Browsing by Subject "Clusters"
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Item Explosion dynamics of van der Waals clusters using 38 nm XUV laser pulses(2016-08) Helal, Ahmed Mohammed; Ditmire, Todd; Keto, John W.; Bengtson, Roger D; Downer, Michael; Ben-Yakar, AdelaThe interaction of intense XUV laser pulses with matter and rare gas cluster has been the focus of the scientific c community for decades. This focus has been sparked by the ongoing efforts to reach microscopy with atomic resolution, leading to a time resolved image on the scale of the atomic motion. The interest in van der Waals clusters appears due to it's similarity with the small bio-molecules, studying the behavior of these cluster will shed some light on how the biomolecules behavior under intense laser pulse. We have conducted a major upgrade to the UT THOR laser system, that enables us to achieve 17.7 nJ of XUV energy, produced by high harmonic generation, which is used to conduct multiple cluster experiments. We investigated the dynamics of rare-gas clusters produced by Ar and Xe gases, the ion time of flight, kinetic energy and electron energy have been measured, the generation of ion kinetic energy of two di different temperatures (6 and 55 eV) due to hydrodynamic expansion was observed. viii For Xe clusters, we observed the generation of unexplained high charge states up to Xe^9+, that could be due to the effect of continuum lowering and inner ionization of the giant resonance 4d-level. We also investigated the dynamics of small molecule clusters. Stating with nitrogen clusters, we noticed a dependence of the ionization ratio between N+ 2 and N+on the cluster size has been noticed. In addition to that nitrogen clusters shows the highest ion kinetic energy generated between all the clusters investigated in this dissertation. The interaction of XUV laser pulses with Methane cluster is studied, we could not detect any high charges of methane fragments such as (CH2+ 4 ). However, we noticed that we generated multiple fragments by breaking C-H bonds (CH+3 ;CH+ 2 ;CH+) in addition to bare carbon with high cluster sizes. The generation of CH+5 , H+ and H+2 was also observed. Studying the partial yield of each of these reveals that the correlation between CH+ 5 and H+ is opposite to what is expected, which might be due to the change of the cluster properties or the expansion dynamic itself (towards more hydrodynamics).Item Galaxy proto-clusters as an interface between structure, cluster, and galaxy formation(2016-05) Chiang, Yi-Kuan; Gebhardt, Karl; Overzier, Roderik; Jogee, Shardha; Milosavljevic, Milos; Finkelstein, Steven; Ouchi, MasamiProto-clusters, the distant progenitor large-scale structures of present day galaxy clusters, represent a key phase of cluster growth during which most of the galaxies were still rapidly forming stars. They are potentially powerful cosmological probes, and are unique laboratories to study dark matter assembly, the cosmic baryon cycle, and the environmental impact on galaxy evolution. Albeit its pivotal role in understanding cluster formation, only a small and heterogeneous sample of proto-clusters has been observed to date. Theoretical characterizations have also remained relatively unexplored. In this dissertation, I present baseline models, detailed theory predictions, and broad observational applications of proto-clusters using state-of-the-art numerical simulations and deep-wide galaxy surveys. A dual focus of both structure formation and galaxy evolution is given throughout the thesis. To prepare for large statistical studies in upcoming surveys like the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX), the Subaru Prime Focus Spectrograph (PFS) survey, and the Wide Field Infrared Survey Telescope (WFIRST) survey, I develop key machinery to connect the main observables of proto-clusters with dark matter structure formation using simulations as a guide. In Chapter 2 and 3, I present, for the first time, a thorough analysis of the main properties of proto-clusters using ~3000 clusters in a set of cosmological N-body simulations and semi-analytic galaxy models. I characterize the growth of proto-clusters and their core halos in size and mass with cosmic time. I show that the progenitor regions of galaxy clusters can already be identified in galaxy surveys at very early times (at least up to z~5), provided that the galaxy overdensities are measured on a sufficiently large scale (5--30 Mpc comoving) and with sufficient statistics. I present the overdensities in matter, dark matter halos, and galaxies as functions of present-day cluster mass, redshift, bias, and selection window size that can be used to interpret the wide range of structures found in real surveys. A table of proto-cluster candidates selected from the literature is provided, and I discuss their properties in light of our simulation predictions. In Chapter 4 I report the discovery of a large sample of proto-cluster candidates in the 1.62 deg^2 COSMOS/UltraVISTA field traced by optical/infrared selected galaxies with photometric redshifts. By comparing properly smoothed three-dimensional galaxy density maps of the observations and a set of matched simulations incorporating the main observational effects, I found 36 candidate structures at 1.610^14} M_sun. With solely photometric redshifts, I successfully rediscover two spectroscopically confirmed structures in this field, suggesting that our algorithm is robust. This work is the first large sample of uniformly selected proto-cluster candidates, providing rich targets for spectroscopic follow-up and subsequent studies of cluster formation. Because of the need of precise galaxy redshifts for density mapping and the prevalence of star formation before quenching, nearly all the proto-clusters known to date were confirmed by spectroscopy of galaxies with strong emission lines. In Chapter 5 I develop a semi-empirical model for Lya escape and generate a set of mock Lya emitter catalogs. This formalism provides a realistic modeling of the galaxy bias, the scatter of the bias, and the stochasticity of the galaxy-dark matter halo connection, which has an enormous potential for studies of the large-scale structure at high redshift. The model suggests that there are two distinct regimes to power a Lya emitter. For massive galaxies, Lya emitters are preferentially