Robust Gravitational Wave Burst Detection and Source Localization in a Network of Interferometers Using Cross Wigner Spectra

We discuss a fast cross-Wigner transform based technique for detecting gravitational wave bursts, and estimating the direction of arrival, using a network of (three) non co-located interferometric detectors. The performances of the detector as a function of signal strength and source location, and the accuracy of the direction of arrival estimation are investigated by numerical simulations.Comment: accepted in Class. Quantum Gravit

A random-effects model for long-term degradation analysis of solid oxide fuel cells

Solid oxide fuel cells (SOFCs) are electrochemical devices converting the chemical energy into electricity with high efficiency and low pollutant emissions. Tough very promising, this technology is still in a developing phase, and degradation at the cell/stack level with operating time is still an issue of major concern. Methods to directly observe degradation modes and to measure their evolution over time are difficult to implement, and indirect performance indicators are adopted, typically related to voltage measurements in long-term tests. In order to describe long-term degradation tests, three components of the voltage measurements should be modelled: the smooth decay of voltage over time for each single unit; the variability of voltage decay among units; and the high-frequency small fluctuations of voltage due to experimental noise and lack of fit. In this paper, we propose an empirical random-effects regression model of polynomial type enabling to evaluate separately these three types of variability. Point and interval estimates are also derived for some performance measures, such as the mean voltage, the prediction of cell voltage, the reliability function and the cell-to-cell variability in SOFC stacks. Finally, the proposed methodology is applied to two real case-studies of long-term degradation tests of SOFC stacks

A New Estimation Algorithm for Interval Censored Data from Repairable Systems

For a minimally repaired system, whose failure process is described by a non-homogeneous Poisson process (NHPP), the classical maximum likelihood estimation procedures cannot be used when the system failures are hidden and detected only at inspection epochs. By assuming that the failure process follows a NHPP with power law intensity function, the Expectation-Maximization (EM) algorithm was recently proposed to estimate the model parameters and a procedure to test the presence of trend in the real failure data of some components of identical medical infusion pumps was discussed. However, the EM algorithm suffers in this application from some limitations due to its complexity and the large computational time required for convergence. This paper proposes a new estimation algorithm which is still iterative but, unlike the EM algorithm, is not based on the expectation of the log-likelihood function with respect to the conditional distribution of the unobserved data, but rather on the expectation of the conditioning variables, that is, of the unknown age of the system at the previous failure. This approach allows one to specify a simpler and much faster estimation procedure. A comparison between the proposed and the EM algorithms shows that the former performs as well as the latter, while requiring a drastically reduced computational burden. In addition, the proposed scheme can be applied to other intensity functions, such as the log-linear and the 2-parameter logarithmic functions. As a result, the test hypothesis of no trend in one of the analyzed datasets, which can not be rejected under the power law intensity function, is instead rejected under the alternative hypothesis of a log-linear intensity function

A Latency-driven Availability Assessment for Multi-Tenant Service Chains

Nowadays, most telecommunication services adhere to the Service Function Chain (SFC) paradigm, where network functions are implemented via software. In particular, container virtualization is becoming a popular approach to deploy network functions and to enable resource slicing among several tenants. The resulting infrastructure is a complex system composed by a huge amount of containers implementing different SFC functionalities, along with different tenants sharing the same chain. The complexity of such a scenario lead us to evaluate two critical metrics: the steady-state availability (the probability that a system is functioning in long runs) and the latency (the time between a service request and the pertinent response). Consequently, we propose a latency-driven availability assessment for multi-tenant service chains implemented via Containerized Network Functions (CNFs). We adopt a multi-state system to model single CNFs and the queueing formalism to characterize the service latency. To efficiently compute the availability, we develop a modified version of the Multidimensional Universal Generating Function (MUGF) technique. Finally, we solve an optimization problem to minimize the SFC cost under an availability constraint. As a relevant example of SFC, we consider a containerized version of IP Multimedia Subsystem, whose parameters have been estimated through fault injection techniques and load tests

