690 research outputs found
The LARES mission: an opportunity to teach general relativity. Frame dragging and Lense-Thirring effect
LARES is an Italian Space Agency mission devoted to test frame-dragging, a prediction of general relativity.
On February 2012 the satellite has been successfully put in orbit with the qualification flight of VEGA, the new European Space Agency launcher. Basic concepts of general relativity are becoming more and more familiar because of the part they play in science fiction movies. But frame-dragging (more formally known as the Lense-Thirring effect), is so peculiar that it is a relatively unknown effect. The idea of this paper is to start from the description of the experiment and then to push some parameters of the experiment to extreme values in order to magnify the effects of relativity. This approach will provide not only the students and general people but also professionals not strictly specialized in general relativity, with increased interest in
gravitational theories
LARES-lab: a thermovacuum facility for research and e-learning. Tests of LARES satellite components and small payloads for e-learning
LARES, an Italian Space Agency satellite, has been launched successfully in 2012. A small thermovacuum facility has been designed and built specifically for performing tests on the optical components of the satellite. Due to the extremely demanding performances of the optical cube corner reflectors, the space conditions have been simulated using the most up-to-date technology available. In particular Sun, Earth and deep space can be simulated in a ultra high vacuum. It is planned to automate the facility so that it can be operated remotely over the internet. The students during the lectures and the researchers from home will be able to perform thermal tests on specimens by exposing them, for specified amount of time, toward Earth, Sun or deep space. They will collect pressures and temperatures and will input additional thermal power through resistive heaters. The paper will first describe the facility and its capabilities showing the tests performed on LARES satellite components but will focus mainly to the planned upgrades that improve its remote use both for research and e-learning
LARES a new satellite specifically designed for testing general relativity
It is estimated that today several hundred operational satellites are orbiting Earth while many more either already re-entered the atmosphere or are no longer operational. On the 13th of February 2012 one more satellite of the Italian Space Agency has been successfully launched. The main difference with respect to all other satellites is its extremely high density that makes LARES (LAser RElativity Satellite) not only the densest satellite but even the densest known orbiting object in the solar system. That implies the non-gravitational perturbations on its surface will have the smallest effects on its orbit with respect to all other artificial orbiting objects. Those design characteristics are required to perform an accurate test of frame dragging and specifically a test of Lense-Thirring effect, predicted by General Relativity. LARES satellite is passive and covered with 92 retroreflectors. Laser pulses, sent from several ground stations, allow an accurate orbit determination. Along with this last aspect and the mentioned special design one has to take into account the effects of the Earth gravitational perturbations due to the deviation from the spherical symmetry of the gravitational potential. To this aim the latest determinations of the Earth gravitational field, produced using gravitational data from several dedicated space missions including GRACE, and the combination of data from three laser ranged satellites is used in the LARES experiment. In spite of its simplicity LARES was a real engineering challenge both in term of manufacturing and testing. The launch was performed with the VEGA qualification flight provided by the European Space Agency. Data acquisition and processing is in progress. The paper will describe the scientific objectives, the status of the experiment, the special feature of the satellite and separation system including some manufacturing issues, and the special tests performed on its retroreflectors
A Distributed Demand-Side Management Framework for the Smart Grid
This paper proposes a fully distributed Demand-Side Management system for
Smart Grid infrastructures, especially tailored to reduce the peak demand of
residential users. In particular, we use a dynamic pricing strategy, where
energy tariffs are function of the overall power demand of customers. We
consider two practical cases: (1) a fully distributed approach, where each
appliance decides autonomously its own scheduling, and (2) a hybrid approach,
where each user must schedule all his appliances. We analyze numerically these
two approaches, showing that they are characterized practically by the same
performance level in all the considered grid scenarios. We model the proposed
system using a non-cooperative game theoretical approach, and demonstrate that
our game is a generalized ordinal potential one under general conditions.
Furthermore, we propose a simple yet effective best response strategy that is
proved to converge in a few steps to a pure Nash Equilibrium, thus
demonstrating the robustness of the power scheduling plan obtained without any
central coordination of the operator or the customers. Numerical results,
obtained using real load profiles and appliance models, show that the
system-wide peak absorption achieved in a completely distributed fashion can be
reduced up to 55%, thus decreasing the capital expenditure (CAPEX) necessary to
meet the growing energy demand
Adaptive Robust Traffic Engineering in Software Defined Networks
One of the key advantages of Software-Defined Networks (SDN) is the
opportunity to integrate traffic engineering modules able to optimize network
configuration according to traffic. Ideally, network should be dynamically
reconfigured as traffic evolves, so as to achieve remarkable gains in the
efficient use of resources with respect to traditional static approaches.
Unfortunately, reconfigurations cannot be too frequent due to a number of
reasons related to route stability, forwarding rules instantiation, individual
flows dynamics, traffic monitoring overhead, etc.
In this paper, we focus on the fundamental problem of deciding whether, when
and how to reconfigure the network during traffic evolution. We propose a new
approach to cluster relevant points in the multi-dimensional traffic space
taking into account similarities in optimal routing and not only in traffic
values. Moreover, to provide more flexibility to the online decisions on when
applying a reconfiguration, we allow some overlap between clusters that can
guarantee a good-quality routing regardless of the transition instant.
We compare our algorithm with state-of-the-art approaches in realistic
network scenarios. Results show that our method significantly reduces the
number of reconfigurations with a negligible deviation of the network
performance with respect to the continuous update of the network configuration.Comment: 10 pages, 8 figures, submitted to IFIP Networking 201
Microscopic description for the emergence of collective dissipation in extended quantum systems
Practical implementations of quantum technology are limited by unavoidable
effects of decoherence and dissipation. With achieved experimental control for
individual atoms and photons, more complex platforms composed by several units
can be assembled enabling distinctive forms of dissipation and decoherence, in
independent heat baths or collectively into a common bath, with dramatic
consequences for the preservation of quantum coherence. The cross-over between
these two regimes has been widely attributed in the literature to the system
units being farther apart than the bath's correlation length. Starting from a
microscopic model of a structured environment (a crystal) sensed by two bosonic
probes, here we show the failure of such conceptual relation, and identify the
exact physical mechanism underlying this cross-over, displaying a sharp
contrast between dephasing and dissipative baths. Depending on the frequency of
the system and, crucially, on its orientation with respect to the crystal axes,
collective dissipation becomes possible for very large distances between
probes, opening new avenues to deal with decoherence in phononic baths
The κ - μ shadowed fading model with arbitrary intercluster correlation
In this paper, we propose a generalization of the
well-known κ-μ shadowed fading model. Based on the clustering
of multipath waves as the baseline model, the novelty of this
new distribution is the addition of an arbitrary correlation for
the scattered components within each cluster. It also inherits
the random fluctuation of the dominant component, which is
assumed to be the same for all clusters. Thus, it unifies a wide
variety of models: Rayleigh, Rician, Rician shadowed, Nakagami-
m, κ-μ and κ-μ shadowed as well as multivariate Rayleigh,
Rician and Rician shadowed. The main statistics of the newly
proposed model, i.e. moment generating function, probability
density function and cumulative density function, are given in
terms of exponentials and powers, and some numerical results
are provided in order to analyze the impact of the arbitrary
intercluster correlation.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec
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