1,721,207 research outputs found
Dynamic Data Reconfiguration for SPMD Programs in Faulty Multicomputer
No full textThe single-program multiple-data (SPMD) paradigm is becoming the most diffuse way to program commercial multicomputers. In this paper we demonstrate that for a wide class of SPMD algorithms it is possible to achieve an efficient fault tolerance avoiding hardware redundancy. We propose a software approach that aims to reconfigure data, thus achieving a good slowdown in computation owing to the fine granularity of the workload to redistribute. In particular, we present and compare three data reconfiguration strategies applied to a problem model that includes a wide class of SPMD iterative algorithms characterized by nonlocal communications among the nodes. The result is that in most of the cases it is better to introduce some communication overhead than to leave idle a few healthy processor
The Optically-Coupled Current-Mirror: a Novel Approach for Linear Transmission of Fast Analogue Signals via Fiber Optics
No full textWe report recent improvements in the performance of a novel circuit topology, the optically-coupled current-mirror (OCCM), that includes optical links in its feedback and forward paths. In this way the input-stage remains Galvanically isolated from the rest of the circuit. The input stage consists on a passive dipole composed only by two components: a LED and a photodiode connected back-to-back. When it is cooled down, eventually close to 77 K, the optical power versus LED-current characteristics assumes a perfectly linear law and the open-loop gain increases by a factor at least x 2, due to the increase of the LED responsivity. The input stage can be connected in series with the anode of different types of ionizing detectors. Originally conceived and operated with success for the readout of the DC component of PMTs biased with cathode grounded, the OCCM has now been optimized for the transmission of fast analogue signals. At present the signal bandwidth approaches 32 MHz. The dynamic range can reach large values by connecting two or more input stages in series, each one associated to a single channel with appropriate gain. To be noted that the only semiconductor devices eventually subject to radiation damage are the LED and the photodiode of the input stage. In this paper we describe recent achievements of the OCCM, and discuss the latest results obtained
Comportamento criogenico di dispositivi optoelettronici per la trasmissione di segnali analogici mediante fibre ottiche
No full textLa trasmissione di un segnale analogico via fibra ottica è tematica di interesse per rivelatori criogenici operanti in strumenti basati a terra oppure imbarcati su satellite. Per meglio comprendere le performance criogeniche dei links ottici analogici, abbiamo investigato il comportamento a bassa temperatura di IR LEDs in AlGaAs, fotodiodi PIN e al Si e di fotodiodi a valanga (APD). I LED al AlGaAs hanno dimostrato un notevole incremento della responsività a 77K e la caratteristica luce-corrente diviene lineare anche se operati a bassa corrente. Al contrario i fotodiodi PIN e al Si mostrano un degrado delle performance quando raffreddati. A 77K, gli APD mostrano invece una responsività pari a quando operati a 300K, ma con una marcata riduzione della tensione di polarizzazione inversa
Cryogenic behaviour of optoelectronic devices for the transmission of analog signals via fiber optics
No full textThe transmission of analog signals via fiber optics is a subject of interest for applications with detectors operating at cryogenic temperature, at ground or on space borne instruments. For those detectors, both thermal and galvanic decoupling shall be required. For a better understanding of the cryogenic performance of cooled optoelectronic devices, we have investigated an infrared AlGaAs LEDs, a Si p-i-n photodiode, a Si photodiode, and an avalanche photodiode (APD). Results of a study related to the photodiode's dark currents at low temperature is presented. In fact, we have clearly measured a strong reduction of the dark current when these devices are cooled dow
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
Gilbert Durand, Introduzione alla mitodologia. Miti e società, (pref. di M. Maffesoli; trad. e cura di V. Grassi), Mimesis, Milano, 2022, pp. 188
No full textSi tratta di una estesa recensione del volume di Gilbert Durand, Introduzione alla mitodologia. Miti e società, (pref. di M. Maffesoli; trad. e cura di V. Grassi), edito da Mimesis, Milano nel 202
Dynamic data reconfiguration for SPMD programs in faulty multicomputers
No full textThe single-program multiple-data (SPMD) paradigm is becoming the most diffuse way to program commercial multicomputers. In this paper we demonstrate that for a wide class of SPMD algorithms it is possible to achieve an efficient fault tolerance avoiding hardware redundancy. We propose a software approach that aims to reconfigure data, thus achieving a good slowdown in computation owing to the fine granularity of the workload to redistribute. In particular, we present and compare three data reconfiguration strategies applied to a problem model that includes a wide class of SPMD iterative algorithms characterized by nonlocal communications among the nodes. The result is that in most of the cases it is better to introduce some communication overhead than to leave idle a few healthy processor
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