Natural Hazards - Drought severity is increasing in Southern Africa which is affecting rain-fed agriculture, the main source of livelihood in most countries in this region. The study assessed the... 相似文献
How tightly should a sample be packed for strain estimation by the Fry method? We address this issue using synthetic simulations of 900 images such that each image contains 200 randomly distributed grains, but differs from other images with respect to the packing tightness and the degree of sorting. Each image is coaxially distorted by various known strain ratios and the strain estimates from distorted images are obtained by the Fry method. The statistical errors in the strain estimates are found to grow larger with the decrease in the packing tightness irrespective of the level of distortion. We demonstrate that a progressive decrease in the packing tightness results in an increasingly clustered nature of grain center distribution and hence the larger errors. These results, obtained from the synthetic images, are corroborated by two natural examples of sandstone, one loosely packed and the other tightly packed. Based on the results of tests on synthetic and natural examples, we recommend that the Fry method should be used only on those samples that have \({>}30\%\) packing density. 相似文献
Natural Hazards - Lightning is one of the most widespread and deadly hazards in Bangladesh. Bangladesh has among the highest death rates of any country. The main objective of this study is to... 相似文献
Soft kaolinite deposits of marine origin are encountered as foundation soils in many parts of the world. The well-developed flocculated structure of kaolinite-bearing marine deposits is amenable to alterations from leaching of pore solution salts, loss of overburden, and secondary compression. Secondary compression causes densification of microstructure that may impact the viscous resistance, soil stiffness, and undrained shear strength of kaolinite-bearing marine deposits. This study examines the influence of secondary compression on viscous resistance and constrained stress–strain modulus of soft kaolinites prepared in synthetic seawater and sodium chloride solutions. The impact of secondary compression on undrained shear strength is interpreted from changes in microstructure, percent monovalent cation concentration, viscous resistance, and constrained stress–strain modulus. Kaolinite specimens experience reduction in void space during secondary compression. Breakdown of edge–face (E–F) and edge–edge (E–E) contacts of kaolinite particles during secondary compression and creation of interlocking zones is observed from scanning electron micrograph studies. Breakdown of E–F and E–E contacts is considered responsible for reduction in constrained stress–strain modulus during secondary compression. Concomitant, creation of interlocking zones at particle contacts increases the viscous resistance of microstructure that enhances the undrained shear strength of soft kaolinites. 相似文献
In this research, deep learning (DL) model is proposed to classify the soil reliability for liquefaction. The applicability of the DL model is tested in comparison with emotional backpropagation neural network (EmBP). The database encompassing cone penetration test of Chi–Chi earthquake. This study uses cone resistance (qc) and peck ground acceleration as inputs for prediction of liquefaction susceptibility of soil. The performance of developed models has been assessed by using various parameters (receiver operating characteristic, sensitivity, specificity, Phi correlation coefficient, Precision–Recall F measure). The performance of DL is excellent. Consistent results obtained from the proposed deep learning model, compared to the EmBP, indicate the robustness of the methodology used in this study. In addition, both the developed model was also tested on global earthquake data. During validation on global data, both the models shows good results based on fitness parameters. The developed classification models a simple, but also efficient decision-making tool in engineering design to quantitatively assess the liquefaction potential. The finding of this paper can be further used to capture the relationship between soil and earthquake parameters.
The goal of this study was to explore prebiotic chemistry in a range of plausible early Earth and Mars atmospheres. To achieve this laboratory continuous flow plasma irradiation experiments were performed on N2/H2/CO/CO2 gas mixtures chosen to represent mildly reducing early Earth and Mars atmospheres derived from a secondary volcanic outgassing of volatiles in chemical equilibrium with magmas near present day oxidation state. Under mildly reducing conditions (91.79% N2, 5.89% H2, 2.21% CO, and 0.11% CO2), simple nitriles are produced in the gas phase with yield (G in molecules per 100 eV), for the key prebiotic marker molecule HCN at G∼1×10−3 (0.1 nmol J−1). In this atmosphere localized HCN concentrations possibly could approach the 10−2 M needed for HCN oligomerization. Yields under mildly oxidizing conditions (45.5% N2, 0.1% H2, 27.2% CO, 27.2% CO2) are significantly less as expected, with HCN at G∼3×10−5 (). Yields in a Triton atmosphere which can be plausibly extrapolated to represent what might be produced in trace CH4 conditions (99.9% N2, 0.1% CH4) are significant with HCN at G∼1×10−2 (1 nmol J−1) and tholins produced. Recently higher methane abundance atmospheres have been examined for their greenhouse warming potential, and higher abundance hydrogen atmospheres have been proposed based on a low early Earth exosphere temperature. A reducing (64.04% N2, 28.8% H2, 3.60% CO2, and 3.56% CH4), representing a high CH4 and H2 abundance early Earth atmosphere had HCN yields of G∼5×10−3 (0.5 nmol J−1). Tholins generated in high methane hydrogen gas mixtures is much less than in a similar mixture without hydrogen. The same mixture with the oxidizing component CO2 removed (66.43% N2, 29.88% H2, 0% CO2, and 3.69% CH4) had HCN yields of G∼1×10−3 (0.1 nmol J−1) but more significant tholin yields. 相似文献
