Notas sueltas sobre el desarrollo de la ciencia en España (Segunda serie)

Ha habido siempre un fondo de aislamiento celtíbero que, a lo largo de los siglos, ha cortado siempre nuestro posible nacer científico. Ha habido cosas muy curiosas y que son casi por completo desconocidas para la mayoría de la gente. Hay partes de nuestra historia que son casi por completo ignoradas.

Pinceladas de veinte años: algunos recuerdos de un plan

Análisis sobre lo conseguido en veinte años (desde los ochenta hasta principios de este siglo) en el campo de la investigación gracias al Plan Nacional de I+D.

El láser, caballo de batalla de la Guerra Fría: algunos detalles de su nacimiento

La historia de uno de los protagonistas tecnológicos del siglo XX, el láser, ha estado salpicada desde antes de sus inicios con las leyendas más descabelladas y las esperanzas más espectaculares. Han pasado ya más de cincuenta años desde su anuncio en los medios de comunicación y, a pesar de todo, sigue manteniendo un protagonismo que muchos otros descubrimientos de esa misma época perdieron hace ya bastante tiempo. Quizás puede ser porque gran parte de los objetivos que se decía que iba a alcanzar aun están pendientes y quizás, también, porque muchos terrenos en los cuales no se pensaba que pudiera incidir, al final tuvo en ellos una importancia destacada.

El láser: orígenes militares y aplicaciones civiles

En los poco más de 50 años que han transcurrido desde la invención del láser, éste ha pasado de ser un instrumento de laboratorio, sólo manejado por investigadores de nuevas tecnologías, a ser un integrante casi habitual de nuestra vida diaria. En muchos casos, su presencia es clara; pero, en otros, pasa casi desapercibido.

La luz, protagonista en 15 ocasiones

Una vez más, la luz ha sido protagonista de un Premio Nobel. Con el concedido a Charles Kao, son ya 15 los científicos o tecnólogos en este campo que, desde 1964, han visto recompensado su trabajo con este galardón. Han sido necesarios 33 años para que la obra de Kao alcance el reconocimiento público con el Nobel, pero, para los profesionales de las comunicaciones, ese reconocimiento surgió tras la publicación de su artículo más emblemático en una prestigiosa revista británica. En 1966 mostró a todos que el material más idóneo para transmitir la luz a su través era la sílice, uno de los materiales más abundantes en la corteza terrestre

Mundo cuántico, relojes y computación

En sus trabajos a lo largo de más de veinte años, el francés Serge Haroche y el americano David Wineland, ambos nacidos en 1944, fueron capaces de observar y medir, con técnicas revolucionarias, comportamientos en sistemas microscópicos antes sólo previstos a través de ecuaciones o mediante experimentos imaginados. Esos trabajos les han valido, en 2012, la concesión del Premio Nobel de Física.

HERMES: towards an integrated toolbox to characterize functional and effective brain connectivity

The analysis of the interdependence between time series has become an important field of research in the last years, mainly as a result of advances in the characterization of dynamical systems from the signals they produce, the introduction of concepts such as generalized and phase synchronization and the application of information theory to time series analysis. In neurophysiology, different analytical tools stemming from these concepts have added to the ?traditional? set of linear methods, which includes the cross-correlation and the coherency function in the time and frequency domain, respectively, or more elaborated tools such as Granger Causality. This increase in the number of approaches to tackle the existence of functional (FC) or effective connectivity (EC) between two (or among many) neural networks, along with the mathematical complexity of the corresponding time series analysis tools, makes it desirable to arrange them into a unified, easy-to-use software package. The goal is to allow neuroscientists, neurophysiologists and researchers from related fields to easily access and make use of these analysis methods from a single integrated toolbox. Here we present HERMES (http://hermes.ctb.upm.es), a toolbox for the Matlab® environment (The Mathworks, Inc), which is designed to study functional and effective brain connectivity from neurophysiological data such as multivariate EEG and/or MEG records. It includes also visualization tools and statistical methods to address the problem of multiple comparisons. We believe that this toolbox will be very helpful to all the researchers working in the emerging field of brain connectivity analysis.

Tu mayor descuido como hombre es mostrar tus debilidades de hombre

Dejarán de admirarte cuando te vean muy humano. Si eres muy fácil, simpático y liviano de carácter, perderás reputación. Así como el varón recatado y discreto es tenido por más hombres que el liviano y hablador. No hay vicio que más te quite autoridad y respeto, porque se opone a la gravedad, a la seriedad y responsabilidad. Un hombre sin sobriedad no puede ser sustancioso, ni sus decisiones están bien fundamentadas, y peor si es ya un anciano, en cuya edad todo el mundo espera que sea sensato y cuerdo. Y aunque este descuido lo tiene mucha gente, no deja de ser incorrecto.

Notas sobre la evaluación en los inicios del plan nacional de I+D

El artículo no pretende ser una historia de la Evaluación en el Sistema C-T español, ni siquiera en sus primeras andaduras en el Primer Plan Nacional de l+D. Es el recuerdo de los primeros años, en los que se gestaron las coordenadas de una estructura que intentaba adecuar la situación científica y tecnológica de España a la del resto de los países avanzados.

