موضوع: "بدون موضوع"
همانگونه که اشاره شد عدد آرام سوزی مهمترین شاخصهی کیفی بنزین موتور میباشد. عدد آرام سوزی بیشتر نمایش دهندهی بنزین مرغوبتر میباشد که نشان میدهد بنزین در مقابل ضربه مقاومتر بوده و موتور راحتتر کار میکند. اهمیت عدد آرام سوزی به ویژه در دهههای اخیر و با بالاتر رفتن ضریب تراکم[2] موتور خودروها بیشتر شده است. [3]. عدد آرام سوزی بنزین مانند اکثر دیگر مشخصات آن از روابط غیر خطی تبعیت نمینمایدکه این غیر خطی بودن به درصدهای حجمی مخلوط تشکیل دهندهی بنزین بستگی دارد. بنابراین جهت مدلسازی آن بایستی از روشهای پیچیدهتری نسبت به روشهای خطی استفاده کرد. بطورکلی و در روشهای آزمایشگاهی، غالب شرکتهای تولید کنندهی بنزین موتور، عدد آرام سوزی آنرا با استفاده از دستگاه CFR[3] که یک موتور تک سیلند دارای شمارشگر ضربه[4] میباشد، اندازهگیری مینمایند.انجام این آزمایش صرفنظر از طول مدت زیاد آزمایش، بعلت استفاده از مواد خالص (نرمال هپتان،ایزو اکتان و تولوئن) دارای هزینهی نسبی زیاد و همراه با ایجاد آلودگی صوتی و شیمیایی است. از طرفی بهعلت هزینهی زیاد خرید دستگاه موتور CFR غالب آزمایشگاههای متوسط و کوچک امکان تهیهی آنرا ندارند که در نتیجه امکان اندازهگیری عدد آرام سوزی بنزین را ندارند.
یکی دیگر از آزمایشهای مهم انجام یافته روی بنزین موتور، آزمایش تقطیر[5] میباشد که شامل اطلاعات مهمی در خصوص بازهی جوش ترکیبات تشکیل دهندهی بنزین موتور میباشد. انجام این آزمایش بعلت سهلالوصول بودن آن در اکثر آزمایشگاههای نفت مرسوم میباشد. هدف از انجام این تحقیق بررسی امکان پیشبینی عدد آرام سوزی بنزین موتور با استفاده از دادههای تقطیر همان نمونه بنزین به روش شبکهی عصبی مصنوعی میباشد.
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ضرورت تحقیق
بحرانهای ناشی از مصرف روزافزون انرژی در کشور ما تبدیل به یک مشکل در مدیریت کلان کشور شده است که علاوه بر آثار سوء زیست
محیطی و بهداشتی باعث آسیب جبران ناپذیر به اقتصاد ملی نیز شده است. و وزارت نفت بهعنوان بزرگترین تأمین کنندهی سوخت مایع در کشور ناگزیر از وارد کردن میزان مورد نیاز افزون بر تولید داخل از خارج میباشد[4]. آنچه قابل ذکر است علیرغم سیاستهای انقباضی دولت جهت خرج از بحران، مصرف فراورده های نفتی ازجمله بنزین روندی صعودی داشته و این به معنی رو به رشد بودن روند ایجاد آلودگیهای ناشی از مصرف اینسوخت فسیلی است. بنابراین لازم است تا علاوه بر مصرف بهینهی بنزین، با ارتقاء استانداردهای فعلی تولید بنزین بهEuro4 [6]و Euro5آلودگی حاصل از مصرف آن به سطوحی پایینتر تقلیل یابد. با توجه به موارد ذکر شده ضرورت تبیین و تعیین روشهای جدیدتری برای تولید فرآوردههای باکیفیت و تواماً نیاز به ایجاد روشهای جدید جهت آزمایش مشخصههای کیفی آن بیش از پیش احساس میشود.
