and kinetic precipitation as self-assembly monitoring techniques and single-crystal X-ray diffraction is key to mapping the realm of molybdenum blue species by establishing spherical {MoV/VI102}-type Keplerates as an important giant molybdenum blue-type species. We additionally rationalize the empirical effect of reducing agent concentration on the formation of all three relevant skeletal types: wheel, lemon and spheres. Whereas both wheels and the lemon-shaped {MoV/VI368} cluster are obtained from weakly reduced molybdenum blue solutions, considerably higher reduced solutions lead to {MoV/VI102}-type Keplerates.

  10. Collective motion and nonequilibrium cluster formation in colonies of gliding bacteria

    CERN Document Server

    Peruani, Fernando; Jakovljevic, Vladimir; Sogaard-Andersen, Lotte; Deutsch, Andreas; Bar, Markus; 10.1103/PhysRevLett.108.098102

    2013-01-01

    We characterize cell motion in experiments and show that the transition to collective motion in colonies of gliding bacterial cells confined to a monolayer appears through the organization of cells into larger moving clusters. Collective motion by non-equilibrium cluster formation is detected for a critical cell packing fraction around 17%. This transition is characterized by a scale-free power-law cluster size distribution, with an exponent $0.88\\pm0.07$, and the appearance of giant number fluctuations. Our findings are in quantitative agreement with simulations of self-propelled rods. This suggests that the interplay of self-propulsion of bacteria and the rod-shape of bacteria is sufficient to induce collective motion.

  11. The Structure, Dynamics and Star Formation Rate of the Orion Nebula Cluster

    CERN Document Server

    Da Rio, Nicola; Jaehnig, Karl

    2014-01-01

    The spatial morphology and dynamical status of a young, still-forming stellar cluster provide valuable clues on the conditions during the star formation event and the processes that regulated it. We analyze the Orion Nebula Cluster (ONC), utilizing the latest censuses of its stellar content and membership estimates over a large wavelength range. We determine the center of mass of the ONC, and study the radial dependence of angular substructure. The core appears rounder and smoother than the outskirts, consistent with a higher degree of dynamical processing. At larger distances the departure from circular symmetry is mostly driven by the elongation of the system, with very little additional substructure, indicating a somewhat evolved spatial morphology or an expanding halo. We determine the mass density profile of the cluster, which is well fitted by a power law that is slightly steeper than a singular isothermal sphere. Together with the ISM density, estimated from average stellar extinction, the mass content...

  12. The galactocentric radius dependent upper mass limit of young star clusters: stochastic star formation ruled out

    CERN Document Server

    Pflamm-Altenburg, Jan; Kroupa, Pavel

    2013-01-01

    It is widely accepted that the distribution function of the masses of young star clusters is universal and can be purely interpreted as a probability density distribution function with a constant upper mass limit. As a result of this picture the masses of the most-massive objects are exclusively determined by the size of the sample. Here we show, with very high confidence, that the masses of the most-massive young star clusters in M33 decrease with increasing galactocentric radius in contradiction to the expectations from a model of a randomly sampled constant cluster mass function with a constant upper mass limit. Pure stochastic star formation is thereby ruled out. We use this example to elucidate how naive analysis of data can lead to unphysical conclusions.

  13. ALFALFA HI Content and Star Formation in Virgo Cluster Early-Type Dwarfs

    CERN Document Server

    Koopmann, R A; Haynes, M P; Brosch, N

    2009-01-01

    The ALFALFA (Arecibo Legacy Fast ALFA) blind survey is providing a census of HI in galaxies of all types in a range of environments. Here we report on ALFALFA results for Virgo Cluster early-type dwarfs between declinations of 4 and 16 degrees. Less than 2% of the Virgo early-type dwarf population is detected, compared to 70-80% of the Im/BCD dwarf population. Most of the dwarfs detected in HI show evidence for ongoing or recent star formation. Early-type galaxies with HI tend to be located in the outer regions of the cluster and to be brighter. Early-type dwarfs with HI may be undergoing morphological transition due to cluster environmental effects.

  14. Formation of binary silver sulfide clusters and sulfur sensitization of photographic process

    Institute of Scientific and Technical Information of China (English)

    彭必先; 崔卫东; 于忠德; 高振; 朱起鹤; 孔繁敖

    1997-01-01

    Formation of silver sulfide binary cluster ions,as well as the effects of silver and sulfur content proportion,the cluster size range,the influence of laser fluence,the UV laser photolysis,etc.,was studied with the laser ablation method and a tandem time-of-flight mass spectrometer.The results show that there exist two different forms of positively charge-bearing cluster ions;[(Ag2S)n Ag] + and [ (Ag2S)n-1 Ag3]+.The most possible forms of the sulfur sensitization centers acting as traps of photoelectrons are [Ag2S] +,[ Ag2S Ag] +,[ Ag2S Ag3]+ and the analogs.

  15. A Study of the Formation of Innovative Clusters As Growth Poles In the Regions of Kazakhstan

    Directory of Open Access Journals (Sweden)

    Anel Kireyeva

    2016-01-01

    Full Text Available The aim of this resarch is to examine the level of innovative process of national economy and to reveal the essence of the cluster approach and indicators of innovative development. Keeping with the previous literature, the present study is determined by the novelty of the problem, concerning the formation and development of innovative clusters as growth poles, as well as large specifics of problems in the framework of use of innovative potential. The study employs method of monitoring of innovative processes in regions; we use method of rating estimation of innovative competitiveness of the region, based on a complex of indicators characterizing the innovation potential of the region: innovative activity and innovative susceptibility. An analysis was showed that Kazakhstan’s regions have substantial differences in the groups of regions for most of the indicators have presented form a tightly located clusters and in the ratings of innovative susceptibility and innovative activity

  16. Star formation in grand-design, spiral galaxies. Young, massive clusters in the near-infrared

    Science.gov (United States)

    Grosbøl, P.; Dottori, H.

    2012-06-01

    Aims: Spiral structure is a prominent feature in many disk galaxies and is often outlined by bright, young objects. We study the distribution of young stellar clusters in grand-design spiral galaxies and thereby determine whether strong spiral perturbations can influence star formation. Methods: Deep, near-infrared JHK-maps were observed for ten nearby, grand-design, spiral galaxies using HAWK-I at the Very Large Telescope. Complete, magnitude-limited candidate lists of star-forming complexes were obtained by searching within the K-band maps. The properties of the complexes were derived from (H - K) - (J - H) diagrams including the identification of the youngest complexes (i.e. ≲7 Myr) and the estimation of their extinction. Results: Young stellar clusters with ages ≲7 Myr have significant internal extinction in the range of AV = 3-7m, while older ones typically have AV pattern, the star formation rate in the arms is higher by a factor of 2-5 than in the inter-arm regions. The CLF in the arms is also shifted towards brighter MK by at least 0.4m. We also detect clusters with colors compatible with Large Magellanic Cloud intermediate age clusters and Milky Way globular clusters. The (J - K) - MK diagram of several galaxies shows, for the brightest clusters, a clear separation between young clusters that are highly attenuated by dust and older ones with low extinction. Conclusions: The gap in the (J - K) - MK diagrams implies that there has been a rapid expulsion of dust at an age around 7 Myr, possibly triggered by supernovae. Strong spiral perturbations concentrate the formation of clusters in the arm regions and shifts their CLF towards brighter magnitudes. Based on observations collected at the European Southern Observatory, Chile; program: ESO 82.B-0331.Appendices A-C are available in electronic form at http://www.aanda.orgThe photometric data are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http

  17. Ions colliding with clusters of fullerenes-Decay pathways and covalent bond formations

    Energy Technology Data Exchange (ETDEWEB)

    Seitz, F.; Zettergren, H.; Chen, T.; Gatchell, M.; Alexander, J. D.; Stockett, M. H.; Schmidt, H. T.; Cederquist, H. [Department of Physics, Stockholm University, S-106 91 Stockholm (Sweden); Rousseau, P.; Chesnel, J. Y.; Capron, M.; Poully, J. C.; Mery, A.; Maclot, S.; Adoui, L. [CIMAP, UMR 6252, CEA/CNRS/ENSICAEN/Universite de Caen Basse-Normandie, bd Henri Becquerel, BP 5133, F-14070 Caen cedex 05 (France); Universite de Caen Basse-Normandie, Esplanade de la Paix, F-14032 Caen (France); Wang, Y.; Martin, F. [Departamento de Quimica, Modulo 13, Universidad Autonoma de Madrid, 28049 Madrid (Spain); Instituto Madrileno de Estudios Avanzados en Nanociencia (IMDEA-Nano), Cantoblanco, 28049 Madrid (Spain); Rangama, J.; Domaracka, A.; Vizcaino, V. [CIMAP, UMR 6252, CEA/CNRS/ENSICAEN/Universite de Caen Basse-Normandie, bd Henri Becquerel, BP 5133, F-14070 Caen cedex 05 (France); and others

    2013-07-21

    We report experimental results for the ionization and fragmentation of weakly bound van der Waals clusters of n C{sub 60} molecules following collisions with Ar{sup 2+}, He{sup 2+}, and Xe{sup 20+} at laboratory kinetic energies of 13 keV, 22.5 keV, and 300 keV, respectively. Intact singly charged C{sub 60} monomers are the dominant reaction products in all three cases and this is accounted for by means of Monte Carlo calculations of energy transfer processes and a simple Arrhenius-type [C{sub 60}]{sub n}{sup +}{yields}C{sub 60}{sup +}+(n-1)C{sub 60} evaporation model. Excitation energies in the range of only {approx}0.7 eV per C{sub 60} molecule in a [C{sub 60}]{sub 13}{sup +} cluster are sufficient for complete evaporation and such low energies correspond to ion trajectories far outside the clusters. Still we observe singly and even doubly charged intact cluster ions which stem from even more distant collisions. For penetrating collisions the clusters become multiply charged and some of the individual molecules may be promptly fragmented in direct knock-out processes leading to efficient formations of new covalent systems. For Ar{sup 2+} and He{sup 2+} collisions, we observe very efficient C{sub 119}{sup +} and C{sub 118}{sup +} formation and molecular dynamics simulations suggest that they are covalent dumb-bell systems due to bonding between C{sub 59}{sup +} or C{sub 58}{sup +} and C{sub 60} during cluster fragmentation. In the Ar{sup 2+} case, it is possible to form even smaller C{sub 120-2m}{sup +} molecules (m= 2-7), while no molecular fusion reactions are observed for the present Xe{sup 20+} collisions.

  18. Formation of conducting nanochannels in diamond-like carbon films

    Science.gov (United States)

    Evtukh, A.; Litovchenko, V.; Semenenko, M.; Yilmazoglu, O.; Mutamba, K.; Hartnagel, H. L.; Pavlidis, D.

    2006-09-01

    A sharp increase of the emission current at high electric fields and a decrease of the threshold voltage after pre-breakdown conditioning of diamond-like carbon (DLC) films have been measured. This effect was observed for DLC-coated silicon tips and GaAs wedges. During electron field emission (EFE) at high electric fields the energy barriers caused by an sp3 phase between sp2 inclusions can be broken, resulting in the formation of conducting nanochannels between the semiconductor-DLC interface and the surface of the DLC film. At high current densities and the resulting local heating, the diamond-like sp3 phase transforms into a conducting graphite-like sp2 phase. As a result an electrical conducting nanostructured channel is formed in the DLC film. The diameter of the conducting nanochannel was estimated from the reduced threshold voltage after pre-breakdown conditioning to be in the range of 5-25 nm. The presence of this nanochannel in an insulating matrix leads to a local enhancement of the electric field and a reduced threshold voltage for EFE. Based on the observed features an efficient method of conducting nanochannel matrix formation in flat DLC films for improved EFE efficiency is proposed. It mainly uses a silicon tip array as an upper electrode in contact with the DLC film. The formation of nanochannels starts at the interface between the tips and the DLC film. This opens new possibilities of aligned and high-density conducting channel formation.

  19. Halpha-Derived Star-Formation Rates For Three z ~ 0.75 EDisCS Galaxy Clusters

    CERN Document Server

    Finn, R A; Poggianti, B M; Rudnick, G; Halliday, C; Milvang-Jensen, B; Pellò, R; Simard, L; Finn, Rose A.; Zaritsky, Dennis; Jr., Donald W. McCarthy; Poggianti, Bianca; Rudnick, Gregory; Halliday, Claire; Milvang-Jensen, Bo; Pello, Roser; Simard, Luc

    2005-01-01

    We present Halpha-derived star-formation rates (SFRs) for three z ~ 0.75 galaxy clusters. Our 1 sigma flux limit corresponds to a star-formation rate of 0.10-0.24 solar mass per year, and our minimum reliable Halpha + [N II] rest-frame equivalent width is 10\\AA. We show that Halpha narrowband imaging is an efficient method for measuring star formation in distant clusters. In two out of three clusters, we find that the fraction of star-forming galaxies increases with projected distance from the cluster center. We also find that the fraction of star-forming galaxies decreases with increasing local galaxy surface density in the same two clusters. We compare the median rate of star formation among star-forming cluster galaxies to a small sample of star-forming field galaxies from the literature and find that the median cluster SFRs are \\~50% less than the median field SFR. We characterize cluster evolution in terms of the mass-normalized integrated cluster SFR and find that the z ~ 0.75 clusters have more SFR per...

  20. Slow quenching of star formation in OMEGAWINGS clusters: galaxies in transition in the local universe

    CERN Document Server

    Paccagnella, Angela; Poggianti, Bianca Maria; Moretti, Alessia; Fritz, Jacopo; Gullieuszik, Marco; Couch, Warrick; Bettoni, Daniela; Cava, Antonio; Fasano, Giovanni; D'Onofrio, Mauro

    2015-01-01

    The star formation quenching depends on environment, but a full understanding of what mechanisms drive it is still missing. Exploiting a sample of galaxies with masses $M_\\ast>10^{9.8}M_\\odot$, drawn from the WIde-field Nearby Galaxy-cluster Survey (WINGS) and its recent extension OMEGAWINGS, we investigate the star formation rate (SFR) as a function of stellar mass (M$_*$) in galaxy clusters at $0.04cluster galaxies with reduced SFRs which is rare in the field. These {\\it transition} galaxies are mainly found within the cluster virial radius ($R_{200}$) but they impact on the SFR-M$_*$ relation only within 0.6R$_{200}$. The ratio of transition to PSF galaxies strongly depends on environment, being larger than 0.6 within 0.3R$_{200}$ and rapidly decreasing with distance, while it is almost flat with $M_*$. As ...

  1. The Link Between the Formation Rates of Clusters and Stars in Galaxies

    CERN Document Server

    Chandar, Rupali; Whitmore, Bradley C

    2015-01-01

    The goal of this paper is to test whether the formation rate of star clusters is proportional to the star formation rate (SFR) in galaxies. As a first step, we present the mass functions of compact clusters younger than 10 Myr in seven star-forming galaxies of diverse masses, sizes, and morphologies: the Large and Small Magellanic Clouds, NGC 4214, NGC 4449, M83, M51, and the Antennae. These cluster mass functions (CMFs) are well represented by power laws, dN/dM~M^b, with similar exponents b=-1.92+/-0.27, but with amplitudes that differ by factors up to ~10^3, corresponding to vast differences in the sizes of the cluster populations in these galaxies. We then normalize these CMFs by the SFRs in the galaxies, derived from dust-corrected H-alpha luminosities, and find that the spread in the amplitudes collapses, with a remaining rms deviation of only sigma_(logA)= 0.2. This is close to the expected dispersion from random uncertainties in the CMFs and SFRs. Thus, the data presented here are consistent with exact...

  2. Star formation activity in a young galaxy cluster at z=0.866

    CERN Document Server

    Laganá, T F; Martins, L P; da Cunha, E

    2016-01-01

    The galaxy cluster RXJ1257$+$4738 at $z=0.866$ is one of the highest redshift clusters with a richness of multi-wavelength data, and thus a good target to study the star formation-density relation at early epochs. Using a sample of spectroscopically-confirmed cluster members, we derive the star formation rates of our galaxies using two methods, (I) the relation between SFR and total infrared luminosity extrapolated from the observed \\textit{Spitzer} MIPS 24$\\mu$m imaging data, and (II) spectral energy distribution (SED) fitting using the MAGPHYS code, including eight different bands. We show that, for this cluster, the SFR-density relation is very weak and seems to be dominated by the two central galaxies and the SFR presents a mild dependence on stellar mass, with more massive galaxies having higher SFR. However, the specific SFR (SSFR) decreases with stellar mass, meaning that more massive galaxies are forming less stars per unit of mass, and thus suggesting that the increase in star-forming members is driv...

  3. Evolutionary-Hierarchical Bases of the Formation of Cluster Model of Innovation Economic Development

    Directory of Open Access Journals (Sweden)

    Yuliya Vladimirovna Dubrovskaya

    2016-10-01

    Full Text Available The functioning of a modern economic system is based on the interaction of objects of different hierarchical levels. Thus, the problem of the study of innovation processes taking into account the mutual influence of the activities of these economic actors becomes important. The paper dwells evolutionary basis for the formation of models of innovation development on the basis of micro and macroeconomic analysis. Most of the concepts recognized that despite a big number of diverse models, the coordination of the relations between economic agents is of crucial importance for the successful innovation development. According to the results of the evolutionary-hierarchical analysis, the authors reveal key phases of the development of forms of business cooperation, science and government in the domestic economy. It has become the starting point of the conception of the characteristics of the interaction in the cluster models of innovation development of the economy. Considerable expectancies on improvement of the national innovative system are connected with the development of cluster and network structures. The main objective of government authorities is the formation of mechanisms and institutions that will foster cooperation between members of the clusters. The article explains that the clusters cannot become the factors in the growth of the national economy, not being an effective tool for interaction between the actors of the regional innovative systems.

  4. Semi analytical description of formation of galaxies and clusters of galaxies

    CERN Document Server

    Demiański, Marek

    2013-01-01

    We apply the well known semi analytical model of formation of DM halos to discuss the process of formation and evolution of the relaxed objects dominated by the DM component (such as the first and dSph galaxies and clusters of galaxies). On the one hand this approach allows us to obtain a simple description of evolution of the first galaxies. On the other hand it reveals links between the observed characteristics of the relaxed DM halos and the initial power spectrum of density perturbations. Results of our analysis of the observed properties of 41 DM dominated dSph galaxies and data of $\\sim 300$ clusters of galaxies are consistent with the $\\Lambda$CDM like power spectrum of initial perturbations down to the scale of $\\sim 10kpc$.

  5. On star formation in stellar systems. I - Photoionization effects in protoglobular clusters

    Science.gov (United States)

    Tenorio-Tagle, G.; Bodenheimer, P.; Lin, D. N. C.; Noriega-Crespo, A.

    1986-01-01

    The progressive ionization and subsequent dynamical evolution of nonhomogeneously distributed low-metal-abundance diffuse gas after star formation in globular clusters are investigated analytically, taking the gravitational acceleration due to the stars into account. The basic equations are derived; the underlying assumptions, input parameters, and solution methods are explained; and numerical results for three standard cases (ionization during star formation, ionization during expansion, and evolution resulting in a stable H II region at its equilibrium Stromgren radius) are presented in graphs and characterized in detail. The time scale of residual-gas loss in typical clusters is found to be about the same as the lifetime of a massive star on the main sequence.

  6. Pitfalls when observationally characterizing the relative formation rates of stars and stellar clusters in galaxies

    CERN Document Server

    Kruijssen, J M Diederik

    2015-01-01

    Stars generally form in aggregates, some of which are bound ('clusters') while others are unbound and disperse on short ($\\sim10$ Myr) timescales ('associations'). The fraction of stars forming in bound clusters ($\\Gamma$) is a fundamental outcome of the star formation process. Recent observational and theoretical work has suggested that $\\Gamma$ increases with the gas surface density ($\\Sigma$) or star formation rate (SFR) surface density ($\\Sigma_{\\rm SFR}$), both within galaxies and between different ones. However, a recent paper by Chandar et al. has challenged these results, showing that the $total$ number of stellar aggregates per unit SFR does not vary systematically with the host galaxy's absolute SFR. In this Letter, we show that no variations are expected when no distinction is made between bound and unbound aggregates, because the sum of these two fractions should be close to unity. We also demonstrate that any scaling of $\\Gamma$ with the absolute SFR is much weaker than with $\\Sigma_{\\rm SFR}$, d...

  7. Binary interactions as a possible scenario for the formation of multiple stellar populations in globular clusters

    CERN Document Server

    Jiang, Dengkai; Li, Lifang

    2014-01-01

    Observations revealed the presence of multiple stellar populations in globular clusters (GCs) that exhibit wide abundance variations and multiple sequences in Hertzsprung-Russell (HR) diagram. We present a scenario for the formation of multiple stellar populations in GCs. In this scenario, initial GCs are single-generation clusters, and our model predicts that the abundance anomalous stars observed in GCs are the merged stars and the accretor stars produced by binary interactions, which are rapidly rotating stars at the moment of their formation and are more massive than normal single stars in the same evolutionary stage. We find that due to their own evolution, these rapidly rotating stars have different surface abundances, effective temperatures and luminosities from normal single stars in the same evolutionary stage. The stellar population with binaries can reproduce two important observational evidences of multiple stellar populations, the Na-O anticorrelation and the multiple sequences in HR diagram. Thi...

  8. Controlled Formation and Vibrational Characterization of Large Solvated Ionic Clusters in Cryogenic Ion Traps

    Science.gov (United States)

    Garand, Etienne; Marsh, Brett; Voss, Jonathan; Duffy, Erin M.

    2016-06-01

    An experimental approach for the formation of solvated ionic clusters and their vibrational spectroscopy will be presented. This recently developed apparatus combines an electrospray ionization source, two temperature controlled cryogenic ion traps and a time-of-flight infrared photofragmentation spectrometer, to allow for a universal and controlled formation and characterization of solvent clusters around ionic core as well as product of ion-molecule reaction. Recent results on the spectroscopy of such solvated ions, will be presented and discussed. In particular, this talk will present the structural evolution of glycylglycine as a function of stepwise solvation, and show how the presence of just a few water can modify the geometry of this model peptide. I will also present results solvation of ion that do not form hydrogen bond or strongly interactions with the solvent.

  9. Slow Quenching of Star Formation in OMEGAWINGS Clusters: Galaxies in Transition in the Local Universe

    Science.gov (United States)

    Paccagnella, A.; Vulcani, B.; Poggianti, B. M.; Moretti, A.; Fritz, J.; Gullieuszik, M.; Couch, W.; Bettoni, D.; Cava, A.; D'Onofrio, M.; Fasano, G.

    2016-01-01

    The star formation quenching depends on environment, but a full understanding of what mechanisms drive it is still missing. Exploiting a sample of galaxies with masses {M}*\\gt {10}9.8{M}⊙ , drawn from the WIde-field Nearby Galaxy-cluster Survey (WINGS) and its recent extension OMEGAWINGS, we investigate the star formation rate (SFR) as a function of stellar mass (M{}*) in galaxy clusters at 0.04\\lt z\\lt 0.07. We use non-member galaxies at 0.02 relation in the two environments, but detect a population of cluster galaxies with reduced SFRs, which is rare in the field. These transition galaxies are mainly found within the cluster virial radius (R200), but they impact on the SFR-M{}* relation only within 0.6R200. The ratio of transition to pure star-forming galaxies strongly depends on environment, being larger than 0.6 within 0.3R200 and rapidly decreasing with distance, while it is almost flat with M*. As galaxies move downward from the SFR-M{}* main sequence, they become redder and present older luminosity- and mass-weighted ages. These trends, together with the analysis of the star formation histories, suggest that transition galaxies have had a reduced SFR for the past 2-5 Gyr. Our results are consistent with the hypothesis that the interaction of galaxies with the intracluster medium via strangulation causes a gradual shut down of star formation, giving birth to an evolved population of galaxies in transition from being star forming to becoming passive.

  10. CONCEPTUAL PROVISIONS OF FORMATION AND DEVELOPMENT OF RESEARCH-ANDPRODUCTION CLUSTERS: INTERNATIONAL EXPERIENCE

    Directory of Open Access Journals (Sweden)

    E. L. Smolyanova

    2012-01-01

    Full Text Available The article considers the conceptual aspects of formation and development of research-andproduction clusters, developed by authors with regard allocated to them the advantages of this form of development of international and regional economy, as well as in accordance with the modern conception of competition, suggesting a need for innovative improvement of the subjects of the regional economy and their associations.

  11. Line-defect mediated formation of hole and Mo clusters in monolayer molybdenum disulfide

    Science.gov (United States)

    Ryu, Gyeong Hee; Lee, Jongyeong; Kim, Na Yeon; Lee, Yeongdong; Kim, Youngchan; Kim, Moon J.; Lee, Changgu; Lee, Zonghoon

    2016-03-01

    The production of hole and Mo cluster by electron beam irradiation in molybdenum disulfide (MoS2), which consists of S-Mo-S layers, is monitored over time using atomic resolution transmission electron microscopy. S vacancies are firstly formed due to knocking off of S atoms and then line defects are induced due to accumulation of S vacancies in MoS2 sheet instead of forming a hole. The line defects tend to be merged at a point and a hole is formed subsequently at the point. Mo atoms tend to be clustered discretely as a nano sheet along the edge of the hole due to difference in displacement threshold energy between Mo and S atoms under electron irradiation. After Mo clusters are nearly separated from MoS2 sheet, the clusters are transformed into body-centered cubic nanocrystal of Mo during prolonged electron beam irradiation. The line defect mediated formation of hole and Mo cluster only occurs within a single grain of monolayer MoS2 sheet.

  12. Cosmology and Astrophysics from Relaxed Galaxy Clusters V: Consistency with Cold Dark Matter Structure Formation

    CERN Document Server

    Mantz, Adam B; Morris, R Glenn

    2016-01-01

    This is the fifth in a series of papers studying the astrophysics and cosmology of massive, dynamically relaxed galaxy clusters. Our sample comprises 40 clusters identified as being dynamically relaxed and hot in Papers I and II of this series. Here we use constraints on cluster mass profiles from X-ray data to test some of the basic predictions of cosmological structure formation in the Cold Dark Matter (CDM) paradigm. We present constraints on the concentration--mass relation for massive clusters, finding a power-law mass dependence with a slope of $\\kappa_m=-0.16\\pm0.07$, in agreement with CDM predictions. For this relaxed sample, the relation is consistent with a constant as a function of redshift (power-law slope with $1+z$ of $\\kappa_\\zeta=-0.17\\pm0.26$), with an intrinsic scatter of $\\sigma_{\\ln c}=0.16\\pm0.03$. We investigate the shape of cluster mass profiles over the radial range probed by the data (typically $\\sim50$kpc--1Mpc), and test for departures from the simple Navarro, Frenk & White (NFW...

  13. KAT-7 Science Verification: Cold Gas, Star Formation, and Substructure in the Nearby Antlia Cluster

    CERN Document Server

    Hess, Kelley M; Carignan, Claude; Passmoor, Sean S; Goedhart, Sharmila

    2015-01-01

    The Antlia Cluster is a nearby, dynamically young structure, and its proximity provides a valuable opportunity for detailed study of galaxy and group accretion onto clusters. We present a deep HI mosaic completed as part of spectral line commissioning of the Karoo Array Telescope (KAT-7), and identify infrared counterparts from the WISE extended source catalog to study neutral atomic gas content and star formation within the cluster. We detect 37 cluster members out to a radius of ~0.9 Mpc with M_HI > 5x10^7 M_Sun. Of these, 35 are new HI detections, 27 do not have previous spectroscopic redshift measurements, and one is the Compton thick Seyfert II, NGC 3281, which we detect in HI absorption. The HI galaxies lie beyond the X-ray emitting region 200 kpc from the cluster center and have experienced ram pressure stripping out to at least 600 kpc. At larger radii, they are distributed asymmetrically suggesting accretion from surrounding filaments. Combining HI with optical redshifts, we perform a detailed dynami...

