arXiv subjects

C. Silvestre

Publications and source records attributed to C. Silvestre.

4 recordsLinked to original sources

arXiv2025

Versatile 3D reconstruction framework for hard X-ray grazing incidence imaging of nanostructures

Coherent imaging techniques such as ptychography offer powerful capabilities for 3D resolution of nanoscale structures. By application in grazing incidence, such techniques may achieve exceptional surface sensitivity as demonstrated by grazing incidence small angle scattering. This requires however an extension of the conventional analysis based on the Distorted Wave Born Approximation which is typically limited to stratified-layer models and statistical descriptions of in-plane structures. The prevailing implementations of reconstruction algorithms for ptychography based on the projection approximation fails to capture the significant multiple scattering that occurs in grazing incidence. We present a ptychographic reconstruction framework that replaces the single-scattering model with a multislice wave-propagation formalism tailored to grazing incidence. The framework supports simultaneous phase retrieval and reconstruction, and can incorporate multiple incidence angles, multiple rotation angles, and flexible experimental geometries into a single inversion. Reconstructions can be initialized from a random guess without strong structural priors, enabling the recovery of complex surface and near-surface nanostructures. This reconstruction framework is applied to both experimental and simulated datasets, demonstrating its versatility.

physics.optics↗

arXiv2025

Leader-Follower Formation Tracking Control of Quadrotor UAVs Using Bearing Measurements

This work addresses the practical problem of distributed formation tracking control of a group of quadrotor vehicles in a relaxed sensing graph topology with a very limited sensor set, where only one leader vehicle can access the global position. Other vehicles in the formation are assumed to only have access to inter-agent bearing (direction) measurements and relative velocities with respect to their neighbor agents. A hierarchical control architecture is adopted for each quadrotor, combining a high-gain attitude inner-loop and an outer-loop bearing-based formation controller with collision avoidance augmentation. The proposed method enables a group of quadrotors to track arbitrary bearing persistently exciting desired formations, including time-varying shapes and rotational maneuvers, such that each quadrotor only requires relative measurements to at least one neighboring quadrotor. The effective performance of the control strategy is validated by numerical simulations in MATLAB and real-world experiments with three quadrotors.

eess.SY↗

arXiv2023

Hard X-ray grazing incidence ptychography: Large field-of-view nanostructure imaging with ultra-high surface sensitivity

We demonstrate a technique that allows highly surface sensitive imaging of nanostructures on planar surfaces over large areas, providing a new avenue for research in materials science, especially for \textit{in situ} applications. The capabilities of hard X-ray grazing incidence ptychography combine aspects from imaging, reflectometry and grazing incidence small angle scattering in providing large field-of-view images with high resolution transverse to the beam, horizontally and along the surface normal. Thus, it yields data with resolutions approaching electron microscopy, in two dimensions, but over much larger areas and with a poorer resolution in the third spatial dimension, along the beam propagation direction. Similar to grazing incidence small angle X-ray scattering, this technique facilitates the characterization of nanostructures across statistically significant surface areas or volumes within potentially feasible time frames for \textit{in situ} experiments, while also providing spatial information.

physics.optics↗

arXiv2010

Position USBL/DVL Sensor-based Navigation Filter in the presence of Unknown Ocean Currents

This paper presents a novel approach to the design of globally asymptotically stable (GAS) position filters for Autonomous Underwater Vehicles (AUVs) based directly on the nonlinear sensor readings of an Ultra-short Baseline (USBL) and a Doppler Velocity Log (DVL). Central to the proposed solution is the derivation of a linear time-varying (LTV) system that fully captures the dynamics of the nonlinear system, allowing for the use of powerful linear system analysis and filtering design tools that yield GAS filter error dynamics. Simulation results reveal that the proposed filter is able to achieve the same level of performance of more traditional solutions, such as the Extended Kalman Filter (EKF), while providing, at the same time, GAS guarantees, which are absent for the EKF.

math.OC↗