Author name code: nelson-george ADS astronomy entries on 2022-09-14 author:"Nelson, George Driver" ------------------------------------------------------------------------ Title: EPO and the Big Education Reform Picture Authors: Nelson, G. D. Bibcode: 2008ASPC..389....3N Altcode: This paper is a summary of the keynote talk delivered at the conference. I have tried to keep the sense of the spoken presentation. Some of the ideas are my own, some are borrowed from colleagues. The biases, and whines are my own. Title: The AAS Resolution on Teaching Evolution Authors: Nelson, George D. Bibcode: 2006AAS...20917402N Altcode: 2006BAAS...38.1152N In September 2005 the AAS adopted a resolution supporting the teaching of evolution, and against the insertion of non-scientific "alternatives to evolution" in the nation’s pre-college science classes. I will discuss the process that the Society followed in writing this resolution while I was Education Officer. Title: PET as a Model for Other Introductory Content Courses Authors: Nelson, George D. Bibcode: 2006AAS...209.0316N Altcode: 2006BAAS...38..895N Western Washington University is the lead institution of the North Cascades and Olympic Science Partnership (NCOSP), a 5-year NSF MathScience Partnership program designed to improve science teaching K-16. The broad scope of the project entails revising science methods courses, developing new science content courses, and providing professional development opportunities to practicing teachers in the region. In collaboration with science faculty from four partner two-year schools, we have developed and implemented a yearlong science content course sequence that uses the Physics for Elementary Teachers (PET) as the curriculum for the first quarter. The second and third quarter courses, developed in-house, cover topics in geology and biology with the common theme of the flow of matter and energy. The philosophy and format of those courses closely mimics PET. Independent assessments of student learning verify the effectiveness of the approach. Title: Astronomy Education at the AAS : The Current State Authors: Nelson, George Bibcode: 2006Spark...1....1N Altcode: No abstract at ADS Title: Expedition Mars Authors: Turner, Martin J. L.; Nelson, George D. Bibcode: 2005PhT....58f..59T Altcode: No abstract at ADS Title: Book Review: EXPEDITION MARS / Springer, 2004 Authors: Nelson, George D. Bibcode: 2005PhT....58f..59N Altcode: No abstract at ADS Title: Keynote Address Authors: Nelson, G. D. Bibcode: 2004ASPC..319...55N Altcode: No abstract at ADS Title: The Colorado MESA Program and CU-LASP: A Model for After School Program/Research Institution Collaboratives Authors: Nelson, G.; Cobabe-Ammann, E. Bibcode: 2004AGUFMED43C..03N Altcode: Colorado MESA is an after school program operating throughout the state with a long track record in promoting science, math and engineering education to largely underserved K-12 student populations. Currently, 81 percent of MESA students are from groups underrepresented in the math/science careers, and 85 percent of MESA students come from low- and moderate-income families. Through a combination of weekly student programs, field trips to universities and industry partners, family orientations, individual academic counseling and required curriculum, Colorado MESA offers an opportunity for students to explore STEM subjects and careers that they might not otherwise have access to - with tangible results. In the Colorado MESA Class of 2003, 97 percent of students planned on entering college this fall, with 86 percent indicating that they will enroll in math/science-based majors. In the last year, the University of Colorado's Laboratory for Atmospheric and Space Physics, a large space and earth sciences institute, has relied on the Colorado MESA program as its primary K-12 partner in Education and Public Outreach. LASP incorporates MESA into its proposal writing opportunities, from E/PO additions to individual research proposals to mission-level educational programs. In addition to funding opportunities, LASP provides scientists and engineers in a variety of contexts and content areas, while MESA works to incorporate those resources into their after school programs. The interface between the after school programs and the research institution requires ongoing communication and coordination in order to evaluate and fine-tune curriculum and activities based on feedback from MESA advisors and teachers. Currently, the MESA/LASP partnership has funded programs in astrobiology, planetary sciences and engineering. Title: Microgravity experiment to understand effect of convection on PVT growth Authors: Singh, N.; Duval, W.; Watson, C.; Nelson, G.; Cacioppo, C.; Naumann, R.; Meyers, N.; Rolin, T.; Griffith, J. Bibcode: 2002cosp...34E1786S Altcode: 2002cosp.meetE1786S We have carried out extensive theoretical and experimental studies on the physical vapour transport (PVT) growth of mercurous halides. To understand the role of thermal convection on quality of crystals, we performed computations that clearly identify the spectrum of convective regimes as a function of gravity level for PVT growth, namely the transition from diffusive, convecto-diffusive, to convective. The experimentally grown crystals in various convective regimes showed