No description available.

No description available.

We examine the globular cluster system (GCS) of the isolated elliptical NGC 720 using the Gemini Multi-Object Spectrograph (GMOS) and have obtained spectra for 241 candidate globular clusters (GCs) extending to a galactocentric radius of 40 kpc. Of the 241 candidates, 120 are confirmed GCs, where 46 are members of the metal-poor, blue, population and 74 are members of the metal-rich, red, population. A (g-i)=0.50 colour split is used to identify the blue and red populations. We measure the full GCS to have a rotational velocity (Vrot) of 50 +/- 7 km/s with a position angle (PA) of 170 +/- 69 degrees. The red population has a Vrot = 97 +/- 14 km/s with PA = 147 +\- 18 degrees and the blue population has a Vrot = 79 +/- 7 km/s with PA = 89 +/- 18 degrees. The full GCS has an average velocity dispersion of 168 +/- 22 km/s, for the red population is 156 +/- 30 km/s and for the blue population is 181 +/- 33 km/s. The velocity dispersion pro file for all populations is constant with increasing radius, suggesting the presence of a dark matter halo. Using a tracer mass estimator, we have measured the mass out to 40 kpc as 1.8(+0.6/-0.1)x10^12 Msun for a potential which traces the dark matter pro file. We also estimate the M/L_V = 30 - 70. This study extends our survey of GCSs to isolated environments. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2011-01-31 11:30:54.389

This dissertation demonstrates new methods for increasing the performance and scalability of high performance networking technologies for use in clustered computing systems, concentrating on Ethernet/High-Speed networking convergence. The motivation behind the improvement of high performance networking technologies and their importance to the viability of modern data centers is discussed first. It then introduces the concepts of high performance networking in a commercial data center context as well as high performance computing (HPC) and describes some of the most important challenges facing such networks in the future. It reviews current relevant literature and discusses problems that are not yet solved. Through a study of existing high performance networks, the most promising features for future networks are identified. Sockets Direct Protocol (SDP) is shown to have unexpected performance issues for commercial applications, due to inefficiencies in handling large numbers of simultaneous connections. The first SDP over eXtended Reliable Connections implementation is developed to reduce connection management overhead, demonstrating that performance issues are related to protocol overhead at the SDP level. Datagram offloading for IP over InfiniBand (IPoIB) is found to work well. In the first work of its kind, hybrid high-speed/Ethernet networks are shown to resolve the issues of SDP underperformance and demonstrate the potential for hybrid high-speed networking local area Remote Direct Memory Access (RDMA) technologies and Ethernet wide area networking for data centers. Given the promising results from these studies, a set of solutions to enhance performance at the local and wide area network level for Ethernet is introduced, providing a scalable, connectionless, socket-compatible, fully RDMA-capable networking technology, datagram-iWARP. A novel method of performing RDMA Write operations (called RDMA Write-Record) and RDMA Read over unreliable datagrams over Ethernet is designed, implemented and tested. It shows its applicability in scientific and commercial application spaces and is applicable to other verbs-based networking interfaces such as InfiniBand. The newly proposed RDMA methods, both for send/recv and RDMA Write-Record, are supplemented with interfaces for both socket-based applications and Message Passing Interface (MPI) applications. An MPI implementation is adapted to support datagram-iWARP. Both scalability and performance improvements are demonstrated for HPC and commercial applications. / Thesis (Ph.D, Electrical & Computer Engineering) -- Queen's University, 2012-09-25 09:43:55.262

No description available.

Nucleases are an essential component of the prokaryotic CRISPR-Cas immunity as well as repair mechanisms within prokaryotic organisms. To better understand the adaptation step of CRISPR-Cas immunity, I have characterized three Cas4 proteins from hyperthermophilic archaea: SSO0001 and SSO1391 from Sulfolobus solfataricus and Pcal_0546 from Pyrobaculum calidifontis. All three proteins have metal-dependent 5′ to 3′ exonuclease and endonuclease activities, while SSO1391 also demonstrates 3′ to 5′ exonuclease activity. Site-directed mutagenesis confirmed that the conserved RecB motif residues are important for the nuclease activity in all three proteins. SSO0001 and Pcal_0546 also exhibit ATP-independent unwinding and cleavage of splayed arm substrates. Structural analysis of SSO0001 showed it is a toroidal decamer with a [4Fe-4S] cluster and Mn2+ ion bound in the active site located inside the internal tunnel. Our results show that Cas4 proteins have the ability to create 3'-DNA overhangs which may contribute to the addition of novel CRISPR spacers.

