Effect of spatial variability on the slope stability using Random Field Numerical Limit Analyses

This paper presents a probabilistic approach to evaluating the geotechnical stability problem by incorporating the stochastic spatial variability of soil property within the numerical limit analyses (NLAs). The undrained shear strength and unit weight of soil are treated as a random field which is characterized by a log-normal distribution and a spatial correlation length. The current calculations use a Cholesky Decomposition technique to incorporate these random properties in NLAs. The Random Field Numerical Limit Analyses are applied to evaluate the effects of spatial variability of soil property on the slope stability and failure mechanism of slope. Monte Carlo iterations are then used to interpret the slope reliability and the dimension for collapsed slope for selected ranges of the coefficient of variation in soil property and the ratio of correlation length to slope height. Finally, the variation in the dimension of collapsed slope is examined in terms of the variability of slope reliability.Japan Society for the Promotion of Science (KAKENHI Grant 25289149

Effects of In-bed Stoichiometric and Flue Gas Recirculation on Combustion and Environmental Performances of a Swirling Fluidized-bed Combustor

This work studied the firing of ground nut/peanut shells in a twin-cyclonic fluidized-bed combustor at the maximum combustor loading (~22.5 kg/h) in the flue gas recirculation (FGR) mode. During the experimental tests, excess air (EA) was fixed at about 60%, while the in-bed stoichiometric ratio (Sb) and FGR ranged from 1.0–1.2 and from 10–25%, respectively. The experimental results showed that nitrogen oxide (NOx) emissions significantly decreased when FGR increased; however, the opposite tendency was found for carbon monoxide (CO) emission. Meanwhile, FGR showed strong effects on both combustion and emission performances, the impacts of Sb were quite low. The FGR of ~10-18% and Sb from 1.0-1.2 appear to be optimum operating conditions for firing ground nut/peanut shells to ensure the lowering of major emissions under the limitations of Thailand’s emission standards, with high combustor efficiency at 99%

Magnetic characterization of synthetic titanomagnetites: Quantifying the recording fidelity of ideal synthetic analogs

A series of four synthetic basalts comprising titanomagnetite (Fe3-xTixO4) grains of varied size and titanium content have been produced by a glass-ceramic method. Complementary characterization techniques of X-ray diffractometry, secondary electron microscopy, and transmission electron microscopy (TEM) demonstrate the reaction product composition consisted of mainly Fe3-xTixO4, pyroxene hedenbergite, fayalite, and SiO2. The samples exhibit bimodal distributions of larger (<2 µm) and smaller Fe3-xTixO4 particles (<50 nm in diameter), the latter found inside pyroxene crystals, as well as the sporadic occurance of dendritic Fe3-xTixO4 structures. Magnetic measurements show their bulk characteristics fall into two groups: Ti-rich titanomagnetite samples with varying Ti content; and near-stoichiometric magnetite. The TEM technique of off-axis electron holography allowed for visualization of the magnetic behavior of the synthetic Fe3-xTixO4 grains. Energy dispersive X-ray analysis and off-axis electron holography confirmed the small Fe3-xTixO4 grains (<50 nm) confined within glassy pyroxene regions to be Fe-rich and single domain, carrying strong magnetic signals, compared to the relatively magnetically weak larger Fe3-xTixO4 grains (x ∼ 0.6). The large grains in the pure magnetite sample are shown to be pseudo-single domain in nature. The quenching process involved in synthesis is considered similar to that of pillow basalts found at mid-ocean ridges and hence the reaction products are thought ideal in terms of characterization and understanding, for the purpose of studying natural systems

Magnetic induction mapping of magnetite chains in magnetotactic bacteria at room temperature and close to the Verwey transition using electron holography

Off-axis electron holography in the transmission electron microscope is used to record magnetic induction maps of closely spaced magnetite crystals in magnetotactic bacteria at room temperature and after cooling the sample using liquid nitrogen. The magnetic microstructure is related to the morphology and crystallography of the particles, and to interparticle interactions. At room temperature, the magnetic signal is dominated by interactions and shape anisotropy, with highly parallel and straight field lines following the axis of each chain of crystals closely. In contrast, at low temperature the magnetic induction undulates along the length of the chain. This behaviour may result from a competition between interparticle interactions and an easy axis of magnetisation that is no longer parallel to the chain axis. The quantitative nature of electron holography also allows the change in magnetisation in the crystals with temperature to be measured