  14. Bouncing, rolling, energy flows, and cluster formation in a two-dimensional vibrated granular gas

    Science.gov (United States)

    Pérez-Ángel, Gabriel; Nahmad-Molinari, Yuri

    2011-10-01

    We study the formation of crystalline clusters for a two-dimensional (2D) sinusoidally vibrated granular gas, with maximum vertical acceleration smaller than gravity, using fully 3D simulations. It is found that this phenomenon arises from the spontaneous segregation of the granulate into two dynamical modes: one of grains that bounce in synchrony with the motion of the sustaining plate (“bouncers”) and another of grains that cease to bounce and simply rolls on the plate, without ever loosing contact with it (“rollers”). These two dynamical categories are quite robust with respect to perturbations. The populations for bouncers and rollers depend on the preparation of the granulate and can be made to take arbitrary values in all the range of accelerations where both dynamical modes are present. It is found that the dynamical mode with the largest population coalesces in clusters under the influence of the other mode, whose grains act as a higher pressure gas that compresses the clusters. In this way it is possible to produce clusters of rollers or clusters of bouncers. A gas made of grains from only one dynamical class shows only weak density fluctuations. When the occupation fractions for both modes are similar, one observes segregation and clusters of both types. The clustering of the gas is monitored using both the average coordination number and the local hexatic order parameter ψ6. Energy flows in the plane are monitored, and it is shown that roller-bouncer collisions increase horizontal kinetic energy, while all other types of collisions reduce this energy. We find that friction with the substrate is the main sink of horizontal energy for these granular gases.

  15. Cosmology and astrophysics from relaxed galaxy clusters - V. Consistency with cold dark matter structure formation

    Science.gov (United States)

    Mantz, A. B.; Allen, S. W.; Morris, R. G.

    2016-10-01

    This is the fifth in a series of papers studying the astrophysics and cosmology of massive, dynamically relaxed galaxy clusters. Our sample comprises 40 clusters identified as being dynamically relaxed and hot in Papers I and II of this series. Here we use constraints on cluster mass profiles from X-ray data to test some of the basic predictions of cosmological structure formation in the cold dark matter (CDM) paradigm. We present constraints on the concentration-mass relation for massive clusters, finding a power-law mass dependence with a slope of κm = -0.16 ± 0.07, in agreement with CDM predictions. For this relaxed sample, the relation is consistent with a constant as a function of redshift (power-law slope with 1 + z of κζ = -0.17 ± 0.26), with an intrinsic scatter of σln c = 0.16 ± 0.03. We investigate the shape of cluster mass profiles over the radial range probed by the data (typically ˜50 kpc-1 Mpc), and test for departures from the simple Navarro-Frenk-White (NFW) form, for which the logarithmic slope of the density profile tends to -1 at small radii. Specifically, we consider as alternatives the generalized NFW (GNFW) and Einasto parametrizations. For the GNFW model, we find an average value of (minus) the logarithmic inner slope of β = 1.02 ± 0.08, with an intrinsic scatter of σβ = 0.22 ± 0.07, while in the Einasto case we constrain the average shape parameter to be α = 0.29 ± 0.04 with an intrinsic scatter of σα = 0.12 ± 0.04. Our results are thus consistent with the simple NFW model on average, but we clearly detect the presence of intrinsic, cluster-to-cluster scatter about the average.

  16. Cosmology and astrophysics from relaxed galaxy clusters – V. Consistency with cold dark matter structure formation

    Energy Technology Data Exchange (ETDEWEB)

    Mantz, A.B.; /KIPAC, Menlo Park /Stanford U., Phys. Dept.; Allen, S.W.; /KIPAC, Menlo Park /Stanford U., Phys. Dept. /SLAC; Morris, R.Glenn; /KIPAC, Menlo Park /SLAC

    2016-07-15

    This is the fifth in a series of papers studying the astrophysics and cosmology of massive, dynamically relaxed galaxy clusters. Our sample comprises 40 clusters identified as being dynamically relaxed and hot in Papers I and II of this series. Here we use constraints on cluster mass profiles from X-ray data to test some of the basic predictions of cosmological structure formation in the cold dark matter (CDM) paradigm. We present constraints on the concentration–mass relation for massive clusters, finding a power-law mass dependence with a slope of κm = -0.16 ± 0.07, in agreement with CDM predictions. For this relaxed sample, the relation is consistent with a constant as a function of redshift (power-law slope with 1 + z of κζ = -0.17 ± 0.26), with an intrinsic scatter of σln c = 0.16 ± 0.03. We investigate the shape of cluster mass profiles over the radial range probed by the data (typically ~50 kpc–1 Mpc), and test for departures from the simple Navarro–Frenk–White (NFW) form, for which the logarithmic slope of the density profile tends to -1 at small radii. Specifically, we consider as alternatives the generalized NFW (GNFW) and Einasto parametrizations. For the GNFW model, we find an average value of (minus) the logarithmic inner slope of β = 1.02 ± 0.08, with an intrinsic scatter of σβ = 0.22 ± 0.07, while in the Einasto case we constrain the average shape parameter to be α = 0.29 ± 0.04 with an intrinsic scatter of σα = 0.12 ± 0.04. Our results are thus consistent with the simple NFW model on average, but we clearly detect the presence of intrinsic, cluster-to-cluster scatter about the average.

  17. Semi analytical description of formation of galaxies and clusters of galaxies

    OpenAIRE

    Demiański, Marek; Doroshkevich, Andrey

    2013-01-01

    We apply the well known semi analytical model of formation of DM halos to discuss the process of formation and evolution of the relaxed objects dominated by the DM component (such as the first and dSph galaxies and clusters of galaxies). On the one hand this approach allows us to obtain a simple description of evolution of the first galaxies. On the other hand it reveals links between the observed characteristics of the relaxed DM halos and the initial power spectrum of density perturbations....

  18. Star Formation Close to Sgr A* and Beyond the Nuclear Cluster

    CERN Document Server

    Yusef-Zadeh, F

    2016-01-01

    Two modes of star formation are involved to explain the origin of young stars near Sgr A*. One is a disk-based mode, which explains the disk of stars orbiting Sgr A*. The other is the standard cloud-based mode observed in the Galactic disk. We discuss each of these modes of star formation and apply these ideas to the inner few parsecs of Sgr A*. In particular, we focus on the latter mode in more detail. We also discuss how the tidal force exerted by the nuclear cluster makes the Roche density approaching zero and contributes to the collapse of molecular clouds located tens of parsecs away from Sgr A*.

  19. Pitfalls when observationally characterizing the relative formation rates of stars and stellar clusters in galaxies

    Science.gov (United States)

    Kruijssen, J. M. Diederik; Bastian, Nate

    2016-03-01

    Stars generally form in aggregates, some of which are bound (`clusters') while others are unbound and disperse on short ({˜ }10 { Myr}) time-scales (`associations'). The fraction of stars forming in bound clusters (Γ) is a fundamental outcome of the star formation process. Recent observational and theoretical work has suggested that Γ increases with the gas surface density (Σ) or star formation rate (SFR) surface density (ΣSFR), both within galaxies and between different ones. However, a recent paper by Chandar et al. has challenged these results, showing that the total number of stellar aggregates per unit SFR does not vary systematically with the host galaxy's absolute SFR. In this Letter, we show that no variations are expected when no distinction is made between bound and unbound aggregates, because the sum of these two fractions should be close to unity. We also demonstrate that any scaling of Γ with the absolute SFR is much weaker than with ΣSFR, due to the mass-radius-SFR relation of star-forming `main-sequence' galaxies. The environmental variation of Γ should therefore be probed as a function of area-normalized quantities, such as Σ or ΣSFR. We present a set of guidelines for meaningful observational tests of cluster formation theories and show that these resolve the reported discrepancy.

  20. Machine-Part cell formation through visual decipherable clustering of Self Organizing Map

    CERN Document Server

    Chattopadhyay, Manojit; Dan, Pranab K; 10.1007/s00170-010-2802-4

    2011-01-01

    Machine-part cell formation is used in cellular manufacturing in order to process a large variety, quality, lower work in process levels, reducing manufacturing lead-time and customer response time while retaining flexibility for new products. This paper presents a new and novel approach for obtaining machine cells and part families. In the cellular manufacturing the fundamental problem is the formation of part families and machine cells. The present paper deals with the Self Organising Map (SOM) method an unsupervised learning algorithm in Artificial Intelligence, and has been used as a visually decipherable clustering tool of machine-part cell formation. The objective of the paper is to cluster the binary machine-part matrix through visually decipherable cluster of SOM color-coding and labelling via the SOM map nodes in such a way that the part families are processed in that machine cells. The Umatrix, component plane, principal component projection, scatter plot and histogram of SOM have been reported in t...

  1. Constraining the high redshift formation of black hole seeds in nuclear star clusters with gas inflows

    CERN Document Server

    Lupi, Alessandro; Devecchi, Bernadetta; Galanti, Giorgio; Volonteri, Marta

    2014-01-01

    In this paper we explore a possible route of black hole seed formation that appeal to a model by Davies, Miller & Bellovary who considered the case of the dynamical collapse of a dense cluster of stellar black holes subjected to an inflow of gas. Here, we explore this case in a broad cosmological context. The working hypotheses are that (i) nuclear star clusters form at high redshifts in pre-galactic discs hosted in dark matter halos, providing a suitable environment for the formation of stellar black holes in their cores, (ii) major central inflows of gas occur onto these clusters due to instabilities seeded in the growing discs and/or to mergers with other gas-rich halos, and that (iii) following the inflow, stellar black holes in the core avoid ejection due to the steepening to the potential well, leading to core collapse and the formation of a massive seed of $<~ 1000\\, \\rm M_\\odot$. We simulate a cosmological box tracing the build up of the dark matter halos and there embedded baryons, and explore...

  2. A Theoretical Assessment of the Formation of IT clusters in Kazakhstan: Approaches and Positive Effects

    Directory of Open Access Journals (Sweden)

    Anel A. Kireyeva

    2016-04-01

    Full Text Available Abstract The aim of this research is to develop new theoretical approaches of the formation of IT clusters in order to strengthen of trend of the innovative industrialization and competitiveness of the country. Keeping with the previous literature, this study determines by the novelty of the problem, concerning the formation of IT clusters, which can become a driving force of transformation due to the interaction, improving efficiency and introducing advanced technology. In this research, we used conceptual approach employs the study of different conceptual views of scientists on a specific research object; structured approach involves determination of properties of a whole object by identifying the different relationships; system approach aims to develop research methods and design of complex objects – systems of different types. This study allows to conclude that IT-clusters will be most effective when they evolve naturally, originating under the action of internal forces of consolidation of  innovative, information and communications infrastructure (industrial parks, techno polis, research laboratories and business incubators, formation of soft infrastructure, that can help to find quick, innovative and creative ways to solve problems.

  3. On the composition of ammonia-sulfuric acid clusters during aerosol particle formation

    CERN Document Server

    Schobesberger, S; Bianchi, F; Rondo, L; Duplissy, J; Kürten, A; Ortega, I K; Metzger, A; Schnitzhofer, R; Almeida, J; Amorim, A; Dommen, J; Dunne, E M; Ehn, M; Gagné, S; Ickes, L; Junninen, H; Hansel, A; Kerminen, V-M; Kirkby, J; Kupc, A; Laaksonen, A; Lehtipalo, K; Mathot, S; Onnela, A; Petäjä, T; Riccobono, F; Santos, F D; Sipilä, M; Tomé, A; Tsagkogeorgas, G; Viisanen, Y; Wagner, P E; Wimmer, D; Curtius, J; Donahue, N M; Baltensperger, U; Kulmala, M; Worsnop, D R

    2014-01-01

    The formation of particles from precursor vapors is an important source of atmospheric aerosol. Research at the Cosmics Leaving OUtdoor Droplets (CLOUD) facility at CERN tries to elucidate which vapors are responsible for this new particle formation, and how in detail it proceeds. Initial measurement campaigns at the CLOUD stainless-steel aerosol chamber focused on investigating particle formation from ammonia (NH3) and sulfuric acid (H2SO4). Experiments were conducted in the presence of water, ozone and sulfur dioxide. Contaminant trace gases were suppressed at the technological limit. For this study, we mapped out the compositions of small NH3-H2SO4 clusters over a wide range of atmospherically relevant environmental conditions. We covered [NH3] in the range from 10. Positively charged clusters grew on average by Δm / Δn = 1.05 and were only observed at sufficiently high [NH3] / [H2SO4]. The H2SO4 molecules of these clusters are partially neutralized by NH3, in close resemblance to the acid-base bindings ...

  4. Silver quantum cluster (ag9 )-grafted graphitic carbon nitride nanosheets for photocatalytic hydrogen generation and dye degradation.

    Science.gov (United States)

    Sridharan, Kishore; Jang, Eunyong; Park, Jung Hyun; Kim, Jong-Ho; Lee, Jung-Ho; Park, Tae Joo

    2015-06-15

    We report the visible-light photocatalytic properties of a composite system consisting of silver quantum clusters [Ag9 (H2 MSA)7 ] (H2 MSA=mercaptosuccinic acid) embedded on graphitic carbon nitride nanosheets (AgQCs-GCN). The composites were prepared through a simple chemical route; their structural, chemical, morphological, and optical properties were characterized by using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy, transmission electron microscopy, UV/Vis diffuse reflectance spectroscopy, and photoluminescence spectroscopy. Embedment of [Ag9 (H2 MSA)7 ] on graphitic carbon nitride nanosheets (GCN) resulted in extended visible-light absorption through multiple single-electron transitions in Ag quantum clusters and an effective electronic structure for hydroxyl radical generation, which enabled increased activity in the photocatalytic degradation of methylene blue and methyl orange dye molecules compared with pristine GCN and silver nanoparticle-grafted GCN (AgNPs-GCN). Similarly, the amount of hydrogen generated by using AgQCs-GCN was 1.7 times higher than pristine GCN. However, the rate of hydrogen generated using AgQCs-GCN was slightly less than that of AgNPs-GCN because of surface hydroxyl radical formation. The plausible photocatalytic processes are discussed in detail.

  5. High resolution infrared spectroscopy of carbon dioxide clusters up to (CO2)13

    OpenAIRE

    Norooz Oliaee, J.; Dehghany, M.; McKellar, A. R. W.; Moazzen-Ahmadi, N.

    2011-01-01

    Thirteen specific infrared bands in the 2350 cm−1 region are assigned to carbon dioxide clusters, (CO2)N, with N = 6, 7, 9, 10, 11, 12 and 13. The spectra are observed in direct absorption using a tuneable infrared laser to probe a pulsed supersonic jet expansion of a dilute mixture of CO2 in He carrier gas. Assignments are aided by cluster structure calculations made using two reliable CO2 intermolecular potential functions. For (CO2)6, two highly symmetric isomers are observed, one with S6 ...

  6. Controllable synthesis and formation mechanism of carbon micro/nano-structural materials

    Science.gov (United States)

    Zhang, Chang'an; Lv, Meijiao; Wang, Xianbao; Li, Jing; Yang, Xuyu; Yang, Jia; Hu, Hao

    2013-10-01

    Three different structures of carbon materials, including carbon spheres, bamboo-like carbon nanotubes and straight carbon nanotubes, were obtained by pyrolysis of iron(II) phthalocyanine with different flow rates of H2 at 1000 °C. The suitable mechanism for formation process of the carbon nanomaterials from spheres to straight nanotubes was suggested. The competing processes between the catalyst forward and the shell growth have been used to explain the formation mechanism of three materials. The controllable synthesis of carbon materials was achieved only by changing the H2 flow rates, and it is important to explore applications of carbon materials with different shapes.

  7. Hα Star Formation Rates for z>1 Galaxy Clusters in the IRAC Shallow Cluster Survey Using WFC3 IR Grism Spectroscopy

    Science.gov (United States)

    Zeimann, Gregory; Stanford, A.; Brodwin, M.; Dey, A.; Stern, D.; Gonzalez, A.

    2011-05-01

    We present new HST WFC3 grism data for 17 z>1 galaxy clusters in the IRAC Shallow Cluster Survey (ISCS). Using the G141 grism (λ = 1.10 - 1.65 μm, 46.5 A/pixel), we identified ˜5-15 new cluster members in each cluster candidate with a visual inspection of emission line galaxies in the reduced 1-d and 2-d spectral extractions. Given the redshift range of the cluster candidates and the wavelength coverage of the G141 grism, the emission line most identified was the blended Hα+NII. Correlations found in the literature between the EW of Hα+NII and the line ratio of NII to Hα were used to deblend the two fluxes. Hα emission was used as an indicator of star formation. Our program is sensitive to an unobscured star formation rate of 4 M⊙ / Year for z=1.5 and a nominal 1:4 ratio of NII to Hα. Concurrent MIPS 24μm data allows for the comparison of different SFR tracers. Whenever possible, we also use the ratio of Hβ/Hα to estimate dust obscuration and correct the SFRs. This dataset allows the study of a wide-range of star formation rates in dense cluster cores during the peak epoch of galaxy formation.

  8. On the formation of sulphuric acid – amine clusters in varying atmospheric conditions and its influence on atmospheric new particle formation

    Directory of Open Access Journals (Sweden)

    I. K. Ortega

    2012-10-01

    Full Text Available Sulphuric acid is a key component in atmospheric new particle formation. However, sulphuric acid alone does not form stable enough clusters to initiate particle formation in atmospheric conditions. Strong bases, such as amines, have been suggested to stabilize sulphuric acid clusters and thus participate in particle formation. We modelled the formation rate of clusters with two sulphuric acid and two amine molecules (JA2B2 at varying atmospherically relevant conditions with respect to concentrations of sulphuric acid ([H2SO4], dimethylamine ([DMA] and trimethylamine ([TMA], temperature and relative humidity (RH. We also tested how the model results change if we assume that the clusters with two sulphuric acid and two amine molecules would act as seeds for heterogeneous nucleation of organic vapours (other than amines with higher atmospheric concentrations than sulphuric acid. The modelled formation rates JA2B2 were functions of sulphuric acid concentration with close to quadratic dependence, which is in good agreement with atmospheric observations of the connection between the particle formation rate and sulphuric acid concentration. The coefficients KA2B2 connecting the cluster formation rate and sulphuric acid concentrations as JA2B2=KA2B2[H2SO4]2 turned out to depend also on amine concentrations, temperature and relative humidity. We compared the modelled coefficients KA2B2 with the corresponding coefficients calculated from the atmospheric observations (Kobs from environments with varying temperatures and levels of anthropogenic influence. By taking into account the modelled behaviour of JA2B2 as a function of [H2SO4], temperature and RH, the atmospheric particle formation rate was reproduced more closely than with the traditional semi-empirical formulae based on sulphuric acid concentration only. The formation rates of clusters with two sulphuric acid and two amine molecules with different amine compositions (DMA or TMA or one of both had

  9. Formate: an Energy Storage and Transport Bridge between Carbon Dioxide and a Formate Fuel Cell in a Single Device.

    Science.gov (United States)

    Vo, Tracy; Purohit, Krutarth; Nguyen, Christopher; Biggs, Brenna; Mayoral, Salvador; Haan, John L

    2015-11-01

    We demonstrate the first device to our knowledge that uses a solar panel to power the electrochemical reduction of dissolved carbon dioxide (carbonate) into formate that is then used in the same device to operate a direct formate fuel cell (DFFC). The electrochemical reduction of carbonate is carried out on a Sn electrode in a reservoir that maintains a constant carbon balance between carbonate and formate. The electron-rich formate species is converted by the DFFC into electrical energy through electron release. The product of DFFC operation is the electron-deficient carbonate species that diffuses back to the reservoir bulk. It is possible to continuously charge the device using alternative energy (e.g., solar) to convert carbonate to formate for on-demand use in the DFFC; the intermittent nature of alternative energy makes this an attractive design. In this work, we demonstrate a proof-of-concept device that performs reduction of carbonate, storage of formate, and operation of a DFFC.

  10. Characterization and prevention of formation damage for fractured carbonate reservoir formations with low permeability

    Institute of Scientific and Technical Information of China (English)

    Shu Yong; Yan Jienian

    2008-01-01

    Stress sensitivity and water blocking in fractured carbonate reservoir formations with low permeability were determined as the main potential damage mechanisms during drilling and completion operations in the ancient buried hill Ordovician reservoirs in the Tarim Basin. Geological structure,lithology, porosity, permeability and mineral components all affect the potential for formation damage.The experimental results showed that the permeability loss was 83.8%-98.6% caused by stress sensitivity,and was 27.9%-48.1% caused by water blocking. Based on the experimental results, several main conclusions concerning stress sensitivity can be drawn as follows: the lower the core permeability and the smaller the core fracture width, the higher the stress sensitivity. Also, stress sensitivity results in lag effect for both permeability recovery and fracture closure. Aimed at the mechanisms of formation damage, a modified low-damage mixed metal hydroxide (MMH) drilling fluid system was developed,which was mainly composed of low-fluorescence shale control agent, filtration control agent, lowfluorescence lubricant and surfactant. The results of experimental evaluation and field test showed that the newly-developed drilling fluid and engineering techniques provided could dramatically increase the return permeability (over 85%) of core samples. This drilling fluid had such advantages as good rheological and lubricating properties, high temperature stability, and low filtration rate (API filtration less than 5 ml after aging at 120 ℃ for 4 hours). Therefore, fractured carbonate formations with low permeability could be protected effectively when drilling with the newly-developed drilling fluid.Meanwhile, field test showed that both penetration rate and bore stability were improved and the soaking time of the drilling fluid with formation was sharply shortened, indicating that the modified MMH drilling fluid could meet the requirements of drilling engineering and geology.

  11. The ACS Nearby Galaxy Survey Treasury. X. Quantifying the Star Cluster Formation Efficiency of Nearby Dwarf Galaxies

    CERN Document Server

    Cook, David O; Dale, Daniel A; Johnson, L Clifton; Weisz, Daniel R; Fouesneau, Morgan; Olsen, Knut A G; Engelbracht, Charles W; Dalcanton, Julianne J

    2012-01-01

    We study the relationship between the field star formation and cluster formation properties in a large sample of nearby dwarf galaxies. We use optical data from the Hubble Space Telescope and from ground-based telescopes to derive the ages and masses of the young (t_age < 100Myr) cluster sample. Our data provides the first constraints on two proposed relationships between the star formation rate of galaxies and the properties of their cluster systems in the low star formation rate regime. The data show broad agreement with these relationships, but significant galaxy-to-galaxy scatter exists. In part, this scatter can be accounted for by simulating the small number of clusters detected from stochastically sampling the cluster mass function. However, this stochasticity does not fully account for the observed scatter in our data suggesting there may be true variations in the fraction of stars formed in clusters in dwarf galaxies. Comparison of the cluster formation and the brightest cluster in our sample gala...

  12. Brown carbon formation from ketoaldehydes of biogenic monoterpenes

    Energy Technology Data Exchange (ETDEWEB)

    Nguyen, Tran B.; Laskin, Alexander; Laskin, Julia; Nizkorodov, Sergey

    2013-04-10

    Sources and chemical composition of the brown carbon are poorly understood, and even less is known about the mechanisms of its atmospheric transformations. This work presents molecular level investigation of the reactive compound ketolimononaldehyde (KLA, C9H14O3), a second generation ozonolysis product of limonene (C10H16), as a potent brown carbon precursor in secondary organic aerosol (SOA) through its reactions with reduced nitrogen compounds such as ammonium ion (NH4+), ammonia, and amino acids. The reactions of synthesized and purified KLA with NH4+ and glycine resulted in the formation of chromophores nearly identical in spectral properties and formation rates to those found in similarly-aged limonene/O3 SOA. Similar chemical reaction processes of limononaldehyde (LA, C10H16O2) and pinonaldehyde (PA, C10H16O2), the first-generation ozonolysis products in the oxidation of limonene and α-pinene, respectively, were also studied, but the resulting products did not exhibit light absorption properties of brown carbon, suggesting that the unique molecular structure of KLA produces visible-light-absorbing compounds. The KLA/NH4+ and KLA/GLY reactions produce water-soluble, hydrolysis-resilient chromophores with high mass absorption coefficients (MAC = 2000-4000 cm2 g-1) at λ ~ 500 nm, precisely at the maximum of the solar emission spectrum. Liquid chromatography was used to isolate the light-absorbing fraction, and UV-Vis, FTIR, NMR and high-resolution mass spectrometry (HR-MS) techniques were used to investigate the structures and chemical properties of the light-absorbing compounds. The KLA browning reaction generates a diverse mixture of light-absorbing compounds, with the majority of the observable products containing 1-4 units of KLA and 0-2 nitrogen atoms. Based on the HR-MS product distribution, conjugated aldol condensates, secondary imines (Schiff bases), and N-heterocycles like pyrroles may contribute in varying degree to the light-absorbing properties

  13. The 100 Myr Star Formation History of NGC 5471 from Cluster and Resolved Stellar Photometry

    CERN Document Server

    García-Benito, Rubén; Díaz, Ángeles I; Apellániz, Jesús Maíz; Cerviño, Miguel

    2011-01-01

    We show that star formation in the giant HII region NGC 5471 has been ongoing during the past 100 Myr. Using HST/WFPC2 F547M and F675W, ground based JHKs, and GALEX FUV and NUV images, we have conducted a photometric study of the star formation history in the massive giant extragalactic HII region NGC 5471 in M101. We perform a photometric study of the colour-magnitude diagram (CMD) of the resolved stars, and an integrated analysis of the main individual star forming clusters and of NGC 5471 as a whole. The integrated UV-optical-nIR photometry for the whole region provides two different reference ages, 8 Myr and 60 Myr, revealing a complex star formation history, clearly confirmed by the CMD resolved stellar photometry analysis. The spatial distribution of the stars shows that the star formation in NGC 5471 has proceeded along the whole region during, at least, the last 100 Myr. The current ionizing clusters are enclosed within a large bubble, which is likely to have been produced by the stars that formed in ...

  14. Non-aqueous formation of the calcium carbonate polymorph vaterite: astrophysical implications

    CERN Document Server

    Day, Sarah J; Parker, Julia E; Evans, Aneurin

    2013-01-01

    We study the formation of calcium carbonate, through the solid-gas interaction of amorphous Ca-silicate with gaseous CO2, at elevated pressures, and link this to the possible presence of calcium carbonate in a number of circumstellar and planetary environments. We use in-situ synchrotron X-Ray powder diffraction to obtain detailed structural data pertaining to the formation of the crystalline calcium carbonate phase vaterite and its evolution with temperature. We found that the metastable calcium carbonate phase vaterite was formed alongside calcite, at elevated CO2 pressure, at room temperature and subsequently remained stable over a large range of temperature and pressure. We report the formation of the calcium carbonate mineral vaterite whilst attempting to simulate carbonate dust grain formation in astrophysical environments. This suggests that vaterite could be a mineral component of carbonate dust and also presents a possible method of formation for vaterite and its polymorphs on planetary surfaces.

  15. The effect of carbon monoxide on planetary haze formation

    Energy Technology Data Exchange (ETDEWEB)

    Hörst, S. M.; Tolbert, M. A, E-mail: sarah.horst@colorado.edu [Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO (United States)

    2014-01-20

    Organic haze plays a key role in many planetary processes ranging from influencing the radiation budget of an atmosphere to serving as a source of prebiotic molecules on the surface. Numerous experiments have investigated the aerosols produced by exposing mixtures of N{sub 2}/CH{sub 4} to a variety of energy sources. However, many N{sub 2}/CH{sub 4} atmospheres in both our solar system and extrasolar planetary systems also contain carbon monoxide (CO). We have conducted a series of atmosphere simulation experiments to investigate the effect of CO on the formation and particle size of planetary haze analogues for a range of CO mixing ratios using two different energy sources, spark discharge and UV. We find that CO strongly affects both number density and particle size of the aerosols produced in our experiments and indicates that CO may play an important, previously unexplored, role in aerosol chemistry in planetary atmospheres.

