Facets for Art Gallery Problems

The Art Gallery Problem (AGP) asks for placing a minimum number of stationary guards in a polygonal region P, such that all points in P are guarded. The problem is known to be NP-hard, and its inherent continuous structure (with both the set of points that need to be guarded and the set of points that can be used for guarding being uncountably infinite) makes it difficult to apply a straightforward formulation as an Integer Linear Program. We use an iterative primal-dual relaxation approach for solving AGP instances to optimality. At each stage, a pair of LP relaxations for a finite candidate subset of primal covering and dual packing constraints and variables is considered; these correspond to possible guard positions and points that are to be guarded. Particularly useful are cutting planes for eliminating fractional solutions. We identify two classes of facets, based on Edge Cover and Set Cover (SC) inequalities. Solving the separation problem for the latter is NP-complete, but exploiting the underlying geometric structure, we show that large subclasses of fractional SC solutions cannot occur for the AGP. This allows us to separate the relevant subset of facets in polynomial time. We also characterize all facets for finite AGP relaxations with coefficients in {0, 1, 2}. Finally, we demonstrate the practical usefulness of our approach. Our cutting plane technique yields a significant improvement in terms of speed and solution quality due to considerably reduced integrality gaps as compared to the approach by Kr\"oller et al.Comment: 29 pages, 18 figures, 1 tabl

Code-switching within the noun phrase: Evidence from three corpora

　 Aims and objectives/purpose/research questions: This study aims to improve our understanding of common switching patterns by examining determiner–noun–adjective complexes in code-switching (CS) in three language pairs (Welsh–English, Spanish–English and Papiamento–Dutch). The languages differ in gender and noun–adjective word order in the noun phrase (NP): (a) Spanish, Welsh, and Dutch have gender; English and Papiamento do not; (b) Spanish, Welsh, and Papiamento prefer post-nominal adjectives; Dutch and English, prenominal ones. We test predictions on determiner language and adjective order derived from generativist accounts and the Matrix Language Frame (MLF) approach. Design/methodology/approach: We draw on three publicly available spoken corpora. For the purposes of these analyses, we re-coded all three datasets identically. From the three re-coded corpora we extracted all monolingual and mixed simplex NPs (DetN) and complex NPs with determiners (determiner–adjective–noun (DetAN/NA)). We then examined the surrounding clause for each to determine the matrix language based on the finite verb. Data and analysis: We analysed the data using a linear regression model in R statistical software to examine the distribution of languages across word class and word order in the corpora. Findings/conclusions: Overall, the generativist predictions are borne out regarding adjective positions but not determiners and the MLF accounts for more of the data. We explore extra-linguistic explanations for the patterns observed. Originality: The current study has provided new empirical data on nominal CS from language pairs not previously considered. Significance/implications: This study has revealed robust patterns across three corpora and taken a step towards disentangling two theoretical accounts. Overall, the findings highlight the importance of comparing multiple language pairs using similar coding.Theoretical and Experimental Linguistic

El book or the libro? Insights from acceptability judgments into determiner/noun code-switches

Objectives/research questions:We used two types of acceptability judgments to experimentally test the predictions of two theoretical models of code-switching regarding the surface realization of the determiner in nominal constructions: lexicalist approaches within the Minimalist Program (MP) versus the Bilingual NP Hypothesis within the Matrix Language Frame Model (MLF).Methodology:Two separate groups of 40 early Spanish-English bilinguals evaluated the acceptability of sentences with code-switches between the determiner and the noun that reflected the predictions of the MP model, the MLF, of both or none. The first group rated them on a Likert scale, while the second group performed a two-alternative forced-choice acceptability task (2AFC).Data and analysis:Ratings from the Likert ratings were subjected to an analysis of variance while results from the 2AFC were analyzed using Thurstone’s Law of Comparative Judgment.Conclusions:Both experiments yielded converging evidence supporting the predictions of the MLF. Results from the 2AFC provided a more detailed picture that suggests also a (smaller) contribution of the language of the determiner.Originality:This is the first study to use acceptability judgments to directly contrast the predictions of these major theoretical models regarding switches between determiner and noun. An additional novelty is the use of the 2AFC and Thurstone’s Law of Comparative Judgment, which yielded a more detailed picture than the more commonly used Likert-scale ratings.Implications:Our results provide further support for Eppler, Luescher, and Deuchar’s recent claim that we can only advance our understanding of grammaticality in code-switching if we combine the insights of the different frameworks rather than considering them in isolation.Theoretical and Experimental Linguistic

