399 research outputs found
Market Games In Finance Education
An electronic share market trading game was introduced to a large first year undergraduate finance course to allow students to experience share market trading. The response from students was positive. We surveyed a sample of 51 of the students in this class who undertook a further one-hour trading session as part of a separate research experiment. These students rate the game as a valuable learning experience. They suggest that their use of the game increased their understanding of share market and the way that prices are set. While the study results cannot be generalised to all students in the course, the results suggest that there are benefits to be gained from including an electronic share market trading game as part of the course
The Medical Library Association Data Services Competency: A Framework for Data Science and Open Science Skills Development
Increasingly, users of health and biomedical libraries need assistance with challenges they face in working with their own and others' data. Librarians have a unique opportunity to provide valuable support and assistance in data science and open science but may need to add to their expertise and skill set to have the most impact. This article describes the rationale for and development of the Medical Library Association Data Services Competency, which outlines a set of five key skills for data services and provides a course of study for gaining these skills
A Study on Marketing Behaviour of Rural Youth Entrepreneurs among Seven Different Ventures
The study was conducted among 210 rural youth entrepreneurs of seven different ventures in Krishnagiri district to assess their marketing behaviour. The entrepreneurial ventures selected for the study were Sericulture, Mushroom Production, Hi-tech nurseries (Polyhouse), Fruit and flower nursery, Fisheries, Poultry farming and Value addition (Tamarind processing and Millet based cookies).
Spitzer and HHT observations of starless cores: masses and environments
We present Spitzer observations of a sample of 12 starless cores selected to
have prominent 24 micron shadows. The Spitzer images show 8 and 24 micron
shadows and in some cases 70 micron shadows; these spatially resolved
absorption features trace the densest regions of the cores. We have carried out
a 12CO (2-1) and 13CO (2-1) mapping survey of these cores with the Heinrich
Hertz Telescope (HHT). We use the shadow features to derive optical depth maps.
We derive molecular masses for the cores and the surrounding environment; we
find that the 24 micron shadow masses are always greater than or equal to the
molecular masses derived in the same region, a discrepancy likely caused by CO
freeze--out onto dust grains. We combine this sample with two additional cores
that we studied previously to bring the total sample to 14 cores. Using a
simple Jeans mass criterion we find that ~ 2/3 of the cores selected to have
prominent 24 micron shadows are collapsing or near collapse, a result that is
supported by millimeter line observations. Of this subset at least half have
indications of 70 micron shadows. All cores observed to produce absorption
features at 70 micron are close to collapse. We conclude that 24 micron
shadows, and even more so the 70 micron ones, are useful markers of cloud cores
that are approaching collapse.Comment: 41 pages, 28 figures, 5 tables; accepted by Ap
Evolutionary Signatures in the Formation of Low-Mass Protostars. II. Towards Reconciling Models and Observations
A long-standing problem in low-mass star formation is the "luminosity
problem," whereby protostars are underluminous compared to the accretion
luminosity expected both from theoretical collapse calculations and arguments
based on the minimum accretion rate necessary to form a star within the
embedded phase duration. Motivated by this luminosity problem, we present a set
of evolutionary models describing the collapse of low-mass, dense cores into
protostars, using the Young & Evans (2005) model as our starting point. We
calculate the radiative transfer of the collapsing cores throughout the full
duration of the collapse in two dimensions. From the resulting spectral energy
distributions, we calculate standard observational signatures to directly
compare to observations. We incorporate several modifications and additions to
the original Young & Evans model in an effort to better match observations with
model predictions. We find that scattering, 2-D geometry, mass-loss, and
outflow cavities all affect the model predictions, as expected, but none
resolve the luminosity problem. A cycle of episodic mass accretion, however,
can resolve this problem and bring the model predictions into better agreement
with observations. Standard assumptions about the interplay between mass
accretion and mass loss in our model give star formation efficiencies
consistent with recent observations that compare the core mass function (CMF)
and stellar initial mass function (IMF). The combination of outflow cavities
and episodic mass accretion reduce the connection between observational Class
and physical Stage to the point where neither of the two common observational
signatures (bolometric temperature and ratio of bolometric to submillimeter
luminosity) can be considered reliable indicators of physical Stage.Comment: 27 pages. Accepted for publication in Ap
Externally Fed Accretion onto Protostars
The asymmetric molecular emission lines from dense cores reveal slow, inward
motion in the clouds' outer regions. This motion is present both before and
after the formation of a central star. Motivated by these observations, we
revisit the classic problem of steady, spherical accretion of gas onto a
gravitating point mass, but now include self-gravity of the gas and impose a
finite, subsonic velocity as the outer boundary condition. We find that the
accretion rate onto the protostar is lower than values obtained for isolated,
collapsing clouds, by a factor that is the Mach number of the outer flow.
