Defensive alliances in graphs: a survey

A set $S$ of vertices of a graph $G$ is a defensive $k$-alliance in $G$ if every vertex of $S$ has at least $k$ more neighbors inside of $S$ than outside. This is primarily an expository article surveying the principal known results on defensive alliances in graph. Its seven sections are: Introduction, Computational complexity and realizability, Defensive $k$-alliance number, Boundary defensive $k$-alliances, Defensive alliances in Cartesian product graphs, Partitioning a graph into defensive $k$-alliances, and Defensive $k$-alliance free sets.Comment: 25 page

Entropy inflection and invisible low-energy states: Defensive alliance example

Lower temperature leads to a higher probability of visiting low-energy states. This intuitive belief underlies most physics-inspired strategies for addressing hard optimization problems. For instance, the popular simulated annealing (SA) dynamics is expected to approach a ground state if the temperature is lowered appropriately. Here, we demonstrate that this belief is not always justified. Specifically, we employ the cavity method to analyze the minimum strong defensive alliance problem and discover a bifurcation in the solution space, induced by an inflection point in the entropy-energy profile. While easily accessible configurations are associated with the lower-free-energy branch, the low-energy configurations are associated with the higher-free-energy branch within the same temperature range. There is a discontinuous phase transition between the high-energy configurations and the ground states, which generally cannot be followed by SA. We introduce an energy-clamping strategy to obtain superior solutions by following the higher-free-energy branch, overcoming the limitations of SA

Estudi bibliomètric any 2014. Campus del Baix Llobregat: EETAC i ESAB

En el present informe s’analitza la producció científica de les dues escoles del Campus del Baix Llobregat, l’Escola d’Enginyeria de Telecomunicació i Aerospacial de Castelldefels (EETAC) i l’Escola Superior d’Agricultura de Barcelona (ESAB) durant el 2014.Postprint (author’s final draft

Textile and clothing industry competitiveness in the Southern African region

This is a study of the relationship between approaches to people management and competitiveness, by examining the case of the textile and clothing industry in Southern Africa. The textile and clothing industry has historically played a major role in many national economies (including many southern African countries) contributing not only to overall economic growth, but also to the creation of significant numbers of relatively well-paid jobs. In the Southern African Region (SAR), the textile and clothing industry has undergone many structural pressures in the face of increased cheap imports from South-East Asian countries – above all, China and Bangladesh - which have resulted in the closure of many firms, and the significant downsizing of many survivors. This study seeks to explore the relationship between HR practice and organizational sustainability in the textile and clothing industry in Southern Africa region, with a particular emphasis on the cases of three countries: South Africa, Mauritius and the Democratic Republic of the Congo. Whilst at very different stages of national development, and with distinct political and developmental histories, all three countries were subject to active industrial policies, including the development of national clothing and textile industries. Again, all have faced the challenge of sustaining these industries in the face of liberalization and intensive competition from the Far East. This study is based on a multi-method approach, combining in-depth interviews with national industry surveys, and the usage of relevant documentary sources. It takes cognizance of the increasing relevance of new HRM practices and discourses to the growing field of Development Studies in the 21st century. The existing HRM literature suggests that there are a number of alternative people management strategies through which firms may secure their competitiveness, most notably strategic approaches to hard HRM (which treats people as an instrument to be strategically deployed to promote competitiveness), soft HRM (which promotes cooperative approaches to managing people) and traditional labour repression (managing people simply as a cost, to be managed in a short-term, un-strategic manner). The literature on HRM in Africa has suggested an alternative paradigm, which combines autocratic paternalism with elements of communitarianism. This study found that the bulk of firms encompassed by the study employed HR policies that recognizably fell within the soft HRM paradigm, enabling high value added production. However, an important exception lies in the area of security of tenure: firms tended to combine high levels of employee involvement and participation; as well as a commitment to human resource development, along with a persistent reliance on the usage of redundancies to adjust changes in the relative need for labour. Hence, this study highlights the limitations of theoretical approaches which see HR strategies as being necessarily coherent and self-reinforcing. Firms may broadly adhere to one approach, whilst adopting aspects of another as needs arise and in response to external pressures. An important exception to this was Mauritius, in which security of tenure appeared to be stronger, perhaps owing to the greater ease of enforcing regulations against illegal imports in a relatively small island country by allowing firms to plan for the future with greater confidence. In contrast, firms in South Africa were characterized by much lower security of tenure, against a backdrop of declining profits, reflecting the competitive challenges posed not only by legitimate low cost imports, but also illegal imports and the proliferation of rural sweatships. One again, this study highlights the relative fragility of the position of many firms and the continued importance of governmental support, most notably in terms of export incentives, support and facilitation in the adoption of new technologies, as well as better policing against illegal imports