1,141 research outputs found
Look before you Hop: Conversational Question Answering over Knowledge Graphs Using Judicious Context Expansion
Fact-centric information needs are rarely one-shot; users typically ask follow-up questions to explore a topic. In such a conversational setting, the user's inputs are often incomplete, with entities or predicates left out, and ungrammatical phrases. This poses a huge challenge to question answering (QA) systems that typically rely on cues in full-fledged interrogative sentences. As a solution, we develop CONVEX: an unsupervised method that can answer incomplete questions over a knowledge graph (KG) by maintaining conversation context using entities and predicates seen so far and automatically inferring missing or ambiguous pieces for follow-up questions. The core of our method is a graph exploration algorithm that judiciously expands a frontier to find candidate answers for the current question. To evaluate CONVEX, we release ConvQuestions, a crowdsourced benchmark with 11,200 distinct conversations from five different domains. We show that CONVEX: (i) adds conversational support to any stand-alone QA system, and (ii) outperforms state-of-the-art baselines and question completion strategies
Bragg Polaritons: Strong Coupling and Amplification in an Unfolded Microcavity
Periodic incorporation of quantum wells inside a one--dimensional Bragg
structure is shown to enhance coherent coupling of excitons to the
electromagnetic Bloch waves. We demonstrate strong coupling of quantum well
excitons to photonic crystal Bragg modes at the edge of the photonic bandgap,
which gives rise to mixed Bragg polariton eigenstates. The resulting Bragg
polariton branches are in good agreement with the theory and allow
demonstration of Bragg polariton parametric amplification.Comment: 4 pages, 4 figure
Efficient Contextualization using Top-k Operators for Question Answering over Knowledge Graphs
Answering complex questions over knowledge bases (KB-QA) faces huge input data with billions of facts, involving millions of entities and thousands of predicates. For efficiency, QA systems first reduce the answer search space by identifying a set of facts that is likely to contain all answers and relevant cues. The most common technique or doing this is to apply named entity disambiguation (NED) systems to the question, and retrieve KB facts for the disambiguated entities. This work presents CLOCQ, an efficient method that prunes irrelevant parts of the search space using KB-aware signals. CLOCQ uses a top-k query processor over score-ordered lists of KB items that combine signals about lexical matching, relevance to the question, coherence among candidate items, and connectivity in the KB graph. Experiments with two recent QA benchmarks for complex questions demonstrate the superiority of CLOCQ over state-of-the-art baselines with respect to answer presence, size of the search space, and runtimes
Conversational Question Answering on Heterogeneous Sources
Conversational question answering (ConvQA) tackles sequential informationneeds where contexts in follow-up questions are left implicit. Current ConvQAsystems operate over homogeneous sources of information: either a knowledgebase (KB), or a text corpus, or a collection of tables. This paper addressesthe novel issue of jointly tapping into all of these together, this wayboosting answer coverage and confidence. We present CONVINSE, an end-to-endpipeline for ConvQA over heterogeneous sources, operating in three stages: i)learning an explicit structured representation of an incoming question and itsconversational context, ii) harnessing this frame-like representation touniformly capture relevant evidences from KB, text, and tables, and iii)running a fusion-in-decoder model to generate the answer. We construct andrelease the first benchmark, ConvMix, for ConvQA over heterogeneous sources,comprising 3000 real-user conversations with 16000 questions, along with entityannotations, completed question utterances, and question paraphrases.Experiments demonstrate the viability and advantages of our method, compared tostate-of-the-art baselines.<br
Oriented polaritons in strongly-coupled asymmetric double quantum well microcavities
Replacing independent single quantum wells inside a strongly-coupled
semiconductor microcavity with double quantum wells produces a special type of
polariton. Using asymmetric double quantum wells in devices processed into
mesas allows the alignment of the electron levels to be voltage-tuned. At the
resonant electronic tunnelling condition, we demonstrate that `oriented
polaritons' are formed, which possess greatly enhanced dipole moments. Since
the polariton-polariton scattering rate depends on this dipole moment, such
devices could reach polariton lasing, condensation and optical nonlinearities
at much lower threshold powers.Comment: 3 figure
Response of a catalytic reaction to periodic variation of the CO pressure: Increased CO_2 production and dynamic phase transition
We present a kinetic Monte Carlo study of the dynamical response of a
Ziff-Gulari-Barshad model for CO oxidation with CO desorption to periodic
variation of the CO presure. We use a square-wave periodic pressure variation
with parameters that can be tuned to enhance the catalytic activity. We produce
evidence that, below a critical value of the desorption rate, the driven system
undergoes a dynamic phase transition between a CO_2 productive phase and a
nonproductive one at a critical value of the period of the pressure
oscillation. At the dynamic phase transition the period-averged CO_2 production
rate is significantly increased and can be used as a dynamic order parameter.
We perform a finite-size scaling analysis that indicates the existence of
power-law singularities for the order parameter and its fluctuations, yielding
estimated critical exponent ratios and . These exponent ratios, together with theoretical symmetry
arguments and numerical data for the fourth-order cumulant associated with the
transition, give reasonable support for the hypothesis that the observed
nonequilibrium dynamic phase transition is in the same universality class as
the two-dimensional equilibrium Ising model.Comment: 18 pages, 10 figures, accepted in Physical Review
Influence of multi-exciton correlations on nonlinear polariton dynamics in semiconductor microcavities
Using two-dimensional spectroscopy, we resolve multi-polariton coherences in quantum wells embedded inside a semiconductor microcavity and elucidate how multi-exciton correlations mediate polariton nonlinear dynamics. We find that polariton correlation strengths depend on spectral overlap with the biexciton resonance and that up to at least four polaritons can be correlated, a higher-order correlation than observed to date among excitons in bare quantum wells. The high-order correlations can be attributed to coupling through the cavity mode, although the role of high-order Coulomb correlations cannot be excluded
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