199 research outputs found
Proceedings of the CUNY Games Conference 5.0
The CUNY Games Network is an organization dedicated to encouraging research, scholarship and teaching in the developing field of games-based learning. We connect educators from every campus and discipline at CUNY and beyond who are interested in digital and non-digital games, simulations, and other forms of interactive teaching and inquiry-based learning. The CUNY Games Conference distills its best cutting-edge interactive presentations into a two-day event to promote and discuss game-based pedagogies in higher education, focusing particularly on non-digital learning activities that faculty can use in the classroom every day. The conference will include workshops lead by CUNY Games Organizers on how to modify existing games for the classroom, how to incorporate elements of play into simulations and critical thinking activities, as well as poster sessions, play testing, and game play. For the digitally minded, we will also offer a workshop in creating computer games in Unity
Proceedings of the CUNY Games Conference 4.0: The Interactive Course
Proceedings of the CUNY Games Conference, held from January 22-23, 2018, at the CUNY Graduate Center and Borough of Manhattan Community College.
Critical Play with History (Panel) - Composition & Storytelling - Health & Cognitive Sciences - Gaming Anthropology: Teaching Culture and Power Through Games and Design (Panel) - Twine & Writing Games - Easy Ideas II - STEM Games - Global Games for Change Catalog (Panel) - Comics & Active Learning - Fact Checking & Research - Computer Science & Game Design - SimGlobal: Building a Serious Roleplay Course for the Social Sciences (Panel) - Role Playing Games, Narrative, & Story - Course Review Through Games - Business & Finance Games - Game Design and Programming in Unity - What’s Your Game Plan? - The Allure of Play in the Classroo
Comments on alternative calculations of the broadening of spectral lines of neutral sodium by H-atom collisions
With the exception of the sodium D-lines recent calculations of line
broadening cross-sections for several multiplets of sodium by Leininger et al
(2000) are in substantial disagreement with cross-sections interpolated from
the tables of Anstee and O'Mara (1995) and Barklem and O'Mara (1997). The
discrepancy is as large as a factor of three for the 3p-4d multiplet. The two
theories are tested by using the results of each to synthesize lines in the
solar spectrum. It is found that generally the data from the theory of Anstee,
Barklem and O'Mara produce the best match to the observed solar spectrum. It is
found, using a simple model for reflection of the optical electron by the
potential barrier between the two atoms, that the reflection coefficient is too
large for avoided crossings with the upper states of subordinate lines to
contribute to line broadening, supporting the neglect of avoided ionic
crossings by Anstee, Barklem and O'Mara for these lines. The large
discrepancies between the two sets of calculations is a result of an
approximate treatment of avoided ionic crossings for these lines by Leininger
et al (2000).Comment: 18 pages, 5 ps figures included, to appear in J Phys B: At. Mol. Opt.
Phy
Evolution of a 3 \msun star from the main sequence to the ZZ Ceti stage: the role played by element diffusion
The purpose of this paper is to present new full evolutionary calculations
for DA white dwarf stars with the major aim of providing a physically sound
reference frame for exploring the pulsation properties of the resulting models
in future communications. Here, white dwarf evolution is followed in a
self-consistent way with the predictions of time dependent element diffusion
and nuclear burning. In addition, full account is taken of the evolutionary
stages prior to the white dwarf formation. In particular, we follow the
evolution of a 3 \msun model from the zero-age main sequence (the adopted
metallicity is Z=0.02) all the way from the stages of hydrogen and helium
burning in the core up to the thermally pulsing phase. After experiencing 11
thermal pulses, the model is forced to evolve towards its white dwarf
configuration by invoking strong mass loss episodes. Further evolution is
followed down to the domain of the ZZ Ceti stars on the white dwarf cooling
branch. Emphasis is placed on the evolution of the chemical abundance
distribution due to diffusion processes and the role played by hydrogen burning
during the white dwarf evolution. Furthermore, the implications of our
evolutionary models for the main quantities relevant for adiabatic pulsation
analysis are discussed. Interestingly, the shape of the Ledoux term is markedly
smoother as compared with previous detailed studies of white dwarfs. This is
translated into a different behaviour of the Brunt-Vaisala frequency.Comment: 11 pages, 11 figures, accepted for publication in MNRA
Near-IR spectroscopic ages of massive star clusters in M82
Like other starburst galaxies, M82 hosts compact, massive young star clusters
that are interesting both in their own right and as benchmarks for population
synthesis models. Can spectral synthesis models at resolutions around 1000
adequately reproduce the near-IR spectral features and the energy distribution
of these clusters between 0.8 and 2.4 microns? How do the derived cluster
properties compare with previous results from optical studies?