در این راستا تلاش شده است با داشتن دادههای سریعالحصول و سهلالوصول به دست آمده از آزمایش تقطیر بنزین، عدد آرام سوزی آنرا که علاوه بر عدم امکان خرید دستگاه موتورCFR برای اکثر آزمایشگاهها، آزمایشی طولانی مدت، پرهزینه و آلاینده میباشد را با دقتی قابل قبول پیش بینی کرده و بهدست آوریم.
عنوان : The Impact of Speech Rate on Iranian Intermediate EFL Learners`s Listening Comprehension Ability
Islamic Azad University
Rasht Branch
Faculty of Human Sciences
Department of English Language
Presented in partial fulfillment of the requirements for (M.A.) degree
Title:
The Impact of Speech Rate on Iranian Intermediate EFL Learners`s Listening Comprehension Ability
Supervisor:
Dr. Morteza Khoda Bandehlou
Date:
(Novamber,2015)
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Table of Contents
Title Page
Abstract 1
: Introduction
1.0 Introduction. 2
1.2 Theoretical Framework. 4
1 .3 statement of problem.. 5
1.4. Significant of the study. 7
1.5. Research Question of the study. 7
1.6. Hypothese of study. 7
1.7. Definitions of Key Terms. 8
1.8. Summary. 8
:
2.0 Introduction. 9
2.1What is listening?. 11
2.3 Theory of listening comprehension. 15
2.4 Listening strategies. 15
2.5 One-way listening versus two way listening. 17
2.6 General proficiency in listening comprehension. 19
2.7 Empirical research about listening comprehension. 20
2.8 Role’s of listeners in the classroom.. 22
2.9 Relation between listening and speaking. 23
2.10 General framework about the speech rate. 25
2.11 Defining speech rate terminology. 26
2.12 Speech rate and Preceding research. 27
2.13 speech rate and different effect on listening. 29
2.14 Standard speech rate in English. 30
2.15 Speech rate and interlocutor. 33
2.16 Appropriate speech rate. 34
2.17 Natural rate vs slow rate. 36
2.18 Control speech rate vs. slow speech rate. 38
2.19 Problem of speech rate. 40
- 20 Modified speech rate and listening. 41
3.0 Introduction. 43
3.1 Design of the study. 44
3.2 Participants. 45
3.3 Materials. 45
3.4 Procedures. 46
3.5 Methods of analyzing data. 47
3.6 Summary. 47
:
4.0. Introduction. 47
4.1. Data analysis and findings. 48
4.1.1. Descriptive Analysis of the Data. 48
4.2. Results of Hypothesis Testing. 52
4.3. Summary. 53
General Discussion
5.1 General Discussion. 53
5.2 Pedagogical implication. 54
5.3 Limitation of the study. 55
5.4 Suggestion for further research. 56
References. 57
Appendixes….. 65
Appendix A(OPT Test). 62
Appendix B.. 67
Appendix C.. 71
List of Tables
Title Page
Table(1) shows the “normal” and the “slow” SR ranges adopted. Table 1 Note. NS: normal speeds, 3-Sp: 3-second pauses, DA: deliberate articulation The Listening. 27
Table(2) :Measuring unit 32
Table(3): Standard speech rate. 32
Table (4):Showed different speech rate (ideal speech rate). 41
Table4. 1. 49
Table4. 2. Descriptive analysis of pre and posttest in both groups. 50
Table4.3.The results of T-TEST to examine the differences between pre and. 50
post test in control and experimental 50
Table 4.4. Mean and adjusted means of listening comprehension test in post test 50
Table4.5.listening comprehension covariance in both groups. 51
List of Figures
Title Page
Figure1.1. the Diagram of the Design of the Study. 44
Figure4.1. level of listening comprehension in both groups (experimental, control). 49
Figure4.2. means of listening comprehension in post test in both groups. 52
Abstract
The aim of the present study was to investigate the Impact of Speech Rate on Iranian Intermediate EFL Learners’ Listening Comprehension Ability. To achieve this purpose, forty four participants intermediate language learners were selected based on their scores on a knowledge on an OPT Test as the randomly assigned to two groups experimental and control group. Each group was exposed to as pre-test and post-test. At the end of the experiment, to see whether or not any changes happened regarding their comprehension with two different rate of speech .the results suggested that the participants who receive slow speech rate have higher listening comprehension ability after posttest comparing to control group.
