Single-Active-Electron Approximation for Describing Molecules in Ultrashort Laser Pulses
NASA Astrophysics Data System (ADS)
Saenz, Alejandro; Awasthi, Manohar; Vanne, Yulian; Castro, Alberto; Decleva, Piero
2008-05-01
A numerical approach that allows for the solution of the time-dependent Schr"odinger equation (TDSE) describing molecules exposed to intense short laser pulses was developed. The molecular response to the strong field is described within the single-active electron approximation (SAE). The method is applied to molecular hydrogen and the validity of the SAE is investigated by comparing the ionization and electronic excitation yields to full two-electron solutions of the TDSE. The present results are also used to investigate the validity of approximate SAE methods like the molecular Ammosov-Delone-Krainov and the strong-field approximation. Finally, results for larger molecules like O2, N2, and C2H2 (acetylene) are presented.
Approximate Bruechner orbitals in electron propagator calculations
Ortiz, J.V.
1999-12-01
Orbitals and ground-state correlation amplitudes from the so-called Brueckner doubles approximation of coupled-cluster theory provide a useful reference state for electron propagator calculations. An operator manifold with hold, particle, two-hole-one-particle and two-particle-one-hole components is chosen. The resulting approximation, third-order algebraic diagrammatic construction [2ph-TDA, ADC (3)] and 3+ methods. The enhanced versatility of this approximation is demonstrated through calculations on valence ionization energies, core ionization energies, electron detachment energies of anions, and on a molecule with partial biradical character, ozone.
Gutzwiller approximation in strongly correlated electron systems
NASA Astrophysics Data System (ADS)
Li, Chunhua
Gutzwiller wave function is an important theoretical technique for treating local electron-electron correlations nonperturbatively in condensed matter and materials physics. It is concerned with calculating variationally the ground state wave function by projecting out multi-occupation configurations that are energetically costly. The projection can be carried out analytically in the Gutzwiller approximation that offers an approximate way of calculating expectation values in the Gutzwiller projected wave function. This approach has proven to be very successful in strongly correlated systems such as the high temperature cuprate superconductors, the sodium cobaltates, and the heavy fermion compounds. In recent years, it has become increasingly evident that strongly correlated systems have a strong propensity towards forming inhomogeneous electronic states with spatially periodic superstrutural modulations. A good example is the commonly observed stripes and checkerboard states in high- Tc superconductors under a variety of conditions where superconductivity is weakened. There exists currently a real challenge and demand for new theoretical ideas and approaches that treats strongly correlated inhomogeneous electronic states, which is the subject matter of this thesis. This thesis contains four parts. In the first part of the thesis, the Gutzwiller approach is formulated in the grand canonical ensemble where, for the first time, a spatially (and spin) unrestricted Gutzwiller approximation (SUGA) is developed for studying inhomogeneous (both ordered and disordered) quantum electronic states in strongly correlated electron systems. The second part of the thesis applies the SUGA to the t-J model for doped Mott insulators which led to the discovery of checkerboard-like inhomogeneous electronic states competing with d-wave superconductivity, consistent with experimental observations made on several families of high-Tc superconductors. In the third part of the thesis, new
Electronic Flux Density beyond the Born-Oppenheimer Approximation.
Schild, Axel; Agostini, Federica; Gross, E K U
2016-05-19
In the Born-Oppenheimer approximation, the electronic wave function is typically real-valued and hence the electronic flux density (current density) seems to vanish. This is unfortunate for chemistry, because it precludes the possibility to monitor the electronic motion associated with the nuclear motion during chemical rearrangements from a Born-Oppenheimer simulation of the process. We study an electronic flux density obtained from a correction to the electronic wave function. This correction is derived via nuclear velocity perturbation theory applied in the framework of the exact factorization of electrons and nuclei. To compute the correction, only the ground state potential energy surface and the electronic wave function are needed. For a model system, we demonstrate that this electronic flux density approximates the true one very well, for coherent tunneling dynamics as well as for over-the-barrier scattering, and already for mass ratios between electrons and nuclei that are much larger than the true mass ratios. PMID:26878256
NASA Astrophysics Data System (ADS)
Agrawal, Divya
Dual-beam ELF/VLF wave generation experiments performed at the High-frequency Active Auroral Research Program (HAARP) HF transmitter in Gakona, Alaska are critically compared with the predictions of a newly developed ionospheric high frequency (HF) heating model that accounts for the simultaneous propagation and absorption of multiple HF beams. The dual-beam HF heating experiments presented herein consist of two HF beams transmitting simultaneously: one amplitude modulated (AM) HF beam modulates the conductivity of the lower ionosphere in the extremely low frequency (ELF, 30 Hz to 3 kHz) and/or very low frequency (VLF, 3 kHz to 30 kHz) band while a second HF beam broadcasts a continuous waveform (CW) signal, modifying the efficiency of ELF/VLF conductivity modulation and thereby the efficiency of ELF/VLF wave generation. Ground-based experimental observations are used together with the predictions of the theoretical model to identify the property of the received ELF/VLF wave that is most sensitive to the effects of multi-beam HF heating, and that property is determined to be the ELF/VLF signal magnitude. The dependence of the generated ELF/VLF wave magnitude on several HF transmission parameters (HF power, HF frequency, and modulation waveform) is then experimentally measured and analyzed within the context of the multi-beam HF heating model. For all cases studied, the received ELF/VLF wave magnitude as a function of transmission parameter is analyzed to identify the dependence on the ambient D-region electron density (Ne) and/or electron temperature ( Te), in turn identifying the HF transmission parameters that provide significant independent information regarding the ambient conditions of the D-region ionosphere. A theoretical analysis is performed to determine the conditions under which the effects of Ne and Te can be decoupled, and the results of this analysis are applied to identify an electron density profile that can reproduce the unusually high level of ELF
Temporal relaxation of electrons in multi-term approximation
Loffhagen, D.; Winkler, R.
1995-12-31
The study of the temporal relaxation of energetic electrons in weakly ionized, spatially homogeneous, collision dominated plasmas under the action of an electric field constitutes a topic of widespread interest (e.g. problems of plasma light sources, gas laser physics, swarm techniques, after-glow decay). Starting point for the electron kinetic investigations is the nonstationary Boltzmann equation. When choosing a fixed direction of the electric field, usually the solution of this electron kinetic equation is based on the Legendre polynomial expansion of the velocity distribution function leading to a hierarchy of partial differential equations. Conventionally this expansion is truncated after two terms (two-term approximation of the velocity distribution) and a quasi-stationary treatment of the distribution anisotropy is adopted. These two approximations are almost generally used in investigations of the temporal relaxation of electrons in collision dominated, weakly ionized plasmas. However, this approach is incorrect in several cases of practical interest. Based upon recent studies of the electron relaxation a new and very efficient technique for the solution of the electron Boltzmann equation in strict nonstationary multi-term approximation has been developed. First results on the electron relaxation in a time-independent electric field for a model gas plasma using this new approach have already been presented in. This paper reports results for the temporal relaxation of electrons in various real inert and molecular gas plasmas.
No surprise in the first Born approximation for electron scattering.
Lentzen, M
2014-01-01
In a recent article it is argued that the far-field expansion of electron scattering, a pillar of electron diffraction theory, is wrong (Treacy and Van Dyck, 2012). It is further argued that in the first Born approximation of electron scattering the intensity of the electron wave is not conserved to first order in the scattering potential. Thus a "mystery of the missing phase" is investigated, and the supposed flaw in scattering theory is seeked to be resolved by postulating a standing spherical electron wave (Treacy and Van Dyck, 2012). In this work we show, however, that these theses are wrong. A review of the essential parts of scattering theory with careful checks of the underlying assumptions and limitations for high-energy electron scattering yields: (1) the traditional form of the far-field expansion, comprising a propagating spherical wave, is correct; (2) there is no room for a missing phase; (3) in the first Born approximation the intensity of the scattered wave is conserved to first order in the scattering potential. The various features of high-energy electron scattering are illustrated by wave-mechanical calculations for an explicit target model, a Gaussian phase object, and for a Si atom, considering the geometric conditions in high-resolution transmission electron microscopy. PMID:24216157
Quasielastic electron-deuteron scattering in the weak binding approximation
Ethier, Jacob J.; Doshi, Nidhi P.; Malace, Simona P.; Melnitchouk, Wally
2014-06-01
We perform a global analysis of all available electron-deuteron quasielastic scattering data using Q^2-dependent smearing functions that describe inclusive inelastic e-d scattering within the weak binding approximation. We study the dependence of the cross sections on the deuteron wave function and the off-shell extrapolation of the elastic electron-nucleon cross section, which show particular sensitivity at x >> 1. The excellent overall agreement with data over a large range of Q^2 and x suggest a limited need for effects beyond the impulse approximation, with the exception of the very high-x or very low-Q^2 regions, where short-distance effects in the deuteron become more relevant.
Two-electron ionization and stabilization beyond the dipole approximation
Staudt, Andreas; Keitel, Christoph H.
2006-04-15
A two-dimensional model atom is employed to study the ionization behavior of helium subjected to strong laser fields in the high-frequency regime. The evolution of the system is studied by means of numerical integration of the Schroedinger equation beyond the dipole approximation. Ionization probabilities of the two-electron atom in highly intense laser fields have been calculated for different pulse shapes. It is confirmed that the mutual repulsion between the two electrons as well as the length of the laser pulses significantly alter the ionization probabilities of the system. Nondipole effects are shown to lead to a considerable increase of the ionization probabilities. For certain laser pulse shapes, a regime of ionization suppression is investigated which exists in addition to two-electron stabilization. The applicability of our model scheme to the case of heliumlike systems is discussed, and it is shown that stabilization may also occur in these systems, and how it is altered in dependence of the nuclear charge.
Electron correlation effects beyond the random phase approximation
NASA Astrophysics Data System (ADS)
Fan, J. D.; Malozovsky, Y. M.
2016-04-01
The methods that have been used to deal with a many-particle system can be basically sorted into three types: Hamiltonian, field theory and phenomenological method. The first two methods are more popular. Traditionally, the Hamiltonian method has been widely adopted in the conventional electronic theory for metals, alloys and semiconductors. Basically, the mean-field approximation (MFA) that has been working well for a weakly coupled system like a metal is employed to simplify a Hamiltonian corresponding to a particular electron system. However, for a strongly coupled many-particle system like a cuprate superconductor MFA should in principle not apply. Therefore, the field theory on the basis of Green’s function and the Feynman diagrams must be invoked. In this method, one is however more familiar with the random phase approximation (RPA) that gives rise to the same results as MFA because of being short of the information for higher-order terms of interaction. For a strongly coupled electron system, it is obvious that one has to deal with higher-order terms of a pair interaction to get a correct solution. Any ignorance of the higher-order terms implies that the more sophisticated information contained in those terms is discarded. However, to date one has not reached a consensus on how to deal with the higher-order terms beyond RPA. We preset here a method that is termed the diagrammatic iteration approach (DIA) and able to derive higher-order terms of the interaction from the information of lower-order ones on the basis of Feynman diagram, with which one is able to go beyond RPA step by step. It is in principle possible that all of higher-order terms can be obtained, and then sorted to groups of diagrams. It turns out that each of the groups can be replaced by an equivalent one, forming a diagrammatic Dyson-equation-like relation. The diagrammatic solution is eventually “translated” to a four-dimensional integral equation. The method can be applied to a
Quasiparticle electronic structure of bismuth telluride in the GW approximation
NASA Astrophysics Data System (ADS)
Kioupakis, Emmanouil; Tiago, Murilo L.; Louie, Steven G.
2010-12-01
The quasiparticle band structure of bismuth telluride (Bi2Te3) , an important thermoelectric material that exhibits topologically insulating surface states, is calculated from first principles in the GW approximation. The quasiparticle energies are evaluated in fine detail in the first Brillouin zone using a Wannier-function interpolation method, allowing the accurate determination of the location of the band extrema (which is in the mirror plane) as well as the values of the quasiparticle band gap (0.17 eV) and effective-mass tensors. Spin-orbit interaction effects were included. The valence band exhibits two distinct maxima in the mirror plane that differ by just 1 meV, giving rise to one direct and one indirect band gap of very similar magnitude. The effective-mass tensors are in reasonable agreement with experiment. The Wannier interpolation coefficients can be used for the tight-binding parametrization of the band structure. Our work elucidates the electronic structure of Bi2Te3 and sheds light on its exceptional thermoelectric and topologically insulating properties.
Quasiparticle electronic structure of bismuth telluride in the GW approximation
Kioupakis, Emmanouil; Tiago, Murilo L; Louie, Steven G.
2010-01-01
The quasiparticle band structure of bismuth telluride Bi2Te3 , an important thermoelectric material that exhibits topologically insulating surface states, is calculated from first principles in the GW approximation. The quasiparticle energies are evaluated in fine detail in the first Brillouin zone using a Wannier-function interpo- lation method, allowing the accurate determination of the location of the band extrema which is in the mirror plane as well as the values of the quasiparticle band gap 0.17 eV and effective-mass tensors. Spin-orbit interaction effects were included. The valence band exhibits two distinct maxima in the mirror plane that differ by just 1 meV, giving rise to one direct and one indirect band gap of very similar magnitude. The effective- mass tensors are in reasonable agreement with experiment. The Wannier interpolation coefficients can be used for the tight-binding parametrization of the band structure. Our work elucidates the electronic structure of Bi2Te3 and sheds light on its exceptional thermoelectric and topologically insulating properties.
Electron correlation within the relativistic no-pair approximation.
Almoukhalalati, Adel; Knecht, Stefan; Jensen, Hans Jørgen Aa; Dyall, Kenneth G; Saue, Trond
2016-08-21
This paper addresses the definition of correlation energy within 4-component relativistic atomic and molecular calculations. In the nonrelativistic domain the correlation energy is defined as the difference between the exact eigenvalue of the electronic Hamiltonian and the Hartree-Fock energy. In practice, what is reported is the basis set correlation energy, where the "exact" value is provided by a full Configuration Interaction (CI) calculation with some specified one-particle basis. The extension of this definition to the relativistic domain is not straightforward since the corresponding electronic Hamiltonian, the Dirac-Coulomb Hamiltonian, has no bound solutions. Present-day relativistic calculations are carried out within the no-pair approximation, where the Dirac-Coulomb Hamiltonian is embedded by projectors eliminating the troublesome negative-energy solutions. Hartree-Fock calculations are carried out with the implicit use of such projectors and only positive-energy orbitals are retained at the correlated level, meaning that the Hartree-Fock projectors are frozen at the correlated level. We argue that the projection operators should be optimized also at the correlated level and that this is possible by full Multiconfigurational Self-Consistent Field (MCSCF) calculations, that is, MCSCF calculations using a no-pair full CI expansion, but including orbital relaxation from the negative-energy orbitals. We show by variational perturbation theory that the MCSCF correlation energy is a pure MP2-like correlation expression, whereas the corresponding CI correlation energy contains an additional relaxation term. We explore numerically our theoretical analysis by carrying out variational and perturbative calculations on the two-electron rare gas atoms with specially tailored basis sets. In particular, we show that the correlation energy obtained by the suggested MCSCF procedure is smaller than the no-pair full CI correlation energy, in accordance with the underlying
Peng, Degao; Yang, Yang; Zhang, Peng; Yang, Weitao
2014-12-01
In this article, we develop systematically second random phase approximations (RPA) and Tamm-Dancoff approximations (TDA) of particle-hole and particle-particle channels for calculating molecular excitation energies. The second particle-hole RPA/TDA can capture double excitations missed by the particle-hole RPA/TDA and time-dependent density-functional theory (TDDFT), while the second particle-particle RPA/TDA recovers non-highest-occupied-molecular-orbital excitations missed by the particle-particle RPA/TDA. With proper orbital restrictions, these restricted second RPAs and TDAs have a formal scaling of only O(N(4)). The restricted versions of second RPAs and TDAs are tested with various small molecules to show some positive results. Data suggest that the restricted second particle-hole TDA (r2ph-TDA) has the best overall performance with a correlation coefficient similar to TDDFT, but with a larger negative bias. The negative bias of the r2ph-TDA may be induced by the unaccounted ground state correlation energy to be investigated further. Overall, the r2ph-TDA is recommended to study systems with both single and some low-lying double excitations with a moderate accuracy. Some expressions on excited state property evaluations, such as ⟨Ŝ(2)⟩ are also developed and tested. PMID:25481124
Peng, Degao; Yang, Yang; Zhang, Peng; Yang, Weitao
2014-12-07
In this article, we develop systematically second random phase approximations (RPA) and Tamm-Dancoff approximations (TDA) of particle-hole and particle-particle channels for calculating molecular excitation energies. The second particle-hole RPA/TDA can capture double excitations missed by the particle-hole RPA/TDA and time-dependent density-functional theory (TDDFT), while the second particle-particle RPA/TDA recovers non-highest-occupied-molecular-orbital excitations missed by the particle-particle RPA/TDA. With proper orbital restrictions, these restricted second RPAs and TDAs have a formal scaling of only O(N{sup 4}). The restricted versions of second RPAs and TDAs are tested with various small molecules to show some positive results. Data suggest that the restricted second particle-hole TDA (r2ph-TDA) has the best overall performance with a correlation coefficient similar to TDDFT, but with a larger negative bias. The negative bias of the r2ph-TDA may be induced by the unaccounted ground state correlation energy to be investigated further. Overall, the r2ph-TDA is recommended to study systems with both single and some low-lying double excitations with a moderate accuracy. Some expressions on excited state property evaluations, such as 〈S{sup ^2}〉 are also developed and tested.
NASA Astrophysics Data System (ADS)
Peng, Degao; Yang, Yang; Zhang, Peng; Yang, Weitao
2014-12-01
In this article, we develop systematically second random phase approximations (RPA) and Tamm-Dancoff approximations (TDA) of particle-hole and particle-particle channels for calculating molecular excitation energies. The second particle-hole RPA/TDA can capture double excitations missed by the particle-hole RPA/TDA and time-dependent density-functional theory (TDDFT), while the second particle-particle RPA/TDA recovers non-highest-occupied-molecular-orbital excitations missed by the particle-particle RPA/TDA. With proper orbital restrictions, these restricted second RPAs and TDAs have a formal scaling of only O(N4). The restricted versions of second RPAs and TDAs are tested with various small molecules to show some positive results. Data suggest that the restricted second particle-hole TDA (r2ph-TDA) has the best overall performance with a correlation coefficient similar to TDDFT, but with a larger negative bias. The negative bias of the r2ph-TDA may be induced by the unaccounted ground state correlation energy to be investigated further. Overall, the r2ph-TDA is recommended to study systems with both single and some low-lying double excitations with a moderate accuracy. Some expressions on excited state property evaluations, such as < hat{S}2rangle are also developed and tested.
Chasing the limits of the one electron approximation
Kędziera, Dariusz; Mentel, Łukasz M.
2014-10-06
Rapid progress in the development of computational methods for quantum chemistry is not properly balanced by the development of basis sets. Even in the case of few-electron systems it is hard to find basis set which are able to reproduce the ECG benchmarks with the mhartree accuracy. In this paper we show early work on improvements of the basis sets for small atomic and molecular systems. As a starting point the ground state of lithium atom and the lowest states of lithium dimer will be investigated. The exploratory optimization of the exponents of primitive gaussians will be based on even tempered scheme combined with CISD method.
Chasing the limits of the one electron approximation
NASA Astrophysics Data System (ADS)
Kedziera, Dariusz; Mentel, Łukasz M.
2014-10-01
Rapid progress in the development of computational methods for quantum chemistry is not properly balanced by the development of basis sets. Even in the case of few-electron systems it is hard to find basis set which are able to reproduce the ECG benchmarks with the mhartree accuracy. In this paper we show early work on improvements of the basis sets for small atomic and molecular systems. As a starting point the ground state of lithium atom and the lowest states of lithium dimer will be investigated. The exploratory optimization of the exponents of primitive gaussians will be based on even tempered scheme combined with CISD method.
NASA Astrophysics Data System (ADS)
Chatterjee, Koushik; Pernal, Katarzyna
2012-11-01
Starting from Rowe's equation of motion we derive extended random phase approximation (ERPA) equations for excitation energies. The ERPA matrix elements are expressed in terms of the correlated ground state one- and two-electron reduced density matrices, 1- and 2-RDM, respectively. Three ways of obtaining approximate 2-RDM are considered: linearization of the ERPA equations, obtaining 2-RDM from density matrix functionals, and employing 2-RDM corresponding to an antisymmetrized product of strongly orthogonal geminals (APSG) ansatz. Applying the ERPA equations with the exact 2-RDM to a hydrogen molecule reveals that the resulting ^1Σ _g^+ excitation energies are not exact. A correction to the ERPA excitation operator involving some double excitations is proposed leading to the ERPA2 approach, which employs the APSG one- and two-electron reduced density matrices. For two-electron systems ERPA2 satisfies a consistency condition and yields exact singlet excitations. It is shown that 2-RDM corresponding to the APSG theory employed in the ERPA2 equations yields excellent singlet excitation energies for Be and LiH systems, and for the N2 molecule the quality of the potential energy curves is at the coupled cluster singles and doubles level. ERPA2 nearly satisfies the consistency condition for small molecules that partially explains its good performance.
NASA Astrophysics Data System (ADS)
Maggio, Emanuele; Kresse, Georg
2016-06-01
The correlation energy of the homogeneous electron gas is evaluated by solving the Bethe-Salpeter equation (BSE) beyond the Tamm-Dancoff approximation for the electronic polarization propagator. The BSE is expected to improve on the random-phase approximation, owing to the inclusion of exchange diagrams. For instance, since the BSE reduces in second order to Møller-Plesset perturbation theory, it is self-interaction free in second order. Results for the correlation energy are compared with quantum Monte Carlo benchmarks and excellent agreement is observed. For low densities, however, we find imaginary eigenmodes in the polarization propagator. To avoid the occurrence of imaginary eigenmodes, an approximation to the BSE kernel is proposed that allows us to completely remove this issue in the low-electron-density region. We refer to this approximation as the random-phase approximation with screened exchange (RPAsX). We show that this approximation even slightly improves upon the standard BSE kernel.
Born Hartree Bethe approximation in the theory of inelastic electron molecule scattering
NASA Astrophysics Data System (ADS)
Kretinin, I. Yu; Krisilov, A. V.; Zon, B. A.
2008-11-01
We propose a new approximation in the theory of inelastic electron atom and electron molecule scattering. Taking into account the completeness property of atomic and molecular wavefunctions, considered in the Hartree approximation, and using Bethe's parametrization for electronic excitations during inelastic collisions via the mean excitation energy, we show that the calculation of the inelastic total integral cross-sections (TICS), in the framework of the first Born approximation, involves only the ground-state wavefunction. The final analytical formula obtained for the TICS, i.e. for the sum of elastic and inelastic ones, contains no adjusting parameters. Calculated TICS for electron scattering by light atoms and molecules (He, Ne, and H2) are in good agreement within the experimental data; results show asymptotic coincidence for heavier ones (Ar, Kr, Xe and N2).
Krasilnikov, M. B. Kudryavtsev, A. A.; Kapustin, K. D.
2014-12-15
It is shown that the local approximation for computing the electron distribution function depends both on the ratio between the energy relaxation length and a characteristic plasma length and on the ratio between heating and ambipolar electric fields. In particular, the local approximation is not valid at the discharge periphery even at high pressure due to the fact that the ambipolar electric field practically always is larger than the heating electric field.
NASA Technical Reports Server (NTRS)
Rule, D. W.
1977-01-01
The first born approximation (FBA) is applied to the calculation of single electron loss cross sections for various ions and atoms containing from one to seven electrons. Screened hydrogenic wave functions were used for the states of the electron ejected from the projectile, and Hartree-Fock elastic and incoherent scattering factors were used to describe the target. The effect of the target atom on the scaling of projectile ionization cross sections with respect to the projectile nuclear charge was explored in the case of hydrogen-like ions. Scaling of the cross section with respect to the target nuclear charge for electron loss by Fe (+25) in collision with neutral atoms ranging from H to Fe is also examined. These results were compared to those of the binary encounter approximation and to the FBA for the case of ionization by completely stripped target ions.
Robust validation of approximate 1-matrix functionals with few-electron harmonium atoms
Cioslowski, Jerzy; Piris, Mario; Matito, Eduard
2015-12-07
A simple comparison between the exact and approximate correlation components U of the electron-electron repulsion energy of several states of few-electron harmonium atoms with varying confinement strengths provides a stringent validation tool for 1-matrix functionals. The robustness of this tool is clearly demonstrated in a survey of 14 known functionals, which reveals their substandard performance within different electron correlation regimes. Unlike spot-testing that employs dissociation curves of diatomic molecules or more extensive benchmarking against experimental atomization energies of molecules comprising some standard set, the present approach not only uncovers the flaws and patent failures of the functionals but, even more importantly, also allows for pinpointing their root causes. Since the approximate values of U are computed at exact 1-densities, the testing requires minimal programming and thus is particularly suitable for rapid screening of new functionals.
Robust validation of approximate 1-matrix functionals with few-electron harmonium atoms
NASA Astrophysics Data System (ADS)
Cioslowski, Jerzy; Piris, Mario; Matito, Eduard
2015-12-01
A simple comparison between the exact and approximate correlation components U of the electron-electron repulsion energy of several states of few-electron harmonium atoms with varying confinement strengths provides a stringent validation tool for 1-matrix functionals. The robustness of this tool is clearly demonstrated in a survey of 14 known functionals, which reveals their substandard performance within different electron correlation regimes. Unlike spot-testing that employs dissociation curves of diatomic molecules or more extensive benchmarking against experimental atomization energies of molecules comprising some standard set, the present approach not only uncovers the flaws and patent failures of the functionals but, even more importantly, also allows for pinpointing their root causes. Since the approximate values of U are computed at exact 1-densities, the testing requires minimal programming and thus is particularly suitable for rapid screening of new functionals.
Gidopoulos, Nikitas I.; Gross, E. K. U.
2014-01-01
A novel treatment of non-adiabatic couplings is proposed. The derivation is based on a theorem by Hunter stating that the wave function of the complete system of electrons and nuclei can be written, without approximation, as a Born–Oppenheimer (BO)-type product of a nuclear wave function, X(R), and an electronic one, ΦR(r), which depends parametrically on the nuclear configuration R. From the variational principle, we deduce formally exact equations for ΦR(r) and X(R). The algebraic structure of the exact nuclear equation coincides with the corresponding one in the adiabatic approximation. The electronic equation, however, contains terms not appearing in the adiabatic case, which couple the electronic and the nuclear wave functions and account for the electron–nuclear correlation beyond the BO level. It is proposed that these terms can be incorporated using an optimized local effective potential. PMID:24516183
Second-order Born approximation for the ionization of molecules by electron and positron impact
Dal Cappello, C.; Rezkallah, Z.; Houamer, S.; Charpentier, I.; Hervieux, P. A.; Ruiz-Lopez, M. F.; Dey, R.; Roy, A. C.
2011-09-15
Second-order Born approximation is applied to study the ionization of molecules. The initial and final states are described by single-center wave functions. For the initial state a Gaussian wave function is used while for the ejected electron it is a distorted wave. Results of the present model are compared with recent (e,2e) experiments on the water molecule. Preliminary results are also presented for the ionization of the thymine molecule by electrons and positrons.
Gerasimov, R. E. Fadin, V. S.
2015-01-15
An analysis of approximations used in calculations of radiative corrections to electron-proton scattering cross section is presented. We investigate the difference between the relatively recent Maximon and Tjon result and the Mo and Tsai result, which was used in the analysis of experimental data. We also discuss the proton form factors ratio dependence on the way we take into account radiative corrections.
NASA Astrophysics Data System (ADS)
Yan, Xin-Zhong
2011-07-01
The discrete Fourier transform is approximated by summing over part of the terms with corresponding weights. The approximation reduces significantly the requirement for computer memory storage and enhances the numerical computation efficiency with several orders without losing accuracy. As an example, we apply the algorithm to study the three-dimensional interacting electron gas under the renormalized-ring-diagram approximation where the Green’s function needs to be self-consistently solved. We present the results for the chemical potential, compressibility, free energy, entropy, and specific heat of the system. The ground-state energy obtained by the present calculation is compared with the existing results of Monte Carlo simulation and random-phase approximation.
Uniform electron gases. II. The generalized local density approximation in one dimension
Loos, Pierre-François Ball, Caleb J.; Gill, Peter M. W.
2014-05-14
We introduce a generalization (gLDA) of the traditional Local Density Approximation (LDA) within density functional theory. The gLDA uses both the one-electron Seitz radius r{sub s} and a two-electron hole curvature parameter η at each point in space. The gLDA reduces to the LDA when applied to the infinite homogeneous electron gas but, unlike the LDA, it is also exact for finite uniform electron gases on spheres. We present an explicit gLDA functional for the correlation energy of electrons that are confined to a one-dimensional space and compare its accuracy with LDA, second- and third-order Møller-Plesset perturbation energies, and exact calculations for a variety of inhomogeneous systems.
Nishikawa, Takeshi
2014-07-15
Most conventional atomic models in a plasma do not treat the effect of the plasma on the free-electron state density. Using a nearest neighbor approximation, the state densities in hydrogenic plasmas for both bound and free electrons were evaluated and the effect of the plasma on the atomic model (especially for the state density of the free electron) was studied. The model evaluates the electron-state densities using the potential distribution formed by the superposition of the Coulomb potentials of two ions. The potential from one ion perturbs the electronic state density on the other. Using this new model, one can evaluate the free-state density without making any ad-hoc assumptions. The resulting contours of the average ionization degree, given as a function of the plasma temperature and density, are shifted slightly to lower temperatures because of the effect of the increasing free-state density.
Rittmeyer, Simon P; Meyer, Jörg; Juaristi, J Iñaki; Reuter, Karsten
2015-07-24
We assess the accuracy of vibrational damping rates of diatomic adsorbates on metal surfaces as calculated within the local-density friction approximation (LDFA). An atoms-in-molecules (AIM) type charge partitioning scheme accounts for intramolecular contributions and overcomes the systematic underestimation of the nonadiabatic losses obtained within the prevalent independent-atom approximation. The quantitative agreement obtained with theoretical and experimental benchmark data suggests the LDFA-AIM scheme as an efficient and reliable approach to account for electronic dissipation in ab initio molecular dynamics simulations of surface chemical reactions. PMID:26252696
Schiwietz, G.; Grande, P. L.
2011-11-15
Recent developments in the theoretical treatment of electronic energy losses of bare and screened ions in gases are presented. Specifically, the unitary-convolution-approximation (UCA) stopping-power model has proven its strengths for the determination of nonequilibrium effects for light as well as heavy projectiles at intermediate to high projectile velocities. The focus of this contribution will be on the UCA and its extension to specific projectile energies far below 100 keV/u, by considering electron-capture contributions at charge-equilibrium conditions.
The second Born approximation for the double ionization of N2 by electron impact
NASA Astrophysics Data System (ADS)
Lamy, P.; Dal Cappello, C.; Charpentier, I.; Ruiz-Lopez, M. F.; Hervieux, P. A.
2016-07-01
In their (e,3e) and (e,3-1e) experiments of the double ionization (DI) of the outermost orbital of N2, Li et al (2012 J. Phys. B: At. Mol. Opt. Phys. 45 135201) recently showed that the process is largely dominated by a two-step-2 mechanism, which is a double interaction of the incident electron with the target. From a theoretical point of view, this should entail the use of the second Born approximation. In the past, very few theoretical calculations had been carried out this way because it requires a difficult numerical triple integration. We propose here to take into account the second Born approximation for the DI of N2 by using the closure approximation. The initial state is described by a single-center wave function derived from the usual multi-center wave function obtained in the self-consistent-field Hartree–Fock method using the linear combination of atomic orbitals-molecular orbital (LCAO-MO) approximation. The final state describes the interaction between each of the ejected electrons and the target by a Coulomb wave and the interaction between the two ejected electrons with the use of the Gamow factor. We calculate differential cross sections using the same kinematic conditions as Li et al (intermediate incident energy about 600 eV) for (e,3e) and (e,3-1e) DI of N2. The results show that the model does not allow a shift of the variation of the four-fold differential cross section near the momentum transfer to be obtained nor its opposite when we include the contribution given by the second Born approximation, as in (e,3-1e) experiments.
Yao, Y. X.; Liu, Jun; Wang, Cai-Zhuang; Ho, Kai-Ming
2014-01-23
We generalized the commonly used Gutzwiller approximation for calculating the electronic structure and total energy of strongly correlated electron systems. In our method, the evaluation of one-body and two-body density matrix elements of the Hamiltonian is simplified using a renormalization approximation to achieve better scaling of the computational effort as a function of system size. To achieve a clear presentation of the concept and methodology, we describe the detailed formalism for a finite hydrogen system with minimal basis set. We applied the correlation matrix renormalization approximation approach to a H_{2} dimer and H_{8} cubic fragment with minimal basis sets, as well as a H_{2} molecule with a large basis set. The results compare favorably with sophisticated quantum chemical calculations. We believe our approach can serve as an alternative way to build up the exchange-correlation energy functional for an improved density functional theory description of systems with strong electron correlations.
Melting curves of metals with excited electrons in the quasiharmonic approximation
NASA Astrophysics Data System (ADS)
Minakov, D. V.; Levashov, P. R.
2015-12-01
We present melting curves of aluminum, copper, and nickel calculated on the basis of a quasiharmonic approximation. The dependence of a phonon density of states on electron temperature is taken into account for both thermodynamic properties and a mean square displacement of atoms. Linear expansion coefficients are strongly dependent on an approximation of the exchange-correlation functional; the generalized gradient approximation gives better results at normal conditions. Using the Lindemann criterion we obtain good agreement with experimental pressure dependences of the melting temperature for Al and Cu. In the case of Ni we consider a spin polarization effect to reproduce a recent first-principle simulation and shock-wave data. However, our melting curve is located significantly higher than static experimental points. We also consider a thermal excitation of electrons in a crystal and investigate the dependence of the melting temperature on the electronic one at normal and elevated densities. Hardening of the crystal structure for all the metals is obtained in our simulation; this effect might be confirmed experimentally owing to a relatively long lifetime of the two-temperature state.
A revised electronic Hessian for approximate time-dependent density functional theory.
Ziegler, Tom; Seth, Michael; Krykunov, Mykhaylo; Autschbach, Jochen
2008-11-14
Time-dependent density functional theory (TD-DFT) at the generalized gradient level of approximation (GGA) has shown systematic errors in the calculated excitation energies. This is especially the case for energies representing electron transitions between two separated regions of space or between orbitals of different spatial extents. It will be shown that these limitations can be attributed to the electronic ground state Hessian G(GGA). Specifically, we shall demonstrate that the Hessian G(GGA) can be used to describe changes in energy due to small perturbations of the electron density (Deltarho), but it should not be applied to one-electron excitations involving the density rearrangement (Deltarho) of a full electron charge. This is in contrast to Hartree-Fock theory where G(HF) has a trust region that is accurate for both small perturbations and one-electron excitations. The large trust radius of G(HF) can be traced back to the complete cancellation of Coulomb and exchange terms in Hartree-Fock (HF) theory representing self-interaction (complete self-interaction cancellation, CSIC). On the other hand, it is shown that the small trust radius for G(GGA) can be attributed to the fact that CSIC is assumed for GGA in the derivation of G(GGA) although GGA (and many other approximate DFT schemes) exhibits incomplete self-interaction cancellation (ISIC). It is further shown that one can derive a new matrix G(R-DFT) with the same trust region as G(HF) by taking terms due to ISIC properly into account. Further, with TD-DFT based on G(R-DFT), energies for state-to-state transitions represented by a one-electron excitation (psi(i)-->psi(a)) are approximately calculated as DeltaE(ai). Here DeltaE(ai) is the energy difference between the ground state Kohn-Sham Slater determinant and the energy of a Kohn-Sham Slater determinant where psi(i) has been replaced by psi(a). We make use of the new Hessian in two numerical applications involving charge-transfer excitations. It is
Niu, Y. F.; Paar, N.; Vretenar, D.; Meng, J.
2011-04-15
We introduce a self-consistent microscopic theoretical framework for modeling the process of electron capture on nuclei in stellar environment, based on relativistic energy density functionals. The finite-temperature relativistic mean-field model is used to calculate the single-nucleon basis and the occupation factors in a target nucleus, and J{sup {pi}}=0{sup {+-}}, 1{sup {+-}}, and 2{sup {+-}} charge-exchange transitions are described by the self-consistent finite-temperature relativistic random-phase approximation. Cross sections and rates are calculated for electron capture on {sup 54,56}Fe and {sup 76,78}Ge in stellar environment, and results compared with predictions of similar and complementary model calculations.
Compton scattering cross section for inner-shell electrons in the relativistic impulse approximation
NASA Astrophysics Data System (ADS)
Stutz, G. E.
2014-01-01
Total Compton scattering cross sections and inelastic scattering factors for bound electron states of several elements have been evaluated in the framework of the relativistic impulse approximation (RIA). The accuracy of different approximate expressions for the singly differential cross section within the RIA is discussed. Accurate evaluations of bound state scattering factors require the use of the full RIA expression. Compton scattering from K-shell electrons dominates over the photoelectric absorption at higher energies. Energy values at which the Compton interaction become the main process of creation of K-shell vacancies are assessed. The role of binding effects in Compton processes at lower energies are clearly evidenced by the computed total cross sections. Calculated K-shell ionization total cross sections, defined as the sum of the photoelectric absorption and the Compton scattering cross sections, are in good agreement with available experimental data. The total Compton cross section for the 2s atomic orbital exhibits a shoulder-like structure, which can be traced back to the node structure of the 2s wave function.
Generalized gradient approximation for the exchange-correlation hole of a many-electron system
Perdew, J.P.; Burke, K.; Wang, Y.
1996-12-01
We construct a generalized gradient approximation (GGA) for the density {ital n}{sub xc}({ital r},{ital r}+{ital u}) at position {ital r}+{ital u} of the exchange-correlation hole surrounding an electron at {ital r}, or more precisely for its system and spherical average {l_angle}{ital n}{sub xc}({ital u}){r_angle}=(4{pi}){sup {minus}1}{integral}{ital d}{Omega}{sub {ital u}}{ital N}{sup {minus}1}{integral}{ital d}{sup 3}{ital r} {ital n}({ital r}){ital n}{sub xc}({ital r},{ital r}+{ital u}). Starting from the second-order density gradient expansion, which involves the local spin densities {ital n}{sub {up_arrow}}({ital r}),{ital n}{sub {down_arrow}}({ital r}) and their gradients {nabla}{ital n}{sub {up_arrow}}({ital r}),{nabla}{ital n}{sub {down_arrow}}({ital r}), we cut off the spurious large-{ital u} contributions to restore those exact conditions on the hole that the local spin density (LSD) approximation respects. Our GGA hole recovers the Perdew-Wang 1991 and Perdew-Burke-Ernzerhof GGA{close_quote}s for the exchange-correlation energy, which therefore respect the same powerful hole constraints as LSD. When applied to real systems, our hole model provides a more detailed test of these energy functionals, and also predicts the observable electron-electron structure factor. {copyright} {ital 1996 The American Physical Society.}
Roemelt, Michael; Guo, Sheng; Chan, Garnet K-L
2016-05-28
A novel approach to strongly contracted N-electron valence perturbation theory (SC-NEVPT2) as a means of describing dynamic electron correlation for quantum chemical density matrix renormalization group (DMRG) calculations is presented. In this approach the strongly contracted perturber functions are projected onto a renormalized Hilbert space. Compared to a straightforward implementation of SC-NEVPT2 with DMRG wavefunctions, the computational scaling and storage requirements are reduced. This favorable scaling opens up the possibility of calculations with larger active spaces. A specially designed renormalization scheme ensures that both the electronic ground state and the perturber functions are well represented in the renormalized Hilbert space. Test calculations on the N2 and [Cu2O2(en)2](2+) demonstrate some key properties of the method and indicate its capabilities. PMID:27250285
NASA Astrophysics Data System (ADS)
Roemelt, Michael; Guo, Sheng; Chan, Garnet K.-L.
2016-05-01
A novel approach to strongly contracted N-electron valence perturbation theory (SC-NEVPT2) as a means of describing dynamic electron correlation for quantum chemical density matrix renormalization group (DMRG) calculations is presented. In this approach the strongly contracted perturber functions are projected onto a renormalized Hilbert space. Compared to a straightforward implementation of SC-NEVPT2 with DMRG wavefunctions, the computational scaling and storage requirements are reduced. This favorable scaling opens up the possibility of calculations with larger active spaces. A specially designed renormalization scheme ensures that both the electronic ground state and the perturber functions are well represented in the renormalized Hilbert space. Test calculations on the N2 and [Cu2O2(en)2]2+ demonstrate some key properties of the method and indicate its capabilities.
Electron-impact excitation of carbon and silicon in the distorted-wave approximation
NASA Technical Reports Server (NTRS)
Pindzola, M. S.; Bhatia, A. K.; Temkin, A.
1977-01-01
The 3P to 1D electron-impact excitation cross section within the ground configuration of both neutral carbon and silicon is calculated in the distorted-wave approximation of the two-state Hartree-Fock coupled equations. An essential element of the present treatment is that orthogonality to core orbitals is not assumed in deriving equations for the scattering orbitals. A local adiabatic polarization potential is also added to the distorted-wave equations. Both elements are necessary in getting good agreement with close-coupling results for carbon to low impacting energies. The agreement is sufficiently good that predictions for silicon should be accurate to within a factor of 2.
NASA Astrophysics Data System (ADS)
Nedzinskas, R.; Karpus, V.; Čechavičius, B.; Kavaliauskas, J.; Valušis, G.
2015-06-01
A simple analytical method for electron energy spectrum calculations of cylindrical quantum dots (QDs) and quantum rods (QRs) is presented. The method is based on a replacement of an actual QD or QR hamiltonian with an approximate one, which allows for a separation of variables. Though this approach is known in the literature, it is essentially expanded in the present paper by taking into account a discontinuity of the effective mass, which is of importance in actual semiconductor heterostructures, e.g., InGaAs QDs or QRs embedded in GaAs matrix. Several examples of InGaAs QDs and QRs are considered—their energy spectrum calculations show that the suggested method yields reliable results both for the ground and excited states. The proposed analytical model is verified by numerical calculations, results of which coincide with an accuracy of ∼1 meV.
Partial Antisymmetry and Approximate Primitive Wave Functions for Interacting Electronic Groups.
NASA Astrophysics Data System (ADS)
Vergenz, Robert Allan
The partial antisymmetry (PA) theorem of W. H. Adams (Chem. Phys. Letters, 68, 511 (1979)) shows that if one can determine an N-electron eigenfunction of a certain non-linear operator, then one can use the eigenfunction, without using full antisymmetry (FA), to calculate an eigenvalue of the Schrodinger Hamiltonian for the system. The operator neither depends on nor commutes with the antisymmetrizer, but involves partial antisymmetrizers. This work provides an initial numerical test of a new approach to calculating approximate interatomic interaction energies based on the PA theorem. Interaction energies were calculated for X ^1Sigma^{+}_ {rm g} Ne_2, Li_2 and Na_2, X^1Sigma^{+} LiNa, X^2Sigma^{+} _{rm g} Li_2 ^{+}, x ^7Sigma ^{+}_{rm u} N_2, x ^3Sigma ^{+}_{rm u} Li_2 and Na_2, x ^3Sigma^{+} LiNa and ionic and covalent configurations of X ^1Sigma^{+} LiF, all at several internuclear distances. Spin-coupled products of single determinants approximated the atomic wave functions, and accurate HF atomic bases were used. Three methods were used: the conventional method based on FA, the PA approach, and a method based on a hybrid set of assumptions. Results were compared with accurate potential curves from the literature. In nine cases of the eleven, including both bonding and repulsive interactions, the PA approximation gave results that were better or roughly the same as those using FA. In these cases there is thus no penalty exacted for the use of PA, though it is shown to be easier to use.
Electronic structure of ordered and disordered alloys in the atomic-sphere approximation
Singh, P.P.; Gonis, A.
1994-12-31
Based on the idea of charge-neutral atomic spheres the authors have calculated the electronic structure of ordered and disordered Cu-Zn, Ni-Pt, and Al-Li alloys using the linear muffin-tin orbital (LMTO) method and the Korringa-Kohn-Rostoker coherent potential approximation (KKR CPA) method in the atomic-sphere approximation (ASA), respectively. The equilibrium lattice constants and the formation energies of ordered alloys obtained with the LMTO-ASA method show that the calculations done with charge-neutral atomic spheres are closer to the experimental results than the conventional equivolume atomic-sphere-type calculations. In the case of disordered alloys, the authors find that charge-neutral atomic spheres are essential for the stability of these alloys within the KKR-ASA CPA method where the Madelung type contribution is neglected. Their results clearly indicate that for disordered alloys any future implementation of a full-potential method within the single-site CPA should be carried out with charge-neutral cells rather than the Wigner-Seitz cells.
NASA Astrophysics Data System (ADS)
Mourenas, D.; Artemyev, A. V.; Agapitov, O. V.; Krasnoselskikh, V.; Li, W.
2014-12-01
The distribution of trapped energetic electrons inside the Earth's radiation belts is the focus of intense studies aiming at better describing the evolution of the space environment in the presence of various disturbances induced by the solar wind or by an enhanced lightning activity. Such studies are usually performed by means of comparisons with full numerical simulations solving the Fokker-Planck quasi-linear diffusion equation for the particle distribution function. Here we present for the first time approximate but realistic analytical solutions for the electron distribution, which are shown to be in good agreement with exact numerical solutions in situations where resonant scattering of energetic electrons by whistler mode hiss, lightning-generated or chorus waves, is the dominant process. Quiet time distributions are well recovered, as well as the evolution of energized relativistic electron distributions during disturbed geomagnetic conditions. It is further shown that careful comparisons between the analytical solutions and measured distributions may allow to infer important bounce- and drift-averaged wave characteristics (such as wave amplitude). It could also help to improve the global understanding of underlying physical phenomena.
NASA Astrophysics Data System (ADS)
Feng, Yue
Plasma is currently a hot topic and it has many significant applications due to its composition of both positively and negatively charged particles. The energy distribution function is important in plasma science since it characterizes the ability of the plasma to affect chemical reactions, affect physical outcomes, and drive various applications. The Boltzmann Transport Equation is an important kinetic equation that provides an accurate basis for characterizing the distribution function---both in energy and space. This dissertation research proposes a multi-term approximation to solve the Boltzmann Transport Equation by treating the relaxation process using an expansion of the electron distribution function in Legendre polynomials. The elastic and 29 inelastic cross sections for electron collisions with nitrogen molecules (N2) and singly ionized nitrogen molecules ( N+2 ) have been used in this application of the Boltzmann Transport Equation. Different numerical methods have been considered to compare the results. The numerical methods discussed in this thesis are the implicit time-independent method, the time-dependent Euler method, the time-dependent Runge-Kutta method, and finally the implicit time-dependent relaxation method by generating the 4-way grid with a matrix solver. The results show that the implicit time-dependent relaxation method is the most accurate and stable method for obtaining reliable results. The results were observed to match with the published experimental data rather well.
NASA Astrophysics Data System (ADS)
Schindlmayr, Arno
2013-02-01
The GW approximation for the electronic self-energy is an important tool for the quantitative prediction of excited states in solids, but its mathematical exploration is hampered by the fact that it must, in general, be evaluated numerically even for very simple systems. In this paper I describe a nontrivial model consisting of two electrons on the surface of a sphere, interacting with the normal long-range Coulomb potential, and show that the GW self-energy, in the absence of self-consistency, can in fact be derived completely analytically in this case. The resulting expression is subsequently used to analyze the convergence of the energy gap between the highest occupied and the lowest unoccupied quasiparticle orbital with respect to the total number of states included in the spectral summations. The asymptotic formula for the truncation error obtained in this way, whose dominant contribution is proportional to the cutoff energy to the power -3/2, may be adapted to extrapolate energy gaps in other systems.
Singh, Kunwar Pal; Arya, Rashmi; Malik, Anil K.
2015-09-14
We have investigated the effect of initial phase on error in electron energy obtained using paraxial approximation to study electron acceleration by a focused laser pulse in vacuum using a three dimensional test-particle simulation code. The error is obtained by comparing the energy of the electron for paraxial approximation and seventh-order correction description of the fields of Gaussian laser. The paraxial approximation predicts wrong laser divergence and wrong electron escape time from the pulse which leads to prediction of higher energy. The error shows strong phase dependence for the electrons lying along the axis of the laser for linearly polarized laser pulse. The relative error may be significant for some specific values of initial phase even at moderate values of laser spot sizes. The error does not show initial phase dependence for a circularly laser pulse.
UAVSAR Active Electronically Scanned Array
NASA Technical Reports Server (NTRS)
Sadowy, Gregory, A.; Chamberlain, Neil F.; Zawadzki, Mark S.; Brown, Kyle M.; Fisher, Charles D.; Figueroa, Harry S.; Hamilton, Gary A.; Jones, Cathleen E.; Vorperian, Vatche; Grando, Maurio B.
2011-01-01
The Uninhabited Airborne Vehicle Synthetic Aperture Radar (UAVSAR) is a pod-based, L-band (1.26 GHz), repeatpass, interferometric, synthetic aperture radar (InSAR) used for Earth science applications. Repeat-pass interferometric radar measurements from an airborne platform require an antenna that can be steered to maintain the same angle with respect to the flight track over a wide range of aircraft yaw angles. In order to be able to collect repeat-pass InSAR data over a wide range of wind conditions, UAVSAR employs an active electronically scanned array (AESA). During data collection, the UAVSAR flight software continuously reads the aircraft attitude state measured by the Embedded GPS/INS system (EGI) and electronically steers the beam so that it remains perpendicular to the flight track throughout the data collection
NASA Astrophysics Data System (ADS)
Galler, Anna; Gunacker, Patrik; Tomczak, Jan; Thunström, Patrik; Held, Karsten
Recently, approaches such as the dynamical vertex approximation (D ΓA) or the dual-fermion method have been developed. These diagrammatic approaches are going beyond dynamical mean field theory (DMFT) by including nonlocal electronic correlations on all length scales as well as the local DMFT correlations. Here we present our efforts to extend the D ΓA methodology to ab-initio materials calculations (ab-initio D ΓA). Our approach is a unifying framework which includes both GW and DMFT-type of diagrams, but also important nonlocal correlations beyond, e.g. nonlocal spin fluctuations. In our multi-band implementation we are using a worm sampling technique within continuous-time quantum Monte Carlo in the hybridization expansion to obtain the DMFT vertex, from which we construct the reducible vertex function using the two particle-hole ladders. As a first application we show results for transition metal oxides. Support by the ERC project AbinitioDGA (306447) is acknowledged.
NASA Astrophysics Data System (ADS)
Armstrong, N. M. R.; Mortimer, K. D.; Kong, T.; Bud'ko, S. L.; Canfield, P. C.; Basov, D. N.; Timusk, T.
2016-04-01
Icosahedral quasicrystals are characterised by the absence of a distinct Drude peak in their low-frequency optical conductivity and the same is true of their crystalline approximants. We have measured the optical conductivity of i-GdCd?, an icosahedral quasicrystal, and two approximants, GdCd? and YCd?. We find that there is a significant difference in the optical properties of these compounds. The approximants have a zero frequency peak, characteristic of a metal, whereas the quasicrystal has a striking minimum. This is the first example where the transport properties of a quasicrystal and its approximant differ in such a fundamental way. Using a generalised Drude model introduced by Mayou, we find that our data are well described by this model. It implies that the quantum diffusion of electron wave packets through the periodic and quasiperiodic lattices is responsible for these dramatic differences: in the approximants, the transport is superdiffusive, whereas the quasicrystals show subdiffusive motion of the electrons.
Serov, Vladislav V.
2011-12-15
We have implemented the paraxial approximation followed by the time-dependent Hartree-Fock method with a frozen core for the single impact ionization of atoms and two-atomic molecules. It reduces the original scattering problem to the solution of a five-dimensional time-dependent Schroedinger equation. Using this method, we calculated the multifold differential cross section of the impact single ionization of the helium atom, the hydrogen molecule, and the nitrogen molecule from the impact of intermediate-energy electrons. Our results for He and H{sub 2} are quite close to the experimental data. Surprisingly, for N{sub 2} the agreement is good for the paraxial approximation combined with first Born approximation but worse for pure paraxial approximation, apparently because of the insufficiency of the frozen-core approximation.
Gosling, J.T.; Bame, S.J.; Feldman, W.C.; Mcomas, D.J.; Phillips, J.L. ); Goldstein, B.E. )
1993-11-05
Enhanced fluxes of suprathermal electrons are commonly observed upstream of corotating forward and reverse shocks in the solar wind at heliocentric distances beyond [approximately]2 AU by the Los Alamos plasma experiment on Ulysses. The average duration of these events, which are most intense immediately upstream from the shocks and which fade with increasing distance from them, is [approximately]2.4 days near 5 AU. These events are caused by the leakage of shock-heated electrons into the upstream region. The upstream regions of these shocks face back toward the SUN along the interplanetary magnetic field, so these leaked electrons commonly counterstream relative to the normal solar wind electron heat flux. The observations suggest that conservation of magnetic moment and scattering typically limit the sunward propagation of these electrons as beams to field-aligned distances of [approximately]15 AU. Although it seems unlikely that these shock-associated events are an important source of counterstreaming events near 1 AU, remnants of the backstreaming beams may contribute importantly to the diffuse solar wind halo electron population there. 13 refs., 3 figs.
NASA Technical Reports Server (NTRS)
Gosling, J. T.; Bame, S. J.; Feldman, W. C.; Mccomas, D. J.; Phillips, J. L.; Goldstein, B. E.
1993-01-01
Enhanced fluxes of suprathermal electrons are commonly observed upstream of corotating forward and reverse shocks in the solar wind at heliocentric distances beyond approximately 2 AU by the Los Alamos plasma experiment on Ulysses. The average duration of these events, which are most intense immediately upstream from the shocks and which fade with increasing distance from them, is approximately 2.4 days near 5 AU. These events are caused by the leakage of shock-heated electrons into the upstream region. The upstream regions of these shocks face back toward the Sun along the interplanetary magnetic field, so these leaked electrons commonly counterstream relative to the normal solar wind electron heat flux. The observations suggest that conservation of magnetic moment and scattering typically limit the sunward propagation of these electrons as beams to field-aligned distances of approximately 15 AU. Although it seems unlikely that these shock-associated events are an important source of counterstreaming events near 1 AU, remnants of the backstreaming beams may contribute importantly to the diffuse solar wind halo electron population there.
UAVSAR Active Electronically-Scanned Array
NASA Technical Reports Server (NTRS)
Sadowy, Gregory; Brown, Kyle; Chamberlain, Neil; Figueroa, Harry; Fisher, Charlie; Grando, Maurio; Hamilton, Gary; Vorperian, Vatche; Zawadzki, Mark
2010-01-01
The Uninhabited Airborne Vehicle Synthetic Aperture Radar (UAVSAR) L-band (1.2-1.3 GHz) repeat pass, interferometric synthetic aperture radar (InSAR) used for Earth science applications. Using complex radar images collected during separate passes on time scales of hours to years, changes in surface topography can be measured. The repeat-pass InSAR technique requires that the radar look angle be approximately the same on successive passes. Due to variations in aircraft attitude between passes, antenna beam steering is required to replicate the radar look angle. This paper describes an active, electronically steered array (AESA) that provides beam steering capability in the antenna azimuth plane. The array contains 24 transmit/receive modules generating 2800 W of radiated power and is capable of pulse-to-pulse beam steering and polarization agility. Designed for high reliability as well as serviceability, all array electronics are contained in single 178cm x 62cm x 12 cm air-cooled panel suitable for operation up 60,000 ft altitude.
NASA Technical Reports Server (NTRS)
Rule, D. W.
1977-01-01
The first Born approximation (FBA) is applied to the calculation of single-electron-loss cross sections for various ions and atoms containing from one to seven electrons. Screened hydrogenic wave functions are used for the states of the electron ejected from the projectile, and Hartree-Fock elastic and incoherent scattering factors are used to describe the target. The effect of the target atom on the scaling of projectile ionization cross sections with respect to the projectile nuclear charge is explored in the case of hydrogenlike ions. Also examined is the scaling of the cross section with respect to the target nuclear charge for electron loss by Fe(25+) in collision with neutral atoms ranging from H to Fe. These results are compared with those of the binary-encounter approximation (BEA) and with the FBA for the case of ionization by completely stripped target ions. Electron-loss cross sections are also calculated for the ions O(i+) (i = 3-7) and N(i+) (i = 0-6) in collision with He targets in the energy range of approximately 0.1 to 100 MeV/nucleon. These results are found to be in excellent agreement with the available data near the peak of the ionization cross section.
J. Adam, Jr.; Franz Gross; Sabine Jeschonnek; Paul Ulmer; J.W. Van Orden
2002-05-01
Using the covariant spectator theory and the transversity formalism, the unpolarized, coincidence cross section for deuteron electrodisintegration, d(e, e'p)n, is studied. The relativistic kinematics are reviewed, and simple theoretical formulae for the relativistic impulse approximation (RIA) are derived and discussed. Numerical predictions for the scattering in the high Q{sup 2} region obtained from the RIA and five other approximations are presented and compared. We concluded that measurements of the unpolarized coincidence cross section and the asymmetry A{sub phi}, to an accuracy that will distinguish between different theoretical models, is feasible over most of the wide kinematic range accessible at Jefferson Lab.
Liu, Fang; Lin, Lin; Vigil-Fowler, Derek; Lischner, Johannes; Kemper, Alexander F.; Sharifzadeh, Sahar; Jornada, Felipe H. da; Deslippe, Jack; Yang, Chao; and others
2015-04-01
We present a numerical integration scheme for evaluating the convolution of a Green's function with a screened Coulomb potential on the real axis in the GW approximation of the self energy. Our scheme takes the zero broadening limit in Green's function first, replaces the numerator of the integrand with a piecewise polynomial approximation, and performs principal value integration on subintervals analytically. We give the error bound of our numerical integration scheme and show by numerical examples that it is more reliable and accurate than the standard quadrature rules such as the composite trapezoidal rule. We also discuss the benefit of using different self energy expressions to perform the numerical convolution at different frequencies.
Chalupský, Jakub Yanai, Takeshi
2013-11-28
The derivation, implementation, and validation of a new approximation to the two-electron spin–orbit coupling (SOC) terms is reported. The approximation, referred to as flexible nuclear screening spin–orbit, is based on the effective one-electron spin–orbit operator and accounts for two-electron SOC effects by screening nuclear charges. A highly flexible scheme for the nuclear screening is developed, mainly using parameterization based on ab initio atomic SOC calculations. Tabulated screening parameters are provided for contracted and primitive Gaussian-type basis functions of the ANO-RCC basis set for elements from H to Cm. The strategy for their adaptation to any other Gaussian basis set is presented and validated. A model to correct for the effect of splitting of transition metal d orbitals on their SOC matrix elements is introduced. The method is applied to a representative set of molecules, and compared to exact treatment and other approximative approaches at the same level of relativistic theory. The calculated SOC matrix elements are in very good agreement with their “exact” values; deviation below 1% is observed on average. The presented approximation is considered to be generally applicable, simple to implement, highly efficient, and accurate.
NASA Astrophysics Data System (ADS)
Chalupský, Jakub; Yanai, Takeshi
2013-11-01
The derivation, implementation, and validation of a new approximation to the two-electron spin-orbit coupling (SOC) terms is reported. The approximation, referred to as flexible nuclear screening spin-orbit, is based on the effective one-electron spin-orbit operator and accounts for two-electron SOC effects by screening nuclear charges. A highly flexible scheme for the nuclear screening is developed, mainly using parameterization based on ab initio atomic SOC calculations. Tabulated screening parameters are provided for contracted and primitive Gaussian-type basis functions of the ANO-RCC basis set for elements from H to Cm. The strategy for their adaptation to any other Gaussian basis set is presented and validated. A model to correct for the effect of splitting of transition metal d orbitals on their SOC matrix elements is introduced. The method is applied to a representative set of molecules, and compared to exact treatment and other approximative approaches at the same level of relativistic theory. The calculated SOC matrix elements are in very good agreement with their "exact" values; deviation below 1% is observed on average. The presented approximation is considered to be generally applicable, simple to implement, highly efficient, and accurate.
NASA Astrophysics Data System (ADS)
Predota, Milan; Cummings, Peter T.; Chialvo, Ariel A.
The adiabatic nuclear and electronic sampling method (ANES), originally formulated as an efficient Monte Carlo algorithm for systems with fluctuating charges, is applied to the simulation of a polarizable water model with induced dipole moments. Structural, thermodynamic and dipolar properties obtained by ANES and a newer algorithm, the pair approximation for polarization interaction (PAPI), are compared with full iteration. With the best parameters, the inaccuracy of both approximate methods was found to be comparable with the uncertainty of the full iteration. The PAPI method with iteration radius equal to the second minimum of the oxygen-oxygen correlation function is, depending on the convergence tolerance, 10-15 times faster than the full iteration for 256 molecules, and yields very accurate structure and thermodynamics with deviation about 0.3%. When the iteration radius is increased to the cutoff distance, exact results are recovered at the cost of decreased efficiency. The ANES method with small nuclear displacements proved to inefficiently sample the configurational space. Simulations at low electronic temperatures with large nuclear displacements are inaccurate for up to 100 electronic moves, and increasing this number would make the simulations as slow as the full iteration. The most accurate and efficient adiabatic ANES simulations are those with infinite electronic temperature, large nuclear displacements and 1-10 electronic moves. The extra freedom of induced dipoles in the ANES method at high electronic temperatures modifies the observed dipolar properties; however, the question of whether the dielectric constant is also modified needs further consideration.
Two-photon approximation in the theory of electron recombination in hydrogen
Solovyev, D.; Labzowsky, L.
2010-06-15
A rigorous quantum electrodynamics theory of the multiphoton decay of excited states in a hydrogen atom is presented. The ''two-photon'' approximation is formulated which is limited by the one- and two-photon transitions including cascade transitions with two-photon links. This may be helpful for the strict description of the recombination process in a hydrogen atom and, in principle, for the history of hydrogen recombination in the early universe.
Collective motion of two-electron atom in hyperspherical adiabatic approximation
Mohamed, A. S.; Nikitin, S. I.
2015-03-30
This work is devoted to calculate bound states in the two-electron atoms. The separation of variables has carried out in hyper spherical coordinate system (R, θ, α). Assuming collective motion of the electrons, where the hper angle (α∼π/4) and (θ∼π). The separation of the rotational variables leads to system of differential equations with more simple form as compared with non restricted motion. Energy of doubly excited P{sup e} and D{sup 0} states are calculated semi classically by using quantization condition of Bohr -Somerfield. The results compared with previously published data.
Kilcrease, D. P.; Brookes, S.
2013-08-19
The modeling of NLTE plasmas requires the solution of population rate equations to determine the populations of the various atomic levels relevant to a particular problem. The equations require many cross sections for excitation, de-excitation, ionization and recombination. Additionally, a simple and computational fast way to calculate electron collisional excitation cross-sections for ions is by using the plane-wave Born approximation. This is essentially a high-energy approximation and the cross section suffers from the unphysical problem of going to zero near threshold. Various remedies for this problem have been employed with varying degrees of success. We present a correction procedure formore » the Born cross-sections that employs the Elwert–Sommerfeld factor to correct for the use of plane waves instead of Coulomb waves in an attempt to produce a cross-section similar to that from using the more time consuming Coulomb Born approximation. We compare this new approximation with other, often employed correction procedures. Furthermore, we also look at some further modifications to our Born Elwert procedure and its combination with Y.K. Kim's correction of the Coulomb Born approximation for singly charged ions that more accurately approximate convergent close coupling calculations.« less
Kilcrease, D. P.; Brookes, S.
