title: Quantitative characterization of the multiscale mechanical properties of low-permeability sandstone roofs of coal seams based on nanoindentation and triaxial tests and its implications for CO2 geological sequestration

authors: Cao, F

abstract: Microstructural heterogeneity of low-permeability sandstone roofs of deep unmineable coal seams due to diagenesis significantly affects rock mechanical behavior, greatly impacting the sealing potential of in situ CO2 sequestration and the structural stability of the geological formation. However, little is known about how the microstructure of different mineral groups influences the multiscale mechanical behavior of deep sandstone. This study proposes a new method for quantitatively characterizing the multiscale mechanical properties of low-permeability sandstone and shows the mechanisms responsible for mechanical failure at the micro-, meso-, and macroscale. Triaxial compression tests and targeted nanoindentation tests were conducted to assess the micro- and macroscale mechanical properties of different types of sandstone. The micro- and macroscale experiments were coupled with numerical simulations of compression using a unified cohesive model based on Voronoi polygons to clarify the multiscale mechanical behavior. The results indicate that quartz, the primary mineral component of the sandstones examined, exhibits the strongest micromechanical properties, followed by feldspar, calcite, and clay minerals. Compared to polycrystalline quartz, monocrystalline quartz has a more stable microstructure and is mechanically stronger. The macro-mechanical properties of tight sandstone samples are weakened by increased microstructural inhomogeneity and larger grain size. This leads to a higher likelihood of splitting damage, characterized by a high degree of discrete and weak stress sensitivity. The major conclusion is that the positive rhythm lithofacies of medium-grained sandstone to siltstone are the most favorable for efficient CO2 sequestration in deep unmineable coal seams.

text: Quantitative characterization of the multiscale mechanical properties of low-permeability sandstone roofs of coal seams based on nanoindentation and triaxial tests and its implications for CO2 geological sequestration Microstructural heterogeneity of low-permeability sandstone roofs of deep unmineable coal seams due to diagenesis significantly affects rock mechanical behavior, greatly impacting the sealing potential of in situ CO2 sequestration and the structural stability of the geological formation. However, little is known about how the microstructure of different mineral groups influences the multiscale mechanical behavior of deep sandstone. This study proposes a new method for quantitatively characterizing the multiscale mechanical properties of low-permeability sandstone and shows the mechanisms responsible for mechanical failure at the micro-, meso-, and macroscale. Triaxial compression tests and targeted nanoindentation tests were conducted to assess the micro- and macroscale mechanical properties of different types of sandstone. The micro- and macroscale experiments were coupled with numerical simulations of compression using a unified cohesive model based on Voronoi polygons to clarify the multiscale mechanical behavior. The results indicate that quartz, the primary mineral component of the sandstones examined, exhibits the strongest micromechanical properties, followed by feldspar, calcite, and clay minerals. Compared to polycrystalline quartz, monocrystalline quartz has a more stable microstructure and is mechanically stronger. The macro-mechanical properties of tight sandstone samples are weakened by increased microstructural inhomogeneity and larger grain size. This leads to a higher likelihood of splitting damage, characterized by a high degree of discrete and weak stress sensitivity. The major conclusion is that the positive rhythm lithofacies of medium-grained sandstone to siltstone are the most favorable for efficient CO2 sequestration in deep unmineable coal seams.

year: 2025

title: The boundedness principle characterizes second category subsets

authors: Broughan, Kevin A.

abstract: Converses are proved for the Osgood (the Principle of Uniform Boundedness), Dini, and other well known. theorems. The notion of a continuous step function on a topological space is defined and a class of spaces identified for which each lower semicontinuous function is the pointwise limit of a monotonically increasing sequence of step functions.

text: The boundedness principle characterizes second category subsets Converses are proved for the Osgood (the Principle of Uniform Boundedness), Dini, and other well known. theorems. The notion of a continuous step function on a topological space is defined and a class of spaces identified for which each lower semicontinuous function is the pointwise limit of a monotonically increasing sequence of step functions.

year: 1977

title: How usable is a smartphone with a Māori-language interface?

authors: Mato, Paora James

subjects: Mäori

abstract: Major languages dominate contemporary technologies. For Mäori, there is opportunity to engage with some technologies using their language and to participate within Mäori- language communities in various digital media. A smartphone launched by Two Degrees Mobile Limited provides a Mäori- language interface option. An initial pilot study indicated users will engage with this interface, but when pushed for time will switch the interface to the English- language option. This paper reports on a study undertaken to test the usability of the smartphone Mäorilanguage interface. Participants reported diffi culties and some frustration as they struggled with new words and unfamiliar uses of words. They also expressed disappointment at poor translations and arbitrary truncations. The feedback highlights perceived shortcomings encountered when technologies that are normally developed and used in a major language are translated for use in minority Indigenous languages. Mäori-language strategies that consider using translated application interfaces should be cognisant of such issues.

text: How usable is a smartphone with a Māori-language interface? Major languages dominate contemporary technologies. For Mäori, there is opportunity to engage with some technologies using their language and to participate within Mäori- language communities in various digital media. A smartphone launched by Two Degrees Mobile Limited provides a Mäori- language interface option. An initial pilot study indicated users will engage with this interface, but when pushed for time will switch the interface to the English- language option. This paper reports on a study undertaken to test the usability of the smartphone Mäorilanguage interface. Participants reported diffi culties and some frustration as they struggled with new words and unfamiliar uses of words. They also expressed disappointment at poor translations and arbitrary truncations. The feedback highlights perceived shortcomings encountered when technologies that are normally developed and used in a major language are translated for use in minority Indigenous languages. Mäori-language strategies that consider using translated application interfaces should be cognisant of such issues.

year: 2016