635 research outputs found
Observations of Binary Stars with the Differential Speckle Survey Instrument. III. Measures below the Diffraction Limit of the WIYN Telescope
In this paper, we study the ability of CCD- and electron-multiplying-CCD-based speckle imaging to obtain reliable astrometry and photometry of binary stars below the diffraction limit of the WIYN 3.5 m Telescope. We present a total of 120 measures of binary stars, 75 of which are below the diffraction limit. The measures are divided into two groups that have different measurement accuracy and precision. The first group is composed of standard speckle observations, that is, a sequence of speckle images taken in a single filter, while the second group consists of paired observations where the two observations are taken on the same observing run and in different filters. The more recent paired observations were taken simultaneously with the Differential Speckle Survey Instrument, which is a two-channel speckle imaging system. In comparing our results to the ephemeris positions of binaries with known orbits, we find that paired observations provide the opportunity to identify cases of systematic error in separation below the diffraction limit and after removing these from consideration, we obtain a linear measurement uncertainty of 3-4 mas. However, if observations are unpaired or if two observations taken in the same filter are paired, it becomes harder to identify cases of systematic error, presumably because the largest source of this error is residual atmospheric dispersion, which is color dependent. When observations are unpaired, we find that it is unwise to report separations below approximately 20 mas, as these are most susceptible to this effect. Using the final results obtained, we are able to update two older orbits in the literature and present preliminary orbits for three systems that were discovered by Hipparcos
Observations of Binary Stars with the Differential Speckle Survey Instrument. II. Hipparcos Stars Observed in 2010 January and June
The results of 497 speckle observations of Hipparcos stars and selected other targets are presented. Of these, 367 were resolved into components and 130 were unresolved. The data were obtained using the Differential Speckle Survey Instrument at the WIYN 3.5 m Telescope. (The WIYN Observatory is a joint facility of the University of Wisconsin-Madison, Indiana University, Yale University, and the National Optical Astronomy Observatories.) Since the first paper in this series, the instrument has been upgraded so that it now uses two electron-multiplying CCD cameras. The measurement precision obtained when comparing to ephemeris positions of binaries with very well known orbits is approximately 1-2 mas in separation and better than 0°.6 in position angle. Differential photometry is found to be in very good agreement with Hipparcos measures in cases where the comparison is most relevant. We derive preliminary orbits for two systems
Differential gene expression during compensatory sprouting of dendrites in the auditory system of the cricket Gryllus bimaculatus
Neurones that lose their presynaptic partners because of injury usually retract or die. However, when the auditory interneurones of the cricket Gryllus bimaculatus are denervated, dendrites respond by growing across the midline and forming novel synapses with the opposite auditory afferents. Suppression subtractive hybridization was used to detect transcriptional changes 3 days after denervation. This is a stage at which we demonstrate robust compensatory dendritic sprouting. Whereas 49 unique candidates were down-regulated, no sufficiently up-regulated candidates were identified at this time point. Several candidates identified in this study are known to influence the translation and degradation of proteins in other systems. The potential role of these factors in the compensatory sprouting of cricket auditory interneurones in response to denervation is discussed. © 2009 The Royal Entomological Society
Electrochemical oxidation of CO on Cu single crystals under alkaline conditions
We perform a joint experimental-theoretical study of the electrochemical
oxidation of CO on copper (Cu) under alkaline conditions. Using cyclic
voltammetry on Cu single crystal surfaces, we demonstrate that both Cu terraces
and steps show CO oxidation activity at potentials just slightly positive
(0.03-0.14 V) of the thermodynamic equilibrium potential. The overpotentials
are 0.23-0.12 V lower than that of gold (approx. 0.26 V), which up until now
has been considered to be the most active catalyst for this process. Our
theoretical calculations suggest that Cu's activity arises from the
advantageous combination of simultaneous *OH adsorption under CO oxidation
potentials and surmountable *CO-*OH coupling barriers. Experimentally observed
onset potentials are in agreement with the computed onsets of *OH adsorption.
We furthermore show that the onsets of *OH adsorption on steps are more
affected by *CO-*OH interactions than on terraces due to a stronger competitive
adsorption. Overall, Cu(100) shows the lowest overpotential (0.03 V) of the
facets considered.Comment: 16 pages, 3 figures plus supplementary informatio
Religious Extremism and Global Violence: What We Knew before September 11 and Why We Ignored It
Diamond Solitaire
We investigate the game of peg solitaire on different board shapes, and find
those of diamond or rhombus shape have interesting properties. When one peg
captures many pegs consecutively, this is called a sweep. Rhombus boards of
side 6 have the property that no matter which peg is missing at the start, the
game can be solved to one peg using a maximal sweep of length 16. We show how
to construct a solution on a rhombus board of side 6i, where the final move is
a maximal sweep of length r, where r=(9i-1)(3i-1) is a "rhombic matchstick
number".Comment: 11 pages, 12 figure
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