1,721,093 research outputs found
Non-uniform C-section phasers for enhanced design flexibility in Radio Analog Signal Processing
No full textA non-uniform C-section phaser is introduced as a powerful approach to enhance the design flexibility of uniform phasers. Moreover, an efficient synthesis technique is provided to design such phasers. Two design examples are presented. The first example is a single non-uniform C-section phaser. The second one is a cascaded double non-uniform C-section phaser featuring larger group delay swing and bandwidth, and hence higher resolution in Radio Analog Signal Processing (R-ASP).</p
Enhanced Bandwidth and Diversity in Real-Time Analog Signal Processing (R-ASP) Using Nonuniform C-Section Phasers
No full textWe show that a continuously nonuniform coupled-line C-section phaser, as the limiting case of the step-discontinuous coupled-line multisection commensurate and non-commensurate phasers, provides enhanced bandwidth and diversity in real-time analog signal processing (R-ASP). The phenomenology of the component is explained in comparison with the step-discontinuous using multiple-reflection theory and a simple synthesis procedure is provided. The bandwidth enhancement results from the suppression of spurious group delay harmonics or quasi-harmonics, while the diversity enhancement results from the greater level of freedom provided by the continuous nature of the nonuniform profile of the phaser. These statements are supported by theoretical and experimental results.</p
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
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
Coupled-resonator arrays for sensing applications
No full textMicrowave sensing for nondestructive detection, diagnosis, and imaging has been of great interest for many decades. Sensing methods are commonly classified as either probe-based or antenna-based according to near-field or far-field applications, respectively. Various resonant probe-based approaches have been reported previously and these have promoted the capabilities of single-probe detectors. However, most of these existing approaches still require raster scanning for information acquisition, so it is impossible to achieve large-scale sensing in one shot. Alternatively, leaky-wave antennas with high-scanning-rate beam steering can be utilized for sensing applications, but drawbacks still exist and limit their utility. Firstly, as traveling-wave structures, leaky-wave antennas feature large working bandwidth and cannot be applied to narrow-band scenarios. Secondly, in most of the literature, leaky-wave antennas can achieve high-scanning-rate beam steering at the cost of large structure loss, which significantly reduces the radiation efficiency of the antenna and hence lowers signal-to-noise ratio (SNR) and sensing quality. To address the challenges of using single resonant probes or leaky-wave antennas, probe arrays and antenna arrays based on coupled-resonator networks are proposed in this thesis. For the first contribution, multiple-probe sensors based on coupled resonators are pro-posed. Both the extraction approach based on coupling matrix theory and the design principle minimizing condition number have been illustrated. The two-port and one-port sensor have been designed and numerical examples together with experimental results have been provided to validate the technique. Compared with existing single probe designs, the multiple-probe structure has the advantage of significantly reducing scanning time by enabling the one shot approach. For the second contribution, a new approach to design extremely high scanning rate beam steering antennas is proposed. The feeding structure for the frequency-steering antenna based on coupled resonators has been demonstrated. Two examples with 50 MHz and 100 MHz bandwidths are designed to illustrate the proposed technique. Experimental validation was also provided for the 50 MHz bandwidth example, which significantly enhance the scanning rate without sacrificing radiation efficiency. For the third contribution, conventional coupling matrix theory is introduced into the sensing application. Modifications to the coupling theory and its subsequent integration with formulations for sensing and imaging provide new approaches to the design of sensing arrays.</p
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
Enhancing microwave imaging by exploiting diversity
No full textMicrowaves can penetrate optically opaque materials without harmful ionizing effects, and thus provide distinct advantages over x-ray imaging in various fields, including security-screening, remote sensing, medical imaging, through-wall imaging, civil and industrial applications. However, conventional microwave imaging methods, such as synthetic aperture radar (SAR) or phased array methods, generally rely on mechanical or electrical scanning to collect the spatial data and the resulting imaging speed and complexity remain challenges for constructing microwave imaging systems. In this thesis, I investigate the use of diversity techniques to develop high-speed, low-profile and low-cost microwave imaging systems. Firstly, I propose a single-shot frequency-diverse near-field imaging system by exploiting a frequency diversity technique based on high-scanning-rate leaky-wave antennas (LWAs). Frequency diversity is an all-electronic technique and can achieve data collection by sweeping frequency without mechanical moving parts or active switching circuit component. In addition, the potential performance of the LWA design is analyzed by introducing a figure of merit based on sensing capacity. It is revealed that a transceiver LWA with a high scanning rate is very effective for providing independent measurement modes. Analytical, simulation and experimental results are provided to characterize and demonstrate the proposed system and show that it can provide image reconstruction across narrow bandwidths. Building on frequency diversity techniques, I investigate the use of high scanning-rate leaky-wave antennas in a multiple-input multiple-output (MIMO) configuration to achieve both frequency and spatial diversity in an imaging system. Compared with frequency-diversity only and spatial-diversity only imaging systems, the proposed system can provide enhanced imaging performance by leveraging both spatial and frequency diversity simultaneously. In addition, an extended Rytov approximation (xRA), recently shown to provide accurate reconstructions for high permittivity and electrically large sized low-loss objects, is also included in this approach. Numerical and experimental examples demonstrate that the proposed system with xRA can accurately estimate the contrast function amplitude and the positions of dielectric scatterers in an imaging region. Apart from frequency and spatial diversity techniques, I investigate the use of pattern diversity for reducing the number of required measurement nodes in utilizing xRA for radio frequency (RF) imaging. For indoor RF imaging using radio tomographic imaging (RTI), 20-40 WiFi nodes are usually utilized around the imaging region. This implies that a conventional WiFi network must be supplemented with additional WiFi nodes specifically dedicated to the imaging application. The proposed approach is to exploit antenna pattern diversity so that each node can collect multiple independent measurements from the same measurement location, thereby decreasing the number of measurement nodes required. Simulation results are provided to verify the RF imaging approach with reduced measurement nodes, which demonstrates the potential of using pattern diversity. In all the research contributions described, analyses, simulations and/or experimental results are utilized to demonstrate the effectiveness of my new and novel approaches to microwave imaging.</p
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