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Sample records for absorption electron transport

  1. Effective light absorption and absolute electron transport rates in the coral Pocillopora damicornis.

    PubMed

    Szabó, Milán; Wangpraseurt, Daniel; Tamburic, Bojan; Larkum, Anthony W D; Schreiber, Ulrich; Suggett, David J; Kühl, Michael; Ralph, Peter J

    2014-10-01

    Pulse Amplitude Modulation (PAM) fluorometry has been widely used to estimate the relative photosynthetic efficiency of corals. However, both the optical properties of intact corals as well as past technical constrains to PAM fluorometers have prevented calculations of the electron turnover rate of PSII. We used a new Multi-colour PAM (MC-PAM) in parallel with light microsensors to determine for the first time the wavelength-specific effective absorption cross-section of PSII photochemistry, σII(λ), and thus PAM-based absolute electron transport rates of the coral photosymbiont Symbiodinium both in culture and in hospite in the coral Pocillopora damicornis. In both cases, σII of Symbiodinium was highest in the blue spectral region and showed a progressive decrease towards red wavelengths. Absolute values for σII at 440 nm were up to 1.5-times higher in culture than in hospite. Scalar irradiance within the living coral tissue was reduced by 20% in the blue when compared to the incident downwelling irradiance. Absolute electron transport rates of P. damicornis at 440 nm revealed a maximum PSII turnover rate of ca. 250 electrons PSII(-1) s(-1), consistent with one PSII turnover for every 4 photons absorbed by PSII; this likely reflects the limiting steps in electron transfer between PSII and PSI. Our results show that optical properties of the coral host strongly affect light use efficiency of Symbiodinium. Therefore, relative electron transport rates do not reflect the productivity rates (or indeed how the photosynthesis-light response is parameterised). Here we provide a non-invasive approach to estimate absolute electron transport rates in corals. PMID:25146689

  2. Time-resolved X-ray Absorption Spectroscopy for Electron Transport Study in Warm Dense Gold

    NASA Astrophysics Data System (ADS)

    Lee, Jong-Won; Bae, Leejin; Engelhorn, Kyle; Heimann, Philip; Ping, Yuan; Barbrel, Ben; Fernandez, Amalia; Beckwith, Martha Anne; Cho, Byoung-Ick; GIST Team; IBS Team; LBNL Collaboration; SLAC Collaboration; LLNL Collaboration

    2015-11-01

    The warm dense Matter represents states of which the temperature is comparable to Fermi energy and ions are strongly coupled. One of the experimental techniques to create such state in the laboratory condition is the isochoric heating of thin metal foil with femtosecond laser pulses. This concept largely relies on the ballistic transport of electrons near the Fermi-level, which were mainly studied for the metals in ambient conditions. However, they were barely investigated in warm dense conditions. We present a time-resolved x-ray absorption spectroscopy measured for the Au/Cu dual layered sample. The front Au layer was isochorically heated with a femtosecond laser pulse, and the x-ray absorption changes around L-edge of Cu, which was attached on the backside of Au, was measured with a picosecond resolution. Time delays between the heating of the `front surface' of Au layer and the alternation of x-ray spectrum of Cu attached on the `rear surface' of Au indicate the energetic electron transport mechanism through Au in the warm dense conditions. IBS (IBS-R012-D1) and the NRF (No. 2013R1A1A1007084) of Korea.

  3. Effect of electron collisions on transport coefficients induced by the inverse bremsstrahlung absorption in plasmas

    SciTech Connect

    Bendib, A.; Tahraoui, A.; Bendib, K.; Mohammed El Hadj, K.; Hueller, S.

    2005-03-01

    The transport coefficients of fully ionized plasmas under the influence of a high-frequency electric field are derived solving numerically the electron Fokker-Planck equation using a perturbation method, parametrized as a function of the electron mean-free-path {lambda}{sub ei} compared to the spatial scales L. The isotropic and anisotropic contributions of the inverse bremsstrahlung heating are considered. Electron-electron collision terms are kept in the analysis, which allows us to consider with sufficient accuracy to describe plasmas with arbitrary atomic number Z. Practical numerical fits of the transport coefficients are proposed as functions of Z and the collisionality parameter {lambda}{sub ei}/L.

  4. Ferrocene-Substituted Naphthalenediimide with Broad Absorption and Electron-Transport Properties in the Segregated-Stack Structure.

    PubMed

    Takai, Atsuro; Sakamaki, Daisuke; Seki, Shu; Matsushita, Yoshitaka; Takeuchi, Masayuki

    2016-05-23

    A new naphthalenediimide (NDI) molecule, where two ferrocene (Fc) units were directly attached to both imide nitrogens (Fc-NDI-Fc), was synthesized. The Fc units provide high crystallinity to Fc-NDI-Fc with good solubility to conventional organic solvents. The Fc units also work as electron-donating substituents, in contrast to the electron-deficient NDI unit, resulting in broad charge-transfer absorption of Fc-NDI-Fc from the UV region to 1500 nm in the solid state. The crystal structure analysis revealed that Fc-NDI-Fc formed a segregated-stack structure. The DFT calculation based on the crystal structure showed that the NDI π-orbitals extended over two axes. The extended π-network of the NDI units led to the electron-transport properties of Fc-NDI-Fc, which was confirmed using a flash-photolysis time-resolved microwave conductivity technique. PMID:27061109

  5. Temporally resolved characterization of shock-heated foam target with Al absorption spectroscopy for fast electron transport study

    SciTech Connect

    Yabuuchi, T.; Sawada, H.; Wei, M. S.; Beg, F. N.; Regan, S. P.; Anderson, K.; Betti, R.; Hund, J.; Paguio, R. R.; Saito, K. M.; Stephens, R. B.; Key, M. H.; Mackinnon, A. J.; McLean, H. S.; Patel, P. K.; Wilks, S. C.

    2012-09-15

    The CH foam plasma produced by a laser-driven shock wave has been characterized by a temporally resolved Al 1s-2p absorption spectroscopy technique. A 200 mg/cm{sup 3} foam target with Al dopant was developed for this experiment, which used an OMEGA EP [D. D. Meyerhofer et al., J. Phys.: Conf. Ser. 244, 032010 (2010)] long pulse beam with an energy of 1.2 kJ and 3.5 ns pulselength. The plasma temperatures were inferred with the accuracy of 5 eV from the fits to the measurements using an atomic physics code. The results show that the inferred temperature is sustained at 40-45 eV between 6 and 7 ns and decreases to 25 eV at 8 ns. 2-D radiation hydrodynamic simulations show a good agreement with the measurements. Application of the shock-heated foam plasma platform toward fast electron transport experiments is discussed.

  6. Lipids: Absorption and transport

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Due to the hydrophobic nature of lipids, dietary fat is handled differently than protein or carbohydrate with respect with digestion and absorption. Dietary fats are broken down throughout the gastrointestinal system. A unique group of enzymes and cofactors allows this process to proceed in an eff...

  7. Backscattering and absorption coefficients for electrons: Solutions of invariant embedding transport equations using a method of convergence

    SciTech Connect

    Figueroa, C.; Brizuela, H.; Heluani, S. P.

    2014-05-21

    The backscattering coefficient is a magnitude whose measurement is fundamental for the characterization of materials with techniques that make use of particle beams and particularly when performing microanalysis. In this work, we report the results of an analytic method to calculate the backscattering and absorption coefficients of electrons in similar conditions to those of electron probe microanalysis. Starting on a five level states ladder model in 3D, we deduced a set of integro-differential coupled equations of the coefficients with a method know as invariant embedding. By means of a procedure proposed by authors, called method of convergence, two types of approximate solutions for the set of equations, namely complete and simple solutions, can be obtained. Although the simple solutions were initially proposed as auxiliary forms to solve higher rank equations, they turned out to be also useful for the estimation of the aforementioned coefficients. In previous reports, we have presented results obtained with the complete solutions. In this paper, we present results obtained with the simple solutions of the coefficients, which exhibit a good degree of fit with the experimental data. Both the model and the calculation method presented here can be generalized to other techniques that make use of different sorts of particle beams.

  8. The impact of cell-specific absorption properties on the correlation of electron transport rates measured by chlorophyll fluorescence and photosynthetic oxygen production in planktonic algae.

    PubMed

    Blache, Ulrich; Jakob, Torsten; Su, Wanwen; Wilhelm, Christian

    2011-08-01

    Photosynthesis-irradiance (P-E)-curves describe the photosynthetic performance of autotrophic organisms. From these P-E-curves the photosynthetic parameters α-slope, P(max), and E(k) can be deduced which are often used to characterize and to compare different organisms or organisms in acclimation to different environmental conditions. Particularly, for in situ-measurements of P-E curves of phytoplankton the analysis of variable chlorophyll fluorescence proved its potential as a sensitive and rapid method. By using Chlorella vulgaris (Trebouxiophyceae), Nannochloropsis salina (Eustigmatophyceae), Skeletonema costatum and Cyclotella meneghiniana (Bacillariophyceae), the present study investigated the influence of cellular bio-optical properties on the correlation of the photosynthetic parameters derived from fluorescence-based P-E-curves with photosynthetic parameters obtained from the measurement of oxygen evolution. It is demonstrated that small planktonic algae show a wide range of cellular absorptivity which was subject to species-specifity, growth stage and environmental conditions, e.g. nutrient limitation. This variability in bio-optical properties resulted in a great deviation of relative electron transport rates (rETRs) from oxygen-based photosynthesis rates. Thus, the photosynthetic parameters α-slope and P(max) derived from rETRs strongly depend on the specific cellular absorptivity and cannot be used to compare the photosynthetic performance of cells with different optical properties. However, it was shown that E(k) is independent of cellular absorptivity and could be used to compare samples with unknown optical properties. PMID:21571541

  9. Performance Analysis of Solution Transportation Absorption Chiller

    NASA Astrophysics Data System (ADS)

    Kiani, Behdad; Hamamoto, Yoshinori; Akisawa, Atsushi; Kashiwagi, Takao

    Thermally activated advanced absorption cycles are considered promising candidates to replace CFCs, HCFCs and HFCs for residential and commercial applications. In such absorption systems, it is desirable to utilize the waste heat from industries for heating and cooling applications in commercial and residential sectors. For this purpose, it is necessary to transport energy over some distance because the waste heat source and demand are generally located apart from each other. Transportation of steam, hot water or chilled water requires high construction costs for insulation. There is an efficient method of energy transportation using absorption system called “ Solution Transportation Absorption System (STA)”. The solution is transported at an ambient temperature so that tube-insulations not required. This paper shows the simulation of the abovementioned system and the optimal result, using mathematical optimization. The optimum system with industry‧s waste heat utilization is obtained. At the end, the effect on the pollution emission and energy conservation is obtained.

  10. The electronic absorption edge of petroleum

    SciTech Connect

    Mullins, O.C.; Mitra-Kirtley, S.; Zhu, Yifu

    1992-09-01

    The electronic absorption spectra of more than 20 crude oils and asphaltenes are examined. The spectral location of the electronic absorption edge varies over a wide range, from the near-infrared for heavy oils and asphaltenes to the near-UV for gas condensates. The functional form of the electronic absorption edge for all crude oils (measured) is characteristic of the {open_quotes}Urbach tail,{close_quotes} a phenomenology which describes electronic absorption edges in wide-ranging materials. The crude oils all show similar Urbach widths, which are significantly larger than those generally found for various materials but are similar to those previously reported for asphaltenes. Monotonically increasing absorption at higher photon energy continues for all crude oils until the spectral region is reached where single-ring aromatics dominate absorption. However, the rate of increasing absorption at higher energies moderates, thereby deviating from the Urbach behavior. Fluorescence emission spectra exhibit small red shifts from the excitation wavelength and small fluorescence peak widths in the Urbach regions of different crude oils, but show large red shifts and large peak widths in spectral regions which deviate from the Urbach behavior. This observation implies that the Urbach spectral region is dominated by lowest-energy electronic absorption of corresponding chromophores. Thus, the Urbach tail gives a direct measure of the population distribution of chromophores in crude oils. Implied population distributions are consistent with thermally activated growth of large chromophores from small ones. 12 refs., 8 figs.

  11. Measurement of electron-spin transports in GaAs quantum wells using a transmission-grating-sampled circular dichroism absorption spectroscopy

    SciTech Connect

    Yu, Hua-Liang; Fang, Shaoyin; Wen, Jinhui; Lai, Tianshu

    2014-11-07

    A transmission-grating-sampled circular dichroism absorption spectroscopy (TGS-CDAS) and its theoretical model are developed sensitively to measure decay dynamics of a transient spin grating (TSG). A binary transmission grating with the same period as TSG is set behind TSG. It allows only a same small part of each period in TSG measured by circular dichroism absorption effect of a probe. In this way, the zero average of spin-dependent effects measured over a whole period in TSG is avoided so that TGS-CDAS has a high sensitivity to spin evolution in TSG. Spin transport experiments are performed on GaAs/AlGaAs quantum wells. Experimental results prove the feasibility and reliability of TGS-CDAS.

  12. Measurement of electron-spin transports in GaAs quantum wells using a transmission-grating-sampled circular dichroism absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Yu, Hua-Liang; Fang, Shaoyin; Wen, Jinhui; Lai, Tianshu

    2014-11-01

    A transmission-grating-sampled circular dichroism absorption spectroscopy (TGS-CDAS) and its theoretical model are developed sensitively to measure decay dynamics of a transient spin grating (TSG). A binary transmission grating with the same period as TSG is set behind TSG. It allows only a same small part of each period in TSG measured by circular dichroism absorption effect of a probe. In this way, the zero average of spin-dependent effects measured over a whole period in TSG is avoided so that TGS-CDAS has a high sensitivity to spin evolution in TSG. Spin transport experiments are performed on GaAs/AlGaAs quantum wells. Experimental results prove the feasibility and reliability of TGS-CDAS.

  13. Electronic transport in graphene

    NASA Astrophysics Data System (ADS)

    Zhang, Yuanbo

    This dissertation focuses on the electronic transport properties of graphene, a single atomic layer of graphite. Graphene is a novel two-dimensional system in which electron transport is effectively governed by the relativistic quantum theory. We discover a variety of new phenomenon which stem from the "relativistic" nature of the electron dynamics in graphene. An unusual quantum Hall (QH) effect is discovered in graphene at low temperatures and strong magnetic fields. Unlike conventional two-dimensional electron systems, in graphene the observed quantization condition is characterized by half integers rather than integers. Our investigation of the magneto-oscillations in resistance reveals a Berry's phase of pi associated with the electron motion in graphene. The half-integer quantization, as well as the Berry's phase, is attributed to the peculiar topology of the graphene band structure with a linear dispersion relation and vanishing mass near the Dirac point, which can be described by relativistic quantum electrodynamics. This is further confirmed by our measurement of the effective carrier mass, m*, which obeys Einstein's equation: E = m*c*2 where c* ≈ c/300 is the effective speed of light for electrons in graphene. The availability of high magnetic fields up to 45 Tesla allows us to study the magneto-transport in graphene in the extreme quantum limit. Under such condition, we discover new sets of QH states at filling factors nu = 0, +/-1, +/-4, indicating the lifting of the four-fold degeneracy of the previously observed QH states at nu = +/-4(|n|+1/2), where n is the Landau level index. In particular, the presence of the nu = 0, +/-1 QH states indicates that the Landau level at the charge neutral Dirac point splits into four sub-levels, lifting both sublattice and spin degeneracy, thereby potentially indicating a many-body correlation in this LL. The QH effect at nu = +/-4 is investigated in tilted magnetic fields and is attributed to lifting of the n

  14. Vapor absorption refrigeration in road transport vehicles

    SciTech Connect

    Horuz, I.

    1999-08-01

    This study includes an experimental investigation into the use of vapor absorption refrigeration (VAR) systems in road transport vehicles using the waste heat in the exhaust gases of the main propulsion unit as the energy source. This would provide an alternative to the conventional vapor compression refrigeration system and its associated internal combustion engine. The performance of a VAR system fired by natural gas is compared with that of the same system driven by engine exhaust gases. This showed that the exhaust-gas-driven system produced the same performance characteristics as the gas-fired system. It also suggested that, with careful design, inserting the VAR system generator into the main engine exhaust system need not impair the performance of the vehicle propulsion unit. A comparison of the capital and running costs of the conventional and proposed alternative system is made. Suggestions are also made regarding operation of the VAR system during off-road/slow running conditions.

  15. Electron Temperature Gradient Mode Transport

    SciTech Connect

    Horton, W.; Kim, J.-H.; Hoang, G. T.; Park, H.; Kaye, S. M.; LeBlanc, B. P.

    2008-05-14

    Anomalous electron thermal losses plays a central role in the history of the controlled fusion program being the first and most persistent form of anomalous transport across all toroidal magnetic confinement devices. In the past decade the fusion program has made analysis and simulations of electron transport a high priority with the result of a clearer understanding of the phenomenon, yet still incomplete. Electron thermal transport driven by the electron temperature gradient is examined in detail from theory, simulation and power balance studies in tokamaks with strong auxiliary heating.

  16. Thermal transport: Cool electronics

    NASA Astrophysics Data System (ADS)

    Cho, Jungwan; Goodson, Kenneth E.

    2015-02-01

    Although heat removal in electronics at room temperature is typically governed by a hierarchy of conduction and convection phenomena, heat dissipation in cryogenic electronics can face a fundamental limit analogous to that of black-body emission of electromagnetic radiation.

  17. Electron transport through molecular junctions

    NASA Astrophysics Data System (ADS)

    Zimbovskaya, Natalya A.; Pederson, Mark R.

    2011-12-01

    At present, metal-molecular tunnel junctions are recognized as important active elements in molecular electronics. This gives a strong motivation to explore physical mechanisms controlling electron transport through molecules. In the last two decades, an unceasing progress in both experimental and theoretical studies of molecular conductance has been demonstrated. In the present work we give an overview of theoretical methods used to analyze the transport properties of metal-molecular junctions as well as some relevant experiments and applications. After a brief general description of the electron transport through molecules we introduce a Hamiltonian which can be used to analyze electron-electron, electron-phonon and spin-orbit interactions. Then we turn to description of the commonly used transport theory formalisms including the nonequilibrium Green’s functions based approach and the approach based on the “master” equations. We discuss the most important effects which could be manifested through molecules in electron transport phenomena such as Coulomb, spin and Frank-Condon blockades, Kondo peak in the molecular conductance, negative differential resistance and some others. Bearing in mind that first principles electronic structure calculations are recognized as the indispensable basis of the theory of electron transport through molecules, we briefly discuss the main equations and some relevant applications of the density functional theory which presently is often used to analyze important characteristics of molecules and molecular clusters. Finally, we discuss some kinds of nanoelectronic devices built using molecules and similar systems such as carbon nanotubes, various nanowires and quantum dots.

  18. Monte Carlo Transport for Electron Thermal Transport

    NASA Astrophysics Data System (ADS)

    Chenhall, Jeffrey; Cao, Duc; Moses, Gregory

    2015-11-01

    The iSNB (implicit Schurtz Nicolai Busquet multigroup electron thermal transport method of Cao et al. is adapted into a Monte Carlo transport method in order to better model the effects of non-local behavior. The end goal is a hybrid transport-diffusion method that combines Monte Carlo Transport with a discrete diffusion Monte Carlo (DDMC). The hybrid method will combine the efficiency of a diffusion method in short mean free path regions with the accuracy of a transport method in long mean free path regions. The Monte Carlo nature of the approach allows the algorithm to be massively parallelized. Work to date on the method will be presented. This work was supported by Sandia National Laboratory - Albuquerque and the University of Rochester Laboratory for Laser Energetics.

  19. Methods development for electron transport

    NASA Astrophysics Data System (ADS)

    Ganapol, Barry D.

    1992-04-01

    This report consists of two code manuals and an article recently published in the proceedings of the American Nuclear Society Mathematics and Computation Topical Meeting held in Pittsburgh. In these presentations, deterministic calculational methods simulating electron transport in solids are detailed. The first method presented (Section 2) is for the solution of the Spencer-Lewis equation in which electron motion is characterized by continuous slowing down theory and a pathlength formulation. The FN solution to the standard monoenergetic transport equation for electron transport with isotropic scattering in finite media is given in Section 3. For both codes, complete flow charts, operational instructions and sample problems are included. Finally, in Section 4, an application of the multigroup formulation of electron transport in an infinite medium is used to verify an equivalent SN formulation. For this case, anisotropic scattering is also included.

  20. Electron transport in bipyridinium films.

    PubMed

    Raymo, Françisco M; Alvarado, Robert J

    2004-01-01

    Bipyridinium dications are versatile building blocks for the assembly of functional materials. In particular, their reliable electrochemical response has encouraged the design of electroactive films. Diverse and elegant experimental strategies to coat metallic and semiconducting electrodes with bipyridinium compounds have, in fact, emerged over the past two decades. The resulting interfacial assemblies span from a few nanometers to several micrometers in thickness. They incorporate from a single molecular layer to large collections of entangled polymer chains. They transport electrons efficiently from the electrode surface to the film/solution interface and vice versa. Electron self-exchange between and the physical diffusion of the bipyridinium building blocks conspire in defining the charge transport properties of these fascinating electroactive assemblies. Often, the matrix of electron-deficient bipyridinium dications can be exploited to entrap electron-rich analytes. Electrostatic interactions promote the supramolecular association of the guests with the surface-confined host matrix. Furthermore, chromophoric sites can be coupled to the bipyridinium dications to produce photosensitive arrays capable of harvesting light and generating current. Thus, thorough investigations on the fundamental properties of these functional molecule-based materials can lead to promising applications in electroanalysis and solar energy conversion, while contributing to advances in the basic understanding of electron transport in interfacial assemblies. PMID:15293340

  1. Regulation of Intestinal Glucose Absorption by Ion Channels and Transporters

    PubMed Central

    Chen, Lihong; Tuo, Biguang; Dong, Hui

    2016-01-01

    The absorption of glucose is electrogenic in the small intestinal epithelium. The major route for the transport of dietary glucose from intestinal lumen into enterocytes is the Na+/glucose cotransporter (SGLT1), although glucose transporter type 2 (GLUT2) may also play a role. The membrane potential of small intestinal epithelial cells (IEC) is important to regulate the activity of SGLT1. The maintenance of membrane potential mainly depends on the activities of cation channels and transporters. While the importance of SGLT1 in glucose absorption has been systemically studied in detail, little is currently known about the regulation of SGLT1 activity by cation channels and transporters. A growing line of evidence suggests that cytosolic calcium ([Ca2+]cyt) can regulate the absorption of glucose by adjusting GLUT2 and SGLT1. Moreover, the absorption of glucose and homeostasis of Ca2+ in IEC are regulated by cation channels and transporters, such as Ca2+ channels, K+ channels, Na+/Ca2+ exchangers, and Na+/H+ exchangers. In this review, we consider the involvement of these cation channels and transporters in the regulation of glucose uptake in the small intestine. Modulation of them may be a potential strategy for the management of obesity and diabetes. PMID:26784222

  2. Quantification of Water Absorption and Transport in Parchment

    NASA Astrophysics Data System (ADS)

    Herringer, Susan N.; Bilheux, Hassina Z.; Bearman, Greg

    Neutron radiography was utilized to quantify water absorption and desorption in parchment at the High Flux Isotope Reactor CG-1D imaging facility at Oak Ridge National Laboratory (ORNL). Sequential 60s radiographs of sections of a 15th century parchment were taken as the parchment underwent wetting and drying cycles. This provided time-resolved visualization and quantification of water absorption and transport in parchment.

  3. Electronic Transport in Carbon Nanomaterials

    SciTech Connect

    Lopez-Benzanilla, Alejandro; Meunier, Vincent; Sumpter, Bobby G; Roche, Stephan; Cruz Silva, Eduardo

    2012-01-01

    Over the past decade, transport measurements on individual single-wall nanotubes have played a prominent role in developing our understanding of this novel carbon conductor. These measurements have identified both metallic and semiconducting nanotubes, determined their dominant electronic scattering mechanisms, and elucidated in great detail the properties of their quantized energy spectrum. Recent technological breakthroughs in nanotube device fabrication and electronic measurement have made possible experiments of unprecedented precision that reveal new and surprising phenomena. In this review, we present the fundamental properties of nanotubes side by side with the newest discoveries and also discuss some of the most exciting emerging directions.

  4. Mesoscopic electronics beyond DC transport

    NASA Astrophysics Data System (ADS)

    di Carlo, Leonardo

    Since the inception of mesoscopic electronics in the 1980's, direct current (dc) measurements have underpinned experiments in quantum transport. Novel techniques complementing dc transport are becoming paramount to new developments in mesoscopic electronics, particularly as the road is paved toward quantum information processing. This thesis describes seven experiments on GaAs/AlGaAs and graphene nanostructures unified by experimental techniques going beyond traditional dc transport. Firstly, dc current induced by microwave radiation applied to an open chaotic quantum dot is investigated. Asymmetry of mesoscopic fluctuations of induced current in perpendicular magnetic field is established as a tool for separating the quantum photovoltaic effect from classical rectification. A differential charge sensing technique is next developed using integrated quantum point contacts to resolve the spatial distribution of charge inside a double quantum clot. An accurate method for determining interdot tunnel coupling and electron temperature using charge sensing is demonstrated. A two-channel system for detecting current noise in mesoscopic conductors is developed, enabling four experiments where shot noise probes transmission properties not available in dc transport and Johnson noise serves as an electron thermometer. Suppressed shot noise is observed in quantum point contacts at zero parallel magnetic field, associated with the 0.7 structure in conductance. This suppression evolves with increasing field into the shot-noise signature of spin-lifted mode degeneracy. Quantitative agreement is found with a phenomenological model for density-dependent mode splitting. Shot noise measurements of multi-lead quantum-dot structures in the Coulomb blockade regime distill the mechanisms by which Coulomb interaction and quantum indistinguishability correlate electron flow. Gate-controlled sign reversal of noise cross correlation in two capacitively-coupled dots is observed, and shown to

  5. Electron Transport in Hall Thrusters

    NASA Astrophysics Data System (ADS)

    McDonald, Michael Sean

    Despite high technological maturity and a long flight heritage, computer models of Hall thrusters remain dependent on empirical inputs and a large part of thruster development to date has been heavily experimental in nature. This empirical approach will become increasingly unsustainable as new high-power thrusters tax existing ground test facilities and more exotic thruster designs stretch and strain the boundaries of existing design experience. The fundamental obstacle preventing predictive modeling of Hall thruster plasma properties and channel erosion is the lack of a first-principles description of electron transport across the strong magnetic fields between the cathode and anode. In spite of an abundance of proposed transport mechanisms, accurate assessments of the magnitude of electron current due to any one mechanism are scarce, and comparative studies of their relative influence on a single thruster platform simply do not exist. Lacking a clear idea of what mechanism(s) are primarily responsible for transport, it is understandably difficult for the electric propulsion scientist to focus his or her theoretical and computational tools on the right targets. This work presents a primarily experimental investigation of collisional and turbulent Hall thruster electron transport mechanisms. High-speed imaging of the thruster discharge channel at tens of thousands of frames per second reveals omnipresent rotating regions of elevated light emission, identified with a rotating spoke instability. This turbulent instability has been shown through construction of an azimuthally segmented anode to drive significant cross-field electron current in the discharge channel, and suggestive evidence points to its spatial extent into the thruster near-field plume as well. Electron trajectory simulations in experimentally measured thruster electromagnetic fields indicate that binary collisional transport mechanisms are not significant in the thruster plume, and experiments

  6. Electronic transport in unconventional superconductors

    SciTech Connect

    Graf, M.J.

    1998-12-31

    The author investigates the electron transport coefficients in unconventional superconductors at low temperatures, where charge and heat transport are dominated by electron scattering from random lattice defects. He discusses the features of the pairing symmetry, Fermi surface, and excitation spectrum which are reflected in the low temperature heat transport. For temperatures {kappa}{sub B}T {approx_lt} {gamma} {much_lt} {Delta}{sub 0}, where {gamma} is the bandwidth of impurity induced Andreev states, certain eigenvalues become universal, i.e., independent of the impurity concentration and phase shift. Deep in the superconducting phase ({kappa}{sub B}T {approx_lt} {gamma}) the Wiedemann-Franz law, with Sommerfeld`s value of the Lorenz number, is recovered. He compares the results for theoretical models of unconventional superconductivity in high-{Tc} and heavy fermion superconductors with experiment. The findings show that impurities are a sensitive probe of the low-energy excitation spectrum, and that the zero-temperature limit of the transport coefficients provides an important test of the order parameter symmetry.

  7. Ab-initio computation of electronic, and transport properties of wurtzite aluminum nitride (W-AlN) and microwave absorption properties of multi-walled carbon nanotubes (outer diameter 20-30 nanometers)-epoxy composites

    NASA Astrophysics Data System (ADS)

    Nwigboji, Ifeanyi Humphrey

    In Section I, We report findings from several ab-initio, self-consistent calculations of electronic and transport properties of wurtzite aluminum nitride (w-AlN). Our calculations utilized a local density approximation (LDA) potential and the linear combination of Gaussian orbitals (LCGO). Unlike some other density functional theory (DFT) calculations, we employed the Bagayoko, Zhao, and Williams' method, enhanced by Ekuma and Franklin (BZW-EF). The BZW-EF method verifiably leads to the minima of the occupied energies; these minima, the low laying unoccupied energies, and related wave functions provide the most variationally and physically valid density functional theory (DFT) description of the ground states of materials under study. With multiple oxidation states of Al (Al3+ to Al) and the availability of N3- to N, the BZW-EF method required several sets of self-consistent calculations with different ionic species as input. The binding energy for (Al3+ & N3-) as input was 1.5 eV larger in magnitude than those for other input choices; the results discussed here are those from the calculation that led to the absolute minima of the occupied energies with this input. Our calculated, direct band gap for w-AlN, at the Gamma point, is 6.28 eV, in excellent agreement with the 6.28 eV experimental value at 5K. We discuss the bands, total and partial densities of states, and calculated, effective masses. In section II, multi-walled carbon nanotubes (MWCNTs)-epoxy composites with MWCNTs of outer diameters (OD) of 20-30nm was fabricated. The MWCNT loadings in the composites were controlled from 1-10 wt. %. An Agilent PNA Network analyzer was utilized in the measurements of microwave absorption (MA) properties of these MWCNTs-epoxy composites over a wide frequency range of 1-26.5GHz.The measurement results showed that MA strongly depends on MWCNTs loadings in the composites. In addition, the microwave reflection, transmission, and dielectric permittivity of the MWCNTs

  8. Absorption and Transport of Sea Cucumber Saponins from Apostichopus japonicus

    PubMed Central

    Li, Shuai; Wang, Yuanhong; Jiang, Tingfu; Wang, Han; Yang, Shuang; Lv, Zhihua

    2016-01-01

    The present study is focused on the intestinal absorption of sea cucumber saponins. We determined the pharmacokinetic characteristics and bioavailability of Echinoside A and Holotoxin A1; the findings indicated that the bioavailability of Holotoxin A1 was lower than Echinoside A. We inferred that the differences in chemical structure between compounds was a factor that explained their different characteristics of transport across the intestine. In order to confirm the absorption characteristics of Echinoside A and Holotoxin A1, we examined their transport across Caco-2 cell monolayer and effective permeability by single-pass intestinal perfusion. The results of Caco-2 cell model indicate that Echinoside A is transported by passive diffusion, and not influenced by the exocytosis of P-glycoprotein (P-gp, expressed in the apical side of Caco-2 monolayers as the classic inhibitor). The intestinal perfusion also demonstrated well the absorption of Echinoside A and poor absorption of Holotoxin A1, which matched up with the result of the Caco-2 cell model. The results demonstrated our conjecture and provides fundamental information on the relationship between the chemical structure of these sea cucumber saponins and their absorption characteristics, and we believe that our findings build a foundation for the further metabolism study of sea cucumber saponins and contribute to the further clinical research of saponins. PMID:27322290

  9. Absorption and Transport of Sea Cucumber Saponins from Apostichopus japonicus.

    PubMed

    Li, Shuai; Wang, Yuanhong; Jiang, Tingfu; Wang, Han; Yang, Shuang; Lv, Zhihua

    2016-01-01

    The present study is focused on the intestinal absorption of sea cucumber saponins. We determined the pharmacokinetic characteristics and bioavailability of Echinoside A and Holotoxin A₁; the findings indicated that the bioavailability of Holotoxin A₁ was lower than Echinoside A. We inferred that the differences in chemical structure between compounds was a factor that explained their different characteristics of transport across the intestine. In order to confirm the absorption characteristics of Echinoside A and Holotoxin A₁, we examined their transport across Caco-2 cell monolayer and effective permeability by single-pass intestinal perfusion. The results of Caco-2 cell model indicate that Echinoside A is transported by passive diffusion, and not influenced by the exocytosis of P-glycoprotein (P-gp, expressed in the apical side of Caco-2 monolayers as the classic inhibitor). The intestinal perfusion also demonstrated well the absorption of Echinoside A and poor absorption of Holotoxin A₁, which matched up with the result of the Caco-2 cell model. The results demonstrated our conjecture and provides fundamental information on the relationship between the chemical structure of these sea cucumber saponins and their absorption characteristics, and we believe that our findings build a foundation for the further metabolism study of sea cucumber saponins and contribute to the further clinical research of saponins. PMID:27322290

  10. Electronic transport in amorphous carbon

    SciTech Connect

    Sullivan, J.P.; Friedmann, T.A.

    1997-12-01

    Electronic transport in a-C films has been the subject of considerable debate. In this study, combined stress relaxation and electrical transport studies were used to identify the transport mechanism in a-C films prepared by pulsed-laser deposition. The stress relaxation was modeled by a first-order kinetic reaction involving transformation of 4-fold coordinated carbon atoms to 3-fold coordinated carbon atoms, and the distribution of activation energies for this process was determined. The activation energies were found to range from about 1 eV to over 2 eV, and using these activation energies, the increase in 3-fold carbon concentration with time-temperature annealing was obtained. Conductivity measurements were also performed as a function of time-temperature annealing. It was found that the conductivity of a-C films is exponentially proportional to increases in 3-fold carbon concentration. This result can be explained by thermally activated hopping along carbon 3-fold chains combined with chain-to-chain tunneling. From the data, a typical chain length was estimated to consist of 13 carbon atoms. The heterogeneous nature of the conductivity may explain the spatially localized electron emission which is observed in a-C assuming a tunnel barrier emission model.

  11. Molecular shock response of explosives: electronic absorption spectroscopy

    SciTech Connect

    Mcgrne, Shawn D; Moore, David S; Whitley, Von H; Bolme, Cindy A; Eakins, Daniel E

    2009-01-01

    Electronic absorption spectroscopy in the range 400-800 nm was coupled to ultrafast laser generated shocks to begin addressing the question of the extent to which electronic excitations are involved in shock induced reactions. Data are presented on shocked polymethylmethacrylate (PMMA) thin films and single crystal pentaerythritol tetranitrate (PETN). Shocked PMMA exhibited thin film interference effects from the shock front. Shocked PETN exhibited interference from the shock front as well as broadband increased absorption. Relation to shock initiation hypotheses and the need for time dependent absorption data (future experiments) is briefly discussed.

  12. Electronic structure and optic absorption of phosphorene under strain

    NASA Astrophysics Data System (ADS)

    Duan, Houjian; Yang, Mou; Wang, Ruiqiang

    2016-07-01

    We studied the electronic structure and optic absorption of phosphorene (monolayer of black phosphorus) under strain. Strain was found to be a powerful tool for the band structure engineering. The in-plane strain in armchair or zigzag direction changes the effective mass components along both directions, while the vertical strain only has significant effect on the effective mass in the armchair direction. The band gap is narrowed by compressive in-plane strain and tensile vertical strain. Under certain strain configurations, the gap is closed and the energy band evolves to the semi-Dirac type: the dispersion is linear in the armchair direction and is gapless quadratic in the zigzag direction. The band-edge optic absorption is completely polarized along the armchair direction, and the polarization rate is reduced when the photon energy increases. Strain not only changes the absorption edge (the smallest photon energy for electron transition), but also the absorption polarization.

  13. Absorption and Transport of Fluorescent Brighteners by Microorganisms

    PubMed Central

    Darken, Marjorie A.

    1962-01-01

    The absorption of brighteners by living cells and their transport to subsequent growth is described. Brighteners are highly fluorescent, ultraviolet-absorbing compounds which appear to be essentially nontoxic, stable biological markers. They have been effectively absorbed by growing cultures of bacteria, yeasts, actinomycetes, and higher fungi, with active growth centers evidencing the greatest flourescence. Images FIG. 2 FIG. 3 FIG. 4 FIG. 5 FIG. 6 FIG. 7 FIG. 8 FIG. 9 FIG. 10-11 PMID:14025111

  14. Absorption and transport of milk calcium by infant rats

    SciTech Connect

    Blake, H.H.; Henning, S.J. )

    1988-01-01

    All previous studies of Ca absorption in the developing animal have used simple salts of Ca. The aims of the current study are (1) to determine the predominant form of Ca in rat milk and (2) to compare the absorption of milk Ca and CaCl{sub 2}. In vivo-labeled rat milk was obtained by injecting lactating dams with {sup 45}CaCl{sub 2}. Distribution of {sup 45}Ca in the cream, whey, and casein fractions was determined by differential centrifugation, the values being 0.3, 5, and 95%, respectively. To study Ca absorption, rats aged 14 and 28 days received either {sup 45}Ca-milk or {sup 45}CaCl{sub 2} by intragastric intubation. At 14 days, transport of milk Ca into the carcass was significantly slower than that of CaCl{sub 2}, although by 6 h postintubation both had plateaued at {approximately}92% of dose. At 28 days, the time course of transport was the same for the two forms of Ca, and the plateau was not significantly different from that at 14 days. In the younger animals, more Ca from milk than from CaCl{sub 2} was retained in gastrointestinal tissue. Quantitation of {sup 45}Ca in various segments of the gastrointestinal tract showed that the greater retention of milk Ca occurred in the stomach, the duodenum, and the distal jejunum. The authors conclude that milk Ca is efficiently absorbed by the suckling rat, possibly in a protein-bound form. The mechanism of the absorptive process awaits further investigation.

  15. Charge Transport and Light Absorption in Conjugated Systems from Extended HÜCKEL Method and Marcus Theory

    NASA Astrophysics Data System (ADS)

    To, Tran Thinh; Adams, Stefan

    2012-06-01

    A simple first principle model was developed based on extended Hückel-type orbital calculation, Marcus electron transport theory and two-dimensional-electron-gas model for the treatment of charge transport in conjugated polymers. Though simple and easy to compute, the effect of the applied electric-field is factored in. Based on this, a complete one-dimensional device model with a single layer of conjugated polymer sandwiched between two electrodes was developed with poly(3-hexylthiophene) (P3HT) as a case study. Simulated J-V curves show that π-π charge transport is much more pronounced than intra-chain transport, hence agree with previous findings. Using the same framework, we also calculated the absorption spectra of P3HT by considering the electronic energy barrier for electronic transitions that would satisfy Franck-Condon principle. Absorption spectra closely harmonize to experimental UV-Vis result. The model also reveals intra-chain electronic transitions to be the dominant absorption mechanism. All parameters of the model are obtained from either ab-initio Density Functional Theory (DFT) or Molecular Dynamics (MD) calculations, so that this model is capable of predicting charge transport and light absorption properties of new conjugated polymers without introducing fit parameters.

  16. Coupled electron-photon radiation transport

    SciTech Connect

    Lorence, L.; Kensek, R.P.; Valdez, G.D.; Drumm, C.R.; Fan, W.C.; Powell, J.L.

    2000-01-17

    Massively-parallel computers allow detailed 3D radiation transport simulations to be performed to analyze the response of complex systems to radiation. This has been recently been demonstrated with the coupled electron-photon Monte Carlo code, ITS. To enable such calculations, the combinatorial geometry capability of ITS was improved. For greater geometrical flexibility, a version of ITS is under development that can track particles in CAD geometries. Deterministic radiation transport codes that utilize an unstructured spatial mesh are also being devised. For electron transport, the authors are investigating second-order forms of the transport equations which, when discretized, yield symmetric positive definite matrices. A novel parallelization strategy, simultaneously solving for spatial and angular unknowns, has been applied to the even- and odd-parity forms of the transport equation on a 2D unstructured spatial mesh. Another second-order form, the self-adjoint angular flux transport equation, also shows promise for electron transport.

  17. Infrared electronic absorption in a single-component molecular metal.

    PubMed

    Kobayashi, Akiko; Sasa, Masaaki; Suzuki, Wakako; Fujiwara, Emiko; Tanaka, Hisashi; Tokumoto, Madoka; Okano, Yoshinori; Fujiwara, Hideki; Kobayashi, Hayao

    2004-01-21

    The infrared spectra of the crystal of transition metal complex molecules with extended-TTF ligands, Ni(tmdt)2, which is the first single-component molecular metal that has a stable metallic state even at low temperatures, exhibited an extremely low-energy electronic absorption around 2200 cm-1 (tmdt = trimethylenetetrathiafulvalenedithiolate). The systematic shift of the absorption peaks for molecules similar to Ni(tmdt)2, which range from metallic to semiconducting crystals, shows that the single-component molecular conductors are composed of molecules with unprecedentedly small HOMO-LUMO gaps. PMID:14719914

  18. PREDICTING DRUG DISPOSITION, ABSORPTION / ELIMINATION / TRANSPORTER INTERPLAY AND THE ROLE OF FOOD ON DRUG ABSORPTION

    PubMed Central

    Custodio, Joseph M.; Wu, Chi-Yuan; Benet, Leslie Z.

    2008-01-01

    The ability to predict drug disposition involves concurrent consideration of many chemical and physiological variables and the effect of food on the rate and extent of availability adds further complexity due to postprandial changes in the gastrointestinal (GI) tract. A system that allows for the assessment of the multivariate interplay occurring following administration of an oral dose, in the presence or absence of meal, would greatly benefit the early stages of drug development. This is particularly true in an era when the majority of new molecular entities are highly permeable, poorly soluble, extensively metabolized compounds (BDDCS Class 2), which present the most complicated relationship in defining the impact of transporters due to the marked effects of transporter-enzyme interplay. This review evaluates the GI luminal environment by taking into account the absorption / transport / elimination interplay and evaluates the physiochemical property issues by taking into account the importance of solubility, permeability and metabolism. We concentrate on the BDDCS and its utility in predicting drug disposition. Furthermore, we focus on the effect of food on the extent of drug availability (F), which appears to follow closely what might be expected if a significant effect of high fat meals is inhibition of transporters. That is, high fat meals and lipidic excipients would be expected to have little effect on F for Class 1 drugs; they would increase F of Class 2 drugs, while decreasing F for Class 3 drugs. PMID:18199522

  19. Electron transport analysis in water vapor

    NASA Astrophysics Data System (ADS)

    Kawaguchi, Satoru; Takahashi, Kazuhiro; Satoh, Kohki; Itoh, Hidenori

    2016-07-01

    A reliable set of electron collision cross sections for water vapor, including elastic, rotational, vibrational, and electronic excitation, electron attachment, and ionization cross sections, is estimated by the electron swarm method. In addition, anisotropic electron scattering for elastic and rotational excitation collisions is considered in the cross section set. Electron transport coefficients such as electron drift velocity, longitudinal diffusion coefficient, and effective ionization coefficient are calculated from the cross section set by Monte Carlo simulation in a wide range of E/N values, where E and N are the applied electric field and the number density of H2O molecules, respectively. The calculated transport coefficients are in good agreement with those measured. The obtained results confirm that the anisotropic electron scattering is important for the calculation at low E/N values. Furthermore, the cross section set assuming the isotropic electron scattering is proposed for practical use.

  20. Two-photon absorption of few-electron heavy ions

    SciTech Connect

    Surzhykov, A.; Indelicato, P.; Santos, J. P.; Amaro, P.; Fritzsche, S.

    2011-08-15

    The two-photon absorption of few-electron ions has been studied by using second-order perturbation theory and Dirac's relativistic equation. Within this framework, the general expressions for the excitation cross sections and rates are derived including a full account of the higher-order multipole terms in the expansion of the electron-photon interaction. While these expressions can be applied to any ion, independent of its particular shell structure, detailed computations are carried out for the two-photon absorption of hydrogen-, helium-, and berylliumlike ions and are compared with the available theoretical and experimental data. The importance of relativistic and nondipole effects in the analysis and computation of induced two-photon transitions is pointed out. Moreover, we discuss the potential of these transitions for atomic parity-violation studies in the high-Z domain.

  1. Electron paramagnetic resonance and optical absorption spectral studies on chalcocite

    NASA Astrophysics Data System (ADS)

    Reddy, S. Lakshmi; Fayazuddin, Md.; Frost, Ray L.; Endo, Tamio

    2007-11-01

    A chalcocite mineral sample of Shaha, Congo is used in the present study. An electron paramagnetic resonance (EPR) study on powdered sample confirms the presence of Mn(II), Fe(III) and Cu(II). Optical absorption spectrum indicates that Fe(III) impurity is present in octahedral structure whereas Cu(II) is present in rhombically distorted octahedral environment. Mid-infrared results are due to water and sulphate fundamentals.

  2. Electron paramagnetic resonance and optical absorption spectral studies on chalcocite.

    PubMed

    Reddy, S Lakshmi; Fayazuddin, Md; Frost, Ray L; Endo, Tamio

    2007-11-01

    A chalcocite mineral sample of Shaha, Congo is used in the present study. An electron paramagnetic resonance (EPR) study on powdered sample confirms the presence of Mn(II), Fe(III) and Cu(II). Optical absorption spectrum indicates that Fe(III) impurity is present in octahedral structure whereas Cu(II) is present in rhombically distorted octahedral environment. Mid-infrared results are due to water and sulphate fundamentals. PMID:17324611

  3. NASA three-laser airborne differential absorption lidar system electronics

    NASA Technical Reports Server (NTRS)

    Allen, R. J.; Copeland, G. D.

    1984-01-01

    The system control and signal conditioning electronics of the NASA three laser airborne differential absorption lidar (DIAL) system are described. The multipurpose DIAL system was developed for the remote measurement of gas and aerosol profiles in the troposphere and lower stratosphere. A brief description and photographs of the majority of electronics units developed under this contract are presented. The precision control system; which includes a master control unit, three combined NASA laser control interface/quantel control units, and three noise pulse discriminator/pockels cell pulser units; is described in detail. The need and design considerations for precision timing and control are discussed. Calibration procedures are included.

  4. Membrane Transporters and Folate Homeostasis; Intestinal Absorption, Transport into Systemic Compartments and Tissues

    PubMed Central

    Zhao, Rongbao; Matherly, Larry H.; Goldman, I. David

    2013-01-01

    Folates, the generic term for the family of B vitamins, are derived entirely from dietary sources, and are key one-carbon donors required for de novo nucleotide and methionine synthesis. These highly hydrophilic molecules utilize genetically distinct and functionally diverse transport systems to enter cells: the reduced folate carrier (RFC), the proton-coupled folate transporter (PCFT), and the folate receptors. Each plays a unique role in mediating folate transport across epithelia and into systemic tissues. With the recent discovery of the mechanism of intestinal folate absorption, and the clarification of the genetic basis for the autosomal recessive disorder, hereditary folate malabsorption, involving loss-of-function mutations in PCFT protein, it is now possible to piece together how these folate transporters contribute, both individually and collectively, to folate homeostasis in humans. This review focuses on the physiological roles of these major folate transporters with a brief consideration of their impact on the pharmacological activities of antifolates. PMID:19173758

  5. Electron Transport in Water Vapour

    NASA Astrophysics Data System (ADS)

    Kawaguchi, Satoru; Satoh, Kohki; Itoh, Hidenori

    2015-09-01

    Sets of electron collision cross sections for water vapour previously reported are examined by comparing calculated electron swarm parameters with measured parameters. Further, reliable cross section set of water vapour is estimated by the electron swarm method using Monte Carlo simulation to ensure the accuracy of the swarm parameter calculation. The values of an electron drift velocity, a longitudinal diffusion coefficient, and an effective ionisation coefficient calculated from Yousfi and Benabdessadok's set and those calculated from Itikawa and Mason's set do not necessarily agree with measured data. A new cross section set of water vapour, which consists of three kinds of rotational excitation, two kinds of vibrational excitation, three kinds of electron attachment, twenty-six kinds of electronic excitation, and six kinds of ionisation cross sections, and an elastic collision cross section, is estimated, and an anisotropic electron scattering for elastic and rotational excitation collision is considered. The swarm parameters calculated from the estimated cross section set is in good agreement with measured data in a wide range of reduced electric field.

  6. Absorption and transport of cholesterol autoxidation derivatives in rabbits

    SciTech Connect

    Peng, S.K.; Morin, R.J.; Phillips, G.A.; Xia, G.Z.

    1986-03-01

    Spontaneously autoxidized products of cholesterol have been demonstrated to be angiotoxic and possibly atherogenic. This study investigates the absorption and transport of these cholesterol oxidation derivatives (COD's) as compared to cholesterol. /sup 14/C-labeled cholesterol autoxidized by incubation in a 60/sup 0/C water bath for 5 weeks, then suspended in gelatin and given to New Zealand white rabbits by gastric gavage. Rabbits were sacrificed 24 hours after treatment. COD's were separated by thin layer chromatography (TLC) and radioactivities of each COD and cholesterol were measured. Percentages of each COD and cholesterol in the original mixture before administration and in the rabbits' serum after administration are almost identical, suggesting that the rates of absorption of COD's are not significantly different from that of cholesterol. Lipoproteins were fractionated by ultracentrifugation into VLDL, LDL and HDL. Radioactivities of each COD separated by TLC in each lipoprotein fraction showed that cholestane-3..beta..,5..cap alpha..,6..beta..-triol, 7..cap alpha..- and 7..beta..-hydroxycholesterol and 7-ketocholesterol were predominantly present in VLDL (3 x serum concentration) and 25-hydroxycholesterol was predominantly in LDL (2.5 x serum concentration). HDL contained only minute amounts of COD's. The increased levels of COD's in VLDL and LDL may contribute to the atherogenicity of these lipoprotein.

