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Deniz Gunduz - One of the best experts on this subject based on the ideXlab platform.
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on the Distortion Energy tradeoff for zero delay transmission of a gaussian source over the awgn channel
Information Theory Workshop, 2015Co-Authors: Erman Koken, Ertem Tuncel, Deniz GunduzAbstract:An achievable scheme for zero-delay transmission of an i.i.d. Gaussian source over an additive white Gaussian channel with no bandwidth limitation is introduced, and its Energy-Distortion performance is analyzed. By the nature of the problem, one must transmit each source sample separately but can use the channel infinitely many times. We introduce an outage concept, and analyze the expected Distortion conditioned on no outage. We show that the proposed scheme can approach to the asymptotical decay for large enough Energy for arbitrary outage probability. The proposed scheme builds on separation of source and channel coding, whereby the source is quantized with a high-resolution optimal quantizer. In the high Energy-to-noise ratio (ENR) regime, the minimum Energy required to obtain a given Distortion level in the proposed scheme can approach arbitrarily close the Shannon bound, which can only be achieved using infinite delay.
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on the asymptotic Distortion Energy tradeoff for zero delay transmission of a gaussian source over the awgn channel
International Symposium on Information Theory, 2015Co-Authors: Erman Koken, Ertem Tuncel, Deniz GunduzAbstract:An achievable scheme for zero-delay transmission of an i.i.d. Gaussian source over an additive white Gaussian noise channel with no bandwidth limitation is introduced, and its Energy-Distortion performance is analyzed. By the nature of the problem, one must transmit each source sample separately but can use the channel infinitely many times. The proposed scheme builds on separation of source and channel coding, whereby the source is quantized into “equiprobable” cells so that the output can be seen as a message suitable for channel coding. Moreover, as the number of quantization cells go to infinity, the channel capacity can be approached with arbitrarily small error. In the high Energy-to-noise ratio regime, the minimum Energy required to obtain a given Distortion level in the proposed scheme can come as close as 3dB to the Shannon bound, which can only be achieved using infinite delay.
Erman Koken - One of the best experts on this subject based on the ideXlab platform.
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on the Distortion Energy tradeoff for zero delay transmission of a gaussian source over the awgn channel
Information Theory Workshop, 2015Co-Authors: Erman Koken, Ertem Tuncel, Deniz GunduzAbstract:An achievable scheme for zero-delay transmission of an i.i.d. Gaussian source over an additive white Gaussian channel with no bandwidth limitation is introduced, and its Energy-Distortion performance is analyzed. By the nature of the problem, one must transmit each source sample separately but can use the channel infinitely many times. We introduce an outage concept, and analyze the expected Distortion conditioned on no outage. We show that the proposed scheme can approach to the asymptotical decay for large enough Energy for arbitrary outage probability. The proposed scheme builds on separation of source and channel coding, whereby the source is quantized with a high-resolution optimal quantizer. In the high Energy-to-noise ratio (ENR) regime, the minimum Energy required to obtain a given Distortion level in the proposed scheme can approach arbitrarily close the Shannon bound, which can only be achieved using infinite delay.
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on the asymptotic Distortion Energy tradeoff for zero delay transmission of a gaussian source over the awgn channel
International Symposium on Information Theory, 2015Co-Authors: Erman Koken, Ertem Tuncel, Deniz GunduzAbstract:An achievable scheme for zero-delay transmission of an i.i.d. Gaussian source over an additive white Gaussian noise channel with no bandwidth limitation is introduced, and its Energy-Distortion performance is analyzed. By the nature of the problem, one must transmit each source sample separately but can use the channel infinitely many times. The proposed scheme builds on separation of source and channel coding, whereby the source is quantized into “equiprobable” cells so that the output can be seen as a message suitable for channel coding. Moreover, as the number of quantization cells go to infinity, the channel capacity can be approached with arbitrarily small error. In the high Energy-to-noise ratio regime, the minimum Energy required to obtain a given Distortion level in the proposed scheme can come as close as 3dB to the Shannon bound, which can only be achieved using infinite delay.
K N Houk - One of the best experts on this subject based on the ideXlab platform.
