872 research outputs found
Direct Access for Conjunctive Queries with Negation
Given a conjunctive query and a database , a direct access to
the answers of over is the operation of returning, given an
index , the answer for some order on its answers. While
this problem is -hard in general with respect to combined
complexity, many conjunctive queries have an underlying structure that allows
for a direct access to their answers for some lexicographical ordering that
takes polylogarithmic time in the size of the database after a polynomial time
precomputation. Previous work has precisely characterised the tractable classes
and given fine-grained lower bounds on the precomputation time needed depending
on the structure of the query.
In this paper, we generalise these tractability results to the case of signed
conjunctive queries, that is, conjunctive queries that may contain negative
atoms. Our technique is based on a class of circuits that can represent
relational data. We first show that this class supports tractable direct access
after a polynomial time preprocessing. We then give bounds on the size of the
circuit needed to represent the answer set of signed conjunctive queries
depending on their structure. Both results combined together allow us to prove
the tractability of direct access for a large class of conjunctive queries. On
the one hand, we recover the known tractable classes from the literature in the
case of positive conjunctive queries. On the other hand, we generalise and
unify known tractability results about negative conjunctive queries -- that is,
queries having only negated atoms. In particular, we show that the class of
-acyclic negative conjunctive queries and the class of bounded nest set
width negative conjunctive queries admit tractable direct access
The development of the Helicopter Non-Technical Skills (HeliNOTS) behavioural marker systems
Acknowledgements The authors would like to thank all of the pilots, technical crew personnel, CRM trainers, and aviation consultants for taking the time to participate in this study. Funding This research was collaboratively funded by the ESRC and Bristow Helicopters [grant number: ES/P000681/1].Peer reviewedPublisher PD
'Having a grand view of what the day entailsâ : a qualitative investigation of the non-technical skills utilised by Mountain Guides.
Peer reviewedPublisher PD
Impact of poloxamer 188 (Pluronic F-68) additive on cell mechanical properties, quantification by real-time deformability cytometry
Advances in cellular therapies have led to the development of new approaches for cell product purification and formulation, e.g., utilizing cell endogenous properties such as size and deformability as a basis for separation from potentially harmful undesirable by-products. However, commonly used additives such as Pluronic F-68 and other poloxamer macromolecules can change the mechanical properties of cells and consequently alter their processing. In this paper, we quantified the short-term effect of Pluronic F-68 on the mechanotype of three different cell types (Jurkat cells, red blood cells, and human embryonic kidney cells) using real-time deformability cytometry. The impact of the additive concentration was assessed in terms of cell size and deformability. We observed that cells respond progressively to the presence of Pluronic F-68 within first 3 h of incubation and become significantly stiffer (p-value < 0.001) in comparison to a serum-free control and a control containing serum. We also observed that the short-term response manifested as cell stiffening is true (p-value < 0.001) for the concentration reaching 1% (w/v) of the poloxamer additive in tested buffers. Additionally, using flow cytometry, we assessed that changes in cell deformability triggered by addition of Pluronic F-68 are not accompanied by size or viability alterations
Wide-field optical imaging on ELAIS N1, ELAIS N2, First Look Survey and Lockman Hole: observations and source catalogues
We present u-, g-, r-, i- and z-band optical images and associated catalogues taken primarily with the Isaac Newton Telescope Wide Field Camera on the European Large Area ISO Survey (ELAIS) N1 and N2, First Look Survey and Lockman Hole fields comprising a total of 1000 h of integration time over 80 deg^2 and approximately 4.3 million objects. In this paper we outline the observations and data processing and characterize the completeness, reliability, photometric and astrometric accuracy of this data set. All images have been photometrically calibrated using the Sloan Digital Sky Survey and a uniform and homogeneous data set is composed over all the observed fields. Magnitude limits are u, g, r, i, z of 23.9, 24.5, 24.0, 23.3, 22.0 (AB, 5Ï). These data have been used for optical identification of past and ongoing projects including the surveys ELAIS, Spitzer Wide-Area Infrared Extragalactic Survey, Spitzer Extragalactic Representative Volume Survey and Herschel Multi-tiered Extragalactic Survey
APM 08279+5255: an ultraluminous BAL quasar at a redshift z=3.87
We report on the discovery of a highly luminous, broad absorption line quasar
at a redshift of which is positionally coincident, within one
arcsecond, with the IRAS FSC source F08279+5255. A chance alignment of the
quasar and the IRAS source is extremely unlikely and we argue that the optical
and FIR flux are different manifestations of the same object. With an R-band
magnitude of 15.2, and an IRAS 60\mum flux of 0.51\jy, APM 08279+5255 is
(apparently) easily the most intrinsically luminous object known, with
L_{Bol}\sim5\times10^{15}L_{\odot}}. Imaging suggests that gravitational
lensing may play a role in amplifying the intrinsic properties of the system.
