Electroactive Biofilms: Current Status and Future Research Needs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Borole, Abhijeet P; Reguera, Gemma; Ringeisen, Bradley

2011-01-01

Electroactive biofilms generated by electrochemically active microorganisms have many potential applications in bioenergy and chemicals production. This review assesses the effects of microbiological and process parameters on enrichment of such biofilms as well as critically evaluates the current knowledge of the mechanisms of extracellular electron transfer in BES systems. First we discuss the role of biofilm forming microorganisms vs. planktonic microorganisms. Physical, chemical and electrochemical parameters which dictate the enrichment and subsequent performance of the biofilms are discussed. Potential dependent biological parameters including biofilm growth rate, specific electron transfer rate and others and their relationship to BES system performance ismore » assessed. A review of the mechanisms of electron transfer in BES systems is included followed by a discussion of biofilm and its exopolymeric components and their electrical conductivity. A discussion of the electroactive biofilms in biocathodes is also included. Finally, we identify the research needs for further development of the electroactive biofilms to enable commercial applications.« less

Mechanistic information from the first volume profile analysis for a reversible intermolecular electron-transfer reaction involving pentaammine(isonicotinamide)ruthenium and cytochrome c

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baensch, B.; Meier, M.; Martinez, P.

1994-10-12

The reversible intermolecular electron-transfer reaction between pentaammine(isonicotinamide)ruthenium(II/III) and horse-heart cytochrome c iron(III/II) was subjected to a detailed kinetic and thermodynamic study as a function of temperature and pressure. Theoretical calculations based on the Marcus-Hush theory were employed to predict all rate and equilibrium constants as well as activation parameters. There is an excellent agreement between the kinetically and thermodynamically determined equilibrium constants and associated pressure parameters. These data are used to construct a volume profile for the overall process, from which it follows that the transition state lies halfway between the reactant and product states on a volume basis. Themore » reorganization in the transition state has reached a similar degree in both directions of the electron-transfer process and corresponds to a {lambda}{sup {double_dagger}} value of 0.44 for this reversible reaction. This is the first complete volume profile analysis for a reversible intermolecular electron-transfer reaction.« less

Role of protein fluctuation correlations in electron transfer in photosynthetic complexes.

PubMed

Nesterov, Alexander I; Berman, Gennady P

2015-04-01

We consider the dependence of the electron transfer in photosynthetic complexes on correlation properties of random fluctuations of the protein environment. The electron subsystem is modeled by a finite network of connected electron (exciton) sites. The fluctuations of the protein environment are modeled by random telegraph processes, which act either collectively (correlated) or independently (uncorrelated) on the electron sites. We derived an exact closed system of first-order linear differential equations with constant coefficients, for the average density matrix elements and for their first moments. Under some conditions, we obtained analytic expressions for the electron transfer rates and found the range of parameters for their applicability by comparing with the exact numerical simulations. We also compared the correlated and uncorrelated regimes and demonstrated numerically that the uncorrelated fluctuations of the protein environment can, under some conditions, either increase or decrease the electron transfer rates.

Reactive trajectories of the Ru2+/3+ self-exchange reaction and the connection to Marcus' theory.

PubMed

Tiwari, Ambuj; Ensing, Bernd

2016-12-22

Outer sphere electron transfer between two ions in aqueous solution is a rare event on the time scale of first principles molecular dynamics simulations. We have used transition path sampling to generate an ensemble of reactive trajectories of the self-exchange reaction between a pair of Ru 2+ and Ru 3+ ions in water. To distinguish between the reactant and product states, we use as an order parameter the position of the maximally localised Wannier center associated with the transferring electron. This allows us to align the trajectories with respect to the moment of barrier crossing and compute statistical averages over the path ensemble. We compare our order parameter with two typical reaction coordinates used in applications of Marcus theory of electron transfer: the vertical gap energy and the solvent electrostatic potential at the ions.

Quantitative Probes of Electron-Phonon Coupling in an Organic Charge-Transfer Material

NASA Astrophysics Data System (ADS)

Rury, Aaron; Sorenson, Shayne; Driscoll, Eric; Dawlaty, Jahan

While organic charge transfer (CT) materials may provide alternatives to inorganic materials in electronics and photonics applications, properties central to applications remain understudied in these organic materials. Specifically, electron-phonon coupling plays a pivotal role in electronic applications yet this coupling in CT materials remains difficult to directly characterize. To better understand the suitability of organic CT materials for electronic applications, we have devised an experimental technique that can directly assess electron-phonon coupling in a model organic CT material. Upon non-resonant interaction with an ultrafast laser pulse, we show that coherent excitation of Raman-active lattice vibrations of quinhydrone, a 1:1 co-crystal of the hydroquinone and p-benzoquinone, modulates the energies of electronic transitions probed by a white light pulse. Using a well-established theoretical framework of vibrational quantum beat spectra across the probe bandwidth, we quantitatively extract the parameters describing these electronic transitions to characterize electron-phonon coupling in this material. In conjunction with temperature-dependent resonance Raman measurements, we assess the hypothesis that several sharp transitions in the near-IR correspond to previously unknown excitonic states of this material. These results and their interpretation set the foundation for further elucidation of the one of the most important parameters in the application of organic charge-transfer materials to electronics and photonics.

A molecularly based theory for electron transfer reorganization energy.

PubMed

Zhuang, Bilin; Wang, Zhen-Gang

2015-12-14

Using field-theoretic techniques, we develop a molecularly based dipolar self-consistent-field theory (DSCFT) for charge solvation in pure solvents under equilibrium and nonequilibrium conditions and apply it to the reorganization energy of electron transfer reactions. The DSCFT uses a set of molecular parameters, such as the solvent molecule's permanent dipole moment and polarizability, thus avoiding approximations that are inherent in treating the solvent as a linear dielectric medium. A simple, analytical expression for the free energy is obtained in terms of the equilibrium and nonequilibrium electrostatic potential profiles and electric susceptibilities, which are obtained by solving a set of self-consistent equations. With no adjustable parameters, the DSCFT predicts activation energies and reorganization energies in good agreement with previous experiments and calculations for the electron transfer between metallic ions. Because the DSCFT is able to describe the properties of the solvent in the immediate vicinity of the charges, it is unnecessary to distinguish between the inner-sphere and outer-sphere solvent molecules in the calculation of the reorganization energy as in previous work. Furthermore, examining the nonequilibrium free energy surfaces of electron transfer, we find that the nonequilibrium free energy is well approximated by a double parabola for self-exchange reactions, but the curvature of the nonequilibrium free energy surface depends on the charges of the electron-transferring species, contrary to the prediction by the linear dielectric theory.

Cellular Assays for Ferredoxins: A Strategy for Understanding Electron Flow through Protein Carriers That Link Metabolic Pathways.

PubMed

Atkinson, Joshua T; Campbell, Ian; Bennett, George N; Silberg, Jonathan J

2016-12-27

The ferredoxin (Fd) protein family is a structurally diverse group of iron-sulfur proteins that function as electron carriers, linking biochemical pathways important for energy transduction, nutrient assimilation, and primary metabolism. While considerable biochemical information about individual Fd protein electron carriers and their reactions has been acquired, we cannot yet anticipate the proportion of electrons shuttled between different Fd-partner proteins within cells using biochemical parameters that govern electron flow, such as holo-Fd concentration, midpoint potential (driving force), molecular interactions (affinity and kinetics), conformational changes (allostery), and off-pathway electron leakage (chemical oxidation). Herein, we describe functional and structural gaps in our Fd knowledge within the context of a sequence similarity network and phylogenetic tree, and we propose a strategy for improving our understanding of Fd sequence-function relationships. We suggest comparing the functions of divergent Fds within cells whose growth, or other measurable output, requires electron transfer between defined electron donor and acceptor proteins. By comparing Fd-mediated electron transfer with biochemical parameters that govern electron flow, we posit that models that anticipate energy flow across Fd interactomes can be built. This approach is expected to transform our ability to anticipate Fd control over electron flow in cellular settings, an obstacle to the construction of synthetic electron transfer pathways and rational optimization of existing energy-conserving pathways.

Electrode redox reactions with polarizable molecules.

PubMed

Matyushov, Dmitry V

2018-04-21

A theory of redox reactions involving electron transfer between a metal electrode and a polarizable molecule in solution is formulated. Both the existence of molecular polarizability and its ability to change due to electron transfer distinguish this problem from classical theories of interfacial electrochemistry. When the polarizability is different between the oxidized and reduced states, the statistics of thermal fluctuations driving the reactant over the activation barrier becomes non-Gaussian. The problem of electron transfer is formulated as crossing of two non-parabolic free energy surfaces. An analytical solution for these free energy surfaces is provided and the activation barrier of electrode electron transfer is given in terms of two reorganization energies corresponding to the oxidized and reduced states of the molecule in solution. The new non-Gaussian theory is, therefore, based on two theory parameters in contrast to one-parameter Marcus formulation for electrode reactions. The theory, which is consistent with the Nernst equation, predicts asymmetry between the cathodic and anodic branches of the electrode current. They show different slopes at small electrode overpotentials and become curved at larger overpotentials. However, the curvature of the Tafel plot is reduced compared to the Marcus-Hush model and approaches the empirical Butler-Volmer form with different transfer coefficients for the anodic and cathodic currents.

Electrode redox reactions with polarizable molecules

NASA Astrophysics Data System (ADS)

Matyushov, Dmitry V.

2018-04-01

A theory of redox reactions involving electron transfer between a metal electrode and a polarizable molecule in solution is formulated. Both the existence of molecular polarizability and its ability to change due to electron transfer distinguish this problem from classical theories of interfacial electrochemistry. When the polarizability is different between the oxidized and reduced states, the statistics of thermal fluctuations driving the reactant over the activation barrier becomes non-Gaussian. The problem of electron transfer is formulated as crossing of two non-parabolic free energy surfaces. An analytical solution for these free energy surfaces is provided and the activation barrier of electrode electron transfer is given in terms of two reorganization energies corresponding to the oxidized and reduced states of the molecule in solution. The new non-Gaussian theory is, therefore, based on two theory parameters in contrast to one-parameter Marcus formulation for electrode reactions. The theory, which is consistent with the Nernst equation, predicts asymmetry between the cathodic and anodic branches of the electrode current. They show different slopes at small electrode overpotentials and become curved at larger overpotentials. However, the curvature of the Tafel plot is reduced compared to the Marcus-Hush model and approaches the empirical Butler-Volmer form with different transfer coefficients for the anodic and cathodic currents.

Fragment-based Quantum Mechanical/Molecular Mechanical Simulations of Thermodynamic and Kinetic Process of the Ru2+-Ru3+ Self-Exchange Electron Transfer.

PubMed

Zeng, Xiancheng; Hu, Xiangqian; Yang, Weitao

2012-12-11

A fragment-based fractional number of electron (FNE) approach, is developed to study entire electron transfer (ET) processes from the electron donor region to the acceptor region in condensed phase. Both regions are described by the density-fragment interaction (DFI) method while FNE as an efficient ET order parameter is applied to simulate the electron transfer process. In association with the QM/MM energy expression, the DFI-FNE method is demonstrated to describe ET processes robustly with the Ru 2+ -Ru 3+ self-exchange ET as a proof-of-concept example. This method allows for systematic calculations of redox free energies, reorganization energies, and electronic couplings, and the absolute ET rate constants within the Marcus regime.

Electron transfer from a carbon nanotube into vacuum under high electric fields

NASA Astrophysics Data System (ADS)

Filip, L. D.; Smith, R. C.; Carey, J. D.; Silva, S. R. P.

2009-05-01

The transfer of an electron from a carbon nanotube (CNT) tip into vacuum under a high electric field is considered beyond the usual one-dimensional semi-classical approach. A model of the potential energy outside the CNT cap is proposed in order to show the importance of the intrinsic CNT parameters such as radius, length and vacuum barrier height. This model also takes into account set-up parameters such as the shape of the anode and the anode-to-cathode distance, which are generically portable to any modelling study of electron emission from a tip emitter. Results obtained within our model compare well to experimental data. Moreover, in contrast to the usual one-dimensional Wentzel-Kramers-Brillouin description, our model retains the ability to explain non-standard features of the process of electron field emission from CNTs that arise as a result of the quantum behaviour of electrons on the surface of the CNT.

Ligand electronic parameters as a measure of the polarization of the C≡O bond in [M(CO)(x)L(y)]n complexes and of the relative stabilization of [M(CO)(x)L(y)](n/n+1) species.

PubMed

Zobi, Fabio

2010-11-15

The electronic description of octahedral (fac-[M(CO)(3)L(3)](n), with M = Re, Ru, and Mn, and [Cr(CO)(5)L](n)), square-planar (cis-[Pt(CO)(2)L(2)](n)), and tetrahedral ([Ni(CO)(3)L](n)) carbonyl complexes (where L = monodentate ligand) was obtained via density functional theory and natural population analyses in order to understand what effects are probed in these species by vibrational spectroscopy and electrochemistry as a function of the ligand electronic parameter of the associated L. The analysis indicates that while ligand electronic parameters may be considered as a measure of the net donor power of the ligand, the net transfer of the electron density (or charge) does not occur from the ligand to the metal ion. In [M(CO)(x)L(y)](n) carbonyl species, the charge transfer occurs from the ligand L to the oxygen atom of the bound carbon monoxides. This charge transfer translates into changes of the polarization (or permanent dipole) and the covalency of the C≡O bonds, and it is this effect that is probed in IR spectroscopy. As the analysis shifts from IR radiations to electrochemical potentials, the parameters best describe the relative thermodynamic stability of the oxidized and reduced [M(CO)(x)L(y)](n/n+1) species. No relationship is found between the metal natural charge of the [M(CO)(x)L(y)](n) fragments analyzed and the parameters. Brief considerations are given on the possible design of CO-releasing molecules.

Storage and retrieval of quantum information with a hybrid optomechanics-spin system

NASA Astrophysics Data System (ADS)

Feng, Zhi-Bo; Zhang, Jian-Qi; Yang, Wan-Li; Feng, Mang

2016-08-01

We explore an efficient scheme for transferring the quantum state between an optomechanical cavity and an electron spin of diamond nitrogen-vacancy center. Assisted by a mechanical resonator, quantum information can be controllably stored (retrieved) into (from) the electron spin by adjusting the external field-induced detuning or coupling. Our scheme connects effectively the cavity photon and the electron spin and transfers quantum states between two regimes with large frequency difference. The experimental feasibility of our protocol is justified with accessible laboratory parameters.

Note: electronic circuit for two-way time transfer via a single coaxial cable with picosecond accuracy and precision.

PubMed

Prochazka, Ivan; Kodet, Jan; Panek, Petr

2012-11-01

We have designed, constructed, and tested the overall performance of the electronic circuit for the two-way time transfer between two timing devices over modest distances with sub-picosecond precision and a systematic error of a few picoseconds. The concept of the electronic circuit enables to carry out time tagging of pulses of interest in parallel to the comparison of the time scales of these timing devices. The key timing parameters of the circuit are: temperature change of the delay is below 100 fs/K, timing stability time deviation better than 8 fs for averaging time from minutes to hours, sub-picosecond time transfer precision, and a few picoseconds time transfer accuracy.

Crystallochromy of perylene pigments: Interference between Frenkel excitons and charge-transfer states

NASA Astrophysics Data System (ADS)

Gisslén, Linus; Scholz, Reinhard

2009-09-01

The optical properties of perylene-based pigments are arising from the interplay between neutral molecular excitations and charge transfer between adjacent molecules. In the crystalline phase, these excitations are coupled via electron and hole transfer, two quantities relating directly to the width of the conduction and valence band in the crystalline phase. Based on the crystal structure determined by x-ray diffraction, density-functional theory (DFT) and Hartree-Fock are used for the calculation of the electronic states of a dimer of stacked molecules. The resulting transfer parameters for electron and hole are used in an exciton model for the coupling between Frenkel excitons and charge-transfer states. The deformation of the positively or negatively charged molecular ions with respect to the neutral ground state is calculated with DFT and the geometry in the optically excited state is deduced from time-dependent DFT and constrained DFT. All of these deformations are interpreted in terms of the elongation of an effective internal vibration which is used subsequently in the exciton model for the crystalline phase. A comparison between the calculated dielectric function and the observed optical spectra allows to deduce the relative energetic position of Frenkel excitons and the charge-transfer state involving stack neighbors, a key parameter for various electronic and optoelectronic device applications. For five out of six perylene pigments studied in the present work, this exciton model results in excellent agreement between calculated and observed optical properties.

Distal [FeS]-Cluster Coordination in [NiFe]-Hydrogenase Facilitates Intermolecular Electron Transfer

PubMed Central

Petrenko, Alexander; Stein, Matthias

2017-01-01

Biohydrogen is a versatile energy carrier for the generation of electric energy from renewable sources. Hydrogenases can be used in enzymatic fuel cells to oxidize dihydrogen. The rate of electron transfer (ET) at the anodic side between the [NiFe]-hydrogenase enzyme distal iron–sulfur cluster and the electrode surface can be described by the Marcus equation. All parameters for the Marcus equation are accessible from Density Functional Theory (DFT) calculations. The distal cubane FeS-cluster has a three-cysteine and one-histidine coordination [Fe4S4](His)(Cys)3 first ligation sphere. The reorganization energy (inner- and outer-sphere) is almost unchanged upon a histidine-to-cysteine substitution. Differences in rates of electron transfer between the wild-type enzyme and an all-cysteine mutant can be rationalized by a diminished electronic coupling between the donor and acceptor molecules in the [Fe4S4](Cys)4 case. The fast and efficient electron transfer from the distal iron–sulfur cluster is realized by a fine-tuned protein environment, which facilitates the flow of electrons. This study enables the design and control of electron transfer rates and pathways by protein engineering. PMID:28067774

Modeling time-coincident ultrafast electron transfer and solvation processes at molecule-semiconductor interfaces

NASA Astrophysics Data System (ADS)

Li, Lesheng; Giokas, Paul G.; Kanai, Yosuke; Moran, Andrew M.

2014-06-01

Kinetic models based on Fermi's Golden Rule are commonly employed to understand photoinduced electron transfer dynamics at molecule-semiconductor interfaces. Implicit in such second-order perturbative descriptions is the assumption that nuclear relaxation of the photoexcited electron donor is fast compared to electron injection into the semiconductor. This approximation breaks down in systems where electron transfer transitions occur on 100-fs time scale. Here, we present a fourth-order perturbative model that captures the interplay between time-coincident electron transfer and nuclear relaxation processes initiated by light absorption. The model consists of a fairly small number of parameters, which can be derived from standard spectroscopic measurements (e.g., linear absorbance, fluorescence) and/or first-principles electronic structure calculations. Insights provided by the model are illustrated for a two-level donor molecule coupled to both (i) a single acceptor level and (ii) a density of states (DOS) calculated for TiO2 using a first-principles electronic structure theory. These numerical calculations show that second-order kinetic theories fail to capture basic physical effects when the DOS exhibits narrow maxima near the energy of the molecular excited state. Overall, we conclude that the present fourth-order rate formula constitutes a rigorous and intuitive framework for understanding photoinduced electron transfer dynamics that occur on the 100-fs time scale.

The effect of twisted D–D–π–A configuration on electron transfer and photo-physics characteristics

NASA Astrophysics Data System (ADS)

Liu, Yunpeng; Li, Yuanzuo; Song, Peng; Ma, Fengcai; Yang, Yanhui

2018-05-01

Two D-D-π-A organic dyes (M45, M46) with dithieno[3,2-b:2‧,3‧-d]pyrrole (DTP) units as election donors in two perpendicular directions, were investigated using density functional theory (DFT) and time-dependent DFT. The ground-state geometries, the absorption, the electronic structures, the charge density difference and molecular electrostatic potential were obtained. To simulate a more realistic performance, all calculations were based on gas condition and dichloromethane solvent. Photoelectric parameters were evaluated by the following factors: the light harvesting efficiency, electron injection driving force, the excited lifetime and vertical dipole moment. Meanwhile, the polarisability and hyperpolarisability were investigated to further explain the relationship between non-linear optical properties and efficiency. The direction of the DTP obviously affects the twisted degree of molecule, forming a better coplanarity on the donor 2 of M45, which results in stronger charge transfer interactions. Furthermore, M45 possesses significant advantages in geometric structure, absorption band and intramolecular charge transfer mechanism. These critical parameters supported the higher performance of M45 in comparison with M46. Moreover, four dyes were designed by the substitution of donor 2, which further verify the influence of the twisted donor 2 on electron transfer and photoelectric properties of D-D-π-A configuration.

A theoretical-electron-density databank using a model of real and virtual spherical atoms.

PubMed

Nassour, Ayoub; Domagala, Slawomir; Guillot, Benoit; Leduc, Theo; Lecomte, Claude; Jelsch, Christian

2017-08-01

A database describing the electron density of common chemical groups using combinations of real and virtual spherical atoms is proposed, as an alternative to the multipolar atom modelling of the molecular charge density. Theoretical structure factors were computed from periodic density functional theory calculations on 38 crystal structures of small molecules and the charge density was subsequently refined using a density model based on real spherical atoms and additional dummy charges on the covalent bonds and on electron lone-pair sites. The electron-density parameters of real and dummy atoms present in a similar chemical environment were averaged on all the molecules studied to build a database of transferable spherical atoms. Compared with the now-popular databases of transferable multipolar parameters, the spherical charge modelling needs fewer parameters to describe the molecular electron density and can be more easily incorporated in molecular modelling software for the computation of electrostatic properties. The construction method of the database is described. In order to analyse to what extent this modelling method can be used to derive meaningful molecular properties, it has been applied to the urea molecule and to biotin/streptavidin, a protein/ligand complex.

Charge transfer complex between 2,3-diaminopyridine with chloranilic acid. Synthesis, characterization and DFT, TD-DFT computational studies

NASA Astrophysics Data System (ADS)

Al-Ahmary, Khairia M.; Habeeb, Moustafa M.; Al-Obidan, Areej H.

2018-05-01

New charge transfer complex (CTC) between the electron donor 2,3-diaminopyridine (DAP) with the electron acceptor chloranilic (CLA) acid has been synthesized and characterized experimentally and theoretically using a variety of physicochemical techniques. The experimental work included the use of elemental analysis, UV-vis, IR and 1H NMR studies to characterize the complex. Electronic spectra have been carried out in different hydrogen bonded solvents, methanol (MeOH), acetonitrile (AN) and 1:1 mixture from AN-MeOH. The molecular composition of the complex was identified to be 1:1 from Jobs and molar ratio methods. The stability constant was determined using minimum-maximum absorbances method where it recorded high values confirming the high stability of the formed complex. The solid complex was prepared and characterized by elemental analysis that confirmed its formation in 1:1 stoichiometric ratio. Both IR and NMR studies asserted the existence of proton and charge transfers in the formed complex. For supporting the experimental results, DFT computations were carried out using B3LYP/6-31G(d,p) method to compute the optimized structures of the reactants and complex, their geometrical parameters, reactivity parameters, molecular electrostatic potential map and frontier molecular orbitals. The analysis of DFT results strongly confirmed the high stability of the formed complex based on existing charge transfer beside proton transfer hydrogen bonding concordant with experimental results. The origin of electronic spectra was analyzed using TD-DFT method where the observed λmax are strongly consisted with the computed ones. TD-DFT showed the contributed states for various electronic transitions.

Electron transfer complex between nitrous oxide reductase and cytochrome c552 from Pseudomonas nautica: kinetic, nuclear magnetic resonance, and docking studies.

PubMed

Dell'acqua, Simone; Pauleta, Sofia R; Monzani, Enrico; Pereira, Alice S; Casella, Luigi; Moura, José J G; Moura, Isabel

2008-10-14

The multicopper enzyme nitrous oxide reductase (N 2OR) catalyzes the final step of denitrification, the two-electron reduction of N 2O to N 2. This enzyme is a functional homodimer containing two different multicopper sites: CuA and CuZ. CuA is a binuclear copper site that transfers electrons to the tetranuclear copper sulfide CuZ, the catalytic site. In this study, Pseudomonas nautica cytochrome c 552 was identified as the physiological electron donor. The kinetic data show differences when physiological and artificial electron donors are compared [cytochrome vs methylviologen (MV)]. In the presence of cytochrome c 552, the reaction rate is dependent on the ET reaction and independent of the N 2O concentration. With MV, electron donation is faster than substrate reduction. From the study of cytochrome c 552 concentration dependence, we estimate the following kinetic parameters: K m c 552 = 50.2 +/- 9.0 muM and V max c 552 = 1.8 +/- 0.6 units/mg. The N 2O concentration dependence indicates a K mN 2 O of 14.0 +/- 2.9 muM using MV as the electron donor. The pH effect on the kinetic parameters is different when MV or cytochrome c 552 is used as the electron donor (p K a = 6.6 or 8.3, respectively). The kinetic study also revealed the hydrophobic nature of the interaction, and direct electron transfer studies showed that CuA is the center that receives electrons from the physiological electron donor. The formation of the electron transfer complex was observed by (1)H NMR protein-protein titrations and was modeled with a molecular docking program (BiGGER). The proposed docked complexes corroborated the ET studies giving a large number of solutions in which cytochrome c 552 is placed near a hydrophobic patch located around the CuA center.

Ru–protein–Co biohybrids designed for solar hydrogen production: understanding electron transfer pathways related to photocatalytic function† †Electronic supplementary information (ESI) available: Time traces of photocatalysis, additional EPR spectra and parameters, UV-visible spectroscopy data, and kinetic fits of TA traces. See DOI: 10.1039/c6sc03121h Click here for additional data file.

PubMed Central

Soltau, Sarah R.; Dahlberg, Peter D.; Niklas, Jens; Poluektov, Oleg G.; Mulfort, Karen L.

2016-01-01

A series of Ru–protein–Co biohybrids have been prepared using the electron transfer proteins ferredoxin (Fd) and flavodoxin (Fld) as scaffolds for photocatalytic hydrogen production. The light-generated charge separation within these hybrids has been monitored by transient optical and electron paramagnetic resonance spectroscopies. Two distinct electron transfer pathways are observed. The Ru–Fd–Co biohybrid produces up to 650 turnovers of H2 utilizing an oxidative quenching mechanism for Ru(ii)* and a sequential electron transfer pathway via the native [2Fe–2S] cluster to generate a Ru(iii)–Fd–Co(i) charge separated state that lasts for ∼6 ms. In contrast, a direct electron transfer pathway occurs for the Ru–ApoFld–Co biohybrid, which lacks an internal electron relay, generating Ru(i)–ApoFld–Co(i) charge separated state that persists for ∼800 μs and produces 85 turnovers of H2 by a reductive quenching mechanism for Ru(ii)*. This work demonstrates the utility of protein architectures for linking donor and catalytic function via direct or sequential electron transfer pathways to enable stabilized charge separation which facilitates photocatalysis for solar fuel production. PMID:28451142

Millisecond newly born pulsars as efficient accelerators of electrons

NASA Astrophysics Data System (ADS)

Osmanov, Zaza; Mahajan, Swadesh; Machabeli, George; Chkheidze, Nino

2015-09-01

The newly born millisecond pulsars are investigated as possible energy sources for creating ultra-high energy electrons. The transfer of energy from the star rotation to high energy electrons takes place through the Landau damping of centrifugally driven (via a two stream instability) electrostatic Langmuir waves. Generated in the bulk magnetosphere plasma, such waves grow to high amplitudes, and then damp, very effectively, on relativistic electrons driving them to even higher energies. We show that the rate of transfer of energy is so efficient that no energy losses might affect the mechanism of particle acceleration; the electrons might achieve energies of the order of 1018 eV for parameters characteristic of a young star.

A unified diabatic description for electron transfer reactions, isomerization reactions, proton transfer reactions, and aromaticity.

PubMed

Reimers, Jeffrey R; McKemmish, Laura K; McKenzie, Ross H; Hush, Noel S

2015-10-14

While diabatic approaches are ubiquitous for the understanding of electron-transfer reactions and have been mooted as being of general relevance, alternate applications have not been able to unify the same wide range of observed spectroscopic and kinetic properties. The cause of this is identified as the fundamentally different orbital configurations involved: charge-transfer phenomena involve typically either 1 or 3 electrons in two orbitals whereas most reactions are typically closed shell. As a result, two vibrationally coupled electronic states depict charge-transfer scenarios whereas three coupled states arise for closed-shell reactions of non-degenerate molecules and seven states for the reactions implicated in the aromaticity of benzene. Previous diabatic treatments of closed-shell processes have considered only two arbitrarily chosen states as being critical, mapping these states to those for electron transfer. We show that such effective two-state diabatic models are feasible but involve renormalized electronic coupling and vibrational coupling parameters, with this renormalization being property dependent. With this caveat, diabatic models are shown to provide excellent descriptions of the spectroscopy and kinetics of the ammonia inversion reaction, proton transfer in N2H7(+), and aromaticity in benzene. This allows for the development of a single simple theory that can semi-quantitatively describe all of these chemical phenomena, as well as of course electron-transfer reactions. It forms a basis for understanding many technologically relevant aspects of chemical reactions, condensed-matter physics, chemical quantum entanglement, nanotechnology, and natural or artificial solar energy capture and conversion.

Diagnostic criteria for the characterization of quasireversible electron transfer reactions by cyclic square wave voltammetry.

PubMed

Mann, Megan A; Helfrick, John C; Bottomley, Lawrence A

2014-08-19

Theory for cyclic square wave voltammetry of quasireversible electron transfer reactions is presented and experimentally verified. The impact of empirical parameters on the shape of the current-voltage curve is examined. From the trends, diagnostic criteria enabling the use of this waveform as a tool for mechanistic analysis of electrode reaction processes are presented. These criteria were experimentally confirmed using Eu(3+)/Eu(2+), a well-established quasireversible analyte. Using cyclic square wave voltammetry, both the electron transfer coefficient and rate were calculated for this analyte and found to be in excellent agreement with literature. When properly applied, these criteria will enable nonexperts in voltammetry to assign the electrode reaction mechanism and accurately measure electrode reaction kinetics.

Reference dosimetry study for 3 MEV electron beam accelerator in malaysia

NASA Astrophysics Data System (ADS)

Ali, Noriah Mod; Sunaga, Hiromi; Tanaka, Ryuichi

1995-09-01

An effective quality assurance programme is initiated for the use of the electron beam with energies up to 3 MeV. The key element of the programme is the establishment of a relationship between the standardised beam to the routine technique which is employed to verify the beam parameter. A total absorbing calorimeter was adopted as a suitable reference system and when used in combination with the electron current densitymeter (ECD) will enable to determine the mean energy for electron with energies between 1 to 3 MeV. An appropriate method of transfering the standard parameter is studied and the work that is expected to optimise the accuracy attainable with routine check-up of the irradiation parameter are presented.

Coherence parameter measurements for neon and hydrogen

NASA Astrophysics Data System (ADS)

Wright, Robert; Hargreaves, Leigh; Khakoo, Murtadha; Zatsarinny, Oleg; Bartschat, Klaus; Stauffer, Al

2015-09-01

We present recent coherence parameter measurements for excitation of neon and hydrogen by 50 eV electrons. The measurements were made using a crossed electron/gas beam spectrometer, featuring a hemispherically selected electron energy analyzer for detecting scattered electrons and double-reflection VUV polarization analyzer to register fluorescence photons. Time-coincidence counting methods on the electron and photon signals were employed to determine Stokes Parameters at each scattering angle, with data measured at angles between 20 - 115 degrees. The data are compared with calculated results using the B-Spline R-Matrix (BSR) and Relativistic Distorted Wave (RDW) approaches. Measurements were made of both the linear (Plin and γ) and circular (Lperp) parameters for the lowest lying excited states in these two targets. We particularly focus on results in the Lperp parameter, which shows unusual behavior in these particular targets, including strong sign changes implying reversal of the angular momentum transfer. In the case of neon, the unusual behavior is well captured by the BSR, but not by other models.

Marcus Bell-Shaped Electron Transfer Kinetics Observed in an Arrhenius Plot.

PubMed

Waskasi, Morteza M; Kodis, Gerdenis; Moore, Ana L; Moore, Thomas A; Gust, Devens; Matyushov, Dmitry V

2016-07-27

The Marcus theory of electron transfer predicts a bell-shaped dependence of the reaction rate on the reaction free energy. The top of the "inverted parabola" corresponds to zero activation barrier when the electron-transfer reorganization energy and the reaction free energy add up to zero. Although this point has traditionally been reached by altering the chemical structures of donors and acceptors, the theory suggests that it can also be reached by varying other parameters of the system including temperature. We find here dramatic evidence of this phenomenon from experiments on a fullerene-porphyrin dyad. Following photoinduced electron transfer, the rate of charge recombination shows a bell-shaped dependence on the inverse temperature, first increasing with cooling and then decreasing at still lower temperatures. This non-Arrhenius rate law is a result of a strong, approximately hyperbolic temperature variation of the reorganization energy and the reaction free energy. Our results provide potentially the cleanest confirmation of the Marcus energy gap law so far since no modification of the chemical structure is involved.

Theory of runaway electrons in ITER: Equations, important parameters, and implications for mitigation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boozer, Allen H., E-mail: ahb17@columbia.edu

2015-03-15

The plasma current in ITER cannot be allowed to transfer from thermal to relativistic electron carriers. The potential for damage is too great. Before the final design is chosen for the mitigation system to prevent such a transfer, it is important that the parameters that control the physics be understood. Equations that determine these parameters and their characteristic values are derived. The mitigation benefits of the injection of impurities with the highest possible atomic number Z and the slowing plasma cooling during halo current mitigation to ≳40 ms in ITER are discussed. The highest possible Z increases the poloidal flux consumptionmore » required for each e-fold in the number of relativistic electrons and reduces the number of high energy seed electrons from which exponentiation builds. Slow cooling of the plasma during halo current mitigation also reduces the electron seed. Existing experiments could test physics elements required for mitigation but cannot carry out an integrated demonstration. ITER itself cannot carry out an integrated demonstration without excessive danger of damage unless the probability of successful mitigation is extremely high. The probability of success depends on the reliability of the theory. Equations required for a reliable Monte Carlo simulation are derived.« less

Resonant electronic excitation energy transfer by Dexter mechanism in the quantum dot system

NASA Astrophysics Data System (ADS)

Samosvat, D. M.; Chikalova-Luzina, O. P.; Vyatkin, V. M.; Zegrya, G. G.

2016-11-01

In present work the energy transfer between quantum dots by the exchange (Dexter) mechanism is analysed. The interdot Coulomb interaction is taken into consideration. It is assumed that the quantum dot-donor and the quantum dot-acceptor are made from the same compound A3B5 and embedded in the matrix of other material creating potential barriers for electron and holes. The dependences of the energy transfer rate on the quantum-dot system parameters are found using the Kane model that provides the most adequate description spectra of semiconductors A3B5. Numerical calculations show that the rate of the energy transfer by Dexter mechanism is comparable to the rate of the energy transfer by electrostatic mechanism at the distances approaching to the contact ones.

Electron emission from transfer ionization reaction in 30 keV amu‑1 He 2+ on Ar collision

NASA Astrophysics Data System (ADS)

Amaya-Tapia, A.; Antillón, A.; Estrada, C. D.

2018-06-01

A model is presented that describes the transfer ionization process in H{e}2++Ar collision at a projectile energy of 30 keV amu‑1. It is based on a semiclassical independent-particle close-coupling method that yields a reasonable agreement between calculated and experimental values of the total single-ionization and single-capture cross sections. It is found that the transfer ionization reaction is predominantly carried out through simultaneous capture and ionization, rather than by sequential processes. The transfer-ionization differential cross section in energy that is obtained satisfactorily reproduces the global behavior of the experimental data. Additionally, the probabilities of capture and ionization as function of the impact parameter for H{e}2++A{r}+ and H{e}++A{r}+ collisions are calculated, as far as we know, for the first time. The results suggest that the model captures essential elements that describe the two-electron transfer ionization process and could be applied to systems and processes of two electrons.

Estimating contrast transfer function and associated parameters by constrained non-linear optimization.

PubMed

Yang, C; Jiang, W; Chen, D-H; Adiga, U; Ng, E G; Chiu, W

2009-03-01

The three-dimensional reconstruction of macromolecules from two-dimensional single-particle electron images requires determination and correction of the contrast transfer function (CTF) and envelope function. A computational algorithm based on constrained non-linear optimization is developed to estimate the essential parameters in the CTF and envelope function model simultaneously and automatically. The application of this estimation method is demonstrated with focal series images of amorphous carbon film as well as images of ice-embedded icosahedral virus particles suspended across holes.

Ab Initio Analysis of Auger-Assisted Electron Transfer.

PubMed

Hyeon-Deuk, Kim; Kim, Joonghan; Prezhdo, Oleg V

2015-01-15

Quantum confinement in nanoscale materials allows Auger-type electron-hole energy exchange. We show by direct time-domain atomistic simulation and analytic theory that Auger processes give rise to a new mechanism of charge transfer (CT) on the nanoscale. Auger-assisted CT eliminates the renown Marcus inverted regime, rationalizing recent experiments on CT from quantum dots to molecular adsorbates. The ab initio simulation reveals a complex interplay of the electron-hole and charge-phonon channels of energy exchange, demonstrating a variety of CT scenarios. The developed Marcus rate theory for Auger-assisted CT describes, without adjustable parameters, the experimental plateau of the CT rate in the region of large donor-acceptor energy gap. The analytic theory and atomistic insights apply broadly to charge and energy transfer in nanoscale systems.

Protein electron transfer: Dynamics and statistics

NASA Astrophysics Data System (ADS)

Matyushov, Dmitry V.

2013-07-01

Electron transfer between redox proteins participating in energy chains of biology is required to proceed with high energetic efficiency, minimizing losses of redox energy to heat. Within the standard models of electron transfer, this requirement, combined with the need for unidirectional (preferably activationless) transitions, is translated into the need to minimize the reorganization energy of electron transfer. This design program is, however, unrealistic for proteins whose active sites are typically positioned close to the polar and flexible protein-water interface to allow inter-protein electron tunneling. The high flexibility of the interfacial region makes both the hydration water and the surface protein layer act as highly polar solvents. The reorganization energy, as measured by fluctuations, is not minimized, but rather maximized in this region. Natural systems in fact utilize the broad breadth of interfacial electrostatic fluctuations, but in the ways not anticipated by the standard models based on equilibrium thermodynamics. The combination of the broad spectrum of static fluctuations with their dispersive dynamics offers the mechanism of dynamical freezing (ergodicity breaking) of subsets of nuclear modes on the time of reaction/residence of the electron at a redox cofactor. The separation of time-scales of nuclear modes coupled to electron transfer allows dynamical freezing. In particular, the separation between the relaxation time of electro-elastic fluctuations of the interface and the time of conformational transitions of the protein caused by changing redox state results in dynamical freezing of the latter for sufficiently fast electron transfer. The observable consequence of this dynamical freezing is significantly different reorganization energies describing the curvature at the bottom of electron-transfer free energy surfaces (large) and the distance between their minima (Stokes shift, small). The ratio of the two reorganization energies establishes the parameter by which the energetic efficiency of protein electron transfer is increased relative to the standard expectations, thus minimizing losses of energy to heat. Energetically efficient electron transfer occurs in a chain of conformationally quenched cofactors and is characterized by flattened free energy surfaces, reminiscent of the flat and rugged landscape at the stability basin of a folded protein.

Protein electron transfer: Dynamics and statistics.

PubMed

Matyushov, Dmitry V

2013-07-14

Electron transfer between redox proteins participating in energy chains of biology is required to proceed with high energetic efficiency, minimizing losses of redox energy to heat. Within the standard models of electron transfer, this requirement, combined with the need for unidirectional (preferably activationless) transitions, is translated into the need to minimize the reorganization energy of electron transfer. This design program is, however, unrealistic for proteins whose active sites are typically positioned close to the polar and flexible protein-water interface to allow inter-protein electron tunneling. The high flexibility of the interfacial region makes both the hydration water and the surface protein layer act as highly polar solvents. The reorganization energy, as measured by fluctuations, is not minimized, but rather maximized in this region. Natural systems in fact utilize the broad breadth of interfacial electrostatic fluctuations, but in the ways not anticipated by the standard models based on equilibrium thermodynamics. The combination of the broad spectrum of static fluctuations with their dispersive dynamics offers the mechanism of dynamical freezing (ergodicity breaking) of subsets of nuclear modes on the time of reaction/residence of the electron at a redox cofactor. The separation of time-scales of nuclear modes coupled to electron transfer allows dynamical freezing. In particular, the separation between the relaxation time of electro-elastic fluctuations of the interface and the time of conformational transitions of the protein caused by changing redox state results in dynamical freezing of the latter for sufficiently fast electron transfer. The observable consequence of this dynamical freezing is significantly different reorganization energies describing the curvature at the bottom of electron-transfer free energy surfaces (large) and the distance between their minima (Stokes shift, small). The ratio of the two reorganization energies establishes the parameter by which the energetic efficiency of protein electron transfer is increased relative to the standard expectations, thus minimizing losses of energy to heat. Energetically efficient electron transfer occurs in a chain of conformationally quenched cofactors and is characterized by flattened free energy surfaces, reminiscent of the flat and rugged landscape at the stability basin of a folded protein.

Structure and charge transfer correlated with oxygen content for a Y0.8Ca0.2Ba2Cu3Oy (y = 6.84 6.32) system: a positron study

NASA Astrophysics Data System (ADS)

Cao, Shixun; Li, Lingwei; Liu, Fen; Li, Wenfeng; Chi, Changyun; Jing, Chao; Zhang, Jincang

2005-05-01

The structure and charge transfer correlated with oxygen content are studied by measuring the positron lifetime parameters of the Y0.8Ca0.2Ba2Cu3Oy system with a large range of oxygen content (y = 6.84-6.32). The local electron density ne is evaluated from the positron lifetime data. The positron lifetime parameters show a clear change around y = 6.50 where the compounds undergo the orthorhombic-tetragonal phase transition. The effect of ne and oxygen content on the structure, charge transfer and superconductivity are discussed. With the decrease of oxygen content y, O(4) tends to the Cu(1) site, causing carrier localization, and accordingly, the decrease of ne. This would prove that the localized carriers (electrons and holes) in the Cu-O chain region have great influence on the superconductivity by affecting the charge transfer between the reservoir layers and the conducting layers. The positron annihilation mechanism and its relation with superconductivity are also discussed.

Electron quantum dynamics in atom-ion interaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sabzyan, H., E-mail: sabzyan@sci.ui.ac.ir; Jenabi, M. J.

2016-04-07

Electron transfer (ET) process and its dependence on the system parameters are investigated by solving two-dimensional time-dependent Schrödinger equation numerically using split operator technique. Evolution of the electron wavepacket occurs from the one-electron species hydrogen atom to another bare nucleus of charge Z > 1. This evolution is quantified by partitioning the simulation box and defining regional densities belonging to the two nuclei of the system. It is found that the functional form of the time-variations of these regional densities and the extent of ET process depend strongly on the inter-nuclear distance and relative values of the nuclear charges, whichmore » define the potential energy surface governing the electron wavepacket evolution. Also, the initial electronic state of the single-electron atom has critical effect on this evolution and its consequent (partial) electron transfer depending on its spreading extent and orientation with respect to the inter-nuclear axis.« less

Theoretical rate constants of super-exchange hole transfer and thermally induced hopping in DNA.

PubMed

Shimazaki, Tomomi; Asai, Yoshihiro; Yamashita, Koichi

2005-01-27

Recently, the electronic properties of DNA have been extensively studied, because its conductivity is important not only to the study of fundamental biological problems, but also in the development of molecular-sized electronics and biosensors. We have studied theoretically the reorganization energies, the activation energies, the electronic coupling matrix elements, and the rate constants of hole transfer in B-form double-helix DNA in water. To accommodate the effects of DNA nuclear motions, a subset of reaction coordinates for hole transfer was extracted from classical molecular dynamics (MD) trajectories of DNA in water and then used for ab initio quantum chemical calculations of electron coupling constants based on the generalized Mulliken-Hush model. A molecular mechanics (MM) method was used to determine the nuclear Franck-Condon factor. The rate constants for two types of mechanisms of hole transfer-the thermally induced hopping (TIH) and the super-exchange mechanisms-were determined based on Marcus theory. We found that the calculated matrix elements are strongly dependent on the conformations of the nucleobase pairs of hole-transferable DNA and extend over a wide range of values for the "rise" base-step parameter but cluster around a particular value for the "twist" parameter. The calculated activation energies are in good agreement with experimental results. Whereas the rate constant for the TIH mechanism is not dependent on the number of A-T nucleobase pairs that act as a bridge, the rate constant for the super-exchange process rapidly decreases when the length of the bridge increases. These characteristic trends in the calculated rate constants effectively reproduce those in the experimental data of Giese et al. [Nature 2001, 412, 318]. The calculated rate constants were also compared with the experimental results of Lewis et al. [Nature 2000, 406, 51].

Modeling the free energy surfaces of electron transfer in condensed phases

NASA Astrophysics Data System (ADS)

Matyushov, Dmitry V.; Voth, Gregory A.

2000-10-01

We develop a three-parameter model of electron transfer (ET) in condensed phases based on the Hamiltonian of a two-state solute linearly coupled to a harmonic, classical solvent mode with different force constants in the initial and final states (a classical limit of the quantum Kubo-Toyozawa model). The exact analytical solution for the ET free energy surfaces demonstrates the following features: (i) the range of ET reaction coordinates is limited by a one-sided fluctuation band, (ii) the ET free energies are infinite outside the band, and (iii) the free energy surfaces are parabolic close to their minima and linear far from the minima positions. The model provides an analytical framework to map physical phenomena conflicting with the Marcus-Hush two-parameter model of ET. Nonlinear solvation, ET in polarizable charge-transfer complexes, and configurational flexibility of donor-acceptor complexes are successfully mapped onto the model. The present theory leads to a significant modification of the energy gap law for ET reactions.

MS-CASPT2 study of hole transfer in guanine-indole complexes using the generalized Mulliken-Hush method: effective two-state treatment.

PubMed

Butchosa, C; Simon, S; Blancafort, L; Voityuk, A

2012-07-12

Because hole transfer from nucleobases to amino acid residues in DNA-protein complexes can prevent oxidative damage of DNA in living cells, computational modeling of the process is of high interest. We performed MS-CASPT2 calculations of several model structures of π-stacked guanine and indole and derived electron-transfer (ET) parameters for these systems using the generalized Mulliken-Hush (GMH) method. We show that the two-state model commonly applied to treat thermal ET between adjacent donor and acceptor is of limited use for the considered systems because of the small gap between the ground and first excited states in the indole radical cation. The ET parameters obtained within the two-state GMH scheme can deviate significantly from the corresponding matrix elements of the two-state effective Hamiltonian based on the GMH treatment of three adiabatic states. The computed values of diabatic energies and electronic couplings provide benchmarks to assess the performance of less sophisticated computational methods.

Diagnostic Criteria for the Characterization of Electrode Reactions with Chemically Coupled Reactions Preceding the Electron Transfer by Cyclic Square Wave Voltammetry.

PubMed

Helfrick, John C; Mann, Megan A; Bottomley, Lawrence A

2016-08-18

Theory for cyclic square wave voltammetry of electrode reactions with chemical reactions preceding the electron transfer is presented. Theoretical voltammograms were calculated following systematic variation of empirical parameters to assess their impact on the shape of the voltammogram. From the trends obtained, diagnostic criteria for this mechanism were deduced. When properly applied, these criteria will enable non-experts in voltammetry to assign the electrode reaction mechanism and accurately measure reaction kinetics. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effects of G-Quadruplex Topology on Electronic Transfer Integrals

PubMed Central

Sun, Wenming; Varsano, Daniele; Di Felice, Rosa

2016-01-01

G-quadruplex is a quadruple helical form of nucleic acids that can appear in guanine-rich parts of the genome. The basic unit is the G-tetrad, a planar assembly of four guanines connected by eight hydrogen bonds. Its rich topology and its possible relevance as a drug target for a number of diseases have stimulated several structural studies. The superior stiffness and electronic π-π overlap between consecutive G-tetrads suggest exploitation for nanotechnologies. Here we inspect the intimate link between the structure and the electronic properties, with focus on charge transfer parameters. We show that the electronic couplings between stacked G-tetrads strongly depend on the three-dimensional atomic structure. Furthermore, we reveal a remarkable correlation with the topology: a topology characterized by the absence of syn-anti G-G sequences can better support electronic charge transfer. On the other hand, there is no obvious correlation of the electronic coupling with usual descriptors of the helix shape. We establish a procedure to maximize the correlation with a global helix shape descriptor. PMID:28335314

Electrochemistry at a Metal Nanoparticle on a Tunneling Film: A Steady-State Model of Current Densities at a Tunneling Ultramicroelectrode.

PubMed

Hill, Caleb M; Kim, Jiyeon; Bard, Allen J

2015-09-09

Here, a new methodology is proposed for treating electrochemical current densities in metal-insulator-metal nanoparticle (M-I-MNP) systems. The described model provides broad, practical insights about MNP-mediated electron transfer to redox species in solution, where electron transfer from the underlying electrode to a MNP via tunneling and heterogeneous electron transfer from the MNP to redox species in solution are treated as sequential steps. Tunneling is treated through an adaptation of the Simmons model of tunneling in metal-insulator-metal structures, and explicit equations are provided for tunneling currents, which demonstrate the effect of various experimental parameters, such as insulator thickness and MNP size. Overall, a general approach is demonstrated for determining experimental conditions where tunneling will have a measurable impact on the electrochemistry of M-I-MNP systems.

Electron lenses for head-on beam-beam compensation in RHIC

DOE PAGES

Gu, X.; Fischer, W.; Altinbas, Z.; ...

2017-02-17

Two electron lenses (e-lenses) have been in operation during 2015 RHIC physics run as part of a head-on beam-beam compensation scheme. While the RHIC lattice was chosen to reduce the beam-beam induced resonance driving terms, the electron lenses reduced the beam-beam induced tune spread. This has been demonstrated for the first time. The beam-beam compensation scheme allows for higher beam-beam parameters and therefore higher intensities and luminosity. In this paper, we detailed the design considerations and verification of the electron beam parameters of the RHIC e-lenses. Lastly, longitudinal and transverse alignments with ion beams and the transverse beam transfer functionmore » (BTF) measurement with head-on electron-proton beam are presented.« less

Electron lenses for head-on beam-beam compensation in RHIC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gu, X.; Fischer, W.; Altinbas, Z.

Two electron lenses (e-lenses) have been in operation during 2015 RHIC physics run as part of a head-on beam-beam compensation scheme. While the RHIC lattice was chosen to reduce the beam-beam induced resonance driving terms, the electron lenses reduced the beam-beam induced tune spread. This has been demonstrated for the first time. The beam-beam compensation scheme allows for higher beam-beam parameters and therefore higher intensities and luminosity. In this paper, we detailed the design considerations and verification of the electron beam parameters of the RHIC e-lenses. Lastly, longitudinal and transverse alignments with ion beams and the transverse beam transfer functionmore » (BTF) measurement with head-on electron-proton beam are presented.« less

Estimates of electronic coupling for excess electron transfer in DNA

NASA Astrophysics Data System (ADS)

Voityuk, Alexander A.

2005-07-01

Electronic coupling Vda is one of the key parameters that determine the rate of charge transfer through DNA. While there have been several computational studies of Vda for hole transfer, estimates of electronic couplings for excess electron transfer (ET) in DNA remain unavailable. In the paper, an efficient strategy is established for calculating the ET matrix elements between base pairs in a π stack. Two approaches are considered. First, we employ the diabatic-state (DS) method in which donor and acceptor are represented with radical anions of the canonical base pairs adenine-thymine (AT) and guanine-cytosine (GC). In this approach, similar values of Vda are obtained with the standard 6-31G* and extended 6-31++G** basis sets. Second, the electronic couplings are derived from lowest unoccupied molecular orbitals (LUMOs) of neutral systems by using the generalized Mulliken-Hush or fragment charge methods. Because the radical-anion states of AT and GC are well reproduced by LUMOs of the neutral base pairs calculated without diffuse functions, the estimated values of Vda are in good agreement with the couplings obtained for radical-anion states using the DS method. However, when the calculation of a neutral stack is carried out with diffuse functions, LUMOs of the system exhibit the dipole-bound character and cannot be used for estimating electronic couplings. Our calculations suggest that the ET matrix elements Vda for models containing intrastrand thymine and cytosine bases are essentially larger than the couplings in complexes with interstrand pyrimidine bases. The matrix elements for excess electron transfer are found to be considerably smaller than the corresponding values for hole transfer and to be very responsive to structural changes in a DNA stack.

Theory for electron transfer from a mixed-valence dimer with paramagnetic sites to a mononuclear acceptor

NASA Astrophysics Data System (ADS)

Bominaar, E. L.; Achim, C.; Borshch, S. A.

1999-06-01

Polynuclear transition-metal complexes, such as Fe-S clusters, are the prosthetic groups in a large number of metalloproteins and serve as temporary electron storage units in a number of important redox-based biological processes. Polynuclearity distinguishes clusters from mononuclear centers and confers upon them unique properties, such as spin ordering and the presence of thermally accessible excited spin states in clusters with paramagnetic sites, and fractional valencies in clusters of the mixed-valence type. In an earlier study we presented an effective-mode (EM) analysis of electron transfer from a binuclear mixed-valence donor with paramagnetic sites to a mononuclear acceptor which revealed that the cluster-specific attributes have an important impact on the kinetics of long-range electron transfer. In the present study, the validity of these results is tested in the framework of more detailed theories which we have termed the multimode semiclassical (SC) model and the quantum-mechanical (QM) model. It is found that the qualitative trends in the rate constant are the same in all treatments and that the semiclassical models provide a good approximation of the more rigorous quantum-mechanical description of electron transfer under physiologically relevant conditions. In particular, the present results corroborate the importance of electron transfer via excited spin states in reactions with a low driving force and justify the use of semiclassical theory in cases in which the QM model is computationally too demanding. We consider cases in which either one or two donor sites of a dimer are electronically coupled to the acceptor. In the case of multiconnectivity, the rate constant for electron transfer from a valence-delocalized (class-III) donor is nonadditive with respect to transfer from individual metal sites of the donor and undergoes an order-of-magnitude change by reversing the sign of the intradimer metal-metal resonance parameter (β). In the case of single connectivity, the rate constant for electron transfer from a valence-localized (class-II) donor can readily be tuned over several orders of magnitude by introducing differences in the electronic potentials at the two metal sites of the donor. These results indicate that theories of cluster-based electron transfer, in order to be realistic, need to consider both intrinsic electronic structure and extrinsic interactions of the cluster with the protein environment.

Heat and metal transfer in gas metal arc welding using argon and helium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Joensson, P.G.; Eagar, T.W.; Szekely, J.

1995-04-01

This article describes a theoretical investigation on the arc parameters and metal transfer in gas metal arc welding (GMAW) of mild steel using argon and helium shielding gases. Major differences in the predicted arc parameters were determined to be due to large differences in thermophysical properties. Various findings from the study include that an arc cannot be struck in a pure helium atmosphere without the assistance of metal vapor, that a strong electromagnetic cathode force affects the fluid flow and heat transfer in the helium arc, providing a possible explanation for the experimentally observed globular transfer mode and that themore » tapering of t electrode in an argon arc is caused by electron condensation on the side of the electrode.« less

Spin qubit transport in a double quantum dot

NASA Astrophysics Data System (ADS)

Zhao, Xinyu; Hu, Xuedong

Long distance spin communication is a crucial ingredient to scalable quantum computer architectures based on electron spin qubits. One way to transfer spin information over a long distance on chip is via electron transport. Here we study the transport of an electron spin qubit in a double quantum dot by tuning the interdot detuning voltage. We identify a parameter regime where spin relaxation hot-spots can be avoided and high-fidelity spin transport is possible. Within this parameter space, the spin transfer fidelity is determined by the operation speed and the applied magnetic field. In particular, near zero detuning, a proper choice of operation speed is essential to high fidelity. In addition, we also investigate the modification of the effective g-factor by the interdot detuning, which could lead to a phase error between spin up and down states. The results presented in this work could be a useful guidance for experimentally achieving high-fidelity spin qubit transport. We thank financial support by US ARO via Grant W911NF1210609.

Interfacial Charge Transfer States in Condensed Phase Systems

NASA Astrophysics Data System (ADS)

Vandewal, Koen

2016-05-01

Intermolecular charge transfer (CT) states at the interface between electron-donating (D) and electron-accepting (A) materials in organic thin films are characterized by absorption and emission bands within the optical gap of the interfacing materials. CT states efficiently generate charge carriers for some D-A combinations, and others show high fluorescence quantum efficiencies. These properties are exploited in organic solar cells, photodetectors, and light-emitting diodes. This review summarizes experimental and theoretical work on the electronic structure and interfacial energy landscape at condensed matter D-A interfaces. Recent findings on photogeneration and recombination of free charge carriers via CT states are discussed, and relations between CT state properties and optoelectronic device parameters are clarified.

Study of metal transfer in CO2 laser+GMAW-P hybrid welding using argon-helium mixtures

NASA Astrophysics Data System (ADS)

Zhang, Wang; Hua, Xueming; Liao, Wei; Li, Fang; Wang, Min

2014-03-01

The metal transfer in CO2 Laser+GMAW-P hybrid welding by using argon-helium mixtures was investigated and the effect of the laser on the mental transfer is discussed. A 650 nm laser, in conjunction with the shadow graph technique, is used to observe the metal transfer process. In order to analyze the heat input to the droplet and the droplet internal current line distribution. An optical emission spectroscopy system was employed to estimate default parameter and optimized plasma temperature, electron number densities distribution. The results indicate that the CO2 plasma plume have a significant impact to the electrode melting, droplet formation, detachment, impingement onto the workpiece and weld morphology. Since the current distribution direction flow changes to the keyhole, to obtain a metal transfer mode of one droplet per pulse, the welding parameters should be adjusted to a higher pulse time (TP) and a lower voltage.

On the Theory of Oxidation-Reduction Reactions Involving Electron Transfer. V. Comparison and Properties of Electrochemical and Chemical Rate Constants

DOE R&D Accomplishments Database

Marcus, R. A.

1962-01-01

Using a theory of electron transfers which takes cognizance of reorganization of the medium outside the inner coordination shell and of changes of bond lengths inside it, relations between electrochemical and related chemical rate constants are deduced and compared with the experimental data. A correlation is found, without the use of arbitrary parameters. Effects of weak complexes with added electrolytes are included under specified conditions. The deductions offer a way of coordinating a variety of data in the two fields, internally as well as with each those in another. For example, the rate of oxidation or reduction of a series of related reactants by one reagent is correlated with that of another and with that of the corresponding electrochemical oxidation-reduction reaction, under certain specified conditions. These correlations may also provide a test for distinguishing an electron from an atom transfer mechanism. (auth)

Toward simulating complex systems with quantum effects

NASA Astrophysics Data System (ADS)

Kenion-Hanrath, Rachel Lynn

Quantum effects like tunneling, coherence, and zero point energy often play a significant role in phenomena on the scales of atoms and molecules. However, the exact quantum treatment of a system scales exponentially with dimensionality, making it impractical for characterizing reaction rates and mechanisms in complex systems. An ongoing effort in the field of theoretical chemistry and physics is extending scalable, classical trajectory-based simulation methods capable of capturing quantum effects to describe dynamic processes in many-body systems; in the work presented here we explore two such techniques. First, we detail an explicit electron, path integral (PI)-based simulation protocol for predicting the rate of electron transfer in condensed-phase transition metal complex systems. Using a PI representation of the transferring electron and a classical representation of the transition metal complex and solvent atoms, we compute the outer sphere free energy barrier and dynamical recrossing factor of the electron transfer rate while accounting for quantum tunneling and zero point energy effects. We are able to achieve this employing only a single set of force field parameters to describe the system rather than parameterizing along the reaction coordinate. Following our success in describing a simple model system, we discuss our next steps in extending our protocol to technologically relevant materials systems. The latter half focuses on the Mixed Quantum-Classical Initial Value Representation (MQC-IVR) of real-time correlation functions, a semiclassical method which has demonstrated its ability to "tune'' between quantum- and classical-limit correlation functions while maintaining dynamic consistency. Specifically, this is achieved through a parameter that determines the quantumness of individual degrees of freedom. Here, we derive a semiclassical correction term for the MQC-IVR to systematically characterize the error introduced by different choices of simulation parameters, and demonstrate the ability of this approach to optimize MQC-IVR simulations.

First-principles calculation of photo-induced electron transfer rate constants in phthalocyanine-C60 organic photovoltaic materials: Beyond Marcus theory

NASA Astrophysics Data System (ADS)

Lee, Myeong H.; Dunietz, Barry D.; Geva, Eitan

2014-03-01

Classical Marcus theory is commonly adopted in solvent-mediated charge transfer (CT) process to obtain the CT rate constant, but it can become questionable when the intramolecular vibrational modes dominate the CT process as in OPV devices because Marcus theory treats these modes classically and therefore nuclear tunneling is not accounted for. We present a computational scheme to obtain the electron transfer rate constant beyond classical Marcus theory. Within this approach, the nuclear vibrational modes are treated quantum-mechanically and a short-time approximation is avoided. Ab initio calculations are used to obtain the basic parameters needed for calculating the electron transfer rate constant. We apply our methodology to phthalocyanine(H2PC)-C60 organic photovoltaic system where one C60 acceptor and one or two H2PC donors are included to model the donor-acceptor interface configuration. We obtain the electron transfer and recombination rate constants for all accessible charge transfer (CT) states, from which the CT exciton dynamics is determined by employing a master equation. The role of higher lying excited states in CT exciton dynamics is discussed. This work is pursued as part of the Center for Solar and Thermal Energy Conversion, an Energy Frontier Research Center funded by the US Department of Energy Office of Science, Office of Basic Energy Sciences under 390 Award No. DE-SC0000957.

Anisotropic rotational diffusion studied by passage saturation transfer electron paramagnetic resonance

NASA Astrophysics Data System (ADS)

Robinson, Bruce H.; Dalton, Larry R.

1980-01-01

The stochastic Liouville equation for the spin density matrix is modified to consider the effects of Brownian anisotropic rotational diffusion upon electron paramagnetic resonance (EPR) and saturation transfer electron paramagnetic resonance (ST-EPR) spectra. Spectral shapes and the ST-EPR parameters L″/L, C'/C, and H″/H defined by Thomas, Dalton, and Hyde at X-band microwave frequencies [J. Chem. Phys. 65, 3006 (1976)] are examined and discussed in terms of the rotational times τ∥ and τ⊥ and in terms of other defined correlation times for systems characterized by magnetic tensors of axial symmetry and for systems characterized by nonaxially symmetric magnetic tensors. For nearly axially symmetric magnetic tensors, such as nitroxide spin labels studied employing 1-3 GHz microwaves, ST-EPR spectra for systems undergoing anisotropic rotational diffusion are virtually indistinguishable from spectra for systems characterized by isotropic diffusion. For nonaxially symmetric magnetic tensors, such as nitroxide spin labels studied employing 8-35 GHz microwaves, the high field region of the ST-EPR spectra, and hence the H″/H parameter, will be virtually indistinguishable from spectra, and parameter values, obtained for isotropic diffusion. On the other hand, the central spectral region at x-band microwave frequencies, and hence the C'/C parameter, is sensitive to the anisotropic diffusion model provided that a unique and static relationship exists between the magnetic and diffusion tensors. Random labeling or motion of the spin label relative to the biomolecule whose hydrodynamic properties are to be investigated will destroy spectral sensitivity to anisotropic motion. The sensitivity to anisotropic motion is enhanced in proceeding to 35 GHz with the increased sensitivity evident in the low field half of the EPR and ST-EPR spectra. The L″/L parameter is thus a meaningful indicator of anisotropic motion when compared with H″/H parameter analysis. However, consideration of spectral shapes suggests that the C'/C parameter definition is not meaningfully extended from 9.5 to 35 GHz. Alternative definitions of the L″/L and C'/C parameters are proposed for those microwave frequencies for which the electron Zeeman anisotropy is comparable to or greater than the electron-nitrogen nuclear hyperfine anisotropy.

A Combined Theoretical and Experimental Study of Dissociation of Charge Transfer States at the Donor-Acceptor Interface of Organic Solar Cells.

PubMed

Tscheuschner, Steffen; Bässler, Heinz; Huber, Katja; Köhler, Anna

2015-08-13

The observation that in efficient organic solar cells almost all electron-hole pairs generated at the donor-acceptor interface escape from their mutual coulomb potential remains to be a conceptual challenge. It has been argued that it is the excess energy dissipated in the course of electron or hole transfer at the interface that assists this escape process. The current work demonstrates that this concept is unnecessary to explain the field dependence of electron-hole dissociation. It is based upon the formalism developed by Arkhipov and co-workers as well as Baranovskii and co-workers. The key idea is that the binding energy of the dissociating "cold" charge-transfer state is reduced by delocalization of the hole along the polymer chain, quantified in terms of an "effective mass", as well as the fractional strength of dipoles existent at the interface in the dark. By covering a broad parameter space, we determine the conditions for efficient electron-hole dissociation. Spectroscopy of the charge-transfer state on bilayer solar cells as well as measurements of the field dependence of the dissociation yield over a broad temperature range support the theoretical predictions.

Investigations on the Influence of Parameters During Electron Beam Surface Hardening Using the Flash Technique

NASA Astrophysics Data System (ADS)

Grafe, S.; Hengst, P.; Buchwalder, A.; Zenker, R.

2018-06-01

The electron beam hardening (EBH) process is one of today’s most innovative industrial technologies. Due to the almost inertia-free deflection of the EB (up to 100 kHz), the energy transfer function can be adapted locally to the component geometry and/or loading conditions. The current state-of-the-art technology is that of EBH with continuous workpiece feed. Due to the large range of parameters, the potentials and limitations of EBH using the flash technique (without workpiece feed) have not been investigated sufficiently to date. The aim of this research was to generate surface isothermal energy transfer within the flash field. This paper examines the effects of selected process parameters on the EBH surface layer microstructure and the properties achieved when treating hardened and tempered C45E steel. When using constant point distribution within the flash field and a constant beam current, surface isothermal energy input was not generated. However, by increasing the deflection frequency, point density and beam current, a more homogeneous EBH surface layer microstructure could be achieved, along with higher surface hardness and greater surface hardening depths. Furthermore, using temperature-controlled power regulation, surface isothermal energy transfer could be realised over a larger area in the centre of the sample.

Ultra high energy electrons powered by pulsar rotation.

PubMed

Mahajan, Swadesh; Machabeli, George; Osmanov, Zaza; Chkheidze, Nino

2013-01-01

A new mechanism of particle acceleration, driven by the rotational slow down of the Crab pulsar, is explored. The rotation, through the time dependent centrifugal force, can efficiently excite unstable Langmuir waves in the electron-positron (hereafter e(±)) plasma of the star magnetosphere. These waves, then, Landau damp on electrons accelerating them in the process. The net transfer of energy is optimal when the wave growth and the Landau damping times are comparable and are both very short compared to the star rotation time. We show, by detailed calculations, that these are precisely the conditions for the parameters of the Crab pulsar. This highly efficient route for energy transfer allows the electrons in the primary beam to be catapulted to multiple TeV (~ 100 TeV) and even PeV energy domain. It is expected that the proposed mechanism may, unravel the puzzle of the origin of ultra high energy cosmic ray electrons.

The influence of the distance between the donor-acceptor groups of polymethine dyes on their photovoltaic properties

NASA Astrophysics Data System (ADS)

Seliverstova, E.; Ibrayev, N.

2018-01-01

Spectral-luminescent and photovoltaic properties of polymethine dyes of various structures are studied. It is shown that an increase in the length of the methylene chain between the active chromophores leads to a red-wave shift of the absorption and fluorescence spectra. Significant changes in the absorptivity and lifetime of fluorescence do not occur in this case. The best photovoltaic parameters have cells sensitized with shorter dye molecules. It is shown, that for a longer dye the resistance associated with electron recombination on the TiO2/electrolyte surface is much higher than the electron transfer resistance in the semiconductor, which reduces the efficiency of electron transfer in the solar cell, sensitized with longer dye molecules.

Determination of equilibrium electron temperature and times using an electron swarm model with BOLSIG+ calculated collision frequencies and rate coefficients

DOE PAGES

Pusateri, Elise N.; Morris, Heidi E.; Nelson, Eric M.; ...

2015-08-04

Electromagnetic pulse (EMP) events produce low-energy conduction electrons from Compton electron or photoelectron ionizations with air. It is important to understand how conduction electrons interact with air in order to accurately predict EMP evolution and propagation. An electron swarm model can be used to monitor the time evolution of conduction electrons in an environment characterized by electric field and pressure. Here a swarm model is developed that is based on the coupled ordinary differential equations (ODEs) described by Higgins et al. (1973), hereinafter HLO. The ODEs characterize the swarm electric field, electron temperature, electron number density, and drift velocity. Importantmore » swarm parameters, the momentum transfer collision frequency, energy transfer collision frequency, and ionization rate, are calculated and compared to the previously reported fitted functions given in HLO. These swarm parameters are found using BOLSIG+, a two term Boltzmann solver developed by Hagelaar and Pitchford (2005), which utilizes updated cross sections from the LXcat website created by Pancheshnyi et al. (2012). We validate the swarm model by comparing to experimental effective ionization coefficient data in Dutton (1975) and drift velocity data in Ruiz-Vargas et al. (2010). In addition, we report on electron equilibrium temperatures and times for a uniform electric field of 1 StatV/cm for atmospheric heights from 0 to 40 km. We show that the equilibrium temperature and time are sensitive to the modifications in the collision frequencies and ionization rate based on the updated electron interaction cross sections.« less

Supramolecular aromaticity

NASA Astrophysics Data System (ADS)

Karabıyık, Hande; Sevinçek, Resul; Karabıyık, Hasan

2014-05-01

We report experimental and theoretical evidences for supramolecular aromaticity as a new concept to be widely used in researches about molecular crystals. CSD survey regarding frequently encountered resonance-assisted H-bonds (RAHBs) in formic acid, formamide, formimidamide, formic acid-formamide, and formamide-formimidamide dimers shows that supramolecular quasirings formed by RAHBs have remarkable electronic delocalization within themselves, which is reminiscent of aromaticity at supramolecular level. This study criticizes and reevaluates the validity of conventional judgment which states that ring systems formed by intermolecular H-bonds cannot be aromatic. Thus, the term aromaticity can be extended to supramolecular systems formed by RAHBs. Supramolecular aromaticity has a multi-fold nature involving both σ- and π-delocalization, and σ-delocalization through RAHBs takes on a task of compensating σ-deficiency within quasirings. Atomic composition in donor-acceptor set of the dimers is descriptive for supramolecular aromaticity. We revised bond-valence parameters for RAHBs and they suggest that hypervalent character of H atoms is more pronounced than their hypovalent character in RAHBs. The σ-delocalized bonding within H-bonded quasirings necessitates hypervalent character of H atoms. Quantum chemical calculations based on adiabatic Hydrogen Atom Transfer (HAT) between the monomers reveal that topological parameters at ring critical points (RCPs) of the quasirings correlate well with Shannon's entropic aromaticity index. The presence of additional LP orbital on O atoms implying more diffused LP-orbitals in donor-acceptor set leads to the formation of resonance-disabling states reducing supramolecular aromaticity of a quasiring and energetic cost of the electron transfer between the monomers. There is a nonignorable electron transfer between the monomers even in the cases where H atoms are close to donor or acceptor atom. NBO analyses have revealed that formally vacant LP* orbitals on H-atoms in TS geometries mediate intermolecular electron transfer as a result of the hyperconjugative stereoelectronic interactions.

