The QAP-polytope and the graph isomorphism problem

In this paper we propose a geometric approach to solve the Graph Isomorphism (GI in short) problem. Given two graphs \(G_1, G_2\), the GI problem is to decide if the given graphs are isomorphic i.e., there exists an edge preserving bijection between the vertices of the two graphs. We propose an Integer Linear Program (ILP) that has a non-empty solution if and only if the given graphs are isomorphic. The convex hull of all possible solutions of the ILP has been studied in literature as the Quadratic Assignment Problem (QAP) polytope. We study the feasible region of the linear programming relaxation of the ILP and show that the given graphs are isomorphic if and only if this region intersects with the QAP-polytope. As a consequence, if the graphs are not isomorphic, the feasible region must lie entirely outside the QAP-polytope. We study the facial structure of the QAP-polytope with the intention of using the facet defining inequalities to eliminate the feasible region outside the polytope. We determine two new families of facet defining inequalities of the QAP-polytope and show that all the known facet defining inequalities are special instances of a general inequality. Further we define a partial ordering on each exponential sized family of facet defining inequalities and show that if there exists a common minimal violated inequality for all points in the feasible region outside the QAP-polytope, then we can solve the GI problem in polynomial time. We also study the general case when there are k such inequalities and give an algorithm for the GI problem that runs in time exponential in k.     

Les différences de salaire au sein de l'Union européenne

Les auteurs recherchent les déterminants des écarts salariaux au sein de l'Union européenne selon la position dans la distribution des salaires, suivant en cela la méthode proposée par Firpo, Fortin et Lemieux (2009) et par Fortin, Lemieux et Firpo (2011). Ils expliquent ces écarts à la fois par un effet de composition et par un effet de structure. Ce dernier effet, plus puissant, dépend surtout des facteurs non observés, alors que l'effet de composition peut ětre attribué principalement au niveau de diplôme, à la profession, à la fréquence des fonctions d'encadrement et, dans une moindre mesure, au secteur d'activité.     

Un-American: Latina high school students’ testimonios of American and white conflation in the middle of nowhere

Abstract

Using a combination of counter-storytelling, testimonios, and Chicana feminist epistemology, I report on the findings of an ethnographic study that explores and analyzes the educational experiences of geographically isolated Latina high school students in a rural city in Wyoming. I demonstrate the labeling of these students by peers and teachers as ‘Un-American’ and the ways in which such a label is embedded in intersecting hegemonic discourses of whiteness, rurality and nationhood. It is through such labeling that white privilege is established and maintained and the immediate and future educational biographies of Latina/o students highly circumscribed.     

Single Parenting and Child Behavior Problems in Kindergarten

Two waves of data from a sample of 89 poor and near-poor single black mothers and their preschool children were used to study the influences of parenting stress, physical discipline practices, and nonresident fathers’ relations with their children on behavior problems in kindergarten. The results indicate that higher levels of parent stress, more frequent spanking, and less frequent father–child contact at time 1 were associated with increased teacher-reported behavior problems at time 2. In addition, more frequent contact between nonresident biological fathers and their children moderated the negative effect of harsh discipline by mothers on subsequent child behavior problems. Specifically, when contact with the father was low, maternal spanking resulted in elevated levels of behavior problems; with average contact, this negative effect of spanking was muted; and with high contact, spanking was not associated with increased behavior problems in kindergarten. The implications of these findings for future research and policy are discussed.     

Catalog competition: Theory and experimental evidence

This paper compares the standard location-then-pricing Hotelling duopoly with a catalog competition game in which firms simultaneously decide locations and prices. We consider a three-location space and continuous pricing and fully characterize the unique symmetric equilibrium. In both games, firms employ mixed strategies, producing a mainstream product more often than a specialized one. In the catalog game, prices are always above the marginal cost of production, whereas in the sequential model, prices converge to the marginal cost when firms produce the same variety. We experimentally test our theoretical predictions in the laboratory, finding strong evidence in favor of most of them.     

Fathers' involvement and child behavior problems in poor African American single-mother families

The present study examined the effects of nonresident fathers' involvement-measured by the frequency of fathers' contact with their children and the quality of fathers' parenting-on their children's behavior problems. Using data from a subsample of African American single and non-cohabiting mothers from the Fragile Families and Child Wellbeing study, results indicate that more frequent contact between fathers and their child and fathers' more adequate parenting were associated indirectly with fewer child behavior problems transmitted through more adequate parenting by mothers. The quality of mothers' parenting was associated positively with the quality of the mother-father relationship and with both the quality and the frequency of the fathers' contacts with their child. Policy and practice implications are discussed.     

