Viscothermal instability in Keplerian disc and formation of overdense regions

Viscosity have a significant effect in evolution of accretion disc. In this paper, we investigate the thermal effect of viscosity in the accretion disc that may cause instability to produce overdense regions through it. For this purpose, the linear perturbation method is used to investigate instability on this so-called viscothermal effect. The results show that instability can occur in accretion disc so that larger overdense regions are formed at far greater distance of protostar. This mechanism may explain formation of larger protoplanets farther from protostars.     

Spatial correlation between groundwater seepage faces and fault zone in high bedrock channel: method and application

The groundwater may recharge the surface water bodies through seepage faces and springs.The spatial correlation between the fault zones and the groundwater seepage faces results in deep understanding of the hydrogeologic regime,especially where there is no monitoring boreholes.Locating these recharging zones by conventional methods is a challenging task;particularly in areas where(1)there is no hydrogeologic monitoring boreholes or reliable data,(2)private pumps withdraw the stream,and(3)intense canopy limits the use of drones and satellite images.This paper aims to study the relationship between the fault zones and occurrence of the groundwater seepage faces by using the high resolution handheld thermal imaging cameras as a tool to locate the seepage faces along a small river in the Damavand County,north of Iran.The correlation between the structural geology features and occurrence of the groundwater seepage faces revealed that the stream in the study area is being recharged by the groundwater at extensive fault zones.Additionally,this study suggests that the handheld thermal imaging cameras are a useful robust tools to evaluate the surface-groundwater interaction.However,it is essential to use the field structural geologic and hydrogeologic observations to interpret the thermal images.     

Field experiments to improve the efficacy of gargoor (fish trap) fishery in Kuwait’s waters

Fish traps were investigated to understand the effects of season, bait type, trap size, and trap soak time on catch rates, catch composition, and trap loss rates from March 2004 to September 2005, to improve the performance and management of Kuwait’s gargoor (cage style fish trap) fishery, which used to be the nation’s most important one in terms of value and landings volume. Catch rates were the highest in April/May (5-8 kg/trap haul) and again in December (7 kg/trap haul). Bait type and trap size also affected catch rates and species composition. Of the seven baits tested, the best catch rates, >5 kg/trap haul, occurred with cuttlefish (Sepia pharaonis), but wolf-herring (Chirocentrus dorab) and mullet (Liza klunzingeri) also produced good results (4-5 kg/trap haul). Within the five tested sizes, the two largest-sized traps captured more fish and larger size fish. Analysis of variance (ANOVA) showed significant differences of catch rate among traps with different baits as well as among traps of different sizes. Duncan test further revealed these differences between two specific baits and sizes. Cluster Analysis of species composition showed more differences among different baits than among different trap sizes. Longer soak times did not result in larger catch rates, but increased trap loss. About 10-day soak time resulted in trap loss 7%, while 40-day soak time could result in a loss of around 20%. Consequently, it is recommended that the gargoor be checked every 10 or fewer days. The average overall catch rate during the study period was lower than that of 1980s (4.5 vs. 5.8 kg/trap haul), indicating a possible decline of fish abundance in Kuwait’s waters. It is recommended that the number of gargoor fishing boats and gargoors from each boat should be limited to allow stock rehabilitation.     

The fast Hankel transform1

An efficient algorithm is presented to compute the Hankel transform. The algorithm yields simultaneously all the required weights for a given order of the Bessel function using the fast Fourier transform. An additional shift is introduced to the filter abscissa besides Koefoed's shift to give a better filter performance.     

Major ion chemistry of groundwaters in the Bahar area, Hamadan, western Iran

Hydrochemical investigations were carried out in Bahar area, Hamadan, western Iran, to assess the chemical composition of groundwater. The area falls in a semi-arid type of climate. In this area, groundwater has been exploited over the past century mainly for irrigation and water supply. A total of 135 representative groundwater samples were collected from different wells to monitor the water chemistry of various ions. Chemical analysis of the groundwater shows that the mean concentration of the cations is of the order Ca²⁺>Mg ²⁺>Na⁺>K⁺, while that for anions is SO₄^2–>HCO₃^–>Cl^–>NO₃^–. Statistical analyses indicate positive correlation between the following pairs of parameters Cl^– and Mg ²⁺ (r=0.71), Cl^– and Na⁺ (r=0.76), HCO₃^– and Na⁺ (r=0.56), SO₄^2– and Mg²⁺ (r=0.76), SO₄^2– and Na⁺ (r=0.69). Water presents a large spatial variability of the chemical facies (Ca-HCO₃, Ca-SO₄, Mg-HCO₃, Mg-SO₄, Na-HCO₃) which is in relation to their interaction with the geological formations of the basin (carbonates, dolomite and various silicates) and evaporation. The hydrochemical types Ca-HCO₃ and Ca-SO₄ dominate the largest part of the studied area. The dissolution of halite, calcite, dolomite, and gypsum explains part of the contained Na ⁺, Ca²⁺, Mg²⁺, Cl^–, SO₄^2– and HCO₃^–, but other processes, such as cation exchange and weathering of aluminosilicates also contribute to the water composition.     

