No description available.

A stable dual-wavelength Tm:Ho co-doped fiber laser operating above 2 mu m based on cascaded single mode-multimode-single mode (SMS) all-fiber structures has been proposed and experimentally demonstrated for the first time.

by Cheong Lik-ming. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1995. / Includes bibliographical references. / Abstract / Acknowledgments / Chapter Chapter I --- Introduction --- p.1 / Chapter 1.1 --- Definitions of Optical Solitons --- p.1 / Chapter 1.2 --- A Brief History of Optical Solitons --- p.2 / Chapter 1.3 --- Generation of Optical Solitons --- p.4 / Chapter 1.4 --- About the Thesis --- p.6 / References --- p.8 / Chapter Chapter II --- General Theory of Optical Solitons --- p.10 / Chapter 2.1 --- Propagation Equation of Optical Solitons --- p.10 / Chapter 2.2 --- Solving of the NLSE --- p.16 / Chapter 2.2.1 --- Inverse Scattering Transform --- p.17 / Chapter 2.2.2 --- Split-Step Fourier Method --- p.20 / Chapter 2.3 --- Fundamental Solitons --- p.22 / Chapter 2.4 --- Higher Order Solitons --- p.25 / References --- p.27 / Chapter Chapter III --- Modeling of Soliton Generation Systems Part I: Gain Switching and Spectral Windowing --- p.29 / Chapter 3.1 --- General Descriptions --- p.29 / Chapter 3.2 --- About the Gain Switching and Spectral Windowing Method --- p.30 / Chapter 3.3 --- Gain Switching of Semiconductor Laser Diodes --- p.30 / Chapter 3.3.1 --- Rate Equations of Semiconductor Laser Diodes --- p.31 / Chapter 3.3.2 --- Analysis of Gain Switching Pulses --- p.35 / Chapter 3.3.3 --- Propagation of Gain Switching Pulses in Optical Fibers --- p.42 / Chapter 3.4 --- Spectral Windowing --- p.47 / Chapter 3.5 --- Erbium-Doped Fiber Amplifier --- p.50 / Chapter 3.5.1 --- Theoretical Model of Erbium-Doped Fiber Amplifier --- p.51 / Chapter 3.5.2 --- Pulse Evolutions in Erbium-Doped Fiber Amplifier --- p.54 / Chapter 3.5.3 --- Analysis of Amplification for Gain Switching Pulses --- p.55 / Chapter 3.6 --- Optimal Condition for the Gain Switching and Spectral Windowing Method --- p.60 / References --- p.61 / Chapter Chapter IV --- Modeling of Soliton Generation Systems Part II: Fiber Ring Laser --- p.64 / Chapter 4.1 --- General Descriptions --- p.64 / Chapter 4.2 --- About the Fiber Ring Laser Method --- p.65 / Chapter 4.3 --- Principles of the Fiber Ring Laser --- p.66 / Chapter 4.4 --- Mathematical Model of the Fiber Ring Laser --- p.67 / Chapter 4.4.1 --- Cross Phase Modulation --- p.68 / Chapter 4.4.2 --- Evolution Equations in Ordinary Optical Fibers --- p.70 / Chapter 4.4.3 --- Evolution Equations in Erbium-Doped Fibers --- p.71 / Chapter 4.4.4 --- Description of Polarization Controllers --- p.72 / Chapter 4.5 --- Analysis of Optical Pulses Generated from Fiber Ring Lasers --- p.74 / Chapter 4.5.1 --- Properties of the Mode Locking Process --- p.74 / Chapter 4.5.2 --- Pulse Width Analysis --- p.79 / Chapter 4.5.3 --- Constant Pulse Width Analysis --- p.88 / Chapter 4.5.4 --- Self-Starting Process --- p.91 / Chapter 4.6 --- Stimulated Raman Scattering in Fiber Ring Lasers --- p.94 / Chapter 4.6.1 --- Mathematical Descriptions of Stimulated Raman Scattering --- p.95 / Chapter 4.6.2 --- Effects of Stimulated Raman Scattering on Fiber Ring Lasers --- p.98 / Chapter 4.7 --- Comparison of the Two Methods --- p.100 / References --- p.102 / Chapter Chapter V --- Experimental Investigation of Fiber Ring Lasers --- p.105 / Chapter 5.1 --- Experimental Setup --- p.105 / Chapter 5.2 --- Experimental Results --- p.106 / Chapter 5.3 --- Discussions --- p.117 / References --- p.122 / Chapter Chapter VI --- Conclusion --- p.123 / Chapter Chapter VII --- Future Extensions --- p.127 / Appendix I Solving the NLSE by the Inverse Scattering Transform --- p.A1 / Appendix II Solving the NLSE by the Split-Step Fourier Method --- p.A9 / Appendix III Parameter Listing --- p.A12

