WOS

Permanent URI for this collectionhttps://ada.atilim.edu.tr/handle/123456789/18

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Now showing 1 - 20 of 4294

Citation - WoS: 4
Optimum Dragline Selection for Strip Coal Mines
(inst Mining Metallurgy, 1998) Erdem, B; Çelebi, N; Pasamehmetoglu, AG; Department of Civil Engineering
A model is presented by means of which the optimal dragline selection may be made. An outline is given of the methodology that was adopted in developing a series of generic algorithms to first define and then formularize the need to extend the working bench under a nat-lying topography and coal seam. Rehandle percentages were calculated for four generalized extended bench geometries, in each of which the percentage rehandle varied according to the relative positions of the extended bench and pit. A set of geometric and simulative equations was developed on which a model for the optimal selection of a dragline was based. Finally, a typical application was tested through the use of data associated with a hypothetical strip-mining operation.
Citation - WoS: 0
Unit cost analysis model for stripping of open-pit lignite mines
(inst Mining Metallurgy, 1998) Çelebi, N; Pasamehmetoglu, AG; Karpuz, C; Department of Civil Engineering
[No Abstract Available]
Citation - WoS: 0
Complexity Engineering, Evolution and Optimality of Structures
(Morgan Kaufmann Pub inc, 1999) Kundu, S
Complexity Engineering deals with harnessing the power of Cellular Automata (CA) like simple models to solve real life difficult and complex engineering problems, dealing with systems that have very simple components that collectively exhibit complex behaviors. The state transition rules are generally fixed in a CA, but evolution of the rules, is considered here. To evolve the local rules, we use the Genetic Algorithm (GA) model. The example application described here will serve to demonstrate that the GAs can discover CA rules that give rise to emergent computational strategies by self-organization and exhibit globally coordinated tasks for optimization, with simple local interactions only.
Citation - WoS: 8
Citation - Scopus: 8
Electroinitiated Polymerization of 2-Allylphenol
(Springer-verlag, 2000) Cihaner, A; Önal, AM; Chemical Engineering
Redox behaviour of 2-allylphenol (2APhOH) was studied by using cyclic voltammetry (CV) and electroinitiated polymerization was conducted at the measured peak potentials. Constant potential electrolysis (CPE) of the monomer was carried out in acetonitrile-sodium perchlorate, solvent-electrolyte couple, at room temperature. Polymerization of the monomer yielded insoluble polymer films on the surface of the electrode together with the low molecular weight polymers in the bulk of the solution. The structural analysis of the polymers were carried by H-1-NMR and FTIR spectroscopy. Molecular weight of the soluble polymer was determined by GPC. Thermal properties of the polymer film and soluble polymer were studied by DSC. The course of electroinitiated polymerization was monitored by in-situ UV-VIS spectroscopy.
Citation - WoS: 1
The Generalized Divergence Theorem and Its Application To Harmonic Maps
(Pergamon-elsevier Science Ltd, 2001) García-Río, E; Kupeli, DN
A survey of divergence theorems in semi-Riemannian geometry is made. The generalization of a divergence theorem to vector fields along a map is given in semi-Riemannian geometry and an application of it is made in Riemannian geometry to obtain some sufficient conditions for a map to be harmonic.
Citation - WoS: 5
Citation - Scopus: 5
Electrochemical Polymerization of 4-Allylanisole
(Pergamon-elsevier Science Ltd, 2001) Cihaner, A; Testereci, HN; Önal, AM; Chemical Engineering
Electrochemical polymerization of 3-allylanisole (4AA). via constant potential electrolysis, has been investigated in acetonitrile using two different supporting electrolytes. Redox behavior of the monomer was also studied in the same solvent-electrolyte couples at room temperature. Electrochemical polymerization of the monomer yielded insoluble polymer films on the electrode surface, which bears a very low conductivity, together with the low molecular weight polymers in the bulk of the solution. The decrease in the monomer concentration, during the electrochemical polymerization. was monitored by taking the cyclic voltammogram of the electrolysis solution. The effect of temperature on the rate of electrochemical polymerization was: also studied. The polymers were characterized by taking the H-1-NMR and FTIR spectra. Molecular weight of the soluble polymer was determined by vapor pressure osmometry. Thermal analysis of the polymer film and soluble polymer were done by DSC. (C) 2001 Elsevier Science Ltd. All rights reserved.
