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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

ALMA Observations of Starless Core Substructure in Ophiuchus

Kirk, H., Dunham, M. M., Francesco, J. Di, Johnstone, D., Offner, S. S. R., Sadavoy, S. I., Tobin, J. J., Arce, H. G., Bourke, T. L., Mairs, S., Myers, P. C., Pineda, J. E., Schnee, S., Shirley, Y. L. 31 March 2017 (has links)
Compact substructure is expected to arise in a starless core as mass becomes concentrated in the central region likely to form a protostar. Additionally, multiple peaks may form if fragmentation occurs. We present Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 2 observations of 60 starless and protostellar cores in the Ophiuchus molecular cloud. We detect eight compact substructures which are >15 '' from the nearest Spitzer young stellar object. Only one of these has strong evidence for being truly starless after considering ancillary data, e.g., from Herschel and X-ray telescopes. An additional extended emission structure has tentative evidence for starlessness. The number of our detections is consistent with estimates from a combination of synthetic observations of numerical simulations and analytical arguments. This result suggests that a similar ALMA study in the Chamaeleon. I cloud, which detected no compact substructure in starless cores, may be due to the peculiar evolutionary state of cores in that cloud.
2

Correlations in the Cosmic Far-infrared Background at 250, 350, and 500 μm Reveal Clustering of Star-forming Galaxies

Viero, Marco Paolo 23 February 2011 (has links)
We demonstrate the application of CMB techniques to measure the clustering of infrared emitting star-forming galaxies. We detect correlations in the cosmic far-infrared background due to the clustering of star-forming galaxies in observations made with the Balloon-borne Large Aperture Submillimeter Telescope, BLAST, at 250, 350, and 500μm. We perform jackknife and other tests to confirm the reality of the signal. The measured correlations are well fit by a power law over scales of 5–25 arcminutes, with ∆I/I = 15.1 ± 1.7%. We adopt a specific model for submillimeter sources in which the contribution to clustering comes from sources in the redshift ranges 1.3≤z≤2.2, 1.5≤z≤2.7,and1.7≤z≤3.2,at 250, 350 and 500 μm, respectively. With these distributions, our measurement of the power spectrum, P(kθ), corresponds to linear bias parameters, b = 3.8±0.6,3.9±0.6 and 4.4±0.7, respectively. We further interpret the results in terms of the halo model, and find that at the smaller scales, the simplest halo model fails to fit our results. One way to improve the fit is to increase the radius at which dark matter halos are artificially truncated in the model, which is equivalent to having some star-forming galaxies at z ≥ 1 located in the outskirts of groups and clusters. In the context of this model we find a minimum halo mass required to host a galaxy is log(Mmin/M⊙) = 11.5+0.4, and we derive effective biases beff = 2.2 ± 0.2, 2.4 ± 0.2, −0.1 and 2.6 ± 0.2, and effective masses log(Meff/M⊙) = 12.9 ± 0.3, 12.8 ± 0.2, and 12.7 ± 0.2 , at 250, 350 and 500 μm, corresponding to spatial correlation lengths of r0 = 4.9, 5.0, and 5.2 ±0.7 h−1 Mpc, respectively. Finally, we discuss implications for clustering measurement strategies with Herschel and Planck.
3

Correlations in the Cosmic Far-infrared Background at 250, 350, and 500 μm Reveal Clustering of Star-forming Galaxies

