| Disentangling the Dynamical Mechanisms for Cluster Galaxy Evolution |
FEB 2008 |
15 pages |
| Authors:
Xiaolei Zhang; NAVAL RESEARCH LAB WASHINGTON DC REMOTE SENSING DIV
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 | The determination of the dynamical causes of the morphological Butcher-Oemler (BO) effect, or the rapid transformation of a large population of late-type galaxies to earlier Hubble types in the rich cluster environment between intermediate redshifts and the local universe, has been an important unsolved problem that is central to our understanding of the general problems of galaxy formation and evolution. In this article, we survey the existing proposed mechanisms for ... |
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| Radiometric Characterization of a New Photovoltaic Cell Unit for Powering Modulating Retroreflectors |
19 JUN 2007 |
18 pages |
| Authors:
Xiaolei Zhang; James Murphy; G. C. Gilbreath; NAVAL RESEARCH LAB WASHINGTON DC REMOTE SENSING DIV
|
| We describe the experimental procedures and results of a detailed radiometric characterization of a new photovoltaic (PV) wafer unit intended for powering the Multiple Quantum Well (MQW) Modulating Retroreflector (MRR) using natural sunlight and/or system laser light as energy input, to enable autonomous operation of free-space optical data link using the MQW-MRR. Our initial measurements show that the PV wafer unit has an average power conversion efficiency of 7% to ... |
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| The Potential-Density Phase-Shift Method for Determining the Corotation Radii in Spiral and Barred Galaxies |
JUN 2007 |
25 pages |
| Authors:
Xiaolei Zhang; Ronald J. Buta; NAVAL RESEARCH LAB WASHINGTON DC REMOTE SENSING DIV
|
| We have developed a new method for determining the corotation radii of density waves in disk galaxies, which makes use of the calculated radial distribution of an azimuthal phase shift between the potential and density wave patterns. The approach originated from improved theoretical understanding of the relation between the morphology and kinematics of galaxies and of the dynamical interaction between density waves and the basic-state disk stars, which results in ... |
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| Design Considerations for the Second-Generation NPOI Fringe Tracker and Science Beam Combiner |
18 DEC 2006 |
30 pages |
| Authors:
Xiaolei Zhang; Tom Armstrong; Sergio Restaino; Dave Mozurkewich; NAVAL RESEARCH LAB WASHINGTON DC REMOTE SENSING DIV
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| We describe the motivations for and the conceptual design of the second-generation back-end beam combiner and fringe tracker for the Navy Prototype Optical Interferometer. The new back end is expected to result in much-improved data quality and sensitivity compared to the existing back end. It will also enable the observation of geostationary satellites in the visible and near infrared regions of the spectrum. |
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| Characterization of the Optical Throughput Performance of Navy Prototype Optical Interferometer (NPOI) |
MAY 2006 |
13 pages |
| Authors:
Xiaolei Zhang; J. T. Armstrong; III Clark James A.; G. C. Gilbreath; Robert Lucke; Sergio Restaino; David Mozurkewich; James A. Benson; Donald J. Hutter; Nat White; NAVAL RESEARCH LAB WASHINGTON DC REMOTE SENSING DIV
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| We have developed an approach for systematically investigating the optical throughput performance of the different segments of a Michelson stellar interferometer, and applied it to the characterization of the Navy Prototype Optical Interferometer (NPOI). We report the results of the first phase of throughput measurements on NPOI, as well as some of the lessons learned. Since the current generation of ground-based optical interferometers all suffers from varying degree of throughput ... |
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| On the Generation of the Hubble Sequence Through an Internal Secular Dynamical Process |
2004 |
11 pages |
| Authors:
Xiaolei Zhang; NAVAL RESEARCH LAB WASHINGTON DC
|
| The secular evolution process, which slowly transforms the morphology of a galaxy over its lifetime, could naturally account for observed properties of the great majority of physical galaxies if both stellar and gaseous accretion processes are taken into account. As an emerging paradigm for galaxy evolution, its dynamical foundation had been established in the past few years, and its observational consequences are yet to be fully explored. The secular evolution ... |
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| The Fizeau Interferometer Testbed |
Mar 2003 |
10 pages |
| Authors:
Xiaolei Zhang; Kenneth G Carpenter; Richard G Lyon; Hubert Huet; Joe Marzouk; Gregory Solyar; NAVAL RESEARCH LAB WASHINGTON DC REMOTE SENSING DIV
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| The Fizeau Interferometer Testbed (FIT) is a collaborative effort between NASA's Goddard Space Flight Center, the Naval Research Laboratory, Sigma Space Corporation, and the University of Maryland. The testbed will be used to explore the principles of and the requirements for the full, as well as the pathfinder, Stellar Imager mission concept. It has a long term goal of demonstrating closed-loop control of a sparse array of numerous articulated mirrors ... |
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| Secular Evolution of Spiral Galaxies |
2003 |
18 pages |
| Authors:
Xiaolei Zhang; NAVAL RESEARCH LAB WASHINGTON DC REMOTE SENSING DIV
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| It is now a well established fact that galaxies undergo significant morphological transformation during their lifetimes, manifesting as an evolution along the Hubble sequence from the late to the early Hubble types. The physical processes commonly believed to be responsible for this observed evolution trend, i.e. the major and minor mergers, as well as gas accretion under a barred potential, though demonstrated applicability to selected types of galaxies, on the ... |
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