2013-08-19
The modeling of NLTE plasmas requires the solution of population rate equations to determine the populations of the various atomic levels relevant to a particular problem. The equations require many cross sections for excitation, de-excitation, ionization and recombination. Additionally, a simple and computational fast way to calculate electron collisional excitation cross-sections for ions is by using the plane-wave Born approximation. This is essentially a high-energy approximation and the cross section suffers from the unphysical problem of going to zero near threshold. Various remedies for this problem have been employed with varying degrees of success. We present a correction procedure for the Born cross-sections that employs the Elwert–Sommerfeld factor to correct for the use of plane waves instead of Coulomb waves in an attempt to produce a cross-section similar to that from using the more time consuming Coulomb Born approximation. We compare this new approximation with other, often employed correction procedures. Furthermore, we also look at some further modifications to our Born Elwert procedure and its combination with Y.K. Kim's correction of the Coulomb Born approximation for singly charged ions that more accurately approximate convergent close coupling calculations.
Nisius, D.; Janssens, R.V.F.; Ahmad, I.
1995-08-01
The FMA has proven to be an ideal instrument for the detailed study of the decay of microsecond isomers behind the focal plane following mass selection. In reactions leading to the population of nuclei with isomeric lifetimes longer than their flight time through the device, decay gamma rays and conversion electrons can be detected in an environment free from the backgrounds of prompt radiation and delta electrons. This was a very successful technique to study proton (h{sub 11/2}){sup n} seniority isomers in nuclei with Z > 64 and N {approximately} 82. Since isomeric decay gamma rays are emitted isotropically, conversion electrons are essential for the assignment of multipolarities in these nuclei. Furthermore, the low-energy transitions that depopulate isomeric states are typically highly converted and can escape gamma-ray detection, but they can be identified by their conversion electrons.
Lagrangian approach to the semirelativistic electron dynamics in the mean-field approximation
NASA Astrophysics Data System (ADS)
Dixit, Anant; Hinschberger, Yannick; Zamanian, Jens; Manfredi, Giovanni; Hervieux, Paul-Antoine
2013-09-01
We derive a mean-field model that is based on a two-component Pauli-like equation and incorporates quantum, spin, and relativistic effects up to second order in 1/c. Using a Lagrangian approach, we obtain the self-consistent charge and current densities that act as sources in the Maxwell equations. A physical interpretation is provided for the second-order corrections to the sources. The Maxwell equations are also expanded to the same order. The resulting self-consistent model constitutes a suitable semirelativistic approximation to the full Dirac-Maxwell equations.
NASA Astrophysics Data System (ADS)
Gráf, Lukáš; Čížek, Martin
2014-09-01
A two dimensional model for the electron interaction with molecular vibrations in molecular junctions is proposed. Alternatively the model can be applied to tunneling through a cylindrical nano-structure. The transmission function is calculated accurately numerically. The exact results are then compared with various approximations: (1) completely frozen vibrations for very light molecule, (2) Chase approximation for very heavy molecule, and (3) discrete-state-in-continuum model in resonant regime. The validity of these approximations is discussed in terms of the characteristic time-scales and coupling strengths. The excitation of the vibrational degree of freedom and the emergence of prominent threshold structures in the strong coupling regime are discussed in more details.
Dynamic screening of an ion in a degenerate electron gas within the second-order Born approximation
NASA Astrophysics Data System (ADS)
Nersisyan, Hrachya B.; Fernández-Varea, José M.; Arista, Néstor R.
2015-07-01
The dynamic Friedel sum rule (FSR) is derived within the second-order Born (B2) approximation for an ion that moves in a fully degenerate electron gas and for an arbitrary spherically-symmetric electron-ion interaction potential. This results in an implicit equation for the dynamic B2 screening parameter which depends on the ion atomic number Z1 unlike the first-order Born (B1) dynamic screening parameter reported earlier by some authors. Furthermore, for typical metallic densities our analytical results for the Yukawa and hydrogenic potentials are compared, for both positive and negative ions, to the exact screening parameters calculated self-consistently by imposing the exact dynamic FSR requirement to the scattering phase shifts. The B1 and B2 screening parameters agree excellently with the exact values at large velocities, while at moderate and low velocities the B1 approximation deviates from the exact solution whereas the B2 approximation still remains close to it. In addition, a Padé approximant to the Born series yields a further improvement of the perturbative approach, showing an excellent agreement on the whole velocity range in the case of antiprotons.
Electron-deuteron scattering in the equal-time formalism: beyond the impulse approximation
D.R. Phillips; Stephen Wallace; N.K. Devine
2004-11-01
Using a three-dimensional formalism that includes relativistic kinematics, the effects of negative-energy states, approximate boosts of the two-body system, and current conservation, we calculate the electromagnetic form factors of the deuteron up to Q{sup 2} of 4 GeV{sup 2}. This is done using a dynamical boost for two-body systems with spin. We first compute form factors in impulse approximation, but then also add an isoscalar meson-exchange current of pion range that involves the gamma-pi contact operator associated with pseudovector pi-N coupling. We also consider effects of the rho-pi-gamma meson-exchange current. The experimentally measured quantities A, B, and t20 are calculated over the kinematic range probed in recent Jefferson Laboratory experiments. The rho-pi-gamma meson-exchange current provides significant strength in A at large Q{sup 2} and the gamma-pi contact-term exchange current shifts t20, providing good agreement with the JLab data. Relativistic effects and the gamma-pi meson-exchange current do not provide an explanation of the B observable, but the rho-pi-gamma current could help to provide agreement if a nonstandard value is used for the tensor rho-N coupling that enters this contribution.
Spencer, James S; Thom, Alex J W
2016-02-28
We describe further details of the stochastic coupled cluster method and a diagnostic of such calculations, the shoulder height, akin to the plateau found in full configuration interaction quantum Monte Carlo. We describe an initiator modification to stochastic coupled cluster theory and show that initiator calculations can at times be extrapolated to the unbiased limit. We apply this method to the 3D 14-electron uniform electron gas and present complete basis set limit values of the coupled cluster singles and doubles (CCSD) and previously unattainable coupled cluster singles and doubles with perturbative triples (CCSDT) correlation energies for up to r(s) = 2, showing a requirement to include triple excitations to accurately calculate energies at high densities. PMID:26931682
NASA Astrophysics Data System (ADS)
Korotin, M. A.; Pchelkina, Z. V.; Skorikov, N. A.; Efremov, A. V.; Anisimov, V. I.
2016-07-01
Based on the coherent potential approximation, the method of calculating the electronic structure of nonstoichiometric and hyperstoichiometric compounds with strong electron correlations and spin-orbit coupling has been developed. This method can be used to study both substitutional and interstitial impurities, which is demonstrated based on the example of the hyperstoichiometric UO2.12 compound. The influence of the coherent potential on the electronic structure of compounds has been shown for the nonstoichiometric UO1.87 containing vacancies in the oxygen sublattice as substitutional impurities, for stoichiometric UO2 containing vacancies in the oxygen sublattice and oxygen as an interstitial impurity, and for hyperstoichiometric UO2.12 with excess oxygen also as interstitial impurity. In the model of the uniform distribution of impurities, which forms the basis of the coherent potential approximation, the energy spectrum of UO2.12 has a metal-like character.
Electron-Phonon Coupling and Energy Flow in a Simple Metal beyond the Two-Temperature Approximation
NASA Astrophysics Data System (ADS)
Waldecker, Lutz; Bertoni, Roman; Ernstorfer, Ralph; Vorberger, Jan
2016-04-01
The electron-phonon coupling and the corresponding energy exchange are investigated experimentally and by ab initio theory in nonequilibrium states of the free-electron metal aluminium. The temporal evolution of the atomic mean-squared displacement in laser-excited thin freestanding films is monitored by femtosecond electron diffraction. The electron-phonon coupling strength is obtained for a range of electronic and lattice temperatures from density functional theory molecular dynamics simulations. The electron-phonon coupling parameter extracted from the experimental data in the framework of a two-temperature model (TTM) deviates significantly from the ab initio values. We introduce a nonthermal lattice model (NLM) for describing nonthermal phonon distributions as a sum of thermal distributions of the three phonon branches. The contributions of individual phonon branches to the electron-phonon coupling are considered independently and found to be dominated by longitudinal acoustic phonons. Using all material parameters from first-principles calculations except the phonon-phonon coupling strength, the prediction of the energy transfer from electrons to phonons by the NLM is in excellent agreement with time-resolved diffraction data. Our results suggest that the TTM is insufficient for describing the microscopic energy flow even for simple metals like aluminium and that the determination of the electron-phonon coupling constant from time-resolved experiments by means of the TTM leads to incorrect values. In contrast, the NLM describing transient phonon populations by three parameters appears to be a sufficient model for quantitatively describing electron-lattice equilibration in aluminium. We discuss the general applicability of the NLM and provide a criterion for the suitability of the two-temperature approximation for other metals.
NASA Astrophysics Data System (ADS)
Kalenkov, Mikhail S.; Zaikin, Andrei D.
2015-07-01
We extend the quasiclassical formalism for diffusive superconductors by deriving anisotropic (gradient) corrections to the Usadel equation. We demonstrate that in a number of physical situations such corrections may play a crucial role, being responsible for the effects which cannot be recovered within the standard Usadel approximation. One of them is the so-called photoelectric effect in superconductors and superconducting-normal (SN) hybrid structures. Provided a superconducting part of the system is irradiated by an external ac electromagnetic field, the charge imbalance develops and a nonvanishing dc voltage is induced across the SN interface. In the presence of magnetic impurities in a superconductor the magnitude of this effect becomes large and can easily be detected in modern experiments.
NASA Astrophysics Data System (ADS)
Hahn, Torsten; Liebing, Simon; Kortus, Jens; Pederson, Mark
The correction of the self-interaction error that is inherent to all standard density functional theory (DFT) calculations is an object of increasing interest. We present our results on the application of the recently developed Fermi-orbital based approach for the self-interaction correction (FO-SIC) to a set of different molecular systems. Our study covers systems ranging from simple diatomic to large organic molecules. Our focus lies on the direct estimation of the ionization potential from orbital eigenvalues and on the ordering of electronic levels in metal-organic molecules. Further, we show that the Fermi orbital positions in structurally similar molecules appear to be transferable. Support by DFG FOR1154 is greatly acknowledged.
NASA Astrophysics Data System (ADS)
Sandalov, I.; Lundin, U.; Eriksson, O.
The diagrammatic strong-coupling perturbation theory (SCPT) for correlated electron systems is developed for intersite Coulomb interaction and for a nonorthogonal basis set. The construction is based on iterations of exact closed equations for many-electron Green functions (GFs) for Hubbard operators in terms of functional derivatives with respect to external sources. The graphs, which do not contain the contributions from the fluctuations of the local population numbers of the ion states, play a special role: a one-to-one correspondence is found between the subset of such graphs for the many-electron GFs and the complete set of Feynman graphs of weak-coupling perturbation theory (WCPT) for single-electron GFs. This fact is used for formulation of the approximation of renormalized Fermions (ARF) in which the many-electron quasi-particles behave analogously to normal Fermions. Then, by analyzing: (a) Sham's equation, which connects the self-energy and the exchange-correlation potential in density functional theory (DFT); and (b) the Galitskii and Migdal expressions for the total energy, written within WCPT and within ARF SCPT, a way we suggest a method to improve the description of the systems with correlated electrons within the local density approximation (LDA) to DFT. The formulation, in terms of renormalized Fermions LDA (RF LDA), is obtained by introducing the spectral weights of the many-electron GFs into the definitions of the charge density, the overlap matrices, effective mixing and hopping matrix elements, into existing electronic structure codes, whereas the weights themselves have to be found from an additional set of equations. Compared with LDA+U and self-interaction correction (SIC) methods, RF LDA has the advantage of taking into account the transfer of spectral weights, and, when formulated in terms of GFs, also allows for consideration of excitations and nonzero temperature. Going beyond the ARF SCPT, as well as RF LDA, and taking into account the
Wasilewski, J.; Staemmler, V.; Koch, S.
1988-08-01
Extensive ab initio calculations at coupled-electron-pair approximation and multireference configuration interaction levels have been performed for the two lowest states X /sup 2/..sigma../sup +/ and A/sup 2/Pi of HeNe/sup +/. Spin-orbit coupling has been included on a semiempirical basis in order to account for the strong mixing between the X /sup 2/..sigma../sub 1/2//sup +/ and A/sub 2//sup 2/Pi/sub 1/2/ components, which influences the properties of both these states in the experimentally observed region at large internuclear distances.
NASA Astrophysics Data System (ADS)
Kellö, Vladimir; Sadlej, Andrzej J.; Hess, Bernd A.
1996-08-01
Relativistic effects and electron correlation effects on the dipole moments of the coinage metal hydrides are investigated and compared employing one-component (scalar) relativistic approximations based on the mass-velocity and Darwin operator and, alternatively, the Douglas-Kroll-transformed spin-averaged no-pair Hamiltonian. The former of the two operators is found to perform quite accurately for CuH and AgH. For AuH the limits of the Pauli approximation seem to be reached, as can be inferred from a comparison with the values obtained within the spin-averaged Douglas-Kroll no-pair formalism. The coupled cluster calculations in the Douglas-Kroll no-pair approximation for relativistic effects establish the dipole moment values of the coinage metal hydrides as equal to 1.05 a.u. for CuH, 1.14 a.u. for AgH and 0.52 for AuH. The corresponding non-relativistic results are 1.14 a.u., 1.36 a.u., and 1.22 a.u., respectively. Some formal problems arising in applications of the Douglas-Kroll no-pair approximation are discussed. It is shown that the Hellmann-Feynman theorem leads to a rather complicated form of the first-order energy change due to external perturbation. The usual expectation value formula is, however, valid through terms proportional to 1/c4 and can be used in most applications. The invariance property with respect to a shift in the external potential is addressed for the Douglas-Kroll no-pair approximation in a finite basis set.
NASA Astrophysics Data System (ADS)
Korona, Tatiana
2012-02-01
A possibility to calculate electron affinities (EAs) by a software devised for electron excitations is exploited to examine the accuracy of a partly local EA-EOM-CCSD method. In the proposed approach local approximations are applied to the ground-state coupled cluster wave function, while the EAs themselves are obtained in a full configurational space. The results of a numerical test for 14 molecules show that already with standard local settings the method reproduces the nonlocal EAs with the average error of 0.009 eV. Since the EA-EOM step of the calculation requires less computational resources than the computation of the CCSD ground state, the proposed hybrid approach can become a valuable tool for obtaining the EAs for molecules, which are too large for a canonical CCSD calculation, but still small enough for the EA-EOM step to be performed in a nonlocal way.
NASA Technical Reports Server (NTRS)
Bickers, N. E.; Scalapino, D. J.; White, S. R.
1989-01-01
A semianalytical approach is described for strongly correlated electronic systems which satisfies microscopic conservation laws, treats strong frequency and momentum dependences, and provides information on both static and dynamic properties. This approach may be used to treat large systems and temperatures lower than those currently accessible to finite-temperature quantum Monte Carlo techniques. Examples of such systems include heavy-electron compounds, organic Bechegaard salts, bis-(ethylenedithiolo)-TTF superconductors, and the oxide superconductors. The technique is based on the derivation and self-consistent solution of infinite-order conserving approximations. The technique is used to derive a low-temperature phase diagram and dynamic correlation functions for the two-dimensional Hubbard lattice model.
Samuha, Shmuel; Mugnaioli, Enrico; Grushko, Benjamin; Kolb, Ute; Meshi, Louisa
2014-12-01
The crystal structure of the novel Al77Rh15Ru8 phase (which is an approximant of decagonal quasicrystals) was determined using modern direct methods (MDM) applied to automated electron diffraction tomography (ADT) data. The Al77Rh15Ru8 E-phase is orthorhombic [Pbma, a = 23.40 (5), b = 16.20 (4) and c = 20.00 (5) Å] and has one of the most complicated intermetallic structures solved solely by electron diffraction methods. Its structural model consists of 78 unique atomic positions in the unit cell (19 Rh/Ru and 59 Al). Precession electron diffraction (PED) patterns and high-resolution electron microscopy (HRTEM) images were used for the validation of the proposed atomic model. The structure of the E-phase is described using hierarchical packing of polyhedra and a single type of tiling in the form of a parallelogram. Based on this description, the structure of the E-phase is compared with that of the ε6-phase formed in Al-Rh-Ru at close compositions. PMID:25449623
NASA Astrophysics Data System (ADS)
Cassam-Chenaï, Patrick; Suo, Bingbing; Liu, Wenjian
2015-07-01
We introduce the electron-nucleus mean-field configuration-interaction (EN-MFCI) approach. It consists in building an effective Hamiltonian for the electrons taking into account a mean field due to the nuclear motion and, conversely, in building an effective Hamiltonian for the nuclear motion taking into account a mean field due to the electrons. The eigenvalue problems of these Hamiltonians are solved in basis sets giving partial eigensolutions for the active degrees of freedom (DOF's), that is to say, either for the electrons or for nuclear motion. The process can be iterated or electron and nuclear motion DOF's can be contracted in a CI calculation. In the EN-MFCI reduction of the molecular Schrödinger equation to an electronic and a nuclear problem, the electronic wave functions do not depend parametrically upon nuclear coordinates. So, it is different from traditional adiabatic methods. Furthermore, when contracting electronic and nuclear functions, a direct product basis set is built in contrast with methods which treat electrons and nuclei on the same footing, but where electron-nucleus explicitly correlated coordinates are used. Also, the EN-MFCI approach can make use of the partition of molecular DOF's into translational, rotational, and internal DOF's. As a result, there is no need to eliminate translations and rotations from the calculation, and the convergence of vibrational levels is facilitated by the use of appropriate internal coordinates. The method is illustrated on diatomic molecules.
Production of radioisotopes by direct electron activation.
Weeks, K J; O'Shea, P G
1998-04-01
High-energy electrons bombarded on materials can induce radioactivity by either directly knocking out neutrons or by first converting a fraction of the electron kinetic energy into electromagnetic energy, with subsequent neutron emission induced by the photons produced. The purpose of this paper was to develop a calculation method for estimating neutron emission and radionuclide production by high-energy (15-25 MeV) electrons directly interacting with a nucleus. The reaction (e,n) is considered using the method of virtual photons. The cross section for electron bombardment of lead, tantalum, rhenium, and tungsten targets is calculated. The electron cross sections are roughly 100 times less than the corresponding photon cross sections. The cross section increases monotonically with incident energy. A traveling wave linear accelerator was used for a qualitative test of the magnitude and energy dependence of the calculated cross sections. Tantalum was bombarded with electrons and the resultant emission of neutrons was inferred from the induced activation of 180Ta. The energy dependence and magnitude of the calculated electron cross sections agree with experiment within experimental uncertainties. It is concluded that accurate estimates of electron activation via the direct process is possible. PMID:9571615
NASA Astrophysics Data System (ADS)
Pederson, Mark R.; Heaton, Richard A.; Harrison, Joseph G.
1989-01-01
The uniform-density electron gas is studied within the framework of the Wannier-function (WF) formulation of the self-interaction-corrected local-spin-density approximation (SIC-LSD). While the results of the present work follow rigorously from a variational formulation, they may also be qualitatively understood in terms of the local-bonding-site concept introduced by Mott in his theory of the metal-insulator transition. SIC-LSD admits metallic-state solutions at ordinary electron densities just as in traditional LSD theory. The result of introducing SIC to the metallic state is an overall downward shift of the LSD eigenvalues. This shift is largest for states near k=0 and vanishes for states near the Fermi energy ɛF. As such, the orbital energies at ɛF are found to be in exact agreement with both the exchange-only version of LSD and Hartree-Fock (HF). Beyond metallic-state solutions, this formulation of SIC-LSD also admits insulator solutions at very low electron densities and may thus have important application to the problem of Wigner crystallization.
NASA Astrophysics Data System (ADS)
Bensadiq, A.; Zaari, H.; Benyoussef, A.; El Kenz, A.
2016-09-01
Using the density functional theory, the electronic structure; density of states, band structure and exchange couplings of Tb Ni4 Si compound have been investigated. Magnetic and magnetocaloric properties of this material have been studied using Monte Carlo Simulation (MCS) and Mean Field Approximation (MFA) within a three dimensional Ising model. We calculated the isothermal magnetic entropy change, adiabatic temperature change and relative cooling power (RCP) for different external magnetic field and temperature. The highest obtained isothermal magnetic entropy change is of -14.52 J kg-1 K-1 for a magnetic field of H=4 T. The adiabatic temperature reaches a maximum value equal to 3.7 K and the RCP maximum value is found to be 125.12 J kg-1 for a field magnetic of 14 T.
Electricity/Electronics Systems. Laboratory Activities.
ERIC Educational Resources Information Center
Sutherland, Barbara, Ed.
This electricity/electronics guide provides teachers with learning activities for secondary students. Introductory materials include an instructional planning outline and worksheet, an outline of essential elements, a list of objectives, a course description, and a content outline. The guide contains 35 modules on the following topics: electrical…
NASA Astrophysics Data System (ADS)
Kurzweil, Yair; Head-Gordon, Martin
2009-07-01
We develop a method that can constrain any local exchange-correlation potential to preserve basic exact conditions. Using the method of Lagrange multipliers, we calculate for each set of given Kohn-Sham orbitals a constraint-preserving potential which is closest to the given exchange-correlation potential. The method is applicable to both the time-dependent (TD) and independent cases. The exact conditions that are enforced for the time-independent case are Galilean covariance, zero net force and torque, and Levy-Perdew virial theorem. For the time-dependent case we enforce translational covariance, zero net force, Levy-Perdew virial theorem, and energy balance. We test our method on the exchange (only) Krieger-Li-Iafrate (xKLI) approximate-optimized effective potential for both cases. For the time-independent case, we calculated the ground state properties of some hydrogen chains and small sodium clusters for some constrained xKLI potentials and Hartree-Fock (HF) exchange. The results (total energy, Kohn-Sham eigenvalues, polarizability, and hyperpolarizability) indicate that enforcing the exact conditions is not important for these cases. On the other hand, in the time-dependent case, constraining both energy balance and zero net force yields improved results relative to TDHF calculations. We explored the electron dynamics in small sodium clusters driven by cw laser pulses. For each laser pulse we compared calculations from TD constrained xKLI, TD partially constrained xKLI, and TDHF. We found that electron dynamics such as electron ionization and moment of inertia dynamics for the constrained xKLI are most similar to the TDHF results. Also, energy conservation is better by at least one order of magnitude with respect to the unconstrained xKLI. We also discuss the problems that arise in satisfying constraints in the TD case with a non-cw driving force.
Kurzweil, Yair; Head-Gordon, Martin
2009-07-15
We develop a method that can constrain any local exchange-correlation potential to preserve basic exact conditions. Using the method of Lagrange multipliers, we calculate for each set of given Kohn-Sham orbitals a constraint-preserving potential which is closest to the given exchange-correlation potential. The method is applicable to both the time-dependent (TD) and independent cases. The exact conditions that are enforced for the time-independent case are Galilean covariance, zero net force and torque, and Levy-Perdew virial theorem. For the time-dependent case we enforce translational covariance, zero net force, Levy-Perdew virial theorem, and energy balance. We test our method on the exchange (only) Krieger-Li-Iafrate (xKLI) approximate-optimized effective potential for both cases. For the time-independent case, we calculated the ground state properties of some hydrogen chains and small sodium clusters for some constrained xKLI potentials and Hartree-Fock (HF) exchange. The results (total energy, Kohn-Sham eigenvalues, polarizability, and hyperpolarizability) indicate that enforcing the exact conditions is not important for these cases. On the other hand, in the time-dependent case, constraining both energy balance and zero net force yields improved results relative to TDHF calculations. We explored the electron dynamics in small sodium clusters driven by cw laser pulses. For each laser pulse we compared calculations from TD constrained xKLI, TD partially constrained xKLI, and TDHF. We found that electron dynamics such as electron ionization and moment of inertia dynamics for the constrained xKLI are most similar to the TDHF results. Also, energy conservation is better by at least one order of magnitude with respect to the unconstrained xKLI. We also discuss the problems that arise in satisfying constraints in the TD case with a non-cw driving force.
NASA Astrophysics Data System (ADS)
Martin-Samos, Layla; Bussi, Giovanni
2009-08-01
We present here SaX (Self-energies and eXcitations), a plane-waves package aimed at electronic-structure and optical-properties calculations in the GW framework, namely using the GW approximation for quasi-particle properties and the Bethe-Salpeter equation for the excitonic effects. The code is mostly written in FORTRAN90 in a modern style, with extensive use of data abstraction (i.e. objects). SaX employs state of the art techniques and can treat large systems. The package is released with an open source license and can be also download from http://www.sax-project.org/. Program summaryProgram title: SaX (Self-energies and eXcitations) Catalogue identifier: AEDF_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEDF_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: GNU General Public License No. of lines in distributed program, including test data, etc.: 779 771 No. of bytes in distributed program, including test data, etc.: 4 894 755 Distribution format: tar.gz Programming language: FORTRAN, plus some C utilities Computer: Linux PC, Linux clusters, IBM-SP5 Operating system: Linux, Aix Has the code been vectorised or parallelized?: Yes RAM: depending on the system complexity Classification: 7.3 External routines: Message-Passing Interface (MPI) to perform parallel computations. ESPRESSO ( http://www.quantum-espresso.org) Nature of problem: SaX is designed to calculate the electronic band-structure of semiconductors, including quasi-particle effects and optical properties including excitonic effects. Solution method: The electronic band-structure is calculated using the GW approximation for the self-energy operator. The optical properties are calculated solving the Bethe-Salpeter equation in the GW approximation. The wavefunctions are expanded on a plane-waves basis set, using norm-conserving pseudopotentials. Restrictions: Many objects are non-local matrix represented in plane wave basis
Matakatsu, Hitoshi; Blair, Seth S
2008-09-23
Signaling via the large protocadherin Fat (Ft), regulated in part by its binding partner Dachsous (Ds) and the Golgi-resident kinase Four-jointed (Fj), is required for a variety of developmental functions in Drosophila. Ft and, to a lesser extent, Ds suppress overgrowth of the imaginal discs from which appendages develop and regulate the Hippo pathway [1-5] (reviewed in [6]). Ft, Ds, and Fj are also required for normal planar cell polarity (PCP) in the wing, abdomen, and eye and for the normal patterning of appendages, including the spacing of crossveins in the wing and the segmentation of the leg tarsus (reviewed in [7-9]). Ft signaling was recently shown to be negatively regulated by the atypical myosin Dachs [10, 11]. We identify here an additional negative regulator of Ft signaling in growth control, PCP, and appendage patterning, the Approximated (App) protein. We show that App encodes a member of the DHHC family, responsible for the palmitoylation of selected cytoplasmic proteins, and provide evidence that App acts by controlling the normal subcellular localization and activity of Dachs. PMID:18804377
Bannwarth, Christoph; Grimme, Stefan
2015-04-16
We show that the electronic circular dichroism (ECD) of delocalized π-systems represents a worst-case scenario for Tamm-Dancoff approximated (TDA) linear response methods. We mainly consider density functional theory (TDA-DFT) variants together with range-separated hybrids, but the conclusions also apply for other functionals as well as the configuration interaction singles (CIS) approaches. We study the effect of the TDA for the computation of ECD spectra in some prototypical extended π-systems. The C76 fullerene, a chiral carbon nanotube fragment, and [11]helicene serve as model systems for inherently chiral, π-chromophores. Solving the full linear response problem is inevitable in order to obtain accurate ECD spectra for these systems. For the C76 fullerene and the nanotube fragment, TDA and CIS approximated methods yield spectra in the origin-independent velocity gauge formalism of incorrect sign which would lead to the assignment of the opposite (wrong) absolute configuration. As a counterexample, we study the ECD of an α-helix polypeptide chain. Here, the lowest-energy transitions are dominated by localized excitations within the individual peptide units, and TDA methods perform satisfactorily. The results may have far-reaching implications for simple semiempirical methods which often employ TDA and CIS for huge molecules. Our recently presented simplified time-dependent DFT approach proves to be an excellent low-cost linear response method which together with range-separated density functionals like ωB97X-D3 produces ECD spectra in very good agreement with experiment. PMID:25798823
NASA Technical Reports Server (NTRS)
Desantis, A.
1994-01-01
In this paper the approximation problem for a class of optimal compensators for flexible structures is considered. The particular case of a simply supported truss with an offset antenna is dealt with. The nonrational positive real optimal compensator transfer function is determined, and it is proposed that an approximation scheme based on a continued fraction expansion method be used. Comparison with the more popular modal expansion technique is performed in terms of stability margin and parameters sensitivity of the relative approximated closed loop transfer functions.
Liu, Jie; Liang, WanZhen
2011-07-01
We present the analytical expression and computer implementation for the second-order energy derivatives of the electronic excited state with respect to the nuclear coordinates in the time-dependent density functional theory (TDDFT) with Gaussian atomic orbital basis sets. Here, the Tamm-Dancoff approximation to the full TDDFT is adopted, and therefore the formulation process of TDDFT excited-state Hessian is similar to that of configuration interaction singles (CIS) Hessian. However, due to the replacement of the Hartree-Fock exchange integrals in CIS with the exchange-correlation kernels in TDDFT, many quantitative changes in the derived equations are arisen. The replacement also causes additional technical difficulties associated with the calculation of a large number of multiple-order functional derivatives with respect to the density variables and the nuclear coordinates. Numerical tests on a set of test molecules are performed. The simulated excited-state vibrational frequencies by the analytical Hessian approach are compared with those computed by CIS and the finite-difference method. It is found that the analytical Hessian method is superior to the finite-difference method in terms of the computational accuracy and efficiency. The numerical differentiation can be difficult due to root flipping for excited states that are close in energy. TDDFT yields more exact excited-state vibrational frequencies than CIS, which usually overestimates the values. PMID:21744894
NASA Astrophysics Data System (ADS)
Neese, Frank; Wennmohs, Frank; Hansen, Andreas
2009-03-01
Coupled-electron pair approximations (CEPAs) and coupled-pair functionals (CPFs) have been popular in the 1970s and 1980s and have yielded excellent results for small molecules. Recently, interest in CEPA and CPF methods has been renewed. It has been shown that these methods lead to competitive thermochemical, kinetic, and structural predictions. They greatly surpass second order Møller-Plesset and popular density functional theory based approaches in accuracy and are intermediate in quality between CCSD and CCSD(T) in extended benchmark studies. In this work an efficient production level implementation of the closed shell CEPA and CPF methods is reported that can be applied to medium sized molecules in the range of 50-100 atoms and up to about 2000 basis functions. The internal space is spanned by localized internal orbitals. The external space is greatly compressed through the method of pair natural orbitals (PNOs) that was also introduced by the pioneers of the CEPA approaches. Our implementation also makes extended use of density fitting (or resolution of the identity) techniques in order to speed up the laborious integral transformations. The method is called local pair natural orbital CEPA (LPNO-CEPA) (LPNO-CPF). The implementation is centered around the concepts of electron pairs and matrix operations. Altogether three cutoff parameters are introduced that control the size of the significant pair list, the average number of PNOs per electron pair, and the number of contributing basis functions per PNO. With the conservatively chosen default values of these thresholds, the method recovers about 99.8% of the canonical correlation energy. This translates to absolute deviations from the canonical result of only a few kcal mol-1. Extended numerical test calculations demonstrate that LPNO-CEPA (LPNO-CPF) has essentially the same accuracy as parent CEPA (CPF) methods for thermochemistry, kinetics, weak interactions, and potential energy surfaces but is up to 500
Gain-Scheduled Approximations to H-Infinity Controllers for the F/A-18 Active Aeroelastic Wing
NASA Technical Reports Server (NTRS)
Lind, Rick
1999-01-01
The Active Aeroelastic Wing will demonstrate technologies related to aeroservoelastic effects such as wing twist and load minimization. This paper presents a control design based on H-infinity synthesis that simultaneously considers the multiple objectives associated with handling qualities, actuator limitations, and loads. The controller is realized as a filter and gain set approximation to a state-space H-infinity controller. This approximation allows scheduling of the controller over a flight envelope.
NASA Technical Reports Server (NTRS)
Shevade, A. V.; Ryan, M. A.; Homer, M. L.; Jewell, A. D.; Zhou, H.; Manatt, K.; Kisor, A. K.
2005-01-01
We report a Quantitative Structure-Activity Relationships (QSAR) study using Genetic Function Approximations (GFA) to describe the polymer-carbon composite sensor activities in the JPL Electronic Nose, when exposed to chemical vapors at parts-per-million concentration levels.
Active pixel sensor array with electronic shuttering
NASA Technical Reports Server (NTRS)
Fossum, Eric R. (Inventor)
2002-01-01
An active pixel cell includes electronic shuttering capability. The cell can be shuttered to prevent additional charge accumulation. One mode transfers the current charge to a storage node that is blocked against accumulation of optical radiation. The charge is sampled from a floating node. Since the charge is stored, the node can be sampled at the beginning and the end of every cycle. Another aspect allows charge to spill out of the well whenever the charge amount gets higher than some amount, thereby providing anti blooming.
Gudmundsson, V.; Palsson, G. )
1994-05-15
We investigate the static nonlinear screening of a single point charge (Coulombic impurity) by a two-dimensional electron gas (2DEG) in a strong perpendicular magnetic field at low temperature. The electron-electron interactions are treated in the Hartree-Fock approximation (HFA). The results are compared to earlier results for Hartree interacting electrons showing quite different screening properties due to the enhancement of the spin splitting of the Landau levels within the HFA. The possibility of different occupation of the spin levels of the impurity and the surrounding 2DEG is discussed in light of experiments.
NASA Astrophysics Data System (ADS)
Chatterjee, Koushik; Pastorczak, Ewa; Jawulski, Konrad; Pernal, Katarzyna
2016-06-01
A perfect-pairing generalized valence bond (GVB) approximation is known to be one of the simplest approximations, which allows one to capture the essence of static correlation in molecular systems. In spite of its attractive feature of being relatively computationally efficient, this approximation misses a large portion of dynamic correlation and does not offer sufficient accuracy to be generally useful for studying electronic structure of molecules. We propose to correct the GVB model and alleviate some of its deficiencies by amending it with the correlation energy correction derived from the recently formulated extended random phase approximation (ERPA). On the examples of systems of diverse electronic structures, we show that the resulting ERPA-GVB method greatly improves upon the GVB model. ERPA-GVB recovers most of the electron correlation and it yields energy barrier heights of excellent accuracy. Thanks to a balanced treatment of static and dynamic correlation, ERPA-GVB stays reliable when one moves from systems dominated by dynamic electron correlation to those for which the static correlation comes into play.
ERIC Educational Resources Information Center
Wetsel, Grover C., Jr.
1978-01-01
Calculates the energy-band structure of noninteracting electrons in a one-dimensional crystal using exact and approximate methods for a rectangular-well atomic potential. A comparison of the two solutions as a function of potential-well depth and ratio of lattice spacing to well width is presented. (Author/GA)
NASA Technical Reports Server (NTRS)
Gonzalez, W. D.; Pinto, O., Jr.; Mendes, O., Jr.; Mozer, F. S.
1986-01-01
Large plasmaspheric electric fields at L is approximately 2 measured by the S3-3 satellite during strong geomagnetic activity are reported. Since these measurements have amplitudes comparable to those of the local corotation electric field, during such events the plasmasphere is expected to get strongly altered event at such low L-values. Furthermore, those measurements could contribute to the understanding of the physics of the convection/electric field penetration to the low latitude plasmaphere as well as the disturbed dynamo, during strong geomagnetic activity. For this purpose, critical parameters related to geomagnetic activity are also presented for the reported electric field events.
NASA Technical Reports Server (NTRS)
Cattell, C.; Dombeck, J.; Preiwisch, A.; Thaller, S.; Vo, P.; Wilson, L. B., III; Wygant, J.; Mende, S. B.; Frey, H. U.; Ilie, R.; Lu, G.
2011-01-01
During an interval when the interplanetary magnetic field was large and primarily duskward and southward, a stable region of auroral emission was observed on 17 August 2001 by IMAGE at 16 magnetic local time, poleward of the main aurora, for 1 h, from before the onset of a large substorm through the recovery phase. In a region where ions showed the energy dispersion expected for the cusp, strong field \\aligned currents and Poynting flux were observed by Polar (at 1.8 RE in the Southern Hemisphere) as it transited field lines mapping to the auroral spot in the Northern Hemisphere. The data are consistent with the hypothesis that the long \\lasting electron auroral spot maps to the magnetopause region where reconnection was occurring. Under the assumption of conjugacy between the Northern and Southern hemispheres on these field lines, the Polar data suggest that the electrons on these field lines were accelerated by Alfven waves and/or a quasi \\static electric field, primarily at altitudes below a few RE since the in situ Poynting flux (mapped to 100 km) is comparable to the energy flux of the emission while the mapped in situ electron energy flux is much smaller. This event provides the first example of an emission due to electrons accelerated at low altitudes at the foot point of a region of quasi \\steady dayside reconnection. Cluster data in the magnetotail indicate that the Poynting flux from the reconnection region during this substorm is large enough to account for the observed nightside aurora.
Sato, Shunsuke A; Taniguchi, Yasutaka; Shinohara, Yasushi; Yabana, Kazuhiro
2015-12-14
We develop methods to calculate electron dynamics in crystalline solids in real-time time-dependent density functional theory employing exchange-correlation potentials which reproduce band gap energies of dielectrics; a meta-generalized gradient approximation was proposed by Tran and Blaha [Phys. Rev. Lett. 102, 226401 (2009)] (TBm-BJ) and a hybrid functional was proposed by Heyd, Scuseria, and Ernzerhof [J. Chem. Phys. 118, 8207 (2003)] (HSE). In time evolution calculations employing the TB-mBJ potential, we have found it necessary to adopt the predictor-corrector step for a stable time evolution. We have developed a method to evaluate electronic excitation energy without referring to the energy functional which is unknown for the TB-mBJ potential. For the HSE functional, we have developed a method for the operation of the Fock-like term in Fourier space to facilitate efficient use of massive parallel computers equipped with graphic processing units. We compare electronic excitations in silicon and germanium induced by femtosecond laser pulses using the TB-mBJ, HSE, and a simple local density approximation (LDA). At low laser intensities, electronic excitations are found to be sensitive to the band gap energy: they are close to each other using TB-mBJ and HSE and are much smaller in LDA. At high laser intensities close to the damage threshold, electronic excitation energies do not differ much among the three cases. PMID:26671367
NASA Astrophysics Data System (ADS)
Sato, Shunsuke A.; Taniguchi, Yasutaka; Shinohara, Yasushi; Yabana, Kazuhiro
2015-12-01
We develop methods to calculate electron dynamics in crystalline solids in real-time time-dependent density functional theory employing exchange-correlation potentials which reproduce band gap energies of dielectrics; a meta-generalized gradient approximation was proposed by Tran and Blaha [Phys. Rev. Lett. 102, 226401 (2009)] (TBm-BJ) and a hybrid functional was proposed by Heyd, Scuseria, and Ernzerhof [J. Chem. Phys. 118, 8207 (2003)] (HSE). In time evolution calculations employing the TB-mBJ potential, we have found it necessary to adopt the predictor-corrector step for a stable time evolution. We have developed a method to evaluate electronic excitation energy without referring to the energy functional which is unknown for the TB-mBJ potential. For the HSE functional, we have developed a method for the operation of the Fock-like term in Fourier space to facilitate efficient use of massive parallel computers equipped with graphic processing units. We compare electronic excitations in silicon and germanium induced by femtosecond laser pulses using the TB-mBJ, HSE, and a simple local density approximation (LDA). At low laser intensities, electronic excitations are found to be sensitive to the band gap energy: they are close to each other using TB-mBJ and HSE and are much smaller in LDA. At high laser intensities close to the damage threshold, electronic excitation energies do not differ much among the three cases.
Sato, Shunsuke A.; Taniguchi, Yasutaka; Shinohara, Yasushi; Yabana, Kazuhiro
2015-12-14
We develop methods to calculate electron dynamics in crystalline solids in real-time time-dependent density functional theory employing exchange-correlation potentials which reproduce band gap energies of dielectrics; a meta-generalized gradient approximation was proposed by Tran and Blaha [Phys. Rev. Lett. 102, 226401 (2009)] (TBm-BJ) and a hybrid functional was proposed by Heyd, Scuseria, and Ernzerhof [J. Chem. Phys. 118, 8207 (2003)] (HSE). In time evolution calculations employing the TB-mBJ potential, we have found it necessary to adopt the predictor-corrector step for a stable time evolution. We have developed a method to evaluate electronic excitation energy without referring to the energy functional which is unknown for the TB-mBJ potential. For the HSE functional, we have developed a method for the operation of the Fock-like term in Fourier space to facilitate efficient use of massive parallel computers equipped with graphic processing units. We compare electronic excitations in silicon and germanium induced by femtosecond laser pulses using the TB-mBJ, HSE, and a simple local density approximation (LDA). At low laser intensities, electronic excitations are found to be sensitive to the band gap energy: they are close to each other using TB-mBJ and HSE and are much smaller in LDA. At high laser intensities close to the damage threshold, electronic excitation energies do not differ much among the three cases.
NASA Astrophysics Data System (ADS)
Boettger, J. C.
2000-09-01
A simple approximation is developed for the two-electron spin-orbit coupling terms generated by the Douglas-Kroll-Hess transformation, in the context of density-functional theory (DFT). For the special case of an isolated atom, the two-electron spin-orbit matrix element for each pair of basis functions of type l is replaced with the spin-orbit matrix element for a point charge -Q(l) placed at the origin; where Q(l)=0,2,10,28,... . Application of this screened-nuclear-spin-orbit (SNSO) approximation to linear combination of Gaussian-type orbital (LCGTO) DFT calculations on Ce, Ta, and Pu atoms yields spin-orbit splittings that agree with results from a numerical solution of the Dirac-Kohn-Sham equations to within about 6%. This is a marked improvement over the nuclear-only spin-orbit approximation, which systematically overestimates spin-orbit splittings; in some cases by as much as 100%. Crystalline LCGTO DFT calculations on the fcc phases of the light-actinide metals Th-->Pu, using a multiatom generalization of the SNSO approximation, yield atomic volumes that are in excellent agreement with results from full-potential linear-augmented-plane-wave calculations.
Mizutani, U; Inukai, M; Sato, H; Zijlstra, E S; Lin, Q
2014-05-16
There are three key electronic parameters in elucidating the physics behind the Hume–Rothery electron concentration rule: the square of the Fermi diameter (2kF)2, the square of the critical reciprocal lattice vector and the electron concentration parameter or the number of itinerant electrons per atom e/a. We have reliably determined these three parameters for 10 Rhombic Triacontahedron-type 2/1–2/1–2/1 (N = 680) and 1/1–1/1–1/1 (N = 160–162) approximants by making full use of the full-potential linearized augmented plane wave-Fourier band calculations based on all-electron density-functional theory. We revealed that the 2/1–2/1–2/1 approximants Al13Mg27Zn45 and Na27Au27Ga31 belong to two different sub-groups classified in terms of equal to 126 and 109 and could explain why they take different e/a values of 2.13 and 1.76, respectively. Among eight 1/1–1/1–1/1 approximants Al3Mg4Zn3, Al9Mg8Ag3, Al21Li13Cu6, Ga21Li13Cu6, Na26Au24Ga30, Na26Au37Ge18, Na26Au37Sn18 and Na26Cd40Pb6, the first two, the second two and the last four compounds were classified into three sub-groups with = 50, 46 and 42; and were claimed to obey the e/a = 2.30, 2.10–2.15 and 1.70–1.80 rules, respectively.
NASA Astrophysics Data System (ADS)
Weber, F.; Distl, H.
2015-11-01
This paper derives an approximate collocated control solution for the mitigation of multi-mode cable vibration by semi-active damping with negative stiffness based on the control force characteristics of clipped linear quadratic regulator (LQR). The control parameters are derived from optimal modal viscous damping and corrected in order to guarantee that both the equivalent viscous damping coefficient and the equivalent stiffness coefficient of the semi-active cable damper force are equal to their desired counterparts. The collocated control solution with corrected control parameters is numerically validated by free decay tests of the first four cable modes and combinations of these modes. The results of the single-harmonic tests demonstrate that the novel approach yields 1.86 times more cable damping than optimal modal viscous damping and 1.87 to 2.33 times more damping compared to a passive oil damper whose viscous damper coefficient is optimally tuned to the targeted mode range of the first four modes. The improvement in case of the multi-harmonic vibration tests, i.e. when modes 1 and 3 and modes 2 and 4 are vibrating at the same time, is between 1.55 and 3.81. The results also show that these improvements are obtained almost independent of the cable anti-node amplitude. Thus, the proposed approximate real-time applicable collocated semi-active control solution which can be realized by magnetorheological dampers represents a promising tool for the efficient mitigation of stay cable vibrations.
Activities of the Research Laboratory of Electronics
NASA Astrophysics Data System (ADS)
Allen, Jonathan; Kleppner, Daniel
1991-08-01
This progress report contains both a statement of research objectives and a summary of research efforts for research projects listed. Partial contents include: (1) submicron structures technology and research; (2) microstructural evolution in thin films of electronic materials; (3) focused ion beam fabrication; (4) chemical reaction dynamics at surfaces; (5) measurement of electron-phonon interactions through large-amplitude phonon excitation; (6) chemical beam epitaxy of compound semiconductors; (7) high-frequency InAlAs/InGaAs metal-insulator-doped semiconductor field-effect transistors for telecommunications; (8) novel superconducting tunneling structures; (9) optics and quantum electronics; (10) superconducting electronic devices; (11) synchrotron X ray studies of surface disordering; (12) semiconductor surface studies; (13) single electron transistors; (14) quantum optics and photonics; (15) plasma dynamics; (16) electromagnetic wave theory and applications; (17) radio astronomy; (18) digital signal processing; (19) speech processing; (20) custom integrated circuits; (21) speech communication; (22) sensory communications; (23) signal transmission in the auditory system; and (24) linguistics.
Active Pixel Sensors for electron microscopy
NASA Astrophysics Data System (ADS)
Denes, P.; Bussat, J.-M.; Lee, Z.; Radmillovic, V.
2007-09-01
The technology used for monolithic CMOS imagers, popular for cell phone cameras and other photographic applications, has been explored for charged particle tracking by the high-energy physics community for several years. This technology also lends itself to certain imaging detector applications in electron microscopy. We have been developing such detectors for several years at Lawrence Berkeley National Laboratory, and we and others have shown that this technology can offer excellent point-spread function, direct detection and high readout speed. In this paper, we describe some of the design constraints peculiar to electron microscopy and summarize where such detectors could play a useful role.
Proynov, Emil; Liu, Fenglai; Shao, Yihan; Kong, Jing
2012-01-01
In a recent letter [E. Proynov, Y. Shao, and J. Kong, Chem. Phys. Lett. 493, 381 (2010)10.1016/j.cplett.2010.05.029], Becke's B05 model of nondynamic electron correlation in density functional theory was implemented self-consistently with computational efficiency (the “SCF-RI-B05” scheme). Important modifications of the algorithm were done in order to make the self-consistency feasible. In the present work, we give a complete account of the SCF-RI-B05 algorithm, including all the formulae for the analytical representation of the B05 functional and for its self-consistent field (SCF) potential. The average performance of the SCF-RI-B05 method reported in the above letter was somewhat less accurate, compared to the original B05 implementation, mainly because the parameters of the original B05 model were optimized with post-local-spin-density calculations. In this work, we report improved atomization energies with SCF-RI-B05, based on a SCF re-optimization of its four linear parameters. The re-optimized SCF-RI-B05 scheme is validated also on reaction barriers, and on the subtle energetics of NO dimer, an exemplary system of strong nondynamic correlation. It yields both the binding energy and the singlet-triplet splitting of the NO dimer correctly, and close to the benchmarks reported in the literature. PMID:22280739
Moreau, John W; Sharp, Thomas G
2004-01-01
Microfossils preserved in chert from the;1.9 Ga Gunflint Formation (Schreiber Beach, Ontario, Canada) were studied with transmission electron microscopy (TEM) and analytical TEM (ATEM). Our goals were to uncover the style of silicification relative to the distribution of organic matter, and to evaluate the distribution and evolution of organic matter, at submicroscopic spatial scales. Petrographically the microfossils typically display filamentous or coccoidal morphologies, and consist of quartz crystals surrounded by kerogen along grain boundaries. ATEM analysis revealed that quartz associated with kerogen consists of 200-500nm-sized, round crystallites, whereas the chert matrix is comprised of randomly oriented, polygonal microquartz (5-10 microm). Silica spheroids found within some fossils consist of quartz subgrains in an amorphous to poorly crystalline matrix, suggesting that precipitation of opaline silica on organic matter occurred with subsequent but incomplete transformation to quartz. Some coccoidal microfossils surround large euhedral quartz crystals (up to 5 microm in diameter) that appeared to have influenced the distribution of kerogen during crystal growth. These euhedral quartz crystals commonly contain elongated (50-100 nm) iron-rich crystallites. Energy-loss, near-edge structure analysis of kerogen associated with a coccoidal microfossil showed that it is composed of amorphous carbon with no evidence of graphitization. TEM results revealed significant differences in the style of silicification between microbe-shaped microfossils and their surrounding chert matrix, as well as the presence of amorphous kerogen. PMID:15253838
Active plasmonic devices via electron spin.
Baron, C A; Elezzabi, A Y
2009-04-27
A class of active terahertz devices that operate via particle plasmon oscillations is introduced for ensembles consisting of ferromagnetic and dielectric micro-particles. By utilizing an interplay between spin-orbit interaction manifesting as anisotropic magnetoresistance and the optical distance between ferromagnetic particles, a multifaceted paradigm for device design is demonstrated. Here, the phase accumulation of terahertz radiation across the device is actively modulated via the application of an external magnetic field. An active plasmonic directional router and an active plasmonic cylindrical lens are theoretically explored using both an empirical approach and finite-difference time-domain calculations. These findings are experimentally supported. PMID:19399088
Electric Propulsion Electronics Activities in Europe
NASA Astrophysics Data System (ADS)
Gollor, Matthias; Weinberg, Simon; Galantini, Paolo; Boss, Michael; Bourguignon, Eric; de la Cruz, Frederico
2008-09-01
For European space missions the importance of electric propulsion is growing strongly. The initial drivers of this development were programs of the European Space Agency and projects of the European national space agencies. In addition, electric propulsion is getting more and more acceptance from European commercial satellite manufacturers. European space industry, represented by individual companies, has developed specific and broad-use solutions for the electronics dedicated to powering and controlling electric propulsion systems.
NASA Astrophysics Data System (ADS)
McClain, James; Lischner, Johannes; Watson, Thomas; Matthews, Devin A.; Ronca, Enrico; Louie, Steven G.; Berkelbach, Timothy C.; Chan, Garnet Kin-Lic
2016-06-01
We use ab initio coupled-cluster theory to compute the spectral function of the uniform electron gas at a Wigner-Seitz radius of rs=4 . The coupled-cluster approximations we employ go significantly beyond the diagrammatic content of state-of-the-art G W theory. We compare our calculations extensively to G W and G W -plus-cumulant theory, illustrating the strengths and weaknesses of these methods in capturing the quasiparticle and satellite features of the electron gas. Our accurate calculations further allow us to address the long-standing debate over the occupied bandwidth of metallic sodium. Our findings indicate that the future application of coupled-cluster theory to condensed phase material spectra is highly promising.
Liu, Ran; Wang, Chuan-Kui; Li, Zong-Liang
2016-01-01
Based on the ab initio calculation, a method of one-dimension transmission combined with three-dimension correction approximation (OTCTCA) is developed to investigate electron-transport properties of molecular junctions. The method considers that the functional molecule provides a spatial distribution of effective potential field for the electronic transport. The electrons are injected from one electrode by bias voltage, then transmit through the potential field around the functional molecule, at last are poured into the other electrode with a specific transmission probability which is calculated from one-dimension Schrödinger equation combined with three-dimension correction. The electron-transport properties of alkane diamines and 4, 4′-bipyridine molecular junctions are studied by applying OTCTCA method. The numerical results show that the conductance obviously exponentially decays with the increase of molecular length. When stretching molecular junctions, steps with a certain width are presented in conductance traces. Especially, in stretching process of 4, 4′-bipyridine molecular junction, if the terminal N atom is broken from flat part of electrode tip and exactly there is a surface Au atom on the tip nearby the N atom, the molecule generally turns to absorb on the surface Au atom, which further results in another lower conductance step in the traces as the experimental probing. PMID:26911451
Liu, Ran; Wang, Chuan-Kui; Li, Zong-Liang
2016-01-01
Based on the ab initio calculation, a method of one-dimension transmission combined with three-dimension correction approximation (OTCTCA) is developed to investigate electron-transport properties of molecular junctions. The method considers that the functional molecule provides a spatial distribution of effective potential field for the electronic transport. The electrons are injected from one electrode by bias voltage, then transmit through the potential field around the functional molecule, at last are poured into the other electrode with a specific transmission probability which is calculated from one-dimension Schrödinger equation combined with three-dimension correction. The electron-transport properties of alkane diamines and 4, 4'-bipyridine molecular junctions are studied by applying OTCTCA method. The numerical results show that the conductance obviously exponentially decays with the increase of molecular length. When stretching molecular junctions, steps with a certain width are presented in conductance traces. Especially, in stretching process of 4, 4'-bipyridine molecular junction, if the terminal N atom is broken from flat part of electrode tip and exactly there is a surface Au atom on the tip nearby the N atom, the molecule generally turns to absorb on the surface Au atom, which further results in another lower conductance step in the traces as the experimental probing. PMID:26911451
NASA Astrophysics Data System (ADS)
Liu, Ran; Wang, Chuan-Kui; Li, Zong-Liang
2016-02-01
Based on the ab initio calculation, a method of one-dimension transmission combined with three-dimension correction approximation (OTCTCA) is developed to investigate electron-transport properties of molecular junctions. The method considers that the functional molecule provides a spatial distribution of effective potential field for the electronic transport. The electrons are injected from one electrode by bias voltage, then transmit through the potential field around the functional molecule, at last are poured into the other electrode with a specific transmission probability which is calculated from one-dimension Schrödinger equation combined with three-dimension correction. The electron-transport properties of alkane diamines and 4, 4‧-bipyridine molecular junctions are studied by applying OTCTCA method. The numerical results show that the conductance obviously exponentially decays with the increase of molecular length. When stretching molecular junctions, steps with a certain width are presented in conductance traces. Especially, in stretching process of 4, 4‧-bipyridine molecular junction, if the terminal N atom is broken from flat part of electrode tip and exactly there is a surface Au atom on the tip nearby the N atom, the molecule generally turns to absorb on the surface Au atom, which further results in another lower conductance step in the traces as the experimental probing.
NASA Astrophysics Data System (ADS)
García-García, J.; Oriols, X.; Martín, F.; Suñé, J.
1996-12-01
Carrier scattering in the Wigner formalism has been introduced for the simulation of dissipative electron transport in resonant tunnelling diodes. Two approaches have been considered: the relaxation time approximation and the Boltzmann collision operator. The relaxation time and transition rates have been evaluated and have been introduced in the discretized version of the Liouville equation to obtain the Wigner distribution function and the current density. Not only phonon scattering, but also ionized impurity scattering has been accounted for in both approaches. We have compared the two scattering models on the basis of the I-V characteristics which have been simulated under various temperature and doping conditions. The results clearly reveal a lower current peak in the Boltzmann collision operator approach. Since the results of both approaches are divergent and since no clear computation advantages are obtained from the relaxation time approximation, we prefer the use of the more realistic Boltzmann collision operator for the simulation of dissipative electron transport in resonant tunnelling diodes.
Yoriyaz, Helio; Moralles, Mauricio; Tarso Dalledone Siqueira, Paulo de; Costa Guimaraes, Carla da; Belonsi Cintra, Felipe; Santos, Adimir dos
2009-11-15
Purpose: Radiopharmaceutical applications in nuclear medicine require a detailed dosimetry estimate of the radiation energy delivered to the human tissues. Over the past years, several publications addressed the problem of internal dose estimate in volumes of several sizes considering photon and electron sources. Most of them used Monte Carlo radiation transport codes. Despite the widespread use of these codes due to the variety of resources and potentials they offered to carry out dose calculations, several aspects like physical models, cross sections, and numerical approximations used in the simulations still remain an object of study. Accurate dose estimate depends on the correct selection of a set of simulation options that should be carefully chosen. This article presents an analysis of several simulation options provided by two of the most used codes worldwide: MCNP and GEANT4. Methods: For this purpose, comparisons of absorbed fraction estimates obtained with different physical models, cross sections, and numerical approximations are presented for spheres of several sizes and composed as five different biological tissues. Results: Considerable discrepancies have been found in some cases not only between the different codes but also between different cross sections and algorithms in the same code. Maximum differences found between the two codes are 5.0% and 10%, respectively, for photons and electrons.Conclusion: Even for simple problems as spheres and uniform radiation sources, the set of parameters chosen by any Monte Carlo code significantly affects the final results of a simulation, demonstrating the importance of the correct choice of parameters in the simulation.
NASA Astrophysics Data System (ADS)
Grimme, Stefan; Bannwarth, Christoph
2016-08-01
The computational bottleneck of the extremely fast simplified Tamm-Dancoff approximated (sTDA) time-dependent density functional theory procedure [S. Grimme, J. Chem. Phys. 138, 244104 (2013)] for the computation of electronic spectra for large systems is the determination of the ground state Kohn-Sham orbitals and eigenvalues. This limits such treatments to single structures with a few hundred atoms and hence, e.g., sampling along molecular dynamics trajectories for flexible systems or the calculation of chromophore aggregates is often not possible. The aim of this work is to solve this problem by a specifically designed semi-empirical tight binding (TB) procedure similar to the well established self-consistent-charge density functional TB scheme. The new special purpose method provides orbitals and orbital energies of hybrid density functional character for a subsequent and basically unmodified sTDA procedure. Compared to many previous semi-empirical excited state methods, an advantage of the ansatz is that a general eigenvalue problem in a non-orthogonal, extended atomic orbital basis is solved and therefore correct occupied/virtual orbital energy splittings as well as Rydberg levels are obtained. A key idea for the success of the new model is that the determination of atomic charges (describing an effective electron-electron interaction) and the one-particle spectrum is decoupled and treated by two differently parametrized Hamiltonians/basis sets. The three-diagonalization-step composite procedure can routinely compute broad range electronic spectra (0-8 eV) within minutes of computation time for systems composed of 500-1000 atoms with an accuracy typical of standard time-dependent density functional theory (0.3-0.5 eV average error). An easily extendable parametrization based on coupled-cluster and density functional computed reference data for the elements H-Zn including transition metals is described. The accuracy of the method termed sTDA-xTB is first
Grimme, Stefan; Bannwarth, Christoph
2016-08-01
The computational bottleneck of the extremely fast simplified Tamm-Dancoff approximated (sTDA) time-dependent density functional theory procedure [S. Grimme, J. Chem. Phys. 138, 244104 (2013)] for the computation of electronic spectra for large systems is the determination of the ground state Kohn-Sham orbitals and eigenvalues. This limits such treatments to single structures with a few hundred atoms and hence, e.g., sampling along molecular dynamics trajectories for flexible systems or the calculation of chromophore aggregates is often not possible. The aim of this work is to solve this problem by a specifically designed semi-empirical tight binding (TB) procedure similar to the well established self-consistent-charge density functional TB scheme. The new special purpose method provides orbitals and orbital energies of hybrid density functional character for a subsequent and basically unmodified sTDA procedure. Compared to many previous semi-empirical excited state methods, an advantage of the ansatz is that a general eigenvalue problem in a non-orthogonal, extended atomic orbital basis is solved and therefore correct occupied/virtual orbital energy splittings as well as Rydberg levels are obtained. A key idea for the success of the new model is that the determination of atomic charges (describing an effective electron-electron interaction) and the one-particle spectrum is decoupled and treated by two differently parametrized Hamiltonians/basis sets. The three-diagonalization-step composite procedure can routinely compute broad range electronic spectra (0-8 eV) within minutes of computation time for systems composed of 500-1000 atoms with an accuracy typical of standard time-dependent density functional theory (0.3-0.5 eV average error). An easily extendable parametrization based on coupled-cluster and density functional computed reference data for the elements H-Zn including transition metals is described. The accuracy of the method termed sTDA-xTB is first
Observations on Electronic Networks: Appropriate Activities for Learning.
ERIC Educational Resources Information Center
Levin, James A.; And Others
1989-01-01
Discussion of the use of electronic networks for learning activities highlights the Noon Observation Project in which students in various locations measured the length of a noontime shadow to determine the earth's circumference. Electronic pen pals are discussed, and the roles of the network and of the class are described. (LRW)
Cleaning and activation of beryllium-copper electron multiplier dynodes.
NASA Technical Reports Server (NTRS)
Pongratz, M. B.
1972-01-01
Description of a cleaning and activation procedure followed in preparing beryllium-copper dynodes for electron multipliers used in sounding-rocket experiments to detect auroral electrons. The initial degreasing step involved a 5-min bath in trichloroethylene in an ultrasonic cleaner. This was followed by an ultrasonic rinse in methanol and by a two-step acid pickling treatment to remove the oxides. Additional rinsing in water and methanol was followed by activation in a stainless-steel RF induction oven.
Activation entropy of electron transfer reactions
NASA Astrophysics Data System (ADS)
Milischuk, Anatoli A.; Matyushov, Dmitry V.; Newton, Marshall D.
2006-05-01
We report microscopic calculations of free energies and entropies for intramolecular electron transfer reactions. The calculation algorithm combines the atomistic geometry and charge distribution of a molecular solute obtained from quantum calculations with the microscopic polarization response of a polar solvent expressed in terms of its polarization structure factors. The procedure is tested on a donor-acceptor complex in which ruthenium donor and cobalt acceptor sites are linked by a four-proline polypeptide. The reorganization energies and reaction energy gaps are calculated as a function of temperature by using structure factors obtained from our analytical procedure and from computer simulations. Good agreement between two procedures and with direct computer simulations of the reorganization energy is achieved. The microscopic algorithm is compared to the dielectric continuum calculations. We found that the strong dependence of the reorganization energy on the solvent refractive index predicted by continuum models is not supported by the microscopic theory. Also, the reorganization and overall solvation entropies are substantially larger in the microscopic theory compared to continuum models.
Probing active electron transfer branch in photosystem I reaction center.
NASA Astrophysics Data System (ADS)
Savikhin, Sergei; Dashdorj, Naranbaatar; Xu, Wu; Martinsson, Peter; Chitnis, Parag
2003-03-01
Complimentary point mutations were introduced at the primary electron acceptor sites in A and B branches of the photosystem I (PS I) reaction center (RC) from Synechocystis sp. PCC 6803 and their effect on the kinetics of the electron transfer process was studied by means of ultrafast pump-probe spectroscopy. The results indicate that in these species the electron transfer occurs primarily along the A-branch. Previous optical experiments on PS I complexes from Chlorella sorokiniana demonstrated that both branches of RC are equally active. That suggests that the directionality of electron transfer in PS I is species dependent.
Javaid, Saqib; Javed Akhtar, M.
2014-07-14
We have investigated the behavior of orthoferrite LaFeO{sub 3} at ambient conditions and under pressure using DFT (generalized gradient approximation (GGA)) + U approach. Ground state electronic (band gap) and magnetic properties are considerably improved due to the Hubbard correction. Moreover, the experimentally observed pressure-driven phase transition, namely, the simultaneous occurrence of spin crossover, isostructural volume collapse, and drastic reduction in electrical resistance (electronic phase transition) is nicely described by GGA + U calculations. In particular, despite a sharp drop in resistance, a small band gap still remains in the low spin state indicating an insulator to semiconductor phase transition, in good agreement with the experiments but in contrast to GGA, which predicts metallic behavior in low spin state. We discuss the origin of variation in electronic structure of LaFeO{sub 3} in low spin state as obtained from GGA to GGA + U methods. These results emphasize the importance of correlation effects in describing the pressure-driven phase transition in LaFeO{sub 3} and other rare-earth orthoferrites.