Keywords: Listening Comprehension, Speech Rate, EFL.
Chapter one
1.0 Introduction
This study is the importance of EFL learner’s rate’s of speech, which is essential pre request skills for speaking because that was influenced on listening comprehension of interlocutors so good listeners become good communicators. Although there is the lack of enough research and the systematic investigation about the listening comprehension (Joiner, 1986; Long, 1987; Dunkel,1991; Rubin, 1994; Mendelsohn, 1998) because there is a belief about the this happen that without the natural exposure to spoken language we can’t acquire listening comprehension ability while other skills should be thought through directional instruction in school setting (Herron &Sedy,1991; Schmidt-Rinehart,1992). This belief showed that there is an important attention of researchers on the language and the lack of materials available for teachers who emphasize role of listening for the students L2 learning. When nonnative listeners have problem for understanding a passage , they usually complain that language is spoken too fast (white,1987) but if they practice listening they can reinforce their speaking and better perceive message .According to Rivers (1966,pp.196, 204) an advocate for listening comprehension , ”Speaking does not of itself constitute communication unless what is said is comprehended by another person… teaching the comprehension of spoken speech is there for of primary importance if the communication aim is to be reached.’ Listening comprehension is important for both teacher and student, Chastain (1976) language teachers and students want to overlook the importance of listening comprehension skill. They do because they fail to developing attention on functional listening comprehension they just attention on fix completely ,speaking, because information processing time factor as an important in listening comprehension.L2 learners have difficulty recognize different part of message ,they can’t separate any noise , syntax and functional, and other part of sentence even in their language therefore they are not good listener when they are contacted with fast speech sound they confused, this happen reflected a question that often heard, ”Do you speak…? ” Obviously, one cannot speak a language unless can understand it .Listening comprehension process is internal not subject to direct and external observation and make correction. Also , since the teachers in their classrooms have little experience for providing class activities for improving students listening comprehension ability they can’t be prepare suitable activity for guidance of learners .The learners for learning to speak English first should learn to understand real language situations to comprehend purpose of native speakers in their speaking .Previous studies showed that many students who go to another country are much less able to perceive native speech than they are to create message ,incomplete as that native speakers can understand. This showed that listening comprehension is necessary for language learning and communicating to real language situation to the teachers and students want to achieve in communication goals. Psychologists describe listening as the comprehending meaning of stream of verbal symbols. Listening comprehension is the most important part of language learning means of the students can’t learn the language without comprehension of it. In spite of learner would like to perceive second language speakers they want to comprehend different speed of speech sound. When students listen to speech sound for making sense of it they should understand perfectly at the first of all gist of native speaker said as part of important skills, listener contrast to reader who has opportunity to go back for understanding, they can’t go back to the next so speaker should have enough knowledge about the speaking and interlocutor for adopting simplified input that called foreign talk to non-native speakers by using a slower speech rate. According to (Dunkel, 1991; Rost, 2001; Vandergrift, 2007) Listening is an important language skill to develop second language acquisition. Listening comprehension in the classroom for some of the learners want to perceive oral presentation of her teacher is the same way need to struggle with listening comprehension they will struggle to learn material presented orally. According to grift (2007) one of the reasons might be that learners are not taught how to learn listening effectively. If the teachers aware of some factors that affect listening comprehension helps them better provide the needs of their students in the fact that how the learners listen, has essential effect on learners job and on the better relationships with others for students listen to get information and enjoyment, to learn and understand Because according to some researchers we remember between 25 percent and 50 percent of what we listen. It means that when we talk with others for 10 minutes, they pay attention to less than half of the conversation. Clearly, listening comprehension is a skill that the learner can improve it by better listening and productivity and the learner should avoid the conflict and misunderstandings as well as their ability to effect in their communication.
