321 research outputs found
A descriptive and evaluative bibliography of films in secondary school literature
Thesis (Ed.M.)--Boston UniversitySTATEMENT OF THE PROBLEM.-- This thesis was written to compile a descriptive and evaluative bibliography of films which might supplement instruction in literature from grades seven through twelve.
JUSTIFICATION.-- Such a study, to the best of the writers' knowledge, is non-existent. In order to conserve unnecessary expenditure of time and effort by teachers in search of films appropriate to their units of instruction, such a listing must be devised. Commercial catalogs often list such important data as: title, running time, producer, and cost; but they rarely give an objective description of the content of the film as related to the objectives of teaching literature as stated in the publication of The National Council of Teachers of English.
PROCEDURE.-- The writers considered themselves a basic evaluation committee formed to appraise a large number of educational films related to teaching literature. In order to substantiate their appraisals, they invited large numbers of teachers to attend the twice-weekly preview showings. A check-list comprised of thirteen items to analyze the films from a pedagogical point of view was devised and circulated among the evaluators attending. Forty-seven films were obtained from Boston University School of Public Relations, The Boston Public Library, The University of New Hampshire, and leading producers of such films who offered full cooperation to the writers throughout the nine-week period of the showings [TRUNCATED]
The Multiple Origin of Blue Straggler Stars: Theory vs. Observations
In this chapter we review the various suggested channels for the formation
and evolution of blue straggler stars (BSSs) in different environments and
their observational predictions. These include mass transfer during binary
stellar evolution - case A/B/C and D (wind Roche-lobe overflow) mass transfer,
stellar collisions during single and binary encounters in dense stellar
cluster, and coupled dynamical and stellar evolution of triple systems. We also
explore the importance of the BSS and binary dynamics in stellar clusters. We
review the various observed properties of BSSs in different environments (halo
and bulge BSSs, BSSs in globular clusters and BSSs in old open clusters), and
compare the current observations with the theoretical predictions for BSS
formation. We try to constrain the likely progenitors and processes that play a
role in the formation of BSSs and their evolution. We find that multiple
channels of BSS formation are likely to take part in producing the observed
BSSs, and we point out the strengths and weaknesses of each the formation
channel in respect to the observational constraints. Finally we point out
directions to further explore the origin of BSS, and highlight eclipsing binary
BSSs as important observational tool.Comment: Chapter 11, in Ecology of Blue Straggler Stars, H.M.J. Boffin, G.
Carraro & G. Beccari (Eds), Astrophysics and Space Science Library, Springe
An Analytic Model for Blue Straggler Formation in Globular Clusters
We present an analytic model for blue straggler formation in globular
clusters. We assume that blue stragglers are formed only through stellar
collisions and binary star evolution, and compare our predictions to observed
blue straggler numbers taken from the catalogue of Leigh, Sills & Knigge
(2011). We can summarize our key results as follows: (1) Binary star evolution
consistently dominates blue straggler production in all our best-fitting
models. (2) In order to account for the observed sub-linear dependence of blue
straggler numbers on the core masses (Knigge, Leigh & Sills 2009), the core
binary fraction must be inversely proportional to the total cluster luminosity
and should always exceed at least a few percent. (3) In at least some clusters,
blue straggler formation must be enhanced by dynamical encounters (either via
direct collisions or by stimulating mass-transfer to occur by altering the
distribution of binary orbital parameters) relative to what is expected by
assuming a simple population of binaries evolving in isolation. (4) The
agreement between the predictions of our model and the observations can be
improved by including blue stragglers that form outside the core but later
migrate in due to dynamical friction. (5) Longer blue straggler lifetimes are
preferred in models that include blue stragglers formed outside the core since
this increases the fraction that will have sufficient time to migrate in via
dynamical friction.Comment: 11 pages, 4 figures, accepted for publication in MNRA
Small-N Collisional Dynamics: Pushing Into the Realm of Not-So-Small-N
In this paper, we study small-N gravitational dynamics involving up to six
objects. We perform a large suite of numerical scattering experiments involving
single, binary, and triple stars. This is done using the FEWBODY numerical
scattering code, which we have upgraded to treat encounters involving triple
stars. We focus on outcomes that result in direct physical collisions between
stars, within the low angular momentum and high absolute orbital energy regime.
The dependence of the collision probability on the number of objects involved
in the interaction, N, is found for fixed total energy and angular momentum.
Our results are consistent with a collision probability that increases
approximately as N^2. Interestingly, this is also what is expected from the
mean free path approximation in the limit of very large N. A more thorough
exploration of parameter space will be required in future studies to fully
explore this potentially intriguing connection. This study is meant as a first
step in an on-going effort to extend our understanding of small-N collisional
dynamics beyond the three- and four-body problems and into the realm of
larger-N.Comment: 11 pages, 6 figures, 2 tables; accepted for publication in MNRAS;
updated to match published versio
The Anisotropic Spatial Distribution of Hypervelocity Stars
We study the distribution of angular positions and angular separations of
unbound hypervelocity stars (HVSs). HVSs are spatially anisotropic at the
3-sigma level. The spatial anisotropy is significant in Galactic longitude, not
in latitude, and the inclusion of lower velocity, possibly bound HVSs reduces
the significance of the anisotropy. We discuss how the observed distribution of
HVSs may be linked to their origin. In the future, measuring the distribution
of HVSs in the southern sky will provide additional constraints on the spatial
anisotropy and the origin of HVSs.Comment: 4 pages, accepted to ApJ Letter
The Blue Stragglers of the Old Open Cluster NGC 188
The old (7 Gyr) open cluster NGC 188 has yielded a wealth of astrophysical
insight into its rich blue straggler population. Specifically, the NGC 188 blue
stragglers are characterized by: A binary frequency of 80% for orbital periods
less than days;Typical orbital periods around 1000 days;Typical
secondary star masses of 0.5 M; At least some white dwarf companion
stars; Modestly rapid rotation; A bimodal radial spatial distribution;
Dynamical masses greater than standard stellar evolution masses (based on
short-period binaries); Under-luminosity for dynamical masses (short-period
binaries). Extensive -body modeling of NGC 188 with empirical initial
conditions reproduces the properties of the cluster, and in particular the
main-sequence solar-type binary population. The current models also reproduce
well the binary orbital properties of the blue stragglers, but fall well short
of producing the observed number of blue stragglers. This deficit could be
resolved by reducing the frequency of common-envelope evolution during Roche
lobe overflow. Both the observations and the -body models strongly indicate
that the long-period blue-straggler binaries - which dominate the NGC 188 blue
straggler population - are formed by asymptotic-giant (primarily) and red-giant
mass transfer onto main sequence stars. The models suggest that the few
non-velocity-variable blue stragglers formed from mergers or collisions.
