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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
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Publication Metadata only Chaos in rotating triatomic clusters(Editions Physique, 1997) Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129Lyapunov exponent distributions of rotating triatomic Lennard-Jones clusters are calculated to analyze the effects of the vibrational and rotational motion on the extent of chaotic behavior. Initial momentum components are assigned to atoms either to rotate the clusters around symmetry axes or to generate random angular momenta. In both cases, it is seen that the initial kinetic energy assigned to vibrational modes is the dominant factor which determines the degree of chaos.Publication Metadata only Influence of competitive hydrogen bonding between hard and soft segments on the properties of siloxane and polyether-based segmented copolymers.(Amer Chemical Soc, 1999) Department of Chemistry; Department of Chemistry; N/A; Yılgör, İskender; Burgaz, Engin; Metin, Burak; Yurtsever, İsmail Ersin; Yılgör, Emel; Faculty Member; Undergraduate Student; Undergraduate Student; Faculty Member; Researcher; Department of Chemistry; College of Sciences; College of Sciences; N/A; 24181; 17956; N/A; N/A; 40527N/APublication Metadata only Crystal structure of tetrasodium octaeuropium(ii) [octaphosphido(3-)]-bis[diphosphido(4-)]tetraaluminate(iii),NA 4EU8[AL4P8(P2) 2](Walter de Gruyter, 1998) Carrillo-Cabrera, W.; Peters, K.; Von Schnering, H.G.; Department of Chemistry; Somer, Mehmet Suat; Faculty Member; Department of Chemistry; College of Sciences; 178882N/APublication Metadata only Hydrophilic polyurethaneurea membranes: influence of soft block composition on the water vapor permeation rates(Elsevier Sci Ltd, 1999) Department of Chemistry; Department of Chemistry; Yılgör, İskender; Yılgör, Emel; Faculty Member; Researcher; Department of Chemistry; College of Sciences; College of Sciences; 24181; 40527High molecular weight segmented polyurethaneurea (PUU) copolymers based on an aliphatic diisocyanate, bis(4-isocyanatocyclohexyl)methane and mixed hydrophilic and hydrophobic soft segments were prepared. Hydrophilic blocks consisted of poly(ethyleneoxide) (PEO) of molecular weight 1450 g/mol, whereas the hydrophobic blocks were poly(tetramethylene oxide) of molecular weight 2000 g/mol. Ethylene diamine was used as the chain extender. Hard segment contents of the copolymers were kept constant at 18%, whereas PEO contents were varied between 0% and 50% by weight. Water vapor permeation rates (WVPR) of thin films (23-178 mu m) cast from dimethylformamide solutions were determined. In studies performed at 23 degrees C and 50% relative humidity, the relationship between PEO content and WVPR followed an S-shaped curve. For copolymers containing up to about 15% by weight of PEG, WVPR were fairly low. This was followed by a region where WVPR increased continuously for membranes containing between 15% and 30% PEG. Further increase in PEO content above 30% did not influence the WVPR substantially. There was also a dramatic increase in WVPR with an increase in temperature from 23 degrees C to 37 degrees C. Activation energy of permeation was determined to be 91.5 kJ for PUU containing 22.0% by weight of PEG. Equilibrium water absorption levels of PUU containing different levels of PEO in their backbone structures followed a similar trend to that of WVPR. Hydrophilic PUUs showed good tensile properties and mechanical integrity even at very high levels of water absorption.Publication Metadata only A two-dimensional Monte Carlo polymerization of 5-membered rings(Scientific Technical Research Council Turkey, 1997) Esentürk, O.; Pamuk, H. A.; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129A modification of the kinetic growth model in two dimensions for the polymerization of 5-membered rings is presented. The preliminary results reveal the validity of the modified model.Publication Metadata only A theoretical study of structural defects in conjugated polymers(Elsevier Science Sa, 1999) Yurtsever, Mine; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129Accurate ab-initio calculations are performed for pyrrole and thiophene oligomers bonded through alpha and beta carbons. The thermodynamical stabilitiy of all possible binding types including the branched forms of tetramers and pentamers are compared. Employing the probabilities obtained from these calculations, a Monte Carlo type growth scheme is applied to predict branching as functions of the chain length and temperature. A high degree of branching for polypyrrole is reported whereas the linear chains dominate the structure of polythiophene.Publication Metadata only Quantum chaos: a route through mixed-mode