  7. Transport experiments with Dirac electrons

    NASA Astrophysics Data System (ADS)

    Checkelsky, Joseph George

    This thesis presents transport experiments performed on solid state systems in which the behavior of the charge carriers can be described by the Dirac equation. Unlike the massive carriers in a typical material, in these systems the carriers behave like massless fermions with a photon-like dispersion predicted to greatly modify their spin and charge transport properties. The first system studied is graphene, a crystalline monolayer of carbon arranged in a hexagonal lattice. The band structure calculated from the hexagonal lattice has the form of the massless Dirac Hamiltonian. At the charge neutral Dirac point, we find that application of a magnetic field drives a transition to an insulating state. We also study the thermoelectric properties of graphene and find that the states near the Dirac point have a unique response compared to those at higher charge density. The second system is the 3D topological insulator Bi2Se3, where a Dirac-like dispersion for states on the 2D surface of the insulating 3D crystal arises as a result of the topology of the 3D bands and time reversal symmetry. To access the transport properties of the 2D states, we suppress the remnant bulk conduction channel by chemical doping and electrostatic gating. In bulk crystals we find strong quantum corrections to transport at low temperature when the bulk conduction channel is maximally suppressed. In microscopic crystals we are able better to isolate the surface conduction channel properties. We identify in-gap conducting states that have relatively high mobility compared to the bulk and exhibit weak anti-localization, consistent with predictions for protected 2D surface states with strong spin-orbit coupling.

  8. EPR and electronic absorption spectra of copper bearing turquoise mineral

    NASA Astrophysics Data System (ADS)

    Sharma, K. B. N.; Moorthy, L. R.; Reddy, B. J.; Vedanand, S.

    1988-10-01

    Electron paramagnetic resonance and optical absorption spectra of turquoise have been studied both at room and low temperatures. It is concluded from the EPR spectra that the ground state of Cu 2+ ion in turquoise is 2A g(d x2- y2) and it is sited in an elongated rhombic octahedron (D 2π). The observed absorption bands at 14970 and 18354 cm -1 are assigned at 2A g→ 2B 1 g( dx2- y2→ xy) and 2A g→[ su2B 3g(d x 2-y 2→d yz) respectively assuming D 2π symmetry which are inconsistent with EPR studies. The three bands in the NIR region are attributed to combinations of fundamental modes of the H 2O molecule present in the sample.

  9. The Electron Transport Chain: An Interactive Simulation

    ERIC Educational Resources Information Center

    Romero, Chris; Choun, James

    2014-01-01

    This activity provides students an interactive demonstration of the electron transport chain and chemiosmosis during aerobic respiration. Students use simple, everyday objects as hydrogen ions and electrons and play the roles of the various proteins embedded in the inner mitochondrial membrane to show how this specific process in cellular…

  10. Electron transport through single carbon nanotubes

    SciTech Connect

    Schenkel, Thomas; Chai, G.; Heinrich, H.; Chow, L.; Schenkel, T.

    2007-08-01

    We report on the transport of energetic electrons through single, well aligned multi-wall carbon nanotubes (CNT). Embedding of CNTs in a protective carbon fiber coating enables the application of focused ion beam based sample preparation techniques for the non-destructive isolation and alignment of individual tubes. Aligned tubes with lengths of 0.7 to 3 mu m allow transport of 300 keV electrons in a transmission electron microscope through their hollow cores at zero degree incident angles and for a misalignment of up to 1 degree.

  11. Electronic transport across linear defects in graphene

    NASA Astrophysics Data System (ADS)

    L C Pereira, Ana; J Paez, Carlos; B Rodrigues, João Nuno; M R Peres, Nuno

    Graphene is being proposed for a variety of new electronic devices. However, the required high-quality electrical properties are affected by the formation of polycrystalline structures, which are practically unavoidable by the growth methods known so far. As such, the scattering problem of an electron off a grain boundary becomes relevant. We investigate the low-energy electronic transport across grain boundaries in graphene ribbons and in?nite ?akes. Using the recursive Green's-function method, we compute the electronic transmittance across different types of grain boundaries in graphene ribbons and ?akes. We use the charge and current density spatial distributions to enhance our understanding of their electronic transport properties, and ?nd that electronic transport depends both on the grain boundaries' microscopic details and on their orientation. We consider extended linear defects of type 585 and 5757, and also a spatial region where the grain boundary is composed by the superposition of two monolayer domains. In addition, we employ the transfer-matrix formalism to analytically study the electronic transport across a class of zigzag grain boundaries with periodicity 3. We ?nd that these grain boundaries give rise to intervalley scattering.

  12. Absorption effects in electron-sulfur-dioxide collisions

    SciTech Connect

    Machado, L. E.; Sugohara, R. T.; Santos, A. S. dos; Lee, M.-T.; Iga, I.; Souza, G. L. C. de; Homem, M. G. P.; Michelin, S. E.; Brescansin, L. M.

    2011-09-15

    A joint experimental-theoretical study on electron-SO{sub 2} collisions in the low and intermediate energy range is reported. More specifically, experimental elastic differential, integral, and momentum transfer cross sections in absolute scale are measured in the 100-1000 eV energy range using the relative-flow technique. Calculated elastic differential, integral, and momentum transfer cross sections as well as grand-total and total absorption cross sections are also presented in the 1-1000 eV energy range. A complex optical potential is used to represent the electron-molecule interaction dynamics, whereas the Schwinger variational iterative method combined with the distorted-wave approximation is used to solve the scattering equations. Comparison of the present results is made with the theoretical and experimental results available in the literature.

  13. Vibrational mode mediated electron transport in molecular transistors

    NASA Astrophysics Data System (ADS)

    Santamore, Deborah; Lambert, Neill; Nori, Franco

    2013-03-01

    We investigate the steady-state electronic transport through a suspended dimer molecule coupled to leads. When strongly coupled to a vibrational mode, the electron transport is enhanced at the phonon resonant frequency and higher-order resonances. The temperature and bias determines the nature of the phonon-assisted resonances, with clear absorption and emission peaks. The strong coupling also induces a Frank-Condon-like blockade, suppressing the current between the resonances. We compare an analytical polaron transformation method to two exact numerical methods: the Hierarchy equations of motion and an exact diagonalization in the Fock basis. In the steady-state, our two numerical results are an exact match and qualitatively reflect the main features of the polaron treatment. Our results also indicate the possibility of compensating the current decrease due to the thermal environment.

  14. Model Comparison for Electron Thermal Transport

    NASA Astrophysics Data System (ADS)

    Moses, Gregory; Chenhall, Jeffrey; Cao, Duc; Delettrez, Jacques

    2015-11-01

    Four electron thermal transport models are compared for their ability to accurately and efficiently model non-local behavior in ICF simulations. Goncharov's transport model has accurately predicted shock timing in implosion simulations but is computationally slow and limited to 1D. The iSNB (implicit Schurtz Nicolai Busquet electron thermal transport method of Cao et al. uses multigroup diffusion to speed up the calculation. Chenhall has expanded upon the iSNB diffusion model to a higher order simplified P3 approximation and a Monte Carlo transport model, to bridge the gap between the iSNB and Goncharov models while maintaining computational efficiency. Comparisons of the above models for several test problems will be presented. This work was supported by Sandia National Laboratory - Albuquerque and the University of Rochester Laboratory for Laser Energetics.

  15. Absorption of intense microwaves and ion acoustic turbulence due to heat transport

    SciTech Connect

    De Groot, J.S.; Liu, J.M.; Matte, J.P.

    1994-02-04

    Measurements and calculations of the inverse bremsstrahlung absorption of intense microwaves are presented. The isotropic component of the electron distribution becomes flat-topped in agreement with detailed Fokker-Planck calculations. The plasma heating is reduced due to the flat-topped distributions in agreement with calculations. The calculations show that the heat flux at high microwave powers is very large, q{sub max} {approx} 0.3 n{sub e}v{sub e}T{sub e}. A new particle model to, calculate the heat transport inhibition due to ion acoustic turbulence in ICF plasmas is also presented. One-dimensional PIC calculations of ion acoustic turbulence excited due to heat transport are presented. The 2-D PIC code is presently being used to perform calculations of heat flux inhibition due to ion acoustic turbulence.

  16. Filamentous bacteria transport electrons over centimetre distances.

    PubMed

    Pfeffer, Christian; Larsen, Steffen; Song, Jie; Dong, Mingdong; Besenbacher, Flemming; Meyer, Rikke Louise; Kjeldsen, Kasper Urup; Schreiber, Lars; Gorby, Yuri A; El-Naggar, Mohamed Y; Leung, Kar Man; Schramm, Andreas; Risgaard-Petersen, Nils; Nielsen, Lars Peter

    2012-11-01

    Oxygen consumption in marine sediments is often coupled to the oxidation of sulphide generated by degradation of organic matter in deeper, oxygen-free layers. Geochemical observations have shown that this coupling can be mediated by electric currents carried by unidentified electron transporters across centimetre-wide zones. Here we present evidence that the native conductors are long, filamentous bacteria. They abounded in sediment zones with electric currents and along their length they contained strings with distinct properties in accordance with a function as electron transporters. Living, electrical cables add a new dimension to the understanding of interactions in nature and may find use in technology development. PMID:23103872

  17. Photosynthetic electron transport system promotes synthesis of Au-nanoparticles.

    PubMed

    Shabnam, Nisha; Pardha-Saradhi, P

    2013-01-01

    In this communication, a novel, green, efficient and economically viable light mediated protocol for generation of Au-nanoparticles using most vital organelle, chloroplasts, of the plant system is portrayed. Thylakoids/chloroplasts isolated from Potamogeton nodosus (an aquatic plant) and Spinacia oleracea (a terrestrial plant) turned Au³⁺ solutions purple in presence of light of 600 µmol m⁻² s⁻¹ photon flux density (PFD) and the purple coloration intensified with time. UV-Vis spectra of these purple colored solutions showed absorption peak at ∼545 nm which is known to arise due to surface plasmon oscillations specific to Au-nanoparticles. However, thylakoids/chloroplasts did not alter color of Au³⁺ solutions in dark. These results clearly demonstrated that photosynthetic electron transport can reduce Au³⁺ to Au⁰ which nucleate to form Au-nanoparticles in presence of light. Transmission electron microscopic studies revealed that Au-nanoparticles generated by light driven photosynthetic electron transport system of thylakoids/chloroplasts were in range of 5-20 nm. Selected area electron diffraction and powder X-ray diffraction indicated crystalline nature of these nanoparticles. Energy dispersive X-ray confirmed that these nanoparticles were composed of Au. To confirm the potential of light driven photosynthetic electron transport in generation of Au-nanoparticles, thylakoids/chloroplasts were tested for their efficacy to generate Au-nanoparticles in presence of light of PFD ranging from 60 to 600 µmol m⁻² s⁻¹. The capacity of thylakoids/chloroplasts to generate Au-nanoparticles increased remarkably with increase in PFD, which further clearly demonstrated potential of light driven photosynthetic electron transport in reduction of Au³⁺ to Au⁰ to form nanoparticles. The light driven donation of electrons to metal ions by thylakoids/chloroplasts can be exploited for large scale production of nanoparticles. PMID:23976990

  18. Electronic transport through nanotube contacts and devices

    NASA Astrophysics Data System (ADS)

    Buia, Calin Ioan

    2003-10-01

    Carbon nanotubes are materials with amazing mechanical and electronic properties, which makes them suitable for building nanoscale electronic devices and circuits. However, their electronic transport properties are not yet fully understood. In this study we aim to investigate the electronic transport through nanotube/nanotube contacts. Our calculations are based on Land auer-Buttiker formalism. The transmission function is computed using a Green's functions technique and a tight-binding hamiltonian. Two types of geometries are considered: parallel contact and concentric contact. Additionally we analyze the behavior of a nanotube Y-junction. We find that out of all the properties of individual nanotubes, chirality and symmetry have the most important effect on the electronic transport. As a rule, armchair/armchair and metallic zigzag/zigzag contacts show the best conduction. This is explained by the perfect in-registry atomic arrangement they can provide. The contact length and the local arrangement of the atoms in the contact area are factors that further influence the conductance. We found that in optimal conditions (i.e. in-registry atomic arrangement), a contact length of ˜10 nm is enough to achieve the same conductance as a perfect nanotube. Beyond that the conductance is modulated by quantum interference effects, due to the formation of a resonant cavity in the contact area. For concentric contacts, the states between which the electron hops when passing from one tube to the other must have compatible rotational symmetries, otherwise, the corresponding conduction channel will be suppressed. This results can be used to predict the electronic transport through various setups, including nanotube bundles and multiwall nanotubes.

  19. Time-Resolved IR-Absorption Spectroscopy of Hot-Electron Dynamics in Satellite and Upper Conduction Bands in GaP

    NASA Technical Reports Server (NTRS)

    Cavicchia, M. A.; Alfano, R. R.

    1995-01-01

    The relaxation dynamics of hot electrons in the X6 and X7 satellite and upper conduction bands in GaP was directly measured by femtosecond UV-pump-IR-probe absorption spectroscopy. From a fit to the induced IR-absorption spectra the dominant scattering mechanism giving rise to the absorption at early delay times was determined to be intervalley scattering of electrons out of the X7 upper conduction-band valley. For long delay times the dominant scattering mechanism is electron-hole scattering. Electron transport dynamics of the upper conduction band of GaP has been time resolved.

  20. Femtosecond X-ray absorption study of electron localization in photoexcited anatase TiO2

    NASA Astrophysics Data System (ADS)

    Santomauro, F. G.; Lübcke, A.; Rittmann, J.; Baldini, E.; Ferrer, A.; Silatani, M.; Zimmermann, P.; Grübel, S.; Johnson, J. A.; Mariager, S. O.; Beaud, P.; Grolimund, D.; Borca, C.; Ingold, G.; Johnson, S. L.; Chergui, M.

    2015-10-01

    Transition metal oxides are among the most promising solar materials, whose properties rely on the generation, transport and trapping of charge carriers (electrons and holes). Identifying the latter’s dynamics at room temperature requires tools that combine elemental and structural sensitivity, with the atomic scale resolution of time (femtoseconds, fs). Here, we use fs Ti K-edge X-ray absorption spectroscopy (XAS) upon 3.49 eV (355 nm) excitation of aqueous colloidal anatase titanium dioxide nanoparticles to probe the trapping dynamics of photogenerated electrons. We find that their localization at Titanium atoms occurs in <300 fs, forming Ti3+ centres, in or near the unit cell where the electron is created. We conclude that electron localization is due to its trapping at pentacoordinated sites, mostly present in the surface shell region. The present demonstration of fs hard X-ray absorption capabilities opens the way to a detailed description of the charge carrier dynamics in transition metal oxides.

  1. Femtosecond X-ray absorption study of electron localization in photoexcited anatase TiO2.

    PubMed

    Santomauro, F G; Lübcke, A; Rittmann, J; Baldini, E; Ferrer, A; Silatani, M; Zimmermann, P; Grübel, S; Johnson, J A; Mariager, S O; Beaud, P; Grolimund, D; Borca, C; Ingold, G; Johnson, S L; Chergui, M

    2015-01-01

    Transition metal oxides are among the most promising solar materials, whose properties rely on the generation, transport and trapping of charge carriers (electrons and holes). Identifying the latter's dynamics at room temperature requires tools that combine elemental and structural sensitivity, with the atomic scale resolution of time (femtoseconds, fs). Here, we use fs Ti K-edge X-ray absorption spectroscopy (XAS) upon 3.49 eV (355 nm) excitation of aqueous colloidal anatase titanium dioxide nanoparticles to probe the trapping dynamics of photogenerated electrons. We find that their localization at Titanium atoms occurs in <300 fs, forming Ti(3+) centres, in or near the unit cell where the electron is created. We conclude that electron localization is due to its trapping at pentacoordinated sites, mostly present in the surface shell region. The present demonstration of fs hard X-ray absorption capabilities opens the way to a detailed description of the charge carrier dynamics in transition metal oxides. PMID:26437873

  2. Femtosecond X-ray absorption study of electron localization in photoexcited anatase TiO2

    PubMed Central

    Santomauro, F. G.; Lübcke, A.; Rittmann, J.; Baldini, E.; Ferrer, A.; Silatani, M.; Zimmermann, P.; Grübel, S.; Johnson, J. A.; Mariager, S. O.; Beaud, P.; Grolimund, D.; Borca, C.; Ingold, G.; Johnson, S.L.; Chergui, M.

    2015-01-01

    Transition metal oxides are among the most promising solar materials, whose properties rely on the generation, transport and trapping of charge carriers (electrons and holes). Identifying the latter’s dynamics at room temperature requires tools that combine elemental and structural sensitivity, with the atomic scale resolution of time (femtoseconds, fs). Here, we use fs Ti K-edge X-ray absorption spectroscopy (XAS) upon 3.49 eV (355 nm) excitation of aqueous colloidal anatase titanium dioxide nanoparticles to probe the trapping dynamics of photogenerated electrons. We find that their localization at Titanium atoms occurs in <300 fs, forming Ti3+ centres, in or near the unit cell where the electron is created. We conclude that electron localization is due to its trapping at pentacoordinated sites, mostly present in the surface shell region. The present demonstration of fs hard X-ray absorption capabilities opens the way to a detailed description of the charge carrier dynamics in transition metal oxides. PMID:26437873

  3. Enhancement of cellular uptake, transport and oral absorption of protease inhibitor saquinavir by nanocrystal formulation

    PubMed Central

    He, Yuan; Xia, Deng-ning; Li, Qiu-xia; Tao, Jin-song; Gan, Yong; Wang, Chi

    2015-01-01

    Aim: Saquinavir (SQV) is the first protease inhibitor for the treatment of HIV infection, but with poor solubility. The aim of this study was to prepare a colloidal nanocrystal suspension for improving the oral absorption of SQV. Methods: SQV nanocrystals were prepared using anti-solvent precipitation–high pressure homogenization method. The nanocrystals were characterized by a Zetasizer and transmission electron microscopy (TEM). Their dissolution, cellular uptake and transport across the human colorectal adenocarcinoma cell line (Caco-2) monolayer were investigated. Bioimaging of ex vivo intestinal sections of rats was conducted with confocal laser scanning microscopy. Pharmacokinetic analysis was performed in rats administered nanocrystal SQV suspension (50 mg/kg, ig), and the plasma SQV concentrations were measured with HPLC. Results: The SQV nanocrystals were approximately 200 nm in diameter, with a uniform size distribution. The nanocrystals had a rod-like shape under TEM. The dissolution, cellular uptake, and transport across a Caco-2 monolayer of the nanocrystal formulation were significantly improved compared to those of the coarse crystals. The ex vivo intestinal section study revealed that the fluorescently labeled nanocrystals were located in the lamina propria and the epithelium of the duodenum and jejunum. Pharmacokinetic study showed that the maximal plasma concentration (Cmax) was 2.16-fold of that for coarse crystalline SQV suspension, whereas the area under the curve (AUC) of nanocrystal SQV suspension was 1.95-fold of that for coarse crystalline SQV suspension. Conclusion: The nanocrystal drug delivery system significantly improves the oral absorption of saquinavir. PMID:26256404

  4. Detection of electron paramagnetic resonance absorption using frequency modulation.

    PubMed

    Hirata, Hiroshi; Kuyama, Toshifumi; Ono, Mitsuhiro; Shimoyama, Yuhei

    2003-10-01

    A frequency modulation (FM) method was developed to measure electron paramagnetic resonance (EPR) absorption. The first-derivative spectrum of 1,1-diphenyl-2-picrylhydrazyl (DPPH) powder was measured with this FM method. Frequency modulation of up to 1.6 MHz (peak-to-peak) was achieved at a microwave carrier frequency of 1.1 GHz. This corresponds to a magnetic field modulation of 57microT (peak-to-peak) at 40.3 mT. By using a tunable microwave resonator and automatic control systems, we achieved a practical continuous-wave (CW) EPR spectrometer that incorporates the FM method. In the present experiments, the EPR signal intensity was proportional to the magnitude of frequency modulation. The background signal at the modulation frequency (1 kHz) for EPR detection was also proportional to the magnitude of frequency modulation. An automatic matching control (AMC) system reduced the amplitude of noise in microwave detection and improved the baseline stability. Distortion of the spectral lineshape was seen when the spectrometer settings were not appropriate, e.g., with a lack of the open-loop gain in automatic tuning control (ATC). FM is an alternative to field modulation when the side-effect of field modulation is detrimental for EPR detection. The present spectroscopic technique based on the FM scheme is useful for measuring the first derivative with respect to the microwave frequency in investigations of electron-spin-related phenomena. PMID:14511592

  5. Detection of electron paramagnetic resonance absorption using frequency modulation

    NASA Astrophysics Data System (ADS)

    Hirata, Hiroshi; Kuyama, Toshifumi; Ono, Mitsuhiro; Shimoyama, Yuhei

    2003-10-01

    A frequency modulation (FM) method was developed to measure electron paramagnetic resonance (EPR) absorption. The first-derivative spectrum of 1,1-diphenyl-2-picrylhydrazyl (DPPH) powder was measured with this FM method. Frequency modulation of up to 1.6 MHz (peak-to-peak) was achieved at a microwave carrier frequency of 1.1 GHz. This corresponds to a magnetic field modulation of 57 μT (peak-to-peak) at 40.3 mT. By using a tunable microwave resonator and automatic control systems, we achieved a practical continuous-wave (CW) EPR spectrometer that incorporates the FM method. In the present experiments, the EPR signal intensity was proportional to the magnitude of frequency modulation. The background signal at the modulation frequency (1 kHz) for EPR detection was also proportional to the magnitude of frequency modulation. An automatic matching control (AMC) system reduced the amplitude of noise in microwave detection and improved the baseline stability. Distortion of the spectral lineshape was seen when the spectrometer settings were not appropriate, e.g., with a lack of the open-loop gain in automatic tuning control (ATC). FM is an alternative to field modulation when the side-effect of field modulation is detrimental for EPR detection. The present spectroscopic technique based on the FM scheme is useful for measuring the first derivative with respect to the microwave frequency in investigations of electron-spin-related phenomena.

  6. Transport coefficients for electrons in Hg vapor

    NASA Astrophysics Data System (ADS)

    Dujko, Sasa; White, Ron; Petrovic, Zoran

    2012-06-01

    Transport coefficients and distribution functions are calculated for electrons in Hg vapor under swarm conditions using a multi term theory for solving the Boltzmann equation, over a range of E/N values and temperatures relevant to lamp discharges. It is shown that for higher E/N the electron distribution is non-thermal for all Hg vapor temperatures considered, and that the speed distribution function significantly deviates from a Maxwellian under these conditions. Our work has been motivated, in part, by recent suggestions that highly accurate data for transport coefficients required as input in fluid models of Hg vapor lamp discharges may significantly improve the existing models. Current models of such lamps require a knowledge of the plasma electrical conductivity, which can be calculated from the cross sections for electron scattering in Hg vapor and mobility coefficients presented in this work. The effect of metastable atoms on the swarm parameters is also discussed. The influence of a magnetic field on electron transport coefficients in Hg vapor is investigated over a range of B/N values and angles between the fields.

  7. Regulation of Photosynthetic Electron Transport and Photoinhibition

    PubMed Central

    Roach, Thomas; Krieger-Liszkay, Anja Krieger

    2014-01-01

    Photosynthetic organisms and isolated photosystems are of interest for technical applications. In nature, photosynthetic electron transport has to work efficiently in contrasting environments such as shade and full sunlight at noon. Photosynthetic electron transport is regulated on many levels, starting with the energy transfer processes in antenna and ending with how reducing power is ultimately partitioned. This review starts by explaining how light energy can be dissipated or distributed by the various mechanisms of non-photochemical quenching, including thermal dissipation and state transitions, and how these processes influence photoinhibition of photosystem II (PSII). Furthermore, we will highlight the importance of the various alternative electron transport pathways, including the use of oxygen as the terminal electron acceptor and cyclic flow around photosystem I (PSI), the latter which seem particularly relevant to preventing photoinhibition of photosystem I. The control of excitation pressure in combination with the partitioning of reducing power influences the light-dependent formation of reactive oxygen species in PSII and in PSI, which may be a very important consideration to any artificial photosynthetic system or technical device using photosynthetic organisms. PMID:24678670

  8. Electron ripple injection concept for transport control

    SciTech Connect

    Choe, W.; Ono, M.; Hwang, Y.S.

    1992-01-01

    Recent experiments in many devices have provided firm evidence that the edge radial electric field profile differs between L- and H-modes, and that these fields can greatly modify transport in tokamak plasmas. A nonintrusive method for inducing radial electric field based on electron ripple injection is being developed by the CDX-U group. This technique utilizes a pair of special coils to create a local magnetic field ripple to trap the electrons at the edge of the plasma. The trapped electrons then drift into the plasma due to the [del]B drift. An ECH power is applied to accelerate electrons to sufficient perpendicular energy to penetrate into the plasma. Application of ECH power to the trapped electrons should provide the desired 20 A of electron current with electrons of a few keV of energy and v[perpendicular]/v[parallel] [much gt] 1. A controlled experiment to investigate the physics of ECH aided ripple injection has been designed on CDX-U. With the set of ripple coils designed for CDX-U, a ripple fraction of [delta] ([double bond] [del]B/B[sub av]) [approximately] 5% is attainable. At this ripple fraction, electrons are trapped if v[perpendicular]/v[parallel] [much gt] 1> (2[delta])[sup [minus][1/2

  9. The effect of electron-electron interaction induced dephasing on electronic transport in graphene nanoribbons

    SciTech Connect

    Kahnoj, Sina Soleimani; Touski, Shoeib Babaee; Pourfath, Mahdi E-mail: pourfath@iue.tuwien.ac.at

    2014-09-08

    The effect of dephasing induced by electron-electron interaction on electronic transport in graphene nanoribbons is theoretically investigated. In the presence of disorder in graphene nanoribbons, wavefunction of electrons can set up standing waves along the channel and the conductance exponentially decreases with the ribbon's length. Employing the non-equilibrium Green's function formalism along with an accurate model for describing the dephasing induced by electron-electron interaction, we show that this kind of interaction prevents localization and transport of electrons remains in the diffusive regime where the conductance is inversely proportional to the ribbon's length.

  10. Single-molecule junctions beyond electronic transport

    NASA Astrophysics Data System (ADS)

    Aradhya, Sriharsha V.; Venkataraman, Latha

    2013-06-01

    The idea of using individual molecules as active electronic components provided the impetus to develop a variety of experimental platforms to probe their electronic transport properties. Among these, single-molecule junctions in a metal-molecule-metal motif have contributed significantly to our fundamental understanding of the principles required to realize molecular-scale electronic components from resistive wires to reversible switches. The success of these techniques and the growing interest of other disciplines in single-molecule-level characterization are prompting new approaches to investigate metal-molecule-metal junctions with multiple probes. Going beyond electronic transport characterization, these new studies are highlighting both the fundamental and applied aspects of mechanical, optical and thermoelectric properties at the atomic and molecular scales. Furthermore, experimental demonstrations of quantum interference and manipulation of electronic and nuclear spins in single-molecule circuits are heralding new device concepts with no classical analogues. In this Review, we present the emerging methods being used to interrogate multiple properties in single molecule-based devices, detail how these measurements have advanced our understanding of the structure-function relationships in molecular junctions, and discuss the potential for future research and applications.

  11. Self-consistent electron transport in tokamaks

    SciTech Connect

    Gatto, R.; Chavdarovski, I.

    2007-09-15

    Electron particle, momentum, and energy fluxes in axisymmetric toroidal devices are derived from a version of the action-angle collision operator that includes both diffusion and drag in action-space [D. A. Hitchcock, R. D. Hazeltine, and S. M. Mahajan, Phys. Fluids 26, 2603 (1983); H. E. Mynick, J. Plasma Phys. 39, 303 (1988)]. A general result of the theory is that any contribution to transport originating directly from the toroidal frequency of the particle motion is constrained to be zero when the electron temperature is equal to the ion temperature. In particular, this constraint applies to those components of the particle and energy fluxes that are proportional to the magnetic shear, independent of the underlying turbulence and of whether the particles are trapped or untrapped. All the total fluxes describing collisionless transport of passing electrons in steady-state magnetic turbulence contain contributions proportional to the conventional thermodynamic drives, which are always outward, and contributions proportional to the magnetic shear, which have both magnitude and sign dependent on the ion-electron temperature ratio. The turbulent generalization of Ohm's law includes a hyper-resistive term, which flattens the current density profile on a fast time scale, and a turbulent electric field, which can have both signs depending on the electron-ion temperature ratio.

  12. Self-consistent electron transport in tokamaks

    NASA Astrophysics Data System (ADS)

    Gatto, R.; Chavdarovski, I.

    2007-09-01

    Electron particle, momentum, and energy fluxes in axisymmetric toroidal devices are derived from a version of the action-angle collision operator that includes both diffusion and drag in action-space [D. A. Hitchcock, R. D. Hazeltine, and S. M. Mahajan, Phys. Fluids 26, 2603 (1983); H. E. Mynick, J. Plasma Phys. 39, 303 (1988)]. A general result of the theory is that any contribution to transport originating directly from the toroidal frequency of the particle motion is constrained to be zero when the electron temperature is equal to the ion temperature. In particular, this constraint applies to those components of the particle and energy fluxes that are proportional to the magnetic shear, independent of the underlying turbulence and of whether the particles are trapped or untrapped. All the total fluxes describing collisionless transport of passing electrons in steady-state magnetic turbulence contain contributions proportional to the conventional thermodynamic drives, which are always outward, and contributions proportional to the magnetic shear, which have both magnitude and sign dependent on the ion-electron temperature ratio. The turbulent generalization of Ohm's law includes a hyper-resistive term, which flattens the current density profile on a fast time scale, and a turbulent electric field, which can have both signs depending on the electron-ion temperature ratio.

  13. Anomalous electronic transport in boron carbides

    NASA Astrophysics Data System (ADS)

    Emin, D.; Samara, G. A.; Wood, C.

    The boron carbides are composed of icosahedral units, B12 and B11C1, linked together by strong intericosahedral bonds. With such distributions of icosahedral and intericosahedral compositions, boron carbides, B/sub 1-x/C/sub x/, are single phase over 0.1 less than or equal to x less than or equal to 0.2. The electronic transport properties of the boron carbides were examined within this single-phase region. Results are inconsistent with conventional analyses of both itinerant and hopping transport. Most striking are Seebeck coefficients which are both large and rapidly increasing functions of temperature despite thermally activated dc conductivities. These results manifest the hopping of small bipolaronic holes between carbon-containing icosahedral that are inequivalent in energy and electron-lattice coupling strength. Under hydrostatic pressures up to approx. 25 kbar, the dc conductivities increase with pressure. This anomalous behavior for hopping conduction reflects the distinctive structure and bonding of these materials.

  14. Electron transport fluxes in potato plateau regime

    SciTech Connect

    Shaing, K.C.; Hazeltine, R.D.

    1997-12-01

    Electron transport fluxes in the potato plateau regime are calculated from the solutions of the drift kinetic equation and fluid equations. It is found that the bootstrap current density remains finite in the region close to the magnetic axis, although it decreases with increasing collision frequency. This finite amount of the bootstrap current in the relatively collisional regime is important in modeling tokamak startup with 100{percent} bootstrap current. {copyright} {ital 1997 American Institute of Physics.}

  15. Understanding charge transport in molecular electronics.

    PubMed

    Kushmerick, J J; Pollack, S K; Yang, J C; Naciri, J; Holt, D B; Ratner, M A; Shashidhar, R

    2003-12-01

    For molecular electronics to become a viable technology the factors that control charge transport across a metal-molecule-metal junction need to be elucidated. We use an experimentally simple crossed-wire tunnel junction to interrogate how factors such as metal-molecule coupling, molecular structure, and the choice of metal electrode influence the current-voltage characteristics of a molecular junction. PMID:14976024

  16. Electronic transport in methylated fragments of DNA

    NASA Astrophysics Data System (ADS)

    de Almeida, M. L.; Oliveira, J. I. N.; Lima Neto, J. X.; Gomes, C. E. M.; Fulco, U. L.; Albuquerque, E. L.; Freire, V. N.; Caetano, E. W. S.; de Moura, F. A. B. F.; Lyra, M. L.

    2015-11-01

    We investigate the electronic transport properties of methylated deoxyribonucleic-acid (DNA) strands, a biological system in which methyl groups are added to DNA (a major epigenetic modification in gene expression), sandwiched between two metallic platinum electrodes. Our theoretical simulations apply an effective Hamiltonian based on a tight-binding model to obtain current-voltage curves related to the non-methylated/methylated DNA strands. The results suggest potential applications in the development of novel biosensors for molecular diagnostics.

  17. Electronic transport in methylated fragments of DNA

    SciTech Connect

    Almeida, M. L. de; Oliveira, J. I. N.; Lima Neto, J. X.; Gomes, C. E. M.; Fulco, U. L. Albuquerque, E. L.; Freire, V. N.; Caetano, E. W. S.; Moura, F. A. B. F. de; Lyra, M. L.

    2015-11-16

    We investigate the electronic transport properties of methylated deoxyribonucleic-acid (DNA) strands, a biological system in which methyl groups are added to DNA (a major epigenetic modification in gene expression), sandwiched between two metallic platinum electrodes. Our theoretical simulations apply an effective Hamiltonian based on a tight-binding model to obtain current-voltage curves related to the non-methylated/methylated DNA strands. The results suggest potential applications in the development of novel biosensors for molecular diagnostics.

  18. Electronic transport in smectic liquid crystals

    NASA Astrophysics Data System (ADS)

    Shiyanovskaya, I.; Singer, K. D.; Twieg, R. J.; Sukhomlinova, L.; Gettwert, V.

    2002-04-01

    Time-of-flight measurements of transient photoconductivity have revealed bipolar electronic transport in phenylnaphthalene and biphenyl liquid crystals (LC), which exhibit several smectic mesophases. In the phenylnaphthalene LC, the hole mobility is significantly higher than the electron mobility and exhibits different temperature and phase behavior. Electron mobility in the range ~10-5 cm2/V s is temperature activated and remains continuous at the phase transitions. However, hole mobility is nearly temperature independent within the smectic phases, but is very sensitive to smectic order, 10-3 cm2/V s in the smectic-B (Sm-B) and 10-4 cm2/V s in the smectic-A (Sm-A) mesophases. The different behavior for holes and electron transport is due to differing transport mechanisms. The electron mobility is apparently controlled by rate-limiting multiple shallow trapping by impurities, but hole mobility is not. To explain the lack of temperature dependence for hole mobility within the smectic phases we consider two possible polaron transport mechanisms. The first mechanism is based on the hopping of Holstein small polarons in the nonadiabatic limit. The polaron binding energy and transfer integral values, obtained from the model fit, turned out to be sensitive to the molecular order in smectic mesophases. A second possible scenario for temperature-independent hole mobility involves the competion between two different polaron mechanisms involving so-called nearly small molecular polarons and small lattice polarons. Although the extracted transfer integrals and binding energies are reasonable and consistent with the model assumptions, the limited temperature range of the various phases makes it difficult to distinguish between any of the models. In the biphenyl LCs both electron and hole mobilities exhibit temperature activated behavior in the range of 10-5 cm2/V s without sensitivity to the molecular order. The dominating transport mechanism is considered as multiple trapping

  19. Composite Transport Coefficient for Electron Thermal Energy

    NASA Astrophysics Data System (ADS)

    Coppi, B.; Daughton, W.

    1996-11-01

    A series of experiments by the Alcator C-Mod machine over a range of heating conditions (ohmic to strongly r.f. heated) has led to the construction of a composite transport coefficient for the electron thermal energy. This is represented by the difference of two terms: one corresponding to an outflow of thermal energy and the other one corresponding to an inflow. There are theoretical arguments(B. Coppi and F. Pegoraro, Phys. Fluids B) 3 p. 2582 (1991) in support of a composite transport coefficient involving the elements of a transport matrix with an inflow term related for instance to the features of the current density profile relative to those of the electron temperature. In deriving the transport coefficient D_e^th that has been used to simulate the Alcator C-Mod plasmas, we have assumed that the driving factor of the underlying modes is the plasma pressure gradient. Thus D_e^th ∝ D_e^o [β_p* - C] where β_p* = (8π p* / B_p^2), p* ≡ -r(dp/dr) is evaluated at the point of maximum pressure gradient, C ≈ 3/16 is a positive numerical coefficient and D_e^o ∝ I_p/(nT)^5/6 is basically the Coppi-Mazzucato-Gruber diffusion coefficient introduced earlier to reproduce the results of experiments with ohmic heating. Supported in part by the U.S. Department of Energy

  20. Electronic transport properties in graphene oxide frameworks

    NASA Astrophysics Data System (ADS)

    Zhu, P.; Cruz-Silva, E.; Meunier, V.

    2014-02-01

    The electronic transport properties in multiterminal graphene oxide framework (GOF) materials are investigated using a combination of theoretical and computational methods. GOFs make up four-terminal [origin=c]90H-shaped GNR-L-GNR junctions where sandwiched boronic acid molecules (L) are covalently linked to two graphene nanoribbons (GNRs) of different edge chiralities. The transport properties are governed by both tunneling and quasiresonant regimes. We determine how the presence of linker molecules affects the transport properties and establish that the through-molecule transport properties can be tuned by varying the chemical composition of the pillar molecules but are not significantly modified when changing the type of electrodes from zigzag GNRs to armchair GNRs. In addition, we find that in multilinker systems containing two parallel molecules in the device area, the coupling between the molecules can lead to both constructive and destructive quantum interferences. We also examine the inability of the classical Kirchhoff's superposition law to account for electron flow in multilinker GOF nanonetworks.

  1. Electron ripple injection concept for transport control

    SciTech Connect

    Choe, W.; Ono, M.; Hwang, Y.S.

    1992-10-01

    Recent experiments in many devices have provided firm evidence that the edge radial electric field profile differs between L- and H-modes, and that these fields can greatly modify transport in tokamak plasmas. A nonintrusive method for inducing radial electric field based on electron ripple injection is being developed by the CDX-U group. This technique utilizes a pair of special coils to create a local magnetic field ripple to trap the electrons at the edge of the plasma. The trapped electrons then drift into the plasma due to the {del}B drift. An ECH power is applied to accelerate electrons to sufficient perpendicular energy to penetrate into the plasma. Application of ECH power to the trapped electrons should provide the desired 20 A of electron current with electrons of a few keV of energy and v{perpendicular}/v{parallel} {much_gt} 1. A controlled experiment to investigate the physics of ECH aided ripple injection has been designed on CDX-U. With the set of ripple coils designed for CDX-U, a ripple fraction of {delta} ({double_bond} {del}B/B{sub av}) {approximately} 5% is attainable. At this ripple fraction, electrons are trapped if v{perpendicular}/v{parallel} {much_gt} 1> (2{delta}){sup {minus}{1/2}} {approx}3. A resonant cavity box was fabricated for efficient heating of the trapped electrons. It is also capable of measuring the effect of the field ripple in conjunction with trapped electrons. Some preliminary results are given.

  2. Chiral electron transport in CVD bilayer graphene

    NASA Astrophysics Data System (ADS)

    Lee, Kyunghoon; Eo, Yun Suk; Kurdak, Cagliyan; Zhong, Zhaohui

    2014-03-01

    Charge carriers in bilayer graphene have a parabolic energy spectrum. Due to this band structure they are massive quasiparticles having a finite density of state at zero energy like other non-relativistic charge carriers in conventional two dimensional materials. However, they are massive Dirac fermions which have a chiral nature similar to the case of massless Dirac fermions in single layer graphene. Coupling of pseudospin and motion of charge carrier via chirality can result in dramatic consequence for transport in bipolar regime like Klein tunneling, Fabry-Perot interference, collimation of charge carrier, Veslago lens, etc. However, little attention has been paid to chiral dependent electron transport in bilayer graphene. Here we study these properties by probing phase coherent transport behavior in CVD bilayer graphene devices with sub-200nm channel length. Complex Fabry-Perot interference patterns are observed in resonant cavities defined by local gating. By applying Fourier analysis technique, we successfully analyze and identify the origin of each individual interference pattern in bipolar and monopolar regime. Our initial results also hint at the observation of cloaking of electronic states against chiral electrons in bilayer graphene.

  3. Conditioner for a helically transported electron beam

    SciTech Connect

    Wang, Changbiao

    1992-05-01

    The kinetic theory is developed to investigate a conditioner for a helically transported electron beam. Linear expressions for axial velocity spread are derived. Numerical simulation is used to check the theoretical results and examine nonlinear aspects of the conditioning process. The results show that in the linear regime the action of the beam conditioner on a pulsed beam mainly depends on the phase at which the beam enters the conditioner and depends only slightly on the operating wavelength. In the nonlinear regime, however, the action of the conditioner strongly depends on the operating wavelength and only slightly upon the entrance phase. For a properly chosen operating wavelength, a little less than the electron`s relativistic cyclotron wavelength, the conditioner can decrease the axial velocity spread of a pulsed beam down to less than one-third of its initial value.

  4. Simultaneous enhancements in photon absorption and charge transport of bismuth vanadate photoanodes for solar water splitting

    NASA Astrophysics Data System (ADS)

    Kim, Tae Woo; Ping, Yuan; Galli, Giulia A.; Choi, Kyoung-Shin

    2015-10-01

    n-Type bismuth vanadate has been identified as one of the most promising photoanodes for use in a water-splitting photoelectrochemical cell. The major limitation of BiVO4 is its relatively wide bandgap (~2.5 eV), which fundamentally limits its solar-to-hydrogen conversion efficiency. Here we show that annealing nanoporous bismuth vanadate electrodes at 350 °C under nitrogen flow can result in nitrogen doping and generation of oxygen vacancies. This gentle nitrogen treatment not only effectively reduces the bandgap by ~0.2 eV but also increases the majority carrier density and mobility, enhancing electron-hole separation. The effect of nitrogen incorporation and oxygen vacancies on the electronic band structure and charge transport of bismuth vanadate are systematically elucidated by ab initio calculations. Owing to simultaneous enhancements in photon absorption and charge transport, the applied bias photon-to-current efficiency of nitrogen-treated BiVO4 for solar water splitting exceeds 2%, a record for a single oxide photon absorber, to the best of our knowledge.

  5. Electron transport parameters in NF3

    NASA Astrophysics Data System (ADS)

    Lisovskiy, V.; Yegorenkov, V.; Ogloblina, P.; Booth, J.-P.; Martins, S.; Landry, K.; Douai, D.; Cassagne, V.

    2014-03-01

    We present electron transport parameters (the first Townsend coefficient, the dissociative attachment coefficient, the fraction of electron energy lost by collisions with NF3 molecules, the average and characteristic electron energy, the electron mobility and the drift velocity) in NF3 gas calculated from published elastic and inelastic electron-NF3 collision cross-sections using the BOLSIG+ code. Calculations were performed for the combined RB (Rescigno 1995 Phys. Rev. E 52 329, Boesten et al 1996 J. Phys. B: At. Mol. Opt. Phys. 29 5475) momentum-transfer cross-section, as well as for the JB (Joucoski and Bettega 2002 J. Phys. B: At. Mol. Opt. Phys. 35 783) momentum-transfer cross-section. In addition, we have measured the radio frequency (rf) breakdown curves for various inter-electrode gaps and rfs, and from these we have determined the electron drift velocity in NF3 from the location of the turning point in these curves. These drift velocity values are in satisfactory agreement with those calculated by the BOLSIG+ code employing the JB momentum-transfer cross-section.

  6. Electronic transport in graphene-based heterostructures

    SciTech Connect

    Tan, J. Y.; Avsar, A.; Balakrishnan, J.; Taychatanapat, T.; O'Farrell, E. C. T.; Eda, G.; Castro Neto, A. H.; Koon, G. K. W.; Özyilmaz, B.; Watanabe, K.; Taniguchi, T.

    2014-05-05

    While boron nitride (BN) substrates have been utilized to achieve high electronic mobilities in graphene field effect transistors, it is unclear how other layered two dimensional (2D) crystals influence the electronic performance of graphene. In this Letter, we study the surface morphology of 2D BN, gallium selenide (GaSe), and transition metal dichalcogenides (tungsten disulfide (WS{sub 2}) and molybdenum disulfide (MoS{sub 2})) crystals and their influence on graphene's electronic quality. Atomic force microscopy analysis shows that these crystals have improved surface roughness (root mean square value of only ∼0.1 nm) compared to conventional SiO{sub 2} substrate. While our results confirm that graphene devices exhibit very high electronic mobility (μ) on BN substrates, graphene devices on WS{sub 2} substrates (G/WS{sub 2}) are equally promising for high quality electronic transport (μ ∼ 38 000 cm{sup 2}/V s at room temperature), followed by G/MoS{sub 2} (μ ∼ 10 000 cm{sup 2}/V s) and G/GaSe (μ ∼ 2200 cm{sup 2}/V s). However, we observe a significant asymmetry in electron and hole conduction in G/WS{sub 2} and G/MoS{sub 2} heterostructures, most likely due to the presence of sulphur vacancies in the substrate crystals. GaSe crystals are observed to degrade over time even under ambient conditions, leading to a large hysteresis in graphene transport making it a less suitable substrate.

  7. Local atomic order, electronic structure and electron transport properties of Cu-Zr metallic glasses

    SciTech Connect

    Antonowicz, J. Pietnoczka, A.; Pękała, K.; Latuch, J.; Evangelakis, G. A.

    2014-05-28

    We studied atomic and electronic structures of binary Cu-Zr metallic glasses (MGs) using combined experimental and computational methods including X-ray absorption fine structure spectroscopy, electrical resistivity, thermoelectric power (TEP) measurements, molecular dynamics (MD) simulations, and ab-initio calculations. The results of MD simulations and extended X-ray absorption fine structure analysis indicate that atomic order of Cu-Zr MGs and can be described in terms of interpenetrating icosahedral-like clusters involving five-fold symmetry. MD configurations were used as an input for calculations of theoretical electronic density of states (DOS) functions which exhibits good agreement with the experimental X-ray absorption near-edge spectra. We found no indication of minimum of DOS at Fermi energy predicted by Mott's nearly free electron (NFE) model for glass-forming alloys. The theoretical DOS was subsequently used to test Mott's model describing the temperature variation of electrical resistivity and thermoelectric power of transition metal-based MGs. We demonstrate that the measured temperature variations of electrical resistivity and TEP remain in a contradiction with this model. On the other hand, the experimental temperature dependence of electrical resistivity can be explained by incipient localization of conduction electrons. It is shown that weak localization model works up to relatively high temperatures when localization is destroyed by phonons. Our results indicate that electron transport properties of Cu-Zr MGs are dominated by localization effects rather than by electronic structure. We suggest that NFE model fails to explain a relatively high glass-forming ability of binary Cu-Zr alloys.

  8. Local atomic order, electronic structure and electron transport properties of Cu-Zr metallic glasses

    NASA Astrophysics Data System (ADS)

    Antonowicz, J.; Pietnoczka, A.; Pekała, K.; Latuch, J.; Evangelakis, G. A.

    2014-05-01

    We studied atomic and electronic structures of binary Cu-Zr metallic glasses (MGs) using combined experimental and computational methods including X-ray absorption fine structure spectroscopy, electrical resistivity, thermoelectric power (TEP) measurements, molecular dynamics (MD) simulations, and ab-initio calculations. The results of MD simulations and extended X-ray absorption fine structure analysis indicate that atomic order of Cu-Zr MGs and can be described in terms of interpenetrating icosahedral-like clusters involving five-fold symmetry. MD configurations were used as an input for calculations of theoretical electronic density of states (DOS) functions which exhibits good agreement with the experimental X-ray absorption near-edge spectra. We found no indication of minimum of DOS at Fermi energy predicted by Mott's nearly free electron (NFE) model for glass-forming alloys. The theoretical DOS was subsequently used to test Mott's model describing the temperature variation of electrical resistivity and thermoelectric power of transition metal-based MGs. We demonstrate that the measured temperature variations of electrical resistivity and TEP remain in a contradiction with this model. On the other hand, the experimental temperature dependence of electrical resistivity can be explained by incipient localization of conduction electrons. It is shown that weak localization model works up to relatively high temperatures when localization is destroyed by phonons. Our results indicate that electron transport properties of Cu-Zr MGs are dominated by localization effects rather than by electronic structure. We suggest that NFE model fails to explain a relatively high glass-forming ability of binary Cu-Zr alloys.

  9. Electron density compression and oscillating effects on laser energy absorption in overdense plasma targets.

    PubMed

    Ge, Z Y; Zhuo, H B; Yu, W; Yang, X H; Yu, T P; Li, X H; Zou, D B; Ma, Y Y; Yin, Y; Shao, F Q; Peng, X J

    2014-03-01

    An analytical model for energy absorption during the interaction of an ultrashort, ultraintense laser with an overdense plasma is proposed. Both the compression effect of the electron density profile and the oscillation of the electron plasma surface are self-consistently included, which exhibit significant influences on the laser energy absorption. Based on our model, the general scaling law of the compression effect depending on laser strength and initial density is derived, and the temporal variation of the laser absorption due to the boundary oscillating effect is presented. It is found that due to the oscillation of the electron plasma surface, the laser absorption rate will vibrate periodically at ω or 2ω frequency for the p-polarized and s-polarized laser, respectively. The effect of plasma collision on the laser absorption has also been investigated, which shows a considerable rise in absorption with increasing electron-ion collision frequency for both polarizations. PMID:24730955

  10. Characterization of the electronic structure of silicon nanoparticles using x-ray absorption and emission

    NASA Astrophysics Data System (ADS)

    Montoya Vaverka, April Susan

    Resolving open questions regarding transport in nanostructures can have a huge impact on a broad range of future technologies such as light harvesting for energy. Silicon has potential to be used in many of these applications. Understanding how the band edges of nanostructures move as a function of size, surface termination and assembly is of fundamental importance in understanding the transport properties of these materials. In this thesis work I have investigated the change in the electronic structure of silicon nanoparticle assemblies as the surface termination is changed. Nanoparticles are synthesized using a thermal evaporation technique and sizes are determined using atomic force microscopy (AFM). By passivating the particles with molecules containing alcohol groups we are able to modify the size dependent band edge shifts. Both the valence and conduction bands are measured using synchrotron based x-ray absorption spectroscopy (XAS) and soft x-ray fluorescence (SXF) techniques. Particles synthesized via recrystallization of amorphous silicon/SiO2 multilayers of thicknesses below 10 rim are also investigated using the synchrotron techniques. These samples also show quantum confinement effects but the electronic structure is different from those synthesized via evaporation methods. The total bandgap is determined for all samples measured. The origins of these differences in the electronic structures are discussed.

