Science.gov

Sample records for formation drives cluster

  1. Gene cloning, purification, and characterization of two cyanobacterial NifS homologs driving iron-sulfur cluster formation.

    PubMed

    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.

  2. Equilibrium Star Cluster Formation

    NASA Astrophysics Data System (ADS)

    Tan, Jonathan C.; Krumholz, Mark R.; McKee, Christopher F.

    2006-04-01

    We argue that rich star clusters take at least several local dynamical times to form and so are quasi-equilibrium structures during their assembly. Observations supporting this conclusion include morphologies of star-forming clumps, momentum flux of protostellar outflows from forming clusters, age spreads of stars in the Orion Nebula cluster (ONC) and other clusters, and the age of a dynamical ejection event from the ONC. We show that these long formation timescales are consistent with the expected star formation rate in turbulent gas, as recently evaluated by Krumholz & McKee. Finally, we discuss the implications of these timescales for star formation efficiencies, the disruption of gas by stellar feedback, mass segregation of stars, and the longevity of turbulence in molecular clumps.

  3. Persistence drives gene clustering in bacterial genomes

    PubMed Central

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

    2008-01-01

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

  4. Formation and Assembly of Massive Star Clusters

    NASA Astrophysics Data System (ADS)

    McMillan, Stephen

    open access to state-of- the-art simulation techniques within a modern, modular software environment. We will follow the gravitational collapse of 0.1-10 million-solar mass gas clouds through star formation and coalescence into a star cluster, modeling in detail the coupling of the gas and the newborn stars. We will study the effects of star formation by detecting accreting regions of gas in self-gravitating, turbulent, MHD, FLASH models that we will translate into collisional dynamical systems of stars modeled with an N-body code, coupled together in the AMUSE framework. Our FLASH models will include treatments of radiative transfer from the newly formed stars, including heating and radiative acceleration of the surrounding gas. Specific questions to be addressed are: (1) How efficiently does the gas in a star forming region form stars, how does this depend on mass, metallicity, and other parameters, and what terminates star formation? What observational predictions can be made to constrain our models? (2) How important are different mechanisms for driving turbulence and removing gas from a cluster: accretion, radiative feedback, and mechanical feedback? (3) How does the infant mortality rate of young clusters depend on the initial properties of the parent cloud? (4) What are the characteristic formation timescales of massive star clusters, and what observable imprints does the assembly process leave on their structure at an age of 10-20 Myr, when formation is essentially complete and many clusters can be observed? These studies are directly relevant to NASA missions at many electromagnetic wavelengths, including Chandra, GALEX, Hubble, and Spitzer. Each traces different aspects of cluster formation and evolution: X-rays trace supernovae, ultraviolet traces young stars, visible colors can distinguish between young blue stars and older red stars, and the infrared directly shows young embedded star clusters.

  5. Polyaspartic acid facilitates oxolation within iron(iii) oxide pre-nucleation clusters and drives the formation of organic-inorganic composites

    NASA Astrophysics Data System (ADS)

    Scheck, J.; Drechsler, M.; Ma, X.; Stöckl, M. T.; Konsek, J.; Schwaderer, J. B.; Stadler, S. M.; De Yoreo, J. J.; Gebauer, D.

    2016-12-01

    The interplay between polymers and inorganic minerals during the formation of solids is crucial for biomineralization and bio-inspired materials, and advanced material properties can be achieved with organic-inorganic composites. By studying the reaction mechanisms, basic questions on organic-inorganic interactions and their role during material formation can be answered, enabling more target-oriented strategies in future synthetic approaches. Here, we present a comprehensive study on the hydrolysis of iron(iii) in the presence of polyaspartic acid. For the basic investigation of the formation mechanism, a titration assay was used, complemented by microscopic techniques. The polymer is shown to promote precipitation in partly hydrolyzed reaction solutions at the very early stages of the reaction by facilitating iron(iii) hydrolysis. In unhydrolyzed solutions, no significant interactions between the polymer and the inorganic solutes can be observed. We demonstrate that the hydrolysis promotion by the polymer can be understood by facilitating oxolation in olation iron(iii) pre-nucleation clusters. We propose that the adsorption of olation pre-nucleation clusters on the polymer chains and the resulting loss in dynamics and increased proximity of the reactants is the key to this effect. The resulting composite material obtained from the hydrolysis in the presence of the polymer was investigated with additional analytical techniques, namely, scanning and transmission electron microscopies, light microscopy, atomic force microscopy, zeta potential measurements, dynamic light scattering, and thermogravimetric analyses. It consists of elastic, polydisperse nanospheres, ca. 50-200 nm in diameter, and aggregates thereof, exhibiting a high polymer and water content.

  6. Formation of Cluster Complexes by Cluster-Cluster-Collisions

    NASA Astrophysics Data System (ADS)

    Ichihashi, Masahiko; Odaka, Hideho

    2015-03-01

    Multi-element clusters are interested in their chemical and physical properties, and it is expected that they are utilized as catalysts, for example. Their properties critically depend on the size, composition and atomic ordering, and it should be important to adjust the above parameters for their functionality. One of the ways to form a multi-element cluster is to employ a low-energy collision between clusters. Here, we show characteristic results obtained in the collision between a neutral Ar cluster and a size-selected Co cluster ion. Low-energy collision experiment was accomplished by using a newly developed merging-beam apparatus. Cobalt cluster ions were produced by laser ablation, and mass-selected. On the other hand, argon clusters were prepared by the supersonic expansion of Ar gas. Both cluster beams were merged together in an ion guide, and ionic cluster complexes were mass-analyzed. In the collision of Co2+ and ArN, Co2Arn+ (n = 1 - 30) were observed, and the total intensity of Co2Arn+ (n >= 1) is inversely proportional to the relative velocity between Co2+ and ArN. This suggests that the charge-induced dipole interaction between Co2+ and a neutral Ar cluster is dominant in the formation of the cluster complex, Co2+Arn.

  7. Galaxy formation through hierarchical clustering

    NASA Technical Reports Server (NTRS)

    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.

  8. Galaxy formation through hierarchical clustering

    NASA Technical Reports Server (NTRS)

    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.

  9. Cluster formation in rarefied water vapour plume

    NASA Astrophysics Data System (ADS)

    Bykov, Nikolay Y.; Gorbachev, Yuriy E.

    2017-07-01

    Mathematical model of water cluster formation has been developed and applied for the Direct Simulation Monte Carlo of water vapour expansion from the reservoir with constant stagnation parameters. The influence of flow rarefaction on plume parameters and on peculiarities of cluster formation process are analyzed. Comparison of simulation results with experimental data is performed.

  10. Star formation and substructure in galaxy clusters

    SciTech Connect

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

    2014-03-10

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

  11. On the formation process of charged clusters

    NASA Astrophysics Data System (ADS)

    Wang, Youmei; Chen, Qi; Yu, M. Y.

    2016-11-01

    The clustering process of charged grains often resembles a formation stage of colloidal and spongy matter, as well as some astrophysical objects. In this paper, molecular dynamics simulation is used to simulate the formation process of clusters of massive charged grains in plasmas. It is found that, from an initially uniform distribution of grains with Maxwellian velocity distribution, a statistically stationary system of clusters, each with different dynamic as well as thermodynamic characteristics, can form. The dependence of the asymptotic, of the final, state of the cluster system on the initial temperature and density of the grains is discussed.

  12. Individualization as Driving Force of Clustering Phenomena in Humans

    PubMed Central

    Mäs, Michael; Flache, Andreas; Helbing, Dirk

    2010-01-01

    One of the most intriguing dynamics in biological systems is the emergence of clustering, in the sense that individuals self-organize into separate agglomerations in physical or behavioral space. Several theories have been developed to explain clustering in, for instance, multi-cellular organisms, ant colonies, bee hives, flocks of birds, schools of fish, and animal herds. A persistent puzzle, however, is the clustering of opinions in human populations, particularly when opinions vary continuously, such as the degree to which citizens are in favor of or against a vaccination program. Existing continuous opinion formation models predict “monoculture” in the long run, unless subsets of the population are perfectly separated from each other. Yet, social diversity is a robust empirical phenomenon, although perfect separation is hardly possible in an increasingly connected world. Considering randomness has not overcome the theoretical shortcomings so far. Small perturbations of individual opinions trigger social influence cascades that inevitably lead to monoculture, while larger noise disrupts opinion clusters and results in rampant individualism without any social structure. Our solution to the puzzle builds on recent empirical research, combining the integrative tendencies of social influence with the disintegrative effects of individualization. A key element of the new computational model is an adaptive kind of noise. We conduct computer simulation experiments demonstrating that with this kind of noise a third phase besides individualism and monoculture becomes possible, characterized by the formation of metastable clusters with diversity between and consensus within clusters. When clusters are small, individualization tendencies are too weak to prohibit a fusion of clusters. When clusters grow too large, however, individualization increases in strength, which promotes their splitting. In summary, the new model can explain cultural clustering in human societies

  13. Individualization as driving force of clustering phenomena in humans.

    PubMed

    Mäs, Michael; Flache, Andreas; Helbing, Dirk

    2010-10-21

    One of the most intriguing dynamics in biological systems is the emergence of clustering, in the sense that individuals self-organize into separate agglomerations in physical or behavioral space. Several theories have been developed to explain clustering in, for instance, multi-cellular organisms, ant colonies, bee hives, flocks of birds, schools of fish, and animal herds. A persistent puzzle, however, is the clustering of opinions in human populations, particularly when opinions vary continuously, such as the degree to which citizens are in favor of or against a vaccination program. Existing continuous opinion formation models predict "monoculture" in the long run, unless subsets of the population are perfectly separated from each other. Yet, social diversity is a robust empirical phenomenon, although perfect separation is hardly possible in an increasingly connected world. Considering randomness has not overcome the theoretical shortcomings so far. Small perturbations of individual opinions trigger social influence cascades that inevitably lead to monoculture, while larger noise disrupts opinion clusters and results in rampant individualism without any social structure. Our solution to the puzzle builds on recent empirical research, combining the integrative tendencies of social influence with the disintegrative effects of individualization. A key element of the new computational model is an adaptive kind of noise. We conduct computer simulation experiments demonstrating that with this kind of noise a third phase besides individualism and monoculture becomes possible, characterized by the formation of metastable clusters with diversity between and consensus within clusters. When clusters are small, individualization tendencies are too weak to prohibit a fusion of clusters. When clusters grow too large, however, individualization increases in strength, which promotes their splitting. In summary, the new model can explain cultural clustering in human societies

  14. Globular Cluster formation in a collapsing supershell

    NASA Astrophysics Data System (ADS)

    Recchi, S.; Wünsch, R.; Palouš, J.; Dinnbier, F.

    2017-10-01

    Primordial clouds are supposed to host the so-called population III stars. These stars are very massive and completely metal-free. The final stage of the life of population III stars with masses between 130 and 260 solar masses is a very energetic hypernova explosion. A hypernova drives a shock, behind which a spherically symmetric very dense supershell forms, which might become gravitationally unstable, fragment, and form stars. In this paper we study under what conditions can an expanding supershell become gravitationally unstable and how the feedback of these supershell stars (SSSs) affects its surroundings. We simulate, by means of a 1-D Eulerian hydrocode, the early evolution of the primordial cloud after the hypernova explosion, the formation of SSSs, and the following evolution, once the SSSs start to release energy and heavy elements into the interstellar medium. Our results indicate that a shell, enriched with nucleosynthetic products from SSSs, propagates inwards, towards the center of the primordial cloud. In a time span of a few Myr, this inward-propagating shell reaches a distance of only a few parsec away from the center of the primordial cloud. Its density is extremely high and its temperature very low, thus the conditions for a new episode of star formation are achieved. We study what fraction of these two distinct populations of stars can remain bound and survive until the present day. We study also under what conditions can this process repeat and form multiple stellar populations. We extensively discuss whether the proposed scenario can help to explain some open questions of the formation mechanism of globular clusters.

  15. Tracking star formation in dwarf cluster galaxies

    NASA Astrophysics Data System (ADS)

    Rude, Cody Millard

    The evolution of galaxies in dense environments can be affected by close encounters with neighboring galaxies and interactions with the intracluster medium (ICM). Dwarf galaxies may be especially susceptible to these effects due to their low mass. The goal of my dissertation research is to look for signs of star formation in cluster dwarf galaxies by measuring and comparing the r- and u-band luminosity functions of 15 low redshift Abell galaxy clusters using archival data from the Canada-France-Hawaii Telescope (CFHT). Luminosity functions, dwarf-to-giant ratios, and blue fractions are measured in four cluster-centric annuli from stacked cluster data. To account for differences in cluster optical richness, each cluster is scaled according to r200, where r200 is the radius of a sphere, centered on the cluster, whose average density is 200 times the critical density of the universe. The outer region of the cluster sample shows an increase in the faint-end slope of the u-band luminosity function relative to the r-band, indicating star formation in dwarf galaxies. The blue fraction for dwarf galaxies steadily rises with increasing cluster-centric radii. The change in the blue fraction of giant galaxies also increases, but at a lower rate. Additionally, the inner regions of clusters ranging from 0.185 < z < 0.7 from the "Cluster Lensing and Supernova survey with Hubble (CLASH)" are used to generate blue- and red-band luminosity functions, dwarf-to-giant ratios, and blue fractions. Comparisons of the inner region of the CLASH and CFHT clusters show an increase in the blue fraction of dwarf galaxies with redshift that is not present in giant galaxies.

  16. Cluster formation and evolution in M51

    NASA Astrophysics Data System (ADS)

    Messa, Matteo Maria; Adamo, Angela

    2015-08-01

    While star formation has been long studied on the single-star scale and on the galaxy scale, the link between these two widely separated scales still needs to be firmly established. LEGUS (Legacy Extra Galactic UV Survey) has collected HST observations of 50 nearby galaxies (closer than 12 Mpc) in five bands, NUV,U,B,V,I. The main goal of this survey is the study of stellar clustering formation and evolution at all scales. The proximity of the galaxies allows us to resolve all the galaxy's components, from stars, to associations, to star clusters.In this poster we will present the cluster population properties of the nearby interacting spiral galaxy M51. M51 is one on the galaxies with the highest SFR in the LEGUS sample. It is certainly one of the most studied nearby galaxies at any wavelength range. The current star cluster analysis is providing multiband luminosities, ages, masses, and extinctions of the huge cluster population sample (more than 10 000 clusters). The cluster population is analyzed as a function of the different galactic environments of M51 (e.g. arm and inter-arm regions, circum-nuclear ring, bar, etc.). The aim is to understand if the cluster properties change as function of the environment where they form and interact.

  17. Star and cluster formation in NGC 1275

    NASA Technical Reports Server (NTRS)

    Richer, Harvey B.; Crabtree, Dennis R.; Fabian, A. C.; Lin, D. N. C.

    1993-01-01

    Luminous, blue, and unresolved objects have been found by imaging the nuclear region of the central galaxy in the Perseus Cluster, NGC 1275. Stellar formation in a cooling flow in which gas clouds confined by weak magnetic fields are allowed to remain at low densities is favored. Cloud-cloud collisions and coagulation in the high cloud density environment at the center of the galaxy then causes some clouds to become gravitationally unstable and to form globular clusters.

  18. A study of globular cluster formation in hierarchical clustering scenarios

    NASA Astrophysics Data System (ADS)

    Pellizza González, L. J.; Tissera, P. B.; García Lambas, D.; Forte, J. C.

    In this work we present preliminary results of a study of the formation of globular clusters (GCs) in hierarchical clustering scenarios. We used hydrodynamical numerical simulations which include star formation and chemical enrichment by supernovae Ia and II in a cosmological framework (Tissera, Lambas y Abadi 1997, Tissera et al. 2001, Mosconi et al. 2001) for the description of the formation of galactic-like objects (GLO) and their stellar populations. Based on these simulations we implemented a model for GC formation, which assumes that GCs are formed in high star formation efficiency periods. Hence, using the star formation history given by the simulations we determined the GC populations formed in each GLO and their astrophysical properties (age, metallicity, colour). We studied the origin of each GC population and found that it is related to violent events (e.g. collapse, mergers). We observed that the simulated GC populations are old (age >8 Gyr), consistently with observations, and that their metallicity is related to the particular kind of event (collapse, orbital decay or final fusion in a merger event). The combination of the different GC populations of a GLO shows, in some cases, a bimodal metallicity and colour distribution cualitatively similar to the ones observed in the GC systems of some galaxies. Nevertheless, the observed parameters of these distributions could not be reproduced cuantitatively. We are working on an improvement of our model (Pellizza González et al. 2003) and also on the use of higher numerical resolution simulations to study this problem.

  19. Quenching star formation in cluster galaxies

    NASA Astrophysics Data System (ADS)

    Taranu, Dan S.; Hudson, Michael J.; Balogh, Michael L.; Smith, Russell J.; Power, Chris; Oman, Kyle A.; Krane, Brad

    2014-05-01

    In order to understand the processes that quench star formation in cluster galaxies, we construct a library of subhalo orbits drawn from Λ cold dark matter cosmological N-body simulations of four rich clusters. We combine these orbits with models of star formation followed by environmental quenching, comparing model predictions with observed bulge and disc colours and stellar absorption line-strength indices of luminous cluster galaxies. Models in which the bulge stellar populations depend only on the galaxy subhalo mass while the disc is quenched upon infall are acceptable fits to the data. An exponential disc quenching time-scale of 3-3.5 Gyr is preferred. Quenching in lower mass groups prior to infall (`pre-processing') provides better fits, with similar quenching time-scales. Models with short (≲1 Gyr) quenching time-scales yield excessively steep cluster-centric gradients in disc colours and Balmer line indices, even if quenching is delayed for several Gyr. The data slightly prefer models where quenching occurs only for galaxies falling within ˜0.5r200. These results imply that the environments of rich clusters must impact star formation rates of infalling galaxies on relatively long time-scales, indicative of gentler quenching mechanisms such as slow `strangulation' over more rapid ram-pressure stripping.

  20. The Formation of Galaxies and Clusters.

    ERIC Educational Resources Information Center

    Gregory, Stephen; Morrison, Nancy D.

    1985-01-01

    Summarizes recent research on the formation of galaxies and clusters, focusing on research examining how the materials in galaxies seen today separated from the universal expansion and collapsed into stable bodies. A list of six nontechnical books and articles for readers with less background is included. (JN)

  1. Globular cluster formation - The fossil record

    NASA Technical Reports Server (NTRS)

    Murray, Stephen D.; Lin, Douglas N. C.

    1992-01-01

    Properties of globular clusters which have remained unchanged since their formation are used to infer the internal pressures, cooling times, and dynamical times of the protocluster clouds immediately prior to the onset of star formation. For all globular clusters examined, it is found that the cooling times are much less than the dynamical times, implying that the protoclusters must have been maintained in thermal equilibrium by external heat sources, with fluxes consistent with those found in previous work, and giving the observed rho-T relation. Self-gravitating clouds cannot be stably heated, so that the Jeans mass forms an upper limit to the cluster masses. The observed dependence of protocluster pressure upon galactocentric position implies that the protocluster clouds were in hydrostatic equilibrium after their formation. The pressure dependence is well fitted by that expected for a quasi-statically evolving background hot gas, shock heated to its virial temperature. The observations and inferences are combined with previous theoretical work to construct a picture of globular cluster formation.

  2. The Formation of Galaxies and Clusters.

    ERIC Educational Resources Information Center

    Gregory, Stephen; Morrison, Nancy D.

    1985-01-01

    Summarizes recent research on the formation of galaxies and clusters, focusing on research examining how the materials in galaxies seen today separated from the universal expansion and collapsed into stable bodies. A list of six nontechnical books and articles for readers with less background is included. (JN)

  3. Globular cluster formation - The fossil record

    NASA Technical Reports Server (NTRS)

    Murray, Stephen D.; Lin, Douglas N. C.

    1992-01-01

    Properties of globular clusters which have remained unchanged since their formation are used to infer the internal pressures, cooling times, and dynamical times of the protocluster clouds immediately prior to the onset of star formation. For all globular clusters examined, it is found that the cooling times are much less than the dynamical times, implying that the protoclusters must have been maintained in thermal equilibrium by external heat sources, with fluxes consistent with those found in previous work, and giving the observed rho-T relation. Self-gravitating clouds cannot be stably heated, so that the Jeans mass forms an upper limit to the cluster masses. The observed dependence of protocluster pressure upon galactocentric position implies that the protocluster clouds were in hydrostatic equilibrium after their formation. The pressure dependence is well fitted by that expected for a quasi-statically evolving background hot gas, shock heated to its virial temperature. The observations and inferences are combined with previous theoretical work to construct a picture of globular cluster formation.

  4. Formation of globular clusters with multiple populations

    NASA Astrophysics Data System (ADS)

    Decressin, T.

    2017-03-01

    Spectroscopic and photometric evidences have led to a complete revision of our understanding of globular clusters with the discovery of multiple stellar populations which differ chemically. Whereas some stars have a chemical composition similar to fields stars, others show large star-to-star variations in light elements (Li to Al) while their composition in iron and heavy elements stay constant. This peculiar chemical pattern can be explained by self-pollution of the intracluster gas occurring in the early evolution of clusters. Here the possible impact from a first generation of fast rotating stars to the early evolution of globular clusters is presented. The high rotation velocity will allow the stars to rotate at the break-up velocity and release matter enrich in H-burning which in turn will produce new stars with a chemical composition in agreement with observations. The massive stars have also an important role to clear the cluster from the remaining gas left after the star formation episodes. If the gas expulsion is fast enough, the strong change in the potential well will lead to the loss of stars occupying the outer part of the cluster. As second generation stars are preferentially born in the cluster centre, the ratio of second to first generation stars will increase over time to match the present ratio determined by observations. Considerations on the properties of low-mass stars still present in globular clusters will also be presented.

  5. The Environmental Factor: Driving the Onset and Early Evolution of High-Mass Stars and Clusters

    NASA Astrophysics Data System (ADS)

    Rivera-Ingraham, Alana; Marston, Anthony; Martin, Peter; Ristorcelli, Isabelle; Juvela, Mika

    2015-08-01

    While the process leading to the formation of low-mass stars is reasonably well established, the origin of their high-mass counterparts, and in particular, the link with the properties and evolution of the parental structures, remains poorly understood. The key role that high-mass stars and massive clusters play in driving the evolution of the ISM, from planetary to galactic scales, makes this study, however, particularly critical.Here we present the latest results from an ongoing Herschel-based project of high-mass star formation in the Outer Galaxy, and which aims to quantify the complex dependence between the final characteristics of young high-mass stars and the early evolution of their local environment.Datasets from the Herschel imaging survey of OB Young Stellar objects (HOBYS; PI. F. Motte) and the Herschel infrared Galactic Plane Survey (Hi-Gal; PI. S. Molinari) Key Programmes are used as a base to carry out an in-depth examination of the cloud physical characteristics, compact source population, and star formation history of those regions with the potential for (and on-going) high-mass star and cluster formation. Results from this study are compelling evidence for the requirement of local external processes, such as stellar feedback (e.g., Convergent Constructive Feedback model; Rivera-Ingraham et al. 2013), in order to counteract the limitations of gravity in the formation and evolution of dense and exotic environments. We will describe how such processes could drive the formation and evolution of the parental host, and therefore influence the final characteristics of the young high-mass stars and clusters (Rivera-Ingraham, et al. 2015a; 2015b, in prep). Our conclusions are further supported by an extensive independent analysis of filamentary properties as a function of Galactic environment (Rivera-Ingraham et al. 2015c; subm), and which we will present as part of the Galactic Cold Cores Key Programme (PI. M. Juvela).

  6. Simulating Stellar Cluster Formation and Early Evolution

    NASA Astrophysics Data System (ADS)

    Wall, Joshua; McMillan, Stephen L. W.; Mac Low, Mordecai-Mark; Ibañez-Mejia, Juan; Portegies Zwart, Simon; Pellegrino, Andrew

    2017-01-01

    We present our current development of a model of stellar cluster formation and evolution in the presence of stellar feedback. We have integrated the MHD code Flash into the Astrophysical Multi-Use Software Environment (AMUSE) and coupled the gas dynamics to an N-body code using a Fujii gravity bridge. Further we have integrated feedback from radiation using the FERVENT module for Flash, supernovae by thermal and kinetic energy injection, and winds by kinetic energy injection. Finally we have developed a method of implementing star formation using the Jeans criterion of the gas. We present initial results from our cluster formation model in a cloud using self-consistent boundary conditions drawn from a model of supernova-driven interstellar turbulence.

  7. Formation History of Old Star Clusters

    NASA Astrophysics Data System (ADS)

    Schweizer, Francois

    Even at the present time globular clusters form during collisions and mergers of gas-rich galaxies by the hundreds. Their subsequent evolution can be traced through observations of merging galaxies and their remnants of different ages all the way to old ellipticals. I shall review what we have learned about the globular-cluster formation process itself and about the evolution of the clusters' color distributions luminosity functions and radial distributions. In brief these observations suggest that 2nd-generation metal-enriched globulars form from giant molecular clouds shocked by the rapid pressure increase in the merger-induced starbursts. By analogy ancient metal-poor globular clusters may have formed in a similar manner from early giant molecular clouds. A prime suspect to have triggered their formation is the general pressure increase occurring during cosmological reionization at z = ~10 - 30. The general nature of this pressure increase would explain why first-generation metal-poor globulars form a nearly universal cluster population

  8. Oak Ridge Institutional Cluster Autotune Test Drive Report

    SciTech Connect

    Jibonananda, Sanyal; New, Joshua Ryan

    2014-02-01

    The Oak Ridge Institutional Cluster (OIC) provides general purpose computational resources for the ORNL staff to run computation heavy jobs that are larger than desktop applications but do not quite require the scale and power of the Oak Ridge Leadership Computing Facility (OLCF). This report details the efforts made and conclusions derived in performing a short test drive of the cluster resources on Phase 5 of the OIC. EnergyPlus was used in the analysis as a candidate user program and the overall software environment was evaluated against anticipated challenges experienced with resources such as the shared memory-Nautilus (JICS) and Titan (OLCF). The OIC performed within reason and was found to be acceptable in the context of running EnergyPlus simulations. The number of cores per node and the availability of scratch space per node allow non-traditional desktop focused applications to leverage parallel ensemble execution. Although only individual runs of EnergyPlus were executed, the software environment on the OIC appeared suitable to run ensemble simulations with some modifications to the Autotune workflow. From a standpoint of general usability, the system supports common Linux libraries, compilers, standard job scheduling software (Torque/Moab), and the OpenMPI library (the only MPI library) for MPI communications. The file system is a Panasas file system which literature indicates to be an efficient file system.

  9. Burst of Star Formation Drives Galactic Bubble

    NASA Technical Reports Server (NTRS)

    2001-01-01

    NASA's Hubble Space Telescope (HST) captures a lumpy bubble of hot gas rising from a cauldron of glowing matter in Galaxy NGC 3079, located 50 million light-years from Earth in the constellation Ursa Major. Astronomers suspect the bubble is being blown by 'winds' or high speed streams of particles, released during a burst of star formation. The bubble's lumpy surface has four columns of gaseous filaments towering above the galaxy's disc that whirl around in a vortex and are expelled into space. Eventually, this gas will rain down on the disc and may collide with gas clouds, compress them, and form a new generation of stars.

  10. In vivo iron–sulfur cluster formation

    PubMed Central

    Raulfs, Estella C.; O'Carroll, Ina P.; Dos Santos, Patricia C.; Unciuleac, Mihaela-Carmen; Dean, Dennis R.

    2008-01-01

    It has been proposed that iron–sulfur [Fe-S] clusters destined for the maturation of [Fe-S] proteins can be preassembled on a molecular scaffold designated IscU. In the present article, it is shown that production of the intact Azotobacter vinelandii [Fe-S] cluster biosynthetic machinery at levels exceeding the amount required for cellular maturation of [Fe-S] proteins results in the accumulation of: (i) apo-IscU, (ii) an oxygen-labile [2Fe-2S] cluster-loaded form of IscU, and (iii) IscU complexed with the S-delivery protein, IscS. It is suggested that these species represent different stages of the [Fe-S] cluster assembly process. Substitution of the IscU Asp39 residue by Ala results in the in vivo trapping of a stoichiometric, noncovalent, nondissociating IscU–IscS complex that contains an oxygen-resistant [Fe-S] species. In aggregate, these results validate the scaffold hypothesis for [Fe-S] cluster assembly and indicate that in vivo [Fe-S] cluster formation is a dynamic process that involves the reversible interaction of IscU and IscS. PMID:18562278

  11. Star Formation in Merging Clusters of Galaxies

    NASA Astrophysics Data System (ADS)

    Mansheim, Alison Seiler

    This thesis straddles two areas of cosmology, each of which are active, rich and plagued by controversy in their own right: merging clusters and the environmental dependence of galaxy evolution. While the greater context of this thesis is major cluster mergers, our individual subjects are galaxies, and we apply techniques traditionally used to study the differential evolution of galaxies with environment. The body of this thesis is drawn from two papers: Mansheim et al. 2016a and Mansheim et al. 2016b, one on each system. Both projects benefited from exquisite data sets assembled as part of the Merging Cluster Collaboration (MC2), and Observations of Redshift Evolution in Large Scale Environments (ORELSE) survey, allowing us to scrutinize the evolutionary states of galaxy populations in multiple lights. Multi-band optical and near-infrared imaging was available for both systems, allowing us to calculate photometric redshifts for completeness corrections, colors (red vs. blue) and stellar masses to view the ensemble properties of the populations in and around each merger. High-resolution spectroscopy was also available for both systems, allowing us to confirm cluster members by measuring spectroscopic redshifts, which are unparalleled in accuracy, and gauge star formation rates and histories by measuring the strengths of certain spectral features. We had the luxury of HST imaging for Musket Ball, allowing us to use galaxy morphology as an additional diagnostic. For Cl J0910, 24 mum imaging allowed us to defeat a most pernicious source of uncertainty. Details on the acquisition and reduction of multi-wavelength data for each system are found within each respective chapter. It is important to note that the research presented in Chapter 3 is based on a letter which had significant space restrictions, so much of the observational details are outsourced to papers written by ORELSE collaboration members. Below is a free-standing summary of each project, drawn from the

  12. Clustering and asymptotic behavior in opinion formation

    NASA Astrophysics Data System (ADS)

    Jabin, Pierre-Emmanuel; Motsch, Sebastien

    2014-12-01

    We investigate the long time behavior of models of opinion formation. We consider the case of compactly supported interactions between agents which are also non-symmetric, including for instance the so-called Krause model. Because of the finite range of interaction, convergence to a unique consensus is not expected in general. We are nevertheless able to prove the convergence to a final equilibrium state composed of possibly several local consensus. This result had so far only been conjectured through numerical evidence. Because of the non-symmetry in the model, the analysis is delicate and is performed in two steps: First using entropy estimates to prove the formation of stable clusters and then studying the evolution in each cluster. We study both discrete and continuous in time models and give rates of convergence when those are available.

  13. Estimation of the driving force for dioxygen formation in photosynthesis.

    PubMed

    Nilsson, Håkan; Cournac, Laurent; Rappaport, Fabrice; Messinger, Johannes; Lavergne, Jérôme

    2016-01-01

    Photosynthetic water oxidation to molecular oxygen is carried out by photosystem II (PSII) over a reaction cycle involving four photochemical steps that drive the oxygen-evolving complex through five redox states Si (i = 0,…, 4). For understanding the catalytic strategy of biological water oxidation it is important to elucidate the energetic landscape of PSII and in particular that of the final S4 → S0 transition. In this short-lived chemical step the four oxidizing equivalents accumulated in the preceding photochemical events are used up to form molecular oxygen, two protons are released and at least one substrate water molecule binds to the Mn4CaO5 cluster. In this study we probed the probability to form S4 from S0 and O2 by incubating YD-less PSII in the S0 state for 2–3 days in the presence of (18)O2 and H2(16)O. The absence of any measurable (16,18)O2 formation by water-exchange in the S4 state suggests that the S4 state is hardly ever populated. On the basis of a detailed analysis we determined that the equilibrium constant K of the S4 → S0 transition is larger than 1.0 × 10(7) so that this step is highly exergonic. We argue that this finding is consistent with current knowledge of the energetics of the S0 to S4 reactions, and that the high exergonicity is required for the kinetic efficiency of PSII.

  14. Star Formation and Young Clusters in Cygnus

    NASA Astrophysics Data System (ADS)

    Reipurth, B.; Schneider, N.

    2008-12-01

    The Great Cygnus Rift harbors numerous very active regions of current or recent star formation. In this part of the sky we look down a spiral arm, s= o regions from only a few hundred pc to several kpc are superposed. The North America and Pelican nebulae, parts of a single giant HII region, are the best known of the Cygnus regions of star formation and are located at a distance of only about 600 pc. Adjacent, but at a distance of about 1.7 kpc, is the Cygnus X region, a ˜10° complex of actively star forming molecular clouds and young clusters. The most massive of these clusters is the 3-4 Myr old Cyg OB2 association, containing several thousand OB stars and akin to the young globular clusters in the LMC. The rich populations of young low and high mass stars and protostars associated with the massive cloud complexes in Cygnus are largely unexplored and deserve systematic study.

  15. Formation and recombination of protonated acetonitrile clusters

    NASA Astrophysics Data System (ADS)

    Plasil, R.; Glosík, J.; Zakouril, P.

    1999-07-01

    Formation of the protonated acetonitrile cluster ions CH3CNH+.CH3CN and their subsequent dissociative recombination with electrons was studied in a high-pressure flowing afterglow using the axially movable Langmuir probe. The first step is the binary proton transfer reaction of H3O+ with CH3CN with the rate coefficient k1 = (5.9±1.9) × 10-9 cm3 s-1. Resulting CH3CNH+ ions further associate with the neutral acetonitrile molecules at pressures 3-5 Torr with the effective binary rate coefficient k2eff = (2.1±0.7) × 10-9 cm3 s-1 forming the clusters H+.(CH3CN)2. Further reaction of these clusters with CH3CN is very slow with the effective binary rate coefficient k3eff = (1.1±0.3) × 10-12 cm3 s-1. The large difference between k2eff and k3eff facilitated the study of dissociative recombination of H+.(CH3CN)2 cluster ions with electrons at thermal energy and pressure p = 4.5-7.0 Torr. The recombination rate coefficient thus obtained is (2.8±1) × 10-6 cm3 s-1.

  16. Formation of young massive clusters from turbulent molecular clouds

    NASA Astrophysics Data System (ADS)

    Fujii, Michiko S.

    2015-08-01

    Young massive clusters are as young as open clusters but more massive and compact compared with typical open clusters. The formation process of young massive clusters is still unclear, and it is an open question whether the formation process is the same for typical open clusters or not. We perform a series of N-body simulations starting from initial conditions constructed from the results of hydrodynamical simulations of turbulent molecular clouds. In our simulations, both open clusters and young massive clusters form when we assume a density-dependent star-formation efficiency. We find that a local star-formation efficiency higher than 50% is necessary for the formation of young massive clusters, but open clusters form from less dense regions with a local star formation efficiency of < 50%. We confirm that the young massive clusters formed in our simulations have mass, size, and density profile similar to those of observed young massive clusters such as NGC 3603 and Trumpler 14. We also find that these simulated clusters evolve via hierarchical mergers of sub-clusters within a few mega years, as is suggested by recent simulations and observations. Although we do not assume initial mass segregation, we observe that the simulated massive clusters show a shallower slope of the mass function (Γ ˜ -1) in the cluster center compared to that of the entire cluster (Γ ˜ -1.3). These values are consistent with those of some young massive clusters in the Milky Way such as Westerlund 1 and Arches.

  17. Accelerating Star Formation in Clusters and Associations

    NASA Astrophysics Data System (ADS)

    Palla, Francesco; Stahler, Steven W.

    2000-09-01

    We use our own, recently developed pre-main-sequence evolutionary tracks to investigate the star formation histories of relatively nearby associations and clusters. We first employ published luminosities and effective temperatures to place the known members of each region in the H-R diagram. We then construct age histograms detailing that region's history. The groups studied include Taurus-Auriga, Lupus, Chamaeleon, ρ Ophiuchi, Upper Scorpius, IC 348, and NGC 2264. This study is the first to analyze a large number of star-forming regions with the same set of theoretical tracks. Our investigation corroborates and extends our previous results on the Orion Nebula Cluster. In all cases, we find that star formation began at a relatively low level some 107 yr in the past and has more recently undergone a steep acceleration. This acceleration, which lasts several million years, is usually continuing through the present epoch. The one clear exception is the OB association Upper Scorpius, where the formation rate climbed upward, peaked, and has now died off. Significantly, this is also the only region of our list that has been largely stripped of molecular gas. The acceleration represents a true physical phenomenon that cannot be explained away by incompleteness of the samples; nor is the pattern of stellar births significantly affected by observational errors or the presence of unresolved binaries. We speculate that increasing star formation activity arises from contraction of the parent cloud. Despite the short timescale for acceleration, the cloud is likely to evolve quasi-statically. Star formation itself appears to be a critical phenomenon, occurring only in locations exceeding some threshold density. The cloud's contraction must reverse itself, and the remnant gas dissipate, in less than 107 yr, even for aggregates containing no massive stars. In this case, molecular outflows from the stars themselves presumably accomplish the task, but the actual dispersal mechanism

  18. Nanodroplet cluster formation in ionic liquid microemulsions.

    PubMed

    Gao, Yanan; Voigt, Andreas; Hilfert, Liane; Sundmacher, Kai

    2008-08-04

    A common ionic liquid (IL), 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF(4)), is used as polar solvent to induce the formation of a reverse bmimBF(4)-in-toluene IL microemulsion with the aid of the nonionic surfactant Triton X-100. The swelling process of the microemulsion droplets by increasing bmimBF(4) content is detected by dynamic light scattering (DLS), conductivity, UV/Vis spectroscopy, and freeze-fracture transmission electron microscopy (FF-TEM). The results show that the microemulsion droplets initially formed are enlarged by the addition of bmimBF(4). However, successive addition of bmimBF(4) lead to the appearance of large-sized microemulsion droplet clusters (200-400 nm). NMR spectroscopic analysis reveal that the special structures and properties of bmimBF(4) and Triton X-100 together with the polar nature of toluene contribute to the formation of such self-assemblies. These unique self-assembled structures of IL-based microemulsion droplet clusters may have some unusual and unique properties with a number of interesting possibilities for potential applications.

  19. How Stellar Feedback Simultaneously Regulates Star Formation and Drives Outflows

    NASA Astrophysics Data System (ADS)

    Hayward, Christopher C.

    2017-07-01

    Stellar-feedback-driven outflows are thought to be a crucial process in galaxy formation, but our physical understanding of them is still rudimentary. I will present an analytical model for how stellar feedback simultaneously regulates star formation and drives outflows. One interesting prediction of the model is that although stellar feedback can efficiently generate outflows in all galaxies at high redshift, it is unable to drive outflows in massive galaxies below z 1. This prediction agrees with the results of state-of-the-art cosmological zoom simulations that include explicit stellar feedback. This model, combined with the aforementioned simulations, suggests that high-redshift galaxies are highly turbulent, disordered and characterized by strong starbursts and subsequent violent outflows, and the suppression of outflows in massive galaxies at z 1 is crucial for the emergence of well-ordered, steadily star-forming disk galaxies.

  20. Spectroscopic Elucidation of First Steps of Supported Bimetallic Cluster Formation

    SciTech Connect

    Kulkarni, A.; Gates, B.C.

    2009-12-23

    Initial steps of bimetallic Ru-Os cluster formation on MgO in the presence of H{sub 2} are analyzed by EXAFS and IR spectroscopy. Ru-Os bond formation takes place after decarbonylation of Ru{sub 3} clusters and subsequently, at higher temperatures, of Os{sub 3} clusters to generate coordinative unsaturation.

  1. Formation of Education Clusters as a Way to Improve Education

    ERIC Educational Resources Information Center

    Aitbayeva, Gul'zamira D.; Zhubanova, Mariyash K.; Kulgildinova, Tulebike A.; Tusupbekova, Gulsum M.; Uaisova, Gulnar I.

    2016-01-01

    The purpose of this research is to analyze basic prerequisites formation and development factors of educational clusters of the world's leading nations for studying the possibility of cluster policy introduction and creating educational clusters in the Republic of Kazakhstan. The authors of this study concluded that educational cluster could be…

  2. Theoretical analysis of the formation driving force and decreased sensitivity for CL-20 cocrystals

    NASA Astrophysics Data System (ADS)

    Zhou, Jun-Hong; Shi, Liang-Wei; Zhang, Chao-Yang; Li, Hong-Zhen; Chen, Min-Bo; Chen, Wei-Ming

    2016-07-01

    Methods that analyze the driving force in the formation of the new energetic cocrystal are proposed in this paper. Various intermolecular interactions in the 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazatetracyclo [5.5.0.05,9.03,11]dodecane (CL-20) cocrystals are compared with those in pure CL-20 and coformer crystals by atom in molecule (AIM) and Hirshfeld surface methods under the supramolecular cluster model. The driving force in the formation of the CL-20 cocrystals is analyzed. The main driving force in the formation of the cocrystal CL-20/HMX comes from the O···H interactions, that in the formation of the cocrystal CL-20/TNT from the O···H and C···O interactions, and that in the formation of the cocrystal CL-20/BTF from the N···H and N···O interactions. Other interactions in the CL-20 cocrystals only contribute to their stabilization. At the same time, the reasons for the decreased impact sensitivity of the CL-20 cocrystals are also analyzed. They are the strengthening of the intermolecular interactions, the reducing of the free space, and the changing of the surrounding of CL-20 molecule in the CL-20 cocrystals in comparison with those in the pure CL-20 crystal.

  3. Sarcomeric Pattern Formation by Actin Cluster Coalescence

    PubMed Central

    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

  4. Dehydration-mediated cluster formation of nanoparticles

    NASA Astrophysics Data System (ADS)

    Ahn, Sungsook; Joon Lee, Sang

    2015-06-01

    Drying procedure is a powerful method to modulate the bottom-up assembly of basic building component. The initially weak attraction between the components screened in a solution strengthens as the solvent evaporates, organizing the components into structures. Drying is process-dependent, irreversible, and nonequilibrated, thus the mechanism and the dynamics are influenced by many factors. Therefore, the interaction of the solvent and the elements during the drying procedure as well as the resulting pattern formations are strongly related. Nonetheless still many things are open in questions in terms of their dynamics. In this study, nanoscale dehydration procedure is experimentally investigated using a nanoparticle (NP) model system. The role of water is verified in a single NP scale and the patterns of collective NP clusters are determined. Stepwise drying procedures are proposed based on the location from which water is removed. Effective water exodus from a unit NP surface enhances the attractive interaction in nanoscale and induces heterogeneous distribution in microscale. This study provides fundamental proof of systematic relation between the dehydration process and the resultant cluster patterns in hierarchical multiscales.

  5. Dehydration-mediated cluster formation of nanoparticles

    PubMed Central

    Ahn, Sungsook; Joon Lee, Sang

    2015-01-01

    Drying procedure is a powerful method to modulate the bottom-up assembly of basic building component. The initially weak attraction between the components screened in a solution strengthens as the solvent evaporates, organizing the components into structures. Drying is process-dependent, irreversible, and nonequilibrated, thus the mechanism and the dynamics are influenced by many factors. Therefore, the interaction of the solvent and the elements during the drying procedure as well as the resulting pattern formations are strongly related. Nonetheless still many things are open in questions in terms of their dynamics. In this study, nanoscale dehydration procedure is experimentally investigated using a nanoparticle (NP) model system. The role of water is verified in a single NP scale and the patterns of collective NP clusters are determined. Stepwise drying procedures are proposed based on the location from which water is removed. Effective water exodus from a unit NP surface enhances the attractive interaction in nanoscale and induces heterogeneous distribution in microscale. This study provides fundamental proof of systematic relation between the dehydration process and the resultant cluster patterns in hierarchical multiscales. PMID:26077841

  6. Counterion-mediated cluster formation by polyphosphoinositides

    PubMed Central

    Wang, Yu-Hsiu; Slochower, David R.; Janmey, Paul A.

    2014-01-01

    Polyphosphoinositides (PPI) and in particular PI(4,5)P2, are among the most highly charged molecules in cell membranes, are important in many cellular signaling pathways, and are frequently targeted by peripheral polybasic proteins for anchoring through electrostatic interactions. Such interactions between PIP2 and proteins containing polybasic stretches depend on the physical state and the lateral distribution of PIP2 within the inner leaflet of the cell's lipid bilayer. The physical chemical properties of PIP2 such as pH-dependent changes in headgroup ionization and area per molecule as determined by experiments together with molecular simulations that predict headgroup conformations at various ionization states have revealed the electrostatic properties and phase behavior of PIP2-containing membranes. This review focuses on recent experimental and computational developments in defining the physical chemistry of PIP2 and its interactions with counterions. Ca2+-induced changes in PIP2 charge, conformation, and lateral structure within the membrane are documented by numerous experimental and computational studies. A simplified electrostatic model successfully predicts the Ca2+-driven formation of PIP2 clusters but cannot account for the different effects of Ca2+ and Mg2+ on PIP2-containing membranes. A more recent computational study is able to see the difference between Ca2+ and Mg2+ binding to PIP2 in the absence of a membrane and without cluster formation. Spectroscopic studies suggest that divalent cation- and multivalent polyamine-induced changes in the PIP2 lateral distribution in model membrane are also different, and not simply related to the net charge of the counterion. Among these differences is the capacity of Ca2+ but not other polycations to induce nm scale clusters of PIP2 in fluid membranes. Recent super resolution optical studies show that PIP2 forms nanoclusters in the inner leaflet of a plasma membrane with a similar size distribution as those

  7. The physics and modes of star cluster formation: observations.

    PubMed

    Lada, Charles J

    2010-02-28

    Stellar clusters are born in cold and dusty molecular clouds and the youngest clusters are embedded to various degrees in a dusty dark molecular material. Such embedded clusters can be considered protocluster systems. The most deeply buried examples are so heavily obscured by dust that they are only visible at infrared wavelengths. These embedded protoclusters constitute the nearest laboratories for a direct astronomical investigation of the physical processes of cluster formation and early evolution. I review the present state of empirical knowledge concerning embedded-cluster systems and discuss the implications for understanding their formation and subsequent evolution to produce bound stellar clusters.

  8. How stellar feedback simultaneously regulates star formation and drives outflows

    NASA Astrophysics Data System (ADS)

    Hayward, Christopher C.; Hopkins, Philip F.

    2017-02-01

    We present an analytic model for how momentum deposition from stellar feedback simultaneously regulates star formation and drives outflows in a turbulent interstellar medium (ISM). Because the ISM is turbulent, a given patch of ISM exhibits sub-patches with a range of surface densities. The high-density patches are 'pushed' by feedback, thereby driving turbulence and self-regulating local star formation. Sufficiently low-density patches, however, are accelerated to above the escape velocity before the region can self-adjust and are thus vented as outflows. When the gas fraction is ≳ 0.3, the ratio of the turbulent velocity dispersion to the circular velocity is sufficiently high that at any given time, of the order of half of the ISM has surface density less than the critical value and thus can be blown out on a dynamical time. The resulting outflows have a mass-loading factor (η ≡ dot{M}_{out}/M_{star }) that is inversely proportional to the gas fraction times the circular velocity. At low gas fractions, the star formation rate needed for local self-regulation, and corresponding turbulent Mach number, declines rapidly; the ISM is 'smoother', and it is actually more difficult to drive winds with large mass-loading factors. Crucially, our model predicts that stellar-feedback-driven outflows should be suppressed at z ≲ 1 in M⋆ ≳ 1010 M⊙ galaxies. This mechanism allows massive galaxies to exhibit violent outflows at high redshifts and then 'shut down' those outflows at late times, thereby enabling the formation of a smooth, extended thin stellar disc. We provide simple fitting functions for η that should be useful for sub-resolution and semi-analytic models.

  9. The High-mass Truncation of the Star Cluster Mass Function: Limits on Massive Cluster Formation

    NASA Astrophysics Data System (ADS)

    Johnson, L. C.; PHAT Team

    2017-01-01

    Long-lived star clusters serve as useful tracers of star formation, and massive clusters in particular are often associated with vigorous star formation activity. We examine how massive cluster formation varies as a function of star formation surface density (ΣSFR) by comparing cluster populations from galaxies that span a wide range of characteristic ΣSFR values. The Panchromatic Hubble Andromeda Treasury (PHAT) survey yielded an unparalleled census of young star clusters in M31 and allows us to examine massive cluster formation in a low intensity star formation environment. We measure the cluster mass function for a sample of 840 young star clusters with ages between 10-300 Myr. The data show clear evidence of a high-mass truncation: only 15 clusters more massive than 104 M⊙ are observed, compared to ~100 expected for a canonical M-2 power-law mass function with the same total number of clusters above the catalog completeness limit. Adopting a Schechter function parameterization, we fit a characteristic truncation mass (Mc) of 8.5×103 M⊙ — the lowest truncation mass ever reported. When combined with previous mass function results, we find that the cluster mass function truncation correlates strongly with the star formation rate surface density, where Mc ∝ ΣSFR1.3. We also find evidence that suggests the observed Mc-ΣSFR relation also holds for globular clusters, linking the two populations via a common formation pathway.

  10. Reversible cluster formation in concentrated monoclonal antibody solutions

    NASA Astrophysics Data System (ADS)

    Godfrin, P. Douglas; Porcar, Lionel; Falus, Peter; Zarraga, Isidro; Wagner, Norm; Liu, Yun

    2015-03-01

    Protein cluster formation in solution is of fundamental interest for both academic research and industrial applications. Recently, industrial scientists are also exploring the effect of reversible cluster formation on biopharmaceutical processing and delivery. However, despite of its importance, the understanding of protein clusters at concentrated solutions remains scientifically very challenging. Using the neutron spin echo technique to study the short time dynamics of proteins in solutions, we have recently systematically studied cluster formation in a few monoclonal antibody (mAb) solutions and their relation with solution viscosity. We show that the existence of anisotropic attraction can cause the formation of finite sized clusters, which increases the solution viscosity. Interestingly, once clusters form at relatively low concentrations, the average size of clusters in solutions remains almost constant over a wide range of concentrations similar to that of micelle formation. For a different mAb we have also investigated, the attraction is mostly induced by hydrophobic patches. As a result, these mAbs form large clusters with loosely linked proteins. In both cases, the formation of clusters all increases the solution viscosity substantially. However, due to different physics origins of cluster formation, solutions viscosities for these two different types of mAbs need to be controlled by different ways.

  11. Converting multiple OC-3c ATM streams to HIPPI to drive an HDTV frame buffer from a workstation cluster

    SciTech Connect

    Tolmie, D.E.; Dornhoff, A.G.; DuBois, A.J.

    1994-12-01

    A group of eight Digital Equipment Corporation Alpha workstations is interconnected with ATM to form a cluster with supercomputer power. For output, each workstation drives a single ``tile`` on an 8-tile high-resolution frame buffer. A special purpose adapter is used to convert the workstation`s ATM format to the frame buffer`s HIPPI format. This paper discusses the rationale behind the workstation farm, and then describes the visualization output path in detail. To provide the system quickly, special emphasis was placed on making the design as simple as possible. The design choices are examined, and the resultant system is described.

  12. MD simulation of cluster formation during sputtering

    NASA Astrophysics Data System (ADS)

    Muramoto, T.; Okai, M.; Yamashita, Y.; Yorizane, K.; Yamamura, Y.

    2001-06-01

    The cluster ejection due to cluster impact on a solid surface is studied through molecular dynamics (MD) simulations. Simulations are performed for Cu cluster impacts on the Cu(1 1 1) surface for cluster energy 100 eV/atom, and for clusters of 6, 13, 28 and 55 atoms. Interatomic interactions are described by the AMLJ-EAM potential. The vibration energy spectrum is independent of the incident cluster size and energy. This comes from the fact that sputtered clusters become stable through the successive fragmentation of nascent large sputtered clusters. The vibration energy spectra for large sputtered clusters have a peak, whose energy corresponds to the melting temperature of Cu. The exponent of the power-law fit of the abundance distribution and the total sputtering yield for the cluster impacts are higher than that for the monatomic ion impacts with the same total energy, where the exponent δ is given by Yn∝ nδ and Yn is the yield of sputtered n-atom cluster. The exponent δ follows a unified function of the total sputtering yield, which is a monotonic increase function, and it is nearly equal to δ ˜ -3 for larger yield.

  13. System identification, adaptive control and formation driving of farm tractors

    NASA Astrophysics Data System (ADS)

    Rekow, Andrew Karl Wilhelm

    Great increases in agricultural productivity and profitability can be gained by increasing the navigational control accuracy of a farm tractor. To maximize accuracy in the presence of environmental uncertainties, a novel technique for on-line parameter identification has been developed. This method combines the Extended Kalman Filter (EKF) and the Least Mean Square (LMS) algorithms and is used to identify key parameters which describe the dynamics of a farm tractor. This algorithm provides a 15:1 improvement in computational efficiency over the traditional EKF, while offering comparable convergence rates and noise rejection properties. Experimental data on a full-sized John Deere tractor shows a 25 percent improvement in lateral accuracy when using then adaptive controller versus a fixed controller over identical trajectories. In addition to parameter identification, farmers require formation driving capability for routine operations. Multiple farm vehicles work cooperatively together to accomplish a common goal. Several formation driving algorithms were developed for these varying requirements. An experimental implementation of a fully autonomous farm vehicle following a human operated lead vehicle demonstrated an accuracy of 10 centimeters in the in-track direction and 10 centimeters in the cross track direction.

  14. The Formation of Young Dense Star Clusters through Mergers

    NASA Astrophysics Data System (ADS)

    Fujii, M. S.; Saitoh, T. R.; Portegies Zwart, S. F.

    2012-07-01

    Young star clusters such as NGC 3603 and Westerlund 1 and 2 in the Milky Way and R136 in the Large Magellanic Cloud are dynamically more evolved than expected based on their current relaxation times. In particular, the combination of a high degree of mass segregation, a relatively low central density, and the large number of massive runaway stars in their vicinity are hard to explain with the monolithic formation of these clusters. Young star clusters can achieve such a mature dynamical state if they formed through the mergers of a number of less massive clusters. The shorter relaxation times of less massive clusters cause them to dynamically evolve further by the time they merge, and the merger product preserves the memory of the dynamical evolution of its constituent clusters. With a series of N-body simulations, we study the dynamical evolution of single massive clusters and those that are assembled through merging smaller clusters together. We find that the formation of massive star clusters through the mergers of smaller clusters can reproduce the currently observed spatial distribution of massive stars, the density, and the characteristics (number and mass distribution) of the stars ejected as runaways from young dense clusters. We therefore conclude that these clusters and possibly other young massive star clusters formed through the mergers of smaller clusters.

  15. THE FORMATION OF YOUNG DENSE STAR CLUSTERS THROUGH MERGERS

    SciTech Connect

    Fujii, M. S.; Portegies Zwart, S. F.; Saitoh, T. R.

    2012-07-01

    Young star clusters such as NGC 3603 and Westerlund 1 and 2 in the Milky Way and R136 in the Large Magellanic Cloud are dynamically more evolved than expected based on their current relaxation times. In particular, the combination of a high degree of mass segregation, a relatively low central density, and the large number of massive runaway stars in their vicinity are hard to explain with the monolithic formation of these clusters. Young star clusters can achieve such a mature dynamical state if they formed through the mergers of a number of less massive clusters. The shorter relaxation times of less massive clusters cause them to dynamically evolve further by the time they merge, and the merger product preserves the memory of the dynamical evolution of its constituent clusters. With a series of N-body simulations, we study the dynamical evolution of single massive clusters and those that are assembled through merging smaller clusters together. We find that the formation of massive star clusters through the mergers of smaller clusters can reproduce the currently observed spatial distribution of massive stars, the density, and the characteristics (number and mass distribution) of the stars ejected as runaways from young dense clusters. We therefore conclude that these clusters and possibly other young massive star clusters formed through the mergers of smaller clusters.

  16. Probing Massive Star Cluster Formation with ALMA

    NASA Astrophysics Data System (ADS)

    Johnson, Kelsey

    2015-08-01

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

  17. The era of star formation in galaxy clusters

    SciTech Connect

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

    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.

