Experimental study on local scour around single oblong pier fitted with a collar in a 180 degree flume bend

In this work, investigation on the development of local scour around an oblong pier in a 180 degree flume bend is presented. Scour hole can cause failure of the bridge especially during the river floods. In this study, the use of oblong collars for reducing the effects of local scour at a bridge pier is presented together with the time aspect of the scour development. Tests were conducted using one oblong pier in positions of 60degree under one flow conditions. The study was conducted using a physical hydraulic model operated under clear-water conditions in cohesionless bed material. In this study, the time development of the local scour around the oblong pier fitted with and without collar plates was studied. Investigated was the effect of size and elevation collar on the time development of scour and its efficacy at preventing scour at a bridge pier. The time development of the scour hole around the model pier with and without a collar installed was compared with similar studies on bridge piers. The results of the model study indicated that the maximum depth of scour is highly dependent on the experimental duration. It was observed that, as the minimum depth of scour occurs for the square collar at width of 3B placed at elevation of 0.1B below the bed and the size of a collar plate increases, the scour decreases. Measuring depth of scouring based on experimental observation, an empirical relation is developed with regression coefficient 95%.     

A simple model for the evolution of supermassive black holes and the quasar population

An empirically motivated model is presented for accretion-dominated growth of supermassive black holes (SMBH) in galaxies, and the implications are studied for the evolution of the quasar population in the Universe. We investigate the core aspects of the quasar population, including space density evolution, evolution of the characteristic luminosity, plausible minimum masses of quasars, the mass function of SMBH and their formation epoch distribution. Our model suggests that the characteristic luminosity in the quasar luminosity function arises primarily as a consequence of a characteristic mass scale above which there is a systematic separation between the black hole and the halo merging rates. At lower mass scales, black hole merging closely tracks the merging of dark haloes. When combined with a declining efficiency of black hole formation with redshift, the model can reproduce the quasar luminosity function over a wide range of redshifts. The observed space density evolution of quasars is well described by formation rates of SMBH above  ∼10⁸  M_⊙  . The inferred mass density of SMBH agrees with that found independently from estimates of the SMBH mass function derived empirically from the quasar luminosity function.     

Ion acoustic solitons in negative ion plasmas with superthermal electrons

Korteweg-de Vries (KdV) equation for electrostatic wave in an unmagnetized negative ion plasma with superthermal electrons is derived using reductive perturbation technique. A generalized Lorentzian distribution (kappa distribution) is assumed for the electrons. The influence of spectral index (kappa) on the soliton is discussed in the presence of the negative ions. It is found that different plasma parameters such as (negative ion temperature, positive ion temperature, negative ion concentration, mass ratio of positive to negative ion) in the presence of superthermal electrons modify the ion acoustic solitary wave structure significantly.     

Magnetoacoustic solitons in dense astrophysical electron-positron-ion plasmas

Nonlinear magnetoacoustic waves in dense electron-positron-ion plasmas are investigated by using three fluid quantum magnetohydrodynamic model. The quantum mechanical effects of electrons and positrons are taken into account due to their Fermionic nature (to obey Fermi statistics) and quantum diffraction effects (Bohm diffusion term) in the model. The reductive perturbation method is employed to derive the Korteweg-de Vries (KdV) equation for low amplitude magnetoacoustic soliton in dense electron-positron-ion plasmas. It is found that positron concentration has significant impact on the phase velocity of magnetoacoustic wave and on the formation of single pulse nonlinear structure. The numerical results are also illustrated by taking into account the plasma parameters of the outside layers of white dwarfs and neutron stars/pulsars.     

Impacts of future land cover and climate change on the water balance in northern Iran

We evaluated the potential impacts of future land cover change and climate variability on hydrological processes in the Neka River basin, northern Iran. This catchment is the main source of water for the intensively cultivated area of Neka County. Hydrological simulations were conducted using the Soil and Water Assessment Tool. An ensemble of 17 CMIP5 climate models was applied to assess changes in temperature and precipitation under the moderate and high emissions scenarios. To generate the business-as-usual scenario map for year 2050 we used the Land Change Modeler. With a combined change in land cover and climate, discharge is expected to decline in all seasons except the end of autumn and winter, based on the inter-model average and various climate models, which illustrated a high degree of uncertainty in discharge projections. Land cover change had a minor influence on discharge relative to that resulting from climate change.     

Limit loads of ship structure components using the elastic modulus adjustment procedure (EMAP)

In this paper, the m_α-tangent method is implemented in conjunction with elastic modulus adjustment procedure (EMAP) and an algorithm has been proposed for limit load estimation. This technique is applied to a number of ship structure components possessing different kinematic redundancies. Specifying spatial variations in the elastic modulus, numerous sets of statically admissible and kinematically admissible stress and strain distributions are generated, and both lower and upper bound limit load multipliers are obtained. Utilizing the lower and upper bound multipliers, accurate limit loads of ship structure components are then determined using the m_α-tangent method. Results are compared with the inelastic finite element results and the available analytical solutions.     

Optimization of design parameters for controlled rocking steel braced dual-frames

A controlled rocking concentrically steel braced frame(CR-CSBF) is introduced as an alternative to conventional methods to prevent major structural damage during large earthquakes. It is equipped with elastic post-tensioned(PT) cables and replaceable devices or fuses to provide overturning resistance and dissipate energy, respectively. Although CR-CSBFs are not officially legalized in globally valid codes for new buildings, it is expected to be presented in them in the near future. The main goal...