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Predicting Construction Contractor Default with Option-Based Credit Models—Models' Performance and Comparison with Financial Ratio Models
No full textNew Donor-Acceptor Random Copolymers with Side-Chains of para-Substituted Dicyano-triphenylamine and Oxadiazole Derivatives : Synthesis, Properties, and Memory Device Applications
No full text近幾年來，高分子材料應用在記憶體元件上引起了廣泛的研究及討論，因為高分子可以透過設計不同的分子結構來改變其光電性質也易於加工，適合應用在元件上。而在高分子種類上，有幾種較具有代表性的種類，像是共軛高分子、非共軛高分子含有聚亞醯胺或是特殊的電子施體或受體基團，另外也有把高分子及奈米金屬顆粒或是有機小分子混掺的材料，這些不同種類的材料目前都有在記憶體元件應用上被深入的研究中。然而，關於不同的高分子結構所造成的影響尚未被深入研究，而在此論文的目標主要是要探討非共軛的亂排高分子使用不同的電子施體及受體對於其光電及熱性質和記憶體元件效應的影響。 在第二章，我們使用了三種噁唑衍生物(2-phenyl-5-(4-vinylphenyl)-1,3,4-oxadiazole (A1), 2-(4-vinylbiphenyl)-5-(4-phenyl) -1,3,4-oxadiazole (A2), and 2-(4-vinylbiphenyl)-5-(4-ethoxyphenyl)-1,3,4-oxadiazole (A3))當作電子受體，另外使用了對位取代氰基的三苯胺當作電子施體來合成高分子並且將兩者利用活性聚合法聚合成側鏈亂排共聚高分子和單聚高分子，並且利用氫譜及元素分析儀鑑定其確切其結構及施體-受體比例(8:2、5:5、2:8)。三苯胺在對位取代氰基之後，化學性質會較穩定而不易產生雙聚體化。從化學結構上來說，A2的共振長度較A1長，A3則因為多引入了一個推電子的乙氧基而增加了電子密度。在吸收光譜上，這些共聚高分子在薄膜態皆有兩根吸收鋒(353奈米、308 ~ 322奈米)分別對應於相關的單聚高分子(PD: 355奈米、PA1: 308奈米、PA2: 330奈米、PA3: 332奈米)，其吸收度則隨著不同的比例變化，另外由光學吸收極限計算可得此系列高分子之能隙在3.11 ~ 3.20電子伏特且會隨著受體含量變多而些微增大。由循環伏安法得到的結果發現這些亂排共聚高分子的HOMO及LUMO能階會與相對應的施體(-5.63電子伏特)或是受體(-2.63 ~ 2.81電子伏特)單聚高分子相同，這是由於這些高分子皆是在側鏈上有各自分離的電子施體和受體，彼此不參與軌域混成。從以上的結果可看出透過不同的化學結構及電子施體-受體的比例可以將高分子調整出不同的光電性質。 在第三章，三個系列的所有高分子都應用在元件製作及測量上，並且使用了二甲基甲醯胺和氯苯兩種溶劑來研究這些高分子所造成的記憶體效應。記憶體元件的構造是將高分子薄膜夾在兩層電極之間的三明治結構，其上層電極是鋁，而下層電極是氧化銦錫。這些元件皆表現出快閃記憶體的性質，且有著低於1伏特的起始電壓，在11000秒的維持時間測試中也有著不錯的穩定性。所有元件皆受到了燈絲理論及空間電荷極限理論的影響，在二甲基甲醯胺的系統中，我們發現到低導電態的電流在經過幾個讀寫迴圈後有變大的情形(10-5 ~ 10-2安培)，當電子受體的含量變多(施體-受體比例為5:5和2:8)或是受體的單聚高分子，此現象更加明顯，這是由於會與鋁金屬鍵結的氮原子含量變多的關係，造成燈絲效應更強烈。另外在結構方面，由於在A3上有一個推電子的乙氧基，使得在噁唑分子上的氮原子有更強的鍵結金屬的能力，使得元件更不容易被關閉，此時則需要更大的反向電壓(-3→-5伏特)才能使元件回到原始的狀態。此外，利用氯苯所製備的高分子膜會較二甲基醯胺平整，而低導電態電流上升的情形在平整的膜上就沒有再顯現出來。本研究探討了高分子之化學結構及溶劑對元件之影響，對於高分子記憶體元件的發展有很大的幫助。In recent years, polymer systems have attracted significant research interest for memory device applications due to their tunable electrical properties through molecular design and good processibility. The representative classes of polymer materials used for fabrication on memories are conjugated polymers, non-conjugated polymers (functional polyimide systems or polymers with specific pendent donor or acceptor moiety) and polymer nanocomposites (metal nanoparticle or fullerene embedded). However, the effects of polymer structure on the memory characteristics have not been fully explored yet. In this thesis, the homopolymers pendant with donors or acceptors and related copolymers containing of both donor and accepter units were synthesized and evaluated on memory devices. n chapter 2, the homopolymers with pendant para-substituted dicyano- triphenylamine (D, as donor) or three different oxadiazole derivatives (2-phenyl-5-(4-vinylphenyl)-1,3,4-oxadiazole (A1), 2-(4-vinylbiphenyl)-5-(4-phenyl)- 1,3,4-oxadiazole (A2), and 2-(4-vinylbiphenyl)-5-(4-ethoxyphenyl)-1,3,4-oxadiazole (A3), as electron acceptor) and also related random copolymers consisting of pendant donor and acceptor moieties (the ratio of donor:acceptor is 8:2, 5:5 and 2:8, respectively) were synthesized by Nitroxide-Mediated Living Free Radical Polymerization (NMP) and characterized by 1H NMR spectrum