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Dissertations / Theses on the topic 'Cluster formation'
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1
Dale, J. E. "Feedback in star cluster formation." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.598249.
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Massive stars emit strong fluxes of ionising radiation and their dynamical impact on their natal clusters is expected to be severe. The outflows generated expel residual gas from the cluster and can potentially gravitationally disrupt it. The loss of its reserves of molecular gas also prevents the cluster forming more stars. Star-formation and star cluster evolution cannot be fully understood without a proper treatment of feedback. I present a novel technique I have developed to allow the inclusion of the effects of ionising radiation in smoothed particle hydrodynamics (SPH) simulations of star clusters. The new algorithm is able to reproduce the results of simple analytical models and also gives results in good agreement with a more sophisticated Monte Carlo radiative transfer code when tested under highly anisotropic conditions. I simulate the effects of ionising radiation in globular clusters and compare my results with one-dimensional calculations with which I find good agreement. I investigate three cases in which different quantities of gas are distributed in my model cluster such that the as becomes fully ionised either during the HII region’s formation phase, or during its expansion phase, or such that the HII region is trapped inside the cluster core. I find gas expulsion to be quite efficient in the calculations in which the HII region escapes the core. I observe an instability in the second calculation which causes the shocked shell driven by the ionisation front to fragment as the HII region exits the core. The instability produces new structure from the smooth gas in the system, but this structure is rapidly destroyed by the radiation field and the effect of the instability on the evolution of the system is minimal. I also simulate feedback in the context of young embedded clusters, a highly inhomogeneous and anisotropic environment. I find that, again, photoionisation is able to produce novel structure in the ambient gas, causing it to fragment into filaments and beads. This fragmentation of the neutral gas, together with compression by hot ionised gas, which decreases the Jeans mass, lead me to conclude that feedback promotes star formation.
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Bailey, Philip John. "Carbide formation and cluster build-up reactions in ruthenium carbonyl cluster chemistry." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335689.
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Bergman, Edward M., and Patrick Lehner. "Industrial cluster formation in European regions. U.S. cluster templates and Austrian evidence." Institut für Wirtschaftsgeographie, Abt. Stadt- und Regionalentwicklung, WU Vienna University of Economics and Business, 1998. http://epub.wu.ac.at/748/1/document.pdf.
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The paper will be organized in the following manner. We first provide a concise review of how industrial trade clusters were developed from available I/O coefficients (see box), including how regional industrial data may be embedded within their "templates". Second, we will review the steps taken, using available industrial concordances, that permit regional data from other advanced national industrial systems to be embedded within these templates. Third, we will illustrate the results of applying the U.S. template for the motor vehicle industrial trade cluster to regions in both Austria and North Carolina over 5-10 year time periods. Finally, we will offer some speculative observations about what the results may indicate about regional cluster development in these two regions. (authors' abstract, ed. M.Putz)Series: SRE - Discussion Papers
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Harris, William E., Stephanie M. Ciccone, Gwendolyn M. Eadie, Oleg Y. Gnedin, Douglas Geisler, Barry Rothberg, and Jeremy Bailin. "GLOBULAR CLUSTER SYSTEMS IN BRIGHTEST CLUSTER GALAXIES. III. BEYOND BIMODALITY." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/622870.
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We present new deep photometry of the rich globular cluster (GC) systems around the Brightest Cluster Galaxies UGC 9799 (Abell 2052) and UGC 10143 (Abell 2147), obtained with the Hubble Space Telescope (HST) ACS and WFC3 cameras. For comparison, we also present new reductions of similar HST/ACS data for the Coma supergiants NGC 4874 and 4889. All four of these galaxies have huge cluster populations (to the radial limits of our data, comprising from 12,000 to 23,000 clusters per galaxy). The metallicity distribution functions (MDFs) of the GCs can still be matched by a bimodal-Gaussian form where the metal-rich and metal-poor modes are separated by similar or equal to 0.8 dex, but the internal dispersions of each mode are so large that the total MDF becomes very broad and nearly continuous from [Fe/H] similar or equal to-2.4 to solar. There are, however, significant differences between galaxies in the relative numbers of metal-rich clusters, suggesting that they underwent significantly different histories of mergers with massive gas-rich halos. Last, the proportion of metal-poor GCs rises especially rapidly outside projected radii R >= 4 R-eff, suggesting the importance of accreted dwarf satellites in the outer halo. Comprehensive models for the formation of GCs as part of the hierarchical formation of their parent galaxies will be needed to trace the systematic change in structure of the MDF with galaxy mass, from the distinctly bimodal form in smaller galaxies up to the broad continuum that we see in the very largest systems.
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Chen, Bo-Gaun. "Cluster formation in supersonic beams of dense fluids." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2015. http://dx.doi.org/10.18452/17441.
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Mit zeitaufgelöster Massenspektrometrie untersuchen wir die Winkelverteilung von Kohlendioxid-Monomeren bei der Streuung von Kohlendioxid-Clustern an einer Si(111)/Siliciumdioxid-Oberfläche unter Ultrahochvakuum-Bedingungen. Die präsen- tierten Studien decken eine große Breite der Clustergrößen, , 1,000 < N < 200,000 Moleküle pro Partikel, ab. Dabei liegt der Fokus auf dem Einfluss der Ausgangsentropie, die durch eine präzise Einstellung des Ausgangsdruckes und der Düsentemperatur realisiert wurde. Es zeigt sich, daß die Streuverteilung direkt den Expansionspfad widerspiegelt, wodurch eine Unterscheidung zwischen Clustern, die durch eine Expansion auf der gasförmigen oder flüssigen Seite des kritischen Punktes und der metstabilen Phase ent- stehen, ermöglicht wird. Um bei den hohen Teilchendichten eine verlässliche Aussage zu ermöglichen, wurden im Vorfeld die Eigenschaften gepulster Molekularstrahlen untersucht, insbesondere deren Abhängigkeit vom Restgasdruck und den Wechselwirkungen mit Strahlblenden. Hierzu diente die elektronische Anregung eines Helium-Strahls. Die Optimierung der Randbedingungen ermöglicht viel kältere Strahlen, so dass Helium-Cluster sogar bei einer Ausgangstemperatur von T = 410.0 K gefunden werden können. Dieses Ergebnis ist für die Cluster-Forschung, die Molekülspektroskopie und Experimente in der Quantenphysik von Bedeutung.Employing pulsed high-pressure supersonic jet expansion and a dedicated setup for the experimental investigation of chemical processes occurring between neutral, van der Waals bound clusters and a solid surface, we report on the angular distribution observed for large carbon dioxide clusters scattered off a Si(111)/Silicon Dioxide surface under ultrahigh vacuum conditions. Scattered particles are detected using angle and time resolved mass spectrometry. The presented studies cover a broad range of cluster sizes, , 1,000 < N < 200,000 molecules per particle. The focus is on the influence of source entropy, realized by accurately setting stagnation pressure and temperature. This thesis demonstrates a dependence of the angular distribution of scattered carbon dioxide monomers on source conditions: the scattering distribution directly reflects the expansion path, allowing us to distinguish between clusters generated via expansion on the gaseous or on the liquid side of the critical point, and an intermediate regime where the expansion passes the metastable gas-liquid region. To optimize the supersonic beam, on the other hand, we reveal a substantial influence of residual gas pressure and beam–skimmer interactions on beam properties, particularly the minimum attainable translational temperature in a model system. This study contains the systematic investigation of supersonic jet expansions of helium, employing the variable distance between the Even-Lavie valve and different types of skimmers. Utilizing the ultra-high precision time-of-flight measurements of electronically tagged particles, the terminal velocities and the spread of particles allow us to correspondingly obtain much colder beams with the same source conditions. As a result, helium clusters can be found even in the jet expansion from a source temperature of T = 410.0 K. This knowledge is of particular interest to cluster science, molecular spectroscopy, and quantum physics.
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Strader, Jay. "Extragalactic globular cluster subpopulations and galaxy formation /." Diss., Digital Dissertations Database. Restricted to UC campuses, 2007. http://uclibs.org/PID/11984.
