709 research outputs found
Inductive Sensor for measuring partial discharges in electrical machines
The research group 'Diagnosis of Electrical Machines and Insulation Materials (DIAMAT) of the University Carlos III of Madrid, has developed an inductive sensor that can detect and measure partial discharge that are characteristic in electrical machines (its analysis allows to estimate the aging degree of the internal insulation)
Optical pumping of charged excitons in unintentionally doped InAs quantum dots
As an alternative to commonly used electrical methods, we have investigated
the optical pumping of charged exciton complexes addressing impurity related
transitions with photons of the appropriate energy. Under these conditions, we
demonstrate that the pumping fidelity can be very high while still maintaining
a switching behavior between the different excitonic species. This mechanism
has been investigated for single quantum dots of different size present in the
same sample and compared with the direct injection of spectator electrons from
nearby donors.Comment: 4 pages and 3 figures submitted to AP
Optimal Input Representation in Neural Systems at the Edge of Chaos
Shedding light on how biological systems represent, process and store information in noisy
environments is a key and challenging goal. A stimulating, though controversial, hypothesis poses
that operating in dynamical regimes near the edge of a phase transition, i.e., at criticality or the âedge
of chaosâ, can provide information-processing living systems with important operational advantages,
creating, e.g., an optimal trade-off between robustness and flexibility. Here, we elaborate on a recent
theoretical result, which establishes that the spectrum of covariance matrices of neural networks
representing complex inputs in a robust way needs to decay as a power-law of the rank, with an
exponent close to unity, a result that has been indeed experimentally verified in neurons of the mouse
visual cortex. Aimed at understanding and mimicking these results, we construct an artificial neural
network and train it to classify images. We find that the best performance in such a task is obtained
when the network operates near the critical point, at which the eigenspectrum of the covariance
matrix follows the very same statistics as actual neurons do. Thus, we conclude that operating near
criticality can also haveâbesides the usually alleged virtuesâthe advantage of allowing for flexible,
robust and efficient input representations.The Spanish Ministry and Agencia Estatal de investigaciĂłn
(AEI) through grant FIS2017-84256-P (European Regional Development Fund)âConsejerĂa de Conocimiento, InvestigaciĂłn Universidad, Junta de AndalucĂaâ and European Regional
Development Fund, Project Ref. A-FQM-175-UGR18 and Project Ref. P20-0017
El majĂșscul impacte d'allĂČ minĂșscul
Tininess Makes a Huge Impact: Semiconducting and Metallic Nanoparticles.Defying the conventions of linguistic repetition, the prefi x nano springs up in all languages with unusual force. Nanostructure, nanofi ber, nanocrystals, nanowires, nanotubes, nanodevice ... These are just a few examples, although you won’t fi nd them in the dictionary. These words have retained some meaning of the root from which they are derived, but should inescapably be contemplated, at best, as distant metaphorical refl ections. The words nanoparticle and nanocrystal will be the focus of this article: What are nanoparticles? When is a nanoparticle a nanocrystal? When is the nanoparticle a quantum dot? What applications can we expect if they are semiconducting or metallic
Multiple Partial Discharge Source Localization in Power Cables through Power Spectral Separation and Time-Domain Reflectometry
Insulated power cables are becoming increasingly popular in today's developing distribution and transportation networks. However, due to aging, deterioration, and various operational and environmental stresses, insulation defects may appear and so the cable needs to be monitored in a timely manner to avoid unexpected failures. Many of these defects are responsible for partial discharge (PD) activity. The localization of the sources of these discharges is a highly decisive facet in the condition-based monitoring of power cables. The techniques for the localization of single-PD defects in insulated power cables are well presented in the current bibliography. However, when several simultaneous PD sources are active, the localization of the sources becomes quite complex. This paper develops an efficient technique for the separation and localization of multiple PD sources in a medium voltage cable. The experimental results are obtained with