1.2 Theoretical Framework
In recent years, there has been a growing of research on the effects of speech modification on L2 listening comprehension. Speech rate research has not been able to precisely define the rate ranges by EFL listeners of different proficiency levels given the disparity among these ranges , according to Zhao (1997) has led to serious methodological flaws and inconsistent results that make the transferability of these conclusions to other contexts almost impossible. Griffiths (1992) studied the effects of speech rates (127, 188, 250 wpm) on the nonnative speaker’s listening comprehension and concluded that the slowest rate was the most comprehensible and the higher rates led to worse comprehension. Teachers and learners should take into account features of slow and natural speech rate and know that both have some advantages and disadvantages. Griffiths (1992) concluded that reducing the velocity of speech rate was positively related to high listening comprehension mean scores . Slow speech rate may be used as a short path practice for comprehending natural speech rate there for comprehending natural speech rate is the optimal objective . This study underlying psychological building block of application of Krashen’s Input Hypothesis (1985) which postulates i+1 input for the learner in the learning and teaching settings. Most of the previous studied about speech rate (e.g., Khatib, 2010; Sakaki, 1996)were carried out on high school in their English books and listening comprehension has been involve in syllabus. Therefore the researcher not only found it useful and practical to have a study in high school but also will compare listening comprehension at two different speech rate therefore main objective whether listening to normal versus slow rate effects on Iranian EFL learners listening comprehension ability or not and investigate the impact of speech rate on intermediate EFL learners’ listening comprehension ability.
کلید واژگان: تکرار ، تکرار مسجع ،تکرار کامل، تکرار دگرگونی واکه
Abstract
This study aimed at analyzing the translation of English reduplicative words to Persian. Reduplication is a morphological process in which the root or stem of a word or a part of it is repeated. McCarthy mentioned three kinds of reduplication, Rhyming reduplication, exact reduplication and Ablaut reduplication. The corpuses on which the study was conducted were English novels and the Persian translation of them. Also the theoretical framework on which the study relied was strategies presented by Davis. By applying Davis’ translation strategies it was found that reduplicative words should not be translated literally if so they would lose the meaning. Moreover, in the struggle of form and meaning, preserving the meaning has superiority over preserving the form.
Keywords: Reduplication, Rhyming reduplication, exact reduplication, Ablaut reduplication.
Table of Contents
Acknowledgments …………………………………………………………..……….I
Abstract …………….…………………………………………………….………. III
Table of contents IV
List of Abbreviations ……………………………………….….…………………VII
1.1 Overview.. 2
1.2 Statement of the problem.. 3
1.3 Significance of the study. 5
1.4 Objectives of the study. 6
1.5 Research Questions 6
1.6 Theoretical Framework. 7
1.7 Limitations of the study. 13
1.8 Definition of key terms. 14
2.1 Introduction. 16
2.2 Reduplication definition. 16
2.2.1 Reduplication and repetitions 21
2.2.2 Types of English reduplicative words 22
2.3 Translation and reduplication 25
2.4 Works done in Iran. 28
2.4 Works done abroad. 28
3.1 Introduction. 32
3.2 Corpus of the study. 32
3.2.1 Justification of the study. 34
3.3 Procedures. 34
3.3.1 Data collection procedure. 34
3.3.2 Data analysis procedure 35
3.4 Design of the study. 35
4.1 Introduction. 37
4.2 Analysis and Results 37
45
5.1 Introduction. 48
5.1 Summary of the study. 48
5.3 Discussing the Results in Terms of the First Research Question. 49
5.4 Discussing the Results in Terms of the Second Research Question. 50
5.5 Discussing the Results in Terms of the Third Research Question. 51
5.6 Pedagogical Implications of the Study. 52
5.6.1 Implications for Translators and Translators Trainers. 52