  16. The formation of the ocean’s anthropogenic carbon reservoir

    Science.gov (United States)

    Iudicone, Daniele; Rodgers, Keith B.; Plancherel, Yves; Aumont, Olivier; Ito, Takamitsu; Key, Robert M.; Madec, Gurvan; Ishii, Masao

    2016-11-01

    The shallow overturning circulation of the oceans transports heat from the tropics to the mid-latitudes. This overturning also influences the uptake and storage of anthropogenic carbon (Cant). We demonstrate this by quantifying the relative importance of ocean thermodynamics, circulation and biogeochemistry in a global biochemistry and circulation model. Almost 2/3 of the Cant ocean uptake enters via gas exchange in waters that are lighter than the base of the ventilated thermocline. However, almost 2/3 of the excess Cant is stored below the thermocline. Our analysis shows that subtropical waters are a dominant component in the formation of subpolar waters and that these water masses essentially form a common Cant reservoir. This new method developed and presented here is intrinsically Lagrangian, as it by construction only considers the velocity or transport of waters across isopycnals. More generally, our approach provides an integral framework for linking ocean thermodynamics with biogeochemistry.

  17. Extragalactic Globular Clusters: Old Spectroscopic Ages and New Views on Their Formation

    CERN Document Server

    Strader, J; Cenarro, A J; Beasley, M A; Forbes, D A; Strader, Jay; Brodie, Jean P.; Beasley, Michael A.; Forbes, Duncan A.

    2005-01-01

    We present the results of a meta-analysis of Keck spectra of extragalactic globular clusters (GCs) in a sample of eight galaxies, ranging from dwarfs to massive ellipticals. We infer ages for the metal-poor and metal-rich GCs in these galaxies through comparisons to Galactic GCs. Both subpopulations appear to be no younger than their Galactic counterparts, with ages ~> 10 Gyr. This is the largest sample of galaxies for which ages have been constrained spectroscopically. Our results support the formation of most GCs in massive galaxies at high redshift. We propose a scenario for the formation of GC subpopulations that synthesizes aspects of both accretion and in situ approaches in the context of galaxy formation through hierarchical merging.

  18. Constraining star formation rates in cool-core brightest cluster galaxies

    CERN Document Server

    Mittal, Rupal; Combes, Francoise

    2015-01-01

    We used broad-band imaging data for 10 cool-core brightest cluster galaxies (BCGs) and conducted a Bayesian analysis using stellar population synthesis to determine the likely properties of the constituent stellar populations. Determination of ongoing star formation rates (SFRs), in particular, has a direct impact on our understanding of the cooling of the intracluster medium (ICM), star formation and AGN-regulated feedback. Our model consists of an old stellar population and a series of young stellar components. We calculated marginalized posterior probability distributions for various model parameters and obtained 68% plausible intervals from them. The 68% plausible interval on the SFRs is broad, owing to a wide range of models that are capable of fitting the data, which also explains the wide dispersion in the star formation rates available in the literature. The ranges of possible SFRs are robust and highlight the strength in such a Bayesian analysis. The SFRs are correlated with the X-ray mass deposition...

  19. Young stellar clusters in the Rosette molecular cloud. Arguments against triggered star formation

    CERN Document Server

    Cambrésy, L; Feher, O; Tóth, L V; Schneider, N

    2013-01-01

    The Rosette complex is a well studied region of the galactic plane which presents the apparent characteristics of a triggered star forming region. This is however still debated as no strong evidence corroborates this statement. In this study, we focus on characterizing the young stellar population in the Rosette to improve our understanding of the processes that regulate the star formation in this region. We propose an original method relying on the joint analysis of the star color and density in the near-infrared. It leads to the mapping of the molecular cloud spatial distribution and the detection of the embedded clusters with their characterization in term of member number and age estimation. We identified 13 clusters, 2 of them are new discoveries, and we estimated that the total number of young stellar objects in the Rosette ranges between 4000 and 8000 members. We found the age distribution of the young clusters is not consistent with a general triggered scenario for the star formation in this molecular...

  20. Ultraviolet Morphologies and Star-Formation Rates of CLASH Brightest Cluster Galaxies

    CERN Document Server

    Donahue, Megan; Fogarty, Kevin; Li, Yuan; Voit, G Mark; Postman, Marc; Koekemoer, Anton; Moustakas, John; Bradley, Larry; Ford, Holland

    2015-01-01

    Brightest cluster galaxies (BCGs) are usually quiescent, but many exhibit star formation. Here we exploit the opportunity provided by rest-frame UV imaging of galaxy clusters in the CLASH (Cluster Lensing and Supernovae with Hubble) Multi-Cycle Treasury Project to reveal the diversity of UV morphologies in BCGs and to compare them with recent simulations of the cool, star-forming gas structures produced by precipitation-driven feedback. All of the CLASH BCGs are detected in the rest-frame UV (280 nm), regardless of their star-formation activity, because evolved stellar populations produce a modest amount of UV light that traces the relatively smooth, symmetric, and centrally peaked stellar distribution seen in the near infrared. Ultraviolet morphologies among the BCGs with strong UV excesses exhibit distinctive knots, multiple elongated clumps, and extended filaments of emission that distinctly differ from the smooth profiles of the UV-quiet BCGs. These structures, which are similar to those seen in the few s...

  1. THE STATE POLICY OF OF CLUSTER FORMS IN ORGANIZATION OF INTERACTION IN AGRARIAN FORMATION

    Directory of Open Access Journals (Sweden)

    Govdya V. V.

    2015-10-01

    Full Text Available The optimization issues of governance and the development of agriculture sector are particularly relevant in times of financial sanctions, implementation of the strategy of import substitution. Integration is the one of these mechanisms. In the article, we have discussed in detail the historical aspect of the appearance agroindustrial integration in Russia. The authors highlighted the negative aspects constraining the development of integration processes in the industry. The agro-industrial complex is considered as a set of regional and microcomplexes. The article identified three main areas of the industry. Its balance is able to provide dynamic and sustainable development of agriculture. Dynamics of the share of industry in the formation of the key indicators of the Russian economy are presented. It demonstrates the need to solve issues of increasing the efficiency of all agrarian formations. The authors proposed industrial and economic way out of the current crisis on the results of the research. The Government support of agriculture is the main instrument of agrarian policy, especially in times of economic crisis. The authors proposed a cluster approach to economic development as a priority. It allows reaching high competitiveness and stability of economic systems of cluster. In the article the advantages of creating clusters in the regional economic system are presented. We have summed up the implementation of the previously developed innovative, systemic management model

  2. On the Formation of Cool, Non-Flowing Cores in Galaxy Clusters via Hierarchical Mergers

    CERN Document Server

    Burns, J O; Norman, M L; Bryan, G L

    2003-01-01

    We present a new model for the creation of cool cores in rich galaxy clusters within a LambdaCDM cosmological framework using the results from high spatial dynamic range, adaptive mesh hydro/N-body simulations. It is proposed that cores of cool gas first form in subclusters and these subclusters merge to create rich clusters with cool, central X-Ray excesses. The rich cool clusters do not possess ``cooling flows'' due to the presence of bulk velocities in the intracluster medium in excess of 1000 km/sec produced by on-going accretion of gas from supercluster filaments. This new model has several attractive features including the presence of substantial core substructure within the cool cores, and it predicts the appearance of cool bullets, cool fronts, and cool filaments all of which have been recently observed with X-Ray satellites. This hierarchical formation model is also consistent with the observation that cool cores in Abell clusters occur preferentially in dense supercluster environments. On the other ...

  3. Formation and evolution of dwarf early-type galaxies in the Virgo cluster I. Internal kinematics

    CERN Document Server

    Toloba, E; Cenarro, A J; Peletier, R F; Gorgas, J; de Paz, A Gil; Munoz-Mateos, J C

    2010-01-01

    We present new medium resolution kinematic data for a sample of 21 dwarf early-type galaxies (dEs) mainly in the Virgo cluster, obtained with the WHT and INT telescopes at the Roque de los Muchachos Observatory (La Palma, Spain). These data are used to study the origin of the dwarf elliptical galaxy population inhabiting clusters. We confirm that dEs are not dark matter dominated galaxies, at least up to the half-light radius. We also find that the observed galaxies in the outer parts of the cluster are mostly rotationally supported systems with disky morphological shapes. Rotationally supported dEs have rotation curves similar to those of star forming galaxies of similar luminosity and follow the Tully-Fisher relation. This is expected if dE galaxies are the descendant of low luminosity star forming systems which recently entered the cluster environment and lost their gas due to a ram pressure stripping event, quenching their star formation activity and transforming into quiescent systems, but conserving the...

  4. Analysis of the static properties of cluster formations in symmetric linear multiblock copolymers.

    Science.gov (United States)

    Fytas, N G; Theodorakis, P E

    2011-06-15

    We use molecular dynamics simulations to study the static properties of a single linear multiblock copolymer chain under poor solvent conditions varying the block length N, the number of blocks n, and the solvent quality by variation of the temperature T. We study the most symmetrical case, where the number of blocks of monomers of type A, n(A), equals that of monomers B, n(B) (n(A) = n(B) = n/2), the length of all blocks is the same irrespective of their type, and the potential parameters are also chosen symmetrically, as for a standard Lennard-Jones fluid. Under poor solvent conditions the chains collapse and blocks with monomers of the same type form clusters, which are phase separated from the clusters with monomers of the other type. We study the dependence of the size of the clusters formed on n, N and T. Furthermore, we discuss our results with respect to recent simulation data on the phase behaviour of such macromolecules, providing a complete picture for the cluster formations in single multiblock copolymer chains under poor solvent conditions.

  5. Modeling AGN Feedback in Cool-Core Clusters: The Formation of Cold Clumps

    CERN Document Server

    Li, Yuan

    2013-01-01

    We perform high-resolution (15-30 pc) adaptive mesh simulations to study the impact of momentum-driven AGN feedback in cool-core clusters, focusing in this paper on the formation of cold clumps. The feedback is jet-driven with an energy determined by the amount of cold gas within 500 pc of the SMBH. When the intra-cluster medium (ICM) in the core of the cluster becomes marginally stable to radiative cooling, with the thermal instability to the free-fall timescale ratio t_{TI}/t_{ff} < 3-10, cold clumps of gas start to form along the propagation direction of the AGN jets. By tracing the particles in the simulations, we find that these cold clumps originate from low entropy (but still hot) gas that is accelerated by the jet to outward radial velocities of a few hundred km/s. This gas is out of hydrostatic equilibrium and so can cool. The clumps then grow larger as they decelerate and fall towards the center of the cluster, eventually being accreted onto the super-massive black hole. The general morphology, s...

  6. The star cluster - field star connection in nearby spiral galaxies. II. Field star and cluster formation histories and their relation

    NARCIS (Netherlands)

    Silva-Villa, E.; Larsen, S.S.

    2011-01-01

    Context. Recent studies have started to cast doubt on the assumption that most stars are formed in clusters. Observational studies of field stars and star cluster systems in nearby galaxies can lead to better constraints on the fraction of stars forming in clusters. Ultimately this may lead to a bet

  7. The Formation of First Generation Stars and Globular Clusters in Protogalactic Clouds

    Energy Technology Data Exchange (ETDEWEB)

    Murray, S

    2003-07-07

    Within collapsing protogalaxies, thermal instability leads to the formation of a population of cool fragments which are confined by the pressure of a residual hot background medium. The critical mass required for the cold clouds to become gravitationally unstable and to form stars is determined by both their internal temperature and external pressure. Massive first generation stars form in primordial clouds with sufficient column density to shield themselves from external UV photons emitted by nearby massive stars or AGNs. Less massive photoionized clouds gain mass due to ram pressure stripping by the residual halo gas. Collisions may also trigger thermal instability and fragmentation into cloudlets. While most cloudlets have substellar masses, the largest become self-gravitating and collapse to form protostellar cores without further fragmentation. The initial stellar mass function is established as these cores capture additional residual cloudlets. Energy dissipation from the mergers ensures that the cluster remains bound in the limit of low star formation efficiency. Dissipation also promotes the formation and retention of the most massive stars in the cluster center. On the scale of the protogalactic clouds, the formation of massive stars generates intense UV radiation which photoionizes gas and quenches star formation in nearby regions. As gas density accumulates in the center of the galactic potential, the self-regulated star formation rate increases. At the location where most of the residual gas can be converted into stars on its internal dynamical timescale, a galaxy attains its asymptotic kinematic structure such as exponential profiles, Tully-Fisher, and Faber-Jackson laws.

  8. Multi-wavelength study of X-ray luminous clusters at z ~ 0.3 I. Star formation activity of cluster galaxies

    CERN Document Server

    Braglia, F G; Biviano, A; Böhringer, H

    2009-01-01

    The current paradigm of cosmic formation and evolution of galaxy clusters foresees growth mostly through merging. Galaxies in the infall region or in the core of a cluster undergo transformations owing to different environmental stresses. For two X-ray luminous clusters at redshift z ~ 0.3 with opposite X-ray morphologies, RXCJ0014.3-3022 and RXCJ2308.3-0211, we assess differences in galaxy populations as a function of cluster topography. Cluster large-scale structure and substructure are determined from the combined photometry in the B, V, and R bands, and from multi-object optical spectroscopy at low resolution. A spectral index analysis is performed, based on the [OII] and Hdelta features, and the D4000 break, available for more than 100 member galaxies per cluster. Combination of spectral indices and FUV-optical colours provides a picture of the star formation history in galaxies. In spite of the potential presence of a small fraction of galaxies with obscured star formation activity, the average star-for...

  9. Suppression of Star Formation in the central 200 kpc of a z = 1.4 Galaxy Cluster

    CERN Document Server

    Grutzbauch, Ruth; Jørgensen, Inger; Varela, Jesus

    2012-01-01

    We present the results of an extended narrow-band H{\\alpha} study of the massive galaxy cluster XMMU J2235.3-2557 at z = 1.39. This paper represents a follow up study to our previous investigation of star-formation in the cluster centre, extending our analysis out to a projected cluster radius of 1.5 Mpc. Using the Near InfraRed Imager and Spectrograph (NIRI) on Gemini North we obtained deep H narrow-band imaging corresponding to the rest-frame wavelength of H{\\alpha} at the cluster's redshift. We identify a total of 163 potential cluster members in both pointings, excluding stars based on their near-IR colours derived from VLT/HAWK-I imaging. Of these 163 objects 14 are spectroscopically confirmed cluster members, and 20% are excess line-emitters. We find no evidence of star formation activity within a radius of 200 kpc of the brightest cluster galaxy in the cluster core. Dust-corrected star formation rates (SFR) of excess emitters outside this cluster quenching radius, RQ \\sim 200 kpc, are on average = 2.7...

  10. Outflow Feedback Regulated Massive Star Formation in Parsec-Scale Cluster Forming Clumps

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Peng; /KIPAC, Menlo Park /Stanford U., Phys.Dept.; Li, Zhi-Yun; /Virginia U., Astron. Dept.; Abel, Tom; /KIPAC, Menlo Park /Stanford U., Phys.Dept.; Nakamura, Fumitaka; /Niigata U.

    2010-02-15

    We investigate massive star formation in turbulent, magnetized, parsec-scale clumps of molecular clouds including protostellar outflow feedback using three dimensional numerical simulations of effective resolution 2048{sup 3}. The calculations are carried out using a block structured adaptive mesh refinement code that solves the ideal MHD equations including self-gravity and implements accreting sink particles. We find that, in the absence of regulation by magnetic fields and outflow feedback, massive stars form readily in a turbulent, moderately condensed clump of {approx} 1,600 M{sub {circle_dot}} (containing {approx} 10{sup 2} initial Jeans masses), along with a cluster of hundreds of lower mass stars. The massive stars are fed at high rates by (1) transient dense filaments produced by large-scale turbulent compression at early times, and (2) by the clump-wide global collapse resulting from turbulence decay at late times. In both cases, the bulk of the massive star's mass is supplied from outside a 0.1 pc-sized 'core' that surrounds the star. In our simulation, the massive star is clump-fed rather than core-fed. The need for large-scale feeding makes the massive star formation prone to regulation by outflow feedback, which directly opposes the feeding processes. The outflows reduce the mass accretion rates onto the massive stars by breaking up the dense filaments that feed the massive star formation at early times, and by collectively slowing down the global collapse that fuel the massive star formation at late times. The latter is aided by a moderate magnetic field of strength in the observed range (corresponding to a dimensionless clump mass-to-flux ratio {lambda} {approx} a few); the field allows the outflow momenta to be deposited more efficiently inside the clump. We conclude that the massive star formation in our simulated turbulent, magnetized, parsec-scale clump is outflow-regulated and clump-fed (ORCF for short). An important implication

  11. Effects of carbonyl bond, metal cluster dissociation, and evaporation rates on predictions of nanotube production in high-pressure carbon monoxide

    Science.gov (United States)

    Scott, Carl D.; Smalley, Richard E.

    2003-01-01

    The high-pressure carbon monoxide (HiPco) process for producing single-wall carbon nanotubes (SWNTs) uses iron pentacarbonyl as the source of iron for catalyzing the Boudouard reaction. Attempts using nickel tetracarbonyl led to no production of SWNTs. This paper discusses simulations at a constant condition of 1300 K and 30 atm in which the chemical rate equations are solved for different reaction schemes. A lumped cluster model is developed to limit the number of species in the models, yet it includes fairly large clusters. Reaction rate coefficients in these schemes are based on bond energies of iron and nickel species and on estimates of chemical rates for formation of SWNTs. SWNT growth is measured by the conformation of CO2. It is shown that the production of CO2 is significantly greater for FeCO because of its lower bond energy as compared with that of NiCO. It is also shown that the dissociation and evaporation rates of atoms from small metal clusters have a significant effect on CO2 production. A high rate of evaporation leads to a smaller number of metal clusters available to catalyze the Boudouard reaction. This suggests that if CO reacts with metal clusters and removes atoms from them by forming MeCO, this has the effect of enhancing the evaporation rate and reducing SWNT production. The study also investigates some other reactions in the model that have a less dramatic influence.

  12. Semi-analytical description of formation of galaxies and clusters of galaxies

    Science.gov (United States)

    Demiański, M.; Doroshkevich, A. G.

    2014-03-01

    We apply the well-known semi-analytical model of formation of the Dark Matter (DM) haloes to discuss properties of the relaxed objects dominated by the DM component (such as the first and dwarf spheroidal galaxies (dSph) and/or clusters of galaxies). This approach allows us to obtain a simple but more detailed description of evolution of the first galaxies. It also reveals links between the observed characteristics of the relaxed DM haloes and the initial power spectrum of density perturbations. Results of our analysis of the observed properties of ˜40 DM dominated galaxies and ˜100 clusters of galaxies are consistent with the Λ cold dark matter like power spectrum of initial perturbations down to the scale of ˜10 kpc. For the DM dominated objects the scaling relations are also discussed.

  13. Formation Mechanism and Binding Energy for Body-Centered Cubic Structure of He+9 Cluster

    Institute of Scientific and Technical Information of China (English)

    ZHANG Jian-Ping; GOU Qing-Quan; LI Ping

    2004-01-01

    The formation mechanism for the body-centered cubic structure of He+9 cluster is proposed and its total energy curve is calculated by the method of a Modified Arrangement Channel Quantum Mechanics. The energy is the function of separation R between the nuclei at the center and an apex of the body-centered cubic structure. The result of the calculation shows that the curve has a minimal energy -25.6669 (a.u.) at R = 2.550ao. The binding energy of He+9 with respect to He+ + 8He was calculated to be 0.8857 a.u. This means that the cluster of He+9 may be formed in the body-centered cubic structure of R = 2.55a0.

  14. Formation, migration, and clustering energies of interstitial He in α-quartz and β-cristobalite

    Science.gov (United States)

    Lin, Kan-Ju; Ding, Hepeng; Demkowicz, Michael J.

    2016-10-01

    Precipitation of implanted helium (He) is detrimental to many nuclear materials. A solid in which implanted He does not precipitate, but rather remains in solution and diffuses readily is potentially of interest for applications requiring resistance to He-induced damage. We use density functional theory (DFT) calculations to examine He interstitial formation, migration, and clustering energies in two SiO2 polymorphs: α-quartz and β-cristobalite. Our findings show greater He solubility and mobility in the latter than in the former. This difference appears to be due primarily to the unlike atomic-level structures of α-quartz and β-cristobalite, rather than their differing densities. Our findings also suggest that He is unlikely to cluster in either material. The behavior of He in α-quartz and β-cristobalite, and similar forms of silica make them promising materials for further investigation for potential use in applications requiring resistance to He-induced damage.

  15. Cluster analysis of particulate matter (PM10) and black carbon (BC) concentrations

    Science.gov (United States)

    Žibert, Janez; Pražnikar, Jure

    2012-09-01

    The monitoring of air-pollution constituents like particulate matter (PM10) and black carbon (BC) can provide information about air quality and the dynamics of emissions. Air quality depends on natural and anthropogenic sources of emissions as well as the weather conditions. For a one-year period the diurnal concentrations of PM10 and BC in the Port of Koper were analysed by clustering days into similar groups according to the similarity of the BC and PM10 hourly derived day-profiles without any prior assumptions about working and non-working days, weather conditions or hot and cold seasons. The analysis was performed by using k-means clustering with the squared Euclidean distance as the similarity measure. The analysis showed that 10 clusters in the BC case produced 3 clusters with just one member day and 7 clusters that encompasses more than one day with similar BC profiles. Similar results were found in the PM10 case, where one cluster has a single-member day, while 7 clusters contain several member days. The clustering analysis revealed that the clusters with less pronounced bimodal patterns and low hourly and average daily concentrations for both types of measurements include the most days in the one-year analysis. A typical day profile of the BC measurements includes a bimodal pattern with morning and evening peaks, while the PM10 measurements reveal a less pronounced bimodality. There are also clusters with single-peak day-profiles. The BC data in such cases exhibit morning peaks, while the PM10 data consist of noon or afternoon single peaks. Single pronounced peaks can be explained by appropriate cluster wind speed profiles. The analysis also revealed some special day-profiles. The BC cluster with a high midnight peak at 30/04/2010 and the PM10 cluster with the highest observed concentration of PM10 at 01/05/2010 (208.0 μg m-3) coincide with 1 May, which is a national holiday in Slovenia and has very strong tradition of bonfire parties. The clustering of

  16. Formation of carbon nanoscrolls from graphene sheet: A molecular dynamics study

    Science.gov (United States)

    Zhang, Danhui; Yang, Houbo

    2016-12-01

    In recent year, carbon nanoscrolls have attracted intensive attention both in theory and experiments for their unique and excellent fundamental properties and the wide range of potential applications. In this paper, the fabrication of carbon nanoscrolls using graphene and carbon nanotubes has been studied by molecular dynamics (MD) method. The formation mechanism of carbon nanoscrolls has been presented convincing explanations. Furthermore, the position and number of carbon nanotubes also influence the formation of carbon nanoscrolls. Our theoretical results will provide researchers a powerful guide and helpful assistance in designing better targeted programs in experiments.

  17. Globular Cluster Abundances and What They Can Tell Us About Galaxy Formation

    CERN Document Server

    Cohen, Judith G

    2009-01-01

    We review the properties of globular clusters which make them useful for studying the Galactic halo, Galactic chemical evolution, and the early stages of the formation of the Milky Way. We review the evidence that GCs have a chemical inventory similar to those of halo field stars. We discuss the abundance ratios for dSph galaxies and show that it is possible to have formed at least part the Galactic halo field stellar population by dissolving globular clusters and/or accreting dSph galaxies but only if this occurred at an early stage in the formation of the Galaxy. We review the constraints on halo formation timescales deduced from the low Mg isotopic ratios in metal-poor halo field dwarfs which indicate that AGB stars did not have time to contribute significantly, while M71 contains two populations, one without and also one with a substantial AGB contribution. We review the limited evidence for GCs with a second population showing additional contributions from SNII, currently confined to Omega Cen, M54, and ...

  18. Formation of Stellar Clusters and the Importance of Thermodynamics for Fragmentation

    CERN Document Server

    Klessen, Ralf S; Glover, Simon C O

    2008-01-01

    We discuss results from numerical simulations of star cluster formation in the turbulent interstellar medium (ISM). The thermodynamic behavior of the star-forming gas plays a crucial role in fragmentation and determines the stellar mass function as well as the dynamic properties of the nascent stellar cluster. This holds for star formation in molecular clouds in the solar neighborhood as well as for the formation of the very first stars in the early universe. The thermodynamic state of the ISM is a result of the balance between heating and cooling processes, which in turn are determined by atomic and molecular physics and by chemical abundances. Features in the effective equation of state of the gas, such as a transition from a cooling to a heating regime, define a characteristic mass scale for fragmentation and so set the peak of the initial mass function of stars (IMF). As it is based on fundamental physical quantities and constants, this is an attractive approach to explain the apparent universality of the...

  19. Fragmentation of neutral carbon clusters formed by high velocity atomic collision; Fragmentation d'agregats de carbone neutres formes par collision atomique a haute vitesse

    Energy Technology Data Exchange (ETDEWEB)

    Martinet, G

    2004-05-01

    The aim of this work is to understand the fragmentation of small neutral carbon clusters formed by high velocity atomic collision on atomic gas. In this experiment, the main way of deexcitation of neutral clusters formed by electron capture with ionic species is the fragmentation. To measure the channels of fragmentation, a new detection tool based on shape analysis of current pulse delivered by semiconductor detectors has been developed. For the first time, all branching ratios of neutral carbon clusters are measured in an unambiguous way for clusters size up to 10 atoms. The measurements have been compared to a statistical model in microcanonical ensemble (Microcanonical Metropolis Monte Carlo). In this model, various structural properties of carbon clusters are required. These data have been calculated with Density Functional Theory (DFT-B3LYP) to find the geometries of the clusters and then with Coupled Clusters (CCSD(T)) formalism to obtain dissociation energies and other quantities needed to compute fragmentation calculations. The experimental branching ratios have been compared to the fragmentation model which has allowed to find an energy distribution deposited in the collision. Finally, specific cluster effect has been found namely a large population of excited states. This behaviour is completely different of the atomic carbon case for which the electron capture in the ground states predominates. (author)

  20. Study of small carbon and semiconductor clusters using negative ion threshold photodetachment spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Arnold, C.C.

    1994-08-01

    The bonding and electronics of several small carbon and semiconductor clusters containing less than ten atoms are probed using negative ion threshold photodetachment (zero electron kinetic energy, or ZEKE) spectroscopy. ZEKE spectroscopy is a particularly advantageous technique for small cluster study, as it combines mass selection with good spectroscopic resolution. The ground and low-lying electronic states of small clusters in general can be accessed by detaching an electron from the ground anion state. The clusters studied using this technique and described in this work are C{sub 6}{sup {minus}}/C{sub 6}, Si{sub n}{sup {minus}}/Si{sub n} (n = 2, 3, 4), Ge{sub 2}{sup {minus}}/Ge{sub 2}, In{sub 2}P{sup {minus}}/In{sub 2}P,InP{sub 2}{sup {minus}}/InP{sup 2}, and Ga{sub 2}As{sup {minus}}. The total photodetachment cross sections of several other small carbon clusters and the ZEKE spectrum of the I{sup {minus}}{center_dot}CH{sub 3}I S{sub N}2 reaction complex are also presented to illustrate the versatility of the experimental apparatus. Clusters with so few atoms do not exhibit bulk properties. However, each specie exhibits bonding properties that relate to the type of bonding found in the bulk. C{sub 6}, as has been predicted, exhibits a linear cumulenic structure, where double bonds connect all six carbon atoms. This double bonding reflects how important {pi} bonding is in certain phases of pure carbon (graphite and fullerenes). The symmetric stretch frequencies observed in the C{sub 6}{sup {minus}} spectra, however, are in poor agreement with the calculated values. Also observed as sharp structure in total photodetachment cross section scans was an excited anion state bound by only {approximately}40 cm{sup {minus}1} relative to the detachment continuum. This excited anion state appears to be a valence bound state, possible because of the high electron affinity of C{sub 6}, and the open shell of the anion.

  1. Cluster-formation in the Rosette molecular cloud at the junctions of filaments

    Science.gov (United States)

    Schneider, N.; Csengeri, T.; Hennemann, M.; Motte, F.; Didelon, P.; Federrath, C.; Bontemps, S.; Di Francesco, J.; Arzoumanian, D.; Minier, V.; André, Ph.; Hill, T.; Zavagno, A.; Nguyen-Luong, Q.; Attard, M.; Bernard, J.-Ph.; Elia, D.; Fallscheer, C.; Griffin, M.; Kirk, J.; Klessen, R.; Könyves, V.; Martin, P.; Men'shchikov, A.; Palmeirim, P.; Peretto, N.; Pestalozzi, M.; Russeil, D.; Sadavoy, S.; Sousbie, T.; Testi, L.; Tremblin, P.; Ward-Thompson, D.; White, G.