NASA Astrophysics Data System (ADS)
Flemming Hansen, D.; Led, Jens J.
2003-08-01
The validity of a series of approximate solutions of the Bloch-McConnell equations normally applied in the analyses of chemically exchanging systems is evaluated, using the electron self-exchange (ESE) in the blue copper protein plastocyanin from Anabaena variabilis as an example. The evaluation is based on a comparison with the results of a complete analysis of the NMR signals of chemically exchanging nuclei that allows an independent and accurate determination of all the involved parameters. The complete analysis is based on the general solution of the Bloch-McConnell equations. It includes a simultaneous analysis of the chemical shift, and the transverse and longitudinal relaxation rates of the observed nuclei as well as the variation of these parameters with the molar fractions of the exchanging species and the rate of the chemical exchange process. The linear prediction model method was used in the data analysis to achieve the highest possible precision. Surprisingly, it is found that the fast exchange condition may not be fulfilled even in cases where a single exchange-averaged NMR signal is observed, and the Larmor frequency and relaxation rates depend linearly on the molar fractions of the exchanging species. In such cases the use of approximate solutions in the analysis of the transverse relaxation rates and the pseudo-contact shifts can lead to erroneous results. In limiting cases close to the fast exchange and slow exchange regimes correct values of some of the parameters can be obtained using the second order approximate solution of the Bloch-McConnell equations. In contrast, the complete analysis of the NMR signals results in an accurate determination of the exchange rates and the NMR parameters of the exchanging sites. This, in turn, can provide information about the structure and function of a protein undergoing chemically exchange. For the investigated plastocyanin the complete analysis results in an accurate determination of the paramagnetic
Topside electron temperature models for low and high solar activity
NASA Astrophysics Data System (ADS)
Pandey, V. K.; Sethi, N. K.; Mahajan, K. K.
It is now well known that in the topside ionosphere thermal conduction from the protonosphere becomes the dominant factor over the heating and loss terms in shaping the ionospheric electron temperature (Te) profile. By analyzing a limited database of incoherent scatter (IS) Te measurements, Mahajan and Pandey [J. Geophys. Res. 85 (1980) 213] reported a correlation between the electron heat flux and electron density in the topside ionosphere. Since attention has been steadily mounting for the empirical modeling of Te, we now exploit the large database of IS measurements of Te and Ne at Arecibo during 1989-1990 (high solar activity), as well as during 1975-1976 (low solar activity) for this purpose. We again find a functional relationship between heat flux and electron density in the topside ionosphere during both the solar activities. These functional relationships are used to generate topside Te profiles.
NASA Astrophysics Data System (ADS)
Busuladžić, M.; Gazibegović-Busuladžić, A.; Milošević, D. B.; Becker, W.
2008-09-01
The strong-field approximation for ionization of diatomic molecules by a strong laser field [D. B. Milošević, Phys. Rev. A 74, 063404 (2006)] is generalized to include rescattering of the ionized electron wave packet off the molecular centers (the electron’s parent ion or the second atom). There are four rescattering contributions to the ionization rate, which are responsible for the high-energy plateau in the electron spectra and which interfere in a complicated manner. The spectra are even more complicated due to the different symmetry properties of the atomic orbitals of which a particular molecular orbital consists. Nevertheless, a comparatively simple condition emerges for the destructive interference of all these contributions, which yields a curve in the (Epf,θ) plane. Here θ is the electron emission angle and Epf is the electron kinetic energy. The resulting suppression of the rescattering plateau can be strong and affect a large area of the (Epf,θ) plane, depending on the orientation of the molecule. We illustrate this using the examples of the 3σg molecular orbital of N2 and the 1πg molecular orbital of O2 for various orientations of these molecules with respect to the laser polarization axis. For N2 , for perpendicular orientation and the equilibrium internuclear distance R0 , we find that the minima of the ionization rate form the curve Epfcos2θ=π2/(2R02) in the (Epf,θ) plane. For O2 the rescattering plateau is absent for perpendicular orientation.
NASA Astrophysics Data System (ADS)
Colle, Renato; Embriaco, Davide; Massini, Michol; Simonucci, Stefano; Taioli, Simone
2004-10-01
Analytic expressions for the direct, resonant, and interference contributions to the differential cross section of a resonant Auger process, produced by the inner-shell photoionization of a linear molecule either “fixed in space” or belonging to a gas of randomly oriented molecules, have been derived following Dill’s procedures [ Dill , Phys. Rev. Lett. 45, 1393 (1980) ], but going beyond the two-step approximation. Angle-resolved Auger spectra of the C2H2 molecule measured on top of the C1s→π* resonance [ Kivimäki , J. Phys. B 30, 4279 (1997) ] have been calculated together with asymmetry parameters, analyzing also the different contributions to the electron angular distributions.
NASA Astrophysics Data System (ADS)
Zaccari, Daniel; Melo, Juan I.; Ruiz de Azúa, Martín C.; Giribet, Claudia G.
2009-02-01
An alternative approach for the calculation of the electron-positron (e-p) contribution to magnetic properties based on two-component Breit-Pauli spinors is presented. In it, the elimination of the small component scheme is applied to the inverse propagator matrix of e-p pairs. The effect of the positronic manifold is expressed as an operator acting on Breit-Pauli spinors. The operator form thus obtained sums up the relativistic correction as a geometric series and as a result a totally different behavior in the vicinity of a nucleus is obtained as compared to the one of the linear response approximation. This feature has deep influence in numerical values of the e-p contribution to the nuclear magnetic shielding of heavy atoms. Numerical calculations carried out for Kr, Xe, and I show that with this approach, the e-p contributions to this property are in good agreement with those of four-component methods.
NASA Astrophysics Data System (ADS)
Guillaume, Stéphane-Olivier; de Abajo, F. Javier García; Henrard, Luc
2013-12-01
An efficient procedure is introduced for the calculation of the optical response of individual and coupled metallic nanoparticles in the framework of the discrete-dipole approximation (DDA). We introduce a modal expansion in the basis set of discrete dipoles and show that a few suitably selected modes are sufficient to compute optical spectra with reasonable accuracy, thus reducing the required numerical effort relative to other DDA approaches. Our method offers a natural framework for the study of localized plasmon modes, including plasmon hybridization. As a proof of concept, we investigate optical extinction and electron energy-loss spectra of monomers, dimers, and quadrumers formed by flat silver squares. This method should find application to the previously prohibited simulation of complex particle arrays.
Jonić, S; Vargas, J; Melero, R; Gómez-Blanco, J; Carazo, J M; Sorzano, C O S
2016-06-01
Cryo-electron microscopy (cryo-EM) of frozen-hydrated preparations of isolated macromolecular complexes is the method of choice to obtain the structure of complexes that cannot be easily studied by other experimental methods due to their flexibility or large size. An increasing number of macromolecular structures are currently being obtained at subnanometer resolution but the interpretation of structural details in such EM-derived maps is often difficult because of noise at these high-frequency signal components that reduces their contrast. In this paper, we show that the method for EM density-map approximation using Gaussian functions can be used for denoising of single-particle EM maps of high (typically subnanometer) resolution. We show its denoising performance using simulated and experimental EM density maps of several complexes. PMID:27085420
Rüger, Robert; van Lenthe, Erik; Heine, Thomas; Visscher, Lucas
2016-05-14
We propose a new method of calculating electronically excited states that combines a density functional theory based ground state calculation with a linear response treatment that employs approximations used in the time-dependent density functional based tight binding (TD-DFTB) approach. The new method termed time-dependent density functional theory TD-DFT+TB does not rely on the DFTB parametrization and is therefore applicable to systems involving all combinations of elements. We show that the new method yields UV/Vis absorption spectra that are in excellent agreement with computationally much more expensive TD-DFT calculations. Errors in vertical excitation energies are reduced by a factor of two compared to TD-DFTB. PMID:27179467
NASA Astrophysics Data System (ADS)
Rüger, Robert; van Lenthe, Erik; Heine, Thomas; Visscher, Lucas
2016-05-01
We propose a new method of calculating electronically excited states that combines a density functional theory based ground state calculation with a linear response treatment that employs approximations used in the time-dependent density functional based tight binding (TD-DFTB) approach. The new method termed time-dependent density functional theory TD-DFT+TB does not rely on the DFTB parametrization and is therefore applicable to systems involving all combinations of elements. We show that the new method yields UV/Vis absorption spectra that are in excellent agreement with computationally much more expensive TD-DFT calculations. Errors in vertical excitation energies are reduced by a factor of two compared to TD-DFTB.
Ionospheric Electron Density during Magnetically Active Times over Istanbul
NASA Astrophysics Data System (ADS)
Naz Erbaş, Bute; Kaymaz, Zerefsan; Ceren Moral, Aysegul; Emine Ceren Kalafatoglu Eyiguler, R. A..
2016-07-01
In this study, we analyze electron density variations over Istanbul using Dynasonde observations during the magnetically active times. In order to perform statistical analyses, we first determined magnetic storms and magnetospheric substorm intervals from October 2012 to October 2015 using Kyoto's magnetic index data. Corresponding ionospheric parameters, such as critical frequency of F2 region (foF2), maximum electron density height (hmF2), total electron density (TEC) etc. were retrieved from Dynasonde data base at Istanbul Technical University's Space Weather Laboratory. To understand the behavior of electron density during the magnetically active times, we remove the background quiet time variations first and then quantify the anomalies. In this presentation, we will report results from our preliminary analyses from the selected cases corresponding to the strong magnetic storms. Initial results show lower electron densities at noon times and higher electron densities in the late afternoon toward sunset times when compared to the electron densities of magnetically quiet times. We also compare the results with IRI and TIEGCM ionospheric models in order to understand the physical and dynamical causes of these variations. During the presentation we will also discuss the role of these changes during the magnetically active times on the GPS communications through ionosphere.
An active expriments with electron gun on the microsatellite
NASA Astrophysics Data System (ADS)
Dokukin, V.; Ruzhin, Yu.
Plasma radio emission in the presence of energetic particle fluxes is a very informative source of knowledge about plasma processes and its parameters in the interaction region. Now there is a big experience of work with election beams in the Earth ionosphere. The new generation of spacecrafts- micro and small satellites give us rather chip possibilities to carry out space orbital experiments. But there is an obstacle to do an active experiments at microsatellite with injection of electron beam-the limited onboard power source. Typically it requires at least tens of Watts to heat the cathode of electron gun and to accelerate the electrons of the beam. The proposal is made to apply ``solar'' electron gun with ``zero'' consumption from satellite powersuppliment. Such type of electron gun could be applied for space experiments at near Earth orbits and for solar or planetary missions.
Hot-electron-mediated surface chemistry: toward electronic control of catalytic activity.
Park, Jeong Young; Kim, Sun Mi; Lee, Hyosun; Nedrygailov, Ievgen I
2015-08-18
nanoparticles on oxide supports and Pt-CdSe-Pt nanodumbbells. We show that the accumulation or depletion of hot electrons on metal nanoparticles, in turn, can also influence catalytic reactions. Mechanisms suggested for hot-electron-induced chemical reactions on a photoexcited plasmonic metal are discussed. We propose that the manipulation of the flow of hot electrons by changing the electrical characteristics of metal-oxide and metal-semiconductor interfaces can give rise to the intriguing capability of tuning the catalytic activity of hybrid nanocatalysts. PMID:26181684
Ulysses observations of electron and proton components in a magnetic cloud and related wave activity
NASA Technical Reports Server (NTRS)
Osherovich, V. A.; Fainberg, J.; Stone, R. G.; MacDowall, R. J.; Phillips, J. L.; Balogh, A.
1995-01-01
In addition to a smooth rotation of the magnetic field vector, magnetic clouds have a low proton temperature T(sub p). Their expansion in the solar wind leads to depletion and therefore the ion component cools down. It has been shown recently that the electron component in magnetic clouds behaves differently: when the cloud expands, electron temperature Te anti correlates with density and therefore Te increases in the cloud, creating favorable conditions for the rise of ion-acoustic waves. For the magnetic cloud observed by Ulysses on June 10 - 12, 1993 at 4.64 AU at S 32.5 deg, we present observations for both electron and proton components and related plasma wave activity. Our results confirm the anti correlation between T(sub e) and electron density and also exhibit a high ratio of T(sub e)/T(sub P) in the cloud. Since Landau damping is not effective for T(sub e)/T(sub p) much greater than 1, Doppler shifted ion acoustic waves are expected in the cloud. Calculation of ion acoustic wave frequencies in the cloud and comparison with observed wave activity confirm this expectation. As in our previous work, we show that the electron component in the cloud obeys a polytropic law with gamma is less than 1 (gamma approximately equals 0.3-0.4). The dynamics of the magnetic cloud are determined to a large degree by the dominating electron pressure.
Development and application of accurate analytical models for single active electron potentials
NASA Astrophysics Data System (ADS)
Miller, Michelle; Jaron-Becker, Agnieszka; Becker, Andreas
2015-05-01
The single active electron (SAE) approximation is a theoretical model frequently employed to study scenarios in which inner-shell electrons may productively be treated as frozen spectators to a physical process of interest, and accurate analytical approximations for these potentials are sought as a useful simulation tool. Density function theory is often used to construct a SAE potential, requiring that a further approximation for the exchange correlation functional be enacted. In this study, we employ the Krieger, Li, and Iafrate (KLI) modification to the optimized-effective-potential (OEP) method to reduce the complexity of the problem to the straightforward solution of a system of linear equations through simple arguments regarding the behavior of the exchange-correlation potential in regions where a single orbital dominates. We employ this method for the solution of atomic and molecular potentials, and use the resultant curve to devise a systematic construction for highly accurate and useful analytical approximations for several systems. Supported by the U.S. Department of Energy (Grant No. DE-FG02-09ER16103), and the U.S. National Science Foundation (Graduate Research Fellowship, Grants No. PHY-1125844 and No. PHY-1068706).
NASA Astrophysics Data System (ADS)
Craco, L.; Faria, J. L. B.
2016-02-01
Iron sulfides are promising candidates for the next generation of rechargeable lithium-ion battery materials. Motivated thereby, we present a detailed study of correlation- and doping-induced electronic reconstruction in troilite. Based on local-density-approximation plus dynamical-mean-field-theory, we stress the importance of multi-orbital Coulomb interactions in concert with first-principles band structure calculations for a consistent understanding of intrinsic Mott-Hubbard insulating state in FeS. We explore the anomalous nature of electron doping-induced insulator-bad metal transition, showing that it is driven by orbital-selective dynamical spectral weight transfer. Our results are relevant for understanding charge dynamics upon electrochemical lithiation of iron monosulfides electrode materials for lithium-ion batteries.
NASA Astrophysics Data System (ADS)
Nagy, Péter R.; Surján, Péter R.; Szabados, Ágnes
2014-01-01
Cross sections of inelastic light scattering accompanied by vibronic excitation in large conjugated carbon structures is assessed at the π-electron level. Intensities of Raman and vibrational Raman optical activity (VROA) spectra of fullerenes are computed, relying on a single electron per atom. When considering only first neighbor terms in the Hamiltonian (a tight-binding (TB) type or Hückel-model), Raman intensities are captured remarkably well, based on comparison with frequency-dependent linear response of the self-consistent field (SCF) method. Resorting to π-electron levels when computing spectral intensities brings a beneficial reduction in computational cost as compared to linear response SCF. At difference with total intensities, the first neighbor TB model is found inadequate for giving the left and right circularly polarized components of the scattered light, especially when the molecular surface is highly curved. To step beyond first neighbor approximation, an effective π-electron Hamiltonian, including interaction of all sites is derived from the all-electron Fockian, in the spirit of the Bloch-equation. Chiroptical cross-sections computed by this novel π-electron method improve upon first-neighbor TB considerably, with no increase in computational cost. Computed VROA spectra of chiral fullerenes, such as C76 and C28, are reported for the first time, both by conventional linear response SCF and effective π-electron models.
Electron beam injection during active experiments. I - Electromagnetic wave emissions
NASA Technical Reports Server (NTRS)
Winglee, R. M.; Kellogg, P. J.
1990-01-01
The wave emissions produced in Echo 7 experiment by active injections of electron beams were investigated to determine the properties of the electromagnetic and electrostatic fields for both the field-aligned and cross-field injection in such experiments and to evaluate the sources of free energy and relative efficiencies for the generation of the VLF and HF emissions. It is shown that, for typical beam energies in active experiments, electromagnetic effects do not substantially change the bulk properties of the beam, spacecraft charging, and plasma particle acceleration. Through simulations, beam-generated whistlers; fundamental z-mode and harmonic x-mode radiation; and electrostatic electron-cyclotron, upper-hybrid, Langmuir, and lower-hybrid waves were identified. The characteristics of the observed wave spectra were found to be sensitive to both the ratio of the electron plasma frequency to the cyclotron frequency and the angle of injection relative to the magnetic field.
NASA Astrophysics Data System (ADS)
Engel, D.; Klews, M.; Wunner, G.
2009-02-01
and to provide a program which allows users to calculate as comprehensively as possible energies, wavelengths, and oscillator strengths of medium-Z atoms and ions up to Z=26 in neutron star magnetic field strengths. Obviously, the method for achieving this goal must be highly efficient since for the calculation of synthetic spectra data of many thousands or even millions of atomic transitions may be required. Solution method: As in previous work on the problem (cf. [3,7]) we exploit the fact that a strong magnetic field results in an approximate decoupling of the dynamics of the electrons parallel and perpendicular to the field. In this adiabatic approximation the single-particle wave functions take the form: ψ(ρ,φ,z)=ϕ(ρ,φ)ṡP(z), where ϕ(ρ,φ) are Landau wave functions, describing the (fast) motion perpendicular to the field, and the P(z) are the longitudinal wave functions, describing the (slow) bound motion along the direction of the field. The spins of the electrons are all aligned antiparallel to the magnetic field and need not be accounted for explicitly. The total N-electron wave function is constructed as a Slater determinant of the single-particle wave functions, and the unknown longitudinal wave functions are determined from the Hartree-Fock equations, which follow from inserting the total N-electron wave function into Schrödinger's variational principle for the total energy. The novel feature of our approach [8] is to use finite-element and B-spline techniques to solve the Hartree-Fock equations for atoms in strong magnetic fields. This is accomplished through the following steps: 1) decomposition of the z-axis into finite elements with quadratically widening element borders; 2) sixth-order B-spline expansion of the single-particle wave functions on the individual finite elements; 3) formulation of the variational principle equivalent to the Hartree-Fock equations in terms of the expansion coefficients. This leads to a simple system of linear
Topside electron temperature models for low and high solar activity
NASA Astrophysics Data System (ADS)
Pandey, V.; Sethi, N.; Mahajan, K.
It is now well known that in the topside ionosphere, thermal conduction from the protonosphere becomes the dominant factor over the "heating" and "loss" terms in shaping the ionospheric electron temperature (Te) profile. By analyzing a limited data base of incoherent scatter (i.s.) Te measurements , Mahajan and Pandey (1980) reported a correlation between the topside electron heat flux and electron density, Ne at 400 km. In the recent years, since attention has been steadily mounting for the empirical modelling of Te, in this paper we exploit the large data base of i.s. measurements of Te and Ne at Arecibo, during 1989 -90 (high solar activity), as well as during 1975-76 ( low solar activity). We again find a functional relationship between heat flux and electron density in the topside ionosphere during both the solar activities. These functional relationships are used to generate topside Te profiles. As the current IRI Te model does not include variations with solar activity, the present work can contribute in improving the topside Te model.
NASA Astrophysics Data System (ADS)
Kosobutsky, A. V.; Basalaev, Yu. M.
2014-12-01
Using first-principles theoretical techniques within density functional theory and many-body perturbation theory we investigated the structural and electronic properties of two LiInSe2 crystal modifications, orthorhombic (β-NaFeO2-type) and tetragonal (CuFeS2-type), focusing on the interband transitions and band gaps. It is found that the Tran-Blaha (TB09) functional predicts LiInSe2 to be a direct-gap semiconductor with a significantly larger band gap as compared with that from common local-density and gradient-corrected functionals. The most accurate values of the fundamental energy gaps are calculated within quasiparticle GW approximation and found to be 2.95 eV for the orthorhombic phase and 2.85 eV for the tetragonal one, with equal pressure coefficients of 63 meV/GPa. Our theoretical results eliminate the uncertainty in the band gap of LiInSe2. Moreover, the data obtained define the upper limit of the band gap of solid solutions (Cu,Li)InSe2 and (Ag,Li)InSe2, which can be of interest for applications in optoelectronics.
Electron-beam-activated zinc selenide and diamond switches
NASA Astrophysics Data System (ADS)
Schoenbach, Karl H.; Kennedy, Mark R.; Joshi, Ravindra P.; Brinkmann, Ralf P.; Ho, Ping-Tong
1992-05-01
Zinc Selenide, in polycrystalline and single crystal form, and chemical vapor deposition (CVD) grown diamond films were studied with respect to their application as materials for electron-beam activated switches. The hold-off fields of the three materials were found to exceed that of semi-insulating gallium arsenide by at least an order of magnitude. Highest hold-off fields for pulsed voltage operation were recorded for diamond at 1.8 MV/cm. The electron-beam induced conductance in the 1 mm thick single crystal zinc selenide switches reached values of 0.5 (Ωcm2)-1 with an electron-beam current density of 20 mA/cm2 at electron-energies of 150 keV. This corresponds to an electron-beam induced reduction of switch resistance from 108 Ω to 2 Ω per square centimeter. The dominant carrier loss mechanism in the single crystal zinc selenide switch was found to be direct recombination of electron-hole pairs. In this material, the current, after electron-beam turn-off, decays hyperbolically with 90% to 10% falitimes in the range of hundreds of nanoseconds. The electron-beam induced conductivity in CVD grown diamond films of 1 micrometer thickness is due to the subnanosecond carrier lifetime less than three orders lower than that of single crystal zinc selenide. Both materials, single crystal zinc selenide and diamond, showed a lock-on effect in current. For diamond it could be demonstrated, as before for gaffium arsenide, that this effect can be suppressed by proper choice of contacts.
NASA Astrophysics Data System (ADS)
Engel, D.; Klews, M.; Wunner, G.
2009-02-01
and to provide a program which allows users to calculate as comprehensively as possible energies, wavelengths, and oscillator strengths of medium-Z atoms and ions up to Z=26 in neutron star magnetic field strengths. Obviously, the method for achieving this goal must be highly efficient since for the calculation of synthetic spectra data of many thousands or even millions of atomic transitions may be required. Solution method: As in previous work on the problem (cf. [3,7]) we exploit the fact that a strong magnetic field results in an approximate decoupling of the dynamics of the electrons parallel and perpendicular to the field. In this adiabatic approximation the single-particle wave functions take the form: ψ(ρ,φ,z)=ϕ(ρ,φ)ṡP(z), where ϕ(ρ,φ) are Landau wave functions, describing the (fast) motion perpendicular to the field, and the P(z) are the longitudinal wave functions, describing the (slow) bound motion along the direction of the field. The spins of the electrons are all aligned antiparallel to the magnetic field and need not be accounted for explicitly. The total N-electron wave function is constructed as a Slater determinant of the single-particle wave functions, and the unknown longitudinal wave functions are determined from the Hartree-Fock equations, which follow from inserting the total N-electron wave function into Schrödinger's variational principle for the total energy. The novel feature of our approach [8] is to use finite-element and B-spline techniques to solve the Hartree-Fock equations for atoms in strong magnetic fields. This is accomplished through the following steps: 1) decomposition of the z-axis into finite elements with quadratically widening element borders; 2) sixth-order B-spline expansion of the single-particle wave functions on the individual finite elements; 3) formulation of the variational principle equivalent to the Hartree-Fock equations in terms of the expansion coefficients. This leads to a simple system of linear
Controlling epileptiform activity with organic electronic ion pumps.
Williamson, Adam; Rivnay, Jonathan; Kergoat, Loïg; Jonsson, Amanda; Inal, Sahika; Uguz, Ilke; Ferro, Marc; Ivanov, Anton; Sjöström, Theresia Arbring; Simon, Daniel T; Berggren, Magnus; Malliaras, George G; Bernard, Christophe
2015-05-27
In treating epilepsy, the ideal solution is to act at a seizure's onset, but only in the affected regions of the brain. Here, an organic electronic ion pump is demonstrated, which directly delivers on-demand pure molecules to specific brain regions. State-of-the-art organic devices and classical pharmacology are combined to control pathological activity in vitro, and the results are verified with electrophysiological recordings. PMID:25866154
Artemisinin Inhibits Chloroplast Electron Transport Activity: Mode of Action
Bharati, Adyasha; Kar, Monaranjan; Sabat, Surendra Chandra
2012-01-01
Artemisinin, a secondary metabolite produced in Artemisia plant species, besides having antimalarial properties is also phytotoxic. Although, the phytotoxic activity of the compound has been long recognized, no information is available on the mechanism of action of the compound on photosynthetic activity of the plant. In this report, we have evaluated the effect of artemisinin on photoelectron transport activity of chloroplast thylakoid membrane. The inhibitory effect of the compound, under in vitro condition, was pronounced in loosely and fully coupled thylakoids; being strong in the former. The extent of inhibition was drastically reduced in the presence of uncouplers like ammonium chloride or gramicidin; a characteristic feature described for energy transfer inhibitors. The compound, on the other hand, when applied to plants (in vivo), behaved as a potent inhibitor of photosynthetic electron transport. The major site of its action was identified to be the QB; the secondary quinone moiety of photosystemII complex. Analysis of photoreduction kinetics of para-benzoquinone and duroquinone suggest that the inhibition leads to formation of low pool of plastoquinol, which becomes limiting for electron flow through photosystemI. Further it was ascertained that the in vivo inhibitory effect appeared as a consequence of the formation of an unidentified artemisinin-metabolite rather than by the interaction of the compound per se. The putative metabolite of artemisinin is highly reactive in instituting the inhibition of photosynthetic electron flow eventually reducing the plant growth. PMID:22719995
NASA Technical Reports Server (NTRS)
Gidley, D. W.; Rich, A.; Van House, J. C.; Zitzewitz, P. W.
1981-01-01
A positronium-formation experiment with a high sensitivity to a possible relation between the helicity of beta particles emitted in nuclear beta decay and the optical asymmetry of biological molecules is presented. The experiment is based on a mechanism in which the electrons in optically active molecules possess a helicity of less than 0.001, too weak to detect in radiolysis experiments, the sign of which depends on the chirality of the isomer. A helicity-dependent asymmetry is sought in the formation of the triplet ground state of positronium when a low-energy beam of polarized positrons of reversible helicity interacts with an optically active substance coating a channel electron multiplier. Asymmetries between positronium decays observed at positive and negative helicities for the same substance can thus be determined with a sensitivity of 0.0001, which represents a factor of 100 improvement over previous positronium experiments.
NASA Technical Reports Server (NTRS)
Richardson, I. G.; Cane, H. V.
2005-01-01
Periodicities of - 155 days in various solar and interplanetary phenomena were first discovered during solar cycle 21 and have been shown t o be intermittently present in other solar cycles. In the current solar cycle (23), they have been reported in solar energetic particle events and interplanetary coronal maSS ejections. We assess whether the "unexpected" October - November 2003 burst of solar activity during the late declining phase of the cycle may have been a manifestation of such a periodic behavior, and hence might have been to =me extent "predictable". If the pattern were to continue, episodes of enhanced activity might be expected around April - May and October, 2004. There was a mod- est increase activity increase in mid-April, 2004 which may conform to this pattern.
12 CFR 7.5003 - Composite authority to engage in electronic activities.
Code of Federal Regulations, 2010 CFR
2010-01-01
... 12 Banks and Banking 1 2010-01-01 2010-01-01 false Composite authority to engage in electronic activities. 7.5003 Section 7.5003 Banks and Banking COMPTROLLER OF THE CURRENCY, DEPARTMENT OF THE TREASURY BANK ACTIVITIES AND OPERATIONS Electronic Activities § 7.5003 Composite authority to engage in electronic activities. Unless otherwise...
12 CFR 7.5008 - Location of a national bank conducting electronic activities.
Code of Federal Regulations, 2010 CFR
2010-01-01
... 12 Banks and Banking 1 2010-01-01 2010-01-01 false Location of a national bank conducting electronic activities. 7.5008 Section 7.5008 Banks and Banking COMPTROLLER OF THE CURRENCY, DEPARTMENT OF THE TREASURY BANK ACTIVITIES AND OPERATIONS Electronic Activities § 7.5008 Location of a national bank conducting electronic activities. A national...
NASA Technical Reports Server (NTRS)
Trump, Jonathan R.; Weiner, Benjamin J.; Scarlata, Claudia; Kocevski, Dale D.; Bell, Eric F.; McGrath, Elizabeth J.; Koo, David C.; Faber, S. M.; Laird, Elise S.; Mozena, Mark; Rangel, Cyprian; Yan, Renbin; Yesuf, Hassen; Atek, Hakim; Dickinson, Mark; Donley, Jennifer L.; Dunlop, James S.; Ferguson, Henry C.; Finkelstein, Steven L.; Grogin, Norman A.; Hathi, Nimish P.; Juneau, Stephanie; Kartaltepe, Jeyhan S.; Koekemoer, Anton M.; Nandra, Kirpal
2011-01-01
We present Hubble Space Telescope Wide Field Camera 3 slitless grism spectroscopy of 28 emission-line galaxies at z approximates 2, in the GOODS-S region of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). The high sensitivity of these grism observations, with > 5-sigma detections of emission lines to f > 2.5 X 10(exp -18( erg/s/ square cm, means that the galaxies in the sample are typically approximately 7 times less massive (median M(star). = 10(exp 9.5)M(solar)) than previously studied z approximates 2 emission-line galaxies. Despite their lower mass, the galaxies have [O-III]/H-Beta ratios which are very similar to previously studied z approximates 2 galaxies and much higher than the typical emission-line ratios of local galaxies. The WFC3 grism allows for unique studies of spatial gradients in emission lines, and we stack the two-dimensional spectra of the galaxies for this purpose. In the stacked data the [O-III] emission line is more spatially concentrated than the H-Beta emission line with 98.1% confidence. We additionally stack the X-ray data (all sources are individually undetected), and find that the average L(sub [O-III])/L(sub 0.5.10keV) ratio is intermediate between typical z approximates 0 obscured active galaxies and star-forming galaxies. Together the compactness of the stacked [O-III] spatial profile and the stacked X-ray data suggest that at least some of these low-mass, low-metallicity galaxies harbor weak active galactic nuclei.
Two-Dimensional Halide Perovskites: Tuning Electronic Activities of Defects
NASA Astrophysics Data System (ADS)
Liu, Yuanyue; Xiao, Hai; Goddard, William A., III
2016-05-01
Two-dimensional (2D) halide perovskites are emerging as promising candidates for nano-electronics and optoelectronics. To realize their full potential, it is important to understand the role of those defects that can strongly impact material properties. In contrast to other popular 2D semiconductors (e.g. transition metal dichalcogenides MX2) for which defects typically induce harmful traps, we show that the electronic activities of defects in 2D perovskites are significantly tunable. For example, even with a fixed lattice orientation, one can change the synthesis conditions to convert a line defect (edge or grain boundary) from electron acceptor to inactive site without deep gap states. We show that this difference originates from the enhanced ionic bonding in these perovskites compared with MX2. The donors tend to have high formation energies, and the harmful defects are difficult to form at a low halide chemical potential. Thus we unveil unique properties of defects in 2D perovskites and suggest practical routes to improve them.
EMITTING ELECTRONS AND SOURCE ACTIVITY IN MARKARIAN 501
Mankuzhiyil, Nijil; Ansoldi, Stefano; Persic, Massimo; Rivers, Elizabeth; Rothschild, Richard; Tavecchio, Fabrizio
2012-07-10
We study the variation of the broadband spectral energy distribution (SED) of the BL Lac object Mrk 501 as a function of source activity, from quiescent to flaring. Through {chi}{sup 2}-minimization we model eight simultaneous SED data sets with a one-zone synchrotron self-Compton (SSC) model, and examine how model parameters vary with source activity. The emerging variability pattern of Mrk 501 is complex, with the Compton component arising from {gamma}-e scatterings that sometimes are (mostly) Thomson and sometimes (mostly) extreme Klein-Nishina. This can be seen from the variation of the Compton to synchrotron peak distance according to source state. The underlying electron spectra are faint/soft in quiescent states and bright/hard in flaring states. A comparison with Mrk 421 suggests that the typical values of the SSC parameters are different in the two sources: however, in both jets the energy density is particle-dominated in all states.
Soft Active Materials for Actuation, Sensing, and Electronics
NASA Astrophysics Data System (ADS)
Kramer, Rebecca Krone
Future generations of robots, electronics, and assistive medical devices will include systems that are soft and elastically deformable, allowing them to adapt their morphology in unstructured environments. This will require soft active materials for actuation, circuitry, and sensing of deformation and contact pressure. The emerging field of soft robotics utilizes these soft active materials to mimic the inherent compliance of natural soft-bodied systems. As the elasticity of robot components increases, the challenges for functionality revert to basic questions of fabrication, materials, and design - whereas such aspects are far more developed for traditional rigid-bodied systems. This thesis will highlight preliminary materials and designs that address the need for soft actuators and sensors, as well as emerging fabrication techniques for manufacturing stretchable circuits and devices based on liquid-embedded elastomers.
NASA Astrophysics Data System (ADS)
Egorov, E. N.; Kalinin, Yu. A.; Koronovsky, A. A.; Trubetskov, D. I.; Khramov, A. E.
2006-10-01
We present the results of studies within the framework of a two-dimensional numerical model of nonlinear nonstationary processes in a nonrelativistic electron beam in the mode of formation of a virtual cathode in the decelerating field without focusing of the electrons by a magnetic field (low-voltage vircator). The results of numerical simulation were qualitatively confirmed by the experiment.
NASA Technical Reports Server (NTRS)
Barghouty, A. F.
2012-01-01
Recent discovery by STEREO A/B of energetic neutral hydrogen is spurring an interest and need for reliable estimates of electron capture cross sections at few MeVs per nucleon as well as for multi-electron ions. Required accuracy in such estimates necessitates detailed and involved quantum-mechanical calculations or expensive numerical simulations. For ENA modeling and similar purposes, a semi-classical approach offers a middle-ground approach. Kuang's semiclassical formalism to calculate electron-capture cross sections for single and multi-electron ions is an elegant and efficient method, but has so far been applied to limited and specific laboratory measurements and at somewhat lower energies. Our goals are to test and extend Kuang s method to all ion-atom and ion-ion collisions relevant to ENA modeling, including multi-electron ions and for K-shell to K-shell transitions.
Robust activation method for negative electron affinity photocathodes
Mulhollan, Gregory A.; Bierman, John C.
2011-09-13
A method by which photocathodes(201), single crystal, amorphous, or otherwise ordered, can be surface modified to a robust state of lowered and in best cases negative, electron affinity has been discovered. Conventional methods employ the use of Cs(203) and an oxidizing agent(207), typically carried by diatomic oxygen or by more complex molecules, for example nitrogen trifluoride, to achieve a lowered electron affinity(404). In the improved activation method, a second alkali, other than Cs(205), is introduced onto the surface during the activation process, either by co-deposition, yo-yo, or sporadic or intermittent application. Best effect for GaAs photocathodes has been found through the use of Li(402) as the second alkali, though nearly the same effect can be found by employing Na(406). Suitable photocathodes are those which are grown, cut from boules, implanted, rolled, deposited or otherwise fabricated in a fashion and shape desired for test or manufacture independently supported or atop a support structure or within a framework or otherwise affixed or suspended in the place and position required for use.
Data Mining Approaches for Modeling Complex Electronic Circuit Design Activities
Kwon, Yongjin; Omitaomu, Olufemi A; Wang, Gi-Nam
2008-01-01
A printed circuit board (PCB) is an essential part of modern electronic circuits. It is made of a flat panel of insulating materials with patterned copper foils that act as electric pathways for various components such as ICs, diodes, capacitors, resistors, and coils. The size of PCBs has been shrinking over the years, while the number of components mounted on these boards has increased considerably. This trend makes the design and fabrication of PCBs ever more difficult. At the beginning of design cycles, it is important to estimate the time to complete the steps required accurately, based on many factors such as the required parts, approximate board size and shape, and a rough sketch of schematics. Current approach uses multiple linear regression (MLR) technique for time and cost estimations. However, the need for accurate predictive models continues to grow as the technology becomes more advanced. In this paper, we analyze a large volume of historical PCB design data, extract some important variables, and develop predictive models based on the extracted variables using a data mining approach. The data mining approach uses an adaptive support vector regression (ASVR) technique; the benchmark model used is the MLR technique currently being used in the industry. The strengths of SVR for this data include its ability to represent data in high-dimensional space through kernel functions. The computational results show that a data mining approach is a better prediction technique for this data. Our approach reduces computation time and enhances the practical applications of the SVR technique.
Activation of cyclic electron flow by hydrogen peroxide in vivo
Strand, Deserah D.; Livingston, Aaron K.; Satoh-Cruz, Mio; Froehlich, John E.; Maurino, Veronica G.; Kramer, David M.
2015-01-01
Cyclic electron flow (CEF) around photosystem I is thought to balance the ATP/NADPH energy budget of photosynthesis, requiring that its rate be finely regulated. The mechanisms of this regulation are not well understood. We observed that mutants that exhibited constitutively high rates of CEF also showed elevated production of H2O2. We thus tested the hypothesis that CEF can be activated by H2O2 in vivo. CEF was strongly increased by H2O2 both by infiltration or in situ production by chloroplast-localized glycolate oxidase, implying that H2O2 can activate CEF either directly by redox modulation of key enzymes, or indirectly by affecting other photosynthetic processes. CEF appeared with a half time of about 20 min after exposure to H2O2, suggesting activation of previously expressed CEF-related machinery. H2O2-dependent CEF was not sensitive to antimycin A or loss of PGR5, indicating that increased CEF probably does not involve the PGR5-PGRL1 associated pathway. In contrast, the rise in CEF was not observed in a mutant deficient in the chloroplast NADPH:PQ reductase (NDH), supporting the involvement of this complex in CEF activated by H2O2. We propose that H2O2 is a missing link between environmental stress, metabolism, and redox regulation of CEF in higher plants. PMID:25870290
Dinpajooh, Mohammadhasan; Martin, Daniel R; Matyushov, Dmitry V
2016-01-01
Enzymes in biology's energy chains operate with low energy input distributed through multiple electron transfer steps between protein active sites. The general challenge of biological design is how to lower the activation barrier without sacrificing a large negative reaction free energy. We show that this goal is achieved through a large polarizability of the active site. It is polarized by allowing a large number of excited states, which are populated quantum mechanically by electrostatic fluctuations of the protein and hydration water shells. This perspective is achieved by extensive mixed quantum mechanical/molecular dynamics simulations of the half reaction of reduction of cytochrome c. The barrier for electron transfer is consistently lowered by increasing the number of excited states included in the Hamiltonian of the active site diagonalized along the classical trajectory. We suggest that molecular polarizability, in addition to much studied electrostatics of permanent charges, is a key parameter to consider in order to understand how enzymes work. PMID:27306204
NASA Astrophysics Data System (ADS)
Dinpajooh, Mohammadhasan; Martin, Daniel R.; Matyushov, Dmitry V.
2016-06-01
Enzymes in biology’s energy chains operate with low energy input distributed through multiple electron transfer steps between protein active sites. The general challenge of biological design is how to lower the activation barrier without sacrificing a large negative reaction free energy. We show that this goal is achieved through a large polarizability of the active site. It is polarized by allowing a large number of excited states, which are populated quantum mechanically by electrostatic fluctuations of the protein and hydration water shells. This perspective is achieved by extensive mixed quantum mechanical/molecular dynamics simulations of the half reaction of reduction of cytochrome c. The barrier for electron transfer is consistently lowered by increasing the number of excited states included in the Hamiltonian of the active site diagonalized along the classical trajectory. We suggest that molecular polarizability, in addition to much studied electrostatics of permanent charges, is a key parameter to consider in order to understand how enzymes work.
Dinpajooh, Mohammadhasan; Martin, Daniel R.; Matyushov, Dmitry V.
2016-01-01
Enzymes in biology’s energy chains operate with low energy input distributed through multiple electron transfer steps between protein active sites. The general challenge of biological design is how to lower the activation barrier without sacrificing a large negative reaction free energy. We show that this goal is achieved through a large polarizability of the active site. It is polarized by allowing a large number of excited states, which are populated quantum mechanically by electrostatic fluctuations of the protein and hydration water shells. This perspective is achieved by extensive mixed quantum mechanical/molecular dynamics simulations of the half reaction of reduction of cytochrome c. The barrier for electron transfer is consistently lowered by increasing the number of excited states included in the Hamiltonian of the active site diagonalized along the classical trajectory. We suggest that molecular polarizability, in addition to much studied electrostatics of permanent charges, is a key parameter to consider in order to understand how enzymes work. PMID:27306204
Indium phosphide negative electron affinity photocathodes: Surface cleaning and activation
NASA Astrophysics Data System (ADS)
Sun, Yun
InP(100) is a very important semi-conductor for many applications. When activated by Cs and oxygen, the InP surface achieves the state of Negative Electron Affinity (NEA) making the Cs+O/InP system a very efficient electron source. Despite many years of study, the chemical cleaning and activation of InP are still not well understood. In our work, we have established an understanding of the basic physics and chemistry for the chemical cleaning and activation of the InP(100) surface. Synchrotron Radiation Photoelectron Spectroscopy is the main technique used in this study because of its high surface sensitivity and ability to identify chemical species present on the surface at each stage of our process. A clean, stoichiometric InP(100) surface is crucial for obtaining high performance of NEA photocathodes. Therefore, the first part of our study focused on the chemical cleaning of InP(100). We found that hydrogen peroxide based solutions alone, originally developed to clean GaAs(100) surfaces and widely used for InP(100), do not result in clean InP(I00) surfaces because oxide is left on the surface. A second cleaning step, which uses acid solutions like HCl or H2SO4, can remove all the oxide and leave a 0.4 ML protective layer of elemental phosphorous on the surface. The elemental phosphorous can be removed by annealing at 330°C and a clean InP(100) surface can be obtained. Cs deposition on InP(100) surface shows clear charge transfer from the Cs ad-atoms to the substrate. When the Cs/InP(100) surface is dosed with oxygen, the charge transfer from the Cs to substrate is reduced and substrate is oxidized. The activation of InP as a NEA photocathode is carried out by an alternating series of steps consisting of Cs deposition and Cs+O co-deposition. Two types of oxygen are found after activation. The first is dissociated oxygen and the other is a di-oxygen species (peroxide or superoxide). The decay of quantum-yield with time and with annealing is studied and changes in
Active Interrogation Using Electronic Neutron Generators for Nuclear Safeguards Applications
NASA Astrophysics Data System (ADS)
Chichester, D. L.; Seabury, E. H.
2009-03-01
Active interrogation, a measurement technique which uses a radiation source to probe materials and generate unique signatures useful for characterizing those materials, is a powerful tool for assaying special nuclear material. The most commonly used technique for performing active interrogation is to use an electronic neutron generator as the probe radiation source. Exploiting the unique operating characteristics of these devices, including their monoenergetic neutron emissions and their ability to operate in pulsed modes, presents a number of options for performing prompt and delayed signature analyses using both photon and neutron sensors. A review of literature in this area shows multiple applications of the active neutron interrogation technique for performing nuclear nonproliferation measurements. Some examples include measuring the plutonium content of spent fuel, assaying plutonium residue in spent fuel hull claddings, assaying plutonium in aqueous fuel reprocessing process streams, and assaying nuclear fuel reprocessing facility waste streams to detect and quantify fissile material. This paper discusses the historical use of this technique and examines its context within the scope and challenges of next-generation nuclear fuel cycles and advanced concept nuclear fuel cycle facilities.
Active Interrogation Using Electronic Neutron Generators for Nuclear Safeguards Applications
David L. Chichester; Edward H. Seabury
2008-08-01
Active interrogation, a measurement technique which uses a radiation source to probe materials and generate unique signatures useful for characterizing those materials, is a powerful tool for assaying special nuclear material. The most commonly used technique for performing active interrogation is to use an electronic neutron generator as the probe radiation source. Exploiting the unique operating characteristics of these devices, including their monoenergetic neutron emissions and their ability to operate in pulsed modes, presents a number of options for performing prompt and delayed signature analyses using both photon and neutron sensors. A review of literature in this area shows multiple applications of the active neutron interrogation technique for performing nuclear nonproliferation measurements. Some examples include measuring the plutonium content of spent fuel, assaying plutonium residue in spent fuel hull claddings, assaying plutonium in aqueous fuel reprocessing process streams, and assaying nuclear fuel reprocessing facility waste streams to detect and quantify fissile material. This paper discusses the historical use of this technique and examines its context within the scope and challenges of next-generation nuclear fuel cycles and advanced concept nuclear fuel cycle facilities.
Metronidazole activation and isolation of Clostridium acetobutylicum electron transport genes.
Santangelo, J D; Jones, D T; Woods, D R
1991-01-01
An Escherichia coli F19 recA, nitrate reductase-deficient mutant was constructed by transposon mutagenesis and shown to be resistant to metronidazole. This mutant was a most suitable host for the isolation of Clostridium acetobutylicum genes on recombinant plasmids, which activated metronidazole and rendered the E. coli F19 strain sensitive to metronidazole. Twenty-five E. coli F19 clones containing different recombinant plasmids were isolated and classified into five groups on the basis of their sensitivity to metronidazole. The clones were tested for nitrate reductase, pyruvate-ferredoxin oxidoreductase, and hydrogenase activities. DNA hybridization and restriction endonuclease mapping revealed that four of the C. acetobutylicum insert DNA fragments on recombinant plasmids were linked in an 11.1-kb chromosomal fragment. DNA sequencing and amino acid homology studies indicated that this DNA fragment contained a flavodoxin gene which encoded a protein of 160 amino acids that activated metronidazole and made the E. coli F19 mutant very sensitive to metronidazole. The flavodoxin and hydrogenase genes which are involved in electron transfer systems were linked on the 11.1-kb DNA fragment from C. acetobutylicum. Images PMID:1991710
NASA Astrophysics Data System (ADS)
Thatribud, Abdulmutta; Pengpan, Teparksorn
2014-09-01
In this work, band gaps of the delafossite Cu-based transparent conducting oxides CuMO2 (M =B,Al,Ga,In) are calculated by density functional theory (DFT) implemented with many-body perturbation theory (MBPT) based on quasiparticle self-consistent GW approximation (QPscGW) and with Tran-Blaha's modified Becke-Johnson functional (DFT-TB09). Their band gaps are explicitly improved from DFT within local density approximation (LDA). Their optical absorption spectra are also calculated by solving Bethe-Salpeter equation (BSE) that includes the electron-hole correlation effect; they show strong excitonic peaks.
Two-Dimensional Halide Perovskites: Tuning Electronic Activities of Defects.
Liu, Yuanyue; Xiao, Hai; Goddard, William A
2016-05-11
Two-dimensional (2D) halide perovskites are emerging as promising candidates for nanoelectronics and optoelectronics. To realize their full potential, it is important to understand the role of those defects that can strongly impact material properties. In contrast to other popular 2D semiconductors (e.g., transition metal dichalcogenides MX2) for which defects typically induce harmful traps, we show that the electronic activities of defects in 2D perovskites are significantly tunable. For example, even with a fixed lattice orientation one can change the synthesis conditions to convert a line defect (edge or grain boundary) from electron acceptor to inactive site without deep gap states. We show that this difference originates from the enhanced ionic bonding in these perovskites compared with MX2. The donors tend to have high formation energies and the harmful defects are difficult to form at a low halide chemical potential. Thus, we unveil unique properties of defects in 2D perovskites and suggest practical routes to improve them. PMID:27100910
Single-Molecule Electronic Monitoring of DNA Polymerase Activity
NASA Astrophysics Data System (ADS)
Marushchak, Denys O.; Pugliese, Kaitlin M.; Turvey, Mackenzie W.; Choi, Yongki; Gul, O. Tolga; Olsen, Tivoli J.; Rajapakse, Arith J.; Weiss, Gregory A.; Collins, Philip G.
Single-molecule techniques can reveal new spatial and kinetic details of the conformational changes occurring during enzymatic catalysis. Here, we investigate the activity of DNA polymerases using an electronic single-molecule technique based on carbon nanotube transistors. Single molecules of the Klenow fragment (KF) of polymerase I were conjugated to the transistors and then monitored via fluctuations in electrical conductance. Continuous, long-term monitoring recorded single KF molecules incorporating up to 10,000 new bases into single-stranded DNA templates. The duration of individual incorporation events was invariant across all analog and native nucleotides, indicating that the precise structure of different base pairs has no impact on the timing of incorporation. Despite similar timings, however, the signal magnitudes generated by certain analogs reveal alternate conformational states that do not occur with native nucleotides. The differences induced by these analogs suggest that the electronic technique is sensing KF's O-helix as it tests the stability of nascent base pairs.
Szenes, G.
2004-09-01
A linear scaling is found for intact biomolecules in the form of ln(Y/S{sub e})-1/S{sub e} where Y, and S{sub e} are the sputtering yield and the electronic stopping power, respectively. The law is in good agreement with the experimental data for valine, leucine, and insulin molecules in various charge states in a broad range of S{sub e}. The thermal spike model of the author is applied and the activation energies of desorption U are obtained from the slope of the semilogarithmic lines. U is considerably higher for neutral leucine molecules than for ions. The Coulomb contribution to U for molecular ions does not depend on S{sub e} in a broad range. During sputtering, the specific heat is approximately 10% of its room temperature value for valine and leucine.
Fosso-Tande, Jacob; Nguyen, Truong-Son; Gidofalvi, Gergely; DePrince, A Eugene
2016-05-10
A large-scale implementation of the complete active space self-consistent field (CASSCF) method is presented. The active space is described using the variational two-electron reduced-density-matrix (v2RDM) approach, and the algorithm is applicable to much larger active spaces than can be treated using configuration-interaction-driven methods. Density fitting or Cholesky decomposition approximations to the electron repulsion integral tensor allow for the simultaneous optimization of large numbers of external orbitals. We have tested the implementation by evaluating singlet-triplet energy gaps in the linear polyacene series and two dinitrene biradical compounds. For the acene series, we report computations that involve active spaces consisting of as many as 50 electrons in 50 orbitals and the simultaneous optimization of 1892 orbitals. For the dinitrene compounds, we find that the singlet-triplet gaps obtained from v2RDM-driven CASSCF with partial three-electron N-representability conditions agree with those obtained from configuration-interaction-driven approaches to within one-third of 1 kcal mol(-1). When enforcing only the two-electron N-representability conditions, v2RDM-driven CASSCF yields less accurate singlet-triplet energy gaps in these systems, but the quality of the results is still far superior to those obtained from standard single-reference approaches. PMID:27065086
Single cell activity reveals direct electron transfer in methanotrophic consortia.
McGlynn, Shawn E; Chadwick, Grayson L; Kempes, Christopher P; Orphan, Victoria J
2015-10-22
Multicellular assemblages of microorganisms are ubiquitous in nature, and the proximity afforded by aggregation is thought to permit intercellular metabolic coupling that can accommodate otherwise unfavourable reactions. Consortia of methane-oxidizing archaea and sulphate-reducing bacteria are a well-known environmental example of microbial co-aggregation; however, the coupling mechanisms between these paired organisms is not well understood, despite the attention given them because of the global significance of anaerobic methane oxidation. Here we examined the influence of interspecies spatial positioning as it relates to biosynthetic activity within structurally diverse uncultured methane-oxidizing consortia by measuring stable isotope incorporation for individual archaeal and bacterial cells to constrain their potential metabolic interactions. In contrast to conventional models of syntrophy based on the passage of molecular intermediates, cellular activities were found to be independent of both species intermixing and distance between syntrophic partners within consortia. A generalized model of electric conductivity between co-associated archaea and bacteria best fit the empirical data. Combined with the detection of large multi-haem cytochromes in the genomes of methanotrophic archaea and the demonstration of redox-dependent staining of the matrix between cells in consortia, these results provide evidence for syntrophic coupling through direct electron transfer. PMID:26375009
Single cell activity reveals direct electron transfer in methanotrophic consortia
NASA Astrophysics Data System (ADS)
McGlynn, Shawn E.; Chadwick, Grayson L.; Kempes, Christopher P.; Orphan, Victoria J.
2015-10-01
Multicellular assemblages of microorganisms are ubiquitous in nature, and the proximity afforded by aggregation is thought to permit intercellular metabolic coupling that can accommodate otherwise unfavourable reactions. Consortia of methane-oxidizing archaea and sulphate-reducing bacteria are a well-known environmental example of microbial co-aggregation; however, the coupling mechanisms between these paired organisms is not well understood, despite the attention given them because of the global significance of anaerobic methane oxidation. Here we examined the influence of interspecies spatial positioning as it relates to biosynthetic activity within structurally diverse uncultured methane-oxidizing consortia by measuring stable isotope incorporation for individual archaeal and bacterial cells to constrain their potential metabolic interactions. In contrast to conventional models of syntrophy based on the passage of molecular intermediates, cellular activities were found to be independent of both species intermixing and distance between syntrophic partners within consortia. A generalized model of electric conductivity between co-associated archaea and bacteria best fit the empirical data. Combined with the detection of large multi-haem cytochromes in the genomes of methanotrophic archaea and the demonstration of redox-dependent staining of the matrix between cells in consortia, these results provide evidence for syntrophic coupling through direct electron transfer.
Gosse, Laurent . E-mail: mauser@univie.ac.at
2006-01-01
This work is concerned with the semiclassical approximation of the Schroedinger-Poisson equation modeling ballistic transport in a 1D periodic potential by means of WKB techniques. It is derived by considering the mean-field limit of a N-body quantum problem, then K-multivalued solutions are adapted to the treatment of this weakly nonlinear system obtained after homogenization without taking into account for Pauli's exclusion principle. Numerical experiments display the behaviour of self-consistent wave packets and screening effects.
Improvement of chaperone activity of 2-Cys peroxiredoxin using electron beam
NASA Astrophysics Data System (ADS)
Hong, Sung Hyun; An, Byung Chull; Lee, Seung Sik; Lee, Jae Taek; Cho, Jae-Hyun; Jung, Hyun Suk; Chung, Byung Yeoup
2012-08-01
The peroxiredoxin protein expressed in Pseudomonas aeruginosa PAO1 (PaPrx) is a typical 2-cysteine peroxiredoxin that has dual functions as both a thioredoxin-dependent peroxidase and molecular chaperone. As the function of PaPrx is regulated by its structural status, in the present study, we examined the effects of electron beam radiation on the structural modifications of PaPrx, as well as changes to PaPrx peroxidase and chaperone functions. It was found that the chaperone activity of PaPrx was increased approximately 3- to 4-fold at 2 kGy when compared to non-irradiated PaPrx, while its peroxidase activity decreased. This corresponded to a shift from the low molecular weight PaPrx species that acts as a peroxidase to the high molecular weight complex that functions as a chaperone, as detected using polyacrylamide gel electrophoresis. We also investigated the influence of the electron beam on physical protein properties such as hydrophobicity and secondary structure. The exposure of the PaPrx hydrophobic domains in response to irradiation reached a peak at 2 kGy and then decreased in a dose-dependent manner at higher doses. In addition, the exposure of β-sheet and random coil elements on the surface of PaPrx was significantly increased following irradiation with an electron beam, whereas exposure of α-helix and turn elements was decreased. These results suggest that irradiated PaPrx may be a potential candidate for use in bio-engineering systems and various industrial applications, due to its enhanced chaperone activity.
Nano-fEM: Protein Localization Using Photo-activated Localization Microscopy and Electron Microscopy
Watanabe, Shigeki; Richards, Jackson; Hollopeter, Gunther; Hobson, Robert J.; Davis, Wayne M.; Jorgensen, Erik M.
2012-01-01
Mapping the distribution of proteins is essential for understanding the function of proteins in a cell. Fluorescence microscopy is extensively used for protein localization, but subcellular context is often absent in fluorescence images. Immuno-electron microscopy, on the other hand, can localize proteins, but the technique is limited by a lack of compatible antibodies, poor preservation of morphology and because most antigens are not exposed to the specimen surface. Correlative approaches can acquire the fluorescence image from a whole cell first, either from immuno-fluorescence or genetically tagged proteins. The sample is then fixed and embedded for electron microscopy, and the images are correlated 1-3. However, the low-resolution fluorescence image and the lack of fiducial markers preclude the precise localization of proteins. Alternatively, fluorescence imaging can be done after preserving the specimen in plastic. In this approach, the block is sectioned, and fluorescence images and electron micrographs of the same section are correlated 4-7. However, the diffraction limit of light in the correlated image obscures the locations of individual molecules, and the fluorescence often extends beyond the boundary of the cell. Nano-resolution fluorescence electron microscopy (nano-fEM) is designed to localize proteins at nano-scale by imaging the same sections using photo-activated localization microscopy (PALM) and electron microscopy. PALM overcomes the diffraction limit by imaging individual fluorescent proteins and subsequently mapping the centroid of each fluorescent spot 8-10. We outline the nano-fEM technique in five steps. First, the sample is fixed and embedded using conditions that preserve the fluorescence of tagged proteins. Second, the resin blocks are sectioned into ultrathin segments (70-80 nm) that are mounted on a cover glass. Third, fluorescence is imaged in these sections using the Zeiss PALM microscope. Fourth, electron dense structures are imaged
Micro- and Nanostructured Materials for Active Devices and Molecular Electronics
Martin, Peter M.; Graff, Gordon L.; Gross, Mark E.; Burrows, Paul E.; Bennett, Wendy D.; Mast, Eric S.; Hall, Michael G.; Bonham, Charles C.; Zumhoff, Mac R.; Williford, Rick E.
2003-10-01
Traditional single layer barrier coatings are not adequate in preventing degradation of the performance of organic molecular electronic and other active devices. Most advanced devices used in display technology now consist of micro and nanostructured small molecule, polymer and inorganic coatings with thin high reactive group 1A metals. This includes organic electronics such as organic light emitting devices (OLED). The lifetimes of these devices rapidly degrades when they are exposed to atmospheric oxygen and water vapor. Thin film photovoltaics and batteries are also susceptible to degradation by moisture and oxygen. Using in-line coating techniques we apply a composite nanostructured inorganic/polymer thin film barrier that restricts moisture and oxygen permeation to undetectable levels using conventional permeation test equipment. We describe permeation mechanisms for this encapsulation coating and flat panel display and other device applications. Permeation through the multilayer barrier coating is defect and pore limited and can be described by Knudsen diffusion involving a long and tortuous path. Device lifetime is also enhanced by the long lag times required to reach the steady state flux regime. Permeation rates in the range of 10-6 cc,g/m2/d have been achieved and OLED device lifetimes. The structure is robust, yet flexible. The resulting device performance and lifetimes will also be described. The barrier film can be capped with a thin film of transparent conductive oxide yielding an engineered nanostructured device for next generation, rugged, lightweight or flexible displays. This enables, for the first time, thin film encapsulation of emissive organic displays.
Campo, Shelly; Janz, Kathleen F; Eckler, Petya; Yang, Jingzhen; Snetselaar, Linda G; Signorini, Alessio
2013-01-01
Background Twitter is a widely used social medium. However, its application in promoting health behaviors is understudied. Objective In order to provide insights into designing health marketing interventions to promote physical activity on Twitter, this exploratory infodemiology study applied both social cognitive theory and the path model of online word of mouth to examine the distribution of different electronic word of mouth (eWOM) characteristics among personal tweets about physical activity in the United States. Methods This study used 113 keywords to retrieve 1 million public tweets about physical activity in the United States posted between January 1 and March 31, 2011. A total of 30,000 tweets were randomly selected and sorted based on numbers generated by a random number generator. Two coders scanned the first 16,100 tweets and yielded 4672 (29.02%) tweets that they both agreed to be about physical activity and were from personal accounts. Finally, 1500 tweets were randomly selected from the 4672 tweets (32.11%) for further coding. After intercoder reliability scores reached satisfactory levels in the pilot coding (100 tweets separate from the final 1500 tweets), 2 coders coded 750 tweets each. Descriptive analyses, Mann-Whitney U tests, and Fisher exact tests were performed. Results Tweets about physical activity were dominated by neutral sentiments (1270/1500, 84.67%). Providing opinions or information regarding physical activity (1464/1500, 97.60%) and chatting about physical activity (1354/1500, 90.27%) were found to be popular on Twitter. Approximately 60% (905/1500, 60.33%) of the tweets demonstrated users’ past or current participation in physical activity or intentions to participate in physical activity. However, social support about physical activity was provided in less than 10% of the tweets (135/1500, 9.00%). Users with fewer people following their tweets (followers) (P=.02) and with fewer accounts that they followed (followings) (P=.04
Mezey, Paul G
2014-09-16
Conspectus Just as complete molecules have no boundaries and have "fuzzy" electron density clouds approaching zero density exponentially at large distances from the nearest nucleus, a physically justified choice for electron density fragments exhibits similar behavior. Whereas fuzzy electron densities, just as any fuzzy object, such as a thicker cloud on a foggy day, do not lend themselves to easy visualization, one may partially overcome this by using isocontours. Whereas a faithful representation of the complete fuzzy density would need infinitely many such isocontours, nevertheless, by choosing a selected few, one can still obtain a limited pictorial representation. Clearly, such images are of limited value, and one better relies on more complete mathematical representations, using, for example, density matrices of fuzzy fragment densities. A fuzzy density fragmentation can be obtained in an exactly additive way, using the output from any of the common quantum chemical computational techniques, such as Hartree-Fock, MP2, and various density functional approaches. Such "fuzzy" electron density fragments properly represented have proven to be useful in a rather wide range of applications, for example, (a) using them as additive building blocks leading to efficient linear scaling macromolecular quantum chemistry computational techniques, (b) the study of quantum chemical functional groups, (c) using approximate fuzzy fragment information as allowed by the holographic electron density theorem, (d) the study of correlations between local shape and activity, including through-bond and through-space components of interactions between parts of molecules and relations between local molecular shape and substituent effects, (e) using them as tools of density matrix extrapolation in conformational changes, (f) physically valid averaging and statistical distribution of several local electron densities of common stoichiometry, useful in electron density databank mining, for
NASA Astrophysics Data System (ADS)
Bolaji, O. S.; Adeniyi, J. O.; Radicella, S. M.; Doherty, P. H.
2012-01-01
Slant total electron content (STEC) data measured by the Global Positioning System receiver at Ilorin, Nigeria, with geographical coordinates 8.47°N, 4.68°E for the year 2009 (a low-activity year) was used to study the diurnal, monthly standard deviation and monthly median value of total electron content (TEC). The vertical total electron content (VTEC) values are estimated from the STEC data. The thin shell approximation with an ionospheric shell height of 350 km was used for the analysis. The diurnal variation of VTEC (DTEC) and its corresponding monthly median variation (MTEC) shows a minimum at presunrise between the hours of 05:00 and 06:00 LT. The DTEC values show a maximum variation range from ˜24 to ˜34 total electron content unit (TECU). The daytime maximum TEC values observed in all the months were broad with a slight daytime depression in May, June, July, and November. The maximum variation of MTEC after slight daytime depression is greater than its variation before the slight daytime depression in the months affected with the month of July as exception. The slight daytime depression was lowest in the month of May and has a value of 0.99 TECU. A postsunset decrease at 20:00 LT with corresponding enhancement 2 h later was observed in the month of March. This post sunset decrease and enhancement in the month of March could be a strong indicator of the abrupt onset of scintillations, plasma bubbles, and spread F phenomenon. The monthly standard deviation depicts summary behavior of all the diurnal variations in each month. Annual and seasonal variations were also investigated.
