15,196 research outputs found
TopSig: Topology Preserving Document Signatures
Performance comparisons between File Signatures and Inverted Files for text
retrieval have previously shown several significant shortcomings of file
signatures relative to inverted files. The inverted file approach underpins
most state-of-the-art search engine algorithms, such as Language and
Probabilistic models. It has been widely accepted that traditional file
signatures are inferior alternatives to inverted files. This paper describes
TopSig, a new approach to the construction of file signatures. Many advances in
semantic hashing and dimensionality reduction have been made in recent times,
but these were not so far linked to general purpose, signature file based,
search engines. This paper introduces a different signature file approach that
builds upon and extends these recent advances. We are able to demonstrate
significant improvements in the performance of signature file based indexing
and retrieval, performance that is comparable to that of state of the art
inverted file based systems, including Language models and BM25. These findings
suggest that file signatures offer a viable alternative to inverted files in
suitable settings and from the theoretical perspective it positions the file
signatures model in the class of Vector Space retrieval models.Comment: 12 pages, 8 figures, CIKM 201
Degradation assessment of industrial composites using thermography
Thermographic inspection is a relatively new technique for Non-Destructive Testing (NDT) which has been gathering increasing interest due to its relatively low cost hardware and extremely fast data acquisition properties. This technique is especially promising in the area of rapid automated damage detection and quantification. In collaboration with a major industry partner from the aerospace sector advanced thermography-based NDT software for impact damaged composites is introduced. The software is based on correlation analysis of time-temperature profiles in combination with an image enhancement process. The prototype software is aiming to a) better visualise the damages in a relatively easy-to-use way and b) automatically and quantitatively measure the properties of the degradation. Knowing that degradation properties play an important role in the identification of degradation types, tests and results on specimens which were artificially damaged have been performed and analyzed.EPSR
Cassini observations of ion and electron beams at Saturn and their relationship to infrared auroral arcs
We present Cassini Visual and Infrared Mapping Spectrometer observations of infrared auroral emissions from the noon sector of Saturn's ionosphere revealing multiple intense auroral arcs separated by dark regions poleward of the main oval. The arcs are interpreted as the ionospheric signatures of bursts of reconnection occurring at the dayside magnetopause. The auroral arcs were associated with upward field-aligned currents, the magnetic signatures of which were detected by Cassini at high planetary latitudes. Magnetic field and particle observations in the adjacent downward current regions showed upward bursts of 100–360 keV light ions in addition to energetic (hundreds of keV) electrons, which may have been scattered from upward accelerated beams carrying the downward currents. Broadband, upward propagating whistler waves were detected simultaneously with the ion beams. The acceleration of the light ions from low altitudes is attributed to wave-particle interactions in the downward current regions. Energetic (600 keV) oxygen ions were also detected, suggesting the presence of ambient oxygen at altitudes within the acceleration region. These simultaneous in situ and remote observations reveal the highly energetic magnetospheric dynamics driving some of Saturn's unusual auroral features. This is the first in situ identification of transient reconnection events at regions magnetically conjugate to Saturn's magnetopause
Statistical Power Supply Dynamic Noise Prediction in Hierarchical Power Grid and Package Networks
One of the most crucial high performance systems-on-chip design challenge is to front their power supply noise sufferance due to high frequencies, huge number of functional blocks and technology scaling down. Marking a difference from traditional post physical-design static voltage drop analysis, /a priori dynamic voltage drop/evaluation is the focus of this work. It takes into account transient currents and on-chip and package /RLC/ parasitics while exploring the power grid design solution space: Design countermeasures can be thus early defined and long post physical-design verification cycles can be shortened. As shown by an extensive set of results, a carefully extracted and modular grid library assures realistic evaluation of parasitics impact on noise and facilitates the power network construction; furthermore statistical analysis guarantees a correct current envelope evaluation and Spice simulations endorse reliable result
The First Reported Infrared Emission from the SN 1006 Remnant
We report results of infrared imaging and spectroscopic observations of the
