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Author name code: nelson-george
ADS astronomy entries on 2022-09-14
author:"Nelson, George Driver"
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Title: EPO and the Big Education Reform Picture
Authors: Nelson, G. D.
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.
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Title: The AAS Resolution on Teaching Evolution
Authors: Nelson, George D.
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.
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Title: PET as a Model for Other Introductory Content Courses
Authors: Nelson, George D.
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.
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Title: Astronomy Education at the AAS : The Current State
Authors: Nelson, George
2006Spark...1....1N Altcode:
No abstract at ADS
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Title: Expedition Mars
Authors: Turner, Martin J. L.; Nelson, George D.
2005PhT....58f..59T Altcode:
No abstract at ADS
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Title: Book Review: EXPEDITION MARS / Springer, 2004
Authors: Nelson, George D.
2005PhT....58f..59N Altcode:
No abstract at ADS
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Title: Keynote Address
Authors: Nelson, G. D.
2004ASPC..319...55N Altcode:
No abstract at ADS
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Title: The Colorado MESA Program and CU-LASP: A Model for After
School Program/Research Institution Collaboratives
Authors: Nelson, G.; Cobabe-Ammann, E.
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.
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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.
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.
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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.
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 <SUP>2</SUP> 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.
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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.
1995ESASP1162...41N Altcode: 1995bsi..book...41N
No abstract at ADS
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Title: Teaching astronomy to children.
Authors: Nelson, G.
1992JRASC..86..225N Altcode:
No abstract at ADS
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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.
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.
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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.
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.
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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.
1984BAAS...16..524N Altcode:
No abstract at ADS
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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.
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
10<SUP>9</SUP> cm<SUP>−3</SUP> and its temperature stayed for many
hours at a fairly constant value of about 6.5 × 10<SUP>6</SUP> 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<SUB>∥</SUB> = 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.
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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.
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.
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Title: Granulation in a main-sequence F-type star
Authors: Nelson, G. D.
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
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Title: Thermal and Continuum Driven Convection in B-Stars
Authors: Nelson, G. D.
1980LNP...114...16N Altcode: 1980IAUCo..51...16N; 1980sttu.coll...16N; 1980LNP...114...16D
No abstract at ADS
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Title: A two-dimensional solar model.
Authors: Nelson, G. D.
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.
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Title: Some comments on the limb shift of solar lines. II: The effect
of granular motions.
Authors: Beckers, J. M.; Nelson, G. D.
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.
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Title: The scale of the solar granulation.
Authors: Nelson, G. D.; Musman, S.
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.
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Title: A line driven Rayleigh-Taylor-type instability in hot stars.
Authors: Nelson, G. D.; Hearn, A. G.
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.
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Title: Convection in the surface layers of the sun and the stars
Authors: Nelson, George Driver
1978PhDT........55N Altcode:
No abstract at ADS
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Title: Convection in the Surface Layers of the Sun and the Stars.
Authors: Nelson, G. D.
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.
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Title: The Scale of Granulation.
Authors: Musman, S. A.; Nelson, G. D.
1977BAAS....9..616M Altcode:
No abstract at ADS
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Title: A dynamical model of solar granulation.
Authors: Nelson, G. D.; Musman, S.
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.
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Title: About the Proper Choice of the Characteristic Length in the
Convection Theory
Authors: Bohm-Vitense, Erika; Nelson, George Driver
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
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Title: The energy balance of granulation.
Authors: Musman, S.; Nelson, G. D.
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.
