Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/207

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Production of precipitated calcium carbonate particles from gypsum waste using venturi tubes as a carbonation zone
(ELSEVIER SCI LTD, THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, OXON, ENGLAND, 01.01.2019) Altiner, Mahmut; Top, Soner; Kaymakoglu, Burcin; Seckin, Ismail Yigit; Vapur, Huseyin; 0000-0002-7428-5999; 0000-0003-3486-4184; 0000-0003-4438-3982; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
In this study, we investigated the production of precipitated calcium carbonate (PCC) particles from desulfurization gypsum (DG) waste using a new experimental apparatus that is divided into two main parts: carbonation and stabilization zones. The solution was circulated via a pump from the stabilization zone to the carbonation zone where different types of Venturi tube were used for the reaction of CO2 with solution to produce PCC particles. The effects of CO2 flow rate, circulation rate, and Venturi types on the properties of the produced PCC particles were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), and particle size analyses. The conductivity and pH values of the solution were monitored during the carbonation. In addition, the reactivity of selected PCC was determined to evaluate its use as a sorbent in a desulfurization unit. The experimental results indicate that the Venturi tube had a strong effect on the reaction time and properties of PCC particles. The use of a Venturi tube resulted in a decrease in the time required for producing PCC particles, which were smooth, well-crystallized, and nano-sized cubic crystals. However, when no Venturi tube was used, hollow spherical crystals formed along with cubic crystals. It was found that the reactivity of selected PCC particles produced using Venturi tube was rather higher (52x10(-4) min(-1)), indicating that the PCC can be used as a sorbent in the desulfurization unit.
Selective removal of cationic micro-pollutants using disulfide-linked network structures
(ROYAL SOC CHEMISTRY, THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND, 207-05-15) Atas, Mehmet Sahin; Dursun, Sami; Akyildiz, Hasan; Citir, Murat; Yavuz, Cafer T.; Yavuz, Mustafa Selman; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü;
Micropollutants are found in all water sources, even after thorough treatments that include membrane filtration. New ones emerge as complex molecules are continuously produced and discarded after used. Treatment methods and sorbent designs are mainly based on non-specific interactions and, therefore, have been elusive. Here, we developed swellable covalent organic polymers (COP) with great affinity towards micropollutants, such as textile industry dyes. Surprisingly, only cationic dyes in aqueous solution were selectively and completely removed. Studies of the COPs surfaces led to a gating capture, where negatively charged layer attracts cationic dyes and moves them inside the swollen gel through diffusive and hydrophobic interaction of the hydrocarbon fragments. Despite its larger molecular size, crystal violet has been taken the most, 13.4 mg g(-1), surpassing all competing sorbents. The maximum adsorption capacity increased from 12.4 to 14.6 mg and from 8.9 to 11.4 mg when the temperature of dye solution was increased from 20 to 70 degrees C. The results indicated that disulfide-linked COPs are attractive candidates for selectively eliminating cationic dyes from industrial wastewater due to exceptional swelling behaviour, low-cost and easy synthesis.
Cation exchange mediated synthesis of bright Au@ZnTe core-shell nanocrystals
(IOP PUBLISHING LTD, TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND, 08.01.2021) Sadeghi, Sadra; Melikov, Rustamzhon; Sahin, Mehmet; Nizamoglu, Sedat; 0000-0002-8569-1626; 0000-0003-2214-7604; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü
The synthesis of heterostructured core-shell nanocrystals has attracted significant attention due to their wide range of applications in energy, medicine and environment. To further extend the possible nanostructures, non-epitaxial growth is introduced to form heterostructures with large lattice mismatches, which cannot be achieved by classical epitaxial growth techniques. Here, we report the synthetic procedure of Au@ZnTe core-shell nanostructures by cation exchange reaction for the first time. For that, bimetallic Au@Ag heterostructures were synthesized by using PDDA as stabilizer and shape-controller. Then, by addition of Te and Zn precursors in a step-wise reaction, the zinc and silver cation exchange was performed and Au@ZnTe nanocrystals were obtained. Structural and optical characterization confirmed the formation of the Au@ZnTe nanocrystals. The optimization of the synthesis led to the bright nanocrystals with a photoluminescence quantum yield up to 27%. The non-toxic, versatile synthetic route, and bright emission of the synthesized Au@ZnTe nanocrystals offer significant potential for future bio-imaging and optoelectronic applications.
