Effect of lateral displacement of a high-altitude platform on cellular interference and handover

A method for predicting movements in cellular coverage caused by lateral drift of a high-altitude platform (a quasi-stationary platform in the stratosphere) is developed. Cells are produced by spot beams generated by horn-type antennas on the platform. It is shown how the carrier-to-interference ratio (CIR) across these cells varies when the antenna payload is steered to accommodate the lateral movement of the platform. The geometry of the antenna beam footprint on the ground is first developed and then applied to a system of many cochannel beams. Pointing strategies are examined, where the pointing angle is calculated to keep, for example, a center cell or an edge cell in the same nominal position before and after the platform drift, and the CIR distribution is calculated. It is shown that the optimum pointing angle depends on the desired level of CIR across the service area, typically lying between 3 +/- 0.75 degrees for a platform drift of 2'km and corresponding to a cell in the middle ring. It is shown that it is necessary for a significant proportion of users to perform a handover to maintain a given CIR after platform drift. The analysis reveals that there is an optimum pointing angle that minimizes the probability of handover for a particular value of drift and CIR

Main Concepts for Two Picture Description Tasks: An Addition to Richardson and Dalton, 2016

Background: Proposition analysis of the discourse of persons with aphasia (PWAs) has a long history, yielding important advancements in our understanding of communication impairments in this population. Recently, discourse measures have been considered primary outcome measures, and multiple calls have been made for improved psychometric properties of discourse measures. Aims: To advance the use of discourse analysis in PWAs by providing Main Concept Analysis checklists and descriptive statistics for healthy control performance on the analysis for the Cat in the Tree and Refused Umbrella narrative tasks utilized in the AphasiaBank database protocol. Methods & Procedures: Ninety-two control transcripts, stratified into four age groups (20–39 years; 40–59; 60–79; 80+), were downloaded from the AphasiaBank database. Relevant concepts were identified, and those spoken by at least one-third of the control sample were considered to be a main concept (MC). A multilevel coding system was used to determine the accuracy and completeness of the MCs produced by control speakers. Outcomes & Results: MC checklists for two discourse tasks are provided. Descriptive statistics are reported and examined to assist readers with evaluation of the normative data. Conclusions: These checklists provide clinicians and researchers with a tool to reliably assess the discourse of PWAs. They also help address the gap in available psychometric data with which to compare PWAs to healthy controls

A Large-Scale Comparison of Main Concept Production Between Persons with Aphasia and Persons Without Brain Injury

Purpose: The purposes of this study are to provide clinicians and researchers with introductory psychometric data for the main concept analysis (MCA), a measure of discourse informativeness, and specifically, to provide descriptive and comparative statistical information about the performance of a large sample of persons not brain injured (PNBIs) and persons with aphasia (PWAs) on AphasiaBank discourse tasks. Method: Transcripts of 5 semi-spontaneous discourse tasks were retrieved from the AphasiaBank database and scored according to detailed checklists and scoring procedures. Transcripts from 145 PNBIs and 238 PWAs were scored; descriptive statistics, median tests, and effect sizes are reported. Results: PWAs demonstrated overall lower informativeness scores and more frequent production of statements that were inaccurate and/or incomplete. Differences between PNBIs and PWAs were observed for all main concept measures and stories. Comparisons of PNBIs and aphasia subtypes revealed significant differences for all groups, although the pattern of differences and strength of effect sizes varied by group and discourse task. Conclusions: These results may improve the investigative and clinical utility of the MCA by providing descriptive and comparative information for PNBIs and PWAs for standardized discourse tasks that can be reliably scored. The results indicate that the MCA is sensitive to differences in discourse as a result of aphasia

Polystyrene Nanocomposites based on Carbazole-Containing Surfactants

New organically-modified clays containing a carbazole unit were prepared and the number of long alkyl chains on the surfactant was varied. The clay was used to prepare polystyrene nanocomposites by both bulk polymerization and melt blending. The dispersion of these clays in the polymer matrix was evaluated using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The thermal stability of the clays and the nanocomposites were analyzed by thermogravimetric analysis (TGA) while the fire properties were evaluated by cone calorimetry. If more than two alkyl chains were present, the gallery spacing is apparently overcrowded, leading to poor dispersion. Bulk polymerization gave nanocomposites with better dispersion and reduced flammability when compared to the melt blending process

Moving Toward Non-transcription Based Discourse Analysis in Stable and Progressive Aphasia

Measurement of communication ability at the discourse level holds promise for predicting how well persons with stable (e.g., stroke-induced), or progressive aphasia navigate everyday communicative interactions. However, barriers to the clinical utilization of discourse measures have persisted. Recent advancements in the standardization of elicitation protocols and the existence of large databases for development of normative references have begun to address some of these barriers. Still, time remains a consistently reported barrier by clinicians. Non-transcription based discourse measurement would reduce the time required for discourse analysis, making clinical utilization a reality. The purpose of this article is to present evidence regarding discourse measures (main concept analysis, core lexicon, and derived efficiency scores) that are well suited to non-transcription based analysis. Combined with previous research, our results suggest that these measures are sensitive to changes following stroke or neurodegenerative disease. Given the evidence, further research specifically assessing the reliability of these measures in clinical implementation is warranted

Synergy Between Nanocomposite Formation and Low Levels of Bromine on Fire Retardancy in Polystyrenes

An organically-modified clay has been prepared using ammonium salts which contain an oligomeric material consisting of vinylbenzyl chloride, styrene and dibromostyrene. The presence of dibromostyrene enhances the flame retardancy of polystyrene nanocomposites compared to both the virgin polymer and polystyrene nanocomposites prepared from non-halogen-containing organically-modified clays. The nanocomposites were prepared both by bulk polymerization and melt blending and they were evaluated by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis and cone calorimetry measurements. Bulk polymerization produced nanocomposites with reduced peak heat release rate, reduced total heat release and improved thermal stability. It is noteworthy that all these improvements were obtained with clay loading as low as 3% and bromine content less than 4%

Improving the system capacity of broadband services using multiple high-altitude platforms

A method of significantly improving the capacity of high-altitude platform (HAP) communications networks operating in the millimeter-wave bands is presented. It is shown how constellations of HAPs can share a common frequency allocation by exploiting the directionality of the user antenna. The system capacity of such constellations is critically affected by the minimum angular separation of the HAPs and the sidelobe level of the user antenna. For typical antenna beamwidths of approximately 5/spl deg/ an inter-HAP spacing of 4 km is sufficient to deliver optimum performance. The aggregate bandwidth efficiency is evaluated, both theoretically using the Shannon equation, and using practical modulation and coding schemes, for multiple HAP configurations delivering either single or multiple cells. For the user antenna beamwidths used, it is shown that capacity increases are commensurate with the increase in the number of platforms, up to 10 HAPs. For increases beyond this the choice of constellation strategy becomes increasingly important