1,103 research outputs found
Local councillors in comparative perspective: drawing conclusions
The chapters of this book contain the first results of our common research project. They show a rich picture of many aspects of local councillors in 16 countries. It is not the intention of the group that this is the final output from the project. On the contrary: these analyses should be only a first step in the use of this valuable dataset. Further analysis and publications are under way and are foreseen in the future
Optical turbulence vertical distribution with standard and high resolution at Mt. Graham
A characterization of the optical turbulence vertical distribution (Cn2
profiles) and all the main integrated astroclimatic parameters derived from the
Cn2 and the wind speed profiles above the site of the Large Binocular Telescope
(Mt. Graham, Arizona, US) is presented. The statistic includes measurements
related to 43 nights done with a Generalized Scidar (GS) used in standard
configuration with a vertical resolution Delta(H)~1 km on the whole 20 km and
with the new technique (HVR-GS) in the first kilometer. The latter achieves a
resolution Delta(H)~20-30 m in this region of the atmosphere. Measurements done
in different periods of the year permit us to provide a seasonal variation
analysis of the Cn2. A discretized distribution of Cn2 useful for the Ground
Layer Adaptive Optics (GLAO) simulations is provided and a specific analysis
for the LBT Laser Guide Star system ARGOS (running in GLAO configuration) case
is done including the calculation of the 'gray zones' for J, H and K bands. Mt.
Graham confirms to be an excellent site with median values of the seeing
without dome contribution epsilon = 0.72", the isoplanatic angle theta0 = 2.5"
and the wavefront coherence time tau0= 4.8 msec. We find that the optical
turbulence vertical distribution decreases in a much sharper way than what has
been believed so far in proximity of the ground above astronomical sites. We
find that 50% of the whole turbulence develops in the first 80+/-15 m from the
ground. We finally prove that the error in the normalization of the
scintillation that has been recently put in evidence in the principle of the GS
technique, affects these measurements with an absolutely negligible quantity
(0.04").Comment: 11 figures. MNRAS, accepte
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WxWindows Interface for CALE
wxWindows is an Open Source, platform independent, User Interface (UI) which has been in development for over eleven years (http://www.wxwindows.org). Currently wxWindows is actively supported for the Linux/Unix (X11, Motif and GTK+), Mac OS 9 and X, all Win32 OSes, MGL, and OS/2 operating systems. wxWindows is written in C++ using an object oriented programming framework; it is a reasonably lightweight API (called wxWidgets) sitting over the native graphics packages of the various platforms it supports. The original version of CALE was written for the basic target platform of Unix using X11 as the graphics package. There have been separate efforts to port the code to Mac OS 9, Mac OS X, Win32, Windows Services for Unix (SFU) and CygWin. Each of these used a variety of different graphical interface approaches and build/make systems. For instance Windows SFU and CygWin could still only use X11 graphics. So could the Win32 version, if a X11 server library and client software were installed. A native Win32 version of CALE was contemplated, but never started. The Macintosh versions were completed but never widely distributed to the users. Given the growing code version support issues, and the slow deviation from the portable code model CALE originally started with, it was desired to come up with a simple graphical UI that would be cross platform portable with only a single code base and build system. During the past two summers, two Laboratory summer students and a CALE team code physicist have worked on porting CALE to the wxWidgets UI. In the summer of 2003 Jeffery Hagelberg (formerly Purdue University, now at the University of California-Davis) started the project. During the spring & summer of 2004 Christopher Egner (Rochester Institute of Technology) completed the work. Paul Amala (A/X-Program at LLNL) supervised the students for their combined 30 weeks of effort. This poster session describes the wxWindows interface as it is implemented in CALE, the level of cross platform portable it actually affords, and the lessons learned during the porting of an existing X11 program to this open source software package. (U
Drift estimation in sparse sequential dynamic imaging, with application to nanoscale fluorescence microscopy.
A major challenge in many modern superresolution fluorescence microscopy techniques at the nanoscale lies in the correct alignment of long sequences of sparse but spatially and temporally highly resolved images. This is caused by the temporal drift of the protein structure, e.g. due to temporal thermal inhomogeneity of the object of interest or its supporting area during the observation process. We develop a simple semiparametric model for drift correction in single-marker switching microscopy. Then we propose an M-estimator for the drift and show its asymptotic normality. This is used to correct the final image and it is shown that this purely statistical method is competitive with state of the art calibration techniques which require the incorporation of fiducial markers in the specimen. Moreover, a simple bootstrap algorithm allows us to quantify the precision of the drift estimate and its effect on the final image estimation. We argue that purely statistical drift correction is even more robust than fiducial tracking, rendering the latter superfluous in many applications. The practicability of our method is demonstrated by a simulation study and by a single-marker switching application. This serves as a prototype for many other typical imaging techniques where sparse observations with high temporal resolution are blurred by motion of the object to be reconstructed
Ground-layer wavefront reconstruction from multiple natural guide stars
Observational tests of ground layer wavefront recovery have been made in open
loop using a constellation of four natural guide stars at the 1.55 m Kuiper
telescope in Arizona. Such tests explore the effectiveness of wide-field seeing
improvement by correction of low-lying atmospheric turbulence with ground-layer
adaptive optics (GLAO). The wavefronts from the four stars were measured
simultaneously on a Shack-Hartmann wavefront sensor (WFS). The WFS placed a 5 x
5 array of square subapertures across the pupil of the telescope, allowing for
wavefront reconstruction up to the fifth radial Zernike order. We find that the
wavefront aberration in each star can be roughly halved by subtracting the
average of the wavefronts from the other three stars. Wavefront correction on
this basis leads to a reduction in width of the seeing-limited stellar image by
up to a factor of 3, with image sharpening effective from the visible to near
infrared wavelengths over a field of at least 2 arc minutes. We conclude that
GLAO correction will be a valuable tool that can increase resolution and
spectrographic throughput across a broad range of seeing-limited observations.Comment: 25 pages, 8 figures, to be published in Astrophys.
Discovery of the Coldest Imaged Companion of a Sun-Like Star
We present the discovery of a brown dwarf or possible planet at a projected
separation of 1.9" = 29 AU around the star GJ 758, placing it between the
separations at which substellar companions are expected to form by core
accretion (~5 AU) or direct gravitational collapse (typically >100 AU). The
object was detected by direct imaging of its thermal glow with Subaru/HiCIAO.
At 10-40 times the mass of Jupiter and a temperature of 550-640 K, GJ 758 B
constitutes one of the few known T-type companions, and the coldest ever to be
imaged in thermal light around a Sun-like star. Its orbit is likely eccentric
and of a size comparable to Pluto's orbit, possibly as a result of
gravitational scattering or outward migration. A candidate second companion is
detected at 1.2" at one epoch.Comment: 5 pages, 3 figures, 2 tables. Accepted for publication in ApJ Letter
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