8,001 research outputs found
Accretion-ejection connection in the young brown dwarf candidate ISO-Cha1 217
As the number of observed brown dwarf outflows is growing it is important to
investigate how these outflows compare to the well studied jets from young
stellar objects. A key point of comparison is the relationship between outflow
and accretion activity and in particular the ratio between the mass outflow and
accretion rates (/). The brown dwarf candidate
ISO-ChaI 217 was discovered by our group, as part of a spectro-astrometric
study of brown dwarfs, to be driving an asymmetric outflow with the
blue-shifted lobe having a position angle of 20. The aim here
is to further investigate the properties of ISO-ChaI 217, the morphology and
kinematics of its outflow, and to better constrain
(/). The outflow is spatially resolved in the
lines and is detected out to 1\farcs6
in the blue-shifted lobe and ~ 1" in the red-shifted lobe. The asymmetry
between the two lobes is confirmed although the velocity asymmetry is less
pronounced with respect to our previous study. Using thirteen different
accretion tracers we measure log() [M/yr]= -10.6
0.4. As it was not possible to measure the effect of extinction on the ISO-ChaI
217 outflow was derived for a range of values of A, up to
a value of A = 2.5 mag estimated for the source extinction. The logarithm
of the mass outflow () was estimated in the range -11.7 to -11.1
for both jets combined. Thus / [\Msun/yr] lies
below the maximum value predicted by magneto-centrifugal jet launching models.
Finally, both model fitting of the Balmer decrements and spectro-astrometric
analysis of the H line show that the bulk of the H I emission comes
from the accretion flow.Comment: accepted by Astronomy & Astrophysic
Searching for Galactic White Dwarf Binaries in Mock LISA Data using an F-Statistic Template Bank
We describe an F-statistic search for continuous gravitational waves from
galactic white-dwarf binaries in simulated LISA Data. Our search method employs
a hierarchical template-grid based exploration of the parameter space. In the
first stage, candidate sources are identified in searches using different
simulated laser signal combinations (known as TDI variables). Since each source
generates a primary maximum near its true "Doppler parameters" (intrinsic
frequency and sky position) as well as numerous secondary maxima of the
F-statistic in Doppler parameter space, a search for multiple sources needs to
distinguish between true signals and secondary maxima associated with other,
"louder" signals. Our method does this by applying a coincidence test to reject
candidates which are not found at nearby parameter space positions in searches
using each of the three TDI variables. For signals surviving the coincidence
test, we perform a fully coherent search over a refined parameter grid to
provide an accurate parameter estimation for the final candidates. Suitably
tuned, the pipeline is able to extract 1989 true signals with only 5 false
alarms. The use of the rigid adiabatic approximation allows recovery of signal
parameters with errors comparable to statistical expectations, although there
is still some systematic excess with respect to statistical errors expected
from Gaussian noise. An experimental iterative pipeline with seven rounds of
signal subtraction and re-analysis of the residuals allows us to increase the
number of signals recovered to a total of 3419 with 29 false alarms.Comment: 29 pages, 11 figures; submitted to Classical and Quantum Gravit
ANIMAC: A Multiprocessor Architecture for Real-Time Computer Animation
Advances in integrated circuit technology have been largely responsible for the growth of the computer graphics industry. This technology promises additional growth through the remainder of the century. This dissertation addresses how this future technology can be harnessed and used to construct very high performance real-time computer graphics systems.
This thesis proposes a new architecture for real-time animation engines. The ANIMAL architecture achieves high performance by utilizing a two-dimensional array of processors that determine visible surfaces in parallel. An array of sixteen processors with only nearest neighbor interprocessor communications can produce real-time shadowed images of scenes containing 100, 000 triangles.
The ANIMAL architecture is based upon analysis and simulations of various parallelization techniques. These simulations suggest that the viewing space be spatially subdivided and that each processor produce a visible surface image for several viewing space subvolumes. Simple assignments of viewing space subvolumes to processors are shown to offer high parallel efficiencies.
Simulations of parallel algorithms were driven with data derived from real scenes since analysis of scene composition suggested that using simplistic models of scene composition might lead to incorrect results.
The ANIMAL architecture required the development of a shadowing algorithm which was tailored to its parallel environment. This algorithm separates shadowing into local and foreign effects. Its implementation allows individual processors to compute shadowing effects for their image regions utilizing only very local information.The design of the ANIMAL processors makes extensive use of new VLSI architectures. A formerly proposed processor per object architecture is used to determine visible surfaces while new processor per object and processor per pixel architectures are used to determine shadowing effects.
It is estimated that the ANIMAL architecture can be realized in the early 1990's. Realizing this architecture will require considerable amounts of hardware and capital yet its cost will not be out of line when compared with today's real time computer graphics systems
A Spiritual Call: Jeremiah’s Call to the Heart And the Stages of Spiritual Progression in Carmelite Spirituality
The aim of this study is first, to identify resonances between Jeremiah 1:10 and the three stages of the spiritual journey as defined by the Carmelites such as John of the Cross and Teresa of Avila (i.e., the stages known as purgative, illuminative and unitive) and then, in light of an in depth understanding of the spiritual senses attributed to Jeremiah 1:10 in its reception history, to evaluate the impact of Jer 1:10 upon the Carmelite conception of the spiritual journey.
