7,515 research outputs found
Efficient and Effective Query Auto-Completion
Query Auto-Completion (QAC) is an ubiquitous feature of modern textual search
systems, suggesting possible ways of completing the query being typed by the
user. Efficiency is crucial to make the system have a real-time responsiveness
when operating in the million-scale search space. Prior work has extensively
advocated the use of a trie data structure for fast prefix-search operations in
compact space. However, searching by prefix has little discovery power in that
only completions that are prefixed by the query are returned. This may impact
negatively the effectiveness of the QAC system, with a consequent monetary loss
for real applications like Web Search Engines and eCommerce. In this work we
describe the implementation that empowers a new QAC system at eBay, and discuss
its efficiency/effectiveness in relation to other approaches at the
state-of-the-art. The solution is based on the combination of an inverted index
with succinct data structures, a much less explored direction in the
literature. This system is replacing the previous implementation based on
Apache SOLR that was not always able to meet the required
service-level-agreement.Comment: Published in SIGIR 202
ALMA polarization observations of the particle accelerators in the hot spot of the radio galaxy 3C 445
We present Atacama Large Millimeter Array (ALMA) polarization observations at
97.5 GHz of the southern hot spot of the radio galaxy 3C 445. The hot spot
structure is dominated by two bright components enshrouded by diffuse emission.
Both components show fractional polarization between 30 and 40 per cent,
suggesting the presence of shocks. The polarized emission of the western
component has a displacement of about 0.5 kpc outward with respect to the total
intensity emission, and may trace the surface of a front shock. Strong
polarization is observed in a thin strip marking the ridge of the hot spot
structure visible from radio to optical. No significant polarization is
detected in the diffuse emission between the main components, suggesting a
highly disordered magnetic field likely produced by turbulence and
instabilities in the downstream region that may be at the origin of the
extended optical emission observed in this hot spot. The polarization
properties support a scenario in which a combination of both multiple and
intermittent shock fronts due to jet dithering, and spatially distributed
stochastic second-order Fermi acceleration processes are present in the hot
spot complex.Comment: 5 pages, 3 figures; accepted for publication in MNRAS Lette
CLIWOC multilingual meteorological dictionary
This dictionary is the first attempt to express the wealth of archaic logbook wind force terms in a form that is comprehensible to the modern-day reader. Oliver and Kington (1970) and Lamb (1982) have drawn attention to the importance of logbooks in climatic studies, and Lamb (1991) offered a conversion scale for early eighteenth century English wind force terms, but no studies have thus far pursued the matter to any greater depth. This text attempts to make good this deficiency, and is derived from the research undertaken by the CLIWOC project1 in which British, Dutch, French and Spanish naval and merchant logbooks from the period 1750 to 1850 were used to derive a global database of climatic information. At an early stage in the project it was apparent that many of the logbook weather terms, whilst conforming to a conventional vocabulary, possessed meanings that were unclear to twenty-first century readers or had changed over time. This was particularly the case for the important element of wind force; but no special plea is entered for the evolution in nautical vocabulary, which often reflected more wide-ranging changes in the respective native languages.The key objective was to translate the archaic vocabulary of the late eighteenth and early nineteenth century mariner into expressions directly comparable with the Beaufort Scale (see Appendix I). Only then could the projects scientific programme be embarked upon. This dictionary is the result of the largest undertaking into logbook studies that has yet been carried out. Several thousand logbooks from British, Dutch, French and Spanish archives were examined, and the exercise offered a unique opportunity to explore the vocabulary of the one hundred year period beginning in 1750. The logbooks from which the raw data have been abstracted range widely across the North and South Atlantic and the Indian Oceans. Only the Pacific, largely in consequence of the paucity of regular naval activity in that area, is not well represented. The range of climates encountered