and element analysis (EA). The para-substituted dicyano groups on triphenylamine improve the stability without the dimerization. The side-chain acceptor A2 shows more conjugated length relative to A1 by introducing another benzene ring, and A3 system further enhances the electronic density by adding terminal electron donating moiety (-OEt). The two thin film absorbance peaks of copolymers at 353 nm and 308 ~ 332 nm belong to the corresponding homopolymers (PD at 355 nm, PA1 at 308 nm, PA2 at 330 nm, PA3 at 332 nm, respectively) and the relative absorbance of two peaks vary with donor and acceptor ratios. The band gaps calculated from absorption edge are in the range of 3.11 ~ 3.20 eV and increase slightly with the larger acceptor content. The HOMO and LUMO energy levels of the random copolymers with different donor and acceptor ratios obtained from cyclic voltammetry (CV) are almost the same with the corresponding HOMO level of donor (-5.63 eV) and LUMO levels of acceptor (-2.63 ~ 2.81 eV), respectively, mainly due to poor hybridization of adjacent donor and acceptor which could be considered as an isolated system. The electronic properties can be well-tuned through different donor-acceptor structures and ratios of the copolymers systems. n chapter 3, the memory device of the random copolymers and homopoymers are fabricated and measured in ambient atmosphere. Different solvents (N,N-dimethyl formamide (DMF) or chlorobenzene (CB)) are chosen for polymer thin film processing. The bistable memory behavior is conducted by a simple sandwich device configuration consisted of spin-coated polymer film between indium-tin oxide (ITO) bottom electrode and aluminum (A1) top electrode. All the polymers exhibit nonvolatile flash type of switching behavior. The memory devices have low turn-on threshold voltage below 1 V and exhibits long retention time of 11000 seconds. The mechanism of the switching behavior is based on filamentary conduction with space charge limited current (SCLC) theory. As the polymer films prepare from DMF, the OFF state current during erasing scan increases from 10-5 A to 10-2 A after several WRER cycles. These phenomena are further obviously demonstrated in the case of the larger acceptor contents of the random copolymers (5:5 and 2:8 donor:acceptor ratio) and homopolymers pendant with acceptor due to the presence of the binding heteroatom (N) on acceptor with Al which contributes to filament conductions. Introducing electron donating ethoxy substituent (A3) which enhance the binding ability of N atom of oxadiazole group makes the memories difficult to turn off and also keep them on the high conductance since the stable filament channel are formed. The memory can still restore to the initial OFF state if the erasing process scan more negatively which also means the enhanced threshold voltage (from -3 V to -5 V) as the acceptor ratio increases. The polymer surface prepared from the CB solution is smooth and the current elevation of OFF state during the erasing switch could not be found. The study demonstrates that pendent donor/acceptor structures and ratio of copolymer and processing condition on the switching characteristics of memory device are fully explored.Contents要 Ibstract IIIontents VIable Captions IXigure Captions