Citation - WoS: 20
Citation - Scopus: 20
Characterization of P-in₂se_{3< Thin Films}
(Kluwer Academic Publ, 2001) Qasrawi, AF; Parlak, M; Erçelebi, Ç; Günal, I; Department of Electrical & Electronics Engineering
Indium selenide thin films were deposited onto glass substrates kept at 150 degreesC by thermal evaporation of alpha -In2Se3. Some of the films were annealed at 150 degreesC and 200 degreesC and they all were found to exhibit p-type conductivity without intentional doping. Scanning electron microscopy (SEM) established that the films have an atomic content of In51Se49. X-ray diffraction (XRD) indicated that the as-grown films were amorphous in nature and became polycrystalline \beta-In2Se3 films after annealing. The analysis of conductivity temperature-dependence measurements in the range 320-100 K revealed that thermal excitation and thermionic emission of the carriers are the predominant conduction mechanisms above 200 K in the amorphous and polycrystalline samples, respectively. The carrier transport below 200 K is due to variable range hopping in all the samples. Hall measurements revealed that the mobility of the polycrystalline films is limited by the scattering of the charged carriers through the grain boundaries above 200 K. (C) 2001 Kluwer Academic Publishers.
Citation - WoS: 56
Citation - Scopus: 59
A curvature condition for a twisted product to be a warped product
(Springer-verlag, 2001) Fernández-López, M; García-Río, E; Kupeli, DN; Ünal, B; Department of Modern Languages
It is shown that a mixed Ricci-flat twisted product semi-Riemannian manifold can be expressed as a warped product semi-Riemannian manifold. Asa consequence, any Einstein twisted product semi-Riemannian manifold is in fact, a warped product serni-Riemannian manifold.
Citation - WoS: 1
Citation - Scopus: 1
Sets of Random Variables With a Given Uncorrelation Structure
(Elsevier Science Bv, 2001) Ostrovska, S; Mathematics
Let xi (1),...,xi (n) be random variables having finite expectations. Denote i(k) := # {(j(1),...,j(k)): 1 less than or equal to j(1) < ... < j(k) less than or equal to n and E (l=1)pi (k) xi (fi) = (l=1)pi (k) E xi (h)}, k = 2,...,n. The finite sequence (i(2),...,i(n)) is called the uncorrelation structure of xi (1),...,xi (n). It is proved that for any given sequence of nonnegative integers (i(2),...,i(n)) satisfying 0 less than or equal to i(k) less than or equal to ((n)(k))and any given nondegenerate probability distributions P-1,...,P-n there exist random variables eta (1),...,eta (n) with respective distributions P-1,...,P-n such that (i(2),...,i(n)) is their uncorrelation structure. (C) 2001 Elsevier Science B.V. All rights reserved.
Citation - WoS: 68
Citation - Scopus: 67
Doubly Warped Products
(Elsevier Science Bv, 2001) Ünal, B; Department of Modern Languages
In this paper we study geodesic completeness of Riemannian doubly warped products and Lorentzian doubly warped products. We give necessary conditions for generalized Robertson-Walker spacetimes with doubly warped product spacial parts to be globally hyperbolic. We also state some results about killing and conformal vector fields of doubly warped products.
Citation - WoS: 33
Synthesis and Characterization of Fluorine-Substituted Polyanilines
(Pergamon-elsevier Science Ltd, 2001) Cihaner, A; Önal, AM; Chemical Engineering
Poly(2-fluoroaniline), P2FAN, poly(3-fluoroaniline). P3FAN. and poly(4-fluoroaniline), P4FAN, have been synthesized from fluorine substituted aniline monomers in aqueous acidic medium using potassium dichromate as oxidizing agent. Characterization of polymer products has been carried out using FTIR, and NMR spectroscopic techniques. Thermal analysis of polyfluoroaniline powders was also investigated using differential scanning calorimetry and thermogravimetric analysis. To compare the structural properties of the polymers, polyfluoroanilines were also synthesized using ammonium peroxydisulfate as oxidizing agent. Polyfluoroanilines synthesized by chemical oxidation were doped by using iodine and the change in the paramagnetic behavior was monitored by electron spin resonance spectroscopy. (C) 2001 Elsevier Science Ltd. All rights reserved.