SN 1006 remnant, carried out with the Spitzer Space Telescope. The 24 micron
image from MIPS clearly shows faint filamentary emission along the northwest
rim of the remnant shell, nearly coincident with the Balmer filaments that
delineate the present position of the expanding shock. The 24 micron emission
traces the Balmer filaments almost perfectly, but lies a few arcsec within,
indicating an origin in interstellar dust heated by the shock. Subsequent
decline in the IR behind the shock is presumably due largely to grain
destruction through sputtering. The emission drops far more rapidly than
current models predict, however, even for a higher proportion of small grains
than would be found closer to the Galactic plane. The rapid drop may result in
part from a grain density that has always been lower -- a relic effect from an
earlier epoch when the shock was encountering a lower density -- but higher
grain destruction rates still seem to be required. Spectra from three positions
along the NW filament from the IRS instrument all show only a featureless
continuum, consistent with thermal emission from warm dust. The dust-to-gas
mass ratio in the pre-shock interstellar medium is lower than that expected for
the Galactic ISM -- as has also been observed in the analysis of IR emission
from other SNRs but whose cause remains unclear. As with other SN Ia remnants,
SN 1006 shows no evidence for dust grain formation in the supernova ejecta.Comment: 24 pages, 6 figure
Design and development of auxiliary components for a new two-stroke, stratified-charge, lean-burn gasoline engine
A unique stepped-piston engine was developed by a group of research engineers at Universiti Teknologi Malaysia (UTM), from 2003 to 2005. The development work undertaken by them engulfs design, prototyping and evaluation over a predetermined period of time which was iterative and challenging in nature. The main objective of the program is to demonstrate local R&D capabilities on small engine work that is able to produce mobile powerhouse of comparable output, having low-fuel consumption and acceptable emission than its crankcase counterpart of similar displacement. A two-stroke engine work was selected as it posses a number of technological challenges, increase in its thermal efficiency, which upon successful undertakings will be useful in assisting the group in future powertrain undertakings in UTM. In its carbureted version, the single-cylinder aircooled engine incorporates a three-port transfer system and a dedicated crankcase breather. These features will enable the prototype to have high induction efficiency and to behave very much a two-stroke engine but equipped with a four-stroke crankcase lubrication system. After a series of analytical work the engine was subjected to a series of laboratory trials. It was also tested on a small watercraft platform with promising indication of its flexibility of use as a prime mover in mobile platform. In an effort to further enhance its technology features, the researchers have also embarked on the development of an add-on auxiliary system. The system comprises of an engine control unit (ECU), a directinjector unit, a dedicated lubricant dispenser unit and an embedded common rail fuel unit. This support system was incorporated onto the engine to demonstrate the finer points of environmental-friendly and fuel economy features. The outcome of this complete package is described in the report, covering the methodology and the final characteristics of the mobile power plant
Molecules in Bipolar Outflows
Bipolar outflows constitute some of the best laboratories to study shock
chemistry in the interstellar medium. A number of molecular species have their
abundance enhanced by several orders of magnitude in the outflow gas, likely as
a combined result of dust mantle disruption and high temperature gas chemistry,
and therefore become sensitive indicators of the physical changes taking place
in the shock. Identifying these species and understanding their chemical
behavior is therefore of high interest both to chemical studies and to our
understanding of the star-formation process. Here we review some of the recent
progress in the study of the molecular composition of bipolar outflows, with
emphasis in the tracers most relevant for shock chemistry. As we discuss, there
has been rapid progress both in characterizing the molecular composition of
certain outflows as well as in modeling the chemical processes likely involved.
However, a number of limitations still affect our understanding of outflow
chemistry. These include a very limited statistical approach in the
observations and a dependence of the models on plane-parallel shocks, which
cannot reproduce the observed wing morphology of the lines. We finish our
contribution by discussing the chemistry of the so-called extremely high
velocity component, which seems different from the rest of the outflow and may
originate in the wind from the very vicinity of the protostar.Comment: 15 pages, 7 figures. Contribution to the IAU Conference "The
Molecular Universe" held in Toledo in June 201
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