NASA Astrophysics Data System (ADS)
Medeiros, Subenia; Araujo, Maeva
2015-03-01
The structural, electronic, vibrational, and optical properties of perovskite CaTiO3 in the cubic, orthorhombic, and tetragonal phase are calculated in the framework of density functional theory (DFT) with different exchange-correlation potentials by CASTEP package. The calculated band structure shows an indirect band gap of 1.88 eV at the Γ-R points in the Brillouin zone to the cubic structure, a direct band gap of 2.41 eV at the Γ- Γ points to the orthorhombic structure, and an indirect band gap of 2.31 eV at theM - Γ points to the tetragonal phase. It is still known that the CaTiO3 has a static dielectric constant that extrapolates to a value greater than 300 at zero temperature, and the dielectric response is dominated by low frequency (ν ~ 90cm-1) polar optical modes in which cation motion opposes oxygen motion. Our calculated lattice parameters, elastic constants, optical properties, and vibrational frequencies are found to be in good agreement with the available theoretical and experimental values. The results for the effective mass in the electron and hole carriers are also presented in this work.
NASA Astrophysics Data System (ADS)
Minjeaud, Sebastian; Pasquetti, Richard
2016-09-01
Due to the extreme conditions required to produce energy by nuclear fusion in tokamaks, simulating the plasma behavior is an important but challenging task. We focus on the edge part of the plasma, where fluid approaches are probably the best suited, and our approach relies on the Braginskii ion-electron model. Assuming that the electric field is electrostatic, this yields a set of 10 strongly coupled and non-linear conservation equations that exhibit multiscale and anisotropy features. The computational domain is a torus of complex geometrical section, that corresponds to the divertor configuration, i.e. with an "X-point" in the magnetic surfaces. To capture the complex physics that is involved, high order methods are used: The time-discretization is based on a Strang splitting, that combines implicit and explicit high order Runge-Kutta schemes, and the space discretization makes use of the spectral element method in the poloidal plane together with Fourier expansions in the toroidal direction. The paper thoroughly describes the algorithms that have been developed, provides some numerical validations of the key algorithms and exhibits the results of preliminary numerical experiments. In particular, we point out that the highest frequency of the system is intermediate between the ion and electron cyclotron frequencies.
Discharge Chamber Primary Electron Modeling Activities in Three-Dimensions
NASA Technical Reports Server (NTRS)
Steuber, Thomas J.
2004-01-01
Designing discharge chambers for ion thrusters involves many geometric configuration decisions. Various decisions will impact discharge chamber performance with respect to propellant utilization efficiency, ion production costs, and grid lifetime. These hardware design decisions can benefit from the assistance of computational modeling. Computational modeling for discharge chambers has been limited to two-dimensional codes that leveraged symmetry for interpretation into three-dimensional analysis. This paper presents model development activities towards a three-dimensional discharge chamber simulation to aid discharge chamber design decisions. Specifically, of the many geometric configuration decisions toward attainment of a worthy discharge chamber, this paper focuses on addressing magnetic circuit considerations with a three-dimensional discharge chamber simulation as a tool. With this tool, candidate discharge chamber magnetic circuit designs can be analyzed computationally to gain insight into factors that may influence discharge chamber performance such as: primary electron loss width in magnetic cusps, cathode tip position with respect to the low magnetic field volume, definition of a low magnetic field region, and maintenance of a low magnetic field region across the grid span. Corroborating experimental data will be obtained from mockup hardware tests. Initially, simulated candidate magnetic circuit designs will resemble previous successful thruster designs. To provide opportunity to improve beyond previous performance benchmarks, off-design modifications will be simulated and experimentally tested.
Federal Register 2010, 2011, 2012, 2013, 2014
2013-01-16
... Agency Information Collection Activities; Comment Request; Formula Grant for the Electronic Application... of Collection: Formula Grant for the Electronic Application System for Indian Education (EASIE). OMB... the Department of Education (ED) requests clearance for the Indian Education Formula Grant...
Tamborrino, Massimiliano
2016-06-01
The first passage time density of a diffusion process to a time varying threshold is of primary interest in different fields. Here, we consider a Brownian motion in presence of an exponentially decaying threshold to model the neuronal spiking activity. Since analytical expressions of the first passage time density are not available, we propose to approximate the curved boundary by means of a continuous two-piecewise linear threshold. Explicit expressions for the first passage time density towards the new boundary are provided. First, we introduce different approximating linear thresholds. Then, we describe how to choose the optimal one minimizing the distance to the curved boundary, and hence the error in the corresponding passage time density. Theoretical means, variances and coefficients of variation given by our method are compared with empirical quantities from simulated data. Moreover, a further comparison with firing statistics derived under the assumption of a small amplitude of the time-dependent change in the threshold, is also carried out. Finally, maximum likelihood and moment estimators of the parameters of the model are derived and applied on simulated data. PMID:27106189
Photon-activated electron hopping in a single-electron trap enhanced by Josephson radiation
NASA Astrophysics Data System (ADS)
Lotkhov, S. V.; Jalali-Jafari, B.; Zorin, A. B.
2016-04-01
Using a Josephson junction interferometer (DC SQUID) as a microwave source for irradiating a single-electron trap, both devices fabricated on the same chip, we study the process of photon-assisted tunneling as an effective mechanism of single photon detection. High sensitivity down to a very small oscillation amplitude v J ˜ 10 nV ≪ E act ≲ h f J and down to low photon absorption rates Γph ˜ (1-50) Hz, as well as a clear threshold type of operation with an activation energy Eact ˜ 400 μeV, is demonstrated for the trap with respect to the microwave photons of frequency fJ ˜ (100-200) GHz. Tunable generation is demonstrated with respect to the power and frequency of the microwave signal produced by the SQUID source biased within the subgap voltage range. A much weaker effect is observed at the higher junction voltages along the quasiparticle branch of the I-V curve; this response mostly appears due to the recombination phonons.
12 CFR 7.5003 - Composite authority to engage in electronic activities.
Code of Federal Regulations, 2011 CFR
2011-01-01
... 12 Banks and Banking 1 2011-01-01 2011-01-01 false Composite authority to engage in electronic activities. 7.5003 Section 7.5003 Banks and Banking COMPTROLLER OF THE CURRENCY, DEPARTMENT OF THE TREASURY BANK ACTIVITIES AND OPERATIONS Electronic Activities § 7.5003 Composite authority to engage...
12 CFR 7.5003 - Composite authority to engage in electronic activities.
Code of Federal Regulations, 2012 CFR
2012-01-01
... 12 Banks and Banking 1 2012-01-01 2012-01-01 false Composite authority to engage in electronic activities. 7.5003 Section 7.5003 Banks and Banking COMPTROLLER OF THE CURRENCY, DEPARTMENT OF THE TREASURY BANK ACTIVITIES AND OPERATIONS Electronic Activities § 7.5003 Composite authority to engage...
12 CFR 7.5003 - Composite authority to engage in electronic activities.
Code of Federal Regulations, 2013 CFR
2013-01-01
... 12 Banks and Banking 1 2013-01-01 2013-01-01 false Composite authority to engage in electronic activities. 7.5003 Section 7.5003 Banks and Banking COMPTROLLER OF THE CURRENCY, DEPARTMENT OF THE TREASURY BANK ACTIVITIES AND OPERATIONS Electronic Activities § 7.5003 Composite authority to engage...
12 CFR 7.5003 - Composite authority to engage in electronic activities.
Code of Federal Regulations, 2014 CFR
2014-01-01
... 12 Banks and Banking 1 2014-01-01 2014-01-01 false Composite authority to engage in electronic activities. 7.5003 Section 7.5003 Banks and Banking COMPTROLLER OF THE CURRENCY, DEPARTMENT OF THE TREASURY BANK ACTIVITIES AND OPERATIONS Electronic Activities § 7.5003 Composite authority to engage...
Using Electronic Neutron Generators in Active Interrogation to Detect Shielded Fissionable Material
D. L. Chichester; E. H. Seabury
2008-10-01
Experiments have been performed at Idaho National Laboratory to study methodology and instrumentation for performing neutron active interrogation die-away analyses for the purpose of detecting shielded fissionable material. Here we report initial work using a portable DT electronic neutron generator with a He-3 fast neutron detector to detect shielded fissionable material including >2 kg quantities of enriched uranium and plutonium. Measurements have been taken of bare material as well as of material hidden within a large plywood cube. Results from this work have demonstrated the efficacy of the die-away neutron measurement technique for quickly detecting the presence of special nuclear material hidden within plywood shields by analyzing the time dependent neutron signals in-between neutron generator pulses. Using a DT electronic neutron generator operating at 300 Hz with a yield of approximately 0.36 x 10**8 neutrons per second, 2.2 kg of enriched uranium hidden within a 0.60 m x 0.60 m x 0.70 m volume of plywood was positively detected with a measurement signal 2-sigma above the passive background within 1 second. Similarly, for a 500 second measurement period a lower detection limit of approaching the gram level could be expected with the same simple set-up.
Ruas, Alexandre; Simonin, Jean-Pierre; Turq, Pierre; Moisy, Philippe
2005-12-01
This work is aimed at a description of the thermodynamic properties of actinide salt solutions at high concentration. The predictive capability of the binding mean spherical approximation (BIMSA) theory to describe the thermodynamic properties of electrolytes is assessed in the case of aqueous solutions of lanthanide(III) nitrate and chloride salts. Osmotic coefficients of cerium(III) nitrate and chloride were calculated from other lanthanide(III) salts properties. In parallel, concentrated binary solutions of cerium nitrate were prepared in order to measure experimentally its water activity and density as a function of concentration, at 25 degrees C. Water activities of several binary solutions of cerium chloride were also measured to check existing data on this salt. Then, the properties of cerium chloride and cerium nitrate solutions were compared within the BIMSA model. Osmotic coefficient values for promethium nitrate and promethium chloride given by this theory are proposed. Finally, water activity measurements were made to examine the fact that the ternary system Ce(NO3)3/HNO3/H2O and the quaternary system Ce(NO3)3/HNO3/N2H5NO3/H2O may be regarded as "simple solutions" (in the sense of Zdanovskii and Mikulin). PMID:16854002
Effectiveness of Electronic Textbooks with Embedded Activities on Student Learning
ERIC Educational Resources Information Center
Porter, Paula L.
2010-01-01
Current versions of electronic textbooks mimic the format and structure of printed textbooks; however, the electronic capabilities of these new versions of textbooks offer the potential of embedding interactive features of web-based learning within the context of a textbook. This dissertation research study was conducted to determine if student…
Communication: Improved pair approximations in local coupled-cluster methods
Schwilk, Max; Werner, Hans-Joachim; Usvyat, Denis
2015-03-28
In local coupled cluster treatments the electron pairs can be classified according to the magnitude of their energy contributions or distances into strong, close, weak, and distant pairs. Different approximations are introduced for the latter three classes. In this communication, an improved simplified treatment of close and weak pairs is proposed, which is based on long-range cancellations of individually slowly decaying contributions in the amplitude equations. Benchmark calculations for correlation, reaction, and activation energies demonstrate that these approximations work extremely well, while pair approximations based on local second-order Møller-Plesset theory can lead to errors that are 1-2 orders of magnitude larger.
Holbrook, Robert J.; Weinberg, David J.; Peterson, Mark D.; Weiss, Emily A.; Meade, Thomas J.
2015-01-01
We describe a mechanism of light activation that initiates protein inhibitory action of a biologically inert Co(III) Schiff base (Co(III)-sb) complex. Photoinduced electron transfer (PET) occurs from a Ru(II) bipyridal complex to a covalently attached Co(III) complex and is gated by conformational changes that occur in tens of nanoseconds. Reduction of the Co(III)-sb by PET initiates displacement of the inert axial imidazole ligands, promoting coordination to active site histidines of α-thrombin. Upon exposure to 455 nm light, the rate of ligand exchange with 4-methylimidazole, a histidine mimic, increases by approximately 5-fold, as observed by NMR spectroscopy. Similarly, the rate of α-thrombin inhibition increases over 5-fold upon irradiation. These results convey a strategy for light activation of inorganic therapeutic agents through PET utilizing redox-active metal centers. PMID:25671465
NASA Astrophysics Data System (ADS)
Bordikar, M. R.; Scales, W. A.; Mahmoudian, A.; Kim, H.; Bernhardt, P. A.; Redmon, R.; Samimi, A. R.; Brizcinski, S.; McCarrick, M. J.
2014-01-01
Recently, narrowband emissions ordered near the H+ (proton) gyrofrequency (fcH) were reported in the stimulated electromagnetic emission (SEE) spectrum during active geomagnetic conditions. This work presents new observations and theoretical analysis of these recently discovered emissions. These emission lines are observed in the stimulated electromagnetic emission (SEE) spectrum when the transmitter is tuned near the second electron gyroharmonic frequency (2fce) during recent ionospheric modification experiments at the High Frequency Active Auroral Research (HAARP) facility near Gakona, Alaska. The spectral lines are typically shifted below and above the pump wave frequency by harmonics of a frequency roughly 10% less than fcH (≈ 800 Hz) with a narrow emission bandwidth less than the O+ gyrofrequency (≈ 50 Hz). However, new observations and analysis of emission lines ordered by a frequency approximately 10% greater than fcH are presented here for the first time as well. The interaction altitude for the heating for all the observations is in the range of 160 km up to 200 km. As described previously, proton precipitation due to active geomagnetic conditions is considered as the reason for the presence of H+ ions known to be a minor background constituent in this altitude region. DMSP satellite observations over HAARP during the heating experiments and ground-based magnetometer and riometer data validate active geomagnetic conditions. The theory of parametric decay instability in multi-ion component plasma including H+ ions as a minority species described in previous work is expanded in light of simultaneously observed preexisting SEE features to interpret the newly reported observations. Impact of active geomagnetic conditions on the SEE spectrum as a diagnostic tool for proton precipitation event characterization is discussed.
Electron bunching in a Penning trap and accelerating process for CO2 gas mixture active medium
NASA Astrophysics Data System (ADS)
Tian, Xiu-Fang; Wu, Cong-Feng; Jia, Qi-Ka
2015-12-01
In PASER (particle acceleration by stimulated emission of radiation), in the presence of an active medium incorporated in a Penning trap, moving electrons can become bunched, and as they get enough energy, they escape the trap forming an optical injector. These bunched electrons can enter the next PASER section filled with the same active medium to be accelerated. In this paper, electron dynamics in the presence of a gas mixture active medium incorporated in a Penning trap is analyzed by developing an idealized 1D model. We evaluate the energy exchange occurring as the train of electrons traverses into the next PASER section. The results show that the oscillating electrons can be bunched at the resonant frequency of the active medium. The influence of the trapped time and population inversion are analyzed, showing that the longer the electrons are trapped, the more energy from the medium the accelerated electrons get, and with the increase of population inversion, the decelerated electrons are virtually unchanged but the accelerated electrons more than double their peak energy values. The simulation results show that the gas active medium needs a lower population inversion to bunch the electrons compared to a solid active medium, so the experimental conditions can easily be achieved. Supported by National Natural Science Foundation of China (10675116) and Major State Basic Research Development Programme of China (2011CB808301)
Dissociative simple ionization of two active electron diatomic systems by fast electron impact
NASA Astrophysics Data System (ADS)
Lahmidi, N.; Joulakian, B.
2005-01-01
The dissociative (e, 2e) ionization of diatomic hydrogen and lithium by fast electrons is studied theoretically as a vertical transition from the lowest vibrational and rotational level of the fundamental electronic state 1Σ+g of H2 (and Li2) to the first dissociative 2Σu state of H2+ (and Li2+). After verification of the perturbative procedure in the non-dissociative case, for which experimental and theoretical results exist, the variation of the multiply differential cross section of the dissociative ionization is studied in a variety of situations to show the particularities of this process and motivate actually realizable complete experiments, which can detect the scattered and ejected electrons in coincidence with the bare detached nucleus. Our results show that the dynamically well understood behaviour in the case of simple (e, 2e) ionization breaks down in the dissociative case, because of the increasing influence of the electron-electron correlation of the two target electrons.
Stochastic resonance in passive and active electronic circuits
Anishchenko, V.S.; Khovanov, I.A.; Shulgin, B.V.
1996-06-01
The phenomenon of stochastic resonance in a bistable system modeling overdamped oscillator is studied by numerical simulations and experiments. Experimental data are compared with theoretical results. Stochastic resonance in Chua{close_quote}s circuit is investigated in detail for different regimes of its own dynamics. The main characteristics of stochastic resonance for different regimes under the adiabatic approximation are compared. {copyright} {ital 1996 American Institute of Physics.}
Rasin, A.
1994-04-01
We discuss the idea of approximate flavor symmetries. Relations between approximate flavor symmetries and natural flavor conservation and democracy models is explored. Implications for neutrino physics are also discussed.
Activity Dependent Global Model of Electron Loss inside the Plasmasphere
NASA Astrophysics Data System (ADS)
Orlova, K.; Spasojevic, M.; Shprits, Y.
2014-12-01
Using data from the CRRES plasma wave experiment, we develop quadratic fits to the mean of the wave amplitude squared for plasmaspheric hiss as a function of Kp, L, and magnetic latitude (λ) for the dayside (6
Development of a novel electron source for active space experiments
NASA Astrophysics Data System (ADS)
Everding, Daniel
2013-01-01
Recent advances in light emitting diode (LED) technology have facilitated a potential remedy to the problems plaguing filament based electron sources. Using spaceworthy LEDs, the photoelectron cathode and its progenitor the ultraviolet cathode (UVC) take advantage of the photoelectric effect to produce electrons for space based experiments. To produce these devices, two species of LED, each producing either ultraviolet or visible radiation, were collected and tested to determine potential photocurrent output. Additionally, materials with requisite photoemission characteristics were collected and tested in vacuum with the LEDs to assess their usefulness as photoelectron sources. Furthermore, circuitry and computer software was compiled, tested, and refined to control the experimental and custodial duties of the UVC and photoelectron cathode while deployed as an electron source in space.
ESTIMATION OF ELECTRON AFFINITY BASED ON STRUCTURE ACTIVITY RELATIONSHIPS
Electron affinity for a wide range of organic molecules was calculated from molecular structure using the chemical reactivity models developed in SPARC. hese models are based on fundamental chemical structure theory applied to the prediction of chemical reactivities for organic m...
Electron-beam activated thermal sputtering of thermoelectric materials.
Wu, J.; He, J.; Han, M-K.; Sootsman, J. R.; Girard, S.; Arachchige, I. U.; Kanatzidis, M. G.; Dravid, V. P.
2011-08-01
Thermoelectricity and Seebeck effect have long been observed and validated in bulk materials. With the development of advanced tools of materials characterization, here we report the first observation of such an effect in the nanometer scale: in situ directional sputtering of several thermoelectric materials inside electron microscopes. The temperature gradient introduced by the electron beam creates a voltage-drop across the samples, which enhances spontaneous sputtering of specimen ions. The sputtering occurs along a preferential direction determined by the direction of the temperature gradient. A large number of nanoparticles form and accumulate away from the beam location as a result. The sputtering and re-crystallization are found to occur at temperatures far below the melting points of bulk materials. The sputtering occurs even when a liquid nitrogen cooling holder is used to keep the overall temperature at -170 C. This unique phenomenon that occurred in the nanometer scale may provide useful clues to understanding the mechanism of thermoelectric effect.
Electron-beam activated thermal sputtering of thermoelectric materials
Wu Jinsong; Dravid, Vinayak P.; He Jiaqing; Han, Mi-Kyung; Sootsman, Joseph R.; Girard, Steven; Arachchige, Indika U.; Kanatzidis, Mercouri G.
2011-08-15
Thermoelectricity and Seebeck effect have long been observed and validated in bulk materials. With the development of advanced tools of materials characterization, here we report the first observation of such an effect in the nanometer scale: in situ directional sputtering of several thermoelectric materials inside electron microscopes. The temperature gradient introduced by the electron beam creates a voltage-drop across the samples, which enhances spontaneous sputtering of specimen ions. The sputtering occurs along a preferential direction determined by the direction of the temperature gradient. A large number of nanoparticles form and accumulate away from the beam location as a result. The sputtering and re-crystallization are found to occur at temperatures far below the melting points of bulk materials. The sputtering occurs even when a liquid nitrogen cooling holder is used to keep the overall temperature at -170 deg. C. This unique phenomenon that occurred in the nanometer scale may provide useful clues to understanding the mechanism of thermoelectric effect.
Active parallel redundancy for electronic integrator-type control circuits
NASA Technical Reports Server (NTRS)
Peterson, R. A.
1971-01-01
Circuit extends concept of redundant feedback control from type-0 to type-1 control systems. Inactive channels are slaves to the active channel, if latter fails, it is rejected and slave channel is activated. High reliability and elimination of single-component catastrophic failure are important in closed-loop control systems.
An electronic control for an electrohydraulic active control landing gear for the F-4 aircraft
NASA Technical Reports Server (NTRS)
Ross, I.
1982-01-01
A controller for an electrohydraulic active control landing gear was developed for the F-4 aircraft. A controller was modified for this application. Simulation results indicate that during landing and rollout over repaired bomb craters the active gear effects a force reduction, relative to the passive gear, or approximately 70%.
NASA Astrophysics Data System (ADS)
Gun'ko, V. M.; Zaulychnyy, Ya. V.; Ilkiv, B. I.; Zarko, V. I.; Nychiporuk, Yu. M.; Pakhlov, E. M.; Ptushinskii, Yu. G.; Leboda, R.; Skubiszewska-Zięba, J.
2011-11-01
Nanosilicas (A-50, A-300, A-500)/activated carbon (AC, SBET = 1520 m2/g) composites were prepared using short-term (5 min) mechanochemical activation (MCA) of powder mixtures in a microbreaker. Smaller silica nanoparticles of A-500 (average diameter dav = 5.5 nm) can more easily penetrate into broad mesopores and macropores of AC microparticles than larger nanoparticles of A-50 (dav = 52.4 nm) or A-300 (dav = 8.1 nm). After MCA of silica/AC, nanopores of non-broken AC nanoparticles remained accessible for adsorbed N2 molecules. According to ultra-soft X-ray emission spectra (USXES), MCA of silica/AC caused formation of chemical bonds Si-O-C; however, Si-C and Si-Si bonds were practically not formed. A decrease in intensity of OKα band in respect to CKα band of silica/AC composites with diminishing sizes of silica nanoparticles is due to both changes in the surface structure of particles and penetration of a greater number of silica nanoparticles into broad pores of AC microparticles and restriction of penetration depth of exciting electron beam into the AC particles.
When electron transfer meets electron transport in redox-active molecular nanojunctions.
Janin, Marion; Ghilane, Jalal; Lacroix, Jean-Christophe
2013-02-13
A scanning electrochemical microscope (SECM) was used to arrange two microelectrodes face-to-face separated by a micrometric gap. Polyaniline (PANI) was deposited electrochemically from the SECM tip side until it bridged the two electrodes. The junctions obtained were characterized by following the current through the PANI as a function of its electrochemical potential measured versus a reference electrode acting as a gate electrode in a solid-state transistor. PANI nanojunctions showed conductances below 100 nS in the oxidized state, indicating control of the charge transport within the whole micrometric gap by a limited number of PANI wires. The SECM configuration makes it possible to observe in the same experiment and in the same current range the electron-transfer and electron-transport processes. These two phenomena are distinguished here and characterized by following the variation of the current with the bias voltage and the scan rate. The electron-transfer current changes with the scan rate, while the charge-transport current varies with the bias voltage. Finally, despite the initially micrometric gap, a junction where the conductance is controlled by a single oligoaniline strand is achieved. PMID:23331168
CMOS Active Pixel Sensor Star Tracker with Regional Electronic Shutter
NASA Technical Reports Server (NTRS)
Yadid-Pecht, Orly; Pain, Bedabrata; Staller, Craig; Clark, Christopher; Fossum, Eric
1996-01-01
The guidance system in a spacecraft determines spacecraft attitude by matching an observed star field to a star catalog....An APS(active pixel sensor)-based system can reduce mass and power consumption and radiation effects compared to a CCD(charge-coupled device)-based system...This paper reports an APS (active pixel sensor) with locally variable times, achieved through individual pixel reset (IPR).
A new active solder for joining electronic components
SMITH,RONALD W.; VIANCO,PAUL T.; HERNANDEZ,CYNTHIA L.; LUGSCHEIDER,E.; RASS,I.; HILLEN,F.
2000-05-11
Electronic components and micro-sensors utilize ceramic substrates, copper and aluminum interconnect and silicon. The joining of these combinations require pre-metallization such that solders with fluxes can wet such combinations of metals and ceramics. The paper will present a new solder alloy that can bond metals, ceramics and composites. The alloy directly wets and bonds in air without the use flux or premetallized layers. The paper will present typical processing steps and joint microstructures in copper, aluminum, aluminum oxide, aluminum nitride, and silicon joints.
Colle, Renato; Embriaco, Davide; Massini, Michol; Simonucci, Stefano; Taioli, Simone
2004-10-01
Analytic expressions for the direct, resonant, and interference contributions to the differential cross section of a resonant Auger process, produced by the inner-shell photoionization of a linear molecule either 'fixed in space' or belonging to a gas of randomly oriented molecules, have been derived following Dill's procedures [Dill et al., Phys. Rev. Lett. 45, 1393 (1980)], but going beyond the two-step approximation. Angle-resolved Auger spectra of the C{sub 2}H{sub 2} molecule measured on top of the C 1s{yields}{pi}* resonance [Kivimaeki et al., J. Phys. B 30, 4279 (1997)] have been calculated together with asymmetry parameters, analyzing also the different contributions to the electron angular distributions.
NASA Technical Reports Server (NTRS)
Dutta, Soumitra
1988-01-01
A model for approximate spatial reasoning using fuzzy logic to represent the uncertainty in the environment is presented. Algorithms are developed which can be used to reason about spatial information expressed in the form of approximate linguistic descriptions similar to the kind of spatial information processed by humans. Particular attention is given to static spatial reasoning.
X-ray imaging of chemically active valence electrons during a pericyclic reaction
NASA Astrophysics Data System (ADS)
Bredtmann, Timm; Ivanov, Misha; Dixit, Gopal
2014-11-01
Time-resolved imaging of chemically active valence electron densities is a long-sought goal, as these electrons dictate the course of chemical reactions. However, X-ray scattering is always dominated by the core and inert valence electrons, making time-resolved X-ray imaging of chemically active valence electron densities extremely challenging. Here we demonstrate an effective and robust method, which emphasizes the information encoded in weakly scattered photons, to image chemically active valence electron densities. The degenerate Cope rearrangement of semibullvalene, a pericyclic reaction, is used as an example to visually illustrate our approach. Our work also provides experimental access to the long-standing problem of synchronous versus asynchronous bond formation and breaking during pericyclic reactions.
X-ray imaging of chemically active valence electrons during a pericyclic reaction
Bredtmann, Timm; Ivanov, Misha; Dixit, Gopal
2014-01-01
Time-resolved imaging of chemically active valence electron densities is a long-sought goal, as these electrons dictate the course of chemical reactions. However, X-ray scattering is always dominated by the core and inert valence electrons, making time-resolved X-ray imaging of chemically active valence electron densities extremely challenging. Here we demonstrate an effective and robust method, which emphasizes the information encoded in weakly scattered photons, to image chemically active valence electron densities. The degenerate Cope rearrangement of semibullvalene, a pericyclic reaction, is used as an example to visually illustrate our approach. Our work also provides experimental access to the long-standing problem of synchronous versus asynchronous bond formation and breaking during pericyclic reactions. PMID:25424639
Magnetic nanoparticle imaging using multiple electron paramagnetic resonance activation sequences
Coene, A. Dupré, L.; Crevecoeur, G.
2015-05-07
Magnetic nanoparticles play an important role in several biomedical applications such as hyperthermia, drug targeting, and disease detection. To realize an effective working of these applications, the spatial distribution of the particles needs to be accurately known, in a non-invasive way. Electron Paramagnetic Resonance (EPR) is a promising and sensitive measurement technique for recovering these distributions. In the conventional approach, EPR is applied with a homogeneous magnetic field. In this paper, we employ different heterogeneous magnetic fields that allow to stabilize the solution of the associated inverse problem and to obtain localized spatial information. A comparison is made between the two approaches and our novel adaptation shows an average increase in reconstruction quality by 5% and is 12 times more robust towards noise. Furthermore, our approach allows to speed up the EPR measurements while still obtaining reconstructions with an improved accuracy and noise robustness compared to homogeneous EPR.
NASA Technical Reports Server (NTRS)
Zdziarski, A. A.; Lightman, A. P.
1985-01-01
A nonthermal model for power-law X-ray and gamma-ray sources is considered. An initial, primary distribution of relativistic electrons is injected and cooled via Compton scattering of soft photons (produced either externally or by the synchrotron mechanism). The scattered photons, constituting a primary gamma-ray source, produce electron-positron pairs that act as a secondary electron injection, which in turn produce a secondary photon spectrum. Pairs formed by a part of the photon spectrum optically thin to pair production are taken into account. The distribution of particles and photons is obtained, and numerical results as well as analytical solutions to certain special cases are presented. For the case of a delta-function primary electron injection it is found that the photon spectrum in the X-ray region is well approximated by a power law, with the energy spectral index alpha(X) lying in the relatively narrow range 0.5-0.9 as the compactness parameter L(x)/R (where L(x) is the X-ray luminosity and R is the source radius) varies over many orders of magnitude. This is proposed as a possible mechanism to explain the universal X-ray spectra observed from active galactic nuclei.
Lichtenberg, C; Krummenacher, I
2016-08-21
Aminotroponiminates (atis) are shown to be redox-active ligands. Under strongly reducing conditions, the result of electron transfer can be controlled by the choice of the metal bound to the ati ligand. Either reversible electron transfer or a reductively induced dimerisation is observed. The latter reaction is (regio- and diastereo-) selective and chemically reversible. PMID:27452905
Federal Register 2010, 2011, 2012, 2013, 2014
2013-03-22
... From the Federal Register Online via the Government Publishing Office ] DEPARTMENT OF EDUCATION Agency Information Collection Activities; eZ-Audit: Electronic Submission of Financial Statements and Compliance Audits AGENCY: Federal Student Aid (FSA), Department of Education (ED). ACTION: Notice....
A semi-quantitative scanning electron microscope (SEK) analytical technique has been developed to examine granular activated carbon (GAC) utilized as media for biomass attachment in liquid waste treatment (combined processes). he procedure allows for the objective monitoring, com...
NASA Astrophysics Data System (ADS)
Meredith, Nigel P.; Horne, Richard B.; Johnstone, Alan D.; Anderson, Roger R.
2000-06-01
The temporal evolution of electron distributions and associated wave activity following substorm injections in the inner magnetosphere are investigated using data from the CRRES satellite. Equatorial electron distributions and concomitant wave spectra outside the plasmapause on the nightside of the Earth are studied as a function of time since injection determined from the auroral-electrojet index (AE). The electron cyclotron harmonic (ECH) wave amplitudes are shown to be very sensitive to small modeling errors in the location of the magnetic equator. They are best understood at the ECH equator, defined by the local maximum in the ECH wave activity in the vicinity of the nominal magnetic equator, suggesting that the ECH equator is a better measure of the location of the true equator. Strong ECH and whistler mode wave amplitudes are associated with the injected distributions and at the ECH equator, in the region 6.0<=L<7.0, exponential fits reveal wave amplitude decay time constants of 6.3+/-1.2 and 4.6+/-0.7 hours, respectively. Pancake electron distributions are seen to develop from injected distributions that are nearly isotropic in velocity space and, in this region, are seen to form on a similar timescale of approximately 4 hours suggesting that both wave types are involved in their production. The timescale for pancake production and wave decay is comparable with the average time interval between substorm events so that the wave-particle interactions are almost continually present in this region leading to a continual supply of electrons to power the diffuse aurora. In the region 3.8<=L<6.0 the timescale for wave decay at the ECH equator is 2.3+/-0.6 and 1.1+/-0.2 hours for ECH waves and whistler mode waves respectively, although the pancakes in this region show no clear evolution as a function of time.
Electron beam injection during active experiments. II - Collisional effects
NASA Technical Reports Server (NTRS)
Winglee, R. M.
1990-01-01
During active beam experiments, the presence of high neutral densities at low altitudes and/or during thruster firings has been observed to modify the spacecraft charging and the properties of the beam. Two-dimensional (three-velocity) electromagnetic particle simulations with ionizing collisions incorporated are used to investigate the modification of the beam-plasma interaction as the neutral density is increased. It is shown that when the spacecraft is uniformly immersed in a neutral cloud, most of the ionization is produced by direct ionization by the beam and its secondaries, rather than via vehicle-induced or wave-induced ionization for the neutral densities considered.
Calculator Function Approximation.
ERIC Educational Resources Information Center
Schelin, Charles W.
1983-01-01
The general algorithm used in most hand calculators to approximate elementary functions is discussed. Comments on tabular function values and on computer function evaluation are given first; then the CORDIC (Coordinate Rotation Digital Computer) scheme is described. (MNS)
NASA Astrophysics Data System (ADS)
Kozlova, I. N.
2016-04-01
We propose a model of functional parameters drift for electronic devices, allowing predicting their lifetime. The method of model parameters estimation is developed. The developed model allows optimizing the accelerated tests modes, taking into account the complex impact of stress factors. The results are applicable for modern electronic devices with a failure rate less than 1 FIT. The results are applicable if the physical and chemical processes leading to electronic devices degradation have an activation mechanism; the activation process is due to the temperature.
NASA Astrophysics Data System (ADS)
Popa, Sorin G.; Shahinpoor, Mohsen
2001-08-01
A novel electronic device capable of sensing and monitoring the myoelectric, polarization wave and electromagnetic activities of the biological systems and in particular the human body is presented. It is known that all the physical and chemical processes within biological systems are associated with polarization, depolarization waves from the brain, neural signals and myoelectric processes that manifest themselves in ionic and dipole motion. The technology developed in our laboratory is based on certain charge motion sensitive electronics. The electronic system developed is capable of sensing the electromagnetic activities of biological systems. The information obtained is then processed by specialized software in order to interpret it from physical and chemical point of view.
NASA Technical Reports Server (NTRS)
Dutta, Soumitra
1988-01-01
Much of human reasoning is approximate in nature. Formal models of reasoning traditionally try to be precise and reject the fuzziness of concepts in natural use and replace them with non-fuzzy scientific explicata by a process of precisiation. As an alternate to this approach, it has been suggested that rather than regard human reasoning processes as themselves approximating to some more refined and exact logical process that can be carried out with mathematical precision, the essence and power of human reasoning is in its capability to grasp and use inexact concepts directly. This view is supported by the widespread fuzziness of simple everyday terms (e.g., near tall) and the complexity of ordinary tasks (e.g., cleaning a room). Spatial reasoning is an area where humans consistently reason approximately with demonstrably good results. Consider the case of crossing a traffic intersection. We have only an approximate idea of the locations and speeds of various obstacles (e.g., persons and vehicles), but we nevertheless manage to cross such traffic intersections without any harm. The details of our mental processes which enable us to carry out such intricate tasks in such apparently simple manner are not well understood. However, it is that we try to incorporate such approximate reasoning techniques in our computer systems. Approximate spatial reasoning is very important for intelligent mobile agents (e.g., robots), specially for those operating in uncertain or unknown or dynamic domains.
Approximate kernel competitive learning.
Wu, Jian-Sheng; Zheng, Wei-Shi; Lai, Jian-Huang
2015-03-01
Kernel competitive learning has been successfully used to achieve robust clustering. However, kernel competitive learning (KCL) is not scalable for large scale data processing, because (1) it has to calculate and store the full kernel matrix that is too large to be calculated and kept in the memory and (2) it cannot be computed in parallel. In this paper we develop a framework of approximate kernel competitive learning for processing large scale dataset. The proposed framework consists of two parts. First, it derives an approximate kernel competitive learning (AKCL), which learns kernel competitive learning in a subspace via sampling. We provide solid theoretical analysis on why the proposed approximation modelling would work for kernel competitive learning, and furthermore, we show that the computational complexity of AKCL is largely reduced. Second, we propose a pseudo-parallelled approximate kernel competitive learning (PAKCL) based on a set-based kernel competitive learning strategy, which overcomes the obstacle of using parallel programming in kernel competitive learning and significantly accelerates the approximate kernel competitive learning for large scale clustering. The empirical evaluation on publicly available datasets shows that the proposed AKCL and PAKCL can perform comparably as KCL, with a large reduction on computational cost. Also, the proposed methods achieve more effective clustering performance in terms of clustering precision against related approximate clustering approaches. PMID:25528318
NASA Astrophysics Data System (ADS)
Behzadi, Hadi; Roonasi, Payman; Assle taghipour, Khatoon; van der Spoel, David; Manzetti, Sergio
2015-07-01
The quantum chemical calculations at the DFT/B3LYP level of theory were carried out on seven quinoxaline compounds, which have been synthesized as anti-Mycobacterium tuberculosis agents. Three conformers were optimized for each compound and the lowest energy structure was found and used in further calculations. The electronic properties including EHOMO, ELUMO and related parameters as well as electron density around oxygen and nitrogen atoms were calculated for each compound. The relationship between the calculated electronic parameters and biological activity of the studied compounds were investigated. Six similar quinoxaline derivatives with possible more drug activity were suggested based on the calculated electronic descriptors. A mechanism was proposed and discussed based on the calculated electronic parameters and bond dissociation energies.
Development of self-assembling nanowires containing electronically active oligothiophenes
NASA Astrophysics Data System (ADS)
Tsai, Wei-Wen
This dissertation discusses the development of conductive one-dimensional nanowires from self-assembling oligothiophene molecules. Self-assembly has been demonstrated to be a promising alternative approach towards high performance, solution processable, and low-cost organic electronics. One of the many challenges in this field is the control of supramolecular morphologies of ordered structures containing pi-conjugated moieties. This research demonstrated several successful strategies to achieve self assembly of conductive nanowires using synergistic interactions combining pi stacking and hydrogen bonding. The first approach used was to develop a hairpin-shaped sexithiophene molecule, which features two arms of the conjugated structure. The diamidocyclohexyl headgroup of this molecule successfully directs the self-assembly from hydrogen bonding among the amides, forming high-aspect-ratio one-dimensional nanowires with well-defined diameters of 3.0 +/- 0.3 nm. The molecular orientation in the nanostructures promotes formation of sexithiophene H and J aggregates that facilitate efficient charge transport. Organic field-effect transistors were fabricated to reveal improved intrinsic hole mobility from films of the nanostructures, 3.46 x 10-6 cm2V-1s-1, which is one order of magnitude higher than films cast from unassembled molecules. Bulk heterojunction solar cells were developed from this molecule and fullerenes utilizing solution-phase fabrication methods. Intimate mix of the molecule and phenyl-C61-butyric acid methyl ester creates structured interfaces for efficient exciton splitting. The charge carrier mobilities of each material are improved by self-assembly in solution and thermal-energy assisted phase separation.The photovoltaic devices achieved the highest open-circuit voltage of 0.62 V, short-circuit current of 1.79 mA/cm2, fill factor of 35%, and power conversion efficiency of 0.48%. Another strategy to one-dimensional nanowires studied here involved the
ERIC Educational Resources Information Center
Floro, Josh N.; Dunton, Genevieve F.; Delfino, Ralph J.
2009-01-01
Convergent validity of accelerometer and electronic diary physical activity data was assessed in children with asthma. Sixty-two participants, ages 9-18 years, wore an accelerometer and reported their physical activity level in quarter-hour segments every 2 hr using the Ambulatory Diary Assessment (ADA). Moderate validity was found between…
Electronic Textiles as Disruptive Designs: Supporting and Challenging Maker Activities in Schools
ERIC Educational Resources Information Center
Kafai, Yasmin B.; Fields, Deborah A.; Searle, Kristin A.
2014-01-01
Electronic textiles are a part of the increasingly popular maker movement that champions existing do-it-yourself activities. As making activities broaden from Maker Faires and fabrication spaces in children's museums, science centers, and community organizations to school classrooms, they provide new opportunities for learning while…
Generalized Gradient Approximation Made Simple
Perdew, J.P.; Burke, K.; Ernzerhof, M.
1996-10-01
Generalized gradient approximations (GGA{close_quote}s) for the exchange-correlation energy improve upon the local spin density (LSD) description of atoms, molecules, and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental constants. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential. {copyright} {ital 1996 The American Physical Society.}
Covariant approximation averaging
NASA Astrophysics Data System (ADS)
Shintani, Eigo; Arthur, Rudy; Blum, Thomas; Izubuchi, Taku; Jung, Chulwoo; Lehner, Christoph
2015-06-01
We present a new class of statistical error reduction techniques for Monte Carlo simulations. Using covariant symmetries, we show that correlation functions can be constructed from inexpensive approximations without introducing any systematic bias in the final result. We introduce a new class of covariant approximation averaging techniques, known as all-mode averaging (AMA), in which the approximation takes account of contributions of all eigenmodes through the inverse of the Dirac operator computed from the conjugate gradient method with a relaxed stopping condition. In this paper we compare the performance and computational cost of our new method with traditional methods using correlation functions and masses of the pion, nucleon, and vector meson in Nf=2 +1 lattice QCD using domain-wall fermions. This comparison indicates that AMA significantly reduces statistical errors in Monte Carlo calculations over conventional methods for the same cost.
Fast approximate motif statistics.
Nicodème, P
2001-01-01
We present in this article a fast approximate method for computing the statistics of a number of non-self-overlapping matches of motifs in a random text in the nonuniform Bernoulli model. This method is well suited for protein motifs where the probability of self-overlap of motifs is small. For 96% of the PROSITE motifs, the expectations of occurrences of the motifs in a 7-million-amino-acids random database are computed by the approximate method with less than 1% error when compared with the exact method. Processing of the whole PROSITE takes about 30 seconds with the approximate method. We apply this new method to a comparison of the C. elegans and S. cerevisiae proteomes. PMID:11535175
The Guiding Center Approximation
NASA Astrophysics Data System (ADS)
Pedersen, Thomas Sunn
The guiding center approximation for charged particles in strong magnetic fields is introduced here. This approximation is very useful in situations where the charged particles are very well magnetized, such that the gyration (Larmor) radius is small compared to relevant length scales of the confinement device, and the gyration is fast relative to relevant timescales in an experiment. The basics of motion in a straight, uniform, static magnetic field are reviewed, and are used as a starting point for analyzing more complicated situations where more forces are present, as well as inhomogeneities in the magnetic field -- magnetic curvature as well as gradients in the magnetic field strength. The first and second adiabatic invariant are introduced, and slowly time-varying fields are also covered. As an example of the use of the guiding center approximation, the confinement concept of the cylindrical magnetic mirror is analyzed.
Spectra of energetic electrons in teh space: dependence on solar activity
NASA Astrophysics Data System (ADS)
Mineev, Yu. V.
2001-08-01
The work examines the dataset of the energetic (0.1-6.0 MeV) electron fluxes and spectra measured on the Prognoz 4-10, IMP 6-8, Ohzora, Soho, and Intercosmos 19 satellites during solar cycles 21-23. The energetic electrons are treated to originate mainly from the Galaxy, the Sun, Jupiter and (in some cases) from the Earth s magnetosphere. The differential electron energy spectra throughout different solar activity cycles and their variations during solar minima and maxima are analyzed. The reasons for the variations in the electron energy spectra are discussed. Simultaneous measurements on near-Earth satellile IMP and Prognoz types showed, that the magnitoshere of Jupiter is a source of near to Earth electrons with energy > 0.3 MeV. The Earth magnetoshere serves a source of energetic electron fluxes. This phenomenon was determined with a help of measurements on anisotropy and asymmetry in fluxes on satellites Prognoz and Intercosmos series. During solar bursts conciderable increasing in electron fluxes with small and middle energies can be observed in the space. Satellites Prognoz and Ohzora for example registrated spectra of space electrons which originated from the Sun. Contribution of different sources into comulative electron spectra in dependence on a level of the solar activity was estimated as a result of series of experiments on a number of satellites.On the basis of measurements on satellites Prognoz, IMP, Ohzora and Soho characteristics of fluxes and spectra of energetic electrons in dependence of solar activity were predicted for 23-rd cycle.
Monotone Boolean approximation
Hulme, B.L.
1982-12-01
This report presents a theory of approximation of arbitrary Boolean functions by simpler, monotone functions. Monotone increasing functions can be expressed without the use of complements. Nonconstant monotone increasing functions are important in their own right since they model a special class of systems known as coherent systems. It is shown here that when Boolean expressions for noncoherent systems become too large to treat exactly, then monotone approximations are easily defined. The algorithms proposed here not only provide simpler formulas but also produce best possible upper and lower monotone bounds for any Boolean function. This theory has practical application for the analysis of noncoherent fault trees and event tree sequences.
NASA Astrophysics Data System (ADS)
Hajra, R.; Tsurutani, B.; Echer, E.
2015-12-01
Relativistic (E > 0.6, > 2.0, and > 4.0 MeV) electrons at geosynchronous orbit during solar cycle 23 are well-correlated with the intervals of high-intensity, long-duration, continuous AE activity (HILDCAA) events. Cluster-4 passes were examined for electromagnetic chorus waves in the 5 < L < 10 and 0 < MLT < 12 region. All the HILDCAA events under study were found to be characterized by enhanced whistler-mode chorus waves and flux enhancements of magnetospheric relativistic electrons of all three energies compared to the pre-event flux levels. CIR magnetic storms followed by HILDCAA events show almost the same relativistic electron signatures. It is concluded that the CIR storms have little to do with the acceleration of relativistic electrons. The response of the energetic electrons to HILDCAAs was found to vary with solar cycle phase. The initial electron fluxes were lower for events occurring during the ascending and solar maximum (AMAX) phases than for events occurring during the descending and solar minimum (DMIN) phases. The flux increases for the DMIN-phase events were > 50% larger than for the AMAX-phase events. It is concluded that electrons are accelerated to relativistic energies most often and most efficiently during the DMIN-phases of the solar cycle. Enhanced E > 0.6 MeV electron fluxes at geosynchronous orbit were first detected ~1 day after the statistical onset of HILDCAAs, E > 2.0 MeV electrons after ~1.5 days, and E > 4.0 MeV electrons after ~2.5 days. It is proposed that relativistic electrons are bootstrapped from high energy electrons: the E > 0.6 MeV electrons are accelerated from HILDCAA-injected E ~100 keV electrons, the E > 2.0 MeV electrons from the E > 0.6 MeV electron population, and consequently the E > 4.0 MeV electrons are accelerated from the E > 2.0 MeV population, etc. Relativistic electron acceleration and decay timescales will be provided for wave-particle investigators to attempt to match their models to empirically derived
NASA Astrophysics Data System (ADS)
Tang, Xuemei; Huang, Lulu; Zhang, Wenyang; Jiang, Ruowei; Zhong, Hongying
2015-03-01
Understanding of the dynamic process of laser-induced ultrafast electron tunneling is still very limited. It has been thought that the photo-catalytic reaction of adsorbents on the surface is either dependent on the number of resultant electron-hole pairs where excess energy is lost to the lattice through coupling with phonon modes, or dependent on irradiation photon wavelength. We used UV (355 nm) laser pulses to excite electrons from the valence band to the conduction band of titanium dioxide (TiO2), zinc oxide (ZnO) and bismuth cobalt zinc oxide (Bi2O3)0.07(CoO)0.03(ZnO)0.9 semiconductor nanoparticles with different photo catalytic properties. Photoelectrons are extracted, accelerated in a static electric field and eventually captured by charge deficient atoms of adsorbed organic molecules. A time-of-flight mass spectrometer was used to detect negative molecules and fragment ions generated by un-paired electron directed bond cleavages. We show that the probability of electron tunneling is determined by the strength of the static electric field and intrinsic electron mobility of semiconductors. Photo-catalytic dissociation or polymerization reactions of adsorbents are highly dependent on the kinetic energy of tunneling electrons as well as the strength of laser influx. By using this approach, photo-activities of phytohormones have been investigated.
Tang, Xuemei; Huang, Lulu; Zhang, Wenyang; Jiang, Ruowei; Zhong, Hongying
2015-01-01
Understanding of the dynamic process of laser-induced ultrafast electron tunneling is still very limited. It has been thought that the photo-catalytic reaction of adsorbents on the surface is either dependent on the number of resultant electron-hole pairs where excess energy is lost to the lattice through coupling with phonon modes, or dependent on irradiation photon wavelength. We used UV (355 nm) laser pulses to excite electrons from the valence band to the conduction band of titanium dioxide (TiO2), zinc oxide (ZnO) and bismuth cobalt zinc oxide (Bi2O3)0.07(CoO)0.03(ZnO)0.9 semiconductor nanoparticles with different photo catalytic properties. Photoelectrons are extracted, accelerated in a static electric field and eventually captured by charge deficient atoms of adsorbed organic molecules. A time-of-flight mass spectrometer was used to detect negative molecules and fragment ions generated by un-paired electron directed bond cleavages. We show that the probability of electron tunneling is determined by the strength of the static electric field and intrinsic electron mobility of semiconductors. Photo-catalytic dissociation or polymerization reactions of adsorbents are highly dependent on the kinetic energy of tunneling electrons as well as the strength of laser influx. By using this approach, photo-activities of phytohormones have been investigated. PMID:25749635
Approximating Integrals Using Probability
ERIC Educational Resources Information Center
Maruszewski, Richard F., Jr.; Caudle, Kyle A.
2005-01-01
As part of a discussion on Monte Carlo methods, which outlines how to use probability expectations to approximate the value of a definite integral. The purpose of this paper is to elaborate on this technique and then to show several examples using visual basic as a programming tool. It is an interesting method because it combines two branches of…
Multicriteria approximation through decomposition
Burch, C. |; Krumke, S.; Marathe, M.; Phillips, C.; Sundberg, E. |
1997-12-01
The authors propose a general technique called solution decomposition to devise approximation algorithms with provable performance guarantees. The technique is applicable to a large class of combinatorial optimization problems that can be formulated as integer linear programs. Two key ingredients of the technique involve finding a decomposition of a fractional solution into a convex combination of feasible integral solutions and devising generic approximation algorithms based on calls to such decompositions as oracles. The technique is closely related to randomized rounding. The method yields as corollaries unified solutions to a number of well studied problems and it provides the first approximation algorithms with provable guarantees for a number of new problems. The particular results obtained in this paper include the following: (1) The authors demonstrate how the technique can be used to provide more understanding of previous results and new algorithms for classical problems such as Multicriteria Spanning Trees, and Suitcase Packing. (2) They show how the ideas can be extended to apply to multicriteria optimization problems, in which they wish to minimize a certain objective function subject to one or more budget constraints. As corollaries they obtain first non-trivial multicriteria approximation algorithms for problems including the k-Hurdle and the Network Inhibition problems.
Multicriteria approximation through decomposition
Burch, C.; Krumke, S.; Marathe, M.; Phillips, C.; Sundberg, E.
1998-06-01
The authors propose a general technique called solution decomposition to devise approximation algorithms with provable performance guarantees. The technique is applicable to a large class of combinatorial optimization problems that can be formulated as integer linear programs. Two key ingredients of their technique involve finding a decomposition of a fractional solution into a convex combination of feasible integral solutions and devising generic approximation algorithms based on calls to such decompositions as oracles. The technique is closely related to randomized rounding. Their method yields as corollaries unified solutions to a number of well studied problems and it provides the first approximation algorithms with provable guarantees for a number of new problems. The particular results obtained in this paper include the following: (1) the authors demonstrate how the technique can be used to provide more understanding of previous results and new algorithms for classical problems such as Multicriteria Spanning Trees, and Suitcase Packing; (2) they also show how the ideas can be extended to apply to multicriteria optimization problems, in which they wish to minimize a certain objective function subject to one or more budget constraints. As corollaries they obtain first non-trivial multicriteria approximation algorithms for problems including the k-Hurdle and the Network Inhibition problems.
Electron transfer activation of a second water channel for proton transport in [FeFe]-hydrogenase
Sode, Olaseni; Voth, Gregory A.
2014-12-14
Hydrogenase enzymes are important because they can reversibly catalyze the production of molecular hydrogen. Proton transport mechanisms have been previously studied in residue pathways that lead to the active site of the enzyme via residues Cys299 and Ser319. The importance of this pathway and these residues has been previously exhibited through site-specific mutations, which were shown to interrupt the enzyme activity. It has been shown recently that a separate water channel (WC2) is coupled with electron transport to the active site of the [FeFe]-hydrogenase. The water-mediated proton transport mechanisms of the enzyme in different electronic states have been studied using the multistate empirical valence bond reactive molecular dynamics method, in order to understand any role WC2 may have in facilitating the residue pathway in bringing an additional proton to the enzyme active site. In a single electronic state A{sup 2−}, a water wire was formed through which protons can be transported with a low free energy barrier. The remaining electronic states were shown, however, to be highly unfavorable to proton transport in WC2. A double amino acid substitution is predicted to obstruct proton transport in electronic state A{sup 2-} by closing a cavity that could otherwise fill with water near the proximal Fe of the active site.
Dynamic defect correlations dominate activated electronic transport in SrTiO3
Snijders, Paul C.; Şen, Cengiz; McConnell, Michael P.; Ma, Ying-Zhong; May, Andrew F.; Herklotz, Andreas; Wong, Anthony T.; Ward, T. Zac
2016-01-01
Strontium titanate (SrTiO3, STO) is a critically important material for the study of emergent electronic phases in complex oxides, as well as for the development of applications based on their heterostructures. Despite the large body of knowledge on STO, there are still many uncertainties regarding the role of defects in the properties of STO, including their influence on ferroelectricity in bulk STO and ferromagnetism in STO-based heterostructures. We present a detailed analysis of the decay of persistent photoconductivity in STO single crystals with defect concentrations that are relatively low but significantly affect their electronic properties. The results show that photo-activated electron transport cannot be described by a superposition of the properties due to independent point defects as current models suggest but is, instead, governed by defect complexes that interact through dynamic correlations. These results emphasize the importance of defect correlations for activated electronic transport properties of semiconducting and insulating perovskite oxides. PMID:27443503
Dynamic defect correlations dominate activated electronic transport in SrTiO3.
Snijders, Paul C; Şen, Cengiz; McConnell, Michael P; Ma, Ying-Zhong; May, Andrew F; Herklotz, Andreas; Wong, Anthony T; Ward, T Zac
2016-01-01
Strontium titanate (SrTiO3, STO) is a critically important material for the study of emergent electronic phases in complex oxides, as well as for the development of applications based on their heterostructures. Despite the large body of knowledge on STO, there are still many uncertainties regarding the role of defects in the properties of STO, including their influence on ferroelectricity in bulk STO and ferromagnetism in STO-based heterostructures. We present a detailed analysis of the decay of persistent photoconductivity in STO single crystals with defect concentrations that are relatively low but significantly affect their electronic properties. The results show that photo-activated electron transport cannot be described by a superposition of the properties due to independent point defects as current models suggest but is, instead, governed by defect complexes that interact through dynamic correlations. These results emphasize the importance of defect correlations for activated electronic transport properties of semiconducting and insulating perovskite oxides. PMID:27443503
Dynamic defect correlated dominate activated electronic transport in SrTiO3
Snijders, Paul C; Sen, Cengiz; McConnell, Michael; Ma, Yingzhong; May, Andrew F; Herklotz, Andreas; Wong, Anthony T; Ward, Thomas Zac
2016-01-01
Strontium titanate (SrTiO3, STO) is a critically important material for the study of emergent electronic phases in complex oxides, as well as for the development of applications based on their heterostructures. Despite the large body of knowledge on STO, there are still many uncertainties regarding the role of defects in the properties of STO, including their influence on ferroelectricity in bulk STO and ferromagnetism in STO-based heterostructures. We present a detailed analysis of the decay of persistent photoconductivity in STO single crystals with defect concentrations that are relatively low but significantly affect their electronic properties. The results show that photo-activated electron transport cannot be described by a superposition of the properties due to independent point defects as current models suggest but is, instead, governed by defect complexes that interact through dynamic correlations. These results emphasize the importance of defect correlations for activated electronic transport properties of semiconducting and insulating perovskite oxides.
Thermally activated electron capture by mobile protons in SiO{sub 2} thin films
Vanheusden, K.; Karna, S.P.; Pugh, R.D.; Warren, W.L.; Fleetwood, D.M.; Devine, R.A.
1998-01-01
The annihilation of mobile protons in thin SiO{sub 2} films by capture of ultraviolet-excited electrons has been analyzed for temperatures between 77 and 500 K. We observe a strong increase in proton annihilation with increasing temperature, and derive an activation energy for electron capture of about 0.2 eV. Based on quantum chemical [(OH){sub 3}Si]{sub 2}{endash}O{endash}H{sup +} cluster calculations, we suggest photoexcitation of electrons from excited vibrational states of the ground electronic (valence band) state to a nearby excited electronic (SiO{sub 2} gap) state. It is argued that the latter excitation can result in H{sup 0} formation at elevated temperatures. {copyright} {ital 1998 American Institute of Physics.}
Electrical activation and electron spin resonance measurements of arsenic implanted in silicon
Hori, Masahiro; Ono, Yukinori; Uematsu, Masashi; Fujiwara, Akira
2015-04-06
The electrical activation of arsenic (As) implanted in Si is investigated with electron spin resonance (ESR), spreading resistance (SR), and secondary ion mass spectroscopy (SIMS). The As ions were implanted with a dose of 1 × 10{sup 12 }cm{sup −2} and subsequently annealed at various temperatures in the range of 500–1100 °C. The ESR measurements at 10 K show that the density of the As donor electrons for all the annealing temperatures is less than 10% of the As atom concentration measured by SIMS. The SR data indicate that the density of conduction band electrons is several times larger than that of the As donor electrons. These results strongly suggest that most of the As donor electrons are ESR inactive at low temperatures.
Zhao, Yimeng; Riley, Nicholas M; Sun, Liangliang; Hebert, Alexander S; Yan, Xiaojing; Westphall, Michael S; Rush, Matthew J P; Zhu, Guijie; Champion, Matthew M; Mba Medie, Felix; Champion, Patricia A DiGiuseppe; Coon, Joshua J; Dovichi, Norman J
2015-01-01
Top-down proteomics offers the potential for full protein characterization, but many challenges remain for this approach, including efficient protein separations and effective fragmentation of intact proteins. Capillary zone electrophoresis (CZE) has shown great potential for separation of intact proteins, especially for differentially modified proteoforms of the same gene product. To date, however, CZE has been used only with collision-based fragmentation methods. Here we report the first implementation of electron transfer dissociation (ETD) with online CZE separations for top-down proteomics, analyzing a mixture of four standard proteins and a complex protein mixture from the Mycobacterium marinum bacterial secretome. Using a multipurpose dissociation cell on an Orbitrap Elite system, we demonstrate that CZE is fully compatible with ETD as well as higher energy collisional dissociation (HCD), and that the two complementary fragmentation methods can be used in tandem on the electrophoretic time scale for improved protein characterization. Furthermore, we show that activated ion electron transfer dissociation (AI-ETD), a recently introduced method for enhanced ETD fragmentation, provides useful performance with CZE separations to greatly increase protein characterization. When combined with HCD, AI-ETD improved the protein sequence coverage by more than 200% for proteins from both standard and complex mixtures, highlighting the benefits electron-driven dissociation methods can add to CZE separations. PMID:25893372
Optimizing the Zeldovich approximation
NASA Technical Reports Server (NTRS)
Melott, Adrian L.; Pellman, Todd F.; Shandarin, Sergei F.
1994-01-01
We have recently learned that the Zeldovich approximation can be successfully used for a far wider range of gravitational instability scenarios than formerly proposed; we study here how to extend this range. In previous work (Coles, Melott and Shandarin 1993, hereafter CMS) we studied the accuracy of several analytic approximations to gravitational clustering in the mildly nonlinear regime. We found that what we called the 'truncated Zeldovich approximation' (TZA) was better than any other (except in one case the ordinary Zeldovich approximation) over a wide range from linear to mildly nonlinear (sigma approximately 3) regimes. TZA was specified by setting Fourier amplitudes equal to zero for all wavenumbers greater than k(sub nl), where k(sub nl) marks the transition to the nonlinear regime. Here, we study the cross correlation of generalized TZA with a group of n-body simulations for three shapes of window function: sharp k-truncation (as in CMS), a tophat in coordinate space, or a Gaussian. We also study the variation in the crosscorrelation as a function of initial truncation scale within each type. We find that k-truncation, which was so much better than other things tried in CMS, is the worst of these three window shapes. We find that a Gaussian window e(exp(-k(exp 2)/2k(exp 2, sub G))) applied to the initial Fourier amplitudes is the best choice. It produces a greatly improved crosscorrelation in those cases which most needed improvement, e.g. those with more small-scale power in the initial conditions. The optimum choice of kG for the Gaussian window is (a somewhat spectrum-dependent) 1 to 1.5 times k(sub nl). Although all three windows produce similar power spectra and density distribution functions after application of the Zeldovich approximation, the agreement of the phases of the Fourier components with the n-body simulation is better for the Gaussian window. We therefore ascribe the success of the best-choice Gaussian window to its superior treatment
Ledvina, Aaron R; Beauchene, Nicole A; McAlister, Graeme C; Syka, John E P; Schwartz, Jae C; Griep-Raming, Jens; Westphall, Michael S; Coon, Joshua J
2010-12-15
Using a modified electron transfer dissociation (ETD)-enabled quadrupole linear ion trap (QLT) mass spectrometer, we demonstrate the utility of IR activation concomitant with ETD ion-ion reactions (activated-ion ETD, AI-ETD). Analyzing 12 strong cation exchanged (SCX) fractions of a LysC digest of human cell protein extract using ETD, collision-activated dissociation (CAD), and AI-ETD, we find that AI-ETD generates 13 405 peptide spectral matches (PSMs) at a 1% false-discovery rate (1% FDR), surpassing both ETD (7 968) and CAD (10 904). We also analyze 12 SCX fractions of a tryptic digest of human cell protein extract and find that ETD produces 6 234 PSMs, AI-ETD 9 130 PSMs, and CAD 15 209 PSMs. Compared to ETD with supplemental collisional activation (ETcaD), AI-ETD generates ∼80% more PSMs for the whole cell lysate digested with trypsin and ∼50% more PSMs for the whole cell lysate digested with LysC. PMID:21062032
Passive and active plasma deceleration for the compact disposal of electron beams
Bonatto, A.; Schroeder, C. B.; Vay, J.-L.; Geddes, C. G. R.; Benedetti, C.; Esarey, E.; Leemans, W. P.
2015-08-15
Plasma-based decelerating schemes are investigated as compact alternatives for the disposal of high-energy beams (beam dumps). Analytical solutions for the energy loss of electron beams propagating in passive and active (laser-driven) schemes are derived. These solutions, along with numerical modeling, are used to investigate the evolution of the electron distribution, including energy chirp and total beam energy. In the active beam dump scheme, a laser-driver allows a more homogeneous beam energy extraction and drastically reduces the energy chirp observed in the passive scheme. These concepts could benefit applications requiring overall compactness, such as transportable light sources, or facilities operating at high beam power.
NASA Astrophysics Data System (ADS)
Chattopadhyay, S.; Bauch, S.; Madsen, L. B.
2015-12-01
We numerically study models of H2 and LiH molecules, aligned collinearly with the linear polarization of the external field, to elucidate the possible role of correlation in the enhanced-ionization (EI) phenomena. Correlation is considered at different levels of approximation with the time-dependent generalized-active-space configuration-interaction method. The results of our studies show that enhanced ionization occurs in multielectron molecules and that correlation is important, and they also demonstrate significant deviations between the results of the single-active-electron approximation and more accurate configuration-interaction methods. We further investigate the role of low-lying excited states in the EI phenomena. With the inclusion of correlation we show strong carrier-envelope-phase effects in the enhanced ionization of the asymmetric heteronuclear LiH -like molecule. The correlated calculation shows an intriguing feature of crossover in enhanced ionization with two carrier-envelope phases at critical internuclear separation.
Computational full electron structure study of biological activity in Cyclophilin A.
