Experimental results of a terrain relative navigation algorithm using a simulated lunar scenario

This paper deals with the problem of the navigation of a lunar lander based on the Terrain Relative Navigation approach. An algorithm is developed and tested on a scaled simulated lunar scenario, over which a tri-axial moving frame has been built to reproduce the landing trajectories. At the tip of the tri-axial moving frame, a long-range and a short-range infrared distance sensor are mounted to measure the altitude. The calibration of the distance sensors is of crucial importance to obtain good measurements. For this purpose, the sensors are calibrated by optimizing a nonlinear transfer function and a bias function using a least squares method. As a consequence, the covariance of the sensors is approximated with a second order function of the distance. The two sensors have two different operation ranges that overlap in a small region. A switch strategy is developed in order to obtain the best performances in the overlapping range. As a result, a single error model function of the distance is found after the evaluation of the switch strategy. Because of different environmental factors, such as temperature, a bias drift is evaluated for both the sensors and properly taken into account in the algorithm. In order to reflect information of the surface in the navigation algorithm, a Digital Elevation Model of the simulated lunar surface has been considered. The navigation algorithm is designed as an Extended Kalman Filter which uses the altitude measurements, the Digital Elevation Model and the accelerations measurements coming from the moving frame. The objective of the navigation algorithm is to estimate the position of the simulated space vehicle during the landing from an altitude of 3 km to a landing site in the proximity of a crater rim. Because the algorithm needs to be updated during the landing, a crater peak detector is conceived in order to reset the navigation filter with a new state vector and new state covariance. Experimental results of the navigation algorithm are presented in the paper

Driven diffusion against electrostatic or effective energy barrier across Alpha-Hemolysin

We analyze the translocation of a charged particle across an Alpha-Hemolysin (aHL) pore in the framework of a driven diffusion over an extended energy barrier generated by the electrical charges of the aHL. A one-dimensional electrostatic potential is extracted from the full 3D solution of the Poisson's equation. We characterize the particle transport under the action of a constant forcing by studying the statistics of the translocation time. We derive an analytical expression of translocation time average that compares well with the results from Brownian dynamic simulations of driven particles over the electrostatic potential. Moreover, we show that the translocation time distributions can be perfectly described by a simple theory which replaces the true barrier by an equivalent structureless square barrier. Remarkably our approach maintains its accuracy also for low-applied voltage regimes where the usual inverse-Gaussian approximation fails. Finally we discuss how the comparison between the simulated time distributions and their theoretical prediction results to be greatly simplified when using the notion of the empirical Laplace transform technique.Comment: RevTeX 4-1, 11 pages, 6 pdf figures, J. Chem. Phys. 2015 in pres

Electric field effect on spin waves and magnetization dynamics: role of magnetic moment current

We show that a static electric field $E_x$ gives rise to a shift of the spin wave dispersion relation $\omega(q_y-q_E)$ in the direction of the wavenumber $q_y$ of the quantity $q_E=-\gamma_LE_x/c^2$. This effect is caused by the magnetic moment current carried by the spin wave itself that generates an additional phase proportional to the electric field, as in the Aharonov-Casher effect. This effect is independent from the possibly present magneto-electric effects of insulating ferromagnets and superimposes to them. By extending this picture to arbitrary magnetization dynamics, we find that the electric field gives rise to a dynamic interaction term which has the same chiral from of the Dzyaloshinskii-Moriya interaction but is fully tunable with the applied electric field.Comment: 6 pages, 2 figures, submitted pape

A Search Algorithm for Stochastic Optimization in Initial Orbit Determination

Optical observations constitute a source of angular measurements of a satellite pass. Commonly, these observations have short durations with respect to the satellite orbit period. As a consequence, the use of classical orbit determination algorithms, as Laplace, Gauss or Escobal methods, give very poor results. This thesis faces with the problem of estimating the orbital parameters of an orbiting object using its optical streak acquired by a telescope or a high accuracy camera. In this thesis a new technique is developed for the Initial Orbit Determination from optical data by exploiting the genetic algorithms. The algorithm works without restrictions on the observer location. A recent challenging problem is the Initial Orbit Determination with space- based observations. This thesis focuses on the problem of determinating the orbital parameters of a satellite from an orbiting observer in LEO, using short time observations. We present the results based on a simulation with the observer on a sun-synchronous orbit with a single observation of just 60 s. Monte Carlo simulations are presented with di erent levels of sensor accuracy to show the reliability of the algorithm. The algorithm is able to yield a candidate solution for each observation. The coplanar case is analyzed and discussed as well. Several test show the reliability of the algorithm varying the number of the observations, the initialization method, the observation period and the noise seed

Temperature dependence of the mean magnon collision time in a spin Seebeck device

Based on the relaxation time approximation, the mean collision time for magnon scattering $\tau_c(T)$ is computed from the experimental spin Seebeck coefficient of a bulk YIG / Pt bilayer. The scattering results to be composed by two processes: the low temperature one, with a $T^{-1/2}$ dependence, is attributed to the scattering by defects and provides a mean free path around 10 $\mu$m; the high temperature one, depending on $T^{-4}$, is associated to the scattering by other magnons. The results are employed to predict the thickness dependence of the spin Seebeck coefficient for thin films.Comment: 13 pages, 4 figures, presented at JEMS 2020, submitted to J.Magn. Magn. Mate

Jacques Bony, L’Esthétique de Nerval

La nostra è un’epoca nella quale l’attenzione al fatto letterario in sé, e alle opere delle scienze umane in generale, appare – inutile disconoscerlo – alquanto ridotta, sacrificata tra la supremazia incontestata delle scienze esatte da un lato e quella delle tecnologie dall’altro. Ancor più rara, quasi eccezionale, appare dunque la circostanza che un testo critico di scrittura raffinata, destinato a pochi specialisti, possa vantare la pubblicazione di una seconda edizione… La prima per i tip..

Dagmar Wieser, Nerval : une poétique du deuil à l’âge romantique

Il lungo saggio di Dagmar Wieser, versione a stampa della tesi, sostenuta all’Università di Berna nel 1998 e diretta da Daniel Sangsue, percorre l’opera del Nostro e focalizza i luoghi nei quali si manifesta una denegazione della Morte – e ancor più un « deuil d’un objet d’amour » (p. 17) – nelle sue variazioni tematiche, enunciative e stilistiche, secondo un approccio metodologico di poetica storica e di metapsicologia ispirata alle teorie freudiane (introduction, pp. 11-24). Il volume si ar..