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43 - Computational linguistics
- from Part II - Language processing
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- By Masayuki Asahara, Assistant Professor in Information Science, Nara Institute of Science and Technology, Yasuharu Den, Associate Professor in Cognitive and Information Sciences, Chiba University, Yuji Matsumoto, Professor in Information Science, Nara Institute of Science and Technology
- Edited by Mineharu Nakayama, Ohio State University, Reiko Mazuka, Duke University, North Carolina, Yasuhiro Shirai, Cornell University, New York
- General editor Ping Li, University of Richmond, Virginia
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- Book:
- The Handbook of East Asian Psycholinguistics
- Published online:
- 05 June 2012
- Print publication:
- 31 August 2006, pp 323-332
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Summary
Introduction
Computational linguistics is a research field which investigates computational mechanisms of language comprehension and production, realizing them as computer programs. Researchers in this field have been working on formal descriptions of lexical, syntactic, semantic, and pragmatic knowledge, and algorithms for parsing and generation, which utilize these descriptions as rules for governing the computational process and heuristics for assigning preference among them. In traditional approaches, these rules and heuristics were designed by expert linguists and computational linguists, but in more recent approaches, they are automatically acquired from large language resources such as text/speech corpora and electronic dictionaries and thesauri. In the following sections, we describe language resources for Japanese computational linguistics, tools for retrieving and processing information in them, and how they are used in computational linguistic studies and can be used in psycholinguistic studies.
Text/speech corpora
Text/speech corpora are the most important resources in computational linguistics. It can be said that the progress of research on a particular language depends heavily on how many good corpora are available in that language. Japan has fallen behind the US and European countries in corpus development and maintenance. Before 1990s, researchers at individual institutes developed small-scale corpora, and no leading organization like the LDC (Linguistics Data Consortium) in the US was formed. We had to wait until the mid 1990s before large-scale Japanese corpora became available.
Table summarizes major text/speech corpora of Japanese which are currently, or will be in the near future, available. They are extensively used in computational linguistic studies of Japanese such as development and tuning of automatic morphological analyzers, syntactic parsers, information retrieval, text summarization, and dialog systems.
Contents
- Masayuki Yamane, Tokyo Institute of Technology, Yoshiyuki Asahara, Kyushu University, Japan
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- Book:
- Glasses for Photonics
- Published online:
- 30 July 2009
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- 11 May 2000, pp v-viii
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Index
- Masayuki Yamane, Tokyo Institute of Technology, Yoshiyuki Asahara, Kyushu University, Japan
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- Glasses for Photonics
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- 30 July 2009
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- 11 May 2000, pp 267-271
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2 - Gradient index glass
- Masayuki Yamane, Tokyo Institute of Technology, Yoshiyuki Asahara, Kyushu University, Japan
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- Glasses for Photonics
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- 30 July 2009
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- 11 May 2000, pp 58-81
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Summary
Introduction
In a conventional optical system, the refractive index within each optical component is considered to be homogeneous. In the design of such systems, the curvatures, thickness, and refractive index of each component are varied independently to optimize the performance of a lens system. It is possible, on the other hand, to manufacture lens elements whose index of refraction varies in a continuous way as a function of spatial coordinate. Such materials, which are often said to be GRadient INdex (GRIN) materials, have various advantages for use in both focusing and imaging purposes.
There are three types of refractive index gradients depending upon the type of symmetry [1–3]. The first is the axial gradient (a-GRIN), in which the refractive index varies in a continuous way along the optical axis. These gradients are particularly useful for replacing aspheric surfaces in monochromatic systems, e.g. in collimators for laser beams.
The second type of gradient is the radial gradient (r-GRIN). The refractive index n in this case varies perpendicular to and continuously outward from the optical axis. This type of gradient index lens, often called a GRIN rod lens when the diameter is small, exhibits the property that light propagating parallel to the optical axis of symmetry can be focused periodically if n varies as an appropriate function of its radial distance from the axis of symmetry. The main applications of gradient index materials in use today are based only on this type of gradient.
