New and simple algorithms for stable flow problems

Stable flows generalize the well-known concept of stable matchings to markets in which transactions may involve several agents, forwarding flow from one to another. An instance of the problem consists of a capacitated directed network, in which vertices express their preferences over their incident edges. A network flow is stable if there is no group of vertices that all could benefit from rerouting the flow along a walk. Fleiner established that a stable flow always exists by reducing it to the stable allocation problem. We present an augmenting-path algorithm for computing a stable flow, the first algorithm that achieves polynomial running time for this problem without using stable allocation as a black-box subroutine. We further consider the problem of finding a stable flow such that the flow value on every edge is within a given interval. For this problem, we present an elegant graph transformation and based on this, we devise a simple and fast algorithm, which also can be used to find a solution to the stable marriage problem with forced and forbidden edges. Finally, we study the stable multicommodity flow model introduced by Kir\'{a}ly and Pap. The original model is highly involved and allows for commodity-dependent preference lists at the vertices and commodity-specific edge capacities. We present several graph-based reductions that show equivalence to a significantly simpler model. We further show that it is NP-complete to decide whether an integral solution exists

Summarizing online user reviews using bicliques

With vast amounts of text being available in electronic format, such as news and social media, automatic multi-document summarization can help extract the most important information. We present and evaluate a novel method for automatic extractive multi-document summarization. The method is purely combinatorial, based on bicliques in the bipartite word-sentence occurrence graph. It is particularly suited for collections of very short, independently written texts (often single sentences) with many repeated phrases, such as customer reviews of products. The method can run in subquadratic time in the number of documents, which is relevant for the application to large collections of documents

Popular edges and dominant matchings

Given a bipartite graph G=(A B, E) with strict preference lists and given an edge e E, we ask if there exists a popular matching in G that contains e. We call this the popular edge problem. A matching M is popular if there is no matching M' such that the vertices that prefer M' to M outnumber those that prefer M to M'. It is known that every stable matching is popular; however G may have no stable matching with the edge e. In this paper we identify another natural subclass of popular matchings called "dominant matchings" and show that if there is a popular matching that contains the edge e, then there is either a stable matching that contains e or adominant matching that contains e. This allows us to design a linear time algorithm for identifying the set of popular edges. When preference lists are complete, we show an O(n3) algorithm to find a popular matching containing a given set of edges or report that none exists, where n = |A| + |B|

Prevalência e fatores associados à prematuridade entre gestantes submetidas à inibição de trabalho de parto prematuro Prevalence and risk factors associated to preterm delivery among pregnant women submitted to preterm labor inhibition treatment

OBJETIVOS: identificar a prevalência de parto prematuro em gestantes submetidas ao tratamento de inibição de trabalho de parto prematuro e analisar os fatores associados. MÉTODOS: estudo transversal, com dados coletados de 163 prontuários de gestantes submetidas a tratamento de inibição de trabalho de parto prematuro atendidas em 1995-2000, no Hospital Universitário da Universidade de São Paulo, Brasil. A variável dependente constituiu-se na ocorrência de parto prematuro e as independentes foram: idade, escolaridade, ocupação, paridade, companheiro, tabagismo, infecção urinária prévia, número de consultas pré-natal e intervalo interpartal. A análise foi feita pelo teste de associação pelo Qui-quadrado e modelos de regressão logística univariado e múltiplo. RESULTADOS: 66,3% das gestantes tiveram filhos prematuros e, em 22,7% dos casos, o parto ocorreu antes de 34 semanas. Houve associação estatística significativa entre parto prematuro e ser nulípara e apresentar número baixo de consultas pré-natal. CONCLUSÕES: atenção especial deve ser dada às gestantes nulíparas e com número reduzido de consulta pré-natal submetidas ao tratamento de inibição de trabalho de parto prematuro, com a finalidade de prevenir esse evento.<br>OBJECTIVES: to identify preterm delivery prevalence in pregnant women submitted to preterm delivery inhibition treatment and to analyze associated factors. METHODS: cross sectional study with data collected from 163 pregnant women medical files seen from 1995-2000 at the University Hospital of the University of São Paulo, Brazil. The dependent variable was preterm delivery and the independent ones were: age, education, job, parity, companion, smoking, prior urinary infection, number of prenatal medical visits and birth interval. Analysis was performed through association by the Chi-square test and univariate and multiple logistic regression models. RESULTS: 66.3% of the women had preterm deliveries and in 22.7% of the cases, delivery occurred before 34 weeks. There was a statistically significant association between preterm birth and no partner, nulliparity and a low number of prenatal visits. CONCLUSIONS: special attention should be given to nulliparous pregnant women with reduced numbers of prenatal medical visits submitted to preterm delivery inhibition treatment with the objective of preventing premature births

Comparação do desenvolvimento motor de lactentes de mães adolescentes e adultas Motor development comparison between infants of adolescent and adult mothers

Este estudo objetivou caracterizar o desempenho motor de bebês de 0 a 16 meses, comparando o de bebês nascidos de mães adolescentes ao de bebês de mães adultas. Participaram 80 bebês, sendo 40 de mães adolescentes e 40 de mães adultas. Os instrumentos avaliativos foram a escala motora infantil de Alberta AIMS (Alberta infant motor scale) e questionário para identificar as características biológicas. Os dados foram analisados estatisticamente. Os resultados da AIMS mostram pior desempenho motor dos bebês de mães adolescentes (p=0,002; p=0,001), além de suas inadequadas aquisições motoras nas posturas prono e em pé. Não foi encontrada associação significativa entre a maioria dos fatores biológicos analisados e o desenvolvimento motor dos bebês. Os resultados sugerem que a idade materna pode ser considerada fator de risco para atraso motor em crianças, porém ressalta-se a interação de diferentes fatores, aqui não controlados, influenciando as aquisições motoras de crianças, tais como as demandas da tarefa e as condições do ambiente.<br>The purpose of the study was to compare motor development of infants aged 0 to 16 months born of teenage mothers to those of adult mothers. Eighty babies were assessed, 40 of which the children of teenage mothers, and 40 of adult mothers. Instruments used were the Alberta infant motor scale (AIMS) and a questionnaire to collect biological information. Data were statistically analysed. Results show teenage mothers' infants to have delayed motor development as compared to adult mothers' ones (p=0.002; p=0.001), as well as their poor motor acquisitions in prone and standing positions. No association was found between infants' motor development and most of the biological factors analysed. Results hence suggest that early maternal age may be considered a risk factor to motor delay in infants, but attention should be paid to other factors such as task requirements and environmental conditions (here not controlled) that may influence the pace of motor acquisition in infants