Xhapter 1 Introduction 1-1 An Overview of Memory 1-2 Polymer Memory Device 3-3 Operating Mechanism for Polymer Memory Device 4-3-1 Filamentary Mechanism 5-3-2 Trapping-Detrapping Mechanism 6-3-3 Charge Transfer Mechanism 7-3-4 Others 9-4 Research Objectives 10eferences 12hapter 2 Synthesis and Characterization of New Donor-Acceptor Random Copolymers with Side-Chains of para-Substituted Dicyano-triphenylamine and Oxadiazole Derivatives 16-1 Introduction 16-1-1 Nitroxide-Mediated Living Free Radical Polymerization 17-2 Experimental Section 19-2-1 Materials 19-2-2 Measurements 19-2-3 Synthesis Monomers 22-2-4 General Procedures of Polymerization 27-3 Results and Discussion 32-3-1 Synthesis and Characterization 32-3-2 Optical Properties 32-3-3 Electrochemical Properties 35-3-4 Thermal Properties 36-4 Conclusions 37eferences 39hapter 3 Memory Device Characteristics of Donor-Acceptor Random Copolymers with Side-Chains of para-Substituted Dicyano-triphenylamine and Oxadiazole Derivatives 66-1 Introduction 66-2 Experimental 67-2-1 Fabrication 67-2-2 Measurement 68-3 Results and Discussion 68-3-1 Performance of Memory Device 68-3-2 Effect of Various Donor-Acceptor Ratios 72-3-3 Effect of Various Acceptors 73-3-4 Effect of Various Coating Solvents 74-3-5 Memory Mechanism 75-4 Conclusions 79eferences 81hapter 4 Conclusions 10
Syntheses of Photoluminescent Noble Metal and Carbon Nanomaterials and Their Applications
No full text發光奈米材料具有高靈敏度、選擇性、以及高光穩定性之特性，故具有應用於生物感測器、細胞顯影劑及顯示器等之潛力。相較於傳統發光半導體量子點使用有毒重金屬為前驅物，此研究主要是以綠色化學方法來合成貴金屬奈米團簇(nanoclusters)以及碳奈米量子點，並應用於不同領域例如環境樣品中重要離子檢測、發光薄膜和催化劑等。整篇論文共分成七個章節，第一章回顧貴金屬奈米團簇和碳奈米量子點的背景知識包含合成、光學性質以及已開發之應用。第二章節，合成可調控放光之氧化鋁奈米及金奈米團簇複合材料並用於改善金奈米團簇的純化過程。經純化的氧化鋁金奈米團簇對於銀離子有更佳的靈敏度，其偵測極限降低了約六倍(從10 nM 降低到1.5 nM)。第三章，於有機溶劑中合成銅奈米團簇聚集體，並進一步研究溶劑對銅奈米團簇”聚集-誘導放光”之影響。此銅奈米團簇聚集體更被用來檢測硫化氫，其偵測極限為500 nM，並被證明能用來分析環境中溫泉水的硫化氫濃度。在第四章，以一鍋合成法(one-pot)來合成金銅奈米團簇，此金銅奈米團簇的螢光對於不同的酸鹼程度會有不同的螢光強度，具有作為pH 感測器潛力。此外，此金銅奈米團簇可用來催化有機染料還原反應。第五章，開發一快速合成法來合成牛血清蛋白金奈米團簇。並利用質譜法以及螢光光譜法被來研究牛血清蛋白金奈米團簇的生長機制。更進一步，牛血清蛋白金奈米團簇被用來檢測汞離子其靈敏度為4 nM。第六章，以一鍋水熱合成法(one-pot hydrothermal route)合成有機矽修飾之碳奈米量子點，此矽修飾之碳奈米量子點的螢光對於溫度293-343 K具有線性響應，此外藉由矽氧鍵(Si–O–S)的作用力，此矽修飾之碳奈米量子點能輕易地被均勻塗覆在玻璃上。第七章，以有機矽修飾之碳奈米量子點為前驅物合成發光矽碳奈米與二氧化矽的奈米複合物(SiC-dots/SiO2 nanocomposites)。藉由控制加熱時間，可合成藍色、綠色、黃褐色放光之矽碳奈米與二氧化矽的奈米複合物。此矽碳奈米與二氧化矽的奈米複合物更被運用於彩色玻璃、電催化材料以及熱微影術。Photoluminescent nanomaterials exhibit great potential for sensing, imaging and visual display because they have advantages of high selectivity and sensitivity, and outstanding photostability. In comparison with conventional semiconductor quantum dots, which use heavy metal ions as precursors, we have developed a series of green approaches for preparation of photoluminescent noble metal and carbon nanomaterials. As-prepared photoluminescent nanomaterials were applied in various fields such as detection of important ions in environmental samples, fabrication of photoluminescent thin films and as catalysts. This dissertation is structured in seven chapters. In Chapter 1, the background of noble metal nanoclusters (NCs) and C-dots including their synthetic routes, optical properties and applications is reviewed in detail. In Chapter 2, alumina nanoparticle supported Au NCs with tunable emission wavelengths were prepared to simplify the purification