We consider the questions of whether the damped Lyman-alpha (DLA) and sub-DLA absorbers in quasar spectra differ intrinsically in metallicity, and whether they could arise in galaxies of different masses. Using the recent measurements of the robust metallicity indicators Zn and S in DLAs and sub-DLAs, we confirm that sub-DLAs have higher mean metallicities than DLAs, especially at z ? 2. We find that the intercept of the metallicity-redshift relation derived from Zn and S is higher than that derived from Fe by 0.5–0.6 dex. We also show that, while there is a correlation between the metallicity and the rest equivalent width of Mg II λ2796 or Fe II λ2599 for DLAs, no correlation is seen for sub-DLAs. Given this, and the similar Mg II or Fe II selection criteria employed in the discovery of both types of systems at lower redshifts, the difference between metallicities of DLAs and sub-DLAs appears to be real and not an artefact of selection. This conclusion is supported by our simulations of Mg II λ2796 and Fe II λ2599 lines for a wide range of physical conditions. On examining the velocity spreads of the absorbers, we find that sub-DLAs show somewhat higher mean and median velocity spreads (Δv), and an excess of systems with Δv > 150 km s?1, than DLAs. Compared to DLAs, the [Mn/Fe] vs. [Zn/H] trend for sub-DLAs appears to be steeper and closer to the trend for Galactic bulge and thick disk stars, possibly suggesting different stellar populations. The absorber data appear to be consistent with galaxy down-sizing. The data are also consistent with the relative number densities of low-mass and high-mass galaxies. It is thus plausible that sub-DLAs arise in more massive galaxies on average than DLAs. 相似文献
Bacterial metal reduction is an important biogeochemical process in anaerobic environments. An understanding of electron transfer pathways from dissimilatory metal-reducing bacteria (DMRB) to solid phase metal (hydr)oxides is important for understanding metal redox cycling in soils and sediments, for utilizing DMRB in bioremedation, and for developing technologies such as microbial fuel cells. Here we hypothesize that the outer membrane cytochromes OmcA and MtrC from Shewanella oneidensis MR-1 are the only terminal reductases capable of direct electron transfer to a hematite working electrode. Cyclic voltammetry (CV) was used to study electron transfer between hematite electrodes and protein films, S. oneidensis MR-1 wild-type cell suspensions, and cytochrome deletion mutants. After controlling for hematite electrode dissolution at negative potential, the midpoint potentials of adsorbed OmcA and MtrC were measured (−201 mV and −163 mV vs. Ag/AgCl, respectively). Cell suspensions of wild-type MR-1, deletion mutants deficient in OmcA (ΔomcA), MtrC (ΔmtrC), and both OmcA and MtrC (ΔmtrC–ΔomcA) were also studied; voltammograms for ΔmtrC–ΔomcA were indistinguishable from the control. When the control was subtracted from the single deletion mutant voltammograms, redox peaks were consistent with the present cytochrome (i.e., ΔomcA consistent with MtrC and ΔmtrC consistent with OmcA). The results indicate that OmcA and MtrC are capable of direct electron exchange with hematite electrodes, consistent with a role as terminal reductases in the S. oneidensis MR-1 anaerobic respiratory pathway involving ferric minerals. There was no evidence for other terminal reductases operating under the conditions investigated. A Marcus-based approach to electron transfer kinetics indicated that the rate constant for electron transfer ket varies from 0.025 s−1 in the absence of a barrier to 63.5 s−1 with a 0.2 eV barrier. 相似文献
Heavy minerals of twenty sediment samples, belonging to polar ice sheet, lake, mainland area and shelf region of Schirmacher
Oasis, east Antarctica, have been studied for their textural characteristics, abundance and provenance determination. The
heavy crop is represented by zircon, tourmaline, rutile, garnet, hypersthene, hornblende, chlorite, enstatite, lawsonite,
kyanite, sillimanite, zoisite, andalusite, spinel, topaz and opaques. The assemblage, in general, is dominated by hornblende-hypersthene-garnet
assemblage, followed by kyanite-sillimanite-andalusite and zircontourmaline-rutile. The high concentration of specific minerals
of metamorphic origin reveals high-grade metamorphic terrain as the primary source. The ZTR ratio is low showing low mineralogical
maturity. An attempt has also been made to compare the trends of heavy minerals of various sub glacial regions with those
of the average values of entire area. 相似文献