Ersin Yurtsever - Academia.edu (original) (raw)

Papers by Ersin Yurtsever

Turkish Journal of Chemistry

In Iran, an arid and semiarid country, the distribution of precipitation is irregular and uneven,... more In Iran, an arid and semiarid country, the distribution of precipitation is irregular and uneven, making the replenishment of reservoirs difficult during periods of scant rainfall. In this paper, a method has been devised to make available the maximum amount of water for irrigation, drinking, and the flow regime of Sofi Creek. The optimal performance of the Eleviyan Dam was evaluated based on reservoir inflows. Before the construction of the dam, 21 years of flow data (October 1973 to September 1994) was measured, and possible low flows were calculated. In this study, 2 scenarios are considered; the first scenario is based on the assumption of an initially full reservoir, and the second is based on the assumption of full dead volume in addition to drinking and utility water. In the first scenario, system shortages were observed in September at all confidence levels and in August at 80% and 90% confidence levels. In the second scenario, considerable shortages were observed in September at all levels, and in August with a 70%-90% and July with a 90% confidence level.

doi:10.3906/kim-1112-16 Competitive hydrogen bonding in aspirin-aspirin and aspirin-leucine inter... more doi:10.3906/kim-1112-16 Competitive hydrogen bonding in aspirin-aspirin and aspirin-leucine interactions Zeynep YURTSEVER1,3, Burak ERMAN2, Ersin YURTSEVER1,∗

International Journal of Mass Spectrometry, 2020

The potential energy surfaces for C À 2 (2 S þ g) interacting with He, Ne and Ar are calculated u... more The potential energy surfaces for C À 2 (2 S þ g) interacting with He, Ne and Ar are calculated using ab initio quantum chemistry methods. The PES are used to carry out coupled-channel quantum scattering calculations for the three systems to obtain the rotationally inelastic scattering cross sections from which the rotationally inelastic state-changing rate coefficients are computed. These rate coefficients are then used to compute thermalisation times of C À 2 in an ion trap employing He, Ne or Ar as different, and possible, buffer gases. A detailed analysis of their comparative collisional efficiencies is presented for guidance in trap modeling studies.

$Research paper thumbnail of {"__content__"=>"Isomeric Broadening of CElectronic Excitation in Helium Droplets: Experiments Meet Theory.", "sub"=>{"__content__"=>"60"}, "sup"=>{"__content__"=>"+"}}$

The journal of physical chemistry letters, Jan 22, 2018

Helium is considered an almost ideal tagging atom for cold messenger spectroscopy experiments. Al... more Helium is considered an almost ideal tagging atom for cold messenger spectroscopy experiments. Although helium is bound very weakly to the ionic molecule of interest, helium tags can lead to shifts and broadenings that we recorded near 963.5 nm in the electronic excitation spectrum of Csolvated with up to 100 helium atoms. Dedicated quantum calculations indicate that the inhomogeneous broadening is due to different binding energies of helium to the pentagonal and hexagonal faces of C, their dependence on the electronic state and the numerous isomeric structures that become available for intermediate coverage. Similar isomeric effects can be expected for optical spectra of most larger molecules surrounded by non-absorbing weakly bound solvent molecules, a situation encountered in many messenger tagging spectroscopy experiments.

Polymer, 2003

In continuing efforts to understand urea phase connectivity in flexible polyurethane foams and it... more In continuing efforts to understand urea phase connectivity in flexible polyurethane foams and its implications on physical properties, LiCl is used to alter the phase-separation behavior of slabstock foams. Comparisons are also drawn with plaque counterparts, which are prepared using the same polyol, isocyanate, and chain extender (water). LiCl is shown to alter the solid-state phase separation behavior of the foams and the plaques in a similar manner. This is confirmed using multiple characterization techniques, which provide information at different scale lengths. The foams and plaques with and without LiCl are shown to possess a microphase separated morphology with interdomain spacings of ca. 100 Å. SAXS and TEM reveal that addition of LiCl reduces the urea aggregation behavior, typical in slabstock polyurethane foams, leading to a loss in the urea phase macro connectivity. Hard segment ordering, as studied by WAXS and FTIR, is shown to be of a similar nature in the plaque and foam, which do not incorporate LiCl. Addition of LiCl leads to a loss in the segmental packing behavior, or micro level connectivity of the urea phase, in both the plaques and corresponding foams, as inferred from WAXS and FTIR. The LiCl additive interacts with the polyol soft segments in an insignificant manner as shown from FTIR and DMA. In addition, foams containing LiCl are found to possess more intact cell windows due to the influence of LiCl on reaction kinetics as well as its effect on the precipitation of the urea phase. The experimental observations are supported by quantum mechanical calculations using a density functional theory approach, where molecular interactions between LiCl and model ether, urethane, and urea compounds are investigated. Interaction geometries of most stable complexes and their stability energies are calculated. Stability energies of ether/LiCl, urethane/LiCl, and urea/LiCl were determined to be 2 189, 2 617, and 2687 kJ/mol, respectively, reinforcing that LiCl interacts predominantly with urea hard segments and in a minimal manner with the polyol soft segments.