Citation - WoS: 25
Citation - Scopus: 28
Crystal Data, Electrical Resistivity, and Hall Mobility of N-Type Agin₅s_{8< Single Crystals}
(Wiley-v C H verlag Gmbh, 2001) Qasrawi, AF; Gasanly, NM; Department of Electrical & Electronics Engineering
The X-ray diffraction has revealed that AgIn5S8 is a single phase crystal of cubic spinel structure. The value of the unit cell parameter for this crystal is 1.08286 nm. The electrical resistivity and Hall effect of n-type AgIn5S8 crystals are measured in the temperature range of 50-400 K. A carrier effective mass of 0.20 m(0), an acceptor to donor concentration ratio of 0.8 and an acoustic phonons deformation potential of 20 eV are identified from the Hall effect measurement. The Hall mobility data art: analyzed assuming the carrier scattering by acoustic and polar optical phonons, and ionized impurities.
Citation - WoS: 9
Citation - Scopus: 11
Effect of Lithium Doping on the Properties of Tl-Based Superconductors
(Iop Publishing Ltd, 2001) Kayed, TS; Özkan, H; Gasanly, NM; Department of Electrical & Electronics Engineering
The effects of lithium doping on the formation and properties of the T1-based superconductors have been studied. Lithium atoms up to around 3 mol.% have been added to the oxides of nominal composition Tl1.8Ba2Ca2.2Cu3Ox, and the usual solid-state reaction method has been applied. Lithium additions in the range 0.23-0.29 mol.% increase the fraction of the Tl-2223 phase and significantly improve the critical temperature of the samples. Higher amounts of lithium additions diminish the Tl-2223 phase, reduce the fraction of the Tl-2212 phase, and cause separate non-superconducting phases to be formed.
Citation - WoS: 18
Citation - Scopus: 19
Crystal Data, Photoconductivity and Carrier Scattering Mechanisms in Cuin₅s_{8< Single Crystals}
(Wiley-v C H verlag Gmbh, 2001) Qasrawi, AF; Gasanly, NM; Department of Electrical & Electronics Engineering
The X-ray diffraction has revealed that CuIn5S8 is a single phase crystal of cubic spinet structure. The value of the unit cell parameter for this crystal is 1.06736 nm. The crystal is assigned to the conventional space group Fd3m. The photocurrent is found to have the characteristic of monomolecular and bimolecular recombination at low and high illumination intensities, respectively. The electrical resistivity and Hall effect of CuIn5S8 crystals are measured in the temperature range of 50-400 K. The crystals are found to be intrinsic and extrinsic above and below 300 K, respectively. An energy band gap of similar to1.35 eV at 0 K, a carrier effective mass of 0.2 m(0), an acceptor to donor concentration ratio of 0.9, an acoustic phonon deformation potential of 10 eV and a nonpolar optical phonon deformation potential of 15 eV are identified from the resistivity and Hall measurements. The Hall mobility data are analyzed assuming the carrier scattering by polar optical phonons, acoustic combined with nonpolar optical phonons, and ionized impurities.
Citation - WoS: 125
Citation - Scopus: 134
Convergence of Generalized Bernstein Polynomials
(Academic Press inc Elsevier Science, 2002) Il'inskii, A; Ostrovska, S; Mathematics
Let f is an element of C[0, 1], q is an element of (0, 1), and B-n(f, q; x) be generalized Bernstein polynomials based on the q-integers. These polynomials were introduced by G. M. Phillips in 1997. We study convergence properties of the sequence {B-n(f, q; x)}(n=1)(infinity). It is shown that in general these properties are essentially different from those in the classical case q = 1. (C) 2002 Elsevier Science (USA).
Citation - WoS: 5
Citation - Scopus: 3
Evaluation of Efficiencies of Diffuse Allochthonous and Autochthonous Nutrient Input Control in Restoration of a Highly Eutrophic Lake
(I W A Publishing, 2002) Muhammetoglu, A; Muhammetoglu, H; Soyupak, S
Mogan Lake is an important recreational area for Metropolitan Ankara-Turkey. It is a shallow eutrophic lake with a dense growth of macrophytes. The main contributors of nutrients and other pollutants to the lake are the creeks carrying the runoff water from the watershed and upland farming land, in addition to the domestic and industrial wastewater discharges from a nearby town and industries. Hydrodynamic and water quality modeling techniques were used to determine the optimum management schemes for the lake restoration and diffuse pollution control. Management scenarios were devised and tested to control allochthonous and autochthonous nutrient inputs to the lake. Phosphorus and nitrogen load reductions were the main test elements for the control of allochthonous nutrient inputs. The scenario analysis revealed that reduction of phosphorus and nitrogen loads from diffused sources will have a marginal effect on controlling eutrophication if macrophyte growth is left uncontrolled. Scenarios employing macrophyte harvesting and sediment dredging have been evaluated for autochthonous nutrient input control. Sediment dredging alone has been shown to yield the most favorable conditions for water quality improvement in Mogan Lake. Further, control of diffuse pollution was an essential final step to achieve an acceptable long-term sustainable water quality improvement in the lake.
