1,721,135 research outputs found
Simulazione numerica di circuiti non lineari a commutazione
No full textIn questo lavoro si vuole illustrare la struttura e le principali caratteristiche di un programma realizzato per effettuare per l'analisi assistita al calcolatore di circuiti non lineari a commutazione. Il programma determina le equazioni di stato della rete sotto esame e le risolve con la tecnica dell'esponenziale di matrice. Per la formulazione delle equazioni di stato è stata sviluppata un'estensione dell'algoritmo proposto da Chua e Lin per le reti lineari attive. Il programma proposto per la simulazione di circuiti contenenti dispositivi elettronici di potenza allo stato solido, pur ricorrendo ad un modello molto semplice (componenti a semiconduttore come interruttori ideali), consente la massima generalità. Per saggiare le capacità del programma sono stati simulati due semplici convertitori. I risultati sono stati confrontati sia con dati sperimentali, sia con simulazioni eseguite con il programma PSPICE. Il confronto ha mostrato un buon accordo tra simulazione e dati sperimentali nei limiti degli errori di misura. I risultati dell'analisi nel dominio del tempo ottenuti con l'algoritmo sviluppato e con PSPICE hanno mostrato un buon accordo dal punto di vista numerico, mentre dal punto di vista dei tempi il codice di calcolo proposto presenta tempi sensibilmente inferiori.
Computer-aided time-domain analysis of switched networks
No full textA new computer-oriented method for an efficient and accurate large-signal time-domain analysis of switched networks consisting of strictly linear elements and of a wide class of switches can be investigated. The switching elements are assumed ideal and the state equation method is adopted for the network description. When a network topology changes, state equations are derived systematically by means of a generalized formulation of the p-port contraint matrices. Each set of equations holds from a switching instant to the next one which is calculated through a Newton-type algorithm. Numerical results are compared with experimental data and SPICE simulations
Self-Adaptive Handoff Management for Mobile Streaming Continuity
No full textSelf-adaptive management and quality adaptation
of multimedia services are open challenges in the heterogeneous
wireless Internet, where different wireless access points potentially
enable anywhere anytime Internet connectivity. One of the
most challenging issues is to guarantee streaming continuity
with maximum quality, despite possible handoffs at multimedia
provi-sioning time. To enable handoff management to self-adapt
to specific application requirements with minimum resource
consumption, this paper offers three main contributions. First, it
proposes a simple way to specify handoff-related service-level
objectives that are focused on quality metrics and tolerable
delay. Second, it presents how to automatically derive from these
objectives a set of parameters to guide system-level configuration
about handoff strategies and dynamic buffer tuning. Third, it
describes the design and implementation of a novel handoff
management infrastructure for maximizing streaming quality
while minimizing resource consumption. Our infrastructure exploits
i) experimentally evaluated tuning diagrams for resource
management and ii) handoff prediction/awareness. The reported
results show the effectiveness of our approach, which permits to
achieve the desired quality-delay tradeoff in common Internet
deployment environments, even in presence of vertical handoffs
Topology Discovery Services for Monitoring the Global Grid
No full textFeature Topic ”An Optical Control Plane for the Grid Community: Opportunities, Challenges and the Vision
Short time scale variability at gamma rays in FSRQs and implications on the current models
No full textWe studied the rapid variability at GeV gamma rays of the flat-spectrum
radio quasar PKS 1222+216, which was recently found by the MAGIC
Cerenkov telescope to display very short variability (minutes time
scale) at hundreds of GeV. We analyzed the time period between 2010
April 29 and June 20, when the source generated a few gamma-ray flares
with flux in the MeV-GeV band in excess of 10^-5 ph cm^-2 s^-1 on daily
basis. We set tight upper limits on the observed doubling time scale
(about 1 hour on 2010 April 30), the smallest measured to date at
MeV-GeV energies, which can constrain the size of the gamma-ray emitting
region. We also studied the spectra measured during two flares (2010
April 30 and June 17-18). The combination of spectral and variability
studies obtained in the present work favors the hypothesis that gamma
rays are generally produced inside the broad-line region (BLR), but
sometimes the dissipation can occur at larger distances, nearby the
infrared torus
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Cross-Network Opportunistic Collection of Urgent Data in Wireless Sensor Networks
No full textUbiquitous smart environments equipped with low-cost and easily-deployable wireless sensor networks (WSNs) and ever-increasing widespread Mobile Ad hoc NETworks (MANETs) are opening brand new opportunities in environmental monitoring. This paper proposes an original solution for WSN/MANET integration based on the primary design guideline of opportunistically exploiting MANET overlays impromptu formed over the WSN to improve and boost the data collection task of a typical WSN. On the one hand, we adopt a cross-layer approach that exploits MANET connections to differentiate and fasten the delivery of sensed urgent data by pushing them over low-latency MANET paths. On the other hand, we take advantage of local cross-layer visibility of the WSN data collection procedures and protocols to carefully control and limit WSN–MANET coordination overhead. We claim that our proposed solution can obtain significant quality of service improvements via differentiation, by granting faster delivery times to urgent data with a very limited cost in most common execution scenarios
- …