5.6.2 Implications for Contrastive Analysts. 52
5.7 Suggestions for Further Research. 53
Refrences. 54
Chapter One:
Introduction
1.1 Overview
Reduplication is a morphological process in which the root or stem of a word or a part of it is repeated. In many languages, reduplication is used in inflections to convey grammatical functions and in lexical derivations to create semantic forms (Nadarajan, 2006).There are different categorization and ideas on reduplication and reduplicative words. For example according to Minkova (2002), there are two kinds of reduplication: full and partial reduplication. Full reduplication involves the exact repetition of the sound or word, while partial reduplication involves reduplication of only a part of a word. He (ibid) mentioned that most reduplications in English are partial reduplication which involves consonant ablaut or vowel alternation (e.g., riff raff, ping pong, chit chat, tip top), rhyme reduplication (e.g., hocus-pocus) and full reduplication (e.g., boo-boo). English reduplications have a certain form class and specific meaning. For example, chit-chat is a noun meaning a light conversation, and a verb meaning to talk informally or to gossip.
Katamba (1993 and 2006) considered reduplication as an affixation process which involves the addition of a free morpheme (not necessarily a bound morpheme) to the beginning, the end or within the base. Moreover there are two different points of view regarding reduplication. The first point states that it is a process whereby phonological material is copied. That is, the segmental content is repeated with various phonological constraints (Marantz 1982).
The second one explains that it is a process whereby a bundle of morpho-syntactic features are copied (Inkelas and Zoll 2005). Broselow and McCarthy (2009) have mentioned three kinds of reduplication used in English mostly for the purpose of informal expressive vocabulary:
- Rhyming reduplication
- Exact reduplication
- Ablaut reduplication
The examples are classified according to this classification mentioned by Broselow and McCarthy (2009). The main point is that, these words (reduplicative words) should not be translated literally. Especially in translation of novels because if they were translated literally their meaning would be lost. The translators’ main task is the analysis of the source text so it’s necessary for s/he to get the exact meaning and message of the source text.
عنوان : Exploring the impact of Pair Work on Writing Performance of Iranian EFL Learners
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Abstract
Collaborative writing has been used in composition research and pedagogy in U.S. educational institutes since the 1970s. Collaborative writing motivates social interaction among writers and their peers via activities such as peer response. Researchers of second language (L2) writing have asserted that pairing students up in writing can promote learning effectiveness in writing field. This paper explored the effects of pair work on improving writings of Iranian EFL learners. This study had a quasi-experimental setting. The participants consisted of 28 EFL students in a language school of Marand at intermediate level, divided into one control and one experimental group. The experimental group was divided into high proficiency and low proficiency groups, the former was called helper and the latter was named writer, making a pair to complement each other. Both had a pretest writing at the first session. The papers were scored manually and were compared with posttest scores which was conducted at the last session in the Excel sheets and figures. To test the variables, descriptive statistics like mean, standard deviation, and significance value were used. To compare mean scores of both groups, independent t-test was used. Then, the data were analyzed by SPSS software. The results showed that writing performance of the experimental group who practiced pair work has a significant difference with the writing ability of the control group who wrote individually. By pair work, the students in the experimental group produced more accurate sentences than the subjects of control group.
