Digital Predistortion in Large-Array Digital Beamforming Transmitters

In this article, we propose a novel digital predistortion (DPD) solution that allows to considerably reduce the complexity resulting from linearizing a set of power amplifiers (PAs) in single-user large-scale digital beamforming transmitters. In contrast to current state-of-the art solutions that assume a dedicated DPD per power amplifier, which is unfeasible in the context of large antenna arrays, the proposed solution only requires a single DPD in order to linearize an arbitrary number of power amplifiers. To this end, the proposed DPD predistorts the signal at the input of the digital precoder based on minimizing the nonlinear distortion of the combined signal at the intended receiver direction. This is a desirable feature, since the resulting emissions in other directions get partially diluted due to less coherent superposition. With this approach, only a single DPD is required, yielding great complexity and energy savings.Comment: 8 pages, Accepted for publication in Asilomar Conference on Signals, Systems, and Computer

Performance Comparison of Constant Envelope and Zero-forcing Precoders in Multiuser Massive MIMO

In this article, the adoption and performance of a constant envelope (CE) type spatial precoder is addressed in large-scale multiuser MIMO based cellular network. We first formulate an efficient computing solution to obtain the antenna samples of such CE precoder. We then evaluate the achievable CE precoder based multiuser downlink (DL) system performance and compare it with the corresponding performance of more ordinary zero-forcing (ZF) spatial precoder. We specifically also analyze how realistic highly nonlinear power amplifiers (PAs) affect the achievable DL performance, as the individual PA units in large-array or massive MIMO systems are expected to be small, cheap and operating close to saturation for increased energy-efficiency purposes. It is shown that the largely reduced peak-to-average power ratio (PAPR) of the PA input signals in the CE precoder based system allows for pushing the PA units harsher towards saturation, while allowing to reach higher signal-to-interference-plus-noise ratio (SINRs) at the intended receivers compared to the classical ZF precoder based system. The obtained results indicate that the CE precoder can outperform the ZF precoder by up to 5-6 dBs, in terms of the achievable SINRs, when the PA units are pushed towards their saturating region. Such large gains are a substantial benefit when seeking to improve the spectral and energy-efficiencies of the mobile cellular networks.Comment: Accepted for publication at IEEE WCNC 201

Role of pseudospin in quasiparticle interferences in epitaxial graphene probed by high-resolution scanning tunneling microscopy

Pseudospin, an additional degree of freedom related to the honeycomb structure of graphene, is responsible of many of the outstanding electronic properties found in this material. This article provides a clear understanding of how such pseudospin impacts the quasiparticle interferences of monolayer (ML) and bilayer (BL) graphene measured by low temperature scanning tunneling microscopy and spectroscopy. We have used this technique to map, with very high energy and space resolution, the spatial modulations of the local density of states of ML and BL graphene epitaxialy grown on SiC(0001), in presence of native disorder. We perform a Fourier transform analysis of such modulations including wavevectors up to unit-vectors of the reciprocal lattice. Our data demonstrate that the quasiparticle interferences associated to some particular scattering processes are suppressed in ML graphene, but not in BL graphene. Most importantly, interferences with 2qF wavevector associated to intravalley backscattering are not measured in ML graphene, even on the images with highest resolution. In order to clarify the role of the pseudospin on the quasiparticle interferences, we use a simple model which nicely captures the main features observed on our data. The model unambiguously shows that graphene's pseudospin is responsible for such suppression of quasiparticle interferences features in ML graphene, in particular for those with 2qF wavevector. It also confirms scanning tunneling microscopy as a unique technique to probe the pseudospin in graphene samples in real space with nanometer precision. Finally, we show that such observations are robust with energy and obtain with great accuracy the dispersion of the \pi-bands for both ML and BL graphene in the vicinity of the Fermi level, extracting their main tight binding parameters

Leptospirosis: toma de muestras y diagnóstico

La leptospirosis es una enfermedad infecto-contagiosa provocada por una bacteria del género Leptospira que afecta a los animales domésticos y silvestres siendo estos una fuente de infección para el hombre. Podemos definir a la leptospirosis como una zoonosis de diagnóstico complejo que provoca pérdidas económicas difíciles de cuantificar. El diagnóstico de la leptospirosis comprende el diagnóstico clínico, bacteriológico, molecular y serológico.Mesa: Leptospirosis.Facultad de Ciencias Veterinaria

Leptospirosis: toma de muestras y diagnóstico

La leptospirosis es una enfermedad infecto-contagiosa provocada por una bacteria del género Leptospira que afecta a los animales domésticos y silvestres siendo estos una fuente de infección para el hombre. Podemos definir a la leptospirosis como una zoonosis de diagnóstico complejo que provoca pérdidas económicas difíciles de cuantificar. El diagnóstico de la leptospirosis comprende el diagnóstico clínico, bacteriológico, molecular y serológico.Mesa: Leptospirosis.Facultad de Ciencias Veterinaria

Leptospirosis: toma de muestras y diagnóstico

La leptospirosis es una enfermedad infecto-contagiosa provocada por una bacteria del género Leptospira que afecta a los animales domésticos y silvestres siendo estos una fuente de infección para el hombre. Podemos definir a la leptospirosis como una zoonosis de diagnóstico complejo que provoca pérdidas económicas difíciles de cuantificar. El diagnóstico de la leptospirosis comprende el diagnóstico clínico, bacteriológico, molecular y serológico.Mesa: Leptospirosis.Facultad de Ciencias Veterinaria

The missing atom as a source of carbon magnetism

Atomic vacancies have a strong impact in the mechanical, electronic and magnetic properties of graphene-like materials. By artificially generating isolated vacancies on a graphite surface and measuring their local density of states on the atomic scale, we have shown how single vacancies modify the electronic properties of this graphene-like system. Our scanning tunneling microscopy experiments, complemented by tight binding calculations, reveal the presence of a sharp electronic resonance at the Fermi energy around each single graphite vacancy, which can be associated with the formation of local magnetic moments and implies a dramatic reduction of the charge carriers' mobility. While vacancies in single layer graphene naturally lead to magnetic couplings of arbitrary sign, our results show the possibility of inducing a macroscopic ferrimagnetic state in multilayered graphene samples just by randomly removing single C atoms.Comment: Accepted for publication in Physical Review Letter

Leptospirosis: técnicas diagnósticas

La Leptospirosis es una enfermedad infecto-contagiosa, causada por una bacteria del género Leptospira que afecta sobre todo a los animales salvajes y domésticos, que sirven como fuente de infección para el hombre. Presenta una epidemiología compleja y distribución cosmopolita, en la que varias especies, principalmente los roedores actúan como hospedadores de mantenimiento de muchas serovariedades en todo el mundo, siendo el hombre y los animales de explotación hospedadores accidentales. Según la clasificación serológica o fenotípica hay más de 225 serovares. Las especies del género Leptospira han sido reclasificadas tomando como base los estudios de ADN. Es por esto que la clasificación fenotípica de leptospiras está siendo reemplazada por la genotípica, en la cual un número de genomoespecies incluyen todas las serovariedades de ambas, L interrogans y L biflexa, habiéndose demostrado heterogeneidad genética.Facultad de Ciencias Veterinaria

La vanguardia artística española a través de la crítica (1912-1936)

Tesis Univ. Complutense de Madrid, 1982.Depto. de Historia del ArteFac. de Geografía e HistoriaTRUEProQuestpu