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The characteristics of microstructure phase transformation and mechanical properties in GPM A30 powder metallurgy high speed steel
No full text本研究是針對榮剛重工生產的粉末高速鋼GPM－A30做特性、組織等方面的探討，企圖以穿透式電子顯微鏡組織為研究方向，配合掃描式電子顯微鏡組織觀察，以及熱膨脹曲線分析，探討高速鋼淬火及各次回火組織之相變態。
隨著淬火溫度的升高，碳化物固溶於基地的量急遽升高，使得基地中的碳含量提高，降低沃斯田鐵組織的Ms溫度，對沃斯田鐵有安定化的作用，故沃斯田鐵再淬火後的殘留比例也急遽升高。淬火溫度提高，強化基地的效果降低，再由於殘留沃斯田鐵增加，使硬度下降。
殘留沃斯田鐵在回火的過程中，分解產生碳化物，而使得Ms溫度提高，有利於麻田散鐵生成。由熱膨脹曲線可知，經三次回火後，殘留沃斯田鐵幾乎已完全分解而不存在。同時，由實驗結果曲線證明，一次回火的效率不大，只有多次回火才能使殘留沃斯田鐵完全（或幾乎完全）相變。
經由顯微組織觀察可以發現，殘留的沃斯田鐵在回火的冷卻過程中會轉變為麻田散鐵，這種新生的板片麻田散鐵（在高碳中，通常為雙晶麻田散鐵）是未經回火，對基地的韌性是有害的，所以必須再進行第二次的回火，使先前硬脆的新生麻田散鐵析出合金碳化物而轉變為強韌的回火麻田散鐵組織，並且兼具適當的硬度與韌性；實驗後證實回火期間沃斯田鐵之催化作用能有效地使基地重新調質，並利用多次回火冷卻的過程來消除殘留沃斯田鐵且逐步相轉變而得到最終回火麻田散鐵的穩定組織。The effect of tempering on the decomposition of retained austenite in a powder metallurgy (PM) high-speed steel, GPM A30, has been monitored with a high-speed dilatometer. The corresponding microstructures of specimens with different tempering cycles have been investigated by a combination of scanning electron microscopy and analytical transformation electron microscopy. The as-quenched structure of the steel studied is composed of retained austenite, untempered martensite and carbides. The results indicate that the complete transformation of retained austenite can be more nearly accomplished by two or triple tempering cycles than by a single long-time cycle. The possible transformation mechanism for the decomposition of retained austenite during multiple tempering cycles is attributed to the invariant-plane-strain of the prior martensitic transformation extending accommodation defects to the adjacent retained austenite, which favors further transformations in the subsequent tempering operations.
There has been intensive research work on retained austenite and lath martensite in low-carbon alloy steels. However, little TEM research work has been carried out on twinned plate martensite with retained austenite in high-carbon alloy steels . It is naturally very difficult to produce electron-transparent samples for TEM (because the high-carbon alloys are quite brittle), but TEM investigation continues to assume greater significance in research.
GPM A30 is a high-carbon grade in commercial P/M high speed steels, and is widely used in such applications as metal cutting tools and metal forming dies. In this work, dilatometric experiments were performed to investigate the tempering response in quench-treated specimens of GPM A30 high speed steel. The resulting scanning electron micrographs and transmission electron micrographs were examined to elucidate the microstructural evolution.目錄
第一章 前 言............................. 1
第二章 文獻回顧............................. 4
2.0 簡介..................................... 4
2.1傳統冶煉鑄造高速鋼與粉末高速鋼之比較...... 4
2.1.1 GPM A30（相當於AISI ASP30）粉末高速鋼...5
2.2 麻田散鐵相變態 ............................6
2.2.1 麻田散鐵的特徵..........................7
2.2.2 麻田散鐵的晶體結構......................8
2.2.3 麻田散鐵的結晶學........................9
2.2.4 麻田散鐵的型態學........................12
2.2.4.1 板條狀麻田散鐵（Lath Martensite）.....13
2.2.4.2 板片狀麻田散鐵 (Plate Martensite).....14
2.2.5 殘留沃斯田鐵 ............................15
2.3合金元素對高速鋼之影響.....................16
