1,624 research outputs found
3 - 14 Micron Spectroscopy of Comets C/2002 O4 (Honig), C/2002 V1 (NEAT), C/2002 X5 (Kudo-Fujikawa), C/2002 Y1 (Juels-Holvorcem), 69P/Taylor, and the Relationships among Grain Temperature, Silicate Band Strength and Structure among Comet Families
We report 3 - 13 micron spectroscopy of 4 comets observed between August 2002
and February 2003: C/2002 O4 (Honig) on August 1, 2002, C/2002 V1 (NEAT) on
Jan. 9 and 10, 2003, C/2002 X5 (Kudo-Fujikawa) on Jan. 9 and 10, 2003, and
C/2002 Y1 (Juels-Holvorcem) on Feb. 20, 2003. In addition, we include data
obtained much earlier on 69P/Taylor (February 9, 1998) but not previously
published. For Comets Taylor, Honig, NEAT, and Kudo-Fujikawa, the silicate
emission band was detected, being approximately 23%, 12%, 15%, and 10%,
respectively, above the continuum. The data for Comet Juels-Holvorcem were of
insufficient quality to detect the presence of a silicate band of comparable
strength to the other three objects, and we place an upper limit of 24% on this
feature. The silicate features in both NEAT and Kudo-Fujikawa contained
structure indicating the presence of crystalline material. Combining these data
with those of other comets, we confirm the correlation between silicate band
strength and grain temperature of Gehrz & Ney (1992) and Williams et al. (1997)
for dynamically new and long period comets, but the majority of Jupiter family
objects may deviate from this relation. The limited data available on Jupiter
family objects suggest that they may have silicate bands that are slightly
different from the former objects. Finally, when compared to the silicate
emission bands observed in pre-main sequence stars, the dynamically new and
long period comets most closely resemble the more evolved stellar systems,
while the limited data (in quantity and quality) on Jupiter family objects seem
to suggest that these have spectra more like the less-evolved stars.Comment: 45 pages, 12 figure
Maximising Social Interactions and Effectiveness within Distance Learning Courses: Cases from Construction
Advanced Internet technologies have revolutionised the delivery of distance learning education. As a result, the physical proximity between learners and the learning providers has become less important. However, whilst the pervasiveness of these technological developments has reached unprecedented levels, critics argue that the student learning experience is still not as effective as conventional face-to-face delivery. In this regard, surveys of distance learning courses reveal that there is often a lack of social interaction attributed to this method of delivery, which tends to leave learners feeling isolated due to a lack of engagement, direction, guidance and support by the tutor. This paper defines and conceptualises this phenomenon by investigating the extent to which distance-learning programmes provide the social interactions of an equivalent traditional classroom setting. In this respect, two distance learning case studies were investigated, covering the UK and Slovenian markets respectively. Research findings identified that delivery success is strongly dependent on the particular context to which the specific distance learning course is
designed, structured and augmented. It is therefore recommended that designers of distance learning courses should balance the tensions and nuances associated with commercial viability and pedagogic effectiveness
VLBA monitoring of Mrk 421 at 15 GHz and 24 GHz during 2011
High-resolution radio observations are ideal for constraining the value of
physical parameters in the inner regions of active-galactic-nucleus jets and
complement results on multiwavelength (MWL) observations. This study is part of
a wider multifrequency campaign targeting the nearby TeV blazar Markarian 421
(z=0.031), with observations in the sub-mm (SMA), optical/IR (GASP), UV/X-ray
(Swift, RXTE, MAXI), and gamma rays (Fermi-LAT, MAGIC, VERITAS). We investigate
the jet's morphology and any proper motions, and the time evolution of physical
parameters such as flux densities and spectral index. The aim of our wider
multifrequency campaign is to try to shed light on questions such as the nature
of the radiating particles, the connection between the radio and gamma-ray
emission, the location of the emitting regions and the origin of the flux
variability. We consider data obtained with the Very Long Baseline Array (VLBA)
over twelve epochs (one observation per month from January to December 2011) at
15 GHz and 24 GHz. We investigate the inner jet structure on parsec scales
through the study of model-fit components for each epoch. The structure of Mrk
421 is dominated by a compact (~0.13 mas) and bright component, with a
one-sided jet detected out to ~10 mas. We identify 5-6 components in the jet
that are consistent with being stationary during the 12-month period studied
here. Measurements of the spectral index agree with those of other works: they
are fairly flat in the core region and steepen along the jet length.
