A Study of Active Galactic Nuclei in Low Surface Brightness Galaxies with Sloan Digital Sky Survey Spectroscopy

Active galactic nuclei (AGN) in low surface brightness galaxies (LSBGs) have received little attention in previous studies. In this paper, we present detailed spectral analysis of 194 LSBGs from the Impey et al. (1996) APM LSBG sample which have been observed spectroscopically by the Sloan Digital Sky Survey Data Release 5 (SDSS DR5). Our elaborate spectral analysis enables us to carry out, for the first time, reliable spectral classification of nuclear activities in LSBGs based on the standard emission line diagnostic diagrams in a rigorous way. Star-forming galaxies are common, as found in about 52% LSBGs. We find, contrary to some of the previous claims, that the fraction of galaxies containing an AGN is significantly lower than that found in nearby normal galaxies of high surface brightness. This is qualitatively in line with the finding of Impey et al. (2001). This result holds true even within each morphological type from Sa to Sc. LSBGs having larger central stellar velocity dispersions, or larger physical sizes, tend to have a higher chance to harbor an AGN. For three AGNs with broad emission lines, the black hole masses estimated from the emission lines are broadly consistent with the well known M-$\sigma_\ast$ relation established for normal galaxies and AGNs.Comment: 5 tables and 14 figure

A THERMODYNAMIC AND FEASIBILITY STUDY OF GREEN SOLVENTS FOR THE FABRICATION OF WATER TREATMENT MEMBRANES

Nonsolvent induced phase separation (NIPS) has been widely used to fabricate polymeric membranes. In NIPS, a polymer is dissolved in a solvent to form a dope solution, which is then cast on a substrate and immersed in a nonsolvent bath, where phase inversion occurs. Petroleum-derived organic solvents, such as N-Methyl-2-Pyrrolidone (NMP) and Dimethylacetamide (DMAc), have been traditionally used to fabricate polymeric membranes via NIPS. However, these solvents may have negative impacts on environmental and human health; therefore, using greener and less toxic solvents, preferably derived from biomass, is of great interest to make membrane fabrication sustainable. In this dissertation, two low-hazard solvents, Methyl 5-(Dimethylamino)-2-Methyl-5-Oxopentanoate (Rhodiasolv® PolarClean) and Gamma-Valerolactone (GVL), were investigated as sole- and as cosolvents to cast Polysulfone (PSf) membranes via NIPS. In the first part of this project, Rhodiasolv PolarClean was studied. PolarClean is a bio-derived, biodegradable, nonflammable and nonvolatile solvent. From cloud point curves, PolarClean shows potential to be a solvent for polysulfone. Membranes prepared with PolarClean were investigated in terms of their morphology, porosity, water permeability and protein rejection, and were compared to membranes prepared with traditional solvents. The pores of polysulfone/PolarClean membranes were sponge-like, and the membranes displayed higher water flux values along with slightly higher solute rejection. On the other hand, PSf/DMAc membrane pores were finger-like with lower water flux and slightly lower solute rejection when compared to PSf/PolarClean membranes. Upon reverse-flow filtration to simulate membrane cleaning, it was observed that the pores of PSf/PolarClean membranes collapsed. To address this issue, GVL was investigated as a sole solvent and a cosolvent with PolarClean to fabricate PSf membranes. Membranes prepared using GVL as a sole solvent were observed to be gelatinous, hence not ideal for filtration. On the other hand, when GVL and PolarClean were used as cosolvents, viable membranes were cast with surface charge and hydrophicility not being significantly different from membranes made using PolarClean alone. Furthermore, the average pore size of membranes decreased as the weight percent of GVL in dope solutions increased. Therefore, the use of PolarClean/GVL as cosolvents shows promise for the fabrication of PSf membranes. With respect to operation, membranes cast from dope solutions containing equal amounts of PolarClean and GVL displayed the most similar flux curves and solute rejection to those made using the traditional solvent tested. Once it was determined that membranes made using PolarClean and GVL as cosolvents were viable and showed similar morphological and operational characteristics to those made using DMAc, the use of PolarClean/GVL cosolvents was then researched at the production scale. In the last portion of this study, a slot die-roll to roll (R2R) system was used to fabricate polysulfone (PSf) ultrafiltration membranes using low-hazard solvents individually and as cosolvents at a production scale. Production-scale membranes were compared structurally, morphologically and operationally to laboratory-scale membranes made using a doctor’s blade. The chemical structure of membranes was not affected by the use of different solvents nor by the differences in scale. On the other hand, cross-sectional images showed that the structures of the membranes were different most likely due to differences in diffusion rates between the different solvents/cosolvents into the nonsolvent, water. Furthermore, it was observed that slot die and doctor’s blade casting methods produced membranes with different roughness values likely due to evaporation time differences between the methods. While to protein filtration, all membranes displayed similar operational parameters, i.e., flux decline, permeability and recovery. Overall, this dissertation shows that membranes fabricated using greener/less toxic solvent mixtures are comparable to membranes cast using petroleum-derived solvents, and are scalable using slot die-R2R

Power of d choices for large-scale bin packing: a loss model

A system with N parallel servers is considered in our thesis. Each server consists of B units of a resource and jobs arrive at this system according to a Poisson process. Each job stays in the system for an exponentially distributed amount of time. Moreover, each job may request different units of the resource from the system. Our goal is to understand how to route arriving jobs to the servers to minimize the probability that an arriving job does not find the required amount of resource at the server, i.e., the goal is to minimize blocking probability. Our motivation arises from the design of cloud computing systems in which the jobs are virtual machines (VMs) that request resources such as memory from a large pool of servers. In our thesis, we consider power-of-d-choices routing, where a job is routed to the server with the largest amount of available resources among d 2 randomly chosen servers. We consider a fluid model that corresponds to the limit as N goes to infinity, and use numerical methods to approximate the blocking probability. Moreover, we also show the simulation for the system

Obscured Binary Quasar Cores in SDSS J104807.74+005543.5?

We report the discovery of a possible close binary system of quasars in SDSS J1048+0055. The [OIII]4959,5007 emission lines are clearly double-peaked, and two discrete radio sources with a projected physical separation of ~20 pc are found in the VLBA milliarcsec resolution image at 8.4 GHz. Each of the [O III]4959,5007 doublets and Hbeta can be well modelled by two Gaussians and the line ratio, [O III]5007/Hbeta ~7, is typical of Seyfert 2 galaxies. No broad component of Hbeta was detected and its [O III]5007 luminosity, L_[OIII] ~ 9.2 times 10^42 erg s^-1, is comparable to luminous quasars and is a few ten times more luminous than typical Seyfert galaxies. One natural interpretation is that SDSS J1048+0055 contains two close quasar-like nuclei and the BLR around them are obscured. Other possible models are also discussed. We suggest that double-peaked narrow emission line profile may be an effective way of selecting candidates of binary black holes with intermediate separation