1,721,016 research outputs found
Periodic dynamics in queuing networks
No full textThis paper deals with state-dependent open Markovian (or exponential) queuing networks, for which arrival and service rates, as well as routing probabilities, may depend on the queue lengths. For a network of this kind, following Mandelbaum and Pats, we provide a formal definition of its associated fluid model, and we focus on the relationships which may occur between the network stochastic dynamics and the deterministic dynamics of its corresponding fluid model, particularly focusing on queuing networks whose fluid models have global periodic attractors
Chaos Based Generation of True Random Bits.
No full textIn this work, referring to some major results achieved in Ergodic Theory, we
discuss a theoretical approach for studying how to generate random bits using
piecewise linear chaotic maps, even taking into account the possible dispersion of
system parameters. In detail, referring to the work developed by Boyarsky and
Gora, we discuss the ergodic theory developed for piecewise affine expanding
transformations, with a special reference to the family of the Sawtooth maps
for truly random number generation.
Ergodic Theory classifies dynamical systems depending on the complexity degree
of their dynamics. Referring to this theoretical framework, we identify a
region within the parameter space in which the Sawtooth map preserves its exactness
property. Even if this work is particularly focused on this special family
of maps, we stress that the proposed approach can be generalized for studying
other piecewise affine maps proposed in literature for ICT applications. Furthermore,
we discuss the link that there exists between the theoretical forms of
entropy developed in Ergodic Theory (e.g., the Kolmogorov-Sinai entropy) and
the classical Shannon entropy for information sources.
This work is organized as in the following: in the next two subsections some
formal definitions about true random number generators are given. In Section 2
we introduce the concept of symbolic dynamics, presenting the family of Sawtooth
maps. Moreover, we prove the exactness property of these systems, considering
a parameter space which covers all those values of practical interest
in true random bit generation. Section 3 is entirely devoted to the analysis
of chaos-based symbolic dynamics, with a discussion on the link existing between
the theoretical forms of entropy developed in the Ergodic Theory (e.g.,
the Kolmogorov-Sinai entropy) and the classical Shannon entropy for information
sources. Conclusions and references close this work
Reliability and safety considerations affecting the design of a radar based railway crossing level passage monitoring system
No full textRailway crossing passage systems are designed to provide a barrier for unwanted intrusion on the railway tracks. Nevertheless an increase in incidents due to cars or trucks stuck in between the barriers are happening with higher frequency. Therefore the authors in this paper propose and discuss three potential configurations for undesired barrier intrusion detection system design, based on radar detectors and focussed their attention on the system reliability and safety aspects. In particular, the radar sensor is identified as the critical component and the configurations analysed accordingly
A smart measurement system with improved low-frequency response to detect moving charged debris
No full textWe propose a smart measurement system with improved low-frequency response to detect moving charged debris, to be used for turbomachinery condition monitoring. The proposed solution has been obtained combining theory, analog hardware design, and a digital postprocessing technique. The outputs of the system are a charge pulse detection digital warning signal, and the measurement of the peak and the width of the pulse. We discuss a theoretical framework, aimed to relax the system bandwidth requirements. In detail, we present an analytical approximation of the expression, describing the measured charge signal in the time domain, and we discuss the design of a charge amplifier whose frequency response can be specifically tailored for the considered application. The proposed solution has been evaluated with experimental results
Gas turbine sensor loop availability driven fall back strategies design
No full textThe design of a new heavy duty gas turbine may imply the exploitation of well proven, as well as, of new sensing technologies and approaches. Nevertheless a key driving point in bringing on the market some innovation resides in the opportunity to implement a flexible sensing system able to optimize the existing compromise among performance, safety, reliability, availability and maintenance (RAMS) parameters. This problem can be solved addressing the possible fall back strategies in case of single or multiple sensors failures through reliability and availability modeling. In this paper, an approach on the modeling of actual sensor configuration dynamic apportionment is presented by means of phase diagrams representation, with the aim of evaluating the advantages and the drawbacks linked to the choice of a certain sensing configuration despite of the sensor technology and relying on failure modes and failure and repair rates knowledge. The simulation results are presented for three different possible sensors configurations on a selected sensor monitoring chain used in gas turbine systems
Distributed UPS control systems reliability analysis
No full textModern power systems should comply with high reliability and availability standards in order to meet customer final expectations and market needs. In this context it is quite obvious that modern uninterruptible power supply (UPS) have started to exploit improvement strategies to achieve higher availability figures over time. At the same time, power, size and performance constraints become stricter placing tight barriers to developers. UPS developers started therefore to design distributed systems where different functions could be allocated to different control board sections. The newly designed systems resulted to have higher availability and improved modularity and expandability. In this paper the authors compare the availability performance of an UPS with a single core control board with a distributed UPS based on multiprocessor control boards. Additionally, a model for the variations of the failure rate due to environmental changes is proposed. In particular, Weibull probability density functions have been considered in order to take into account failure rate changes induced by temperature increase at warmup in a limited time frame
Histogram test of ADCs with chaotic samples
No full textIn this paper we discuss the possible use of chaotic signals for testing Analog to Digital Converters (ADCs). In detail, exploiting a chaos-based discrete-time noise generator, a method for generating test samples with a distribution arbitrarly close to the uniform one is proposed, and their use for the Code Density Test (also known as Histogram Test) of ADC is discussed
A lightweight digital system for the probabilistic characterization of true random bit generators
No full textIn this brief paper we present a low-complexity digital architecture for the probabilistic characterization of ergodic TRBGs. Differently from other methods based on the direct estimation of the generation probabilities of finite sets of binary words, in this study we investigate some theoretical relationships between the autocorrelation function of the binary source and the dynamical symbol generation probabilities, that can be exploited to obtain a probabilistic characterization of the TRBG. The solution is proposed to perform a real-time monitoring of TRBGs, that can be suitably implemented in lightweight digital systems
Metal oxide nanograined chemosensor: Influence of film microstructure on gas sensing
No full textIn this work the case of spherical grains will be discussed in order to point out that the reduction of the sensing film grain size changes the behavior, not always giving a better performance in terms of sensitivity, with respect to large grained films. The model was focused on p-type materials and some
simulation results for YCoO3 are shown and discussed
- …