  18. Reputation drives cooperative behaviour and network formation in human groups.

    PubMed

    Cuesta, Jose A; Gracia-Lázaro, Carlos; Ferrer, Alfredo; Moreno, Yamir; Sánchez, Angel

    2015-01-19

    Cooperativeness is a defining feature of human nature. Theoreticians have suggested several mechanisms to explain this ubiquitous phenomenon, including reciprocity, reputation, and punishment, but the problem is still unsolved. Here we show, through experiments conducted with groups of people playing an iterated Prisoner's Dilemma on a dynamic network, that it is reputation what really fosters cooperation. While this mechanism has already been observed in unstructured populations, we find that it acts equally when interactions are given by a network that players can reconfigure dynamically. Furthermore, our observations reveal that memory also drives the network formation process, and cooperators assort more, with longer link lifetimes, the longer the past actions record. Our analysis demonstrates, for the first time, that reputation can be very well quantified as a weighted mean of the fractions of past cooperative acts and the last action performed. This finding has potential applications in collaborative systems and e-commerce.

  19. Reputation drives cooperative behaviour and network formation in human groups

    PubMed Central

    Cuesta, Jose A.; Gracia-Lázaro, Carlos; Ferrer, Alfredo; Moreno, Yamir; Sánchez, Angel

    2015-01-01

    Cooperativeness is a defining feature of human nature. Theoreticians have suggested several mechanisms to explain this ubiquitous phenomenon, including reciprocity, reputation, and punishment, but the problem is still unsolved. Here we show, through experiments conducted with groups of people playing an iterated Prisoner's Dilemma on a dynamic network, that it is reputation what really fosters cooperation. While this mechanism has already been observed in unstructured populations, we find that it acts equally when interactions are given by a network that players can reconfigure dynamically. Furthermore, our observations reveal that memory also drives the network formation process, and cooperators assort more, with longer link lifetimes, the longer the past actions record. Our analysis demonstrates, for the first time, that reputation can be very well quantified as a weighted mean of the fractions of past cooperative acts and the last action performed. This finding has potential applications in collaborative systems and e-commerce. PMID:25598347

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

    NASA Astrophysics Data System (ADS)

    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. What interactions drive the salivary mucosal pellicle formation?

    PubMed Central

    Gibbins, Hannah L.; Yakubov, Gleb E.; Proctor, Gordon B.; Wilson, Stephen; Carpenter, Guy H.

    2014-01-01

    The bound salivary pellicle is essential for protection of both the enamel and mucosa in the oral cavity. The enamel pellicle formation is well characterised, however the mucosal pellicle proteins have only recently been clarified and what drives their formation is still unclear. The aim of this study was to examine the salivary pellicle on particles with different surface properties (hydrophobic or hydrophilic with a positive or negative charge), to determine a suitable model to mimic the mucosal pellicle. A secondary aim was to use the model to test how transglutaminase may alter pellicle formation. Particles were incubated with resting whole mouth saliva, parotid saliva and submandibular/sublingual saliva. Following incubation and two PBS and water washes bound salivary proteins were eluted with two concentrations of SDS, which were later analysed using SDS-PAGE and Western blotting. Experiments were repeated with purified transglutaminase to determine how this epithelial-derived enzyme may alter the bound pellicle. Protein pellicles varied according to the starting salivary composition and the particle chemistry. Amylase, the single most abundant protein in saliva, did not bind to any particle indicating specific protein binding. Most proteins bound through hydrophobic interactions and a few according to their charges. The hydrophobic surface most closely matched the known salivary mucosal pellicle by containing mucins, cystatin and statherin but an absence of amylase and proline-rich proteins. This surface was further used to examine the effect of added transglutaminase. At the concentrations used only statherin showed any evidence of crosslinking with itself or another saliva protein. In conclusion, the formation of the salivary mucosal pellicle is probably mediated, at least in part, by hydrophobic interactions to the epithelial cell surface. PMID:24921197

  2. Cluster formation in a heterogeneous metapopulation model.

    PubMed

    Silva, Jacques A L

    2016-05-01

    A spatially explicit heterogeneous metapopulation model with two different patch types is analyzed. Some network topologies support a partially synchronized dynamics, a state where two different clusters of patches are formed. Within each cluster the dynamics of all patches are synchronized. The linearized asymptotic stability of the partially synchronized attractor is studied. The transversal stability is analyzed and a simple expression for the transversal Lyapunov number of partially synchronized attractors is obtained.

  3. Star cluster formation in cosmological simulations. I. Properties of young clusters

    DOE PAGES

    Li, Hui; Gnedin, Oleg Y.; Gnedin, Nickolay Y.; ...

    2017-01-03

    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 ismore » $$\\alpha \\approx 1.8\\mbox{–}2$$, 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. As a result, 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.« less

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

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

    Bekki, Kenji

    2017-05-01

    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 on to 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] × 105 M⊙ can accrete more than 105 M⊙ gas from AGB stars of the SCC. We suggest that merging of hierarchical SSCs can play key roles in stellar halo formation around GCs and self-enrichment processes in the early phase of GC formation.

  6. The star cluster formation history of the LMC

    NASA Astrophysics Data System (ADS)

    Baumgardt, H.; Parmentier, G.; Anders, P.; Grebel, E. K.

    2013-03-01

    The Large Magellanic Cloud (LMC) is one of the nearest galaxies to us and is one of only few galaxies where the star formation history can be determined from studying resolved stellar populations. We have compiled a new catalogue of ages, luminosities and masses of LMC star clusters and used it to determine the age distribution and dissolution rate of LMC star clusters. We find that the frequency of massive clusters with masses M > 5000 M⊙ is almost constant between 10 and 200 Myr, showing that the influence of residual gas expulsion is limited to the first 10 Myr of cluster evolution or clusters less massive than 5000 M⊙. Comparing the cluster frequency in that interval with the absolute star formation rate, we find that about 15 per cent of all stars in the LMC were formed in long-lived star clusters that survive for more than 10 Myr. We also find that the mass function of LMC clusters younger than 109 Gyr can be fitted by a power-law mass function N(m) ˜ m-α with slope α = 2.3, while older clusters follow a significantly shallower slope and interpret that this is a sign of either incompleteness or the ongoing dissolution of low-mass clusters. Our data show that for ages older than 200 Myr, about 90 per cent of all clusters are lost per dex of lifetime. The implied cluster dissolution rate is significantly faster than that based on analytic estimates and N-body simulations. Our cluster age data finally show evidence for a burst in cluster formation about 109 yr ago, but little evidence for bursts at other ages.

  7. Bimodal regime in young massive clusters leading to formation of subsequent stellar generations

    NASA Astrophysics Data System (ADS)

    Wunsch, Richard; Palous, Jan; Tenorio-Tagle, Guillermo; Munoz-Tunon, Casiana; Ehlerova, Sona

    2015-08-01

    Massive stars in young massive clusters insert tremendous amounts of mass and energy into their surroundings in the form of stellar winds and supernova ejecta. Mutual shock-shock collisions lead to formation of hot gas, filling the volume of the cluster. The pressure of this gas then drives a powerful cluster wind. However, it has been shown that if the cluster is massive and dense enough, it can evolve in the so called bimodal regime, in which the hot gas inside the cluster becomes thermally unstable and forms dense clumps which are trapped inside the cluster by its gravity.We will review works on the bimodal regime and discuss the implications for the formation of subsequent stellar generations. The mass accumulates inside the cluster and as soon as a high enough column density is reached, the interior of the clumps becomes self-shielded against the ionising radiation of, stars and the clumps collapse and form new stars. The second stellar generation will be enriched by products of the stellar evolution of the first generation, and will be concentrated near the cluster center.

  8. Clustering algorithms for Stokes space modulation format recognition.

    PubMed

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

    2015-06-15

    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.

  9. Extreme Star Formation in the Massive Young Cluster Westerlund 1

    NASA Astrophysics Data System (ADS)

    Hora, Joseph; Kraemer, Kathleen; Megeath, Tom; Gutermuth, Rob; Smith, Howard; Martinez Galarza, Juan Rafael; Guzman Fernandez, Andres; Carey, Sean; Koenig, Xavier; Schneider, Nicola; Motte, Frederique; Bontemps, Sylvain; Adams, Joseph; Simon, Robert; Nguyen-Luong, Quang; Schilke, Peter; Keto, Eric; Fazio, Giovanni; Allen, Lori

    2012-12-01

    We propose to extend Spitzer's study of massive star formation to the massive cluster Westerlund 1, which at ~4 kpc is the closest and most massive 'Super Star Cluster' known in the Galaxy. Star formation may have proceeded differently in this region, having created a higher overall density of coeval massive stars. The proposed observations will allow us to compare star formation in this region to that seen near the Sun, in the massive Cygnus-X complex, and in the outer Galaxy (coming from the studies of W5, the Cycle-5 SMOG project, and GLIMPSE360), and therefore to complete a more representative view of star formation in the Galaxy.

  10. OT2_baltieri_5: Star formation in proto-clusters

    NASA Astrophysics Data System (ADS)

    Altieri, B.

    2011-09-01

    Massive clusters of galaxies have been found to date from as early as 3-4 billion years after the Big Bang. Cosmological simulations using the current cold dark matter model predict that these systems should descend from 'proto-clusters' - early overdensities of massive galaxies that merge hierarchically to form a cluster. These protocluster regions themselves are built up hierarchically and so are expected to contain extremely massive galaxies, progenitors of the quiescent behemoths observed in cores of the present day massive galaxy clusters. Observational evidence for this picture, however, is sparse because high-redshift proto-clusters are rare and difficult to observe. Here we propose to probe with Herschel SPIRE the very beginning of the cluster and massive galaxies formation process by observing 5 proto-clusters at 3formation at such high redshift, to compare the properties of the proto-cluster galaxies with those of field galaxies at similar redshift. Determining whether cluster galaxies differ from field galaxies when the proto-cluster was still forming, tells us whether any of the difference observed today is driven by nature as apposed to nurture.

  11. Formation of plant metabolic gene clusters within dynamic chromosomal regions

    PubMed Central

    Field, Ben; Fiston-Lavier, Anna-Sophie; Kemen, Ariane; Geisler, Katrin; Quesneville, Hadi; Osbourn, Anne E.

    2011-01-01

    In bacteria, genes with related functions often are grouped together in operons and are cotranscribed as a single polycistronic mRNA. In eukaryotes, functionally related genes generally are scattered across the genome. Notable exceptions include gene clusters for catabolic pathways in yeast, synthesis of secondary metabolites in filamentous fungi, and the major histocompatibility complex in animals. Until quite recently it was thought that gene clusters in plants were restricted to tandem duplicates (for example, arrays of leucine-rich repeat disease-resistance genes). However, operon-like clusters of coregulated nonhomologous genes are an emerging theme in plant biology, where they may be involved in the synthesis of certain defense compounds. These clusters are unlikely to have arisen by horizontal gene transfer, and the mechanisms behind their formation are poorly understood. Previously in thale cress (Arabidopsis thaliana) we identified an operon-like gene cluster that is required for the synthesis and modification of the triterpene thalianol. Here we characterize a second operon-like triterpene cluster (the marneral cluster) from A. thaliana, compare the features of these two clusters, and investigate the evolutionary events that have led to cluster formation. We conclude that common mechanisms are likely to underlie the assembly and control of operon-like gene clusters in plants. PMID:21876149

  12. The INfrared Survey of Young Nebulous Clusters (IN-SYNC): Surveying the Dynamics and Star Formation Histories of Young Clusters with APOGEE

    NASA Astrophysics Data System (ADS)

    Covey, Kevin R.; Cottaar, Michiel; Foster, Jonathan B.; Da Rio, Nicola; Tan, Jonathan; Meyer, Michael; Nidever, David L.; Flaherty, Kevin M.; Arce, Hector G.; Rebull, Luisa M.; Chojnowski, S. Drew; Frinchaboy, Peter M.; Hearty, Fred R.; Majewski, Steven R.; Skrutskie, Michael F.; Stassun, Keivan; Wilson, John C.; Zasowski, Gail

    2015-01-01

    Young clusters are the most prolific sites of star formation in the Milky Way, but demographic studies indicate that relatively few of the Milky Way's stellar clusters persist as bound structures for 100 Myrs or longer. Uniform & precise measurements of the stellar populations and internal dynamics of these regions are difficult to obtain, however, particularly for extremely young clusters whose optical visibility is greatly hampered by their parental molecular cloud. The INfrared Survey of Young Nebulous Clusters (IN-SYNC), an SDSS-III ancillary science program, leverages the stability and multiplex capability of the APOGEE spectrograph to obtain high resolution spectra at near-infrared wavelengths, where photospheric emission is better able to penetrate the dusty shrouds that surround sites of active star formation. We summarize our recent measurements of the kinematics and stellar populations of IC 348 and NGC 1333, two young clusters in the Perseus Molecular Cloud, and of the members of the Orion Nebula Cluster (ONC) and L1641 filament in the Orion molecular complex. These measurements highlight the dynamically 'warm' environment within these young clusters, and suggest a range of stellar radii within these quasi-single-age populations. We close with a preview of plans for continuing this work as part of the APOGEE-2 science portfolio: self-consistent measurements of the kinematics and star formation histories for clusters spanning a range of initial conditions and ages will provide a opportunity to disentangle the mechanisms that drive the formation and dissolution of sites of active star formation.

  13. STAR FORMATION IN HIGH-REDSHIFT CLUSTER ELLIPTICALS

    SciTech Connect

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

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

  15. Clustering and Pattern Formation in Chemorepulsive Active Colloids

    NASA Astrophysics Data System (ADS)

    Liebchen, Benno; Marenduzzo, Davide; Pagonabarraga, Ignacio; Cates, Michael E.

    2015-12-01

    We demonstrate that migration away from self-produced chemicals (chemorepulsion) generates a generic route to clustering and pattern formation among self-propelled colloids. The clustering instability can be caused either by anisotropic chemical production, or by a delayed orientational response to changes of the chemical environment. In each case, chemorepulsion creates clusters of a self-limiting area which grows linearly with self-propulsion speed. This agrees with recent observations of dynamic clusters in Janus colloids (albeit not yet known to be chemorepulsive). More generally, our results could inform design principles for the self-assembly of chemorepulsive synthetic swimmers and/or bacteria into nonequilibrium patterns.

  16. Clustering and Pattern Formation in Chemorepulsive Active Colloids.

    PubMed

    Liebchen, Benno; Marenduzzo, Davide; Pagonabarraga, Ignacio; Cates, Michael E

    2015-12-18

    We demonstrate that migration away from self-produced chemicals (chemorepulsion) generates a generic route to clustering and pattern formation among self-propelled colloids. The clustering instability can be caused either by anisotropic chemical production, or by a delayed orientational response to changes of the chemical environment. In each case, chemorepulsion creates clusters of a self-limiting area which grows linearly with self-propulsion speed. This agrees with recent observations of dynamic clusters in Janus colloids (albeit not yet known to be chemorepulsive). More generally, our results could inform design principles for the self-assembly of chemorepulsive synthetic swimmers and/or bacteria into nonequilibrium patterns.

  17. Improving performance through concept formation and conceptual clustering

    NASA Technical Reports Server (NTRS)

    Fisher, Douglas H.

    1992-01-01

    Research from June 1989 through October 1992 focussed on concept formation, clustering, and supervised learning for purposes of improving the efficiency of problem-solving, planning, and diagnosis. These projects resulted in two dissertations on clustering, explanation-based learning, and means-ends planning, and publications in conferences and workshops, several book chapters, and journals; a complete Bibliography of NASA Ames supported publications is included. The following topics are studied: clustering of explanations and problem-solving experiences; clustering and means-end planning; and diagnosis of space shuttle and space station operating modes.

  18. Bottlebrush additives drive formation of vesicle chains in polymer blends

    NASA Astrophysics Data System (ADS)

    Mah, Hui Zhen; Afzali, Pantea; Verduzco, Rafeal; Stein, Gila

    2015-03-01

    The effects of bottlebrush polymer additive with poly (styrene-r-methyl methacrylate) side-chains on the thin film morphology of polystyrene (PS) and poly (methyl methacrylate) (PMMA) blends were studied. Results were compared to PS/PMMA blends with diblock copolymer PS-b-PMMA compatibilizer and without any additive. Thin films were spin casted from toluene onto a ``neutral'' silicon surface and then annealed at a fixed temperature of 150ºC for a range of times (up to 85 mins). The morphology of the films was characterized using optical microscopy and atomic force microscopy. In the absence of any additive, the PS/PMMA blend rapidly de-mixes to form macroscale domains, while high loadings of the PS-b-PMMA additive can compatibilize the blend and suppress phase separation. However, the bottlebrush polymer additive drives the formation of well-organized vesicle chains in the PS/PMMA blend films. This morphology is favored by entropic considerations as the bottlebrush polymers are more stable than linear chains at the PS/PMMA interface and the brush like surface attracts.

  19. Lithium formate ion clusters formation during electrospray ionization: Evidence of magic number clusters by mass spectrometry and ab initio calculations

    SciTech Connect

    Shukla, Anil; Bogdanov, Bogdan

    2015-02-14

    Small cationic and anionic clusters of lithium formate were generated by electrospray ionization and their fragmentations were studied by tandem mass spectrometry. Singly as well as multiply charged clusters were formed with the general formulae, (HCOOLi)nLi+, (HCOOLi)nLimm+, (HCOOLi)nHCOO- and (HCOOLi)n(HCOO)mm-. Several magic number cluster ions were observed in both the positive and negative ion modes although more predominant in the positive ion mode with (HCOOLi)3Li+ being the most abundant and stable cluster ions. Fragmentations of singly charged clusters proceed first by the loss of a dimer unit ((HCOOLi)2) followed by sequential loss of monomer units (HCOOLi). In the case of positive cluster ions, all fragmentations lead to the magic cluster (HCOOLi)3Li+ at higher collision energies which later fragments to dimer and monomer ions in lower abundance. Quantum mechanical calculations performed for smaller cluster ions showed that the trimer ion has a closed ring structure similar to the phenalenylium structure with three closed rings connected to the lithium ion. Further additions of monomer units result in similar symmetric structures for hexamer and nonamer cluster ions. Thermochemical calculations show that trimer cluster ion is relatively more stable than neighboring cluster ions, supporting the experimental observation of a magic number cluster with enhanced stability.

  20. Formation and Levitation of Unconfined Droplet Clusters

    NASA Technical Reports Server (NTRS)

    Liu, S.; Ruff, G. A.

    1999-01-01

    Combustion experiments using arrays of droplets seek to provide a link between single droplet combustion phenomena and the behavior of complex spray combustion systems. Both single droplet and droplet array studies have been conducted in microgravity to better isolate the droplet interaction phenomena and eliminate or reduce the confounding effects of buoyancy-induced convection. In most experiments involving droplet arrays, the droplets are supported on fibers to keep them stationary and close together before the combustion event. The presence of the fiber, however, disturbs the combustion process by introducing a source of heat transfer and asymmetry into the configuration. As the number of drops in a droplet array increases, supporting the drops on fibers becomes less practical because of the cumulative effect of the fibers on the combustion process. The overall objective of this research is to study the combustion of well-characterized drop clusters in a microgravity environment. Direct experimental observations and measurements of the combustion of droplet clusters would fill a large gap in our current understanding of droplet and spray combustion and provide unique experimental data for the verification and improvement of spray combustion models. This paper describes current work on the design and performance of an apparatus to generate and stabilize droplet clusters using acoustic and electrostatic forces.

  1. Formation and Levitation of Unconfined Droplet Clusters

    NASA Technical Reports Server (NTRS)

    Liu, S.; Ruff, G. A.

    1999-01-01

    Combustion experiments using arrays of droplets seek to provide a link between single droplet combustion phenomena and the behavior of complex spray combustion systems. Both single droplet and droplet array studies have been conducted in microgravity to better isolate the droplet interaction phenomena and eliminate or reduce the confounding effects of buoyancy-induced convection. In most experiments involving droplet arrays, the droplets are supported on fibers to keep them stationary and close together before the combustion event. The presence of the fiber, however, disturbs the combustion process by introducing a source of heat transfer and asymmetry into the configuration. As the number of drops in a droplet array increases, supporting the drops on fibers becomes less practical because of the cumulative effect of the fibers on the combustion process. The overall objective of this research is to study the combustion of well-characterized drop clusters in a microgravity environment. Direct experimental observations and measurements of the combustion of droplet clusters would fill a large gap in our current understanding of droplet and spray combustion and provide unique experimental data for the verification and improvement of spray combustion models. This paper describes current work on the design and performance of an apparatus to generate and stabilize droplet clusters using acoustic and electrostatic forces.

  2. Clustered star formation and the origin of stellar masses.

    PubMed

    Pudritz, Ralph E

    2002-01-04

    Star clusters are ubiquitous in galaxies of all types and at all stages of their evolution. We also observe them to be forming in a wide variety of environments, ranging from nearby giant molecular clouds to the supergiant molecular clouds found in starburst and merging galaxies. The typical star in our galaxy and probably in others formed as a member of a star cluster, so star formation is an intrinsically clustered and not an isolated phenomenon. The greatest challenge regarding clustered star formation is to understand why stars have a mass spectrum that appears to be universal. This review examines the observations and models that have been proposed to explain these fundamental issues in stellar formation.

  3. Galactic flows and the formation of stellar clusters

    NASA Astrophysics Data System (ADS)

    Smilgys, Romas; Bonnell, Ian A.

    2017-03-01

    We investigate the formation of stellar clusters from a Galactic scale SPH simulation. The simulation traces star formation over a 5.6 Myr timescale, with local gravitational instabilities resulting in ~ 105 solar masses of star formation in the form of sink particles. We investigate the time evolution of the physical properties of the forming clusters including their half-mass radii, their energies and the depletion time of the gas. Star formation is driven by the large scale flows which compress the gas to higher densities where self gravity takes over and collapse occurs. We show that the more massive clusters (up to ~ 2 × 104 solar masses) gather their material from of order 10 pc due to these large scale motions associated with the spiral arm passage and shock. The bulk of the gas becomes gravitationally bound near 1-2 Myr before sink formation, and in the absence of feedback, significant accretion ongoing on longer timescales. We trace the hierarchical merging process of cluster formation which naturally results in age spreads of order the crossing time of the original region which provides the gas reservoir for the cluster.

  4. The efficiency of star formation in clustered and distributed regions

    NASA Astrophysics Data System (ADS)

    Bonnell, Ian A.; Smith, Rowan J.; Clark, Paul C.; Bate, Matthew R.

    2011-02-01

    We investigate the formation of both clustered and distributed populations of young stars in a single molecular cloud. We present a numerical simulation of a 104 M⊙ elongated, turbulent, molecular cloud and the formation of over 2500 stars. The stars form both in stellar clusters and in a distributed mode, which is determined by the local gravitational binding of the cloud. A density gradient along the major axis of the cloud produces bound regions that form stellar clusters and unbound regions that form a more distributed population. The initial mass function (IMF) also depends on the local gravitational binding of the cloud with bound regions forming full IMFs whereas in the unbound, distributed regions the stellar masses cluster around the local Jeans mass and lack both the high-mass and the low-mass stars. The overall efficiency of star formation is ≈ 15 per cent in the cloud when the calculation is terminated, but varies from less than 1 per cent in the regions of distributed star formation to ≈ 40 per cent in regions containing large stellar clusters. Considering that large-scale surveys are likely to catch clouds at all evolutionary stages, estimates of the (time-averaged) star formation efficiency (SFE) for the giant molecular cloud reported here is only ≈ 4 per cent. This would lead to the erroneous conclusion of slow star formation when in fact it is occurring on a dynamical time-scale.

  5. PHAT Star Clusters in M31: Insight on Environmental Dependence of Star & Cluster Formation

    NASA Astrophysics Data System (ADS)

    Johnson, Lent C.; Dalcanton, Julianne; Seth, Anil; Beerman, Lori; Lewis, Alexia; Fouesneau, Morgan; Weisz, Daniel R.; Andromeda Project Team, PHAT Team

    2015-01-01

    Theoretical studies of star cluster formation suggest that the star formation efficiency (SFE) of a cluster's progenitor cloud dictates whether or not a gravitationally bound grouping will emerge from an embedded region after gas expulsion. I measure the fraction of stars formed in long-lived clusters relative to unbound field stars on a spatial resolved basis in the Andromeda galaxy. These observations test theoretical predictions that star clusters are formed within a hierarchical interstellar medium at peaks in the gas density where local SFEs are enhanced and regions become stellar dominated. Using data from the Panchromatic Hubble Andromeda Treasury (PHAT) survey and ancillary observations of M31's gas phase, I investigate how cluster formation correlates with galactic environment and galaxy-scale properties of the star formation. We construct a sample of >2700 star clusters through a crowd-sourced visual search of the high spatial resolution HST imaging data. Our catalog uses ~2 million image classifications collected by the Andromeda Project citizen science website to provide an unparalleled census of clusters that spans ~4 orders of magnitude in mass (50% completeness at ~500 M⊙ at <100 Myr) and increases the number of known clusters within the PHAT survey footprint by a factor of ~6. Cluster ages and masses are obtained by fitting to color-magnitude diagrams (CMDs) of individually resolved stars within each cluster. Furthermore, we insure our ability to accurately interpret cluster age and mass distributions through careful catalog completeness characterization, made possible by thousands of synthetic cluster tests included during catalog construction work. We combine our high quality cluster sample with spatially resolved star formation histories, derived from CMD fitting of PHAT's photometry of ~117 million resolved field stars. We derived the fraction of stars formed in long-lived clusters and show that only a few percent of coeval stars are found in

  6. Star Formation Activity in a Young Galaxy Cluster at Z = 0.866

    NASA Astrophysics Data System (ADS)

    Laganá, T. F.; Ulmer, M. P.; Martins, L. P.; da Cunha, E.

    2016-07-01

    The galaxy cluster RX J1257+4738 at z = 0.866 is one of the highest redshift clusters with a richness of multi-wavelength data, and is 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 (SFRs) of our galaxies using two methods: (1) the relation between SFR and total infrared luminosity extrapolated from the observed Spitzer Multiband Imaging Photometer for Spitzer 24 μm imaging data; and (2) spectral energy distribution 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 fewer stars per unit of mass, and thus suggesting that the increase in star-forming members is driven by cluster assembly and infall. If the environment is somehow driving the star formation, one would expect a relation between the SSFR and the cluster centric distance, but that is not the case. A possible scenario to explain this lack of correlation is the contamination by infalling galaxies in the inner part of the cluster, which may be on their initial pass through the cluster center. As these galaxies have higher SFRs for their stellar mass, they enhance the mean SSFR in the center of the cluster.

  7. Teenage suicide cluster formation and contagion: implications for primary care

    PubMed Central

    Johansson, Lars; Lindqvist, Per; Eriksson, Anders

    2006-01-01

    Background We have previously studied unintentional as well as intentional injury deaths among teenagers living in the four northernmost counties, forming approximately 55% of Sweden with 908,000 inhabitants in 1991. During this work, we found what we suspected to be a suicide cluster among teenagers and we also suspected contagion since there were links between these cases. In this present study, we investigate the occurrence of suicide clustering among teenagers, analyze cluster definitions, and suggest preventive measures. Methods A retrospective study of teenager suicides autopsied at the Department of Forensic Medicine in Umeå, Sweden, during 1981 through 2000. Police reports, autopsy protocols, and medical records were studied in all cases, and the police officers that conducted the investigation at the scene were interviewed in all cluster cases. Parents of the suicide victims of the first cluster were also interviewed. Two aggregations of teenager suicides were detected and evaluated as possible suicide clusters using the US Centers for Disease Control definition of a suicide cluster. Results Two clusters including six teenagers were confirmed, and contagion was established within each cluster. Conclusion The general practitioner is identified as a key person in the aftermath of a teenage suicide since the general practitioner often meet the family, friends of the deceased, and other acquaintances early in the process after a suicide. This makes the general practitioner suitable to initiate contacts with others involved in the well-being of the young, in order to prevent suicide cluster formation and para-suicidal activities. PMID:16707009

  8. Formation of Globular Clusters in Hierarchical Cosmology: ART and Science

    NASA Astrophysics Data System (ADS)

    Gnedin, Oleg Y.; Prieto, José L.

    We test the hypothesis that globular clusters form in supergiant molecular clouds within high-redshift galaxies. Numerical simulations demonstrate that such large, dense, and cold gas clouds assemble naturally in current hierarchical models of galaxy formation. These clouds are enriched with heavy elements from earlier stars and could produce star clusters in a similar way to nearby molecular clouds. The masses and sizes of the model clusters are in excellent agreement with the observations of young massive clusters. Do these model clusters evolve into globular clusters that we see in our and external galaxies? In order to study their dynamical evolution, we calculate the orbits of model clusters using the outputs of the cosmological simulation of a Milky Way-sized galaxy. We find that at present the orbits are isotropic in the inner 50 kpc of the Galaxy and preferentially radial at larger distances. All clusters located outside 10 kpc from the center formed in the now-disrupted satellite galaxies. The spatial distribution of model clusters is spheroidal, with a power-law density profile consistent with observations. The combination of two-body scattering, tidal shocks, and stellar evolution results in the evolution of the cluster mass function from an initial power law to the observed log-normal distribution. However, not all initial conditions and not all evolution scenarios are consistent with the observed mass function.

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

    SciTech Connect

    Zeimann, Gregory R.; Stanford, S. A.; Brodwin, Mark; Gonzalez, Anthony H.; Mancone, Conor; Snyder, Gregory F.; Stern, Daniel; Eisenhardt, Peter; Dey, Arjun; Moustakas, John

    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 ☉}.

  10. Suppressed star formation by a merging cluster system

    NASA Astrophysics Data System (ADS)

    Mansheim, A. S.; Lemaux, B. C.; Tomczak, A. R.; Lubin, L. M.; Rumbaugh, N.; Wu, P.-F.; Gal, R. R.; Shen, L.; Dawson, W. A.; Squires, G. K.

    2017-07-01

    We examine the effects of an impending cluster merger on galaxies in the large-scale structure (LSS) RX J0910 at z =1.105. Using multiwavelength data, including 102 spectral members drawn from the Observations of Redshift Evolution in Large Scale Environments (ORELSE) survey and precise photometric redshifts, we calculate star formation rates and map the specific star formation rate density of the LSS galaxies. These analyses along with an investigation of the colour-magnitude properties of LSS galaxies indicate lower levels of star formation activity in the region between the merging clusters relative to the outskirts of the system. We suggest that gravitational tidal forces due to the potential of the merging haloes may be the physical mechanism responsible for the observed suppression of star formation in galaxies caught between the merging clusters.

  11. The Star Cluster Mass-Galactocentric Radius Relation: Implications for Cluster Formation

    NASA Astrophysics Data System (ADS)

    Sun, Weijia; de Grijs, Richard; Fan, Zhou; Cameron, Ewan

    2016-01-01

    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 (≲ a few × {10}8 year 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 taking an absolute-value-distance penalty. Both methods yield, within the 1σ to 3σ uncertainties, near-zero slopes in the diagnostic plane, largely irrespective of the maximum age or minimum mass imposed on our sample selection, or of the radial bin size adopted. We conclude that, at least in our four well-studied sample galaxies, star cluster formation does not necessarily require an environment-dependent cluster formation scenario, which thus supports the notion of stochastic star cluster formation as the dominant star cluster-formation process within a given galaxy.

  12. SIGNATURES OF STAR CLUSTER FORMATION BY COLD COLLAPSE

    SciTech Connect

    Kuznetsova, Aleksandra; Hartmann, Lee; Ballesteros-Paredes, Javier

    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.

  13. Signatures of Star Cluster Formation by Cold Collapse

    NASA Astrophysics Data System (ADS)

    Kuznetsova, Aleksandra; Hartmann, Lee; Ballesteros-Paredes, Javier

    2015-12-01

    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.

  14. The Hydrangea simulations: galaxy formation in and around massive clusters

    NASA Astrophysics Data System (ADS)

    Bahé, Yannick M.; Barnes, David J.; Dalla Vecchia, Claudio; Kay, Scott T.; White, Simon D. M.; McCarthy, Ian G.; Schaye, Joop; Bower, Richard G.; Crain, Robert A.; Theuns, Tom; Jenkins, Adrian; McGee, Sean L.; Schaller, Matthieu; Thomas, Peter A.; Trayford, James W.

    2017-10-01

    We introduce the Hydrangea simulations, a suite of 24 cosmological hydrodynamic zoom-in simulations of massive galaxy clusters (M200c = 1014-1015.4 M⊙) with baryon particle masses of ˜106 M⊙. Designed to study the impact of the cluster environment on galaxy formation, they are a key part of the `Cluster-EAGLE' project. They use a galaxy formation model developed for the EAGLE project, which has been shown to yield both realistic field galaxies and hot gas fractions of galaxy groups consistent with observations. The total stellar mass content of the simulated clusters agrees with observations, but central cluster galaxies are too massive, by up to 0.6 dex. Passive satellite fractions are higher than in the field, and at stellar masses Mstar > 1010 M⊙, this environmental effect is quantitatively consistent with observations. The predicted satellite stellar mass function matches data from local cluster surveys. Normalized to total mass, there are fewer low-mass (Mstar ≲ 1010 M⊙) galaxies within the virial radius of clusters than in the field, primarily due to star formation quenching. Conversely, the simulations predict an overabundance of massive galaxies in clusters compared to the field that persists to their far outskirts (>5 r200c). This is caused by a significantly increased stellar mass fraction of (sub-)haloes in the cluster environment, by up to ˜0.3 dex even well beyond r200c. Haloes near clusters are also more concentrated than equally massive field haloes, but these two effects are largely uncorrelated.

  15. Geometric and potential driving formation and evolution of biomolecular surfaces.

    PubMed

    Bates, P W; Chen, Zhan; Sun, Yuhui; Wei, Guo-Wei; Zhao, Shan

    2009-08-01

    This paper presents new geometrical flow equations for the theoretical modeling of biomolecular surfaces in the context of multiscale implicit solvent models. To account for the local variations near the biomolecular surfaces due to interactions between solvent molecules, and between solvent and solute molecules, we propose potential driven geometric flows, which balance the intrinsic geometric forces that would occur for a surface separating two homogeneous materials with the potential forces induced by the atomic interactions. Stochastic geometric flows are introduced to account for the random fluctuation and dissipation in density and pressure near the solvent-solute interface. Physical properties, such as free energy minimization (area decreasing) and incompressibility (volume preserving), are realized by some of our geometric flow equations. The proposed approach for geometric and potential forces driving the formation and evolution of biological surfaces is illustrated by extensive numerical experiments and compared with established minimal molecular surfaces and molecular surfaces. Local modification of biomolecular surfaces is demonstrated with potential driven geometric flows. High order geometric flows are also considered and tested in the present work for surface generation. Biomolecular surfaces generated by these approaches are typically free of geometric singularities. As the speed of surface generation is crucial to implicit solvent model based molecular dynamics, four numerical algorithms, a semi-implicit scheme, a Crank-Nicolson scheme, and two alternating direction implicit (ADI) schemes, are constructed and tested. Being either stable or conditionally stable but admitting a large critical time step size, these schemes overcome the stability constraint of the earlier forward Euler scheme. Aided with the Thomas algorithm, one of the ADI schemes is found to be very efficient as it balances the speed and accuracy.

  16. Chemical abundances in Virgo cluster spirals - what drives the environmental dependence of galaxy metallicity?

    NASA Astrophysics Data System (ADS)

    Ellison, Sara; Skillman, Evan; Chung, Aeree

    2009-08-01

    The Virgo cluster is not only our nearest massive cluster, but its dynamical infancy also renders it an ideal laboratory for studies of cluster formation and galaxy evolution. Given the intense interest in Virgo, it is astounding that only 9 out of over 100 spirals in its firmament have chemical abundance measurements. We propose to simultaneously address this gap in our fundamental knowledge of Virgo cluster spirals and investigate how the metallicity and abundance gradients of star forming galaxies are sensitive to environment. Our sample consists of 13 Virgo cluster spiral galaxies, preferentially gas-poor early types, which complement the existing metallicity measurements. We also sample a range of clustercentric distances (0.3 -- 3 Mpc from M87), local densities and include several galaxies which exhibit evidence for interactions with the intra-cluster medium.

  17. New insights on the formation of nuclear star clusters

    NASA Astrophysics Data System (ADS)

    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.

  18. The gaseous proto-cluster: better characterizing the initial conditions of stellar cluster formation?

    NASA Astrophysics Data System (ADS)

    Lee, Y.-N.; Hennebelle, P.

    2016-12-01

    Cluster formation simulations have always been numerically challenging due to the large range of spatial and temporal scales that vary by orders of magnitudes and multiple physical mechanisms involved. The simulation box is typically of parsec (pc) scale while resolution down to a few astronomical units (AUs) is needed to well resolve individual stars. However, studies of this kind are important for the understanding of the interaction between gravity and turbulence that guides the star formation and the mechanisms through which the possibly self-regulated initial mass function (IMF) is shaped by stellar feedback. Most simulation works have initial conditions that correspond to molecular clouds (MCs), while the actual star formation occurs in a very small volume fraction of the whole simulation box. We present a series of simulations to characterise the early stage of cluster formation, of which a primary stage of gas concentration is noticed. We denote this stage as the gaseous proto-cluster, which forms from gravo-turbulent collapse of the MC. This high-density region is indeed the principle site of star formation. The existence of this primary stage implies that the cluster formation environment is somewhat universal and cluster formation studies could therefore set out from more local conditions, therefore reducing the computational demand.

  19. Lithium formate ion clusters formation during electrospray ionization: Evidence of magic number clusters by mass spectrometry and ab initio calculations.

    PubMed

    Shukla, Anil; Bogdanov, Bogdan

    2015-02-14

    Small cationic and anionic clusters of lithium formate were generated by electrospray ionization and their fragmentations were studied by tandem mass spectrometry (collision-induced dissociation with N2). Singly as well as multiply charged clusters were formed in both positive and negative ion modes with the general formulae, (HCOOLi)nLi(+), (HCOOLi)nLim (m+), (HCOOLi)nHCOO(-), and (HCOOLi)n(HCOO)m (m-). Several magic number cluster (MNC) ions were observed in both the positive and negative ion modes although more predominant in the positive ion mode with (HCOOLi)3Li(+) being the most abundant and stable cluster ion. Fragmentations of singly charged positive clusters proceed first by the loss of a dimer unit ((HCOOLi)2) followed by the loss of monomer units (HCOOLi) although the former remains the dominant dissociation process. In the case of positive cluster ions, all fragmentations lead to the magic cluster (HCOOLi)3Li(+) as the most abundant fragment ion at higher collision energies which then fragments further to dimer and monomer ions at lower abundances. In the negative ion mode, however, singly charged clusters dissociated via sequential loss of monomer units. Multiply charged clusters in both positive and negative ion modes dissociated mainly via Coulomb repulsion. Quantum chemical calculations performed for smaller cluster ions showed that the trimer ion has a closed ring structure similar to the phenalenylium structure with three closed rings connected to the central lithium ion. Further additions of monomer units result in similar symmetric structures for hexamer and nonamer cluster ions. Thermochemical calculations show that trimer cluster ion is relatively more stable than neighboring cluster ions, supporting the experimental observation of a magic number cluster with enhanced stability.

  20. Lithium formate ion clusters formation during electrospray ionization: Evidence of magic number clusters by mass spectrometry and ab initio calculations

    SciTech Connect

    Shukla, Anil; Bogdanov, Bogdan

    2015-02-14

    Small cationic and anionic clusters of lithium formate were generated by electrospray ionization and their fragmentations were studied by tandem mass spectrometry (collision-induced dissociation with N{sub 2}). Singly as well as multiply charged clusters were formed in both positive and negative ion modes with the general formulae, (HCOOLi){sub n}Li{sup +}, (HCOOLi){sub n}Li{sub m}{sup m+}, (HCOOLi){sub n}HCOO{sup −}, and (HCOOLi){sub n}(HCOO){sub m}{sup m−}. Several magic number cluster (MNC) ions were observed in both the positive and negative ion modes although more predominant in the positive ion mode with (HCOOLi){sub 3}Li{sup +} being the most abundant and stable cluster ion. Fragmentations of singly charged positive clusters proceed first by the loss of a dimer unit ((HCOOLi){sub 2}) followed by the loss of monomer units (HCOOLi) although the former remains the dominant dissociation process. In the case of positive cluster ions, all fragmentations lead to the magic cluster (HCOOLi){sub 3}Li{sup +} as the most abundant fragment ion at higher collision energies which then fragments further to dimer and monomer ions at lower abundances. In the negative ion mode, however, singly charged clusters dissociated via sequential loss of monomer units. Multiply charged clusters in both positive and negative ion modes dissociated mainly via Coulomb repulsion. Quantum chemical calculations performed for smaller cluster ions showed that the trimer ion has a closed ring structure similar to the phenalenylium structure with three closed rings connected to the central lithium ion. Further additions of monomer units result in similar symmetric structures for hexamer and nonamer cluster ions. Thermochemical calculations show that trimer cluster ion is relatively more stable than neighboring cluster ions, supporting the experimental observation of a magic number cluster with enhanced stability.

  1. The physics and modes of star cluster formation: simulations.

    PubMed

    Clarke, Cathie

    2010-02-28

    We review progress in numerical simulations of star cluster formation. These simulations involve the bottom-up assembly of clusters through hierarchical mergers, which produces a fractal stellar distribution at young (approx. 0.5 Myr) ages. The resulting clusters are predicted to be mildly aspherical and highly mass-segregated, except in the immediate aftermath of mergers. The upper initial mass function within individual clusters is generally somewhat flatter than for the aggregate population. Recent work has begun to clarify the factors that control the mean stellar mass in a star-forming cloud and also the efficiency of star formation. The former is sensitive to the thermal properties of the gas while the latter depends both on the magnetic field and the initial degree of gravitational boundedness of the natal cloud. Unmagnetized clouds that are initially bound undergo rapid collapse, which is difficult to reverse by ionization feedback or stellar winds.

  2. STAR FORMATION AND RELAXATION IN 379 NEARBY GALAXY CLUSTERS

    SciTech Connect

    Cohen, Seth A.; Hickox, Ryan C.; Wegner, Gary A.

    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.

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

    NASA Astrophysics Data System (ADS)

    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

  4. Actin retrograde flow and actomyosin II arc contraction drive receptor cluster dynamics at the immunological synapse in Jurkat T cells

    PubMed Central

    Yi, Jason; Wu, Xufeng S.; Crites, Travis; Hammer, John A.

    2012-01-01

    Actin retrograde flow and actomyosin II contraction have both been implicated in the inward movement of T cell receptor (TCR) microclusters and immunological synapse formation, but no study has integrated and quantified their relative contributions. Using Jurkat T cells expressing fluorescent myosin IIA heavy chain and F-tractin—a novel reporter for F-actin—we now provide direct evidence that the distal supramolecular activation cluster (dSMAC) and peripheral supramolecular activation cluster (pSMAC) correspond to lamellipodial (LP) and lamellar (LM) actin networks, respectively, as hypothesized previously. Our images reveal concentric and contracting actomyosin II arcs/rings at the LM/pSMAC. Moreover, the speeds of centripetally moving TCR microclusters correspond very closely to the rates of actin retrograde flow in the LP/dSMAC and actomyosin II arc contraction in the LM/pSMAC. Using cytochalasin D and jasplakinolide to selectively inhibit actin retrograde flow in the LP/dSMAC and blebbistatin to selectively inhibit actomyosin II arc contraction in the LM/pSMAC, we demonstrate that both forces are required for centripetal TCR microcluster transport. Finally, we show that leukocyte function–associated antigen 1 clusters accumulate over time at the inner aspect of the LM/pSMAC and that this accumulation depends on actomyosin II contraction. Thus actin retrograde flow and actomyosin II arc contraction coordinately drive receptor cluster dynamics at the immunological synapse. PMID:22219382

  5. Actin retrograde flow and actomyosin II arc contraction drive receptor cluster dynamics at the immunological synapse in Jurkat T cells.

    PubMed

    Yi, Jason; Wu, Xufeng S; Crites, Travis; Hammer, John A

    2012-03-01

    Actin retrograde flow and actomyosin II contraction have both been implicated in the inward movement of T cell receptor (TCR) microclusters and immunological synapse formation, but no study has integrated and quantified their relative contributions. Using Jurkat T cells expressing fluorescent myosin IIA heavy chain and F-tractin-a novel reporter for F-actin-we now provide direct evidence that the distal supramolecular activation cluster (dSMAC) and peripheral supramolecular activation cluster (pSMAC) correspond to lamellipodial (LP) and lamellar (LM) actin networks, respectively, as hypothesized previously. Our images reveal concentric and contracting actomyosin II arcs/rings at the LM/pSMAC. Moreover, the speeds of centripetally moving TCR microclusters correspond very closely to the rates of actin retrograde flow in the LP/dSMAC and actomyosin II arc contraction in the LM/pSMAC. Using cytochalasin D and jasplakinolide to selectively inhibit actin retrograde flow in the LP/dSMAC and blebbistatin to selectively inhibit actomyosin II arc contraction in the LM/pSMAC, we demonstrate that both forces are required for centripetal TCR microcluster transport. Finally, we show that leukocyte function-associated antigen 1 clusters accumulate over time at the inner aspect of the LM/pSMAC and that this accumulation depends on actomyosin II contraction. Thus actin retrograde flow and actomyosin II arc contraction coordinately drive receptor cluster dynamics at the immunological synapse.

  6. Dynamical Formation of Black Hole Binaries in Globular Clusters

    NASA Astrophysics Data System (ADS)

    Rasio, Frederic A.; Chatterjee, Sourav; Kremer, Kyle; Rodriguez, Carl

    2017-08-01

    Theoretical predictions for black holes in field populations of binary stars are extremely sensitive to the assumptions of stellar evolution, leading, for example, to predicted merger rates for binary black holes that span several orders of magnitude. But in dense stellar environments such as globular clusters, binary black holes form by well-understood gravitational interactions. We will present an overview of recent theoretical work on the dynamical formation of black hole binaries based on realistic N-body simulations of globular clusters. By calibrating theoretical models against observed properties of globular clusters, we find that the mergers of dynamically formed binaries could eventually be detected by Advanced LIGO at a rate of at least ~ 100 per year, potentially dominating the overall detection rate of gravitational wave sources. Dynamical processes in globular clusters can also form very naturally the black hole X-ray binaries that have been tentatively identified recently in many Milky Way and extragalactic globular clusters.

  7. From a star cluster ensemble to its formation history

    NASA Astrophysics Data System (ADS)

    Schulz, Christine; Hilker, Michael

    2017-03-01

    The present-day sample of ultra-compact dwarf galaxies (UCDs) and globular clusters (GCs) around NGC 1399 is interpreted to be composed of individual star cluster (SC) populations. It is assumed that such an SC population forms at a constant star-formation rate (SFR), and its mass distribution is described by the embedded cluster mass function (ECMF) up to the upper limit M max. The GCs and UCDs probably formed in interactions of the progenitor galaxies during the assembly of the central Fornax galaxy cluster which is why we use them as tracers of those events. After some corrections, the overall GC/UCD mass function is decomposed into separate SC populations, each described by an ECMF. M max of each ECMF is converted to an SFR according to the SFR-M max relation, revealing the SFRs reached during the assembly of galaxies in the central Fornax galaxy cluster.

  8. The Imprints Of Galactic Environment On Cluster Formation and Evolution

    NASA Astrophysics Data System (ADS)

    Adamo, Angela

    2017-03-01

    Young star clusters (YSCs) appear to be a ubiquitous product of star formation in local galaxies, thus, they can be used to study the star formation process at work in their host galaxies. Moreover, YSCs are intrinsically brighter that single stars, potentially becoming the most important tracers of the recent star formation history in galaxies in the local Universe. In local galaxies, we also witness the presence of a large population of evolved star clusters, commonly called globular clusters (GCs). GCs peak formation history is very close to the redshift (z ~ 2) when the cosmic star formation history reached the maximum. Therefore, GCs are usually associated to extreme star formation episodes in high-redshift galaxies. It is yet not clear whether YSCs and GCs share a similar formation process (same physics under different interstellar medium conditions) and evolution process, and whether the former can be used as progenitor analogs of the latter. In this invited contribution, I review general properties of YSC populations in local galaxies. I will summarise some of the current open questions in the field, with particular emphasis to whether or not galactic environments, where YSCs form, leave imprints on the nested populations. The importance of this rapidly developing field can be crucial in understanding GC formation and possibly the galactic environment condition where this ancient population formed.

  9. Formation of protonated ammonia clusters probed by a femtosecond laser

    SciTech Connect

    Purnell, J.; Wei, S.; Buzza, S.A.; Castleman, A.W. Jr. )

    1993-12-02

    Femtosecond pump-probe techniques combined with a reflection time-of-flight mass spectrometer are employed to investigate the formation mechanisms of protonated ammonia clusters. Pump pulses are employed to excite the ammonia clusters to electronically excited states corresponding to selected A or C' states, while probe pulses with variable delay times are used to ionize the clusters. The results reveal that both the absorption-ionization-dissociation and absorption-dissociation-ionization mechanisms occur in the A state, while the absorption-ionization-dissociation mechanism is the sole one operative in the C' state. 23 refs., 7 figs.

  10. Probing Globular Cluster Formation in Low Metallicity Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Johnson, Kelsey E.; Hunt, Leslie K.; Reines, Amy E.

    2008-12-01

    The ubiquitous presence of globular clusters around massive galaxies today suggests that these extreme star clusters must have been formed prolifically in the earlier universe in low-metallicity galaxies. Numerous adolescent and massive star clusters are already known to be present in a variety of galaxies in the local universe; however most of these systems have metallicities of 12 + log(O/H) > 8, and are thus not representative of the galaxies in which today's ancient globular clusters were formed. In order to better understand the formation and evolution of these massive clusters in environments with few heavy elements, we have targeted several low-metallicity dwarf galaxies with radio observations, searching for newly-formed massive star clusters still embedded in their birth material. The galaxies in this initial study are HS 0822+3542, UGC 4483, Pox 186, and SBS 0335-052, all of which have metallicities of 12 + log(O/H) < 7.75. While no thermal radio sources, indicative of natal massive star clusters, are found in three of the four galaxies, SBS 0335-052 hosts two such objects, which are incredibly luminous. The radio spectral energy distributions of these intense star-forming regions in SBS 0335-052 suggest the presence of ~12,000 equivalent O-type stars, and the implied star formation rate is nearing the maximum starburst intensity limit.

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

    PubMed

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

    2014-11-19

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

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

    NASA Astrophysics Data System (ADS)

    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.

  13. Formation and evolution of star clusters in merging galaxies

    NASA Astrophysics Data System (ADS)

    Zhang, Qing

    2002-04-01

    Recent observations have revealed numerous young massive star clusters, often known as “young globular clusters”. Their formation and evolution are important astrophysical processes and may potentially have cosmological implications. In this work, we focus on the star clusters in the nearest ongoing merger NGC 4038/9 (the “Antennae”). With the Hubble Space Telescope, we identify clusters with all ages, most of which are younger than 20 Myr. Our goal is to study their formation mechanisms, and the relation with the interstellar medium environment, and their evolutionary connection with old globular clusters. We find that their luminosity function and mass function are best described as power laws with indices around -2. The masses of young star clusters cover the range 104 ≤ M ≤ 10 6 M⊙ . This result is distinctly different from that of old globular clusters that has a “preferred” scale at M ≈ 2 × 105 M⊙ . To understand the difference in MF between the young and old star clusters, we conduct a theoretical study on the effects of dynamical disruption of individual clusters on the mass function. We find that, for a wide variety of initial conditions, the mass function develops a characteristic scale, that is remarkably close to the observed one for globular clusters after 12 Gyr. In addition, we find that some radial anisotropy in the initial velocity distribution, especially when decreasing outward, is needed to account for the observed near-uniformity of the mass functions of globular clusters. This is consistent with the observed near-isotropy of the present velocity distributions because clusters on elongated orbits are preferentially destroyed. In order to understand the formation and feedback effects of young star clusters, we have also conducted a multi- wavelength study on the association between young star clusters and their interstellar environment in the Antennae galaxies. This is possible for the first time because various new

  14. The star-formation history of very young clusters

    NASA Technical Reports Server (NTRS)

    Stahler, S. W.

    1985-01-01

    The popular idea that star formation has proceeded sequentially from lowest to highest mass members in open clusters is examined critically. For extremely young clusters, such as NGC 2264 and NGC 6530, this sequential hypothesis is a consequence of the assignment of pre-main-sequence contraction ages to all member stars. However, such ages yield a formation history which is implausible from a physical point of view, since the critical time for the onset of formation at any stellar mass is equal to the pre-main-sequence contraction time for that mass. Moreover, these ages are in conflict with the strong observational evidence that a substantial fraction of cluster members have already reached the main sequence. After reconsideration of the probable main-sequence members, the stellar ages in NGC 2264 and NGC 6530 are consistent with a variety of formation histories, and, in particular, with the view that all stellar masses form in approximately the same interval of time within a given cluster, i.e., that there is no mass-age correlation. A notion closely related to the sequential hypothesis, that the total star-formation rate increases exponentially with time, is subject to the same criticism.

  15. DETECTING STAR FORMATION IN BRIGHTEST CLUSTER GALAXIES WITH GALEX

    SciTech Connect

    Hicks, A. K.; Donahue, M.; Mushotzky, R. E-mail: donahue@pa.msu.ed

    2010-08-20

    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 {>=} 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 which 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 star formation is directly and incontrovertibly related to the cooling gas.

  16. Concomitant formation of different nature clusters and hardening in reactor pressure vessel steels irradiated by heavy ions

    NASA Astrophysics Data System (ADS)

    Fujii, K.; Fukuya, K.; Hojo, T.

    2013-11-01

    Specimens of A533B steels containing 0.04, 0.09 and 0.21 wt%Cu were irradiated at 290 °C to 3 dpa with 3 MeV Fe ions and subjected to atom probe analyses, transmission electron microscopy observations and hardness measurements. The atom probe analysis results showed that two types of solute clusters were formed: Cu-enriched clusters containing Mn, Ni and Si atoms as irradiation-enhanced solute atom clusters and Mn/Ni/Si-enriched clusters as irradiation-induced solute atom clusters. Both cluster types occurred in the highest Cu-content steel and the ratio of Mn/Ni/Si-enriched clusters to Cu-enriched clusters increased with irradiation doses. It was confirmed that the cluster formation was a key factor in the microstructure evolution until the high dose irradiation was reached even in the low Cu content steels though the dislocation loops with much lower density than that of the clusters were observed as matrix damage. The difference in the hardening efficiency due to the difference in the nature of the clusters was small. The irradiation-induced clustering of undersized Si atoms suggested that a clustering driving force other than vacancy-driven diffusion, probably an interstitial mechanism, may become important at higher dose rates.

  17. THE DYNAMICAL STATE OF BRIGHTEST CLUSTER GALAXIES AND THE FORMATION OF CLUSTERS

    SciTech Connect

    Coziol, R.; Andernach, H.; Caretta, C. A.; Alamo-MartInez, K. A.; Tago, E. E-mail: heinz@astro.ugto.mx E-mail: k.alamo@astrosmo.unam.mx

    2009-06-15

    A large sample of Abell clusters of galaxies, selected for the likely presence of a dominant galaxy, is used to study the dynamical properties of the brightest cluster members (BCMs). From visual inspection of Digitized Sky Survey images combined with redshift information we identify 1426 candidate BCMs located in 1221 different redshift components associated with 1169 different Abell clusters. This is the largest sample published so far of such galaxies. From our own morphological classification we find that {approx}92% of the BCMs in our sample are early-type galaxies and 48% are of cD type. We confirm what was previously observed based on much smaller samples, namely, that a large fraction of BCMs have significant peculiar velocities. From a subsample of 452 clusters having at least 10 measured radial velocities, we estimate a median BCM peculiar velocity of 32% of their host clusters' radial velocity dispersion. This suggests that most BCMs are not at rest in the potential well of their clusters. This phenomenon is common to galaxy clusters in our sample, and not a special trait of clusters hosting cD galaxies. We show that the peculiar velocity of the BCM is independent of cluster richness and only slightly dependent on the Bautz-Morgan type. We also find a weak trend for the peculiar velocity to rise with the cluster velocity dispersion. The strongest dependence is with the morphological type of the BCM: cD galaxies tend to have lower relative peculiar velocities than elliptical galaxies. This result points to a connection between the formation of the BCMs and that of their clusters. Our data are qualitatively consistent with the merging-groups scenario, where BCMs in clusters formed first in smaller subsystems comparable to compact groups of galaxies. In this scenario, clusters would have formed recently from the mergers of many such groups and would still be in a dynamically unrelaxed state.

