title: Libtrace: A packet capture and analysis library

authors: Alcock, Shane

subjects: computer science

abstract: This paper introduces libtrace, an open-source software library for reading and writing network packet traces. Libtrace offers performance and usability enhancements compared to other libraries that are currently used. We describe the main features of libtrace and demonstrate how the libtrace programming API enables users to easily develop portable trace analysis tools without needing to consider the details of the capture format, file compression or intermediate protocol headers. We compare the performance of libtrace against other trace processing libraries to show that libtrace offers the best compromise between development effort and program run time. As a result, we conclude that libtrace is a valuable contribution to the passive measurement community that will aid the development of better and more reliable trace analysis and network monitoring tools.

text: Libtrace: A packet capture and analysis library This paper introduces libtrace, an open-source software library for reading and writing network packet traces. Libtrace offers performance and usability enhancements compared to other libraries that are currently used. We describe the main features of libtrace and demonstrate how the libtrace programming API enables users to easily develop portable trace analysis tools without needing to consider the details of the capture format, file compression or intermediate protocol headers. We compare the performance of libtrace against other trace processing libraries to show that libtrace offers the best compromise between development effort and program run time. As a result, we conclude that libtrace is a valuable contribution to the passive measurement community that will aid the development of better and more reliable trace analysis and network monitoring tools.

year: 2012

title: Fabrication and characterisation of nickel/yttria stabilised zirconia cermet anodes for solid oxide fuel cells

authors: Brown, Michael Steven

abstract: The primary objective of this thesis was to study the Ni/YSZ system from powder preparation to electrochemical and morphological characterisation.

Nickel/yttria stabilised zirconia (YSZ) cermet systems are employed as anode materials in high temperature solid oxide fuel cell (SOFC) applications. The ionically conducting YSZ powder was modified, by sintering and milling to vary the particle distribution. This allowed the fabrication of cermet powders with varying particle sizes and therefore microstructures. Bimodal particle distributions were present for the milled YSZ, which indicated two particle sizes. The finest particles were individual YSZ particles of approximately 0.4 μm, and represented the grinding limit, which was independent of calcining temperature. The agglomerate size decreased and the amount of fine YSZ increased as milling times were extended.

A ‘paint’ consisting of the cermet powder (NiO/YSZ), a solvent, and a binder was developed in order to use a wet powder spraying (WPS®) technique, to apply the electrode layer to the electrolyte substrate. By this method, reproducible anodes with good morphological properties were produced. The slurry was prepared with ethanol as the solvent and a PVP binder, to form a stable suspension. 

Anode sintering temperature was studied with results indicating that a temperature of 1300 °C provided the optimum sintering effect. Anodes sintered at 1300 °C showed no agglomeration of NiO. There was no discernable increase of Ni particle size after reducing in hydrogen.

A number of Ni/YSZ cermet anodes consisting of 40 vol% nickel and 60 vol% YSZ were fabricated with varying thickness of the active layer. The anode materials were milled to the appropriate particle sizes, air-sprayed onto YSZ substrates and subsequently sintered to produce the anode component. The thicknesses ranged from 3.5 μm to 54 μm in order to find the minimum thickness of active layer for a high performance anode using the least material. The anodes were studied in an atmosphere of hydrogen, water and nitrogen in a 3-electrode setup. Impedance spectroscopy was carried out at a temperature of 1000 °C.

It was found that approximately 12 μm was the limiting thickness for a low polarisation resistance. Below a thickness of 12 μm, the polarisation resistance increased in an erratic manner as the reaction zone was reduced.

Ni/YSZ cermet anodes consisting of 90 vol% Ni and 10 vol% YSZ were fabricated in order to create an anode with significantly higher polarisation resistance. Hereby a structure-related impedance arc at high frequencies could be examined in detail.  The anode was studied in mixtures of hydrogen, water and nitrogen in a 3-electrode setup. Impedance measurements were carried out at temperatures ranging between 700°C and 1000°C. The present work confirmed that a high frequency arc from impedance spectroscopy data was indeed related to the structure of the cermet. 

Four types of Ni/YSZ anodes were characterised and compared to illustrate similarities and differences from state-of-the-art cermet anodes to coarse structure cermets to two-dimensional Ni anodes with significantly higher polarization resistance. The anode structure-dependent high frequency section of the impedance spectrum was studied.