Significant flux-density variations are detected for the core component. From
our results, we draw an overall scenario in which we estimate a viewing angle
2{\deg} < theta < 5{\deg} and a different jet velocity for the radio and the
high-energy emission regions, such that the respective Doppler factors are
{\delta}r ~3 and {\delta}h.e. ~14.Comment: 9 pages, 4 figure
Analyzing collaborative learning processes automatically
In this article we describe the emerging area of text classification research focused on the problem of collaborative learning process analysis both from a broad perspective and more specifically in terms of a publicly available tool set called TagHelper tools. Analyzing the variety of pedagogically valuable facets of learnersâ interactions is a time consuming and effortful process. Improving automated analyses of such highly valued processes of collaborative learning by adapting and applying recent text classification technologies would make it a less arduous task to obtain insights from corpus data. This endeavor also holds the potential for enabling substantially improved on-line instruction both by providing teachers and facilitators with reports about the groups they are moderating and by triggering context sensitive collaborative learning support on an as-needed basis. In this article, we report on an interdisciplinary research project, which has been investigating the effectiveness of applying text classification technology to a large CSCL corpus that has been analyzed by human coders using a theory-based multidimensional coding scheme. We report promising results and include an in-depth discussion of important issues such as reliability, validity, and efficiency that should be considered when deciding on the appropriateness of adopting a new technology such as TagHelper tools. One major technical contribution of this work is a demonstration that an important piece of the work towards making text classification technology effective for this purpose is designing and building linguistic pattern detectors, otherwise known as features, that can be extracted reliably from texts and that have high predictive power for the categories of discourse actions that the CSCL community is interested in
International comparisons of sectoral energy- and labour-productivity performance. Stylised facts and decomposition of trends
Organization of Block Copolymers using NanoImprint Lithography: Comparison of Theory and Experiments
We present NanoImprint lithography experiments and modeling of thin films of
block copolymers (BCP). The NanoImprint lithography is used to align
perpendicularly lamellar phases, over distances much larger than the natural
lamellar periodicity. The modeling relies on self-consistent field calculations
done in two- and three-dimensions. We get a good agreement with the NanoImprint
lithography setups. We find that, at thermodynamical equilibrium, the ordered
BCP lamellae are much better aligned than when the films are deposited on
uniform planar surfaces
First detection of a VHE gamma-ray spectral maximum from a Cosmic source: H.E.S.S. discovery of the Vela X nebula
The Vela supernova remnant (SNR) is a complex region containing a number of
sources of non-thermal radiation. The inner section of this SNR, within 2
degrees of the pulsar PSR B0833-45, has been observed by the H.E.S.S. gamma-ray
atmospheric Cherenkov detector in 2004 and 2005. A strong signal is seen from
an extended region to the south of the pulsar, within an integration region of
radius 0.8 deg. around the position (RA = 08h 35m 00s, dec = -45 deg. 36'
J2000.0). The excess coincides with a region of hard X-ray emission seen by the
ROSAT and ASCA satellites. The observed energy spectrum of the source between
550 GeV and 65 TeV is well fit by a power law function with photon index = 1.45
+/- 0.09(stat) +/- 0.2(sys) and an exponential cutoff at an energy of 13.8 +/-
2.3(stat) +/- 4.1(sys) TeV. The integral flux above 1 TeV is (1.28 +/- 0.17
(stat) +/- 0.38(sys)) x 10^{-11} cm^{-2} s^{-1}. This result is the first clear
measurement of a peak in the spectral energy distribution from a VHE gamma-ray
source, likely related to inverse Compton emission. A fit of an Inverse Compton
model to the H.E.S.S. spectral energy distribution gives a total energy in
non-thermal electrons of ~2 x 10^{45} erg between 5 TeV and 100 TeV, assuming a
distance of 290 parsec to the pulsar. The best fit electron power law index is
2.0, with a spectral break at 67 TeV.Comment: 5 pages, 4 figures, accepted for publication in Astronomy and
Astrophysics letter
Observations of Mkn 421 in 2004 with H.E.S.S. at large zenith angles
Mkn 421 was observed during a high flux state for nine nights in April and
May 2004 with the fully operational High Energy Stereoscopic System (H.E.S.S.)