Zhou, Wenjin; Rossetto, Allison M; Pang, Xiaodong; Zhou, Linxiang
2016-01-01
Cyclosporine (CsA) is widely used in organ transplant patients to help prevent the patient's body from rejecting the organ. CsA has been shown to be a safe and highly effective immunosuppressive drug that binds with the protein Cyclophilin A (CypA) at active sites. However, the exact mechanism of this binding at the molecular level remains unknown. In this project, we elucidate the binding of CsA to CypA at the molecular level by computing their electron structures and revealing their interactions. We employ a novel technique called electron Computer-Aided Drug Design (eCADD) on the protein's full electron structure along with its hydrophobic pocket and the perturbation theory of the interaction between two wave functions. We have identified the wave function of CypA, the biological active residues and active atoms of CypA and CsA, the interaction site between CypA and CsA, and the hydrogen bonds in the ligand CsA binding site. All these calculated active residues, active atoms, and hydrogen bonds are in good agreement with recorded laboratory experiments and provide guidelines for designing new ligands of CypA. We believe that our eCADD framework can provide researchers with a cost-efficient new method of drug design based on the full electron structure of proteins. PMID:26264861
Equatorial Total Electron Content (TEC) at Low and High Solar Activity
NASA Astrophysics Data System (ADS)
Mene, M. N.; Obrou, O. K.; Kobea, A. T.; Zaka, K. Z.
2007-05-01
Total Electron Content derived from ionosonde data recorded at Korhogo (Lat=9.33 N, Long =5.43 W, Dip = 0.67 S) are compared to the Internatial Reference Ionosphere (IRI) model predicted TEC for high (1999) and low (1994) solar activity conditions. The result shows that the TEC has a solar activity and seasonal dependence. The IRI predicted values are closer to the observed TEC at high solar activity. However, at low solar activity the IRI overestimates the observed TEC. The deviation is more prominent in equinox during the time range 0900 to 2300 local time. The deviation is estimated to 60% of the observed TEC.
Chemical Laws, Idealization and Approximation
NASA Astrophysics Data System (ADS)
Tobin, Emma
2013-07-01
This paper examines the notion of laws in chemistry. Vihalemm ( Found Chem 5(1):7-22, 2003) argues that the laws of chemistry are fundamentally the same as the laws of physics they are all ceteris paribus laws which are true "in ideal conditions". In contrast, Scerri (2000) contends that the laws of chemistry are fundamentally different to the laws of physics, because they involve approximations. Christie ( Stud Hist Philos Sci 25:613-629, 1994) and Christie and Christie ( Of minds and molecules. Oxford University Press, New York, pp. 34-50, 2000) agree that the laws of chemistry are operationally different to the laws of physics, but claim that the distinction between exact and approximate laws is too simplistic to taxonomise them. Approximations in chemistry involve diverse kinds of activity and often what counts as a scientific law in chemistry is dictated by the context of its use in scientific practice. This paper addresses the question of what makes chemical laws distinctive independently of the separate question as to how they are related to the laws of physics. From an analysis of some candidate ceteris paribus laws in chemistry, this paper argues that there are two distinct kinds of ceteris paribus laws in chemistry; idealized and approximate chemical laws. Thus, while Christie ( Stud Hist Philos Sci 25:613-629, 1994) and Christie and Christie ( Of minds and molecules. Oxford University Press, New York, pp. 34--50, 2000) are correct to point out that the candidate generalisations in chemistry are diverse and heterogeneous, a distinction between idealizations and approximations can nevertheless be used to successfully taxonomise them.
Chalasani, P.; Saias, I.; Jha, S.
1996-04-08
As increasingly large volumes of sophisticated options (called derivative securities) are traded in world financial markets, determining a fair price for these options has become an important and difficult computational problem. Many valuation codes use the binomial pricing model, in which the stock price is driven by a random walk. In this model, the value of an n-period option on a stock is the expected time-discounted value of the future cash flow on an n-period stock price path. Path-dependent options are particularly difficult to value since the future cash flow depends on the entire stock price path rather than on just the final stock price. Currently such options are approximately priced by Monte carlo methods with error bounds that hold only with high probability and which are reduced by increasing the number of simulation runs. In this paper the authors show that pricing an arbitrary path-dependent option is {number_sign}-P hard. They show that certain types f path-dependent options can be valued exactly in polynomial time. Asian options are path-dependent options that are particularly hard to price, and for these they design deterministic polynomial-time approximate algorithms. They show that the value of a perpetual American put option (which can be computed in constant time) is in many cases a good approximation to the value of an otherwise identical n-period American put option. In contrast to Monte Carlo methods, the algorithms have guaranteed error bounds that are polynormally small (and in some cases exponentially small) in the maturity n. For the error analysis they derive large-deviation results for random walks that may be of independent interest.
Photoemission Study of Cs-NF3 Activated GaAs(100) Negative Electron Affinity Photocathodes
Liu, Z.; Sun, Y.; Peterson, S.; Pianetta, P.
2008-05-28
GaAs based negative electron affinity photocathodes activated with Cs and NF{sub 3} are used as polarized electron sources for linear accelerators. It is generally believed that the activation layer consists of CsF. The activation layers of Cs-NF{sub 3} on GaAs photocathodes are herein investigated using synchrotron radiation photoelectron spectroscopy (SR-PES). F1s, N1s and other core levels are recorded at photon energies ranging from 70eV to 820eV. Surprisingly, a significant amount of nitrogen is observed in the activation layers. Two distinct species of nitrogen are observed, one of which decreases along with the Fluorine signal as the yield of the photocathode decays with time.
Beyond the Kirchhoff approximation
NASA Technical Reports Server (NTRS)
Rodriguez, Ernesto
1989-01-01
The three most successful models for describing scattering from random rough surfaces are the Kirchhoff approximation (KA), the small-perturbation method (SPM), and the two-scale-roughness (or composite roughness) surface-scattering (TSR) models. In this paper it is shown how these three models can be derived rigorously from one perturbation expansion based on the extinction theorem for scalar waves scattering from perfectly rigid surface. It is also shown how corrections to the KA proportional to the surface curvature and higher-order derivatives may be obtained. Using these results, the scattering cross section is derived for various surface models.
Liu, Ding; Lei, Lecheng; Yang, Bin; Yu, Qingni; Li, Zhongjian
2013-11-01
Pentachlorophenol (PCP) was dechlorinated by electrochemically active bacteria using an electrode as the direct electron donor. Dechlorination efficiency and coulombic efficiency (CE) were investigated. When hydrogen evolution reaction was eliminated by controlling the potential, both dechlorination efficiency and CE increase as the potential decreases, which implied the dechlorination was stimulated by electric current rather than hydrogen gas. Further investigation of the cyclic voltammetry characterization of the medium revealed nearly no redox mediator secreted by the bacteria. Moreover, the comparison of dechlorination experiments carried out with filtered and unfiltered medium provided convincible evidence that the dominating electron transfer mechanism for the dechlorination is direct electron transfer. Additionally, 454 pyrosequencing technique was employed to gain a comprehensive understanding of the biocathodic microbial community. The results showed Proteobacteria, Bacteroidetes and Firmicutes were the three predominant groups. This paper demonstrated the direct electron transfer mechanism could be involved in PCP dechlorination with a biocathode. PMID:24035815
Tkach, N. V. Seti, Ju. A.; Grynyshyn, Yu. B.
2015-04-15
The theory of electron tunneling through an open nanostructure as an active element of a quantum cascade detector is developed, which takes into account the interaction of electrons with confined and interface phonons. Using the method of finite-temperature Green’s functions and the electron-phonon Hamiltonian in the representation of second quantization over all system variables, the temperature shifts and electron-level widths are calculated and the contributions of different electron-phonon-interaction mechanisms to renormalization of the spectral parameters are analyzed depending on the geometrical configuration of the nanosystem. Due to weak electron-phonon coupling in a GaAs/Al{sub 0.34}Ga{sub 0.66}As-based resonant tunneling nanostructure, the temperature shift and rf field absorption peak width are not very sensitive to the electron-phonon interaction and result from a decrease in potential barrier heights caused by a difference in the temperature dependences of the well and barrier band gaps.
NASA Astrophysics Data System (ADS)
Hoffstadt, Thorben; Maas, Jürgen
2015-04-01
To enable a continuous operation of a DEAP transducer, the feeding power electronics must provide the capability to charge and discharge the transducer to enable a continuous voltage adjustment. While in case of energy harvesting applications a bidirectional power electronics is mandatory, for actuator applications also unidirectional power electronics with active discharging circuits can be used. Thus, in this contribution a bidirectional flyback-converter is compared to a unidirectional with different discharging circuits. For this purpose, the design of a resistive and an inductive-resistive discharging circuit is proposed, that are connected in parallel to the DEAP and activated when required. Modulation schemes for both discharging circuits are derived that enable a continuous voltage control. Based on realized prototypes of the investigated topologies the different converters are finally compared to each other.
Active-Space Coupled-Cluster Study of Electronic States of Be₃
Kowalski, Karol; Hirata, So; Wloch, M W.; Piecuch, Piotr; Windus, Theresa L.
2005-08-15
An automated implementation of the active-space coupled-cluster (CC) and equation-of-motion (EOM) CC methods with all singles and doubles, and triples defined via active orbitals (CCSDt, EOMCCSDt) employing Tensor Contraction Engine (TCE), is reported. The TCE-generated CCSDt/ codes are parallel and applicable to closed-and open-shell references. The effectiveness of the new code in describing electronic quasi-degeneracies is illustrated by the CCSDt / EOMCCSDt) calculations for the challenging Be₃system, which is characterized by a large number of low-lying excited states dominated by two-electron transitions and significant high order correlation effects in the ground electronic state. Different strategies for defining triple excitation s within the CCSDt / EOMCCSDt) approach are discussed.
Mankuzhiyil, Nijil; Ansoldi, Stefano; Tavecchio, Fabrizio
2011-05-20
For the high-frequency-peaked BL Lac object Mrk 421, we study the variation of the spectral energy distribution (SED) as a function of source activity, from quiescent to active. We use a fully automatized {chi}{sup 2}-minimization procedure, instead of the 'eyeball' procedure more commonly used in the literature, to model nine SED data sets with a one-zone synchrotron self-Compton (SSC) model and examine how the model parameters vary with source activity. The latter issue can finally be addressed now, because simultaneous broadband SEDs (spanning from optical to very high energy photon) have finally become available. Our results suggest that in Mrk 421 the magnetic field (B) decreases with source activity, whereas the electron spectrum's break energy ({gamma}{sub br}) and the Doppler factor ({delta}) increase-the other SSC parameters turn out to be uncorrelated with source activity. In the SSC framework, these results are interpreted in a picture where the synchrotron power and peak frequency remain constant with varying source activity, through a combination of decreasing magnetic field and increasing number density of {gamma} {<=} {gamma}{sub br} electrons: since this leads to an increased electron-photon scattering efficiency, the resulting Compton power increases, and so does the total (= synchrotron plus Compton) emission.
Sault, A.G. ); Datye, A.K. )
1993-03-01
Activation procedures can have a dramatic effect on the activity of iron-based catalysts for Fischer-Tropsch (F-T) synthesis. CO conversion over a 100 Fe/3 Cu/0.2 K catalyst (parts by weight) can vary by nearly a factor of 3, depending on activation treatment. In contrast, a 100 Fe/5 Cu/4.2 K/25 SiO[sub 2] catalyst displays little dependence of F-T activity on activation treatment. An ultra-high vacuum surface analysis chamber coupled to an atmospheric reactor has been used to measure the surface composition of these catalysts following activation in carbon monoxide at 280[degrees]C, while transmission electron microscopy (TEM) and BET surface area measurements have been used to investigate catalyst morphology. CO activation of the 100 Fe/5 Cu/4.2 K/25 SiO[sub 2] catalyst at 280[degrees]C results in partial reduction of iron to a mixture of Fe[sub x]O and Fe[sub 3]O[sub 4], and an overall surface composition very similar to that obtained following hydrogen activation at 220 or 280[degrees]C, consistent with the invariance of F-T activity with activation treatment for this catalyst. Activation of the 100 Fe/3 Cu/0.2 K catalyst in CO at 280[degrees]C results in the formation of iron carbide particles, growth of graphitic carbon (C[sub g]) filaments, and formation of a thick, porous, C[sub g] layer covering the carbide particles. Differences in F-T activity between the hydrogen- and CO-activated 100 Fe/3 Cu/0.2 K catalyst are discussed in terms of surface composition and catalyst morphology. The difference in sensitivity of the two catalysts to activation conditions is related to differences in the extent of reduction of the catalysts. 45 refs., 4 figs., 1 tab.
Electronic Motion Sensors and Heart Rate as Measures of Physical Activity in Children.
ERIC Educational Resources Information Center
Freedson, Patty S.
1991-01-01
Reviews several mechanical and electronic techniques for monitoring physical activity in children. The paper focuses on motion sensors (Large Scale Integrated Sensor and Caltrac Accelerometer) and heart rate, and it presents recommendations for establishing general guidelines for appropriate use of such monitoring devices with children. (SM)
Federal Register 2010, 2011, 2012, 2013, 2014
2010-04-07
... nancy.kessinger@va.gov . Please refer to ``OMB Control No. 2900-0021'' in any correspondence. During the... AFFAIRS Proposed Information Collection (VA Loan Electronic Reporting Interface (VALERI) System) Activity.... SUMMARY: The Veterans Benefits Administration (VBA), Department of Veterans Affairs (VA), is announcing...
Federal Register 2010, 2011, 2012, 2013, 2014
2013-09-25
... Affairs, 810 Vermont Avenue NW., Washington, DC 20420, (202) 632-7492 or email crystal.rennie@va.gov... AFFAIRS Agency Information Collection (VA Loan Electronic Reporting Interface (VALERI) System) Activity... through www.Regulations.gov , or to Office of Information and Regulatory Affairs, Office of Management...
Federal Register 2010, 2011, 2012, 2013, 2014
2013-06-18
... nancy.kessinger@va.gov . Please refer to ``OMB Control No. 2900-0021'' in any correspondence. During the... AFFAIRS Proposed Information Collection (VA Loan Electronic Reporting Interface (VALERI) System) Activity.... SUMMARY: The Veterans Benefits Administration (VBA), Department of Veterans Affairs (VA), is announcing...
An Electronic Library-Based Learning Environment for Supporting Web-Based Problem-Solving Activities
ERIC Educational Resources Information Center
Tsai, Pei-Shan; Hwang, Gwo-Jen; Tsai, Chin-Chung; Hung, Chun-Ming; Huang, Iwen
2012-01-01
This study aims to develop an electronic library-based learning environment to support teachers in developing web-based problem-solving activities and analyzing the online problem-solving behaviors of students. Two experiments were performed in this study. In study 1, an experiment on 103 elementary and high school teachers (the learning activity…
Constructive approximate interpolation by neural networks
NASA Astrophysics Data System (ADS)
Llanas, B.; Sainz, F. J.
2006-04-01
We present a type of single-hidden layer feedforward neural networks with sigmoidal nondecreasing activation function. We call them ai-nets. They can approximately interpolate, with arbitrary precision, any set of distinct data in one or several dimensions. They can uniformly approximate any continuous function of one variable and can be used for constructing uniform approximants of continuous functions of several variables. All these capabilities are based on a closed expression of the networks.
Dementin, Sébastien; Burlat, Bénédicte; Fourmond, Vincent; Leroux, Fanny; Liebgott, Pierre-Pol; Abou Hamdan, Abbas; Léger, Christophe; Rousset, Marc; Guigliarelli, Bruno; Bertrand, Patrick
2011-07-01
Electrons are transferred over long distances along chains of FeS clusters in hydrogenases, mitochondrial complexes, and many other respiratory enzymes. It is usually presumed that electron transfer is fast in these systems, despite the fact that there has been no direct measurement of rates of FeS-to-FeS electron transfer in any respiratory enzyme. In this context, we propose and apply to NiFe hydrogenase an original strategy that consists of quantitatively interpreting the variations of steady-state activity that result from changing the nature of the FeS clusters which connect the active site to the redox partner, and/or the nature of the redox partner. Rates of intra- and intermolecular electron transfer are deduced from such large data sets. The mutation-induced variations of electron transfer rates cannot be explained by changes in intercenter distances and reduction potentials. This establishes that FeS-to-FeS rate constants are extremely sensitive to the nature and coordination of the centers. PMID:21615141
NASA Technical Reports Server (NTRS)
Rich, A.; Van House, J.; Hegstrom, R. A.
1982-01-01
A dynamical calculation is presented of the helicity induced in an initially unpolarized electron beam after elastic scattering from an optically active medium, a process analogous to the circular polarization induced in unpolarized light following Rayleigh scattering from chiral targets. The calculation is based on the bound helical electron model of a chiral molecule, according to which the major contribution to the helicity is provided by the perturbation of the electron bound state by the spin-orbit interaction of the bound electrons moving in the electric field of the molecular core. The net helicity acquired is found to depend directly on a molecular asymmetry factor and the square of the atomic number of the heaviest atom in an asymmetric environment. For the case of carbon, the induced helicity is on the order of 0.00001, which would account for its lack of observation in a recent experiment. Results may have implications for the origin of optical activity in biological molecules by the differential ionization of D and L isomers by beta-decay electrons.
Sault, A.G. )
1993-03-01
Activation procedures can have a dramatic effect on the activity of iron-based catalysts for Fischer-Tropsch (F-T) synthesis. CO conversion over a 100 Fe/3 Cu/0.2 K catalyst (parts by weight) can vary by nearly a factor of 3, depending on activation. In contrast, a 100 Fe/5 Cu/4.2 K/25 SiO[sub 2] catalyst displays only minor variations in activity with activation conditions. An ultra-high vacuum surface analysis chamber coupled to an atmospheric pressure reactor has been used to measure the surface compositions of these catalysts following various hydrogen activation procedures. Activation of the 100 Fe/3 Cu/0.2 K catalyst in H[sub 2] results in rapid reduction of iron to the metallic state, and segregation of sulfur to the catalyst surface. The sulfur arises from bulk sulfate impurities present in the metal nitrates used to prepare the catalyst. Sulfur coverage increases with both activation time and temperature, due to an increase in the rate of sulfur diffusion with temperature. F-T activity of this catalyst varies inversely with sulfur coverage, consistent with the well-known poisoning effect of sulfur on F-T synthesis. For the 100 Fe/5 Cu/4.2 K/25 SiO[sub 2] catalyst no significant variations in surface composition are observed as a function of hydrogen activation temperature, consistent with the absence of any variations in catalyst activity. Only partial reduction of iron to a mixture of Fe[sub x]O and Fe[sub 3]O[sub 4] is observed for this catalyst for all activation conditions investigated. Using electron beam effects to remove potassium and silica shows that one or both of these components inhibits reduction of iron to the metallic state in the 100 Fe/5 Cu/4.2 K/25 SiO[sub 2] catalyst. 48 refs., 3 tabs.
Huang, Lulu; Tang, Xuemei; Zhang, Wenyang; Jiang, Ruowei; Chen, Disong; Zhang, Juan; Zhong, Hongying
2016-01-01
A new mass spectrometric imaging approach based on laser activated electron tunneling (LAET) was described and applied to analysis of endogenous metabolites of plant leaves. LAET is an electron-directed soft ionization technique. Compressed thin films of semiconductor nanoparticles of bismuth cobalt zinc oxide were placed on the sample plate for proof-of-principle demonstration because they can not only absorb ultraviolet laser but also have high electron mobility. Upon laser irradiation, electrons are excited from valence bands to conduction bands. With appropriate kinetic energies, photoexcited electrons can tunnel away from the barrier and eventually be captured by charge deficient atoms present in neutral molecules. Resultant unpaired electron subsequently initiates specific chemical bond cleavage and generates ions that can be detected in negative ion mode of the mass spectrometer. LAET avoids the co-crystallization process of routinely used organic matrix materials with analyzes in MALDI (matrix assisted-laser desorption ionization) analysis. Thus uneven distribution of crystals with different sizes and shapes as well as background peaks in the low mass range resulting from matrix molecules is eliminated. Advantages of LAET imaging technique include not only improved spatial resolution but also photoelectron capture dissociation which produces predictable fragment ions. PMID:27053227
NASA Astrophysics Data System (ADS)
Huang, Lulu; Tang, Xuemei; Zhang, Wenyang; Jiang, Ruowei; Chen, Disong; Zhang, Juan; Zhong, Hongying
2016-04-01
A new mass spectrometric imaging approach based on laser activated electron tunneling (LAET) was described and applied to analysis of endogenous metabolites of plant leaves. LAET is an electron-directed soft ionization technique. Compressed thin films of semiconductor nanoparticles of bismuth cobalt zinc oxide were placed on the sample plate for proof-of-principle demonstration because they can not only absorb ultraviolet laser but also have high electron mobility. Upon laser irradiation, electrons are excited from valence bands to conduction bands. With appropriate kinetic energies, photoexcited electrons can tunnel away from the barrier and eventually be captured by charge deficient atoms present in neutral molecules. Resultant unpaired electron subsequently initiates specific chemical bond cleavage and generates ions that can be detected in negative ion mode of the mass spectrometer. LAET avoids the co-crystallization process of routinely used organic matrix materials with analyzes in MALDI (matrix assisted-laser desorption ionization) analysis. Thus uneven distribution of crystals with different sizes and shapes as well as background peaks in the low mass range resulting from matrix molecules is eliminated. Advantages of LAET imaging technique include not only improved spatial resolution but also photoelectron capture dissociation which produces predictable fragment ions.
Huang, Lulu; Tang, Xuemei; Zhang, Wenyang; Jiang, Ruowei; Chen, Disong; Zhang, Juan; Zhong, Hongying
2016-01-01
A new mass spectrometric imaging approach based on laser activated electron tunneling (LAET) was described and applied to analysis of endogenous metabolites of plant leaves. LAET is an electron-directed soft ionization technique. Compressed thin films of semiconductor nanoparticles of bismuth cobalt zinc oxide were placed on the sample plate for proof-of-principle demonstration because they can not only absorb ultraviolet laser but also have high electron mobility. Upon laser irradiation, electrons are excited from valence bands to conduction bands. With appropriate kinetic energies, photoexcited electrons can tunnel away from the barrier and eventually be captured by charge deficient atoms present in neutral molecules. Resultant unpaired electron subsequently initiates specific chemical bond cleavage and generates ions that can be detected in negative ion mode of the mass spectrometer. LAET avoids the co-crystallization process of routinely used organic matrix materials with analyzes in MALDI (matrix assisted-laser desorption ionization) analysis. Thus uneven distribution of crystals with different sizes and shapes as well as background peaks in the low mass range resulting from matrix molecules is eliminated. Advantages of LAET imaging technique include not only improved spatial resolution but also photoelectron capture dissociation which produces predictable fragment ions. PMID:27053227
Sun, Han; Cao, Yue; Feng, Leiyu; Chen, Yinguang
2016-01-01
Reducing the recombination probability of photogenerated electrons and holes is pivotal in enhancing the photocatalytic ability of graphitic carbon nitride (g-C3N4). Speeding the departure of photogenerated electrons is the most commonly used method of achieving this. To the best of our knowledge, there is no report on suppressing the recombination of photogenerated electron-hole pairs by immobilizing the electrons with ester functional groups. Here, for the first time the mesoporous g-C3N4 (mpg-C3N4) was integrated with polymethyl methacrylate, a polymer abundant in ester groups, which showed a photocatalytic activity unexpectedly higher than that of the original mpg-C3N4 under visible-light irradiation. Experimental observations, along with theoretical calculations, clarified that the impressive photocatalytic ability of the as-modified mpg-C3N4 was mainly derived from the immobilization of photogenerated electrons via an electron-gripping effect imposed by the ester groups in the polymethyl methacrylate. This novel strategy might also be applied in improving the photocatalytic performance of other semiconductors. PMID:26948968
Active Plasma Lensing for Relativistic Laser-Plasma-Accelerated Electron Beams.
van Tilborg, J; Steinke, S; Geddes, C G R; Matlis, N H; Shaw, B H; Gonsalves, A J; Huijts, J V; Nakamura, K; Daniels, J; Schroeder, C B; Benedetti, C; Esarey, E; Bulanov, S S; Bobrova, N A; Sasorov, P V; Leemans, W P
2015-10-30
Compact, tunable, radially symmetric focusing of electrons is critical to laser-plasma accelerator (LPA) applications. Experiments are presented demonstrating the use of a discharge-capillary active plasma lens to focus 100-MeV-level LPA beams. The lens can provide tunable field gradients in excess of 3000 T/m, enabling cm-scale focal lengths for GeV-level beam energies and allowing LPA-based electron beams and light sources to maintain their compact footprint. For a range of lens strengths, excellent agreement with simulation was obtained. PMID:26565471
NASA Astrophysics Data System (ADS)
Hajra, Rajkumar; Tsurutani, Bruce; Echer, Ezequiel; Gonzalez, Walter
2015-04-01
Radiation belt relativistic (E > 0.6, > 2.0, and > 4.0 MeV) electron acceleration at geosynchronous orbit is studied for solar cycle 23 (1995-2008). High-intensity, long-duration, continuous AE activity (HILDCAA) events are considered as the basis of the analyses. Cluster-4 passes were examined for electromagnetic chorus waves in the 5 < L < 10 and 0 < MLT < 12 region. All the HILDCAA events under study were found to be characterized by enhanced whistler-mode chorus waves and flux enhancements of magnetospheric relativistic electrons of all three energies compared to the pre-event flux levels. The response of the energetic electrons to HILDCAAs was found to vary with solar cycle phase. The initial electron fluxes were lower for events occurring during the ascending and solar maximum (AMAX) phases than for events occurring during the descending and solar minimum (DMIN) phases. The flux increases for the DMIN-phase events were > 50% larger than for the AMAX-phase events. It is concluded that electrons are accelerated to relativistic energies most often and most efficiently during the DMIN-phases of the solar cycle. We propose two possible solar UV-related mechanisms to explain this solar cycle effect. Enhanced E > 0.6 MeV electron fluxes at geosynchronous orbit were first detected ~1 day after the statistical onset of HILDCAAs, E > 2.0 MeV electrons after ~1.5 days, and E > 4.0 MeV electrons after ~2.5 days. We estimated acceleration and decay rates and timescales for the three energy levels, which will be provided for wave-particle investigators to attempt to match their models to empirically derived values.
Huang, Zhangyi; Qi, Jianqi Zhou, Li; Feng, Zhao; Yu, Xiaohe; Gong, Yichao; Yang, Mao; Wei, Nian; Shi, Qiwu; Lu, Tiecheng
2015-12-07
We investigate the ionization and displacement effects of an electron-beam (e-beam) on amorphous Gd{sub 2}Zr{sub 2}O{sub 7} synthesized by the co-precipitation and calcination methods. The as-received amorphous specimens were irradiated under electron beams at different energies (80 keV, 120 keV, and 2 MeV) and then characterized by X-ray diffraction and transmission electron microscopy. A metastable fluorite phase was observed in nanocrystalline Gd{sub 2}Zr{sub 2}O{sub 7} and is proposed to arise from the relatively lower surface and interface energy compared with the pyrochlore phase. Fast crystallization could be induced by 120 keV e-beam irradiation (beam current = 0.47 mA/cm{sup 2}). The crystallization occurred on the nanoscale upon ionization irradiation at 400 °C after a dose of less than 10{sup 17} electrons/cm{sup 2}. Under e-beam irradiation, the activation energy for the grain growth process was approximately 10 kJ/mol, but the activation energy was 135 kJ/mol by calcination in a furnace. The thermally activated ionization process was considered the fast crystallization mechanism.
Countably QC-Approximating Posets
Mao, Xuxin; Xu, Luoshan
2014-01-01
As a generalization of countably C-approximating posets, the concept of countably QC-approximating posets is introduced. With the countably QC-approximating property, some characterizations of generalized completely distributive lattices and generalized countably approximating posets are given. The main results are as follows: (1) a complete lattice is generalized completely distributive if and only if it is countably QC-approximating and weakly generalized countably approximating; (2) a poset L having countably directed joins is generalized countably approximating if and only if the lattice σc(L)op of all σ-Scott-closed subsets of L is weakly generalized countably approximating. PMID:25165730
NASA Technical Reports Server (NTRS)
Simsic, P. L.
1974-01-01
Excitation of neutral atoms by inelastic scattering of incident electrons in gaseous nebulae were investigated using Slater Wave functions to describe the initial and final states of the atom. Total cross sections using the Born Approximation are calculated for: Li(2s yields 2p), Na(3s yields 4p), k(4s yields 4p). The intensity of emitted radiation from gaseous nebulae is also calculated, and Maxwell distribution is employed to average the kinetic energy of electrons.
Approximate Bayesian multibody tracking.
Lanz, Oswald
2006-09-01
Visual tracking of multiple targets is a challenging problem, especially when efficiency is an issue. Occlusions, if not properly handled, are a major source of failure. Solutions supporting principled occlusion reasoning have been proposed but are yet unpractical for online applications. This paper presents a new solution which effectively manages the trade-off between reliable modeling and computational efficiency. The Hybrid Joint-Separable (HJS) filter is derived from a joint Bayesian formulation of the problem, and shown to be efficient while optimal in terms of compact belief representation. Computational efficiency is achieved by employing a Markov random field approximation to joint dynamics and an incremental algorithm for posterior update with an appearance likelihood that implements a physically-based model of the occlusion process. A particle filter implementation is proposed which achieves accurate tracking during partial occlusions, while in cases of complete occlusion, tracking hypotheses are bound to estimated occlusion volumes. Experiments show that the proposed algorithm is efficient, robust, and able to resolve long-term occlusions between targets with identical appearance. PMID:16929730
Electron spin resonance measurement of radical scavenging activity of Aronia melanocarpa fruit juice
Valcheva-Kuzmanova, Stefka; Blagović, Branka; Valić, Srećko
2012-01-01
Background: The fruits of Aronia melanocarpa (Michx.) Elliot contain large amounts of phenolic substances, mainly procyanidins, anthocyanins and other flavonoids, and phenolic acids. The ability of phenolic substances to act as antioxidants has been well established. Objective: In this study, we investigated the radical scavenging activity of A. melanocarpa fruit juice (AMFJ). Materials and Methods: The method used was electron spin resonance (ESR) spectroscopy. The galvinoxyl free radical was used as a scavenging object. AMFJ was added to the galvinoxyl free radical solution. The measure of the radical scavenging activity was the decrease of signal intensity. Results: AMFJ showed a potent antiradical activity causing a strong and rapid decrease of signal intensity as a function of time and juice concentration. This effect of AMFJ was probably due to the activity of its phenolic constituents. Conclusion: The ESR measurements in this study showed a pronounced radical scavenging effect of AMFJ, an important mechanism of its antioxidant activity. PMID:22701293
Lewis, Zakkoyya H; Mayrsohn, Brian G; Rowland, Jennifer L
2014-01-01
Background Electronic activity monitors (such as those manufactured by Fitbit, Jawbone, and Nike) improve on standard pedometers by providing automated feedback and interactive behavior change tools via mobile device or personal computer. These monitors are commercially popular and show promise for use in public health interventions. However, little is known about the content of their feedback applications and how individual monitors may differ from one another. Objective The purpose of this study was to describe the behavior change techniques implemented in commercially available electronic activity monitors. Methods Electronic activity monitors (N=13) were systematically identified and tested by 3 trained coders for at least 1 week each. All monitors measured lifestyle physical activity and provided feedback via an app (computer or mobile). Coding was based on a hierarchical list of 93 behavior change techniques. Further coding of potentially effective techniques and adherence to theory-based recommendations were based on findings from meta-analyses and meta-regressions in the research literature. Results All monitors provided tools for self-monitoring, feedback, and environmental change by definition. The next most prevalent techniques (13 out of 13 monitors) were goal-setting and emphasizing discrepancy between current and goal behavior. Review of behavioral goals, social support, social comparison, prompts/cues, rewards, and a focus on past success were found in more than half of the systems. The monitors included a range of 5-10 of 14 total techniques identified from the research literature as potentially effective. Most of the monitors included goal-setting, self-monitoring, and feedback content that closely matched recommendations from social cognitive theory. Conclusions Electronic activity monitors contain a wide range of behavior change techniques typically used in clinical behavioral interventions. Thus, the monitors may represent a medium by which
Vidal-Limón, Abraham; Águila, Sergio; Ayala, Marcela; Batista, Cesar V; Vazquez-Duhalt, Rafael
2013-05-01
Combined quantum mechanical and molecular mechanical (QM/MM) calculations were used to explore the electron pathway involved in the suicide inactivation of cytochrome P450BM3 from Bacillus megaterium. The suicide inactivation is a common phenomenon observed for heme peroxidases, in which the enzyme is inactivated as a result of self-oxidation mediated by highly oxidizing enzyme intermediates formed during the catalytic cycle. The selected model was a mutant comprising only the heme domain (CYPBM3 21B3) that had been previously evolved to efficiently catalyze hydroxylation reactions with hydrogen peroxide (H2O2) as electron acceptor. An extensive mapping of residues involved in electron transfer routes was obtained from density functional calculations on activated heme (i.e. Compound I) and selected amino acid residues. Identification of oxidizable residues (electron donors) was performed by selectively activating/deactivating different quantum regions. This method allowed a rational identification of key oxidizable targets in order to replace them for less oxidizable residues by site-directed mutagenesis. The residues W96 and F405 were consistently predicted by the QM/MM electron pathway to hold high spin density; single and double mutants of P450BM3 on these positions (W96A, F405L, W96A/F405L) resulted in a more stable variants in the presence of hydrogen peroxide, displaying a similar reaction rate than P450BM3 21B3. Furthermore, mass spectrometry confirmed these oxidation sites and corroborated the possible routes described by QM/MM electron transfer (ET) pathways. PMID:23425936
Approximation by hinge functions
Faber, V.
1997-05-01
Breiman has defined {open_quotes}hinge functions{close_quotes} for use as basis functions in least squares approximations to data. A hinge function is the max (or min) function of two linear functions. In this paper, the author assumes the existence of smooth function f(x) and a set of samples of the form (x, f(x)) drawn from a probability distribution {rho}(x). The author hopes to find the best fitting hinge function h(x) in the least squares sense. There are two problems with this plan. First, Breiman has suggested an algorithm to perform this fit. The author shows that this algorithm is not robust and also shows how to create examples on which the algorithm diverges. Second, if the author tries to use the data to minimize the fit in the usual discrete least squares sense, the functional that must be minimized is continuous in the variables, but has a derivative which jumps at the data. This paper takes a different approach. This approach is an example of a method that the author has developed called {open_quotes}Monte Carlo Regression{close_quotes}. (A paper on the general theory is in preparation.) The author shall show that since the function f is continuous, the analytic form of the least squares equation is continuously differentiable. A local minimum is solved for by using Newton`s method, where the entries of the Hessian are estimated directly from the data by Monte Carlo. The algorithm has the desirable properties that it is quadratically convergent from any starting guess sufficiently close to a solution and that each iteration requires only a linear system solve.
Dynamic defect correlations dominate activated electronic transport in SrTiO3
Snijders, Paul C.; Sen, Cengiz; McConnell, Michael P.; Ma, Ying-Zhong; May, Andrew F.; Herklotz, Andreas; Wong, Anthony T.; Ward, Thomas Zac
2016-07-22
Strontium titanate (SrTiO3, STO) is a critically important material for the study of emergent electronic phases in complex oxides, as well as for the development of applications based on their heterostructures. Despite the large body of knowledge on STO, there are still many uncertainties regarding the role of defects in the properties of STO, including their influence on ferroelectricity in bulk STO and ferromagnetism in STO-based heterostructures. In this paper, we present a detailed analysis of the decay of persistent photoconductivity in STO single crystals with defect concentrations that are relatively low but significantly affect their electronic properties. The resultsmore » show that photo-activated electron transport cannot be described by a superposition of the properties due to independent point defects as current models suggest but is, instead, governed by defect complexes that interact through dynamic correlations. In conclusion, these results emphasize the importance of defect correlations for activated electronic transport properties of semiconducting and insulating perovskite oxides.« less
LICHTENBERGER, DENNIS L.
2002-03-26
This research program is directed at obtaining detailed experimental information on the electronic interactions between metals and organic molecules. These interactions provide low energy pathways for many important chemical and catalytic processes. A major feature of the program is the continued development and application of our special high-resolution valence photoelectron spectroscopy (UPS), and high-precision X-ray core photoelectron spectroscopy (XPS) instrumentation for study of organometallic molecules in the gas phase. The study involves a systematic approach towards understanding the interactions and activation of bound carbonyls, C-H bonds, methylenes, vinylidenes, acetylides, alkenes, alkynes, carbenes, carbynes, alkylidenes, alkylidynes, and others with various monometal, dimetal, and cluster metal species. Supporting ligands include -aryls, alkoxides, oxides, and phosphines. We are expanding our studies of both early and late transition metal species and electron-rich and electron-poor environments in order to more completely understand the electronic factors that serve to stabilize particular organic fragments and intermediates on metals. Additional new directions for this program are being taken in ultra-high vacuum surface UPS, XPS, scanning tunneling microscopy (STM) and atomic force microscopy (AFM) experiments on both physisorbed and chemisorbed organometallic thin films. The combination of these methods provides additional electronic structure information on surface-molecule and molecule-molecule interactions. A very important general result emerging from this program is the identification of a close relationship between the ionization energies of the species and the thermodynamics of the chemical and catalytic reactions of these systems.
Sun, Han; Cao, Yue; Feng, Leiyu; Chen, Yinguang
2016-01-01
Reducing the recombination probability of photogenerated electrons and holes is pivotal in enhancing the photocatalytic ability of graphitic carbon nitride (g-C3N4). Speeding the departure of photogenerated electrons is the most commonly used method of achieving this. To the best of our knowledge, there is no report on suppressing the recombination of photogenerated electron–hole pairs by immobilizing the electrons with ester functional groups. Here, for the first time the mesoporous g-C3N4 (mpg-C3N4) was integrated with polymethyl methacrylate, a polymer abundant in ester groups, which showed a photocatalytic activity unexpectedly higher than that of the original mpg-C3N4 under visible-light irradiation. Experimental observations, along with theoretical calculations, clarified that the impressive photocatalytic ability of the as-modified mpg-C3N4 was mainly derived from the immobilization of photogenerated electrons via an electron-gripping effect imposed by the ester groups in the polymethyl methacrylate. This novel strategy might also be applied in improving the photocatalytic performance of other semiconductors. PMID:26948968
Laser Activated Streak Camera for Measurement of Electron Pulses with Femtosecond Resolution
NASA Astrophysics Data System (ADS)
Zandi, Omid; Desimone, Alice; Wilkin, Kyle; Yang, Jie; Centurion, Martin
2015-05-01
The duration of femtosecond electron pulses used in time-resolved diffraction and microscopy experiments is challenging to measure in-situ. To overcome this problem, we have fabricated a streak camera that uses the time-varying electric field of a discharging parallel plate capacitor. The capacitor is discharged using a laser-activated GaAs photoswitch, resulting in a damped oscillation of the electric field. The delay time between the laser pulse and electron pulse is set so that the front and back halves of the bunch encounter opposite electric fields of the capacitor and are deflected in opposite directions. Thus, the electron bunch appears streaked on the detector with a length proportional to its duration. The temporal resolution of the streak camera is proportional to the maximum value of the electric field and the frequency of the discharge oscillation. The capacitor is charged by high voltage short pulses to achieve a high electric field and prevent breakdown. We have achieved an oscillation frequency in the GHz range by reducing the circuit size and hence its inductance. The camera was used to measure 100 keV electron pulses with up to a million electrons that are compressed transversely by magnetic lenses and longitudinally by an RF cavity. This work was supported mainly by the Air Force Office of Scientific Research, Ultrashort Pulse Laser Matter Interaction program, under grant # FA9550-12-1-0149.
Simčič, Tatjana; Pajk, Franja; Jaklič, Martina; Brancelj, Anton; Vrezec, Al
2014-04-01
Whether electron transport system (ETS) activity could be used as an estimator of crayfish thermal tolerance has been investigated experimentally. Food consumption rate, respiration rates in the air and water, the difference between energy consumption and respiration costs at a given temperature ('potential growth scope', PGS), and ETS activity of Orconectes limosus and Pacifastacus leniusculus were determined over a temperature range of 5-30°C. All concerned parameters were found to be temperature dependent. The significant correlation between ETS activity and PGS indicates that they respond similarly to temperature change. The regression analysis of ETS activity as an estimator of thermal tolerance at the mitochondrial level and PGS as an indicator of thermal tolerance at the organismic level showed the shift of optimum temperature ranges of ETS activity to the right for 2° in O. limosus and for 3° in P. leniusculus. Thus, lower estimated temperature optima and temperatures of optimum ranges of PGS compared to ETS activity could indicate higher thermal sensitivity at the organismic level than at a lower level of complexity (i.e. at the mitochondrial level). The response of ETS activity to temperature change, especially at lower and higher temperatures, indicates differences in the characteristics of the ETSs in O. limosus and P. leniusculus. O. limosus is less sensitive to high temperature. The significant correlation between PGS and ETS activity supports our assumption that ETS activity could be used for the rapid estimation of thermal tolerance in crayfish species. PMID:24679968
Soto-Rodríguez, Jessica; Hemmatian, Zahra; Josberger, Erik E; Rolandi, Marco; Baneyx, François
2016-08-01
Fusion of a palladium-binding peptide to an archaeal rhodopsin promotes intimate integration of the lipid-embedded membrane protein with a palladium hydride protonic contact. Devices fabricated with the palladium-binding deltarhodopsin enable light-activated conversion of protonic currents to electronic currents with on/off responses complete in seconds and a nearly tenfold increase in electrical signal relative to those made with the wild-type protein. PMID:27185384
12 CFR 7.5001 - Electronic activities that are part of, or incidental to, the business of banking.
Code of Federal Regulations, 2011 CFR
2011-01-01
... delivering financial products and services; and (ii) Whether the activity enables the bank to use capacity... electronic capacity and by-products) and § 7.5006 (incidental non-financial data processing), the OCC has... 12 Banks and Banking 1 2011-01-01 2011-01-01 false Electronic activities that are part of,...
12 CFR 7.5001 - Electronic activities that are part of, or incidental to, the business of banking.
Code of Federal Regulations, 2013 CFR
2013-01-01
... delivering financial products and services; and (ii) Whether the activity enables the bank to use capacity... electronic capacity and by-products) and § 7.5006 (incidental non-financial data processing), the OCC has... 12 Banks and Banking 1 2013-01-01 2013-01-01 false Electronic activities that are part of,...
12 CFR 7.5001 - Electronic activities that are part of, or incidental to, the business of banking.
Code of Federal Regulations, 2014 CFR
2014-01-01
... delivering financial products and services; and (ii) Whether the activity enables the bank to use capacity... electronic capacity and by-products) and § 7.5006 (incidental non-financial data processing), the OCC has... 12 Banks and Banking 1 2014-01-01 2014-01-01 false Electronic activities that are part of,...
Noise exposure level while operating electronic arcade games as a leisure time activity.
Mirbod, S M; Inaba, R; Yoshida, H; Nagata, C; Komura, Y; Iwata, H
1992-01-01
In order to study noise levels associated with electronic arcade games, noise measurements were made in 3 selected game centers and 192 samples were taken in each location. The background noise was recorded at a level of 61 dB(A) and 64 dB(C). When the electronic games were performed these levels of noise reached to 88 approximately 90 dB(A). The 1/3 octave bands analyzing sound pressure levels showed that more intense noise levels arose in a frequency range between 0.5 and 2.0 kHz. The computed values for noise pollution levels (LNP) and L90 (fast response A-weighted sound level exceeded 90% of the measurement time) ranged from 93.3 to 96.6 and from 85.1 to 87.3 dB(A), respectively. Concerning our results and according to Melnic (1979), it was estimated that these levels of noise might cause 4-8 dB temporary threshold shift (TTS) at 4.0 kHz in an individual with less than one hour of exposure to such a level of noise. As for the employees of the 3 game centers, the 8-hr equivalent continuous sound levels (Leq,8) were in the range of 80.3 approximately 87.5 dB(A), although their exposure time could not be exactly determined. It was suggested that: 1) The maximum levels should be limited to a reasonable level, either by the manufacturers or by the game center owners; 2) Education programs in industry should inform the employees about other factors outside the work that may affect their hearing; and 3) For policy-making on hearing conservation, recreational warning and standards should be established. PMID:1490870
Feenstra, B.J.; Schooveld, W.A.; Bos, C.
1995-12-31
Electronic properties of superconductors are contemporarily being studied using many different experimental techniques, among which infrared spectrometry, photoelectron spectroscopy and microwave cavity techniques play an important role. The data analysis, however, is complicated by the fact that in these materials the phonon-frequency range overlaps with the one in which the energy gap is expected. This problem can be circumvented by making use of two different sources, one to induce the excitations (the Free Electron Laser in Nieuwegein, The Netherlands, FELIX), and one to study the behavior of these excitations (i.e. quasiparticles). In our case the latter source is monochromatic microwave radiation, transmitted through a thin superconducting film. We measured both a conventional superconductor (NbN, T{sub c} = 17 K) and a high T{sub c} superconductor (SmBa{sub 2}Cu{sub 3}O{sub 7-{delta}}, T{sub c} = 92 K). For NbN we observed a positive change in transmission, followed by a relaxation to a transmission smaller than the original value, after which the starting situation was restored within {approximately} 100 {mu}s. In case of SmBa{sub 2}Cu{sub 3}O{sub 7-{delta}}, the changes persisted above T{sub c}. At very low temperatures we observed slow oscillations ({approximately} 4kHz) in the induced signal, which were absent in NbN. The long time scales can possibly be explained by the so-called bottleneck, i.e. quasiparticles excited with a lot of excess energy lose part of their energy by exciting other quasiparticles. In this case the quasiparticle lifetime is enhanced considerably. The oscillations point towards an intrinsic difference of the low energy excitations, i.e. the symmetry of the pairing.
Federal Register 2010, 2011, 2012, 2013, 2014
2011-02-16
... Collection; Comment Request; Electronic Records; Electronic Signatures AGENCY: Food and Drug Administration... solicits comments on information collection provisions relating to FDA's electronic records and electronic signatures. DATES: Submit either electronic or written comments on the collection of information by April...
Barzegar, Abolfazl
2012-01-01
Dipyridamole (DIP) is a well-known pharmaceutical drug used as a coronary vasodilator and anti-platelet agent in clinics for treating several cardiovascular diseases. Primarily, the therapeutic effects of the drug are attributed to its antioxidant potency. In this research, we aim to declare the unknown antioxidant mechanism of DIP as well as its potent chain-breaking antioxidant activity in polar aqueous medium inside the cells, using different experimental methods and theoretical quantum calculations. Data demonstrated the higher antioxidant capacity of DIP against ROS and free radicals in polar cell's interior. DIP is capable of generating long living and noninvasive DIP• radicals in oxidant condition that leads to an effective “chain-breaking antioxidant” activity. Quantum computational data indicated that DIP antioxidant has more favorable ionization potential than trolox which means DIP has higher antioxidant activity. Also, data showed that the direct hydrogen-transfer is not a favorable process to construct DIP• because of high barrier energy, though electron-transfer process can more easily to produce DIP•+ with the lowest barrier energy. Altogether, the electron donating potency of DIP to reduce ferric ion, having the low anodic oxidation peak potential, producing long lived stable DIP• radicals and protecting myoblast cells from oxidation, proposed the excellent “chain-breaking antioxidant” potency via electron-transfer mechanism of this vasodilator DIP drug in polar aqueous medium. PMID:22745807
Roulling, Frédéric; Godin, Amandine; Cipolla, Alexandre; Collins, Tony; Miyazaki, Kentaro; Feller, Georges
2016-09-01
Cuproxidases are a subset of the blue multicopper oxidases that catalyze the oxidation of toxic Cu(I) ions into less harmful Cu(II) in the bacterial periplasm. Cuproxidases from psychrophilic, mesophilic, and thermophilic bacteria display the canonical features of temperature adaptation, such as increases in structural stability and apparent optimal temperature for activity with environmental temperature as well as increases in the binding affinity for catalytic and substrate copper ions. In contrast, the oxidative activities at 25 °C for both the psychrophilic and thermophilic enzymes are similar, suggesting that the nearly temperature-independent electron transfer rate does not require peculiar adjustments. Furthermore, the structural flexibilities of both the psychrophilic and thermophilic enzymes are also similar, indicating that the firm and precise bindings of the four catalytic copper ions are essential for the oxidase function. These results show that the requirements for enzymatic electron transfer, in the absence of the selective pressure of temperature on electron transfer rates, produce a specific adaptive pattern, which is distinct from that observed in enzymes possessing a well-defined active site and relying on conformational changes such as for the induced fit mechanism. PMID:27315165
Pudasaini, Pushpa Raj; Noh, Joo Hyon; Wong, Anthony T.; Ovchinnikova, Olga S.; Haglund, Amanda V.; Dai, Sheng; Ward, Thomas Zac; Mandrus, David; Rack, Philip D.
2016-02-09
To begin this abstract, amorphous metal-oxide semiconductors offer the high carrier mobilities and excellent large-area uniformity required for high performance, transparent, flexible electronic devices; however, a critical bottleneck to their widespread implementation is the need to activate these materials at high temperatures which are not compatible with flexible polymer substrates. The highly controllable activation of amorphous indium gallium zinc oxide semiconductor channels using ionic liquid gating at room temperature is reported. Activation is controlled by electric field-induced oxygen migration across the ionic liquid-semiconductor interface. In addition to activation of unannealed devices, it is shown that threshold voltages of a transistormore » can be linearly tuned between the enhancement and depletion modes. Finally, the first ever example of transparent flexible thin film metal oxide transistor on a polyamide substrate created using this simple technique is demonstrated. Finally, this study demonstrates the potential of field-induced activation as a promising alternative to traditional postdeposition thermal annealing which opens the door to wide scale implementation into flexible electronic applications.« less
Ping, Z A; Butterfiel, D A
1991-01-01
A spin-labeled p-chloromercuribenzoate (SL-PMB) and a fluorescence probe, 6-acryloyl-2-dimethylaminonaphthalene (Acrylodan), both of which bind to the single SH group located in the active site of papain, were used to investigate the interaction of papain (EC 3.4.22.2) with two protein denaturants. It was found that the active site of papain was highly stable in urea solution, but underwent a large conformational change in guanidine hydrochloride solution. Electron paramagnetic resonance and fluorescence results were in agreement and both paralleled enzymatic activity of papain with respect to both the variation in pH and denaturation. These results strongly suggest that SL-PMB and Acrylodan labels can be used to characterize the physical state of the active site of the enzyme. PMID:1657229
NASA Astrophysics Data System (ADS)
Pudasaini, Pushpa Raj; Noh, Joo Hyon; Wong, Anthony; Haglund, Amada; Ward, Thomas Zac; Mandrus, David; Rack, Philip
Amorphous metal-oxide semiconductors have been extensively studied as an active channel material in thin film transistors due to their high carrier mobility, and excellent large-area uniformity. Here, we report the athermal activation of amorphous indium gallium zinc oxide semiconductor channels by an electric field-induced oxygen migration via gating through an ionic liquid. Using field-induced activation, a transparent flexible thin film transistor is demonstrated on a polyamide substrate with transistor characteristics having a current ON-OFF ratio exceeding 108, and saturation field effect mobility of 8.32 cm2/(V.s) without a post-deposition thermal treatment. This study demonstrates the potential of field-induced activation as an athermal alternative to traditional post-deposition thermal annealing for metal oxide electronic devices suitable for transparent and flexible polymer substrates. Materials Science and Technology Division, ORBL, Oak Ridge, TN 37831, USA.
Wakefields Generated by Electron Beams Passing through a Waveguide Loaded with an Active Medium
Tyukhtin, Andrey; Kanareykin, Alexei; Schoessow, Paul
2006-11-27
The wakefields of a relativistic electron beam passing through a waveguide loaded with an active medium with weak resonant dispersion have been considered. For the calculations in this paper the parameters of the medium are those of a solution of fullerene (C60) in a nematic liquid crystal that exhibits activity in the X-band. It was shown that several of the TM accelerating modes can be amplified for the geometries under consideration; structures in which higher order modes are amplified exhibit essential advantages as PASERs. In particular, the amplification of the highest mode occurs in a structure loaded with a rather thick active medium layer that maximizes the energy stored by the active medium.
Zhu, Xianglong; Hu, Juan; Zhao, Zhenghuan; Sun, Mingjun; Chi, Xiaoqin; Wang, Xiaomin; Gao, Jinhao
2015-02-18
Tyrosinase is an important marker of human diseases such as the neurodegeneration associated with Parkinson's disease and melanoma. Sensitive detection of tyrosinase activity in vitro and inside cells is of great significance to medical diagnostics and skin disorder treatments. With unique photophysical properties, semiconductor quantum dots (QDs) are employed as photoluminescent platforms for various biosensing, in particular for the detection of enzyme activities. In this work, QDs are functionalized with tyrosine and zwitterionic molecules to construct a nanometer-scale scaffold (QD-Tyr conjugate), and this is used to test tyrosinase activity in vitro and inside cells. Tyrosinase oxidizes tyrosine to dopachrome and switches on the electron-transfer access, which relates to fluorescence quenching. High quenching efficiency is achieved by shortening the distance between the electron donors and acceptors, which is attributed to the small size of the conjugated tyrosine. Enzymatic process curves reveal the enhanced enzymatic activity on the conjugated nanoparticle substrate, which leads to highly sensitive detection of tyrosinase (as low as 1 nM). It is also demonstrated that QD-Tyr conjugates can sensitively probe intracellular tyrosinase in melanoma cells, which promises great potential in disease monitoring and medical diagnostics. PMID:25285706
Influence of Humic Acid Complexation with Metal Ions on Extracellular Electron Transfer Activity.
Zhou, Shungui; Chen, Shanshan; Yuan, Yong; Lu, Qin
2015-01-01
Humic acids (HAs) can act as electron shuttles and mediate biogeochemical cycles, thereby influencing the transformation of nutrients and environmental pollutants. HAs commonly complex with metals in the environment, but few studies have focused on how these metals affect the roles of HAs in extracellular electron transfer (EET). In this study, HA-metal (HA-M) complexes (HA-Fe, HA-Cu, and HA-Al) were prepared and characterized. The electron shuttle capacities of HA-M complexes were experimentally evaluated through microbial Fe(III) reduction, biocurrent generation, and microbial azoreduction. The results show that the electron shuttle capacities of HAs were enhanced after complexation with Fe but were weakened when using Cu or Al. Density functional theory calculations were performed to explore the structural geometry of the HA-M complexes and revealed the best binding sites of the HAs to metals and the varied charge transfer rate constants (k). The EET activity of the HA-M complexes were in the order HA-Fe > HA-Cu > HA-Al. These findings have important implications for biogeochemical redox processes given the ubiquitous nature of both HAs and various metals in the environment. PMID:26593782
A behaviour of electron and ion energy and angular distribution during the active APEX experiment
NASA Astrophysics Data System (ADS)
Nemecek, Z.; Safrankova, J.; Prech, L.
1993-10-01
The APEX project (Active Plasma Experiment) involves two spacecrafts moving along the same polar orbit (perigeum 440 km, apogeum 3080 km). The distance between these spacecrafts can be controlled in a wide range - from 1 to 1000 km, enabling a variety of two-point measurements. The principal feature of the experiment is an electron and ion gun, with variable parameters of injected beams, mounted on board the main satellite. Both objects are provided with fast ionelectron energy spectrometers having energy range from 50 eV to 30 keV. The spectrometers cover a full 4p of angular directions. This paper explains experimental possibilities offered by the APEX set-up, especially for the study of artificial disturbances created by the electron gun, and presents first results on the ion and electron distribution function measurements. The most interesting observation is a similarity between the undisturbed energy distribution in the polar region and that resulting from the electron beam-plasma interaction in lower latitudes.
Tang, Xuemei; Huang, Lulu; Zhang, Wenyang; Zhong, Hongying
2015-03-01
Identification of endogenous and exogenous chemicals contained in latent fingerprints is important for forensic science in order to acquire evidence of criminal identities and contacts with specific chemicals. Mass spectrometry has emerged as a powerful technique for such applications without any derivatization or fluorescent tags. Among these techniques, MALDI (Matrix Assisted Laser Desorption Ionization) provides small beam size but has interferences with MALDI matrix materials, which cause ion suppressions as well as limited spatial resolution resulting from uneven distribution of MALDI matrix crystals with different sizes. LAET (Laser Activated Electron Tunneling) described in this work offers capabilities for chemical imaging through electron-directed soft ionization. A special film of semiconductors has been designed for collection of fingerprints. Nanoparticles of bismuth cobalt zinc oxide were compressed on a conductive metal substrate (Al or Cu sticky tape) under 10 MPa pressure. Resultant uniform thin films provide tight and shining surfaces on which fingers are impressed. Irradiation of ultraviolet laser pulses (355 nm) on the thin film instantly generates photoelectrons that can be captured by adsorbed organic molecules and subsequently cause electron-directed ionization and fragmentation. Imaging of latent fingerprints is achieved by visualization of the spatial distribution of these molecular ions and structural information-rich fragment ions. Atomic electron emission together with finely tuned laser beam size improve spatial resolution. With the LAET technique, imaging analysis not only can identify physical shapes but also reveal endogenous metabolites present in females and males, detect contacts with prohibited substances, and resolve overlapped latent fingerprints. PMID:25647159
Influence of Humic Acid Complexation with Metal Ions on Extracellular Electron Transfer Activity
Zhou, Shungui; Chen, Shanshan; Yuan, Yong; Lu, Qin
2015-01-01
Humic acids (HAs) can act as electron shuttles and mediate biogeochemical cycles, thereby influencing the transformation of nutrients and environmental pollutants. HAs commonly complex with metals in the environment, but few studies have focused on how these metals affect the roles of HAs in extracellular electron transfer (EET). In this study, HA-metal (HA-M) complexes (HA-Fe, HA-Cu, and HA-Al) were prepared and characterized. The electron shuttle capacities of HA-M complexes were experimentally evaluated through microbial Fe(III) reduction, biocurrent generation, and microbial azoreduction. The results show that the electron shuttle capacities of HAs were enhanced after complexation with Fe but were weakened when using Cu or Al. Density functional theory calculations were performed to explore the structural geometry of the HA-M complexes and revealed the best binding sites of the HAs to metals and the varied charge transfer rate constants (k). The EET activity of the HA-M complexes were in the order HA-Fe > HA-Cu > HA-Al. These findings have important implications for biogeochemical redox processes given the ubiquitous nature of both HAs and various metals in the environment. PMID:26593782
Dynamic defect correlated dominate activated electronic transport in SrTiO3
Snijders, Paul C; Sen, Cengiz; McConnell, Michael; Ma, Yingzhong; May, Andrew F; Herklotz, Andreas; Wong, Anthony T; Ward, Thomas Zac
2016-01-01
Strontium titanate (SrTiO3, STO) is a critically important material for the study of emergent electronic phases in complex oxides, as well as for the development of applications based on their heterostructures. Despite the large body of knowledge on STO, there are still many uncertainties regarding the role of defects in the properties of STO, including their influence on ferroelectricity in bulk STO and ferromagnetism in STO-based heterostructures. We present a detailed analysis of the decay of persistent photoconductivity in STO single crystals with defect concentrations that are relatively low but significantly affect their electronic properties. The results show that photo-activatedmore » electron transport cannot be described by a superposition of the properties due to independent point defects as current models suggest but is, instead, governed by defect complexes that interact through dynamic correlations. These results emphasize the importance of defect correlations for activated electronic transport properties of semiconducting and insulating perovskite oxides.« less
Influence of Humic Acid Complexation with Metal Ions on Extracellular Electron Transfer Activity
NASA Astrophysics Data System (ADS)
Zhou, Shungui; Chen, Shanshan; Yuan, Yong; Lu, Qin
2015-11-01
Humic acids (HAs) can act as electron shuttles and mediate biogeochemical cycles, thereby influencing the transformation of nutrients and environmental pollutants. HAs commonly complex with metals in the environment, but few studies have focused on how these metals affect the roles of HAs in extracellular electron transfer (EET). In this study, HA-metal (HA-M) complexes (HA-Fe, HA-Cu, and HA-Al) were prepared and characterized. The electron shuttle capacities of HA-M complexes were experimentally evaluated through microbial Fe(III) reduction, biocurrent generation, and microbial azoreduction. The results show that the electron shuttle capacities of HAs were enhanced after complexation with Fe but were weakened when using Cu or Al. Density functional theory calculations were performed to explore the structural geometry of the HA-M complexes and revealed the best binding sites of the HAs to metals and the varied charge transfer rate constants (k). The EET activity of the HA-M complexes were in the order HA-Fe > HA-Cu > HA-Al. These findings have important implications for biogeochemical redox processes given the ubiquitous nature of both HAs and various metals in the environment.
Javan, Ashkan Jebelli; Javan, Marjan Jebeli
2014-12-15
Molecules acting as antioxidants capable of scavenging reactive oxygen species (ROS) are of upmost importance in the living cell. Thymol derivatives exhibit various antioxidant activities and potential health benefits. Exploration of structure-radical scavenging activity (SAR) was approached with a wide range of thymol derivatives. To accomplish this task, the DPPH experimental assay along with quantum-chemical calculations were also employed for these compounds. By comparing the structural properties of the derivatives of interest, their antioxidant activity was explained by the formation of an intramolecular hydrogen bond and the presence of unsaturated double bond (-CHCH substituent) in their radical spices. Moreover, the delocalization of odd electrons in these radicals has been investigated by natural bond orbital analysis and interpretation of spin density maps. Reactivity order of the compound towards the ROS: HO, HOO, and O2(-) was found to be as HO>HOO > O2(-). PMID:25038698
Free energy, entropy and volume of activation for electron transfer reactions in a polar solvent
Manjari, Swati R.; Kim, Hyung J.
2006-07-07
A continuum theory with account of cavity size fluctuations is employed to study free energy, volume and entropy of activation for nonadiabatic electron transfer (ET) reactions in polar solvents. By using a two-sphere cavity description, model calculations are performed for charge separation and recombination processes in acetonitrile under ambient conditions. It is found that the cavity size at the transition state varies with the free energy of reaction as well as with the thermodynamic conditions. In contrast to the Marcus theory predictions, the volume and entropy of activation show a monotonic behavior with the free energy of reaction and a strong correlation with each other. For example, for a given ET process, the volume and entropy of activation have the same sign. Their values for the charge separation and recombination processes are opposite in sign. These findings are in good qualitative agreement with measurements.
Evaluation of antioxidant activity and electronic structure of aspirin and paracetamol
NASA Astrophysics Data System (ADS)
Motozaki, W.; Nagatani, Y.; Kimura, Y.; Endo, K.; Takemura, T.; Kurmaev, E. Z.; Moewes, A.
2011-01-01
We present a study of electronic structure, chemical bonding, and antioxidant activity of phenolic antioxidants (aspirin and paracetamol). X-ray photoelectron and emission spectra of the antioxidants have been simulated by deMon density functional theory (DFT) calculations of the molecules. The chemical bonding of aspirin is characterized by the formation of oxygen 'lone-pair' π-orbitals which can neutralize free radicals and thus be related to antioxidant properties of the drug. In the case of paracetamol the additional nitrogen 'lone pair' is formed which can explain toxicity of the drug. We propose an evaluation method of antioxidant activity based on the relationship between experimental half-wave oxidation potential ( Ep/2 ) and calculated ionization potentials ( IP) by the DFT calculations, and can conclude that paracetamol has the higher antioxidant activity than aspirin.
NASA Astrophysics Data System (ADS)
Blum, Volker; Lau, Vincent; Botari, Tiago; Huhn, William; Lotsch, Bettina V.
2015-03-01
Polymers consisting of bridged heptazine units (often called ``graphitic carbon nitride'' or ``g-C3N4'') show considerable promise as photocatalysts for solar hydrogen evolution. Recent experimental evidence suggests that oligomeric rather than fully polymerized ``g-C3N4'' exhibits increased intrinsic photocatalytic activity. Using density-functional theory (DFT; van der Waals corrected PBE functional for conformers, hybrid DFT and GW for electronic levels), we show that considerable conformational flexibility exists for the heptazine trimers and tetramers. Analysis of HOMO and LUMO locations as well as trends in photocatalytic activity among heptazine oligomers and polymers reveals the NH2 groups of the oligomers as potential charge-transfer sites. We show that conformational variations of the oligomers can lead to significant, electrostatically motivated carrier localization effects. We suggest that NH2 side groups and the intrinsic conformational variations of the oligomeric species lead to the observed enhanced catalytic activity.