HASFC: a MANO-compliant Framework for Availability Management of Service Chains

Most softwarized telco services are conveniently framed as Service Function Chains (SFCs). Indeed, being structured as a combination of interconnected nodes, service chains may suffer from the single point of failure problem, meaning that an individual node malfunctioning could compromise the whole chain operation. To guarantee "highly available" (HA) levels, service providers are required to introduce redundancy strategies to achieve specific availability demands, where cost constraints have to be taken into account as well. Along these lines we propose HASFC (standing for High Availability SFC), a framework designed to support, through a dedicated REST interface, the MANO infrastructure in deploying SFCs with an optimal availability-cost trade off. Our framework is equipped with: i) an availability model builder aimed to construct probabilistic models of the SFC nodes in terms of failure and repair actions; ii) a chaining and selection module to compose the possible redundant SFCs, and extract the best candidates thereof. Beyond providing architectural details, we demonstrate the functionalities of HASFC through a use case which considers the IP Multimedia Subsystem, an SFC-like structure adopted to manage multimedia contents within 4G and 5G networks

Semi-Markov Models for Performance Evaluation of Telecommunication Networks in the Presence of Failures

Planning and deployment of next generation telecommunication networks based on the Third Generation Partnership Project IP Multimedia Subsystem (IMS) must take into account the occurrence of random failures causing performance degradations, in order to assess and maintain the Quality of Service offered by telecommunication service providers to their subscribers. In particular, core network signalling servers of IMS can be modelled as repairable multi-state elements where server states correspond to different performance levels. In this paper, we evaluate IMS signalling network performance in terms of the number of sessions handled by the network per time unit, by adopting a semi-Markov model for the IMS servers, which allows as well for non-exponential probability distributions of sojourn times, as often observed in practical network scenarios. Furthermore, a redundancy optimisation problem is solved in an IMS-based realistic scenario, to the aim of minimizing the deployment cost of a telecommunication network with a given availability requirement

Secure Mobile IPv6 for Mobile Networks based on the 3GPP IP Multimedia Subsystem

The rapid spread of new radio access technologies and the consequent service opportunities have stimulated thetechnical and scientific community to investigate future evolution scenarios for 3rd Generation networks (3G), generically referred to as Beyond-3G or 4G. They are going to be characterized by ever stronger requirements for security, as well as the capability for the final users to experience continuous connectivity and uninterrupted services of IP applications as they move about from one access network to another. Key issues are: i) securityprovision for applications exchanging data in diverse wireless networks; ii) seamless mobility (handoff) between different coverage domains and, in case, access technologies. Since many proposals are based on the use of the Mobile IPv6 protocol, in this paper we analyze the security threats emerging from some Mobile IPv6 mechanisms for mobility management, and we propose a solution against such threats, under the assumption that both end users (mobile or not) are attached to a Mobile IPv6-enabled 3GPP IP Multimedia Subsystem network

