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Articles 10111 - 10140 of 10730
Full-Text Articles in Physical Sciences and Mathematics
Development Of Black Cobalt Selective Absorber On Copper For Solar Collectors, Fi̇gen Kadirgan, Mete Söhmen
Development Of Black Cobalt Selective Absorber On Copper For Solar Collectors, Fi̇gen Kadirgan, Mete Söhmen
Turkish Journal of Chemistry
An eletrolyte is proposed for the deposition of black cobalt selective absorber coating on copper plate. The influence of the electrolyte composition and operating parameters on the properties of black cobalt coatings including optical properties were studied. The optimum conditions to obtain a high absorptance/emittance ratio are described.
Effect Of Temperature On The Electrooxidation Of Some Organic Molecules On Pt Doped Conducting Polymer Coated Electrodes, İpek Beceri̇k, Fehmi̇ Fiçicioğlu, Fi̇gen Kadirgan
Effect Of Temperature On The Electrooxidation Of Some Organic Molecules On Pt Doped Conducting Polymer Coated Electrodes, İpek Beceri̇k, Fehmi̇ Fiçicioğlu, Fi̇gen Kadirgan
Turkish Journal of Chemistry
Polymer modified electrodes are of importance as possible electrocatalysts for various electrode reactions, i.e., platinum incorporated into polypyrrole or polyaniline films are known to be good systems for the electrooxidation of various organic molecules. In this study, the effect of temperature on the electrooxidation of D. glucose and methanol on Pt doped films was investigated, apparent activation energies were calculated and the results were evaluated.
Electrochemical Reduction Of Methyl Cinnamate In The Presence Of 1,3-Bis(4-Methyl Phenylsulphonyloxy)Propane, Mustafa Güllü
Electrochemical Reduction Of Methyl Cinnamate In The Presence Of 1,3-Bis(4-Methyl Phenylsulphonyloxy)Propane, Mustafa Güllü
Turkish Journal of Chemistry
Electrochemical reduction of methyl cinnamate in the presence of a dielectrophile, such as 1,3-bis(4-methyl phenylsulphonyloxy)propane gives two major products: trans- (\pm) methyl 2-phenylcyclopentanecarboxylate and trans- (\pm) methyl 2,3-diphenyl-5-oxo-cyclopentanecarboxylate. The ratio of products basically depends on the electrolysis conditions.
Comparative Mechanistic Studies On The Oxidation Of Aromatic And Aliphatic Hydroxyl Derivatives In An Alkaline Medium At Preanodized Pt, Au And Pt/Au Electrodes In Presence Of Redox Mediators, Sasha Kalcheva, Philip Iotov
Comparative Mechanistic Studies On The Oxidation Of Aromatic And Aliphatic Hydroxyl Derivatives In An Alkaline Medium At Preanodized Pt, Au And Pt/Au Electrodes In Presence Of Redox Mediators, Sasha Kalcheva, Philip Iotov
Turkish Journal of Chemistry
The role of redox mediators obtained from Pt, Au, and Pt/Au electrodes in the process of electrocatalytic oxidation of aromatic/aliphatic hydroxyl derivatives in an alkaline medium has been studied by applying cyclic voltammetry. Phenol and glycerol were used as aromatic and aliphatic hydroxyl derivatives in the electrochemical oxidation experiments. The results revealed that the presence of redox mediators formed by preliminary electrode anodization is crucial for the process of oxidation of aromatic compounds and imposes a different oxidation route for the aliphatic hydroxyl derivatives. The effect of preanodization has been related to the formation and dissolution of the corresponding higher …
