Global design of analog cells using statistical optimization techniques

We present a methodology for automated sizing of analog cells using statistical optimization in a simulation based approach. This methodology enables us to design complex analog cells from scratch within reasonable CPU time. Three different specification types are covered: strong constraints on the electrical performance of the cells, weak constraints on this performance, and design objectives. A mathematical cost function is proposed and a bunch of heuristics is given to increase accuracy and reduce CPU time to minimize the cost function. A technique is also presented to yield designs with reduced variability in the performance parameters, under random variations of the transistor technological parameters. Several CMOS analog cells with complexity levels up to 48 transistors are designed for illustration. Measurements from fabricated prototypes demonstrate the suitability of the proposed methodology

Consideraciones sobre los modelos numéricos de distribución para el análisis de la fisuración del hormigón

Se analizan los modelos de distribución para el análisis de la fisuración del hormigón por el Método de los Elementos Finitos profundizando en el significado del concepto de distribución y en sus implicaciones numéricas. Se establece una longitud característica, consistente con la disipación correcta de la energía de fractura, que permite el paso de ecuaciones constitutivas del tipo tensión desplazamiento al tipo tensión-deformación. Se presentan diversos ejemplos numéricos de aplicación del modelo propuesto en los que se analizan la convergencia con el tamaño y deformación de la malla, la influencia del orden de integración y se comparan los resultados con otras formulaciones.In this paper, smeared models for cracking analysis of concrete are analyzed emphasizing ,on the smeared concept and its numerical implications. A caracteristic length, consistent with the correct fracture energy dissipation is derived. Tliat allows for passing from stressdisplacement type to stress-strain type constitutive equations. Several numerical examples of the application of the proposed model are presented, in which convergency with size and mesh deformation, influence of the numerical integration order, and comparation with other formulations are studied.Peer Reviewe

The relationship between soft X-rays and the 1640 Å feature fluxes in late-type stars

The λ 1640 feature has been observed in a sample of late­ type stars of different luminosity classes. The intensity was measured from IUE low dispersion spectra, and it has been compared with the observed X-ray fluxes, finding a relationship between both quantities for "solar type" stars. The X-ray fluxes derived from this relationship for a reduced sample of stars are consistent with the observed ones in the case of "solar type" stars. "Non solar type" stars exhibit discrepancies that could be explained assuming that the λ 1640 feature is formed by contri­buters other than He II, which supply an important fraction of this emission in "solar type" stars. The obtained empirical relationship has been used to derive the X-ray flux for some stars that have not been observed in the X-ray range

Performance evaluation and limitations of a vision system on a reconfigurable/programmable chip

This paper presents a survey of the characteristics of a vision system implemented in a reconfigurable/programmable chip (FPGA). System limitations and performance have been evaluated in order to derive specifications and constraints for further vision system synthesis. The system hereby reported has a conventional architecture. It consists in a central microprocessor (CPU) and the necessary peripheral elements for data acquisition, data storage and communications. It has been designed to stand alone, but a link to the programming and debugging tools running in a digital host (PC) is provided. In order to alleviate the computational load of the central microprocessor, we have designed a visual co-processor in charge of the low-level image processing tasks. It operates autonomously, commanded by the CPU, as another system peripheral. The complete system, without the sensor, has been implemented in a single reconfigurable chip as a SOPC. The incorporation of a dedicated visual co-processor, with specific circuitry for low-level image processing acceleration, enhances the system throughput outperforming conventional processing schemes. However, time-multiplexing of the dedicated hardware remains a limiting factor for the achievable peak computing power. We have quantified this effect and sketched possible solutions, like replication of the specific image processing hardware. © J.UCS.This work has been partially funded by project FIT-330100-2005-162 of the Spanish Ministry of Industry, Tourism and Commerce. The work of F. J. Sánchez-Fernández is supported by a grant of the Spanish Ministry of Education and Science.Peer Reviewe

On the instability for an incremental problem in elastodynamics

Financiado para publicación en acceso aberto: Universidade de Vigo/CISUGIn this short note, we consider some issues regarding the instability of some elastodynamical problems when the elasticity tensor is not positive definite. By using the so-called logarithmic convexity argument, we prove the instability of solutions when the time derivative of the elasticity tensor is semi-definite negative or it satisfies another restriction on the coefficients. The uniqueness of the solution is also concluded. Finally, a simple one-dimensional example is provided to demonstrate the numerical behaviour of the instability.Ministerio de Ciencia, Innovación y Universidades | Ref. PID2019-105118GB-I0

Las áreas metropolitanas frente al desafío de la competitividad

Las áreas metropolitanas de todo el mundo, y en particular las de América Latina y el Caribe, se enfrentan hoy con importantes problemas. Bastantes de ellos no son nuevos en absoluto, sino que tienen sus raíces en la evolución que dichas áreas han experimentado a lo largo de las últimas décadas. Este es el caso de los problemas fiscales, los relacionados con el transporte urbano y metropolitano, los continuos requerimientos para la dotación de nuevas y mejores infraestructuras, o las crecientes necesidades de cobertura en materia de servicios sociales. En los últimos años han surgido y tomado cuerpo, además, algunas cuestiones que hoy también se consideran claves, como son, por una parte, los problemas medioambientales y de sostenibilidad del crecimiento de las grandes ciudades y áreas metropolitanas y, por otra, la competencia que en no pocos casos se está desarrollando entre ellas, ya sea a escala nacional, continental e incluso global. Todo ello se relaciona muy directamente con un concepto más amplio como es el de la ‘gobernabilidad’ de las aglomeraciones metropolitanas

Colored semi-transparent Cu-Si oxide thin films prepared by magnetron sputtering

Colored semi-transparent Cu-Si oxide thin films have been prepared by reactive magnetron sputtering from a single cathode of copper-silicon composition. Thin films of different composition and optical response were obtained by changing process parameters like the relative amount of copper in the target and the O2/Ar mixture of the reactive plasma gas. The film characteristics were analyzed by several techniques. Their optical properties (refractive index, absorption coefficient, color) have been correlated with the process parameters used in the film preparation as well as with the film stoichiometry and chemistry.Ministerio de Ciencia e Innovación CEN-20072014, MAT2010-18447, MAT2010-21228, CSD2008–00023Junta de Andalucía P09-TEP5283, CTS-518

Combined use of the GGSFT data base and on Board Marine Collected Data to Model the Moho Beneath the Powell Basin, Antarctica

The Powell Basin is a small oceanic basin located at the NE end of the Antarctic Peninsula developed during the Early Miocene and mostly surrounded by the continental crusts of the South Orkney Microcontinent, South Scotia Ridge and Antarctic Peninsula margins. Gravity data from the SCAN 97 cruise obtained with the R/V Hespérides and data from the Global Gravity Grid and Sea Floor Topography (GGSFT) database (Sandwell and Smith, 1997) are used to determine the 3D geometry of the crustal-mantle interface (CMI) by numerical inversion methods. Water layer contribution and sedimentary effects were eliminated from the Free Air anomaly to obtain the total anomaly. Sedimentary effects were obtained from the analysis of existing and new SCAN 97 multichannel seismic profiles (MCS). The regional anomaly was obtained after spectral and filtering processes. The smooth 3D geometry of the crustal mantle interface obtained after inversion of the regional anomaly shows an increase in the thickness of the crust towards the continental margins and a NW-SE oriented axis of symmetry coinciding with the position of an older oceanic spreading axis. This interface shows a moderate uplift towards the western part and depicts two main uplifts to the northern and eastern sectors