Fluctuations in the electron system of a superconductor exposed to a photon flux

We report on fluctuations in the electron system, Cooper pairs and quasiparticles, of a superconducting aluminium film. The superconductor is exposed to pair-breaking photons (1.54 THz), which are coupled through an antenna. The change in the complex conductivity of the superconductor upon a change in the quasiparticle number is read out by a microwave resonator. A large range in radiation power can be chosen by carefully filtering the radiation from a blackbody source. We identify two regimes. At high radiation power, fluctuations in the electron system caused by the random arrival rate of the photons are resolved, giving a straightforward measure of the optical efficiency (48%). At low radiation power fluctuations are dominated by excess quasiparticles, the number of which is measured through their recombination lifetime

Confocal Ellipsoidal Reflector System for a Mechanically Scanned Active Terahertz Imager

We present the design of a reflector system that can rapidly scan and refocus a terahertz beam for high-resolution standoff imaging applications. The proposed optical system utilizes a confocal Gregorian geometry with a small mechanical rotating mirror and an axial displacement of the feed. For operation at submillimeter wavelengths and standoff ranges of many meters, the imaging targets are electrically very close to the antenna aperture. Therefore the main reflector surface must be an ellipse, instead of a parabola, in order to achieve the best imaging performance. Here we demonstrate how a simple design equivalence can be used to generalize the design of a Gregorian reflector system based on a paraboloidal main reflector to one with an ellipsoidal main reflector. The system parameters are determined by minimizing the optical path length error, and the results are validated with numerical simulations from the commercial antenna software package GRASP. The system is able to scan the beam over 0.5 m in cross-range at a 25 m standoff range with less than 1% increase of the half-power beam-width

Time-Delay Multiplexing of Two Beams in a Terahertz Imaging Radar

We demonstrate a time-delay multiplexing technique that doubles the frame rate of a 660–690-GHz imaging radar with minimal additional instrument complexity. This is done by simultaneously projecting two offset, orthogonally polarized radar beams generated and detected by a common source and receiver. Beam splitting and polarization rotation is accomplished with a custom designed waveguide hybrid coupler and twist. A relative time lag of approximately 2 ns between the beams’ waveforms is introduced using a quasi-optical delay line, followed by spatial recombination using a selectively reflective wire grid. This delay is much longer than the approximately 20-ps time-of-flight resolution of the 30-GHz bandwidth radar, permitting the two beams’ reflected signals from a compact target to be easily distinguished in digital post-processing of the single receiver channel

Operation and Maintenance in Solar Plants: Eight study cases

The use of solar photovoltaic generation is growing up nowadays. New developments have been achieved lowering the prices of the modules and their installation. Nevertheless, the operation and maintenance of these plants still needs improvements in order to enhance their efficiency and economic balance. This paper presents a detailed analysis of eight photovoltaic (PV) plants revealing improvements on the monitoring system and the maintenance procedures. The common failures in PV plants have been established and their losses have been estimated. A correct diagnostic method using good information and monitoring systems could have reduced the losses

Surface wave control for large arrays of microwave kinetic inductance detectors

Large ultra-sensitive detector arrays are needed for present and future observatories for far infra-red, submillimeter wave (THz), and millimeter wave astronomy. With increasing array size, it is increasingly important to control stray radiation inside the detector chips themselves, the surface wave. We demonstrate this effect with focal plane arrays of 880 lens-antenna coupled Microwave Kinetic Inductance Detectors (MKIDs). Presented here are near field measurements of the MKID optical response versus the position on the array of a reimaged optical source. We demonstrate that the optical response of a detector in these arrays saturates off-pixel at the $\sim-30$ dB level compared to the peak pixel response. The result is that the power detected from a point source at the pixel position is almost identical to the stray response integrated over the chip area. With such a contribution, it would be impossible to measure extended sources, while the point source sensitivity is degraded due to an increase of the stray loading. However, we show that by incorporating an on-chip stray light absorber, the surface wave contribution is reduced by a factor $>$10. With the on-chip stray light absorber the point source response is close to simulations down to the $\sim-35$ dB level, the simulation based on an ideal Gaussian illumination of the optics. In addition, as a crosscheck we show that the extended source response of a single pixel in the array with the absorbing grid is in agreement with the integral of the point source measurements.Comment: accepted for publication in IEEE Transactions on Terahertz Science and Technolog

Penetrating 3-D Imaging at 4- and 25-m Range Using a Submillimeter-Wave Radar

We show experimentally that a high-resolution imaging radar operating at 576–605 GHz is capable of detecting weapons concealed by clothing at standoff ranges of 4–25 m. We also demonstrate the critical advantage of 3-D image reconstruction for visualizing hidden objects using active-illumination coherent terahertz imaging. The present system can image a torso with <1 cm resolution at 4 m standoff in about five minutes. Greater standoff distances and much higher frame rates should be achievable by capitalizing on the bandwidth, output power, and compactness of solid state Schottky-diode based terahertz mixers and multiplied sources

Machine Learning models for the estimation of the production of large utility-scale photovoltaic plants

Photovoltaic (PV) energy development has increased in the last years mainly based on large utility-scale plants. These plants are characterised by a huge number of panels connected to high-power inverters occupying a large land area. An accurate estimation of the power production of the PV plants is needed for failure detection, identifying production deviations, and the integration of the plants into the power grid. Various studies have used Machine Learning estimation techniques developed on very small PV plants. This paper deals with large utility-scale plants and uses all the available information to represent the non-uniform radiation over the whole studied solar field. Variables measured in up to four meteorological stations and distributed across the plant are used. Three PV plants with 1, 2 and 4 meteorological stations have been used to develop Machine Learning models. The hyperparameters were systematically optimised, demonstrating the improvements by comparing with a simple model based on Multiple Linear Regression. The best results were obtained with the Random Forest technique for the three PV plants, providing a RMS error value ranging from 1.9% to 5.4%. The final models were compared with those found in the literature for tiny PV plants showing in general much better performance

