Einleitung: Steady-State- Muster-ERGs (PERGs) werden in der Glaukomfrühdiagnostik angewandt. Da die transienten PERG-Komponenten N35, P50 und N95 unter schnellen Reizbedingungen nicht zu erkennen sind, können bisher keine Aussagen über die Beteiligung einzelner Retinaschichten an der Reizantwort gemacht werden. Mit der Deconvolution-Methode (CLAD) wurden 2004 akustisch evozierte transiente Antworten aus hochfrequenten Messungen entfaltet. In dieser Arbeit wird CLAD beim PERG validiert um herauszufinden, ob bei Messungen mit hohen Reizfrequenzen deutliche transiente Antworten entfaltet werden. Methodik: Es wurden 3 Reizbedingungen mit nicht-isochronen Stimuli der mittleren Frequenz 16,7 rps verglichen. Der Abstand zwischen 2 Stimuli variierte zwischen 15 und 105 ms, 30 und 90 ms oder 45 und 75 ms, der mittlere Abstand betrug jedoch immer 60 ms. Als Referenz wurden konventionelle transiente (1,4 rps) und Steady-State-Messungen (16,7 rps) durchgeführt. Um sie zu validieren, wurden in einem zweiten Schritt aus den transienten CLAD-Steady-State-Antworten synthetisiert und diese mit der Steady-State-Referenzmessung verglichen. Ergebnisse: Die große Übereinstimmung der synthetisierten Steady-State-Antworten mit der Referenzmessung im Bezug auf Amplitude und –Kurvenform bestätigte, dass die entfalteten transienten Antworten „trotz“ Abweichungen von konventionellen PERG-Antworten plausibel sind. Allerdings hatte der konkrete Stimulusabstand Einfluss auf die PERG-Antwort: die Amplituden der 3 CLAD-Reizbedingungen wichen signifikant voneinander ab. Diskussion: Diese Studie zeigte, dass durch CLAD transiente Reizantworten aus Messungen hoher Frequenz gewonnen werden können. Ob der Einsatz von CLAD Vorteile in der Glaukomfrühdiagnostik erbringt und der exakte retinale Ursprung der Antwortkomponenten ist in künftigen Studien zu validieren. Durch CLAD könnte es in Zukunft möglich werden, auf elektrophysiologischem Wege den Beitrag einzelner Retinaschichten bei Retinapathologien genauer aufzuzeigen.

This study examines the static recovery behaviour of a clad aluminum alloy manufactured by Novelis FusionTM technology after 72% cold rolling. The clad alloy system studied consisted of a core AA6XXX alloy clad on one side with AA3003. The Recovery at the inter-alloy region is compared with the recovery of core AA6XXX at the same depth from the rolling surface. Sample coupons from the inter-alloy region and core AA6XXX were heated isochronally and isothermally, at different temperatures and times, respectively, to probe the recovery kinetics of the X-ray peak broadening, X-ray macro-texture and micro-hardness from the cold rolled state. The recovery of the {220} and {311} X-ray line profiles were observed between the anneals. A pseudo-Voigt fit function was fit to the profile to obtain the defect related information. Recovery in the peak broadening began by 100°C and correlated to a decrease in the hardness. Sharpening of X-ray profiles during recovery is attributed to the microstructural evolution resulting from preferred release of the stored energy due to dislocation rearrangement and annihilation. Kinetic behaviour of the recovery is measured by observing the evolution of X-ray profiles and hardness during isothermal annealing at two different temperatures. Recovery behaviour in the inter-alloy region is measured to be relatively slower than the recovery of the core AA6XXX after same macroscopic pre-strain. Activation energy for recovery is calculated from the isothermal data to deduce a recovery mechanism. The activation energy calculated in core AA6XXX, 1.7eV, is close to the activation energy value for diffusion of Mg in Al (1.3-1.7eV). This indicates a possible role of Mg diffusion in the recovery of AA6XXX. The relatively higher activation energy for recovery of 2.9eV measured in the inter-alloy region may be due to pinning by nano-scale Al-Mn precipitates. The X-ray broadening data is deconvoluted to determine the apparent dislocation content using a modified Williamson-Hall model. The dislocation density measured in the AA6XXX and inter-alloy regions in the deformed and recovered conditions indicates that dislocation density is a suitable parameter that represents the stored energy that drives subsequent structural evolution during recovery. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2011-09-30 19:02:44.02

No description available.