  18. Kinematics of a Massive Star Cluster in Formation

    NASA Astrophysics Data System (ADS)

    Tan, Jonathan

    2014-10-01

    We propose to measure the proper motion stellar kinematics of a massive (~10^4Msun), forming proto-star-cluster to test basic theoretical models of formation. This will be the first time such a measurement has been performed. It requires HST-WFC3/IR and is beyond the practical capabilities of ground-based adaptive optics (AO) observations. In contrast to previously-studied massive, young (<10 Myr-old), already-formed clusters, such as NGC3603, Westerlund 1 or the Arches, our target protocluster, G286.21+0.17 (hereafter G286), is still gas-dominated and undergoing active star formation. It has been carefully selected from a complete survey of ~300 dense molecular gas clumps in a 120 sq. deg. region of the Galactic plane. The cluster is also relatively nearby (~2.5 kpc), but not too close that it would span a prohibitively large angular area or suffer from significant saturation problems. Such massive systems are rare and indeed we are unaware of any equivalent, early-stage (i.e., gas dominated) cluster that is closer. Given the depth of its gravitational potential based on its mass and size, the expected proper motions of many independent sub-clusters of stars are detectable at the ~5 sigma level over a 2-year baseline and global contraction of the cluster can be seen if it is happening even at just ~10% of the free-fall rate.

  19. Stellar Dynamical Processes in Massive Star and Star Cluster Formation

    NASA Astrophysics Data System (ADS)

    Tan, Jonathan; Eyer, L.

    2009-01-01

    We study how high precision astrometric measurements by SIM and GAIA of stars involved in dynamical ejection events from star clusters can constrain theories of massive star and star cluster formation. We focus on the Orion Nebula Cluster (ONC). First, we investigate the scientific potential associated with an accurate measurement of the distance and proper motion of Theta 1 Ori C, which is the most massive star in the cluster and was recently involved (about 4000 years ago) in the ejection of a B star: the Becklin-Neugebauer (BN) star. The motion of the BN star has taken it close to a massive protostar, known as source I, where it appears to have influenced the accretion and outflow activity, most likely by a tidal interaction with the accretion disk. An accurate proper motion measurement of Theta 1 Ori C will constrain BN's initial motion, allowing us to search for deflections caused by the gravitational potential of the massive protostar. Second, we search the Hipparcos catalog for candidate runaway stars, i.e. that have been dynamically ejected from the cluster over the course of the last several Myr. SIM and GAIA observations of these stars will be needed to confirm their origin from the ONC. The results of this study will constrain the star cluster formation timescale and the statistics of the population of ejected stars. JCT acknowledges support from from NSF CAREER grant AST-0645412 and a grant from NASA for SIM Science Studies.

  20. W3 Main, a test case for cluster formation

    NASA Astrophysics Data System (ADS)

    Bik, Arjan

    2013-07-01

    Embedded clusters play an important role in the star formation process: it is in these embedded clusters where most, or even all, young stars are born. In such star-forming regions, stars interact via stellar feedback and dynamical interactions with each other and with the surrounding interstellar medium. Therefore, the understanding of the physical processes operating on scales of a few tens of parsecs becomes fundamental to perceive the impact of star formation on global galactic scales. We use the embedded cluster W3 Main as a test case to derive constraints on the formation of embedded clusters. Deep near-infrared JHK imaging of W3 Main as well as K-band spectroscopy of the massive stars using LUCI1 at the LBT provide us with a detailed picture of this complex region. We combine these data with a large multi-wavelength dataset, ranging from X-rays to radio in order to derive its formation history. Based on the spectroscopy of the massive stars and the presence of hyper-compact HII regions in W3 Main we derive an age spread of 2 -3 Myrs for W3 Main. This age spread is comfirmed by a spatially varying disk fraction of the low-mass stars. The age of the most massive O star IRS2, and the nature of the HII regions suggest that star formation in W3 Main started at least 2-3 Myrs ago, and due to dynamical interactions with dense molecular cores in the surroundings and possible internal triggering, star formation is continuing until the present day. Currently the youngest population is located in the center and may be the latest dense concentration of molecular gas in the contracting cloud, forming the youngest sub cluster around IRS5.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed

    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.

  3. DUST-OBSCURED STAR FORMATION IN INTERMEDIATE REDSHIFT GALAXY CLUSTERS

    SciTech Connect

    Finn, Rose A.; Desai, Vandana; Rudnick, Gregory; Poggianti, Bianca; Bell, Eric F.; Hinz, Joannah; Zaritsky, Dennis; Jablonka, Pascale; Milvang-Jensen, Bo; Moustakas, John; Rines, Kenneth E-mail: jmoustakas@ucsd.ed

    2010-09-01

    We present Spitzer MIPS 24 {mu}m observations of sixteen 0.4 < z < 0.8 galaxy clusters drawn from the ESO Distant Cluster Survey. This is the first large 24 {mu}m survey of clusters at intermediate redshift. The depth of our imaging corresponds to a total IR luminosity of 8 x 10{sup 10} L{sub sun}, just below the luminosity of luminous infrared galaxies (LIRGs), and 6{sup +1}{sub -1}% of M{sub V} < -19 cluster members show 24 {mu}m emission at or above this level. We compare with a large sample of coeval field galaxies and find that while the fraction of cluster LIRGs lies significantly below that of the field, the IR luminosities of the field and cluster galaxies are consistent. However, the stellar masses of the EDisCS LIRGs are systematically higher than those of the field LIRGs. A comparison with optical data reveals that {approx}80% of cluster LIRGs are blue and the remaining 20% lie on the red sequence. Of LIRGs with optical spectra, 88{sup +4} {sub -5}% show [O II] emission with EW([O II]) > 5 A, and {approx}75% exhibit optical signatures of dusty starbursts. On average, the fraction of cluster LIRGs increases with projected clustercentric radius but remains systematically lower than the field fraction over the area probed (<1.5x R {sub 200}). 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 exponentially declining LIRG fraction, with the decline in the field delayed by {approx}1 Gyr relative to the clusters.

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

    SciTech Connect

    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.

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

    NASA Astrophysics Data System (ADS)

    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).

  6. The Formation and Early Evolution of Embedded Massive Star Clusters

    NASA Astrophysics Data System (ADS)

    Barnes, Peter

    We propose to combine Spitzer, WISE, Herschel, and other archival spacecraft data with an existing ground- and space-based mm-wave to near-IR survey of molecular clouds over a large portion of the Milky Way, in order to systematically study the formation and early evolution of massive stars and star clusters, and provide new observational calibrations for a theoretical paradigm of this key astrophysical problem. Central Objectives: The Galactic Census of High- and Medium-mass Protostars (CHaMP) is a large, unbiased, uniform, and panchromatic survey of massive star and cluster formation and early evolution, covering 20°x6° of the Galactic Plane. Its uniqueness lies in the comprehensive molecular spectroscopy of 303 massive dense clumps, which have also been included in several archival spacecraft surveys. Our objective is a systematic demographic analysis of massive star and cluster formation, one which has not been possible without knowledge of our CHaMP cloud sample, including all clouds with embedded clusters as well as those that have not yet formed massive stars. For proto-clusters deeply embedded within dense molecular clouds, analysis of these space-based data will: 1. Yield a complete census of Young Stellar Objects in each cluster. 2. Allow systematic measurements of embedded cluster properties: spectral energy distributions, luminosity functions, protostellar and disk fractions, and how these vary with cluster mass, age, and density. Combined with other, similarly complete and unbiased infrared and mm data, CHaMP's goals include: 3. A detailed comparison of the embedded stellar populations with their natal dense gas to derive extinction maps, star formation efficiencies and feedback effects, and the kinematics, physics, and chemistry of the gas in and around the clusters. 4. Tying the demographics, age spreads, and timescales of the clusters, based on pre-Main Sequence evolution, to that of the dense gas clumps and Giant Molecular Clouds. 5. A

  7. Linked supramolecular building blocks for enhanced cluster formation

    DOE PAGES

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

    2015-01-09

    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 complex assembly process. The ability to covalently link calix[4]arenes at the methylene bridge provides significantly improved control over the introduction of different metal centres to resulting cluster motifs. Clusters assembled from bis-calix[4]arenes and transition metal ions or 3d-4f combinations display characteristic features of the analogous calix[4]arene supported clusters, thereby demonstrating an enhanced and rational approach towards the targeted synthesis of complex and challenging structures.

  8. Linked supramolecular building blocks for enhanced cluster formation

    SciTech Connect

    McLellan, Ross; Palacios, Maria A.; Beavers, Christine M.; Teat, Simon J.; Piligkos, Stergios; Brechin, Euan K.; Dalgarno, Scott J.

    2015-01-09

    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 complex assembly process. The ability to covalently link calix[4]arenes at the methylene bridge provides significantly improved control over the introduction of different metal centres to resulting cluster motifs. Clusters assembled from bis-calix[4]arenes and transition metal ions or 3d-4f combinations display characteristic features of the analogous calix[4]arene supported clusters, thereby demonstrating an enhanced and rational approach towards the targeted synthesis of complex and challenging structures.

  9. Formation and stability of high-spin alkali clusters.

    PubMed

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

    2004-01-09

    Helium nanodroplet isolation has been applied to agglomerate alkali clusters at temperatures of 380 mK. 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, van der Waals-like complexes of metal atoms. We find that sodium and potassium readily form such clusters containing up to 25 atoms. 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.

  10. Formation and Stability of High-Spin Alkali Clusters

    NASA Astrophysics Data System (ADS)

    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.

  11. Confronting the outflow-regulated cluster formation model with observations

    SciTech Connect

    Nakamura, Fumitaka; Li, Zhi-Yun E-mail: zl4h@virginia.edu

    2014-03-10

    Protostellar outflows have been shown theoretically to be capable of maintaining supersonic turbulence in cluster-forming clumps and keeping the star formation rate per free-fall time as low as a few percent. We aim to test two basic predictions of this outflow-regulated cluster formation model, namely, (1) the clump should be close to virial equilibrium and (2) the turbulence dissipation rate should be balanced by the outflow momentum injection rate, using recent outflow surveys toward eight nearby cluster-forming clumps (B59, L1551, L1641N, Serpens Main Cloud, Serpens South, ρ Oph, IC 348, and NGC 1333). We find, for almost all sources, that the clumps are close to virial equilibrium and the outflow momentum injection rate exceeds the turbulence momentum dissipation rate. In addition, the outflow kinetic energy is significantly smaller than the clump gravitational energy for intermediate and massive clumps with M {sub cl} ≳ a few × 10{sup 2} M {sub ☉}, suggesting that the outflow feedback is not enough to disperse the clump as a whole. The number of observed protostars also indicates that the star formation rate per free-fall time is as small as a few percent for all clumps. These observationally based results strengthen the case for outflow-regulated cluster formation.

  12. Shallow junction formation by polyatomic cluster ion implantation

    SciTech Connect

    Takeuchi, Daisuke; Shimada, Norihiro; Matsuo, Jiro; Yamada, Isao

    1996-12-31

    Recent integrated circuits require shallow junctions which are less than 0.1 {mu}m depth. This creates a strong demand for low energy ion beam techniques. Equivalent low-energy and high-current ion beams can be realized quite easily with clusters, because the kinetic energy of the cluster is shared between the constituent atoms. Additionally, cluster-ion beams avoid damage due to excessive charge. We have used polyatomic clusters, decaborane (B{sub 10}H{sub 14}), as a kind of B cluster, in order to form a very shallow p{sup +} junction. A B SIMS profile of B{sub 10}H{sub 14} implanted into Si (100) at 20keV was quite similar to that of B implanted at 2keV. These SIMS measurements revealed that the cluster ion beam can realize equivalent low-energy implantation quite easily. The implantation efficiency achieved was about 90%. The damage induced by B{sub 10}H{sub 14} implantation was completely removed by a 600{degrees}C furnace anneal for 30 min, and implanted B atoms were electrically activated. After rapid thermal annealing (RTA) at 900{degrees}C of a sample prepared with a close of 5{times}10{sup 13} ion/cm{sup 2}, the sheet resistance decreased to about 600W/sq. and the activation efficiency was about 50%. These results show that a polyatomic cluster ion beam is useful for shallow junction formation.

  13. Star Formation in Space and Time: The Orion Nebula Cluster

    NASA Astrophysics Data System (ADS)

    Huff, E. M.; Stahler, Steven W.

    2006-06-01

    We examine the pattern of star birth in the Orion Nebula cluster (ONC), with the goal of discerning the cluster's formation mechanism. Outside the Trapezium, the distribution of stellar masses is remarkably uniform and is not accurately described by the field-star initial mass function. The deconvolved, three-dimensional density of cluster members peaks at the Trapezium stars, which are truly anomalous in mass. Using theoretical pre-main-sequence tracks, we confirm the earlier finding that star formation has accelerated over the past 107 yr. We further show that the rate of acceleration has been the same for all masses. Thus, there is no correlation between stellar age and mass, contrary to previous claims. Finally, the acceleration has been spatially uniform throughout the cluster. Our reconstruction of the parent molecular cloud spawning the cluster shows that it had a mass of 6700 Msolar prior to its destruction by the Trapezium. If the cloud was supported against self-gravity by mildly dissipative turbulence, then it contracted in a quasi-static but accelerating manner. We demonstrate this contraction theoretically through a simple energy argument. The mean turbulent speed increased to its recent value, which is reflected in the present-day stellar velocity dispersion. The current ONC will be gravitationally unbound once cloud destruction is complete, and is destined to become a dispersing OB association. We hypothesize that similarly crowded groups seen at the centers of distant OB associations are also unbound and do not give rise to the Galactic population of open clusters. Finally, accelerating star formation implies that most clumps within giant molecular complexes should have relatively low formation activity. Sensitive infrared surveys could confirm this hypothesis.

  14. WITNESSING THE FORMATION OF A BRIGHTEST CLUSTER GALAXY IN A NEARBY X-RAY CLUSTER

    SciTech Connect

    Rasmussen, Jesper; Mulchaey, John S.; Bai, Lei; Ponman, Trevor J.; Raychaudhury, Somak; Dariush, Ali

    2010-07-10

    The central dominant galaxies in galaxy clusters constitute the most massive and luminous galaxies in the universe. Despite this, the formation of these brightest cluster galaxies (BCGs) and the impact of this on the surrounding cluster environment remain poorly understood. Here we present multiwavelength observations of the nearby poor X-ray cluster MZ 10451, in which both processes can be studied in unprecedented detail. Chandra observations of the intracluster medium (ICM) in the cluster core, which harbors two optically bright early-type galaxies in the process of merging, show that the system has retained a cool core and a central metal excess. This suggests that any merger-induced ICM heating and mixing remain modest at this stage. Tidally stripped stars seen around either galaxy likely represent an emerging intracluster light component, and the central ICM abundance enhancement may have a prominent contribution from in situ enrichment provided by these stars. The smaller of the merging galaxies shows evidence for having retained a hot gas halo, along with tentative evidence for some obscured star formation, suggesting that not all BCG major mergers at low redshift are completely dissipationless. Both galaxies are slightly offset from the peak of the ICM emission, with all three lying on an axis that roughly coincides with the large-scale elongation of the ICM. Our data are consistent with a picture in which central BCGs are built up by mergers close to the cluster core, by galaxies infalling on radial orbits aligned with the cosmological filaments feeding the cluster.

  15. The Inception of Star Cluster Formation: [CII] emission from IRDCs

    NASA Astrophysics Data System (ADS)

    Tan, Jonathan

    2015-10-01

    Most stars are born in clusters. Thus, the processes that may initiate star cluster formation are of fundamental importance throughout astrophysics, from the evolution of stellar populations in galaxies to the formation of planets in protoplanetary disks in these environments. Infrared Dark Clouds (IRDCs) are now recognized as the likely precursors of star clusters. Thus it is important to understand the kinematics, dynamics & formation environments of IRDCs. We propose to utilize the efficient mapping capabilities of upGREAT to map [CII] emission in a sample of 4 IRDCs that we have been studying over the last decade with numerous facilities, including Spitzer, IRAM 30m, IRAM PdBI, Herschel & ALMA. [CII] probes the photodissociation region around the IRDC. Thus it may provide crucial information on the kinematics of the gas that is becoming molecular and joining the IRDC. Different theoretical models of IRDC formation are expected to have different signatures of [CII] kinematics. For example, we are investigating simulations of dense gas formation via either decaying turbulence or triggering by cloud-cloud collisions: these simulations make specific distinguishing predictions for [CII] that can be tested against upGREAT observations. We propose to carry out OTF mapping with SOFIA-upGREAT to study 4 IRDCs with sensitivity of 0.35 K per beam achieved at km/s velocity resolution. From previous studies of [CII] in IRDCs we expect strong detections. We will test observed [CII] spatial and kinematic structures against numerical simulations of various scenarios of IRDC formation to deduce the processes that initiate star cluster formation.

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

    NASA Astrophysics Data System (ADS)

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

    2001-02-01

    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 that 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 (NGC 7648), exhibits signatures of a tidal encounter. Neutral hydrogen observations of that galaxy with the Arecibo radio telescope reveal the presence of ~4×108 Msolar of H I. Arecibo observations of other current or recent star-forming early-type galaxies in Pegasus I indicate smaller amounts of gas in one of them, and only upper limits in others. These observations indicate that NGC 7648 in the Pegasus I cluster owes its present star formation episode to some form of tidal interaction. The same may be true for the other galaxies with centralized star formation, but we cannot rule out the possibility that their outer disks have been removed via ram pressure stripping, followed by rapid quenching of star formation in the central region.

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

    NASA Astrophysics Data System (ADS)

    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.

  18. The Galactic open cluster system: evidence of enhanced formation episodes

    NASA Astrophysics Data System (ADS)

    Piatti, A. E.

    The exciting debate about the existence of signs of enhanced formation of Galactic open clusters (OCs) is revisited here on the basis of a revised age distribution. By using the recently updated 2009 version of the Dias et al. catalogue of 1787 OCs, we found that the present OC's age distribution presents two primary excesses at t ~ 10-15 Myr and 1.5 Gyr. We interpret both excesses as signs of enhanced formation episodes similar to those that occurred in other galaxies (e.g., M 51, NGC 1705). When restricting the OC sample to those located in the solar neighbourhood, with the aim of avoiding incompleteness effects, we also find that these clusters are engraved with clear signs of enhanced formation at both ages.

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

    NASA Astrophysics Data System (ADS)

    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 (z<0.03) groups and clusters of varied richness, morphological type mix, and X-ray luminosity. By studying a large range of environments and considering the spatial distributions of star formation, we probe mechanisms of gas depletion and morphological transformation. The project uses ALFALFA HI observations, optical observations, and digital databases like SDSS, and incorporates work 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.

  20. STAR FORMATION IN THE BULLET CLUSTER. I. THE INFRARED LUMINOSITY FUNCTION AND STAR FORMATION RATE ,

    SciTech Connect

    Sun Mi Chung; Gonzalez, Anthony H.; Clowe, Douglas; Markevitch, Maxim; Zaritsky, Dennis

    2010-12-20

    The Bullet Cluster is a massive galaxy cluster at z = 0.297 undergoing a major supersonic (Mach 3) merger event. Using data from Spitzer MIPS and the Infrared Array Camera, optical imaging, and optical spectroscopy, we present the global star formation rate (SFR) of this unique cluster. Using a 90% spectroscopically complete sample of 37 star-forming MIPS confirmed cluster members out to R < 1.7 Mpc, and the Rieke et al. relation to convert from 24 {mu}m flux to SFR, we calculate an integrated obscured SFR of 267 M{sub sun} yr{sup -1} and a specific SFR of 28 M{sub sun} yr{sup -1} per 10{sup 14} M{sub sun}. The cluster mass normalized integrated SFR of the Bullet Cluster is among the highest in a sample of eight other clusters and cluster mergers from the literature. Five LIRGs and one ULIRG contribute 30% and 40% of the total SFR of the cluster, respectively. To investigate the origin of the elevated specific SFR, we compare the infrared luminosity function (IR LF) of the Bullet Cluster to those of Coma (evolved to z = 0.297) and CL1358+62. The Bullet Cluster IR LF exhibits an excess of sources compared to the IR LFs of the other massive clusters. A Schechter function fit of the Bullet Cluster IR LF yields L* = 44.68 {+-} 0.11 erg s{sup -1}, which is {approx}0.25 and 0.35 dex brighter than L* of evolved Coma and CL1358+62, respectively. The elevated IR LF of the Bullet Cluster relative to other clusters can be explained if we attribute the 'excess' star-forming IR galaxies to a population associated with the infalling group that has not yet been transformed into quiescent galaxies. In this case, the timescale required for quenching star formation in the cluster environment must be longer than the timescale since the group's accretion-a few hundred million years. We suggest that 'strangulation' is likely to be an important process in the evolution of star formation in clusters.

  1. Quenching of the star formation activity in cluster galaxies

    NASA Astrophysics Data System (ADS)

    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% < QF ≤ 80% and QA ≲ 500 Myr for QF > 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 < 0.5), where the hot diffuse X-ray emitting gas of the cluster is located, to the outer regions (R/Rvir > 4). The efficient quenching of the

  2. Star formation in the massive cluster merger Abell 2744

    NASA Astrophysics Data System (ADS)

    Rawle, T. D.; Altieri, B.; Egami, E.; Pérez-González, P. G.; Richard, J.; Santos, J. S.; Valtchanov, I.; Walth, G.; Bouy, H.; Haines, C. P.; Okabe, N.

    2014-07-01

    We present a comprehensive study of star-forming (SF) galaxies in the Hubble Space Telescope (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 SFRUV+IR = 343 ± 10 M⊙ yr-1. Within the central 4 arcmin (1.1 Mpc) radius, the integrated SFR is complete, yielding a total SFRUV+IR = 201 ± 9 M⊙ yr-1. Focusing on obscured star formation, this core region exhibits a total SFRIR = 138 ± 8 M⊙ yr-1, a mass-normalized SFRIR of ΣSFR = 11.2 ± 0.7 M⊙ yr-1 per 1014 M⊙ 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 SFRIR, 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 galaxies with substantial unobscured SF due to extreme stripping (SFRUV/SFRIR up to 3.3). The orientation of the trail, and of material stripped from constituent galaxies, indicates that the passing shock front of the cluster merger was the trigger. Constraints on star formation from both IR and UV are crucial for understanding galaxy evolution within the densest environments.

  3. STAR FORMATION ACTIVITY IN CLASH BRIGHTEST CLUSTER GALAXIES

    SciTech Connect

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

    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.

  4. In situ heat treatment of a tar sands formation after drive process treatment

    SciTech Connect

    Vinegar, Harold J.; Stanecki, John

    2010-09-21

    A method for treating a tar sands formation includes providing a drive fluid to a hydrocarbon containing layer of the tar sands formation to mobilize at least some hydrocarbons in the layer. At least some first hydrocarbons from the layer are produced. Heat is provided to the layer from one or more heaters located in the formation. At least some second hydrocarbons are produced from the layer of the formation. The second hydrocarbons include at least some hydrocarbons that are upgraded compared to the first hydrocarbons produced by using the drive fluid.

  5. The gaseous proto-cluster as a product of gravo-turbulent interaction: modified local environment for stellar cluster formation?

    NASA Astrophysics Data System (ADS)

    Lee, Y.-N.; Hennebelle, P.

    2016-12-01

    Stars are often observed to form in clusters, while the formation of the gaseous proto-cluster precedes that of the stellar cluster. We discuss the assembly of gas via gravo-turbulent reprocessing inside collapsing molecular clouds, and demonstrate that virial equilibrium is established for the gaseous proto-cluster, of which the higher density is favorable for clustered star formation, and that some physical characteristics of the stellar cluster are inherited from the gaseous proto-cluster. We introduce an analytical two-dimensional virial model to account for the quasi-stationary accreting gaseous proto-cluster which has non-negligible rotation. Results are compared to observations and simulations and the fact that gaseous proto-clusters lie on an equilibrium sequence may imply that star formation could be to some extent disentangled from larger scale physics, offering an encouraging explanation for the universality of IMF.

  6. Method of producing drive fluid in situ in tar sands formations

    DOEpatents

    Mudunuri, Ramesh Raju; Jaiswal, Namit; Vinegar, Harold J.; Karanikas, John Michael

    2010-03-23

    Methods of treating a tar sands formation are described herein. Methods for treating a tar sands may include providing heat to at least part of a hydrocarbon layer in the formation from one or more heaters located in the formation. The heat may be allowed to transfer from the heaters to at least a portion of the formation such that a drive fluid is produced in situ in the formation. The drive fluid may move at least some mobilized, visbroken, and/or pyrolyzed hydrocarbons from a first portion of the formation to a second portion of the formation. At least some of the mobilized, visbroken, and/or pyrolyzed hydrocarbons may be produced from the formation.

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

    PubMed

    Tiggesbäumker, Josef; Stienkemeier, Frank

    2007-09-14

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

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

    NASA Astrophysics Data System (ADS)

    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.

  9. Formation of young massive clusters from turbulent molecular clouds

    NASA Astrophysics Data System (ADS)

    Fujii, Michiko; Portegies Zwart, Simon

    2015-08-01

    We simulate the formation and evolution of young star clusters using smoothed-particle hydrodynamics (SPH) and direct N-body methods. We start by performing SPH simulations of the giant molecular cloud with a turbulent velocity field, a mass of 10^4 to 10^6 M_sun, and a density between 17 and 1700 cm^-3. We continue the SPH simulations for a free-fall time scale, and analyze the resulting structure of the collapsed cloud. We subsequently replace a density-selected subset of SPH particles with stars. As a consequence, the local star formation efficiency exceeds 30 per cent, whereas globally only a few per cent of the gas is converted to stars. The stellar distribution is very clumpy with typically a dozen bound conglomerates that consist of 100 to 10000 stars. We continue to evolve the stars dynamically using the collisional N-body method, which accurately treats all pairwise interactions, stellar collisions and stellar evolution. We analyze the results of the N-body simulations at 2 Myr and 10 Myr. From dense massive molecular clouds, massive clusters grow via hierarchical merging of smaller clusters. The shape of the cluster mass function that originates from an individual molecular cloud is consistent with a Schechter function with a power-law slope of beta = -1.73 at 2 Myr and beta = -1.67 at 10 Myr, which fits to observed cluster mass function of the Carina region. The superposition of mass functions have a power-law slope of < -2, which fits the observed mass function of star clusters in the Milky Way, M31 and M83. We further find that the mass of the most massive cluster formed in a single molecular cloud with a mass of M_g scales with 6.1 M_g^0.51 which also agrees with recent observation in M51. The molecular clouds which can form massive clusters are much denser than those typical in the Milky Way. The velocity dispersion of such molecular clouds reaches 20 km/s and it is consistent with the relative velocity of the molecular clouds observed near NGC 3603

  10. Formation of structure in small lead clusters under thermal effect

    NASA Astrophysics Data System (ADS)

    Baidyshev, V. S.; Gafner, Yu. Ya.

    2016-12-01

    The thermal effect on lead clusters with radii up to 5.5 nm has been investigated by the molecular dynamics method using a modified tight-binding potential TB-SMA. The melting of Pb nanoparticles of these sizes is strictly homogeneous, without the formation of a surface liquidlike layer. The primary fcc phase in the particles is retained upon heating in the overwhelming majority of model experiments. An analysis of the structure formation during crystallization has shown that structures with pentagonal symmetry are preferred for lead clusters in this case. It is noted that an increase in the nanoparticle size leads to the dominance of the dodecahedral structure over the icosahedral one.

  11. Cluster Formation Triggered by Filament Collisions in Serpens South

    NASA Astrophysics Data System (ADS)

    Nakamura, Fumitaka

    2015-08-01

    The Serpens South infrared darkcloud consists of several filamentary ridges, some of which fragment into dense clumps. On the basis of CCS, N2H+, SiO observations, we investigated the kinematics and chemical evolution of these filamentary ridges. We find that CCS is extremely strong along the main filament, in particular toward northern precluster clump. We emphasize that Serpens South is the first protocluster clump where strong CCS emission is detected. We identified several ridges with different velocity. These ridges appear to converge toward the protocluster clump, suggesting that the collisions of these ridges may have trigerred cluster formation. The collisions presumably happened within the last half Myr because the chemical evolution calculations indicate that CCS is abundant only in the first half Myr. We also speculate that these filamentary ridges might be formed in a compressed turbulent region created by a larger-scale cloud-cloud collision and subsequent filament collision triggered cluster formation.

  12. Inflammation-induced formation of fat-associated lymphoid clusters

    PubMed Central

    Bénézech, Cécile; Kruglov, Andrei A.; Loo, Yunhua; Nakamura, Kyoko; Zhang, Yang; Nayar, Saba; Jones, Lucy H.; Flores-Langarica, Adriana; McIntosh, Alistair; Marshall, Jennifer; Barone, Francesca; Besra, Gurdyal; Miles, Katherine; Allen, Judith E.; Gray, Mohini; Kollias, George; Cunningham, Adam F.; Withers, David R.; Toellner, Kai Michael; Jones, Nick D.; Veldhoen, Marc; Nedospasov, Sergei A.; McKenzie, Andrew N.J.; Caamaño, Jorge H.

    2015-01-01

    Fat-associated lymphoid clusters (FALCs) are a recently discovered type of lymphoid tissue associated with visceral fat. Here we show that distribution of FALCs was heterogeneous with the pericardium containing large numbers of these clusters. FALCs contributed to the retention of B-1 B cells in the peritoneal cavity through high expression of the chemokine CXCL13 and supported B cell proliferation and germinal center differentiation during peritoneal immune challenges. FALC formation was induced by inflammation, which triggered recruitment of myeloid cells that express tumor necrosis factor (TNF) necessary for TNF receptor-signaling in stromal cells. CD1d-restricted Natural killer T (NKT) cells were likewise required for inducible formation of FALCs. Thus, FALCs support and coordinate innate B and T cell activation during serosal immune responses. PMID:26147686

  13. Cluster formation and percolation in ethanol-water mixtures

    NASA Astrophysics Data System (ADS)

    Gereben, Orsolya; Pusztai, László

    2017-10-01

    Results of systematic molecular dynamics studies of ethanol-water mixtures, over the entire concentration range, were reported previously that agree with experimental X-ray diffraction data. These simulated systems are analyzed in this work to examine cluster formation and percolation, using four different hydrogen bond definitions. Percolation analyses revealed that each mixture (even the one containing 80 mol% ethanol) is above the 3D percolation threshold, with fractal dimensions, df, between 2.6 and 2.9, depending on concentration. Monotype water cluster formation was also studied in the mixtures: 3D water percolation can be found in systems with less than 40 mol% ethanol, with fractal dimensions between 2.53 and 2.84. These observations can be put in parallel with experimental data on some thermodynamic quantities, such as the excess partial molar enthalpy and entropy.

  14. Formation of young massive clusters from turbulent molecular clouds

    NASA Astrophysics Data System (ADS)

    Fujii, Michiko S.; Portegies Zwart, Simon

    2017-03-01

    We simulate the formation and evolution of young star clusters from turbulent molecular clouds using smoothed-particle hydrodynamics and direct N-body methods. We find that the shape of the cluster mass function that originates from an individual molecular cloud is consistent with a Schechter function with power-law slopes of β = -1.73. The superposition of mass functions turn out to have a power-law slope of < -2. The mass of the most massive cluster formed from a single molecular cloud with mass M g scales with 6.1 M 0.51 g. The molecular clouds that tend to form massive clusters are much denser than those typical found in the Milky Way. The velocity dispersion of such molecular clouds reaches 20km s-1 and it is consistent with the relative velocity of the molecular clouds observed near NGC 3603 and Westerlund 2, for which a triggered star formation by cloud-cloud collisions is suggested.

  15. Clustering on Magnesium Surfaces – Formation and Diffusion Energies

    DOE PAGES

    Chu, Haijian; Huang, Hanchen; Wang, Jian

    2017-07-12

    The formation and diffusion energies of atomic clusters on Mg surfaces determine the surface roughness and formation of faulted structure, which in turn affect the mechanical deformation of Mg. This paper reports first principles density function theory (DFT) based quantum mechanics calculation results of atomic clustering on the low energy surfaces {0001} and {more » $$\\bar{1}$$011} . In parallel, molecular statics calculations serve to test the validity of two interatomic potentials and to extend the scope of the DFT studies. On a {0001} surface, a compact cluster consisting of few than three atoms energetically prefers a face-centered-cubic stacking, to serve as a nucleus of stacking fault. On a {$$\\bar{1}$$011} , clusters of any size always prefer hexagonal-close-packed stacking. Adatom diffusion on surface {$$\\bar{1}$$011} is high anisotropic while isotropic on surface (0001). Three-dimensional Ehrlich–Schwoebel barriers converge as the step height is three atomic layers or thicker. FInally, adatom diffusion along steps is via hopping mechanism, and that down steps is via exchange mechanism.« less

  16. Dynamic tubulation of mitochondria drives mitochondrial network formation.

    PubMed

    Wang, Chong; Du, Wanqing; Su, Qian Peter; Zhu, Mingli; Feng, Peiyuan; Li, Ying; Zhou, Yichen; Mi, Na; Zhu, Yueyao; Jiang, Dong; Zhang, Senyan; Zhang, Zerui; Sun, Yujie; Yu, Li

    2015-10-01

    Mitochondria form networks. Formation of mitochondrial networks is important for maintaining mitochondrial DNA integrity and interchanging mitochondrial material, whereas disruption of the mitochondrial network affects mitochondrial functions. According to the current view, mitochondrial networks are formed by fusion of individual mitochondria. Here, we report a new mechanism for formation of mitochondrial networks through KIF5B-mediated dynamic tubulation of mitochondria. We found that KIF5B pulls thin, highly dynamic tubules out of mitochondria. Fusion of these dynamic tubules, which is mediated by mitofusins, gives rise to the mitochondrial network. We further demonstrated that dynamic tubulation and fusion is sufficient for mitochondrial network formation, by reconstituting mitochondrial networks in vitro using purified fusion-competent mitochondria, recombinant KIF5B, and polymerized microtubules. Interestingly, KIF5B only controls network formation in the peripheral zone of the cell, indicating that the mitochondrial network is divided into subzones, which may be constructed by different mechanisms. Our data not only uncover an essential mechanism for mitochondrial network formation, but also reveal that different parts of the mitochondrial network are formed by different mechanisms.

  17. Dynamic tubulation of mitochondria drives mitochondrial network formation

    PubMed Central

    Wang, Chong; Du, Wanqing; Su, Qian Peter; Zhu, Mingli; Feng, Peiyuan; Li, Ying; Zhou, Yichen; Mi, Na; Zhu, Yueyao; Jiang, Dong; Zhang, Senyan; Zhang, Zerui; Sun, Yujie; Yu, Li

    2015-01-01

    Mitochondria form networks. Formation of mitochondrial networks is important for maintaining mitochondrial DNA integrity and interchanging mitochondrial material, whereas disruption of the mitochondrial network affects mitochondrial functions. According to the current view, mitochondrial networks are formed by fusion of individual mitochondria. Here, we report a new mechanism for formation of mitochondrial networks through KIF5B-mediated dynamic tubulation of mitochondria. We found that KIF5B pulls thin, highly dynamic tubules out of mitochondria. Fusion of these dynamic tubules, which is mediated by mitofusins, gives rise to the mitochondrial network. We further demonstrated that dynamic tubulation and fusion is sufficient for mitochondrial network formation, by reconstituting mitochondrial networks in vitro using purified fusion-competent mitochondria, recombinant KIF5B, and polymerized microtubules. Interestingly, KIF5B only controls network formation in the peripheral zone of the cell, indicating that the mitochondrial network is divided into subzones, which may be constructed by different mechanisms. Our data not only uncover an essential mechanism for mitochondrial network formation, but also reveal that different parts of the mitochondrial network are formed by different mechanisms. PMID:26206315

  18. Heating hydrocarbon containing formations in a line drive staged process

    DOEpatents

    Miller, David Scott

    2009-07-21

    Method for treating a hydrocarbon containing formation are described herein. Methods may include providing heat to a first section of the formation with one or more first heaters in the first section. First hydrocarbons may be heated in the first section such that at least some of the first hydrocarbons are mobilized. At least some of the mobilized first hydrocarbons may be produced through a production well located in a second section of the formation. The second section may be located substantially adjacent to the first section. A portion of the second section may be provided some heat from the mobilized first hydrocarbons, but is not conductively heated by heat from the first heaters. Heat may be provided to the second section with one or more second heaters in the second section to further heat the second section.

  19. Molecules as Drives and Witnesses of Star Formation

    NASA Astrophysics Data System (ADS)

    Shustov, B. M.

    2017-07-01

    The progress in understanding the role of molecules in star formation is discussed. After very brief introduction which we note in that no star formation would be possible without molecules at the dawn of the Universe and that molecules are important drivers and witnesses of star formation in the current epoch, we consider observational technologies and emphasize the prospective role of UV observations. Special attention is paid to possibilities of UV spectroscopy with coming space observatory Spektr-UF (World Space Observatory - Ultraviolet; WSO-UV). Only one example (observations of CO-dark clouds) from vast scientific program of the WSO-UV is mentioned. Also very briefly disclosed is a model approach to study complex evolution of very young (prestellar) object focusing on chemical (molecular) evolution.

  20. Anisotropic thermal conduction in cosmological cluster formation simulations

    NASA Astrophysics Data System (ADS)

    Ruszkowski, Mateusz; Parrish, Ian; Brueggen, Marcus

    2009-05-01

    We investigate the role of the magnetothermal instability (MTI) in the cosmological cluster formation simulations. Our simulations self-consistently incorporate the effects of the field amplification by the structure formation (i.e., gravitational collapse and shearing) and by anisotropic thermal conduction, as well as the effects of violent sloshing motions (e.g., due to mergers) that tend to slow down the field growth. We quantify the effects of these processes on the temperature and density profiles, the strength and topology of the magnetic fields as well as the effective thermal conduction in the intarcluster medium.

  1. Cysteine-rich protein 2 accelerates actin filament cluster formation

    PubMed Central

    Shinohara, Satoko; Takaoka, Shunpei; Miyake, Jun

    2017-01-01

    Filamentous actin (F-actin) forms many types of structures and dynamically regulates cell morphology and movement, and plays a mechanosensory role for extracellular stimuli. In this study, we determined that the smooth muscle-related transcription factor, cysteine-rich protein 2 (CRP2), regulates the supramolecular networks of F-actin. The structures of CRP2 and F-actin in solution were analyzed by small-angle X-ray solution scattering (SAXS). The general shape of CRP2 was partially unfolded and relatively ellipsoidal in structure, and the apparent cross sectional radius of gyration (Rc) was about 15.8 Å. The predicted shape, derived by ab initio modeling, consisted of roughly four tandem clusters: LIM domains were likely at both ends with the middle clusters being an unfolded linker region. From the SAXS analysis, the Rc of F-actin was about 26.7 Å, and it was independent of CRP2 addition. On the other hand, in the low angle region of the CRP2-bound F-actin scattering, the intensities showed upward curvature with the addition of CRP2, which indicates increasing branching of F-actin following CRP2 binding. From biochemical analysis, the actin filaments were augmented and clustered by the addition of CRP2. This F-actin clustering activity of CRP2 was cooperative with α-actinin. Thus, binding of CRP2 to F-actin accelerates actin polymerization and F-actin cluster formation. PMID:28813482

  2. Formation and evolution of clumpy tidal tails in globular clusters

    NASA Astrophysics Data System (ADS)

    Di Matteo, P.; Miocchi, P.; Capuzzo Dolcetta, R.

    2004-05-01

    Numerical simulations of a globular cluster orbiting in the central region of a triaxial galaxy have been performed, in order to study the formation and subsequent evolution of tidal tails and their main features. Tails begin to form after about a quarter of the cluster orbital period and tend to lie along its orbit, with a leading tail that precedes the cluster and an outer tail that trails behind it. Tails show clumpy substructures; the most prominent ones (for a globular cluster moving on a quasi-circular orbit around the galaxy) are located at a distance from the cluster center between 50 pc and 80 pc and, after 3 orbital periods, contain about 10% of the cluster mass at that epoch. The morphology of tails and clumps will be compared with available observational data, in particular with that concerning Palomar 5, for which evident clumps in the tails have been detected. Kinematical properties of stars in the tails (line-of-sight velocities and velocity dispersion profiles) will be presented and compared to kinematical data of M15 and ω Centauri, two galactic globular clusters for which there is evidence that the velocity dispersion remains constant at large radii. All the simulations have been performed with our own implementation of a tree-code, that uses a multipolar expansion of the potential truncated at the quadrupole moment and that ran on high performance computers employing an original parallelization approach implemented via MPI routines. The time-integration of the `particles' trajectories is performed by a 2nd order leap-frog algorithm, using individual and variable time-steps. Part of this work has been done using the IBM SP4 platform located at CINECA (Bologna, Italy) thanks to the grant inarm007 obtained in the framework of INAF-CINECA agreements.

  3. Identifying driving gene clusters in complex diseases through critical transition theory

    NASA Astrophysics Data System (ADS)

    Wolanyk, Nathaniel; Wang, Xujing; Hessner, Martin; Gao, Shouguo; Chen, Ye; Jia, Shuang

    A novel approach of looking at the human body using critical transition theory has yielded positive results: clusters of genes that act in tandem to drive complex disease progression. This cluster of genes can be thought of as the first part of a large genetic force that pushes the body from a curable, but sick, point to an incurable diseased point through a catastrophic bifurcation. The data analyzed is time course microarray blood assay data of 7 high risk individuals for Type 1 Diabetes who progressed into a clinical onset, with an additional larger study requested to be presented at the conference. The normalized data is 25,000 genes strong, which were narrowed down based on statistical metrics, and finally a machine learning algorithm using critical transition metrics found the driving network. This approach was created to be repeatable across multiple complex diseases with only progression time course data needed so that it would be applicable to identifying when an individual is at risk of developing a complex disease. Thusly, preventative measures can be enacted, and in the longer term, offers a possible solution to prevent all Type 1 Diabetes.

  4. Dynamical formation of cataclysmic variables in globular clusters

    NASA Astrophysics Data System (ADS)

    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.

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

    SciTech Connect

    Li, Hui; Gnedin, Oleg Y. E-mail: ognedin@umich.edu

    2014-11-20

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

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

    SciTech Connect

    Rawle, T. D.; Egami, E.; Rex, M.; Fiedler, A.; Haines, C. P.; Pereira, M. J.; Portouw, J.; Walth, G.; Edge, A. C.; Smith, G. P.; Altieri, B.; Valtchanov, I.; Perez-Gonzalez, P. G.; Van der Werf, P. P.; Zemcov, M.

    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.

  7. The Driving Force of Frost Boils and Hummocks Formation

    NASA Astrophysics Data System (ADS)

    Shur, Y.; Ping, C.

    2003-12-01

    Formation of frost boils has several aspects to be explained, including the bowl shape of boils, the formation of an organic layer at the periphery of the frost boils, the elevated center of the boils, and resistance of the soil surface to vegetation colonization. Genesis of frost boils and hummocks have been widely attributed to cryoturbation-a complex of seasonally interchanging processes of frost heave and thaw settlement. Existing hypotheses, however, do not consider changes in the upper permafrost as factors of frost boil and hummock formation. Most of features listed above cannot be explained by reversible seasonal changes in the active layer. Frost boils and inter-boil areas form a well-organized and long-term functioning system closely linked to upper permafrost dynamics. Formation of this system starts with the occurrence of vegetation in inter-boil areas in shallow thermal cracks limited by the thickness of the active layer. Vegetation and its decomposition change the thermal properties of the active layer that steadily decreases with formation of aggradational ice and perennial frost heave beneath vegetated inter-boils. Due to the three-dimensional nature of the freezing front, frost heave in inter-boil areas is not perpendicular to the soil surface but is inclined in the direction of the boils, thus forming the bowl shape of boils. The organic matter formed in inter-boil areas intrudes under boils due to formation of frost cracks and thawing of ice lenses and layers at the bottom of the active layer. Penetration of organics along the active layer - permafrost boundary from an inter-boil area leads to formation of additional aggradational ice in the intermediate layer at the top of the permafrost accompanying the intruding organics. This aggradational process reinforces the bowl shape of frost-boils. Accumulation of organic matter at the lower part of the active layer leads to a decrease in active-layer thickness under the boils, which in turn leads to

  8. Roles of dynamical symmetry breaking in driving oblate-prolate transitions of atomic clusters

    SciTech Connect

    Oka, Yurie Yanao, Tomohiro; Koon, Wang Sang

    2015-04-07

    This paper explores the driving mechanisms for structural transitions of atomic clusters between oblate and prolate isomers. We employ the hyperspherical coordinates to investigate structural dynamics of a seven-atom cluster at a coarse-grained level in terms of the dynamics of three gyration radii and three principal axes, which characterize overall mass distributions of the cluster. Dynamics of gyration radii is governed by two kinds of forces. One is the potential force originating from the interactions between atoms. The other is the dynamical forces called the internal centrifugal forces, which originate from twisting and shearing motions of the system. The internal centrifugal force arising from twisting motions has an effect of breaking the symmetry between two gyration radii. As a result, in an oblate isomer, activation of the internal centrifugal force that has the effect of breaking the symmetry between the two largest gyration radii is crucial in triggering structural transitions into prolate isomers. In a prolate isomer, on the other hand, activation of the internal centrifugal force that has the effect of breaking the symmetry between the two smallest gyration radii is crucial in triggering structural transitions into oblate isomers. Activation of a twisting motion that switches the movement patterns of three principal axes is also important for the onset of structural transitions between oblate and prolate isomers. Based on these trigger mechanisms, we finally show that selective activations of specific gyration radii and twisting motions, depending on the isomer of the cluster, can effectively induce structural transitions of the cluster. The results presented here could provide further insights into the control of molecular reactions.

  9. Evidence for aqueous clusters as intermediates during zinc sulfide formation

    NASA Astrophysics Data System (ADS)

    Luther, George W.; Theberge, Stephen M.; Rickard, David T.

    1999-10-01

    Using zinc sulfide as an example, we demonstrate a plausible stepwise process for the formation of minerals from low temperature aqueous solutions. The process occurs with the formation of soluble complexes that aggregate into soluble rings and clusters. The final moiety in solution has a structure similar to the moiety in the first formed solid, which is a restatement of the Ostwald step rule. Titrations of aqueous Zn(II) with bisulfide indicate that sulfide clusters form at concentrations of 20 μM (or less) of metal and bisulfide. Precipitation does not occur according to voltammetric measurements using a mercury electrode and UV-VIS (ultra-violet to visible) spectroscopic data. UV-VIS data and filtration experiments indicate that the material passes through 0.1 μm Nuclepore and 1000 dalton filters. The complexes form rapidly (kf > 108 Ms-1), are kinetically inert to dissociation and thermodynamically strong. Although a neutral complex of 1:1 (ZnS) empirical stoichiometry initially forms, an anionic complex with an empirical 2 Zn:3 S stoichiometry results with continued addition of sulfide. Gel electrophoresis confirms the existence of a cluster that is negatively charged with a molecular mass between 350 and 750 daltons. On the basis of known mineral and thiol complex structures for these systems, a tetrameric cluster unit of Zn4S6(H2O)44- is likely. Molecular mechanic calculations show that this cluster is structurally analogous to ZnS minerals (particularly sphalerite) and is a viable precursor to mineral formation and a product of mineral dissolution. The formation of Zn4S6(H2O)44- can occur from condensation of Zn3S3(H2O)6 rings, which are neutral molecular clusters. The Zn atoms on one Zn3S3(H2O)6 ring combine with the S atoms on another Zn3S3(H2O)6, to lead to higher order clusters with loss of water. The Zn4S64- species form by the cross-linking of two neutral Zn3S3 rings by added sulfide; thus a Zn-S-Zn bridge forms across the rings with subsequent

  10. The Formation and Evolution of Star Clusters in Interacting Galaxies

    NASA Astrophysics Data System (ADS)

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

    2017-08-01

    Observations of globular clusters show that they have universal lognormal mass functions with a characteristic peak at ˜ 2× {10}5 {M}⊙ , but the origin of this peaked distribution is highly debated. Here we investigate the formation and evolution of star clusters (SCs) in interacting galaxies using high-resolution hydrodynamical simulations performed with two different codes in order to mitigate numerical artifacts. We find that massive SCs in the range of ˜ {10}5.5{--}{10}7.5 {M}⊙ 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˜ {10}8{--}{10}12 {{K}} {{cm}}-3, which is ˜ {10}4{--}{10}8 times higher than the typical pressure of the interstellar medium but consistent with recent observations of a pre-super-SC cloud in the Antennae Galaxies. Furthermore, these massive SCs have quasi-lognormal initial mass functions with a peak around ˜ {10}6 {M}⊙ . The number of clusters declines with time due to destructive processes, but the shape and the peak of the mass functions do not change significantly during the course of galaxy collisions. Our results suggest that gas-rich galaxy mergers may provide a favorable environment for the formation of massive SCs such as globular clusters, and that the lognormal mass functions and the unique peak may originate from the extreme high-pressure conditions of the birth clouds and may survive the dynamical evolution.

  11. Turbulence and vorticity in Galaxy clusters generated by structure formation

    NASA Astrophysics Data System (ADS)

    Vazza, F.; Jones, T. W.; Brüggen, M.; Brunetti, G.; Gheller, C.; Porter, D.; Ryu, D.

    2017-01-01

    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 ˜ 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 (˜95 per cent) in the central cluster volume at all epochs. The dissipation via compressive modes is found to be more important (˜30 per cent of the total) only at large radii (≥0.5rvir) and close to merger events. We show that enstrophy (vorticity squared) is good proxy of solenoidal turbulence. All terms ruling the evolution of enstrophy (i.e. baroclinic, compressive, stretching and advective terms) are found to be significant, but in amounts that vary with time and location. Two important trends for the growth of enstrophy in our simulation are identified: first, enstrophy is continuously accreted into the cluster from the outside, and most of that accreted enstrophy is generated near the outer accretion shocks by baroclinic and compressive processes. Secondly, in the cluster interior vortex, stretching is dominant, although the other terms also contribute substantially.

  12. Formation and evolution of star clusters in interacting galaxies

    NASA Astrophysics Data System (ADS)

    Anders, P.

    2006-02-01

    My present PhD thesis "Formation and evolution of star clusters in interacting galaxies" and the associated work was performed in the Galaxy Evolution Group at the Institut für Astrophysik (Georg-August-Universität Göttingen, Germany) under supervision of apl. Prof. Dr. U. Fritze - v. Alvensleben. My co-supervisor - especially for the observational part of the thesis - was Dr. R. de Grijs (Department of Physics & Astronomy, University of Sheffield, UK). In the course of my PhD project I got involved in a number of projects, spanning a wide range of astrophysical topics. The results of these projects are reported in my PhD thesis: * evolutionary synthesis modeling: I played a leading role in the most recent updates of the GALEV code (originally built by U. Fritze - v. Alvensleben). I have implemented gaseous emission effects to the code (see Anders & Fritze - v. Alvensleben 2003). Only due to this update, models for younger ages than before became possible, allowing for more direct and detailed studies of star and star cluster formation processes. In addition, I have implemented a variety of new filter systems (models in a comprehensive set of regularly used filter sets, including all relevant filters on-board the HST, are now available) eliminating the need to transform between different filter systems and avoiding the associated uncertainties. * cluster parameter determination: I have developed and thoroughly tested the AnalySED tool (Anders et al. 2004b). This tool allows for statistically robust parameter determination from multi-wavelength broad-band observations of (initially) star clusters. The AnalySED tool has been successfully applied to a large number of star cluster systems (e.g. Anders et al. 2004a; de Grijs et al. (incl. Anders) 2003a,b,c, 2004; de Grijs & Anders 2006, MNRAS, in press) * uncertainties inherent to evolutionary synthesis modeling and parameter determination: I reported very detailed on a large number of tests on the accuracy of the

  13. Pattern formation of underwater sand ripples with a skewed drive.

    PubMed

    Bundgaard, F; Ellegaard, C; Scheibye-Knudsen, K; Bohr, T; Sams, T

    2004-12-01

    In this paper we present an experimental study of the dynamics of underwater sand ripples when a regular pattern of ripples is subjected to a skewed oscillatory flow, i.e., one not perpendicular to the direction of the ripple crests. Striking patterns with new, superposed ripples on top of the original ones occur very quickly with a characteristic angle, which is, in general, not perpendicular to the flow. A slower, more complex transition then follows, leading to the final state where the ripples are again perpendicular to the flow. We investigate the variation of the superposed pattern as a function of the direction, amplitude, and frequency of the drive, and as a function of the viscosity (by changing the temperature). We quantify the dynamics of the entire transition process and finally study the grain motion around idealized (solid) skewed ripples. This leads to a characteristic mean path of a single particle. The path has a shape close to a parallelogram, with no apparent connection to the pattern of real, superposed ripples. On the other hand, a thin layer of sand sprinkled on the solid ripples leads to qualitatively similar patterns.

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

    NASA Astrophysics Data System (ADS)

    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 < z < 0.09 as a field control sample. Overall, we find agreement between the SFR-M{}* 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.

  15. Sequential clustering of star formations in IC 1396

    NASA Astrophysics Data System (ADS)

    Huang, Ya-Fang; Li, Jin-Zeng

    2013-05-01

    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 near- and 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.

  16. Westerlund 1: monolithic formation of a starburst cluster

    NASA Astrophysics Data System (ADS)

    Negueruela, Ignacio; Clark, J. Simon; Ritchie, Ben; Goodwin, Simon

    2015-08-01

    Westerlund 1 is in all likelihood the most massive young cluster in the Milky Way, with a mass on the order of 105 Msol. We have been observing its massive star population for ten years, measuring radial velocity changes for a substantial fraction of its OB stars and evolved supergiants. The properties of the evolved population are entirely consisting with a single burst of star formation, in excellent agreement with the results of studies based on the lower-mass population.Here we will present two new studies of the cluster: 1) A direct measurement of its average radial velocity and velocity dispersion based on individual measurements for several dozen stars with constant radial velocity and 2) A search for massive stars in its immediate neighbourhood using multi-object spectroscopy.The results of these two studies show that Westerlund 1 is decidedly subvirial and has a systemic radial velocity significantly different from that of nearby gas, which was assumed to provide a dynamical distance by previous authors. Moreover, the dynamical distance is inconsistent with the properties of the high-mass stellar population. In addition, we find that the cluster is completely isolated, with hardly any massive star in its vicinity that could be associated in terms of distance modulus or radial velocity. The cluster halo does not extend much further than five parsec away from the centre. All these properties are very unusual among starburst clusters in the Local Universe, which tend to form in the context of large star-forming regions.Westerlund 1 is thus the best example we have of a starburst cluster formed monolithically.

  17. Foam and cluster structure formation by latex particles at the air/water interface

    NASA Astrophysics Data System (ADS)

    Ruiz-Garcia, Jaime; Gámez-Corrales, Rogelio; Ivlev, Boris I.

    1997-02-01

    We report the formation of two-dimensional foam and cluster structures by spherical polystyrene particles trapped at the air/water interface. The colloidal foam is a transient structure that evolves to the formation of clusters, but clusters can also be formed after deposition of the sample. We also observed the formation of small aggregates, whose formation along with the cluster stabilization can be explained in terms of a balance between electrostatic repulsive and van der Waals attractive interactions.

  18. Star Formation Activity in CLASH Brightest Cluster Galaxies

    NASA Astrophysics Data System (ADS)

    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. Star formation in shocked cluster spirals and their tails

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

    Recent observations of ram pressure stripped spiral galaxies in clusters revealed details of the stripping process, i.e. the truncation of all interstellar medium phases and of star formation (SF) in the disc, 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 intracluster 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 idealized 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 disc and in the near tails, which are easiest to observe. The observed jellyfish morphology is qualitatively reproduced for, both, face-on and edge-on stripping. In edge-on stripping, the interplay between the ICM wind and the disc rotation leads to asymmetries along the ICM wind direction and perpendicular to it. The apparent tail is still part of a highly deformed gaseous and young stellar disc. In both geometries, SF takes place in knots throughout the tail, such that the stars in the tails show no ordered age gradients. Significant SF enhancement in the disc occurs only at radii where the gas will be stripped in due course.

