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Mining learning preferences in web-based instruction: Holists vs. Serialists
Web-based instruction programs are used by learners with diverse knowledge, skills and needs. These differences determine their preferences for the design of Web-based instruction programs and ultimately influence learners' success in using them. Cognitive style has been found to significantly affect learners' preferences of web-based instruction programs. However, the majority of previous studies focus on Field Dependence/Independence. Pask's Holist/Serialist dimension has conceptual links with Field Dependence/Independence but it is left mostly unstudied. Therefore, this study focuses on identifying how this dimension of cognitive style affects learner preferences of Web-based instruction programs. A data mining approach is used to illustrate the difference in preferences between Holists and Serialists. The findings show that there are clear differences in regard to content presentation and navigation support. A set of design features were then produced to help designers incorporate cognitive styles into the development of Web-based instruction programs to ensure that they can accommodate learners' different preferences.This work is partially funded by National Science Council, Taiwan, ROC (NSC 98-2511-S-008-012- MY3; NSC 99-
2511-S-008 -003 -MY2; NSC 99-2631-S-008-001)
The vulnerability of rules in complex work environments: dynamism and uncertainty pose problems for cognition
Many complex work environments rely heavily on cognitive operators using rules. Operators sometimes fail to implement rules, with catastrophic human, social and economic costs. Rule-based error is widely reported, yet the mechanisms of rule vulnerability have received less attention. This paper examines rule vulnerability in the complex setting of airline transport operations. We examined âthe stable approach criteria ruleâ, which acts as a system defence during the approach to land. The study experimentally tested whether system state complexity influenced rule failure. The results showed increased uncertainty and dynamism led to increased likelihood of rule failure. There was also an interaction effect, indicating complexity from different sources can combine to further constrain rule-based response. We discuss the results in relation to recent aircraft accidents and suggest that ârule-based errorâ could be progressed to embrace rule vulnerability, fragility and failure. This better reflects the influence that system behaviour and cognitive variety have on rule-based response. Practitioner Summary: In this study, we examined mechanisms of rule vulnerability in the complex setting of airline transport operations. The results suggest work scenarios featuring high uncertainty and dynamism constrain rule-based response, leading to rules becoming vulnerable, fragile or failing completely. This has significant implications for rule-intensive, safety critical work environments
Dynamic cyber-incident response
Permission to make digital or hard copies of this publication for internal use within NATO and for personal or educational use when for non-profi t or non-commercial purposes is granted providing that copies bear this notice and a full citation on the first page. Any other reproduction or transmission requires prior written permission by NATO CCD COE.Traditional cyber-incident response models have not changed significantly since the early days of the Computer Incident Response with even the most recent incident response life cycle model advocated by the US National Institute of Standards and Technology (Cichonski, Millar, Grance, & Scarfone, 2012) bearing a striking resemblance to the models proposed by early leaders in the field e.g. Carnegie-Mellon University (West-Brown, et al., 2003) and the SANS Institute (Northcutt, 2003). Whilst serving the purpose of producing coherent and effective response plans, these models appear to be created from the perspectives of Computer Security professionals with no referenced academic grounding. They attempt to defend against, halt and recover from a cyber-attack as quickly as possible. However, other actors inside an organisation may have priorities which conflict with these traditional approaches and may ultimately better serve the longer-term goals and objectives of an organisation
Improving the performance of National Centre for Earth Observation (NCEO) code using GPUs
The aim of this study was to investigate the advantages of different tools designed for running code on Graphics Processing Units (GPUs) and specify the types of code best suited for GPU acceleration.
âą Three examples of code were obtained from NCEO scientists for three distinct applications and ported to GPUs on the Natural Environment Research Council (NERC) Earth Observation Data Acquisition and Analysis Service (NEODAAS) MAGEO computing cluster.
âą Comparisons were made between the time taken to run the code on the original Central Processing Unit (CPU) and the MAGEO CPU and GPU.
âą Accelerations of between x30 and x1800 were achieved: more details are provided below.
âą In terms of energy saving this relates to an estimated 93.9% to 99.8% reduction in electricity usage.
