575 research outputs found
Large Scale Question Paraphrase Retrieval with Smoothed Deep Metric Learning
The goal of a Question Paraphrase Retrieval (QPR) system is to retrieve
equivalent questions that result in the same answer as the original question.
Such a system can be used to understand and answer rare and noisy
reformulations of common questions by mapping them to a set of canonical forms.
This has large-scale applications for community Question Answering (cQA) and
open-domain spoken language question answering systems. In this paper we
describe a new QPR system implemented as a Neural Information Retrieval (NIR)
system consisting of a neural network sentence encoder and an approximate
k-Nearest Neighbour index for efficient vector retrieval. We also describe our
mechanism to generate an annotated dataset for question paraphrase retrieval
experiments automatically from question-answer logs via distant supervision. We
show that the standard loss function in NIR, triplet loss, does not perform
well with noisy labels. We propose smoothed deep metric loss (SDML) and with
our experiments on two QPR datasets we show that it significantly outperforms
triplet loss in the noisy label setting
The lithospheric mantle and lower crust-mantle relationships under Scotland: a xenolithic perspective
In the British Isles the majority of volcanic rocks containing upper mantle and lower crustal xenoliths occur in Scotland. Most of the occurrences are of Carboniferous–Permian age. This paper presents new data on the mineral chemistry of spinel lherzolite xenoliths from the five principal Scottish tectonic terranes. Compositional variations among the minerals emphasize the broad lateral heterogeneity of the subcontinental lithospheric mantle across the region. The remarkable range of Al2O3 v. CaO exhibited by the clinopyroxenes compared with data from other ‘xenolith provinces' emphasizes the extremely complex tectonomagmatic history of the Scottish lithosphere. The generalized age increase from southern and central Scotland to the Northern Highland and Hebridean terranes of the north and NW, with concomitant complexity of geological history, is reflected also by trace element and isotopic studies. Reaction relationships in lherzolites from the Hebridean Terrane, owing to pervasive metasomatism, involve secondary growth of sodic feldspar. This, and light REE enrichment of clinopyroxenes, points to involvement of a natro-carbonatitic melt. Most pyroxenitic xenoliths are inferred to form a basal crustal layer with a generally sharp discontinuity above the underlying (dominantly lherzolitic) mantle. A second discontinuity is inferred to separate these ultramafic cumulates from overlying, broadly cognate metagabbroic cumulates
Ranking Kernels for Structures and Embeddings: A Hybrid Preference and Classification Model
n/
Aluminium distribution in an Earth’s non–primitive lower mantle
The aluminium incorporation mechanism of perovskite was explored by means of quantum mechanics in combination with equilibrium/off-equilibrium thermodynamics under the pressure-temperature conditions of the Earth’s lower mantle (from 24 to 80 GPa). Earth’s lower mantle was modelled as a geochemically non-primitive object because of an enrichment by 3 wt% of recycled crustal material (MORB component). The compositional modelling takes into account both chondrite and pyrolite reference models.
The capacity of perovskite to host Al was modelled through an Al2O3 exchange process in an unconstrained Mg-perovskite+Mg-Al-perovskite+free-Al2O3(corundum) system. Aluminium is globally incorporated principally via an increase in the amount of Al bearing perovskite [Mg-Al-pv(80 GPa)/Mg-Al-pv(24 GPa)ï‚»1.17], rather than by an increase in the Al2O3 content of the average chemical composition which changes little (0.11-0.13, mole fraction of Al2O3) and tends to decrease in Al. The Al2O3 distribution in the lower mantle was described through the probability of the occurrence of given compositions of Al bearing perovskite. The probability of finding Mg-Al-perovskite is comparable to Mg-perovskites. Perovskite with Al2O3 mole fraction up to 0.15 has an occurrence probability of ~28% at 24 GPa, increasing up to ~43% at 80 GPa; on the contrary, perovskite compositions in the range 0.19-0.30 Al2O3 mole fraction drop their occurrence probability from 9.8 to 2.0%, over the same P-range. In light of this, the distribution of Al in the lower mantle shows that, among the possible Al bearing perovskite phases, the (Mg0.89Al0.11)(Si0.89Al0.11)O3 composition is the likeliest, providing from 5 to 8% of the bulk perovskite in the pressure range from 24 to 80 GPa. The occurrence of the most Al rich composition, i.e. (Mg0.71Al0.29)(Si0.71Al0.29)O3, is a rare event (probability of occurrence < 1.7%). This study predicts that perovskite may globally host Al2O3 in terms of 4.3 and 4.8 wt% (with respect to the non-primitive lower mantle mass), thus accounting for ~ 90% and 100% of the bulk Al2O3 estimated in the framework of pyrolite and chondrite reference models, respectively. A calcium-ferrite type phase (on the MgAl2O4-NaAlSiO4 join) seems to be the only candidate that can compensate for the 10% gap of the perovskite Al incorporation capacity, in the case of a pyrolite non-primitive lower mantle model
