Spatial distribution and biodiversity of macrofauna in the southeast of the Caspian Sea, Gorgan Bay in relation to environmental conditions

Spatial distribution and biodiversity of macrofauna in the Gorgan Bay, southeast of the Caspian Sea, were studied at fifteen stations in June 2010. Also, depth, temperature, salinity, dissolved oxygen, total organic matter content and sediment particle size were measured in each station. A total 3,356 individuals belonged to eight families and ten species were identified. Polychaeta were numerically dominated groups and Streblospio gynobranchiata, was constant and dominant species with 60.28% of total individuals but Bivalvia with four species had highest species number, though the density of them were low. The maximum density (4,500 ind/m²) was obtained at station 1 while the minimum (411 ind/m²) was observed at station 6. There was not significant correlation between the density of macrofauna with all environmental conditions. In total, six feeding group were considered but surface deposit feeder and deposit feeder were dominant in all stations. The maximum mean species number, diversity, richness, and evenness were obtained, 6.33, 1.46, 1.38 and 0.87, respectively. Based on the M-AMBI and the AMBI classification it seems that bentic environment in Gorgan Bay was not bad but the results of Shannon-Wiener, Margalef and Simpson indices the results were vice versa. In general, the values of the mentioned indices decreased from the western to the eastern part of the bay. Furthermore, the nonmetric multidimensional scaling (nMDS) showed that the structure of the macrofaunal assemblages was divides to six groups.     

Assessing groundwater vulnerability using GIS-based DRASTIC model for Ahmedabad district,India

The present research aims to derive the intrinsic vulnerability of groundwater against contamination using the GIS platform. The study applies DRASTIC model for Ahmedabad district in Gujarat, India. The model uses parameters like depth, recharge, aquifer, soil, topography, vadose zone and hydraulic conductivity, which depict the hydrogeology of the area. The research demonstrates that northern part of district with 46.4% of area is under low vulnerability, the central and southern parts with 48.4% of the area are under moderate vulnerability, while 5.2% of area in the south-east of district is under high vulnerability. It is observed from the study that lower vulnerability in northern part may be mostly due to the greater depth of vadose zone, deeper water tables and alluvial aquifer system with minor clay lenses. The moderate and high vulnerability in central and southern parts of study area may be due to lesser depth to water tables, smaller vadose zone depths, unconfined to semi-confined alluvial aquifer system and greater amount of recharge due to irrigation practices. Further, the map removal and single-parameter sensitivity analysis indicate that groundwater vulnerability index has higher influence of vadose zone, recharge, depth and aquifer parameters for the given study area. The research also contributes to validating the existence of higher concentrations of contaminants/indicators like electrical conductivity, chloride, total dissolved solids, sulphate, nitrate, calcium, sodium and magnesium with respect to groundwater vulnerability status in the study area. The contaminants/indicators exceeding the prescribed limits for drinking water as per Indian Standard 10500 (1991) were mostly found in areas under moderate and high vulnerability. Finally, the research successfully delineates the groundwater vulnerability in the region which can aid land-use policies and norms for activities related to recharge and seepage with respect to existing status of groundwater vulnerability and its quality.     

Inelastic seismic response of stiffening systems and development of demand spectrum: Application to MSSS bridges

A stiffening system is a system that increases its stiffness as it goes under large displacements. Such behavioural characteristic can result from constitutive behaviour or at the structural level often from closure of gaps between various components (sub‐systems) of the structure. An example of the latter situation is multi‐span simply supported (MSSS) bridges under horizontal earthquake ground motion. Unlike softening systems, stiffening systems have not been studied. In addition to the need for more understanding of the seismic response of stiffening systems, there is a need to develop response spectrum that can be used in design. Several parameters including gap size and ratios of sub‐systems stiffness, strength, and mass control the behaviour of a stiffening system. In this study, a simplified stiffening model is developed and over 367 000 cases are analysed to investigate the nonlinear stiffening behaviour and pounding. Parameters considered also include ground motion characteristic. Results are evaluated and compared in terms of displacement and dissipated hysteretic energy. Parameter study results show that, on average, the displacement response is lower for stiffening systems, however, they dissipates higher hysteretic energy, due to higher yield cycles and yield excursions, and can possibly sustain more damage than a bilinear, elastic–plastic system. Using parameter study database, design response spectrum for stiffening systems is also proposed and its practical application is demonstrated through its application to an MSSS bridge. Results of this study goes beyond MSSS bridges and will have application for many structural systems where response is characterized by a stiffening behaviour. Copyright © 2007 John Wiley & Sons, Ltd.     

Wavelet-Hilbert transform-based simulation of pulse-like ground motion

In nonlinear dynamic structural analysis, a suite of pulse-like ground motions is required for the performance-based design of structures near active faults. The dissimilarity in the amplitude and frequency content of the earthquake time series referred to nonstationary properties in temporal and spectral, respectively. An approach is proposed based on the nonstationary properties of the far-field records and the seismological information in an event for simulating pulse-like records. The pulse-like earthquake time history is estimated via the superposition of the residual part of the earthquake with the estimated pulse. The wavelet-based Hilbert transform is utilized to characterize the nonstationary properties, the instantaneous amplitude, and frequencies of far-field records to model residual part. The effects of near-fault and pulse are estimated based on the seismological properties of the region. The validation of the procedure is indicated by comparing simulated time-series, response spectra, and Arias intensity with recorded pulse-like records in two different earthquakes in California; the M_w 6.7 1994 Northridge and the M_w 6.5 1979 Imperial valley.