âą The study highlighted the value of expertise in GPUs and coding such as provided by NEODAA
Distant field BHB stars and the mass of the Galaxy II: Photometry and spectroscopy of UKST candidates 16<B<19.5, 11<R<52 kpc
This is the second in a series of papers presenting a new calculation of the
mass of the Galaxy based on radial velocities and distances for a sample of
faint 16 < B < 21.3 field blue horizontal-branch (BHB) stars. We present
accurate BV CCD photometry and spectra for 142 candidate A-type stars selected
from ub_jr photometry of UK Schmidt telescope plates in six
high-Galactic-latitude fields. Classification of these candidates produces a
sample of 60 BHB stars at distances of 11-52 kpc from the Sun (mean 28 kpc),
with heliocentric line-of-sight velocities accurate to 15 km/s, and distance
errors < 10%. We provide a summary table listing coordinates and velocities of
these stars. The measured dispersion of the radial component of the
Galactocentric velocity for this sample is 108+-10 km/s, in agreement with a
recent study of the distant halo by Sirko and coworkers. Measurements of the Ca
II K line indicate that nearly all the stars are metal-poor with a mean [Fe/H]
= -1.8 with dispersion 0.5. Subsequent papers will describe a second survey of
BHBs to heliocentric distances 70 < R < 125 kpc and present a new estimate of
the mass of the Galaxy.Comment: 16 pages, 15 figures. Accepted for publication in MNRA
Distant Field BHB Stars III: Identification of a probable outer halo stream at Galactocentric distance r = 70 kpc
We present VLT-FORS1 spectra of a sample of 34 faint 20.0 < g* < 21.1 A-type
stars selected from the Sloan Digital Sky Survey Early Data Release, with the
goal of measuring the velocity dispersion of blue horizontal branch (BHB) stars
in the remote Galactic halo, R~80kpc. We show that colour selection with 1.08 <
u*-g* < 1.40 and -0.2 < g*-r* < -0.04 minimises contamination of the sample by
less luminous blue stragglers. In classifying the stars we confine our
attention to the 20 stars with spectra of signal-to-noise ratio > 15 per
Angstrom. Classification produces a sample of eight BHB stars at distances
65-102 kpc from the Sun (mean 80 kpc), which represents the most distant sample
of Galactic stars with measured radial velocities. The dispersion of the
measured radial component of the velocity with respect to the centre of the
Galaxy is 58+-15km/s. This value is anomalously low in comparison with measured
values for stars at smaller distances, as well as for satellites at similar
distances. Seeking an explanation for the low measured velocity dispersion,
further analysis reveals that six of the eight remote BHB stars are plausibly
associated with a single orbit. Three previously known outer halo carbon stars
also appear to belong to this stream. The velocity dispersion of all nine stars
relative to the orbit is only 15+-4 km/s. Further observations along the orbit
are required to trace the full extent of this structure on the sky.Comment: 13 pages, 7 figures. Accepted for publication in MNRA
The stellar content of the Hamburg/ESO survey. III. Field horizontal-branch stars in the Galaxy
We present a sample of 8321 candidate Field Horizontal-Branch (FHB) stars
selected by automatic spectral classification in the digital data base of the
Hamburg/ESO objective-prism survey. The stars are distributed over 8225 square
degrees of the southern sky, at |b| > 30 deg. The average distance of the
sample, assuming that they are all FHB stars, is 9.8 kpc, and distances of up
to ~30 kpc are reached. Moderate-resolution spectroscopic follow-up
observations and UBV photometry of 125 test sample stars demonstrate that the
contamination of the full candidate sample with main-sequence A-type stars is <
16%, while it would be up to 50% in a flux-limited sample at high galactic
latitudes. Hence more than ~6800 of our FHB candidates are expected to be
genuine FHB stars. The candidates are being used as distance probes for
high-velocity clouds and for studies of the structure and kinematics of the
Galactic halo.Comment: A&A, in pres
Radio Jets in Galaxies with Actively Accreting Black Holes: new insights from the SDSS
The majority of nearby radio-loud AGN are found in massive, old elliptical
galaxies with weak emission lines. At high redshifts,however, most known radio
AGN have strong emission lines. In this paper, we examine a subset of radio AGN
with emission lines selected from the Sloan Digital Sky Survey. The probability
for a nearby radio AGN to have emission lines is a strongly decreasing function
of galaxy mass and an increasing function of radio luminosity above 10^25 W/Hz.
Emission line and radio luminosities are correlated, but with large dispersion.
At a given radio power, AGN with small black holes have higher [OIII]
luminosities (which we interpret as higher accretion rates) than AGN with big
black holes. However, if we scale both radio and emission line luminosities by
the black hole mass, we find a correlation between normalized radio power and
accretion rate in Eddington units that is independent of black hole mass. There
is also a clear correlation between normalized radio power and the age of the
stellar population in the galaxy. Present-day AGN with the highest normalized
radio powers are confined to galaxies with small black holes. High-redshift,
high radio-luminosity AGN could be explained if big black holes were similarly
active at earlier cosmic epochs. To investigate why only a small fraction of
emission line AGN become radio loud, we create matched samples of radio-loud
and radio-quiet AGN and compare their host galaxy properties and environments.
The main difference lies in their environments; our local density estimates are
a factor 2 larger around the radio-loud AGN. We propose a scenario in which
radio-loud AGN with emission lines are located in galaxies where accretion of
both cold and hot gas can occur simultaneously. (Abridged)Comment: 18 figures, submitted to MNRA
Kinematics of SDSS subdwarfs: Structure and substructure of the Milky Way halo
We construct a new sample of ~1700 solar neighbourhood halo subdwarfs from
the Sloan Digital Sky Survey, selected using a reduced proper motion diagram.
Radial velocities come from the SDSS spectra and proper motions from the
light-motion curve catalogue of Bramich et al. (2008). Using a photometric
parallax relation to estimate distances gives us the full phase-space
coordinates. Typical velocity errors are in the range 30-50 km/s. This halo
sample is one of the largest constructed to-date and the disc contamination is
at a level of < 1 per cent. This enables us to calculate the halo velocity
dispersion to excellent accuracy. We find that the velocity dispersion tensor
is aligned in spherical polar coordinates and that (sigma_r, sigma_phi,
sigma_theta) = (143 \pm 2, 82 \pm 2, 77 \pm 2) km/s. The stellar halo exhibits
no net rotation, although the distribution of v_phi shows tentative evidence
for asymmetry. The kinematics are consistent with a mildly flattened stellar
density falling with distance like r^{-3.75}. Using the full phase-space
coordinates, we look for signs of kinematic substructure in the stellar halo.
We find evidence for four discrete overdensities localised in angular momentum
and suggest that they may be possible accretion remnants. The most prominent is
the solar neighbourhood stream previously identified by Helmi et al. (1999),
but the remaining three are new. One of these overdensities is potentially
associated with a group of four globular clusters (NGC5466, NGC6934, M2 and
M13) and raises the possibility that these could have been accreted as part of
a much larger progenitor.Comment: 16 pages, 13 figures, MNRAS (in press). Revised following referee's
comments; using new and improved parallax relation. Results and conclusions
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