  20. The Extended Environments of ULIRGS and LIRGS: Clusters in Formation

    NASA Astrophysics Data System (ADS)

    Laag, Edward A.

    2006-12-01

    The environments surrounding Ultra-Luminous Infrared Galaxies (ULIRGS; Lir > 10^12 Lsun) and LIRGs (LIRGS; Lir > 10^11 Lsun) are potential laboratories for studying the formation of galaxy clusters. These proto-clusters likely contain large amounts of mass in the form of dark matter (DM) haloes and are actively accreting galaxies, inducing star formation and AGN activity. In addition, possible companions are frequently seen in the vicinity of ULIRGs. We present preliminary results of a project to study clustering properties of ULIRGs in the FIRST sample. We have obtained wide field of view (FOV) (75’x 65’) ESI R-band sub-arcsecond seeing images with limiting magniudes of R=25 of the fields surrounding 32 (z < 0.35) ULIRGs and LIRGs. To confirm group membership we have obtained spectra using the Shane 3m telescope at Lick Observatory, for many of the galaxies in these fields. In addition, we discuss a new adaptive optics (AO) technique on the horizon for Keck Observatory that would be helpful for this research. A project to obtain redshifts and wide FOV imaging of a larger sample of ULIRGs is ongoing.

  1. The filamentous fungal pellet and forces driving its formation.

    PubMed

    Zhang, Jianguo; Zhang, Jining

    2016-12-01

    Filamentous fungi play an important role not only in the bio-manufacturing of value-added products, but also in bioenergy and environmental research. The bioprocess manipulation of filamentous fungi is more difficult than that of other microbial species because of their different pellet morphologies and the presence of tangled mycelia under different cultivation conditions. Fungal pellets, which have the advantages of harvest ease, low fermentation broth viscosity and high yield of some proteins, have been used for a long time. Many attempts have been made to establish the relationship between pellet and product yield using quantitative approaches. Fungal pellet formation is attributed to the combination of electrostatic interactions, hydrophobicity and specific interactions from spore wall components. Electrostatic interactions result from van der Waals forces and negative charge repulsion from carboxyl groups in the spore wall structure. Electrostatic interactions are also affected by counter-ions (cations) and the physiologic conditions of spores that modify the carboxyl groups. Fungal aggregates are promoted by the hydrophobicity generated by hydrophobins, which form a hydrophobic coat that covers the spore. The specific interactions of spore wall components contribute to spore aggregation through salt bridging. A model of spore aggregation was proposed based on these forces. Additionally, some challenges were addressed, including the limitations of research techniques, the quantitative determination of forces and the complex information of biological systems, to clarify the mechanism of fungal pellet formation.

  2. Simulating radiative feedback and star cluster formation in GMCs - I. Dependence on gravitational boundedness

    NASA Astrophysics Data System (ADS)

    Howard, Corey S.; Pudritz, Ralph E.; Harris, William E.

    2016-09-01

    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, 106 M⊙ 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 initial mass function (IMF) with an efficiency of 20 per cent per free-fall time. We find that radiative feedback only decreases the cluster particle formation efficiency by a few per cent. The initial virial parameter plays a much stronger role in limiting cluster formation, with a spread of cluster formation efficiencies of 37-71 per cent for the most unbound to the most bound model. The total number of clusters increases while the maximum mass cluster decreases with an increasing initial virial parameter, resulting in steeper mass distributions. The star formation rates in our cluster particles are initially consistent with observations but rise to higher values at late times. This suggests that radiative feedback alone is not responsible for dispersing a GMC over the first 5 Myr of cluster formation.

  3. Renewable Formate from C-H Bond Formation with CO2: Using Iron Carbonyl Clusters as Electrocatalysts.

    PubMed

    Loewen, Natalia D; Neelakantan, Taruna V; Berben, Louise A

    2017-09-19

    As a society, we are heavily dependent on nonrenewable petroleum-derived fuels and chemical feedstocks. Rapid depletion of these resources and the increasingly evident negative effects of excess atmospheric CO2 drive our efforts to discover ways of converting excess CO2 into energy dense chemical fuels through selective C-H bond formation and using renewable energy sources to supply electrons. In this way, a carbon-neutral fuel economy might be realized. To develop a molecular or heterogeneous catalyst for C-H bond formation with CO2 requires a fundamental understanding of how to generate metal hydrides that selectively donate H(-) to CO2, rather than recombining with H(+) to liberate H2. Our work with a unique series of water-soluble and -stable, low-valent iron electrocatalysts offers mechanistic and thermochemical insights into formate production from CO2. Of particular interest are the nitride- and carbide-containing clusters: [Fe4N(CO)12](-) and its derivatives and [Fe4C(CO)12](2-). In both aqueous and mixed solvent conditions, [Fe4N(CO)12](-) forms a reduced hydride intermediate, [H-Fe4N(CO)12](-), through stepwise electron and proton transfers. This hydride selectively reacts with CO2 and generates formate with >95% efficiency. The mechanism for this transformation is supported by crystallographic, cyclic voltammetry, and spectroelectrochemical (SEC) evidence. Furthermore, installation of a proton shuttle onto [Fe4N(CO)12](-) facilitates proton transfer to the active site, successfully intercepting the hydride intermediate before it reacts with CO2; only H2 is observed in this case. In contrast, isoelectronic [Fe4C(CO)12](2-) features a concerted proton-electron transfer mechanism to form [H-Fe4C(CO)12](2-), which is selective for H2 production even in the presence of CO2, in both aqueous and mixed solvent systems. Higher nuclearity clusters were also studied, and all are proton reduction electrocatalysts, but none promote C-H bond formation. Thermochemical

  4. Tension stimulation drives tissue formation in scaffold-free systems

    NASA Astrophysics Data System (ADS)

    Lee, Jennifer K.; Huwe, Le W.; Paschos, Nikolaos; Aryaei, Ashkan; Gegg, Courtney A.; Hu, Jerry C.; Athanasiou, Kyriacos A.

    2017-08-01

    Scaffold-free systems have emerged as viable approaches for engineering load-bearing tissues. However, the tensile properties of engineered tissues have remained far below the values for native tissue. Here, by using self-assembled articular cartilage as a model to examine the effects of intermittent and continuous tension stimulation on tissue formation, we show that the application of tension alone, or in combination with matrix remodelling and synthesis agents, leads to neocartilage with tensile properties approaching those of native tissue. Implantation of tension-stimulated tissues results in neotissues that are morphologically reminiscent of native cartilage. We also show that tension stimulation can be translated to a human cell source to generate anisotropic human neocartilage with enhanced tensile properties. Tension stimulation, which results in nearly sixfold improvements in tensile properties over unstimulated controls, may allow the engineering of mechanically robust biological replacements of native tissue.

  5. Diffusion layer formation drives zone migration in travelling wave electrophoresis.

    PubMed

    Booth, William Albert; Edwards, Boyd; Jo, Kyoo; Timperman, Aaron; Schiffbauer, Jarrod

    2017-04-04

    COMSOL finite element modeling software is used to simulate 2D traveling-wave electrophoresis for microfluidic separations and sample concentration. A four-phase AC potential is applied to a periodic interdigitated four-electrode array to produce a longitudinal electric wave that travels through the channel. Charged particles are carried along with the electric wave or left behind, depending on their mobilities. A simplified model of asymmetric electrode reactions resolves the issue of electric double layer shielding at the electrodes. Selective reactions allow for the formation of diffusion layers of charged particles which follow the traveling electric wave. These diffusion layers determine the transport of charged species through the system. Our model reproduces experimental separations of charged species based on mobility. With easy control over the frequency and direction, one may employ this method for concentrating and/or separating charged particles.

  6. Synaptic clustering within dendrites: an emerging theory of memory formation

    PubMed Central

    Kastellakis, George; Cai, Denise J.; Mednick, Sara C.; Silva, Alcino J.; Poirazi, Panayiota

    2015-01-01

    It is generally accepted that complex memories are stored in distributed representations throughout the brain, however the mechanisms underlying these representations are not understood. Here, we review recent findings regarding the subcellular mechanisms implicated in memory formation, which provide evidence for a dendrite-centered theory of memory. Plasticity-related phenomena which affect synaptic properties, such as synaptic tagging and capture, synaptic clustering, branch strength potentiation and spinogenesis provide the foundation for a model of memory storage that relies heavily on processes operating at the dendrite level. The emerging picture suggests that clusters of functionally related synapses may serve as key computational and memory storage units in the brain. We discuss both experimental evidence and theoretical models that support this hypothesis and explore its advantages for neuronal function. PMID:25576663

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

    NASA Astrophysics Data System (ADS)

    Tremblay, Grant Russell

    2011-07-01

    The classical "cooling flow" model historically associated with "cool core" clusters of galaxies fails in the absence of an external, non-gravitational heating mechanism needed to offset catastrophic radiative losses of the X-ray bright intracluster medium (ICM). Numerous proposed solutions exist, including feedback from active galactic nuclei (AGN), which may elegantly calibrate fundamental relationships such as the coupled co-evolution of black holes and the stellar component of their host galaxies. AGN feedback cannot completely offset cooling at all times, however, as the brightest cluster galaxies (BCGs) in cool core clusters harbor extensive warm (˜104 K) and cold (10 < T < 104 K) gas reservoirs whose physical properties are regulated by ongoing star formation and an unknown, non-stellar heating mechanism. We present a doctoral thesis broadly related to these issues, particularly as they pertain to cooling flows, the triggering of AGN activity, and the associated energetic feedback that may play a critical role in heating the ambient environment on tens to hundreds of kiloparsec scales. We begin with a summary of the relevant background material, and in Chapter 2 we present a multiwavelength study of effervescent AGN heating in the cool core cluster Abell 2597. Previously unpublished Chandra X-ray data show the central regions of the hot intracluster medium (ICM) to be highly anisotropic on the scale of the BCG, permeated by a network of kpc-scale X-ray cavities, the largest of which is cospatial in projection with extended 330 MHz radio emission. We present spectral maps of projected, modeled gas properties fit to the X-ray data. The X-ray temperature map reveals two discrete, "hard-edged'' structures, including a ˜15 kpc "cold filament'' and an arc of hot gas which in projection borders the inner edge of the large X-ray cavity. We interpret the latter in the context of the effervescent AGN heating model, in which cavity enthalpy is thermalized as the

  8. Formation and Reactivity of Organo-Functionalized Tin Selenide Clusters.

    PubMed

    Rinn, Niklas; Eußner, Jens P; Kaschuba, Willy; Xie, Xiulan; Dehnen, Stefanie

    2016-02-24

    Reactions of R(1) SnCl3 (R(1) =CMe2 CH2 C(O)Me) with (SiMe3 )2 Se yield a series of organo-functionalized tin selenide clusters, [(SnR(1) )2 SeCl4 ] (1), [(SnR(1) )2 Se2 Cl2 ] (2), [(SnR(1) )3 Se4 Cl] (3), and [(SnR(1) )4 Se6 ] (4), depending on the solvent and ratio of the reactants used. NMR experiments clearly suggest a stepwise formation of 1 through 4 by subsequent condensation steps with the concomitant release of Me3 SiCl. Furthermore, addition of hydrazines to the keto-functionalized clusters leads to the formation of hydrazone derivatives, [(Sn2 (μ-R(3) )(μ-Se)Cl4 ] (5, R(3) =[CMe2 CH2 CMe(NH)]2 ), [(SnR(2) )3 Se4 Cl] (6, R(2) =CMe2 CH2 C(NNH2 )Me), [(SnR(4) )3 Se4 ][SnCl3 ] (7, R(4) =CMe2 CH2 C(NNHPh)Me), [(SnR(2) )4 Se6 ] (8), and [(SnR(4) )4 Se6 ] (9). Upon treatment of 4 with [Cu(PPh3 )3 Cl] and excess (SiMe3 )2 Se, the cluster fragments to form [(R(1) Sn)2 Se2 (CuPPh3 )2 Se2 ] (10), the first discrete Sn/Se/Cu cluster compound reported in the literature. The derivatization reactions indicate fundamental differences between organotin sulfide and organotin selenide chemistry.

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

    NASA Astrophysics Data System (ADS)

    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.

  10. Modeling jet and outflow feedback during star cluster formation

    SciTech Connect

    Federrath, Christoph; Schrön, Martin; Banerjee, Robi; Klessen, Ralf S.

    2014-08-01

    Powerful jets and outflows are launched from the protostellar disks around newborn stars. These outflows carry enough mass and momentum to transform the structure of their parent molecular cloud and to potentially control star formation itself. Despite their importance, we have not been able to fully quantify the impact of jets and outflows during the formation of a star cluster. The main problem lies in limited computing power. We would have to resolve the magnetic jet-launching mechanism close to the protostar and at the same time follow the evolution of a parsec-size cloud for a million years. Current computer power and codes fall orders of magnitude short of achieving this. In order to overcome this problem, we implement a subgrid-scale (SGS) model for launching jets and outflows, which demonstrably converges and reproduces the mass, linear and angular momentum transfer, and the speed of real jets, with ∼1000 times lower resolution than would be required without the SGS model. We apply the new SGS model to turbulent, magnetized star cluster formation and show that jets and outflows (1) eject about one-fourth of their parent molecular clump in high-speed jets, quickly reaching distances of more than a parsec, (2) reduce the star formation rate by about a factor of two, and (3) lead to the formation of ∼1.5 times as many stars compared to the no-outflow case. Most importantly, we find that jets and outflows reduce the average star mass by a factor of ∼ three and may thus be essential for understanding the characteristic mass of the stellar initial mass function.

  11. Long Duration Directional Drives for Star Formation and Photoionization

    SciTech Connect

    Kane, J. O.; Martinez, D. A.; Pound, M. W.; Heeter, R. F.; Villette, B.; Casner, A.; Mancini, R. C.

    2015-06-18

    This research will; confirm the possibility of studying the structure and evolution of star-forming regions of molecular clouds in the laboratory; test the cometary model for the formation of the pillar structures in molecular clouds; assess the effect of magnetic fields on the evolution of structures in molecular clouds; and develop and demonstrate a new, long-duration (60-100 ns), directional source of x-ray radiation that can be used for the study of deeply nonlinear hydrodynamics, hydrodynamic instabilities that occur in the presence of directional radiation, shock-driven and radiatively-driven collapse of dense cores, and photoionization. Due to the iconic status of the pillars of the Eagle Nebula, this research will bring popular attention to plasma physics, HED laboratory physics, and fundamental science at NIF and other experimental facilities. The result will be to both to bring new perspectives to the studies of hydrodynamics in inertial confinement fusion and HED scenarios in general, and to promote interest in the STEM disciplines.

  12. Present star formation in sprials of the Virgo cluster

    NASA Technical Reports Server (NTRS)

    Guiderdoni, B.

    1987-01-01

    From a study of spiral galaxies in the Virgo Cluster (VC), it is shown that the RDDO anemics with smooth arms and no sign of present formation of (massive) stars have HI surface densities below a threshold value of 2 to 5 x 10 to the 20th power atoms/sq cm. This value is very consistent with predictions of theoretical models. It is likely that the HI disks of VC HI-deficient RDDO anemics were deeply affected by ram pressure stripping in the gaseous intracluster medium, while VC HI deficient RDDO spirals were only peripherally stripped.

  13. BURST OF STAR FORMATION DRIVES BUBBLE IN GALAXY'S CORE

    NASA Technical Reports Server (NTRS)

    2002-01-01

    These NASA Hubble Space Telescope snapshots reveal dramatic activities within the core of the galaxy NGC 3079, where a lumpy bubble of hot gas is rising from a cauldron of glowing matter. The picture at left shows the bubble in the center of the galaxy's disk. The structure is more than 3,000 light-years wide and rises 3,500 light-years above the galaxy's disk. The smaller photo at right is a close-up view of the bubble. Astronomers suspect that the bubble is being blown by 'winds' (high-speed streams of particles) released during a burst of star formation. Gaseous filaments at the top of the bubble are whirling around in a vortex and are being expelled into space. Eventually, this gas will rain down upon the galaxy's disk where it may collide with gas clouds, compress them, and form a new generation of stars. The two white dots just above the bubble are probably stars in the galaxy. The close-up reveals that the bubble's surface is lumpy, consisting of four columns of gaseous filaments that tower above the galaxy's disk. The filaments disperse at a height of 2,000 light-years. Each filament is about 75 light-years wide. Velocity measurements taken by the Canada-France-Hawaii Telescope in Hawaii show that the gaseous filaments are ascending at more than 4 million miles an hour (6 million kilometers an hour). According to theoretical models, the bubble formed when ongoing winds from hot stars mixed with small bubbles of very hot gas from supernova explosions. Observations of the core's structure by radio telescopes indicate that those processes are still active. The models suggest that this outflow began about a million years ago. They occur about every 10 million years. Eventually, the hot stars will die, and the bubble's energy source will fade away. Astronomers have seen evidence of previous outbursts from radio and X-ray observations. Those studies show rings of dust and gas and long plumes of material, all of which are larger than the bubble. NGC 3079 is 50

  14. BURST OF STAR FORMATION DRIVES BUBBLE IN GALAXY'S CORE

    NASA Technical Reports Server (NTRS)

    2002-01-01

    These NASA Hubble Space Telescope snapshots reveal dramatic activities within the core of the galaxy NGC 3079, where a lumpy bubble of hot gas is rising from a cauldron of glowing matter. The picture at left shows the bubble in the center of the galaxy's disk. The structure is more than 3,000 light-years wide and rises 3,500 light-years above the galaxy's disk. The smaller photo at right is a close-up view of the bubble. Astronomers suspect that the bubble is being blown by 'winds' (high-speed streams of particles) released during a burst of star formation. Gaseous filaments at the top of the bubble are whirling around in a vortex and are being expelled into space. Eventually, this gas will rain down upon the galaxy's disk where it may collide with gas clouds, compress them, and form a new generation of stars. The two white dots just above the bubble are probably stars in the galaxy. The close-up reveals that the bubble's surface is lumpy, consisting of four columns of gaseous filaments that tower above the galaxy's disk. The filaments disperse at a height of 2,000 light-years. Each filament is about 75 light-years wide. Velocity measurements taken by the Canada-France-Hawaii Telescope in Hawaii show that the gaseous filaments are ascending at more than 4 million miles an hour (6 million kilometers an hour). According to theoretical models, the bubble formed when ongoing winds from hot stars mixed with small bubbles of very hot gas from supernova explosions. Observations of the core's structure by radio telescopes indicate that those processes are still active. The models suggest that this outflow began about a million years ago. They occur about every 10 million years. Eventually, the hot stars will die, and the bubble's energy source will fade away. Astronomers have seen evidence of previous outbursts from radio and X-ray observations. Those studies show rings of dust and gas and long plumes of material, all of which are larger than the bubble. NGC 3079 is 50

  15. Drama of HII regions: Clustered and Triggered Star Formation

    NASA Astrophysics Data System (ADS)

    Li, Jinzeng; YUAN, Jinghua; LIU, Hongli; Wu, Yuefang; Huang, Yafang

    2015-08-01

    Intense ultraviolet radiation from young massive stars ionizes ambient material leading to the formation of HII regions which have keen impact upon the birth of new stars in the vicinities. The strong radiation may be responsible for the dispersal of molecular clouds to hinder star formation, while the expansion of HII regions would collect neutral material to form dense layers which may be gravitationally unstable to collapse to give birth to new stars.In order to understand the star formation process under the influence of HII regions, we have carried out extensive investigations to well selected star-forming regions which all have been profoundly affected by existing massive O type stars. On the basis of multi-wavelength data from mid-infrared to millimeter collected using Spitzer, Herschel, and ground based radio telescope, the physical status of interstellar medium and star formation in these regions have been revealed. Clustered and sequential star formation have been detected toward well known HII regions, such as IC1396 and Sh-155. In a relatively large infrared dust bubble, active star formation is undergoing and the shell is still expanding. Socked features and signs of triggered star formation have been tentatively detected in a relatively small bubble. The dense cores in the Rosette Molecular Complex detected at 1.1 mm using SMA have been speculated to have a likely triggered origin according to their spatial distribution. Although some observational results have been obtained, more efforts are necessary to reach trustworthy conclusions. And more regions will be extensively explored based on multi-wavelength observations, especially the data collected using the Herschel Space Observatory.

  16. Cluster formation in liverwort-associated methylobacteria and its implications

    NASA Astrophysics Data System (ADS)

    Kutschera, U.; Thomas, J.; Hornschuh, M.

    2007-08-01

    Pink-pigmented methylotropic bacteria of the genus Methylobacterium inhabit the surfaces of plant organs. In bryophytes, these methylobacteria enhance cell growth, but the nature of this plant-microbe interaction is largely unknown. In this study, methylobacteria were isolated from the upper surface of the free-living thalli of the liverwort Marchantia polymorpha L. Identification of one strain by 16S ribosomal RNA (rRNA) gene-targeted polymerase chain reaction (PCR) and other data show that these microbes represent an undescribed species of the genus Methylobacterium ( Methylobacterium sp.). The growth-promoting activity of these wild-type methylobacteria was tested and compared with that of the type strain Methylobacterium mesophilicum. Both types of methylobacteria stimulated surface expansion of isolated gemmae from Marchantia polymorpha by about 350%. When suspended in water, the liverwort-associated bacteria ( Methylobacterium sp.) formed dense clusters of up to 600 cells. In liquid cultures of Methylobacterium mesophilicum, single cells were observed, but no clustering occurred. We suggest that the liverwort-associated methylobacteria are co-evolved symbionts of the plants: Cluster formation may be a behavior that enhances the survival of the epiphytic microbes during periods of drought of these desiccation-tolerant lower plants.

  17. Simulating Galaxy Clusters with Dust Formation and Evolution

    NASA Astrophysics Data System (ADS)

    Gjergo, Eda; Granato, Gian Luigi; Murante, Giuseppe; Ragone-Figueroa, Cinthia

    2017-07-01

    In order to investigate basic properties of galaxies, such as the star formation rate and the masses of baryonic components, it is important to account for dust reprocessing. Dust particles absorb and scatter the stars' optical/UV emission, and they re-radiate thermally in the infrared. A combination of simulations and post-processing radiative transfer computations can produce mock data, which can be compared directly to observations. Until now, however, dust properties have only been included in our simulations by means of post-processing assumptions, leaving room for uncertainties, particularly significant at wavelengths shorter than 100 microns. To reduce these uncertainties, we implemented a state-of-the-art treatment of the production and evolution of dust grains within our simulation code, P-GADGET3. This model traces the creation, evolution, and destruction of dust through various processes. It accounts for the diameter of dust particles with a two-grain-size approximation proposed by H. Hirashita. We will present a first result of our new code applied to zoom-in simulations of massive (M_{200} > 3 × 10^4 M_{⊙}) galaxy clusters, focusing in particular to the early stages of assembly of the cluster at high redshift, around z = 2, where the SF activity is at its maximum and the proto-cluster regions are rich of cold, dust-polluted gas.

  18. Gold Cluster Formation on C60 Surfaces: Au-Cluster Beads and Self-Organized Structures

    NASA Astrophysics Data System (ADS)

    Reinke, Petra; Liu, Hui

    2007-03-01

    Petra Reinke, Hui Liu, Department of Materials Science and Engineering, University of Virginia The investigation of C60-Au interaction is central to the advancement of solar cell and nanotechnology applications of C60. C60 grows in a quasi-layer-by-layer mode on a pristine graphite surface and form a special surface structure (coexistence of round and fractal islands). The deposition of Au leads to the formation of a complex array of different surface structures, while the basic island structure of the C60 is preserved. The Au-clusters nucleate preferentially at the graphite-first fullerene layer islands edge forming beadlike structures. A roughness analysis of the fullerene surface indicates the presence of Au atoms embedded in the fullerene surface, situated in the troughs in between the large molecules. The analysis of the spatial and size distributions of Au clusters provides the basis for the development of a qualitative model which describes the relevant surface processes in the Au-fullerene system. The simultaneous deposition of Au and C60 leads to the formation of organized structures, in which Au clusters are embedded in a ring of fullerene molecules with a constant width.

  19. Formation and structure of stable aggregates in binary diffusion-limited cluster-cluster aggregation processes

    NASA Astrophysics Data System (ADS)

    López-López, J. M.; Moncho-Jordá, A.; Schmitt, A.; Hidalgo-Álvarez, R.

    2005-09-01

    Binary diffusion-limited cluster-cluster aggregation processes are studied as a function of the relative concentration of the two species. Both, short and long time behaviors are investigated by means of three-dimensional off-lattice Brownian Dynamics simulations. At short aggregation times, the validity of the Hogg-Healy-Fuerstenau approximation is shown. At long times, a single large cluster containing all initial particles is found to be formed when the relative concentration of the minority particles lies above a critical value. Below that value, stable aggregates remain in the system. These stable aggregates are composed by a few minority particles that are highly covered by majority ones. Our off-lattice simulations reveal a value of approximately 0.15 for the critical relative concentration. A qualitative explanation scheme for the formation and growth of the stable aggregates is developed. The simulations also explain the phenomenon of monomer discrimination that was observed recently in single cluster light scattering experiments.

  20. Formation of Short-Period Binary Pulsars in Globular Clusters.

    PubMed

    Rasio; Pfahl; Rappaport

    2000-03-20

    We present a new dynamical scenario for the formation of short-period binary millisecond pulsars in globular clusters. Our work is motivated by the recent observations of 20 radio pulsars in 47 Tuc. In a dense cluster such as 47 Tuc, most neutron stars acquire binary companions through exchange interactions with primordial binaries. The resulting systems have semimajor axes in the range approximately 0.1-1 AU and neutron star companion masses approximately 1-3 M middle dot in circle. For many of these systems, we find that when the companion evolves off the main sequence and fills its Roche lobe, the subsequent mass transfer is dynamically unstable. This leads to a common envelope phase and the formation of short-period neutron star-white dwarf binaries. For a significant fraction of these binaries, the decay of the orbit due to gravitational radiation will be followed by a period of stable mass transfer driven by a combination of gravitational radiation and tidal heating of the companion. The properties of the resulting short-period binaries match well those of observed binary pulsars in 47 Tuc.

  1. Supergiant molecular clouds and the formation of globular cluster systems

    NASA Astrophysics Data System (ADS)

    Harris, William E.; Pudritz, Ralph E.

    1994-07-01

    Data from several large elliptical and disk galaxies now show that globular clusters more massive than approximately 105 solar mass follow a power-law number distribution by mass, N approximately M-1.7, which is virtually independent of environment. Within observational uncertainty, this relation is identical to the shape of the mass distributions of giant molecular clouds (GMCs) in large spiral galaxies, the cloud cores embedded in GMCs, and giant H II regions in large spiral galaxies. We interpret this within a model whereby globular clusters formed out of dense cores within supergiant molecular clouds (SGMCs) that were present in the early protogalactic epoch. We construct a theory of pressure confined, self-gravitating, isothermal, magnetized molecular clouds and cores, based on the viral theorem and the observed mass spectra, and derive the characteristic physical properties of these parent SGMCs. These turn out to be of the right mass and density range to resemble the Searle-Zinn primordial fragments from which larger galaxies may have assembled. We suggest that the protocluster clouds were supported against gravitational collapse primarily by a combination of magnetic field pressure and Alfvenic turbulence, as is observed to be the case for contemporary molecular clouds. This approach removes the need for arbitrary external heat sources (such as long-lasting AGNs or Population III stars) to keep the clouds stable for long enough times to build up to globular-sized masses and more easily permits the global properties of the emergent clusters to be similar from one galaxy to another. By calculating lifetimes through a standard cloud growth model, we estimate that the principal epoch of globular cluster formation should have begun no earlier than a redshift of z approximately equal to 6.

  2. Survival of Massive Star-forming Galaxies in Cluster Cores Drives Gas-phase Metallicity Gradients: The Effects of Ram Pressure Stripping

    NASA Astrophysics Data System (ADS)

    Gupta, Anshu; Yuan, Tiantian; Martizzi, Davide; Tran, Kim-Vy H.; Kewley, Lisa J.

    2017-06-01

    Recent observations of galaxies in a cluster at z = 0.35 show that their integrated gas-phase metallicities increase with decreasing cluster-centric distance. To test whether ram pressure stripping (RPS) is the underlying cause, we use a semianalytic model to quantify the “observational bias” that RPS introduces into the aperture-based metallicity measurements. We take integral field spectroscopy of local galaxies, remove gas from their outer galactic disks via RPS, and then conduct mock slit observations of cluster galaxies at z = 0.35. Our RPS model predicts a typical cluster-scale metallicity gradient of -0.03 dex/Mpc. By removing gas from the outer galactic disks, RPS introduces a mean metallicity enhancement of +0.02 dex at a fixed stellar mass. This gas removal and subsequent quenching of star formation preferentially removes low-mass cluster galaxies from the observed star-forming population. As only the more massive star-forming galaxies survive to reach the cluster core, RPS produces a cluster-scale stellar mass gradient of -0.05{log}({M}* /{M}⊙ )/Mpc. This mass segregation drives the predicted cluster-scale metallicity gradient of -0.03 dex/Mpc. However, the effects of RPS alone cannot explain the higher metallicities measured in cluster galaxies at z = 0.35. We hypothesize that additional mechanisms including steep internal metallicity gradients and self-enrichment due to gas strangulation are needed to reproduce our observations at z = 0.35.

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

    NASA Astrophysics Data System (ADS)

    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.

  4. Embedded star clusters and the formation of the Oort Cloud

    NASA Astrophysics Data System (ADS)

    Brasser, R.; Duncan, M. J.; Levison, H. F.

    2006-09-01

    < when <ρ>≳10 Mpc. Our models easily produce objects on orbits like that of (90377) Sedna [Brown, M.E., Trujillo, C., Rabinowitz, D., 2004. Astrophys. J. 617, 645-649] within ˜1 Myr in cases where the mean density is 10 Mpc or higher; one needs mean densities of order 10 Mpc to create objects like 2000 CR 105 by this mechanism, which are reasonable (see, e.g., Guthermuth, R.A., Megeath, S.T., Pipher, J.L., Williams, J.P., Allen, L.E., Myers, P.C., Raines, S.N., 2005. Astrophys. J. 632, 397-420). Thus the latter object may also be part of the OC. Close stellar passages can stir the primordial Kuiper Belt to sufficiently high eccentricities ( e≳0.05; Kenyon, S.J., Bromley, B.C., 2002. Astron. J. 123, 1757-1775) that collisions become destructive. From the simulations performed it is determined that there is a 50% or better chance to stir the primordial Kuiper Belt to eccentricities e⩾0.05 at 50 AU when <ρ>≳10 Mpc. The orbit of the new object 2003 UB 313 [Brown, M.E., Trujillo, C.A., Rabinowitz, D.L., 2005. Astrophys. J. 635, L97-L100] is only reproduced for mean cluster densities of the order of 10 Mpc, but in the simulations it could not come to be on its current orbit by this mechanism without disrupting the formation of bodies in the primordial Kuiper Belt down to 20 AU. It is therefore improbable that the latter object is created by this mechanism.

  5. CLUSTERED STAR FORMATION AND OUTFLOWS IN AFGL 2591

    SciTech Connect

    Sanna, A.; Carrasco-Gonzalez, C.; Menten, K. M.; Brunthaler, A.; Reid, M. J.; Moscadelli, L.; Rygl, K. L. J.

    2012-02-01

    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 M{sub Sun }. 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{sup -1}) and perhaps a lower-velocity ({approx}10 km s{sup -1}) wind with an opening angle of about 20 Degree-Sign from the jet axis.

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

    SciTech Connect

    Rathborne, J. M.; Contreras, Y.; Longmore, S. N.; Bastian, N.; Jackson, J. M.; Alves, J. F.; Bally, J.; Foster, J. B.; Garay, G.; Kruijssen, J. M. D.; Testi, L.; Walsh, A. J.

    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.

  7. A Cluster in the Making: ALMA Reveals the Initial Conditions for High-mass Cluster Formation

    NASA Astrophysics Data System (ADS)

    Rathborne, J. M.; Longmore, S. N.; Jackson, J. M.; Alves, J. F.; Bally, J.; Bastian, N.; Contreras, Y.; Foster, J. B.; Garay, G.; Kruijssen, J. M. D.; Testi, L.; Walsh, A. J.

    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.

  8. Selfish Operons: Horizontal Transfer May Drive the Evolution of Gene Clusters

    PubMed Central

    Lawrence, J. G.; Roth, J. R.

    1996-01-01

    A model is presented whereby the formation of gene clusters in bacteria is mediated by transfer of DNA within and among taxa. Bacterial operons are typically composed of genes whose products contribute to a single function. If this function is subject to weak selection or to long periods with no selection, the contributing genes may accumulate mutations and be lost by genetic drift. From a cell's perspective, once several genes are lost, the function can be restored only if all missing genes were acquired simultaneously by lateral transfer. The probability of transfer of multiple genes increases when genes are physically proximate. From a gene's perspective, horizontal transfer provides a way to escape evolutionary loss by allowing colonization of organisms lacking the encoded functions. Since organisms bearing clustered genes are more likely to act as successful donors, clustered genes would spread among bacterial genomes. The physical proximity of genes may be considered a selfish property of the operon since it affects the probability of successful horizontal transfer but may provide no physiological benefit to the host. This process predicts a mosaic structure of modern genomes in which ancestral chromosomal material is interspersed with novel, horizontally transferred operons providing peripheral metabolic functions. PMID:8844169

  9. COSMOLOGICAL MAGNETOHYDRODYNAMIC SIMULATIONS OF CLUSTER FORMATION WITH ANISOTROPIC THERMAL CONDUCTION

    SciTech Connect

    Ruszkowski, M.; Lee, D.; Parrish, I.; Oh, S. Peng E-mail: dongwook@flash.uchicago.edu E-mail: iparrish@astro.berkeley.edu

    2011-10-20

    The intracluster medium (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 whenever the temperature gradient points in the direction opposite to gravitational acceleration. Using cosmological simulations of cluster formation 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 rearrangements 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 the Square Kilometer Array and future X-ray spectroscopic studies with the International X-ray Observatory. We demonstrate that radiative cooling boosts the amplification of the magnetic field by about two orders of magnitude beyond what is expected in the non-radiative cases. This effect is caused by the compression of the gas and frozen-in magnetic field as it accumulates in the cluster center. At z = 0 the field is amplified by a factor of about 10{sup 6} compared to the uniform magnetic field that evolved due to the universal expansion alone. Interestingly, the runs that include both radiative cooling and thermal conduction exhibit stronger magnetic field amplification than purely radiative runs. In these cases, buoyant restoring forces depend on the temperature gradients rather than the steeper entropy gradients. Thus, the ICM is more easily mixed and the winding up of the frozen-in magnetic

  10. Simulating radiative feedback and star cluster formation in GMCs - II. Mass dependence of cloud destruction and cluster properties

    NASA Astrophysics Data System (ADS)

    Howard, Corey S.; Pudritz, Ralph E.; Harris, William E.

    2017-09-01

    The process of radiative feedback in giant molecular clouds (GMCs) is an important mechanism for limiting star cluster formation through the heating and ionization of the surrounding gas. We explore the degree to which radiative feedback affects early (≲5 Myr) cluster formation in GMCs having masses that range from 104 to 106 M⊙ using the flash code. The inclusion of radiative feedback lowers the efficiency of cluster formation by 20-50 per cent relative to hydrodynamic simulations. Two models in particular - 5 × 104 and 105 M⊙ - show the largest suppression of the cluster formation efficiency, corresponding to a factor of ∼2. For these clouds only, the internal energy, a measure of the energy injected by radiative feedback, exceeds the gravitational potential for a significant amount of time. We find a clear relation between the maximum cluster mass, Mc,max, formed in a GMC and the mass of the GMC itself, MGMC: Mc,max ∝ M_{GMC}^{0.81}. This scaling result suggests that young globular clusters at the necessary scale of 106 M⊙ form within host GMCs of masses near ∼5 × 107 M⊙. We compare simulated cluster mass distributions to the observed embedded cluster mass function [d log (N)/dlog (M) ∝ Mβ where β = -1] and find good agreement (β = -0.99 ± 0.14) only for simulations including radiative feedback, indicating this process is important in controlling the growth of young clusters. However, the high star formation efficiencies, which range from 16 to 21 per cent, and high star formation rates compared to locally observed regions suggest other feedback mechanisms are also important during the formation and growth of stellar clusters.

  11. The formation of cluster elliptical galaxies as revealed by extensive star formation.

    PubMed

    Stevens, J A; Ivison, R J; Dunlop, J S; Smail, Ian R; Percival, W J; Hughes, D H; Röttgering, H J A; Van Breugel, W J M; Reuland, M

    2003-09-18

    The most massive galaxies in the present-day Universe are found to lie in the centres of rich clusters. They have old, coeval stellar populations suggesting that the bulk of their stars must have formed at early epochs in spectacular starbursts, which should be luminous phenomena when observed at submillimetre wavelengths. The most popular model of galaxy formation predicts that these galaxies form in proto-clusters at high-density peaks in the early Universe. Such peaks are indicated by massive high-redshift radio galaxies. Here we report deep submillimetre mapping of seven high-redshift radio galaxies and their environments. These data confirm not only the presence of spatially extended regions of massive star-formation activity in the radio galaxies themselves, but also in companion objects previously undetected at any wavelength. The prevalence, orientation, and inferred masses of these submillimetre companion galaxies suggest that we are witnessing the synchronous formation of the most luminous elliptical galaxies found today at the centres of rich clusters of galaxies.

  12. Revisiting the formation of cyclic clusters in liquid ethanol

    NASA Astrophysics Data System (ADS)

    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.

  13. Formation of runaway stars in a star-cluster potential

    NASA Astrophysics Data System (ADS)

    Ryu, Taeho; Leigh, Nathan W. C.; Perna, Rosalba

    2017-09-01

    We study the formation of runaway stars due to binary-binary (2+2) interactions in young star-forming clusters and/or associations. This is done using a combination of analytic methods and numerical simulations of 2+2 scattering interactions, both in isolation and in a homogeneous background potential. We focus on interactions that produce two single stars and a binary, and study the outcomes as a function of the depth of the background potential, within a range typical of cluster cores. As reference parameters for the observational properties, we use those observed for the system of runaway stars AE Aur and μ Col and binary ι Ori. We find that the outcome fractions have no appreciable dependence on the depth of the potential, and neither do the velocities of the ejected single stars. However, as the potential gets deeper and a larger fraction of binaries remain trapped, two binary populations emerge, with the escaped component having higher speeds and shorter semimajor axes than the trapped one. Additionally, we find that the relative angles between the ejected products are generally large. In particular, the angle between the ejected fastest star and the escaped binary is typically ≳120°-135°, with a peak at around 160°. However, as the potential gets deeper, the angle distribution becomes broader. Finally, we discuss the implications of our results for the interpretation of the properties of the runaway stars AE Aur and μ Col.

  14. Hierarchical Cluster Formation in Concentrated Monoclonal Antibody Formulations

    NASA Astrophysics Data System (ADS)

    Godfrin, P. Douglas; Zarzar, Jonathan; Zarraga, Isidro Dan; Porcar, Lionel; Falus, Peter; Wagner, Norman; Liu, Yun

    Reversible cluster formation has been identified as an underlying cause of large solution viscosities observed in some concentrated monoclonal antibody (mAb) formulations. As high solution viscosity prevents the use of subcutaneous injection as a delivery method for some mAbs, a fundamental understanding of the interactions responsible for high viscosities in concentrated mAb solutions is of significant relevance to mAb applications in human health care as well as of intellectual interest. Here, we present a detailed investigation of a well-studied IgG1 based mAb to relate the short time dynamics and microstructure to significant viscosity changes over a range of pharmaceutically relevant physiochemical conditions. Using a combination of experimental techniques, it is found that upon adding Na2SO4, these antibodies dimerize in solution. Proteins form strongly bounded reversible dimers at dilute concentrations that, when concentrated, interact with each other to form loosely bounded, large, transient clusters. The combined effect of forming strongly bounded dimers and a large transient network is a significant increase in the solution viscosity. Strongly bounded, reversible dimers may exist in many IgG1 based mAb systems such that these results contribute to a more comprehensive understanding of the physical mechanisms producing high viscosities in concentrated protein solutions.

  15. Arrays of stochastic oscillators: Nonlocal coupling, clustering, and wave formation.

    PubMed

    Escaff, Daniel; Pinto, Italo'Ivo Lima Dias; Lindenberg, Katja

    2014-11-01

    We consider an array of units each of which can be in one of three states. Unidirectional transitions between these states are governed by Markovian rate processes. The interactions between units occur through a dependence of the transition rates of a unit on the states of the units with which it interacts. This coupling is nonlocal, that is, it is neither an all-to-all interaction (referred to as global coupling), nor is it a nearest neighbor interaction (referred to as local coupling). The coupling is chosen so as to disfavor the crowding of interacting units in the same state. As a result, there is no global synchronization. Instead, the resultant spatiotemporal configuration is one of clusters that move at a constant speed and that can be interpreted as traveling waves. We develop a mean field theory to describe the cluster formation and analyze this model analytically. The predictions of the model are compared favorably with the results obtained by direct numerical simulations.

  16. Formation of Nanometallic Clusters in Silica by Ion Implantation

    SciTech Connect

    Ila, D., Sarkisov, S., Williams, E.K. , Smith, C.C. , Poker, D.B., Hensley, D.K.

    1997-10-01

    We have changed both linear and nonlinear optical properties of suprasil-1 by implanting 2.0 MeV copper, 350 keV tin, 1.5 MeV silver and 3.0 MeV gold.These changes were induced both by over implantation above the threshold fluence for spontaneous cluster formation and by subsequent thermal annealing,and are due to an increase in resonance optical absorption as well as an enhancement of the nonlinear optical properties. Using optical absorption spectrophotometry and Rutherford Backscattering spectrometry, we have measured the cluster size for each heat treatment temperature. Using Z-scan technique we have determined the third order electric susceptibility for each implanted species to be 1.5 x 10(exp -6) esu for Sn nanoclusters, 2.7 x 10(exp -6) esu for Cu nanoclusters, 5 x 10(exp -7) esu for Ag nanoclusters, to 6.5 x 10(exp-7) esu for Au nanoclusters in suprasil- 1.

  17. Formation of compact clusters from high resolution hybrid cosmological simulations

    SciTech Connect

    Richardson, Mark L. A.; Scannapieco, Evan; Gray, William J.

    2013-11-20

    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 and 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 reaction, and then cools to form dense, chemically homogenous clumps of star-forming gas. The formation of these high-redshift clusters may be observable with the next generation of telescopes and the largest of them should survive to the present-day, having properties similar to halo globular clusters.

  18. Star formation in the starburst cluster in NGC 3603

    NASA Astrophysics Data System (ADS)

    Correnti, Matteo; Paresce, Francesco; Aversa, Rossella; Beccari, Giacomo; De Marchi, Guido; Di Criscienzo, Marcella; Pang, Xiaoying; Spezzi, Loredana; Valenti, Elena; Ventura, Paolo

    2012-08-01

    We have used new, deep, visible and near infrared observations of the compact starburst cluster in the giant HII region NGC 3603 and its surroundings with the WFC3 on HST and HAWK-I on the VLT to study in detail the physical properties of its intermediate mass (˜1-3 M⊙) stellar population. We show that after correction for differential extinction and actively accreting stars, and the study of field star contamination, strong evidence remains for a continuous spread in the ages of pre-main sequence stars in the range ˜2 to ˜30 Myr within the temporal resolution available. Existing differences among presently available theoretical models account for the largest possible variation in shape of the measured age histograms within these limits. We also find that this isochronal age spread in the near infrared and visible Colour-Magnitude Diagrams cannot be reproduced by any other presently known source of astrophysical or instrumental scatter that could mimic the luminosity spread seen in our observations except, possibly, episodic accretion. The measured age spread and the stellar spatial distribution in the cluster are consistent with the hypothesis that star formation started at least 20-30 Myrs ago progressing slowly but continuously up to at least a few million years ago. All the stars in the considered mass range are distributed in a flattened oblate spheroidal pattern with the major axis oriented in an approximate South-East-North-West direction, and with the length of the equatorial axis decreasing with increasing age. This asymmetry is most likely due to the fact that star formation occurred along a filament of gas and dust in the natal molecular cloud oriented locally in this direction.

  19. STAR FORMATION IN MASSIVE CLUSTERS VIA BONDI ACCRETION

    SciTech Connect

    Murray, Norman; Chang, Philip E-mail: pchang@cita.utoronto.ca

    2012-02-10

    Essentially all stars form in giant molecular clouds (GMCs). However, inside GMCs, most of the gas does not participate in star formation; rather, denser gas accumulates in clumps in the GMC, with the bulk of the stars in a given GMC forming in a few of the most massive clumps. In the Milky Way, these clumps have masses M{sub cl} {approx}< 5 Multiplication-Sign 10{sup -2} of the GMC, radii r{sub cl} {approx} 1 pc, and free-fall times {tau}{sub cl} {approx} 2 Multiplication-Sign 10{sup 5} yr. We show that clumps inside GMCs should accrete at a modified Bondi accretion rate, which depends on clump mass as M-dot{sub cl}{approx}M{sub cl}{sup 5/4}. This rate is initially rather slow, usually slower than the initial star formation rate inside the clump (we adopt the common assumption that inside the clump, M-dot{sub *}={epsilon}{sub ff}M{sub cl}/{tau}{sub cl}, with {epsilon}{sub ff} Almost-Equal-To 0.017). However, after {approx}2 GMC free-fall times {tau}{sub GMC}, the clump accretion rate accelerates rapidly; formally, the clump can accrete the entire GMC in {approx}3{tau}{sub GMC}. At the same time, the star formation rate accelerates, tracking the Bondi accretion rate. If the GMC is disrupted by feedback from the largest clump, half the stars in that clump form in the final {tau}{sub GMC} before the GMC is disrupted. The theory predicts that the distribution of effective star formation rates, measured per GMC free-fall time, is broad, ranging from {approx}0.001 up to 0.1 or larger and that the mass spectrum of star clusters is flatter than that of clumps, consistent with observations.

  20. Catalytic formation of a nitrogenase iron-sulfur cluster.

    PubMed

    Zheng, L; Dean, D R

    1994-07-22

    Biological nitrogen fixation is catalyzed by nitrogenase, an enzyme comprised of two component proteins called the Fe protein and the MoFe protein. Both nitrogenase component proteins contain metalloclusters. The Azotobacter vinelandii nifS gene product (NifS), which is required for full activation of the nitrogenase component proteins, is a pyridoxal phosphate enzyme and is able to catalyze the desulfurization of L-cysteine to yield sulfur and L-alanine (Zheng, L., White, R. H., Cash, V.L., Jack, R.F., and Dean, D.R. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 2754-2758). An enzyme-bound persulfide that was identified as an intermediate in the cysteine desulfurization reaction catalyzed by NifS has been suggested as a possible S-donor in formation of the iron-sulfide cores of the nitrogenase metalloclusters. In the present work it is shown that NifS is able to effectively catalyze activation of an apo-form of the Fe protein that was prepared by removal of its Fe4S4 cluster using the chelator, alpha,alpha'-dipyridyl. The reconstitution reaction includes apo-Fe protein, NifS, L-cysteine, ferrous ion, dithiothreitol, and MgATP. Reconstitution of the inactive apo-Fe protein catalyzed by NifS results in 80-95% recovery of the original activity and yields an Fe protein having the normal electron paramagnetic resonance spectra properties associated with the Fe protein's Fe4S4 cluster. An altered NifS protein, NifS-Ala325, which lacks the desulfurase activity and is unable to from the NifS-bound persulfide, is not able to catalyze reactivation of the apo-Fe protein. These in vitro results support the proposal that NifS activity provides the inorganic sulfide necessary for in vivo formation of the nitrogenase metalloclusters. Moreover, because NifS has recently been shown to be a member of a highly homologous gene family, it appears that pyridoxal phosphate chemistry might play a general role in iron-sulfur cluster assembly.

  1. The Formation of Cluster Populations Through Direct Galaxy Collisions

    NASA Astrophysics Data System (ADS)

    Peterson, Bradley W.; Smith, Beverly J.; Struck, Curtis

    2016-01-01

    Much progress has been made on the question of how globular clusters form. In particular, the study of extragalactic populations of young, high-mass clusters ("super star clusters") has revealed a class of objects can evolve into globular clusters. The process by which these clusters form, and how many survive long enough to become globular clusters, is not wholly understood. Here, we use new data on the colliding galaxy system Arp 261 to investigate the possibility that young, massive clusters form in greater numbers during direct galaxy collisions, compared to less direct tidal collisions.

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

    NASA Astrophysics Data System (ADS)

    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/π<=0.12) in the whole Hipparcos catalog. On average, our revised distance moduli are decreased by 0.04 mag with respect to Gratton et al. The corresponding age of the GCs is t=11.5+/-2.6 Gyr, where the error bars refer to the 95% confidence range. The relation between the zero-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

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

    PubMed

    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.

  4. Sulfur driven nucleation mode formation in diesel exhaust under transient driving conditions.

    PubMed

    Karjalainen, Panu; Rönkkö, Topi; Pirjola, Liisa; Heikkilä, Juha; Happonen, Matti; Arnold, Frank; Rothe, Dieter; Bielaczyc, Piotr; Keskinen, Jorma

    2014-02-18

    Sulfur driven diesel exhaust nucleation particle formation processes were studied in an aerosol laboratory, on engine dynamometers, and on the road. All test engines were equipped with a combination of a diesel oxidation catalyst (DOC) and a partial diesel particulate filter (pDPF). At steady operating conditions, the formation of semivolatile nucleation particles directly depended on SO2 conversion in the catalyst. The nucleation particle emission was most significant after a rapid increase in engine load and exhaust gas temperature. Results indicate that the nucleation particle formation at transient driving conditions does not require compounds such as hydrocarbons or sulfated hydrocarbons, however, it cannot be explained only by the nucleation of sulfuric acid. A real-world exhaust study with a heavy duty diesel truck showed that the nucleation particle formation occurs even with ultralow sulfur diesel fuel, even at downhill driving conditions, and that nucleation particles can contribute 60% of total particle number emissions. In general, due to sulfur storage and release within the exhaust aftertreatment systems and transients in driving, emissions of nucleation particles can even be the dominant part of modern diesel vehicle exhaust particulate number emissions.

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

    PubMed Central

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

    2014-01-01

    Abstract The inferior olivary nucleus (IO) in in vitro slices from postnatal mice (P5.5–P15.5) spontaneously generates clusters of neurons with synchronous calcium transients, and intracellular recordings from IO neurons suggest that electrical coupling between neighbouring IO neurons may serve as a synchronizing mechanism. Here, we studied the cluster-forming mechanism and find that clusters overlap extensively with an overlap distribution that resembles the distribution for a random overlap model. The average somatodendritic field size of single curly IO neurons was ∼6400 μm2, which is slightly smaller than the average IO cluster size. Eighty-seven neurons with overlapping dendrites were estimated to be contained in the principal olive mean cluster size, and about six non-overlapping curly IO neurons could be contained within the largest clusters. Clusters could also be induced by iontophoresis 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 signify that active dendritic properties contribute to cluster formation. PMID:24042500

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

    PubMed

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

    2014-01-01

    The inferior olivary nucleus (IO) in in vitro slices from postnatal mice (P5.5-P15.5) spontaneously generates clusters of neurons with synchronous calcium transients, and intracellular recordings from IO neurons suggest that electrical coupling between neighbouring IO neurons may serve as a synchronizing mechanism. Here, we studied the cluster-forming mechanism and find that clusters overlap extensively with an overlap distribution that resembles the distribution for a random overlap model. The average somatodendritic field size of single curly IO neurons was ∼6400 μm(2), which is slightly smaller than the average IO cluster size. Eighty-seven neurons with overlapping dendrites were estimated to be contained in the principal olive mean cluster size, and about six non-overlapping curly IO neurons could be contained within the largest clusters. Clusters could also be induced by iontophoresis 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 signify that active dendritic properties contribute to cluster formation.

  7. Dimerization of postsynaptic neuroligin drives synaptic assembly via transsynaptic clustering of neurexin

    PubMed Central

    Shipman, Seth L.; Nicoll, Roger A.

    2012-01-01

    The transsynaptic complex of neuroligin (NLGN) and neurexin forms a physical connection between pre- and postsynaptic neurons that occurs early in the course of new synapse assembly. Both neuroligin and neurexin have, indeed, been proposed to exhibit active, instructive roles in the formation of synapses. However, the process by which these instructive roles play out during synaptogenesis is not well understood. Here, we examine one aspect of postsynaptic neuroligin with regard to its synaptogenic properties: its basal state as a constitutive dimer. We show that dimerization is required for the synaptogenic properties of neuroligin and likely serves to induce presynaptic differentiation via a transsynaptic clustering of neurexin. Further, we introduce chemically inducible, exogenous dimerization domains to the neuroligin molecule, effectively bestowing chemical control of neuroligin dimerization. This allows us to identify the acute requirements of neuroligin dimerization by chemically manipulating the monomeric-to-dimeric conversion of neuroligin. Based on the results of the inducible dimerization experiments, we propose a model in which dimerized neuroligin induces the mechanical clustering of presynaptic molecules as part of a requisite step in the coordinated assembly of a chemical synapse. PMID:23129658

  8. Dimerization of postsynaptic neuroligin drives synaptic assembly via transsynaptic clustering of neurexin.

    PubMed

    Shipman, Seth L; Nicoll, Roger A

    2012-11-20

    The transsynaptic complex of neuroligin (NLGN) and neurexin forms a physical connection between pre- and postsynaptic neurons that occurs early in the course of new synapse assembly. Both neuroligin and neurexin have, indeed, been proposed to exhibit active, instructive roles in the formation of synapses. However, the process by which these instructive roles play out during synaptogenesis is not well understood. Here, we examine one aspect of postsynaptic neuroligin with regard to its synaptogenic properties: its basal state as a constitutive dimer. We show that dimerization is required for the synaptogenic properties of neuroligin and likely serves to induce presynaptic differentiation via a transsynaptic clustering of neurexin. Further, we introduce chemically inducible, exogenous dimerization domains to the neuroligin molecule, effectively bestowing chemical control of neuroligin dimerization. This allows us to identify the acute requirements of neuroligin dimerization by chemically manipulating the monomeric-to-dimeric conversion of neuroligin. Based on the results of the inducible dimerization experiments, we propose a model in which dimerized neuroligin induces the mechanical clustering of presynaptic molecules as part of a requisite step in the coordinated assembly of a chemical synapse.

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

    PubMed

    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

  10. The Insignificance of Major Mergers in Driving Star Formation at z approximately equal to 2

    NASA Technical Reports Server (NTRS)

    Kaviraj, S.; Cohen, S.; Windhorst, R. A.; Silk, J.; O'Connell, R. W.; Dopita, M. A.; Dekel, A.; Hathi, N. P.; Straughn, A.; Rutkowski, M.

    2012-01-01

    We study the significance of major mergers in driving star formation in the early Universe, by quantifying the contribution of this process to the total star formation budget in 80 massive (M(*) > 10(exp 10) Solar M) galaxies at z approx = 2. Employing visually-classified morphologies from rest-frame V-band HST imaging, we find that 55(exp +/-14)% of the star formation budget is hosted by non-interacting late-types, with 27(exp +/-18% in major mergers and 18(exp +/- 6)% in spheroids. Given that a system undergoing a major merger continues to experience star formation driven by other processes at this epoch (e.g. cold accretion, minor mergers), approx 27% is a likely upper limit for the major-merger contribution to star formation activity at this epoch. The ratio of the average specific star formation rate in major mergers to that in the non-interacting late-types is approx 2.2:1, suggesting that the typical enhancement of star formation due to major merging is modest and that just under half the star formation in systems experiencing major mergers is unrelated to the merger itself. Taking this into account, we estimate that the actual major-merger contribution to the star formation budget may be as low as approx 15%. While our study does not preclude a major-merger-dominated. era in the very early Universe, if the major-merger contribution to star formation does not evolve significantly into larger look-back times, then this process has a relatively insignificant role in driving stellar mass assembly over cosmic time.

  11. Star Formation in Galaxy Clusters Over the Past 10 Billion Years

    NASA Astrophysics Data System (ADS)

    Tran, Kim-Vy

    2012-01-01

    Galaxy clusters are the largest gravitationally bound systems in the universe and include the most massive galaxies in the universe; this makes galaxy clusters ideal laboratories for disentangling the nature versus nurture aspect of how galaxies evolve. Understanding how galaxies form and evolve in clusters continues to be a fundamental question in astronomy. The ages and assembly histories of galaxies in rich clusters test both stellar population models and hierarchical formation scenarios. Is star formation in cluster galaxies simply accelerated relative to their counterparts in the lower density field, or do cluster galaxies assemble their stars in a fundamentally different manner? To answer this question, I review multi-wavelength results on star formation in galaxy clusters from Coma to the most distant clusters yet discovered at look-back times of 10 billion years (z 2).