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Sacilotto, Cintia Kulzer. "Industrial cluster relocation : cluster formation, development and technological change in the destination region." Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:22ee5a2d-ea95-4c58-941a-5e6385e03f1a.
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This dissertation presents the first systematic study on cluster relocation, providing a non- random and dynamic analysis of firm relocations. Seeking to contribute to the understanding of cluster relocations and their consequences for the destination region, I explore the process and determinants of a particular cluster relocation and investigate the growth and maintenance of the new cluster through the enhancement of its supplier base, the diffusion of innovations, and advances in technological change. I analyse the differences between first and late mover firms in the process of cluster relocation to unveil the elements that boost relocation. I examine the process of technological change that occurs in the destination region. On one hand, I explore the channels for the diffusion of specific innovations and provide novel evidence for the cluster literature by considering different channels simultaneously. I measure the importance of local and relocated firms for the diffusion of innovations, unveiling the mechanisms by which knowledge spillovers with and among local firms take place. On the other hand, I present a dynamic view of the impact of relocated firms in the new region, providing unique details of technological change and the build-up of absorptive capacity over time. I analyse the changing role of relocated firms in the creation and expansion of local firms' capabilities. The relocation of the Sinos Valley footwear cluster in Brazil is analysed as a case study in this research. After being defined as a 'supercluster' by Schmitz (1995), the cluster collapsed and partially relocated in the end of the 1990s to the northeast of Brazil, and to China, following major changes that affected the competitiveness of the sector. In their attempt to survive, several firms relocated to the Cariri area in the state of Ceará, northeast Brazil. I follow this relocation process using mapping techniques, analysing the diffusion of innovations and technological change processes through an extensive set of interviews and a complete social network analysis.
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Hohertz, Jeremy D. "Formation of a globular cluster via gravitational capture." Oxford, Ohio : Miami University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=miami1217352629.
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Canning, Rebecca Elizabeth Ann. "Star and filament formation in brightest cluster galaxies." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610523.
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Santoro, Fernando. "Semi analytical simulations of primordial star cluster formation." Thesis, University of Sussex, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288843.
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Heays, Katherine Grace. "Cluster formation and stream-bed armouring: a photogrammetric study." Thesis, University of Auckland, 2012. http://hdl.handle.net/2292/13048.
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Clusters are a self organising structures commonly found in natural rivers. They play an important role in river bed dynamics by providing habitat and increasing bed stability. The aim of the present study was to investigate the development of naturally formed cluster microforms from a flattened bed of graded gravel at constant flow rate. The study was laboratory based, and used photogrammetry to observe the behaviour of well graded, cohesionless sediment at flood flow conditions as clusters formed, evolved and disintegrated. Focus was primarily on the cluster formation and sediment movement, and the development of clusters was observed under varying flow rate and grain size distribution. The study of gravel dynamics using coloured particles, coupled with image analysis, has enabled in-depth observation of sediment transport and cluster development. To assist in the study of cluster dynamics, a new application of photogrammetry was developed. A digital particle tracking (DPT) program was successfully applied to recordings of sediment movement over extended experiment durations, and a cluster identification program was developed to monitor cluster evolution. Application of the DPT program to recordings of the gravel bed as it was water worked revealed large spatial and temporal variation of sediment transport rates. Image analysis was used to investigate the progression of armouring, and statistical analysis was applied to surface elevation profiles of the water-worked surface sediment to investigate the effects of armouring. Objective cluster identification was achieved by monitoring the stationary areas of the bed, and designating clusters as areas with stable groups of large particles. This tool was used in combination with DPT to obtain new insights into cluster formation. The complex interactions of clusters with the surrounding bed were studied, and the behavioural trends of cluster formation are presented in this thesis. Surface coverage of clusters on the test section increased over time, with a maximum surface coverage of around 34% observed between all experiments. Particle shape plays a role in cluster formation, where elongate stones form more stable clusters. Clustering is enhanced by the presence of a stationary object on the bed, and the presence of clusters plays a role in attenuating the sediment transport of the surrounding bed.
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Cho, Jaeil. "Globular cluster systems and their implications of galaxy formation." Thesis, Durham University, 2008. http://etheses.dur.ac.uk/2427/.
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In this thesis the spectroscopic and photometric results of the Galactic and extragalactic globular clusters are presented. And their implications on galaxy formation have been investigated. Integrated spectroscopy with a high resolution of 24 Galactic globular clusters were obtained using the Isacc Newton Telescope, from which 21 line indices were carefully measured and calibrated. By comparing with recent simple stellar population models (Thomas et al. 2003 and Lee & Worthey 2005), it is confirmed that Galactic globular clusters are old (~10- 12 Gyr). There is a discrepancy between the two models in low metallicity and the line indices measured have a better fit to Lee & Worthey (2005) model. These is a significant effect of blue horizontal branch stars on the Balmer absorption lines in integrated spectra, which could cause globular clusters to be underestimated their age. Shell in elliptical galaxies are probably signature of recent galaxy merger/interaction. Properties of globular cluster systems (GCSs) in six shell galaxies have been examined and whether this signature can be seen in GCSs have been investigated. The GCSs in shell galaxies are found not to differ noticeably from those in normal elliptical galaxies in the sense and blue subpopulations are consistent with previous studies. This result is contradictory to results by Sikkema et al. (2006), who have found possible young globular clusters in the two galaxies. Using the Advanced Camera for Survey on the Hubble Space telescope, 10 low density early-type galaxies were observed and properties of their GCSs have been investigated to constrain galaxy formation history depending on environments. By comparing results from the Virgo Cluster Survey as a high-density counterpart, both similarities and differences between the two density groups were found. General behaviour of colour distributions of GCSs found in cluster environment are also seen in those in field galaxies; mean colour gets redder as increasing with galaxy luminosity, less bimodal colour distributions are detected in lower galaxy luminosity, and there is a correlation between red colour peak and host galaxy luminosity. However, mean colours of GCS in low-density appear to be slightly bluer than those in high-density at a given galaxy luminosity, which implies that GCS in field environments is either less metal-rich or younger than those in cluster environments. More diverse shape of colour distributions are found in dense region than in low-density region, which would reflects more complicated galaxy formation history in dense region. In spite of finding environmental this effect on galaxy formation, this effect is so subtle that galaxy (final) mass is still a dominant factor to determine galaxy formation and stellar populations in there.
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Fensch, Jérémy. "Star and stellar cluster formation in gas-dominated galaxies." Thesis, Sorbonne Paris Cité, 2017. http://www.theses.fr/2017USPCC207/document.
