Educational Magic Tricks Based on Error-Detection Schemes

Magic tricks based on computer science concepts help grab student attention and can motivate them to delve more deeply. Error detection ideas long used by computer scientists provide a rich basis for working magic; probably the most well known trick of this type is one included in the CS Unplugged activities. This paper shows that much more powerful variations of the trick can be performed, some in an unplugged environment and some with computer assistance. Some of the tricks also show off additional concepts in computer science and discrete mathematics

The Stellar Content of Obscured Galactic Giant H II Regions IV.: NGC3576

We present deep, high angular resolution near-infrared images of the obscured Galactic Giant H II region NGC3576. Our images reach objects to ~3M_sun. We collected high signal-to-noise K-band spectra of eight of the brightest objects, some of which are affected by excess emission and some which follow a normal interstellar reddening law. None of them displayed photospheric features typical of massive OB type stars. This indicates that they are still enshrouded in their natal cocoons. The K-band brightest source (NGC3576 #48) shows CO 2.3 micron bandhead emission, and three others have the same CO feature in absorption. Three sources display spatially unresolved H_2 emission, suggesting dense shocked regions close to the stars. We conclude that the remarkable object NGC3576 #48 is an early-B/late-O star surrounded by a thick circumstellar disk. A number of other relatively bright cluster members also display excess emission in the K-band, indicative of reprocessing disks around massive stars (YSOs). Such emission appears common in other Galactic Giant H II regions we have surveyed. The IMF slope of the cluster, Gamma = -1.51, is consistent with Salpeter's distribution and similar to what has been observed in the Magellanic Cloud clusters and in the periphery of our Galaxy.Comment: 14 pages, 11 figures, accepted for publication in A

NGC 3576 and NGC 3603: Two Luminous Southern HII Regions Observed at High Resolution with the Australia Telescope Compact Array

NGC 3576 (G291.28-0.71; l=291.3o, b=-0.7o) and NGC 3603 (G291.58-0.43; l=291.6o, b=-0.5o) are optically visible, luminous HII regions located at distances of 3.0 kpc and 6.1 kpc, respectively. We present 3.4 cm Australian Telescope Compact Array (ATCA) observations of these two sources in the continuum and the H90a, He90a, C90a and H113b recombination lines with an angular resolution of 7" and a velocity resolution of 2.6 km/s. All four recombination lines are detected in the integrated profiles of the two sources. Broad radio recombination lines are detected in both NGC 3576 (DV_{FWHM}>= 50 km/s) and NGC 3603 (DV_{FWHM}>=70 km/s). In NGC 3576 a prominent N-S velocity gradient (~30 km/s/pc) is observed, and a clear temperature gradient (6000 K to 8000 K) is found from east to west, consistent with a known IR color gradient in the source. In NGC 3603, the H90a, He90a and the H113b lines are detected from 13 individual sources. The Y^+ (He/H) ratios in the two sources range from 0.08+/-0.04 to 0.26+/-0.10. We compare the morphology and kinematics of the ionized gas at 3.4 cm with the distribution of stars, 10 micron emission and H_2O, OH, and CH_3OH maser emission. These comparisons suggest that both NGC 3576 and NGC 3603 have undergone sequential star formation.Comment: 24 pages, 12 Postscript figure

Structure of the Large Magellanic Cloud from 2MASS

We derive structural parameters and evidence for extended tidal debris from star count and preliminary standard candle analyses of the Large Magellanic Cloud based on Two Micron All Sky Survey (2MASS) data. The full-sky coverage and low extinction in K_s presents an ideal sample for structural analysis of the LMC. The star count surface densities and deprojected inclination for both young and older populations are consistent with previous work. We use the full areal coverage and large LMC diameter to Galactrocentric distance ratio to infer the same value for the disk inclination based on perspective. A standard candle analysis based on a sample of carbon long-period variables (LPV) in a narrow color range, 1.6<J-K_s<1.7 allows us to probe the three-dimensional structure of the LMC along the line of sight. The intrinsic brightness distribution of carbon LPVs in selected fields implies that \sigma_M\simlt 0.2^m for this color cut. The sample provides a {\it direct} determination of the LMC disk inclination: $42.3^\circ\pm 7.2^\circ$. Distinct features in the photometric distribution suggest several distinct populations. We interpret this as the presence of an extended stellar component of the LMC, which may be as thick as 14 kpc, and intervening tidal debris at roughly 15 kpc from the LMC.Comment: 24 pages, 9 figures. Submitted to Ap