Electrochemical Characterization Of Al_2 O_3 -Ni Thin Film Selective Surface On Aluminium, Fi̇gen Kadirgan, Ewa Wackelgard, Mete Söhmen
Electrochemical Characterization Of Al_2 O_3 -Ni Thin Film Selective Surface On Aluminium, Fi̇gen Kadirgan, Ewa Wackelgard, Mete Söhmen
Turkish Journal of Chemistry
Solar thermal collectors represent a widely used type of system for the conversion of solar energy. In order to produce selective coatings on aluminium substrates to be used as absorber plates in high efficiency solar collectors, nickel pigmentation was applied to anodically oxidised surfaces. Electrochemical dc methods are used to study the oxidation of aluminium as functions of the following electrolysis conditions: applied current, pH, temperature and concentration of electrolyte. The properties of the oxidised aluminium surfaces are investigated by cyclic voltammetry. Nickel pigmentation of porous aluminium surfaces was also performed as a function of electrochemical pigmentation conditions by ac …
The Effects Of Detergent Pollution On The Corrosion Of Iron And Aluminium, Si̇bel Zor, B. Yazici, M. Erbi̇l
The Effects Of Detergent Pollution On The Corrosion Of Iron And Aluminium, Si̇bel Zor, B. Yazici, M. Erbi̇l
Turkish Journal of Chemistry
The current-potential values were measured with iron or aluminium electrodes in solutions of 3.5% NaCl containing 30, 150, 300 ppm linear alkylbenzene (LAB) and detergents (LAS) at pH8. Polarization resistances (Rp) were determined using the values of current and potentials. The corrosion rates of iron and aluminium were determined in 2 and 4 hour intervals using the Mansfeld-Oldham equation based on the Stern-Geary and Butler-Volmer equations.
Reactions Of N-Aminopyrimidine Derivatives With 1,3-Dicarbonyl Compounds, Zülbi̇ye Önal, Behzat Altural
Reactions Of N-Aminopyrimidine Derivatives With 1,3-Dicarbonyl Compounds, Zülbi̇ye Önal, Behzat Altural
Turkish Journal of Chemistry
The reactions of 1-Amino-pyrimidine derivatives (1) and some 1,3-dicarbonyl compounds (2) were realized in the presence of p-toluensulfonic acid catalyst to give convenient enamine (3) and/or imine derivatives (4). In the same way, the enamine (5) and/or imine derivatives (6) were synthesized using (1) and 1,3-indanedione which is one of the different 1,3-dicarbonyl compounds. The molecular structures of all the prepared compounds were determined by ^1H-nmr, ^{13}C-nmr, i.r. spectra and elemental analyses, and were drawn by taking imine-enamine tautomerism into account.
Autocatalytic Reduction Of Dichloro 5, 10, 15, 20 Tetraphenylporphinatoplatinum(Iv) By 1-Methylimidazole, F. Ece Bulak
Autocatalytic Reduction Of Dichloro 5, 10, 15, 20 Tetraphenylporphinatoplatinum(Iv) By 1-Methylimidazole, F. Ece Bulak
Turkish Journal of Chemistry
It was observed that in toluene solution, excess 1-methyl-imidazole (Melm) reduces dichloro 5, 10, 15, 20 tetraphenyl-porphinatoplatinum(IV) (PtTPPCl_2) to tetraphenylporphinato-platinum(II) (PtTPP) autocatalytically (Fig. 1). There was no Pt(III) intermediate or 1-methylimidazole radical detected by Electron Resonance Spectroscopy (ESR) at 25°C. The reaction was found to be autocatalyzed by the PtTPP product when the 1-methylimidazole to PtTPPCl_2 concentration ratio is about 10^4 or more. From the data obtained it is reasonable to suppose that aggregation of the PtTPP product with PtTPPCl_2 plays an important role in this reduction process.