Nucleases are an essential component of the prokaryotic CRISPR-Cas immunity as well as repair mechanisms within prokaryotic organisms. To better understand the adaptation step of CRISPR-Cas immunity, I have characterized three Cas4 proteins from hyperthermophilic archaea: SSO0001 and SSO1391 from Sulfolobus solfataricus and Pcal_0546 from Pyrobaculum calidifontis. All three proteins have metal-dependent 5′ to 3′ exonuclease and endonuclease activities, while SSO1391 also demonstrates 3′ to 5′ exonuclease activity. Site-directed mutagenesis confirmed that the conserved RecB motif residues are important for the nuclease activity in all three proteins. SSO0001 and Pcal_0546 also exhibit ATP-independent unwinding and cleavage of splayed arm substrates. Structural analysis of SSO0001 showed it is a toroidal decamer with a [4Fe-4S] cluster and Mn2+ ion bound in the active site located inside the internal tunnel. Our results show that Cas4 proteins have the ability to create 3'-DNA overhangs which may contribute to the addition of novel CRISPR spacers.

Nanoclusters have special importance in nanotechnology because of their low dimensionality, which provides electronic, chemical, and magnetic properties that differ from those of the equivalent bulk materials. Suitably controllable self-assembly methods are required in order to incorporate nanoclusters into useful devices. The self-assembly method used in this study employs V-grooves as a template element for nanocluster device fabrication. The V-grooves are fabricated by optical lithography on SiO2/Si wafers and KOH wet etching. Bi clusters deposited on a V-groove form a self-assembled conducting wire. The clusters are produced using an inert gas aggregation source inside an ultra high vacuum compatible system. In order to characterise the assembly process, Bi clusters with different average sizes and velocities are deposited on V-grooves with different widths. The cluster bouncing was found to be the main process in forming the cluster wires. The bouncing angles were smaller than the incident angle, and they are dependent on the cluster size and velocity. For a certain bouncing angle, the wire width reflects the V-groove width because of the fixed bouncing angle. Nanocluster devices were fabricated by depositing the clusters on V-grooves with pre-formed Au/NiCr electrical contacts. The amount of the deposited material required to form an electrically conducting wire was found to be a function of the V-groove width and the wire length. The two point I(V) measurements in the voltage range between -1 and +1V showed linear characteristics for low resistance wires (kΩ), and non-linear characteristics for the high resistance ones (MΩ). The silicon substrate was used as a back gate. Applying a voltage to the gate was found to modify the electrical conduction of the cluster wire. The temperature dependence of the resistance of the nanocluster wires was studied in the temperature range of 4.2-473K, and all of the measured wires showed a negative temperature coefficient of resistance. These measurements allowed a detailed study of the conduction mechanisms through the cluster wires. The study showed that Bi clusters can be used for device fabrication. To size select the clusters prior to using them for the device fabrication, a high transmission mass filter is required. This transmission can be obtained using the von Issendorff and Palmer mass filter if it is operated using the optimum operation conditions. The mass filter consists of two pairs of parallel plates with horizontal openings in Plates 1 and 2, and it operates on the time of flight principle. During this project, the operation conditions of this mass filter were studied using both experiment and simulation. The study showed that the beam deflection angle is a critical factor in optimising the mass filter transmission efficiency. This angle is dependent on the accelerating voltage, ion mass, and the horizontal velocity of the ions. The optimum operation conditions for the mass filter were found and used to study the mass distribution of Pd ions produced by a magnetron sputtering source with variable cluster aggregation length.