1 - Glass properties
- Masayuki Yamane, Tokyo Institute of Technology, Yoshiyuki Asahara, Kyushu University, Japan
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- Glasses for Photonics
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- 30 July 2009
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- 11 May 2000, pp 1-57
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Summary
Introduction
Glass can be made with excellent homogeneity in a variety of forms and sizes, from small fibers to meter-sized pieces. Furthermore, glass can be doped with rare earth ions and microcrystallites and a wide range of properties can be chosen to meet the needs of various applications. These advantages over crystalline materials are based on the unique structural and thermodynamic features of glass materials. Before discussing the special properties of glass, the fundamentals of glass materials are given in this chapter.
Features of glass as an industrial material
Structural features
Atomic arrangement
A glass is defined in ASTM [1] as ‘an inorganic product of fusion which has been cooled to a rigid condition without crystallization’. According to this definition, a glass is a noncrystalline material obtained by a melt-quenching process. Nowadays, noncrystalline materials that can not be distinguished from melt-quenched glasses of the same composition are obtainable by using various techniques such as chemical vapor deposition, sol-gel process, etc. Therefore, most glass scientists regard the term ‘glass’ as covering ‘all noncrystalline solids that show a glass transition’ regardless of their preparation method.
The words ‘noncrystalline solids’ and ‘glass transition’ suggest that a glass cannot be classified either in the category of crystalline materials such as quartz, sapphire, etc. or in the category of liquid. The atomic arrangement of a glass is different from those of crystalline materials and lacks long-range regularity, as schematically shown in Fig. 1.1 [2].
3 - Laser glass
- Masayuki Yamane, Tokyo Institute of Technology, Yoshiyuki Asahara, Kyushu University, Japan
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- Glasses for Photonics
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- 30 July 2009
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- 11 May 2000, pp 82-158
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Summary
Introduction
The laser is a source of monochromatic radiation of high intensity, coherence, and directionality, in the ultraviolet, visible and infrared optical region. The many and varied applications of lasers include laboratory use, research (optical spectroscopy, holography, laser fusion), materials-processing (cutting, scribing, drilling, welding, abrasion), communications, information processing, military (range finders, target designators), and medical use [1]. Glass plays many varied roles in rare-earth laser systems, because glass can be made with uniformly distributed rare-earth concentrations and has great potential as a laser host medium. In addition, rare-earth doped fibers have received growing attention recently. They could have many uses as amplifiers in optical communication systems and as optical sources. Glass waveguide lasers are another interesting subject for the development of compact laser sources and amplifier devices.
This chapter concentrates on laser glass materials containing rare-earth ions, thus excluding crystalline laser materials. To provide an understanding of the properties of laser glass, the chapter begins with a brief summary of the fundamental physics of lasers in Section 3.1. To explain the characteristics of bulk laser glass, representative laser parameters and their host dependences are summarized briefly in Section 3.2. The recent developments of fiber lasers (in Section 3.3) and glass waveguide lasers (in Section 3.4) are reviewed.
Fundamentals of laser physics
Stimulated emission [2, 3]
It is well known that atoms, ions and molecules can exist in certain stationary states, each of which is characterized by levels of the atomic system called quantum numbers.
4 - Nonlinear optical glass
- Masayuki Yamane, Tokyo Institute of Technology, Yoshiyuki Asahara, Kyushu University, Japan
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- Glasses for Photonics
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- 30 July 2009
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- 11 May 2000, pp 159-241
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Summary
Introduction
There has been considerable activity in the development of photonics devices such as all-optical switches and modulators for many applications in optical communication and optical computer systems. The success of such devices depends on the development of nonlinear optical materials. Various types of glass are very attractive materials for these applications, because of their strong nonlinearities and their relatively fast response time, and in addition, they are mechanically durable and are compatible with fiber and waveguide fabrication procedures. They are also very attractive from the basic viewpoint of understanding the physical mechanisms of optical nonlinearities in materials. Generally, optical nonlinearities of glass materials can be divided into two principal categories [1, 2]: resonant and nonresonant.