Viero, Marco Paolo 23 February 2011 (has links)
We demonstrate the application of CMB techniques to measure the clustering of infrared emitting star-forming galaxies. We detect correlations in the cosmic far-infrared background due to the clustering of star-forming galaxies in observations made with the Balloon-borne Large Aperture Submillimeter Telescope, BLAST, at 250, 350, and 500μm. We perform jackknife and other tests to confirm the reality of the signal. The measured correlations are well fit by a power law over scales of 5–25 arcminutes, with ∆I/I = 15.1 ± 1.7%. We adopt a specific model for submillimeter sources in which the contribution to clustering comes from sources in the redshift ranges 1.3≤z≤2.2, 1.5≤z≤2.7,and1.7≤z≤3.2,at 250, 350 and 500 μm, respectively. With these distributions, our measurement of the power spectrum, P(kθ), corresponds to linear bias parameters, b = 3.8±0.6,3.9±0.6 and 4.4±0.7, respectively. We further interpret the results in terms of the halo model, and find that at the smaller scales, the simplest halo model fails to fit our results. One way to improve the fit is to increase the radius at which dark matter halos are artificially truncated in the model, which is equivalent to having some star-forming galaxies at z ≥ 1 located in the outskirts of groups and clusters. In the context of this model we find a minimum halo mass required to host a galaxy is log(Mmin/M⊙) = 11.5+0.4, and we derive effective biases beff = 2.2 ± 0.2, 2.4 ± 0.2, −0.1 and 2.6 ± 0.2, and effective masses log(Meff/M⊙) = 12.9 ± 0.3, 12.8 ± 0.2, and 12.7 ± 0.2 , at 250, 350 and 500 μm, corresponding to spatial correlation lengths of r0 = 4.9, 5.0, and 5.2 ±0.7 h−1 Mpc, respectively. Finally, we discuss implications for clustering measurement strategies with Herschel and Planck.
4

Theoretical investigation of carbon nanotube devices for millimeter/submillimeter wave analog circuits

Daggett, Josephine Anne. January 2009 (has links) (PDF)
Thesis (MS)--Montana State University--Bozeman, 2009. / Typescript. Chairperson, Graduate Committee: James P. Becker. Includes bibliographical references (leaves 96-98).
5

Development of Signal Sources for Millimeter and Submillimeter Wave Output

Kirby, Peter Lund 09 August 2007 (has links)
The objectives of this research lie in the area of millimeter and submillimeter wave signal generation and are directed into two paths that are separate, but related. The first involves the development of a W-Band oscillator using Raytheon's Metamorphic High Electron Mobility Transistor (MHEMT) substrate. The second involves the development of silicon formed rectangular waveguide to replace metallic waveguide, ultimately to be used in THz signal source circuits. An exploration of two different topologies for a W-Band oscillator design utilizing Raytheon s MHEMT substrate is presented. This material will demonstrate the reasoning behind the topology selection and the approach of the design. An evaluation of this first ever W-Band MHEMT oscillator will be presented demonstrating its performance capabilities. Finally, an oscillator design will be presented extending the first successful MHEMT W-Band design. The area of Silicon rectangular waveguide with is covered. A design approach of the silicon waveguide will be discussed. The technology used to fabricate and package the silicon waveguide will be explained. The results of the very first 400 GHz silicon waveguide will be shown and the future efforts will be covered. A silicon micromachined waveguide multiplier using an HBV diode circuit is constructed and successfully demonstrated with an output frequency of 261 GHz, showing little difference between using micromachined waveguide and metal waveguide. Lastly, a power combining frequency multiplier is developed utilizing HBV diodes with an output of 260 GHz. The input and output sections are created using branch line couplers. The results showed good power generation as compared to a single diode multiplier.
6