Eliminating stray radiation inside large area imaging arrays

With increasing array size, it is increasingly important to control stray radiation inside the detector chips themselves. We demonstrate this effect with focal plane arrays of absorber coupled Lumped Element microwave Kinetic Inductance Detectors (LEKIDs) and lens-antenna coupled distributed quarter wavelength Microwave Kinetic Inductance Detectors (MKIDs). In these arrays the response from a point source at the pixel position is at a similar level to the stray response integrated over the entire chip area. For the antenna coupled arrays, we show that this effect can be suppressed by incorporating an on-chip stray light absorber. A similar method should be possible with the LEKID array, especially when they are lens coupled.Comment: arXiv admin note: substantial text overlap with arXiv:1707.0214

Valor de la Resonancia Nuclear Magnética en Ortopedia Oncológica

Presentamos nuestra experiencia preliminar sobre la utilidad diagnóstica de la Resonancia Nuclear Magnética (RM) en la evaluación pre- y postoperatoria de pacientes con tumores musculoesqueléticos. Se han revisado 21 pacientes con tumores caracterizados histológicamente. Del total, 10 casos eran sarcomas de partes blandas, 7 correspondían a tumores óseos y 4 eran metástasis óseas o recidivas locales. Las imágenes se obtuvieron mediante un sistema de RM de campo medio provisto de un imán superconductor operando a 0.5 Teslas. En todos los casos se obtuvieron imágenes T1 y T2, en los planos axial y coronal. Como norma se objetivó un excelente contraste entre la señal de la lesión y la de las estructuras normales adyacentes. Sólo en un caso, un osteosarcoma del extremo proximal del peroné, las imágenes de extensión a partes blandas vecinas resultaron ser negativas en la exploración quirúrgica. El análisis de los cambios de intensidad de la señal no permitieron distinguir la especificidad tisular del tumor, ni diferenciar lesiones benignas y malignas. En nuestra experiencia, la RM nos ha permitido un mejor diagnóstico anatómico de la extensión tumoral, facilitándonos la planificación quirúrgica que requieren las modernas técnicas reconstructivas en ortopedia oncológica.The preliminary experience using Magnetic Resonance imaging for pre- and post-operative assessment of orthopaedic oncologic patients is hereby reported. Twenty-one patients with histologically characterized bone and soft tissue tumors have been reviewed. Seventeen patients had primary musculoskeletal neoplasia: 10 had soft tissue sarcomas and 7 bone tumors. The remained 4 patients consisted of bone metastasis or local racidive. Magnetic resonance images were acquired using a superconductive magnet operating at 0.5 Tesla. T1- and T2-weighted transaxial and coronal images were obtained in all cases. An excellent contrast between the signal of the lesion and the normal adjacent structures was usually obtained. Only in one osteosarcoma of the proximal fibula, an extraosseous extension was presumed but not found during surgical resection. Changes in image intensity did not permit to identify tumor tissue specificity neither distinguish between benign and malignat lesions. In our experience, Magnetic Resonance shows a great advantage in order to determine tumor anatomical extension, providing a useful information for the surgical planning required by current reconstructive techniques in orthopaedic oncology

Dermatitis crónica por sensibilización al níquel en un paciente con fractura del astrágalo tratada mediante osteosíntesis

Se presenta un varón de 25 años, con fractura del astrágalo izquierdo tratada mediante osteosíntesis con 2 tornillos de acero inoxidable con un contenido en níquel del 12-14%. A los 4 meses de la intervención, el paciente desarrolló una dermatitis pruriginosa en cara lateral externa del pie, en la zona cutánea supra-adyacente al lugar de la osteosíntesis. La lesión no cedió con el tratamiento tópico convencional a base de corticoides. Las pruebas epicutáneas realizadas con la batería estándar del Grupo Español de Investigación en Dermatitis de Contacto revelaron un parche positivo vesiculoso (+ +) al sulfato de níquel al 2,5% y al cloruro de cobalto al 1%, ambos aplicados en vaselina, en la lectura a las 48 y 96 horas. En vista de que las lesiones permanecían estables al mes de tratamiento con un potente corticoide en cura oclusiva y antihistamínicos sistémicos, se procedió a retirar los tornillos de osteosíntesis. A los pocos días de la intervención comenzó a desaparecer el prurito y, en el curso de 2 semanas, se produjo la curación completa de la dermatitisSe presenta un varón de 25 años, con fractura del astrágalo izquierdo tratada mediante osteosíntesis con 2 tornillos de acero inoxidable con un contenido en níquel del 12-14%. A los 4 meses de la intervención, el paciente desarrolló una dermatitis pruriginosa en cara lateral externa del pie, en la zona cutánea supra-adyacente al lugar de la osteosíntesis. La lesión no cedió con el tratamiento tópico convencional a base de corticoides. Las pruebas epicutáneas realizadas con la batería estándar del Grupo Español de Investigación en Dermatitis de Contacto revelaron un parche positivo vesiculoso (+ +) al sulfato de níquel al 2,5% y al cloruro de cobalto al 1%, ambos aplicados en vaselina, en la lectura a las 48 y 96 horas. En vista de que las lesiones permanecían estables al mes de tratamiento con un potente corticoide en cura oclusiva y antihistamínicos sistémicos, se procedió a retirar los tornillos de osteosíntesis. A los pocos días de la intervención comenzó a desaparecer el prurito y, en el curso de 2 semanas, se produjo la curación completa de la dermatitis