A New Differential Absorption Lidar to Measure Sub-Hourly Fluctuation of Tropospheric Ozone Profiles in the Baltimore - Washington D.C. Region

Tropospheric ozone profiles have been retrieved from the new ground based National Aeronautics and Space Administration (NASA) Goddard Space Flight Center TROPospheric OZone DIfferential Absorption Lidar (GSFC TROPOZ DIAL) in Greenbelt, MD (38.99 N, 76.84 W, 57 meters ASL) from 400 m to 12 km AGL. Current atmospheric satellite instruments cannot peer through the optically thick stratospheric ozone layer to remotely sense boundary layer tropospheric ozone. In order to monitor this lower ozone more effectively, the Tropospheric Ozone Lidar Network (TOLNet) has been developed, which currently consists of five stations across the US. The GSFC TROPOZ DIAL is based on the Differential Absorption Lidar (DIAL) technique, which currently detects two wavelengths, 289 and 299 nm. Ozone is absorbed more strongly at 289 nm than at 299 nm. The DIAL technique exploits this difference between the returned backscatter signals to obtain the ozone number density as a function of altitude. The transmitted wavelengths are generated by focusing the output of a quadrupled Nd:YAG laser beam (266 nm) into a pair of Raman cells, filled with high pressure hydrogen and deuterium. Stimulated Raman Scattering (SRS) within the focus generates a significant fraction of the pump energy at the first Stokes shift. With the knowledge of the ozone absorption coefficient at these two wavelengths, the range resolved number density can be derived. An interesting atmospheric case study involving the Stratospheric-Tropospheric Exchange (STE) of ozone is shown to emphasize the regional importance of this instrument as well as assessing the validation and calibration of data. The retrieval yields an uncertainty of 16-19 percent from 0-1.5 km, 10-18 percent from 1.5-3 km, and 11-25 percent from 3 km to 12 km. There are currently surface ozone measurements hourly and ozonesonde launches occasionally, but this system will be the first to make routine tropospheric ozone profile measurements in the Baltimore-Washington DC area

Bentho-Pelagic Divergence of Cichlid Feeding Architecture Was Prodigious and Consistent during Multiple Adaptive Radiations within African Rift-Lakes

&lt;b&gt;Background&lt;/b&gt; How particular changes in functional morphology can repeatedly promote ecological diversification is an active area of evolutionary investigation. The African rift-lake cichlids offer a calibrated time series of the most dramatic adaptive radiations of vertebrate trophic morphology yet described, and the replicate nature of these events provides a unique opportunity to test whether common changes in functional morphology have repeatedly facilitated their ecological success.&lt;p&gt;&lt;/p&gt; &lt;b&gt;Methodology/Principal Findings&lt;/b&gt; Specimens from 87 genera of cichlid fishes endemic to Lakes Tanganyka, Malawi and Victoria were dissected in order to examine the functional morphology of cichlid feeding. We quantified shape using geometric morphometrics and compared patterns of morphological diversity using a series of analytical tests. The primary axes of divergence were conserved among all three radiations, and the most prevalent changes involved the size of the preorbital region of the skull. Even the fishes from the youngest of these lakes (Victoria), which exhibit the lowest amount of skull shape disparity, have undergone extensive preorbital evolution relative to other craniofacial traits. Such changes have large effects on feeding biomechanics, and can promote expansion into a wide array of niches along a bentho-pelagic ecomorphological axis.&lt;p&gt;&lt;/p&gt; &lt;b&gt;Conclusions/Significance&lt;/b&gt; Here we show that specific changes in trophic anatomy have evolved repeatedly in the African rift lakes, and our results suggest that simple morphological alterations that have large ecological consequences are likely to constitute critical components of adaptive radiations in functional morphology. Such shifts may precede more complex shape changes as lineages diversify into unoccupied niches. The data presented here, combined with observations of other fish lineages, suggest that the preorbital region represents an evolutionary module that can respond quickly to natural selection when fishes colonize new lakes. Characterizing the changes in cichlid trophic morphology that have contributed to their extraordinary adaptive radiations has broad evolutionary implications, and such studies are necessary for directing future investigations into the proximate mechanisms that have shaped these spectacular phenomena