in this otherwise wide geographic domain gives ample opportunity for the full range of the mariners nautical weather vocabulary to be assessed, from the calms of the Equatorial regions, through the gales of the mid-latitude systems to the fearsome storms of the tropical latitudes. The Trade Winds belts, the Doldrums, the unsettled mid-latitudes, even the icy wastes of the high latitudes, are all embraced in this study. It is not here intended to pass any judgements on the climatological record of the logbooks, and this text seeks only to provide a means of understanding archaic wind force terms and, other than to indicate those items that were not commonly used, no information is given on the frequency with which different terms appeared in the logbooks. Attention is, furthermore, confined to Dutch, English, French and Spanish because these once great imperial powers were the only nations able to support wide-ranging ocean-going fleets with their attendant collections of logbooks and documents over this long period of time. The work is offered to the wider academic community in the hope that they will prove to be of as much value as it has been to the CLIWOC team
Variable stars in the globular cluster M28 (NGC 6626)
We present a new search for variable stars in the Galactic globular cluster
M28 (NGC 6626). The search is based on a series of BVI images obtained with the
SMARTS Consortium's 1.3m telescope at Cerro Tololo Inter-American Observatory,
Chile. The search was carried out using the ISIS v2.2 image subtraction
package. We find a total of 25 variable stars in the field of the cluster, 9
being new discoveries. Of the newly found variables, 1 is an ab-type RR Lyrae
star, 6 are c-type RR Lyrae, and 2 are long-period/semi-regular variables. V22,
previously classified as a type II Cepheid, appears as a bona-fide RRc in our
data. In turn, V20, previously classified as an ab-type RR Lyrae, could not be
properly phased with any reasonable period. The properties of the ab-type RR
Lyrae stars in M28 appear most consistent with an Oosterhoff-intermediate
classification, which is unusual for bona-fide Galactic globulars clusters.
However, the cluster's c-type variables do not clearly support such an
Oosterhoff type, and a hybrid Oosterhoff I/II system is accordingly another
possibility, thus raising the intriguing possibility of multiple populations
being present in M28. Coordinates, periods, and light curves in differential
fluxes are provided for all the detected variables.Comment: A&A, in pres
The Discovery of a Companion to the Lowest Mass White Dwarf
We report the detection of a radial velocity companion to SDSS
J091709.55+463821.8, the lowest mass white dwarf currently known with
M~0.17Msun. The radial velocity of the white dwarf shows variations with a
semi-amplitude of 148.8 km/s and a period of 7.5936 hours, which implies a
companion mass of M > 0.28Msun. The lack of evidence of a companion in the
optical photometry forces any main-sequence companion to be smaller than
0.1Msun, hence a low mass main sequence star companion is ruled out for this
system. The companion is most likely another white dwarf, and we present
tentative evidence for an evolutionary scenario which could have produced it.
However, a neutron star companion cannot be ruled out and follow-up radio
observations are required to search for a pulsar companion.Comment: ApJ, in press. See the Press Release at
http://www.cfa.harvard.edu/press/2007/pr200708.htm
First Results from the LEIR Ionisation Profile Monitors
The role of the Low Energy Ion Ring, LEIR, is to transform long pulses of lead ions from the Linac 3 to short dense bunches for transfer to the LHC. This is accomplished by the accumulation of up to 4 Linac pulses by electron cooling. In order to non-destructively monitor the cooling performance and determine the accumulated beam characteristics, two prototype ionisation profile monitors have been built and were tested during the LEIR commissioning runs with O4+ and Pb54+ ions in 2006. In this paper we present the results obtained with the prototype monitors, the problems encountered and describe the modifications made for the final design. The modified monitors have been installed on the LEIR machine and are waiting for the next ion run planned in August
A -Vertex Kernel for Maximum Internal Spanning Tree
We consider the parameterized version of the maximum internal spanning tree
problem, which, given an -vertex graph and a parameter , asks for a
spanning tree with at least internal vertices. Fomin et al. [J. Comput.
System Sci., 79:1-6] crafted a very ingenious reduction rule, and showed that a
simple application of this rule is sufficient to yield a -vertex kernel.
