240 research outputs found
Taming Existence in RDF Querying
We introduce the recursive, rule-based RDF query language
RDFLog. RDFLog extends previous RDF query languages by arbitrary
quantifier alternation: blank nodes may occur in the scope of all, some,
or none of the universal variables of a rule. In addition RDFLog is aware
of important RDF features such as the distinction between blank nodes,
literals and URIs or the RDFS vocabulary. The semantics of RDFLog is
closed (every answer is an RDF graph), but lifts RDFâs restrictions on
literal and blank node occurrences for intermediary data. We show how
to define a sound and complete operational semantics that can be implemented
using existing logic programming techniques. Using RDFLog
we classify previous approaches to RDF querying along their support for
blank node construction and show equivalence between languages with
full quantifier alternation and languages with only ââ rules
Magnetic structure and dynamics of a strongly one-dimensional cobalt metal-organic framework
We investigate the magnetism of the
Co(OH)(CHO) metal-organic framework which
displays complex inorganic chains separated from each other by distances of 1
to 2 nm, and which orders at ~5.4 K. The zero-field magnetic structure is
determined using neutron powder diffraction: it is mainly antiferromagnetic but
posseses a ferromagnetic component along the -axis. This magnetic
structure persists in presence of a magnetic field. Ac susceptibility
measurements confirm the existence of a single thermally activated regime over
7 decades in frequency () whereas time-dependent relaxation
of the magnetization after saturation in an external field leads to a two times
smaller energy barrier. These experiments probe the slow dynamics of domain
walls within the chains: we propose that the ac measurements are sensitive to
the motion of existing domain walls within the chains, while the magnetization
measurements are governed by the creation of domain walls.Comment: 12 pages, 14 figure
A Novel Method for Studying the Dynamics of Confined Polymers in Nanoparticles in Nanoblends
The advances in new technologies have prompted the need for functional
systems smaller than the gyration radius of polymer chains. Thus, understanding
how nanoconfinement affects polymer properties has been the focus of a lot of
research for over a decade. Polystyrene in particular has been reported to be
strongly affected when nanoconfined as a thin film and specifically its glass
transition temperature (Tg) is reported to decrease with decreasing film
thickness. Tremendous effort has been dedicated to developing methods for
quantifying the large-scale dynamic of nanoconfined polymers: film dewetting,
film contraction, nanobubble inflation, nanoparticle imbedding and healing of
deformed surfaces etc. In this work we describe a novel method to study the
large scale dynamic and nanomechanical properties of nanoconfined polymers in
nanoparticles in nanoblends. Nanoblends of dPS/PBMA were prepared from a
mixture of colloidal suspensions of cross-linked PBMA and traces of dPS
nanoparticles via water evaporation. The polymer blends were prepared at
temperatures well below the glass transition of PS (TgPS) and above the Tg of
cross-linked PBMA particles (TgPBMA). In these conditions we expect the PBMA
particles to deform under capillary pressure to fill the interstices between
them and the glassy PS nanoparticles to remain spherical. During the
preparation of the nanoblends the elastic energy is stored within the deformed
cross-linked PBMA nanoparticles. Upon annealing the films above TgPS, the PBMA
nanoparticles regain their spherical shape and release the stored elastic
energy, which induces the deformation of the PS nanoparticles. Small angle
neutron scattering is then used to monitor the shape evolution of the PS
nanoparticles and to quantify the relaxation dynamics of the polystyrene
nanoparticles
Assessment of chemo-mechanical degradation of concrete sewer pipes through an integrated experimental approach
Foundations of Rule-Based Query Answering
This survey article introduces into the essential concepts and methods underlying rule-based query languages. It covers four complementary areas: declarative semantics based on adaptations of mathematical logic, operational semantics, complexity and expressive power, and optimisation of query evaluation.
The treatment of these areas is foundation-oriented, the foundations having resulted from over four decades of research in the logic programming and database communities on combinations of query languages and rules. These results have later formed the basis for conceiving, improving, and implementing several Web and Semantic Web technologies, in particular query languages such as XQuery or SPARQL for querying relational, XML, and RDF data, and rule languages like the âRule Interchange Framework (RIF)â currently being developed in a working group of the W3C.