Journal of Chemical Sciences, 2012

Quantum dynamics of superelastic collisions involving vibrational levels of MgH + (X 1 +) ions in... more Quantum dynamics of superelastic collisions involving vibrational levels of MgH + (X 1 +) ions in cold traps, interacting with 4 He(1 S) as a buffer gas at relative temperatures down to millikelvins, is discussed using an ab initio computed potential energy surface. The relative efficiency of collisional cooling with respect to collisional quenching of the internal vibrations is examined from the results of the relative sizes of the relevant cross sections in relation to predicting actual behaviour in cold traps. The present study indicates the feasibility of cooling vibrationally 'hot', trapped ions with the buffer gas.

Polymer, 2000

Hydrogen bonding in polydimethylsiloxane and polyether based urethane and urea type segmented cop... more Hydrogen bonding in polydimethylsiloxane and polyether based urethane and urea type segmented copolymers was investigated by infrared spectroscopy, differential scanning calorimetry and quantum mechanical calculations. Hydrogen bonding in model urethane and urea compounds was compared with those of the copolymers, in order to determine the extent of interaction and resulting phase mixing between hard and soft segments in these copolymers. Quantum mechanical calculations were also used to determine the interaction energies due to hydrogen bonding in model urethane and urea compounds. Further, similar calculations were also performed to quantify the interactions between silicone and ether type soft segments, and urea and urethane type hard segments. As expected, these calculations clearly indicated the absence of any interaction between silicones and urea groups, while there was substantial hydrogen bonding between urea groups and the oxygen in the ether type soft segments. Results of FTIR studies and quantum mechanical calculations were in good agreement with thermomechanical behavior and mechanical properties of these copolymers.

The Journal of chemical physics, Jan 7, 2014

The interplay between thermal relaxation and statistical dissociation in binary Morse clusters (A... more The interplay between thermal relaxation and statistical dissociation in binary Morse clusters (AB)N has been investigated using numerical simulations and simple statistical approaches, for a variety of interaction parameters covering miscible and non-miscible regimes. While all clusters exhibit a core/shell phase separation pattern in their most stable, T = 0 structure, different melting mechanisms are identified depending on the ranges and their mismatch, including two-step melting of the surface and the core or premelting as alloying. The preference for emitting A or B particles upon evaporation has been evaluated assuming that the cluster is either thermally equilibrated or vibrationally excited in its ground state structure, and compared to the predictions of the Weisskopf theory. The variations of the dissociation rate constants with increasing energy and the branching ratio between the two channels show significant differences in both cases, especially when the clusters are m...

Polymer, 2014

Quantum mechanical calculations (QMC) and dissipative particle dynamics (DPD) simulations were ut... more Quantum mechanical calculations (QMC) and dissipative particle dynamics (DPD) simulations were utilized to understand the nature of the short and long-range hydrogen bonding and its influence on the microphase morphology in segmented polyurethanes and segmented polyureas prepared without chain extenders through the stoichiometric reactions of hydroxy or amine terminated poly(tetramethylene oxide) (PTMO-1000) with 1,4-phenylene diisocyanate (PPDI) and 1,3-phenylene diisocyanate (MPDI). The possibility of long-range connectivity due to a network of well-ordered hydrogen bonds between symmetrical PPDI and kinked MPDI based model urethane and urea compounds were also investigated. Special emphasis was given on the understanding of the influence of diisocyanate symmetry and nature of the hydrogen bonding between hard segments on the morphology development. QMC results obtained clearly indicated the possibility of long-range ordering of hydrogen bonds between PPDI based urethane and urea groups, while MPDI based systems did not display such a behavior. DPD results strongly supported the QMC studies and clearly demonstrated the possibility of long-range connectivity of hydrogen bonds between urethane and urea groups in PPDI based segmented copolymers, leading to the formation of microphase separated morphologies in these systems, which was not observed in the kinked MPDI based segmented urethane and urea copolymers. Computational results obtained strongly supported the experimental observations reported on the morphology and thermal and mechanical properties of these segmented polyurethanes and polyureas based on PPDI and MPDI.

Physical Review B, 2000

Using a potential recently proposed by Baskes ͓Phys. Rev. Lett. 83, 2592 ͑1999͔͒, we study the in... more Using a potential recently proposed by Baskes ͓Phys. Rev. Lett. 83, 2592 ͑1999͔͒, we study the influence of the many-body interactions on the thermodynamics and chaotic dynamics of small atomic clusters. With standard molecular dynamics simulations as well as parallel tempering Monte Carlo, we calculate the complete heat capacity curves and the variations of the largest Lyapunov exponent with total energy. We observe that increasing the magnitude or decreasing the range of the many-body forces leads to an increase of chaos and a decrease in the melting temperature. Decreasing the range of the many-body interactions also results in a significantly lower latent heat of melting.