Contrasting code-switching theories: insights from Kaqchikel-Spanish code-switched nominal constructions

Theoretical and Experimental Linguistic

Mortality due to violence: application of exploratory analysis techniques on data from an urban area of southeastern Brazil, 1979-1987

An exploratory analysis of gross death rates due to external reasons was carried out in the area of the "Baixada Fluminense", and in the Rio de Janeiro city, covering the 1979 -1987 period. The main goal was to verify mortality trends in the area and period of time specified, in an attempt to investigate a premiss according to wich violence rates have been increasing. Results obtained have show that death rates presented tendency to a non-linear increase throughout this period. A decrease was observed from 1979 to 1983, followed by an increase, since 1984, on to a higher level.Realizou-se análise exploratória das taxas brutas de mortalidade por causas externas, nos municípios da Baixada Fluminense e no Município do Rio de Janeiro, Brasil, no período de 1979 a 1987. Objetivou-se verificar a tendência da mortalidade na área e período especificados para investigar a premissa de que a violência vem crescendo. Os resultados obtidos mostraram que as taxas de mortalidade apresentaram tendência de crescimento não linear ao longo de todo o período. Observou-se decréscimo de 1979 a 1983, seguido de crescimento a partir de 1984 quando as taxas atingem patamares mais elevados

The Messinian Salinity Crisis in the Dacic Basin (SW Romania) and early Zanclean Mediterranean-Eastern Paratethys high sea-level connection

International audienceNew field observations and fossil analyses complete and clarify the strong impact of the Mediterranean sea-level changes linked to the peak of the Messinian Salinity Crisis on the Dacic Basin in southwestern Romania. In addition to the Gilbert-type fan delta already evidenced along the Danube River in the area of Turnu Severin, a new Gilbert-type fan delta is described northward. Early Zanclean bottomset beds are evidenced and dated based on nannofossils at the junction of the two coalescing Gilbert-type fan deltas. A clear sedimentological, morphological and chronologic differentiation is established in the area between the Carpathians Late Miocene piedmont alluvial fans and the early Zanclean Gilbert-type fan deltas. The early Zanclean age of the Hinova clays, where the bottomset beds of the Gilbert-type fan deltas are mostly developed, is confirmed by the occurrence of nannofossil markers of Subzone NN12b and a Bosphorian mollusk macrofauna. Early Zanclean inflow of Mediterranean marine waters into the Dacic Basin is also supported by the record of planktonic foraminifers. In the Dacic Basin, the Messinian Salinity Crisis resulted in the cutting of the Iron Gates by a Carpathians river. Fluvial erosion also affected the residual Pannonian Basin and probably catched the paleo-Tisza River which contributed to the erosion of the Iron Gates and to the fluvial drainage of the partly desiccated Dacic Basin. Arguments are reinforced in favor of a marine gateway between the Mediterranean and Dacic Basin through the Balkans before and after the Messinian Salinity Crisis

Search for heavy neutrinos mixing with tau neutrinos

We report on a search for heavy neutrinos (\nus) produced in the decay D_s\to \tau \nus at the SPS proton target followed by the decay \nudecay in the NOMAD detector. Both decays are expected to occur if \nus is a component of $\nu_{\tau}$.\ From the analysis of the data collected during the 1996-1998 runs with $4.1\times10^{19}$ protons on target, a single candidate event consistent with background expectations was found. This allows to derive an upper limit on the mixing strength between the heavy neutrino and the tau neutrino in the \nus mass range from 10 to 190 $\rm MeV$. Windows between the SN1987a and Big Bang Nucleosynthesis lower limits and our result are still open for future experimental searches. The results obtained are used to constrain an interpretation of the time anomaly observed in the KARMEN1 detector.\Comment: 20 pages, 7 figures, a few comments adde