Tunneling of heat: Beyond linear response regime

NASA Astrophysics Data System (ADS)

Walczak, Kamil; Saroka, David

2018-02-01

We examine nanoscale processes of heat (energy) transfer as carried by electrons tunneling via potential barriers and molecular interconnects between two heat reservoirs (thermal baths). For that purpose, we use Landauer-type formulas to calculate thermal conductance and quadratic correction to heat flux flowing via quantum systems. As an input, we implement analytical expressions for transmission functions related to simple potential barriers and atomic bridges. Our results are discussed with respect to energy of tunneling electrons, temperature, the presence of resonant states, and specific parameters characterizing potential barriers as well as heat carriers. The simplicity of semi-analytical models developed by us allows to fit experimental data and extract crucial information about the values of model parameters. Further investigations are expected for more realistic transmission functions, while time-dependent aspects of nanoscale heat transfer may be addressed by using the concept of wave packets scattered on potential barriers and point-like defects within regular (periodic) nanostructures.

Chemical and quantum simulation of electron transfer through a polypeptide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ungar, L.W.; Voth, G.A.; Newton, M.D.

1999-08-26

Quantum rate theory, molecular dynamics simulations, and semiempirical electronic structure calculations are used to fully investigate electron transfer mediated by a solvated polypeptide for the first time. Using a stationary-phase approximation, the nonadiabatic electron-transfer rate constant is calculated from the nuclear free energies and the electronic coupling between the initial and final states. The former are obtained from quantum path integral and classical molecular dynamics simulations; the latter are calculated using semiempirical electronic structure calculations and the generalized Mulliken-Hush method. Importantly, no parameters are fit to kinetic data. The simulated system consists of a solvated four-proline polypeptide with a tris(bipyridine)rutheniummore » donor group and an oxypentamminecobalt acceptor group. From the simulation data entropy and energy contributions to the free energies are distinguished. Quantum suppression of the barrier, including important solvent contributions, is demonstrated. Although free energy profiles along the reaction coordinate are nearly parabolic, pronounced departures from harmonic behavior are found for the separate energy and entropy functions. Harmonic models of the system are compared to simulation results in order to quantify anharmonic effects. Electronic structure calculations show that electronic coupling elements vary considerably with system conformation, even when the effective donor-acceptor separation remains roughly constant. The calculations indicate that electron transfer in a significant range of conformations linking the polypeptide to the acceptor may contribute to the overall rate constant. After correction for limitations of the solvent model, the simulations and calculations agree well with the experimental activation energy and Arrhenius prefactor.« less

Charge transfer at organic-inorganic interfaces—Indoline layers on semiconductor substrates

NASA Astrophysics Data System (ADS)

Meyenburg, I.; Falgenhauer, J.; Rosemann, N. W.; Chatterjee, S.; Schlettwein, D.; Heimbrodt, W.

2016-12-01

We studied the electron transfer from excitons in adsorbed indoline dye layers across the organic-inorganic interface. The hybrids consist of indoline derivatives on the one hand and different inorganic substrates (TiO2, ZnO, SiO2(0001), fused silica) on the other. We reveal the electron transfer times from excitons in dye layers to the organic-inorganic interface by analyzing the photoluminescence transients of the dye layers after femtosecond excitation and applying kinetic model calculations. A correlation between the transfer times and four parameters have been found: (i) the number of anchoring groups, (ii) the distance between the dye and the organic-inorganic interface, which was varied by the alkyl-chain lengths between the carboxylate anchoring group and the dye, (iii) the thickness of the adsorbed dye layer, and (iv) the level alignment between the excited dye ( π* -level) and the conduction band minimum of the inorganic semiconductor.

Comprehensive photonics-electronics convergent simulation and its application to high-speed electronic circuit integration on a Si/Ge photonic chip

NASA Astrophysics Data System (ADS)

Takeda, Kotaro; Honda, Kentaro; Takeya, Tsutomu; Okazaki, Kota; Hiraki, Tatsurou; Tsuchizawa, Tai; Nishi, Hidetaka; Kou, Rai; Fukuda, Hiroshi; Usui, Mitsuo; Nosaka, Hideyuki; Yamamoto, Tsuyoshi; Yamada, Koji

2015-01-01

We developed a design technique for a photonics-electronics convergence system by using an equivalent circuit of optical devices in an electrical circuit simulator. We used the transfer matrix method to calculate the response of an optical device. This method used physical parameters and dimensions of optical devices as calculation parameters to design a device in the electrical circuit simulator. It also used an intermediate frequency to express the wavelength dependence of optical devices. By using both techniques, we simulated bit error rates and eye diagrams of optical and electrical integrated circuits and calculated influences of device structure change and wavelength shift penalty.

Evaluation of oxygen exposure levels and polyphenolic content of red wines using an electronic panel formed by an electronic nose and an electronic tongue.

PubMed

Rodriguez-Mendez, M L; Apetrei, C; Gay, M; Medina-Plaza, C; de Saja, J A; Vidal, S; Aagaard, O; Ugliano, M; Wirth, J; Cheynier, V

2014-07-15

An electronic panel formed by an electronic nose and an electronic tongue has been used to analyse red wines showing high and low phenolic contents, obtained by flash release and traditional soaking, respectively, and processed with or without micro-oxygenation. Four oxygen transfer rate conditions (0.8, 1.9, 8.0, and 11.9 μl oxygen/bottle/day) were ensured by using synthetic closures with controlled oxygen permeability and storage under controlled atmosphere. Twenty-five chemical parameters associated with the polyphenolic composition, the colour indices and the levels of oxygen were measured in triplicate and correlated with the signals registered (seven replicas) by means of the electronic nose and the electronic tongue using partial least squares regression analysis. The electronic nose and the electronic tongue showed particularly good correlations with those parameters associated with the oxygen levels and, in particular, with the influence of the porosity of the closure to oxygen exposure. In turn, the electronic tongue was particularly sensitive to redox species including oxygen and phenolic compounds. It has been demonstrated that a combined system formed from the electronic nose and the electronic tongue provides information about the chemical composition of both the gas and the liquid phase of red wines. This complementary information improves the capacity to predict values of oxygen-related parameters, phenolic content and colour parameters. Copyright © 2014 Elsevier Ltd. All rights reserved.

Single-molecule interfacial electron transfer dynamics in solar energy conversion

NASA Astrophysics Data System (ADS)

Dhital, Bharat

This dissertation work investigated the parameters affecting the interfacial electron transfer (ET) dynamics in dye-semiconductor nanoparticles (NPs) system by using single-molecule fluorescence spectroscopy and imaging combined with electrochemistry. The influence of the molecule-substrate electronic coupling, the molecular structure, binding geometry on the surface and the molecule-attachment surface chemistry on interfacial charge transfer processes was studied on zinc porphyrin-TiO2 NP systems. The fluorescence blinking measurement on TiO2 NP demonstrated that electronic coupling regulates dynamics of charge transfer processes at the interface depending on the conformation of molecule on the surface. Moreover, semiconductor surface charge induced electronic coupling of molecule which is electrostatically adsorbed on the semiconductor surface also predominantly alters the ET dynamics. Furthermore, interfacial electric field and electron accepting state density dependent ET dynamics has been dissected in zinc porphyrin-TiO2 NP system by observing the single-molecule fluorescence blinking dynamics and fluorescence lifetime with and without applied bias. The significant difference in fluorescence fluctuation and lifetime suggested the modulation of charge transfer dynamics at the interface with external electric field perturbation. Quasi-continuous distribution of fluorescence intensity with applied negative potential was attributed to the faster charge recombination due to reduced density of electron accepting states. The driving force and electron accepting state density ET dependent dynamics has also been probed in zinc porphyrin-TiO2 NP and zinc porphyrin-indium tin oxide (ITO) systems. Study of a molecule adsorbed on two different semiconductors (ITO and TiO2), with large difference in electron densities and distinct driving forces, allows us to observe the changes in rates of back electron transfer process reflected by the suppressed fluorescence blinking of molecule on ITO surface. Finally, the electric field effect on the interface properties has been probed by using surface-enhanced Raman spectroscopy and supported by density functional theory calculations in alizarin-TiO2 system. The perturbation, created by the external potential, has been observed to cause a shift and/or splitting interfacial bond vibrational mode, typical indicator of the coupling energy changes between alizarin and TiO2. Such splitting provides evidence for electric field-dependent electronic coupling changes that have a significant impact on the interfacial electron transfer dynamics.

Chemical and physical investigations on the charge transfer interaction of organic donors with iodine and its application as non-traditional organic conductors

NASA Astrophysics Data System (ADS)

Refat, Moamen S.; Sharshar, T.; Adam, Abdel Majid A.; Elsabawy, Khaled M.; Hemeda, O. M.

2014-09-01

The iso-leucine-iodide and methionine-iodide charge-transfer complexes were prepared and characterized using different spectroscopic techniques. The iodide charge-transfer complexes were synthesized by grinding KI-I2-amino acid with 1:1:1 M ratio in presence of few drops of methanol solvent. The structures of both solid amino acid iodide charge-transfer complexes are discussed with the help of the obtained results of the infrared and Raman laser spectra, Uv-vis. electronic spectra and thermal analyses. The electrical properties (AC resistivity and dielectric constant) of both complexes were investigated. The positron annihilation Doppler broadening (PADB) spectroscopies were also used to probe the structural changes of both complexes. The PADB line-shape parameters (S and W) were found to be dependent on the structure, electronic configuration of the charge transfer complex. The PADB technique is a powerful tool to probe the structural features of the KI-I2-amino acid complexes.

Organic nanowire hierarchy over fabric platform for flexible cold cathode

NASA Astrophysics Data System (ADS)

Maiti, Soumen; Narayan Maiti, Uday; Pal, Shreyasi; Chattopadhyay, Kalyan Kumar

2013-11-01

Organic charge transfer (CT) complexes initiated a growing interest in modern electronic devices owing to their easy processability and unique characteristics. In this work, three-dimensional field emitters comprising metal-organic charge transfer complex nanostructures of AgTCNQ and CuTCNQ (TCNQ, 7,7,8,8-tetracyanoquinodimethane) over flexible fabric substrate are realized. Deliberate control over the reaction parameter during organic solid phase reaction leads to modification in structural parameters of the nanowires (i.e. length, diameter) as well as their arrangement atop the carbon fibers. The optimized arrays of AgTCNQ and CuTCNQ nanowires exhibit excellent field electron emission performance with very low turn-on (1.72 and 2.56 V μm-1) and threshold fields (4.21 and 6.33 V μm-1) respectively, which are comparable to those of the best organic field emitters reported to date. The underlying conducting carbon cloth with special woven-like geometry not only offers a flexible platform for nanowire growth, but also provides an additional field enhancement to ease the electron emission.

Influence of dimension parameters of the gravity heat pipe on the thermal performance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kosa, Ľuboš, E-mail: lubos.kosa@fstroj.uniza.sk; Nemec, Patrik, E-mail: patrik.nemec@fstroj.uniza.sk; Jobb, Marián, E-mail: marian.jobb@fstroj.uniza.sk

Currently the problem with the increasing number of electronic devices is a problem with the outlet Joule heating. Joule heating, also known as ohmic heating and resistive heating, is the process by which the passage of an electric current through a conductor releases heat. Perfect dustproof cooling of electronic components ensures longer life of the equipment. One of more alternatives of heat transfer without the using of mechanical equipment is the use of the heat pipe. Heat pipes are easy to manufacture and maintenance of low input investment cost. The advantage of using the heat pipe is its use inmore » hermetic closed electronic device which is separated exchange of air between the device and the environment. This experiment deals with the influence of changes in the working tube diameter and changing the working fluid on performance parameters. Changing the working fluid and the tube diameter changes the thermal performance of the heat pipe. The result of this paper is finding the optimal diameter with ideal working substance for the greatest heat transfer for 1cm{sup 2} sectional area tube.« less

Influence of the heat transfer on the thermoelastic response of metals on heating by the laser pulse

NASA Astrophysics Data System (ADS)

Sudenkov, Y. V.; Zimin, B. A.; Sventitskaya, V. E.

2018-05-01

The paper presents an analysis of the effect of the heat transfer process in metals on the parameters of thermal stresses under pulsed laser action. The dynamic problem of thermoelasticity is considered as a two-stage process. The first stage is determined by the time of action of the radiation pulse. The second stage is caused by the dynamics of the heat transfer process after the end of the laser pulse. For showing the continuity of thermoelastic and thermoelectric processes, the analysis of the electronic mechanism for the propagation of heat in metals and the results of experimental studies of these processes are presented. The results of the experiments demonstrate the high sensitivity of the parameters of thermoelastic and thermoelectric pulses to the microstructure of metals.

The behavior of exciplex decay processes and interplay of radiationless transition and preliminary reorganization mechanisms of electron transfer in loose and tight pairs of reactants.

PubMed

Kuzmin, Michael G; Soboleva, Irina V; Dolotova, Elena V

2007-01-18

Exciplex emission spectra and rate constants of their decay via internal conversion and intersystem crossing are studied and discussed in terms of conventional radiationless transition approach. Exciplexes of 9-cyanophenanthrene with 1,2,3-trimethoxybenzene and 1,3,5-trimethoxybenzene were studied in heptane, toluene, butyl acetate, dichloromethane, butyronitrile, and acetonitrile. A better description of spectra and rate constants is obtained using 0-0 transition energy and Gauss broadening of vibrational bands rather than the free energy of electron transfer and reorganization energy. The coincidence of parameters describing exciplex emission spectra and dependence of exciplex decay rate constants on energy gap gives the evidence of radiationless quantum transition mechanism rather than thermally activated medium reorganization mechanism of charge recombination in exciplexes and excited charge transfer complexes (contact radical ion pairs) as well as in solvent separated radical ion pairs. Radiationless quantum transition mechanism is shown to provide an appropriate description also for the main features of exergonic excited-state charge separation reactions if fast mutual transformations of loose and tight pairs of reactants are considered. In particular, very fast electron transfer (ET) in tight pairs of reactants with strong electronic coupling of locally excited and charge transfer states can prevent the observation of an inverted region in bimolecular excited-state charge separation even for highly exergonic reactions.

Solvent as electron donor: Donor/acceptor electronic coupling is a dynamical variable

DOE Office of Scientific and Technical Information (OSTI.GOV)

Castner, E.W. Jr.; Kennedy, D.; Cave, R.J.

2000-04-06

The authors combine analysis of measurements by femtosecond optical spectroscopy, computer simulations, and the generalized Mulliken-Hush (GMH) theory in the study of electron-transfer reactions and electron donor-acceptor interactions. The study focus is on ultrafast photoinduced electron-transfer reactions from aromatic amine solvent donors to excited-state acceptors. The experimental results from femtosecond dynamical measurements fall into three categories: six coumarin acceptors reductively quenched by N,N-dimethylaniline (DMA), eight electron-donating amine solvents reductively quenching coumarin 152 (7-(dimethylamino)-4-(trifluoromethyl)-coumarin), and reductive quenching dynamics of two coumarins by DMA as a function of dilution in the nonreactive solvents toluene and chlorobenzene. Applying a combination of molecular dynamicsmore » trajectories, semiempirical quantum mechanical calculations (of the relevant adiabatic electronic states), and GMH theory to the C152/DMA photoreaction, the authors calculate the electron donor/acceptor interaction parameter H{sub DA} at various time frames, H{sub DA} is strongly modulated by both inner-sphere and outer-sphere nuclear dynamics, leading us to conclude that H{sub DA} must be considered as a dynamical variable.« less

Application of the π-accepting ability parameter of N-heterocyclic carbene ligands in iridium complexes for signal amplification by reversible exchange (SABRE).

PubMed

van Weerdenburg, Bram J A; Eshuis, Nan; Tessari, Marco; Rutjes, Floris P J T; Feiters, Martin C

2015-09-21

The new π-accepting ability parameter (PAAP) appears to be the best tool to analyse the electronic properties of NHC ligands in [Ir(H)2(NHC)(Py)3](+) complexes for SABRE. Together with the buried volume, the efficiency of hyperpolarisation transfer in SABRE, depending on the exchange rate of pyridine, can be described.

Parameter-free driven Liouville-von Neumann approach for time-dependent electronic transport simulations in open quantum systems

DOE PAGES

Zelovich, Tamar; Hansen, Thorsten; Liu, Zhen-Fei; ...

2017-03-02

A parameter-free version of the recently developed driven Liouville-von Neumann equation [T. Zelovich et al., J. Chem. Theory Comput. 10(8), 2927-2941 (2014)] for electronic transport calculations in molecular junctions is presented. The single driving rate, appearing as a fitting parameter in the original methodology, is replaced by a set of state-dependent broadening factors applied to the different single-particle lead levels. These broadening factors are extracted explicitly from the self-energy of the corresponding electronic reservoir and are fully transferable to any junction incorporating the same lead model. Furthermore, the performance of the method is demonstrated via tight-binding and extended Hückel calculationsmore » of simple junction models. Our analytic considerations and numerical results indicate that the developed methodology constitutes a rigorous framework for the design of "black-box" algorithms to simulate electron dynamics in open quantum systems out of equilibrium.« less

Parameter-free driven Liouville-von Neumann approach for time-dependent electronic transport simulations in open quantum systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zelovich, Tamar; Hansen, Thorsten; Liu, Zhen-Fei

A parameter-free version of the recently developed driven Liouville-von Neumann equation [T. Zelovich et al., J. Chem. Theory Comput. 10(8), 2927-2941 (2014)] for electronic transport calculations in molecular junctions is presented. The single driving rate, appearing as a fitting parameter in the original methodology, is replaced by a set of state-dependent broadening factors applied to the different single-particle lead levels. These broadening factors are extracted explicitly from the self-energy of the corresponding electronic reservoir and are fully transferable to any junction incorporating the same lead model. Furthermore, the performance of the method is demonstrated via tight-binding and extended Hückel calculationsmore » of simple junction models. Our analytic considerations and numerical results indicate that the developed methodology constitutes a rigorous framework for the design of "black-box" algorithms to simulate electron dynamics in open quantum systems out of equilibrium.« less

Numerical simulation of electron beam welding with beam oscillations

NASA Astrophysics Data System (ADS)

Trushnikov, D. N.; Permyakov, G. L.

2017-02-01

This research examines the process of electron-beam welding in a keyhole mode with the use of beam oscillations. We study the impact of various beam oscillations and their parameters on the shape of the keyhole, the flow of heat and mass transfer processes and weld parameters to develop methodological recommendations. A numerical three-dimensional mathematical model of electron beam welding is presented. The model was developed on the basis of a heat conduction equation and a Navier-Stokes equation taking into account phase transitions at the interface of a solid and liquid phase and thermocapillary convection (Marangoni effect). The shape of the keyhole is determined based on experimental data on the parameters of the secondary signal by using the method of a synchronous accumulation. Calculations of thermal and hydrodynamic processes were carried out based on a computer cluster, using a simulation package COMSOL Multiphysics.

LASER APPLICATIONS AND OTHER TOPICS IN QUANTUM ELECTRONICS On control of kinematic parameters of ultracold neutrons in waveguides

NASA Astrophysics Data System (ADS)

Rivlin, Lev A.

2010-10-01

The possibility of controlling the kinematic parameters of ultracold neutrons (UCNs) is analysed by the example of a waveguide transfer and transformation of 2D images in ultracold neutrons and by the example of an increase in the concentration and deceleration/acceleration of ultracold neutrons during their transport in the waveguide with a variable cross section. The critical parameters of the problem are estimated, which indicates both consistency of the proposed approach and the emerging experimental limitations.

Scaling relationships for nonadiabatic energy relaxation times in warm dense matter: toward understanding the equation of state.

PubMed

Pradhan, Ekadashi; Magyar, Rudolph J; Akimov, Alexey V

2016-11-30

Understanding the dynamics of electron-ion energy transfer in warm dense (WD) matter is important to the measurement of equation of state (EOS) properties and for understanding the energy balance in dynamic simulations. In this work, we present a comprehensive investigation of nonadiabatic electron relaxation and thermal excitation dynamics in aluminum under high pressure and temperature. Using quantum-classical trajectory surface hopping approaches, we examine the role of nonadiabatic couplings and electronic decoherence in electron-nuclear energy transfer in WD aluminum. The computed timescales range from 400 fs to 4.0 ps and are consistent with existing experimental studies. We have derived general scaling relationships between macroscopic parameters of WD systems such as temperature or mass density and the timescales of energy redistribution between quantum and classical degrees of freedom. The scaling laws are supported by computational results. We show that electronic decoherence plays essential role and can change the functional dependencies qualitatively. The established scaling relationships can be of use in modelling of WD matter.

Impact of undamped and damped intramolecular vibrations on the efficiency of photosynthetic exciton energy transfer

NASA Astrophysics Data System (ADS)

Juhász, Imre Benedek; Csurgay, Árpád I.

2018-04-01

In recent years, the role of molecular vibrations in exciton energy transfer taking place during the first stage of photosynthesis attracted increasing interest. Here, we present a model formulated as a Lindblad-type master equation that enables us to investigate the impact of undamped and especially damped intramolecular vibrational modes on the exciton energy transfer, particularly its efficiency. Our simulations confirm the already reported effects that the presence of an intramolecular vibrational mode can compensate the energy detuning of electronic states, thus promoting the energy transfer; and, moreover, that the damping of such a vibrational mode (in other words, vibrational relaxation) can further enhance the efficiency of the process by generating directionality in the energy flow. As a novel result, we show that this enhancement surpasses the one caused by pure dephasing, and we present its dependence on various system parameters (time constants of the environment-induced relaxation and excitation processes, detuning of the electronic energy levels, frequency of the intramolecular vibrational modes, Huang-Rhys factors, temperature) in dimer model systems. We demonstrate that vibrational-relaxation-enhanced exciton energy transfer (VREEET) is robust against the change of these characteristics of the system and occurs in wide ranges of the investigated parameters. With simulations performed on a heptamer model inspired by the Fenna-Matthews-Olson (FMO) complex, we show that this mechanism can be even more significant in larger systems at T = 300 K. Our results suggests that VREEET might be prevalent in light-harvesting complexes.

Polarization correlation study of the electron-impact excitation of neon and argon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khakoo, M.A.; McConkey, J.W.

1986-08-11

The recent development of a circular polarization analyzer for the vacuum ultraviolet spectral region has enabled a Stokes parameter analysis to be carried out for the excitation of neon and argon by 80-eV incident electrons. The results show that the transfer of angular momentum to the atom is positive and is in fact surprisingly ''heliumlike.'' Small deviations from total coherence were observed and are discussed.

Analysis of FORTE data to extract ionospheric parameters

NASA Astrophysics Data System (ADS)

Roussel-Dupré, Robert A.; Jacobson, Abram R.; Triplett, Laurie A.

2001-01-01

The ionospheric transfer function is derived for a spherically symmetric ionosphere with an arbitrary radial electron density profile in the limit where the radio frequencies of interest ω are much larger than the plasma frequency ωpe. An expansion of the transfer function to second order in the parameter X (= ω2pe/ω2) is carried out. In this limit the dispersive properties of the ionosphere are manifested as a frequency-dependent time of arrival that includes quadratic, cubic, and quartic terms in 1/ω. The coefficients of these terms are related to the total electron content (TEC) along the slant path from transmitter to receiver, the product of TEC and the longitudinal magnetic field strength along the slant path, and refractive bending and higher-order electron density profile effects, respectively. By fitting the time of arrival versus frequency of a transionospheric signal to a polynomial in 1/ω it is possible to extract the TEC, the longitudinal magnetic field strength, the peak electron density, and an effective thickness for the ionosphere. This exercise was carried out for a number of transionospheric pulses measured in the VHF by the FORTE satellite receiver and generated by the Los Alamos Portable Pulser. The results are compared with predictions derived from the International Reference Ionosphere and the United States Geological Survey geomagnetic field model.

The multistate impact parameter method for molecular charge exchange in nitrogen

NASA Technical Reports Server (NTRS)

Ioup, J. W.

1980-01-01

The multistate impact parameter method is applied to the calculation of total cross sections for low energy change transfer between nitrogen ions and nitrogen molecules. Experimental data showing the relationships between total cross section and ion energy for various pressures and electron ionization energies were obtained. Calculated and experimental cross section values from the work are compared with the experimental and theoretical results of other investigators.

Theoretical investigation of the charge-transfer properties in different meso-linked zinc porphyrins for highly efficient dye-sensitized solar cells.

PubMed

Namuangruk, Supawadee; Sirithip, Kanokkorn; Rattanatwan, Rattanawelee; Keawin, Tinnagon; Kungwan, Nawee; Sudyodsuk, Taweesak; Promarak, Vinich; Surakhot, Yaowarat; Jungsuttiwong, Siriporn

2014-06-28

The charge transfer effect of different meso-substituted linkages on porphyrin analogue 1 (A1, B1 and C1) was theoretically investigated using density functional theory (DFT) and time-dependent DFT (TDDFT) calculations. The calculated geometry parameters and natural bond orbital analysis reveal that the twisted conformation between porphyrin macrocycle and meso-substituted linkages leads to blocking of the conjugation of the conjugated backbone, and the frontier molecular orbital plot shows that the intramolecular charge transfer of A1, B1 and C1 hardly takes place. In an attempt to improve the photoinduced intramolecular charge transfer ability of the meso-linked zinc porphyrin sensitizer, a strong electron-withdrawing group (CN) was introduced into the anchoring group of analogue 1 forming analogue 2 (A2, B2 and C2). The density difference plot of A2, B2 and C2 shows that the charge transfer properties dramatically improved. The electron injection process has been performed using TDDFT; the direct charge-transfer transition in the A2-(TiO2)38 interacting system takes place; our results strongly indicated that introducing electron-withdrawing groups into the acceptor part of porphyrin dyes can fine-tune the effective conjugation length of the π-spacer and improve intramolecular charge transfer properties, consequently inducing the electron injection process from the anchoring group of the porphyrin dye to the (TiO2)38 surface which may improve the conversion efficiency of the DSSCs. Our calculated results can provide valuable information and a promising outlook for computation-aided sensitizer design with anticipated good properties in further experimental synthesis.

Coupled mode effects on energy transfer in weakly coupled, two-temperature plasmas

NASA Astrophysics Data System (ADS)

Vorberger, J.; Gericke, D. O.

2009-08-01

The effects of collective modes on the temperature relaxation in fully ionized, weakly coupled plasmas are investigated. A coupled mode (CM) formula for the electron-ion energy transfer is derived within the random phase approximation and it is shown how it can be evaluated using standard methods. The CM rates are considerably smaller than rates based on Fermi's golden rule for some parameters and identical for others. It is shown how the CM effects are connected to the occurrence of ion acoustic modes and when they occur. Interestingly, CM effects occur also for plasmas with very high electron temperatures; a regime, where the Landau-Spitzer approach is believed to be accurate.

Out-of-plane heat transfer in van der Waals stacks through electron-hyperbolic phonon coupling

NASA Astrophysics Data System (ADS)

Tielrooij, Klaas-Jan; Hesp, Niels C. H.; Principi, Alessandro; Lundeberg, Mark B.; Pogna, Eva A. A.; Banszerus, Luca; Mics, Zoltán; Massicotte, Mathieu; Schmidt, Peter; Davydovskaya, Diana; Purdie, David G.; Goykhman, Ilya; Soavi, Giancarlo; Lombardo, Antonio; Watanabe, Kenji; Taniguchi, Takashi; Bonn, Mischa; Turchinovich, Dmitry; Stampfer, Christoph; Ferrari, Andrea C.; Cerullo, Giulio; Polini, Marco; Koppens, Frank H. L.

2018-01-01

Van der Waals heterostructures have emerged as promising building blocks that offer access to new physics, novel device functionalities and superior electrical and optoelectronic properties1-7. Applications such as thermal management, photodetection, light emission, data communication, high-speed electronics and light harvesting8-16 require a thorough understanding of (nanoscale) heat flow. Here, using time-resolved photocurrent measurements, we identify an efficient out-of-plane energy transfer channel, where charge carriers in graphene couple to hyperbolic phonon polaritons17-19 in the encapsulating layered material. This hyperbolic cooling is particularly efficient, giving picosecond cooling times for hexagonal BN, where the high-momentum hyperbolic phonon polaritons enable efficient near-field energy transfer. We study this heat transfer mechanism using distinct control knobs to vary carrier density and lattice temperature, and find excellent agreement with theory without any adjustable parameters. These insights may lead to the ability to control heat flow in van der Waals heterostructures.

Real-time radon monitoring at Stromboli volcano: influence of environmental parameters on 222Rn degassing

NASA Astrophysics Data System (ADS)

Cigolini, C.; Ripepe, M.; Poggi, P.; Laiolo, M.

2008-12-01

Two real-time stations for radon monitoring are currently operative at Stromboli volcano. The 222Rn electronic dosimeters are interfaced with an electronic board connected to a radiomodem for wireless data transfer (through a directional antenna) to a receiving station at the volcano observatory (COA). Radon activity data and enviromental parameters (soil temperature and atmospheric pressure) are sampled every 15 minutes and are instantaneously elaborated and transferred via web so that they can be checked in remote. Collected time series show that there is an overall inverse correlation between radon emissions and seasonal temperature variations. Signal processing analysis show that radon emissions in sectors of diffuse degassing are modulated by tidal forces as well. In addition, radon activities recorded at the summit station, located along the summit fracture zone where the gas flux is concentrated, are positively correlated with changes in atmospheric pressure and confirm the occurrence of the 'atmospheric stack effect'. It is not excluded that this process may play an active role in modulating Stromboli explosivity.

Hydrodynamic and thermal modeling of two-dimensional microdroplet arrays for digitized heat transfer

NASA Astrophysics Data System (ADS)

Baird, Eric S.

This document describes hydrodynamic and thermal modeling of two-dimensional microdroplet arrays for use in digitized heat transfer (DHT), a novel active thermal management technique for high power density electronics and integrated microsystems. In DHT, thermal energy is transported by a discrete array of electrostatically activated microdroplets of liquid metals, alloys or aqueous solutions with the potential of supporting significantly higher heat transfer rates than classical air-cooled heat sinks. Actuation methods for dispensing and transporting individual fluid slugs with a high degree of precision and programmability are described, with simple approximate formulae for net forces for steady state and transient velocities in terms of known parameters. A modified cavity flow solver is developed to provide details on the internal flow properties of a translating microdroplet and used to detail the effects of droplet curvature, internal mixing, Peclet number and other parameters on the heat transfer capabilities of a discretized liquid flow. The concept of Nusselt number is generalized to an individual fluid slug and shown to oscillate with a period equal to the droplet's mixing rate. In whole, DHT is demonstrated to be a viable new alternative for achieving the most important objectives of electronic cooling (i.e., minimization of the maximum substrate temperature, reduction of the substrate temperature gradient and removal of substrate hot spots) and a sound fundamental description of the method's electro-, hydro- and thermodynamics is provided.

Electronic energy transfer through non-adiabatic vibrational-electronic resonance. II. 1D spectra for a dimer.

PubMed

Tiwari, Vivek; Jonas, David M

2018-02-28

Vibrational-electronic resonance in photosynthetic pigment-protein complexes invalidates Förster's adiabatic framework for interpreting spectra and energy transfer, thus complicating determination of how the surrounding protein affects pigment properties. This paper considers the combined effects of vibrational-electronic resonance and inhomogeneous variations in the electronic excitation energies of pigments at different sites on absorption, emission, circular dichroism, and hole-burning spectra for a non-degenerate homodimer. The non-degenerate homodimer has identical pigments in different sites that generate differences in electronic energies, with parameters loosely based on bacteriochlorophyll a pigments in the Fenna-Matthews-Olson antenna protein. To explain the intensity borrowing, the excited state vibrational-electronic eigenvectors are discussed in terms of the vibrational basis localized on the individual pigments, as well as the correlated/anti-correlated vibrational basis delocalized over both pigments. Compared to those in the isolated pigment, vibrational satellites for the correlated vibration have the same frequency and precisely a factor of 2 intensity reduction through vibrational delocalization in both absorption and emission. Vibrational satellites for anti-correlated vibrations have their relaxed emission intensity reduced by over a factor 2 through vibrational and excitonic delocalization. In absorption, anti-correlated vibrational satellites borrow excitonic intensity but can be broadened away by the combination of vibronic resonance and site inhomogeneity; in parallel, their vibronically resonant excitonic partners are also broadened away. These considerations are consistent with photosynthetic antenna hole-burning spectra, where sharp vibrational and excitonic satellites are absent. Vibrational-excitonic resonance barely alters the inhomogeneously broadened linear absorption, emission, and circular dichroism spectra from those for a purely electronic excitonic coupling model. Energy transfer can leave excess energy behind as vibration on the electronic ground state of the donor, allowing vibrational relaxation on the donor's ground electronic state to make energy transfer permanent by removing excess energy from the excited electronic state of the dimer.

Electronic energy transfer through non-adiabatic vibrational-electronic resonance. II. 1D spectra for a dimer

NASA Astrophysics Data System (ADS)

Tiwari, Vivek; Jonas, David M.

2018-02-01

Vibrational-electronic resonance in photosynthetic pigment-protein complexes invalidates Förster's adiabatic framework for interpreting spectra and energy transfer, thus complicating determination of how the surrounding protein affects pigment properties. This paper considers the combined effects of vibrational-electronic resonance and inhomogeneous variations in the electronic excitation energies of pigments at different sites on absorption, emission, circular dichroism, and hole-burning spectra for a non-degenerate homodimer. The non-degenerate homodimer has identical pigments in different sites that generate differences in electronic energies, with parameters loosely based on bacteriochlorophyll a pigments in the Fenna-Matthews-Olson antenna protein. To explain the intensity borrowing, the excited state vibrational-electronic eigenvectors are discussed in terms of the vibrational basis localized on the individual pigments, as well as the correlated/anti-correlated vibrational basis delocalized over both pigments. Compared to those in the isolated pigment, vibrational satellites for the correlated vibration have the same frequency and precisely a factor of 2 intensity reduction through vibrational delocalization in both absorption and emission. Vibrational satellites for anti-correlated vibrations have their relaxed emission intensity reduced by over a factor 2 through vibrational and excitonic delocalization. In absorption, anti-correlated vibrational satellites borrow excitonic intensity but can be broadened away by the combination of vibronic resonance and site inhomogeneity; in parallel, their vibronically resonant excitonic partners are also broadened away. These considerations are consistent with photosynthetic antenna hole-burning spectra, where sharp vibrational and excitonic satellites are absent. Vibrational-excitonic resonance barely alters the inhomogeneously broadened linear absorption, emission, and circular dichroism spectra from those for a purely electronic excitonic coupling model. Energy transfer can leave excess energy behind as vibration on the electronic ground state of the donor, allowing vibrational relaxation on the donor's ground electronic state to make energy transfer permanent by removing excess energy from the excited electronic state of the dimer.

Theoretical simulations on the antioxidant mechanism of naturally occurring flavonoid: A DFT approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Praveena, R.; Sadasivam, K.

Synthetic antioxidants such as butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) are found to be toxic, hence non-carcinogenic naturally occurring radical scavengers especially flavonoids have gained considerable importance in the past two decades. In the present investigation, the radical scavenging activity of C-glycosyl flavonoids is evaluated using theoretical approach which could broaden its scope in therapeutic applications. Gas and solvent phase studies of structural and molecular characteristics of C-glycosyl flavonoid, isovitexin is investigated through hydrogen atom transfer mechanism (HAT), Electron transfer-proton transfer (ET–PT) and Sequential proton loss electron transfer (SPLET) by Density functional theory (DFT) using hybrid parameters. The computedmore » values of the adiabatic ionization potential, electron affinity, hardness, softness, electronegativity and electrophilic index indicate that isovitexin possess good radical scavenging activity. The behavior of different –OH groups in polyphenolic compounds is assessed by considering electronic effects of the neighbouring groups and the overall geometry of molecule which in turn helps in analyzing the antioxidant capacity of the polyphenolic molecule. The studies indicate that the H–atom abstraction from 4’–OH site is preferred during the radical scavenging process. From Mulliken spin density analysis and FMOs, B–ring is found to be more delocalized center and capable of electron donation. Comparison of antioxidant activity of vitexin and isovitexin leads to the conclusion that isovitexin acts as a better radical scavenger. This is an evidence for the importance of position of glucose unit in the flavonoid.« less

Electronic structure and optical properties of Si, Ge and diamond in the lonsdaleite phase.

PubMed

De, Amrit; Pryor, Craig E

2014-01-29

Crystalline semiconductors may exist in different polytypic phases with significantly different electronic and optical properties. In this paper, we calculate the electronic structure and optical properties of diamond, Si and Ge in the lonsdaleite (hexagonal diamond) phase using a transferable model empirical pseudopotential method with spin–orbit interactions. We calculate their band structures and extract various relevant parameters. Differences between the cubic and hexagonal phases are highlighted by comparing their densities of states. While diamond and Si remain indirect gap semiconductors in the lonsdaleite phase, Ge transforms into a direct gap semiconductor with a much smaller bandgap. We also calculate complex dielectric functions for different optical polarizations and find strong optical anisotropy. We further provide expansion parameters for the dielectric functions in terms of Lorentz oscillators.

Numerical modeling of heat-transfer and the influence of process parameters on tailoring the grain morphology of IN718 in electron beam additive manufacturing

DOE PAGES

Raghavan, Narendran; Dehoff, Ryan; Pannala, Sreekanth; ...

2016-04-26

The fabrication of 3-D parts from CAD models by additive manufacturing (AM) is a disruptive technology that is transforming the metal manufacturing industry. The correlation between solidification microstructure and mechanical properties has been well understood in the casting and welding processes over the years. This paper focuses on extending these principles to additive manufacturing to understand the transient phenomena of repeated melting and solidification during electron beam powder melting process to achieve site-specific microstructure control within a fabricated component. In this paper, we have developed a novel melt scan strategy for electron beam melting of nickel-base superalloy (Inconel 718) andmore » also analyzed 3-D heat transfer conditions using a parallel numerical solidification code (Truchas) developed at Los Alamos National Laboratory. The spatial and temporal variations of temperature gradient (G) and growth velocity (R) at the liquid-solid interface of the melt pool were calculated as a function of electron beam parameters. By manipulating the relative number of voxels that lie in the columnar or equiaxed region, the crystallographic texture of the components can be controlled to an extent. The analysis of the parameters provided optimum processing conditions that will result in columnar to equiaxed transition (CET) during the solidification. Furthermore, the results from the numerical simulations were validated by experimental processing and characterization thereby proving the potential of additive manufacturing process to achieve site-specific crystallographic texture control within a fabricated component.« less

Synthesis and characterization of highly conductive charge-transfer complexes using positron annihilation spectroscopy

NASA Astrophysics Data System (ADS)

Adam, Abdel Majid A.; Refat, Moamen S.; Sharshar, T.; Heiba, Z. K.

Molecular charge-transfer complexes of the tetramethylethylenediamine (TMEDA) with picric acid (Pi-OH), benzene-1,4-diol (QL), tin(IV) tetrachloride (SnCl4), iodine, bromine, and zinc chloride (ZnCl2) have been synthesized and investigated by elemental and thermal analysis, electronic, infrared, Raman and proton-NMR, energy-dispersive X-ray spectroscopy, X-ray powder diffraction and positron annihilation lifetime spectroscopy, and scanning electron microscopy. In this work, three types of acceptors π-acceptors (Pi-OH and QL), σ-acceptors (iodine and bromine), and vacant orbital acceptors (SnCl4 and ZnCl2) were covered. The results of elemental analysis indicated that the CT complexes were formed with ratios 1:1 and 1:2 for QL, SnCl4, and ZnCl2 acceptors and iodine, Pi-OH, and Br2 acceptors, respectively. The type of chelating between the TMEDA donor and the mentioned acceptors depends upon the behavior of both items. The positron annihilation lifetime parameters were found to be dependent on the structure, electronic configuration, and the power of acceptors. The correlation between these parameters and the molecular weight and biological activities of studied complexes was also observed. Regarding the electrical properties, the AC conductivity and the dielectric coefficients were measured as a function of frequency at room temperature. The TMEDA charge-transfer complexes were screened against antibacterial (Escherichia coli, Staphylococcus aureus, Bacillus subtilis, and Pseudomonas aeruginosa) and antifungal (Aspergillus flavus and Candida albicans) activities.

The Kinetics of Heterogeneous Electron Transfer Reactions in Polar Solvents

DTIC Science & Technology

1994-04-20

focussed on systems for which rate constants and activation parameters are available as a function of the solvent, and as a function of temperature . The... temperature . The role of reactant structure in determining the kinetic parameters is also considered. Double layer effects both at unmodified and...that the Gibbs activation energy to form a monovalent cation from a neutral molecule via electrooxidation is different from that to form a monovalent

Experimental verification of orbital engineering at the atomic scale: Charge transfer and symmetry breaking in nickelate heterostructures

NASA Astrophysics Data System (ADS)

Phillips, Patrick J.; Rui, Xue; Georgescu, Alexandru B.; Disa, Ankit S.; Longo, Paolo; Okunishi, Eiji; Walker, Fred; Ahn, Charles H.; Ismail-Beigi, Sohrab; Klie, Robert F.

2017-05-01

Epitaxial strain, layer confinement, and inversion symmetry breaking have emerged as powerful new approaches to control the electronic and atomic-scale structural properties of complex metal oxides. Trivalent rare-earth (RE) nickelate R E NiO3 heterostructures have been shown to be exemplars since the orbital occupancy, degeneracy, and, consequently, electronic/magnetic properties can be altered as a function of epitaxial strain, layer thickness, and superlattice structure. One recent example is the tricomponent LaTiO3-LaNiO3-LaAlO3 superlattice which exhibits charge transfer and orbital polarization as the result of its interfacial dipole electric field. A crucial step towards control of these parameters for future electronic and magnetic device applications is to develop an understanding of both the magnitude and range of the octahedral network's response towards interfacial strain and electric fields. An approach that provides atomic-scale resolution and sensitivity towards the local octahedral distortions and orbital occupancy is therefore required. Here, we employ atomic-resolution imaging coupled with electron spectroscopies and first-principles theory to examine the role of interfacial charge transfer and symmetry breaking in a tricomponent nickelate superlattice system. We find that nearly complete charge transfer occurs between the LaTiO3 and LaNiO3 layers, resulting in a mixed Ni2 +/Ni3 + valence state. We further demonstrate that this charge transfer is highly localized with a range of about 1 unit cell within the LaNiO3 layers. We also show how Wannier-function-based electron counting provides a simple physical picture of the electron distribution that connects directly with formal valence charges. The results presented here provide important feedback to synthesis efforts aimed at stabilizing new electronic phases that are not accessible by conventional bulk or epitaxial film approaches.

Effect of anode polarization on biofilm formation and electron transfer in Shewanella oneidensis/graphite felt microbial fuel cells.

PubMed

Pinto, David; Coradin, Thibaud; Laberty-Robert, Christel

2018-04-01

In microbial fuel cells, electricity generation is assumed by bacterial degradation of low-grade organics generating electrons that are transferred to an electrode. The nature and efficiency of the electron transfer from the bacteria to the electrodes are determined by several chemical, physical and biological parameters. Specifically, the application of a specific potential at the bioanode has been shown to stimulate the formation of an electro-active biofilm, but the underlying mechanisms remain poorly understood. In this study, we have investigated the effect of an applied potential on the formation and electroactivity of biofilms established by Shewanella oneidensis bacteria on graphite felt electrodes in single- and double-chamber reactor configurations in oxic conditions. Using amperometry, cyclic voltammetry, and OCP/Power/Polarization curves techniques, we showed that a potential ranging between -0.3V and +0.5V (vs. Ag/AgCl/KCl sat.) and its converse application to a couple of electrodes leads to different electrochemical behaviors, anodic currents and biofilm architectures. For example, when the bacteria were confined in the anodic compartment of a double-chamber cell, a negative applied potential (-0.3V) at the bioanode favors a mediated electron transfer correlated with the progressive formation of a biofilm that fills the felt porosity and bridges the graphite fibers. In contrast, a positive applied potential (+0.3V) at the bioanode stimulates a direct electron transfer resulting in the fast-bacterial colonization of the fibers only. These results provide significant insight for the understanding of the complex bacteria-electrode interactions in microbial fuel cells. Copyright © 2017 Elsevier B.V. All rights reserved.

Theory of electron transfer and molecular state in DNA

NASA Astrophysics Data System (ADS)

Endres, Robert Gunter

2002-09-01

In this thesis, a mechanism for long-range electron transfer in DNA and a systematic search for high conductance DNA are developed. DNA is well known for containing the genetic code of all living species. On the other hand, there are some experimental indications that DNA can mediate effectively long-range electron transfer leading to the concept of chemistry at a distance. This can be important for DNA damage and healing. In the first part of the thesis, a possible mechanism for long-range electron transfer is introduced. The weak distance dependent electron transfer was experimentally observed using transition metal intercalators for donor and acceptor. In our model calculations, the transfer is mediated by the molecular analogue of a Kondo bound state well known from solid state physics of mixed-valence rare-earth compounds. We believe this is quite realistic, since localized d orbitals of the transition metal ions could function as an Anderson impurity embedded in a reservoir of rather delocalized molecular orbitals of the intercalator ligands and DNA pi orbitals. The effective Anderson model is solved with a physically intuitive variational ansatz as well as with the essentially exact DMRG method. The electronic transition matrix element, which is important because it contains the donor-acceptor distance dependence, is obtained with the Mulliken-Hush algorithm as well as from Born-Oppenheimer potential energy surfaces. Our possible explanation of long-range electron transfer is put in context to other more conventional mechanisms which also could lead to similar behavior. Another important issue of DNA is its possible use for nano-technology. Although DNA's mechanical properties are excellent, the question whether it can be conducting and be used for nano-wires is highly controversial. Experimentally, DNA shows conducting, semi-conducting and insulating properties. Motivated by these wide ranging experimental results on the conductivity of DNA, we have embarked on a theoretical effort to ascertain what conditions might induce such remarkable behavior. We use a combination of an ab initio density functional theory method and a parameterized Huckel-Slater-Koster model. Our focus here is to examine whether any likely DNA structures or environments can yield reduced activation gaps to conduction or enhanced electronic overlaps. In particular, we study a hypothetical stretched ribbon structure, A-, and B-form DNA, and the effects of counterions and humidity. Unlike solids, DNA and other molecules are considered soft condensed matter. Hence, we study the influence of vibrations upon the electronic structure of DNA. We calculate parameters for charge transfer rates between adjacent bases. We find good agreement between our estimated rates and recent experimental data assuming that torsional vibrations limit the charge transfer most significantly.

Different electronic and charge-transport properties of four organic semiconductors Tetraazaperopyrenes derivatives

NASA Astrophysics Data System (ADS)

Shi, Yarui; Wei, Huiling; Liu, Yufang

2015-03-01

Tetraazaperopyrenes (TAPPs) derivatives are high-performance n-type organic semiconductor material families with the remarkable long-term stabilities. The charge carrier mobilities in TAPPs derivatives crystals were calculated by the density functional theory (DFT) method combined with the Marcus-Hush electron-transfer theory. The existence of considerable C-H…F-C bonding defines the conformation of the molecular structure and contributes to its stability. We illustrated how it is possible to control the electronic and charge-transport parameters of TAPPs derivatives as a function of the positions, a type of the substituents. It is found that the core substitution of TAPPs has a drastic influence on the charge-transport mobilities. The maximum electron mobility value of the core-brominated 2,9-bis (perfluoroalkyl)-substituted TAPPs is 0.521 cm2 V-1 s-1, which appear in the orientation angle 95° and 275°. The results demonstrate that the TAPPs with bromine substituents in ortho positions exhibit the best charge-transfer efficiency among the four different TAPP derivatives.

Atomic bonding effects in annular dark field scanning transmission electron microscopy. I. Computational predictions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Odlyzko, Michael L.; Mkhoyan, K. Andre, E-mail: mkhoyan@umn.edu; Himmetoglu, Burak

2016-07-15

Annular dark field scanning transmission electron microscopy (ADF-STEM) image simulations were performed for zone-axis-oriented light-element single crystals, using a multislice method adapted to include charge redistribution due to chemical bonding. Examination of these image simulations alongside calculations of the propagation of the focused electron probe reveal that the evolution of the probe intensity with thickness exhibits significant sensitivity to interatomic charge transfer, accounting for observed thickness-dependent bonding sensitivity of contrast in all ADF-STEM imaging conditions. Because changes in image contrast relative to conventional neutral atom simulations scale directly with the net interatomic charge transfer, the strongest effects are seen inmore » crystals with highly polar bonding, while no effects are seen for nonpolar bonding. Although the bonding dependence of ADF-STEM image contrast varies with detector geometry, imaging parameters, and material temperature, these simulations predict the bonding effects to be experimentally measureable.« less

Poly(methylene blue) functionalized graphene modified carbon ionic liquid electrode for the electrochemical detection of dopamine.

PubMed

Sun, Wei; Wang, Yuhua; Zhang, Yuanyuan; Ju, Xiaomei; Li, Guangjiu; Sun, Zhenfan

2012-11-02

An ionic liquid 1-butylpyridinium hexafluorophosphate based carbon ionic liquid electrode (CILE) was used as the substrate electrode and a poly(methylene blue) (PMB) functionalized graphene (GR) composite film was co-electrodeposited on CILE surface by cyclic voltammetry. The PMB-GR/CILE exhibited better electrochemical performances with higher conductivity and lower electron transfer resistance. Electrochemical behavior of dopamine (DA) was further investigated by cyclic voltammetry and a pair of well-defined redox peaks appeared with the peak-to-peak separation (ΔE(p)) as 0.058V in 0.1 mol L(-1) pH 6.0 phosphate buffer solution, which proved a fast quasi-reversible electron transfer process on the modified electrode. Electrochemical parameters of DA on PMB-GR/CILE were calculated with the electron transfer number as 1.83, the charge transfer coefficients as 0.70, the apparent heterogeneous electron transfer rate constant as 1.72 s(-1) and the diffusional coefficient (D) as 3.45×10(-4) cm(2) s(-1), respectively. Under the optimal conditions with differential pulse voltammetric measurement, the linear relationship between the oxidation peak current of DA and its concentration was obtained in the range from 0.02 to 800.0 μmol L(-1) with the detection limit as 5.6 nmol L(-1) (3σ). The coexisting substances exhibited no interference and PMB-GR/CILE was applied to the detection of DA injection samples and human urine samples with satisfactory results. Copyright © 2012 Elsevier B.V. All rights reserved.

Electrochemistry of hemoglobin entrapped in a Nafion/nano-ZnO film on carbon ionic liquid electrode.

PubMed

Sun, Wei; Zhai, ZiQin; Wang, DanDan; Liu, ShuFeng; Jiao, Kui

2009-02-01

A stable composite film composed of the ionomer Nafion, the ZnO nanoparticle and the protein hemoglobin was cast on the surface of an ionic liquid modified carbon paste electrode (CILE) to establish a modified electrode denoted as Nafion/nano-ZnO/Hb/CILE. UV-vis and FT-IR spectrum showed that hemoglobin in the film retained its native conformation. The electrochemical behaviors of hemoglobin entrapped in the film were carefully investigated with cyclic voltammetry. A pair of well-defined and quasi-reversible redox voltammetric peaks for Hb Fe(III)/Fe(II) was obtained with the standard potential (E(0)') located at -0.344 V (vs. SCE) in phosphate buffer solution (PBS, pH 7.0), which was attributed to the direct electron transfer of Hb with electrode in the microenvironments of ZnO nanoparticle and ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF(6)). The electrochemical parameters of Hb in the composite film were further carefully calculated with the results of the electron-transfer rate constant (k(s)) as 0.139 s(-1), the charge transfer coefficient (alpha) as 0.413 and the number of electron transferred (n) as 0.95. The Hb modified electrode showed good electrocatalytic ability toward the reduction of trichloroacetic acid (TCA).

Tight-Binding Study of Polarons in Two-Dimensional Systems: Implications for Organic Field-Effect Transistor Materials

NASA Astrophysics Data System (ADS)

Lei, Jie

2011-03-01

In order to understand the electronic and transport properties of organic field-effect transistor (FET) materials, we theoretically studied the polarons in two-dimensional systems using a tight-binding model with the Holstein type and Su--Schrieffer--Heeger type electron--lattice couplings. By numerical calculations, it was found that a carrier accepts four kinds of localization, which are named the point polaron, two-dimensional polaron, one-dimensional polaron, and the extended state. The degree of localization is sensitive to the following parameters in the model: the strength and type of electron--lattice couplings, and the signs and relative magnitudes of transfer integrals. When a parameter set for a single-crystal phase of pentacene is applied within the Holstein model, a considerably delocalized hole polaron is found, consistent with the bandlike transport mechanism.

The central active site arginine in sulfite oxidizing enzymes alters kinetic properties by controlling electron transfer and redox interactions.

PubMed

Hsiao, Ju-Chun; McGrath, Aaron P; Kielmann, Linda; Kalimuthu, Palraj; Darain, Farzana; Bernhardt, Paul V; Harmer, Jeffrey; Lee, Mihwa; Meyers, Kimberley; Maher, Megan J; Kappler, Ulrike

2018-01-01

A central conserved arginine, first identified as a clinical mutation leading to sulfite oxidase deficiency, is essential for catalytic competency of sulfite oxidizing molybdoenzymes, but the molecular basis for its effects on turnover and substrate affinity have not been fully elucidated. We have used a bacterial sulfite dehydrogenase, SorT, which lacks an internal heme group, but transfers electrons to an external, electron accepting cytochrome, SorU, to investigate the molecular functions of this arginine residue (Arg78). Assay of the SorT Mo centre catalytic competency in the absence of SorU showed that substitutions in the central arginine (R78Q, R78K and R78M mutations) only moderately altered SorT catalytic properties, except for R78M which caused significant reduction in SorT activity. The substitutions also altered the Mo-centre redox potentials (Mo VI/V potential lowered by ca. 60-80mV). However, all Arg78 mutations significantly impaired the ability of SorT to transfer electrons to SorU, where activities were reduced 17 to 46-fold compared to SorT WT , precluding determination of kinetic parameters. This was accompanied by the observation of conformational changes in both the introduced Gln and Lys residues in the crystal structure of the enzymes. Taking into account data collected by others on related SOE mutations we propose that the formation and maintenance of an electron transfer complex between the Mo centre and electron accepting heme groups is the main function of the central arginine, and that the reduced turnover and increases in K Msulfite are caused by the inefficient operation of the oxidative half reaction of the catalytic cycle in enzymes carrying these mutations. Copyright © 2017 Elsevier B.V. All rights reserved.

Charge-density analysis of a protein structure at subatomic resolution: the human aldose reductase case.

PubMed

Guillot, Benoît; Jelsch, Christian; Podjarny, Alberto; Lecomte, Claude

2008-05-01

The valence electron density of the protein human aldose reductase was analyzed at 0.66 angstroms resolution. The methodological developments in the software MoPro to adapt standard charge-density techniques from small molecules to macromolecular structures are described. The deformation electron density visible in initial residual Fourier difference maps was significantly enhanced after high-order refinement. The protein structure was refined after transfer of the experimental library multipolar atom model (ELMAM). The effects on the crystallographic statistics, on the atomic thermal displacement parameters and on the structure stereochemistry are analyzed. Constrained refinements of the transferred valence populations Pval and multipoles Plm were performed against the X-ray diffraction data on a selected substructure of the protein with low thermal motion. The resulting charge densities are of good quality, especially for chemical groups with many copies present in the polypeptide chain. To check the effect of the starting point on the result of the constrained multipolar refinement, the same charge-density refinement strategy was applied but using an initial neutral spherical atom model, i.e. without transfer from the ELMAM library. The best starting point for a protein multipolar refinement is the structure with the electron density transferred from the database. This can be assessed by the crystallographic statistical indices, including Rfree, and the quality of the static deformation electron-density maps, notably on the oxygen electron lone pairs. The analysis of the main-chain bond lengths suggests that stereochemical dictionaries would benefit from a revision based on recently determined unrestrained atomic resolution protein structures.

Resonant electronic excitation energy transfer by exchange mechanism in the quantum dot system

NASA Astrophysics Data System (ADS)

Chikalova-Luzina, O. P.; Samosvat, D. M.; Vyatkin, V. M.; Zegrya, G. G.

2017-11-01

A microscopic theory of nonradiative resonance energy transfer between spherical A3B5 semiconductor quantum dots by the exchange mechanism is suggested. The interdot Coulomb interaction is taken into consideration. It is assumed that the quantum dot-donor and the quantum dot-acceptor are made from the same A3B5 compound and are embedded in the matrix of another material that produces potential barriers for electrons and holes. The dependences of the energy transfer rate on the quantum-dot system parameters are found in the frame of the Kane model that provides the most adequate description of the real spectra of A3B5 semiconductors. The analytical treatment is carried out with using the density matrix method, which enabled us to perform an energy transfer analysis both in the weak-interaction approximation and in the strong-interaction approximation. The numerical calculations showed the saturation of the energy transfer rate at the distances between the donor and the acceptor approaching the contact one. The contributions of the exchange and direct Coulomb intractions can be of the same order at the small distances and can have the same value in the saturation range.

Electron Raman scattering in a strained ZnO/MgZnO double quantum well

NASA Astrophysics Data System (ADS)

Mojab-abpardeh, M.; Karimi, M. J.

2018-02-01

In this work, the electron Raman scattering in a strained ZnO / MgZnO double quantum wells is studied. The energy eigenvalues and the wave functions are obtained using the transfer matrix method. The effects of Mg composition, well width and barrier width on the internal electric field in well and barrier layers are investigated. Then, the influences of these parameters on the differential cross-section of electron Raman scattering are studied. Results indicate that the position, magnitude and the number of the peaks depend on the Mg composition, well width and barrier width.

Effect of magnetic ion Ni doping for Cu in the CuO 2 plane on electronic structure and superconductivity on Y123 cuprate

NASA Astrophysics Data System (ADS)

Cao, Shixun; Li, Pinglin; Cao, Guixin; Zhang, Jincang

2003-05-01

The YBa2Cu3-xNixO7-δ with x=0-0.4 have been studied using positron annihilation technique. The changes of positron annihilation parameters with the Ni substitution concentration x are given. From the change of electronic density ne and Tc, it would prove that the localized carriers (electron and hole) in Cu-O chain and CuO2 planes have enormous influence on superconductivity by affecting charge transfer between the reservoir layer and CuO2 planes.

Exciton-to-Dopant Energy Transfer in Mn-Doped Cesium Lead Halide Perovskite Nanocrystals.

PubMed

Parobek, David; Roman, Benjamin J; Dong, Yitong; Jin, Ho; Lee, Elbert; Sheldon, Matthew; Son, Dong Hee

2016-12-14

We report the one-pot synthesis of colloidal Mn-doped cesium lead halide (CsPbX 3 ) perovskite nanocrystals and efficient intraparticle energy transfer between the exciton and dopant ions resulting in intense sensitized Mn luminescence. Mn-doped CsPbCl 3 and CsPb(Cl/Br) 3 nanocrystals maintained the same lattice structure and crystallinity as their undoped counterparts with nearly identical lattice parameters at ∼0.2% doping concentrations and no signature of phase separation. The strong sensitized luminescence from d-d transition of Mn 2+ ions upon band-edge excitation of the CsPbX 3 host is indicative of sufficiently strong exchange coupling between the charge carriers of the host and dopant d electrons mediating the energy transfer, essential for obtaining unique properties of magnetically doped quantum dots. Highly homogeneous spectral characteristics of Mn luminescence from an ensemble of Mn-doped CsPbX 3 nanocrystals and well-defined electron paramagnetic resonance spectra of Mn 2+ in host CsPbX 3 nanocrystal lattices suggest relatively uniform doping sites, likely from substitutional doping at Pb 2+ . These observations indicate that CsPbX 3 nanocrystals, possessing many superior optical and electronic characteristics, can be utilized as a new platform for magnetically doped quantum dots expanding the range of optical, electronic, and magnetic functionality.

In vivo quantification of demyelination and recovery using compartment-specific diffusion MRI metrics validated by electron microscopy.

PubMed

Jelescu, Ileana O; Zurek, Magdalena; Winters, Kerryanne V; Veraart, Jelle; Rajaratnam, Anjali; Kim, Nathanael S; Babb, James S; Shepherd, Timothy M; Novikov, Dmitry S; Kim, Sungheon G; Fieremans, Els

2016-05-15

There is a need for accurate quantitative non-invasive biomarkers to monitor myelin pathology in vivo and distinguish myelin changes from other pathological features including inflammation and axonal loss. Conventional MRI metrics such as T2, magnetization transfer ratio and radial diffusivity have proven sensitivity but not specificity. In highly coherent white matter bundles, compartment-specific white matter tract integrity (WMTI) metrics can be directly derived from the diffusion and kurtosis tensors: axonal water fraction, intra-axonal diffusivity, and extra-axonal radial and axial diffusivities. We evaluate the potential of WMTI to quantify demyelination by monitoring the effects of both acute (6weeks) and chronic (12weeks) cuprizone intoxication and subsequent recovery in the mouse corpus callosum, and compare its performance with that of conventional metrics (T2, magnetization transfer, and DTI parameters). The changes observed in vivo correlated with those obtained from quantitative electron microscopy image analysis. A 6-week intoxication produced a significant decrease in axonal water fraction (p<0.001), with only mild changes in extra-axonal radial diffusivity, consistent with patchy demyelination, while a 12-week intoxication caused a more marked decrease in extra-axonal radial diffusivity (p=0.0135), consistent with more severe demyelination and clearance of the extra-axonal space. Results thus revealed increased specificity of the axonal water fraction and extra-axonal radial diffusivity parameters to different degrees and patterns of demyelination. The specificities of these parameters were corroborated by their respective correlations with microstructural features: the axonal water fraction correlated significantly with the electron microscopy derived total axonal water fraction (ρ=0.66; p=0.0014) but not with the g-ratio, while the extra-axonal radial diffusivity correlated with the g-ratio (ρ=0.48; p=0.0342) but not with the electron microscopy derived axonal water fraction. These parameters represent promising candidates as clinically feasible biomarkers of demyelination and remyelination in the white matter. Copyright © 2016 Elsevier Inc. All rights reserved.

The Effects of Channel Curvature and Protrusion Height on Nucleate Boiling and the Critical Heat Flux of a Simulated Electronic Chip

DTIC Science & Technology

1994-05-01

parameters and geometry factor. 57 3.2 Laminar sublayer and buffer layer thicknesses for geometry of Mudawar and Maddox.ŝ 68 3.3 Correlation constants...transfer from simulated electronic chip heat sources that are flush with the flow channel wall. Mudawar and Maddox2" have studied enhanced surfaces...bias error was not estimated; however, the percentage of heat loss measured compares with that previously reported by Mudawar and Maddox19 for a

Commissioning of the Electron-Positron Collider VEPP-2000 after the Upgrade

NASA Astrophysics Data System (ADS)

Shatunov, Yu.; Belikov, O.; Berkaev, D.; Gorchakov, K.; Zharinov, Yu.; Zemlyanskii, I.; Kasaev, A.; Kirpotin, A.; Koop, I.; Lysenko, A.; Motygin, S.; Perevedentsev, E.; Prosvetov, V.; Rabusov, D.; Rogovskii, Yu.; Senchenko, A.; Timoshenko, M.; Shatilov, D.; Shatunov, P.; Shvarts, D.

2018-05-01

The VEPP-2000 electron-positron collider has been operating at BINP since 2010. Applying the concept of round colliding beams allows us to reach the record value of the beam-beam parameter, ξ 0.12. The VEPP-2000 upgrade, including the connection to the new BINP Injection Complex, the improvement of the BEP booster, and the BEP-VEPP-2000 transfer channels for operation at 1 GeV, substantially increases the installation luminosity. Data collection is in progress.

Electron-transfer mediator for a NAD-glucose dehydrogenase-based glucose sensor.

PubMed

Kim, Dong-Min; Kim, Min-yeong; Reddy, Sanapalli S; Cho, Jaegeol; Cho, Chul-ho; Jung, Suntae; Shim, Yoon-Bo

2013-12-03

A new electron-transfer mediator, 5-[2,5-di (thiophen-2-yl)-1H-pyrrol-1-yl]-1,10-phenanthroline iron(III) chloride (FePhenTPy) oriented to the nicotinamide adenine dinucleotide-dependent-glucose dehydrogenase (NAD-GDH) system was synthesized through a Paal-Knorr condensation reaction. The structure of the mediator was confirmed by Fourier-transform infrared spectroscopy, proton and carbon nucler magnetic resonance spectroscopy, and mass spectroscopy, and its electron-transfer characteristic for a glucose sensor was investigated using voltammetry and impedance spectroscopy. A disposable amperometric glucose sensor with NAD-GDH was constructed with FePhenTPy as an electron-transfer mediator on a screen printed carbon electrode (SPCE) and its performance was evaluated, where the addition of reduces graphene oxide (RGO) to the mediator showed the enhanced sensor performance. The experimental parameters to affect the analytical performance and the stability of the proposed glucose sensor were optimized, and the sensor exhibited a dynamic range between 30 mg/dL and 600 mg/dL with the detection limit of 12.02 ± 0.6 mg/dL. In the real sample experiments, the interference effects by acetaminophen, ascorbic acid, dopamine, uric acid, caffeine, and other monosaccharides (fructose, lactose, mannose, and xylose) were completely avoided through coating the sensor surface with the Nafion film containing lead(IV) acetate. The reliability of proposed glucose sensor was evaluated by the determination of glucose in artificial blood and human whole blood samples.

Predicting the photoinduced electron transfer thermodynamics in polyfluorinated 1,3,5-triarylpyrazolines based on multiple linear free energy relationships†

PubMed Central

Verma, Manjusha; Chaudhry, Aneese F.; Fahrni, Christoph J.

2010-01-01

The photophysical properties of 1,3,5-triarylpyrazolines are strongly influenced by the nature and position of substituents attached to the aryl-rings, rendering this fluorophore platform well suited for the design of fluorescent probes utilizing a photoinduced electron transfer (PET) switching mechanism. To explore the tunability of two key parameters that govern the PET thermodynamics, the excited state energy ΔE00 and acceptor potential E(A/A−), a library of polyfluoro-substituted 1,3-diaryl-5-phenyl-pyrazolines was synthesized and characterized. The observed trends for the PET parameters were effectively captured through multiple Hammett linear free energy relationships (LFER) using a set of independent substituent constants for each of the two aryl rings. Given the lack of experimental Hammett constants for polyfluoro substituted aromatics, theoretically derived constants based on the electrostatic potential at the nucleus (EPN) of carbon atoms were employed as quantum chemical descriptors. The performance of the LFER was evaluated with a set of compounds that were not included in the training set, yielding a mean unsigned error of 0.05 eV for the prediction of the combined PET parameters. The outlined LFER approach should be well suited to design and optimize the performance of cation-responsive 1,3,5-triarylpyrazolines. PMID:19343239

Low-Field Nuclear Polarization Using Nitrogen Vacancy Centers in Diamonds

NASA Astrophysics Data System (ADS)

Hovav, Y.; Naydenov, B.; Jelezko, F.; Bar-Gill, N.

2018-02-01

It was recently demonstrated that bulk nuclear polarization can be obtained using nitrogen vacancy (NV) color centers in diamonds, even at ambient conditions. This is based on the optical polarization of the NV electron spin, and using several polarization transfer methods. One such method is the nuclear orientation via electron spin locking (NOVEL) sequence, where a spin-locked sequence is applied on the NV spin, with a microwave power equal to the nuclear precession frequency. This was performed at relatively high fields, to allow for both polarization transfer and noise decoupling. As a result, this scheme requires accurate magnetic field alignment in order preserve the NV properties. Such a requirement may be undesired or impractical in many practical scenarios. Here we present a new sequence, termed the refocused NOVEL, which can be used for polarization transfer (and detection) even at low fields. Numerical simulations are performed, taking into account both the spin Hamiltonian and spin decoherence, and we show that, under realistic parameters, it can outperform the NOVEL sequence.

Ballistic-diffusive approximation for the thermal dynamics of metallic nanoparticles in nanocomposite materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shirdel-Havar, A. H., E-mail: Amir.hushang.shirdel@gmail.com; Masoudian Saadabad, R.

2015-03-21

Based on ballistic-diffusive approximation, a method is presented to model heat transfer in nanocomposites containing metal nanoparticles. This method provides analytical expression for the temperature dynamics of metallic nanoparticles embedded in a dielectric medium. In this study, nanoparticles are considered as spherical shells, so that Boltzmann equation is solved using ballistic-diffusive approximation to calculate the electron and lattice thermal dynamics in gold nanoparticles, while thermal exchange between the particles is taken into account. The model was used to investigate the influence of particle size and metal concentration of the medium on the electron and lattice thermal dynamics. It is shownmore » that these two parameters are crucial in determining the nanocomposite thermal behavior. Our results showed that the heat transfer rate from nanoparticles to the matrix decreases as the nanoparticle size increases. On the other hand, increasing the metal concentration of the medium can also decrease the heat transfer rate.« less

First-principles simulation for strong and ultra-short laser pulse propagation in dielectrics

NASA Astrophysics Data System (ADS)

Yabana, K.

