Characterization of high-power white leds for VLC applications

During the last years, visible light communications (VLC) have been proposed for providing connectivity while ensuring satisfactory illumination in both indoor environments and also specific outdoor scenarios without the need of deploying complex infrastructures for that purpose. Transmission for VLC is carried out through lightemitting diodes (LEDs), which correspond to semiconductors based on PN-junction materials with a direct gap. In this sense, the current flow plays a major role in the behavior and performance of these devices for VLC. Therefore, characterizing the electrical response of high-power white LED results mandatory for the successful implementation of VLC. At this point, it is worth noting that the electrical characterization is usually not available for high-power LEDs since, in fact, determining these characterization results challenging. In this sense, there exist some measurement instruments such as LCRs or impedance analyzers typically employed for characterizing materials and passive electrical components. However, these kinds of instruments are subject to a limited input impedance and a maximum value of forwarding current. In this work, the electrical characterization of the LED LXHL-BW02 of Luxeon is analyzed to show that typically commercial instrumentation for characterizing these devices is limited for high-power LEDs, which may provide polluted results when these limitations are not considered. After that, the characterization of the LXHL-BW02 based on a lock-in amplifier is proposed.This research was co-financed by Comunidad de Madrid and the FSE/FEDER Program under grant SINFOTON2-CM (S2018/NMT-4326), the Universidad Carlos III de Madrid under grant 2020/00038/001, and the Ministerio de Ciencia e Innovación and Agencia Estatal de Investigación (PID2019-109072RB-C31), and the European Regional Development Fund (ERDF) EXP 00119337/IDI-2019029

An enhanced method for dynamic characterization of high-power LEDs for visible light communication applications

Visible light communications (VLC) have been proposed for several applications beyond the traditional indoor scenarios, from vehicular to underwater communications. The common element in all these applications is the use of light-emitting diodes (LEDs) in which the forward current that flows through each LED plays a major role. Therefore, knowing the electrical equivalent of the LEDs is a useful tool for the proper design of the VLC systems. Currently, some measurement instruments exist, such as the LCR (inductance, capacitance, and resistance) meters or impedance analyzers to characterize the main parameters of the LEDs. However, these instruments and measurement procedures are subject to satisfying some requirements, such as a minimum value of the input impedance or the maximum forward current. In this work, the LED LXHL-BW02 is used to obtain its equivalent circuit, using different measurement methods and traditional methods of measurement with our proposed method. The equivalent model is implemented on the simulation tool LTSPICE. Our alternative method can be used for determining the electrical equivalent circuit of LEDs subject to high current variations at very high frequencies, in the MHz range, i.e., in an operating range for VLC applications.This research was co-financed by Comunidad de Madrid and the FSE/FEDER Program under grant SINFOTON2-CM (S2018/NMT-4326), the Madrid Government (Comunidad de Madrid) under the Multiannual Agreement with UC3M in the line of “Fostering Young Doctors Research” (GEOVEOLUZ-CM-UC3M), and in the context of the V PRICIT (Regional Programme of Research and Technological Innovation, and the Ministerio de Ciencia e Innovación and Agencia Estatal de Investigación (PID2019-109072RB-C31) and under the CDTI (Centre for the Development of Industrial Technology, Ministerio de Ciencia e Innovación) throughthe European Regional Development Fund (ERDF) EXP 00119337/IDI-2019029

Influence of atmospheric conditions on the power production of utility-scale wind turbines in yaw misalignment

