211 research outputs found
Integrated Laboratory Demonstrations of Multi-Object Adaptive Optics on a Simulated 10-Meter Telescope at Visible Wavelengths
One important frontier for astronomical adaptive optics (AO) involves methods
such as Multi-Object AO and Multi-Conjugate AO that have the potential to give
a significantly larger field of view than conventional AO techniques. A second
key emphasis over the next decade will be to push astronomical AO to visible
wavelengths. We have conducted the first laboratory simulations of wide-field,
laser guide star adaptive optics at visible wavelengths on a 10-meter-class
telescope. These experiments, utilizing the UCO/Lick Observatory's Multi-Object
/ Laser Tomography Adaptive Optics (MOAO/LTAO) testbed, demonstrate new
techniques in wavefront sensing and control that are crucial to future on-sky
MOAO systems. We (1) test and confirm the feasibility of highly accurate
atmospheric tomography with laser guide stars, (2) demonstrate key innovations
allowing open-loop operation of Shack-Hartmann wavefront sensors (with errors
of ~30 nm) as will be needed for MOAO, and (3) build a complete error budget
model describing system performance. The AO system maintains a performance of
32.4% Strehl on-axis, with 24.5% and 22.6% at 10" and 15", respectively, at a
science wavelength of 710 nm (R-band) over the equivalent of 0.8 seconds of
simulation. The MOAO-corrected field of view is ~25 times larger in area than
that limited by anisoplanatism at R-band. Our error budget is composed of terms
verified through independent, empirical experiments. Error terms arising from
calibration inaccuracies and optical drift are comparable in magnitude to
traditional terms like fitting error and tomographic error. This makes a strong
case for implementing additional calibration facilities in future AO systems,
including accelerometers on powered optics, 3D turbulators, telescope and LGS
simulators, and external calibration ports for deformable mirrors.Comment: 29 pages, 11 figures, submitted to PAS
Moonlighting Proteins Hal3 and Vhs3 Form a Heteromeric PPCDC with Ykl088w in Yeast CoA Biosynthesis
Premi a l'excel·lència investigadora. 2010Unlike most other organisms, the essential five-step Coenzyme A biosynthetic pathway has not been fully resolved in yeast. Specifically, the gene(s) encoding the phosphopantothenoylcysteine decarboxylase (PPCDC) activity still remains unidentified. Sequence homology analyses suggest three candidates, namely Ykl088w, Hal3 and Vhs3, as putative PPCDC enzymes in Saccharomyces cerevisiae. Interestingly, Hal3 and Vhs3 have been characterized as negative regulatory subunits of the Ppz1 protein phosphatase. Here we show that YKL088w does not encode a third Ppz1 regulatory subunit, and that the essential roles of Ykl088w and the Hal3/Vhs3 pair are complementary, cannot be interchanged and can be attributed to PPCDC-related functions. We demonstrate that while known eukaryotic PPCDCs are homotrimers, the active yeast enzyme is a heterotrimer which consists of Ykl088w and Hal3/Vhs3 monomers that separately provides two essential catalytic residues. Our results unveil Hal3/Vhs3 as moonlighting proteins, involved in both CoA biosynthesis and protein phosphatase regulation
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Wind prediction with multiple guide stars reduces tomographic errors and expands MOAO field of regard
Liger for Next Generation Keck AO: Filter Wheel and Pupil Design
Liger is a next-generation near-infrared imager and integral field
spectrograph (IFS) for the W.M. Keck Observatory designed to take advantage of
the Keck All-Sky Precision Adaptive Optics (KAPA) upgrade. Liger will operate
at spectral resolving powers between R4,000 - 10,000 over a wavelength
range of 0.8-2.4m. Liger takes advantage of a sequential imager and
spectrograph design that allows for simultaneous observations between the two
channels using the same filter wheel and cold pupil stop. We present the design
for the filter wheels and pupil mask and their location and tolerances in the
optical design. The filter mechanism is a multi-wheel design drawing from the
heritage of the current Keck/OSIRIS imager single wheel design. The Liger
multi-wheel configuration is designed to allow future upgrades to the number
and range of filters throughout the life of the instrument. The pupil mechanism
is designed to be similarly upgradeable with the option to add multiple pupil
mask options. A smaller wheel mechanism allows the user to select the desired
pupil mask with open slots being designed in for future upgrade capabilities.