Infrared multiple photon dissociation spectroscopy of protonated histidine and 4-phenyl imidazole
(ELSEVIER, 2012) Hinton, Christopher S.; Oomens, Jos; Citir, Murat; Steill, Jeffrey D; Armentrout, P. B.; 0000-0002-6666-4980; AGÜ; Citir, Murat
The gas-phase structures of protonated histidine (His) and the side-chain model, protonated 4-phenyl imidazole (PhIm), are examined by infrared multiple photon dissociation (IRMPD) action spectroscopy utilizing light generated by the free electron laser FELIX. To identify the structures present in the experimental studies, the measured IRMPD spectra are compared to spectra calculated at a B3LYP/6–311+G(d,p) level of theory. Relative energies of various conformers are provided by single point energy calculations carried out at the B3LYP, B3P86, and MP2(full) levels using the 6–311+G(2d,2p) basis set. On the basis of these experiments and calculations, the IRMPD action spectrum for H+(His) is characterized by a mixture of [N,N] and [N,CO] conformers, with the former dominating. These conformers have the protonated nitrogen atom of imidazole adjacent to the side-chain (N) hydrogen bonding to the backbone amino nitrogen (N) and to the backbone carbonyl oxygen, respectively. Comparison of the present results to recent IRMPD studies of protonated histamine, the radical His•+ cation, H+(HisArg), H2 2+(HisArg), and M+(His), where M+ = Li+, Na+, K+, Rb+, and Cs+, allows evaluation of the vibrational motions associated with the observed bands.
Thermochemistry of alkali metal cation interactions with histidine: Influence of the side chain
(American Chemical Society, 2012) Armentrout, P. B.; Citir, Murat; Chen, Yu; Rodgers, M. T.; 0000-0002-7957-110X; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Citir, Murat
The interactions of alkali metal cations (M+ = Na+ , K+ , Rb+ , Cs+ ) with the amino acid histidine (His) are examined in detail. Experimentally, bond energies are determined using threshold collision-induced dissociation of the M+ (His) complexes with xenon in a guided ion beam tandem mass spectrometer. Analyses of the energy dependent cross sections provide 0 K bond energies of 2.31 ± 0.11, 1.70 ± 0.08, 1.42 ± 0.06, and 1.22 ± 0.06 eV for complexes of His with Na+ , K+ , Rb+ , and Cs+ , respectively. All bond dissociation energy (BDE) determinations include consideration of unimolecular decay rates, internal energy of reactant ions, and multiple ion-neutral collisions. These experimental results are compared to values obtained from quantum chemical calculations conducted previously at the MP2(full)/6-311+G(2d,2p), B3LYP/6-311+G(2d,2p), and B3P86/6-311+G(2d,2p) levels with geometries and zero point energies calculated at the B3LYP/6-311+G(d,p) level where Rb and Cs use the Hay−Wadt effective core potential and basis set augmented with additional polarization functions (HW*). Additional calculations using the def2-TZVPPD basis set with B3LYP geometries were conducted here at all three levels of theory. Either basis set yields similar results for Na+ (His) and K+ (His), which are in reasonable agreement with the experimental BDEs. For Rb+ (His) and Cs+ (His), the HW* basis set and ECP underestimate the experimental BDEs, whereas the def2-TZVPPD basis set yields results in good agreement. The effect of the imidazole side chain on the BDEs is examined by comparing the present results with previous thermochemistry for other amino acids. Both polarizability and the local dipole moment of the side chain are influential in the energetics.
The photoionization cross section of a hydrogenic impurity in a multi-layered spherical quantum dot
(AIP Publishing1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501, 2012) Sahin, Mehmet; Tek, Firdes; Erdinc, Ahmet; 0000-0002-9419-1711; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Şahin, Mehmet
In this study, we have investigated the photoionization cross section of an on-center hydrogenic impurity in a multi-layered spherical quantum dot. The electronic energy levels and their wave functions have been determined fully numerically by shooting method. Also, we have calculated the binding energy of the impurity by using these energy values. The photoionization cross section has also been computed as a function of the layer thickness and normalized photon energies. We have discussed in detail the possible physical reasons behind the changes in the binding energies and photoionization cross section. It is observed that both the binding energies and the photoionization cross sections depend strongly on the layer thickness and photon energies. (C) 2012 American Institute of Physics.