Here we propose a novel way to use the same reduction rule, resulting in an
improved -vertex kernel. Our algorithm applies first a greedy procedure
consisting of a sequence of local exchange operations, which ends with a
local-optimal spanning tree, and then uses this special tree to find a
reducible structure. As a corollary of our kernel, we obtain a deterministic
algorithm for the problem running in time
Estudio experimental comparativo de la estabilidad de distintos tutores externos
Se investigó la rigidez de 11 diferentes montajes de tutores externos usando un
modelo experimental con tibias cadavéricas a las cuales se realizaba una osteotomía transversal
mediodiafisaria perpendicular al eje longitudinal del hueso, creando entre ambos segmentos
una brecha de 35 mm, simulando una fractura. Mediante dispositivos de medición diseñados y
construidos especialmente para este estudio se logró cuantificar los desplazamientos que se
producen en el foco de fractura ante cargas de compresión axial, torsión y flexiones anteroposterior
y mediolateral. Se determinó en cada ensayo la carga segura y carga máxima previamente
definidas. La mayor rigidez a la compresión axial se observó en el tutor Orthofix a la
torsión y a la flexión anteroposterior en el Kronner biplanar y a la flexión mediolateral en el
tutor AO triangulado. Se determina la rigidez total porcentual de cada montaje como índice
que representa el funcionamiento promedio del mismo en todas las modalidades de carga. Se
consideran las indicaciones, ventajas, complicaciones y fundamentalmente la biología de la
consolidación ósea en referencia a los fijadores externos. Se concluye sobre el cuidado con
que debe ser conducida la carga de un miembro con fractura inestable, ya que la mayoría de
los montajes permiten más de 1 mm de movimiento en la brecha de la fractura con una carga
axial baja.The stiffness of 11 different device configurations of external fixation was investigated
in an experimental model using human cadaveric tibia. After application of the different
devices, a diaphyseal osteotomy allowing removal of a 35 mm bone segment was performed in
the specimens. Displacements of the bone fragments at the osteotomy site induced by compresion
loading, torsion, and both anteroposterior and mediolateral flexion were measured with
dispositives designed for this experiment. Maximal load and that required for inducing 1 mm
displacement were recorded. The higher stiffness corresponded to the Orthofix fixator in axial
compression, the Kronner biplanar device in anteroposterior flexion, and the triangular configuration
of the AO device in mediolateral flexion. A total stiffness index of each configuration
as an average of the behavior against all loading modahties was obtained. The indications, advantages,
complications and the biology of bone consolidation wien regards to external fixation
are considered. As conclusion, progressive loading of the extremity with unstable fracture requires
a close monitorization, since most of the device configurations analyzed allow more than
1 mm displacement of bone fragments at the fracture site, even with low axial loading
Clues to NaCN formation
ALMA is providing us essential information on where certain molecules form.
Observing where these molecules emission arises from, the physical conditions
of the gas, and how this relates with the presence of other species allows us
to understand the formation of many species, and to significantly improve our
knowledge of the chemistry that occurs in the space. We studied the molecular
distribution of NaCN around IRC +10216, a molecule detected previously, but
whose origin is not clear. High angular resolution maps allow us to model the
abundance distribution of this molecule and check suggested formation paths. We
modeled the emission of NaCN assuming local thermal equilibrium (LTE)
conditions. These profiles were fitted to azimuthal averaged intensity profiles
to obtain an abundance distribution of NaCN. We found that the presence of NaCN
seems compatible with the presence of CN, probably as a result of the
photodissociation of HCN, in the inner layers of the ejecta of IRC +10216.
However, similar as for CH 3 CN, current photochemical models fail to reproduce
this CN reservoir. We also found that the abundance peak of NaCN appears at a
radius of 3 x 10 15 cm, approximately where the abundance of NaCl, suggested to
be the parent species, starts to decay. However, the abundance ratio shows that
the NaCl abundance is lower than that obtained for NaCN. We expect that the LTE
assumption might result in NaCN abundances higher than the real ones. Updated
photochemical models, collisional rates, and reaction rates are essential to
determine the possible paths of the NaCN formation.Comment: 7 pages, 10 figures. Accepted for publication in A&A letter
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