by Kwok Kin Wing. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1990. / Bibliography: leaves 126-128. / Acknowledgement / Abstract / Chapter 1. --- Introduction --- p.1 / Chapter 1.1 --- General Background --- p.1 / Chapter 1.2 --- Previous Studies on Injection Moulded Short Fibre Reinforced Composites --- p.4 / Chapter 1.3 --- Scope of the Present Work --- p.6 / Chapter 2. --- Theory --- p.8 / Chapter 2.1 --- Elastic Moduli of Injection Moulded Short Fibre Reinforced Composites --- p.8 / Chapter 2.1.1 --- Elastic Properties of an Anisotropic Solid --- p.10 / Chapter 2.1.2 --- Elastic Moduli of a Unidirectional Lamina --- p.12 / Chapter 2.1.3 --- Laminate Theory for the Elastic Moduli of Short Fibre Reinforced Composites --- p.21 / Chapter 2.1.4 --- Out-of-Plane Elastic Moduli of Injection Moulded Short Fibre Reinforced Composites --- p.31 / Chapter 2.2 --- Thermal Conductivity of Injection Moulded Short Fibre Reinforced Composites --- p.32 / Chapter 2.2.1 --- Thermal Conductivity of a Unidirectional Lamina --- p.32 / Chapter 2.2.2 --- Laminate Theory for the Thermal Conductivity of a Multidirectional Laminate --- p.35 / Chapter 2.2.3 --- In-plane Thermal Conductivity of Injection Moulded Short Fibre Reinforced Composites --- p.36 / Chapter 3. --- Expeirimental Techniques --- p.37 / Chapter 3.1 --- Determination of the Elastic Moduli by Ultrasonic Techniques --- p.37 / Chapter 3.1.1 --- Theory of Measurement --- p.37 / Chapter 3.1.2 --- Ultrasonic Measurement --- p.40 / Chapter 3.2 --- Determination of the Thermal Diffusivity by Laser Flash Radiometry --- p.49 / Chapter 3.2.1 --- Theory of Measurement --- p.49 / Chapter 3.2.2 --- Thermal Diffusivity Measurement --- p.51 / Chapter 3.3 --- Fibre Orientation and Length Measurements --- p.57 / Chapter 3.4 --- Density Measurement --- p.58 / Chapter 4 . --- Results and Discussion --- p.60 / Chapter 4.1 --- Composites and Polymers Studied in the Present Work --- p.60 / Chapter 4.2 --- Elastic Moduli and Thermal Conductivity of the Fibres and Polymer Matrices --- p.60 / Chapter 4.3 --- Fibre Orientation and Aspect Ratio --- p.67 / Chapter 4.4 --- Elastic Moduli of the Composites --- p.74 / Chapter 4.4.1 --- General Features --- p.74 / Chapter 4.4.2 --- Comparison between Theory and Experiment --- p.77 / Chapter 4.5 --- Thermal Conductivity of the Composites --- p.90 / Chapter 4.5.1 --- Thickness and Width Dependence of the Thermal Diffusivity of the Composites --- p.90 / Chapter 4.5.2 --- Comparison between Theory and Experiment --- p.104 / Chapter 5. --- Conclusion --- p.113 / Chapter Appendix A --- Tables of Data --- p.115 / References --- p.126