A generalized analysis of multiple-clad cylindrical dielectric structures with step-index profiles is presented. This analysis yields unified expressions for fields, dispersion equation and cutoff conditions for weakly guiding optical fibers with step-index but otherwise arbitrary profiles. The formulation focuses on triple-clad fibers, but can accommodate single and double-clad fibers as special limiting cases. Using the generalized solutions, transmission properties of several types of specialty fibers for broadband applications, including dispersion-shifted, dispersion-flattened, and dispersion compensating fibers, are studied. Improved designs for dispersion-shifted and dispersion compensating fibers are achieved. Fiber parameters and material compositions for the improved designs are provided. The proposed design for the dispersion-shifted fiber yields zero second-order as well as third-order dispersion at the 1.55 micrometer wavelength. The dispersion compensating fiber proposed here provides a large negative dispersion of about -400 ps/nm.km at the 1.55 micrometer wavelength for the fundamental mode. Numerical results for dispersion characteristics, cutoff wavelengths, and radial field distributions are provided. / Master of Science

The need for lighter weight vehicles to improve fuel efficiency is becoming increasingly imperative. Sheet magnesium alloys offer the potential as a light weight material for use in the transportation industry due to their high specific strength and stiffness. In fact, magnesium alloys have the highest strength-to-weight ratio of all the common structural metals. Though the demand for light weight materials is present and sheet magnesium is available, the use of these materials in automotive applications has been rather limited due to high production costs and poor corrosion performance and formability. A promising process to produce wrought magnesium sheet in a more cost effective manner is Twin Roll Casting (TRC). In addition, enhanced corrosion resistance and ductility may be realized in these sheet alloys with the possible introduction of a clad layer during the TRC process thereby producing a laminate sheet where the surface properties are different from the core. The focus of this research was to investigate the potential of cladding magnesium alloy AZ31 material during the TRC process. As part of this research, a thermal fluid mathematical model of the TRC process was developed, which was then further refined to include the addition of a clad layer during the process. The TRC model was validated through experimental work conducted at the Pohang Institute of Science and Technology (POSTECH University), where TRC experiments of AZ31 were conducted under various casting conditions. The as-cast microstructure of the AZ31 sheets were characterized and measurements of the secondary dendrite arm spacing (SDAS) made at the mid-region were compared to predicted microstructures from the TRC model based on solidification history. The predicted SDAS matched with the measured values, thus, validating the model. Using the validated TRC model the feasibility of adding a clad layer was assessed and various simulations were conducted to observe the effects of cast speed, cast thickness, and clad material on the thermal history and temperature profile in both the clad and core domains. The material properties and clad thickness did not seem to impact the temperature profiles significantly, while the cast speed and initial temperature dictated whether or not the cast would be successful. Using these operational parameters a process window was created (based on the CANMET facility) to illustrate the feasibility of casting and cladding during TRC. This window is beneficial for future experimentation and understanding the effects of these casting parameters.

The topic of this thesis is solar pump Nd-doped double-clad fiber laser, the main characteristic of this research is we use nature and low pollution source pump unique laser gain medium. By using Neodymium-doped double-clad fiber in form of waveguide structure to replace Neodymium-doped glass, Neodymium-doped yttrium aluminum garnet crystals that have large cross-section area of the volume in the past¡F natural sunlight is used as pumped source in instead of diode laser, pulsed Xenon lamp, Krypton arc lamp¡Ketc. In order to reduce the use of electric power source and decrease the pollution . By using Solar concentration system, we focus average sunlight power density (800W/m2) to very high power density. In application, If lasers are needed in remote locations where sunlight is abundant and other forms of energy sources are scarce, this kind of solar energy usage is not a bad idea.

This study aims to experimentally explore the possibility to join the two pieces of low-carbon steel and Cu-Ni alloy as the cladding material into a thick clad steel plate during a Friction Stir Lap Welding¡]FSLW¡^process without a probe. Two methods are employed to enhance the welding strength. Firstly, a layer of nickel is coated on the low-carbon steel to prevent it from oxidizing during the welding process. Secondly, the surface of the low-carbon steel is knurled to increase the contact area between the welding surfaces. Experimental results show that Ni-coating can effectively prevent the generation of oxidation and improve the welding strength. According to the tensile test using a plate of Cu-Ni alloy with a thickness of 4 mm, the welding strength of the clad steel plate with Ni-coating is about 2.3 times greater than that without Ni-coating. Moreover, according to the impact test, the clad steel plate with Ni-coating can absorb more impact energy than that without Ni-coating. This difference increases with increasing thickness of the plate. It is also found that the welding strength at the center of joints using the Ni-coating is greater than that at the substrate of copper-nickel alloy. For the clad steel plate with knurling, since it is difficult to fill the gap between the patterns of knurling, the increase in the contact area between the welding surfaces has been offset. Hence, the welding strength of the clad steel plate with knurling is less than that with Ni-coating.