2016-05-01

We develop a computational approach for interaction between strong laser pulse and dielectrics based on time-dependent density functional theory (TDDFT). In this approach, a key ingredient is a solver to simulate electron dynamics in a unit cell of solids under a time-varying electric field that is a time-dependent extension of the static band calculation. This calculation can be regarded as a constitutive relation, providing macroscopic electric current for a given electric field applied to the medium. Combining the solver with Maxwell equations for electromagnetic fields of the laser pulse, we describe propagation of laser pulses in dielectrics without any empirical parameters. An important output from the coupled Maxwell+TDDFT simulation is the energy transfer from the laser pulse to electrons in the medium. We have found an abrupt increase of the energy transfer at certain laser intensity close to damage threshold. We also estimate damage threshold by comparing the transferred energy with melting and cohesive energies. It shows reasonable agreement with measurements.

Exciplex formation in bimolecular photoinduced electron-transfer investigated by ultrafast time-resolved infrared spectroscopy.

PubMed

Koch, Marius; Letrun, Romain; Vauthey, Eric

2014-03-12

The dynamics of bimolecular photoinduced electron-transfer reactions has been investigated with three donor/acceptor (D/A) pairs in tetrahydrofuran (THF) and acetonitrile (ACN) using a combination of ultrafast spectroscopic techniques, including time-resolved infrared absorption. For the D/A pairs with the highest driving force of electron transfer, all transient spectroscopic features can be unambiguously assigned to the excited reactant and the ionic products. For the pair with the lowest driving force, three additional transient infrared bands, more intense in THF than in ACN, with a time dependence that differs from those of the other bands are observed. From their frequency and solvent dependence, these bands can be assigned to an exciplex. Moreover, polarization-resolved measurements point to a relatively well-defined mutual orientation of the constituents and to a slower reorientational time compared to those of the individual reactants. Thanks to the minimal overlap of the infrared signature of all transient species in THF, a detailed reaction scheme including the relevant kinetic and thermodynamic parameters could be deduced for this pair. This analysis reveals that the formation and recombination of the ion pair occur almost exclusively via the exciplex.

A new method to calculate the beam charge for an integrating current transformer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu Yuchi; Han Dan; Zhu Bin

2012-09-15

The integrating current transformer (ICT) is a magnetic sensor widely used to precisely measure the charge of an ultra-short-pulse charged particle beam generated by traditional accelerators and new laser-plasma particle accelerators. In this paper, we present a new method to calculate the beam charge in an ICT based on circuit analysis. The output transfer function shows an invariable signal profile for an ultra-short electron bunch, so the function can be used to evaluate the signal quality and calculate the beam charge through signal fitting. We obtain a set of parameters in the output function from a standard signal generated bymore » an ultra-short electron bunch (about 1 ps in duration) at a radio frequency linear electron accelerator at Tsinghua University. These parameters can be used to obtain the beam charge by signal fitting with excellent accuracy.« less

Progress and Perspectives of Plasmon-Enhanced Solar Energy Conversion.

PubMed

Cushing, Scott K; Wu, Nianqiang

2016-02-18

Plasmonics allows extraordinary control of light, making it attractive for application in solar energy harvesting. In metal-semiconductor heterojunctions, plasmons can enhance photoconversion in the semiconductor via three mechanisms, including light trapping, hot electron/hole transfer, and plasmon-induced resonance energy transfer (PIRET). To understand the plasmonic enhancement, the metal's geometry, constituent metal, and interface must be viewed in terms of the effects on the plasmon's dephasing and decay route. To simplify design of plasmonic metal-semiconductor heterojunctions for high-efficiency solar energy conversion, the parameters controlling the plasmonic enhancement can be distilled to the dephasing time. The plasmonic geometry can then be further refined to optimize hot carrier transfer, PIRET, or light trapping.

Control voltage and power fluctuations when connecting wind farms

NASA Astrophysics Data System (ADS)

Berinde, Ioan; Bǎlan, Horia; Oros Pop, Teodora Susana

2015-12-01

Voltage, frequency, active power and reactive power are very important parameters in terms of power quality. These parameters are followed when connecting any power plant, the more the connection of wind farms. Connecting wind farms to the electricity system must not cause interference outside the limits set by regulations. Modern solutions for fast and automatic voltage control and power fluctuations using electronic control systems of reactive power flows. FACTS (Flexible Alternating Current Transmision System) systems, established on the basis of power electronic circuits ensure control of electrical status quantities to achieve the necessary transfer of power to the power grid. FACTS devices can quickly control parameters and sizes of state power lines, such as impedance line voltages and phase angles of the voltages of the two ends of the line. Their use can lead to improvement in power system operation by increasing the transmission capacity of power lines, power flow control lines, improved static and transient stability reserve.

Effects of anisotropic electron-ion interactions in atomic photoelectron angular distributions

NASA Technical Reports Server (NTRS)

Dill, D.; Starace, A. F.; Manson, S. T.

1974-01-01

The photoelectron asymmetry parameter beta in LS-coupling is obtained as an expansion into contributions from alternative angular momentum transfers j sub t. The physical significance of this expansion of beta is shown to be that: (1) the electric dipole interaction transfers to the atom a charcteristic single angular momentum j sub t = sub o, where sub o is the photoelectron's initial orbital momentum; and (2) angular momentum transfers indicate the presence of anisotropic interaction of the outgoing photoelectron with the residual ion. For open shell atoms the photoelectron-ion interaction is generally anisotropic; photoelectron phase shifts and electric dipole matrix elements depend on both the multiplet term of the residual ion and the total orbital momentum of the ion-photoelectron final state channel. Consequently beta depends on the term levels of the residual ion and contains contributions from all allowed values of j sub t. Numerical calculations of the asymmetry parameters and partial cross sections for photoionization of atomic sulfur are presented.

Quantum mechanical theory of dynamic nuclear polarization in solid dielectrics.

PubMed

Hu, Kan-Nian; Debelouchina, Galia T; Smith, Albert A; Griffin, Robert G

2011-03-28

Microwave driven dynamic nuclear polarization (DNP) is a process in which the large polarization present in an electron spin reservoir is transferred to nuclei, thereby enhancing NMR signal intensities. In solid dielectrics there are three mechanisms that mediate this transfer--the solid effect (SE), the cross effect (CE), and thermal mixing (TM). Historically these mechanisms have been discussed theoretically using thermodynamic parameters and average spin interactions. However, the SE and the CE can also be modeled quantum mechanically with a system consisting of a small number of spins and the results provide a foundation for the calculations involving TM. In the case of the SE, a single electron-nuclear spin pair is sufficient to explain the polarization mechanism, while the CE requires participation of two electrons and a nuclear spin, and can be used to understand the improved DNP enhancements observed using biradical polarizing agents. Calculations establish the relations among the electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) frequencies and the microwave irradiation frequency that must be satisfied for polarization transfer via the SE or the CE. In particular, if δ, Δ < ω(0I), where δ and Δ are the homogeneous linewidth and inhomogeneous breadth of the EPR spectrum, respectively, we verify that the SE occurs when ω(M) = ω(0S) ± ω(0I), where ω(M), ω(0S) and ω(0I) are, respectively, the microwave, and the EPR and NMR frequencies. Alternatively, when Δ > ω(0I) > δ, the CE dominates the polarization transfer. This two-electron process is optimized when ω(0S(1))-ω(0S(2)) = ω(0I) and ω(M)~ω(0S(1)) or ω(0S(2)), where ω(0S(1)) and ω(0S(2)) are the EPR Larmor frequencies of the two electrons. Using these matching conditions, we calculate the evolution of the density operator from electron Zeeman order to nuclear Zeeman order for both the SE and the CE. The results provide insights into the influence of the microwave irradiation field, the external magnetic field, and the electron-electron and electron-nuclear interactions on DNP enhancements.

Photoinduced Bimolecular Electron Transfer from Cyano Anions in Ionic Liquids

DOE PAGES

Wu, Boning; Liang, Min; Maroncelli, Mark; ...

2015-10-26

Ionic liquids with electron-donating anions are used to investigate rates and mechanisms of photoinduced bimolecular electron transfer to the photoexcited acceptor 9,10-dicyanoanthracene (9,10-DCNA). The set of five cyano anion ILs studied comprises the 1-ethyl-3-methylimidazolium cation paired with each of these five anions: selenocyanate, thiocyanate, dicyanamide, tricyanomethanide, and tetracyano-borate. Measurements with these anions dilute in acetonitrile and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)-amide show that the selenocyanate and tricyanomethanide anions are strong quenchers of the 9,10-DCNA fluorescence, thiocyanate is a moderately strong quencher, dicyanamide is a weak quencher, and no quenching is observed for tetracyanoborate. Quenching rates are obtained from both time-resolved fluorescence transients andmore » time-integrated spectra. Finally, application of a Smoluchowski diffusion-and-reaction model showed that the complex kinetics observed can be fit using only two adjustable parameters, D and V 0, where D is the relative diffusion coefficient between donor and acceptor and V 0 is the value of the electronic coupling at donor-acceptor contact.« less

Thermodynamic and electron paramagnetic resonance characterization of flavin in succinate dehydrogenase.

PubMed

Ohnishi, T; King, T E; Salerno, J C; Blum, H; Bowyer, J R; Maida, T

1981-06-10

Thermodynamic parameters of succinate dehydrogenase flavin were determined potentiometrically from the analysis of free radical signal levels as a function of the oxidation-reduction potential. Midpoint redox potentials of consecutive 1-electron transfer steps are -127 and -31 mV at pH 7.0. This corresponds to a stability constant of intermediate stability, 2.5 x 10(-2), which suggests flavin itself may be a converter from n = 2 to n = 1 electron transfer steps. The pK values of the free radical (FlH . in equilibrium Fl . -) and the fully reduced form (FlH2 in equilibrium FlH-) were estimated as 8.0 +/- 0.2 and 7.7 +/- 0.2, respectively. Succinate dehydrogenase flavosemiquinone elicits an EPR spectrum at g = 2.00 with a peak to peak width of 1.2 mT even in the protonated form, suggesting the delocalization in the unpaired electron density. A close proximity of succinate dehydrogenase flavin and iron-sulfur cluster S-1 was demonstrated based on the enhancement of flavin spin relaxation by Center S-1.

Intramolecular and Lattice Dynamics in V6-nIVVnV O7(OCH3)12 Crystal

NASA Astrophysics Data System (ADS)

Yablokov, Yu. V.; Augustyniak-Jabłokow, M. A.; Borshch, S.; Daniel, C.; Hartl, H.

2006-08-01

Multi-nuclear mixed-valence clusters V4IVV2VO7(OCH3)12 were studied by X-band EPR in the temperature range 4.2-300 K. An isotropic exchange interactions between four VIV ions with individual spin Si=1/2 determine the energy levels structure of the compound with the total spin states S=0, 1, and 2, which are doubled and split due to the extra electron transfer. The spin-Hamiltonian approach was used for the analysis of the temperature dependences of the EPR spectra parameters and the cluster dynamics. Two types of the electron transfer are assumed: the single jump transfer leading to the splitting of the total spin states by intervals comparable in magnitude with the exchange parameter J≈100-150cm-1 and the double jump one resulting in dynamics. The dependence of the transition ratesνtr on the energy of the total spin states was observed. In particular, in the range 300-220 K the νtr ≈0.7×1010 cm-1 and below 180 K the νtr≈1×1010 cm-1 was estimated. The g-factors of the spin states were shown to depend on the values of the intermediate spins. A phase transition in the T-range 210-180 K leading to the change in the initial VIV ions localization was discovered.

UV-Vis spectroscopy and density functional study of solvent effect on the charge transfer band of the n → σ* complexes of 2-Methylpyridine and 2-Chloropyridine with molecular iodine

NASA Astrophysics Data System (ADS)

Gogoi, Pallavi; Mohan, Uttam; Borpuzari, Manash Protim; Boruah, Abhijit; Baruah, Surjya Kumar

2017-03-01

UV-Vis spectroscopy has established that Pyridine substitutes form n→σ* charge transfer (CT) complexes with molecular Iodine. This study is a combined approach of purely experimental UV-Vis spectroscopy, Multiple linear regression theory and Computational chemistry to analyze the effect of solvent upon the charge transfer band of 2-Methylpyridine-I2 and 2-Chloropyridine-I2 complexes. Regression analysis verifies the dependence of the CT band upon different solvent parameters. Dielectric constant and refractive index are considered among the bulk solvent parameters and Hansen, Kamlet and Catalan parameters are taken into consideration at the molecular level. Density Functional Theory results explain well the blue shift of the CT bands in polar medium as an outcome of stronger donor acceptor interaction. A logarithmic relation between the bond length of the bridging atoms of the donor and the acceptor with the dielectric constant of the medium is established. Tauc plot and TDDFT study indicates a non-vertical electronic transition in the complexes. Buckingham and Lippert Mataga equations are applied to check the Polarizability effect on the CT band.

Numerical model of the plasma formation at electron beam welding

NASA Astrophysics Data System (ADS)

Trushnikov, D. N.; Mladenov, G. M.

2015-01-01

The model of plasma formation in the keyhole in liquid metal as well as above the electron beam welding zone is described. The model is based on solution of two equations for the density of electrons and the mean electron energy. The mass transfer of heavy plasma particles (neutral atoms, excited atoms, and ions) is taken into account in the analysis by the diffusion equation for a multicomponent mixture. The electrostatic field is calculated using the Poisson equation. Thermionic electron emission is calculated for the keyhole wall. The ionization intensity of the vapors due to beam electrons and high-energy secondary and backscattered electrons is calibrated using the plasma parameters when there is no polarized collector electrode above the welding zone. The calculated data are in good agreement with experimental data. Results for the plasma parameters for excitation of a non-independent discharge are given. It is shown that there is a need to take into account the effect of a strong electric field near the keyhole walls on electron emission (the Schottky effect) in the calculation of the current for a non-independent discharge (hot cathode gas discharge). The calculated electron drift velocities are much bigger than the velocity at which current instabilities arise. This confirms the hypothesis for ion-acoustic instabilities, observed experimentally in previous research.

Hybridization-controlled charge transfer and induced magnetism at correlated oxide interfaces

PubMed Central

Grisolia, M.N.; Arora, A.; Valencia, S.; Varela, M.; Abrudan, R.; Weschke, E.; Schierle, E.; Rault, J.E.; Rueff, J.-P.; Barthélémy, A.; Santamaria, J.; Bibes, M.

2015-01-01

At interfaces between conventional materials, band bending and alignment are classically controlled by differences in electrochemical potential. Applying this concept to oxides in which interfaces can be polar and cations may adopt a mixed valence has led to the discovery of novel two-dimensional states between simple band insulators such as LaAlO3 and SrTiO3. However, many oxides have a more complex electronic structure, with charge, orbital and/or spin orders arising from strong Coulomb interactions between transition metal and oxygen ions. Such electronic correlations offer a rich playground to engineer functional interfaces but their compatibility with the classical band alignment picture remains an open question. Here we show that beyond differences in electron affinities and polar effects, a key parameter determining charge transfer at correlated oxide interfaces is the energy required to alter the covalence of the metal-oxygen bond. Using the perovskite nickelate (RNiO3) family as a template, we probe charge reconstruction at interfaces with gadolinium titanate GdTiO3. X-ray absorption spectroscopy shows that the charge transfer is thwarted by hybridization effects tuned by the rare-earth (R) size. Charge transfer results in an induced ferromagnetic-like state in the nickelate, exemplifying the potential of correlated interfaces to design novel phases. Further, our work clarifies strategies to engineer two-dimensional systems through the control of both doping and covalence. PMID:27158255

Hybridization-controlled charge transfer and induced magnetism at correlated oxide interfaces

NASA Astrophysics Data System (ADS)

Grisolia, M. N.; Varignon, J.; Sanchez-Santolino, G.; Arora, A.; Valencia, S.; Varela, M.; Abrudan, R.; Weschke, E.; Schierle, E.; Rault, J. E.; Rueff, J.-P.; Barthélémy, A.; Santamaria, J.; Bibes, M.

2016-05-01

At interfaces between conventional materials, band bending and alignment are classically controlled by differences in electrochemical potential. Applying this concept to oxides in which interfaces can be polar and cations may adopt a mixed valence has led to the discovery of novel two-dimensional states between simple band insulators such as LaAlO3 and SrTiO3. However, many oxides have a more complex electronic structure, with charge, orbital and/or spin orders arising from strong Coulomb interactions at and between transition metal and oxygen ions. Such electronic correlations offer a rich playground to engineer functional interfaces but their compatibility with the classical band alignment picture remains an open question. Here we show that beyond differences in electron affinities and polar effects, a key parameter determining charge transfer at correlated oxide interfaces is the energy required to alter the covalence of the metal-oxygen bond. Using the perovskite nickelate (RNiO3) family as a template, we probe charge reconstruction at interfaces with gadolinium titanate GdTiO3. X-ray absorption spectroscopy shows that the charge transfer is thwarted by hybridization effects tuned by the rare-earth (R) size. Charge transfer results in an induced ferromagnetic-like state in the nickelate, exemplifying the potential of correlated interfaces to design novel phases. Further, our work clarifies strategies to engineer two-dimensional systems through the control of both doping and covalence.

Catalytic Proton Coupled Electron Transfer from Metal Hydrides to Titanocene Amides, Hydrazides and Imides: Determination of Thermodynamic Parameters Relevant to Nitrogen Fixation.

PubMed

Pappas, Iraklis; Chirik, Paul J

2016-10-03

The hydrogenolysis of titanium-nitrogen bonds in a series of bis(cyclopentadienyl) titanium amides, hydrazides and imides by proton coupled electron transfer (PCET) is described. Twelve different N-H bond dissociation free energies (BDFEs) among the various nitrogen-containing ligands were measured or calculated, and effects of metal oxidation state and N-ligand substituent were determined. Two metal hydride complexes, (η 5 -C 5 Me 5 )(py-Ph)Rh-H (py-Ph = 2-pyridylphenyl, [Rh]-H) and (η 5 -C 5 R 5 )(CO) 3 Cr-H ([Cr] R -H, R= H, Me) were evaluated for formal H atom transfer reactivity and were selected due to their relatively weak M-H bond strengths yet ability to activate and cleave molecular hydrogen. Despite comparable M-H BDFEs, disparate reactivity between the two compounds was observed and was traced to the vastly different acidities of the M-H bonds and overall redox potentials of the molecules. With [Rh]-H, catalytic syntheses of ammonia, silylamine and N,N-dimethylhydrazine have been accomplished from the corresponding titanium(IV) complex using H 2 as the stoichiometric H atom source. The data presented in this study provides the thermochemical foundation for the synthesis of NH 3 by proton coupled electron transfer at a well-defined transition metal center.

Charge transfer complex studies between some non-steroidal anti-inflammatory drugs and π-electron acceptors

NASA Astrophysics Data System (ADS)

Duymus, Hulya; Arslan, Mustafa; Kucukislamoglu, Mustafa; Zengin, Mustafa

2006-12-01

Charge transfer (CT) complexes of some non-steroidal anti-inflammatory drugs, naproxen and etodolac which are electron donors with some π-acceptors, such as tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano- p-benzoquinone (DDQ), p-chloranil ( p-CHL), have been investigated spectrophotometrically in chloroform at 21 °C. The coloured products are measured spectrophotometrically at different wavelength depending on the electronic transition between donors and acceptors. Beer's law is obeyed and colours were produced in non-aqueous media. All complexes were stable at least 2 h except for etodolac with DDQ stable for 5 min. The equilibrium constants of the CT complexes were determined by the Benesi-Hildebrand equation. The thermodynamic parameters Δ H, Δ S, Δ G° were calculated by Van't Hoff equation. Stochiometries of the complexes formed between donors and acceptors were defined by the Job's method of the continuous variation and found in 1:1 complexation with donor and acceptor at the maximum absorption bands in all cases.

Calculation of rates of exciton dissociation into hot charge-transfer states in model organic photovoltaic interfaces

NASA Astrophysics Data System (ADS)

Vázquez, Héctor; Troisi, Alessandro

2013-11-01

We investigate the process of exciton dissociation in ordered and disordered model donor/acceptor systems and describe a method to calculate exciton dissociation rates. We consider a one-dimensional system with Frenkel states in the donor material and states where charge transfer has taken place between donor and acceptor. We introduce a Green's function approach to calculate the generation rates of charge-transfer states. For disorder in the Frenkel states we find a clear exponential dependence of charge dissociation rates with exciton-interface distance, with a distance decay constant β that increases linearly with the amount of disorder. Disorder in the parameters that describe (final) charge-transfer states has little effect on the rates. Exciton dissociation invariably leads to partially separated charges. In all cases final states are “hot” charge-transfer states, with electron and hole located far from the interface.

The active site of hen egg-white lysozyme: flexibility and chemical bonding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Held, Jeanette, E-mail: jeanette.netzel@uni-bayreuth.de; Smaalen, Sander van

Chemical bonding at the active site of lysozyme is analyzed on the basis of a multipole model employing transferable multipole parameters from a database. Large B factors at low temperatures reflect frozen-in disorder, but therefore prevent a meaningful free refinement of multipole parameters. Chemical bonding at the active site of hen egg-white lysozyme (HEWL) is analyzed on the basis of Bader’s quantum theory of atoms in molecules [QTAIM; Bader (1994 ▶), Atoms in Molecules: A Quantum Theory. Oxford University Press] applied to electron-density maps derived from a multipole model. The observation is made that the atomic displacement parameters (ADPs) ofmore » HEWL at a temperature of 100 K are larger than ADPs in crystals of small biological molecules at 298 K. This feature shows that the ADPs in the cold crystals of HEWL reflect frozen-in disorder rather than thermal vibrations of the atoms. Directly generalizing the results of multipole studies on small-molecule crystals, the important consequence for electron-density analysis of protein crystals is that multipole parameters cannot be independently varied in a meaningful way in structure refinements. Instead, a multipole model for HEWL has been developed by refinement of atomic coordinates and ADPs against the X-ray diffraction data of Wang and coworkers [Wang et al. (2007), Acta Cryst. D63, 1254–1268], while multipole parameters were fixed to the values for transferable multipole parameters from the ELMAM2 database [Domagala et al. (2012), Acta Cryst. A68, 337–351] . Static and dynamic electron densities based on this multipole model are presented. Analysis of their topological properties according to the QTAIM shows that the covalent bonds possess similar properties to the covalent bonds of small molecules. Hydrogen bonds of intermediate strength are identified for the Glu35 and Asp52 residues, which are considered to be essential parts of the active site of HEWL. Furthermore, a series of weak C—H⋯O hydrogen bonds are identified by means of the existence of bond critical points (BCPs) in the multipole electron density. It is proposed that these weak interactions might be important for defining the tertiary structure and activity of HEWL. The deprotonated state of Glu35 prevents a distinction between the Phillips and Koshland mechanisms.« less

Measurement and analysis of electronic energy transfer between Tb 3+ and Eu 3+ ions in Cs 2NaY 1-x-y Tb xEu yCl 6

NASA Astrophysics Data System (ADS)

Moran, Diane M.; May, P. Stanley; Richardson, F. S.

1994-08-01

Electronic energy-transfer processes between Tb 3+5D 4) and Eu 3+ ( 7F 0, 7F 1) ions in crystalline Cs 2NaY 1-x-yTb xEu yCl 6 compounds are examined over a wide range of relative Tb 3+ and Eu 3+ concentrations (at sample temperature of 77 and 295 K). In these systems, the Tb 3+ and Eu 3+ ions are located at centrosymmetric (O h) sites surrounded by six Cl - ions, and the minimum distance between these sites is ≈ 7.6 Å. The host lattice has a cubic structure (space group O h5-Fm3m), and the phonon spectrum of this lattice has a cut-off frequency of ≈ 300 cm -1. The optical spectra of Tb 3+ and Eu 3+ in Cs 2NaYCl 6 exhibit relatively sparse line structures, consisting almost entirely of magnetic-dipole origin lines and one-phonon-assisted electric-dipole vibronic lines that reflect O h selection rules and have relatively low oscillator strenghts. Overlap between Tb 3+ ( 5D 4) emission and Eu 3+ ( 7F 0, 7F 1) absorption spectra occurs only within the Tb 3+ ( 5D 4 → 7 F 4 and Eu 3+ ( 7F 0, 7F 1 → 5D 0 transition regions, and resonances between individual lines in these regions are used to identify possible pathways for Tb 3+ ( 5D 4)-to-Eu 3+ ( 7F 0, 7F 1) energy transfer. Rates of energy transfer are determined from time-resolved Tb 3+ ( 5D 4) luminescence intersity measurements, analyzed in terms of two different models for representing donor (Tb 3+)-acceptor (Eu 3+) site distributions in Cs 2NaY 1-x-yTb xEu yCl 6 systems. In one model, donor-accepator site distances are represented by a continuous radial distribution function, whereas in the second model, these distances are represented by a discrete distribution function. Both models are used to analyze donor luminescence decay data in terms of rate parameters that reflect specific mechanistic contributions to electronic energy transfer. Both electron-exchange and multipole-multipole mechanisms are considered in the analyses. Results from these analyses, combined with spectral overlap considerations and comparisons of 77 versus 295 K rate data, suggest an electric-quadrupole/electric-dipole mechanism in which a 5D 4(T 1g → 7F 4(T 1g) electric-quadrupole transition on Tb 3+ excites a 7F 0(A 1g) + v4(t 1u → 5D 0(A 1g) electric-dipole (vibronic) transition on Eu 3+. Rate data obtained on systems of stoichiometric formulae Cs 2NaY 0.95-xTb xEu 0.05Cl 6 show that Tb 3+( 5D 4)- to-Eu 3+ ( 7F 0, 7F 1) energy-transfer rates a Tb 3+-Tb 3+ energy-migration processes when tx > 0.05. Direct calculations of Tb 3+ ( 5D 4)-Eu 3+ ( 7F 0, 7F 1) and Tb 3+ ( 5D 4-Tb 3+ ( 7F 6) multipole-multipole interaction parameters are performed, and the parameters obtained from these calculations are compared to those derived from parametric fits of experimentally observed rate data. Discrepancies between calculated and ovserved rate parameters are large, and possible explanations for these discrepancies are discussed.

A detailed study of the magnetism of chiral {Cr₇M} rings: an investigation into parametrization and transferability of parameters.

PubMed

Garlatti, Elena; Albring, Morten A; Baker, Michael L; Docherty, Rebecca J; Mutka, Hannu; Guidi, Tatiana; Garcia Sakai, Victoria; Whitehead, George F S; Pritchard, Robin G; Timco, Grigore A; Tuna, Floriana; Amoretti, Giuseppe; Carretta, Stefano; Santini, Paolo; Lorusso, Giulia; Affronte, Marco; McInnes, Eric J L; Collison, David; Winpenny, Richard E P

2014-07-09

Compounds of general formula [Cr7MF3(Etglu)(O2C(t)Bu)15(Phpy)] [H5Etglu = N-ethyl-d-glucamine; Phpy = 4-phenylpyridine; M = Zn (1), Mn (2), Ni (3)] have been prepared. The structures contain an irregular octagon of metal sites formed around the penta-deprotonated Etglu(5-) ligand; the chirality of N-ethyl-d-glucamine is retained in the final product. The seven Cr(III) sites have a range of coordination environments, and the divalent metal site is crystallographically identified and has a Phpy ligand attached to it. By using complementary experimental techniques, including magnetization and specific heat measurements, inelastic neutron scattering, and electron paramagnetic resonance spectroscopy, we have investigated the magnetic features of this family of {Cr7M} rings. Microscopic parameters of the spin Hamiltonian have been determined as a result of best fits of the different experimental data, allowing a direct comparison with corresponding parameters found in the parent compounds. We examine whether these parameters can be transferred between compounds and compare them with those of an earlier family of heterometallic rings.

12 CFR 1005.14 - Electronic fund transfer service provider not holding consumer's account.

Code of Federal Regulations, 2012 CFR

2012-01-01

... 12 Banks and Banking 8 2012-01-01 2012-01-01 false Electronic fund transfer service provider not... PROTECTION ELECTRONIC FUND TRANSFERS (REGULATION E) § 1005.14 Electronic fund transfer service provider not holding consumer's account. (a) Provider of electronic fund transfer service. A person that provides an...

12 CFR 1005.14 - Electronic fund transfer service provider not holding consumer's account.

Code of Federal Regulations, 2013 CFR

2013-01-01

... 12 Banks and Banking 8 2013-01-01 2013-01-01 false Electronic fund transfer service provider not... PROTECTION ELECTRONIC FUND TRANSFERS (REGULATION E) General § 1005.14 Electronic fund transfer service provider not holding consumer's account. (a) Provider of electronic fund transfer service. A person that...

12 CFR 1005.14 - Electronic fund transfer service provider not holding consumer's account.

Code of Federal Regulations, 2014 CFR

2014-01-01

... 12 Banks and Banking 8 2014-01-01 2014-01-01 false Electronic fund transfer service provider not... PROTECTION ELECTRONIC FUND TRANSFERS (REGULATION E) General § 1005.14 Electronic fund transfer service provider not holding consumer's account. (a) Provider of electronic fund transfer service. A person that...

Kinetic and mechanism of the oxidation of chromium(III) complex with anthranil- N, N-diacetic acid by periodate ion in acidic aqueous solutions

NASA Astrophysics Data System (ADS)

Ali, Ismat H.

2015-06-01

The kinetics of oxidation of [CrIII(atda)(H2O)2] (atda = anthranil- N, N-diacetato) complex by IO{4/-} was studied spectrophotometrically in aqueous solutions with pH range 2.20-3.34, 0.30 M ionic strength and in 20.0-40.0°C temperature range. The rate law of the reaction exhibited saturation kinetics. Values of the rate constant for the electron transfer process, the equilibrium constant for dissociation of [CrIII (atda)(H2O)2] to [CrIII (atda) (H2O)OH]+ + H+ and the pre-equilibrium formation constant were calculated. The thermodynamic activation parameters are reported. It is proposed that electron transfer proceeds through an inner-sphere mechanism via coordination of the IVII to chromium(III).

Electric-field-driven electron-transfer in mixed-valence molecules.

PubMed

Blair, Enrique P; Corcelli, Steven A; Lent, Craig S

2016-07-07

Molecular quantum-dot cellular automata is a computing paradigm in which digital information is encoded by the charge configuration of a mixed-valence molecule. General-purpose computing can be achieved by arranging these compounds on a substrate and exploiting intermolecular Coulombic coupling. The operation of such a device relies on nonequilibrium electron transfer (ET), whereby the time-varying electric field of one molecule induces an ET event in a neighboring molecule. The magnitude of the electric fields can be quite large because of close spatial proximity, and the induced ET rate is a measure of the nonequilibrium response of the molecule. We calculate the electric-field-driven ET rate for a model mixed-valence compound. The mixed-valence molecule is regarded as a two-state electronic system coupled to a molecular vibrational mode, which is, in turn, coupled to a thermal environment. Both the electronic and vibrational degrees-of-freedom are treated quantum mechanically, and the dissipative vibrational-bath interaction is modeled with the Lindblad equation. This approach captures both tunneling and nonadiabatic dynamics. Relationships between microscopic molecular properties and the driven ET rate are explored for two time-dependent applied fields: an abruptly switched field and a linearly ramped field. In both cases, the driven ET rate is only weakly temperature dependent. When the model is applied using parameters appropriate to a specific mixed-valence molecule, diferrocenylacetylene, terahertz-range ET transfer rates are predicted.

Effects of anisotropic electron-ion interactions in atomic photoelectron angular distributions

NASA Technical Reports Server (NTRS)

Dill, D.; Starace, A. F.; Manson, S. T.

1975-01-01

A summary of the angular momentum transfer formulation of the differential photoionization cross section is presented and photoionization amplitudes in LS coupling are considered. The application of the theoretical concepts and relations developed is illustrated with the aid of an example involving the calculation of the angular distribution of photoelectrons ionized from atomic sulfur according to a certain reaction. The investigation shows that anisotropic electron-ion interactions in atomic sulfur lead to measurable differences between photoelectron angular distribution asymmetry parameters corresponding to alternative ionic term levels.

The target material influence on the current pulse during high power pulsed magnetron sputtering

NASA Astrophysics Data System (ADS)

Moens, Filip; Konstantinidis, Stéphanos; Depla, Diederik

2017-10-01

The current-time characteristic during high power pulsed magnetron sputtering is measured under identical conditions for seventeen different target materials. Based on physical processes such as gas rarefaction, ion-induced electron emission, and electron impact ionization, two test parameters were derived that significantly correlate with specific features of the current-time characteristic: i) the peak current is correlated to the momentum transfer between the sputtered material and the argon gas, ii) while the observed current plateau after the peak is connected to the metal ionization rate.

Free energy functionals for polarization fluctuations: Pekar factor revisited.

PubMed

Dinpajooh, Mohammadhasan; Newton, Marshall D; Matyushov, Dmitry V

2017-02-14

The separation of slow nuclear and fast electronic polarization in problems related to electron mobility in polarizable media was considered by Pekar 70 years ago. Within dielectric continuum models, this separation leads to the Pekar factor in the free energy of solvation by the nuclear degrees of freedom. The main qualitative prediction of Pekar's perspective is a significant, by about a factor of two, drop of the nuclear solvation free energy compared to the total (electronic plus nuclear) free energy of solvation. The Pekar factor enters the solvent reorganization energy of electron transfer reactions and is a significant mechanistic parameter accounting for the solvent effect on electron transfer. Here, we study the separation of the fast and slow polarization modes in polar molecular liquids (polarizable dipolar liquids and polarizable water force fields) without relying on the continuum approximation. We derive the nonlocal free energy functional and use atomistic numerical simulations to obtain nonlocal, reciprocal space electronic and nuclear susceptibilities. A consistent transition to the continuum limit is introduced by extrapolating the results of finite-size numerical simulation to zero wavevector. The continuum nuclear susceptibility extracted from the simulations is numerically close to the Pekar factor. However, we derive a new functionality involving the static and high-frequency dielectric constants. The main distinction of our approach from the traditional theories is found in the solvation free energy due to the nuclear polarization: the anticipated significant drop of its magnitude with increasing liquid polarizability does not occur. The reorganization energy of electron transfer is either nearly constant with increasing the solvent polarizability and the corresponding high-frequency dielectric constant (polarizable dipolar liquids) or actually noticeably increases (polarizable force fields of water).

Laser-induced forward transfer (LIFT) of congruent voxels

NASA Astrophysics Data System (ADS)

Piqué, Alberto; Kim, Heungsoo; Auyeung, Raymond C. Y.; Beniam, Iyoel; Breckenfeld, Eric

2016-06-01

Laser-induced forward transfer (LIFT) of functional materials offers unique advantages and capabilities for the rapid prototyping of electronic, optical and sensor elements. The use of LIFT for printing high viscosity metallic nano-inks and nano-pastes can be optimized for the transfer of voxels congruent with the shape of the laser pulse, forming thin film-like structures non-lithographically. These processes are capable of printing patterns with excellent lateral resolution and thickness uniformity typically found in 3-dimensional stacked assemblies, MEMS-like structures and free-standing interconnects. However, in order to achieve congruent voxel transfer with LIFT, the particle size and viscosity of the ink or paste suspensions must be adjusted to minimize variations due to wetting and drying effects. When LIFT is carried out with high-viscosity nano-suspensions, the printed voxel size and shape become controllable parameters, allowing the printing of thin-film like structures whose shape is determined by the spatial distribution of the laser pulse. The result is a new level of parallelization beyond current serial direct-write processes whereby the geometry of each printed voxel can be optimized according to the pattern design. This work shows how LIFT of congruent voxels can be applied to the fabrication of 2D and 3D microstructures by adjusting the viscosity of the nano-suspension and laser transfer parameters.

Towards a First-Principles Determination of Effective Coulomb Interactions in Correlated Electron Materials: Role of Intershell Interactions

NASA Astrophysics Data System (ADS)

Seth, Priyanka; Hansmann, Philipp; van Roekeghem, Ambroise; Vaugier, Loig; Biermann, Silke

2017-08-01

The determination of the effective Coulomb interactions to be used in low-energy Hamiltonians for materials with strong electronic correlations remains one of the bottlenecks for parameter-free electronic structure calculations. We propose and benchmark a scheme for determining the effective local Coulomb interactions for charge-transfer oxides and related compounds. Intershell interactions between electrons in the correlated shell and ligand orbitals are taken into account in an effective manner, leading to a reduction of the effective local interactions on the correlated shell. Our scheme resolves inconsistencies in the determination of effective interactions as obtained by standard methods for a wide range of materials, and allows for a conceptual understanding of the relation of cluster model and dynamical mean field-based electronic structure calculations.

Towards a First-Principles Determination of Effective Coulomb Interactions in Correlated Electron Materials: Role of Intershell Interactions.

PubMed

Seth, Priyanka; Hansmann, Philipp; van Roekeghem, Ambroise; Vaugier, Loig; Biermann, Silke

2017-08-04

The determination of the effective Coulomb interactions to be used in low-energy Hamiltonians for materials with strong electronic correlations remains one of the bottlenecks for parameter-free electronic structure calculations. We propose and benchmark a scheme for determining the effective local Coulomb interactions for charge-transfer oxides and related compounds. Intershell interactions between electrons in the correlated shell and ligand orbitals are taken into account in an effective manner, leading to a reduction of the effective local interactions on the correlated shell. Our scheme resolves inconsistencies in the determination of effective interactions as obtained by standard methods for a wide range of materials, and allows for a conceptual understanding of the relation of cluster model and dynamical mean field-based electronic structure calculations.

Proton transfer in microbial electrolysis cells

DOE PAGES

Borole, Abhijeet P.; Lewis, Alex J.

2017-02-15

Proton transfer and electron transfer are of prime importance in the development of microbial electrochemical cells. While electron transfer is primarily controlled by biology, proton transfer is controlled by process engineering and cell design. To develop commercially feasible technologies around the concept of a bioelectrochemical cell, real feedstocks have to be explored and associated limitations have to be identified. Here in this study, the proton transfer rate was quantified for a microbial electrolysis cell (MEC) and its dependence on process parameters was investigated using a proton balance model. The reaction system consisted of a biomass-derived pyrolytic aqueous stream as amore » substrate producing hydrogen in a flow-through MEC. The proton transfer rate increased with anode flow rate and organic loading rate up to a maximum of 0.36 ± 0.01 moles per m 2 per h, equivalent to a hydrogen production rate of 9.08 L per L per day. Higher rates of hydrogen production, reaching 11.7 ± 0.2 L per L per day were achieved, when additional protons were provided via the cathode buffer. Electrochemical impedance spectroscopy shows that proton transfer was the dominant resistance in the production of hydrogen. The quantification of proton transfer rates for MECs with potential for biorefinery application and the demonstration of high hydrogen production rates approaching those required for commercial consideration indicate the strong potential of this technology for renewable hydrogen production. Understanding the transport phenomenon in bioelectrochemical cells is of great significance since these systems have potential for wide-ranging applications including energy production, bioremediation, chemical and nanomaterial synthesis, electro-fermentation, energy storage, desalination, and produced water treatment. Electron transfer in anode biofilms has been investigated extensively, but proton transfer studies are also important, since many cathodic half reactions require protons as the reactant. Determination of transport rates via proton balance was investigated in microbial electrolysis cells, which can be applied to other forms of microbial electrochemical systems. Lastly, these systems have a unique niche in the development of future biorefineries as a means of recovering energy from waste streams with potential for water recycle, making them an integral part of the water–energy nexus focus area.« less

Proton transfer in microbial electrolysis cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Borole, Abhijeet P.; Lewis, Alex J.

Proton transfer and electron transfer are of prime importance in the development of microbial electrochemical cells. While electron transfer is primarily controlled by biology, proton transfer is controlled by process engineering and cell design. To develop commercially feasible technologies around the concept of a bioelectrochemical cell, real feedstocks have to be explored and associated limitations have to be identified. Here in this study, the proton transfer rate was quantified for a microbial electrolysis cell (MEC) and its dependence on process parameters was investigated using a proton balance model. The reaction system consisted of a biomass-derived pyrolytic aqueous stream as amore » substrate producing hydrogen in a flow-through MEC. The proton transfer rate increased with anode flow rate and organic loading rate up to a maximum of 0.36 ± 0.01 moles per m 2 per h, equivalent to a hydrogen production rate of 9.08 L per L per day. Higher rates of hydrogen production, reaching 11.7 ± 0.2 L per L per day were achieved, when additional protons were provided via the cathode buffer. Electrochemical impedance spectroscopy shows that proton transfer was the dominant resistance in the production of hydrogen. The quantification of proton transfer rates for MECs with potential for biorefinery application and the demonstration of high hydrogen production rates approaching those required for commercial consideration indicate the strong potential of this technology for renewable hydrogen production. Understanding the transport phenomenon in bioelectrochemical cells is of great significance since these systems have potential for wide-ranging applications including energy production, bioremediation, chemical and nanomaterial synthesis, electro-fermentation, energy storage, desalination, and produced water treatment. Electron transfer in anode biofilms has been investigated extensively, but proton transfer studies are also important, since many cathodic half reactions require protons as the reactant. Determination of transport rates via proton balance was investigated in microbial electrolysis cells, which can be applied to other forms of microbial electrochemical systems. Lastly, these systems have a unique niche in the development of future biorefineries as a means of recovering energy from waste streams with potential for water recycle, making them an integral part of the water–energy nexus focus area.« less

Influence of Coherent Tunneling and Incoherent Hopping on the Charge Transfer Mechanism in Linear Donor-Bridge-Acceptor Systems.

PubMed

Li, Guangqi; Govind, Niranjan; Ratner, Mark A; Cramer, Christopher J; Gagliardi, Laura

2015-12-17

The mechanism of charge transfer has been observed to change from tunneling to hopping with increasing numbers of DNA base pairs in polynucleotides and with the length of molecular wires. The aim of this paper is to investigate this transition by examining the population dynamics using a tight-binding Hamiltonian with model parameters to describe a linear donor-bridge-acceptor (D-B-A) system. The model includes a primary vibration and an electron-vibration coupling at each site. A further coupling of the primary vibration with a secondary phonon bath allows the system to dissipate energy to the environment and reach a steady state. We apply the quantum master equation (QME) approach, based on second-order perturbation theory in a quantum dissipative system, to examine the dynamical processes involved in charge-transfer and follow the population transfer rate at the acceptor, ka, to shed light on the transition from tunneling to hopping. With a small tunneling parameter, V, the on-site population tends to localize and form polarons, and the hopping mechanism dominates the transfer process. With increasing V, the population tends to be delocalized and the tunneling mechanism dominates. The competition between incoherent hopping and coherent tunneling governs the mechanism of charge transfer. By varying V and the total number of sites, we also examine the onset of the transition from tunneling to hopping with increasing length.

Calcium induced ATP synthesis: Isotope effect, magnetic parameters and mechanism

NASA Astrophysics Data System (ADS)

Buchachenko, A. L.; Kuznetsov, D. A.; Breslavskaya, N. N.; Shchegoleva, L. N.; Arkhangelsky, S. E.

2011-03-01

ATP synthesis by creatine kinase with calcium ions is accompanied by 43Ca/ 40Ca isotope effect: the enzyme with 43Ca 2+ was found to be 2.0 ± 0.3 times more active than enzymes, in which Ca 2+ ions have nonmagnetic nuclei 40Ca. The effect demonstrates that primary reaction in ATP synthesis is electron transfer between reaction partners, Сa( HO)n2+ ( n ⩽ 3) and Ca 2+(ADP) 3-. It generates ion-radical pair, in which spin conversion results in the isotope effect. Magnetic parameters (g-factors and HFC constants a( 43Ca) and a( 31P)) confirm that namely terminal oxygen atom of the ADP ligand in the complex Ca 2+(ADP) 3- donates electron to the Ca( HO)n2+ ion.

Multiple electron processes of He and Ne by proton impact

NASA Astrophysics Data System (ADS)

Terekhin, Pavel Nikolaevich; Montenegro, Pablo; Quinto, Michele; Monti, Juan; Fojon, Omar; Rivarola, Roberto

2016-05-01

A detailed investigation of multiple electron processes (single and multiple ionization, single capture, transfer-ionization) of He and Ne is presented for proton impact at intermediate and high collision energies. Exclusive absolute cross sections for these processes have been obtained by calculation of transition probabilities in the independent electron and independent event models as a function of impact parameter in the framework of the continuum distorted wave-eikonal initial state theory. A binomial analysis is employed to calculate exclusive probabilities. The comparison with available theoretical and experimental results shows that exclusive probabilities are needed for a reliable description of the experimental data. The developed approach can be used for obtaining the input database for modeling multiple electron processes of charged particles passing through the matter.

Electron-neutrino charged-current quasi-elastic scattering in MINERvA

NASA Astrophysics Data System (ADS)

Wolcott, Jeremy

2014-03-01

The electron-neutrino charged-current quasi-elastic (CCQE) cross-section on nuclei is an important input parameter to appearance-type neutrino oscillation experiments. Current experiments typically work from the muon neutrino CCQE cross-section and apply corrections from theoretical arguments to obtain a prediction for the electron neutrino CCQE cross-section, but to date there has been no precise experimental verification of these estimates at an energy scale appropriate to such experiments. We present the current status of a direct measurement of the electron neutrino CCQE differential cross-section as a function of the squared four-momentum transfer to the nucleus, Q2, in MINERvA. This talk will discuss event selection, background constraints, and the flux prediction used in the calculation.

Modelling excitonic-energy transfer in light-harvesting complexes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kramer, Tobias; Kreisbeck, Christoph

The theoretical and experimental study of energy transfer in photosynthesis has revealed an interesting transport regime, which lies at the borderline between classical transport dynamics and quantum-mechanical interference effects. Dissipation is caused by the coupling of electronic degrees of freedom to vibrational modes and leads to a directional energy transfer from the antenna complex to the target reaction-center. The dissipative driving is robust and does not rely on fine-tuning of specific vibrational modes. For the parameter regime encountered in the biological systems new theoretical tools are required to directly compare theoretical results with experimental spectroscopy data. The calculations require tomore » utilize massively parallel graphics processor units (GPUs) for efficient and exact computations.« less

Quantum tunneling resonant electron transfer process in Lorentzian plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hong, Woo-Pyo; Jung, Young-Dae, E-mail: ydjung@hanyang.ac.kr; Department of Applied Physics and Department of Bionanotechnology, Hanyang University, Ansan, Kyunggi-Do 426-791

The quantum tunneling resonant electron transfer process between a positive ion and a neutral atom collision is investigated in nonthermal generalized Lorentzian plasmas. The result shows that the nonthermal effect enhances the resonant electron transfer cross section in Lorentzian plasmas. It is found that the nonthermal effect on the classical resonant electron transfer cross section is more significant than that on the quantum tunneling resonant charge transfer cross section. It is shown that the nonthermal effect on the resonant electron transfer cross section decreases with an increase of the Debye length. In addition, the nonthermal effect on the quantum tunnelingmore » resonant electron transfer cross section decreases with increasing collision energy. The variation of nonthermal and plasma shielding effects on the quantum tunneling resonant electron transfer process is also discussed.« less

Ultrafast direct electron transfer at organic semiconductor and metal interfaces.

PubMed

Xiang, Bo; Li, Yingmin; Pham, C Huy; Paesani, Francesco; Xiong, Wei

2017-11-01

The ability to control direct electron transfer can facilitate the development of new molecular electronics, light-harvesting materials, and photocatalysis. However, control of direct electron transfer has been rarely reported, and the molecular conformation-electron dynamics relationships remain unclear. We describe direct electron transfer at buried interfaces between an organic polymer semiconductor film and a gold substrate by observing the first dynamical electric field-induced vibrational sum frequency generation (VSFG). In transient electric field-induced VSFG measurements on this system, we observe dynamical responses (<150 fs) that depend on photon energy and polarization, demonstrating that electrons are directly transferred from the Fermi level of gold to the lowest unoccupied molecular orbital of organic semiconductor. Transient spectra further reveal that, although the interfaces are prepared without deliberate alignment control, a subensemble of surface molecules can adopt conformations for direct electron transfer. Density functional theory calculations support the experimental results and ascribe the observed electron transfer to a flat-lying polymer configuration in which electronic orbitals are found to be delocalized across the interface. The present observation of direct electron transfer at complex interfaces and the insights gained into the relationship between molecular conformations and electron dynamics will have implications for implementing novel direct electron transfer in energy materials.

Contribution of direct electron transfer mechanisms to overall electron transfer in microbial fuel cells utilising Shewanella oneidensis as biocatalyst.

PubMed

Fapetu, Segun; Keshavarz, Taj; Clements, Mark; Kyazze, Godfrey

2016-09-01

To investigate the contribution of direct electron transfer mechanisms to electricity production in microbial fuel cells by physically retaining Shewanella oneidensis cells close to or away from the anode electrode. A maximum power output of 114 ± 6 mWm(-2) was obtained when cells were retained close to the anode using a dialysis membrane. This was 3.5 times more than when the cells were separated away from the anode. Without the membrane the maximum power output was 129 ± 6 mWm(-2). The direct mechanisms of electron transfer contributed significantly to overall electron transfer from S. oneidensis to electrodes, a result that was corroborated by another experiment where S. oneidensis cells were entrapped in alginate gels. S. oneidensis transfers electrons primarily by direct electron transfer as opposed to mediated electron transfer.

Suppression of BRCA2 by Mutant Mitochondrial DNA in Prostate Cancer

DTIC Science & Technology

2011-05-01

Briefly, the electron transfer activities of complex I/III (NADH dehydrogenase/cytochrome bc1 complex: catalyzes the electron transfer from NADH to...ferricytochrome c) and complex II/III (succinate dehydrogenase/cytochrome bc1 complex: catalyzes the electron transfer from succinate to ferricytochrome...The electron transfer activity of complex IV (cytochrome c oxidase: catalyzes the final step of the respiratory chain by transferring electrons from

Electrochemical Measurement of Electron Transfer Kinetics by Shewanella oneidensis MR-1*

PubMed Central

Baron, Daniel; LaBelle, Edward; Coursolle, Dan; Gralnick, Jeffrey A.; Bond, Daniel R.

2009-01-01

Shewanella oneidensis strain MR-1 can respire using carbon electrodes and metal oxyhydroxides as electron acceptors, requiring mechanisms for transferring electrons from the cell interior to surfaces located beyond the cell. Although purified outer membrane cytochromes will reduce both electrodes and metals, S. oneidensis also secretes flavins, which accelerate electron transfer to metals and electrodes. We developed techniques for detecting direct electron transfer by intact cells, using turnover and single turnover voltammetry. Metabolically active cells attached to graphite electrodes produced thin (submonolayer) films that demonstrated both catalytic and reversible electron transfer in the presence and absence of flavins. In the absence of soluble flavins, electron transfer occurred in a broad potential window centered at ∼0 V (versus standard hydrogen electrode), and was altered in single (ΔomcA, ΔmtrC) and double deletion (ΔomcA/ΔmtrC) mutants of outer membrane cytochromes. The addition of soluble flavins at physiological concentrations significantly accelerated electron transfer and allowed catalytic electron transfer to occur at lower applied potentials (−0.2 V). Scan rate analysis indicated that rate constants for direct electron transfer were slower than those reported for pure cytochromes (∼1 s−1). These observations indicated that anodic current in the higher (>0 V) window is due to activation of a direct transfer mechanism, whereas electron transfer at lower potentials is enabled by flavins. The electrochemical dissection of these activities in living cells into two systems with characteristic midpoint potentials and kinetic behaviors explains prior observations and demonstrates the complementary nature of S. oneidensis electron transfer strategies. PMID:19661057

Reorganization energy upon charging a single molecule on an insulator measured by atomic force microscopy

NASA Astrophysics Data System (ADS)

Fatayer, Shadi; Schuler, Bruno; Steurer, Wolfram; Scivetti, Ivan; Repp, Jascha; Gross, Leo; Persson, Mats; Meyer, Gerhard

2018-05-01

Intermolecular single-electron transfer on electrically insulating films is a key process in molecular electronics1-4 and an important example of a redox reaction5,6. Electron-transfer rates in molecular systems depend on a few fundamental parameters, such as interadsorbate distance, temperature and, in particular, the Marcus reorganization energy7. This crucial parameter is the energy gain that results from the distortion of the equilibrium nuclear geometry in the molecule and its environment on charging8,9. The substrate, especially ionic films10, can have an important influence on the reorganization energy11,12. Reorganization energies are measured in electrochemistry13 as well as with optical14,15 and photoemission spectroscopies16,17, but not at the single-molecule limit and nor on insulating surfaces. Atomic force microscopy (AFM), with single-charge sensitivity18-22, atomic-scale spatial resolution20 and operable on insulating films, overcomes these challenges. Here, we investigate redox reactions of single naphthalocyanine (NPc) molecules on multilayered NaCl films. Employing the atomic force microscope as an ultralow current meter allows us to measure the differential conductance related to transitions between two charge states in both directions. Thereby, the reorganization energy of NPc on NaCl is determined as (0.8 ± 0.2) eV, and density functional theory (DFT) calculations provide the atomistic picture of the nuclear relaxations on charging. Our approach presents a route to perform tunnelling spectroscopy of single adsorbates on insulating substrates and provides insight into single-electron intermolecular transport.

Hydrated Electron Transfer to Nucleobases in Aqueous Solutions Revealed by Ab Initio Molecular Dynamics Simulations.

PubMed

Zhao, Jing; Wang, Mei; Fu, Aiyun; Yang, Hongfang; Bu, Yuxiang

2015-08-03

We present an ab initio molecular dynamics (AIMD) simulation study into the transfer dynamics of an excess electron from its cavity-shaped hydrated electron state to a hydrated nucleobase (NB)-bound state. In contrast to the traditional view that electron localization at NBs (G/A/C/T), which is the first step for electron-induced DNA damage, is related only to dry or prehydrated electrons, and a fully hydrated electron no longer transfers to NBs, our AIMD simulations indicate that a fully hydrated electron can still transfer to NBs. We monitored the transfer dynamics of fully hydrated electrons towards hydrated NBs in aqueous solutions by using AIMD simulations and found that due to solution-structure fluctuation and attraction of NBs, a fully hydrated electron can transfer to a NB gradually over time. Concurrently, the hydrated electron cavity gradually reorganizes, distorts, and even breaks. The transfer could be completed in about 120-200 fs in four aqueous NB solutions, depending on the electron-binding ability of hydrated NBs and the structural fluctuation of the solution. The transferring electron resides in the π*-type lowest unoccupied molecular orbital of the NB, which leads to a hydrated NB anion. Clearly, the observed transfer of hydrated electrons can be attributed to the strong electron-binding ability of hydrated NBs over the hydrated electron cavity, which is the driving force, and the transfer dynamics is structure-fluctuation controlled. This work provides new insights into the evolution dynamics of hydrated electrons and provides some helpful information for understanding the DNA-damage mechanism in solution. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Numerical model of the plasma formation at electron beam welding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Trushnikov, D. N., E-mail: trdimitr@yandex.ru; The Department for Welding Production and Technology of Constructional Materials, Perm National Research Polytechnic University, Perm 614990; Mladenov, G. M., E-mail: gmmladenov@abv.bg

2015-01-07

The model of plasma formation in the keyhole in liquid metal as well as above the electron beam welding zone is described. The model is based on solution of two equations for the density of electrons and the mean electron energy. The mass transfer of heavy plasma particles (neutral atoms, excited atoms, and ions) is taken into account in the analysis by the diffusion equation for a multicomponent mixture. The electrostatic field is calculated using the Poisson equation. Thermionic electron emission is calculated for the keyhole wall. The ionization intensity of the vapors due to beam electrons and high-energy secondarymore » and backscattered electrons is calibrated using the plasma parameters when there is no polarized collector electrode above the welding zone. The calculated data are in good agreement with experimental data. Results for the plasma parameters for excitation of a non-independent discharge are given. It is shown that there is a need to take into account the effect of a strong electric field near the keyhole walls on electron emission (the Schottky effect) in the calculation of the current for a non-independent discharge (hot cathode gas discharge). The calculated electron drift velocities are much bigger than the velocity at which current instabilities arise. This confirms the hypothesis for ion-acoustic instabilities, observed experimentally in previous research.« less

Electron transfer and conformational change in complexes of trimethylamine dehydrogenase and electron transferring flavoprotein.

PubMed

Jones, Matthew; Talfournier, Francois; Bobrov, Anton; Grossmann, J Günter; Vekshin, Nikolai; Sutcliffe, Michael J; Scrutton, Nigel S

2002-03-08

The trimethylamine dehydrogenase-electron transferring flavoprotein (TMADH.ETF) electron transfer complex has been studied by fluorescence and absorption spectroscopies. These studies indicate that a series of conformational changes occur during the assembly of the TMADH.ETF electron transfer complex and that the kinetics of assembly observed with mutant TMADH (Y442F/L/G) or ETF (alpha R237A) complexes are much slower than are the corresponding rates of electron transfer in these complexes. This suggests that electron transfer does not occur in the thermodynamically most favorable state (which takes too long to form), but that one or more metastable states (which are formed more rapidly) are competent in transferring electrons from TMADH to ETF. Additionally, fluorescence spectroscopy studies of the TMADH.ETF complex indicate that ETF undergoes a stable conformational change (termed structural imprinting) when it interacts transiently with TMADH to form a second, distinct, structural form. The mutant complexes compromise imprinting of ETF, indicating a dependence on the native interactions present in the wild-type complex. The imprinted form of semiquinone ETF exhibits an enhanced rate of electron transfer to the artificial electron acceptor, ferricenium. Overall molecular conformations as probed by small-angle x-ray scattering studies are indistinguishable for imprinted and non-imprinted ETF, suggesting that changes in structure likely involve confined reorganizations within the vicinity of the FAD. Our results indicate a series of conformational events occur during the assembly of the TMADH.ETF electron transfer complex, and that the properties of electron transfer proteins can be affected lastingly by transient interaction with their physiological redox partners. This may have significant implications for our understanding of biological electron transfer reactions in vivo, because ETF encounters TMADH at all times in the cell. Our studies suggest that caution needs to be exercised in extrapolating the properties of in vitro interprotein electron transfer reactions to those occurring in vivo.

31 CFR 208.3 - Payment by electronic funds transfer.

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2011-07-01

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48 CFR 18.124 - Electronic funds transfer.

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2011-10-01

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48 CFR 18.124 - Electronic funds transfer.

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2013-10-01

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31 CFR 208.3 - Payment by electronic funds transfer.

Code of Federal Regulations, 2012 CFR

2012-07-01

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48 CFR 18.123 - Electronic funds transfer.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 48 Federal Acquisition Regulations System 1 2010-10-01 2010-10-01 false Electronic funds transfer. 18.123 Section 18.123 Federal Acquisition Regulations System FEDERAL ACQUISITION REGULATION... Electronic funds transfer. Electronic funds transfer payments may be waived for acquisitions to support...

48 CFR 18.124 - Electronic funds transfer.

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2012-10-01

... 48 Federal Acquisition Regulations System 1 2012-10-01 2012-10-01 false Electronic funds transfer. 18.124 Section 18.124 Federal Acquisition Regulations System FEDERAL ACQUISITION REGULATION... Electronic funds transfer. Electronic funds transfer payments may be waived for acquisitions to support...

48 CFR 18.124 - Electronic funds transfer.

Code of Federal Regulations, 2014 CFR

2014-10-01

... 48 Federal Acquisition Regulations System 1 2014-10-01 2014-10-01 false Electronic funds transfer. 18.124 Section 18.124 Federal Acquisition Regulations System FEDERAL ACQUISITION REGULATION... Electronic funds transfer. Electronic funds transfer payments may be waived for acquisitions to support...

Quantifying Environmental Effects on the Decay of Hole Transfer Couplings in Biosystems.

PubMed

Ramos, Pablo; Pavanello, Michele

2014-06-10

In the past two decades, many research groups worldwide have tried to understand and categorize simple regimes in the charge transfer of such biological systems as DNA. Theoretically speaking, the lack of exact theories for electron-nuclear dynamics on one side and poor quality of the parameters needed by model Hamiltonians and nonadiabatic dynamics alike (such as couplings and site energies) on the other are the two main difficulties for an appropriate description of the charge transfer phenomena. In this work, we present an application of a previously benchmarked and linear-scaling subsystem density functional theory (DFT) method for the calculation of couplings, site energies, and superexchange decay factors (β) of several biological donor-acceptor dyads, as well as double stranded DNA oligomers composed of up to five base pairs. The calculations are all-electron and provide a clear view of the role of the environment on superexchange couplings in DNA-they follow experimental trends and confirm previous semiempirical calculations. The subsystem DFT method is proven to be an excellent tool for long-range, bridge-mediated coupling and site energy calculations of embedded molecular systems.

Quantitative analysis of intramolecular exciplex and electron transfer in a double-linked zinc porphyrin-fullerene dyad.

PubMed

Al-Subi, Ali Hanoon; Niemi, Marja; Tkachenko, Nikolai V; Lemmetyinen, Helge

2012-10-04

Photoinduced charge transfer in a double-linked zinc porphyrin-fullerene dyad is studied. When the dyad is excited at the absorption band of the charge-transfer complex (780 nm), an intramolecular exciplex is formed, followed by the complete charge separated (CCS) state. By analyzing the results obtained from time-resolved transient absorption and emission decay measurements in a range of solvents with different polarities, we derived a dependence between the observable lifetimes and internal parameters controlling the reaction rate constants based on the semiquantum Marcus electron-transfer theory. The critical value of the solvent polarity was found to be ε(r) ≈ 6.5: in solvents with higher dielectric constants, the energy of the CCS state is lower than that of the exciplex and the relaxation takes place via the CCS state predominantly, whereas in solvents with lower polarities the energy of the CCS state is higher and the exciplex relaxes directly to the ground state. In solvents with moderate polarities the exciplex and the CCS state are in equilibrium and cannot be separated spectroscopically. The degree of the charge shift in the exciplex relative to that in the CCS state was estimated to be 0.55 ± 0.02. The electronic coupling matrix elements for the charge recombination process and for the direct relaxation of the exciplex to the ground state were found to be 0.012 ± 0.001 and 0.245 ± 0.022 eV, respectively.

Electrical transport engineering of semiconductor superlattice structures

NASA Astrophysics Data System (ADS)

Shokri, Aliasghar

2014-04-01

We investigate the influence of doping concentration on band structures of electrons and electrical transmission in a typical aperiodic semiconductor superlattice consisting of quantum well and barrier layers, theoretically. For this purpose, we assume that each unit cell of the superlattice contains alternately two types of material GaAs (as a well) and GaAlAs (as a barrier) with six sublayers of two materials. Our calculations are based on the generalized Kronig-Penny (KP) model and the transfer matrix method within the framework of the parabolic conductance band effective mass approximation in the coherent regime. This model reduces the numerical calculation time and enables us to use the transfer matrix method to investigate transport in the superlattices. We show that by varying the doping concentration and geometrical parameters, one can easily block the transmission of the electrons. The numerical results may be useful in designing of nanoenergy filter devices.

Photoinduced electron transfer from semiconductor quantum dots to metal oxide nanoparticles

PubMed Central

Tvrdy, Kevin; Frantsuzov, Pavel A.; Kamat, Prashant V.

2011-01-01

Quantum dot-metal oxide junctions are an integral part of next-generation solar cells, light emitting diodes, and nanostructured electronic arrays. Here we present a comprehensive examination of electron transfer at these junctions, using a series of CdSe quantum dot donors (sizes 2.8, 3.3, 4.0, and 4.2 nm in diameter) and metal oxide nanoparticle acceptors (SnO2, TiO2, and ZnO). Apparent electron transfer rate constants showed strong dependence on change in system free energy, exhibiting a sharp rise at small driving forces followed by a modest rise further away from the characteristic reorganization energy. The observed trend mimics the predicted behavior of electron transfer from a single quantum state to a continuum of electron accepting states, such as those present in the conduction band of a metal oxide nanoparticle. In contrast with dye-sensitized metal oxide electron transfer studies, our systems did not exhibit unthermalized hot-electron injection due to relatively large ratios of electron cooling rate to electron transfer rate. To investigate the implications of these findings in photovoltaic cells, quantum dot-metal oxide working electrodes were constructed in an identical fashion to the films used for the electron transfer portion of the study. Interestingly, the films which exhibited the fastest electron transfer rates (SnO2) were not the same as those which showed the highest photocurrent (TiO2). These findings suggest that, in addition to electron transfer at the quantum dot-metal oxide interface, other electron transfer reactions play key roles in the determination of overall device efficiency. PMID:21149685

Photoinduced electron transfer from semiconductor quantum dots to metal oxide nanoparticles.

PubMed

Tvrdy, Kevin; Frantsuzov, Pavel A; Kamat, Prashant V

2011-01-04

Quantum dot-metal oxide junctions are an integral part of next-generation solar cells, light emitting diodes, and nanostructured electronic arrays. Here we present a comprehensive examination of electron transfer at these junctions, using a series of CdSe quantum dot donors (sizes 2.8, 3.3, 4.0, and 4.2 nm in diameter) and metal oxide nanoparticle acceptors (SnO(2), TiO(2), and ZnO). Apparent electron transfer rate constants showed strong dependence on change in system free energy, exhibiting a sharp rise at small driving forces followed by a modest rise further away from the characteristic reorganization energy. The observed trend mimics the predicted behavior of electron transfer from a single quantum state to a continuum of electron accepting states, such as those present in the conduction band of a metal oxide nanoparticle. In contrast with dye-sensitized metal oxide electron transfer studies, our systems did not exhibit unthermalized hot-electron injection due to relatively large ratios of electron cooling rate to electron transfer rate. To investigate the implications of these findings in photovoltaic cells, quantum dot-metal oxide working electrodes were constructed in an identical fashion to the films used for the electron transfer portion of the study. Interestingly, the films which exhibited the fastest electron transfer rates (SnO(2)) were not the same as those which showed the highest photocurrent (TiO(2)). These findings suggest that, in addition to electron transfer at the quantum dot-metal oxide interface, other electron transfer reactions play key roles in the determination of overall device efficiency.

Coexistence of ferromagnetism and superconductivity in iron based pnictides: a time resolved magnetooptical study.

PubMed

Pogrebna, A; Mertelj, T; Vujičić, N; Cao, G; Xu, Z A; Mihailovic, D

2015-01-13

Ferromagnetism and superconductivity are antagonistic phenomena. Their coexistence implies either a modulated ferromagnetic order parameter on a lengthscale shorter than the superconducting coherence length or a weak exchange coupling between the itinerant superconducting electrons and the localized ordered spins. In some iron based pnictide superconductors the coexistence of ferromagnetism and superconductivity has been clearly demonstrated. The nature of the coexistence, however, remains elusive since no clear understanding of the spin structure in the superconducting state has been reached and the reports on the coupling strength are controversial. We show, by a direct optical pump-probe experiment, that the coupling is weak, since the transfer of the excess energy from the itinerant electrons to ordered localized spins is much slower than the electron-phonon relaxation, implying the coexistence without the short-lengthscale ferromagnetic order parameter modulation. Remarkably, the polarization analysis of the coherently excited spin wave response points towards a simple ferromagnetic ordering of spins with two distinct types of ferromagnetic domains.

Photoactive layer based on T-shaped benzimidazole dyes used for solar cell: from photoelectric properties to molecular design

NASA Astrophysics Data System (ADS)

Xu, Beibei; Li, Yuanzuo; Song, Peng; Ma, Fengcai; Sun, Mengtao

2017-03-01

Three benzimidazole-based organic dyes, possessing the same triphenylamine donors and cyanoacrylic acid acceptors with the bithiophene π-bridges combined in different nuclear positions of benzimidazole, were investigated in the utility of dye-sensitizer solar cells. The structure, molecular orbital and energy, absorption spectra and some important parameters (such as light harvesting efficiency (LHE), electron injection driving force, the electron injection time, chemical reactivity parameters, vertical dipole moment as well as interaction models of dye-I2) were obtained according to Newns-Anderson model and DFT calculation. The process and strength of charge transfer and separation were visualized with charge different density and index of spatial extent (S, D and Δq). Current work paid attention to the new T-shaped dyes to reveal the relation between the structure and photoelectric performance. Furthermore, nine dyes (substitution of alkyl chains and π-bridges) have been designed and characterized to screen promising sensitizer candidates with excellent photo-electronic properties.

Electron-transfer reactions of cobalt(III) complexes. 1. The kinetic investigation of the reduction of various surfactant cobalt(III) complexes by iron(II) in surface active ionic liquids

NASA Astrophysics Data System (ADS)

Nagaraj, Karuppiah; Senthil Murugan, Krishnan; Thangamuniyandi, Pilavadi; Sakthinathan, Subramanian

2015-05-01

The kinetics of outer sphere electron transfer reaction of surfactant cobalt(III) complex ions, cis-[Co(en)2(C12H25NH2)2]3+ (1), cis-[Co(dp)2(C12H25NH2)2]3+ (2), cis-[Co(trien)(C12H25NH2)2]3+ (3), cis-[Co(bpy)2(C12H25NH2)2]3+ (4) and cis-[Co(phen)2(C12H25NH2)2]3+ (5) (en: ethylenediamine, dp: diaminopropane, trien : triethylenetetramine, bpy: 2,2‧-bipyridyl, phen: 1,10-phenanthroline and C12H25NH2 : dodecylamine) have been interrogated by Fe2+ ion in ionic liquid (1-butyl-3-methylimidazoliumbromide) medium at different temperatures (298, 303, 308, 313, 318 and 323 K) by the spectrophotometry method under pseudo first order conditions using an excess of the reductant. Experimentally the reactions were found to be of second order and the electron transfer as outer sphere. The second order rate constant for the electron transfer reaction in ionic liquids was found to increase with increase in the concentration of all these surfactant cobalt(III) complexes. Among these complexes (from en to phen ligand), complex containing the phenanthroline ligand rate is higher compared to other complexes. By assuming the outer sphere mechanism, the results have been explained based on the presence of aggregated structures containing cobalt(III) complexes at the surface of ionic liquids formed by the surfactant cobalt(III) complexes in the reaction medium. The activation parameters (enthalpy of activation ΔH‡ and entropy of activation ΔS‡) of the reaction have been calculated which substantiate the kinetics of the reaction.

Electrochemical control over photoinduced electron transfer and trapping in CdSe-CdTe quantum-dot solids.