    2012-04-01

    Aims: For many years feedback processes generated by OB-stars in molecular clouds, including expanding ionization fronts, stellar winds, or UV-radiation, have been proposed to trigger subsequent star formation. However, hydrodynamic models including radiation and gravity show that UV-illumination has little or no impact on the global dynamical evolution of the cloud. Instead, gravitational collapse of filaments and/or merging of filamentary structures can lead to building up dense high-mass star-forming clumps. However, the overall density structure of the cloud has a large influence on this process, and requires a better understanding. Methods: The Rosette molecular cloud, irradiated by the NGC 2244 cluster, is a template region for triggered star-formation, and we investigated its spatial and density structure by applying a curvelet analysis, a filament-tracing algorithm (DisPerSE), and probability density functions (PDFs) on Herschel column density maps, obtained within the HOBYS key program. Results: The analysis reveals not only the filamentary structure of the cloud but also that all known infrared clusters except one lie at junctions of filaments, as predicted by turbulence simulations. The PDFs of sub-regions in the cloud show systematic differences. The two UV-exposed regions have a double-peaked PDF we interprete as caused by shock compression, while the PDFs of the center and other cloud parts are more complex, partly with a power-law tail. A deviation of the log-normal PDF form occurs at AV ≈ 9m for the center, and around 4m for the other regions. Only the part of the cloud farthest from the Rosette nebula shows a log-normal PDF. Conclusions: The deviations of the PDF from the log-normal shape typically associated with low- and high-mass star-forming regions at AV ≈ 3-4m and 8-10m, respectively, are found here within the very same cloud. This shows that there is no fundamental difference in the density structure of low- and high-mass star

  2. Evolution of collisionless systems of gravitating masses, and the formation of galaxies and galaxy clusters

    Energy Technology Data Exchange (ETDEWEB)

    Doroshkevich, A.G.; Klypin, A.A.

    1981-03-01

    A series of dissipation-free models are investigated for the formation of structure in elliptical galaxies or rich clusters of galaxies by the rapid relaxation process. Using the method of macroparticles, the evolution of two types of systems comprising approx.10/sup 4/ particles is computed numerically: a) a system of superposed homogeneous oblate ellipsoids differing widely in mass and initial density; b) successive accretion of a set of low-density envelopes. In all cases an extended, flattened power-law surface-density profile develops, in good agreement with the profiles observed. The relationship between the parameters of the initial and final distributions is discussed.

  3. The Red Sequence of High-Redshift Clusters: a Comparison with Cosmological Galaxy Formation Models

    OpenAIRE

    Menci, N.; Rosati, P.; Gobat, R.; Strazzullo, V.; Rettura, A.; S. Mei; Demarco, R.

    2008-01-01

    We compare the results from a semi-analytic model of galaxy formation with spectro-photometric observations of distant galaxy clusters observed in the range 0.8< z< 1.3. We investigate the properties of their red sequence (RS) galaxies and compare them with those of the field at the same redshift. In our model we find that i) a well-defined, narrow RS is obtained already by z= 1.2; this is found to be more populated than the field RS, analogously to what observed and predicted at z=0; ii) the...

  4. STAR FORMATION HISTORY OF THE MILKY WAY HALO TRACED BY THE OOSTERHOFF DICHOTOMY AMONG GLOBULAR CLUSTERS

    Energy Technology Data Exchange (ETDEWEB)

    Jang, Sohee; Lee, Young-Wook, E-mail: ywlee2@yonsei.ac.kr [Center for Galaxy Evolution Research and Department of Astronomy, Yonsei University, Seoul 120-749 (Korea, Republic of)

    2015-06-22

    In our recent investigation of the Oosterhoff dichotomy in the multiple population paradigm, we have suggested that the RR Lyrae variables in the globular clusters (GCs) of Oosterhoff groups I, II, and III are produced mostly by first, second, and third generation stars (G1, G2, and G3), respectively. Here we show, for the first time, that the observed dichotomies in the inner and outer halo GCs can be naturally reproduced when these models are extended to all metallicity regimes, while maintaining reasonable agreements in the horizontal-branch type versus [Fe/H] correlations. In order to achieve this, however, specific star formation histories are required for the inner and outer halos. In the inner halo GCs, the star formation commenced and ceased earlier with a relatively short formation timescale between the subpopulations (∼0.5 Gyr), while in the outer halo, the formation of G1 was delayed by ∼0.8 Gyr with a more extended timescale between G1 and G2 (∼1.4 Gyr). This is consistent with the dual origin of the Milky Way halo. Despite the difference in detail, our models show that the Oosterhoff period groups observed in both outer and inner halo GCs are all manifestations of the “population-shift” effect within the instability strip, for which the origin can be traced back to the two or three discrete episodes of star formation in GCs.

  5. Theory and methods to development of strategy of formation and develop-ment of researchand-production clusters

    Directory of Open Access Journals (Sweden)

    Y. A. Ahenbah

    2012-01-01

    Full Text Available The research-and-production cluster is one of the effective forms of regional development giving steady synergetic effect, providing an intensification of the regional industry and business and promoting increase of a standard of living of the population. Formation of research-and-production clusters represents difficult process, to estimate which productivity it is represented only in long-term prospect. This circumstance causes need of use at formation of research-and-production clusters of tools of strategic management.

  6. Brightest cluster galaxy formation in the cluster C0037-2522: flattening of the dark matter cusp

    CERN Document Server

    Nipoti, C; Ciotti, L; Treu, T; Rosati, P

    2003-01-01

    The X-ray cluster C0337-2522 at redshift $z=0.59$ hosts in its core a group of five elliptical galaxies. Using N-body simulations we show that a multiple merging event among the five galaxies is expected to take place in the next few Gyrs, forming a central brightest cluster galaxy. We also find indications that dynamical friction heating associated with this event is likely to modify the central slope of the cluster dark matter density profile.

  7. Dynamics of the Tidal Fields and Formation of Star Clusters in Galaxy Mergers

    CERN Document Server

    Renaud, Florent

    2010-01-01

    In interacting galaxies, strong tidal forces disturb the global morphology of the progenitors and give birth to the long stellar, gaseous and dusty tails often observed. In addition to this destructive effect, tidal forces can morph into a transient, protective setting called compressive mode. Such modes then shelter the matter in their midst by increasing its gravitational binding energy. This thesis focuses on the study of this poorly known regime by quantifying its properties thanks to numerical and analytical tools applied to a spectacular merging system of two galaxies, commonly known as the Antennae galaxies. N-body simulations of this pair yield compressive modes in the regions where observations reveal a burst of star formation. Furthermore, characteristic time- and energy scales of these modes match well those of self-gravitating substructures such as star clusters and tidal dwarf galaxies. These results suggest that the compressive modes of tidal fields plays an important role in the formation and e...

  8. Effect of Mn cluster on the formation of superoxide radicals in photoinhibition of photosystem Ⅱ

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    To further realize the action of superoxide radicals (O-2) in photoinhibition of photosystem Ⅱ (PS Ⅱ),we employed 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a spin trap, associated with EPR spectroscopy, to study the effect of illumination time on O-*2 formation during high light photoinhibition in PS Ⅱ membranes and Mn-depleted PS Ⅱ membranes. Results indicated that the removal of Mn cluster from PSⅡmembranes has a strong influence on the dynamnics of superoxide formation.The relative mechanism was also discussed.These novel findings may further promote the studies of the structure and function of PSⅡand the mechanism of photoinhibition.

  9. The Lost Dwarfs of Centaurus A and the Formation of its Dark Globular Clusters

    CERN Document Server

    Bovill, Mia Sauda; Ricotti, Massimo; Taylor, Matthew A

    2016-01-01

    We present theoretical constraints for the formation of the newly discovered dark star clusters (DSCs) with high mass-to-light (M/L) ratios, from Taylor et al (2015). These compact stellar systems photometrically resemble globular clusters (GCs) but have dynamical M/L ratios of ~ 10 - 100, closer to the expectations for dwarf galaxies. The baryonic properties of the dark star clusters (DSCs) suggest their host dark matter halos likely virialized at high redshift with M > 10^8 M_sun. We use a new set of high-resolution N-body simulations of Centaurus A to determine if there is a set of z=0 subhalos whose properties are in line with these observations. While we find such a set of subhalos, when we extrapolate the dark matter density profiles into the inner 20 pc, no dark matter halo associated with Centaurus A in our simulations, at any redshift, can replicate the extremely high central mass densities of the DSCs. Among the most likely options for explaining 10^5 - 10^7 M_sun within 10 pc diameter subhalos is t...

  10. Cluster-formation in the Rosette molecular cloud at the junctions of filaments

    CERN Document Server

    Schneider, N; Hennemann, M; Motte, F; Didelon, P; Federrath, C; Bontemps, S; Di Francesco, J; Arzoumanian, D; Minier, V; André, Ph; Hill, T; Zavagno, A; Nguyen-Luong, Q; Attard, M; Bernard, J -Ph; Elia, D; Fallscheer, C; Griffin, M; Kirk, J; Klessen, R; Könyves, V; Martin, P; Men'shchikov, A; Palmeirim, P; Peretto, N; Pestalozzi, M; Russeil, D; Sadavoy, S; Sousbie, T; Testi, L; Tremblin, P; Ward-Thompson, D; White, G

    2012-01-01

    For many years feedback processes generated by OB-stars in molecular clouds, including expanding ionization fronts, stellar winds, or UV-radiation, have been proposed to trigger subsequent star formation. However, hydrodynamic models including radiation and gravity show that UV-illumination has little or no impact on the global dynamical evolution of the cloud. The Rosette molecular cloud, irradiated by the NGC2244 cluster, is a template region for triggered star-formation, and we investigated its spatial and density structure by applying a curvelet analysis, a filament-tracing algorithm (DisPerSE), and probability density functions (PDFs) on Herschel column density maps, obtained within the HOBYS key program. The analysis reveals not only the filamentary structure of the cloud but also that all known infrared clusters except one lie at junctions of filaments, as predicted by turbulence simulations. The PDFs of sub-regions in the cloud show systematic differences. The two UV-exposed regions have a double-peak...

  11. Ultra Violet Escape Fractions from Giant Molecular Clouds During Early Cluster Formation

    CERN Document Server

    Howard, Corey S; Klessen, Ralf S

    2016-01-01

    The UV photon escape fraction from molecular clouds is a key parameter for understanding the ionization of the Interstellar Medium (ISM), and extragalactic processes, such as cosmic reionization. We present the ionizing photon flux and the corresponding photon escape fraction (f$_{esc}$) arising as a consequence of star cluster formation in a turbulent, 10$^6$ M$_{\\odot}$ GMC, simulated using the code FLASH. We make use of sink particles to represent young, star-forming clusters coupled with a radiative transfer scheme to calculate the emergent UV flux. We find that the ionizing photon flux across the cloud boundary is highly variable in time and space due to the turbulent nature of the intervening gas. The escaping photon fraction remains at $\\sim$5% for the first 2.5 Myr, followed by two pronounced peaks at 3.25 and 3.8 Myr with a maximum f$_{esc}$ of 30% and 37%, respectively. These peaks are due to the formation of large HII regions, that expand into regions of lower density and some of which reach the cl...

  12. THE CLUSTERED NATURE OF STAR FORMATION. PRE-MAIN-SEQUENCE CLUSTERS IN THE STAR-FORMING REGION NGC 602/N90 IN THE SMALL MAGELLANIC CLOUD

    Energy Technology Data Exchange (ETDEWEB)

    Gouliermis, Dimitrios A.; Gennaro, Mario [Max Planck Institute for Astronomy, Koenigstuhl 17, 69117 Heidelberg (Germany); Schmeja, Stefan [Zentrum fuer Astronomie der Universitaet Heidelberg, Institut fuer Theoretische Astrophysik, Albert-Ueberle-Str. 2, 69120 Heidelberg (Germany); Dolphin, Andrew E. [Raytheon Company, P.O. Box 11337, Tucson, AZ 85734 (United States); Tognelli, Emanuele; Prada Moroni, Pier Giorgio [Dipartimento di Fisica ' Enrico Fermi' , Universita di Pisa, largo Pontecorvo 3, Pisa I-56127 (Italy)

    2012-03-20

    Located at the tip of the wing of the Small Magellanic Cloud (SMC), the star-forming region NGC 602/N90 is characterized by the H II nebular ring N90 and the young cluster of pre-main-sequence (PMS) and early-type main-sequence stars NGC 602, located in the central area of the ring. We present a thorough cluster analysis of the stellar sample identified with Hubble Space Telescope/Advanced Camera for Surveys in the region. We show that apart from the central cluster low-mass PMS stars are congregated in 13 additional small, compact sub-clusters at the periphery of NGC 602, identified in terms of their higher stellar density with respect to the average background density derived from star counts. We find that the spatial distribution of the PMS stars is bimodal, with an unusually large fraction ({approx}60%) of the total population being clustered, while the remaining is diffusely distributed in the intercluster area, covering the whole central part of the region. From the corresponding color-magnitude diagrams we disentangle an age difference of {approx}2.5 Myr between NGC 602 and the compact sub-clusters, which appear younger, on the basis of comparison of the brighter PMS stars with evolutionary models, which we accurately calculated for the metal abundance of the SMC. The diffuse PMS population appears to host stars as old as those in NGC 602. Almost all detected PMS sub-clusters appear to be centrally concentrated. When the complete PMS stellar sample, including both clustered and diffused stars, is considered in our cluster analysis, it appears as a single centrally concentrated stellar agglomeration, covering the whole central area of the region. Considering also the hot massive stars of the system, we find evidence that this agglomeration is hierarchically structured. Based on our findings, we propose a scenario according to which the region NGC 602/N90 experiences an active clustered star formation for the last {approx}5 Myr. The central cluster NGC 602 was

  13. Where does the gas fueling star formation in brightest cluster galaxies originate?

    Science.gov (United States)

    Molendi, S.; Tozzi, P.; Gaspari, M.; De Grandi, S.; Gastaldello, F.; Ghizzardi, S.; Rossetti, M.

    2016-11-01

    Aims: We investigate the relationship between X-ray cooling and star formation in brightest cluster galaxies (BCGs). Methods: We present an X-ray spectral analysis of the inner regions, 10-40 kpc, of six nearby cool core clusters (z < 0.35) observed with Chandra ACIS. This sample is selected on the basis of the high star formation rate (SFR) observed in the BCGs. We restrict our search for cooling gas to regions that are roughly cospatial with the starburst. We fit single- and multi-temperature mkcflow models to constrain the amount of isobarically cooling intracluster medium. Results: We find that in all clusters, below a threshold temperature ranging between 0.9 and 3 keV, only upper limits can be obtained. In four out of six objects, the upper limits are significantly below the SFR and in two, namely A1835 and A1068, they are less than a tenth of the SFR. Conclusions: Our results suggests that a number of mechanisms conspire to hide the cooling signature in our spectra. In a few systems the lack of a cooling signature may be attributed to a relatively long delay time between the X-ray cooling and the star burst. However, for A1835 and A1068, where the X-ray cooling time is shorter than the timescale of the starburst, a possible explanation is that the region where gas cools out of the X-ray phase extends to very large radii, likely beyond the core of these systems.

  14. Monte Carlo studies of drug nucleation 1: formation of crystalline clusters of bicalutamide in water.

    Science.gov (United States)

    Persson, Rasmus; Nordholm, Sture; Perlovich, German; Lindfors, Lennart

    2011-03-31

    A computational method of predicting the effects of the metastability of drug solutions is sought. A simple extension of our in silicio approach to thermodynamic drug solubility is tested on the drug bicalutamide for which we performed vapor pressure measurements complementing earlier measurements of aqueous solubility and crystal-water interfacial tension. The free energy of formation of an N-cluster of the drug molecule is estimated semiempirically by use of an Einstein model of the crystal in which experiment supplies the crystal structure, enthalpy of sublimation, and Einstein frequency of vibration. The rigid drug clusters with N from 2 to 14 are extracted from the bulk crystal by minimization of either cluster energy or radius of gyration. The free energy of hydration is estimated by Monte Carlo simulation combined with simplified response theory based on the OPLS-AA/COMPASS force field for the drug-water interaction and the TIP4P water model. The results have been interpreted in terms of an apparent crystal-water interfacial tension according to classical nucleation theory. The energy-minimal and radius of gyration-minimal clusters seem to give very similar crystal-water interfacial tensions for both the monoclinic and the triclinic polymorph. The interfacial tension of the monoclinic polymorph is significantly higher (by around 20%) than that of the triclinic polymorph in accordance with experiment. For the triclinic polymorph a substantial overestimation of the interfacial tension compared to estimates from crystal nucleation experiments is found, mitigated somewhat by an empirical scaling of the simulated binding energies and free energies of hydration.

  15. Fast formation of statistically reliable FDG parametric images based on clustering and principal components

    Energy Technology Data Exchange (ETDEWEB)

    Kimura, Y. [Positron Medical Center, Tokyo Metropolitan Institute of Gerontology, Naka, Itabashi, Tokyo (Japan); Senda, M. [Foundation for Biomedical Research and Innovation, 7F Chamber of Commerce, Minatojima-Nakamachi, Chuo, Kobe (Japan); Alpert, N.M. [Division of Nuclear Medicine, Massachusetts General Hospital, Boston, MA (United States)]. E-mail: alpert@pet.mgh.harvard.edu

    2002-02-07

    Formation of parametric images requires voxel-by-voxel estimation of rate constants, a process sensitive to noise and computationally demanding. A model-based clustering method for a two-parameter model (CAKS) was extended to the FDG three-parameter model. The concept was to average voxels with similar kinetic signatures to reduce noise. Voxel kinetics were categorized by the first two principal components of the tissue time-activity curves for all voxels. k{sub 2} and k{sub 3} were estimated cluster-by-cluster, and K{sub 1} was estimated voxel-by-voxel within clusters. When CAKS was applied to simulated images with noise levels similar to brain FDG scans, estimation bias was well suppressed, and estimation errors were substantially smaller - 1.3 times for K{sub i} and 1.5 times for k{sub 3} - than those of conventional voxel-based estimation. The statistical reliability of voxel-level estimation by CAKS was comparable with ROI analysis including 100 voxels. CAKS was applied to clinical cases with Alzheimer's disease (ALZ) and cortico basal degeneration (CBD). In ALZ, the affected regions had low K{sub i}(K{sub 1}k{sub 3}/(k{sub 2}+k{sub 3})) and k{sub 3}. In CBD, K{sub i} was low, but k{sub 3} was preserved. These results were consistent with ROI-based kinetic analysis. Because CAKS decreased the number of invoked estimations, the calculation time was reduced substantially. In conclusion, CAKS has been extended to allow parametric imaging of a three-compartment model. The method is computationally efficient, with low bias and excellent noise properties. (author)

  16. Star formation history of the Milky Way halo traced by the Oosterhoff dichotomy among globular clusters

    CERN Document Server

    Jang, Sohee

    2015-01-01

    In our recent investigation of the Oosterhoff dichotomy in the multiple population paradigm (Jang et al. 2014), we have suggested that the RR Lyrae variables in the Oosterhoff groups I, II, and III globular clusters (GCs) are produced mostly by the first, second, and third generation stars (G1, G2, and G3), respectively. Here we show, for the first time, that the observed dichotomies in the inner and outer halo GCs can be naturally reproduced when these models are extended to all metallicity regimes, while maintaining reasonable agreements in the horizontal-branch type versus [Fe/H] correlations. In order to achieve this, however, specific star formation histories are required for the inner and outer halos. In the inner halo GCs, the star formation commenced and ceased earlier with relatively short formation timescale between the subpopulations (~0.5 Gyr), while in the outer halo, the formation of G1 was delayed by ~0.8 Gyr with more extended timescale between G1 and G2 (~1.4 Gyr). This is consistent with the...

  17. Massive Star Formation Rates and Radial Distributions from Halpha Imaging of 84 Virgo Cluster and Isolated Spiral Galaxies

    CERN Document Server

    Koopmann, R A; Koopmann, Rebecca A.; Kenney, Jeffrey D. P.

    2002-01-01

    The massive star formation properties of 55 Virgo Cluster and 29 isolated S0-Scd spiral galaxies are compared via analyses of R and Halpha surface photometry and integrated fluxes as functions of Hubble type and central R light concentration. The total massive star formation rates in Virgo Cluster spirals have been reduced by factors up to 2.5 in the median compared to isolated spirals. The inner disk star formation rates of most Virgo Cluster spirals are similar or enhanced by factors up to 2.5 in the median, while outer disk star formation rates are reduced by factors up to 7.1 in the median. Thus the reduction in total star formation of Virgo Cluster spirals is caused primarily by truncation of the star-forming disks. The star formation morphologies of Virgo Cluster spirals compared to isolated spirals can be divided into four categories: normal (27%), anemic (6%), enhanced (15%), and truncated (52%). Several galaxies with truncated star-forming disks have anemic inner disks, but the majority have normal-e...

  18. Surveying approaches to the formation of carbon-carbon bonds between a pyran and an adjacent ring

    OpenAIRE

    Frein, Jeffrey D.; Rovis, Tomislav

    2006-01-01

    We have examined several methods for the stereoselective formation of carbon-carbon bonds between contiguous rings where a stereogenic center is already present. The approaches investigated were a [1,3] oxygen to carbon rearrangement of cyclic vinyl acetals, an intermolecular enolsilane addition into an in situ generated oxocarbenium ion, an intramolecular conjugate addition of tethered alkoxy enones, and epimerization of several α-pyranyl cycloalkanones. These routes have been found to be co...

  19. Calculation of the vibrational frequencies of carbon clusters and fullerenes with empirical potentials.

    Science.gov (United States)

    Do, Hainam; Besley, Nicholas A

    2015-02-07

    Vibrational frequencies for carbon clusters, fullerenes and nanotubes evaluated using empirical carbon-carbon potentials are presented. For linear and cyclic clusters, frequencies evaluated with the reactive empirical bond order (REBO) potential provide the closest agreement with experiment. The mean absolute deviation (MAD) between experiment and the calculated harmonic frequencies is 79 cm(-1) for the bending modes and 76 cm(-1) for the stretching modes. The effects of anharmonicity are included via second order vibrational perturbation theory and tend to increase the frequency of the bending modes while the stretching modes have negative shifts in the region of 20-60 cm(-1), with larger shifts for the higher frequency modes. This results in MADs for the bending and stretching modes of 84 cm(-1) and 58 cm(-1), respectively. For the fullerene molecule C60, the high frequency modes are predicted to have harmonic frequencies that are significantly higher than experiment, and this is not corrected by accounting for anharmonicity. This overestimation of experimental observed frequencies is also evident in the calculated frequencies of the G band in nanotubes. This suggests that the REBO potential is not optimal for these larger systems and it is shown that adjustment of the parameters within the potential leads to closer agreement with experiment, particularly if higher and lower frequency modes are considered separately.

  20. High resolution infrared spectroscopy of carbon dioxide clusters up to (CO2)13.

    Science.gov (United States)

    Norooz Oliaee, J; Dehghany, M; McKellar, A R W; Moazzen-Ahmadi, N

    2011-07-28

    Thirteen specific infrared bands in the 2350 cm(-1) region are assigned to carbon dioxide clusters, (CO(2))(N), with N = 6, 7, 9, 10, 11, 12 and 13. The spectra are observed in direct absorption using a tuneable infrared laser to probe a pulsed supersonic jet expansion of a dilute mixture of CO(2) in He carrier gas. Assignments are aided by cluster structure calculations made using two reliable CO(2) intermolecular potential functions. For (CO(2))(6), two highly symmetric isomers are observed, one with S(6) symmetry (probably the more stable form), and the other with S(4) symmetry. (CO(2))(13) is also symmetric (S(6)), but the remaining clusters are asymmetric tops with no symmetry elements. The observed rotational constants tend to be slightly (≈2%) smaller than those from the predicted structures. The bands have increasing vibrational blueshifts with increasing cluster size, similar to those predicted by the resonant dipole-dipole interaction model but significantly larger in magnitude.

  1. Distinct Short-Range Order Is Inherent to Small Amorphous Calcium Carbonate Clusters (<2 nm)

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Shengtong [Physical Chemistry, University of Konstanz, Universitätsstrasse 10 78457 Konstanz Germany; School of Chemical Engineering, State Key Laboratory of Chemical Engineering, Shanghai Key Laboratory of Multiphase Materials Chemical Engineering, East China University of Science and Technology, 130 Meilong Road Shanghai 200237 P.R. China; Chevrier, Daniel M. [Department of Chemistry and Institute for Research in Materials, Dalhousie University, Halifax Nova Scotia B3H 4R2 Canada; Zhang, Peng [Department of Chemistry and Institute for Research in Materials, Dalhousie University, Halifax Nova Scotia B3H 4R2 Canada; Gebauer, Denis [Physical Chemistry, University of Konstanz, Universitätsstrasse 10 78457 Konstanz Germany; Cölfen, Helmut [Physical Chemistry, University of Konstanz, Universitätsstrasse 10 78457 Konstanz Germany

    2016-09-09

    Amorphous intermediate phases are vital precursors in the crystallization of many biogenic minerals. While inherent short-range orders have been found in amorphous calcium carbonates (ACCs) relating to different crystalline forms, it has never been clarified experimentally whether such orders already exist in very small clusters less than 2 nm in size. Here, we studied the stability and structure of 10,12-pentacosadiynoic acid (PCDA) protected ACC clusters with a core size of ca. 1.4 nm consisting of only seven CaCO3 units. Ligand concentration and structure are shown to be key factors in stabilizing the ACC clusters. More importantly, even in such small CaCO3 entities, a proto-calcite short-range order can be identified but with a relatively high degree of disorder that arises from the very small size of the CaCO3 core. Our findings support the notion of a structural link between prenucleation clusters, amorphous intermediates, and final crystalline polymorphs, which appears central to the understanding of polymorph selection.

  2. Theoretical studies of zirconium and carbon clusters with molecular dynamics simulations

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, B.

    1993-08-01

    In this dissertation, we will present a systematic study of structures of fullerenes ranging from C{sub 20} to C{sub 100} by introducing a novel scheme. Using our new scheme, we not only reproduce all known fullerene structures but also successfully predicted several other fullerene structures which were confirmed by experiments. By utilizing the tight-binding molecular-dynamic (TBMD) simulation, we also studied the dynamical behavior of fullerenes: Vibrations, thermal disintegration of individual clusters as well as collisions between fullerenes. If the beauty of carbon fullerene is not enough, people found that carbon can also form tubules and even speculated that they can form three-dimensional graphite-like networks. By extending our fullerene structure searching scheme, we performed a search for the ground-state structure of three dimensional carbon network. We found the most stable structure people ever proposed for simple cubic based networks. From the difference of this new form of carbon and graphite in the electronic and vibrational properties, we propose an experimental probe to identify these novel three-dimensional carbon networks.

  3. Proximity gettering of C3H5 carbon cluster ion-implanted silicon wafers for CMOS image sensors: Gettering effects of transition metal, oxygen, and hydrogen impurities

    Science.gov (United States)

    Kurita, Kazunari; Kadono, Takeshi; Okuyama, Ryousuke; Hirose, Ryo; Onaka-Masada, Ayumi; Koga, Yoshihiro; Okuda, Hidehiko

    2016-12-01

    A new technique is described for manufacturing silicon wafers with the highest capability yet reported for gettering transition metallic, oxygen, and hydrogen impurities in CMOS image sensor fabrication. It is demonstrated that this technique can implant wafers simultaneously with carbon and hydrogen elements that form the projection range by using hydrocarbon compounds. Furthermore, these wafers can getter oxygen impurities out-diffused from the silicon substrate to the carbon cluster ion projection range during heat treatment. Therefore, they can reduce the formation of transition metals and oxygen-related defects in the device active regions and improve electrical performance characteristics, such as dark current and image lag characteristics. The new technique enables the formation of high-gettering-capability sinks for transition metals, oxygen, and hydrogen impurities under device active regions of CMOS image sensors. The wafers formed by this technique have the potential to significantly reduce dark current in advanced CMOS image sensors.

