Showing papers by "Istanbul Technical University published in 2000"

Heightened Odds of Large Earthquakes Near Istanbul: An Interaction-Based Probability Calculation

Abstract: We calculate the probability of strong shaking in Istanbul, an urban center of 10 million people, from the description of earthquakes on the North Anatolian fault system in the Marmara Sea during the past 500 years and test the resulting catalog against the frequency of damage in Istanbul during the preceding millennium. Departing from current practice, we include the time-dependent effect of stress transferred by the 1999 moment magnitude M = 7.4 Izmit earthquake to faults nearer to Istanbul. We find a 62 ± 15% probability (one standard deviation) of strong shaking during the next 30 years and 32 ± 12% during the next decade.

When did the western Anatolian grabens begin to develop

Abstract: Abstract To solve a long-lasting controversy on the timing and mechanism of generation of the western Anatolian graben system, new data have been collected from a mapping project in western Anatolia, which reveal that initially north-south trending graben basins were formed under an east-west extensional regime during Early Miocene times. The extensional openings associated with approximately north-south trending oblique slip faults provided access for calc-alkaline, hybrid magmas to reach the surface. A north-south extensional regime began during Late Miocene time. During this period a major breakaway fault was formed. Part of the lower plate was uplifted and cropped out later in the Bozdağ, Horst, and above the upper plate approximately north-south trending cross-grabens were developed. Along these fault systems, alkaline basalt lavas were extruded. The north-south extension was interrupted at the end of Late Miocene or Early Pliocene times, as evidenced by a regional horizontal erosional surface which developed across Neogene rocks, including Upper Miocene-Lower Pliocene strata. This erosion nearly obliterated the previously formed topographic irregularities, including the Bozdağ elevation. Later, the erosional surface was disrupted and the structures which controlled development of the Lower-Upper Miocene rocks were cut by approximately east-west trending normal faults formed by rejuvenated north-south extension. This has led to development of the present-day east-west trending grabens during Plio-Quaternary time.

Coseismic and Postseismic Fault Slip for the 17 August 1999, M = 7.5, Izmit, Turkey Earthquake.

Abstract: We use Global Positioning System (GPS) observations and elastic half-space models to estimate the distribution of coseismic and postseismic slip along the Izmit earthquake rupture. Our results indicate that large coseismic slip (reaching 5.7 meters) is confined to the upper 10 kilometers of the crust, correlates with structurally distinct fault segments, and is relatively low near the hypocenter. Continued surface deformation during the first 75 days after the earthquake indicates an aseismic fault slip of as much as 0.43 meters on and below the coseismic rupture. These observations are consistent with a transition from unstable (episodic large earthquakes) to stable (fault creep) sliding at the base of the seismogenic zone.

Dynamic oscillatory shear testing of foods — selected applications

Abstract: An ideal solid material will respond to an applied load by deforming finitely and recovering that deformation upon removal of the load. Such a response is called “elastic”. Ideal elastic materials obey Hooke's law, which describes a direct proportionality between the stress (σ) and strain (γ) via a proportionality constant called modulus (G), i.e., σ=Gγ. An ideal fluid will deform and continue to deform as long as the load is applied. The material will not recover from its deformation when the load is removed. This response is called “viscous”. The flow of simple viscous materials is described by Newton's law, which constitutes a direct proportionality between the shear stress and the shear rate ( γ ), i.e., σ=η γ . The proportionality constant η is called the shear viscosity. From energy considerations, elastic behavior represents complete recovery of energy expended during deformation, whereas viscous flow represents complete loss of energy as all the energy supplied during deformation is dissipated as heat. Ideal elastic and ideal viscous behaviors present two extreme responses of materials to external stresses. As the terms imply, these are only applicable for “ideal” materials. Real materials, however, exhibit a wide array of responses between viscous and elastic. Most materials exhibit some viscous and some elastic behavior simultaneously and are called “viscoelastic”. Almost all foods, both liquid and solid, belong to this group. The viscoelastic properties of materials are determined by transient or dynamic methods. The transient methods include stress relaxation (application of constant and instantaneous strain and measuring decaying stress with respect to time) and creep (application of constant and instantaneous stress and measuring increasing strain with time). Though such methods are fairly easy to perform, there are several limitations. Major among them is that the material response cannot be determined as a function of frequency.