  11. Characterization of the Electronic Structure of Silicon Nanoparticles Using X-ray Absorption and Emission

    SciTech Connect

    Vaverka, April Susan Montoya

    2008-01-01

    Resolving open questions regarding transport in nanostructures can have a huge impact on a broad range of future technologies such as light harvesting for energy. Silicon has potential to be used in many of these applications. Understanding how the band edges of nanostructures move as a function of size, surface termination and assembly is of fundamental importance in understanding the transport properties of these materials. In this thesis work I have investigated the change in the electronic structure of silicon nanoparticle assemblies as the surface termination is changed. Nanoparticles are synthesized using a thermal evaporation technique and sizes are determined using atomic force microscopy (AFM). By passivating the particles with molecules containing alcohol groups we are able to modify the size dependent band edge shifts. Both the valence and conduction bands are measured using synchrotron based x-ray absorption spectroscopy (XAS) and soft x-ray fluorescence (SXF) techniques. Particles synthesized via recrystallization of amorphous silicon/SiO2 multilayers of thicknesses below 10 nm are also investigated using the synchrotron techniques. These samples also show quantum confinement effects but the electronic structure is different from those synthesized via evaporation methods. The total bandgap is determined for all samples measured. The origins of these differences in the electronic structures are discussed.

  12. Calculation tool for transported geothermal energy using two-step absorption process

    DOE Data Explorer

    Kyle Gluesenkamp

    2016-02-01

    This spreadsheet allows the user to calculate parameters relevant to techno-economic performance of a two-step absorption process to transport low temperature geothermal heat some distance (1-20 miles) for use in building air conditioning. The parameters included are (1) energy density of aqueous LiBr and LiCl solutions, (2) transportation cost of trucking solution, and (3) equipment cost for the required chillers and cooling towers in the two-step absorption approach. More information is available in the included public report: "A Technical and Economic Analysis of an Innovative Two-Step Absorption System for Utilizing Low-Temperature Geothermal Resources to Condition Commercial Buildings"

  13. Electron and proton absorption calculations for a graphite/epoxy composite model. [large space structures

    NASA Technical Reports Server (NTRS)

    Long, E. R., Jr.

    1979-01-01

    The Bethe-Bloch stopping power relations for inelastic collisions were used to determine the absorption of electron and proton energy in cured neat epoxy resin and the absorption of electron energy in a graphite/epoxy composite. Absorption of electron energy due to bremsstrahlung was determined. Electron energies from 0.2 to 4.0 MeV and proton energies from 0.3 to 1.75 MeV were used. Monoenergetic electron energy absorption profiles for models of pure graphite, cured neat epoxy resin, and graphite/epoxy composites are reported. A relation is determined for depth of uniform energy absorption in a composite as a function of fiber volume fraction and initial electron energy. Monoenergetic proton energy absorption profiles are reported for the neat resin model. A relation for total proton penetration in the epoxy resin as a function of initial proton energy is determined. Electron energy absorption in the composite due to bremsstrahlung is reported. Electron and proton energy absorption profiles in cured neat epoxy resin are reported for environments approximating geosynchronous earth orbit.

  14. Electron Transport in Short Peptide Single Molecules

    NASA Astrophysics Data System (ADS)

    Cui, Jing; Brisendine, Joseph; Ng, Fay; Nuckolls, Colin; Koder, Ronald; Venkarataman, Latha

    We present a study of the electron transport through a series of short peptides using scanning tunneling microscope-based break junction method. Our work is motivated by the need to gain a better understanding of how various levels of protein structure contribute to the remarkable capacity of proteins to transport charge in biophysical processes such as respiration and photosynthesis. We focus here on short mono, di and tri-peptides, and probe their conductance when bound to gold electrodes in a native buffer environment. We first show that these peptides can bind to gold through amine, carboxyl, thiol and methyl-sulfide termini. We then focus on two systems (glycine and alanine) and show that their conductance decays faster than alkanes terminated by the same linkers. Importantly, our results show that the peptide bond is less conductive than a sigma carbon-carbon bond. This work was supported in part by NSF-DMR 1507440.

  15. Unconventional dc Transport in Rashba Electron Gases.

    PubMed

    Brosco, Valentina; Benfatto, Lara; Cappelluti, Emmanuele; Grimaldi, Claudio

    2016-04-22

    We discuss the transport properties of a disordered two-dimensional electron gas with strong Rashba spin-orbit coupling. We show that in the high-density regime where the Fermi energy overcomes the energy associated with spin-orbit coupling, dc transport is accurately described by a standard Drude's law, due to a nontrivial compensation between the suppression of backscattering and the relativistic correction to the quasiparticle velocity. On the contrary, when the system enters the opposite dominant spin-orbit regime, Drude's paradigm breaks down and the dc conductivity becomes strongly sensitive to the spin-orbit coupling strength, providing a suitable tool to test the entanglement between spin and charge degrees of freedom in these systems. PMID:27152815

  16. Unconventional dc Transport in Rashba Electron Gases

    NASA Astrophysics Data System (ADS)

    Brosco, Valentina; Benfatto, Lara; Cappelluti, Emmanuele; Grimaldi, Claudio

    2016-04-01

    We discuss the transport properties of a disordered two-dimensional electron gas with strong Rashba spin-orbit coupling. We show that in the high-density regime where the Fermi energy overcomes the energy associated with spin-orbit coupling, dc transport is accurately described by a standard Drude's law, due to a nontrivial compensation between the suppression of backscattering and the relativistic correction to the quasiparticle velocity. On the contrary, when the system enters the opposite dominant spin-orbit regime, Drude's paradigm breaks down and the dc conductivity becomes strongly sensitive to the spin-orbit coupling strength, providing a suitable tool to test the entanglement between spin and charge degrees of freedom in these systems.

  17. Correlated quantum transport of density wave electrons.

    PubMed

    Miller, J H; Wijesinghe, A I; Tang, Z; Guloy, A M

    2012-01-20

    Recently observed Aharonov-Bohm quantum interference of the period h/2e in charge density wave rings strongly suggests that correlated density wave electron transport is a cooperative quantum phenomenon. The picture discussed here posits that quantum solitons nucleate and transport current above a Coulomb blockade threshold field. We propose a field-dependent tunneling matrix element and use the Schrödinger equation, viewed as an emergent classical equation as in Feynman's treatment of Josephson tunneling, to compute the evolving macrostate amplitudes, finding excellent quantitative agreement with voltage oscillations and current-voltage characteristics in NbSe(3). A proposed phase diagram shows the conditions favoring soliton nucleation versus classical depinning. PMID:22400766

  18. Electronic transport properties of silicon clusters

    NASA Astrophysics Data System (ADS)

    Matsuura, Yukihito

    2016-02-01

    The electronic transport properties of silicon clusters were examined via theoretical calculations using the first-principles method. Additionally, p-type doping and n-type doping were analyzed by calculating conductance and current of boron- and phosphorus-doped silicon clusters. The p-type doping and n-type doping provided a new transmission peak at an energy level around the Fermi level to increase conductance. Furthermore, simultaneous boron and phosphorus doping resulted in noticeable rectifying characteristics, with the current drive in forward bias being three times higher than that in the reverse bias. A p-n junction was achieved even on a molecular scale.

  19. Cytochrome f function in photosynthetic electron transport.

    PubMed Central

    Whitmarsh, J; Cramer, W A

    1979-01-01

    The questions of whether the stoichiometry of the turnover of cytochrome f, and the time-course of its reduction subsequent to a light flash, are consistent with efficient function in noncyclic electron transport have been investigated. Measurements were made of the absorbance change at the 553-nm alpha-band maximum relative to a reference wavelength. In the dark cytochrome f is initially fully reduced, oxidized by a 0.3-s flash, and reduced again in the dark period after the flash. In the presence of gramicidin at 18 degrees C, the dark reduction was characterized by a half-time of 25-30 ms, stoichiometries of cytochrome f:chlorophyll and P700:chlorophyll of 1:670 and 1:640, respectively, and a short time delay. The time delay in the dark reduction of cytochrome f, which is expected for a component in an intermediate position in the chain, becomes more apparent in the presence of valinomycin and K+. Under these conditions the half-time for cytochrome f dark reduction is 130-150 ms, and the delay is approximately equal to 20 ms. The measured value for the activation energy of the dark reduction of cytochrome f (11 +/- 1 kcal/mol) is the same as that for noncyclic electron transport in steady-state light. A sigmoidal time-course for the reduction of cytochrome f has been calculated for a simple linear electron transport chain. The kinetics for reduction of cytochrome f predicted by the calculation, in the presence of valinomycin and K+, are in reasonably good agreement with the experimental data. There is an appreciable amount of data in the literature to document complex properties of cytochrome f after illumination with short flashes, and evidence for complexity in a light-minus-dark transition. The data presented here, obtained after a long flash that should establish steady-state conditions, either fulfill or are consistent with the basic criteria for efficient function of cytochrome f in noncyclic electron transport. PMID:262417

  20. Electron heat transport down steep temperature gradients

    SciTech Connect

    Matte, J.P.; Virmont, J.

    1982-12-27

    Electron heat transport is studied by numerically solving the Fokker-Planck equation, with a spherical harmonic representation of the distribution function. The first two terms (f/sub 0/, f/sub 1/) suffice, even in steep temperature gradients. Deviations from the Spitzer-Haerm law appear for lambda/L/sub T/ ((mean free path)/(temperature gradient length))> or approx. =0.01, as a result of non-Maxwellian f/sub 0/. For lambda/L/sub T/> or approx. =1, the heat flux is (1/3) of the free-streaming value. In intermediate cases, a harmonic law describes well the hottest part of the plasma.

  1. Electronic transport properties of (fluorinated) metal phthalocyanine

    NASA Astrophysics Data System (ADS)

    Fadlallah, M. M.; Eckern, U.; Romero, A. H.; Schwingenschlögl, U.

    2016-01-01

    The magnetic and transport properties of the metal phthalocyanine (MPc) and F16MPc (M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn and Ag) families of molecules in contact with S-Au wires are investigated by density functional theory within the local density approximation, including local electronic correlations on the central metal atom. The magnetic moments are found to be considerably modified under fluorination. In addition, they do not depend exclusively on the configuration of the outer electronic shell of the central metal atom (as in isolated MPc and F16MPc) but also on the interaction with the leads. Good agreement between the calculated conductance and experimental results is obtained. For M = Ag, a high spin filter efficiency and conductance is observed, giving rise to a potentially high sensitivity for chemical sensor applications.

  2. Conditioner for a helically transported electron beam

    SciTech Connect

    Wang, Changbiao.

    1992-05-01

    The kinetic theory is developed to investigate a conditioner for a helically transported electron beam. Linear expressions for axial velocity spread are derived. Numerical simulation is used to check the theoretical results and examine nonlinear aspects of the conditioning process. The results show that in the linear regime the action of the beam conditioner on a pulsed beam mainly depends on the phase at which the beam enters the conditioner and depends only slightly on the operating wavelength. In the nonlinear regime, however, the action of the conditioner strongly depends on the operating wavelength and only slightly upon the entrance phase. For a properly chosen operating wavelength, a little less than the electron's relativistic cyclotron wavelength, the conditioner can decrease the axial velocity spread of a pulsed beam down to less than one-third of its initial value.

  3. Fermionic thermocoherent state: Efficiency of electron transport

    NASA Astrophysics Data System (ADS)

    Karmakar, Anirban; Gangopadhyay, Gautam

    2016-02-01

    On the basis of the fermionic coherent state of Cahill and Glauber [Phys. Rev. A 59, 1538 (1999)], 10.1103/PhysRevA.59.1538, we have introduced here the fermionic thermocoherent state in terms of the quasiprobability distribution which shows the appropriate thermal and coherent limits as in the bosonic case or the Glauber-Lachs state. It is shown that the fermionic thermocoherent state can be realized as a displaced thermal state of fermions. Its relation with the fermionic displaced number state and the fermion-added coherent state are explored in the spirit of the bosonic case. We have investigated the nature of the average current and the suppression of noise due to the thermocoherent character of the source. The theory is applied to the problem of electronic conduction. A modification of the Landauer conductance formula is suggested which reflects the role of nonzero coherence of the source in electron transport.

  4. Magnetoacoustic transport in narrow electron channels

    NASA Astrophysics Data System (ADS)

    Aizin, Gregory; Gumbs, Godfrey; Pepper, M.

    2000-03-01

    We develop a theory of the effect due to a small perpendicular magnetic field on the quantized acoustoelectric current induced by a surface acoustic wave (SAW) in a narrow electron channel. The quasi one-dimensional channel is formed in a piezoelectric GaAs/AlGaAs semiconductor structure by a split gate technique with the gate voltage beyond pinch-off. The current is the result of the trapping of electrons in the SAW induced moving quantum dots and the transfer of electrons residing in these dots through the channel. It has been observed recently (J. Cunningham, et al., Phys. Rev.B, 1999) that in small magnetic fields the acoustoelectric current oscillates as a function of magnetic field. Based on a simple model for the quantized acoustoelecric transport in a narrow channel (G. Gumbs et al., Phys. Rev.B, Rapid Commun., 60, N20, R13954, 1999) we develop a theory for these oscillations. The case when one electron is captured in the dot is considered, and the period, the amplitude, and the phase of the current oscillations as a function of the system's parameters are obtained and analyzed.

  5. DNA sequencing via transverse electronic transport

    NASA Astrophysics Data System (ADS)

    Lagerqvist, Johan; Zwolak, Michael; di Ventra, Massimiliano

    2006-03-01

    Recently, it was theoretically shown that transverse current measurements could be used to distinguish the different bases of single stranded DNA. [1] If electrodes are embedded in a device, e.g., a nanopore, which allows translocation of ss-DNA, the strand can be sequenced by continuous measurement of the current in the direction perpendicular to the DNA backbone. [1] However, variations of the electronic signatures of each base in a real device due to structural fluctuations, counter-ions, water and other sources of noise will be important obstacles to overcome in order to make this theoretical proposal a reality. In order to explore these effects we have coupled molecular dynamics simulations with transport calculations to obtain the real time transverse current of ss-DNA translocating into a nanopore. We find that distributions of currents for each base are indeed different even in the presence of all the sources of noise discussed above. These results support even more the original proposal [1] that fast DNA sequencing could be done using transverse current measurements. Work supported by the National Humane Genome Research Institute. [1] M. Zwolak and M. Di Ventra, ``Electronic Signature of DNA Nucleotides via Transverse Transport'', Nano Lett. 5, 421 (2005).

  6. Simultaneous enhancements in photon absorption and charge transport of bismuth vanadate photoanodes for solar water splitting

    PubMed Central

    Kim, Tae Woo; Ping, Yuan; Galli, Giulia A.; Choi, Kyoung-Shin

    2015-01-01

    n-Type bismuth vanadate has been identified as one of the most promising photoanodes for use in a water-splitting photoelectrochemical cell. The major limitation of BiVO4 is its relatively wide bandgap (∼2.5 eV), which fundamentally limits its solar-to-hydrogen conversion efficiency. Here we show that annealing nanoporous bismuth vanadate electrodes at 350 °C under nitrogen flow can result in nitrogen doping and generation of oxygen vacancies. This gentle nitrogen treatment not only effectively reduces the bandgap by ∼0.2 eV but also increases the majority carrier density and mobility, enhancing electron–hole separation. The effect of nitrogen incorporation and oxygen vacancies on the electronic band structure and charge transport of bismuth vanadate are systematically elucidated by ab initio calculations. Owing to simultaneous enhancements in photon absorption and charge transport, the applied bias photon-to-current efficiency of nitrogen-treated BiVO4 for solar water splitting exceeds 2%, a record for a single oxide photon absorber, to the best of our knowledge. PMID:26498984

  7. Ion age transport: developing devices beyond electronics

    NASA Astrophysics Data System (ADS)

    Demming, Anna

    2014-03-01

    There is more to current devices than conventional electronics. Increasingly research into the controlled movement of ions and molecules is enabling a range of new technologies. For example, as Weihua Guan, Sylvia Xin Li and Mark Reed at Yale University explain, 'It offers a unique opportunity to integrate wet ionics with dry electronics seamlessly'. In this issue they provide an overview of voltage-gated ion and molecule transport in engineered nanochannels. They cover the theory governing these systems and fabrication techniques, as well as applications, including biological and chemical analysis, and energy conversion [1]. Studying the movement of particles in nanochannels is not new. The transport of materials in rock pores led Klinkenberg to describe an analogy between diffusion and electrical conductivity in porous rocks back in 1951 [2]. And already in 1940, Harold Abramson and Manuel Gorin noted that 'When an electric current is applied across the living human skin, the skin may be considered to act like a system of pores through which transfer of substances like ragweed pollen extract may be achieved both by electrophoretic and by diffusion phenomena' [3]. Transport in living systems through pore structures on a much smaller scale has attracted a great deal of research in recent years as well. The selective transport of ions and small organic molecules across the cell membrane facilitates a number of functions including communication between cells, nerve conduction and signal transmission. Understanding these processes may benefit a wide range of potential applications such as selective separation, biochemical sensing, and controlled release and drug delivery processes. In Germany researchers have successfully demonstrated controlled ionic transport through nanopores functionalized with amine-terminated polymer brushes [4]. The polymer nanobrushes swell and shrink in response to changes in temperature, thus opening and closing the nanopore passage to ionic

  8. Optical absorption properties of electron bubbles and experiments on monitoring individual electron bubbles in liquid helium

    NASA Astrophysics Data System (ADS)

    Guo, Wei

    When a free electron is injected into liquid helium, it forms a microscopic bubble essentially free of helium atoms, which is referred to as an electron bubble. It represents a fine example of a quantum-mechanical particle confined in a potential well. In this dissertation, we describe our studies on bubble properties, especially the optical absorption properties of ground state electron bubbles and experiments on imaging individual electron bubbles in liquid helium. We studied the effect of zero-point and thermal fluctuations on the shape of ground state electron bubbles in liquid helium. The results are used to determine the line shape for the 1S to 1P optical transition. The calculated line shape is in very good agreement with the experimental measurements of Grimes and Adams. For 1S to 2P transition, the obtained transition line width agrees well with the measured data of Zipfel over a range of pressure up to 15 bars. Fluctuations in the bubble shape also make other "unallowed" transitions possible. The transition cross-sections from the 1S state to the 1D and 2D states are calculated with magnitude approximately two orders smaller than that of the 1S to 1P and 2P transitions. In our electron bubble imaging experiments, a planar ultrasonic transducer was used to generate strong sound wave pulse in liquid helium. The sound pulse passed through the liquid so as to produce a transient negative pressure over a large volume (˜ 1 cm3). An electron bubble that was passed by the sound pulse exploded for a fraction of a microsecond and grew to have a radius of around 10 microns. While the bubble had this large size it was illuminated with a flash lamp and its position was recorded. In this way, we can determine its position. Through the application of a series of sound pulses, we can then take images along the track of individual electrons. The motion of individual electron bubbles has been successfully monitored. Interesting bubble tracks that may relate to electrons

  9. Ion age transport: developing devices beyond electronics

    NASA Astrophysics Data System (ADS)

    Demming, Anna

    2014-03-01

    There is more to current devices than conventional electronics. Increasingly research into the controlled movement of ions and molecules is enabling a range of new technologies. For example, as Weihua Guan, Sylvia Xin Li and Mark Reed at Yale University explain, 'It offers a unique opportunity to integrate wet ionics with dry electronics seamlessly'. In this issue they provide an overview of voltage-gated ion and molecule transport in engineered nanochannels. They cover the theory governing these systems and fabrication techniques, as well as applications, including biological and chemical analysis, and energy conversion [1]. Studying the movement of particles in nanochannels is not new. The transport of materials in rock pores led Klinkenberg to describe an analogy between diffusion and electrical conductivity in porous rocks back in 1951 [2]. And already in 1940, Harold Abramson and Manuel Gorin noted that 'When an electric current is applied across the living human skin, the skin may be considered to act like a system of pores through which transfer of substances like ragweed pollen extract may be achieved both by electrophoretic and by diffusion phenomena' [3]. Transport in living systems through pore structures on a much smaller scale has attracted a great deal of research in recent years as well. The selective transport of ions and small organic molecules across the cell membrane facilitates a number of functions including communication between cells, nerve conduction and signal transmission. Understanding these processes may benefit a wide range of potential applications such as selective separation, biochemical sensing, and controlled release and drug delivery processes. In Germany researchers have successfully demonstrated controlled ionic transport through nanopores functionalized with amine-terminated polymer brushes [4]. The polymer nanobrushes swell and shrink in response to changes in temperature, thus opening and closing the nanopore passage to ionic

  10. Variables Affecting Two Electron Transport System Assays

    PubMed Central

    Burton, G. Allen; Lanza, Guy R.

    1986-01-01

    Several methodological variables were critical in two commonly used electron transport activity assays. The dehydrogenase assay based on triphenyl formazan production exhibited a nonlinear relationship between formazan production (dehydrogenase activity) and sediment dilution, and linear formazan production occurred for 1 h in sediment slurries. Activity decreased with increased time of sediment storage at 4°C. Extraction efficiencies of formazan from sediment varied with alcohol type; methanol was unsatisfactory. Phosphate buffer (0.06 M) produced higher activity than did either U.S. Environmental Protection Agency reconstituted hard water or Tris buffer sediment diluents. Intracellular formazan crystals were dissolved within minutes when in contact with immersion oil. Greater crystal production (respiration) detected by a tetrazolium salt assay occurred at increased substrate concentrations. Test diluents containing macrophyte exudates produced greater activity than did phosphate buffer, U.S. Environmental Protection Agency water, or ultrapure water diluents. Both assays showed decreases in sediment or bacterial activity through time. PMID:16347067

  11. Electronic transport and dynamics in correlated heterostructures

    NASA Astrophysics Data System (ADS)

    Mazza, G.; Amaricci, A.; Capone, M.; Fabrizio, M.

    2015-05-01

    We investigate by means of the time-dependent Gutzwiller approximation the transport properties of a strongly correlated slab subject to Hubbard repulsion and connected with to two metallic leads kept at a different electrochemical potential. We focus on the real-time evolution of the electronic properties after the slab is connected to the leads and consider both metallic and Mott insulating slabs. When the correlated slab is metallic, the system relaxes to a steady state that sustains a finite current. The zero-bias conductance is finite and independent of the degree of correlations within the slab as long as the system remains metallic. On the other hand, when the slab is in a Mott insulating state, the external bias leads to currents that are exponentially activated by charge tunneling across the Mott-Hubbard gap, consistent with the Landau-Zener dielectric breakdown scenario.

  12. Laser damage in silicon: Energy absorption, relaxation, and transport

    SciTech Connect

    Rämer, A. Rethfeld, B.; Osmani, O.

    2014-08-07

    Silicon irradiated with an ultrashort 800 nm-laser pulse is studied theoretically using a two temperature description that considers the transient free carrier density during and after irradiation. A Drude model is implemented to account for the highly transient optical parameters. We analyze the importance of considering these density-dependent parameters as well as the choice of the Drude collision frequency. In addition, degeneracy and transport effects are investigated. The importance of each of these processes for resulting calculated damage thresholds is studied. We report damage thresholds calculations that are in very good agreement with experimental results over a wide range of pulse durations.

  13. PGR5-PGRL1-Dependent Cyclic Electron Transport Modulates Linear Electron Transport Rate in Arabidopsis thaliana.

    PubMed

    Suorsa, Marjaana; Rossi, Fabio; Tadini, Luca; Labs, Mathias; Colombo, Monica; Jahns, Peter; Kater, Martin M; Leister, Dario; Finazzi, Giovanni; Aro, Eva-Mari; Barbato, Roberto; Pesaresi, Paolo

    2016-02-01

    Plants need tight regulation of photosynthetic electron transport for survival and growth under environmental and metabolic conditions. For this purpose, the linear electron transport (LET) pathway is supplemented by a number of alternative electron transfer pathways and valves. In Arabidopsis, cyclic electron transport (CET) around photosystem I (PSI), which recycles electrons from ferrodoxin to plastoquinone, is the most investigated alternative route. However, the interdependence of LET and CET and the relative importance of CET remain unclear, largely due to the difficulties in precise assessment of the contribution of CET in the presence of LET, which dominates electron flow under physiological conditions. We therefore generated Arabidopsis mutants with a minimal water-splitting activity, and thus a low rate of LET, by combining knockout mutations in PsbO1, PsbP2, PsbQ1, PsbQ2, and PsbR loci. The resulting Δ5 mutant is viable, although mature leaves contain only ∼ 20% of wild-type naturally less abundant PsbO2 protein. Δ5 plants compensate for the reduction in LET by increasing the rate of CET, and inducing a strong non-photochemical quenching (NPQ) response during dark-to-light transitions. To identify the molecular origin of such a high-capacity CET, we constructed three sextuple mutants lacking the qE component of NPQ (Δ5 npq4-1), NDH-mediated CET (Δ5 crr4-3), or PGR5-PGRL1-mediated CET (Δ5 pgr5). Their analysis revealed that PGR5-PGRL1-mediated CET plays a major role in ΔpH formation and induction of NPQ in C3 plants. Moreover, while pgr5 dies at the seedling stage under fluctuating light conditions, Δ5 pgr5 plants are able to survive, which underlines the importance of PGR5 in modulating the intersystem electron transfer. PMID:26687812

  14. The effects of excipients on transporter mediated absorption.

    PubMed

    Goole, Jonathan; Lindley, David J; Roth, Wyatt; Carl, Stephen M; Amighi, Karim; Kauffmann, Jean-Michel; Knipp, Gregory T

    2010-06-30

    Traditionally most pharmaceutical excipients used for peroral dosage forms have been considered to be inert, although they have been known to play an important role in governing the release of the active pharmaceutical ingredient (API) required for the desired therapeutic effect. Of considerable interest is the emerging data demonstrating that many of these "inert" excipients may produce subtle changes that could directly or indirectly alter the activity of membrane-spanning proteins such as transporters. In this way, excipients could be altering the overall ADMET properties of an incorporated drug thereby affecting its intended therapeutic efficacy and/or enhancing adverse side effects. Therefore, given this recent evidence, it seems necessary to review what has been reported in the literature on interactions of excipients with human physiological entities, particularly transporters. As of today, safety/toxicity evaluations are typically based on the appearance of gross morphological changes rather than the effects on a cellular level, the ability of excipients in modifying the pharmacological activity of an active drug could lead to toxicity evaluation in routine for each additive used in oral formulations. Further knowledge on this subject will enable formulators to make more rational decisions in dosage form design and will help answer the question of whether certain excipients should be considered active pharmaceutical components of formulations. PMID:20417699

  15. Study of electron transition energies between anions and cations in spinel ferrites using differential UV-vis absorption spectra

    NASA Astrophysics Data System (ADS)

    Xue, L. C.; Wu, L. Q.; Li, S. Q.; Li, Z. Z.; Tang, G. D.; Qi, W. H.; Ge, X. S.; Ding, L. L.

    2016-07-01

    It is very important to determine electron transition energies (Etr) between anions and different cations in order to understand the electrical transport and magnetic properties of a material. Many authors have analyzed UV-vis absorption spectra using the curve (αhν)2 vs E, where α is the absorption coefficient and E(=hν) is the photon energy. Such an approach can give only two band gap energies for spinel ferrites. In this paper, using differential UV-vis absorption spectra, dα/dE vs E, we have obtained electron transition energies (Etr) between the anions and cations, Fe2+ and Fe3+ at the (A) and [B] sites and Ni2+ at the [B] sites for the (A)[B]2O4 spinel ferrite samples CoxNi0.7-xFe2.3O4 (0.0≤x≤0.3), CrxNi0.7Fe2.3-xO4 (0.0≤x≤0.3) and Fe3O4. We suggest that the differential UV-vis absorption spectra should be accepted as a general analysis method for determining electron transition energies between anions and cations.

  16. Effects of Cu deficiency on photosynthetic electron transport

    SciTech Connect

    Droppa, M.; Terry, N.; Horvath, G.

    1984-04-01

    The role of copper (Cu) in photosynthetic electron transport was explored by using Cu deficiency in sugar beet as an experimental approach. Copper influenced electron transport at two sites in addition to plastocyanin. Under mild deficiency (0.84 nmol of Cu per cm/sup 2/ of leaf area), electron transport between the two photosystems (PS) is inhibited but not electron transport within PS I or PS II measured separately. The chlorophyll/plastoquinone ratio was normal in Cu-deficient plants. However, the breakpoint in the Arrhenius plot of electron transport was shifted towards a higher temperature. It is concluded that Cu is necessary to maintain the appropriate membrane fluidity to ensure the mobility of plastoquinone molecules to transfer electrons between the two photosystems. Under severe deficiency (0.22 nmol of Cu per cm/sup 2/ of leaf area) both PS II and PS I electron transports were inhibited and to the same extent. PS II electron transport activity could not be restored by adding artifical electron donors. Polypeptides with M/sub r/s of 28,000 and 13,500 were missing in Cu-deficient chloroplast membranes. In PS II particles prepared from normal chloroplasts of spinach, 2 atoms of Cu per reaction center are present. We conclude that Cu influences PS II electron transport either directly, by participation in electron transfer as a constituent of an electron carrier, or indirectly, via the polypeptide composition of the membrane in the PS II complex.

  17. Perpendicular electron heating by absorption of auroral kilometric radiation

    NASA Technical Reports Server (NTRS)

    Morgan, D. D.; Menietti, J. D.; Winglee, R. M.; Wong, H. K.

    1994-01-01

    We investigate the possibility of perpendicular heating of electrons and the generation of '90 deg -electron conics' by particle diffusion in velocity space due to wave-particle interaction with intense auroral kilometric radiation. This interaction is made possible by the downward shift in the R-X cutoff below the electron cyclotron frequency that occurs in the presence of warm plasma. We stimulate this condition and solve the diffusion equation using a finite difference algorithm. The results show strong perpendicular electron heating and indicate that the main characteristics of an electron conic distribution can be reproduced under these conditions.

  18. Lactobacillus plantarum WCFS1 Electron Transport Chains▿

    PubMed Central

    Brooijmans, R. J. W.; de Vos, W. M.; Hugenholtz, J.

    2009-01-01

    Lactobacillus plantarum WCFS1 requires both heme and menaquinone to induce respiration-like behavior under aerobic conditions. The addition of these compounds enhanced both biomass production, without progressive acidification, and the oxygen consumption rate. When both heme and menaquinone were present, L. plantarum WCFS1 was also able to reduce nitrate. The ability to reduce nitrate was severely inhibited by the glucose levels that are typically found in L. plantarum growth media (1 to 2% [vol/vol] glucose). In contrast, comparable mannitol levels did not inhibit the reduction of nitrate. L. plantarum reduced nitrate with concomitant formation of nitrite and ammonia. Genes that encode a bd-type cytochrome (cydABCD) and a nitrate reductase (narGHJI) were identified in the genome of L. plantarum. The narGHJI operon is part of a cluster of genes that includes the molybdopterin cofactor biosynthesis genes and narK. Besides a menaquinone source, isogenic mutants revealed that cydA and ndh1 are required for the aerobic-respiration-like response and narG for nitrate reduction. The ndh1 mutant was still able to reduce nitrate. The existence of a nonredundant branched electron transport chain in L. plantarum WCFS1 that is capable of using oxygen or nitrate as a terminal electron acceptor is proposed. PMID:19346351

  19. Electron scattering and transport in liquid argon

    SciTech Connect

    Boyle, G. J.; Cocks, D. G.; White, R. D.; McEachran, R. P.

    2015-04-21

    The transport of excess electrons in liquid argon driven out of equilibrium by an applied electric field is revisited using a multi-term solution of Boltzmann’s equation together with ab initio liquid phase cross-sections calculated using the Dirac-Fock scattering equations. The calculation of liquid phase cross-sections extends previous treatments to consider multipole polarisabilities and a non-local treatment of exchange, while the accuracy of the electron-argon potential is validated through comparison of the calculated gas phase cross-sections with experiment. The results presented highlight the inadequacy of local treatments of exchange that are commonly used in liquid and cluster phase cross-section calculations. The multi-term Boltzmann equation framework accounting for coherent scattering enables the inclusion of the full anisotropy in the differential cross-section arising from the interaction and the structure factor, without an a priori assumption of quasi-isotropy in the velocity distribution function. The model, which contains no free parameters and accounts for both coherent scattering and liquid phase screening effects, was found to reproduce well the experimental drift velocities and characteristic energies.

  20. Electron scattering and transport in liquid argon.

    PubMed

    Boyle, G J; McEachran, R P; Cocks, D G; White, R D

    2015-04-21

    The transport of excess electrons in liquid argon driven out of equilibrium by an applied electric field is revisited using a multi-term solution of Boltzmann's equation together with ab initio liquid phase cross-sections calculated using the Dirac-Fock scattering equations. The calculation of liquid phase cross-sections extends previous treatments to consider multipole polarisabilities and a non-local treatment of exchange, while the accuracy of the electron-argon potential is validated through comparison of the calculated gas phase cross-sections with experiment. The results presented highlight the inadequacy of local treatments of exchange that are commonly used in liquid and cluster phase cross-section calculations. The multi-term Boltzmann equation framework accounting for coherent scattering enables the inclusion of the full anisotropy in the differential cross-section arising from the interaction and the structure factor, without an a priori assumption of quasi-isotropy in the velocity distribution function. The model, which contains no free parameters and accounts for both coherent scattering and liquid phase screening effects, was found to reproduce well the experimental drift velocities and characteristic energies. PMID:25903897

  1. Role of villus microcirculation in intestinal absorption of glucose: coupling of epithelial with endothelial transport

    PubMed Central

    Pappenheimer, J R; Michel, C C

    2003-01-01

    Capillaries in jejunal villi can absorb nutrients at rates several hundred times greater (per gram tissue) than capillaries in other tissues, including contracting skeletal muscle and brain. We here present an integrative hypothesis to account for these exceptionally large trans-endothelial fluxes and their relation to epithelial transport. Equations are developed for estimating concentration gradients of glucose across villus capillary walls, along paracellular channels and across subjunctional lateral membranes of absorptive cells. High concentrations of glucose discharged across lateral membranes to subjunctional intercellular spaces are delivered to abluminal surfaces of villus capillaries by convection-diffusion in intercellular channels without significant loss of concentration. Post-junctional paracellular transport thus provides the series link between epithelial and endothelial transport and makes possible the large trans-endothelial concentration gradients required for absorption to blood. Our analysis demonstrates that increases of villus capillary blood flow and permeability-surface area product (PS) are essential components of absorptive mechanisms: epithelial transport of normal digestive loads could not be sustained without concomitant increases in capillary blood flow and PS. The low rates of intestinal absorption found in anaesthetised animals may be attributed to inhibition of normal villus microvascular responses to epithelial transport. PMID:12937296

  2. Quantum mechanical study of the coupling of plasmon excitations to atomic-scale electron transport

    SciTech Connect

    Song Peng; Nordlander, Peter; Gao Shiwu

    2011-02-21

    The coupling of optical excitation and electron transport through a sodium atom in a plasmonic dimer junction is investigated using time-dependent density functional theory. The optical absorption and dynamic conductance is determined as a function of gap size. Surface plasmons are found to couple to atomic-scale transport through several different channels including dipolar, multipolar, and charge transfer plasmon modes. These findings provide insight into subnanoscale couplings of plasmons and atoms, a subject of general interest in plasmonics and molecular electronics.

  3. Vibrationally dependent electron-electron interactions in resonant electron transport through single-molecule junctions

    NASA Astrophysics Data System (ADS)

    Erpenbeck, A.; Härtle, R.; Bockstedte, M.; Thoss, M.

    2016-03-01

    We investigate the role of electronic-vibrational coupling in resonant electron transport through single-molecule junctions, taking into account that the corresponding coupling strengths may depend on the charge and excitation state of the molecular bridge. Within an effective-model Hamiltonian approach for a molecule with multiple electronic states, this requires to extend the commonly used model and include vibrationally dependent electron-electron interaction. We use Born-Markov master equation methods and consider selected models to exemplify the effect of the additional interaction on the transport characteristics of a single-molecule junction. In particular, we show that it has a significant influence on local cooling and heating mechanisms, it may result in negative differential resistance, and it may cause pronounced asymmetries in the conductance map of a single-molecule junction.

  4. Absorption of infrared radiation by electrons in the field of a neutral hydrogen atom

    NASA Technical Reports Server (NTRS)

    Stallcop, J. R.

    1974-01-01

    An analytical expression for the absorption coefficient is developed from a relationship between the cross-section for inverse bremsstrahlung absorption and the cross-section for electron-atom momentum transfer; it is accurate for those photon frequencies v and temperatures such that hv/kT is small. The determination of the absorption of infrared radiation by free-free transitions of the negative hydrogen ion has been extended to higher temperatures. A simple analytical expression for the absorption coefficient has been derived.

  5. Twin-peaks absorption spectra of excess electron in ionic liquids

    NASA Astrophysics Data System (ADS)

    Musat, Raluca M.; Kondoh, Takafumi; Yoshida, Yoichi; Takahashi, Kenji

    2014-07-01

    The solvated electron in room temperature ionic liquids (RTILs) has been the subject of several investigations and several reports exist on its nature and absorption spectrum. These studies concluded that the solvated electron exhibits an absorption spectrum peaking in the 1000-1400 nm region; a second absorption band peaking in the UV region has been assigned to the hole or dication radicals simultaneously formed in the system. Here we report on the fate of the excess electron in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, P14+/NTf2- using nanosecond pulse radiolysis. Scavenging experiments allowed us to record and disentangle the complex spectrum measured in P14+/NTf2-. We identified a bi-component absorption spectrum, due to the solvated electron, the absorption maxima located at 1080 nm and around 300 nm, as predicted by previous ab-initio molecular dynamics simulations for the dry excess electron. We also measured the spectra using different ionic liquids and confirmed the same feature of two absorption peaks. The present results have important implications for the characterization of solvated electrons in ionic liquids and better understanding of their structure and reactivity.

  6. Electronic absorption by Ti3+ ions and electron delocalization in synthetic blue rutile

    NASA Astrophysics Data System (ADS)

    Khomenko, V. M.; Langer, K.; Rager, H.; Fett, A.

    Polarized absorption spectra, σ and π, in the spectral range 30000-400 cm-1 (3.71-0.05 eV) were obtained on crystal slabs // [001] of deep blue rutile at various temperatures from 88 to 773 K. The rutile crystals were grown in Pt-capsules from carefully dried 99.999% TiO2 rutile powder at 50 kbar/1500 °C using graphite heating cells in a belt-type apparatus. Impurities were below the detection limits of the electron microprobe (about 0.005 wt% for elements with Z>=13). The spectra are characterized by an unpolarized absorption edge at 24300 cm-1, two weak and relatively narrow (Δν1/2 3500-4000 cm-1), slightly σ-polarized bands ν1 at 23500 cm-1 and ν2 at 18500 cm-1, and a complex, strong band system in the NIR (near infra red) with sharp weak peaks in the region of the OH stretching fundamentals superimposed on the NIR system in the σ-spectra. The NIR band system and the UV edge produce an absorption minimum in both spectra, σ and π, at 21000 cm-1, i.e. in the blue, which explains the colour of the crystals. Bands ν1 and ν2 are assigned to dd transitions to the Jahn-Teller split upper Eg state of octahedral Ti3+. The NIR band system can be fitted as a sum of three components. Two of them are partly π-polarized, nearly Gaussian bands, both with large half widths 6000-7000 cm-1, ν3 at 12000 cm-1 and the most intense ν4 at 6500 cm-1. The third NIR band ν5 of a mixed Lorentz-Gaussian shape with a maximum at 3000 cm-1 forms a shoulder on the low-energy wing of ν4. Energy positions, half band widths and temperature behaviour of these bands are consistent with a small polaron type of Ti3+Ti4+ charge transfer (CT). Polarization dependence of CT bands can be explained on the basis of the structural model of defect rutile by Bursill and Blanchin (1983) involving interstitial titanium. Two OH bands at 3322 and 3279 cm-1 in σ-spectra show different stability during annealing, indicating two different positions of proton in the rutile structure, one of them

  7. Designing a beam transport system for RHIC's electron lens

    SciTech Connect

    Gu, X.; Pikin, A.; Okamura, M.; Fischer, W.; Luo, Y.; Gupta, R.; Hock, J.; Raparia, D.

    2011-03-28

    We designed two electron lenses to apply head-on beam-beam compensation for RHIC; they will be installed near IP10. The electron-beam transport system is an important subsystem of the entire electron-lens system. Electrons are transported from the electron gun to the main solenoid and further to the collector. The system must allow for changes of the electron beam size inside the superconducting magnet, and for changes of the electron position by 5 mm in the horizontal- and vertical-planes.

  8. Low temperature charge transport and microwave absorption of carbon coated iron nanoparticles–polymer composite films

    SciTech Connect

    Prasad, V.

    2012-06-15

    Highlights: ► Carbon coated Fe nanoparticle–PVC composite films were prepared by solution casting method. ► A low electrical percolation threshold of 2.2 was achieved. ► The low temperature electrical conductivity follows variable range hopping type conduction. ► An EMI shielding of 18 dB was achieved in 200 micron thick film. -- Abstract: In this paper, the low temperature electrical conductivity and microwave absorption properties of carbon coated iron nanoparticles–polyvinyl chloride composite films are investigated for different filler fractions. The filler particles are prepared by the pyrolysis of ferrocene at 980 °C and embedded in polyvinyl chloride matrix. The high resolution transmission electron micrographs of the filler material have shown a 5 nm thin layer graphitic carbon covering over iron particles. The room temperature electrical conductivity of the composite film changes by 10 orders of magnitude with the increase of filler concentration. A percolation threshold of 2.2 and an electromagnetic interference shielding efficiency (EMI SE) of ∼18.6 dB in 26.5–40 GHz range are observed for 50 wt% loading. The charge transport follows three dimensional variable range hopping conduction.

  9. Transition in electron transport in a cylindrical Hall thruster

    SciTech Connect

    Parker, J. B.; Raitses, Y.; Fisch, N. J.

    2010-08-30

    Through the use of high-speed camera and Langmuir probe measurements in a cylindrical Hall thruster, we report the discovery of a rotating spoke of increased plasma density and light emission which correlates with increased electron transport across the magnetic field. As cathode electron emission is increased, a sharp transition occurs where the spoke disappears and electron transport decreases. This suggests that a significant fraction of the electron current might be directed through the spoke.

  10. Transition in Electron Transport in a Cylindrical Hall Thruster

    SciTech Connect

    J.B. Parker, Y. Raitses, and N.J. Fisch

    2010-06-02

    Through the use of high-speed camera and Langmuir probe measurements in a cylindrical Hall thruster, we report the discovery of a rotating spoke of increased plasma density and light emission which correlates with increased electron transport across the magnetic field. As cathode electron emission is increased, a sharp transition occurs where the spoke disappears and electron transport decreases. This suggests that a significant fraction of the electron current might be directed through the spoke.

  11. Enhanced carrier collection efficiency and reduced quantum state absorption by electron doping in self-assembled quantum dot solar cells

    SciTech Connect

    Li, Tian E-mail: dage@ece.umd.edu; Dagenais, Mario E-mail: dage@ece.umd.edu; Lu, Haofeng; Fu, Lan; Tan, Hark Hoe; Jagadish, Chennupati

    2015-02-02

    Reduced quantum dot (QD) absorption due to state filling effects and enhanced electron transport in doped QDs are demonstrated to play a key role in solar energy conversion. Reduced QD state absorption with increased n-doping is observed in the self-assembled In{sub 0.5}Ga{sub 0.5}As/GaAs QDs from high resolution below-bandgap external quantum efficiency (EQE) measurement, which is a direct consequence of the Pauli exclusion principle. We also show that besides partial filling of the quantum states, electron-doping produces negatively charged QDs that exert a repulsive Coulomb force on the mobile electrons, thus altering the electron trajectory and reducing the probability of electron capture, leading to an improved collection efficiency of photo-generated carriers, as indicated by an absolute above-bandgap EQE measurement. The resulting redistribution of the mobile electron in the planar direction is further validated by the observed photoluminescence intensity dependence on doping.

  12. The induction of microsomal electron transport enzymes.

    PubMed

    Waterman, M R; Estabrook, R W

    1983-01-01

    Liver endoplasmic reticulum contains as NADPH-dependent electron transport complex where the family of hemeproteins, termed cytochrome P-450, serve as catalysts for the oxidation of a variety of different organic chemicals. The content and inventory of the types of cytochrome P-450 is readily modified following in vivo treatment of animals with 'inducing agents' such as barbiturates, steroids and polycyclic hydrocarbons. Recent studies have applied the methods of molecular biology to evaluate changes in the transcription and translation of genomic information occurring concomitant with the initiation of synthesis of various types of cytochrome P-450. The ability to isolate unique cytochrome P-450 proteins and to prepare specific antibodies now permits the study of in vitro translation of mRNA and the preparation of specific cDNAs. The present review summarizes the historic background leading to current concepts of cytochrome P-450 induction and describes recent advances in our knowledge of the regulation of cytochrome P-450 synthesis in the liver. PMID:6353196

  13. Electron transport through functionalized carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Bruque, Nicolas; Pandey, Rajeev; Khalid Ashraf, Md.; Lake, Roger

    2008-03-01

    Single molecule functionalization of single walled carbon nanotubes (CNT)s by B. R. Goldsmith, et. al. [1] and single molecule bridges of single wall CNTs by X. Guo, et. al. [2] are elegant examples of CNT contacts to individual molecules for electronic applications. CNTs are of the same physical size as the molecule they contact providing a well-defined covalent bond between CNT electrodes and a molecule. The above two systems are studied to determine how a chemical absorbate and linker influence transport through metallic CNTs. The first system consists of a stand alone metallic CNT with a single oxygen adsorption site, matching a proposed final chemical process for a HNO3 oxidation and reduction process. The second system consists of a CNT-Amide-(CH)n-Amide-CNT structure in which both CNTs are metallic. Transmission calculations, using our DFT (FIREBALL)-NEGF code show that the amide linker suppresses transmission compared to a direct CNT-polyene linkage studied in [3]. 1. B. R. Goldsmith, et. al., Science, 315, 77 (2007). 2. X. Guo, et. al. Science, 311, 356 (2006). 3. N. Bruque, et. al. Phys. Rev. B, 76, 205322 (2007).

  14. Electronic and Ionic Transport Dynamics in Organolead Halide Perovskites.

    PubMed

    Li, Dehui; Wu, Hao; Cheng, Hung-Chieh; Wang, Gongming; Huang, Yu; Duan, Xiangfeng

    2016-07-26

    Ion migration has been postulated as the underlying mechanism responsible for the hysteresis in organolead halide perovskite devices. However, the electronic and ionic transport dynamics and how they impact each other in organolead halide perovskites remain elusive to date. Here we report a systematic investigation of the electronic and ionic transport dynamics in organolead halide perovskite microplate crystals and thin films using temperature-dependent transient response measurements. Our study reveals that thermally activated ionic and electronic conduction coexist in perovskite devices. The extracted activation energies suggest that the electronic transport is easier, but ions migrate harder in microplates than in thin films, demonstrating that the crystalline quality and grain boundaries can fundamentally modify electronic and ionic transport in perovskites. These findings offer valuable insight on the electronic and ionic transport dynamics in organolead halide perovskites, which is critical for optimizing perovskite devices with reduced hysteresis and improved stability and efficiency. PMID:27315525

  15. Beam Transport Devices for the 10 kW IR Free Electron Laser

    SciTech Connect

    Lawrence Dillon-Townes; Michael Bevins; David Kashy; Stephanie Slachtouski; Ronald Lassiter; George Neil; Michelle D. Shinn; Joseph Gubeli; Christopher Behre; David Douglas; David W. Waldman; George Biallas; Lawrence Munk; Christopher Gould

    2005-05-01

    Beam transport components for the 10kW IR Free Electron Laser (FEL) at Thomas Jefferson National Accelerator Facility (Jefferson Lab) were designed to manage (1) electron beam transport and (2) photon beam transport. An overview of the components will be presented in this paper. The electron beam transport components were designed to address RF heating, maintain an accelerator transport vacuum of 1 x 10{sup -8} torr, deliver photons to the optical cavity, and provide 50 kW of beam absorption during the energy recovery process. The components presented include a novel shielded bellows, a novel zero length beam clipper, a one decade differential pumping station with a 7.62 cm (3.0 inch) aperture, and a 50 kW beam dump. The photon beam transport components were designed to address the management of photons delivered by the accelerator transport. The optical cavity manages the photons and optical transport delivers the 10 kW of laser power to experimental labs. The optical cavity component presented is a unique high reflector vessel and the optical transport component presented is a turning mirror cassette.

