1,720,968 research outputs found
Optical Binding Forces on Gold or Silver Nanoparticles
No full text以線性極化平面電磁波或Gaussian光束，照射金、銀奈米二聚體(dimer)，產生表面電漿子共振(surface plasmon resonance；SPR)，並出現控制著兩粒子穩定距離的光束縛力(optical binding force)。在幾種波長下，由多重中心展開法(multiple-multipole expansions method)計算電磁場，並透過Maxwell應力張量得知粒子所受光力，與二聚體間距改變的關係。結果顯示，在各波長下，粒子會出現幾個穩定平衡距離，並束縛住彼此，而這距離皆為略小於在介質中波長的整數倍。在這些特定的距離下，當兩粒子靠近或遠離時，二聚體間的光力會如同彈簧般，產生斥力或吸力，且當二聚體相距一倍波長時，這虛擬彈簧中的恢復力與彈簧常數往往是最大的，表示這是最穩定的狀態，此外，兩粒子球心連線(中心線)總是傾向於垂直電場極化的方向。至於由不相同的兩粒子所組成的異型二聚體，其穩定平衡距離仍然存在，但會出現光泳力，驅使整個二聚體系統作剛體運動。另一方面，以Gaussian光束為光源時，會產生朝向中心的梯度力，對平衡位置產生影響，甚至破壞。而三顆粒子所組成的三聚體，同樣以接近介質中波長的距離，保持平衡，並仍有光泳力的產生。 除此之外，任意角度平面波，照射金奈米桿的平均吸收與散射效應，及金奈米桿的去極化效率(depolarization ratio)，也在本文作討論。結果指出，金奈米桿的長軸表面電漿子共振(longitudinal SPR；LSPR)，會隨著桿的細長比(aspect ratio；AR)增加而紅位移。至於金奈米桿的去極化效率，與LSPR並無太大關係，但會隨著AR值加大而增加，且紅位移。This study theoretically investigates that plasmon-mediated optical forces, exerted on metal dimers, consisting of two gold or silver nanoparticles (NPs), induced by the normal illumination of a linearly polarized plane wave or Gaussian beam. Using the multiple multipole method, we analyzed the optical force in terms of Maxwell’s stress tensor versus the inter-particles distance for some specific wavelengths. Numerical results show that for a given wavelength there are several stable equilibrium distances between NPs, which is slightly shorter than some integer multiples of the wavelength in medium, for metal dimer acting as bonded together. At these specific distances, the optical force between dimer will become a repulsive or an attractive force when the two NPs are close to or away from each other. The spring constant of the restoring force at the first stable equilibrium is always the maximum, indicating that the first stable equilibrium distance is the most stable one. Moreover, the central line of a dimer tends to be perpendicular to the polarization of light. For a heterodimer, which consists of two NPs of different sizes or different materials, the phenomenon of stable equilibrium distance still exists but with a net driving photophoretic force to move the heterodimer. In addition, a Gaussian beam provides a gradient force reducing the stability of these equilibriums. For a trimer, consisting of three gold NPs, there still exists stable distance between NPs and also a photophoretic force. Moreover, the average scattering and absorption efficiencies as well as depolarization ratio of a randomly oriented gold nanorod are also studied. Our results indicate that the depolarization spectrum is broader than those of scattering and absorption efficiencies. The maximum depolarization ratio can be raised and the corresponding wavelength (not at the longitudinal SPR) is red-shifted by increasing the aspect ratio
An Investigation on predictors of REITs Returns in America
No full text本研究主要探討美國不動產投資信託(REITs)報酬率的預測因子，利用兩種檢定模型：簡單線性迴歸模型與複回歸歸模型檢視每個預測因子的解釋能力，推導出美國REITs報酬率的資產定價模型。本研究共選取五個預測因子，分別為：公司規模、週轉率、帳面價值與市場價值比(B/M)、益本比(E/P)、股利與股價比(D/P)。同時，根據Fama and French(1993)的三因子模型，探討市場風險溢酬(Rm-Rf)因子、規模溢酬因子(SMB)以及淨值市值比溢酬(HML)因子對於REITs報酬的解釋能力。由於美國REITs市場在1990年之後，產生結構上的變化，因此，本文將探討1990年之前以及1990年之後兩個時期，REITs報酬率之預測因子的解釋能力，經由實證分析發現，在1990年之前，只有公司規模因子具有預測力，能夠解釋REITs報酬的變異，而在1990年之後，五個預測因子皆能夠解釋REITs報酬的變異；另外，在三因子模型表現方面，在1990年之前，市場溢酬因子以及HML無法解釋REITs報酬的變異；相反的，在1990年之後，市場溢酬因子與高淨值市值比的投資組合則會有較佳的解釋能力。
最後，本文進行穩健性檢定（robustness test），判斷其是否能夠與複迴歸檢定模型產出一致的結果。實證發現，在穩健性檢定之下，也能夠得到較一致的結論，即兩種不同的檢定統計方法可以產出具有一致的結果。In this study, we mainly discuss the predictors of the rate of return of American real estate investment trust (REITs). We totally choose five factors as the predictor and use two kinds of models: The simple linear regression model and the multiple linear regression models to examine the explanation ability of each predictor. The five factors are company size, turnover ratio, book to market ratio (BM), earnings to price ratio (EP), and dividend to price ratio (DP). At the same time, according to three factor model of Fama and French (1993), we examine the relation among excess return of REITs and three factors: market risk premium factor (Rm-Rf) , size premium factor (SMB) and book to market ratio premium factor (HML). Because there was a structure change in the REITs market that occurred after 1990, we will discuss the explanation ability of predictors of the two different sub-periods: pre-1990 and post-1990. The determinations of the expected return of REITs differ in the sub-periods. In the pre-1990 sub-period, only size factor predict expected REITs returns. In the post-1990 sub-period, size factor, turnover ratio, BM ratio, EP ratio, and DP ratio predict expected REITs returns. In the three factor model analysis, the market risk premium, and book to market ratio premium (HML) could predict the excess REITs returns in the post-1990 sub-period. The most important concept is that we find that the explanation ability of the predictors is very different in the two sub-periods. More specially, the explanation ability of predictors in the post-1990 is better than in the pre-1990.第一節 緒論………………………………………………1
第二節 文獻回顧…………………………………………3
第三節 方法論……………………………………………5
3-1.節 資料來源與變數衡量 …………………………………5
3-2.節 檢定模型 ………………………………………………6
第四節 實證結果…………………………………………9
4-1節 預測變數之基本統計量 ………………………………9
4-2節 橫斷面迴歸模型之實證結果 …………………………13
4-3節 時間序列之三因子模型實證結果 ……………………17
4-4節 穩健性檢定(robustness test)之分析結果 ………20
第五節 結論 ……………………………………………22
參考文獻 …………………………………………………2
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
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
- …