significant variation in the quality. This indicated the necessity of a microgravity experiment, on the growth of Hg Cl2 crystal, to identify the effect of gravity driven convection2 on the quality of crystals. A Space exp eriment was carried out in the Spacehab module on STS-77. H g2 Cl2 crystals grown in microgravity environment were evaluated by X-ray and optical methods. A comparison was made to ground-based grown crystals to determine the effect of convection on the homogeneity of crystals. Title: Chromosome aberrations in human lymphocytes induced by 250 MeV protons: effects of dose, dose rate and shielding Authors: George, K.; Willingham, V.; Wu, H.; Gridley, D.; Nelson, G.; Cucinotta, F. A. Bibcode: 2002AdSpR..30..891G Altcode: Although the space radiation environment consists predominantly of energetic protons, astronauts inside a spacecraft are chronically exposed to both primary particles as well as secondary particles that are generated when the primary particles penetrate the spacecraft shielding. Secondary neutrons and secondary charged particles can have an LET value that is greater than the primary protons and, therefore, produce a higher relative biological effectiveness (RBE). Using the accelerator facility at Loma Linda University, we exposed human lymphocytes in vitro to 250 MeV protons with doses ranging from 0 to 60 cGy at three different dose rates: a low dose rate of 7.5 cGy/h, an intermediate dose rate of 30 cGy/h and a high dose rate of 70 cGy/min. The effect of 15 g/cm 2 aluminum shielding on the induction of chromosome aberrations was investigated for each dose rate. After exposure, lymphocytes were incubated in growth medium containing phytohemagglutinin (PHA) and chromosome spreads were collected using a chemical-induced premature chromosome condensation (PCC) technique. Aberrations were analyzed using the fluorescence in situ hybridization (FISH) technique with three different colored chromosome-painting probes. The frequency of reciprocal and complex-type chromosome exchanges were compared in shielded and unshielded samples. Title: Genetic and Molecular Dosimetry of HZE Radiation (US-1 RADIAT) Authors: Nelson, G.; Schubert, W. W.; Kazarians, G. A.; Richards, G. F.; Benton, E. V.; Benton, E. R.; Henke, R. P. Bibcode: 1995ESASP1162...41N Altcode: 1995bsi..book...41N No abstract at ADS Title: Teaching astronomy to children. Authors: Nelson, G. Bibcode: 1992JRASC..86..225N Altcode: No abstract at ADS Title: Microwave and X-ray observations of delayed brightenings at sites remote from the primary flare locations Authors: Nakajima, H.; Dennis, B. R.; Hoyng, P.; Nelson, G.; Kosugi, T.; Kai, K. Bibcode: 1985ApJ...288..806N Altcode: Five examples of solar flares observed with the 17-GHz interferometer at Nobeyama in which a secondary microwave burst occurred at a distance of 100,000 km to 1,000,000 km from the primary flare site are presented. The secondary microwave burst in all five cases had a similar time profile to the primary burst with a delay of 2 to 25 s. The velocity of a triggering agent inferred from this delay and spatial separation is 10,000 km to 100,000 km/s. The intensity of the secondary burst was a factor of 3 to 25 smaller than that of the primary burst in all events except for one case in which it was a factor of 2 larger. The polarization degree of the secondary burst at 17 GHz was 35 percent, significantly higher than the average value for typical impulsive bursts. Two of the events were accompanied by meterwave type III/V bursts located high in the corona between the primary and secondary sites. For two of the other events, X-ray images of the secondary source were obtained with the hard-X-ray imaging spectrometer on the Solar Maximum Mission. These observations strongly suggest that the distant microwave bursts were produced by electrons with energies of 10 keV to 100 keV which were channeled along a huge loop from the main flare site to the remote location. Title: Microwave and X-ray observations of delayed brightenings at sites remote from the primary flare locations Authors: Nakajima, H.; Dennis, B. R.; Hoyng, P.; Nelson, G.; Kosugi, T.; Kai, K. Bibcode: 1984STIN...8433326N Altcode: Five examples of solar flares observed with the 17-GHz interferometer at Nobeyama in which a secondary microwave burst occurred at a distance of 100,000 km to 1,000,000 km from the primary flare site are presented. The secondary microwave burst in all five cases had a similar time profile to the primary burst with a delay of 2 to 25 s. The velocity of a triggering agent inferred from this delay and spatial separation is 10,000 km to 100,000 km/s. The intensity of the secondary burst was a factor of 3 to 25 smaller than that of the primary burst in all events except for one case in which it was a factor of 2 larger. The polarization degree of the secondary burst at 17 GHz was 35%, significantly higher than the average value for typical impulsive bursts. Two of the events were accompanied by meterwave type III/V bursts located high in the corona between the primary and secondary sites. For two of the other events, X-ray images of he secondary source were obtained with the hard-X-ray imaging spectrometer on the Solar Maximum Mission. These observations strongly suggest that the distant microwave bursts