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Nous étudions la formation d’étoiles et d’amas d’étoiles dans les galaxies dominées par le gaz. Ce terme réfère en premier lieu aux galaxies de l’époque du pic de formation d’étoiles dans l’histoire de l’Univers, qui s’est déroulé vers z ~ 2, mais aussi à leurs analogues locaux, les galaxies naines de marées. En premier lieu, en utilisant des simulations numériques, nous montrons que les galaxies massives typiques de z=2, avec une fraction de gaz d’environ 50%, forment des structures gazeuses massives (10**7-8 masses solaires) et liées gravitationnellement, appelées grumeaux dans la suite. Ces grumeaux ne se forment dans des galaxies avec une fraction de gaz inférieure à 25%. Nous présentons ensuite une étude observationnelle d’un analogue local de grumeaux de galaxies à z=2, la galaxie naine de marée NGC 5291N. Une analyse des raies d’émission de cette galaxie montre la présence de chocs sur les pourtours de l’objet. La photométrie des amas d’étoiles de cette galaxie montre que les amas les plus jeunes (< 10 millions d’années) sont significativement moins massifs que les amas plus âgés. Ceci peut être le signe de fusions progressives d’amas et/ou d’une forte activité de formation stellaire dans ce système il y a environ 500 millions d’années.Dans un second lieu nous étudions comment la fraction de gaz influe sur la formation d’étoiles et d’amas stellaires dans des fusions de galaxies à z=2. En utilisant des simulations numériques nous montrons que ces fusions n’augmentent que relativement peu le taux de formation d’étoiles et d’amas stellaires comparativement aux fusions de galaxies locales, à faible fraction de gaz. Nous montrons que ceci est due à une saturation de plusieurs facteurs physiques, qui sont déjà présents naturellement dans les galaxies isolées à z=2 et sont donc comparativement peu accentués par les fusions. Il s’agit de la turbulence du gaz, des zones de champ de marée compressif et des flux de matières vers le noyau de la galaxie. Nous montrons aussi que les structures stellaires formées au sein des grumeaux de gaz sont préservées par la fusion : elles sont éjectées des disques et orbitent dans le halo de la galaxie résultante de la fusion, où elles peuvent devenir les progéniteurs de certains amas globulairesWe study the formation of stars and stellar clusters in gas-dominated galaxies. This term primarily refers to galaxies from the epoch of the peak of the cosmic star formation history, which occurred at z ~ 2, but also to their local analogues, the tidal dwarf galaxies.Firstly, using numerical simulations, we show that the massive galaxies at z = 2, which have a gas fraction of about 50%, form massive (10**7-8 solar masses) and gravitationally bound structures, which we call clumps thereafter. These clumps do not form in galaxies with a gas fraction below 25%. We then present an observational study of a local analogue of a z = 2 galactic clump, which is the tidal dwarf galaxy NGC 5291N. The analysis of emission lines show the presence of shocks on the outskirts of the object. Photometry of this galaxy’s stellar clusters show that the youngest clusters (< 10 million years) are significantly less massive than older clusters. This could be the sign of ongoing cluster mergers and/or of a strong star formation activity in this system about 500 million years ago).Secondly, we study how the gas fraction impacts the formation of stars and stellar clusters in galaxy mergers at z = 2. Using numerical simulations we show that these mergers only slightly increase the star and stellar cluster formation rate, compared to local galaxy mergers, which have a lower gas fraction. We show that this is due to the saturation of several physical quantities, which are already strong in isolated z=2 galaxies and are thus less enhanced by the merger. These factors are gas turbulence, compressive tides and nuclear gas inflows, We also show that the stellar structures formed in the gaseous clumps are preserved by the fusion: they are ejected from the disk and orbit in the halo of the remnant galaxy, where they may become the progenitors of some globular clusters
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Rudick, Craig S. "The Formation and Evolution of Intracluster Light: Simulations and Observations." Case Western Reserve University School of Graduate Studies / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=case1282831433.
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Cooke, Elizabeth A. "How to build a cluster : the formation and evolution of galaxies in high-redshift clusters and protoclusters." Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/35454/.
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High redshift galaxy protoclusters are the precursors of today’s massive clusters; the sites of formation of the most massive galaxies in the present-day Universe. By studying these immature structures we can directly analyse the formation of galaxies in the densest environments without relying on extrapolations from low redshift. Finding protoclusters is challenging due to the need for very wide and deep surveys. Radio-loud active galactic nuclei (RLAGN) have been shown to preferentially reside in overdense environments at z > 1. By using these bright radio sources as beacons, protoclusters may be efficiently selected, without the need for large, blind surveys. In this thesis I study the properties of galaxies in high redshift (z > 1.3) clusters and protoclusters selected around RLAGN. Using a sample of 37 clusters and protoclusters from the Clusters Around Radio-Loud AGN (CARLA) survey, I show that the protocluster galaxies have an approximately unevolving, red observed-frame i'-[3.6] colour across 1.3 < z < 3.2. This is at odds with the simple models which are commonly used to explain the cluster red sequence in the local Universe, which predict cluster galaxy colours to become more blue at higher redshifts. Taking the full cluster population into account, I show that the formation of stars within the majority of massive cluster galaxies occurs over at least 2 Gyr, and peaks at z ~ 2–3. This is consistent with the cosmic star formation history, with star formation ending in clusters at 1 < z < 2. I further show that massive galaxies at z > 2 must have assembled within 0.5 Gyr of them forming a significant fraction of their stars. This means that few massive galaxies in z > 2 protoclusters could have formed via dry mergers. Some of the CARLA structures exhibit signs of being mature, collapsed clusters. In a pilot project, I report on the discovery of a z = 1.58 cluster with a strong red sequence around the RLAGN 7C 1753+6311. I demonstrate that the cluster has an enhanced quiescent galaxy fraction that is three times that of the control field. I also show that this enhancement is mass dependent: 91 +/- 9% of the M* > 10^10.5 Msun cluster galaxies are quiescent, compared to only 36 +/- 2% of field galaxies, whereas the fraction of quiescent galaxies with lower masses is the same in the cluster and field environments. This is in contrast to low redshift studies which have shown that mass and environmental effects on quenching star formation are separable. In the literature there is some debate as to whether RLAGN preferentially reside in clusters of a certain stage of collapse. The presence of a dense core and a well-formed, quiescent red sequence suggest that 7C1753+6311 resides within a mature cluster. This means that distant RLAGN do not solely reside in young, uncollapsed protoclusters, rather they can be found in clusters in a wide range of evolutionary states. Finally I present results from surveys of Halpha emitters in the fields around three high redshift RLAGN. I find that there is more dust-obscured star formation in protocluster galaxies than in similarly-selected control field galaxies at z ~ 2.5 and there is tentative evidence of a higher fraction of starbursting galaxies in the denser environment. However, on average I do not find a difference between the star formation rate (SFR)-mass relations of the protocluster and field galaxies and so conclude that the SFR of these galaxies at z ~ 2.5 is governed predominantly by galaxy mass and not the host environment. The stellar mass distribution of the protocluster galaxies is also skewed towards higher masses and there is a significant lack of low mass (M < 10^10 Msun) galaxies within the protocluster core. These results have implications for future protocluster surveys. The lack of low mass galaxies affects the level of overdensity which is detected. If only high mass galaxies are considered, the density of the protocluster field may be over-estimated. This means that it is important when quantifying protoclusters to compare their mass functions, rather than simply number overdensities. I also find that some radio galaxies do not reside in the centre, or densest region of the surrounding structure, meaning the overdensity measured in an aperture centred on the RLAGN will be underestimated. This means that future studies of (proto)clusters around RLAGN should use larger fields of view in order to establish the existence of a (proto)cluster.
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Lin, Pei. "First-principles calculations of helium cluster formation in palladium tritides." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/41103.
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The accumulation of helium atoms in metals or metal tritides is known to result in the formation of helium bubbles in the lattice and to cause degradation of the material. Helium is introduced either through neutron transmutation reaction or via the radioactive decay of tritium. We have performed first-principles calculations of interstitial helium inside Pd and Pd tritide using density functional theory (DFT) and the projector augmented-wave (PAW) method within the generalized gradient approximation (GGA). We model the growth process of an interstitial helium cluster and find that when the size of the cluster reaches to five atoms, the cluster can induce an energetically favorable vacancy with a self-trapping mechanism. The cluster growth mechanism of interstitial helium is addressed by investigating the associated energetics, cluster configurations, and electronic structural properties.
In addition, we study the diffusion properties of helium in palladium-based compounds by performing the nudged elastic band (NEB) calculations. Our computational models propose that by loading the lattice with hydrogen atoms at certain concentration, or substituting with alloying metals can modify the diffusivity by increasing its migration barrier, which may impede the cluster formation in the beginning stage.
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Corbett, Jennifer Leontine. "Sodium-cluster complexes : probability of formation, stability and mass spectra." Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/41966.
