6,231 research outputs found
The Effect of Discovery Systems on Online Journal Usage: A Longitudinal Study
Many academic libraries are implementing discovery services as a way of giving their users a single comprehensive search option for all library resources. These tools are designed to change the research experience, yet very few studies have investigated the impact of discovery service implementation. This study examines one aspect of that impact by asking whether usage of publisher-hosted journal content changes after implementation of a discovery tool. Libraries that have begun using the four major discovery services have seen an increase in usage of this content, suggesting that for this particular type of material, discovery services have a positive impact on use. Though all discovery services significantly increased usage relative to a no discovery service control group, some had a greater impact than others, and there was extensive variation in usage change among libraries using the same service. Future phases of this study will look at other types of content
The Effect of Discovery Systems on Online Journal Usage: A Longitudinal Study
Many academic libraries are implementing discovery services as a way of giving their users a single comprehensive search option for all library resources. These tools are designed to change the research experience, yet very few studies have investigated the impact of discovery service implementation. This study examines one aspect of that impact by asking whether usage of publisher-hosted journal content changes after implementation of a discovery tool. Libraries that have begun using the four major discovery services have seen an increase in usage of this content, suggesting that for this particular type of material, discovery services have a positive impact on use. Though all discovery services significantly increased usage relative to a no discovery service control group, some had a greater impact than others, and there was extensive variation in usage change among libraries using the same service. Future phases of this study will look at other types of content
Regeneration in gap models: priority issues for studying forest responses to climate change
Recruitment algorithms in forest gap models are examined with particular regard to their suitability for simulating forest ecosystem responses to a changing climate. The traditional formulation of recruitment is found limiting in three areas. First, the aggregation of different regeneration stages (seed production, dispersal, storage, germination and seedling establishment) is likely to result in less accurate predictions of responses as compared to treating each stage separately. Second, the relatedassumptions that seeds of all species are uniformly available and that environmental conditions are homogeneous, are likely to cause overestimates of future species diversity and forest migration rates. Third, interactions between herbivores (ungulates and insect pests) and forest vegetation are a big unknown with potentially serious impacts in many regions. Possible strategies for developing better gap model representations for the climate-sensitive aspects of each of these key areas are discussed. A working example of a relatively new model that addresses some of these limitations is also presented for each case. We conclude that better models of regeneration processes are desirable for predicting effects of climate change, but that it is presently impossible to determine what improvements can be expected without carrying out rigorous tests for each new formulation
Protostellar collapse and fragmentation using an MHD GADGET
Although the influence of magnetic fields is regarded as vital in the star
formation process, only a few magnetohydrodynamics (MHD) simulations have been
performed on this subject within the smoothed particle hydrodynamics (SPH)
method. This is largely due to the unsatisfactory treatment of non-vanishing
divergence of the magnetic field. Recently smoothed particle
magnetohydrodynamics (SPMHD) simulations based on Euler potentials have proven
to be successful in treating MHD collapse and fragmentation problems, however
these methods are known to have some intrinsical difficulties. We have
performed SPMHD simulations based on a traditional approach evolving the
magnetic field itself using the induction equation. To account for the
numerical divergence, we have chosen an approach that subtracts the effects of
numerical divergence from the force equation, and additionally we employ
artificial magnetic dissipation as a regularization scheme. We apply this
realization of SPMHD to a widely known setup, a variation of the 'Boss &
Bodenheimer standard isothermal test case', to study the impact of the magnetic
fields on collapse and fragmentation. In our simulations, we concentrate on
setups, where the initial magnetic field is parallel to the rotation axis. We
examine different field strengths and compare our results to other findings
reported in the literature. We are able to confirm specific results found
elsewhere, namely the delayed onset of star formation for strong fields,
accompanied by the tendency to form only single stars. We also find that the
'magnetic cushioning effect', where the magnetic field is wound up to form a
'cushion' between the binary, aids binary fragmentation in a case, where
previously only formation of a single protostar was expected.Comment: 18 pages, 11 figures. Final version (with revisions). Accepted to
MNRA
The ISM in spiral galaxies: can cooling in spiral shocks produce molecular clouds?
We investigate the thermodynamics of the ISM and the formation of molecular
hydrogen through numerical simulations of spiral galaxies. The model follows
the chemical, thermal and dynamical response of the disc to an external spiral
potential. Self-gravity and magnetic fields are not included. The calculations
demonstrate that gas can cool rapidly when subject to a spiral shock. Molecular
clouds in the spiral arms arise through a combination of compression of the ISM
by the spiral shock and orbit crowding. These results highlight that local
self-gravity is not required to form molecular clouds. Self-shielding provides
a sharp transition density, below which gas is essentially atomic, and above
which the molecular gas fraction is >0.001. The timescale for gas to move
between these regimes is very rapid (<~1 Myr). From this stage, the majority of
gas generally takes between 10 to 20 Myr to obtain high H fractions (>50
%). Although our calculations are unable to resolve turbulent motions on scales
smaller than the spiral arm and do not include self-gravity. True cloud
formation timescales are therefore expected to be even shorter.