Several remarkable short-period double-lined binaries point to the importance
of subsequent dynamical exchange encounters, and provide at least one example
of a likely collisional origin for a blue straggler.Comment: Chapter 3, in Ecology of Blue Straggler Stars, H.M.J. Boffin, G.
Carraro & G. Beccari (Eds), Astrophysics and Space Science Library, Springe
Parents, but not their children, demonstrate greater delay discounting with resource scarcity
BACKGROUND: Individuals with obesity tend to discount the future (delay discounting), focusing on immediate gratification. Delay discounting is reliably related to indicators of economic scarcity (i.e., insufficient resources), including lower income and decreased educational attainment in adults. It is unclear whether the impact of these factors experienced by parents also influence child delay discounting between the ages of 8 and 12-years in families with obesity.
METHODS: The relationship between indices of family income and delay discounting was studied in 452 families with parents and 6-12-year-old children with obesity. Differences in the relationships between parent economic, educational and Medicaid status, and parent and child delay discounting were tested.
RESULTS: Results showed lower parent income (p = 0.019) and Medicaid status (p = 0.021) were differentially related to greater parent but not child delay discounting among systematic responders.
CONCLUSIONS: These data suggest differences in how indicators of scarcity influence delay discounting for parents and children, indicating that adults with scarce resources may be shaped to focus on immediate needs instead of long-term goals. It is possible that parents can reduce the impact of economic scarcity on their children during preadolescent years. These findings suggest a need for policy change to alleviate the burden of scarce conditions and intervention to modify delay discounting rate and to improve health-related choices and to address weight disparities
Are Child and Adolescent Responses to Placebo Higher in Major Depression than in Anxiety Disorders? A Systematic Review of Placebo-Controlled Trials
BACKGROUND: In a previous report, we hypothesized that responses to placebo were high in child and adolescent depression because of specific psychopathological factors associated with youth major depression. The purpose of this study was to compare the placebo response rates in pharmacological trials for major depressive disorder (MDD), obsessive compulsive disorder (OCD) and other anxiety disorders (AD-non-OCD). METHODOLOGY AND PRINCIPAL FINDINGS: We reviewed the literature relevant to the use of psychotropic medication in children and adolescents with internalized disorders, restricting our review to double-blind studies including a placebo arm. Placebo response rates were pooled and compared according to diagnosis (MDD vs. OCD vs. AD-non-OCD), age (adolescent vs. child), and date of publication. From 1972 to 2007, we found 23 trials that evaluated the efficacy of psychotropic medication (mainly non-tricyclic antidepressants) involving youth with MDD, 7 pertaining to youth with OCD, and 10 pertaining to youth with other anxiety disorders (N = 2533 patients in placebo arms). As hypothesized, the placebo response rate was significantly higher in studies on MDD, than in those examining OCD and AD-non-OCD (49.6% [range: 17-90%] vs. 31% [range: 4-41%] vs. 39.6% [range: 9-53], respectively, ANOVA F = 7.1, p = 0.002). Children showed a higher stable placebo response within all three diagnoses than adolescents, though this difference was not significant. Finally, no significant effects were found with respect to the year of publication. CONCLUSION: MDD in children and adolescents appears to be more responsive to placebo than other internalized conditions, which highlights differential psychopathology
MMT Hypervelocity Star Survey. II. Five New Unbound Stars
We present the discovery of five new unbound hypervelocity stars (HVSs) in
the outer Milky Way halo. Using a conservative estimate of Galactic escape
velocity, our targeted spectroscopic survey has now identified 16 unbound HVSs
as well as a comparable number of HVSs ejected on bound trajectories. A
Galactic center origin for the HVSs is supported by their unbound velocities,
the observed number of unbound stars, their stellar nature, their ejection time
distribution, and their Galactic latitude and longitude distribution. Other
proposed origins for the unbound HVSs, such as runaway ejections from the disk
or dwarf galaxy tidal debris, cannot be reconciled with the observations. An
intriguing result is the spatial anisotropy of HVSs on the sky, which possibly
reflects an anisotropic potential in the central 10-100 pc region of the
Galaxy. Further progress requires measurement of the spatial distribution of
HVSs over the southern sky. Our survey also identifies seven B supergiants
associated with known star-forming galaxies; the absence of B supergiants
elsewhere in the survey implies there are no new star-forming galaxies in our
survey footprint to a depth of 1-2 Mpc.Comment: 10 pages, submitted to Ap
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