were produced by electrons with energies of 10 keV to 100 keV which were channeled along a huge loop from the main flare site to the remote location. Title: Microwave and X-ray Observations of Delayed Brightenings at Sites Remote from the Primary Flare Locations Authors: Nakajima, H.; Dennis, B. R.; Hoyng, P.; Nelson, G.; Kosugi, T.; Kai, K. Bibcode: 1984BAAS...16..524N Altcode: No abstract at ADS Title: Observations of a POST Flare Radio Burst in X-Rays Authors: Svestka, Z.; Hoyng, P.; van Tend, W.; Boelee, A.; de Jager, C.; Stewart, R. T.; Acton, L. W.; Bruner, E. C.; Gabriel, A. H.; Rapley, C. G.; de Jager, C.; LaFleur, H.; Nelson, G.; Simnett, G. M.; van Beek, H. F.; Wagner, W. J. Bibcode: 1982SoPh...75..305S Altcode: More than six hours after the two-ribbon flare of 21 May 1980, the hard X-ray spectrometer aboard the SMM imaged an extensive arch above the flare region which proved to be the lowest part of a stationary post-flare noise storm recorded at the same time at Culgoora. The X-ray arch extended over 3 or more arc minutes to a projected distance of 95 000 km, and its real altitude was most probably between 110 000 and 180 000 km. The mean electron density in the cloud was close to 109 cm−3 and its temperature stayed for many hours at a fairly constant value of about 6.5 × 106 K. The bent crystal spectrometer aboard the SMM confirms that the arch emission was basically thermal. Variations in brightness and energy spectrum at one of the supposed footpoints of the arch seem to correlate in time with radio brightness suggesting that suprathermal particles from the radio noise regions dumped in variable quantities into the low corona and transition layer; these particles may have contributed to the population of the arch, after being trapped and thermalized. The arch extended along the H∥ = 0 line thus apparently hindering any upward movement of the upper loops reconnected in the flare process. There is evidence from Culgoora that this obstacle may have been present above the flare since 15-30 min after its onset. Title: Optical and radio observations of the 1980 March 29, April 30, and June 7 flares Authors: Rust, D. M.; Benz, A.; Hurford, G. J.; Nelson, G.; Pick, M.; Ruzdjak, V. Bibcode: 1981ApJ...244L.179R Altcode: Ground-based solar observations are analyzed for three of the flares discussed in the accompanying Solar Maximum Mission reports. The principal conclusions are that H-alpha begins to brighten several minutes before the impulsive, hard X-ray bursts, that the preflare heating and impulsive phases of the three flares occurred in loop-shaped structures of about 3500 km semidiameter, and that after the impulsive phase a much larger volume (about 200 times) of flare plasma was present for the flare main phase. Evidence is presented for the escape of 100-500 keV electrons into the larger volume and into the corona during the impulsive phase. For the April 30 flare, the inferred origin of the hard X-ray burst is near the feet of the magnetic loops. Title: Granulation in a main-sequence F-type star Authors: Nelson, G. D. Bibcode: 1980ApJ...238..659N Altcode: The modal approach developed by Nelson and Musman (1977) is used to investigate convection in an F-type main-sequence star (effective temperature of 7300 K, g = 10,000 cm per sec per sec). The convective velocities and intensity contrasts are found to be larger than in the sun. Even though the convective flux is less than 1% of the total flux at a mean optical depth of unity, the spectral-energy distribution is strongly reddened as a result of the fluctuating opacity. This has important implications in the conversion scale from observed colors to effective temperature. The scale of the surface granulation is expected to be in the range 1000-5000 km. Calculations of the combined H-He I and He II convection zones support the prediction of Toomre et al. (1976) that the stable region between the zones is well mixed Title: Thermal and Continuum Driven Convection in B-Stars Authors: Nelson, G. D. Bibcode: 1980LNP...114...16N Altcode: 1980IAUCo..51...16N; 1980sttu.coll...16N; 1980LNP...114...16D No abstract at ADS Title: A two-dimensional solar model. Authors: Nelson, G. D. Bibcode: 1978SoPh...60....5N Altcode: We present a two-dimensional, nearly flux constant solar atmosphere which includes a physical model of granulation. If the inhomogeneous character of the solar photosphere is neglected in the construction of empirical models, the result is an underestimate of the temperature gradient in the layers below τ ∼ 0.5 and an overestimate of the convective flux penetration into the observable layers. The two-dimensional model adequately reproduces the mean limb darkening, the magnitude and center-to-limb variation of the intensity fluctuations, and the rms vertical and horizontal convective velocities. Title: Some comments on the limb shift of solar lines. II: The effect of granular motions. Authors: Beckers, J. M.; Nelson, G. D. Bibcode: 1978SoPh...58..243B Altcode: The well-known correlation between granulation intensity and velocity fluctuations causes a shift of the average line position called the `convective blue shift'. It is argued that this convective blue shift is most likely reponsible for the limb effect of solar Fraunhofer lines. To explain the