From innovation to diversification: a simple competitive model

Few attempts have been proposed in order to describe the statistical features and historical evolution of the export bipartite matrix countries/products. An important standpoint is the introduction of a products network, namely a hierarchical forest of products that models the formation and the evolution of commodities. In the present article, we propose a simple dynamical model where countries compete with each other to acquire the ability to produce and export new products. Countries will have two possibilities to expand their export: innovating, i.e. introducing new goods, namely new nodes in the product networks, or copying the productive process of others, i.e. occupying a node already present in the same network. In this way, the topology of the products network and the country-product matrix evolve simultaneously, driven by the countries push toward innovation.Comment: 8 figures, 8 table

On the Complexity of Query Result Diversification

Query result diversification is a bi-criteria optimization problem for ranking query results. Given a database D, a query Q and a positive integer k, it is to find a set of k tuples from Q(D) such that the tuples are as relevant as possible to the query, and at the same time, as diverse as possible to each other. Subsets of Q(D) are ranked by an objective function defined in terms of relevance and diversity. Query result diversification has found a variety of applications in databases, information retrieval and operations research. This paper studies the complexity of result diversification for relational queries. We identify three problems in connection with query result diversification, to determine whether there exists a set of k tuples that is ranked above a bound with respect to relevance and diversity, to assess the rank of a given k-element set, and to count how many k-element sets are ranked above a given bound. We study these problems for a variety of query languages and for three objective functions. We establish the upper and lower bounds of these problems, all matching, for both combined complexity and data complexity. We also investigate several special settings of these problems, identifying tractable cases. 1

On the suitability of intent spaces for IR diversification

This is an electronic version of the paper presented at the International Workshop on Diversity in Document Retrieval (DDR 2012), held in Seattle on 2012Recent developments in Information Retrieval diversity are based on the consideration of a space of information need aspects, a notion which takes different forms in the literature. The choice of a suitable aspect space for diversification is a critical issue when designing an IR diversification strategy, which has not been explicitly addressed to some depth in the literature. This paper aims to identify relevant properties of the aspect space which may help the system designer in making a suitable choice in selecting and configuring this space, and diagnosing malfunctions of the diversification algorithms. In particular, we identify the mutual information between aspects and documents as a meaningful magnitude, in terms of which anomalous cases can be characterized. We further seek to discern favorable cases through a combination of theoretic and empirical analysis.This work is supported by the Spanish Government (TIN2011-28538-C02-01), and the Government of Madrid (S2009TIC-1542)

Gene duplication drives genome expansion in a major lineage of Thaumarchaeota

Acknowledgements This work and P.O.S. were financially supported by UKRI through the NERC grant NE/R001529/1. In addition, C.G.-R. and T.A.W. were both supported by a Royal Society University Research Fellowship (URF150571 and UF140626). C.Q. was funded through an MRC fellowship (MR/M50161X/1) as part of the CLoud Infrastructure for Microbial Genomics (CLIMB) consortium (MR/L015080/1). S.R. was funded through the BBSRC grant BB/R015171/1. The Thames Metagenome Database was funded through the NERC grants NE/M011674/1, NE/M011259/1 and NE/M01133X/1. We thank Dr Tony Travis for his support with Biolinux and acknowledge Prof Jim Prosser for his critical reading of the manuscript. The authors would also like to acknowledge the support of the Maxwell computer cluster funded by the University of Aberdeen.Peer reviewedPublisher PD