single-end-based measurements using a high-frequency current transformer in a laboratory environment. The data processing based on the spectral characteristics of the signals is carried out by using the power ratios technique in order to determine the presence of different types of PD. Once the signals are separated, the PD sources can be localized with an individualized analysis of each source through time-domain reflectometry. The proposed methodology can be very valuable to improve the location diagnostic capability of the condition-based monitoring solutions, especially for underground cables.This work was supported in part by the Ministry of Economy and Competitiveness of Spain (MINECO), in part by the European Regional Development Fund (ERDF) under Contract DPI2015-66478-C2-1-R (MINECO/FEDER, European Union), and in part by the Academy of Finland under Grant 30941
Design of highly stabilized nanocomposite inks based on biodegradable polymer-matrix and gold nanoparticles for Inkjet Printing
Nowadays there is a worldwide growing interest in the Inkjet Printing technology owing to its potentially high levels of geometrical complexity, personalization and resolution. There is also social concern about usage, disposal and accumulation of plastic materials. In this work, it is shown that sugar-based biodegradable polyurethane polymers exhibit outstanding properties as polymer-matrix for gold nanoparticles composites. These materials could reach exceptional stabilization levels, and demonstrated potential as novel robust inks for Inkjet based Printing. Furthermore, a physical comparison among different polymers is discussed based on stability and printability experiments to search for the best ink candidate. The University of Seville logo was printed by employing those inks, and the presence of gold was confirmed by ToF-SIMS. This approach has the potential to open new routes and applications for fabrication of enhanced biomedical nanometallic-sensors using stabilized AuNP.Spanish Ministerio de EconomĂa y Competitividad MINECO, (Grants Nos. CTQ2016- 78703-P and MAT2016-78703-P)Junta de AndalucĂa (Consolidation Grant for Research Group FQM135 and 2017/FQM-386, P-2018/809)University of Seville (V y VI Plan Propio PP2016-5937
Shielding effect of power transformers tanks in the ultra-high-frequency detection of partial discharges
Partial discharges (PD) measurement is a well-known technique for judgment of the condition of power transformer offline. Phase-resolved PD measurement is a normalized technique for PD tests, but noise, especially by PD-measurements onsite is sometimes difficult to reject, and a post-processing of a pattern is necessary to separate different sources. Higher-frequency-detection devices and processing strategies are useful for PD classification and identification. Recently, ultra-high-frequency (UHF) detection by means of antennas has been shown to be a promising detection system for both offline and online PD-measurements. However, it is necessary to assess whether PD source separation and classification is possible by means of pulse analysis because some additional UHF noise sources are coupled to the detected signals, and it is not clear whether different sources produce different pulses. In this study, the attenuation effect of the metallic tank of a power transformer on the inner PD activity when measured outside the tank was studied. Additionally, experiments were conducted to detect and characterize two different PD sources (internal and external discharges) using two antennas measuring the same phenomenon inside and outside of a transformer. It will also be shown that broadband UHF signals are useful for PD recognition and that a deep study of frequencies below 500 MHz can separate PD occurring inside from those occurring outside when measured with an antenna outside the tank.This research has been supported by the Spanish Science and Technology Ministry under contract DPI 2009-14628- C03-02 and by the Madrid Regional Government and Universidad Carlos III de Madrid under contract CCG10- UC3M/DPI-4627. Tests have been made in the High Voltage Research and Tests Laboratory of Universidad Carlos III de Madrid (LINEALT).Publicad
Sensor inductivo para la medida de descargas parciales en måquinas eléctricas
El grupo de investigaciĂłn âDiagnĂłstico de MĂĄquinas ElĂ©ctricas y Materiales Aislantes (DIAMAT)â de la Universidad Carlos III de Madrid, ha desarrollado un sensor inductivo que permite detectar y medir las descargas parciales caracterĂsticas en mĂĄquinas elĂ©ctricas (cuyo anĂĄlisis permite estimar el grado de envejecimiento del aislamiento interno)
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