  12. Cluster Formation Triggered by Filament Collisions in Serpens South

    NASA Astrophysics Data System (ADS)

    Nakamura, Fumitaka; Sugitani, Koji; Tanaka, Tomohiro; Nishitani, Hiroyuki; Dobashi, Kazuhito; Shimoikura, Tomomi; Shimajiri, Yoshito; Kawabe, Ryohei; Yonekura, Yoshinori; Mizuno, Izumi; Kimura, Kimihiko; Tokuda, Kazuki; Kozu, Minato; Okada, Nozomi; Hasegawa, Yutaka; Ogawa, Hideo; Kameno, Seiji; Shinnaga, Hiroko; Momose, Munetake; Nakajima, Taku; Onishi, Toshikazu; Maezawa, Hiroyuki; Hirota, Tomoya; Takano, Shuro; Iono, Daisuke; Kuno, Nario; Yamamoto, Satoshi

    2014-08-01

    The Serpens South infrared dark cloud consists of several filamentary ridges, some of which fragment into dense clumps. On the basis of CCS (JN = 43-32), HC3N (J = 5-4), N2H+ (J = 1-0), and SiO (J = 2-1, v = 0) observations, we investigated the kinematics and chemical evolution of these filamentary ridges. We find that CCS is extremely abundant along the main filament in the protocluster clump. We emphasize that Serpens South is the first cluster-forming region where extremely strong CCS emission is detected. The CCS-to-N2H+ abundance ratio is estimated to be about 0.5 toward the protocluster clump, whereas it is about 3 in the other parts of the main filament. We identify six dense ridges with different V LSR. These ridges appear to converge toward the protocluster clump, suggesting that the collisions of these ridges may have triggered cluster formation. The collisions presumably happened within a few × 105 yr because CCS is abundant only for a short time. The short lifetime agrees with the fact that the number fraction of Class I objects, whose typical lifetime is 0.4 × 105 yr, is extremely high, about 70% in the protocluster clump. In the northern part, two ridges appear to have partially collided, forming a V-shape clump. In addition, we detected strong bipolar SiO emission that is due to the molecular outflow blowing out of the protostellar clump, as well as extended weak SiO emission that may originate from the filament collisions.

  13. CLUSTER FORMATION TRIGGERED BY FILAMENT COLLISIONS IN SERPENS SOUTH

    SciTech Connect

    Nakamura, Fumitaka; Kawabe, Ryohei; Shinnaga, Hiroko; Sugitani, Koji; Tanaka, Tomohiro; Kimura, Kimihiko; Tokuda, Kazuki; Kozu, Minato; Okada, Nozomi; Hasegawa, Yutaka; Ogawa, Hideo; Nishitani, Hiroyuki; Mizuno, Izumi; Dobashi, Kazuhito; Shimoikura, Tomomi; Shimajiri, Yoshito; Kameno, Seiji; Momose, Munetake; Nakajima, Taku; and others

    2014-08-20

    The Serpens South infrared dark cloud consists of several filamentary ridges, some of which fragment into dense clumps. On the basis of CCS (J{sub N} = 4{sub 3}-3{sub 2}), HC{sub 3}N (J = 5-4), N{sub 2}H{sup +} (J = 1-0), and SiO (J = 2-1, v = 0) observations, we investigated the kinematics and chemical evolution of these filamentary ridges. We find that CCS is extremely abundant along the main filament in the protocluster clump. We emphasize that Serpens South is the first cluster-forming region where extremely strong CCS emission is detected. The CCS-to-N{sub 2}H{sup +} abundance ratio is estimated to be about 0.5 toward the protocluster clump, whereas it is about 3 in the other parts of the main filament. We identify six dense ridges with different V {sub LSR}. These ridges appear to converge toward the protocluster clump, suggesting that the collisions of these ridges may have triggered cluster formation. The collisions presumably happened within a few × 10{sup 5} yr because CCS is abundant only for a short time. The short lifetime agrees with the fact that the number fraction of Class I objects, whose typical lifetime is 0.4 × 10{sup 5} yr, is extremely high, about 70% in the protocluster clump. In the northern part, two ridges appear to have partially collided, forming a V-shape clump. In addition, we detected strong bipolar SiO emission that is due to the molecular outflow blowing out of the protostellar clump, as well as extended weak SiO emission that may originate from the filament collisions.

  14. Formation of failure matrix and failure-free control algorithm for multi-sectioned Switched-reluctance drive

    NASA Astrophysics Data System (ADS)

    Odnokopylov, G.; Rozayev, I.

    2014-10-01

    We review fault-tolerant switched reluctance drive with sectioning of the three-phase stator winding. In the operating process of an electric drive, there will be continuous monitoring of the operating state on the basis of a developed algorithm to analyse drive operability and formation tabulate a failure matrix. The paper introduces a failure-free control algorithm for multi-section switch - reluctance motor with formation the assignment values of amplitude phase currents taking into account the failure matrix. We show that in an emergency such single failure or multiple failure in switched-reluctance drive it is possible to provide reduction of torque fall and pro-gressively stock depletion with providing fault-tolerance of drive system. A method of residual life evaluation is proposed on the basis of calculating the coefficient of operability of the electric drive system that gives possibility to control the endurance of electric drive in real time from operational to completely unusable.

  15. Lack of nuclear clusters in dwarf spheroidal galaxies: implications for massive black holes formation and the cusp/core problem

    NASA Astrophysics Data System (ADS)

    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.

  16. Cationic cluster formation versus disproportionation of low-valent indium and gallium complexes of 2,2'-bipyridine

    PubMed Central

    Lichtenthaler, Martin R.; Stahl, Florian; Kratzert, Daniel; Heidinger, Lorenz; Schleicher, Erik; Hamann, Julian; Himmel, Daniel; Weber, Stefan; Krossing, Ingo

    2015-01-01

    Group 13 MI compounds often disproportionate into M0 and MIII. Here, however, we show that the reaction of the MI salt of the weakly coordinating alkoxyaluminate [GaI(C6H5F)2]+[Al(ORF)4]− (RF=C(CF3)3) with 2,2'-bipyridine (bipy) yields the paramagnetic and distorted octahedral [Ga(bipy)3]2+•{[Al(ORF)4]−}2 complex salt. While the latter appears to be a GaII compound, both, EPR and DFT investigations assign a ligand-centred [GaIII{(bipy)3}•]2+ radical dication. Surprisingly, the application of the heavier homologue [InI(C6H5F)2]+[Al(ORF)4]− leads to aggregation and formation of the homonuclear cationic triangular and rhombic [In3(bipy)6]3+, [In3(bipy)5]3+ and [In4(bipy)6]4+ metal atom clusters. Typically, such clusters are formed under strongly reductive conditions. Analysing the unexpected redox-neutral cationic cluster formation, DFT studies suggest a stepwise formation of the clusters, possibly via their triplet state and further investigations attribute the overall driving force of the reactions to the strong In−In bonds and the high lattice enthalpies of the resultant ligand stabilized [M3]3+{[Al(ORF)4]−}3 and [M4]4+{[Al(ORF)4]−}4 salts. PMID:26478464

  17. Undergraduate ALFALFA Team: Analysis of Spatially-Resolved Star-Formation in Nearby Galaxy Groups and Clusters

    NASA Astrophysics Data System (ADS)

    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.

  18. Globular cluster systems in nearby dwarf galaxies - III. Formation efficiencies of old globular clusters

    NASA Astrophysics Data System (ADS)

    Georgiev, Iskren Y.; Puzia, Thomas H.; Goudfrooij, Paul; Hilker, Michael

    2010-08-01

    We investigate the origin of the shape of the globular cluster (GC) system scaling parameters as a function of galaxy mass, i.e. specific frequency (SN), specific luminosity (SL), specific mass (SM) and specific number () of GCs. In the low-mass galaxy regime (MV >~ -16 mag), our analysis is based on Hubble Space Telescope/Advanced Camera for Surveys observations of GC populations of faint, mainly late-type dwarf galaxies in low-density environments. In order to sample the entire range in galaxy mass (MV = -11 to -23mag =106- 1011Lsolar), environment and morphology we augment our sample with data of spiral and elliptical galaxies from the literature, in which old GCs are reliably detected. This large data set confirms (irrespective of the galaxy type) the increase in the specific frequencies of GCs above and below a galaxy magnitude of MV ~= -20mag. Over the full mass range, the SL value of early-type galaxies is, on average, twice that of late types. To investigate the observed trends, we derive theoretical predictions of GC system scaling parameters as a function of host galaxy mass based on the models of Dekel and Birnboim in which star formation processes are regulated by stellar and supernova feedback below a stellar mass of 3 × 1010Msolar and by virial shocks above it. We find that the analytical model describes remarkably well the shape of the GC system scaling parameter distributions with a universal specific GC formation efficiency, η, which relates the total mass in GCs to the total galaxy halo mass. Early-type and late-type galaxies show a similar mean value of η = 5.5 × 10-5, with an increasing scatter towards lower galaxy masses. This can be due to the enhanced stochastic nature of the star and star-cluster formation processes for such systems. Some massive galaxies have excess η values compared to what is expected from the mean model prediction for galaxies more luminous than MV ~= -20mag (LV >~ 1010Lsolar). This may be attributed to a very

  19. On the formation of cD galaxies and their parent clusters

    NASA Astrophysics Data System (ADS)

    Tovmassian, Hrant M.; Andernach, Heinz

    2012-12-01

    In order to study the mechanism of the formation of cD galaxies, we search for possible dependencies between the K-band luminosity of cD galaxies and the parameters of their host clusters which we select to have a dominant cD galaxy, corresponding to a cluster morphology of Bautz-Morgan type I (BM I). As a comparison sample we use cD galaxies in clusters where they are not dominant, which we define here as non-BM I (NBMI) type clusters. We find that for 71 BM I clusters the absolute K-band luminosity of cD galaxies 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 BM I 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 X-ray luminosity of BM I clusters depends on the cluster velocity dispersion, while in NBMI clusters such a correlation is absent. These findings favour the cannibalism scenario for the formation of cD galaxies. We suggest that cD galaxies in clusters of BM I type were formed and evolved preferentially in one and the same cluster. In contrast, cD galaxies in NBMI-type clusters were either originally formed in clusters that later merged with groups or clusters to form the current cluster, or are now in the process of merging.

  20. The enhancement mechanism of glycolic acid on the formation of atmospheric sulfuric acid-ammonia molecular clusters

    NASA Astrophysics Data System (ADS)

    Zhang, Haijie; Kupiainen-Määttä, Oona; Zhang, Xiuhui; Molinero, Valeria; Zhang, Yunhong; Li, Zesheng

    2017-05-01

    Highly oxidized multifunctional organic molecules, which span a wide range of low volatilities, are capable of driving particle formation as well as the initial growth of particles in the atmosphere. However, their participant mechanism in new particle formation still remains largely ambiguous. Here we present an investigation of the potentially participant mechanism of the simplest hydroxyl acid, glycolic acid (GA) on clusters formation by sulfuric acid (SA) and ammonia (A). Density functional theory calculations at the M062X/6-311++G(3df,3pd) level of theory combining with atmospheric cluster dynamics code simulations of (𝐒𝐀)xṡ𝐀yṡ(𝐆𝐀)z cluster (y≤x + z ≤ 3) systems at different temperatures (298, 278, 258, 238, and 218 K) give direct evidence of the enhancement effect of GA on the formation rates of SA-A-based clusters at high concentration of GA and T = 238 K and 218 K. Moreover, within GA's enhancement concentrations, the enhancement strength R of GA presents a positive dependence on its atmospheric concentrations and a negative dependence on temperature. A competitive relationship between SA and GA has been identified through the negative dependence of R on the concentrations of SA. The influence of A on R is more complex that R first increases, reaching a maximum value, and then decreases with the increasing concentration of A. Finally, the combination of the traced growth paths of the system with the enhancement strength of GA suggests a "catalytic" enhancement mechanism of GA where GA acts as a mediate bridge for the formation of pure SA-A-based clusters.

  1. Resolving Star Formation, Multiphase ISM Structure, and Wind Driving with MHD and RHD Models of Galactic Disks

    NASA Astrophysics Data System (ADS)

    Ostriker, Eve

    Current studies of star and galaxy formation have concluded that energetic feedback from young stars and supernovae (SNe) is crucial, both for controlling observed interstellar medium (ISM) properties and star formation rates in the Milky Way and other galaxies, and for driving galactic winds that govern the baryon abundance in dark matter halos. However, in many numerical studies of the ISM, energy inputs have not been implemented self-consistently with the evolving rate of gravitational collapse to make stars, or have considered only isolated star-forming clouds without a realistic galactic environment (including sheared rotation and externally-originating SNe), or have not directly incorporated radiation, magnetic, and chemical effects that are important or even dominant. In models of galaxy formation and evolution in the cosmic context, galactic winds are indispensable but highly uncertain as the physics of superbubble evolution and radiation-gas interactions cannot be resolved. Our central objectives are (1) to address the above limitations of current models, developing self-consistent simulations of the multiphase ISM in disk galaxies that resolve both star formation and stellar feedback, covering the range of scales needed to connect star cluster formation to galactic superwind ejection, and the range of environments from dwarfs to ULIRGs; and (2) to analyze the detailed properties of the gas, magnetic field, radiation field, and star formation/SNe in our simulations, including dependencies on local galactic disk environment, and to connect intrinsic properties with observable diagnostics. The proposed project will employ the Athena code for numerical magneto-hydrodynamic (MHD) and radiation-hydrodynamic (RHD) simulations, using comprehensive physics modules that have been developed, tested, and demonstrated in sample simulations. We will consider local ``shearing box'' disk models with gas surface density Sigma = 2 - 10,000 Msun/pc^2, and a range of stellar

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

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed

    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. Graphical Abstract ᅟ.

  4. Formation and Combustion of Unconfined Drop Clusters in Microgravity

    NASA Technical Reports Server (NTRS)

    Liu, S.; Craig, G.; Zhang, Y.; Ruff, G. A.

    1997-01-01

    Single-drop and droplet array studies have become common methods to isolate and investigate the effects of any of the complexities that enter into the drop combustion process. Microgravity environments are required to allow larger drops to be studied while minimizing or eliminating the confounding effects of buoyancy. Based on the results from current isolated drop, drop array, and spray studies funded through the Microgravity Science and Applications Division, it has become clear that even with the effects of buoyancy removed, the extrapolation of results from droplet array studies to spray flames is difficult. The problem occurs because even the simplest spray systems introduce complexities of multi-disperse drop sizes and drop-drop interactions, coupled with more complicated fluid dynamics. Not only do these features make the interpretation of experimental data difficult, they also make the problem very difficult to analyze computationally. Group combustion models, in which the interaction between droplets is treated on a statistical manner, have become a popular method to investigate the behavior of large numbers of interacting droplets, particularly through the work of Ryan et al. and Bellan and co-workers. While these models idealize the actual spray systems to a point where they can be treated computationally, the experimental analogy to these models is difficult to achieve because it requires the formation and Combustion of drop clusters without the effects of buoyancy. Therefore, even though these models have provided useful and insightful information, the verification of the results by direct comparison with experimental data is still lacking.

  5. Risky Driving, Mental Health, and Health-Compromising Behaviors: Risk Clustering in Late Adolescents and Adults

    PubMed Central

    Sommers, Marilyn S.; Fargo, Jamison D.

    2014-01-01

    Background Health-compromising behaviors in adolescents and adults co-occur. Because motor vehicle crashes are the leading cause of death and disability for these age groups, understanding the association between risky driving and other health compromising behaviors is critical. Methods We performed a secondary analysis of data from a randomized controlled trial of an intervention for participants who screened positive for risky driving and problem drinking. Using baseline data, we examined relationships among conduct behavior problems before and after age 15, depressive symptoms, sleep, problem drinking, and risky driving (hostile, reckless and drinking and driving) in late adolescents ages 18–24 (n= 110) and adults ages 25–44 (n= 202). We developed a measurement model for the entire sample using confirmatory factor analysis, which was then specified as a multi-group structural equation model. Results Late adolescents and adults had some similar associations for pathways through problem drinking to drinking and driving; depression to reckless driving; and conduct behavior problems after 15 to hostile driving. Late adolescents, however, had more complex relationships: depressive symptoms and conduct behavior problems before 15 were associated with more risky driving behaviors through multiple pathways and males reported more risky driving. Conclusions Risky driving is associated with other health-compromising behaviors and mental health factors. It is a multidimensional phenomenon more pronounced in late adolescence than adulthood. In order to promote safe driving, the findings support the need to consider behaviors that are a health threat in the late adolescent population during driving training and licensure. PMID:24814717

  6. Risky driving, mental health, and health-compromising behaviours: risk clustering in late adolescents and adults.

    PubMed

    McDonald, Catherine C; Sommers, Marilyn S; Fargo, Jamison D

    2014-12-01

    Health-compromising behaviours in adolescents and adults co-occur. Because motor vehicle crashes are the leading cause of death and disability for these age groups, understanding the association between risky driving and other health-compromising behaviours is critical. We performed a secondary analysis of data from a randomised controlled trial of an intervention for participants who screened positive for risky driving and problem drinking. Using baseline data, we examined relationships among conduct behaviour problems before and after age 15 years, depressive symptoms, sleep, problem drinking, and risky driving (hostile, reckless and drinking and driving) in late adolescents ages 18-24 (n=110) years, and adults ages 25-44 (n=202) years. We developed a measurement model for the entire sample using confirmatory factor analysis, which was then specified as a multigroup structural equation model. Late adolescents and adults had some similar associations for pathways through problem drinking to drinking and driving; depression to reckless driving; and conduct behaviour problems after 15 years of age to hostile driving. Late adolescents, however, had more complex relationships: depressive symptoms and conduct behaviour problems before 15 years of age were associated with more risky driving behaviours through multiple pathways, and males reported more risky driving. Risky driving is associated with other health-compromising behaviours and mental health factors. It is a multidimensional phenomenon more pronounced in late adolescence than adulthood. In order to promote safe driving, the findings support the need to consider behaviours that are a health threat in the late adolescent population during driving training and licensure. NCT00164294. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.

  7. The influence of feedback from massive stars on the formation and emergence of massive clusters

    NASA Astrophysics Data System (ADS)

    Dale, James E.

    2017-03-01

    Massive star clusters are of fundamental importance both observationally, since they are visible at such great distances, and theoretically, because of their influence on the large-scale ISM. Understanding stellar feedback is a prerequisite for making sense of their formation and early evolution, since feedback influences cluster structure, star formation efficiency, and sets the timescales on which clusters emerge from their parent clouds to become optically visible. I review the progress made in understanding these issues from a numerical perspective.

  8. A density-dependent switch drives stochastic clustering and polarization of signaling molecules.

    PubMed

    Jilkine, Alexandra; Angenent, Sigurd B; Wu, Lani F; Altschuler, Steven J

    2011-11-01

    Positive feedback plays a key role in the ability of signaling molecules to form highly localized clusters in the membrane or cytosol of cells. Such clustering can occur in the absence of localizing mechanisms such as pre-existing spatial cues, diffusional barriers, or molecular cross-linking. What prevents positive feedback from amplifying inevitable biological noise when an un-clustered "off" state is desired? And, what limits the spread of clusters when an "on" state is desired? Here, we show that a minimal positive feedback circuit provides the general principle for both suppressing and amplifying noise: below a critical density of signaling molecules, clustering switches off; above this threshold, highly localized clusters are recurrently generated. Clustering occurs only in the stochastic regime, suggesting that finite sizes of molecular populations cannot be ignored in signal transduction networks. The emergence of a dominant cluster for finite numbers of molecules is partly a phenomenon of random sampling, analogous to the fixation or loss of neutral mutations in finite populations. We refer to our model as the "neutral drift polarity model." Regulating the density of signaling molecules provides a simple mechanism for a positive feedback circuit to robustly switch between clustered and un-clustered states. The intrinsic ability of positive feedback both to create and suppress clustering is a general mechanism that could operate within diverse biological networks to create dynamic spatial organization.

  9. A Density-Dependent Switch Drives Stochastic Clustering and Polarization of Signaling Molecules

    PubMed Central

    Jilkine, Alexandra; Angenent, Sigurd B.; Wu, Lani F.; Altschuler, Steven J.

    2011-01-01

    Positive feedback plays a key role in the ability of signaling molecules to form highly localized clusters in the membrane or cytosol of cells. Such clustering can occur in the absence of localizing mechanisms such as pre-existing spatial cues, diffusional barriers, or molecular cross-linking. What prevents positive feedback from amplifying inevitable biological noise when an un-clustered “off” state is desired? And, what limits the spread of clusters when an “on” state is desired? Here, we show that a minimal positive feedback circuit provides the general principle for both suppressing and amplifying noise: below a critical density of signaling molecules, clustering switches off; above this threshold, highly localized clusters are recurrently generated. Clustering occurs only in the stochastic regime, suggesting that finite sizes of molecular populations cannot be ignored in signal transduction networks. The emergence of a dominant cluster for finite numbers of molecules is partly a phenomenon of random sampling, analogous to the fixation or loss of neutral mutations in finite populations. We refer to our model as the “neutral drift polarity model.” Regulating the density of signaling molecules provides a simple mechanism for a positive feedback circuit to robustly switch between clustered and un-clustered states. The intrinsic ability of positive feedback both to create and suppress clustering is a general mechanism that could operate within diverse biological networks to create dynamic spatial organization. PMID:22102805

  10. Induction of peptide bond dipoles drives cooperative helix formation in the (AAQAA)3 peptide.

    PubMed

    Huang, Jing; MacKerell, Alexander D

    2014-08-19

    Cooperativity is a central feature in the formation of secondary structures in proteins. However, the driving forces behind this cooperativity are poorly understood. The present work shows that the cooperativity of helix formation in the acetyl-(AAQAA)3-NH2 peptide is significantly enhanced using an empirical force field that explicitly includes the treatment of electronic polarizability. Polarizable simulations yield helical content consistent with experimental measurements and indicate that the dependence of helical content on temperature is improved over additive models, though further sampling is required to fully validate this conclusion. Cooperativity is indicated by the peptide sampling either the coiled state or long helices with relatively low populations of short helices. The cooperativity is shown to be associated with enhanced dipole moments of the peptide backbone upon helix formation. These results indicate the polarizable force field to more accurately model peptide-folding cooperativity based on its physically realistic treatment of electronic polarizability.

  11. Induction of Peptide Bond Dipoles Drives Cooperative Helix Formation in the (AAQAA)3 Peptide

    PubMed Central

    Huang, Jing; MacKerell, Alexander D.

    2014-01-01

    Cooperativity is a central feature in the formation of secondary structures in proteins. However, the driving forces behind this cooperativity are poorly understood. The present work shows that the cooperativity of helix formation in the acetyl-(AAQAA)3-NH2 peptide is significantly enhanced using an empirical force field that explicitly includes the treatment of electronic polarizability. Polarizable simulations yield helical content consistent with experimental measurements and indicate that the dependence of helical content on temperature is improved over additive models, though further sampling is required to fully validate this conclusion. Cooperativity is indicated by the peptide sampling either the coiled state or long helices with relatively low populations of short helices. The cooperativity is shown to be associated with enhanced dipole moments of the peptide backbone upon helix formation. These results indicate the polarizable force field to more accurately model peptide-folding cooperativity based on its physically realistic treatment of electronic polarizability. PMID:25140435

  12. Star Formation and Early Evolution of Young Clusters

    NASA Astrophysics Data System (ADS)

    Gregorio-Hetem, J.; Fernandes, B.; Santos-Silva, T.; Montmerle, T.; Hetem, A.

    2017-07-01

    Characterizing large samples of young stars and studying the dynamical evolution of stellar clusters are the main subjects of this paper. The review is based on multi-band observations of star-forming regions, as well as the clustering properties observed in the spatial distribution of stars in young clusters, compared with N-body simulations that reproduce their fractal sub-structures. These are recent observational and theoretical results related to the early phases of the clusters evolution, whose initial star-forming conditions could be under effect of ionizing sources.

  13. Formation of cold ion-neutral clusters using superfluid helium nanodroplets

    NASA Astrophysics Data System (ADS)

    Falconer, Travis M.; Lewis, William K.; Bemish, Raymond J.; Miller, Roger E.; Glish, Gary L.

    2010-05-01

    A strategy for forming and detecting cold ion-neutral clusters using superfluid helium nanodroplets is described. Sodium cations generated via thermionic emission are directed toward a beam of helium droplets that can also pick up neutral molecules and form a cluster with the captured Na+. The composition of the clusters is determined by mass spectrometric analysis following a desolvation step. It is shown that the polar molecules H2O and HCN are picked up and form ion-neutral clusters with sizes and relative abundances that are in good agreement with those predicted by the statistics used to describe neutral cluster formation in helium droplets. [Na(H2O)n]+ clusters containing six to 43 water molecules were observed, a size range of sodiated water clusters difficult to access in the gas phase. Clusters containing N2 were in lower abundance than expected, suggesting that the desolvation process heats the clusters sufficiently to dissociate those containing nonpolar molecules.

  14. APP-dependent glial cell line-derived neurotrophic factor gene expression drives neuromuscular junction formation.

    PubMed

    Stanga, Serena; Zanou, Nadège; Audouard, Emilie; Tasiaux, Bernadette; Contino, Sabrina; Vandermeulen, Gaëlle; René, Frédérique; Loeffler, Jean-Philippe; Clotman, Frédéric; Gailly, Philippe; Dewachter, Ilse; Octave, Jean-Noël; Kienlen-Campard, Pascal

    2016-05-01

    Besides its crucial role in the pathogenesis of Alzheimer's disease, the knowledge of amyloid precursor protein (APP) physiologic functions remains surprisingly scarce. Here, we show that APP regulates the transcription of the glial cell line-derived neurotrophic factor (GDNF). APP-dependent regulation of GDNF expression affects muscle strength, muscular trophy, and both neuronal and muscular differentiation fundamental for neuromuscular junction (NMJ) maturation in vivo In a nerve-muscle coculture model set up to modelize NMJ formation in vitro, silencing of muscular APP induces a 30% decrease in secreted GDNF levels and a 40% decrease in the total number of NMJs together with a significant reduction in the density of acetylcholine vesicles at the presynaptic site and in neuronal maturation. These defects are rescued by GDNF expression in muscle cells in the conditions where muscular APP has been previously silenced. Expression of GDNF in muscles of amyloid precursor protein null mice corrected the aberrant synaptic morphology of NMJs. Our findings highlight for the first time that APP-dependent GDNF expression drives the process of NMJ formation, providing new insights into the link between APP gene regulatory network and physiologic functions.-Stanga, S., Zanou, N., Audouard, E., Tasiaux, B., Contino, S., Vandermeulen, G., René, F., Loeffler, J.-P., Clotman, F., Gailly, P., Dewachter, I., Octave, J.-N., Kienlen-Campard, P. APP-dependent glial cell line-derived neurotrophic factor gene expression drives neuromuscular junction formation. © FASEB.

  15. Effects of Formation Epoch Distribution on X-Ray Luminosity and Temperature Functions of Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Enoki, Motohiro; Takahara, Fumio; Fujita, Yutaka

    2001-07-01

    We investigate statistical properties of galaxy clusters in the context of a hierarchical clustering scenario, taking into account their formation epoch distribution; this study is motivated by the recent finding by Fujita and Takahara that X-ray clusters form a fundamental plane in which the mass and the formation epoch are regarded as two independent parameters. Using the formalism that discriminates between major mergers and accretion, the epoch of a cluster formation is identified with that of the last major merger. Since tiny mass accretion following formation does not much affect the core structure of clusters, the properties of X-ray emission from clusters are determined by the total mass and density at their formation time. Under these assumptions, we calculate X-ray luminosity and temperature functions of galaxy clusters. We find that the behavior of the luminosity function differs from the model that does not take into account formation epoch distribution; the behavior of the temperature function, however, is not much different. In our model, the luminosity function is shifted to a higher luminosity and shows no significant evolution up to z~1, independent of cosmological models. The clusters are populated on the temperature-luminosity plane, with a finite dispersion. Since the simple scaling model in which the gas temperature is equal to the virial temperature fails to reproduce the observed luminosity-temperature relation, we also consider a model that takes into account the effects of preheating. The preheating model reproduces the observations much more accurately.

  16. Low Temperature Kinetics of the First Steps of Water Cluster Formation

    SciTech Connect

    Roussel, V.; Capron, M.; Bourgalais, J.; Benidar, A.; Japser, A. W.; Klippenstein, S. J.; Biennier, L; Le Picard, S. D.

    2016-03-17

    We present a combined experimental and theoretical low temperature kinetic study of water cluster formation. Water cluster growth takes place in low temperature (23-69 K) supersonic flows. The observed kinetics of formation of water clusters are reproduced with a kinetic model based on theoretical predictions for the first steps of clusterization. The temperature-and pressure-dependent association and dissociation rate coefficients are predicted with an ab initio transition state theory based master equation approach over a wide range of temperatures (20-100 K) and pressures (10(-6) - 10 bar).

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

    NASA Astrophysics Data System (ADS)

    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.

  18. THE GLOBULAR CLUSTER SYSTEM OF NGC 4636 AND FORMATION OF GLOBULAR CLUSTERS IN GIANT ELLIPTICAL GALAXIES

    SciTech Connect

    Park, Hong Soo; Lee, Myung Gyoon; Hwang, Ho Seong; Kim, Sang Chul; Arimoto, Nobuo; Yamada, Yoshihiko; Tamura, Naoyuki; Onodera, Masato E-mail: mglee@astro.snu.ac.kr E-mail: sckim@kasi.re.kr E-mail: yoshihiko.yamada@nao.ac.jp E-mail: monodera@phys.ethz.ch

    2012-11-10

    We present a spectroscopic analysis of the metallicities, ages, and alpha-elements of the globular clusters (GCs) in the giant elliptical galaxy (gE) NGC 4636 in the Virgo Cluster. Line indices of the GCs are measured from the integrated spectra obtained with Faint Object Camera and Spectrograph on the Subaru 8.2 m Telescope. We derive [Fe/H] values of 59 GCs based on the Brodie and Huchra method, and [Z/H], age, and [{alpha}/Fe] values of 33 GCs from the comparison of the Lick line indices with single stellar population models. The metallicity distribution of NGC 4636 GCs shows a hint of a bimodality with two peaks at [Fe/H] = -1.23({sigma} = 0.32) and -0.35({sigma} = 0.19). The age spread is large from 2 Gyr to 15 Gyr and the fraction of young GCs with age <5 Gyr is about 27%. The [{alpha}/Fe] of the GCs shows a broad distribution with a mean value [{alpha}/Fe] Almost-Equal-To 0.14 dex. The dependence of these chemical properties on the galactocentric radius is weak. We also derive the metallicities, ages, and [{alpha}/Fe] values for the GCs in other nearby gEs (M87, M49, M60, NGC 5128, NGC 1399, and NGC 1407) from the line index data in the literature using the same methods as used for NGC 4636 GCs. The metallicity distribution of GCs in the combined sample of seven gEs including NGC 4636 is found to be bimodal, supported by the KMM test with a significance level of >99.9%. All these gEs harbor some young GCs with ages less than 5 Gyr. The mean age of the metal-rich GCs ([Fe/H] >-0.9) is about 3 Gyr younger than that of the metal-poor GCs. The mean value of [{alpha}/Fe] of the gE GCs is smaller than that of the Milky Way GCs. We discuss these results in the context of GC formation in gEs.

  19. The Ghosts of Galaxies: Tidal Debris and the Formation of Clusters

    NASA Astrophysics Data System (ADS)

    West, Michael

    2004-07-01

    Intergalactic stellar populations and tidal debris are now recognized as important components of galaxy clusters. This project examines the interrelated processes of galaxy destruction, recycling of tidal debris, and creation of dwarf galaxies and intergalactic star clusters, all of which are part of the grand scheme of cluster formation. We propose deep multicolor imaging of two examples of newly created tidal debris, the spectacular plumes in the Centaurus and Coma clusters. The Centaurus observations will extend our earlier work, which demonstrated the existence of tidal debris dwarf galaxies and star cluster in the body of the Centaurus plume. Deep ACS/WFC observations can determine rough ages and cluster membership, better characterizing the new debris. The Coma observations will reproduce this work for a second plume feature, in the quintessential rich cluster of galaxies. Parallel WFPC2 observations will investigate the central intracluster spaces at the bottom of the each cluster's potential, where older debris is thickest.

  20. Isotope enrichment during the formation of water clusters in supersonic free jet expansions. [p

    SciTech Connect

    Kay, B.D.; Castleman, A.W. Jr.

    1983-03-15

    Presently, investigation of the dynamics, energetics, and structure of microscopic molecular clusters constitutes an active area of research in chemical physics. Herein the RRKM theory of primary isotope effects is extended to qualitatively predict isotope enrichment in water cluster formation. The theoretical model is verified experimentally by neutral free jet expansion modulated molecular beam mass spectrometry of mixed (H/sub 2/O)/sub m/(D/sub 2/O)/sub n/ clusters. The results further support the previously presented mechanism for neutral cluster growth in free jet expansions. The observed enrichment factors (approx.30%) suggest that techniques involving clustering may find practical applications in the area of isotope separation.

  1. Westerlund 1: monolithic formation of a starburst cluster

    NASA Astrophysics Data System (ADS)

    Negueruela, Ignacio; Clark, J. Simon; Ritchie, Ben W.; Goodwin, Simon P.

    2017-03-01

    Westerlund 1 is in all likelihood the most massive young cluster in the Milky Way, with a mass on the order of 105 M ⊙. To determine its bulk properties we have made multi-epoch radial velocity measurements for a substantial fraction of its OB stars and evolved supergiants and obtained multi-object spectroscopy of candidate cluster members in its locale. The results of these two studies show that Westerlund 1 is apparently subvirial and appears completely isolated, with hardly any massive star in its vicinity that could be associated with it in terms of distance modulus or radial velocity. The cluster halo does not extend much further than five parsec away from the centre. All these properties are very unusual among starburst clusters in the Local Universe, which tend to form in the context of large star-forming regions.

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

    PubMed

    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

  3. Formation, structures, and reactivities of niobium oxide cluster ions

    SciTech Connect

    Deng, H.T.; Kerns, K.P.; Castleman, A.W. Jr.

    1996-08-01

    Niobium oxide cluster ions are produced by a laser-induced plasma source. The cluster distribution, collision-induced dissociation (CID), and cluster reactivities are studied using a triple-quadrupole mass spectrometer. CID experiments on the cluster ions Nb{sub 3}O{sub 7-9}{sup +}, Nb{sub 4}O{sub 9-11}{sup +}, and Nb{sub 5}O{sub 12}{sup +} reveal that their building blocks are Nb{sub 2}O{sub 5}, NbO{sub 2}{sup +}, NbO{sub 3}, Nb{sub 3}O{sub 7}{sup +}, O, and O{sub 2}, whereby the cluster stoichiometry is assigned to have the general form (NbO{sub 3}){sub m}(NbO{sub 2}){sub n}(O){sub 0-4}{sup +}. The trends in the ionization potentials of these species are estimated in terms of the CID fragments produced. Nb{sub 3}O{sub 8-9}{sup +} and Nb{sub 4}O{sub 11}{sup +} cluster ions evidently form via the adsorption of one oxygen atom or molecule onto the cluster surface. Nb{sub 3}O{sub 7}{sup +}, Nb{sub 4}O{sub 9}{sup +}, and Nb{sub 5}O{sub 12}{sup +} have strong reactivities to abstract an oxygen atom from oxygen-containing molecules and adsorb small hydrocarbons at near thermal energies. In particular, the reactivity of the oxygen atom or molecule in the oxide clusters Nb{sub 3}O{sub 8-9}{sup +} and Nb{sub 4}O{sub 11}{sup +} is consistent with our suggestions that it has a radical oxygen character. 37 refs., 8 figs., 1 tab.

  4. Identifying mechanisms driving formation of granuloma-associated fibrosis during Mycobacterium tuberculosis infection.

    PubMed

    Warsinske, Hayley C; DiFazio, Robert M; Linderman, Jennifer J; Flynn, JoAnne L; Kirschner, Denise E

    2017-09-21

    Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), is a pulmonary pathogen of major global concern. A key feature of Mtb infection in primates is the formation of granulomas, dense cellular structures surrounding infected lung tissue. These structures serve as the main site of host-pathogen interaction in TB, and thus to effectively treat TB we must clarify mechanisms of granuloma formation and their function in disease. Fibrotic granulomas are associated with both good and bad disease outcomes. Fibrosis can serve to isolate infected tissue from healthy tissue, but it can also cause difficulty breathing as it leaves scars. Little is known about fibrosis in TB, and data from non-human primates is just beginning to clarify the picture. This work focuses on constructing a hybrid multi-scale model of fibrotic granuloma formation, in order to identify mechanisms driving development of fibrosis in Mtb infected lungs. We combine dynamics of molecular, cellular, and tissue scale models from previously published studies to characterize the formation of two common sub-types of fibrotic granulomas: peripherally fibrotic, with a cuff of collagen surrounding granulomas, and centrally fibrotic, with collagen throughout granulomas. Uncertainty and sensitivity analysis, along with large simulation sets, enable us to identify mechanisms differentiating centrally versus peripherally fibrotic granulomas. These findings suggest that heterogeneous cytokine environments exist within granulomas and may be responsible for driving tissue scale morphologies. Using this model we are primed to better understand the complex structure of granulomas, a necessity for developing successful treatments for TB. Copyright © 2017 Elsevier Ltd. All rights reserved.

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

    PubMed

    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.

  6. Entropy Drives the Formation of Salt Bridges in the Protein GB3.

    PubMed

    Zhang, Ning; Wang, Yefei; An, Liaoyuan; Song, Xiangfei; Huang, Qingshan; Liu, Zhijun; Yao, Lishan

    2017-06-19

    Salt bridges are very common in proteins. But what drives the formation of protein salt bridges is not clear. In this work, we determined the strength of four salt bridges in the protein GB3 by measuring the ΔpKa values of the basic residues that constitute the salt bridges with a highly accurate NMR titration method at different temperatures. The results show that the ΔpKa values increase with temperature, thus indicating that the salt bridges are stronger at higher temperatures. Fitting of ΔpKa values to the van't Hoff equation yields positive ΔH and ΔS values, thus indicating that entropy drives salt-bridge formation. Molecular dynamics simulations show that the protein and solvent make opposite contributions to ΔH and ΔS. Specifically, the enthalpic gain contributed from the protein is more than offset by the enthalpic loss contributed from the solvent, whereas the entropic gain originates from the desolvation effect. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  7. BUDHIES II: a phase-space view of H I gas stripping and star formation quenching in cluster galaxies

    NASA Astrophysics Data System (ADS)

    Jaffé, Yara L.; Smith, Rory; Candlish, Graeme N.; Poggianti, Bianca M.; Sheen, Yun-Kyeong; Verheijen, Marc A. W.

    2015-04-01

    We investigate the effect of ram-pressure from the intracluster medium on the stripping of H I gas in galaxies in a massive, relaxed, X-ray bright, galaxy cluster at z = 0.2 from the Blind Ultra Deep H I Environmental Survey (BUDHIES). We use cosmological simulations, and velocity versus position phase-space diagrams to infer the orbital histories of the cluster galaxies. In particular, we embed a simple analytical description of ram-pressure stripping in the simulations to identify the regions in phase-space where galaxies are more likely to have been sufficiently stripped of their H I gas to fall below the detection limit of our survey. We find a striking agreement between the model predictions and the observed location of H I-detected and non-detected blue (late-type) galaxies in phase-space, strongly implying that ram-pressure plays a key role in the gas removal from galaxies, and that this can happen during their first infall into the cluster. However, we also find a significant number of gas-poor, red (early-type) galaxies in the infall region of the cluster that cannot easily be explained with our model of ram-pressure stripping alone. We discuss different possible additional mechanisms that could be at play, including the pre-processing of galaxies in their previous environment. Our results are strengthened by the distribution of galaxy colours (optical and UV) in phase-space, that suggests that after a (gas-rich) field galaxy falls into the cluster, it will lose its gas via ram-pressure stripping, and as it settles into the cluster, its star formation will decay until it is completely quenched. Finally, this work demonstrates the utility of phase-space diagrams to analyse the physical processes driving the evolution of cluster galaxies, in particular H I gas stripping.

  8. An H-alpha survey of cluster spirals - Comparison of star formation in clusters and the field

    NASA Technical Reports Server (NTRS)

    Moss, C.; Whittle, M.

    1993-01-01

    In an objective prism survey of eight nearby Abell clusters, we have detected H-alpha emission from 77 out of a total of 201 CGCG spiral galaxies. We find that detection of H alpha emission is approximately independent of galaxy absolute magnitude, distance to the cluster center, and the presence of a bar. However, tidally distorted spirals are much more likely to be detected than undistorted spirals. Furthermore, there is a strong tendency for tidally distorted spirals to have compact nuclear emission rather than more extended disk-wide emission. When compared to field spirals, we find that late-type (Sc and Sc-Irr) cluster spirals have less H alpha emission, while early-type (Sa and Sab) cluster spirals can have significantly enhanced emission. The enhanced emission is most likely to be due to tidally induced star formation from galaxy-galaxy interactions.

  9. Hierarchical Star Formation in Turbulent Media: Evidence from Young Star Clusters

    NASA Astrophysics Data System (ADS)

    Grasha, Kathryn; Elmegreen, Bruce; Calzetti, Daniela

    2017-01-01

    We present an analysis of the positions and ages of star clusters in eight local galaxies and find a correlation between the age difference and separation of cluster pairs. We infer that cluster formation is correlated in time such that clusters that are close to each have similar ages. In addition, the age between cluster pairs increases with their separation to the 0.3 - 0.6 power, close to the expected slope of 0.5 that would arise in a turbulent-driven interstellar medium. This suggests that not only is star formation hierarchical both in space and in time, but that the duration of star formation depends on the region of interest: smaller regions will form stars over a shorter time frame whereas larger regions form stars over a longer time frame.

  10. Behavior of Ac during Gd{sub 2}Cl{sub 3} condensed cluster formation

    SciTech Connect

    Mikheev, N.B.; Kamenskaya, A.N.; Rumer, I.A.

    1994-11-01

    The behavior of tracer {sup 228}Ac during Gd{sub 2}Cl{sub 3} condensed cluster formation is studied. The cluster is prepared by electrochemical reduction of GdCl{sub 3}. Actinium does not cocrystallize with the Gd{sub 2}Cl{sub 3} cluster. Its behavior is similar to that of La under analogous conditions. A number of hypotheses requiring further refinement is proposed to explain the results.

  11. Study of the formation of fragments with different clusterization methods

    NASA Astrophysics Data System (ADS)

    Singh, Jaivir; Puri, Rajeev K.

    2001-10-01

    We present a comparison of different clusterization methods based on simple spatial correlation, spatial-momentum correlation and energy minimization (simulated annealing) by simulating the reactions of O + Ag/Br within the quantum molecular dynamics model. We find that the response of different clusterization algorithms depends on the asymmetry of the reaction. The momentum correlation methods recognize the fragments between 60-100 fm c-1, whereas the simple spatial-correlation method needs a much longer time. The response of a larger nucleon-nucleon cross section as well as of momentum-dependent interaction depends on the clusterization algorithm one is using. It is maximal with the spatial correlation method, whereas it is minimal with the energy minimization method. Interestingly, in the presence of a larger nucleon-nucleon cross section, the momentum cut and energy minimization methods yield a similar evolution. This is true at higher incident energies where the frequency of nucleon-nucleon collisions is very large.

  12. Cluster formation of transmembrane proteins due to hydrophobic mismatching.

    PubMed

    Schmidt, Ulrich; Guigas, Gernot; Weiss, Matthias

    2008-09-19

    Membranes are the defining envelopes of living cells. At this boundary a multitude of transmembrane proteins mediate signal and mass transfer between cells and their environment. Clustering of these proteins is a frequent and often vital phenomenon that relies at least in part on membrane-mediated interactions. Indeed, the mismatch between proteins' hydrophobic transmembrane domains and the surrounding lipid bilayer has been predicted to facilitate clustering, yet unequivocal quantitative data in support of these predictions have been lacking. Here, we have used coarse-grained membrane simulations to thoroughly address the clustering of transmembrane proteins in detail. Our results emphasize the universal nature of membrane-mediated attraction which relaxes the need for a plethora of fine-tuned interactions between membrane proteins.

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

    PubMed

    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

  14. First-principles simulations of hydrogen peroxide formation catalyzed by small neutral gold clusters.

    PubMed

    Kacprzak, Katarzyna A; Akola, Jaakko; Häkkinen, Hannu

    2009-08-14

    Energetics and dynamical pathways for hydrogen peroxide formation from H(2) and O(2) bound to neutral gold dimers and tetramers have been investigated by applying several strategies: T = 0 K geometry optimizations, constrained Car-Parrinello molecular dynamics simulations at T = 300 K and metadynamics at T = 300 K. The competing reaction channels for water and hydrogen peroxide formation have been found and characterized. In each case, the reaction barriers for Au cluster catalyzed proton transfer are less than 1 eV. Water formation is a competitive reaction channel, and the relative weight of H(2)O and H(2)O(2) products may depend on the chosen Au cluster size. Dynamic simulations demonstrate the significance of the geometric fluxionality of small catalytic Au clusters. These results indicate that neutral Au clusters could work as catalysts in aerobic H(2)O(2) formation in ambient conditions.

  15. Modeling Massive Cluster Formation with Stellar Feedback using Flash and AMUSE

    NASA Astrophysics Data System (ADS)

    McMillan, Stephen; Wall, Joshua; Mac Low, Mordecai-Mark

    2015-08-01

    Star cluster formation is a complex astrophysical problem combining multiple competing physical processes in a challenging computational environment, placing stringent demands on both software and hardware. Current simulations still fall short of a realistic description of the physical processes at work in star-forming regions. We are developing a hybrid simulation code to explore the formation and assembly of massive star clusters by combining the magnetohydrodynamics code Flash and the AMUSE software environment. Flash handles gas dynamics and star formation through cloud collapse, while AMUSE manages the dynamics and evolution of stars and binary systems. The gravitational interaction between the gas and the stars is treated via a symplectic gravity bridge between the codes in AMUSE. Radiative, wind, and supernova feedback are followed in FLASH based on information provided by the AMUSE system. We present some early results of this work, focusing on cluster formation and assembly, and including simplified models of feedback to study gas expulsion and cluster survival.

  16. Molecular dynamics simulation of helium cluster diffusion and bubble formation in bulk tungsten

    NASA Astrophysics Data System (ADS)

    Li, Xiao-Chun; Shu, Xiaolin; Tao, Peng; Yu, Yi; Niu, Guo-Jiang; Xu, Yuping; Gao, Fei; Luo, Guang-Nan

    2014-12-01

    Molecular dynamics (MD) simulations have been performed to investigate the diffusion behavior of helium (He) clusters in tungsten (W), because their diffusion properties provide basic knowledge in understanding the He bubble formation. The binding energy between He and He cluster is shown to be positive, and thus, He is easy to form bubbles by self-trapping. The mean squared displacements (MSDs) were employed to determine the diffusivities of He clusters with different sizes at different temperatures. The He bubble formation at different temperatures with 1% He was also investigated. It is revealed that the formation of He bubbles is strongly associated with the temperature and the diffusivities of the He clusters in W. The results demonstrate the initial stage of the He bubble formation and growth in W.

  17. From collisions to clusters: first steps of sulphuric acid nanocluster formation dynamics

    NASA Astrophysics Data System (ADS)

    Loukonen, Ville; Bork, Nicolai; Vehkamäki, Hanna

    2014-08-01

    The clustering of sulphuric acid with base molecules is one of the main pathways of new-particle formation in the Earth's atmosphere. First step in the clustering process is likely the formation of a (sulphuric acid)1(base)1(water)n cluster. Here, we present results from direct first-principles molecular dynamics collision simulations of (sulphuric acid)1(water)0, 1 + (dimethylamine) → (sulphuric acid)1(dimethylamine)1(water)0, 1 cluster formation processes. The simulations indicate that the sticking factor in the collisions is unity: the interaction between the molecules is strong enough to overcome the possible initial non-optimal collision orientations. No post-collisional cluster break up is observed. The reasons for the efficient clustering are (i) the proton transfer reaction which takes place in each of the collision simulations and (ii) the subsequent competition over the proton control. As a consequence, the clusters show very dynamic ion pair structure, which differs from both the static structure optimisation calculations and the equilibrium first-principles molecular dynamics simulations. In some of the simulation runs, water mediates the proton transfer by acting as a proton bridge. In general, water is able to notably stabilise the formed clusters by allocating a fraction of the released clustering energy.

  18. The richness of the globular cluster system of NGC 3923: Clues to elliptical galaxy formation

    NASA Technical Reports Server (NTRS)

    Zepf, Stephen E.; Geisler, Doug; Ashman, Keith M.

    1994-01-01

    We present new data on the globular cluster system of the elliptical galaxy NGC 3923 which show that it has the most globular clusters per unit luminosity of any noncluster elliptical yet observed, with S(sub N) = 6.4 +/- 1.4. NGC 3923 is also among the brightest ellipticals outside of a galaxy cluster for which the number of globular clusters has been determined. Our observation of a large number of clusters per unit luminosity (high S(sub N)-value) for a bright elliptical in a sparse environment is consistent with the suggestion of Djorgovski and Santiago that the number of globular clusters is a power-law function of the luminosity with an exponent greater than 1. We relate this higher specific frequency of globular clusters in more luminous galaxies to other observations which indicate that the physical conditions within elliptical galaxies at the time of their formation were dependent on galaxy mass.

  19. Point Defect Cluster Formation in Iron Displacement Cascades Up to 50 keV

    SciTech Connect

    Stoller, R.E.

    1998-11-30

    The results of molecular dynamics displacement cascade simulations in iron at energies up to 50 keV and temperatures of 100, 600, and 900K are summarized, with a focus on the characterization of interstitial and vacancy clusters that are formed directly within the cascade. The fraction of the surviving point defects contained in clusters, and the size distributions of these in-cascade clusters have been determined. Although the formation of true vacancy clusters appears to be inhibited in iron, a significant degree of vacancy site correlation was observed. These well correlated arrangements of vacancies can be considered nascent clusters, and they have been observed to coalesce during longer term Monte Carlo simulations which permit short range vacancy diffusion. Extensive interstitial clustering was observed. The temperature and cascade energy dependence of the cluster size distributions are discussed in terms of their relevance to microstructural evolution and mechanical property changes in irradiated iron-based alloys.

  20. Formation of biomolecule clusters in a supersonic jet: An example of molecular recognition?

    SciTech Connect

    Meffert, Anja; Moritz, Fritz; Dey, Michael; Grotemeyer, Juergen

    1995-04-01

    In this paper some results of the formation of biomolecular clusters in a supersonic beam are discussed. The clusters from nucleobases and nucleosides are formed by laser desorption and are probed by multiphoton ionization. It is shown that complementary nucleobase pairs as found in DNA can be observed in preference to noncomplementary base pairs. Association constants for the formation of free nucleobases and nucleosides in the gas phase are calculated.

  1. Molecular Dynamics Simulation Study of the Influence of Cluster Geometry on Formation of C60 Fullerene Clusters in Aqueous Solution.

    PubMed

    Kim, Hojin; Bedrov, Dmitry; Smith, Grant D

    2008-02-01

    We have performed atomistic molecular dynamics simulations of linear (1-dimensional), planar (2-dimensional), and icosahedral (3-dimensional) clusters of C60 fullerenes in aqueous solution in order to investigate the influence of cluster geometry on their free energy of formation. As was found in our previous study of the potential of mean force (PMF) as a function of separation for a single pair of fullerenes in aqueous solution, the interaction between fullerenes for all cluster geometries was dominated by direct fullerene-fullerene interactions and not by water-induced hydrophobic interactions. A coarse-grained implicit solvent (CGIS) potential, given by the PMF for the fullerene pair in water obtained from atomistic simulations, was found to describe well the free energy of formation of the linear cluster, indicating that many-body effects, i.e., the influence of neighboring fullerenes on the water-induced interaction between a fullerene pair, are negligible for the 1-dimensional geometry. For the 2-dimensional and particularly the 3-dimensional geometry, however, many-body effects were found to strongly influence hydration, leading to complete dehydration of the central fullerene at close fullerene-fullerene separations for the icosahedral cluster. This strong influence of geometry on hydration translates into water-induced interactions that, while remaining repulsive, as is found for the fullerene pair, are not well described by the two-body CGIS potential obtained from the isolated fullerene pair, particularly for the 3-dimensional geometry.

  2. Star Formation in the Cluster Merger DLSCL J0916.2+2953

    NASA Astrophysics Data System (ADS)

    Mansheim, A. S.; Lemaux, B. C.; Dawson, W. A.; Lubin, L. M.; Wittman, D.; Schmidt, S.

    2017-01-01

    We investigate star formation in DLSCL J0916.2+2953, a dissociative merger of two clusters at z = 0.53 that has progressed {1.1}-0.4+1.3 Gyr since the 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({{H}}δ ), EW([{{O}} {{II}}]), and {D}n(4000) measured from the composite spectra of 64 cluster and 153 coeval field galaxies. We supplement Keck DEep Imaging Multi-Object Spectrograph spectra with DLS and Hubble Space Telescope imaging, to determine the color, stellar mass, and morphology of each galaxy. We also 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 North cluster is currently active, and that the South cluster is currently post-starburst, having undergone a recent star formation event. Although the North activity could be latent or long-term merger effects, a young blue stellar population and irregular geometry suggest the cluster was still forming prior the collision. Even though the South activity coincides with the time of the merger, the blue early-type population could be a result of secular cluster processes. The evidence suggests that the dearth or surfeit of activity is indiscernible from normal cluster galaxy evolution.

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    A fraction of brightest cluster galaxies (BCGs) show bright emission in the ultraviolet 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 broad-band photometric data. Here, we study the optical spectra of a sample of 19 BCGs hosted by X-ray luminous galaxy clusters at 0.15 Cluster Comparison Project sample. We identify plausible star formation histories of the galaxies by fitting simple stellar populations 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 four 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 BCGs. We constrain the mass contribution of these young components to the total stellar mass to be typically between 1 and 3 per cent, but rising to 7 per cent in Abell 1835. We find that the four of the BCGs with strong evidence for recent star formation (and only these four galaxies) are found within a projected distance of 5 kpc of their host cluster's X-ray peak, and the diffuse, X-ray gas surrounding the BCGs exhibits a ratio of the radiative cooling-to-free-fall time (tc/tff) of ≤10. These are also some of the clusters with the lowest central entropy. Our results are consistent with the predictions of the precipitation-driven star formation and active galactic nucleus feedback model, in which the radiatively cooling diffuse gas is subject to local thermal instabilities once the instability parameter tc/tff falls below ˜10, leading to the condensation and precipitation of cold gas. The number of galaxies in our sample where the host cluster satisfies all the

  4. Dynein Clusters into Lipid Microdomains on Phagosomes to Drive Rapid Transport toward Lysosomes

    PubMed Central

    Rai, Ashim; Pathak, Divya; Thakur, Shreyasi; Singh, Shampa; Dubey, Alok Kumar; Mallik, Roop

    2016-01-01

    Summary Diverse cellular processes are driven by motor proteins that are recruited to and generate force on lipid membranes. Surprisingly little is known about how membranes control the force from motors and how this may impact specific cellular functions. Here, we show that dynein motors physically cluster into microdomains on the membrane of a phagosome as it matures inside cells. Such geometrical reorganization allows many dyneins within a cluster to generate cooperative force on a single microtubule. This results in rapid directed transport of the phagosome toward microtubule minus ends, likely promoting phagolysosome fusion and pathogen degradation. We show that lipophosphoglycan, the major molecule implicated in immune evasion of Leishmania donovani, inhibits phagosome motion by disrupting the clustering and therefore the cooperative force generation of dynein. These findings appear relevant to several pathogens that prevent phagosome-lysosome fusion by targeting lipid microdomains on phagosomes. PMID:26853472

  5. Dynein Clusters into Lipid Microdomains on Phagosomes to Drive Rapid Transport toward Lysosomes.

    PubMed

    Rai, Ashim; Pathak, Divya; Thakur, Shreyasi; Singh, Shampa; Dubey, Alok Kumar; Mallik, Roop

    2016-02-11

    Diverse cellular processes are driven by motor proteins that are recruited to and generate force on lipid membranes. Surprisingly little is known about how membranes control the force from motors and how this may impact specific cellular functions. Here, we show that dynein motors physically cluster into microdomains on the membrane of a phagosome as it matures inside cells. Such geometrical reorganization allows many dyneins within a cluster to generate cooperative force on a single microtubule. This results in rapid directed transport of the phagosome toward microtubule minus ends, likely promoting phagolysosome fusion and pathogen degradation. We show that lipophosphoglycan, the major molecule implicated in immune evasion of Leishmania donovani, inhibits phagosome motion by disrupting the clustering and therefore the cooperative force generation of dynein. These findings appear relevant to several pathogens that prevent phagosome-lysosome fusion by targeting lipid microdomains on phagosomes. Copyright © 2016 The Authors. Published by Elsevier Inc. All rights reserved.