  16. Electronic absorption spectra of some arylidene pyrazolone derivatives

    NASA Astrophysics Data System (ADS)

    Mahmoud, M. R.; El-Kashef, H. S.; El-Hamide, R. Abd

    The u.v. and visible spectra of some 1 - phenyl - 3 - methyl - 4 - arylidene - 2 - pyrazolin - 5 - one derivatives are investigated in pure and mixed organic solvents as well as in aqueous buffer solutions. Electronic transitions have been identified as either locally excited or predominantly charge transfer states. Moreover, the spectra of the hydroxy derivatives in proton acceptor solvents (DMF, DMSO, ethanol) are characterized by an extra band located at longer wavelengths, which is ascribed to an intermolecular CT transition. This involves an electron transfer from the lone pair of electrons of the oxygen atom of the solvent molecules (ψ ol) to the antibonding orbital of the substituent OH group. The spectral shifts are discussed in terms of medium effects and in relation to molecular structure. The variation of absorbance with pH is utilized for the determination of p K a for the dimethylamino and hydroxy derivatives.

  17. Profile modification and hot electron temperature from resonant absorption at modest intensity

    SciTech Connect

    Albritton, J.R.; Langdon, A.B.

    1980-10-13

    Resonant absorption is investigated in expanding plasmas. The momentum deposition associated with the ejection of hot electrons toward low density via wavebreaking readily exceeds that of the incident laser radiation and results in significant modification of the density profile at critical. New scaling of hot electron temperature with laser and plasma parameters is presented.

  18. Characterization of intestinal absorption of mizoribine mediated by concentrative nucleoside transporters in rats.

    PubMed

    Mori, Nobuhiro; Yokooji, Tomoharu; Kamio, Yoshihiro; Murakami, Teruo

    2008-05-31

    Mizoribine, an imidazole nucleoside, is an inhibitor of purine synthesis and has been used as an orally available immunosuppressive agent in human renal transplantation. In the present study, the intestinal absorption of mizoribine was characterized by examining the contribution of concentrative nucleoside transporters (CNT1, CNT2) in rats. When mizoribine was administered orally in conscious rats, the bioavailability of mizoribine estimated by urinary excretion percentage of unchanged mizoribine was a dose dependent: 53.1+/-6.0% at 5 mg/kg and 24.0+/-5.1% at 20 mg/kg. In in-situ loop studies, the disappearance rate, or absorption rate, of mizoribine from the intestinal lumen was comparable between 1 and 5 mg/kg, but significantly lower at 25 mg/kg. Coadministration of adenosine (a substrate of both CNT1 and CNT2), thymidine (a CNT1 substrate) and inosine (a CNT2 substrate) significantly suppressed the intestinal mizoribine absorption, depending on the nucleoside concentrations coadministered. Gemcitabine (a pyrimidine nucleoside analogue, a CNT1 substrate) and ribavirin (a purine nucleoside analog, a CNT2 substrate) also significantly suppressed the mizoribine intestinal absorption. Bile salts such as sodium cholate and sodium glycocholate (10 mM) also significantly suppressed the intestinal mizoribine absorption, but not ribavirin absorption. Mizoribine is an amphoteric compound, however, the suppression of intestinal absorption by bile salts was not ascribed to the electrostatic interaction or micellar formation between mizoribine and bile salts. In conclusion, the intestinal absorption of mizoribine is mediated by CNT1 and CNT2, and nucleoside-derived drugs such as gemcitabine and ribavirin can suppress the intestinal absorption of mizoribine. Bile salts such as sodium glycocholate were also found to cause interaction with mizoribine. PMID:18371949

  19. Multi-photon absorption in the channeling of electrons in an external field

    NASA Astrophysics Data System (ADS)

    Yaralov, V.

    2016-07-01

    Following the methods developed for atom ionization by alternating electric field the probability of multi-photon absorption of photons of the strong external laser field by channeled electron (extraction of electron from the channel) have been calculated for different strengths of the monochromatic external field. The emission spectra of 54 MeV electron channeled in diamond crystal planes (110) are shown for different values of the resonant laser field of a frequency close to the transition frequency in the channel taking into account multi-photon absorption. It is shown that the multi-photon phenomena give some contribution to the total level width.

  20. Absorption and blood/cellular transport of folate and cobalamin: Pharmacokinetic and physiological considerations.

    PubMed

    Alpers, David H

    2016-07-01

    The systems involving folate and cobalamin have several features in common: 1) their dietary forms require luminal digestion for absorption; 2) intestinal bacteria in the upper intestine synthesize and utilize both vitamins, creating possible competition for the nutrients; 3) there is one major intestinal brush border protein essential for absorption; 4) both are subject to extensive entero-hepatic circulation. Finally, human mutations have confirmed the role of specific transporters and receptors in these processes. There are other features, however, that distinguish the metabolism of these vitamins: 1) upper intestinal bacteria tend to produce folate, while cobalamin (cbl) utilization is more common; 2) cbl absorption requires a luminal binding protein, but folate does not; 3) folate absorption can occur throughout the small bowel, but the cbl receptor, cubilin, is restricted to the distal half of the small bowel; 4) movement into cells uses transporters, exchangers, and symporters, whereas cbl is transferred by receptor-mediated endocytosis; 5) folate is carried in the blood mostly in red blood cells, whereas cbl is carried on specific binding-proteins; 6) folate can enter cells via multiple systems, but cbl uptake into all tissues use the transcobalamin receptor (TC-R), with the asialoglycoprotein receptor (ASGP-R) present in hepatocytes for uptake of haptocorrin-cbl (HC-cbl) complexes. In summary, the systems for absorption and distribution of folate and cobalamin are complex. These complexities help to explain the variable clinical responses after oral administration of the vitamins, especially when provided as supplements. PMID:26586110

  1. Loss of anion transport without increased sodium absorption characterizes newborn porcine cystic fibrosis airway epithelia.

    PubMed

    Chen, Jeng-Haur; Stoltz, David A; Karp, Philip H; Ernst, Sarah E; Pezzulo, Alejandro A; Moninger, Thomas O; Rector, Michael V; Reznikov, Leah R; Launspach, Janice L; Chaloner, Kathryn; Zabner, Joseph; Welsh, Michael J

    2010-12-10

    Defective transepithelial electrolyte transport is thought to initiate cystic fibrosis (CF) lung disease. Yet, how loss of CFTR affects electrolyte transport remains uncertain. CFTR⁻(/)⁻ pigs spontaneously develop lung disease resembling human CF. At birth, their airways exhibit a bacterial host defense defect, but are not inflamed. Therefore, we studied ion transport in newborn nasal and tracheal/bronchial epithelia in tissues, cultures, and in vivo. CFTR⁻(/)⁻ epithelia showed markedly reduced Cl⁻ and HCO₃⁻ transport. However, in contrast to a widely held view, lack of CFTR did not increase transepithelial Na(+) or liquid absorption or reduce periciliary liquid depth. Like human CF, CFTR⁻(/)⁻ pigs showed increased amiloride-sensitive voltage and current, but lack of apical Cl⁻ conductance caused the change, not increased Na(+) transport. These results indicate that CFTR provides the predominant transcellular pathway for Cl⁻ and HCO₃⁻ in porcine airway epithelia, and reduced anion permeability may initiate CF airway disease. PMID:21145458

  2. Synergetic second and third harmonic electron cyclotron power absorption in TCV: experiment and Fokker-Planck modeling

    NASA Astrophysics Data System (ADS)

    Gnesin, Silvano; Goodman, Timothy; Coda, Stefano; Decker, Joan; Peysson, Yves

    2010-11-01

    The TCV tokamak is equipped with nine electron cyclotron (EC) wave gyrotron/launcher systems: six 0.5 MW in the 2nd harmonic X-mode (X2) and three 0.5 MW in the 3rd harmonic X-mode (X3). TCV experiments have been expressly devised to study the X2/X3 interplay, especially through the dynamics and transport properties of the suprathermal electron population generated primarily by X2 and its influence on the X3 wave absorption. Fokker Planck modeling of X2/X3 TCV experiments with the quasilinear fully relativistic LUKE code, coupled with the C3PO ray-tracing module and the R5X2 bremsstrahlung module, is presented here. Two series of experiments are discussed: 1) X2/X3 synergy when both X2 (82.7 GHz) and X3 (118 GHz) waves are injected into the plasma and 2) X2/X3 synergetic absorption at the same frequency (82.7 GHz). The role of suprathermal electron transport has been investigated by comparing the bremsstrahlung emission measured by a hard X-ray camera with the simulated signal.

  3. Breaking the barriers of all-polymer solar cells: Solving electron transporter and morphology problems

    NASA Astrophysics Data System (ADS)

    Gavvalapalli, Nagarjuna

    All-polymer solar cells (APSC) are a class of organic solar cells in which hole and electron transporting phases are made of conjugated polymers. Unlike polymer/fullerene solar cell, photoactive material of APSC can be designed to have hole and electron transporting polymers with complementary absorption range and proper frontier energy level offset. However, the highest reported PCE of APSC is 5 times less than that of polymer/fullerene solar cell. The low PCE of APSC is mainly due to: i) low charge separation efficiency; and ii) lack of optimal morphology to facilitate charge transfer and transport; and iii) lack of control over the exciton and charge transport in each phase. My research work is focused towards addressing these issues. The charge separation efficiency of APSC can be enhanced by designing novel electron transporting polymers with: i) broad absorption range; ii) high electron mobility; and iii) high dielectric constant. In addition to with the above parameters chemical and electronic structure of the repeating unit of conjugated polymer also plays a role in charge separation efficiency. So far only three classes of electron transporting polymers, CN substituted PPV, 2,1,3-benzothiadiazole derived polymers and rylene diimide derived polymers, are used in APSC. Thus to enhance the charge separation efficiency new classes of electron transporting polymers with the above characteristics need to be synthesized. I have developed a new straightforward synthetic strategy to rapidly generate new classes of electron transporting polymers with different chemical and electronic structure, broad absorption range, and high electron mobility from readily available electron deficient monomers. In APSCs due to low entropy of mixing, polymers tend to micro-phase segregate rather than forming the more useful nano-phase segregation. Optimizing the polymer blend morphology to obtain nano-phase segregation is specific to the system under study, time consuming, and not

  4. Theoretical analysis of electronic absorption spectra of vitamin B12 models

    NASA Astrophysics Data System (ADS)

    Andruniow, Tadeusz; Kozlowski, Pawel M.; Zgierski, Marek Z.

    2001-10-01

    Time-dependent density-functional theory (TD-DFT) is applied to analyze the electronic absorption spectra of vitamin B12. To accomplish this two model systems were considered: CN-[CoIII-corrin]-CN (dicyanocobinamide, DCC) and imidazole-[CoIII-corrin]-CN (cyanocobalamin, ImCC). For both models 30 lowest excited states were calculated together with transition dipole moments. When the results of TD-DFT calculations were directly compared with experiment it was found that the theoretical values systematically overestimate experimental data by approximately 0.5 eV. The uniform adjustment of the calculated transition energies allowed detailed analysis of electronic absorption spectra of vitamin B12 models. All absorption bands in spectral range 2.0-5.0 eV were readily assigned. In particular, TD-DFT calculations were able to explain the origin of the shift of the lowest absorption band caused by replacement of the-CN axial ligand by imidazole.

  5. Coronal and interplanetary transport of solar energetic protons and electrons

    NASA Astrophysics Data System (ADS)

    Wibberenz, G.; Kunow, H.; Iwers, B.; Kecskemety, K.; Somogyi, A.

    1989-09-01

    Data from the Helios 1 and 2 and the Prognoz 6 spacecraft are used to separate coronal and interplanetary propagation effects for two solar particle events on December 27, 1977 and January 1, 1978. The results confirm the concept of two different coronal propagation regimes. In both regimes electrons are transported more efficiently than protons. Possible explanations for the fast transport of electrons and the different behavior of electrons and protons are considered.

  6. Streamer-induced transport in electron temperature gradient turbulence

    SciTech Connect

    Hauff, T.; Jenko, F.

    2009-10-15

    The question if and how streamers (i.e., radially elongated vortices) can lead to an enhancement of the electron heat transport in electron temperature gradient turbulence is addressed. To this aim, the electrons are treated as passive tracers, and their decorrelation mechanisms with respect to the advecting electrostatic potential are studied. A substantial transport enhancement is found in a wide region of parameter space.

  7. Involvement of intestinal uptake transporters in the absorption of azithromycin and clarithromycin in the rat.

    PubMed

    Garver, Eric; Hugger, Erin D; Shearn, Shawn P; Rao, Anuradha; Dawson, Paul A; Davis, Charles B; Han, Chao

    2008-12-01

    Macrolide antibiotics azithromycin (AZI) and clarithromycin (CLARI) are large molecular weight compounds and are substrates for apically polarized efflux transporters such as P-glycoprotein, which can potentially restrict intestinal absorption. However, despite these undesired physicochemical and biopharmaceutical properties, AZI and CLARI exhibit moderate to excellent p.o. bioavailability in preclinical species and humans. Intestinal uptake transporters, such as organic anion transporting polypeptides (OATPs), can facilitate the uptake of drugs that are substrates and hence increase p.o. absorption. The present study was designed to determine whether the intestinal Oatps are involved in absorption of these macrolides. AZI or CLARI was dosed p.o. to Sprague-Dawley rats after p.o. administration with vehicle or rifamycin SV (RIF), an OATP inhibitor. The p.o. exposures of AZI and CLARI were reduced 65 and 45%, respectively, when coadministered with an optimized RIF regimen. The p.o. RIF had no affect on the total blood clearance of these macrolides and most likely did not cause induction of metabolizing enzymes and/or transporters. Therefore, the results suggest that inhibition of an RIF-sensitive uptake transporter such as Oatp along the rat gastrointestinal tract was responsible for reduced p.o. exposure of AZI and CLARI. In addition, AZI and CLARI caused inhibition of taurocholate uptake in rat Oatp1a5-transfected Madin-Darby canine kidney cell monolayers. The in vitro and in vivo results suggest that the intestinal Oatps are involved in the p.o. absorption of AZI and CLARI in the rat. PMID:18755851

  8. Amino acid absorption and homeostasis in mice lacking the intestinal peptide transporter PEPT1.

    PubMed

    Nässl, Anna-Maria; Rubio-Aliaga, Isabel; Fenselau, Henning; Marth, Mena Katharina; Kottra, Gabor; Daniel, Hannelore

    2011-07-01

    The intestinal peptide transporter PEPT1 mediates the uptake of di- and tripeptides derived from dietary protein breakdown into epithelial cells. Whereas the transporter appears to be essential to compensate for the reduced amino acid delivery in patients with mutations in amino acid transporter genes, such as in cystinuria or Hartnup disease, its physiological role in overall amino acid absorption is still not known. To assess the quantitative importance of PEPT1 in overall amino acid absorption and metabolism, PEPT1-deficient mice were studied by using brush border membrane vesicles, everted gut sacs, and Ussing chambers, as well as by transcriptome and proteome analysis of intestinal tissue samples. Neither gene expression nor proteome profiling nor functional analysis revealed evidence for any compensatory changes in the levels and/or function of transporters for free amino acids in the intestine. However, most plasma amino acid levels were increased in Pept1(-/-) compared with Pept1(+/+) animals, suggesting that amino acid handling is altered. Plasma appearance rates of (15)N-labeled amino acids determined after intragastric administration of a low dose of protein remained unchanged, whereas administration of a large protein load via gavage revealed marked differences in plasma appearance of selected amino acids. PEPT1 seems, therefore, important for overall amino acid absorption only after high dietary protein intake when amino acid transport processes are saturated and PEPT1 can provide additional absorption capacity. Since renal amino acid excretion remained unchanged, elevated basal concentrations of plasma amino acids in PEPT1-deficient animals seem to arise mainly from alterations in hepatic amino acid metabolism. PMID:21350187

  9. A Guide to Electronic Multipoles in Photon Scattering and Absorption

    NASA Astrophysics Data System (ADS)

    Lovesey, Stephen William; Balcar, Ewald

    2013-02-01

    The practice of replacing matrix elements in atomic calculations by those of convenient operators with strong physical appeal has a long history, and in condensed matter physics it is perhaps best known through use of operator equivalents in electron resonance by Elliott and Stevens. Likewise, electronic multipoles, created with irreducible spherical-tensors, to represent charge-like and magnetic-like quantities are widespread in modern physics. Examples in recent headlines include a magnetic charge (a monopole), an anapole (a dipole) and a triakontadipole (a magnetic-like atomic multipole of rank 5). In this communication, we aim to guide the reader through use of atomic, spherical multipoles in photon scattering, and resonant Bragg diffraction and dichroic signals in particular. Applications to copper oxide CuO and neptunium dioxide (NpO2) are described. In keeping with it being a simple guide, there is sparse use in the communication of algebra and expressions are gathered from the published literature and not derived, even when central to the exposition. An exception is a thorough grounding, contained in an Appendix, for an appropriate version of the photon scattering length based on quantum electrodynamics. A theme of the guide is application of symmetry in scattering, in particular constraints imposed on results by symmetry in crystals. To this end, a second Appendix catalogues constraints on multipoles imposed by symmetry in crystal point-groups.

  10. Unified theory of electron-phonon renormalization and phonon-assisted optical absorption

    NASA Astrophysics Data System (ADS)

    Patrick, Christopher E.; Giustino, Feliciano

    2014-09-01

    We present a theory of electronic excitation energies and optical absorption spectra which incorporates energy-level renormalization and phonon-assisted optical absorption within a unified framework. Using time-independent perturbation theory we show how the standard approaches for studying vibronic effects in molecules and those for addressing electron-phonon interactions in solids correspond to slightly different choices for the non-interacting Hamiltonian. Our present approach naturally leads to the Allen-Heine theory of temperature-dependent energy levels, the Franck-Condon principle, the Herzberg-Teller effect and to phonon-assisted optical absorption in indirect band gap materials. In addition, our theory predicts sub-gap phonon-assisted optical absorption in direct gap materials, as well as an exponential edge which we tentatively assign to the Urbach tail. We also consider a semiclassical approach to the calculation of optical absorption spectra which simultaneously captures energy-level renormalization and phonon-assisted transitions and is especially suited to first-principles electronic structure calculations. We demonstrate this approach by calculating the phonon-assisted optical absorption spectrum of bulk silicon.

  11. Electron transient transport in CdTe polycrystalline films

    NASA Astrophysics Data System (ADS)

    Ramírez-Bon, R.; Sánchez-Sinencio, F.; González de la Cruz, G.; Zelaya, O.

    1991-11-01

    Electron transient currents between coplanar electrodes have been measured in intrinsic polycrystalline films of CdTe, by means of the time of flight technique. The experimental results: electron transient current vs time, transit time vs voltage and the temperature dependence of the electron drift mobility, show features characteristics of dispersive electrical transport similar to that observed in disordered solids.

  12. Transporter-targeted cholic acid-cytarabine conjugates for improved oral absorption.

    PubMed

    Zhang, Dong; Li, Dongpo; Shang, Lei; He, Zhonggui; Sun, Jin

    2016-09-10

    Cytarabine has a poor oral absorption due to its rapid deamination and poor membrane permeability. Bile acid transporters are highly expressed both in enterocytes and hepatocytes and to increase the oral bioavailability and investigate the potential application of cytarabine for liver cancers, a transporter- recognizing prodrug strategy was applied to design and synthesize four conjugates of cytarabine with cholic acid (CA), chenodeoxycholic acid (CDCA), hyodeoxycholic acid (HDCA) and ursodeoxycholic acid (UDCA). The anticancer activities against HepG2 cells were evaluated by MTT assay and the role of bile acid transporters during cellular transport was investigated in a competitive inhibition experiment. The in vitro and in vivo metabolic stabilities of these conjugates were studied in rat plasma and liver homogenates. Finally, an oral bioavailability study was conducted in rats. All the cholic acid-cytarabine conjugates (40μM) showed potent antiproliferative activities (up to 70%) against HepG2 cells after incubation for 48h. The addition of bile acids could markedly reduce the antitumor activities of these conjugates. The N(4)-ursodeoxycholic acid conjugate of cytarabine (compound 5) exhibited optimal stability (t1/2=90min) in vitro and a 3.9-fold prolonged half-life of cytarabine in vivo. More importantly, compound 5 increased the oral bioavailability 2-fold compared with cytarabine. The results of the present study suggest that the prodrug strategy based on the bile acid transporters is suitable for improving the oral absorption and the clinical application of cytarabine. PMID:27377011

  13. Terahertz quantum transport in semiconductor nanostructures with the UCSB free electron lasers

    SciTech Connect

    Allen, S.J.

    1995-12-31

    Quantum transport in semiconductor nanostructures takes on new dimensions in the presence of intense terahertz electric fields. Terahertz frequencies lift us into the regime where the scattering and relaxation is not so important and strong terahertz electric fields provided by the UCSB FEL`s explore non-linear dynamics far from the perturbative limit. New quantum transport channels that are assisted by the absorption or emission of a photon appear in current voltage characteristics. We will describe some of these experiments, the new phenomena they expose and the potential impact on future terahertz semiconductor electronics.

  14. Relativistic Electron Transport Through Carbon Foils

    NASA Astrophysics Data System (ADS)

    Seliger, M.; Takasi, K.; Reinhold, C. O.; Takabayashi, Y.; Ito, T.; Komaki, K.; Azuma, T.; Yamazaki, Y.; Yamazaki, Y.

    We present a theoretical study of convoy electron emission resulting from transmission of relativistic 390 MeV/amu Ar17+ ions through carbon foils of various thicknesses. Our approach is based on a Langevin equation describing the random walk of the electron initially bound to the argon nucleus and later in the continuum. The calculated spectra of ejected electrons in the forward direction exhibit clear signatures of multiple scattering and are found to be in good agreement with recent experimental data.

  15. Terahertz electromodulation spectroscopy of electron transport in GaN

    SciTech Connect

    Engelbrecht, S. G.; Arend, T. R.; Kersting, R.; Zhu, T.; Kappers, M. J.

    2015-03-02

    Time-resolved terahertz (THz) electromodulation spectroscopy is applied to investigate the high-frequency transport of electrons in gallium nitride at different doping concentrations and densities of threading dislocations. At THz frequencies, all structures reveal Drude transport. The analysis of the spectral response provides the fundamental transport properties, such as the electron scattering time and the electrons' conductivity effective mass. We observe the expected impact of ionized-impurity scattering and that scattering at threading dislocations only marginally affects the high-frequency mobility.

  16. Spin transport in tilted electron vortex beams

    NASA Astrophysics Data System (ADS)

    Basu, Banasri; Chowdhury, Debashree

    2014-12-01

    In this paper we have enlightened the spin related issues of tilted Electron vortex beams. We have shown that in the skyrmionic model of electron we can have the spin Hall current considering the tilted type of electron vortex beam. We have considered the monopole charge of the tilted vortex as time dependent and through the time variation of the monopole charge we can explain the spin Hall effect of electron vortex beams. Besides, with an external magnetic field we can have a spin filter configuration.

  17. Relativistic effects on cyclotron wave absorption by an energetic electron tail in the PLT tokamak

    SciTech Connect

    Mazzucato, E.; Efthimion, P.; Fidone, I.

    1984-07-01

    Electron cyclotron wave absorption by mildly relativistic electrons in the low density regime of the PLT tokamak is investigated. Appreciable wave damping is found for vertical propagation at frequencies of 50, 60, and 70 GHz when the spatially constant cyclotron frequency is 89 GHz. The perpendicular temperature T/sub perpendicular/(v/sub parallel/) of the fast tail is also measured from emission of radiation in the same direction. The results obtained are in satisfactory agreement with the theory of wave emission and absorption.

  18. Polarization and absorption effects in electron-helium scattering at 30--400 eV

    SciTech Connect

    Thirumalai, D.; Truhlar, D.G.; Brandt, M.A.; Eades, R.A.; Dixon, D.A.

    1982-06-01

    We report several calculations of the differential, integral, and momentum-transfer cross sections for elastic scattering, and of the absorption cross sections (for the sum of all electronically inelastic and ionization processes) for electron-He collisions at 30--400 eV. We consider two basically different approaches to include the effect of absorption, i.e., loss of flux from the initial channel. The first is the matrix effective potential (MEP) based on a variational calculation of the polarization potential; this models absorption by including a pseudochannel whose properties are based on a variational adiabatic polarization potential. This method predicts both the absorption and elastic cross sections. The second method involves phenomenological absorption (A) potentials, calibrated against experimental absorption cross sections. These potentials, when combined with static (S), exchange (E), and real polarization (P) potentials form an SEPA optical model potential that is used to predict the elastic cross sections. The MEP model based on the variational polarization potential predicts the absorption cross sections with an average absolute error of 28% at 30 and 50 eV and 5% at 100--400 eV. It predicts the elastic integral cross sections with an average absolute error of 8% over the whole energy range. The SEPA models, including a nonadiabatic polarization potential, predict the elastic integral cross sections with average absolute errors of 12 or 6%, depending on the shape function (i.e., r dependence) of the absorption potential. The adiabatic approximation for polarization is less accurate than the nonadiabatic one, even when absorption effects are included. Five new calculations of the differential cross sections at each of five impact energies are compared to experimental results in detail.

  19. Polarization and absorption effects in electron-helium scattering at 30-400 eV

    NASA Astrophysics Data System (ADS)

    Thirumalai, Devarajan; Truhlar, Donald G.; Brandt, Maynard A.; Eades, Robert A.; Dixon, David A.

    1982-06-01

    We report several calculations of the differential, integral, and momentum-transfer cross sections for elastic scattering, and of the absorption cross sections (for the sum of all electronically inelastic and ionization processes) for electron-He collisions at 30-400 eV. We consider two basically different approaches to include the effect of absorption, i.e., loss of flux from the initial channel. The first is the matrix effective potential (MEP) based on a variational calculation of the polarization potential; this models absorption by including a pseudochannel whose properties are based on a variational adiabatic polarization potential. This method predicts both the absorption and elastic cross sections. The second method involves phenomenological absorption (A) potentials, calibrated against experimental absorption cross sections. These potentials, when combined with static (S), exchange (E), and real polarization (P) potentials form an SEPA optical model potential that is used to predict the elastic cross sections. The MEP model based on the variational polarization potential predicts the absorption cross sections with an average absolute error of 28% at 30 and 50 eV, and 5% at 100-400 eV. It predicts the elastic integral cross sections with an average absolute error of 8% over the whole energy range. The SEPA models, including a nonadiabatic polarization potential, predict the elastic integral cross sections with average absolute errors of 12 or 6%, depending on the shape function (i.e., r dependence) of the absorption potential. The adiabatic approximation for polarization is less accurate than the nonadiabatic one, even when absorption effects are included. Five new calculations of the differential cross sections at each of five impact energies are compared to experimental results in detail.

  20. Absorption of Vitamin A and Carotenoids by the Enterocyte: Focus on Transport Proteins

    PubMed Central

    Reboul, Emmanuelle

    2013-01-01

    Vitamin A deficiency is a public health problem in most developing countries, especially in children and pregnant women. It is thus a priority in health policy to improve preformed vitamin A and/or provitamin A carotenoid status in these individuals. A more accurate understanding of the molecular mechanisms of intestinal vitamin A absorption is a key step in this direction. It was long thought that β-carotene (the main provitamin A carotenoid in human diet), and thus all carotenoids, were absorbed by a passive diffusion process, and that preformed vitamin A (retinol) absorption occurred via an unidentified energy-dependent transporter. The discovery of proteins able to facilitate carotenoid uptake and secretion by the enterocyte during the past decade has challenged established assumptions, and the elucidation of the mechanisms of retinol intestinal absorption is in progress. After an overview of vitamin A and carotenoid fate during gastro-duodenal digestion, our focus will be directed to the putative or identified proteins participating in the intestinal membrane and cellular transport of vitamin A and carotenoids across the enterocyte (i.e., Scavenger Receptors or Cellular Retinol Binding Proteins, among others). Further progress in the identification of the proteins involved in intestinal transport of vitamin A and carotenoids across the enterocyte is of major importance for optimizing their bioavailability. PMID:24036530

  1. Non-nuclear electron transport channels in hollow molecules

    NASA Astrophysics Data System (ADS)

    Zhao, Jin; Petek, Hrvoje

    2014-08-01

    Electron transport in inorganic semiconductors and metals occurs through delocalized bands formed by overlapping electron orbitals. Strong correlation of electronic wave functions with the ionic cores couples the electron and lattice motions, leading to efficient interaction and scattering that degrades coherent charge transport. By contrast, unoccupied electronic states at energies near the vacuum level with diffuse molecular orbitals may form nearly-free-electron bands with density maxima in non-nuclear interstitial voids, which are subject to weaker electron-phonon interaction. The position of such bands typically above the frontier orbitals, however, renders them unstable with respect to electronic interband relaxation and therefore unsuitable for charge transport. Through electronic-structure calculations, we engineer stable, non-nuclear, nearly-free-electron conduction channels in low-dimensional molecular materials by tailoring their electrostatic and polarization potentials. We propose quantum structures of graphane-derived Janus molecular sheets with spatially isolated conducting and insulating regions that potentially exhibit emergent electronic properties, as a paradigm for molecular-scale non-nuclear charge conductors; we also describe tuning of their electronic properties by application of external fields and calculate their electron-acoustic-phonon interaction.

  2. Theoretical calculations on the electron absorption spectra of selected Polycyclic Aromatic Hydrocarbons (PAH) and derivatives

    NASA Technical Reports Server (NTRS)

    Du, Ping

    1993-01-01

    As a theoretical component of the joint effort with the laboratory of Dr. Lou Allamandola to search for potential candidates for interstellar organic carbon compound that are responsible for the visible diffuse interstellar absorption bands (DIB's), quantum mechanical calculations were performed on the electron absorption spectra of selected polycyclic aromatic hydrocarbons (PAH) and derivatives. In the completed project, 15 different species of naphthalene, its hydrogen abstraction and addition derivatives, and corresponding cations and anions were studied. Using semiempirical quantum mechanical method INDO/S, the ground electronic state of each species was evaluated with restricted Hartree-Fock scheme and limited configuration interaction. The lowest energy spin state for each species was used for electron absorption calculations. Results indicate that these calculations are accurate enough to reproduce the spectra of naphthalene cation and anion observed in neon matrix. The spectral pattern of the hydrogen abstraction and addition derivatives predicted based on these results indicate that the electron configuration of the pi orbitals of these species is the dominant determinant. A combined list of 19 absorptions calculated from 4500 A to 10,400 A were compiled and suggested as potential candidates that are relevant for the DIB's absorptions. Continued studies on pyrene and derivatives revealed the ground state symmetries and multiplicities of its neutral, anionic, and cationic species. Spectral calculations show that the cation (B(sub 3g)-2) and the anion (A(sub u)-2) are more likely to have low energy absorptions in the regions between 10 kK and 20 kK, similar to naphthalene. These absorptions, together with those to be determined from the hydrogen abstraction and addition derivatives of pyrene, can be used to provide additional candidates and suggest experimental work in the search for interstellar compounds that are responsible for DIB's.

  3. Photosynthetic, respiratory and extracellular electron transport pathways in cyanobacteria.

    PubMed

    Lea-Smith, David J; Bombelli, Paolo; Vasudevan, Ravendran; Howe, Christopher J

    2016-03-01

    Cyanobacteria have evolved elaborate electron transport pathways to carry out photosynthesis and respiration, and to dissipate excess energy in order to limit cellular damage. Our understanding of the complexity of these systems and their role in allowing cyanobacteria to cope with varying environmental conditions is rapidly improving, but many questions remain. We summarize current knowledge of cyanobacterial electron transport pathways, including the possible roles of alternative pathways in photoprotection. We describe extracellular electron transport, which is as yet poorly understood. Biological photovoltaic devices, which measure electron output from cells, and which have been proposed as possible means of renewable energy generation, may be valuable tools in understanding cyanobacterial electron transfer pathways, and enhanced understanding of electron transfer may allow improvements in the efficiency of power output. This article is part of a Special Issue entitled Organization and dynamics of bioenergetic systems in bacteria, edited by Conrad Mullineaux. PMID:26498190

  4. Angular dependent transport of auroral electrons in the upper atmosphere

    NASA Technical Reports Server (NTRS)

    Lummerzheim, D.; Rees, M. H.; Anderson, H. R.

    1989-01-01

    The transport of auroral electrons through the upper atmosphere is analyzed. The transport equation is solved using a discrete-ordinate method, including elastic and inelastic scattering of electrons (resulting in changes of pitch angle) and degradation in energy as the electrons penetrate into the atmosphere. The transport equation is solved numerically for the electron intensity as a function of altitude, pitch angle, and energy. In situ measurements of the pitch angle and energy distribution of precipitating electrons over an auroral arc provide boundary conditions for the calculation. Model calculations were carried out with various different phase functions for elastic and inelastic collisions to attempt changing the angular scattering, but the observed pitch angle distributions remain unexplained. It is suggested that mechanisms other than collisional scattering influence the angular distribution of auroral electrons at or below 300 km altitude in the low-energy domain.

  5. Ballistic electron transport in wrinkled superlattices

    NASA Astrophysics Data System (ADS)

    Mitran, T. L.; Nemnes, G. A.; Ion, L.; Dragoman, Daniela

    2016-07-01

    Inspired by the problem of elastic wave scattering on wrinkled interfaces, we studied the scattering of ballistic electrons on a wrinkled potential energy region. The electron transmission coefficient depends on both wrinkle amplitude and periodicity, having different behaviors for positive and negative scattering potential energies. For scattering on potential barriers, minibands appear in the electron transmission, as in superlattices, whereas for scattering on periodic potential wells the transmission coefficient has a more complex form. Besides suggesting that tuning of electron transmission is possible by modifying the scattering potential via voltages on wrinkled gate electrodes, our results emphasize the analogies between ballistic electrons and elastic waves even in scattering problems on non-typical configurations.

  6. Sources of hot electrons in laser-plasma interaction with emphasis on Raman and turbulence absorption

    SciTech Connect

    Estabrook, K.; Kruer, W.L.; Phillion, D.W.; Turner, R.E.; Campbell, E.M.

    1982-04-06

    Heating targets with high power lasers results in a sizable fraction of the absorbed energy going into electrons of temperature much greater than thermal which can pre-heat the pellet core and accelerate fast ion blowoff which results in poor momentum transfer and hence poor compression efficiency. The present emphasis is to build lasers of higher frequency, ..omega../sub 0/, which at the same W/cm/sup 2/ results in more absorption into cooler electrons. Two physical reasons are that the laser can propagate to a higher electron density, n, infinity..omega../sub 0//sup 2/ resulting in more collisional inverse bremsstrahlung absorption proportional to n, and because the hot temperatures from some plasma absorption processes increase as the oscillatory velocity of an electron in the laser electric field v/sub 0//c = eE/(m/sub e/..omega../sub 0/). The heated electron temperatures from other plasma processes (Raman for example approx.(m/sub e//2)v/sup 2//sub phase/ and the higher laser frequency helps by increasing the competing collisional absorption and decreasing the Raman gain.

  7. Ab initio calculation of the electronic absorption spectrum of liquid water

    NASA Astrophysics Data System (ADS)

    Martiniano, Hugo F. M. C.; Galamba, Nuno; Cabral, Benedito J. Costa

    2014-04-01

    The electronic absorption spectrum of liquid water was investigated by coupling a one-body energy decomposition scheme to configurations generated by classical and Born-Oppenheimer Molecular Dynamics (BOMD). A Frenkel exciton Hamiltonian formalism was adopted and the excitation energies in the liquid phase were calculated with the equation of motion coupled cluster with single and double excitations method. Molecular dynamics configurations were generated by different approaches. Classical MD were carried out with the TIP4P-Ew and AMOEBA force fields. The BLYP and BLYP-D3 exchange-correlation functionals were used in BOMD. Theoretical and experimental results for the electronic absorption spectrum of liquid water are in good agreement. Emphasis is placed on the relationship between the structure of liquid water predicted by the different models and the electronic absorption spectrum. The theoretical gas to liquid phase blue-shift of the peak positions of the electronic absorption spectrum is in good agreement with experiment. The overall shift is determined by a competition between the O-H stretching of the water monomer in liquid water that leads to a red-shift and polarization effects that induce a blue-shift. The results illustrate the importance of coupling many-body energy decomposition schemes to molecular dynamics configurations to carry out ab initio calculations of the electronic properties in liquid phase.

  8. Ab initio calculation of the electronic absorption spectrum of liquid water

    SciTech Connect

    Martiniano, Hugo F. M. C.; Galamba, Nuno; Cabral, Benedito J. Costa

    2014-04-28

    The electronic absorption spectrum of liquid water was investigated by coupling a one-body energy decomposition scheme to configurations generated by classical and Born-Oppenheimer Molecular Dynamics (BOMD). A Frenkel exciton Hamiltonian formalism was adopted and the excitation energies in the liquid phase were calculated with the equation of motion coupled cluster with single and double excitations method. Molecular dynamics configurations were generated by different approaches. Classical MD were carried out with the TIP4P-Ew and AMOEBA force fields. The BLYP and BLYP-D3 exchange-correlation functionals were used in BOMD. Theoretical and experimental results for the electronic absorption spectrum of liquid water are in good agreement. Emphasis is placed on the relationship between the structure of liquid water predicted by the different models and the electronic absorption spectrum. The theoretical gas to liquid phase blue-shift of the peak positions of the electronic absorption spectrum is in good agreement with experiment. The overall shift is determined by a competition between the O–H stretching of the water monomer in liquid water that leads to a red-shift and polarization effects that induce a blue-shift. The results illustrate the importance of coupling many-body energy decomposition schemes to molecular dynamics configurations to carry out ab initio calculations of the electronic properties in liquid phase.

  9. Functional studies of Drosophila zinc transporters reveal the mechanism for dietary zinc absorption and regulation

    PubMed Central

    2013-01-01

    Background Zinc is key to the function of many proteins, but the process of dietary zinc absorption is not well clarified. Current knowledge about dietary zinc absorption is fragmented, and mostly derives from incomplete mammalian studies. To gain a comprehensive picture of this process, we systematically characterized all zinc transporters (that is, the Zip and ZnT family members) for their possible roles in dietary zinc absorption in a genetically amenable model organism, Drosophila melanogaster. Results A set of plasma membrane-resident zinc transporters was identified to be responsible for absorbing zinc from the lumen into the enterocyte and the subsequent exit of zinc to the circulation. dZip1 and dZip2, two functionally overlapping zinc importers, are responsible for absorbing zinc from the lumen into the enterocyte. Exit of zinc to the circulation is mediated through another two functionally overlapping zinc exporters, dZnT1, and its homolog CG5130 (dZnT77C). Somewhat surprisingly, it appears that the array of intracellular ZnT proteins, including the Golgi-resident dZnT7, is not directly involved in dietary zinc absorption. By modulating zinc status in different parts of the body, we found that regulation of dietary zinc absorption, in contrast to that of iron, is unresponsive to bodily needs or zinc status outside the gut. The zinc transporters that are involved in dietary zinc absorption, including the importers dZip1 and dZip2, and the exporter dZnT1, are respectively regulated at the RNA and protein levels by zinc in the enterocyte. Conclusions Our study using the model organism Drosophila thus starts to reveal a comprehensive sketch of dietary zinc absorption and its regulatory control, a process that is still incompletely understood in mammalian organisms. The knowledge gained will act as a reference for future mammalian studies, and also enable an appreciation of this important process from an evolutionary perspective. PMID:24063361

  10. Fast electron generation and transport in a turbulent, magnetized plasma

    SciTech Connect

    Stoneking, W.R.

    1994-05-01

    The nature of fast electron generation and transport in the Madison Symmetric Torus (MST) reversed field pinch (RFP) is investigated using two electron energy analyzer (EEA) probes and a thermocouple calorimeter. The parallel velocity distribution of the fast electron population is well fit by a drifted Maxwellian distribution with temperature of about 100 eV and drift velocity of about 2 {times} 10{sup 6} m/s. Cross-calibration of the EEA with the calorimeter provides a measurement of the fast electron perpendicular temperature of 30 eV, much lower than the parallel temperature, and is evidence that the kinetic dynamo mechanism (KDT) is not operative in MST. The fast electron current is found to match to the parallel current at the edge, and the fast electron density is about 4 {times} 10{sup 11} cm{sup {minus}3} independent of the ratio of the applied toroidal electric field to the critical electric field for runaways. First time measurements of magnetic fluctuation induced particle transport are reported. By correlating electron current fluctuations with radial magnetic fluctuations the transported flux of electrons is found to be negligible outside r/a{approximately}0.9, but rises the level of the expected total particle losses inside r/a{approximately}0.85. A comparison of the measured diffusion coefficient is made with the ausilinear stochastic diffusion coefficient. Evidence exists that the reduction of the transport is due to the presence of a radial ambipolar electric field of magnitude 500 V/m, that acts to equilibrate the ion and electron transport rates. The convective energy transport associated with the measured particle transport is large enough to account for the observed magnetic fluctuation induced energy transport in MST.

  11. Effect of absorption of D-glucose and water on paracellular transport in rat duodenum-jejunum.

    PubMed

    O'Rourke, M; Shi, X; Gisolfi, C; Schedl, H

    1995-03-01

    Paracellular transport is thought to be a major absorptive pathway for small nutrient molecules. The authors used in vivo in situ perfusion of rat duodenum-proximal jejunum to examine paracellular transport using lactulose as a probe. They perfused solutions with a constant lactulose concentration but varied initial D-glucose concentration (range 12-176 mM) to open paracellular pathways and to increase water absorption, thereby optimizing potential for paracellular transport of lactulose and other solutes in its molecular weight range. All solutions contained sodium chloride to approach isotonicity. Water absorption was measured as the difference in weight of solution perfused and sample collected. Absorption of D-glucose increased with mean luminal D-glucose concentration, and water absorption more than doubled (from 0.12 +/- 0.03 to 0.26 +/- 0.05 mL/min per g dry wt of segment) as mean luminal glucose concentration was increased from 10 to 80 mM. Lactulose absorption was at the threshold of detection and did not correlate with D-glucose or water absorption. Expressed as percent per segment, D-glucose absorption ranged from 29-50%, and the lactulose absorption rate was 4-5%. The fraction of D-glucose absorption that could be attributed to lactulose absorptive pathways was 12% at the highest rate of water absorption. In conclusion, based on lactulose as a probe, under conditions of opening tight junctions by D-glucose, the paracellular component of D-glucose absorption was of the order of 1/10 of total D-glucose absorption (ie, not a major absorptive pathway. PMID:7879819

  12. Non-nuclear Electron Transport Channels in Hollow Molecules

    SciTech Connect

    Zhao, Jin; Petek, Hrvoje

    2014-08-15

    Electron transport in inorganic semiconductors and metals occurs through delocalized bands formed by overlapping electron orbitals. Strong correlation of electronic wave functions with the ionic cores couples the electron and lattice motions, leading to efficient interaction and scattering that degrades coherent charge transport. By contrast, unoccupied electronic states at energies near the vacuum level with diffuse molecular orbitals may form nearly-free-electron bands with density maxima in non-nuclear interstitial voids, which are subject to weaker electron-phonon interaction. The position of such bands typically above the frontier orbitals, however, renders them unstable with respect to electronic interband relaxation and therefore unsuitable for charge transport. Through electronic-structure calculations, we engineer stable, non-nuclear, nearly-free-electron conduction channels in low-dimensional molecular materials by tailoring their electrostatic and polarization potentials. We propose quantum structures of graphane-derived Janus molecular sheets with spatially isolated conducting and insulating regions that potentially exhibit emergent electronic properties, as a paradigm for molecular-scale non-nuclear charge conductors; we also describe tuning of their electronic properties by application of external fields and calculate their electron–acoustic-phonon interaction.

  13. Involvement of active sodium transport in the rectal absorption of gentamicin sulfate in the presence and absence of absorption-promoting adjuvants.

    PubMed

    Fix, J A; Porter, P A; Leppert, P S

    1983-06-01

    The involvement of active sodium transport in the rectal absorption of gentamicin sulfate was examined in rats, employing aqueous microenemas of known total ionic strength (mu) in the presence or absence of absorption-promoting adjuvants. Rectal gentamicin bio-availability, which is negligible (1 +/- 1.2%) at an ionic strength of 0.15 without adjuvants, is significantly (p less than 0.01) increased by including adjuvants in the formulation (sodium salicylate, 12 +/- 4.0%; sodium-5-bromosalicylate, 59 +/- 15.1%; disodium ethylene (dinitrilo)tetraacetate, 24 +/- 9.3%). Pretreating the rectal mucosa cells with ouabain, a specific inhibitor of active sodium transport, significantly (p less than 0.01) reduced gentamicin absorption in response to all three adjuvants. In contrast to previous findings with sodium chloride, high ionic strength choline chloride (mu = 1.056) did not promote gentamicin absorption. The data indicate that active sodium transport is an integral component of rectal absorption of water-soluble compounds and may be involved in the mechanism of action of absorption-promoting adjuvants. PMID:6875833

  14. Advanced simulation of electron heat transport in fusion plasmas

    SciTech Connect

    Lin, Zhihong; Xiao, Y.; Klasky, Scott A; Lofstead, J.

    2009-01-01

    Electron transport in burning plasmas is more important since fusion products first heat electrons. First-principles simulations of electron turbulence are much more challenging due to the multi-scale dynamics of the electron turbulence, and have been made possible by close collaborations between plasma physicists and computational scientists. The GTC simulations of collisionless trapped electron mode (CTEM) turbulence show that the electron heat transport exhibits a gradual transition from Bohm to gyroBohm scaling when the device size is increased. The deviation from the gyroBohm scaling can be induced by large turbulence eddies, turbulence spreading, and non-diffusive transport processes. Analysis of radial correlation function shows that CTEM turbulence eddies are predominantly microscopic but with a significant tail in the mesoscale. A comprehensive analysis of kinetic and fluid time scales shows that zonal flow shearing is the dominant decorrelation mechanism. The mesoscale eddies result from a dynamical process of linear streamers breaking by zonal flows and merging of microscopic eddies. The radial profile of the electron heat conductivity only follows the profile of fluctuation intensity on a global scale, whereas the ion transport tracks more sensitively the local fluctuation intensity. This suggests the existence of a nondiffusive component in the electron heat flux, which arises from the ballistic radial E x B drift of trapped electrons due to a combination of the presence of mesoscale eddies and the weak de-tuning of the toroidal precessional resonance that drives the CTEM instability. On the other hand, the ion radial excursion is not affected by the mesoscale eddies due to a parallel decorrelation, which is not operational for the trapped electrons because of a bounce averaging process associated with the electron fast motion along magnetic field lines. The presence of the nondiffusive component raises question on the applicability of the usual

  15. Advanced Simulation of Electron Heat Transport in Fusion Plasmas

    SciTech Connect

    Lin, Z.; Xiao, Y.; Holod, I.; Zhang, W. L.; Deng, Wenjun; Klasky, Scott A; Lofstead, J.; Kamath, Chandrika; Wichmann, Nathan

    2009-01-01

    Electron transport in burning plasmas is more important since fusion products first heat electrons. First-principles simulations of electron turbulence are much more challenging due to the multi-scale dynamics of the electron turbulence, and have been made possible by close collaborations between plasma physicists and computational scientists. The GTC simulations of collisionless trapped electron mode (CTEM) turbulence show that the electron heat transport exhibits a gradual transition from Bohm to gyroBohm scaling when the device size is increased. The deviation from the gyroBohm scaling can be induced by large turbulence eddies, turbulence spreading, and non-diffusive transport processes. Analysis of radial correlation function shows that CTEM turbulence eddies are predominantly microscopic but with a significant tail in the mesoscale. A comprehensive analysis of kinetic and fluid time scales shows that zonal flow shearing is the dominant decorrelation mechanism. The mesoscale eddies result from a dynamical process of linear streamers breaking by zonal flows and merging of microscopic eddies. The radial profile of the electron heat conductivity only follows the profile of fluctuation intensity on a global scale, whereas the ion transport tracks more sensitively the local fluctuation intensity. This suggests the existence of a nondiffusive component in the electron heat flux, which arises from the ballistic radial E x B drift of trapped electrons due to a combination of the presence of mesoscale eddies and the weak de-tuning of the toroidal precessional resonance that drives the CTEM instability. On the other hand, the ion radial excursion is not affected by the mesoscale eddies due to a parallel decorrelation, which is not operational for the trapped electrons because of a bounce averaging process associated with the electron fast motion along magnetic field lines. The presence of the nondiffusive component raises question on the applicability of the usual

  16. Electronic transport and lasing in microstructures

    SciTech Connect

    Lax, M.

    1992-01-01

    We consider the interaction of hot carriers with hot phonons in a quantum well. Transport is considered in the transverse direction and tunneling through the well barriers. Time-dependent transport effects down to the femto-second regime are included, as are strong and/or microwave fields, with negative resistance effects. Resonant tunneling assisted by phonon relaxation and infra-red radiation will be explored. The limitations on transmission of information due to partition noise, as influenced by the design of semiconductor feedback lasers will be considered. The use of light scattering and decision theory to detect shell-like aerosols is examined.

  17. Light absorption and electrical transport in Si:O alloys for photovoltaics

    SciTech Connect

    Mirabella, S.; Crupi, I.; Miritello, M.; Simone, F.; Di Martino, G.; Di Stefano, M. A.; Di Marco, S.; Priolo, F.

    2010-11-15

    Thin films (100-500 nm) of the Si:O alloy have been systematically characterized in the optical absorption and electrical transport behavior, by varying the Si content from 43 up to 100 at. %. Magnetron sputtering or plasma enhanced chemical vapor deposition have been used for the Si:O alloy deposition, followed by annealing up to 1250 deg. C. Boron implantation (30 keV, 3-30x10{sup 14} B/cm{sup 2}) on selected samples was performed to vary the electrical sheet resistance measured by the four-point collinear probe method. Transmittance and reflectance spectra have been extracted and combined to estimate the absorption spectra and the optical band gap, by means of the Tauc analysis. Raman spectroscopy was also employed to follow the amorphous-crystalline (a-c) transition of the Si domains contained in the Si:O films. The optical absorption and the electrical transport of Si:O films can be continuously and independently modulated by acting on different parameters. The light absorption increases (by one decade) with the Si content in the 43-100 at. % range, determining an optical band gap which can be continuously modulated into the 2.6-1.6 eV range, respectively. The a-c phase transition in Si:O films, causing a significant reduction in the absorption coefficient, occurs at increasing temperatures (from 600 to 1100 deg. C) as the Si content decreases. The electrical resistivity of Si:O films can be varied among five decades, being essentially dominated by the number of Si grains and by the doping. Si:O alloys with Si content in the 60-90 at. % range (named oxygen rich silicon films), are proved to join an appealing optical gap with a viable conductivity, being a good candidate for increasing the conversion efficiency of thin-film photovoltaic cell.