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Accurate knowledge of aerosol size and composition is important for the understanding of their effects on both the atmosphere and the health of those who inhale them. Ultrafine aerosols (0.25 nm to 10 nm radius) and small clusters (2 molecules to 0.25 nm radius) can only be detected down to radii of a few nanometers and no chemical information is provided. A photoion spectrometer was previously built and is used to dope clusters and ultrafine aerosols with Na atoms. The subsequent Na-cluster complexes are then ionized by a UV laser. This technique is currently believed to be the softest ionization method available. Calculations were done to predict the efficiency of this system because a direct comparison with other systems cannot be made over the complete size range. These calculations include, the probability of a particle colliding with a Na atom in the oven, the average lifetime of Na-cluster complexes and their photoionization efficiency. Calculations in this thesis focus on the collision probability and include predictions as to the most efficient temperature of the Na oven for Na pick up. The temperature of the Na oven was also found to experimentally agree with the calculations, because the vapor pressure of Na plays a significant role in the collision probability. Characterization of the sodium doping technique was done through experiments comparing direct XUV ionization with UV ionization of small Na doped clusters. The fragmentation of acetic acid clusters was characterized for the monomer and oligomers up to the tetramer. It was found that up to two acetic acid molecules evaporated from the clusters. The Na doping technique also reveals a significant difference in the size distribution as seen by UV and XUV laser ionization for large dimethyl ether and acetic acid clusters, and a smaller yet visible difference for large water clusters. Different UV wavelengths were also investigated including wavelengths above and below the ionization energy of a lone Na atom. The Na doping technique was found to be a softer technique than direct ionization with XUV light, because no fragmentation of molecules occurred and evaporation was minimized.
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Thomas, Claire F. "Environmental dependence of star formation in field and cluster galaxies." Thesis, Liverpool John Moores University, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.439066.
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Akizuki, Makoto. "Gas Cluster Ion-Solid Surface Interaction and Thin Film Formation." Kyoto University, 1999. http://hdl.handle.net/2433/181783.
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Haack, Alexander [Verfasser]. "Theoretical Investigations on Cluster Formation in Mass Spectrometry / Alexander Haack." Wuppertal : Universitätsbibliothek Wuppertal, 2020. http://d-nb.info/1207005800/34.
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Adamo, A., J. E. Ryon, M. Messa, H. Kim, K. Grasha, D. O. Cook, D. Calzetti, et al. "Legacy ExtraGalactic UV Survey with The Hubble Space Telescope: Stellar Cluster Catalogs and First Insights Into Cluster Formation and Evolution in NGC 628." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/624449.
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We report the large effort that is producing comprehensive high-level young star cluster (YSC) catalogs for a significant fraction of galaxies observed with the Legacy ExtraGalactic UV Survey (LEGUS) Hubble treasury program. We present the methodology developed to extract cluster positions, verify their genuine nature, produce multiband photometry (from NUV to NIR), and derive their physical properties via spectral energy distribution fitting analyses. We use the nearby spiral galaxy NGC 628 as a test case for demonstrating the impact that LEGUS will have on our understanding of the formation and evolution of YSCs and compact stellar associations within their host galaxy. Our analysis of the cluster luminosity function from the UV to the NIR finds a steepening at the bright end and at all wavelengths suggesting a dearth of luminous clusters. The cluster mass function of NGC 628 is consistent with a power-law distribution of slopes similar to-2 and a truncation of a few times 10(5) M-circle dot. After their formation, YSCs and compact associations follow different evolutionary paths. YSCs survive for a longer time frame, confirming their being potentially bound systems. Associations disappear on timescales comparable to hierarchically organized star-forming regions, suggesting that they are expanding systems. We find massindependent cluster disruption in the inner region of NGC 628, while in the outer part of the galaxy there is little or no disruption. We observe faster disruption rates for low mass (<= 10(4) M-circle dot) clusters, suggesting that a massdependent component is necessary to fully describe the YSC disruption process in NGC 628.
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Shim, Young Hak. "Design of a cluster analysis heuristic for the configuration and capacity management of manufacturing cells." Diss., Texas A&M University, 2003. http://hdl.handle.net/1969.1/5905.
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This dissertation presents the configuration and capacity management of manufacturing cells using cluster analysis. A heuristic based on cluster analysis is developed to solve cell formation in cellular manufacturing systems (CMS). The clustering heuristic is applied for cell formation considering processing requirement (CFOPR) as well as various manufacturing factors (CFVMF). The proposed clustering heuristic is developed by employing a new solving structure incorporating hierarchical and non-hierarchical clustering methods. A new similarity measure is constructed by modifying the Jarccard similarity and a new assignment algorithm is proposed by employing the new pairwise exchange method. In CFOPR, the clustering heuristic is modified by adding a feedback step and more exact allocation rules. Grouping efficacy is employed as a measure to evaluate solutions obtained from the heuristic. The clustering heuristic for CFOPR was evaluated on 23 test problems taken from the literature in order to compare with other approaches and produced the best solution in 18 out of 23 and the second best in the remaining problems. These solutions were obtained in a considerably short time and even the largest test problem was solved in around one and a half seconds. In CFVMF, the machine capacity was first ensured, and then manufacturing cells were configured to minimize intercellular movements. In order to ensure the machine capacity, the duplication of machines and the split of operations are allowed and operations are assigned into duplicated machines by the largest-first rule. The clustering heuristic for CFVMF proposes a new similarity measure incorporating processing requirement, material flow and machine workload and a new machine-part matrix representing material flow and processing time assigned to multiple identical machines. Also, setup time, which has not been clearly addressed in existing research, is discussed in the solving procedure. The clustering heuristic for CFVMF employs two evaluation measures such as the number of intercellular movements and grouping efficacy. In two test problems taken from the literature, the heuristic for CFVMF produced the same results, but the trade-off problem between the two evaluation measures is proposed to consider the goodness of grouping.
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Messa, M., A. Adamo, G. Östlin, D. Calzetti, K. Grasha, E. K. Grebel, F. Shabani, et al. "The young star cluster population of M51 with LEGUS – I. A comprehensive study of cluster formation and evolution." OXFORD UNIV PRESS, 2018. http://hdl.handle.net/10150/626277.
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Recently acquired WFC3 UV (F275W and F336W) imaging mosaics under the Legacy Extragalactic UV Survey (LEGUS), combined with archival ACS data of M51, are used to study the young star cluster (YSC) population of this interacting system. Our newly extracted source catalogue contains 2834 cluster candidates, morphologically classified to be compact and uniform in colour, for which ages, masses and extinction are derived. In this first work we study the main properties of the YSC population of the whole galaxy, considering a mass-limited sample. Both luminosity and mass functions follow a power-law shape with slope -2, but at high luminosities and masses a dearth of sources is observed. The analysis of the mass function suggests that it is best fitted by a Schechter function with slope -2 and a truncation mass at 1.00 +/- 0.12 x 10(5) M-circle dot . Through Monte Carlo simulations, we confirm this result and link the shape of the luminosity function to the presence of a truncation in the mass function. A mass limited age function analysis, between 10 and 200 Myr, suggests that the cluster population is undergoing only moderate disruption. We observe little variation in the shape of the mass function at masses above 1 x 10(4) M-circle dot over this age range. The fraction of star formation happening in the form of bound clusters in M51 is similar to 20 per cent in the age range 10-100 Myr and little variation is observed over the whole range from 1 to 200 Myr.
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Nuur, Cali. "Cluster Dynamics and Industrial Policy in Peripheral Regions : a study of cluster formation as a local development process." Doctoral thesis, Stockholm : Department of Industrial Economics and Management, Royal Institute of Technology : Arbetslivsinstitutet, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-475.
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Usui, Hiroaki. "IONIZED CLUSTER BEAM TECHNIQUES: Formation of Cluster Beams by Vaporized Solid Materials and Their Applications to Film Depositions." Kyoto University, 1987. http://hdl.handle.net/2433/74708.
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Tsai, Chao-Wei. "Star cluster formation in the nuclear regions of nearby spiral galaxies." Diss., Restricted to subscribing institutions, 2009. http://proquest.umi.com/pqdweb?did=1997620851&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
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Perrett, Kathryn. "The globular cluster system of M31, keys to its formation history." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/NQ63443.pdf.
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Wang, Yan. "Chinese entrepreneurship and cluster formation : multi-case studies from east China." Thesis, University of Central Lancashire, 2011. http://clok.uclan.ac.uk/3718/.