CdWO{sub 4} polymorphs: Selective preparation, electronic structures, and photocatalytic activities
Yan, Tingjiang; Li, Liping; Tong, Wenming; Zheng, Jing; Wang, Yunjian; Li, Guangshe
2011-02-15
This work explored the selective synthesis of polymorphs of CdWO{sub 4} in either tetragonal or monoclinic phase by optimizing the experimental parameters. Systematic characterization indicated that both polymorphs possessed similar spherical morphologies but different structural building blocks. Electronic structures calculations for both polymorphs demonstrated the same constructions of conduction band or valence band, while the conduction band widths of both polymorphs were quite different. Both CdWO{sub 4} polymorphs exhibited good photocatalytic activity for degradation of methyl orange under UV light irradiation. When comparing to some other well-known tungstate oxide materials, the photocatalytic activity was found to follow such a consequence, monoclinic CdWO{sub 4{approx}}monoclinic ZnWO{sub 4}>tetragonal CdWO{sub 4}>tetragonal CaWO{sub 4}. The specific photocatalytic activity of monoclinic CdWO{sub 4} was even higher than that of commercial TiO{sub 2} photocatalyst (Degussa P25). The increased activity from the tetragonal CdWO{sub 4} to the monoclinic was consistent with the trend of the decreased symmetry, and this could be explained in terms of the geometric structures and electronic structures for both polymorphs. -- Graphical abstract: Monoclinic CdWO{sub 4} exhibited a much higher photocatalytic activity than the tetragonal form owing to the lower symmetry, more distorted geometric structure, and the dispersive band configuration. Display Omitted Research highlights: > Polymorphs of CdWO{sub 4} in either tetragonal or monoclinic phase were selectively synthesized. > Both polymorphs possessed similar spherical morphologies, while the relevant structural building blocks were different. > Photocatalytic activities of CdWO{sub 4} polymorphs depended strongly on the symmetry, geometric structure, as well as band configuration.
'LTE-diffusion approximation' for arc calculations
NASA Astrophysics Data System (ADS)
Lowke, J. J.; Tanaka, M.
2006-08-01
This paper proposes the use of the 'LTE-diffusion approximation' for predicting the properties of electric arcs. Under this approximation, local thermodynamic equilibrium (LTE) is assumed, with a particular mesh size near the electrodes chosen to be equal to the 'diffusion length', based on De/W, where De is the electron diffusion coefficient and W is the electron drift velocity. This approximation overcomes the problem that the equilibrium electrical conductivity in the arc near the electrodes is almost zero, which makes accurate calculations using LTE impossible in the limit of small mesh size, as then voltages would tend towards infinity. Use of the LTE-diffusion approximation for a 200 A arc with a thermionic cathode gives predictions of total arc voltage, electrode temperatures, arc temperatures and radial profiles of heat flux density and current density at the anode that are in approximate agreement with more accurate calculations which include an account of the diffusion of electric charges to the electrodes, and also with experimental results. Calculations, which include diffusion of charges, agree with experimental results of current and heat flux density as a function of radius if the Milne boundary condition is used at the anode surface rather than imposing zero charge density at the anode.
NASA Astrophysics Data System (ADS)
Wang, Kaiti; Lin, Ching-Huei; Wang, Lu-Yin; Hada, Tohru; Nishimura, Yukitoshi; Turner, Drew L.; Angelopoulos, Vassilis
2014-12-01
Changes in pitch angle distributions of electrons with energies from a few eV to 1 MeV at dipolarization sites in Earth's magnetotail are investigated statistically to determine the extent to which adiabatic acceleration may contribute to these changes. Forty-two dipolarization events from 2008 and 2009 observed by Time History of Events and Macroscale Interactions during Substorms probes covering the inner plasma sheet from 8 RE to 12 RE during geomagnetic activity identified by the AL index are analyzed. The number of observed events with cigar-type distributions (peaks at 0° and 180°) decreases sharply below 1 keV after dipolarization because in many of these events, electron distributions became more isotropized. From above 1 keV to a few tens of keV, however, the observed number of cigar-type events increases after dipolarization and the number of isotropic events decreases. These changes can be related to the ineffectiveness of Fermi acceleration below 1 keV (at those energies, dipolarization time becomes comparable to electron bounce time). Model-calculated pitch angle distributions after dipolarization with the effect of betatron and Fermi acceleration tested indicate that these adiabatic acceleration mechanisms can explain the observed patterns of event number changes over a large range of energies for cigar events and isotropic events. Other factors still need to be considered to assess the observed increase in cigar events around 2 keV. Indeed, preferential directional increase/loss of electron fluxes, which may contribute to the formation of cigar events, was observed. Nonadiabatic processes to accelerate electrons in a parallel direction may also be important for future study.
Toyama, Toshizo; Wada-Takahashi, Satoko; Takamichi, Maomi; Watanabe, Kiyoko; Yoshida, Ayaka; Yoshino, Fumihiko; Miyamoto, Chihiro; Maehata, Yojiro; Sugiyama, Shuta; Takahashi, Shun-Suke; Todoki, Kazuo; Lee, Masaichi-Chang-Il; Hamada, Nobushiro
2014-12-01
Jixueteng, the dried stem of Spatholobus suberectus Dunn (Leguminosae), is a traditional Chinese herbal medicine that is commonly classified as a herb that promotes blood circulation and can be used to treat blood stasis. The aim of this study was to examine the reactive oxygen species (ROS) scavenging activity of Jixueteng and other herbal medicines. The ROS scavenging activities of the water extracts of Jixueteng, Cnidium officinale and Salvia miltiorrhiza were examined using an electron spin resonance (ESR) technique and faint luminescence measurement. The ESR signal intensities of the superoxide anion (O2·) and hydroxyl radical (HO·) were reduced more by Jixueteng than the other herbal medicines we tested. High photon emission intensity to hydrogen peroxide (H202) and HO· was observed in Jixueteng using the XYZ chemiluminescence system that was used as faint luminescence measurement and analysis. The results of the present study revealed that the ROS scavenging activity of 8% Jixueteng was the strongest among the herbal medicines we tested. It has been reported that Jixueteng includes various polyphenols. In the ROS scavenging activity by Jixueteng, it is supposed that the antioxidant activity caused by these polyphenols would contribute greatly. In conclusion, a water extract component of Jixueteng had potent free radical scavenging activity and an antioxidative effect that inhibited the oxidative actions of O2·⁻, H2O2 and HO·. Therefore, Jixueteng represents a promising therapeutic drug for reactive oxygen-associated pathologies. PMID:25632478
Features of the electronic structure of the active center of an HbS molecule
NASA Astrophysics Data System (ADS)
Novoselov, D. Yu.; Korotin, Dm. M.; Anisimov, V. I.
2016-01-01
Features of the electronic structure of the nonprotein part of the mutant form of the human hemoglobin molecule, HbS, are studied along with the magnetic state of the iron ion that is the "nucleus" of the active center of the molecule. It is found that the mutant form of the HbS molecule differs from a normal hemoglobin molecule by the distortion of the local environment of the iron ion, which changes the energy level splitting by a crystal field. As a result of ab initio calculations, the magnetic transition in the iron atom from the high-spin state to the low-spin state upon the addition of molecular oxygen to hemoglobin molecule is reproduced. It is established for the first time that a change in the crystal and electronic structure of the active center as a result of a mutation can lead to a substantial change in the energy of the bond between the active center of the hemoglobin molecule and an oxygen molecule.
GPS-Total electron content variability in Brazil during low solar activity
NASA Astrophysics Data System (ADS)
Mendes da Costa, A.; Vilas Boas, J.; Fonseca Junior, E.
Variations of ionospheric Total Electron Content (TEC) have been calculated using GPS data obtained over a low latitude station Presidente Prudente, Brazil (22.1o S; 51.4o W ) in 1997, a period of low solar activity. Two hourly TEC averages are presented for the period. Diurnal, seasonal, solar activity variations and the Equatorial Anomaly effects are discussed. TEC diurnal means compared with IRI-95 predictions for equinoxes and solstices months showed that IRI-95 systematically overestimates the observed values. Pre-midnight TEC enhancements were observed all over the year, except in May and June. The TEC values measured reproduce the same general trend of the TEC observations over Cachoeira Paulista, Brazil (22.5o S 45o W). The "fountain" effect seems to be more effective at Presidente Prudente because of its lower magnetic dip latitude. A correlation between TEC experimental values and low solar flux (62 < F10.7 < 116 flux units) emphasizes the inadequacy of IRI to model low latitude TEC values at low solar activity periods. These are the first results obtained using TEC-GPS technique for total electron content measureme n t s at low latitudes in Brazil.
Mineev, Y.V.; Spir'kova, E.S.
1986-05-01
In January 1976, the Interplanetary Magnetospheric Study (IMS) began. During the period January-March 1976, geomagnetic disturbances coincided mainly with a recurring sequence of earth passages through sector structures in the interplanetary magnetic field (IMF). In March, unusually large enhancements in energetic electron fluxes were recorded by Prognoz 4. The observations were made during intersections of the flanks of the transition region (TR) in conditions of enhanced geomagnetic activity, and the enhancements were of significant duration. Intense bursts of these particles were also observed in the outer magnetosphere at high latitudes. We discuss possible mechanisms for creating such formations.
Active Microwave Pulse Compressor Using an Electron-Beam Triggered Switch
NASA Astrophysics Data System (ADS)
Ivanov, O. A.; Lobaev, M. A.; Vikharev, A. L.; Gorbachev, A. M.; Isaev, V. A.; Hirshfield, J. L.; Gold, S. H.; Kinkead, A. K.
2013-03-01
A high-power active microwave pulse compressor is described that operates by modulating the quality factor of an energy storage cavity by means of mode conversion controlled by a triggered electron-beam discharge across a switch cavity. This Letter describes the principle of operation, the design of the switch cavity, the configuration used for the tests, and the experimental results. The pulse compressor produced output pulses with 140-165 MW peak power, record peak power gains of 16∶1-20∶1, and FWHM pulse duration of 16-20 ns at a frequency of 11.43 GHz.
Active microwave pulse compressor using an electron-beam triggered switch.
Ivanov, O A; Lobaev, M A; Vikharev, A L; Gorbachev, A M; Isaev, V A; Hirshfield, J L; Gold, S H; Kinkead, A K
2013-03-15
A high-power active microwave pulse compressor is described that operates by modulating the quality factor of an energy storage cavity by means of mode conversion controlled by a triggered electron-beam discharge across a switch cavity. This Letter describes the principle of operation, the design of the switch cavity, the configuration used for the tests, and the experimental results. The pulse compressor produced output pulses with 140-165 MW peak power, record peak power gains of 16∶1-20∶1, and FWHM pulse duration of 16-20 ns at a frequency of 11.43 GHz. PMID:25166547
9-fluorenemethanol: an internal electron donor to fine tune olefin polymerization activity.
Gnanakumar, Edwin S; Rao Chokkapu, Eswara; Kunjir, Shrikant; Ajithkumar, T G; Rajamohanan, P R; Chakraborty, Debashis; Gopinath, Chinnakonda S
2014-06-28
A new MgCl2 based molecular adduct has been synthesized with 9-fluorenemethanol (9FM) as a novel internal electron donor (IED), along with ethanol (EtOH) (MgCl2·n9FM·xEtOH). The above molecular adduct has been subjected to a variety of structural, spectroscopic and morphological characterization techniques. The results of the solid state (13)C CPMAS NMR technique suggests the coordination of 9FM to MgCl2. Observation of a low angle diffraction peak at 2θ = 5.7° (d = 15.5 Å) underscores the coordination of 9FM along the z-axis, and ethanol in the molecular adduct. Active Ziegler-Natta catalysts were prepared by two different synthesis methods; the conventional method to obtain a high surface area active catalyst, and other one with 9FM as an integral part of the active catalyst in order to study the influence of 9FM as an IED over the active sites. The active catalysts were also characterized thoroughly with different analytical tools. The XRD results show (003) facets of δ-MgCl2 (α-MgCl2) for the conventional (non-conventional) titanated catalyst. Results of the ethylene polymerization activity study reveals that the conventionally prepared highly porous active catalyst shows 1.7-2.5 times higher activity than the non-conventional prepared catalyst; however, the latter shows a low molecular weight distribution and confirms the role of the Lewis base as an IED. PMID:24810354
Activity-Dependent Synaptic Plasticity of a Chalcogenide Electronic Synapse for Neuromorphic Systems
NASA Astrophysics Data System (ADS)
Li, Yi; Zhong, Yingpeng; Zhang, Jinjian; Xu, Lei; Wang, Qing; Sun, Huajun; Tong, Hao; Cheng, Xiaoming; Miao, Xiangshui
2014-05-01
Nanoscale inorganic electronic synapses or synaptic devices, which are capable of emulating the functions of biological synapses of brain neuronal systems, are regarded as the basic building blocks for beyond-Von Neumann computing architecture, combining information storage and processing. Here, we demonstrate a Ag/AgInSbTe/Ag structure for chalcogenide memristor-based electronic synapses. The memristive characteristics with reproducible gradual resistance tuning are utilised to mimic the activity-dependent synaptic plasticity that serves as the basis of memory and learning. Bidirectional long-term Hebbian plasticity modulation is implemented by the coactivity of pre- and postsynaptic spikes, and the sign and degree are affected by assorted factors including the temporal difference, spike rate and voltage. Moreover, synaptic saturation is observed to be an adjustment of Hebbian rules to stabilise the growth of synaptic weights. Our results may contribute to the development of highly functional plastic electronic synapses and the further construction of next-generation parallel neuromorphic computing architecture.
Lichtenberger, D.L.
1992-01-01
Purpose of this research program is to obtain experimental information on the different fundamental ways metals bond and activate organic molecules. Our approach has been to directly probe the electronic interactions between metals and molecules through a wide variety of ionization spectroscopies and other techniques, and to investigate the relationships with bonding modes, structures, and chemical behavior. During this period, we have (1) characterized the electronic features of diphosphines and monophosphines in their coordination to metals, (2) carried out theoretical and experimental investigations of the bonding capabilities of C[sub 60] to transition metals, (3) developed techniques for the imaging of single molecules on gold substrates that emphasizes the electronic backbonding from the metal to the molecule, (4) obtained the high resolution photoelectron spectrum of pure C[sub 70] in the gas phase, (5) compared the bonding of [eta][sup 3]- acetylide ligands to the bonding of other small organic molecules with metals, and (6) reported the photoelectron spectra and bonding of [eta][sup 3]-cyclopropenyl groups to metals.
Activity-Dependent Synaptic Plasticity of a Chalcogenide Electronic Synapse for Neuromorphic Systems
Li, Yi; Zhong, Yingpeng; Zhang, Jinjian; Xu, Lei; Wang, Qing; Sun, Huajun; Tong, Hao; Cheng, Xiaoming; Miao, Xiangshui
2014-01-01
Nanoscale inorganic electronic synapses or synaptic devices, which are capable of emulating the functions of biological synapses of brain neuronal systems, are regarded as the basic building blocks for beyond-Von Neumann computing architecture, combining information storage and processing. Here, we demonstrate a Ag/AgInSbTe/Ag structure for chalcogenide memristor-based electronic synapses. The memristive characteristics with reproducible gradual resistance tuning are utilised to mimic the activity-dependent synaptic plasticity that serves as the basis of memory and learning. Bidirectional long-term Hebbian plasticity modulation is implemented by the coactivity of pre- and postsynaptic spikes, and the sign and degree are affected by assorted factors including the temporal difference, spike rate and voltage. Moreover, synaptic saturation is observed to be an adjustment of Hebbian rules to stabilise the growth of synaptic weights. Our results may contribute to the development of highly functional plastic electronic synapses and the further construction of next-generation parallel neuromorphic computing architecture. PMID:24809396
Li, Yi; Zhong, Yingpeng; Zhang, Jinjian; Xu, Lei; Wang, Qing; Sun, Huajun; Tong, Hao; Cheng, Xiaoming; Miao, Xiangshui
2014-01-01
Nanoscale inorganic electronic synapses or synaptic devices, which are capable of emulating the functions of biological synapses of brain neuronal systems, are regarded as the basic building blocks for beyond-Von Neumann computing architecture, combining information storage and processing. Here, we demonstrate a Ag/AgInSbTe/Ag structure for chalcogenide memristor-based electronic synapses. The memristive characteristics with reproducible gradual resistance tuning are utilised to mimic the activity-dependent synaptic plasticity that serves as the basis of memory and learning. Bidirectional long-term Hebbian plasticity modulation is implemented by the coactivity of pre- and postsynaptic spikes, and the sign and degree are affected by assorted factors including the temporal difference, spike rate and voltage. Moreover, synaptic saturation is observed to be an adjustment of Hebbian rules to stabilise the growth of synaptic weights. Our results may contribute to the development of highly functional plastic electronic synapses and the further construction of next-generation parallel neuromorphic computing architecture. PMID:24809396
Yu, Ki Jun; Kuzum, Duygu; Hwang, Suk-Won; Kim, Bong Hoon; Juul, Halvor; Kim, Nam Heon; Won, Sang Min; Chiang, Ken; Trumpis, Michael; Richardson, Andrew G; Cheng, Huanyu; Fang, Hui; Thompson, Marissa; Bink, Hank; Talos, Delia; Seo, Kyung Jin; Lee, Hee Nam; Kang, Seung-Kyun; Kim, Jae-Hwan; Lee, Jung Yup; Huang, Younggang; Jensen, Frances E; Dichter, Marc A; Lucas, Timothy H; Viventi, Jonathan; Litt, Brian; Rogers, John A
2016-07-01
Bioresorbable silicon electronics technology offers unprecedented opportunities to deploy advanced implantable monitoring systems that eliminate risks, cost and discomfort associated with surgical extraction. Applications include postoperative monitoring and transient physiologic recording after percutaneous or minimally invasive placement of vascular, cardiac, orthopaedic, neural or other devices. We present an embodiment of these materials in both passive and actively addressed arrays of bioresorbable silicon electrodes with multiplexing capabilities, which record in vivo electrophysiological signals from the cortical surface and the subgaleal space. The devices detect normal physiologic and epileptiform activity, both in acute and chronic recordings. Comparative studies show sensor performance comparable to standard clinical systems and reduced tissue reactivity relative to conventional clinical electrocorticography (ECoG) electrodes. This technology offers general applicability in neural interfaces, with additional potential utility in treatment of disorders where transient monitoring and modulation of physiologic function, implant integrity and tissue recovery or regeneration are required. PMID:27088236
NASA Astrophysics Data System (ADS)
Onda, Kunizo; Ejiri, Masaki; Itikawa, Yukikazu
A downward electron differential number flux, the absolute photoemission rate for the (0, 1) band of the first negative band system of the molecular nitrogen ion, and the number density of thermal electrons were simultaneously measured by the sounding rocket S-310JA-8 launched toward active auroral arcs at a substorm expansion phase on April 4, 1984, from Syowa Station in Antarctica. We apply the Monte Carlo method to analyze these observed results. The MSIS-86 model is employed to represent the atmospheric number density and temperature in the aurora observed by this experiment. Only N2, O, and O2 are taken into account as constituent elements of the atmosphere. Electrons are injected downward into the upper atmosphere at the altitude of 200 km, at which the downward electron differential number flux was measured. An initial electron energy is considered in the range of 0.1-18 keV. It is assumed that an initial pitch angle is uniformly distributed in the range of [0, π/2]. Excitation and ionization rates of N2, O, and O2 are calculated as a function of altitude, the initial pitch angle, and the initial electron energy. Production and emission rates of the N2+ 1N (0, 1) band are deduced by using these calculated rates. Time variation of the observed absolute intensity of this band is reasonably well reproduced by the Monte Carlo method combined with the measured electron number flux.
Second derivatives for approximate spin projection methods
Thompson, Lee M.; Hratchian, Hrant P.
2015-02-07
The use of broken-symmetry electronic structure methods is required in order to obtain correct behavior of electronically strained open-shell systems, such as transition states, biradicals, and transition metals. This approach often has issues with spin contamination, which can lead to significant errors in predicted energies, geometries, and properties. Approximate projection schemes are able to correct for spin contamination and can often yield improved results. To fully make use of these methods and to carry out exploration of the potential energy surface, it is desirable to develop an efficient second energy derivative theory. In this paper, we formulate the analytical second derivatives for the Yamaguchi approximate projection scheme, building on recent work that has yielded an efficient implementation of the analytical first derivatives.
NASA Astrophysics Data System (ADS)
Duy Nguyen, Ngoc; Phu Dang, Van; Le, Anh Quoc; Hien Nguyen, Quoc
2014-12-01
Colloidal solutions of 1 mM gold nanoparticles (AuNPs) were synthesized by γ-ray Co-60 and electron beam irradiation using 1% water soluble chitosan (WSC) with different molecular weight (Mw) as stabilizer. The AuNPs size measured from TEM images was of 7.1 and 15.1 nm for electron beam and γ-ray Co-60, respectively. The AuNPs sizes of 9.8, 15.1 and 22.4 nm stabilized by different WSC Mw of 155 × 103, 78 × 103 and 29 × 103 g mol-1, respectively, were also synthesized by γ-ray Co-60 irradiation. Antioxidant activity of AuNPs with different size from 7.1 to 20.0 nm was investigated using free radical 2,2‧-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS•+). Results indicated that the smaller size of AuNPs exhibited higher antioxidant activity. In particular, the antioxidant efficiency was of nearly 100, 75, 65, 52 and 30% for 7.1, 9.8, 15.1, 20.0 nm AuNPs and WSC 0.1%, respectively, at the same reaction time of 270 min. Thus, due to the compatibility of WSC and the unique property of AuNPs, the pure colloidal AuNPs/WSC solutions synthesized by irradiation method can be potentially applied in biomedicine, cosmetics and in other fields as well.
Effect of Electronic Messaging on Physical Activity Participation among Older Adults
Antoine Parker, Chantrell; Ellis, Rebecca
2016-01-01
The purpose of this study was to determine if electronic messaging would increase min of aerobic physical activity (PA) among older adults. Participants were active older adults (n = 28; M age = 60 years, SD = 5.99, and range = 51–74 years). Using an incomplete within-subjects crossover design, participants were randomly assigned to begin the 4-week study receiving the treatment condition (a morning and evening text message) or the control condition (an evening text message). Participants self-reported min of completed aerobic PA by cell phone text. The 1-way within-subjects ANOVA showed significant group differences (p < 0.05). Specifically, when participants were in the treatment condition, they reported significantly greater average weekly min of aerobic PA (M = 96.88 min, SD = 62.9) compared to when they completed the control condition (M = 71.68 min, SD = 40.98). Electronic messaging delivered via cell phones was effective at increasing min of aerobic PA among older adults. PMID:27293891
Faddeev random-phase approximation for molecules
Degroote, Matthias; Van Neck, Dimitri; Barbieri, Carlo
2011-04-15
The Faddeev random-phase approximation is a Green's function technique that makes use of Faddeev equations to couple the motion of a single electron to the two-particle-one-hole and two-hole-one-particle excitations. This method goes beyond the frequently used third-order algebraic diagrammatic construction method: all diagrams involving the exchange of phonons in the particle-hole and particle-particle channel are retained, but the phonons are now described at the level of the random-phase approximation, which includes ground-state correlations, rather than at the Tamm-Dancoff approximation level, where ground-state correlations are excluded. Previously applied to atoms, this paper presents results for small molecules at equilibrium geometry.
Van Zeeland, Michael; Heidbrink, W.; Nazikian, Raffi; Austin, M. E.; Cheng, C Z; Chu, M. S.; Gorelenkov, Nikolai; Holcomb, C T; Hyatt, A. W.; Kramer, G.; Lohr, J.T.; Mckee, G. R.; Petty, C C.; Prater, R.; Solomon, W. M.; Spong, Donald A
2009-01-01
Neutral beam injection into reversed magnetic shear DIII-D plasmas produces a variety of Alfvenic activity including toroidicity and ellipticity induced Alfven eigenmodes (TAE/EAE, respectively) and reversed shear Alfven eigenmodes (RSAE) as well as their spatial coupling. These modes are studied during the discharge current ramp phase when incomplete current penetration results in a high central safety factor and strong drive due to multiple higher order resonances. It is found that ideal MHD modelling of eigenmode spectral evolution, coupling and structure are in excellent agreement with experimental measurements. It is also found that higher radial envelope harmonic RSAEs are clearly observed and agree with modelling. Some discrepancies with modelling such as that due to up/down eigenmode asymmetries are also pointed out. Concomitant with the Alfvenic activity, fast ion (FIDA) spectroscopy shows large reductions in the central fast ion profile, the degree of which depends on the Alfven eigenmode amplitude. Interestingly, localized electron cyclotron heating (ECH) near the mode location stabilizes RSAE activity and results in significantly improved fast ion confinement relative to discharges with ECH deposition on axis. In these discharges, RSAE activity is suppressed when ECH is deposited near the radius of the shear reversal point and enhanced with deposition near the axis. The sensitivity of this effect to deposition power and current drive phasing as well as ECH modulation are presented.
NASA Astrophysics Data System (ADS)
Lee, Jung-Wook; Lee, Soo-Hyoung; Kim, Yong-Hoon; Park, Sung Kyu
2014-09-01
A simple and versatile route of forming sol-gel-derived metal oxide n-type electron transport layers (ETLs) for flexible inverted polymer solar cells (PSCs) is proposed using low-temperature photochemical activation process. The photochemical activation, which is induced by deep ultraviolet irradiation on sol-gel films, allows formation of metal oxide n-type ETLs such as zinc oxide (ZnO) and indium gallium zinc oxide films at a low temperature. Compared to poly(3-hexylthiophene)/phenyl-C61-butyric acid methyl ester inverted PSCs with thermally annealed ZnO ETLs (optimized efficiency of 3.26 ± 0.03 %), the inverted PSCs with photo-activated ZnO ETLs showed an improved efficiency of 3.60 ± 0.02 %. The enhanced photovoltaic property is attributed to efficient charge collection from low overall series resistance and high surface area-to-geometric area ratio by the photo-activated ZnO ETLs.
Electron Spin Resonance (ESR) detection of active oxygen species and organic phases in Martian soils
NASA Technical Reports Server (NTRS)
Tsay, Fun-Dow; Kim, Soon Sam; Liang, Ranty H.
1989-01-01
The presence of active oxygen species (O(-), O2(-), O3(-)) and other strong oxidants (Fe2O3 and Fe3O4) was invoked in interpretations of the Viking biological experiments and a model was also suggested for Martian surface chemistry. The non-biological interpretations of the biological results gain futher support as no organic compounds were detected in the Viking pyrolysis-gas chromatography mass spectrometer (GCSM) experiments at concentrations as low as 10 ppb. Electron spin resonance (ESR) measures the absorption of microwaves by a paramagnetic and/or ferromagnetic center in the presence of an external field. In many instances, ESR has the advantage of detailed submicroscopic identification of the transient species and/or unstable reaction intermediates in their environments. Since the higly active oxygen species (O(-), O2(-), O3(-), and R-O-O(-)) are all paramagnetic in nature, they can be readily detected in native form by the ESR method. Active oxygen species likely to occur in the Martian surface samples were detected by ESR in UV-irradiated samples containing MgO. A miniaturized ESR spectrometer system can be developed for the Mars Rover Sample Return Mission. The instrument can perform the following in situ Martian samples analyses: detection of active oxygen species; characterization of Martian surface chemistry and photooxidation processes; and searching for organic compounds in the form of free radicals preserved in subsoils, and detection of microfossils with Martian carbonate sediments.
A study of electrically active traps in AlGaN/GaN high electron mobility transistor
NASA Astrophysics Data System (ADS)
Yang, Jie; Cui, Sharon; Ma, T. P.; Hung, Ting-Hsiang; Nath, Digbijoy; Krishnamoorthy, Sriram; Rajan, Siddharth
2013-10-01
We have studied electron conduction mechanisms and the associated roles of the electrically active traps in the AlGaN layer of an AlGaN/GaN high electron mobility transistor structure. By fitting the temperature dependent I-V (Current-Voltage) curves to the Frenkel-Poole theory, we have identified two discrete trap energy levels. Multiple traces of I-V measurements and constant-current injection experiment all confirm that the main role of the traps in the AlGaN layer is to enhance the current flowing through the AlGaN barrier by trap-assisted electron conduction without causing electron trapping.
Tao, Mangjuan; Shi, Zhilu; Cheng, Rui; Zhang, Jing; Li, Baoxin; Jin, Yan
2015-09-15
Sensitive and reliable study of the activity of polynucleotide kinase (PNK) and its potential inhibitors is of great importance for biochemical interaction related to DNA phosphorylation as well as development of kinase-targeted drug discovery. To achieve facile and reliable detection of PNK activity, we report here a novel fluorescence method for PNK assay based on a combination of exonuclease cleavage reaction and photo-induced electron transfer (PIET) by using T4 PNK as a model target. The fluorescence of 3'-carboxyfluorescein-labeled DNA probe (FDNA) is effectively quenched by deoxyguanosines at the 5' end of its complementary DNA (cDNA) due to an effective PIET between deoxyguanosines and fluorophore. Whereas FDNA/cDNA hybrid is phosphorylated by PNK and then immediately cleaved by lambda exonuclease (λ exo), fluorescence is greatly restored due to the break of PIET. This homogeneous PNK activity assay does not require a complex design by taking advantage of the quenching ability of deoxyguanosines, making the proposed strategy facile and cost-effective. The activity of PNK can be sensitively detected in the range of 0.005 to 10 U mL(-1) with a detection limit of 2.1×10(-3) U mL(-1). Research on inhibition efficiency of different inhibitors demonstrated that it can be explored to evaluate inhibition capacity of inhibitors. The application for detection of PNK activity in complex matrix achieved satisfactory results. Therefore, this PIET strategy opens a promising avenue for studying T4 PNK activity as well as evaluating PNK inhibitors, which is of great importance for discovering kinase-targeted drugs. PMID:26050629
Nature and the Sign of Stress-Activated Electronic Charge Carriers in Rocks
NASA Astrophysics Data System (ADS)
Freund, F.
2013-12-01
When rocks are subjected to increasing uniaxial stress, highly mobile charge carriers become activated, which have the remarkable ability to flow out of the stressed rock volume, spreading into and through adjacent less stressed or unstressed rocks. Two basic questions arise: (i) What is the nature - and the sign - of these charge carriers and (ii) How do they exist in the rocks before being activated by stress? A large body of evidence is available that points to a positive sign, consistent with defect electrons, which (in semiconductor parlance) are called 'holes'. Holes that reside in the oxygen anion sublattice, associated with O 2sp-type energy states at the upper edge of the valence band, are called 'positive holes'. The positive holes exist in rocks in form of dormant, electrically inactive peroxy defects. Ever so slight deformation, leading to grain-grain sliding, can break the peroxy bonds and activate positive holes. Electrons that are co-activated by the same process cannot flow out of the stressed rock volume into the unstressed rocks. This leads to charge separation and, hence, to a potential difference similar to a battery voltage. In order to experimentally confirm the positive sign of the positive hole charge carriers flowing out of a given stressed rock volume, certain rules have to be obeyed. If not, unreliable results may be obtained, even negative outflow currents, seemingly inconsistent with the postulated positive sign of the positive hole charge carriers. Such errors can be avoided by taking into account that the charge outflow occurs in response to a 'battery potential', V, rapidly evolving between stressed and unstressed or less stressed parts of the rock. The current I given by Ohm's Law, I=V/R, is then limited by the internal resistance R. A second complicating factor arises from the fact that, as the positive holes are stress-activated and begin to flow out, they simultaneously recombine, returning to the dormant state. The ensuing
EUV-driven ionospheres and electron transport on extrasolar giant planets orbiting active stars
NASA Astrophysics Data System (ADS)
Chadney, J. M.; Galand, M.; Koskinen, T. T.; Miller, S.; Sanz-Forcada, J.; Unruh, Y. C.; Yelle, R. V.
2016-03-01
The composition and structure of the upper atmospheres of extrasolar giant planets (EGPs) are affected by the high-energy spectrum of their host stars from soft X-rays to the extreme ultraviolet (EUV). This emission depends on the activity level of the star, which is primarily determined by its age. In this study, we focus upon EGPs orbiting K- and M-dwarf stars of different ages - ɛ Eridani, AD Leonis, AU Microscopii - and the Sun. X-ray and EUV (XUV) spectra for these stars are constructed using a coronal model. These spectra are used to drive both a thermospheric model and an ionospheric model, providing densities of neutral and ion species. Ionisation - as a result of stellar radiation deposition - is included through photo-ionisation and electron-impact processes. The former is calculated by solving the Lambert-Beer law, while the latter is calculated from a supra-thermal electron transport model. We find that EGP ionospheres at all orbital distances considered (0.1-1 AU) and around all stars selected are dominated by the long-lived H+ ion. In addition, planets with upper atmospheres where H2 is not substantially dissociated (at large orbital distances) have a layer in which H3+ is the major ion at the base of the ionosphere. For fast-rotating planets, densities of short-lived H3+ undergo significant diurnal variations, with the maximum value being driven by the stellar X-ray flux. In contrast, densities of longer-lived H+ show very little day/night variability and the magnitude is driven by the level of stellar EUV flux. The H3+ peak in EGPs with upper atmospheres where H2 is dissociated (orbiting close to their star) under strong stellar illumination is pushed to altitudes below the homopause, where this ion is likely to be destroyed through reactions with heavy species (e.g. hydrocarbons, water). The inclusion of secondary ionisation processes produces significantly enhanced ion and electron densities at altitudes below the main EUV ionisation peak, as
NASA Astrophysics Data System (ADS)
Blum, L. W.; Halford, A.; Millan, R.; Bonnell, J. W.; Goldstein, J.; Usanova, M.; Engebretson, M.; Ohnsted, M.; Reeves, G.; Singer, H.; Clilverd, M.; Li, X.
2015-07-01
Electromagnetic ion cyclotron (EMIC) waves have been suggested to be a cause of radiation belt electron loss to the atmosphere. Here simultaneous, magnetically conjugate measurements are presented of EMIC wave activity, measured at geosynchronous orbit and on the ground, and energetic electron precipitation, seen by the Balloon Array for Radiation belt Relativistic Electron Losses (BARREL) campaign, on two consecutive days in January 2013. Multiple bursts of precipitation were observed on the duskside of the magnetosphere at the end of 18 January and again late on 19 January, concurrent with particle injections, substorm activity, and enhanced magnetospheric convection. The structure, timing, and spatial extent of the waves are compared to those of the precipitation during both days to determine when and where EMIC waves cause radiation belt electron precipitation. The conjugate measurements presented here provide observational support of the theoretical picture of duskside interaction of EMIC waves and MeV electrons leading to radiation belt loss.
Emelyanova, Larisa; Ashary, Zain; Cosic, Milanka; Negmadjanov, Ulugbek; Ross, Gracious; Rizvi, Farhan; Olet, Susan; Kress, David; Sra, Jasbir; Tajik, A Jamil; Holmuhamedov, Ekhson L; Shi, Yang; Jahangir, Arshad
2016-07-01
Mitochondria are critical for maintaining normal cardiac function, and a deficit in mitochondrial energetics can lead to the development of the substrate that promotes atrial fibrillation (AF) and its progression. However, the link between mitochondrial dysfunction and AF in humans is still not fully defined. The aim of this study was to elucidate differences in the functional activity of mitochondrial oxidative phosphorylation (OXPHOS) complexes and oxidative stress in right atrial tissue from patients without (non-AF) and with AF (AF) who were undergoing open-heart surgery and were not significantly different for age, sex, major comorbidities, and medications. The overall functional activity of the electron transport chain (ETC), NADH:O2 oxidoreductase activity, was reduced by 30% in atrial tissue from AF compared with non-AF patients. This was predominantly due to a selective reduction in complex I (0.06 ± 0.007 vs. 0.09 ± 0.006 nmol·min(-1)·citrate synthase activity(-1), P = 0.02) and II (0.11 ± 0.012 vs. 0.16 ± 0.012 nmol·min(-1)·citrate synthase activity(-1), P = 0.003) functional activity in AF patients. Conversely, complex V activity was significantly increased in AF patients (0.21 ± 0.027 vs. 0.12 ± 0.01 nmol·min(-1)·citrate synthase activity(-1), P = 0.005). In addition, AF patients exhibited a higher oxidative stress with increased production of mitochondrial superoxide (73 ± 17 vs. 11 ± 2 arbitrary units, P = 0.03) and 4-hydroxynonenal level (77.64 ± 30.2 vs. 9.83 ± 2.83 ng·mg(-1) protein, P = 0.048). Our findings suggest that AF is associated with selective downregulation of ETC activity and increased oxidative stress that can contribute to the progression of the substrate for AF. PMID:27199126
Laarmann, T.; Rusek, M.; Schulz, J.; Castro, A.R.B. de; Guertler, P.; Laasch, W.; Moeller, T.
2005-08-05
The ionization dynamics of Ar and Xe clusters irradiated with intense vacuum ultraviolet light from a free-electron laser is investigated using photoelectron spectroscopy. Clusters comprising between 70 and 900 atoms were irradiated with femtosecond pulses at 95 nm wavelength ({approx}13 eV photon energy) and a peak intensity of {approx}4x10{sup 12} W/cm{sup 2}. A broad thermal distribution of emitted electrons from clusters with a maximum kinetic energy up to 30-40 eV is observed. The observation of relatively low-energy photoelectrons is in good agreement with calculations using a time-dependent Thomas-Fermi model and gives experimental evidence of an outer ionization process of the clusters, due to delayed thermoelectronic emission.
1996-10-01
This study deals with the effects of chemical surface treatment of active carbons on their capacity to adsorb different organic pollutants in water. In particular, it explores the role of electrostatic adsorbate/adsorbent interactions and the consequences of the amphoteric nature of carbon surfaces. We contrast the behavior of chemically different carbons in adsorbing vastly different aromatic solutes. For example, nitrobenzene is a very weak Lewis acid that possesses the electron-withdrawing NO{sub 2} group, while aniline is a predominantly cationic species at pH < 4.6 that also possesses the electron-donating NH{sub 2} group.
Cavity approximation for graphical models.
Rizzo, T; Wemmenhove, B; Kappen, H J
2007-07-01
We reformulate the cavity approximation (CA), a class of algorithms recently introduced for improving the Bethe approximation estimates of marginals in graphical models. In our formulation, which allows for the treatment of multivalued variables, a further generalization to factor graphs with arbitrary order of interaction factors is explicitly carried out, and a message passing algorithm that implements the first order correction to the Bethe approximation is described. Furthermore, we investigate an implementation of the CA for pairwise interactions. In all cases considered we could confirm that CA[k] with increasing k provides a sequence of approximations of markedly increasing precision. Furthermore, in some cases we could also confirm the general expectation that the approximation of order k , whose computational complexity is O(N(k+1)) has an error that scales as 1/N(k+1) with the size of the system. We discuss the relation between this approach and some recent developments in the field. PMID:17677405
Approximate circuits for increased reliability
Hamlet, Jason R.; Mayo, Jackson R.
2015-08-18
Embodiments of the invention describe a Boolean circuit having a voter circuit and a plurality of approximate circuits each based, at least in part, on a reference circuit. The approximate circuits are each to generate one or more output signals based on values of received input signals. The voter circuit is to receive the one or more output signals generated by each of the approximate circuits, and is to output one or more signals corresponding to a majority value of the received signals. At least some of the approximate circuits are to generate an output value different than the reference circuit for one or more input signal values; however, for each possible input signal value, the majority values of the one or more output signals generated by the approximate circuits and received by the voter circuit correspond to output signal result values of the reference circuit.
Approximate circuits for increased reliability
Hamlet, Jason R.; Mayo, Jackson R.
2015-12-22
Embodiments of the invention describe a Boolean circuit having a voter circuit and a plurality of approximate circuits each based, at least in part, on a reference circuit. The approximate circuits are each to generate one or more output signals based on values of received input signals. The voter circuit is to receive the one or more output signals generated by each of the approximate circuits, and is to output one or more signals corresponding to a majority value of the received signals. At least some of the approximate circuits are to generate an output value different than the reference circuit for one or more input signal values; however, for each possible input signal value, the majority values of the one or more output signals generated by the approximate circuits and received by the voter circuit correspond to output signal result values of the reference circuit.
Structural optimization with approximate sensitivities
NASA Technical Reports Server (NTRS)
Patnaik, S. N.; Hopkins, D. A.; Coroneos, R.
1994-01-01
Computational efficiency in structural optimization can be enhanced if the intensive computations associated with the calculation of the sensitivities, that is, gradients of the behavior constraints, are reduced. Approximation to gradients of the behavior constraints that can be generated with small amount of numerical calculations is proposed. Structural optimization with these approximate sensitivities produced correct optimum solution. Approximate gradients performed well for different nonlinear programming methods, such as the sequence of unconstrained minimization technique, method of feasible directions, sequence of quadratic programming, and sequence of linear programming. Structural optimization with approximate gradients can reduce by one third the CPU time that would otherwise be required to solve the problem with explicit closed-form gradients. The proposed gradient approximation shows potential to reduce intensive computation that has been associated with traditional structural optimization.
NASA Astrophysics Data System (ADS)
Chanlek, N.; Herbert, J. D.; Jones, R. M.; Jones, L. B.; Middleman, K. J.; Militsyn, B. L.
2015-09-01
In this paper we report the first time demonstration under extremely high vacuum (XHV) conditions of the influence of O2, CO2, CO, N2, H2 and CH4 on the quantum efficiency (QE) of negative electron affinity (NEA) gallium arsenide (GaAs) photocathodes activated with Cs and NF3. The photocathodes were exposed to a small quantity (<0.25 Langmuirs) of each gas species under test in a vacuum chamber with a typical base pressure of 1.5× {{10}-11} mbar, thereby minimising the influence of the residual gas in the photocathode response. It was found that exposure to N2, H2 and CH4 does not affect the QE of the photocathodes, whereas exposure to O2 and CO2 lead to a substantial reduction in the QE of the photocathodes. Only small degradation in the QE under CO exposure was observed. Compared to those activated with Cs and O2 in our previous study [1], photocathodes activated with Cs and NF3 are more stable, especially under exposure to CO.
Lipidomic analysis and electron transport chain activities in C57BL/6J mouse brain mitochondria
Kiebish, Michael A.; Han, Xianlin; Cheng, Hua; Lunceford, Adam; Clarke, Catherine F.; Moon, Hwi; Chuang, Jeffrey H.; Seyfried, Thomas N.
2011-01-01
The objective of this study was to characterize the lipidome and electron transport chain activities in purified non-synaptic (NS) and synaptic (Syn) mitochondria from C57BL/6J mouse cerebral cortex. Contamination from subcellular membranes, especially myelin, has hindered past attempts to accurately characterize the lipid composition of brain mitochondria. An improved Ficoll and sucrose discontinuous gradient method was employed that yielded highly enriched mitochondrial populations free of myelin contamination. The activities of Complexes I, II, III, and II/III were lower in Syn than in NS mitochondria, while Complexes I/III and IV activities were similar in both populations. Shotgun lipidomics showed that levels of cardiolipin (Ptd2Gro) were lower, whereas levels of ceramide and phosphatidylserine were higher in Syn than in NS mitochondria. Coenzyme Q9 and Q10 was also lower in Syn than in NS mitochondria. Gangliosides, phosphatidic acid, sulfatides, and cerebrosides were undetectable in brain mitochondria. The distribution of Ptd2Gro molecular species was similar in both populations and formed a unique pattern, consisting of seven major molecular species groups, when arranged according to mass to charge ratios. Remodeling involving choline and ethanolamine phosphoglycerides could explain Ptd2Gro heterogeneity. NS and Syn mitochondrial lipidomic heterogeneity could influence energy metabolism, which may contribute to metabolic compartmentation of the brain. PMID:18373617
Vicentini, Chiara B; Guccione, Salvatore; Giurato, Laura; Ciaccio, Rebecca; Mares, Donatella; Forlani, Giuseppe
2005-05-18
Four series of new pyrazoles, namely, 5 4-carboxypyrazolo-3-tert-butylcarboxamide and 6 4-carboxypyrazolo-3-cyclopropylcarboxamide derivatives and 10 pyrazolo[3,4-d][1,3]thiazine-4-one and 9 pyrazolo[3,4-d][1,3]thiazine-4-thione derivatives, were synthesized and screened as potential inhibitors of photosynthetic electron transport. The structures were confirmed by 1H NMR, elemental, and IR analyses. Their biological activity was evaluated in vitro as the ability to interfere with the light-driven reduction of ferricyanide by isolated spinach chloroplasts. Only a few compounds exhibited excellent inhibitory properties in the micromolar range, comparable to those of commercial herbicides sharing the same target, such as diuron, lenacil, and hexazinone. Nevertheless, most of the remaining molecules exerted a remarkable inhibition in the millimolar range. Combined with previous results on 6 pyrazolo[1,5-a][1,3,5]triazine-2,4-dione and 4 pyrazolo[1,5-c][1,3,5]thiadiazine-2-one derivatives, these data allowed a comprehensive analysis of structure-activity relationship. Molecular modeling studies were undertaken to rationalize the structural determinants of activity in terms of shape, size, and molecular fields. Results suggested that the inhibitory potential of these compounds is associated mainly with their electrostatic properties. PMID:15884806
Electronics drivers for high voltage dielectric electro active polymer (DEAP) applications
NASA Astrophysics Data System (ADS)
Zhang, Zhe; Andersen, Michael A. E.
2015-04-01
Dielectric electro active polymer (DEAP) can be used in actuation, sensing and energy harvesting applications, but driving the DEAP based actuators and generators has three main challenges from a power electronics standpoint, i.e. high voltage (around 2.5 kV), nonlinearity, and capacitive behavior. In this paper, electronics divers for heating valves, loud speakers, incremental motors, and energy harvesting are reviewed, studied and developed in accordance with their corresponding specifications. Due to the simplicity and low power capacity (below 10W), the reversible Fly-back converters with both magnetic and piezoelectric transformers are employed for the heating valve and incremental motor application, where only ON/OFF regulation is adopted for energy saving; as for DEAP based energy harvesting, the noisolated Buck/Boost converter is used, due to the system high power capacity (above 100W), but the voltage balancing across the series-connected high voltage IGBTs is a critical issue and accordingly a novel gate driver circuitry is proposed and equipped; due to the requirements of the audio products, such as low distortion and noise, the multi-level Buck converter based Class-D amplifier, because of its high control linearity, is implemented for the loud speaker applications. A synthesis among those converter topologies and control techniques is given; therefore, for those DEAP based applications, their diversity and similarity of electronics drivers, as well as the key technologies employed are analyzed. Therefore a whole picture of how to choose the proper topologies can be revealed. Finally, the design guidelines in order to achieve high efficiency and reliability are discussed.
Role of Many-Electron Dynamics in High Harmonic Generation
Gordon, Ariel; Kaertner, Franz X.; Rohringer, Nina; Santra, Robin
2006-06-09
High harmonic generation (HHG) in many-electron atoms is studied theoretically. The breakdown of the frozen-core single active electron approximation is demonstrated, as it predicts roughly the same radiation amplitude in all noble gases. This is in contradiction with experiments, where heavier noble gases are known to emit much stronger HHG radiation than lighter ones. This experimental behavior of the noble gases can be qualitatively reproduced when many-electron dynamics, within a simple approximation, is taken into account.
Can Distributional Approximations Give Exact Answers?
ERIC Educational Resources Information Center
Griffiths, Martin
2013-01-01
Some mathematical activities and investigations for the classroom or the lecture theatre can appear rather contrived. This cannot, however, be levelled at the idea given here, since it is based on a perfectly sensible question concerning distributional approximations that was posed by an undergraduate student. Out of this simple question, and…
Metabolic transistor strategy for controlling electron transfer chain activity in Escherichia coli
Wu, Hui; Tuli, Leepika; Bennett, George N.; San, Ka-Yiu
2015-01-01
A novel strategy to finely control a large metabolic flux by using a “metabolic transistor” approach was established. In this approach a small change in the level or availability of an essential component for the process is controlled by adding a competitive reaction that affects a precursor or an intermediate in its biosynthetic pathway. The change of the basal level of the essential component, considered as a base current in a transistor, has a large effect on the flux through the major pathway. In this way, the fine-tuning of a large flux can be accomplished. The “metabolic transistor” strategy was applied to controlling electron transfer chain function by manipulation of the quinone synthesis pathway in Escherichia coli. The achievement of a theoretical yield of lactate production under aerobic conditions via this strategy upon manipulation of the biosynthetic pathway of the key participant, ubiquinone-8 (Q8), in an E. coli strain provides an in vivo, genetically tunable means to control the activity of the electron transfer chain and manipulate the production of reduced products while limiting consumption of oxygen to a defined amount. PMID:25596510
Bai, Mingsian R; Lin, Yuanpei; Lai, Jienwen
2002-02-01
Electronic delay has been a critical problem in active noise control (ANC) systems. This is true whether a feedforward structure or a feedback structure is adopted. In particular, excessive delays would create a causality problem in a feedforward ANC system of a finite-length duct. This paper suggests a multirate signal-processing approach for minimizing the electronic delay in the control loop. In this approach, digital controllers are required in decimation and interpolation of discrete-time signals. The computation efficiency is further enhanced by a polyphase method, where the phases of low-pass finite impulse response (FIR) filters must be carefully designed to avoid unnecessary delays. Frequency domain optimization procedures based on H1, H2, and Hinfinity norms, respectively, are utilized in the FIR filter design. The proposed method was implemented by using a floating-point digital signal processor. Experimental results showed that the multirate approach remains effective for suppressing a broadband (200-600 Hz) noise in a duct with a minimum upstream measurement microphone placement of 20 cm. PMID:11863193
Electronic origins of photocatalytic activity in d0 metal organic frameworks
Nasalevich, Maxim A.; Hendon, Christopher H.; Santaclara, Jara G.; Svane, Katrine; van der Linden, Bart; Veber, Sergey L.; Fedin, Matvey V.; Houtepen, Arjan J.; van der Veen, Monique A.; Kapteijn, Freek; Walsh, Aron; Gascon, Jorge
2016-01-01
Metal-organic frameworks (MOFs) containing d0 metals such as NH2-MIL-125(Ti), NH2-UiO-66(Zr) and NH2-UiO-66(Hf) are among the most studied MOFs for photocatalytic applications. Despite structural similarities, we demonstrate that the electronic properties of these MOFs are markedly different. As revealed by quantum chemistry, EPR measurements and transient absorption spectroscopy, the highest occupied and lowest unoccupied orbitals of NH2-MIL-125(Ti) promote a long lived ligand-to-metal charge transfer upon photoexcitation, making this material suitable for photocatalytic applications. In contrast, in case of UiO materials, the d-orbitals of Zr and Hf, are too low in binding energy and thus cannot overlap with the π* orbital of the ligand, making both frontier orbitals localized at the organic linker. This electronic reconfiguration results in short exciton lifetimes and diminishes photocatalytic performance. These results highlight the importance of orbital contributions at the band edges and delineate future directions in the development of photo-active hybrid solids. PMID:27020767
Electronic origins of photocatalytic activity in d0 metal organic frameworks
NASA Astrophysics Data System (ADS)
Nasalevich, Maxim A.; Hendon, Christopher H.; Santaclara, Jara G.; Svane, Katrine; van der Linden, Bart; Veber, Sergey L.; Fedin, Matvey V.; Houtepen, Arjan J.; van der Veen, Monique A.; Kapteijn, Freek; Walsh, Aron; Gascon, Jorge
2016-03-01
Metal-organic frameworks (MOFs) containing d0 metals such as NH2-MIL-125(Ti), NH2-UiO-66(Zr) and NH2-UiO-66(Hf) are among the most studied MOFs for photocatalytic applications. Despite structural similarities, we demonstrate that the electronic properties of these MOFs are markedly different. As revealed by quantum chemistry, EPR measurements and transient absorption spectroscopy, the highest occupied and lowest unoccupied orbitals of NH2-MIL-125(Ti) promote a long lived ligand-to-metal charge transfer upon photoexcitation, making this material suitable for photocatalytic applications. In contrast, in case of UiO materials, the d-orbitals of Zr and Hf, are too low in binding energy and thus cannot overlap with the π* orbital of the ligand, making both frontier orbitals localized at the organic linker. This electronic reconfiguration results in short exciton lifetimes and diminishes photocatalytic performance. These results highlight the importance of orbital contributions at the band edges and delineate future directions in the development of photo-active hybrid solids.
De Novo Sequencing of Heparan Sulfate Oligosaccharides by Electron-Activated Dissociation
Huang, Yu; Yu, Xiang; Mao, Yang; Costello, Catherine E.; Zaia, Joseph; Lin, Cheng
2014-01-01
Structural characterization of highly sulfated glycosaminoglycans (GAGs) by collisionally activated dissociation (CAD) is challenging because of the extensive sulfate losses mediated by free protons. While removal of the free protons may be achieved through the use of derivatization, metal cation adducts, and/or electrospray supercharging reagents, these steps add complexity to the experimental workflow. It is therefore desirable to develop an analytical approach for GAG sequencing that does not require derivatization or addition of reagents to the electrospray solution. Electron detachment dissociation (EDD) can produce extensive and informative fragmentation for GAGs without the need to remove free protons from the precursor ions. However, EDD is an inefficient process, often requiring consumption of large sample quantities (typically several micrograms), particularly for highly sulfated GAG ions. Here, we report that with improved instrumentation, optimization of the ionization and ion transfer parameters, and enhanced EDD efficiency, it is possible to generate highly informative EDD spectra of highly sulfated GAGs on the liquid chromatography (LC) time-scale, with consumption of only a few nanograms of sample. We further show that negative electron transfer dissociation (NETD) is an even more effective fragmentation technique for GAG sequencing, producing fewer sulfate losses while consuming smaller amount of samples. Finally, a simple algorithm was developed for de novo HS sequencing based on their high resolution tandem mass spectra. These results demonstrate the potential of EDD and NETD as sensitive analytical tools for detailed, high-throughput, de novo structural analyses of highly sulfated GAGs. PMID:24224699
Electronic origins of photocatalytic activity in d0 metal organic frameworks.
Nasalevich, Maxim A; Hendon, Christopher H; Santaclara, Jara G; Svane, Katrine; van der Linden, Bart; Veber, Sergey L; Fedin, Matvey V; Houtepen, Arjan J; van der Veen, Monique A; Kapteijn, Freek; Walsh, Aron; Gascon, Jorge
2016-01-01
Metal-organic frameworks (MOFs) containing d(0) metals such as NH2-MIL-125(Ti), NH2-UiO-66(Zr) and NH2-UiO-66(Hf) are among the most studied MOFs for photocatalytic applications. Despite structural similarities, we demonstrate that the electronic properties of these MOFs are markedly different. As revealed by quantum chemistry, EPR measurements and transient absorption spectroscopy, the highest occupied and lowest unoccupied orbitals of NH2-MIL-125(Ti) promote a long lived ligand-to-metal charge transfer upon photoexcitation, making this material suitable for photocatalytic applications. In contrast, in case of UiO materials, the d-orbitals of Zr and Hf, are too low in binding energy and thus cannot overlap with the π* orbital of the ligand, making both frontier orbitals localized at the organic linker. This electronic reconfiguration results in short exciton lifetimes and diminishes photocatalytic performance. These results highlight the importance of orbital contributions at the band edges and delineate future directions in the development of photo-active hybrid solids. PMID:27020767
Dale, Gregory E.; Woloshun, Keith A.; Kelsey IV, Charles T.; Olivas, Eric R.; Holloway, Michael A.; Hurtle, Ken P.; Romero, Frank P.; Dalmas, Dale A.; Chemerisov, Sergey D.; Vandegrift, George F.; Tkac, Peter; Makarashvili, Vakho; Jonah, Charles D.; Harvey, James T.
2013-04-19
{sup 99m}Tc, the daughter isotope of {sup 99}Mo, is the most commonly used radioisotope for nuclear medicine in the United States. Under the direction of the National Nuclear Security Administration (NNSA), Los Alamos National Laboratory (LANL) and Argonne National Laboratory (ANL) are partnering with North Star Medical Technologies to demonstrate the viability of large-scale {sup 99}Mo production using electron accelerators. In this process, {sup 99}Mo is produced in an enriched {sup 100}Mo target through the {sup 100}Mo({gamma},n){sup 99}Mo reaction. Five experiments have been performed to date at ANL to demonstrate this process. This paper reviews the current status of these activities, specifically the design and performance of the helium gas target cooling system.
[ELECTRONIC LOGBOOK: LEARNING TOOL AND TEACHING AID FOR THE EVALUATION OF LEARNING ACTIVITIES].
Scantamburlo, G; Vierset, V; Bonnet, P; Verpoorten, D; Delfosse, C; Ansseau, M
2016-04-01
A LogBook is a learning tool and teaching aid I where clinical settings lived during training courses are provided. A LogBook is basically a journal which evidences learning and skills. LogBook provides a means for monitoring student learning, both for the student and for the instructor. It provides a feedback loop for the evaluation of learning activities. This LogBook has been developed for the student's training in psychiatry but it may be extended to all medical disciplines. The authors have developed an electronic logbook to support learning and assessment. In the context of Europe, it has become necessary to set up a LogBook of uniform learning outcomes to assist medical students. PMID:27295902
Trost, Barry M; Debien, Laurent
2015-09-16
α-Trifluoromethyl-styrenes, trifluoromethyl-enynes, and dienes undergo palladium-catalyzed trimethylenemethane cycloadditions under mild reaction conditions. The trifluoromethyl group serves as a unique σ-electron-withdrawing group for the activation of the olefin toward the cycloaddition. This method allows for the formation of exomethylene cyclopentanes bearing a quaternary center substituted by the trifluoromethyl group, compounds of interest for the pharmaceutical, agrochemical, and materials industries. In the diene series, the cycloaddition operates in a [3 + 4] and/or [3 + 2] manner to give rise to seven- and/or five-membered rings. This transformation greatly improves the scope of the TMM cycloaddition technology and provides invaluable insights into the reaction mechanism. PMID:26291872
Active local oscillator power stabilization for a hot electron bolometer heterodyne receiver
NASA Astrophysics Data System (ADS)
Hayton, D. J.; Gao, J. R.; Kooi, J. W.; Ren, Y.; Zhang, W.; de Lange, G.
2012-09-01
We report on the application of a new technique for actively stabilizing the power of a far infrared gas laser as the local oscillator (LO) in a superconducting hot electron bolometer (HEB) heterodyne receiver system at 2.5 THz. The technique utilizes PID feedback control of the local oscillator intensity by means of a voice-coil based swing arm actuator placed in the beam path. The HEB itself is used as a direct detector to measure incident LO power whilst simultaneously continuing to function as heterodyne mixer. Results presented here demonstrate a factor of 50 improvement in the measured total power and spectroscopic Allan variance time. Allan times of 30 seconds and 25 seconds respectively are shown for large and small area HEB's with a measured effective noise fluctuation bandwidth of 12 MHz. The technique is versatile and can be applied to any LO source and at any LO frequency.
Gao, Shan; Zheng, Zhenbing; Huan, Li; Wang, Guangce
2016-01-01
Photosynthetic performances and glucose-6-phosphate dehydrogenase (G6PDH) activity in Physcomitrella patens changed greatly during salt stress and recovery. In P. patens, the cyclic electron flow around photosystem (PS) I was much more tolerant to high salt stress than PSII. After high salt stress, the PSII activity recovered much more slowly than that of PSI, which was rapidly restored to pretreatment levels even as PSII was almost inactivate. This result suggested that after salt stress the recovery of the cyclic electron flow around PSI was independent of PSII activity. In addition, G6PDH activity and NADPH content increased under high salt stress. When G6PDH activity was inhibited by glucosamine (Glucm, a G6PDH inhibitor), the cyclic electron flow around PSI and the NADPH content decreased significantly. Additionally, after recovery in liquid medium containing Glucm, the PSI activity was much lower than in liquid medium without Glucm. These results suggested the PSI activity was affected significantly by G6PDH activity and the NADPH content. Based on the above results, we propose that G6PDH in P. patens has a close relationship with the photosynthetic process, possibly providing NADPH for the operation of the cyclic electron flow around PSI during salt stress and promoting the restoration of PSI. PMID:26887288
12 CFR 7.5001 - Electronic activities that are part of, or incidental to, the business of banking.
Code of Federal Regulations, 2010 CFR
2010-01-01
... 12 Banks and Banking 1 2010-01-01 2010-01-01 false Electronic activities that are part of, or incidental to, the business of banking. 7.5001 Section 7.5001 Banks and Banking COMPTROLLER OF THE CURRENCY... activities that are part of, or incidental to, the business of banking. (a) Purpose. This section...
Approximate Genealogies Under Genetic Hitchhiking
Pfaffelhuber, P.; Haubold, B.; Wakolbinger, A.
2006-01-01
The rapid fixation of an advantageous allele leads to a reduction in linked neutral variation around the target of selection. The genealogy at a neutral locus in such a selective sweep can be simulated by first generating a random path of the advantageous allele's frequency and then a structured coalescent in this background. Usually the frequency path is approximated by a logistic growth curve. We discuss an alternative method that approximates the genealogy by a random binary splitting tree, a so-called Yule tree that does not require first constructing a frequency path. Compared to the coalescent in a logistic background, this method gives a slightly better approximation for identity by descent during the selective phase and a much better approximation for the number of lineages that stem from the founder of the selective sweep. In applications such as the approximation of the distribution of Tajima's D, the two approximation methods perform equally well. For relevant parameter ranges, the Yule approximation is faster. PMID:17182733
Gas pressure and electron density at the level of the active zone of hollow cathode arc discharges
NASA Technical Reports Server (NTRS)
Minoo, M. H.
1984-01-01
A model for the longitudinal variations of the partial pressures of electrons, ions, and neutral particles is proposed as a result of an experimental study of pressure variations at the level of the active zone as a function of the various discharge parameters of a hollow cathode arc. The cathode region where the temperature passes through its maximum is called active zone. The proposed model embodies the very important variations which the partial electron and neutral particles pressures undergo at the level of the active zone.
NASA Astrophysics Data System (ADS)
De Geronimo, G.; Deptuch, G.; Dragone, A.; Radeka, V.; Rehak, P.; Castoldi, A.; Fazzi, A.; Gatti, E.; Guazzoni, C.; Rijssenbeek, M.; Dulinski, W.; Besson, A.; Deveaux, M.; Winter, M.
2006-11-01
A new type of active pixel sensors (APSs) to track charged particles for particle physics experiments or to count number of electrons that cross any pixel at the focal plane of electron microscopes is described. The electric field of desirable shape is created inside the active volume of the pixel introducing the drift component in the movement of the signal electrons towards charge collecting electrodes. The electric field results from the flow of ˜100 mA/cm 2 hole currents within individual pixels of the sensor. The proposed sensor is produced using a standard industrially available complementary metal oxide silicon (CMOS) process. There are two main advantages of the proposed detectors when compared to the present (February 2005) state-of-the-art, i.e. field-free APS sensors. The first advantage of a field-assisted transport mechanism is the reduction of the charge collection time and of the sharing of the signal electrons between adjacent pixels by diffusion. The second advantage is the freedom to use both kinds of MOS transistors within each pixel of the sensor. Thus, the full functional power of CMOS circuits can be embedded in situ. As an example, 16-bit scalers will be implemented in each pixel of the sensor for electron microscopy. The reduced collection time combined with the state-of-the-art electronics within each pixel provides the most complete information about the position and the timing of incident charged particles for particle physics experiments. Position resolution of new sensors was computationally simulated to be a few microns, that is, the same as the resolution of standard APSs. Moreover, the active depth of the sensor and the associate electronics is less than about 20 μm and a thinned down sensor together with its beryllium backing can have a total thickness of less than 0.1% of one radiation length. The reduction of the thickness of the detector reduces the amount of multiple scattering within the detector. The determination of the
NASA Astrophysics Data System (ADS)
Sahal-Bréchot, Sylvie; Dimitrijević, Milan; Nessib, Nabil
2014-06-01
"Stark broadening" theory and calculations have been extensively developed for about 50 years. The theory can now be considered as mature for many applications, especially for accurate spectroscopic diagnostics and modeling, in astrophysics, laboratory plasma physics and technological plasmas, as well. This requires the knowledge of numerous collisional line profiles. In order to meet these needs, the "SCP" (semiclassical perturbation) method and numerical code were created and developed. The SCP code is now extensively used for the needs of spectroscopic diagnostics and modeling, and the results of the published calculations are displayed in the STARK-B database. The aim of the present paper is to introduce the main approximations leading to the impact of semiclassical perturbation method and to give formulae entering the numerical SCP code, in order to understand the validity conditions of the method and of the results; and also to understand some regularities and systematic trends. This would also allow one to compare the method and its results to those of other methods and codes.
