350 research outputs found
About Norms and Causes
Knowing the norms of a domain is crucial, but there exist no repository of
norms. We propose a method to extract them from texts: texts generally do not
describe a norm, but rather how a state-of-affairs differs from it. Answers
concerning the cause of the state-of-affairs described often reveal the
implicit norm. We apply this idea to the domain of driving, and validate it by
designing algorithms that identify, in a text, the "basic" norms to which it
refers implicitly
Une expérience de sémantique inférentielle
We develop a system which must be able to perform the same inferences that a human reader of an accident report can do and more particularly to determine the apparent causes of the accident. We describe the general framework in which we are situated, linguistic and semantic levels of the analysis and the inference rules used by the system
The role of time in considering collections
The paper concerns the understanding of plurals in the framework of Artificial Intelligence and emphasizes the role of time. The construction of collection(s) and their evolution across time is often crucial and has to be accounted for. The paper contrasts a "de dicto" collection where the collection can be considered as persisting over these situations even if its members change with a "de re" collection whose composition does not vary through time. It expresses different criteria of choice between the two interpretations (de re and de dicto) depending on the context of enunciation
The Ray Bundle method for calculating weak magnification by gravitational lenses
We present here an alternative method for calculating magnifications in
gravitational lensing calculations -- the Ray Bundle method. We provide a
detailed comparison between the distribution of magnifications obtained
compared with analytic results and conventional ray-shooting methods. The Ray
Bundle method provides high accuracy in the weak lensing limit, and is
computationally much faster than (non-hierarchical) ray shooting methods to a
comparable accuracy.
The Ray Bundle method is a powerful and efficient technique with which to
study gravitational lensing within realistic cosmological models, particularly
in the weak lensing limit.Comment: 9 pages Latex, 8 figures, submitted to MNRA
Root development and heavy metal phytoextraction efficiency: comparison of different plant species in the field
Heavy metal phytoextraction is a soil remediation technique which implies the optimal use of plants to remove contamination from soil. Plants must thus be tolerant to heavy metals, adapted to soil and climate characteristics and able to take up large amounts of heavy metals. Their roots must also fit the spatial distribution of pollution. Their different root systems allow plants to adapt to their environment and be more or less efficient in element uptake. To assess the impact of the root system on phytoextraction efficiency in the field, we have studied the uptake and root systems (root length and root size) of various high biomass plants (Brassica juncea, Nicotiana tabacum, Zea mays and Salix viminalis) and one hyperaccumulator (Thlaspi caerulescens) grown in a Zn, Cu and Cd contaminated soil and compared them with total heavy metal distribution in the soil. Changes from year to year have been studied for an annual (Zea mays) and a perennial plant (Salix viminalis) to assess the impact of the climate on root systems and the evolution of efficiency with time and growth. In spite of a small biomass, T. caerulescens was the most efficient plant for Cd and Zn removal because of very high concentrations in the shoots. The second most efficient were plants combining high metal concentrations and high biomass (willows for Cd and Zn and tobacco for Cu and Cd). A large cumulative root density/aboveground biomass ratio (LA/B), together with a relative larger proportion of fine roots compared to other plants seemed to be additional favourable characteristics for increased heavy metal uptake by T. caerulescens. In general, for all plants correlations were found between L A/B and heavy metal concentrations in shoots (r=0.758***, r=0.594***, r=0.798*** (P<0.001) for Cd, Cu and Zn concentrations resp.). Differences between years were significant because of variations in climatic conditions for annual plants or because of growth for perennial plants. The plants exhibited also different root distributions along the soil profile: T. caerulescens had a shallow root system and was thus best suited for shallow contamination (0.2 m) whereas maize and willows were the most efficient in colonising the soil at depth and thus more applicable for deep contamination (0.7 m). In the field situation, no plant was able to fit the contamination properly due to heterogeneity in soil contamination. This points out to the importance and the difficulty of choosing plant species according to depth and heterogeneity of localisation of the pollutio
Challenging the principle of compositionality in interpreting natural language texts
The paper aims at emphasizing that, even relaxed, the hypothesis of
compositionality has to face many problems when used for interpreting natural
language texts. Rather than fixing these problems within the compositional
framework, we believe that a more radical change is necessary, and propose
another approach
Age Determination of Six Intermediate-age SMC Star Clusters with HST/ACS
We present a photometric analysis of the star clusters Lindsay 1, Kron 3,
NGC339, NGC416, Lindsay 38, and NGC419 in the Small Magellanic Cloud (SMC),
observed with the Hubble Space Telescope Advanced Camera for Surveys (ACS) in
the F555W and F814W filters. Our color magnitude diagrams (CMDs) extend ~3.5
mag deeper than the main-sequence turnoff points, deeper than any previous
data. Cluster ages were derived using three different isochrone models: Padova,
Teramo, and Dartmouth, which are all available in the ACS photometric system.
Fitting observed ridgelines for each cluster, we provide a homogeneous and
unique set of low-metallicity, single-age fiducial isochrones. The cluster CMDs
are best approximated by the Dartmouth isochrones for all clusters, except for
NGC419 where the Padova isochrones provided the best fit. The CMD of NGC419
shows several main-sequence turn-offs, which belong to the cluster and to the
SMC field. We thus derive an age range of 1.2-1.6 Gyr for NGC419.
Interestingly, our intermediate-age star clusters have a metallicity spread of
~0.6 dex, which demonstrates that the SMC does not have a smooth, monotonic
age-metallicity relation. We find an indication for centrally concentrated blue
straggler star candidates in NGC416, while for the other clusters these are not
present. Using the red clump magnitudes, we find that the closest cluster,
NGC419 (~50kpc), and the farthest cluster, Lindsay 38 (~67kpc), have a relative
distance of ~17kpc, which confirms the large depth of the SMC.Comment: 25 pages, 45 Figure
Study of the reactivity of silica supported tantalum catalysts with oxygen followed by in situ HEROS
We report on the reactivity of grafted tantalum organometallic catalysts with molecular oxygen. The changes in the local Ta electronic structure were followed by in situ high-energy resolution off-resonant spectroscopy (HEROS). The results revealed agglomeration and formation of Ta dimers, which cannot be reversed. The process occurs independently of starting grafted complex
- …