The aim of the study was to find out the relationship between the DP and the tensile properties of different regenerated cellulose fibers. During the process to make regenerated cellulose fibers from wood, the reduction in DP of cellulose is a necessary process to enable fiber extrusion. The reduction of the DP is usually from 1000 to 350 (Coley 1953). The reduction in DP is necessary, first to make the cellulose soluble, and then further decrease in DP is required to control the viscosity of the solution to minimize the mechanical difficulties during processing faced. It is a fact that the reduction in DP is a compromise which is necessary, as reduction in DP means reduction in tensile properties of the fiber produced. The reduction in DP is optimized to make the process both processing and the final product more feasible. The relation in DP and the strength of the fibers is rather obvious i.e. higher the DP higher the tensile strength, but researchers have different views regarding the relationship. By the experiments performed by us we tried to come to a conclusion regarding the difference in opinions. Different types of regenerated cellulose fibers were collected from various sources. Both wet and dry tenacities of 19 different viscose, bamboo viscose, kupro viscose, modal and Tencel fibers were determined. The fiber linear density was also measured, but for some samples we had to take the fiber density value as provided by the manufacturer, due to the limitation of the instrument regarding the fiber length and low fiber linear density. Then out of all the samples 10 were selected (based on our and company’s interest). SEC analysis was used to determine the DP of the samples. These tests were not carried out by us but by MoRe Research. The results of both the analysis were gathered, analyzed and commented upon. / Program: Master Programme in Textile Technology

Fiber Bragg gratings have become an important element in the fields of telecommunications and fiber optical sensing. Their small size, light weight and high tunability have made them ideal for many unique applications. In this paper the fabrication of these devices is investigated. Following a review of current literature and a discussion of the mechanisms underlying the photosensitivity of optical fibers, a new technique for writing fiber Bragg gratings is presented. This technique uses a diode-pumped Nd:YAG laser operating at 266 nm with pulse energies up to 137 ��J per pulse to write high quality gratings in standard optical fiber. This technique allows for the writing of variable wavelength gratings using a standard diffractive optical element (phase mask). The new technique has much lower setup and laser stability requirements than the conventional methods of writing variable wavelength fiber Bragg gratings. Furthermore, it is found to be very tunable and extremely robust, allowing for extended writing times. A preliminary study of the time evolution of the writing process is also presented. It is evident that the process of grating inscription is very complicated and is not always adequately described by current models. In addition. it appears that the process is strongly dependent upon pulse energy and is accelerated by simultaneous heating of the fiber with a C0��� laser and by heating due to the writing laser. A brief study of the thermal stability of different gratings is then given to determine some of the thermal stability properties of the fiber Bragg gratings written at OSU. / Graduation date: 2001

In response to the energy needs of modern society and emerging ecological concerns, the pursuit of novel, low-cost, and environmentally friendly energy conversion and storage systems has raised significant interest. Among various energy conversion and storage systems, fuel cells have become a primary research focus since they convert chemical energy directly into electrical energy with high efficiency and low pollutant emissions. For example, direct methanol fuel cells (DMFCs), which supply the electrical energy by converting methanol to energy, are an ideal fuel cell system for applications in electric vehicles and electronic portable devices due to their relatively quick start-up, rapid response to catalyst loading, and low operating temperature. However, the wide commercial use of DMFCs in advanced hybrid electric vehicles and electronic portable devices is hampered by their high cost, poor durability, and relatively low energy and power densities. In order to address these problems, their research focuses on the development of highly active electrode catalysts coupled with a suitable electrode structure for the oxidation of methanol at the anode and the reduction of oxygen at the cathode to attain high efficiency of DMFCs, and subsequently lowering the cost. In this dissertation, the fabrication of novel platinum and platinum alloy nanoparticle-loaded carbon nanofibers (CNFs) for use as electrodes in DMFCs is demonstrated through electrospinning, carbonization, and deposition. The resulting CNF-based electrodes possess the properties of high electroactive surface area, good catalytic abilities towards the oxidation of methanol and the reduction of oxygen, and great long-time stability. As a result, DMFCs using these CNFs-supported platinum and platinum alloy nanoparticles as electrodes offer many advantages, such as improved electrocatalytic abilities, long-term stability, easy fabrication, low cost, and environmental benignity. Therefore, this new technology opens up new opportunities to develop high-performance electrode materials in the future for high-performance DMFCs, which are one of the promising power sources for consumer devices and electric vehicles, and play a critical role in solving the worldwide critical energy issue.