  4. Using young massive star clusters to understand star formation and feedback in high-redshift-like environments

    CERN Document Server

    Longmore, Steven; Battersby, Cara; Bally, John; Kruijssen, J M Diederik; Dale, James; Henshaw, Jonathan; Walker, Daniel; Rathborne, Jill; Testi, Leonardo; Ott, Juergen; Ginsburg, Adam

    2016-01-01

    The formation environment of stars in massive stellar clusters is similar to the environment of stars forming in galaxies at a redshift of 1 - 3, at the peak star formation rate density of the Universe. As massive clusters are still forming at the present day at a fraction of the distance to high-redshift galaxies they offer an opportunity to understand the processes controlling star formation and feedback in conditions similar to those in which most stars in the Universe formed. Here we describe a system of massive clusters and their progenitor gas clouds in the centre of the Milky Way, and outline how detailed observations of this system may be able to: (i) help answer some of the fundamental open questions in star formation and (ii) quantify how stellar feedback couples to the surrounding interstellar medium in this high-pressure, high-redshift analogue environment.

  5. A carbon-cluster laser ion source for TRIGA-TRAP

    Energy Technology Data Exchange (ETDEWEB)

    Smorra, C; Eberhardt, K [Johannes Gutenberg-Universitaet Mainz, Institut fuer Kernchemie, Fritz-Strassmann Weg 2, D-55128 Mainz (Germany); Blaum, K [Ruprecht-Karls-Universitaet Heidelberg, Physikalisches Institut, Philosophenweg 12, D-69120 Heidelberg (Germany); Eibach, M; Ketelaer, J; Ketter, J; Knuth, K [Johannes Gutenberg-Universitaet Mainz, Institut fuer Physik, Staudingerweg 7, D-55128 Mainz (Germany); Nagy, Sz, E-mail: smorrac@uni-mainz.d [Max-Planck-Institut fuer Kernphysik, Saupfercheckweg 1, D-69117 Heidelberg (Germany)

    2009-08-14

    A new laser ablation ion source was developed and tested for the Penning trap mass spectrometer TRIGA-TRAP in order to provide carbon-cluster ions for absolute mass calibration. Ions of different cluster sizes up to C{sup +}{sub 24} were successfully produced, covering the mass range up to the heavy actinide elements. The ions were captured in a Penning trap, and their time-of-flight cyclotron resonances recorded in order to determine their cyclotron frequency. Furthermore, the same ion source was used to produce GdO{sup +} ions from a gadolinium target in sufficient amount for mass spectrometry purposes. The design of the source and its characteristics are presented.

  6. The Evolution of Star Formation Activity in Cluster Galaxies Over $0.15

    CERN Document Server

    Wagner, Cory R; Brodwin, Mark; Stanford, S A; Snyder, Gregory F; Stern, Daniel

    2016-01-01

    We explore 7.5 billion years of evolution in the star formation activity of massive ($M_{\\star}>10^{10.1}\\,M_{\\odot}$) cluster galaxies using a sample of 25 clusters over $0.15Cluster Lensing And Supernova survey with Hubble and 11 clusters over $1Cluster Survey. Galaxy morphologies are determined visually using high-resolution Hubble Space Telescope images. Using the spectral energy distribution fitting code CIGALE, we measure star formation rates, stellar masses, and 4000 \\AA\\ break strengths. The latter are used to separate quiescent and star-forming galaxies (SFGs). From $z\\sim1.3$ to $z\\sim0.2$, the specific star formation rate (sSFR) of cluster SFGs and quiescent galaxies decreases by factors of three and four, respectively. Over the same redshift range, the sSFR of the entire cluster population declines by a factor of 11, from $0.48\\pm0.06\\;\\mathrm{Gyr}^{-1}$ to $0.043\\pm0.009\\;\\mathrm{Gyr}^{-1}$. This strong overall sSFR evolution is driven by t...

  7. Interconversion between formate and hydrogen carbonate by tungsten-containing formate dehydrogenase-catalyzed mediated bioelectrocatalysis

    Directory of Open Access Journals (Sweden)

    Kento Sakai

    2015-09-01

    Full Text Available We have focused on the catalytic properties of tungsten-containing formate dehydrogenase (FoDH1 from Methylobacterium extorquens AM1 to construct a bioelectrochemical interconversion system between formate (HCOO− and hydrogen carbonate (HCO3−. FoDH1 catalyzes both of the HCOO oxidation and the HCO3− reduction with several artificial dyes. The bi-molecular reaction rate constants between FoDH1 and the artificial electron acceptors and NAD+ (as the natural electron acceptor show the property called a linear free energy relationship (LFER, indicating that FoDH1 would have no specificity to NAD+. Similar LFER is also observed for the catalytic reduction of HCO3−. The reversible reaction between HCOO− and HCO3− through FoDH1 has been realized on cyclic voltammetry by using methyl viologen (MV as a mediator and by adjusting pH from the thermodynamic viewpoint. Potentiometric measurements have revealed that the three redox couples, MV2+/MV·−+, HCOO−/HCO3−, FoDH1 (ox/red, reach an equilibrium in the bulk solution when the two-way bioelectrocatalysis proceeds in the presence of FoDH1 and MV. The steady-state voltammograms with two-way bioelectrocatalytic properties are interpreted on a simple model by considering the solution equilibrium.

  8. The challenging task of determining star formation rates: the case of a massive stellar burst in the brightest cluster galaxy of Phoenix galaxy cluster

    CERN Document Server

    Mittal, Rupal; Whelan, John T; Bruzual, Gustavo

    2016-01-01

    Star formation in galaxies at the center of cooling-flow galaxy clusters is an important phenomenon in the context of formation and evolution of massive galaxies in the Universe. Yet, star formation rates (SFRs) in such systems continue to be elusive. We use our Bayesian-motivated spectral energy distribution (SED)-fitting code, BAYESCOOL, to estimate the plausible SFR values in the brightest cluster galaxy of a massive, X-ray luminous galaxy cluster, Phoenix. Previous studies of Phoenix have resulted in the highest measurement of SFR for any galaxy, with the estimates reaching up to 1000 solar masses/yr. However, very few number of models have been considered in those studies. BAYESCOOL allows us to probe a large parameter space. We consider two models for star formation history, instantaneous bursts and continuous star formation, a wide range of ages for the old and the young stellar population, along with other discrete parameters, such as the initial mass function, metallicities, internal extinction and e...

  9. The challenging task of determining star formation rates: the case of a massive stellar burst in the brightest cluster galaxy of Phoenix galaxy cluster

    Science.gov (United States)

    Mittal, Rupal; McDonald, M.; Whelan, John T.; Bruzual, Gustavo

    2017-03-01

    Star formation in galaxies at the centre of cooling-flow galaxy clusters is an important phenomenon in the context of formation and evolution of massive galaxies in the Universe. Yet, star formation rates (SFRs) in such systems continue to be elusive. We use our Bayesian-motivated spectral energy distribution (SED)-fitting code, BAYESCOOL, to estimate the plausible SFR values in the brightest cluster galaxy of a massive, X-ray luminous galaxy cluster, Phoenix. Previous studies of Phoenix have resulted in the highest measurement of SFR for any galaxy, with the estimates reaching up to 1000 M⊙ yr-1. However, a very small number of models have been considered in those studies. BAYESCOOL allows us to probe a large parameter space. We consider two models for star formation history, instantaneous bursts and continuous star formation, a wide range of ages for the old and the young stellar population, along with other discrete parameters, such as the initial mass function, metallicities, internal extinction and extinction law. We find that in the absence of any prior except that the maximum cooling rate Phoenix. The SFR dependence on the extinction is a reflection of the standard age-extinction degeneracy, which can be overcome by using a prior on one of the two quantities in question.

  10. Formation of clusters composed of C60 molecules via self-assembly in critical fluids

    Science.gov (United States)

    Fukuda, Takahiro; Ishii, Koji; Kurosu, Shunji; Whitby, Raymond; Maekawa, Toru

    2007-04-01

    Fullerenes are promising candidates for intelligent, functional nanomaterials because of their unique mechanical, electronic and chemical properties. However, it is necessary to invent some efficient but relatively simple methods of producing structures composed of fullerenes for the development of nanomechatronic, nanoelectronic and biochemical devices and sensors. In this paper, we show that various structures such as straight fibres, networks formed by fibres, wide sheets and helical structures, which are composed of C60 molecules, are created by placing C60-crystals in critical ethane, carbon dioxide and xenon even though C60 molecules do not dissolve or disperse in the above fluids. It is supposed, judging by the intermolecular potentials between C60 and C60, between C60 and ethane, and between ethane and ethane, that C60-clusters grow with the assistance of solvent molecules, which are trapped between C60 molecules under critical conditions. This room-temperature self-assembly cluster growth process in critical fluids may open up a new methodology of forming structures built up with fullerenes without the need for any ultra-fine processing technologies.

  11. Molecular clouds toward the super star cluster NGC 3603; possible evidence for a cloud-cloud collision in triggering the cluster formation

    Energy Technology Data Exchange (ETDEWEB)

    Fukui, Y.; Ohama, A.; Hanaoka, N.; Furukawa, N.; Torii, K.; Hasegawa, K.; Fukuda, T.; Soga, S.; Moribe, N.; Kuroda, Y.; Hayakawa, T.; Kuwahara, T.; Yamamoto, H.; Okuda, T. [Department of Astrophysics, Nagoya University, Chikusa-ku, Nagoya 464-8602 (Japan); Dawson, J. R. [School of Mathematics and Physics, University of Tasmania, Sandy Bay Campus, Churchill Avenue, Sandy Bay, TAS 7005 (Australia); Mizuno, N.; Kawamura, A. [National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Onishi, T.; Maezawa, H. [Department of Astrophysics, Graduate School of Science, Osaka Prefecture University, 1-1 Gakuen-cho, Sakai, Osaka 599-8531 (Japan); Mizuno, A., E-mail: fukui@a.phys.nagoya-u.ac.jp [Solar-terrestrial Environment Laboratory, Nagoya University, Chikusa-ku, Nagoya 464-8601 (Japan)

    2014-01-01

    We present new large field observations of molecular clouds with NANTEN2 toward the super star cluster NGC 3603 in the transitions {sup 12}CO(J = 2-1, J = 1-0) and {sup 13}CO(J = 2-1, J = 1-0). We suggest that two molecular clouds at 13 km s{sup –1} and 28 km s{sup –1} are associated with NGC 3603 as evidenced by higher temperatures toward the H II region, as well as morphological correspondence. The mass of the clouds is too small to gravitationally bind them, given their relative motion of ∼20 km s{sup –1}. We suggest that the two clouds collided with each other 1 Myr ago to trigger the formation of the super star cluster. This scenario is able to explain the origin of the highest mass stellar population in the cluster, which is as young as 1 Myr and is segregated within the central sub-pc of the cluster. This is the second super star cluster along with Westerlund 2 where formation may have been triggered by a cloud-cloud collision.

  12. Deep near-infrared imaging of W3 Main: constraints on stellar cluster formation

    Science.gov (United States)

    Bik, A.; Stolte, A.; Gennaro, M.; Brandner, W.; Gouliermis, D.; Hußmann, B.; Tognelli, E.; Rochau, B.; Henning, Th.; Adamo, A.; Beuther, H.; Pasquali, A.; Wang, Y.

    2014-01-01

    Context. Embedded clusters like W3 Main are complex and dynamically evolving systems that represent an important phase in the star formation process. Aims: We aim to characterize of the entire stellar content of W3 Main in a statistical sense, which will then identify possible differences in the evolutionary phase of the stellar populations and find clues about the formation mechanism of this massive embedded cluster. Methods: Deep JHKs imaging is used to derive the disk fraction, Ks-band luminosity functions, and mass functions for several subregions in W3 Main. A two-dimensional completeness analysis using artificial star experiments is applied as a crucial ingredient for assessing realistic completeness limits for our photometry. Results: We find an overall disk fraction of 7.7 ± 2.3%, radially varying from 9.4 ± 3.0% in the central 1 pc to 5.6 ± 2.2% in the outer parts of W3 Main. The mass functions derived for three subregions are consistent with a Kroupa and Chabrier mass function. The mass function of IRSN3 is complete down to 0.14 M⊙ and shows a break at M ~ 0.5 M⊙. Conclusions: We interpret the higher disk fraction in the center as evidence that the cluster center is younger. We find that the evolutionary sequence observed in the low-mass stellar population is consistent with the observed age spread among the massive stars. An analysis of the mass function variations does not show evidence of mass segregation. W3 Main is currently still actively forming stars, showing that the ionizing feedback of OB stars is confined to small areas (~0.5 pc). The FUV feedback might be influencing large regions of the cluster as suggested by the low overall disk fraction. Based on data acquired using the Large Binocular Telescope (LBT). The LBT is an international collaboration among institutions in Germany, Italy, and the United States. LBT Corporation partners are LBT Beteiligungsgesellschaft, Germany, representing the Max Planck Society, the Astrophysical

  13. Carbon cluster mass calibration at the double Penning trap mass spectrometer TRIGA-TRAP

    Energy Technology Data Exchange (ETDEWEB)

    Smorra, Christian [Physikalisches Institut, Universitaet Heidelberg (Germany); Institut fuer Kernchemie, Universitaet Mainz (Germany); Blaum, Klaus [Physikalisches Institut, Universitaet Heidelberg (Germany); Max-Planck Institut fuer Kernphysik, Heidelberg (Germany); Eberhardt, Klaus [Institut fuer Kernchemie, Universitaet Mainz (Germany); Eibach, Martin; Ketelaer, Jens; Ketter, Jochen; Knuth, Konstantin [Institut fuer Physik, Universitaet Mainz (Germany); Herfurth, Frank [GSI, Helmholtzzentrum fuer Schwerionenforschung GmbH, Darmstadt (Germany); Nagy, Szilard [Max-Planck Institut fuer Kernphysik, Heidelberg (Germany)

    2009-07-01

    TRIGA-TRAP is a facility which aims for mass measurements on neutron-rich short-lived fission products and actinides with relative mass uncertainties of 10{sup -7} and below. To this end the cyclotron frequency of a stored ion in a Penning trap is determined. In high-precision mass spectrometry the investigation of systematic errors is of utmost importance. In order to demonstrate the accuracy of the measured values, various carbon cluster ions have been used in cross reference measurements. The results are presented and the accuracy limit of TRIGA-TRAP is discussed.

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

    Science.gov (United States)

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

    2006-04-01

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

  15. Carbon cluster diagnostics-I: Direct Recoil Spectroscopy (DRS) of Ar+ and Kr+ bombarded graphite

    CERN Document Server

    Ahmad, Shoaib; Qayyum, A; Ahmad, B; Bahar, K; Arshed, W

    2016-01-01

    Measurements of the energy spectra of multiply charged positive and negative carbon ions recoiling from graphite surface under 100 and 150 keV argon and krypton ion bombardment are presented. With the energy spectrometer set at recoil angle of 79.5 degrees, direct recoil (DR) peaks have been observed with singly as well as multiply charged carbon ions , where n = 1 to 6. These monatomic and cluster ions have been observed recoiling with the characteristic recoil energy E(DR) . We have observed sharp DR peaks. A collimated projectile beam with small divergence is supplemented with a similar collimation before the energy analyzer to reduce the background of sputtered ions due to scattered projectiles.

  16. Effects of the Equation of State on the Formation of Star Clusters

    CERN Document Server

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

    2003-01-01

    We study the effect of varying the equation of state on the formation of stellar clusters in turbulent molecular clouds, using three-dimensional, smoothed particle hydrodynamics simulations. Our results show that the equation of state helps determine how strongly self-gravitating gas fragments. The degree of fragmentation decreases with increasing adiabatic index gamma in the range 0.2 1 probably results in the formation of isolated and massive stars. Fragmentation and collapse ceases entirely for gamma > 1.4 as expected from analytic arguments. The mass spectrum of overdense gas clumps is roughly log-normal for non-self-gravitating turbulent gas, but changes to a power-law under the action of gravity. The spectrum of collapsed cores, on the other hand, remains log-normal for gamma 1. The density PDFs approach log-normal, with widths that decrease with increasing gamma. Primordial gas may have effective gamma > 1, in which case these results could help explain why models of the formation of the first stars te...

  17. From large scale gas compression to cluster formation in the Antennae overlap region

    CERN Document Server

    Herrera, Cinthya N; Nesvadba, Nicole P H

    2011-01-01

    We present a detailed observational analysis of how merger-driven turbulence may regulate the star-formation efficiency during galaxy interactions and set the initial conditions for the formation of super star clusters. Using VLT/SINFONI, we obtained near-infrared imaging spectroscopy of a small region in the Antennae overlap region, coincident with the supergiant molecular cloud 2 (SGMC 2). We find extended H2 line emission across much of the 600 pc field-of-view, traced at sub-arcsecond spatial resolution. The data also reveal a compact H2 source with broad lines and a dynamical mass Mdyn 10^7 Msun, which has no observable Brg or K-band continuum emission, and no obvious counterpart in the 6 cm radio continuum. Line ratios indicate that the H2 emission of both sources is powered by shocks, making these lines a quantitative tracer of the dissipation of turbulent kinetic energy. The turbulence appears to be driven by the large-scale gas dynamics, and not by feedback from star formation. We propose a scenario ...

  18. Formation and evolution of heavy sub-structures in the centre of galaxy clusters: the local effect of dark energy

    CERN Document Server

    Sedda, Manuel Arca; Merafina, Marco

    2016-01-01

    We discuss how the centres of galaxy clusters evolve in time, showing the results of a series of direct N-body simulations. In particular, we followed the evolution of a galaxy cluster with a mass $M_{clus} \\simeq 10^{14} $M$_{\\odot}$ in different configurations. The dynamical evolution of the system leads in all the cases to the formation of dense and massive sub-structures in the cluster centre, that form in consequence of a series of collisions and merging among galaxies travelling in the cluster core. We investigate how the structural properties of the main merging product depends on the characteristics of those galaxies that contributed to its formation.

  19. On the formation of sulphuric acid-amine clusters in varying atmospheric conditions and its influence on atmospheric new particle formation

    Directory of Open Access Journals (Sweden)

    P. Paasonen

    2012-05-01

    Full Text Available Sulphuric acid is a key component in atmospheric new particle formation. However, sulphuric acid alone does not form stable enough clusters to initiate particle formation in atmospheric conditions. Strong bases, such as amines, have been suggested to stabilize sulphuric acid clusters and thus participate in particle formation. We modelled the formation rate of clusters with two sulphuric acid and two amine molecules (JA2B2 at varying atmospherically relevant conditions with respect to concentrations of sulphuric acid ([H2SO4], dimethylamine ([DMA] and trimethylamine ([TMA], temperature and relative humidity (RH. The modelled formation rates JA2B2 were functions of sulphuric acid concentration with close to quadratic dependence, which is in good agreement with atmospheric observations of the connection between the particle formation rate and sulphuric acid concentration. The coefficients KA2B2 connecting the cluster formation rate and sulphuric acid concentrations as JA2B2 = KA2B2[H2SO4]2 turned out to depend also on amine concentrations, temperature and relative humidity. We tested how the model results change if the clusters with two sulphuric acid and two amine molecules are assumed to act as seeds for heterogeneous nucleation of organic vapours (other than amines with higher atmospheric concentrations than sulphuric acid. We also compared the modelled coefficients KA2B2 with the corresponding coefficients calculated from the atmospheric observations (Kobs from environments with varying temperatures and levels of anthropogenic influence. By taking into account the modelled behaviour of JA2B2 as a function of [H2SO4], temperature and RH, the atmospheric particle formation rate was reproduced more closely than with the

  20. From Boron Cluster to Two-Dimensional Boron Sheet on Cu(111) Surface: Growth Mechanism and Hole Formation

    OpenAIRE

    Hongsheng Liu; Junfeng Gao; Jijun Zhao

    2013-01-01

    As attractive analogue of graphene, boron monolayers have been theoretically predicted. However, due to electron deficiency of boron atom, synthesizing boron monolayer is very challenging in experiments. Using first-principles calculations, we explore stability and growth mechanism of various boron sheets on Cu(111) substrate. The monotonic decrease of formation energy of boron cluster BN with increasing cluster size and low diffusion barrier for a single B atom on Cu(111) surface ensure cont...

  1. Star Formation in the Extreme Outer Galaxy: Digel Cloud 2 Clusters

    CERN Document Server

    Yasui, Chikako; Tokunaga, Alan T; Terada, Hiroshi; Saito, Masao

    2007-01-01

    As a first step for studying star formation in the extreme outer Galaxy (EOG), we obtained deep near-infrared images of two embedded clusters at the northern and southern CO peaks of Cloud 2, which is one of the most distant star forming regions in the outer Galaxy (galactic radius R_g ~ 19 kpc). With high spatial resolution (FWHM ~ 0".35) and deep imaging (K ~ 21 mag) with the IRCS imager at the Subaru telescope, we detected cluster members with a mass detection limit of < 0.1 M_{sun}, which is well into the substellar regime. These high quality data enables a comparison of EOG to those in the solar neighborhood on the same basis for the first time. Before interpreting the photometric result, we have first constructed the NIR color-color diagram (dwarf star track, classical T Tauri star (CTTS) locus, reddening law) in the Mauna Kea Observatory filter system and also for the low metallicity environment since the metallicity in EOG is much lower than those in the solar neighborhood. The estimated stellar de...

  2. Constraining ultra-compact dwarf galaxy formation with galaxy clusters in the local universe

    CERN Document Server

    Pfeffer, Joel; Baumgardt, Holger; Griffen, Brendan F

    2016-01-01

    We compare the predictions of a semi-analytic model for ultra-compact dwarf galaxy (UCD) formation by tidal stripping to the observed properties of globular clusters (GCs) and UCDs in the Fornax and Virgo clusters. For Fornax we find the predicted number of stripped nuclei agrees very well with the excess number of GCs$+$UCDs above the GC luminosity function. GCs$+$UCDs with masses $>10^{7.3}$ M$_\\odot$ are consistent with being entirely formed by tidal stripping. Stripped nuclei can also account for Virgo UCDs with masses $>10^{7.3}$ M$_\\odot$ where numbers are complete by mass. For both Fornax and Virgo, the predicted velocity dispersions and radial distributions of stripped nuclei are consistent with that of UCDs within $\\sim$50-100 kpc but disagree at larger distances where dispersions are too high and radial distributions too extended. Stripped nuclei are predicted to have radially biased anisotropies at all radii, agreeing with Virgo UCDs at clustercentric distances larger than 50 kpc. However, ongoing ...

  3. The Lost Dwarfs of Centaurus A and the Formation of its Dark Globular Clusters

    Science.gov (United States)

    Bovill, Mia Sauda; Puzia, Thomas H.; Ricotti, Massimo; Taylor, Matthew A.

    2016-11-01

    We present theoretical constraints for the formation of the newly discovered dark star clusters (DSCs) with high mass-to-light ({ M }/{ L }) ratios, from Taylor et al. These compact stellar systems photometrically resemble globular clusters (GCs) but have dynamical { M }/{ L } ratios of ˜10-100, closer to the expectations for dwarf galaxies. The baryonic properties of the DSCs suggest that their host dark matter halos likely virialized at high redshift with { M }\\gt {10}8{M}⊙ . We use a new set of high-resolution N-body simulations of Centaurus A to determine whether there is a set of z = 0 subhalos whose properties are in line with these observations. While we find such a set of subhalos, when we extrapolate the dark matter density profiles into the inner 20 pc, no dark matter halo associated with Centaurus A in our simulations, at any redshift, can replicate the extremely high central mass densities of the DSCs. Among the most likely options for explaining 105-{10}7{M}⊙ within subhalos of 10 pc diameter is the presence of a central massive black hole (BH). We therefore propose that the DSCs are remnant cusps of stellar systems surrounding the central BHs of dwarf galaxies that have been almost completely destroyed by interactions with Centaurus A.

  4. Star formation quenching in simulated group and cluster galaxies: When, how, and why?

    CERN Document Server

    Bahe, Yannick M

    2014-01-01

    Star formation is observed to be suppressed in group and cluster galaxies compared to the field. To gain insight into the quenching process, we have analysed ~2000 galaxies formed in the GIMIC suite of cosmological hydrodynamical simulations. The time of quenching varies from ~2 Gyr before accretion (first crossing of r200,c) to >4 Gyr after, depending on satellite and host mass. Once begun, quenching is rapid (>~ 500 Myr) in low-mass galaxies (M* < 10^10 M_Sun), but significantly more protracted for more massive satellites. The simulations predict a substantial role of outflows driven by ram pressure -- but not tidal forces -- in removing the star-forming interstellar matter (ISM) from satellite galaxies, especially dwarfs (M* ~ 10^9 M_Sun) where they account for nearly two thirds of ISM loss in both groups and clusters. Immediately before quenching is complete, this fraction rises to ~80% even for Milky Way analogues (M* ~ 10^10.5 M_Sun) in groups (M_host ~ 10^13.5 M_Sun). We show that (i) ISM stripping ...

  5. The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. V. Constraints on Formation Scenarios

    CERN Document Server

    Renzini, A; Cassisi, S; King, I R; Milone, A P; Ventura, P; Anderson, J; Bedin, L R; Bellini, A; Brown, T M; Piotto, G; van der Marel, R P; Barbuy, B; Dalessandro, E; Hidalgo, S; Marino, A F; Ortolani, S; Salaris, M; Sarajedini, A

    2015-01-01

    We build on the evidence provided by our Legacy Survey of Galactic globular clusters (GC) to submit to a crucial test four scenarios currently entertained for the formation of multiple stellar generations in GCs. The observational constraints on multiple generations to be fulfilled are manifold, including GC specificity, ubiquity, variety, predominance, discreteness, supernova avoidance, p-capture processing, helium enrichment and mass budget. We argue that scenarios appealing to supermassive stars, fast rotating massive stars and massive interactive binaries violate in an irreparable fashion two or more among such constraints. Also the scenario appealing to AGB stars as producers of the material for next generation stars encounters severe difficulties, specifically concerning the mass budget problem and the detailed chemical composition of second generation stars. We qualitatively explore ways possibly allowing one to save the AGB scenario, specifically appealing to a possible revision of the cross section o...

  6. LoCuSS: The slow quenching of star formation in cluster galaxies and the need for pre-processing

    CERN Document Server

    Haines, C P; Smith, G P; Egami, E; Babul, A; Finoguenov, A; Ziparo, F; McGee, S L; Rawle, T D; Okabe, N; Moran, S M

    2015-01-01

    We present a study of the spatial distribution and kinematics of star-forming galaxies in 30 massive clusters at 0.15cluster members. The fraction (f_SF) of star-forming cluster galaxies rises steadily with cluster-centric radius, increasing fivefold by 2r200, but remains well below field values even at 3r200. This suppression of star formation at large radii cannot be reproduced by models in which star formation is quenched in infalling field galaxies only once they pass within r200 of the cluster, but is consistent with some of them being first pre-processed within galaxy groups. Despite the increasing f_SF-radius trend, the surface density of star-forming galaxies actually declines steadily with radius, falling ~15x from the core to 2r200. This requires star-formation to survive within recently accreted spirals for 2--3Gyr to build up the apparent over-density of star-forming galaxies within clusters...

  7. Wide- and contact-binary formation in substructured young stellar clusters

    Science.gov (United States)

    Dorval, J.; Boily, C. M.; Moraux, E.; Roos, O.

    2017-02-01

    We explore with collisional gravitational N-body models the evolution of binary stars in initially fragmented and globally subvirial clusters of stars. Binaries are inserted in the (initially) clumpy configurations so as to match the observed distributions of the field-binary-stars' semimajor axes a and binary fraction versus primary mass. The dissolution rate of wide binaries is very high at the start of the simulations, and is much reduced once the clumps are eroded by the global infall. The transition between the two regimes is sharper as the number of stars N is increased, from N = 1.5 k up to 80 k. The fraction of dissolved binary stars increases only mildly with N, from ≈15 per cent to ≈25 per cent for the same range in N. We repeated the calculation for two initial system mean number densities of 6 per pc3 (low) and 400 per pc3 (high). We found that the longer free-fall time of the low-density runs allows for prolonged binary-binary interactions inside clumps and the formation of very tight (a ≈ 0.01 au) binaries by exchange collisions. This is an indication that the statistics of such compact binaries bear a direct link to their environment at birth. We also explore the formation of wide (a ≳ 5 × 104 au) binaries and find a low (≈0.01 per cent) fraction mildly bound to the central star cluster. The high-precision astrometric mission Gaia could identify them as outflowing shells or streams.