     

New firm formation in old industrial regions – a study of entrepreneurial in-migrants in Bergslagen,Sweden

The article examines new firm formation in the old industrial region (OIR) of Bergslagen in Sweden, and in particular the role of in-migrants. The study is based on longitudinal georeferenced microdata (1993–2008) compiled by Statistics Sweden and providing information on individuals' attachments to the Swedish labour market, as well as workplaces and firms, education, income, and family composition. This specially commissioned database enabled the characterization and analysis of emerging forms of entrepreneurship and self-employment, as well as the socio-economics of the labour market. The longitudinal data allowed the authors to trace actions taken by individuals over time. The results indicate that new firm formation is related to private services, rather than to the traditional manufacturing sector and public services that currently dominate the regional labour market. Self-employed in-migrants are active in other sectors than non-migrants, and show some distinct features in terms of their lower age, better education, and more often non-Nordic background. The study showed that both in-migration and return migration had a positive, significant, and substantial effect on migrants' decision to start a business when a number of other individual characteristics had been controlled for.     

Influence of random heterogeneity of the friction angle on bearing capacity factor Nγ

ABSTRACT

Probabilistic methods in geotechnical engineering have received a lot of attention during the last decade and different methodologies are used to capture the inherent variability of soil in different geotechnical engineering problems. In this paper, numerical simulations are conducted to obtain the bearing capacity factor, N_γ, for a purely frictional heterogenous soil where the friction angle is modelled as randomly distributed throughout the domain and the effect of its spatial variability on N_γ is investigated. A finite element method, based on the upper bound limit analysis was combined with random field theory and linear programming to develop a probabilistic analysis. Monte Carlo simulations were performed and the effect of the variability of the friction angle defined by statistical parameters on the bearing capacity factor was investigated. Results show that the mean bearing capacity factor N_γ of a footing on a spatially variable cohesionless soil is generally higher than the deterministic N_γ obtained from a constant mean value. Increasing the heterogeneity of the friction angle by an increase in the coefficient of variation generally increases this deviation. This can be explained by the nonlinearity of the relationship between N_γ and the friction angle.     

Crustal structure of northern Egypt from joint inversion of receiver functions and surface wave dispersion velocities

In this study, we used a combined inversion of body wave receiver functions and surface wave dispersion measurements to provide constraints on the crustal structure of northern Egypt. The two techniques are complementary to each other: receiver functions (RFs) are sensitive to shear-wave velocity contrasts, while surface wave dispersion (SWD) measurements are sensitive to finite variations of shear-wave velocity with depth. A database of 122 teleseismic events digitally recorded by the Egyptian National Seismological Network (ENSN) stations has been used as well. To enhance the resulting RFs at each ENSN station, the H-k stacking method was applied. A joint inversion process between the resulting receiver functions and the surface wave dispersion curves was applied as well. We have produced three averaged velocity structure models for distinct geographic and tectonic provinces namely Sinai, eastern desert, and western desert from east to the west respectively. These models will deeply help in estimation the epicenter distance of earthquake, focal mechanism solutions, and earthquake hazard analysis in northern Egypt. An obvious image of the subsurface structure has been determined which shows that generally the crustal structure of northern Egypt consists of three layers covered with a sequence of sediments that differs in thickness from across the region except in the Sharm area where the sedimentary cover is absent. The obtained results indicate that crustal thickness differs from east to west and reaches its maximum value of about 36 km at Siwa station (SWA) in the western desert and its minimum value of about 28 km at Sharm station (SHR) of the southern tip of the Sinai Peninsula. The Vp/Vs ratio varies between 1.71 and 2.07 in northern Egypt. Generally, the high values (1.93) of (Vp/Vs) at SWA station may reflect the well-known rich aquifer with fully saturated sediments of the Swia Oasis in the Western Desert. Moreover, the highest value (2.07) of (Vp/Vs) at BNS station may be attributed to the widespread recently discovered hydrocarbon fields at the Beni-Suef Basin along the Eastern Desert. Finally, an integrated geophysical and hydrological study of the dimensions and physical properties of the aquifer and hydrocarbon fields at SWA and BNS stations to confirm if they are sufficient to produce the elevated Vp/Vs ratios or not become essential and highly recommended.     

Probabilistic failure analysis of riprap as riverbank protection under flood uncertainties

Existing riverbank riprap could face the risk of failure if the flood regime changes in future. Additionally, changed sediment transport in rivers, as a possible result of climate change, impacts the failure risk of flood protection measures. Evaluation of this potential failure is the primary issue of riprap stability and safety assessment. The consequences of the bank failure are probably uncontrolled erosion and flooding with disastrous consequences in residential areas or damage to infrastructures. Thus, a probabilistic analysis of riprap failure considering different mechanisms due to the flood and sediment transport uncertainties is required to assess embankment stability. In this article, the concept of a probabilistic assessment model based on Monte Carlo simulation method, moment analysis methods, and Rosenblueth point estimation method are presented to define the failure risk of riprap as the river bank protection. The probability of failure in different modes, namely direct block erosion, toe scouring and overtopping, has been defined by taking into account the river bed level variation based on bedload transport described with a probabilistic function of the peak discharge. The result of three models comparison revealed a good agreement (the average deviation of less than 2%) in estimation of riprap failure probability. This model is a strategical tool to search the critical river reaches and helps to evaluate the risk maps. So that, the model could cover the engineering aspect of environmental stability in the rivers with riprap as the bank protections.