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Cluster is not a new phenomenon, having existed in different forms for a long time. Although a large amount of work has been dedicated to cluster research (Marshall, 1920; Krugman, 1995; Schmitz 1997; Porter, 1998; Wilson and Popp, 2003), there is still a lack of convincing explanations as to how and why clusters are created. Reviewing the different definitions of ‘cluster’ from previous studies, produces the interesting finding that most of the cluster definitions neglect one key element – the ‘actor’ – that is, the individuals who are involved in the process of founding new businesses that give rise to cluster formation. Recognising the values and shortcomings of the extant studies on clusters, this thesis aims to establish a conceptual framework and attempt to advance the understanding of the cluster formation process from an alternative view. The purpose is to answer the research questions of how and why cluster are formed, how different actors interact with key institutional factors relevant to cluster creation and how these actors themselves make sense of the cluster creation process, particularly in the Chinese context. This research employs a qualitative approach comprising semi-structured in-depth interviews, which seek to uncover the depth and richness of the living experiences of different actors with the SME clusters. Fieldwork was completed in multi-phases involving a preliminary data collection in phase one, followed by a further data collection in the second and subsequent phases through re-interviewing the key informants. The findings of the three empirical case studies echoed the claims that the very notion of a cluster is a dynamic, and for some a ‘Chaotic’ one (Martin and Sunley, 2003). This highlights the importance of a comprehensive framework to address the complex web of elements that are involved in cluster formation. The result of the thesis also indicates that individual (entrepreneurs & social relations), and the social interactions among individuals and their institutional context are the key ingredients for forming clusters. It is suggested that the established conceptual framework, based upon the theories of institutionalisation, social embeddedness and sensemaking, can help to fill the gap in the extant cluster research and pave the way for future research.
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SHAH, VIVEK. "PARALLEL CLUSTER FORMATION FOR SECURED COMMUNICATION IN WIRELESS AD HOC NETWORKS." University of Cincinnati / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1097709696.
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Tirumalai, Nakul. "LCPlace: A Novel VLSI Placement Methodology based on large cluster formation." University of Cincinnati / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1396530925.
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Bressert, Eli Walter. "The initial distribution of stars." Thesis, University of Exeter, 2012. http://hdl.handle.net/10036/3890.
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The primary focus of my PhD is to quantify the spatial distribution of star-forming environments from optical to radio wavelengths using data from the Hubble Space Telescope, the Very Large Telescope, the Spitzer Space Telescope, the Herschel Space Observatory, and the Caltech Submillimeter Observatory. Towards the end of my PhD study I have developed theoretical models. With these observational and theoretical avenues I have led a series of research projects to (1) quantify the initial spatial structure of pre-stellar cores and proto-stars, (2) test whether massive stars can form in isolation or not, (3) and develop a theoretical model on how young massive clusters form. These research projects have been fruitful as my collaborators and I have shown that pre-stellar cores and stars form in a smooth continuum of surface densities from a few to thousands of stars per pc^2. These two works have important implications on our understanding of what a young stellar cluster is and how star forming environments can evolve to form field star populations or gravitationally bound clusters. In my second study my collaborators and I found evidence for isolated massive star formation in the active star forming region 30 Doradus, in the Large Magellanic Cloud. The result impacts the field of the initial mass function and star formation models. Massive stars forming in isolation is consistent with a stochastically sampled initial mass function. Additionally, the result would put constraints on theoretical models on massive star formation. Continuing my work on massive star forming environments my collaborators and I have developed a theoretical model on how young massive clusters form. From the models we argue that feedback energies can be contained by the gravitational potential well of the massive progenitors. Furthermore, we predict the physical properties the massive cluster progenitors in terms of initial gas mass, radii and flux brightness to enable a search for these objects in Galactic plane surveys and upcoming telescopes. Using the common thread of spatial distribution analysis of star formation I describe my future research plans, which entails studies on extragalactic scales in the conclusion.
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Kuntschner, Harald. "The star formation history of early-type galaxies in the Fornax cluster." Thesis, Durham University, 1998. http://etheses.dur.ac.uk/4849/.
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We have measured central line strengths and line-strength gradients for a complete sample of early-type galaxies in the Fornax cluster, comprising 11 elliptical and 11 lenticular galaxies, more luminous than M(_B) = -17. We find that the centres of Fornax ellipticals follow the locus of galaxies of fixed age in Worthey's models and have metallicities varying roughly from half solar to 2.5 times solar. Line-strength gradients indicate that elliptical galaxies do not show age gradients with radius but do exhibit a decrease of ~ 0.4 dex in [Fe/H] between the centre and one effective radius. The centres of lenticular galaxies however exhibit a substantial spread to younger luminosity weighted ages indicating a more extended star formation history. Metallicity gradients are generally shallower than for ellipticals. Five of the faint S0s have experienced a central starburst on top of an underlying older stellar population. Our conclusions are based on several age/metallicity diagnostic diagrams in the Lick/IDS system comprising established indices such as [MgFe] and Hβ as well as new and more sensitive indices such as C4668, Fe3 and Hγ(_A). The inferred difference in the age distribution between lenticular and elliptical galaxies is a robust conclusion as the models generate consistent relative ages using different age and metallicity indicators even though the absolute ages remain uncertain. The absolute age uncertainty is caused by the effects of non-solar abundance ratios which are not accounted for in the stellar population models. We find that Es are generally overabundant in magnesium where the most luminous galaxies show stronger overabundances. The luminosity weighted stellar populations of young S0s are consistent with solar abundance ratios, however the bulges of the two large S0s in our sample have [Mg/Fe] > 0. We have analysed in detail the sources of scatter in the Mg-crg relation by investigating the effects of age, metallicity and [Mg/Fe] variations. We find that young stellar populations are responsible for most of the scatter towards weak Mg-absorption. However, for the roughly coeval ellipticals the scatter at a given ctq is correlated with [Mg/Fe variations; metallicity and age effects seem to be less important. The young luminosity weighted ages of the faint S0s in the Fornax cluster are consistent with the recent discovery that the fraction of S0 galaxies in intermediate redshift clusters is a factor of 2-3 lower than found locally, and suggests that a fraction of the cluster spiral galaxy population has evolved into these faint S0s in the 5 Gyrs interval from z = 0.5 to the present. One of the proposed transformation mechanisms is the galaxy harassment picture. The properties of young S0s with large bulge to disk ratios in our sample are remarkably similar to the proposed end-products of galaxy harassment. However, we note that there are young disky S0s which are unlikely to be the result of harassment. Two of the faintest lenticular galaxies in our sample have blue continua and extremely strong Balmer-line absorption suggesting starbursts < 2 Gyrs ago.
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Jones, Christopher William. "Dynamics, formation and segregation of the cytoplasmic chemoreceptor cluster in Rhodobacter sphaeroides." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:73ce27e2-260e-4b1d-a746-cf7e7df6a02e.
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The internal organisation of bacteria is far more complex than originally thought. Many components of the cell have specific localisation patterns. Proteins are localised to many different regions of the cell by numerous mechanisms, and often their function depends on correct localisation. Bacterial and plasmid DNA are also highly organised and actively positioned. These tightly regulated positioning patterns ensure stable maintenance of genetic material. Members of the ParA/MinD family of ATPases are responsible for the segregation of a large number of bacterial chromosomes and plasmids. Recently members of this family have been shown to position and segregate protein complexes. One such complex is the cytoplasmic chemosensory cluster of Rhodobacter sphaeroides. This large complexes are segregated from a single cluster positioned at the mid-cell to two clusters at 1/4, 3/4 positions by the ParA homologue PpfA using the nucleoid as a scaffold. This ensures that each daughter cell inherits a cluster. This study sought to investigate this cytoplasmic chemosensory cluster, and its positioning and segregation by PpfA through the cell cycle. The use of fluorescence recovery after photobleaching revealed that like membrane bound chemoreceptor arrays the cytoplasmic cluster of R. sphaeroides is a highly stable complex. The difference seen between the cytoplasmic cluster and the data reported for the membrane bound cluster of Escherichia coli is probably due to the lack of membrane helping hold the array together. Investigation of the role of PpfA in segregation of the cytoplasmic cluster, using fluorescence imaging and single molecule tracking with a range of mutants through the cell cycle, suggest that it uses a mechanism unlike any reported for ParA homologues. Single molecule tracking of PpfA molecules shows that the chemoreceptor TlpT stabilises PpfA molecules resulting in slower diffusion of PpfA molecules at the cluster. The use of a ΔppfA mutant shows that PpfA restrains the movement of the cluster, together these results suggest a model in which TlpT stabilises PpfA’s interaction with the nucleoid and PpfA positions the cluster.