The intentional yaw misalignment of leading, upwind turbines in a wind farm, termed wake steering, has demonstrated potential as a collective control approach for wind farm power maximization. The optimal control strategy and the resulting effect of wake steering on wind farm power production are in part dictated by the power degradation of the upwind yaw misaligned wind turbines. In the atmospheric boundary layer, the wind speed and direction may vary significantly over the wind turbine rotor area, depending on atmospheric conditions and stability, resulting in freestream turbine power production which is asymmetric as a function of the direction of yaw misalignment and which varies during the diurnal cycle. In this study, we propose a model for the power production of a wind turbine in yaw misalignment based on aerodynamic blade elements, which incorporates the effects of wind speed and direction changes over the turbine rotor area in yaw misalignment. The proposed model can be used for the modeling of the angular velocity, aerodynamic torque, and power production of an arbitrary yaw misaligned wind turbine based on the incident velocity profile, wind turbine aerodynamic properties, and turbine control system. A field experiment is performed using multiple utility-scale wind turbines to characterize the power production of yawed freestream operating turbines depending on the wind conditions, and the model is validated using the experimental data. The resulting power production of a yaw misaligned variable speed wind turbine depends on a nonlinear interaction between the yaw misalignment, the atmospheric conditions, and the wind turbine control system

VINTAGE TECHNIQUE IN VASCULAR SURGERY: LUMBAR SYMPATHECTOMY IN CRITICAL LIMB ISCHEMIA

Introduction: Tromboangiitis Obliterans or Buerguer's disease is one of the expresions of the peripheral arterial disease; its main feauture is the absence of average distal outflow that precludes direct revascularization surgery; lumbar sympathectomy was carried out to treat this condition with acceptable results but nowadays this technique is described as obsolete; many young vascular surgeons have not even heard about it and most of them have never seen a lumbar sympathectomy for the treatment of patients with critical limb ischemia. Case report: A 39-year-old woman admitted with critical limb ischemia due to popliteal artery occlusion without average distal outflow, treated by a lumbar sympathectomy as a resource technique. Discussion: Today, endovascular treatment is the first option for the critical limb ischemia in most cases; althoug tromboangiitis obliterans is less frequent nowadays, exists, and this is one of the situations where endovascular treatment does not work; what's more, direct surgery is also not possible. Conclusions: Lumbar sympathectomy can work not only in this scenary of Buerguer's disease; it can be used as resource technique when the first approach with direct surgery has failed and there is not more options to limb salvage; thus, lumbar sympathectomy should be part of the therapeutic arsenal of any vascular surgeon

Pastores trashumantes del Neolítico antiguo en un entorno de alta montaña: secuencia crono-cultural de la Cova de Els Trocs (San Feliú de Veri, Huesca)

This paper presents the preliminary results of the excavation of the “Els Trocs’’ Cave, developed in the context of the research project “The pathways of the Neolithic”. The careful and detailed work of excavation and recording has revealed a complex stratigraphy in which, thanks to the radiocarbon dates on short-lived samples (cereal seeds, human bones and domestic animal remains), it has been possible to distinguish four different periods of occupation inside the cave. With this information and some preliminary analyses of part of the materials (pottery, flint and faunal remains), we have documented the presence of a human group in the mountain pastures of the axial Pyrennes, at a very early stage (beginning of the last third of the Vlth millennium cal. BC), with a transhumant pastoral economy. It was a fully neolithic population with clear evidences of the use of wheat and barley, despite they did not cultivate around the close environment of this cave, where complex burial rituals had been also documented.Este trabajo presenta los resultados preliminares obtenidos en la excavación de la Cova de Els Trocs, desarrollada dentro del proyecto de investigación "Los caminos del Neolítico". La minuciosa labor de excavación y de registro ha permitido establecer una compleja secuencia estratigráfica en la que, gracias a una veintena de dataciones radiocarbónicas sobre eventos singulares de vida corta (semillas de cereal, huesos humanos y fauna doméstica), se han podido diferenciar cuatro momentos de ocupación distintos de la cueva. Con estos datos y algunos análisis, también preliminares, de parte del registro (cerámica, sílex y restos faunísticos), se ha podido definir, en una época muy temprana (inicios del último tercio del VI milenio cal. BC.), la presencia en los pastos de montaña del Pirineo axial de un grupo humano que desarrolla una actividad pastoril trashumante. Una población plenamente neolitizada, que conoce el trigo y la cebada, aunque no los cultive en el entorno de la cueva, y que, a tenor de ciertas evidencias, practica complejos rituales tanatológicos