Ghimire, Govinda; Yi, Yi; Derylo, Maksymilian A; Baker, Lane A; Ito, Takashi
2015-11-10
This paper reports the electrochemical behavior of redox-active microdomains in thin films of ferrocene-containing diblock copolymers, polystyrene-block-poly(2-(acryloyloxy)ethyl ferrocenecarboxylate) (PS-b-PAEFc). PS-b-PAEFc with different PAEFc volume fractions (PS154-b-PAEFc51, PS154-b-PAEFc26, and PS154-b-PAEFc12, where the subscripts represent the polymerization degree of each block; f(PAEFc) = 0.47, 0.30, and 0.17, respectively) was synthesized by sequential atom transfer radical polymerization. PS-b-PAEFc films of controlled thicknesses (20-160 nm) were prepared on gold substrates via spin-coating and characterized by ellipsometry. Microdomains were observed via atomic force microscopy on the surfaces of PS154-b-PAEFc51 and PS154-b-PAEFc26 thin films but not on the surfaces of PS154-b-PAEFc12 thin films. Electrochemical behavior of films was assessed by cyclic voltammetry and chronocoulometry in acetonitrile solution. The redox potential of ferrocene moieties was similar (ca. + 0.29 V vs Fc(+)/Fc) regardless of fPAEFc and film thickness. For PS154-b-PAEFc51 and PS154-b-PAEFc26, thicker films afforded larger faradaic peak currents and exhibited diffusion-controlled voltammograms at faster sweep rates. PS154-b-PAEFc26 produced voltammograms less influenced by solvent-induced swelling than PS154-b-PAEFc51, reflecting the improved morphological stability of PAEFc microdomains by redox-inert PS frameworks. In contrast, PS154-b-PAEFc12 films yielded similar faradaic peak currents regardless of film thickness and exhibited voltammograms indicative of surface-confined species. These observations suggest that PS154-b-PAEFc51 and PS154-b-PAEFc26 films contain continuous PAEFc microdomains extending from the electrode to the surface, in contrast to the PS154-b-PAEFc12 films which contain isolated PAEFc microdomains buried within the PS matrix. Electron propagation took place only through PAEFc microdomains that could electrically communicate with the underlying
The Effect of Excess Electron and hole on CO2 Adsorption and Activation on Rutile (110) surface.
Yin, Wen-Jin; Wen, Bo; Bandaru, Sateesh; Krack, Matthias; Lau, M W; Liu, Li-Min
2016-01-01
CO2 capture and conversion into useful chemical fuel attracts great attention from many different fields. In the reduction process, excess electron is of key importance as it participates in the reaction, thus it is essential to know whether the excess electrons or holes affect the CO2 conversion. Here, the first-principles calculations were carried out to explore the role of excess electron on adsorption and activation of CO2 on rutile (110) surface. The calculated results demonstrate that CO2 can be activated as CO2 anions or CO2 cation when the system contains excess electrons and holes. The electronic structure of the activated CO2 is greatly changed, and the lowest unoccupied molecular orbital of CO2 can be even lower than the conduction band minimum of TiO2, which greatly facilities the CO2 reduction. Meanwhile, the dissociation process of CO2 undergoes an activated CO2(-) anion in bend configuration rather than the linear, while the long crossing distance of proton transfer greatly hinders the photocatalytic reduction of CO2 on the rutile (110) surface. These results show the importance of the excess electrons on the CO2 reduction process. PMID:26984417
The Effect of Excess Electron and hole on CO2 Adsorption and Activation on Rutile (110) surface
NASA Astrophysics Data System (ADS)
Yin, Wen-Jin; Wen, Bo; Bandaru, Sateesh; Krack, Matthias; Lau, Mw; Liu, Li-Min
2016-03-01
CO2 capture and conversion into useful chemical fuel attracts great attention from many different fields. In the reduction process, excess electron is of key importance as it participates in the reaction, thus it is essential to know whether the excess electrons or holes affect the CO2 conversion. Here, the first-principles calculations were carried out to explore the role of excess electron on adsorption and activation of CO2 on rutile (110) surface. The calculated results demonstrate that CO2 can be activated as CO2 anions or CO2 cation when the system contains excess electrons and holes. The electronic structure of the activated CO2 is greatly changed, and the lowest unoccupied molecular orbital of CO2 can be even lower than the conduction band minimum of TiO2, which greatly facilities the CO2 reduction. Meanwhile, the dissociation process of CO2 undergoes an activated CO2‑ anion in bend configuration rather than the linear, while the long crossing distance of proton transfer greatly hinders the photocatalytic reduction of CO2 on the rutile (110) surface. These results show the importance of the excess electrons on the CO2 reduction process.
The Effect of Excess Electron and hole on CO2 Adsorption and Activation on Rutile (110) surface
Yin, Wen-Jin; Wen, Bo; Bandaru, Sateesh; Krack, Matthias; Lau, MW; Liu, Li-Min
2016-01-01
CO2 capture and conversion into useful chemical fuel attracts great attention from many different fields. In the reduction process, excess electron is of key importance as it participates in the reaction, thus it is essential to know whether the excess electrons or holes affect the CO2 conversion. Here, the first-principles calculations were carried out to explore the role of excess electron on adsorption and activation of CO2 on rutile (110) surface. The calculated results demonstrate that CO2 can be activated as CO2 anions or CO2 cation when the system contains excess electrons and holes. The electronic structure of the activated CO2 is greatly changed, and the lowest unoccupied molecular orbital of CO2 can be even lower than the conduction band minimum of TiO2, which greatly facilities the CO2 reduction. Meanwhile, the dissociation process of CO2 undergoes an activated CO2− anion in bend configuration rather than the linear, while the long crossing distance of proton transfer greatly hinders the photocatalytic reduction of CO2 on the rutile (110) surface. These results show the importance of the excess electrons on the CO2 reduction process. PMID:26984417
Mathematical algorithms for approximate reasoning
NASA Technical Reports Server (NTRS)
Murphy, John H.; Chay, Seung C.; Downs, Mary M.
1988-01-01
Most state of the art expert system environments contain a single and often ad hoc strategy for approximate reasoning. Some environments provide facilities to program the approximate reasoning algorithms. However, the next generation of expert systems should have an environment which contain a choice of several mathematical algorithms for approximate reasoning. To meet the need for validatable and verifiable coding, the expert system environment must no longer depend upon ad hoc reasoning techniques but instead must include mathematically rigorous techniques for approximate reasoning. Popular approximate reasoning techniques are reviewed, including: certainty factors, belief measures, Bayesian probabilities, fuzzy logic, and Shafer-Dempster techniques for reasoning. A group of mathematically rigorous algorithms for approximate reasoning are focused on that could form the basis of a next generation expert system environment. These algorithms are based upon the axioms of set theory and probability theory. To separate these algorithms for approximate reasoning various conditions of mutual exclusivity and independence are imposed upon the assertions. Approximate reasoning algorithms presented include: reasoning with statistically independent assertions, reasoning with mutually exclusive assertions, reasoning with assertions that exhibit minimum overlay within the state space, reasoning with assertions that exhibit maximum overlay within the state space (i.e. fuzzy logic), pessimistic reasoning (i.e. worst case analysis), optimistic reasoning (i.e. best case analysis), and reasoning with assertions with absolutely no knowledge of the possible dependency among the assertions. A robust environment for expert system construction should include the two modes of inference: modus ponens and modus tollens. Modus ponens inference is based upon reasoning towards the conclusion in a statement of logical implication, whereas modus tollens inference is based upon reasoning away
Exponential approximations in optimal design
NASA Technical Reports Server (NTRS)
Belegundu, A. D.; Rajan, S. D.; Rajgopal, J.
1990-01-01
One-point and two-point exponential functions have been developed and proved to be very effective approximations of structural response. The exponential has been compared to the linear, reciprocal and quadratic fit methods. Four test problems in structural analysis have been selected. The use of such approximations is attractive in structural optimization to reduce the numbers of exact analyses which involve computationally expensive finite element analysis.
Approximate factorization with source terms
NASA Technical Reports Server (NTRS)
Shih, T. I.-P.; Chyu, W. J.
1991-01-01
A comparative evaluation is made of three methodologies with a view to that which offers the best approximate factorization error. While two of these methods are found to lead to more efficient algorithms in cases where factors which do not contain source terms can be diagonalized, the third method used generates the lowest approximate factorization error. This method may be preferred when the norms of source terms are large, and transient solutions are of interest.
Galiazzo, F; Pedersen, J Z; Civitareale, P; Schiesser, A; Rotilio, G
1989-01-01
Manganese accumulation was studied by room-temperature electron spin resonance (ESR) spectroscopy in Saccharomyces cerevisiae grown in the presence of increasing amounts of MnSO4. Mn2+ retention was nearly linear in intact cells for fractions related to both low-molecular-mass and macromolecular complexes ('free' and 'bound' Mn2+, respectively). A deviation from linearity was observed in cell extracts between the control value and 0.1 mM Mn2+, indicating more efficient accumulation at low Mn2+ concentrations. The difference in slopes between the two straight lines describing Mn2+ retention at concentrations lower and higher than 0.1 mM, respectively, was quite large for the free Mn2+ fraction. Furthermore it was unaffected by subsequent dialyses of the extracts, showing stable retention in the form of low-molecular-mass complexes. In contrast, the slope of the line describing retention of 'bound' Mn2+ at concentrations higher than 0.1 mM became less steep after subsequent dialyses of the cell extracts. This result indicates that the macromolecule-bound Mn2+ was essentially associated with particulate structures. In contrast to Cu2+, Mn2+ had no effect on the major enzyme activities involved in oxygen metabolism except for a slight increase of cyanide-resistant Mn-superoxide dismutase activity, due to dialyzable Mn2+ complexes. PMID:2562042
NASA Astrophysics Data System (ADS)
Humplik, Thomas; Stirrup, Emily K.; Grillet, Anne M.; Grant, Richard P.; Allen, Ashley N.; Wesolowski, Daniel E.; Roberts, Christine C.
2016-07-01
The transient transport of electrolytes in thermally-activated batteries is studied using electron probe micro-analysis (EPMA), demonstrating the robust capability of EPMA as a useful tool for studying and quantifying mass transport within porous materials, particularly in difficult environments where classical flow measurements are challenging. By tracking the mobility of bromine and potassium ions from the electrolyte stored within the separator into the lithium silicon anode and iron disulfide cathode, we are able to quantify the transport mechanisms and physical properties of the electrodes including permeability and tortuosity. Due to the micron to submicron scale porous structure of the initially dry anode, a fast capillary pressure driven flow is observed into the anode from which we are able to set a lower bound on the permeability of 10-1 mDarcy. The transport into the cathode is diffusion-limited because the cathode originally contained some electrolyte before activation. Using a transient one-dimensional diffusion model, we estimate the tortuosity of the cathode electrode to be 2.8 ± 0.8.
Visible light active TiO 2 films prepared by electron beam deposition of noble metals
NASA Astrophysics Data System (ADS)
Hou, Xing-Gang; Ma, Jun; Liu, An-Dong; Li, De-Jun; Huang, Mei-Dong; Deng, Xiang-Yun
2010-03-01
TiO 2 films prepared by sol-gel method were modified by electron beam deposition of noble metals (Pt, Pd, and Ag). Effects of noble metals on the chemical and surface characteristics of the films were studied using XPS, TEM and UV-Vis spectroscopy techniques. Photocatalytic activity of modified TiO 2 films was evaluated by studying the degradation of methyl orange dye solution under visible light UV irradiation. The result of TEM reveals that most of the surface area of TiO 2 is covered by tiny particles of noble metals with diameter less than 1 nm. Broad red shift of UV-Visible absorption band of modified photocatalysts was observed. The catalytic degradation of methyl orange in aqueous solutions under visible light illumination demonstrates a significant enhancement of photocatalytic activity of these films compared with the un-loaded films. The photocatalytic efficiency of modified TiO 2 films by this method is affected by the concentration of impregnating solution.
NASA Astrophysics Data System (ADS)
Herrera, A.; Gómez, M.; Packard, T. T.; Fernández de Puelles, M. L.
2014-03-01
Measuring electron transport system (ETS) activity in zooplankton provides an index of respiration, theoretically, the potential respiration rate. We apply the ETS technique to estimate potential respiration and carbon demand from the zooplankton community in the upper 200 m of the water column near the Balearic Islands. The investigation was focused on two areas with different oceanographic conditions: the Balearic and Algerian subbasins. It compared the biomass, potential respiration and specific potential respiration of different size fractions (53-200, 200-500, > 500 μm) in both areas. In these regions the largest contribution to respiration was found in the larger sizes. The specific respiration (per unit biomass) was greater in smaller fractions, indicating that they have a more active metabolism. Both biomass and potential respiration increased in the Algerian subbasin and for both regions biomass and potential respiration were greater in shallow waters over the continental shelf (< 200 m). Using Kleiber's law as a tool to investigate the relationships between these two variables, we found that the exponential relation coefficient (b) was less than 0.75, indicating that the respiration was depressed (shifted down). In cultures and in eutrophic ocean waters (upwelling areas) b normally is greater than 0.75, consequently we intuit that the low value of b over the Balearic and Algerian subbasins indicates that the zooplankton is not well fed and that they are living under oligotrophic stress.
NASA Astrophysics Data System (ADS)
Li, Libo; Ma, Yue; Xie, Jingchen; Yang, Xiuchun; Wang, Heng; Tian, Haiyan; Mu, Hongjing; Wang, Wentao
2015-10-01
A new copper plating bath without Pd activation for electroless deposition on polyimide (PI) film is reported. The characteristics of Cu coatings on the PI via electroless plating and the effects of operating parameters on the coating coverage are discussed. The pre-treatment and plating processes are further optimized based on orthogonal experiment methods, involving variations of multiple process parameters. The electroless copper coating was characterized by scanning electron microscopy and atomic force microscopy, while the composition and crystalline structure are estimated by energy dispersive spectrometer and x-ray diffraction, respectively. These results show that the crystalline copper layer on the PI surface after electroless plating is dense, continuous and uniform. The joint tensile experiment is used to measure the adhesive strength of the coating with palladium-free and palladium activation, and the former is higher. Furthermore, the pre-treatment method proposed in this work without using palladium compounds is considered to be environmentally friendly. In addition, it provides a new concept of electroless Cu plating on the PI, which is generally difficult to plate due to its hydrophobic nature.
Díaz, Ana C; Fernández Gimenez, Analía V; Mendiara, Sara N; Fenucci, Jorge L
2004-05-19
Free radical scavenging properties of hepatopancreas extracts of Pleoticus muelleri were evaluated by electron paramagnetic spin resonance spectrometry methods (EPR) against the stable 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical. The present study was carried out to characterize different physiological stages of the shrimp under environmental and nutritional stress, evaluating the effect on growth, survival, and functional morphology of the hepatopancreas. Feeding trials were carried out on juveniles (1 g initial weight) held in aquaria. Each diet, with different concentrations of vitamins A and E, was tested in triplicate groups during 25 days. The control groups were fed with fresh squid mantle and with a vitamin-free diet. For all of the diets, the extracts exhibited strong DPPH radical scavenging activity, suggesting that the tissue is a powerful natural antioxidant. Individuals fed with different concentrations of vitamin E showed the strongest effect on the DPPH radicals, reducing the DPPH radicals to 50%, after an incubation period of 3 min. In contrast, the extracts of control animals, fed with squid mantle, had the weakest antioxidant activity (4%). These data indicated that the presence of vitamin E in the diet can provide immediate protection against free radicals. PMID:15137874
Approximating random quantum optimization problems
NASA Astrophysics Data System (ADS)
Hsu, B.; Laumann, C. R.; Läuchli, A. M.; Moessner, R.; Sondhi, S. L.
2013-06-01
We report a cluster of results regarding the difficulty of finding approximate ground states to typical instances of the quantum satisfiability problem k-body quantum satisfiability (k-QSAT) on large random graphs. As an approximation strategy, we optimize the solution space over “classical” product states, which in turn introduces a novel autonomous classical optimization problem, PSAT, over a space of continuous degrees of freedom rather than discrete bits. Our central results are (i) the derivation of a set of bounds and approximations in various limits of the problem, several of which we believe may be amenable to a rigorous treatment; (ii) a demonstration that an approximation based on a greedy algorithm borrowed from the study of frustrated magnetism performs well over a wide range in parameter space, and its performance reflects the structure of the solution space of random k-QSAT. Simulated annealing exhibits metastability in similar “hard” regions of parameter space; and (iii) a generalization of belief propagation algorithms introduced for classical problems to the case of continuous spins. This yields both approximate solutions, as well as insights into the free energy “landscape” of the approximation problem, including a so-called dynamical transition near the satisfiability threshold. Taken together, these results allow us to elucidate the phase diagram of random k-QSAT in a two-dimensional energy-density-clause-density space.
Razafinjanahary, H.; Rogemond, F.; Chermette, H.
1994-08-15
The MS-LSD method remains a method of interest when rapidity and small computer resources are required; its main drawback is some lack of accuracy, mainly due to the muffin-tin distribution of the potential. In the case of large clusters or molecules, the use of an empty sphere to fill, in part, the large intersphere region can improve greatly the results. Calculations bearing on C{sub 60} has been undertaken to underline this trend, because, on the one hand, the fullerenes exhibit a remarkable possibility to fit a large empty sphere in the center of the cluster and, on the other hand, numerous accurate calculations have already been published, allowing quantitative comparison with results. The author`s calculations suggest that in case of added empty sphere the results compare well with the results of more accurate calculations. The calculated electron affinity for C{sub 60} and C{sub 60}{sup {minus}} are in reasonable agreement with experimental values, but the stability of C{sub 60}{sup 2-} in gas phase is not found. 35 refs., 3 figs., 5 tabs.
First use of a high-sensitivity active pixel sensor array as a detector for electron microscopy
NASA Astrophysics Data System (ADS)
Xuong, Nguyen-Huu; Milazzo, Anna-Clare; LeBlanc, Philippe; Duttweiler, Fred; Bouwer, James; Peltier, Steve; Ellisman, Mark; Denes, Peter; Bieser, Fred; Matis, Howard S.; Wieman, Howard; Kleinfelder, Stuart
2004-06-01
There is an urgent need to replace film and CCD cameras as recording instruments for transmission electron microscopy (TEM). Film is too cumbersome to process and CCD cameras have low resolution, marginal to poor signal-to-noise ratio for single electron detection and high spatial distortion. To find a replacement device, we have tested a high sensitivity active pixel sensor (APS) array currently being developed for nuclear physics. The tests were done at 120 keV in a JEOL 1200 electron microscope. At this energy, each electron produced on average a signal-tonoise ratio about 20/1. The spatial resolution was also excellent with the full width at half maximum (FWHM) about 20 microns. Since it is very radiation tolerant and has almost no spatial distortion, the above tests showed that a high sensitivity CMOS APS array holds great promise as a direct detection device for electron microscopy.
Pshenichnyuk, Stanislav A; Modelli, Alberto; Lazneva, Eleonora F; Komolov, Alexei S
2016-05-01
Electron-accepting properties, and in particular resonance dissociative electron attachment (DEA) to ascorbic acid (AA), are investigated by means of DEA spectroscopy in vacuo. The experimental features are assigned in silico and discussed in relation to expected dissociative electron transfer processes in vivo with the support of density functional theory calculations and the polarizable continuum model. It is shown that formation of the two most abundant AA metabolites in living cells, namely monodehydroascorbic acid and dehydroascorbic acid, can be stimulated by cellular electron transfer to AA under reductive conditions. Prooxidant effects caused by AA are suggested to be mediated by hydroxyl radicals formation via the DEA mechanism. The involvement of excited electronic states under UV-irradiation in plants could open additional DEA channels leading to specific AA activity forbidden under dark state conditions. PMID:27074645
Approximation methods in gravitational-radiation theory
NASA Technical Reports Server (NTRS)
Will, C. M.
1986-01-01
The observation of gravitational-radiation damping in the binary pulsar PSR 1913 + 16 and the ongoing experimental search for gravitational waves of extraterrestrial origin have made the theory of gravitational radiation an active branch of classical general relativity. In calculations of gravitational radiation, approximation methods play a crucial role. Recent developments are summarized in two areas in which approximations are important: (a) the quadrupole approxiamtion, which determines the energy flux and the radiation reaction forces in weak-field, slow-motion, source-within-the-near-zone systems such as the binary pulsar; and (b) the normal modes of oscillation of black holes, where the Wentzel-Kramers-Brillouin approximation gives accurate estimates of the complex frequencies of the modes.
The Cell Cycle Switch Computes Approximate Majority
NASA Astrophysics Data System (ADS)
Cardelli, Luca; Csikász-Nagy, Attila
2012-09-01
Both computational and biological systems have to make decisions about switching from one state to another. The `Approximate Majority' computational algorithm provides the asymptotically fastest way to reach a common decision by all members of a population between two possible outcomes, where the decision approximately matches the initial relative majority. The network that regulates the mitotic entry of the cell-cycle in eukaryotes also makes a decision before it induces early mitotic processes. Here we show that the switch from inactive to active forms of the mitosis promoting Cyclin Dependent Kinases is driven by a system that is related to both the structure and the dynamics of the Approximate Majority computation. We investigate the behavior of these two switches by deterministic, stochastic and probabilistic methods and show that the steady states and temporal dynamics of the two systems are similar and they are exchangeable as components of oscillatory networks.
Solar activity variability in the IRI at high latitudes: Comparisons with GPS total electron content
NASA Astrophysics Data System (ADS)
Themens, David R.; Jayachandran, P. T.
2016-04-01
Total electron content (TEC) measurements from 10 dual-frequency GPS receivers in the Canadian High Arctic Ionospheric Network (CHAIN) are used to evaluate the performance of International Reference Ionosphere (IRI)-2007 within the Canadian sector. Throughout the region, we see systematic underestimation of daytime TEC, particularly at solar maximum, where summer and equinox root-mean-square errors reach as high as 14 total electron content units, 1 TECU = 1016 el m-2 (TECU). It is also shown that the use of a monthly IG index, in place of the IRI's standard IG12 index, leads to an improvement in TEC specification by up to 3 TECU in the polar cap and up to 6 TECU in the subauroral region during periods of short-term, large amplitude changes in solar activity. On diurnal timescales, variability in TEC is found to be underestimated by the IRI, during equinox periods, by up to 40% at subauroral latitudes and up to 70% in the polar cap region. During the winter, diurnal variations are overestimated by up to 40% in the subauroral region and are underestimated within the polar cap by up to 80%. Using collocated ionosonde data, we find IRI bottomside TEC to be within 1 TECU of observation with errors largest during the equinoxes. For the topside we find good agreement during the winter but significant underestimation of topside TEC by the IRI during summer and equinox periods, exceeding 6 TECU at times. By ingesting measured NmF2 into the IRI, we show that the topside thickness parameterization is the source of the bulk of the observed TEC errors.
Roux, Yoann; Ricoux, Rémy; Avenier, Frédéric; Mahy, Jean-Pierre
2015-01-01
Development of artificial systems, capable of delivering electrons to metal-based catalysts for the reductive activation of dioxygen, has been proven very difficult for decades, constituting a major scientific lock for the elaboration of environmentally friendly oxidation processes. Here we demonstrate that the incorporation of a flavin mononucleotide (FMN) in a water-soluble polymer, bearing a locally hydrophobic microenvironment, allows the efficient reduction of the FMN by NADH. This supramolecular entity is then capable of catalysing a very fast single-electron reduction of manganese(III) porphyrin by splitting the electron pair issued from NADH. This is fully reminiscent of the activity of natural reductases such as the cytochrome P450 reductases with kinetic parameters, which are three orders of magnitude faster compared with other artificial systems. Finally, we show as a proof of concept that the reduced manganese porphyrin activates dioxygen and catalyses the oxidation of organic substrates in water. PMID:26419885
Roux, Yoann; Ricoux, Rémy; Avenier, Frédéric; Mahy, Jean-Pierre
2015-01-01
Development of artificial systems, capable of delivering electrons to metal-based catalysts for the reductive activation of dioxygen, has been proven very difficult for decades, constituting a major scientific lock for the elaboration of environmentally friendly oxidation processes. Here we demonstrate that the incorporation of a flavin mononucleotide (FMN) in a water-soluble polymer, bearing a locally hydrophobic microenvironment, allows the efficient reduction of the FMN by NADH. This supramolecular entity is then capable of catalysing a very fast single-electron reduction of manganese(III) porphyrin by splitting the electron pair issued from NADH. This is fully reminiscent of the activity of natural reductases such as the cytochrome P450 reductases with kinetic parameters, which are three orders of magnitude faster compared with other artificial systems. Finally, we show as a proof of concept that the reduced manganese porphyrin activates dioxygen and catalyses the oxidation of organic substrates in water. PMID:26419885
Approximation by fully complex multilayer perceptrons.
Kim, Taehwan; Adali, Tülay
2003-07-01
We investigate the approximation ability of a multilayer perceptron (MLP) network when it is extended to the complex domain. The main challenge for processing complex data with neural networks has been the lack of bounded and analytic complex nonlinear activation functions in the complex domain, as stated by Liouville's theorem. To avoid the conflict between the boundedness and the analyticity of a nonlinear complex function in the complex domain, a number of ad hoc MLPs that include using two real-valued MLPs, one processing the real part and the other processing the imaginary part, have been traditionally employed. However, since nonanalytic functions do not meet the Cauchy-Riemann conditions, they render themselves into degenerative backpropagation algorithms that compromise the efficiency of nonlinear approximation and learning in the complex vector field. A number of elementary transcendental functions (ETFs) derivable from the entire exponential function e(z) that are analytic are defined as fully complex activation functions and are shown to provide a parsimonious structure for processing data in the complex domain and address most of the shortcomings of the traditional approach. The introduction of ETFs, however, raises a new question in the approximation capability of this fully complex MLP. In this letter, three proofs of the approximation capability of the fully complex MLP are provided based on the characteristics of singularity among ETFs. First, the fully complex MLPs with continuous ETFs over a compact set in the complex vector field are shown to be the universal approximator of any continuous complex mappings. The complex universal approximation theorem extends to bounded measurable ETFs possessing a removable singularity. Finally, it is shown that the output of complex MLPs using ETFs with isolated and essential singularities uniformly converges to any nonlinear mapping in the deleted annulus of singularity nearest to the origin. PMID:12816570
Wavelet Sparse Approximate Inverse Preconditioners
NASA Technical Reports Server (NTRS)
Chan, Tony F.; Tang, W.-P.; Wan, W. L.
1996-01-01
There is an increasing interest in using sparse approximate inverses as preconditioners for Krylov subspace iterative methods. Recent studies of Grote and Huckle and Chow and Saad also show that sparse approximate inverse preconditioner can be effective for a variety of matrices, e.g. Harwell-Boeing collections. Nonetheless a drawback is that it requires rapid decay of the inverse entries so that sparse approximate inverse is possible. However, for the class of matrices that, come from elliptic PDE problems, this assumption may not necessarily hold. Our main idea is to look for a basis, other than the standard one, such that a sparse representation of the inverse is feasible. A crucial observation is that the kind of matrices we are interested in typically have a piecewise smooth inverse. We exploit this fact, by applying wavelet techniques to construct a better sparse approximate inverse in the wavelet basis. We shall justify theoretically and numerically that our approach is effective for matrices with smooth inverse. We emphasize that in this paper we have only presented the idea of wavelet approximate inverses and demonstrated its potential but have not yet developed a highly refined and efficient algorithm.
Approximate entropy of network parameters.
West, James; Lacasa, Lucas; Severini, Simone; Teschendorff, Andrew
2012-04-01
We study the notion of approximate entropy within the framework of network theory. Approximate entropy is an uncertainty measure originally proposed in the context of dynamical systems and time series. We first define a purely structural entropy obtained by computing the approximate entropy of the so-called slide sequence. This is a surrogate of the degree sequence and it is suggested by the frequency partition of a graph. We examine this quantity for standard scale-free and Erdös-Rényi networks. By using classical results of Pincus, we show that our entropy measure often converges with network size to a certain binary Shannon entropy. As a second step, with specific attention to networks generated by dynamical processes, we investigate approximate entropy of horizontal visibility graphs. Visibility graphs allow us to naturally associate with a network the notion of temporal correlations, therefore providing the measure a dynamical garment. We show that approximate entropy distinguishes visibility graphs generated by processes with different complexity. The result probes to a greater extent these networks for the study of dynamical systems. Applications to certain biological data arising in cancer genomics are finally considered in the light of both approaches. PMID:22680542
Approximate entropy of network parameters
NASA Astrophysics Data System (ADS)
West, James; Lacasa, Lucas; Severini, Simone; Teschendorff, Andrew
2012-04-01
We study the notion of approximate entropy within the framework of network theory. Approximate entropy is an uncertainty measure originally proposed in the context of dynamical systems and time series. We first define a purely structural entropy obtained by computing the approximate entropy of the so-called slide sequence. This is a surrogate of the degree sequence and it is suggested by the frequency partition of a graph. We examine this quantity for standard scale-free and Erdös-Rényi networks. By using classical results of Pincus, we show that our entropy measure often converges with network size to a certain binary Shannon entropy. As a second step, with specific attention to networks generated by dynamical processes, we investigate approximate entropy of horizontal visibility graphs. Visibility graphs allow us to naturally associate with a network the notion of temporal correlations, therefore providing the measure a dynamical garment. We show that approximate entropy distinguishes visibility graphs generated by processes with different complexity. The result probes to a greater extent these networks for the study of dynamical systems. Applications to certain biological data arising in cancer genomics are finally considered in the light of both approaches.
Relativistic regular approximations revisited: An infinite-order relativistic approximation
Dyall, K.G.; van Lenthe, E.
1999-07-01
The concept of the regular approximation is presented as the neglect of the energy dependence of the exact Foldy{endash}Wouthuysen transformation of the Dirac Hamiltonian. Expansion of the normalization terms leads immediately to the zeroth-order regular approximation (ZORA) and first-order regular approximation (FORA) Hamiltonians as the zeroth- and first-order terms of the expansion. The expansion may be taken to infinite order by using an un-normalized Foldy{endash}Wouthuysen transformation, which results in the ZORA Hamiltonian and a nonunit metric. This infinite-order regular approximation, IORA, has eigenvalues which differ from the Dirac eigenvalues by order E{sup 3}/c{sup 4} for a hydrogen-like system, which is a considerable improvement over the ZORA eigenvalues, and similar to the nonvariational FORA energies. A further perturbation analysis yields a third-order correction to the IORA energies, TIORA. Results are presented for several systems including the neutral U atom. The IORA eigenvalues for all but the 1s spinor of the neutral system are superior even to the scaled ZORA energies, which are exact for the hydrogenic system. The third-order correction reduces the IORA error for the inner orbitals to a very small fraction of the Dirac eigenvalue. {copyright} {ital 1999 American Institute of Physics.}
[Bond selective chemistry beyond the adiabatic approximation
Butler, L.J.
1993-02-28
The adiabatic Born-Oppenheimer potential energy surface approximation is not valid for reaction of a wide variety of energetic materials and organic fuels; coupling between electronic states of reacting species plays a key role in determining the selectivity of the chemical reactions induced. This research program initially studies this coupling in (1) selective C-Br bond fission in 1,3- bromoiodopropane, (2) C-S:S-H bond fission branching in CH[sub 3]SH, and (3) competition between bond fission channels and H[sub 2] elimination in CH[sub 3]NH[sub 2].
Gadgets, approximation, and linear programming
Trevisan, L.; Sudan, M.; Sorkin, G.B.; Williamson, D.P.
1996-12-31
We present a linear-programming based method for finding {open_quotes}gadgets{close_quotes}, i.e., combinatorial structures reducing constraints of one optimization problems to constraints of another. A key step in this method is a simple observation which limits the search space to a finite one. Using this new method we present a number of new, computer-constructed gadgets for several different reductions. This method also answers a question posed by on how to prove the optimality of gadgets-we show how LP duality gives such proofs. The new gadgets improve hardness results for MAX CUT and MAX DICUT, showing that approximating these problems to within factors of 60/61 and 44/45 respectively is N P-hard. We also use the gadgets to obtain an improved approximation algorithm for MAX 3SAT which guarantees an approximation ratio of .801. This improves upon the previous best bound of .7704.
Pankratov, I. M. E-mail: rjzhou@ipp.ac.cn; Zhou, R. J. E-mail: rjzhou@ipp.ac.cn; Hu, L. Q.
2015-07-15
Peculiar phenomena were observed during experiments with runaway electrons: rapid changes in the synchrotron spot and its intensity that coincided with stepwise increases in the electron cyclotron emission (ECE) signal (cyclotron radiation of suprathermal electrons). These phenomena were initially observed in TEXTOR (Tokamak Experiment for Technology Oriented Research), where these events only occurred in the current decay phase or in discharges with thin stable runaway beams at a q = 1 drift surface. These rapid changes in the synchrotron spot were interpreted by the TEXTOR team as a fast pitch angle scattering event. Recently, similar rapid changes in the synchrotron spot and its intensity that coincided with stepwise increases in the non-thermal ECE signal were observed in the EAST (Experimental Advanced Superconducting Tokamak) runaway discharge. Runaway electrons were located around the q = 2 rational magnetic surface (ring-like runaway electron beam). During the EAST runaway discharge, stepwise ECE signal increases coincided with enhanced magnetohydrodynamic (MHD) activity. This behavior was peculiar to this shot. In this paper, we show that these non-thermal ECE step-like jumps were related to the abrupt growth of suprathermal electrons induced by bursting electric fields at reconnection events during this MHD plasma activity. Enhancement of the secondary runaway electron generation also occurred simultaneously. Local changes in the current-density gradient appeared because of local enhancement of the runaway electron generation process. These current-density gradient changes are considered to be a possible trigger for enhancement of the MHD plasma activity and the rapid changes in runaway beam behavior.
Heat pipe transient response approximation
NASA Astrophysics Data System (ADS)
Reid, Robert S.
2002-01-01
A simple and concise routine that approximates the response of an alkali metal heat pipe to changes in evaporator heat transfer rate is described. This analytically based routine is compared with data from a cylindrical heat pipe with a crescent-annular wick that undergoes gradual (quasi-steady) transitions through the viscous and condenser boundary heat transfer limits. The sonic heat transfer limit can also be incorporated into this routine for heat pipes with more closely coupled condensers. The advantages and obvious limitations of this approach are discussed. For reference, a source code listing for the approximation appears at the end of this paper. .
A Multi-Purpose Modular Electronics Integration Node for Exploration Extravehicular Activity
NASA Technical Reports Server (NTRS)
Hodgson, Edward; Papale, William; Wichowski, Robert; Rosenbush, David; Hawes, Kevin; Stankiewicz, Tom
2013-01-01
As NASA works to develop an effective integrated portable life support system design for exploration Extravehicular activity (EVA), alternatives to the current system s electrical power and control architecture are needed to support new requirements for flexibility, maintainability, reliability, and reduced mass and volume. Experience with the current Extravehicular Mobility Unit (EMU) has demonstrated that the current architecture, based in a central power supply, monitoring and control unit, with dedicated analog wiring harness connections to active components in the system has a significant impact on system packaging and seriously constrains design flexibility in adapting to component obsolescence and changing system needs over time. An alternative architecture based in the use of a digital data bus offers possible wiring harness and system power savings, but risks significant penalties in component complexity and cost. A hybrid architecture that relies on a set of electronic and power interface nodes serving functional models within the Portable Life Support System (PLSS) is proposed to minimize both packaging and component level penalties. A common interface node hardware design can further reduce penalties by reducing the nonrecurring development costs, making miniaturization more practical, maximizing opportunities for maturation and reliability growth, providing enhanced fault tolerance, and providing stable design interfaces for system components and a central control. Adaptation to varying specific module requirements can be achieved with modest changes in firmware code within the module. A preliminary design effort has developed a common set of hardware interface requirements and functional capabilities for such a node based on anticipated modules comprising an exploration PLSS, and a prototype node has been designed assembled, programmed, and tested. One instance of such a node has been adapted to support testing the swingbed carbon dioxide and humidity
NASA Astrophysics Data System (ADS)
Rioult, Maxime; Belkhou, Rachid; Magnan, Hélène; Stanescu, Dana; Stanescu, Stefan; Maccherozzi, Francesco; Rountree, Cindy; Barbier, Antoine
2015-11-01
The direct conversion of solar light into chemical energy or fuel through photoelectrochemical water splitting is promising as a clean hydrogen production solution. Ti-doped hematite (Ti:α-Fe2O3) is a potential key photoanode material, which despite its optimal band gap, excellent chemical stability, abundance, non-toxicity and low cost, still has to be improved. Here we give evidence of a drastic improvement of the water splitting performances of Ti-doped hematite photoanodes upon a HCl wet-etching. In addition to the topography investigation by atomic force microscopy, a detailed determination of the local electronic structure has been carried out in order to understand the phenomenon and to provide new insights in the understanding of solar water splitting. Using synchrotron radiation based spectromicroscopy (X-PEEM), we investigated the X-ray absorption spectral features at the L3 Fe edge of the as grown surface and of the wet-etched surface on the very same sample thanks to patterning. We show that HCl wet etching leads to substantial surface modifications of the oxide layer including increased roughness and chemical reduction (presence of Fe2 +) without changing the band gap. We demonstrate that these changes are profitable and correlated to the drastic changes of the photocatalytic activity.
Use of an active wire Bθ cell for electron beam conditioning
NASA Astrophysics Data System (ADS)
Murphy, D. P.; Myers, M. C.; Weidman, D. J.; Antoniades, J. A.; Fernsler, R. F.; Meger, R. A.
1996-10-01
The propagation of intense, relativistic electron beams in air is subject to the resistive hose instability. Conditioning the beam prior to injecting it into the air can extend its range by reducing the hose growth rate and by reducing the initial spatial perturbations that seed the hose instability. Experiments have been performed using the SuperIBEX accelerator (Ipeak=10-30 kA, E=4.5 MeV, 40 ns full width at half-maximum) to develop conditioning cells that suppress the hose. This paper describes the performance of an active wire Bθ cell that is used in conjunction with an ion focused regime (IFR) cell. The IFR cell detunes the instability by producing a head-to-tail radius taper on the beam. The wire cell maintains this radius taper while producing an emittance taper that is necessary to suppress the hose growth. In addition, the wire cell reduces the initial beam perturbations through the anharmonic centering force associated with the wire current and its azimuthal magnetic field Bθ. The ability of the Bθ cell to reduce the beam offset with a minimal increase in the beam radius gives it several advantages over the use of a simple, thick scattering foil to perform the radius taper to emittance taper conversion. The SuperIBEX beam propagation distance, in terms of the betatron oscillation scale length, was extended to ˜10λβ using these cells.
The Electron Runaround: Understanding Electric Circuit Basics Through a Classroom Activity
NASA Astrophysics Data System (ADS)
Singh, Vandana
2010-05-01
Several misconceptions abound among college students taking their first general physics course, and to some extent pre-engineering physics students, regarding the physics and applications of electric circuits. Analogies used in textbooks, such as those that liken an electric circuit to a piped closed loop of water driven by a water pump, do not completely resolve these misconceptions. Mazur and Knight,2 in particular, separately note that such misconceptions include the notion that electric current on either side of a light bulb in a circuit can be different. Other difficulties and confusions involve understanding why the current in a parallel circuit exceeds the current in a series circuit with the same components, and include the role of the battery (where students may assume wrongly that a dry cell battery is a fixed-current rather than a fixed-voltage device). A simple classroom activity that students can play as a game can resolve these misconceptions, providing an intellectual as well as a hands-on understanding. This paper describes the "Electron Runaround," first developed by the author to teach extremely bright 8-year-old home-schooled children the basics of electric circuits and subsequently altered (according to the required level of instruction) and used for various college physics courses.
A Ku band 5 bit MEMS phase shifter for active electronically steerable phased array applications
NASA Astrophysics Data System (ADS)
Sharma, Anesh K.; Gautam, Ashu K.; Farinelli, Paola; Dutta, Asudeb; Singh, S. G.
2015-03-01
The design, fabrication and measurement of a 5 bit Ku band MEMS phase shifter in different configurations, i.e. a coplanar waveguide and microstrip, are presented in this work. The development architecture is based on the hybrid approach of switched and loaded line topologies. All the switches are monolithically manufactured on a 200 µm high resistivity silicon substrate using 4 inch diameter wafers. The first three bits (180°, 90° and 45°) are realized using switched microstrip lines and series ohmic MEMS switches whereas the fourth and fifth bits (22.5° and 11.25°) consist of microstrip line sections loaded by shunt ohmic MEMS devices. Individual bits are fabricated and evaluated for performance and the monolithic device is a 5 bit Ku band (16-18 GHz) phase shifter with very low average insertion loss of the order of 3.3 dB and a return loss better than 15 dB over the 32 states with a chip area of 44 mm2. A total phase shift of 348.75° with phase accuracy within 3° is achieved over all of the states. The performance of individual bits has been optimized in order to achieve an integrated performance so that they can be implemented into active electronically steerable antennas for phased array applications.
A tutorial on activity-based costing of electronic health records.
Federowicz, Marie H; Grossman, Mila N; Hayes, Bryant J; Riggs, Joseph
2010-01-01
As the American Recovery and Restoration Act of 2009 allocates $19 billion to health information technology, it will be useful for health care managers to project the true cost of implementing an electronic health record (EHR). This study presents a step-by-step guide for using activity-based costing (ABC) to estimate the cost of an EHR. ABC is a cost accounting method with a "top-down" approach for estimating the cost of a project or service within an organization. The total cost to implement an EHR includes obvious costs, such as licensing fees, and hidden costs, such as impact on productivity. Unlike other methods, ABC includes all of the organization's expenditures and is less likely to miss hidden costs. Although ABC is used considerably in manufacturing and other industries, it is a relatively new phenomenon in health care. ABC is a comprehensive approach that the health care field can use to analyze the cost-effectiveness of implementing EHRs. In this article, ABC is applied to a health clinic that recently implemented an EHR, and the clinic is found to be more productive after EHR implementation. This methodology can help health care administrators assess the impact of a stimulus investment on organizational performance. PMID:20042937
Zalibera, Michal; Staško, Andrej; Šlebodová, Anna; Jančovičová, Viera; Čermáková, Tatiana; Brezová, Vlasta
2008-09-15
The antioxidant properties of 15 honey samples from different floral sources and various Slovak regions were investigated by means of electron paramagnetic resonance spectroscopy. Cation radical of ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) diammonium salt), DPPH (1,1-diphenyl-2-picrylhydrazyl) and hydroxyl radicals generated by the photochemical decomposition of hydrogen peroxide were used as oxidants. The antioxidant activities found with ABTS(+), expressed as trolox equivalent antioxidant capacity (TEAC), ranged from 0.15 to 1.14mmolkg(-1), and those determined with DPPH, from 0.04 to 0.32mmolkg(-1). TEAC values correlated well with results found by elimination of DPPH, and both values revealed a linear relationship with the concentration of phenolics obtained with the Folin-Ciocalteu phenol test (expressed as gallic acid equivalents, GAE). The colour coordinates (CIE L(∗)a(∗)b(∗)), as well as reflectance spectra determined for original honeys using a white background, demonstrated that the colour difference (ΔE(∗)) and coordinate b(∗) interrelate with TEAC values. The radical-scavenging capacities (RSC) of the honey samples determined in the experiments with photochemically decomposed hydrogen peroxide, generating reactive OH radicals in the presence of spin trapping agent, differ from those found with ABTS(+) and DPPH. Here, probably, the reactive OH radicals, having higher redox potential, are scavenged by a variety of compounds not effective with ABTS(+) and DPPH (e.g., saccharides, proteins). PMID:26049247
Xie, Xiujun; Gu, Wenhui; Gao, Shan; Lu, Shan; Li, Jian; Pan, Guanghua; Wang, Guangce; Shen, Songdong
2013-01-01
The xanthophyll cycle (Xc), which involves violaxanthin de-epoxidase (VDE) and the zeaxanthin epoxidase (ZEP), is one of the most rapid and efficient responses of plant and algae to high irradiance. High light intensity can activate VDE to convert violaxanthin (Vx) to zeaxanthin (Zx) via antheraxanthin (Ax). However, it remains unclear whether VDE remains active under low light or dark conditions when there is no significant accumulation of Ax and Zx, and if so, how the ΔpH required for activation of VDE is built. In this study, we used salicylaldoxime (SA) to inhibit ZEP activity in the intertidal macro-algae Ulva sp. (Ulvales, Chlorophyta) and then characterized VDE under low light and dark conditions with various metabolic inhibitors. With inhibition of ZEP by SA, VDE remained active under low light and dark conditions, as indicated by large accumulations of Ax and Zx at the expense of Vx. When PSII-mediated linear electron transport systems were completely inhibited by SA and DCMU, alternative electron transport systems (i.e., cyclic electron transport and chlororespiration) could maintain VDE activity. Furthermore, accumulations of Ax and Zx decreased significantly when SA, DCMU, or DBMIB together with an inhibitor of chlororespiration (i.e., propyl gallate (PG)) were applied to Ulva sp. This result suggests that chlororespiration not only participates in the build-up of the necessary ΔpH, but that it also possibly influences VDE activity indirectly by diminishing the oxygen level in the chloroplast. PMID:24250793
Pythagorean Approximations and Continued Fractions
ERIC Educational Resources Information Center
Peralta, Javier
2008-01-01
In this article, we will show that the Pythagorean approximations of [the square root of] 2 coincide with those achieved in the 16th century by means of continued fractions. Assuming this fact and the known relation that connects the Fibonacci sequence with the golden section, we shall establish a procedure to obtain sequences of rational numbers…
NASA Astrophysics Data System (ADS)
Sabashvili, Andro; Östlund, Stellan; Granath, Mats
2013-08-01
We calculate the single-particle spectral function for doped bilayer graphene in the low energy limit, described by two parabolic bands with zero band gap and long range Coulomb interaction. Calculations are done using thermal Green's functions in both the random phase approximation (RPA) and the fully self-consistent GW approximation. Consistent with previous studies RPA yields a spectral function which, apart from the Landau quasiparticle peaks, shows additional coherent features interpreted as plasmarons, i.e., composite electron-plasmon excitations. In the GW approximation the plasmaron becomes incoherent and peaks are replaced by much broader features. The deviation of the quasiparticle weight and mass renormalization from their noninteracting values is small which indicates that bilayer graphene is a weakly interacting system. The electron energy loss function, Im[-ɛq-1(ω)] shows a sharp plasmon mode in RPA which in the GW approximation becomes less coherent and thus consistent with the weaker plasmaron features in the corresponding single-particle spectral function.
NASA Astrophysics Data System (ADS)
Takeshima, Tsuguhide; Takeuchi, Hiroshi; Egawa, Toru; Konaka, Shigehiro
2005-01-01
The molecular structure of arecoline (methyl 1,2,5,6-tetrahydro-1-methylnicotinate, ? has been determined by gas electron diffraction. Diffraction patterns were taken at about 370 K. Structural constraints for the data analysis were obtained from MP2/6-31G** calculations. Vibrational mean amplitudes and shrinkage corrections were calculated from the force constants obtained from the gas-phase vibrational frequencies and the B3LYP/6-31G** calculations. The electron diffraction data were well reproduced by assuming the mixture of four conformers. The determined structural parameters ( rg (Å) and ∠ (°)) for the main conformer with 3 σ in parentheses are as follows: < rg(N-C ring)>=1.456(4); rg(N-C methyl)=1.451 (d.p.); rg(C dbnd6 C)=1.339(9); < rg(C-C)>=1.512(3); rg(O-C methyl)=1.434(5); rg(C(O)-O)=1.355 (d.p.); rg(C dbnd6 O)=1.209(4); the out-of-plane angle of the methyl group=50.3(23); ∠C ringN ringC ring=112.8(30); ∠N ringC ringC ring(H 2)=110.5(16); <∠C ringC ringC ring>=118.4(5); ∠C dbnd6 CC(O)=116.8(7); ∠CC dbnd6 O=127.6(9); ∠CC-O=109.8(8), where the angle brackets denote averaged values and d.p. denotes dependent parameters. Fixing the abundances of the minor conformers, Ax-s- cis and Ax-s- trans, at the theoretical values (13% in total), those of the Eq-s- cis and Eq-s- trans conformers were determined to be 46(16) and 41(16)%, respectively. Here Ax and Eq denote the axial and equatorial directions of the N-CH 3 bond and s- cis and s- trans show the orientation of the methoxycarbonyl group expressed by the configuration of the C dbnd6 O and C dbnd6 C bonds. The N⋯O carbonyl distances of the Eq-s- cis and Ax-s- cis conformers are 4.832(13) and 4.874(16) Å, respectively. They are close to the N⋯N distance of the most abundant conformer of nicotine, 4.885(6) Å, suggesting that the Eq-s- cis and Ax-s- cis conformers have nicotinic activity.
Surface Activation of Electrocatalysis at Oxide Electrodes. Concerted Electron-Proton Transfer
Gagliardi, Christopher J.; Jurss, Jonah W.; Thorp, H. Holden; Meyer, Thomas J.
2011-03-21
Dramatic rate enhancements are observed for the oxidation of phenols, including tyrosine, at indium-tin oxide electrodes modified by the addition of the electron-transfer relays [M^{II}(bpy)_{2}(4,4'-(HO)_{2}P(O)CH_{2})_{2}bpy)]^{2+} (M = Ru, Os) with clear evidence for the importance of proton-coupled electron transfer and concerted electron-proton transfer.
Energetic electrons, hard x-ray emission and MHD activity studies in the IR-T1 tokamak.
Agah, K Mikaili; Ghoranneviss, M; Elahi, A Salar
2015-01-01
Determinations of plasma parameters as well as the Magnetohydrodynamics (MHD) activity, energetic electrons energy and energy confinement time are essential for future fusion reactors experiments and optimized operation. Also some of the plasma information can be deduced from these parameters, such as plasma equilibrium, stability, and MHD instabilities. In this contribution we investigated the relation between energetic electrons, hard x-ray emission and MHD activity in the IR-T1 Tokamak. For this purpose we used the magnetic diagnostics and a hard x-ray spectroscopy in IR-T1 tokamak. A hard x-ray emission is produced by collision of the runaway electrons with the plasma particles or limiters. The mean energy was calculated from the slope of the energy spectrum of hard x-ray photons. PMID:25882736
NASA Astrophysics Data System (ADS)
Härtling, Thomas; Reitzig, Manuela; Mayer, Anton; Wetzel, Christiane; Röder, Olaf; Schreiber, Jürgen; Opitz, Jörg
2012-02-01
Secure proof of sterilization processes on packaging materials is an important issue in many economic sectors. In this context, electron beam sterilization is a highly effective low temperature technique. However, verifying the application of a sufficient electron dose is still difficult - especially on products with complex geometry. Here we report on an optical, hence fast and contactless approach which gives reliable evidence of a successful e-beam treatment. The technique is based on placing a suitable marker material (rare-earth based particles) inside or as a coating on the packaging material. By electron irradiation these particles change their optical properties and thus indicate the successful application of the electron beam.
Obradović, Aleksandar Lj.; Joksimović, Srđan; Poe, Michael M.; Ramerstorfer, Joachim; Varagic, Zdravko; Namjoshi, Ojas; Batinić, Bojan; Radulović, Tamara; Marković, Bojan; Roth, Brian; Sieghart, Werner; Cook, James M.; Savić, Miroslav M.
2014-01-01
Enormous progress in understanding the role of four populations of benzodiazepine-sensitive GABAA receptors was paralleled by the puzzling findings suggesting that substantial separation of behavioral effects may be accomplished by apparently non-selective modulators. We report on SH-I-048A, a newly-synthesized chiral positive modulator of GABAA receptors characterized by exceptional subnanomolar affinity, high efficacy and non-selectivity. Its influence on behavior was assessed in Wistar rats and contrasted to that obtained with 2 mg/kg diazepam. SH-I-048A reached micromolar concentrations in brain tissue, while the unbound fraction in brain homogenate was around 1.5%. The approximated electrophysiological responses, which estimated free concentrations of SH-I-048A or diazepam are able to elicit, suggested a similarity between the 10 mg/kg dose of the novel ligand and 2 mg/kg diazepam; however, SH-I-048A was relatively more active at α1- and α5-containing GABAA receptors. Behaviorally, SH-I-048A induced sedative, muscle relaxant and ataxic effects, reversed mechanical hyperalgesia 24 hours after injury, while it was devoid of clear anxiolytic actions and did not affect water-maze performance. While lack of clear anxiolytic actions may be connected with an enhanced potentiation at α1-containing GABAA receptors, the observed behavior in the rotarod, water maze and peripheral nerve injury tests was possibly affected by its prominent action at receptors containing the α5 subunit. The current results encourage further innovative approaches aimed at linking in vitro and in vivo data in order to help define fine-tuning mechanisms at four sensitive receptor populations that underlie subtle differences in behavioral profiles of benzodiazepine site ligands. PMID:24472579
Obradović, Aleksandar Lj; Joksimović, Srđan; Poe, Michael M; Ramerstorfer, Joachim; Varagic, Zdravko; Namjoshi, Ojas; Batinić, Bojan; Radulović, Tamara; Marković, Bojan; Roth, Brian L; Sieghart, Werner; Cook, James M; Savić, Miroslav M
2014-03-20
Enormous progress in understanding the role of four populations of benzodiazepine-sensitive GABAA receptors was paralleled by the puzzling findings suggesting that substantial separation of behavioral effects may be accomplished by apparently non-selective modulators. We report on SH-I-048A, a newly synthesized chiral positive modulator of GABAA receptors characterized by exceptional subnanomolar affinity, high efficacy and non-selectivity. Its influence on behavior was assessed in Wistar rats and contrasted to that obtained with 2mg/kg diazepam. SH-I-048A reached micromolar concentrations in brain tissue, while the unbound fraction in brain homogenate was around 1.5%. The approximated electrophysiological responses, which estimated free concentrations of SH-I-048A or diazepam are able to elicit, suggested a similarity between the 10mg/kg dose of the novel ligand and 2mg/kg diazepam; however, SH-I-048A was relatively more active at α1- and α5-containing GABAA receptors. Behaviorally, SH-I-048A induced sedative, muscle relaxant and ataxic effects, reversed mechanical hyperalgesia 24h after injury, while it was devoid of clear anxiolytic actions and did not affect water-maze performance. While lack of clear anxiolytic actions may be connected with an enhanced potentiation at α1-containing GABAA receptors, the observed behavior in the rotarod, water maze and peripheral nerve injury tests was possibly affected by its prominent action at receptors containing the α5 subunit. The current results encourage further innovative approaches aimed at linking in vitro and in vivo data in order to help define fine-tuning mechanisms at four sensitive receptor populations that underlie subtle differences in behavioral profiles of benzodiazepine site ligands. PMID:24472579
NASA Technical Reports Server (NTRS)
Choi, B. H.; Poe, R. T.
1977-01-01
A detailed vibrational-rotational (V-R) close-coupling formulation of electron-diatomic-molecule scattering is developed in which the target molecular axis is chosen to be the z-axis and the resulting coupled differential equation is solved in the moving body-fixed frame throughout the entire interaction region. The coupled differential equation and asymptotic boundary conditions in the body-fixed frame are given for each parity, and procedures are outlined for evaluating V-R transition cross sections on the basis of the body-fixed transition and reactance matrix elements. Conditions are discussed for obtaining identical results from the space-fixed and body-fixed formulations in the case where a finite truncated basis set is used. The hybrid theory of Chandra and Temkin (1976) is then reformulated, relevant expressions and formulas for the simultaneous V-R transitions of the hybrid theory are obtained in the same forms as those of the V-R close-coupling theory, and distorted-wave Born-approximation expressions for the cross sections of the hybrid theory are presented. A close-coupling approximation that conserves the internuclear axis component of the incident electronic angular momentum (l subscript z-prime) is derived from the V-R close-coupling formulation in the moving body-fixed frame.
Analytic approximate radiation effects due to Bremsstrahlung
Ben-Zvi I.
2012-02-01
The purpose of this note is to provide analytic approximate expressions that can provide quick estimates of the various effects of the Bremsstrahlung radiation produced relatively low energy electrons, such as the dumping of the beam into the beam stop at the ERL or field emission in superconducting cavities. The purpose of this work is not to replace a dependable calculation or, better yet, a measurement under real conditions, but to provide a quick but approximate estimate for guidance purposes only. These effects include dose to personnel, ozone generation in the air volume exposed to the radiation, hydrogen generation in the beam dump water cooling system and radiation damage to near-by magnets. These expressions can be used for other purposes, but one should note that the electron beam energy range is limited. In these calculations the good range is from about 0.5 MeV to 10 MeV. To help in the application of this note, calculations are presented as a worked out example for the beam dump of the R&D Energy Recovery Linac.
Behera, Sushant Kumar; Deb, Pritam; Ghosh, Arghya
2016-08-17
The rational design of metalloprotein hybrid structures and precise calculations for understanding the role of the interfacial electronic structure in regulating the HER activity of water splitting sites and their microscopic effect for obtaining robust hydrogen evolution possess great promise for developing highly efficient nano-bio hybrid HER catalysts. Here, we employ high-accuracy linear-scaling density functional theory calculations using a near-complete basis set and a minimal parameter implicit solvent model within the self-consistent calculations, on silver (Ag) ions assimilated on bacteriorhodopsin (bR) at specific binding sites. Geometry optimization indicates the formation of active sites at the interface of the metalloprotein complex and the density of states reflects the metallic nature of the active sites. The reduced value of the canonical orbital gap indicates the state of dynamic nature after Ag ion assimilation on active sites and smooth electron transfer. These incorporated active protein sites are more efficient in electrolytic splitting of water than pristine sites due to their low value of Gibbs free energy for the HER in terms of hydrogen coverages. Volcano plot analysis and the free energy diagram are compared for understanding the hydrogen evolution efficiency. Moreover, the essential role of the interfacial electronic properties in regulating the HER catalytic activity of water splitting sites and enhancing the efficiency is elucidated. PMID:27499158
NASA Astrophysics Data System (ADS)
Mukherjee, Dibyendu; Ivanov, Ilia; Khomami, Bamin
2012-02-01
Photosynthetic protein complex, Photosystem I (PS I) activates a light-induced (λ=680 nm) directional electron transfer chain that initiates at the lumenal side (mid-point potential, Em(P700/ P700+)˜+0.4 V) and terminates at the stromal side (Em(FA; FB; FX)˜-0.7 V) of PS I. In an effort to harness this photo-electrochemical activity of PS I in future bio-hybrid photovoltaic devices, precise electrochemical measurements have been used to investigate the photo-activated properties of PS I monolayers assembled on C9-alkanethiolate SAM/Au substrates. These measurements demonstrate, for the first time, a light-induced energetic electron transfer from the Au donor facilitated by photoexcitation of the reaction center P700 in PS I complexes. Furthermore, electrochemical impedance spectroscopy measurements, when fitted with equivalent electrical circuit models, reveal a light-induced reduction in the charge transfer resistance at the PS I/SAM-electrolyte interface. These observations, in conjunction with measurements for the transient electronic behavior, reveal the underlying mechanistic picture for the photo-excited electronic activities in PS I monolayer assembly on SAM/Au substrates.
How Does an Activity Theory Model Help to Know Better about Teaching with Electronic-Exercise-Bases?
ERIC Educational Resources Information Center
Abboud-Blanchard, Maha; Cazes, Claire
2012-01-01
The research presented in this paper relies on Activity Theory and particularly on Engestrom's model, to better understand the use of Electronic-Exercise-Bases (EEB) by mathematics teachers. This theory provides a holistic approach to illustrate the complexity of the EEB integration. The results highlight reasons and ways of using EEB and show…
ERIC Educational Resources Information Center
Toktarova, Vera Ivanovna
2015-01-01
The present study considers issues related to the planning and implementation of the system of pedagogical management of learning activities of students in the context of modern electronic educational environment of the higher education institution. As a methodological basis considered a differentiated approach based on flexible individual…
NASA Astrophysics Data System (ADS)
Odekirk, Bruce
1983-01-01
A study of the characteristics of extrinsic, ceramic SrTiO(,3) and TiO(,2) is presented. These materials have been known to assist in the photoelectrochemical dissociation of water without undergoing decomposition, but their wide intrinsic bandgaps (3.0-3.2 eV) make them unsuitable for efficient solar energy conversion. Consequently, a wide variety of samples were studied in the highly extrinsic state, produced both by the introduction of impurities and by strong reduction. Electrical conductivity (throughout the range 10 (LESSTHEQ) T (LESSTHEQ) 500 K), thermopower, and photoconductivity were all measured, and compared to photoelectrochemical (PEC) cell performance. Single crystal samples of strongly reduced TiO(,2) were similarly examined for comparison with the ceramic materials. It was found that oxygen vacancies produced upon high temperature reduction of undoped SrTiO(,3) form O(,V) -impurity bands, with activation energies in the range 0.03 -0.075 eV (for n = 10('17) - 10('13) cm('-3)). Impurity band formation was also found in La-doped SrTiO(,3) for {La} (GREATERTHEQ) 0.2%, and the spectral response confirmed expectations from dark conductivity measurements that the conduction and impurity bands are fully merged with a substantial band tail when {La} = 1.0%. This resulted in the diminution of the optical bandgap from (DBLTURN) 3.2 eV to (DBLTURN) 2.8 eV, and with that, significantly enhanced photoanode performance was obtained. The behavior of (sigma) with reduction for La:SrTiO(,3) confirmed that the defect structure at room temperature consists of controlled atomic imperfection under oxidizing conditions, which gives way to a controlled valency mechanism upon reduction. This transition produces a semiconducting material. High temperature reduction of undoped TiO(,2) was found to produce a large number of donor defects, with room temperature conductionband electron densities in the range n = 10('17) - 10('19 )cm('-3). Ta-doped TiO(,2) ceramics demonstrated
Yu, Huogen; Tian, Jing; Chen, Feng; Wang, Ping; Wang, Xuefei
2015-01-01
For a high-performance cocatalyst-modified photocatalyst, an effective interfacial separation of photogenerated electron from its corresponding holes and its following reduction reaction at the active sites are highly required. However, it is difficult for a single-component cocatalyst to simultaneously realize the crucial functions. In this study, an effective interfacial transfer of photogenerated electrons and its following rapid oxygen-reduction can be easily realized in a dual electron-cocatalyst modified Fe(III)/rGO-TiO2 photocatalyst, where the rGO nanosheets function as an electron-transfer mediator for the effective transfer of photogenerated electrons from the TiO2 surface while the Fe(III) cocatalyst serves as an electron-reduction active site to promote the following interfacial oxygen reduction. In this case, the rGO nanosheets were firstly loaded on the TiO2 nanoparticle surface by a hydrothermal method and then the Fe(III) cocatalyst was further modified on the rGO nanosheets by an impregnation method to prepare the Fe(III)/rGO-TiO2 photocatalyst. It was found that the dual electron-cocatalyst modified Fe(III)/rGO-TiO2 photocatalyst showed an obviously higher photocatalytic performance than the naked TiO2 and single-cocatalyst modified photocatalysts (such as Fe(III)/TiO2 and rGO-TiO2) owing to the synergistic effect of rGO and Fe(III) bi-cocatalysts. The present work can provide some new insights for the smart design of high-efficiency photocatalytic materials. PMID:26272870
One sign ion mobile approximation
NASA Astrophysics Data System (ADS)
Barbero, G.