in Namibia. The observations were carried out at zenith angles of
60--65, which result in an average energy threshold of 1.5 TeV
and a collection area reaching 2~km at 10~TeV. Roughly 7000 photons from
Mkn~421 were accumulated with an average gamma-ray rate of 8 photons/min. The
overall significance of the detection exceeds 100 standard deviations. The
light-curve of integrated fluxes above 2~TeV shows changes of the diurnal flux
up to a factor of 4.3. For nights of high flux, intra-night variability is
detected with a decay time of less than 1 hour. The time averaged energy
spectrum is curved and is well described by a power-law with a photon index
\egamm and an exponential cutoff at \ecut~TeV and an average integral flux
above 2~TeV of 3 Crab flux units. Significant variations of the spectral shape
are detected with a spectral hardening as the flux increases. Contemporaneous
multi-wavelength observations at lower energies (X-rays and gamma-rays above
~GeV) indicate smaller relative variability amplitudes than seen
above 2~TeV during high flux state observed in April 2004.Comment: 5 pages, 4 figures, published in A&
Arthropod Distribution In A Tropical Rainforest: Tackling A Four Dimensional Puzzle
Quantifying the spatio-temporal distribution of arthropods in tropical rainforests represents a first step towards scrutinizing the global distribution of biodiversity on Earth. To date most studies have focused on narrow taxonomic groups or lack a design that allows partitioning of the components of diversity. Here, we consider an exceptionally large dataset (113,952 individuals representing 5,858 species), obtained from the San Lorenzo forest in Panama, where the phylogenetic breadth of arthropod taxa was surveyed using 14 protocols targeting the soil, litter, understory, lower and upper canopy habitats, replicated across seasons in 2003 and 2004. This dataset is used to explore the relative influence of horizontal, vertical and seasonal drivers of arthropod distribution in this forest. We considered arthropod abundance, observed and estimated species richness, additive decomposition of species richness, multiplicative partitioning of species diversity, variation in species composition, species turnover and guild structure as components of diversity. At the scale of our study (2km of distance, 40m in height and 400 days), the effects related to the vertical and seasonal dimensions were most important. Most adult arthropods were collected from the soil/litter or the upper canopy and species richness was highest in the canopy. We compared the distribution of arthropods and trees within our study system. Effects related to the seasonal dimension were stronger for arthropods than for trees. We conclude that: (1) models of beta diversity developed for tropical trees are unlikely to be applicable to tropical arthropods; (2) it is imperative that estimates of global biodiversity derived from mass collecting of arthropods in tropical rainforests embrace the strong vertical and seasonal partitioning observed here; and (3) given the high species turnover observed between seasons, global climate change may have severe consequences for rainforest arthropods.1012SolVin-Solvay SASTRIUnited Nations Environment ProgrammeSmithsonian Institution (Walcott Fund)European Science FoundationGlobal Canopy ProgrammeCzech Science foundation GACR grant [14-36098G]European Social FundCzech Ministry of Education [CZ.1.07/2.3.00/20.0064]U.S. National Science Fundation [DEB-0841885]Australian Research Council [FT100100040]Conselho Nacional de Desenvolvimento CientĂfico e TecnolĂłgico (CNPq)"Investissement d'Avenir'' grant [ANR-10-LABX-25-01]Norwegian Research CouncilGrant Agency of the Czech Republic [14-36098G
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