4,243 research outputs found
Innovative observing strategy and orbit determination for Low Earth Orbit Space Debris
We present the results of a large scale simulation, reproducing the behavior
of a data center for the build-up and maintenance of a complete catalog of
space debris in the upper part of the low Earth orbits region (LEO). The
purpose is to determine the performances of a network of advanced optical
sensors, through the use of the newest orbit determination algorithms developed
by the Department of Mathematics of Pisa (DM). Such a network has been proposed
to ESA in the Space Situational Awareness (SSA) framework by Carlo Gavazzi
Space SpA (CGS), Istituto Nazionale di Astrofisica (INAF), DM, and Istituto di
Scienza e Tecnologie dell'Informazione (ISTI-CNR). The conclusion is that it is
possible to use a network of optical sensors to build up a catalog containing
more than 98% of the objects with perigee height between 1100 and 2000 km,
which would be observable by a reference radar system selected as comparison.
It is also possible to maintain such a catalog within the accuracy requirements
motivated by collision avoidance, and to detect catastrophic fragmentation
events. However, such results depend upon specific assumptions on the sensor
and on the software technologies
Orbit Determination with the two-body Integrals
We investigate a method to compute a finite set of preliminary orbits for
solar system bodies using the first integrals of the Kepler problem. This
method is thought for the applications to the modern sets of astrometric
observations, where often the information contained in the observations allows
only to compute, by interpolation, two angular positions of the observed body
and their time derivatives at a given epoch; we call this set of data
attributable. Given two attributables of the same body at two different epochs
we can use the energy and angular momentum integrals of the two-body problem to
write a system of polynomial equations for the topocentric distance and the
radial velocity at the two epochs. We define two different algorithms for the
computation of the solutions, based on different ways to perform elimination of
variables and obtain a univariate polynomial. Moreover we use the redundancy of
the data to test the hypothesis that two attributables belong to the same body
(linkage problem). It is also possible to compute a covariance matrix,
describing the uncertainty of the preliminary orbits which results from the
observation error statistics. The performance of this method has been
investigated by using a large set of simulated observations of the Pan-STARRS
project.Comment: 23 pages, 1 figur
Nanoscale roughness and morphology affect the IsoElectric Point of titania surfaces
We report on the systematic investigation of the role of surface nanoscale
roughness and morphology on the charging behaviour of nanostructured titania
(TiO2) surfaces in aqueous solutions. IsoElectric Points (IEPs) of surfaces
have been characterized by direct measurement of the electrostatic double layer
interactions between titania surfaces and the micrometer-sized spherical silica
probe of an atomic force microscope in NaCl aqueous electrolyte. The use of a
colloidal probe provides well-defined interaction geometry and allows
effectively probing the overall effect of nanoscale morphology. By using
supersonic cluster beam deposition to fabricate nanostructured titania films,
we achieved a quantitative control over the surface morphological parameters.