Nonresonant nonlinear glasses range from optical glasses to high-refractive-index glasses such as heavy-metal oxide glasses and chalcogenide glasses, and resonant nonlinear glasses including composite glasses containing semiconductor or metal microcrystallites. These have been the subject of investigation, although further developments in photonics switching and information processing will depend critically on the continuing development of improved glass materials. In this chapter, we first give a brief survey of the fundamentals of nonlinear optics and their applications, and then describe the physical mechanisms, the fabrication, and the characteristics of nonlinear glass materials and several examples of their application.
5 - Magneto-optical glass
- Masayuki Yamane, Tokyo Institute of Technology, Yoshiyuki Asahara, Kyushu University, Japan
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- Glasses for Photonics
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- 30 July 2009
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- 11 May 2000, pp 242-266
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Introduction
The research into materials with a high magneto-optical effect is always an interesting matter because these materials are extensively used as magnetic field sensors and optical isolators. Glass materials are of interest for these applications because they are transparent in the visible and near infrared spectral region and can be readily formed into complex shapes such as optical fibers. One of the magneto-optical effects, the Faraday effect in glass is a well-known phenomenon. The primary trend of the studies is, therefore, to develop and produce glass compositions having a large specific Faraday rotation and low absorption in the visible and near infrared regions.
Generally the Verdet constant, a measure of the Faraday rotation of the materials, is considered to be of two types depending upon the ion or ions that are incorporated in glass: diamagnetic or paramagnetic. Most normal network former and modifier ions in glass would give rise to diamagnetic rotation. The rare-earth and transition ions are examples of paramagnetic ions. Diamagnetic glasses generally have small and positive Verdet constants, which are almost independent of temperature, whereas paramagnetic glasses usually have large and negative Verdet constants, which are generally inversely proportional to temperature. The Faraday effects of various glasses are presented and discussed in this chapter.
Frontmatter
- Masayuki Yamane, Tokyo Institute of Technology, Yoshiyuki Asahara, Kyushu University, Japan
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- Book:
- Glasses for Photonics
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- 30 July 2009
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- 11 May 2000, pp i-iv
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Glasses for Photonics
- Masayuki Yamane, Yoshiyuki Asahara
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- Published online:
- 30 July 2009
- Print publication:
- 11 May 2000
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This book is an introduction to recent progress in the development and application of glass with special photonics properties. Glass has a number of structural and practical advantages over crystalline materials, including excellent homogeneity, variety of form and size, and the potential for doping with a variety of dopant materials. Glasses with photonic properties have great potential and are expected to play a significant role in the next generation of multimedia systems. Fundamentals of glass materials are explained in the first chapter, and the book then proceeds to a discussion of gradient index glass, laser glasses, nonlinear optical glasses and magneto-optical glasses. Beginning with the basic theory, the book discusses actual problems, performance and applications of glasses. The book will be of value to graduate students, researchers and professional engineers working in materials science, chemistry and physics with an interest in photonics and glass with special properties.
Preface
- Masayuki Yamane, Tokyo Institute of Technology, Yoshiyuki Asahara, Kyushu University, Japan
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- Book:
- Glasses for Photonics
- Published online:
- 30 July 2009
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- 11 May 2000, pp ix-x
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Summary
Glass can be doped with rare earth ions, high refractive index ions and microcrystallites which give it great potential as a photonic medium. The practical advances of these types of glass are expected to have significant roles in multimedia systems in the next generation.
This book is thus an introduction to the theory and recent progress in the technology of glass with special photonic properties, for graduate students, practising engineers and scientists, who wish to supplement their theoretical and practical knowledge of this field with the material science aspects. Hence, this book is intended to be comprehensive enough for an introductory course and be easily readable by practising engineers who are interested in and desire an overview of this field.
Although this book is designed with the purpose of providing a fundamental review of materials with special optical properties, another goal is to provide practical and useful information about developments over the last 10 years in this rapidly changing field. It is impossible, however, to describe all the innovations which have been developed over the last 10 years and omissions are inevitable in a compilation of the size of this book. References to work with respect to the range of glasses examined in this book are given as references to the tables in each chapter. Readers interested in specific data will be able to refer to the original literature. Even so, there remains the possibility of serious omission, for which we beg, in advance, the reader's pardon.