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

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Citation Count: 6
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 Count: 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 Count: 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 Count: 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 Count: 9
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 Count: 38
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 Count: 25
Crystal data, electrical resistivity, and Hall mobility of n-type AgIn₅S₈ 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 Count: 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 Count: 20
Characterization of p-In₂Se₃ 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 Count: 57
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 Count: 19
Crystal data, photoconductivity and carrier scattering mechanisms in CuIn₅S₈ 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 Count: 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 Count: 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 Count: 65
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 Count: 7
Photoelectronic and electrical properties of InS crystals
(Iop Publishing Ltd, 2002) Qasrawi, AF; Gasanly, NM; Department of Electrical & Electronics Engineering
To identify the localized levels in InS single crystals, the dark electrical conductivity, current-voltage characteristics and photoconductivity measurements were carried out in the temperature range of 10-350 K. Temperature dependence of dark electrical conductivity and the space-charge limited current studies indicate the presence of a single discrete trapping level located at (10 +/- 2) meV below the conduction band with a density of about 4.8 x 10(11) cm(-3). The conductivity data above 110 K reveal an additional two independent donor levels with activation energies of (50 +/- 2) and (164 +/- 4) meV indicating the extrinsic nature of conductivity. The spectral distribution of photocurrent in the photon energy range of 0.8-3.1 eV reveals an indirect band gap of (1.91 +/- 0.04) eV. The photocurrent-illumination intensity dependence follows the law I-ph proportional to F-gamma, with gamma being 1.0 and 0.5 at low and high illumination intensities indicating the domination of monomolecular and bimolecular recombination, respectively. It is observed that the photocurrent increases in the temperature range of 10 K up to T-m = 110 K and decreases or remains constant for 110 K < T < 160 K and increases again above 160 K. The temperature dependence of the photocurrent reveals an additional shallow impurity level with activation energies of 3 meV.
Citation Count: 1
The local Mobius equation and decomposition theorems in Riemannian geometry
(Canadian Mathematical Soc, 2002) Fernández-López, M; García-Río, E; Kupeli, DN
A partial differential equation, the local Mobius equation, is introduced in Riemannian geometry which completely characterizes the local twisted product structure of a Riemannian manifold. Also the characterizations of warped product and product structures of Riemannian manifolds are made by the local Mobius equation and an additional partial differential equation.
Citation Count: 9
Carrier scattering mechanisms in GaS_0.5Se_0.5 layered crystals
(Wiley-v C H verlag Gmbh, 2002) Qasrawi, AF; Gasanly, NM; Department of Electrical & Electronics Engineering
Systematic dark electrical resistivity and Hall mobility measurements have been carried out in the temperature range 150-400 K on n-type GaS0.5Se0.5 layered crystals. The analysis of temperature dependent electrical resistivity and carrier concentration reveals the extrinsic type of conduction with a donor impurity level located at 0.44 eV, donor and acceptor concentrations of 3.4x10(17) and 4.1x10(17) cm(-1), respectively, and an electron effective mass of 0.41 m(o). The Hall mobility is limited by the electron-phonon short-range interactions scattering at high temperatures combined with the ionized impurity scattering at low temperatures. The electron-phonon short-range interactions scattering mobility analysis reveals an electron-phonon coupling constant of 0.25 and conduction band deformation potential of 5.57 eV/Angstrom.
Citation Count: 1
Spectroelectrochemical investigation of pentacarbonyl(pyrazine)metal(0) (metal = Cr, Mo, W) complexes of group 6 elements
(Walter de Gruyter Gmbh, 2002) Yaman, SO; Esentürk, E; Kayran, C; Önal, AM
The electrochemical behaviour of pentacarbony l(pyrazine) metal (0) complexes of the group 6 elements was studied by cyclic voltammetry in dichloromethane-(n-Bu)(4)NBF4 solvent-electrolyte couple at -20 degreesC vs. Ag/Ag+ or SCE reference electrode. Constant potential electrolyses of the complexes were carried out at their first oxidation peak potentials and monitored in situ by UV-Vis spectrometry. Electrolysis of W(CO)(5)pz produces [W(CO)(5)pz](+) and a similar electrochemical mechanism is expected both for Cr(CO)(5)pz and Mo(CO)(5)pz complexes. In situ low temperature constant current ESR electrolysis also confirmed the production of [W(CO)(5)pz](+) after the electron transfer.
Citation Count: 11
Vulnerability of groundwater to pollution from agricultural diffuse sources: a case study
(I W A Publishing, 2002) Muhammetoglu, H; Muhammetoglu, A; Soyupak, S
Kumluca, near Antalya in Turkey, is an important plain with its intensive agricultural activities employing greenhouses. The chemical fertilizer application practices caused excessive increases of the nitrogen, phosphorus and salinity within groundwater. A study has been initiated to assess the present state of the groundwater pollution problem of Kumluca Plain. A total of nine measurement and sampling stations have been selected to represent different depths groundwater table, different types of agricultural activities and different soil types. The magnitudes of the parameters: temperature, salinity and conductivity, nitrate, nitrite, ammonia, orthophosphate and fecal coliform were determined for groundwater. Soil samples collected from the stations have been analyzed for several parameters such as texture, total salinity, total nitrogen, and total phosphorus. The measurement and analyses results of the groundwater showed wide spatial variations depending on factors such as the quality of irrigation water, depth groundwater, soil characteristics, type and age of agriculture and hydrology. Groundwater vulnerabilities to pollution have been analyzed using the SEEPAGE Model approach. Furthermore the soil, aquifer and groundwater characteristics, which will be utilized to establish "cause" and "effect" relationships in future, have been clarified.
Citation Count: 3
Effect of magnetic field and γ irradiation on the properties of Tl-2212 superconducting tape
(Wiley-v C H verlag Gmbh, 2002) Kayed, TS; Ercan, I; Mathematics; Department of Electrical & Electronics Engineering
The critical temperature and critical current of Tl-2212 superconducting sample in the form of a tape have been studied near T-c under magnetic field and gamma irradiation. T-c decreases from 109 to 94 K with increase of magnetic field up to 300 mT. In 77-109 K range, J(c) decreases rapidly in low fields up to around 50 mT followed by a very slow decrease in J(c) up to 300 mT. T-c of the sample did not change up to 100 MR gamma dose and then started to decrease from 109 to 102 K with increase of gamma dose up to 800 MR, most of the change taking place in high doses. The critical currents of the sample decreased steadily with gamma irradiation up to 600 MR after which no further change was noticed.

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