PubMed

Boehme, Simon C; Walvis, T Ardaan; Infante, Ivan; Grozema, Ferdinand C; Vanmaekelbergh, Daniël; Siebbeles, Laurens D A; Houtepen, Arjan J

2014-07-22

Understanding and controlling charge transfer between different kinds of colloidal quantum dots (QDs) is important for devices such as light-emitting diodes and solar cells and for thermoelectric applications. Here we study photoinduced electron transfer between CdTe and CdSe QDs in a QD film. We find that very efficient electron trapping in CdTe QDs obstructs electron transfer to CdSe QDs under most conditions. Only the use of thiol ligands results in somewhat slower electron trapping; in this case the competition between trapping and electron transfer results in a small fraction of electrons being transferred to CdSe. However, we demonstrate that electron trapping can be controlled and even avoided altogether by using the unique combination of electrochemistry and transient absorption spectroscopy. When the Fermi level is raised electrochemically, traps are filled with electrons and electron transfer from CdTe to CdSe QDs occurs with unity efficiency. These results show the great importance of knowing and controlling the Fermi level in QD films and open up the possibility of studying the density of trap states in QD films as well as the systematic investigation of the intrinsic electron transfer rates in donor-acceptor films.

The R package 'RLumModel': Simulating charge transfer in quartz

NASA Astrophysics Data System (ADS)

Friedrich, Johannes; Kreutzer, Sebastian; Schmidt, Christoph

2017-04-01

Kinetic models of quartz luminescence have gained an important role for predicting experimental results and for understanding charge transfers in (natural) quartz as well as for other dosimetric materials, e.g., Al2O3:C. We present the R package 'RLumModel', offering an easy-to-use tool for simulating quartz luminescence signals (TL, OSL, LM-OSL and RF) based on five integrated and published parameter sets as well as the possibility to use own parameters. Simulation commands can be created (a) using the Risø Sequence Editor, (b) a built-in SAR sequence generator or (c) self-explanatory keywords for customised sequences. Results can be analysed seamlessly using the R package 'Luminescence' along with a visualisation of concentrations of electrons and holes in every trap/centre as well as in the valence and conduction band during all stages of the simulation. Modelling luminescence signals can help understanding charge transfer processes occurring in nature or during measurements in the laboratory. This will lead to a better understanding of several processes concerning geoscientific questions, because quartz is the second most abundant mineral in the Earth's continental crust.

Hot-electron transfer in quantum-dot heterojunction films.

PubMed

Grimaldi, Gianluca; Crisp, Ryan W; Ten Brinck, Stephanie; Zapata, Felipe; van Ouwendorp, Michiko; Renaud, Nicolas; Kirkwood, Nicholas; Evers, Wiel H; Kinge, Sachin; Infante, Ivan; Siebbeles, Laurens D A; Houtepen, Arjan J

2018-06-13

Thermalization losses limit the photon-to-power conversion of solar cells at the high-energy side of the solar spectrum, as electrons quickly lose their energy relaxing to the band edge. Hot-electron transfer could reduce these losses. Here, we demonstrate fast and efficient hot-electron transfer between lead selenide and cadmium selenide quantum dots assembled in a quantum-dot heterojunction solid. In this system, the energy structure of the absorber material and of the electron extracting material can be easily tuned via a variation of quantum-dot size, allowing us to tailor the energetics of the transfer process for device applications. The efficiency of the transfer process increases with excitation energy as a result of the more favorable competition between hot-electron transfer and electron cooling. The experimental picture is supported by time-domain density functional theory calculations, showing that electron density is transferred from lead selenide to cadmium selenide quantum dots on the sub-picosecond timescale.

Thermodynamic and kinetic studies of As2O3 toxicological effects on human insulin in generation diabetes mellitus

NASA Astrophysics Data System (ADS)

Mohsennia, Mohsen; Motaharinejad, Atieh; Rafiee-Pour, Hossain-Ali; Torabbeigi, Marzieh

2017-12-01

The interaction of arsenic trioxide with human insulin was investigated by circular dichroism (CD), cyclic voltammetry and electrophoresis techniques. The interfacial behavior of insulin in presence of As2O3 onto the Ag electrode surface was studied at 310 K in phosphate buffer solution (PBS). According to Far-UV CD spectroscopy results, As2O3 caused to decrease in structural compactness and variety of alpha helix into beta structures. Near-UV CD indicated that As2O3 dissociates disulfide linkage in insulin structure. The kinetic parameters, including charge-transfer coefficient and apparent heterogeneous electron transfer rate constant were also determined. The thermodynamic parameters of insulin denaturation in presence of arsenic trioxide were calculated and reported. The obtained results indicated strong adsorption of insulin in presence of arsenic trioxide onto the Ag surface via chemisorptions.

Method for extracting relevant electrical parameters from graphene field-effect transistors using a physical model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boscá, A., E-mail: alberto.bosca@upm.es; Dpto. de Ingeniería Electrónica, E.T.S.I. de Telecomunicación, Universidad Politécnica de Madrid, Madrid 28040; Pedrós, J.

2015-01-28

Due to its intrinsic high mobility, graphene has proved to be a suitable material for high-speed electronics, where graphene field-effect transistor (GFET) has shown excellent properties. In this work, we present a method for extracting relevant electrical parameters from GFET devices using a simple electrical characterization and a model fitting. With experimental data from the device output characteristics, the method allows to calculate parameters such as the mobility, the contact resistance, and the fixed charge. Differentiated electron and hole mobilities and direct connection with intrinsic material properties are some of the key aspects of this method. Moreover, the method outputmore » values can be correlated with several issues during key fabrication steps such as the graphene growth and transfer, the lithographic steps, or the metalization processes, providing a flexible tool for quality control in GFET fabrication, as well as a valuable feedback for improving the material-growth process.« less

Control voltage and power fluctuations when connecting wind farms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Berinde, Ioan, E-mail: ioan-berinde@yahoo.com; Bălan, Horia, E-mail: hbalan@mail.utcluj.ro; Oros, Teodora Susana, E-mail: teodoraoros-87@yahoo.com

2015-12-23

Voltage, frequency, active power and reactive power are very important parameters in terms of power quality. These parameters are followed when connecting any power plant, the more the connection of wind farms. Connecting wind farms to the electricity system must not cause interference outside the limits set by regulations. Modern solutions for fast and automatic voltage control and power fluctuations using electronic control systems of reactive power flows. FACTS (Flexible Alternating Current Transmision System) systems, established on the basis of power electronic circuits ensure control of electrical status quantities to achieve the necessary transfer of power to the power grid.more » FACTS devices can quickly control parameters and sizes of state power lines, such as impedance line voltages and phase angles of the voltages of the two ends of the line. Their use can lead to improvement in power system operation by increasing the transmission capacity of power lines, power flow control lines, improved static and transient stability reserve.« less

Electron-transfer oxidation properties of DNA bases and DNA oligomers.

PubMed

Fukuzumi, Shunichi; Miyao, Hiroshi; Ohkubo, Kei; Suenobu, Tomoyoshi

2005-04-21

Kinetics for the thermal and photoinduced electron-transfer oxidation of a series of DNA bases with various oxidants having the known one-electron reduction potentials (E(red)) in an aqueous solution at 298 K were examined, and the resulting electron-transfer rate constants (k(et)) were evaluated in light of the free energy relationship of electron transfer to determine the one-electron oxidation potentials (E(ox)) of DNA bases and the intrinsic barrier of the electron transfer. Although the E(ox) value of GMP at pH 7 is the lowest (1.07 V vs SCE) among the four DNA bases, the highest E(ox) value (CMP) is only 0.19 V higher than that of GMP. The selective oxidation of GMP in the thermal electron-transfer oxidation of GMP results from a significant decrease in the pH dependent oxidation potential due to the deprotonation of GMP*+. The one-electron reduced species of the photosensitizer produced by photoinduced electron transfer are observed as the transient absorption spectra when the free energy change of electron transfer is negative. The rate constants of electron-transfer oxidation of the guanine moieties in DNA oligomers with Fe(bpy)3(3+) and Ru(bpy)3(3+) were also determined using DNA oligomers containing different guanine (G) sequences from 1 to 10 G. The rate constants of electron-transfer oxidation of the guanine moieties in single- and double-stranded DNA oligomers with Fe(bpy)3(2+) and Ru(bpy)3(3+) are dependent on the number of sequential guanine molecules as well as on pH.

EPR parameters of L-α-alanine radicals in aqueous solution: a first-principles study

NASA Astrophysics Data System (ADS)

Janbazi, Mehdi; T. Azar, Yavar; Ziaie, Farhood

2018-07-01

EPR (electron paramagnetic resonance) response for a wide range of possible alanine radicals has been analysed employing quantum chemical methods. The strong correlation between geometry and EPR parameter structure of these radicals has been shown in this research work. Significant solvent effect on EPR parameters has been shown employing both explicit and implicit solvent models. In a relatively good agreement with the experiment, stable conformation of these radicals in acidic and basic conditions was determined, and a new conformation was suggested based on possible proton transfer in the intermediate pH range. The employed methodology along with experimental results may be used for the characterisation of different radiation-induced amino acid radicals.

Nuclear conversion theory: molecular hydrogen in non-magnetic insulators

NASA Astrophysics Data System (ADS)

Ilisca, Ernest; Ghiglieno, Filippo

2016-09-01

The hydrogen conversion patterns on non-magnetic solids sensitively depend upon the degree of singlet/triplet mixing in the intermediates of the catalytic reaction. Three main `symmetry-breaking' interactions are brought together. In a typical channel, the electron spin-orbit (SO) couplings introduce some magnetic excitations in the non-magnetic solid ground state. The electron spin is exchanged with a molecular one by the electric molecule-solid electron repulsion, mixing the bonding and antibonding states and affecting the molecule rotation. Finally, the magnetic hyperfine contact transfers the electron spin angular momentum to the nuclei. Two families of channels are considered and a simple criterion based on the SO coupling strength is proposed to select the most efficient one. The denoted `electronic' conversion path involves an emission of excitons that propagate and disintegrate in the bulk. In the other denoted `nuclear', the excited electron states are transients of a loop, and the electron system returns to its fundamental ground state. The described model enlarges previous studies by extending the electron basis to charge-transfer states and `continui' of band states, and focuses on the broadening of the antibonding molecular excited state by the solid conduction band that provides efficient tunnelling paths for the hydrogen conversion. After working out the general conversion algebra, the conversion rates of hydrogen on insulating and semiconductor solids are related to a few molecule-solid parameters (gap width, ionization and affinity potentials) and compared with experimental measures.

14 CFR 1274.931 - Electronic funds transfer payment methods.

Code of Federal Regulations, 2011 CFR

2011-01-01

... 14 Aeronautics and Space 5 2011-01-01 2010-01-01 true Electronic funds transfer payment methods... COOPERATIVE AGREEMENTS WITH COMMERCIAL FIRMS Other Provisions and Special Conditions § 1274.931 Electronic funds transfer payment methods. Electronic Funds Transfer Payment Methods July 2002 Payments under this...

77 FR 40459 - Electronic Fund Transfers (Regulation E); Correction

Federal Register 2010, 2011, 2012, 2013, 2014

2012-07-10

... Electronic Fund Transfers (Regulation E); Correction AGENCY: Bureau of Consumer Financial Protection. ACTION... published the Final Rule (77 FR 6194), which implements the Electronic Fund Transfer Act, and the official... Sec. 1005.3(a) in the interim final rule, Electronic Fund Transfers (Regulation E), published on...

14 CFR 1274.931 - Electronic funds transfer payment methods.

Code of Federal Regulations, 2013 CFR

2013-01-01

... 14 Aeronautics and Space 5 2013-01-01 2013-01-01 false Electronic funds transfer payment methods... COOPERATIVE AGREEMENTS WITH COMMERCIAL FIRMS Other Provisions and Special Conditions § 1274.931 Electronic funds transfer payment methods. Electronic Funds Transfer Payment Methods July 2002 Payments under this...

Electric-field-driven electron-transfer in mixed-valence molecules

DOE Office of Scientific and Technical Information (OSTI.GOV)

Blair, Enrique P., E-mail: enrique-blair@baylor.edu; Corcelli, Steven A., E-mail: scorcell@nd.edu; Lent, Craig S., E-mail: lent@nd.edu

2016-07-07

Molecular quantum-dot cellular automata is a computing paradigm in which digital information is encoded by the charge configuration of a mixed-valence molecule. General-purpose computing can be achieved by arranging these compounds on a substrate and exploiting intermolecular Coulombic coupling. The operation of such a device relies on nonequilibrium electron transfer (ET), whereby the time-varying electric field of one molecule induces an ET event in a neighboring molecule. The magnitude of the electric fields can be quite large because of close spatial proximity, and the induced ET rate is a measure of the nonequilibrium response of the molecule. We calculate themore » electric-field-driven ET rate for a model mixed-valence compound. The mixed-valence molecule is regarded as a two-state electronic system coupled to a molecular vibrational mode, which is, in turn, coupled to a thermal environment. Both the electronic and vibrational degrees-of-freedom are treated quantum mechanically, and the dissipative vibrational-bath interaction is modeled with the Lindblad equation. This approach captures both tunneling and nonadiabatic dynamics. Relationships between microscopic molecular properties and the driven ET rate are explored for two time-dependent applied fields: an abruptly switched field and a linearly ramped field. In both cases, the driven ET rate is only weakly temperature dependent. When the model is applied using parameters appropriate to a specific mixed-valence molecule, diferrocenylacetylene, terahertz-range ET transfer rates are predicted.« less

Disruption of the ndhF1 gene affects Chl fluorescence through state transition in the Cyanobacterium Synechocystis sp. PCC 6803, resulting in apparent high efficiency of photosynthesis.

PubMed

Ogawa, Takako; Harada, Tetsuyuki; Ozaki, Hiroshi; Sonoike, Kintake

2013-07-01

In Synechocystis sp. PCC 6803, the disruption of the ndhF1 gene (slr0844), which encodes a subunit of one of the NDH-1 complexes (NDH-1L complex) serving for respiratory electron transfer, causes the largest change in Chl fluorescence induction kinetics among the kinetics of 750 disruptants searched in the Fluorome, the cyanobacterial Chl fluorescence database. The cause of the explicit phenotype of the ndhF1 disruptant was examined by measurements of the photosynthetic rate, Chl fluorescence and state transition. The results demonstrate that the defects in respiratory electron transfer obviously have great impact on Chl fluorescence in cyanobacteria. The inactivation of NDH-1L complexes involving electron transfer from NDH-1 to plastoquinone (PQ) would result in the oxidation of the PQ pool, leading to the transition to State 1, where the yield of Chl fluorescence is high. Apparently, respiration, although its rate is far lower than that of photosynthesis, could affect Chl fluorescence through the state transition as leverage. The disruption of the ndhF1 gene caused lower oxygen-evolving activity but the estimated electron transport rate from Chl fluorescence measurements was faster in the mutant than in the wild-type cells. The discrepancy could be ascribed to the decreased level of non-photochemical quenching due to state transition. One must be cautious when using the Chl fluorescence parameter to estimate photosynthesis in mutants defective in state transition.

Range parameters of slow gold ions implanted into light targets

NASA Astrophysics Data System (ADS)

Kuzmin, V.

2009-08-01

Interatomic potentials for Au-C, Au-B, Au-N and Au-Si systems, calculated with density-functional theory (DFT) methods, have been used to evaluate the range parameters of gold in B, Si, BN and SiC films at energies of about 10-400 keV. The potentials have been employed to describe scattering angles of a projectile and to calculate the nuclear stopping powers and the higher moments of the energy, transferred in single collisions. Utilizing these findings the range parameters have been obtained by the standard transport theory and by Monte-Carlo simulations. A velocity proportional electronic stopping was included into the consideration. The approach developed corresponds completely to the standard classical scheme of the calculation of range parameters. Good agreement between the computed range parameters and available experimental data allow us to conclude that correlation effects between the nuclear and electronic stopping can be neglected in the energy range in question. Moreover, it is proven for the first time that the model by Grande, et al. [P.L. Grande, F.C. Zawislak, D. Fink, M. Behar, Nucl. Instr. and Meth. B 61 (1991) 282], which relies on the importance of correlation effects, contains inherent contradictions.

Temperature gradients due to adiabatic plasma expansion in a magnetic nozzle

NASA Astrophysics Data System (ADS)

Sheehan, J. P.; Longmier, B. W.; Bering, E. A.; Olsen, C. S.; Squire, J. P.; Ballenger, M. G.; Carter, M. D.; Cassady, L. D.; Díaz, F. R. Chang; Glover, T. W.; Ilin, A. V.

2014-08-01

A mechanism for ambipolar ion acceleration in a magnetic nozzle is proposed. The plasma is adiabatic (i.e., does not exchange energy with its surroundings) in the diverging section of a magnetic nozzle so any energy lost by the electrons must be transferred to the ions via the electric field. Fluid theory indicates that the change in plasma potential is proportional to the change in average electron energy. These predictions were compared to measurements in the VX-200 experiment which has conditions conducive to ambipolar ion acceleration. A planar Langmuir probe was used to measure the plasma potential, electron density, and electron temperature for a range of mass flow rates and power levels. Axial profiles of those parameters were also measured, showing consistency with the adiabatic ambipolar fluid theory.

Laser-Material Interactions for Flexible Applications.

PubMed

Joe, Daniel J; Kim, Seungjun; Park, Jung Hwan; Park, Dae Yong; Lee, Han Eol; Im, Tae Hong; Choi, Insung; Ruoff, Rodney S; Lee, Keon Jae

2017-07-01

The use of lasers for industrial, scientific, and medical applications has received an enormous amount of attention due to the advantageous ability of precise parameter control for heat transfer. Laser-beam-induced photothermal heating and reactions can modify nanomaterials such as nanoparticles, nanowires, and two-dimensional materials including graphene, in a controlled manner. There have been numerous efforts to incorporate lasers into advanced electronic processing, especially for inorganic-based flexible electronics. In order to resolve temperature issues with plastic substrates, laser-material processing has been adopted for various applications in flexible electronics including energy devices, processors, displays, and other peripheral electronic components. Here, recent advances in laser-material interactions for inorganic-based flexible applications with regard to both materials and processes are presented. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effect of the structure of imidazolium cations in [BF4](-)-type ionic liquids on direct electrochemistry and electrocatalysis of horseradish peroxidase in Nafion films.

PubMed

Lu, Lu; Huang, Xirong; Qu, Yinbo

2011-10-01

The direct electrochemistry and bioelectrocatalysis of horseradish peroxidase (HRP) in Nafion films at glassy carbon electrode (GCE) was investigated in three [BF(4)](-)-type room-temperature ionic liquids (ILs) to understand the structural effect of imidazolium cations. The three ILs are 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim][BF(4)]), 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF(4)]) and 1-hexyl-3-methylimidazolium tetrafluoroborate ([Hmim][BF(4)]). A small amount of water in the three ILs is indispensable for maintaining the electrochemical activity of HRP in Nafion films, and the optimum water contents decrease with the increase of alkyl chain length on imidazole ring. Analysis shows that the optimum water contents are primarily determined by the hydrophilicity of ILs used. In contrast to aqueous medium, ILs media facilitate the direct electron transfer of HRP, and the electrochemical parameters obtained in different ILs are obviously related to the nature of ILs. The direct electron transfer between HRP and GCE is a surface-confined quasi-reversible single electron transfer process. The apparent heterogeneous electron transfer rate constant decreases gradually with the increase of alkyl chain length on imidazole ring, but the changing extent is relatively small. The electrocatalytic reduction current of H(2)O(2) at the present electrode decreases obviously with the increase of alkyl chain length, and the mass transfer of H(2)O(2) via diffusion in ILs should be responsible for the change. In addition, the modified electrode has good stability and reproducibility; the ability to tolerate high levels of F(-) has been greatly enhanced due to the use of Nafion film. When an appropriate mediator is included in the sensing layer, a sensitive nonaqueous biosensor could be fabricated. Copyright © 2011 Elsevier B.V. All rights reserved.

14 CFR § 1260.69 - Electronic funds transfer payment methods.

Code of Federal Regulations, 2014 CFR

2014-01-01

... 14 Aeronautics and Space 5 2014-01-01 2014-01-01 false Electronic funds transfer payment methods... GRANTS AND COOPERATIVE AGREEMENTS General Special Conditions § 1260.69 Electronic funds transfer payment methods. Electronic Funds Transfer Payment Methods October 2000 (a) Payments under this grant will be made...

14 CFR 1260.69 - Electronic funds transfer payment methods.

Code of Federal Regulations, 2013 CFR

2013-01-01

... 14 Aeronautics and Space 5 2013-01-01 2013-01-01 false Electronic funds transfer payment methods... COOPERATIVE AGREEMENTS General Special Conditions § 1260.69 Electronic funds transfer payment methods. Electronic Funds Transfer Payment Methods October 2000 (a) Payments under this grant will be made by the...

14 CFR 1260.69 - Electronic funds transfer payment methods.

Code of Federal Regulations, 2012 CFR

2012-01-01

... 14 Aeronautics and Space 5 2012-01-01 2012-01-01 false Electronic funds transfer payment methods... COOPERATIVE AGREEMENTS General Special Conditions § 1260.69 Electronic funds transfer payment methods. Electronic Funds Transfer Payment Methods October 2000 (a) Payments under this grant will be made by the...

14 CFR 1260.69 - Electronic funds transfer payment methods.

Code of Federal Regulations, 2011 CFR

2011-01-01

... 14 Aeronautics and Space 5 2011-01-01 2010-01-01 true Electronic funds transfer payment methods... COOPERATIVE AGREEMENTS General Special Conditions § 1260.69 Electronic funds transfer payment methods. Electronic Funds Transfer Payment Methods October 2000 (a) Payments under this grant will be made by the...

Bands dispersion and charge transfer in β-BeH2

NASA Astrophysics Data System (ADS)

Trivedi, D. K.; Galav, K. L.; Joshi, K. B.

2018-04-01

Predictive capabilities of ab-initio method are utilised to explore bands dispersion and charge transfer in β-BeH2. Investigations are carried out using the linear combination of atomic orbitals method at the level of density functional theory. The crystal structure and related parameters are settled by coupling total energy calculations with the Murnaghan equation of state. Electronic bands dispersion from PBE-GGA is reported. The PBE-GGA, and PBE0 hybrid functional, show that β-BeH2 is a direct gap semiconductor with 1.18 and 2.40 eV band gap. The band gap slowly decreases with pressure and beyond l00 GPa overlap of conduction and valence bands at the r point is observed. Charge transfer is studied by means of Mullikan population analysis.

DFT study of electron absorption and emission spectra of pyramidal LnPc(OAc) complexes of some lanthanide ions in the solid state

NASA Astrophysics Data System (ADS)

Hanuza, J.; Godlewska, P.; Lisiecki, R.; Ryba-Romanowski, W.; Kadłubański, P.; Lorenc, J.; Łukowiak, A.; Macalik, L.; Gerasymchuk, Yu.; Legendziewicz, J.

2018-05-01

The electron absorption and emission spectra were measured for the pyramidal LnPc(OAc) complexes in the solid state and co-doped in silica glass, where Ln = Er, Eu and Ho. The theoretical electron spectra were determined from the quantum chemical DFT calculation using four approximations CAM-B3LYP/LANL2DZ, CAM-B3LYP/CC-PVDZ, B3LYP/LANL2DZ and B3LYP/CC-PVDZ. It was shown that the best agreement between the calculated and experimental structural parameters and spectroscopic data was reached for the CAM-B3LYP/LANL2DZ model. The emission spectra were measured using the excitations both in the ligand and lanthanide absorption ranges. The possibility of energy transfer between the phthalocyanine ligand and excited states of lanthanide ions was discussed. It was shown that the back energy transfer from metal states to phthalocyanine state is responsible for the observed emission of the studied complexes both in the polycrystalline state and silica glass.

DFT study of electron absorption and emission spectra of pyramidal LnPc(OAc) complexes of some lanthanide ions in the solid state.

PubMed

Hanuza, J; Godlewska, P; Lisiecki, R; Ryba-Romanowski, W; Kadłubański, P; Lorenc, J; Łukowiak, A; Macalik, L; Gerasymchuk, Yu; Legendziewicz, J

2018-05-05

The electron absorption and emission spectra were measured for the pyramidal LnPc(OAc) complexes in the solid state and co-doped in silica glass, where Ln=Er, Eu and Ho. The theoretical electron spectra were determined from the quantum chemical DFT calculation using four approximations CAM-B3LYP/LANL2DZ, CAM-B3LYP/CC-PVDZ, B3LYP/LANL2DZ and B3LYP/CC-PVDZ. It was shown that the best agreement between the calculated and experimental structural parameters and spectroscopic data was reached for the CAM-B3LYP/LANL2DZ model. The emission spectra were measured using the excitations both in the ligand and lanthanide absorption ranges. The possibility of energy transfer between the phthalocyanine ligand and excited states of lanthanide ions was discussed. It was shown that the back energy transfer from metal states to phthalocyanine state is responsible for the observed emission of the studied complexes both in the polycrystalline state and silica glass. Copyright © 2018. Published by Elsevier B.V.

CarbAl Heat Transfer Material

NASA Technical Reports Server (NTRS)

Fink, Richard

2015-01-01

The increasing use of power electronics, such as high-current semiconductor devices and modules, within space vehicles is driving the need to develop specialty thermal management materials in both the packaging of these discrete devices and the packaging of modules consisting of these device arrays. Developed by Applied Nanotech, Inc. (ANI), CarbAl heat transfer material is uniquely characterized by its low density, high thermal diffusivity, and high thermal conductivity. Its coefficient of thermal expansion (CTE) is similar to most power electronic materials, making it an effective base plate substrate for state-of-the-art silicon carbide (SiC) super junction transistors. The material currently is being used to optimize hybrid vehicle inverter packaging. Adapting CarbAl-based substrates to space applications was a major focus of the SBIR project work. In Phase I, ANI completed modeling and experimentation to validate its deployment in a space environment. Key parameters related to cryogenic temperature scaling of CTE, thermal conductivity, and mechanical strength. In Phase II, the company concentrated on improving heat sinks and thermally conductive circuit boards for power electronic applications.

Nodeless vibrational amplitudes and quantum nonadiabatic dynamics in the nested funnel for a pseudo Jahn-Teller molecule or homodimer

NASA Astrophysics Data System (ADS)

Peters, William K.; Tiwari, Vivek; Jonas, David M.

2017-11-01

The nonadiabatic states and dynamics are investigated for a linear vibronic coupling Hamiltonian with a static electronic splitting and weak off-diagonal Jahn-Teller coupling through a single vibration with a vibrational-electronic resonance. With a transformation of the electronic basis, this Hamiltonian is also applicable to the anti-correlated vibration in a symmetric homodimer with marginally strong constant off-diagonal coupling, where the non-adiabatic states and dynamics model electronic excitation energy transfer or self-exchange electron transfer. For parameters modeling a free-base naphthalocyanine, the nonadiabatic couplings are deeply quantum mechanical and depend on wavepacket width; scalar couplings are as important as the derivative couplings that are usually interpreted to depend on vibrational velocity in semiclassical curve crossing or surface hopping theories. A colored visualization scheme that fully characterizes the non-adiabatic states using the exact factorization is developed. The nonadiabatic states in this nested funnel have nodeless vibrational factors with strongly avoided zeroes in their vibrational probability densities. Vibronic dynamics are visualized through the vibrational coordinate dependent density of the time-dependent dipole moment in free induction decay. Vibrational motion is amplified by the nonadiabatic couplings, with asymmetric and anisotropic motions that depend upon the excitation polarization in the molecular frame and can be reversed by a change in polarization. This generates a vibrational quantum beat anisotropy in excess of 2/5. The amplitude of vibrational motion can be larger than that on the uncoupled potentials, and the electronic population transfer is maximized within one vibrational period. Most of these dynamics are missed by the adiabatic approximation, and some electronic and vibrational motions are completely suppressed by the Condon approximation of a coordinate-independent transition dipole between adiabatic states. For all initial conditions investigated, the initial nonadiabatic electronic motion is driven towards the lower adiabatic state, and criteria for this directed motion are discussed.

Nodeless vibrational amplitudes and quantum nonadiabatic dynamics in the nested funnel for a pseudo Jahn-Teller molecule or homodimer.

PubMed

Peters, William K; Tiwari, Vivek; Jonas, David M

2017-11-21

The nonadiabatic states and dynamics are investigated for a linear vibronic coupling Hamiltonian with a static electronic splitting and weak off-diagonal Jahn-Teller coupling through a single vibration with a vibrational-electronic resonance. With a transformation of the electronic basis, this Hamiltonian is also applicable to the anti-correlated vibration in a symmetric homodimer with marginally strong constant off-diagonal coupling, where the non-adiabatic states and dynamics model electronic excitation energy transfer or self-exchange electron transfer. For parameters modeling a free-base naphthalocyanine, the nonadiabatic couplings are deeply quantum mechanical and depend on wavepacket width; scalar couplings are as important as the derivative couplings that are usually interpreted to depend on vibrational velocity in semiclassical curve crossing or surface hopping theories. A colored visualization scheme that fully characterizes the non-adiabatic states using the exact factorization is developed. The nonadiabatic states in this nested funnel have nodeless vibrational factors with strongly avoided zeroes in their vibrational probability densities. Vibronic dynamics are visualized through the vibrational coordinate dependent density of the time-dependent dipole moment in free induction decay. Vibrational motion is amplified by the nonadiabatic couplings, with asymmetric and anisotropic motions that depend upon the excitation polarization in the molecular frame and can be reversed by a change in polarization. This generates a vibrational quantum beat anisotropy in excess of 2/5. The amplitude of vibrational motion can be larger than that on the uncoupled potentials, and the electronic population transfer is maximized within one vibrational period. Most of these dynamics are missed by the adiabatic approximation, and some electronic and vibrational motions are completely suppressed by the Condon approximation of a coordinate-independent transition dipole between adiabatic states. For all initial conditions investigated, the initial nonadiabatic electronic motion is driven towards the lower adiabatic state, and criteria for this directed motion are discussed.

The influence of dielectric relaxation on intramolecular electron transfer

NASA Astrophysics Data System (ADS)

Heitele, H.; Michel-Beyerle, M. E.; Finckh, P.

1987-07-01

An unusually strong temperature dependence on the intramolecular electron-transfer rate has been observed for bridged donor-acceptor compounds in propylene glycol solution. In the frame of recent electron-transfer theories this effect reflects the influence of dielectric relaxation dynamics on electron transfer. With increasing dielectric relaxation time a smooth transition from non-adiabatic to solvent-controlled adiabatic behaviour is observed. The electron transfer rate in the solvent-controlled adiabatic limit is dominated by an inhomogeneous distribution of relaxation times.

Study of the spray to globular transition in gas metal arc welding: a spectroscopic investigation

NASA Astrophysics Data System (ADS)

Valensi, F.; Pellerin, S.; Castillon, Q.; Boutaghane, A.; Dzierzega, K.; Zielinska, S.; Pellerin, N.; Briand, F.

2013-06-01

The gas metal arc welding (GMAW) process is strongly influenced by the composition of the shielding gas. In particular, addition of CO2 increases the threshold current for the transition from unstable globular to more stable spray transfer mode. We report on the diagnostics—using optical emission spectroscopy—of a GMAW plasma in pure argon and in mixtures of argon, CO2 and N2 while operated in spray and globular transfer modes. The spatially resolved plasma parameters are obtained by applying the Abel transformation to laterally integrated emission data. The Stark widths of some iron lines are used to determine both electron density and temperature, and line intensities yield relative contents of neutral and ionized iron to argon. Our experimental results indicate a temperature drop on the arc axis in the case of spray arc transfer. This drop reduces with addition of N2 and disappears in globular transfer mode when CO2 is added. Despite the temperature increase, the electron density decreases with CO2 concentration. The highest concentration of iron is observed in the plasma column upper part (close to the anode) and for GMAW with CO2. Our results are compared with recently published works where the effect of non-homogeneous metal vapour concentration has been taken into account.

Flavins in Coastal Marine Sediments: New Perspectives on Diagenetic Electron Transfer

NASA Astrophysics Data System (ADS)

Monteverde, D.; Berelson, W.; Baronas, J. J.; Sanudo-Wilhelmy, S. A.

2016-02-01

Coastal marine sediments play a critical role in the global cycling of metals and nutrients, many of which undergo diagenetic alteration. Central to these transformations are redox reactions where electron-rich organic matter is oxidized via transfer to terminal electron acceptors (NO3-, MnOx, FeOx, SO42-). The flavins (flavin adenine dinucleotide [FAD], flavin mononucleotide [FMN], and riboflavin [B2]) are microbially synthesized organic coenzymes that perform both single and double electron transfer and are known to mediate reduction of insoluble metal oxides. Culture experiments have found high rates of flavin excretion in metal-reducing Shewanella and Geobacter species, however environmental measurements of these highly labile molecules have not been previously reported. Here we present porewater measurements of FAD, FMN, and B2 from San Pedro Basin. This California Borderland basin is silled, suboxic, 900 m deep, and experiences high sedimentation. Flavin concentrations ranged from pico- (FAD: 0- 60 pM; B2: 40 - 90 pM) to nanomolar (FMN: 0.4 - 1.2 nM). The concentration cascade of FMN>B2>FAD fits well within culture experiments. Interestingly, profiles of all three flavins show a near linear increase with depth from 0-30 cm and a relatively steady concentration from 30-45 cm, supporting likely in situ production. Additionally, the flavins showed a negative correlation with dissolved Fe (R2 = 0.7 for FMN, 0.8 for FAD, and 0.9 for B2), which decreased linearly with depth from 160µM to 65µM. We discuss hypothesized mechanisms controlling flavin concentrations based on a suite of sediment geochemical parameters (dissolved Fe, Mn, TCO2, δ13C, NH3, DOM, and SO42-) as well as implications for microbial redox syntrophy. These data provide a critical link between the extensive culture-based mechanistic understanding of flavin function and the sedimentary environment. Furthermore, these results demonstrate that flavins likely serve as a significant electron transfer intermediaries in the marine sediment carbon cycle.

Large amplitude Fourier transformed ac voltammetry at a rotating disc electrode: a versatile technique for covering Levich and flow rate insensitive regimes in a single experiment.

PubMed

Bano, Kiran; Kennedy, Gareth F; Zhang, Jie; Bond, Alan M

2012-04-14

The theory for large amplitude Fourier transformed ac voltammetry at a rotating disc electrode is described. Resolution of time domain data into dc and ac harmonic components reveals that the mass transport for the dc component is controlled by convective-diffusion, while the background free higher order harmonic components are flow rate insensitive and mainly governed by linear diffusion. Thus, remarkable versatility is available; Levich behaviour of the dc component limiting current provides diffusion coefficient values and access to higher harmonics allows fast electrode kinetics to be probed. Two series of experiments (dc and ac voltammetry) have been required to extract these parameters; here large amplitude ac voltammetry with RDE methodology is used to demonstrate that kinetics and diffusion coefficient information can be extracted from a single experiment. To demonstrate the power of this approach, theoretical and experimental comparisons of data obtained for the reversible [Ru(NH(3))(6)](3+/2+) and quasi-reversible [Fe(CN)(6)](3-/4-) electron transfer processes are presented over a wide range of electrode rotation rates and with different concentrations and electrode materials. Excellent agreement of experimental and simulated data is achieved, which allows parameters such as electron transfer rate, diffusion coefficient, uncompensated resistance and others to be determined using a strategically applied approach that takes into account the different levels of sensitivity of each parameter to the dc or the ac harmonic.

12 CFR 205.15 - Electronic fund transfer of government benefits.

Code of Federal Regulations, 2011 CFR

2011-01-01

... 12 Banks and Banking 2 2011-01-01 2011-01-01 false Electronic fund transfer of government benefits. 205.15 Section 205.15 Banks and Banking FEDERAL RESERVE SYSTEM BOARD OF GOVERNORS OF THE FEDERAL RESERVE SYSTEM ELECTRONIC FUND TRANSFERS (REGULATION E) § 205.15 Electronic fund transfer of government...

12 CFR 1005.3 - Coverage.

Code of Federal Regulations, 2014 CFR

2014-01-01

...-time electronic fund transfer from a consumer's account. The consumer must authorize the transfer. (ii... one-time electronic fund transfer (in providing a check to a merchant or other payee for the MICR... transfer. A consumer authorizes a one-time electronic fund transfer from his or her account to pay the fee...

Case A and B evolution towards electron capture supernova

NASA Astrophysics Data System (ADS)

Siess, L.; Lebreuilly, U.

2018-06-01

Context. Most super-asymptotic giant branch (SAGB) stars are expected to end their life as oxygen-neon white dwarfs rather than electron capture supernovae (ECSN). The reason is ascribed to the ability of the second dredge-up to significantly reduce the mass of the He core and of the efficient AGB winds to remove the stellar envelope before the degenerate core reaches the critical mass for the activation of electron capture reactions. Aims: In this study, we investigate the formation of ECSN through case A and case B mass transfer. In these scenarios, when Roche lobe overflow stops, the primary has become a helium star. With a small envelope left, the second dredge-up is prevented, potentially opening new paths to ECSN. Methods: We compute binary models using our stellar evolution code BINSTAR. We consider three different secondary masses of 8, 9, and 10 M⊙ and explore the parameter space, varying the companion mass, orbital period, and input physics. Results: Assuming conservative mass transfer, with our choice of secondary masses all case A systems enter contact either during the main sequence or as a consequence of reversed mass transfer when the secondary overtakes its companion during core helium burning. Case B systems are able to produce ECSN progenitors in a relatively small range of periods (3 ≲ P(d) ≤ 30) and primary masses (10.9 ≤ M/M⊙≤ 11.5). Changing the companion mass has little impact on the primary's fate as long as the mass ratio M1/M2 remains less than 1.4-1.5, above which evolution to contact becomes unavoidable. We also find that allowing for systemic mass loss substantially increases the period interval over which ECSN can occur. This change in the binary physics does not however affect the primary mass range. We finally stress that the formation of ECSN progenitors through case A and B mass transfer is very sensitive to adopted binary and stellar physics. Conclusions: Close binaries provide additional channels for ECSN but the parameter space is rather constrained likely making ECSN a rare event.

Modular Homogeneous Chromophore–Catalyst Assemblies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mulfort, Karen L.; Utschig, Lisa M.

2016-05-17

Photosynthetic reaction center (RC) proteins convert incident solar energy to chemical energy through a network of molecular cofactors which have been evolutionarily tuned to couple efficient light-harvesting, directional electron transfer, and long-lived charge separation with secondary reaction sequences. These molecular cofactors are embedded within a complex protein environment which precisely positions each cofactor in optimal geometries along efficient electron transfer pathways with localized protein environments facilitating sequential and accumulative charge transfer. By contrast, it is difficult to approach a similar level of structural complexity in synthetic architectures for solar energy conversion. However, by using appropriate self-assembly strategies, we anticipate thatmore » molecular modules, which are independently synthesized and optimized for either light-harvesting or redox catalysis, can be organized into spatial arrangements that functionally mimic natural photosynthesis. In this Account, we describe a modular approach to new structural designs for artificial photosynthesis which is largely inspired by photosynthetic RC proteins. We focus on recent work from our lab which uses molecular modules for light-harvesting or proton reduction catalysis in different coordination geometries and different platforms, spanning from discrete supramolecular assemblies to molecule–nanoparticle hybrids to protein-based biohybrids. Molecular modules are particularly amenable to high-resolution characterization of the ground and excited state of each module using a variety of physical techniques; such spectroscopic interrogation helps our understanding of primary artificial photosynthetic mechanisms. In particular, we discuss the use of transient optical spectroscopy, EPR, and X-ray scattering techniques to elucidate dynamic structural behavior and light-induced kinetics and the impact on photocatalytic mechanism. Two different coordination geometries of supramolecular photocatalyst based on the [Ru(bpy)3]2+ (bpy = 2,2'-bipyridine) light-harvesting module with cobaloxime-based catalyst module are compared, with progress in stabilizing photoinduced charge separation identified. These same modules embedded in the small electron transfer protein ferredoxin exhibit much longer charge-separation, enabled by stepwise electron transfer through the native [2Fe-2S] cofactor. We anticipate that the use of interchangeable, molecular modules which can interact in different coordination geometries or within entirely different structural platforms will provide important fundamental insights into the effect of environment on parameters such as electron transfer and charge separation, and ultimately drive more efficient designs for artificial photosynthesis.« less

Effect of electronic excitation on high-temperature flows behind strong shock waves

DOE Office of Scientific and Technical Information (OSTI.GOV)

Istomin, V. A.; Kustova, E. V.

2014-12-09

In the present paper, a strongly non-equilibrium one-dimensional steady-state flow behind the plane shock wave is studied. We consider a high-temperature chemically reacting five-component ionized mixture of nitrogen species (N{sub 2}/N{sub 2}{sup 2}/N/N{sup +}/e{sup −}) taking into account electronic degrees of freedom in N and N{sup +} (170 and 625 electronic energy levels respectively), and electronic-rotational-vibrational modes in N{sub 2} and N{sub 2}{sup +} (5 and 7 electronic terms). Non-equilibrium reactions of ionization, dissociation, recombination and charge-transfer are included to the kinetic scheme. The system of governing equations is written under the assumption that translation and internal energy relaxation ismore » fast whereas chemical reactions and ionization proceed on the macroscopic gas-dynamics time-scale. The developed model is applied to simulate the flow behind a plane shock wave under initial conditions characteristic for the spacecraft re-entry from an interplanetary flight (Hermes and Fire II experiments). Fluid-dynamic parameters behind the shock wave as well as transport coefficients and the heat flux are calculated for the (N{sub 2}/N{sub 2}{sup +}/N/N{sup +}/e{sup −}) mixture. The effect of electronic excitation on kinetics, dynamics and heat transfer is analyzed. Whereas the contribution of electronic degrees of freedom to the flow macroparameters is negligible, their influence on the heat flux is found to be important under conditions of Hermes re-entry.« less

Nuclear conversion theory: molecular hydrogen in non-magnetic insulators

PubMed Central

Ghiglieno, Filippo

2016-01-01

The hydrogen conversion patterns on non-magnetic solids sensitively depend upon the degree of singlet/triplet mixing in the intermediates of the catalytic reaction. Three main ‘symmetry-breaking’ interactions are brought together. In a typical channel, the electron spin–orbit (SO) couplings introduce some magnetic excitations in the non-magnetic solid ground state. The electron spin is exchanged with a molecular one by the electric molecule–solid electron repulsion, mixing the bonding and antibonding states and affecting the molecule rotation. Finally, the magnetic hyperfine contact transfers the electron spin angular momentum to the nuclei. Two families of channels are considered and a simple criterion based on the SO coupling strength is proposed to select the most efficient one. The denoted ‘electronic’ conversion path involves an emission of excitons that propagate and disintegrate in the bulk. In the other denoted ‘nuclear’, the excited electron states are transients of a loop, and the electron system returns to its fundamental ground state. The described model enlarges previous studies by extending the electron basis to charge-transfer states and ‘continui’ of band states, and focuses on the broadening of the antibonding molecular excited state by the solid conduction band that provides efficient tunnelling paths for the hydrogen conversion. After working out the general conversion algebra, the conversion rates of hydrogen on insulating and semiconductor solids are related to a few molecule–solid parameters (gap width, ionization and affinity potentials) and compared with experimental measures. PMID:27703681

Photophysical parameters and fluorescence quenching of 7-diethylaminocoumarin (DEAC) laser dye

NASA Astrophysics Data System (ADS)

El-Mossalamy, E. H.; Obaid, A. Y.; El-Daly, S. A.

2011-10-01

The optical properties including electronic absorption spectrum, emission spectrum, fluorescence quantum yield, and dipole moment of electronic transition of 7-diethylaminocoumarin (DEAC) laser dye have been measured in different solvents. Both electronic absorption and fluorescence spectra are red shifted as the polarity of the medium increases, indicating that the dipole moment of molecule increases on excitation. The fluorescence quantum yield of DEAC decreases as the polarity of solvent increases, a result of the role of solvent polarity in stabilization of the twisting of the intramolecular charge transfer (TICT) in excited state, which is a non-emissive state, as well as hydrogen bonding with the hetero-atom of dye. The emission spectrum of DEAC has also been measured in cationic (CTAC) and anionic (SDS) micelles, the intensity increases as the concentration of surfactant increases, and an abrupt change in emission intensity is observed at critical micelle concentration (CMC) of surfactant. 2×10 -3 mol dm -3 of DEAC gives laser emission in the blue region on pumping with nitrogen laser ( λex=337.1 nm). The laser parameters such as tuning range, gain coefficient ( α), emission cross section ( σe), and half-life energy have been calculated in different solvents, namely acetone, dioxane , ethanol, and dimethyforamide (DMF). The photoreactivity of DEAC has been studied in CCl 4 at a wavelength of 366 nm. The values of photochemical yield ( ϕc) and rate constant ( k) are determined. The interaction of organic acceptors such as picric acid (PA), tetracyanoethylene (TCNE), and 7,7,8,8-tetracynoquinonedimethane (TCNQ) with DEAC is also studied using fluorescence measurements in acetonitrile (CH 3CN); from fluorescence quenching study we assume the possible electron transfer from excited donor DEAC to organic acceptor forming non-emissive exciplex.

Identification of New Potential Scientific and Technology Areas for DoD Application. Summary of Activities

DTIC Science & Technology

1986-07-31

designer will be able to more rapid- ly assemble a total software package from perfected modules that can be easily de - bugged or replaced with more...antinuclear interactions e. gravitational effects of antimatter 2. possible machine parameters and lattice design 3. electron and stochastic cooling needs 4...implementation, reliability requirements; development of design environments and of experimental methodology; technology transfer methods from

12 CFR 205.14 - Electronic fund transfer service provider not holding consumer's account.

Code of Federal Regulations, 2010 CFR

2010-01-01

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Code of Federal Regulations, 2013 CFR

2013-01-01

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Code of Federal Regulations, 2014 CFR

2014-01-01

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12 CFR 205.14 - Electronic fund transfer service provider not holding consumer's account.

Code of Federal Regulations, 2011 CFR

2011-01-01

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12 CFR 205.14 - Electronic fund transfer service provider not holding consumer's account.

Code of Federal Regulations, 2012 CFR

2012-01-01

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An Ab Initio Exciton Model Including Charge-Transfer Excited States

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Xin; Parrish, Robert M.; Liu, Fang

Here, the Frenkel exciton model is a useful tool for theoretical studies of multichromophore systems. We recently showed that the exciton model could be used to coarse-grain electronic structure in multichromophoric systems, focusing on singly excited exciton states. However, our previous implementation excluded charge-transfer excited states, which can play an important role in light-harvesting systems and near-infrared optoelectronic materials. Recent studies have also emphasized the significance of charge-transfer in singlet fission, which mediates the coupling between the locally excited states and the multiexcitonic states. In this work, we report on an ab initio exciton model that incorporates charge-transfer excited statesmore » and demonstrate that the model provides correct charge-transfer excitation energies and asymptotic behavior. Comparison with TDDFT and EOM-CC2 calculations shows that our exciton model is robust with respect to system size, screening parameter, and different density functionals. Inclusion of charge-transfer excited states makes the exciton model more useful for studies of singly excited states and provides a starting point for future construction of a model that also includes double-exciton states.« less

An Ab Initio Exciton Model Including Charge-Transfer Excited States

DOE PAGES

Li, Xin; Parrish, Robert M.; Liu, Fang; ...

2017-06-15

Here, the Frenkel exciton model is a useful tool for theoretical studies of multichromophore systems. We recently showed that the exciton model could be used to coarse-grain electronic structure in multichromophoric systems, focusing on singly excited exciton states. However, our previous implementation excluded charge-transfer excited states, which can play an important role in light-harvesting systems and near-infrared optoelectronic materials. Recent studies have also emphasized the significance of charge-transfer in singlet fission, which mediates the coupling between the locally excited states and the multiexcitonic states. In this work, we report on an ab initio exciton model that incorporates charge-transfer excited statesmore » and demonstrate that the model provides correct charge-transfer excitation energies and asymptotic behavior. Comparison with TDDFT and EOM-CC2 calculations shows that our exciton model is robust with respect to system size, screening parameter, and different density functionals. Inclusion of charge-transfer excited states makes the exciton model more useful for studies of singly excited states and provides a starting point for future construction of a model that also includes double-exciton states.« less

An Ab Initio Exciton Model Including Charge-Transfer Excited States.

PubMed

Li, Xin; Parrish, Robert M; Liu, Fang; Kokkila Schumacher, Sara I L; Martínez, Todd J

2017-08-08

The Frenkel exciton model is a useful tool for theoretical studies of multichromophore systems. We recently showed that the exciton model could be used to coarse-grain electronic structure in multichromophoric systems, focusing on singly excited exciton states [ Acc. Chem. Res. 2014 , 47 , 2857 - 2866 ]. However, our previous implementation excluded charge-transfer excited states, which can play an important role in light-harvesting systems and near-infrared optoelectronic materials. Recent studies have also emphasized the significance of charge-transfer in singlet fission, which mediates the coupling between the locally excited states and the multiexcitonic states. In this work, we report on an ab initio exciton model that incorporates charge-transfer excited states and demonstrate that the model provides correct charge-transfer excitation energies and asymptotic behavior. Comparison with TDDFT and EOM-CC2 calculations shows that our exciton model is robust with respect to system size, screening parameter, and different density functionals. Inclusion of charge-transfer excited states makes the exciton model more useful for studies of singly excited states and provides a starting point for future construction of a model that also includes double-exciton states.

Electron transport in NH3/NO2 sensed buckled antimonene

NASA Astrophysics Data System (ADS)

Srivastava, Anurag; Khan, Md. Shahzad; Ahuja, Rajeev

2018-04-01

The structural and electronic properties of buckled antimonene have been analysed using density functional theory based ab-initio approach. Geometrical parameters in terms of bond length and bond angle are found close to the single ruffle mono-layer of rhombohedral antimony. Inter-frontier orbital analyses suggest localization of lone pair electrons at each atomic centre. Phonon dispersion along with high symmetry point of Brillouin zone does not signify any soft mode. With an electronic band gap of 1.8eV, the quasi-2D nano-surface has been further explored for NH3/NO2 molecules sensing and qualities of interaction between NH3/NO2 gas and antimonene scrutinized in terms of electronic charges transfer. A current-voltage characteristic has also been analysed, using Non Equilibrium Green's function (NEGF), for antimonene, in presence of incoming NH3/NO2 molecules.

Transport coefficients in nonequilibrium gas-mixture flows with electronic excitation.

PubMed

Kustova, E V; Puzyreva, L A

2009-10-01

In the present paper, a one-temperature model of transport properties in chemically nonequilibrium neutral gas-mixture flows with electronic excitation is developed. The closed set of governing equations for the macroscopic parameters taking into account electronic degrees of freedom of both molecules and atoms is derived using the generalized Chapman-Enskog method. The transport algorithms for the calculation of the thermal-conductivity, diffusion, and viscosity coefficients are proposed. The developed theoretical model is applied for the calculation of the transport coefficients in the electronically excited N/N(2) mixture. The specific heats and transport coefficients are calculated in the temperature range 50-50,000 K. Two sets of data for the collision integrals are applied for the calculations. An important contribution of the excited electronic states to the heat transfer is shown. The Prandtl number of atomic species is found to be substantially nonconstant.

Anomalous single-electron transfer in common-gate quadruple-dot single-electron devices with asymmetric junction capacitances

NASA Astrophysics Data System (ADS)

Imai, Shigeru; Ito, Masato

2018-06-01

In this paper, anomalous single-electron transfer in common-gate quadruple-dot turnstile devices with asymmetric junction capacitances is revealed. That is, the islands have the same total number of excess electrons at high and low gate voltages of the swing that transfers a single electron. In another situation, two electrons enter the islands from the source and two electrons leave the islands for the source and drain during a gate voltage swing cycle. First, stability diagrams of the turnstile devices are presented. Then, sequences of single-electron tunneling events by gate voltage swings are investigated, which demonstrate the above-mentioned anomalous single-electron transfer between the source and the drain. The anomalous single-electron transfer can be understood by regarding the four islands as “three virtual islands and a virtual source or drain electrode of a virtual triple-dot device”. The anomalous behaviors of the four islands are explained by the normal behavior of the virtual islands transferring a single electron and the behavior of the virtual electrode.

An experimental and theoretical study of a hydrogen-bonded complex: O-phenylenediamine with 2,6-pyridinedicarboxylic acid

NASA Astrophysics Data System (ADS)

Ghasemi, Khaled; Rezvani, Ali Reza; Habibi-Khorassani, Sayyed Mostafa; Shahraki, Mehdi; Shokrollahi, Ardeshir; Moghimi, Abolghasem; Tamandani, Halimeh Kord; Gavahi, Sara

2015-11-01

The hydrogen-bonded complex, [(OPDH)+(dipicH)-.H2O], between o-phenylenediamine (OPD) and 2,6-pyridinedicarboxylic acid (dipicH2) has been characterized in water by the 1H, 13C NMR and IR spectroscopies. The crystal structure showed that the edge to face C-H⋯π and C-O⋯π stacking interactions between the dipicH2 and OPD rings play an extra significant role in the formation of the hydrogen-bonded complex and supported the H-bonding interactions. The proton transfer also investigated theoretically in gas phase and thermodynamic parameters such as ΔH‡, ΔG‡, ΔS‡ were calculated for this process. Moreover, intramolecular hydrogen-bonding interaction has been recognized by calculating the electron density ρ(r) and Laplacian ∇2ρ(r) at the bond critical point (BCP) using Atoms-In-Molecule (AIM) method and also the interaction between electron acceptor (σ*) of OH with the lone pair of the nitrogen atom as an electron donor using Natural Bond Orbital (NBO) analysis. In addition, the protonation constants of dipicH2 and OPD and the equilibrium constants for the dipic-OPD (1:1) proton transfer system were obtained by the potentiometric pH titration method using the Hyperquad 2008 program. The stoichiometry of the proton transfer species in the solution confirmed the solid state result.

Cyclic Nanostructures of Tungsten Oxide (WO3) n   (n = 2-6) as NO x Gas Sensor: A Theoretical Study.

PubMed

Izadyar, Mohammad; Jamsaz, Azam

2014-01-01

Today's WO3-based gas sensors have received a lot of attention, because of important role as a sensitive layer for detection of the small quantities of  NO x . In this research, a theoretical study has been done on the sensing properties of different cyclic nanoclusters of (WO3) n   (n = 2-6) for NO x   (x = 1,2) gases. Based on the calculated adsorption energies by B3LYP and X3LYP functionals, from the different orientations of  NO x molecule on the tungsten oxide clusters, O-N⋯W was preferred. Different sizes of the mentioned clusters have been analyzed and W2O6 cluster was chosen as the best candidate for NO x detection from the energy viewpoint. Using the concepts of the chemical hardness and electronic charge transfer, some correlations between the energy of adsorption and interaction energy have been established. These analyses confirmed that the adsorption energy will be boosted with charge transfer enhancement. However, the chemical hardness relationship is reversed. Finally, obtained results from the natural bond orbital and electronic density of states analysis confirmed the electronic charge transfer from the adsorbates to WO3 clusters and Fermi level shifting after adsorption, respectively. The last parameter confirms that the cyclic clusters of tungsten oxide can be used as NO x gas sensors.

Cyclic Nanostructures of Tungsten Oxide (WO3)n  (n = 2–6) as NOx Gas Sensor: A Theoretical Study

PubMed Central

Izadyar, Mohammad; Jamsaz, Azam

2014-01-01

Today's WO3-based gas sensors have received a lot of attention, because of important role as a sensitive layer for detection of the small quantities of  NOx. In this research, a theoretical study has been done on the sensing properties of different cyclic nanoclusters of (WO3)n  (n = 2–6) for NOx  (x = 1,2) gases. Based on the calculated adsorption energies by B3LYP and X3LYP functionals, from the different orientations of  NOx molecule on the tungsten oxide clusters, O–N⋯W was preferred. Different sizes of the mentioned clusters have been analyzed and W2O6 cluster was chosen as the best candidate for NOx detection from the energy viewpoint. Using the concepts of the chemical hardness and electronic charge transfer, some correlations between the energy of adsorption and interaction energy have been established. These analyses confirmed that the adsorption energy will be boosted with charge transfer enhancement. However, the chemical hardness relationship is reversed. Finally, obtained results from the natural bond orbital and electronic density of states analysis confirmed the electronic charge transfer from the adsorbates to WO3 clusters and Fermi level shifting after adsorption, respectively. The last parameter confirms that the cyclic clusters of tungsten oxide can be used as NOx gas sensors. PMID:25544841

Apparatus and method of direct water cooling several parallel circuit cards each containing several chip packages

DOEpatents

Cipolla, Thomas M [Katonah, NY; Colgan, Evan George [Chestnut Ridge, NY; Coteus, Paul W [Yorktown Heights, NY; Hall, Shawn Anthony [Pleasantville, NY; Tian, Shurong [Mount Kisco, NY

2011-12-20

A cooling apparatus, system and like method for an electronic device includes a plurality of heat producing electronic devices affixed to a wiring substrate. A plurality of heat transfer assemblies each include heat spreaders and thermally communicate with the heat producing electronic devices for transferring heat from the heat producing electronic devices to the heat transfer assemblies. The plurality of heat producing electronic devices and respective heat transfer assemblies are positioned on the wiring substrate having the regions overlapping. A heat conduit thermally communicates with the heat transfer assemblies. The heat conduit circulates thermally conductive fluid therethrough in a closed loop for transferring heat to the fluid from the heat transfer assemblies via the heat spreader. A thermally conductive support structure supports the heat conduit and thermally communicates with the heat transfer assemblies via the heat spreader transferring heat to the fluid of the heat conduit from the support structure.

Exploring the relevance of thiophene rings as bridge unit in acceptor-bridge-donor dyes on self-aggregation and performance in DSSCs.

PubMed

Zarate, Ximena; Saavedra-Torres, Mario; Rodriguez-Serrano, Angela; Gomez, Tatiana; Schott, Eduardo

2018-04-30

The possibility of dye charge recombination in DSSCs remains a challenge for the field. This consists of: (a) back-transfer from the TiO 2 to the oxidized dye and (b) intermolecular electron transfer between dyes. The latter is attributed to dye aggregation due to dimeric conformations. This leads to poor electron injection which decreases the photocurrent conversion efficiency. Most organic sensitizers are characterized by an Acceptor-Bridge-Donor (A-Bridge-D) arrangement that is commonly employed to provide charge separation and, therefore, lowering the unwanted back-transfer. Here, we address the intermolecular electron transfer by studying the dimerization and photovoltaic performance of a group of A-Bridge-D structured dyes. Specifically, eight famous sulfur containing π-bridges were analyzed (A and D remained fixed). Through quantum mechanical and molecular dynamics approaches, it was found that the formation of weakly stabilized dimers is allowed. The dyes with covalently bonded and fused thiophene rings as Bridges, 6d and 7d as well as 8d with a fluorene, would present high aggregation and, therefore, high probability of recombination processes. Conversely, using TiO 2 cluster and surface models, delineated the shortest bridges to improve the adsorption energy and the stability of the system. Finally, the elongation of the bridge up to 2 and 3 units and their photovoltaic parameters were studied. These results showed that all the sensitizers are able to provide similar photocurrent outcomes, regardless of whether the bridge is elongated. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Acid/base-regulated reversible electron transfer disproportionation of N–N linked bicarbazole and biacridine derivatives† †Electronic supplementary information (ESI) available: Experimental information, synthesis and characterization data, NMR spectra, solid state NMR data, X-ray data, ESR spectra, UV-Vis-NIR spectra, fluorescence spectra, kinetic experiments, theoretical calculations, Tables S1–S8, Scheme S1, Fig. S1–12, References. CCDC 1025063, 1038914, 1049677 and 1040722. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5sc00946d

PubMed Central

Pandit, Palash; Yamamoto, Koji; Nakamura, Toshikazu; Nishimura, Katsuyuki; Kurashige, Yuki; Yanai, Takeshi; Nakamura, Go; Masaoka, Shigeyuki; Furukawa, Ko; Yakiyama, Yumi; Kawano, Masaki

2015-01-01

Regulation of electron transfer on organic substances by external stimuli is a fundamental issue in science and technology, which affects organic materials, chemical synthesis, and biological metabolism. Nevertheless, acid/base-responsive organic materials that exhibit reversible electron transfer have not been well studied and developed, owing to the difficulty in inventing a mechanism to associate acid/base stimuli and electron transfer. We discovered a new phenomenon in which N–N linked bicarbazole (BC) and tetramethylbiacridine (TBA) derivatives undergo electron transfer disproportionation by acid stimulus, forming their stable radical cations and reduced species. The reaction occurs through a biradical intermediate generated by the acid-triggered N–N bond cleavage reaction of BC or TBA, which acts as a two electron acceptor to undergo electron transfer reactions with two equivalents of BC or TBA. In addition, in the case of TBA the disproportionation reaction is highly reversible through neutralization with NEt3, which recovers TBA through back electron transfer and N–N bond formation reactions. This highly reversible electron transfer reaction is possible due to the association between the acid stimulus and electron transfer via the acid-regulated N–N bond cleavage/formation reactions which provide an efficient switching mechanism, the ability of the organic molecules to act as multi-electron donors and acceptors, the extraordinary stability of the radical species, the highly selective reactivity, and the balance of the redox potentials. This discovery provides new design concepts for acid/base-regulated organic electron transfer systems, chemical reagents, or organic materials. PMID:29218181

Rate of Interfacial Electron Transfer through the 1,2,3-Triazole Linkage

PubMed Central

Devaraj, Neal K.; Decreau, Richard A.; Ebina, Wataru; Collman, James P.; Chidsey, Christopher E. D.

2012-01-01

The rate of electron transfer is measured to two ferrocene and one iron tetraphenylporphyrin redox species coupled through terminal acetylenes to azide-terminated thiol monolayers by the Cu(I)-catalyzed azide–alkyne cycloaddition (a Sharpless “click” reaction) to form the 1,2,3-triazole linkage. The high yield, chemoselectivity, convenience, and broad applicability of this triazole formation reaction make such a modular assembly strategy very attractive. Electron-transfer rate constants from greater than 60,000 to 1 s−1 are obtained by varying the length and conjugation of the electron-transfer bridge and by varying the surrounding diluent thiols in the monolayer. Triazole and the triazole carbonyl linkages provide similar electronic coupling for electron transfer as esters. The ability to vary the rate of electron transfer to many different redox species over many orders of magnitude by using modular coupling chemistry provides a convenient way to study and control the delivery of electrons to multielectron redox catalysts and similar interfacial systems that require controlled delivery of electrons. PMID:16898751

Electronic couplings and on-site energies for hole transfer in DNA: Systematic quantum mechanical/molecular dynamic study

NASA Astrophysics Data System (ADS)

Voityuk, Alexander A.

2008-03-01

The electron hole transfer (HT) properties of DNA are substantially affected by thermal fluctuations of the π stack structure. Depending on the mutual position of neighboring nucleobases, electronic coupling V may change by several orders of magnitude. In the present paper, we report the results of systematic QM/molecular dynamic (MD) calculations of the electronic couplings and on-site energies for the hole transfer. Based on 15ns MD trajectories for several DNA oligomers, we calculate the average coupling squares ⟨V2⟩ and the energies of basepair triplets XG +Y and XA +Y, where X, Y =G, A, T, and C. For each of the 32 systems, 15 000 conformations separated by 1ps are considered. The three-state generalized Mulliken-Hush method is used to derive electronic couplings for HT between neighboring basepairs. The adiabatic energies and dipole moment matrix elements are computed within the INDO/S method. We compare the rms values of V with the couplings estimated for the idealized B-DNA structure and show that in several important cases the couplings calculated for the idealized B-DNA structure are considerably underestimated. The rms values for intrastrand couplings G-G, A-A, G-A, and A-G are found to be similar, ˜0.07eV, while the interstrand couplings are quite different. The energies of hole states G+ and A+ in the stack depend on the nature of the neighboring pairs. The XG +Y are by 0.5eV more stable than XA +Y. The thermal fluctuations of the DNA structure facilitate the HT process from guanine to adenine. The tabulated couplings and on-site energies can be used as reference parameters in theoretical and computational studies of HT processes in DNA.

Parameter transferability within homogeneous regions and comparisons with predictions from a priori parameters in the eastern United States

NASA Astrophysics Data System (ADS)

Chouaib, Wafa; Alila, Younes; Caldwell, Peter V.

2018-05-01

The need for predictions of flow time-series persists at ungauged catchments, motivating the research goals of our study. By means of the Sacramento model, this paper explores the use of parameter transfer within homogeneous regions of similar climate and flow characteristics and makes comparisons with predictions from a priori parameters. We assessed the performance using the Nash-Sutcliffe (NS), bias, mean monthly hydrograph and flow duration curve (FDC). The study was conducted on a large dataset of 73 catchments within the eastern US. Two approaches to the parameter transferability were developed and evaluated; (i) the within homogeneous region parameter transfer using one donor catchment specific to each region, (ii) the parameter transfer disregarding the geographical limits of homogeneous regions, where one donor catchment was common to all regions. Comparisons between both parameter transfers enabled to assess the gain in performance from the parameter regionalization and its respective constraints and limitations. The parameter transfer within homogeneous regions outperformed the a priori parameters and led to a decrease in bias and increase in efficiency reaching a median NS of 0.77 and a NS of 0.85 at individual catchments. The use of FDC revealed the effect of bias on the inaccuracy of prediction from parameter transfer. In one specific region, of mountainous and forested catchments, the prediction accuracy of the parameter transfer was less satisfactory and equivalent to a priori parameters. In this region, the parameter transfer from the outsider catchment provided the best performance; less-biased with smaller uncertainty in medium flow percentiles (40%-60%). The large disparity of energy conditions explained the lack of performance from parameter transfer in this region. Besides, the subsurface stormflow is predominant and there is a likelihood of lateral preferential flow, which according to its specific properties further explained the reduced efficiency. Testing the parameter transferability using criteria of similar climate and flow characteristics at ungauged catchments and comparisons with predictions from a priori parameters are a novelty. The ultimate limitations of both approaches are recognized and recommendations are made for future research.

Protein control of true, gated, and coupled electron transfer reactions.

PubMed

Davidson, Victor L

2008-06-01

Electron transfer (ET) through and between proteins is a fundamental biological process. The rates of ET depend upon the thermodynamic driving force, the reorganization energy, and the degree of electronic coupling between the reactant and product states. The analysis of protein ET reactions is complicated by the fact that non-ET processes might influence the observed ET rate in kinetically complex biological systems. This Account describes studies of the methylamine dehydrogenase-amicyanin-cytochrome c-551i protein ET complex that have revealed the influence of several features of the protein structure on the magnitudes of the physical parameters for true ET reactions and how they dictate the kinetic mechanisms of non-ET processes that sometimes influence protein ET reactions. Kinetic and thermodynamic studies, coupled with structural information and biochemical data, are necessary to fully describe the ET reactions of proteins. Site-directed mutagenesis can be used to elucidate specific structure-function relationships. When mutations selectively alter the electronic coupling, reorganization energy, or driving force for the ET reaction, it becomes possible to use the parameters of the ET process to determine how specific amino acid residues and other features of the protein structure influence the ET rates. When mutations alter the kinetic mechanism for ET, one can determine the mechanisms by which non-ET processes, such as protein conformational changes or proton transfers, control the rates of ET reactions and how specific amino acid residues and certain features of the protein structure influence these non-ET reactions. A complete description of the mechanism of regulation of biological ET reactions enhances our understanding of metabolism, respiration, and photosynthesis at the molecular level. Such information has important medical relevance. Defective protein ET leads to production of the reactive oxygen species and free radicals that are associated with aging and many disease states. Defective ET within the respiratory chain also causes certain mitochondrial myopathies. An understanding of the mechanisms of regulation of protein ET is also of practical value because it provides a logical basis for the design of applications utilizing redox enzymes, such as enzyme-based electrode sensors and fuel cells.

Electronic transmission in non-linear potential profile of GaAs/AlxGa1-xAs biased quantum well structure

NASA Astrophysics Data System (ADS)

Meghoufel, F. Z.; Bentata, S.; Terkhi, S.; Bendahma, F.; Cherid, S.

2013-05-01

We study the effect of the nonlinearity on electrons transmission properties in a double barriers structure GaAs/AlxGa1-xAs superlattices. The nonlinearity is introduced as an effective potential in the Schrödinger equation and translates the electronic Colombian repulsion. We have used the transfer matrix formalism and the plane wave functions approximation to solve numerically the equation and calculate the electronic transmission coefficient. We have shown the occurrence of two allowed states within the same well instead of a single, translating the presence of two resonant states at two different energies. The first allowed state intensity strongly decreases with increasing the nonlinear parameter, whereas the second one called the degeneracy state increases. Both the two states evolve towards higher resonances energies.

Lateral engineering of surface states - towards surface-state nanoelectronics.

PubMed

García de Abajo, F J; Cordón, J; Corso, M; Schiller, F; Ortega, J E

2010-05-01

Patterned metal surfaces can host electron quantum waves that display interference phenomena over distances of a few nanometres, thus providing excellent information carriers for future atomic-scale devices. Here we demonstrate that collimation and waveguiding of surface electrons can be realized in silver-induced strain dislocation networks on Cu(111) surfaces, as a conceptual proof-of-principle of surface-state nanoelectronics (SSNE). The Ag/Cu(111) system exhibits featured surface bands with gaps at the Fermi energy, which are basic requirements for a potential SSNE material. We establish a solid analogy between the behavior of surface-state electrons and surface plasmons in patterned metal surfaces, thus facilitating the transfer of existing knowledge on plasmonic structures to the new scenario presented by engineered electronic surface-state nanostructures, with the advantage of a 1000-fold reduction in wavelength and geometrical parameters.

On the physics of electron transfer (drift) in the substance: about the reason of “abnormal” fast transfer of electrons in the plasma of tokamak and at known Bohm’s diffusion

NASA Astrophysics Data System (ADS)

Boriev, I. A.