L '(CO)/L-FIR RELATIONS WITH CO ROTATIONAL LADDERS OF GALAXIES ACROSS THE HERSCHEL SPIRE ARCHIVE

Kamenetzky, J., Rangwala, N., Glenn, J., Maloney, P. R., Conley, A. 26 September 2016 (has links)
We present a catalog of all CO (J = 4-3 through J = 13-12), [ C I], and [ N II] lines available from extragalactic spectra from the Herschel SPIRE Fourier Transform Spectrometer (FTS) archive combined with observations of the low-J CO lines from the literature and from the Arizona Radio Observatory. This work examines the relationships between L-FIR, L'(CO), and L-CO/L-CO,L-1-0. We also present a new method for estimating probability distribution functions from marginal signal-to-noise ratio Herschel FTS spectra, which takes into account the instrumental "ringing" and the resulting highly correlated nature of the spectra. The slopes of log(L-FIR) versus log (L'(CO)) are linear for all mid- to high-J CO lines and slightly sublinear if restricted to (ultra) luminous infrared galaxies ((U) LIRGs). The mid-to high-J CO luminosity relative to CO J - 1-0 increases with increasing L-FIR, indicating higher excitement of the molecular gas, although these ratios do not exceed similar to 180. For a given bin in L-FIR, the luminosities relative to CO J = 1-0 remain relatively flat from J = 6-5 through J = 13-12, across three orders of magnitude of L-FIR. A single component theoretical photodissociation region (PDR) model cannot match these flat SLED shapes, although combinations of PDR models with mechanical heating added qualitatively match the shapes, indicating the need for further comprehensive modeling of the excitation processes of warm molecular gas in nearby galaxies.
7

Metamaterial devices in terahertz range. / 太赫茲波的超材料器件之研究 / Tai he zi bo de chao cai liao qi jian zhi yan jiu

January 2009 (has links)
Chen, Mengyu. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 110-116). / Abstracts in English and Chinese. / Abstract --- p.I / Acknowledgments --- p.V / Table of Contents --- p.VI / List of Tables and Figures --- p.VIII / List of Abbreviations and Symbol --- p.XII / Chapter Chapter 1: --- Introduction --- p.1 / Chapter 1.1 --- Left-handed material --- p.1 / Chapter 1.1.1 --- Left-handed transmission --- p.1 / Chapter 1.1.2 --- Corrected physical laws and sub-wavelength imaging --- p.4 / Chapter 1.1.3 --- Methods to realized Left-handed Material --- p.5 / Chapter 1.2 --- The meaning of this work --- p.8 / Chapter 1.3 --- Organization of the thesis --- p.8 / Chapter Chapter 2: --- Basic theory and Metamaterial Devices --- p.11 / Chapter 2.1 --- Left-handed Metamaterials --- p.11 / Chapter 2.1.1 --- Metal wire arrays structure --- p.11 / Chapter 2.1.2 --- SRR structure --- p.14 / Chapter 2.1.3 --- SRR plus wire arrays structure --- p.20 / Chapter 2.1.4 --- Development and Fishnet structure --- p.22 / Chapter 2.2 --- Transmission line model --- p.26 / Chapter 2.2.1 --- Transmission line theory --- p.26 / Chapter 2.2.2 --- Transmission line model of SRR plus wire arrays structure --- p.27 / Chapter 2.2.3 --- Transmission line model of Fishnet structure --- p.29 / Chapter 2.3 --- Electric Metamaterial Devices --- p.32 / Chapter 2.3.1 --- The dielectric property of SRR --- p.32 / Chapter 2.3.2 --- Active Metamaterial Devices --- p.34 / Chapter 2.4 --- Other Metamaterial Devices --- p.36 / Chapter 2.4.1 --- Metamaterial Electromagnetic Cloak --- p.36 / Chapter 2.4.2 --- Metamaterial based Perfect absorber --- p.39 / Chapter 2.5 --- Homogenization and effective material parameters --- p.40 / Chapter Chapter 3: --- Metamaterial devices fabrication --- p.43 / Chapter 3.1 --- Introduction --- p.43 / Chapter 3.2 --- Photolithography --- p.44 / Chapter 3.2.1 --- Process description --- p.45 / Chapter 3.2.2 --- Parameter Selection --- p.50 / Chapter 3.3 --- E-beam Evaporation and lift-off --- p.51 / Chapter 3.3.1 --- E-beam evaporation --- p.51 / Chapter 3.3.2 --- Lift-off --- p.53 / Chapter 3.4 --- Flexible metamaterial and double-layer device --- p.54 / Chapter 3.4.1 --- Polyimide brief introduction --- p.54 / Chapter 3.4.2 --- Double-layer structure and fabrication --- p.57 / Chapter Chapter 4: --- Simulation and Experiment Method --- p.61 / Chapter 4.1 --- Numerical simulation methods and software --- p.61 / Chapter 4.1.1 --- Time domain solver --- p.61 / Chapter 4.1.2 --- Frequency domain solver --- p.62 / Chapter 4.2 --- High Frequency Structure Simulator (HFSS) --- p.63 / Chapter 4.2.1 --- Introduction --- p.63 / Chapter 4.2.2 --- Simulation Process --- p.64 / Chapter 4.2.3 --- Parameter Retrieve Method --- p.67 / Chapter 4.3 --- Terahertz Time Domain spectroscopy system --- p.71 / Chapter 4.3.1 --- Introduction --- p.71 / Chapter 4.3.2 --- System Setup --- p.73 / Chapter 4.3.3 --- Photoconductive Antennas --- p.75 / Chapter 4.3.4 --- Data Analysis Method --- p.77 / Chapter Chapter 5: --- Simulation and Experiment Results and Analysis --- p.82 / Chapter 5.1 --- SRR structure based Metamaterial Devices --- p.82 / Chapter 5.1.1 --- SRR based left-handed material --- p.82 / Chapter 5.1.2 --- Electric Metamaterial Devices with different substrate --- p.84 / Chapter 5.2 --- Fishnet structure based metamaterial devices --- p.94 / Chapter 5.2.1 --- Dual-band Polarization-Insensitive Left-handed Metamaterial --- p.94 / Chapter Chapter 6: --- Conclusion --- p.106 / Chapter 6.1 --- Conclusion and potential application --- p.106 / Chapter 6.2 --- Future work --- p.108 / References --- p.110 / Publication list --- p.116
8

