1,720,963 research outputs found
Analysis of Weak and Complex Impact-Echo Signal
No full text本研究主旨在於利用一個有效的訊號處理方法，以檢測隱藏於敲擊回音訊號中的微弱訊號，或複雜的幾何情況造成回傳的應力波互相干擾，以期提升敲擊回音法的極限，有效提升工程品質。
黃鍔院士所提出的訊號處理方法是利用經驗模態分解法將原訊號內的各本質模態函數析出，林佳慶[14]率先利用此法將敲擊回音訊號進行經驗模態分解，再對本質模態函數進行快速傅立葉轉換，結果顯示，此法能得到更清楚且具物理意義的頻譜。
本研究先以有限元素軟體模擬四種狀況的孔洞，分別為1. 孔洞直徑4cm，8cm，12cm，保護層深度皆為6cm。2. 孔洞直徑6cm，保護層深度分別為12cm、18cm、24cm。3. 兩孔洞間距小。4. 孔洞上方有鋼筋干擾。最後進行模型試驗。經由數值算例和模型試驗分析比較，此法確實有效的提取出隱藏於敲擊回音內微弱及複雜的訊號，或是互相干擾的應力波。而且由回音訊號的傅立葉頻譜發現，孔洞的回音訊號大都具有數個大小相似的尖峰群。
配合短時傅利葉轉換，可觀察各本質模態函數的時頻分布，即可判斷出各本質模態函數所代表的物理意義。其中表面波能量消散最快；內部缺陷回音訊號能量消散次之；模態振動能量最大，消散最慢
Deformation and Stability of an Elastica Constrained by Curved Surfaces
No full text本文中我們考慮在底部平面兩端夾持(clamped-clamped)的彈性樑(elastica)在受到頂部牆面側向壓縮後的變形及穩定性。我們考慮三種頂部牆面:分別為凹面(concave)、凸面(convex)及平面(plane)。首先建立受壓縮彈性樑的變形軌跡圖，接著由振動法決定各式變形的穩定性。當頂部牆面以半靜態方式(quasi-statically)壓縮時，我們架設實驗驗證理論上預測的變形演變。當頂部牆面為平面時，free fold(與牆面發生點接觸前的變形)恰接觸到牆面時，壓縮外力會減少到零。當頂部牆面不再是平面時，此現象就不見得存在。當頂部牆面不再是平面，線接觸變形的多樣性會受到破壞。當頂部牆面為凹面時，頂面不會發生二次挫曲，反而是底部平面兩端的線接觸持續變長。當頂部牆面為凸面不會發生頂部線接觸。In this paper we consider the deformation and stability of a clamped-clamped elastica resting on a bottom plane and pressed by a top wall laterally. Three types of top walls are considered; they are concave, convex, and plane surfaces. Deformation maps of the pressed elastica are first constructed. The stability of various deformation patterns is determined via a vibration method. The theoretical predictions on the deformation evolution when the top wall presses quasi-statically are verified experimentally. In the case of plane top wall, the external pressing force reduces to zero whenever the free fold of a previous deformation starts to touch the wall. In the case when the top wall is not a plane, this is in general no longer true. The multiplicity of line-contact deformations in the case of plane top wall is destroyed when the top wall is curved. No secondary buckling will occur when the top wall is concave. Instead, line contact on the sides of the bottom plane will develop. In the case when the top wall is convex, no line contact on the top wall is possible
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
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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