Caratterizzazione della dinamica produttiva di pascoli naturali italiani

This work studies herbage production and its seasonal distribution in indigenous pastures, and analyses the relationship between the environmental factors (soil, clima, vegetation) and the productivity of these resources. The investigations have been carried on during the period 1983-90 by the joint activity of 10 different University Istitutions in 23 different environments distributed along the Italian peninsula and the main islands. For each environment, pasture production has been measured with the Corrall and Fenlon method, analysing the more important vegetational and ecological conditions; altogether the total yearly production and the seasonal pattern of herbage production have been detected on 104 pastures. The total herbage yield is not significantly influenced by the latitudinal gradient, and the overall regional (alps, central Appenine, south Apennine and islands) production is about 2.3 t ha-1 year-1 The wide range (0.5-6.3 t ha-1 year-1) of herbage production, on small or medium scale, seems to be due to evident changeof environmental or management factors. Five types of seasonal distribution of herbage growth are evidenced with multivariate analysis methods, based on the growing season and the amplitude of the growth. With mean temperature above 12°C and total rainfall below 800 mm, herbage distribution shows a standstill during summer period and an evident regrowth in autumn. On the contrary, for the 4 other distribution types, the winter standstill become important, and the types are distinct by summer growth amplitude and by the growing season lenght. With cluster analysis method, for each type of herbage distribution, have been pointed out under-types characterized by interannual herbage production variation. Among the environmental factors, vegetation characheristics, expressed as Pasture Value following Daget and Poissonet seems to be strictly correlated with total production. The comparative poor role played by the soil and climatic factor, may be due to the strong past and present antropic influence, related with management and utilization techniques. Il presente lavoro ha come scopo l'approfondimento delle conoscenze sulla produzione e sulla distribuzione stagionale della crescita dell'erba dei pascoli naturali, nonché l'analisi delle interazioni tra i fattori ambientali, pedo-climatici e vegetazionali, e la risposta produttiva di queste risorse. La ricerca è stata condotta nel periodo 1983-90 da 10 diverse Istituzioni Universitarie, in 23 ambienti differenti, distribuiti lungo tutta la penisola e le isole maggiori. Per ogni ambiente, con il metodo di rilievo di Corrall e Fenlon, è stata saggiata la risposta produttiva di pascoli rappresentativi delle principali situazioni vegetazionali e di giacitura; complessivamente sono state rilevate la produzione totale annua e la curva di produttività media pluriennale di 104 pascoli. Riguardo la produzione annua complessiva si è osservato che essa non presenta variazioni significative lungo il gradiente latitudinale, collocandosi tra le diverse regioni (alpina, centro appenninica, suq, appenninica e insulare) attorno a 2.3 t ha-1 anno-1. La fitomassa raccolta è soggetta invece a variazioni sensibili (0.5-6.3 t ha-1 anno-1) riconducibili a fattori ambientali e gestionali che si esprimono su piccola e media scala. Con metodi di analisi multivariata si sono individuate 5 tipologie distributive della crescita dell'erba, in rapporto alla stagione vegetativa e alle variazioni dell'intensità di crescita nel corso della stagione stessa. Con temperature medie e precipitazioni annue rispettivamente maggiori di 12°C e minori di 800 mm, risulta evidente la stasi vegetativa nel trimestre estivo e la ripresa vegetativa autunnale. Nel caso opposto la stasi è invernale e le 4 tipologie afferenti a questo modello, sono distinguibili dall'entità della crescita nei mesi estivi e dalla durata della stagione vegetativa. Per ogni tipologia produttiva, sono state evidenziate, tramite l'analisi cluster, sotto-tipologie distinte per la variabilità produttiva interannuale. Tra i fattori ambientali, la vegetazione, espressa attraverso l'indice del valore pastorale di Daget e Poissonet, presenta una buona capacità predittiva nei confronti del livello produttivo dei pascoli. Il contributo comparativamente modesto offerto dai fattori pedoclimatici sembra attribuibile alla forte influenza antropica, pregressa e attuale, attraverso le cure colturali e l'utilizzazione

Buffered high charge spectrally-peaked proton beams in the relativistic-transparency regime

Spectrally-peaked proton beams of high charge (Ep » 8 MeV, DE » 4 MeV, N » 50 nC ) have been observed from the interaction of an intense laser (>1019 W cm−2) with ultrathin CH foils, as measured by spectrally-resolved full beam profiles. These beams are reproducibly generated for foil thicknesses 5–100 nm, and exhibit narrowing divergence with decreasing target thickness down to »8 for 5 nm. Simulations demonstrate that the narrow energy spread feature is a result of buffered acceleration of protons. The radiation pressure at the front of the target results in asymmetric sheath fields which permeate throughout the target, causing preferential forward acceleration. Due to their higher charge- to-mass ratio, the protons outrun a carbon plasma driven in the relativistic transparency regime