TABLE of CONTENTS
| ACKNOWLEDGEMENTS | i |
| ABSTRACT | ii |
| TABLE of CONTENTS | iii |
| CHAPTER I INTRODUCTION | |
| 1.1. Introduction | 2 |
| 1.2. Statement of the Problem | 2 |
| 1.3. Purpose of the Study | 3 |
| 1.4. Research Questions | 3 |
| 1.5. Significance of the Study | 4 |
| 1.6. Organization of the Study | 5 |
| 1.7. Definition of the Terms | 6 |
| 1.8. Summary | 6 |
| CHAPTER II REVIEW OF RELATED LITERATURE | |
| 2.1. Introduction | 8 |
| 2. 2. The philosophy behind this study: Sociocultural perspective | 8 |
| 2.2.1. Writing in Vygotsky’s school of thought | 10 |
| 2.2.1.1. More Knowledgeable Other or MKO | 10 |
| 2.2.1.2. Elaboration of ZPD | 11 |
| 2.3. Scaffolding in classroom situations | 12 |
| 2.3.1. Facilitative methods in scaffolding | 13 |
| 2.3.2. Characteristics and Critical Features of Scaffolded Instruction | 14 |
| 2.3.3. Challenges and Benefits of Scaffolding | 15 |
| 2.3.3.1. Challenges | 15 |
| 2.3.3. 2. Benefits | 16 |
| 2.3.4. Peer interaction: a good illustration and system of scaffolding | 17 |
| 2.4. Mediation and Writing | 17 |
| 2.5. Accuracy | 19 |
| 2.6. Writing English and pair work an important issue in Iranian context | 19 |
| 2.7. Arguments for and against pair work in writing: To use it or not to? | 21 |
| 2.8. Small groups or large ones? Which yields better results? | 23 |
| 2.9. Advantages of pair work | 24 |
| 2.10. A Large Number of Literature Supporting Pair Work | 26 |
| 2.11. Summary | 33 |
| CHAPTER III DESIGN AND METHODOLOGY | |
| 3.1. Introduction | 35 |
| 3.2. Design of the Study | 35 |
| 3.2.1.Procedure | 37 |
| 3.3. Site of the Study | 42 |
| 3.4. Participants of the Study | 42 |
| 3.5. Research Instruments | 42 |
| 3.6. Data Collection | 43 |
| 3.7. Data Analysis | 43 |
| 3.7.1. Accuracy Measurement | 43 |
| 3.8. Summary | 44 |
| CHAPTER IV FINDINGS | |
| 4.1. Introduction | 46 |
| 4.2. Background Information | 46 |
| 4.2.1. Students’ Background Information | 46 |
| 4.2.3. Language Instructor’s Background Information | 47 |
| 4.3. Research Question | 47 |
| 4.5. Summary | 54 |
| CHAPTER V DISCUSSION and CONCLUSION | |
| 5.1. Introduction | 56 |
| 5.2. Summary of the Study | 56 |
| 5.3. Discussion | 57 |
| 5.4. Pedagogical Implications | 59 |
| 5.5. Recommendations for Future Research | 61 |
| 5.6. Limitations of the Study | 62 |
| 5.8. Conclusion | 62 |
| REFERENCES | 64 |
| APPENDICES | 75 |
CHAPTER I
INTRODUCTION
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Introduction
Writing is a difficult task to perform. This problem is more evident in Iranian private institutes which are based on communication-focused instruction, providing little opportunity for learners to focus on writing skills in the limited class time. This is while demands for professional writing are increasing in academic settings. One way of overcoming this problem is exercising pair work. Pair work is great for practicing various language skills, vocabulary checks, and completing worksheets. Working in pairs gives individual students a lot of practice time. Groups give students the opportunity to create more complex texts, explore relationships between characters, pool knowledge together, and have a more social learning environment. Additionally, there is a better chance for self-correction or peer correction and for a discussion on a wider range of thoughts and opinions in a large size. This social interaction and dialogue with others are considered crucial for learning by social interactionist’ theorists, such as Vygotsky (2000), who stated that learning involves the internalization of social interaction processes, which helps the learner progress from complex to conceptual thinking. Generally speaking, the smaller the group, the more each member acts and the less chance there is that someone will be left out.
