Morphologically-Identified Merging Galaxies in the SWIRE Fields

We investigate the evolutional and environmental effects on star formation efficiency for more than 400 merging galaxies. The ~400 merging systems, with photometric redshifts smaller than 0.7, are obtained from a catalog of ~15000 morphologically identified merging galaxies derived from observations of the Canada-France-Hawaii Telescope. We also obtained the IR data of the merging galaxies from the Spitzer Wide-area InfraRed Extragalactic Survey (SWIRE). The redshift differences \Delta z between the member galaxies of these merging pairs show a large distribution with 0 < \Delta z < 0.4. We divide our merging pairs into two sub-samples with \Delta z 0.05 for further analyses. We find a statistically significant anti-correlation between the specific star formation rate (SSFR) and the separation of the merging galaxies for both sub-samples. Our analyses also show that although most of the merging systems do have enhanced star formation activity, only very rare ones display extremely high SFRs. Additionally, the SSFR of the merging galaxies also decreases when the magnitude difference between two member galaxies becomes large. However, we find that for the merging pairs with large luminosity contrast, the fainter components show higher SSFR than the brighter ones. Finally, there is a higher fraction of gas-poor mergers in galaxy clusters, and the SSFR of gas-rich mergers is reduced in cluster environments.Comment: 32 pages, 12 figures and 7 tables; accepted for publication in Ap

The mid-infrared Tully-Fisher relation: Spitzer Surface Photometry

The availability of photometric imaging of several thousand galaxies with the Spitzer Space Telescope enables a mid-infrared calibration of the correlation between luminosity and rotation in spiral galaxies. The most important advantage of the new calibration in the 3.6 micron band, IRAC ch.1, is photometric consistency across the entire sky. Additional advantages are minimal obscuration, observations of flux dominated by old stars, and sensitivity to low surface brightness levels due to favorable backgrounds. Through Spitzer cycle 7 roughly 3000 galaxies had been observed and images of these are available at the Spitzer archive. In cycle 8 a program called Cosmic Flows with Spitzer has been initiated that will increase by 1274 the available sample of spiral galaxies with inclinations greater than 45 degrees from face-on suitable for distance measurements. This paper describes procedures based on the photometry package Archangel that are being employed to analyze both the archival and the new data in a uniform way. We give results for 235 galaxies, our calibrator sample for the Tully-Fisher relation. Galaxy magnitudes are determined with uncertainties held below 0.05 mag for normal spiral systems. A subsequent paper will describe the calibration of the [3.6] luminosity-rotation relation.Comment: Accepted for publication in The Astronomical Journal, 12 pages, 9 figure

SYSTEM MODELING AND MATERIAL DEVELOPMENT FOR STANDALONE THERMOELECTRIC POWER GENERATORS

This dissertation addresses the need to develop a scalable and standalone power generator for personal, commercial, and military transportation and communication systems. The standalone thermoelectric power generator (TPG) converts heat to electrical power in a unique way that does not draw on conventional power sources like batteries. A TPG is comprised of four main components: a heat source, thermoelectric modules, a heat sink, and thermal insulation. For system modeling and materials development purposes, the dissertation invented the first pyrophoric heated standalone TPG, solid-state renewable heat source, and two-component nanocomposite thermoelectric power generation material. In this work, the first pyrophoric heated standalone thermoelectric power generator was designed, fabricated, and tested. The bases of the system were four porous silicon carbide combustors for the exothermic reaction of pyrophoric iron powder with oxygen. These combustors provided a heat source of 2,800 to 5,600 W to the heat sinks (through TE modules) at conditions suitable for a standalone, pyrophoric iron fueled TE power generator. The system integrated with 16 commercial bismuth telluride thermoelectric modules to produce 140 to 280 W of electrical power with a TE power conversion efficiency of ~5%. This demonstration represents an order-of-magnitude improvement in portable electrical power from thermoelectrics and hydrocarbon fuel, and a notable increase in the conversion efficiency compared with other published works. To optimize the TE heat-to-power conversion performance of the TPG, numerical simulations were performed with computational fluid dynamics (CFD) using FLUENT. The temperature dependent material properties of bismuth telluride, effects of air flow rate (6 – 14 m/s) at 300 K, and effects of thermoelectric element thickness (4 – 8 mm) on temperature gradient generated across the module are investigated under constant power input (7.5 W). The obtained results reveal that all geometric parameters have important effect on the thermal performance of thermoelectric power generation module. The optimized single TE element thickness is 7 mm for electrical power generation of 0.47 W at temperature difference of 138 K. The TE heat-to-power conversion efficiency is 6.3%. The first solid-state renewable heat source (without the use of hydrocarbons) were created with porous silicon carbide combustors coated with pyrophoric 1-3 micron-sized iron particles mixture. The thermal behavior and ignition characteristics of iron particles and mixtures were investigated. The mixture include activate carbon and sodium chloride, in which iron is the main ingredient used as fuel. The final mixture composition is determined to consist of iron powder, activate carbon, and sodium chloride with a weight ratio of approximately 5/1/1. The mixture generated two-peak DSC curves featured higher ignition temperatures of 431.53°C and 554.85°C with a higher heat generation of 9366 J/g than single iron particles. The enhancement of figure-of-merit ZT or efficiency of thermoelectric materials is dependent on reducing the thermal conductivity. This dissertation synthesized and characterized the advanced two-component Si-Ge nanocomposites with a focus on lowering the thermal conductivity. The ball-milled two-component Si-Ge material demonstrated 50% reduction in thermal conductivity than the single component material used in the radioisotope thermoelectric generators and 10% reduction than the p-type SiGe alloy