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analyzing reaction rates with the Distortion interaction activation strain model
Angewandte Chemie, 2017Co-Authors: Matthias F Bickelhaupt, K N HoukAbstract:The activation strain or Distortion/interaction model is a tool to analyze activation barriers that determine reaction rates. For bimolecular reactions, the activation energies are the sum of the energies to distort the reactants into geometries they have in transition states plus the interaction energies between the two distorted molecules. The Energy required to distort the molecules is called the activation strain or Distortion Energy. This Energy is the principal contributor to the activation barrier. The transition state occurs when this activation strain is overcome by the stabilizing interaction Energy. Following the changes in these energies along the reaction coordinate gives insights into the factors controlling reactivity. This model has been applied to reactions of all types in both organic and inorganic chemistry, including substitutions and eliminations, cycloadditions, and several types of organometallic reactions.
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Bimodal Evans–Polanyi Relationships in Dioxirane Oxidations of sp3 C–H: Non-perfect Synchronization in Generation of Delocalized Radical Intermediates
2017Co-Authors: Fengjiao Liu, Ye Mei, Zhongyue Yang, K N HoukAbstract:The selectivities in C–H oxidations of a variety of compounds by DMDO have been explored with density functional theory. There is a linear Evans–Polanyi-type correlation for saturated substrates. Activation energies correlate with reaction energies or, equivalently, BDEs (ΔH‡sat = 0.91*BDE – 67.8). Unsaturated compounds, such as alkenes, aromatics, and carbonyls, exhibit a different correlation for allylic and benzylic C–H bonds (ΔH‡unsat = 0.35*BDE – 13.1). Bernasconi’s Principle of Non-Perfect Synchronization (NPS) is found to operate here. The origins of this phenomenon were analyzed by a Distortion/Interaction model. Computations indicate early transition states for H-abstractions from allylic and benzylic C–H bonds, but later transition states for the saturated. The reactivities are mainly modulated by the Distortion Energy and the degree of dissociation of the C–H bond. While the increase in barrier with higher BDE is not unexpected from the Evans−Polanyi relationship, two separate correlations, one for saturated compounds, and one for unsaturated leading to delocalized radicals, were unexpected
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Diels–Alder Reactivities of Benzene, Pyridine, and Di‑, Tri‑, and Tetrazines: The Roles of Geometrical Distortions and Orbital Interactions
2016Co-Authors: Yunfang Yang, Yong Liang, Fang Liu, K N HoukAbstract:The cycloadditions of benzene and ten different azabenzenes (pyridine, three diazines, three triazines, and three tetrazines) with the ethylene dienophile have been explored with density functional theory (M06-2X) and analyzed with the Distortion/interaction model. Activation barriers correlate closely with both Distortion energies and interaction energies over an activation Energy range of 45 kcal/mol. The replacement of CH with N increases Diels–Alder reactivity due not only to the more favorable orbital interaction, but also to a decrease in Distortion Energy. The rates of reactions are greatly influenced by the nature of the bonds being formed: two CC bonds > one CC bond, and one CN bond > two CN bonds. The activation Energy of Diels–Alder reactions correlates very well with reaction energies and with the NICS(0) values of the aromatic dienes. The Distortion Energy of the Diels–Alder reaction transition states mostly arises from the diene out-of-plane Distortion Energy
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Mechanism and Selectivity of N‑Triflylphosphoramide Catalyzed (3+ + 2) Cycloaddition between Hydrazones and Alkenes
