Showing papers by "Istanbul Technical University published in 2002"

Families of scroll grid attractors

Abstract: In this paper a new family of scroll grid attractors is presented. These families are classified into three called 1D-, 2D- and 3D-grid scroll attractors depending on the location of the equilibrium points in state space. The scrolls generated from 1D-, 2D- and 3D-grid scroll attractors are located around the equilibrium points on a line, on a plane or in 3D, respectively. Due to the generalization of the nonlinear characteristics, it is possible to increase the number of scrolls in all state variable directions. A number of strange attractors from the scroll grid attractor families are presented. They have been experimentally verified using current feedback opamps. Also Lur'e representations are given for the scroll grid attractor families.

Capital budgeting techniques using discounted fuzzy versus probabilistic cash flows

Abstract: Risk analysis involves the development of the probability distribution for the measure of effectiveness. The risk associated with an investment alternative is generally either given as the possibility of an unfavorable value of the measure of effectiveness or measured by the variance of the measure of effectiveness. In an uncertain economic decision environment, an expert's knowledge about discounting cash flows consists of a lot of vagueness instead of randomness. Cash amounts and interest rates are usually estimated by using educated guesses based on expected values or other statistical techniques to obtain them. Fuzzy numbers can capture the difficulties in estimating these parameters. In this paper, the formulas for the analyses of fuzzy present value, fuzzy equivalent uniform annual value, fuzzy future value, fuzzy benefit-cost ratio, and fuzzy payback period are developed and given some numeric examples. Then the examined cash flows are expanded to geometric and trigonometric cash flows and using these cash flows fuzzy present value, fuzzy future value, and fuzzy annual value formulas are developed for both discrete compounding and continuous compounding.

Ozone treatment of textile effluents and dyes: effect of applied ozone dose, pH and dye concentration

Abstract: The ozonation of wastewater supplied from a treatment plant (Samples A and B) and dye-bath effluent (Sample C) from a dyeing and finishing mill and acid dye solutions in a semi-batch reactor has been examined to explore the impact of ozone dose, pH, and initial dye concentration. Results revealed that the apparent rate constants were raised with increases in applied ozone dose and pH, and decreases in initial dye concentration. While the color removal efficiencies of both wastewater Samples A and C for 15 min ozonation at high ozone dosage were 95 and 97%, respectively, these were 81 and 87%, respectively at low ozone dosage. The chemical oxygen demand (COD) and dissolved organic carbon (DOC) removal efficiencies at several ozone dose applications for a 15 min ozonation time were in the ranges of 15–46% and 10–20%, respectively for Sample A and 15–33% and 9–19% respectively for Sample C. Ozone consumption per unit color, COD and DOC removal at any time was found to be almost the same while the applied ozone dose was different. Ozonation could improve the BOD5 (biological oxygen demand) COD ratio of Sample A by 1.6 times with 300 mg dm−3 ozone consumption. Ozonation of acid dyes was a pseudo-first order reaction with respect to dye. Increases in dye concentration increased specific ozone consumption. Specific ozone consumption for Acid Red 183 (AR-183) dye solution with a concentration of 50 mg dm−3 rose from 0.32 to 0.72 mg-O3 per mg dye decomposed as the dye concentration was increased to 500 mg dm−3. © 2002 Society of Chemical Industry

Virtual-topology adaptation for WDM mesh networks under dynamic traffic

Abstract: We present a new approach to the virtual-topology reconfiguration problem for wavelength-routed, optical wide-area networks under dynamic traffic demand. By utilizing the measured Internet backbone traffic characteristics, an adaptation mechanism is proposed to follow the changes in traffic without assuming that the future traffic pattern is known. In that sense, our work differs from previous studies which redesign the virtual-topology according to an expected (or known) traffic pattern, and then modify the connectivity to reach the target topology. The key idea of our approach is to adapt the underlying optical connectivity by measuring the actual traffic load on lightpaths continuously (periodically based on a measurement period) and reacting promptly to the imbalances caused by fluctuations in the traffic by adding or deleting one lightpath at a time. We aim to correct the encountered load imbalance directly, either by tearing down a lightpath that is lightly loaded or by setting up a new lightpath when congestion occurs. We introduce high and low watermark parameters on lightpath loads to detect any over/underutilized lightpath, and to trigger an adaptation step. The adaptation method is evaluated through simulations and the effect of system parameters (high and low watermarks, length of the measurement period) are investigated.

