Showing papers by "Istanbul Technical University published in 1995"

Tectonic Evolution of the Tibetan Plateau: A Working Hypothesis Based on the Archipelago Model of Orogenesis

Abstract: The geology of the Tibetan Plateau is interpreted within the framework of archipelago orogenesis, with the relief of the plateau owing its origin to the Neogene subduction of the Indian continental lithosphere under Tibet. Late Precambrian back-arc spreading resulted in the genesis of island arcs and back-arc basins south of the Angaran craton. A magmatic front is located at or near the position of the Kunlun Mountains. The part including and south of the Tianshan and Neimonide was separated from the Angaraland and formed microcontinents as well as numerous back-arc basins and remnant arcs in China. The Early Paleozoic basins collapsed behind the Kunlun magmatic front to form the Tianshan, Qilian, and other mountains. A part ofthe accretionary complex to the south of the Kunlun Arc was split off to form Late Paleozoic and Early Mesozoic island arcs and back-arc basins to the northeast of the Bangong/Nujiang suture. The collapse of those basins before the end of the Triassic caused the accretion of the arc...

Syn-rift sedimentation and structural development of the Gediz and Büyük Menderes graben, western Turkey

Abstract: The Buyuk Menderes and Gediz graben of western Turkey developed during Miocene to Recent extension in the Aegean region. New mapping of structures and sedimentary lithofacies in exhumed basin-fill strata is used to reconstruct the evolution of the graben. Field evidence shows that extension was primarily accommodated by tilted fault-blocks 0.2–0.8 km wide, bounded by planar faults, with some modification by antithetic faulting. The basins are faulted on both margins, although they are highly asymmetric, with dominant 9footwall9 margins characterized by steeper topography and greater thicknesses of exhumed strata. Within exhumed graben-fill sequences, lacustrine, axial fluvial, and laterally-derived sedimentary facies can be identified. Palaeocurrent orientations, divergent wedge geometries and intra-basin unconformities all indicate that exposed sediments are syn-tectonic. The present day map patterns demonstrate that the position of graben-bounding faults has migrated basinward with time. As a result, large-scale erosion and recycling of the uplifted basin fill have created extensive footwall-derived alluvial fans. These displace the axial drainage towards the hanging-wall margins, away from the locus of greatest subsidence.

Applied Hydrogeology for Scientists and Engineers

Abstract: Introduction Hydrogeology of Groundwater Reservoirs Groundwater Flow Properties Aquifer Properties Groundwater Flow Laws Water Wells Field Measurements Steady-State Flow Aquifer Tests Porous Medium Aquifer Tests Fractured Medium Aquifer Tests Well Test Nonlinear Flow Aquifer Tests Index

Plane surface suddenly set in motion in a non-Newtonian fluid

Abstract: The flow field of a fluid being called “the third order fluid” or the “fluid of grade three” is considered for a non-Newtonian flow in the vicinity of a plane wall, suddenly set in motion. The velocity field of the flow is described by a fourth order, non-linear partial differential equation. The solution of this differential equation shows that for short time a strong non-Newtonian effect is present in the velocity field. However, for long time the velocity field becomes a Newtonian one.

Basinward migration of rift-border faults: Implications for facies distributions and preservation potential

Abstract: Basinward migration of half-graben footwall margins occurs throughout the active Aegean extensional province and has significant implications for facies distributions and preservation potential in synrift fills worldwide. Recognition of this phenomenon is particularly important for predicting the preservation and distribution of hydrocarbon reservoirs in rift basins. Using an example from the Gediz graben of western Turkey, it is shown that basinward migration of footwall margins exhumes proximal facies of lateral sedimentary systems, severely limiting their preservation potential and providing a ready source of easily erodible material. This in turn leads to the generation of extensive footwall-derived depositional systems, which frequently displace axial drainage systems toward the hanging-wall dip slope.

A fully-dispersive nonlinear wave model and its numerical solutions

Abstract: A set of fully-dispersive nonlinear wave equations is derived by introducing a velocity expression with a few vertical-dependence functions and then applying the Galerkin method, which provides an optimum combination of the verticaldependence functions to express an arbitrary velocity field under wave motion. The obtained equations can describe nonlinear non-breaking waves under general conditions, such as nonlinear random waves with a wide-banded spectrum at an arbitrary depth including very shallow and far deep water depths. The single component forms of the new wave equations, one of which is referred to here as "time-dependent nonlinear mild-slope equation", are shown to produce various existing wave equations such as Boussinesq and mild-slope equations as their degenerate forms. Numerical examples with comparison to experimental data are given to demonstrate the validity of the present wave equations and their high performance in expressing not only wave profiles but also velocity fields.

Differential and integral sensitivity formulations and shape optimization by BEM

Abstract: Two different formulations for shape design sensitivity analysis are provided for heat conducting solids. The material derivative concept and the adjoint variable method of analysis are the common techniques utilized in the two formulations. It is found that complementary boundary integral equations arise in the case of the integral sensitivity analysis. Numerical solutions of the primary and adjoint equations are achieved by the BEM, whilst shape configurations are discretized by means of ray and height functions. Several 2-D constrained shape optimization problems are solved by the proposed numerical solution techniques.

