Earth-Venus Mission Analysis via Weak Capture and Nonlinear Orbit Control

Exploration of Venus is recently driven by the interest of the scientific community in understanding the evolution of Earth-size planets, and is leading the implementation of missions that can benefit from new design techniques and technology. In this work, we investigate the possibility to implement a microsatellite exploration mission to Venus, taking advantage of (i) weak capture, and (ii) nonlinear orbit control. This research considers the case of a microsatellite, equipped with a high-thrust and a low-thrust propulsion system, and placed in a highly elliptical Earth orbit, not specifically designed for the Earth-Venus mission of interest. In particular, to minimize the propellant mass, phase (i) of the mission was designed to inject the microsatellite into a low-energy capture around Venus, at the end of the interplanetary arc. The low-energy capture is designed in the dynamical framework of the circular restricted 3-body problem associated with the Sun-Venus system. Modeling the problem with the use of the Hamiltonian formalism, capture trajectories can be characterized based on their state while transiting in the equilibrium region about the collinear libration point L1. Low-energy capture orbits are identified that require the minimum velocity change to be established. These results are obtained using the General Mission Analysis Tool, which implements planetary ephemeris. After completing the ballistic capture, phase (ii) of the mission starts, and it is aimed at driving the microsatellite toward the operational orbit about Venus. The transfer maneuver is based on the use of low-thrust propulsion and nonlinear orbit control. Convergence toward the desired operational orbit is investigated and is proven analytically using the Lyapunov stability theory, in conjunction with the LaSalle invariance principle, under certain conditions related to the orbit perturbing accelerations and the low-thrust magnitude. The numerical results prove that the mission profile at hand, combining low-energy capture and low-thrust nonlinear orbit control, represents a viable and effective strategy for microsatellite missions to Venus

Codesign for discovery in social sciences and humanities:addressing the heterogeneous needs of a community in digital scholarship

GoTriple is a novel discovery platform for Social Sciences and Humanities (SSH) in Europe. Discovery is a phase of research where scholars seek to locate resources for their work, such as publications or previous projects. The paper details the work done for involving the SSH community in the codesign of GoTriple, focusing on the research discovery activities. It is an investigation of the user needs and barriers toward digital discovery for the SSH community, conducted through codesign. This work encompassed interviews, a questionnaire, codesign workshops and evaluation activities. The paper reports on some outcomes for the codesign and how user needs were identified and served by novel designs supporting discovery for SSH. This process of design is both concerned with creating digital tools for discovery and with the creation of a community of users that could make the platform thrive. The main contribution of the work is therefore the identification of the user needs for digital discovery in SSH and a series of insights on the design with the user community. The paper comprises a report on how codesign principles do support such work

Two Variables Algorithms for Solving the Stochastic Equilibrium Assignment with Variable Demand: Performance Analysis and Effects of Path Choice Models

In this paper a general fixed-point approach dealing with multi-user (stochastic) equilibrium assignment with variable demand is proposed. The main focus is on (i) the implementation and comparison of different algorithm solutions based on successive averages methods calculated on one (arc flows, arc costs) and on two variables (arc flows and path satisfaction; arc costs and demand flows); (ii) the effects of algorithm efficiency on different path choice models and/or travel demand choice models. In terms of the best performing algorithmic solution, the effects of different path choice models, such as Multinomial Logit model, C-Logit model and Multinomial Probit model were implemented, and algorithmic efficiency was investigated w.r.t. a real network

scheduled synchronisation based on a mesoscopic flow model with speed dispersion

Abstract This paper proposes a method for netwok signal setting design, based on enhacements of an existing coordination method aiming: 1) to extend the existing approach in order to address the Traffic Control through Scheduled Synchronisation (i.e 'one step' optimisation of stage matrix, green timings, and node offsets ); 2) to extend the considered Mesoscopic Traffic Flow model (TRAFFMED) to the vehicle platoon speed dispersion; 3) to build up a solution method suitable for both off-line and on-line applications. The proposed optimisation method is an application of the Simulated Annealing meta-heuristic. Some numerical applications are proposed, specifically analysing 'two step' optimisation (synchronisation), and'one step' optimisation (scheduled synchronisation), for off-line (pre-timed strategy) and on-line applications (on-line computation strategy). A grid network was considered as case study and the effectiveness of the proposed strategies were evaluated by comparing the obtained results with those computed through commercial (benchmark) and in-house codes

Nonlinear anisotropic dielectric metasurfaces for ultrafast nanophotonics

We report on the broadband transient optical response from anisotropic nanobrick amorphous silicon particles, exhibiting Mie-type resonances. A quantitative model is developed to identify and disentangle the three physical processes that govern the ultrafast changes of the nanobrick optical properties, namely two-photon absorption, free-carrier relaxation, and lattice heating. We reveal a set of operating windows where ultrafast all-optical modulation of transmission is achieved with full return to zero in 20 ps. This is made possible due to the interplay between the competing nonlinear processes and despite the slow (nanosecond) internal lattice dynamics. The observed ultrafast switching behavior can be independently engineered for both or- thogonal polarizations using the large anisotropy of nanobricks thus allowing ultrafast anisotropy control. Our results categorically ascertain the potential of all-dielectric resonant nanophotonics as a platform for ultrafast optical devices, and reveal the pos- sibility for ultrafast polarization-multiplexed displays and polarization rotators

CAESAR II Tool: Complementary Analyses for Emergency Planning Based on Seismic Risks Impact Evaluations

Italy is a country with high seismic hazard, however since the delay in the seismic classification of the national territory, most of the existing building heritage does not comply with the current technical standards for buildings. The seismic events that have hit different Italian regions in recent years have highlighted the complexity of the challenge for the public bodies both in the emergency management and post‐event reconstruction and in the planning of effective risk prevention and mitigation measures to be implemented in ‘peacetime’. These difficulties concern, in particular, the capacity to properly manage the financial and technical resources available and to identify the intervention priorities throughout the entire emergency cycle. For correct management, the priority is to quantify and localize, through simulations, the quantification of probable damages and to evaluate in terms of cost‐benefits the possible alternative strategies for mitigation, also taking into account the potential, in terms of cost‐effectiveness, of integrated measures for seismic and energy retrofitting. In this framework, the project CAESAR II (Complementary Analyses for Emergency planning based on Seismic Risks impact evaluations) has been developed as a Decision Support System for Public Authorities in charge of developing Disaster Risk Reduction plans, with the possibility of programming mid to long‐term investments for public and private properties, as well as defining custom financial support mechanisms and tax incentives

Coupling of electron and vibrational spectroscopy with false colour imaging for the investigation of natural dyes in historical fabrics (15th-18th centuries)

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Generation of 85-fs pulses at 13 μm for ultrabroadband pump-probe spectroscopy

We report on a near-infrared non-collinear optical parametric amplifier (NOPA) based on periodically poled stoichiometric lithium tantalate. The NOPA generates mu J-energy pulses with spectrum spanning the 1-1.7 mu m wavelength range, which are compressed to nearly transform-limited 8.5 fs duration by a deformable mirror. By synchronizing this source with a sub-10-fs visible NOPA, we demonstrate an unprecedented combination of temporal resolution and spectral coverage in two-colour pump-probe spectroscopy. (C) 2009 Optical Society of Americ