Homogeneous hypersurfaces and totally geodesic submanifolds

This Ph.D. thesis deals with the study of certain classes of submanifolds in the presence of symmetry. Namely, results have been derived regarding the theory of submanifolds in Riemannian homogeneous spaces with a special emphasis on symmetric spaces. In this dissertation, we will focus on two of the most natural classes of submanifolds that one can study in Riemannian manifolds. These are homogeneous hypersurfaces and totally geodesic submanifolds. Regarding the first ones, we will conclude the classification of homogeneous hypersurfaces in symmetric spaces of rank one, by finishing the classification in quaternionic hyperbolic spaces. As for totally geodesic submanifolds, we will derive different classifications. In particular, we will classify totally geodesic submanifolds in the following spaces: in products of symmetric spaces of rank one, in exceptional symmetric spaces, and in Hopf-Berger spheres

A 64-channel inductively-powered neural recording sensor array

This paper reports a 64-channel inductively powered neural recording sensor array. Neural signals are acquired, filtered, digitized and compressed in the channels. Additionally, each channel implements a local auto-calibration mechanism which configures the transfer characteristics of the recording site. The system has two operation modes; in one case the information captured by the channels is sent as uncompressed raw data; in the other, feature vectors extracted from the detected neural spikes are transmitted. Data streams coming from the channels are serialized by an embedded digital processor and transferred to the outside by means of the same inductive link used for powering the system. Simulation results show that the power consumption of the complete system is 377μW.Ministerio de Ciencia e Innovación TEC2009-0844

A low-power reconfigurable ADC for biomedical sensor interfaces

This paper presents a 12-bit low-voltage low-power reconfigurable Analog-to-Digital Converter (ADC). The design employs Switched Capacitor (SC) techniques and implements a Successive Approximation (SA) algorithm. The ADC can be tuned to handle a large variety of biopotential signals, with digitally selectable resolution and input signal amplitude. It achieves 10.4-bit of effective resolution sampling at 56kS/s, with a power consumption below 3μW from a 1V voltage supply.Ministerio de Educación y Ciencia TEC2006-03022Junta de Andalucía TIC-0281

A power efficient neural spike recording channel with data bandwidth reduction

This paper presents a mixed-signal neural spike recording channel which features, as an added value, a simple and low-power data compression mechanism. The channel uses a band-limited differential low noise amplifier and a binary search data converter, together with other digital and analog blocks for control, programming and spike characterization. The channel offers a self-calibration operation mode and it can be configured both for signal tracking (to raw digitize the acquired neural waveform) and feature extraction (to build a first-order PWL approximation of the spikes). The prototype has been fabricated in a standard CMOS 0.13μm and occupies 400μm×400μm. The overall power consumption of the channel during signal tracking is 2.8μW and increases to 3.0μW average when the feature extraction operation mode is programmed.Ministerio de Ciencia e Innovación TEC2009-08447Junta de Andalucía TIC-0281

A self-calibration circuit for a neural spike recording channel

This paper presents a self-calibration circuit for a neural spike recording channel. The proposed design tunes the bandwidth of the signal acquisition Band-Pass Filter (BPF), which suffers from process variations corners. It also performs the adjustment of the Programmable Gain Amplifier (PGA) gain to maximize the input voltage range of the analog-to-digital conversion. The circuit, which consists on a frequency-controlled signal generator and a digital processor, operates in foreground, is completely autonomous and integrable in an estimated area of 0.026mm 2 , with a power consumption around 450nW. The calibration procedure takes less than 250ms to select the configuration whose performance is closest to the required one.Ministerio de Ciencia e Innovación TEC2009-08447Junta de Andalucía TIC-0281

Hopf fibrations and totally geodesic submanifolds

We classify totally geodesic submanifolds in Hopf-Berger spheres, which constitute a special family of homogeneous spaces diffeomorphic to spheres constructed via Hopf fibrations. As a byproduct of our investigations, we have discovered very intriguing examples of totally geodesic submanifolds. In particular, we stand out the following three: totally geodesic submanifolds isometric to real projective spaces, uncountably many isometric but non-congruent totally geodesic submanifolds, and a totally geodesic submanifold that is not extrinsically homogeneous. Remarkably, all these examples only arise in certain Hopf-Berger spheres with positive curvature.Comment: Minor changes. To appear in JEMS (Journal of the European Mathematical Society

Self-calibration of neural recording sensors

This paper reports a calibration system for automatically adjusting the bandpass and gain characteristics of programmable E×G sensors. The calibration mechanism of the bandpass characteristic is based on a mixed-signal tuning loop which uses as feedback signal the output of the data converter following the signal conditioning of the E×G sensor. Intended high-pass and low-pass frequency poles of the transfer function are injected into the loop by means of a direct frequency synthesizer followed by a smoothing atenuator.Ministerio de Ciencia e Innovación TEC2012-3363

Ulva Genus as Alternative Crop: Nutritional and Functional Properties

Use of seaweed by humans is an ancient practice. In Asian countries, the use of them in human and animal feed, traditional medicine, and compost in agriculture is well documented. Since the twenty-first century begins, the scientific interest for seaweed had increased in Occidental countries. Ulva or Enteromorpha is a green macroalgae genus that raises and cultivates around the world. It has salinity tolerance and growth with diverse nitrogen ratios, be able to farm them in aquaculture systems. Scientific studies seen in this genus an interesting profile of chemical compounds: The protein is similar in quantity and quality to soy or some animal products; dietetic fiber percentage is elevated (>40%), being around 40% soluble fiber of them. In addition, fiber fraction presents Ulvan, a complex sulfated polysaccharide that presents antiviral, antihyperlipidemic, and antidiabetic effect in animal assays. Moreover, antioxidant and phytochemical profile has not being totally elucidated, giving important opportunities to scientific community for explode consciously this biological resource

Evaluación de técnicas de control modulares en un convertidor elevador síncrono con rendimiento elevado a baja carga con el uso de MOSFET de SiC

XXIV Seminario Anual de Automática, Electrónica Industrial e Instrumentación 2017 (SAAEI'17), Valencia (España)Este artículo se centra en convertidores bidireccionales de alta tensión para ser utilizados como interfaz entre baterías y celdas de un convertidor modular multinivel (MMC), para poder dotar de almacenamiento distribuido a un transformador de estado sólido (SST). Dichos convertidores han de tener un rendimiento elevado a media y baja carga, así como un rizado de corriente reducido, debido a los procesos de carga y descarga de la batería. En este trabajo se analiza el uso de MOSFET de SiC como solución para cumplir con los dos requisitos anteriores. En primer lugar, la implementación de un control de frecuencia variable que permita mantener el rendimiento a baja carga. Y en segundo lugar, el uso de un convertidor modular y de distintas técnicas de control para reducir el rizado de corriente. En este trabajo se resumen distintos resultados experimentales del uso de MOSFET de SiC con el control de frecuencia variable, así como una comparativa de las técnicas de control. Estos resultados se han obtenido mediante un convertidor modular con entrada en paralelo y salida en paralelo (IPOP) basado en tres módulos (3kW por módulo) de un elevador síncrono, para una conversión de 400V a 800V y 9kW de potencia máxim