We performed a systematical exploration of the electrical double layer
properties in different interaction regimes characterized by different ratios
of characteristic nanometric lengths of the system: the surface rms roughness
Rq, the correlation length {\xi} and the Debye length {\lambda}D. We observed a
remarkable reduction by several pH units of IEP on rough nanostructured
surfaces, with respect to flat crystalline rutile TiO2. In order to explain the
observed behavior of IEP, we consider the roughness-induced self-overlap of the
electrical double layers as a potential source of deviation from the trend
expected for flat surfaces.Comment: 63 pages, including 7 figures and Supporting Informatio
A Possibility to Build Isolated Masonry Housing in High Seismic Zones Using Rubber Seismic Isolators
New residential buildings in developing countries often have inadequate seismic protection, particularly for masonry. Such material is widely preferred because the cost and application are relatively cheap. To decrease the vulnerability, an interesting option is represented by seismic isolation, but the cost should remain relatively low, and this is the reason why rubber isolation with few pads remains the most suitable technical solution to adopt. In this study, we deal with a newly conceived low-cost seismic isolation system for masonry buildings relying on elastomeric bearings. The elastomeric isolator here proposed consists of few layers of rubber pads and fiber lamina, making it cheaper comparing to the conventional isolators. A detailed 3D finite element (FE) analysis to predict the behavior of the low-cost rubber isolator undergoing moderate deformations is carried out. A Yeoh hyperelasticity model with coefficients estimated through available experimental data is assumed for rubber pads. Having so derived the shear behavior, such isolation system is implemented at a structural level into a two stories masonry house prototype, identifying the 3D model with a damped nonlinear spring model, so making the FE analysis computationally inexpensive. For masonry, a concrete damage plasticity (CDP) model available in the commercial FE code Abaqus is adopted. A nonlinear static-pushover analysis is conducted to assess the performance of the isolated building. To simulate a realistic condition under seismic event, a ground motion data is applied to observe the dynamic behavior of the building by monitoring the damage level of masonry. Through a-posterior estimation, it is also possible to monitor the deformation of the isolators during the seismic excitation, to determine whether the isolator is capable of resisting shear deformations in different angles. According to the results obtained, quite good isolation is obtained with the system proposed, with immediate applicability at a structural level
Vulcanization degree influence on the mechanical properties of Fiber Reinforced Elastomeric Isolators made with reactivated EPDM
Rubber is well known as the basic material for some structural devices, such as seaport fenders and seismic isolators. In practice, to seismically isolate a structure it is necessary to interpose between the foundation and the superstructure a rubber device that increases the period of the superstructure, a feature that allows the structure to be “transparent” to the seismic excitation. A seismic isolator is constituted typically by a package of several rubber pads 1–2 cm thick vertically interspersed with either steel laminas or FRP dry textiles suitably treated. In this latter case the isolator is called FREI (Fiber Reinforced Elastomeric Isolator). FREIs exhibit light weight, easy installation and low cost. In this study, recycled rubber in the form of reactivated EPDM has been used to produce very low cost FREIs, combined with glass fiber reinforcement. To be ready for structural application, the rubber used must be vulcanized correctly to properly create the polymer crosslinking. However, all rubber mechanical properties are strongly affected by curing temperature and curing time. Here, the mechanical properties of a typology of FREI conceived and produced by the authors in prototypes are evaluated through a series of experimental tests and numerical computations, taking into account the different levels of vulcanization degree. Shore A hardness test, uniaxial tensile test, and relaxation test have been conducted and verified through Finite Element (FE) modeling. All collected data allow to precisely determine the curing time and temperature to use in the industrial production to obtain optimal output mechanical properties for FREIs
The evolution of the orbit distance in the double averaged restricted 3-body problem with crossing singularities
We study the long term evolution of the distance between two Keplerian
confocal trajectories in the framework of the averaged restricted 3-body
problem. The bodies may represent the Sun, a solar system planet and an
asteroid. The secular evolution of the orbital elements of the asteroid is
computed by averaging the equations of motion over the mean anomalies of the
asteroid and the planet. When an orbit crossing with the planet occurs the
averaged equations become singular. However, it is possible to define piecewise
differentiable solutions by extending the averaged vector field beyond the
singularity from both sides of the orbit crossing set. In this paper we improve
the previous results, concerning in particular the singularity extraction
technique, and show that the extended vector fields are Lipschitz-continuous.
Moreover, we consider the distance between the Keplerian trajectories of the
small body and of the planet. Apart from exceptional cases, we can select a
sign for this distance so that it becomes an analytic map of the orbital
elements near to crossing configurations. We prove that the evolution of the
'signed' distance along the averaged vector field is more regular than that of
the elements in a neighborhood of crossing times. A comparison between averaged
and non-averaged evolutions and an application of these results are shown using
orbits of near-Earth asteroids.Comment: 29 pages, 8 figure
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