A Modified Potentiometric Method For The Estimation Of Phenol In Aqueous Systems, Farhat Huma, Muhammad Jaffar, Khalid Masud
A Modified Potentiometric Method For The Estimation Of Phenol In Aqueous Systems, Farhat Huma, Muhammad Jaffar, Khalid Masud
Turkish Journal of Chemistry
A modified potentiometric titration is proposed for the estimation of phenol in aqueous systems. The method is evolved on the basis of a critical dependence of pH on log V rather than simple V, as used in conventional potentiometric titrations. The method incorporates titrants in a concentration range several orders of magnitude greater than that of phenol in the aqueous phase. Derivative potentiometric curves so obtained provide a clear exposition of the equivalence point and the overall error is found to be between \pm 1.0 and 1.5%. The range of phenol concentration investigated was from 10^{-2} to 10^{-3} M. and …
Electrochemical Behaviour Of Hexa[4-(Phenylazo) Phenoxy]Cyclotriphasphazene, Necati̇ Menek, Günseli̇ Turgut, Mustafa Odabaşioğlu
Electrochemical Behaviour Of Hexa[4-(Phenylazo) Phenoxy]Cyclotriphasphazene, Necati̇ Menek, Günseli̇ Turgut, Mustafa Odabaşioğlu
Turkish Journal of Chemistry
The polarographic and voltammetric behaviour of hexa[4-(phenylazo)phenoxy]cyclotriphasphazene in tetrahydrofuran-water 50% (v/v) was studied at room temperature using various electrochemical techniques. In this study, the reduction of the azo group to the amino group of the organophosphazenes compound was observed as the electrode reaction. An electrode reaction mechanism was suggested for the compound.
Synthesis, Structural And Thermal Studies Of Titanium(Iv) Complexes Of N-Alkyl Phenothiazines, Jaldappa Seetharamappa, Boregowda Keshavan
Synthesis, Structural And Thermal Studies Of Titanium(Iv) Complexes Of N-Alkyl Phenothiazines, Jaldappa Seetharamappa, Boregowda Keshavan
Turkish Journal of Chemistry
New coordination compounds of the type [Ti(C_2O_4)_2L]2H_2O where L=N-alkyl phenothiazines (NAPs) were synthesised and characterised by elemental analyses, molar conductance, magnetic, thermal and spectral data. The spectral data suggest the bidentate nature of NAPs in the complexes. An octahedral structure is proposed for all the complexes. Thermal studies were used to evaluate the kinetic and thermodynamic parameters.
Weak Localization In Disordered Two-Dimensional Crystals With Half-Filled Band, E.P. Nakhmedov, T. Kaya
Weak Localization In Disordered Two-Dimensional Crystals With Half-Filled Band, E.P. Nakhmedov, T. Kaya
Turkish Journal of Physics
Effect of subtitutional impurities on electron localization in two dimensional (2D) lattice near the middle of the band is studied. Calculation of density of the electronic states, \rho (\varepsilon ), increases logaritmically in the middle of the band. This singularity in the density of states of noninteracting electron gas on lattice gives rise to anomalous dependencies of thermodynamic quantities on the temperature. The quantum correction to the conductivity of a nonintreracting electron gas due to Umklapp electron--impurity scattering is calculated. This correction to the conductivity is shown to compete with that from the localization corrrection for a Normal scattering process. …
Algebraic Implementation Of Gauss' Law, Andrzej Herdegen
Algebraic Implementation Of Gauss' Law, Andrzej Herdegen
Turkish Journal of Physics
A C^*-algebraic model may be constructed for the description of asymptotic fields in quantum electrodynamics. In this model charged fields carry the asymptotic Coulomb field of associated charged particles.
Differentiating Type Of Muscle Movement Via Ar Modeling And Neural Network Classification, Beki̇r Karlik
Differentiating Type Of Muscle Movement Via Ar Modeling And Neural Network Classification, Beki̇r Karlik
Turkish Journal of Electrical Engineering and Computer Sciences
The aim of this study is to classify electromyogram (EMG) signals for controlling multifunction proshetic devices. An artificial neural network (ANN) implementation was used for this purpose. Autoregressive (AR) parameters of $a_1, a_2, a_3, a_4$ and their signal power obtained from different arm muscle motions were applied to the input of ANN, which is a multilayer perceptron. At the output layer, for 5000 iterations, six movements were distinguished at a high accuracy of 97.6%.