Search for vector-boson resonances decaying to a top quark and bottom quark in the lepton plus jets final state in pp collisions at s=13 TeV with the ATLAS detector

A search for new charged massive gauge bosons, W, is performed with the ATLAS detector at the LHC. Data were collected in proton–proton collisions at a center-of-mass energy of s=13 TeV and correspond to an integrated luminosity of 36.1 fb. This analysis searches for W bosons in the W→tb¯ decay channel in final states with an electron or muon plus jets. The search covers resonance masses between 0.5 and 5.0 TeV and considers right-handed W bosons. No significant deviation from the Standard Model (SM) expectation is observed and upper limits are set on the W→tb¯ cross section times branching ratio and the W boson effective couplings as a function of the W boson mass. For right-handed W bosons with coupling to the SM particles equal to the SM weak coupling constant, masses below 3.15 TeV are excluded at the 95% confidence level. This search is also combined with a previously published ATLAS result for W→tb¯ in the fully hadronic final state. Using the combined searches, right-handed W bosons with masses below 3.25 TeV are excluded at the 95% confidence level.Peer Reviewe

Search for heavy particles decaying into a top-quark pair in the fully hadronic final state in pp collisions at s =13 TeV with the ATLAS detector

A search for new particles decaying into a pair of top quarks is performed using proton-proton collision data recorded with the ATLAS detector at the Large Hadron Collider at a center-of-mass energy of s=13 TeV corresponding to an integrated luminosity of 36.1 fb-1. Events consistent with top-quark pair production and the fully hadronic decay mode of the top quarks are selected by requiring multiple high transverse momentum jets including those containing b-hadrons. Two analysis techniques, exploiting dedicated top-quark pair reconstruction in different kinematic regimes, are used to optimize the search sensitivity to new hypothetical particles over a wide mass range. The invariant mass distribution of the two reconstructed top-quark candidates is examined for resonant production of new particles with various spins and decay widths. No significant deviation from the Standard Model prediction is observed and limits are set on the production cross-section times branching fraction for new hypothetical Z′ bosons, dark-matter mediators, Kaluza-Klein gravitons and Kaluza-Klein gluons. By comparing with the predicted production cross sections, the Z′ boson in the topcolor-assisted-technicolor model is excluded for masses up to 3.1-3.6 TeV, the dark-matter mediators in a simplified framework are excluded in the mass ranges from 0.8 to 0.9 TeV and from 2.0 to 2.2 TeV, and the Kaluza-Klein gluon is excluded for masses up to 3.4 TeV, depending on the decay widths of the particles.Peer Reviewe

Search for pairs of highly collimated photon-jets in pp collisions at s =13 TeV with the ATLAS detector

Results of a search for the pair production of photon-jets - collimated groupings of photons - in the ATLAS detector at the Large Hadron Collider are reported. Highly collimated photon-jets can arise from the decay of new, highly boosted particles that can decay to multiple photons collimated enough to be identified in the electromagnetic calorimeter as a single, photonlike energy cluster. Data from proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 36.7 fb-1, were collected in 2015 and 2016. Candidate photon-jet pair production events are selected from those containing two reconstructed photons using a set of identification criteria much less stringent than that typically used for the selection of photons, with additional criteria applied to provide improved sensitivity to photon-jets. Narrow excesses in the reconstructed diphoton mass spectra are searched for. The observed mass spectra are consistent with the Standard Model background expectation. The results are interpreted in the context of a model containing a new, high-mass scalar particle with narrow width, X, that decays into pairs of photon-jets via new, light particles, a. Upper limits are placed on the cross section times the product of branching ratios σ×B(X→aa)×B(a→γγ)2 for 200 GeV<mX<2 TeV and for ranges of ma from a lower mass of 100 MeV up to between 2 and 10 GeV, depending upon mX. Upper limits are also placed on σ×B(X→aa)×B(a→3π0)2 for the same range of mX and for ranges of ma from a lower mass of 500 MeV up to between 2 and 10 GeV.Peer Reviewe

