Relaciones de similitud y valor discriminativo de los indicadores bibliométricos: el caso de los indicadores de Scimago Journal and Country Rank aplicados a las revistas generalistas de paleontología

Los objetivos de este trabajo son: (1) analizar las relaciones de similitud de los indicadores bibliométricos; y (2) estudiar el valor de estos para discriminar/agrupar revistas científicas. Como unidades de estudio se utilizaron los 15 indicadores brindados por SCImago Journal Rank (SCImagoJR), aplicados a las 11 revistas paleontológicas generalistas listadas en dicha fuente durante el lapso 1999-2013. Las relaciones de similitud entre los indicadores se estimaron mediante un fenograma, mientras que el valor de los indicadores para agrupar/discriminar revistas se estimó mediante un análisis de componentes principales. Los resultados permiten concluir que, al menos para las revistas consideradas en este estudio, los 15 indicadores utilizados por SCImagoJR muestran redundancia por grupos, debido a las correlaciones existentes entre indicadores de producción, por una parte, y de citación, por otra. Sin embargo, esto es válido solo a los efectos de agrupar las revistas, ya que al considerar cada indicador por separado se aprecian variaciones entre los mismos, que permiten establecer una caracterización más específica de cada revista e, incluso, colaboran a explicar los resultados del análisis multivariado. Por otra parte, los resultados coinciden con los obtenidos por otros autores al reunir en un mismo grupo al SJR y al número de citas/documento en un período de dos años y en otro al índice h y al indicador número total de citas en un lapso de tres años.

Discarge compilation from The Global River Discharge (RivDIS) Project

The Global River Discharge (RivDIS) data set contains monthly discharge measurements for 1018 stations located throughout the world. The period of record varies widely from station to station, with a mean of 21.5 years. These data were digitized from published UNESCO archives by Charles Voromarty, Balaze Fekete, and B.A. Tucker of the Complex Systems Research Center (CSRC) at the University of New Hampshire. River discharge is typically measured through the use of a rating curve that relates local water level height to discharge. This rating curve is used to estimate discharge from the observed water level. The rating curves are periodically rechecked and recalibrated through on-site measurement of discharge and river stage.

Noise Figure Measurement of Differential Amplifiers Using non-Ideal Baluns

This paper analyzes the noise and gain measurement of microwave differential amplifiers using two passive baluns. A general model of the baluns is considered, including potential losses and phase/amplitude unbalances. This analysis allows de-embedding the actual gain and noise performance of the isolated amplifier by using single-ended measurements of the cascaded system and baluns. Finally, measured results from two amplifier prototypes are used to validate the theoretical principles.

Dual-Band Tunable Recursive Active Filter

This letter presents a novel recursive active filter topology that provides dual-band performance, with independent tuning capability in both bands. The dual-band operation is achieved by using two independent feedback lines. Additionally, linear phase shifters based on left-handed cells are included in these two branches in order to tune the center frequency of both pass bands.

A De-Embedding Method to Characterize Differential

This paper analyses the noise and gain measurement of microwave differential amplifiers using two passive baluns. A model of the baluns that includes potential losses and unbalances has been considered. This analysis allows to de-embed the actual performance of the differential device from the single-ended measurements of the two-port cascaded system and the baluns. The method has been validated with measured results from a fully-differential amplifier prototype.

Medidas de propiedades dieléctricas de materiales de construcción mediante elipsometría

A set of measurements of electromagnetic properties of building materials is presented in this work. The method is based on the measurement of the polarization state of the reflected signal from the material under study at a fixed angle of incidence. From the measured data, by using the Fresnel equations, it has been obtained the dielectric constant. Measurements were done by using two horn antennas at the frequency of 9 GHz. The obtained results are compared with the free space reflexion and transmission Fresnel method and other reflection methods based on a conductor waveguide. The method explained in this work can be used for other type of materials and its main advantage is the non-destructive character and the ease implementation.

Método de desembebido para la caracterización de amplificadores diferenciales usando baluns pasivos

This paper analyses the noise and gain measurement of microwave differential amplifiers using two passive baluns. A model of the baluns that includes potential losses and unbalances has been considered. This analysis allows de-embedding actual performance of the differential device from the single-ended measurements of the two-port cascaded system and the baluns. The method has been validated with measured results from a fully-differential amplifier prototype.

Diseño de una rectena de onda completa de triple frecuencia

Modern communication systems use multifrequency or broadband antennas in order to provide multiple communication services. One of the biggest problems associated to all these systems comes from their batteries life cycle. Nowadays, great efforts are being undertaken in order to harvest energy from as many places as possible. In addition, if the two cycles of the corresponding wave could be used, it would be good in order to increase the RF-DC power conversion. This paper presents a multifrequency and full wave-rectifying antenna for microwave application

Sistema de enfoque basado en dos espejos elípticos y un espejo plano rotatorio para un radar a 300 GHz

A focusing system for a 300 GHz radar with two target distances (5m and 10m) is proposed, having 1cm resolution in both cases. The focusing system is based on a gaussian telescope scheme and it has been designed using gaussian beam quasi-optical propagation theory with a homemade Matlab analysis tool. It has been translated into a real focusing system based on two elliptical mirrors and a plane mirror in order to have scanning capabilities and validated using the commercial antenna software GRASP