Coeval plutonism and metamorphism in a latest Oligocene metamorphic core complex in northwest Turkey

Abstract: A metamorphic core complex of latest Oligocene age crops out in the Kazdag˘ mountain range in northwest Turkey. The footwall of the core complex consists of gneiss, amphibolite and marble metamorphosed at 5 ± 1 kbar and 640° ± 50 °C. The average muscovite and biotite Rb/Sr ages from the gneisses are 19 Ma and 22 Ma, respectively, and imply high temperature metamorphism during latest Oligocene times. The hangingwall is made up of an unmetamorphosed Lower Tertiary oceanic accretionary melange with Upper Cretaceous eclogite lenses. The hangingwall and footwall are separated by an extensional ductile shear zone, two kilometres thick. Mylonites and underlying high-grade metamorphic rocks show a N-trending mineral lineation with the structural fabrics indicat- ing down-dip, top-to-the-north shear sense. The shear zone, the accretionary melange and the high- grade metamorphic rocks are cut by an undeformed granitoid with a 21 Ma Rb/Sr biotite age, analytically indistinguishable from the Rb/Sr biotite ages in the surrounding footwall gneisses. The estimated pressure of the metamorphism, and that of the granitoid emplacement, indicate that the high-grade metamorphic rocks were rapidly exhumed at ~ 24 Ma from a depth of ~ 14 km to ~ 7 km by activity along the shear zone. The subsequent exhumation of the metamorphic rocks to the surface occurred during Pliocene-Quaternary times in a transpressive ridge between two overstepping fault segments of the North Anatolian Fault zone. The high-grade metamorphic rocks of the Kazdag ˘ range are surrounded by voluminous calc-alkaline volcanic and plutonic rocks of Late Oligocene-Early Miocene age, which formed above the northward-dipping Hellenic subduction zone. The magmatic arc setting of the core complex and stratigraphic evidence for subdued topography in northwest Turkey prior to the onset of extension suggest that the latest Oligocene regional extension was primarily related to the roll-back of the subduction zone rather than to the gravitational collapse.

Current-mode all-pass filters using current differencing buffered amplifier and a new high-Q bandpass filter configuration

Abstract: A new configuration realizing first-order canonical current processing all-pass filters based on current differencing buffered amplifier, a recently introduced active element, is proposed. Using this configuration, two types of first-order current-mode all-pass filters are derived. They employ only a single active element and a bare minimum number of passive components. No component-matching constrains are required. Because of the high performance of the current differencing buffered amplifier, they are suitable for wideband applications. The derived filters are cascadable because of their high output impedances and they use fewer active and/or passive components compared to their previously reported counterparts. As an application of the proposed first-order all-pass networks, a new current-mode high-Q bandpass filter, which offers a number of advantages over its counterparts, is also given.

Recyling of plastic wastes via pyrolysis

Abstract: Pyrolysis for the simultaneous generation of oils and gases can be convenient to obtain hydrocarbons and even to recover crude petrochemicals or to generate energy from waste plastics A Gray–King apparatus has been used to pyrolyze waste polyethylene (PE), polystyrene (PS), both separately and with different compositions Thermogravimetric analysis of waste plastics indicated the critical temperatures, which should be effective for pyrolysis The chosen heating rate was low in order to achieve higher liquid yields The results showed that waste PS yielded higher liquid, and waste PE yielded higher gaseous products The dominant liquid product of PS waste was styrene whereas for waste PE, prophenylbenzene was the dominant pyrolysis product

Use of Gamma Distribution in Hydrological Analysis

Abstract: In this study, amounts of daily rainfall and the ascension curve of the hydrograph are investigated. In both cases, the 2-parameter gamma distribution is used. The distribution is fitted to the amounts of daily rainfall and to the differences between the flows of successive days on the ascension curve of the hydrograph. The shape and scale parameters of the distribution, in both cases, are estimated in a monthly time interval. A 30-year daily rainfall series and a 35-year daily runoff series are used for the application. It may be seen that the distribution fits very well to the rainfall data and also that the ascension curve of the hydrograph can easily be represented by the distribution.