This thesis covers the development of high-resolution model spectra of simple-stellar-populations (SSP) to be used in the measurement of the ages, metallicities and chemical abundances of unresolved extragalactic globular clusters (GCs). The models are compared to low- and high-resolution spectra of GCs in the Milky Way and M31 galaxies, whose properties are already known, to establish the effectiveness of both the SSP spectral grid and of the direct spectral fitting procedure employed in this work. The model SSP spectra were created using Dotter et al. (2007) isochrones, populated using the flux derived from a grid of stellar spectra, weighted by the Kroupa (2001) mass function. Models with varying mass loss from the red giant branch and varying numbers of He-burning stars were generated. The spectral grid currently covers a parameter range of 2 to 15 Gyrs in age, and -2.5 to 0 dex in [Fe/H] at an [alpha/Fe] of +0.4 dex. Metallicities derived for Milky Way GCs from Lick index comparisons to the model grid are in good agreement with values in the literature. The stellar spectral grid, from which the GC spectra are generated, has been created using ATLAS9 and SYNTHE. The spectra are at a resolution of R = 100,000 and cover a wavelength range from 3000 - 9000 Angstroms. Extensive work was undertaken in creating appropriate lists of atomic and molecular transition oscillator strength (log gf) values for this spectral grid. An automated program was created to alter the strengths of millions of atomic transition lines in the Kurucz atomic line lists to fit a model spectrum of appropriate parameters to that of the red-giant star Arcturus and to the Solar spectrum at shorter wavelengths (3000 - 3727 Angstroms). Comparisons to these observed spectra were made manually for several molecular lines and band-heads, and log gf values changed en-mass for all the lines of a given molecular species. The SSP spectra were compared to low-resolution spectra of Milky Way GCs. Integrated-light spectra of a large number of Galactic GCs were obtained from three sources: the Schiavon et al. (2005) Library of Integrated Spectra of Galactic Globular Clusters, taken using the Ritchey-Chretien spectrograph on the Blanco 4m telescope at Cerro Tololo Inter-American Observatory; spectra obtained through private communication with M. Bessell using the Double Beam Spectrograph on the 2.3m telescope at Siding Springs Observatory; and spectra obtained using the Robert Stobie Spectrograph on the 11m diameter Southern African Large Telescope. With resolutions of 1500 to 2800, abundances of individual elements could not be determined, but overall ages and metallicities were derived. The model spectra were fitted to the observed spectra using a Chi^2 minimisation procedure over large wavelength regions to fully utilise the information available in the spectra. Derived metallicity values were in agreement with literature values. However, age determinations were not consistent with those derived from photometric methods and had large associated uncertainties. The lack of age information in the spectra at such resolutions is a similar result to that found by other studies using the Schiavon data (eg. Mendel et al., 2007; Koleva et al., 2008). The SSP spectral grid was used to determine ages, metallicities and individual elemental abundances of three clusters (GCM06, GC5 and GC10) in the outer halo of M31. High-resolution spectra from Keck-HIRES were obtained through private communication with D. Forbes. Age and metallicity determinations were made simultaneously by fitting un-blended FeI lines and the H-beta and H-gamma lines. Diagnostic analysis (such as that done by Colucci et al., 2009) and simultaneous fitting of the FeI lines alone gave unrealistic age values that tended towards the lower limits (2 Gyrs) of the age grid. The age and metallicities derived in this work for these clusters are consistent with those found by Alves-Brito et al. (2009) using the same data. Abundances of a number of elements were derived from the high-resolution spectra. An overall enhancement of alpha-elements (from measurements of Ca, Si and Ti) was seen in all three clusters ([alpha/Fe] = 0.67 +/- 0.2, 0.63 +/- 0.2 and 0.5 +/- 0.2 dex for clusters GCM06, GC5 and GC10 respectively) which is greater than that found for other M31 GCs (Puzia et al., 2005; Colucci et al., 2009). A depletion in Mg compared to the other alpha-elements is seen, in accordance with patterns seen in both Milky Way and M31 GCs (Gratton et al., 2004; Colucci et al., 2009). All three clusters show varying levels of enhancements and depletion in the other measured elements (C, Sc, V, Cr, Mn, Ni, Ba), none of which follow the trends seen in Milky Way clusters. Comparisons to high-resolution spectra of Milky Way GCs, for which abundance ratios are known from the measurement of individual stars, need to be made to establish the accuracy of this elemental-abundance analysis. Overall, the system presented in this thesis is well designed to be used in the analysis of integrated-light spectra from distant, unresolved GCs. The uncertainties in the derived ages are still larger than desired, but the metallicity determination is very consistent when tested against clusters of known metallicities.