2011-12-01
The electrical response of an electrolytic cell to an external excitation is discussed in the simple case where only one group of positive and negative ions is present. The particular case where the diffusion coefficients of the negative ions, Dm, is very small with respect to that of the positive ions, Dp, is considered. In this framework, it is discussed under what conditions the one mobile approximation, in which the negative ions are assumed fixed, works well. The analysis is performed by assuming that the external excitation is sinusoidal with circular frequency ω, as that used in the impedance spectroscopy technique. In this framework, we show that there exists a circular frequency, ω*, such that for ω > ω*, the one mobile ion approximation works well. We also show that for Dm ≪ Dp, ω* is independent of Dm.
Testing the frozen flow approximation
NASA Technical Reports Server (NTRS)
Lucchin, Francesco; Matarrese, Sabino; Melott, Adrian L.; Moscardini, Lauro
1993-01-01
We investigate the accuracy of the frozen-flow approximation (FFA), recently proposed by Matarrese, et al. (1992), for following the nonlinear evolution of cosmological density fluctuations under gravitational instability. We compare a number of statistics between results of the FFA and n-body simulations, including those used by Melott, Pellman & Shandarin (1993) to test the Zel'dovich approximation. The FFA performs reasonably well in a statistical sense, e.g. in reproducing the counts-in-cell distribution, at small scales, but it does poorly in the crosscorrelation with n-body which means it is generally not moving mass to the right place, especially in models with high small-scale power.
Golubic, Rajna; May, Anne M.; Benjaminsen Borch, Kristin; Overvad, Kim; Charles, Marie-Aline; Diaz, Maria Jose Tormo; Amiano, Pilar; Palli, Domenico; Valanou, Elisavet; Vigl, Matthaeus; Franks, Paul W.; Wareham, Nicholas; Ekelund, Ulf; Brage, Soren
2014-01-01
Objective To examine the validity of the Recent Physical Activity Questionnaire (RPAQ) which assesses physical activity (PA) in 4 domains (leisure, work, commuting, home) during past month. Methods 580 men and 1343 women from 10 European countries attended 2 visits at which PA energy expenditure (PAEE), time at moderate-to-vigorous PA (MVPA) and sedentary time were measured using individually-calibrated combined heart-rate and movement sensing. At the second visit, RPAQ was administered electronically. Validity was assessed using agreement analysis. Results RPAQ significantly underestimated PAEE in women [median(IQR) 34.1 (22.1, 52.2) vs. 40.6 (32.4, 50.9) kJ/kg/day, 95%LoA: −44.4, 63.4 kJ/kg/day) and in men (43.7 (29.0, 69.0) vs. 45.5 (34.1, 57.6) kJ/kg/day, 95%LoA: −47.2, 101.3 kJ/kg/day]. Using individualised definition of 1MET, RPAQ significantly underestimated MVPA in women [median(IQR): 62.1 (29.4, 124.3) vs. 73.6 (47.8, 107.2) min/day, 95%LoA: −130.5, 305.3 min/day] and men [82.7 (38.8, 185.6) vs. 83.3 (55.1, 125.0) min/day, 95%LoA: −136.4, 400.1 min/day]. Correlations (95%CI) between subjective and objective estimates were statistically significant [PAEE: women, rho = 0.20 (0.15–0.26); men, rho = 0.37 (0.30–0.44); MVPA: women, rho = 0.18 (0.13–0.23); men, rho = 0.31 (0.24–0.39)]. When using non-individualised definition of 1MET (3.5 mlO2/kg/min), MVPA was substantially overestimated (∼30 min/day). Revisiting occupational intensity assumptions in questionnaire estimation algorithms with occupational group-level empirical distributions reduced median PAEE-bias in manual (25.1 kJ/kg/day vs. −9.0 kJ/kg/day, p<0.001) and heavy manual workers (64.1 vs. −4.6 kJ/kg/day, p<0.001) in an independent hold-out sample. Conclusion Relative validity of RPAQ-derived PAEE and MVPA is comparable to previous studies but underestimation of PAEE is smaller. Electronic RPAQ may be used in large-scale epidemiological studies including surveys
Revisiting Twomey's approximation for peak supersaturation
NASA Astrophysics Data System (ADS)
Shipway, B. J.
2015-04-01
Twomey's seminal 1959 paper provided lower and upper bound approximations to the estimation of peak supersaturation within an updraft and thus provides the first closed expression for the number of nucleated cloud droplets. The form of this approximation is simple, but provides a surprisingly good estimate and has subsequently been employed in more sophisticated treatments of nucleation parametrization. In the current paper, we revisit the lower bound approximation of Twomey and make a small adjustment that can be used to obtain a more accurate calculation of peak supersaturation under all potential aerosol loadings and thermodynamic conditions. In order to make full use of this improved approximation, the underlying integro-differential equation for supersaturation evolution and the condition for calculating peak supersaturation are examined. A simple rearrangement of the algebra allows for an expression to be written down that can then be solved with a single lookup table with only one independent variable for an underlying lognormal aerosol population. While multimodal aerosol with N different dispersion characteristics requires 2N+1 inputs to calculate the activation fraction, only N of these one-dimensional lookup tables are needed. No additional information is required in the lookup table to deal with additional chemical, physical or thermodynamic properties. The resulting implementation provides a relatively simple, yet computationally cheap, physically based parametrization of droplet nucleation for use in climate and Numerical Weather Prediction models.
ERIC Educational Resources Information Center
Wijtmans, Maikel; van Rens, Lisette; van Muijlwijk-Koezen, Jacqueline E.
2014-01-01
Interactive teaching with larger groups of students can be a challenge, but the use of mobile electronic devices by students (smartphones, tablets, laptops) can be used to improve classroom interaction. We have examined several types of tasks that can be electronically enacted in classes and practical courses using these devices: multiple choice…
Federal Register 2010, 2011, 2012, 2013, 2014
2011-09-16
...FinCEN is proposing to require electronic filing of certain Bank Secrecy Act (BSA) reports not later than June 30, 2012. This requirement will significantly enhance the quality of our electronic data, improve our analytic capabilities in supporting law enforcement requirements and result in significant reduction in real costs to the United States Government and ultimately to U.S. taxpayers.......
Mehl, Matthias R; Robbins, Megan L; Deters, Fenne Große
2012-05-01
This article introduces a novel observational ambulatory monitoring method called the electronically activated recorder (EAR). The EAR is a digital audio recorder that runs on a handheld computer and periodically and unobtrusively records snippets of ambient sounds from participants' momentary environments. In tracking moment-to-moment ambient sounds, it yields acoustic logs of people's days as they naturally unfold. In sampling only a fraction of the time, it protects participants' privacy and makes large observational studies feasible. As a naturalistic observation method, it provides an observer's account of daily life and is optimized for the objective assessment of audible aspects of social environments, behaviors, and interactions (e.g., habitual preferences for social settings, idiosyncratic interaction styles, subtle emotional expressions). This article discusses the EAR method conceptually and methodologically, reviews prior research with it, and identifies three concrete ways in which it can enrich psychosomatic research. Specifically, it can (a) calibrate psychosocial effects on health against frequencies of real-world behavior; (b) provide ecological observational measures of health-related social processes that are independent of self-report; and (c) help with the assessment of subtle and habitual social behaviors that evade self-report but have important health implications. An important avenue for future research lies in merging traditional self-report-based ambulatory monitoring methods with observational approaches such as the EAR to allow for the simultaneous yet methodologically independent assessment of inner, experiential aspects (e.g., loneliness) and outer, observable aspects (e.g., social isolation) of real-world social processes to reveal their unique effects on health. PMID:22582338
Mehl, Matthias R.; Robbins, Megan L.; Deters, Fenne große
2012-01-01
This article introduces a novel, observational ambulatory monitoring method called the Electronically Activated Recorder or EAR. The EAR is a digital audio recorder that runs on a handheld computer and periodically and unobtrusively records snippets of ambient sounds from participants’ momentary environments. In tracking moment-to-moment ambient sounds, it yields acoustic logs of people’s days as they naturally unfold. In sampling only a fraction of the time, it protects participants’ privacy and makes large observational studies feasible. As a naturalistic observation method, it provides an observer’s account of daily life and is optimized for the objective assessment of audible aspects of social environments, behaviors, and interactions (e.g., habitual preferences for social settings, idiosyncratic interaction styles, and subtle emotional expressions). The article discusses the EAR method conceptually and methodologically, reviews prior research with it, and identifies three concrete ways in which it can enrich psychosomatic research. Specifically, it can (a) calibrate psychosocial effects on health against frequencies of real-world behavior, (b) provide ecological, observational measures of health-related social processes that are independent of self-report, and (c) help with the assessment of subtle and habitual social behaviors that evade self-report but have important health implications. An important avenue for future research lies in merging traditional, self-report based ambulatory monitoring methods with observational approaches such as the EAR to allow for the simultaneous yet methodologically independent assessment of inner, experiential (e.g., loneliness) and outer, observable aspects (e.g., social isolation) of real-world social processes to reveal their unique effects on health. PMID:22582338
Approximate Counting of Graphical Realizations
2015-01-01
In 1999 Kannan, Tetali and Vempala proposed a MCMC method to uniformly sample all possible realizations of a given graphical degree sequence and conjectured its rapidly mixing nature. Recently their conjecture was proved affirmative for regular graphs (by Cooper, Dyer and Greenhill, 2007), for regular directed graphs (by Greenhill, 2011) and for half-regular bipartite graphs (by Miklós, Erdős and Soukup, 2013). Several heuristics on counting the number of possible realizations exist (via sampling processes), and while they work well in practice, so far no approximation guarantees exist for such an approach. This paper is the first to develop a method for counting realizations with provable approximation guarantee. In fact, we solve a slightly more general problem; besides the graphical degree sequence a small set of forbidden edges is also given. We show that for the general problem (which contains the Greenhill problem and the Miklós, Erdős and Soukup problem as special cases) the derived MCMC process is rapidly mixing. Further, we show that this new problem is self-reducible therefore it provides a fully polynomial randomized approximation scheme (a.k.a. FPRAS) for counting of all realizations. PMID:26161994
Computer Experiments for Function Approximations
Chang, A; Izmailov, I; Rizzo, S; Wynter, S; Alexandrov, O; Tong, C
2007-10-15
This research project falls in the domain of response surface methodology, which seeks cost-effective ways to accurately fit an approximate function to experimental data. Modeling and computer simulation are essential tools in modern science and engineering. A computer simulation can be viewed as a function that receives input from a given parameter space and produces an output. Running the simulation repeatedly amounts to an equivalent number of function evaluations, and for complex models, such function evaluations can be very time-consuming. It is then of paramount importance to intelligently choose a relatively small set of sample points in the parameter space at which to evaluate the given function, and then use this information to construct a surrogate function that is close to the original function and takes little time to evaluate. This study was divided into two parts. The first part consisted of comparing four sampling methods and two function approximation methods in terms of efficiency and accuracy for simple test functions. The sampling methods used were Monte Carlo, Quasi-Random LP{sub {tau}}, Maximin Latin Hypercubes, and Orthogonal-Array-Based Latin Hypercubes. The function approximation methods utilized were Multivariate Adaptive Regression Splines (MARS) and Support Vector Machines (SVM). The second part of the study concerned adaptive sampling methods with a focus on creating useful sets of sample points specifically for monotonic functions, functions with a single minimum and functions with a bounded first derivative.
Approximate reasoning using terminological models
NASA Technical Reports Server (NTRS)
Yen, John; Vaidya, Nitin
1992-01-01
Term Subsumption Systems (TSS) form a knowledge-representation scheme in AI that can express the defining characteristics of concepts through a formal language that has a well-defined semantics and incorporates a reasoning mechanism that can deduce whether one concept subsumes another. However, TSS's have very limited ability to deal with the issue of uncertainty in knowledge bases. The objective of this research is to address issues in combining approximate reasoning with term subsumption systems. To do this, we have extended an existing AI architecture (CLASP) that is built on the top of a term subsumption system (LOOM). First, the assertional component of LOOM has been extended for asserting and representing uncertain propositions. Second, we have extended the pattern matcher of CLASP for plausible rule-based inferences. Third, an approximate reasoning model has been added to facilitate various kinds of approximate reasoning. And finally, the issue of inconsistency in truth values due to inheritance is addressed using justification of those values. This architecture enhances the reasoning capabilities of expert systems by providing support for reasoning under uncertainty using knowledge captured in TSS. Also, as definitional knowledge is explicit and separate from heuristic knowledge for plausible inferences, the maintainability of expert systems could be improved.
Approximate Counting of Graphical Realizations.
Erdős, Péter L; Kiss, Sándor Z; Miklós, István; Soukup, Lajos
2015-01-01
In 1999 Kannan, Tetali and Vempala proposed a MCMC method to uniformly sample all possible realizations of a given graphical degree sequence and conjectured its rapidly mixing nature. Recently their conjecture was proved affirmative for regular graphs (by Cooper, Dyer and Greenhill, 2007), for regular directed graphs (by Greenhill, 2011) and for half-regular bipartite graphs (by Miklós, Erdős and Soukup, 2013). Several heuristics on counting the number of possible realizations exist (via sampling processes), and while they work well in practice, so far no approximation guarantees exist for such an approach. This paper is the first to develop a method for counting realizations with provable approximation guarantee. In fact, we solve a slightly more general problem; besides the graphical degree sequence a small set of forbidden edges is also given. We show that for the general problem (which contains the Greenhill problem and the Miklós, Erdős and Soukup problem as special cases) the derived MCMC process is rapidly mixing. Further, we show that this new problem is self-reducible therefore it provides a fully polynomial randomized approximation scheme (a.k.a. FPRAS) for counting of all realizations. PMID:26161994
Sun, Bo; Zhang, Ping; Zhao, Xian-Geng
2008-02-28
The electronic structure and properties of PuO2 and Pu2O3 have been studied from first principles by the all-electron projector-augmented-wave method. The local density approximation+U and the generalized gradient approximation+U formalisms have been used to account for the strong on-site Coulomb repulsion among the localized Pu 5f electrons. We discuss how the properties of PuO2 and Pu2O3 are affected by the choice of U as well as the choice of exchange-correlation potential. Also, oxidation reaction of Pu2O3, leading to formation of PuO2, and its dependence on U and exchange-correlation potential have been studied. Our results show that by choosing an appropriate U, it is promising to correctly and consistently describe structural, electronic, and thermodynamic properties of PuO2 and Pu2O3, which enable the modeling of redox process involving Pu-based materials possible. PMID:18315070
Wang, Shuzhi; Zhang, Daoyong; Pan, Xiangliang
2013-09-01
Cadmium (Cd) shows high toxicity to aquatic microalgae. Many studies showed that Cd inhibited activities of photosystem II (PSII) but the effects of heavy metals on photosystem I (PSI) and cyclic electron flow (CEF) were still controversial and unclear. The effects of CdCl2 on the activities of PSI, PSII and CEF in Chlorella pyrenoidosa was measured simultaneously in the present study. In presence of 200μM of Cd, ultrastructure of some cells was strongly modified. Cd exposure led to decrease of the activities of photosynthetic oxygen evolution and respiration. PSII was more sensitive to Cd treatment than PSI. Cd treatment showed significant inhibition on the photochemical quantum yield and electron transport rate of PSII. Cd increased the quantum yield of non-light-induced non-photochemical fluorescence quenching, indicating the damage of PSII. The activity of PSI showed tolerance to Cd treatment with concentration less than 100μM in the experiment. Linear electron flow (LEF) made significant contribution to the photochemical quantum yield of PSI of the untreated cells, but decreased with increasing Cd concentration. The contribution of CEF to the yield of PSI increased with increasing Cd concentration. The activation of CEF after exposure to Cd played an essential role for the protection of PSI. PMID:23726885
Strong washout approximation to resonant leptogenesis
NASA Astrophysics Data System (ADS)
Garbrecht, Björn; Gautier, Florian; Klaric, Juraj
2014-09-01
We show that the effective decay asymmetry for resonant Leptogenesis in the strong washout regime with two sterile neutrinos and a single active flavour can in wide regions of parameter space be approximated by its late-time limit ɛ=Xsin(2varphi)/(X2+sin2varphi), where X=8πΔ/(|Y1|2+|Y2|2), Δ=4(M1-M2)/(M1+M2), varphi=arg(Y2/Y1), and M1,2, Y1,2 are the masses and Yukawa couplings of the sterile neutrinos. This approximation in particular extends to parametric regions where |Y1,2|2gg Δ, i.e. where the width dominates the mass splitting. We generalise the formula for the effective decay asymmetry to the case of several flavours of active leptons and demonstrate how this quantity can be used to calculate the lepton asymmetry for phenomenological scenarios that are in agreement with the observed neutrino oscillations. We establish analytic criteria for the validity of the late-time approximation for the decay asymmetry and compare these with numerical results that are obtained by solving for the mixing and the oscillations of the sterile neutrinos. For phenomenologically viable models with two sterile neutrinos, we find that the flavoured effective late-time decay asymmetry can be applied throughout parameter space.
NASA Astrophysics Data System (ADS)
Ito, Junji; Hanaki, Yasunari; Shen, Qing; Toyoda, Taro
2012-12-01
In order to decrease the consumption of precious metals used in the catalytic converters used in automobiles, we studied the relationship between the catalytic activity of Pt/alumina (Pt/Al2O3) and the relaxation process of photoexcited electrons. Firstly, we studied the relationship between the size of the Pt particles in Pt/Al2O3 and catalytic performance. Secondly, the relationship between the size of the Pt particles in Pt/Al2O3 and the decay time of the excited electrons was studied using an improved transient grating (TG) technique. The results showed that faster decay of the excited electrons leads to greater oxidation rates. The decay time obtained with the improved TG technique gives an indication of the time that the exited electrons take to return to the ground state. According to studies utilizing FT-IR, one of the processes necessary for quickly generating CO2 with Pt is that the electron in the Ptsbnd O bond moves to the Pt side and that the Pt+ becomes Pt metal. Thus, the decay time obtained with the improved TG technique corresponds to the process whereby Pt+ returns to Pt metal. Thus, we found that the consumption of precious metals can be reduced by increasing the speed of the decay of the excited electrons.
Deng, Chunnuan; Pan, Xiangliang; Zhang, Daoyong
2015-02-01
Pollution with antibiotics poses a great risk to aquatic ecosystems. Although some toxic effects of antibiotics on photosystem II (PSII) have been documented, their toxicity to photosystem I (PSI) is still unclear. In this study, effects of ofloxacin on activities of both PSI and PSII of Microcystis aeruginosa (Kützing) Kützing were investigated. Exposure to 0.1 mg L(-)(1) ofloxacin led to increases in contents of chlorophyll a and carotenoids and photosynthetic activity of M. aeruginosa. PSI activity and its electron transport were not affected by 0.1 mg L(-)(1) ofloxacin. When M. aeruginosa was exposed to ≥10 mg L(-)(1) ofloxacin, the electron transport rates of PSI and PSII, the yield of cyclic electron flow (CEF) and the contribution of linear electron flow (LEF) to PSI decreased whereas Y(NA) (limitation of donor side of PSI) and Y(NO) (the quantum yield of non-regulated energy dissipation in PSII) significantly increased. CEF had a significant contribution to alleviating the inhibitory effect of ofloxacin on PSI of M. aeruginosa treated with low concentrations of ofloxacin. The protective role CEF for tolerance of PSI to the toxicity of ofloxacin decreased with increasing ofloxacin concentration. PMID:25209631
NASA Astrophysics Data System (ADS)
Jones, L. B.; Rozhkov, S. A.; Bakin, V. V.; Kosolobov, S. N.; Militsyn, B. L.; Scheibler, H. E.; Smith, S. L.; Terekhov, A. S.
2009-08-01
A Free-Electron Laser (FEL) places many exacting demands on a Negative Electron Affinity (NEA) photocathode, such as the need for an ultra-fast response time, low energy spread for emitted electrons, high quantum efficiency (Q.E.) and a high average photocurrent. However, these key requirements are conflicting, and cannot be fulfilled by conventional photocathode design. For example, to achieve ˜10 ps response time, the photocathode active layer should be thinned to ˜100-150 nm, but this thickness is insufficient to provide near-complete absorption of light with hv≈ɛg so high Q.E. cannot be achieved. Complete optical absorption and high Q.E. can be obtained using a thin active layer at higher photon energies, but this generates photoelectrons with excess kinetic energy within the semiconductor. These photoelectrons do not thermalise in a thin active layer, so yield a broad energy distribution in the emitted electrons. Moreover, cooling of the conventional semiconductor photocathode structure is ineffective due to its fragility, so it cannot be pressed firmly to a heat sink to attain good thermal contact. Consequently, the maximum CW photocurrent is limited to a few miiliamps. The goal of our work is to develop a new design of NEA-photocathode which is optimised for FEL applications.
Dynamical Vertex Approximation for the Hubbard Model
NASA Astrophysics Data System (ADS)
Toschi, Alessandro
A full understanding of correlated electron systems in the physically relevant situations of three and two dimensions represents a challenge for the contemporary condensed matter theory. However, in the last years considerable progress has been achieved by means of increasingly more powerful quantum many-body algorithms, applied to the basic model for correlated electrons, the Hubbard Hamiltonian. Here, I will review the physics emerging from studies performed with the dynamical vertex approximation, which includes diagrammatic corrections to the local description of the dynamical mean field theory (DMFT). In particular, I will first discuss the phase diagram in three dimensions with a special focus on the commensurate and incommensurate magnetic phases, their (quantum) critical properties, and the impact of fluctuations on electronic lifetimes and spectral functions. In two dimensions, the effects of non-local fluctuations beyond DMFT grow enormously, determining the appearance of a low-temperature insulating behavior for all values of the interaction in the unfrustrated model: Here the prototypical features of the Mott-Hubbard metal-insulator transition, as well as the existence of magnetically ordered phases, are completely overwhelmed by antiferromagnetic fluctuations of exponentially large extension, in accordance with the Mermin-Wagner theorem. Eventually, by a fluctuation diagnostics analysis of cluster DMFT self-energies, the same magnetic fluctuations are identified as responsible for the pseudogap regime in the holed-doped frustrated case, with important implications for the theoretical modeling of the cuprate physics.
Analysing organic transistors based on interface approximation
Akiyama, Yuto; Mori, Takehiko
2014-01-15
Temperature-dependent characteristics of organic transistors are analysed thoroughly using interface approximation. In contrast to amorphous silicon transistors, it is characteristic of organic transistors that the accumulation layer is concentrated on the first monolayer, and it is appropriate to consider interface charge rather than band bending. On the basis of this model, observed characteristics of hexamethylenetetrathiafulvalene (HMTTF) and dibenzotetrathiafulvalene (DBTTF) transistors with various surface treatments are analysed, and the trap distribution is extracted. In turn, starting from a simple exponential distribution, we can reproduce the temperature-dependent transistor characteristics as well as the gate voltage dependence of the activation energy, so we can investigate various aspects of organic transistors self-consistently under the interface approximation. Small deviation from such an ideal transistor operation is discussed assuming the presence of an energetically discrete trap level, which leads to a hump in the transfer characteristics. The contact resistance is estimated by measuring the transfer characteristics up to the linear region.
NASA Astrophysics Data System (ADS)
Kastlunger, Georg; Stadler, Robert
2015-03-01
To define the conductance of single-molecule junctions with a redox functionality in an electrochemical cell, two conceptually different electron transport mechanisms, namely, coherent tunneling and vibrationally induced hopping, compete with each other, where implicit parameters of the setup such as the length of the molecule and the applied gate voltage decide which mechanism is the dominant one. Although coherent tunneling is most efficiently described within Landauer theory and the common theoretical treatment of electron hopping is based on Marcus theory, both theories are adequate for the processes they describe without introducing accuracy-limiting approximations. For a direct comparison, however, it has to be ensured that the crucial quantities obtained from electronic structure calculations, i.e., the transmission function T (E ) in Landauer theory and the transfer integral V , the reorganization energy λ , and the driving force Δ G0 in Marcus theory, are derived from similar grounds, as pointed out by Nitzan and coworkers in a series of publications. In this paper our framework is a single-particle picture, for which we perform density functional theory calculations for the conductance corresponding to both transport mechanisms for junctions with the central molecule containing one, two, or three Ruthenium centers, from which we extrapolate our results in order to define the critical length of the transition point of the two regimes which we identify at 5.76nm for this type of molecular wire. We also discuss trends in the dependence on an electrochemically induced gate potential.
Improved non-approximability results
Bellare, M.; Sudan, M.
1994-12-31
We indicate strong non-approximability factors for central problems: N{sup 1/4} for Max Clique; N{sup 1/10} for Chromatic Number; and 66/65 for Max 3SAT. Underlying the Max Clique result is a proof system in which the verifier examines only three {open_quotes}free bits{close_quotes} to attain an error of 1/2. Underlying the Chromatic Number result is a reduction from Max Clique which is more efficient than previous ones.
Quantum tunneling beyond semiclassical approximation
NASA Astrophysics Data System (ADS)
Banerjee, Rabin; Ranjan Majhi, Bibhas
2008-06-01
Hawking radiation as tunneling by Hamilton-Jacobi method beyond semiclassical approximation is analysed. We compute all quantum corrections in the single particle action revealing that these are proportional to the usual semiclassical contribution. We show that a simple choice of the proportionality constants reproduces the one loop back reaction effect in the spacetime, found by conformal field theory methods, which modifies the Hawking temperature of the black hole. Using the law of black hole mechanics we give the corrections to the Bekenstein-Hawking area law following from the modified Hawking temperature. Some examples are explicitly worked out.
Fermion tunneling beyond semiclassical approximation
NASA Astrophysics Data System (ADS)
Majhi, Bibhas Ranjan
2009-02-01
Applying the Hamilton-Jacobi method beyond the semiclassical approximation prescribed in R. Banerjee and B. R. Majhi, J. High Energy Phys.JHEPFG1029-8479 06 (2008) 09510.1088/1126-6708/2008/06/095 for the scalar particle, Hawking radiation as tunneling of the Dirac particle through an event horizon is analyzed. We show that, as before, all quantum corrections in the single particle action are proportional to the usual semiclassical contribution. We also compute the modifications to the Hawking temperature and Bekenstein-Hawking entropy for the Schwarzschild black hole. Finally, the coefficient of the logarithmic correction to entropy is shown to be related with the trace anomaly.
The structural physical approximation conjecture
NASA Astrophysics Data System (ADS)
Shultz, Fred
2016-01-01
It was conjectured that the structural physical approximation (SPA) of an optimal entanglement witness is separable (or equivalently, that the SPA of an optimal positive map is entanglement breaking). This conjecture was disproved, first for indecomposable maps and more recently for decomposable maps. The arguments in both cases are sketched along with important related results. This review includes background material on topics including entanglement witnesses, optimality, duality of cones, decomposability, and the statement and motivation for the SPA conjecture so that it should be accessible for a broad audience.
Wagner, Heiko; Jakob, Torsten; Lavaud, Johann; Wilhelm, Christian
2016-05-01
Alternative electron sinks are an important regulatory mechanism to dissipate excessively absorbed light energy particularly under fast changing dynamic light conditions. In diatoms, the cyclic electron transport (CET) around Photosystem II (PS II) is an alternative electron transport pathway (AET) that contributes to avoidance of overexcitation under high light illumination. The combination of nitrogen limitation and high-intensity irradiance regularly occurs under natural conditions and is expected to force the imbalance between light absorption and the metabolic use of light energy. The present study demonstrates that under N limitation, the amount of AET and the activity of CETPSII in the diatom Phaeodactylum tricornutum were increased. Thereby, the activity of CETPSII was linearly correlated with the amount of AET rates. It is concluded that CETPSII significantly contributes to AET in P. tricornutum. Surprisingly, CETPSII was found to be activated already at the end of the dark period under N-limited conditions. This coincided with a significantly increased degree of reduction of the plastoquinone (PQ) pool. The analysis of the macromolecular composition of cells of P. tricornutum under N-limited conditions revealed a carbon allocation in favor of carbohydrates during the light period and their degradation during the dark phase. A possible linkage between the activity of CETPSII and degree of reduction of the PQ pool on the one side and the macromolecular changes on the other is discussed. PMID:26650230
N2 activation by an iron complex with a strong electron-donating iminophosphorane ligand.
Suzuki, Tatsuya; Wasada-Tsutsui, Yuko; Ogawa, Takahiko; Inomata, Tomohiko; Ozawa, Tomohiro; Sakai, Yoichi; Fryzuk, Michael D; Masuda, Hideki
2015-10-01
A new tridentate cyclopentane-bridged iminophosphorane ligand, N-(2-diisopropylphosphinophenyl)-P,P-diisopropyl-P-(2-(2,6-diisopropylphenylamido)cyclopent-1-enyl)phosphoranimine (NpNPiPr), was synthesized and used in the preparation of a diiron dinitrogen complex. The reaction of the iron complex FeBr(NpNPiPr) with KC8 under dinitrogen yielded the dinuclear dinitrogen Fe complex [Fe(NpNPiPr)]2(μ-N2), which was characterized by X-ray analysis and resonance Raman and NMR spectroscopies. The X-ray analysis revealed a diiron complex bridged by the dinitrogen molecule, with each metal center coordinated by an NpNPiPr ligand and dinitrogen in a trigonal-monopyramidal geometry. The N–N bond length is 1.184(6) Å, and resonance Raman spectra indicate that the N–N stretching mode ν(14N2/15N2) is 1755/1700 cm–1. The magnetic moment of [Fe(NpNPiPr)]2(μ-N2) in benzene-d6 solution, as measured by 1H NMR spectroscopy by the Evans method, is 6.91μB (S = 3). The Mössbauer spectrum at 78 K showed δ = 0.73 mm/s and ΔEQ = 1.83 mm/s. These findings suggest that the iron ions are divalent with a high-spin configuration and that the N2 molecule has (N═N)2– character. Density functional theory calculations performed on [Fe(NpNPiPr)]2(μ-N2) also suggested that the iron is in a high-spin divalent state and that the coordinated dinitrogen molecule is effectively activated by π back-donation from the two iron ions (dπ) to the dinitrogen molecule (πx* and πy*). This is supported by cooperation between a large negative charge on the iminophosphorane ligand and strong electron donation and effective orbital overlap between the iron dπ orbitals and N2 π* orbitals supplied by the phosphine ligand. PMID:26135343
Wavelet Approximation in Data Assimilation
NASA Technical Reports Server (NTRS)
Tangborn, Andrew; Atlas, Robert (Technical Monitor)
2002-01-01
Estimation of the state of the atmosphere with the Kalman filter remains a distant goal because of high computational cost of evolving the error covariance for both linear and nonlinear systems. Wavelet approximation is presented here as a possible solution that efficiently compresses both global and local covariance information. We demonstrate the compression characteristics on the the error correlation field from a global two-dimensional chemical constituent assimilation, and implement an adaptive wavelet approximation scheme on the assimilation of the one-dimensional Burger's equation. In the former problem, we show that 99%, of the error correlation can be represented by just 3% of the wavelet coefficients, with good representation of localized features. In the Burger's equation assimilation, the discrete linearized equations (tangent linear model) and analysis covariance are projected onto a wavelet basis and truncated to just 6%, of the coefficients. A nearly optimal forecast is achieved and we show that errors due to truncation of the dynamics are no greater than the errors due to covariance truncation.
Plasma Physics Approximations in Ares
Managan, R. A.
2015-01-08
Lee & More derived analytic forms for the transport properties of a plasma. Many hydro-codes use their formulae for electrical and thermal conductivity. The coefficients are complex functions of Fermi-Dirac integrals, F_{n}( μ/θ ), the chemical potential, μ or ζ = ln(1+e^{ μ/θ} ), and the temperature, θ = kT. Since these formulae are expensive to compute, rational function approximations were fit to them. Approximations are also used to find the chemical potential, either μ or ζ . The fits use ζ as the independent variable instead of μ/θ . New fits are provided for A^{α} (ζ ),A^{β} (ζ ), ζ, f(ζ ) = (1 + e^{-μ/θ})F_{1/2}(μ/θ), F_{1/2}'/F_{1/2}, F_{c}^{α}, and F_{c}^{β}. In each case the relative error of the fit is minimized since the functions can vary by many orders of magnitude. The new fits are designed to exactly preserve the limiting values in the non-degenerate and highly degenerate limits or as ζ→ 0 or ∞. The original fits due to Lee & More and George Zimmerman are presented for comparison.
Vacancy-rearrangement theory in the first Magnus approximation
Becker, R.L.
1984-01-01
In the present paper we employ the first Magnus approximation (M1A), a unitarized Born approximation, in semiclassical collision theory. We have found previously that the M1A gives a substantial improvement over the first Born approximation (B1A) and can give a good approximation to a full coupled channels calculation of the mean L-shell vacancy probability per electron, p/sub L/, when the L-vacancies are accompanied by a K-shell vacancy (p/sub L/ is obtained experimentally from measurements of K/sub ..cap alpha../-satellite intensities). For sufficiently strong projectile-electron interactions (sufficiently large Z/sub p/ or small v) the M1A ceases to reproduce the coupled channels results, but it is accurate over a much wider range of Z/sub p/ and v than the B1A. 27 references.
NASA Technical Reports Server (NTRS)
Coyne, L.; Hovatter, W.; Sweeney, M.
1983-01-01
Experimental data concerning emission of light upon dehydration as a function of preheating and pre-gamma-irradiation are correlated with reported studies of electron-spin resonance (ESR) activity after similar pretreatments. The effect of these pretreatments on the kaolin-promoted incorporation of glycine into peptide oligomers in a wet/cold, hot/dry fluctuating environment is compared to their effect on the ESR and luminescent signals. The existence of spectroscopically active centers appears to be loosely anticorrelated with reaction yield; these yields are increased by increasing the overall energy content of the material. It is concluded that some part of the chemical yield is produced by a mechanism involving intrinsic, excited electronic states of the clay crystal lattice. These states may be derived from thermally, interfacially, and/or mechanically induced charge reorganization within interspersed energy levels in the band structure of the material.
Interior, building 810, view to west from approximately midhangar. Area ...
Interior, building 810, view to west from approximately mid-hangar. Area of photo encompasses approximately 1/4 of the interior space, with the KC-10 tanker aircraft and the figures beneath it giving an idea of scale, 90mm lens plus electronic flash fill lightening. - Travis Air Force Base, B-36 Hangar, Between Woodskill Avenue & Ellis, adjacent to Taxiway V & W, Fairfield, Solano County, CA
NASA Technical Reports Server (NTRS)
Chua, D.; Parks, G. K.; Brittnacher, M. J.; Peria, W.; Germany, G. A.; Spann, J. F., Jr.; Carlson, C.; Rose, M. Franklin (Technical Monitor)
2000-01-01
The Polar Ultraviolet Imager (UVI) observes auroral responses to incident solar wind pressure pulses and interplanetary shocks such as those associated with coronal mass ejections. The arrival of a CME pressure pulse at the front of the magnetosphere results in highly disturbed geomagnetic conditions and a substantial increase in both dayside and nightside auroral precipitation. Our observations show a simultaneous brightening over broad areas of the dayside and nightside aurora in response to a pressure pulse, indicating that more magnetospheric regions participate as sources for auroral precipitation than during isolated substorms. We estimate the average energies of incident auroral electrons using Polar UVI images and compare the precipitation energies during pressure pulse associated events to those during isolated auroral substorms. Electron precipitation during substorms has average energies greater than 10 keV and is structured both in local time and magnetic latitude. For auroral intensifications following the arrival of a pressure pulse or interplanetary shock, electron precipitation is less spatially structured and has greater ux of lower energy electrons (Eave _ 7 keV) than during isolated substorm, onsets. The average energies of the precipitating electrons inferred from UVI are consistent with those measured in-situ by the FAST spacecraft. These observations quantify the differences between global and local auroral precipitation processes and will provide a valuable experimental check for models of sudden storm commencements and magnetospheric response to perturbations in the solar wind.
Interplay of approximate planning strategies.
Huys, Quentin J M; Lally, Níall; Faulkner, Paul; Eshel, Neir; Seifritz, Erich; Gershman, Samuel J; Dayan, Peter; Roiser, Jonathan P
2015-03-10
Humans routinely formulate plans in domains so complex that even the most powerful computers are taxed. To do so, they seem to avail themselves of many strategies and heuristics that efficiently simplify, approximate, and hierarchically decompose hard tasks into simpler subtasks. Theoretical and cognitive research has revealed several such strategies; however, little is known about their establishment, interaction, and efficiency. Here, we use model-based behavioral analysis to provide a detailed examination of the performance of human subjects in a moderately deep planning task. We find that subjects exploit the structure of the domain to establish subgoals in a way that achieves a nearly maximal reduction in the cost of computing values of choices, but then combine partial searches with greedy local steps to solve subtasks, and maladaptively prune the decision trees of subtasks in a reflexive manner upon encountering salient losses. Subjects come idiosyncratically to favor particular sequences of actions to achieve subgoals, creating novel complex actions or "options." PMID:25675480
Approximating metal-insulator transitions
NASA Astrophysics Data System (ADS)
Danieli, Carlo; Rayanov, Kristian; Pavlov, Boris; Martin, Gaven; Flach, Sergej
2015-12-01
We consider quantum wave propagation in one-dimensional quasiperiodic lattices. We propose an iterative construction of quasiperiodic potentials from sequences of potentials with increasing spatial period. At each finite iteration step, the eigenstates reflect the properties of the limiting quasiperiodic potential properties up to a controlled maximum system size. We then observe approximate Metal-Insulator Transitions (MIT) at the finite iteration steps. We also report evidence on mobility edges, which are at variance to the celebrated Aubry-André model. The dynamics near the MIT shows a critical slowing down of the ballistic group velocity in the metallic phase, similar to the divergence of the localization length in the insulating phase.
Strong shock implosion, approximate solution
NASA Astrophysics Data System (ADS)
Fujimoto, Y.; Mishkin, E. A.; Alejaldre, C.
1983-01-01
The self-similar, center-bound motion of a strong spherical, or cylindrical, shock wave moving through an ideal gas with a constant, γ= cp/ cv, is considered and a linearized, approximate solution is derived. An X, Y phase plane of the self-similar solution is defined and the representative curved of the system behind the shock front is replaced by a straight line connecting the mappings of the shock front with that of its tail. The reduced pressure P(ξ), density R(ξ) and velocity U1(ξ) are found in closed, quite accurate, form. Comparison with numerically obtained results, for γ= {5}/{3} and γ= {7}/{5}, is shown.
Magnus approximation in neutrino oscillations
NASA Astrophysics Data System (ADS)
Acero, Mario A.; Aguilar-Arevalo, Alexis A.; D'Olivo, J. C.
2011-04-01
Oscillations between active and sterile neutrinos remain as an open possibility to explain some anomalous experimental observations. In a four-neutrino (three active plus one sterile) mixing scheme, we use the Magnus expansion of the evolution operator to study the evolution of neutrino flavor amplitudes within the Earth. We apply this formalism to calculate the transition probabilities from active to sterile neutrinos with energies of the order of a few GeV, taking into account the matter effect for a varying terrestrial density.
Approximate analytic solutions to the NPDD: Short exposure approximations
NASA Astrophysics Data System (ADS)
Close, Ciara E.; Sheridan, John T.
2014-04-01
There have been many attempts to accurately describe the photochemical processes that take places in photopolymer materials. As the models have become more accurate, solving them has become more numerically intensive and more 'opaque'. Recent models incorporate the major photochemical reactions taking place as well as the diffusion effects resulting from the photo-polymerisation process, and have accurately described these processes in a number of different materials. It is our aim to develop accessible mathematical expressions which provide physical insights and simple quantitative predictions of practical value to material designers and users. In this paper, starting with the Non-Local Photo-Polymerisation Driven Diffusion (NPDD) model coupled integro-differential equations, we first simplify these equations and validate the accuracy of the resulting approximate model. This new set of governing equations are then used to produce accurate analytic solutions (polynomials) describing the evolution of the monomer and polymer concentrations, and the grating refractive index modulation, in the case of short low intensity sinusoidal exposures. The physical significance of the results and their consequences for holographic data storage (HDS) are then discussed.
Surface-active element effects on the shape of GTA, laser, and electron-beam welds
Heiple, C.R.; Roper, J.R.; Stagner, R.T.; Aden, R.J.
1983-03-01
Laser and electron-beam welds were passed across selenium-doped zones in 21-6-9 stainless steel. The depth/width (d/w) ratio of a defocused laser weld with a weld pool shape similar to a GTA weld increased by over 200% in a zone where 66 ppm selenium had been added. Smaller increases were observed in selenium-doped zones for a moderately defocused electron beam weld with a higher d/w ratio in undoped base metal. When laser or electron beam weld penetration was by a keyhole mechanism, no change in d/w ratio occurred in selenium-doped zones. The results confirm the surface-tension-driven fluid-flow model for the effect of minor elements on GTA weld pool shape. Other experimental evidence bearing on the effect of minor elements on GTA weld penetration is summarized.
Pc1-2 activity and energetic electron precipitation in the polar cap
NASA Astrophysics Data System (ADS)
Francia, Patrizia; De Lauretis, Marcello; Regi, Mauro; Pezzopane, Michael; Alfonsi, Lucilla; Spogli, Luca
2016-04-01
A possible driver of the precipitation of magnetospheric energetic electron is represented by EMIC or Pc1-2 magnetospheric waves, which can induce the electron precipitation process through pitch angle scattering by gyro-resonant interaction. We present a study on the correlation between the occurrence of Pc1-2 waves and the precipitation of energetic electrons in the high latitude ionosphere. We used ULF geomagnetic measurements at Mario Zucchelli Station (Terra Nova Bay, Antarctica) to identify Pc1-2 events. In correspondence to such events, analyses are done to look for possible signatures of the precipitating particles in the ionospheric parameters provided by the ionosonde and GPS receiver at Mario Zucchelli Station.
Activity-dependent global model of electron loss inside the plasmasphere
NASA Astrophysics Data System (ADS)
Orlova, Ksenia; Spasojevic, Maria; Shprits, Yuri
2014-06-01
Using data from the CRRES plasma wave experiment, we develop quadratic fits to the mean of the wave amplitude squared for plasmaspheric hiss as a function of Kp, L, and magnetic latitude (λ) for the dayside (6 < magnetic local time (MLT) ≤ 21) and nightside (21 < MLT ≤ 6) magnetic local time sectors. The empirical model of hiss waves is used to compute quasi-linear pitch angle diffusion coefficients for energetic, relativistic, and ultrarelativistic electrons in the energy range of 1 keV to 10 MeV. In our calculations, we account for changes in hiss wave normal angle and plasma density with increasing λ. Electron lifetimes are then calculated from the diffusion coefficients and parameterized as a function of energy, Kp, and L. Coefficients for both the hiss model and the electron lifetimes are provided and can be easily incorporated into existing diffusion, convection, and particle tracing codes.
Photoelectron spectroscopy and the dipole approximation
Hemmers, O.; Hansen, D.L.; Wang, H.
1997-04-01
Photoelectron spectroscopy is a powerful technique because it directly probes, via the measurement of photoelectron kinetic energies, orbital and band structure in valence and core levels in a wide variety of samples. The technique becomes even more powerful when it is performed in an angle-resolved mode, where photoelectrons are distinguished not only by their kinetic energy, but by their direction of emission as well. Determining the probability of electron ejection as a function of angle probes the different quantum-mechanical channels available to a photoemission process, because it is sensitive to phase differences among the channels. As a result, angle-resolved photoemission has been used successfully for many years to provide stringent tests of the understanding of basic physical processes underlying gas-phase and solid-state interactions with radiation. One mainstay in the application of angle-resolved photoelectron spectroscopy is the well-known electric-dipole approximation for photon interactions. In this simplification, all higher-order terms, such as those due to electric-quadrupole and magnetic-dipole interactions, are neglected. As the photon energy increases, however, effects beyond the dipole approximation become important. To best determine the range of validity of the dipole approximation, photoemission measurements on a simple atomic system, neon, where extra-atomic effects cannot play a role, were performed at BL 8.0. The measurements show that deviations from {open_quotes}dipole{close_quotes} expectations in angle-resolved valence photoemission are observable for photon energies down to at least 0.25 keV, and are quite significant at energies around 1 keV. From these results, it is clear that non-dipole angular-distribution effects may need to be considered in any application of angle-resolved photoelectron spectroscopy that uses x-ray photons of energies as low as a few hundred eV.
The use of neural networks for approximation of nuclear data
Korovin, Yu. A.; Maksimushkina, A. V.
2015-12-15
The article discusses the possibility of using neural networks for approximation or reconstruction of data such as the reaction cross sections. The quality of the approximation using fitting criteria is also evaluated. The activity of materials under irradiation is calculated from data obtained using neural networks.
Crystal chemistry and chemical order in ternary quasicrystals and approximants
NASA Astrophysics Data System (ADS)
Gómez, Cesar Pay; Tsai, An Pang
2014-01-01
In this work we review our current understanding of structure, stability and formation of icosahedral quasicrystals and approximants. The work has special emphasis on Cd-Yb type phases, but several concepts are generalized to other families of icosahedral quasicrystals and approximants. The paper handles topics such as chemical order and site preference at the cluster level for ternary phases, valence electron concentration and its influence on formation and composition, fundamental building blocks and cluster linkages, and the similarities and differences between different families of icosahedral quasicrystals and approximants.
Streb, Judith; Kammer, Thomas; Spitzer, Manfred; Hille, Katrin
2015-01-01
This paper reports accelerometer and electronic dairy data on typical daily activities of 139 school students from grade six and nine. Recordings covered a typical school day for each student and lasted on average for 23 h. Screen activities (watching television and using the computer) are compared to several other activities performed while sitting (e.g., playing, eating, sitting in school, and doing homework). Body movement was continuously recorded by four accelerometers and transformed into a motion sore. Our results show that extremely low motion scores, as if subjects were freezing, emerge to a greater extent in front of screens compared to other investigated activities. Given the substantial amount of time young people spend in front of screens and the rising obesity epidemic, our data suggest a mechanism for the association of screen time and obesity. PMID:25955531
Streb, Judith; Kammer, Thomas; Spitzer, Manfred; Hille, Katrin
2015-01-01
This paper reports accelerometer and electronic dairy data on typical daily activities of 139 school students from grade six and nine. Recordings covered a typical school day for each student and lasted on average for 23 h. Screen activities (watching television and using the computer) are compared to several other activities performed while sitting (e.g., playing, eating, sitting in school, and doing homework). Body movement was continuously recorded by four accelerometers and transformed into a motion sore. Our results show that extremely low motion scores, as if subjects were freezing, emerge to a greater extent in front of screens compared to other investigated activities. Given the substantial amount of time young people spend in front of screens and the rising obesity epidemic, our data suggest a mechanism for the association of screen time and obesity. PMID:25955531
Fink, Daniel; Weibert, Bernhard; Winter, Rainer F
2016-05-01
Tetraruthenium macrocycles with 1,4-divinylphenylene and diarylamine-substituted isophthalic acids as the sides display up to eight one-electron redox steps and rich electrochromic behaviour with strong absorptions of the dications in the near infrared and of the tetra- and hexacations at low energies in the visible. PMID:27067796
Biogenic hydroxysulfate green rust, a potential electron acceptor for SRB activity
NASA Astrophysics Data System (ADS)
Zegeye, Asfaw; Huguet, Lucie; Abdelmoula, Mustapha; Carteret, Cédric; Mullet, Martine; Jorand, Frédéric
2007-11-01
Microbiological reduction of a biogenic sulfated green rust (GR2(SO42-)), was examined using a sulfate reducing bacterium ( Desulfovibrio alaskensis). Experiments investigated whether GR2(SO42-) could serve as a sulfate source for D. alaskensis anaerobic respiration by analyzing mineral transformation. Batch experiments were conducted using lactate as the electron donor and biogenic GR2(SO42-) as the electron acceptor, at circumneutral pH in unbuffered medium. GR2(SO42-) transformation was monitored with time by X-ray diffraction (XRD), Transmission Mössbauer Spectroscopy (TMS), Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS). The reduction of sulfate anions and the formation of iron sulfur mineral were clearly identified by XPS analyses. TMS showed the formation of additional mineral as green rust (GR) and vivianite. XRD analyses discriminated the type of the newly formed GR as GR1. The formed GR1 was GR1(CO32-) as indicated by DRIFTS analysis. Thus, the results presented in this study indicate that D. alaskensis cells were able to use GR2(SO42-) as an electron acceptor. GR1(CO32-), vivianite and an iron sulfur compound were formed as a result of GR2(SO42-) reduction by D. alaskensis. Hence, in environments where geochemical conditions promote biogenic GR2(SO42-) formation, this mineral could stimulate the anaerobic respiration of sulfate reducing bacteria.
Federal Register 2010, 2011, 2012, 2013, 2014
2010-06-15
... through http://www.Regulations.gov ; or to VA's OMB Desk Officer, OMB Human Resources and Housing Branch..., (202) 461-7485, FAX (202) 273-0443 or e-mail denise.mclamb@va.gov . Please refer to ``OMB Control No... AFFAIRS Agency Information Collection (VA Loan Electronic Reporting Interface (VALERI) System)...
An Active Reading Intervention for the Electronic Career Development Course (eCDC) Program
ERIC Educational Resources Information Center
Isreal, Kenith R.
2013-01-01
Electronic books have rapidly moved through the entertainment community and are rapidly making their way into the academic environment. Public and private schools, libraries and training organizations use eBooks for research and instruction. This study sought to enhance the learning habits of students taking self-paced correspondence courses…
Federal Register 2010, 2011, 2012, 2013, 2014
2011-07-08
... Information Systems Technology Architecture (VistA). DATES: Written comments and recommendations on the... written comments on the collection of information through Federal Docket Management System (FDMS) at http... attorney by veterans who have medical information recorded in VHA electronic health records...
Federal Register 2010, 2011, 2012, 2013, 2014
2012-02-29
..., while moving forward with the electronic filing requirement. \\11\\ See 76 FR 57799, September 16, 2011...- based service may be accessed at http://bsaefiling.fincen.treas.gov/main.html . \\8\\ See 76 FR 57799. \\9... 75 FR 63545, October 15, 2010 and 76 FR 4747, January 26, 2011. Office of Management and Budget...
Description and Assessment of Activities Oriented to Enhance a First Course on Power Electronics
ERIC Educational Resources Information Center
Fernandez, C.; Zumel, P.; Sanz, M.; Lazaro, A.; Barrado, A.
2011-01-01
The ongoing search for excellence in education requires the review and renewal of teaching strategies, concentrating efforts on courses that are not attractive to students or are considered to be unsuccessful. This paper is focused on an undergraduate power electronics course in which students had poor academic results in the past. The actions…
Approximate equations of state in two-temperature plasma mixtures
Ramshaw, John D.; Cook, Andrew W.
2014-02-15
Approximate thermodynamic state relations for multicomponent atomic and molecular gas mixtures are often constructed by artificially partitioning the mixture into its constituent materials and requiring the separated materials to be in temperature and pressure equilibrium. Iterative numerical algorithms have been employed to enforce this equilibration and compute the resulting approximate state relations in single-temperature mixtures. In partially ionized gas mixtures, there is both theoretical and empirical evidence that equilibrating the chemical potentials, number densities, or partial pressures of the free electrons is likely to produce more accurate results than equilibrating the total pressures. Moreover, in many situations of practical interest the free electrons and heavy particles have different temperatures. In this paper, we present a generalized algorithm for equilibrating the heavy-particle and electron temperatures and a third user-specified independent thermodynamic variable in a two-temperature plasma mixture. Test calculations based on the equilibration of total pressure vs. electron pressure are presented for three different mixtures.
Regulation of electron transfer processes affects phototrophic mat structure and activity.
Ha, Phuc T; Renslow, Ryan S; Atci, Erhan; Reardon, Patrick N; Lindemann, Stephen R; Fredrickson, James K; Call, Douglas R; Beyenal, Haluk
2015-01-01
Phototrophic microbial mats are among the most diverse ecosystems in nature. These systems undergo daily cycles in redox potential caused by variations in light energy input and metabolic interactions among the microbial species. In this work, solid electrodes with controlled potentials were placed under mats to study the electron transfer processes between the electrode and the microbial mat. The phototrophic microbial mat was harvested from Hot Lake, a hypersaline, epsomitic lake located near Oroville (Washington, USA). We operated two reactors: graphite electrodes were polarized at potentials of -700 mVAg/AgCl [cathodic (CAT) mat system] and +300 mVAg/AgCl [anodic (AN) mat system] and the electron transfer rates between the electrode and mat were monitored. We observed a diel cycle of electron transfer rates for both AN and CAT mat systems. Interestingly, the CAT mats generated the highest reducing current at the same time points that the AN mats showed the highest oxidizing current. To characterize the physicochemical factors influencing electron transfer processes, we measured depth profiles of dissolved oxygen (DO) and sulfide in the mats using microelectrodes. We further demonstrated that the mat-to-electrode and electrode-to-mat electron transfer rates were light- and temperature-dependent. Using nuclear magnetic resonance (NMR) imaging, we determined that the electrode potential regulated the diffusivity and porosity of the microbial mats. Both porosity and diffusivity were higher in the CAT mats than in the AN mats. We also used NMR spectroscopy for high-resolution quantitative metabolite analysis and found that the CAT mats had significantly higher concentrations of osmoprotectants such as betaine and trehalose. Subsequently, we performed amplicon sequencing across the V4 region of the 16S rRNA gene of incubated mats to understand the impact of electrode potential on microbial community structure. These data suggested that variation in the
Regulation of electron transfer processes affects phototrophic mat structure and activity
Ha, Phuc T.; Renslow, Ryan S.; Atci, Erhan; Reardon, Patrick N.; Lindemann, Stephen R.; Fredrickson, James K.; Call, Douglas R.; Beyenal, Haluk
2015-01-01
Phototrophic microbial mats are among the most diverse ecosystems in nature. These systems undergo daily cycles in redox potential caused by variations in light energy input and metabolic interactions among the microbial species. In this work, solid electrodes with controlled potentials were placed under mats to study the electron transfer processes between the electrode and the microbial mat. The phototrophic microbial mat was harvested from Hot Lake, a hypersaline, epsomitic lake located near Oroville (Washington, USA). We operated two reactors: graphite electrodes were polarized at potentials of -700 mVAg/AgCl [cathodic (CAT) mat system] and +300 mVAg/AgCl [anodic (AN) mat system] and the electron transfer rates between the electrode and mat were monitored. We observed a diel cycle of electron transfer rates for both AN and CAT mat systems. Interestingly, the CAT mats generated the highest reducing current at the same time points that the AN mats showed the highest oxidizing current. To characterize the physicochemical factors influencing electron transfer processes, we measured depth profiles of dissolved oxygen (DO) and sulfide in the mats using microelectrodes. We further demonstrated that the mat-to-electrode and electrode-to-mat electron transfer rates were light- and temperature-dependent. Using nuclear magnetic resonance (NMR) imaging, we determined that the electrode potential regulated the diffusivity and porosity of the microbial mats. Both porosity and diffusivity were higher in the CAT mats than in the AN mats. We also used NMR spectroscopy for high-resolution quantitative metabolite analysis and found that the CAT mats had significantly higher concentrations of osmoprotectants such as betaine and trehalose. Subsequently, we performed amplicon sequencing across the V4 region of the 16S rRNA gene of incubated mats to understand the impact of electrode potential on microbial community structure. These data suggested that variation in the
Jin, Xiaoyan; Mok, Eun Kyung; Baek, Ji-Won; Park, Sang-Hyun; Hwang, Seong-Ju
2015-10-15
The electronic coupling and photocatalytic activity of Ag{sub 2}CO{sub 3}–TiO{sub 2} nanocomposite can be optimized by the fine-tuning of the band position of titanium oxide with nitrogen doping. The increase of the valence band energy of TiO{sub 2} by N-doping leads not only to the enhanced absorption of visible light but also to the promoted hole transfer from Ag{sub 2}CO{sub 3} to TiO{sub 2}, resulting in the efficient spatial separation of photogenerated electrons and holes. While the undoped Ag{sub 2}CO{sub 3}–TiO{sub 2} nanocomposite shows an inferior photocatalytic activity to the pure Ag{sub 2}CO{sub 3}, the photocatalyst performance of N-doped nanocomposite is better than those of Ag{sub 2}CO{sub 3} and undoped Ag{sub 2}CO{sub 3}–TiO{sub 2} nanocomposite. This observation underscores a significant enhancement of the photocatalytic activity of nanocomposite upon N-doping, a result of enhanced electronic coupling between the hybridized species. The present results clearly demonstrate the importance of the fine-tuning of band position in optimizing the photocatalytic activity of hybrid-type photocatalysts. - Highlights: • The band position of Ag{sub 2}CO{sub 3}–TiO{sub 2} can be effectively tailored by nitrogen doping. • The N-doping leads to the improvement of charge separation. • The N-doped Ag{sub 2}CO{sub 3}–TiO{sub 2} shows high photocatalytic activity.
Strong washout approximation to resonant leptogenesis
Garbrecht, Björn; Gautier, Florian; Klaric, Juraj E-mail: florian.gautier@tum.de
2014-09-01
We show that the effective decay asymmetry for resonant Leptogenesis in the strong washout regime with two sterile neutrinos and a single active flavour can in wide regions of parameter space be approximated by its late-time limit ε=Xsin(2φ)/(X{sup 2}+sin{sup 2}φ), where X=8πΔ/(|Y{sub 1}|{sup 2}+|Y{sub 2}|{sup 2}), Δ=4(M{sub 1}-M{sub 2})/(M{sub 1}+M{sub 2}), φ=arg(Y{sub 2}/Y{sub 1}), and M{sub 1,2}, Y{sub 1,2} are the masses and Yukawa couplings of the sterile neutrinos. This approximation in particular extends to parametric regions where |Y{sub 1,2}|{sup 2}>> Δ, i.e. where the width dominates the mass splitting. We generalise the formula for the effective decay asymmetry to the case of several flavours of active leptons and demonstrate how this quantity can be used to calculate the lepton asymmetry for phenomenological scenarios that are in agreement with the observed neutrino oscillations. We establish analytic criteria for the validity of the late-time approximation for the decay asymmetry and compare these with numerical results that are obtained by solving for the mixing and the oscillations of the sterile neutrinos. For phenomenologically viable models with two sterile neutrinos, we find that the flavoured effective late-time decay asymmetry can be applied throughout parameter space.
Function approximation in inhibitory networks.
Tripp, Bryan; Eliasmith, Chris
2016-05-01
In performance-optimized artificial neural networks, such as convolutional networks, each neuron makes excitatory connections with some of its targets and inhibitory connections with others. In contrast, physiological neurons are typically either excitatory or inhibitory, not both. This is a puzzle, because it seems to constrain computation, and because there are several counter-examples that suggest that it may not be a physiological necessity. Parisien et al. (2008) showed that any mixture of excitatory and inhibitory functional connections could be realized by a purely excitatory projection in parallel with a two-synapse projection through an inhibitory population. They showed that this works well with ratios of excitatory and inhibitory neurons that are realistic for the neocortex, suggesting that perhaps the cortex efficiently works around this apparent computational constraint. Extending this work, we show here that mixed excitatory and inhibitory functional connections can also be realized in networks that are dominated by inhibition, such as those of the basal ganglia. Further, we show that the function-approximation capacity of such connections is comparable to that of idealized mixed-weight connections. We also study whether such connections are viable in recurrent networks, and find that such recurrent networks can flexibly exhibit a wide range of dynamics. These results offer a new perspective on computation in the basal ganglia, and also perhaps on inhibitory networks within the cortex. PMID:26963256
Interplay of approximate planning strategies
Huys, Quentin J. M.; Lally, Níall; Faulkner, Paul; Eshel, Neir; Seifritz, Erich; Gershman, Samuel J.; Dayan, Peter; Roiser, Jonathan P.
2015-01-01
Humans routinely formulate plans in domains so complex that even the most powerful computers are taxed. To do so, they seem to avail themselves of many strategies and heuristics that efficiently simplify, approximate, and hierarchically decompose hard tasks into simpler subtasks. Theoretical and cognitive research has revealed several such strategies; however, little is known about their establishment, interaction, and efficiency. Here, we use model-based behavioral analysis to provide a detailed examination of the performance of human subjects in a moderately deep planning task. We find that subjects exploit the structure of the domain to establish subgoals in a way that achieves a nearly maximal reduction in the cost of computing values of choices, but then combine partial searches with greedy local steps to solve subtasks, and maladaptively prune the decision trees of subtasks in a reflexive manner upon encountering salient losses. Subjects come idiosyncratically to favor particular sequences of actions to achieve subgoals, creating novel complex actions or “options.” PMID:25675480
Multidimensional stochastic approximation Monte Carlo.
Zablotskiy, Sergey V; Ivanov, Victor A; Paul, Wolfgang
2016-06-01
Stochastic Approximation Monte Carlo (SAMC) has been established as a mathematically founded powerful flat-histogram Monte Carlo method, used to determine the density of states, g(E), of a model system. We show here how it can be generalized for the determination of multidimensional probability distributions (or equivalently densities of states) of macroscopic or mesoscopic variables defined on the space of microstates of a statistical mechanical system. This establishes this method as a systematic way for coarse graining a model system, or, in other words, for performing a renormalization group step on a model. We discuss the formulation of the Kadanoff block spin transformation and the coarse-graining procedure for polymer models in this language. We also apply it to a standard case in the literature of two-dimensional densities of states, where two competing energetic effects are present g(E_{1},E_{2}). We show when and why care has to be exercised when obtaining the microcanonical density of states g(E_{1}+E_{2}) from g(E_{1},E_{2}). PMID:27415383
Decision analysis with approximate probabilities
NASA Technical Reports Server (NTRS)
Whalen, Thomas
1992-01-01
This paper concerns decisions under uncertainty in which the probabilities of the states of nature are only approximately known. Decision problems involving three states of nature are studied. This is due to the fact that some key issues do not arise in two-state problems, while probability spaces with more than three states of nature are essentially impossible to graph. The primary focus is on two levels of probabilistic information. In one level, the three probabilities are separately rounded to the nearest tenth. This can lead to sets of rounded probabilities which add up to 0.9, 1.0, or 1.1. In the other level, probabilities are rounded to the nearest tenth in such a way that the rounded probabilities are forced to sum to 1.0. For comparison, six additional levels of probabilistic information, previously analyzed, were also included in the present analysis. A simulation experiment compared four criteria for decisionmaking using linearly constrained probabilities (Maximin, Midpoint, Standard Laplace, and Extended Laplace) under the eight different levels of information about probability. The Extended Laplace criterion, which uses a second order maximum entropy principle, performed best overall.
Multidimensional stochastic approximation Monte Carlo
NASA Astrophysics Data System (ADS)
Zablotskiy, Sergey V.; Ivanov, Victor A.; Paul, Wolfgang
2016-06-01
Stochastic Approximation Monte Carlo (SAMC) has been established as a mathematically founded powerful flat-histogram Monte Carlo method, used to determine the density of states, g (E ) , of a model system. We show here how it can be generalized for the determination of multidimensional probability distributions (or equivalently densities of states) of macroscopic or mesoscopic variables defined on the space of microstates of a statistical mechanical system. This establishes this method as a systematic way for coarse graining a model system, or, in other words, for performing a renormalization group step on a model. We discuss the formulation of the Kadanoff block spin transformation and the coarse-graining procedure for polymer models in this language. We also apply it to a standard case in the literature of two-dimensional densities of states, where two competing energetic effects are present g (E1,E2) . We show when and why care has to be exercised when obtaining the microcanonical density of states g (E1+E2) from g (E1,E2) .