A Weighted Multidimensional Index of Child Well-Being Which Incorporates Children’s Individual Perceptions

It has been a decade since a landmark piece of work on child well-being measurement based on a summary index was developed in the United States, the Index of Child and Youth Well-Being. Several research studies, both in the U.S. and Europe, followed on from this work. Despite these studies’ valuable contribution, scope exists for further improvements at the methodological level. In the present paper we draw the methodological basis for a new, micro-based summary child well-being index in which children’s views on their own well-being assume a central role and distinct weights (based on the children’s perceptions) to each component that is included in the index are used. Based on 914 pairs of responses of Portuguese children and their carers, the newly proposed index was tested vis-à-vis other methodologies. The econometric estimations show that the significance of all potential well-being determinants (e.g., age, school cycle, mother’s and father’s level of education) remains the same across the distinct methods of calculation of child well-being indexes. However, the consideration of subjective components (degrees of importance and weights) allowed to evidence that the most relevant determinants of child well-being are the set of variables related to the child’s parents, namely education and professional status. In particular, when compared to their counterparts, children whose fathers have higher education degrees reveal an increased overall well-being by around 25 %, whereas children whose fathers are unemployed present a decreased well-being by around 11 %.     

Single Mothers,Nonresident Fathers,and Preschoolers’ Socioemotional Development: Social Support,Psychological Well-Being,and Parenting Quality

ABSTRACT

Using data from two waves of a short-term longitudinal study, the influences of mothers’ social support with respect to parenting from nonresident fathers and significant others on behavioral outcomes among poor and near-poor preschool-aged Black children were examined. The sample consisted of 99 single Black mothers—each with a preschool-aged child (ages 3 and 5 years old, respectively, at Time 1 and Time 2)—who were current and former welfare recipients. Results revealed protective effects of nonresident fathers’ presence in the context of mothers’ parenting stress and depressive symptoms at Time 1 that appeared to operate through decreases in the negative influences of these variables on the children's development of behavior problems 1.5 to 2 years later. Greater availability of instrumental support from significant others, including nonresident fathers, was associated with more adequate parenting at Time 1, and through the latter, with fewer child behavior problems at Time 2. Implications of these findings for program and policy interventions are discussed. Nonresident fathers are described in the Appendix.     

The intellectual and scientific basis of science,technology and innovation research

There has been a considerable increase in the literature devoted to innovation in the past few decades. This research area is characterized by prolific interdisciplinary connections and no single domain is able to embrace all aspects of science, technology and innovation. By analyzing nearly 60,000 references included in the 1442 articles published between 1974 and 2007 in the area's seed journal, Research Policy (RP), we have uncovered the following patterns: (1) the most important sources of knowledge are associated with “core” economics (mostly mainstream) and management sources, even though the importance of innovation-related sources has been rising; (2) the degree of autonomy of science, technology and innovation research is still weak, revealing its incipience and lack of a unified theoretical framework; (3) the most influential authors and studies follow heterodox approaches, namely the evolutionary approach (e.g. Richard R. Nelson) and the European approach to innovation (e.g. Keith Pavitt and Chris Freeman), although it is rather surprising that one of the most widely recognized founding fathers of innovation-related studies, Joseph Schumpeter, is absent from the top-10 cited authors list; and (4) the ranking of the most influential studies highlights the relevance of the evolutionary paradigm, with its focus on the capabilities and routines of firms, and the policy-driven nature of topics, evidencing the pervasiveness of the literature on the National System of Innovation.     

Nonresident Fathers’ Parenting,Maternal Mastery and Child Development in Poor African American Single-Mother Families

This study examines the relationships between and among economic hardship, mothers’ depressive symptoms, nonresident fathers’ parenting, mothers’ parenting and mastery, and their children’s behavioral and cognitive development in poor African American single-mother families. Informed by stress-coping and family process theoretical perspectives, this study estimates the effects of nonresident fathers’ parenting and maternal mastery on child developmental outcomes. Analyses use the first three waves of longitudinal data from a subsample of single, African American and noncohabiting mothers with low income in the Fragile Families and Child Wellbeing Study. Results suggest that nonresident fathers’ parenting is indirectly associated with children’s behavior problems and cognitive development transmitted through mothers’ parenting and mastery. Maternal mastery is also found to be one of the most influential predictors of both developmental outcomes of children. Policy and practice implications of these findings are discussed.