Effect of Heat Treatment on the Flotation of Turkish Lignites

Abstract: Unlike bituminous coals which oxidize upon heat treatment, lower rank coals such as lignites have been found to exhibit improved hydrophobicity on heating. Microflotation tests, zeta potential and infrared measurements have been carried out to understand the flotation behavior of four different lower-rank coals of varying ash and moisture contents. While Yenikoy and Saray coals exhibited improved floatability, Alpagut and Soma coals showed either no improvement or adverse effect upon thermal treatment. The zeta potential values of heat treated samples showed drastic changes compared to the original sample. Interaction of anionic and cationic surfactants with the original and heat treated coals was tested to find out their effect on flotation. A quantitative approach was adapted to correlate the flotation response and the quantity of hydrophobic and hydrophilic groups in coal as determined by infrared measurements. It is shown that the amount of hydrophobic and hydrophilic groups in coal dictates whether a...

The λ-phase transitions in NH4Cl

Abstract: We show here the correlations between the volume changes and the vibrational frequencies of the disorder-induced Raman modes of NH4Cl near the λ-phase transitions of first order (P=0), tricritical (P⋍1.6 kbar) and second order (P⋍2.8 kbar). We obtain the values of the mode Gruneisen parameter for each phonon across the λ-phase transitions and use them to predict the Raman frequencies for the phonon modes studied as functions of temperature in the λ-phase change regions. Our calculated frequencies for the M-point phonons of v7 (93 cm−1) and v5 (144 cm−1) of NH4Cl are in good agreement with our observed Raman frequencies. This shows that the method employed here is satisfactory for predicting the Raman frequencies from the volume changes near the λ-phase transitions in the NH4Cl system.

Electrokinetic Properties of Some Hydrated Boron Minerals

Abstract: Electrokinetic properties of a series of boron minerals, i.e., colemanite, ulexite, inderite, and tunellite, are investigated using the microelectrophoresis technique. Colemanite exhibits an isoelectric point at pH 10.5. Ulexite, inderite, and tunellite yield practically no isoelectric point in the pH range of 7 to 11. While ulexite remains negatively charged, inderite and tunellite show positive charges in the pH range studied. The potential determining ions for these minerals are the constituent lattice cations, Ca 2+ , Mg 2+ , and Sr 2+ , and the anion, B 4 O 2- 7 . The H + and OH - ions which indirectly control the ratio of HCO - 3 /CO 2- 3 are also the potential determining ions for the hydrated boron minerals studied. The electrokinetic results generally support the adsorption of oppositely charged flotation collectors on boron minerals through electrostatic attraction.

The effect of heat treatment on corrosion behavior of laser surface melted 304L stainless steel

Abstract: Laser surface melting (LSM) improves the passivation and pitting behavior of 304L stainless steel. This improvement was attributed to microstructural modification, mainly to increased δ-ferrite content, and elimination and/or redistribution of sulfur based inclusions. In this study, in order to clarify the role of microstructural changes that took place during LSM on electrochemical behavior, laser surface melted 304L grade stainless steel was heat treated at 1050 °C. A detailed analysis of the electrochemical behavior of as-received, laser surface melted and laser surface melted + heat treated 304L in sulfuric acid and sodium chloride solutions was conducted. Effects of laser surface melting and post heat treatment on pit morphology was also investigated.

Measuring elongational properties of mozzarella cheese

Abstract: A vertical uniaxial extension apparatus was developed for determining elongational properties of Mozzarella cheese over the course of one month of refrigerated storage. Cheese specimens suspended in hot oil (4OC) first 'underwent melting and then stretching under the influence of a constant force. Samples did not break even afier 400% extension. Strain rate and sample temperature both increased during a test. Transient elongational (TE) viscosity of Mozarella cheese decreased with increasing strain rate and sample temperature. Proteolysis of caseins in Mozzarella, determined by gel electrophoresis, did not alter its TE viscosity to an extent measurable by our method.

Oxidative polymerization of pyrrole in polymer matrix

Abstract: The oxidative matrix polymerization of pyrrole (Py) by Ce(IV) in the presence of Polyacrylic acid (PAA) has been studied to obtain water-soluble and insoluble products. The role of the PAA, Pyrrole, and Ce(IV) concentration, order of component addition, the structure of polymer matrix [PAA, Hydroxy Ethyl Cellulose (HES), Poly-N-vinylpyrrolidone (PVP)], and model unit of PAA (propionic acid), on the polymerization system were investigated. Interaction of PAA with insoluble polypyrrole (PPy) and the interpolymer complex formation were investigated along with the aggregation of PPy onto the matrix polymer followed by spectral shifts. FTIR results of insoluble products obtained from the PAA-Py-Ce(IV) system and solubility of the system is explained in light of the mechanism of the polymerization of pyrrole on the polymer matrix. © 1995 John Wiley & Sons, Inc.

Characteristics of safflower seed oils of Turkish origin

Abstract: Technological characteristics of oils extracted from seventeen varieties of safflower seeds (Carthamus tinctorius L.) of Turkish origin were investigated for their utilization prospects in the food industry and in other industrial sectors. Standard procedures were applied to determine the technological characteristics of seventeen varieties of safflower seeds and the safflower seed oils; fatty acid compositions were determined by gas-liquid chromatography. Results show that safflower seed oils are suitable both for food and industrial purposes.