4,744 research outputs found

    The Spectacular Ionized Interstellar Medium of NGC55

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    We present deep Halpha+[NII], [SII] (6716,6731A) and [OII] (3726,3729A) images of the highly inclined, actively star--forming SBm galaxy NGC 55, located in the nearby Sculptor Group. Due to its proximity, NGC 55 provides a unique opportunity to study the disk--halo interface in a late--type galaxy with unprecedented spatial resolution. Our images reveal a spectacular variety of ionized gas features, ranging from giant HII region complexes, to supergiant filamentary and shell features, to patches of very faint diffuse emission. Many of these features protrude well above the plane of the galaxy, including a very faint fragmented shell of emission which is visible at 2.6 kpc above the disk. We identify candidate `chimneys' extending out of the disk, which could be the conduits into the halo for hot gas around disk star-forming regions, and could also provide low-density paths for the passage of UV photons from the disk to the halo. Several of the identified chimneys are `capped' with clumps of ionized gas, one of which, located at 1.5 kpc above the disk plane, appears to be the site of recent star formation. Emission--line ratios ([OII]/Halpha+[NII], [SII]/Halpha+[NII]) constrain the ionization mechanism of the gas, and our images allow the first measurement of [OII]/Halpha+[NII] in extra-planar diffuse ionized gas. The diffuse gas is characterized by emission--line ratios which are enhanced on average by a factor of two compared to those of bright HII regions. Each line ratio increases in value smoothly from the cores of HII regions, through the haloes of HII regions, into the diffuse ionized gas. Such a continuous trend is predicted by models in which the diffuse gas is ionized by photons produced by massive stars in HII regions.Comment: 19 pages, including 4 figures, plus 2 external tables. Accepted for publication in the Astronomical Journal. Compressed, postscript versions of the plates are available at ftp://skysrv.pha.jhu.edu/ferguson

    Life cycle evolution and systematics of Campanulariid hydrozoans

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    Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2004The purpose of this thesis is to study campanulariid life cycle evolution and systematics. The Campanulariidae is a hydrozoan family with many life cycle variations, and provide an excellent model system to study life cycle evolution. Additionally, the unique campanulariid Obelia medusae may have been "re-invented" from ancestors without medusae. Chapter 1 reviews campanulariid life cycles and taxonomy. Chapter 2 presents a phylogeny based on 18S rDNA, calmodulin, L6S rDNA and cytochrome c oxidase I (COI). Ancestral life cycles are reconstructed using parsimony. Medusa loss is common, and Obelia may derive from ancestors with typical medusae. Taxonomic results are discussed in Chapter 3. Bilardia, a nominal campanulariid, appears phylogenetic ally distant, while Bonneviella spp. (Bonneviellidae), are nested within the Campanulariidae. Campanulariid genera are not monophyletic. Orthopyxis integra and elytia gracilis may represent cryptic species, while Obelia longissima may be cosmopolitan. Chapter 4 investigates Obelia geniculata phylogeography. Japanese and North Atlantic 16S rDNA and COI sequences are calibrated against the opening of the Bering Strait. Substitution rates are faster than in anthozoans and comparable to non-cnidarian invertebrates. Comparison of Pacific and Atlantic sequences suggests cryptic species exist. Finally, hydroids in New Brunswick, Canada and Iceland may have survived the last glaciation.Funding for my thesis was provided by WHOI Academic Programs, an NSF PEET grant to Cliff Cunningham (DEB-9978131), WHOI Ocean Ventures Fund, the Society for Integrative and Comparative Biology, WHOI Biology, and the MIT-Italy club

    THE INFLUENCE OF MICROWAVE OVENS ON THE DEMAND FOR FRESH AND FROZEN POTATOES

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    Growth in the number of homes with microwave ovens has changed food preferences and preparation methods. The objective of this study was to determine the impact that microwave oven ownership has had on the demand for fresh and frozen potatoes. Using data from the 1970-88 period, demand equations were estimated for fresh potatoes, frozen potatoes in the retail market and frozen potatoes in the food service market. Results indicate that increases in the percentage of homes that own microwave ovens have shifted demand outward for fresh potatoes but inward for frozen potatoes. If potato processors can develop a microwave frozen French fry that satisfies consumers, microwave ovens could boost the demand for frozen potatoes along with the increase in demand for fresh potatoes.Demand and Price Analysis,

    EFFECTS OF pH ON LOCOMOTER ACTIVITY AND DRIFT OF STREAM INSECTS

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    The Threat Effect of Participation in Active Labor Market Programs on Job Search Behavior of Migrants in Germany

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    Labor market programs may affect unemployed individuals' behavior before they enroll. Such ex ante effects may differ according to ethnic origin. We apply a novel method that relates self-reported perceived treatment rates and job search behavioral outcomes, such as the reservation wage or search intensity, to each other. We compare German native workers with migrants with a Turkish origin or Central and Eastern European (including Russian) background. Job search theory is used to derive theoretical predictions. We examine the omnibus ex ante effect of the German ALMP system, using the novel IZA Evaluation Data Set, which includes self-reported assessments of the variables of interest as well as an unusually detailed amount of information on behavior, attitudes and past outcomes. We find that the ex ante threat effect on the reservation wage and search effort varies considerably among the groups considered.unemployment duration, immigrants, active labor market policy, policy evaluation, reservation wage, program evaluation, expectations, search effort

    The threat effect of participation in active labor market programs on job search behavior of migrants in Germany

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    Labor market programs may affect unemployed individualsā€™ behavior before they enroll. Such ex ante effects may differ according to ethnic origin. We apply a novel method that relates self-reported perceived treatment rates and job search behavĀ­ioral outcomes, such as the reservation wage or search intensity, to each other. We compare German native workers with migrants with a Turkish origin or Central and Eastern European (including Russian) background. Job search theory is used to deĀ­rive theoretical predictions. We examine the omnibus ex ante effect of the German ALMP system, using the novel IZA Evaluation Data Set, which includes self-reported assessments of the variables of interest as well as an unusually detailed amount of inĀ­formation on behavior, attitudes and past outcomes. We find that the ex ante threat effect on the reservation wage and search effort varies considerably among the groups considered.Immigrants; policy evaluation; reservation wage; search effort; expectations; unemployĀ­ment duration; program evaluation; active labor market policy.

    The National School Lunch Program: Background, Trends, and Issues

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    The National School Lunch Program (NSLP) is the Nationā€™s second largest food and nutrition assistance program. In 2006, it operated in over 101,000 public and nonprofit private schools and provided over 28 million low-cost or free lunches to children on a typical school day at a Federal cost of $8 billion for the year. This report provides background information on the NSLP, including historical trends and participant characteristics. It also addresses steps being taken to meet challenges facing administrators of the program, including tradeoffs between nutritional quality of foods served, costs, and participation, as well as between program access and program integrity.National School Lunch Program, child nutrition, obesity, food assistance, Agricultural and Food Policy, Health Economics and Policy, Public Economics,
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