  18. Electron transport in single molecules: from benzene to graphene.

    PubMed

    Chen, F; Tao, N J

    2009-03-17

    Electron movement within and between molecules--that is, electron transfer--is important in many chemical, electrochemical, and biological processes. Recent advances, particularly in scanning electrochemical microscopy (SECM), scanning-tunneling microscopy (STM), and atomic force microscopy (AFM), permit the study of electron movement within single molecules. In this Account, we describe electron transport at the single-molecule level. We begin by examining the distinction between electron transport (from semiconductor physics) and electron transfer (a more general term referring to electron movement between donor and acceptor). The relation between these phenomena allows us to apply our understanding of single-molecule electron transport between electrodes to a broad range of other electron transfer processes. Electron transport is most efficient when the electron transmission probability via a molecule reaches 100%; the corresponding conductance is then 2e(2)/h (e is the charge of the electron and h is the Planck constant). This ideal conduction has been observed in a single metal atom and a string of metal atoms connected between two electrodes. However, the conductance of a molecule connected to two electrodes is often orders of magnitude less than the ideal and strongly depends on both the intrinsic properties of the molecule and its local environment. Molecular length, means of coupling to the electrodes, the presence of conjugated double bonds, and the inclusion of possible redox centers (for example, ferrocene) within the molecular wire have a pronounced effect on the conductance. This complex behavior is responsible for diverse chemical and biological phenomena and is potentially useful for device applications. Polycyclic aromatic hydrocarbons (PAHs) afford unique insight into electron transport in single molecules. The simplest one, benzene, has a conductance much less than 2e(2)/h due to its large LUMO-HOMO gap. At the other end of the spectrum, graphene

  19. X-ray absorption study of the electronic structure of Mn-doped amorphous Si

    SciTech Connect

    Arenholz, Elke; Zeng, Li; Huegel, A.; Helgren, E.; Hellman, F.; Piamonteze, C.; Arenholz, E.

    2008-03-08

    The electronic structure of Mn in amorphous Si (a-Mn{sub x}Si{sub 1?x}) is studied by X-ray absorption spectroscopy at the Mn L{sub 3,2} edges for x = 0.005-0.18. Except the x = 0.005 sample, which shows a slight signature of Mn{sup 2+} atomic multiplets associated with a local Mn moment, all samples have broad and featureless L{sub 3,2} absorption peaks, corresponding to an itinerant state for all 3d electrons. The broad X-ray absorption spectra exclude the possibility of a localized 3d moment and explain the unexpectedly quenched Mn moment in this magnetically-doped amorphous semiconductor. Such a fully delocalized d state of Mn dopant in Si has not been previously suggested.

  20. RHIC electron lens beam transport system design considerations

    SciTech Connect

    Gu, X.; Pikin, A.; Okamura, M.; Fischer, W.; Luo, Y.; Gupta, R.; Hock, J.; Jain, A.; Raparia, D.

    2010-10-01

    To apply head-on beam-beam compensation for RHIC, two electron lenses are designed and will be installed at IP10. Electron beam transport system is one of important subsystem, which is used to transport electron beam from electron gun side to collector side. This system should be able to change beam size inside superconducting magnet and control beam position with 5 mm in horizontal and vertical plane. Some other design considerations for this beam transport system are also reported in this paper. The head-on beam-beam effect is one of important nonlinear source in storage ring and linear colliders, which have limited the luminosity improvement of many colliders, such as SppS, Tevatron and RHIC. In order to enhance the performance of colliders, beam-beam effects can be compensated with direct space charge compensation, indirect space charge compensation or betatron phase cancellation scheme. Like other colliders, indirect space charge compensation scheme (Electron Lens) was also proposed for Relativistic Heavy Ion Collider (RHIC) beam-beam compensation at Brookhaven National Laboratory. The two similar electron lenses are located in IR10 between the DX magnets. One RHIC electron lens consists of one DC electron gun, one superconducting magnet, one electron collector and beam transport system.

  1. Nano-structured electron transporting materials for perovskite solar cells

    NASA Astrophysics Data System (ADS)

    Liu, Hefei; Huang, Ziru; Wei, Shiyuan; Zheng, Lingling; Xiao, Lixin; Gong, Qihuang

    2016-03-01

    Organic-inorganic hybrid perovskite solar cells have been developing rapidly in the past several years, and their power conversion efficiency has reached over 20%, nearing that of polycrystalline silicon solar cells. Because the diffusion length of the hole in perovskites is longer than that of the electron, the performance of the device can be improved by using an electron transporting layer, e.g., TiO2, ZnO and TiO2/Al2O3. Nano-structured electron transporting materials facilitate not only electron collection but also morphology control of the perovskites. The properties, morphology and preparation methods of perovskites are reviewed in the present article. A comprehensive understanding of the relationship between the structure and property will benefit the precise control of the electron transporting process and thus further improve the performance of perovskite solar cells.

  2. Nano-structured electron transporting materials for perovskite solar cells.

    PubMed

    Liu, Hefei; Huang, Ziru; Wei, Shiyuan; Zheng, Lingling; Xiao, Lixin; Gong, Qihuang

    2016-03-17

    Organic-inorganic hybrid perovskite solar cells have been developing rapidly in the past several years, and their power conversion efficiency has reached over 20%, nearing that of polycrystalline silicon solar cells. Because the diffusion length of the hole in perovskites is longer than that of the electron, the performance of the device can be improved by using an electron transporting layer, e.g., TiO2, ZnO and TiO2/Al2O3. Nano-structured electron transporting materials facilitate not only electron collection but also morphology control of the perovskites. The properties, morphology and preparation methods of perovskites are reviewed in the present article. A comprehensive understanding of the relationship between the structure and property will benefit the precise control of the electron transporting process and thus further improve the performance of perovskite solar cells. PMID:26457406

  3. Improved inline model for nonlocal electron transport in HYDRA

    NASA Astrophysics Data System (ADS)

    Marinak, M. M.; Kerbel, G. D.; Patel, M. V.; Robey, H.; Ridgers, C. P.; Kingham, R. J.

    2014-10-01

    The nonlocal electron transport model in HYDRA has been improved in several respects. The original multigroup model has been extended to include the cascade in energy as particles slow down, yielding a more accurate range. The model was also extended to account for contributions to the energy loss rate due to bound electrons. These are among the important modifications that have enabled the package to simulate classes of suprathermal electrons. We show recent calculations using the model that suggest superthermal electrons could be having a significant effect on performance of cryogenic capsule implosions on the National Ignition Facility. We evaluate the nonlocal transport model's accuracy by comparison with an electron VFP code. Comparisons assess the accuracy of the calculated thermal transport for plasmas relevant to NIF experiments. This work was performed under the auspices of the Lawrence Livermore National Security, LLC, (LLNS) under Contract No. DE-AC52-07NA27344.

  4. SUPPRESSION OF ENERGETIC ELECTRON TRANSPORT IN FLARES BY DOUBLE LAYERS

    SciTech Connect

    Li, T. C.; Drake, J. F.; Swisdak, M.

    2012-09-20

    During flares and coronal mass ejections, energetic electrons from coronal sources typically have very long lifetimes compared to the transit times across the systems, suggesting confinement in the source region. Particle-in-cell simulations are carried out to explore the mechanisms of energetic electron transport from the corona to the chromosphere and possible confinement. We set up an initial system of pre-accelerated hot electrons in contact with ambient cold electrons along the local magnetic field and let it evolve over time. Suppression of transport by a nonlinear, highly localized electrostatic electric field (in the form of a double layer) is observed after a short phase of free-streaming by hot electrons. The double layer (DL) emerges at the contact of the two electron populations. It is driven by an ion-electron streaming instability due to the drift of the back-streaming return current electrons interacting with the ions. The DL grows over time and supports a significant drop in temperature and hence reduces heat flux between the two regions that is sustained for the duration of the simulation. This study shows that transport suppression begins when the energetic electrons start to propagate away from a coronal acceleration site. It also implies confinement of energetic electrons with kinetic energies less than the electrostatic energy of the DL for the DL lifetime, which is much longer than the electron transit time through the source region.

  5. Study of Electron Transport and Amplification in Diamond

    SciTech Connect

    Ben-Zvi, Ilan; Muller, Erik

    2015-01-05

    The development of the Diamond Amplified Photocathode (DAP) has produced significant results under our previous HEP funded efforts both on the fabrication of working devices and the understanding of the underlying physics governing its performance. The results presented here substantiate the use of diamond as both a secondary electron amplifier for high-brightness, high-average-current electron sources and as a photon and particle detector in harsh radiation environments. Very high average current densities (>10A/cm2) have been transported through diamond material. The transport has been measured as a function of incident photon energy and found to be in good agreement with theoretical models. Measurements of the charge transport for photon energies near the carbon K-edge (290 eV for sp3 bonded carbon) have provided insight into carrier loss due to diffusion; modeling of this aspect of charge transport is underway. The response of diamond to nanosecond x-ray pulses has been measured; in this regime the charge transport is as expected. Electron emission from hydrogenated diamond has been measured using both electron and x-ray generated carriers; a gain of 178 has been observed for electron-generated carriers. The energy spectrum of the emitted electrons has been measured, providing insight into the electron affinity and ultimately the thermal emittance. The origin of charge trapping in diamond has been investigated for both bulk and surface trapping

  6. Conditioner for a helically transported electron beam

    SciTech Connect

    Wang, C.

    1992-05-01

    The kinetic theory is developed to investigate a conditioner for a helically imported electron beam. Linear expressions for axial velocity spread are derived. Numerical simulation is used to check the theoretical results and examine nonlinear aspects of the conditioning process. The results show that in the linear regime the action of the beam conditioner on a pulsed beam mainly depends on the phase at which the beam enters the conditioner and depends only slightly on the operating wavelength. In the nonlinear regime, however, the action of the conditioner strongly depends on the operating wavelength and only slightly upon the entrance phase. For a properly chosen operating wavelength, a little less than the electron`s relativistic cyclotron wavelength, the conditioner can decrease the axial velocity spread of a pulsed beam down to less than one-third of its initial value.

  7. Coherent electron transport in a helical nanotube

    NASA Astrophysics Data System (ADS)

    Liang, Guo-Hua; Wang, Yong-Long; Du, Long; Jiang, Hua; Kang, Guang-Zhen; Zong, Hong-Shi

    2016-09-01

    The quantum dynamics of carriers bound to helical tube surfaces is investigated in a thin-layer quantization scheme. By numerically solving the open-boundary Schrödinger equation in curvilinear coordinates, geometric effect on the coherent transmission spectra is analysed in the case of single propagating mode as well as multimode. It is shown that, the coiling endows the helical nanotube with different transport properties from a bent cylindrical surface. Fano resonance appears as a purely geometric effect in the conductance, the corresponding energy of quasibound state is obviously influenced by the torsion and length of the nanotube. We also find new plateaus in the conductance. The transport of double-degenerate mode in this geometry is reminiscent of the Zeeman coupling between the magnetic field and spin angular momentum in quasi-one-dimensional structure.

  8. Analysis of the ionosphere-plasmasphere transport of superthermal electrons. I - Transport in the plasmasphere

    NASA Technical Reports Server (NTRS)

    Khazanov, George V.; Gombosi, Tamas I.; Nagy, Andrew F.; Koen, Mikhail A.

    1992-01-01

    Analytical solutions are developed for the kinetic equation which describes the transport of superthermal electrons in the terrestrial plasmasphere, together with a relationship which makes it possible to calculate the transparency of the plasmasphere to these electrons. In addition, analytic expressions are presented for the heating rate of the thermal plasma due to the passage of these superthermal electrons through the plasmasphere.

  9. A Deterministic Transport Code for Space Environment Electrons

    NASA Technical Reports Server (NTRS)

    Nealy, John E.; Chang, C. K.; Norman, Ryan B.; Blattnig, Steve R.; Badavi, Francis F.; Adamczyk, Anne M.

    2010-01-01

    A deterministic computational procedure has been developed to describe transport of space environment electrons in various shield media. This code is an upgrade and extension of an earlier electron code. Whereas the former code was formulated on the basis of parametric functions derived from limited laboratory data, the present code utilizes well established theoretical representations to describe the relevant interactions and transport processes. The shield material specification has been made more general, as have the pertinent cross sections. A combined mean free path and average trajectory approach has been used in the transport formalism. Comparisons with Monte Carlo calculations are presented.

  10. Neoclassical electron transport in tokamaks with neutral-beam injection

    SciTech Connect

    Helander, P.; Akers, R.J.

    2005-04-15

    The collisional interaction between neutral-beam ions and bulk plasma electrons leads to convective transport of particles and energy similar to the well-known Ware pinch. These transport fluxes are calculated, and it is found that the particle flux is outward when the neutral beams are in the same direction as the plasma current and inward otherwise, while the opposite holds for the electron heat transport. This effectively shifts the neutral-beam fueling profile approximately one fast-ion banana width outward during coinjection and inward during counterinjection, and could help to explain why very different plasma behavior is sometimes observed when the direction of the plasma current is reversed.

  11. Effects of anomalous transport on lower hybrid electron heating

    SciTech Connect

    McCoy, M.G.; Harvey, R.W.

    1981-02-01

    The transport of electron energy out of tokamaks is known to be far greater than that calculated using classical and neoclassical theory. However, low levels of non-axisymmetric magnetic field turbulence can couple the fast transport of electrons parallel to the magnetic field lines to radial transport, thus providing a plausible explanation for observed energy confinement. These models further predict that the electron loss rate is proportional to v/sub parallel bars/. This has subsequently been found to be consistent with data for runaway electrons in PLT, at energies up to 1 MeV. Recently it has been pointed out by Chan, Chiu and Ohkawa that anomalous transport processes should be taken into account in attempting to determine steady state electron distribution functions for cases involving RF electron tail heating, particularly in view of the v/sub parallel bars/ dependence of the loss rate. In this work these physical processes are modeled through a 2-D nonlinear program which describes the evolution of the electron distribution function in velocity magnitude; (v) and plasma radius (r), and which studies the efficiency of tail electron heating.

  12. Electronic correlation and transport properties of nuclear fuel materials

    NASA Astrophysics Data System (ADS)

    Yin, Quan; Kutepov, Andrey; Haule, Kristjan; Kotliar, Gabriel; Savrasov, Sergey Y.; Pickett, Warren E.

    2011-11-01

    The electronic structures and transport properties of a series of actinide monocarbides, mononitrides, and dioxides are studied systematically using a combination of density-functional theory and dynamical mean-field theory. The studied materials present different electronic correlation strength and degree of localization of 5f electrons, where a metal-insulator boundary naturally lies within. In the spectral function of Mott-insulating uranium oxide, a resonance peak is observed in both theory and experiment and may be understood as a generalized Zhang-Rice state. We also investigate the interplay between electron-electron and electron-phonon interactions, both of which are responsible for the transport in the metallic compounds. Our findings allow us to gain insight in the roles played by different scattering mechanisms, and suggest how to improve their thermal conductivities.

  13. Electronic correlation and transport properties of nuclear fuel materials

    SciTech Connect

    Yin Quan; Kutepov, Andrey; Haule, Kristjan; Kotliar, Gabriel; Savrasov, Sergey Y.; Pickett, Warren E.

    2011-11-15

    The electronic structures and transport properties of a series of actinide monocarbides, mononitrides, and dioxides are studied systematically using a combination of density-functional theory and dynamical mean-field theory. The studied materials present different electronic correlation strength and degree of localization of 5f electrons, where a metal-insulator boundary naturally lies within. In the spectral function of Mott-insulating uranium oxide, a resonance peak is observed in both theory and experiment and may be understood as a generalized Zhang-Rice state. We also investigate the interplay between electron-electron and electron-phonon interactions, both of which are responsible for the transport in the metallic compounds. Our findings allow us to gain insight in the roles played by different scattering mechanisms, and suggest how to improve their thermal conductivities.

  14. X-ray absorption spectroscopy elucidates the impact of structural disorder on electron mobility in amorphous zinc-tin-oxide thin films

    SciTech Connect

    Siah, Sin Cheng E-mail: buonassisi@mit.edu; Lee, Yun Seog; Buonassisi, Tonio E-mail: buonassisi@mit.edu; Lee, Sang Woon; Gordon, Roy G.; Heo, Jaeyeong; Shibata, Tomohiro; Segre, Carlo U.

    2014-06-16

    We investigate the correlation between the atomic structures of amorphous zinc-tin-oxide (a-ZTO) thin films grown by atomic layer deposition (ALD) and their electronic transport properties. We perform synchrotron-based X-ray absorption spectroscopy at the K-edges of Zn and Sn with varying [Zn]/[Sn] compositions in a-ZTO thin films. In extended X-ray absorption fine structure (EXAFS) measurements, signal attenuation from higher-order shells confirms the amorphous structure of a-ZTO thin films. Both quantitative EXAFS modeling and X-ray absorption near edge spectroscopy (XANES) reveal that structural disorder around Zn atoms increases with increasing [Sn]. Field- and Hall-effect mobilities are observed to decrease with increasing structural disorder around Zn atoms, suggesting that the degradation in electron mobility may be correlated with structural changes.

  15. Electronic transport in Si:P δ -doped wires

    NASA Astrophysics Data System (ADS)

    Smith, J. S.; Drumm, D. W.; Budi, A.; Vaitkus, J. A.; Cole, J. H.; Russo, S. P.

    2015-12-01

    Despite the importance of Si:P δ -doped wires for modern nanoelectronics, there are currently no computational models of electron transport in these devices. In this paper we present a nonequilibrium Green's function model for electronic transport in a δ -doped wire, which is described by a tight-binding Hamiltonian matrix within a single-band effective-mass approximation. We use this transport model to calculate the current-voltage characteristics of a number of δ -doped wires, achieving good agreement with experiment. To motivate our transport model we have performed density-functional calculations for a variety of δ -doped wires, each with different donor configurations. These calculations also allow us to accurately define the electronic extent of a δ -doped wire, which we find to be at least 4.6 nm.

  16. A Deterministic Computational Procedure for Space Environment Electron Transport

    NASA Technical Reports Server (NTRS)

    Nealy, John E.; Chang, C. K.; Norman, Ryan B.; Blattnig, Steve R.; Badavi, Francis F.; Adamcyk, Anne M.

    2010-01-01

    A deterministic computational procedure for describing the transport of electrons in condensed media is formulated to simulate the effects and exposures from spectral distributions typical of electrons trapped in planetary magnetic fields. The primary purpose for developing the procedure is to provide a means of rapidly performing numerous repetitive transport calculations essential for electron radiation exposure assessments for complex space structures. The present code utilizes well-established theoretical representations to describe the relevant interactions and transport processes. A combined mean free path and average trajectory approach is used in the transport formalism. For typical space environment spectra, several favorable comparisons with Monte Carlo calculations are made which have indicated that accuracy is not compromised at the expense of the computational speed.

  17. Increasing oral absorption of polar neuraminidase inhibitors: a prodrug transporter approach applied to oseltamivir analogue.

    PubMed

    Gupta, Deepak; Varghese Gupta, Sheeba; Dahan, Arik; Tsume, Yasuhiro; Hilfinger, John; Lee, Kyung-Dall; Amidon, Gordon L

    2013-02-01

    Poor oral absorption is one of the limiting factors in utilizing the full potential of polar antiviral agents. The neuraminidase target site requires a polar chemical structure for high affinity binding, thus limiting oral efficacy of many high affinity ligands. The aim of this study was to overcome this poor oral absorption barrier, utilizing prodrug to target the apical brush border peptide transporter 1 (PEPT1). Guanidine oseltamivir carboxylate (GOCarb) is a highly active polar antiviral agent with insufficient oral bioavailability (4%) to be an effective therapeutic agent. In this report we utilize a carrier-mediated targeted prodrug approach to improve the oral absorption of GOCarb. Acyloxy(alkyl) ester based amino acid linked prodrugs were synthesized and evaluated as potential substrates of mucosal transporters, e.g., PEPT1. Prodrugs were also evaluated for their chemical and enzymatic stability. PEPT1 transport studies included [(3)H]Gly-Sar uptake inhibition in Caco-2 cells and cellular uptake experiments using HeLa cells overexpressing PEPT1. The intestinal membrane permeabilities of the selected prodrugs and the parent drug were then evaluated for epithelial cell transport across Caco-2 monolayers, and in the in situ rat intestinal jejunal perfusion model. Prodrugs exhibited a pH dependent stability with higher stability at acidic pHs. Significant inhibition of uptake (IC(50) <1 mM) was observed for l-valyl and l-isoleucyl amino acid prodrugs in competition experiments with [(3)H]Gly-Sar, indicating a 3-6 times higher affinity for PEPT1 compared to valacyclovir, a well-known PEPT1 substrate and >30-fold increase in affinity compared to GOCarb. The l-valyl prodrug exhibited significant enhancement of uptake in PEPT1/HeLa cells and compared favorably with the well-absorbed valacyclovir. Transepithelial permeability across Caco-2 monolayers showed that these amino acid prodrugs have a 2-5-fold increase in permeability as compared to the parent drug and

  18. Electron-phonon interactions in silicon: Mean free paths, related distributions and transport characteristics

    NASA Astrophysics Data System (ADS)

    Akkerman, Avraham; Murat, Michael

    2015-05-01

    The mean free path (MFP) for electron-phonon interactions in pure silicon is an important characteristic needed both for low energy electron transport calculations using Boltzmann transport equation, and for Monte Carlo simulations. Full band calculations present a basic (though complicated) approach to the solution of the problem. Simpler approaches based on analytical presentation of the scattering rates have also been used; however they are valid for a restricted range of electron energies, below 2 eV. In this paper we introduce a hybrid method that utilizes the density of energy states calculated from the full band calculations for electron energies larger than 2 eV, allowing to extend the analytical approach for energies up to 5 eV, where the impact ionization becomes the dominant mechanism of electron interactions within bulk silicon. The resulting MFPs as function of electron energy and lattice temperature, together with the integral probability distribution for given energy losses by phonon emission (or energy gain by absorption of phonons) form the database for Monte Carlo calculations. Using this method, we calculate the electron diffusivity and mobility as function of the electron and lattice temperatures. These parameters are important for solution of the two temperature model, used for calculations of the track structure created by swift ions and nanosecond laser beams.

  19. Electron Trapping and Charge Transport by Large Amplitude Whistlers

    NASA Technical Reports Server (NTRS)

    Kellogg, P. J.; Cattell, C. A.; Goetz, K.; Monson, S. J.; Wilson, L. B., III

    2010-01-01

    Trapping of electrons by magnetospheric whistlers is investigated using data from the Waves experiment on Wind and the S/WAVES experiment on STEREO. Waveforms often show a characteristic distortion which is shown to be due to electrons trapped in the potential of the electrostatic part of oblique whistlers. The density of trapped electrons is significant, comparable to that of the unperturbed whistler. Transport of these trapped electrons to new regions can generate potentials of several kilovolts, Trapping and the associated potentials may play an important role in the acceleration of Earth's radiation belt electrons.

  20. Multidimensional electron-photon transport with standard discrete ordinates codes

    SciTech Connect

    Drumm, C.R.

    1995-12-31

    A method is described for generating electron cross sections that are compatible with standard discrete ordinates codes without modification. There are many advantages of using an established discrete ordinates solver, e.g. immediately available adjoint capability. Coupled electron-photon transport capability is needed for many applications, including the modeling of the response of electronics components to space and man-made radiation environments. The cross sections have been successfully used in the DORT, TWODANT and TORT discrete ordinates codes. The cross sections are shown to provide accurate and efficient solutions to certain multidimensional electronphoton transport problems.

  1. Electronic transport in phosphorus-doped silicon nanocrystal networks.

    PubMed

    Stegner, A R; Pereira, R N; Klein, K; Lechner, R; Dietmueller, R; Brandt, M S; Stutzmann, M; Wiggers, H

    2008-01-18

    We have investigated the role of doping and paramagnetic states on the electronic transport of networks assembled from freestanding Si nanocrystals (Si-NCs). Electrically detected magnetic resonance (EDMR) studies on Si-NCs films, which show a strong increase of conductivity with doping of individual Si-NCs, reveal that P donors and Si dangling bonds contribute to dark conductivity via spin-dependent hopping, whereas in photoconductivity, these states act as spin-dependent recombination centers of photogenerated electrons and holes. Comparison between EDMR and conventional electron paramagnetic resonance shows that different subsets of P-doped nanocrystals contribute to the different transport processes. PMID:18232904

  2. Translating Molecular Physiology of Intestinal Transport into Pharmacologic Treatment of Diarrhea: Stimulation of Na+ Absorption

    PubMed Central

    Singh, Varsha; Yang, Jianbo; Chen, Tiane-e; Zachos, Nick; Kovbasnjuk, Olga; Verkman, Alan; Donowitz, Mark

    2013-01-01

    Diarrheal diseases remain a leading cause of morbidity and mortality for children in developing countries while representing an important cause of morbidity worldwide. The WHO recommended low osmolarity oral rehydration solutions plus zinc save lives in patients with acute diarrhea1, but there are no approved, safe drugs which have been shown to be effective against most causes of acute diarrhea. Identification of abnormalities in electrolyte handling by the intestine in diarrhea, including increased intestinal anion secretion and reduced Na+ absorption, suggest a number of potential drug targets. This is based on the view that successful drug therapy for diarrhea will result from correcting the abnormalities in electrolyte transport that are pathophysiologic for diarrhea. We review the molecular mechanisms of physiologic regulation of intestinal ion transport and changes that occur in diarrhea and the status of drugs being developed to correct the transport abnormalities in Na+ absorption which occur in diarrhea. Mechanisms of Cl− secretion and approaches to anti-Cl− secretory therapies of diarrhea are discussed in a companion review. PMID:24184676

  3. Translating molecular physiology of intestinal transport into pharmacologic treatment of diarrhea: stimulation of Na+ absorption.

    PubMed

    Singh, Varsha; Yang, Jianbo; Chen, Tiane-e; Zachos, Nicholas C; Kovbasnjuk, Olga; Verkman, Alan S; Donowitz, Mark

    2014-01-01

    Diarrheal diseases remain a leading cause of morbidity and mortality for children in developing countries, while representing an important cause of morbidity worldwide. The World Health Organization recommended that low osmolarity oral rehydration solutions plus zinc save lives in patients with acute diarrhea, but there are no approved, safe drugs that have been shown to be effective against most causes of acute diarrhea. Identification of abnormalities in electrolyte handling by the intestine in diarrhea, including increased intestinal anion secretion and reduced Na(+) absorption, suggest a number of potential drug targets. This is based on the view that successful drug therapy for diarrhea will result from correcting the abnormalities in electrolyte transport that are pathophysiologic for diarrhea. We review the molecular mechanisms of physiologic regulation of intestinal ion transport and changes that occur in diarrhea and the status of drugs being developed to correct the transport abnormalities in Na(+) absorption that occur in diarrhea. Mechanisms of Cl(-) secretion and approaches to anti-Cl(-) secretory therapies of diarrhea are discussed in a companion review. PMID:24184676

  4. Role of interface band structure on hot electron transport

    NASA Astrophysics Data System (ADS)

    Garramone, John J.

    Knowledge of electron transport through materials and interfaces is fundamentally and technologically important. For example, metal interconnects within integrated circuits suffer increasingly from electromigration and signal delay due to an increase in resistance from grain boundary and sidewall scattering since their dimensions are becoming shorter than the electron mean free path. Additionally, all semiconductor based devices require the transport of electrons through materials and interfaces where scattering and parallel momentum conservation are important. In this thesis, the inelastic and elastic scattering of hot electrons are studied in nanometer thick copper, silver and gold films deposited on silicon substrates. Hot electrons are electron with energy greater than kBT above the Fermi level (EF). This work was performed utilizing ballistic electron emission microscopy (BEEM) which is a three terminal scanning tunneling microscopy (STM) technique that measures the percentage of hot electrons transmitted across a Schottky barrier interface. Hot electron attenuation lengths of the metals were extracted by measuring the BEEM current as a function of metal overlayer thickness for both hot electron and hot hole injection at 80 K and under ultra high vacuum. The inelastic and elastic scattering lengths were extracted by fitting the energetic dependence of the measured attenuation lengths to a Fermi liquid based model. A sharp increase in the attenuation length is observed at low injection energies, just above the Schottky barrier height, only for metals on Si(001) substrates. In contrast, the attenuation length measured on Si(111) substrates shows a sharp decrease. These results indicate that interface band structure and parallel momentum conservation have significant impact upon the transport of hot electrons across non epitaxial metal-semiconductor interfaces. In addition, they help to separate effects upon hot electron transport that are inherent to the metal

  5. Treating electron transport in MCNP{sup trademark}

    SciTech Connect

    Hughes, H.G.

    1996-12-31

    The transport of electrons and other charged particles is fundamentally different from that of neutrons and photons. A neutron, in aluminum slowing down from 0.5 MeV to 0.0625 MeV will have about 30 collisions; a photon will have fewer than ten. An electron with the same energy loss will undergo 10{sup 5} individual interactions. This great increase in computational complexity makes a single- collision Monte Carlo approach to electron transport unfeasible for many situations of practical interest. Considerable theoretical work has been done to develop a variety of analytic and semi-analytic multiple-scattering theories for the transport of charged particles. The theories used in the algorithms in MCNP are the Goudsmit-Saunderson theory for angular deflections, the Landau an theory of energy-loss fluctuations, and the Blunck-Leisegang enhancements of the Landau theory. In order to follow an electron through a significant energy loss, it is necessary to break the electron`s path into many steps. These steps are chosen to be long enough to encompass many collisions (so that multiple-scattering theories are valid) but short enough that the mean energy loss in any one step is small (for the approximations in the multiple-scattering theories). The energy loss and angular deflection of the electron during each step can then be sampled from probability distributions based on the appropriate multiple- scattering theories. This subsumption of the effects of many individual collisions into single steps that are sampled probabilistically constitutes the ``condensed history`` Monte Carlo method. This method is exemplified in the ETRAN series of electron/photon transport codes. The ETRAN codes are also the basis for the Integrated TIGER Series, a system of general-purpose, application-oriented electron/photon transport codes. The electron physics in MCNP is similar to that of the Integrated TIGER Series.

  6. Study of electron transport in hydrocarbon gases

    NASA Astrophysics Data System (ADS)

    Hasegawa, H.; Date, H.

    2015-04-01

    The drift velocity and the effective ionization coefficient of electrons in the organic gases, C2H2, C2H4, C2H6, CH3OH, C2H5OH, C6H6, and C6H5CH3, have been measured over relatively wide ranges of density-reduced electric fields (E/N) at room temperature (around 300 K). The drift velocity was measured, based on the arrival-time spectra of electrons by using a double-shutter drift tube over the E/N range from 300 to 2800 Td, and the effective ionization coefficient (α - η) was determined by the steady-state Townsend method from 150 to 3000 Td. Whenever possible, these parameters were compared with those available in the literature. It has been shown that the swarm parameters for these gases have specific tendencies, depending on their molecular configurations.

  7. Conditioner for a helically transported electron beam

    SciTech Connect

    Wang, C.

    1992-05-01

    The kinetic theory is developed to investigate a conditioner for a helically imported electron beam. Linear expressions for axial velocity spread are derived. Numerical simulation is used to check the theoretical results and examine nonlinear aspects of the conditioning process. The results show that in the linear regime the action of the beam conditioner on a pulsed beam mainly depends on the phase at which the beam enters the conditioner and depends only slightly on the operating wavelength. In the nonlinear regime, however, the action of the conditioner strongly depends on the operating wavelength and only slightly upon the entrance phase. For a properly chosen operating wavelength, a little less than the electron's relativistic cyclotron wavelength, the conditioner can decrease the axial velocity spread of a pulsed beam down to less than one-third of its initial value.

  8. Anomalous cross field electron transport in a Hall effect thruster

    SciTech Connect

    Boniface, C.; Garrigues, L.; Hagelaar, G. J. M.; Boeuf, J. P.; Gawron, D.; Mazouffre, S.

    2006-10-16

    The origin of anomalous electron transport across the magnetic field in the channel of a Hall effect thruster has been the subject of controversy, and the relative importance of electron-wall collisions and plasma turbulence on anomalous transport is not clear. From comparisons between Fabry-Perot measurements and hybrid model calculations of the ion velocity profile in a 5 kW Hall effect thruster, we deduce that one and the same mechanism is responsible for anomalous electron transport inside and outside the Hall effect thruster channel. This suggests that the previous assumption that Bohm anomalous conductivity is dominant outside the thruster channel whereas electron-wall conductivity prevails inside the channel is not valid.

  9. TOPICAL REVIEW: Electron transport in indium arsenide nanowires

    NASA Astrophysics Data System (ADS)

    Dayeh, Shadi A.

    2010-02-01

    The vapor--liquid--solid growth of semiconductor nanowires led to the implementation of engineered electronic and optoelectronic one-dimensional nanostructures with outstanding promise for device applications. To realize this promise, detailed understanding and control over their growth, crystal structure, and transport properties and their combined impact on device performance is vital. Here, we review our work on electron transport in InAs nanowires in a variety of device schemes. First, we provide a brief introduction and historical perspective on growth and transport studies in InAs NWs. Second, we discuss and present experimental measurements of ballistic transport in InAs nanowires over ~200 nm length scale, which indicates a large electron mean free path and correlates with the high electron mobility measured on similar nanowires. Third, we devise a device model that enables accurate estimation of transport coefficients from field-effect transistor measurements by taking into account patristic device components. We utilize this model to reveal the impact of surface states, diameter, lateral and vertical fields, as well as crystal structure, on electron transport and transport coefficient calculation. We show in these studies that electron transport in InAs nanowires is dominated by surface state effects that introduce measurement artifacts in parameter extraction, reduce electron mobility for smaller diameters, and degrade the subthreshold characteristics of transistors made of Zinc Blende InAs nanowires. This device model is also used for isolating vertical and lateral field effects on electron transport in nanowire transistor channels and explaining observed negative differential conductance and mobility degradation at high injection fields, which is supported by electro-thermal simulations and microstructure failure analysis. We adopt the concept of lack of inversion symmetry in polar III-V materials and the resultant spontaneous polarization charges

  10. Potential benefits of triethylamine as n-electron donor in the estimation of forskolin by electronic absorption and emission spectroscopy

    NASA Astrophysics Data System (ADS)

    Raju, Gajula; Ram Reddy, A.

    2016-02-01

    Diterpenoid forskolin was isolated from Coleus forskolii. The electronic absorption and emission studies of forskolin were investigated in various solvents with an aim to improve its detection limits. The two chromophores present in the diterpenoid are not conjugated leading to the poor absorption and emission of UV light. The absorption and fluorescence spectra were solvent specific. In the presence of a monodentate ligand, triethylamine the detection of forskolin is improved by 3.63 times in ethanol with the fluorescence method and 3.36 times in DMSO by the absorption spectral method. The longer wavelength absorption maximum is blue shifted while the lower energy fluorescence maximum is red shifted in the presence of triethylamine. From the wavelength of fluorescence maxima of the exciplex formed between excited forskolin and triethylamine it is concluded that the order of reactivity of hydroxyl groups in the excited state forskolin is in the reverse order to that of the order of the reactivity of hydroxyl groups in its ground state.

  11. Non-uniform absorption of terahertz radiation on superconducting hot electron bolometer microbridges

    SciTech Connect

    Miao, W.; Zhang, W.; Zhong, J. Q.; Shi, S. C.; Delorme, Y.; Lefevre, R.; Feret, A.; Vacelet, T.

    2014-02-03

    We interpret the experimental observation of a frequency-dependence of superconducting hot electron bolometer (HEB) mixers by taking into account the non-uniform absorption of the terahertz radiation on the superconducting HEB microbridge. The radiation absorption is assumed to be proportional to the local surface resistance of the HEB microbridge, which is computed using the Mattis-Bardeen theory. With this assumption the dc and mixing characteristics of a superconducting niobium-nitride (NbN) HEB device have been modeled at frequencies below and above the equilibrium gap frequency of the NbN film.

  12. Quasi-two dimensional simulations of electron thermal transport

    NASA Astrophysics Data System (ADS)

    Holder, B.; Horton, W.

    2003-10-01

    There exist two leading theoretical turbulent transport models which are driven by the electron temperature gradient and induce anomalous electron transport in tokamaks: (1) electron temperature gradient (ETG) and (2) trapped-electron mode (TEM) turbulence [1,2]. In ETG turbulence, the instability leads to the formation of small scale (on the order of q ρe R/L_Te and c / ω_pe) vortices which provide transport via the toroidal curvature analog of Rayleigh-Benard convection. In contrast, the larger scale (on the order of ρ_s) TEM/ITG turbulence has no clear critical electron temperature gradient and can be driven by the density gradient alone or the ion temperature gradient. Thus, we present 2D psuedo-spectral simulations of these two models and constrast their electron transport properties. Particular attention is given to the scaling of the anomalous heat flux with the electron temperature gradient, holding other parameters fixed. 1. G. G.Craddock, et al., Phys. Plasmas 1 (6), 1877 (1994). 2. D.A. Baver, P.W. Terry, and R. Gatto, Phys. Plasmas 9 (8), 3318 (2002).

  13. Loss of anion transport without increased sodium absorption characterizes newborn porcine cystic fibrosis airway epithelia

    PubMed Central

    Chen, Jeng-Haur; Stoltz, David A.; Karp, Philip H.; Ernst, Sarah E.; Pezzulo, Alejandro A.; Moninger, Thomas O.; Rector, Michael V.; Reznikov, Leah R.; Launspach, Janice L.; Chaloner, Kathryn; Zabner, Joseph; Welsh, Michael J.

    2011-01-01

    SUMMARY Defective transepithelial electrolyte transport is thought to initiate cystic fibrosis (CF) lung disease. Yet, how loss of CFTR affects electrolyte transport remains uncertain. CFTR−/− pigs spontaneously develop lung disease resembling human CF. At birth, their airways exhibit a bacterial host defense defect, but are not inflamed. Therefore, we studied ion transport in newborn nasal and tracheal/bronchial epithelia in tissue, cultures, and in vivo. CFTR−/− epithelia showed markedly reduced Cl− and HCO3− transport. However, in contrast to a widely held view, lack of CFTR did not increase transepithelial Na+ or liquid absorption or reduce periciliary liquid depth. Like human CF, CFTR−/− pigs showed increased amiloride-sensitive voltage and current, but lack of apical Cl− conductance caused the change, not increased Na+ transport. These results indicate that CFTR provides the predominant transcellular pathway for Cl− and HCO3− in porcine airway epithelia, and reduced anion permeability may initiate CF airway disease. PMID:21145458

  14. Study of electron transport in hydrocarbon gases

    SciTech Connect

    Hasegawa, H.; Date, H.

    2015-04-07

    The drift velocity and the effective ionization coefficient of electrons in the organic gases, C{sub 2}H{sub 2}, C{sub 2}H{sub 4}, C{sub 2}H{sub 6}, CH{sub 3}OH, C{sub 2}H{sub 5}OH, C{sub 6}H{sub 6}, and C{sub 6}H{sub 5}CH{sub 3}, have been measured over relatively wide ranges of density-reduced electric fields (E/N) at room temperature (around 300 K). The drift velocity was measured, based on the arrival-time spectra of electrons by using a double-shutter drift tube over the E/N range from 300 to 2800 Td, and the effective ionization coefficient (α − η) was determined by the steady-state Townsend method from 150 to 3000 Td. Whenever possible, these parameters were compared with those available in the literature. It has been shown that the swarm parameters for these gases have specific tendencies, depending on their molecular configurations.

  15. Excitonic emission and absorption resonances in V0.25W0.75Se2 single crystals grown by direct vapour transport technique

    NASA Astrophysics Data System (ADS)

    Solanki, G. K.; Pataniya, Pratik; Sumesh, C. K.; Patel, K. D.; Pathak, V. M.

    2016-05-01

    A systematic study on emission and absorption spectra of vanadium mixed tungsten diselenide single crystals grown by direct vapour transport (DVT) technique is reported. The grown crystals were characterized by energy dispersive analysis of X-ray (EDAX), which gives the confirmation about the stoichiometry. The structural characterizations were accomplished by X-ray diffraction (XRD), surface morphology and transmission electron microscopy (TEM). These characterizations were indicating the growth of V0.25W0.75Se2 single crystal from vapour phase. The optical response of this material has been observed by combination of UV-vis-NIR spectroscopy and photo luminescence (PL) spectroscopy. A detailed study of excitonic emission and absorption resonances was carried out on grown crystals. The energy band gap was calculated for indirect allowed transition with absorbed and emitted phonon. Additionally, absorption tail for grown crystal is found to obey the Urbach's rule.

  16. Donor-acceptor electron transport mediated by solitons.

    PubMed

    Brizhik, L S; Piette, B M A G; Zakrzewski, W J

    2014-11-01

    We study the long-range electron and energy transfer mediated by solitons in a quasi-one-dimensional molecular chain (conjugated polymer, alpha-helical macromolecule, etc.) weakly bound to a donor and an acceptor. We show that for certain sets of parameter values in such systems an electron, initially located at the donor molecule, can tunnel to the molecular chain, where it becomes self-trapped in a soliton state, and propagates to the opposite end of the chain practically without energy dissipation. Upon reaching the end, the electron can either bounce back and move in the opposite direction or, for suitable parameter values of the system, tunnel to the acceptor. We estimate the energy efficiency of the donor-acceptor electron transport depending on the parameter values. Our calculations show that the soliton mechanism works for the parameter values of polypeptide macromolecules and conjugated polymers. We also investigate the donor-acceptor electron transport in thermalized molecular chains. PMID:25493866

  17. Donor-acceptor electron transport mediated by solitons

    NASA Astrophysics Data System (ADS)

    Brizhik, L. S.; Piette, B. M. A. G.; Zakrzewski, W. J.

    2014-11-01

    We study the long-range electron and energy transfer mediated by solitons in a quasi-one-dimensional molecular chain (conjugated polymer, alpha-helical macromolecule, etc.) weakly bound to a donor and an acceptor. We show that for certain sets of parameter values in such systems an electron, initially located at the donor molecule, can tunnel to the molecular chain, where it becomes self-trapped in a soliton state, and propagates to the opposite end of the chain practically without energy dissipation. Upon reaching the end, the electron can either bounce back and move in the opposite direction or, for suitable parameter values of the system, tunnel to the acceptor. We estimate the energy efficiency of the donor-acceptor electron transport depending on the parameter values. Our calculations show that the soliton mechanism works for the parameter values of polypeptide macromolecules and conjugated polymers. We also investigate the donor-acceptor electron transport in thermalized molecular chains.

  18. Evidence for global electron transportation into the jovian inner magnetosphere.

    PubMed

    Yoshioka, K; Murakami, G; Yamazaki, A; Tsuchiya, F; Kimura, T; Kagitani, M; Sakanoi, T; Uemizu, K; Kasaba, Y; Yoshikawa, I; Fujimoto, M

    2014-09-26

    Jupiter's magnetosphere is a strong particle accelerator that contains ultrarelativistic electrons in its inner part. They are thought to be accelerated by whistler-mode waves excited by anisotropic hot electrons (>10 kiloelectron volts) injected from the outer magnetosphere. However, electron transportation in the inner magnetosphere is not well understood. By analyzing the extreme ultraviolet line emission from the inner magnetosphere, we show evidence for global inward transport of flux tubes containing hot plasma. High-spectral-resolution scanning observations of the Io plasma torus in the inner magnetosphere enable us to generate radial profiles of the hot electron fraction. It gradually decreases with decreasing radial distance, despite the short collisional time scale that should thermalize them rapidly. This indicates a fast and continuous resupply of hot electrons responsible for exciting the whistler-mode waves. PMID:25258073

  19. Electronic Band Structure and Sub-band-gap Absorption of Nitrogen Hyperdoped Silicon

    PubMed Central

    Zhu, Zhen; Shao, Hezhu; Dong, Xiao; Li, Ning; Ning, Bo-Yuan; Ning, Xi-Jing; Zhao, Li; Zhuang, Jun

    2015-01-01

    We investigated the atomic geometry, electronic band structure, and optical absorption of nitrogen hyperdoped silicon based on first-principles calculations. The results show that all the paired nitrogen defects we studied do not introduce intermediate band, while most of single nitrogen defects can introduce intermediate band in the gap. Considering the stability of the single defects and the rapid resolidification following the laser melting process in our sample preparation method, we conclude that the substitutional nitrogen defect, whose fraction was tiny and could be neglected before, should have considerable fraction in the hyperdoped silicon and results in the visible sub-band-gap absorption as observed in the experiment. Furthermore, our calculations show that the substitutional nitrogen defect has good stability, which could be one of the reasons why the sub-band-gap absorptance remains almost unchanged after annealing. PMID:26012369

  20. Aerosol Sources, Absorption, and Intercontinental Transport: Synergies Among Models, Remote Sensing, and Atmospheric Measurements

    NASA Technical Reports Server (NTRS)

    Chin, Mian; Chu, Allen; Levy, Robert; Remer, Lorraine; Kaufman, Yoram; Dubovik, Oleg; Holben, Brent; Eck, Tom; Anderson, Tad; Quinn, Patricia

    2004-01-01

    Aerosol climate forcing is one of the largest uncertainties in assessing the anthropogenic impact on the global climate system. This uncertainty arises from the poorly quantified aerosol sources, especially black carbon emissions, our limited knowledge of aerosol mixing state and optical properties, and the consequences of intercontinental transport of aerosols and their precursors. Here we use a global model GOCART to simulate atmospheric aerosols, including sulfate, black carbon, organic carbon, dust, and sea salt, from anthropogenic, .biomass burning, and natural sources. We compare the model calculated aerosol extinction and absorption with those quantities from the ground-based sun photometer measurements from AERON" at several different wavelengths and the field observations from ACE-Asia, and model calculated total aerosol optical depth and fine mode fractions with the MODIS satellite retrieval. We will also estimate the intercontinental transport of pollution and dust aerosols from their source regions to other areas in different seasons.

  1. Aerosol Sources, Absorption, and Intercontinental Transport: Synergies among Models, Remote Sensing, and Atmospheric Measurements

    NASA Technical Reports Server (NTRS)

    Chin, Mian; Ginoux, Paul; Dubovik, Oleg; Holben, Brent; Kaufman, Yoram; chu, Allen; Anderson, Tad; Quinn, Patricia

    2003-01-01

    Aerosol climate forcing is one of the largest uncertainties in assessing the anthropogenic impact on the global climate system. This uncertainty arises from the poorly quantified aerosol sources, especially black carbon emissions, our limited knowledge of aerosol mixing state and optical properties, and the consequences of intercontinental transport of aerosols and their precursors. Here we use a global model GOCART to simulate atmospheric aerosols, including sulfate, black carbon, organic carbon, dust, and sea salt, from anthropogenic, biomass burning, and natural sources. We compare the model calculated aerosol extinction and absorption with those quantities from the ground-based sun photometer measurements from AERONET at several different wavelengths and the field observations from ACE-Asia, and model calculated total aerosol optical depth and fine mode fractions with the MODIS satellite retrieval. We will also estimate the intercontinental transport of pollution and dust aerosols from their source regions to other areas in different seasons.

  2. Collisionless absorption, hot electron generation, and energy scaling in intense laser-target interaction

    SciTech Connect

    Liseykina, T.; Mulser, P.; Murakami, M.

    2015-03-15

    Among the various attempts to understand collisionless absorption of intense and superintense ultrashort laser pulses, a whole variety of models and hypotheses has been invented to describe the laser beam target interaction. In terms of basic physics, collisionless absorption is understood now as the interplay of the oscillating laser field with the space charge field produced by it in the plasma. A first approach to this idea is realized in Brunel's model the essence of which consists in the formation of an oscillating charge cloud in the vacuum in front of the target, therefore frequently addressed by the vague term “vacuum heating.” The investigation of statistical ensembles of orbits shows that the absorption process is localized at the ion-vacuum interface and in the skin layer: Single electrons enter into resonance with the laser field thereby undergoing a phase shift which causes orbit crossing and braking of Brunel's laminar flow. This anharmonic resonance acts like an attractor for the electrons and leads to the formation of a Maxwellian tail in the electron energy spectrum. Most remarkable results of our investigations are the Brunel like spectral hot electron distribution at the relativistic threshold, the minimum of absorption at Iλ{sup 2}≅(0.3−1.2)×10{sup 21} Wcm{sup −2}μm{sup 2} in the plasma target with the electron density of n{sub e}λ{sup 2}∼10{sup 23}cm{sup −3}μm{sup 2}, the drastic reduction of the number of hot electrons in this domain and their reappearance in the highly relativistic domain, and strong coupling, beyond expectation, of the fast electron jets with the return current through Cherenkov emission of plasmons. The hot electron energy scaling shows a strong dependence on intensity in the moderately relativistic domain Iλ{sup 2}≅(10{sup 18}−10{sup 20}) Wcm{sup −2}μm{sup 2}, a scaling in vague accordance with current published estimates in the range Iλ{sup 2}≅(0.14−3.5)×10{sup 21} Wcm{sup −2}

  3. Collisionless absorption, hot electron generation, and energy scaling in intense laser-target interaction

    NASA Astrophysics Data System (ADS)

    Liseykina, T.; Mulser, P.; Murakami, M.

