131,007 research outputs found
Interventions, Productions and Collaborations:the relationship between RAI and visual artists
No full textOn the 17th May 1952, before RAI Radiotelevisione Italiana Studios began their regular broadcast from Milan, the Spatialist painter and sculptor Lucio Fontana broadcast his own experimental ‘artwork’ on Italian television, beginning a fruitful relationship between RAI and visual artists. For some, it provided careers as designers and art directors, such as the painter Mario Sasso and the Arte Povera artist Pino Pascali, while for others, who were given unique access to RAI’s television apparatus, it was an opportunity to explore their own artistic experimentations with an expensive and exclusive medium, such as Carlo Quartucci and Gianni Toti. RAI also hosted seminal artists’ performances on screen including John Cage and Fabio Mauri. This article, based on documents and interviews collected during the Arts and Humanities Research Council funded project REWINDItalia, discusses these and other seminal cases as well as tracing and assessing the history of this fruitful and complex exchange between RAI and visual artists
On the Electrical Aging of the Insulation in PWM-Fed High-Speed Electric Machines: Analysis, Modelling, and Mitigation
No full textThis doctoral thesis represents the completion of a three-year research activity that has been carried out as part of the Ph.D. program in Electrical and Information Engineering, XXXII cycle, of the Polytechnic University of Bari, Italy. The work that is presented in this document addresses some specific aspects of the broader topic of reliability in high-frequency electric drives, which is the early failure of inverter-fed AC machine insulation systems due to the very high dv/dt’s of modern fast switching converters. A selection of the most important research works that have been published in the literature on this subject is reviewed here and can be found in the reference. These works have greatly contributed to the progression of the research and thesis. Hopefully, the content presented in this document will also add a modest contribution to this topic that is becoming more and more relevant in today's electric drive applications.
The background of the thesis, the motivations, and ideas laying behind the research activity carried on the topic of insulation aging are presented. The role of electrification in many application areas and the benefits that the transition to cleaner energy forms can bring to the cause of environment and climate preservation are discussed. In this promising energy transition process, high-speed machines and high-frequency power electronics converters are key technologies to enable enormous energy-saving and to boost the penetration of more electrical systems in both industry and transportation sectors. The growing market diffusion of high-frequency electric drives is driven by the fast developments in the new generation of power switching devices, which are based on silicon carbide and gallium nitride composites, the so-called wide bandgap semiconductor materials. Thanks to these new materials, which present better properties than silicon with respect to breakdown electric field, electron mobility, and thermal stability, modern power switches can operate at higher commutation frequency, with lower losses and higher junction temperature than previous generations. Alongside the numerous advantages of high-frequency devices, new issues arise for their practical implementation because of their fast commutation transients at turn-on and turn-off. In fact, the very short rise and fall time of the applied voltage pulses, in the order of tens of nanoseconds, is source of increased electromagnetic interference that can negatively affect the surrounding low-power electronics, common-mode voltage can appear across the shaft of the machine leading to the circulation of currents along the bearings and subsequent mechanical deterioration, and increased stress on the motor turn insulation. The higher electrical stress on the insulation is the cause of partial discharges within the weak spots of the system, small sparks that delaminate the dielectric material, eventually leading to a turn short circuit and to the fault.
The winding insulation system is a fundamental component of any electric machine, functionally required for the operation of the electromechanical conversion mechanism. The breakdown of the insulation inhibits the operation of the machine, which must be re-wound to be put in service again. Due to the high dv/dt’s in high-frequency power electronic converters, two phenomena occur that can threaten the life duration of motor insulation systems. Voltage waveform reflections along the cable that connects the inverter and the machine produce high overvoltage at the motor terminals when the rise time of the PWM voltage pulses is short. Furthermore, due to the parasitic capacitances of the winding insulation, the distribution of the voltage across the coil is such that, when the pulses are applied to the winding, the first turns are exposed to the higher share of the voltage. Consequently, within the defects of the insulation system, such as air pockets or small clearances, partial discharges are triggered by the electric field exceeding the dielectric strength of the air. Partial discharges are ionic discharge events that modify the physical and chemical properties of the material, making it weaker over time until it cannot sustain the normal field anymore. At this point, the irreversible fault occurs, and the machine must be put out of service. Many studies in the literature have investigated the role of partial discharge on shortening the life of winding insulation systems, and the main effects of PWM voltages on the partial discharge characteristics have been identified.