1.2. Statement of the Problem
Writing in English has gained a significant eminence in recent years in Iran. The reason behind it can be that in universities of Iran writing articles and dissertations, at different educational levels (BA, MA and PhD) by the students of all majors, accompanies various privileges for their writers as well as academic achievements. For the growing body of academia, even board members of scientific faculties are required to submit at least two papers in English at international journals to retain their positions or promote. This has created a flood of writing demands who yearn to acquire writing skills for fulfilling their above-mentioned academic tasks towards language institutes. This challenges the teachers to explore new ways for improving this skill which is the most difficult one (among 4 skills of listening, speaking, reading, and writing) for L2 learners to master. The difficulty lies not only in generating and organizing ideas, but also in translating them into readable and recognizable text. The skills involved in writing are highly complex. L2 learners have to pay attention to higher level skills of planning and organizing as well as lower level skills of spelling, punctuation, word choice, and so on (Poynton ,1996). The difficulty becomes even more highlighted if their language proficiency is weak (Richards, 2002). According to a broad literature review by the author of this paper, one important strategy for improving EFL writers can be using the techniques of pair work with their related strategies in classroom contexts. By working in pairs, you gain experience and understanding about how tasks are often undertaken in the workshops. The successful completion of a group assignment usually means that you have acquired many very important skills, particularly communication, analytical and interpersonal skills, which are highly valued by the instructors. The capacity to listen, question, persuade, respect the opinions of others, help, share and participate is of lifelong value. Working with others also allows for the assignments to be broken into smaller tasks and the workload to be distributed evenly. By working together, students are able to bounce ideas off each other and learn from each other as well. Members can contribute different skills and thus the group can achieve more than individual members could on their own. As a result, this study will endeavor to explore some strategies of pair work and their effects on the writing skills of the learners.
2-1 قسمت مکانیکی دستگاه 20 ژول 47
2-2 سیستم تخلیه و دمش گاز 49
2-3 سیستم الکتریکی دستگاه 50
2-4 نصب و راه اندازی و آزمایشات اولیه 57
3- پایش پرتوی 61
62
مراجع : 66
فهرست شکل ها
شکل 1-1 ) نمای شماتیک دو دستگاه پلاسمای کانونی 3
شکل 1-2) دو نمونه از تصاویر مربوط به کاربرد پلاسمای کانونی 5
شکل1-3)طرحی از پلاسمای کانونی و مدار مربوط به آن 7
شکل 1-5) نمایی از دستگاه نانوفوکوس 15
شکل 1-6) تصویر بیرونی دستگاه نانوفوکوس 16
شکل 1-7) 17
شکل 1-8) سیگنال های الکتریکی مربوط به ولتاژ، مشتق جریان و جریان 18
