1,720,976 research outputs found
A V band singly balanced diode mixer for space application
Full text linkThe paper describes the design of a V band single balanced mixer to be employed in the front end of an on-board receiver for space applications. The V band receiver is a demonstrator for the use of different monolithic processes and interconnection/assembly technologies in space applications at such high frequencies. The receiver front-end consists of a multi-stage LNA amplification followed by an image reject filter, the mixer and a frequency doubler for the local oscillator. All the chips are mounted over an LTTC substrate using bumps/hot vias technology. Chip to chip interconnection is provided by coplanar wave guide on LTTC. The mixer employs a rat race 180° hybrid to balance the local oscillator and a couple of Schottky diodes as mixing elements. The technology employed is a 0.15μm pHMET process that offers diodes with a cut off frequency higher that 300GHz. The choices made for the mixer type and topology starting from the system specifications are covered in the paper along with the actual description of the circuit design
Design of L and X band class E power amplifiers with GaAs pHEMT technology for space SAR
No full textThe paper describes the design of class E power amplifiers for SAR space applications, exploiting a 0.35-um pHEMT GaAs process. An L-band 10-Watt push-pull hybrid amplifier has been designed and implemented. The HPA features 73% PAE and 81% drain efficiency at 1.275 GHz. The performances of the class E HPA are also compared with a class AB HPA, exploiting the same technology. Class E design was also evaluated at X band, which for this technology is beyond the limit for the devices' class E operation capability. Two different prototype amplifiers were designed exploiting different device periphery. The single-cell amplifier delivers about 31 dBm output power with 64% peak PAE, whereas the double-cell circuit features 27 dBm output power with 70% peak PAE. These prototype amplifiers prove the possibility to use this process for the design of X band MMIC HPA for SAR space applications operating with high efficiency
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Analysis of dielectric constant behavior of thermally treated SU-8 polymer up to 18 GHz
No full textSu-8 polymer has excellent potential for application in process manufacturing. This paper presents the effects of thermal stress on the electromagnetic properties of SU-8 polymer, showing the frequency-dependent microwave response of the material. The procedure follows the international standard method for assessing the quality of components and devices for space qualification as thermal stress simulates the aging process. The polymer has been used as a base layer to fabricate passive devices in the coplanar waveguide (CPW) configuration. Resonating structures and delay lines, with different sizes, have been manufactured on a SU-8 layer spun on a high resistivity silicon wafer. The material's dielectric constant has been calculated by measuring the microwave response of the devices before and after the thermal processes. We have recorded data in a broadband range, from 2 GHz to 18 GHz, and the conclusive comparison allows us to identify a frequency dependence of the electromagnetic performances of SU-8 polymer and confirms the possibility to use it for medium-and long-term microwave space applications. Specifically, minor changes of the electrical matching have been recorded in the Ku-band, from 12 GHz to 18 GHz, making the polymer reliable for current space communications
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
A Technique to Design MMICs for Space Applications and High Production Yields
No full textIn this paper a MMIC design technique, oriented to the optimization of the production yields, is illustrated together with the obtained results.
This method, based on a sensitivity analysis, i.e. on the circuit behavior for variations of passive elements from their nominal value, and on the contemporary determination of the production yields, allows the identification the circuit elements to obtain high production yield. Moreover it allows an appropriate choice of the circuit topology.
As example, this technique has been applied to design a MMIC to be employed on equipments where a high number of devices is required
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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