    2015-03-01

    Among the various attempts to understand collisionless absorption of intense and superintense ultrashort laser pulses, a whole variety of models and hypotheses has been invented to describe the laser beam target interaction. In terms of basic physics, collisionless absorption is understood now as the interplay of the oscillating laser field with the space charge field produced by it in the plasma. A first approach to this idea is realized in Brunel's model the essence of which consists in the formation of an oscillating charge cloud in the vacuum in front of the target, therefore frequently addressed by the vague term "vacuum heating." The investigation of statistical ensembles of orbits shows that the absorption process is localized at the ion-vacuum interface and in the skin layer: Single electrons enter into resonance with the laser field thereby undergoing a phase shift which causes orbit crossing and braking of Brunel's laminar flow. This anharmonic resonance acts like an attractor for the electrons and leads to the formation of a Maxwellian tail in the electron energy spectrum. Most remarkable results of our investigations are the Brunel like spectral hot electron distribution at the relativistic threshold, the minimum of absorption at I λ 2 ≅ ( 0.3 - 1.2 ) × 10 21 Wcm - 2 μ m 2 in the plasma target with the electron density of n e λ 2 ˜ 10 23 cm - 3 μ m 2 , the drastic reduction of the number of hot electrons in this domain and their reappearance in the highly relativistic domain, and strong coupling, beyond expectation, of the fast electron jets with the return current through Cherenkov emission of plasmons. The hot electron energy scaling shows a strong dependence on intensity in the moderately relativistic domain I λ 2 ≅ ( 10 18 - 10 20 ) Wcm - 2 μ m 2 , a scaling in vague accordance with current published estimates in the range I λ 2 ≅ ( 0.14 - 3.5 ) × 10 21 Wcm - 2 μ m 2 , and again a distinct power increase beyond I = 3.5 × 10 21 Wcm

  4. Depth-selective X-ray absorption spectroscopy by detection of energy-loss Auger electrons

    NASA Astrophysics Data System (ADS)

    Isomura, Noritake; Soejima, Narumasa; Iwasaki, Shiro; Nomoto, Toyokazu; Murai, Takaaki; Kimoto, Yasuji

    2015-11-01

    A unique X-ray absorption spectroscopy (XAS) method is proposed for depth profiling of chemical states in material surfaces. Partial electron yield mode detecting energy-loss Auger electrons, called the inelastic electron yield (IEY) mode, enables a variation in the probe depth. As an example, Si K-edge XAS spectra for a well-defined multilayer sample (Si3N4/SiO2/Si) have been investigated using this method at various kinetic energies. We found that the peaks assigned to the layers from the top layer to the substrate appeared in the spectra in the order of increasing energy loss relative to the Auger electrons. Thus, the probe depth can be changed by the selection of the kinetic energy of the energy loss electrons in IEY-XAS.

  5. Support Effects on Electronic Behaviors of Gold Nanoparticles Studied by X-Ray Absorption Fine Structure

    SciTech Connect

    Li Zhongrui; Yan Wensheng; Wei Shiqiang

    2007-02-02

    The electronic properties of gold nanoparticles supported on different supports were studied with X-ray absorption fine structure (XAFS). It was found that the tunability of the d-electron distribution in the nano-sized Au clusters can be realized by selective supporting. The Au atoms in the clusters gain 5d electrons when supported on SiO2, and lose 5d electrons when loaded over MgO, Al2O3, and TiO2. Contractions in bond lengths of between 0.5 and 1.6% from bulk metal values were observed from EXAFS data. This work demonstrates that the important role of the different supports in the 5d-charge distribution of Au nanoparticles and usefulness of XAFS in probing the electronic behavior of noble metal nanoparticles.

  6. Dissipationless electron transport in photon-dressed nanostructures.

    PubMed

    Kibis, O V

    2011-09-01

    It is shown that the electron coupling to photons in field-dressed nanostructures can result in the ground electron-photon state with a nonzero electric current. Since the current is associated with the ground state, it flows without the Joule heating of the nanostructure and is nondissipative. Such a dissipationless electron transport can be realized in strongly coupled electron-photon systems with the broken time-reversal symmetry--particularly, in quantum rings and chiral nanostructures dressed by circularly polarized photons. PMID:21981519

  7. Electron Collision Cross Sections for the Cl2 Molecule from Electron Transport Coefficients

    NASA Astrophysics Data System (ADS)

    Tuan, Do Anh; Jeon, Byung-Hoon

    2011-08-01

    The measured electron transport coefficients (electron drift velocity, Townsend first ionization coefficient, electron attachment coefficient, and density-normalized effective ionization coefficient) in pure Cl2 have been analyzed to derive the currently best available electron collision cross section set of the elastic and inelastic electron collision cross sections for the Cl2 molecule using an electron swarm study and a two-term approximation of the Boltzmann equation for energy. The electron transport coefficients calculated using the derived cross sections are consistent with the experimental data over a wide range of E/N values (ratio of the electric field E to the neutral number density N). The present electron collision cross section set for the Cl2 molecule is the best available so far for quantitative numerical modeling plasma discharges for processing procedures with materials containing Cl2 molecules.

  8. Effect of dephasing on DNA sequencing via transverse electronic transport

    SciTech Connect

    Zwolak, Michael; Krems, Matt; Pershin, Yuriy V; Di Ventra, Massimiliano

    2009-01-01

    We study theoretically the effects of dephasing on DNA sequencing in a nanopore via transverse electronic transport. To do this, we couple classical molecular dynamics simulations with transport calculations using scattering theory. Previous studies, which did not include dephasing, have shown that by measuring the transverse current of a particular base multiple times, one can get distributions of currents for each base that are distinguishable. We introduce a dephasing parameter into transport calculations to simulate the effects of the ions and other fluctuations. These effects lower the overall magnitude of the current, but have little effect on the current distributions themselves. The results of this work further implicate that distinguishing DNA bases via transverse electronic transport has potential as a sequencing tool.

  9. Electron-Transport Properties of Few-Layer Black Phosphorus.

    PubMed

    Xu, Yuehua; Dai, Jun; Zeng, Xiao Cheng

    2015-06-01

    We perform the first-principles computational study of the effect of number of stacking layers and stacking style of the few-layer black phosphorus (BPs) on the electronic properties, including transport gap, current-voltage (i-v) relation, and differential conductance. Our computation is based on the nonequilibrium Green's function approach combined with density functional theory calculations. Specifically, we compute electron-transport properties of monolayer BP, bilayer BP, and trilayer BP as well as bilayer BPs with AB-, AA-, or AC-stacking. We find that the stacking number has greater influence on the transport gap than the stacking type. Conversely, the stacking type has greater influence on i-v curve and differential conductance than on the transport gap. This study offers useful guidance for determining the number of stacking layers and the stacking style of few-layer BP sheets in future experimental measurements and for potential applications in nanoelectronic devices. PMID:26266491

  10. Mitochondrial ROS Produced via Reverse Electron Transport Extend Animal Lifespan

    PubMed Central

    Scialò, Filippo; Sriram, Ashwin; Fernández-Ayala, Daniel; Gubina, Nina; Lõhmus, Madis; Nelson, Glyn; Logan, Angela; Cooper, Helen M.; Navas, Plácido; Enríquez, Jose Antonio; Murphy, Michael P.; Sanz, Alberto

    2016-01-01

    Summary Increased production of reactive oxygen species (ROS) has long been considered a cause of aging. However, recent studies have implicated ROS as essential secondary messengers. Here we show that the site of ROS production significantly contributes to their apparent dual nature. We report that ROS increase with age as mitochondrial function deteriorates. However, we also demonstrate that increasing ROS production specifically through respiratory complex I reverse electron transport extends Drosophila lifespan. Reverse electron transport rescued pathogenesis induced by severe oxidative stress, highlighting the importance of the site of ROS production in signaling. Furthermore, preventing ubiquinone reduction, through knockdown of PINK1, shortens lifespan and accelerates aging; phenotypes that are rescued by increasing reverse electron transport. These results illustrate that the source of a ROS signal is vital in determining its effects on cellular physiology and establish that manipulation of ubiquinone redox state is a valid strategy to delay aging. PMID:27076081

  11. Imaging electronic trap states in perovskite thin films with combined fluorescence and femtosecond transient absorption microscopy

    DOE PAGESBeta

    Xiao, Kai; Ma, Ying -Zhong; Simpson, Mary Jane; Doughty, Benjamin; Yang, Bin

    2016-04-22

    Charge carrier trapping degrades the performance of organometallic halide perovskite solar cells. To characterize the locations of electronic trap states in a heterogeneous photoactive layer, a spatially resolved approach is essential. Here, we report a comparative study on methylammonium lead tri-iodide perovskite thin films subject to different thermal annealing times using a combined photoluminescence (PL) and femtosecond transient absorption microscopy (TAM) approach to spatially map trap states. This approach coregisters the initially populated electronic excited states with the regions that recombine radiatively. Although the TAM images are relatively homogeneous for both samples, the corresponding PL images are highly structured. Themore » remarkable variation in the PL intensities as compared to transient absorption signal amplitude suggests spatially dependent PL quantum efficiency, indicative of trapping events. Furthermore, detailed analysis enables identification of two trapping regimes: a densely packed trapping region and a sparse trapping area that appear as unique spatial features in scaled PL maps.« less

  12. Imaging Electronic Trap States in Perovskite Thin Films with Combined Fluorescence and Femtosecond Transient Absorption Microscopy.

    PubMed

    Simpson, Mary Jane; Doughty, Benjamin; Yang, Bin; Xiao, Kai; Ma, Ying-Zhong

    2016-05-01

    Charge carrier trapping degrades the performance of organometallic halide perovskite solar cells. To characterize the locations of electronic trap states in a heterogeneous photoactive layer, a spatially resolved approach is essential. Here, we report a comparative study on methylammonium lead tri-iodide perovskite thin films subject to different thermal annealing times using a combined photoluminescence (PL) and femtosecond transient absorption microscopy (TAM) approach to spatially map trap states. This approach coregisters the initially populated electronic excited states with the regions that recombine radiatively. Although the TAM images are relatively homogeneous for both samples, the corresponding PL images are highly structured. The remarkable variation in the PL intensities as compared to transient absorption signal amplitude suggests spatially dependent PL quantum efficiency, indicative of trapping events. Detailed analysis enables identification of two trapping regimes: a densely packed trapping region and a sparse trapping area that appear as unique spatial features in scaled PL maps. PMID:27103096

  13. Progress in Simulating Turbulent Electron Thermal Transport in NSTX

    SciTech Connect

    Guttenfelder, Walter; Kaye, S. M.; Ren, Y.; Bell, R. E.; Hammett, G. W.; LeBlanc, B. P.; Mikkelsen, D. R.; Peterson, J. L.; Nevins, W. M.; Candy, J.; Yuh, H.

    2013-07-17

    Nonlinear simulations based on multiple NSTX discharge scenarios have progressed to help differentiate unique instability mechanisms and to validate with experimental turbulence and transport data. First nonlinear gyrokinetic simulations of microtearing (MT) turbulence in a high-beta NSTX H-mode discharge predict experimental levels of electron thermal transport that are dominated by magnetic flutter and increase with collisionality, roughly consistent with energy confinement times in dimensionless collisionality scaling experiments. Electron temperature gradient (ETG) simulations predict significant electron thermal transport in some low and high beta discharges when ion scales are suppressed by E x B shear. Although the predicted transport in H-modes is insensitive to variation in collisionality (inconsistent with confinement scaling), it is sensitive to variations in other parameters, particularly density gradient stabilization. In reversed shear (RS) Lmode discharges that exhibit electron internal transport barriers, ETG transport has also been shown to be suppressed nonlinearly by strong negative magnetic shear, s<<0. In many high beta plasmas, instabilities which exhibit a stiff beta dependence characteristic of kinetic ballooning modes (KBM) are sometimes found in the core region. However, they do not have a distinct finite beta threshold, instead transitioning gradually to a trapped electron mode (TEM) as beta is reduced to zero. Nonlinear simulations of this "hybrid" TEM/KBM predict significant transport in all channels, with substantial contributions from compressional magnetic perturbations. As multiple instabilities are often unstable simultaneously in the same plasma discharge, even on the same flux surface, unique parametric dependencies are discussed which may be useful for distinguishing the different mechanisms experimentally.

  14. Collective microdynamics and noise suppression in dispersive electron beam transport

    SciTech Connect

    Gover, Avraham; Dyunin, Egor; Duchovni, Tamir; Nause, Ariel

    2011-12-15

    A general formulation is presented for deep collective interaction micro-dynamics in dispersive e-beam transport. In the regime of transversely coherent interaction, the formulation is applicable to both coherent and random temporal modulation of the electron beam. We demonstrate its use for determining the conditions for suppressing beam current noise below the classical shot-noise level by means of transport through a dispersive section with a small momentum compaction parameter.

  15. Simulation of electron transport in quantum well devices

    NASA Technical Reports Server (NTRS)

    Miller, D. R.; Gullapalli, K. K.; Reddy, V. R.; Neikirk, D. P.

    1992-01-01

    Double barrier resonant tunneling diodes (DBRTD) have received much attention as possible terahertz devices. Despite impressive experimental results, the specifics of the device physics (i.e., how the electrons propagate through the structure) are only qualitatively understood. Therefore, better transport models are warranted if this technology is to mature. In this paper, the Lattice Wigner function is used to explain the important transport issues associated with DBRTD device behavior.

  16. Coherently driven, ultrafast electron-phonon dynamics in transport junctions

    SciTech Connect

    Szekely, Joshua E.; Seideman, Tamar

    2014-07-28

    Although the vast majority of studies of transport via molecular-scale heterojunctions have been conducted in the (static) energy domain, experiments are currently beginning to apply time domain approaches to the nanoscale transport problem, combining spatial with temporal resolution. It is thus an opportune time for theory to develop models to explore both new phenomena in, and new potential applications of, time-domain, coherently driven molecular electronics. In this work, we study the interaction of a molecular phonon with an electronic wavepacket transmitted via a conductance junction within a time-domain model that treats the electron and phonon on equal footing and spans the weak to strong electron-phonon coupling strengths. We explore interference between two coherent energy pathways in the electronic subspace, thus complementing previous studies of coherent phenomena in conduction junctions, where the stationary framework was used to study interference between spatial pathways. Our model provides new insights into phase decoherence and population relaxation within the electronic subspace, which have been conventionally treated by density matrix approaches that often rely on phenomenological parameters. Although the specific case of a transport junction is explored, our results are general, applying also to other instances of coupled electron-phonon systems.

  17. Quercetin inhibits intestinal iron absorption and ferroportin transporter expression in vivo and in vitro.

    PubMed

    Lesjak, Marija; Hoque, Rukshana; Balesaria, Sara; Skinner, Vernon; Debnam, Edward S; Srai, Surjit K S; Sharp, Paul A

    2014-01-01

    Balancing systemic iron levels within narrow limits is critical for maintaining human health. There are no known pathways to eliminate excess iron from the body and therefore iron homeostasis is maintained by modifying dietary absorption so that it matches daily obligatory losses. Several dietary factors can modify iron absorption. Polyphenols are plentiful in human diet and many compounds, including quercetin--the most abundant dietary polyphenol--are potent iron chelators. The aim of this study was to investigate the acute and longer-term effects of quercetin on intestinal iron metabolism. Acute exposure of rat duodenal mucosa to quercetin increased apical iron uptake but decreased subsequent basolateral iron efflux into the circulation. Quercetin binds iron between its 3-hydroxyl and 4-carbonyl groups and methylation of the 3-hydroxyl group negated both the increase in apical uptake and the inhibition of basolateral iron release, suggesting that the acute effects of quercetin on iron transport were due to iron chelation. In longer-term studies, rats were administered quercetin by a single gavage and iron transporter expression measured 18 h later. Duodenal FPN expression was decreased in quercetin-treated rats. This effect was recapitulated in Caco-2 cells exposed to quercetin for 18 h. Reporter assays in Caco-2 cells indicated that repression of FPN by quercetin was not a transcriptional event but might be mediated by miRNA interaction with the FPN 3'UTR. Our study highlights a novel mechanism for the regulation of iron bioavailability by dietary polyphenols. Potentially, diets rich in polyphenols might be beneficial for patients groups at risk of iron loading by limiting the rate of intestinal iron absorption. PMID:25058155

  18. Transport Properties of III-N Hot Electron Transistors

    NASA Astrophysics Data System (ADS)

    Suntrup, Donald J., III

    Unipolar hot electron transistors (HETs) represent a tantalizing alternative to established bipolar transistor technologies. During device operation electrons are injected over a large emitter barrier into the base where they travel along the device axis with very high velocity. Upon arrival at the collector barrier, high-energy electrons pass over the barrier and contribute to collector current while low-energy electrons are quantum mechanically reflected back into the base. Designing the base with thickness equal to or less than the hot electron mean free path serves to minimize scattering events and thus enable quasi-ballistic operation. Large current gain is achieved by increasing the ratio of transmitted to reflected electrons. Although III-N HETs have undergone substantial development in recent years, there remain ample opportunities to improve key device metrics. In order to engineer improved device performance, a deeper understanding of the operative transport physics is needed. Fortunately, the HET provides fertile ground for studying several prominent electron transport phenomena. In this thesis we present results from several studies that use the III-N HET as both emitter and analyzer of hot electron momentum states. The first provides a measurement of the hot electron mean free path and the momentum relaxation rate in GaN; the second relies on a new technique called electron injection spectroscopy to investigate the effects of barrier height inhomogeneity in the emitter. To supplement our analysis we develop a comprehensive theory of coherent electron transport that allows us to model the transfer characteristics of complex heterojunctions. Such a model provides a theoretical touchstone with which to compare our experimental results. While these studies are of potential interest in their own right, we interpret the results with an eye toward improving next-generation device performance.

  19. Ab-initio calculations of the hydrogen-uranium system. Part I: Surface phenomena, absorption, transport and trapping

    SciTech Connect

    Taylor, Christopher D; Lillard, R Scott

    2009-01-01

    Density functional theory was applied to the initial steps of uranium hydriding: surface phenomena, absorption, bulk transport and trapping. H adsorbs exothermically to the (0 0 1) surface, yet H absorption into the bulk is endothermic, with off-center octahedral absorption having the lowest absorption energy of 0.39 eV, relative to molecular H{sub 2}. H absorption in interstitial sites causes a local softening of the bulk modulus. Diffusion of H in unstrained {alpha}-U has a barrier of 0.6 eV. The energy of H absorption adjacent to the chemical impurities C, S, Si was lowered by an amount proportional to the size of the impurity atom, and the resulting lattice strain Si > S > C. Thus, impurities may promote hydriding by providing surfaces or prestrained zones for H uptake.

  20. Electronic measurement and control of spin transport in silicon

    NASA Astrophysics Data System (ADS)

    Appelbaum, Ian; Huang, Biqin; Monsma, Douwe J.

    2007-05-01

    The spin lifetime and diffusion length of electrons are transport parameters that define the scale of coherence in spintronic devices and circuits. As these parameters are many orders of magnitude larger in semiconductors than in metals, semiconductors could be the most suitable for spintronics. So far, spin transport has only been measured in direct-bandgap semiconductors or in combination with magnetic semiconductors, excluding a wide range of non-magnetic semiconductors with indirect bandgaps. Most notable in this group is silicon, Si, which (in addition to its market entrenchment in electronics) has long been predicted a superior semiconductor for spintronics with enhanced lifetime and transport length due to low spin-orbit scattering and lattice inversion symmetry. Despite this promise, a demonstration of coherent spin transport in Si has remained elusive, because most experiments focused on magnetoresistive devices; these methods fail because of a fundamental impedance mismatch between ferromagnetic metal and semiconductor, and measurements are obscured by other magnetoelectronic effects. Here we demonstrate conduction-band spin transport across 10μm undoped Si in a device that operates by spin-dependent ballistic hot-electron filtering through ferromagnetic thin films for both spin injection and spin detection. As it is not based on magnetoresistance, the hot-electron spin injection and spin detection avoids impedance mismatch issues and prevents interference from parasitic effects. The clean collector current shows independent magnetic and electrical control of spin precession, and thus confirms spin coherent drift in the conduction band of silicon.

  1. Electronic states of DNA and M-DNA studied by optical absorption

    NASA Astrophysics Data System (ADS)

    Tsuburaya, Makoto; Sakamoto, Hirokazu; Mizoguchi, Kenji

    2014-02-01

    To unveil the electronic states of divalent metal ion incorporated M-DNAs, where M is Mg, Mn, Ni, Co, or Fe, optical absorption spectra have been studied in aqueous solutions of single-stranded (SS) 30mer DNA of poly(dA) (adenine), poly(dG) (guanine), poly(dT) (thymine), poly(dC) (cytosine), salmon-sperm DNA (B-DNA), and M-DNA. The absorption spectrum of the double-stranded (DS) B-DNA can be reproduced with the sum of the four absorption spectra of the SS oligo-DNAs in the ratio corresponding to the composition of B-DNA. This observation suggests that the interactions between complementary strands of DS DNA are negligibly weaker than the bandwidths of the optical spectra. In the metal-incorporated M-DNAs, except for Fe-DNA, the absorption spectra show no significant qualitative change from that of B-DNA. Quantitatively, however, the absorption intensity decreases by ≈15% uniquely in a DS poly(dA)-poly(dT) solution with adding MCl2, while nothing happens quantitatively and qualitatively in any SS oligo-DNA and DS poly(dG)-poly(dC) solutions, suggesting some suppression of the electronic excitation only in the Adenine-M-Thymine complex. In contrast, remarkable differences have been observed in Fe-DNA, prepared with FeCl2 and B-DNA. New absorption bands appear in the intragap energy of Fe-DNA, in addition to the suppression of the interband absorption peak of DNA at 4.8 eV. The intragap absorption is attributed to the appearance of Fe3+ species with the same spectral feature as that of FeCl3, that is, purely ionic Fe3+ species. This observation suggests that FeCl2+B-DNA forms Fe-DNA with hydrated Fe3+ ions with ionic bonds. Thus, it is concluded that the charge transfer from Fe2+ to DNA has occurred in Fe-DNA and that the transferred charges are expected to be located in the nearby bases.

  2. Theoretical modeling of low-energy electronic absorption bands in reduced cobaloximes

    DOE PAGESBeta

    Bhattacharjee, Anirban; Chavarot-Kerlidou, Murielle; Dempsey, Jillian L.; Gray, Harry B.; Fujita, Etsuko; Muckerman, James T.; Fontecave, Marc; Artero, Vincent; Arantes, Guilherme M.; Field, Martin J.

    2014-08-11

    Here, we report that the reduced Co(I) states of cobaloximes are powerful nucleophiles that play an important role in the hydrogen-evolving catalytic activity of these species. In this work we have analyzed the low energy electronic absorption bands of two cobaloxime systems experimentally and using a variety of density functional theory and molecular orbital ab initio quantum chemical approaches. Overall we find a reasonable qualitative understanding of the electronic excitation spectra of these compounds but show that obtaining quantitative results remains a challenging task.

  3. Theoretical modeling of low-energy electronic absorption bands in reduced cobaloximes

    SciTech Connect

    Bhattacharjee, Anirban; Chavarot-Kerlidou, Murielle; Dempsey, Jillian L.; Gray, Harry B.; Fujita, Etsuko; Muckerman, James T.; Fontecave, Marc; Artero, Vincent; Arantes, Guilherme M.; Field, Martin J.

    2014-08-11

    Here, we report that the reduced Co(I) states of cobaloximes are powerful nucleophiles that play an important role in the hydrogen-evolving catalytic activity of these species. In this work we have analyzed the low energy electronic absorption bands of two cobaloxime systems experimentally and using a variety of density functional theory and molecular orbital ab initio quantum chemical approaches. Overall we find a reasonable qualitative understanding of the electronic excitation spectra of these compounds but show that obtaining quantitative results remains a challenging task.

  4. Theoretical Modeling of Low Energy Electronic Absorption Bands in Reduced Cobaloximes

    PubMed Central

    Bhattacharjee, Anirban; Chavarot-Kerlidou, Murielle; Dempsey, Jillian L.; Gray, Harry B.; Fujita, Etsuko; Muckerman, James T.; Fontecave, Marc; Artero, Vincent; Arantes, Guilherme M.; Field, Martin J.

    2015-01-01

    The reduced Co(I) states of cobaloximes are powerful nucleophiles that play an important role in the hydrogen-evolving catalytic activity of these species. In this work we have analyzed the low energy electronic absorption bands of two cobaloxime systems experimentally and using a variety of density functional theory and molecular orbital ab initio quantum chemical approaches. Overall we find a reasonable qualitative understanding of the electronic excitation spectra of these compounds but show that obtaining quantitative results remains a challenging task. PMID:25113847

  5. Electronic transport in polycrystalline samples of icosahedral phases

    NASA Astrophysics Data System (ADS)

    Vekilov, Yu. Kh.; Chernikov, M. A.; Dolinichek, Ya.

    2016-01-01

    The low-temperature electronic transport in polycrystals of quasicrystalline phases with an icosahedral structure has been analyzed within the model of the granular electronic system. In this model, the grains (drops) of a metallic icosahedral phase are surrounded by extended defects and grain boundaries, which create an insulating environment. The electron transport in this model is determined by the size quantization of electronic states inside metallic grains, by intergranular tunneling, and by electrostatic barriers. Depending on the temperature and structural state of the system, the hopping conductivity with variable lengths of jumps in the Efros-Shklovskii or Mott regime is observed with predominantly elastic cotunneling. In the case of strong intergranular coupling, the system passes into the metallic regime with the exponential temperature dependence of the electrical conductivity.

  6. Contactless electronic transport in a bio-molecular junction

    SciTech Connect

    Hossain, Faruque M. Al-Dirini, Feras; Skafidas, Efstratios

    2014-07-28

    Molecular electronics hold promise for next generation ultra-low power, nano-scale integrated electronics. The main challenge in molecular electronics is to make a reliable interface between molecules and metal electrodes. Interfacing metals and molecules detrimentally affects the characteristics of nano-scale molecular electronic devices. It is therefore essential to investigate alternative arrangements such as contact-less tunneling gaps wherever such configurations are feasible. We conduct ab initio density functional theory and non-equilibrium Green's functions calculations to investigate the transport properties of a biocompatible glycine molecular junction. By analyzing the localized molecular orbital energy distributions and transmission probabilities in the transport-gap, we find a glycine molecule confined between two gold electrodes, without making a contact, is energetically stable and possesses high tunneling current resembling an excellent ohmic-like interface.

  7. Ozone absorption spectroscopy in search of low-lying electronic states

    NASA Technical Reports Server (NTRS)

    Anderson, S. M.; Mauersberger, K.

    1995-01-01

    A spectrometer capable of detecting ozone absorption features 9 orders of magnitude weaker than the Hartley band has been employed to investigate the molecule's near-infrared absorption spectrum. At this sensitivity a wealth of information on the low-lying electronically excited states often believed to play a role in atmospheric chemistry is available in the form of vibrational and rotational structure. We have analyzed these spectra using a combination of digital filtering and isotope substitution and find evidence for three electronically excited states below 1.5 eV. The lowest of these states is metastable, bound by approximately 0.1 eV and probably the (3)A2 rather than the (3)B2 state. Its adiabatic electronic energy is 1.24 +/- 0.01 eV, slightly above the dissociation energy of the ground state. Two higher states, at 1.29 +/- 0.03 and 1.48 +/- 0.03 eV are identified as the (3)B2 and the (3)B1, respectively. Combined with other recent theoretical and experimental data on the low-lying electronic states of ozone, these results imply that these are, in fact, the lowest three excited states; that is, there are no electronically excited states of ozone lying below the energy of O(3P) + O2((3)Sigma(-), v = 0). Some of the implications for atmospheric chemistry are considered.

  8. Elastic and absorption cross sections for electron-nitrous oxide collisions

    NASA Astrophysics Data System (ADS)

    Lee, M.-T.; Iga, I.; Homem, M. G.; Machado, L. E.; Brescansin, L. M.

    2002-06-01

    In this work, we present a joint theoretical-experimental study on electron-N2O collisions in the intermediate energy range. More specifically, calculated and measured elastic differential, integral, and momentum-transfer cross sections, as well as calculated total and absorption cross sections are reported. The measurements were performed using a crossed electron-beam-molecular-beam geometry. The angular distribution of the scattered electrons was converted to absolute cross sections using the relative-flow technique. Theoretically, a complex optical potential is used to represent the electron-molecule interaction dynamics in the present calculation. The Schwinger variational iterative method combined with the distorted-wave approximation is used to solve the scattering equations. The comparison of the present calculated results with the measured results as well as with the existing experimental and theoretical data shows good agreement.

  9. Study of Electron Transport and Amplification in Diamond

    SciTech Connect

    Muller, Erik M.; Ben-Zvi, Ilan

    2013-03-31

    As a successful completion of this award, my group has demonstrated world-leading electron gain from diamond for use in a diamond-amplified photocathode. Also, using high-resolution photoemission measurements we were able to uncover exciting new physics of the electron emission mechanisms from hydrogen terminated diamond. Our work, through the continued support of HEP, has resulted in a greater understanding of the diamond material science, including current limits, charge transport modeling, and spatial uniformity.

  10. Origin of electronic transport of lithium phthalocyanine iodine crystal

    SciTech Connect

    Koike, Noritake; Oda, Masato; Shinozuka, Yuzo

    2013-12-04

    The electronic structures of Lithium Phthalocyanine Iodine are investigated using density functional theory. Comparing the band structures of several model crystals, the metallic conductivity of highly doped LiPcI{sub x} can be explained by the band of doped iodine. These results reveal that there is a new mechanism for electronic transport of doped organic semiconductors that the dopant band plays the main role.

  11. Two-stream approach to electron transport and thermalization

    SciTech Connect

    Stamnes, K.

    1981-04-01

    An explicit solution to the electron transport and energy degradation problem is presented in the two-stream approximation. The validity of this simple approach is discussed, and it is shown that it can be extended to high electron energies (appropriate for applications to auroras) provided the coupling between the two streams, described by the backscatter ratio, is correctly estimated. A simple formula for the backscatter ratio which can be used at all energies is derived.

  12. Colloquium: Transport in strongly correlated two dimensional electron fluids

    NASA Astrophysics Data System (ADS)

    Spivak, B.; Kravchenko, S. V.; Kivelson, S. A.; Gao, X. P. A.

    2010-04-01

    An overview of the measured transport properties of the two dimensional electron fluids in high mobility semiconductor devices with low electron densities is presented as well as some of the theories that have been proposed to account for them. Many features of the observations are not easily reconciled with a description based on the well understood physics of weakly interacting quasiparticles in a disordered medium. Rather, they reflect new physics associated with strong correlation effects, which warrant further study.

  13. The Role of Sodium-Dependent Glucose Transporter 1 and Glucose Transporter 2 in the Absorption of Cyanidin-3-O-β-Glucoside in Caco-2 Cells

    PubMed Central

    Zou, Tang-Bin; Feng, Dan; Song, Gang; Li, Hua-Wen; Tang, Huan-Wen; Ling, Wen-Hua

    2014-01-01

    Anthocyanins have multiple biological activities of benefit to human health. While a few studies have been conducted to evaluate the bioavailability of anthocyanins, the mechanisms of their absorption mechanism remain ill-defined. In the present study, we investigated the absorption mechanism of cyanidin-3-O-β-glucoside (Cy-3-G) in human intestinal epithelial (Caco-2) cells. Cy-3-G transport was assessed by measuring the absorptive and efflux direction. Inhibition studies were conducted using the pharmacological agents, phloridzin, an inhibitor of sodium-dependent glucose transporter 1 (SGLT1), or phloretin, an inhibitor of glucose transporter 2 (GLUT2). The results showed that phloridzin and phloretin significantly inhibited the absorption of Cy-3-G. In addition, Caco-2 cells transfected with small interfering RNA (siRNA) specific for SGLT1 or GLUT2 showed significantly decreased Cy-3-G absorption. These siRNA transfected cells also showed a significantly decreased rate of transport of Cy-3-G compared with the control group. These findings suggest that Cy-3-G absorption is dependent on the activities of SGLT1 and GLUT2 in the small intestine and that SGLT1 and GLUT2 could be a limiting step for the bioavailability of Cy-3-G. PMID:25314643

  14. The role of sodium-dependent glucose transporter 1 and glucose transporter 2 in the absorption of cyanidin-3-o-β-glucoside in Caco-2 cells.

    PubMed

    Zou, Tang-Bin; Feng, Dan; Song, Gang; Li, Hua-Wen; Tang, Huan-Wen; Ling, Wen-Hua

    2014-10-01

    Anthocyanins have multiple biological activities of benefit to human health. While a few studies have been conducted to evaluate the bioavailability of anthocyanins, the mechanisms of their absorption mechanism remain ill-defined. In the present study, we investigated the absorption mechanism of cyanidin-3-O-β-glucoside (Cy-3-G) in human intestinal epithelial (Caco-2) cells. Cy-3-G transport was assessed by measuring the absorptive and efflux direction. Inhibition studies were conducted using the pharmacological agents, phloridzin, an inhibitor of sodium-dependent glucose transporter 1 (SGLT1), or phloretin, an inhibitor of glucose transporter 2 (GLUT2). The results showed that phloridzin and phloretin significantly inhibited the absorption of Cy-3-G. In addition, Caco-2 cells transfected with small interfering RNA (siRNA) specific for SGLT1 or GLUT2 showed significantly decreased Cy-3-G absorption. These siRNA transfected cells also showed a significantly decreased rate of transport of Cy-3-G compared with the control group. These findings suggest that Cy-3-G absorption is dependent on the activities of SGLT1 and GLUT2 in the small intestine and that SGLT1 and GLUT2 could be a limiting step for the bioavailability of Cy-3-G. PMID:25314643

  15. Electron transport in magnetrons by a posteriori Monte Carlo simulations

    NASA Astrophysics Data System (ADS)

    Costin, C.; Minea, T. M.; Popa, G.

    2014-02-01

    Electron transport across magnetic barriers is crucial in all magnetized plasmas. It governs not only the plasma parameters in the volume, but also the fluxes of charged particles towards the electrodes and walls. It is particularly important in high-power impulse magnetron sputtering (HiPIMS) reactors, influencing the quality of the deposited thin films, since this type of discharge is characterized by an increased ionization fraction of the sputtered material. Transport coefficients of electron clouds released both from the cathode and from several locations in the discharge volume are calculated for a HiPIMS discharge with pre-ionization operated in argon at 0.67 Pa and for very short pulses (few µs) using the a posteriori Monte Carlo simulation technique. For this type of discharge electron transport is characterized by strong temporal and spatial dependence. Both drift velocity and diffusion coefficient depend on the releasing position of the electron cloud. They exhibit minimum values at the centre of the race-track for the secondary electrons released from the cathode. The diffusion coefficient of the same electrons increases from 2 to 4 times when the cathode voltage is doubled, in the first 1.5 µs of the pulse. These parameters are discussed with respect to empirical Bohm diffusion.

  16. Molecular electronics: Some views on transport junctions and beyond

    PubMed Central

    Joachim, Christian; Ratner, Mark A.

    2005-01-01

    The field of molecular electronics comprises a fundamental set of issues concerning the electronic response of molecules as parts of a mesoscopic structure and a technology-facing area of science. We will overview some important aspects of these subfields. The most advanced ideas in the field involve the use of molecules as individual logic or memory units and are broadly based on using the quantum state space of the molecule. Current work in molecular electronics usually addresses molecular junction transport, where the molecule acts as a barrier for incoming electrons: This is the fundamental Landauer idea of “conduction as scattering” generalized to molecular junction structures. Another point of view in terms of superexchange as a guiding mechanism for coherent electron transfer through the molecular bridge is discussed. Molecules generally exhibit relatively strong vibronic coupling. The last section of this overview focuses on vibronic effects, including inelastic electron tunneling spectroscopy, hysteresis in junction charge transport, and negative differential resistance in molecular transport junctions. PMID:15956192

  17. Remote plasmon-induced heat transfer probed by the electronic transport of a gold nanowire

    NASA Astrophysics Data System (ADS)

    Mennemanteuil, M.-M.; Buret, M.; Cazier, N.; Colas-Des-Francs, G.; Bouhelier, A.; Besbes, M.; Ben-Abdallah, P.

    2016-07-01

    We show in this paper that the heat generated by the optical excitation of resonant plasmonic antennas and diffusing along a simple glass/air interface disturbs the electron transport of a nearby conductive element. By probing the temperature-dependent resistance of a gold nanowire Rnw(T ) , we quantitatively analyze the impact of a resonant absorption of the laser by the antennas. We find that the temperature rise at the nanowire induced by the laser absorption of a distant nanoparticle may exceed that of a direct illumination of the nanowire itself. We also find that a global calibration of the temperature-dependent resistance underestimates the heat generated locally by the laser. The local temperatures deduced from resistance variations are verified by numerical simulations with a very satisfactory agreement.

  18. Photosynthetic electron transport and specific photoprotective responses in wheat leaves under drought stress.

    PubMed

    Zivcak, Marek; Brestic, Marian; Balatova, Zuzana; Drevenakova, Petra; Olsovska, Katarina; Kalaji, Hazem M; Yang, Xinghong; Allakhverdiev, Suleyman I

    2013-11-01

    The photosynthetic responses of wheat (Triticum aestivum L.) leaves to different levels of drought stress were analyzed in potted plants cultivated in growth chamber under moderate light. Low-to-medium drought stress was induced by limiting irrigation, maintaining 20 % of soil water holding capacity for 14 days followed by 3 days without water supply to induce severe stress. Measurements of CO2 exchange and photosystem II (PSII) yield (by chlorophyll fluorescence) were followed by simultaneous measurements of yield of PSI (by P700 absorbance changes) and that of PSII. Drought stress gradually decreased PSII electron transport, but the capacity for nonphotochemical quenching increased more slowly until there was a large decrease in leaf relative water content (where the photosynthetic rate had decreased by half or more). We identified a substantial part of PSII electron transport, which was not used by carbon assimilation or by photorespiration, which clearly indicates activities of alternative electron sinks. Decreasing the fraction of light absorbed by PSII and increasing the fraction absorbed by PSI with increasing drought stress (rather than assuming equal absorption by the two photosystems) support a proposed function of PSI cyclic electron flow to generate a proton-motive force to activate nonphotochemical dissipation of energy, and it is consistent with the observed accumulation of oxidized P700 which causes a decrease in PSI electron acceptors. Our results support the roles of alternative electron sinks (either from PSII or PSI) and cyclic electron flow in photoprotection of PSII and PSI in drought stress conditions. In future studies on plant stress, analyses of the partitioning of absorbed energy between photosystems are needed for interpreting flux through linear electron flow, PSI cyclic electron flow, along with alternative electron sinks. PMID:23860828

  19. ELECTRONIC AND TRANSPORT PROPERTIES OF THERMOELECTRIC Ru2Si3

    NASA Astrophysics Data System (ADS)

    Singh, David J.; Parker, David

    2013-10-01

    We report calculations of the doping and temperature dependent thermopower of Ru2Si3 based on Boltzmann transport theory and the first principles electronic structure. We find that the performance reported to date can be significantly improved by optimization of the doping level and that ultimately n-type should have higher ZT than p-type.

  20. Investigation of electron beam transport in a helical undulator

    SciTech Connect

    Jeong, Y.U.; Lee, B.C.; Kim, S.K.

    1995-12-31

    Lossless transport of electrons through the undulator is essential for CW operation of the FELs driven by recirculating electrostatic accelerators. We calculate the transport ratio of an electron beam in a helical undulator by using a 3-D simulation code and compare the results with the experimental results. The energy and the current of the electron beam are 400 keV and 2 A, respectively. The 3-D distribution of the magnetic field of a practical permanent-magnet helical undulator is measured and is used in the calculations. The major parameters of the undutlator are : period = 32 mm, number of periods = 20, number of periods in adiabatic region = 3.5, magnetic field strength = 1.3 kG. The transport ratio is very sensitive to the injection condition of the electron beam such as the emittance, the diameter, the divergence, etc.. The injection motion is varied in the experiments by changing the e-gun voltage or the field strength of the focusing magnet located at the entrance of the undulator. It is confirmed experimentally and with simulations that most of the beam loss occurs at the adiabatic region of the undulator regardless of the length of the adiabatic region The effect of axial guiding magnetic field on the beam finish is investigated. According to the simulations, the increase of the strength of axial magnetic field from 0 to 1 kG results in the increase of the transport ratio from 15 % to 95%.

  1. Transport Experiments on 2D Correlated Electron Physics in Semiconductors

    SciTech Connect

    Tsui, Daniel

    2014-03-24

    This research project was designed to investigate experimentally the transport properties of the 2D electrons in Si and GaAs, two prototype semiconductors, in several new physical regimes that were previously inaccessible to experiments. The research focused on the strongly correlated electron physics in the dilute density limit, where the electron potential energy to kinetic energy ratio rs>>1, and on the fractional quantum Hall effect related physics in nuclear demagnetization refrigerator temperature range on samples with new levels of purity and controlled random disorder.

  2. Electron energy transport and magnetic curvature driven modes

    SciTech Connect

    Coppi, B.; Tang, W.M.

    1984-10-01

    A transport coefficient for anomalous electron thermal conduction is constructed on the basis of the so-called Principle of Profile Consistency. It is assumed that the relevant modes in plasma where a substantial fraction of the electron population is magnetically trapped produce magnetic reconnection at a microscopic level and are driven by the combined effects of the plasma pressure gradient and the magnetic field curvature. Consequently, the scaling for the electron energy confinement time exhibits a strongly favorable dependence on the radius of magnetic curvature.

  3. Ferroelectric polarization driven optical absorption and charge carrier transport in CH3NH3PbI3/TiO2-based photovoltaic cells

    NASA Astrophysics Data System (ADS)

    Feng, Hong-Jian

    2015-09-01

    Time-dependent density-functional theory(TD-DFT) calculations show that photogenerated electrons accumulate at the interface of CH3NH3PbI3/TiO2. Electrons transport from CH3NH3PbI3 side to TiO2 side, and the recombination of charge carriers is significantly reduced in this heterostructure. This can unambiguously explain why the power conversion efficiency and the open-circuit voltage are so high in the mesoporous TiO2 with an ultrathin layer of the hybrid halide perovskites. The calculated absorption spectrum of CH3NH3PbI3 agrees well with the experimental measurements. Our TD-DFT calculations confirm the connection between the ferroelectric polarization and the optical absorption. The polarization is caused by the combination of stereochemical activity of the lone pair of Pb-6s2 and the distortions of the organic moieties. Ti-3d states play crucial role in the formation of electron-hole pairs and make TiO2 as an electron transport material.

  4. Suppression of infrared absorption in nanostructured metals by controlling Faraday inductance and electron path length.

    PubMed

    Han, Sang Eon

    2016-02-01

    Nanostructured metals have been intensively studied for optical applications over the past few decades. However, the intrinsic loss of metals has limited the optical performance of the metal nanostructures in diverse applications. In particular, light concentration in metals by surface plasmons or other resonances causes substantial absorption in metals. Here, we avoid plasmonic excitations for low loss and investigate methods to further suppress loss in nanostructured metals. We demonstrate that parasitic absorption in metal nanostructures can be significantly reduced over a broad band by increasing the Faraday inductance and the electron path length. For an example structure, the loss is reduced in comparison to flat films by more than an order of magnitude over most of the very broad spectrum between short and long wavelength infrared. For a photodetector structure, the fraction of absorption in the photoactive material increases by two orders of magnitude and the photoresponsivity increases by 15 times because of the selective suppression of metal absorption. These findings could benefit many metal-based applications that require low loss such as photovoltaics, photoconductive detectors, solar selective surfaces, infrared-transparent defrosting windows, and other metamaterials. PMID:26906830

  5. Atomistic simulations of divacancy defects in armchair graphene nanoribbons: Stability, electronic structure, and electron transport properties

    NASA Astrophysics Data System (ADS)

    Zhao, Jun; Zeng, Hui; Wei, Jianwei; Li, Biao; Xu, Dahai

    2014-01-01

    Using the first principles calculations associated with nonequilibrium Green's function, we have studied the electronic structures and quantum transport properties of defective armchair graphene nanoribbon (AGNR) in the presence of divacancy defects. The triple pentagon-triple heptagon (555-777) defect in the defective AGNR is energetically more favorable than the pentagon-octagon-pentagon (5-8-5) defect. Our calculated results reveal that both 5-8-5-like defect and 555-777-like defect in AGNR could improve the electron transport. It is anticipated that defective AGNRs can exhibit large range variations in transport behaviors, which are strongly dependent on the distributions of the divacancy defect.

  6. Optimal-transport formulation of electronic density-functional theory

    NASA Astrophysics Data System (ADS)

    Buttazzo, Giuseppe; De Pascale, Luigi; Gori-Giorgi, Paola

    2012-06-01

    The most challenging scenario for Kohn-Sham density-functional theory, that is, when the electrons move relatively slowly trying to avoid each other as much as possible because of their repulsion (strong-interaction limit), is reformulated here as an optimal transport (or mass transportation theory) problem, a well-established field of mathematics and economics. In practice, we show that to solve the problem of finding the minimum possible internal repulsion energy for N electrons in a given density ρ(r) is equivalent to find the optimal way of transporting N-1 times the density ρ into itself, with the cost function given by the Coulomb repulsion. We use this link to set the strong-interaction limit of density-functional theory on firm ground and to discuss the potential practical aspects of this reformulation.

  7. Neoclassical electron and ion transport in toroidally rotating plasmas

    SciTech Connect

    Sugama, H.; Horton, W.

    1997-06-01

    Neoclassical transport processes of electrons and ions are investigated in detail for toroidally rotating axisymmetric plasmas with large flow velocities on the order of the ion thermal speed. The Onsager relations for the flow-dependent neoclassical transport coefficients are derived from the symmetry properties of the drift kinetic equation with the self-adjoint collision operator. The complete neoclassical transport matrix with the Onsager symmetry is obtained for the rotating plasma consisting of electrons and single-species ions in the Pfirsch{endash}Schl{umlt u}ter and banana regimes. It is found that the inward banana fluxes of particles and toroidal momentum are driven by the parallel electric field, which are phenomena coupled through the Onsager symmetric off-diagonal coefficients to the parallel currents caused by the radial thermodynamic forces conjugate to the inward fluxes, respectively. {copyright} {ital 1997 American Institute of Physics.}

  8. First-principles calculation of electronic structure and optical absorption of BN ZnO

    NASA Astrophysics Data System (ADS)

    Zhang, Xiao; Schleife, Andre

    2015-03-01

    The α-BN structure of ZnO, a nonequilibrium phase with a transition pressure of 25 GPa, has been found in nano structures of ZnO. The structural difference between the BN structure and the equilibrium wurtzite structure can play an important role for applications of nanostructured ZnO. In order to understand the difference, first principles calculations have been performed on both phases. The electronic structure is computed using the GW method based on Density Functional Theory and HSE hybrid functional calculations. The GW method includes the quasiparticle effects due to the screened electron-electron interaction which gives an accurate description of the electronic band structure and density of states. After that, by solving the Bethe-Salpeter Equation for the optical polarization function, which take excitonic effects into account, we have achieved an accurate description of optical absorption spectra for both structures. We find a good agreement with experimental and previous computational results for WZ structure, and predict the absorption for the BN structure. The BN structure shows a larger band gap and we found a very large optical anisotropy: The gap for extraordinary light polarization is almost 0.7eV larger than that for ordinary light polarization.

  9. Solvent effects on the resonance Raman and electronic absorption spectra of bacteriochlorophyll a cation radical

    SciTech Connect

    Misono, Yasuhito; Itoh, Koichi; Limanatara, Leenawaty; Koyama, Yasushi

    1996-02-08

    Resonance Raman and electronic absorption spectra of bacteriocholrophyll a cation radical (BChl a{sup .+}) were recorded in 14 different kinds of solvents. The frequency of the ring-breathing Raman band of BChl a{sup .+} was in the region of 1596-1599 cm{sup -1} in solvents forming the pentacoordinated state in neutral bacteriochlorophyll a (BChl a), while it was in the region of 1584-1588 cm{sup -1} in solvents forming the hexacoordinated state. BChl a{sup .+} exhibited a key absorption band in the regions 546-554 and 557-563 nm in the above penta- and hexa-coordinating solvents. Therefore, it has been concluded that the penta- and hexa-coordinated states are retained even after conversion of BChl a into BChl a{sup .+} (one-electron oxidization). Application of this rule to the case of 2-propanol solution showed transformation from the penta- to the hexa-coordinated state upon one-electron oxidation in this particular solution. The coordination states of BChl a{sup .+} could be correlated with the donor number(DN) and the Taft parameters, {Beta} and {pi}{sup *}, of the solvent: The hexacoordinated state was formed in solvents with DN >= 18 or {Beta} > 0.5 showing higher electron donating power, while the pentacoordinated state was formed in solvents with {pi}{sup *} > 0.65 showing higher dielectric stabilization. 27 refs., 8 figs., 3 tabs.

  10. Interplay between structural and electronic properties of various fullerene derivatives, and their absorption spectra

    NASA Astrophysics Data System (ADS)

    Park, Sora; Ahn, Jeung Sun; Kwon, Young-Kyun

    2011-03-01

    Using density functional theory (DFT), we investigate the geometrical structures and electronic properties of various fullerene derivatives formed by attaching several kinds of addends on C60 through [2+2] cycloaddition. Various forms of such derivatives are modeled by considering different kinds, different positions and different numbers of addends to study how structural configurations will affect their electronic structures. Our results reveal that some derivatives with certain symmetries determined by the configuration of addends may have wider energy gap than that of pristine C60 . This suggests that absorption properties could be adjusted by controlling the addends configurations. To describe the excited state properties, such as absorption spectra, of various C60 derivatives more accurately, we performed time-dependent (TD) DFT calculations. We find the position and the intensity of the peak of absorption spectra of derivatives are affected by the specific symmetry of the derivatives defined by the configurations of the addends. To explore such peculiar effects, we analyze the charge distribution and orbital mixing characters.