Was the Late Triassic orogeny in Turkey caused by the collision of an oceanic plateau

Abstract: A belt of Late Triassic deformation and metamorphism (Cimmeride Orogeny) extends east-west for 1100 km in northern Turkey. It is proposed that this was caused by the collision and partial accretion of an Early-Middle Triassic oceanic plateau with the southern continental margin of Laurasia. The upper part of this oceanic plateau is recognized as a thick Lower-Middle Triassic metabasite-marble-phyllite complex, named the Niltifer Unit, which covers an area of 120 000 km 2 with an estimated volume of mafic rocks of 2 x 105 km 3. The mafic sequence, which has thin stratigraphic intercalations of hemipelagic limestone and shale, shows consistent within-plate geochemical signatures. The Niliifer Unit has undergone a high-pressure greenschist facies metamorphism, but also includes tectonic slices of eclogite and blueschist with latest Triassic isotopic ages, produced during the attempted subduction of the plateau. The short period for the orogeny (< 15 Ma; Norian-Hettangian) is further evidence for the oceanic plateau origin of the Cimmeride Orogeny. The accretion of the Niltifer Plateau produced strong uplift and compressional deformation in the hanging wall. A large and thick clastic wedge, fed from the granitic basement of the Laurasia, represented by a thick Upper Triassic arkosic sandstone sequence in northwest Turkey, engulfed the subduction zone and the Niltifer Plateau. An east-west trending belt of latest Triassic deformation and regional metamorphism extends for over 1100 km in northern Turkey. The Early Mesozoic deformation (but not the regional metamorphism) was known previously ($eng6r 1979; Bergougnan & Fourquin 1982) and was referred to as the Cimmeride deformation ($eng6r et al. 1984). The Cimmeride deformation was ascribed to the closure of the Palaeotethys ocean following the collision of a Cimmerian continental sliver with the southern margin of Laurasia ($eng6r 1979; Seng6r et al. 1984). Here, an alternative explanation, involving the collision and partial accretion of an oceanic plateau to the southern margin of Laurasia, is proposed for the origin of the latest Triassic deformation and metamorphism in northern Turkey. A tectonic map of Turkey and the surrounding region is shown in Fig. 1. During the Palaeozoic and Mesozoic, the various continental blocks that make up present-day Turkey were situated on the continental margins of the Tethys Ocean. The Pontides, which comprise the Strandja, istanbul and Sakarya Zones, show Laurasian stratigraphic affinities, while the Anatolide-Tauride Block and the Klr~ehir Massif are tectonically and stratigraphically related to Gondwana ($eng6r & Yllmaz 1981; Okay et aL 1996; Okay & Ttiystiz 2000). The istanbul Zone is a continental fragment, which was translated south from the Odessa Shelf with the Cretaceous opening of the oceanic West Black Sea Basin (Fig. 1; Okay et al. 1994). Its stratigraphy is similar to that of the Scythian and Moesian platforms, with a fully developed Palaeozoic sedimentary sequence unconformably overlain by Triassic and younger sedimentary rocks (Haas 1968; Dean et al. 1997; G6rtir et al. 1997). In the Istanbul Zone, a weak latest Triassic deformation is marked by an unconformity between the Norian siliciclastic turbidites and the overlying Upper Cretaceous carbonates. The Strandja Zone consists of a Late Hercynian metamorphic and granitic basement unconformably overlain by Lower Triassic-Middle Jurassic sedimentary rocks (Chatalov 1988; Okay et al. 1996). The Anatol ide-Tauride Block and the Klr~ehir Massif are also devoid of Triassic metamorphism, and of any significant Triassic deformation. Several well studied Lower Mesozoic stratigraphic sections in the Taurides, including those in the Bornova Flysch Zone (Erdo~an et al. 1990.). and in the central Taurides (Gutnic et al. 1979; Ozgti11997), show a continuous transition between Triassic and Jurassic with no evidence of an intervening deformation phase. The pre-Jurassic thrusting, described by Monod & Akay (1984) from a small locality in the central Taurides, is as yet of unknown significance. Late Triassic deformation and regional metamorphism in Turkey are predominantly found in the Sakarya Zone, which will form the main subject of this paper. From: BOZKURT, E., WINCHESTER, J. A. & PIPER, J. D. A. (eds) Tectonics and Magmatism in Turkey and the Surrounding Area. Geological Society, London, Special Publications, 173, 25-41.1-86239-064-9/00/$15.00 (C) The Geological Society of London 2000.

Biochar from the Straw-Stalk of Rapeseed Plant

Abstract: Agricultural residues are an important and inexpensive bioresource for energy production. In this study the slow pyrolysis technique has been applied to the straw and stalk of rapeseed plant, and the effects of temperature and heating rate on the yields and characteristics of the solid products (biochars) have been investigated. Experiments were performed in a tubular reactor under nitrogen atmosphere at constant heating rate (5 °C min-1) and varying temperatures (400−900 °C) and at constant temperature (800 °C) and varying heating rates (5, 10, 15, °C min-1). The biochars obtained are carbon rich, reactive, and relatively pollution-free potential solid biofuels.