We analyse the spectra of 5 massive clusters in M82, using data acquired with
the spectrograph SpeX on the InfraRed Telescope Facility (NASA/IRTF) and a new
population synthesis tool with a highly improved near-IR extension, based on a
recent collection of empirical and theoretical spectra of red supergiant stars.
We obtain excellent fits across the near-IR with models at quasi-solar
metallicity and a solar neighbourhood extinction law. Spectroscopy breaks a
strong degeneracy between age and extinction in the near-IR colours in the red
supergiant-dominated phase of evolution. The estimated near-IR ages cluster
between 9 and 30 Myr, i.e. the ages at which the molecular bands due to
luminous red supergiants are strongest in the current models. They do not
always agree with optical spectroscopic ages. Adding optical data sometimes
leads to the rejection of the solar neighbourhood extinction law. This is not
surprising considering small-scale structure around the clusters, but it has no
significant effect on the near-IR based spectroscopic ages. [abridged]Comment: 14 pages, 20 figures, uses aa.cl
The X-ray spectrum of the newly discovered accreting millisecond pulsar IGR J17511-3057
We report on an XMM-Newton observation of the accreting millisecond pulsar,
IGR J17511-3057. Pulsations at 244.8339512(1) Hz are observed with an RMS
pulsed fraction of 14.4(3)%. A precise solution for the P_orb=12487.51(2)s
binary system is derived. The measured mass function indicates a main sequence
companion with a mass between 0.15 and 0.44 Msun. The XMM-Newton spectrum of
the source can be modelled by at least three components, multicoloured disc
emission, thermal emission from the NS surface and thermal Comptonization
emission. Spectral fit of the XMM-Newton data and of the RXTE data, taken in a
simultaneous temporal window, constrain the Comptonization parameters: the
electron temperature, kT_e=51(+6,-4) keV, is rather high, while the optical
depth (tau=1.34(+0.03,-0.06)) is moderate. The energy dependence of the pulsed
fraction supports the interpretation of the cooler thermal component as coming
from the accretion disc, and indicates that the Comptonizing plasma surrounds
the hot spots on the NS surface, which provide the seed photons. Signatures of
reflection, such as a broadened iron K-alpha emission line and a Compton hump
at 30 keV ca., are also detected. We derive from the smearing of the reflection
component an inner disc radius of ~> 40 km for a 1.4 Msun neutron star, and an
inclination between 38{\deg} and 68{\deg}. XMM-Newton also observed two type-I
X-ray bursts, probably ignited in a nearly pure helium environment. No
photospheric radius expansion is observed, thus leading to an upper limit on
the distance to the source of 10 kpc. A lower limit of 6.5 kpc can be also set
if it is assumed that emission during the decaying part of the burst involves
the whole neutron star surface. Pulsations observed during the burst decay are
compatible with being phase locked, and have a similar amplitude, than
pre-burst pulsations.Comment: 16 pages, 10 figures, 4 tables, accepted for publication in MNRA
Alpha-decay branching ratios of near-threshold states in 19Ne and the astrophysical rate of 15O(alpha,gamma)19Ne
The 15O(alpha,gamma)19Ne reaction is one of two routes for breakout from the
hot CNO cycles into the rp process in accreting neutron stars. Its
astrophysical rate depends critically on the decay properties of excited states
in 19Ne lying just above the 15O + alpha threshold. We have measured the
alpha-decay branching ratios for these states using the p(21Ne,t)19Ne reaction
at 43 MeV/u. Combining our measurements with previous determinations of the
radiative widths of these states, we conclude that no significant breakout from
the hot CNO cycle into the rp process in novae is possible via
15O(alpha,gamma)19Ne, assuming current models accurately represent their
temperature and density conditions
Three-micron spectra of AGB stars and supergiants in nearby galaxies
The dependence of stellar molecular bands on the metallicity is studied using
infrared L-band spectra of AGB stars (both carbon-rich and oxygen-rich) and
M-type supergiants in the Large and Small Magellanic Clouds (LMC and SMC) and
in the Sagittarius Dwarf Spheroidal Galaxy. The spectra cover SiO bands for
oxygen-rich stars, and acetylene (C2H2), CH and HCN bands for carbon-rich AGB