The effect of dilute nitrogen on nonlinear optical properties of the InGaAsN/GaAs single quantum wells
(SPRINGER, 2012) Sahin, Mehmet; Koksal, Koray; 0000-0002-9419-1711; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Sahin, Mehmet
In this study, we investigate the linear and third order nonlinear optical properties of InGaAsN/GaAs depending on nitrogen content and laser dressing parameter. As theoretical models, band anticrossing and model solid theory are used. In order to obtain the electronic properties of the quantum well, the finite difference method is used. The laser beam affects the electronic properties of the quantum well by changing the shape of the confinement potential. This modification of the potential is determined by laser dressing parameter. By using dilute amount of nitrogen, conduction band and the depth of quantum well can be controlled. The strain which is introduced due to the presence of nitrogen can be compensated by using indium atoms. The electronic and the linear and third order nonlinear optical properties of InGaAsN/GaAs quantum well structure are obtained.
The linear optical properties of a multi-shell spherical quantum dot of a parabolic confinement for cases with and without a hydrogenic impurity
(IOP Publishing Ltd, 2012) Sahin, Mehmet; Koksal, Koray; 0000-0002-9419-1711; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Sahin, Mehmet
Throughout this work, we aim to explore the linear optical properties of a semiconductor multi-shell spherical quantum dot with and without a hydrogenic donor impurity. The core and well layers are defined by the parabolic electronic potentials in the radial direction. The energy levels and corresponding wavefunctions of the structure are calculated by using the shooting technique in the framework of the effective-mass approximation. We investigate the intersublevel absorption coefficients of a single electron and the hydrogenic donor impurity comparatively as a function of the photon energy. In addition, we carry out the effect of a donor impurity and the layer thickness on the oscillator strengths and magnitude and position of absorption coefficient peaks. We illustrate the electron probability distribution and variation of the energy levels in cases with and without the impurity for different thicknesses of layers. This kind of structure gives an opportunity to tune and control the absorption coefficient of the system by changing three different thickness parameters. Also it provides a possibility to separate 0s and 1p electrons in different regions of the quantum dot.
A detailed investigation of the electronic properties of a multi-layer spherical quantum dot with a parabolic confinement
(ELSEVIER, 2012) Akgul, Selcuk; Koksal, Koray; Sahin, Mehmet; 0000-0002-9419-1711; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Sahin, Mehmet
In this work, we aim a detailed investigation of the electronic properties of a spherical multi-layer quantum dot with and without a hydrogenic impurity. The structure is introduced in the form of core/ shell/well/shell layers. The core and well layers are defined by the parabolic electronic potentials. We carry out the effect of the core radius and layer thickness on the energy levels, their wave functions, binding energies of the impurity and the probability distributions. In order to determine the sublevel eigenvalues and eigenfunctions, the Schrodinger equation is solved full numerically by shooting ¨ method in the frame of the effective mass approximation. The results are analyzed in detail as a function of the layer thicknesses and their probable physical reasons are tried to be explained. It is found that the electronic properties and impurity binding energies are strongly depending on the layer thicknesses.
The electronic properties of a core/shell/well/shell spherical quantum dot with and without a hydrogenic impurity
(AIP Publishing1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501, 2012) Sahin, Mehmet; Tas, Hatice; 0000-0002-9419-1711; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Şahin, Mehmet
In this study, we have performed a detailed investigation of the electronic properties of a core/shell/well/shell multi-layered spherical quantum dot, such as energy eigenvalues, wave functions, electron probability distribution and binding energies. The energy eigenvalues and their wave functions of the considered structure have been calculated for cases with and without an on-center impurity. For this purpose, the Schr¨odinger equation has been numerically solved by using the shooting method in the effective mass approximation for a finite confining potential. The electronic properties have been examined for different core radii, barrier thickness and well widths in a certain potential. The results have been analyzed in detail as a function of the layer thickness and their physical reasons have been interpreted. It has found that the electronic properties are strongly depending on the layer thickness.
