The selection of an electric propulsion subsystem architecture for high-power space missions

The arise of high-power electric propulsion is paving the way towards new horizons of space exploration. Hall thrusters represent a promising propulsion concept, able to fulfil challenging mission requirements for both commercial and exploration applications. This technology offers several benefits in terms of flexibility of operation, extensive lifetime and high reliability. However, the design of a high-power electric propulsion subsystem (E-PROP) still presents challenges to address. Filling the corresponding technological gaps will open new market opportunities, owing mainly to the extension of mission capabilities and the reduction of the overall mission costs. Therefore, investigations of innovative technology alternatives will allow to identify the most promising E-PROP architectures for various high-power mission scenarios. One of the most critical trade-off to perform is between a high-power monolithic thruster and a cluster of thrusters of lower power. Another criticality is the amount of propellant necessary to perform high delta-v missions. The high price of xenon prompted the investigation on alternative propellants, such as krypton. The propellant selection should consider the impact on different aspects of the platform design, including performance, system complexity and mission costs. Last, due to the high-power levels that the E-PROP shall manage, a different architecture can be implemented by adopting the direct-drive approach, i.e. a direct and non-isolated connection between the solar array and the thruster. However, even if the disruptive direct-drive technology allows a significant reduction in the EP system mass and cost, its implementation rises additional challenges to the design of the spacecraft power subsystem. This paper analyses the impact of innovative architecture solutions on the design of a high-power E-PROP. In the framework of this research, we first carried out an extensive investigation of possible mission scenarios and we derived corresponding mission requirements and constrains. Then, we performed three technological trade-offs: monolithic 20 kW vs 5 kW cluster configuration, Xe vs Kr propellant and direct-drive vs standard PPU. All the analysis are based on the experimental data obtained during the 5 kW and 20 kW thrusters development and characterisation at SITAEL. We characterized each design option through several figures of merit, evaluating them for each identified mission scenario. We exploited an Analytical Hierarchy Process for the trade-off analyses and a Monte Carlo method to perform the preliminary evaluation of the trade-off weights. The analyses are based on the research activities that are currently ongoing at SITAEL and PoliTo in the framework of 20 kW E-PROP development programmes. The results of the work highlight the effects of each architecture alternative on both platform design and mission performance

A major QTL is associated with berry grape texture characteristics

Berry texture and berry skin mechanical properties are traits with high agronomic relevance because they are related to quality parameters and marketing requirements of wine, table, and raisin grapes. Searching for QTLs linked to berry texture, an F1 population of 152 individuals and their parents were used in this study. These F1 plants were obtained crossing Raboso Veronese, a seeded black wine grape cultivar, and Sultanina, a seedless white grape variety, especially used for raisins. Density flotation was applied for berry sorting improving the management of many and highly variable genotypes, irrespective of the quantification of specific molecule classes. Berries were evaluated for technological ripeness parameters and mechanical properties. Texture parameters were taken as raw data and as data normalised on berry dimensions, i.e., berry diameter or surface or volume. SSR molecular markers were used to produce a genetic map and a major QTL for berry texture was found on chromosome 18 with traits related to berry firmness showing a phenotypical explained variance higher than 60 %, and traits related to berry resilience, springiness and cohesiveness showing a variance higher than 50 %. Surprisingly, this QTL showed to be associated with SSR markers linked to VviAGL11, the main gene linked to seedlessness. VviAGL11 expression and co-expression profiling during grape ripening was evaluated using available information; this data suggested a role for this gene on the texture of a ripe berry

Metadynamics simulations rationalize the conformational effects induced by N-methylation of RGD cyclohexapeptides

Cyclopeptides are a promising class of compounds with favourable pharmacokinetic characteristics that can be used as therapeutics in modulation of protein-protein interactions. Nevertheless their application has been limited due to the difficulties to predict in silico their three-dimensional structure and inhibitory activity. Because of these challenges, their optimization for specific biological targets has been mainly based on empirical approaches. Computational tools could be fundamental in accelerating the drug design process, reducing the efforts dedicated to expensive and time-consuming compound synthesis. In this scenario a detailed conformational search of ligands followed by docking calculations is highly recommendable to achieve reliable computational predictability. We have developed a multi-stage computational protocol[1] able to i. predict the affinity of a set of cyclopeptides for different integrins, ii. rationalize the interplay between conformational equilibria and receptor affinity. The protocol relies on the combination of enhanced sampling molecular dynamics technique (Bias-Exchange Metadynamics), docking calculations and re-scoring via Molecular Mechanics/Generalized-Born Surface Area. The reliability of our method was tested investigating the impact of single and multiple N-methylation on the equilibrium conformations of five RGD (Arg-Gly-Asp) cyclohexapeptides that were generated to increase their selectivity towards \u3b1IIb\u3b23 integrin.[2] We obtained excellent results: the conformational sampling was in good agreement with available NMR data and we were able to discriminate between binders and non-binders. Additionally we offered a structural rationale for why N-methylation increases peptides affinities towards a specific integrin. Herein we have shown that Metadynamics can represent a promising in silico screening strategy, opening new perspectives in the application of cyclopeptides as therapeutic inhibitors. We expect that this combination of techniques will be successfully exploited in future to predict the conformational effects of methylation and other chemical modifications in cyclopeptides