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Electron heating and electron-phonon scattering in AlGaAs/GaAs two-dimensional electron system
No full text在這篇論文裡，我們研究了在0.3 K ~ 4 K溫度範圍內，砷化鋁鎵/砷化鎵二維電子系統其電子-聲子散射對於溫度改變的反應，而我們主要是量測電子-聲子散射機率τep-1 Te p的p值。在樣品LM 4646的量測中，由於其量子井中做了delta摻雜，使得我們能夠以隨溫度改變之縱向電阻 Rxx(T) 當作溫度計來求得特定電流所對應到的電子溫度。實驗結果顯示，在零磁場時p = 2.3 2、在負磁阻的範圍內p = 1.6~1.8 2，以及在SdH震盪範圍內p = 0.9~1.0 1。而由p 2變化至p 1似乎是以絕緣態-量子霍爾相變的交叉點為分界。在另一塊樣品LM 4640的量測中，其量子井並無做delta摻雜，因此我們是以隨溫度改變之SdH震盪的振幅來當作溫度計，並發現p = 0.7~1.0 1在此SdH範圍內。而與文獻上理論計算和實驗結果的比較下，我們可以解釋在樣品LM 4646中，在零磁場以及負磁阻的範圍內，系統中動態屏蔽的聲頻壓電散射為主要的電子-聲子散射機制因此導致了p 2的行為。而在樣品LM 4640中，在SdH範圍裡量測到p 1，也表示無屏蔽的聲頻壓電散射在此系統中為主要的電子-聲子散射機制。至於在樣品LM 4646中，由p 2(零磁場以及負磁阻範圍)至p 1(SdH範圍)的變化在過去並沒有被觀察到，其變化的行為似乎也可能與絕緣態-量子霍爾相變有某些相關。而我們也需要進一步的實驗來研究其背後可能的機制。In this thesis, we studied the temperature behavior of electron-phonon scattering in the temperature range of 0.3 K T 4 K, in AlGaAs/GaAs two-dimensional electron systems. We focused on determining the temperature exponent p of electron-phonon scattering rate τep-1 Te p. In sample LM 4646 which has delta doping in the quantum well, we used the temperature dependence of longitudinal resistance Rxx(T) as thermometer to find the corresponding electron temperature Te. The experimental results showed that p = 2.3 2 at B=0 T and p = 1.6~1.8 2 in the negative magnetoresistance (NMR) regime, and p = 0.9~1.0 1 in the SdH regime. The “critical point” of this transition from p 2 to p 1 is very close to the crossover of insulator to Quantum Hall transition. On the other hand, in sample LM 4640 which is a typical modulation-doped heterostructure, p = 0.7~1.0 1 was found in the SdH regime by using the temperature-dependent amplitude of SdH oscillations as a thermometer. Comparing with theoretical calculations and experimental results in literatures, we can explain the value of p 2 in sample LM 4646, at B=0 T and in the NMR regime, that dynamically screened piezoelectric scattering dominates. And p 1 in sample LM 4640, in the SdH regime, implies that the unscreened piezoelectric scattering is relatively important. But the transition from p 2 (small magnetic field regime) to p 1 (SdH regime) in sample LM 4646 has not been observed in the past, which is probably associated with the I-QH transition, and further works are needed to explore the underlying mechanisms.Chapter 1ntroduction to electron transport in semiconductors 1.1 Introduction..............................................................................................................1.2 The Drude model......................................................................................................1.3 Electrons in periodic potentials－Band structures...................................................3.4 Effective mass..........................................................................................................6.5 Densities of states.....................................................................................................7.6 Scattering process.....................................................................................................9.6.2 Electron-impurity scattering..........................................................................10 1.6.2 Electron-phonon scattering............................................................................12eferences....................................................................................................................15hapter 2ransport in a two-dimensional electron system 16.1 Semiconductors heterostructures............................................................................16.2 Classical Hall effect................................................................................................17.3 Two-dimensional electron transport under perpendicular magnetic field－Landau levels......................................................................................................................20.4 Shubnikov-de Haas Oscillations............................................................................23.5 Quantum Hall effect...............................................................................................25.6 Weak localization...................................................................................................29eferences....................................................................................................................31hapter 3lectron heating and electron-phonon scattering at zero magnetic field 32.1 Introduction............................................................................................................32.2 The two bath model................................................................................................33.3 Experimental setup.................................................................................................36.4 Experimental results I：Sample LM 4646.............................................................37.5 Experimental results II：Sample LM 4640............................................................41.6 Discussions.............................................................................................................42.7 Conclusions............................................................................................................49eferences....................................................................................................................50hapter 4lectron heating and electron-phonon scattering in a perpendicular magnetic field 51.1 Introduction............................................................................................................51.2 Current scaling.......................................................................................................52.3 Experimental setup.................................................................................................56.4 Experimental results I：Sample LM 4646.............................................................56.5 Experimental results II：Sample LM 4640............................................................61.6 Discussions.............................................................................................................65.7 Conclusions............................................................................................................71eferences....................................................................................................................72hapter 5onclusion 73onclusion....................................................................................................................7
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
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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