Coverage of the article is deliberately limited to declarative languages in a classical setting: issues such as query answering in F-Logic or in description logics, or the relationship of query answering to reactive rules and events, are not addressed
Molecular biogeography of prickly lettuce (lactuca serriola l.) shows traces of recent range expansion
Prickly lettuce (Lactuca serriola L., Asteraceae), a wild relative of cultivated lettuce, is an autogamous species which greatly expanded throughout Western and Northern Europe during the last 2 centuries. Here, we present a large-scale biogeographic genetic analysis performed on a dataset represented by 2622 individuals from 110 wild European populations. Thirty-two maternally inherited chloroplast RFLP-markers and 10 nuclear microsatellite loci were used. Microsatellites revealed low genetic variation and high inbreeding coefficients within populations, as well as strong genetic differentiation between populations, which was in accordance with the autogamous breeding system. Analysis of molecular variance based clustering indicated the presence of 3 population clusters, which showed strong geographical patterns. One cluster occupied United Kingdom and part of Northern Europe, and characterized populations with a single predominant genotype. The second mostly combined populations from Northern Europe, while the third cluster grouped populations particularly from Southern Europe. Kriging of gene diversity for L. serriola corroborated northwards and westwards spread from Central (Eastern) Europe. Significant lower genetic diversity characterized the newly colonized parts of the range compared to the historical ones, confirming the importance of founder effects. Stronger pattern of isolation by distance was assessed in the newly colonized areas than in the historical areas (Mantelâs r = 0.20). In the newly colonized areas, populations at short geographic distances were genetically more similar than those in the historical areas. Our results corroborate the speciesâ recent and rapid northward and westward colonization from Eastern Europe, as well as a decrease of genetic diversity in recently established populations
Anthropologie des déplacements et nouvelles logiques urbaines
Michel Agier, directeur dâĂ©tudes De lâethnographie des marges Ă lâanthropologie de la ville Cette direction dâĂ©tudes sâest composĂ©e en 2008-2009 de deux sĂ©minaires : un sĂ©minaire principal, de recherche (« De lâethnographie des marges Ă lâanthropologie de la ville ») et un atelier de recherche collectif (« Limites du politique, Politiques des limites »). Dâautre part, jâai poursuivi cette annĂ©e encore un sĂ©minaire semestriel dâIntroduction aux recherches sur les rĂ©fugiĂ©s et lâasile, principal..
Environmental changes during the onset of the Late Pliensbachian Event (Early Jurassic) in the Cardigan Bay Basin, Wales
The Late Pliensbachian Event (LPE), in the Early Jurassic, is associated with a perturbation in the global carbon cycle (positive carbon isotope excursion (CIE) of âŒ2ââ°), cooling of âŒ5ââC, and the deposition of widespread regressive facies. Cooling during the late Pliensbachian has been linked to enhanced organic matter burial and/or disruption of thermohaline ocean circulation due to a sea level lowstand of at least regional extent. Orbital forcing had a strong influence on the Pliensbachian environments and recent studies show that the terrestrial realm and the marine realm in and around the Cardigan Bay Basin, UK, were strongly influenced by orbital climate forcing. In the present study we build on the previously published data for long eccentricity cycle E459â±â1 and extend the palaeoenvironmental record to include E458â±â1. We explore the environmental and depositional changes on orbital timescales for the Llanbedr (Mochras Farm) core during the onset of the LPE. Clay mineralogy, X-ray fluorescence (XRF) elemental analysis, isotope ratio mass spectrometry, and palynology are combined to resolve systematic changes in erosion, weathering, fire, grain size, and riverine influx. Our results indicate distinctively different environments before and after the onset of the LPE positive CIE and show increased physical erosion relative to chemical weathering. We also identify five swings in the climate, in tandem with the 405âkyr eccentricity minima and maxima. Eccentricity maxima are linked to precessionally repeated occurrences of a semi-arid monsoonal climate with high fire activity and relatively coarser sediment from terrestrial runoff. In contrast, 405âkyr minima in the Mochras core are linked to a more persistent, annually wet climate, low fire activity, and relatively finer-grained deposits across multiple precession cycles. The onset of the LPE positive CIE did not impact the expression of the 405âkyr cycle in the proxy records; however, during the second pulse of heavier carbon (13C) enrichment, the clay minerals record a change from dominant chemical weathering to dominant physical erosion
Anthropologie des déplacements, nouvelles logiques urbaines
Michel Agier, directeur dâĂ©tudes De lâethnographie des marges Ă lâanthropologie de la ville Cette direction dâĂ©tudes sâest composĂ©e en 2007-2008 de deux sĂ©minaires : un sĂ©minaire principal, de recherche, « De lâethnographie des marges Ă lâanthropologie de la ville » et un atelier de recherche collectif, « Limites du politique, politiques des limites ». Par ailleurs, un sĂ©minaire dâIntroduction aux recherches sur les rĂ©fugiĂ©s et lâasile a Ă©tĂ© donnĂ© principalement mais non exclusivement Ă lâatt..
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