Neural Classifiers For Learning Higher-Order Correlations, Marifi Güler
Neural Classifiers For Learning Higher-Order Correlations, Marifi Güler
Turkish Journal of Physics
Studies by various authors suggest that higher-order networks can be more powerful and are biologically more plausible with respect to the more traditional multilayer networks. These architectures make explicit use of nonlinear interactions between input variables in the form of higher-order units or product units. If it is known a priori that the problem to be implemented possesses a given set of invariances like in the translation, rotation, and scale invariant pattern recognition problems, those invariances can be encoded, thus eliminating all higher-order terms which are incompatible with the invariances. In general, however, it is a serious set-back that the …
Ordering Due To Disorder In Frustrated Quantum Magnetic Systems, Taner Yildirim
Ordering Due To Disorder In Frustrated Quantum Magnetic Systems, Taner Yildirim
Turkish Journal of Physics
The phenomenon of order by disorder in frustrated magnetic systems is reviewed. Disorder (thermal or quantum fluctuations) may sometimes give rise to long range ordering in systems with frustration, where one must often consider the selection among classically degenerate ground states which are not equivalent by any symmetry. The lowest order effects of quantum fluctuations in such frustrated systems usually resolves the continues degeneracy of the ground state manifold into discrete Ising--type degeneracy. A unique ground state selection out of this Ising degenerate manifold then occurs due to higher order effects of quantum fluctuations. For systems such as face-centered cubic …
Diverging Strains Near Threshold: Breakdown Of The Elastic Description Of A Charge Density Wave Model, Muhittin Mungan, Susan N. Coppersmith, Valeri M. Vinokur
Diverging Strains Near Threshold: Breakdown Of The Elastic Description Of A Charge Density Wave Model, Muhittin Mungan, Susan N. Coppersmith, Valeri M. Vinokur
Turkish Journal of Physics
We analyze the strains near threshold in 1-d charge density wave models at zero temperature and strong pinning. We show that in these models local strains diverge near the depinning threshold and characterize the scaling behavior of the phenomenon. This helps quantify when the underlying elastic description breaks down and plastic effects have to be included.
Photon Counting In Astrophotometry. Fundamentals And Some Advices For Beginners, Romualdas Kalytis
Photon Counting In Astrophotometry. Fundamentals And Some Advices For Beginners, Romualdas Kalytis
Turkish Journal of Physics
The beginners in astrophotometry are reminded of fundamentals of photon counting. Several advices for new users of electrophotometric technics are given.
Kinematics Of Rs Cvn And W Uma Binaries In The Hipparcos Catalogue, Zeki̇ Aslan, Tuncay Özdemi̇r, Cahi̇t Yeşi̇lyaprak, Ahmet İskender
Kinematics Of Rs Cvn And W Uma Binaries In The Hipparcos Catalogue, Zeki̇ Aslan, Tuncay Özdemi̇r, Cahi̇t Yeşi̇lyaprak, Ahmet İskender
Turkish Journal of Physics
Space motions of RS CVn and W UMa binaries have been calculated using parallaxes and proper motions from Hipparcos catalogue and radial velocities from the literature. We have calculating the mean motions and velocity dispersions. We have excluded those binaries with relative parallax errors \geq 0.5. The comparison of the asymmetric drift, velocity ellipsoids and vertex deviation with those of main sequence stars given by Dehnen and Binney indicates that both RS CVn and W UMa binaries have kinematics similar to main sequence stars slightly bluer than the Parenago's discontinuity and B-V \simeq 0.62. Implication of this has been discussed.