2018-03-01

An analysis of the problem of so-called “abnormal” fast transfer of electrons in tokamak plasma, which turned out much faster than the result of accepted calculation, is given. Such transfer of hot electrons leads to unexpectedly fast destruction of the inner tokamak wall with ejection of its matter in plasma volume, what violates a condition of plasma confinement for controlled thermonuclear fusion. It is shown, taking into account real physics of electron drift in the gas (plasma) and using the conservation law for momentum of electron transfer (drift), that the drift velocity of elastically scattered electrons should be significantly greater than that of accepted calculation. The reason is that the relaxation time of the momentum of electron transfer, to which the electron drift velocity is proportional, is significantly greater (from 16 up to 4 times) than the electron free path time. Therefore, generally accepted replacement of the relaxation time, which is unknown a priori, by the electron free path time, leads to significant (16 times for thermal electrons) underestimation of electron drift velocity (mobility). This result means, that transfer of elastically (and isotropically) scattered electrons in the gas phase should be so fast, and corresponds to multiplying coefficient (16), introduced by D. Bohm to explain the observed by him “abnormal” fast diffusion of electrons.

Marcus equation

DOE R&D Accomplishments Database

1998-09-21

In the late 1950s to early 1960s Rudolph A. Marcus developed a theory for treating the rates of outer-sphere electron-transfer reactions. Outer-sphere reactions are reactions in which an electron is transferred from a donor to an acceptor without any chemical bonds being made or broken. (Electron-transfer reactions in which bonds are made or broken are referred to as inner-sphere reactions.) Marcus derived several very useful expressions, one of which has come to be known as the Marcus cross-relation or, more simply, as the Marcus equation. It is widely used for correlating and predicting electron-transfer rates. For his contributions to the understanding of electron-transfer reactions, Marcus received the 1992 Nobel Prize in Chemistry. This paper discusses the development and use of the Marcus equation. Topics include self-exchange reactions; net electron-transfer reactions; Marcus cross-relation; and proton, hydride, atom and group transfers.

Coupled sensitizer-catalyst dyads: electron-transfer reactions in a perylene-polyoxometalate conjugate.

PubMed

Odobel, Fabrice; Séverac, Marjorie; Pellegrin, Yann; Blart, Errol; Fosse, Céline; Cannizzo, Caroline; Mayer, Cédric R; Elliott, Kristopher J; Harriman, Anthony

2009-01-01

Ultrafast discharge of a single-electron capacitor: A variety of intramolecular electron-transfer reactions are apparent for polyoxometalates functionalized with covalently attached perylene monoimide chromophores, but these are restricted to single-electron events. (et=electron transfer, cr=charge recombination, csr=charge-shift reaction, PER=perylene, POM=polyoxometalate).A new strategy is introduced that permits covalent attachment of an organic chromophore to a polyoxometalate (POM) cluster. Two examples are reported that differ according to the nature of the anchoring group and the flexibility of the linker. Both POMs are functionalized with perylene monoimide units, which function as photon collectors and form a relatively long-lived charge-transfer state under illumination. They are reduced to a stable pi-radical anion by electrolysis or to a protonated dianion under photolysis in the presence of aqueous triethanolamine. The presence of the POM opens up an intramolecular electron-transfer route by which the charge-transfer state reduces the POM. The rate of this process depends on the molecular conformation and appears to involve through-space interactions. Prior reduction of the POM leads to efficient fluorescence quenching, again due to intramolecular electron transfer. In most cases, it is difficult to resolve the electron-transfer products because of relatively fast reverse charge shift that occurs within a closed conformer. Although the POM can store multiple electrons, it has not proved possible to use these systems as molecular-scale capacitors because of efficient electron transfer from the one-electron-reduced POM to the excited singlet state of the perylene monoimide.

Directing the path of light-induced electron transfer at a molecular fork using vibrational excitation

NASA Astrophysics Data System (ADS)

Delor, Milan; Archer, Stuart A.; Keane, Theo; Meijer, Anthony J. H. M.; Sazanovich, Igor V.; Greetham, Gregory M.; Towrie, Michael; Weinstein, Julia A.

2017-11-01

Ultrafast electron transfer in condensed-phase molecular systems is often strongly coupled to intramolecular vibrations that can promote, suppress and direct electronic processes. Recent experiments exploring this phenomenon proved that light-induced electron transfer can be strongly modulated by vibrational excitation, suggesting a new avenue for active control over molecular function. Here, we achieve the first example of such explicit vibrational control through judicious design of a Pt(II)-acetylide charge-transfer donor-bridge-acceptor-bridge-donor 'fork' system: asymmetric 13C isotopic labelling of one of the two -C≡C- bridges makes the two parallel and otherwise identical donor→acceptor electron-transfer pathways structurally distinct, enabling independent vibrational perturbation of either. Applying an ultrafast UVpump(excitation)-IRpump(perturbation)-IRprobe(monitoring) pulse sequence, we show that the pathway that is vibrationally perturbed during UV-induced electron transfer is dramatically slowed down compared to its unperturbed counterpart. One can thus choose the dominant electron transfer pathway. The findings deliver a new opportunity for precise perturbative control of electronic energy propagation in molecular devices.

Exciton-phonon coupling in diindenoperylene thin films

NASA Astrophysics Data System (ADS)

Heinemeyer, U.; Scholz, R.; Gisslén, L.; Alonso, M. I.; Ossó, J. O.; Garriga, M.; Hinderhofer, A.; Kytka, M.; Kowarik, S.; Gerlach, A.; Schreiber, F.

2008-08-01

We investigate exciton-phonon coupling and exciton transfer in diindenoperylene (DIP) thin films on oxidized Si substrates by analyzing the dielectric function determined by variable-angle spectroscopic ellipsometry. Since the molecules in the thin-film phase form crystallites that are randomly oriented azimuthally and highly oriented along the surface normal, DIP films exhibit strongly anisotropic optical properties with uniaxial symmetry. This anisotropy can be determined by multiple sample analysis. The thin-film spectrum is compared with a monomer spectrum in solution, which reveals similar vibronic subbands and a Huang-Rhys parameter of S≈0.87 for an effective internal vibration at ℏωeff=0.17eV . However, employing these parameters the observed dielectric function of the DIP films cannot be described by a pure Frenkel exciton model, and the inclusion of charge-transfer (CT) states becomes mandatory. A model Hamiltonian is parametrized with density-functional theory calculations of single DIP molecules and molecule pairs in the stacking geometry of the thin-film phase, revealing the vibronic coupling constants of DIP in its excited and charged states together with electron and hole transfer integrals along the stack. From a fit of the model calculation to the observed dielectric tensor, we find the lowest CT transition E00CT at 0.26±0.05eV above the neutral molecular excitation energy E00F , which is an important parameter for device applications.

Twenty Years of Rad-Hard K14 SPAD in Space Projects

PubMed Central

Michálek, Vojtěch; Procházka, Ivan; Blažej, Josef

2015-01-01

During last two decades, several photon counting detectors have been developed in our laboratory. One of the most promising detector coming from our group silicon K14 Single Photon Avalanche Diode (SPAD) is presented with its valuable features and space applications. Based on the control electronics, it can be operated in both gated and non-gated mode. Although it was designed for photon counting detection, it can be employed for multiphoton detection as well. With respect to control electronics employed, the timing jitter can be as low as 20 ps RMS. Detection efficiency is about 40 % in range of 500 nm to 800 nm. The detector including gating and quenching circuitry has outstanding timing stability. Due to its radiation resistivity, the diode withstands 100 krad gamma ray dose without parameters degradation. Single photon detectors based on K14 SPAD were used for planetary altimeter and atmospheric lidar in MARS92/96 and Mars Surveyor ’98 space projects, respectively. Recent space applications of K14 SPAD comprises LIDAR and mainly time transfer between ground stations and artificial satellites. These include Laser Time Transfer, Time Transfer by Laser Link, and European Laser Timing projects. PMID:26213945

Optical properties of humic substances and CDOM: relation to structure.

PubMed

Boyle, Erin S; Guerriero, Nicolas; Thiallet, Anthony; Del Vecchio, Rossana; Blough, Neil V

2009-04-01

The spectral dependencies of absorption and fluorescence emission (emission maxima (lamdamax), quantum yields (phi), and mean lifetimes (taum)) were acquired for a commercial lignin, Suwannee River humic (SRHA) and fulvic (SRFA) acids, and a series solid phase extracts (C18) from the Middle Atlantic Bight (MAB extracts). These parameters were compared with the relative average size and total lignin phenol content (TLP). TLP was strongly correlated with absorption at 280 and 355 nm for the MAB extracts, SRHA, and SRFA. The spectral dependence of lamdamax, phi), and taum was very similar for all samples, suggesting a common photophysical and thus structural basis. A strong decrease of phi and taum with increasing average size indicates that intramolecular interactions must be important. When combined with previous work, the results lead us to conclude that the optical properties commonly associated with terrestrial humic substances and chromophoric dissolved organic matter arise primarily from an ensemble of partially oxidized lignins derived from vascular plant sources. Theyfurther provide additional support for an electronic interaction model in which intramolecular energy transfer, excited-state electron transfer, as well as charge transfer likely play important roles in producing the observed optical and photochemical properties of these materials.

Enhanced bimolecular exchange reaction through programmed coordination of a five-coordinate oxovanadium complex for efficient redox mediation in dye-sensitized solar cells.

PubMed

Oyaizu, Kenichi; Hayo, Noriko; Sasada, Yoshito; Kato, Fumiaki; Nishide, Hiroyuki

2013-12-07

Electrochemical reversibility and fast bimolecular exchange reaction found for VO(salen) gave rise to a highly efficient redox mediation to enhance the photocurrent of a dye-sensitized solar cell, leading to an excellent photovoltaic performance with a conversion efficiency of 5.4%. A heterogeneous electron-transfer rate constant at an electrode (k0) and a second-order rate constant for an electron self-exchange reaction (k(ex)) were proposed as key parameters that dominate the charge transport property, which afforded a novel design concept for the mediators based on their kinetic aspects.

Ultrasonic power transfer from a spherical acoustic wave source to a free-free piezoelectric receiver: Modeling and experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shahab, S.; Gray, M.; Erturk, A., E-mail: alper.erturk@me.gatech.edu

2015-03-14

Contactless powering of small electronic components has lately received growing attention for wireless applications in which battery replacement or tethered charging is undesired or simply impossible, and ambient energy harvesting is not a viable solution. As an alternative to well-studied methods of contactless energy transfer, such as the inductive coupling method, the use of ultrasonic waves transmitted and received by piezoelectric devices enables larger power transmission distances, which is critical especially for deep-implanted electronic devices. Moreover, energy transfer by means of acoustic waves is well suited in situations where no electromagnetic fields are allowed. The limited literature of ultrasonic acousticmore » energy transfer is mainly centered on proof-of-concept experiments demonstrating the feasibility of this method, lacking experimentally validated modeling efforts for the resulting multiphysics problem that couples the source and receiver dynamics with domain acoustics. In this work, we present fully coupled analytical, numerical, and experimental multiphysics investigations for ultrasonic acoustic energy transfer from a spherical wave source to a piezoelectric receiver bar that operates in the 33-mode of piezoelectricity. The fluid-loaded piezoelectric receiver under free-free mechanical boundary conditions is shunted to an electrical load for quantifying the electrical power output for a given acoustic source strength of the transmitter. The analytical acoustic-piezoelectric structure interaction modeling framework is validated experimentally, and the effects of system parameters are reported along with optimal electrical loading and frequency conditions of the receiver.« less

Electron Beam Melting and Refining of Metals: Computational Modeling and Optimization

PubMed Central

Vutova, Katia; Donchev, Veliko

2013-01-01

Computational modeling offers an opportunity for a better understanding and investigation of thermal transfer mechanisms. It can be used for the optimization of the electron beam melting process and for obtaining new materials with improved characteristics that have many applications in the power industry, medicine, instrument engineering, electronics, etc. A time-dependent 3D axis-symmetrical heat model for simulation of thermal transfer in metal ingots solidified in a water-cooled crucible at electron beam melting and refining (EBMR) is developed. The model predicts the change in the temperature field in the casting ingot during the interaction of the beam with the material. A modified Pismen-Rekford numerical scheme to discretize the analytical model is developed. These equation systems, describing the thermal processes and main characteristics of the developed numerical method, are presented. In order to optimize the technological regimes, different criteria for better refinement and obtaining dendrite crystal structures are proposed. Analytical problems of mathematical optimization are formulated, discretized and heuristically solved by cluster methods. Using important for the practice simulation results, suggestions can be made for EBMR technology optimization. The proposed tool is important and useful for studying, control, optimization of EBMR process parameters and improving of the quality of the newly produced materials. PMID:28788351

Thermal transfer structures coupling electronics card(s) to coolant-cooled structure(s)

DOEpatents

David, Milnes P; Graybill, David P; Iyengar, Madhusudan K; Kamath, Vinod; Kochuparambil, Bejoy J; Parida, Pritish R; Schmidt, Roger R

2014-12-16

Cooling apparatuses and coolant-cooled electronic systems are provided which include thermal transfer structures configured to engage with a spring force one or more electronics cards with docking of the electronics card(s) within a respective socket(s) of the electronic system. A thermal transfer structure of the cooling apparatus includes a thermal spreader having a first thermal conduction surface, and a thermally conductive spring assembly coupled to the conduction surface of the thermal spreader and positioned and configured to reside between and physically couple a first surface of an electronics card to the first surface of the thermal spreader with docking of the electronics card within a socket of the electronic system. The thermal transfer structure is, in one embodiment, metallurgically bonded to a coolant-cooled structure and facilitates transfer of heat from the electronics card to coolant flowing through the coolant-cooled structure.

General purpose pulse shape analysis for fast scintillators implemented in digital readout electronics

NASA Astrophysics Data System (ADS)

Asztalos, Stephen J.; Hennig, Wolfgang; Warburton, William K.

2016-01-01

Pulse shape discrimination applied to certain fast scintillators is usually performed offline. In sufficiently high-event rate environments data transfer and storage become problematic, which suggests a different analysis approach. In response, we have implemented a general purpose pulse shape analysis algorithm in the XIA Pixie-500 and Pixie-500 Express digital spectrometers. In this implementation waveforms are processed in real time, reducing the pulse characteristics to a few pulse shape analysis parameters and eliminating time-consuming waveform transfer and storage. We discuss implementation of these features, their advantages, necessary trade-offs and performance. Measurements from bench top and experimental setups using fast scintillators and XIA processors are presented.

Relativistic energy-dispersion relations of 2D rectangular lattices

NASA Astrophysics Data System (ADS)

Ata, Engin; Demirhan, Doğan; Büyükkılıç, Fevzi

2017-04-01

An exactly solvable relativistic approach based on inseparable periodic well potentials is developed to obtain energy-dispersion relations of spin states of a single-electron in two-dimensional (2D) rectangular lattices. Commutation of axes transfer matrices is exploited to find energy dependencies of the wave vector components. From the trace of the lattice transfer matrix, energy-dispersion relations of conductance and valence states are obtained in transcendental form. Graphical solutions of relativistic and nonrelativistic transcendental energy-dispersion relations are plotted to compare how lattice parameters V0, core and interstitial size of the rectangular lattice affects to the energy-band structures in a situation core and interstitial diagonals are of equal slope.

Numerical study of vorticity-enhanced heat transfer

NASA Astrophysics Data System (ADS)

Wang, Xiaolin; Alben, Silas

2013-11-01

Vortices produced by vibrated reeds and flapping foils can improve heat transfer efficiency in electronic hardware. Vortices enhance forced convection by boundary layer separation and thermal mixing in the bulk flow. In this work, we modeled and simulated the fluid flow and temperature in a 2-D channel flow with vortices injected at the upstream boundary. We classified four types of vortex streets depending on the Reynolds number and vortices' strengths and spacings, and studied the different vortex dynamics in each situation. We then used Lagrangian coherent structures (LCS) to study the effect of the vortices on mixing and determined how the Nusselt number and Coefficients of performance vary with flow parameters and Peclet numbers.

A new silicon detector telescope for measuring the linear energy transfer distribution over the range from 0.2 to 400 keV/micrometer in space.

PubMed

Doke, T; Hayashi, T; Hasebe, N; Kikuchi, J; Kono, S; Murakami, T; Sakaguchi, T; Takahashi, K; Takashima, T

1996-12-01

A new telescope consisting of three two-dimensional position-sensitive silicon detectors which can measure the linear energy transfer (LET) distribution over the range from 0.2 to 400keV/micrometers has been developed as a real-time radiation monitor in manned spacecraft. First, the principle of LET measurement and its design method are described. Second, suitable electronic parameters for the LET measurement are experimentally determined. Finally the telescope performance is investigated by using, relativistic heavy ions. The first in-flight test of this type of telescope on the US Space Shuttle (STS-84) is scheduled for May, 1997.

Experimental approach to the anion problem in DFT calculation of the partial charge transfer during adsorption at electrochemical interfaces

NASA Astrophysics Data System (ADS)

Marichev, V. A.

2005-08-01

In DFT calculation of the charge transfer (Δ N), anions pose a special problem since their electron affinities are unknown. There is no method for calculating reasonable values of the absolute electronegativity ( χA) and chemical hardness ( ηA) for ions from data of species themselves. We propose a new approach to the experimental measurement of χA at the condition: Δ N = 0 at which η values may be neglected and χA = χMe. Electrochemical parameters corresponding to this condition may be obtained by the contact electric resistance method during in situ investigation of anion adsorption in the particular system anion-metal.

Ultrafast forward and backward electron transfer dynamics of coumarin 337 in hydrogen-bonded anilines as studied with femtosecond UV-pump/IR-probe spectroscopy.

PubMed

Ghosh, Hirendra N; Verma, Sandeep; Nibbering, Erik T J

2011-02-10

Femtosecond infrared spectroscopy is used to study both forward and backward electron transfer (ET) dynamics between coumarin 337 (C337) and the aromatic amine solvents aniline (AN), N-methylaniline (MAN), and N,N-dimethylaniline (DMAN), where all the aniline solvents can donate an electron but only AN and MAN can form hydrogen bonds with C337. The formation of a hydrogen bond with AN and MAN is confirmed with steady state FT-IR spectroscopy, where the C═O stretching vibration is a direct marker mode for hydrogen bond formation. Transient IR absorption measurements in all solvents show an absorption band at 2166 cm(-1), which has been attributed to the C≡N stretching vibration of the C337 radical anion formed after ET. Forward electron transfer dynamics is found to be biexponential with time constants τ(ET)(1) = 500 fs, τ(ET)(2) = 7 ps in all solvents. Despite the presence of hydrogen bonds of C337 with the solvents AN and MAN, no effect has been found on the forward electron transfer step. Because of the absence of an H/D isotope effect on the forward electron transfer reaction of C337 in AN, hydrogen bonds are understood to play a minor role in mediating electron transfer. In contrast, direct π-orbital overlap between C337 and the aromatic amine solvents causes ultrafast forward electron transfer dynamics. Backward electron transfer dynamics, in contrast, is dependent on the solvent used. Standard Marcus theory explains the observed backward electron transfer rates.

Monoenergetic ion acceleration and Rayleigh-Taylor instability of the composite target irradiated by the laser pulse

NASA Astrophysics Data System (ADS)

Khudik, Vladimir; Yi, S. Austin; Shvets, Gennady

2012-10-01

Acceleration of ions in the two-specie composite target irradiated by a circularly polarized laser pulse is studied analytically and via particle-in-cell (PIC) simulations. A self-consistent analytical model of the composite target is developed. In this model, target parameters are stationary in the center of mass of the system: heavy and light ions are completely separated from each other and form two layers, while electrons are bouncing in the potential well formed by the laser ponderomotive and electrostatic potentials. They are distributed in the direction of acceleration by the Boltzmann law and over velocities by the Maxwell-Juttner law. The laser pulse interacts directly only with electrons in a thin sheath layer, and these electrons transfer the laser pressure to the target ions. In the fluid approximation it is shown, the composite target is still susceptible to the Rayleigh-Taylor instability [1]. Using PIC simulations we found the growth rate of initially seeded perturbations as a function of their wavenumber for different composite target parameters and compare it with analytical results. Useful scaling laws between this rate and laser pulse pressure and target parameters are discussed.[4pt] [1] T.P. Yu, A. Pukhov, G. Shvets, M. Chen, T. H. Ratliff, S. A. Yi, and V. Khudik, Phys. Plasmas, 18, 043110 (2011).

Photo-induced electron transfer method

DOEpatents

Wohlgemuth, R.; Calvin, M.

1984-01-24

The efficiency of photo-induced electron transfer reactions is increased and the back transfer of electrons in such reactions is greatly reduced when a photo-sensitizer zinc porphyrin-surfactant and an electron donor manganese porphyrin-surfactant are admixed into phospholipid membranes. The phospholipids comprising said membranes are selected from phospholipids whose head portions are negatively charged. Said membranes are contacted with an aqueous medium in which an essentially neutral viologen electron acceptor is admixed. Catalysts capable of transferring electrons from reduced viologen electron acceptor to hydrogen to produce elemental hydrogen are also included in the aqueous medium. An oxidizable olefin is also admixed in the phospholipid for the purpose of combining with oxygen that coordinates with oxidized electron donor manganese porphyrin-surfactant.

Allosteric control of internal electron transfer in cytochrome cd1 nitrite reductase

PubMed Central

Farver, Ole; Kroneck, Peter M. H.; Zumft, Walter G.; Pecht, Israel

2003-01-01

Cytochrome cd1 nitrite reductase is a bifunctional multiheme enzyme catalyzing the one-electron reduction of nitrite to nitric oxide and the four-electron reduction of dioxygen to water. Kinetics and thermodynamics of the internal electron transfer process in the Pseudomonas stutzeri enzyme have been studied and found to be dominated by pronounced interactions between the c and the d1 hemes. The interactions are expressed both in dramatic changes in the internal electron-transfer rates between these sites and in marked cooperativity in their electron affinity. The results constitute a prime example of intraprotein control of the electron-transfer rates by allosteric interactions. PMID:12802018

Kinetics of the Reduction of Metalloproteins by Chromous Ion

PubMed Central

Dawson, J. W.; Gray, H. B.; Holwerda, R. A.; Westhead, E. W.

1972-01-01

The reduction of Cu(330) in Rhus vernicifera laccase by chromous ion is 30% faster than reduction of Cu(614) at room temperature [pH 4.8, μ = 0.1 (NaCl)], and two parallel first-order paths, attributed to heterogeneity of the protein, are observed at both wavelengths. The reactions of stellacyanin, spinach and French-bean plastocyanins, and cytochrome c with chromous ion under similar conditions are faster than that with laccase by factors of 102 to 104, and are first order in protein concentration. Comparison of rates and activation parameters for the reduction of “blue” copper in laccase, stellacyanin, and the two plastocyanins indicates that reduction of the Cu(614) site in laccase may occur by intramolecular electron transfer from one of the Cu(330) sites. Our value of ΔH‡ (17.4 kcal/mol) for the chromous ion reduction of cytochrome c is consistent with a mechanism in which major conformational changes in the protein must accompany electron transfer. PMID:4500552

Enhanced electronic excitation energy transfer between dye molecules incorporated in nano-scale media with apparent fractal dimensionality

NASA Astrophysics Data System (ADS)

Yefimova, Svetlana L.; Rekalo, Andrey M.; Gnap, Bogdan A.; Viagin, Oleg G.; Sorokin, Alexander V.; Malyukin, Yuri V.

2014-09-01

In the present study, we analyze the efficiency of Electronic Excitation Energy Transfer (EEET) between two dyes, an energy donor (D) and acceptor (A), concentrated in structurally heterogeneous media (surfactant micelles, liposomes, and porous SiO2 matrices). In all three cases, highly effective EEET in pairs of dyes has been found and cannot be explained by Standard Förster-type theory for homogeneous solutions. Two independent approaches based on the analysis of either the D relative quantum yield () or the D fluorescence decay have been used to study the deviation of experimental results from the theoretical description of EEET process. The observed deviation is quantified by the apparent fractal distribution of molecules parameter . We conclude that the highly effective EEET observed in the nano-scale media under study can be explained by both forced concentration of the hydrophobic dyes within nano-volumes and non-uniform cluster-like character of the distribution of D and A dye molecules within nano-volumes.

Dynamics driving function: new insights from electron transferring flavoproteins and partner complexes.

PubMed

Toogood, Helen S; Leys, David; Scrutton, Nigel S

2007-11-01

Electron transferring flavoproteins (ETFs) are soluble heterodimeric FAD-containing proteins that function primarily as soluble electron carriers between various flavoprotein dehydrogenases. ETF is positioned at a key metabolic branch point, responsible for transferring electrons from up to 10 primary dehydrogenases to the membrane-bound respiratory chain. Clinical mutations of ETF result in the often fatal disease glutaric aciduria type II. Structural and biophysical studies of ETF in complex with partner proteins have shown that ETF partitions the functions of partner binding and electron transfer between (a) a 'recognition loop', which acts as a static anchor at the ETF-partner interface, and (b) a highly mobile redox-active FAD domain. Together, this enables the FAD domain of ETF to sample a range of conformations, some compatible with fast interprotein electron transfer. This 'conformational sampling' enables ETF to recognize structurally distinct partners, whilst also maintaining a degree of specificity. Complex formation triggers mobility of the FAD domain, an 'induced disorder' mechanism contrasting with the more generally accepted models of protein-protein interaction by induced fit mechanisms. We discuss the implications of the highly dynamic nature of ETFs in biological interprotein electron transfer. ETF complexes point to mechanisms of electron transfer in which 'dynamics drive function', a feature that is probably widespread in biology given the modular assembly and flexible nature of biological electron transfer systems.

Massively Parallel Real-Time TDDFT Simulations of Electronic Stopping Processes

NASA Astrophysics Data System (ADS)

Yost, Dillon; Lee, Cheng-Wei; Draeger, Erik; Correa, Alfredo; Schleife, Andre; Kanai, Yosuke

Electronic stopping describes transfer of kinetic energy from fast-moving charged particles to electrons, producing massive electronic excitations in condensed matter. Understanding this phenomenon for ion irradiation has implications in modern technologies, ranging from nuclear reactors, to semiconductor devices for aerospace missions, to proton-based cancer therapy. Recent advances in high-performance computing allow us to achieve an accurate parameter-free description of these phenomena through numerical simulations. Here we discuss results from our recently-developed large-scale real-time TDDFT implementation for electronic stopping processes in important example materials such as metals, semiconductors, liquid water, and DNA. We will illustrate important insight into the physics underlying electronic stopping and we discuss current limitations of our approach both regarding physical and numerical approximations. This work is supported by the DOE through the INCITE awards and by the NSF. Part of this work was performed under the auspices of U.S. DOE by LLNL under Contract DE-AC52-07NA27344.

Parallel Large-scale Semidefinite Programming for Strong Electron Correlation: Using Correlation and Entanglement in the Design of Efficient Energy-Transfer Mechanisms

DTIC Science & Technology

2014-09-24

which nature uses strong electron correlation for efficient energy transfer, particularly in photosynthesis and bioluminescence, (ii) providing an...strong electron correlation for efficient energy transfer, particularly in photosynthesis and bioluminescence, (ii) providing an innovative paradigm...efficient energy transfer, particularly in photosynthesis and bioluminescence, (ii) providing an innovative paradigm for energy transfer in photovoltaic

Golden rule kinetics of transfer reactions in condensed phase: The microscopic model of electron transfer reactions in disordered solid matrices

NASA Astrophysics Data System (ADS)

Basilevsky, M. V.; Odinokov, A. V.; Titov, S. V.; Mitina, E. A.

2013-12-01

The algorithm for a theoretical calculation of transfer reaction rates for light quantum particles (i.e., the electron and H-atom transfers) in non-polar solid matrices is formulated and justified. The mechanism postulated involves a local mode (an either intra- or inter-molecular one) serving as a mediator which accomplishes the energy exchange between the reacting high-frequency quantum mode and the phonon modes belonging to the environment. This approach uses as a background the Fermi golden rule beyond the usually applied spin-boson approximation. The dynamical treatment rests on the one-dimensional version of the standard quantum relaxation equation for the reduced density matrix, which describes the frequency fluctuation spectrum for the local mode under consideration. The temperature dependence of a reaction rate is controlled by the dimensionless parameter ξ0 = ℏω0/kBT where ω0 is the frequency of the local mode and T is the temperature. The realization of the computational scheme is different for the high/intermediate (ξ0 < 1 - 3) and for low (ξ0 ≫ 1) temperature ranges. For the first (quasi-classical) kinetic regime, the Redfield approximation to the solution of the relaxation equation proved to be sufficient and efficient in practical applications. The study of the essentially quantum-mechanical low-temperature kinetic regime in its asymptotic limit requires the implementation of the exact relaxation equation. The coherent mechanism providing a non-vanishing reaction rate has been revealed when T → 0. An accurate computational methodology for the cross-over kinetic regime needs a further elaboration. The original model of the hopping mechanism for electronic conduction in photosensitive organic materials is considered, based on the above techniques. The electron transfer (ET) in active centers of such systems proceeds via local intra- and intermolecular modes. The active modes, as a rule, operate beyond the kinetic regimes, which are usually postulated in the existing theories of the ET. Our alternative dynamic ET model for local modes immersed in the continuum harmonic medium is formulated for both classical and quantum regimes, and accounts explicitly for the mode/medium interaction. The kinetics of the energy exchange between the local ET subsystem and the surrounding environment essentially determine the total ET rate. The efficient computer code for rate computations is elaborated on. The computations are available for a wide range of system parameters, such as the temperature, external field, local mode frequency, and characteristics of mode/medium interaction. The relation of the present approach to the Marcus ET theory and to the quantum-statistical reaction rate theory [V. G. Levich and R. R. Dogonadze, Dokl. Akad. Nauk SSSR, Ser. Fiz. Khim. 124, 213 (1959); J. Ulstrup, Charge Transfer in Condensed Media (Springer, Berlin, 1979); M. Bixon and J. Jortner, Adv. Chem. Phys. 106, 35 (1999)] underlying it is discussed and illustrated by the results of computations for practically important target systems.

Golden rule kinetics of transfer reactions in condensed phase: the microscopic model of electron transfer reactions in disordered solid matrices.

PubMed

Basilevsky, M V; Odinokov, A V; Titov, S V; Mitina, E A

2013-12-21

The algorithm for a theoretical calculation of transfer reaction rates for light quantum particles (i.e., the electron and H-atom transfers) in non-polar solid matrices is formulated and justified. The mechanism postulated involves a local mode (an either intra- or inter-molecular one) serving as a mediator which accomplishes the energy exchange between the reacting high-frequency quantum mode and the phonon modes belonging to the environment. This approach uses as a background the Fermi golden rule beyond the usually applied spin-boson approximation. The dynamical treatment rests on the one-dimensional version of the standard quantum relaxation equation for the reduced density matrix, which describes the frequency fluctuation spectrum for the local mode under consideration. The temperature dependence of a reaction rate is controlled by the dimensionless parameter ξ0 = ℏω0/k(B)T where ω0 is the frequency of the local mode and T is the temperature. The realization of the computational scheme is different for the high/intermediate (ξ0 < 1 - 3) and for low (ξ0 ≫ 1) temperature ranges. For the first (quasi-classical) kinetic regime, the Redfield approximation to the solution of the relaxation equation proved to be sufficient and efficient in practical applications. The study of the essentially quantum-mechanical low-temperature kinetic regime in its asymptotic limit requires the implementation of the exact relaxation equation. The coherent mechanism providing a non-vanishing reaction rate has been revealed when T → 0. An accurate computational methodology for the cross-over kinetic regime needs a further elaboration. The original model of the hopping mechanism for electronic conduction in photosensitive organic materials is considered, based on the above techniques. The electron transfer (ET) in active centers of such systems proceeds via local intra- and intermolecular modes. The active modes, as a rule, operate beyond the kinetic regimes, which are usually postulated in the existing theories of the ET. Our alternative dynamic ET model for local modes immersed in the continuum harmonic medium is formulated for both classical and quantum regimes, and accounts explicitly for the mode∕medium interaction. The kinetics of the energy exchange between the local ET subsystem and the surrounding environment essentially determine the total ET rate. The efficient computer code for rate computations is elaborated on. The computations are available for a wide range of system parameters, such as the temperature, external field, local mode frequency, and characteristics of mode/medium interaction. The relation of the present approach to the Marcus ET theory and to the quantum-statistical reaction rate theory [V. G. Levich and R. R. Dogonadze, Dokl. Akad. Nauk SSSR, Ser. Fiz. Khim. 124, 213 (1959); J. Ulstrup, Charge Transfer in Condensed Media (Springer, Berlin, 1979); M. Bixon and J. Jortner, Adv. Chem. Phys. 106, 35 (1999)] underlying it is discussed and illustrated by the results of computations for practically important target systems.

Electron Tunneling in Lithium Ammonia Solutions Probed by Frequency-Dependent Electron-Spin Relaxation Studies

PubMed Central

Maeda, Kiminori; Lodge, Matthew T.J.; Harmer, Jeffrey; Freed, Jack H.; Edwards, Peter P.

2012-01-01

Electron transfer or quantum tunneling dynamics for excess or solvated electrons in dilute lithium-ammonia solutions have been studied by pulse electron paramagnetic resonance (EPR) spectroscopy at both X- (9.7 GHz) and W-band (94 GHz) frequencies. The electron spin-lattice (T1) and spin-spin (T2) relaxation data indicate an extremely fast transfer or quantum tunneling rate of the solvated electron in these solutions which serves to modulate the hyperfine (Fermi-contact) interaction with nitrogen nuclei in the solvation shells of ammonia molecules surrounding the localized, solvated electron. The donor and acceptor states of the solvated electron in these solutions are the initial and final electron solvation sites found before, and after, the transfer or tunneling process. To interpret and model our electron spin relaxation data from the two observation EPR frequencies requires a consideration of a multi-exponential correlation function. The electron transfer or tunneling process that we monitor through the correlation time of the nitrogen Fermi-contact interaction has a time scale of (1–10)×10−12 s over a temperature range 230–290K in our most dilute solution of lithium in ammonia. Two types of electron-solvent interaction mechanisms are proposed to account for our experimental findings. The dominant electron spin relaxation mechanism results from an electron tunneling process characterized by a variable donor-acceptor distance or range (consistent with such a rapidly fluctuating liquid structure) in which the solvent shell that ultimately accepts the transferring electron is formed from random, thermal fluctuations of the liquid structure in, and around, a natural hole or Bjerrum-like defect vacancy in the liquid. Following transfer and capture of the tunneling electron, further solvent-cage relaxation with a timescale of ca. 10−13 s results in a minor contribution to the electron spin relaxation times. This investigation illustrates the great potential of multi-frequency EPR measurements to interrogate the microscopic nature and dynamics of ultra fast electron transfer or quantum-tunneling processes in liquids. Our results also impact on the universal issue of the role of a host solvent (or host matrix, e.g. a semiconductor) in mediating long-range electron transfer processes and we discuss the implications of our results with a range of other materials and systems exhibiting the phenomenon of electron transfer. PMID:22568866

A consistent S-Adenosylmethionine force field improved by dynamic Hirshfeld-I atomic charges for biomolecular simulation

NASA Astrophysics Data System (ADS)

Saez, David Adrian; Vöhringer-Martinez, Esteban

2015-10-01

S-Adenosylmethionine (AdoMet) is involved in many biological processes as cofactor in enzymes transferring its sulfonium methyl group to various substrates. Additionally, it is used as drug and nutritional supplement to reduce the pain in osteoarthritis and against depression. Due to the biological relevance of AdoMet it has been part of various computational simulation studies and will also be in the future. However, to our knowledge no rigorous force field parameter development for its simulation in biological systems has been reported. Here, we use electronic structure calculations combined with molecular dynamics simulations in explicit solvent to develop force field parameters compatible with the AMBER99 force field. Additionally, we propose new dynamic Hirshfeld-I atomic charges which are derived from the polarized electron density of AdoMet in aqueous solution to describe its electrostatic interactions in biological systems. The validation of the force field parameters and the atomic charges is performed against experimental interproton NOE distances of AdoMet in aqueous solution and crystal structures of AdoMet in the cavity of three representative proteins.

Optimization of design and operating parameters of a space-based optical-electronic system with a distributed aperture.

PubMed

Tcherniavski, Iouri; Kahrizi, Mojtaba

2008-11-20

Using a gradient optimization method with objective functions formulated in terms of a signal-to-noise ratio (SNR) calculated at given values of the prescribed spatial ground resolution, optimization problems of geometrical parameters of a distributed optical system and a charge-coupled device of a space-based optical-electronic system are solved for samples of the optical systems consisting of two and three annular subapertures. The modulation transfer function (MTF) of the distributed aperture is expressed in terms of an average MTF taking residual image alignment (IA) and optical path difference (OPD) errors into account. The results show optimal solutions of the optimization problems depending on diverse variable parameters. The information on the magnitudes of the SNR can be used to determine the number of the subapertures and their sizes, while the information on the SNR decrease depending on the IA and OPD errors can be useful in design of a beam combination control system to produce the necessary requirements to its accuracy on the basis of the permissible deterioration in the image quality.

Effect of Hypoeutectic Boron Additions on the Grain Size and Mechanical Properties of Ti-6Al-4V Manufactured with Powder Bed Electron Beam Additive Manufacturing

NASA Astrophysics Data System (ADS)

Mahbooba, Zaynab; West, Harvey; Harrysson, Ola; Wojcieszynski, Andrzej; Dehoff, Ryan; Nandwana, Peeyush; Horn, Timothy

2017-03-01

In additive manufacturing, microstructural control is feasible via processing parameter alteration. However, the window for parameter variation for certain materials, such as Ti-6Al-4V, is limited, and alternative methods must be employed to customize microstructures. Grain refinement and homogenization in cast titanium alloys has been demonstrated through the addition of hypoeutectic concentrations of boron. This work explores the influence of 0.00 wt.%, 0.25 wt.%, 0.50 wt.%, and 1.0 wt.% boron additions on the microstructure and bulk mechanical properties of Ti-6Al-4V samples fabricated in an Arcam A2 electron beam melting (EBM) system with commercial processing parameters for Ti-6Al-4V. Analyses of EBM fabricated Ti-6Al-4V + B indicate that the addition of 0.25-1.0 wt.% boron progressively refines the grain structure, and it improves hardness and elastic modulus. Despite a reduction in size, the β grain structure remained columnar as a result of directional heat transfer during EBM fabrication.

Natural convection of Al2O3-water nanofluid in a wavy enclosure

NASA Astrophysics Data System (ADS)

Leonard, Mitchell; Mozumder, Aloke K.; Mahmud, Shohel; Das, Prodip K.

2017-06-01

Natural convection heat transfer and fluid flow inside enclosures filled with fluids, such as air, water or oil, have been extensively analysed for thermal enhancement and optimisation due to their applications in many engineering problems, including solar collectors, electronic cooling, lubrication technologies, food processing and nuclear reactors. In comparison, little effort has been given to the problem of natural convection inside enclosures filled with nanofluids, while the addition of nanoparticles into a fluid base to alter thermal properties can be a feasible solution for many heat transfer problems. In this study, the problem of natural convection heat transfer and fluid flow inside a wavy enclosure filled with Al2O3-water nanofluid is investigated numerically using ANSYS-FLUENT. The effects of surface waviness and aspect ratio of the wavy enclosure on the heat transfer and fluid flow are analysed for various concentrations of Al2O3 nanoparticles in water. Flow fields and temperature fields are investigated and heat transfer rate is examined for different values of Rayleigh number. Results show that heat transfer within the enclosure can be enhanced by increasing surface waviness, aspect ratio or nanoparticles volume fraction. Changes in surface waviness have little effect on the heat transfer rate at low Rayleigh numbers, but when Ra ≥ 105 heat transfer increases with the increase of surface waviness from zero to higher values. Increasing the aspect ratio causes an increase in heat transfer rate, as the Rayleigh number increases the effect of changing aspect ratio is more apparent with the greatest heat transfer enhancement seen at higher Rayleigh numbers. Nanoparticles volume fraction has a little effect on the average Nusselt number at lower Rayleigh numbers when Ra ≥ 105 average Nusselt number increases with the increase of volume fraction. These findings provide insight into the heat transfer effects of using Al2O3-water nanofluid as a heat transfer medium and the effects of changing geometrical parameters, which will help in developing novel geometries with enhanced and controlled heat-transfer for solar collectors, electronic cooling, and food processing industries.

Opto-electronic conversion logic behaviour through dynamic modulation of electron/energy transfer states at the TiO2-carbon quantum dot interface.

PubMed

Wang, Fang; Zhang, Yonglai; Liu, Yang; Wang, Xuefeng; Shen, Mingrong; Lee, Shuit-Tong; Kang, Zhenhui

2013-03-07

Here we show a bias-mediated electron/energy transfer process at the CQDs-TiO(2) interface for the dynamic modulation of opto-electronic properties. Different energy and electron transfer states have been observed in the CQDs-TNTs system due to the up-conversion photoluminescence and the electron donation/acceptance properties of the CQDs decorated on TNTs.

Gyrokinetic turbulence: between idealized estimates and a detailed analysis of nonlinear energy transfers

NASA Astrophysics Data System (ADS)

Teaca, Bogdan; Jenko, Frank; Told, Daniel

2017-04-01

Using large resolution numerical simulations of gyrokinetic (GK) turbulence, spanning an interval ranging from the end of the fluid scales to the electron gyroradius, we study the energy transfers in the perpendicular direction for a proton-electron plasma in a slab equilibrium magnetic geometry. The plasma parameters employed here are relevant to kinetic Alfvén wave turbulence in solar wind conditions. In addition, we use an idealized test representation for the energy transfers between two scales, to aid our understanding of the diagnostics applicable to the nonlinear cascade in an infinite inertial range. For GK turbulence, a detailed analysis of nonlinear energy transfers that account for the separation of energy exchanging scales is performed. Starting from the study of the energy cascade and the scale locality problem, we show that the general nonlocal nature of GK turbulence, captured via locality functions, contains a subset of interactions that are deemed local, are scale invariant (i.e. a sign of asymptotic locality) and possess a locality exponent that can be recovered directly from measurements on the energy cascade. It is the first time that GK turbulence is shown to possess an asymptotic local component, even if the overall locality of interactions is nonlocal. The results presented here and their implications are discussed from the perspective of previous findings reported in the literature and the idea of universality of GK turbulence.

New series of aromatic/ five-membered heteroaromatic butanesulfonyl hydrazones as potent biological agents: Synthesis, physicochemical and electronic properties

NASA Astrophysics Data System (ADS)

Hamurcu, Fatma; Mamaş, Serhat; Ozdemir, Ummuhan Ozmen; Gündüzalp, Ayla Balaban; Senturk, Ozan Sanlı

2016-08-01

The aromatic/five-membered heteroaromatic butanesulfonylhydrazone derivatives; 5-bromosalicylaldehydebutanesulfonylhydrazone(1), 2-hydroxy-1-naphthaldehydebutane sulfonylhydrazone(2), indole-3-carboxaldehydebutanesulfonylhydrazone (3), 2-acetylfuran- carboxyaldehydebutanesulfonylhydrazone(4), 2-acetylthiophenecarboxyaldehydebutane- sulfonylhydrazone(5) and 2-acetyl-5-chlorothiophenecarboxyaldehydebutanesulfonyl hydrazone (6) were synthesized by the reaction of butane sulfonic acid hydrazide with aldehydes/ketones and characterized by using elemental analysis, 1H NMR, 13C NMR and FT-IR technique. Their geometric parameters and electronic properties consist of global reactivity descriptors were also determined by theoretical methods. The electrochemical behavior of the butanesulfonylhydrazones were investigated by using cyclic voltammetry (CV), controlled potential electrolysis and chronoamperometry (CA) techniques. The number of electrons transferred (n), diffusion coefficient (D) and standard heterogeneous rate constants (ks) were determined by electrochemical methods.

Study of ring influence and electronic response to proton transfer reactions. Reaction electronic flux analysis.

PubMed

Herrera, Barbara

2011-05-01

In this article, a theoretical study of 1-5 proton transfers is presented. Two model systems which represent 1-5 proton transfer, 3-hidroxy-2-propenimine and salicyldenaniline have been studied as shown in Fig. 1. For this purpose, a DFT/B3LYP/6-311+G**, reaction force and reaction electronic flux analysis is made. The obtained results indicate that both proton transfers exhibit energetic and electronic differences emphasizing the role of the neighbor ring and the impact of conjugation on electronic properties.

Coherent Electron Transfer at the Ag / Graphite Heterojunction Interface

NASA Astrophysics Data System (ADS)

Tan, Shijing; Dai, Yanan; Zhang, Shengmin; Liu, Liming; Zhao, Jin; Petek, Hrvoje

2018-03-01

Charge transfer in transduction of light to electrical or chemical energy at heterojunctions of metals with semiconductors or semimetals is believed to occur by photogenerated hot electrons in metal undergoing incoherent internal photoemission through the heterojunction interface. Charge transfer, however, can also occur coherently by dipole coupling of electronic bands at the heterojunction interface. Microscopic physical insights into how transfer occurs can be elucidated by following the coherent polarization of the donor and acceptor states on the time scale of electronic dephasing. By time-resolved multiphoton photoemission spectroscopy (MPP), we investigate the coherent electron transfer from an interface state that forms upon chemisorption of Ag nanoclusters onto graphite to a σ symmetry interlayer band of graphite. Multidimensional MPP spectroscopy reveals a resonant two-photon transition, which dephases within 10 fs completing the coherent transfer.

Food Antioxidants: Chemical Insights at the Molecular Level.

PubMed

Galano, Annia; Mazzone, Gloria; Alvarez-Diduk, Ruslán; Marino, Tiziana; Alvarez-Idaboy, J Raúl; Russo, Nino

2016-01-01

In this review, we briefly summarize the reliability of the density functional theory (DFT)-based methods to accurately predict the main antioxidant properties and the reaction mechanisms involved in the free radical-scavenging reactions of chemical compounds present in food. The analyzed properties are the bond dissociation energies, in particular those involving OH bonds, electron transfer enthalpies, adiabatic ionization potentials, and proton affinities. The reaction mechanisms are hydrogen-atom transfer, proton-coupled electron transfer, radical adduct formation, single electron transfer, sequential electron proton transfer, proton-loss electron transfer, and proton-loss hydrogen-atom transfer. Furthermore, the chelating ability of these compounds and its role in decreasing or inhibiting the oxidative stress induced by Fe(III) and Cu(II) are considered. Comparisons between theoretical and experimental data confirm that modern theoretical tools are not only able to explain controversial experimental facts but also to predict chemical behavior.

On generalized Mulliken-Hush approach of electronic transfer: Inclusion of non-zero off-diagonal diabatic dipole moment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kryachko, E.S.

1999-06-03

The electronic coupling between the initial and final diabatic states is the major factor that determines the rate of electron transfer. A general formula for the adiabatic-to-diabatic mixing angle in terms of the electronic dipole moments is derived within a two-state model. It expresses the electronic coupling determining the rate of electronic transfer in terms of the off-diagonal diabatic dipole moment.

Photo-induced electron transfer method

DOEpatents

Wohlgemuth, Roland; Calvin, Melvin

1984-01-01

The efficiency of photo-induced electron transfer reactions is increased and the back transfer of electrons in such reactions is greatly reduced when a photo-sensitizer zinc porphyrin-surfactant and an electron donor manganese porphyrin-surfactant are admixed into phospho-lipid membranes. The phospholipids comprising said membranes are selected from phospholipids whose head portions are negatively charged. Said membranes are contacted with an aqueous medium in which an essentially neutral viologen electron acceptor is admixed. Catalysts capable of transfering electrons from reduced viologen electron acceptor to hydrogen to produce elemental hydrogen are also included in the aqueous medium. An oxidizable olefin is also admixed in the phospholipid for the purpose of combining with oxygen that coordinates with oxidized electron donor manganese porphyrin-surfactant.

Electron transport in the two-dimensional channel material - zinc oxide nanoflake

NASA Astrophysics Data System (ADS)

Lai, Jian-Jhong; Jian, Dunliang; Lin, Yen-Fu; Ku, Ming-Ming; Jian, Wen-Bin

2018-03-01

ZnO nanoflakes of 3-5 μm in lateral size and 15-20 nm in thickness are synthesized. The nanoflakes are used to make back-gated transistor devices. Electron transport in the ZnO nanoflake channel between source and drain electrodes are investigated. In the beginning, we argue and determine that electrons are in a two-dimensional system. We then apply Mott's two-dimensional variable range hopping model to analyze temperature and electric field dependences of resistivity. The disorder parameter, localization length, hopping distance, and hopping energy of the electron system in ZnO nanoflakes are obtained and, additionally, their temperature behaviors and dependences on room-temperature resistivity are presented. On the other hand, the basic transfer characteristics of the channel material are carried out, as well, and the carrier concentration, the mobility, and the Fermi wavelength of two-dimensional ZnO nanoflakes are estimated.

Application of Electron-Transfer Theory to Several Systems of Biological Interest

DOE R&D Accomplishments Database

Marcus, R. A.; Sutin, N.

1985-03-23

Electron-transfer reaction rates are compared with theoretically calculated values for several reactions in the bacterial photosynthetic reaction center. A second aspect of the theory, the cross-relation, is illustrated using protein-protein electron transfers.

Synergistic electron transfer effect-based signal amplification strategy for the ultrasensitive detection of dopamine.

PubMed

Lu, Qiujun; Chen, Xiaogen; Liu, Dan; Wu, Cuiyan; Liu, Meiling; Li, Haitao; Zhang, Youyu; Yao, Shouzhuo

2018-05-15

The selective and sensitive detection of dopamine (DA) is of great significance for the identification of schizophrenia, Huntington's disease, and Parkinson's disease from the perspective of molecular diagnostics. So far, most of DA fluorescence sensors are based on the electron transfer from the fluorescence nanomaterials to DA-quinone. However, the limited electron transfer ability of the DA-quinone affects the level of detection sensitivity of these sensors. In this work, based on the DA can reduce Ag + into AgNPs followed by oxidized to DA-quinone, we developed a novel silicon nanoparticles-based electron transfer fluorescent sensor for the detection of DA. As electron transfer acceptor, the AgNPs and DA-quinone can quench the fluorescence of silicon nanoparticles effectively through the synergistic electron transfer effect. Compared with traditional fluorescence DA sensors, the proposed synergistic electron transfer-based sensor improves the detection sensitivity to a great extent (at least 10-fold improvement). The proposed sensor shows a low detection limit of DA, which is as low as 0.1 nM under the optimal conditions. This sensor has potential applicability for the detection of DA in practical sample. This work has been demonstrated to contribute to a substantial improvement in the sensitivity of the sensors. It also gives new insight into design electron transfer-based sensors. Copyright © 2018. Published by Elsevier B.V.

Quantifying electron transfer reactions in biological systems: what interactions play the major role?

NASA Astrophysics Data System (ADS)

Sjulstok, Emil; Olsen, Jógvan Magnus Haugaard; Solov'Yov, Ilia A.

2015-12-01

Various biological processes involve the conversion of energy into forms that are usable for chemical transformations and are quantum mechanical in nature. Such processes involve light absorption, excited electronic states formation, excitation energy transfer, electrons and protons tunnelling which for example occur in photosynthesis, cellular respiration, DNA repair, and possibly magnetic field sensing. Quantum biology uses computation to model biological interactions in light of quantum mechanical effects and has primarily developed over the past decade as a result of convergence between quantum physics and biology. In this paper we consider electron transfer in biological processes, from a theoretical view-point; namely in terms of quantum mechanical and semi-classical models. We systematically characterize the interactions between the moving electron and its biological environment to deduce the driving force for the electron transfer reaction and to establish those interactions that play the major role in propelling the electron. The suggested approach is seen as a general recipe to treat electron transfer events in biological systems computationally, and we utilize it to describe specifically the electron transfer reactions in Arabidopsis thaliana cryptochrome-a signaling photoreceptor protein that became attractive recently due to its possible function as a biological magnetoreceptor.

ELECTRON TRANSFER MECHANISM AT THE SOLID-LIQUID INTERFACE OF PHYLLOSILICATES

EPA Science Inventory

Interfacial electron transfer processes on clay minerals have significant impact in natural environments and geochemical systems. Nitrobenzene was used as molecular probes to study the electron transfer mechanism at the solid-water interfaces of Fe-containing phyllosicates. For...

Electron Capture Supernovae from Close Binary Systems

NASA Astrophysics Data System (ADS)

Poelarends, Arend J. T.; Wurtz, Scott; Tarka, James; Cole Adams, L.; Hills, Spencer T.

2017-12-01

We present the first detailed study of the Electron Capture Supernova Channel (ECSN Channel) for a primary star in a close binary star system. Progenitors of ECSN occupy the lower end of the mass spectrum of supernova progenitors and are thought to form the transition between white dwarf progenitors and core-collapse progenitors. The mass range for ECSN from close binary systems is thought to be wider than the range for single stars, because of the effects of mass transfer on the helium core. Using the MESA stellar evolution code, we explored the parameter space of initial primary masses between 8 and 17 {M}⊙ , using a large grid of models. We find that the initial primary mass and the mass transfer evolution are important factors in the final fate of stars in this mass range. Mass transfer due to Roche lobe overflow during and after carbon burning causes the core to cool down so that it avoids neon ignition, even in helium-free cores with masses up to 1.52 {M}⊙ , which in single stars would ignite neon. If the core is able to contract to high enough densities for electron captures to commence, we find that, for the adopted Ledoux convection criterion, the initial mass range for the primary to evolve into an ECSN is between 13.5 and 17.6 {M}⊙ . The mass ratio, initial period, and mass-loss efficiency only marginally affect the predicted ranges.

Synthesis, and spectroscopic studies of charge transfer complex of 1,2-dimethylimidazole as an electron donor with π-acceptor 2,4-dinitro-1-naphthol in different polar solvents

NASA Astrophysics Data System (ADS)

Miyan, Lal; Khan, Ishaat M.; Ahmad, Afaq

2015-07-01

The charge transfer (CT) complex of 1,2-dimethylimidazole (DMI) as an electron donor with π acceptor 2,4-dinitro-1-naphthol (DNN) has been studied spectrophotometrically in different solvents like chloroform, acetonitrile, methanol, methylene chloride, etc. at room temperature. The CT complex which is formed through the transfer of lone pair electrons from DMI to DNN exhibits well resolved CT bands and the regions of these bands were remarkably different from those of the donor and acceptor. The stoichiometry of the CT complex was found to be 1:1 by a straight-line method between donor and acceptor with maximum absorption bands. The novel CT complex has been characterized by FTIR, TGA-DTA, powder XRD, 1H NMR and 13C NMR spectroscopic techniques. The Benesi-Hildebrand equation has been used to determine the formation constant (KCT), molar extinction coefficient (εCT), standard gibbs free energy (ΔG°) and other physical parameters of the CT complex. The formation constant recorded higher values and molar extinction coefficient recorded lower values in chloroform compared with methylene chloride, methanol and acetonitrile, confirming the strong interaction between the molecular orbital's of donor and acceptor in the ground state in less polar solvent. This CT complex has been studied by absorption spectra of donor 1,2-dimethylimidazole (DMI) and acceptor 2,4-dinitro-1-naphthol (DNN) by using the spectrophotometric technique in various solvents at room temperature.

Systems approach to excitation-energy and electron transfer reaction networks in photosystem II complex: model studies for chlorophyll a fluorescence induction kinetics.

PubMed

Matsuoka, Takeshi; Tanaka, Shigenori; Ebina, Kuniyoshi

2015-09-07

Photosystem II (PS II) is a protein complex which evolves oxygen and drives charge separation for photosynthesis employing electron and excitation-energy transfer processes over a wide timescale range from picoseconds to milliseconds. While the fluorescence emitted by the antenna pigments of this complex is known as an important indicator of the activity of photosynthesis, its interpretation was difficult because of the complexity of PS II. In this study, an extensive kinetic model which describes the complex and multi-timescale characteristics of PS II is analyzed through the use of the hierarchical coarse-graining method proposed in the authors׳ earlier work. In this coarse-grained analysis, the reaction center (RC) is described by two states, open and closed RCs, both of which consist of oxidized and neutral special pairs being in quasi-equilibrium states. Besides, the PS II model at millisecond scale with three-state RC, which was studied previously, could be derived by suitably adjusting the kinetic parameters of electron transfer between tyrosine and RC. Our novel coarse-grained model of PS II can appropriately explain the light-intensity dependent change of the characteristic patterns of fluorescence induction kinetics from O-J-I-P, which shows two inflection points, J and I, between initial point O and peak point P, to O-J-D-I-P, which shows a dip D between J and I inflection points. Copyright © 2015 Elsevier Ltd. All rights reserved.

Tunneling induced electron transfer between separated protons

NASA Astrophysics Data System (ADS)

Vindel-Zandbergen, Patricia; Meier, Christoph; Sola, Ignacio R.

2018-04-01

We study electron transfer between two separated protons using local control theory. In this symmetric system one can favour a slow transfer by biasing the algorithm, achieving high efficiencies for fixed nuclei. The solution can be parametrized using a sequence of a pump followed by a dump pulse that lead to tunneling-induced electron transfer. Finally, we study the effect of the nuclear kinetic energy on the efficiency. Even in the absence of relative motion between the protons, the spreading of the nuclear wave function is enough to reduce the yield of electronic transfer to less than one half.

X.400: The Standard for Message Handling Systems.

ERIC Educational Resources Information Center

Swain, Leigh; Tallim, Paula

1990-01-01

Profiles X.400, the Open Systems Interconnection (OSI) Application layer standard that supports interpersonal electronic mail services, facsimile transfer, electronic data interchange, electronic funds transfer, electronic publishing, and electronic invoicing. Also discussed are an electronic directory to support message handling, compatibility…

Application of Degenerately Doped Metal Oxides in the Study of Photoinduced Interfacial Electron Transfer.

PubMed

Farnum, Byron H; Morseth, Zachary A; Brennaman, M Kyle; Papanikolas, John M; Meyer, Thomas J

2015-06-18

Degenerately doped In2O3:Sn semiconductor nanoparticles (nanoITO) have been used to study the photoinduced interfacial electron-transfer reactivity of surface-bound [Ru(II)(bpy)2(4,4'-(PO3H2)2-bpy)](2+) (RuP(2+)) molecules as a function of driving force over a range of 1.8 eV. The metallic properties of the ITO nanoparticles, present within an interconnected mesoporous film, allowed for the driving force to be tuned by controlling their Fermi level with an external bias while their optical transparency allowed for transient absorption spectroscopy to be used to monitor electron-transfer kinetics. Photoinduced electron transfer from excited-state -RuP(2+*) molecules to nanoITO was found to be dependent on applied bias and competitive with nonradiative energy transfer to nanoITO. Back electron transfer from nanoITO to oxidized -RuP(3+) was also dependent on the applied bias but without complication from inter- or intraparticle electron diffusion in the oxide nanoparticles. Analysis of the electron injection kinetics as a function of driving force using Marcus-Gerischer theory resulted in an experimental estimate of the reorganization energy for the excited-state -RuP(3+/2+*) redox couple of λ* = 0.83 eV and an electronic coupling matrix element, arising from electronic wave function overlap between the donor orbital in the molecule and the acceptor orbital(s) in the nanoITO electrode, of Hab = 20-45 cm(-1). Similar analysis of the back electron-transfer kinetics yielded λ = 0.56 eV for the ground-state -RuP(3+/2+) redox couple and Hab = 2-4 cm(-1). The use of these wide band gap, degenerately doped materials provides a unique experimental approach for investigating single-site electron transfer at the surface of oxide nanoparticles.

Chemical and charge transfer studies on interfaces of a conjugated polymer and ITO

NASA Astrophysics Data System (ADS)

David, Tanya M. S.; Arasho, Wondwosson; Smith, O'Neil; Hong, Kunlun; Bonner, Carl; Sun, Sam-Shajing

2017-08-01

Conjugated oligomers and polymers are very attractive for potential future plastic electronic and opto-electronic device applications such as plastic photo detectors and solar cells, thermoelectric devices, field effect transistors, and light emitting diodes. Understanding and optimizing charge transport between an active polymer layer and conductive substrate is critical to the optimization of polymer based electronic and opto-electronic devices. This study focused on the design, synthesis, self-assembly, and electron transfers and transports of a phosphonic acid end-functionalized polyphenylenevinylene (PPV) that was covalently attached and self-assembled onto an Indium Tin Oxide (ITO) substrate. This study demonstrated how atomic force microscopy (AFM) can be an effective characterization technique in conjunction with conventional electron transfer methods, including cyclic voltammetry (CV), towards determining electron transfer rates in polymer and polymer/conductor interface systems. This study found that the electron transfer rates of covalently attached and self-assembled films were much faster than the spin coated films. The knowledge from this study can be very useful for designing potential polymer based electronic and opto-electronic thin film devices.

Electron transfer by excited benzoquinone anions: slow rates for two-electron transitions.

PubMed

Zamadar, Matibur; Cook, Andrew R; Lewandowska-Andralojc, Anna; Holroyd, Richard; Jiang, Yan; Bikalis, Jin; Miller, John R

2013-09-05

Electron transfer (ET) rate constants from the lowest excited state of the radical anion of benzoquinone, BQ(-•)*, were measured in THF solution. Rate constants for bimolecular electron transfer reactions typically reach the diffusion-controlled limit when the free-energy change, ΔG°, reaches -0.3 eV. The rate constants for ET from BQ(-•)* are one-to-two decades smaller at this energy and do not reach the diffusion-controlled limit until -ΔG° is 1.5-2.0 eV. The rates are so slow probably because a second electron must also undergo a transition to make use of the energy of the excited state. Similarly, ET, from solvated electrons to neutral BQ to form the lowest excited state, is slow, while fast ET is observed at a higher excited state, which can be populated in a transition involving only one electron. A simple picture based on perturbation theory can roughly account for the control of electron transfer by the need for transition of a second electron. The picture also explains how extra driving force (-ΔG°) can restore fast rates of electron transfer.

Charge transfer complex of some nervous and brain drugs - Part 1: Synthesis, spectroscopic, analytical and biological studies on the reaction between haloperidol antipsychotic drugs with π-acceptors

NASA Astrophysics Data System (ADS)

El-Habeeb, Abeer A.; Al-Saif, Foziah A.; Refat, Moamen S.

2013-02-01

Donor-acceptor interactions between the electron donor haloperidol (HPL) and π-acceptors like 7,7,8,8-tetracyanoquinodimethane (TCNQ) and picric acid (PA) have been studied spectrophotometrically in CH3OH solvent. The donor-acceptor (charge transfer complexes) were discussed in terms of formation constant (KCT), molar extinction coefficient (ɛCT), standard free energy (ΔGo), oscillator strength (ƒ), transition dipole moment (μ), resonance energy (RN) and ionization potential (ID). The stoichiometry of these complexes was found to be 1:1 M ratio and having the formulas [(HPL)(TCNQ)] and [(HPL)(PA)], respectively. The charge transfer interaction was successfully applied to determine of HPL drug using mentioned common π-acceptors also, the results obtained herein are satisfactory for estimation of HPL compound in the pharmaceutical form. The formed solid charge-transfer complexes were also isolated and characterized using elemental analysis, conductivity, (infrared, Raman, and 1H NMR) spectra and X-ray powder diffraction (XRD). The experimental data of elemental analyses are in agreement with calculated data. The infrared spectra of both HPL complexes are confirming the participation of sbnd OH of 4-hydroxy-1-piperidyl moiety in the donor-acceptor chelation. The morphological surface of the resulted charge transfer complexes were investigated using scanning electron microscopy (SEM). The thermogravimetric analysis (TG/DTG) and differential scanning calorimetry (DSC) techniques were performed to give knowledge about the thermal stability behavior of the synthesized charge transfer complexes. Thermodynamic parameters were computed from the thermal decomposition data. These complexes were also tested for their antimicrobial activity against six different microorganisms, and the results were compared with the parent drug.

Flavins in Marine Sediments: A Potentially Ubiquitous Intermediary In Microbial Electron Transfer

NASA Astrophysics Data System (ADS)

Monteverde, D.; Sylvan, J. B.; Suffridge, C.; Berelson, W.; Sanudo-Wilhelmy, S. A.; Baronas, J. J.

2016-12-01

The flavins (riboflavin, flavin mononucleotide [FMN], flavin adenine dinucleotide [FA­­D]) are a class of organic compounds synthesized by organisms to assist in redox reactions. They represent the largest class of required coenzymes, rivaled only by iron in the number of unique enzymes they bind. In addition to internal use, cultured metal-reducing organisms such as Shewanella and Geobacter have been known to release flavins into the extracellular pool to aid in external electron transfer. So called "electron shuttles" can allow organisms to overcome unfavorable geochemical zonation by transferring electrons onto a relatively distant insoluble acceptor. Despite the extensive culture work, flavins have not been systematically measured in the environment. Here we present the first set of flavin profiles from the water column and pore waters of a marine environment. Samples were taken from San Pedro Basin, a 900 meter deep, silled basin, with high seasonal inputs of organic carbon, low bottom water oxygen concentrations, and laminated sediments - making it ideal to explore variations in sediment geochemical zonations. Dissolved flavin concentrations in the water column and pore waters collected from two cores were preconcentrated via solid phase extraction and measured via LC/MS. Flavin profiles are compared to a suite of geochemical parameters as well as sediment microbial 16s rRNA data. Preliminary results show that FMN is typically an order of magnitude higher concentration than riboflavin (800-300pM versus 100-50pM). Porewater concentrations were elevated over water column values for all analytes (ranging from 100-2000pM) and displayed an increasing trend with depth in both cores. This increasing trend correlated with a decrease in dissolved Fe (ranging from 160 µM in surface sediments to 65 µM at 40 cm) and shifts in microbial diversity from sediments shallower than 5 cm depth dominated by Delta- and Gammaproteobacteria to subsurface sediments dominated by Chloroflexi and Archaea at 20-40 cm. These first environmental profiles of flavins in the marine environmental support previous observations of the importance of electron transfer intermediaries in culture and point to an important role for flavins in modern marine microbial communities.

Evidence that Additions of Grignard Reagents to Aliphatic Aldehydes Do Not Involve Single-Electron-Transfer Processes.

PubMed

Otte, Douglas A L; Woerpel, K A

2015-08-07

Addition of allylmagnesium reagents to an aliphatic aldehyde bearing a radical clock gave only addition products and no evidence of ring-opened products that would suggest single-electron-transfer reactions. The analogous Barbier reaction also did not provide evidence for a single-electron-transfer mechanism in the addition step. Other Grignard reagents (methyl-, vinyl-, t-Bu-, and triphenylmethylmagnesium halides) also do not appear to add to an alkyl aldehyde by a single-electron-transfer mechanism.

Evidence for protein conformational change at a Au(110)/protein interface

NASA Astrophysics Data System (ADS)

Messiha, H. L.; Smith, C. I.; Scrutton, N. S.; Weightman, P.

2008-07-01

Evidence is presented that reflection anisotropy spectroscopy (RAS) can provide real-time measurements of conformational change in proteins induced by electron transfer reactions. A bacterial electron transferring flavoprotein (ETF) has been modified so as to adsorb on an Au(110) electrode and enable reversible electron transfer to the protein cofactor in the absence of mediators. Reversible changes are observed in the RAS of this protein that are interpreted as arising from conformational changes accompanying the transfer of electrons.

Enhanced electron transfer kinetics through hybrid graphene-carbon nanotube films.

PubMed

Henry, Philémon A; Raut, Akshay S; Ubnoske, Stephen M; Parker, Charles B; Glass, Jeffrey T

2014-11-01

We report the first study of the electrochemical reactivity of a graphenated carbon nanotube (g-CNT) film. The electron transfer kinetics of the ferri-ferrocyanide couple were examined for a g-CNT film and compared to the kinetics to standard carbon nanotubes (CNTs). The g-CNT film exhibited much higher catalytic activity, with a heterogeneous electron-transfer rate constant, k 0 , approximately two orders of magnitude higher than for standard CNTs. Scanning electron microscopy and Raman spectroscopy were used to correlate the higher electron transfer kinetics with the higher edge-density of the g-CNT film.

Enzymatic cellulose oxidation is linked to lignin by long-range electron transfer

PubMed Central

Westereng, Bjørge; Cannella, David; Wittrup Agger, Jane; Jørgensen, Henning; Larsen Andersen, Mogens; Eijsink, Vincent G.H.; Felby, Claus

2015-01-01

Enzymatic oxidation of cell wall polysaccharides by lytic polysaccharide monooxygenases (LPMOs) plays a pivotal role in the degradation of plant biomass. While experiments have shown that LPMOs are copper dependent enzymes requiring an electron donor, the mechanism and origin of the electron supply in biological systems are only partly understood. We show here that insoluble high molecular weight lignin functions as a reservoir of electrons facilitating LPMO activity. The electrons are donated to the enzyme by long-range electron transfer involving soluble low molecular weight lignins present in plant cell walls. Electron transfer was confirmed by electron paramagnetic resonance spectroscopy showing that LPMO activity on cellulose changes the level of unpaired electrons in the lignin. The discovery of a long-range electron transfer mechanism links the biodegradation of cellulose and lignin and sheds new light on how oxidative enzymes present in plant degraders may act in concert. PMID:26686263

Correlation between energy deposition and molecular damage from Auger electrons: A case study of ultra-low energy (5-18 eV) electron interactions with DNA.

PubMed

Rezaee, Mohammad; Hunting, Darel J; Sanche, Léon

2014-07-01

The present study introduces a new method to establish a direct correlation between biologically related physical parameters (i.e., stopping and damaging cross sections, respectively) for an Auger-electron emitting radionuclide decaying within a target molecule (e.g., DNA), so as to evaluate the efficacy of the radionuclide at the molecular level. These parameters can be applied to the dosimetry of Auger electrons and the quantification of their biological effects, which are the main criteria to assess the therapeutic efficacy of Auger-electron emitting radionuclides. Absorbed dose and stopping cross section for the Auger electrons of 5-18 eV emitted by(125)I within DNA were determined by developing a nanodosimetric model. The molecular damages induced by these Auger electrons were investigated by measuring damaging cross section, including that for the formation of DNA single- and double-strand breaks. Nanoscale films of pure plasmid DNA were prepared via the freeze-drying technique and subsequently irradiated with low-energy electrons at various fluences. The damaging cross sections were determined by employing a molecular survival model to the measured exposure-response curves for induction of DNA strand breaks. For a single decay of(125)I within DNA, the Auger electrons of 5-18 eV deposit the energies of 12.1 and 9.1 eV within a 4.2-nm(3) volume of a hydrated or dry DNA, which results in the absorbed doses of 270 and 210 kGy, respectively. DNA bases have a major contribution to the deposited energies. Ten-electronvolt and high linear energy transfer 100-eV electrons have a similar cross section for the formation of DNA double-strand break, while 100-eV electrons are twice as efficient as 10 eV in the induction of single-strand break. Ultra-low-energy electrons (<18 eV) substantially contribute to the absorbed dose and to the molecular damage from Auger-electron emitting radionuclides; hence, they should be considered in the dosimetry calculation of such radionuclides. Moreover, absorbed dose is not an appropriate physical parameter for nanodosimetry. Instead, stopping cross section, which describes the probability of energy deposition in a target molecule can be an appropriate nanodosimetric parameter. The stopping cross section is correlated with a damaging cross section (e.g., cross section for the double-strand break formation) to quantify the number of each specific lesion in a target molecule for each nuclear decay of a single Auger-electron emitting radionuclide.

