Levels of reality: portraiture in African art

African Studies Center Working Paper No. 3

Pacific Islands' Bilateral Trade: The Role of Remoteness and of Transport Costs

Bilateral trade of geographically distant countries is likely to be negatively affected by the distance separating them from their trading partners and positively affected by their remoteness, defined as the average weighted distance between two countries with weights reflecting the absorptive capacity of the partner country. In presence of competitive transport costs, the effect of remoteness and distance is diluted. An augmented gravity model applied to the Pacific islands' bilateral trade from 1980 to 2004 shows that a doubling of the elasticity of distance would decrease their average bilateral trade by 80 per cent. Remoteness positively affects the Pacific islands' bilateral trade, but does not compensate for the negative effect of distance. The opposite is found for the Caribbean islands, where the elasticity of trade with respect to remoteness is eight times bigger than that for the Pacific islands. ...bilateral trade, remoteness, transport costs, infrastructure, gravity model, Pacific islands

Vectorised Spreading Activation algorithm for centrality measurement

Spreading Activation is a family of graph-based algorithms widely used in areas such as information retrieval, epidemic models, and recommender systems. In this paper we introduce a novel Spreading Activation (SA) method that we call Vectorised Spreading Activation (VSA). VSA algorithms, like “traditional” SA algorithms, iteratively propagate the activation from the initially activated set of nodes to the other nodes in a network through outward links. The level of the node’s activation could be used as a centrality measurement in accordance with dynamic model-based view of centrality that focuses on the outcomes for nodes in a network where something is fl owing from node to node across the edges. Representing the activation by vectors allows the use of the information about various dimensionalities of the fl ow and the dynamic of the fl ow. In this capacity, VSA algorithms can model multitude of complex multidimensional network fl ows. We present the results of numerical simulations on small synthetic social networks and multi dimensional network models of folksonomies which show that the results of VSA propagation are more sensitive to the positions of the initial seed and to the community structure of the network than the results produced by traditional SA algorithms. We tentatively conclude that the VSA methods could be instrumental to develop scalable and computationally effi cient algorithms which could achieve synergy between computation of centrality indexes with detection of community structures in networks. Based on our preliminary results and on improvements made over previous studies, we foresee advances and applications in the current state of the art of this family of algorithms and their applications to centrality measurement

Conditions for Obtaining Nontrivial Knots from Collections of Vectors

We explore under what conditions one can obtain a nontrivial knot, given a collection of n vectors. First, we show how to get a crossing from any 3 vectors equal in magnitude, by arbitrarily picking 2 vectors and identifying the sufficient and necessary criteria for picking a third vector that will guarantee a crossing when the vectors are reordered. We also show that it’s always possible for a set of vectors to be reordered to form the unknot, if they sum to ~0 when added together. Our main results are restricted to sets of n vectors that, when reordered appropriately, project to a regular n-gon in R 2 . We prove that if n = 6, we cannot form a nontrivial knot with our vectors. The first nontrivial knot possible (31) is when n = 7, and the first 41 knot possible is when n = 8. We prove that if n ≥ 7, we can always reorder the vectors to get a projection of a nontrivial knot, and also provide an algorithm to choose how to reorder the vectors to get such a knot

El problema del actor clave

Se describe un procedimiento para identificar actores clave en una red social. Un supuesto básico es que la selección optima depende de los fines de dicha selección. De acuerdo con ello, se articulan dos metas genéricas, referidas al problema del actor clave en términos positivos y negativos. Primero se propone un procedimiento para identificar actores clave con el objetivo de difundir algo de manera óptima en la red, valiéndose de los actores clave como semillas. El segundo procedimiento identifica actores clave con el objetivo de perturbar o fragmentar la red eliminando algunos de sus nodos. Los indicadores de centralidad habituales no son óptimos para este propósito, por lo que se proponen nuevos indicadores.A procedure is described for finding sets of key players in a social network. A key assumption is that the optimal selection of key players depends on what they are needed for. Accordingly, two generic goals are articulated, referring to key player problem in positive (KPP-1) and negative (KPP-2) terms. KPP-1 is defined as the identification of key players for the purpose of optimally diffusing something through the network by using the key players as seeds. KPP-2 is defined as the identification of key players for the purpose of disrupting or fragmenting the network by removing the key nodes. It is found that off-the-shelf centrality measures are not optimal for solving either generic problem, and therefore new measures are presented

The role of negative maternal affective states and infant temperament in early interactions between infants with cleft lip and their mothers

OBJECTIVES: The study examined the early interaction between mothers and their infants with cleft lip, assessing the role of maternal affective state and expressiveness and differences in infant temperament. METHODS: Mother-infant interactions were assessed in 25 2-month-old infants with cleft lip and 25 age-matched healthy infants. Self-report and behavioral observations were used to assess maternal depressive symptoms and expressions. Mothers rated infant temperament. RESULTS: Infants with cleft lip were less engaged and their mothers showed more difficulty in interaction than control group dyads. Mothers of infants with cleft lip displayed more negative affectivity, but did not report more self-rated depressive symptoms than control group mothers. No group differences were found in infant temperament. CONCLUSIONS: In order to support the mother's experience and facilitate her ongoing parental role, findings highlight the importance of identifying maternal negative affectivity during early interactions, even when they seem have little awareness of their depressive symptoms

A New Tariff Database for Selected Least Developed Countries

This paper presents a new hand-gathered database on tariff rates for 18 least developed countries and Korea at the 4-digit level in HS 1988 and SITC revision 2. The database contains one observation per country and per decade starting from the 1970s to 2000/2002. Over time, the tariff schemes of the LDCs follow a symmetric bell-shaped distribution with low rates in the 1970s, which are raised in the 1980s, and then lowered or kept constant in the 1990s and substantially lowered in 2000/02. The analysis in the paper shows that the LDCs have already lowered their average tariff rates to those levels considered ‘optimal’ by many economists and that they have not shifted the protection over time, keeping the highest rates on labor-intensive and on medium skill manufactures and the lowest rates on mineral products.Tariff Rates, Protection, Commercial Policy, Least developed countries