Subset sum problems with digraph constraints

We introduce and study optimization problems which are related to the well-known Subset Sum problem. In each new problem, a node-weighted digraph is given and one has to select a subset of vertices whose total weight does not exceed a given budget. Some additional constraints called digraph constraints and maximality need to be satisfied. The digraph constraint imposes that a node must belong to the solution if at least one of its predecessors is in the solution. An alternative of this constraint says that a node must belong to the solution if all its predecessors are in the solution. The maximality constraint ensures that no superset of a feasible solution is also feasible. The combination of these constraints provides four problems. We study their complexity and present some approximation results according to the type of input digraph, such as directed acyclic graphs and oriented trees.     

Reclaiming the future: (In)visible dirt borders in Sammy Baloji’s mining photomontages

ABSTRACT

This paper analyses how Baloji’s photographic work Essay on Urban Planning and Mémoire/Kolwezi rely on the dialectic of visibility/invisibility of mining dirt to reveal similarities as well as discrepancies between past and present in capital and labour flows. Conflating archives of humans on display and photographs of abandoned mining sites, Baloji’s figurations of mining dirt unravel how perceptions of dirt were used by the colonial system to impose geographies of exclusion that have become invisible. While they expose how postindependence Congo has failed to appropriate its resources, Baloji’s images of artisanal miners working with mining dirt further epitomise how the disposable objects (often dematerialised via the web) consumed in rich nations involve the disposable lives of workers in the Congo within material dirt borders one can no longer see.     

The Residential Mobility of Seniors Among Different Residential Forms: Analysis of Metropolitan and Rural Issues for Six Contrasted Regions in Québec,Canada

The purpose of this research is to describe and analyze the residential mobility of senior citizens, between 2006 and 2011, among different residential forms in rural and metropolitan areas in the province of Quebec (Canada). A systematic analysis of residential form variability in territories that include both metropolitan and rural areas is performed. First, a typology of residential forms is proposed using a principal component analysis and a hierarchical cluster analysis on environment-related and housing variables. Second, the residential mobility of seniors among these different residential forms is analyzed. The results reveal a certain amount of residential stability among seniors, except where specific conditions are met, such as the death of a spouse or the onset of health problems limiting day-to-day activities. For those who moved, high-rise habitat areas and mixed areas with older rental apartments held the greatest attraction. However, suburban areas attracted the largest number of seniors because these areas account for a sizeable portion of the real estate market.     

From Foster Care to Adoption and Guardianship: A Twenty-First Century Challenge

For nearly four decades, child welfare policy and practice have focused on the achievement of legal permanence for children in foster care. Although federal child welfare policy has resulted in the movement of children from state custody to legally permanent adoptive or guardianship families, little is known about the quality and enduring nature of these placements. A significant challenge of the twenty-first century child welfare system is how to ensure the well-being of children currently living with adoptive parents or guardians. This paper discusses child welfare policy and trends related to post-permanency well-being, including the decrease in Title IV-E foster care caseloads nationwide and the simultaneous increase in Title IV-E adoptive and guardianship caseloads. We highlight the needs of a twenty-first century child welfare system, including increased federal efforts to ensure child permanence and well-being after legal adoption or guardianship has been achieved, as well as more rigorous longitudinal and interdisciplinary research focused on the post-permanency adjustment of children and their families.     

Participatory Art as a Social Practice of Commoning to Reinvent the Right to the City

The right to the city is a concept that helps rethink spatial–social dynamics, which has recently reinvigorated the field of organization studies. Following Lefebvre and considering the failure of both the market and the state, other scholars pinpoint the need to rethink social–spatial and geographical–historical relations. They do so by theorizing the city as a host for urban commons. Collective and non-commodified, these spatial–social experiences need to be constantly reproduced and preserved through commoning practices in the struggle against spatial injustice. A case study shows that a civil society organization (CSO) uses participatory art to (re)produce urban commons at the level of a local community and to redress partially spatial injustice. We theorize participatory art-making as a social practice of commoning, i.e., a process of organizing for the commons—collective art-based activities to serve a community—and of the common—to (re)produce a community while performing them. Such commoning practices are not only about sharing urban resources but also about using and experiencing differently urban spaces. By making participatory artworks in public spaces and co-designing street furniture with residents of poor areas, TDA helps to better cope with the tensions between residents and local authorities and between amateurs and professional artists. By negotiating the long-term implementation of these creative artworks in the public space with public authorities, TDA has fostered the empowerment of inhabitants as they have experienced citizens’ reappropriation of some public spaces in Marseille.     

