Empirical modeling of low-frequency dispersive effects due to traps and thermal phenomena in III-V FET's

The modeling of low-frequency dispersive effects due to surface state densities, deep level traps and thermal phenomena plays an important role in the large-signal performance prediction of III-V FET's. This paper describes an empirical modeling approach to accurately predict deviations between static and dynamic drain current characteristics caused by dispersive effects in III-V devices operating at microwave frequencies. It is based on reasonable assumptions and can easily be embedded in nonlinear FET models to be used in Harmonic-Balance tools for circuit analysis and design. Experimental and simulated results, for HEMT's and GaAs MESFET's of different manufacturers, that confirm the validity of the new approach, are presented and discussed together with the characterization procedures require

ANTENA DE SEGUIMIENTO EN ACIMUT PARA COMUNICACIONES VIA SATELITE

We present in this paper a first step of a feasibility study about a geo-satellite link from aeronautical, maritime and land mobiles, where the antenna provides a mechanical scanning in azimuth, based on a new beam tracking system.The novelty of this system is on the radiating element, which provides simultaneously at the input of the control card, the signals of both beams. This system avoids the waiting time due to the state change of the beam switch in a classical process.A laboratory prototype of the antenna has been designed, manufactured and measured, to demonstrate the possibilities of the developed technolog

La participación laboral de las mujeres: un reto para el bienestar social.

Este trabajo ha sido posible gracias a la cobertura de los proyectos de investigación “Riesgos y oportunidades a lo largo del curso de la vida en las sociedades postindustriales” (CICYT. Sec2003-06799), dirigido por Esping-Andersen (Universitat Pompeu Fabra) y “Nuevos Riesgos Sociales y Trayectorias de las Políticas del Bienestar” (NURSOPOB) (MEC, Plan Nacional de I+D+I), dirigidos por Luis Moreno (Unidad de Políticas Comparadas, CSIC). Agradezco a ambos el apoyo que me han prestado para poderle llevar a cabo, y de forma muy particular, a Ana Arriba y Luis Moreno, por sus comentarios y colaboración en versiones anteriores del mismo

Usefulness of NGS for diagnosis of dominant beta-thalassemia and unstable hemoglobinopathies in five clinical cases

Unstable hemoglobinopathies (UHs) are rare anemia disorders (RADs) characterized by abnormal hemoglobin (Hb) variants with decreased stability. UHs are therefore easily precipitating, causing hemolysis and, in some cases, leading to dominant beta-thalassemia (dBTHAL). The clinical picture of UHs is highly heterogeneous, inheritance pattern is dominant, instead of recessive as in more prevalent major Hb syndromes, and may occur de novo. Most cases of UHs are not detected by conventional testing, therefore diagnosis requires a high index of suspicion of the treating physician. Here, we highlight the importance of next generation sequencing (NGS) methodologies for the diagnosis of patients with dBTHAL and other less severe UH variants. We present five unrelated clinical cases referred with chronic hemolytic anemia, three of them with severe blood transfusion dependent anemia. Targeted NGS analysis was performed in three cases while whole exome sequencing (WES) analysis was performed in two cases. Five different UH variants were identified correlating with patients' clinical manifestations. Four variants were related to the beta-globin gene (Hb Bristol-Alesha, Hb Debrousse, Hb Zunyi, and the novel Hb Mokum) meanwhile one case was caused by a mutation in the alpha-globin gene leading to Hb Evans. Inclusion of alpha and beta-globin genes in routine NGS approaches for RADs has to be considered to improve diagnosis' efficiency of RAD due to UHs. Reducing misdiagnoses and underdiagnoses of UH variants, especially of the severe forms leading to dBTHAL would also facilitate the early start of intensive or curative treatments for these patients.Genetics of disease, diagnosis and treatmen

The role of molecular genetics in diagnosing familial hematuria(s)

Familial microscopic hematuria (MH) of glomerular origin represents a heterogeneous group of monogenic conditions involving several genes, some of which remain unknown. Recent advances have increased our understanding and our ability to use molecular genetics for diagnosing such patients, enabling us to study their clinical characteristics over time. Three collagen IV genes, COL4A3, COL4A4, and COL4A5 explain the autosomal and X-linked forms of Alport syndrome (AS), and a subset of thin basement membrane nephropathy (TBMN). A number of X-linked AS patients follow a milder course reminiscent of that of patients with heterozygous COL4A3/COL4A4 mutations and TBMN, while at the same time a significant subset of patients with TBMN and familial MH progress to chronic kidney disease (CKD) or end-stage kidney disease (ESKD). A mutation in CFHR5, a member of the complement factor H family of genes that regulate complement activation, was recently shown to cause isolated C3 glomerulopathy, presenting with MH in childhood and demonstrating a significant risk for CKD/ESKD after 40 years old. Through these results molecular genetics emerges as a powerful tool for a definite diagnosis when all the above conditions enter the differential diagnosis, while in many at-risk related family members, a molecular diagnosis may obviate the need for another renal biopsy

A Coherent Small/Large Signal FET model Based on Neuronal Architectures 1

A modular neural network architecture for accurate small/large signal microwave MESFET/HEMT modeling is presented. This is achieved by means of an original neural architecture having two main modules. A network captures the nonlinear dynamic Pulsed I/V characteristic of the device, which is mainly responsible of the large signal behavior, while the second network estimates the high order derivatives at the operation point, which are responsible of the IMD behaviour, by means of a neural network and then it locally reconstructs the current function by means of a third order Taylor series around that point. Finally, in order to have a maximum of coherence, the two networks are combined into a global model by means of a simple fuzzy controller. Computer simulations and experimental measurements validate this flexible modeling technique

Pseudo-random pulsed IV characterisation system for GAAS MESFET/HEMT devices

A novel experimental system for observing the dependence of the trapping states on electric field for GaAs MESFET/HEMT devices is presented. The new procedure employs a pseudo-random pulse characterisation system for observing the memory effect in these devices. The results indicate that the trapping effect is more serious than may be thought

Analysis of microstrip line step-discontinuities and its application to a cascaded configuration

An abrupt change in microstrip linewidth, commonly called a microstrip impedance step, is a discontinuity that appears frequently in MMICs, such as, stepped impedance transformers and matching networks for example. Therefore, the accurate description of these step-discontinuties is important for the computer-aided design of conventional and monolithic MICs. In this work we have studied the set of modes that appears in a boxed microstrip in order to apply modal analysis in the spectral domain to the study of simple and cascaded step discontinuities. In order to check its precision, our method has been applied to a nine section low-pass filter, made up of a cascade of microstrip step discontinuities. Several filters have been designed, built and tested at different frequencies. We have compared these designs with Touchstone and shown that at low frequencies both methods give similar results, but when the frequency is higher, the Touchstone results are farther from the experimental results than the design obtained with the modal analysis method

Electric field dependency of traps in mesfet/hemt devices

A new measurement procedure for observing the dependence of the frequency dispersion effect on electric field for GaAs MESFET/HEMT devices is presented. The new procedure employs a statistically based pulse I/V measurement system for observing the memory effect in these devices. The results indicate, possibly for the first time, the true extent of the effects of the traps in these devices