Heat Pulse Studies Of The Emission And Absorption Of Acoustic Phonons In Gaas Quantum Wells And Wires, A. J. Kent
Heat Pulse Studies Of The Emission And Absorption Of Acoustic Phonons In Gaas Quantum Wells And Wires, A. J. Kent
Turkish Journal of Physics
This paper reviews some recent experiments in which heat pulse techniques have been used to study the interaction of acoustic phonons with electrons in semiconductor quantum wells and wires. Heat pulse experiments provide temporal and spatial resolution of the phonons that are emitted or absorbed by the electrons and so give more detailed information about the electron-phonon interaction than can be obtained by other methods (e.g. transport measurements). Phonon experiments demonstrate clearly the effect of the electron confinement on the carrier-phonon interaction and the overall energy loss rate due to acoustic phonon emission. A qualitative explanation of the results is …
Modelling Of Devices For Optoelectronic Applications: The Quantum Confined Stark Effect And Self-Electrooptic Effect Devices, Eckehard Scholl
Modelling Of Devices For Optoelectronic Applications: The Quantum Confined Stark Effect And Self-Electrooptic Effect Devices, Eckehard Scholl
Turkish Journal of Physics
Electro-optical effects, such as the Franz-Keldysh effect in bulk materials or the quantum confined Stark effect in quantum well structures, lead to strong optoelectronic nonlinearities which form the basis for optical modulators and optically bistable devices. They result from a modification of the optical absorption properties by an applied electric field and are particularly pronounced in the case of low dimensional semiconductors. We review theoretical modelling and computer simulations of such optoelectronic devices in particular for ZnSe based quantum well structures, where excitonic features dominate even at room temperature. The field dependent absorption spectra are calculated by a many-body theory …
Stability Of Quasi-Two-Dimensional Bipolarons, R. Tuğrul Senger, Ati̇lla Erçelebi̇
Stability Of Quasi-Two-Dimensional Bipolarons, R. Tuğrul Senger, Ati̇lla Erçelebi̇
Turkish Journal of Physics
The stability criteria of quasi-two-dimensional dimensional bipolarons have been studied within the framework of strong coupling and path-integral theories. It is shown that the critical values of the electron-phonon coupling constant (\alpha), and the ratio of dielectric constants (\eta = \epsilon_{\infty}/\epsilon_{0}) exhibit some non-trivial features as the effective dimensionality is tuned from three to two.
Band-Gap Renormalization In Quantum Wires, K. Güven, C. R. Bennett, B. Tanatar
Band-Gap Renormalization In Quantum Wires, K. Güven, C. R. Bennett, B. Tanatar
Turkish Journal of Physics
Improved techniques in semiconductor fabrication increased the interest in quantum wire structures, because of their opto-electronic device application possibilities. Many-body interactions among the electrons and holes in the wire lead to the band-gap renormalization (BGR), which in turn affect the optical properties of the system. We study the BGR within the random-phase approximation incorporating the dynamical effects, and investigate the density dependence.
Light Emission From Travelling Space Charge Domains, M. Hostut, N. Balkan
Light Emission From Travelling Space Charge Domains, M. Hostut, N. Balkan
Turkish Journal of Physics
We report light emission from n-doped GaAs epilayers associated with impact ionization when the device is biased in the negative difference resistance (NDR) regime (F > 3.5 kV cm^{-1}). Spectral distribution of the emitted light (electroluminescence) has been measured to identify the energy distribution of the recombining electron-hole pairs. Electron temperatures, calculated from the high energy tail of the electroluminescence spectra, show that the light emission is due to the recombination of the impact ionized holes with the background, channel, and the travelling space charge electrons. The range of the electron temperatures obtained indicate that the contribution to the light emission …
The Orbit Center Dependence Of The Energy Levels In A Multiple Quantum Wells Under External Tilted Magnetic And Electric Fields, R. Amca, Y. Ergün, H. Sari, S. Elagöz, İ. Sökmen
The Orbit Center Dependence Of The Energy Levels In A Multiple Quantum Wells Under External Tilted Magnetic And Electric Fields, R. Amca, Y. Ergün, H. Sari, S. Elagöz, İ. Sökmen
Turkish Journal of Physics
An analytical solution to the Schrödinger equation for a multiple quantum well system subjected to an externally applied electric field the growth direction and an externally applied tilted magnetic field are obtained and the results are discussed. The energy dependence energy spectrum of the system as a function of the external electric field and the orbit center is also discussed.