‘Are we to become a gender university?’ Facets of resistance to a gender equality project

Gender equality (GE) is something ‘we cannot not want’. Indeed, the pursuit of equal rights, responsibilities and opportunities for all women and men throughout a society freed from gendered oppression is widely visible in recent organizational GE initiatives. In practice, however, GE initiatives often fail in challenging gendered norms and at effecting deep‐seated change. In fact, GE measures tend to encounter resistance, with a gap between saying and doing. Using a GE project at a Swedish university, we examined the changing nature of reactions to GE objectives seeking to understand why gender inequality persists in academia. We used ‘resistance’ to identify multiple, complex reactions to the project, focusing on the discursive practices of GE. Focusing our contextual analysis on change and changes in reactions enabled a process‐oriented analysis that revealed gaps where change is possible. Thus, we argue that studying change makes it possible to identify points in time where gendered discriminatory norms are more likely to occur. However, analysing discursive practices does not itself lead to change nor to action. Rather, demands for change must start with answering, in a collaborative way, what problem we are trying to solve when we start a new GE project, in order to be relevant to the specific context. Otherwise, GE risks being the captive of consensus politics and gender inequality will persist.     

A simple two-stage design for quantitative responses with application to a study in diabetic neuropathic pain

Two-stage designs offer substantial advantages for early phase II studies. The interim analysis following the first stage allows the study to be stopped for futility, or more positively, it might lead to early progression to the trials needed for late phase II and phase III. If the study is to continue to its second stage, then there is an opportunity for a revision of the total sample size. Two-stage designs have been implemented widely in oncology studies in which there is a single treatment arm and patient responses are binary. In this paper the case of two-arm comparative studies in which responses are quantitative is considered. This setting is common in therapeutic areas other than oncology. It will be assumed that observations are normally distributed, but that there is some doubt concerning their standard deviation, motivating the need for sample size review. The work reported has been motivated by a study in diabetic neuropathic pain, and the development of the design for that trial is described in detail.     

The generalized log-gamma mixture model with covariates: local influence and residual analysis

In a sample of censored survival times, the presence of an immune proportion of individuals who are not subject to death, failure or relapse, may be indicated by a relatively high number of individuals with large censored survival times. In this paper the generalized log-gamma model is modified for the possibility that long-term survivors may be present in the data. The model attempts to separately estimate the effects of covariates on the surviving fraction, that is, the proportion of the population for which the event never occurs. The logistic function is used for the regression model of the surviving fraction. Inference for the model parameters is considered via maximum likelihood. Some influence methods, such as the local influence and total local influence of an individual are derived, analyzed and discussed. Finally, a data set from the medical area is analyzed under the log-gamma generalized mixture model. A residual analysis is performed in order to select an appropriate model. The authors would like to thank the editor and referees for their helpful comments. This work was supported by CNPq, Brazil.     

A copula-based Markov chain model for the analysis of binary longitudinal data

A fully parametric first-order autoregressive (AR(1)) model is proposed to analyse binary longitudinal data. By using a discretized version of a copula, the modelling approach allows one to construct separate models for the marginal response and for the dependence between adjacent responses. In particular, the transition model that is focused on discretizes the Gaussian copula in such a way that the marginal is a Bernoulli distribution. A probit link is used to take into account concomitant information in the behaviour of the underlying marginal distribution. Fixed and time-varying covariates can be included in the model. The method is simple and is a natural extension of the AR(1) model for Gaussian series. Since the approach put forward is likelihood-based, it allows interpretations and inferences to be made that are not possible with semi-parametric approaches such as those based on generalized estimating equations. Data from a study designed to reduce the exposure of children to the sun are used to illustrate the methods.     

Bayesian robustness of the compound Poisson distribution under bidimensional prior: an application to the collective risk model

The distribution of the aggregate claims in one year plays an important role in Actuarial Statistics for computing, for example, insurance premiums when both the number and size of the claims must be implemented into the model. When the number of claims follows a Poisson distribution the aggregated distribution is called the compound Poisson distribution. In this article we assume that the claim size follows an exponential distribution and later we make an extensive study of this model by assuming a bidimensional prior distribution for the parameters of the Poisson and exponential distribution with marginal gamma. This study carries us to obtain expressions for net premiums, marginal and posterior distributions in terms of some well-known special functions used in statistics. Later, a Bayesian robustness study of this model is made. Bayesian robustness on bidimensional models was deeply treated in the 1990s, producing numerous results, but few applications dealing with this problem can be found in the literature.