1,721,361 research outputs found
Vertical QoS Mapping over Wireless Interfaces
No full textThis article focuses on the problem of quality of service mapping between layers in a cascade. Protocol stacks in telecommunications networks are
composed of functional layers. QoS provision depends on the performance achieved at each layer and is based on functions performed at layer
interfaces. In practice, QoS derives from reliable physical and link layers that can offer specific transport services to upper network layers. The
data flows (or bundles of flows) generated by the upper layers (e.g., the network layers) are forwarded down to a physical interface that transports the information along a channel that provides, if possible, the expected QoS to the upper layers. The action is called vertical QoS mapping and poses many challenges for a communication scientist, in particular if it is applied to wireless interfaces.
This article states the definition of vertical QoS mapping, proposes a formal separation between technology-dependent and technology-indepen-
dent layers, models each functional layer as a battery of buffers, generalizes the relation between layers through a chain of buffers in a cascade, formalizes the theoretical problems of vertical QoS mapping, and suggests possible solutions that use dynamic bandwidth allocation schemes
A New SVDD Approach to Reliable and Explainable AI
No full textSafety engineering and artificial intelligence are two fields that still need investigation on their reciprocal interactions. Safety should be guaranteed when autonomous decision may lead to risk for the environment and the human. The present work addresses how support vector data description (SVDD) can be redesigned to detect safety regions in a cyber-physical system with zero statistical error. Rule-based knowledge extraction is also presented, to let the SVDD be understandable. Two applications are considered for performance evaluation: domain name server tunneling detection and region of attraction estimation of dynamic systems. Results demonstrate how the new SVDD and its intelligible representation are both suitable in designing safety regions, still maximizing the space of the working conditions
Health assessment and ambient vibration testing of the “Ponte delle Torri” of Spoleto during the 2016–2017 Central Italy seismic sequence
No full textThe Ponte delle Torri is a large medieval masonry bridge, one of the main architectural heritage of Spoleto, Italy. The location of the bridge is less than 50 km from the main epicenters of the recent Central Italy earthquakes (Mw > 5.0) that occurred between August 2016 and February 2017. In addition, some minor quakes of the sequence (Mw between 3.0 and 4.0) occurred within 10 km from the bridge, causing some damages and fear among the population around Spoleto. In this context, the present paper aims at contributing to understand the effects on the structural health of the bridge by analyzing the ambient vibration data acquired before, during and after the seismic sequence, as changes in the dynamic behavior of the structure might indicate the evolution of the state of damage of the monument. In particular, vibration data were processed by modal analysis techniques for mutual validation of the extracted modal parameters. Environmental and vibration data were simultaneously acquired to take into account the seasonal effects on the dynamic behavior. Through a preliminary finite-element model (FEM) the modal shapes were obtained to choose the positions where to locate the sensors for the vibration spot acquisition session of June 2015. The same positions were acquired in October 2016 and at the end of May 2017. Subsequently, a more detailed FEM was produced based on a 3D reconstruction by structure-from-motion stereo-photogrammetry technique with high-resolution photos from unmanned aerial vehicle of the bridge. The model was validated through comparison with the damage pattern experienced by the bridge and then used for assessing the seismic safety by means of both, nonlinear dynamic and static push-over analyses. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature
A measurement-based adaptive control mechanism for pricing in telecommunication networks
No full textResource allocation in satellite networks: certainty equivalent approaches versus sensitivity estimation algorithms
No full textIn this paper, we consider a resource allocation problem for a satellite network, where variations of fading conditions are added to those of traffic load. Since the capacity of the system is finite and divided in finite discrete portions, the resource allocation problem reveals to be a discrete stochastic programming one, which is typically NP-hard. We propose a new approach based on the minimization over a discrete constraint set using an estimation of the gradient, obtained through a 'relaxed continuous extension' of the performance measure. The computation of the gradient estimation is based on the infinitesimal perturbation analysis technique, applied on a stochastic fluid model of the network. No closed-forms of the performance measure, nor additional feedback concerning the state of the system, and very mild assumptions on the probabilistic properties about the statistical processes involved in the problem are requested. Such optimization approach is compared with a dynamic programming algorithm that maintains a perfect knowledge about the state of the satellite network (traffic load statistics and fading levels). The comparison shows that the sensitivity estimation capability of the proposed algorithm allows to maintain the optimal resource allocation in dynamic conditions and it is able to provide even better performance than the one reached by employing the dynamic programming approach