Provisos for classic linear oscillator design methods. New linear oscillator design based on the NDF/RRT

In this paper, the classic oscillator design methods are reviewed, and their strengths and weaknesses are shown. Provisos for avoiding the misuse of classic methods are also proposed. If the required provisos are satisfied, the solutions provided by the classic methods (oscillator start-up linear approximation) will be correct. The provisos verification needs to use the NDF (Network Determinant Function). The use of the NDF or the most suitable RRT (Return Relation Transponse), which is directly related to the NDF, as a tool to analyze oscillators leads to a new oscillator design method. The RRT is the "true" loop-gain of oscillators. The use of the new method is demonstrated with examples. Finally, a comparison of NDF/RRT results with the HB (Harmonic Balance) simulation and practical implementation measurements prove the universal use of the new methods.

Transpose return relation method for designing low noise oscillators

In this paper, a new linear method for optimizing compact low noise oscillators for RF/MW applications will be presented. The first part of this paper makes an overview of Leeson's model. It is pointed out, and it is demonstrates that the phase noise is always the same inside the oscillator loop. It is presented a general phase noise optimization method for reference plane oscillators. The new method uses Transpose Return Relations (RRT) as true loop gain functions for obtaining the optimum values of the elements of the oscillator, whatever scheme it has. With this method, oscillator topologies that have been designed and optimized using negative resistance, negative conductance or reflection coefficient methods, until now, can be studied like a loop gain method. Subsequently, the main disadvantage of Leeson's model is overcome, and now it is not only valid for loop gain methods, but it is valid for any oscillator topology. The last section of this paper lists the steps to be performed to use this method for proper phase noise optimization during the linear design process and before the final non-linear optimization. The power of the proposed RRT method is shown with its use for optimizing a common oscillator, which is later simulated using Harmonic Balance (HB) and manufactured. Then, the comparison of the linear, HB and measurements of the phase noise are compared.

Comments and remarks over classic linear loop-gain method for oscillator design and analysis. New proposed method based on NDF/RRT

Abstract. This paper describes a new and original method for designing oscillators based on the Normalized Determinant Function (NDF) and Return Relations (RRT)- Firstly, a review of the loop-gain method will be performed. The loop-gain method pros, cons and some examples for exploring wrong solutions provided by this method will be shown. This method produces in some cases wrong solutions because some necessary conditions have not been fulfilled. The required necessary conditions to assure a right solution will be described. The necessity of using the NDF or the Transpose Return Relations (RRT), which are related with the True Loop-Gain, to test the additional conditions will be demonstrated. To conclude this paper, the steps for oscillator design and analysis, using the proposed NDF/RRj method, will be presented. The loop-gain wrong solutions will be compared with the NDF/RRj and the accuracy of this method to estimate the oscillation frequency and QL will be demonstrated. Some additional examples of plane reference oscillators (Z/Y/T), will be added and they will be analyzed with the new NDF/RRj proposed method, even these oscillators cannot be analyzed using the classic loop gain method.

Impact of N2 plasma power discharge on AlGaN/GaN HEMT performance

The effects of power and time conditions of in situ N2 plasma treatment, prior to silicon nitride (SiN) passivation, were investigated on an AlGaN/GaN high-electron mobility transistor (HEMT). These studies reveal that N2 plasma power is a critical parameter to control the SiN/AlGaN interface quality, which directly affects the 2-D electron gas density. Significant enhancement in the HEMT characteristics was observed by using a low power N2 plasma pretreatment. In contrast, a marked gradual reduction in the maximum drain-source current density (IDS max) and maximum transconductance (gm max), as well as in fT and fmax, was observed as the N2 plasma power increases (up to 40% decrease for 210 W). Different mechanisms were proposed to be dominant as a function of the discharge power range. A good correlation was observed between the device electrical characteristics and the surface assessment by atomic force microscopy and Kelvin force microscopy techniques.

From arrays of THz antennas to large-area emitters

Arrays of coherently driven photomixers with antenna (antenna emitter arrays, AEAs) have been evaluated as a possibility to overcome the power limitations of individual conventional photomixers with antenna (?antenna emitters?, AEs) for the generation of continuous-wave (CW) THz radiation. In this paper, ?large area emitters? (LAEs) are proposed as an alternative approach, and compared with AEAs. In this antenna-free new scheme of photomixing, the THz radiation originates directly from the acceleration of photo-induced charge carriers generated within a large semiconductor area. The quasi-continuous distribution of emitting elements corresponds to a high-density array and results in favorable radiation profiles without side lobes. Moreover, the achievable THz power is expected to outnumber even large AEAs. Last not least, the technological challenge of fabricating LAEs appears to be significantly less demanding.

Receptores homodinos a 300 GHz basados en tecnología CMOS

Using CMOS transistors for terahertz detection is currently a disruptive technology that offers the direct integration of a terahertz detector with video preamplifiers. The detectors are based on the resistive mixer concept and its performance mainly depends on the following parameters: type of antenna, electrical parameters (gate to drain capacitor and channel length of the CMOS device) and foundry. Two different 300 GHz detectors are discussed: a single transistor detector with a broadband antenna and a differential pair driven by a resonant patch antenna.