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Impostazione e gestione della sicurezza del lavoro: un approccio validato per le unita' estrattive
No full textNoise and dust emissions from non-metal mining activities: analysis of suitable techniques of measurement, prediction and control
No full textPolyol-functionalized thin-film composite membranes with improved transport properties and boron removal in reverse osmosis
No full textA novel test rig to investigate under-platform damper dynamics
No full textIn the field of turbomachinery, vibration amplitude is often reduced by dissipating the kinetic energy of the blades with devices that utilize dry friction. Under-platform dampers, for example, are often placed in the underside of two consecutive turbine blades. Dampers are kept in contact with the under-platform of the respective blades by means of the cen-trifugal force. If the damper is well designed, vibration of blades instigate a relative motion between the under-platform and the damper. A friction force, that is a non-conservative force, arises in the contact and partly dissipates the vibration energy. Several contact mod-els are available in the literature to simulate the contact between the damper and the under-platform. However, the actual dynamics of the blade-damper interaction have not fully understood yet. Several test rigs have been previously developed to experimentally investigate the performance of under-platform dampers. The majority of these experimen-tal setups aim to evaluate the overall damper efficiency in terms of reduction in response amplitude of the blade for a given exciting force that simulates the aerodynamic loads. Unfortunately, the experimental data acquired on the blade dynamics do not provide enough information to understand the damper dynamics. Therefore, the uncertainty on the damper behavior remains a big issue. In this work, a novel experimental test rig has been developed to extensively investigate the damper dynamic behavior. A single replaceable blade is clamped in the rig with a speci-fic clamping device. With this device the blade root is pressed against a groove machined in the test rig. The pushing force is controllable and measurable, to better simulate the actual centrifugal load acting on the blade. Two dampers, one on each side of the blade, are in con-tact with the blade under-platforms and with platforms on force measuring supports. These supports have been specifically designed to measure the contact forces on the dam-per. The contact forces on the blade are computed by post processing the measured forces and assuming the static equilibrium of the damper. The damper kinematics is rebuilt by using the relative displacement, measured with a differential laser, between the damper and the blade under-platform. This article describes the main concepts behind this new approach and explains the design and working of this novel test rig. Moreover, the influence of the damper contact forces on the dynamic behavior of the blade is discussed in the result section
Exact solutions for static analysis of laminated, box and sandwich beams by refined layer-wise theory
No full textFrequent Itemsets Mining for Big Data: A Comparative Analysis
No full textItemset mining is a well-known exploratory data mining technique used to discover interesting correlations hidden in a data collection. Since it supports different targeted analyses, it is profitably exploited in a wide range of different domains, ranging from network traffic data to medical records. With the increasing amount of generated data, different scalable algorithms have been developed, exploiting the advantages of distributed computing frameworks, such as Apache Hadoop and Spark. This paper reviews Hadoop- and Spark-based scalable algorithms addressing the frequent itemset mining problem in the Big Data domain through both theoretical and experimental comparative analyses. Since the itemset mining task is computationally expensive, its distribution and parallelization strategies heavily affect memory usage, load balancing, and communication costs. A detailed discussion of the algorithmic choices of the distributed methods for frequent itemset mining is followed by an experimental analysis comparing the performance of state-of-the-art distributed implementations on both synthetic and real datasets. The strengths and weaknesses of the algorithms are thoroughly discussed with respect to the dataset features (e.g., data distribution, average transaction length, number of records), and specific parameter settings. Finally, based on theoretical and experimental analyses, open research directions for the parallelization of the itemset mining problem are presented
Empirical derivation of upper and lower bounds of NBTI aging for embedded cores
No full textIn deeply scaled CMOS technologies, device aging causes transistor performance parameters to degrade over time. While reliable models to accurately assess these degradations are available for devices and circuits, the extension to these models for estimating the aging of microprocessor cores is not trivial and there is no well accepted model in the literature. This work proposes a methodology for deriving an NBTI-induced aging model for embedded cores. Since aging can only be determined on a netlist, we use an empirical approach based on characterizing the model using a set of open synthesizable embedded cores, which allows us to establish a link between the aging at the transistor level and the aging from the core perspective in terms of maximum frequency degradation. Using this approach, we were able to (1) prove the independence of the aging on the workloads which run by the cores, and (2) calculate upper and lower bounds for the "aging factor" that can be used for a generic embedded processor. Results show that our method yields very good accuracy in predicting the frequency degradation of cores due to NBTI aging effect, and can be used with confidence when the netlist of the cores is not available
Design and implementation of a belief-propagation scheduler for multicast traffic in input-queued switches
No full textScheduling multicast traffic in input-queued switches to maximize throughput requires solving a hard combinatorial optimization problem in a very short time. This task advocates the design of algorithms that are simple to implement and efficient in terms of performance. We propose a new scheduling algorithm, based on message passing and inspired by the belief propagation paradigm, meant to approximate the provably-optimal scheduling policy for multicast traffic. We design and implement both a software and a hardware version of the algorithm, the latter running on a NetFPGA. We compare the performance and the power consumption of the two versions when integrated in a software router. Our main findings are that our algorithm outperforms other centralized greedy scheduling policies, achieving a better tradeoff between complexity and performance, and it is amenable to practical high-performance implementations
Critical remarks on the Italian research assessment exercise VQR 2011-2014
No full textFor nearly a decade, several national exercises have been implemented for assessing the Italian research performance, from the viewpoint of universities and other research institutions. The penultimate one - i.e., the VQR 2004-2010, which adopted a hybrid evaluation approach based on bibliometric analysis and peer review - suffered heavy criticism at a national and international level. The architecture of the subsequent exercise - i.e., the VQR 2011-2014, still in progress - is partly similar to that of the previous one, except for a few presumed improvements. Nevertheless, this other exercise is suffering heavy criticism too. This paper presents a structured discussion of the VQR 2011-2014, collecting and organizing some critical arguments so far emerged, and developing them in detail. Some of the major vulnerabilities of the VQR 2011-2014 are: (1) the fact that evaluations cover a relatively small fraction of the scientific publications produced by the researchers involved in the evaluation, (2) incorrect and anachronistic use of the journal metrics (i.e., ISI Impact Factor and similar ones) for assessing individual papers, and (3) conceptually misleading criteria for normalizing and aggregating the bibliometric indicators in use