Learning to bid in revenue-maximizing auctions

We consider the problem of the optimization of bidding strategies in prior-dependent revenue-maximizing auctions, when the seller fixes the reserve prices based on the bid distributions. Our study is done in the setting where one bidder is strategic. Using a variational approach, we study the complexity of the original objective and we introduce a relaxation of the objective functional in order to use gradient descent methods. Our approach is simple, general and can be applied to various value distributions and revenue-maximizing mechanisms. The new strategies we derive yield massive uplifts compared to the traditional truthfully bidding strategy

Data management in distributed shared virtual worlds

Research efforts in Virtual Worlds domain have been mainly devoted to user interfaces, communication supports and consistency issues. To the best of our knowledge, no works clearly focused on the global problem of managing virtual world’s data. The promise of future large persistent virtual worlds, evolving during a long period of time and with large number of participants makes the question of data management even more crucial. This paper introduces the global problem of managing data in virtual worlds and reports our research work in using data management services for virtual worlds platforms

Implementation of a method to determine sub-nanomolar concentrations of iron in seawater and its application to the study of marine iron biogeochemistry at the ocean-shelf interface

The aim of this study was to improve our understanding of the marine iron cycle using a newly implemented technique to measure dissolved iron in seawater. The setting up of a flow-injection analyser with chemiluminescence detection (FIACL) for Fe(II) proved to be non-trivial. Extensive work was undertaken to solve problems relating to our limited level of understanding of the CL reaction, and the variable behaviour of the resins prepared to preconcentrate iron. An analyser for Fe(II)+(III) was optimised, and careful assessment of data demonstrated the high quality of the information interpreted in this study, from the Celtic Sea shelf edge (Northeast Atlantic), and from the North Scotia Ridge (Southern Ocean).The distribution of iron at the Celtic Sea shelf edge was examined, and was used to provide a conceptual framework for future studies. Dissolved Fe (< 0.4 µm) concentrations were measured in samples from nine vertical profiles taken across the continental slope (160 – 2950 m water depth). Dissolved iron concentrations varied between 0.2 and 5.4 nM, and the resulting detailed section showed evidence of a range of processes influencing the iron distributions. The presence of elevated levels of dissolved Fe near the seafloor was consistent with release of Fe from in situ particulate organic matter remineralisation at two upper slope stations, and possibly of pore water release upon resuspension on shelf. Lateral transport of dissolved iron was evident in an intermediate nepheloid layer and its advection along an isopycnal. Surface waters at the shelf break also showed evidence of vertical mixing of deeper iron-rich waters. The data also suggest some degree of stabilisation of relatively high concentrations of iron, presumably through ligand association or as colloids. The possibility of iron limitation of phytoplankton at the shelf edge was not ruled out despite obvious depletion of nitrate. This study supports the view that export of dissolved iron laterally to the ocean’s interior from shelf and coastal zones may have important implications for the global budget of oceanic iron.A set of surface samples collected on a survey between the Falkland Islands and South Georgia were analysed for total dissolvable iron. Results suggested a source of benthic iron near South Georgia. A shift in photo-physiology of phytoplankton towards South Georgia was probably influenced by the transition from iron-limited to iron-replete populations. These results therefore strongly support the hypothesis that South Georgia may be a "pulse-point" of iron to high-nutrient low-chlorophyll waters

Impacts of regular and random noise on the behaviour, growth and development of larval Atlantic cod (<i>Gadus morhua</i>)

Anthropogenic noise impacts behaviour and physiology in many species, but responses could change with repeat exposures. As repeat exposures can vary in regularity, identifying regimes with less impact is important for regulation. We use a 16-day split-brood experiment to compare effects of regular and random acoustic noise (playbacks of recordings of ships), relative to ambient-noise controls, on behaviour, growth and development of larval Atlantic cod (Gadus morhua). Short-term noise caused startle responses in newly hatched fish, irrespective of rearing noise. Two days of both regular and random noise regimes reduced growth, while regular noise led to faster yolk sac use. After 16 days, growth in all three sound treatments converged, although fish exposed to regular noise had lower body width–length ratios. Larvae with lower body width–length ratios were easier to catch in a predator-avoidance experiment. Our results demonstrate that the timing of acoustic disturbances can impact survival-related measures during development. Much current work focuses on sound levels, but future studies should consider the role of noise regularity and its importance for noise management and mitigation measures

Are aerobic fitness and repeated sprint ability linked to fatigue in professional soccer match-play? A pilot study

This investigation examined the association between aerobic fitness and repeated sprint ability and match-related fatigue in 9 professional outfield soccer players. Aerobic fitness using maximal aerobic speed (MAS) was determined via a continuous progressive incremental running test conducted on a motorised treadmill. A repeated sprint ability test (6 successive 6 s sprints separated by 20 s passive recovery) was performed on a non-motorised treadmill to determine mean and best sprint times and a percentage decrement score (%PD). A total of 114 observations of physical performance derived using computerised time motion analyses were collected from 33 matches. Correlations between fitness test and match-play measures were examined for 1) accumulated fatigue: percentage difference between halves for total distance covered per minute, distance run at high-intensities (HIR, actions for 1s duration, >19.1 km/h) per minute, mean recovery time between high-intensity runs, and percentage difference between the distance covered in HIR in the first 5- and 15-minute periods versus the final 5- and 15-minute periods respectively in normal time; and for 2) transient fatigue: percentage difference between the distance covered in HIR in a peak 5-minute period and the subsequent 5-minute period and for the latter compared to the mean for all other 5-minute periods. No significant relationships were observed between MAS and fatigue scores (magnitude of associations: trivial to large). For mean and best sprint times and %PD, the only reported significant correlation (r=0.77, magnitude of association: very large, p<0.05) was between %PD and the % difference across halves for mean recovery time between high-intensity runs (magnitude of other associations: small to large). Criterion measures from tests of aerobic fitness and repeated sprint ability might not accurately depict a player’s capacity to resist fatigue during professional soccer competition