La temporalit\ue0 nel poema di Nikolay Gogol' "Anime morte"
Lo scopo della tesi \ue8 quello di analizzare i diversi aspetti della temporalit\ue0 nel poema di Gogol' "Anime morte", attraverso lo studio sia delle figure del tempo (la Storia, il calendario, l'orologio, ecc.), sia delle strutture (tempo dell'azione e tempo della lettura), grazie all'ausilio di importanti studi sulla temporalit\ue0 effettuati in ambiente formalista e pi\uf9 tardi. L'attenzione mirata a scandagliare la dimensione temporale nelle sue pi\uf9 diverse coordinate ha portato a constatare una sorta di collaborazione di queste ultime. Sembra che le varianti della temporalit\ue0 nel poema di Gogol', al di l\ue0 da una condizione di irrilevanza che la critica tende ad osservare per questa dimensione, si muovano tutte nella stessa direzione: rallentando, dilatando e nullificando l'esistenza. Una sensazione che viene senza dubbio rappresentata dal singolo momento pietrificato (il vero protagonista temporale del poema) dove la condizione di nullit\ue0 dei protagonisti appare in tutta la sua tragica espressivit\ue0.The purpose of this research is to analyze the various aspects of temporality in the poem of Gogol' "Dead Souls", both through the study of the figures of the time (the history, calendar, clock, etc..) and structures (action time and time of reading) and with the support of important studies carried out by formalists and later. The attention paid to probe the temporal dimension in its various coordinates led to finding some sort of collaboration of the latter. It seems that variants of temporality in the poem of Gogol', far from a condition of irrelevance that critics tend to look for this dimension, all move in the same direction, slows down, nullifying the existence and expanding. A feeling that is undoubtedly represented by the single moment petrified (the real protagonist of the poem time) where the condition of invalidity of the main characters appear in all its tragic expression
Fe-periclase reactivity at Earth's lower mantle conditions: Ab-initio geochemical modelling
Intrinsic and extrinsic stability of the (Mg,Fe)O solid mixture in the Fe-Mg-Si-O system at high P, T conditions relevant to
the Earth\u2019s mantle is investigated by the combination of quantum mechanical calculations (Hartree- 26 Fock/DFT hybrid
scheme), cluster expansion techniques and statistical thermodynamics. Iron in the (Mg,Fe)O binary mixture is assumed to
be either in the low spin (LS) or in the high spin (HS) state. Un-mixing at solid state is observed only for the LS condition
in the 23\u201342 GPa pressure range, whereas HS does not give rise to un-mixing. LS (Mg,Fe)O un-mixings are shown to be able
to incorporate iron by subsolidus reactions with a reservoir of a virtual bridgmanite composition, for a maximum total enrichment
of 0.22 FeO. At very high P (up to 130/3150 GPa/K), a predominant (0.7 phase proportion), iron-rich Fe-periclase
mixture (Mg0.50Fe0.50)O is formed, and it coexists, at constrained phase composition conditions, with two iron-poor assemblages
[(Mg0.90Fe0.10)O and (Mg0.825Fe0.175)O]. These theoretical results agree with the compositional variability and frequency
of occurrence observed in lower mantle Fe-periclase from diamond inclusions and from HP-HT synthesis
products. The density difference among the Fe-periclase phases increases up to 10%, between 24 and 130 GPa. The calculated
bulk Fe/Mg partitioning coefficient between the bridgmanite reservoir and Fe-periclase, Kd, is 0.64 at 24 GPa; it then
drops to 0.19 at 80 GPa, and becomes quasi-invariant (0.18\u20130.16) in the lowermost portion of the Earth\u2019s mantle (80\u2013
130 GPa). These Kd-values represent an approximate estimate for the Fe/Mg-partitioning between actual bridgmanite and
Fe-periclase. Consequently, our Kd-values agree with experimental measurements and theoretical determinations, hinting
that iron preferentially dissolves in periclase with respect to all the other iron-bearing phases of the lower mantle. The continuous
change up to 80 GPa (2000 km depth) of the products (compositions and phase proportions) over the MgO-FeO
binary causes geochemical heterogeneities throughout the lower mantle, but it does not give rise to any sharp discontinuity.
In this view, anomalies like the ULVZs, explained with a local and abrupt change of density, do not seem primarily ascribable
to the mixing behavior and reactivity of (Mg,Fe)O at subsolidus
MSWI fly ash steam washing, aimed to reach a condition of non- hazardous waste and to their possible reuse.
- …