No description available.

Clad metals are extensively used for their multi-functionality and their optimal combination of quality and cost. Roll bonding is an effective and economic processing approach to making clad metals. This dissertation presents an experimental investigation of the roll cladding process as well as thermo-mechanical modeling of mechanism for roll bonding of clad metals. The objectives of this research are to investigate the bonding mechanism of dissimilar metals in a warm rolling process and to advance the knowledge of the roll cladding process. To accomplish the objectives, aluminum 1100 sheet (Al 1100) and stainless steel 304 sheet (SST 304) are bonded by warm rolling under controlled conditions. The 180 degrees peel test is used to determine the bonding property of those clad metals. The experimental results show that the rolling thickness reduction and the entry temperature are two major factors of bonding strength. Minimum thickness reduction at a particular entry temperature is required to bond Al 1100 and SST 304. Increasing of either thickness reduction or entry temperature significantly improves the bonding strength between the two metals. X-ray microanalysis is also performed to characterize the diffusion state at the bonding interface. The diffusion coefficients of aluminum and iron are estimated through experimental method. A thermo-mechanical model was developed to describe the rolling plastic deformation of component metal sheets and the diffusion evolution during a roll bonding process of dissimilar metals. The effect of various rolling conditions on the contact area ratio was quantitatively discussed. Finite element simulation of 2-D diffusion under the rolling created boundary conditions was performed. The peel strength during the diffusion evolution was predicted by the integrated roll bonding model. The modeling predictions correspond to the experimental results well. The correspondence validates the effectiveness of the thermo-mechanical roll bonding model. Based on experimental observation, this research presents a bonding mechanism for the roll cladding process of dissimilar metals. The roll bonding model can help optimize rolling parameters for varying bonding strength depending on the demands of the application. It can also provide insights into design and analysis of rolling bonding process of other groups of dissimilar metal sheets.

The need for lighter weight vehicles to improve fuel efficiency is becoming increasingly imperative. Sheet magnesium alloys offer the potential as a light weight material for use in the transportation industry due to their high specific strength and stiffness. In fact, magnesium alloys have the highest strength-to-weight ratio of all the common structural metals. Though the demand for light weight materials is present and sheet magnesium is available, the use of these materials in automotive applications has been rather limited due to high production costs and poor corrosion performance and formability. A promising process to produce wrought magnesium sheet in a more cost effective manner is Twin Roll Casting (TRC). In addition, enhanced corrosion resistance and ductility may be realized in these sheet alloys with the possible introduction of a clad layer during the TRC process thereby producing a laminate sheet where the surface properties are different from the core. The focus of this research was to investigate the potential of cladding magnesium alloy AZ31 material during the TRC process. As part of this research, a thermal fluid mathematical model of the TRC process was developed, which was then further refined to include the addition of a clad layer during the process. The TRC model was validated through experimental work conducted at the Pohang Institute of Science and Technology (POSTECH University), where TRC experiments of AZ31 were conducted under various casting conditions. The as-cast microstructure of the AZ31 sheets were characterized and measurements of the secondary dendrite arm spacing (SDAS) made at the mid-region were compared to predicted microstructures from the TRC model based on solidification history. The predicted SDAS matched with the measured values, thus, validating the model. Using the validated TRC model the feasibility of adding a clad layer was assessed and various simulations were conducted to observe the effects of cast speed, cast thickness, and clad material on the thermal history and temperature profile in both the clad and core domains. The material properties and clad thickness did not seem to impact the temperature profiles significantly, while the cast speed and initial temperature dictated whether or not the cast would be successful. Using these operational parameters a process window was created (based on the CANMET facility) to illustrate the feasibility of casting and cladding during TRC. This window is beneficial for future experimentation and understanding the effects of these casting parameters.