CymA and Exogenous Flavins Improve Extracellular Electron Transfer and Couple It to Cell Growth in Mtr-Expressing Escherichia coli

DOE PAGES

Jensen, Heather M.; TerAvest, Michaela A.; Kokish, Mark G.; ...

2016-03-22

Introducing extracellular electron transfer pathways into heterologous organisms offers the opportunity to explore fundamental biogeochemical processes and to biologically alter redox states of exogenous metals for various applications. While expression of the MtrCAB electron nanoconduit from Shewanella oneidensis MR-1 permits extracellular electron transfer in Escherichia coli, the low electron flux and absence of growth in these cells limits their practicality for such applications. In this paper, we investigate how the rate of electron transfer to extracellular Fe(III) and cell survival in engineered E. coli are affected by mimicking different features of the S. oneidensis pathway: the number of electron nanoconduits,more » the link between the quinol pool and MtrA, and the presence of flavin-dependent electron transfer. While increasing the number of pathways does not significantly improve the extracellular electron transfer rate or cell survival, using the native inner membrane component, CymA, significantly improves the reduction rate of extracellular acceptors and increases cell viability. Strikingly, introducing both CymA and riboflavin to Mtr-expressing E. coli also allowed these cells to couple metal reduction to growth, which is the first time an increase in biomass of an engineered E. coli has been observed under Fe 2O 3 (s) reducing conditions. Overall and finally, this work provides engineered E. coli strains for modulating extracellular metal reduction and elucidates critical factors for engineering extracellular electron transfer in heterologous organisms.« less

CymA and Exogenous Flavins Improve Extracellular Electron Transfer and Couple It to Cell Growth in Mtr-Expressing Escherichia coli

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jensen, Heather M.; TerAvest, Michaela A.; Kokish, Mark G.

Introducing extracellular electron transfer pathways into heterologous organisms offers the opportunity to explore fundamental biogeochemical processes and to biologically alter redox states of exogenous metals for various applications. While expression of the MtrCAB electron nanoconduit from Shewanella oneidensis MR-1 permits extracellular electron transfer in Escherichia coli, the low electron flux and absence of growth in these cells limits their practicality for such applications. In this paper, we investigate how the rate of electron transfer to extracellular Fe(III) and cell survival in engineered E. coli are affected by mimicking different features of the S. oneidensis pathway: the number of electron nanoconduits,more » the link between the quinol pool and MtrA, and the presence of flavin-dependent electron transfer. While increasing the number of pathways does not significantly improve the extracellular electron transfer rate or cell survival, using the native inner membrane component, CymA, significantly improves the reduction rate of extracellular acceptors and increases cell viability. Strikingly, introducing both CymA and riboflavin to Mtr-expressing E. coli also allowed these cells to couple metal reduction to growth, which is the first time an increase in biomass of an engineered E. coli has been observed under Fe 2O 3 (s) reducing conditions. Overall and finally, this work provides engineered E. coli strains for modulating extracellular metal reduction and elucidates critical factors for engineering extracellular electron transfer in heterologous organisms.« less

Flavin Charge Transfer Transitions Assist DNA Photolyase Electron Transfer

NASA Astrophysics Data System (ADS)

Skourtis, Spiros S.; Prytkova, Tatiana; Beratan, David N.

2007-12-01

This contribution describes molecular dynamics, semi-empirical and ab-initio studies of the primary photo-induced electron transfer reaction in DNA photolyase. DNA photolyases are FADH--containing proteins that repair UV-damaged DNA by photo-induced electron transfer. A DNA photolyase recognizes and binds to cyclobutatne pyrimidine dimer lesions of DNA. The protein repairs a bound lesion by transferring an electron to the lesion from FADH-, upon photo-excitation of FADH- with 350-450 nm light. We compute the lowest singlet excited states of FADH- in DNA photolyase using INDO/S configuration interaction, time-dependent density-functional, and time-dependent Hartree-Fock methods. The calculations identify the lowest singlet excited state of FADH- that is populated after photo-excitation and that acts as the electron donor. For this donor state we compute conformationally-averaged tunneling matrix elements to empty electron-acceptor states of a thymine dimer bound to photolyase. The conformational averaging involves different FADH--thymine dimer confromations obtained from molecular dynamics simulations of the solvated protein with a thymine dimer docked in its active site. The tunneling matrix element computations use INDO/S-level Green's function, energy splitting, and Generalized Mulliken-Hush methods. These calculations indicate that photo-excitation of FADH- causes a π→π* charge-transfer transition that shifts electron density to the side of the flavin isoalloxazine ring that is adjacent to the docked thymine dimer. This shift in electron density enhances the FADH--to-dimer electronic coupling, thus inducing rapid electron transfer.

Atomic bonding effects in annular dark field scanning transmission electron microscopy. II. Experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Odlyzko, Michael L.; Held, Jacob T.; Mkhoyan, K. Andre, E-mail: mkhoyan@umn.edu

2016-07-15

Quantitatively calibrated annular dark field scanning transmission electron microscopy (ADF-STEM) imaging experiments were compared to frozen phonon multislice simulations adapted to include chemical bonding effects. Having carefully matched simulation parameters to experimental conditions, a depth-dependent bonding effect was observed for high-angle ADF-STEM imaging of aluminum nitride. This result is explained by computational predictions, systematically examined in the preceding portion of this study, showing the propagation of the converged STEM beam to be highly sensitive to net interatomic charge transfer. Thus, although uncertainties in experimental conditions and simulation accuracy remain, the computationally predicted experimental bonding effect withstands the experimental testing reportedmore » here.« less

An analytical model for bio-electronic organic field-effect transistor sensors

NASA Astrophysics Data System (ADS)

Macchia, Eleonora; Giordano, Francesco; Magliulo, Maria; Palazzo, Gerardo; Torsi, Luisa

2013-09-01

A model for the electrical characteristics of Functional-Bio-Interlayer Organic Field-Effect Transistors (FBI-OFETs) electronic sensors is here proposed. Specifically, the output current-voltage characteristics of a streptavidin (SA) embedding FBI-OFET are modeled by means of the analytical equations of an enhancement mode p-channel OFET modified according to an ad hoc designed equivalent circuit that is also independently simulated with pspice. An excellent agreement between the model and the experimental current-voltage output characteristics has been found upon exposure to 5 nM of biotin. A good agreement is also found with the SA OFET parameters graphically extracted from the device transfer I-V curves.

Theory of low transitions in CO discharge lasers

NASA Technical Reports Server (NTRS)

Sidney, B. D.; Mcinuille, R. M.; Smith, N. S.; Hassan, H. A.

1976-01-01

A self consistent theoretical model which couples the electron and heavy particle finite rate kinetics with the optical and fluid dynamic processes has been employed to identify the various parameters and explain the mechanism responsible for producing low lying transitions in slow flowing CO lasers. It is found that lasing on low lying transitions can be achieved at low temperatures for low pressures (or low flow rates) together with high partial pressures of the He and N2. The role of N2 has been identified as an additive responsible for reducing the electron temperature to a range where the transfer of electrical power to the lower vibrational modes of CO is optimum.

Photoinduced electron transfer between benzyloxy dendrimer phthalocyanine and benzoquinone

NASA Astrophysics Data System (ADS)

Zhang, Tiantian; Ma, Dongdong; Pan, Sujuan; Wu, Shijun; Jiang, Yufeng; Zeng, Di; Yang, Hongqin; Peng, Yiru

2016-10-01

Photo-induced electron transfer (PET) is an important and fundamental process in natural photosynthesis. To mimic such interesting PET process, a suitable donor and acceptor couple were properly chosen. Dendrimer phthalocyanines and their derivatives have emerged as promising materials for artificial photosynthesis systems. In this paper, the electron transfer between the light harvest dendrimer phthalocyanine (donor) and the 1,4-benzoquinone (acceptor) was studied by UV/Vis and fluorescence spectroscopic methods. It was found that fluorescence of phthalocyanine was quenched by benzoquinone (BQ) via excited state electron transfer, from the phthalocyanine to the BQ upon excitation at 610 nm. The Stern-Volmer constant (KSV) of electron transfer was calculated. Our study suggests that this dendritic phthalocyanine is an effective new electron donor and transmission complex and could be used as a potential artificial photosynthesis system.

Long-range electron transfer in porphyrin-containing [2]-rotaxanes: tuning the rate by metal cation coordination.

PubMed

Andersson, Mikael; Linke, Myriam; Chambron, Jean-Claude; Davidsson, Jan; Heitz, Valérie; Hammarström, Leif; Sauvage, Jean-Pierre

2002-04-24

A series of [2]-rotaxanes has been synthesized in which two Zn(II)-porphyrins (ZnP) electron donors were attached as stoppers on the rod. A macrocycle attached to a Au(III)-porphyrin (AuP+) acceptor was threaded on the rod. By selective excitation of either porphyrin, we could induce an electron transfer from the ZnP to the AuP+ unit that generated the same ZnP*+-AuP* charge-transfer state irrespective of which porphyrin was excited. Although the reactants were linked only by mechanical or coordination bonds, electron-transfer rate constants up to 1.2x10(10) x s(-1) were obtained over a 15-17 A edge-to-edge distance between the porphyrins. The resulting charge-transfer state had a relatively long lifetime of 10-40 ns and was formed in high yield (>80%) in most cases. By a simple variation of the link between the reactants, viz. a coordination of the phenanthroline units on the rotaxane rod and ring by either Ag+ or Cu+, we could enhance the electron-transfer rate from the ZnP to the excited 3AuP+. We interpret our data in terms of an enhanced superexchange mechanism with Ag+ and a change to a stepwise hopping mechanism with Cu+, involving the oxidized Cu(phen)22+ unit as a real intermediate. When the ZnP unit was excited instead, electron transfer from the excited 1ZnP to AuP+ was not affected, or even slowed, by Ag+ or Cu+. We discuss this asymmetry in terms of the different orbitals involved in mediating the reaction in an electron- and a hole-transfer mechanism. Our results show the possibility to tune the rates of electron transfer between noncovalently linked reactants by a convenient modification of the link. The different effect of Ag+ and Cu+ on the rate with ZnP and AuP+ excitation shows an additional possibility to control the electron-transfer reactions by selective excitation. We also found that coordination of the Cu+ introduced an energy-transfer reaction from 1ZnP to Cu(phen)2+ (k = 5.1x10(9) x s(-1)) that proceeded in competition with electron transfer to AuP+ and was followed by a quantitative energy transfer to give the 3ZnP state (k = 1.5x10(9) x s(-1)).

A molecular shift register based on electron transfer

NASA Technical Reports Server (NTRS)

Hopfield, J. J.; Onuchic, Josenelson; Beratan, David N.

1988-01-01

An electronic shift-register memory at the molecular level is described. The memory elements are based on a chain of electron-transfer molecules and the information is shifted by photoinduced electron-transfer reactions. This device integrates designed electronic molecules onto a very large scale integrated (silicon microelectronic) substrate, providing an example of a 'molecular electronic device' that could actually be made. The design requirements for such a device and possible synthetic strategies are discussed. Devices along these lines should have lower energy usage and enhanced storage density.

Surface Redox Chemistry of Immobilized Nanodiamond: Effects of Particle Size and Electrochemical Environment

NASA Astrophysics Data System (ADS)

Gupta, S.; McDonald, B.; Carrizosa, S. B.

2017-07-01

The size of the diamond particle is tailored to nanoscale (nanodiamond, ND), and the ND surface is engineered targeting specific (electrochemical and biological) applications. In this work, we investigated the complex surface redox chemistry of immobilized ND layer on conductive boron-doped diamond electrode with a broad experimental parameter space such as particle size (nano versus micron), scan rate, pH (cationic/acidic versus anionic/basic), electrolyte KCl concentration (four orders of magnitude), and redox agents (neutral and ionic). We reported on the significant enhancement of ionic currents while recording reversible oxidation of neutral ferrocene methanol (FcMeOH) by almost one order of magnitude than traditional potassium ferricyanide (K3Fe(CN)6) redox agent. The current enhancement is inversely related to ND particle diameter in the following order: 1 μm << 1000 nm < 100 nm < 10 nm ≤ 5 nm < 2 nm. We attribute the current enhancement to concurrent electrocatalytic processes, i.e. the electron transfer between redox probes and electroactive surface functional (e.g. hydroxyl, carboxyl, epoxy) moieties and the electron transfer mediated by adsorbed FcMeOH+ (or Fe(CN) 6 3+ ) ions onto ND surface. The first process is pH dependent since it depends upon ND surface functionalities for which the electron transfer is coupled to proton transfer. The adsorption mediated process is observed most apparently at slower scan rates owing to self-exchange between adsorbed FcMeOH+ ions and FcMeOH redox agent molecules in diffusion-limited bulk electrolyte solution. Alternatively, it is hypothesized that the surface functionality and defect sites ( sp 2-bonded C shell and unsaturated bonds) give rise to surface electronic states with energies within the band gap (midgap states) in undoped ND. These surface states serve as electron donors (and acceptors) depending upon their bonding (and antibonding) character and, therefore, they can support electrocatalytic redox processes in the presence of specific redox-active molecules via feedback mechanism. Apparently, FcMeOH+ tended to have electrostatic affinity for negatively charged ND surface functionalities, corroborated by present experiments. We also attempted to study biocatalytic process using model metalloprotein (cytochrome c; Cyt c) immobilized on ND particles for investigating interfacial electron transfer kinetics and compared with those of functionalized graphene (graphene oxide; GO and reduced GO). The findings are discussed in terms of interplay of sp 3-bonded C (ND core) and sp 2-bonded C (ND shell and graphene-based systems).

Geophysical monitoring of solute transport in dual-domain environments through laboratory experiments, field-scale solute tracer tests, and numerical simulation

NASA Astrophysics Data System (ADS)

Swanson, Ryan David

The advection-dispersion equation (ADE) fails to describe non-Fickian solute transport breakthrough curves (BTCs) in saturated porous media in both laboratory and field experiments, necessitating the use of other models. The dual-domain mass transfer (DDMT) model partitions the total porosity into mobile and less-mobile domains with an exchange of mass between the two domains, and this model can reproduce better fits to BTCs in many systems than ADE-based models. However, direct experimental estimation of DDMT model parameters remains elusive and model parameters are often calculated a posteriori by an optimization procedure. Here, we investigate the use of geophysical tools (direct-current resistivity, nuclear magnetic resonance, and complex conductivity) to estimate these model parameters directly. We use two different samples of the zeolite clinoptilolite, a material shown to demonstrate solute mass transfer due to a significant internal porosity, and provide the first evidence that direct-current electrical methods can track solute movement into and out of a less-mobile pore space in controlled laboratory experiments. We quantify the effects of assuming single-rate DDMT for multirate mass transfer systems. We analyze pore structures using material characterization methods (mercury porosimetry, scanning electron microscopy, and X-ray computer tomography), and compare these observations to geophysical measurements. Nuclear magnetic resonance in conjunction with direct-current resistivity measurements can constrain mobile and less-mobile porosities, but complex conductivity may have little value in relation to mass transfer despite the hypothesis that mass transfer and complex conductivity lengths scales are related. Finally, we conduct a geoelectrical monitored tracer test at the Macrodispersion Experiment (MADE) site in Columbus, MS. We relate hydraulic and electrical conductivity measurements to generate a 3D hydraulic conductivity field, and compare to hydraulic conductivity fields estimated through ordinary kriging and sequential Gaussian simulation. Time-lapse electrical measurements are used to verify or dismiss aspects of breakthrough curves for different hydraulic conductivity fields. Our results quantify the potential for geophysical measurements to infer on single-rate DDMT parameters, show site-specific relations between hydraulic and electrical conductivity, and track solute exchange into and out of less-mobile domains.

Advanced electron microscopy characterization of tri-layer rare-earth oxide superlattices

NASA Astrophysics Data System (ADS)

Phillips, Patrick; Disa, Ankit; Ismail-Beigi, Sohrab; Klie, Robert; University of Illinois-Chicago Team; Yale University Team

2015-03-01

Rare-earth nickelates are known to display complex electronic and magnetic behaviors owed to a very localized and sensitive Ni-site atomic and electronic structure. Toward realizing the goal of manipulating of the energetic ordering of Ni d orbitals and 2D conduction, the present work focuses on the experimental characterization of thin film superlattice structures consisting of alternating layers of LaTiO3 and LaNiO3 sandwiched between a dull insulator, LaAlO3. Using advanced scanning transmission electron microscopy (STEM)-based methods, properties such as interfacial sharpness, electron transfer, O presence, and local electronic structure can be probed at the atomic scale, and will be discussed at length. By combining both energy dispersive X-ray (EDX) and electronic energy loss (EEL) spectroscopies in an aberration-corrected STEM, it is possible to attain energy and spatial resolutions of 0.35 eV and 100 pm, respectively. Focus of the talk will remain not only on the aforementioned properties, but will also include details and parameters of the acquisitions to facilitate future characterization at this level.

12 CFR 1005.6 - Liability of consumer for unauthorized transfers.

Code of Federal Regulations, 2012 CFR

2012-01-01

... transfers. 1005.6 Section 1005.6 Banks and Banking BUREAU OF CONSUMER FINANCIAL PROTECTION ELECTRONIC FUND TRANSFERS (REGULATION E) § 1005.6 Liability of consumer for unauthorized transfers. (a) Conditions for..., for an unauthorized electronic fund transfer involving the consumer's account only if the financial...

Stabilization of non-productive conformations underpins rapid electron transfer to electron-transferring flavoprotein.

PubMed

Toogood, Helen S; van Thiel, Adam; Scrutton, Nigel S; Leys, David

2005-08-26

Crystal structures of protein complexes with electron-transferring flavoprotein (ETF) have revealed a dual protein-protein interface with one region serving as anchor while the ETF FAD domain samples available space within the complex. We show that mutation of the conserved Glu-165beta in human ETF leads to drastically modulated rates of interprotein electron transfer with both medium chain acyl-CoA dehydrogenase and dimethylglycine dehydrogenase. The crystal structure of free E165betaA ETF is essentially identical to that of wild-type ETF, but the crystal structure of the E165betaA ETF.medium chain acyl-CoA dehydrogenase complex reveals clear electron density for the FAD domain in a position optimal for fast interprotein electron transfer. Based on our observations, we present a dynamic multistate model for conformational sampling that for the wild-type ETF. medium chain acyl-CoA dehydrogenase complex involves random motion between three distinct positions for the ETF FAD domain. ETF Glu-165beta plays a key role in stabilizing positions incompatible with fast interprotein electron transfer, thus ensuring high rates of complex dissociation.

Utility of positron annihilation lifetime technique for the assessment of spectroscopic data of some charge-transfer complexes derived from N-(1-Naphthyl)ethylenediamine dihydrochloride

NASA Astrophysics Data System (ADS)

Refat, Moamen S.; Adam, Abdel Majid A.; Sharshar, T.; Saad, Hosam A.; Eldaroti, Hala H.

2014-03-01

In this work, structural, thermal, morphological, pharmacological screening and positron annihilation lifetime measurements were performed on the interactions between a N-(1-Naphthyl)ethylenediamine dihydrochloride (NEDA·2HCl) donor and three types of acceptors to characterize these CT complexes. The three types of acceptors include π-acceptors (quinol and picric acid), σ-acceptors (iodine) and vacant orbital acceptors (tin(IV) tetrachloride and zinc chloride). The positron annihilation lifetime parameters were found to be dependent on the structure, electronic configuration, the power of acceptors and molecular weight of the CT complexes. The positron annihilation lifetime spectroscopy can be used as a probe for the formation of charge-transfer (CT) complexes.

Mixed stack charge transfer crystals: Crossing the neutral-ionic borderline by chemical substitution

NASA Astrophysics Data System (ADS)

Castagnetti, Nicola; Masino, Matteo; Rizzoli, Corrado; Girlando, Alberto; Rovira, Concepció

2018-02-01

We report extensive structural and spectroscopic characterization of four mixed stack charge-transfer (ms-CT) crystals formed by the electron donor 3,3',5 ,5' -tetramethylbenzidine (TMB) with Chloranil (CA), Bromanil (BA), 2,5-difluoro-tetracyanoquinodimethane (TCNQF2), and tetrafluoro-tetracyanoquinodimethane (TCNQF4). Together with the separately studied TMB-TCNQ [Phys. Rev. B 95, 024101 (2017), 10.1103/PhysRevB.95.024101] the TMB-acceptor series spans a wide range of degree of CT, from about 0.14 to 0.91, crossing the neutral-ionic interface, yet retaining similar packing and donor-acceptor CT integrals. First principle calculations of key phenomenological parameters allow us to get insight into the factors determining the degree of CT and other relevant physical properties.

77 FR 34127 - Financial Management Service; Proposed Collection of Information: Electronic Transfer Account...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-06-08

... Information: Electronic Transfer Account (ETA) Financial Agency Agreement AGENCY: Financial Management Service... of information described below: Title: Electronic Transfer Account (ETA) Financial Agency Agreement... public and other Federal agencies to take this opportunity to comment on a continuing information...

31 CFR 208.4 - Waivers.

Code of Federal Regulations, 2011 CFR

2011-07-01

...) Payment by electronic funds transfer is not required in the following cases: (1) Where an individual: (i... are not required to be made by electronic funds transfer, unless and until such payments become... waiver request with Treasury certifying that payment by electronic funds transfer would impose a hardship...

12 CFR 1005.7 - Initial disclosures.

Code of Federal Regulations, 2012 CFR

2012-01-01

... disclosures required by this section at the time a consumer contracts for an electronic fund transfer service or before the first electronic fund transfer is made involving the consumer's account. (b) Content of... Banks and Banking BUREAU OF CONSUMER FINANCIAL PROTECTION ELECTRONIC FUND TRANSFERS (REGULATION E...

Solvent effects on the oxidation (electron transfer) reaction of [Fe(CN) 6] 4- by [Co(NH 3) 5pz] 3+

NASA Astrophysics Data System (ADS)

Muriel, F.; Jiménez, R.; López, M.; Prado-Gotor, R.; Sánchez, F.

2004-03-01

Solvent effects on the title reaction were studied in different reaction media constituted by water and organic cosolvents (methanol, tert-butyl alcohol, ethyleneglycol and glucose) at 298.2 K. The results are considered in light of the Marcus-Hush approach for electron transfer reactions. Variations of the electron transfer rate constant are shown to be mainly due to changes in the reaction free energy. On the other hand the energies of the MMCT band, corresponding to the optical electron transfer within the ion pair [Fe(CN) 6] 4-/[Co(NH 3) 5pz] 3+, in the different reaction media, have been obtained. The activation free energies of the thermal electron transfer process have been calculated from the band ( Eop) data, and compared with those obtained from the kinetic study. Quantitative agreement is found between the two series of data. This shows the possibility of estimating activation free energies for electron transfer reactions from static (optical) measurements.

Theory of even-parity states and two-photon spectra of conjugated polymers

NASA Astrophysics Data System (ADS)

McWilliams, P. C. M.; Hayden, G. W.; Soos, Z. G.

1991-04-01

The two-photon absorption (TPA) spectrum of interacting π electrons in conjugated polymers is shown to be qualitatively different from any single-particle description, including the Hartree-Fock limit. Alternating transfer integrals t(1+/-δ) along the backbone lead to a weak TPA below the one-photon gap Eg for arbitrarily weak correlations at δ=0, for intermediate correlations at δ=0.07 in polyenes, and for strong correlations at any δ<1. More intense TPA is derived from two-electron transfer across Eg; this even-parity state shifts from 2Eg in single-particle theory to Eg in the limit of strong correlations in Hubbard models and is around 1.5Eg for Pariser-Parr-Pople (PPP) parameters. The PPP model, which accounts for one- and two-photon excitations of finite polyenes, is extended to even-parity states in polydiacetylenes (PDA's), polyacetylene (PA), and polysilanes (PS's). Previous experimental data for PDA and PS support both the strong TPA above Eg and weak TPA slightly below Eg for δ=0.15 in PDA and above Eg for δ~0.3 in PS. The strong TPA expected around 1.5Eg in isolated PA strands shifts to ~Eg due to interchain π-electron dispersion forces. TPA intensities in correlated states are shown to reflect both ionicity and mean-square charge separation. The even-parity states of conjugated polymers, like those of polyenes, show qualitatively different features associated with electron-electron correlations.

Microscopic dynamics research on the "mature" process of dye-sensitized solar cells after injection of highly concentrated electrolyte.

PubMed

Liang, Zhongguan; Liu, Weiqing; Chen, Jun; Hu, Linhua; Dai, Songyuan

2015-01-21

After injection of electrolyte, the internal three-dimensional solid-liquid penetration system of dye-sensitized solar cells (DSCs) can take a period of time to reach "mature" state. This paper studies the changes of microscopic processes of DSCs including TiO2 energy-level movement, localized state distribution, charge accumulation, electron transport, and recombination dynamics, from the beginning of electrolyte injection to the time of reached mature state. The results show that the microscopic dynamics process of DSCs exhibited a time-dependent behavior and achieved maturity ∼12 h after injecting the electrolyte into DSCs. Within 0-12 h, several results were observed: (1) the conduction band edge of TiO2 moved slightly toward negative potential direction; (2) the localized states in the band gap of TiO2 was reduced according to the same distribution law; (3) the transport resistance in TiO2 film increased, and electron transport time was prolonged as the time of maturity went on, which indicated that the electron transport process is impeded gradually; (4) the recombination resistance at the TiO2/electrolyte (EL) interface increases, and electron lifetime gradually extends, therefore, the recombination process is continuously suppressed. Furthermore, results suggest that the parameters of EL/Pt-transparent conductive oxide (TCO) interface including the interfacial capacitance, electron-transfer resistance, and transfer time constant would change with time of maturity, indicating that the EL/Pt-TCO interface is a potential factor affecting the mature process of DSCs.

Kinetics of triscarbonato uranyl reduction by aqueous ferrous iron: a theoretical study.

PubMed

Wander, Matthew C F; Kerisit, Sebastien; Rosso, Kevin M; Schoonen, Martin A A

2006-08-10

Uranium is a pollutant whose mobility is strongly dependent on its oxidation state. While U(VI) in the form of the uranyl cation is readily reduced by a range of natural reductants, by contrast complexation of uranyl by carbonate greatly reduces its reduction potential and imposes increased electron transfer (ET) distances. Very little is known about the elementary processes involved in uranium reduction from U(VI) to U(V) to U(IV) in general. In this study, we examine the theoretical kinetics of ET from ferrous iron to triscarbonato uranyl in aqueous solution. A combination of molecular dynamics (MD) simulations and density functional theory (DFT) electronic structure calculations is employed to compute the parameters that enter into Marcus' ET model, including the thermodynamic driving forces, reorganization energies, and electronic coupling matrix elements. MD simulations predict that two ferrous iron atoms will bind in an inner-sphere fashion to the three-membered carbonate ring of triscarbonato uranyl, forming the charge-neutral ternary Fe(2)UO(2)(CO(3))(3)(H(2)O)(8) complex. Through a sequential proton-coupled electron-transfer mechanism (PCET), the first ET step converting U(VI) to U(V) is predicted by DFT to occur with an electronic barrier that corresponds to a rate on the order of approximately 1 s(-1). The second ET step converting U(V) to U(IV) is predicted to be significantly endergonic. Therefore, U(V) is a stabilized end product in this ET system, in agreement with experiment.

Bidirectional Photoinduced Electron Transfer in Ruthenium(II)-Tris-bipyridyl-Modified PpcA, a Multi-heme c -Type Cytochrome from Geobacter sulfurreducens

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kokhan, Oleksandr; Ponomarenko, Nina S.; Pokkuluri, P. Raj

PpcA, a tri-heme cytochrome c7 from Geobacter sulfurreducens was investigated as a model for photosensitizer-initiated electron transfer within a multi-heme "molecular wire" protein architecture. E. coli expression of PpcA was found to be tolerant of cysteine site-directed mutagenesis, demonstrated by the successful expression of natively folded proteins bearing cysteine mutations at a series of sites selected to vary characteristically with respect to the three -CXXCH- heme binding domains. A preliminary survey of 5 selected mutants found that the introduced cysteines can be readily covalently linked to a Ru(II)-(2,2'-bpy)2(4-bromomethyl-4’-methyl-2,2'-bpy) photosensitizer (where bpy = bipyridine), and that the linked constructs support bothmore » photo-oxidative and photo-reductive quenching of the photosensitizer excited-state, depending upon the initial heme redox state. For photo-oxidative electron transfer, apparent heme reduction risetimes were found to vary from 7 x 10-12 s to 5 x 10-8 s, depending upon the site of photosensitizer linking. The excited-state electron transfers are about 103-fold faster than any previously reported photosensitizer-redox protein covalently linked construct. Preliminary conformational analysis using molecular dynamics simulations shows that rates for electron transfer track both the distance and pathways for electron transfer. Two mutants with the fastest charge transfer rates, A23C and K29C, showed a significant role of specific paths for electron transfer. While K29C labeled mutant was expected to have approximately 0.8Å greater donor-acceptor distance, it showed 20-fold faster charge separation rate. Clear evidence for inter-heme electron transfer within the multi-heme protein is not detected within the lifetimes of the charge separated states. These results demonstrate an opportunity to develop multi-heme c-cytochromes for investigation of electron transfer in protein "molecular wires" and to serve as frameworks for metalloprotein designs that support multiple electron transfer redox chemistry.« less

Photoemission of Energetic Hot Electrons Produced via Up-Conversion in Doped Quantum Dots.

PubMed

Dong, Yitong; Parobek, David; Rossi, Daniel; Son, Dong Hee

2016-11-09

The benefits of the hot electrons from semiconductor nanostructures in photocatalysis or photovoltaics result from their higher energy compared to that of the band-edge electrons facilitating the electron-transfer process. The production of high-energy hot electrons usually requires short-wavelength UV or intense multiphoton visible excitation. Here, we show that highly energetic hot electrons capable of above-threshold ionization are produced via exciton-to-hot-carrier up-conversion in Mn-doped quantum dots under weak band gap excitation (∼10 W/cm 2 ) achievable with the concentrated solar radiation. The energy of hot electrons is as high as ∼0.4 eV above the vacuum level, much greater than those observed in other semiconductor or plasmonic metal nanostructures, which are capable of performing energetically and kinetically more-challenging electron transfer. Furthermore, the prospect of generating solvated electron is unique for the energetic hot electrons from up-conversion, which can open a new door for long-range electron transfer beyond short-range interfacial electron transfer.

Programming interfacial energetic offsets and charge transfer in β-Pb 0.33V 2O 5/quantum-dot heterostructures: Tuning valence-band edges to overlap with midgap states

DOE PAGES

Pelcher, Kate E.; Milleville, Christopher C.; Wangoh, Linda; ...

2016-12-06

Here, semiconductor heterostructures for solar energy conversion interface light-harvesting semiconductor nanoparticles with wide-band-gap semiconductors that serve as charge acceptors. In such heterostructures, the kinetics of charge separation depend on the thermodynamic driving force, which is dictated by energetic offsets across the interface. A recently developed promising platform interfaces semiconductor quantum dots (QDs) with ternary vanadium oxides that have characteristic midgap states situated between the valence and conduction bands. In this work, we have prepared CdS/β-Pb 0.33V 2O 5 heterostructures by both linker-assisted assembly and surface precipitation and contrasted these materials with CdSe/β-Pb 0.33V 2O 5 heterostructures prepared by the samemore » methods. Increased valence-band (VB) edge onsets in X-ray photoelectron spectra for CdS/β-Pb 0.33V 2O 5 heterostructures relative to CdSe/β-Pb 0.33V 2O 5 heterostructures suggest a positive shift in the VB edge potential and, therefore, an increased driving force for the photoinduced transfer of holes to the midgap state of β-Pb 0.33V 2O 5. This approach facilitates a ca. 0.40 eV decrease in the thermodynamic barrier for hole injection from the VB edge of QDs suggesting an important design parameter. Transient absorption spectroscopy experiments provide direct evidence of hole transfer from photoexcited CdS QDs to the midgap states of β-Pb 0.33V 2O 5 NWs, along with electron transfer into the conduction band of the β-Pb 0.33V 2O 5 NWs. Hole transfer is substantially faster and occurs at <1-ps time scales, whereas completion of electron transfer requires 5—30 ps depending on the nature of the interface. The differentiated time scales of electron and hole transfer, which are furthermore tunable as a function of the mode of attachment of QDs to NWs, provide a vital design tool for designing architectures for solar energy conversion. More generally, the approach developed here suggests that interfacing semiconductor QDs with transition-metal oxide NWs exhibiting intercalative midgap states yields a versatile platform wherein the thermodynamics and kinetics of charge transfer can be systematically modulated to improve the efficiency of charge separation across interfaces.« less

Programming interfacial energetic offsets and charge transfer in β-Pb 0.33V 2O 5/quantum-dot heterostructures: Tuning valence-band edges to overlap with midgap states

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pelcher, Kate E.; Milleville, Christopher C.; Wangoh, Linda

Here, semiconductor heterostructures for solar energy conversion interface light-harvesting semiconductor nanoparticles with wide-band-gap semiconductors that serve as charge acceptors. In such heterostructures, the kinetics of charge separation depend on the thermodynamic driving force, which is dictated by energetic offsets across the interface. A recently developed promising platform interfaces semiconductor quantum dots (QDs) with ternary vanadium oxides that have characteristic midgap states situated between the valence and conduction bands. In this work, we have prepared CdS/β-Pb 0.33V 2O 5 heterostructures by both linker-assisted assembly and surface precipitation and contrasted these materials with CdSe/β-Pb 0.33V 2O 5 heterostructures prepared by the samemore » methods. Increased valence-band (VB) edge onsets in X-ray photoelectron spectra for CdS/β-Pb 0.33V 2O 5 heterostructures relative to CdSe/β-Pb 0.33V 2O 5 heterostructures suggest a positive shift in the VB edge potential and, therefore, an increased driving force for the photoinduced transfer of holes to the midgap state of β-Pb 0.33V 2O 5. This approach facilitates a ca. 0.40 eV decrease in the thermodynamic barrier for hole injection from the VB edge of QDs suggesting an important design parameter. Transient absorption spectroscopy experiments provide direct evidence of hole transfer from photoexcited CdS QDs to the midgap states of β-Pb 0.33V 2O 5 NWs, along with electron transfer into the conduction band of the β-Pb 0.33V 2O 5 NWs. Hole transfer is substantially faster and occurs at <1-ps time scales, whereas completion of electron transfer requires 5—30 ps depending on the nature of the interface. The differentiated time scales of electron and hole transfer, which are furthermore tunable as a function of the mode of attachment of QDs to NWs, provide a vital design tool for designing architectures for solar energy conversion. More generally, the approach developed here suggests that interfacing semiconductor QDs with transition-metal oxide NWs exhibiting intercalative midgap states yields a versatile platform wherein the thermodynamics and kinetics of charge transfer can be systematically modulated to improve the efficiency of charge separation across interfaces.« less

Quantum Calculations of Electron Tunneling in Respiratory Complex III.

PubMed

Hagras, Muhammad A; Hayashi, Tomoyuki; Stuchebrukhov, Alexei A

2015-11-19

The most detailed and comprehensive to date study of electron transfer reactions in the respiratory complex III of aerobic cells, also known as bc1 complex, is reported. In the framework of the tunneling current theory, electron tunneling rates and atomistic tunneling pathways between different redox centers were investigated for all electron transfer reactions comprising different stages of the proton-motive Q-cycle. The calculations reveal that complex III is a smart nanomachine, which under certain conditions undergoes conformational changes gating electron transfer, or channeling electrons to specific pathways. One-electron tunneling approximation was adopted in the tunneling calculations, which were performed using hybrid Broken-Symmetry (BS) unrestricted DFT/ZINDO levels of theory. The tunneling orbitals were determined using an exact biorthogonalization scheme that uniquely separates pairs of tunneling orbitals with small overlaps out of the remaining Franck-Condon orbitals with significant overlap. Electron transfer rates in different redox pairs show exponential distance dependence, in agreement with the reported experimental data; some reactions involve coupled proton transfer. Proper treatment of a concerted two-electron bifurcated tunneling reaction at the Q(o) site is given.

Electronic properties of doped and defective NiO: A quantum Monte Carlo study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shin, Hyeondeok; Luo, Ye; Ganesh, Panchapakesan

NiO is a canonical Mott (or charge-transfer) insulator and as such is notoriously difficult to describe using density functional theory (DFT) based electronic structure methods. Doped Mott insulators such as NiO are of interest for various applications but rigorous theoretical descriptions are lacking. Here, we use quantum Monte Carlo methods, which very accurately include electron-electron interactions, to examine energetics, charge- and spin-structures of NiO with various point defects, such as vacancies or substitutional doping with potassium. The formation energy of a potassium dopant is significantly lower than for a Ni vacancy, making potassium an attractive monovalent dopant for NiO. Wemore » compare our results with DFT results that include an on-site Hubbard U (DFT+U) to account for correlations and find relatively large discrepancies for defect formation energies as well as for charge and spin redistributions in the presence of point defects. Finally, it is unlikely that single-parameter fixes of DFT may be able to obtain accurate accounts of anything but a single parameter, e.g., band gap; responses that, maybe in addition to the band gap, depend in subtle and complex ways on ground state properties, such as charge and spin densities, are likely to contain quantitative and qualitative errors.« less

Electronic properties of doped and defective NiO: A quantum Monte Carlo study

DOE PAGES

Shin, Hyeondeok; Luo, Ye; Ganesh, Panchapakesan; ...

2017-12-28

NiO is a canonical Mott (or charge-transfer) insulator and as such is notoriously difficult to describe using density functional theory (DFT) based electronic structure methods. Doped Mott insulators such as NiO are of interest for various applications but rigorous theoretical descriptions are lacking. Here, we use quantum Monte Carlo methods, which very accurately include electron-electron interactions, to examine energetics, charge- and spin-structures of NiO with various point defects, such as vacancies or substitutional doping with potassium. The formation energy of a potassium dopant is significantly lower than for a Ni vacancy, making potassium an attractive monovalent dopant for NiO. Wemore » compare our results with DFT results that include an on-site Hubbard U (DFT+U) to account for correlations and find relatively large discrepancies for defect formation energies as well as for charge and spin redistributions in the presence of point defects. Finally, it is unlikely that single-parameter fixes of DFT may be able to obtain accurate accounts of anything but a single parameter, e.g., band gap; responses that, maybe in addition to the band gap, depend in subtle and complex ways on ground state properties, such as charge and spin densities, are likely to contain quantitative and qualitative errors.« less

Two-Centre Convergent Close-Coupling Approach to Ion-Atom Collisions: Current Progress

NASA Astrophysics Data System (ADS)

Kadyrov, Alisher; Abdurakhmanov, Ilkhom; Bailey, Jackson; Bray, Igor

2016-09-01

There are two versions of the convergent close-coupling (CCC) approach to ion-atom collisions: quantum-mechanical (QM-CCC) and semi-classical (SC-CCC). Recently, both implementations have been extended to include electron-transfer channels. The SC-CCC approach has been applied to study the excitation and the electron-capture processes in proton-hydrogen collisions. The integral alignment parameter A20 for polarization of Lyman- α emission and the cross sections for excitation and electron-capture into the lowest excited states have been calculated for a wide range of the proton impact energies. It has been established that for convergence of the results a very wide range of impact parameters (typically, 0-50 a.u.) is required due to extremely long tails of transition probabilities for transitions into the 2 p states at high energies. The QM-CCC approach allowed to obtain an accurate solution of proton-hydrogen scattering problem including all underlying processes, namely, direct scattering and ionisation, and electron capture into bound and continuum states of the projectile. In this presentation we give a general overview of current progress in applications of the two-centre CCC approach to ion-atom and atom-atom collisions. The work is supported by the Australian Research Council.

Electrobioremediation of oil spills.

PubMed

Daghio, Matteo; Aulenta, Federico; Vaiopoulou, Eleni; Franzetti, Andrea; Arends, Jan B A; Sherry, Angela; Suárez-Suárez, Ana; Head, Ian M; Bestetti, Giuseppina; Rabaey, Korneel

2017-05-01

Annually, thousands of oil spills occur across the globe. As a result, petroleum substances and petrochemical compounds are widespread contaminants causing concern due to their toxicity and recalcitrance. Many remediation strategies have been developed using both physicochemical and biological approaches. Biological strategies are most benign, aiming to enhance microbial metabolic activities by supplying limiting inorganic nutrients, electron acceptors or donors, thus stimulating oxidation or reduction of contaminants. A key issue is controlling the supply of electron donors/acceptors. Bioelectrochemical systems (BES) have emerged, in which an electrical current serves as either electron donor or acceptor for oil spill bioremediation. BES are highly controllable and can possibly also serve as biosensors for real time monitoring of the degradation process. Despite being promising, multiple aspects need to be considered to make BES suitable for field applications including system design, electrode materials, operational parameters, mode of action and radius of influence. The microbiological processes, involved in bioelectrochemical contaminant degradation, are currently not fully understood, particularly in relation to electron transfer mechanisms. Especially in sulfate rich environments, the sulfur cycle appears pivotal during hydrocarbon oxidation. This review provides a comprehensive analysis of the research on bioelectrochemical remediation of oil spills and of the key parameters involved in the process. Copyright © 2017 Elsevier Ltd. All rights reserved.

Charge transfer from TiO2 into adsorbed benzene diazonium compounds

NASA Astrophysics Data System (ADS)

Merson, A.; Dittrich, Th.; Zidon, Y.; Rappich, J.; Shapira, Yoram

2004-08-01

Electron transfer from sol-gel-prepared TiO2 into adsorbed benzene diazonium compounds has been investigated using cyclic voltammetry, x-ray photoelectron spectroscopy, contact potential difference, and surface photovoltage spectroscopy. The results show that the potential of maximum electron transfer depends strongly on the dipole moment of the benzene compound. Two reactive surface sites at which electron transfer occurs have been identified.

Direct Observation of Excimer-Mediated Intramolecular Electron Transfer in a Cofacially-Stacked Perylene Bisimide Pair.

PubMed

Sung, Jooyoung; Nowak-Król, Agnieszka; Schlosser, Felix; Fimmel, Benjamin; Kim, Woojae; Kim, Dongho; Würthner, Frank

2016-07-27

We have elucidated excimer-mediated intramolecular electron transfer in cofacially stacked PBIs tethered by two phenylene-butadiynylene loops. The electron transfer between energetically equivalent PBIs is revealed by the simultaneous observation of the PBI radical anion and cation bands in the transient absorption spectra. The fluorescence decay time of the excimer states is in good agreement with the rise time of PBI radical bands in transient absorption spectra suggesting that the electron transfer dynamics proceed via the excimer state. We can conclude that the excimer state effectuates the efficient charge transfer in the cofacially stacked PBI dimer.

Electronic Structure and Transport in Magnetic Multilayers

DOE Office of Scientific and Technical Information (OSTI.GOV)

None

2008-02-18

ORNL assisted Seagate Recording Heads Operations in the development of CIPS pin Valves for application as read sensors in hard disk drives. Personnel at ORNL were W. H. Butler and Xiaoguang Zhang. Dr. Olle Heinonen from Seagate RHO also participated. ORNL provided codes and materials parameters that were used by Seagate to model CIP GMR in their heads. The objectives were to: (1) develop a linearized Boltzmann transport code for describing CIP GMR based on realistic models of the band structure and interfaces in materials in CIP spin valves in disk drive heads; (2) calculate the materials parameters needed asmore » inputs to the Boltzmann code; and (3) transfer the technology to Seagate Recording Heads.« less

Simulation of the Focal Spot of the Accelerator Bremsstrahlung Radiation

NASA Astrophysics Data System (ADS)

Sorokin, V.; Bespalov, V.

2016-06-01

Testing of thick-walled objects by bremsstrahlung radiation (BR) is primarily performed via high-energy quanta. The testing parameters are specified by the focal spot size of the high-energy bremsstrahlung radiation. In determining the focal spot size, the high- energy BR portion cannot be experimentally separated from the low-energy BR to use high- energy quanta only. The patterns of BR focal spot formation have been investigated via statistical modeling of the radiation transfer in the target material. The distributions of BR quanta emitted by the target for different energies and emission angles under normal distribution of the accelerated electrons bombarding the target have been obtained, and the ratio of the distribution parameters has been determined.

Thermodynamic and Kinetic Requirements in Anaerobic Methane Oxidizing Consortia Exclude Hydrogen, Acetate, and Methanol as Possible Electron Shuttles.

PubMed

Sørensen, K.B.; Finster, K.; Ramsing, N.B.

2001-07-01

Anaerobic methane oxidation (AMO) has long remained an enigma in microbial ecology. In the process the net reaction appears to be an oxidation of methane with sulfate as electron acceptor. In order to explain experimental data such as effects of inhibitors and isotopic signals in biomarkers it has been suggested that the process is carried out by a consortium of bacteria using an unknown compound to shuttle electrons between the participants. The overall change in free energy during AMO with sulfate is very small (?22 kJ mol-1) at in situ concentrations of methane and sulfate. In order to share the available free energy between the members of the consortium, the concentration of the intermediate electron shuttle compound becomes crucial. Diffusive flux of a substrate (i.e, the electron shuttle) between bacteria requires a stable concentration gradient where the concentration is higher in the producing organism than in the consuming organism. Since changes in concentrations cause changes in reaction free energies, the diffusive flux of a catabolic product/substrate between bacteria is associated with a net loss of available energy. This restricts maximal inter-bacterial distances in consortia composed of stationary bacteria. A simple theoretical model was used to describe the relationship between inter-bacterial distances and the energy lost due to concentration differences in consortia. Key parameters turned out to be the permissible concentration range of the electron shuttle in the consortium (i.e., the concentration range that allows both participants to gain sufficient energy) and the stoichiometry of the partial reactions. The model was applied to two known consortia degrading ethanol and butyrate and to four hypothetical methane-oxidizing consortia (MOC) based on interspecies transfer of hydrogen, methanol, acetate, or formate, respectively. In the first three MOCs the permissible distances between producers and consumers of the transferred compounds were less than two times prokaryotic cell wall diameters. Consequently, it is not possible that a MOC can be based on inter-species transfer of hydrogen, methanol, or acetate. Formate, on the other hand, is a possible shuttle candidate provided the bacteria are attached to one another. In general the model predicts that members of consortia thriving on low energy such as the MOC must adhere to each other and utilize a compound for the exchange of electrons that has a high permissible concentration range and a high diffusion coefficient and transfers as many electrons as possible per molecule.

12 CFR 1005.6 - Liability of consumer for unauthorized transfers.

Code of Federal Regulations, 2014 CFR

2014-01-01

... transfers. 1005.6 Section 1005.6 Banks and Banking BUREAU OF CONSUMER FINANCIAL PROTECTION ELECTRONIC FUND TRANSFERS (REGULATION E) General § 1005.6 Liability of consumer for unauthorized transfers. (a) Conditions... this section, for an unauthorized electronic fund transfer involving the consumer's account only if the...

12 CFR 1005.6 - Liability of consumer for unauthorized transfers.

Code of Federal Regulations, 2013 CFR

2013-01-01

... transfers. 1005.6 Section 1005.6 Banks and Banking BUREAU OF CONSUMER FINANCIAL PROTECTION ELECTRONIC FUND TRANSFERS (REGULATION E) General § 1005.6 Liability of consumer for unauthorized transfers. (a) Conditions... this section, for an unauthorized electronic fund transfer involving the consumer's account only if the...

Single-Molecule Interfacial Electron Transfer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, H. Peter

This project is focused on the use of single-molecule high spatial and temporal resolved techniques to study molecular dynamics in condensed phase and at interfaces, especially, the complex reaction dynamics associated with electron and energy transfer rate processes. The complexity and inhomogeneity of the interfacial ET dynamics often present a major challenge for a molecular level comprehension of the intrinsically complex systems, which calls for both higher spatial and temporal resolutions at ultimate single-molecule and single-particle sensitivities. Combined single-molecule spectroscopy and electrochemical atomic force microscopy approaches are unique for heterogeneous and complex interfacial electron transfer systems because the static andmore » dynamic inhomogeneities can be identified and characterized by studying one molecule at a specific nanoscale surface site at a time. The goal of our project is to integrate and apply these spectroscopic imaging and topographic scanning techniques to measure the energy flow and electron flow between molecules and substrate surfaces as a function of surface site geometry and molecular structure. We have been primarily focusing on studying interfacial electron transfer under ambient condition and electrolyte solution involving both single crystal and colloidal TiO 2 and related substrates. The resulting molecular level understanding of the fundamental interfacial electron transfer processes will be important for developing efficient light harvesting systems and broadly applicable to problems in fundamental chemistry and physics. We have made significant advancement on deciphering the underlying mechanism of the complex and inhomogeneous interfacial electron transfer dynamics in dyesensitized TiO 2 nanoparticle systems that strongly involves with and regulated by molecule-surface interactions. We have studied interfacial electron transfer on TiO 2 nanoparticle surfaces by using ultrafast single-molecule spectroscopy and electrochemical AFM metal tip scanning microscopy, focusing on understanding the interfacial electron transfer dynamics at specific nanoscale electron transfer sites with high-spatially and temporally resolved topographic-and-spectroscopic characterization at individual molecule basis, characterizing single-molecule rate processes, reaction driving force, and molecule-substrate electronic coupling. One of the most significant characteristics of our new approach is that we are able to interrogate the complex interfacial electron transfer dynamics by actively pin-point energetic manipulation of the surface interaction and electronic couplings, beyond the conventional excitation and observation.« less

Electron phonon coupling in Ni-based binary alloys with application to displacement cascade modeling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Samolyuk, German D.; Stocks, George Malcolm; Stoller, Roger E.

Energy transfer between lattice atoms and electrons is an important channel of energy dissipation during displacement cascade evolution in irradiated materials. On the assumption of small atomic displacements, the intensity of this transfer is controlled by the strength of electron–phonon (el–ph) coupling. The el–ph coupling in concentrated Ni-based alloys was calculated using electronic structure results obtained within the coherent potential approximation. It was found that Ni 0.5Fe 0.5, Ni 0.5Co 0.5 and Ni 0.5Pd 0.5 are ordered ferromagnetically, whereas Ni 0.5Cr 0.5 is nonmagnetic. Since the magnetism in these alloys has a Stoner-type origin, the magnetic ordering is accompanied bymore » a decrease of electronic density of states at the Fermi level, which in turn reduces the el–ph coupling. Thus, the el–ph coupling values for all alloys are approximately 50% smaller in the magnetic state than for the same alloy in a nonmagnetic state. As the temperature increases, the calculated coupling initially increases. After passing the Curie temperature, the coupling decreases. The rate of decrease is controlled by the shape of the density of states above the Fermi level. Introducing a two-temperature model based on these parameters in 10 keV molecular dynamics cascade simulation increases defect production by 10–20% in the alloys under consideration.« less

Electron phonon coupling in Ni-based binary alloys with application to displacement cascade modeling

DOE PAGES

Samolyuk, German D.; Stocks, George Malcolm; Stoller, Roger E.

2016-04-01

Energy transfer between lattice atoms and electrons is an important channel of energy dissipation during displacement cascade evolution in irradiated materials. On the assumption of small atomic displacements, the intensity of this transfer is controlled by the strength of electron–phonon (el–ph) coupling. The el–ph coupling in concentrated Ni-based alloys was calculated using electronic structure results obtained within the coherent potential approximation. It was found that Ni 0.5Fe 0.5, Ni 0.5Co 0.5 and Ni 0.5Pd 0.5 are ordered ferromagnetically, whereas Ni 0.5Cr 0.5 is nonmagnetic. Since the magnetism in these alloys has a Stoner-type origin, the magnetic ordering is accompanied bymore » a decrease of electronic density of states at the Fermi level, which in turn reduces the el–ph coupling. Thus, the el–ph coupling values for all alloys are approximately 50% smaller in the magnetic state than for the same alloy in a nonmagnetic state. As the temperature increases, the calculated coupling initially increases. After passing the Curie temperature, the coupling decreases. The rate of decrease is controlled by the shape of the density of states above the Fermi level. Introducing a two-temperature model based on these parameters in 10 keV molecular dynamics cascade simulation increases defect production by 10–20% in the alloys under consideration.« less

Theoretical study of the hydrogen abstraction of substituted phenols by nitrogen dioxide as a source of HONO.

PubMed

Shenghur, Abraham; Weber, Kevin H; Nguyen, Nhan D; Sontising, Watit; Tao, Fu-Ming

2014-11-20

The mild yet promiscuous reactions of nitrogen dioxide (NO2) and phenolic derivatives to produce nitrous acid (HONO) have been explored with density functional theory calculations. The reaction is found to occur via four distinct pathways with both proton coupled electron transfer (PCET) and hydrogen atom transfer (HAT) mechanisms available. While the parent reaction with phenol may not be significant in the gas phase, electron donating groups in the ortho and para positions facilitate the reduction of nitrogen dioxide by electronically stabilizing the product phenoxy radical. Hydrogen bonding groups in the ortho position may additionally stabilize the nascent resonantly stabilized radical product, thus enhancing the reaction. Catechol (ortho-hydroxy phenol) has a predicted overall free energy change ΔG(0) = -0.8 kcal mol(-1) and electronic activation energy Ea = 7.0 kcal mol(-1). Free amines at the ortho and para positions have ΔG(0) = -3.8 and -1.5 kcal mol(-1); Ea = 2.3 and 2.1 kcal mol(-1), respectively. The results indicate that the hydrogen abstraction reactions of these substituted phenols by NO2 are fast and spontaneous. Hammett constants produce a linear correlation with bond dissociation energy (BDE) demonstrating that the BDE is the main parameter controlling the dark abstraction reaction. The implications for atmospheric chemistry and ground-level nitrous acid production are discussed.

What Hinders Electron Transfer Dissociation (ETD) of DNA Cations?

NASA Astrophysics Data System (ADS)

Hari, Yvonne; Leumann, Christian J.; Schürch, Stefan

2017-12-01

Radical activation methods, such as electron transfer dissociation (ETD), produce structural information complementary to collision-induced dissociation. Herein, electron transfer dissociation of 3-fold protonated DNA hexamers was studied to gain insight into the fragmentation mechanism. The fragmentation patterns of a large set of DNA hexamers confirm cytosine as the primary target of electron transfer. The reported data reveal backbone cleavage by internal electron transfer from the nucleobase to the phosphate linker leading either to a•/ w or d/ z• ion pairs. This reaction pathway contrasts with previous findings on the dissociation processes after electron capture by DNA cations, suggesting multiple, parallel dissociation channels. However, all these channels merely result in partial fragmentation of the precursor ion because the charge-reduced DNA radical cations are quite stable. Two hypotheses are put forward to explain the low dissociation yield of DNA radical cations: it is either attributed to non-covalent interactions between complementary fragments or to the stabilization of the unpaired electron in stacked nucleobases. MS3 experiments suggest that the charge-reduced species is the intact oligonucleotide. Moreover, introducing abasic sites significantly increases the dissociation yield of DNA cations. Consequently, the stabilization of the unpaired electron by π-π-stacking provides an appropriate rationale for the high intensity of DNA radical cations after electron transfer. [Figure not available: see fulltext.

75 FR 33681 - Electronic Fund Transfers

Federal Register 2010, 2011, 2012, 2013, 2014

2010-06-15

... FEDERAL RESERVE SYSTEM 12 CFR Part 205 [Regulation E; Docket No. R-1343] Electronic Fund Transfers June 4, 2010. AGENCY: Board of Governors of the Federal Reserve System. ACTION: Final rule; correction..., published on June 4, 2010 (75 FR 31665) make the following correction: PART 205--ELECTRONIC FUND TRANSFERS...

Quantification of free convection for embarked QFN64 electronic package: An experimental and numerical survey

NASA Astrophysics Data System (ADS)

Baïri, A.

2017-08-01

Embarked Quad Flat Non-lead (QFN) electronic devices are equipped with a significant number of sensors used for flight parameters measurement purposes. Their accuracy directly depends on the package thermal state. Flight safety therefore depends on the reliability of these QFNs, whose junction temperature must remain as low as possible while operating. The QFN64 is favored for these applications. In the operating power range considered here (0.01-0.1W), the study shows that radiative heat transfer is negligible with respect to natural convective exchanges. It is then essential to quantify the convective heat transfer coefficient on its different areas so that the arrangement is properly dimensioned. This is the objective of this work. The device is welded on a PCB which may be inclined with respect to the horizontal plane by an angle ranging from 0° to 90°. Numerical approach results are confirmed by thermal and electrical measurements carried out on prototypes for all power-inclination angle combinations. The correlations here proposed help determine the natural convective heat transfer coefficient in any area of the assembly. This work allowed to thermally characterize and certify a new QFN64 package equipped with sensors designed for aeronautics, currently under industrialization process.

Synthesis, spectroscopic, thermal and antimicrobial investigations of charge-transfer complexes formed from the drug procaine hydrochloride with quinol, picric acid and TCNQ

NASA Astrophysics Data System (ADS)

Adam, Abdel Majid A.

2012-12-01

Intermolecular charge-transfer or proton-transfer complexes between the drug procaine hydrochloride (PC-HCl) as a donor and quinol (QL), picric acid (PA) or 7,7',8,8'-tetracyanoquinodimethane (TCNQ) as a π-acceptor have been synthesized and spectroscopically studied in methanol at room temperature. Based on elemental analyses and photometric titrations, the stoichiometry of the complexes (donor:acceptor molar ratios) was determined to be 1:1 for all three complexes. The formation constant (KCT), molar extinction coefficient (ɛCT) and other spectroscopic data have been determined using the Benesi-Hildebrand method and its modifications. The newly synthesized CT complexes have been characterized via elemental analysis, IR, Raman, 1H NMR, and electronic absorption spectroscopy. The morphological features of these complexes were investigated using scanning electron microscopy (SEM), and the sharp, well-defined Bragg reflections at specific 2θ angles have been identified from the powder X-ray diffraction patterns. Thermogravimetric analyses (TGAs) and kinetic thermodynamic parameters were also used to investigate the thermal stability of the synthesized solid CT complexes. Finally, the CT complexes were screened for their antibacterial and antifungal activities against various bacterial and fungal strains, and only the complex obtained using picric acid exhibited moderate antibacterial activity against all of the tested strains.

Design and engineering of photosynthetic light-harvesting and electron transfer using length, time, and energy scales.

PubMed

Noy, Dror; Moser, Christopher C; Dutton, P Leslie

2006-02-01

Decades of research on the physical processes and chemical reaction-pathways in photosynthetic enzymes have resulted in an extensive database of kinetic information. Recently, this database has been augmented by a variety of high and medium resolution crystal structures of key photosynthetic enzymes that now include the two photosystems (PSI and PSII) of oxygenic photosynthetic organisms. Here, we examine the currently available structural and functional information from an engineer's point of view with the long-term goal of reproducing the key features of natural photosystems in de novo designed and custom-built molecular solar energy conversion devices. We find that the basic physics of the transfer processes, namely, the time constraints imposed by the rates of incoming photon flux and the various decay processes allow for a large degree of tolerance in the engineering parameters. Moreover, we find that the requirements to guarantee energy and electron transfer rates that yield high efficiency in natural photosystems are largely met by control of distance between chromophores and redox cofactors. Thus, for projected de novo designed constructions, the control of spatial organization of cofactor molecules within a dense array is initially given priority. Nevertheless, constructions accommodating dense arrays of different cofactors, some well within 1 nm from each other, still presents a significant challenge for protein design.

A technique for measuring vertically and horizontally polarized microwave brightness temperatures using electronic polarization-basis rotation

NASA Technical Reports Server (NTRS)

Gasiewski, Albin J.

1992-01-01

This technique for electronically rotating the polarization basis of an orthogonal-linear polarization radiometer is based on the measurement of the first three feedhorn Stokes parameters, along with the subsequent transformation of this measured Stokes vector into a rotated coordinate frame. The technique requires an accurate measurement of the cross-correlation between the two orthogonal feedhorn modes, for which an innovative polarized calibration load was developed. The experimental portion of this investigation consisted of a proof of concept demonstration of the technique of electronic polarization basis rotation (EPBR) using a ground based 90-GHz dual orthogonal-linear polarization radiometer. Practical calibration algorithms for ground-, aircraft-, and space-based instruments were identified and tested. The theoretical effort consisted of radiative transfer modeling using the planar-stratified numerical model described in Gasiewski and Staelin (1990).

Volume-energy parameters for heat transfer to supercritical fluids

NASA Technical Reports Server (NTRS)

Kumakawa, A.; Niino, M.; Hendricks, R. C.; Giarratano, P. J.; Arp, V. D.

1986-01-01

Reduced Nusselt numbers of supercritical fluids from different sources were grouped by several volume-energy parameters. A modified bulk expansion parameter was introduced based on a comparative analysis of data scatter. Heat transfer experiments on liquefied methane were conducted under near-critical conditions in order to confirm the usefulness of the parameters. It was experimentally revealed that heat transfer characteristics of near-critical methane are similar to those of hydrogen. It was shown that the modified bulk expansion parameter and the Gibbs-energy parameter grouped the heat transfer data of hydrogen, oxygen and methane including the present data on near-critical methane. It was also indicated that the effects of surface roughness on heat transfer were very important in grouping the data of high Reynolds numbers.

Inner reorganization limiting electron transfer controlled hydrogen bonding: intra- vs. intermolecular effects.

PubMed

Martínez-González, Eduardo; Frontana, Carlos

2014-05-07

In this work, experimental evidence of the influence of the electron transfer kinetics during electron transfer controlled hydrogen bonding between anion radicals of metronidazole and ornidazole, derivatives of 5-nitro-imidazole, and 1,3-diethylurea as the hydrogen bond donor, is presented. Analysis of the variations of voltammetric EpIcvs. log KB[DH], where KB is the binding constant, allowed us to determine the values of the binding constant and also the electron transfer rate k, confirmed by experiments obtained at different scan rates. Electronic structure calculations at the BHandHLYP/6-311++G(2d,2p) level for metronidazole, including the solvent effect by the Cramer/Truhlar model, suggested that the minimum energy conformer is stabilized by intramolecular hydrogen bonding. In this structure, the inner reorganization energy, λi,j, contributes significantly (0.5 eV) to the total reorganization energy of electron transfer, thus leading to a diminishment of the experimental k.

Development of a Simple Electron Transfer and Polarization Model and Its Application to Biological Systems.

PubMed

Diller, David J

2017-01-10

Here we present a new method for point charge calculation which we call Q ET (charges by electron transfer). The intent of this work is to develop a method that can be useful for studying charge transfer in large biological systems. It is based on the intuitive framework of the Q EQ method with the key difference being that the Q ET method tracks all pairwise electron transfers by augmenting the Q EQ pseudoenergy function with a distance dependent cost function for each electron transfer. This approach solves the key limitation of the Q EQ method which is its handling of formally charged groups. First, we parametrize the Q ET method by fitting to electrostatic potentials calculated using ab initio quantum mechanics on over 11,000 small molecules. On an external test set of over 2500 small molecules the Q ET method achieves a mean absolute error of 1.37 kcal/mol/electron when compared to the ab initio electrostatic potentials. Second, we examine the conformational dependence of the charges on over 2700 tripeptides. With the tripeptide data set, we show that the conformational effects account for approximately 0.4 kcal/mol/electron on the electrostatic potentials. Third, we test the Q ET method for its ability to reproduce the effects of polarization and electron transfer on 1000 water clusters. For the water clusters, we show that the Q ET method captures about 50% of the polarization and electron transfer effects. Finally, we examine the effects of electron transfer and polarizability on the electrostatic interaction between p38 and 94 small molecule ligands. When used in conjunction with the Generalized-Born continuum solvent model, polarization and electron transfer with the Q ET model lead to an average change of 17 kcal/mol on the calculated electrostatic component of ΔG.

Phylogenetic analysis of proteins associated in the four major energy metabolism systems: photosynthesis, aerobic respiration, denitrification, and sulfur respiration.

PubMed

Tomiki, Takeshi; Saitou, Naruya

2004-08-01

The four electron transfer energy metabolism systems, photosynthesis, aerobic respiration, denitrification, and sulfur respiration, are thought to be evolutionarily related because of the similarity of electron transfer patterns and the existence of some homologous proteins. How these systems have evolved is elusive. We therefore conducted a comprehensive homology search using PSI-BLAST, and phylogenetic analyses were conducted for the three homologous groups (groups 1-3) based on multiple alignments of domains defined in the Pfam database. There are five electron transfer types important for catalytic reaction in group 1, and many proteins bind molybdenum. Deletions of two domains led to loss of the function of binding molybdenum and ferredoxin, and these deletions seem to be critical for the electron transfer pattern changes in group 1. Two types of electron transfer were found in group 2, and all its member proteins bind siroheme and ferredoxin. Insertion of the pyridine nucleotide disulfide oxidoreductase domain seemed to be the critical point for the electron transfer pattern change in this group. The proteins belonging to group 3 are all flavin enzymes, and they bind flavin adenine dinucleotide (FAD) or flavin mononucleotide (FMN). Types of electron transfer in this group are divergent, but there are two common characteristics. NAD(P)H works as an electron donor or acceptor, and FAD or FMN transfers electrons from/to NAD(P)H. Electron transfer functions might be added to these common characteristics by the addition of functional domains through the evolution of group 3 proteins. Based on the phylogenetic analyses in this study and previous studies, we inferred the phylogeny of the energy metabolism systems as follows: photosynthesis (and possibly aerobic respiration) and the sulfur/nitrogen assimilation system first diverged, then the sulfur/nitrogen dissimilation system was produced from the latter system.

Predicting the Rate Constant of Electron Tunneling Reactions at the CdSe-TiO2 Interface.

PubMed

Hines, Douglas A; Forrest, Ryan P; Corcelli, Steven A; Kamat, Prashant V

2015-06-18

Current interest in quantum dot solar cells (QDSCs) motivates an understanding of the electron transfer dynamics at the quantum dot (QD)-metal oxide (MO) interface. Employing transient absorption spectroscopy, we have monitored the electron transfer rate (ket) at this interface as a function of the bridge molecules that link QDs to TiO2. Using mercaptoacetic acid, 3-mercaptopropionic acid, 8-mercaptooctanoic acid, and 16-mercaptohexadecanoic acid, we observe an exponential attenuation of ket with increasing linker length, and attribute this to the tunneling of the electron through the insulating linker molecule. We model the electron transfer reaction using both rectangular and trapezoidal barrier models that have been discussed in the literature. The one-electron reduction potential (equivalent to the lowest unoccupied molecular orbital) of each molecule as determined by cyclic voltammetry (CV) was used to estimate the effective barrier height presented by each ligand at the CdSe-TiO2 interface. The electron transfer rate (ket) calculated for each CdSe-ligand-TiO2 interface using both models showed the results in agreement with the experimentally determined trend. This demonstrates that electron transfer between CdSe and TiO2 can be viewed as electron tunneling through a layer of linking molecules and provides a useful method for predicting electron transfer rate constants.

Proton-coupled electron transfer versus hydrogen atom transfer: generation of charge-localized diabatic states.

PubMed

Sirjoosingh, Andrew; Hammes-Schiffer, Sharon

2011-03-24

The distinction between proton-coupled electron transfer (PCET) and hydrogen atom transfer (HAT) mechanisms is important for the characterization of many chemical and biological processes. PCET and HAT mechanisms can be differentiated in terms of electronically nonadiabatic and adiabatic proton transfer, respectively. In this paper, quantitative diagnostics to evaluate the degree of electron-proton nonadiabaticity are presented. Moreover, the connection between the degree of electron-proton nonadiabaticity and the physical characteristics distinguishing PCET from HAT, namely, the extent of electronic charge redistribution, is clarified. In addition, a rigorous diabatization scheme for transforming the adiabatic electronic states into charge-localized diabatic states for PCET reactions is presented. These diabatic states are constructed to ensure that the first-order nonadiabatic couplings with respect to the one-dimensional transferring hydrogen coordinate vanish exactly. Application of these approaches to the phenoxyl-phenol and benzyl-toluene systems characterizes the former as PCET and the latter as HAT. The diabatic states generated for the phenoxyl-phenol system possess physically meaningful, localized electronic charge distributions that are relatively invariant along the hydrogen coordinate. These diabatic electronic states can be combined with the associated proton vibrational states to generate the reactant and product electron-proton vibronic states that form the basis of nonadiabatic PCET theories. Furthermore, these vibronic states and the corresponding vibronic couplings may be used to calculate rate constants and kinetic isotope effects of PCET reactions.

49 CFR 225.37 - Optical media transfer and electronic submission.

Code of Federal Regulations, 2012 CFR

2012-10-01

... 49 Transportation 4 2012-10-01 2012-10-01 false Optical media transfer and electronic submission..., AND INVESTIGATIONS § 225.37 Optical media transfer and electronic submission. (a) A railroad has the option of submitting the following reports, updates, and amendments by way of optical media (CD-ROM), or...

49 CFR 225.37 - Optical media transfer and electronic submission.

Code of Federal Regulations, 2013 CFR

2013-10-01

... 49 Transportation 4 2013-10-01 2013-10-01 false Optical media transfer and electronic submission..., AND INVESTIGATIONS § 225.37 Optical media transfer and electronic submission. (a) A railroad has the option of submitting the following reports, updates, and amendments by way of optical media (CD-ROM), or...

49 CFR 225.37 - Optical media transfer and electronic submission.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 49 Transportation 4 2011-10-01 2011-10-01 false Optical media transfer and electronic submission..., AND INVESTIGATIONS § 225.37 Optical media transfer and electronic submission. (a) A railroad has the option of submitting the following reports, updates, and amendments by way of optical media (CD-ROM), or...

