1,720,961 research outputs found
An Efficient Plane-Waves Superposition Method for Improved Spatial Correlation in Simulated Reverberation Chambers
Get PDFAccurate Rayleigh propagation environments within an ideal reverberation chamber (RC) are synthesized computationally using a superposition of plane-waves (PWs). Randomness in the electro-magnetic (EM) field distribution is achieved by synthesizing many field realizations featuring slant-polarized PWs with randomly defined transverse field components. These PWs propagate along a large number of predefined and uniformly distributed directions determined only once via an efficient spiraling sampling scheme over the unit sphere. Comparisons with theoretical Rayleigh field statistics indicate that the proposed method yields random EM field distributions that in several cases follow more closely the field spatial correlation properties, for comparable numerical burden, than other available numerical techniques. Finally, a formula relating the number of PWs to the size of a desired RC analysis volume was provided
Computational RF Dosimetry of Rodents Cohorts in a Realistic Reverberation Chambers at 900 MHz
No full textReverberation chambers (RCs) have been widely employed in bioelectromagnetic large-scale rodent bioassays, to investigate potential effects of lifetime RF exposures. Numerical RF dosimetry has been of the utmost importance in determining the range of exposures, in terms of whole-body and organ specific absorption rate (SAR), and its uniformity across large animal cohorts, and therefore may influence key decisions in the design of in-vivo animal studies (exposure levels, number of animals per room, etc.). In this work, we expand prior research on rodents' numerical dosimetry in RCs based on a realistic RC configuration, comprising a mode stirrer and various types of antennas. The exposure prediction modeling involves a MonteCarlo (MC) approach recently developed by the authors, taking into account the animals size distribution, as well as their posture, position and orientation within individual cages. The feasibility of conducting whole-RC dosimetry within a multivariate MC framework for large rodent cohorts at 900 MHz was demonstrated, showing larger whole-body SAR (wbSAR) variability than previously estimated, and suggesting that exposures in some of the cages may be consistently higher or lower than a cohort mean wbSAR target
Computational RF Dosimetry of Rodents Cohorts in a Realistic Reverberation Chambers at 900 MHz
No full textMonte-Carlo Based Numerical Dosimetry in Reverberation Chamber Exposure Systems Employed for in-Vivo Rodent Bioassays
Get PDFA Monte-Carlo based computational approach for the statistical characterization of the whole-body specific absorption rate (wbSAR) variability in large cohorts of rodents exposed to radio-frequency (RF) energy in reverberation chambers (RCs) is applied to adult male rat exposures illustrative of those in a US National Toxicology Program (NTP) cancer bioassay. A large number of 3D electromagnetic field realizations fulfilling Rayleigh fading properties were generated within an electrically-large volume representative of an ideal RC, yielding granular wbSAR distributions for an ensemble of 96 homogeneous rodent models with random mass distribution, postures, positions and orientations. Two case studies were addressed: a “momentary exposure” with each rat fixed in posture, position and orientation, and a “day-long exposure” in which the position, orientation and posture were varied randomly for each subsequent Rayleigh field realization. Over 500 and 2500 field realizations or “snapshots”, respectively, the rats’ instantaneous wbSARs, as well as their individual time-averaged wbSARs, were found to be well fit by lognormal distributions. The large variability in instantaneous wbSARs in the cohort was due in part to the inherent Rayleigh field variability in RCs (70-80%) and in part to weight, posture and position variations (20-30%), while the effect of cage location was found to be small over day-long exposures. Averaging the exposure over field realizations substantially reduces the range of wbSARs in the cohort. Hence, when RF-induced thermal effects are studied, the relevant exposure metric (wbSAR averaged over appropriate times) features a narrower range than instantaneous wbSAR, which is the relevant metric in studies dealing with non-thermal effects. Compared to previous studies, the present approach was found to be computationally more efficient enabling thus a Monte-Carlo analysis by varying concurrently the incident field and the animals posture, position, and orientation. In practice, it can inform the choice of wbSAR targets in rodent bioassay, allowing to identify possible dose-effect trends while avoiding undue thermal stress
On the Correlation Between Incident Power Density and Temperature Increase for Exposures at Frequencies Above 6 GHz
Get PDFInternational guidelines/standards for human exposure to electromagnetic fields have recently been revised to update the dosimetric reference limits (DRLs or basic restrictions) and exposure reference levels (ERLs), specifically for frequencies above 6 GHz. At such frequencies, the ERL is defined in terms of incident power density (IPD) and used as a practical quantity to assess compliance with DRLs (absorbed or epithelial power density) and therefore appropriately limits temperature elevation at the body surface. In the exposure standards, IPD is spatially averaged over an area of 4 cm(2) below 30 GHz and 1 cm(2) above 30 GHz, however the definition of IPD is given in a theoretical manner. With the progress in the development of product safety compliance assessment standards, one concern has been how to define the IPD considering practical measurement procedures. Two definitions or averaging methods were considered: using IPD vectors normal to the averaging surface and using magnitude (norm) of IPD vectors. As the exposure guidelines are intended to prevent excessive tissue heating, statistical analysis was therefore undertaken to investigate which IPD metric better correlates with the temperature increase. To this end, a large data set for several exposure scenarios was collected by different research institutions. The analysis of the obtained results is presented and shows that both definitions have high correlation with temperature rise, with slightly better correlation (0.9 vs. 0.8) for the definition using the magnitude of IPD vectors
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
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