Measurement of W±Z production cross sections and gauge boson polarisation in pp collisions at √s=13TeV with the ATLAS detector

This paper presents measurements of WZ production cross sections in pp collisions at a centre-of-mass energy of 13 TeV. The data were collected in 2015 and 2016 by the ATLAS experiment at the Large Hadron Collider, and correspond to an integrated luminosity of 36.1fb-1. The WZ candidate events are reconstructed using leptonic decay modes of the gauge bosons into electrons and muons. The measured inclusive cross section in the detector fiducial region for a single leptonic decay mode is σW±Z→ℓ′νℓℓfid.=63.7±1.0(stat.)±2.3(syst.)±1.4(lumi.) fb, reproduced by the next-to-next-to-leading-order Standard Model prediction of 61.5-1.3+1.4 fb. Cross sections for WZ and WZ production and their ratio are presented as well as differential cross sections for several kinematic observables. An analysis of angular distributions of leptons from decays of W and Z bosons is performed for the first time in pair-produced events in hadronic collisions, and integrated helicity fractions in the detector fiducial region are measured for the W and Z bosons separately. Of particular interest, the longitudinal helicity fraction of pair-produced vector bosons is also measured.We acknowledge the support of ANPCyT, Argentina; YerPhI, Armenia; ARC, Australia; BMWFW and FWF, Austria; ANAS, Azerbaijan; SSTC, Belarus; CNPq and FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; CONICYT, Chile; CAS, MOST and NSFC, China; COLCIENCIAS, Colombia; MSMT CR, MPO CR and VSC CR, Czech Republic; DNRF and DNSRC, Denmark; IN2P3-CNRS, CEA-DRF/IRFU, France; SRNSFG, Georgia; BMBF, HGF, and MPG, Germany; GSRT, Greece; RGC, Hong Kong SAR, China; ISF and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; NWO, Netherlands; RCN, Norway; MNiSW and NCN, Poland; FCT, Portugal; MNE/IFA, Romania; MES of Russia and NRC KI, Russian Federation; JINR; MESTD, Serbia; MSSR, Slovakia; ARRS and MIZŠ, Slovenia; DST/NRF, South Africa; MINECO, Spain; SRC and Wallenberg Foundation, Sweden; SERI, SNSF and Cantons of Bern and Geneva, Switzerland; MOST, Taiwan; TAEK, Turkey; STFC, UK; DOE and NSF, USA. In addition, individual groups and members have received support from BCKDF, CANARIE, CRC and Compute Canada, Canada; COST, ERC, ERDF, Horizon 2020, and Marie Skłodowska-Curie Actions, European Union; Investissements d’ Avenir Labex and Idex, ANR, France; DFG and AvH Foundation, Germany; Herakleitos, Thales and Aristeia programmes co-financed by EU-ESF and the Greek NSRF, Greece; BSF-NSF and GIF, Israel; CERCA Programme Generalitat de Catalunya, Spain; The Royal Society and Leverhulme Trust, UK. The crucial computing support from all WLCG partners is acknowledged gratefully, in particular from CERN, the ATLAS Tier-1 facilities at TRIUMF (Canada), NDGF (Denmark, Norway, Sweden), CC-IN2P3 (France), KIT/GridKA (Germany), INFN-CNAF (Italy), NL-T1 (Netherlands), PIC (Spain), ASGC (Taiwan), RAL (UK) and BNL (USA), the Tier-2 facilities worldwide and large non-WLCG resource providers. Major contributors of computing resources are listed in Ref. [106].Peer Reviewe