1,083 research outputs found
Comparing knowledge sources for nominal anaphora resolution
We compare two ways of obtaining lexical knowledge for antecedent selection in other-anaphora
and definite noun phrase coreference. Specifically, we compare an algorithm that relies on links
encoded in the manually created lexical hierarchy WordNet and an algorithm that mines corpora
by means of shallow lexico-semantic patterns. As corpora we use the British National
Corpus (BNC), as well as the Web, which has not been previously used for this task. Our
results show that (a) the knowledge encoded in WordNet is often insufficient, especially for
anaphor-antecedent relations that exploit subjective or context-dependent knowledge; (b) for
other-anaphora, the Web-based method outperforms the WordNet-based method; (c) for definite
NP coreference, the Web-based method yields results comparable to those obtained using
WordNet over the whole dataset and outperforms the WordNet-based method on subsets of the
dataset; (d) in both case studies, the BNC-based method is worse than the other methods because
of data sparseness. Thus, in our studies, the Web-based method alleviated the lexical knowledge
gap often encountered in anaphora resolution, and handled examples with context-dependent relations
between anaphor and antecedent. Because it is inexpensive and needs no hand-modelling
of lexical knowledge, it is a promising knowledge source to integrate in anaphora resolution systems
How many Ultra High Energy Cosmic Rays could we expect from Centaurus A?
The Pierre Auger Observatory has associated a few ultra high energy cosmic
rays with the direction of Centaurus A. This source has been deeply studied in
radio, infrared, X-ray and -rays (MeV-TeV) because it is the nearest
radio-loud active galactic nuclei.
Its spectral energy distribution or spectrum shows two main peaks, the low
energy peak, at an energy of eV, and the high energy peak, at about
150 keV.
There is also a faint very high energy (E 100 GeV) -ray
emission fully detected by the High Energy Stereoscopic System experiment. In
this work we describe the entire spectrum, the two main peaks with a
Synchrotron/Self-Synchrotron Compton model and, the Very High Energy emission
with a hadronic model. We consider p and interactions. For the
p interaction, we assume that the target photons are those produced at
150 keV in the leptonic processes. On the other hand, for the pp interaction we
consider as targets the thermal particle densities in the lobes. Requiring a
satisfactory description of the spectra at very high energies with p
interaction we obtain an excessive luminosity in ultra high energy cosmic rays
(even exceeding the Eddington luminosity). However, when considering pp
interaction to describe the -spectrum, the obtained number of ultra
high energy cosmic rays are in agreement with Pierre Auger observations.
Moreover, we calculate the possible neutrino signal from pp interactions on a
Km neutrino telescope using Monte Carlo simulations.Comment: Accepted in Ap
Glycine attenuates Fanconi syndrome induced by maleate or ifosfamide in rats
Glycine attenuates Fanconi syndrome induced by maleate or ifosfamide in rats. It has become widely recognized that glycine (Gly) depletion predisposes isolated proximal tubules (PT) to necrotic cell damage induced by diverse insults and that Gly replacement in vitro is highly cytoprotective. However, the effectiveness of supplementation with Gly in vivo, where blood and tissue Gly normally are maintained at high levels, is incompletely defined. Our aim was to assess whether: (a) supplementation of Gly in drinking water of rats would attenuate the proximal tubule damage and the Fanconi syndrome (FS) induced by maleate (Mal), a classical proximal tubule toxin, or ifosfamide (IFO), an antineoplastic drug; and (b) to explore the mechanisms responsible for such effects, since Gly supplementation might be especially beneficial in treating the FS, where the kidney tends to waste amino acids. Rats received daily injection of Mal (2 mmol/kg) for two days without or with oral supplementation of 2% Gly. IFO, 50 mg/kg, was injected daily for five days without or with oral Gly. Control rats were injected with saline, without or with oral Gly. The results demonstrated that both Mal and IFO induced a FS characterized by wasting of amino and organic acids, glucose, and electrolytes, along with elevated plasma creatinine (Crn) and BUN, and decreased Crn clearance rate. Light microscopy revealed a necrotic lesion in the proximal tubules of the Mal group, but no necrosis after IFO. Gly strongly ameliorated the severity of renal necrosis and/or dysfunction induced by Mal or IFO, with significant decreases in total and fractional excretion of Na+, K+, PO43− and glucose, decreased plasma BUN and Crn, and increased Crn clearance. Analysis of freeze-clamped cortical tissue showed substantial depletion of [Gly], [ATP] and [GSH] along with increased GSSG in Mal or IFO groups and correction of [Gly] and [ATP] with Gly supplementation, but no improvement with Gly of reduced gluthatione [GSH] or the ratio of reduced to oxidized gluthatione (GSH/GSSG). 31P-NMR analysis of the renal cortex indicated a decrease in Pi and various membrane phospholipids in Mal and IFO rats and prevention of this damage with Gly. These observations demonstrate that oral supplementation of Gly can provide protection against Mal or IFO-induced renal tubular cell dysfunction and structural damage. The lack of effect on glutathione oxidation and depletion suggests an action distal to toxin uptake and intracellular interactions, which is similar to the characteristics of Gly cytoprotection against diverse insults in vitro. The results also suggest modification by Gly of the primary toxicity of the agents and effects on phospholipid synthesis that could contribute to repair
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