Higher-dimensional perfect fluid collapse in $$ gravity

In this paper, we analyze higher-dimensional spherical perfect fluid collapse in \(f(R,T)\) theory for minimally coupled models. We use Darmois junction conditions by taking Lemaître-Tolman-Bondi geometry as an interior region and Schwarzschild metric as an exterior spacetime. The solution of field equations is obtained for constant scalar curvature. We determine mass in two regions of the collapsing object and discuss the formation of apparent horizons. We conclude that modified curvature term tends to slow down the collapse rate.     

Lithosphere formation in the central Slave Craton (Canada): plume subcretion or lithosphere accretion?

Major-element compositions of minerals in peridotite xenoliths from the Lac de Gras kimberlites provide constraints on the mode of lithosphere formation beneath the central Slave Craton, Canada. Magnesia contents of reconstructed whole rocks correlate positively with NiO and negatively with CaO contents, consistent with variable partial melt extraction. Alumina and Cr₂O₃ contents are broadly positively correlated, suggestive of melt depletion in the absence of a Cr–Al phase. Garnet modes are high at a given Al₂O₃ content (a proxy for melt depletion), falling about a 7 GPa melt depletion model. These observations, combined with high olivine Mg# and major-element relationships of FeO-poor peridotites (<7.5 wt%) indicative of melt loss at pressures >3 GPa (residual FeO content being a sensitive indicator of melt extraction pressure), and similar high pressures of last equilibration (∼4.2 to 5.8 GPa), provide multiple lines of evidence that the mantle beneath the central Slave Craton has originated as a residue from high-pressure melting, possibly during plume subcretion. Apparent low melt depletion pressures for high-FeO peridotites (>7.5 wt%) could suggest formation in an oceanic setting, followed by subduction to their depth of entrainment. However, these rocks, which are characterised by low SiO₂ contents (<43 wt%), are more likely to be the result of post-melting FeO-addition, leading to spuriously low estimates of melt extraction pressures. They may have reacted with a silica-undersaturated melt that dissolved orthopyroxene, or experienced olivine injection by crystallising melts. A secular FeO-enrichment of parts of the deep mantle lithosphere is supported by lower average Mg# in xenolithic olivine (91.7) compared to olivine inclusions in diamond (92.6).     

A coupling of mixed and continuous Galerkin finite element methods for poroelasticity II: the discrete-in-time case

In this paper, we formulate a finite element procedure for approximating the coupled fluid and mechanics in Biot’s consolidation model of poroelasticity. Here, we approximate the pressure by a mixed finite element method and the displacements by a Galerkin method. Theoretical convergence error estimates are derived in a discrete-in-time setting. Of particular interest is the case when the lowest-order Raviart–Thomas approximating space or cell-centered finite differences are used in the mixed formulation and continuous piecewise linear approximations are used for displacements. This approach appears to be the one most frequently applied to existing reservoir engineering simulators.     

Drought and institutional adaptation in the Great Plains of Alberta and Saskatchewan, 1914–1939

Agriculture in the southern Great Plains of Canada has been particularly vulnerable to prolonged episodes of drought. Using climate data and a precipitation minus potential evapotranspiration index, the extent of the region’s exposure to drought is examined. Between 1914 and 1917, the Dry Belt was particularly vulnerable to drought, whereas after 1928, a much larger region known as the Palliser Triangle covering most of southern Alberta and Saskatchewan was much more exposed to drought. These droughts provoked major institutional adaptation, in particular the establishment of the Special Areas Board by the Government of Alberta, and the creation of the Prairie Farm Rehabilitation Administration by the Government of Canada. Both organizations have proved to be relatively permanent public adaptations to the natural hazard of drought in the region. Moreover, these earlier experiences with prolonged drought as well as institution-building may be of value in helping the residents of the Palliser Triangle adapt to predicted climate changes in the future as well as anticipate some of the barriers to effective institutional adaptation.     

