Contributors to this issue

Contributors to this issue     

Unemployment Transitions among Brazilians in the United States and Canada

This study uses the job search framework to examine the unemployment experiences of Brazilian immigrants in the North American labour force. Primary data gathered in Canada and the United States is used in these analyses. The model generally used to monitor transitions among the native‐born was modified to make it more appropriate to the immigrant experience. To do this a composite model was constructed that incorporates variables unique to the immigrant experience. Event history analyses revealed that, in general, job search theory is very relevant for examining the transitions of immigrants. However, not all standard measures behaved as predicted (e.g. reservation wage). Several immigrant specific variables were very significant (e.g. target earner and legal status) and improved the overall model fit. Brazilians who worked primarily with other co‐ethnics were more likely to become re‐employed than those who did not, while working for a Brazilian employer had no effect on being re‐employed. US/Canadian comparisons also revealed that residents of Canada endured longer periods of unemployment. We believe this result is because Canadian residents had greater access to public services and, as such, were able to have higher reservation wages.     

The Development of State Welfare in the Asian NICs with Special Reference to Taiwan

This paper explores Taiwan's welfare development from its specific politico-economic situation. Although education and public health are well developed in Taiwan and social insurance is expanding to cover more and more Taiwanese people, the govenmental welfare effort is still too low to meet the welfare needs of the public. This is especially so given our discovery that military servicemen and related groups receive over 70% of the welfare expenditure of the central government while the disadvantaged receive only around 3%. Furthermore, political crises are often accompanied by a significant growth in social expenditure, implying that the purpose of state welfare is to maintain the stability of the Taiwanese state rather than to protect the well-being of Taiwanese people. Political isolation forces the Kuomintang (KMT) to secure Taiwan's role in the international community via economic growth. The development of state welfare cannot be allowed to have a negative effect on this highest priority. The limited resources, therefore, are allocated to economic goals as well as to the KMT–state apparatus in order to keep the KMT in power. However, the democratization of Taiwanese politics since the 1980s has forced the KMT to consolidate its legitimacy from the people and the improvement of social welfare is one measure for this purpose. Whether or not Taiwan becomes a Western-style welfare state through the expansion of state welfare in the near future, it furnishes a useful example with which to examine existing welfare theories.     

Penta-Extensions of Hereditary Classes of Graphs

Penta is the configuration shown in figure 1(a), where continuous lines represent edges and dotted lines represent non-edges. The vertex u in figure 1(a) is called the center of Penta. A graph G is called a pentagraph if every induced subgraph H of G has a vertex v which is not a center of induced Penta in H. The class of pentagraphs is a common generalization of chordal [triangulated] graphs and Mahadev graphs. We construct a polynomial-time algorithm that either find a maximum stable set of G or concludes that G is not a pentagraph. We propose a method for extending α-polynomial hereditary classes based on induced Pentas.     

The 2-Edge-Connected Subgraph Polyhedron

We study the polyhedron P(G) defined by the convex hull of 2-edge-connected subgraphs of G where multiple copies of edges may be chosen. We show that each vertex of P(G) is also a vertex of the LP relaxation. Given the close relationship with the Graphical Traveling Salesman problem (GTSP), we examine how polyhedral results for GTSP can be modified and applied to P(G). We characterize graphs for which P(G) is integral and study how this relates to a similar result for GTSP. In addition, we show how one can modify some classes of valid inequalities for GTSP and produce new valid inequalities and facets for P(G).     

Clustering Binary Oligonucleotide Fingerprint Vectors for DNA Clone Classification Analysis

We considered the problem of clustering binarized oligonucleotide fingerprints that attempts to identify clusters. Oligonucleotide fingerprinting is a powerful DNA array based method to characterize cDNA and rRNA libraries and has many applications including gene expression profiling and DNA clone classification. DNA clone classification is the main application for the problem considered in this paper. Most of the existing approaches for clustering use normalized real intensity values and thus do not treat positive and negative hybridization signals equally. This is demonstrated in a series of recent publications where a discrete approach typically useful in the classification of microbial rRNA clones has been proposed. In the discrete approach, hybridization intensities are normalized and thresholds are set such that a value of 1 represents hybridization, a value of 0 represents no hybridization, and an N represents unknown, which is also called a missing value. A combinatorial optimization problem is then formulated attempting to cluster the fingerprints and resolve the missing values simultaneously. It has been examined that missing values cause much difficulty in clustering analysis and most clustering methods are very sensitive to them. In this paper, we turned a little back to the traditional clustering problem, which takes in no missing values but with the revised goal to stabilize the number of clusters and maintain the clustering quality. We adopted the binarizing scheme used in the discrete approach as it is shown to be typically useful for the clone classifications. We formulated such a problem into another combinatorial optimization problem. The computational complexity of this new clustering problem and its relationships to the discrete approach and the traditional clustering problem were studied. We have designed an exact algorithm for the new clustering problem, which is an A* search algorithm for finding a minimum number of clusters. The experimental results on two commonly tested real datasets demonstrated that the A* search algorithm runs fast and performs better than some popular hierarchical clustering methods, in terms of separating clones that have different characteristics with respect to the given oligonucleotide probes.Supported by NSERC and CFI.Supported by NSERC.Supported partially by NSERC, CFI, and NNSF Grant 60373012.     

Maximizing Profits of Routing in WDM Networks

Let G = (V, E) be a ring (or chain) network representing an optical wavelength division multiplexing (WDM) network with k channels, where each edge e_j has an integer capacity c_j. A request s_i,t_i is a pair of two nodes in G. Given m requests s_i,t_i, i = 1, 2, ..., m, each with a profit value p_i, we would like to design/route a k-colorable set of paths for some (may not be all) of the m requests such that each edge e_j in G is used at most c_j times and the total profit of the set of designed paths is maximized. Here two paths cannot have the same color (channel) if they share some common edge(s).This problem arises in optical communication networks. In this paper, we present a polynomial-time algorithm to solve the problem when G is a chain. When G is a ring, however, the optimization problem is NP-hard (Wan and Liu, 1998), we present a 2-approximation algorithm based on our solution to the chain network. Similarly, some results in a bidirected chain and a bidirected ring are obtained.