Towards comprehensive characterisation and modelling of the forming and wrinkling mechanics of engineering fabrics

Through a combination of direct measurement and inverse modelling, a route to characterising the main mechanical forming properties of engineering fabric is demonstrated. The process involves just two experimental tests, a cantilever bending test and a modified version of the uniaxial bias extension test. The mechanical forming properties of a twill weave carbon fabric have been determined, including estimates of the in-plane bending stiffness and the torsional stiffness of a sheared fabric. As a result of measuring and incorporating all the main mechanical properties of the fabric in forming simulations (tensile, shear, out-of-plane bending, in-plane bending & torsion), the specimen size-dependent shear kinematics and wrinkling response measured in experiments, is faithfully reproduced in simulations of the uniaxial bias extension (UBE) test

Palladium based catalysts for oxygen reduction in polymer electrolyte membrane fuel cells

PhD ThesisAn important issue in low temperature polymer electrolyte membrane fuel cells (PEMFC) is the lack of alternative catalysts to platinum for the oxygen reduction reaction (ORR). The high cost and potential limited availability of platinum restricts its long term use for large scale applications in PEMFC. Consequently, there is a great interest in alternative catalysts to platinum for PEMFC. In this research a systematic study of the synthesis and optimization of carbon-supported palladium and palladium alloy nanoparticle electrocatalysts is reported. The catalysts investigated were Pd, Pd-Au, Pd- Co, Pd-Fe and Pd-Ti supported on carbon black (Vulcan XC-72R). At least two different atomic metal to metal ratios for bimetallic catalysts were investigated. All catalysts were initially evaluated for the ORR by voltammetry in a three-electrode cell. Different reducing agents, including hydrogen, ethylene glycol (EG), formaldehyde and sodium borohydride were used for the synthesis of Pd nanoparticles. The use of EG led to Pd nanoparticles with the highest ORR activity; this synthetic method was optimised by adjusting the pH of the system. Pd nanoparticles of approximately 6 nm diameter dispersed on carbon black with exchange current densities for the ORR of ca. 1.0 x 10-11 A cm-2 were obtained. Two synthetic procedures were chosen for the preparation of bimetallic catalysts: simultaneous co-deposition of both metals on the carbon support and deposition of the second metal on carbon-supported Pd. Pd-Co alloy with atomic ratio Pd:Co 4:1 exhibited improved ORR activity compared to Pd/C after being heat treated at 300 ºC under H flow. The effect of heat treatment under H flow on 22 the ORR activity and physicochemical properties was also studied. Pure Pd particles exhibited sintering after heat treatment; the presence of Au, Co and Fe decreased the degree of sintering and the presence of Ti did not affect Pd particle growth. Pd and Pd-Co were evaluated in low temperature hydrogen PEMFC, and Pd was tested as cathode catalysts in hydrogen polybenzimidazole (PBI) based high temperature PEMFC, and in direct methanol fuel cells (DMFC). Optimized Pd and Pd-Co catalysts were tested in a hydrogen low temperature PEMFC and the results were compared to those of the state of the art commercial Pt catalyst. With approximately 1.7 times higher metal loading than Pt (still significantly lower cost) the fuel cell with the Pd cathode gave better performance than that with Pt operating with air at 40 ºC. A comparative study of Pd and Pt was carried out in DMFC using different methanol concentrations and under different operating conditions. At methanol concentrations of 5 M and higher, the Pd cathode based cell performed better than that with Pt at 60 ºC with air. A pseudo one dimensional model for Nafion® -based low temperature hydrogen PEMFC was developed to simulate the influence of cathode catalyst, metal loading, electrode thickness and different operating conditions on the cell voltage and current density output. The model considered mass transport through a thin film electrolyte and through porous media but not gas flow along the channels of the cell. The model closely predicted experimental results at 20 and 40 ºC. Above 40 ºC cell performance did not improve experimentally as was predicted by the model; this lack of improvement was attributed to the decrease of oxygen permeability through Nafion® caused by the lower humidity at higher temperatures. Predicted results showed that enhanced fuel cell performance in the whole current density range could be achieved by increasing metal loading in the cathode whilst maintaining the catalyst layer thickness, which could be practically achieved by increasing the metal content of the carbon-supported catalyst

日本の重要伝統的建造物群保存地区の評価方法と地域マネジメントの変遷について : 西洋近代における地域保存政策との比較研究から

早大学位記番号:新7802早稲田大

Mobile mentoring conversations and the role of participant teachers

Abstract. The aim of this thesis is to explore the practices in Finn Church Aid’s Mobile Mentoring project by analyzing the teachers’ online conversations. This study seeks to improve the North-South engagements, especially in the context of teacher professional development. The research questions address the development of the online conversations, the positions of participants, mentor-mentee, and the effect on teachers’ professional development. From a theoretical perspective this research is located under the postcolonial paradigm, which is discussed together with the pedagogical postcolonial framework, Learning Through Other Eyes, and Bhabha’s Third Space. Topics regarding mobile learning, teacher’s professional development and mobile mentoring are also discussed. Participating teachers were originally from Uganda, the mentees, and from Finland, the mentor. The twelve weeks conversation was analyzed following a dialogical methodology. The findings of this analysis were divided into two parts: firstly, the four modules showed the development of the conversations and were used a reorientation for the summary of the findings. Secondly, the research questions were directly addressed based on the most representative segments of conversation. The research found that the development of the conversations followed multilateral interactions, however there was a slight change towards multilateral interactions as weeks past. Moreover, the mentees positioned themselves as respondents and the mentor as a guide of the conversations. Nonetheless, there were times when some mentees took the leading role. Finally, the mobile mentoring conversations followed an inquiry based mentoring model which allowed mentees to contextualize their reflections to their own setting. Some alternatives for mobile mentoring in similar contexts are suggested. Further research needs to analyze other elements of mobile mentoring project such as the curriculum or the participant’s perceptions

Cryptanalysis of a new chaotic cryptosystem based on ergodicity

This paper analyzes the security of a recent cryptosystem based on the ergodicity property of chaotic maps. It is shown how to obtain the secret key using a chosen-ciphertext attack. Some other design weaknesses are also shown.Comment: 10 pages, 5 figure

Simultaneous analysis of elastic scattering and transfer/breakup channels for the 6He+208Pb reaction at energies near the Coulomb barrier

The elastic and alpha-production channels for the 6He+208Pb reaction are investigated at energies around the Coulomb barrier (E_{lab}=14, 16, 18, 22, and 27 MeV). The effect of the two-neutron transfer channels on the elastic scattering has been studied within the Coupled-Reaction-Channels (CRC) method. We find that the explicit inclusion of these channels allows a simultaneous description of the elastic data and the inclusive alpha cross sections at backward angles. Three-body Continuum-Discretized Coupled-Channels (CDCC) calculations are found to reproduce the elastic data, but not the transfer/breakup data. The trivially-equivalent local polarization potential (TELP) derived from the CRC and CDCC calculations are found to explain the features found in previous phenomenological optical model calculations for this system.Comment: 7 pages, 6 figures (replaced with updated version

Lorenz System Parameter Determination and Application to Break the Security of Two-channel Chaotic Cryptosystems

This paper describes how to determine the parameter values of the chaotic Lorenz system used in a two-channel cryptosystem. The geometrical properties of the Lorenz system are used firstly to reduce the parameter search space, then the parameters are exactly determined, directly from the ciphertext, through the minimization of the average jamming noise power created by the encryption process.Comment: 5 pages, 5 figures Preprint submitted to IEEE T. Cas II, revision of authors name spellin