The main approaches commonly adopted today for the mitigation of the electrical stress on the insulation are the use of inverter output filters, very effective but generally bulky and costly and that often reduce the dynamic performance of the drive, and the combined design of converter and machine to minimize the length of the cables, which has practical limitations in high-speed drives due to the different scaling of the two parts.
Three are three main goals of the research activity presented in this doctoral thesis. The first objective is to achieve a better understanding of the effects of electrical aging on motor insulation, to develop a practical method for the estimation of the aging progression through the measure of electrical quantities such as voltage and current. The second goal is the development of an accurate and easy-to-tune model of the drive components in the high-frequency domain, to be used for both improving the drive design and performing advanced diagnosis features. The third objective is to investigate possible approaches for the mitigation of electrical aging in high-speed electrical machines. Two possibilities are taken into consideration to this purpose: the active regulation of the dv/dt to limit the overvoltage at the motor terminals, and the use of multilevel converters to reduce the voltage stress by increasing the number of voltage levels.
To achieve a deep understanding of the aging phenomenon from a macroscopic point of view, i.e. by mean of easily measurable electrical quantities, a series of electrical aging test has been performed on a group of motors while their characteristics were cyclically measured. The data collected during this aging campaign, together with the experimental setup that has been developed, are presented in the thesis. The data are statistically used to build some indicators of the insulation condition that can be used as an estimation of the aging progression in the insulation system. The first indicator is obtained through the measure of the machine characteristic impedances at different aging steps, while the second and the third are calculated from the high-frequency response of the phase current when a voltage pulse is applied.
Accurate models of the electric drive system in the high-frequency domain are required to both improve designs from a system point of view and to include advanced predictive diagnosis features in the drive control system. A series of high-frequency motor models are reviewed and analyzed in this thesis based on the findings from the electrical aging campaign performed. A first modeling approach is made using a lumped-parameter model of the machine and an automatic identification procedure. To improve both accuracy and model tuning time, a second model is proposed, which is based on the automatic identification of an analytical rational function with the measured data. The fitting algorithm that has been employed is described in the thesis, and results are shown about the achieved accuracy level.
The experimental data collected during the electrical aging tests and the developed high-frequency models of the drive components are used to investigate some possible approaches for the mitigation of the electrical stress on the winding insulation system of electric machines. The first method that is considered is the idea of using the estimation of the winding insulation aging conditions as a feedback for an advanced control system for the active regulation of the dv/dt of the PWM pulses to the purpose of extending the life of the drive while optimizing efficiency and performance. Such a system requires different parts to properly function, an effective estimator, a controller based on an optimization algorithm, and a set of active gate drivers. In this thesis, the idea is explored by simulation with some simplifications. The second overvoltage mitigation approach is to have a multilevel voltage waveform applied to the motor instead of a train of PWM pulses. In this way, the level of the overvoltage applied to the motor is reduced, and so is the electrical stress on the insulation. To this purpose, in this thesis, a cascaded H-bridge multilevel converter is compared to a conventional 2-level inverter operating on the same load conditions and with the same overvoltage level at the motor terminals. A simulation model is used to compare the losses, the efficiency, and the thermal requirements in both cases
A Single-Cell-Based Injection Method for Circulating Current Control in MMC