Exploratory Factor Analysis of Wireline Logs Using a Float-Encoded Genetic Algorithm

In the paper, a novel inversion approach is used for the solution of the problem of factor analysis. The float-encoded genetic algorithm as a global optimization method is implemented to extract factor variables using open-hole logging data. The suggested statistical workflow is used to give a reliable estimate for not only the factors but also the related petrophysical properties in hydrocarbon formations. In the first step, the factor loadings and scores are estimated by Jöreskog’s fast approximate method, which are gradually improved by the genetic algorithm. The forward problem is solved to calculate wireline logs directly from the factor scores. In each generation, the observed and calculated well logs are compared to update the factor population. During the genetic algorithm run, the average fitness of factor populations is maximized to give the best fit between the observed and theoretical data. By using the empirical relation between the first factor and formation shaliness, the shale volume is estimated along the borehole. Permeability as a derived quantity also correlates with the first factor, which allows its determination from an independent source. The estimation results agree well with those of independent deterministic modeling and core measurements. Case studies from Hungary and the USA demonstrate the feasibility of the global optimization based factor analysis, which provides a useful tool for improved reservoir characterization.     

ENSO and IOD analysis on the occurrence of floods in Pakistan

Different techniques have been used to discuss the existence of significant relation between the El Nino Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). Various studies present their interaction and influence on the natural disasters (i.e. drought, flood, etc.) over large parts of the globe. This study uses a Markov chain method to investigate the relation between the ENSO and IOD for the period of 62 years (1950–2011) and aggregates their influence on the occurrence of floods in Pakistan. Both data sets show similarities in the formation of transition matrices and expected number of visits from one state to another. The strong values of 2-dimensional correlation and high self-communication of the transition states confirm the existence of a possible relation between ENSO and IOD data. Moreover, significant values of dependency and stationary test endorse the applicability of the Markov chain analyses. The independent analysis shows that strong events of both data sets are co-occurred in the same flood years. During the study period maximum number of floods was observed during summer monsoon season. However, further analysis shows that after 1970, Pakistan observed the highest percentage of floods occurred per year during El Nino, Non-ENSO and positive IOD years. These observations and results demonstrate that climate variability especially ENSO and IOD should be incorporated into disaster risk analyses and policies in Pakistan.     

Assessing the impacts of rainfall intensity and urbanization on storm runoff in an arid catchment

In the past few decades, rapid urbanization has occurred in many regions of the Kingdom of Saudi Arabia due to increasing population and urban development. Additionally, the effects of global warming on rainfall characteristics have been observed. This rapid change in urbanization and climate change has cause significant changes in the nature of land surfaces and rainfall patterns, which affect the runoff process and the amount of surface runoff during floods. This study investigated the effect of urbanization and rainfall intensity for Hafr Al-Batin watershed located in Saudi Arabia. For this purpose, a hydrologic model, HEC-HMS, was adopted to simulate the flow of different rainfall intesities and urbanization levels. Simulated results showed that for a 100-year storm, a 24-h duration, and an urbanization level of 80%, the peak flow was 213% higher than the estimated current peak and the runoff volume was 112% higher than the current runoff volume. These results show a strong linear correlation between the level of urbanization and both peak discharge and runoff volume. Furthermore, the results indicate that for short return periods, the peak flow is more sensitive to the level of urbanization compared to long periods.     

