2,613 research outputs found
Multitemporal dendrogeomorphological analysis of slope instability in Upper Orcia Valley (Southern Tuscany, Italy)
The Upper Orcia Valley (Southern Tuscany, Italy) is a key site for the
comprehension of denudation processes typically acting in Mediterranean
badlands (calanchi) areas, thanks to the availability of long-lasting
erosion monitoring datasets and the rapidity of erosion processes development.
These features make the area suitable as an open air laboratory
for the study of badlands dynamic and changes in geoheritage due to
erosion (i.e. active geomorphosites).
Decadal multitemporal investigations on the erosion rates and the
geomorphological dynamics of the study area allowed to highlight a decrease
in the average water erosion rates during the last 60 years. More in
detail, a reduction of bare land and, consequently, of erosion processes
effectiveness and a contemporary increasing frequency of mass wasting
events were recorded. These trends can be partly related to the land cover
changes occurred in the study area from the 1950s onwards, which
consist of the significant increase of reforestation practices and important
other forms of human impacts on slopes, mainly land levelling for
agricultural exploitation.
In order to better identify the most significant phases of geomorphological
instability occurred in this area during the last decades, an
integrated approach based on multitemporal geomorphological mapping
and dendrogeomorphology analysis on specimen of Pinus nigra Arn.
was used. In detail, trees colonizing a denudation slope located in the
surrounding of the Radicofani town (Tuscany, Italy) and characterized
by calanchi and shallow mass movements deposits, were analyzed for
the 1985-2012 time period. The analysis of the growth anomaly indexes
and of compression wood allowed to determine a spatio-temporal differentiation
along the slope and respect to an undisturbed reference site.
The negative anomaly index results to be more pronounced in the trees
located on the investigated slope with respect to the ones sampled in
a non-disturbed area. Compression wood characterizes trees on slope
sectors mainly affected by runoff and/or mass movements with a different
persistence. Erosion rates were finally calculated through dendrogeomorphological
analysis on tree roots exposure (0.31-3 cm/y runoff
prevailing; 5.86-27.5 cm/y, mass movements prevailing). Dendrogeomorphological
results are in accordance with those obtained in the investigated
areas with multitemporal photogrammetric and geomorphologic
analyses
On the computation of reducible invariant tori on a parallel computer
We present an algorithm for the computation of reducible invariant tori of discrete dynamical systems that is suitable for tori of dimensions larger than 1. It is based on a quadratically convergent scheme that approximates, at the same time, the Fourier series of the torus, its Floquet transformation, and its Floquet matrix. The Floquet matrix describes the linearization of the dynamics around the torus and, hence, its linear stability. The algorithm presents a high degree of parallelism, and the computational effort grows linearly with the number of Fourier modes needed to represent the solution. For these reasons it is a very good option to compute quasi-periodic solutions with several basic frequencies. The paper includes some examples (flows) to show the efficiency of the method in a parallel computer. In these flows we compute invariant tori of dimensions up to 5, by taking suitable sections
Transport and invariant manifolds near L3 in the Earth-Moon Bicircular model
This paper focuses on the role of to organise trajectories for a particle going from Earth to Moon and viceversa, and entering or leaving the Earth-Moon system. As a first model, we have considered the planar Bicircular problem to account for the gravitational effect of the Sun on the particle. The first step has been to compute a family of hyperbolic quasi-periodic orbits near . Then, the computation of their stable and unstable manifolds provides connections between Earth and Moon, and also generates trajectories that enter and leave the Earth-Moon system. Finally, by means of numerical simulations based on the JPL ephemeris we show that these connections can guide the journey of lunar ejecta towards the Earth
Using invariant manifolds to capture an asteroid near the L3 point of the Earth-Moon Bicircular model
This paper focuses on the capture of Near-Earth Asteroids (NEAs) in a neighbourhood of the point of the Earth-Moon system. The dynamical model for the motion of the asteroid is the planar Earth-Moon-Sun Bicircular problem (BCP). It is known that the point of the Restricted Three-Body Problem is replaced, in the BCP, by a periodic orbit of centre saddle type, with a family of mildly hyperbolic tori that is born from the elliptic direction of this periodic orbit. It is remarkable that some pieces of the stable manifolds of these tori escape (backward in time) the Earth-Moon system and become nearly circular orbits around the Sun. In this work we compute this family of invariant tori and also high order approximations to their stable/unstable manifolds. We show how to use these manifolds to compute an impulsive transfer of a NEA to an invariant tori near . As an example, we study the capture of the asteroid in its approach of 2006. We show that there are several opportunities for this capture, with different costs. It is remarkable that one of them requires a as low as 20
Noise-induced macroscopic bifurcations in globally-coupled chaotic units
Large populations of globally-coupled identical maps subjected to independent
additive noise are shown to undergo qualitative changes as the features of the
stochastic process are varied. We show that for strong coupling, the collective
dynamics can be described in terms of a few effective macroscopic degrees of
freedom, whose deterministic equations of motion are systematically derived
through an order parameter expansion.Comment: Phys. Rev. Lett., accepte
On the station keeping of a Solar sail in the Elliptic Sun-Earth system
In this work we focus on the dynamics of a solar sail in the Sun Earth Elliptic Restricted Three-Body Problem with solar radiation pressure. The considered situation is the motion of a sail close to the point, but displacing the equilibrium point with the sail so that it is possible to have continuous communication with the Earth. In previous works we derived a station keeping strategy for this situation but using the Circular RTBP as a model. In this paper we discuss the effect of the eccentricity in the region close to the sail-displaced point of the Circular RTBP. Then we show how to use the information on this dynamics to design a station keeping strategy. Finally, we apply these results to the GeoStorm mission, including errors in the sail orientation and on the estimation of the position of the sail in the simulations
Effective Reducibility of Quasi-Periodic Linear Equations close to Constant Coefficients
Let us consider the differential equation where A is an elliptic constant matrix and Q depends on time in a quasi-periodic (and analytic) way. It is also assumed that the eigenvalues of A and the basic frequencies of Q satisfy a diophantine condition. Then it is proved that this system can be reduced to where is exponentially small in , and the linear change of variables that performs such a reduction is also quasi-periodic with the same basic frequencies as Q. The results are illustrated and discussed in a practical example
Theory of Materials and Finishes 1
Exam paper for second semester: Theory of Materials and Finishes
Metal Microelectromechanical Resonator Exhibiting Fast Human Activity Detection
This work presents a MEMS resonator used as an ultra-high resolution water vapor sensor (humidity sensing) to detect human activity through finger movement as a demonstrator example. This microelectromechanical resonator is designed as a clamped-clamped beam fabricated using the top metal layer of a commercial CMOS technology (0.35 ÎŒm CMOS-AMS) and monolithically integrated with conditioning and readout circuitry. Sensing is performed through the resonance frequency change due to the addition of water onto the clamped clamped beam coming from the moisture created by the evaporation of water in the human body. The sensitivity and high-speed response to the addition of water onto the metal bridge, as well as the quick dewetting of the surface, make it suitable for low-power human activity sensing
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