stars. The equivalent width of acetylene is found to be high even at low
metallicity. The high C2H2 abundance can be explained with a high
carbon-to-oxygen (C/O) ratio for lower metallicity carbon stars. In contrast,
the HCN equivalent width is low: fewer than half of the extra-galactic carbon
stars show the 3.5micron HCN band, and only a few LMC stars show high HCN
equivalent width. HCN abundances are limited by both nitrogen and carbon
elemental abundances. The amount of synthesized nitrogen depends on the initial
mass, and stars with high luminosity (i.e. high initial mass) could have a high
HCN abundance. CH bands are found in both the extra-galactic and Galactic
carbon stars. None of the oxygen-rich LMC stars show SiO bands, except one
possible detection in a low quality spectrum. The limits on the equivalent
widths of the SiO bands are below the expectation of up to 30angstrom for LMC
metallicity. Several possible explanations are discussed. The observations
imply that LMC and SMC carbon stars could reach mass-loss rates as high as
their Galactic counterparts, because there are more carbon atoms available and
more carbonaceous dust can be formed. On the other hand, the lack of SiO
suggests less dust and lower mass-loss rates in low-metallicity oxygen-rich
stars. The effect on the ISM dust enrichment is discussed.Comment: accepted for A&
Modeling the actinides with disordered local moments
A first-principles disordered local moment (DLM) picture within the
local-spin-density and coherent potential approximations (LSDA+CPA) of the
actinides is presented. The parameter free theory gives an accurate description
of bond lengths and bulk modulus. The case of -Pu is studied in
particular and the calculated density of states is compared to data from
photo-electron spectroscopy. The relation between the DLM description, the
dynamical mean field approach and spin-polarized magnetically ordered modeling
is discussed.Comment: 6 pages, 4 figure
Active megadetachment beneath the western United States
Geodetic data, interpreted in light of seismic imaging, seismicity, xenolith studies, and the late Quaternary geologic history of the northern Great Basin, suggest that a subcontinental-scale extensional detachment is localized near the Moho. To first order, seismic yielding in the upper crust at any given latitude in this region occurs via an M7 earthquake every 100 years. Here we develop the hypothesis that since 1996, the region has undergone a cycle of strain accumulation and release similar to “slow slip events” observed on subduction megathrusts, but yielding occurred on a subhorizontal surface 5–10 times larger in the slip direction, and at temperatures >800°C. Net slip was variable, ranging from 5 to 10 mm over most of the region. Strain energy with moment magnitude equivalent to an M7 earthquake was released along this “megadetachment,” primarily between 2000.0 and 2005.5. Slip initiated in late 1998 to mid-1999 in northeastern Nevada and is best expressed in late 2003 during a magma injection event at Moho depth beneath the Sierra Nevada, accompanied by more rapid eastward relative displacement across the entire region. The event ended in the east at 2004.0 and in the remainder of the network at about 2005.5. Strain energy thus appears to have been transmitted from the Cordilleran interior toward the plate boundary, from high gravitational potential to low, via yielding on the megadetachment. The size and kinematic function of the proposed structure, in light of various proxies for lithospheric thickness, imply that the subcrustal lithosphere beneath Nevada is a strong, thin plate, even though it resides in a high heat flow tectonic regime. A strong lowermost crust and upper mantle is consistent with patterns of postseismic relaxation in the southern Great Basin, deformation microstructures and low water content in dunite xenoliths in young lavas in central Nevada, and high-temperature microstructures in analog surface exposures of deformed lower crust. Large-scale decoupling between crust and upper mantle is consistent with the broad distribution of strain in the upper crust versus the more localized distribution in the subcrustal lithosphere, as inferred by such proxies as low P wave velocity and mafic magmatism
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