Kelvin–Helmholtz instability in a weakly ionized layer

We study the linear theory of Kelvin–Helmholtz instability in a layer of ions and neutrals with finite thickness. In the short wavelength limit the thickness of the layer has a negligible effect on the growing modes. However, perturbations with wavelength comparable to layer’s thickness are significantly affected by the thickness of the layer. We show that the thickness of the layer has a stabilizing effect on the two dominant growing modes. Transition between the modes not only depends on the magnetic strength, but also on the thickness of the layer.     

Salinization of groundwater in arid and semi-arid zones: an example from Tajarak,western Iran

Study of the groundwater samples from Tajarak area, western Iran, was carried out in order to assess their chemical compositions and suitability for agricultural purposes. All of the groundwaters are grouped into two categories: relatively low mineralized of Ca–HCO₃ and Na–HCO₃ types and high mineralized waters of Na–SO₄ and Na–Cl types. The chemical evolution of groundwater is primarily controlled by water–rock interactions mainly weathering of aluminosilicates, dissolution of carbonate minerals and cation exchange reactions. Calculated values of pCO₂ for the groundwater samples range from 2.34 × 10⁻⁴ to 1.07 × 10⁻¹ with a mean value of 1.41 × 10⁻² (atm), which is above the pCO₂ of the earth’s atmosphere (10^−3.5). The groundwater is oversaturated with respect to calcite, aragonite and dolomite and undersaturated with respect to gypsum, anhydrite and halite. According to the EC and SAR the most dominant classes (C3-S1, C4-S1 and C4-S2) were found. With respect to adjusted SAR (adj SAR), the sodium (Na⁺) content in 90% of water samples in group A is regarded as low and can be used for irrigation in almost all soils with little danger of the development of harmful levels of exchangeable Na⁺, while in 40 and 37% of water samples in group B the intensity of problem is moderate and high, respectively. Such water, when used for irrigation will lead to cation exchange and Na⁺ is adsorbed on clay minerals while calcium (Ca²⁺) and magnesium (Mg²⁺) are released to the liquid phase. The salinity hazard is regarded as medium to high and special management for salinity control is required. Thus, the water quality for irrigation is low, providing the necessary drainage to avoid the build-up of toxic salt concentrations.     

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...     

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.     

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.     

Approximate formulas for rotational effects in earthquake engineering

The paper addresses the issue of researching into the engineering characteristics of rotational strong ground motion components and rotational effects in structural response. In this regard, at first, the acceleration response spectra of rotational components are estimated in terms of translational ones. Next, new methods in order to consider the effects of rotational components in seismic design codes are presented by determining the effective structural parameters in the rotational loading of structures due only to the earthquake rotational components. Numerical results show that according to the frequency content of rotational components, the contribution of the rocking components to the seismic excitation of short period structures can never be ignored. During strong earthquakes, these rotational motions may lead to the unexpected overturning or local structural damages for the low-rise multi-story buildings located on soft soil. The arrangement of lateral-load resisting system in the plan, period, and aspect ratio of the system can severely change the seismic loading of wide symmetric buildings under the earthquake torsional component.     

Formation of fluctuations in a molecular slab via isobaric thermal instability

Frictional heating by the ion-neutral drift is calculated and its effect on the isobaric thermal instability is studied. Ambipolar drift heating of a one-dimensional self-gravitating magnetized molecular slab is used under the assumptions of quasi-magnetohydrostatic and local ionization equilibrium. We see that ambipolar drift heating is inversely proportional to density and its value in some regions of the slab can be significantly larger than the average heating rates of cosmic rays and turbulent motions. The results show that isobaric thermal instability can occur in some regions of the slab, and thus it may produce slab fragmentation and formation of astronomical unit scale condensations.     

Validation of soil moisture simulation with a distributed hydrologic model (WetSpa)

The objective of this paper is to test the ability of a spatially distributed hydrologic model (WetSpa) to simulate soil moisture. The test is conducted in the Baron Fork river basin (Oklahoma, USA), where soil moisture has been recorded on a daily basis at the WEST site soil moisture monitoring station of the Oklahoma Mesonet. The model is calibrated by comparing hourly simulated and observed river flows at Eldon gaging station from October 1, 1995 to December 31, 1996. The model performance to predict hourly river flows is verified by comparing model estimates and observations from January 1, 1997 to December 31, 2000. Next, the model predictions of soil moisture are compared with observations of WEST site soil moisture monitoring station for the same validation period. The observations are well reproduced by the model with errors that are within range of the observation accuracy, although the predictions show somewhat more abrupt temporal fluctuations as the whole root zone is considered to react instantaneously to precipitation events. The good performance compared to other studies is especially attributed to the quality of the rainfall data provided by weather radars. It is concluded that the performance of the model to predict soils moisture is promising, although spatial patterns still have to be verified.