The mass budget of the disc is dominated by cold gas residing in the spiral
arms. Between 50 and 75 % of this gas is in the atomic phase. When this gas
leaves the spiral arm and drops below the self-shielding limit it is heated by
the galactic radiation field. Consequently, most of the volume in the interarm
regions is filled with warm atomic gas. However, some cold spurs and clumps can
survive in interarm regions for periods comparable to the interarm passage
timescale. Altogether between 7 and 40% of the gas in our disc is molecular,
depending on the surface density of the calculation, with approximately 20%
molecular for a surface density comparable to the solar neighbourhood.Comment: 16 pages, 19 figures, accepted for publication in MNRA
SnoopCGH: software for visualizing comparative genomic hybridization data
Summary: Array-based comparative genomic hybridization (CGH) technology is used to discover and validate genomic structural variation, including copy number variants, insertions, deletions and other structural variants (SVs). The visualization and summarization of the array CGH data outputs, potentially across many samples, is an important process in the identification and analysis of SVs. We have developed a software tool for SV analysis using data from array CGH technologies, which is also amenable to short-read sequence data
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The Stardust – a successful encounter with the remarkable comet Wild 2
On January 2, 2004 the Stardust spacecraft completed a close flyby of comet Wild2 (P81). Flying at a relative speed of 6.1 km/s within 237km of the 5 km nucleus, the spacecraft took 72 close-in images, measured the flux of impacting particles and did TOF mass spectrometry
Laughlin-Jastrow-correlated Wigner crystal in a strong magnetic field
We propose a new ground state trial wavefunction for a two-dimensional Wigner
crystal in a strong perpendicular magnetic field. The wavefunction includes
Laughlin-Jastrow correlations between electron pairs, and may be interpreted as
a crystal state of composite fermions or composite bosons. Treating the power
of the Laughlin-Jastrow factor as a variational parameter, we use quantum
Monte Carlo simulations to compute the energy of these new states. We find that
our wavefunctions have lower energy than existing crystalline wavefunctions in
the lowest Landau level. Our results are consistent with experimental
observations of the filling factor at which the transition between the
fractional quantum Hall liquid and the Wigner crystal occurs for electron
systems. Exchange contributions to the wavefunctions are estimated
quantitatively and shown to be negligible for sufficiently small filling
factors
The Eye of the Tornado - an isolated, high mass young stellar object near the Galactic centre
We present infrared (AAT, UKIRT) and radio (VLA, SEST) observations of the
Eye of the Tornado, a compact source apparently near the head of the Tornado
Nebula. The near-infrared Br-gamma and He I lines are broad (FWHM 40 and 30
km/s, respectively) and have a line centre at Vlsr = -205 km/s. This
corresponds to a feature at the same velocity in the 12CO J=1-0 line profile.
The kinematic velocity derived from Galactic rotation places the Eye at the
distance of the Galactic Centre (i.e. 8.5 kpc) and separated (probably
foreground) from the Tornado Nebula. Four knots of emission are seen in the
Br-gamma line and at 6 and 20 cm. Together with the flat radio spectral index,
we confirm that the Eye contains ionized gas, but that this is embedded within
a dense molecular core. The spectral energy distribution can be modelled as a
two-component blackbody + greybody, peaking at far-IR wavelengths. The knots
are UC HII regions, and the core contains a luminous (2 x 10^4 Lsun), embedded,
massive young stellar source. We also propose a geometrical model for the Eye
to account for both its spectral energy distribution and its morphology.Comment: 25 pages, including 5 figures. Accepted by Monthly Notices of the
Royal Astronomical Society on 27/10/0
Emotional valence and arousal affect reading in an interactive way: neuroimaging evidence for an approach-withdrawal framework
A growing body of literature shows that the emotional content of verbal material affects reading, wherein emotional words are given processing priority compared to neutral words. Human emotions can be conceptualised within a two-dimensional model comprised of emotional valence and arousal (intensity). These variables are at least in part distinct, but recent studies report interactive effects during implicit emotion processing and relate these to stimulus-evoked approach-withdrawal tendencies. The aim of the present study was to explore how valence and arousal interact at the neural level, during implicit emotion word processing. The emotional attributes of written word stimuli were orthogonally manipulated based on behavioural ratings from a corpus of emotion words. Stimuli were presented during an fMRI experiment while 16 participants performed a lexical decision task, which did not require explicit evaluation of a word's emotional content. Results showed greater neural activation within right insular cortex in response to stimuli evoking conflicting approach-withdrawal tendencies (i.e., positive high-arousal and negative low-arousal words) compared to stimuli evoking congruent approach vs. withdrawal tendencies (i.e., positive low-arousal and negative high-arousal words). Further, a significant cluster of activation in the left extra-striate cortex was found in response to emotional than neutral words, suggesting enhanced perceptual processing of emotionally salient stimuli. These findings support an interactive two-dimensional approach to the study of emotion word recognition and suggest that the integration of valence and arousal dimensions recruits a brain region associated with interoception, emotional awareness and sympathetic functions
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