No full textModular multilevel converters are becoming more and more attractive for many high-voltage high-power applications. However, due to their topology and operation they present technical challenges in the implementation of the control system, such as balancing of the submodule capacitor voltages and suppressing the circulating currents. The circulating current introduces additional power losses, increases the current stress on power devices and reduces their lifetime. The aim of this paper is to propose an innovative control technique for the elimination of the circulating current by injecting a low-frequency alternating signal into a single submodule of each converter arm, to also achieve a reduction of the voltage ripple across capacitor, beneficial to extend their lifetime. Experimental results performed on a seven-levels converter are presented to validate the proposed technique and assess its performance in comparison with state-of-the-art approaches
An Innovative Single-Cell-Based Injection Method to Improve Efficiency and Reliability of MMC with Low Implementation Burden
No full textModular multilevel converters are increasingly gaining popularity in various high-voltage and high-power applications. However, their operation poses some technical challenges in implementing the control system, including issues, such as balancing submodule capacitor voltages and mitigating circulating currents. The presence of circulating currents leads to additional power losses, increases thermal stress on the power devices, and shortens their lifetime. This article introduces an innovative control technique to eliminate circulating currents by injecting a low-frequency alternating signal into a single submodule of each converter arm. The proposed method not only addresses circulating current mitigation but is also able to reduce capacitor voltage ripple and peak arm current, thereby enhancing the overall converter's lifespan and efficiency. Results of experimental tests on a seven-level converter are presented to prove the effectiveness of the proposed technique and compare its performance with existing state-of-the-art approaches
A 3-D numerical study of pollutant dispersion in a coastal current interacting with a headland
No full textExpanding the phenotype of the rare neuronal ceroid lipofuscinoses (ncl) 10
No full textExpanding the phenotype of the rare Neuronal Ceroid Lipofuscinoses
(NCL) 10
Di Maggio C1, Bernardini L2, Masuelli L4, Aiello C5, Giorgi D3, Pollini
L1, Torres B2, Bertini E S5, Leuzzi V1
1Dept HumNeurosc, Univ Sapienza, Rome, Italy, 2Cytogen Unit, IRCCS
Casa Sollievo Soffer, San Giovanni Rotondo (FG), Italy, 3Dept Head-
Neck, Div Ophth, Univ Sapienza, Rome, Italy, 4Dept Experimental Med, Univ Sapienza, Rome, Italy, 5Unit Musc Neur Dis, Bam Ges
Childr Hosp, Rome, Italy
Background:NCL type 10 is caused by a deficiency in cathepsin D
(CTSD), a lysosomal protease involved in proteolytic degradation, cell
invasion and apoptosis, which results in a severe congenital phenotype
with rapid progression to exitus and a milder form with a later onset with
ataxia, dementia and retinopathy.
Case Report: This 3,5-year-old girl was born from consanguineous parents
after a pregnancy complicated by fetal ascites since the 6th month. Previous
pregnancies were normal. She presented development delay during the first
months of life. Neurological regression was observed at 26 months of life. At
28 months she showed: facial dysmorphism, acquired microcephaly,
apostural status with profound hypotonia, unresponsiveness to visual stimulation.
EEG showed a multifocal epileptic pattern. Brain MRI showed a
generalized cortical atrophy. On CSF examination folate was low (43.2
nmol/L; r.v. 63–111). An extensive neurometabolic work-up failed to detect
any alteration. She eventually developed optic atrophy with “salt and pepper”
retinopathy. ERGwere not evocable. Echocardiogram revealed a slight thickening
of the interventricular septum. Ultrastructural analysis of the skin detected
vacuolated fibroblasts, osmophilic deposits, fingerprint-like structures,
lipopigment storage in the cytoplasm of a lymphocyte, suggesting NCL.
Results: SNP-array analysis was negative for CNVs but disclosed a high
rate of regions of homozygosity(about 9%; ROH), among which a ROH
of about 3.5 Mb within 11p15.511p15.4 genomic region,including
NCL10 locus (CTSD gene). NGS panel for NCL detected a homozygous
causative variant in CTSD gene (c.308T>A; p. L103Q).
Discussion: With respect to other patients so far reported (11) our case
presents an intermediate phenotype and age of onset. Heart involvement,
reported in several NCL types, is emerging as a possible second target of
the disease. Further study is required to support CSF folate as a metabolic
biomarker of the disease
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Theoretical Investigation and Experimental Verification of the Nonanalytic Form of the Conversion Equations in a Frequency Divider by Two
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