  8. Neutral hydrogen gas, past and future star formation in galaxies in and around the `Sausage' merging galaxy cluster

    Science.gov (United States)

    Stroe, Andra; Oosterloo, Tom; Röttgering, Huub J. A.; Sobral, David; van Weeren, Reinout; Dawson, William

    2015-09-01

    CIZA J2242.8+5301 (z = 0.188, nicknamed `Sausage') is an extremely massive (M200 ˜ 2.0 × 1015 M⊙), merging cluster with shock waves towards its outskirts, which was found to host numerous emission line galaxies. We performed extremely deep Westerbork Synthesis Radio Telescope H I observations of the `Sausage' cluster to investigate the effect of the merger and the shocks on the gas reservoirs fuelling present and future star formation (SF) in cluster members. By using spectral stacking, we find that the emission line galaxies in the `Sausage' cluster have, on average, as much H I gas as field galaxies (when accounting for the fact cluster galaxies are more massive than the field galaxies), contrary to previous studies. Since the cluster galaxies are more massive than the field spirals, they may have been able to retain their gas during the cluster merger. The large H I reservoirs are expected to be consumed within ˜0.75-1.0 Gyr by the vigorous SF and active galactic nuclei activity and/or driven out by the outflows we observe. We find that the star formation rate (SFR) in a large fraction of H α emission line cluster galaxies correlates well with the radio broad-band emission, tracing supernova remnant emission. This suggests that the cluster galaxies, all located in post-shock regions, may have been undergoing sustained SFR for at least 100 Myr. This fully supports the interpretation proposed by Stroe et al. and Sobral et al. that gas-rich cluster galaxies have been triggered to form stars by the passage of the shock.

  9. Structure of protonated carbon dioxide clusters: infrared photodissociation spectroscopy and ab initio calculations.

    Science.gov (United States)

    Douberly, G E; Ricks, A M; Ticknor, B W; Duncan, M A

    2008-02-07

    The infrared photodissociation spectra (IRPD) in the 700 to 4000 cm(-1) region are reported for H+ (CO2)n clusters (n = 1-4) and their complexes with argon. Weakly bound Ar atoms are attached to each complex upon cluster formation in a pulsed electric discharge/supersonic expansion cluster source. An expanded IRPD spectrum of the H+ (CO2)Ar complex, previously reported in the 2600-3000 cm(-1) range [Dopfer, O.; Olkhov, R.V.; Roth, D.; Maier, J.P. Chem. Phys. Lett. 1998, 296, 585-591] reveals new vibrational resonances. For n = 2 to 4, the vibrational resonances involving the motion of the proton are observed in the 750 to 1500 cm(-1) region of the spectrum, and by comparison to the predictions of theory, the structure of the small clusters are revealed. The monomer species has a nonlinear structure, with the proton binding to the lone pair of an oxygen. In the dimer, this nonlinear configuration is preserved, with the two CO2 units in a trans configuration about the central proton. Upon formation of the trimer, the core CO2 dimer ion undergoes a rearrangement, producing a structure with near C2v symmetry, which is preserved upon successive CO2 solvation. While the higher frequency asymmetric CO2 stretch vibrations are unaffected by the presence of the weakly attached Ar atom, the dynamics of the shared proton motions are substantially altered, largely due to the reduction in symmetry of each complex. For n = 2 to 4, the perturbation due to Ar leads to blue shifts of proton stretching vibrations that involve motion of the proton mostly parallel to the O-H+-O axis of the core ion. Moreover, proton stretching motions perpendicular to this axis exhibit smaller shifts, largely to the red. Ab initio (MP2) calculations of the structures, complexation energies, and harmonic vibrational frequencies are also presented, which support the assignments of the experimental spectra.

  10. Photospheric carbon and oxygen abundances of F-G type stars in the Pleiades cluster

    CERN Document Server

    Takeda, Yoichi; Honda, Satoshi

    2016-01-01

    In order to investigate the carbon-to-oxygen ratio of the young open cluster M45 (Pleiades), the C and O abundances of selected 32 F-G type dwarfs (in the effective temperature range of Teff~5800-7600K and projected rotational velocity range of vesini~10-110km/s) belonging to this cluster were determined by applying the synthetic spectrum-fitting technique to C I 5380 and O I 6156-8 lines. The non-LTE corrections for these C I and O I lines were found to be practically negligible (less than a few hundredths dex). The resulting C and O abundances (along with the Fe abundance) turned out nearly uniform without any systematic dependence upon Teff or vesini. We found, however, in spite of almost solar Fe abundance ([Fe/H]~0), carbon turned out to be slightly subsolar ([C/H]~-0.1) while oxygen slightly supersolar ([O/H]~+0.1). This lead to a conclusion that [C/O] ratio was moderately subsolar (~-0.2) in the primordial gas from which these Pleiades stars were formed ~120--130 Myr ago. Interestingly, similarly young...

  11. Constraining star formation rates in cool-core brightest cluster galaxies

    Science.gov (United States)

    Mittal, Rupal; Whelan, John T.; Combes, Françoise

    2015-07-01

    We used broad-band imaging data for 10 cool-core brightest cluster galaxies (BCGs) and conducted a Bayesian analysis using stellar population synthesis to determine the likely properties of the constituent stellar populations. Determination of ongoing star formation rates (SFRs), in particular, has a direct impact on our understanding of the cooling of the intracluster medium (ICM), star formation and AGN-regulated feedback. Our model consists of an old stellar population and a series of young stellar components. We calculated marginalized posterior probability distributions for various model parameters and obtained 68 per cent plausible intervals from them. The 68 per cent plausible interval on the SFRs is broad, owing to a wide range of models that are capable of fitting the data, which also explains the wide dispersion in the SFRs available in the literature. The ranges of possible SFRs are robust and highlight the strength in such a Bayesian analysis. The SFRs are correlated with the X-ray mass deposition rates (the former are factors of 4-50 lower than the latter), implying a picture where the cooling of the ICM is a contributing factor to star formation in cool-core BCGs. We find that 9 out of 10 BCGs have been experiencing starbursts since 6 Gyr ago. While four out of nine BCGs seem to require continuous SFRs, five out of nine seem to require periodic star formation on intervals ranging from 20 to 200 Myr. This time-scale is similar to the cooling time of the ICM in the central (<5 kpc) regions.

  12. Root Cluster Formation and Citrate Exudation of White Lupin (Lupinus albus L.) as Related to Phosphorus Availability

    Institute of Scientific and Technical Information of China (English)

    Chun-Jian LI; Rui-Xia LIANG

    2005-01-01

    A split-root system was used to investigate whether the external or internal P concentration controls root cluster formation and citrate exudation in white lupin (Lupinus albus L.) grown under controlled conditions. In spite of low P concentrations in the shoots and roots of the -P plant, its dry weight was not reduced compared with the +P plant. Supplying external P (0.25 mmol/L) to one root halfresulted in an increase in P concentration not only in the shoot, but also in the P-deprived root half, indicating P cycling within the plants. Omitting P from both split-root pots stimulated root cluster formation in both root halves,whereas P supply to one root halfstimulated root cluster formation at the beginning of the treatment. Neither P supply to just one root half continuously nor resupply of P to one root half after 19 d of P starvation inhibited root cluster formation on the P-deprived side, although the concentration of P in this root half and shoot increased markedly. The results indicate that root cluster formation in L. albus is controlled by both shoot and root P concentrations. The rates of citrate exudation by both root halves with P deficiency were higher than those of the one root half supplied with P only. In the treatment with one root half supplied with P, the rates of citrate exudation by either the P-supplied or -deprived root halves were almost the same,regardless of P concentration in the roots. The results suggest that internal P concentration controls root cluster formation and citrate exudation in white lupin, but these processes may be regulated by different mechanisms.

  13. Gas Giants in Hot Water: Inhibiting Giant Planet Formation and Planet Habitability in Dense Star Clusters Through Cosmic Time

    CERN Document Server

    Thompson, Todd A

    2012-01-01

    I show that the temperature of nuclear star clusters, starburst clusters in M82, compact high-z galaxies, and some globular clusters of the Galaxy likely exceeded the ice line temperature (T_Ice ~ 150-170 K) during formation for a time comparable to the planet formation timescale. The protoplanetary disks within these systems will thus not have an ice line, decreasing the total material available for building protoplanetary embryos, inhibiting the formation of gas- and ice-giants if they form by core accretion, and prohibiting habitability. Planet formation by gravitational instability is similarly suppressed because Toomre's Q > 1 in all but the most massive disks. I discuss these results in the context of the observed lack of planets in 47 Tuc. I predict that a similar search for planets in the globular cluster NGC 6366 ([Fe/H] = -0.82) should yield detections, whereas (counterintuitively) the relatively metal-rich globular clusters NGC 6440, 6441, and 6388 should be devoid of giant planets. The characteris...

  14. Fusion process of Lennard-Jones clusters: global minima and magic numbers formation

    DEFF Research Database (Denmark)

    Solov'yov, Ilia; Solov'yov, Andrey V.; Greiner, Walter

    2004-01-01

    We present a new theoretical framework for modeling the fusion process of Lennard–Jones (LJ) clusters. Starting from the initial tetrahedral cluster configuration, adding new atoms to the system and absorbing its energy at each step, we find cluster growing paths up to the cluster size of 150 atoms...

  15. Formation of global energy minimim structures in the growth process of Lennard-Jones clusters

    DEFF Research Database (Denmark)

    Solov'yov, Ilia; Koshelev, Andrey; Shutovich, Andrey

    2003-01-01

    We present a new theoretical framework for modelling the cluster growing process. Starting from the initial tetrahedral cluster configuration, adding new atoms to the system and absorbing its energy at each step, we find cluster growing paths up to the cluster sizes of 150 atoms. We demonstrate t...

  16. Analytic and computational micromechanics of clustering and interphase effects in carbon nanotube composites.

    Energy Technology Data Exchange (ETDEWEB)

    Seidel, Gary D.; Hammerand, Daniel Carl; Lagoudas, Dimitris C. (Texas A& M University, College Station, TX)

    2006-01-01

    Effective elastic properties for carbon nanotube reinforced composites are obtained through a variety of micromechanics techniques. Using the in-plane elastic properties of graphene, the effective properties of carbon nanotubes are calculated utilizing a composite cylinders micromechanics technique as a first step in a two-step process. These effective properties are then used in the self-consistent and Mori-Tanaka methods to obtain effective elastic properties of composites consisting of aligned single or multi-walled carbon nanotubes embedded in a polymer matrix. Effective composite properties from these averaging methods are compared to a direct composite cylinders approach extended from the work of Hashin and Rosen (1964) and Christensen and Lo (1979). Comparisons with finite element simulations are also performed. The effects of an interphase layer between the nanotubes and the polymer matrix as result of functionalization is also investigated using a multi-layer composite cylinders approach. Finally, the modeling of the clustering of nanotubes into bundles due to interatomic forces is accomplished herein using a tessellation method in conjunction with a multi-phase Mori-Tanaka technique. In addition to aligned nanotube composites, modeling of the effective elastic properties of randomly dispersed nanotubes into a matrix is performed using the Mori-Tanaka method, and comparisons with experimental data are made. Computational micromechanical analysis of high-stiffness hollow fiber nanocomposites is performed using the finite element method. The high-stiffness hollow fibers are modeled either directly as isotropic hollow tubes or equivalent transversely isotropic effective solid cylinders with properties computed using a micromechanics based composite cylinders method. Using a representative volume element for clustered high-stiffness hollow fibers embedded in a compliant matrix with the appropriate periodic boundary conditions, the effective elastic properties

  17. Formation of ordered CoAl alloy clusters by the plasma-gas condensation technique

    OpenAIRE

    Toyohiko J., Konno; Saeki, Yamamuro; Kenji, Sumiyama

    2001-01-01

    CoxAl1-x alloy clusters were synthesized from a mixture of Co and Al metal vapors generated by the sputtering of pure metal targets. We observed that the produced alloy clusters were uniform in size, ranging from approximately 20 nm for Al-rich clusters to 10 nm for Co-rich clusters. For a wide average composition range (x?0.4-0.7), the alloy clusters have the ordered B2 (CsCl-type) structure. In the Co-rich cluster aggregates (x=0.76), the clusters are composed of face-centered-cubic (fcc) C...

  18. In Situ Formation of Carbon Nanomaterials on Bulk Metallic Materials

    Directory of Open Access Journals (Sweden)

    J. Y. Xu

    2014-01-01

    Full Text Available Carbon nanomaterials were synthesized in situ on bulk 316L stainless steel, pure cobalt, and pure nickel by hybrid surface mechanical attrition treatment (SMAT. The microstructures of the treated samples and the resulted carbon nanomaterials were investigated by SEM and TEM characterizations. Different substrates resulted in different morphologies of products. The diameter of carbon nanomaterials is related to the size of the nanograins on the surface layer of substrates. The possible growth mechanism was discussed. Effects of the main parameters of the synthesis, including the carbon source and gas reactant composition, hydrogen, and the reaction temperature, were studied. Using hybrid SMAT is proved to be an effective way to synthesize carbon nanomaterials in situ on surfaces of metallic materials.

  19. A multiwavelength photometric census of AGN and star formation activity in the brightest cluster galaxies of X-ray selected clusters

    Science.gov (United States)

    Green, T. S.; Edge, A. C.; Stott, J. P.; Ebeling, H.; Burgett, W. S.; Chambers, K. C.; Draper, P. W.; Metcalfe, N.; Kaiser, N.; Wainscoat, R. J.; Waters, C.

    2016-09-01

    Despite their reputation as being `red and dead', the unique environment inhabited by brightest cluster galaxies (BCGs) can often lead to a self-regulated feedback cycle between radiatively cooling intracluster gas and star formation and active galactic nucleus (AGN) activity in the BCG. However the prevalence of `active' BCGs, and details of the feedback involved, are still uncertain. We have performed an optical, UV and mid-IR photometric analysis of the BCGs in 981 clusters at 0.03 AGN and/or star formation activity within the BCG. We find that whilst the majority of BCGs are consistent with being passive, at least 14 per cent of our BCGs show a significant colour offset from passivity in at least one colour index. And, where available, supplementary spectroscopy reveals the majority of these particular BCGs show strong optical emission lines. On comparing BCG `activity' with the X-ray luminosity of the host cluster, we find that BCGs showing a colour offset are preferentially found in the more X-ray luminous clusters, indicative of the connection between BCG `activity' and the intracluster medium.

  20. Carbon nanomaterial Formation on Fresh-Reduced Iron by Converted Natural Gas

    Science.gov (United States)

    Nebesnyi, A.; Kotov, V.; Sviatenko, A.; Filonenko, D.; Khovavko, A.; Bondarenko, B.

    2017-02-01

    The mechanism of carbon nanomaterial formation at moderate temperatures while processing fresh-reduced iron by products of air conversion of natural gas is considered. It is shown that under given conditions, the size and the shape of the resulting carbon are dependent on the temperature and the size of microscopic iron grains formed during reduction. These iron grains are the catalyzer of the reaction of carbon monoxide disproportionation. It is concluded that the formation of a nucleus of the new carbon phase occurs at the contact boundaries of neighboring grains of newly reduced iron with the subsequent formation in these places of ring-shaped carbon cuffs. Nanotubes are forming as a result of further carbon crystallization, and separation of iron particles from the main mass is occurring, i.e., there is a fragmentation of the substance of the catalyst. According to the results of laboratory studies, the optimum temperature of carbon nanotube formation in the environment of converted gas is 600-650 °C. The evidence of the hypothesis that the mechanism of the reaction of carbon monoxide disproportionation flows through the intermediate stage of iron oxides formation is given.

  1. Gas giants in hot water: inhibiting giant planet formation and planet habitability in dense star clusters through cosmic time

    Science.gov (United States)

    Thompson, Todd A.

    2013-05-01

    I show that the temperature of nuclear star clusters, starburst clusters in M82, compact high-z galaxies and some globular clusters of the Galaxy likely exceeded the ice-line temperature (TIce ≈ 150-170 K) during formation for a time comparable to the planet formation time-scale. The protoplanetary discs within these systems will thus, not have an ice line, decreasing the total material available for building protoplanetary embryos, inhibiting the formation of gas- and ice-giants if they form by core accretion, and prohibiting habitability. Planet formation by gravitational instability is similarly suppressed because Toomre's Q > 1 in all but the most massive discs. I show that cluster irradiation can in many cases dominate the thermodynamics and structure of passive and active protoplanetary discs for semi-major axes larger than ˜1-5 au. I discuss these results in the context of the observed lack of planets in 47 Tuc. I predict that a similar search for planets in the globular cluster NGC 6366 ([Fe/H] = -0.82) should yield detections, whereas (counterintuitively) the relatively metal-rich globular clusters NGC 6440, 6441 and 6388 should be devoid of giant planets. The characteristic stellar surface density above which TIce is exceeded in star clusters is ˜ 6 × 103 M⊙ pc- 2 f- 1/2dg, MW, where fdg, MW is the dust-to-gas ratio of the embedding material, normalized to the Milky Way value. Simple estimates suggest that ˜5-50 per cent of the stars in the universe formed in an environment exceeding this surface density. Future microlensing planet searches that directly distinguish between the bulge and disc planet populations of the Galaxy and M31 can test these predictions. Caveats and uncertainties are detailed.

  2. Compound nucleus formation probability PCN defined within the dynamical cluster-decay model

    Science.gov (United States)

    Chopra, Sahila; Kaur, Arshdeep; Gupta, Raj K.

    2015-01-01

    With in the dynamical cluster-decay model (DCM), the compound nucleus fusion/ formation probability PCN is defined for the first time, and its variation with CN excitation energy E* and fissility parameter χ is studied. In DCM, the (total) fusion cross section σfusion is sum of the compound nucleus (CN) and noncompound nucleus (nCN) decay processes, each calculated as the dynamical fragmentation process. The CN cross section σCN is constituted of the evaporation residues (ER) and fusion-fission (ff), including the intermediate mass fragments (IMFs), each calculated for all contributing decay fragments (A1, A2) in terms of their formation and barrier penetration probabilities P0 and P. The nCN cross section σnCN is determined as the quasi-fission (qf) process where P0=1 and P is calculated for the entrance channel nuclei. The calculations are presented for six different target-projectile combinations of CN mass A~100 to superheavy, at various different center-of-mass energies with effects of deformations and orientations of nuclei included in it. Interesting results are that the PCN=1 for complete fusion, but PCN <1 or ≪1 due to the nCN conribution, depending strongly on both E* and χ.

  3. Compound nucleus formation probability PCN defined within the dynamical cluster-decay model

    Directory of Open Access Journals (Sweden)

    Chopra Sahila

    2015-01-01

    Full Text Available With in the dynamical cluster-decay model (DCM, the compound nucleus fusion/ formation probability PCN is defined for the first time, and its variation with CN excitation energy E* and fissility parameter χ is studied. In DCM, the (total fusion cross section σfusion is sum of the compound nucleus (CN and noncompound nucleus (nCN decay processes, each calculated as the dynamical fragmentation process. The CN cross section σCN is constituted of the evaporation residues (ER and fusion-fission (ff, including the intermediate mass fragments (IMFs, each calculated for all contributing decay fragments (A1, A2 in terms of their formation and barrier penetration probabilities P0 and P. The nCN cross section σnCN is determined as the quasi-fission (qf process where P0=1 and P is calculated for the entrance channel nuclei. The calculations are presented for six different target-projectile combinations of CN mass A~100 to superheavy, at various different center-of-mass energies with effects of deformations and orientations of nuclei included in it. Interesting results are that the PCN=1 for complete fusion, but PCN <1 or ≪1 due to the nCN conribution, depending strongly on both E* and χ.

  4. Search for Signal on Percolation Cluster Formation in Nucleus-Nucleus Collisions at Relativistic Energies

    CERN Document Server

    Abdinov, O B; Kuznetsov, A A; Suleymanov, M K; Vodopyanov, A S; Vokal, S

    2005-01-01

    The appearance of the strongly interacting matter mixed phase (MP)has been suggested to consider to understand qualitatively the regime change existence in the behavior of some centrality depending characteristics of events. The MP has been predicted by QCD for the temperatures around the critical temperature Tc and could be formed as a result of nucleon percolation in the density nuclear matter. Our main goal is to get a new experimental confirmation of the percolation cluster formation as an accompanying effect of the MP formation. To reach the goal, the experimental data on Kr+Em - reaction at 0.95 GeV/nuc and Au+Em - reaction at 10.6 GeV/nucl. with a number of target fragments N_h > 8, have been analyzed. The behavior of the distributions of the target and the projectile fragments has been studied. The experimental data have been compared of the data coming from the cascade-evaporation model. We can conclude that: -- the centrality of the collision could be defined as a number of the target g-fragments in...

  5. Outflow Feedback Regulated Massive Star Formation in Parsec-Scale Cluster Forming Clumps

    CERN Document Server

    Wang, Peng; Abel, Tom; Nakamura, Fumitaka

    2009-01-01

    (Abridged) We investigate massive star formation in turbulent, magnetized, parsec-scale clumps of molecular clouds including protostellar outflow feedback using Enzo-based MHD simulations with accreting sink particles and effective resolution $2048^3$. We find that, in the absence of regulation by magnetic fields and outflow feedback, massive stars form readily in a turbulent, moderately condensed clump of $\\sim 1,600$ solar masses, along with a cluster of hundreds of lower mass stars. The massive stars are fed at high rates by (1) transient dense filaments produced by large-scale turbulent compression at early times, and (2) by the clump-wide global collapse resulting from turbulence decay at late times. In both cases, the bulk of the massive star's mass is supplied from outside a 0.1 pc-sized "core" that surrounds the star. In our simulation, the massive star is clump-fed rather than core-fed. The need for large-scale feeding makes the massive star formation prone to regulation by outflow feedback, which di...

  6. Carbon Formation and Metal Dusting in Hot-Gas Cleanup Systems of Coal Gasifiers

    Energy Technology Data Exchange (ETDEWEB)

    Tortorelli, Peter F.; Judkins, Roddie R.; DeVan, Jackson H.; Wright, Ian G.

    1995-12-31

    There are several possible materials/systems degradation modes that result from gasification environments with appreciable carbon activities. These processes, which are not necessarily mutually exclusive, include carbon deposition, carburization, metal dusting, and CO disintegration of refractories. Carbon formation on solid surfaces occurs by deposition from gases in which the carbon activity (a sub C) exceeds unity. The presence of a carbon layer CO can directly affect gasifier performance by restricting gas flow, particularly in the hot gas filter, creating debris (that may be deposited elsewhere in the system or that may cause erosive damage of downstream components), and/or changing the catalytic activity of surfaces.

  7. Recent development in electrolytic formation of carbon nanotubes in molten salts

    Directory of Open Access Journals (Sweden)

    Chen G.Z.

    2003-01-01

    Full Text Available This article reviews the recent research development in the electrolytic production of carbon nano-tubes in molten salts. The experimental procedure and product morphologies of the electrolytic method are described in details. Different hypotheses of the carbon nano-tube formation mechanism in molten salts, particularly it relation with the erosion of the cathode, are compared and discussed. It is anticipated that the electrolytic method can potentially become a cheap and continuous process for the production of curved carbon nano-tubes, carbon sheathed metal nanowires and other carbon based nano-structures.

  8. The ACS Virgo Cluster Survey XV. The Formation Efficiencies of Globular Clusters in Early-Type Galaxies: The Effects of Mass and Environment

    CERN Document Server

    Peng, Eric W; Cote, Patrick; Takamiya, Marianne; West, Michael J; Blakeslee, John P; Chen, Chin-Wei; Ferrarese, Laura; Mei, Simona; Tonry, John L; West, Andrew A

    2008-01-01

    The fraction of stellar mass contained in globular clusters (GCs), also measured by number as the specific frequency, is a fundamental quantity that reflects both a galaxy's early star formation and its entire merging history. We present specific frequencies, luminosities, and mass fractions for the globular cluster systems of 100 early-type galaxies in the ACS Virgo Cluster Survey, the largest homogeneous catalog of its kind. We find that 1) GC mass fractions can be high in both giants and dwarfs, but are universally low in galaxies with intermediate luminosities. 2) The behavior of specific frequency across galaxy mass is dominated by the blue GCs. 3) The GC fractions of low-mass galaxies exhibit a dependence on environment. Nearly all dwarf galaxies with high GC fractions are within 1 Mpc of the cD galaxy M87, presenting the first strong evidence that GC formation in dwarfs is biased toward dense environments. 4) GC formation in central dwarfs is biased because their stars form earliest and most intensely....

  9. Highly efficient conversion of superoxide to oxygen using hydrophilic carbon clusters.

    Science.gov (United States)

    Samuel, Errol L G; Marcano, Daniela C; Berka, Vladimir; Bitner, Brittany R; Wu, Gang; Potter, Austin; Fabian, Roderic H; Pautler, Robia G; Kent, Thomas A; Tsai, Ah-Lim; Tour, James M

    2015-02-24

    Many diseases are associated with oxidative stress, which occurs when the production of reactive oxygen species (ROS) overwhelms the scavenging ability of an organism. Here, we evaluated the carbon nanoparticle antioxidant properties of poly(ethylene glycolated) hydrophilic carbon clusters (PEG-HCCs) by electron paramagnetic resonance (EPR) spectroscopy, oxygen electrode, and spectrophotometric assays. These carbon nanoparticles have 1 equivalent of stable radical and showed superoxide (O2 (•-)) dismutase-like properties yet were inert to nitric oxide (NO(•)) as well as peroxynitrite (ONOO(-)). Thus, PEG-HCCs can act as selective antioxidants that do not require regeneration by enzymes. Our steady-state kinetic assay using KO2 and direct freeze-trap EPR to follow its decay removed the rate-limiting substrate provision, thus enabling determination of the remarkable intrinsic turnover numbers of O2 (•-) to O2 by PEG-HCCs at >20,000 s(-1). The major products of this catalytic turnover are O2 and H2O2, making the PEG-HCCs a biomimetic superoxide dismutase.

  10. Investigation of the plasma processability of natural carbon bearing formations

    Science.gov (United States)

    Molchanov, V. P.

    2017-01-01

    In the south of the Russian Far East, a new perspective source of minerals was pioneered, which is the metal-bearing high carbon rocks of the Ruzhinskaya square. The rocks are rich in crystalline graphite, gold, platinum and carbon nanostructures (fullerene, nanotubes and diamond-like carbon). The technique of extraction of ultrapure (99.98%) crystalline graphite from these rocks has been developed using hydrometallugical methods. The obtained graphite was used as a raw material for plasma-chemical tests succeeded in the separation of nanodimensional carbon structures, part of which could be inherited from the natural graphite-bearing rocks. The results of investigation will be used in the development of resource-saving technology of minerals extraction.

  11. Cluster formation, evolution and size distribution in Fe-Cu alloy: Analysis by XAFS, XRD and TEM

    Energy Technology Data Exchange (ETDEWEB)

    Cammelli, S., E-mail: sebastiano.cammelli@psi.c [LNM, NES, Paul Scherrer Institute, 5232 Villigen PSI (Switzerland); Fachbereich C - Physik, Bergische Universitaet Wuppertal, Gauss-Str. 20, 42097 Wuppertal (Germany); Degueldre, C. [LNM, NES, Paul Scherrer Institute, 5232 Villigen PSI (Switzerland); Cervellino, A. [SLS, Paul Scherrer Institute, 5232 Villigen PSI (Switzerland); Abolhassani, S.; Kuri, G.; Bertsch, J. [LNM, NES, Paul Scherrer Institute, 5232 Villigen PSI (Switzerland); Luetzenkirchen-Hecht, D.; Frahm, R. [Fachbereich C - Physik, Bergische Universitaet Wuppertal, Gauss-Str. 20, 42097 Wuppertal (Germany)

    2010-03-15

    Fe-Cu alloys containing 1.3 at.% copper were studied as model systems for cluster formation in reactor pressure vessel steels. The samples were annealed at 775 K for different times and subsequently analyzed using X-ray absorption fine structure spectroscopy at the Cu-K-edge, X-ray diffraction and transmission electron microscopy. The results show that copper cluster formation might occur even with short annealing times. These clusters of about 1 nm size can switch easily from bcc iron-like structures to fcc copper, if the local copper concentration is high enough. While a short annealing time of 2.5 h at 775 K maintains a good dilution of copper in the bcc iron matrix, annealing for 312 h leads to large fcc copper precipitates. A linear combination analysis suggests that in the sample annealed 8 h, copper clusters are mostly formed with the same structure as the matrix. A co-existence of bcc and fcc clusters is obtained for 115 h of annealing. Transmission electron microscopy indicates the presence of precipitates as large as 60 nm size for an annealing time of 312 h, and X-ray diffraction provided complementary data about the clusters size distributions in all of the four samples.