49 CFR 225.37 - Optical media transfer and electronic submission.

Code of Federal Regulations, 2014 CFR

2014-10-01

... 49 Transportation 4 2014-10-01 2014-10-01 false Optical media transfer and electronic submission..., AND INVESTIGATIONS § 225.37 Optical media transfer and electronic submission. (a) A railroad has the option of submitting the following reports, updates, and amendments by way of optical media (CD-ROM), or...

76 FR 708 - Electronic Funds Transfer of Depository Taxes; Correction

Federal Register 2010, 2011, 2012, 2013, 2014

2011-01-06

... DEPARTMENT OF THE TREASURY Internal Revenue Service 26 CFR Parts 1, 31, 40, and 301 [TD 9507] RIN 1545-BJ13 Electronic Funds Transfer of Depository Taxes; Correction AGENCY: Internal Revenue Service... Electronic Funds Transfer (EFT). The temporary and final regulations provide rules under which depositors...

76 FR 709 - Electronic Funds Transfer of Depository Taxes; Correction

Federal Register 2010, 2011, 2012, 2013, 2014

2011-01-06

... DEPARTMENT OF THE TREASURY Internal Revenue Service 26 CFR Parts 40 and 301 [TD 9507] RIN 1545-BJ13 Electronic Funds Transfer of Depository Taxes; Correction AGENCY: Internal Revenue Service (IRS...) providing guidance relating to Federal tax deposits (FTDs) by Electronic Funds Transfer (EFT). The temporary...

78 FR 49365 - Electronic Fund Transfers (Regulation E); Correction

Federal Register 2010, 2011, 2012, 2013, 2014

2013-08-14

... BUREAU OF CONSUMER FINANCIAL PROTECTION 12 CFR Part 1005 [Docket No. CFPB-2012-0050] RIN 3170-AA33 Electronic Fund Transfers (Regulation E); Correction AGENCY: Bureau of Consumer Financial Protection. ACTION... 2013 Final Rule, which along with three other final rules \\1\\ implements the Electronic Fund Transfer...

75 FR 52485 - Electronic Funds Transfer of Depository Taxes; Correction

Federal Register 2010, 2011, 2012, 2013, 2014

2010-08-26

... DEPARTMENT OF THE TREASURY Internal Revenue Service 26 CFR Parts 1, 31, 40, and 301 [REG-153340-09] RIN 1545-BJ13 Electronic Funds Transfer of Depository Taxes; Correction AGENCY: Internal Revenue... to Federal tax deposits (FTDs) by Electronic Funds Transfer (EFT). FOR FURTHER INFORMATION CONTACT...

76 FR 67153 - Federal Acquisition Regulation; Submission for OMB Review; Payment by Electronic Fund Transfer

Federal Register 2010, 2011, 2012, 2013, 2014

2011-10-31

...; Submission for OMB Review; Payment by Electronic Fund Transfer AGENCY: Department of Defense (DOD), General... collection requirement concerning payment by electronic fund transfer. A notice was published in the Federal... technological collection techniques or other forms of information technology. DATES: Submit comments on or...

40 CFR Table I-2 to Subpart I - Examples of Fluorinated GHGs and Fluorinated Heat Transfer Fluids Used by the Electronics Industry

Code of Federal Regulations, 2012 CFR

2012-07-01

... Fluorinated Heat Transfer Fluids Used by the Electronics Industry I Table I-2 to Subpart I Protection of... REPORTING Electronics Manufacturing Pt. 98, Subpt. I, Table I-2 Table I-2 to Subpart I—Examples of Fluorinated GHGs and Fluorinated Heat Transfer Fluids Used by the Electronics Industry Product type...

On judgement of electron transfer between two regions divided by the separatrix of confronting divergent magnetic fields applied to an inductively coupled plasma

NASA Astrophysics Data System (ADS)

Sugawara, Hirotake; Yamamoto, Tappei

2016-09-01

In order to quantitatively evaluate the electron confinement effect of the confronting divergent magnetic fields (CDMFs) applied to an inductively coupled plasma, we analyzed the electron transfer between two regions divided by the separatrix of the CDMFs in Ar at 0.67 Pa at 300 K using a Monte Carlo method. A conventional transfer judgement was simply based on the electron passage across the separatrix from the upstream source region to the downstream diffusion region. An issue was an overestimation of the transfer due to temporary stay of electrons in the downstream region. Electrons may pass the downstream region during their gyration even in case they are effectively bound to the upstream region, where their guiding magnetic flux lines run. More than half of the transfers were temporary ones and such seeming transfers were relevantly excluded from the statistics by introducing a newly chosen criterion based on the passage of electron gyrocenters across the separatrix and collisional events in the downstream region. Simulation results showed a tendency that the ratio of the temporary transfers excluded was higher under stronger magnetic fields because of higher cyclotron frequency. Work supported by JSPS Kakenhi Grant Number 16K05626.

The role of defects in Fe(II) – goethite electron transfer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andrade de Notini, Luiza; Latta, Drew; Neumann, Anke

Despite accumulating experimental evidence for Fe(II)-Fe(III) oxide electron transfer, computational chemical calculations suggest that oxidation of sorbed Fe(II) is not energetically feasible unless defects are present. Here we used isotope specific 57Fe Mössbauer spectroscopy to investigate whether Fe(II)-goethite electron transfer is influenced by defects. Specifically, we heated the mineral to try to anneal the goethite surface and ground goethite to try to create defects. We found that heating goethite results in less oxidation of sorbed Fe(II) by goethite. When goethite was re-ground after heating, electron transfer was partially restored. X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) ofmore » heated and ground goethite confirm that heating and grinding alter the surface structure of the goethite. We propose that the heating process annealed the surface and decreased the number of sites where electron transfer could occur. Our experimental findings suggest that surface defects play an important role in Fe(II)-goethite electron transfer as suggested by computational calculations. Our finding that defects influence heterogeneous Fe(II)-goethite electron transfer has important implications for Fe(II) driven recrystallization of Fe oxides, as well as X and Y.« less

Nonadiabatic dynamics of electron transfer in solution: Explicit and implicit solvent treatments that include multiple relaxation time scales

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schwerdtfeger, Christine A.; Soudackov, Alexander V.; Hammes-Schiffer, Sharon, E-mail: shs3@illinois.edu

2014-01-21

The development of efficient theoretical methods for describing electron transfer (ET) reactions in condensed phases is important for a variety of chemical and biological applications. Previously, dynamical dielectric continuum theory was used to derive Langevin equations for a single collective solvent coordinate describing ET in a polar solvent. In this theory, the parameters are directly related to the physical properties of the system and can be determined from experimental data or explicit molecular dynamics simulations. Herein, we combine these Langevin equations with surface hopping nonadiabatic dynamics methods to calculate the rate constants for thermal ET reactions in polar solvents formore » a wide range of electronic couplings and reaction free energies. Comparison of explicit and implicit solvent calculations illustrates that the mapping from explicit to implicit solvent models is valid even for solvents exhibiting complex relaxation behavior with multiple relaxation time scales and a short-time inertial response. The rate constants calculated for implicit solvent models with a single solvent relaxation time scale corresponding to water, acetonitrile, and methanol agree well with analytical theories in the Golden rule and solvent-controlled regimes, as well as in the intermediate regime. The implicit solvent models with two relaxation time scales are in qualitative agreement with the analytical theories but quantitatively overestimate the rate constants compared to these theories. Analysis of these simulations elucidates the importance of multiple relaxation time scales and the inertial component of the solvent response, as well as potential shortcomings of the analytical theories based on single time scale solvent relaxation models. This implicit solvent approach will enable the simulation of a wide range of ET reactions via the stochastic dynamics of a single collective solvent coordinate with parameters that are relevant to experimentally accessible systems.« less

Wireless energizing system for an automated implantable sensor.

PubMed

Swain, Biswaranjan; Nayak, Praveen P; Kar, Durga P; Bhuyan, Satyanarayan; Mishra, Laxmi P

2016-07-01

The wireless drive of an automated implantable electronic sensor has been explored for health monitoring applications. The proposed system comprises of an automated biomedical sensing system which is energized through resonant inductive coupling. The implantable sensor unit is able to monitor the body temperature parameter and sends back the corresponding telemetry data wirelessly to the data recoding unit. It has been observed that the wireless power delivery system is capable of energizing the automated biomedical implantable electronic sensor placed over a distance of 3 cm from the power transmitter with an energy transfer efficiency of 26% at the operating resonant frequency of 562 kHz. This proposed method ensures real-time monitoring of different human body temperatures around the clock. The monitored temperature data have been compared with a calibrated temperature measurement system to ascertain the accuracy of the proposed system. The investigated technique can also be useful for monitoring other body parameters such as blood pressure, bladder pressure, and physiological signals of the patient in vivo using various implantable sensors.

Nonlinear stability of solar type III radio bursts. II - Application to observations near 1 AU

NASA Technical Reports Server (NTRS)

Goldstein, M. L.; Smith, R. A.; Papadopoulos, K.

1979-01-01

A set of rate equations including strong turbulence effects and anomalous resistivity are solved using parameters which model several solar type III bursts. Analysis of these bursts has led to quantitative comparisons between several of the observed phenomena and the theory. Through use of an analytic model for the time evolution of the energetic electron exciter, it is found that the exciter distributions observed at 1 AU are unstable to the excitation of the linear bump-in-tail instability, amplifying Langmuir waves above the threshold for the oscillating two-stream instability (OTSI). The OTSI and the attendant anomalous resistivity produce a rapid spectral transfer of Langmuir waves to short wavelengths, out of resonance with the electron exciter. In addition, the various parameters needed to model the bursts are extrapolated inside 1 AU with similar results. Finally, reabsorption of the Langmuir waves by the beam is shown to be unimportant in all cases, even at 0.1 AU.

Cyclic Square Wave Voltammetry of Surface-Confined Quasireversible Electron Transfer Reactions.

PubMed

Mann, Megan A; Bottomley, Lawrence A

2015-09-01

The theory for cyclic square wave voltammetry of surface-confined quasireversible electrode reactions is presented and experimentally verified. Theoretical voltammograms were calculated following systematic variation of empirical parameters to assess their impact on the shape of the voltammogram. From the trends obtained, diagnostic criteria for this mechanism were deduced. These criteria were experimentally confirmed using two well-established surface-confined analytes. When properly applied, these criteria will enable non-experts in voltammetry to assign the electrode reaction mechanism and accurately measure electrode reaction kinetics.

The role of solitons in charge and energy transfer in 1D molecular chains

NASA Astrophysics Data System (ADS)

Ivić , Zoran

1998-03-01

The idea that polarons and solitons could play the crucial role in the transport processes in biological structures, has been critically reexamined on the basis of the general theory of self-trapping phenomena. The criteria which enable one to determine conditions for the existence and stability of polarons and solitons and to determine their character, in dependence of the values of the basic physical parameters of the system, were formulated. Validity of the so-called Davydov's soliton model was discussed on the basis of these criteria. It was found that the original Davydov's proposal, based upon the idea of the soliton creation due to the single excitation (particle, vibron, etc.) self-trapping, cannot explain the intramolecular energy transfer in α-helix and acetanilide. However, Davydov theory is flexible enough to describe the single electron transfer in some systems (α-helix and acetanilide for example). In the many-particle systems, dressing effect, due to the quantum nature of phonons, may cause the creation of the bound states of the several excitons in the molecular chain. The possibility of creation of the soliton states of this type is discussed for the simple Fröhlich's one-dimensional model. The regions of the system parameter space where different mechanisms dominate the behaviour of such entities are characterized.

A Quantitative Theoretical Framework For Protein-Induced Fluorescence Enhancement-Förster-Type Resonance Energy Transfer (PIFE-FRET).

PubMed

Lerner, Eitan; Ploetz, Evelyn; Hohlbein, Johannes; Cordes, Thorben; Weiss, Shimon

2016-07-07

Single-molecule, protein-induced fluorescence enhancement (PIFE) serves as a molecular ruler at molecular distances inaccessible to other spectroscopic rulers such as Förster-type resonance energy transfer (FRET) or photoinduced electron transfer. In order to provide two simultaneous measurements of two distances on different molecular length scales for the analysis of macromolecular complexes, we and others recently combined measurements of PIFE and FRET (PIFE-FRET) on the single molecule level. PIFE relies on steric hindrance of the fluorophore Cy3, which is covalently attached to a biomolecule of interest, to rotate out of an excited-state trans isomer to the cis isomer through a 90° intermediate. In this work, we provide a theoretical framework that accounts for relevant photophysical and kinetic parameters of PIFE-FRET, show how this framework allows the extraction of the fold-decrease in isomerization mobility from experimental data, and show how these results provide information on changes in the accessible volume of Cy3. The utility of this model is then demonstrated for experimental results on PIFE-FRET measurement of different protein-DNA interactions. The proposed model and extracted parameters could serve as a benchmark to allow quantitative comparison of PIFE effects in different biological systems.

Dynamics and mechanism of UV-damaged DNA repair in indole-thymine dimer adduct: molecular origin of low repair quantum efficiency.

PubMed

Guo, Xunmin; Liu, Zheyun; Song, Qinhua; Wang, Lijuan; Zhong, Dongping

2015-02-26

Many biomimetic chemical systems for repair of UV-damaged DNA showed very low repair efficiency, and the molecular origin is still unknown. Here, we report our systematic characterization of the repair dynamics of a model compound of indole-thymine dimer adduct in three solvents with different polarity. By resolving all elementary steps including three electron-transfer processes and two bond-breaking and bond-formation dynamics with femtosecond resolution, we observed the slow electron injection in 580 ps in water, 4 ns in acetonitrile, and 1.38 ns in dioxane, the fast back electron transfer without repair in 120, 150, and 180 ps, and the slow bond splitting in 550 ps, 1.9 ns, and 4.5 ns, respectively. The dimer bond cleavage is clearly accelerated by the solvent polarity. By comparing with the biological repair machine photolyase with a slow back electron transfer (2.4 ns) and a fast bond cleavage (90 ps), the low repair efficiency in the biomimetic system is mainly determined by the fast back electron transfer and slow bond breakage. We also found that the model system exists in a dynamic heterogeneous C-clamped conformation, leading to a stretched dynamic behavior. In water, we even identified another stacked form with ultrafast cyclic electron transfer, significantly reducing the repair efficiency. Thus, the comparison of the repair efficiency in different solvents is complicated and should be cautious, and only the dynamics by resolving all elementary steps can finally determine the total repair efficiency. Finally, we use the Marcus electron-transfer theory to analyze all electron-transfer reactions and rationalize all observed electron-transfer dynamics.

Proton Form Factor Puzzle and the CEBAF Large Acceptance Spectrometer (CLAS) two-photon exchange experiment

NASA Astrophysics Data System (ADS)

Rimal, Dipak

The electromagnetic form factors are the most fundamental observables that encode information about the internal structure of the nucleon. The electric (GE) and the magnetic ( GM) form factors contain information about the spatial distribution of the charge and magnetization inside the nucleon. A significant discrepancy exists between the Rosenbluth and the polarization transfer measurements of the electromagnetic form factors of the proton. One possible explanation for the discrepancy is the contributions of two-photon exchange (TPE) effects. Theoretical calculations estimating the magnitude of the TPE effect are highly model dependent, and limited experimental evidence for such effects exists. Experimentally, the TPE effect can be measured by comparing the ratio of positron-proton elastic scattering cross section to that of the electron-proton [R = sigma(e +p)/sigma(e+p)]. The ratio R was measured over a wide range of kinematics, utilizing a 5.6 GeV primary electron beam produced by the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson Lab. This dissertation explored dependence of R on kinematic variables such as squared four-momentum transfer (Q2) and the virtual photon polarization parameter (epsilon). A mixed electron-positron beam was produced from the primary electron beam in experimental Hall B. The mixed beam was scattered from a liquid hydrogen (LH2) target. Both the scattered lepton and the recoil proton were detected by the CEBAF Large Acceptance Spectrometer (CLAS). The elastic events were then identified by using elastic scattering kinematics. This work extracted the Q2 dependence of R at high epsilon(epsilon > 0.8) and the $epsilon dependence of R at approx 0.85 GeV2. In these kinematics, our data confirm the validity of the hadronic calculations of the TPE effect by Blunden, Melnitchouk, and Tjon. This hadronic TPE effect, with additional corrections contributed by higher excitations of the intermediate state nucleon, largely reconciles the Rosenbluth and the polarization transfer measurements of the electromagnetic form factors.

Golden rule kinetics of transfer reactions in condensed phase: The microscopic model of electron transfer reactions in disordered solid matrices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Basilevsky, M. V.; Mitina, E. A.; Odinokov, A. V.

The algorithm for a theoretical calculation of transfer reaction rates for light quantum particles (i.e., the electron and H-atom transfers) in non-polar solid matrices is formulated and justified. The mechanism postulated involves a local mode (an either intra- or inter-molecular one) serving as a mediator which accomplishes the energy exchange between the reacting high-frequency quantum mode and the phonon modes belonging to the environment. This approach uses as a background the Fermi golden rule beyond the usually applied spin-boson approximation. The dynamical treatment rests on the one-dimensional version of the standard quantum relaxation equation for the reduced density matrix, whichmore » describes the frequency fluctuation spectrum for the local mode under consideration. The temperature dependence of a reaction rate is controlled by the dimensionless parameter ξ{sub 0}=ℏω{sub 0}/k{sub B}T where ω{sub 0} is the frequency of the local mode and T is the temperature. The realization of the computational scheme is different for the high/intermediate (ξ{sub 0} < 1 − 3) and for low (ξ{sub 0}≫ 1) temperature ranges. For the first (quasi-classical) kinetic regime, the Redfield approximation to the solution of the relaxation equation proved to be sufficient and efficient in practical applications. The study of the essentially quantum-mechanical low-temperature kinetic regime in its asymptotic limit requires the implementation of the exact relaxation equation. The coherent mechanism providing a non-vanishing reaction rate has been revealed when T→ 0. An accurate computational methodology for the cross-over kinetic regime needs a further elaboration. The original model of the hopping mechanism for electronic conduction in photosensitive organic materials is considered, based on the above techniques. The electron transfer (ET) in active centers of such systems proceeds via local intra- and intermolecular modes. The active modes, as a rule, operate beyond the kinetic regimes, which are usually postulated in the existing theories of the ET. Our alternative dynamic ET model for local modes immersed in the continuum harmonic medium is formulated for both classical and quantum regimes, and accounts explicitly for the mode/medium interaction. The kinetics of the energy exchange between the local ET subsystem and the surrounding environment essentially determine the total ET rate. The efficient computer code for rate computations is elaborated on. The computations are available for a wide range of system parameters, such as the temperature, external field, local mode frequency, and characteristics of mode/medium interaction. The relation of the present approach to the Marcus ET theory and to the quantum-statistical reaction rate theory [V. G. Levich and R. R. Dogonadze, Dokl. Akad. Nauk SSSR, Ser. Fiz. Khim. 124, 213 (1959); J. Ulstrup, Charge Transfer in Condensed Media (Springer, Berlin, 1979); M. Bixon and J. Jortner, Adv. Chem. Phys. 106, 35 (1999)] underlying it is discussed and illustrated by the results of computations for practically important target systems.« less

Electron shuttles in biotechnology.

PubMed

Watanabe, Kazuya; Manefield, Mike; Lee, Matthew; Kouzuma, Atsushi

2009-12-01

Electron-shuttling compounds (electron shuttles [ESs], or redox mediators) are essential components in intracellular electron transfer, while microbes also utilize self-produced and naturally present ESs for extracellular electron transfer. These compounds assist in microbial energy metabolism by facilitating electron transfer between microbes, from electron-donating substances to microbes, and/or from microbes to electron-accepting substances. Artificially supplemented ESs can create new routes of electron flow in the microbial energy metabolism, thereby opening up new possibilities for the application of microbes to biotechnology processes. Typical examples of such processes include halogenated-organics bioremediation, azo-dye decolorization, and microbial fuel cells. Herein we suggest that ESs can be applied widely to create new microbial biotechnology processes.

Spectroscopic (FT-IR, FT-Raman and UV-Visible) investigations, NMR chemical shielding anisotropy (CSA) parameters of 2,6-Diamino-4-chloropyrimidine for dye sensitized solar cells using density functional theory.

PubMed

Gladis Anitha, E; Joseph Vedhagiri, S; Parimala, K

2015-02-05

The molecular structure, geometry optimization, vibrational frequencies of organic dye sensitizer 2,6-Diamino-4-chloropyrimidine (DACP) were studied based on Hartree-Fock (HF) and density functional theory (DFT) using B3LYP methods with 6-311++G(d,p) basis set. Ultraviolet-Visible (UV-Vis) spectrum was investigated by time dependent DFT (TD-DFT). Features of the electronic absorption spectrum in the UV-Visible regions were assigned based on TD-DFT calculation. The absorption bands are assigned to transitions. The interfacial electron transfer between semiconductor TiO2 electrode and dye sensitizer DACP is due to an electron injection process from excited dye to the semiconductor's conduction band. The observed and the calculated frequencies are found to be in good agreement. The energies of the frontier molecular orbitals (FMOS) have also been determined. The chemical shielding anisotropic (CSA) parameters are calculated from the NMR analysis, Stability of the molecule arising from hyperconjugative interactions and charge delocalization has been analyzed using natural bond orbital (NBO) analysis. Copyright © 2014 Elsevier B.V. All rights reserved.

Using the plasmon linewidth to calculate the time and efficiency of electron transfer between gold nanorods and graphene.

PubMed

Hoggard, Anneli; Wang, Lin-Yung; Ma, Lulu; Fang, Ying; You, Ge; Olson, Jana; Liu, Zheng; Chang, Wei-Shun; Ajayan, Pulickel M; Link, Stephan

2013-12-23

We present a quantitative analysis of the electron transfer between single gold nanorods and monolayer graphene under no electrical bias. Using single-particle dark-field scattering and photoluminescence spectroscopy to access the homogeneous linewidth, we observe broadening of the surface plasmon resonance for gold nanorods on graphene compared to nanorods on a quartz substrate. Because of the absence of spectral plasmon shifts, dielectric interactions between the gold nanorods and graphene are not important and we instead assign the plasmon damping to charge transfer between plasmon-generated hot electrons and the graphene that acts as an efficient acceptor. Analysis of the plasmon linewidth yields an average electron transfer time of 160 ± 30 fs, which is otherwise difficult to measure directly in the time domain with single-particle sensitivity. In comparison to intrinsic hot electron decay and radiative relaxation, we furthermore calculate from the plasmon linewidth that charge transfer between the gold nanorods and the graphene support occurs with an efficiency of ∼10%. Our results are important for future applications of light harvesting with metal nanoparticle plasmons and efficient hot electron acceptors as well as for understanding hot electron transfer in plasmon-assisted chemical reactions.

Comparison of Regression Analysis and Transfer Function in Estimating the Parameters of Central Pulse Waves from Brachial Pulse Wave.

PubMed

Chai, Rui; Xu, Li-Sheng; Yao, Yang; Hao, Li-Ling; Qi, Lin

2017-01-01

This study analyzed ascending branch slope (A_slope), dicrotic notch height (Hn), diastolic area (Ad) and systolic area (As) diastolic blood pressure (DBP), systolic blood pressure (SBP), pulse pressure (PP), subendocardial viability ratio (SEVR), waveform parameter (k), stroke volume (SV), cardiac output (CO), and peripheral resistance (RS) of central pulse wave invasively and non-invasively measured. Invasively measured parameters were compared with parameters measured from brachial pulse waves by regression model and transfer function model. Accuracy of parameters estimated by regression and transfer function model, was compared too. Findings showed that k value, central pulse wave and brachial pulse wave parameters invasively measured, correlated positively. Regression model parameters including A_slope, DBP, SEVR, and transfer function model parameters had good consistency with parameters invasively measured. They had same effect of consistency. SBP, PP, SV, and CO could be calculated through the regression model, but their accuracies were worse than that of transfer function model.

Mechanism and analyses for extracting photosynthetic electrons using exogenous quinones - what makes a good extraction pathway?

PubMed

Longatte, G; Rappaport, F; Wollman, F-A; Guille-Collignon, M; Lemaître, F

2016-08-04

Plants or algae take many benefits from oxygenic photosynthesis by converting solar energy into chemical energy through the synthesis of carbohydrates from carbon dioxide and water. However, the overall yield of this process is rather low (about 4% of the total energy available from sunlight is converted into chemical energy). This is the principal reason why recently many studies have been devoted to extraction of photosynthetic electrons in order to produce a sustainable electric current. Practically, the electron transfer occurs between the photosynthetic organism and an electrode and can be assisted by an exogenous mediator, mainly a quinone. In this regard, we recently reported on a method involving fluorescence measurements to estimate the ability of different quinones to extract photosynthetic electrons from a mutant of Chlamydomonas reinhardtii. In the present work, we used the same kind of methodology to establish a zone diagram for predicting the most suitable experimental conditions to extract photoelectrons from intact algae (quinone concentration and light intensity) as a function of the purpose of the study. This will provide further insights into the extraction mechanism of photosynthetic electrons using exogenous quinones. Indeed fluorescence measurements allowed us to model the capacity of photosynthetic algae to donate electrons to an exogenous quinone by considering a numerical parameter called "open center ratio" which is related to the Photosystem II acceptor redox state. Then, using it as a proxy for investigating the extraction of photosynthetic electrons by means of an exogenous quinone, 2,6-DCBQ, we suggested an extraction mechanism that was globally found consistent with the experimentally extracted parameters.

Sensitization of ultra-long-range excited-state electron transfer by energy transfer in a polymerized film

PubMed Central

Ito, Akitaka; Stewart, David J.; Fang, Zhen; Brennaman, M. Kyle; Meyer, Thomas J.

2012-01-01

Distance-dependent energy transfer occurs from the Metal-to-Ligand Charge Transfer (MLCT) excited state to an anthracene-acrylate derivative (Acr-An) incorporated into the polymer network of a semirigid poly(ethyleneglycol)dimethacrylate monolith. Following excitation, to Acr-An triplet energy transfer occurs followed by long-range, Acr-3An—Acr-An → Acr-An—Acr-3An, energy migration. With methyl viologen dication (MV2+) added as a trap, Acr-3An + MV2+ → Acr-An+ + MV+ electron transfer results in sensitized electron transfer quenching over a distance of approximately 90 Å. PMID:22949698

40 CFR Table I-2 to Subpart I of... - Examples of Fluorinated GHGs and Fluorinated Heat Transfer Fluids Used by the Electronics Industry

Code of Federal Regulations, 2013 CFR

2013-07-01

... Fluorinated Heat Transfer Fluids Used by the Electronics Industry I Table I-2 to Subpart I of Part 98... GREENHOUSE GAS REPORTING Electronics Manufacturing Pt. 98, Subpt. I, Table I-2 Table I-2 to Subpart I of Part 98—Examples of Fluorinated GHGs and Fluorinated Heat Transfer Fluids Used by the Electronics Industry...

48 CFR 252.232-7011 - Payments in Support of Emergencies and Contingency Operations.

Code of Federal Regulations, 2011 CFR

2011-10-01

.... Internal Revenue Code. (ix) Electronic funds transfer banking information. (A) The Contractor shall include electronic funds transfer banking information on the invoice only if required elsewhere in this contract. (B) If electronic funds transfer banking information is not required to be on the invoice, in order for...

76 FR 52862 - Time for Payment of Certain Excise Taxes, and Quarterly Excise Tax Payments for Small Alcohol...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-08-24

... 40 Cigars and cigarettes, Claims, Electronic fund transfers, Excise taxes, Labeling, Packaging and... that are not required to pay taxes through electronic funds transfer (EFT), this first payment period..., Electronic funds transfers, Excise taxes, Exports, Food additives, Fruit juices, Labeling, Liquors, Packaging...

Co-adsorption of water and oxygen on GaN: Effects of charge transfer and formation of electron depletion layer.

PubMed

Wang, Qi; Puntambekar, Ajinkya; Chakrapani, Vidhya

2017-09-14

Species from ambient atmosphere such as water and oxygen are known to affect electronic and optical properties of GaN, but the underlying mechanism is not clearly known. In this work, we show through careful measurement of electrical resistivity and photoluminescence intensity under various adsorbates that the presence of oxygen or water vapor alone is not sufficient to induce electron transfer to these species. Rather, the presence of both water and oxygen is necessary to induce electron transfer from GaN that leads to the formation of an electron depletion region on the surface. Exposure to acidic gases decreases n-type conductivity due to increased electron transfer from GaN, while basic gases increase n-type conductivity and PL intensity due to reduced charge transfer from GaN. These changes in the electrical and optical properties, as explained using a new electrochemical framework based on the phenomenon of surface transfer doping, suggest that gases interact with the semiconductor surface through electrochemical reactions occurring in an adsorbed water layer present on the surface.

The interaction of trimethylamine dehydrogenase and electron-transferring flavoprotein.

PubMed

Shi, Weiwei; Mersfelder, John; Hille, Russ

2005-05-27

The interaction between the physiological electron transfer partners trimethylamine dehydrogenase (TMADH) and electron-transferring flavoprotein (ETF) from Methylophilus methylotrophus has been examined with particular regard to the proposal that the former protein "imprints" a conformational change on the latter. The results indicate that the absorbance change previously attributed to changes in the environment of the FAD of ETF upon binding to TMADH is instead caused by electron transfer from partially reduced, as-isolated TMADH to ETF. Prior treatment of the as-isolated enzyme with the oxidant ferricenium essentially abolishes the observed spectral change. Further, when the semiquinone form of ETF is used instead of the oxidized form, the mirror image of the spectral change seen with as-isolated TMADH and oxidized ETF is observed. This is attributable to a small amount of electron transfer in the reverse of the physiological direction. Kinetic determination of the dissociation constant and limiting rate constant for electron transfer within the complex of (reduced) TMADH with (oxidized) ETF is reconfirmed and discussed in the context of a recently proposed model for the interaction between the two proteins that involves "structural imprinting" of ETF.

Effect of hypoeutectic boron additions on the grain size and mechanical properties of Ti-6Al-4V manufactured with powder bed electron beam additive manufacturing

DOE PAGES

Mahbooba, Zaynab; West, Harvey; Harrysson, Ola; ...

2016-12-02

In additive manufacturing, microstructural control is feasible via processing parameter alteration. However, the window for parameter variation for certain materials, such as Ti-6Al-4V, is limited, and alternative methods must be employed to customize microstructures. Grain refinement and homogenization in cast titanium alloys has been demonstrated through the addition of hypoeutectic concentrations of boron. This work explores the influence of 0.00 wt.%, 0.25 wt.%, 0.50 wt.%, and 1.0 wt.% boron additions on the microstructure and bulk mechanical properties of Ti-6Al-4V samples fabricated in an Arcam A2 electron beam melting (EBM) system with commercial processing parameters for Ti-6Al-4V. Analyses of EBM fabricatedmore » Ti-6Al-4V + B indicate that the addition of 0.25–1.0 wt.% boron progressively refines the grain structure, and it improves hardness and elastic modulus. Furthermore, despite a reduction in size, the β grain structure remained columnar as a result of directional heat transfer during EBM fabrication.« less

Triphenylamine-based fluorescent NLO phores with ICT characteristics: Solvatochromic and theoretical study

NASA Astrophysics Data System (ADS)

Katariya, Santosh B.; Patil, Dinesh; Rhyman, Lydia; Alswaidan, Ibrahim A.; Ramasami, Ponnadurai; Sekar, Nagaiyan

2017-12-01

The static first and second hyperpolarizability and their related properties were calculated for triphenylamine-based "push-pull" dyes using the B3LYP, CAM-B3LYP and BHHLYP functionals in conjunction with the 6-311+G(d,p) basis set. The electronic coupling for the electron transfer reaction of the dyes were calculated with the generalized Mulliken-Hush method. The results obtained were correlated with the polarizability parameter αCT , first hyperpolarizability parameter βCT, and the solvatochromic descriptor of 〈 γ〉 SD obtained by the solvatochromic method. The dyes studied show a high total first order hyperpolarizability (70-238 times) and second order hyperpolarizability (412-778 times) compared to urea. Among the three functionals, the CAM-B3LYP and BHHLYP functionals show hyperpolarizability values closer to experimental values. Experimental absorption and emission wavelengths measured for all the synthesized dyes are in good agreement with those predicted using the time-dependent density functional theory. The theoretical examination on non-linear optical properties was performed on the key parameters of polarizability and hyperpolarizability. A remarkable increase in non-linear optical response is observed on insertion of benzothiazole unit compared to benzimidazole unit.

Effect of hypoeutectic boron additions on the grain size and mechanical properties of Ti-6Al-4V manufactured with powder bed electron beam additive manufacturing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mahbooba, Zaynab; West, Harvey; Harrysson, Ola

In additive manufacturing, microstructural control is feasible via processing parameter alteration. However, the window for parameter variation for certain materials, such as Ti-6Al-4V, is limited, and alternative methods must be employed to customize microstructures. Grain refinement and homogenization in cast titanium alloys has been demonstrated through the addition of hypoeutectic concentrations of boron. This work explores the influence of 0.00 wt.%, 0.25 wt.%, 0.50 wt.%, and 1.0 wt.% boron additions on the microstructure and bulk mechanical properties of Ti-6Al-4V samples fabricated in an Arcam A2 electron beam melting (EBM) system with commercial processing parameters for Ti-6Al-4V. Analyses of EBM fabricatedmore » Ti-6Al-4V + B indicate that the addition of 0.25–1.0 wt.% boron progressively refines the grain structure, and it improves hardness and elastic modulus. Furthermore, despite a reduction in size, the β grain structure remained columnar as a result of directional heat transfer during EBM fabrication.« less

Optical determination of charge transfer times from indoline dyes to ZnO in solid state dye-sensitized solar cells

NASA Astrophysics Data System (ADS)

Meyenburg, I.; Hofeditz, N.; Ruess, R.; Rudolph, M.; Schlettwein, D.; Heimbrodt, W.

2018-05-01

We studied the electron transfer at the interface of organic-inorganic hybrids consisting of indoline derivatives (D149 and D131) on ZnO substrates using a new optical method. We revealed the electron transfer times from the excited dye, e.g. the excitons formed in the dye aggregates to the ZnO substrate by analyzing the photoluminescence transients of the excitons after femtosecond excitation and applying kinetic model calculations. We reveal the changes of the electron transfer times by applying electrical bias. Pushing the Fermi energy of the ZnO substrate towards the excited dye level the transfer time gets longer and eventually the electron transfer is suppressed. The level alignment between the excited dye state and the ZnO Fermi-level is estimated. The excited state of D131 is about 100 meV higher than the respective state of D149 compared to the ZnO conduction band. This leads to shorter electron transfer times and eventually to higher quantum efficiencies of the solar cells.

Structural, electronic, and thermodynamic properties of curium dioxide: Density functional theory calculations

NASA Astrophysics Data System (ADS)

Hou, Ling; Li, Wei-Dong; Wang, Fangwei; Eriksson, Olle; Wang, Bao-Tian

2017-12-01

We present a systematic investigation of the structural, magnetic, electronic, mechanical, and thermodynamic properties of CmO2 with the local density approximation (LDA)+U and the generalized gradient approximation (GGA)+U approaches. The strong Coulomb repulsion and the spin-orbit coupling (SOC) effects on the lattice structures, electronic density of states, and band gaps are carefully studied, and compared with other A O2 (A =U , Np, Pu, and Am). The ferromagnetic configuration with half-metallic character is predicted to be energetically stable while a charge-transfer semiconductor is predicted for the antiferromagnetic configuration. The elastic constants and phonon spectra show that the fluorite structure is mechanically and dynamically stable. Based on the first-principles phonon density of states, the lattice vibrational energy is calculated using the quasiharmonic approximation. Then, the Gibbs free energy, thermal expansion coefficient, specific heat, and entropy are obtained and compared with experimental data. The mode Grüneisen parameters are presented to analyze the anharmonic properties. The Slack relation is applied to obtain the lattice thermal conductivity in temperature range of 300-1600 K. The phonon group velocities are also calculated to investigate the heat transfer. For all these properties, if available, we compare the results of CmO2 with other A O2 .

Electrochemistry and electrocatalysis of myoglobin immobilized in sulfonated graphene oxide and Nafion films.

PubMed

Chen, Guiying; Sun, Hong; Hou, Shifeng

2016-06-01

In this study, sulfonated graphene oxide (SGO) was synthesized and characterized by Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). It was used to make Mb-SGO-Nafion composite films by coating myoglobin (Mb) on the glassy carbon electrodes (GCE). Positions of the Soret absorption bands suggested that Mb retained its native conformation in the films. Mb-SGO-Nafion film modified electrode showed a pair of well-defined and nearly reversible cyclic voltammetry peaks at around -0.39 V versus saturated calomel electrode (SCE) in pH 7.0 buffers, characteristic of heme Fe(III)/Fe(II) redox couples. Electrochemical parameters such as electron transfer rate constant (ks) and formal potential (E(o')) were estimated by fitting the data of square-wave voltammetry with nonlinear regression analysis. Experimental data demonstrated that the electron transfer between Mb and electrode was greatly facilitated and showed good electrocatalytic properties toward various substrates, such as H2O2 and NaNO2, with significant lowering of reduction overpotential. Copyright © 2016. Published by Elsevier Inc.

Electrocatalytic effect of polyvinyl pyrrolidone capped platinum nanoparticles electrodeposited on platinum electrode for ammonia oxidation

NASA Astrophysics Data System (ADS)

Mayedwa, Noluthando; Matinise, Nolubabalo; Mongwaketsi, Nametso; Maaza, Malik

2018-05-01

The aim of this work was to study structural and kinetic parameters as well as the mechanism of platinum nanoparticles (PtNP) reduced with sodium borohydride (NaBH4) and capped with polyvinyl pyrrolidone (PVP). The nanoparticles were supported on Pt electrode for ammonia oxidation in fuel cell application. X-ray diffraction (XRD) was used to study structural composition and high resolution transmission electron microscopy (HRTEM) was used for morphological study of the nanoalloy. The electrocatalysts were studied in alkaline solution of potassium hydroxide (KOH) by cyclic voltammetry (CV), square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS). CV showed that the ammonia oxidation over potential for PtNP was -431 mV and with exchange current density of 1.726 × 10-4 A. EIS showed that the charge transfer resistance (Rct) of PtNP was the lowest (Rct = 1.943 × 106 Ω) compared to that of bare Pt working electrode (2.0604 × 106 Ω), indicating that the Pt nanoparticles have good conductivity and played an important role in accelerating the transfer of electrons.

A new generation of effective core potentials for correlated calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bennett, Michael Chandler; Melton, Cody A.; Annaberdiyev, Abdulgani

Here, we outline ideas on desired properties for a new generation of effective core potentials (ECPs) that will allow valence-only calculations to reach the full potential offered by recent advances in many-body wave function methods. The key improvements include consistent use of correlated methods throughout ECP constructions and improved transferability as required for an accurate description of molecular systems over a range of geometries. The guiding principle is the isospectrality of all-electron and ECP Hamiltonians for a subset of valence states. We illustrate these concepts on a few first- and second-row atoms (B, C, N, O, S), and we obtainmore » higher accuracy in transferability than previous constructions while using semi-local ECPs with a small number of parameters. In addition, the constructed ECPs enable many-body calculations of valence properties with higher (or same) accuracy than their all-electron counterparts with uncorrelated cores. This implies that the ECPs include also some of the impacts of core-core and core-valence correlations on valence properties. The results open further prospects for ECP improvements and refinements.« less

Infrared spectroscopic study of CaFe0.7Co0.3O3

NASA Astrophysics Data System (ADS)

Zhang, C. X.; Xia, H. L.; Dai, Y. M.; Qiu, Z. Y.; Sui, Q. T.; Long, Y. W.; Qiu, X. G.

2017-08-01

Temperature-dependent infrared spectroscopy has been investigated for CaFe0.7Co0.3O3 which undergoes a ferromagnetic transition at TC≈177 K . It is observed that the spectral weight is transferred from ˜4800 -14 000 cm-1 to ˜0 -4800 cm-1 as the temperature is lowered around TC. Such a large-range spectral weight transfer is attributed to the Hund's interaction. The phonons in CaFe0.7Co0.3O3 show minor asymmetric line shapes, implying relatively weak electron-phonon coupling compared with the parent compound CaFeO3. The optical conductivity also reveals a broad peak structure in the range of ˜700 -1500 cm-1. Fit by the model of single-polaron absorption, the broad peak is interpreted by the excitation of polarons. From the fitting parameters of the polaron peak, we estimate the electron-phonon coupling constant α ˜ 0.4 -0.5 , implying that CaFe0.7Co0.3O3 falls into the weak-coupling regime.

A Transfer Hamiltonian Model for Devices Based on Quantum Dot Arrays

PubMed Central

Illera, S.; Prades, J. D.; Cirera, A.; Cornet, A.

2015-01-01

We present a model of electron transport through a random distribution of interacting quantum dots embedded in a dielectric matrix to simulate realistic devices. The method underlying the model depends only on fundamental parameters of the system and it is based on the Transfer Hamiltonian approach. A set of noncoherent rate equations can be written and the interaction between the quantum dots and between the quantum dots and the electrodes is introduced by transition rates and capacitive couplings. A realistic modelization of the capacitive couplings, the transmission coefficients, the electron/hole tunneling currents, and the density of states of each quantum dot have been taken into account. The effects of the local potential are computed within the self-consistent field regime. While the description of the theoretical framework is kept as general as possible, two specific prototypical devices, an arbitrary array of quantum dots embedded in a matrix insulator and a transistor device based on quantum dots, are used to illustrate the kind of unique insight that numerical simulations based on the theory are able to provide. PMID:25879055

Increasing the productivity of glycopeptides analysis by using higher-energy collision dissociation-accurate mass-product-dependent electron transfer dissociation.

PubMed

Saba, Julian; Dutta, Sucharita; Hemenway, Eric; Viner, Rosa

2012-01-01

Currently, glycans are attracting attention from the scientific community as potential biomarkers or as posttranslational modifications (PTMs) of therapeutic proteins. However, structural characterization of glycoproteins and glycopeptides remains analytically challenging. Here, we report on the implementation of a novel acquisition strategy termed higher-energy collision dissociation-accurate mass-product-dependent electron transfer dissociation (HCD-PD-ETD) on a hybrid linear ion trap-orbitrap mass spectrometer. This acquisition strategy uses the complementary fragmentations of ETD and HCD for glycopeptides analysis in an intelligent fashion. Furthermore, the approach minimizes user input for optimizing instrumental parameters and enables straightforward detection of glycopeptides. ETD spectra are only acquired when glycan oxonium ions from MS/MS HCD are detected. The advantage of this approach is that it streamlines data analysis and improves dynamic range and duty cycle. Here, we present the benefits of HCD-PD-ETD relative to the traditional alternating HCD/ETD for a trainer set containing twelve-protein mixture with two glycoproteins: human serotransferrin, ovalbumin and contaminations of two other: bovine alpha 1 acid glycoprotein (bAGP) and bovine fetuin.

Improper ferroelectric polarization in a perovskite driven by intersite charge transfer and ordering

NASA Astrophysics Data System (ADS)

Chen, Wei-Tin; Wang, Chin-Wei; Wu, Hung-Cheng; Chou, Fang-Cheng; Yang, Hung-Duen; Simonov, Arkadiy; Senn, M. S.

2018-04-01

It is of great interest to design and make materials in which ferroelectric polarization is coupled to other order parameters such as lattice, magnetic, and electronic instabilities. Such materials will be invaluable in next-generation data storage devices. Recently, remarkable progress has been made in understanding improper ferroelectric coupling mechanisms that arise from lattice and magnetic instabilities. However, although theoretically predicted, a compact lattice coupling between electronic and ferroelectric (polar) instabilities has yet to be realized. Here we report detailed crystallographic studies of a perovskite HgAMn3A'Mn4BO12 that is found to exhibit a polar ground state on account of such couplings that arise from charge and orbital ordering on both the A'- and B-sites, which are themselves driven by a highly unusual MnA '-MnB intersite charge transfer. The inherent coupling of polar, charge, orbital, and hence magnetic degrees of freedom make this a system of great fundamental interest, and demonstrating ferroelectric switching in this and a host of recently reported hybrid improper ferroelectrics remains a substantial challenge.

A transfer hamiltonian model for devices based on quantum dot arrays.

PubMed

Illera, S; Prades, J D; Cirera, A; Cornet, A

2015-01-01

We present a model of electron transport through a random distribution of interacting quantum dots embedded in a dielectric matrix to simulate realistic devices. The method underlying the model depends only on fundamental parameters of the system and it is based on the Transfer Hamiltonian approach. A set of noncoherent rate equations can be written and the interaction between the quantum dots and between the quantum dots and the electrodes is introduced by transition rates and capacitive couplings. A realistic modelization of the capacitive couplings, the transmission coefficients, the electron/hole tunneling currents, and the density of states of each quantum dot have been taken into account. The effects of the local potential are computed within the self-consistent field regime. While the description of the theoretical framework is kept as general as possible, two specific prototypical devices, an arbitrary array of quantum dots embedded in a matrix insulator and a transistor device based on quantum dots, are used to illustrate the kind of unique insight that numerical simulations based on the theory are able to provide.

A new generation of effective core potentials for correlated calculations

DOE PAGES

Bennett, Michael Chandler; Melton, Cody A.; Annaberdiyev, Abdulgani; ...

2017-12-12

Here, we outline ideas on desired properties for a new generation of effective core potentials (ECPs) that will allow valence-only calculations to reach the full potential offered by recent advances in many-body wave function methods. The key improvements include consistent use of correlated methods throughout ECP constructions and improved transferability as required for an accurate description of molecular systems over a range of geometries. The guiding principle is the isospectrality of all-electron and ECP Hamiltonians for a subset of valence states. We illustrate these concepts on a few first- and second-row atoms (B, C, N, O, S), and we obtainmore » higher accuracy in transferability than previous constructions while using semi-local ECPs with a small number of parameters. In addition, the constructed ECPs enable many-body calculations of valence properties with higher (or same) accuracy than their all-electron counterparts with uncorrelated cores. This implies that the ECPs include also some of the impacts of core-core and core-valence correlations on valence properties. The results open further prospects for ECP improvements and refinements.« less

Preparation, characteristics, convection and applications of magnetic nanofluids: A review

NASA Astrophysics Data System (ADS)

Kumar, Aditya; Subudhi, Sudhakar

2018-02-01

Magnetic nanofluids (MNfs), the colloidal suspension of ferromagnetic nanomaterial, have been taken into research fascinatingly. After contemplating its distinctive interesting properties and unique eximious features it offers innumerous application not only in heat transfer field but also immensely prevalent in medical, biological, aerospace, electronics and solar sciences. This review paper epitomizes and perusing the research work done on heat transfer application of MNfs and encapsulate it for the future research support. Moreover, numerical and experimental, both the approaches has been included for the insightful analysis of phenomenon to apprehend augmentation in heat transfer by MNfs. This article first underlines the importance of appropriate methods of preparation of MNfs as well as its effects on the thermophysical properties of MNfs. Subsequently, the paper comprehended the descriptive analysis of augmentation of convection heat transfer and the effect of magnetic field on the behavior MNfs. Additionally, the effect of magnetic field intensity has been taken as a pertinent parameter and correlations have been developed for thermal conductivity, viscosity and heat transfer coefficient based on the reviewed data. The paper concluded with the tremendous applications of the MNfs and the futuristic plan to support the potential areas for future research.

Analysis of modes of heat transfer in baking Indian rice pan cake (Dosa,) a breakfast food.

PubMed

Venkateshmurthy, K; Raghavarao, K S M S

2015-08-01

Heat transfer by individual modes is estimated during baking of rice (Oryza sativa) pan cake (Dosa), a traditional food. The mathematical expressions proposed could be used to modify the baking oven for controlling the individual modes of heat transfer to obtain the desired product texture, colour and flavour. Conduction from the rotating hot plate is found to be the most prominent mode of heat transfer and is critical for obtaining the desired product characteristics such as texture and flavour. Temperature profiles along the thickness of Dosa are obtained and compared with those obtained experimentally. Heat transfer parameters such as thermal conductivity and emissivity of Dosa are determined (0.42 W/m K and 0.31, respectively). The effect of material of construction of the hot plate such as alloy steel, teflon coated aluminum, cast iron and stainless steel on product texture was studied and stainless steel was found to give good surface finish to the product, which was confirmed by scanning electron microscope. Sensory evaluation was carried out to evaluate the product acceptability. The thermal efficiency of the baking oven was 51.5%.

In-situ sequential laser transfer and laser reduction of graphene oxide films

NASA Astrophysics Data System (ADS)

Papazoglou, S.; Petridis, C.; Kymakis, E.; Kennou, S.; Raptis, Y. S.; Chatzandroulis, S.; Zergioti, I.

2018-04-01

Achieving high quality transfer of graphene on selected substrates is a priority in device fabrication, especially where drop-on-demand applications are involved. In this work, we report an in-situ, fast, simple, and one step process that resulted in the reduction, transfer, and fabrication of reduced graphene oxide-based humidity sensors, using picosecond laser pulses. By tuning the laser illumination parameters, we managed to implement the sequential printing and reduction of graphene oxide flakes. The overall process lasted only a few seconds compared to a few hours that our group has previously published. DC current measurements, X-Ray Photoelectron Spectroscopy, X-Ray Diffraction, and Raman Spectroscopy were employed in order to assess the efficiency of our approach. To demonstrate the applicability and the potential of the technique, laser printed reduced graphene oxide humidity sensors with a limit of detection of 1700 ppm are presented. The results demonstrated in this work provide a selective, rapid, and low-cost approach for sequential transfer and photochemical reduction of graphene oxide micro-patterns onto various substrates for flexible electronics and sensor applications.

Multiple electron injection dynamics in linearly-linked two dye co-sensitized nanocrystalline metal oxide electrodes for dye-sensitized solar cells.

PubMed

Shen, Qing; Ogomi, Yuhei; Park, Byung-wook; Inoue, Takafumi; Pandey, Shyam S; Miyamoto, Akari; Fujita, Shinsuke; Katayama, Kenji; Toyoda, Taro; Hayase, Shuzi

2012-04-07

Understanding the electron transfer dynamics at the interface between dye sensitizer and semiconductor nanoparticle is very important for both a fundamental study and development of dye-sensitized solar cells (DSCs), which are a potential candidate for next generation solar cells. In this study, we have characterized the ultrafast photoexcited electron dynamics in a newly produced linearly-linked two dye co-sensitized solar cell using both a transient absorption (TA) and an improved transient grating (TG) technique, in which tin(IV) 2,11,20,29-tetra-tert-butyl-2,3-naphthalocyanine (NcSn) and cis-diisothiocyanato-bis(2,2'-bipyridyl-4,4'-dicarboxylato)ruthenium(II) bis(tetrabutylammonium) (N719) are molecularly and linearly linked and are bonded to the surface of a nanocrystalline tin dioxide (SnO(2)) electrode by a metal-O-metal linkage (i.e. SnO(2)-NcSn-N719). By comparing the TA and TG kinetics of NcSn, N719, and hybrid NcSn-N719 molecules adsorbed onto both of the SnO(2) and zirconium dioxide (ZrO(2)) nanocrystalline films, the forward and backward electron transfer dynamics in SnO(2)-NcSn-N719 were clarified. We found that there are two pathways for electron injection from the linearly-linked two dye molecules (NcSn-N719) to SnO(2). The first is a stepwise electron injection, in which photoexcited electrons first transfer from N719 to NcSn with a transfer time of 0.95 ps and then transfer from NcSn to the conduction band (CB) of SnO(2) with two timescales of 1.6 ps and 4.2 ps. The second is direct photoexcited electron transfer from N719 to the CB of SnO(2) with a timescale of 20-30 ps. On the other hand, back electron transfer from SnO(2) to NcSn is on a timescale of about 2 ns, which is about three orders of magnitude slower compared to the forward electron transfer from NcSn to SnO(2). The back electron transfer from NcSn to N719 is on a timescale of about 40 ps, which is about one order slower compared to the forward electron transfer from N719 to NcSn. These results demonstrate that photoexcited electrons can be effectively injected into SnO(2) from both of the N719 and NcSn dyes.

12 CFR 205.9 - Receipts at electronic terminals; periodic statements.

Code of Federal Regulations, 2011 CFR

2011-01-01

... RESERVE SYSTEM ELECTRONIC FUND TRANSFERS (REGULATION E) § 205.9 Receipts at electronic terminals; periodic..., a financial institution shall make a receipt available to a consumer at the time the consumer initiates an electronic fund transfer at an electronic terminal. The receipt shall set forth the following...

12 CFR 205.9 - Receipts at electronic terminals; periodic statements.

Code of Federal Regulations, 2013 CFR

2013-01-01

... RESERVE SYSTEM ELECTRONIC FUND TRANSFERS (REGULATION E) § 205.9 Receipts at electronic terminals; periodic..., a financial institution shall make a receipt available to a consumer at the time the consumer initiates an electronic fund transfer at an electronic terminal. The receipt shall set forth the following...

12 CFR 205.9 - Receipts at electronic terminals; periodic statements.

Code of Federal Regulations, 2014 CFR

2014-01-01

... RESERVE SYSTEM ELECTRONIC FUND TRANSFERS (REGULATION E) § 205.9 Receipts at electronic terminals; periodic..., a financial institution shall make a receipt available to a consumer at the time the consumer initiates an electronic fund transfer at an electronic terminal. The receipt shall set forth the following...

12 CFR 205.9 - Receipts at electronic terminals; periodic statements.

Code of Federal Regulations, 2010 CFR

2010-01-01

... RESERVE SYSTEM ELECTRONIC FUND TRANSFERS (REGULATION E) § 205.9 Receipts at electronic terminals; periodic..., a financial institution shall make a receipt available to a consumer at the time the consumer initiates an electronic fund transfer at an electronic terminal. The receipt shall set forth the following...

12 CFR 205.9 - Receipts at electronic terminals; periodic statements.

Code of Federal Regulations, 2012 CFR

2012-01-01

... RESERVE SYSTEM ELECTRONIC FUND TRANSFERS (REGULATION E) § 205.9 Receipts at electronic terminals; periodic..., a financial institution shall make a receipt available to a consumer at the time the consumer initiates an electronic fund transfer at an electronic terminal. The receipt shall set forth the following...

Ultrafast above-threshold dynamics of the radical anion of a prototypical quinone electron-acceptor.

PubMed

Horke, Daniel A; Li, Quansong; Blancafort, Lluís; Verlet, Jan R R

2013-08-01

Quinones feature prominently as electron acceptors in nature. Their electron-transfer reactions are often highly exergonic, for which Marcus theory predicts reduced electron-transfer rates because of a free-energy barrier that occurs in the inverted region. However, the electron-transfer kinetics that involve quinones can appear barrierless. Here, we consider the intrinsic properties of the para-benzoquinone radical anion, which serves as the prototypical electron-transfer reaction product involving a quinone-based acceptor. Using time-resolved photoelectron spectroscopy and ab initio calculations, we show that excitation at 400 and 480 nm yields excited states that are unbound with respect to electron loss. These excited states are shown to decay on a sub-40 fs timescale through a series of conical intersections with lower-lying excited states, ultimately to form the ground anionic state and avoid autodetachment. From an isolated electron-acceptor perspective, this ultrafast stabilization mechanism accounts for the ability of para-benzoquinone to capture and retain electrons.

Mg line formation in late-type stellar atmospheres. I. The model atom

NASA Astrophysics Data System (ADS)

Osorio, Y.; Barklem, P. S.; Lind, K.; Belyaev, A. K.; Spielfiedel, A.; Guitou, M.; Feautrier, N.

2015-07-01

Context. Magnesium is an element of significant astrophysical importance, often traced in late-type stars using lines of neutral magnesium, which is expected to be subject to departures from local thermodynamic equilibrium (LTE). The importance of Mg , together with the unique range of spectral features in late-type stars probing different parts of the atom, as well as its relative simplicity from an atomic physics point of view, makes it a prime target and test bed for detailed ab initio non-LTE modelling in stellar atmospheres. Previous non-LTE modelling of spectral line formation has, however, been subject to uncertainties due to lack of accurate data for inelastic collisions with electrons and hydrogen atoms. Aims: In this paper we build and test a Mg model atom for spectral line formation in late-type stars with new or recent inelastic collision data and no associated free parameters. We aim to reduce these uncertainties and thereby improve the accuracy of Mg non-LTE modelling in late-type stars. Methods: For the low-lying states of Mg i, electron collision data were calculated using the R-matrix method. Hydrogen collision data, including charge transfer processes, were taken from recent calculations by some of us. Calculations for collisional broadening by neutral hydrogen were also performed where data were missing. These calculations, together with data from the literature, were used to build a model atom. This model was then employed in the context of standard non-LTE modelling in 1D (including average 3D) model atmospheres in a small set of stellar atmosphere models. First, the modelling was tested by comparisons with observed spectra of benchmark stars with well-known parameters. Second, the spectral line behaviour and uncertainties were explored by extensive experiments in which sets of collisional data were changed or removed. Results: The modelled spectra agree well with observed spectra from benchmark stars, showing much better agreement with line profile shapes than with LTE modelling. The line-to-line scatter in the derived abundances shows some improvements compared to LTE (where the cores of strong lines must often be ignored), particularly when coupled with averaged 3D models. The observed Mg emission features at 7 and 12 μm in the spectra of the Sun and Arcturus, which are sensitive to the collision data, are reasonably well reproduced. Charge transfer with H is generally important as a thermalising mechanism in dwarfs, but less so in giants. Excitation due to collisions with H is found to be quite important in both giants and dwarfs. The R-matrix calculations for electron collisions also lead to significant differences compared to when approximate formulas are employed. The modelling predicts non-LTE abundance corrections ΔA(Mg )NLTE-LTE in dwarfs, both solar metallicity and metal-poor, to be very small (of order 0.01 dex), even smaller than found in previous studies. In giants, corrections vary greatly between lines, but can be as large as 0.4 dex. Conclusions: Our results emphasise the need for accurate data of Mg collisions with both electrons and H atoms for precise non-LTE predictions of stellar spectra, but demonstrate that such data can be calculated and that ab initio non-LTE modelling without resort to free parameters is possible. In contrast to Li and Na, where only the introduction of charge transfer processes has led to differences with respect to earlier non-LTE modelling, the more complex case of Mg finds changes due to improvements in the data for collisional excitation by electrons and hydrogen atoms, as well as due to the charge transfer processes. Grids of departure coefficients and abundance corrections for a range of stellar parameters are planned for a forthcoming paper.

Proximity effects across oxide-interfaces of superconductor-insulator-ferromagnet hybrid heterostructure.

PubMed

Prajapat, C L; Singh, Surendra; Bhattacharya, D; Ravikumar, G; Basu, S; Mattauch, S; Zheng, Jian-Guo; Aoki, T; Paul, Amitesh

2018-02-27

A case study of electron tunneling or charge-transfer-driven orbital ordering in superconductor (SC)-ferromagnet (FM) interfaces has been conducted in heteroepitaxial YBa 2 Cu 3 O 7 (YBCO)/La 0.67 Sr 0.33 MnO 3 (LSMO) multilayers interleaved with and without an insulating SrTiO 3 (STO) layer between YBCO and LSMO. X-ray magnetic circular dichroism experiments revealed anti-parallel alignment of Mn magnetic moments and induced Cu magnetic moments in a YBCO/LSMO multilayer. As compared to an isolated LSMO layer, the YBCO/LSMO multilayer displayed a (50%) weaker Mn magnetic signal, which is related to the usual proximity effect. It was a surprise that a similar proximity effect was also observed in a YBCO/STO/LSMO multilayer, however, the Mn signal was reduced by 20%. This reduced magnetic moment of Mn was further verified by depth sensitive polarized neutron reflectivity. Electron energy loss spectroscopy experiment showed the evidence of Ti magnetic polarization at the interfaces of the YBCO/STO/LSMO multilayer. This crossover magnetization is due to a transfer of interface electrons that migrate from Ti (4+)-δ to Mn at the STO/LSMO interface and to Cu 2+ at the STO/YBCO interface, with hybridization via O 2p orbitals. So charge-transfer driven orbital ordering is the mechanism responsible for the observed proximity effect and Mn-Cu anti-parallel coupling in YBCO/STO/LSMO. This work provides an effective pathway in understanding the aspect of long range proximity effect and consequent orbital degeneracy parameter in magnetic coupling.

Photocatalytic Conversion of Nitrobenzene to Aniline through Sequential Proton-Coupled One-Electron Transfers from a Cadmium Sulfide Quantum Dot

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jensen, Stephen C.; Bettis Homan, Stephanie; Weiss, Emily A.

2016-01-28

This paper describes the use of cadmium sulfide quantum dots (CdS QDs) as visible-light photocatalysts for the reduction of nitrobenzene to aniline through six sequential photoinduced, proton-coupled electron transfers. At pH 3.6–4.3, the internal quantum yield of photons-to-reducing electrons is 37.1% over 54 h of illumination, with no apparent decrease in catalyst activity. Monitoring of the QD exciton by transient absorption reveals that, for each step in the catalytic cycle, the sacrificial reductant, 3-mercaptopropionic acid, scavenges the excitonic hole in ~5 ps to form QD•–; electron transfer to nitrobenzene or the intermediates nitrosobenzene and phenylhydroxylamine then occurs on the nanosecondmore » time scale. The rate constants for the single-electron transfer reactions are correlated with the driving forces for the corresponding proton-coupled electron transfers. This result suggests, but does not prove, that electron transfer, not proton transfer, is rate-limiting for these reactions. Nuclear magnetic resonance analysis of the QD–molecule systems shows that the photoproduct aniline, left unprotonated, serves as a poison for the QD catalyst by adsorbing to its surface. Performing the reaction at an acidic pH not only encourages aniline to desorb but also increases the probability of protonated intermediates; the latter effect probably ensures that recruitment of protons is not rate-limiting.« less

a Time-Dependent Many-Electron Approach to Atomic and Molecular Interactions

NASA Astrophysics Data System (ADS)

Runge, Keith

A new methodology is developed for the description of electronic rearrangement in atomic and molecular collisions. Using the eikonal representation of the total wavefunction, time -dependent equations are derived for the electronic densities within the time-dependent Hartree-Fock approximation. An averaged effective potential which ensures time reversal invariance is used to describe the effect of the fast electronic transitions on the slower nuclear motions. Electron translation factors (ETF) are introduced to eliminate spurious asymptotic couplings, and a local ETF is incorporated into a basis of traveling atomic orbitals. A reference density is used to describe local electronic relaxation and to account for the time propagation of fast and slow motions, and is shown to lead to an efficient integration scheme. Expressions for time-dependent electronic populations and polarization parameters are given. Electronic integrals over Gaussians including ETFs are derived to extend electronic state calculations to dynamical phenomena. Results of the method are in good agreement with experimental data for charge transfer integral cross sections over a projectile energy range of three orders of magnitude in the proton-Hydrogen atom system. The more demanding calculations of integral alignment, state-to-state integral cross sections, and differential cross sections are found to agree well with experimental data provided care is taken to include ETFs in the calculation of electronic integrals and to choose the appropriate effective potential. The method is found to be in good agreement with experimental data for the calculation of charge transfer integral cross sections and state-to-state integral cross sections in the one-electron heteronuclear Helium(2+)-Hydrogen atom system and in the two-electron system, Hydrogen atom-Hydrogen atom. Time-dependent electronic populations are seen to oscillate rapidly in the midst of collision event. In particular, multiple exchanges of the electron are seen to occur in the proton-Hydrogen atom system at low collision energies. The concepts and results derived from the approach provide new insight into the dynamics of nuclear screening and electronic rearrangement in atomic collisions.

Quantum state transfer in double-quantum-well devices

NASA Technical Reports Server (NTRS)

Jakumeit, Jurgen; Tutt, Marcel; Pavlidis, Dimitris

1994-01-01

A Monte Carlo simulation of double-quantum-well (DQW) devices is presented in view of analyzing the quantum state transfer (QST) effect. Different structures, based on the AlGaAs/GaAs system, were simulated at 77 and 300 K and optimized in terms of electron transfer and device speed. The analysis revealed the dominant role of the impurity scattering for the QST. Different approaches were used for the optimization of QST devices and basic physical limitations were found in the electron transfer between the QWs. The maximum transfer of electrons from a high to a low mobility well was at best 20%. Negative differential resistance is hampered by the almost linear rather than threshold dependent relation of electron transfer on electric field. By optimizing the doping profile the operation frequency limit could be extended to 260 GHz.

Dioxygen in Polyoxometalate Mediated Reactions.

PubMed

Weinstock, Ira A; Schreiber, Roy E; Neumann, Ronny

2018-03-14

In this review article, we consider the use of molecular oxygen in reactions mediated by polyoxometalates. Polyoxometalates are anionic metal oxide clusters of a variety of structures that are soluble in liquid phases and therefore amenable to homogeneous catalytic transformations. Often, they are active for electron transfer oxidations of a myriad of substrates and upon reduction can be reoxidized by molecular oxygen. For example, the phosphovanadomolybdate, H 5 PV 2 Mo 10 O 40 , can oxidize Pd(0) thereby enabling aerobic reactions catalyzed by Pd and H 5 PV 2 Mo 10 O 40 . In a similar vein, polyoxometalates can stabilize metal nanoparticles, leading to additional transformations. Furthermore, electron transfer oxidation of other substrates such as halides and sulfur-containing compounds is possible. More uniquely, H 5 PV 2 Mo 10 O 40 and its analogues can mediate electron transfer-oxygen transfer reactions where oxygen atoms are transferred from the polyoxometalate to the substrate. This unique property has enabled correspondingly unique transformations involving carbon-carbon, carbon-hydrogen, and carbon-metal bond activation. The pathway for the reoxidation of vanadomolybdates with O 2 appears to be an inner-sphere reaction, but the oxidation of one-electron reduced polyoxotungstates has been shown through intensive research to be an outer-sphere reaction. Beyond electron transfer and electron transfer-oxygen transfer aerobic transformations, there a few examples of apparent dioxygenase activity where both oxygen atoms are donated to a substrate.

Picture of the Week: Hacking the bio-nano interface for better biofuels

Science.gov Websites

) influence electron transfer between the enzyme and the electrode to determine the best placement of enzymes compounds) influence electron transfer between the enzyme and the electrode to determine the best placement studied how three quinones (a class of organic compounds) influence electron transfer between the enzyme

Intramolecular electron-transfer rates in mixed-valence triarylamines: measurement by variable-temperature ESR spectroscopy and comparison with optical data.

PubMed

Lancaster, Kelly; Odom, Susan A; Jones, Simon C; Thayumanavan, S; Marder, Seth R; Brédas, Jean-Luc; Coropceanu, Veaceslav; Barlow, Stephen

2009-02-11

The electron spin resonance spectra of the radical cations of 4,4'-bis[di(4-methoxyphenyl)amino]tolane, E-4,4'-bis[di(4-methoxyphenyl)amino]stilbene, and E,E-1,4-bis{4-[di(4-methoxyphenyl)amino]styryl}benzene in dichloromethane exhibit five lines over a wide temperature range due to equivalent coupling to two 14N nuclei, indicating either delocalization between both nitrogen atoms or rapid intramolecular electron transfer on the electron spin resonance time scale. In contrast, those of the radical cations of 1,4-bis{4-[di(4-methoxyphenyl)amino]phenylethynyl}benzene and E,E-1,4-bis{4-[di(4-n-butoxyphenyl)amino]styryl}-2,5-dicyanobenzene exhibit line shapes that vary strongly with temperature, displaying five lines at room temperature and only three lines at ca. 190 K, indicative of slow electron transfer on the electron spin resonance time scale at low temperatures. The rates of intramolecular electron transfer in the latter compounds were obtained by simulation of the electron spin resonance spectra and display an Arrhenius temperature dependence. The activation barriers obtained from Arrhenius plots are significantly less than anticipated from Hush analyses of the intervalence bands when the diabatic electron-transfer distance, R, is equated to the N[symbol: see text]N distance. Comparison of optical and electron spin resonance data suggests that R is in fact only ca. 40% of the N[symbol: see text]N distance, while the Arrhenius prefactor indicates that the electron transfer falls in the adiabatic regime.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Norris, J.R.; Budil, D.E.; Gast, P.

The orientation of the principal axes of the primary electron donor triplet state measured in single crystals of photosynthetic reaction centers is compared to the x-ray structures of the bacteria Rhodobacter (Rb.) sphaeroides R-26 and Rhodopseudomonas (Rps.) viridis. The primary donor of Rps. viridis is significantly different from that of Rb. sphaeroides. The measured directions of the axes indicate that triplet excitation is almost completely localized on the L-subunit half of the dimer in Rps. viridis but is more symmetrically distributed on the dimeric donor in Rb. sphaeroides R-26. The large reduction of the zero field splitting parameters relative tomore » monomeric bacteriochlorophyll triplet in vitro suggests significant participation of asymmetrical charge transfer electronic configurations in the special pair triplet state of both organisms.« less

Optical diagnosis and theoretical simulation of laser induced lead plasma spectrum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hong Bofu; Chuan Songchen; Bao Yuanman

2012-01-15

Plasmas generated during incipient laser ablation of lead in air were studied using emission spectroscopy and fast photography by an intensified charge coupled device (ICCD) camera. An improved plasma emission model was introduced, invoking one-dimensional radiative transfer, to describe the observed emission spectra, while taking into account Gaussian intensity distribution of the laser used to form plasma. The effects of different parameters to the fitting results are discussed. The plasma temperature got by Saha-Boltzmann plot method and the electron number density got by line broadening method were compared with the fitting results. We also found that the distribution of plasmamore » temperature is more uniform than that of the electron number density in the radial direction.« less

Probing ultrafast changes of spin and charge density profiles with resonant XUV magnetic reflectivity at the free-electron laser FERMI.

PubMed

Gutt, C; Sant, T; Ksenzov, D; Capotondi, F; Pedersoli, E; Raimondi, L; Nikolov, I P; Kiskinova, M; Jaiswal, S; Jakob, G; Kläui, M; Zabel, H; Pietsch, U

2017-09-01

We report the results of resonant magnetic XUV reflectivity experiments performed at the XUV free-electron laser FERMI. Circularly polarized XUV light with the photon energy tuned to the Fe M 2,3 edge is used to measure resonant magnetic reflectivities and the corresponding Q -resolved asymmetry of a Permalloy/Ta/Permalloy trilayer film. The asymmetry exhibits ultrafast changes on 240 fs time scales upon pumping with ultrashort IR laser pulses. Depending on the value of the wavevector transfer Q z , we observe both decreasing and increasing values of the asymmetry parameter, which is attributed to ultrafast changes in the vertical spin and charge density profiles of the trilayer film.