Journal of Inorganic and Organometallic Polymers and Materials, 2011

Molecular dynamics and mesoscale dynamics simulation techniques were used to investigate the effe... more Molecular dynamics and mesoscale dynamics simulation techniques were used to investigate the effect of hydrogen bonding on the microphase separation, morphology and various physicochemical properties of segmented silicone-urea copolymers. Model silicone-urea copolymers investigated were based on the stoichiometric combinations of a,x-aminopropyl terminated polydimethylsiloxane (PDMS) oligomers with number average molecular weights ranging from 700 to 15,000 g/mole and bis(4-isocyanatocyclohexyl)methane (HMDI). Urea hard segment contents of the copolymers, which were determined by the PDMS molecular weight, were in 1.7-34% by weight range. Since no chain extenders were used, urea hard segments in all copolymers were of uniform length. Simulation results clearly demonstrated the presence of very good microphase separation in all silicone-urea copolymers, even for the copolymer with 1.7% by weight hard segment content. Experimentally reported enhanced properties of these materials were shown to stem from strong hydrogen bond interactions which leads to the aggregation of urea hard segments and reinforcement of the PDMS.

Physical Review E, 2005

The dynamics and thermodynamics of melting in two-dimensional Coulomb clusters is revisited using... more The dynamics and thermodynamics of melting in two-dimensional Coulomb clusters is revisited using molecular dynamics and Monte Carlo simulations. Several parameters are considered, including the Lindemann index, the largest Lyapunov exponent and the diffusion constant. In addition to the orientational and radial melting processes, isomerizations and complex size effects are seen to occur in a very similar way to atomic and molecular clusters. The results are discussed in terms of the energy landscape represented through disconnectivity graphs, with proper attention paid to the broken ergodicity problems in simulations. Clusters bound by 1/r 3 and e −κr /r forces, and heterogeneous clusters made of singly-and doubly-charged species, are also studied, as well as the evolution toward larger systems.

Physical Review A, 2011

The stable structures and melting dynamics of clusters of identical ions bound by linear octupole... more The stable structures and melting dynamics of clusters of identical ions bound by linear octupole radiofrequency traps are theoretically investigated by global optimization methods and molecular dynamics simulations. By varying the cluster sizes in the range of 10-1000 ions and the extent of trap anisotropy by more than one order of magnitude, we find a broad variety of stable structures based on multiple rings at small sizes evolving into tubular geometries at large sizes. The binding energy of these clusters is well represented by two contributions arising from isotropic linear and octupolar traps. The structures generally exhibit strong size effects, and chiral arrangements spontaneously emerge in many crystals. Sufficiently large clusters form nested, coaxial tubes with different thermal stabilities. As in isotropic octupolar clusters, the inner tubes melt at temperatures that are lower than the overall melting point.

$Research paper thumbnail of Vibrational quenching at ultralow energies: Calculations of the Li_{2}(^{1}Σ_{g}^{+};ν⪢0)+He superelastic scattering cross sections$

Physical Review A, 2006

Accurate quantum calculations have been carried out at ultralow energies ͑from 10 −2 to 10 −6 cm ... more Accurate quantum calculations have been carried out at ultralow energies ͑from 10 −2 to 10 −6 cm −1 ͒ for the vibrational deexcitation of Li 2 ͑ 1 ⌺ g + ͒ by collisions with He, starting from a broad range of initial highly excited vibrational levels. The results indicate the clear dominance of a few transitions with the smallest ⌬ changes and show the overall deexcitation cross sections to markedly depend on the initial vibrational state of the molecule, in line with earlier results on H 2 +He ͓Balakrishan et al. Phys. Rev. Lett. 80, 3224 ͑1998͔͒ vibrational quenching. A connection is made with very recent measurements on the vibrational quenching of ultracold Cs 2 molecules in optical traps that were instead found to behave in a very different manner. Numerical experiments on the present system as well as on the H 3 reaction strongly suggest a possible explanation for such differences.

$Research paper thumbnail of Quenching of internal rotations versus collisional cooling at ultralow energies for weakly interacting partners: Cs_{2}(^{3}Σ_{u}^{+}) with ^{3,4}He$

Physical Review A, 2010

Quantum-scattering calculations at ultralow (close to 10 −6 cm −1) collision energies are carried... more Quantum-scattering calculations at ultralow (close to 10 −6 cm −1) collision energies are carried out for the Cs dimer in its spin-stretched triplet state, interacting with helium. An ab initio potential energy surface is computed and employed, while the target molecule is kept in its ground vibrational state and several excitated initial rotational states are considered in the quantum dynamics. The highly anisotropic interaction is seen to cause, in spite of its weakness, internal energy quenching rates comparable with the efficiency of the collisional cooling of relative kinetic energies. The rates of spin-flip processes are also analyzed and compared with pure rotational quenching events.