The inter-sublevel optical properties of a spherical quantum dot-quantum well with and without a donor impurity
(AIP Publishing1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501, 2012) Tas, Hatice; Sahin, Mehmet; 0000-0002-9419-1711; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Şahin, Mehmet
In this study, we have investigated the inter-sublevel optical properties of a core/shell/well/shell spherical quantum dot with the form of quantum dot-quantum well heterostructure. In order to determine the energy eigenvalues and corresponding wave functions, the Schr¨odinger equation has been solved full numerically by using shooting method in the effective mass approximation for a finite confining potential. The inter-sublevel optical absorption and the oscillator strength between ground (1s) and excited (1p) states have been examined based on the computed energies and wave functions. Also, the effect of a hydrogenic donor impurity, located at the center of the multi-shell spherical quantum dot (MSQD), has been researched for different core radii (R1), shell thicknesses (Ts) and well widths (Tw) in certain potential. It is observed that the oscillator strengths and the absorption coefficients are strongly depend on the core radii and layer thicknesses of the MSQD.
DISSOLUTION OF MIXED ZINC-CARBON AND ALKALINE BATTERY POWDERS IN SULPHURIC ACID USING ASCORBIC/OXALIC ACID AS A REDUCTANT
(JOHN WILEY & SONS, 2012) Kaya, Muammer; Kursunoglu, Sait; 0000-0002-1680-5482; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Kursunoglu, Sait
The aim of this study was to investigate the effectiveness of ascorbic (C6H8O6) / oxalic (C2H2O4) acid as a reductant for the simultaneous recovery of zinc and manganese from a spent and mixed zinc-carbon and alkaline battery powder in sulphuric acid leaching. The effects of sulfuric acid concentration, ascorbic/oxalic acid dosages, reaction temperature and leaching time on the zinc and manganese dissolutions were investigated according to 2(k) full factorial experimental design; then, a simple optimization study was carried out for the best reductant. The optimum reductive acid leaching conditions were determined at 3 hours leaching time, 70 degrees C leaching temperature, 0.5M sulfuric acid concentration, 13 g/L ascorbic acid dosage, 1/20 g/mL solid/liquid ratio and 200 rpm stirring speed. Under these conditions, the dissolution efficiencies were 99.9% for Zn and 99.3% for Mn. When our results were compared with the previous results, our findings were better than previous studies. In addition, the manganese dissolution kinetics was undertaken, and the activation energy was found to be 7.04 kJ/mol. Selective precipitations of Zn and Mn from acid solutions were carried out using NaOH and KOH. Using 3M NaOH as precipitating agent at room temperature and at pH 8; 95.4% of Zn and at pH 10; 93.7% of Mn were precipitated from the leaching solution. Under the same conditions, using 3 M KOH at pH 8; 91.6% of Zn and at pH 10, 96.4% of Mn were precipitated. Based on the experimental results obtained, an appropriate flow sheet was proposed to recover zinc and manganese.
Recovery of Manganese from Spent Batteries Using Activated Carbon Powder as Reductant in Sulfuric Acid Solution
(ASIAN JOURNAL OF CHEMISTRY, 11/100 RAJENDRA NAGAR, SECTOR 3,, SAHIBABAD 201 005, GHAZIABAD, INDIA, 2013) Kursunoglu, Sait; Kaya, Muammer; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü;
Recovery of manganese from spent batteries was investigated using activated carbon powder as a reducing agent in sulfuric acid solution. The effects of four different leaching parameters (sulfuric acid concentration, amount of activated carbon powder, temperature and time) on the leaching of manganese from spent batteries were investigated using central composite design technique. The maximum manganese recovery conditions were determined as 1 M of sulfuric acid concentration, 3 g of activated carbon powder, 80 degrees C of temperature and 3 h of leaching time. Under these conditions, the recovery of manganese was 86.39 % and pH value of the solution was 0.77. According to the reductive acid leaching results, an empirical second order equation for manganese recovery based on four investigated parameters was calculated. The observed values of manganese recoveries using model equation were found to be in a good agreement with the predicted values (R-2 = 0.92).