Effect of ion nitriding on fatigue behaviour of AISI 4140 steel

Abstract: Ion nitriding has become a popular thermo-chemical surface treatment, which is being used to develop fatigue and wear characteristics of steels. Besides the increased strength, the formation of high compressive residual stresses in the case region causes remarkable improvement in fatigue properties of steels. In this study, the effect of case depth on fatigue performance of AISI 4140 low alloy steel has been investigated by conducting a series of rotary bending fatigue tests at the frequency of 95 Hz, on hour glass shaped, 4 mm diameter specimens, which had been ion nitrided at 748 K for 1, 3, 8 and 16 h. Up to 50% improvement in fatigue strength of the steel has been attained by ion nitriding, depending on the case depth formed during the process. The comparison of test results between ion and liquid nitrided specimens having the same case and core properties, has shown that a 12% increase in fatigue strength could be reached by ion nitriding with respect to conventional, salt bath nitriding process. An attempt was made to establish some empirical relationships between the parameters defining relative case depth, which consider case depth and specimen size together, and fatigue strength of ion nitrided steel. It was obtained that the subsurface ‘fish eye’ type crack formation is the dominant fatigue crack initiation mechanism in ion nitrided AISI 4140 steel, and a map has been constructed to illustrate the locations of crack origins depending upon the case depth and the cyclic stress acting on specimens. It was also tried to explain the conditions promoting the ‘fish eye’ crack formation by analysing the combined effects of residual and applied stress patterns as well as inclusion size.

Analysis of input-output clustering for determining centers of RBFN

Abstract: The key point in design of radial basis function networks is to specify the number and the locations of the centers. Several heuristic hybrid learning methods, which apply a clustering algorithm for locating the centers and subsequently a linear least-squares method for the linear weights, have been previously suggested. These hybrid methods can be put into two groups, which will be called as input clustering (IC) and input-output clustering (IOC), depending on whether the output vector is also involved in the clustering process. The idea of concatenating the output vector to the input vector in the clustering process has independently been proposed by several papers in the literature although none of them presented a theoretical analysis on such procedures, but rather demonstrated their effectiveness in several applications. The main contribution of this paper is to present an approach for investigating the relationship between clustering process on input-output training samples and the mean squared output error in the context of a radial basis function network (RBFN). We may summarize our investigations in that matter as follows: (1) A weighted mean squared input-output quantization error, which is to be minimized by IOC, yields an upper bound to the mean squared output error. (2) This upper bound and consequently the output error can be made arbitrarily small (zero in the limit case) by decreasing the quantization error which can be accomplished through increasing the number of hidden units.

Predicting Bursting Strength of Cotton Plain Knitted Fabrics Using Intelligent Techniques

Abstract: The bursting strength of cotton plain knitted fabrics is predicted before manufacturing using intelligent techniques of neural network and neuro-fuzzy approaches in this re search. Among many parameters that affect fabric bursting strength, fabric weight, yarn breaking strength, and yarn breaking elongation are input elements for the predictions. In this research, both the multi-layer feed-forward neural network and adaptive network- based fuzzy inference system, a combination of a radial basis neural network and the Sugeno-Takagi fuzzy system, are studied. Both systems have the ability to learn training data successfully, and testing errors are small enough to give an approximate knowledge of the bursting strength of the fabric to be knitted.

Robust sliding-mode control for the uncertain MIMO aircraft model F-18

Abstract: Robust flight control laws based on variable structure control (VSC) theory and Lyapunov V-function method are designed for a simplified aircraft model F-18. A min-max control (MMC) and VSC laws are derived, for multi-input multi-output (MIMO) systems with plant uncertainties and input disturbance. Two types of robust feedback controllers MMC and VSC for uncertain MIMO systems are considered. For both cases the existence conditions of a stable sliding mode and the robust asymptotic stability in uncertain MIMO systems by MMC and VSC are investigated. For the design of an MMC and VSC, measurable states and sliding surface are chosen so that the zero dynamics of the system are stable. An application of tracking and positioning of VSC of longitudinal dynamics is presented. Finally, simulation results are presented to show the effectiveness of the design methods.