  6. Learning Drives Differential Clustering of Axodendritic Contacts in the Barn Owl Auditory System

    PubMed Central

    McBride, Thomas J.; Rodriguez-Contreras, Adrian; Trinh, Angela; Bailey, Robert; DeBello, William M.

    2008-01-01

    Computational models predict that experience-driven clustering of coactive synapses is a mechanism for information storage. This prediction has remained untested, because it is difficult to approach through time-lapse analysis. Here, we exploit a unique feature of the barn owl auditory localization pathway that permits retrospective analysis of prelearned and postlearned circuitry: owls reared wearing prismatic spectacles develop an adaptive microcircuit that coexists with the native one but can be analyzed independently based on topographic location. To visualize the clustering of axodendritic contacts (potential synapses) within these zones, coactive axons were labeled by focal injection of fluorescent tracer and their target dendrites labeled with an antibody directed against CaMKII (calcium/calmodulin-dependent protein kinase type II, α subunit). Using high-resolution confocal imaging, we measured the distance from each contact to its nearest neighbor on the same branch of dendrite. We found that the distribution of intercontact distances for the adaptive zone was shifted dramatically toward smaller values compared with distributions for either the maladaptive zone of the same animals or the adaptive zone of normal juveniles, which indicates that a dynamic clustering of contacts had occurred. Moreover, clustering in the normal zone was greater in normal juveniles than in prism-adapted owls, indicative of declustering. These data demonstrate that clustering is bidirectionally adjustable and tuned by behaviorally relevant experience. The microanatomical configurations in all zones of both experimental groups matched the functional circuit strengths that were assessed by in vivo electrophysiological mapping. Thus, the observed changes in clustering are appropriately positioned to contribute to the adaptive strengthening and weakening of auditory-driven responses. PMID:18596170

  7. Formation of Disulfide Bridges Drives Oligomerization, Membrane Pore Formation, and Translocation of Fibroblast Growth Factor 2 to Cell Surfaces*

    PubMed Central

    Müller, Hans-Michael; Steringer, Julia P.; Wegehingel, Sabine; Bleicken, Stephanie; Münster, Maximilian; Dimou, Eleni; Unger, Sebastian; Weidmann, Georg; Andreas, Helena; García-Sáez, Ana J.; Wild, Klemens; Sinning, Irmgard; Nickel, Walter

    2015-01-01

    Fibroblast growth factor 2 (FGF2) is a key signaling molecule in tumor-induced angiogenesis. FGF2 is secreted by an unconventional secretory mechanism that involves phosphatidylinositol 4,5-bisphosphate-dependent insertion of FGF2 oligomers into the plasma membrane. This process is regulated by Tec kinase-mediated tyrosine phosphorylation of FGF2. Molecular interactions driving FGF2 monomers into membrane-inserted FGF2 oligomers are unknown. Here we identify two surface cysteines that are critical for efficient unconventional secretion of FGF2. They represent unique features of FGF2 as they are absent from all signal-peptide-containing members of the FGF protein family. We show that phosphatidylinositol 4,5-bisphosphate-dependent FGF2 oligomerization concomitant with the generation of membrane pores depends on FGF2 surface cysteines as either chemical alkylation or substitution with alanines impairs these processes. We further demonstrate that the FGF2 variant forms lacking the two surface cysteines are not secreted from cells. These findings were corroborated by experiments redirecting a signal-peptide-containing FGF family member from the endoplasmic reticulum/Golgi-dependent secretory pathway into the unconventional secretory pathway of FGF2. Cis elements known to be required for unconventional secretion of FGF2, including the two surface cysteines, were transplanted into a variant form of FGF4 without signal peptide. The resulting FGF4/2 hybrid protein was secreted by unconventional means. We propose that the formation of disulfide bridges drives membrane insertion of FGF2 oligomers as intermediates in unconventional secretion of FGF2. PMID:25694424

  8. Formation of disulfide bridges drives oligomerization, membrane pore formation, and translocation of fibroblast growth factor 2 to cell surfaces.

    PubMed

    Müller, Hans-Michael; Steringer, Julia P; Wegehingel, Sabine; Bleicken, Stephanie; Münster, Maximilian; Dimou, Eleni; Unger, Sebastian; Weidmann, Georg; Andreas, Helena; García-Sáez, Ana J; Wild, Klemens; Sinning, Irmgard; Nickel, Walter

    2015-04-03

    Fibroblast growth factor 2 (FGF2) is a key signaling molecule in tumor-induced angiogenesis. FGF2 is secreted by an unconventional secretory mechanism that involves phosphatidylinositol 4,5-bisphosphate-dependent insertion of FGF2 oligomers into the plasma membrane. This process is regulated by Tec kinase-mediated tyrosine phosphorylation of FGF2. Molecular interactions driving FGF2 monomers into membrane-inserted FGF2 oligomers are unknown. Here we identify two surface cysteines that are critical for efficient unconventional secretion of FGF2. They represent unique features of FGF2 as they are absent from all signal-peptide-containing members of the FGF protein family. We show that phosphatidylinositol 4,5-bisphosphate-dependent FGF2 oligomerization concomitant with the generation of membrane pores depends on FGF2 surface cysteines as either chemical alkylation or substitution with alanines impairs these processes. We further demonstrate that the FGF2 variant forms lacking the two surface cysteines are not secreted from cells. These findings were corroborated by experiments redirecting a signal-peptide-containing FGF family member from the endoplasmic reticulum/Golgi-dependent secretory pathway into the unconventional secretory pathway of FGF2. Cis elements known to be required for unconventional secretion of FGF2, including the two surface cysteines, were transplanted into a variant form of FGF4 without signal peptide. The resulting FGF4/2 hybrid protein was secreted by unconventional means. We propose that the formation of disulfide bridges drives membrane insertion of FGF2 oligomers as intermediates in unconventional secretion of FGF2.

  9. STAR FORMATION AND UV COLORS OF THE BRIGHTEST CLUSTER GALAXIES IN THE REPRESENTATIVE XMM-NEWTON CLUSTER STRUCTURE SURVEY

    SciTech Connect

    Donahue, Megan; Bruch, Seth; Wang, Emily; Voit, G. Mark; Hicks, Amalia K.; Haarsma, Deborah B.; Croston, Judith H.; Pratt, Gabriel W.; O'Connell, Robert W.

    2010-06-01

    We present UV broadband photometry and optical emission-line measurements for a sample of 32 brightest cluster galaxies (BCGs) in clusters of the Representative XMM-Newton Cluster Structure Survey (REXCESS) with z = 0.06-0.18. The REXCESS clusters, chosen to study scaling relations in clusters of galaxies, have X-ray measurements of high quality. The trends of star formation and BCG colors with BCG and host properties can be investigated with this sample. The UV photometry comes from the XMM-Newton Optical Monitor, supplemented by existing archival Galaxy Evolution Explorer photometry. We detected H{alpha} and forbidden line emission in seven (22%) of these BCGs, in optical spectra obtained using the Southern Astrophysical Research Goodman spectrograph. All of these emission-line BCGs occupy clusters classified as cool cores (CCs) based on the central cooling time in the cluster core, for an emission-line incidence rate of 70% for BCGs in REXCESS CC clusters. Significant correlations between the H{alpha} equivalent widths, excess UV production in the BCG, and the presence of dense, X-ray bright intracluster gas with a short cooling time are seen, including the fact that all of the H{alpha} emitters inhabit systems with short central cooling times and high central intracluster medium densities. Estimates of the star formation rates based on H{alpha} and UV excesses are consistent with each other in these seven systems, ranging from 0.1to8 solar masses per year. The incidence of emission-line BCGs in the REXCESS sample is intermediate, somewhat lower than in other X-ray-selected samples ({approx}35%), and somewhat higher than but statistically consistent with optically selected, slightly lower redshift BCG samples ({approx}10%-15%). The UV-optical colors (UVW1 - R {approx}4.7 {+-} 0.3) of REXCESS BCGs without strong optical emission lines are consistent with those predicted from templates and observations of ellipticals dominated by old stellar populations. We see no

  10. Gas Stripping, Turbulence, and Wake Formation in Cluster Mergers

    NASA Astrophysics Data System (ADS)

    Ricker, P. M.; Sarazin, C. L.; Kempner, J. C.; Calder, A. C.; Dursi, L. J.; Fryxell, B.; Lamb, D. Q.; Olson, K.; Rosner, R.; Timmes, F. X.; Truran, J. W.; Tufo, H.; Zingale, M.

    2001-12-01

    We present results from high-resolution (sub-kpc) hydro + dark matter simulations of the interaction of subclusters with the intracluster medium during the initial stages of a galaxy cluster merger. Using the adaptive-mesh code FLASH, we study the development of fluid instabilities along the contact surface and in the wake produced by this interaction. We examine the role of shock waves and instability-induced turbulence in the stripping of gas from the dense subcluster core. We discuss the observability of merger-induced turbulence, and we compare our results to the observed clusters Abell 85 and Abell 3667. This research has been supported by the U.S. Department of Energy under grant no. B341495 to the ASCI Flash Center at the University of Chicago.

  11. Synaptic efficacy cluster formation across the dendrite via STDP.

    PubMed

    Iannella, Nicolangelo; Tanaka, Shigeru

    2006-07-31

    The role of spike-timing-dependent plasticity (STDP) in shaping the strength of a synapse located on the dendritic tree has gained recent interest. Previous theoretical studies using STDP have mostly used simplified integrate-and-fire models to investigate the evolution of synaptic efficacy with time. Such studies usually show that the final weight distribution is unimodal or bimodal resulting from a multiplicative or additive STDP rule, respectively. However, very little is known about how STDP shapes the spatial organization of synaptic efficacies. Here, for the first time, we demonstrate that spatial clustering of synaptic efficacies can occur on the dendrite via STDP, where changes in synaptic efficacy are driven by timing differences between synaptic inputs and the generation of local dendritic spikes. Specifically, when the model neuron is stimulated by two independent groups of correlated afferent inputs, the synaptic efficacies from each group, are not only spatially clustered on the dendrite but also spatially complementary to each other.

  12. Extended Star Formation in the Intermediate-age Large Magellanic Cloud Star Cluster NGC 2209

    NASA Astrophysics Data System (ADS)

    Keller, Stefan C.; Mackey, A. Dougal; Da Costa, Gary S.

    2012-12-01

    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.

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

    SciTech Connect

    Keller, Stefan C.; Mackey, A. Dougal; Da Costa, Gary S.

    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.

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

    SciTech Connect

    Matzner, Christopher D.; Jumper, Peter H.

    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.

  15. Cluster Formation and Evolution on Semiconductor and Insulator Surfaces

    DTIC Science & Technology

    1988-01-01

    Abrupt, Defect-Free Interfaces," Phys. Rev. Lett. 62, 1568-1572 (1989). 40. T.J. Wagener, Yongjun Hu, Y. Gao, M.B. Jost, J.H. Weaver, N. Spencer, and...Monmouth, New Jersey, May 1988. 9. Yongjun Hu, T.J. Wagener, Y. Gao, and J.H. Weaver, "Cluster Growth and the Evolution of Empty Electronic States," 35th

  16. Modelling the formation of galaxy clusters in MOND

    NASA Astrophysics Data System (ADS)

    Nusser, Adi; Pointecouteau, Etienne

    2006-03-01

    We use a one-dimensional hydrodynamical code to study the evolution of spherically symmetric perturbations in the framework of modified Newtonian dynamics (MOND). The code evolves spherical gaseous shells in an expanding Universe by employing a MOND-type relationship between the fluctuations in the density field and the gravitational force, g. We focus on the evolution of initial density perturbations of the form δi~r-si for 0 < s < 3. A shell is initially cold and remains so until it encounters the shock formed by the earlier collapse of shells nearer to the centre. During the early epochs g is sufficiently large and shells move according to Newtonian gravity. As the physical size of the perturbation increases with time, g gets smaller and the evolution eventually becomes MOND-dominated. However, the density in the inner collapsed regions is large enough that they re-enter the Newtonian regime. The evolved gas temperature and density profiles tend to a universal form that is independent of the slope, s, and of the initial amplitude. An analytic explanation of this intriguing result is offered. Over a wide range of scales, the temperature, density and entropy profiles in the simulations depend on radius roughly like r0.5, r-1.5 and r1.5, respectively. We compare our results with XMM-Newton and Chandra observations of clusters. The temperature profiles of 16 observed clusters are either flat or show a mild decrease at R>~ 200kpc. MOND profiles show a significant increase that cannot be reconciled with the data. Our simulated MOND clusters are substantially denser than the observed clusters. It remains to be seen whether these difficulties persist in three-dimensional hydrodynamical simulations with generic initial conditions.

  17. Rupture of Stochastically Occurring Vesicle Clusters Limits Bilayer Formation on Alkane-PEG-Type Supports: Uncoupling Clustering from Surface Coverage.

    PubMed

    Peel, Matthew J; Cross, Stephen J; Birkholz, Oliver; Aladağ, Amine; Piehler, Jacob; Peel, Suman

    2015-08-18

    Polymer-supported bilayers (PSBs) are a recognized tool for drug discovery through function-interaction analysis of membrane proteins. While silica-supported bilayers (SSBs) spontaneously form from surface-adsorbed vesicles, successful PSB formation via a similar method has thus far been limited by an insufficient understanding of the underlying vesicle-remodelling processes. Here, we generated a polymer support through the incubation of poly-L-lysine conjugated to alkyl-chain-terminated poly(ethylene)glycol on silica. This polymer-coated silica substrate yielded efficient vesicle adsorption and spontaneous bilayer formation, thereby providing a rare opportunity to address the mechanism of PSB formation and compare it to that of SSB. The combined use of super-resolution imaging, kinetics, and simulations indicates that the rupture of stochastically formed vesicle clusters is the rate-limiting step, which is an order of magnitude higher for silica than for polymer-coated silica. This was confirmed by directly demonstrating increased rupture rates for surface adsorbed multivesicle assemblies formed by vesicle cross-linking in solution. On the basis of this key insight we surmised that a low propensity of cluster rupture can be compensated for by an increase in the number density of clusters: the deposition of a mixture of oppositely charged vesicles resulted in bilayer formation on another alkane-PEG type of interface, which despite efficient vesicle adsorption otherwise fails to support spontaneous bilayer formation. This potentially provides a universal strategy for promoting bilayer formation on resistant surfaces without resorting to modifying the surface itself. Therefore, multivesicle assemblies with tailored geometries not only could facilitate bilayer formation on polymers with interesting functional properties but also could instigate the exploration of vesicle architecture for other processes involving vesicle remodelling such as drug delivery.

  18. Observational constraints on star cluster formation theory. I. The mass-radius relation

    NASA Astrophysics Data System (ADS)

    Pfalzner, S.; Kirk, H.; Sills, A.; Urquhart, J. S.; Kauffmann, J.; Kuhn, M. A.; Bhandare, A.; Menten, K. M.

    2016-02-01

    Context. Stars form predominantly in groups usually denoted as clusters or associations. The observed stellar groups display a broad spectrum of masses, sizes, and other properties, so it is often assumed that there is no underlying structure in this diversity. Aims: Here we show that the assumption of an unstructured multitude of cluster or association types might be misleading. Current data compilations of clusters in the solar neighbourhood show correlations among cluster mass, size, age, maximum stellar mass, etc. In this first paper we take a closer look at the correlation of cluster mass and radius. Methods: We use literature data to explore relations in cluster and molecular core properties in the solar neighbourhood. Results: We show that for embedded clusters in the solar neighbourhood a clear correlation exists between cluster mass and half-mass radius of the form Mc = CRcγ with γ = 1.7 ± 0.2. This correlation holds for infrared K-band data, as well as for X-ray sources and clusters containing a hundred stars up to those consisting of a few tens of thousands of stars. The correlation is difficult to verify for clusters containing fewer than 30 stars owing to low-number statistics. Dense clumps of gas are the progenitors of the embedded clusters. We find almost the same slope for the mass-size relation of dense, massive clumps as for the embedded star clusters. This might point to a direct translation from gas to stellar mass: however, it is difficult to relate size measurements for clusters (stars) to those for gas profiles. Taking multiple paths for clump mass into cluster mass into account, we obtain an average star-formation efficiency of 18%+9.3-5.7 for the embedded clusters in the solar neighbourhood. Conclusions: The derived mass-radius relation gives constraints for the theory of clustered star formation. Analytical models and simulations of clustered star formation have to reproduce this relation in order to be realistic.

  19. Two channels for the formation of compact dwarf galaxies in clusters of galaxies

    NASA Astrophysics Data System (ADS)

    Martinović, Nemanja; Micic, Miroslav

    2017-10-01

    We have identified two channels for the formation of compact dwarf galaxies in the Illustris simulation by reconstructing mass and distance histories of candidates located in the vicinity of the simulation's most massive cluster galaxies. One channel is tidal stripping of Milky Way-mass galaxies that form outside of clusters and eventually sink into them, spiralling in towards central massive objects. The second channel of formation is an in situ formation (in reference to the parent cluster) of dwarf mass galaxies, with negligible evolution and limited change in stellar mass. We find 19 compact dwarf galaxies at the centres of 14 clusters, consistent with observations: 30 per cent of these have an external origin while 70 per cent are formed in situ.

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

    SciTech Connect

    Zinkle, S.J.; Snead, L.L.; Edwards, D.J.

    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.

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

    PubMed

    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.

  2. Drama of HII regions: Clustered and Triggered Star Formation

    NASA Astrophysics Data System (ADS)

    Li, Jin-Zeng; Yuan, Jinghua; Liu, Hong-Li; Wu, Yuefang; Huang, Ya-Fang

    2017-03-01

    In order to understand the star formation process under the influence of H ii regions, we have carried out extensive investigations to well selected star-forming regions which all have been profoundly affected by existing massive O type stars. On the basis of multi-wavelength data from mid-infrared to millimeter collected using Spitzer, Herschel, and ground based radio telescopes, the physical status of interstellar medium and star formation in these regions have been revealed. In a relatively large infrared dust bubble, active star formation is undergoing and the shell is still expanding. Signs of compressed gas and triggered star formation have been tentatively detected in a relatively small bubble. The dense cores in the Rosette Molecular Complex detected at 1.1 mm using SMA have been speculated to have a likely triggered origin according to their spatial distribution. Although some observational results have been obtained, more efforts are necessary to reach trustworthy conclusions.

  3. The rise and fall of star formation in z ˜ 0.2 merging galaxy clusters

    NASA Astrophysics Data System (ADS)

    Stroe, Andra; Sobral, David; Dawson, William; Jee, M. James; Hoekstra, Henk; Wittman, David; van Weeren, Reinout J.; Brüggen, Marcus; Röttgering, Huub J. A.

    2015-06-01

    CIZA J2242.8+5301 (`Sausage') and 1RXS J0603.3+4213 (`Toothbrush') are two low-redshift (z ˜ 0.2), massive (˜2 × 1015 M⊙), 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 Å). We robustly separate between Hα and higher redshift emitters using a combination of optical multiband (B, g, V, r, i, z) and spectroscopic data. We build Hα 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) Hα emitters above a star formation rate (SFR) of 0.17 M⊙ yr-1 surprisingly located in close proximity to the shock fronts, embedded in very hot intracluster medium plasma. The SFR density for the cluster population is at least at the level of typical galaxies at z ˜ 2. Down to the same SFR, the possibly dynamically more evolved `Toothbrush' cluster has only nine Hα galaxies. The cluster Hα galaxies fall on the SFR-stellar mass relation z ˜ 0.2 for the field. However, the `Sausage' cluster has an Hα emitter density >20 times that of blank fields. If the shock passes through gas-rich cluster galaxies, the compressed gas could collapse into dense clouds and excite star formation for a few 100 Myr. This process ultimately leads to a rapid consumption of the molecular gas, accelerating the transformation of gas-rich field spirals into cluster S0s or ellipticals.

  4. The SAMI Galaxy Survey: Cluster properties and the impact on galaxy star formation

    NASA Astrophysics Data System (ADS)

    Owers, Matt S.

    2015-08-01

    The SAMI Galaxy Survey will provide resolved spectroscopy for around 3000 galaxies. Of those galaxies, ~600 have been selected to be members of eight massive clusters of galaxies. These eight clusters were the subject of a deep redshift survey using the AAOmega multi-object spectrograph with the aim of characterising the cluster dynamical properties (galaxy membership, cluster mass and substructure). Seven of the clusters also have existing Chandra and/or XMM-Newton X-ray data. In this talk I will describe the global characteristics of the clusters, such as the total masses and merging status, which have been measured using the combination of the redshift and X-ray data. These data are also used to provide a more physical description of galaxy environment local to the SAMI targets. Preliminary results will be presented on the environments of galaxies with evidence for environmentally impacted star formation properties, as indicated by the resolved information provided by the SAMI data.

  5. Mining the UKIDSS Galactic Plane Survey: star formation and embedded clusters

    NASA Astrophysics Data System (ADS)

    Solin, O.; Ukkonen, E.; Haikala, L.

    2012-06-01

    Context. Data mining techniques must be developed and applied to analyse the large public data bases containing hundreds to thousands of millions entries. Aims: We develop methods for locating previously unknown stellar clusters from the UKIDSS Galactic Plane Survey (GPS) catalogue data. Methods: The cluster candidates are computationally searched from pre-filtered catalogue data using a method that fits a mixture model of Gaussian densities and background noise using the expectation maximization algorithm. The catalogue data contains a significant number of false sources clustered around bright stars. A large fraction of these artefacts were automatically filtered out before or during the cluster search. The UKIDSS data reduction pipeline tends to classify marginally resolved stellar pairs and objects seen against variable surface brightness as extended objects (or "galaxies" in the archive parlance). 10% or 66 × 106 of the sources in the UKIDSS GPS catalogue brighter than 17m in the K band are classified as "galaxies". Young embedded clusters create variable NIR surface brightness because the gas/dust clouds in which they were formed scatters the light from the cluster members. Such clusters appear therefore as clusters of "galaxies" in the catalogue and can be found using only a subset of the catalogue data. The detected "galaxy clusters" were finally screened visually to eliminate the remaining false detections due to data artefacts. Besides the embedded clusters the search also located locations of non clustered embedded star formation. Results: The search covered an area of 1302 deg2 and 137 previously unknown cluster candidates and 30 previously unknown sites of star formation were found. Appendices A-C are available in electronic form at http://www.anda.org

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

    PubMed

    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.

  7. Alpha-cluster preformation factor within cluster-formation model for odd-A and odd-odd heavy nuclei

    NASA Astrophysics Data System (ADS)

    Saleh Ahmed, Saad M.

    2017-06-01

    The alpha-cluster probability that represents the preformation of alpha particle in alpha-decay nuclei was determined for high-intensity alpha-decay mode odd-A and odd-odd heavy nuclei, 82 < Z < 114, 111 < N < 174. This probability was calculated using the energy-dependent formula derived from the formulation of clusterisation states representation (CSR) and the hypothesised cluster-formation model (CFM) as in our previous work. Our previous successful determination of phenomenological values of alpha-cluster preformation factors for even-even nuclei motivated us to expand the work to cover other types of nuclei. The formation energy of interior alpha cluster needed to be derived for the different nuclear systems with considering the unpaired-nucleon effect. The results showed the phenomenological value of alpha preformation probability and reflected the unpaired nucleon effect and the magic and sub-magic effects in nuclei. These results and their analyses presented are very useful for future work concerning the calculation of the alpha decay constants and the progress of its theory.

  8. Velocity Drives Greater Power Observed During Back Squat Using Cluster Sets.

    PubMed

    Oliver, Jonathan M; Kreutzer, Andreas; Jenke, Shane C; Phillips, Melody D; Mitchell, Joel B; Jones, Margaret T

    2016-01-01

    This investigation compared the kinetics and kinematics of cluster sets (CLU) and traditional sets (TRD) during back squat in trained (RT) and untrained (UT) men. Twenty-four participants (RT = 12, 25 ± 1 year, 179.1 ± 2.2 cm, 84.6 ± 2.1 kg; UT = 12, 25 ± 1 year, 180.1 ± 1.8 cm, 85.4 ± 3.8 kg) performed TRD (4 × 10, 120-second rest) and CLU (4 × (2 × 5) 30 seconds between clusters; 90 seconds between sets) with 70% one repetition maximum, randomly. Kinematics and kinetics were sampled through force plate and linear position transducers. Resistance-trained produced greater overall force, velocity, and power; however, similar patterns were observed in all variables when comparing conditions. Cluster sets produced significantly greater force in isolated repetitions in sets 1-3, while consistently producing greater force due to a required reduction in load during set 4 resulting in greater total volume load (CLU, 3302.4 ± 102.7 kg; TRD, 3274.8 ± 102.8 kg). Velocity loss was lessened in CLU resulting in significantly higher velocities in sets 2 through 4. Furthermore, higher velocities were produced by CLU during later repetitions of each set. Cluster sets produced greater power output for an increasing number of repetitions in each set (set 1, 5 repetitions; sets 2 and 3, 6 repetitions; set 4, 8 repetitions), and the difference between conditions increased over subsequent sets. Time under tension increased over each set and was greater in TRD. This study demonstrates greater power output is driven by greater velocity when back squatting during CLU; therefore, velocity may be a useful measure by which to assess power.

  9. Formation of a protocluster: A virialized structure from gravoturbulent collapse. I. Simulation of cluster formation in a collapsing molecular cloud

    NASA Astrophysics Data System (ADS)

    Lee, Yueh-Ning; Hennebelle, Patrick

    2016-06-01

    Context. Stars are often observed to form in clusters and it is therefore important to understand how such a region of concentrated mass is assembled out of the diffuse medium. The properties of such a region eventually prescribe the important physical mechanisms and determine the characteristics of the stellar cluster. Aims: We study the formation of a gaseous protocluster inside a molecular cloud and associate its internal properties with 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. Methods: We performed high resolution magnetohydrodynamic (MHD) simulations of gaseous protoclusters forming in molecular clouds collapsing under self-gravity. We determined ellipsoidal cluster regions via gas kinematics and sink particle distribution, permitting us to determine the mass, size, and aspect ratio of the cluster. We studied the cluster properties, such as kinetic and gravitational energy, and made links to the parent cloud. Results: The gaseous protocluster is formed out of global collapse of a molecular cloud and has non-negligible rotation owing 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. This dense entity is a result of the interplay between turbulence and gravity. We identify such regions in simulations and compare the gas and sink particles to observed star-forming clumps and embedded clusters, respectively. The gaseous protocluster inferred from simulation results presents a mass-size relation that is compatible with observations. We stress that the stellar cluster radius, although clearly correlated with the gas cluster radius, depends sensitively on its definition. Energy analysis is performed to confirm that the gaseous protocluster is a product of gravoturbulent reprocessing and that the support of turbulent

  10. Extended magnetohydrodynamic simulations of field reversed configuration formation and sustainment with rotating magnetic field current drive

    SciTech Connect

    Milroy, R. D.; Kim, C. C.; Sovinec, C. R.

    2010-06-15

    Three-dimensional simulations of field reversed configuration (FRC) formation and sustainment with rotating magnetic field (RMF) current drive have been performed with the NIMROD code [C. R. Sovinec et al., J. Comput. Phys. 195, 355 (2004)]. The Hall term is a zeroth order effect with strong coupling between Fourier components, and recent enhancements to the NIMROD preconditioner allow much larger time steps than was previously possible. Boundary conditions to capture the effects of a finite length RMF antenna have been added, and simulations of FRC formation from a uniform background plasma have been performed with parameters relevant to the translation, confinement, and sustainment-upgrade experiment at the University of Washington [H. Y. Guo, A. L. Hoffman, and R. D. Milroy, Phys. Plasmas 14, 112502 (2007)]. The effects of both even-parity and odd-parity antennas have been investigated, and there is no evidence of a disruptive instability for either antenna type. It has been found that RMF effects extend considerably beyond the ends of the antenna, and that a large n=0 B{sub t}heta can develop in the open-field line region, producing a back torque opposing the RMF.

  11. Extended magnetohydrodynamic simulations of field reversed configuration formation and sustainment with rotating magnetic field current drive

    NASA Astrophysics Data System (ADS)

    Milroy, R. D.; Kim, C. C.; Sovinec, C. R.

    2010-06-01

    Three-dimensional simulations of field reversed configuration (FRC) formation and sustainment with rotating magnetic field (RMF) current drive have been performed with the NIMROD code [C. R. Sovinec et al., J. Comput. Phys. 195, 355 (2004)]. The Hall term is a zeroth order effect with strong coupling between Fourier components, and recent enhancements to the NIMROD preconditioner allow much larger time steps than was previously possible. Boundary conditions to capture the effects of a finite length RMF antenna have been added, and simulations of FRC formation from a uniform background plasma have been performed with parameters relevant to the translation, confinement, and sustainment-upgrade experiment at the University of Washington [H. Y. Guo, A. L. Hoffman, and R. D. Milroy, Phys. Plasmas 14, 112502 (2007)]. The effects of both even-parity and odd-parity antennas have been investigated, and there is no evidence of a disruptive instability for either antenna type. It has been found that RMF effects extend considerably beyond the ends of the antenna, and that a large n =0 Bθ can develop in the open-field line region, producing a back torque opposing the RMF.

  12. Canonical free-energy barrier of particle and polymer cluster formation

    NASA Astrophysics Data System (ADS)

    Zierenberg, Johannes; Schierz, Philipp; Janke, Wolfhard

    2017-02-01

    A common approach to study nucleation rates is the estimation of free-energy barriers. This usually requires knowledge about the shape of the forming droplet, a task that becomes notoriously difficult in macromolecular setups starting with a proper definition of the cluster boundary. Here we demonstrate a shape-free determination of the free energy for temperature-driven cluster formation in particle as well as polymer systems. Combined with rigorous results on equilibrium droplet formation, this allows for a well-defined finite-size scaling analysis of the effective interfacial free energy at a fixed density. We first verify the theoretical predictions for the formation of a liquid droplet in a supersaturated particle gas by generalized-ensemble Monte Carlo simulations of a Lennard-Jones system. Going one step further, we then generalize this approach to cluster formation in a dilute polymer solution. Our results suggest an analogy with particle condensation, when the macromolecules are interpreted as extended particles.

  13. Impact of a star formation efficiency profile on the evolution of open clusters

    NASA Astrophysics Data System (ADS)

    Shukirgaliyev, B.; Parmentier, G.; Berczik, P.; Just, A.

    2017-09-01

    Aims: We study the effect of the instantaneous expulsion of residual star-forming gas on star clusters in which the residual gas has a density profile that is shallower than that of the embedded cluster. This configuration is expected if star formation proceeds with a given star-formation efficiency per free-fall time in a centrally concentrated molecular gas clump. Methods: We performed direct N-body simulations whose initial conditions were generated by the program "mkhalo" from the package "falcON", adapted for our models. Our model clusters initially had a Plummer profile and are in virial equilibrium with the gravitational potential of the cluster-forming clump. The residual gas contribution was computed based on a local-density driven clustered star formation model. Our simulations included mass loss by stellar evolution and the tidal field of a host galaxy. Results: We find that a star cluster with a minimum global star formation efficiency (SFE) of 15 percent is able to survive instantaneous gas expulsion and to produce a bound cluster. Its violent relaxation lasts no longer than 20 Myr, independently of its global SFE and initial stellar mass. At the end of violent relaxation, the bound fractions of the surviving clusters with the same global SFEs are similar, regardless of their initial stellar mass. Their subsequent lifetime in the gravitational field of the Galaxy depends on their bound stellar masses. Conclusions: We therefore conclude that the critical SFE needed to produce a bound cluster is 15 percent, which is roughly half the earlier estimates of 33 percent. Thus we have improved the survival likelihood of young clusters after instantaneous gas expulsion. Young clusters can now survive instantaneous gas expulsion with a global SFEs as low as the SFEs observed for embedded clusters in the solar neighborhood (15-30 percent). The reason is that the star cluster density profile is steeper than that of the residual gas. However, in terms of the

  14. Experimental studies of complex crater formation under cluster implantation of solids

    NASA Astrophysics Data System (ADS)

    Prasalovich, S.; Popok, V.; Persson, P.; Campbell, E. E. B.

    2005-10-01

    The results of a systematic study of surface defect formation after energetic Arn+ (n = 12, 22, 32, 54) and Xen+ (n = 4, 16) cluster ion implantation into silicon and sapphire are presented. Implantation energies vary from 3 to 18 keV/ion. Two cases of comparative studies are carried out: the same cluster species are implanted into two different substrates, i.e. Arn+ cluster ions into silicon and sapphire and two different cluster species Arn+ and Xen+ are implanted into the same kind of substrate (silicon). Atomic force, scanning electron and transmission electron microscopies (AFM, SEM and TEM) are used to study the implanted samples. The analysis reveals the formation of two types of surface erosion defects: simple and complex (with centrally positioned hillock) craters. It is found that the ratio of simple to complex crater formation as well as the hillock dimensions depend strongly on the cluster species, size and impact energy as well as on the type of substrate material. Qualitative models describing the two comparative cases of cluster implantation, the case of different cluster species and the case of different substrate materials, are proposed.

  15. Observation of small cluster formation in concentrated monoclonal antibody solutions and its implications to solution viscosity.

    PubMed

    Yearley, Eric J; Godfrin, Paul D; Perevozchikova, Tatiana; Zhang, Hailiang; Falus, Peter; Porcar, Lionel; Nagao, Michihiro; Curtis, Joseph E; Gawande, Pradad; Taing, Rosalynn; Zarraga, Isidro E; Wagner, Norman J; Liu, Yun

    2014-04-15

    Monoclonal antibodies (mAbs) are a major class of biopharmaceuticals. It is hypothesized that some concentrated mAb solutions exhibit formation of a solution phase consisting of reversibly self-associated aggregates (or reversible clusters), which is speculated to be responsible for their distinct solution properties. Here, we report direct observation of reversible clusters in concentrated solutions of mAbs using neutron spin echo. Specifically, a stable mAb solution is studied across a transition from dispersed monomers in dilute solution to clustered states at more concentrated conditions, where clusters of a preferred size are observed. Once mAb clusters have formed, their size, in contrast to that observed in typical globular protein solutions, is observed to remain nearly constant over a wide range of concentrations. Our results not only conclusively establish a clear relationship between the undesirable high viscosity of some mAb solutions and the formation of reversible clusters with extended open structures, but also directly observe self-assembled mAb protein clusters of preferred small finite size similar to that in micelle formation that dominate the properties of concentrated mAb solutions.

  16. Hierarchical Star Formation in Turbulent Media: Evidence from Young Star Clusters

    NASA Astrophysics Data System (ADS)

    Grasha, K.; Elmegreen, B. G.; Calzetti, D.; Adamo, A.; Aloisi, A.; Bright, S. N.; Cook, D. O.; Dale, D. A.; Fumagalli, M.; Gallagher, J. S., III; Gouliermis, D. A.; Grebel, E. K.; Kahre, L.; Kim, H.; Krumholz, M. R.; Lee, J. C.; Messa, M.; Ryon, J. E.; Ubeda, L.

    2017-06-01

    We present an analysis of the positions and ages of young star clusters in eight local galaxies to investigate the connection between the age difference and separation of cluster pairs. We find that star clusters do not form uniformly but instead are distributed so that the age difference increases with the cluster pair separation to the 0.25-0.6 power, and that the maximum size over which star formation is physically correlated ranges from ˜200 pc to ˜1 kpc. The observed trends between age difference and separation suggest that cluster formation is hierarchical both in space and time: clusters that are close to each other are more similar in age than clusters born further apart. The temporal correlations between stellar aggregates have slopes that are consistent with predictions of turbulence acting as the primary driver of star formation. The velocity associated with the maximum size is proportional to the galaxy’s shear, suggesting that the galactic environment influences the maximum size of the star-forming structures.

  17. A Multi-Wavelength Study of AGN and Star Formation in Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Atlee, David Wesley; Martini, P.

    2011-01-01

    Clusters of galaxies have long been used as laboratories for the study of galaxy evolution because the processes that impact morphology and star-formation rates (SFRs) in dense environments occur most rapidly in clusters. We present results from a study of AGN and star-formation in 8 low-redshift galaxy clusters. We construct spectral energy distributions (SEDs) from visible and MIR observations of cluster galaxies and fit model SEDs to the observed fluxes. These fits measure stellar masses and SFRs of the cluster members, which we use to predict the X-ray luminosity of each cluster member. X-ray luminosities in excess of the predictions indicate the presence of an AGN. AGN can also be identified from their model SEDs. The AGN selected by these two techniques are largely disjoint: only 8 out of 44 AGN are identified in X-rays and from their model SEDs. We find a positive correlation between SFR and radius within the host cluster, consistent with the SFR--density relation, but there is no apparent correlation between radius and accretion rate. However, the relationship between AGN accretion and host star-formation in cluster AGN hosts does not significantly differ from the relationship shown by z≈0.8 field AGNs and their hosts. Since SFR correlates with radius, field galaxies at z=0 must have larger SFRs relative to their black hole growth than field galaxies at z≈0.8. This is consistent with evolution in the MBH--Mbulge relation. We also measure the fractions of cluster members with star-formation and AGN to determine the AGN duty cycle in star-forming galaxies. At time of writing, results are pending. I am grateful to The Ohio State University and the Spitzer grant program for supporting this work.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

  20. Exploring Star Formation in Cluster Galaxies with the Herschel Space Observatory

    NASA Astrophysics Data System (ADS)

    Rawle, Tim; Rex, M.; Egami, E.; Chung, S.; Fadda, D.; Lensing Survey, Herschel

    2011-05-01

    Nominally designed to locate high-redshift galaxies magnified by 44 massive foreground clusters, the ``Herschel Lensing Survey'' (HLS; PI: Egami) also provides deep 5-band, far-infrared (FIR) imaging of the galaxies contained within those clusters. For sources at these redshifts (z 0.2-0.4), Herschel photometry spans the peak of the dust component, allowing us to constrain the dust properties, measure total infrared luminosity and hence derive obscured star formation rate. Although a large fraction of galaxies in massive clusters are quiescent early-types and therefore remain undetected by Herschel, the far-infrared highlights regions of activity within the system. The FIR effectively probes the transitional phases of cluster galaxy evolution, exposing starburst mechanisms such as tidal interactions and mergers, as well as the remnants of the as-yet un-quenched in-fall population. Here we focus on two particular, contrasting clusters at z 0.3: the famous merging system known as the Bullet Cluster, and a relatively undisturbed cluster MS2137. We locate the FIR-bright cluster members and characterize their dust component, allowing us to study the distribution of star formation in the two systems as a function of morphology and local environment. In addition, we investigate an intriguing subpopulation of FIR-luminous galaxies with dust component SEDs that do not conform to the templates derived from local field galaxies, yet are also unlike any sources observed at higher redshift.

  1. Flux dependence of cluster formation in neutron-irradiated weld material

    NASA Astrophysics Data System (ADS)

    Bergner, F.; Ulbricht, A.; Hein, H.; Kammel, M.

    2008-03-01

    The effect of neutron flux on the formation of irradiation-induced clusters in reactor pressure vessel (RPV) steels is an unresolved issue. Small-angle neutron scattering was measured for a neutron-irradiated RPV weld material containing 0.22 wt% impurity Cu. The experiment was focused on the influence of neutron flux on the formation of irradiation-induced clusters at fixed fluence. The aim was to separate and tentatively interpret the effect of flux on the characteristics of the cluster size distribution. We have observed a pronounced effect of neutron flux on cluster size, whereas the total volume fraction of irradiation-induced clusters is insensitive to the level of flux. The result is compatible with a rate theory model according to which the range of applied fluxes covers the transition from a flux-independent regime at lower fluxes to a regime of decelerating cluster growth. The results are confronted with measured irradiation-induced changes of mechanical properties. Despite the observed flux effect on cluster size, both yield stress increase and transition temperature shift turned out to be independent of flux. This is in agreement with the volume fraction of irradiation-induced clusters being insensitive to the level of flux.

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

    NASA Astrophysics Data System (ADS)

    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 <2 to 1400 pptv, [H2SO4] 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]<0.1 to 1. For larger values of [NH3] / [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

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

    NASA Astrophysics Data System (ADS)

    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 < 2 to 1400 pptv, [H2SO4] from 3.3 × 106 to 1.4 × 109 cm-3 (0.1 to 56 pptv), 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] < 0.1 to 1. For larger values of [NH3] / [H2SO4], the composition of NH3-H2SO4 clusters was characterized by the number of NH3 molecules m added for each added H2SO4 molecule n (Δm/Δ n), where n is in the range 4-18 (negatively charged clusters) or 1-17 (positively charged clusters). For negatively charged clusters, Δ m/Δn saturated between 1 and 1.4 for [NH3] / [H2SO4] > 10. Positively

  4. A parsec-resolution simulation of the Antennae galaxies: formation of star clusters during the merger

    NASA Astrophysics Data System (ADS)

    Renaud, Florent; Bournaud, Frédéric; Duc, Pierre-Alain

    2015-01-01

    We present a hydrodynamical simulation of an Antennae-like galaxy merger at parsec resolution, including a multicomponent 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 pericentre passages, the starburst is spatially extended and forms many star clusters. However, the starburst associated with 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 to globular clusters. Monitoring the evolution of a few clusters reveals the diversity of formation scenarios including the gathering and merger of gas clumps, the monolithic formation and the hierarchical formation in sub-structures inside a single cloud. Two stellar objects formed in the simulation yield the same properties as ultracompact dwarf galaxies. They share the same formation scenario than the most massive clusters, but have a larger radius either since birth, or get it after a violent interaction with the galactic centre. The diversity of environments across space and time in a galaxy merger can account for the diversity of the stellar objects formed, both in terms of mass and size.

  5. Kinesin-12 motors cooperate to suppress microtubule catastrophes and drive the formation of parallel microtubule bundles

    PubMed Central

    Drechsler, Hauke; McAinsh, Andrew D.

    2016-01-01

    Human Kinesin-12 (hKif15) plays a crucial role in assembly and maintenance of the mitotic spindle. These functions of hKif15 are partially redundant with Kinesin-5 (Eg5), which can cross-link and drive the extensile sliding of antiparallel microtubules. Although both motors are known to be tetramers, the functional properties of hKif15 are less well understood. Here we reveal how single or multiple Kif15 motors can cross-link, transport, and focus the plus-ends of intersecting microtubules. During transport, Kif15 motors step simultaneously along both microtubules with relative microtubule transport driven by a velocity differential between motor domain pairs. Remarkably, this differential is affected by the underlying intersection geometry: the differential is low on parallel and extreme on antiparallel microtubules where one motor domain pair becomes immobile. As a result, when intersecting microtubules are antiparallel, canonical transport of one microtubule along the other is allowed because one motor is firmly attached to one microtubule while it is stepping on the other. When intersecting microtubules are parallel, however, Kif15 motors can drive (biased) parallel sliding because the motor simultaneously steps on both microtubules that it cross-links. These microtubule rearrangements will focus microtubule plus-ends and finally lead to the formation of parallel bundles. At the same time, Kif15 motors cooperate to suppress catastrophe events at polymerizing microtubule plus-ends, raising the possibility that Kif15 motors may synchronize the dynamics of bundles that they have assembled. Thus, Kif15 is adapted to operate on parallel microtubule substrates, a property that clearly distinguishes it from the other tetrameric spindle motor, Eg5. PMID:26969727

  6. Kinesin-12 motors cooperate to suppress microtubule catastrophes and drive the formation of parallel microtubule bundles.

    PubMed

    Drechsler, Hauke; McAinsh, Andrew D

    2016-03-22

    Human Kinesin-12 (hKif15) plays a crucial role in assembly and maintenance of the mitotic spindle. These functions of hKif15 are partially redundant with Kinesin-5 (Eg5), which can cross-link and drive the extensile sliding of antiparallel microtubules. Although both motors are known to be tetramers, the functional properties of hKif15 are less well understood. Here we reveal how single or multiple Kif15 motors can cross-link, transport, and focus the plus-ends of intersecting microtubules. During transport, Kif15 motors step simultaneously along both microtubules with relative microtubule transport driven by a velocity differential between motor domain pairs. Remarkably, this differential is affected by the underlying intersection geometry: the differential is low on parallel and extreme on antiparallel microtubules where one motor domain pair becomes immobile. As a result, when intersecting microtubules are antiparallel, canonical transport of one microtubule along the other is allowed because one motor is firmly attached to one microtubule while it is stepping on the other. When intersecting microtubules are parallel, however, Kif15 motors can drive (biased) parallel sliding because the motor simultaneously steps on both microtubules that it cross-links. These microtubule rearrangements will focus microtubule plus-ends and finally lead to the formation of parallel bundles. At the same time, Kif15 motors cooperate to suppress catastrophe events at polymerizing microtubule plus-ends, raising the possibility that Kif15 motors may synchronize the dynamics of bundles that they have assembled. Thus, Kif15 is adapted to operate on parallel microtubule substrates, a property that clearly distinguishes it from the other tetrameric spindle motor, Eg5.

  7. Anthropogenic disruption to the seismic driving of beach ridge formation: The Sendai coast, Japan.

    PubMed

    Goff, James; Knight, Jasper; Sugawara, Daisuke; Terry, James P

    2016-02-15

    The expected geomorphic after-effects of the Mw 9.0 Tōhoku-oki earthquake of 11 March 2011 (eastern Japan) are summarized by a schematic model of seismic driving, which details seismogenic disturbances to sediment systems that affect the rate or timing of sediment delivery to coastlines over timescales of 10(2)-10(4)years. The immediate physical environmental responses to this high-magnitude earthquake included a large tsunami and extensive region-wide slope failures. Normally, slope failures within mountain catchments would have significant impacts on Japan's river and coastal geomorphology in the coming decades with, for example, a new beach ridge expected to form within 20-100 years on the Sendai Plain. However, human activity has significantly modified the rate and timing of geomorphic processes of the region, which will have impacts on likely geomorphic responses to seismic driving. For example, the rivers draining into Sendai Bay have been dammed, providing sediment traps that will efficiently capture bedload and much suspended sediment in transit through the river system. Instead of the expected ~1 km of coastal progradation and formation of a ~3m high beach ridge prior to the next large tsunami, it is likely that progradation of the Sendai Plain will continue to slow or even cease as a result of damming of river systems and capture of river sediments behind dams. The resulting reduction of fluvial sediment delivery to the coast due to modification of rivers inadvertently makes seawalls and other engineered coastal structures even more necessary than they would be otherwise.

  8. Reassessing the formation of the inner Oort cloud in an embedded star cluster

    NASA Astrophysics Data System (ADS)

    Brasser, R.; Duncan, M. J.; Levison, H. F.; Schwamb, M. E.; Brown, M. E.

    2012-01-01

    We re-examine the formation of the inner Oort comet cloud while the Sun was in its birth cluster with the aid of numerical simulations. This work is a continuation of an earlier study (Brasser, R., Duncan, M.J., Levison, H.F. [2006]. Icarus 184, 59-82) with several substantial modifications. First, the system consisting of stars, planets and comets is treated self-consistently in our N-body simulations, rather than approximating the stellar encounters with the outer Solar System as hyperbolic fly-bys. Second, we have included the expulsion of the cluster gas, a feature that was absent previously. Third, we have used several models for the initial conditions and density profile of the cluster - either a Hernquist or Plummer potential - and chose other parameters based on the latest observations of embedded clusters from the literature. These other parameters result in the stars being on radial orbits and the cluster collapses. Similar to previous studies, in our simulations the inner Oort cloud is formed from comets being scattered by Jupiter and Saturn and having their pericentres decoupled from the planets by perturbations from the cluster gas and other stars. We find that all inner Oort clouds formed in these clusters have an inner edge ranging from 100 AU to a few hundred AU, and an outer edge at over 100,000 AU, with little variation in these values for all clusters. All inner Oort clouds formed are consistent with the existence of (90377) Sedna, an inner Oort cloud dwarf planetoid, at the inner edge of the cloud: Sedna tends to be at the innermost 2% for Plummer models, while it is 5% for Hernquist models. We emphasise that the existence of Sedna is a generic outcome. We define a 'concentration radius' for the inner Oort cloud and find that its value increases with increasing number of stars in the cluster, ranging from 600 AU to 1500 AU for Hernquist clusters and from 1500 AU to 4000 AU for Plummer clusters. The increasing trend implies that small star

  9. Confronting models of star formation quenching in galaxy clusters with archival Spitzer data

    NASA Astrophysics Data System (ADS)

    Rudnick, Gregory

    Large scale structures in the universe form hierarchically: small structures merge to form larger ones. Over the same epoch where these structures experience significant growth, the fraction of star forming galaxies within them decreases, and at a faster rate than for field galaxies. It is now widely accepted that there must be physical processes at work in these dense environments to actively quench star formation. However, despite no shortage of candidate mechanisms, sophisticated cosmological simulations still cannot reproduce the star formation rate distributions within dense environments, such as galaxy clusters. Insufficient observational constraints are a primary obstacle to further progress. In particular, the interpretation of observations of nearby clusters relies on untested assumptions about the properties of galaxies before they entered the dense cluster environment at higher redshifts. Clearly, direct constraints on these properties are required. Our group has assembled two data sets designed to address these concerns. The first focuses on an intermediate wide-field cluster sample and the second focuses on a well-matched low-redshift cluster sample. We will use these samples, along with sophisticated models of hierarchical galaxy formation, to meet the following objectives: 1. Directly measure the SFR distribution of the progenitors of present-day cluster galaxies. We will use ground-based spectroscopy to identify cluster members within four virial radii of eight intermediate-redshift clusters. We will couple this with archival Spitzer/MIPS data to measure the SFRs of galaxies out to the cluster outskirts. 2. Measure the SFR distribution of the present-day cluster galaxies using Spitzer and WISE. Robust N-body simulations tell us statistically which galaxies at intermediate redshifts will have entered the cluster virial radius by the current epoch. By combining our wide-field coverage at high redshift with our local cluster sample, we will determine

  10. THE FORMATION OF COSMIC FULLERENES FROM AROPHATIC CLUSTERS

    SciTech Connect

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

    2012-12-10

    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.

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

    NASA Astrophysics Data System (ADS)

    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.

  12. Clusters of high-mass protostars: From extreme clouds to mini-bursts of star formation

    NASA Astrophysics Data System (ADS)

    Motte, Frédérique; Louvet, Fabien; Nguyen Lu'O'Ng, Quang

    2017-03-01

    Herschel revealed high-density cloud filaments of several pc3, which are forming clusters of OB-type stars. Counting Herschel protostars gives a direct measure of the mass of stars forming in a period of ~105 yrs, the ``instantaneous'' star formation activity. Given their activity, these so-called mini-starburst cloud ridges could be seen as ``miniature and instant models'' of starburst galaxies. Their characteristics could shed light on the origin of massive clusters.

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

    NASA Astrophysics Data System (ADS)

    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.

  14. The ALMA view of the Antennae galaxy collision: How galaxy interaction triggers the formation of super star clusters

    NASA Astrophysics Data System (ADS)

    Herrera, Cinthya N.; Boulanger, François; Falgarone, Edith G.; Pineau Des Forêts, Guillaume; García-Burillo, Santiago; Iono, Daisuke; Guillard, Pierre

    The Antennae galaxies are a spectacular example of a burst of star formation triggered by the encounter of two galaxies, being an ideal source to understand how the dynamics of galaxy mergers drives star formation. We present archive ALMA CO(3-2) and VLT near-IR H2 spectro-imaging observations, and new ALMA 13CO(2-1) and dust continuum observations, at ~50 pc resolution. Combining tracers of density and velocity structure of the gas and its energetics, we demonstrate that star formation involves a complex interplay of merger-driven gas dynamics and turbulence, and the dissipation of the gas kinetic energy. We focus on a compact, bright H2 source, associated with cold molecular gas and dust continuum emission, located where the velocity gradient in the interaction region is observed to be the largest. The characteristics of this source suggest that we are witnessing the formation, initiated by turbulent dissipation, of a cloud massive enough (~4×106M⊙) to form a super star cluster within 1 Myr.

  15. First-principles molecular dynamics simulations of (sulfuric acid)1(dimethylamine)1 cluster formation

    NASA Astrophysics Data System (ADS)

    Loukonen, Ville; Bork, Nicolai; Vehkamäki, Hanna

    2013-05-01

    The clustering process (sulfuric acid) + (base)→(sulfuric acid)1(base)1 is of fundamental importance in the atmospheric new-particle formation. Especially interesting are the collisions where a proton transfer reaction can happen, as the reaction often leads to relatively strongly bound clusters. Here, we studied the clustering process of (sulfuric acid) + (dimethylamine) → (sulfuric acid)1(dimethylamine)1 using first-principles molecular dynamics simulations. The collision of the two molecules was simulated starting with various spatial orientations and the evolution of the cluster was followed in the NVE ensemble. The simulations suggest that the proton transfer reaction takes place regardless of the intial collision orientation. However, due to the energy released in the process, the newly-formed cluster is not able to reach the minimun energy configuration, which might affect the following growth processes.

  16. Modeling the formation of ion clusters by applying classical nucleation theory

    NASA Astrophysics Data System (ADS)

    Yue, G. K.

    Experiments have been conducted to study the clustering of atmospheric trace gases around ion cores (Castleman and Tang, 1972; Searcy and Fenn, 1974; Castleman, 1978). The classical liquid-drop model is used to investigate this ion-induced formation mechanism. Results obtained from models of the distribution of Pb(+)-(H2O)n and H(+)-(H2O)n type clusters under various conditions are compared with experimental results. The distribution of water-ion clusters in the atmosphere as a function of altitude is calculated. In situ measurements of the water-ion cluster distributions in the upper atmosphere are then compared with present predictions. It is concluded that the classical nucleation theory can be used to predict rough estimates for ion cluster sizes under many conditions.

  17. Modeling the formation of ion clusters by applying classical nucleation theory. [aerosol mechanisms

    NASA Technical Reports Server (NTRS)

    Yue, G. K.

    1981-01-01

    Experiments have been conducted to study the clustering of atmospheric trace gases around ion cores (Castleman and Tang, 1972; Searcy and Fenn, 1974; Castleman, 1978). The classical liquid-drop model is used to investigate this ion-induced formation mechanism. Results obtained from models of the distribution of Pb(+)-(H2O)n and H(+)-(H2O)n type clusters under various conditions are compared with experimental results. The distribution of water-ion clusters in the atmosphere as a function of altitude is calculated. In situ measurements of the water-ion cluster distributions in the upper atmosphere are then compared with present predictions. It is concluded that the classical nucleation theory can be used to predict rough estimates for ion cluster sizes under many conditions.

  18. SUPERMASSIVE BLACK HOLE FORMATION VIA GAS ACCRETION IN NUCLEAR STELLAR CLUSTERS

    SciTech Connect

    Davies, Melvyn B.; Coleman Miller, M.; Bellovary, Jillian M.

    2011-10-20

    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 timescales due to the nearly free-fall inflow of self-gravitating gas with a mass comparable to or larger than that of the clusters. This process increases the velocity dispersion to the point where 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{sup 5} M{sub sun} or larger.

  19. The rarity of star formation in brightest cluster galaxies as measured by WISE

    NASA Astrophysics Data System (ADS)

    Fraser-McKelvie, Amelia; Brown, Michael J. I.; Pimbblet, Kevin A.