Citation - WoS: 6
Some Examples in Cogalois Theory With Applications To Elementary Fleld Arithmetic
(World Scientific Publ Co Pte Ltd, 2002) Albu, Toma
The aim of this paper is to provide some examples in Cogalois Theory showing that the property of a field extension to be radical (resp. Kneser, or Cogalois) is not transitive and is not inherited by subextensions. Our examples refer especially to extensions of type Q(root r + root d)/Q. We also effectively calculate the Cogalois groups of these extensions. A series of applications to elementary arithmetic of fields, like: for what n, d is an element of N* is root n + root d a sum of radicals of positive rational numbers when is (n0)root a(0) a finite sum of monomials of form c center dot(n1)root a(1)(j1) ... (nr)root a(r)(jr), where r, j(1), ... , j(r) is an element of N*, c is an element of Q*, and a(0), ... , a(r) is an element of Q(+)(*) are also presented.
Citation - WoS: 7
Citation - Scopus: 9
Cesaro Asymptotics for Orthogonal Polynomials on the Unit Circle and Classes of Measures
(Academic Press inc Elsevier Science, 2002) Golinskii, L; Khrushchev, S; Mathematics
The convergence in L-2(T) of the even approximants of the Wall continued fractions is extended to the Cesaro-Nevai class CN, which is defined as the class of probability measures sigma with lim(n-->infinity) 1/n Sigma(k=0)(n-1) \a(k)\ = 0, (a(n))(ngreater than or equal to0) being the Geronimus parameters of sigma. We show that CN contains universal measures, that is, probability measures for which the sequence (\phi(n)\(2) dsigma)(ngreater than or equal to0) is dense in the set of all probability measures equipped with the weak-* topology. We also consider the "opposite" Szego class which consists of measures with Sigma(n=0)(infinity) (1-\a(n)\(2))(1/2) < infinity and describe it in terms of Hessenberg matrices. (C) 2002 Elsevier Science (USA).
Citation - WoS: 2
On Radical Field Extensions of Prime Exponent
(World Scientific Publ Co Pte Ltd, 2002) Albu, Toma
In this paper we investigate finite separable radical extensions K subset of L of prime exponent via the concept of G-Cogalois extension. As particular cases we retrieve some older results in I. Kaplansky [9] and A. Baker and H. M. Stark [7] concerning such radical extensions.
Citation - WoS: 20
Citation - Scopus: 21
Electrochemical Behaviour and Electrochemical Polymerization of Fluoro-Substituted Anilines
(Wiley, 2002) Cihaner, A; Önal, AM; Chemical Engineering
The electrochemical behaviour of three fluoro-substituted aniline monomers, 2-fluoroaniline (2FAN), 3-fluoroaniline (3FAN) and 4-fluoroaniline (4FAN), was investigated in aqueous acidic and organic media by means of cyclic voltammetry (CV) studies. Constant potential electrolysis (CPE) of the monomers in acetonitrile-water mixture (1: 1 by volume) using NaClO4 as supporting electrolyte yielded soluble polymers. The mechanism of electrochemical polymerization was investigated using in situ electron spin resonance (ESR) and in situ UV-VIS spectroscopic techniques for one of the monomers (4FAN). Both CV and in situ LTV-VIS measurements indicated that the polymers obtained are in the emeraldine base form. In situ ESR studies indicated that electrochemical polymerization involves a radical-cation as an intermediate. Characterization of polymer products have been carried out using FTIR and NMR spectroscopic techniques, and thermal behaviour was studied using differential scanning calorimetry (DSC). It was found that conductivity can be imparted to assynthesized polyfluoroanilines via iodine doping. (C) 2002 Society of Chemical Industry.

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