  12. The chloroplast NifS-like protein of Arabidopsis thaliana is required for iron-sulfur cluster formation in ferredoxin.

    Science.gov (United States)

    Ye, Hong; Garifullina, Gulnara F; Abdel-Ghany, Salah E; Zhang, Lihong; Pilon-Smits, Elizabeth A H; Pilon, Marinus

    2005-02-01

    Plastids are known to be able to synthesize their own iron-sulfur clusters, but the biochemical machinery responsible for this process is not known. In this study it is investigated whether CpNifS, the chloroplastic NifS-like cysteine desulfurase of Arabidopsis thaliana (L.) Heynh. is responsible for the release of sulfur from cysteine for the biogenesis of iron-sulfur (Fe-S) clusters in chloroplasts. Using an in vitro reconstitution assay it was found that purified CpNifS was sufficient for Fe-S cluster formation in ferredoxin in the presence of cysteine and a ferrous iron salt. Antibody-depletion experiments using stromal extract showed that CpNifS is also essential for the Fe-S cluster formation activity of chloroplast stroma. The activity of CpNifS in the stroma was 50- to 80-fold higher than that of purified CpNifS on a per-protein basis, indicating that other stromal factors cooperate in Fe-S cluster formation. When stromal extract was separated on a gel-filtration column, most of the CpNifS eluted as a dimer of 86 kDa, but a minor fraction of the stromal CpNifS eluted at a molecular weight of approx. 600 kDa, suggesting the presence of a multi-protein complex. The possible nature of the interacting proteins is discussed.

  13. HERSCHEL OBSERVATIONS OF THE W3 GMC: CLUES TO THE FORMATION OF CLUSTERS OF HIGH-MASS STARS

    Energy Technology Data Exchange (ETDEWEB)

    Rivera-Ingraham, A. [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4 (Canada); Martin, P. G.; Luong, Q. Nguyen; Roy, A. [Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, ON M5S 3H8 (Canada); Polychroni, D. [Department of Astrophysics, Astronomy and Mechanics, Faculty of Physics, University of Athens, Panepistimiopolis, 15784 Zografos, Athens (Greece); Motte, F.; Schneider, N.; Hennemann, M.; Men' shchikov, A.; Andre, Ph.; Arzoumanian, D.; Hill, T.; Minier, V. [Laboratoire AIM, CEA/IRFU-CNRS/INSU-Universite Paris Diderot, CEA-Saclay, F-91191 Gif-sur-Yvette Cedex (France); Bontemps, S. [Universite Bordeaux, LAB, UMR 5804, F-33270 Floirac (France); Bernard, J.-Ph. [CNRS, IRAP, 9 Avenue colonel Roche, BP 44346, F-31028 Toulouse cedex 4 (France); Di Francesco, J.; Fallscheer, C. [National Research Council Canada, Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada); Elia, D.; Pezzuto, S. [INAF-Istituto di Astrofisica e Planetologia Spaziali, via Fosso del Cavaliere 100, I-00133 Rome (Italy); Li, J. Z. [National Astronomical Observatories, Chinese Academy of Sciences, Beijing (China); and others

    2013-04-01

    The W3 GMC is a prime target for the study of the early stages of high-mass star formation. We have used Herschel data from the HOBYS key program to produce and analyze column density and temperature maps. Two preliminary catalogs were produced by extracting sources from the column density map and from Herschel maps convolved to 500 {mu}m resolution. Herschel reveals that among the compact sources (FWHM < 0.45 pc), W3 East, W3 West, and W3 (OH) are the most massive and luminous and have the highest column density. Considering the unique properties of W3 East and W3 West, the only clumps with ongoing high-mass star formation, we suggest a 'convergent constructive feedback' scenario to account for the formation of a cluster with decreasing age and increasing system/source mass toward the innermost regions. This process, which relies on feedback by high-mass stars to ensure the availability of material during cluster formation, could also lead to the creation of an environment suitable for the formation of Trapezium-like systems. In common with other scenarios proposed in other HOBYS studies, our results indicate that an active/dynamic process aiding in the accumulation, compression, and confinement of material is a critical feature of the high-mass star/cluster formation, distinguishing it from classical low-mass star formation. The environmental conditions and availability of triggers determine the form in which this process occurs, implying that high-mass star/cluster formation could arise from a range of scenarios: from large-scale convergence of turbulent flows to convergent constructive feedback or mergers of filaments.

  14. Herschel Observations of the W3 GMC: Clues to the Formation of Clusters of High-mass Stars

    Science.gov (United States)

    Rivera-Ingraham, A.; Martin, P. G.; Polychroni, D.; Motte, F.; Schneider, N.; Bontemps, S.; Hennemann, M.; Men'shchikov, A.; Nguyen Luong, Q.; André, Ph.; Arzoumanian, D.; Bernard, J.-Ph.; Di Francesco, J.; Elia, D.; Fallscheer, C.; Hill, T.; Li, J. Z.; Minier, V.; Pezzuto, S.; Roy, A.; Rygl, K. L. J.; Sadavoy, S. I.; Spinoglio, L.; White, G. J.; Wilson, C. D.

    2013-04-01

    The W3 GMC is a prime target for the study of the early stages of high-mass star formation. We have used Herschel data from the HOBYS key program to produce and analyze column density and temperature maps. Two preliminary catalogs were produced by extracting sources from the column density map and from Herschel maps convolved to 500 μm resolution. Herschel reveals that among the compact sources (FWHM < 0.45 pc), W3 East, W3 West, and W3 (OH) are the most massive and luminous and have the highest column density. Considering the unique properties of W3 East and W3 West, the only clumps with ongoing high-mass star formation, we suggest a "convergent constructive feedback" scenario to account for the formation of a cluster with decreasing age and increasing system/source mass toward the innermost regions. This process, which relies on feedback by high-mass stars to ensure the availability of material during cluster formation, could also lead to the creation of an environment suitable for the formation of Trapezium-like systems. In common with other scenarios proposed in other HOBYS studies, our results indicate that an active/dynamic process aiding in the accumulation, compression, and confinement of material is a critical feature of the high-mass star/cluster formation, distinguishing it from classical low-mass star formation. The environmental conditions and availability of triggers determine the form in which this process occurs, implying that high-mass star/cluster formation could arise from a range of scenarios: from large-scale convergence of turbulent flows to convergent constructive feedback or mergers of filaments. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

  15. LoCuSS: THE SLOW QUENCHING OF STAR FORMATION IN CLUSTER GALAXIES AND THE NEED FOR PRE-PROCESSING

    Energy Technology Data Exchange (ETDEWEB)

    Haines, C. P. [Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Correo Central, Santiago (Chile); Pereira, M. J.; Egami, E.; Rawle, T. D. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Smith, G. P.; Ziparo, F.; McGee, S. L. [School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham, B15 2TT (United Kingdom); Babul, A. [Department of Physics and Astronomy, University of Victoria, 3800 Finnerty Road, Victoria, BC, V8P 1A1 (Canada); Finoguenov, A. [Department of Physics, University of Helsinki, Gustaf Hällströmin katu 2a, FI-0014 Helsinki (Finland); Okabe, N. [Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), P.O. Box 23-141, Taipei 10617, Taiwan (China); Moran, S. M., E-mail: cphaines@das.uchile.cl [Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States)

    2015-06-10

    We present a study of the spatial distribution and kinematics of star-forming galaxies in 30 massive clusters at 0.15 < z < 0.30, combining wide-field Spitzer 24 μm and GALEX near-ultraviolet imaging with highly complete spectroscopy of cluster members. The fraction (f{sub SF}) of star-forming cluster galaxies rises steadily with cluster-centric radius, increasing fivefold by 2r{sub 200}, but remains well below field values even at 3r{sub 200}. This suppression of star formation at large radii cannot be reproduced by models in which star formation is quenched in infalling field galaxies only once they pass within r{sub 200} of the cluster, but is consistent with some of them being first pre-processed within galaxy groups. Despite the increasing f{sub SF}-radius trend, the surface density of star-forming galaxies actually declines steadily with radius, falling ∼15× from the core to 2r{sub 200}. This requires star formation to survive within recently accreted spirals for 2–3 Gyr to build up the apparent over-density of star-forming galaxies within clusters. The velocity dispersion profile of the star-forming galaxy population shows a sharp peak of 1.44 σ{sub ν} at 0.3r{sub 500}, and is 10%–35% higher than that of the inactive cluster members at all cluster-centric radii, while their velocity distribution shows a flat, top-hat profile within r{sub 500}. All of these results are consistent with star-forming cluster galaxies being an infalling population, but one that must also survive ∼0.5–2 Gyr beyond passing within r{sub 200}. By comparing the observed distribution of star-forming galaxies in the stacked caustic diagram with predictions from the Millennium simulation, we obtain a best-fit model in which star formation rates decline exponentially on quenching timescales of 1.73 ± 0.25 Gyr upon accretion into the cluster.

  16. Accretion of pristine gas and dilution during the formation of multiple-population globular clusters

    Science.gov (United States)

    D'Ercole, A.; D'Antona, F.; Vesperini, E.

    2016-10-01

    We study the interaction of the early spherical GC wind powered by Type II supernovae (SNe II) with the surrounding ambient medium consisting of the gaseous disc of a star-forming galaxy at redshift z ≳ 2. The bubble formed by the wind eventually breaks out of the disc, and most of the wind moves directly out of the galaxy and is definitively lost. The fraction of the wind moving nearly parallel to the galactic plane carves a hole in the disc which will contract after the end of the SN activity. During the interval of time between the end of the SN explosions and the `closure' of the hole, very O-poor stars (the Extreme population) can form out of the super-AGB (asymptotic giant branch) ejecta collected in the GC centre. Once the hole contracts, the AGB ejecta mix with the pristine gas, allowing the formation of stars with an oxygen abundance intermediate between that of the very O-poor stars and that of the pristine gas. We show that this mechanism may explain why Extreme populations are present only in massive clusters, and can also produce a correlation between the spread in helium and the cluster mass. Finally, we also explore the possibility that our proposed mechanism can be extended to the case of multiple populations showing bimodality in the iron content, with the presence of two populations characterized by a small difference in [Fe/H]. Such a result can be obtained taking into account the contribution of delayed SN II.

  17. Palladium on Nitrogen-Doped Mesoporous Carbon: A Bifunctional Catalyst for Formate-Based, Carbon-Neutral Hydrogen Storage.

    Science.gov (United States)

    Wang, Fanan; Xu, Jinming; Shao, Xianzhao; Su, Xiong; Huang, Yanqiang; Zhang, Tao

    2016-02-08

    The lack of safe, efficient, and economical hydrogen storage technologies is a hindrance to the realization of the hydrogen economy. Reported herein is a reversible formate-based carbon-neutral hydrogen storage system that is established over a novel catalyst comprising palladium nanoparticles supported on nitrogen-doped mesoporous carbon. The support was fabricated by a hard template method and nitridated under a flow of ammonia. Detailed analyses demonstrate that this bicarbonate/formate redox equilibrium is promoted by the cooperative role of the doped nitrogen functionalities and the well-dispersed, electron-enriched palladium nanoparticles.

  18. Multi-seeded multi-mode formation of embedded clusters in the RMC: Structured star formation toward the south-east boundary

    CERN Document Server

    Smith, J Z L M D

    2005-01-01

    The Rosette Molecular Complex contains embedded clusters with diverse properties and origins. We have previously explored the shell mode of formation in the north (Regions A & B) and the massive concentrations in the ridge (Region C). Here, we explore star formation towards the south of the complex, Region D, based on data from the spatially complete 2 Micron All Sky Survey. We find that stars are forming prolifically throughout this region in a highly structured mode with both clusters and loose aggregates detected. The most prominent cluster (Region D1) lies in the north-center. This cluster is over 20 pc to the south of the Monoceros ridge, the interface of the emerging young OB cluster NGC 2244 with its ambient molecular clouds. In addition, there are several branches stemming from AFGL 961 in Region C and extending to the south-east boundary of the cloud. We invoke a tree model to interpret this pattern, corresponding to probable tracks of abrupt turbulent excitation and subsequent decay. Alternative...

  19. Seafloor-precipitated carbonate fans in the Neoproterozoic Rainstorm Member, Johnnie Formation, Death Valley Region, USA

    OpenAIRE

    Pruss, Sara Brady; Corsetti, Frank A.; Fischer, Woodward W.

    2008-01-01

    Cm-sized carbonate seafloor fans occur in the Neoproterozoic Rainstorm Member of the Johnnie Formation, Death Valley, USA. The fans formed in a mixed carbonate-clastic succession near storm wave base at the base of parasequences on a storm-dominated ramp. Petrographic observations indicate that the fans were originally precipitated as aragonite and later inverted to calcite during diagenesis. Although not directly dated, the Rainstorm Member preserves a large magnitude negative carbon isotopi...

  20. Formation of CuInS{sub 2}-carbon multilayers in the spray ILGAR process

    Energy Technology Data Exchange (ETDEWEB)

    Camus, Christian; Abou-Ras, Daniel; Allsop, Nicholas A.; Gledhill, Sophie E.; Koehler, Tristan; Lauermann, Iver; Lux-Steiner, Martha C.; Fischer, Christian-Herbert [Helmholtz Zentrum Berlin fuer Materialien und Energie, Glienicker Str. 100, 14109 Berlin (Germany); Rappich, Joerg [Helmholtz Zentrum Berlin fuer Materialien und Energie, Kekulestr. 5, 12489 Berlin (Germany)

    2010-01-15

    In this paper, the incorporation of carbon into CuInS{sub 2} (CIS) thin films is described as observed in spray ion layer gas reaction (ILGAR) deposition of such thin films. It is shown that this carbon incorporation leads to the formation of a CIS-carbon multilayer stack. Its growth mechanism is explained by the interaction of the copper and indium precursor compounds used in the deposition process. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  1. Formation and transformation of a short range ordered iron carbonate precursor

    DEFF Research Database (Denmark)

    Dideriksen, Knud; Frandsen, Cathrine; Bovet, Nicolas

    2015-01-01

    Fe(II)-carbonates, such as siderite, form in environments where O2 is scarce, e.g., during marine sediment diagenesis, corrosion and possibly CO2 sequestration, but little is known about their formation pathways. We show that early precipitates from carbonate solutions containing 0.1M Fe(II) with...

  2. The Effect of Carbon Source and Fluoride Concentrations in the "Streptococcus Mutans" Biofilm Formation

    Science.gov (United States)

    Paulino, Tony P.; Andrade, Ricardo O.; Bruschi-Thedei, Giuliana C. M.; Thedei, Geraldo, Jr.; Ciancaglini, Pietro

    2004-01-01

    The main objective of this class experiment is to show the influence of carbon source and of different fluoride concentrations on the biofilm formation by the bacterium "Streptococcus mutans." The observation of different biofilm morphology as a function of carbon source and fluoride concentration allows an interesting discussion regarding the…

  3. Trace-Element Analyses of Carbonate Minerals in the Gunflint Banded Iron Formation

    Science.gov (United States)

    Pun, Aurora; Papike, James J.; Shearer, C. K.

    2002-01-01

    We report on the petrography, mineralogy and trace-element abundances of individual carbonate grains in the Early Proterozoic Gunflint BIF (Banded Iron Formation). Trace-element data may be used as environmental recorders of the fluid evolution from which the various carbonate phases precipitated. Additional information is contained in the original extended abstract.

  4. Structure and Turbulence in Simulated Galaxy Clusters and the Implications for the Formation of Radio Halos

    CERN Document Server

    Hallman, Eric J

    2011-01-01

    We track the histories of massive clusters of galaxies formed within a cosmological hydrodynamic simulation. Specifically, we track the time evolution of the energy in random bulk motions of the intracluster medium and X-ray measures of cluster structure and their relationship to cluster mergers. We aim to assess the viability of the turbulent re-acceleration model for the generation of giant radio halos by comparing the level of turbulent kinetic energy in simulated clusters with the observed properties of radio halo clusters, giving particular attention to the association of radio halos to clusters with disturbedX-ray structures. The evolution of X-ray cluster structure and turbulence kinetic energy, k, in simulations can then inform us about the expected lifetime of radio halos and the fraction of clusters as a function of redshift expected to host them. We find strong statistical correlation of disturbed structure measures and the presence of enhancements in k. Specifically, quantitatively "disturbed", ra...

  5. A Site-Specific Phosphorylation of the Focal Adhesion Kinase Controls the Formation of Spheroid Cell Clusters

    DEFF Research Database (Denmark)

    Beck, Hans Christian; Gosau, Martin; Kristensen, Lars Peter

    2014-01-01

    Human dental follicle cells (DFCs) are ectomesenchymal multipotent stem cells that form spheroid cell clusters (SCCs) under serum free medium cell culture conditions (SFM). Until today, molecular mechanisms for the formation of SCCs are unknown. In this study a quantitative phosphoproteomics...

  6. GALEX Observations of "Passive Spirals" in the Cluster Cl 0024+17: Clues to the Formation of S0 Galaxies

    CERN Document Server

    Moran, S M; Treu, T; Salim, S; Rich, R M; Smith, G P; Kneib, J P; Moran, Sean M.; Ellis, Richard S.; Treu, Tommaso; Salim, Samir; Smith, Graham P.; Kneib, Jean-Paul

    2006-01-01

    We present new results from deep GALEX UV imaging of the cluster Cl 0024+17 at z~0.4. Rest-frame far UV emission is detected from a large fraction of so-called ``passive spiral galaxies'' -a significant population which exhibits spiral morphology with little or no spectroscopic evidence for ongoing star formation. This population is thought to represent infalling galaxies whose star formation has been somehow truncated by environmental processes, possibly in morphological transition to S0 galaxies. Compared to normal cluster spirals, we find that passive spirals are redder in FUV-optical color, while exhibiting much stronger UV emission than cluster E/S0s - as expected for recently-truncated star formation. By modeling the different temporal sensitivities of UV and spectroscopic data to recent activity, we show that star formation in passive spirals decayed on timescales of less than 1 Gyr, consistent with `gas starvation' - a process where the cluster environment prevents cold gas from accreting onto the spi...

  7. Constraining the high-redshift formation of black hole seeds in nuclear star clusters with gas inflows

    NARCIS (Netherlands)

    Lupi, A.; Colpi, M.; Devecchi, B.; Galanti, G.; Volonteri, M.

    2014-01-01

    In this paper, we explore a possible route of black hole seed formation that appeals to a model by Davies, Miller & Bellovary who considered the case of the dynamical collapse of a dense cluster of stellar black holes subjected to an inflow of gas. Here, we explore this case in a broad cosmological

  8. Star Formation Rates in Cooling Flow Clusters: A UV Pilot Study with Archival XMM-Newton Optical Monitor Data

    Science.gov (United States)

    Hicks, A. K.; Mushotzky, R.

    2006-01-01

    We have analyzed XMM-Newton Optical Monitor (OM) UV (180-400 nm) data for a sample of 33 galaxies. 30 are cluster member galaxies, and nine of these are central cluster galaxies (CCGs) in cooling flow clusters having mass deposition rates which span a range of 8 - 525 Solar Mass/yr. By comparing the ratio of UV to 2MASS J band fluxes, we find a significant UV excess in many, but not all, cooling flow CCGs, a finding consistent with the outcome of previous studies based on optical imaging data (McNamara & O'Connell 1989; Cardiel, Gorgas, & Aragon-Salamanca 1998; Crawford et al. 1999). This UV excess is a direct indication of the presence of young massive stars, and therefore recent star formation, in these galaxies. Using the Starburst99 spectral energy distribution (SED) model of continuous star formation over a 900 Myr period, we derive star formation rates of 0.2 - 219 solar Mass/yr for the cooling flow sample. For 2/3 of this sample it is possible to equate Chandra/XMM cooling flow mass deposition rates with UV inferred star formation rates, for a combination of starburst lifetime and IMF slope. This is a pilot study of the well populated XMM UV cluster archive and a more extensive follow up study is currently underway.

  9. Neutral hydrogen gas, past and future star-formation in galaxies in and around the 'Sausage' merging galaxy cluster

    CERN Document Server

    Stroe, Andra; Rottgering, Huub J A; Sobral, David; van Weeren, Reinout; Dawson, William

    2015-01-01

    CIZA J2242.8+5301 ($z = 0.188$, nicknamed 'Sausage') is an extremely massive ($M_{200}\\sim 2.0 \\times 10^{15}M_\\odot$ ), merging cluster with shock waves towards its outskirts, which was found to host numerous emission-line galaxies. We performed extremely deep Westerbork Synthesis Radio Telescope HI observations of the 'Sausage' cluster to investigate the effect of the merger and the shocks on the gas reservoirs fuelling present and future star formation (SF) in cluster members. By using spectral stacking, we find that the emission-line galaxies in the 'Sausage' cluster have, on average, as much HI gas as field galaxies (when accounting for the fact cluster galaxies are more massive than the field galaxies), contrary to previous studies. Since the cluster galaxies are more massive than the field spirals, they may have been able to retain their gas during the cluster merger. The large HI reservoirs are expected to be consumed within $\\sim0.75-1.0$ Gyr by the vigorous SF and AGN activity and/or driven out by t...

  10. Theoretical realization of cluster-assembled hydrogen storage materials based on terminated carbon atomic chains.

    Science.gov (United States)

    Liu, Chun-Sheng; An, Hui; Guo, Ling-Ju; Zeng, Zhi; Ju, Xin

    2011-01-14

    The capacity of carbon atomic chains with different terminations for hydrogen storage is studied using first-principles density functional theory calculations. Unlike the physisorption of H(2) on the H-terminated chain, we show that two Li (Na) atoms each capping one end of the odd- or even-numbered carbon chain can hold ten H(2) molecules with optimal binding energies for room temperature storage. The hybridization of the Li 2p states with the H(2)σ orbitals contributes to the H(2) adsorption. However, the binding mechanism of the H(2) molecules on Na arises only from the polarization interaction between the charged Na atom and the H(2). Interestingly, additional H(2) molecules can be bound to the carbon atoms at the chain ends due to the charge transfer between Li 2s2p (Na 3s) and C 2p states. More importantly, dimerization of these isolated metal-capped chains does not affect the hydrogen binding energy significantly. In addition, a single chain can be stabilized effectively by the C(60) fullerenes termination. With a hydrogen uptake of ∼10 wt.% on Li-coated C(60)-C(n)-C(60) (n = 5, 8), the Li(12)C(60)-C(n)-Li(12)C(60) complex, keeping the number of adsorbed H(2) molecules per Li and stabilizing the dispersion of individual Li atoms, can serve as better building blocks of polymers than the (Li(12)C(60))(2) dimer. These findings suggest a new route to design cluster-assembled hydrogen storage materials based on terminated sp carbon chains.

  11. M4C9 +(M = Ti, V): New gas phase clusters

    Indian Academy of Sciences (India)

    R Selvan; L Gowrishankar; T Pradeep

    2001-10-01

    New metal-carbon clusters, M4C9 +(M = Ti, V), generated using a combined thermal arc discharge evaporation set-up, have been studied with quadrupole mass spectrometry. Reactivities of these clusters have been investigated by means of association reactions with H2O. Metal-carbon clusters of other compositions have also been studied. We speculate on the mechanism of formation of larger metal-carbon clusters.

  12. A large Hα survey of star formation in relaxed and merging galaxy cluster environments at z ∼ 0.15-0.3

    Science.gov (United States)

    Stroe, Andra; Sobral, David; Paulino-Afonso, Ana; Alegre, Lara; Calhau, João; Santos, Sergio; van Weeren, Reinout

    2017-03-01

    We present the first results from the largest Hα survey of star formation and active galactic nucleus activity in galaxy clusters. Using nine different narrow-band filters, we select >3000 Hα emitters within 19 clusters and their larger scale environment over a total volume of 1.3 × 105 Mpc3. The sample includes both relaxed and merging clusters, covering the 0.15-0.31 redshift range and spanning from 5 × 1014 to 30 × 1014 M⊙. We find that the Hα luminosity function for merging clusters has a higher characteristic density ϕ* compared to relaxed clusters. ϕ* drops from cluster core to cluster outskirts for both merging and relaxed clusters, with the merging cluster values ∼0.3 dex higher at each projected radius. The characteristic luminosity L* drops over the 0.5-2.0 Mpc distance from the cluster centre for merging clusters and increases for relaxed objects. Among disturbed objects, clusters hosting large-scale shock waves (traced by radio relics) are overdense in Hα emitters compared to those with turbulence in their intracluster medium (traced by radio haloes). We speculate that the increase in star formation activity in disturbed, young, massive galaxy clusters can be triggered by interactions between gas-rich galaxies, shocks and/or the intracluster medium, as well as accretion of filaments and galaxy groups. Our results indicate that disturbed clusters represent vastly different environments for galaxy evolution compared to relaxed clusters or average field environments.

  13. The evolution of and starburst-agn connection in luminous and ultraluminous infrared galaxies and their link to globular cluster formation

    Science.gov (United States)

    Fiorenza, Stephanie Lynn

    The evolutionary connection between nuclear starbursts and active galactic nuclei (AGN) in luminous infrared galaxies (LIRGs; 1011 Tukey-Kramer method of statistical analysis, and fit an exponential curve to the data to describe the expected amount of decrease in SFR seen for a U/LIRG in my sample over a given change in starburst age. Finally, I find evidence that the stellar mass and starburst mass fractions influence whether a U/LIRG in my sample will have a strong AGN and SFR, respectively. I compare the SFR-Mstar relationship seen in my sample with those predicted by models and found from previous observations. I find that the U/LIRGs with older starbursts (>125 Myr) agree with previous results, while those with younger starbursts show a large dispersion in Mstar. I conclude that this is supporting evidence that the star formation histories and timescales at which the IR power sources in U/LIRGs evolve are responsible for the scatter found for the SFR-Mstar relationship. U/LIRGs that form from merging gas-rich disk galaxies could also represent a stage of galaxy evolution involving heavy formation of globular clusters (GCs). It has been suggested that a large number of stellar clusters form during the merging of two gas-rich disk galaxies, leading to open and young massive clusters with the latter likely evolving into GCs. Furthering our understanding of GC formation can uncover the connection between GCs and their host galaxies, which could, at some point during their formation or evolution, be U/LIRGs. To understand GC formation in the context of hierarchical galaxy formation, it is necessary to understand the origin of their abundance patterns. To this effort, I use SDSS spectra from Data Release 8 and 9 to estimate carbon (C) abundances for five GCs by matching synthetic spectra, created with TURBOSPECTRUM using atmospheric parameters derived from the Segue Stellar Parameter Pipeline, with observed spectra at the CH G-band feature. I find large spreads in

  14. MOLECULAR DYNAMICS SIMULATIONS OF FILLED AND EMPTY CAGE-LIKE WATER CLUSTERS IN LIQUID WATER AND THEIR SIGNIFICANCE TO GAS HYDRATE FORMATION MECHANISMS

    Institute of Scientific and Technical Information of China (English)

    GUO Guangjun; ZHANG Yigang; ZHAO Yajuan

    2003-01-01

    Molecular dynamics simulations are performed to observe the evolutions of 512 and 51262 cage-like water clusters filled with or without a methane molecule immersed in bulk liquid water at 250 K and 230 K. The lifetimes of these clusters are calculated according to their Lindemann index δ (t) using the criteria of δ≥0.07. For both the filled and empty clusters, we find the dynamics of bulk water determines the lifetimes of cage-like water clusters, and that the lifetime of 512 62 cage-like cluster is the same as that of 512 cage-like cluster. Although the methane molecule indeed makes the filled cage-like cluster more stable than the empty one, the empty cage-like cluster still has chance to be long-lived compared with the filled clusters. These observations support the labile cluster hypothesis on the formation mechanisms of gas hydrates.