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Holfinger, Steven James. "PANC-1 Migration And Cluster Formation Is A Result Of Random Migration." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1308332896.
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Turner, Thomas Daniel. "Molecular self-assembly, nucleation kinetics and cluster formation associated with solution crystallisation." Thesis, University of Leeds, 2015. http://etheses.whiterose.ac.uk/11929/.
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The structural pathway from a single molecule to clustering through to nucleation during a crystallisation process is not fully understood. As such the solution state structure, nucleation kinetics and phase transformation kinetics of p-Aminobenzoic (PABA) acid are probed using a combination of in-situ crystallisation characterisation techniques and nucleation kinetic analysis methods. The solubility of alpha PABA is measured in a number of solvents where van’t Hoff analysis shows that solute-solute interactions are probable in all solvents. Solution state FTIR studies reveal the presence of a distribution of solvated monomer and carboxylic acid dimer species in acetonitrile solutions. This provides a link between solution state structural synthons and the carboxylic acid dimer structural synthon of the alpha PABA solid phase. Isothermal nucleation kinetic analysis reveals that calculated interfacial tension, γeff, values are found to be low for an organic material; where γeff values are 0.85 – 1.31 mJ/m2 in ethanol and 2.36 – 2.60 mJ/m2 in water. Due to this the critical cluster sizes are in the region of 0.48 – 1.98 nm. Poly-thermal kinetic analysis reveals a nucleation mechanism change from instantaneous to progressive as a function of decreasing solubility in ethanol, acetonitrile and water. This is caused by an increase in attachment frequency due to decreasing de-solvation free energy of PABA found from molecular dynamics simulations, this in combination with increasing γeff causes the thermodynamic component of the nucleation rate to become limiting. Isothermal and poly-thermal X-ray scattering studies of PABA nucleation reveal the formation of large liquid-like clusters of PABA, >40nm, in the under-saturated state. These Nano-scale assemblies increase in size and structural ordering, indicated by an increase in fractal dimensionality from 1 – 2 as a function of driving force. The Guinier region of the high q structures is found to increase from Rg = 0.46nm to 0.53 nm which indicates a population of monomers and dimers of PABA in the supersaturated state. This was confirmed as the carboxylic acid dimer structure from form factor fitting of known structural synthons of the alpha phase. In-situ XRD studies of the polymorphic phase transformation of the beta-alpha phase, indicates that the dissolution and growth processes are consistent with zero order nucleation kinetics and first and zero order kinetics respectively with the latter seemingly temperature dependant. UV/Vis analysis in combination with the XRD data reveal the transformation is a dissolution controlled process explained by particle morphology. The transformation temperature was also estimated from the growth and dissolution rate constants as 22.8 – 23.6 °C.
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Rosander, Christian. "Characteristics of convective cloud cluster formationover Thailand through satellite image analysis." Thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-303916.
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Weather forecasting relies on the availability of observational data as input parameters. However,such data are not readily available, because of difficulties to collect weather data due toinaccessibility to many places in the world, such as oceans or mountain regions. For this reason,satellite surveillance is a suitable tool to observe the atmosphere in regions where it is notpossible by other means. This master thesis is a study of convective cloud cluster formation over Thailand, conductedthrough satellite image analysis. Characteristics of cloud cluster formations are investigatedthrough an implementation of the Maximum Spatial Correlation Technique (MASCOTTE),described by Carvalho and Jones (2001). This method allows tracking of convective cloud systemsthrough region based analysis of satellite images. The aim of this study is to investigate whether satellite image analysis, through the implementationof the MASCOTTE methodology, can provide characteristics of convective cloud systems,in order to discern convective systems by intensity, accurately enough to be able to discernsevere thunderstorms from ordinary thunderstorms. The annual distribution of the occurrenceof life cycles detected through the analysis is studied, as well as their monthly distribution ofmean and maximum life times. Moreover, the yearly distribution of life cycle mean and minimumbrightness temperatures are analysed, as well as the number of detected split and mergeevents. This is followed by a comparison of life cycle structural properties to investigate thepossibility to use individual parameters, alone or in combination with each other, as indicatorsof the degree of convective activity within life cycles. Yearly distributions were studied in order to verify if this method could reveal seasonal variations,such as the onset period of the wet season, in terms of the occurrence of life cycles andtheir life time. The findings of this study verified that the most convectively intense life cycles exist under theinfluence of the Inter Tropical Convergence Zone (ITCZ), during the onset and beginning ofthe monsoon season. Analysis of life cycle structural properties, showed that properties likemean and minimum brightness temperature as well as fractional convective area, could be usedas indicators to discern between life cycles with different level of convective activity. However,it is concluded that studies, including ground-based remote sensing technologies such asRADAR/LIDAR, as well as data from rawinsondes, needs to be conducted in order to clarifyif it is possible to use this methodology to successfully discern severe thunderstorms fromordinary thunderstorms.Tillgängligheten av meteorologiska mätdata är väsentlig för att kunna prognostisera väder. Idag är tillgängligheten på dessa data relativt gles, bland annat på grund av svårigheter att mäta på många platser runt om i världen, t.ex över världshaven eller vid otillgängliga bergsområden. Därför är satellitövervakning ett bra alternativ till andra typer av väderobservationer, eftersom denna teknik kan tillhandahålla mätdata över stora områden som annars inte är möljiga att samla data från. Denna magisteruppsats är en studie om egenskaper hos konvektiv molnbildning över Thailand. Studien är genomförd med hjälp av satellitbildsanalys. Egenskaper hos olika konvektiva molnceller har studerats genom att använda en metod baserad på ”the Maximum Spatial Correlation Technique” (MASCOTTE), beskriven av Carvalho and Jones (2001). Tanken bakom denna metod är att hitta och följa utvecklingen av olika konvektiva molnceller baserat på deras storlek och temperatur. Målet med studien är att undersöka hurvida denna metoden kan ge kunskap som leder till att man kan skilja på konvektiva celler, genom intensitetsskillnader, med tillräcklig noggrannhet för att kunna urskilja vanliga konvektiva celler från intensiva celler. För att få en uppfattning om förekomsten av intensiva konvektiva system, har antalet detekterade livscykler per månad studerats. För sedan att få en bild av hurvida deras livscykler skiljer sig åt över året, har även egenskaper som medellivslängd och maximal livslängd studerats. Dessutom studerades den årliga fördelningen av livscyklernas medel och minimum temperaturer, samt förekomsten av delningar och sammanslagningar av konvektiva celler. För att finna kunskap om skillnader i intensitet mellan individuella livscykler, har egenskaper som medel och minimum temperatur analyserats. Dessutom har andelen moln med extremt låg temperatur studerats i syfte att kunna använda dessa parametrar som intensitetsindikatorer vid satellitbildsanalys. Resultaten i denna studie visar att de mest intensiva konvektiva molnsystemen (kraftigaste åskvädren), förekommer under påverkan av ITCZ (Inter Tropical Convergence Zone), under antågandet och början av regnperioden. Studier av de konvektiva systemens egenskaper visade att parametrar, som andelen extremt kallt område i molnceller (fractional convective area), och livscyklernas medel och minimum temperaturer, skulle kunna användas som intensitetsindikatorer för att skilja på olika livscykler med avseende på deras styrka i intensitet. Slutsatsen av studien är att det behövs fler studier där andra typer av meteorologiska mätdata, såsom RADAR/LIDAR och sonderingsdata är involverade, för att skaffa ytterligare kunskap om hur man genom satellitbildsanalys kan urskilja kraftiga åskväder.