2.3.1碳(C)....................................16
2.3.2鎢(W)....................................17
2.3.3鉬(Mo)...................................18
2.3.4鉻(Cr)....... ............................18
2.3.5釩(V)....................................19
2.3.6鈷(Co)...................................19
2.4高速鋼碳化物的探討.........................20
2.4.1高速鋼中碳化物的種類.....................20
2.4.2合金碳化物對高速鋼的影響.................22
2.4.3 合金鋼碳化物相變態模式..................22
2.5高速鋼之熱處理.............................23
2.5.1高速鋼的淬火硬化與深冷處理...............23
2.5.2含V、Mo、Cr等合金鋼之回火，通常可以分成下列五個階段： .....................................24
2.5.3高速鋼的回火熱處理.......................26
第三章 實驗方法..............................34
3.1實驗材料...................................40
3.2 實驗流程..................................41
3.2掃描式電子顯微鏡(SEM)的觀察和EDAX之半定量成份分析
...........................................42
3.3熱處理試棒的製作及使用儀器.................42
3.4穿透式電子顯微鏡（TEM）的試片製作及觀察....43
第四章 粉末高速鋼GPM A30相變態研究............49
4.1最佳淬火溫度之選擇.........................49
4.1.1前 言...................................49
4.1.2晶粒大小與淬火溫度之關係.................49
4.2熱膨脹曲線之探討...........................53
4.2.1前 言...................................53
4.2.2高速工具鋼熱處理之膨脹曲線...............53
4.3顯微組織觀察...............................57
4.3.1原有狀態（As Received）的顯微組織........57
4.3.2淬火狀態的顯微組織.......................58
4.3.2.1固溶淬火溫度的影響.....................58
4.3.2.2 1160℃×3min淬火後之SEM顯微組織........58
4.3.2.3 1160℃×3min淬火後之TEM顯微組織........59
4.3.3回火狀態的顯微組織.......................61
4.3.3.1 SEM顯微組織...........................61
4.3.3.2 TEM顯微組織...........................64
第五章 結 論...............................106
第六章 建議未來工作.........................108
參考文獻.....................................10
Design and Implementation of a Baseband Receiver for DVB-T/H Standard
No full text本論文探討歐規數位電視地面/手持廣播系統(DVB-T/H)之特色與規格。此外，基頻通道模型在本論文中也予以討論，其中通道效應包含多路徑衰減通道(Multipath Fading Effect)、加成性白色高斯雜訊(AWGN)、載波頻率漂移(Carrier Frequency Offset)、取樣時脈漂移(Sampling Clock Offset)、以及相位雜訊(Phase Noise)。根據此規格以及通道模型，本論文提出一基頻接收機，包含各模組之演算法，電路設計，以及硬體實做。為了支援移動接收之機能，本論文提出一通道估測及補償之演算法，並結合一兩階段模式偵測、符元時間偵測、載波頻率漂移與取樣時脈漂移之估測、補償及追蹤、2/4/8K FFT處理器、相位調整、軟性輸出解映射器及軟性輸入維特比解碼器。此外，為了降低系統之複雜度，於模式增測及整數載波頻率漂移之估測等處予以硬體簡化。為了解調傳輸參數訊號，一BCH解碼器也於本論文提出及設計。透過輸出訊噪比(Output SNR)取代位元錯誤率(BER)來做為決定最佳位元數之指標，進行全系統之定點數模擬。最後經由全系統之效能模擬及全系統之Verilog RTL程式之實做與驗證，證明本論文所提出之DVB-T/H基頻接收機之良好效能。In this thesis, the features and specification of Europe DVB-T/H standard have been delineated. Besides, a baseband channel model has been discussed, including multipath fading effect, AWGN, CFO effect, SCO effect, and phase noise. Based on the standard and a baseband equivalent channel model, a baseband receiver is proposed, including algorithms, circuit design and Verilog RTL code implementation. To support mobile reception, this thesis proposes the channel estimation and equalization algorithm and combines algorithms of a two-stage mode detection, symbol timing detection, CFO as well as SCO estimation and compensation, 2/4/8K FFT processor, phase modification soft-output de-mapper and soft-input Viterbi decoder. In addition, to reduce the hardware complexity, the GI mode detection module and integer CFO module have been modified; to decode the TPS signal, a BCH decoder is designed and implemented as well. Through output SNR instead of bit error rate (BER) as the metric of the word-length determination, the optimal word-length can be obtained. By means of system performance simulation and verification of whole Verilog RTL code, the proposed DVB-T/H baseband receiver is proven to work well.Contents i