A comprehensive Word Study is undertaken of six task verbs from Jer 1:10, presented as three pairs: to root out (נתש) and to pull down (נחץ), to destroy (אבד) and to throw down (הרס), to build (בנה) and to plant (נטע). This analysis offers support for the alignment and resonances of the task verbs with the three stages of the spiritual journey. The Word Study also suggests that for the spiritual sense, the Hebrew text may provide a typology of a three-stage progression, in which two stages of purification (described by two pairs of negative task verbs) are necessary before the holiest and whole-hearted stage of unification is effected (described by the positive pair of task verbs). In addition, the repeated proximate position of task verbs to the themes of “turning” and “the heart” suggest that the verbs may work to turn the heart to the Lord, who continues to love his people despite their spiritual adultery and other sins.
The evidence reviewed in the Word Study is supported by the reception history and indicates that Jer 1:10 may offer a significant and early spiritual model. This verse directly impacts upon Paul and Origen in the early era of Christianity. Based on Origen’s interpretation, it is possible that Jer 1:10 offers a biblical model for the tri-partite spiritual journey which precedes the conception of spiritual stages by Pseudo-Dionysius, who is often considered the originator of the purgative, illuminative and unitive concepts. In a number of ways, Origen’s spiritual interpretation seems to be carried through Christian tradition and may challenge oft-assumed Platonic or Neoplatonic sources of the spiritual journey.
However, the impact of Jer 1:10 upon the Carmelites Saints John of the Cross and Teresa of Avila is diffuse and indirect. No direct citation or echo of Jer 1:10 has been identified in their writings. Nonetheless, like Origen’s interpretation of Jer 1:10, John recognizes successive stages of spiritual “destruction” (purgation and illumination) designed to open space in the soul for God, allowing for a third phase of “construction” (i.e., union). Jer 1:10 may offer insight into the earliest theological seeds of the spiritual journey, with echoes and resonances throughout the ages
Classical T Tauri-like Outflow Activity in the Brown Dwarf Mass Regime
Over the last number of years spectroscopic studies have strongly supported
the assertion that protostellar accretion and outflow activity persists to the
lowest masses. In this paper we present the results of our latest investigation
of brown dwarf (BD) outflow activity and report on the discovery of two new
outflows. Here ISO-Oph 32 is shown to drive a blue-shifted outflow with a
radial velocity of 10-20 km/s and spectro-astrometric analysis constrains the
position angle of this outflow to 240 +/- 7 degrees. The BD candidate ISO-Cha1
217 is found to have a bipolar outflow bright in several key forbidden lines
(radial velocity = -20 km/s, +40 km/s) and with a PA of 190-210 degrees. A
striking feature of the ISO-Cha1 217 outflow is the strong asymmetry between
the red and blue-shifted lobes. This asymmetry is revealed in the relative
brightness of the two lobes (red-shifted lobe is brighter), the factor of two
difference in radial velocity (the red-shifted lobe is faster) and the
difference in the electron density (again higher in the red lobe). Such
asymmetries are common in jets from low mass protostars and the observation of
a marked asymmetry at such a low mass supports the idea that BD outflow
activity is scaled down from low mass protostellar activity.
In addition to presenting these new results, a comprehensive comparison is
made between BD outflow activity and jets launched by CTTSs. In particular, the
application of current methods for investigating the excitation conditions and
mass loss rates in CTT jets to BD spectra is explored.Comment: Accepted by Astrophysical Journa
Cannabinoid signalling in TNF-alpha induced IL-8 release
Original article can be found at: http://www.sciencedirect.com/science/journal/00142999 Copyright Elsevier B.V. DOI : 10.1016/j.ejphar.2006.04.015Peer reviewe
Influence of virtual reality training on the roadside crossing judgements of child pedestrians
The roadside crossing judgments of children aged 7, 9, and 11 years were assessed relative to controls before and after training with a computer-simulated traffic environment. Trained children crossed more quickly, and their estimated crossing times became better aligned with actual crossing times. They crossed more promptly, missed fewer safe opportunities to cross, accepted smaller traffic gaps without increasing the number of risky crossings, and showed better conceptual understanding of the factors to be considered when making crossing judgments. All age groups improved to the same extent, and there was no deterioration when children were retested 8 months later. The results are discussed in relation to theoretical arguments concerning the extent to which children's pedestrian judgments are amenable to training
Physical parameters of the Cen X-3 system
Photographic spectra of Cen X-3 show that the primary star has a spectral type near 06.5 with weak, variable emission at wavelength 4640 and 4686. No orbital motion of the emission or absorption lines is detected; for the latter the upper limit is approximately + or - 50 km/s. Analysis of the available data indicates that the primary is a factor of 2-3 less massive than expected from normal evolutionary models while the X-ray source has a solar mass near 1.5
Development and application of a catchment scale pesticide fate and transport model for use in drinking water risk assessment
This paper describes the development and application of IMPT (Integrated Model for Pesticide Transport), a parameter-efficient tool for predicting diffuse-source pesticide concentrations in surface waters used for drinking water supply. The model was applied to a small UK headwater catchment with high frequency (8 h) pesticide monitoring data and to five larger catchments (479–1653 km2) with sampling approximately every 14 days. Model performance was good for predictions of both flow (Nash Sutcliffe Efficiency generally > 0.59 and PBIAS < 10%) and pesticide concentrations, although low sampling frequency in the larger catchments is likely to mask the true episodic nature of exposure. The computational efficiency of the model, along with the fact that most of its parameters can be derived from existing national soil property data mean that it can be used to rapidly predict pesticide exposure in multiple surface water resources to support operational and strategic risk assessments
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