  11. Electronic relaxation dynamics of PCDA-PDA studied by transient absorption spectroscopy.

    PubMed

    Joung, Joonyoung F; Baek, Junwoo; Kim, Youngseo; Lee, Songyi; Kim, Myung Hwa; Yoon, Juyoung; Park, Sungnam

    2016-08-17

    Photo-curable polymers originating from 10,12-pentacosadiynoic acid (PCDA-PDA) are commonly used polydiacetylenes (PDAs). PCDA-PDA exhibits thermochromic properties undergoing a unique colorimetric transition from blue to red as the temperature is increased from low to high. In this work, we have carefully studied the temperature-dependent optical properties of PCDA-PDA by using UV-visible absorption, FTIR, Raman, and transient absorption (TA) spectroscopy in combination with quantum chemical calculations. Temperature-dependent UV-visible absorption spectra indicate that PCDA-PDA exhibits reversible thermochromic properties up to 60 °C and its thermochromic properties become irreversible above 60 °C. Such distinct thermochromic properties are also manifested in TA signals so that the electronically excited PCDA-PDA relaxes to the ground state via an intermediate state at 20 °C (blue form) but it relaxes directly back to the ground state at 80 °C (red form). The electronic relaxation dynamics of PCDA-PDA are comprehensively analyzed based on different kinetic models by using the global fitting analysis method. The intermediate state in the blue form of PCDA-PDA is clearly found to be responsible for fluorescence quenching. FTIR and Raman spectroscopy and quantum chemical calculations confirm that the H-bonds between the carboxylic acid groups in PCDA-PDA are broken at high temperatures leading to an irreversible structural change of PCDA-PDA. PMID:27492212

  12. The electronic absorption study of imide anion radicals in terms of time dependent density functional theory

    NASA Astrophysics Data System (ADS)

    Andrzejak, Marcin; Sterzel, Mariusz; Pawlikowski, Marek T.

    2005-07-01

    The absorption spectra of the N-(2,5-di- tert-butylphenyl) phthalimide ( 1-), N-(2,5-di- tert-butylphenyl)-1,8-naphthalimide ( 2-) and N-(2,5-di- tert-butylphenyl)-perylene-3,4-dicarboximide ( 3-) anion radicals are studied in terms of time dependent density functional theory (TDDFT). For these anion radicals a large number electronic states (from 30 to 60) was found in the visible and near-IR regions (5000-45000 cm -1). In these regions the TD/B3LYP treatment at the 6-1+G* level is shown to reproduce satisfactorily the empirical absorption spectra of all three anion radicals studied. The most apparent discrepancies between purely electronic theory and the experiment could be found in the excitation region corresponding to D0→ D1 transitions in the 2- and 3- molecules. For these species we argue that the structures seen in the lowest energy part of the absorptions of the 2- and 3- species are very likely due to Franck-Condon (FC) activity of the totally symmetric vibrations not studied in this Letter.

  13. Electronic band gaps and transport in Cantor graphene superlattices

    NASA Astrophysics Data System (ADS)

    Xu, Yi; He, Ying; Yang, Yanfang; Zhang, Huifang

    2015-04-01

    The electronic band gap and transport in Cantor graphene superlattices are investigated theoretically. It is found that such fractal structure can possess an unusual Dirac point located at the energy corresponding to the zero-averaged wave number (zero- k ‾) . The location of the Dirac point shifts to lower energy with the increase of order number. The zero- k ‾ gap is robust against the lattice constants and less sensitive to the incidence angle. Moreover, multi-Dirac-points may appear by adjusting the lattice constants and the order, and an expression for their location is derived. The control of electron transport in such fractal structure may lead to potential applications in graphene-based electronic devices.

  14. Electron transport mechanisms in polymer-carbon sphere composites

    NASA Astrophysics Data System (ADS)

    Nieves, Cesar A.; Ramos, Idalia; Pinto, Nicholas J.; Zimbovskaya, Natalya A.

    2016-07-01

    A set of uniform carbon microspheres (CSs) whose diameters have the order of 0.125 μm to 10 μm was prepared from aqueous sucrose solution by means of hydrothermal carbonization of sugar molecules. A pressed pellet was composed by mixing CSs with polyethylene oxide (PEO). Electrical characterization of the pellet was carried out showing Ohmic current-voltage characteristics and temperature-dependent conductivity in the range of 80 K electron transport. It was shown that thermally induced electron tunneling between adjacent spheres may take on an important part in the electron transport through the CS/PEO composites.

  15. Electron transport in naphthylamine-based organic compounds

    NASA Astrophysics Data System (ADS)

    Tse, S. C.; Kwok, K. C.; So, S. K.

    2006-12-01

    Two naphthylamine-based hole transporters, namely, N ,N'-diphenyl-N ,N'-bis(1-naphthyl)(1,1'-biphenyl)-4,4'diamine (NPB) and 4,4',4″-tris(n-(2-naphthyl)-n-phenyl-amino)-triphenylamine (2TNATA), were found to possess electron transporting (ET) abilities. From time-of-flight measurements, values of electron mobilities for NPB and 2TNATA are (6-9)×10-4 and (1-3)×10-4cm2/Vs, respectively, under an applied electric field range of 0.04-0.8MV/cm at 290K. An organic light-emitting diode that employed NPB as the ET material was demonstrated. The electron conducting mechanism of NPB and 2TNATA in relation to the Marcus theory [Rev. Mod. Phys. 65, 599 (1993)] from quantum chemistry will be discussed.

  16. Advanced electronic displays and their potential in future transport aircraft

    NASA Technical Reports Server (NTRS)

    Hatfield, J. J.

    1981-01-01

    It is pointed out that electronic displays represent one of the keys to continued integration and improvement of the effectiveness of avionic systems in future transport aircraft. An employment of modern electronic display media and generation has become vital in connection with the increases in modes and functions of modern aircraft. Requirements for electronic systems of future transports are examined, and a description is provided of the tools which are available for cockpit integration, taking into account trends in information processing and presentation, trends in integrated display devices, and trends concerning input/output devices. Developments related to display media, display generation, and I/O devices are considered, giving attention to a comparison of CRT and flat-panel display technology, advanced HUD technology and multifunction controls. Integrated display formats are discussed along with integrated systems and cockpit configurations.

  17. Study of Acceleration, Transport and Dephasing of Hot Electrons in Solid Density Plasmas Irradiated with Ultra Intense Laser Pulses

    NASA Astrophysics Data System (ADS)

    Cho, B. I.; Osterholz, J.; Bernstein, A. C.; Dyer, G. M.; Ditmire, T.

    2008-04-01

    We have characterized the transport of hot electrons in solid targets by coherent transition radiation (CTR). CTR was observed from the rear side of aluminum foils irradiated with the THOR laser (800 nm, 40 fs, 600 mJ, 2 x 10^19 W/cm^2) at the University of Texas at Austin. In the experiment, two distinct beams of hot electrons are emitted simultaneously from the target rear side. This observation shows that two different mechanisms, namely resonance absorption and j x B heating, accelerate the electrons at the target front side. These two distinct beams propagate through aluminum foils with different spatial and temporal characteristics and electron temperatures. The interpretation is confirmed by calculations of the electron acceleration and transport inside the target.

  18. Controlled electrostatic assembly of quantum dots vis-à-vis their electronic coupling and transport gap.

    PubMed

    Ghosh, Batu; Pal, Amlan J

    2011-05-28

    We correlate the electronic coupling between quantum dots and the transport gap of nanoparticle-passivated Si substrates. We vary the length of the stabilizers of CdS nanoparticles, which in turn alters the particle-to-particle separation and hence the electronic coupling between them. We also control the electronic coupling using time-restricted electrostatic-assembly of quantum dots, using short periods of time so that an incomplete monolayer or a sub-monolayer of CdS forms. In such a sub-monolayer, the nanoparticles remain isolated from each other with a controllable particle-to-particle separation. From electronic absorption spectroscopy of multilayer films and atomic force microscopy of a monolayer, we evidenced sub-monolayer formation in the controlled electrostatic assembly process. We measure the current-voltage characteristics of nanoparticle-passivated substrates with a scanning tunnelling microscope; we show that the transport gap of nanoparticle-passivated substrates depends on the electronic coupling between CdS particles in the monolayer. PMID:21465033

  19. Enhancing light absorption within the carrier transport length in quantum junction solar cells.

    PubMed

    Fu, Yulan; Hara, Yukihiro; Miller, Christopher W; Lopez, Rene

    2015-09-10

    Colloidal quantum dot (CQD) solar cells have attracted tremendous attention because of their tunable absorption spectrum window and potentially low processing cost. Recently reported quantum junction solar cells represent a promising approach to building a rectifying photovoltaic device that employs CQD layers on each side of the p-n junction. However, the ultimate efficiency of CQD solar cells is still highly limited by their high trap state density in both p- and n-type CQDs. By modeling photonic structures to enhance the light absorption within the carrier transport length and by ensuring that the carrier generation and collection efficiencies were both augmented, our work shows that overall device current density could be improved. We utilized a two-dimensional numerical model to calculate the characteristics of patterned CQD solar cells based on a simple grating structure. Our calculation predicts a short circuit current density as high as 31  mA/cm2, a value nearly 1.5 times larger than that of the conventional flat design, showing the great potential value of patterned quantum junction solar cells. PMID:26368966

  20. Full-potential theoretical investigations of electron inelastic mean free paths and extended x-ray absorption fine structure in molybdenum.

    PubMed

    Chantler, C T; Bourke, J D

    2014-04-01

    X-ray absorption fine structure (XAFS) spectroscopy is one of the most robust, adaptable, and widely used structural analysis tools available for a range of material classes from bulk solids to aqueous solutions and active catalytic structures. Recent developments in XAFS theory have enabled high-accuracy calculations of spectra over an extended energy range using full-potential cluster modelling, and have demonstrated particular sensitivity in XAFS to a fundamental electron transport property-the electron inelastic mean free path (IMFP). We develop electron IMFP theory using a unique hybrid model that simultaneously incorporates second-order excitation losses, while precisely accounting for optical transitions dictated by the complex band structure of the solid. These advances are coupled with improved XAFS modelling to determine wide energy-range absorption spectra for molybdenum. This represents a critical test case of the theory, as measurements of molybdenum K-edge XAFS represent the most accurate determinations of XAFS spectra for any material. We find that we are able to reproduce an extended range of oscillatory structure in the absorption spectrum, and demonstrate a first-time theoretical determination of the absorption coefficient of molybdenum over the entire extended XAFS range utilizing a full-potential cluster model. PMID:24651638

  1. Resonant two-photon absorption of extreme-ultraviolet free-electron-laser radiation in helium

    SciTech Connect

    Nagasono, Mitsuru; Suljoti, Edlira; Pietzsch, Annette; Hennies, Franz; Wellhoefer, Michael; Hoeft, Jon-Tobias; Martins, Michael; Wurth, Wilfried; Foehlisch, Alexander; Treusch, Rolf; Feldhaus, Josef; Schneider, Jochen R.

    2007-05-15

    We have investigated the nonlinear response of helium to intense extreme-ultraviolet radiation from the free-electron laser in Hamburg (FLASH). We observe a spectral feature between 24 and 26 eV electron kinetic energy in photoemission which shows a quadratic fluence dependence. The feature is explained as a result of subsequent processes involving a resonant two-photon absorption process into doubly excited levels of even parity (N=5 and 6), radiative decay to the doubly excited states in the vicinity of the He{sup +} (N=2) ionization threshold and finally the photoionization of the inner electron by the radiation of the next microbunches. This observation suggests that even-parity states, which have been elusive to be measured with the low pulse energy of synchrotron radiation sources, can be investigated with the intense radiation of FLASH. This also demonstrates a first step to bring nonlinear spectroscopy into the xuv and soft-x-ray regime.

  2. Two-dimensional stanane: strain-tunable electronic structure, high carrier mobility, and pronounced light absorption.

    PubMed

    Liu, Xiuhong; Wang, Yu; Li, Feng; Li, Yafei

    2016-06-01

    By means of state-of-the-art density functional theory (DFT) computations, we systematically studied the structural, electronic, and optical properties of a novel two dimensional material, namely stanane (SnH). According to our computational results, stanane is semiconducting with a direct band gap of 1.00 eV, which can be flexibly tuned by applying an external strain. Remarkably, stanane has much higher electron and hole mobilities than those of a MoS2 monolayer at room temperature. Moreover, stanane has rather strong optical absorption in the visible as well as infrared regions of the solar spectrum. These results provide many useful insights for the wide application of stanane in electronics and optoelectronics. PMID:27181028

  3. Pressure dependence of Hexanitrostilbene Raman/ electronic absorption spectra to validate DFT EOS

    NASA Astrophysics Data System (ADS)

    Farrow, Darcie; Alam, Kathleen; Martin, Laura; Fan, Hongyou; Kay, Jeffrey; Wixom, Ryan

    2015-06-01

    Due to its thermal stability and low vapor pressure, Hexanitrostilbene (HNS) is often used in high-temperature or vacuum applications as a detonator explosive or in mild detonating fuse. Toward improving the accuracy of the equation of state used in hydrodynamic simulations of the performance of HNS, we have measured the Raman and electronic absorption spectra of this material under static pressure in a diamond anvil cell. Density functional theory calculations were used to simulate the pressure dependence of the Raman/Electronic spectra along the Hugoniot and 300K isotherm for comparison and to aid in interpreting the data. We will discuss changes in the electronic structure of HNS under pressure, validation of a DFT predicted equation of state (EOS), and using this data as a basis for understanding future pulsed Raman measurements on dynamically compressed HNS samples.

  4. Electronic absorption spectra of H₂C₆O⁺ isomers: produced by ion-molecule reactions.

    PubMed

    Chakraborty, Arghya; Fulara, Jan; Maier, John P

    2015-01-01

    Three absorption systems with origins at 354, 497, and 528 nm were detected after mass-selected deposition of H2C6O(+) in a 6 K neon matrix. The ions were formed by the reaction of C2O with HC4H(+) in a mixture of C3O2 and diacetylene in a hot cathode source, or by dissociative ionization of tetrabromocyclohexadienone. The 497 and 354 nm systems are assigned to the 1(2)A″ ← X(2)A″ and 2(2)A″ ← X(2)A″ electronic transitions of B(+), (2-ethynylcycloallyl)methanone cation, and the 528 nm absorption to the 1(2)A2 ← X(2)B1 transition of F(+), 2-ethynylbut-3-yn-1-enone-1-ylide, on the basis of calculated excitation energies with CASPT2. PMID:25495044

  5. Electronic structure investigation of highly compressed aluminum with K edge absorption spectroscopy.

    PubMed

    Benuzzi-Mounaix, A; Dorchies, F; Recoules, V; Festa, F; Peyrusse, O; Levy, A; Ravasio, A; Hall, T; Koenig, M; Amadou, N; Brambrink, E; Mazevet, S

    2011-10-14

    The electronic structure evolution of highly compressed aluminum has been investigated using time resolved K edge x-ray absorption spectroscopy. A long laser pulse (500 ps, I(L)≈8×10(13) W/cm(2)) was used to create a uniform shock. A second ps pulse (I(L)≈10(17)  W/cm(2)) generated an ultrashort broadband x-ray source near the Al K edge. The main target was designed to probe aluminum at reshocked conditions up to now unexplored (3 times the solid density and temperatures around 8 eV). The hydrodynamical conditions were obtained using rear side visible diagnostics. Data were compared to ab initio and dense plasma calculations, indicating potential improvements in either description. This comparison shows that x-ray-absorption near-edge structure measurements provide a unique capability to probe matter at these extreme conditions and severally constrains theoretical approaches currently used. PMID:22107398

  6. Electron transport and photophosphorylation by Photosystem I in vivo in plants and cyanobacteria.

    PubMed

    Fork, D C; Herbert, S K

    1993-06-01

    Recently, a number of techniques, some of them relatively new and many often used in combination, have given a clearer picture of the dynamic role of electron transport in Photosystem I of photosynthesis and of coupled cyclic photophosphorylation. For example, the photoacoustic technique has detected cyclic electron transport in vivo in all the major algal groups and in leaves of higher plants. Spectroscopic measurements of the Photosystem I reaction center and of the changes in light scattering associated with thylakoid membrane energization also indicate that cyclic photophosphorylation occurs in living plants and cyanobacteria, particularly under stressful conditions.In cyanobacteria, the path of cyclic electron transport has recently been proposed to include an NAD(P)H dehydrogenase, a complex that may also participate in respiratory electron transport. Photosynthesis and respiration may share common electron carriers in eukaryotes also. Chlororespiration, the uptake of O2 in the dark by chloroplasts, is inhibited by excitation of Photosystem I, which diverts electrons away from the chlororespiratory chain into the photosynthetic electron transport chain. Chlororespiration in N-starved Chlamydomonas increases ten fold over that of the control, perhaps because carbohydrates and NAD(P)H are oxidized and ATP produced by this process.The regulation of energy distribution to the photosystems and of cyclic and non-cyclic phosphorylation via state 1 to state 2 transitions may involve the cytochrome b 6-f complex. An increased demand for ATP lowers the transthylakoid pH gradient, activates the b 6-f complex, stimulates phosphorylation of the light-harvesting chlorophyll-protein complex of Photosystem II and decreases energy input to Photosystem II upon induction of state 2. The resulting increase in the absorption by Photosystem I favors cyclic electron flow and ATP production over linear electron flow to NADP and 'poises' the system by slowing down the flow of

  7. Ultrafast electron transport in graphene and magnetic nanostructures

    NASA Astrophysics Data System (ADS)

    Turchinovich, Dmitry

    2016-03-01

    Ultrafast terahertz spectroscopy is an ideal tool for observation of dynamics of charge, lattice and spin in solids on the most elementary timescale: in the regime ωτ ~ 1, where ω is the electromagnetic wave oscillation frequency, and τ is the characteristic timescale at which the fundamental phenomena in the three subsystems comprising the solid occur. In this paper two case studies will be discussed. (i) Ultrafast electron transport in graphene. We will show, that the free-carrier conductivity of graphene in arbitrary ultrafast, (sub-)picosecond electric fields is defined by the thermodynamic balance maintained within the electronic structure of graphene acting as thermalized electron gas. Within this simple thermodynamic picture, the electron gas quasi-instantaneously increases its temperature by absorbing the energy of driving ultrafast electric field, and at the same time cools down via a time-retarded, few picosecond-long process of phonon emission. The asymmetry in electron heating and cooling dynamics leads to heat accumulation in the electron population of graphene, concomitantly lowering the chemical potential for hotter electrons, and thereby reducing the intraband conductivity of graphene - an effect crucially important for understanding of ultrafast graphene transistors and photodetectors. (ii) We will also discuss the fundamental observation of spin-controlled electron conduction of Fermilevel electrons in ferromagnetic metals, and will directly quantify the Mott picture of conduction in ferromagnets - the effect directly employed in modern magnetic sensor technologies such as giant magnetoresistance.

  8. Electronic structure and absorption spectrum of biexciton obtained by using exciton basis

    SciTech Connect

    Shiau, Shiue-Yuan; Combescot, Monique; Chang, Yia-Chung

    2013-09-15

    We approach the biexciton Schrödinger equation not through the free-carrier basis as usually done, but through the free-exciton basis, exciton–exciton interactions being treated according to the recently developed composite boson many-body formalism which allows an exact handling of carrier exchange between excitons, as induced by the Pauli exclusion principle. We numerically solve the resulting biexciton Schrödinger equation with the exciton levels restricted to the ground state and we derive the biexciton ground state as well as the bound and unbound excited states as a function of hole-to-electron mass ratio. The biexciton ground-state energy we find, agrees reasonably well with variational results. Next, we use the obtained biexciton wave functions to calculate optical absorption in the presence of a dilute exciton gas in quantum well. We find an asymmetric peak with a characteristic low-energy tail, identified with the biexciton ground state, and a set of Lorentzian-like peaks associated with biexciton unbound states, i.e., exciton–exciton scattering states. Last, we propose a pump–probe experiment to probe the momentum distribution of the exciton condensate. -- Highlights: •New composite boson many-body theory is used to derive exactly the biexciton Schrödinger equation using the exciton basis. •We solved the 2D and 3D biexciton ground- and excited-state binding energies for various electron-to-hole mass ratios. •The absorption spectrum shows an asymmetric low-energy peak identified with the biexciton ground state. •High-energy Lorentzian-like peaks in the absorption spectrum are associated with the exciton–exciton scattering states. •The exciton gas momentum distribution can be determined by the absorption spectrum via the biexciton wave functions.

  9. Hot Electrons and Energy Transport in Metals at MK Temperatures.

    NASA Astrophysics Data System (ADS)

    Roukes, Michael Lee

    Using a new technique involving the generation of hot carriers, we directly measure energy loss lifetimes for electrons in impure metals at mK temperatures. At these temperatures very weak inelastic scattering processes determine energy transport out of the electron gas. A temperature difference between the electron gas and the lattice can be induced by applying an extremely small electric field (of order 1 (mu)V/cm at 25 mK). This temperature difference reflects the rate at which electrons lose energy to the surroundings. The experiment is carried out using a pair of interdigitated thin film resistors mounted on a millidegree demagnetization cryostat: we obtain electron temperature directly by observing current fluctuations. Noise generated by the resistors is measured using an ultra-sensitive two -channel dc SQUID system, providing femtoamp resolution at KHz frequencies. A dc voltage applied across one resistor imposes the bias field causing electron heating. Phonon temperature in the metal lattice is obtained by measuring noise from a second (unbiased) resistor, which is tightly coupled thermally to the first (biased). Our measurements show that electron heating follows an E('2/5) power law in the regime where electron temperature is largely determined by the electric field, E. This implies a T('-3) law for the energy loss lifetime, suggesting electron -acoustic phonon processes dominate. In the mK temperature regime the conductivity is impurity limited and remains ohmic, even as the electrons heat. Assuming a T('3) dependence and extrapolating our measured rates to higher temperatures, we find agreement with electron-phonon rates measured above 1K in clean bulk metals. This contrasts with results from weak localization experiments showing a power law differing from T('3) and much faster rates. This difference arises because weak localization experiments measure the electron phase coherence lifetime; our electron heating experiments, however, measure an energy

  10. Electronic structure of some adenosine receptor antagonists. III. Quantitative investigation of the electronic absorption spectra of alkyl xanthines

    NASA Astrophysics Data System (ADS)

    Moustafa, H.; Shalaby, Samia H.; El-sawy, K. M.; Hilal, Rifaat

    2002-07-01

    Quantitative and comparative investigation of the electronic absorption spectra of theophylline, caffeine and their derivatives is reported. The spectra of theophylline, caffeine and theobromine were compared to establish the predominant tautomeric species in solution. This comparison, analysis of solvent effects and assignments of the observed transitions via MO computations indicate the exits of only one tautomeric species in solution that is the N7 form. A low-lying triplet state was identified which corresponds to a HOMO-LUMO transition. This relatively long-lived T 1 state is always less polar than the ground state and may very well underlie the photochemical reactivity of alkyl xanthines. Substituents of different electron donating or withdrawing strengths and solvent effects are investigated and analyzed. The present analysis is facilitated via computer deconvolution of the observed spectra and MO computation.

  11. Hypouricemic effects of novel concentrative nucleoside transporter 2 inhibitors through suppressing intestinal absorption of purine nucleosides.

    PubMed

    Hiratochi, Masahiro; Tatani, Kazuya; Shimizu, Kazuo; Kuramochi, Yu; Kikuchi, Norihiko; Kamada, Noboru; Itoh, Fumiaki; Isaji, Masayuki

    2012-09-01

    We have developed concentrative nucleoside transporter 2 (CNT2) inhibitors as a novel pharmacological approach for improving hyperuricemia by inhibiting intestinal absorption of purines. Dietary purine nucleosides are absorbed in the small intestines by CNTs expressed in the apical membrane. In humans, the absorbed purine nucleosides are rapidly degraded to their final end product, uric acid, by xanthine oxidase. Based on the expression profile of human CNTs in digestive tract tissues, we established a working hypothesis that mainly CNT2 contributes to the intestinal absorption of purine nucleosides. In order to confirm this possibility, we developed CNT2 inhibitors and found that (2R,3R,4S,5R)-2-(6-amino-8-{[3'-(3-aminopropoxy)-biphenyl-4-ylmethyl]-amino}-9H-purin-9-yl)-5-hydroxymethyl-tetrahydrofuran-3,4-diol (KGO-2142) and 1-[3-(5-{[1-((2R,3R,4S,5R)-3,4-dihydroxy-5-hydroxymethyl-tetrahydrofuran-2-yl)-1H-benzimidazol-2-ylamino]-methyl}-2-ethoxyphenoxy)-propyl]-piperidine-4-carboxylic acid amide (KGO-2173) were inhibitory. These CNT2 inhibitors had potent inhibitory activity against inosine uptake via human CNT2, but they did not potently interfere with nucleoside uptake via human CNT1, CNT3 or equilibrative nucleoside transporters (ENTs) in vitro. After oral administration of KGO-2173 along with [(14)C]-inosine, KGO-2173 significantly decreased the urinary excretion of radioactivity at 6 and 24h in rats. Since dietary purine nucleosides are not utilized in the body and are excreted into the urine rapidly, this decrease in radioactivity in the urine represented the inhibitory activity of KGO-2173 toward the absorption of [(14)C]-inosine in the small intestines. KGO-2142 almost completely inhibited dietary RNA-induced hyperuricemia and the increase in urinary excretion of uric acid in cebus monkeys. These novel CNT2 inhibitors, KGO-2142 and KGO-2173, could be useful therapeutic options for the treatment of hyperuricemia. PMID:22709993

  12. Hybrid Simulation of Laser-Plasma Interactions and Fast Electron Transport in Inhomogeneous Plasma

    SciTech Connect

    Cohen, B I; Kemp, A; Divol, L

    2009-05-27

    A new framework is introduced for kinetic simulation of laser-plasma interactions in an inhomogenous plasma motivated by the goal of performing integrated kinetic simulations of fast-ignition laser fusion. The algorithm addresses the propagation and absorption of an intense electromagnetic wave in an ionized plasma leading to the generation and transport of an energetic electron component. The energetic electrons propagate farther into the plasma to much higher densities where Coulomb collisions become important. The high-density plasma supports an energetic electron current, return currents, self-consistent electric fields associated with maintaining quasi-neutrality, and self-consistent magnetic fields due to the currents. Collisions of the electrons and ions are calculated accurately to track the energetic electrons and model their interactions with the background plasma. Up to a density well above critical density, where the laser electromagnetic field is evanescent, Maxwell's equations are solved with a conventional particle-based, finite-difference scheme. In the higher-density plasma, Maxwell's equations are solved using an Ohm's law neglecting the inertia of the background electrons with the option of omitting the displacement current in Ampere's law. Particle equations of motion with binary collisions are solved for all electrons and ions throughout the system using weighted particles to resolve the density gradient efficiently. The algorithm is analyzed and demonstrated in simulation examples. The simulation scheme introduced here achieves significantly improved efficiencies.

  13. Simulation of laser-plasma interactions and fast-electron transport in inhomogeneous plasma

    SciTech Connect

    Cohen, B.I. Kemp, A.J.; Divol, L.

    2010-06-20

    A new framework is introduced for kinetic simulation of laser-plasma interactions in an inhomogeneous plasma motivated by the goal of performing integrated kinetic simulations of fast-ignition laser fusion. The algorithm addresses the propagation and absorption of an intense electromagnetic wave in an ionized plasma leading to the generation and transport of an energetic electron component. The energetic electrons propagate farther into the plasma to much higher densities where Coulomb collisions become important. The high-density plasma supports an energetic electron current, return currents, self-consistent electric fields associated with maintaining quasi-neutrality, and self-consistent magnetic fields due to the currents. Collisions of the electrons and ions are calculated accurately to track the energetic electrons and model their interactions with the background plasma. Up to a density well above critical density, where the laser electromagnetic field is evanescent, Maxwell's equations are solved with a conventional particle-based, finite-difference scheme. In the higher-density plasma, Maxwell's equations are solved using an Ohm's law neglecting the inertia of the background electrons with the option of omitting the displacement current in Ampere's law. Particle equations of motion with binary collisions are solved for all electrons and ions throughout the system using weighted particles to resolve the density gradient efficiently. The algorithm is analyzed and demonstrated in simulation examples. The simulation scheme introduced here achieves significantly improved efficiencies.

  14. Current Issues in Electron and Positron Transport Theory

    NASA Astrophysics Data System (ADS)

    Robson, Robert

    2007-10-01

    In this paper we review the current status of transport theory for low energy electrons or positrons in gases, in the context of both kinetic theory and fluid modelling. In particular, we focus on the following issues: (i) Muliterm vs two-term representation of the velocity distribution function in solution of Boltzmann's equation; (ii) the effect of non-conservative collisions (attachment, ionization, positron annihilation) on transport properties; (iii) the enduring electron- hydrogen vibrational cross section controversy and possible implications for the Boltzmann equation itself; (iv) closure of the fluid equations and the heat flux ansatz; and (v) correct use of swarm transport coefficients in fluid modelling of low temperature plasmas. Both hydrodynamic and non-hydrodynamic examples will be given, with attention focussed on the Franck-Hertz experiment, particularly the ``window'' of fields in which oscillations of transport properties are produced, and the way in which electric and magnetic fields combine to affect transport properties. In collaboration with co-authors Z. LJ. Petrovi'c, Institute of Physics Belgrade, and R.D. White, James Cook University.

  15. Experiments on viscous transport in pure-electron plasmas

    SciTech Connect

    Kriesel, Jason M.; Driscoll, C. Fred

    1999-12-10

    Viscous transport in pure-electron plasmas is a rearrangement of particles due to like-particle interactions, eventually leading to a confined global thermal equilibrium state. The measured transport is observed to be proportional to the shear in the total (ExB+diamagnetic) fluid rotation of the plasma, for both hollow and monotonic rotation profiles. We determine the local kinematic viscosity, {kappa}, from measurements of the local flux of electrons. The measured viscosity is 50-10{sup 4} times larger than expected from classical transport due to short-range velocity-scattering collisions, but is within a factor of 10 of recent theories by O'Neil and Dubin of transport due to long-range drift collisions. The measured viscosity scales with magnetic field and plasma length roughly as {kappa}{proportional_to}B/L. This scaling suggests a finite-length transport enhancement caused by particles interacting multiple times as they bounce axially between the ends of the plasma.

  16. Electronic structure of barium strontium titanate by soft-x-ray absorption spectroscopy

    SciTech Connect

    Uehara, Y.; Underwood, J.H.; Gullikson, E.M.; Perera, R.C.C.

    1997-04-01

    Perovskite-type titanates, such as Strontium Titanate (STO), Barium Titanate (BTO), and Lead Titanate (PTO) have been widely studied because they show good electric and optical properties. In recent years, thin films of Barium Strontium Titanate (BST) have been paid much attention as dielectrics of dynamic random access memory (DRAM) capacitors. BST is a better insulator with a higher dielectric constant than STO and can be controlled in a paraelectric phase with an appropriate ratio of Ba/Sr composition, however, few studies have been done on the electronic structure of the material. Studies of the electronic structure of such materials can be beneficial, both for fundamental physics research and for improving technological applications. BTO is a famous ferroelectric material with a tetragonal structure, in which Ti and Ba atoms are slightly displaced from the lattice points. On the other hand, BST keeps a paraelectric phase, which means that the atoms are still at the cubic lattice points. It should be of great interest to see how this difference of the local structure around Ti atoms between BTO and BST effects the electronic structure of these two materials. In this report, the authors present the Ti L{sub 2,3} absorption spectra of STO, BTO, and BST measured with very high accuracy in energy of the absorption features.

  17. Effect of compression on the electronic, optical and transport properties of MoS2/graphene-based junctions

    NASA Astrophysics Data System (ADS)

    Ghorbani-Asl, Mahdi; Bristowe, Paul D.; Koziol, K.; Heine, Thomas; Kuc, Agnieszka

    2016-06-01

    Electronic, optical and transport properties of the MoS2/graphene heterostructure have been investigated as function of applied uniaxial compression normal to the interface plane using first principles calculations and a non-equilibrium Green’s function approach. The results show that a small compressive load (∼1 GPa) can open up the band gap (∼12 meV), reduce the optical absorption coefficient (∼7%), redshift the absorption spectrum, and create non-Ohmic I –V characteristics that depend on the magnitude of applied bias. This suggests that graphene/MoS2 heterostructure can be suitable for electromechanical and photomechanical devices where the electronic, optical and transport properties can be tuned by an appropriate application of bias and mechanical deformations.

  18. Visible to deep ultraviolet range optical absorption of electron irradiated borosilicate glass

    NASA Astrophysics Data System (ADS)

    Wang, Tie-Shan; Duan, Bing-Huang; Tian, Feng; Peng, Hai-Bo; Chen, Liang; Zhang, Li-Min; Yuan, Wei

    2015-07-01

    To study the room-temperature stable defects induced by electron irradiation, commercial borosilicate glasses were irradiated by 1.2 MeV electrons and then ultraviolet (UV) optical absorption (OA) spectra were measured. Two characteristic bands were revealed before irradiation, and they were attributed to silicon dangling bond (E’-center) and Fe3+ species, respectively. The existence of Fe3+ was confirmed by electron paramagnetic resonance (EPR) measurements. After irradiation, the absorption spectra revealed irradiation-induced changes, while the content of E’-center did not change in the deep ultraviolet (DUV) region. The slightly reduced OA spectra at 4.9 eV was supposed to transform Fe3+ species to Fe2+ species and this transformation leads to the appearance of 4.3 eV OA band. By calculating intensity variation, the transformation of Fe was estimated to be about 5% and the optical absorption cross section of Fe2+ species is calculated to be 2.2 times larger than that of Fe3+ species. Peroxy linkage (POL, ≡Si-O-O-Si≡), which results in a 3.7 eV OA band, is speculated not to be from Si-O bond break but from Si-O-B bond, Si-O-Al bond, or Si-O-Na bond break. The co-presence defect with POL is probably responsible for 2.9-eV OA band. Project supported by the Fundamental Research Funds for the Central Universities of China (Grant No. lzujbky-2014-16).

  19. Electronic transport in benzodifuran single-molecule transistors

    NASA Astrophysics Data System (ADS)

    Xiang, An; Li, Hui; Chen, Songjie; Liu, Shi-Xia; Decurtins, Silvio; Bai, Meilin; Hou, Shimin; Liao, Jianhui

    2015-04-01

    Benzodifuran (BDF) single-molecule transistors have been fabricated in electromigration break junctions for electronic measurements. The inelastic electron tunneling spectrum validates that the BDF molecule is the pathway of charge transport. The gating effect is analyzed in the framework of a single-level tunneling model combined with transition voltage spectroscopy (TVS). The analysis reveals that the highest occupied molecular orbital (HOMO) of the thiol-terminated BDF molecule dominates the charge transport through Au-BDF-Au junctions. Moreover, the energy shift of the HOMO caused by the gate voltage is the main reason for conductance modulation. In contrast, the electronic coupling between the BDF molecule and the gold electrodes, which significantly affects the low-bias junction conductance, is only influenced slightly by the applied gate voltage. These findings will help in the design of future molecular electronic devices.Benzodifuran (BDF) single-molecule transistors have been fabricated in electromigration break junctions for electronic measurements. The inelastic electron tunneling spectrum validates that the BDF molecule is the pathway of charge transport. The gating effect is analyzed in the framework of a single-level tunneling model combined with transition voltage spectroscopy (TVS). The analysis reveals that the highest occupied molecular orbital (HOMO) of the thiol-terminated BDF molecule dominates the charge transport through Au-BDF-Au junctions. Moreover, the energy shift of the HOMO caused by the gate voltage is the main reason for conductance modulation. In contrast, the electronic coupling between the BDF molecule and the gold electrodes, which significantly affects the low-bias junction conductance, is only influenced slightly by the applied gate voltage. These findings will help in the design of future molecular electronic devices. Electronic supplementary information (ESI) available: The fabrication procedure for BDF single

  20. Linear delta-f simulations of nonlocal electron heat transport

    SciTech Connect

    Brunner, S.; Valeo, E.; Krommes, J.A.

    2000-01-27

    Nonlocal electron heat transport calculations are carried out by making use of some of the techniques developed previously for extending the delta f method to transport time scale simulations. By considering the relaxation of small amplitude temperature perturbations of a homogeneous Maxwellian background, only the linearized Fokker-Planck equation has to be solved, and direct comparisons can be made with the equivalent, nonlocal hydrodynamic approach. A quasineutrality-conserving algorithm is derived for computing the self-consistent electric fields driving the return currents. In the low-collisionality regime, results illustrate the importance of taking account of nonlocality in both space and time.

  1. Temperature dependence of electronic transport property in ferroelectric polymer films

    NASA Astrophysics Data System (ADS)

    Zhao, X. L.; Wang, J. L.; Tian, B. B.; Liu, B. L.; Zou, Y. H.; Wang, X. D.; Sun, S.; Sun, J. L.; Meng, X. J.; Chu, J. H.

    2014-10-01

    The leakage current mechanism of ferroelectric copolymer of polyvinylidene fluoride with trifluoroethylene prepared by Langmuir-Blodgett was investigated in the temperature range from 100 K to 350 K. The electron as the dominant injected carrier was observed in the ferroelectric copolymer films. The transport mechanisms in copolymer strongly depend on the temperature and applied voltage. From 100 K to 200 K, Schottky emission dominates the conduction. With temperature increasing, the Frenkel-Poole emission instead of the Schottky emission to conduct the carrier transport. When the temperature gets to 260 K, the leakage current becomes independent of temperature, and the space charge limited current conduction was observed.

  2. LDRD project 151362 : low energy electron-photon transport.

    SciTech Connect

    Kensek, Ronald Patrick; Hjalmarson, Harold Paul; Magyar, Rudolph J.; Bondi, Robert James; Crawford, Martin James

    2013-09-01

    At sufficiently high energies, the wavelengths of electrons and photons are short enough to only interact with one atom at time, leading to the popular %E2%80%9Cindependent-atom approximation%E2%80%9D. We attempted to incorporate atomic structure in the generation of cross sections (which embody the modeled physics) to improve transport at lower energies. We document our successes and failures. This was a three-year LDRD project. The core team consisted of a radiation-transport expert, a solid-state physicist, and two DFT experts.

  3. Extracellular Electron Transport (EET): Metal Cycling in Extreme Places

    NASA Astrophysics Data System (ADS)

    Nealson, K. H.

    2014-12-01

    Extracellular electron transport, or EET, is the process whereby bacteria either donate electrons to an electron acceptor (usually insoluble), or take up electrons from and electron donor (usually insoluble) that is located outside the cell. Iron cycling is inherently linked to EET, as both reduced iron (electron donors), and oxidized iron (electron acceptors) can be found as insoluble minerals, and require specialized molecular machines to accomplish these extracellular geobiological reactions. Bacteria in the group Shewanella are able to catalyze EET in both directions, and are involved with a number of different iron conversions, but are not good role models for extreme conditions - to our knowledge there are no shewanellae that are tolerant to extremes of temperature or pH, the two usual. This being said, when cells are energy starved via limitation for electron acceptors, they respond by turning on the system(s) for EET. Thus, in this presentation the known mechanism(s) of EET will be discussed, along with recent findings and reports of EET-capable organisms from a variety of extreme environments. From these data, I put forward the hypothesis that there are many microbes (many of them from extreme environments) that will be resistant to cultivation by "standard microbiological methods", yet lend themselves well to cultivation via electrochemical methods.

  4. Impurity transport in trapped electron mode driven turbulence

    SciTech Connect

    Mollen, A.; Fueloep, T.; Moradi, S.; Pusztai, I.

    2013-03-15

    Trapped electron mode turbulence is studied by gyrokinetic simulations with the GYRO code and an analytical model including the effect of a poloidally varying electrostatic potential. Its impact on radial transport of high-Z trace impurities close to the core is thoroughly investigated, and the dependence of the zero-flux impurity density gradient (peaking factor) on local plasma parameters is presented. Parameters such as ion-to-electron temperature ratio, electron temperature gradient, and main species density gradient mainly affect the impurity peaking through their impact on mode characteristics. The poloidal asymmetry, the safety factor, and magnetic shear have the strongest effect on impurity peaking, and it is shown that under certain scenarios where trapped electron modes are dominant, core accumulation of high-Z impurities can be avoided. We demonstrate that accounting for the momentum conservation property of the impurity-impurity collision operator can be important for an accurate evaluation of the impurity peaking factor.

  5. Geometric effects in the electronic transport of deformed nanotubes

    NASA Astrophysics Data System (ADS)

    Santos, Fernando; Fumeron, Sébastien; Berche, Bertrand; Moraes, Fernando

    2016-04-01

    Quasi-two-dimensional systems may exibit curvature, which adds three-dimensional influence to their internal properties. As shown by da Costa (1981 Phys. Rev. A 23 1982-7), charged particles moving on a curved surface experience a curvature-dependent potential which greatly influence their dynamics. In this paper, we study the electronic ballistic transport in deformed nanotubes. The one-electron Schrödinger equation with open boundary conditions is solved numerically with a flexible MAPLE code made available as supplementary data. We find that the curvature of the deformations indeed has strong effects on the electron dynamics, suggesting its use in the design of nanotube-based electronic devices.

  6. Geometric effects in the electronic transport of deformed nanotubes.

    PubMed

    Santos, Fernando; Fumeron, Sébastien; Berche, Bertrand; Moraes, Fernando

    2016-04-01

    Quasi-two-dimensional systems may exibit curvature, which adds three-dimensional influence to their internal properties. As shown by da Costa (1981 Phys. Rev. A 23 1982-7), charged particles moving on a curved surface experience a curvature-dependent potential which greatly influence their dynamics. In this paper, we study the electronic ballistic transport in deformed nanotubes. The one-electron Schrödinger equation with open boundary conditions is solved numerically with a flexible MAPLE code made available as supplementary data. We find that the curvature of the deformations indeed has strong effects on the electron dynamics, suggesting its use in the design of nanotube-based electronic devices. PMID:26900666

  7. Spatially resolved study of primary electron transport in magnetic cusps

    SciTech Connect

    Hubble, Aimee A.; Foster, John E.

    2012-01-15

    Spatially resolved primary electron current density profiles were measured using a planar Langmuir probe in the region above a magnetic cusp in a small ion thruster discharge chamber. The probe current maps obtained were used to study the electron collection mechanics in the cusp region in the limit of zero gas flow and no plasma production, and they allowed for the visualization of primary electron transport through the cusp. Attenuation coefficients and loss widths were calculated as a function of probe distance above the anode at various operating conditions. Finally, the collection mechanics between two magnetic cusps were studied and compared. It was found that primary electron collection was dominated by the upstream magnet ring.

  8. First principles electron transport simulations in the Kondo regime

    NASA Astrophysics Data System (ADS)

    Rungger, Ivan; Radonjic, Milos; Appelt, Wilhelm; Chioncel, Liviu; Droghetti, Andrea

    When magnetic atoms, molecules or thin films are brought into contact with metals the electron-electron interaction leads to the appearance of the correlated Kondo state at low temperatures. In this talk we will present results for the electronic structure and conductance in the Kondo regime of recent STM and break junction experiments for stable radical molecules, which correspond to spin half molecular magnets. We will outline the methodological approach to evaluate the conductance of such systems from first principles, as implemented in the Smeagol electron transport code. The method combines the density functional theory (DFT) with Anderson impurity solvers within the continuum time quantum Monte Carlo (CTQMC) and numerical renormalization group (NRG) approaches.

  9. The macro response Monte Carlo method for electron transport

    SciTech Connect

    Svatos, M M

    1998-09-01

    The main goal of this thesis was to prove the feasibility of basing electron depth dose calculations in a phantom on first-principles single scatter physics, in an amount of time that is equal to or better than current electron Monte Carlo methods. The Macro Response Monte Carlo (MRMC) method achieves run times that are on the order of conventional electron transport methods such as condensed history, with the potential to be much faster. This is possible because MRMC is a Local-to-Global method, meaning the problem is broken down into two separate transport calculations. The first stage is a local, in this case, single scatter calculation, which generates probability distribution functions (PDFs) to describe the electron's energy, position and trajectory after leaving the local geometry, a small sphere or "kugel" A number of local kugel calculations were run for calcium and carbon, creating a library of kugel data sets over a range of incident energies (0.25 MeV - 8 MeV) and sizes (0.025 cm to 0.1 cm in radius). The second transport stage is a global calculation, where steps that conform to the size of the kugels in the library are taken through the global geometry. For each step, the appropriate PDFs from the MRMC library are sampled to determine the electron's new energy, position and trajectory. The electron is immediately advanced to the end of the step and then chooses another kugel to sample, which continues until transport is completed. The MRMC global stepping code was benchmarked as a series of subroutines inside of the Peregrine Monte Carlo code. It was compared to Peregrine's class II condensed history electron transport package, EGS4, and MCNP for depth dose in simple phantoms having density inhomogeneities. Since the kugels completed in the library were of relatively small size, the zoning of the phantoms was scaled down from a clinical size, so that the energy deposition algorithms for spreading dose across 5-10 zones per kugel could be tested. Most

  10. Fabrication and electronic transport studies of single nanocrystal systems

    SciTech Connect

    Klein, D L

    1997-05-01

    Semiconductor and metallic nanocrystals exhibit interesting electronic transport behavior as a result of electrostatic and quantum mechanical confinement effects. These effects can be studied to learn about the nature of electronic states in these systems. This thesis describes several techniques for the electronic study of nanocrystals. The primary focus is the development of novel methods to attach leads to prefabricated nanocrystals. This is because, while nanocrystals can be readily synthesized from a variety of materials with excellent size control, means to make electrical contact to these nanocrystals are limited. The first approach that will be described uses scanning probe microscopy to first image and then electrically probe surfaces. It is found that electronic investigations of nanocrystals by this technique are complicated by tip-sample interactions and environmental factors such as salvation and capillary forces. Next, an atomic force microscope technique for the catalytic patterning of the surface of a self assembled monolayer is described. In principle, this nano-fabrication technique can be used to create electronic devices which are based upon complex arrangements of nanocrystals. Finally, the fabrication and electrical characterization of a nanocrystal-based single electron transistor is presented. This device is fabricated using a hybrid scheme which combines electron beam lithography and wet chemistry to bind single nanocrystals in tunneling contact between closely spaced metallic leads. In these devices, both Au and CdSe nanocrystals show Coulomb blockade effects with characteristic energies of several tens of meV. Additional structure is seen the transport behavior of CdSe nanocrystals as a result of its electronic structure.

  11. Contribution of Abcc4-Mediated Gastric Transport to the Absorption and Efficacy of Dasatinib

    PubMed Central

    Fujita, Ken-ichi; Li, Lie; Gibson, Alice A.; Janke, Laura J.; Williams, Richard T.; Schuetz, John D.; Sparreboom, Alex; Baker, Sharyn D.

    2013-01-01

    Purpose Several oral multikinase inhibitors are known to interact in vitro with the human ATP-binding cassette transporter ABCC4 (MRP4), but the in vivo relevance of this interaction remains poorly understood. We hypothesized that host ABCC4 activity may influence the pharmacokinetic profile of dasatinib and subsequently affect its antitumor properties. Experimental Design Transport of dasatinib was studied in cells transfected with human ABCC4 or the ortholog mouse transporter, Abcc4. Pharmacokinetic studies were done in wildtype and Abcc4-null mice. The influence of Abcc4-deficiency on dasatinib efficacy was evaluated in a model of Ph+ acute lymphoblastic leukemia (ALL) by injection of luciferase-positive, p185(BCR-ABL)-expressing Arf(−/−) pre-B cells. Results Dasatinib accumulation was significantly changed in cells over-expressing ABCC4 or Abcc4 compared to control cells (P<0.001). Deficiency of Abcc4 in vivo was associated with a 1.75-fold decrease in systemic exposure to oral dasatinib, but had no influence on the pharmacokinetics of i.v. dasatinib. Abcc4 was found to be highly expressed in the stomach, and dasatinib efflux from isolated mouse stomachs ex vivo was impaired by Abcc4-deficiency (P<0.01), without any detectable changes in gastric pH. Abcc4-null mice receiving dasatinib had an increase in leukemic burden, based on bioluminescence imaging, and decreased overall survival compared to wildtype mice (P=0.048). Conclusions This study suggests that Abcc4 in the stomach facilitates the oral absorption of dasatinib, and it possibly plays a similar role for other orally-administered substrates, such as acetylsalicylic acid. This phenomenon also provides a mechanistic explanation for the malabsorption of certain drugs following gastric resection. PMID:23794731

  12. Chronic intermittent psychological stress promotes macrophage reverse cholesterol transport by impairing bile acid absorption in mice

    PubMed Central

    Silvennoinen, Reija; Quesada, Helena; Kareinen, Ilona; Julve, Josep; Kaipiainen, Leena; Gylling, Helena; Blanco-Vaca, Francisco; Escola-Gil, Joan Carles; Kovanen, Petri T; Lee-Rueckert, Miriam

    2015-01-01

    Psychological stress is a risk factor for atherosclerosis, yet the pathophysiological mechanisms involved remain elusive. The transfer of cholesterol from macrophage foam cells to liver and feces (the macrophage-specific reverse cholesterol transport, m-RCT) is an important antiatherogenic pathway. Because exposure of mice to physical restraint, a model of psychological stress, increases serum levels of corticosterone, and as bile acid homeostasis is disrupted in glucocorticoid-treated animals, we investigated if chronic intermittent restraint stress would modify m-RCT by altering the enterohepatic circulation of bile acids. C57Bl/6J mice exposed to intermittent stress for 5 days exhibited increased transit through the large intestine and enhanced fecal bile acid excretion. Of the transcription factors and transporters that regulate bile acid homeostasis, the mRNA expression levels of the hepatic farnesoid X receptor (FXR), the bile salt export pump (BSEP), and the intestinal fibroblast growth factor 15 (FGF15) were reduced, whereas those of the ileal apical sodium-dependent bile acid transporter (ASBT), responsible for active bile acid absorption, remained unchanged. Neither did the hepatic expression of cholesterol 7α-hydroxylase (CYP7A1), the key enzyme regulating bile acid synthesis, change in the stressed mice. Evaluation of the functionality of the m-RCT pathway revealed increased fecal excretion of bile acids that had been synthesized from macrophage-derived cholesterol. Overall, our study reveals that chronic intermittent stress in mice accelerates m-RCT specifically by increasing fecal excretion of bile acids. This novel mechanism of m-RCT induction could have antiatherogenic potential under conditions of chronic stress. PMID:25969465

  13. Chronic intermittent psychological stress promotes macrophage reverse cholesterol transport by impairing bile acid absorption in mice.

