Multimethods and separate static typechecking in a language with C++-like object model

The goal of this paper is the description and analysis of multimethod implementation in a new object-oriented, class-based programming language called OOLANG. The implementation of the multimethod typecheck and selection, deeply analyzed in the paper, is performed in two phases in order to allow static typechecking and separate compilation of modules. The first phase is performed at compile time, while the second is executed at link time and does not require the modules' source code. OOLANG has syntax similar to C++; the main differences are the absence of pointers and the realization of polymorphism through subsumption. It adopts the C++ object model and supports multiple inheritance as well as virtual base classes. For this reason, it has been necessary to define techniques for realigning argument and return value addresses when performing multimethod invocations.Comment: 15 pages, 18 figure

OS-Assisted Task Preemption for Hadoop

This work introduces a new task preemption primitive for Hadoop, that allows tasks to be suspended and resumed exploiting existing memory management mechanisms readily available in modern operating systems. Our technique fills the gap that exists between the two extremes cases of killing tasks (which waste work) or waiting for their completion (which introduces latency): experimental results indicate superior performance and very small overheads when compared to existing alternatives

Cross-Saturation Effects in IPM Motors and Related Impact on Sensorless Control

Permanent-magnet-assisted synchronous reluctance motors are well suited to zero-speed sensorless control because of their inherently salient behavior. However, the cross-saturation effect can lead to large errors on the position estimate, which is based on the differential anisotropy. These errors are quantified in this paper as a function of the working point. The errors that are calculated are then found to be in good accordance with the purposely obtained experimental measurement

Combustibilità di fuliggini da olio trattate e tal quali in atmosfera a diverso tenore di ossigeno

Lo scopo della presente tesi è stato quello di studiare la combustibilità sia di fuliggini da olio combustibile tal quali sia di quelle sottoposte a preliminare lisciviazione per il recupero di metalli quali vanadio e nichel. Da un punto di vista sperimentale si è proceduto ad una caratterizzazione chimica-fisica e morfologica dei campioni al fine di meglio interpretare i dati successivi sulla combustibilità. Si è proceduto poi ad un’analisi comparativa delle caratteristiche di combustibilità delle fuliggini, tal quali e lisciviate, con i due campioni di carbone commerciale mediante analisi termogravimetrica e termocinetica condotta in atmosfera a diverso tenore di ossigeno (21, 12 e 6% vol.) ed in azoto, al fine di valutare anche l’effetto del tenore di ossigeno sul range di combustibilità

Sleep-like slow oscillations improve visual classification through synaptic homeostasis and memory association in a thalamo-cortical model

The occurrence of sleep passed through the evolutionary sieve and is widespread in animal species. Sleep is known to be beneficial to cognitive and mnemonic tasks, while chronic sleep deprivation is detrimental. Despite the importance of the phenomenon, a complete understanding of its functions and underlying mechanisms is still lacking. In this paper, we show interesting effects of deep-sleep-like slow oscillation activity on a simplified thalamo-cortical model which is trained to encode, retrieve and classify images of handwritten digits. During slow oscillations, spike-timing-dependent-plasticity (STDP) produces a differential homeostatic process. It is characterized by both a specific unsupervised enhancement of connections among groups of neurons associated to instances of the same class (digit) and a simultaneous down-regulation of stronger synapses created by the training. This hierarchical organization of post-sleep internal representations favours higher performances in retrieval and classification tasks. The mechanism is based on the interaction between top-down cortico-thalamic predictions and bottom-up thalamo-cortical projections during deep-sleep-like slow oscillations. Indeed, when learned patterns are replayed during sleep, cortico-thalamo-cortical connections favour the activation of other neurons coding for similar thalamic inputs, promoting their association. Such mechanism hints at possible applications to artificial learning systems.Comment: 11 pages, 5 figures, v5 is the final version published on Scientific Reports journa

Impact of cross-saturation in sensorless control of transverse-laminated synchronous reluctance motors

Synchronous reluctance (SyR) motors are well suited to a zero-speed sensorless control, because of their inherently salient behavior. However, the cross-saturation effect can lead to large errors on the position estimate, which is based on the differential anisotropy. These errors are quantified in the paper, as a function of the working point. The so-calculated errors are then found in good accordance with the purposely obtained experimental measurements. The impact of the amplitude of the carrier voltage is then pointed out, leading to a mixed (carrier injection plus electromotive force estimation) control scheme. Last, a scheme of this type is used, with a commercial transverse-laminated SyR motor. The robustness against cross-saturation is shown, in practice, and the obtained drive performance is pointed out proving to be effective for a general-purpose applicatio

Position-sensorless control of permanent-magnet-assisted synchronous reluctance motor

The sensorless control of permanent-magnet-assisted synchronous reluctance (PMASR) motors is investigated, in order to conjugate the advantages of the sensorless control with full exploitation of the allowed operating area, for a given inverter. An additional pulsating flux is injected in the d-axis direction at low and zero speed, while it is dropped out, at large speed, to save voltage and additional loss. A flux-observer-based control scheme is used, which includes an accurate knowledge of the motor magnetic behavior. This leads, in general, to good robustness against load variations, by counteracting the magnetic cross saturation effect. Moreover, it allows an easy and effective correspondence between the wanted torque and flux and the set values of the chosen control variables, that is d-axis flux and q-axis current. Experimental verification of the proposed method is given, both steady-state and dynamic performance are outlined. A prototype PMASR motor will be used to this aim, as part of a purposely assembled prototype drive, for light traction application (electric scooter