dynamics(Scientific and Technical research Council of Turkey - TUBITAK/Türkiye Bilimsel ve Teknik Araştırma Kurumu, 1997) Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129The quantal-classical mixed-mode dynamics provides a convenient tool for studying the transition from classical to quantum dynamics. In this work nonlinearly coupled oscillator systems whose classical motion display chaos are investigated under the time-dependent self-consistent-field approach so that one of the modes can be treated quantum mechanically. Lyapunov exponents for the mixed-mode system are defined through the use of Hamilton-Jacobi-like equations of motion for the quantal wavepacket. The classical modes seem to be more regularized when they are under the effect of quantum fields, however the Lyapunov exponents of the mixed-mode dynamics agree extremely well with those from classical calculations showing that chaos still survives in the mixed-mode philosophy.Publication Metadata only Tetrarubidium nonagermanide(4-) ethylenediamine, Rb-4[Ge-9][en](Wiley, 1998) Carrillo-Cabrera, Wilder; Peters, Eva Maria; Peters, Karl; von Schnering, Hans Georg; Department of Chemistry; Somer, Mehmet Suat; Faculty Member; Department of Chemistry; College of Sciences; 178882Orange crystals of Rbd(4)[Ge-9][en] are obtained after the exchange reaction of a solution of 'NaGe2.25' (precursor) in ethylenediamine (en) with solid RbI at 363 K, followed by slow cooling. The compound is very sensitive to oxidation and hydrolysis. The thermal decomposition in dynamic vacuum starts at 350 K with the complete loss of en followed by the sublimation of Rb in four steps (Rb8Ge25, Rb8Ge44, RbxGe136 with x less than or equal to 16, Ge). The Raman spectrum shows the characteristic bands of the [Ge-9](4-) anion (151, 163, 185 and 222 cm(-1)). Rb-4[Ge-9][en] crystallizes in a new structure type (space group P2(1)/m; a=15.353 Angstrom, b = 16.434 Angstrom, c = 15.539 Angstrom, beta =113.75 degrees; Z = 6; Pearson code mP198-40), which can be described as a hierarchical derivative of the structures of Al4YbMo2 and CrB4 (initiators) formed by partial atom-to-aggregate replacement: B-4[square 1][Cr] (=) over cap Al-4[Yb][Mo](2) (=) over cap Rb-4[Ge-9][en](1-2). Three crystal lographic independent [Ge-9](4-) clusters with different orientations are embedded in a Lt-connected 46(5) net formed by the Rb atoms, a network of condensed tetraasteranes. The clusters are distorted monocapped tetragonal antiprisms with D-1(Ge-Ge) = 2.57 Angstrom (16 x) and D-2(Ge-Ge) = 2.84 Angstrom (4x). The atoms of clusters with D1 and D2 lie at the surface of a rotational ellipsoid (a=b=2.136 Angstrom, c=2.431 Angstrom). The en molecules are located in open channels along [(1) over bar 0 1]. The coordinations [Ge-9] Rb-12/14 and Rb [Ge-9](4/12) en(2/8) show that the first step of solvation do not separate the cations from the cluster anions.Publication Metadata only The [Sn-5](2-) cluster compound [K-(2,2,2-crypt)](2)Sn-5 - Synthesis, crystal structure, Raman spectrum, and hierarchical relationship to CaIn2(Wiley, 1999) Carrillo-Cabrera, Wilder; Peters, Eva-Maria; Peters, Karl; Kaupp, Martin; von Schnering, Hans Georg; Department of Chemistry; Somer, Mehmet Suat; Faculty Member; Department of Chemistry; College of Sciences; 178882Dark red crystals of [K-(2,2,2)-crypt)](2)Sn-5 precipitate after the reaction of (2,2,2)-crypt with a solution of K1.33Sn in liquid ammonia at room temperature. The compound is sensitive to oxidation and hydrolysis. The sequence of Raman bands (104, 120, 133 and 180 cm(-1)) is characteristic for the trigonal bipyramidal closo-[Sn-5](2-) cluster anion. The wave numbers correspond with the data from Hartree-Fock calculations (114, 128, 142 and 187 cm(-1)). The compound crystallizes trigonally (a = 11.736 Angstrom, c = 22.117 Angstrom, Z = 2, space group (No. 165); Pearson code hP262), isotypic with [Na-(2,2,2)-crypt)](2)Pb-5. The atoms of the cluster show strange anisotropic displacements, which are perfectly reducible to a helical rigid-body motion around and along [001] (libration: +/-9.5 degrees; translation +/-0.29 Angstrom). The structure can be described as a hierarchical derivative of the initiator CaIn2 (P6(3)/mmc, hP6), generated by an atom-to-aggregate replacement: [Ca][In](2) = [Sn-5][K @ C36H72N4O12](2). Thus, the distribution of the [Sn-5](2-) Zint1 anions is hexagonal primitive, and the cation complexes are located close to the centers of trigonal superprisms formed by Sn5 clusters.Publication Metadata only A new antiaromatic compound: 1,4-biphenylenequinone synthesis and trapping reactions(American Chemical Society (ACS), 1997) Kılıç, Hamdullah; Balcı, Metin; Department of Chemistry; Yurtsever, İsmail Ersin; Faculty Member; Department of Chemistry; College of Sciences; 7129N/A