center-to-limb variation of this limb effect it is essential that both horizontal and vertical motions in the granulation are considered. The effects of a variation in the granulation properties across the Sun on large scale velocity pattern observations are discussed. Abnormal granulation patterns observed inactive regions and at the boundaries of supergranules could be responsible for part or all of the `downflow' observed there. Title: The scale of the solar granulation. Authors: Nelson, G. D.; Musman, S. Bibcode: 1978ApJ...222L..69N Altcode: The observed scale of granulation is derived as a consequence of a physical model. At scales smaller than granulation, horizontal radiative transport reduces temperature fluctuations and the resultant buoyancy forces in the surface layers. At scales only slightly larger than granulation, the dynamical pressure required to drive horizontal motions changes the opacity sufficiently to reduce the apparent contrast. This raises the possibility that the dark center of an exploding granule may actually be hot below the surface. The maximum possible horizontal extent of a surface-driven convective flow is estimated as 4.5 times granular scale. Title: A line driven Rayleigh-Taylor-type instability in hot stars. Authors: Nelson, G. D.; Hearn, A. G. Bibcode: 1978A&A....65..223N Altcode: The existence of a Rayleigh-Taylor-type instability in the atmospheres of hot stars, driven by the radiative force associated with impurity ion resonance lines, is demonstrated. In a hot star with an effective temperature of 50,000 K, the instability will grow exponentially with a time scale of approximately 50 s in the layers where the stellar wind velocity is 5% of the thermal velocity of the ion. As a result, radially symmetric stellar winds driven by resonance line radiative forces will break up in small horizontal scale lengths. The energy fed into the instability provides a possible source of mechanical heating in the atmosphere for a chromosphere or corona. Title: Convection in the surface layers of the sun and the stars Authors: Nelson, George Driver Bibcode: 1978PhDT........55N Altcode: No abstract at ADS Title: Convection in the Surface Layers of the Sun and the Stars. Authors: Nelson, G. D. Bibcode: 1978PhDT.........1N Altcode: A two-dimensional steady-state model of the convection in the surface layers of the sun and stars is developed. Radiative energy transport through the inhomogeneous photosphere is described with the two-dimensional transfer equation in the gray Eddington approximation. The magnitude and extent of the vertical velocity overshoot as a function of cell size and drag length is discussed. Title: The Scale of Granulation. Authors: Musman, S. A.; Nelson, G. D. Bibcode: 1977BAAS....9..616M Altcode: No abstract at ADS Title: A dynamical model of solar granulation. Authors: Nelson, G. D.; Musman, S. Bibcode: 1977ApJ...214..912N Altcode: We construct a steady-state model of solar granulation with a simplified horizontal structure. As in our previous model the transfer of radiation dominates the energy balance and determines the temperature fluctuations. The turbulent drag force which we include in a simplified form balances the buoyancy created by the temperature fluctuations. Penetration of velocity and temperature fluctuations are similar to those observed. The small-scale turbulence generated by granular motions may be an important contributor to observed unresolved motions but cannot account for the total. Title: About the Proper Choice of the Characteristic Length in the Convection Theory Authors: Bohm-Vitense, Erika; Nelson, George Driver Bibcode: 1976ApJ...210..741B Altcode: It is known that convection sets in rather abruptly for stars with Teff < Tb, where Tb depends on the luminosity. The boundary line Tb(L) goes through the H-R diagram from late A or early F main-sequence stars to late F or early G supergiants. In the mixing length approach to the theory of convection the exact theoretical position of this boundary temperature depends on the assumptions about the size of the mixing length 1. We make the assumption that the red boundary of the Cepheid instability strip agrees with the line Tb(L). If we also assume 1 = n pressure scale height H, with n being the same constant for all stars, we find 1 H to give the correct Tb(L). If we assume the region of large instability to determine 1, the relation 1 R2 also gives approximately the correct Tb(L). We do not think, however, that the latter relation has any physical significance. Subject headings: convection - stars: Cepheids - stars: chromosphere - stars: interiors Title: The energy balance of granulation. Authors: Musman, S.; Nelson, G. D. Bibcode: 1976ApJ...207..981M Altcode: We construct columnar models of the solar granulation based on the balance of convective energy carried by a vertical velocity field and radiation. A specified velocity field and perturbation of the radiative flux determines the variation of temperature fluctuations with height. For a nominal model we compute the variation of contrast with wavelength and heliocentric angle. We conclude that the observed temperature fluctuations cannot be produced by the observed velocities alone, but require either a modified radiation field or turbulent energy transport, or both.