2014Co-Authors: Xin Hong, Modhu Sudan Maji, Yunfang Yang, Magnus Rueping, Hatice Başpınar Küçük, K N HoukAbstract:Brønsted acid catalyzed (3+ + 2) cycloadditions between hydrazones and alkenes provide a general approach to pyrazolidines. The acidity of the Brønsted acid is crucial for the catalytic efficiency: the less acidic phosphoric acids are ineffective, while highly acidic chiral N-triflylphosphoramides are very efficient and can promote highly enantioselective cycloadditions. The mechanism and origins of catalytic efficiencies and selectivities of these reactions have been explored with density functional theory (M06-2X) calculations. Protonation of hydrazones by N-triflylphosphoramide produces hydrazonium–phosphoramide anion complexes. These ion-pair complexes are very reactive in (3+ + 2) cycloadditions with alkenes, producing pyrazolidine products. Alternative 1,3-dipolar (3 + 2) cycloadditions with the analogous azomethine imines are much less favorable due to the endergonic isomerization of hydrazone to azomethine imine. With N-triflylphosphoramide catalyst, only a small Distortion of the ion-pair complex is required to achieve its geometry in the (3+ + 2) cycloaddition transition state. In contrast, the weak phosphoric acid does not protonate the hydrazone, and only a hydrogen-bonded complex is formed. Larger Distortion Energy is required for the hydrogen-bonded complex to achieve the “ion-pair” geometry in the cycloaddition transition state, and a significant barrier is found. On the basis of this mechanism, we have explained the origins of enantioselectivities when a chiral N-triflylphosphoramide catalyst is employed. We also report the experimental studies that extend the substrate scope of alkenes to ethyl vinyl ethers and thioethers
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enhanced reactivity in dioxirane c h oxidations via strain release a computational and experimental study
Journal of Organic Chemistry, 2013Co-Authors: Lufeng Zou, Robert S Paton, Albert Eschenmoser, Timothy R Newhouse, Phil S Baran, K N HoukAbstract:The site selectivities and stereoselectivities of C–H oxidations of substituted cyclohexanes and trans-decalins by dimethyldioxirane (DMDO) were investigated computationally with quantum mechanical density functional theory (DFT). The multiconfiguration CASPT2 method was employed on model systems to establish the preferred mechanism and transition state geometry. The reaction pathway involving a rebound step is established to account for the retention of stereochemistry. The oxidation of sclareolide with dioxirane reagents is reported, including the oxidation by the in situ generated tBu-TFDO, a new dioxirane that better discriminates between C–H bonds on the basis of steric effects. The release of 1,3-diaxial strain in the transition state contributes to the site selectivity and enhanced equatorial C–H bond reactivity for tertiary C–H bonds, a result of the lowering of Distortion Energy. In addition to this strain release factor, steric and inductive effects contribute to the rates of C–H oxidation by di...
Aravind Asthagiri - One of the best experts on this subject based on the ideXlab platform.
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water adsorption on olivine 010 surfaces effect of alkali and transition metal cation doping
Journal of Chemical Physics, 2019Co-Authors: David R Cole, Aravind AsthagiriAbstract:: Dopants have the potential to locally modify water-olivine interactions, which can impact geological processes, such as weathering, CO2 sequestration, and abiotic hydrocarbon generation. As a first step in understanding the role of dopants on the water structure and chemistry at water-olivine interfaces, water monomer adsorption on alkaline earth (AE) and transition metal (TM) doped forsterite(010) [Mg2SiO4(010)] surfaces was studied using density functional theory (DFT). Dopants that occur in olivine minerals were considered and consisted of Ca, Sr, and Ba for the AE dopants and Cr, Mn, Fe, Co, and Ni for the TM dopants. The water molecule adsorbs on the olivine surface through a metal-water bond (Me-Ow) and a hydrogen bond with an adjacent surface lattice oxygen (Ox-Hw). A frontier orbital analysis reveals that the 1b2, 3a1, and 1b1 (HOMO) of the water molecule are involved in the bonding. All of the TM dopants show strong net Me-Ow covalent bonding between 3a1 and 1b1 water orbitals and TM d states, while the AE dopants except for Mg2SiO4(010) show negligible Me-Ow covalent bonding. Both the AE and TM dopants show similar hydrogen bonding features involving both the 1b2 and 3a1 orbitals. While the AE cations show an overall lower Me-Ow covalent interaction, the AE dopants have strong electrostatic interactions between the positive metal cation and the negatively charged water dipole. A bonding model incorporating a linear combination of the covalent Me-Ow bond, the Ox-Hw hydrogen bond, the electrostatic interaction between the dopant cation and the H2O molecule, and the surface Distortion Energy is needed to capture the variation in the DFT adsorption energies on the olivine surfaces. The bonding analysis is able to identify the dominant contributions to water-dopant interactions and can serve as a basis for future studies of more realistic water-olivine interfaces.