The birth of nanotechnology era has revolutionized materials science, catalysis and field of optoelectronics. Novel and unique phenomena emerge when material dimensions are reduced to ultra-small size regime and enter nanometre (2-100 nm) realm. Such novel materials are expected to replace bulk materials, offering lower cost of manufacturing and enabling progress in many areas such as solar cell, drug delivery, quantum communication and computing, catalysis and sensing applications. With the progress in nanomaterial synthesis and fabrication, the need for the state-of-art characterization techniques became obvious; such techniques help to establish a complete understanding of the nature and interactions of nanosized materials. In this thesis, the first part focuses on the synthesis of gold and ruthenium clusters, namely Au8, Au9, Au101, Ru3, Ru4 and AuRu3, using the well-established synthetic protocols in the literature. Apart from the standard lab-based characterization techniques such as nuclear magnetic resonance (NMR), UV-visible spectroscopy (UV-vis) and Fourier Transform Infra-red (FTIR), a less explored but useful technique far infra-red (far IR) spectroscopy, available at the Australian Synchrotron (AS), was employed to investigate the vibrational modes in these clusters. Peaks in the experimental far IR spectra were assigned unambiguously to specific vibrations by comparing with the ones generated via DFT calculations with the help of collaborators, group of Professor Gregory Metha, University of Adelaide. For the Au9 cluster, three significant gold core vibrations are observed at 157, 177 and 197 cm-1 in the experimental spectrum. In the case of the Ru3 cluster, only a single ruthenium core vibration is identified within the spectrum, at 150 cm-1 with the calculated force constant, k = 0.33 mdyne/Å. The Ru4 cluster exhibits two metal core vibrations at 153 and 170 cm-1 with force constants of 0.35 and 0.53 mdyne/Å, respectively. Substitution with a gold atom yielding a mixed metal AuRu3 cluster shifts the core transitions toward higher wavenumbers at 177 and 299 cm-1 with an increase in force constants to 0.37 and 1.65 mdyne/Å, respectively. This is attributed to the change in chemical composition and geometry of the metal cluster core. A combination of the DFT calculations and high quality synchrotron-based experimental measurements allowed the full assignment of the key transitions in these clusters. Next, these clusters were fabricated into heterogeneous catalysts by depositing on different metal oxide nanopowders. Synchrotron X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) studies were performed at the Australian Synchrotron and the Photon Factory synchrotron in Japan to investigate the electronic structure of Au8, Au9 and Au101 on TiO2 catalysts. The XPS analysis reveals that “as-deposited” Au8 and Au9 retain some un-aggregated clusters while Au101 show bulk-like gold. These findings are in line with TEM observations, where the aggregates (large particles, > 2 nm) of Au8, Au9 and Au101 are hardly seen under HRTEM. UV-visible diffuse reflectance spectroscopy (UV-vis DRS) studies show the absence of localised surface plasmon resonance (LSPR) peaks in these “as-deposited” clusters, suggesting they are below 2 nm in size. Importantly, the XAS spectrum of “as-deposited” Au9 clusters estimates that 60% of pure, un-aggregated Au9 clusters and 40% of bulk gold in the sample. Upon calcination under O2 and combined O2 and H2 (O2-H2), Au8, Au9 and Au101 clusters form larger nanoparticles (> 2 nm) with the appearance of LSPE peak in UV-vis DR spectra. In addition, majority of the phosphine ligands (that stabilise the gold core) dislodge and form phosphine oxide-like species by interacting with oxygen on the TiO2 surface. The third part focused on testing the catalytic performance of the supported Au8, Au9, Au101, Ru3, Ru4 and AuRu3 clusters on different TiO2, SiO2, ZnO and ZrO2 in benzyl alcohol oxidation. Au101-based catalysts display the highest catalytic activity with a turn-over frequency (TOF) up to 0.69 s-1. The high catalytic activity is attributed to the formation of large Au nanoparticles (> 2 nm) that coincides with the partial removal of capping ligands. Au8 and Au9 clusters which contain NO3- counter anions are found to be inactive in benzyl alcohol oxidation. Further work shows that the presence of NO3- species diminishes the catalytic activity. Monometallic ruthenium clusters, Ru3 and Ru4, are found to be inactive yet the bimetallic AuRu3 clusters are active in benzyl alcohol oxidation, suggesting the synergistic effect between ruthenium and gold metal. Investigation of catalytic testing parameters reveals that tuning selectivity of the product is possible through manipulating the reaction temperature. Finally, a joint experiment with Prof. Wojtek Wlodarski’s group at RMIT, Melbourne was undertaken to test the sensing ability of Au9 clusters for hydrogen detection. Au9 clusters were deposited onto radio-frequency (RF) sputtered WO3 films at two different concentrations; 0.01(S1) and 0.1(S2) mg/mL. It was found that the optimal temperatures for sensor S1 and S2 were 300 °C and 350 °C, respectively. The sensor with lower Au9 concentration (S1) displays a faster response and recovery time, and a higher sensitivity toward H2. HRTEM studies reveal that the sensor S1 contain a significant population of sub-5 nm Au nanoparticles which might be responsible for a faster rate of H2 adsorption and dissociation. The key finding in this study suggest that the addition of catalytic layer such as ultra-small Au9 clusters results in improved sensitivity and dynamic performance (response and recovery time) of H2 sensors. In summary, this thesis demonstrated that cluster-based nanomaterials have wide range of applications spanning from catalysis to sensing. Further improvements in material synthesis and use of multiple complimentary characterization techniques allowed better understanding of the nature of the key active species (metal nanoparticles) assisting design of catalysts and sensors with enhanced performance.