    2014-10-01

    We present the mid-infrared star formation rates of 245 X-ray selected, nearby (z < 0.1) brightest cluster galaxies (BCGs). A homogeneous and volume limited sample of BCGs was created by X-ray selecting clusters with Lx > 1 × 1044 erg s- 1. The Wide-Field Infrared Survey Explorer (WISE) All WISE Data Release provides the first measurement of the 12 μm star formation indicator for all BCGs in the nearby Universe. Perseus A and Cygnus A are the only galaxies in our sample to have star formation rates of > 40 M⊙ yr- 1, indicating that these two galaxies are highly unusual at current times. Stellar populations of 99 ± 0.6 per cent of local BCGs are (approximately) passively evolving, with star formation rates of < 10 M⊙ yr- 1. We find that in general, star formation produces only modest BCG growth at the current epoch.

  20. On the fraction of star formation occurring in bound stellar clusters

    NASA Astrophysics Data System (ADS)

    Kruijssen, J. M. Diederik

    2012-11-01

    We present a theoretical framework in which bound stellar clusters arise naturally at the high-density end of the hierarchy of the interstellar medium (ISM). Due to short free-fall times, these high-density regions achieve high local star formation efficiencies, enabling them to form bound clusters. Star-forming regions of lower density remain substructured and gas-rich, ending up unbound when the residual gas is expelled. Additionally, the tidal perturbation of star-forming regions by nearby, dense giant molecular clouds imposes a minimum density contrast required for the collapse to a bound cluster. The fraction of all star formation that occurs in bound stellar clusters (the cluster formation efficiency, hereafter CFE) follows by integration of these local clustering and survival properties over the full density spectrum of the ISM, and hence is set by galaxy-scale physics. We derive the CFE as a function of observable galaxy properties, and find that it increases with the gas surface density, from Γ ˜ 1 per cent in low-density galaxies to a peak value of Γ ˜ 70 per cent at densities of Σg ˜ 103 M⊙ pc-2. This explains the observation that the CFE increases with the star formation rate density in nearby dwarf, spiral and starburst galaxies. Indeed, comparing our model results with observed galaxies yields excellent agreement. The model is applied further by calculating the spatial variation of the CFE within single galaxies. We also consider the variation of the CFE with cosmic time and show that it increases with redshift, peaking in high-redshift, gas-rich disc galaxies. It is estimated that up to 30-35 per cent of all stars in the Universe once formed in bound stellar clusters. We discuss how our theory can be verified with Gaia and ALMA, and provide possible implementations for theoretical work and for simulations of galaxy formation and evolution.

  1. Star formation trends in the unrelaxed, post-merger cluster A2255

    SciTech Connect

    Tyler, K. D.; Rieke, G. H.; Bai, L.

    2014-10-10

    The effects of dense environments on normal field galaxies are still up for debate despite much study since Abell published his catalog of nearby clusters in 1958. There are changes in color, morphology, and star formation properties when galaxies fall into groups and clusters, but the specifics of how and where these modifications occur are not fully understood. To look for answers, we focused on star-forming galaxies in A2255, an unrelaxed cluster thought to have recently experienced a merger with another cluster or large group. We used Hα, MIPS 24 μm, and WISE 22 μm to estimate total star formation rates (SFRs) and Sloan Digital Sky Survey photometry to find stellar masses (M {sub *}) for galaxies out to ∼5 r {sub 200}. We compared the star-forming cluster galaxies with the field SFR-mass distribution and found no enhancement or suppression of star formation in currently star-forming galaxies of high mass (log (M {sub *}/M {sub ☉}) ≳ 10). This conclusion holds out to very large distances from the cluster center. However, the core (r {sub proj} < 3 Mpc) has a much lower fraction of star-forming galaxies than anywhere else in the cluster. These results indicate that for the mass range studied here, the majority of the star formation suppression occurs in the core on relatively short timescales, without any enhancement prior to entering the central region. If any significant enhancement or quenching of star formation occurs, it will be in galaxies of lower mass (log (M {sub *}/M {sub ☉}) < 10).

  2. Numerical analysis of bubble-cluster formation in an ultrasonic field

    NASA Astrophysics Data System (ADS)

    Kim, Donghyun; Son, Gihun

    2016-11-01

    Bubble-cluster formation in an ultrasonic field is investigated numerically solving the conservation equations of mass, momentum and energy. The liquid-gas interface is calculated using the volume-of-fluid method with variable gas density to consider the bubble compressibility. The effect of liquid-gas phase change is also included as the interface source terms of the mass and energy equations. The numerical approach is tested through the simulation of the expansion and contraction motion of a compressed bubble adjacent to a wall. When the bubble is placed in an ultrasonic field, it oscillates radially and then collapses violently. Numerical simulation is also performed for bubble-cluster formation induced by an ultrasonic generator, where the generated bubbles are merged into a macrostructure along the acoustic flow field. The effects of ultrasonic power and frequency, liquid properties and pool temperature on the bubble-cluster formation are investigated. This work was supported by the Korea Institute of Energy Research.

  3. GLOBULAR CLUSTER FORMATION EFFICIENCIES FROM BLACK HOLE X-RAY BINARY FEEDBACK

    SciTech Connect

    Justham, Stephen; Peng, Eric W.; Schawinski, Kevin

    2015-08-10

    We investigate a scenario in which feedback from black hole X-ray binaries (BHXBs) sometimes begins inside young star clusters before strong supernova (SN) feedback. Those BHXBs could reduce the gas fraction inside embedded young clusters while maintaining virial equilibrium, which may help globular clusters (GCs) to stay bound when SN-driven gas ejection subsequently occurs. Adopting a simple toy model with parameters guided by BHXB population models, we produce GC formation efficiencies consistent with empirically inferred values. The metallicity dependence of BHXB formation could naturally explain why GC formation efficiency is higher at lower metallicity. For reasonable assumptions about that metallicity dependence, our toy model can produce a GC metallicity bimodality in some galaxies without a bimodality in the field-star metallicity distribution.

  4. Oxalate Formation in Titanium-Carbon Dioxide Anionic Clusters Studied by Infrared Photodissociation Spectroscopy

    NASA Astrophysics Data System (ADS)

    Dodson, Leah G.; Thompson, Michael C.; Weber, J. Mathias

    2017-06-01

    Carbon-carbon bond formation during carbon dioxide fixation would enable bulk synthesis of hydrocarbon chains, generally through formation of an oxalate intermediate. In this talk, we demonstrate the formation of [Ti(CO_{2})_{y}]^{-} (y = 4-6) gas phase clusters with an oxalate ligand bearing significant (> 1 e^{-}) negative charge. Gas phase anionic clusters were generated using laser ablation of a titanium metal target in the presence of a CO_{2} expansion, and the infrared photodissociation spectra were measured from 950-2400 cm^{-1}, revealing vibrations characteristic of the oxalate anion. The molecular structure of these clusters was identified by comparing the experimental vibrational spectra with density functional theory calculations.

  5. The formation mechanism of clusters produced by laser ablation of solid sodium azide

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Shen, Ruiqi; Wu, Lizhi; Ye, Yinghua; Hu, Yan; Zhu, Peng

    2013-02-01

    The mass spectra of sodium azide (NaN3) cluster ions, produced by 532 nm laser ablation of a solid NaN3 sample, were measured by a time-of-flight (TOF) mass spectrometer. The spectra showed that most of the cluster ions could be ascribed to the following series: Nan-, (NaN3)n-, Na(NaN3)n-, N3(NaN3)n-, Nan+, Nan(NaN3)+ and Na2(NaN3)n+. According to the possible distribution of the ions, possible formation mechanisms of NaN3 clusters are proposed.

  6. Analysis of radiation-induced small Cu particle cluster formation in aqueous CuCl2

    USGS Publications Warehouse

    Jayanetti, Sumedha; Mayanovic, Robert A.; Anderson, Alan J.; Bassett, William A.; Chou, I.-Ming

    2001-01-01

    Radition-induced small Cu particle cluster formation in aqueous CuCl2 was analyzed. It was noticed that nearest neighbor distance increased with the increase in the time of irradiation. This showed that the clusters approached the lattice dimension of bulk copper. As the average cluster size approached its bulk dimensions, an increase in the nearest neighbor coordination number was found with the decrease in the surface to volume ratio. Radiolysis of water by incident x-ray beam led to the reduction of copper ions in the solution to themetallic state.

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

    PubMed

    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.

  8. Shocks and Cool Cores: An ALMA View of Massive Galaxy Cluster Formation at High Redshifts

    NASA Astrophysics Data System (ADS)

    Basu, Kaustuv

    2017-07-01

    These slides present some recent results on the Sunyaev-Zel'dovich (SZ) effect imaging of galaxy cluster substructures. The advantage of SZ imaging at high redshifts or in the low density cluster outskirts is already well-known. Now with ALMA a combination of superior angular resolution and high sensitivity is available. One example is the first ALMA measurement of a merger shock at z=0.9 in the famous El Gordo galaxy cluster. Here comparison between SZ, X-ray and radio data enabled us to put constraints on the shock Mach number and magnetic field strength for a high-z radio relic. Second example is the ALMA SZ imaging of the core region of z=1.4 galaxy cluster XMMU J2235.2-2557. Here ALMA data provide an accurate measurement of the thermal pressure near the cluster center, and from a joint SZ/X-ray analysis we find clear evidence for a reduced core temperature. This result indicate that a cool core establishes itself early enough in the cluster formation history while the gas accumulation is still continuing. The above two ALMA measurements are among several other recent SZ results that shed light on the formation process of massive clusters at high redshifts.

  9. FORMATION OF COMPACT STELLAR CLUSTERS BY HIGH-REDSHIFT GALAXY OUTFLOWS. III. OBSERVABILITY AND CONNECTION TO HALO GLOBULAR CLUSTERS

    SciTech Connect

    Gray, William J.; Scannapieco, Evan

    2011-12-01

    The early universe hosted a large population of low-mass virialized 'minihalos', that were not massive enough to form stars on their own. While most minihalos were photoevaporated by ionizing photons from star-forming galaxies, these galaxies also drove large outflows, which in some cases would have reached the minihalos in advance of ionization fronts. In the previous papers in this series, we carried out high-resolution, three-dimensional adaptive mesh refinement simulations of outflow-minihalo interactions that included non-equilibrium chemistry, radiative cooling, and turbulent mixing. We found that, for a fiducial set of parameters, minihalos were transformed into dense, chemically homogenous stellar clusters. Here we conduct a suite of simulations that follow these interactions over a wide range of parameters including minihalo mass, minihalo formation redshift, outflow energy, outflow redshift, distance, concentration, and spin. In almost all cases, the shocked minihalos form molecules through non-equilibrium reactions and then cool rapidly to become compact, chemically homogenous stellar clusters. Furthermore, we show that the unique properties of these clusters make them a prime target for direct study with the next generation of telescopes, and that there are many reasons to suspect that their low-redshift counterparts are the observed population of halo globular clusters.

  10. The formation of NGC 3603 young starburst cluster: `prompt' hierarchical assembly or monolithic starburst?

    NASA Astrophysics Data System (ADS)

    Banerjee, Sambaran; Kroupa, Pavel

    2015-02-01

    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. The stellar radiative and mechanical feedback to the residual gas energizes the latter until it escapes the system. The newly born gas-free young cluster eventually readjusts with the corresponding mass-loss. Based on the observed substructured morphologies of many young stellar associations, it is alternatively suggested that even the smooth-profiled massive clusters are also assembled from migrating less massive subclusters. A very young (age ≈ 1 Myr), massive (>104 M⊙) star cluster like the Galactic NGC 3603 young cluster (HD 97950) is an appropriate testbed for distinguishing between the above `monolithic' and `hierarchical' formation scenarios. A recent study by Banerjee & Kroupa demonstrates that the monolithic scenario remarkably reproduces the HD 97950 cluster. In particular, its shape, internal motion and the mass distribution of stars are found to follow naturally and consistently from a single model calculation undergoing ≈70 per cent by mass gas dispersal. In this 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 various modes of subclustering in both absence and presence of a background gas potential. Unlike the above monolithic initial system that reproduces HD 97950 very well, the same is found to be prohibitive with hierarchical assembly alone (with/without a gas potential). Only those systems which assemble promptly into a single cluster (in ≲1 Myr) from a close separation (all within ≲2 pc) could match the observed density profile of HD 97950 after a similar gas removal. These results therefore suggest that the NGC 3603 young cluster has formed essentially

  11. The axolotl limb blastema: cellular and molecular mechanisms driving blastema formation and limb regeneration in tetrapods

    PubMed Central

    McCusker, Catherine; Bryant, Susan V.

    2015-01-01

    Abstract The axolotl is one of the few tetrapods that are capable of regenerating complicated biological structures, such as complete limbs, throughout adulthood. Upon injury the axolotl generates a population of regeneration‐competent limb progenitor cells known as the blastema, which will grow, establish pattern, and differentiate into the missing limb structures. In this review we focus on the crucial early events that occur during wound healing, the neural−epithelial interactions that drive the formation of the early blastema, and how these mechanisms differ from those of other species that have restricted regenerative potential, such as humans. We also discuss how the presence of cells from the different axes of the limb is required for the continued growth and establishment of pattern in the blastema as described in the polar coordinate model, and how this positional information is reprogrammed in blastema cells during regeneration. Multiple cell types from the mature limb stump contribute to the blastema at different stages of regeneration, and we discuss the contribution of these types to the regenerate with reference to whether they are “pattern‐forming” or “pattern‐following” cells. Lastly, we explain how an engineering approach will help resolve unanswered questions in limb regeneration, with the goal of translating these concepts to developing better human regenerative therapies. PMID:27499868

  12. CO J = 2-1 LINE EMISSION IN CLUSTER GALAXIES AT z {approx} 1: FUELING STAR FORMATION IN DENSE ENVIRONMENTS

    SciTech Connect

    Wagg, Jeff; Pope, Alexandra; Alberts, Stacey; Armus, Lee; Desai, Vandana; Brodwin, Mark; Bussmann, Robert S.; Dey, Arjun; Jannuzi, Buell; Le Floc'h, Emeric; Melbourne, Jason; Stern, Daniel

    2012-06-20

    We present observations of CO J = 2-1 line emission in infrared-luminous cluster galaxies at z {approx} 1 using the IRAM Plateau de Bure Interferometer. Our two primary targets are optically faint, dust-obscured galaxies (DOGs) found to lie within 2 Mpc of the centers of two massive (>10{sup 14} M{sub Sun }) galaxy clusters. CO line emission is not detected in either DOG. We calculate 3{sigma} upper limits to the CO J = 2-1 line luminosities, L'{sub CO} < 6.08 Multiplication-Sign 10{sup 9} and <6.63 Multiplication-Sign 10{sup 9} K km s{sup -1} pc{sup 2}. Assuming a CO-to-H{sub 2} conversion factor derived for ultraluminous infrared galaxies in the local universe, this translates to limits on the cold molecular gas mass of M{sub H{sub 2}}< 4.86 Multiplication-Sign 10{sup 9} M{sub Sun} and M{sub H{sub 2}}< 5.30 Multiplication-Sign 10{sup 9} M{sub Sun }. Both DOGs exhibit mid-infrared continuum emission that follows a power law, suggesting that an active galactic nucleus (AGN) contributes to the dust heating. As such, estimates of the star formation efficiencies in these DOGs are uncertain. A third cluster member with an infrared luminosity, L{sub IR} < 7.4 Multiplication-Sign 10{sup 11} L{sub Sun }, is serendipitously detected in CO J = 2-1 line emission in the field of one of the DOGs located roughly two virial radii away from the cluster center. The optical spectrum of this object suggests that it is likely an obscured AGN, and the measured CO line luminosity is L'{sub CO} = (1.94 {+-} 0.35) Multiplication-Sign 10{sup 10} K km s{sup -1} pc{sup 2}, which leads to an estimated cold molecular gas mass M{sub H{sub 2}}= (1.55{+-}0.28) Multiplication-Sign 10{sup 10} M{sub Sun }. A significant reservoir of molecular gas in a z {approx} 1 galaxy located away from the cluster center demonstrates that the fuel can exist to drive an increase in star formation and AGN activity at the outskirts of high-redshift clusters.

  13. Gas cluster ion beam assisted NiPt germano-silicide formation on SiGe

    SciTech Connect

    Ozcan, Ahmet S.; Lavoie, Christian; Jordan-Sweet, Jean; Alptekin, Emre; Zhu, Frank; Leith, Allen; Pfeifer, Brian D.; LaRose, J. D.; Russell, N. M.

    2016-04-21

    We report the formation of very uniform and smooth Ni(Pt)Si on epitaxially grown SiGe using Si gas cluster ion beam treatment after metal-rich silicide formation. The gas cluster ion implantation process was optimized to infuse Si into the metal-rich silicide layer and lowered the NiSi nucleation temperature significantly according to in situ X-ray diffraction measurements. This novel method which leads to more uniform films can also be used to control silicide depth in ultra-shallow junctions, especially for high Ge containing devices, where silicidation is problematic as it leads to much rougher interfaces.

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

    SciTech Connect

    Aharon, Danor; Perets, Hagai B.

    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.

  15. The Evolution of Star Formation Activity in Cluster Galaxies Over 0.15 < z < 1.5

    NASA Astrophysics Data System (ADS)

    Wagner, Cory R.

    In this thesis, we explore 7.5 billion years of evolution in cluster galaxy star formation activity using a sample of 11 high-redshift (1 < z < 1.5) clusters from the IRAC Shallow Cluster Survey, and 25 low-redshift (0.15 < z < 1) clusters from The Cluster Lensing And Supernova survey with Hubble. We compare cluster galaxy star formation to that of the field over 0.15 < z < 1.5 using 8000 galaxies from the UltraVISTA survey. Mid-infrared star formation rates are measured using Spitzer 24 mum data for isolated high-redshift galaxies. We calculate rest-frame ultraviolet star formation rates for low-redshift cluster members using Hubble Space Telescope observations. Using publically available mid-infrared and ultraviolet data for our field sample, we empirically derive scaling relations to adjust low-redshift cluster galaxy ultraviolet star formation rates to mid-infrared levels. We classify cluster galaxy morphology by visual inspection, and use quantitatively measured morphologies for field galaxies. Cluster late-type galaxies at z > 1 show enhanced star formation activity relative to the field, and account for nearly 90% of the overall star formation activity in high-redshift clusters. While high-redshift early-type galaxies are substantially quenched relative to cluster late-types, they still contribute 13% of the total cluster star formation activity. With early-type fractions increasing from 34 to 56% from z 1.5 → 1.16, we find that new cluster early-type galaxies are likely being formed around z 1.4. The fraction of early-type galaxies that are star-forming drops from 29 to 11% over this period, yet their specific star formation rates are roughly constant. These factors suggest that the events that created these new galaxies, possibly mergers, were both recent and gas-rich. With typical coverages of 50% of z < 1 cluster virial radii, we can only probe the cores of low-redshift clusters. We find that in this regime, the star formation activity of cluster

  16. Star cluster dynamics.

    PubMed

    Vesperini, Enrico

    2010-02-28

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

  17. Initial conditions of formation of starburst clusters: constraints from stellar dynamics

    NASA Astrophysics Data System (ADS)

    Banerjee, Sambaran; Kroupa, Pavel

    2015-08-01

    Recent high resolution observations of dense regions of molecular clouds and massive gaseous clumps with instruments like Herschel and ALMA have revealed intricate and filamentary overdensity structures in them. Such progenitors of massive starburst clusters are in contrast with smooth, centrally-pronounced profiles of the latter. In this work, we intend to constrain massive, substructured stellar distributions that would evolve to cluster-like profiles at very young ages (~Myr), as seen in starburst clusters. Taking the well observed NGC3603 Young Cluster (NYC) as an example, we compute the infall and final merger of filament-like compact (0.1-0.3 pc) subclusters, totalling 10000 M_sun, from a range of spatial scales and modes of sub-clustering, using direct N-body calculations. These calculations infer an allowable span of approx. 2.5 pc from which the subclusters can fall in a gas potential and merge to form a single centrally-dense structure in near dynamical equilibrium, within the young age of NYC (1-2 Myr). However, these merged clusters are too compact and centrally overdense compared to typical young clusters. Our N-body calculations, beginning from such compact initial conditions, show that even stellar wind and supernova mass loss, dynamical heating from retaining black holes, external tidal field and heating due to tight O-star binaries together cannot expand these clusters to their observed sizes, even in 100 Myr. Hence an explosive gas dispersal phase seems essential for forming starburst and other young clusters observed in the Milky Way and in the Local Group which can expand the clusters to their observed sizes and concentrations; including that for NYC with approx. 30% clump star formation efficiency. However, some observed massive but highly extended (>10 pc) , >10 Myr old clusters better fit a slow (several Myr timescale) gas dispersal from parsec-scale initial profiles, which can be the future of embedded systems like W3 Main.

  18. GAS RESERVOIRS AND STAR FORMATION IN A FORMING GALAXY CLUSTER AT zbsime0.2

    SciTech Connect

    Jaffe, Yara L.; Poggianti, Bianca M.; Verheijen, Marc A. W.; Deshev, Boris Z.; Van Gorkom, Jacqueline H.

    2012-09-10

    We present first results from the Blind Ultra-Deep H I Environmental Survey of the Westerbork Synthesis Radio Telescope. Our survey is the first direct imaging study of neutral atomic hydrogen gas in galaxies at a redshift where evolutionary processes begin to show. In this Letter we investigate star formation, H I content, and galaxy morphology, as a function of environment in Abell 2192 (at z = 0.1876). Using a three-dimensional visualization technique, we find that Abell 2192 is a cluster in the process of forming, with significant substructure in it. We distinguish four structures that are separated in redshift and/or space. The richest structure is the baby cluster itself, with a core of elliptical galaxies that coincides with (weak) X-ray emission, almost no H I detections, and suppressed star formation. Surrounding the cluster, we find a compact group where galaxies pre-process before falling into the cluster, and a scattered population of 'field-like' galaxies showing more star formation and H I detections. This cluster proves to be an excellent laboratory to understand the fate of the H I gas in the framework of galaxy evolution. We clearly see that the H I gas and the star formation correlate with morphology and environment at z {approx} 0.2. In particular, the fraction of H I detections is significantly affected by the environment. The effect starts to kick in in low-mass groups that pre-process the galaxies before they enter the cluster. Our results suggest that by the time the group galaxies fall into the cluster, they are already devoid of H I.

  19. THE RICH GLOBULAR CLUSTER SYSTEM OF ABELL 1689 AND THE RADIAL DEPENDENCE OF THE GLOBULAR CLUSTER FORMATION EFFICIENCY

    SciTech Connect

    Alamo-Martínez, K. A.; González-Lópezlira, R. A.; Blakeslee, J. P.; Côté, P.; Ferrarese, L.; Jee, M. J.; Jordán, A.; Meurer, G. R.; Peng, E. W.; West, M. J.

    2013-09-20

    We study the rich globular cluster (GC) system in the center of the massive cluster of galaxies Abell 1689 (z = 0.18), one of the most powerful gravitational lenses known. With 28 Hubble Space Telescope/Advanced Camera for Surveys orbits in the F814W bandpass, we reach a magnitude I{sub 814} = 29 with ∼>90% completeness and sample the brightest ∼5% of the GC system. Assuming the well-known Gaussian form of the GC luminosity function (GCLF), we estimate a total population of N{sup total}{sub GC}= 162,850{sup +75,450}{sub -51,310} GCs within a projected radius of 400 kpc. As many as half of the GCs may comprise an intracluster component. Even with the sizable uncertainties, which mainly result from the uncertain GCLF parameters, this system is by far the largest GC population studied to date. The specific frequency S{sub N} is high, but not uncommon for central galaxies in massive clusters, rising from S{sub N} ≈ 5 near the center to ∼12 at large radii. Passive galaxy fading would increase S{sub N} by ∼20% at z = 0. We construct the radial mass profiles of the GCs, stars, intracluster gas, and lensing-derived total mass, and we compare the mass fractions as a function of radius. The estimated mass in GCs, M{sub GC}{sup total} = 3.9 × 10{sup 10} M{sub ☉}, is comparable to ∼80% of the total stellar mass of the Milky Way. The shape of the GC mass profile appears intermediate between those of the stellar light and total cluster mass. Despite the extreme nature of this system, the ratios of the GC mass to the baryonic and total masses, and thus the GC formation efficiency, are typical of those in other rich clusters when comparing at the same physical radii. The GC formation efficiency is not constant, but varies with radius, in a manner that appears similar for different clusters; we speculate on the reasons for this similarity in profile.

  20. Formation of the Fe-S cluster of ferredoxin in lysed spinach chloroplasts. [Spinacia oleracea

    SciTech Connect

    Takahashi, Yasuhiro; Mitsui, Akira; Matsubara, Hiroshi )

    1991-01-01

    In vitro formation of the {sup 35}S-labeled Fe-S cluster of ferredoxin (Fd) has been achieved by incubating apo-Fd and ({sup 35}S)cysteine with osmotically lysed chloroplasts of spinach (Spinacia oleracea). Correct integration of the {sup 35}S-labeled Fe-S cluster into Fd was verified on the basis of the following: (a) Under nondenaturing conditions, {sup 35}S-labeled holo-Fd showed the same electrophoretic mobility as authentic holo-Fd; (b) {sup 35}S-labeled holo-Fd showed an ability to bind Fd-NADP{sup +} reductase; (c) the {sup 35}S-labeled moiety was removed from the Fd polypeptide by TCA treatment but not by 2-mercaptoethanol treatment; (d) externally added pea II apo-Fd was converted to {sup 35}S-labeled holo-Fd. This reconstitution was dependent on both ATP and light, and formation of the {sup 35}S-labeled Fe-S cluster was observed upon addition of ATP or when an ATP generation-system was constructed in the light. In contrast, ATP-consuming systems abolished the Fe-S cluster formation. A non-hydrolyzable ATP analog was unable to serve as an ATP substitute, indicating the requirement of ATP hydrolysis for cluster formation. GTP was able to substitute for ATP, but CTP and UTP were less effective. Fe-S cluster formation in lysed chloroplasts was stimulated by light even in the presence of added ATP. Light stimulation was inhibited by DCMU or methyl viologen but not by NH{sub 4}{sup +}. NADPH was able to substitute for light, indicating that light energy is required for the production of reducing compounds such as NADPH in addition to the generation of ATP.

  1. Alloy Formation of Supported Gold Nanoparticles at Their Transition from Clusters to Solids: Does Size Matter?

    NASA Astrophysics Data System (ADS)

    Boyen, H.-G.; Ethirajan, A.; Kästle, G.; Weigl, F.; Ziemann, P.; Schmid, G.; Garnier, M. G.; Büttner, M.; Oelhafen, P.

    2005-01-01

    Gold nanoclusters of a size approaching the molecular limit (<3 nm) were prepared on Si substrates in order to study alloy formation on the nanometer scale. For this purpose, indium atoms are deposited on top of the gold particles at room temperature and the formation of AuIn2 is studied by x-ray photoelectron spectroscopy insitu. It is observed that the alloy formation takes place independent of whether the particles electronically are in an insulating molecular or in a metallic state. Most important, however, closed packed full-shell clusters containing 55 Au atoms are found to exhibit an outstanding stability against alloying despite a large negative heat of formation of the bulk Au-In system. Thus, Au55 clusters may play a significant role in the design of nanoscaled devices where chemical inertness is of crucial importance.

  2. Formation of regular polyicosahedral structure during growth of large Lennard-Jones clusters from their global minimum

    NASA Astrophysics Data System (ADS)

    Polak, Wiesław Z.

    2016-08-01

    Simulated growth of four global-minimum Lennard-Jones clusters of sizes N = 561, 823, 850 and 923, representing multishell icosahedra and decahedron, always leads to formation of regular polyicosahedral clusters. Observation of cluster structure evolution revealed that new atoms form anti-Mackay islands spreading over the cluster surface by making strong island-island junctions at cluster edges. Analysis of potential energies of atoms composing different local structures shows that energy-driven preference for decahedral arrangement of several atoms initiating the junction of pentagonal symmetry on the cluster surface is responsible for kinetic effect in the cluster growth.

  3. INFRARED AND ULTRAVIOLET STAR FORMATION IN BRIGHTEST CLUSTER GALAXIES IN THE ACCEPT SAMPLE

    SciTech Connect

    Hoffer, Aaron S.; Donahue, Megan; Hicks, Amalia; Barthelemy, R. S. E-mail: donahue@pa.msu.edu E-mail: ramon.s.barthelemy@wmich.edu

    2012-03-01

    We present infrared (IR) and ultraviolet (UV) photometry for a sample of brightest cluster galaxies (BCGs). The BCGs are from a heterogeneous but uniformly characterized sample, the Archive of Chandra Cluster Entropy Profile Tables (ACCEPT), of X-ray galaxy clusters from the Chandra X-ray telescope archive with published gas temperature, density, and entropy profiles. We use archival Galaxy Evolution Explorer (GALEX), Spitzer Space Telescope, and Two Micron All Sky Survey (2MASS) observations to assemble spectral energy distributions (SEDs) and colors for BCGs. We find that while the SEDs of some BCGs follow the expectation of red, dust-free old stellar populations, many exhibit signatures of recent star formation in the form of excess UV or mid-IR emission, or both. We establish a mean near-UV (NUV) to 2MASS K color of 6.59 {+-} 0.34 for quiescent BCGs. We use this mean color to quantify the UV excess associated with star formation in the active BCGs. We use both fits to a template of an evolved stellar population and library of starburst models and mid-IR star formation relations to estimate the obscured star formation rates (SFRs). We show that many of the BCGs in X-ray clusters with low central gas entropy exhibit enhanced UV (38%) and mid-IR emission (43%) from 8 to 160 {mu}m, above that expected from an old stellar population. These excesses are consistent with ongoing star formation activity in the BCG, star formation that appears to be enabled by the presence of high-density, X-ray-emitting intergalactic gas in the core of the cluster of galaxies. This hot, X-ray-emitting gas may provide the enhanced ambient pressure and some of the fuel to trigger star formation. This result is consistent with previous works that showed that BCGs in clusters with low central gas entropies host H{alpha} emission-line nebulae and radio sources, while clusters with high central gas entropy exhibit none of these features. GALEX UV and Spitzer mid-IR measurements combined

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

    NASA Astrophysics Data System (ADS)

    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.

  5. Universal few-body physics and cluster formation

    NASA Astrophysics Data System (ADS)

    Greene, Chris H.; Giannakeas, P.; Pérez-Ríos, J.

    2017-07-01

    A recent rejuvenation of experimental and theoretical interest in the physics of few-body systems has provided deep, fundamental insights into a broad range of problems. Few-body physics is a cross-cutting discipline not restricted to conventional subject areas such as nuclear physics or atomic or molecular physics. To a large degree, the recent explosion of interest in this subject has been sparked by dramatic enhancements of experimental capabilities in ultracold atomic systems over the past decade, which now permit atoms and molecules to be explored deep in the quantum mechanical limit with controllable two-body interactions. This control, typically enabled by magnetic or electromagnetically dressed Fano-Feshbach resonances, allows, in particular, access to the range of universal few-body physics, where two-body scattering lengths far exceed all other length scales in the problem. The Efimov effect, where three particles experiencing short-range interactions can counterintuitively exhibit an infinite number of bound or quasibound energy levels, is the most famous example of universality. Tremendous progress in the field of universal Efimov physics has taken off, driven particularly by a combination of experimental and theoretical studies in the past decade, and prior to the first observation in 2006, by an extensive set of theoretical studies dating back to 1970. Because experimental observations of Efimov physics have usually relied on resonances or interference phenomena in three-body recombination, this connects naturally with the processes of molecule formation in a low-temperature gas of atoms or nucleons, and more generally with N -body recombination processes. Some other topics not closely related to the Efimov effect are also reviewed in this article, including confinement-induced resonances for explorations of lower-dimensionality systems, and some chemically interesting systems with longer-range forces such as the ion-atom-atom recombination problem.

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

    NASA Technical Reports Server (NTRS)

    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.

  7. Star Formation in Intermediate Redshift 0.2 < z < 0.7 Brightest Cluster Galaxies

    NASA Astrophysics Data System (ADS)

    Cooke, Kevin C.; O'Dea, Christopher P.; Baum, Stefi A.; Tremblay, Grant R.; Cox, Isabella G.; Gladders, Michael

    2016-12-01

    We present a multi-wavelength photometric and spectroscopic study of 42 Brightest Cluster Galaxies (BCGs) in two samples of galaxy clusters chosen for a gravitational lensing study. The study’s initial sample combines 25 BCGs from the Cluster Lensing and Supernova Survey with Hubble sample and 37 BCGs from the Sloan Giant Arcs Survey with a total redshift range of 0.2< z< 0.7. Using archival GALEX, Hubble Space Telescope, Wide-Field Infrared Survey Explorer, Herschel, and Very Large Array 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 active galactic nucleus (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 suggest that star formation is no longer a significant channel for galaxy growth for z ≤slant 1. Instead, stellar growth (of the order of a factor of at least two) during this period is expected to occur mainly via minor dry mergers.

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

    PubMed

    Kürten, Andreas; Jokinen, Tuija; 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

    2014-10-21

    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 though the neutral particles are stable against evaporation from the SA dimer onward, the formation rates of particles at 1.7-nm size, which contain about 10 SA molecules, are up to 4 orders of magnitude smaller compared with those of the dimer due to coagulation and wall loss of particles before they reach 1.7 nm in diameter. This demonstrates that neither the atmospheric particle formation rate nor its dependence on SA can simply be interpreted in terms of cluster evaporation or the molecular composition of a critical nucleus.

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

    PubMed Central

    Kürten, Andreas; Jokinen, Tuija; 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 though the neutral particles are stable against evaporation from the SA dimer onward, the formation rates of particles at 1.7-nm size, which contain about 10 SA molecules, are up to 4 orders of magnitude smaller compared with those of the dimer due to coagulation and wall loss of particles before they reach 1.7 nm in diameter. This demonstrates that neither the atmospheric particle formation rate nor its dependence on SA can simply be interpreted in terms of cluster evaporation or the molecular composition of a critical nucleus. PMID:25288761

  10. The Location, Clustering, and Propagation of Massive Star Formation in Giant Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Ochsendorf, Bram B.; Meixner, Margaret; Chastenet, Jérémy; Tielens, Alexander G. G. M.; Roman-Duval, Julia

    2016-11-01

    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 data set of ∼600 massive young stellar objects, ∼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. However, whether a cloud is associated with an SC does not depend on either the cloud’s mass or global surface density. These results reveal a connection between different generations of massive stars on timescales up to 10 Myr. We compare our work with Galactic studies and discuss our findings in terms of GMC collapse, triggered star formation, and a potential dichotomy between low- and high-mass star formation.

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

    NASA Astrophysics Data System (ADS)

    Ochsendorf, Bram; Meixner, Margaret; Chastenet, Jeremy; Tielens, A. G. G. M.; Roman-Duval, Julia

    2017-01-01

    Massive stars are key players in the evolution of galaxies, yet their formation pathway remains unclear. In this talk, I will highlight results from a project utilizing 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 have employed this data to quantitatively study the location and clustering of massive star formation and its relation to the internal structure of GMCs. The main results are as follows: (1) Massive stars do not typically form at the highest column densities nor centers of their parent GMCs. (2) Massive star formation clusters over multiple generations and on size scales much smaller than the size of the parent GMC. (3) The rate of massive star formation is significantly boosted in clouds near SCs. Yet, comparison of molecular clouds associated with SCs with those that are not reveals no significant difference in their global properties. These results reveal a connection between different generations of massive stars on timescales up to 10 Myr. I will compare our findings with Galactic studies and discuss this in terms of GMC collapse, triggered star formation, and a potential dichotomy between low- and high-mass star formation.

  12. PROGRESSIVE STAR FORMATION IN THE YOUNG GALACTIC SUPER STAR CLUSTER NGC 3603

    SciTech Connect

    Beccari, Giacomo; Spezzi, Loredana; De Marchi, Guido; Andersen, Morten; Paresce, Francesco; Young, Erick; Panagia, Nino; Bond, Howard; Balick, Bruce; 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

    2010-09-10

    Early Release Science observations of the cluster NGC 3603 with the WFC3 on the refurbished Hubble Space Telescope allow us to study its recent star formation history. Our analysis focuses on stars with H{alpha} 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 H{alpha} 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.

  13. Entropy-driven formation of large icosahedral colloidal clusters by spherical confinement

    NASA Astrophysics Data System (ADS)

    de Nijs, Bart; Dussi, Simone; Smallenburg, Frank; Meeldijk, Johannes D.; Groenendijk, Dirk J.; Filion, Laura; Imhof, Arnout; van Blaaderen, Alfons; Dijkstra, Marjolein

    2015-01-01

    Icosahedral symmetry, which is not compatible with truly long-range order, can be found in many systems, such as liquids, glasses, atomic clusters, quasicrystals and virus-capsids. To obtain arrangements with a high degree of icosahedral order from tens of particles or more, interparticle attractive interactions are considered to be essential. Here, we report that entropy and spherical confinement suffice for the formation of icosahedral clusters consisting of up to 100,000 particles. Specifically, by using real-space measurements on nanometre- and micrometre-sized colloids, as well as computer simulations, we show that tens of thousands of hard spheres compressed under spherical confinement spontaneously crystallize into icosahedral clusters that are entropically favoured over the bulk face-centred cubic crystal structure. Our findings provide insights into the interplay between confinement and crystallization and into how these are connected to the formation of icosahedral structures.

  14. Two-Dimensional Nanoparticle Cluster Formation in Supercritical Fluid CO2.

    PubMed

    Wang, Joanna S; Wai, Chien M; Brown, Gail J; Apt, Scott D

    2016-05-10

    Supercritical fluid carbon dioxide (sc-CO2) is capable of depositing nanoparticles in small structures of silicon substrates because of its gas-like penetration, liquid-like solvation abilities, and near-zero surface tension. In nanometer-sized shallow wells on silicon surface, formation of two-dimensional (2D) monolayer metal nanoparticle (NP) clusters can be achieved using the sc-CO2 deposition method. Nanoparticles tend to fill nanostructured holes first, and then, if sufficient nanoparticles are available, they will continue to cover the flat areas nearby, unless defects or other surface imperfections are available. In addition, SEM images of two-dimensional gold (Au) nanoparticle clusters formed on a flat silicon surface with two to a dozen or more of the nanoparticles are provided to illustrate the patterns of nanoparticle cluster formation in sc-CO2.

  15. Accretion-driven star formation in central dominant galaxies in X-ray clusters

    NASA Astrophysics Data System (ADS)

    Sarazin, C. L.; Oconnell, R. W.

    1983-05-01

    Analytical and observational evidence for the formation of low-mass stars in the gas accreting in the central dominant galaxies in clusters is presented. Observations of the (U-V) and (K-V) color gradients in accreting galaxies are suggested to reveal colors altered by the appearance of young stars, e.g., the excess blue and the A star spectrum detected in NGC 1275. Low-temperature X ray line emissions from accreting galaxies have been partially surveyed with the result that 10 pct of the brightest cluster galaxies in a magnitude-limited sample show evidence of significant accretion. Photometric data from the quasar 3C 48, located in a galaxy with a very blue population, also suggests low-mass star formation, especially when compared to measurements of NGC 1275, which has the highest accretion rate among observed central dominant cluster galaxies. The quasar, however, would not be accreting interstellar gas.

  16. Turbulent Coagulation of Solid Particles in Molten Aluminium—Kinetics of Cluster Formation

    NASA Astrophysics Data System (ADS)

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

    Removal of inclusions plays a key role in the process of aluminum recycling. Many research works focus on the behaviors of inclusions in molten metal, such as particle coagulation. To reveal its mechanism water model experiments have been performed by some researchers including the authors' group. In the present research, experiments of particle coagulation were carried out with molten Al including SiC particles in a mechanically agitated system. Particle coagulation and formation of clusters were observed under turbulent flow of the molten Al. The number of clusters in the metal decreased with agitating time whilst the size increased. 3-D analysis of the clusters in solidified Al was implemented by X-ray micro CT in SPring-8. A 3-D image analysis was adopted to a number of sliced 2-D images, and the size and structure of the SiC cluster were analyzed.

  17. X-ray irradiation-induced formation of luminescent silver clusters in nanoporous matrices.

    PubMed

    Coutino-Gonzalez, Eduardo; Grandjean, Didier; Roeffaers, Maarten; Kvashnina, Kristina; Fron, Eduard; Dieu, Bjorn; De Cremer, Gert; Lievens, Peter; Sels, Bert; Hofkens, Johan

    2014-02-09

    We report the formation of luminescent silver clusters in zeolites by a fast, highly accurate, and controlled activation of silver ions entrapped in sodalite cages of LTA and FAU zeolites using high-brilliance soft X-rays. The activated luminescent samples were investigated by employing a combination of stationary and time-resolved spectroscopic techniques.

  18. Real-Time Characterization of Formation and Breakup of Iridium Clusters in Highly Dealuminated Zeolite Y

    SciTech Connect

    Uzun, Alper; Gates, Bruce C.

    2009-01-15

    The chemistry of formation of iridium clusters from mononuclear iridium diethylene complexes anchored in dealuminated Y zeolite, and their subsequent breakup -- all including changes in the metal-metal, metal-support, and metal-ligand interactions -- is demonstrated by time-resolved EXAFS, XANES, and IR spectroscopy.

  19. The Link between the Formation Rates of Clusters and Stars in Galaxies

    NASA Astrophysics Data System (ADS)

    Chandar, Rupali; Fall, S. Michael; Whitmore, Bradley C.

    2015-09-01

    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}\\propto {M}β , with similar exponents β =-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 Hα luminosities, and find that the spread in the amplitudes collapses, with a remaining rms deviation of only σ ({log}A)=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 proportionality between the formation rates of stars and clusters. However, the data also permit weak deviations from proportionality, at the factor of two level, within the statistical uncertainties. We find the same spread in amplitudes when we normalize the mass functions of much older clusters, with ages in the range 100-400 Myr, by the current SFR. This is another indication of the general similarity among the cluster populations of different galaxies.

  20. Cluster formation by allelomimesis in real-world complex adaptive systems

    NASA Astrophysics Data System (ADS)

    Juanico, Dranreb Earl; Monterola, Christopher; Saloma, Caesar

    2005-04-01

    Animal and human clusters are complex adaptive systems and many organize in cluster sizes s that obey the frequency distribution D(s)∝s-τ . The exponent τ describes the relative abundance of the cluster sizes in a given system. Data analyses reveal that real-world clusters exhibit a broad spectrum of τ values, 0.7 (tuna fish schools) ⩽τ⩽4.61 (T4 bacteriophage gene family sizes). Allelomimesis is proposed as an underlying mechanism for adaptation that explains the observed broad τ spectrum. Allelomimesis is the tendency of an individual to imitate the actions of others and two cluster systems have different τ values when their component agents display unequal degrees of allelomimetic tendencies. Cluster formation by allelomimesis is shown to be of three general types: namely, blind copying, information-use copying, and noncopying. Allelomimetic adaptation also reveals that the most stable cluster size is formed by three strongly allelomimetic individuals. Our finding is consistent with available field data taken from killer whales and marmots.

  1. Changing role of carrier gas in formation of ethanol clusters by adiabatic expansion

    NASA Astrophysics Data System (ADS)

    Abu-samha, Mahmoud; Ryding, Mauritz J.; Uggerud, Einar; Sæthre, Leif J.; Børve, Knut J.

    2017-07-01

    Adiabatic expansion of molecular vapors is a celebrated method for producing pure and mixed clusters of relevance in both applied and fundamental studies. The present understanding of the relationship between experimental conditions and the structure of the clusters formed is incomplete. We explore the role of the backing/carrier gas during adiabatic expansion of ethanol vapors with regard to cluster production and composition. Single-component clusters of ethanol were produced over a wide size-range by varying the rare gas (He, Ar) backing pressure, with Ar being more efficient than He in promoting the formation of pure ethanol clusters. However, at stagnation pressures Ps>1.34 (4 ) bar and temperature 49 (2) °C, synchrotron-based valence and inner-shell photoelectron spectroscopy reveals condensation of Ar carrier gas on the clusters. Theoretical calculations of cluster geometries as well as chemical shifts in carbon 1s ionization energies confirm that the experimental observations are consistent with an ethanol core covered by an outer shell of argon. Experiments on the 1-propanol/Ar system display a similar pattern as described for ethanol/Ar, indicating a broader range of validity of the results.

  2. Star formation activity of intermediate redshift cluster galaxies out to the infall regions

    NASA Astrophysics Data System (ADS)

    Gerken, B.; Ziegler, B.; Balogh, M.; Gilbank, D.; Fritz, A.; Jäger, K.

    2004-07-01

    We present a spectroscopic analysis of two galaxy clusters at z≈0.2, out to ˜4 Mpc. The two clusters VMF73 and VMF74 as identified by \\citet{VMFJQH98} were observed with multiple object spectroscopy using MOSCA at the Calar Alto 3.5 m telescope. Both clusters lie in the ROSAT Position Sensitive Proportional Counter field R285 and were selected from the X-ray Dark Cluster Survey \\citep{GBCZ04} that provides optical V- and I-band data. VMF73 and VMF74 are located at respective redshifts of z=0.25 and z=0.18 with velocity dispersions of 671 km s-1 and 442 km s-1, respectively. Both cluster velocity dispersions are consistent with Gaussians. The spectroscopic observations reach out to ˜2.5 virial radii. Line strength measurements of the emission lines Hα and [O II]λ3727 are used to assess the star formation activity of cluster galaxies which show radial and density dependences. The mean and median of both line strength distributions as well as the fraction of star forming galaxies increase with increasing clustercentric distance and decreasing local galaxy density. Except for two galaxies with strong Hα and [O II] emission, all of the cluster galaxies are normal star forming or passive galaxies. Our results are consistent with other studies that show the truncation in star formation occurs far from the cluster centre. Table A.1 is only available in electronic from at http//www.edpsciences.org

  3. Mechanism of Acetylcholine Receptor Cluster Formation Induced by DC Electric Field

    PubMed Central

    Zhang, Hailong Luke; Peng, H. Benjamin

    2011-01-01

    Background The formation of acetylcholine receptor (AChR) cluster is a key event during the development of the neuromuscular junction. It is induced through the activation of muscle-specific kinase (MuSK) by the heparan-sulfate proteoglycan agrin released from the motor axon. On the other hand, DC electric field, a non-neuronal stimulus, is also highly effective in causing AChRs to cluster along the cathode-facing edge of muscle cells. Methodology/Principal Findings To understand its molecular mechanism, quantum dots (QDs) were used to follow the movement of AChRs as they became clustered under the influence of electric field. From analyses of trajectories of AChR movement in the membrane, it was concluded that diffuse receptors underwent Brownian motion until they were immobilized at sites of cluster formation. This supports the diffusion-mediated trapping model in explaining AChR clustering under the influence of this stimulus. Disrupting F-actin cytoskeleton assembly and interfering with rapsyn-AChR interaction suppressed this phenomenon, suggesting that these are integral components of the trapping mechanism induced by the electric field. Consistent with the idea that signaling pathways are activated by this stimulus, the localization of tyrosine-phosphorylated forms of AChR β-subunit and Src was observed at cathodal AChR clusters. Furthermore, disrupting MuSK activity through the expression of a kinase-dead form of this enzyme abolished electric field-induced AChR clustering. Conclusions These results suggest that DC electric field as a physical stimulus elicits molecular reactions in muscle cells in the form of cathodal MuSK activation in a ligand-free manner to trigger a signaling pathway that leads to cytoskeletal assembly and AChR clustering. PMID:22046365

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

    NASA Astrophysics Data System (ADS)

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

    2008-10-01

    We compare the results from a state-of-the-art semianalytic model of galaxy formation with spectrophotometric 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 (1) 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 is observed and predicted at z = 0; (2) 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 ≈5 times smaller than the corresponding field value; (3) 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 Gyr; and (4) the predicted distribution of stellar ages of RS galaxies at z = 1.2 peaks at 3.7 Gyr for both cluster and field populations; 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 ΔU - V ≈ 0.07 of the observed cluster RS scatter 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.

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

    PubMed

    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.

  6. The formation and evolution of M33 as revealed by its star clusters

    NASA Astrophysics Data System (ADS)

    San Roman, Izaskun

    2012-03-01

    Numerical simulations based on the Lambda-Cold Dark Matter (Λ-CDM) model predict a scenario consistent with observational evidence in terms of the build-up of Milky Way-like halos. Under this scenario, large disk galaxies derive from the merger and accretion of many smaller subsystems. However, it is less clear how low-mass spiral galaxies fit into this picture. The best way to answer this question is to study the nearest example of a dwarf spiral galaxy, M33. We will use star clusters to understand the structure, kinematics and stellar populations of this galaxy. Star clusters provide a unique and powerful tool for studying the star formation histories of galaxies. In particular, the ages and metallicities of star clusters bear the imprint of the galaxy formation process. We have made use of the star clusters to uncover the formation and evolution of M33. In this dissertation, we have carried out a comprehensive study of the M33 star cluster system, including deep photometry as well as high signal-to-noise spectroscopy. In order to mitigate the significant incompleteness presents in previous catalogs, we have conducted ground-based and space-based photometric surveys of M33 star clusters. Using archival images, we have analyzed 12 fields using the Advanced Camera for Surveys Wide Field Channel onboard the Hubble Space Telescope (ACS/HST) along the major axis of the galaxy. We present integrated photometry and color-magnitude diagrams for 161 star clusters in M33, of which 115 were previously uncataloged. This survey extends the depth of the existing M33 cluster catalogs by ˜ 1 mag. We have expanded our search through a photometric survey in a 1° x 1° area centered on M33 using the MegaCam camera on the 3.6m Canada-France-Hawaii Telescope (CFHT). In this work we discuss the photometric properties of the sample, including color-color diagrams of 599 new candidate stellar clusters, and 204 confirmed clusters. Comparisons with models of simple stellar populations

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

    NASA Astrophysics Data System (ADS)

    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 < 1m. The cluster luminosity function (CLF) is well-fitted by a power law with an exponent of around -2 and displays no evidence of a high luminosity cut-off. The brightest cluster complexes in the disk reach luminosities of MK = -15.5m or estimated masses of 106 M⊙. At radii with a strong, two-armed spiral 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

  8. Frataxin Accelerates [2Fe-2S] Cluster Formation on the Human Fe–S Assembly Complex

    PubMed Central

    Fox, Nicholas G.; Das, Deepika; Chakrabarti, Mrinmoy; Lindahl, Paul A.; Barondeau, David P.

    2015-01-01

    Iron–sulfur (Fe–S) clusters function as protein cofactors for a wide variety of critical cellular reactions. In human mitochondria, a core Fe–S assembly complex [called SDUF and composed of NFS1, ISD11, ISCU2, and frataxin (FXN) proteins] synthesizes Fe–S clusters from iron, cysteine sulfur, and reducing equivalents and then transfers these intact clusters to target proteins. In vitro assays have relied on reducing the complexity of this complicated Fe–S assembly process by using surrogate electron donor molecules and monitoring simplified reactions. Recent studies have concluded that FXN promotes the synthesis of [4Fe-4S] clusters on the mammalian Fe–S assembly complex. Here the kinetics of Fe–S synthesis reactions were determined using different electron donation systems and by monitoring the products with circular dichroism and absorbance spectroscopies. We discovered that common surrogate electron donor molecules intercepted Fe–S cluster intermediates and formed high-molecular weight species (HMWS). The HMWS are associated with iron, sulfide, and thiol-containing proteins and have properties of a heterogeneous solubilized mineral with spectroscopic properties remarkably reminiscent of those of [4Fe-4S] clusters. In contrast, reactions using physiological reagents revealed that FXN accelerates the formation of [2Fe-2S] clusters rather than [4Fe-4S] clusters as previously reported. In the preceding paper [Fox, N. G., et al. (2015) Biochemistry 54, DOI: 10.1021/bi5014485], [2Fe-2S] intermediates on the SDUF complex were shown to readily transfer to uncomplexed ISCU2 or apo acceptor proteins, depending on the reaction conditions. Our results indicate that FXN accelerates a rate-limiting sulfur transfer step in the synthesis of [2Fe-2S] clusters on the human Fe–S assembly complex. PMID:26016518

  9. Repetitive motor learning induces coordinated formation of clustered dendritic spines in vivo.

    PubMed

    Fu, Min; Yu, Xinzhu; Lu, Ju; Zuo, Yi

    2012-02-19

    Many lines of evidence suggest that memory in the mammalian brain is stored with distinct spatiotemporal patterns. Despite recent progresses in identifying neuronal populations involved in memory coding, the synapse-level mechanism is still poorly understood. Computational models and electrophysiological data have shown that functional clustering of synapses along dendritic branches leads to nonlinear summation of synaptic inputs and greatly expands the computing power of a neural network. However, whether neighbouring synapses are involved in encoding similar memory and how task-specific cortical networks develop during learning remain elusive. Using transcranial two-photon microscopy, we followed apical dendrites of layer 5 pyramidal neurons in the motor cortex while mice practised novel forelimb skills. Here we show that a third of new dendritic spines (postsynaptic structures of most excitatory synapses) formed during the acquisition phase of learning emerge in clusters, and that most such clusters are neighbouring spine pairs. These clustered new spines are more likely to persist throughout prolonged learning sessions, and even long after training stops, than non-clustered counterparts. Moreover, formation of new spine clusters requires repetition of the same motor task, and the emergence of succedent new spine(s) accompanies the strengthening of the first new spine in the cluster. We also show that under control conditions new spines appear to avoid existing stable spines, rather than being uniformly added along dendrites. However, succedent new spines in clusters overcome such a spatial constraint and form in close vicinity to neighbouring stable spines. Our findings suggest that clustering of new synapses along dendrites is induced by repetitive activation of the cortical circuitry during learning, providing a structural basis for spatial coding of motor memory in the mammalian brain.

  10. Globular cluster formation from gravitational tidal effects of merging and interacting galaxies

    NASA Astrophysics Data System (ADS)

    Bekki, K.; Forbes, Duncan A.; Beasley, M. A.; Couch, W. J.

    2002-10-01

    We investigate the spatial, kinematic and chemical properties of globular cluster systems formed in merging and interacting galaxies using N-body-smoothed particle hydrodynamics (SPH) simulations. Although we cannot resolve individual clusters in our simulation, we assume that they form in collapsing molecular clouds when the local external gas pressure exceeds 105kB (where kB is the Boltzmann constant). Several simulations are carried out for a range of initial conditions and galaxy mass ratios. The input model spirals are given a halo globular cluster system similar to those observed for the Milky Way and M31. Gravitational tidal effects during galaxy merging and interaction lead to a dramatic increase in gas pressure, which exceeds our threshold and hence triggers new globular cluster formation. We investigate the properties of the globular cluster system in the remnant galaxy, such as the number density, the specific frequency, kinematic properties and the metallicity distribution. Different orbital conditions and mass ratios give rise to a range in globular cluster properties, particularly for the interaction models. Our key results are the following: the newly formed metal-rich clusters are concentrated at the centre of the merger remnant elliptical, whereas the metal-poor ones are distributed to the outer parts because of strong angular momentum transfer. The dissipative merging of present-day spirals, including chemical evolution, results in metal-rich clusters with a mean metallicity that is super-solar, i.e. much higher than is observed in elliptical galaxies. If elliptical galaxies form by dissipative major mergers, then they must do so at very early epochs when their discs contained low-metallicity gas. Our simulations show that the specific frequency can be increased in a dissipative major merger. However, when this occurs it results in a ratio of metal-poor to metal-rich clusters that is less than one, contrary to the ratio observed in many elliptical

  11. Evidence of enhanced formation episodes in the Galactic open cluster system

    NASA Astrophysics Data System (ADS)

    Piatti, A. E.

    2010-04-01

    Aims: The exciting debate about the existence of signs of enhanced formation of Galactic open clusters (OCs) is revisited here on the basis of a revised age distribution. Methods: The data were taken from the recently updated 2009 version of the Dias et al.'s 1787 OC catalogue. Results: We found that the present OC's age distribution presents two primary excesses at t ~ 10-15 Myr and 1.5 Gyr, which are signs of enhanced formation episodes similar to those that occurred in other galaxies (e.g., M 51, NGC 1705). When restricting the OC sample to those located in the solar neighbourhood, with the aim of avoiding incompleteness effects, we also find that these clusters are engraved with clear signs of enhanced formation at both ages.

