Publications | Clément Sebastiao webpage

Research

The Trade-off Between Directness and Coverage in Transport Network Growththe Trade-off Between Directness and Coverage in Transport Network Growth

Clément S, Anastassia V, Ane Rahbek V, Luca Maria A, Michael S,

Paper

In
Applied Network Science

Designing spatial networks, such as transport networks, commonly deals with the problem of how to best connect a set of locations through a set of links. In practice, it can be crucial to order the implementation of the links in a way that facilitates early functioning of the network during growth, like in bicycle networks. However, it is unclear how this early functional structure can be achieved by different growth processes. Here, we systematically study the growth of connected planar networks, quantifying functionality of the growing network structure. We compare random growth with various greedy and human-designed, manual growth strategies. We evaluate our results via the fundamental performance metrics of directness and coverage, finding non-trivial trade-offs between them. Manual strategies fare better than greedy strategies on both metrics, while random strategies perform worst and are unlikely to be Pareto efficient. Centrality-based greedy strategies tend to perform best for directness but are worse than random strategies for coverage, while coverage-based greedy strategies can achieve maximum global coverage as fast as possible but perform as poorly for directness as random strategies. Directness-based greedy strategies get stuck in local optimum traps. These results hold for a number of stylized urban transport network topologies. Our insights are crucial for applications where the order in which links are added to a spatial network is important, such as in urban or regional transport network design problems.
Long‐Standing Optically Excited Magnetic States in ZnO Nanoparticles

Adrien S, Clément S, Olivier M,

Paper

In
physica status solidi (RRL)–Rapid Research Letters

The spectral dependence of the light-induced magnetic states generated in zinc oxide nanoparticles by illumination during an electron paramagnetic resonance (EPR) experiment is studied for three incident light wavelengths (451, 405, and 370 nm). The minimal wavelength excitation is found to be in the visible violet region, very close to 405 nm for all of the light-induced EPR lines. This points to a close relationship between their originating centers, despite the difference in their dynamics previously revealed by saturation recovery measurements. The study of the light-induced signals decay with time (after illumination removal) and with temperature (under constant illumination) confirms the existence of two groups of lines characterized by different dynamics. The quite unusual persistence of these magnetic states after excitation removal opens promising possibilities for encoding information within semiconducting nanoparticles.