A multifractal model of crack coalescence in rocks

Geometric characteristics of fractal sets of cracks are investigated from the standpoint of their coalescence. A 1D computer model, in which a realistic character of forms of crack sets is achieved through the inducing of sets with the use of the multiplicative cascade procedure, is considered. The investigation is aimed at the determination of conditions of coalescence of cracks organized as a superposition of fractal subsets of a unified set of cracks. The process of crack coalescence is investigated for three different values of the coalescence criterion. The geometric characteristics of the sets of cracks that are necessary for the transition of the crack coalescence process into an avalanche-like stage are estimated.     

Dynamics of a moored barge under regular and random waves

Developments in the study of wave forces and construction techniques in deep water by the offshore oil industry have increased the use of marine terminals at deep water locations. A thorough understanding of moored ship dynamics when subjected to waves, wind and current combined with the use of flexible mooring lines would help to design berthing terminals for exposed areas. In this paper, the three dimensional problem of wave interactions with a barge moored to a single point is dealt with, based on the finite element method. The effect of flexibility of the mooring line and the point of mooring on the response of the barge as well as the mooring line tension is investigated. The paper compares the numerical results with model tests carried out on a barge moored to a fixed support under regular and random waves in head sea. The effect of stiffness of the mooring line on the barge response for different mooring points is discussed, which would be useful for the designers. The effect of viscous damping is also considered. The analytical results are in good agreement with the experimental results in both regular and random waves.     

Oxygen isotope and geochemical variations in the Missouri River

Oxygen isotope ratios in streamflow of the Missouri River basin vary geographically due to differences in source precipitation and the integration of waters from upstream regions. Average '¹⁸O values in the Missouri River main stem systematically increase from less than -17‰ in the headwaters to about -9‰ in the lower basin. Seasonal variations at a given location result from fluctuations in meteoric precipitation, residence time in reservoirs and groundwater systems, evaporation, and snowmelt. Average water chemistry values are successfully predicted for the upstream stations of two reaches on the lower Missouri River based on changes in discharge along each reach and water quality measurements collected at the downstream stations. Source regions for some dissolved ions found in the lower Missouri River are also identified. Sodium and sulfate originate predominantly from the basin above Sioux City, Iowa, while nitrate is largely derived from agricultural regions below Sioux City.     

Determination of crustal movements in Turkey by terrestrial geodetic methods

In Turkey, neotectonic activity originated from the collision of the Arabian and Anatolian land masses during the Middle Miocene. As a result of the collision, westward escape of the Anatolian block introduced E-W compression in Western Turkey which began to be relieved by N-S extension. The North Anatolian Fault (NAF) is the major active strike-slip fault that was formed under the neotectonic regime. The rates of the motion along this fault estimated by several authors are in the range of 0.4–2.9 cm/a according to kinematic data. In Turkey, the first studies of crustal movements by geodetic methods were started in the west section of the NAF in 1972. So far, individual activities and studies coordinated by multidisciplinary projects have been realized in this region. The results obtained from available geodetic data indicate the motion of the Anatolian block relative to Eurasia.     

Mean wind-direction shear through a forest canopy

The equations of motion applying to the wind field in a forest canopy are simplified to a balance between the shearing stress gradient and either the form-drag of the leaves in the upper dense canopy, or the overall horizontal pressure gradient in the more open space beneath. The equations imply that, in descending through the forest, the stress and wind vectors turn through an angle which depends on the forest characteristics and on the stability and the speed of the airflow above the forest. The turning is roughly confirmed by an overall average measured on a very flat site near Thetford, Norfolk, covered by an extensive uniform pine forest.     

Determination of organophosphorus insecticide residues in the rice paddies

In most rice paddies in Mazandaran Province, diazinon is applied to control Chilo suppressalis. Due to the extensive application of insecticides in the rice paddies of the Caspian coasts of Iran, this investigation was carried out on the rice fields in order to obtain the necessary data and information on the concentration of insecticide residues. A total of 125 samples were taken from five areas of Amol township in 2007. Then, according to the analysis of variance procedures, the water samples were statistically analyzed after the spraying of diazinon. Results indicate that the insecticide was used frequently to control stem boring caterpillar of rice. The residuals of this toxic chemical were observed in the majority of stations from the day after the spraying until one to two months later. The greatest level of diazinon was observed in station 1 in amount of 1.14 ppm. This study revealed that the physical and chemical properties of the studied diazinon such as fumigation characteristic as well as the ecological conditions and soil type influence the reduction and eventual removal of the insecticides during the cultivation and harvest periods.     

New seismic data in the Mozambique Channel

This paper presents seismic reflection and refraction data from the Mozambique Channel, collected between 1971 and 1973. A deep sedimentary basin (up to 5 km of sediments) opens southwards to the Mozambique Basin, and is bounded to the east by the Davie Ridge and beyond by the marginal plateau of Malagasy. A continuous reflector (C), possibly of Cretaceous age, is identified between layers having seismic interval velocities of 2.4–2.8 km/s and 3.1–3.4 km/s. The deepest sediments have velocities of 4.5–4.9 km/s and overlie a layer with velocity 5.5 km/s, which may be volcanic in the north-east of the Channel.The crust occupying most of the Channel is probably pre-Cretaceous in age, and may be largely continental in nature. This is supported by subdued magnetic anomalies and the possibility of a continuous Karroo sedimentary section across the northern Channel. The oceanic crust of the Mozambique Basin may extend as far north as 24°S, into the western Channel only. The problem of the origin of the Mozambique Channel remains unresolved, although a long sedimentary history indicates that Malagasy may have separated from Mainland Africa prior to Karroo times. The Davie Ridge may possibly represent a relict strike-slip fault, which permitted movement along a north-south line.