less dusty and slightly less metal enriched, while their ages and star formation rates are indistinguishable from other star-forming galaxies of the same mass. In contrast, low mass Lya emitters M_star<10^9 M_sun) are dominated by young objects with recent or ongoing starburst, with a gas phase metallicity diluted by cold accretion. In Chapter 6 I report a newly discovered large-scale structure at z=2.44 in the HETDEX Pilot Survey. On a scale of a few tens of (comoving) Mpc, this structure shows a complex overdensity of Lya emitters, which coincides with broad-band selected galaxies in the COSMOS/UltraVISTA photometric and zCOSMOS spectroscopic catalogs, as well as overdensities of intergalactic gas revealed by Lya absorption maps. I use the mock Lya emitter catalogs constructed in Chapter 5 to predict the cosmic evolution of this structure, and confirm that part of the structure will collapse to form a galaxy cluster with 10^14.5+-0.4 M_sun by z=0. The galaxies inside this structure have a higher median stellar mass than those outside the structure. The overdense region also shows a boost in the number of extended Lya nebulae, and a marginal excess of active galactic nuclei relative to the field, supporting a scenario of accelerated galaxy evolution in cluster progenitors. Building upon the success of finding and characterizing the z=2.44 proto-cluster in the HETDEX Pilot Survey, in Chapter 7 I use the same mock Lya emitter catalogs to evaluate the baseline performance of a large proto-cluster search in the upcoming HETDEX survey. Based on the correlation between galaxy overdensity and the z=0 descendant halo mass calibrated in the simulation, I predict that several hundred 1.910^14.5 M_sun will be discovered in the 8.5 Gpc^3 of space surveyed by HETDEX. This sample will open up a rich, new area of statistical investigations of both structure formation and galaxy evolution processes inside dense structures. The future for this field is bright, as we are entering an era of Gpc^3 surveys beyond the local Universe. In Chapter 8 I close this thesis by providing a future outlook. Specific research directions with great potential to blossom are highlighted. With the theoretical and observational advancements laid out in this dissertation, we now have a much more solid foundation of this fascinating subject.Item Interaction of clusters with ultra short X-ray free electron laser pulses(2012-08) Kandadai, Nirmala Krishna; Ditmire, Todd R.; Hallock, G. A.Biomolecular imaging has become one of the most exciting potential applications of the Linear Coherent Light Source (LCLS), which is a source of intense femtosecond X-rays. It has been predicted that a highly intense pulse with pulse lengths on the order of a few femtoseconds should be sufficient to capture the image of a biomolecule before it is destroyed. However, the rate at which a large biomolecule explodes during exposure is a large unknown, and will likely be one of the major factors in determining if such imaging will succeed. Clusters were chosen as a size dependant model system, ideal to study the evolution of complex systems in X-ray fields. From earlier intense near-infrared (IR) experiments, it is known that depending on size and Z constitution, clusters explode by Coulomb or hydrodynamic forces. These two limits have very different cluster explosion times and signatures. Coulomb explosion is too fast to allow imaging, whereas a hydrodynamically expanding cluster is a much slower process. The ionization process leading to cluster explosion is strongly wavelength dependent as one passes from IR through XUV to the X-ray regime because the kinetic energy of the released electrons determines the charge imbalance within the cluster, and therefore, determines the explosion dynamics. Unlike in previous experiments performed with near IR or XUV pulses, irradiation by photons at the LCLS will lead to the ejection of energetic photo- and Auger- electrons which could easily escape from the cluster, leaving behind positive ions. The buildup of this charge during exposure can lead to a Coulomb explosion of the sample. On the other hand, if the charge accumulates, the photoelectrons will be held inside the cluster, where they could contribute to the cluster temperature and form a nanoplasma and expand hydrodynamically. The main goal of the thesis was to study the explosion dynamics of clusters generated due to their interaction with intense X-rays and look at its dependencies on the X-ray energy, photon fluence, absorption cross sections, sample constituency and sample size. This thesis also compares the results from X-rays with the corresponding results obtained using ultrashort XUV and Infrared lasers.Item Rovibrational spectroscopy calculations using a Weyl-Heisenberg wavelet basis and classical phase space truncation(2006-08) Lombardini, Richard Luzi; Poirier, Bill; Glab, Wallace; Gibson, Thomas; Gellene, GregNew basis set methods are examined regarding quantum mechanical calculations of energy levels and wave functions of bound systems. The first method (I) involves compact orthogonal wavelets as the basis set which is subsequently truncated using the guidance of a classical phase space picture of the system. In this dissertation, the first application of this technique to a real molecular system (neon dimer) is presented, and many of the technical details are developed for its use on any arbitrary system. Although in many respects, neon dimer represents a "worst-case scenario" for the method, it is still competitive with another state-of-the-art scheme applied to the same system. The second method (II) greatly improves the computed accuracies of the first through the introduction of phase space region operators, which increase the efficiency K/N of the basis set, where N is the number of basis functions needed to calculate K energy eigenvalues to a given level of accuracy. For one model system, the absolute error of the computed energy levels is reduced by nearly 4 orders of magnitude, as compared to method I. Finally, a new parallel algorithm for matrix diagonalization (method III) is introduced, which uses a modified subspace iteration method. The new method exhibits great parallel scalability, making it possible to determine many thousands of accurate eigenvalues for sparse matrices of order N approximately N ~ 106 or larger.