Data-Driven Power System Optimal Decision Making Strategy under Wildfire Events

Wildfire activities are increasing in the western United States in recent years, causing escalating threats to power systems. This paper developed an optimal and data-driven decision-making framework that improves power system resilience under wildfire risks. An optimal load shedding plan is formulated based on optimal power flow analysis. To avoid power system cascading failure caused by wildfire, we added additional transmission line flow constraints based on the identification of power lines with high ignition risk. Finally, a data-driven method is developed, leveraging multiple machine learning techniques, to model the complex correlations between input wildfire scenarios and the output power management strategy with significantly reduced computational complexities. The proposed data-driven decision-making framework can reduce the safety impacts on the electricity consumers, improve power system resilience under wildfire events

Study of the Microbial Diversity of a Newly Discovered East Antarctic Freshwater Lake, L27C, and of a Perennially Ice-Covered Lake Untersee

The microbial communities that reside within freshwater lakes of Schirmacher and Untersee Oases in East Antarctica must cope with extreme conditions that may include cold temperature, annual freeze-thaw cycles, exposure to UV radiation, especially during the austral summer months, low light beneath thick ice-cover, followed by seasonal darkness. The objective of this study was to assess the microbial biodiversity and distribution from samples taken from two freshwater lakes (L27C and Lake Untersee) that were collected during the Tawani 2008 International Antarctic Expedition that conducted research in this region of Antarctica. L27C is a small, previously unreported lake residing 2 km WNW of Maitri Station at Schirmacher Oasis. Biodiversity and distribution of microorganisms within the lake were studied using both culture-independent and culture-dependent methodologies based upon the analysis of eubacterial 16S rRNA gene sequences. Lake Untersee, a perennially ice-covered, ultra-oligotrophic, lake in the Otto-von-Gruber-Gebirge (Gruber Mountains) of central Dronning Maud Land was also sampled and the microbial diversity was analyzed by eubacterial 16S rRNA gene sequences derived from pure cultures. Direct culturing of water samples from each lake on separate R2A growth medium exhibited a variety of microorganisms including: Janthinobacterium, Hymenobacter, Sphingamonas, Subtercola, Deinococcus, Arthrobacter, Flavobacterium, Polaromonas, Rhodoferax and Duganella. The evaluation of samples from L27C through culture-independent methodology identified a rich microbial diversity consisting of six different phyla of bacteria. The culture-independent analysis also displayed the majority of bacteria (56%) belonged to the Class gamma-proteobacteria within the phylum Proteobacteria. Within the Class gamma-proteobacteria, Acinetobacter dominated (48%) the total microbial load. Overall, L27C exhibited 7 different phyla of bacteria and 20 different genera. Statistical analysis (Shannon-Weaver Diversity Index and Simpson Diversity Index) of the biodiversity of L27C displayed a moderately rich and diverse community. Investigations of the biodiversity and distribution of microorganisms in these lakes will help further our understanding of how the physical environment impact the structure and function within these microbially dominated ecosystems

Infrared Properties of a Complete Sample of Star-Forming Dwarf Galaxies

We present a study of a large, statistically complete sample of star-forming dwarf galaxies using mid-infrared observations from the {\it Spitzer Space Telescope}. The relationships between metallicity, star formation rate (SFR) and mid-infrared color in these systems show that the galaxies span a wide range of properties. However, the galaxies do show a deficit of 8.0 \um\ polycyclic aromatic hydrocarbon emission as is apparent from the median 8.0 \um\ luminosity which is only 0.004 \lstarf\ while the median $B$-band luminosity is 0.05 \lstarb. Despite many of the galaxies being 8.0 \um\ deficient, there is about a factor of 4 more extremely red galaxies in the [3.6] $-$ [8.0] color than for a sample of normal galaxies with similar optical colors. We show correlations between the [3.6] $-$ [8.0] color and luminosity, metallicity, and to a lesser extent SFRs that were not evident in the original, smaller sample studied previously. The luminosity--metallicity relation has a flatter slope for dwarf galaxies as has been indicated by previous work. We also show a relationship between the 8.0 \um\ luminosity and the metallicity of the galaxy which is not expected given the competing effects (stellar mass, stellar population age, and the hardness of the radiation field) that influence the 8.0 \um\ emission. This larger sample plus a well-defined selection function also allows us to compute the 8.0 \um\ luminosity function and compare it with the one for the local galaxy population. Our results show that below 10$^{9}$ $L$\solar, nearly all the 8.0 \um\ luminosity density of the local universe arises from dwarf galaxies that exhibit strong \ha\ emission -- i.e., 8.0 \um\ and \ha\ selection identify similar galaxy populations despite the deficit of 8.0 \um\ emission observed in these dwarfs.Comment: 13 pages, 11 figures, Published in Ap