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Simanton, Lesley Ann. "Star Cluster Populations in the Spiral Galaxy M101." University of Toledo / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1437587267.
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Emmoth, Anna. "The Legitimacy Process that Supports the Formation and Development of Cluster Initiatives : The Case of a Tourism Cluster Initiative in Dalarna." Licentiate thesis, Karlstads universitet, Centrum för tjänsteforskning, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-42021.
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Today, large public investments are being made with the aim of creating and developing cooperation between businesses in inter-organizational networks. Such initiatives are commonly denoted cluster initiatives and their underlying purpose are to spur innovation and regional growth. Much research has been conducted in this field, but relatively few studies have examined the process of cluster initiatives. By following the case of a regional cluster project within the tourism industry in the region of Dalarna, Sweden, the objective of this thesis is to deepen the understanding of the formation and development process of cluster initiatives. The investigation has been conducted by examining two main themes; the internal relationships within the cluster initiative and the relationships between the cluster initiative and its external stakeholders, such as funding agencies, regional government and local businesses. The analysis is based on a legitimacy perspective and indicates that the coordinating body of the cluster initiative, the hub, principally deals with a legitimation process. What occurs within the cluster initiative, between the members themselves and between the members and the hub, is legitimation. This also applies to external relationships, between the hub and its external stakeholders. A prerequisite for the realization of its mission is that the hub obtain and sustain legitimacy; legitimacy for itself, for the other members, for the idea, for the different activities and for the industry as such.
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Young, Teresa Marie. "Statistical thermodynamics of cluster formation in dilute colloidal and coarse-grained protein solutions." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 206 p, 2010. http://proquest.umi.com/pqdweb?did=1997524011&sid=2&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Ikeda, Keisuke. "Physicochemical study on Alzheimer's amyloid-β fibril formation mediated by GM1 ganglioside cluster." 京都大学 (Kyoto University), 2009. http://hdl.handle.net/2433/124045.
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Bai, Lei. "The Effects of Dense Cluster Environments on Galaxies and Intracluster Dust." Diss., The University of Arizona, 2007. http://hdl.handle.net/10150/193609.
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Dense cluster environment influences the properties of galaxies and their evolution. In order to understand this environmental effect and how it evolves with time, we study the infrared (IR) properties of galaxies in three rich clusters. The IR luminosities provide us with extinction-free measurements of the star formation rates (SFRs) of these cluster galaxies. We find a strong evolution in the IR luminosity function (LF) of two z ∼ 0:8 clusters when compared to two local clusters. The evolution rate of the IR LF found in these clusters is consistent with the evolution in field IR LFs. The similar evolution rate found in very different environments favors some internal mechanism, e.g., the gradual consumption of the gas fuel in galaxies, as being responsible for much of the star formation evolution. The mass-normalized integrated SFRs within 0.5R₂₀₀ of these clusters also shows an evolution trend, ∝ (1 + z)5. But this evolution has large scatter and may be affected by the mass selection effect of the sample. In the dense cluster core regions (r < 0.3 Mpc), we find evidence for enhanced SFR suppression. A substantial fraction of members in MS 1054-03 (z ∼ 0.8) are still forming stars actively. This cannot be explained by the scenario where the cluster is only passively accreting star-forming galaxies from the surrounding field, after which their star formation is quenched quickly. We also study the extended IR emission from the intracluster dust (ICD) in A2029. We only find weak signals at 24 and 70 μm and obtain upper limits for the ICD emission.
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Sheehan, Patrick D., Josh A. Eisner, Rita K. Mann, and Jonathan P. Williams. "A VLA SURVEY FOR FAINT COMPACT RADIO SOURCES IN THE ORION NEBULA CLUSTER." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/622165.
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We present Karl G. Jansky Very Large Array 1.3, 3.6, and 6 cm continuum maps of compact radio sources in the Orion Nebular Cluster (ONC). We mosaicked 34 arcmin(2) at 1.3 cm, 70 arcmin(2) at 3.6 cm and 109 arcmin(2) at 6 cm, containing 778 near-infrared detected young stellar objects and 190 Hubble Space Telescope-identified proplyds (with significant overlap between those characterizations). We detected radio emission from 175 compact radio sources in the ONC, including 26 sources that were detected for the first time at these wavelengths. For each detected source, we fitted a simple free-free and dust emission model to characterize the radio emission. We extrapolate the free-free emission spectrum model for each source to ALMA bands to illustrate how these measurements could be used to correctly measure protoplanetary disk dust masses from submillimeter flux measurements. Finally, we compare the fluxes measured in this survey with previously measured fluxes for our targets, as well as four separate epochs of 1.3 cm data, to search for and quantify the variability of our sources.
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Scandariato, Gaetano. "The Initial Mass Function of the Orion Nebula Cluster from Near-Infrared Photometry." Doctoral thesis, Università di Catania, 2012. http://hdl.handle.net/10761/1027.
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The main goal of this thesis is the complete characterization of the IMF of the Orion Nebula Cluster (ONC) down to the Brown Dwarfs (BDs) regime, using ground-based Near-Infrared (NIR) photometric observations. The data taken in the framework of the Hubble Space Telescope (HST) Treasury Program on the ONC have been obtained with the wide-field imager Infrared Side Port Imager (ISPI) at the Blanco 4m telescope of CTIO, and cover an area of about 0.25 square degrees roughly centered on Theta1OriC. We observed the region in the JHKS bands with exposure times of 330 s. As a result of our survey, we provide
2MASS-calibrated astrometry and photometry for ~7000 sources in the ONC region.
Analyzing our photometric sample, we derive the contamination-completeness corrected (J,J-H) CMDs of the ONC, canceling out the contribution from the contaminant population. We also develop a statistical algorithm, which combines the CMD of the ONC with our reference isochrone and, taking into account the presence of extinction and NIR excess, derives the intrinsic Luminosity Function (LF) of the cluster. We finally combine the LF with our empirical NIR isochrone to derive a statistical estimate of the IMF at different distances from the cluster center. We find that the mass distribution of the cluster is peaked at ~0.16 M and falls off crossing the hydrogen burning limit, continuously decreasing in the BDs domain down to ~0.03 M . We also find that the substellar-to-stellar objects ratio in the ONC decreases with increasing distance from the cluster center, suggesting that BDs are preferentially formed in the deep gravitational potential well where the most massive stars of the Trapezium cluster are also found.
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Yu, Pui-ling, and 余佩玲. "Strong ram-pressure stripping and widespread star formation in the high-velocity system towards the center of the Perseus cluster." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2015. http://hdl.handle.net/10722/211150.
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I present spectroscopic imaging of the high-velocity system (HVS) towards the central cD galaxy (NGC 1275) in the Perseus Cluster at a high spectral resolution for the first time. Previous observation suggests that the HVS is a highly inclined dusty and gas-rich galaxy moving towards the center of NGC 1275 at a high speed of 3000 km/s relative to the systemic velocity of NGC 1275 through the hot intracluster medium (ICM). If this is the case, then the HVS should be undergoing intense ram-pressure stripping. However, there is tentative evidence for ram-pressure stripping in the HVS, and furthermore confined to a small region of the galaxy. Previous observations also point out that at the location where the HVS is seen, there are many star clusters seen towards the inner region of NGC 1275. The separation of young star clusters between those belong to NGC 1275 and those belong to the HVS is, however, not clearly defined.
The primary scientific objectives are to (i) search for evidence for ram-pressure stripping in the HVS, as well as signs of tidal interactions between the HVS and NGC 1275; and (ii) separate the numerous young star clusters seen towards the entire NGC 1275 into those associated with the HVS and those associated with NGC 1275. NGC 1275 and the HVS were observed simultaneously with the use of Potsdam Multi-Aperture Spectrophotometer. The main emission lines being studied are the Hα & [NII]λ6548,6483 lines in NGC 1275 and the HVS. I present maps of intensity distribution, velocity field and velocity dispersion of the Hαemission of the HVS, as well as the line ratio of the [NII] doublets lines to the Hα line in the HVS.