The thesis concludes with recommendations for further investigations.

text: Fabrication and characterisation of nickel/yttria stabilised zirconia cermet anodes for solid oxide fuel cells The primary objective of this thesis was to study the Ni/YSZ system from powder preparation to electrochemical and morphological characterisation.

Nickel/yttria stabilised zirconia (YSZ) cermet systems are employed as anode materials in high temperature solid oxide fuel cell (SOFC) applications. The ionically conducting YSZ powder was modified, by sintering and milling to vary the particle distribution. This allowed the fabrication of cermet powders with varying particle sizes and therefore microstructures. Bimodal particle distributions were present for the milled YSZ, which indicated two particle sizes. The finest particles were individual YSZ particles of approximately 0.4 μm, and represented the grinding limit, which was independent of calcining temperature. The agglomerate size decreased and the amount of fine YSZ increased as milling times were extended.

A ‘paint’ consisting of the cermet powder (NiO/YSZ), a solvent, and a binder was developed in order to use a wet powder spraying (WPS®) technique, to apply the electrode layer to the electrolyte substrate. By this method, reproducible anodes with good morphological properties were produced. The slurry was prepared with ethanol as the solvent and a PVP binder, to form a stable suspension. 

Anode sintering temperature was studied with results indicating that a temperature of 1300 °C provided the optimum sintering effect. Anodes sintered at 1300 °C showed no agglomeration of NiO. There was no discernable increase of Ni particle size after reducing in hydrogen.

A number of Ni/YSZ cermet anodes consisting of 40 vol% nickel and 60 vol% YSZ were fabricated with varying thickness of the active layer. The anode materials were milled to the appropriate particle sizes, air-sprayed onto YSZ substrates and subsequently sintered to produce the anode component. The thicknesses ranged from 3.5 μm to 54 μm in order to find the minimum thickness of active layer for a high performance anode using the least material. The anodes were studied in an atmosphere of hydrogen, water and nitrogen in a 3-electrode setup. Impedance spectroscopy was carried out at a temperature of 1000 °C.

It was found that approximately 12 μm was the limiting thickness for a low polarisation resistance. Below a thickness of 12 μm, the polarisation resistance increased in an erratic manner as the reaction zone was reduced.

Ni/YSZ cermet anodes consisting of 90 vol% Ni and 10 vol% YSZ were fabricated in order to create an anode with significantly higher polarisation resistance. Hereby a structure-related impedance arc at high frequencies could be examined in detail.  The anode was studied in mixtures of hydrogen, water and nitrogen in a 3-electrode setup. Impedance measurements were carried out at temperatures ranging between 700°C and 1000°C. The present work confirmed that a high frequency arc from impedance spectroscopy data was indeed related to the structure of the cermet. 

Four types of Ni/YSZ anodes were characterised and compared to illustrate similarities and differences from state-of-the-art cermet anodes to coarse structure cermets to two-dimensional Ni anodes with significantly higher polarization resistance. The anode structure-dependent high frequency section of the impedance spectrum was studied.

The thesis concludes with recommendations for further investigations.

year: 1998

title: Comment

authors: Mitchell, Linda

abstract: This issue of Early Childhood Folio has a diverse range of articles focusing on highly relevant and current pedagogical issues. Several involve case studies, where in-depth analysis enables opportunities for learning and development afforded by pedagogy and the environment to be highlighted. Some offer new methodological approaches, including the use of a “mosaic approach” to investigate “voices” of child and adult participants, kaupapa Māori methodology to illustrate culturally valid forms of assessment within contemporary Māori early childhood settings, and the use of a model of participation in home-based settings

text: Comment This issue of Early Childhood Folio has a diverse range of articles focusing on highly relevant and current pedagogical issues. Several involve case studies, where in-depth analysis enables opportunities for learning and development afforded by pedagogy and the environment to be highlighted. Some offer new methodological approaches, including the use of a “mosaic approach” to investigate “voices” of child and adult participants, kaupapa Māori methodology to illustrate culturally valid forms of assessment within contemporary Māori early childhood settings, and the use of a model of participation in home-based settings

year: 2012