Vertical-cavity semiconductor optical amplifiers (VCSOAs) as optical sensing elements

Semiconductor Optical Amplifiers (SOAs) have mainly found application in optical telecommunication networks for optical signal regeneration, wavelength switching or wavelength conversion. The objective of this paper is to report the use of semiconductor optical amplifiers for optical sensing taking into account their optical bistable properties. As it was previously reported, some semiconductor optical amplifiers, including Fabry-Perot and Distributed-Feedback Semiconductor Optical Amplifiers (FPSOAs and DFBSOAs), may exhibit optical bistability. The characteristics of the attained optical bistability in this kind of devices are strongly dependent on different parameters including wavelength, temperature or applied bias current and small variations lead to a change on their bistable properties. As in previous analyses for Fabry-Perot and DFB SOAs, the variations of these parameters and their possible application for optical sensing are reported in this paper for the case of the Vertical-Cavity Semiconductor Optical Amplifier (VCSOA). When using a VCSOA, the input power needed for the appearance of optical bistability is one order of magnitude lower than that needed in edge-emitting devices. This feature, added to the low manufacturing costs of VCSOAs and the ease to integrate them in 2-D arrays, makes the VCSOA a very promising device for its potential use in optical sensing applications.

Photonic switching architectures with logic cells

Possible switching architectures, with Optically Programmable Logic Cells - OPLCs - will be reported in this paper. These basic units, previously employed by us for some other applications mainly in optical computing, will be employed as main elements to switch optical communications signals. The main aspect to be considered is that because the nternal components of these cells have nonlinear behaviors, namely either pure bistable or SEED-like properties, several are the possibilities to be obtained. Moreover, because their properties are dependent, under certain condition, of the signal wavelength, they are apt to be employed in WDM systems and the final result will depend on the orresponding optical signal frequency. We will give special emphasis to the case where self-routing is achieved, namely to structures of the Batcher or Banyan type. In these cases, as it will be shown, there is the possibility to route any packet input to a certain direction according to its first bits. The number of possible outputs gives the number of bits needed to route signals. An advantage of this configuration is that a very versatile behavior may be allowed. The main one is the possibility to obtain configurations with different kinds of behavior, namely, Strictly Nonblocking, Wide-Sense Nonblocking or Rearrangeably Nonblocking as well as to eliminate switching conflicts at a certain intermediate stages.

Photonic processing subsystem based on visual cortex architecture

Optical signal processing in any living being is more complex than the one obtained in artificial systems. Cortex architecture, although only partly known, gives some useful ideas to be employed in communications. To analyze some of these structures is the objective of this paper. One of the main possibilities reported is handling signals in a parallel way. As it is shown, according to the signal characteristics each signal impinging onto a single input may be routed to a different output. At the same time, identical signals, coming to different inputs, may be routed to the same output without internal conflicts. This is due to the change of some of their characteristics in the way out when going through the intermediate levels. The simulation of this architecture is based on simple logic cells. The basis for the proposed architecture is the five layers of the mammalian retina and the first levels of the visual cortex.

Coder/decoder with an optical programmable logic cell

A major research area is the representation of knowledge for a given application in a compact manner such that desired information relating to this knowledge is easily recoverable. A complicated procedure may be required to recover the information from the stored representation and convert it back to usable form. Coder/decoder are the devices dedicated to that task. In this paper the capabilities that an Optical Programmable Logic Cell offers as a basic building block for coding and decoding are analyzed. We have previously published an Optically Programmable Logic Cells (OPLC), for applications as a chaotic generator or as basic element for optical computing. In optical computing previous studies these cells have been analyzed as full-adder units, being this element a basic component for the arithmetic logic structure in computing. Another application of this unit is reported in this paper. Coder and decoder are basic elements in computers, for example, in connections between processors and memory addressing. Moreover, another main application is the generation of signals for machine controlling from a certain instruction. In this paper we describe the way to obtain a coder/decoder with the OPLC and which type of applications may be the best suitable for this type of cell.

Logic cells as basic structures to add/drop WDM information signals

Nowadays, in order to take advantage of fiber optic bandwidth, any optical communications system tends to be WDM. The way to extract a channel, characterized by a wavelength, from the optical fiber is to filter the specific wavelength. This gives the systems a low degree of freedom due to the fact of the static character of most of the employed devices. In this paper we will present a different way to extract channels from an optical fiber with WDM transmission. The employed method is based on an Optically Programmable Logic Cells (OPLC) previously published by us, for other applications as a chaotic generator or as basic element for optical computing. In this paper we will describe the configuration of the OPLC to be employed as a dropping device. It acts as a filter because it will extract the data carried by a concrete wavelength. It does depend, internally, on the wavelength. We will show how the intensity of the signal is able to select the chosen information from the line. It will be also demonstrated that a new idea of redundant information it is the way of selecting the concrete wavelength. As a matter of fact this idea is apparently the only way to use the OPLC as a dropping device. Moreover, based on these concepts, a similar way to route signals to different routes is reported. The basis is the use of photonic switching configurations, namely Batcher or Bayan structures, where the unit switching cells are the above indicated OPLCs.

Low-power vertical cavity NAND gate

The study of the Vertical-Cavity Semiconductor Optical Amplifiers (VCSOAs) for optical signal processing applications is increasing his interest. Due to their particular structure, the VCSOAs present some advantages when compared to their edge-emitting counterparts including low manufacturing costs, high coupling efficiency to optical fibers and the ease to fabricate 2-D arrays of this kind of devices. As a consequence, all-optical logic gates based on VCSOAs may be very promising devices for their use in optical computing and optical switching in communications. Moreover, since all the boolean logic functions can be implemented by combining NAND logic gates, the development of a Vertical-Cavity NAND gate would be of particular interest. In this paper, the characteristics of the dispersive optical bistability appearing on a VCSOA operated in reflection are studied. A progressive increment of the number of layers compounding the top Distributed Bragg Reflector (DBR) of the VCSOA results on a change on the shape of the appearing bistability from an S-shape to a clockwise bistable loop. This resulting clockwise bistability has high on-off contrast ratio and input power requirements one order of magnitude lower than those needed for edge-emitting devices. Based on these results, an all-optical vertical-cavity NAND gate with high on-off contrast ratio and an input power for operation of only 10|i\V will be reported in this paper.