Jadeite–chloritoid–glaucophane–lawsonite blueschists in north-west Turkey: unusually high P/T ratios in continental crust

Abstract: Sodic metapelites with jadeite, chloritoid, glaucophane and lawsonite form a coherent regional metamorphic sequence, several tens of square kilometres in size, and over a kilometre thick, in the Orhaneli region of northwest Turkey. The low-variance mineral assemblage in the sodic metapelites is quartz + phengite + jadeite + glaucophane + chloritoid + lawsonite. The associated metabasites are characterized by sodic amphibole + lawsonite ± garnet paragenesis. The stable coexistence of jadeite + chloritoid + glaucophane + lawsonite, not reported before, indicates metamorphic pressures of 24 ± 3 kbar and temperatures of 430 ± 30 °C for the peak blueschist facies conditions. These P–T conditions correspond to a geotherm of 5 °C km−1, one of the lowest recorded in continental crustal rocks. The low geotherm, and the known rate of convergence during the Cretaceous subduction suggest low shear stresses at the top of the downgoing continental slab.

Creation of a complex butterfly attractor using a novel Lorenz-Type system

Abstract: A novel Lorenz-type system of nonlinear differential equations is proposed. Unlike the original Lorenz system, where the chaotic dynamics remain confined to the positive half-space with respect to the Z state variable due to a limiting threshold effect, the proposed system enables bipolar swing of this state variable. In addition, the classical set of parameters (a, b, c) controlling the behavior of the Lorenz system are reduced to a single parameter, namely a. Two possible modes of operation are admitted by the system; switching between these two modes results in the creation of a complex butterfly chaotic attractor. Numerical simulations and results from an experimental setup are presented.

A new method for dynamic analysis of mistuned bladed disks based on the exact relationship between tuned and mistuned systems

Abstract: A new method for the dynamic analysis of mistuned bladed disks is presented. The method is based on exact calculation of the response of a mistimed system using response levels for the tuned assembly togeher with a modification matrix constructed from the frequency response function (FRF) matrix of the tamed system and a matrix describing the mistuning. The train advantages of the method are its efficiency and accuracy, which allow the use of large finite element models of practical bladed disk assemblies in parametric studies of mistuning effects on vibration amplitudes. A new method of calculating the FRF matrix of the tuned system using a sector model is also developed so as to improve the efficiency of the method even further, making the proposed method a very attractive tool for mistuning steadies. various numerical aspects of the proposed method are addressed and its accuracy and efficiency are demonstrated using representative test cases

Synthesis and Characterization of Macrophotoinitiators of Poly(∊-caprolactone) and Their Use in Block Copolymerization

Abstract: Novel end-chain and midchain functional macrophotoinitiators of poly(-caprolactone) have been synthesized. For this purpose, mono- and dihydroxy functional photoinitiators namely, benzoin (B) and 2-hydroxy-2-methyl-1-phenyl propan-1-one (HMPP), Darocure 1173, and 2-hydroxy-1-(4-(2-hydroxy- ethoxy)phenyl)-2-methyl propan-1-one (HE-HMPP), Irgacure 2959, respectively, were used as initiators for the stannous-2-ethylhexanoate (Sn(Oct)2) catalyzed living ring-opening polymerization of -caprolactone. The gpc and IR, H NMR, UV, and fluorescence spectroscopic studies revealed that low-polydispersity poly(-caprolactone) with desired photoinitiator functionality at the end or in the middle of the chain were obtained. These prepolymers were used to induce radical polymerization of methyl methacrylate (MMA) upon irradiation via R-cleavage of the incorporated phenyl ketone groups. While end-chain functional macrophotoiniators led to the formation of both homo and block copolymers, only block copolymers of -CL and MMA were formed with midchain functional macrophotoinitiator. Successful blocking has been confirmed by a strong change in the molecular weight of the prepolymer and the block copolymer as well as by NMR spectral measurements.

Shopping behaviour and preferences in e-commerce of Turkish and American university students: Implications from cross-cultural design

Abstract: With internationalization of commerce and business and with increased use of e-business and e-commerce, it is important to ensure that these systems can be effectively utilized across cultural boundaries. To increase effectiveness, appropriate changes and modifications in the systems may be required. With this in mind, a survey of 300 Turkish university students was undertaken to assess their on-line shopping and behaviour preferences, and these were compared with the results derived from 64 US university students. The results provide guidelines for specific design of features for the Turkish population that may not be necessary for the US population.

Rubber Elasticity of Poly(N-isopropylacrylamide) Gels at Various Charge Densities

Abstract: The mechanical properties and the swelling behavior of a series of N-isopropylacrylamide copolymers with the sodium salt of 2-acrylamido-2-methylpropanesulfonic acid were investigated. The increase...