SFG synthesis of general high-order all-pass and all-pole current transfer functions using CFTAs.

PubMed

Tangsrirat, Worapong

2014-01-01

An approach of using the signal flow graph (SFG) technique to synthesize general high-order all-pass and all-pole current transfer functions with current follower transconductance amplifiers (CFTAs) and grounded capacitors has been presented. For general nth-order systems, the realized all-pass structure contains at most n + 1 CFTAs and n grounded capacitors, while the all-pole lowpass circuit requires only n CFTAs and n grounded capacitors. The resulting circuits obtained from the synthesis procedure are resistor-less structures and especially suitable for integration. They also exhibit low-input and high-output impedances and also convenient electronic controllability through the g m-value of the CFTA. Simulation results using real transistor model parameters ALA400 are also included to confirm the theory.

SFG Synthesis of General High-Order All-Pass and All-Pole Current Transfer Functions Using CFTAs

PubMed Central

Tangsrirat, Worapong

2014-01-01

An approach of using the signal flow graph (SFG) technique to synthesize general high-order all-pass and all-pole current transfer functions with current follower transconductance amplifiers (CFTAs) and grounded capacitors has been presented. For general nth-order systems, the realized all-pass structure contains at most n + 1 CFTAs and n grounded capacitors, while the all-pole lowpass circuit requires only n CFTAs and n grounded capacitors. The resulting circuits obtained from the synthesis procedure are resistor-less structures and especially suitable for integration. They also exhibit low-input and high-output impedances and also convenient electronic controllability through the g m-value of the CFTA. Simulation results using real transistor model parameters ALA400 are also included to confirm the theory. PMID:24688375

A summary of the OV1-19 satellite dose, depth dose, and linear energy transfer spectral measurements

NASA Technical Reports Server (NTRS)

Cervini, J. T.

1972-01-01

Measurements of the biophysical and physical parameters in the near earth space environment, specifically, the Inner Van Allen Belt are discussed. This region of space is of great interest to planners of the Skylab and the Space Station programs because of the high energy proton environment, especially during periods of increased solar activity. Many physical measurements of charged particle flux, spectra, and pitch angle distribution have been conducted and are programmed in the space radiation environment. Such predictions are not sufficient to accurately predict the effects of space radiations on critical biological and electronic systems operating in these environments. Some of the difficulties encountered in transferring from physical data to a prediction of the effects of space radiation on operational systems are discussed.

Structure-dependent magnetoresistance and spin-transfer torque in antiferromagnetic Fe |MgO |FeMn |Cu tunnel junctions

NASA Astrophysics Data System (ADS)

Jia, Xingtao; Tang, Huimin; Wang, Shizhuo; Qin, Minghui

2017-02-01

We predict large magnetoresistance (MR) and spin transfer torque (STT) in antiferromagnetic Fe |MgO |FeMn |Cu tunnel junctions based on first-principles scattering theory. MR as large as ˜100 % is found in one junction. Magnetic dynamic simulations show that STT acting on the antiferromagnetic order parameter dominates the spin dynamics, and an electronic bias of order 10-1mV and current density of order 105Acm-2 can switches a junction of three-layer MgO, they are about one order smaller than that in Fe |MgO |Fe junction with the same barrier thickness, respectively. The multiple scattering in the antiferromagnetic region is considered to be responsible for the enhanced spin torque and smaller switching current density.

Role of coherence and delocalization in photo-induced electron transfer at organic interfaces

NASA Astrophysics Data System (ADS)

Abramavicius, V.; Pranculis, V.; Melianas, A.; Inganäs, O.; Gulbinas, V.; Abramavicius, D.

2016-09-01

Photo-induced charge transfer at molecular heterojunctions has gained particular interest due to the development of organic solar cells (OSC) based on blends of electron donating and accepting materials. While charge transfer between donor and acceptor molecules can be described by Marcus theory, additional carrier delocalization and coherent propagation might play the dominant role. Here, we describe ultrafast charge separation at the interface of a conjugated polymer and an aggregate of the fullerene derivative PCBM using the stochastic Schrödinger equation (SSE) and reveal the complex time evolution of electron transfer, mediated by electronic coherence and delocalization. By fitting the model to ultrafast charge separation experiments, we estimate the extent of electron delocalization and establish the transition from coherent electron propagation to incoherent hopping. Our results indicate that even a relatively weak coupling between PCBM molecules is sufficient to facilitate electron delocalization and efficient charge separation at organic interfaces.

Alternative ground states enable pathway switching in biological electron transfer

DOE PAGES

Abriata, Luciano A.; Alvarez-Paggi, Damian; Ledesma, Gabirela N.; ...

2012-10-10

Electron transfer is the simplest chemical reaction and constitutes the basis of a large variety of biological processes, such as photosynthesis and cellular respiration. Nature has evolved specific proteins and cofactors for these functions. The mechanisms optimizing biological electron transfer have been matter of intense debate, such as the role of the protein milieu between donor and acceptor sites. Here we propose a mechanism regulating long-range electron transfer in proteins. Specifically, we report a spectroscopic, electrochemical, and theoretical study on WT and single-mutant CuA redox centers from Thermus thermophilus, which shows that thermal fluctuations may populate two alternative ground-state electronicmore » wave functions optimized for electron entry and exit, respectively, through two different and nearly perpendicular pathways. In conclusion, these findings suggest a unique role for alternative or “invisible” electronic ground states in directional electron transfer. Moreover, it is shown that this energy gap and, therefore, the equilibrium between ground states can be fine-tuned by minor perturbations, suggesting alternative ways through which protein–protein interactions and membrane potential may optimize and regulate electron–proton energy transduction.« less

Ultrafast Electron Transfer Kinetics in the LM Dimer of Bacterial Photosynthetic Reaction Center from Rhodobacter sphaeroides.

PubMed

Sun, Chang; Carey, Anne-Marie; Gao, Bing-Rong; Wraight, Colin A; Woodbury, Neal W; Lin, Su

2016-06-23

It has become increasingly clear that dynamics plays a major role in the function of many protein systems. One system that has proven particularly facile for studying the effects of dynamics on protein-mediated chemistry is the bacterial photosynthetic reaction center from Rhodobacter sphaeroides. Previous experimental and computational analysis have suggested that the dynamics of the protein matrix surrounding the primary quinone acceptor, QA, may be particularly important in electron transfer involving this cofactor. One can substantially increase the flexibility of this region by removing one of the reaction center subunits, the H-subunit. Even with this large change in structure, photoinduced electron transfer to the quinone still takes place. To evaluate the effect of H-subunit removal on electron transfer to QA, we have compared the kinetics of electron transfer and associated spectral evolution for the LM dimer with that of the intact reaction center complex on picosecond to millisecond time scales. The transient absorption spectra associated with all measured electron transfer reactions are similar, with the exception of a broadening in the QX transition and a blue-shift in the QY transition bands of the special pair of bacteriochlorophylls (P) in the LM dimer. The kinetics of the electron transfer reactions not involving quinones are unaffected. There is, however, a 4-fold decrease in the electron transfer rate from the reduced bacteriopheophytin to QA in the LM dimer compared to the intact reaction center and a similar decrease in the recombination rate of the resulting charge-separated state (P(+)QA(-)). These results are consistent with the concept that the removal of the H-subunit results in increased flexibility in the region around the quinone and an associated shift in the reorganization energy associated with charge separation and recombination.

Photoinduced electron transfer in covalent ruthenium-anthraquinone dyads: relative importance of driving-force, solvent polarity, and donor-bridge energy gap.

PubMed

Hankache, Jihane; Wenger, Oliver S

2012-02-28

Four rigid rod-like molecules comprised of a Ru(bpy)(3)(2+) (bpy = 2,2'-bipyridine) photosensitizer, a 9,10-anthraquinone electron acceptor, and a molecular bridge connecting the two redox partners were synthesized and investigated by optical spectroscopic and electrochemical means. An attempt was made to assess the relative importance of driving-force, solvent polarity, and bridge variation on the rates of photoinduced electron transfer in these molecules. Expectedly, introduction of tert-butyl substituents in the bipyridine ligands of the ruthenium complex and a change in solvent from dichloromethane to acetonitrile lead to a significant acceleration of charge transfer rates. In dichloromethane, photoinduced electron transfer is not competitive with the inherent excited-state deactivation processes of the photosensitizer. In acetonitrile, an increase in driving-force by 0.2 eV through attachment of tert-butyl substituents to the bpy ancillary ligands causes an increase in electron transfer rates by an order of magnitude. Replacement of a p-xylene bridge by a p-dimethoxybenzene spacer entails an acceleration of charge transfer rates by a factor of 3.5. In the dyads from this study, the relative order of importance of individual influences on electron transfer rates is therefore as follows: solvent polarity ≥ driving-force > donor-bridge energy gap.

Regio-Selective Intramolecular Hydrogen/Deuterium Exchange in Gas-Phase Electron Transfer Dissociation

NASA Astrophysics Data System (ADS)

Hamuro, Yoshitomo

2017-05-01

Protein backbone amide hydrogen/deuterium exchange mass spectrometry (HDX-MS) typically utilizes enzymatic digestion after the exchange reaction and before MS analysis to improve data resolution. Gas-phase fragmentation of a peptic fragment prior to MS analysis is a promising technique to further increase the resolution. The biggest technical challenge for this method is elimination of intramolecular hydrogen/deuterium exchange (scrambling) in the gas phase. The scrambling obscures the location of deuterium. Jørgensen's group pioneered a method to minimize the scrambling in gas-phase electron capture/transfer dissociation. Despite active investigation, the mechanism of hydrogen scrambling is not well-understood. The difficulty stems from the fact that the degree of hydrogen scrambling depends on instruments, various parameters of mass analysis, and peptide analyzed. In most hydrogen scrambling investigations, the hydrogen scrambling is measured by the percentage of scrambling in a whole molecule. This paper demonstrates that the degree of intramolecular hydrogen/deuterium exchange depends on the nature of exchangeable hydrogen sites. The deuterium on Tyr amide of neurotensin (9-13), Arg-Pro-Tyr-Ile-Leu, migrated significantly faster than that on Ile or Leu amides, indicating the loss of deuterium from the original sites is not mere randomization of hydrogen and deuterium but more site-specific phenomena. This more precise approach may help understand the mechanism of intramolecular hydrogen exchange and provide higher confidence for the parameter optimization to eliminate intramolecular hydrogen/deuterium exchange during gas-phase fragmentation.

Regio-Selective Intramolecular Hydrogen/Deuterium Exchange in Gas-Phase Electron Transfer Dissociation.

PubMed

Hamuro, Yoshitomo

2017-05-01

Protein backbone amide hydrogen/deuterium exchange mass spectrometry (HDX-MS) typically utilizes enzymatic digestion after the exchange reaction and before MS analysis to improve data resolution. Gas-phase fragmentation of a peptic fragment prior to MS analysis is a promising technique to further increase the resolution. The biggest technical challenge for this method is elimination of intramolecular hydrogen/deuterium exchange (scrambling) in the gas phase. The scrambling obscures the location of deuterium. Jørgensen's group pioneered a method to minimize the scrambling in gas-phase electron capture/transfer dissociation. Despite active investigation, the mechanism of hydrogen scrambling is not well-understood. The difficulty stems from the fact that the degree of hydrogen scrambling depends on instruments, various parameters of mass analysis, and peptide analyzed. In most hydrogen scrambling investigations, the hydrogen scrambling is measured by the percentage of scrambling in a whole molecule. This paper demonstrates that the degree of intramolecular hydrogen/deuterium exchange depends on the nature of exchangeable hydrogen sites. The deuterium on Tyr amide of neurotensin (9-13), Arg-Pro-Tyr-Ile-Leu, migrated significantly faster than that on Ile or Leu amides, indicating the loss of deuterium from the original sites is not mere randomization of hydrogen and deuterium but more site-specific phenomena. This more precise approach may help understand the mechanism of intramolecular hydrogen exchange and provide higher confidence for the parameter optimization to eliminate intramolecular hydrogen/deuterium exchange during gas-phase fragmentation. Graphical Abstract ᅟ.

Toxicity prediction of PHDDs and phenols in the light of nucleic acid bases and DNA base pair interaction.

PubMed

Mondal Roy, Sutapa; Roy, Debesh R; Sahoo, Suban K

2015-11-01

The applicability of Density Functional Theory (DFT) based descriptors for the development of quantitative structure-toxicity relationships (QSTR) is assessed for two different series of toxic aromatic compounds, viz., polyhalogenated dibenzo-p-dioxins (PHDDs) and phenols (PHs). A series of 20 compounds each for PHDDs and PHs with their experimental toxicities (IC50 and IGC50) is chosen in the present study to develop DFT based efficient quantum chemical parameters (QCPs) for explaining the toxin potential of the considered compounds. A systematic analysis to find out the electron donation/acceptance nature of these selected compounds with the considered model biosystems, viz., nucleic acid (NA) bases and DNA base pairs, is performed to identify potential QCPs. Accordingly, PHDDs is found to be electron acceptors whereas phenols as donors, during their interaction with biosystems. Two parameter regression model is carried out comprising global charge transfer (ΔN), and local Fukui Function's for nucleophilic attack (fk(+)) for PHDDs and the same for electrophilic attack (fk(-)) in case of PHs. It is heartening to note that our chosen descriptors, viz, charge transfer (ΔN) and Fukui Function (fk(±)) plays a crucial role by explaining more than 90% of the observed toxic behavior (in terms of correlation-coefficient, R) of PHDDs and PHs. The developed QCPs, viz., ΔN and fk(±) can be added as the new descriptors in the QSTR parlance. Copyright © 2015 Elsevier Inc. All rights reserved.

CRADA Payment Options | NCI Technology Transfer Center | TTC

Cancer.gov

NCI TTC CRADA PAYMENT OPTIONS: Electronic Payments by Wire Transfer via Fedwire, Mail a check to the Institute or Center, or Automated Clearing House (ACH)/Electronic Funds Transfer (ETF) payments via Pay.gov (NCI ONLY).

Understanding the Charge Transfer at the Interface of Electron Donors and Acceptors: TTF–TCNQ as an Example

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, Changwon; Atalla, Viktor; Smith, Sean

Charge transfer between an electron donor and an electron acceptor is widely accepted as being independent of their relative configurations if the interaction between them is weak; however, the limit of this concept for an interacting system has not yet been well established. Our study of prototypical electron donor–acceptor molecules, tetrathiafulvalene–tetracyanoquinodimethane, using density functional theory based on an advanced functional, clearly demonstrates that for interacting molecules, their configurational arrangement is as important as their individual electronic properties in the asymptotic limit to determine the charge transfer direction. For the first time, we demonstrate that by changing their relative orientation, onemore » can reverse the charge transfer direction of the pair, causing the molecules to exchange roles as donor and acceptor. In conclusion, our theory has important implications for understanding the interfacial charge-transfer mechanism of hybrid systems and related phenomena.« less

Sulfate-reducing bacteria: Microbiology and physiology

NASA Technical Reports Server (NTRS)

Peck, H. D.

1985-01-01

The sulfate reducing bacteria, the first nonphotosynthetic anaerobic bacteria demonstrated to contain c type cytochromes, perform electron transfer coupled to phosphorylation. A new bioenergetic scheme for the formation of a proton gradient for growth of Desulfovibrio on organic substrates and sulfate involving vectors electron transfer and consistent with the cellular localization of enzymes and electron transfer components was proposed. Hydrogen is produced in the cytoplasm from organic substrates and, as a permease molecule diffuses rapidly across the cytoplasmic membrane, it is oxidized to protons and electrons by the periplasmic hydrogenase. The electrons only are transferred across the cytoplasmic membrane to the cytoplasm where they are used to reduce sulfate to sulfide. The protons are used for transport or to drive a reversible ATPOSE. The net effect is the transfer of protons across the cytoplasmic membrane with the intervention of a proton pump. This type of H2 cycling is relevant to the bioenergetics of other types of anaerobic microorganisms.

Understanding the Charge Transfer at the Interface of Electron Donors and Acceptors: TTF–TCNQ as an Example

DOE PAGES

Park, Changwon; Atalla, Viktor; Smith, Sean; ...

2017-06-16

Charge transfer between an electron donor and an electron acceptor is widely accepted as being independent of their relative configurations if the interaction between them is weak; however, the limit of this concept for an interacting system has not yet been well established. Our study of prototypical electron donor–acceptor molecules, tetrathiafulvalene–tetracyanoquinodimethane, using density functional theory based on an advanced functional, clearly demonstrates that for interacting molecules, their configurational arrangement is as important as their individual electronic properties in the asymptotic limit to determine the charge transfer direction. For the first time, we demonstrate that by changing their relative orientation, onemore » can reverse the charge transfer direction of the pair, causing the molecules to exchange roles as donor and acceptor. In conclusion, our theory has important implications for understanding the interfacial charge-transfer mechanism of hybrid systems and related phenomena.« less

Nanoantioxidant-driven plasmon enhanced proton-coupled electron transfer

NASA Astrophysics Data System (ADS)

Sotiriou, Georgios A.; Blattmann, Christoph O.; Deligiannakis, Yiannis

2015-12-01

Proton-coupled electron transfer (PCET) reactions involve the transfer of a proton and an electron and play an important role in a number of chemical and biological processes. Here, we describe a novel phenomenon, plasmon-enhanced PCET, which is manifested using SiO2-coated Ag nanoparticles functionalized with gallic acid (GA), a natural antioxidant molecule that can perform PCET. These GA-functionalized nanoparticles show enhanced plasmonic response at near-IR wavelengths, due to particle agglomeration caused by the GA molecules. Near-IR laser irradiation induces strong local hot-spots on the SiO2-coated Ag nanoparticles, as evidenced by surface enhanced Raman scattering (SERS). This leads to plasmon energy transfer to the grafted GA molecules that lowers the GA-OH bond dissociation enthalpy by at least 2 kcal mol-1 and therefore facilitates PCET. The nanoparticle-driven plasmon-enhancement of PCET brings together the so far unrelated research domains of nanoplasmonics and electron/proton translocation with significant impact on applications based on interfacial electron/proton transfer.Proton-coupled electron transfer (PCET) reactions involve the transfer of a proton and an electron and play an important role in a number of chemical and biological processes. Here, we describe a novel phenomenon, plasmon-enhanced PCET, which is manifested using SiO2-coated Ag nanoparticles functionalized with gallic acid (GA), a natural antioxidant molecule that can perform PCET. These GA-functionalized nanoparticles show enhanced plasmonic response at near-IR wavelengths, due to particle agglomeration caused by the GA molecules. Near-IR laser irradiation induces strong local hot-spots on the SiO2-coated Ag nanoparticles, as evidenced by surface enhanced Raman scattering (SERS). This leads to plasmon energy transfer to the grafted GA molecules that lowers the GA-OH bond dissociation enthalpy by at least 2 kcal mol-1 and therefore facilitates PCET. The nanoparticle-driven plasmon-enhancement of PCET brings together the so far unrelated research domains of nanoplasmonics and electron/proton translocation with significant impact on applications based on interfacial electron/proton transfer. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr04942c

Electron energy distribution function, effective electron temperature, and dust charge in the temporal afterglow of a plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Denysenko, I. B.; Azarenkov, N. A.; Kersten, H.

2016-05-15

Analytical expressions describing the variation of electron energy distribution function (EEDF) in an afterglow of a plasma are obtained. Especially, the case when the electron energy loss is mainly due to momentum-transfer electron-neutral collisions is considered. The study is carried out for different EEDFs in the steady state, including Maxwellian and Druyvesteyn distributions. The analytical results are not only obtained for the case when the rate for momentum-transfer electron-neutral collisions is independent on electron energy but also for the case when the collisions are a power function of electron energy. Using analytical expressions for the EEDF, the effective electron temperaturemore » and charge of the dust particles, which are assumed to be present in plasma, are calculated for different afterglow durations. An analytical expression for the rate describing collection of electrons by dust particles for the case when the rate for momentum-transfer electron-neutral collisions is independent on electron energy is also derived. The EEDF profile and, as a result, the effective electron temperature and dust charge are sufficiently different in the cases when the rate for momentum-transfer electron-neutral collisions is independent on electron energy and when the rate is a power function of electron energy.« less

Molecular dynamics simulations give insight into the conformational change, complex formation, and electron transfer pathway for cytochrome P450 reductase

PubMed Central

Sündermann, Axel; Oostenbrink, Chris

2013-01-01

Cytochrome P450 reductase (CYPOR) undergoes a large conformational change to allow for an electron transfer to a redox partner to take place. After an internal electron transfer over its cofactors, it opens up to facilitate the interaction and electron transfer with a cytochrome P450. The open conformation appears difficult to crystallize. Therefore, a model of a human CYPOR in the open conformation was constructed to be able to investigate the stability and conformational change of this protein by means of molecular dynamics simulations. Since the role of the protein is to provide electrons to a redox partner, the interactions with cytochrome P450 2D6 (2D6) were investigated and a possible complex structure is suggested. Additionally, electron pathway calculations with a newly written program were performed to investigate which amino acids relay the electrons from the FMN cofactor of CYPOR to the HEME of 2D6. Several possible interacting amino acids in the complex, as well as a possible electron transfer pathway were identified and open the way for further investigation by site directed mutagenesis studies. PMID:23832577

Exciton dispersion in molecular solids

NASA Astrophysics Data System (ADS)

Cudazzo, Pierluigi; Sottile, Francesco; Rubio, Angel; Gatti, Matteo

2015-03-01

The investigation of the exciton dispersion (i.e. the exciton energy dependence as a function of the momentum carried by the electron-hole pair) is a powerful approach to identify the exciton character, ranging from the strongly localised Frenkel to the delocalised Wannier-Mott limiting cases. We illustrate this possibility at the example of four prototypical molecular solids (picene, pentacene, tetracene and coronene) on the basis of the parameter-free solution of the many-body Bethe-Salpeter equation. We discuss the mixing between Frenkel and charge-transfer excitons and the origin of their Davydov splitting in the framework of many-body perturbation theory and establish a link with model approaches based on molecular states. Finally, we show how the interplay between the electronic band dispersion and the exchange electron-hole interaction plays a fundamental role in setting the nature of the exciton. This analysis has a general validity holding also for other systems in which the electron wavefunctions are strongly localized, as in strongly correlated insulators.

Simple glucose reduction route for one-step synthesis of copper nanofluids

NASA Astrophysics Data System (ADS)

Shenoy, U. Sandhya; Shetty, A. Nityananda

2014-01-01

One-step method has been employed in the synthesis of copper nanofluids. Copper nitrate is reduced by glucose in the presence of sodium lauryl sulfate. The synthesized particles are characterized by X-ray diffraction technique for the phase structure; electron diffraction X-ray analysis for chemical composition; transmission electron microscopy and field emission scanning electron microscopy for the morphology; Fourier-transform infrared spectroscopy and ultraviolet-visible spectroscopy for the analysis of ingredients of the solution. Thermal conductivity, sedimentation and rheological measurements have also been carried out. It is found that the reaction parameters have considerable effect on the size of the particle formed and rate of the reaction. The techniques confirm that the synthesized particles are copper. The reported method showed promising increase in the thermal conductivity of the base fluid and is found to be reliable, simple and cost-effective method for preparing heat transfer fluids with higher stability.

Electronic structure, elasticity, bonding features and mechanical behaviour of zinc intermetallics: A DFT study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fatima, Bushra, E-mail: bushrafatima25@gmail.com; Acharya, Nikita; Sanyal, Sankar P.

2016-05-06

The structural stability, electronic structure, elastic and mechanical properties of TiZn and ZrZn intermetallics have been studied using ab-initio full potential linearized augmented plane wave (FP-LAPW) method within generalized gradient approximation for exchange and correlation potentials. The various structural parameters, such as lattice constant (a{sub 0}), bulk modulus (B), and its pressure derivative (B’) are analysed and compared. The investigation of elastic constants affirm that both TiZn and ZrZn are elastically stable in CsCl (B{sub 2} phase) structure. The electronic structures have been analysed quantitatively from the band structure which reveals the metallic nature of these compounds. To better illustratemore » the nature of bonding and charge transfer, we have also studied the Fermi surfaces. The three well known criterion of ductility namely Pugh’s rule, Cauchy’s pressure and Frantsevich rule elucidate the ductile nature of these compounds.« less

Theoretical investigation of the structural, elastic, electronic and optical properties of the ternary indium sulfide layered structures AInS2 (A = K, Rb and Cs)

NASA Astrophysics Data System (ADS)

Bouchenafa, M.; Sidoumou, M.; Halit, M.; Benmakhlouf, A.; Bouhemadou, A.; Maabed, S.; Bentabet, A.; Bin-Omran, S.

2018-02-01

Ab initio calculations were performed to investigate the structural, elastic, electronic and optical properties of the ternary layered systems AInS2 (A = K, Rb and Cs). The calculated structural parameters are in good agreement with the existing experimental data. Analysis of the electronic band structure shows that the three studied materials are direct band-gap semiconductors. Density of states, charge transfers and charge density distribution maps were computed and analyzed. Numerical estimations of the elastic moduli and their related properties for single-crystal and polycrystalline aggregates were predicted. The optical properties were calculated for incident radiation polarized along the [100], [010] and [001] crystallographic directions. The studied materials exhibit a noticeable anisotropic behaviour in the elastic and optical properties, which is expected due to the symmetry and the layered nature of these compounds.

Retuning the Catalytic Bias and Overpotential of a [NiFe]-Hydrogenase via a Single Amino Acid Exchange at the Electron Entry/Exit Site

PubMed Central

2017-01-01

The redox chemistry of the electron entry/exit site in Escherichia coli hydrogenase-1 is shown to play a vital role in tuning biocatalysis. Inspired by nature, we generate a HyaA-R193L variant to disrupt a proposed Arg–His cation−π interaction in the secondary coordination sphere of the outermost, “distal”, iron–sulfur cluster. This rewires the enzyme, enhancing the relative rate of H2 production and the thermodynamic efficiency of H2 oxidation catalysis. On the basis of Fourier transformed alternating current voltammetry measurements, we relate these changes in catalysis to a shift in the distal [Fe4S4]2+/1+ redox potential, a previously experimentally inaccessible parameter. Thus, metalloenzyme chemistry is shown to be tuned by the second coordination sphere of an electron transfer site distant from the catalytic center. PMID:28697596

Electron transfer across a thermal gradient

PubMed Central

Craven, Galen T.

2016-01-01

Charge transfer is a fundamental process that underlies a multitude of phenomena in chemistry and biology. Recent advances in observing and manipulating charge and heat transport at the nanoscale, and recently developed techniques for monitoring temperature at high temporal and spatial resolution, imply the need for considering electron transfer across thermal gradients. Here, a theory is developed for the rate of electron transfer and the associated heat transport between donor–acceptor pairs located at sites of different temperatures. To this end, through application of a generalized multidimensional transition state theory, the traditional Arrhenius picture of activation energy as a single point on a free energy surface is replaced with a bithermal property that is derived from statistical weighting over all configurations where the reactant and product states are equienergetic. The flow of energy associated with the electron transfer process is also examined, leading to relations between the rate of heat exchange among the donor and acceptor sites as functions of the temperature difference and the electronic driving bias. In particular, we find that an open electron transfer channel contributes to enhanced heat transport between sites even when they are in electronic equilibrium. The presented results provide a unified theory for charge transport and the associated heat conduction between sites at different temperatures. PMID:27450086

Ultrafast Electron Transfer across a Nanocapsular Wall: Coumarins as Donors, Viologen as Acceptor, and Octa Acid Capsule as the Mediator.

PubMed

Chuang, Chi-Hung; Porel, Mintu; Choudhury, Rajib; Burda, Clemens; Ramamurthy, V

2018-01-11

Results of our study on ultrafast electron transfer (eT) dynamics from coumarins (coumarin-1, coumarin-480, and coumarin-153) incarcerated within octa acid (OA) capsules as electron donors to methyl viologen dissolved in water as acceptor are presented. Upon photoexcitation, coumarin inside the OA capsule transfers an electron to the acceptor electrostatically attached to the capsule leading to a long-lived radical-ion pair separated by the OA capsular wall. This charge-separated state returns to the neutral ground state via back electron transfer on the nanosecond time scale. This system allows for ultrafast electron transfer processes through a molecular wall from the apolar capsular interior to the highly polar (aqueous) environment on the femtosecond time scale. Employing femtosecond transient absorption spectroscopy, distinct rates of both forward (1-25 ps) and backward eT (700-1200 ps) processes were measured. Further understanding of the energetics is provided using Rehm-Weller analysis for the investigated photoinduced eT reactions. The results provide the rates of the eT across a molecular wall, akin to an isotropic solution, depending on the standard free energy of the reaction. The insights from this work could be utilized in the future design of efficient electron transfer processes across interfaces separating apolar and polar environments.

Numerical Modeling and Optimization of Warm-water Heat Sinks

NASA Astrophysics Data System (ADS)

Hadad, Yaser; Chiarot, Paul

2015-11-01

For cooling in large data-centers and supercomputers, water is increasingly replacing air as the working fluid in heat sinks. Utilizing water provides unique capabilities; for example: higher heat capacity, Prandtl number, and convection heat transfer coefficient. The use of warm, rather than chilled, water has the potential to provide increased energy efficiency. The geometric and operating parameters of the heat sink govern its performance. Numerical modeling is used to examine the influence of geometry and operating conditions on key metrics such as thermal and flow resistance. This model also facilitates studies on cooling of electronic chip hot spots and failure scenarios. We report on the optimal parameters for a warm-water heat sink to achieve maximum cooling performance.

Correlation between energy deposition and molecular damage from Auger electrons: A case study of ultra-low energy (5–18 eV) electron interactions with DNA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rezaee, Mohammad, E-mail: Mohammad.Rezaee@USherbrooke.ca; Hunting, Darel J.; Sanche, Léon

2014-07-15

Purpose: The present study introduces a new method to establish a direct correlation between biologically related physical parameters (i.e., stopping and damaging cross sections, respectively) for an Auger-electron emitting radionuclide decaying within a target molecule (e.g., DNA), so as to evaluate the efficacy of the radionuclide at the molecular level. These parameters can be applied to the dosimetry of Auger electrons and the quantification of their biological effects, which are the main criteria to assess the therapeutic efficacy of Auger-electron emitting radionuclides. Methods: Absorbed dose and stopping cross section for the Auger electrons of 5–18 eV emitted by{sup 125}I withinmore » DNA were determined by developing a nanodosimetric model. The molecular damages induced by these Auger electrons were investigated by measuring damaging cross section, including that for the formation of DNA single- and double-strand breaks. Nanoscale films of pure plasmid DNA were prepared via the freeze-drying technique and subsequently irradiated with low-energy electrons at various fluences. The damaging cross sections were determined by employing a molecular survival model to the measured exposure–response curves for induction of DNA strand breaks. Results: For a single decay of{sup 125}I within DNA, the Auger electrons of 5–18 eV deposit the energies of 12.1 and 9.1 eV within a 4.2-nm{sup 3} volume of a hydrated or dry DNA, which results in the absorbed doses of 270 and 210 kGy, respectively. DNA bases have a major contribution to the deposited energies. Ten-electronvolt and high linear energy transfer 100-eV electrons have a similar cross section for the formation of DNA double-strand break, while 100-eV electrons are twice as efficient as 10 eV in the induction of single-strand break. Conclusions: Ultra-low-energy electrons (<18 eV) substantially contribute to the absorbed dose and to the molecular damage from Auger-electron emitting radionuclides; hence, they should be considered in the dosimetry calculation of such radionuclides. Moreover, absorbed dose is not an appropriate physical parameter for nanodosimetry. Instead, stopping cross section, which describes the probability of energy deposition in a target molecule can be an appropriate nanodosimetric parameter. The stopping cross section is correlated with a damaging cross section (e.g., cross section for the double-strand break formation) to quantify the number of each specific lesion in a target molecule for each nuclear decay of a single Auger-electron emitting radionuclide.« less

Correlation between energy deposition and molecular damage from Auger electrons: A case study of ultra-low energy (5–18 eV) electron interactions with DNA

PubMed Central

Rezaee, Mohammad; Hunting, Darel J.; Sanche, Léon

2015-01-01

Purpose The present study introduces a new method to establish a direct correlation between biologically related physical parameters (i.e., stopping and damaging cross sections, respectively) for an Auger-electron emitting radionuclide decaying within a target molecule (e.g., DNA), so as to evaluate the efficacy of the radionuclide at the molecular level. These parameters can be applied to the dosimetry of Auger electrons and the quantification of their biological effects, which are the main criteria to assess the therapeutic efficacy of Auger-electron emitting radionuclides. Methods Absorbed dose and stopping cross section for the Auger electrons of 5–18 eV emitted by 125I within DNA were determined by developing a nanodosimetric model. The molecular damages induced by these Auger electrons were investigated by measuring damaging cross section, including that for the formation of DNA single- and double-strand breaks. Nanoscale films of pure plasmid DNA were prepared via the freeze-drying technique and subsequently irradiated with low-energy electrons at various fluences. The damaging cross sections were determined by employing a molecular survival model to the measured exposure–response curves for induction of DNA strand breaks. Results For a single decay of 125I within DNA, the Auger electrons of 5–18 eV deposit the energies of 12.1 and 9.1 eV within a 4.2-nm3 volume of a hydrated or dry DNA, which results in the absorbed doses of 270 and 210 kGy, respectively. DNA bases have a major contribution to the deposited energies. Ten-electronvolt and high linear energy transfer 100-eV electrons have a similar cross section for the formation of DNA double-strand break, while 100-eV electrons are twice as efficient as 10 eV in the induction of single-strand break. Conclusions Ultra-low-energy electrons (<18 eV) substantially contribute to the absorbed dose and to the molecular damage from Auger-electron emitting radionuclides; hence, they should be considered in the dosimetry calculation of such radionuclides. Moreover, absorbed dose is not an appropriate physical parameter for nanodosimetry. Instead, stopping cross section, which describes the probability of energy deposition in a target molecule can be an appropriate nanodosimetric parameter. The stopping cross section is correlated with a damaging cross section (e.g., cross section for the double-strand break formation) to quantify the number of each specific lesion in a target molecule for each nuclear decay of a single Auger-electron emitting radionuclide. PMID:24989405

Electronic Transfer of School Records.

ERIC Educational Resources Information Center

Yeagley, Raymond

2001-01-01

Describes the electronic transfer of student records, notably the use of a Web-server named CHARLOTTE sponsored by the National Forum on Education Statistics and an Electronic Data Exchange system named SPEEDE/ExPRESS. (PKP)

Application of lab derived kinetic biodegradation parameters at the field scale

NASA Astrophysics Data System (ADS)

Schirmer, M.; Barker, J. F.; Butler, B. J.; Frind, E. O.

2003-04-01

Estimating the intrinsic remediation potential of an aquifer typically requires the accurate assessment of the biodegradation kinetics, the level of available electron acceptors and the flow field. Zero- and first-order degradation rates derived at the laboratory scale generally overpredict the rate of biodegradation when applied to the field scale, because limited electron acceptor availability and microbial growth are typically not considered. On the other hand, field estimated zero- and first-order rates are often not suitable to forecast plume development because they may be an oversimplification of the processes at the field scale and ignore several key processes, phenomena and characteristics of the aquifer. This study uses the numerical model BIO3D to link the laboratory and field scale by applying laboratory derived Monod kinetic degradation parameters to simulate a dissolved gasoline field experiment at Canadian Forces Base (CFB) Borden. All additional input parameters were derived from laboratory and field measurements or taken from the literature. The simulated results match the experimental results reasonably well without having to calibrate the model. An extensive sensitivity analysis was performed to estimate the influence of the most uncertain input parameters and to define the key controlling factors at the field scale. It is shown that the most uncertain input parameters have only a minor influence on the simulation results. Furthermore it is shown that the flow field, the amount of electron acceptor (oxygen) available and the Monod kinetic parameters have a significant influence on the simulated results. Under the field conditions modelled and the assumptions made for the simulations, it can be concluded that laboratory derived Monod kinetic parameters can adequately describe field scale degradation processes, if all controlling factors are incorporated in the field scale modelling that are not necessarily observed at the lab scale. In this way, there are no scale relationships to be found that link the laboratory and the field scale, accurately incorporating the additional processes, phenomena and characteristics, such as a) advective and dispersive transport of one or more contaminants, b) advective and dispersive transport and availability of electron acceptors, c) mass transfer limitations and d) spatial heterogeneities, at the larger scale and applying well defined lab scale parameters should accurately describe field scale processes.

Production of vibrationally excited N 2 by electron impact

NASA Astrophysics Data System (ADS)

Campbell, L.; Brunger, M. J.; Cartwright, D. C.; Teubner, P. J. O.

2004-08-01

Energy transfer from electrons to neutral gases and ions is one of the dominant electron cooling processes in the ionosphere, and the role of vibrationally excited N 2 in this is particularly significant. We report here the results from a new calculation of electron energy transfer rates ( Q) for vibrational excitation of N 2, as a function of the electron temperature Te. The present study was motivated by the development of a new cross-section compilation for vibrational excitation processes in N 2 which supercedes those used in the earlier calculations of the electron energy transfer rates. We show that the energy dependence and magnitude of these cross sections, particularly in the region of the well-known 2Π g resonance in N 2, significantly affect the calculated values of Q. A detailed comparison between the current and previous calculated electron energy transfer rates is made and coefficients are provided so that these rates for transitions from level 0 to levels 1-10 can be calculated for electron temperatures less than 6000 K.

Photogeneration of Charge Carriers in Bilayer Assemblies of Conjugated Rigid-Rod Polymers

DTIC Science & Technology

1994-07-08

photoinduced electron transfer and exciplex formation at the bilayer interface. Thus photocarrier generation on photoexcitation of the conjugated rigid...rod polymers in the bilayer occurs by photoinduced electron transfer, forming intermolecular exciplexes which dissociate efficiently in electric field...photogeneration, conjugated rigid-rod polymers, is. MACI COD bilayer assemblies, electron transfer, exciplexes . 11. SEOJUTY CLASUICA 10. 51(11MIE CLASSIMIAVION

Telematics and satellites. Part 1: Information systems

NASA Astrophysics Data System (ADS)

Burke, W. R.

1980-06-01

Telematic systems are identified and described. The applications are examined emphasizing the role played by satellite links. The discussion includes file transfer, examples of distributed processor systems, terminal communication, information retrieval systems, office information systems, electronic preparation and publishing of information, electronic systems for transfer of funds, electronic mail systems, record file transfer characteristics, intra-enterprise networks, and inter-enterprise networks.

Is back-electron transfer process in Betaine-30 coherent?

NASA Astrophysics Data System (ADS)

Rafiq, Shahnawaz; Scholes, Gregory D.

2017-09-01

The possible role of coherent vibrational motion in ultrafast photo-induced electron transfer remains unclear despite considerable experimental and theoretical advances. We revisited this problem by tracking the back-electron transfer (bET) process in Betaine-30 with broadband pump-probe spectroscopy. Dephasing time constant of certain high-frequency vibrations as a function of solvent shows a trend similar to the ET rates. In the purview of Bixon-Jortner model, high-frequency quantum vibrations bridge the reactant-product energy gap by providing activationless vibronic channels. Such interaction reduces the effective coupling significantly and thereby the coherence effects are eliminated due to energy gap fluctuations, making the back-electron transfer incoherent.

Exciton Scattering approach for conjugated macromolecules: from electronic spectra to electron-phonon coupling

NASA Astrophysics Data System (ADS)

Tretiak, Sergei

2014-03-01

The exciton scattering (ES) technique is a multiscale approach developed for efficient calculations of excited-state electronic structure and optical spectra in low-dimensional conjugated macromolecules. Within the ES method, the electronic excitations in the molecular structure are attributed to standing waves representing quantum quasi-particles (excitons), which reside on the graph. The exciton propagation on the linear segments is characterized by the exciton dispersion, whereas the exciton scattering on the branching centers is determined by the energy-dependent scattering matrices. Using these ES energetic parameters, the excitation energies are then found by solving a set of generalized ``particle in a box'' problems on the graph that represents the molecule. All parameters can be extracted from quantum-chemical computations of small molecular fragments and tabulated in the ES library for further applications. Subsequently, spectroscopic modeling for any macrostructure within considered molecular family could be performed with negligible numerical effort. The exciton scattering properties of molecular vertices can be further described by tight-binding or equivalently lattice models. The on-site energies and hopping constants are obtained from the exciton dispersion and scattering matrices. Such tight-binding model approach is particularly useful to describe the exciton-phonon coupling, energetic disorder and incoherent energy transfer in large branched conjugated molecules. Overall the ES applications accurately reproduce the optical spectra compared to the reference quantum chemistry results, and make possible to predict spectra of complex macromolecules, where conventional electronic structure calculations are unfeasible.

Microbial Biofilm Voltammetry: Direct Electrochemical Characterization of Catalytic Electrode-Attached Biofilms▿ †

PubMed Central

Marsili, Enrico; Rollefson, Janet B.; Baron, Daniel B.; Hozalski, Raymond M.; Bond, Daniel R.

2008-01-01

While electrochemical characterization of enzymes immobilized on electrodes has become common, there is still a need for reliable quantitative methods for study of electron transfer between living cells and conductive surfaces. This work describes growth of thin (<20 μm) Geobacter sulfurreducens biofilms on polished glassy carbon electrodes, using stirred three-electrode anaerobic bioreactors controlled by potentiostats and nondestructive voltammetry techniques for characterization of viable biofilms. Routine in vivo analysis of electron transfer between bacterial cells and electrodes was performed, providing insight into the main redox-active species participating in electron transfer to electrodes. At low scan rates, cyclic voltammetry revealed catalytic electron transfer between cells and the electrode, similar to what has been observed for pure enzymes attached to electrodes under continuous turnover conditions. Differential pulse voltammetry and electrochemical impedance spectroscopy also revealed features that were consistent with electron transfer being mediated by an adsorbed catalyst. Multiple redox-active species were detected, revealing complexity at the outer surfaces of this bacterium. These techniques provide the basis for cataloging quantifiable, defined electron transfer phenotypes as a function of potential, electrode material, growth phase, and culture conditions and provide a framework for comparisons with other species or communities. PMID:18849456

Real-time electron transfer in respiratory complex I

PubMed Central

Verkhovskaya, Marina L.; Belevich, Nikolai; Euro, Liliya; Wikström, Mårten; Verkhovsky, Michael I.

2008-01-01

Electron transfer in complex I from Escherichia coli was investigated by an ultrafast freeze-quench approach. The reaction of complex I with NADH was stopped in the time domain from 90 μs to 8 ms and analyzed by electron paramagnetic resonance (EPR) spectroscopy at low temperatures. The data show that after binding of the first molecule of NADH, two electrons move via the FMN cofactor to the iron–sulfur (Fe/S) centers N1a and N2 with an apparent time constant of ≈90 μs, implying that these two centers should have the highest redox potential in the enzyme. The rate of reduction of center N2 (the last center in the electron transfer sequence) is close to that predicted by electron transfer theory, which argues for the absence of coupled proton transfer or conformational changes during electron transfer from FMN to N2. After fast reduction of N1a and N2, we observe a slow, ≈1-ms component of reduction of other Fe/S clusters. Because all elementary electron transfer rates between clusters are several orders of magnitude higher than this observed rate, we conclude that the millisecond component is limited by a single process corresponding to dissociation of the oxidized NAD+ molecule from its binding site, where it prevents entry of the next NADH molecule. Despite the presence of approximately one ubiquinone per enzyme molecule, no transient semiquinone formation was observed, which has mechanistic implications, suggesting a high thermodynamic barrier for ubiquinone reduction to the semiquinone radical. Possible consequences of these findings for the proton translocation mechanism are discussed. PMID:18316732

Dexter energy transfer pathways

PubMed Central

Skourtis, Spiros S.; Liu, Chaoren; Antoniou, Panayiotis; Virshup, Aaron M.; Beratan, David N.

2016-01-01

Energy transfer with an associated spin change of the donor and acceptor, Dexter energy transfer, is critically important in solar energy harvesting assemblies, damage protection schemes of photobiology, and organometallic opto-electronic materials. Dexter transfer between chemically linked donors and acceptors is bridge mediated, presenting an enticing analogy with bridge-mediated electron and hole transfer. However, Dexter coupling pathways must convey both an electron and a hole from donor to acceptor, and this adds considerable richness to the mediation process. We dissect the bridge-mediated Dexter coupling mechanisms and formulate a theory for triplet energy transfer coupling pathways. Virtual donor–acceptor charge-transfer exciton intermediates dominate at shorter distances or higher tunneling energy gaps, whereas virtual intermediates with an electron and a hole both on the bridge (virtual bridge excitons) dominate for longer distances or lower energy gaps. The effects of virtual bridge excitons were neglected in earlier treatments. The two-particle pathway framework developed here shows how Dexter energy-transfer rates depend on donor, bridge, and acceptor energetics, as well as on orbital symmetry and quantum interference among pathways. PMID:27382185

Dexter energy transfer pathways.

PubMed

Skourtis, Spiros S; Liu, Chaoren; Antoniou, Panayiotis; Virshup, Aaron M; Beratan, David N

2016-07-19

Energy transfer with an associated spin change of the donor and acceptor, Dexter energy transfer, is critically important in solar energy harvesting assemblies, damage protection schemes of photobiology, and organometallic opto-electronic materials. Dexter transfer between chemically linked donors and acceptors is bridge mediated, presenting an enticing analogy with bridge-mediated electron and hole transfer. However, Dexter coupling pathways must convey both an electron and a hole from donor to acceptor, and this adds considerable richness to the mediation process. We dissect the bridge-mediated Dexter coupling mechanisms and formulate a theory for triplet energy transfer coupling pathways. Virtual donor-acceptor charge-transfer exciton intermediates dominate at shorter distances or higher tunneling energy gaps, whereas virtual intermediates with an electron and a hole both on the bridge (virtual bridge excitons) dominate for longer distances or lower energy gaps. The effects of virtual bridge excitons were neglected in earlier treatments. The two-particle pathway framework developed here shows how Dexter energy-transfer rates depend on donor, bridge, and acceptor energetics, as well as on orbital symmetry and quantum interference among pathways.

Effect of proton transfer on the electronic coupling in DNA

NASA Astrophysics Data System (ADS)

Rak, Janusz; Makowska, Joanna; Voityuk, Alexander A.

2006-06-01

The effects of single and double proton transfer within Watson-Crick base pairs on donor-acceptor electronic couplings, Vda, in DNA are studied on the bases of quantum chemical calculations. Four dimers [AT,AT], [GC,GC], [GC,AT] and [GC,TA)] are considered. Three techniques - the generalized Mulliken-Hush scheme, the fragment charge method and the diabatic states method - are employed to estimate Vda for hole transfer between base pairs. We show that both single- and double proton transfer (PT) reactions may substantially affect the electronic coupling in DNA. The electronic coupling in [AT,AT] is predicted to be most sensitive to PT. Single PT within the first base pair in the dimer leads to increase in the hole transfer efficiency by a factor of 4, while proton transfer within the second pair should substantially, by 2.7 times, decrease the rate of charge transfer. Thus, directional asymmetry of the PT effects on the electronic coupling is predicted. The changes in the Vda matrix elements correlate with the topological properties of orbitals of donor and acceptor and can be qualitatively rationalized in terms of resonance structures of donor and acceptor. Atomic pair contributions to the Vda matrix elements are also analyzed.

Ultrafast electron and hole transfer dynamics of a solar cell dye containing hole acceptors on mesoporous TiO2 and Al2O3.

PubMed

Scholz, Mirko; Flender, Oliver; Boschloo, Gerrit; Oum, Kawon; Lenzer, Thomas

2017-03-08

The stability of dye cations against recombination with conduction band electrons in mesoporous TiO 2 electrodes is a key property for improving light harvesting in dye-sensitised solar cells. Using ultrafast transient broadband absorption spectroscopy, we monitor efficient intramolecular hole transfer in the solar cell dye E6 having two peripheral triarylamine acceptors. After photoexcitation, two hole transfer mechanisms are identified: a concerted mechanism for electron injection and hole transfer (2.4 ps) and a sequential mechanism with time constants of 3.9 ps and 30 ps. This way the dye retards unwanted recombination with a TiO 2 conduction band electron by quickly moving the hole further away from the surface. Contact of the E6/TiO 2 surface with the solvent acetonitrile has almost no influence on the electron injection and hole transfer kinetics. Fast hole transfer (2.8 ps) is also observed on a "non-injecting" Al 2 O 3 surface generating a radical cation-radical anion species with a lifetime of 530 ps. The findings confirm the good intramolecular hole transfer properties of this dye on both thin films. In contrast, intramolecular hole transfer does not occur in the mid-polar organic solvent methyl acetate. This is confirmed by TDDFT calculations suggesting a polarity-induced reduction of the driving force for hole transfer. In methyl acetate, only the relaxation of the initially photoexcited core chromophore is observed including solvent relaxation processes of the electronically excited state S 1 /ICT.

Antioxidant activity of selenenamide-based mimic as a function of the aromatic thiols nucleophilicity, a DFT-SAPE model.

PubMed

Kheirabadi, Ramesh; Izadyar, Mohammad

2018-05-18

The mechanism of action of the selenenamide 1 as a mimic of the glutathione peroxidase (GPx) was investigated by the density functional theory. The solvent-assisted proton exchange procedure was applied to model the catalytic behavior and antioxidant activity of this mimic. To have an insight into the charge transfer effect, different aromatic thiols, including electron donating substituents on the phenyl ring were considered. The catalytic behavior of the selenenamide was modeled in a four-step mechanism, described by the oxidation of the mimic, the reduction of the obtained product, selenoxide, the reduction of the selenenylsulfide and dehydration of selenenic acid. On the basis of the activation parameters, the final step of the proposed mechanism is the rate determining states of the catalytic cycle. Turnover frequency (TOF) analysis showed that the electron donating groups at the para-position of the phenyl ring of the PhSH do not affect the catalytic activity of the selenenamide in contrast to p-methyl thiophenol which indicates the highest nucleophilicity. The evaluation of the electronic contribution of the various donating groups on the phenyl ring of the aromatic thiols shows that the antioxidant activity of the selenenamide sufficiently increases in the presence of the electron-donating substitutions. Finally, the charge transfer process at the rate-determining state was investigated based on the natural bond orbital analysis. Copyright © 2018 Elsevier Ltd. All rights reserved.

Communication: Fragment-based Hamiltonian model of electronic charge-excitation gaps and gap closure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Valone, S. M.; Pilania, G.; Liu, X. Y.

2015-11-14

Capturing key electronic properties such as charge excitation gaps within models at or above the atomic scale presents an ongoing challenge to understanding molecular, nanoscale, and condensed phase systems. One strategy is to describe the system in terms of properties of interacting material fragments, but it is unclear how to accomplish this for charge-excitation and charge-transfer phenomena. Hamiltonian models such as the Hubbard model provide formal frameworks for analyzing gap properties but are couched purely in terms of states of electrons, rather than the states of the fragments at the scale of interest. The recently introduced Fragment Hamiltonian (FH) modelmore » uses fragments in different charge states as its building blocks, enabling a uniform, quantum-mechanical treatment that captures the charge-excitation gap. These gaps are preserved in terms of inter-fragment charge-transfer hopping integrals T and on-fragment parameters U{sup (FH)}. The FH model generalizes the standard Hubbard model (a single intra-band hopping integral t and on-site repulsion U) from quantum states for electrons to quantum states for fragments. We demonstrate that even for simple two-fragment and multi-fragment systems, gap closure is enabled once T exceeds the threshold set by U{sup (FH)}, thus providing new insight into the nature of metal-insulator transitions. This result is in contrast to the standard Hubbard model for 1d rings, for which Lieb and Wu proved that gap closure was impossible, regardless of the choices for t and U.« less

Molecular Electronic Coupling Controls Charge Recombination Kinetics in Organic Solar Cells of Low Bandgap Diketopyrrolopyrrole, Carbazole, and Thiophene Polymers

PubMed Central

2013-01-01

Low-bandgap diketopyrrolopyrrole- and carbazole-based polymer bulk-heterojunction solar cells exhibit much faster charge carrier recombination kinetics than that encountered for less-recombining poly(3-hexylthiophene). Solar cells comprising these polymers exhibit energy losses caused by carrier recombination of approximately 100 mV, expressed as reduction in open-circuit voltage, and consequently photovoltaic conversion efficiency lowers in more than 20%. The analysis presented here unravels the origin of that energy loss by connecting the limiting mechanism governing recombination dynamics to the electronic coupling occurring at the donor polymer and acceptor fullerene interfaces. Previous approaches correlate carrier transport properties and recombination kinetics by means of Langevin-like mechanisms. However, neither carrier mobility nor polymer ionization energy helps understanding the variation of the recombination coefficient among the studied polymers. In the framework of the charge transfer Marcus theory, it is proposed that recombination time scale is linked with charge transfer molecular mechanisms at the polymer/fullerene interfaces. As expected for efficient organic solar cells, small electronic coupling existing between donor polymers and acceptor fullerene (Vif < 1 meV) and large reorganization energy (λ ≈ 0.7 eV) are encountered. Differences in the electronic coupling among polymer/fullerene blends suffice to explain the slowest recombination exhibited by poly(3-hexylthiophene)-based solar cells. Our approach reveals how to directly connect photovoltaic parameters as open-circuit voltage to molecular properties of blended materials. PMID:23662167

Electronic Data Interchange: Using Technology to Exchange Transcripts.

ERIC Educational Resources Information Center

Stewart, John T.

1994-01-01

Describes the Florida Automated System for Transferring Educational Records (FASTER) project, which permits the electronic exchange of student transcripts; uses of similar electronic data interchange (EDI) programs in other states; and the national SPEEDE/ExPRESS project, which uses a standard format for transferring electronic transcripts.…

Electronic coupling in long-range electron transfer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Newton, M.D.

1996-12-31

One of the quantities crucial in controlling electron transfer (et) kinetics is the donor/acceptor electronic coupling integral (HDA). Recent theoretical models for HDA will be presented, and the results of ab initio computational implementation will be reported and analyzed for several metal-to-metal ligand charge transfer processes in complex molecular aggregates. New procedures for defining diabatic states, including a generalization of the Mulliken-Hush model, allow applications to optical and excited state as well as ground state et in a many-state framework.

Identifying dominant controls on hydrologic parameter transfer from gauged to ungauged catchments: a comparative hydrology approach

USGS Publications Warehouse

Singh, R.; Archfield, S.A.; Wagener, T.

2014-01-01

Daily streamflow information is critical for solving various hydrologic problems, though observations of continuous streamflow for model calibration are available at only a small fraction of the world’s rivers. One approach to estimate daily streamflow at an ungauged location is to transfer rainfall–runoff model parameters calibrated at a gauged (donor) catchment to an ungauged (receiver) catchment of interest. Central to this approach is the selection of a hydrologically similar donor. No single metric or set of metrics of hydrologic similarity have been demonstrated to consistently select a suitable donor catchment. We design an experiment to diagnose the dominant controls on successful hydrologic model parameter transfer. We calibrate a lumped rainfall–runoff model to 83 stream gauges across the United States. All locations are USGS reference gauges with minimal human influence. Parameter sets from the calibrated models are then transferred to each of the other catchments and the performance of the transferred parameters is assessed. This transfer experiment is carried out both at the scale of the entire US and then for six geographic regions. We use classification and regression tree (CART) analysis to determine the relationship between catchment similarity and performance of transferred parameters. Similarity is defined using physical/climatic catchment characteristics, as well as streamflow response characteristics (signatures such as baseflow index and runoff ratio). Across the entire US, successful parameter transfer is governed by similarity in elevation and climate, and high similarity in streamflow signatures. Controls vary for different geographic regions though. Geology followed by drainage, topography and climate constitute the dominant similarity metrics in forested eastern mountains and plateaus, whereas agricultural land use relates most strongly with successful parameter transfer in the humid plains.

Disentangling specific versus generic doping mechanisms in oxide heterointerfaces

NASA Astrophysics Data System (ADS)

Gabel, J.; Zapf, M.; Scheiderer, P.; Schütz, P.; Dudy, L.; Stübinger, M.; Schlueter, C.; Lee, T.-L.; Sing, M.; Claessen, R.

2017-05-01

More than a decade after the discovery of the two-dimensional electron system (2DES) at the interface between the band insulators LaAlO3 (LAO) and SrTiO3 (STO) its microscopic origin is still under debate. Several explanations have been proposed, the main contenders being electron doping by oxygen vacancies and electronic reconstruction, i.e., the redistribution of electrons to the interface to minimize the electrostatic energy in the polar LAO film. However, no experiment thus far could provide unambiguous information on the microscopic origin of the interfacial charge carriers. Here we utilize a novel experimental approach combining photoelectron spectroscopy (PES) with highly brilliant synchrotron radiation and apply it to a set of samples with varying key parameters that are thought to be crucial for the emergence of interfacial conductivity. Based on microscopic insight into the electronic structure, we obtain results tipping the scales in favor of polar discontinuity as a generic, robust driving force for the 2DES formation. Likewise, other functionalities such as magnetism or superconductivity might be switched in all-oxide devices by polarity-driven charge transfer.

Electronic charge rearrangement at metal/organic interfaces induced by weak van der Waals interactions

NASA Astrophysics Data System (ADS)

Ferri, Nicola; Ambrosetti, Alberto; Tkatchenko, Alexandre

2017-07-01

Electronic charge rearrangements at interfaces between organic molecules and solid surfaces play a key role in a wide range of applications in catalysis, light-emitting diodes, single-molecule junctions, molecular sensors and switches, and photovoltaics. It is common to utilize electrostatics and Pauli pushback to control the interface electronic properties, while the ubiquitous van der Waals (vdW) interactions are often considered to have a negligible direct contribution (beyond the obvious structural relaxation). Here, we apply a fully self-consistent Tkatchenko-Scheffler vdW density functional to demonstrate that the weak vdW interactions can induce sizable charge rearrangements at hybrid metal/organic systems (HMOS). The complex vdW correlation potential smears out the interfacial electronic density, thereby reducing the charge transfer in HMOS, changes the interface work functions by up to 0.2 eV, and increases the interface dipole moment by up to 0.3 Debye. Our results suggest that vdW interactions should be considered as an additional control parameter in the design of hybrid interfaces with the desired electronic properties.

The Laser ablation of a metal foam: The role of electron-phonon coupling and electronic heat diffusivity

NASA Astrophysics Data System (ADS)

Rosandi, Yudi; Grossi, Joás; Bringa, Eduardo M.; Urbassek, Herbert M.

2018-01-01

The incidence of energetic laser pulses on a metal foam may lead to foam ablation. The processes occurring in the foam may differ strongly from those in a bulk metal: The absorption of laser light, energy transfer to the atomic system, heat conduction, and finally, the atomistic processes—such as melting or evaporation—may be different. In addition, novel phenomena take place, such as a reorganization of the ligament network in the foam. We study all these processes in an Au foam of average porosity 79% and an average ligament diameter of 2.5 nm, using molecular dynamics simulation. The coupling of the electronic system to the atomic system is modeled by using the electron-phonon coupling, g, and the electronic heat diffusivity, κe, as model parameters, since their actual values for foams are unknown. We show that the foam coarsens under laser irradiation. While κe governs the homogeneity of the processes, g mainly determines their time scale. The final porosity reached is independent of the value of g.

Untangling the drivers of nonlinear systems with information theory

NASA Astrophysics Data System (ADS)

Wing, S.; Johnson, J.

2017-12-01

Many systems found in nature are nonlinear. The drivers of the system are often nonlinearly correlated with one another, which makes it a challenge to understand the effects of an individual driver. For example, solar wind velocity (Vsw) and density (nsw) are both found to correlate well with radiation belt fluxes and are thought to be drivers of the magnetospheric dynamics; however, the Vsw is anti-correlated with nsw, which can potentially confuse interpretation of these relationships as causal or coincidental. Information theory can untangle the drivers of these systems, describe the underlying dynamics, and offer constraints to modelers and theorists, leading to better understanding of the systems. Two examples are presented. In the first example, the solar wind drivers of geosynchronous electrons with energy range of 1.8-3.5 MeV are investigated using mutual information (MI), conditional mutual information (CMI), and transfer entropy (TE). The information transfer from Vsw to geosynchronous MeV electron flux (Je) peaks with a lag time (t) of 2 days. As previously reported, Je is anticorrelated with nsw with a lag of 1 day. However, this lag time and anticorrelation can be attributed mainly to the Je(t + 2 days) correlation with Vsw(t) and nsw(t + 1 day) anticorrelation with Vsw(t). Analyses of solar wind driving of the magnetosphere need to consider the large lag times, up to 3 days, in the (Vsw, nsw) anticorrelation. Using CMI to remove the effects of Vsw, the response of Je to nsw is 30% smaller and has a lag time < 24 hr, suggesting that the loss mechanism due to nsw or solar wind dynamic pressure has to start operating in < 24 hr. nsw transfers about 36% as much information as Vsw (the primary driver) to Je. Nonstationarity in the system dynamics are investigated using windowed TE. When the data is ordered according to high or low transfer entropy it is possible to understand details of the triangle distribution that has been identified between Je(t + 2 days) vs. Vsw(t). In the second example, the previously identified causal parameters of the solar cycle such as the solar polar field, meridional flow, polar faculae (proxy for polar field), dipole axis strength, are investigated. We discuss the response lag times of the sunspot numbers and information transferred to the sunspot numbers from the dynamic time series of these parameters.

Electronic structure measurements of metal-organic solar cell dyes using x-ray absorption spectroscopy

NASA Astrophysics Data System (ADS)

Johnson, Phillip S.

The focus of this thesis is twofold: to report the results of X-ray absorption studies of metal-organic dye molecules for dye-sensitized solar cells and to provide a basic training manual on X-ray absorption spectroscopy techniques and data analysis. The purpose of our research on solar cell dyes is to work toward an understanding of the factors influencing the electronic structure of the dye: the choice of the metal, its oxidation state, ligands, and cage structure. First we study the effect of replacing Ru in several common dye structures by Fe. First-principles calculations and X-ray absorption spectroscopy at the C 1s and N 1s edges are combined to investigate transition metal dyes in octahedral and square planar N cages. Octahedral molecules are found to have a downward shift in the N 1s-to-pi* transition energy and an upward shift in C 1s-to-pi* transition energy when Ru is replaced by Fe, explained by an extra transfer of negative charge from Fe to the N ligands compared to Ru. For the square planar molecules, the behavior is more complex because of the influence of axial ligands and oxidation state. Next the crystal field parameters for a series of phthalocyanine and porphyrins dyes are systematically determined using density functional calculations and atomic multiplet calculations with polarization-dependent X-ray absorption spectra. The polarization dependence of the spectra provides information on orbital symmetries which ensures the determination of the crystal field parameters is unique. A uniform downward scaling of the calculated crystal field parameters by 5-30% is found to be necessary to best fit the spectra. This work is a part of the ongoing effort to design and test new solar cell dyes. Replacing the rare metal Ru with abundant metals like Fe would be a significant advance for dye-sensitized solar cells. Understanding the effects of changing the metal centers in these dyes in terms of optical absorption, charge transfer, and electronic structure enables the systematic design of new dyes using less expensive materials.

Electron transfer statistics and thermal fluctuations in molecular junctions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goswami, Himangshu Prabal; Harbola, Upendra

2015-02-28

We derive analytical expressions for probability distribution function (PDF) for electron transport in a simple model of quantum junction in presence of thermal fluctuations. Our approach is based on the large deviation theory combined with the generating function method. For large number of electrons transferred, the PDF is found to decay exponentially in the tails with different rates due to applied bias. This asymmetry in the PDF is related to the fluctuation theorem. Statistics of fluctuations are analyzed in terms of the Fano factor. Thermal fluctuations play a quantitative role in determining the statistics of electron transfer; they tend tomore » suppress the average current while enhancing the fluctuations in particle transfer. This gives rise to both bunching and antibunching phenomena as determined by the Fano factor. The thermal fluctuations and shot noise compete with each other and determine the net (effective) statistics of particle transfer. Exact analytical expression is obtained for delay time distribution. The optimal values of the delay time between successive electron transfers can be lowered below the corresponding shot noise values by tuning the thermal effects.« less

Electron transfer reactivity of the aqueous iron(IV)–oxo complex. Outer-sphere vs proton-coupled electron transfer

DOE PAGES

Bataineh, Hajem; Pestovsky, Oleg; Bakac, Andreja

2016-06-18

Here, the kinetics of oxidation of organic and inorganic reductants by aqueous iron(IV) ions, Fe IV(H 2O) 5O 2+ (hereafter Fe IV aqO 2+), are reported. The substrates examined include several water-soluble ferrocenes, hexachloroiridate(III), polypyridyl complexes M(NN) 3 2+ (M = Os, Fe and Ru; NN = phenanthroline, bipyridine and derivatives), HABTS–/ABTS 2–, phenothiazines, Co II(dmgBF 2) 2, macrocyclic nickel(II) complexes, and aqueous cerium(III). Most of the reductants were oxidized cleanly to the corresponding one-electron oxidation products, with the exception of phenothiazines which produced the corresponding oxides in a single-step reaction, and polypyridyl complexes of Fe(II) and Ru(II) that generatedmore » ligand-modified products. Fe IV aqO 2+ oxidizes even Ce(III) (E 0 in 1 M HClO 4 = 1.7 V) with a rate constant greater than 10 4 M –1 s –1. In 0.10 M aqueous HClO 4 at 25 °C, the reactions of Os(phen) 3 2+ (k = 2.5 × 10 5 M –1 s –1), IrCl 6 3– (1.6 × 10 6), ABTS 2– (4.7 × 10 7), and Fe(cp)(C 5H 4CH 2OH) (6.4 × 10 7) appear to take place by outer sphere electron transfer (OSET). The rate constants for the oxidation of Os(phen) 3 2+ and of ferrocenes remained unchanged in the acidity range 0.05 < [H+] < 0.10 M, ruling out prior protonation of Fe IV aqO 2+ and further supporting the OSET assignment. A fit to Marcus cross-relation yielded a composite parameter (log k 22 + E 0 Fe/0.059) = 17.2 ± 0.8, where k 22 and E 0 Fe are the self-exchange rate constant and reduction potential, respectively, for the Fe IV aqO 2+/Fe III aqO + couple. Comparison with literature work suggests k 22 < 10 –5 M –1 s –1 and thus E 0(Fe IV aqO 2+/Fe III aqO +) > 1.3 V. For proton-coupled electron transfer, the reduction potential is estimated at E 0 (Fe IV aqO 2+, H +/Fe III aqOH 2+) ≥ 1.95 V.« less

Polarizable atomic multipole-based force field for DOPC and POPE membrane lipids

NASA Astrophysics Data System (ADS)

Chu, Huiying; Peng, Xiangda; Li, Yan; Zhang, Yuebin; Min, Hanyi; Li, Guohui

2018-04-01

A polarizable atomic multipole-based force field for the membrane bilayer models 1,2-dioleoyl-phosphocholine (DOPC) and 1-palmitoyl-2-oleoyl-phosphatidylethanolamine (POPE) has been developed. The force field adopts the same framework as the Atomic Multipole Optimized Energetics for Biomolecular Applications (AMOEBA) model, in which the charge distribution of each atom is represented by the permanent atomic monopole, dipole and quadrupole moments. Many-body polarization including the inter- and intra-molecular polarization is modelled in a consistent manner with distributed atomic polarizabilities. The van der Waals parameters were first transferred from existing AMOEBA parameters for small organic molecules and then optimised by fitting to ab initio intermolecular interaction energies between models and a water molecule. Molecular dynamics simulations of the two aqueous DOPC and POPE membrane bilayer systems, consisting of 72 model molecules, were then carried out to validate the force field parameters. Membrane width, area per lipid, volume per lipid, deuterium order parameters, electron density profile, etc. were consistent with experimental values.

Introduction of gold nanoparticles into myoglobin-Nafion film for direct electrochemistry application.

PubMed

Xie, Wenting; Kong, Linlin; Kan, Meixiu; Han, Dongmei; Wang, Xueji; Zhang, Hui-Min

2010-10-01

An effective myoglobin-Nafion film is prepared by introducing gold nanoparticles in through a simple procedure by ion-exchange combined with electrochemical reduction. Gold nanoparticles are highly dispersed in myoglobin-Nafion film with an average size of 2.3 +/- 0.2 nm. The electrochemical behavior of myoglobin entrapped in the film has been carefully investigated with cyclic voltammetry. The results show that the introduction of gold nanoparticles into myoglobin-Nafion film makes the direct electron transfer of myoglobin efficient. A pair of well-defined redox peaks for myoglobin heme Fe(II)/Fe(III) is observed with a formal potential of -0.150 V in 0.1 M phosphate buffer (pH 7.0). The electrochemical parameters of myoglobin in the composite film are further calculated with the results of the electron-transfer rate constant (k(s)) as 0.93 s(-1) and the charge transfer coefficient (alpha) as 0.69. The experimental results also demonstrate that the immobilized myoglobin retains its electrocatalytic activity for the reduction of hydrogen peroxide and the catalytic reduction peak of myoglobin appear in a linear relationship with H2O2 concentration in the range of 10.0-235.0 microM with correlation coefficient of 0.9970. Thus fabricated Au/Mb/Nafion electrode should give a new approach for developing redox protein or enzyme-based biosensors.

Extracellular electron transfer mechanisms between microorganisms and minerals.

PubMed

Shi, Liang; Dong, Hailiang; Reguera, Gemma; Beyenal, Haluk; Lu, Anhuai; Liu, Juan; Yu, Han-Qing; Fredrickson, James K

2016-10-01

Electrons can be transferred from microorganisms to multivalent metal ions that are associated with minerals and vice versa. As the microbial cell envelope is neither physically permeable to minerals nor electrically conductive, microorganisms have evolved strategies to exchange electrons with extracellular minerals. In this Review, we discuss the molecular mechanisms that underlie the ability of microorganisms to exchange electrons, such as c-type cytochromes and microbial nanowires, with extracellular minerals and with microorganisms of the same or different species. Microorganisms that have extracellular electron transfer capability can be used for biotechnological applications, including bioremediation, biomining and the production of biofuels and nanomaterials.