شکل 1-9 19
شکل 2-1) بلوک دیاگرام کلی طراحی دستگاه های پلاسمای کانونی 28
شکل 2-2) تصویری از بالا از دستگاه 29
شکل 2-3) میله آند همراه با عایق دور آن و لایه تفلون جدا کننده 32
شکل 2-4) برشی عمودی از دستگاه 35
شکل3-1) دستگاه پلاسمای کانونی کوچک 20 ژول که بر روی میز استیل دو طبقه نصب شده است. 46
شکل 3-2) اندازه های قسمت های مختلف دستگاه بر حسب میلی متر 48
شکل 3-3) سیستم کلی دستگاه 20 ژول 50
شکل3-4) نمای تابلو فرمان 52
شکل 3-5) شمای دستگاه کنترل الکترونیکی 54
شکل 3-6) بلوک دیاگرام کلی دستگاه 55
شکل 3-7) شمای کلی از طرح دستگاه پلاسمای کانونی 20 ژول 56
شکل3-8) نمونه ای از سیگنال مشتق جریان 58
شکل 3-9) نمونه ای ازسیگنال مشتق جریان 59
شکل 3-10) نمونه ای ازسیگنال جریان 59
شکل 3-11) تغییرات فرکانس تخلیه با فشار در ولتاز تخلیه 16 کیلو ولت 60
شکل 3-12) آرایش TLDهای نصب شده در اطراف دستگاه20 ژول 61
فهرست جدول ها
جدول1-1مشخصات دستگاه های پلاسمای كانونی موجود در مرکزCCHEN 20
جدول 2-1) مشخصات الکتریکی چند دستگاه پلاسمای کانونی 24
جدول3-1) اسامی برخی از وسایل موجود در آزمایشگاه پلاسمای کانونی کوچک در پژوهشکده فیزیک پلاسما 43
جدول 3-2) مشخصات دستگاه پلاسمای کانونی 20 ژول 47
فصل اول
عملکرد
پلاسمای کانونی
1-
1-1 دستگاه پلاسمای کانونی:
پلاسمای کانونی دستگاهی از خانواده Z-پینچهای دینامیک است. این دستگاه از دو الکترود هم محور تشکیل می شود که در پایین به وسیله یک عایق از هم جدا می شوند و الکترود بیرونی نقش کاتد و الکترود داخلی نقش آند را بازی می کندو فضایبین آن ها را گازی با فشار پایین پر کرده است.]2و1[
الکترود ها معمولا از جنس مس یا فولاد ضد زنگ ساخته می شوند. جنس عایق در این دستگاه ها ممکن است، چینی، سرامیک، یا تفلون باشد.در این دستگاهاعمال یک ولتاژ بالا به شکل پالسی بیناین دو الکترود هم محور سبب وقوع تخلیه الکتریکی بین دو الکترود میشود که در نتیجه آنیک ستون پلاسمای داغ(با دمای در حدود چند کیلو الکترون ولت)، چگال (در حدود 3-cm1019 -1018) وبا عمر کوتاه (درحدودns200-50) بر روی محور الکترود داخلی تولید میگردد.
این دستگاه در دهه 1960 میلادی به طور مستقل توسط فیلیپوف در شوروی و مدر در ایالات متحده آمریکا به دو مدل متفاوت طراحی و ساخته شد که به نام مخترعینشان نامیده می شوند. تفاوت این دو مدل در نسبت طول الکترود داخلی(L)به قطرآن(D) است.درنوع فیلیپوف 1 (در حدود 2/0 یا کمتر) و در نوع مدر 1 (در حدود 5 یا بیشتر) است(شکل 1-1)]2و1[
این اختلاف منجر به تفاوت هایی در فرآیندهای فیزیکی به ویژه در مرحله اول تخلیه می شود، اما در نهایت شاهد نتایج مشابهی در هر دو نوع هستیم. یعنی تشکیل پلاسمایی داغ و چگال با مشخصات ذکر شده در پاراگراف بالا، که منبعی غنی از انواع مختلف تابش های نوترونی، الکترومغناطیسی، الکترونی، پرتو ایکس نرم و سخت و انواع پدیده های پلاسمایی است.]3[
همچنین دستگاههای پلاسمای کانونی ترکیبی (هیبرید) با نسبت های2-1 نیز ساخته شده اند.]5و4[
پلاسمای کانونی ماشینی ارزان و کارآمد برای مطالعه امواج ضربه، پدیده پینچ و کانونی شدن، ناپایداریهای مختلف پلاسما و پدیده های متعدد دیگری است که در آن پلاسما می تواند تا شرایط گداخت گرم شده و مقادیر قابل ملاحظه ای پرتو ایکس نرم و سخت، انواع یون های پرانرژی، پرتوهای الکترون نسبیتی و در صورتی که گاز به کار رفته حاوی دوتریم باشد،نوترون های حاصل از گداخت هسته ای گسیل نماید]6[.
شکل 1-1 ) نمای شماتیک دو دستگاه پلاسمای کانونی
[1]Plasma Focus
[2] Z-Pinch
[3]Filipov
[4]Mather