Provenance and Palaeoweathering Attributes of Proterozoic Rock Formations from the Son Valley,Central India

The characteristics of source rocks and weathering of Palaeoproterozoic phyllitic rock of Mahakoshal Group and Mesoproterozoic shales and siliciclastics of Vindhyan Supergroup exposed in Son Valley, Central India have been investigated by analyzing their chemical compositions. The investigations pertaining to the relationship between major-elements were carried out along Parshoi, Chitrangi, and Markundi areas of Son valley, Central, India. The studied rock strata have been classified into three categories namely phyllitic rocks, shales and sandstone.The A-CN-K ternary diagram, CIW, CIA, MIA, and ICV values indicate about the similar provenance or source rocks subjected to severe chemical weathering, under dry and hot-humid climates in a basic and acidic environment with changing lower to higher PCO₂ of continental flora. Various geochemical discriminantts diagrams, elemental ratios suggest that rocks are derived from post-Archaean-Proterozoic igneous source. The igneous source was mainly granite with a minor contribution of granodioritic rock, in a passive margin setting. The sediments responsible for formation of shale and sandstones were most likely deposited in the interglacial period in between the Mesoproterozoic and Neoproterozoic glacial times. Compositionally the sandstones is distinctive of cratonic environments with their passive continental margin setting. However, the phyllities of Mahakoshal Group suggests their formation under lower weathering conditions in dry climatic conditions which were operating on more intermediate to basic igneous rocks with abundance of mafic minerals.     

Response mechanism of post-earthquake slopes under heavy rainfall

This paper uses the catastrophic landslide that occurred in Zhongxing Town, Dujiangyan City, as an example to study the formation mechanism of landslides induced by heavy rainfall in the post-Wenchuan earthquake area. The deformation characteristics of a slope under seismic loading were investigated via a shaking table test. The results show that a large number of cracks formed in the slope due to the tensile and shear forces of the vibrations, and most of the cracks had angles of approximately 45° with respect to the horizontal. A series of flume tests were performed to show how the duration and intensity of rainfall influence the responses of the shaken and non-shaken slopes. Wetting fronts were recorded under different rainfall intensities, and the depth of rainfall infiltration was greater in the shaken slope than in the non-shaken slope because the former experienced a greater extreme rainfall intensity under the same early rainfall and rainfall duration conditions. At the beginning of the rainfall infiltration experiment, the pore water pressure in the slope was negative, and settling occurred at the top of the slope. With increasing rainfall, the pore water pressure changed from negative to positive, and cracks were observed on the back surface of the slope and the shear outlet of the landslide on the front of the slope. The shaken slope was more susceptible to crack formation than the non-shaken slope under the same rainfall conditions. A comparison of the responses of the shaken and non-shaken slopes under heavy rainfall revealed that cracks formed by earthquakes provided channels for infiltration. Soil particles in the cracks of slopes were washed away, and the pore water pressure increased rapidly, especially the transient pore water pressure in the slope caused by short-term concentrated rainfall which decreased rock strength and slope stability.     

Pico- and Nanophytoplankton Dynamics in Two Coupled but Contrasting Coastal Bays in the NW Mediterranean Sea (France)

Due to its ecological context, the Toulon bay represents a site of scientific interest to study temporal plankton distribution, particularly pico- and nanophytoplankton dynamics. A monthly monitoring was performed during a two-year cycle (October 2013–December 2015) at two coupled sampling sites, referred to as Little and Large bays, which had different morphometric characteristics and human pressures. Flow cytometry analyses highlighted the fact that pico- and nanophytoplankton were more abundant in the eutrophic Little bay. Furthermore, it evidenced two community structures across the Toulon bays: at times, a co-dominance of picoeukaryotes, nanoeukaryotes, Synechococcus 1-like cells and Prochlorococcus-like cells was found, and at other times, a Synechococcus 1-like dominated community existed. The alternation of one structure or the other can be explained by a combined action of temperature regime, nutrient conditions and degree of contamination. This study showed that pico- and nanophytoplankton dynamics were mainly driven by temperature in both sites, as in other temperate Mediterranean regions. Thus, the community was mainly composed of picoeukaryotes and Prochlorococcus-like cells in the winter (<?15 °C), while it was dominated by Synechococcus 1-like cells in the summer (>?20 °C). Additionally, the multiple human stressors in the Little bay seemed to affect the increase in abundance of Synechococcus 1-like cells as they were preferentially observed in the Large bay.