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water adsorption on olivine 010 surfaces effect of alkali and transition metal cation doping
Journal of Chemical Physics, 2019Co-Authors: David R Cole, Aravind AsthagiriAbstract:Dopants have the potential to locally modify water-olivine interactions, which can impact geological processes, such as weathering, CO2 sequestration, and abiotic hydrocarbon generation. As a first step in understanding the role of dopants on the water structure and chemistry at water-olivine interfaces, water monomer adsorption on alkaline earth (AE) and transition metal (TM) doped forsterite(010) [Mg2SiO4(010)] surfaces was studied using density functional theory (DFT). Dopants that occur in olivine minerals were considered and consisted of Ca, Sr, and Ba for the AE dopants and Cr, Mn, Fe, Co, and Ni for the TM dopants. The water molecule adsorbs on the olivine surface through a metal-water bond (Me–Ow) and a hydrogen bond with an adjacent surface lattice oxygen (Ox–Hw). A frontier orbital analysis reveals that the 1b2, 3a1, and 1b1 (HOMO) of the water molecule are involved in the bonding. All of the TM dopants show strong net Me–Ow covalent bonding between 3a1 and 1b1 water orbitals and TM d states, while the AE dopants except for Mg2SiO4(010) show negligible Me–Ow covalent bonding. Both the AE and TM dopants show similar hydrogen bonding features involving both the 1b2 and 3a1 orbitals. While the AE cations show an overall lower Me–Ow covalent interaction, the AE dopants have strong electrostatic interactions between the positive metal cation and the negatively charged water dipole. A bonding model incorporating a linear combination of the covalent Me–Ow bond, the Ox–Hw hydrogen bond, the electrostatic interaction between the dopant cation and the H2O molecule, and the surface Distortion Energy is needed to capture the variation in the DFT adsorption energies on the olivine surfaces. The bonding analysis is able to identify the dominant contributions to water-dopant interactions and can serve as a basis for future studies of more realistic water-olivine interfaces.Dopants have the potential to locally modify water-olivine interactions, which can impact geological processes, such as weathering, CO2 sequestration, and abiotic hydrocarbon generation. As a first step in understanding the role of dopants on the water structure and chemistry at water-olivine interfaces, water monomer adsorption on alkaline earth (AE) and transition metal (TM) doped forsterite(010) [Mg2SiO4(010)] surfaces was studied using density functional theory (DFT). Dopants that occur in olivine minerals were considered and consisted of Ca, Sr, and Ba for the AE dopants and Cr, Mn, Fe, Co, and Ni for the TM dopants. The water molecule adsorbs on the olivine surface through a metal-water bond (Me–Ow) and a hydrogen bond with an adjacent surface lattice oxygen (Ox–Hw). A frontier orbital analysis reveals that the 1b2, 3a1, and 1b1 (HOMO) of the water molecule are involved in the bonding. All of the TM dopants show strong net Me–Ow covalent bonding between 3a1 and 1b1 water orbitals and TM d states, wh...
Ertem Tuncel - One of the best experts on this subject based on the ideXlab platform.
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on the Distortion Energy tradeoff for zero delay transmission of a gaussian source over the awgn channel
Information Theory Workshop, 2015Co-Authors: Erman Koken, Ertem Tuncel, Deniz GunduzAbstract:An achievable scheme for zero-delay transmission of an i.i.d. Gaussian source over an additive white Gaussian channel with no bandwidth limitation is introduced, and its Energy-Distortion performance is analyzed. By the nature of the problem, one must transmit each source sample separately but can use the channel infinitely many times. We introduce an outage concept, and analyze the expected Distortion conditioned on no outage. We show that the proposed scheme can approach to the asymptotical decay for large enough Energy for arbitrary outage probability. The proposed scheme builds on separation of source and channel coding, whereby the source is quantized with a high-resolution optimal quantizer. In the high Energy-to-noise ratio (ENR) regime, the minimum Energy required to obtain a given Distortion level in the proposed scheme can approach arbitrarily close the Shannon bound, which can only be achieved using infinite delay.
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on the asymptotic Distortion Energy tradeoff for zero delay transmission of a gaussian source over the awgn channel
International Symposium on Information Theory, 2015Co-Authors: Erman Koken, Ertem Tuncel, Deniz GunduzAbstract:An achievable scheme for zero-delay transmission of an i.i.d. Gaussian source over an additive white Gaussian noise channel with no bandwidth limitation is introduced, and its Energy-Distortion performance is analyzed. By the nature of the problem, one must transmit each source sample separately but can use the channel infinitely many times. The proposed scheme builds on separation of source and channel coding, whereby the source is quantized into “equiprobable” cells so that the output can be seen as a message suitable for channel coding. Moreover, as the number of quantization cells go to infinity, the channel capacity can be approached with arbitrarily small error. In the high Energy-to-noise ratio regime, the minimum Energy required to obtain a given Distortion level in the proposed scheme can come as close as 3dB to the Shannon bound, which can only be achieved using infinite delay.