Moreover, the region of infall surrounding the protostar spreads out more
slowly, at a speed close to the subsonic, incoming velocity. Our calculation,
while highly idealized, provides insight into two longstanding problems -- the
surprisingly low accretion luminosities of even the most deeply embedded
stellar sources, and the failure so far to detect spatially extended,
supersonic infall within their parent dense cores. Indeed, the observed
subsonic contraction in the outer regions of dense cores following star
formation appears to rule out a purely hydrodynamic origin for these clouds.Comment: accepted by MNRA
The Initial Conditions of Clustered Star Formation. II. N2H+ Observations of the Ophiuchus B Core
We present a Nobeyama 45 m Radio Telescope map and Australia Telescope
Compact Array pointed observations of N2H+ 1-0 emission towards the clustered,
low mass star forming Oph B Core within the Ophiuchus molecular cloud. We
compare these data with previously published results of high resolution NH3
(1,1) and (2,2) observations in Oph B. We use 3D Clumpfind to identify emission
features in the single-dish N2H+ map, and find that the N2H+ `clumps' match
well similar features previously identified in NH3 (1,1) emission, but are
frequently offset to clumps identified at similar resolution in 850 micron
continuum emission. Wide line widths in the Oph B2 sub-Core indicate
non-thermal motions dominate the Core kinematics, and remain transonic at
densities n ~ 3 x 10^5 cm^-3 with large scatter and no trend with N(H2).
Non-thermal motions in Oph B1 and B3 are subsonic with little variation, but
also show no trend with H2 column density. Over all Oph B, non-thermal N2H+
line widths are substantially narrower than those traced by NH3, making it
unlikely NH3 and N2H+ trace the same material, but the v_LSR of both species
agree well. We find evidence for accretion in Oph B1 from the surrounding
ambient gas. The NH3/N2H+ abundance ratio is larger towards starless Oph B1
than towards protostellar Oph B2, similar to recent observational results in
other star-forming regions. Small-scale structure is found in the ATCA N2H+ 1-0
emission, where emission peaks are again offset from continuum emission. In
particular, the ~1 M_Sun B2-MM8 clump is associated with a N2H+ emission
minimum and surrounded by a broken ring-like N2H+ emission structure,
suggestive of N2H+ depletion. We find a strong general trend of decreasing N2H+
abundance with increasing N(H2) in Oph B which matches that found for NH3.Comment: 55 pages (manuscript), 15 figures, ApJ accepte
The Dust Emissivity Spectral Index in the Starless Core TMC-1C
In this paper we present a dust emission map of the starless core TMC-1C
taken at 2100 microns. Along with maps at 160, 450, 850 and 1200 microns, we
study the dust emissivity spectral index from the (sub)millimeter spectral
energy distribution, and find that it is close to the typically assumed value
of beta = 2. We also map the dust temperature and column density in TMC-1C, and
find that at the position of the dust peak (A_V ~ 50), the
line-of-sight-averaged temperature is ~7 K. Employing simple Monte Carlo
modeling, we show that the data are consistent with a constant value for the
emissivity spectral index over the whole map of TMC-1C.Comment: 11 pages, including 5 pages of figures. Accepted to Ap
The Millimeter Astronomy Legacy Team 90 GHz (MALT90) Pilot Survey
We describe a pilot survey conducted with the Mopra 22-m radio telescope in
preparation for the Millimeter Astronomy Legacy Team Survey at 90 GHz (MALT90).
We identified 182 candidate dense molecular clumps using six different
selection criteria and mapped each source simultaneously in 16 different lines
near 90 GHz. We present a summary of the data and describe how the results of
the pilot survey shaped the design of the larger MALT90 survey. We motivate our
selection of target sources for the main survey based on the pilot detection
rates and demonstrate the value of mapping in multiple lines simultaneously at
high spectral resolution.Comment: Accepted to ApJS. 23 pages and 16 figures. Full resolution version
with an appendix showing all the data (12.1 MB) is available at
http://malt90.bu.edu/publications/Foster_2011_Malt90Pilot.pd
Triggering Collapse of the Presolar Dense Cloud Core and Injecting Short-Lived Radioisotopes with a Shock Wave. I. Varied Shock Speeds
The discovery of decay products of a short-lived radioisotope (SLRI) in the
Allende meteorite led to the hypothesis that a supernova shock wave transported
freshly synthesized SLRI to the presolar dense cloud core, triggered its
self-gravitational collapse, and injected the SLRI into the core. Previous
multidimensional numerical calculations of the shock-cloud collision process
showed that this hypothesis is plausible when the shock wave and dense cloud
core are assumed to remain isothermal at ~10 K, but not when compressional
heating to ~1000 K is assumed. Our two-dimensional models (Boss et al. 2008)
with the FLASH2.5 adaptive mesh refinement (AMR) hydrodynamics code have shown
that a 20 km/sec shock front can simultaneously trigger collapse of a 1 solar
mass core and inject shock wave material, provided that cooling by molecular
species such as H2O, CO, and H2 is included. Here we present the results for
similar calculations with shock speeds ranging from 1 km/sec to 100 km/sec. We
find that shock speeds in the range from 5 km/sec to 70 km/sec are able to
trigger the collapse of a 2.2 solar mass cloud while simultaneously injecting
shock wave material: lower speed shocks do not achieve injection, while higher
speed shocks do not trigger sustained collapse. The calculations continue to
support the shock-wave trigger hypothesis for the formation of the solar
system, though the injection efficiencies in the present models are lower than
desired.Comment: 39 pages, 14 figures. in press, Ap
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