Restoring groundwater levels after tunneling: a numerical simulation approach to tunnel sealing decision-making

Tunneling is often unpopular with local residents and environmentalists, and can cause aquifer damage. Tunnel sealing is sometimes used to avoid groundwater leakage into the tunnel, thereby mitigating the damage. Due to the high cost of sealing operations, a detailed hydrogeological investigation should be conducted as part of the tunneling project to determine the impact of sealing, and groundwater modeling is an accurate method that can aid decision-making. Groundwater-level drawdown induced by the construction of the Headrace water-conveyance tunnel in Sri Lanka dried up 456 wells. Due to resulting socio-environmental problems, tunnel sealing was decided as a remedy solution. However, due to the expectation of significant delays and high costs of sealing, and because the water pressure in the tunnel may prevent groundwater seepage into the tunnel during operation, there was another (counter) decision that the tunnel could remain unsealed. This paper describes groundwater modeling carried out using MODFLOW to determine which option—sealed or unsealed tunnel—is more effective in groundwater level recovery. The Horizontal Flow Barrier and River packages of MODFLOW were used to simulate sealed and unsealed tunnels, respectively. The simulation results showed that only through tunnel sealing can the groundwater level be raised to preexisting levels after 18 years throughout the study area. If the tunnel remains unsealed, about 1 million m³/year of water conveyed by the tunnel will seep into the aquifer, reducing the operational capacity of the tunnel as a transport scheme. In conclusion, partial tunnel sealing in high-impact sections is recommended.

     

Dynamics of charged dust particles in protoplanetary discs

We study the effect of an imposed magnetic field on the motion of charged dust particles in magnetically active regions of a protoplanetary disc. Assuming a power law structure for the vertical and the toroidal components of the magnetic field for the regions beyond magnetically dead region of the disc, the radial and the vertical velocities of the charged particles, in the asymptotic case of small particles, are calculated analytically. While grains with radii smaller than a critical radius significantly are affected by the magnetic force, motion of the particles with larger radii is independent of the magnetic field. The critical radius depends on the magnetic geometry and the charge of the grains. Assuming that a grain particle has one elementary charge and the physical properties of the disc correspond to a minimum-mass solar nebula, we show that only micron-sized grains are affected by the magnetic force. Also, charge polarity determines direction of the radial velocity. For such small particles, both the radial and the vertical velocities increase due to the magnetic force.     

Seismotectonics and consequences of the 1930s large earthquakes in eastern Mazandaran,north of Iran

Early in the 1930s,two relatively large earthquakes (Kosout,magnitude 6.8,and Talarrud,magnitude 5.8) shook the eastern Mazandaran,northern Iran.Despite the his...     

Rayleigh wave separation using high-resolution time-frequency polarization filter

Obtaining geological information from seismic data motivates researchers to innovate and improve seismic wave processing tools. Polarization-based methods have received much attention regarding their ability to discriminate between different phases of the seismic wave based on polarity. Combining the intuitive definition of polarity in the frequency domain (monochromatic waves) with the non-stationary properties provided by time-domain methods, time-frequency approaches are attracting widespread interest because they localize the information extracted from the seismic waves in the joint time and frequency domains. Due to the lack of high-resolution time-frequency maps, the time-frequency polarization approach was not able to resolve specific temporal polarity changes in the seismic signal. The main objective of this study was to devise a robust time-frequency-based polarization filtering method using high-resolution polarization attributes obtained directly from the sparse time-frequency map without using Eigen analysis or analytic signals. The method proposed here utilizes a computationally effective sparsity-based adaptive S-transform to obtain a high-resolution polarization map of an inherently non-stationary seismogram for the entire frequency content of the signal at different times. The superiority of the proposed method over the S-transform method was verified using synthetic and real data sets to calculate the polarization attributes in the time-frequency domain and separate the Rayleigh waves from the seismogram.