On-off Dual Channel Coding as a Team Decision Problem
No full textWe consider the 'single-letter' ('one-shot' or 'zero-delay') source-channel coding of a sensor's measurements in the presence of two channels as a constrained team decision theory problem. Under a global power constraint and quadratic distortion measure, the action space of coding strategies is restricted to on-off (transmission or silence) decisions. The latter are communicated to the decoder through a binary side channel, whereas in case of transmission the uncoded analog measurement is sent over the main communication channel between the transmitter and the receiver. By further restrictions on the behavior of the encoder, suboptimal team control strategies are derived in closed form, along with their parameters that stem from a numerical optimization problem. The distortion of the resulting strategy is compared with other schemes under non-Gaussian source and noise
Test of FBG sensors for monitoring high pressure pipes
No full textFibre Bragg Grating (FBG) sensors are increasingly being used on a wide range of civil, industrial and aerospace structures. The sensors are created inside optical fibres (usually standard telecommunication fibres); the optical fibres technology allows to install the sensors on structures working in harsh environments, since the materials are almost insensitive to corrosion, the monitoring system can be positioned far away from the sensors without sensible signal losses, and there is no risk of electric discharge. FBG sensors can be used to create strain gages, thermometers or accelerometers, depending on the coating on the grating, on the way the grating is fixed to the structure, and on the presence of a specifically designed interface that can act as a transducer. This paper describes a test of several different FBG sensors to monitor an high pressure pipe that feeds the hydraulic actuators of a 6 degrees-of-freedom shaking table at the ENEA Casaccia research centre. A bare FBG sensor and a copper coated FBG sensor have been glued on the pipe. A third sensor has been mounted on a special interface to amplify the vibrations; this last sensor can be placed on the steel pipe by a magnetic mounting system, that also allows the its removal. All the sensor are placed parallel to the axis of the pipe. The analysis of the data recorded when the shaking table is operated will allow to determine which kind of sensor is best suited for structural monitoring of high pressure pipelines. © 2017 SPIE
Reliable AI Through SVDD and Rule Extraction
No full textThe proposed paper addresses how Support Vector Data Description (SVDD) can be used to detect safety regions with zero statistical error. It provides a detailed methodology for the applicability of SVDD in real-life applications, such as Vehicle Platooning, by addressing common machine learning problems such as parameter tuning and handling large data sets. Also, intelligible analytics for knowledge extraction with rules is presented: it is targeted to understand safety regions of system parameters. Results are shown by feeding data through simulation to the train of different rule extraction mechanisms
Aluminium based protective coatings produced on AISI 304 stainless. Journ. de Phys. IV 3,877-880 ,
No full textThe diffision of Aluminium is one of the most promising methods to build superficial coatings for stainless
steel protection.
Heat treatments at 800 OC performed on rods of AISI 304 steel, Aluminium coated by means of
electrodeposition, displayed the possibility of forming intermetallic compounds. Depending on the
duration of the heat treatment and on the cooling kinetics, these compounds can be continuous.
At high cooling kinetics (water cooling) a two-phase structure composed of y' (Ni3Al) and y
(substitutional solid solution) is obtained.
At slow cooling rates (in furnace), a substitutional solid solution and some precipitates of y' (Ni3Al) and
p (NiAl) can be observed.
At intermediate cooling rates (oil cooling and air cooling), only the substitutional solution and the y' phase
are present.
Using furnace cooling from 800 OC until 500 OC, permanence at this temperature for I92 h and cooling
furnace, the two-phase structure obtained is composed of the substitutional solid solution and the j3 (NiAl)
phase.
The existence of these phases and their composition have been reported by X-ray diffraction patterns and
microanalysis.
The possibility of forming a natural composite, constituted by a hard phase of aluminides diffised in a
substitutional solid solution, has an important consequence on the mechanical and protection properties of
these coatings. Moreover, the diffusion of Al improves the adhesion of coatings
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