I find that the line ratio of [NII]/Hα is less than 0.1 throughout the entire body of the HVS, indicating metallicity is low in the HVS. I also find that the metallicity is decreasing with distance from the center, just like other normal spiral galaxies. I demonstrate that a large fraction of the young star clusters seen towards the inner regions of NGC 1275 are closely associated with bright Hα-emitting regions in the HVS, and trace the overall Hα-emitting body of the HVS, suggesting that some young star clusters are associated to the HVS. I find that there are two distributions of young star clusters in color-color space, providing a way to separate out the star clusters likely belong to the HVS. I present evidence that the HVS is experiencing intense ram-pressure stripping and also evidence suggesting that the HVS is possibly tidally interacting with NGC 1275.
The results demonstrate that the HVS is a dusty, gas-rich, low-metallicity galaxy that has been disrupted by ram-pressure stripping and possibly also tidal interactions. I show that the HVS exhibit widespread and vigorous (~3.6 MM_⊙ yr^(-1)) star formation over the last at least ~0.1 Gyr. The vigorous SFR of the HVS is in contrast to what suggested by the observed low metallicity (suggestive of relatively weak star-formation activity over the recent history). The SFR of the HVS is likely to be triggered by the same process that produces global distortion on the HVS, here ram pressure stripping and possibly tidal interaction are in consideration.published_or_final_version
Physics
Master
Master of Philosophy
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Starostina, А. "Cluster model of territorial community development program." Thesis, Sumy State University, 2017. http://essuir.sumdu.edu.ua/handle/123456789/55778.
Full textAbstract:
The mechanism of development program
formation for territorial community based on the cluster
approach has been offered. The mechanism is based on
a conceptual cluster model of programs. This model
includes four clusters: cluster of objects that form the
capability of territorial community, cluster of objects
that form "overcapability" of the community; cluster of
objects that define the focus area of the territorial
community; and a cluster of objects that do not meet the
overall focus area of local community, but generate
some profit. Based on different cluster layout in
program, four versions of a mathematical model of the
program have been developed.
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Pozzo, Monica. "The effect of high-mass stars on low-mass star formation." Thesis, Keele University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366445.
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Kriwattanawong, Wichean. "The formation and evolution of the galaxy population in the nearby cluster abell 1367." Thesis, Liverpool John Moores University, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.502762.
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Peralta-Quirós, Tatiana. "Exploring the relationship between destination accessibility, cluster formation and employment growth in Kendall Square." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/82847.
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Thesis (S.M. in Transportation)--Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 175-177).
The exploration of the links between transportation and land use highlights the cyclical relation of accessibility, activities and transit demand. Agglomeration theory focuses on the benefits in productivity that arise from high employment density areas when companies operate in the same sector; while cluster theory examines these centers more closely and stresses the importance of relationships among companies, as well as links to input services and employment. Previous research (Pushkarev & Zupan 1977) demonstrated that high trip density is unsustainable without an efficient public transportation system. This high employment density center fosters a unique kind of industry, focusing on the cutting edge of technology and research, bio-tech and technology start-ups. The location of Kendall Square, next to the Massachusetts Institute of Technology (MIT), and supporting transportation infrastructure make it highly accessible. This thesis explores Kendall Square, as well as other employment centers in the Greater Boston Area, in order to determine if Kendall may be considered an employment cluster. Utilizing census data, this thesis looks at employment changes, industries and worker types to explore Kendall's uniqueness. The study of the area also includes the evolution of commuting patterns (trip length distribution, trip origins, modal splits) in the last 30 years. In order to better understand current trends, it also utilizes employee interviews and MBTA service usage. Three transportation models for the Greater Boston Area that replicate socio-economic and transportation infrastructure conditions of 1990, 2000 and 2010, created using modeling software packages, TransCAD and Cube Voyager, are used to analyze the modal accessibility of each destination for those time periods. Accessibility measures are then utilized to develop a series of linear regression models that explore the relative importance of each modal accessibility measure on employment density and employment changes. The results suggest that transit accessibility is the most important modal measure to support high employment density areas. In order to continue fostering employment growth planners must provide a transit service capable of sustaining the employment changes for the region.
by Tatiana Peralta-Quirós.
S.M.in Transportation
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Perkins, Rachel A. "Business Clustering as a Collaboration Strategy for Small Tourism Businesses Contributing to Regional Destination Branding." Thesis, Griffith University, 2021. http://hdl.handle.net/10072/407570.
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Effective branding for destinations encourages visitation and ensures the financial stability of regions that rely on tourist expenditure. Literature reveals however, that the destination branding process is not straightforward, particularly in regional destinations of which Australia’s tourism industry is largely comprised. Scholars advocate for collaboration as a solution to enacting destination branding, but, the feasibility and practicality of working together presents many challenges. It is therefore crucial that collaboration is further understood by honing in on the collaborative strategy ‘business clustering’ to effectively unpack collaboration complexities. Business clustering combines the skills, talents and attributes of multiple stakeholders within a geographic region and has proven to be a successful strategy for enhancing destination branding. Surprisingly, past research has only investigated clusters that already exist in a region. Until the present thesis, there was no research that explored how these clusters are created, leaving a gap in academic knowledge and subsequently leaving regions without a cluster unable to reap its benefits.
The overarching research question of this thesis seeks to understand how small tourism businesses progress through the steps of cluster formation to contribute to destination branding. This thesis will explore the complexities of collaboration, identifying the role and contribution of stakeholder typologies and stakeholder networks to the contribution of cluster formation. The research adopted a participatory action research (PAR) design to bring together academics and industry to create practical knowledge. The study involved 19 stakeholders from local businesses, the local tourism organization and the local council in the Granite Belt region, the regional tourism organization for South-East Queensland and the state tourism organization in Queensland, Australia. Data collection occurred over 11 phases of enquiry during a two year period, resulting in a 45 file dataset which was thematically analysed by the researcher in Excel and NVIVO.
This thesis includes three journal papers. Paper 1 is a systematic narrative literature review that investigates the challenges of destination branding for small tourism businesses in regional areas, by exploring the concepts of collaboration. The findings from this paper emphasised the need for empirical research aimed at trialling how stakeholder collaboration can be implemented effectively from initiation. Papers 2 and 3 are empirical. Paper 2 is the first empirical paper in this domain that forms a tourism business cluster, subsequently reporting on the phases and steps to cluster formation. The cluster enabled participants to contribute to the destination brand in their region through the conceptualisation of an event that celebrates local artisan providers. The event is due to be hosted in the future after experiencing COVID-19 setbacks. Paper 3 provides critical insights into stakeholder typologies and stakeholder networks during the cluster formation process. The paper uncovers the degree to which different stakeholders types are helpful and/or harmful to the cluster formation process and contributes the Stakeholder Helpfulness Continuum (SHC), which depicts helpful and harmful stakeholder actions. It also offers insights into the composition of stakeholder networks pre and post cluster formation and the usefulness of the cluster in enhancing these stakeholder networks.
This thesis offers an array of new, significant contributions to theory, to practice and to methodology. Theoretically this thesis offers entirely new insights to the tourism collaboration literature, offering an empirically-tested Total Cluster Formation Framework (TCFF) which delivers insights on forming a business cluster, transferable to other collaboration forms. This thesis also contributes significantly to the stakeholder literature, offering insights to stakeholder typology with the development of the SHC which provides guidance on helpful and harmful stakeholder behaviour as it pertains to collaboration. Practically, this thesis offers guides for industry in creating and achieving effective cluster formation and other types of collaboration. The step-by-step TCFF can be followed by industry to form collaborations and the SHC provides useful insights to managing and understanding different stakeholder types and their behaviours. In terms of the methodological contribution, this thesis provides an insightful expansion of PAR as it is applied in the context of regional tourism as well as offering an expansion of new literature review techniques.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Dept Tourism, Sport & Hot Mgmt
Griffith Business School
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Barlović, Robert. "Traffic jams cluster formation in low-dimensional cellular automata models for highway and city traffic /." [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=969248830.
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