1,721,012 research outputs found
Techniques for the synchronisation and demodulation of fast frequency hopped M-ary frequency shift keying
No full textIn this thesis we consider the synchronisation and demodulation of fast frequency hopped M-ary FSK with convolutional coding in the presence of jamming, multiple access noise, frequency uncertainty and random frequency variations. We consider three modulation formats, 4-FSK, 8-FSK and 16-FSK and describe a family of 1/2 rate constraint length 7 symbol-based convolutional codes. We investigate the performance of the proposed systems with 2nd order diversity, in addition to the 1/2 rate encoding, and highlight the worst-case partial-band tone jammer waveform for such schemes. Consideration is given to a receiver based upon the offset FFT, where these transforms are then processed in order to achieve maximum a posteriori carier frequency synchronisation, demodulation and decoding of the received signal. Two hop-by-hop AGC techniques are described, the SNORM and the DMAX techniques; the former normalises the OFFT amplitudes with reference to the total power within the OFFT whilst the latter performs the normalisation based upon the maximum amplitude slot present within the OFFT. The worst-case partial-band tone jammer is generalised for the OFFT receiver when transform sizes exceed the modulation set size. A Viterbi frequency synchroniser is presented. This technique combines frequency synchronisation with the soft decision decoding of the convolutional code. By considering both the mean and the standard deviation of the signal slot amplitudes across the four OFFT slots which comprise each branch metric of the Viterbi decoding process, a novel modified metric is derived. This metric alters the worst-case partial-band jammer from a single tone to a more broad-band dammer waveform. An improvement in the worst-case partial-band tone jamming BER performance is experienced with all modulation formats for large OFFTs and for OFFTs of all sizes for modulation formats where M ≥ 8. The AWGN GER performance is degraded by 0.5-0.7 dB. The Viterbi frequency synchroniser is shown to degrade the BER peformance for 8-FSK by approximately 0.75 dB when compared to perfect carrier frequency synchronisation. The metric is also shown to increase the number of simultaneous users in an FFH 8-FSK multiple access environment, especially when the power control of the different accesses in the system is poor. Implementation of the synchroniser and metric calculation are investigated and the performance of 8-FSK with 4-bit quantisation of the soft decision information is shown to degrade the BER performance by 0.25 dB. Coarse code and carrier frequency synchronisation methods for spread spectrum communications in general are reviewed. The requirement for additional intermediate frequency tones in order to achieve frequency synchronisation is shown to be unnecessary when MFSK detection uses the OFFT. Two techniques for the synchronisation of fast frequency hopped MFSK are described and analysed in AWGN. These are the bandwidth identifcation algorithm and the tone folding detector. These are compared with a Viterbi based detector which exploits the structure which is inherent within the convolutionally encoded data sequence. The superiority of the Viterbi detector is shown and the technique is modified to utilise the modified metric calculation which was developed for demodulation. A jammer classifier is described, based upon mean output of the DMAX AGC in order to allow thresholding to be achieved in the presence of different jammer types.</p
Stress Corrosion Cracking and Crack Tip Characterization of Alloy X-750 in Light Water Reactor Environments
No full textStress corrosion cracking (SCC) susceptibility of Inconel Alloy X-750 in the HTH condition has been evaluated in high purity water at 93 and 288°C under Boiling Water Reactor Normal Water Chemistry (NWC) and Hydrogen Water Chemistry (HWC) conditions. SCC crack growth rates of approximately 1.1x10-7 mm/s (K=28 MPa√m) under NWC conditions and 1.4x10-8 mm/s (K=28 MPa√m) under HWC in high purity water at 288°C were observed. The environmental conditions were changed from NWC to HWC during constant K loading, and the crack growth rate immediately slowed down by approximately one order of magnitude. The alloy was also tested in HWC at 93°C.
No SCC crack growth was observed at K= 35 MPa√m for the length of time tested at 93°C. The fracture mode transitioned from predominantly transgranular cracking under fatigue conditions to a mixture of intergranular, pseudo-intergranular, and a small amount of transgranular fracture in constant stress intensity SCC. Pseudo-intergranular cracking is when a crack propagates directly adjacent to the grain boundary carbides and not actually on the grain boundary.
The SCC crack tips were characterized with scanning electron microscopy (SEM) and 3D Atom
Probe Tomography (APT). The SEM analysis was focused on the fractographic analysis and crackpropagation mode. The crack was observed to propagate adjacent to grain boundary carbides (pseudo-intergranular) and along a boundary with high coherency where no carbides were present (intergranular). The small and localized areas of transgranular cracking were occasionally seen between two regions of intergranular cracking.
The APT reconstructions of the crack tips and crack wall identified several key features contributing to the SCC process: 1) Preferential oxygen transport occurs in either a finger-like or crystallographic morphology extending from the crack tip region. These regions are enriched in both oxygen and oxide with the oxide being a chromium-nickel spinel. 2) The matrix ahead of each finger-like “tunnel” is enriched in oxygen and predominantly chromium oxide. This indicates that oxygen is diffusing ahead of the crack tip into the bulk material. 3) The oxygen that penetrates directly into the base material from the crack walls in an ordered manner suggests that it is controlled by crystallographic features. 4) The main SCC crack tip is full of predominantly oxide phase and, to a lesser extent, metal atoms. The very crack tip forms a spinel of chromium and nickel oxides. Iron oxide begins to contribute to the oxide spinel approximately 25-30 nm from the actual tip. 5) The γ’ precipitates that are directly adjacent to each crack tip and crack wall were deficient in aluminum content. The aluminum content in the bulk γ ’ was approximately 6.6 at % and the near-crack γ ’ aluminum content ranged from 2.5-3.5 at %. The range of affected γ ’ was approximately 100 nm wide
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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