Quantifying variation in the ability of yeasts to attract Drosophila melanogaster

Yeasts that invade and colonise fruit significantly enhance the volatile chemical diversity of this ecosystem. These modified bouquets are thought to be more attractive to Drosophila flies than the fruit alone, but the variance of attraction in natural yeast populations is uncharacterised. Here we investigate how a range of yeast isolates affect the attraction of female D. melanogaster to fruit in a simple two choice assay comparing yeast to sterile fruit. Of the 43 yeast isolates examined, 33 were attractive and seven repellent to the flies. The results of isolate-versus-isolate comparisons provided the same relative rankings. Attractiveness varied significantly by yeast, with the strongly fermenting Saccharomyces species generally being more attractive than the mostly respiring non-Saccharomyces species (P = 0.0035). Overall the habitat (fruit or other) from which the isolates were directly sampled did not explain attraction (P = 0.2352). However, yeasts isolated from fruit associated niches were more attractive than those from non-fruit associated niches (P = 0.0188) regardless of taxonomic positioning. These data suggest that while attractiveness is primarily correlated with phylogenetic status, the ability to attract Drosophila is a labile trait among yeasts that is potentially associated with those inhabiting fruit ecosystems. Preliminary analysis of the volatiles emitted by four yeast isolates in grape juice show the presence/absence of ethanol and acetic acid were not likely explanations for the observed variation in attraction. These data demonstrate variation among yeasts for their ability to attract Drosophila in a pattern that is consistent with the hypothesis that certain yeasts are manipulating fruit odours to mediate interactions with their Drosophila dispersal agent. © 2013 Palanca et al

Small-scale biomass-fired cogeneration, pellet production or district heating: new criteria for selecting the most profitable solution

In this paper the possible use of heat surplus from a biomass-fired cogeneration unit, for treating a share of the biomass and produce a new and more performing fuel like pellet, is proposed and discussed. Such a fuel could be easily stored and then distributed, for a more widespread and diffused utilization close to the consumers, for heating purposes. This form of energy storage makes time and geographical shift of heat utilization possible, also in small-scale applications. A technical-economical comparison is carried out and discussed between the above mentioned system and a district heating supplied by a traditional biomass boiler, or a conventional chip-fired cogeneration plant without pellets production. The paper also focuses on the opportunities and challenges deriving from the energy use of a specific biomass resource: olive pomace. The technical feasibility and the economical profitability of different plant solutions are investigated. To a methodological contribution, related to the description and modeling of the proposed conversion processes, some case-studies are joined, based on efficiencies and costs suggested by the most recent literature and field tests

Short-term operation of a hybrid minigrid under load and renewable production uncertainty

Properly sized and operated hybrid minigrids can assure good-quality electricity to rural households at an affordable price. A system composed by renewable sources, a diesel generator and batteries can be a cheaper option, but it requires daily operation in order to reduce fuel consumption, to assure fuel availability, and to avoid quick degradation of the batteries. Variability in load and renewable generation introduces uncertainties that must be considered in order to assure a proper operation, thus reducing the curtailment of both load and renewable production. This paper proposes a procedure for short-term operation of a hybrid minigrid in order to cope with errors in forecasting of both load and renewable generation. A probabilistic tool based on Monte Carlo simulations and mixedinteger programming is developed to estimate the optimal working point of the diesel generator and batteries. The Monte Carlo scenarios are singularly optimized, thus defining several optimal schedules that are combined to define the proposed stochastic commitment and dispatchment. The methodology is supported by numerical case studies that even confirm the applicability of Monte Carlo simulations to the short-term operation