2,180 research outputs found
To Use Constructed-Response Questions, Or Not To Use Constructed-Response Questions? That Is The Question
Advocates of Constructed Response (CR) questions argue that CR questions provide a different assessment of student knowledge than is available from Multiple Choice (MC) questions. If that is the case, and if the benefit in terms of improved assessment is substantial, then it follows that grade outcomes using CR questions should be different from those using MC questions. We investigate this using a large dataset composed of individual assessment results from thousands of students in introductory economics classes at a large public university. Empirical analysis of our large sample of students indicates that a switch to an all-MC format would result in grade changes that are in the “small” to moderate range when compared to grade changes that occur between assessments. This evidence suggests that CR questions could be abandoned at relatively little cost in grading accuracy. However, there are other arguments in favour of keeping CR questions. In particular, it has been suggested that students perceive a mix of CR and MC as “fairer” than an assessment composed exclusively of one or the other question type. Further, some instructors believe that CR questions encourage students to study harder. We provide survey evidence that supports both arguments.Principles of Economics Assessment; Multiple Choice; Constructed Response; Free Response; Essay
Laser-only adaptive optics achieves significant image quality gains compared to seeing-limited observations over the entire sky
Adaptive optics laser guide star systems perform atmospheric correction of
stellar wavefronts in two parts: stellar tip-tilt and high-spatial-order
laser-correction. The requirement of a sufficiently bright guide star in the
field-of-view to correct tip-tilt limits sky coverage. Here we show an
improvement to effective seeing without the need for nearby bright stars,
enabling full sky coverage by performing only laser-assisted wavefront
correction. We used Robo-AO, the first robotic AO system, to comprehensively
demonstrate this laser-only correction. We analyze observations from four years
of efficient robotic operation covering 15,000 targets and 42,000 observations,
each realizing different seeing conditions. Using an autoguider (or a
post-processing software equivalent) and the laser to improve effective seeing
independent of the brightness of a target, Robo-AO observations show a 39+/-19%
improvement to effective FWHM, without any tip-tilt correction. We also
demonstrate that 50% encircled-energy performance without tip-tilt correction
remains comparable to diffraction-limited, standard Robo-AO performance.
Faint-target science programs primarily limited by 50% encircled-energy (e.g.
those employing integral field spectrographs placed behind the AO system) may
see significant benefits to sky coverage from employing laser-only AO.Comment: Accepted for publication in The Astronomical Journal. 7 pages, 6
figure
Some American Dolomites
These rocks are among the important building materials of the country and have a wide distribution. We secured a few typical specimens from different sections, in order to make a comparison of their chemical composition. The specimens analyzed are all used as building stones in their respective localities
Multiplicity of the Galactic Senior Citizens: A high-resolution search for cool subdwarf companions
Cool subdwarfs are the oldest members of the low mass stellar population.
Mostly present in the galactic halo, subdwarfs are characterized by their low
metallicity. Measuring their binary fraction and comparing it to solar
metallicity stars could give key insights into the star formation process early
in the history of the Milky Way. However, because of their low luminosity and
relative rarity in the solar neighborhood, binarity surveys of cool subdwarfs
have suffered from small sample sizes and incompleteness. Previous surveys have
suggested that the binary fraction of red subdwarfs is much lower than for
their main sequence cousins. Using the highly efficient RoboAO system, we
present the largest yet high-resolution survey of subdwarfs, sensitive to
angular separations, down to 0.15 arcsec, and contrast ratios, up to 6
magnitude difference, invisible in past surveys. Of 344 target cool subdwarfs,
40 are in multiple systems, 16 newly discovered, for a binary fraction of 11.6
percent and 1.8 percent error. We also discovered 6 triple star systems for a
triplet fraction of 1.7 percent and 0.7 percent error. Comparisons to similar
surveys of solar metallicity dwarf stars gives a 3 sigma disparity in
luminosity between companion stars, with subdwarfs displaying a shortage of low
contrast companions.Comment: 13 pages, 10 figures, submitted to Ap
High-speed imaging and wavefront sensing with an infrared avalanche photodiode array
Infrared avalanche photodiode arrays represent a panacea for many branches of
astronomy by enabling extremely low-noise, high-speed and even photon-counting
measurements at near-infrared wavelengths. We recently demonstrated the use of
an early engineering-grade infrared avalanche photodiode array that achieves a
correlated double sampling read noise of 0.73 e- in the lab, and a total noise
of 2.52 e- on sky, and supports simultaneous high-speed imaging and tip-tilt
wavefront sensing with the Robo-AO visible-light laser adaptive optics system
at the Palomar Observatory 1.5-m telescope. We report here on the improved
image quality achieved simultaneously at visible and infrared wavelengths by
using the array as part of an image stabilization control-loop with
adaptive-optics sharpened guide stars. We also discuss a newly enabled survey
of nearby late M-dwarf multiplicity as well as future uses of this technology
in other adaptive optics and high-contrast imaging applications.Comment: Accepted to Astrophysical Journal. 8 pages, 3 figures and 1 tabl
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