Visual SLAM for 3D large-scale seabed acquisition employing underwater vehicles

This paper presents a novel technique to align partial 3D reconstructions of the seabed acquired by a stereo camera mounted on an autonomous underwater vehicle. Vehicle localization and seabed mapping is performed simultaneously by means of an Extended Kalman Filter. Passive landmarks are detected on the images and characterized considering 2D and 3D features. Landmarks are re-observed while the robot is navigating and data association becomes easier but robust. Once the survey is completed, vehicle trajectory is smoothed by a Rauch-Tung-Striebel filter obtaining an even better alignment of the 3D views and yet a large-scale acquisition of the seabed

Local map update for large scale SLAM

A technique for simultaneous localisation and mapping (SLAM) for large scale scenarios is presented. This solution is based on the use of independent submaps of a limited size to map large areas. In addition, a global stochastic map, containing the links between adjacent submaps, is built. The information in both levels is corrected every time a loop is closed: local maps are updated with the information from overlapping maps, and the global stochastic map is optimised by means of constrained minimisation

Investigating the impact of small versus large firms on economic performance of countries and industries

Following earlier work by Audretsch et al. (2002), we assume that an optimal size-class structure exists, in terms of achieving maximal economic growth rates. Such an optimal structure is likely to exist as economies need a balance between the core competences of large firms (such as exploitation of economies of scale) and those of smaller firms (such as flexibility and exploration of new ideas). Accordingly, changes in size-class structure (i.e., changes in the relative shares in economic activity accounted for by micro, small, medium-sized and large firms) may affect macro-economic growth. Using a unique data base of the EU-27 countries for the period 2002-2008 for five broad sectors of economic activity and four size-classes, we find empirical support which suggests that, on average for these countries over this period, the share of micro and large firms may have been ‘above optimum’ (particularly in lower income EU countries) whereas the share of medium-sized firms may have been ‘below optimum’ (particularly in higher income EU countries). This evidence suggests that the transition from a ‘managed’ to an ‘entrepreneurial’ economy (Audretsch and Thurik, 2001) has not been completed yet in all countries of the EU-27. Keywords: small firms, large firms, size-classes, macro-economic performance

Do innovation and human capital explain the productivity gap between small and large firms?

Empirical evidence is compelling that large firms are more productive than small firms. The hypothesis in this paper is that the productivity differences between small and large firms are associated with two of the main determinants of a firm’s performance: the human and technological capital that firms incorporate. We suggest that the contribution of these factors in explaining the productivity-size gap might not only be due to the fact that large firms make a more extensive use of them, but also because large firms obtain higher returns from their investment in human and technological capital. The evidence we obtain for a comprehensive sample of Spanish manufacturing firms (1990-2002) supports this hypothesis, which has important implications for the effectiveness of policies designed to improve productivity in SMEs by stimulating innovation and the use of more skilled workers.

A characterization of cooperative TU-games with large monotonic core

[cat] El concepte de joc cooperatiu amb large core és introduït per Sharkey (1982) i el de Population Monotonic Allocation Scheme és definit per Sprumont (1990). Inspirat en aquests conceptes, Moulin (1990) introdueix la noció de large monotonic core donant una caracterització per a jocs de tres jugadors. En aquest document provem que tots els jocs amb large monotonic core són convexes. A més, donem un criteri efectiu per determinar si un joc té large monotonic core o no, i daquí obtenim una caracterització pel cas de quatre jugadors.

A characterization of cooperative TU-games with large monotonic core

[cat] El concepte de joc cooperatiu amb large core és introduït per Sharkey (1982) i el de Population Monotonic Allocation Scheme és definit per Sprumont (1990). Inspirat en aquests conceptes, Moulin (1990) introdueix la noció de large monotonic core donant una caracterització per a jocs de tres jugadors. En aquest document provem que tots els jocs amb large monotonic core són convexes. A més, donem un criteri efectiu per determinar si un joc té large monotonic core o no, i daquí obtenim una caracterització pel cas de quatre jugadors.

Fish colonization of artificial reefs in a large Neotropical reservoir: material type and successional changes

Artificial reefs have barely been used in Neotropical reservoirs (about five studies in three reservoirs), despite their potential as a fishery management tool to create new habitats and also to understand fish ecology. We experimentally assessed how reef material (ceramic, concrete, and PVC) and time modulated fish colonization of artificial reefs deployed in Itaipu Reservoir, a large reservoir of the mainstem Parana´ River, Brazil. Fish richness, abundance, and biomass were significantly greater in the reef treatments than at control sites. Among the experimental reefs, ceramic followed by the concrete treatments were the materials most effectively colonized, harboring the majority of the 13 fish species recorded. Although dependent on material type, many of the regularities of ecological successions were also observed in the artificial reefs, including decelerating increases in species richness, abundance, mean individual size, and species loss rates with time and decelerating decreases of species gain and turnover rates. Species composition also varied with material type and time, together with suites of life history traits: more equilibrium species (i.e., fishes of intermediate size that often exhibit parental care and produce fewer but larger offspring) of the Winemiller-Rose model of fish life histories prevailed in later successional stages. Overall, our study suggests that experimental reefs are a promising tool to understand ecological succession of fish assemblages, particularly in tropical ecosystems given their high species richness and low seasonality

Effects of solar activity and climate variability on large floods in Switzerland

The paper presents the variability of major floods in Switzerland for the period 1800-2008 from a summer index (INU). The index is constructed from the damage caused by flooding, with the aim of establishing the possible influence of the solar and climate variability on the major floods. The coincidence of flood-rich periods with those observed in other regions of different climate and fluvial regimes suggests that climate forcings and changes in the general circulation of the atmosphere are those who govern the appearance of these high-frequency temporal clusters.