Feasibility Of Fabrication Of Heteroepitaxial Ge_X Si_{1-X}/Si(111) Structure By Pulsed Nd: Yag Laser, R. N. Al-Rawi, R. A. Ismail, R. N. Mousis
Feasibility Of Fabrication Of Heteroepitaxial Ge_X Si_{1-X}/Si(111) Structure By Pulsed Nd: Yag Laser, R. N. Al-Rawi, R. A. Ismail, R. N. Mousis
Turkish Journal of Physics
Heteroepitaxial Ge_x Si_{1-x} alloy layers have been formed by 10 ms and 300 \mu s laser pulse induced mixing of pure germanium films and Si(111) substrates where Ge films of thickness (500-1250) Å are thermally evaporated onto Si(111) under vacuum pressure \sim 10^{-5} Torr. The near surface of the sample then undergoes rapid melting and regrowth processes during each pulse from a free running Nd; YAG laser. The alloy layers are (4.6-6.5) \mum thick and have a Ge fraction of x = 6-8.2%.
Electronic And Lattice Thermal Conductivity Of Bi_{1-X} Sb_X And Ag-Sb-Te Systems, Sabi̇r Ali̇yev, Agami̇rza Movsum-Zadeh, Sadiyar Ragimov, Eldar Zulfigarov
Electronic And Lattice Thermal Conductivity Of Bi_{1-X} Sb_X And Ag-Sb-Te Systems, Sabi̇r Ali̇yev, Agami̇rza Movsum-Zadeh, Sadiyar Ragimov, Eldar Zulfigarov
Turkish Journal of Physics
An investigation of the electronic (\aleph_e) and lattice (\aleph_L) parts of the thermal conductivity for samples of Bi_{1-x} Sb_x (0,02 < X < 0,12) and system of Ag-Sb-Te was carried out in the temperature interval 6-300K. Separation of \aleph_L and \aleph_e has been made by suppressing \aleph_e in magnetic field. The experimental data of \aleph_L and \aleph_e have been compared, respectively, with Gallaway's theory and with a theory which takes into account the inelastic character of scattering. It is observed that the Lorentz number L calculated by using the experimental values of \aleph_e and thermomagnetic coefficients is smaller than its Zommerfeld's value L_0 in high doping Bi_{0.88}Sb_{0.12}. A satisfactory agreement between the theory and the experiment allows to conclude that besides the normal and U-processes in Bi_{1-x}Sb_x the defects of mass also plays a considerable role in scattering. It is observed that \aleph_L of single phase samples Ag_{0.82}Sb_{1.18}Te_{2.18} is smaller than AgSbTe_2 samples. It is shown that this is due to the presence of p-Ag_2 Te in AgSbTe_2. It is established that the high concentration of intrinsic defects plays a considerable role in scattering for Ag-Sb-Te as well.
Planar Linkages And Algebraic Sets, Henry C. King
Planar Linkages And Algebraic Sets, Henry C. King
Turkish Journal of Mathematics
No abstract provided.
Electron Liquid Beyond The Random Phase Approximation, Mehmet Tomak, Ceyhun Bulutay
Electron Liquid Beyond The Random Phase Approximation, Mehmet Tomak, Ceyhun Bulutay
Turkish Journal of Physics
A deeper understanding of low-dimensional and small-scale electronic systems requires an accurate characterization of the many-electron effects. Based on the electron liquid (EL) model, these many-body effects in the three-dimensional (3D) and two-dimensional (2D) electronic systems are dealt going beyond the random phase approximation within the zero-temperature framework. The dielectric formulation of the many-body problem is recapitulated and the longitudinal dielectric function of the EL is obtained using the self-consistent local-field correction scheme, known as STLS, under a general spin-valley degeneracy. Extensive explicit expressions are provided for the use of other researchers. The performance of this formalism is compared in …
Magnetic Excitations In Random Anisotropic Magnets, İbrahim Avgin
Magnetic Excitations In Random Anisotropic Magnets, İbrahim Avgin
Turkish Journal of Physics
A study is made for the magnetic excitations and their Anderson localization properties for a Heisenberg ferromagnet with random anisotropic fields. The system is assumed to be in a strong applied field so that complete spin alignment is established. The magnetic excitations, i.e., the harmonic spin waves, are computed using coherent-field-anisotropy approximation (a version of coherent potential approximation of the electronic problem). The spin wave shift and damping are calculated using the computed coherent field which is a complex function of energy approximating the random medium as a mean field level. The localizaton of the excitations are calculated by adopting …