  15. Improving Osteoblast Response In Vitro by a Nanostructured Thin Film with Titanium Carbide and Titanium Oxides Clustered around Graphitic Carbon.

    Directory of Open Access Journals (Sweden)

    Giovanni Longo

    Full Text Available Recently, we introduced a new deposition method, based on Ion Plating Plasma Assisted technology, to coat titanium implants with a thin but hard nanostructured layer composed of titanium carbide and titanium oxides, clustered around graphitic carbon. The nanostructured layer has a double effect: protects the bulk titanium against the harsh conditions of biological tissues and in the same time has a stimulating action on osteoblasts.The aim of this work is to describe the biological effects of this layer on osteoblasts cultured in vitro. We demonstrate that the nanostructured layer causes an overexpression of many early genes correlated to proteins involved in bone turnover and an increase in the number of surface receptors for α3β1 integrin, talin, paxillin. Analyses at single-cell level, by scanning electron microscopy, atomic force microscopy, and single cell force spectroscopy, show how the proliferation, adhesion and spreading of cells cultured on coated titanium samples are higher than on uncoated titanium ones. Finally, the chemistry of the layer induces a better formation of blood clots and a higher number of adhered platelets, compared to the uncoated cases, and these are useful features to improve the speed of implant osseointegration.In summary, the nanostructured TiC film, due to its physical and chemical properties, can be used to protect the implants and to improve their acceptance by the bone.

  16. Geological Sequestration of CO2 by Hydrous Carbonate Formation with Reclaimed Slag

    Energy Technology Data Exchange (ETDEWEB)

    Von L. Richards; Kent Peaslee; Jeffrey Smith

    2008-02-06

    The concept of this project is to develop a process that improves the kinetics of the hydrous carbonate formation reaction enabling steelmakers to directly remove CO2 from their furnace exhaust gas. It is proposed to bring the furnace exhaust stream containing CO2 in contact with reclaimed steelmaking slag in a reactor that has an environment near the unit activity of water resulting in the production of carbonates. The CO2 emissions from the plant would be reduced by the amount sequestered in the formation of carbonates. The main raw materials for the process are furnace exhaust gases and specially prepared slag.

  17. Origin of abnormal formation of pearlite in medium-carbon steel under nonequilibrium conditions of heating

    Science.gov (United States)

    Mirzaev, D. A.; Yakovleva, I. L.; Tereshchenko, N. A.; Urtsev, V. N.; Degtyarev, V. N.; Shmakov, A. V.

    2016-06-01

    The structure and kinetics of the formation of austenite in medium-carbon steel during shortterm heating above the temperature Ac 1 followed by accelerated cooling are analyzed. It has been shown that the abnormal formation of pearlite in steel results from the concentrational and structural inhomogeneity of austenite, as well as the presence of carbide particles in ferrite areas.

  18. Formation and vibrational structure of Si nano-clusters in ZnO matrix

    Energy Technology Data Exchange (ETDEWEB)

    Garcia-Serrano, J. [Universidad Autonoma del Estado de Hidalgo, Hidalgo (Mexico); Pal, U. [Universidad Autonoma de Puebla, Puebla (Mexico); Koshizaki, N.; Sasaki, T. [National Institute of Materials and Chemical Research, Ibaraki (Japan)

    2001-02-01

    We have studied the formation and vibrational structure of Si nano-clusters in ZnO matrix prepared by radio-frequency (r.f.) co-sputtering, and characterized by Transmission Electron Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS) and Infrared (IR) spectroscopy techniques. The composite films of Si/ZnO were grown o quartz substrates by co-sputtering of Si and ZnO targets. TEM images show a homogeneous distribution of clusters in the matrix with average size varied from 3.7 nm to 34 nm depending on the temperature of annealing. IR absorption measurements revealed the bands correspond to the modes of vibrations of Si{sub 3} in its triangular geometrical structure. By analysing the IR absorption and XPS spectra we found that the nano-clusters consist of a Si{sub 3} core and a SiO{sub x} cap layer. With the increase of annealing temperature, the vibrational states of Si changed from the triplet {sup 3}B1(C2{sub v}) and {sup 3}A'{sub 2}(D{sub 3h}) states to its singlet ground state {sup 1}A{sub 1}(C2{sub v}) and the oxidation state of Si in SiO{sub x} increased. The evolution of the local atomic structure of the Si nano-clusters with the variation of Si content in the film and with the variation of the temperature of annealing are discussed. [Spanish] Se estudia la formacion y estructura vibracional de nano-cumulos de Si en matriz de ZnO preparados por la tecnica de radio-frecuencia (r.f.) co-sputtering, y caracterizados por Microscopia Electronica de Transmision (TEM), Espectroscopia Fotoelectronica de rayos X (XPS) y Espectroscopia de Infrarrojo (IR). Las peliculas compositas de Si/ZnO fueron crecidas sobre sustratos de cuarzo mediante el co-sputtering de blancos de Si y ZnO. Las imagenes de TEM mostraron una distribucion homogenea de cumulos en la matriz con un tamano promedio de 3.7 nm a 34 nm dependiendo de la temperatura de tratamiento. Las mediciones de IR relevaron las bandas correspondientes a los modos de vibracion de Si{sub 3} en su estructura

  19. Techniques for Representation of Regional Clusters in Geographical In-formation Systems

    Directory of Open Access Journals (Sweden)

    Adriana REVEIU

    2011-01-01

    Full Text Available This paper provides an overview of visualization techniques adapted for regional clusters presentation in Geographic Information Systems. Clusters are groups of companies and insti-tutions co-located in a specific geographic region and linked by interdependencies in providing a related group of products and services. The regional clusters can be visualized by projecting the data into two-dimensional space or using parallel coordinates. Cluster membership is usually represented by different colours or by dividing clusters into several panels of a grille display. Taking into consideration regional clusters requirements and the multilevel administrative division of the Romania’s territory, I used two cartograms: NUTS2- regions and NUTS3- counties, to illustrate the tools for regional clusters representation.

  20. Formation of anomalous globular clusters with metallicity spreads: A unified picture

    CERN Document Server

    Bekki, Kenji

    2016-01-01

    Recent observations have revealed that at least 8 globular clusters (GCs) in the Galaxy show internal abundance spreads in [Fe/H]. We investigate the origin of these `anomalous' GCs using numerical simulations of GCs in the dwarfs orbiting around the Galaxy and chemical evolution model of dwarfs hosting the GCs. The principal results are as follows. GCs formed in a host dwarf galaxy with a total mass of ~ 10^10 M_sun can merge to form a single nuclear GC before the host is completely destroyed by the Galaxy, if they are massive (> 3*10^5 M_sun) and if they are formed in the inner region (R<400 pc). The GC merger remnants can capture field stars during its spiral-in to nuclear regions. If two GCs are formed from star formation events separated by ~300 Myr in their host dwarf, then the new GC formed from GC merging can have [Fe/H] spread of 0.2 dex and [Ba/Fe] spread of 0.3 dex. GCs formed from GC merging can show variety of internal abundance spreads depending on the details of their hosts' chemical evoluti...

  1. Recent galaxy mergers and residual star formation of red sequence galaxies in galaxy clusters

    CERN Document Server

    Sheen, Yun-Kyeong; Ree, Chang H; Jaffé, Yara; Demarco, Ricardo; Treister, Ezequiel

    2016-01-01

    This study explored the GALEX ultraviolet (UV) properties of optical red sequence galaxies in 4 rich Abell clusters at z \\leq 0.1. In particular, we tried to find a hint of merger-induced recent star formation (RSF) in red sequence galaxies. Using the NUV - r' colors of the galaxies, RSF fractions were derived based on various criteria for post-merger galaxies and normal galaxies. Following k-correction, about 36% of the post-merger galaxies were classified as RSF galaxies with a conservative criterion (NUV - r' \\leq 5), and that number was doubled (~ 72%) when using a generous criterion (NUV - r' \\leq 5.4). The trend was the same when we restricted the sample to galaxies within 0.5xR_{200}. Post-merger galaxies with strong UV emission showed more violent, asymmetric features in the deep optical images. The RSF fractions did not show any trend along the clustocentric distance within R_{200}. We performed a Dressler-Shectman test to check whether the RSF galaxies had any correlation with the sub-structures in ...

  2. Galaxy and cluster formation in a universe dominated by cold dark matter

    Energy Technology Data Exchange (ETDEWEB)

    Primack, J.R.

    1984-07-01

    The dark matter (DM) that appears to be gravitationally dominant on all astronomical scales larger than the cores of galaxies can be classified, on the basis of its characteristic free-streaming damping mass M/sub D/, as hot (M/sub D/ approx. 10/sup 15/ M/sub mass/), warm (M/sub D/ approx. 10/sup 11/ M/sub mass/), or cold (M/sub D < 10/sup 8/ M/sub mass/). For the case of cold DM, the shape of the DM fluctuation spectrum is determined by (a) the primordial spectrum (on scales larger than the horizon), and (b) stagspansion, the stagnation of the growth of DM fluctuations that enter the horizon while the universe is still radiation-dominated. An attractive feature of the cold dark matter hypothesis is its considerable predictive power: the post-recombination fluctuation spectrum is calculable, and it in turn governs the formation of galaxies and clusters. Good agreement with the data is obtained for a Zeldovich spectrum of primordial fluctuations.

  3. WS2 layer formation on multi-walled carbon nanotubes

    Science.gov (United States)

    Whitby, R. L. D.; Hsu, W. K.; Boothroyd, C. B.; Brigatti, K. S.; Kroto, H. W.; Walton, D. R. M.

    Time-dependent powder X-ray-diffraction analyses reveal that the conversion of WO3 into WS2 on carbon nanotube surfaces in the presence of H2S is a one-step process. The WS2 layers grow simultaneously along the tube in the radial and axial directions.

  4. Formation of silicon carbide nanorods from wood-based carbons

    NARCIS (Netherlands)

    Hata, T; Castro, [No Value; Fujisawa, M; Imamura, Y; Bonnamy, S; Bronsveld, P; Kikuchi, H

    2005-01-01

    Man-made ceramic wood similar to petrified wood found in nature can be used at high temperature as the high oxidation rate of carbon above 500 degrees C is suppressed by a mu m thin SiC coating similar to the shuttle's heat shield. Possible applications are in the field of energy production, e.g., g

  5. Methods and systems for the formation of cyclic carbonates

    Science.gov (United States)

    Hatton, Trevor Alan; Jamison, Timothy F; Kozak, Jennifer Aiden; Simeon, Fritz; Wu, Jie

    2014-12-30

    Described herein are inventive methods for synthesis of cyclic carbonates from CO.sub.2 and epoxide. In some embodiments, the methods are carried out in the presence of a catalyst comprising an electrophilic halogen. In some embodiments, the methods are carried out in a flow reactor.

  6. Megaparsec-Scale Triggers for Star Formation: Clusters and Filaments of Galaxies in the Horologium-Reticulum Supercluster

    CERN Document Server

    Fleenor, Matthew C

    2009-01-01

    Specific indications of star-formation are presented within cluster and filament galaxies that are members of the Horologium-Reticulum supercluster (HRS, z ~0.06). These indicators arise from multi-wavelength observations, primarily emission lines from optical spectroscopy and faint excess from radio continuum (1.4 GHz) photometry. HRS galaxies exhibiting current star formation are consistent with previous studies in that the star-forming populations organize around megaparsec-scale filament axes as well as near the cluster core. Therefore with support from optical photometry, mechanisms for triggering star formation in these galaxies are most likely due to merger interactions in lower density (and lower velocity) environments and possible bursts prior to stripping within the higher density (and higher velocity) environments.

  7. The rise and fall of star-formation in $\\bf z\\sim0.2$ merging galaxy clusters

    CERN Document Server

    Stroe, Andra; Dawson, William; Jee, M James; Hoekstra, Henk; Wittman, David; van Weeren, Reinout J; Brüggen, Marcus; Röttgering, Huub J A

    2014-01-01

    CIZA J2242.8+5301 (`Sausage') and 1RXS J0603.3+4213 (`Toothbrush') are two low-redshift ($z\\sim0.2$), massive ($\\sim2\\times10^{15}M_\\odot$), post-core passage merging clusters, which host shock waves traced by diffuse radio emission. To study their star-formation properties, we uniformly survey the `Sausage' and `Toothbrush' clusters in broad and narrow band filters and select a sample of $201$ and $463$ line emitters, down to a rest-frame equivalent width ($13${\\AA}). We robustly separate between H$\\alpha$ and higher redshift emitters using a combination of optical multi-band (B, g, V, r, i, z) and spectroscopic data. We build H$\\alpha$ luminosity functions for the entire cluster region, near the shock fronts, and away from the shock fronts and find striking differences between the two clusters. In the dynamically younger, $1$ Gyr old `Sausage' cluster we find numerous ($59$) H$\\alpha$ emitters above a star-formation rate (SFR) of $0.17$ M$_{\\odot}$ yr$^{-1}$ surprisingly located in close proximity to the sh...

  8. Gene cloning, purification, and characterization of two cyanobacterial NifS homologs driving iron-sulfur cluster formation.

    Science.gov (United States)

    Kato, S; Mihara, H; Kurihara, T; Yoshimura, T; Esaki, N

    2000-11-01

    Iron-sulfur proteins are essential in the photosynthetic system and many other biological processes. We have isolated and characterized enzymes driving the formation of iron-sulfur clusters from Synechocystis sp. PCC6803. Two genes (slr0387 and sll0704), showing similarity to nifS of Azotobacter vinelandii, were cloned, and their gene products (SsCsdl and SsCsd2) were purified. They catalyzed the desulfuration of L-cysteine. Reconstitution of a [2Fe-2S] cluster of cyanobacterial ferredoxin proceeded much faster in the presence of L-cysteine and either of these enzymes than when using sodium sulfide. These results suggest that SsCsdl and SsCsd2 facilitate the iron-sulfur cluster assembly by producing inorganic sulfur from L-cysteine. Synechocystis sp. PCC6803 has no gene coding for a protein with similarity to the N-terminal domain of NifU of A. vinelandii, which is believed to cooperate with NifS to assemble iron-sulfur clusters. Thus, the cluster formation in the cyanobacterium probably proceeds through a mechanism that is different from that in A. vinelandii.

  9. The Epipolythiodiketopiperazine Gene Cluster in Claviceps purpurea: Dysfunctional Cytochrome P450 Enzyme Prevents Formation of the Previously Unknown Clapurines.

    Directory of Open Access Journals (Sweden)

    Julian Dopstadt

    Full Text Available Claviceps purpurea is an important food contaminant and well known for the production of the toxic ergot alkaloids. Apart from that, little is known about its secondary metabolism and not all toxic substances going along with the food contamination with Claviceps are known yet. We explored the metabolite profile of a gene cluster in C. purpurea with a high homology to gene clusters, which are responsible for the formation of epipolythiodiketopiperazine (ETP toxins in other fungi. By overexpressing the transcription factor, we were able to activate the cluster in the standard C. purpurea strain 20.1. Although all necessary genes for the formation of the characteristic disulfide bridge were expressed in the overexpression mutants, the fungus did not produce any ETPs. Isolation of pathway intermediates showed that the common biosynthetic pathway stops after the first steps. Our results demonstrate that hydroxylation of the diketopiperazine backbone is the critical step during the ETP biosynthesis. Due to a dysfunctional enzyme, the fungus is not able to produce toxic ETPs. Instead, the pathway end-products are new unusual metabolites with a unique nitrogen-sulfur bond. By heterologous expression of the Leptosphaeria maculans cytochrome P450 encoding gene sirC, we were able to identify the end-products of the ETP cluster in C. purpurea. The thioclapurines are so far unknown ETPs, which might contribute to the toxicity of other C. purpurea strains with a potentially intact ETP cluster.

  10. The Epipolythiodiketopiperazine Gene Cluster in Claviceps purpurea: Dysfunctional Cytochrome P450 Enzyme Prevents Formation of the Previously Unknown Clapurines

    Science.gov (United States)

    Tudzynski, Paul; Humpf, Hans-Ulrich

    2016-01-01

    Claviceps purpurea is an important food contaminant and well known for the production of the toxic ergot alkaloids. Apart from that, little is known about its secondary metabolism and not all toxic substances going along with the food contamination with Claviceps are known yet. We explored the metabolite profile of a gene cluster in C. purpurea with a high homology to gene clusters, which are responsible for the formation of epipolythiodiketopiperazine (ETP) toxins in other fungi. By overexpressing the transcription factor, we were able to activate the cluster in the standard C. purpurea strain 20.1. Although all necessary genes for the formation of the characteristic disulfide bridge were expressed in the overexpression mutants, the fungus did not produce any ETPs. Isolation of pathway intermediates showed that the common biosynthetic pathway stops after the first steps. Our results demonstrate that hydroxylation of the diketopiperazine backbone is the critical step during the ETP biosynthesis. Due to a dysfunctional enzyme, the fungus is not able to produce toxic ETPs. Instead, the pathway end-products are new unusual metabolites with a unique nitrogen-sulfur bond. By heterologous expression of the Leptosphaeria maculans cytochrome P450 encoding gene sirC, we were able to identify the end-products of the ETP cluster in C. purpurea. The thioclapurines are so far unknown ETPs, which might contribute to the toxicity of other C. purpurea strains with a potentially intact ETP cluster. PMID:27390873

  11. Star Clusters

    OpenAIRE

    Gieles, M.

    1993-01-01

    Star clusters are observed in almost every galaxy. In this thesis we address several fundamental problems concerning the formation, evolution and disruption of star clusters. From observations of (young) star clusters in the interacting galaxy M51, we found that clusters are formed in complexes of stars and star clusters. These complexes share similar properties with giant molecular clouds, from which they are formed. Many (70%) of the young clusters will not survive the fist 10 Myr, due to t...

  12. Carbon and oxygen isotope variations of the Middle-Late Triassic Al Aziziyah Formation, northwest Libya

    Science.gov (United States)

    Moustafa, Mohamed S. H.; Pope, Michael C.; Grossman, Ethan L.; Mriheel, Ibrahim Y.

    2016-06-01

    This study presents the δ13C and δ18O records from whole rock samples of the Middle-Late Triassic (Ladinian-Carnian) Al Aziziyah Formation that were deposited on a gently sloping carbonate ramp within the Jifarah Basin of Northwest Libya. The Al Aziziyah Formation consists of gray limestone, dolomite, and dolomitic limestone interbedded with shale. The Ghryan Dome and Kaf Bates sections were sampled and analyzed for carbon and oxygen isotope chemostratigraphy to integrate high-resolution carbon isotope data with an outcrop-based stratigraphy, to provide better age control of the Al Aziziyah Formation. This study also discusses the relation between the facies architecture of the Al Aziziyah Formation and the carbon isotope values. Seven stages of relative sea level rise and fall within the Ghryan Dome were identified based on facies stacking patterns, field observations and carbon stable isotopes. The Al Aziziyah Formation δ13C chemostratigraphic curve can be partially correlated with the Triassic global δ13C curve. This correlation indicates that the Al Aziziyah Formation was deposited during the Ladinian and early Carnian. No straight-forward relationship is seen between δ13C and relative sea level probably because local influences complicated systematic environmental and diagenetic isotopic effects associated with sea level change.

  13. Molecular dynamics simulation of melting and crystallization processes of polyethylene clusters confined in armchair single-walled carbon nanotubes.

    Science.gov (United States)

    Zhou, Zhou; Wang, Jinjian; Zhu, Xiaolei; Lu, Xiaohua; Guan, Wenwen; Yang, Yuchen

    2015-01-01

    The confined interaction is important to understand the melting and crystallization of polymers within single-wall carbon tube (SWNT). However, it is difficult for us to observe this interaction. In the current work, the structures and behaviors of melting and crystallization for polyethylene (PE) clusters confined in armchair single-walled carbon nanotubes ((n,n)-SWNTs) are investigated and examined based on molecular dynamics (MD) simulations. The nonbonded energies, structures, Lindemman indices, radial density distributions, and diffusion coefficients are used to demonstrate the features of melting phase transition for PE clusters confined in (n,n)-SWNTs. The chain end-to-end distance (R(n)) and chain end-to-end distribution are used to examine the flexibility of the PE chain confined in SWNT. The global orientational order parameter (P2) is employed to reveal the order degree of whole PE polymer. The effect of polymerization degree on melting temperature and the influence of SWNT chirality on structure of PE cluster are examined and discussed. Results demonstrate that within the confined environment of SWNT, PE clusters adopt novel co-axial crystalline layer structure, in which parallel chains of each layer are approximately vertical to tube axis. The disordered-ordered transformation of PE chains in each layer is an important structural feature for crystallization of confined PE clusters. SWNTs have a considerable effect on the structures and stabilities of the confined PE clusters.

  14. Kinetics of austenite formation during continuous heating in a low carbon steel

    OpenAIRE

    Oliveira, Fernando Lucas Gonçalves e; Andrade, Margareth Spangler; Cota, André Barros

    2007-01-01

    The kinetics and microstructural evolution of austenite formation in a low carbon steel, with initial microstructure composed of ferrite and pearlite, were studied during continuous heating, by using dilatometric analysis and measurements of microstructural parameters. The formation of austenite was observed to occur in two stages: (a) pearlite dissolution and (b) ferrite to austenite transformation. The critical temperatures of austenite formation in continuous heating increase with increasi...

  15. Distribution of star formation rates during the rapid assembly of NGC 1399 as deduced from its globular cluster system

    CERN Document Server

    Schulz, C; Kroupa, P; Pflamm-Altenburg, J

    2016-01-01

    Ultra-compact dwarf galaxies (UCDs) share many properties with globular clusters (GCs) and are found in similar environments. A large sample of UCDs and GCs around NGC 1399, the central giant elliptical of the Fornax galaxy cluster, is used to infer their formation history and also that of NGC 1399. We assumed that all GCs and UCDs in our sample are star clusters (SCs) and used them as tracers of past star formation activities. After correcting our GC/UCD sample for mass loss, we interpreted their overall mass function to be a superposition of SC populations that formed coevally during different times. The SC masses of each population were distributed according to the embedded cluster mass function (ECMF), a pure power law with the slope $-\\beta$ and a stellar upper mass limit, $M_{\\mathrm{max}}$, which depended on the star formation rate (SFR). We decomposed the observed GC/UCD mass function into individual SC populations and converted $M_{\\mathrm{max}}$ of each SC population to an SFR. The overall distribut...

  16. Undergraduate ALFALFA Team: Analysis of Spatially-Resolved Star-Formation in Nearby Galaxy Groups and Clusters

    Science.gov (United States)

    Finn, Rose; Collova, Natasha; Spicer, Sandy; Whalen, Kelly; Koopmann, Rebecca A.; Durbala, Adriana; Haynes, Martha P.; Undergraduate ALFALFA Team

    2017-01-01

    As part of the Undergraduate ALFALFA Team, we are conducting a survey of the gas and star-formation properties of galaxies in 36 groups and clusters in the local universe. The galaxies in our sample span a large range of galactic environments, from the centers of galaxy groups and clusters to the surrounding infall regions. One goal of the project is to map the spatial distribution of star-formation; the relative extent of the star-forming and stellar disks provides important information about the internal and external processes that deplete gas and thus drive galaxy evolution. We obtained wide-field H-alpha observations with the WIYN 0.9m telescope at Kitt Peak National Observatory for galaxies in the vicinity of the MKW11 and NRGb004 galaxy groups and the Abell 1367 cluster. We present a preliminary analysis of the relative size of the star-forming and stellar disks as a function of galaxy morphology and local galaxy density, and we calculate gas depletion times using star-formation rates and HI gas mass. We will combine these results with those from other UAT members to determine if and how environmentally-driven gas depletion varies with the mass and X-ray properties of the host group or cluster. This work has supported by NSF grants AST-0847430, AST-1211005 and AST-1637339.

  17. Formation of globular clusters in atomic-cooling halos via rapid gas condensation and fragmentation during the epoch of reionization

    CERN Document Server

    Kimm, Taysun; Rosdahl, Joakim; Yi, Sukyoung

    2015-01-01

    We investigate the formation of metal-poor globular clusters (GCs) at the center of two dark matter halos with $M_{halo}\\sim4\\times10^7\\,M_\\odot$ at $z>10$ using cosmological radiation-hydrodynamics simulations. We find that very compact ($\\lesssim$ 1 pc) and massive ($\\sim6\\times10^5\\,M_\\odot$) clusters form rapidly when pristine gas collapses isothermally with the aid of efficient Ly$\\alpha$ emission during the transition from molecular-cooling halos to atomic-cooling halos. Because the local free-fall time of dense star-forming gas is very short ($\\ll 1\\,{\\rm Myr}$), a large fraction of the collapsed gas is turned into stars before stellar feedback processes blow out the gas and shut down star formation. Although the early stage of star formation is limited to a small region of the central star-forming disk, we find that the disk quickly fragments due to metal enrichment from supernovae. Sub-clusters formed in the fragmented clouds eventually merge with the main cluster at the center. We estimate using a s...

  18. Negative Ion Photoelectron Spectroscopy Reveals Thermodynamic Advantage of Organic Acids in Facilitating Formation of Bisulfate Ion Clusters: Atmospheric Implications

    Energy Technology Data Exchange (ETDEWEB)

    Hou, Gao-Lei; Lin, Wei; Deng, Shihu; Zhang, Jian; Zheng, Weijun; Paesani, Francesco; Wang, Xue B.

    2013-03-07

    Recent lab and field measurements have indicated critical roles of organic acids in enhancing new atmospheric aerosol formation. Such findings have stimulated theoretical studies with the aim of understanding interaction of organic acids with common aerosol nucleation precursors like bisulfate (HSO4-). In this Letter, we report a combined negative ion photoelectron spectroscopic and theoretical investigation of molecular clusters formed by HSO4- with succinic acid (SUA, HO2C(CH2)2CO2H), HSO4-(SUA)n (n = 0-2), along with HSO4-(H2O)n and HSO4-(H2SO4)n. It is found that one SUA molecule can stabilize HSO4- by ca. 39 kcal/mol, triple the corresponding value that one water molecule is capable of (ca. 13 kcal/mol). Molecular dynamics simulations and quantum chemical calculations reveal the most plausible structures of these clusters and attribute the stability of these clusters due to formation of strong hydrogen bonds. This work provides direct experimental evidence showing significant thermodynamic advantage by involving organic acid molecules to promote formation and growth in bisulfate clusters and aerosols.

  19. Lack of nuclear clusters in dwarf spheroidal galaxies: implications for massive black holes formation and the cusp/core problem

    Science.gov (United States)

    Arca-Sedda, Manuel; Capuzzo-Dolcetta, Roberto

    2017-01-01

    One of the leading scenarios for the formation of nuclear star clusters in galaxies is related to the orbital decay of globular clusters (GCs) and their subsequent merging, though alternative theories are currently debated. The availability of high-quality data for structural and orbital parameters of GCs allows us to test different nuclear star cluster formation scenarios. The Fornax dwarf spheroidal (dSph) galaxy is the heaviest satellite of the Milky Way and it is the only known dSph hosting five GCs, whereas there are no clear signatures for the presence of a central massive black hole. For this reason, it represents a suited place to study the orbital decay process in dwarf galaxies. In this paper, we model the future evolution of the Fornax GCs simulating them and the host galaxy by means of direct N-body simulations. Our simulations also take into account the gravitational field generated by the Milky Way. We found that if the Fornax galaxy is embedded in a standard cold dark matter halo, the nuclear cluster formation would be significantly hampered by the high central galactic mass density. In this context, we discuss the possibility that infalling GCs drive the flattening of the galactic density profile, giving a possible alternative explanation to the so-called cusp/core problem. Moreover, we briefly discuss the link between GC infall process and the absence of massive black holes in the centre of dSphs.

  20. Thermodynamic analysis of