  12. Acceleration of raindrop formation due to the tangling-clustering instability in a turbulent stratified atmosphere

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

    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- to 100 -μ m droplets. Observations show that this process takes only 15-20 min. 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), 10.1063/1.4816643] results in the formation of droplet clusters with drastically increased droplet number densities. The mechanism of the tangling clustering instability is much more effective than the previously considered by us the inertial clustering instability caused by the centrifugal effect of turbulent vortices. This is the reason of strong enhancement of the collision-coalescence rate inside the clusters. The mean-field theory of the droplet growth developed in this study can be useful for explanation of the observed fast growth of cloud droplets in warm clouds from the initial 1 -μ m -size droplets to 40- to 50 -μ m -size droplets within 15-20 min.

  13. Free energy of cluster formation and a new scaling relation for the nucleation rate

    SciTech Connect

    Tanaka, Kyoko K.; Tanaka, Hidekazu; Diemand, Jürg; Angélil, Raymond

    2014-05-21

    Recent very large molecular dynamics simulations of homogeneous nucleation with (1 − 8) × 10{sup 9} Lennard-Jones atoms [J. Diemand, R. Angélil, K. K. Tanaka, and H. Tanaka, J. Chem. Phys. 139, 074309 (2013)] allow us to accurately determine the formation free energy of clusters over a wide range of cluster sizes. This is now possible because such large simulations allow for very precise measurements of the cluster size distribution in the steady state nucleation regime. The peaks of the free energy curves give critical cluster sizes, which agree well with independent estimates based on the nucleation theorem. Using these results, we derive an analytical formula and a new scaling relation for nucleation rates: ln J{sup ′}/η is scaled by ln S/η, where the supersaturation ratio is S, η is the dimensionless surface energy, and J{sup ′} is a dimensionless nucleation rate. This relation can be derived using the free energy of cluster formation at equilibrium which corresponds to the surface energy required to form the vapor-liquid interface. At low temperatures (below the triple point), we find that the surface energy divided by that of the classical nucleation theory does not depend on temperature, which leads to the scaling relation and implies a constant, positive Tolman length equal to half of the mean inter-particle separation in the liquid phase.

  14. Acceleration of raindrop formation due to the tangling-clustering instability in a turbulent stratified atmosphere.

    PubMed

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

    2015-07-01

    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- to 100-μm droplets. Observations show that this process takes only 15-20 min. 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. The mechanism of the tangling clustering instability is much more effective than the previously considered by us the inertial clustering instability caused by the centrifugal effect of turbulent vortices. This is the reason of strong enhancement of the collision-coalescence rate inside the clusters. The mean-field theory of the droplet growth developed in this study can be useful for explanation of the observed fast growth of cloud droplets in warm clouds from the initial 1-μm-size droplets to 40- to 50-μm-size droplets within 15-20 min.

  15. miR-322/-503 cluster is expressed in the earliest cardiac progenitor cells and drives cardiomyocyte specification

    PubMed Central

    Shen, Xiaopeng; Soibam, Benjamin; Benham, Ashley; Xu, Xueping; Chopra, Mani; Peng, Xiaoping; Yu, Wei; Bao, Wenjing; Liang, Rui; Azares, Alon; Liu, Peijun; Gunaratne, Preethi H.; Mercola, Mark; Cooney, Austin J.; Schwartz, Robert J.; Liu, Yu

    2016-01-01

    Understanding the mechanisms of early cardiac fate determination may lead to better approaches in promoting heart regeneration. We used a mesoderm posterior 1 (Mesp1)-Cre/Rosa26-EYFP reporter system to identify microRNAs (miRNAs) enriched in early cardiac progenitor cells. Most of these miRNA genes bear MESP1-binding sites and active histone signatures. In a calcium transient-based screening assay, we identified miRNAs that may promote the cardiomyocyte program. An X-chromosome miRNA cluster, miR-322/-503, is the most enriched in the Mesp1 lineage and is the most potent in the screening assay. It is specifically expressed in the looping heart. Ectopic miR-322/-503 mimicking the endogenous temporal patterns specifically drives a cardiomyocyte program while inhibiting neural lineages, likely by targeting the RNA-binding protein CUG-binding protein Elav-like family member 1 (Celf1). Thus, early miRNAs in lineage-committed cells may play powerful roles in cell-fate determination by cross-suppressing other lineages. miRNAs identified in this study, especially miR-322/-503, are potent regulators of early cardiac fate. PMID:27512039

  16. Using Herschel Far-Infrared Photometry to Constrain Star Formation Rates in CLASH Cluster Galaxies

    NASA Astrophysics Data System (ADS)

    Larson, Rebecca L.; Postman, Marc; Fogarty, Kevin

    2016-01-01

    The Cluster Lensing And Supernova survey with Hubble (CLASH) program obtained broadband images of 25 massive galaxy clusters in 16 passbands from the UV to the near-IR. The data was taken with the Wide-field Camera 3 (WFC3), and the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST). These 25 clusters have also been observed in the mid-IR by Spitzer IRAC, the far-IR by the Herschel Space Observatory PACS and SPIRE, and in the x-ray by the Chandra and XMM observatories. We focused on the two brightest cluster galaxies (BCGs) in the survey (MACS1931.8-2653 and RXJ1532.9+3021) that have reddening-corrected UV-derived star formation rates (SFRs) > 100 M⊙ yr-1 as measured by Fogarty et al (2015). The inclusion of Herschel data provides unique constraints on dust content and independent estimates of the star formation rates in these interesting galaxies. We performed photometry on the five Herschel bands (100-500μm), and removed any contamination from other cluster members. We fit a UV-FIR SED to each galaxy to measure the bolometric dust luminosity (Lbol), which we use to derive the FIR obscured SFR. We calculate the sum of the measured UV unobscured SFR from the HST photometry and the FIR obscured SFR from the Herschel photometry to get a total SFR for these two BCGs. We compared this to the reddening-corrected SFRs and found they were in agreement within error. This confirms that the Kennicutt and Calzetti methods for calculating star formation rates are both applicable for these highly star-forming massive cluster galaxies.

  17. The Role of Dynamics in the Formation of Cataclysmic Variables in Globular Clusters

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

    Internal dynamics and stellar interactions in the high-density environments of globular clusters are likely to play a key role in the formation and evolution of X-ray sources in these stellar systems.Observational evidence in support of the role dynamical interactions in the formation of X-ray sources comes from a number of observational studies showing that the number of X-ray sources in globular clusters is correlated with the cluster stellar encounter rate.We present here the results of a survey of Monte-Carlo simulations exploring the role of dynamics in the formation of cataclysmic variables (CVs). Our simulations show a correlation between the number of CVs and the stellar encounter rate as found in observational studies and illustrate the dynamical path leading to this correlation.We also study the spatial distribution of CVs in clusters and find that they are more concentrated than single stars with masses close to those of turn-off stars at 12 Gyr. This trend is stronger for the population of CVs formed from primordial binaries undergoing exchange encounters.

  18. Glass formation and cluster evolution in the rapidly solidified monatomic metallic liquid Ta under high pressure

    NASA Astrophysics Data System (ADS)

    Jiang, Dejun; Wen, Dadong; Tian, Zean; Liu, Rangsu

    2016-12-01

    Molecular dynamics (MD) simulations have been performed to examine the glass formation and cluster evolution during the rapid solidification of monatomic metallic liquid Ta under high pressure. The atomic structures in the systems are characterized by the radical distribution function (RDF), Honeycutt-Anderson (H-A) bond-type index method and cluster-type index method (CTIM). It is observed that the defective icosahedra play the critical role in the formation of Ta monatomic metallic glasses (MGs) rather than (12 0 12 0) perfect icosahedra, which have been identified as the basic local atomic units in many multi-component MGs. With the increase of pressure P, the fraction of icosahedral type clusters decreases remarkably in Ta MGs, while the fraction of bcc type clusters rises evidently. The evolution of vitrification degree (DSRO or DMRO) of the rapidly cooled metal Ta system further reveals that a higher pressure P is disadvantageous to the formation of Ta monatomic MGs. The weaker glass forming ability (GFA) of liquid metal Ta obtained under higher pressure P can be contributed to the decrease of DSRO or DMRO which is induced by increasing high pressure P to some extent.

  19. Formation of the structures from dusty clusters in neon dc discharge under cooling

    NASA Astrophysics Data System (ADS)

    Polyakov, D. N.; Shumova, V. V.; Vasilyak, L. M.

    2016-11-01

    The formation of structures consisted of dusty clusters in plasma at the discharge tube cooling to a temperature of liquid nitrogen was discovered. The dependence of the reduced electric field in the positive column of a discharge on gas temperature was experimentally measured. Depending on the pressure of neon were observed the different structural transitions in the regions of growing current-voltage characteristics at low discharge currents ≤ 1 mA. It was found that the regions of existence of structured clusters and the regions of structural transitions were characterized by the higher values of the reduced electric field than the regions of destruction of ordered structures.

  20. Dehydrogenation of gaseous hydrogen-containing molecules: The formation of elemental and molecular clusters

    SciTech Connect

    Chen, Z.Y.; Walder, G.J.; Castleman, A.W. Jr. )

    1994-01-15

    A general concept employing the dehydrogenation of hydrogen-containing organic and inorganic compounds is shown to readily affect the production of a wide variety of elemental and binary clusters. Hydrogen-containing molecules such as C[sub 2]H[sub 4], NH[sub 3], SiH[sub 4], H[sub 2]S, or H[sub 2]O, are introduced into an extremely energetic plasma generated from laser irradiation of a metal surface; this plasma dehydrogenates the molecules to produce nascent C, N, Si, S, and O atoms. These C, N, Si, S, and O atoms can react with metal atoms or ions contained in the plasma and form metallocarbohedrenes or metal-carbide, metal-nitride, metal-silicide, metal-sulfide, or metal-oxide clusters. Alternatively, individual constituents may associate to produce pure elemental clusters such as those comprised of carbon or silicon. In principle, this technique can be applied to all gaseous hydrogen-containing compounds. The results of the present study provide an alternative way (in some cases it could be the only feasible way) to generate clusters of these materials. Study of the ensuing distributions provides unique insight into the cluster-formation mechanisms involving this type of cluster source.

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

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    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.

  2. Simulation of XenArm Cluster Formation in a Molecular Beam: Comparison with Photoelectron Spectroscopy

    NASA Astrophysics Data System (ADS)

    Amar, Francois G.; Preston, Thomas J.

    2006-03-01

    We perform direct MD simulations of the formation of mixed XenArm clusters (500clusters and compare them to the experimental spectra of Tchaplyguine et al[1]. The predicted spectra are calculated as the sum of final state energy shifts of the ionized atoms (within the cluster) relative to the isolated gas phase ion using a self-consistent polarization formalism. We use the results of our earlier calculations on pure argon and xenon clusters [2] to determine the appropriate inelastic mean free path value for the signal electrons leaving the mixed clusters. These results allow us to gain a refined understanding of the size, stoichiometry, and core/shell structure of these mixed clusters. [1] M. Tchaplyguine, et al, Phys. Rev A 69, 031201 (2004); [2] F. Amar, et al, JCP 122, 244717 (2005).

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

    PubMed

    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.

  4. Formation mechanism of atomic cluster structures in Al-Mg alloy during rapid solidification processes

    SciTech Connect

    Liu Fengxiang; Liu Rangsu Hou Zhaoyang; Liu Hairong; Tian Zean; Zhou Lili

    2009-02-15

    The rapid solidification processes of Al{sub 50}Mg{sub 50} liquid alloy consisting of 50,000 atoms have been simulated by using molecular dynamics method based on the effective pair potential derived from the pseudopotential theory. The formation mechanisms of atomic clusters during the rapid solidification processes have been investigated adopting a new cluster description method-cluster-type index method (CTIM). The simulated partial structure factors are in good agreement with the experimental results. And Al-Mg amorphous structure characterized with Al-centered icosahedral topological short-range order (SRO) is found to form during the rapid solidification processes. The icosahedral cluster plays a key role in the microstructure transition. Besides, it is also found that the size distribution of various clusters in the system presents a magic number sequence of 13, 19, 23, 25, 29, 31, 33, 37, .... The magic clusters are more stable and mainly correspond to the incompact arrangements of linked icosahedra in the form of rings, chains or dendrites. And each magic number point stands correspondingly for one certain combining form of icosahedra. This magic number sequence is different from that generated in the solidification structure of liquid Al and those obtained by methods of gaseous deposition and ionic spray, etc.

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

    SciTech Connect

    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.

  6. DISSIPATIONLESS FORMATION AND EVOLUTION OF THE MILKY WAY NUCLEAR STAR CLUSTER

    SciTech Connect

    Antonini, Fabio; Capuzzo-Dolcetta, Roberto; Mastrobuono-Battisti, Alessandra; Merritt, David

    2012-05-10

    In one widely discussed model for the formation of nuclear star clusters (NSCs), massive globular clusters spiral into the center of a galaxy and merge to form the nucleus. It is now known that at least some NSCs coexist with supermassive black holes (SMBHs); this is the case, for instance, in the Milky Way. In this paper, we investigate how the presence of an SMBH at the center of the Milky Way impacts the merger hypothesis for the formation of its NSC. Starting from a model consisting of a low-density nuclear stellar disk and the SMBH, we use direct N-body simulations to follow the successive inspiral and merger of globular clusters. The clusters are started on circular orbits of radius 20 pc, and their initial masses and radii are set up in such a way as to be consistent with the galactic tidal field at that radius. These clusters, decayed orbitally in the central region due to their large mass, were followed in their inspiral events; as a result, the total accumulated mass by Almost-Equal-To 10 clusters is about 1.5 Multiplication-Sign 10{sup 7} M{sub Sun }. Each cluster is disrupted by the SMBH at a distance of roughly 1 pc. The density profile that results after the final inspiral event is characterized by a core of roughly this radius and an envelope with density that falls off {rho} {approx} r{sup -2}. These properties are similar to those of the Milky Way NSC, with the exception of the core size, which in the Milky Way is somewhat smaller. But by continuing the evolution of the model after the final inspiral event, we find that the core shrinks substantially via gravitational encounters in a time (when scaled to the Milky Way) of 10 Gyr as the stellar distribution evolves toward a Bahcall-Wolf cusp. We also show that the luminosity function of the Milky Way NSC is consistent with the hypothesis that 1/2 of the mass comes from old ({approx}10 Gyr) stars, brought in by globular clusters, with the other half due to continuous star formation. We conclude that

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

    NASA Astrophysics Data System (ADS)

    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

  8. Multicolor photometry of the merging galaxy cluster A2319: Dynamics and star formation properties

    SciTech Connect

    Yan, Peng-Fei; Yuan, Qi-Rong; Zhang, Li; Zhou, Xu E-mail: yuanqirong@njnu.edu.cn

    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{sub −70}{sup +91} km s{sup –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 {sub 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

  9. The Formation and Evolution of the Large Magellanic Cloud from Selected Clusters and Star Fields

    NASA Astrophysics Data System (ADS)

    Olsen, Knut Anders Grova

    We have obtained deep Hubble Space Telescope color-magnitude diagrams of fields centered on the six old LMC globular clusters NGC 1754, NGC 1835, WGC 1898, NGC 1916, NGC 2005, and NGC 2019. The data have been carefully calibrated and the effects of crowding on the photometric accuracy have been thoroughly investigated. The observations have been used to produce V-I,V color-magnitude diagrams of the clusters and of the background field stars, which we have separated from each other through a statistical cleaning technique. The cluster color-magnitude diagrams show that the clusters are old, with main sequence turnoffs at V~ 22.5 and well-developed horizontal branches. We used the slopes of the red giant branches to measure the abundances, which we find to be 0.3 dex higher, on average, than previously measured spectroscopic abundances. In two cases there is significant variable reddening across at least part of the image, but only for NGC 1916 does differential reddening preclude accurate measurements of the CMD characteristics. The mean reddenings of the clusters, measured both from the color of the red giant branch and through comparison with Milky Way clusters, are <=0.10 magnitudes in E(B-V) in all cases. By matching tbe color-magnitude diagrams of the clusters to fiducial sequences of the Milky Way globular clusters M3, M5, and M55, we find that the mean difference of the LMC and Milky Way cluster ages is 1.0 ± 1.2 Gyr, calculated such that a positive difference indicates that the LMC clusters are older. Through Monte Carlo simulations, errors in the individual measurements of the ages relative to Milky Way clusters are found to be ~<1.0 Gyr. We find a similar chronology by comparing the horizontal branch morphologies and abundances with HB evolutionary tracks, assuming that age is the 'second parameter'. These results imply that the LMC formed at the same time as the Milky Way Galaxy. The evolution of the LMC following its formation has been studied through

  10. Canonical free-energy barrier of particle and polymer cluster formation

    PubMed Central

    Zierenberg, Johannes; Schierz, Philipp; Janke, Wolfhard

    2017-01-01

    A common approach to study nucleation rates is the estimation of free-energy barriers. This usually requires knowledge about the shape of the forming droplet, a task that becomes notoriously difficult in macromolecular setups starting with a proper definition of the cluster boundary. Here we demonstrate a shape-free determination of the free energy for temperature-driven cluster formation in particle as well as polymer systems. Combined with rigorous results on equilibrium droplet formation, this allows for a well-defined finite-size scaling analysis of the effective interfacial free energy at a fixed density. We first verify the theoretical predictions for the formation of a liquid droplet in a supersaturated particle gas by generalized-ensemble Monte Carlo simulations of a Lennard-Jones system. Going one step further, we then generalize this approach to cluster formation in a dilute polymer solution. Our results suggest an analogy with particle condensation, when the macromolecules are interpreted as extended particles. PMID:28240262

  11. Ultraviolet Morphology and Unobscured UV Star Formation Rates of CLASH Brightest Cluster Galaxies

    NASA Astrophysics Data System (ADS)

    Donahue, Megan; Connor, Thomas; Fogarty, Kevin; Li, Yuan; Voit, G. Mark; Postman, Marc; Koekemoer, Anton; Moustakas, John; Bradley, Larry; Ford, Holland

    2015-06-01

    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 Cluster Lensing and Supernovae with Hubble (CLASH) 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 star-forming BCGs observed in the UV at low redshift, are suggestive of bi-polar streams of clumpy star formation, but not of spiral arms or large, kiloparsec-scale disks. Based on the number of streams and lack of culprit companion galaxies, these streams are unlikely to have arisen from multiple collisions with gas-rich galaxies. These star-forming UV structures are morphologically similar to the cold-gas structures produced in simulations of precipitation-driven active galactic nucleus feedback in which jets uplift low-entropy gas to greater altitudes, causing it to condense. Unobscured star formation rates estimated from CLASH UV images using the Kennicutt relation range up to 80 {{M}⊙ } y{{r}-1} in the most extended and highly structured systems. The circumgalactic gas-entropy threshold for star formation in CLASH BCGs at z ˜ 0.2-0.5 is indistinguishable from that for clusters at z\\lt 0.2.

  12. Formation of high-mass cluster ions from compound semiconductors using time-of-flight secondary ion mass spectrometry with cluster primary ions.

    PubMed

    Goacher, Robyn E; Luo, Hong; Gardella, Joseph A

    2008-05-01

    The detection of high-mass, nonstoichiometric, GaxAsy and InxPy secondary ion clusters using time-of-flight secondary ion mass spectrometry is reported for the first time. The GaxAsy and InxPy clusters are detected in both positive and negative ion spectra and extend to masses of at least 6000 dalton (Da). Consecutive clusters differ by the addition of one gallium (indium) atom. This leads to nonstoichiometric clusters at high mass (i.e., Ga15As3 at 1270 Da) which are metastable above a critical mass. The relative secondary ion yields of high-mass GaxAsy clusters detected using several primary ion sources (Cs+, Bi+, Bi3+, Bi32+, Bi52+, C60+, and C602+) are compared. The relative secondary ion yield of high-mass GaxAsy clusters is significantly enhanced by the use of cluster primary ions and the best relative secondary ion yield is obtained using Bi3+ primary ions. An application of the high-mass GaxAsy clusters is presented, in which these clusters are utilized to distinguish between contaminant levels of Ga and bulk GaAs structure in a depth profile of a MnAs/GaAs heterojunction. These results illustrate improved analysis of inorganic materials using cluster primary ions and break the paradigm of stoichiometric secondary cluster ion formation for SIMS of inorganic compounds.

  13. Capturing a Star Formation Burst in Galaxies Infalling onto the Cluster A1367

    NASA Astrophysics Data System (ADS)

    Gavazzi, G.; Cortese, L.; Boselli, A.; Iglesias-Paramo, J.; Vílchez, J. M.; Carrasco, L.

    2003-11-01

    The discovery of a striking astrophysical laboratory in the cluster of galaxies A1367 by Sakai and coworkers is confirmed with independent imaging and spectroscopic observations and further investigated in the present analysis. Two giant and 10 dwarf/H II galaxies, members of a group, are simultaneously undergoing a burst of star formation. Redshift measurements suggest that the group galaxies are in the process of falling into the cluster at very high speed. We explore two possible mechanisms that could have triggered the short-lived stellar burst that we are witnessing: the first, internal to the group itself, via tidal interactions among its members, the hypothesis favored by Sakai et al.; the second associated with the high-velocity infall of the group galaxies into the cluster intergalactic medium. We present evidence in favor of and against the two hypotheses.

  14. Reversible light-controlled formation and evaporation of rubidium clusters in nanoporous silica.

    PubMed

    Burchianti, A; Bogi, A; Marinelli, C; Maibohm, C; Mariotti, E; Moi, L

    2006-10-13

    We observe reversible light assisted formation and evaporation of rubidium clusters embedded in nanoporous silica. Metallic nanoparticles are cyclically produced and evaporated by weak blue-green and near-infrared light, respectively. The atoms photodetached from the huge surface of the silica matrix build up clusters, whereas cluster evaporation is increased by induced surface plasmon excitation. Frequency tuning of light activates either one process or the other and the related changes of glass transparency become visible to the naked eye. We demonstrate that the porous silica, loaded with rubidium, shows memory of illumination sequences behaving as a rereadable and rewritable optical medium. These processes take place as a consequence of the strong confinement of atoms and particles at the nanoscale.

  15. C2-domain mediated nano-cluster formation increases calcium signaling efficiency

    PubMed Central

    Bonny, Mike; Hui, Xin; Schweizer, Julia; Kaestner, Lars; Zeug, André; Kruse, Karsten; Lipp, Peter

    2016-01-01

    Conventional protein kinase Cs (cPKCs) are key signaling proteins for transducing intracellular Ca2+ signals into downstream phosphorylation events. However, the lifetime of individual membrane-bound activated cPKCs is an order of magnitude shorter than the average time needed for target-protein phosphorylation. Here, we employed intermolecular Förster resonance energy transfer (FRET) in living cells combined with computational analysis to study the spatial organization of cPKCs bound to the plasma membrane. We discovered Ca2+-dependent cPKC nano-clusters that significantly extend cPKC’s plasma-membrane residence time. These protein patterns resulted from self-assembly mediated by Ca2+-binding C2-domains, which are widely used for membrane-targeting of Ca2+-sensing proteins. We also established clustering of other unrelated C2-domain containing proteins, suggesting that nano-cluster formation is a key step for efficient cellular Ca2+-signaling. PMID:27808106

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

    SciTech Connect

    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.

  17. C2-domain mediated nano-cluster formation increases calcium signaling efficiency.

    PubMed

    Bonny, Mike; Hui, Xin; Schweizer, Julia; Kaestner, Lars; Zeug, André; Kruse, Karsten; Lipp, Peter

    2016-11-03

    Conventional protein kinase Cs (cPKCs) are key signaling proteins for transducing intracellular Ca(2+) signals into downstream phosphorylation events. However, the lifetime of individual membrane-bound activated cPKCs is an order of magnitude shorter than the average time needed for target-protein phosphorylation. Here, we employed intermolecular Förster resonance energy transfer (FRET) in living cells combined with computational analysis to study the spatial organization of cPKCs bound to the plasma membrane. We discovered Ca(2+)-dependent cPKC nano-clusters that significantly extend cPKC's plasma-membrane residence time. These protein patterns resulted from self-assembly mediated by Ca(2+)-binding C2-domains, which are widely used for membrane-targeting of Ca(2+)-sensing proteins. We also established clustering of other unrelated C2-domain containing proteins, suggesting that nano-cluster formation is a key step for efficient cellular Ca(2+)-signaling.

  18. THE EVOLUTION OF DUSTY STAR FORMATION IN GALAXY CLUSTERS TO z = 1: SPITZER INFRARED OBSERVATIONS OF THE FIRST RED-SEQUENCE CLUSTER SURVEY

    SciTech Connect

    Webb, T. M. A.; O'Donnell, D.; Coppin, Kristen; Faloon, Ashley; Geach, James E.; Noble, Allison; Yee, H. K. C.; Gilbank, David; Ellingson, Erica; Gladders, Mike; Muzzin, Adam; Wilson, Gillian; Yan, Renbin

    2013-10-01

    We present the results of an infrared (IR) study of high-redshift galaxy clusters with the MIPS camera on board the Spitzer Space Telescope. We have assembled a sample of 42 clusters from the Red-Sequence Cluster Survey-1 over the redshift range 0.3 < z < 1.0 and spanning an approximate range in mass of 10{sup 14-15} M {sub ☉}. We statistically measure the number of IR-luminous galaxies in clusters above a fixed inferred IR luminosity of 2 × 10{sup 11} M {sub ☉}, assuming a star forming galaxy template, per unit cluster mass and find it increases to higher redshift. Fitting a simple power-law we measure evolution of (1 + z){sup 5.1±1.9} over the range 0.3 < z < 1.0. These results are tied to the adoption of a single star forming galaxy template; the presence of active galactic nuclei, and an evolution in their relative contribution to the mid-IR galaxy emission, will alter the overall number counts per cluster and their rate of evolution. Under the star formation assumption we infer the approximate total star formation rate per unit cluster mass (ΣSFR/M {sub cluster}). The evolution is similar, with ΣSFR/M {sub cluster} ∼ (1 + z){sup 5.4±1.9}. We show that this can be accounted for by the evolution of the IR-bright field population over the same redshift range; that is, the evolution can be attributed entirely to the change in the in-falling field galaxy population. We show that the ΣSFR/M {sub cluster} (binned over all redshift) decreases with increasing cluster mass with a slope (ΣSFR/M{sub cluster}∼M{sub cluster}{sup -1.5±0.4}) consistent with the dependence of the stellar-to-total mass per unit cluster mass seen locally. The inferred star formation seen here could produce ∼5%-10% of the total stellar mass in massive clusters at z = 0, but we cannot constrain the descendant population, nor how rapidly the star-formation must shut-down once the galaxies have entered the cluster environment. Finally, we show a clear decrease in the number of IR

  19. Ions colliding with clusters of fullerenes--decay pathways and covalent bond formations.

    PubMed

    Seitz, F; Zettergren, H; Rousseau, P; Wang, Y; Chen, T; Gatchell, M; Alexander, J D; Stockett, M H; Rangama, J; Chesnel, J Y; Capron, M; Poully, J C; Domaracka, A; Méry, A; Maclot, S; Vizcaino, V; Schmidt, H T; Adoui, L; Alcamí, M; Tielens, A G G M; Martín, F; Huber, B A; Cederquist, H

    2013-07-21

    We report experimental results for the ionization and fragmentation of weakly bound van der Waals clusters of n C60 molecules following collisions with Ar(2+), He(2+), and Xe(20+) at laboratory kinetic energies of 13 keV, 22.5 keV, and 300 keV, respectively. Intact singly charged C60 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 [C60]n(+) → C60(+)+(n-1)C60 evaporation model. Excitation energies in the range of only ~0.7 eV per C60 molecule in a [C60]13(+) 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(2+) and He(2+) collisions, we observe very efficient C119(+) and C118(+) formation and molecular dynamics simulations suggest that they are covalent dumb-bell systems due to bonding between C59(+) or C58(+) and C60 during cluster fragmentation. In the Ar(2+) case, it is possible to form even smaller C120-2m(+) molecules (m = 2-7), while no molecular fusion reactions are observed for the present Xe(20+) collisions.

  20. Nitrogen affects cluster root formation and expression of putative peptide transporters

    PubMed Central

    Paungfoo-Lonhienne, Chanyarat; Schenk, Peer M.; Lonhienne, Thierry G. A.; Brackin, Richard; Meier, Stefan; Rentsch, Doris; Schmidt, Susanne

    2009-01-01

    Non-mycorrhizal Hakea actites (Proteaceae) grows in heathland where organic nitrogen (ON) dominates the soil nitrogen (N) pool. Hakea actites uses ON for growth, but the role of cluster roots in ON acquisition is unknown. The aim of the present study was to ascertain how N form and concentration affect cluster root formation and expression of peptide transporters. Hydroponically grown plants produced most biomass with low molecular weight ON>inorganic N>high molecular weight ON, while cluster roots were formed in the order no-N>ON>inorganic N. Intact dipeptide was transported into roots and metabolized, suggesting a role for the peptide transporter (PTR) for uptake and transport of peptides. HaPTR4, a member of subgroup II of the NRT1/PTR transporter family, which contains most characterized di- and tripeptide transporters in plants, facilitated transport of di- and tripeptides when expressed in yeast. No transport activity was demonstrated for HaPTR5 and HaPTR12, most similar to less well characterized transporters in subgroup III. The results provide further evidence that subgroup II of the NRT1/PTR family contains functional di- and tripeptide transporters. Green fluorescent protein fusion proteins of HaPTR4 and HaPTR12 localized to tonoplast, and plasma- and endomembranes, respectively, while HaPTR5 localized to vesicles of unknown identity. Grown in heathland or hydroponic culture with limiting N supply or starved of nutrients, HaPTR genes had the highest expression in cluster roots and non-cluster roots, and leaf expression increased upon re-supply of ON. It is concluded that formation of cluster roots and expression of PTR are regulated in response to N supply. PMID:19380419

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

    NASA Astrophysics Data System (ADS)

    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 < z < 0.7. We find reasonable agreement with clustering measurements from the Galaxy and Mass Assembly Survey, but find larger discrepancies for some stellar mass ranges and separation scales with respect to measurements from the Sloan Digital Sky Survey and the VIMOS Public Extragalactic Redshift Survey, depending on the GALFORM model used.

  2. Ions colliding with clusters of fullerenes—Decay pathways and covalent bond formations

    NASA Astrophysics Data System (ADS)

    Seitz, F.; Zettergren, H.; Rousseau, P.; Wang, Y.; Chen, T.; Gatchell, M.; Alexander, J. D.; Stockett, M. H.; Rangama, J.; Chesnel, J. Y.; Capron, M.; Poully, J. C.; Domaracka, A.; Méry, A.; Maclot, S.; Vizcaino, V.; Schmidt, H. T.; Adoui, L.; Alcamí, M.; Tielens, A. G. G. M.; Martín, F.; Huber, B. A.; Cederquist, H.

    2013-07-01

    We report experimental results for the ionization and fragmentation of weakly bound van der Waals clusters of n C60 molecules following collisions with Ar2 +, He2 +, and Xe20 + at laboratory kinetic energies of 13 keV, 22.5 keV, and 300 keV, respectively. Intact singly charged C60 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_{60}]_n^+ → C_{60}+ + (n-1)C_{60} evaporation model. Excitation energies in the range of only ˜0.7 eV per C60 molecule in a [C_{60}]_{13}^+ 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 Ar2 + and He2 + collisions, we observe very efficient C_{119}+ and C_{118}+ formation and molecular dynamics simulations suggest that they are covalent dumb-bell systems due to bonding between C_{59}+ or C_{58}+ and C60 during cluster fragmentation. In the Ar2 + case, it is possible to form even smaller C_{120-2m}+ molecules (m = 2-7), while no molecular fusion reactions are observed for the present Xe20 + collisions.

  3. KAT-7 science verification: cold gas, star formation, and substructure in the nearby Antlia Cluster

    NASA Astrophysics Data System (ADS)

    Hess, Kelley M.; Jarrett, T. H.; Carignan, Claude; Passmoor, Sean S.; Goedhart, Sharmila

    2015-09-01

    The Antlia Cluster is a nearby, dynamically young structure, and its proximity provides a valuable opportunity for detailed study of galaxy and group accretion on to clusters. We present a deep H I mosaic completed as part of spectral line commissioning of the Karoo Array Telescope (KAT-7), and identify infrared counterparts from the Widefield Infrared Survey Explorer extended source catalogue 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_{H I}>5× 10^7 M⊙. Of these, 35 are new H I detections, 27 do not have previous spectroscopic redshift measurements, and one is the Compton thick Seyfert II, NGC 3281, which we detect in H I absorption. The H I galaxies lie beyond the X-ray-emitting region 200 kpc from the cluster centre 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 H I with optical redshifts, we perform a detailed dynamical analysis of the internal substructure, identify large infalling groups, and present the first compilation of the large-scale distribution of H I and star-forming galaxies within the cluster. We find that elliptical galaxy NGC 3268 is at the centre of the oldest substructure and argue that NGC 3258 and its companion population are more recent arrivals. Through the presence of H I and ongoing star formation, we rank substructures with respect to their relative time since accretion on to Antlia.

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

    SciTech Connect

    Seitz, F.; Zettergren, H.; Chen, T.; Gatchell, M.; Alexander, J. D.; Stockett, M. H.; Schmidt, H. T.; Cederquist, H.; Rousseau, P.; Chesnel, J. Y.; Capron, M.; Poully, J. C.; Mery, A.; Maclot, S.; Adoui, L.; Wang, Y.; Martin, F.; Rangama, J.; Domaracka, A.; Vizcaino, V. [CIMAP, UMR 6252, CEA 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.

  5. nIFTy cosmology: the clustering consistency of galaxy formation models

    NASA Astrophysics Data System (ADS)

    Pujol, Arnau; Skibba, Ramin A.; Gaztañaga, Enrique; Benson, Andrew; Blaizot, Jeremy; Bower, Richard; Carretero, Jorge; Castander, Francisco J.; Cattaneo, Andrea; Cora, Sofia A.; Croton, Darren J.; Cui, Weiguang; Cunnama, Daniel; De Lucia, Gabriella; Devriendt, Julien E.; Elahi, Pascal J.; Font, Andreea; Fontanot, Fabio; Garcia-Bellido, Juan; Gargiulo, Ignacio D.; Gonzalez-Perez, Violeta; Helly, John; Henriques, Bruno M. B.; Hirschmann, Michaela; Knebe, Alexander; Lee, Jaehyun; Mamon, Gary A.; Monaco, Pierluigi; Onions, Julian; Padilla, Nelson D.; Pearce, Frazer R.; Power, Chris; Somerville, Rachel S.; Srisawat, Chaichalit; Thomas, Peter A.; Tollet, Edouard; Vega-Martínez, Cristian A.; Yi, Sukyoung K.

    2017-07-01

    We present a clustering comparison of 12 galaxy formation models [including semi-analytic models (SAMs) and halo occupation distribution (HOD) models] all run on halo catalogues and merger trees extracted from a single Λ cold dark matter N-body simulation. We compare the results of the measurements of the mean halo occupation numbers, the radial distribution of galaxies in haloes and the two-point correlation functions (2PCF). We also study the implications of the different treatments of orphan (galaxies not assigned to any dark matter subhalo) and non-orphan galaxies in these measurements. Our main result is that the galaxy formation models generally agree in their clustering predictions but they disagree significantly between HOD and SAMs for the orphan satellites. Although there is a very good agreement between the models on the 2PCF of central galaxies, the scatter between the models when orphan satellites are included can be larger than a factor of 2 for scales smaller than 1 h-1 Mpc. We also show that galaxy formation models that do not include orphan satellite galaxies have a significantly lower 2PCF on small scales, consistent with previous studies. Finally, we show that the 2PCF of orphan satellites is remarkably different between SAMs and HOD models. Orphan satellites in SAMs present a higher clustering than in HOD models because they tend to occupy more massive haloes. We conclude that orphan satellites have an important role on galaxy clustering and they are the main cause of the differences in the clustering between HOD models and SAMs.

  6. Observing the real time formation of phosphine-ligated gold clusters by electrospray ionization mass spectrometry

    SciTech Connect

    Ligare, Marshall R.; Johnson, Grant E.; Laskin, Julia

    2017-01-01

    Early stages of the reduction and nucleation of solution-phase gold clusters are largely unknown. This is due, in part, to the high reaction rates and the complexity of the cluster synthesis process. Through the addition of a diphosphine ligand, 1-4,Bis(diphenylphosphino)butane (L4) to the gold precursor, chloro(triphenylphosphine) gold(I) (Au(PPh3)Cl), in methanol organometallic complexes of the type, [Au(L4)x(L4O)y(PPh3)z]+, are formed. These complexes lower the rate of reduction so that the reaction can be directly monitored from 1 min to over an hour using on-line electrospray ionization mass spectrometry (ESI-MS). Our results indicate that the formation of Au8(L4)42+, Au9(L4)4H2+ and Au10(L4)52+ cationic clusters occurs through different reaction pathways that may be kinetically controlled either through the reducing agent concentration or the extent of oxidation of L4. Through comparison of selected ion chronograms our results indicate that Au2(L4)2H+ may be an intermediate in the formation of Au8(L4)42+and Au10(L4)52+ while a variety of chlorinated clusters are involved in the formation of Au9(L4)4H2+. Additionally, high-resolution mass spectrometry was employed to identify 53 gold containing species produced under highly oxidative conditions. New intermediate species are identified which help understand how different gold cluster nuclearities can be stabilized during the growth process.

  7. Importance of the initial conditions for star formation - III. Statistical properties of embedded protostellar clusters

    NASA Astrophysics Data System (ADS)

    Girichidis, Philipp; Federrath, Christoph; Allison, Richard; Banerjee, Robi; Klessen, Ralf S.

    2012-03-01

    We investigate the formation of protostellar clusters during the collapse of dense molecular cloud cores with a focus on the evolution of potential and kinetic energy, the degree of substructure and the early phase of mass segregation. Our study is based on a series of hydrodynamic simulations of dense cores, where we vary the initial density profile and the initial turbulent velocity. In the three-dimensional adaptive mesh refinement simulations, we follow the dynamical formation of filaments and protostars until a star formation efficiency of 20 per cent. Despite the different initial configurations, the global ensemble of all protostars in a setup shows a similar energy evolution and forms sub-virial clusters with an energy ratio Ekin/|Epot|˜ 0.2. Concentrating on the innermost central region, the clusters show a roughly virialized energy balance. However, the region of virial balance only covers the innermost ˜10-30 per cent of all the protostars. In all simulations with multiple protostars, the total kinetic energy of the protostars is higher than the kinetic energy of the gas cloud, although the protostars only contain 20 per cent of the total mass. The clusters vary significantly in size, mass and number of protostars, and show different degrees of substructure and mass segregation. Flat density profiles and compressive turbulent modes produce more subclusters than centrally concentrated profiles and solenoidal turbulence. We find that dynamical relaxation and hence dynamical mass segregation is very efficient in all cases from the very beginning of the nascent cluster, i.e. during a phase when protostars constantly form and accrete.

  8. Linking star formation and galaxy kinematics in the massive cluster Abell 2163

    NASA Astrophysics Data System (ADS)

    Menacho, Veronica; Verdugo, Miguel

    2015-02-01

    The origin of the morphology-density relation is still an open question in galaxy evolution. It is most likely driven by the combination of the efficient star formation in the highest peaks of the mass distribution at high-z and the transformation by environmental processes at later times as galaxies fall into more massive halos. To gain additional insights about these processes we study the kinematics, star formation and structural properties of galaxies in Abell 2163 a very massive (~4×1015 M⊙, Holz & Perlmutter 2012) merging cluster at z = 0.2. We use high resolution spectroscopy with VLT/VIMOS to derive rotation curves and dynamical masses for galaxies that show regular kinematics. Galaxies that show irregular rotation are also analysed to study the origin of their distortion. This information is combined with stellar masses and structural parameters obtained from high quality CFHT imaging. From narrow band photometry (2.2m/WFI), centered on the redshifted Hα line, we obtain star formation rates. Although our sample is still small, field and cluster galaxies lie in a similar Tully-Fisher relation as local galaxies. Controlling by additional parameters like SFRs or bulge-to-disk ratio do not affect this result. We find however that ~50% of the cluster galaxies display irregular kinematics in contrast to what is found in the field at similar redshifts (~30%, Böhm et al. 2004) and in agreement with other studies in clusters (e.g. Bösch et al. 2013, Kutdemir et al. 2010) which points out to additional processes operating in clusters that distort the galaxy kinematics.

  9. Formation history of old open clusters constrained by detailed asteroseismology of red giant stars observed by Kepler

    NASA Astrophysics Data System (ADS)

    Corsaro, E.; Lee, Y.-N.; García, R. A.; Hennebelle, P.; Mathur, S.; Beck, P. G.; Mathis, S.; Stello, D.; Bouvier, J.

    2016-12-01

    Stars originate by the gravitational collapse of a turbulent molecular cloud, often forming clusters of thousands of stars. Stellar clusters therefore play an important role in our understanding of star formation, a fundamental problem in astrophysics that is difficult to investigate because pre-stellar cores are typically obscured by dust. Thanks to a Bayesian analysis of about 50 red giants of NGC 6791 and NGC 6819, two old open clusters observed by NASA Kepler, we characterize thousands of individual oscillation modes. We show for the first time how the measured asteroseismic properties lead us to a discovery about the rotation history of these clusters. Finally, our findings are compared to 3D hydrodynamical simulations for stellar cluster formation to put strong constraints on the physical processes of turbulence and rotation, which are in action in the early formation stage of the stellar clusters.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Technical Reports Server (NTRS)

    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.

  12. Laminin-111 Peptides Conjugated to Fibrin Hydrogels Promote Formation of Lumen Containing Parotid Gland Cell Clusters.

    PubMed

    Nam, Kihoon; Jones, Joshua P; Lei, Pedro; Andreadis, Stelios T; Baker, Olga J

    2016-06-13

    Previous studies showed that mouse submandibular gland cells form three-dimensional structures when grown on Laminin-111 gels. The use of Laminin-111 for tissue bioengineering is complicated due to its lack of purity. By contrast, the use of synthetic peptides derived from Laminin-111 is beneficial due to their high purity and easy manipulation. Two Laminin-111 peptides have been identified for salivary cells: the A99 peptide corresponding to the α1 chain from Laminin-111 and the YIGSR peptide corresponding to the β1 chain from Laminin-111, which are important for cell adhesion and migration. We created three-dimensional salivary cell clusters using a modified fibrin hydrogel matrix containing immobilized Laminin-111 peptides. Results indicate that the YIGSR peptide improved morphology and lumen formation in rat parotid Par-C10 cells as compared to cells grown on unmodified fibrin hydrogel. Moreover, a combination of both peptides not only allowed the formation of functional three-dimensional salivary cell clusters but also increased attachment and number of cell clusters. In summary, we demonstrated that fibrin hydrogel decorated with Laminin-111 peptides supports attachment and differentiation of salivary gland cell clusters with mature lumens.

  13. Spectroscopic study of formation, evolution and interaction of M31 and M33 with star clusters

    NASA Astrophysics Data System (ADS)

    Fan, Zhou; Yang, Yanbin

    2016-02-01

    The recent studies show that the formation and evolution process of the nearby galaxies are still unclear. By using the Canada France Hawaii Telescope (CFHT) 3.6m telescope, the PanDAS shows complicated substructures (dwarf satellite galaxies, halo globular clusters, extended clusters, star streams, etc.) in the halo of M31 to ~150 kpc from the center of galaxy and M31-M33 interaction has been studied. In our work, we would like to investigate formation, evolution and interaction of M31 and M33, which are the nearest two spiral galaxies in Local Group. The star cluster systems of the two galaxies are good tracers to study the dynamics of the substructures and the interaction. Since 2010, the Xinglong 2.16m, Lijiang 2.4m and MMT 6.5m telescopes have been used for our spectroscopic observations. The radial velocities and Lick absorption-line indices can thus be measured with the spectroscopy and then ages, metallicities and masses of the star clusters can be fitted with the simple stellar population models. These parameters could be used as the input physical parameters for numerical simulations of M31-M33 interaction.

  14. Understanding the In-Situ Star Formation in a z=1.7 Cluster Core Galaxy

    NASA Astrophysics Data System (ADS)

    Webb, Tracy

    2014-10-01

    We have discovered a rare beast of a central galaxy within a z=1.7 rich galaxy cluster (estimated ~4x10^14 Msun), forming stars at a prodigious rate of 1200 Msun/yr. This system is infrared bright and its SED and the detection of PAHs at the cluster redshift, implies the IR luminosity is dominated by star formation. Such an extreme system has to date, only been confirmed in the z=0.6 Phoenix cluster (McDonald et al. 2012, 2013, 2014), whereas this object is observed at a much earlier and more active epoch of galaxy and cluster evolution. Here we propose deep HST imaging with WFC3 F160W/F105W to investigate the morphology of the BCG galaxy and its nearest neighbours. Our main goal is to understand the physical processes fuelling the intense starburst, be it a major merger or infalling gas from a cooling flow. We will also characterize the morphological properties (with color information) of the central BCG. These data will be the first of their kind at this redshift and will relate overall formation and evolution of the central galaxy massive parent halo at a cosmological epoch where these processes may begin to dominate.

  15. Investigating star formation properties of galaxies in massive clusters with Herschel and ALMA

    NASA Astrophysics Data System (ADS)

    Wu, John F.; Baker, Andrew J.; Aguirre, Paula; Barkats, D.; Halpern, Mark; Hilton, Matt; Hughes, John Patrick; Infante, Leopoldo; Lindner, Robert; Marriage, Tobias; Menanteau, Felipe; Sifon, Cristobal; Weiss, Axel; ACT Collaboration

    2016-01-01

    I will present results from an investigation of star formation properties of galaxies residing in two massive z ~ 1 clusters (including the 'El Gordo' merger) that were initially selected via their Sunyaev-Zeldovich decrements by the Atacama Cosmology Telescope (ACT) southern survey. This study uses new Herschel Space Observatory and Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 2 observations, which provide information about the dust and cold gas content of galaxies in our targeted clusters. We have detected CO (4-3) and [CI] in individual star-forming cluster galaxies, and also measured stacked continuum and spectral line fluxes at long (e.g., far-infrared, submillimeter, and radio) wavelengths. We use these results to explore the relations between star formation and local environment and cluster dynamical state.This work has been supported by (i) an award issued by JPL/Caltech in association with Herschel, which is a European Space Agency Cornerstone Mission with significant participation by NASA, and (ii) the National Science Foundation through award GSSP SOSPA2-018 from the National Radio Astronomy Observatory, which is operated under cooperative agreement by Associated Universities, Inc.

  16. The structure, dynamics, and star formation rate of the Orion nebula cluster

    SciTech Connect

    Da Rio, Nicola; Tan, Jonathan C.; Jaehnig, Karl

    2014-11-01

    The spatial morphology and dynamical status of a young, still-forming stellar cluster provide valuable clues to 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, which is 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 interstellar medium density, which is estimated from average stellar extinction, the mass content of the ONC is insufficient by a factor ∼1.8 to reproduce the observed velocity dispersion from virialized motions, in agreement with previous assessments that the ONC is moderately supervirial. This may indicate recent gas dispersal. Based on the latest estimates for the age spread in the system and our density profiles, we find that at the half-mass radius, 90% of the stellar population formed within ∼5-8 free-fall times (t {sub ff}). This implies a star formation efficiency per t {sub ff} of ε{sub ff} ∼ 0.04-0.07 (i.e., relatively slow and inefficient star formation rates during star cluster formation).

  17. Divalent cation-induced cluster formation by polyphosphoinositides in model membranes.

    PubMed

    Wang, Yu-Hsiu; Collins, Agnieszka; Guo, Lin; Smith-Dupont, Kathryn B; Gai, Feng; Svitkina, Tatyana; Janmey, Paul A

    2012-02-22

    Polyphosphoinositides (PPIs) and in particular phosphatidylinositol-(4,5)-bisphosphate (PI4,5P2), control many cellular events and bind with variable levels of specificity to hundreds of intracellular proteins in vitro. The much more restricted targeting of proteins to PPIs in cell membranes is thought to result in part from the formation of spatially distinct PIP2 pools, but the mechanisms that cause formation and maintenance of PIP2 clusters are still under debate. The hypothesis that PIP2 forms submicrometer-sized clusters in the membrane by electrostatic interactions with intracellular divalent cations is tested here using lipid monolayer and bilayer model membranes. Competitive binding between Ca(2+) and Mg(2+) to PIP2 is quantified by surface pressure measurements and analyzed by a Langmuir competitive adsorption model. The physical chemical differences among three PIP2 isomers are also investigated. Addition of Ca(2+) but not Mg(2+), Zn(2+), or polyamines to PIP2-containing monolayers induces surface pressure drops coincident with the formation of PIP2 clusters visualized by fluorescence, atomic force, and electron microscopy. Studies of bilayer membranes using steady-state probe-partitioning fluorescence resonance energy transfer (SP-FRET) and fluorescence correlation spectroscopy (FCS) also reveal divalent metal ion (Me(2+))-induced cluster formation or diffusion retardation, which follows the trend: Ca(2+) ≫ Mg(2+) > Zn(2+), and polyamines have minimal effects. These results suggest that divalent metal ions have substantial effects on PIP2 lateral organization at physiological concentrations, and local fluxes in their cytoplasmic levels can contribute to regulating protein-PIP2 interactions.

  18. Regulation of Star Formation amidst Heating and Cooling in Galaxies and Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Vaddi, Sravani

    Galaxy clusters are the largest gravitationally bound systems in the Universe and often host the largest galaxies (known as the brightest cluster galaxies (BCG)) at its centers. These BCG's are embedded in hot 1-10 keV X-ray gas. A subset of galaxy clusters known as cool-core clusters show sharply peaked X-ray emission and high central densities, demonstrating cooling of the surrounding halo gas in timescales much shorter than a Hubble time. These observations led to the development of a simple cooling flow model. In the absence of an external heating process, a cooling flow model predicts that the hot intracluster medium gas in these dense cores would hydrostatically cool, generating cooling flows in the center of the cluster. This cooled gas will eventually collapse to form stars and contribute to the bulk of galaxy mass. The rates of star formation actually observed in the clusters however are far less than predicted by the cooling flow model, suggesting a non-gravitational heating source. Active galactic nuclei (AGN), galaxies hosting a supermassive black hole that ejects outflows via accretion, is currently the leading heating mechanism (referred to as AGN feedback) explaining the observed deficit in the star formation rates. AGN feedback also offers an elegant explanation to the observed black hole and galaxy co-evolution. Much of the evidence for AGN feedback has been obtained from studies focussed on galaxy clusters and luminous massive systems with little evidence that it occurs in more typical systems in the local universe. Our research investigates this less explored area to address the importance of AGN heating in the regulation of star formation in typical early type galaxies in the local universe. We selected a sample of 200+ early type, low redshift galaxies and carried out a multiple wavelength study using archival observed in the UV, IR and radio. Our results suggest that early type galaxies in the current epoch are rarely powerful AGN and AGN

  19. The mechanics of bacterial cluster formation on plant leaf surfaces as revealed by bioreporter technology.

    PubMed

    Tecon, Robin; Leveau, Johan H J

    2012-05-01

    Bacteria that colonize the leaves of terrestrial plants often occur in clusters whose size varies from a few to thousands of cells. For the formation of such bacterial clusters, two non-mutually exclusive but very different mechanisms may be proposed: aggregation of multiple cells or clonal reproduction of a single cell. Here we assessed the contribution of both mechanisms on the leaves of bean plants that were colonized by the bacterium Pantoea agglomerans. In one approach, we used a mixture of green and red fluorescent P. agglomerans cells to populate bean leaves. We observed that this resulted in clusters made up of only one colour as well as two-colour clusters, thus providing evidence for both mechanisms. Another P. agglomerans bioreporter, designed to quantify the reproductive success of bacterial colonizers by proxy to the rate at which green fluorescent protein is diluted from dividing cells, revealed that during the first hours on the leaf surface, many bacteria were dividing, but not staying together and forming clusters, which is suggestive of bacterial relocation. Together, these findings support a dynamic model of leaf surface colonization, where both aggregative and reproductive mechanisms take place. The bioreporter-based approach we employed here should be broadly applicable towards a more quantitative and mechanistic understanding of bacterial colonization of surfaces in general. © 2012 Society for Applied Microbiology and Blackwell Publishing Ltd.

  20. Effect of Temperature on Morphology of Metallic Iron and Formation of Clusters of Iron Ore Pellets

    NASA Astrophysics Data System (ADS)

    de Alencar, Jean Philippe Santos Gherardi; de Resende, Valdirene Gonzaga; de Castro, Luiz Fernando Andrade

    2016-02-01

    The increase of the reduction temperature in direct reduction furnaces has been a recurring tool due to the benefits that it provides to the process. However, its increase cannot be performed without taking into account some considerations, since the sticking phenomenon is directly correlated with it and could lead to permeability problems and reactor performance. An analysis of the formation of pellets clusters at different temperatures was carried out with focus on morphological characterization of reduced materials to better understand the causes and effects of these actions. The results showed a correlation between the morphology of the metallic iron present in the samples and the clustering index. At low reduction temperatures, 1123 K (850 °C), the iron formed is eroded and deformed and the cluster hardly remains after tumbling. When forming iron with fibrous structure, 1223 K (950 °C), the clustering index increases because of anchor points which make the material to stick together. Finally, under the effect of high temperature and long time, it generates fresh precipitated iron, enhancing the resistance of the clusters so that they cannot be separated.

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

    NASA Astrophysics Data System (ADS)

    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.

  2. Star Formation in the Dense Environment of Young Clusters: A FORCAST Imaging Survey

    NASA Astrophysics Data System (ADS)

    Mundy, Lee

    2012-10-01

    We propose a multi-wavelength FORCAST survey of 6-8 dense star-forming regions within 1kpc. This survey will image multiple fields in each target cluster with the 11, 19, 31 and 37 micron bands, including an estimated 100 young stellar objects (YSO) with bright mid-IR emission. The results will fill in YSO information for the cluster centers where previous studies based on Spitzer, WISE, and IRAS were saturated and/or suffered from source confusion. In addition, these observations will help fill the 10-40 micron gap in the spectral energy distributions of YSOs in these fields, and will help characterize the spatial extent of the 31 micron and 37micron emission. FORCAST's high spatial resolution will be an improvement by a factor of two over the Spitzer 24 micron images. The proposed survey will provide better statistics on bright young cluster stars which will help test current theories of clustered star formation: Turbulent Core Collapse and Competitive Accretion. Specifically, the data will improve our knowledge of the protostellar luminosity and temperature distributions in the dense regions of forming clusters, which constrain these models (Offner and Mckee 2011; Myers 2011). In addition, the extent of the 31 and 37 micron emission (unresolved compared to 5-10") will provide direct information on Competitive Accretion.

  3. Identification of the progenitors of rich clusters and member galaxies in rapid formation at z > 2

    NASA Astrophysics Data System (ADS)

    Shimakawa, Rhythm; Kodama, Tadayuki; Tadaki, Ken-ichi; Tanaka, Ichi; Hayashi, Masao; Koyama, Yusei

    2014-06-01

    We present the results of near-infrared spectroscopy of Hα emitters (HAEs) associated with two protoclusters around radio galaxies (PKS 1138-262 at z = 2.2 and USS 1558-003 at z = 2.5) with the Multi-Object Infrared Camera and Spectrograph (MOIRCS) on the Subaru telescope. Among the HAE candidates constructed from our narrow-band imaging, we have confirmed membership of 27 and 36 HAEs for the respective protoclusters, with a success rate of 70 per cent of our observed targets. The large number of spectroscopically confirmed members per cluster has enabled us for the first time to reveal the detailed kinematical structures of the protoclusters at z > 2. The clusters show prominent substructures such as clumps, filaments and velocity gradients, suggesting that they are still in the midst of rapid construction to grow to rich clusters at later times. We also estimate the dynamical masses of the clusters and substructures, assuming their local virialization. The inferred masses (˜1014 M⊙) of the protocluster cores are consistent with their being typical progenitors of the present-day most massive class of galaxy clusters (˜1015 M⊙) if we take into account the typical mass growth history of clusters. We then calculate the integrated star formation rates of the protocluster cores normalized by the dynamical masses and compare these with lower redshift descendants. We see a marked increase of star-forming activities in the cluster cores, by almost three orders of magnitude, as we go back in time to 11 billion years ago; this scales as (1 + z)6.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    SciTech Connect

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

    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.

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