Linear and nonlinear optical properties of GaAs/Al(x)Ga1-xAs/GaAs/Al(y)Ga1-yAs multi-shell spherical quantum dot
(AIP Publishing, 2013) Kavruk, Ahmet Emre; Sahin, Mehmet; Koc, Fatih; 0000-0002-4751-2340; 0000-0002-9419-1711; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Sahin, Mehmet
In this work, the optical properties of GaAs/AlxGa1-xAs/GaAs/AlyGa1-yAs multi-shell quantum dot heterostructure have been studied as a function of Al doping concentrations for cases with and without a hydrogenic donor atom. It has been observed that the absorption coefficient strength and/or resonant absorption wavelength can be adjusted by changing the Al content of inner-barrier and/or outer-barrier regions. Besides, it has been shown that the donor atom has an important effect on the control of the electronic and optical properties of the structure. The results have been presented as a function of the Al contents of the inner-barrier x and outer-barrier y regions and probable physical reasons have been discussed. (c) 2013 AIP Publishing LLC.
A highly selective whole cell biocatalysis method for the production of two major bioactive conjugated linoleic acid isomers
(ELSEVIER, 2013) Khaskheli, Abid Ali; Talpur, Farah N.; (Demir, Ayhan S.; Cebeci, Aysun; Jawaid, Sana; 0000-0002-6158-8798; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Cebeci, Aysun
Conjugated linoleic acid (CLA) is well known potential anticarcinogenic, antiatherogenic and a number of other therapeutic qualities bearing substance. In the present study we have isolated Lactobacillus plantarum from local dairy buffalo milk and used as a whole cell biocatalyst, for selective CLA isomer production from linoleic acid (LA). Quantitative analysis revealed that the cis-9, trans-11 CLA comprised of 51% (w/w), while trans-10, cis-12 CLA accounted for 49% (w/w) of total CLA produced by L. plantarum. The product formation and quantitation was monitored by the spectrophotometric method and the individual isomers separation was done with GC–FID. After optimization of biotransformation conditions such as pH, LA concentration, effect of preincubation, fermentation time; the highest CLA production (19.07% conversion) was achieved at 120 h in the presence of 1.62 mg ml−1 of LA. The results revealed that the bacterium is an efficient biocatalyst for the production of two major bioactive CLA isomers using LA as a substrate.
Proton-conducting blend membranes of Nafion/poly(vinylphosphonic acid) for proton exchange membrane fuel cells
(SPRINGER, 2013) Acar, Oktay; Celik, Sevim Unugur; Bozkurt, Ayhan; Ata, Ali; Tokumasu, Takashi; Miyamoto, Akira; Sen, Unal; 0000-0003-4201-370X; 0000-0001-6055-2817; 0000-0003-3736-5049; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Sen, Unal
Nafion/poly(vinylphosphonic acid) blends were synthesized and characterized in this work. Poly(vinylphosphonic acid), PVPA, was synthesized by the free-radical polymerization of vinylphosphonic acid. Then Nafion/PVPA blend membranes were prepared by means of film casting from Nafion/PVPA solutions with several molar ratios of PVPA repeat unit to – SO3H. Homogeneous Nafion/PVPA films were produced. Nafion–PVPA interactions were studied by Fourier transform infrared (FT-IR) spectroscopy. Thermal properties were investigated via thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The TGA results illustrated that all of these Nafion/PVPA electrolytes are thermally stable up to 400 °C. The membrane properties were further characterized by studying their morphologies using scanning electron microscopy (SEM). The proton conductivity of the Nafion/P(VPA)3 blend membrane was 1.1×10−5 S/cm in an anhydrous state at 130 °C. The conductivities of the blends increased by at least three orders of magnitude upon hydration, exceeding 10−2 S/cm with RH=50 % at ambient temperature
Estimation of Protease Activity by Use of the Mixolab
(ELSEVIER, 2013) Kahraman, Kevser; Koksel, H.; 0000-0002-2786-3944; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Kahraman, Kevser
It is known that the preharvest attack on wheat by some heteropterous insects (Eurygaster spp., Aelia spp., and Nysius huttoni) reduces the breadmaking quality of the resulting wheat flour (Lorenz and Meredith 1988, Swallow and Every 1991, Harriri et al 2000). The problem is quite common in Mediterranean, Middle Eastern, and East European countries. Before harvest, these insects inject their salivary secretions into maturing wheat ears when they feed. Following attack by the insect, the grain matures normally, but a light-colored opaque patch surrounds the site where the insect pierced the grain. The penetration point is visible as a small dark spot in the middle of this patch. The damaged area is softer and usually collapses when pressed by a fingernail. The secretions contain proteases that break down the gluten structure during mixing and fermentation (Kretovich 1944; Every et al 1998; Sivri et al 1998, 1999).