An ideal pupil would match the shape of the image formed of the primary and
would track its rotation. For different pupil shapes without tracking we model
the additional exposure time needed to achieve the same signal to noise of an
ideal pupil and determine that a set of fixed masks of different shapes
provides a mechanically simpler system with little compromise in performance.Comment: 9 pages, 7 figures, 1 tabl
Liger for Next Generation Keck Adaptive Optics: Opto-Mechanical Dewar for Imaging Camera and Slicer
Liger is a next generation adaptive optics (AO) fed integral field
spectrograph (IFS) and imager for the W. M. Keck Observatory. This new
instrument is being designed to take advantage of the upgraded AO system
provided by Keck All-Sky Precision Adaptive-optics (KAPA). Liger will provide
higher spectral resolving power (R4,000-10,000), wider wavelength
coverage (0.8-2.4 m), and larger fields of view than any current
IFS. We present the design and analysis for a custom-made dewar chamber for
characterizing the Liger opto-mechanical system. This dewar chamber is designed
to test and assemble the Liger imaging camera and slicer IFS components while
being adaptable for future experiments. The vacuum chamber will operate below
Torr with a cold shield that will be kept below 90 K. The dewar test
chamber will be mounted to an optical vibration isolation platform and further
isolated from the cryogenic and vacuum systems with bellows. The cold head and
vacuums will be mounted to a custom cart that will also house the electronics
and computer that interface with the experiment. This test chamber will provide
an efficient means of calibrating and characterizing the Liger instrument and
performing future experiments.Comment: 8 pages, 6 figure
The global oscillation network group site survey. II. Results
The Global Oscillation Network Group (GONG) Project will place a network of instruments around the world to observe solar oscillations as continuously as possible for three years. The Project has now chosen the six network sites based on analysis of survey data from fifteen sites around the world. The chosen sites are: Big Bear Solar Observatory, California; Mauna Loa Solar Observatory, Hawaii; Learmonth Solar Observatory, Australia; Udaipur Solar Observatory, India; Observatorio del Teide, Tenerife; and Cerro Tololo Interamerican Observatory, Chile.
Total solar intensity at each site yields information on local cloud cover, extinction coefficient, and transparency fluctuations. In addition, the performance of 192 reasonable components analysis. An accompanying paper describes the analysis methods in detail; here we present the results of both the network and individual site analyses.
The selected network has a duty cycle of 93.3%, in good agreement with numerical simulations. The power spectrum of the network observing window shows a first diurnal sidelobe height of 3 × 10⁻⁴ with respect to the central component, an improvement of a factor of 1300 over a single site. The background level of the network spectrum is lower by a factor of 50 compared to a single-site spectrum
The Role of UPF0157 in the Folding of M. tuberculosis Dephosphocoenzyme A Kinase and the Regulation of the Latter by CTP
BACKGROUND:Targeting the biosynthetic pathway of Coenzyme A (CoA) for drug development will compromise multiple cellular functions of the tubercular pathogen simultaneously. Structural divergence in the organization of the penultimate and final enzymes of CoA biosynthesis in the host and pathogen and the differences in their regulation mark out the final enzyme, dephosphocoenzyme A kinase (CoaE) as a potential drug target. METHODOLOGY/PRINCIPAL FINDINGS:We report here a complete biochemical and biophysical characterization of the M. tuberculosis CoaE, an enzyme essential for the pathogen's survival, elucidating for the first time the interactions of a dephosphocoenzyme A kinase with its substrates, dephosphocoenzyme A and ATP; its product, CoA and an intrinsic yet novel inhibitor, CTP, which helps modulate the enzyme's kinetic capabilities providing interesting insights into the regulation of CoaE activity. We show that the mycobacterial enzyme is almost 21 times more catalytically proficient than its counterparts in other prokaryotes. ITC measurements illustrate that the enzyme follows an ordered mechanism of substrate addition with DCoA as the leading substrate and ATP following in tow. Kinetic and ITC experiments demonstrate that though CTP binds strongly to the enzyme, it is unable to participate in DCoA phosphorylation. We report that CTP actually inhibits the enzyme by decreasing its Vmax. Not surprisingly, a structural homology search for the modeled mycobacterial CoaE picks up cytidylmonophosphate kinases, deoxycytidine kinases, and cytidylate kinases as close homologs. Docking of DCoA and CTP to CoaE shows that both ligands bind at the same site, their interactions being stabilized by 26 and 28 hydrogen bonds respectively. We have also assigned a role for the universal Unknown Protein Family 0157 (UPF0157) domain in the mycobacterial CoaE in the proper folding of the full length enzyme. CONCLUSIONS/SIGNIFICANCE:In view of the evidence presented, it is imperative to assign a greater role to the last enzyme of Coenzyme A biosynthesis in metabolite flow regulation through this critical biosynthetic pathway
The global oscillation network group site survey. II. Results
The Global Oscillation Network Group (GONG) Project will place a network of instruments around the world to observe solar oscillations as continuously as possible for three years. The Project has now chosen the six network sites based on analysis of survey data from fifteen sites around the world. The chosen sites are: Big Bear Solar Observatory, California; Mauna Loa Solar Observatory, Hawaii; Learmonth Solar Observatory, Australia; Udaipur Solar Observatory, India; Observatorio del Teide, Tenerife; and Cerro Tololo Interamerican Observatory, Chile.
Total solar intensity at each site yields information on local cloud cover, extinction coefficient, and transparency fluctuations. In addition, the performance of 192 reasonable components analysis. An accompanying paper describes the analysis methods in detail; here we present the results of both the network and individual site analyses.
The selected network has a duty cycle of 93.3%, in good agreement with numerical simulations. The power spectrum of the network observing window shows a first diurnal sidelobe height of 3 × 10⁻⁴ with respect to the central component, an improvement of a factor of 1300 over a single site. The background level of the network spectrum is lower by a factor of 50 compared to a single-site spectrum
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