Observing the galactic plane with the Balloon-borne Large-Aperture Submillimeter Telescope

Marsden, Gaelen 05 1900 (has links)
Stars form from collapsing massive clouds of gas and dust. The UV and optical light emitted by a forming or recently-formed star is absorbed by the surrounding cloud and is re-radiated thermally at infrared and submillimetre wavelengths. Observations in the submillimetre spectrum are uniquely sensitive to star formation in the early Universe, as the peak of the thermal emission is redshifted to submillimetre wavelengths. The coolest objects in star forming regions in our own Galaxy, including heavily-obscured proto-stars and starless gravitationally-bound clumps, are also uniquely bright in the submillimetre spectrum. The Earth's atmosphere is mostly opaque at these wavelengths, however, limiting the spectral coverage and sensitivity achievable from ground-based observatories. The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) observes the sky from an altitude of 40 km, above 99.5% of the atmosphere, using a long-duration scientific balloon platform. BLAST observes at 3 broad-band wavelengths spanning 250-500 micron, taking advantage of detector technology developed for the space-based instrument SPIRE, scheduled for launch in 2008. The greatly-enhanced atmospheric transmission at float altitudes, increased detector sensitivity and large number of detector elements allow BLAST to survey much larger fields in a much smaller time than can be accomplished with ground-based instruments. It is expected that in a single 10-day flight, BLAST will detect ~10000 extragalactic sources, ~100 times the number detected in 10 years of ground-based observations, and 1000s of Galactic star-forming sources, a large fraction of which are not seen by infrared telescopes. The instrument has performed 2 scientific flights, in the summer of 2005 and winter of 2006, for a total of 16 days of observing time. This thesis discusses the design of the instrument, performance of the flights, and presents the analysis of 2 of the fields observed during the first flight. A failure in the optical system during the first flight precluded sensitive extragalactic observations, so the majority of the flight was spent observing Galactic targets. We anticipate exciting extragalactic and Galactic results from the 2006 data.
9

Theoretical, numerical and experimental studies of the optical behaviour of few-mode power detectors for submillimetre and far-infrared astronomy

Thomas, Christopher Niall January 2012 (has links)
No description available.
10

Tracing the evolution of submillimeter selected galaxies

Alaghband-Zadeh, Susannah January 2013 (has links)
No description available.

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