Activation of methane by Os+: Guided-ion-beam and theoretical studies
(CHEMM, 2013) Armentrout P.B.; Parke, Laura; Hinton, Christopher; Citir, Murat; 0000-0002-7957-110X; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Citir, Murat
Activation of methane by the third-row transition-metal cation Os + is studied experimentally by examining the kinetic energy dependence of reactions of Os+ with CH4 and CD4 using guided-ion-beam tandem mass spectrometry. A flow tube ion source produces Os+ in its electronic ground state and primarily in the ground spin-orbit level. Dehydrogenation to form [Os,C,2 H]++H2 is exothermic, efficient, and the only process observed at low energies for reaction of Os+ with methane, whereas OsH+ dominates the product spectrum at higher energies. The kinetic energy dependences of the cross sections for several endothermic reactions are analyzed to give 0K bond dissociation energies (in eV) of D0(Os+-C)=6.20±0. 21, D0(Os+-CH)=6.77±0.15, and D0(Os +-CH3)=3.00±0.17. Because it is formed exothermically, D0(Os+-CH2) must be greater than 4.71eV, and a speculative interpretation suggests the exothermicity exceeds 0.6eV. Quantum chemical calculations at the B3LYP/def2-TZVPP level show reasonable agreement with the experimental bond energies and with previous theoretical values available. Theory also provides the electronic structures of the product species as well as intermediates and transition states along the reactive potential energy surfaces. Notably, the structure of the dehydrogenation product is predicted to be HOsCH+, rather than OsCH2+, in contrast to previous work.
A model for the recombination and radiative lifetime of trions and biexcitons in spherically shaped semiconductor nanocrystals
(AIP Publishing1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501, 2013) Şahin, Mehmet; Koç, Fatih; 0000-0002-4751-2340; 0000-0002-9419-1711; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Şahin, Mehmet
In this letter, we propose a different model to determine the recombination oscillator strength of trions and biexcitons for bound and unbound cases in the effective mass approximation. The validity of our model has been confirmed by the radiative lifetime of the trion and biexciton in a spherical quantum dot. The results show that the model works with sufficient accuracy in comparison with results of more complex methods such as quantum Monte Carlo techniques and atomistic calculations.
Formation of resistant starch from amylotype corn starch and determination of the functional properties
(CODON PUBLICATIONS, 2013) Kahraman, Kevser; KÖKSEL, HAMİT; 0000-0002-2786-3944; AGÜ, Mühendislik Fakültesi, Malzeme Bilimi ve Nanoteknoloji Mühendisliği Bölümü; Kahraman, Kevser
High amylose corn starch was hydrolysed with HCl at 40 °C for 0.5-2.0 h. Then the native and acid-modified starch samples were subjected to 2 different heat treatments (HT). In HT1, heat treated/autoclaved samples were dried after storage and in HT2, heat treated/autoclaved samples were dried without storage. Relative quantities of high- and medium-molecular weight fractions decreased and relative quantities of low-molecular weight fractions increased as a result of acid modification. Resistant starch (RS) contents of the acid-modified starches were between 15.7- 16.4% and increased up to 29.4% due to HT1 and up to 17.5% due to HT2. The results indicated that RS contents of the high amylose starch can be increased by HT and storing prior to drying. Rapid ViscoAnalayser viscosity values decreased as the acid modification level increased. Water absorption and solubility values of the samples prepared with both heat treatments were higher than those of the native starch and hydrolysates. Emulsifying capacity/ stability values of soy protein solution supplemented with the hydrolysates and heat treated samples were higher than those supplemented with the native and heat treated native starch.

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