3,306 research outputs found
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
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
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
Revisiting Size-Based Scheduling with Estimated Job Sizes
We study size-based schedulers, and focus on the impact of inaccurate job
size information on response time and fairness. Our intent is to revisit
previous results, which allude to performance degradation for even small errors
on job size estimates, thus limiting the applicability of size-based
schedulers.
We show that scheduling performance is tightly connected to workload
characteristics: in the absence of large skew in the job size distribution,
even extremely imprecise estimates suffice to outperform size-oblivious
disciplines. Instead, when job sizes are heavily skewed, known size-based
disciplines suffer.
In this context, we show -- for the first time -- the dichotomy of
over-estimation versus under-estimation. The former is, in general, less
problematic than the latter, as its effects are localized to individual jobs.
Instead, under-estimation leads to severe problems that may affect a large
number of jobs.
We present an approach to mitigate these problems: our technique requires no
complex modifications to original scheduling policies and performs very well.
To support our claim, we proceed with a simulation-based evaluation that covers
an unprecedented large parameter space, which takes into account a variety of
synthetic and real workloads.
As a consequence, we show that size-based scheduling is practical and
outperforms alternatives in a wide array of use-cases, even in presence of
inaccurate size information.Comment: To be published in the proceedings of IEEE MASCOTS 201
International Standards for the Induction Motor Efficiency Evaluation: a Critical Analysis of the Stray-Load Losses Determination
Motor efficiency has to be measured or calculated in accordance with international standards. The most important standards are the IEEE 112-B, IEC 34-2, and JEC 3 . In this paper, a comparison of the measurement procedures defined by these international standards is reported, together with some comments on the prescribed methodologies. The comparison is based on experimental results obtained by tests on four general-purpose three-phase induction motors. The stray-load loss measurement represents a critical key for the correct evaluation of the motor efficiency. For this reason, a critical analysis of this type of losses has been performed. In particular, in order to understand which are the most critical quantities that influence their evaluation, the stray-load loss sensitivity to the measurement errors is analyzed. In the final part of the paper the temperature influence, on the conventional iron losses, is experimentally analyzed. The performed tests show that the temperature difference between the no-load test and the motor real operative conditions is not negligible
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
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
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