Cut-Simulation and Impredicativity

We investigate cut-elimination and cut-simulation in impredicative (higher-order) logics. We illustrate that adding simple axioms such as Leibniz equations to a calculus for an impredicative logic -- in our case a sequent calculus for classical type theory -- is like adding cut. The phenomenon equally applies to prominent axioms like Boolean- and functional extensionality, induction, choice, and description. This calls for the development of calculi where these principles are built-in instead of being treated axiomatically.Comment: 21 page

A Phenomenological Study of the Use of Humor as a Teaching Tool by Middle and High School Teachers

The purpose of this transcendental phenomenological study was to understand perceptions of instructional classroom humor used to help students learn and master new material, among teachers at middle and high schools in rural Appalachia districts. Using humor in the classroom is generally defined as deliberate planning and utilization of subject relevant humor in an attempt to improve students’ learning outcomes. Rural Appalachia was defined as the area geographically located in or near the Appalachian Mountain range, and the dominant socioeconomic culture found there. The theories guiding this study were (a) Bandura’s social learning theory, as it describes the way students learn from observing others and through vicarious experiences, such as teachers’ use of humor, (b) Vygotsky’s social development theory as it relates to the idea of children learning first socially then individually, and (c) the incongruence theory of humor as supported by Kant, as it provides an explanation for humor as the act of understanding something unexpected. Data were collected through interviews, a focus group interview, and classroom observations conducted with 10 purposefully selected middle and high school teachers who used humor in the classroom. Data were analyzed using a modified version of Moustakas’ seven steps, as described by Creswell. Analysis revealed humor use fell into three major themes: relationships, instruction, and environment

SMOKING IS A STRONG INDEPENDENT PREDICTOR FOR FUNCTIONAL SIGNIFICANCE OF INTERMEDIATE CORONARY LESIONS

Refiere un ejercicio para mejorar el estilo del periodista. Evoca la necesidad de escribir al menos con claridad corrección y naturalida

Limits on Quaoar's Atmosphere

Here we present high cadence photometry taken by the Acquisition Camera on Gemini South, of a close passage by the ~540 km radius Kuiper belt object, (50000) Quaoar, of a r' = 20.2 background star. Observations before and after the event show that the apparent impact parameter of the event was 0."019 ± 0."004, corresponding to a close approach of 580 ± 120 km to the center of Quaoar. No signatures of occultation by either Quaoar's limb or its potential atmosphere are detectable in the relative photometry of Quaoar and the target star, which were unresolved during closest approach. From this photometry we are able to put constraints on any potential atmosphere Quaoar might have. Using a Markov chain Monte Carlo and likelihood approach, we place pressure upper limits on sublimation supported, isothermal atmospheres of pure N_2, CO, and CH_4. For N_2 and CO, the upper limit surface pressures are 1 and 0.7 μbar, respectively. The surface temperature required for such low sublimation pressures is ~33 K, much lower than Quaoar's mean temperature of ~44 K measured by others. We conclude that Quaoar cannot have an isothermal N_2 or CO atmosphere. We cannot eliminate the possibility of a CH_4 atmosphere, but place upper surface pressure and mean temperature limits of ~138 nbar and ~44 K, respectively

Photometric Observations Constraining the Size, Shape, and Albedo of 2003 El61, a Rapidly Rotating, Pluto-Sized Object in the Kuiper Belt

We present measurements at optical wavelengths of the spectral reflectance, rotational light curve, and solar phase curve of 2003 EL61. With apparent visual magnitude 17.5 at 51 AU from the sun, this newly discovered member of the classical Kuiper Belt is now the third brightest KBO after Pluto and 2005 FY9. Our observations reveal an unambiguous, double-peaked rotational light curve with period 3.9154 +/- 0.0002 hours and peak to peak amplitude 0.28 +/- 0.04 mag. This is the fastest rotation period reliably determined for any body in the solar system larger than 100 km. Assuming the body has relaxed over time to the shape taken by a homogenous fluid body, our observations tightly constrain the shape and density. Given the mass we recently determined for 2003 EL61 from the orbit of a small satellite, we also constrain the size and albedo. We find a total length of 1960 to 2500 km, a mean density of 2600 to 3340 kg m-3, and a visual albedo greater than 0.6. We also measure a neutral reflectance at visible wavelengths and a linear phase curve with slope varying from 0.09 mag deg-1 in the B band to 0.13 mag deg-1 in the I band. The absolute V-band magnitude is 0.444+/-0.021.Comment: 27 pages, six figure

Kuiper Belt Occultation Predictions

Here we present observations of seven large Kuiper Belt objects. From these observations, we extract a point source catalog with ∼0.01″ precision, and astrometry of our target Kuiper Belt objects with 0.04–0.08″ precision within that catalog. We have developed a new technique to predict the future occurrence of stellar occultations by Kuiper Belt objects. The technique makes use of a maximum likelihood approach which determines the best-fit adjustment to cataloged orbital elements of an object. Using simulations of a theoretical object, we discuss the merits and weaknesses of this technique compared to the commonly adopted ephemeris offset approach. We demonstrate that both methods suffer from separate weaknesses, and thus together provide a fair assessment of the true uncertainty in a particular prediction. We present occultation predictions made by both methods for the seven tracked objects, with dates as late as 2015. Finally, we discuss observations of three separate close passages of Quaoar to field stars, which reveal the accuracy of the element adjustment approach, and which also demonstrate the necessity of considering the uncertainty in stellar position when assessing potential occultations

In-polar InN grown by plasma-assisted molecular beam epitaxy

We study the effect of different deposition conditions on the properties of In-polar InN grown by plasma-assisted molecular beam epitaxy. GaN buffer layers grown in the Ga-droplet regime prior to the InN deposition significantly improved the surface morphology of InN films grown with excess In flux. Using this approach, In-polar InN films have been realized with room temperature electron mobilities as high as 2250 cm(2)/V s. We correlate electron concentrations in our InN films with the unintentionally incorporated impurities, oxygen and hydrogen. A surface electron accumulation layer of 5.11x10(13) cm(-2) is measured for In-polar InN. Analysis of optical absorption data provides a band gap energy of similar to 0.65 eV for the thickest InN films. (c) 2006 American Institute of Physics