process. Purified Al2O3 NPs@Au NCs revealed six-fold better sensitivity (from limit of detection (LOD) 10 nM to 1.5 nM) towards silver ions. In Chapter 3, luminescent Cu NC aggregates were prepared in the presence of organic solvent. The relation between aggregation-induced emission behavior and organic solvent was investigated. As-prepared Cu NC aggregates were utilized to detect hydrogen sulfide (LOD: 500 nM), and their practicality was validated by detection of hydrogen sulfide in hot spring water samples. In Chapter 4, a one-pot approach to synthesize bimetallic AuCu NCs was developed. The AuCu NCs revealed interesting pH-dependent photoluminescent behavior, and exhibited their potential as pH sensors and organic dye reduction catalysts. In Chapter 5, a facile method to prepare bovine serum albumin gold nanoclusters (BSA-Au NCs) is reported. The growth mechanism of BSA-Au NCs was studied by mass spectroscopy and photoluminescence measurements. The work laid solid foundation for synthesis of dual-emission metal NCs. In Chapter 6, organosilane-functionalized carbon nanodots (SiC-dots) were synthesized by a simple one-pot hydrothermal route. The photoluminescence of SiC-dots revealed reversible temperature response (293–343 K). Through Si–O–Si bonding, temperature-sensitive photoluminescent SiC-dot films could be easily fabricated on glass substrates without aggregation. In Chapter 7, SiC-dots/SiO2 nanocomposites were prepared from SiC-dots (in Chapter 6). By controlling the heat treatment time, blue, green, and tan (yellow-brown) photoluminescent SiC-dots/SiO2 nanocomposites were achieved. The potential applications for colourful windows, electrocatalysis and lithographic patterning of SiC-dots/SiO2 nanocomposites were demonstrated
Mems Microwell and Microcolumn Arrays: Novel Methods for High-Throughput Cell-Based Assays
No full textAlthough the cell-based assay is becoming more popular for high throughput drug screening and the functional characterization of disease- associated genes, most researchers in these areas do not use it because it is a complex and expensive process. We wanted to create a simple method of performing an on-chip cell-based assay. To do this , we used micro- electro-mechanical systems (MEMS) to fabricate a microwell array chip comprised of a glass substrate covered with a photoresist film patterned to form multiple microwells and tested it in two reverse transfection experiments, an exogenous gene expression study and an endogenous gene knockdown study. It was used effectively in both. Then, using the same MEMS technology, we fabricated a complementary microcolumn array to be used as a drug carrier device to topically apply drugs to cells cultured in the microwell array. We tested the effectiveness of microwell- microcolumn on-chip cell-based assay by using it in experiments to identify epidermal growth factor receptor (EGFR) activity inhibitors, for which it was found to provide effective high throughput and high content functional screening. In conclusion, this new method of cell -based screening proved to be a simple and efficient method of characterizing gene function and discovering drug leads
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
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