For nearly two decades inclusion compounds (ICs) have been formed by threading polymer chains into the cyclic starches, cyclodextrins (CDs). Non-covalently bonded crystalline ICs have been formed by threading CDs, onto guest nylon-6 (N6) chains. When excess N6 is employed, non-stoichiometric (n-s)-N6-CD-ICs with partially uncovered and dangling N6 chains result. We have been studying the constrained crystallization of the N6 chains dangling from (n-s)-N6-CD-ICs in comparison with bulk N6 samples, as a function of N6 molecular weights, lengths of uncovered N6 chains, and the CD host used. While the crystalline CD lattice is stable to ~ 300° C, the uncovered and dangling, yet constrained, N6 chains may crystallize below, or be molten above ~225° C. In the IC channels formed with host α- and γ-CDs containing 6 and 8 glucose units, respectively, single and pairs of side-by-side N6 chains can be threaded and included. In the α-CD-ICs the ~ 0.5nm channels are separated by ~ 1.4nm, while in γ-CD-ICs the ~ 1nm channels are ~ 1.7 nm apart, with each γ-CD channel including two N6 chains. The constrained dangling chains in the dense (n-s)-N6-CD-IC brushes crystallize faster and to a greater extent than those in bulk N6 melts, and this behavior is enhanced as the molecular weights/chain lengths of N6 are increased. Furthermore, when added at low concentrations (n-s)-N6-CD-ICs serve as effective nucleating agents for the bulk crystallization of N6 from the melt. Because of the biodegradable/bioabsorbable nature of CDs, (n-s)-polymer-CD-ICs can provide environmentally favorable, non-toxic nucleants for enhancing the melt crystallization of polymers and improving their properties.

Tortuosity factor is often used to characterize the structure of the pore volume in fibrous porous media. This work involves the determination of tortuosity using computational fluid dynamic (CFD) simulation and particle tracking analysis. A new method has been adopted to generate 3-D geometry for modeling fibrous porous structures using ANSYS® Parametric Design Language (APDL). Computation fluid dynamics has been used to simulate permeability of modeled 3-D fiberweb structures. The simulated permeability results are in good agreement with the models proposed by other authors. The experimental results were found to be slightly higher compared to simulated results and existing models due to the layered configuration of the samples. Permeability is found to be significantly influenced by fiber diameter, and porosity as well as fiberweb thickness. The relationship between air permeability and fiberweb thickness has been used to develop an indirect method for determination of tortuosity factor. Tortuosity factor has also been determined using a more direct method involving CFD simulation and Particle Tracking analysis. Different models established using the direct and indirect methods of determination show that tortuosity is significantly influenced by porosity, fiber diameter and fiberweb thickness, whereas the models available in the literature express tortuosity as a function of porosity only.

It is a well known fact that the quality of a fabric is tied to the non-uniformity of fabric properties. Although methods have been suggested to measure certain physical properties of fabrics (mass, handle, strength, comfort, permeability), there has been no single method that is industrially accepted to characterize and quantify distribution of some of these fabric properties or non-uniformities. Therefore, the purpose of this research was to investigate and suggest a new method to fill this need. During this research, data about fabric properties were obtained either directly from images of fabric appearances or indirectly from on-line measurements of yarn diameters. The yarn diameters captured through a line-scan camera were mapped into a 2-D fabric matrix by assigning each point of the yarn to a specific location (x, y) within the 2-D fabric matrix. The gray-scale image of a 2-D fabric matrix was called a virtual fabric and provided the basic information on the uniformity of the fabric property. Variance-area curves were developed to characterize and quantify non-uniformity of actual and virtual fabrics in two dimensions. Certain irregularity features such as vertical and horizontal streaks and random cloudiness produced variance-area curves that are dependent on the shape of the unit area. Thus the difference between these curves became a new way to measure isotropy features of fabric properties. Theoretical relationships between yarns and their virtual fabrics were derived using only the internal correlation information of the given underlying yarns