List of Figures iv
List of Tables vii
1 Introduction 1
1.1 Motivation of Thesis 1
1.2 Introduction of Digital Video Broadcasting 3
1.2.1 Comparison of DVB-S, DVB-C, DVB-T, and DVB-H 4
1.3 Comparison of Various Existing Mobile Digital TV Standards 5
1.4 Organization of Thesis 7
2 Principle of OFDM and DVB-T/H 9
2.1 Introduction 9
2.2 Principle of OFDM 9
2.3 DVB-T/H Standard 17
2.3.1 Hierarchy Information 19
2.3.2 OFDM Frame Structure 21
3 Baseband Channel Model 27
3.1 Introduction 27
3.2 Wireless Channel 28
3.2.1 Multipath Fading Channel 28
3.2.1.1 Static Channel Model 28
3.2.1.2 Dynamic Channel Model 30
3.2.2 Additive White Gaussian Noise 32
3.3 Receiver Impairment 33
3.3.1 Carrier Frequency Offset 33
3.3.2 Sampling Clock Offset 34
3.3.3 Phase Noise 35
4 Low-Complexity Channel Estimation and Equalization for Mobile DVB-T/H System 37
4.1 Introduction 37
4.2 Derivation of ICI Response 38
4.3 Channel Estimation 40
4.3.1 2D-RLS Time Domain Interpolation 40
4.3.1.1 Shift Invariant Property 41
4.3.1.2 SISA 2D-RLS Interpolator 43
4.3.1.3 Computation Reduction 48
4.3.2 Frequency Domain Interpolation 54
4.4 ICI Response Approximation 56
4.5 ICI Mitigation 58
4.5.1 Zero-Forcing ICI Equalization 58
4.5.2 Parallel ICI Cancellation 65
4.6 Simulation Result 67
5 DVB-T/H System Design 75
5.1 Introduction 75
5.2 Transmitter Architecture 76
5.2.1 Block Diagram 76
5.2.2 Inner Coder 77
5.2.3 Inner Interleaver 79
5.2.4 Constellation Mapping 81
5.2.5 Frame adaptation 84
5.3 Receiver Architecture 85
5.3.1 Block Diagram 85
5.3.2 Mode Detection 86
5.3.2.1 FFT Mode Detection 87
5.3.2.2 GI Mode Detection 90
5.3.3 Symbol Timing Detection 93
5.3.4 CFO Estimation 97
5.3.4.1 Fractional CFO Estimation 98
5.3.4.2 Integer CFO Estimation 99
5.3.5 Joint WLS Estimation 102
5.3.6 Carrier Recovery Loop 104
5.3.6.1 Loop Filter 104
5.3.6.2 CFO Compensation 105
5.3.6.3 SCO Compensation 105
5.3.7 Phase Modification 107
5.3.8 Scattered Pilot Detection 108
5.3.9 Channel Estimation 110
5.3.10 ICI Mitigation 111
5.3.11 TPS Demodulation 112
5.3.11.1 TPS Demodulation 112
5.3.11.2 BCH Decoder 113
5.3.12 De-mapper 115
5.3.13 Outer Receiver 118
5.4 System Simulation 119
6 Hardware Implementation 125
6.1 Introduction 125
6.2 Fix Point Simulation 125
6.3 Circuit Design 131
6.3.1 CORDIC 131
6.3.2 Piecewise Linear Approximation 133
6.3.3 Mode Detection 134
6.3.4 Symbol Timing Detection and Fractional CFO Estimation 136
6.3.5 Integer CFO Estimation 138
6.3.6 FFT Module 139
6.3.7 Joint WLS Estimation 140
6.3.8 Carrier Recovery Loop 140
6.3.9 Phase Modification 142
6.3.10 Scatter Pilot Detection 143
6.3.11 Channel Estimation 144
6.3.12 ICI Mitigation 146
6.3.13 TPS Demodulation 147
6.3.14 Resource Sharing 153
6.3.15 Gated Clock 155
6.3.16 Saving in Complexity 157
6.4 Simulation Result 158
7 Conclusion 165
Reference 16
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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