The optical spectrum of the quasar clearly reveals the presence of three
potential lensing galaxies, \mg absorption systems at and ,
and a \ly absorption system at . We estimate the total amplification of
the optical component to be , but, due to the larger scale of the
emitting region, would expect the infrared amplification to be significantly
less. Even making the conservative assumption that all wavelengths are
amplified by a factor 40, APM 08279+5255 still possesses a phenomenal
luminosity of \simgt 10^{14L_{\odot}}, indicating that it belongs to a small,
but significant population of high--redshift, hyperluminous objects with
copious infrared emission.Comment: 15 Pages with Four figures. Accepted for publication in the
Astrophysical Journa
An Overdensity of Extremely Red Objects Around Faint Mid-IR galaxies
We have searched for Extremely Red Objects (EROs) around faint mid-IR
selected galaxies in ELAIS fields. We find a significant overdensity, by
factors of 2 to 5, of these EROs compared to field EROs in the same region and
literature random field ERO counts. The excess is similar to that found
previously in the fields of known high redshift quasars and AGN. While with the
present data it cannot be definitely shown whether the overdensity is
physically connected to the mid-IR source, a derived radial distribution does
suggest this. The fraction of EROs among K-selected galaxies is high in the
mid-IR fields in agreement with the picture that the EROs responsible for the
overdensity are members of high redshift clusters of galaxies. We find R-K>5
selected EROs to be more clustered around the mid-IR galaxies than I-K>4 EROs,
though statistics are weak because of small numbers. However, this would be
consistent with a cluster/galaxy group scenario if, as we argue, the former
colour selection finds preferentially more strongly clustered early type
galaxies, whereas the latter selection includes a larger fraction of dusty
EROs. Finally, using the mid-IR data, we are able to limit the fraction of
ULIRG type very dusty EROs at K<18 magnitude to less than 10% of the total ERO
population.Comment: A&A, accepted, 13 pages and 5 ps-fig
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Does "Liking" Lead to Loving? The Impact of Joining a Brand's Social Network on Marketing Outcomes
Does âlikingâ a brand on Facebook cause a person to view it more favorably? Or is âlikingâ simply a symptom of being fond of a brand? We disentangle these possibilities and find evidence for the latter: brand attitudes and purchasing are predicted by consumersâ preexisting fondness for brands and are the same regardless of when and whether consumers âlikeâ brands. In addition, we explore possible second-order effects, examining whether âlikingâ brands might cause consumersâ friends to view that brand more favorably. When consumers see that a friend has âlikedâ a brand, they are less likely to buy the brand relative to a more meaningful social endorsement: learning that a friend likes a brand, in the offline sense. Taken together, five experiments and two meta-analyses (N > 14,000) suggest that turning âlikingâ into improved brand attitudes and increased purchasing by either consumers or their friends may require more than just the click of a button
Number Counts of Bright Extremely Red Objects: Evolved Massive Galaxies at z~1
We present results on number counts of Extremely Red Objects (EROs) in a 2850
arcmin^2 near-infrared survey performed in European Large Area ISO Survey
(ELAIS) fields at K<17.5. Counts of EROs are extended to brighter levels than
available previously, giving 0.002 +/- 0.001 arcmin^-2 at K<16.5 and consistent
numbers with literature values at fainter magnitudes. Photometric redshifts
from HYPERZ as well as GRASIL model SEDs of galaxies imply that our EROs are
located in the range z=0.7-1.5, with the bulk of the population at z~1. Taking
advantage of the ISO data in the fields, we use mid-IR detections to constrain
the number of dusty EROs, and also discuss the superior capabilities of Spitzer
Space Telescope to detect dusty EROs. Both the mid-IR data and the use of
colour-colour diagrammes indicate that at most 10-20% of the EROs in this
bright regime are dusty starbursting systems. The space density of our EROs,
interpreted to be counterparts of local >2-3L^star massive galaxies at around
z~1, is estimated to be approx. 2x10^-5 Mpc^-3, which is consistent with local
values. Furthermore, the cumulative number counts at our bright magnitudes are
remarkably well fitted by pure luminosity evolution models.Comment: A&A, accepted, 14 pages and 8 ps-fig
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