    PubMed

    Silvennoinen, Reija; Quesada, Helena; Kareinen, Ilona; Julve, Josep; Kaipiainen, Leena; Gylling, Helena; Blanco-Vaca, Francisco; Escola-Gil, Joan Carles; Kovanen, Petri T; Lee-Rueckert, Miriam

    2015-05-11

    Psychological stress is a risk factor for atherosclerosis, yet the pathophysiological mechanisms involved remain elusive. The transfer of cholesterol from macrophage foam cells to liver and feces (the macrophage-specific reverse cholesterol transport, m-RCT) is an important antiatherogenic pathway. Because exposure of mice to physical restraint, a model of psychological stress, increases serum levels of corticosterone, and as bile acid homeostasis is disrupted in glucocorticoid-treated animals, we investigated if chronic intermittent restraint stress would modify m-RCT by altering the enterohepatic circulation of bile acids. C57Bl/6J mice exposed to intermittent stress for 5 days exhibited increased transit through the large intestine and enhanced fecal bile acid excretion. Of the transcription factors and transporters that regulate bile acid homeostasis, the mRNA expression levels of the hepatic farnesoid X receptor (FXR), the bile salt export pump (BSEP), and the intestinal fibroblast growth factor 15 (FGF15) were reduced, whereas those of the ileal apical sodium-dependent bile acid transporter (ASBT), responsible for active bile acid absorption, remained unchanged. Neither did the hepatic expression of cholesterol 7α-hydroxylase (CYP7A1), the key enzyme regulating bile acid synthesis, change in the stressed mice. Evaluation of the functionality of the m-RCT pathway revealed increased fecal excretion of bile acids that had been synthesized from macrophage-derived cholesterol. Overall, our study reveals that chronic intermittent stress in mice accelerates m-RCT specifically by increasing fecal excretion of bile acids. This novel mechanism of m-RCT induction could have antiatherogenic potential under conditions of chronic stress. PMID:25969465

  14. Quantum Transport of Electrons through Graphene and Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Das, Shambhu K.

    Quantum transport of electrons through graphene has attracted increased interest in the field of nano-technology. Quantum transport through mesoscopic systems explains a wide range of interesting experimental findings, such as: rectification, switching mechanism and transistor actions. We focused our research on the quantum transmission of electrons through graphene and carbon nanotubes. Graphene and nanotube devices operated between source and drain shows a peculiar negative differential resistance behavior (NDR) while drawing current-voltage characteristics. This property is used in many electronic devices. The main feature of graphene is that the electron has zero effective mass at Dirac points, but gains mass when the graphene sheet is folded into a nanotube. Scientists have analyzed the vanishing mass of the electron inside graphene and explain the observed mass gain through Higgs mechanism. We focus our study on the Klein Paradox which deals with the reflection probability greater than one as well as a negative transmission probability. This has been predicted by Oscar Klein and remained a mystery until 1929; the Klein Paradox finally was proven with experimental and theoretical evidence by Geim and Novoselov. In the case of graphene, conductivity is an exponential function of temperature, whereas nanotubes follow a power law. This is a very characteristic feature of quantum dots.

  15. Nonlocal electron transport in magnetized plasmas with arbitrary atomic number

    SciTech Connect

    Bennaceur-Doumaz, D.; Bendib, A.

    2006-09-15

    The numerical solution of the steady-state electron Fokker-Planck equation perturbed with respect to a global equilibrium is presented in magnetized plasmas with arbitrary atomic number Z. The magnetic field is assumed to be constant and the electron-electron collisions are described by the Landau collision operator. The solution is derived in the Fourier space and in the framework of the diffusive approximation which captures the spatial nonlocal effects. The transport coefficients are deduced and used to close a complete set of nonlocal electron fluid equations. This work improves the results of A. Bendib et al. [Phys. Plasmas 9, 1555 (2002)] and of A. V. Brantov et al. [Phys. Plasmas 10, 4633 (2003)] restricted to the local and nonlocal high-Z plasma approximations, respectively. The influence of the magnetic field on the nonlocal effects is discussed. We propose also accurate numerical fits of the relevant transport coefficients with respect to the collisionality parameter {lambda}{sub ei}/L and the atomic number Z, where L is the typical scale length and {lambda}{sub ei} is the electron-ion mean-free-path.

  16. Turbulent electron transport in edge pedestal by electron temperature gradient turbulence

    SciTech Connect

    Singh, R.; Jhang, Hogun; Diamond, P. H.

    2013-11-15

    We present a model for turbulent electron thermal transport at the edge pedestal in high (H)-mode plasmas based on electron temperature gradient (ETG) turbulence. A quasi-linear analysis of electrostatic toroidal ETG modes shows that both turbulent electron thermal diffusivity and hyper-resistivity exhibits the Ohkawa scaling in which the radial correlation length of turbulence becomes the order of electron skin depth. Combination of the Ohkawa scales and the plasma current dependence results in a novel confinement scaling inside the pedestal region. It is also shown that ETG turbulence induces a thermoelectric pinch, which may accelerate the density pedestal formation.

  17. Transport in organic single-crystal microbelt for conformal electronics

    NASA Astrophysics Data System (ADS)

    Cui, Nan; Tong, Yanhong; Tang, Qingxin; Liu, Yichun

    2016-03-01

    We showed the advantages of flexible rubrene organic single-crystal microbelts in high-performance devices and circuits towards conformal electronics. The anisotropic transport based on the only one organic microbelt was studied by a "cross-channel" method, and the rubrene microbelt showed the highest mobility up to 26 cm2/V s in the length direction. Based on an individual rubrene microbelt, the organic single-crystal circuit with good adherence on a pearl ball and the gain as high as 18 was realized. These results present great potential for applications of organic single-crystal belts in the next-generation conformal electronics.

  18. Helicity and transport in electron MHD heat pulses

    SciTech Connect

    Stenzel, R.L.; Urrutia, J.M.

    1996-02-01

    Electrons are heated locally and temporally in a uniform magnetoplasma by applying a short current pulse to a loop antenna. The resultant heat pulse, satisfying electron MHD conditions ({omega}{sub {ital ce}}{sup {minus}1}{lt}{Delta}{ital t}{lt}{omega}{sub {ital ci}}{sup {minus}1}), generates helicity due to twisting of field lines by diamagnetic drifts. Heat convection and diffusion cool the pulse, which reduces its propagation to zero. The stationary temperature profile decays by cross-field transport conserving volume-integrated heat. {copyright} {ital 1996 The American Physical Society.}

  19. Electron transporting organic materials with an exceptional large scale homeotropic molecular orientation.

    PubMed

    Zhao, Huan; He, Zhiqun; Xu, Min; Liang, Chunjun; Kumar, Sandeep

    2016-03-28

    An electron transporting anthraquinone derivative demonstrated a stable large-scale homeotropic alignment on an open substrate surface, which substantially improved its charge carrier mobility. The electron mobility (μ(E)) increased by two orders of magnitude from 3.2 × 10(-4) cm(2) V(-1) s(-1) for the film without alignment to 1.2 × 10(-2) cm(2) V(-1) s(-1) for the homeotropically aligned film. A distinct enhancement in the UV absorption spectra of the films around the short wavelength range was observed to be associated with the molecular alignments. These alignments are less sensitive to the substrate under test. The anchoring force of the columnar stacks appears to be related to the nature of the material associated with the strong interaction between the molecules and substrate interface. PMID:26949167

  20. Ponderomotive effects on magnetic fields and electron transport under ignitor conditions

    SciTech Connect

    Mason, R.J.; Glinsky, M.; Tabak, M.

    1994-12-31

    The Fast Ignitor ICF concept will use bright source lasers to induce thermonuclear ignition. The absorption of ultra-intense laser pulses at target surfaces has been predicted to generate relativistic electrons and self-magnetic fields exceeding 100 MG. The authors have used the implicit multi-fluid code ANTHEM to track the emitted hot electrons from the corona, where they drive a fast expansion of the ions, to the dense target interior where they are slowed and absorbed into the background by collisions. In the absence of ponderomotive effects, the external magnetic field has the usual thermoelectric polarity, while a weaker field with reversed polarity is produced below critical. The authors will discuss field and transport changes associated with the inclusion of ponderomotive influences.

  1. Electronic absorption band broadening and surface roughening of phthalocyanine double layers by saturated solvent vapor treatment

    SciTech Connect

    Kim, Jinhyun; Yim, Sanggyu

    2012-10-15

    Variations in the electronic absorption (EA) and surface morphology of three types of phthalocyanine (Pc) thin film systems, i.e. copper phthalocyanine (CuPc) single layer, zinc phthalocyanine (ZnPc) single layer, and ZnPc on CuPc (CuPc/ZnPc) double layer film, treated with saturated acetone vapor were investigated. For the treated CuPc single layer film, the surface roughness slightly increased and bundles of nanorods were formed, while the EA varied little. In contrast, for the ZnPc single layer film, the relatively high solubility of ZnPc led to a considerable shift in the absorption bands as well as a large increase in the surface roughness and formation of long and wide nano-beams, indicating a part of the ZnPc molecules dissolved in acetone, which altered their molecular stacking. For the CuPc/ZnPc film, the saturated acetone vapor treatment resulted in morphological changes in mainly the upper ZnPc layer due to the significantly low solubility of the underlying CuPc layer. The treatment also broadened the EA band, which involved a combination of unchanged CuPc and changed ZnPc absorption.

  2. Optical Absorption and Electron Paramagnetic Resonance studies of two different solid solutions of Pyralspite Garnet

    NASA Astrophysics Data System (ADS)

    Watanabe, S.; Espinoza, S. R. Q.; Chubaci, J. F. D.; Cano, N. F.; Cornejo, D. R.

    2015-04-01

    Two different solid solutions of pyralspite garnet have been investigated as to their optical absorption and EPR properties. The absorption band around 9850 cm-1 is due to Fe2+. After heating above 950 °C we found this band diminishes considerably; which was interpreted as Fe2+ loosing an electron to become Fe3+. The EPR spectrum of sample consisted of a straight line with angular coefficient of about 176°. After 600°C/1hr annealing, the spectrum starts deviating from a straight line. A strong typical EPR signal is observed around g = 2.0 after annealing at 850°C. We assume that with high temperature annealing a large number of Fe2+ are converted to Fe3+ as the optical absorption has shown. These results were also confirmed by chemical reaction. The susceptibility vs. magnetic field measurement has shown that the samples annealed at temperatures below 850°C present normal paramagnetic behavior, however, annealed above 900 °C, they show hysteresis, namely ferromagnetic behavior.

  3. Femtosecond x-ray absorption spectroscopy with hard x-ray free electron laser

    SciTech Connect

    Katayama, Tetsuo; Togashi, Tadashi; Tono, Kensuke; Kameshima, Takashi; Inubushi, Yuichi; Sato, Takahiro; Hatsui, Takaki; Yabashi, Makina; Obara, Yuki; Misawa, Kazuhiko; Bhattacharya, Atanu; Kurahashi, Naoya; Ogi, Yoshihiro; Suzuki, Toshinori

    2013-09-23

    We have developed a method of dispersive x-ray absorption spectroscopy with a hard x-ray free electron laser (XFEL), generated by a self-amplified spontaneous emission (SASE) mechanism. A transmission grating was utilized for splitting SASE-XFEL light, which has a relatively large bandwidth (ΔE/E ∼ 5 × 10{sup −3}), into several branches. Two primary split beams were introduced into a dispersive spectrometer for measuring signal and reference spectra simultaneously. After normalization, we obtained a Zn K-edge absorption spectrum with a photon-energy range of 210 eV, which is in excellent agreement with that measured by a conventional wavelength-scanning method. From the analysis of the difference spectra, the noise ratio was evaluated to be ∼3 × 10{sup −3}, which is sufficiently small to trace minute changes in transient spectra induced by an ultrafast optical laser. This scheme enables us to perform single-shot, high-accuracy x-ray absorption spectroscopy with femtosecond time resolution.

  4. The kinetic model for slow photoinduced electron transport in the reaction centers of purple bacteria.

    PubMed

    Serdenko, T V; Barabash, Y M; Knox, P P; Seifullina, N Kh

    2016-12-01

    The present work is related to the investigation of slow kinetics of electron transport in the reaction centers (RCs) of Rhodobacter sphaeroides. Experimental data on the absorption kinetics of aqueous solutions of reaction centers at different modes of photoexcitation are given. It is shown that the kinetics of oxidation and reduction of RCs are well described by the sum of three exponential functions. This allows to suggest a two-level kinetic model for electron transport in the RC as a system of four electron-conformational states which correspond to three balance differential equations combined with state equation. The solution of inverse problem made it possible to obtain the rate constant values in kinetic equations for different times and intensities of exciting light. Analysis of rate constant values in different modes of RC excitation allowed to suggest that two mechanisms of structural changes are involved in RC photo-oxidation. One mechanism leads to the increment of the rate of electron return, another one-to its drop. Structural changes were found out to occur in the RCs under incident light. After light was turned off, the reduction of RCs was determined by the second mechanism. PMID:27271854

  5. The kinetic model for slow photoinduced electron transport in the reaction centers of purple bacteria

    NASA Astrophysics Data System (ADS)

    Serdenko, T. V.; Barabash, Y. M.; Knox, P. P.; Seifullina, N. Kh.

    2016-06-01

    The present work is related to the investigation of slow kinetics of electron transport in the reaction centers (RCs) of Rhodobacter sphaeroides. Experimental data on the absorption kinetics of aqueous solutions of reaction centers at different modes of photoexcitation are given. It is shown that the kinetics of oxidation and reduction of RCs are well described by the sum of three exponential functions. This allows to suggest a two-level kinetic model for electron transport in the RC as a system of four electron-conformational states which correspond to three balance differential equations combined with state equation. The solution of inverse problem made it possible to obtain the rate constant values in kinetic equations for different times and intensities of exciting light. Analysis of rate constant values in different modes of RC excitation allowed to suggest that two mechanisms of structural changes are involved in RC photo-oxidation. One mechanism leads to the increment of the rate of electron return, another one—to its drop. Structural changes were found out to occur in the RCs under incident light. After light was turned off, the reduction of RCs was determined by the second mechanism.

  6. First principle studies on the electronic structures and absorption spectra in KMgF 3 crystal with fluorine vacancy

    NASA Astrophysics Data System (ADS)

    Cheng, Fang; Liu, Tingyu; Zhang, Qiren; Qiao, Hailin; Zhou, Xiuwen

    2010-08-01

    The experiments indicate that the perfect KMgF 3 crystal has no absorption in the visible range, however the electron irradiation induces a complex absorption spectrum. The absorption spectra can be decomposed by five Gaussian bands peaking at 2.5 eV (488 nm), 3.4 eV (359 nm), 4.2 eV (295 nm), 4.6 eV (270 nm) and 5.2 eV (239 nm), respectively. The purpose of this paper is to seek the origins of the absorption bands. The electronic structures and absorption spectra either for the perfect KMgF 3 or for KMgF 3: VF+ with electrical neutrality have been studied by using density functional theory code CASTEP with the lattice structure optimized. The calculation results predicate that KMgF 3: VF+ also exhibits five absorption bands caused by the existence of the fluorine ion vacancy VF+ and the five absorption bands well coincide with the experimental results. It is believable that the five absorption bands are related to VF+ in KMgF 3 crystal produced by the electron irradiation.

  7. Electron heat transport from stochastic fields in gyrokinetic simulationsa)

    NASA Astrophysics Data System (ADS)

    Wang, E.; Nevins, W. M.; Candy, J.; Hatch, D.; Terry, P.; Guttenfelder, W.

    2011-05-01

    GYRO is used to examine the perturbed magnetic field structure generated by electromagnetic gyrokinetic simulations of the CYCLONE base case as βe is varied from 0.1% to 0.7%, as investigated by J. Candy [Phys. Plasmas 12, 072307 (2005)]. Poincare surface of section plots obtained from integrating the self-consistent magnetic field demonstrates widespread stochasticity for all nonzero values of βe. Despite widespread stochasticity of the perturbed magnetic fields, no significant increase in electron transport is observed. The magnetic diffusion, dm [A. B. Rechester and M. N. Rosenbluth, Phys. Rev. Lett 40, 38 (1978)], is used to quantify the degree of stochasticity and related to the electron heat transport for hundreds of time slices in each simulation.

  8. Electron heat transport from stochastic fields in gyrokinetic simulations

    SciTech Connect

    Wang, E.; Nevins, W. M.; Candy, J.; Hatch, D.; Terry, P.; Guttenfelder, W.

    2011-05-15

    GYRO is used to examine the perturbed magnetic field structure generated by electromagnetic gyrokinetic simulations of the CYCLONE base case as {beta}{sub e} is varied from 0.1% to 0.7%, as investigated by J. Candy [Phys. Plasmas 12, 072307 (2005)]. Poincare surface of section plots obtained from integrating the self-consistent magnetic field demonstrates widespread stochasticity for all nonzero values of {beta}{sub e}. Despite widespread stochasticity of the perturbed magnetic fields, no significant increase in electron transport is observed. The magnetic diffusion, d{sub m}[A. B. Rechester and M. N. Rosenbluth, Phys. Rev. Lett 40, 38 (1978)], is used to quantify the degree of stochasticity and related to the electron heat transport for hundreds of time slices in each simulation.

  9. Electron beam transport for the LBL IR-FEL

    SciTech Connect

    Staples, J.; Edighoffer, J.; Kim, Kwang-Je

    1992-07-01

    The infrared flee-electron laser (IR-FEL) proposed by LBL as part of the Combustion Dynamics Research Laboratory (CDRL) consists of a multiple-pass accelerator with superconducting cavities supplying a 55 MeV 12 mA beam to an undulator within a 24-meter optical cavity. Future options include deceleration through the same cavities for energy recovery and reducing the power in the beam dump. The electron transport system from the injector through the cavities and undulator must satisfy conditions of high order achromaticity, isochronicity, unity first-order transport matrix around the recirculation loop, variable betatron match into the undulator, ease of operation and economical implementation. This paper presents a workable solution that satisfies these requirements.

  10. Two-point model for electron transport in EBT

    SciTech Connect

    Chiu, S.C.; Guest, G.E.

    1980-01-01

    The electron transport in EBT is simulated by a two-point model corresponding to the central plasma and the edge. The central plasma is assumed to obey neoclassical collisionless transport. The edge plasma is assumed turbulent and modeled by Bohm diffusion. The steady-state temperatures and densities in both regions are obtained as functions of neutral influx and microwave power. It is found that as the neutral influx decreases and power increases, the edge density decreases while the core density increases. We conclude that if ring instability is responsible for the T-M mode transition, and if stability is correlated with cold electron density at the edge, it will depend sensitively on ambient gas pressure and microwave power.

  11. Nanoscale electron transport at the surface of a topological insulator

    PubMed Central

    Bauer, Sebastian; Bobisch, Christian A.

    2016-01-01

    The use of three-dimensional topological insulators for disruptive technologies critically depends on the dissipationless transport of electrons at the surface, because of the suppression of backscattering at defects. However, in real devices, defects are unavoidable and scattering at angles other than 180° is allowed for such materials. Until now, this has been studied indirectly by bulk measurements and by the analysis of the local density of states in close vicinity to defect sites. Here, we directly measure the nanoscale voltage drop caused by the scattering at step edges, which occurs if a lateral current flows along a three-dimensional topological insulator. The experiments were performed using scanning tunnelling potentiometry for thin Bi2Se3 films. So far, the observed voltage drops are small because of large contributions of the bulk to the electronic transport. However, for the use of ideal topological insulating thin films in devices, these contributions would play a significant role. PMID:27098939

  12. Nanoscale electron transport at the surface of a topological insulator

    NASA Astrophysics Data System (ADS)

    Bauer, Sebastian; Bobisch, Christian A.

    2016-04-01

    The use of three-dimensional topological insulators for disruptive technologies critically depends on the dissipationless transport of electrons at the surface, because of the suppression of backscattering at defects. However, in real devices, defects are unavoidable and scattering at angles other than 180° is allowed for such materials. Until now, this has been studied indirectly by bulk measurements and by the analysis of the local density of states in close vicinity to defect sites. Here, we directly measure the nanoscale voltage drop caused by the scattering at step edges, which occurs if a lateral current flows along a three-dimensional topological insulator. The experiments were performed using scanning tunnelling potentiometry for thin Bi2Se3 films. So far, the observed voltage drops are small because of large contributions of the bulk to the electronic transport. However, for the use of ideal topological insulating thin films in devices, these contributions would play a significant role.

  13. Nanoscale electron transport at the surface of a topological insulator.

    PubMed

    Bauer, Sebastian; Bobisch, Christian A

    2016-01-01

    The use of three-dimensional topological insulators for disruptive technologies critically depends on the dissipationless transport of electrons at the surface, because of the suppression of backscattering at defects. However, in real devices, defects are unavoidable and scattering at angles other than 180° is allowed for such materials. Until now, this has been studied indirectly by bulk measurements and by the analysis of the local density of states in close vicinity to defect sites. Here, we directly measure the nanoscale voltage drop caused by the scattering at step edges, which occurs if a lateral current flows along a three-dimensional topological insulator. The experiments were performed using scanning tunnelling potentiometry for thin Bi2Se3 films. So far, the observed voltage drops are small because of large contributions of the bulk to the electronic transport. However, for the use of ideal topological insulating thin films in devices, these contributions would play a significant role. PMID:27098939

  14. Ballistic electron transport in stubbed quantum waveguides: Experiment and theory

    NASA Astrophysics Data System (ADS)

    Debray, P.; Raichev, O. E.; Vasilopoulos, P.; Rahman, M.; Perrin, R.; Mitchell, W. C.

    2000-04-01

    We present results of experimental and theoretical investigations of electron transport through stub-shaped waveguides or electron stub tuners (ESTs) in the ballistic regime. Measurements of the conductance G as a function of voltages, applied to different gates Vi (i=bottom, top, and side) of the device, show oscillations in the region of the first quantized plateau that we attribute to reflection resonances. The oscillations are rather regular and almost periodic when the height h of the EST cavity is small compared to its width. When h is increased, the oscillations become less regular and broad depressions in G appear. A theoretical analysis, which accounts for the electrostatic potential formed by the gates in the cavity region, and a numerical computation of the transmission probabilities successfully explains the experimental observations. An important finding for real devices, defined by surface Schottky gates, is that the resonance minima result from size quantization along the transport direction of the EST.

  15. Ab Initio Electronic Relaxation Times and Transport in Noble Metals

    NASA Astrophysics Data System (ADS)

    Mustafa, Jamal I.; Bernardi, Marco; Neaton, Jeffrey B.; Louie, Steven G.

    Relaxation times employed to study electron transport in metals are typically assumed to be constants and obtained empirically using the Drude model. Here, we employ ab initio calculations to compute the electron-phonon relaxation times of Cu, Ag, and Au, and find that they vary significantly on the Fermi surface, spanning ~15 -45 fs. We compute room temperature resistivities in excellent agreement with experiment by combining GW bandstructures, Wannier-interpolated band velocities, and ab initio relaxation times. Our calculations are compared to other approximations used for the relaxation times. Additionally, an importance sampling scheme is introduced to speed up the convergence of resistivity and transport calculations by sampling directly points on the Fermi surface. This work was supported by NSF Grant No. DMR15-1508412 and U.S. DOE under Contract No. DE-AC02-05CH11231. Computational resources have been provided by DOE at LBNL's NERSC facility.

  16. Dietary Lipid and Carbohydrate Interactions: Implications on Lipid and Glucose Absorption, Transport in Gilthead Sea Bream (Sparus aurata) Juveniles.

    PubMed

    Castro, Carolina; Corraze, Geneviève; Basto, Ana; Larroquet, Laurence; Panserat, Stéphane; Oliva-Teles, Aires

    2016-06-01

    A digestibility trial was performed with gilthead sea bream juveniles (IBW = 72 g) fed four diets differing in lipid source (fish oil, FO; or a blend of vegetable oil, VO) and starch content (0 %, CH-; or 20 %, CH+) to evaluate the potential interactive effects between carbohydrates and VO on the processes involved in digestion, absorption and transport of lipids and glucose. In fish fed VO diets a decrease in lipid digestibility and in cholesterol (C), High Density Lipoprotein(HDL)-C and Low Density Lipoprotein (LDL)-C (only in CH+ group) were recorded. Contrarily, dietary starch induced postprandial hyperglycemia and time related alterations on serum triacylglycerol (TAG), phospholipid (PL) and C concentrations. Fish fed a CH+ diet presented lower serum TAG than CH- group at 6 h post-feeding, and the reverse was observed at 12 h post-feeding for TAG and PL. Lower serum C and PL at 6 h post-feeding were recorded only in VOCH+ group. No differences between groups were observed in hepatic and intestinal transcript levels of proteins involved in lipid transport and hydrolysis (FABP, DGAT, GPAT, MTP, LPL, LCAT). Lower transcript levels of proteins related to lipid transport (ApoB, ApoA1, FABP2) were observed in the intestine of fish fed the CH+ diet, but remained unchanged in the liver. Overall, transcriptional mechanisms involved in lipid transport and absorption were not linked to changes in lipid serum and digestibility. Dietary starch affected lipid absorption and transport, probably due to a delay in lipid absorption. This study suggests that a combination of dietary VO and starch may negatively affect cholesterol absorption and transport. PMID:27023202

  17. Transport of electron beams with initial transverse-longitudinal correlation

    NASA Astrophysics Data System (ADS)

    Harris, J. R.; Lewellen, J. W.; Poole, B. R.

    2013-08-01

    When an electron beam whose current varies in time is extracted from a DC gun, the competition between the time-dependent space charge force and the time-independent focusing force will cause a correlation between radius, divergence, current, and position along the beam. This correlation will determine the beam's configuration in trace space, and together with the design of the downstream transport system, will determine the quality of the transport solutions that can be obtained, including the amplitude of the mismatch oscillations occurring in each slice of the beam. Recent simulations of a simplified diode with Pierce-type focusing operating at nonrelativistic voltages indicated that the radius and divergence of beams extracted from such guns can be approximated to high accuracy as linear functions of current. Here, we consider the impact of this dependence on the beam configuration in trace space and investigate the implications for matching and transport of such correlated beams in uniform linear focusing channels.

  18. Transport of solar electrons in the turbulent interplanetary magnetic field

    NASA Astrophysics Data System (ADS)

    Ablaßmayer, J.; Tautz, R. C.; Dresing, N.

    2016-01-01

    The turbulent transport of solar energetic electrons in the interplanetary magnetic field is investigated by means of a test-particle Monte-Carlo simulation. The magnetic fields are modeled as a combination of the Parker field and a turbulent component. In combination with the direct calculation of diffusion coefficients via the mean-square displacements, this approach allows one to analyze the effect of the initial ballistic transport phase. In that sense, the model complements the main other approach in which a transport equation is solved. The major advancement is that, by recording the flux of particles arriving at virtual detectors, intensity and anisotropy-time profiles can be obtained. Observational indications for a longitudinal asymmetry can thus be explained by tracing the diffusive spread of the particle distribution. The approach may be of future help for the systematic interpretation of observations for instance by the solar terrestrial relations observatory (STEREO) and advanced composition explorer (ACE) spacecrafts.

  19. Intrinsic electronic and transport properties of graphyne sheets and nanoribbons.

    PubMed

    Wu, Wenzhi; Guo, Wanlin; Zeng, Xiao Cheng

    2013-10-01

    Graphyne, a two-dimensional carbon allotrope like graphene but containing doubly and triply bonded carbon atoms, has been proven to possess amazing electronic properties as graphene. Although the electronic, optical, and mechanical properties of graphyne and graphyne nanoribbons (NRs) have been previously studied, their electron transport behaviors have not been understood. Here we report a comprehensive study of the intrinsic electronic and transport properties of four distinct polymorphs of graphyne (α, β, γ, and 6,6,12-graphynes) and their nanoribbons (GyNRs) using density functional theory coupled with the non-equilibrium Green's function (NEGF) method. Among the four graphyne sheets, 6,6,12-graphyne displays notable directional anisotropy in the transport properties. Among the GyNRs, those with armchair edges are nonmagnetic semiconductors whereas those with zigzag edges can be either antiferromagnetic or nonmagnetic semiconductors. Among the armchair GyNRs, the α-GyNRs and 6,6,12-GyNRs exhibit distinctive negative differential resistance (NDR) behavior. On the other hand, the zigzag α-GyNRs and zigzag 6,6,12-GyNRs exhibit symmetry-dependent transport properties, that is, asymmetric zigzag GyNRs behave as conductors with nearly linear current-voltage dependence, whereas symmetric GyNRs produce very weak currents due to the presence of a conductance gap around the Fermi level under finite bias voltages. Such symmetry-dependent behavior stems from different coupling between π* and π subbands. Unlike α- and 6,6,12-GyNRs, both zigzag β-GyNRs and zigzag γ-GyNRs exhibit NDR behavior regardless of the symmetry. PMID:23949158

  20. Electron transport in the dissimilatory iron reducer, GS-15

    USGS Publications Warehouse

    Gorby, Y.A.; Lovley, D.R.

    1991-01-01

    Mechanisms for electron transport to Fe(III) were investigated in GS-15, anovel anaerobic microorganism which can obtain energy for growth hy coupling the complete oxidation of organic acids or aromatic compounds to the reduction of Fe(III) to Fe(II). The results indicate that Fe(III) reduction proceeds through a type b cytochrome and a membrane-bound Fe(III) reductase which is distinct from the nitrate reductase.

  1. Mitochondrial Electron Transport and Glycolysis are coupled in Articular Cartilage

    PubMed Central

    Martin, James A.; Martini, Anne; Molinari, Alexander; Morgan, Walter; Ramalingam, Wendy; Buckwalter, Joseph A.; McKinley, Todd O.

    2012-01-01

    Objective Although the majority of the ATP in chondrocytes is made by glycolysis rather than by oxidative phosphorylation in mitochondria there is evidence to suggest that reactive oxygen species produced by mitochondrial electron transport help to maintain cellular redox balance in favor of glycolysis. The objective of this study was to test this hypothesis by determining if rotenone, which inhibits electron transport and blocks oxidant production inhibits glycolytic ATP synthesis. Design Bovine osteochondral explants were treated with rotenone, an electron transport inhibitor; or oligomycin an ATP synthase inhibitor; or 2-fluoro-2-deoxy-D-glucose, a glycolysis inhibiter; or peroxide, an exogenous oxidant; or mitoquinone, a mitochondria-targeted anti-oxidant. Cartilage extracts were assayed for ATP, NAD+, and NADH, and culture medium was assayed for pyruvate and lactate after 24 hours of treatment. Imaging studies were used to measure superoxide production in cartilage. Results Rotenone and 2-fluoro-2-deoxy-D-glucose caused a significant decline in cartilage ATP (p < 0.001). In contrast, ATP levels were not affected by oligomycin. Peroxide treatment blocked rotenone effects on ATP, while treatment with MitoQ significantly suppressed ATP levels. Rotenone and 2-fluoro-2-deoxy-D-glucose caused a significant decline in pyruvate, but not in lactate production. NADH:NAD+ ratios decreased significantly in both rotenone and 2-fluoro-2-deoxy-D-glucose-treated explants (p < 0.05). Rotenone also significantly reduced superoxide production Conclusions These findings showing a link between glycolysis and electron transport are consistent with previous reports on the critical need for oxidants to support normal chondrocyte metabolism. They suggest a novel role for mitochondria in cartilage homeostasis that is independent of oxidative phosphorylation. PMID:22305999

  2. Infrared absorption and electron paramagnetic resonance studies of vinyl radical in noble-gas matrices

    SciTech Connect

    Tanskanen, Hanna; Khriachtchev, Leonid; Raesaenen, Markku; Feldman, Vladimir I.; Sukhov, Fedor F.; Orlov, Aleksei Yu.; Tyurin, Daniil A.

    2005-08-08

    Vinyl radicals produced by annealing-induced reaction of mobilized hydrogen atoms with acetylene molecules in solid noble-gas matrices (Ar, Kr, and Xe) were characterized by Fourier transform infrared and electron paramagnetic resonance (EPR) spectroscopies. The hydrogen atoms were generated from acetylene by UV photolysis or fast electron irradiation. Two vibrational modes of the vinyl radical ({nu}{sub 7} and {nu}{sub 5}) were assigned in IR absorption studies. The assignment is based on data for various isotopic substitutions (D and {sup 13}C) and confirmed by comparison with the EPR measurements and density-functional theory calculations. The data on the {nu}{sub 7} mode is in agreement with previous experimental and theoretical results whereas the {nu}{sub 5} frequency agrees well with the computational data but conflicts with the gas-phase IR emission results.

  3. Bound states in optical absorption of semiconductor quantum wells containing a two-dimensional electron Gas

    PubMed

    Huard; Cox; Saminadayar; Arnoult; Tatarenko

    2000-01-01

    The dependence of the optical absorption spectrum of a semiconductor quantum well on two-dimensional electron concentration n(e) is studied using CdTe samples. The trion peak (X-) seen at low n(e) evolves smoothly into the Fermi edge singularity at high n(e). The exciton peak (X) moves off to high energy, weakens, and disappears. The X,X- splitting is linear in n(e) and closely equal to the Fermi energy plus the trion binding energy. For Cd0.998Mn0.002Te quantum wells in a magnetic field, the X,X- splitting reflects unequal Fermi energies for M = +/-1/2 electrons. The data are explained by Hawrylak's theory of the many-body optical response including spin effects. PMID:11015866

  4. Electron bubbles in liquid helium: Density functional calculations of infrared absorption spectra

    SciTech Connect

    Grau, Victor; Barranco, Manuel; Mayol, Ricardo; Pi, Marti

    2006-02-01

    Within density functional theory, we have calculated the energy of the transitions from the ground state to the first two excited states in the electron bubbles in liquid helium at pressures from zero to about the solidification pressure. For {sup 4}He at low temperatures, our results are in very good agreement with infrared absorption experiments. Above a temperature of {approx}2 K, we overestimate the energy of the 1s-1p transition. We attribute this to the break down of the Franck-Condon principle due to the presence of helium vapor inside the bubble. Our results indicate that the 1s-2p transition energies are sensitive not only to the size of the electron bubble, but also to its surface thickness. We also present results for the infrared transitions in the case of liquid {sup 3}He, for which we lack experimental data.

  5. Self-amplified spontaneous emission free electron laser devices and nonideal electron beam transport

    NASA Astrophysics Data System (ADS)

    Lazzarino, L. L.; Di Palma, E.; Anania, M. P.; Artioli, M.; Bacci, A.; Bellaveglia, M.; Chiadroni, E.; Cianchi, A.; Ciocci, F.; Dattoli, G.; Di Giovenale, D.; Di Pirro, G.; Ferrario, M.; Gatti, G.; Giannessi, L.; Mostacci, A.; Musumeci, P.; Petralia, A.; Petrillo, V.; Pompili, R.; Rau, J. V.; Rossi, A. R.; Sabia, E.; Vaccarezza, C.; Villa, F.

    2014-11-01

    We have developed, at the SPARC test facility, a procedure for a real time self-amplified spontaneous emission free electron laser (FEL) device performance control. We describe an actual FEL, including electron and optical beam transport, through a set of analytical formulas, allowing a fast and reliable on-line "simulation" of the experiment. The system is designed in such a way that the characteristics of the transport elements and the laser intensity are measured and adjusted, via a real time computation, during the experimental run, to obtain an on-line feedback of the laser performances. The detail of the procedure and the relevant experimental results are discussed.

  6. Electronic transport in VO{sub 2}—Experimentally calibrated Boltzmann transport modeling

    SciTech Connect

    Kinaci, Alper; Rosenmann, Daniel; Chan, Maria K. Y. E-mail: mchan@anl.gov; Kado, Motohisa; Ling, Chen; Zhu, Gaohua; Banerjee, Debasish E-mail: mchan@anl.gov

    2015-12-28

    Materials that undergo metal-insulator transitions (MITs) are under intense study, because the transition is scientifically fascinating and technologically promising for various applications. Among these materials, VO{sub 2} has served as a prototype due to its favorable transition temperature. While the physical underpinnings of the transition have been heavily investigated experimentally and computationally, quantitative modeling of electronic transport in the two phases has yet to be undertaken. In this work, we establish a density-functional-theory (DFT)-based approach with Hubbard U correction (DFT + U) to model electronic transport properties in VO{sub 2} in the semiconducting and metallic regimes, focusing on band transport using the Boltzmann transport equations. We synthesized high quality VO{sub 2} films and measured the transport quantities across the transition, in order to calibrate the free parameters in the model. We find that the experimental calibration of the Hubbard correction term can efficiently and adequately model the metallic and semiconducting phases, allowing for further computational design of MIT materials for desirable transport properties.

  7. Free-free absorption of infrared radiation in collisions of electrons with neutral rare-gas atoms

    NASA Technical Reports Server (NTRS)

    Stallcop, J. R.

    1974-01-01

    A relationship between the inverse bremsstrahlung absorption cross section and the electron neutral momentum transfer cross section has been utilized to determine the infrared free-free continuum absorption coefficient for the negative ions of helium, neon, argon, krypton, and xenon. The values of the momentum transfer cross section for this calculation have been obtained from experimental measurements. Analytical expressions for the absorption coefficient have also been developed. From the results of this calculation, it is possible to determine the absorption coefficient per unit electron density per neutral atom for temperatures in the range from 2500 to 25,000 K. The results are compared with those from tabulations of previous calculations and those computed from theoretical values of the phase shifts for the elastic scattering of electrons by neutral atoms.

  8. Comparative analysis of discrete and continuous absorption weighting estimators used in Monte Carlo simulations of radiative transport in turbid media.

    PubMed

    Hayakawa, Carole K; Spanier, Jerome; Venugopalan, Vasan

    2014-02-01

    We examine the relative error of Monte Carlo simulations of radiative transport that employ two commonly used estimators that account for absorption differently, either discretely, at interaction points, or continuously, between interaction points. We provide a rigorous derivation of these discrete and continuous absorption weighting estimators within a stochastic model that we show to be equivalent to an analytic model, based on the radiative transport equation (RTE). We establish that both absorption weighting estimators are unbiased and, therefore, converge to the solution of the RTE. An analysis of spatially resolved reflectance predictions provided by these two estimators reveals no advantage to either in cases of highly scattering and highly anisotropic media. However, for moderate to highly absorbing media or isotropically scattering media, the discrete estimator provides smaller errors at proximal source locations while the continuous estimator provides smaller errors at distal locations. The origin of these differing variance characteristics can be understood through examination of the distribution of exiting photon weights. PMID:24562029

  9. Comparative analysis of discrete and continuous absorption weighting estimators used in Monte Carlo simulations of radiative transport in turbid media

    PubMed Central

    Hayakawa, Carole K.; Spanier, Jerome; Venugopalan, Vasan

    2014-01-01

    We examine the relative error of Monte Carlo simulations of radiative transport that employ two commonly used estimators that account for absorption differently, either discretely, at interaction points, or continuously, between interaction points. We provide a rigorous derivation of these discrete and continuous absorption weighting estimators within a stochastic model that we show to be equivalent to an analytic model, based on the radiative transport equation (RTE). We establish that both absorption weighting estimators are unbiased and, therefore, converge to the solution of the RTE. An analysis of spatially resolved reflectance predictions provided by these two estimators reveals no advantage to either in cases of highly scattering and highly anisotropic media. However, for moderate to highly absorbing media or isotropically scattering media, the discrete estimator provides smaller errors at proximal source locations while the continuous estimator provides smaller errors at distal locations. The origin of these differing variance characteristics can be understood through examination of the distribution of exiting photon weights. PMID:24562029

  10. The role of electron-impact vibrational excitation in electron transport through gaseous tetrahydrofuran

    SciTech Connect

    Duque, H. V.; Do, T. P. T.; Konovalov, D. A.; White, R. D.; Brunger, M. J. E-mail: darryl.jones@flinders.edu.au; Jones, D. B. E-mail: darryl.jones@flinders.edu.au

    2015-03-28

    In this paper, we report newly derived integral cross sections (ICSs) for electron impact vibrational excitation of tetrahydrofuran (THF) at intermediate impact energies. These cross sections extend the currently available data from 20 to 50 eV. Further, they indicate that the previously recommended THF ICS set [Garland et al., Phys. Rev. A 88, 062712 (2013)] underestimated the strength of the electron-impact vibrational excitation processes. Thus, that recommended vibrational cross section set is revised to address those deficiencies. Electron swarm transport properties were calculated with the amended vibrational cross section set, to quantify the role of electron-driven vibrational excitation in describing the macroscopic swarm phenomena. Here, significant differences of up to 17% in the transport coefficients were observed between the calculations performed using the original and revised cross section sets for vibrational excitation.

  11. Charge transport and injection in amorphous organic electronic materials

    NASA Astrophysics Data System (ADS)

    Tse, Shing Chi

    This thesis presents how we use various measuring techniques to study the charge transport and injection in organic electronic materials. Understanding charge transport and injection properties in organic solids is of vital importance for improving performance characteristics of organic electronic devices, including organic-light-emitting diodes (OLEDs), photovoltaic cells (OPVs), and field effect transistors (OFETs). The charge transport properties of amorphous organic materials, commonly used in organic electronic devices, are investigated by the means of carrier mobility measurements. Transient electroluminescence (EL) technique was used to evaluate the electron mobility of an electron transporting material--- tris(8-hydroxyquinoline) aluminum (Alq3). The results are in excellent agreement with independent time-of-flight (TOF) measurements. Then, the effect of dopants on electron transport was also examined. TOF technique was also used to examine the effects of tertiary-butyl (t-Bu) substitutions on anthracene derivatives (ADN). All ADN compounds were found to be ambipolar. As the degree of t-Bu substitution increases, the carrier mobilities decrease progressively. The reduction of carrier mobilities with increasing t-butylation can be attributed to a decrease in the charge-transfer integral or the wavefunction overlap. In addition, from TOF measurements, two naphthylamine-based hole transporters, namely, N,N'-diphenyl-N,N'-bis(1-naphthyl)(1,1'-biphenyl)-4,4'diamine (NPB) and 4,4',4"-tris(n-(2-naphthyl)-n-phenyl-amino)-triphenylamine (2TNATA) were found to possess electron-transporting (ET) abilities. An organic light-emitting diode that employed NPB as the ET material was demonstrated. The electron conducting mechanism of NPB and 2TNATA in relation to the hopping model will be discussed. Furthermore, the ET property of NPB applied in OLEDs will also be examined. Besides transient EL and TOF techniques, we also use dark-injection space-charge-limited current

  12. Theoretical investigations into the electronic structures and electron transport properties of fluorine and carbonyl end-functionalized quarterthiophenes.

    PubMed

    Li, Qian; Duan, Yuai; Gao, Hong-Ze; Su, Zhong-Мin; Geng, Yun

    2015-06-01

    In this work, we concentrate on systematic investigation on the fluorination and carbonylation effect on electron transport properties of thiophene-based materials with the aim of seeking and designing electron transport materials. Some relative factors, namely, frontier molecular orbital (FMO), vertical electron affinity (VEA), electron reorganization energy (λele), electron transfer integral (tele), electron drift mobility (μele) and band structures have been calculated and discussed based on density functional theory. The results show that the introduction of fluorine atoms and carbonyl group especially for the latter could effectively increase EA and reduce λele, which is beneficial to the improvement of electron transport performance. Furthermore, these introductions could also affect the tele by changing molecular packing manner and distribution of FMO. Finally, according to our calculation, the 3d system is considered to be a promising electron transport material with small λele, high electron transport ability and good ambient stability. PMID:25909689

  13. Distribution of tunnelling times for quantum electron transport

    NASA Astrophysics Data System (ADS)

    Rudge, Samuel L.; Kosov, Daniel S.

    2016-03-01

    In electron transport, the tunnelling time is the time taken for an electron to tunnel out of a system after it has tunnelled in. We define the tunnelling time distribution for quantum processes in a dissipative environment and develop a practical approach for calculating it, where the environment is described by the general Markovian master equation. We illustrate the theory by using the rate equation to compute the tunnelling time distribution for electron transport through a molecular junction. The tunnelling time distribution is exponential, which indicates that Markovian quantum tunnelling is a Poissonian statistical process. The tunnelling time distribution is used not only to study the quantum statistics of tunnelling along the average electric current but also to analyse extreme quantum events where an electron jumps against the applied voltage bias. The average tunnelling time shows distinctly different temperature dependence for p- and n-type molecular junctions and therefore provides a sensitive tool to probe the alignment of molecular orbitals relative to the electrode Fermi energy.

  14. Multidimensional electron-photon transport with standard discrete ordinates codes

    SciTech Connect

    Drumm, C.R.

    1997-04-01

    A method is described for generating electron cross sections that are comparable with standard discrete ordinates codes without modification. There are many advantages of using an established discrete ordinates solver, e.g. immediately available adjoint capability. Coupled electron-photon transport capability is needed for many applications, including the modeling of the response of electronics components to space and man-made radiation environments. The cross sections have been successfully used in the DORT, TWODANT and TORT discrete ordinates codes. The cross sections are shown to provide accurate and efficient solutions to certain multidimensional electron-photon transport problems. The key to the method is a simultaneous solution of the continuous-slowing-down (CSD) portion and elastic-scattering portion of the scattering source by the Goudsmit-Saunderson theory. The resulting multigroup-Legendre cross sections are much smaller than the true scattering cross sections that they represent. Under certain conditions, the cross sections are guaranteed positive and converge with a low-order Legendre expansion.

  15. Energy level control: toward an efficient hot electron transport

    PubMed Central

    Jin, Xiao; Li, Qinghua; Li, Yue; Chen, Zihan; Wei, Tai-Huei; He, Xingdao; Sun, Weifu

    2014-01-01

    Highly efficient hot electron transport represents one of the most important properties required for applications in photovoltaic devices. Whereas the fabrication of efficient hot electron capture and lost-cost devices remains a technological challenge, regulating the energy level of acceptor-donor system through the incorporation of foreign ions using the solution-processed technique is one of the most promising strategies to overcome this obstacle. Here we present a versatile acceptor-donor system by incorporating MoO3:Eu nanophosphors, which reduces both the ‘excess' energy offset between the conduction band of acceptor and the lowest unoccupied molecular orbital of donor, and that between the valence band and highest occupied molecular orbital. Strikingly, the hot electron transfer time has been shortened. This work demonstrates that suitable energy level alignment can be tuned to gain the higher hot electron/hole transport efficiency in a simple approach without the need for complicated architectures. This work builds up the foundation of engineering building blocks for third-generation solar cells. PMID:25099864

  16. Distribution of tunnelling times for quantum electron transport.

    PubMed

    Rudge, Samuel L; Kosov, Daniel S

    2016-03-28

    In electron transport, the tunnelling time is the time taken for an electron to tunnel out of a system after it has tunnelled in. We define the tunnelling time distribution for quantum processes in a dissipative environment and develop a practical approach for calculating it, where the environment is described by the general Markovian master equation. We illustrate the theory by using the rate equation to compute the tunnelling time distribution for electron transport through a molecular junction. The tunnelling time distribution is exponential, which indicates that Markovian quantum tunnelling is a Poissonian statistical process. The tunnelling time distribution is used not only to study the quantum statistics of tunnelling along the average electric current but also to analyse extreme quantum events where an electron jumps against the applied voltage bias. The average tunnelling time shows distinctly different temperature dependence for p- and n-type molecular junctions and therefore provides a sensitive tool to probe the alignment of molecular orbitals relative to the electrode Fermi energy. PMID:27036425

  17. Electron transport through a quantum dot assisted by cavity photons

    NASA Astrophysics Data System (ADS)

    Abdullah, Nzar Rauf; Tang, Chi-Shung; Manolescu, Andrei; Gudmundsson, Vidar

    2013-11-01

    We investigate transient transport of electrons through a single quantum dot controlled by a plunger gate. The dot is embedded in a finite wire with length Lx assumed to lie along the x-direction with a parabolic confinement in the y-direction. The quantum wire, originally with hard-wall confinement at its ends, ±Lx/2, is weakly coupled at t = 0 to left and right leads acting as external electron reservoirs. The central system, the dot and the finite wire, is strongly coupled to a single cavity photon mode. A non-Markovian density-matrix formalism is employed to take into account the full electron-photon interaction in the transient regime. In the absence of a photon cavity, a resonant current peak can be found by tuning the plunger-gate voltage to lift a many-body state of the system into the source-drain bias window. In the presence of an x-polarized photon field, additional side peaks can be found due to photon-assisted transport. By appropriately tuning the plunger-gate voltage, the electrons in the left lead are allowed to undergo coherent inelastic scattering to a two-photon state above the bias window if initially one photon was present in the cavity. However, this photon-assisted feature is suppressed in the case of a y-polarized photon field due to the anisotropy of our system caused by its geometry.

  18. Electron transport through a quantum dot assisted by cavity photons.

    PubMed

    Abdullah, Nzar Rauf; Tang, Chi-Shung; Manolescu, Andrei; Gudmundsson, Vidar

    2013-11-20

    We investigate transient transport of electrons through a single quantum dot controlled by a plunger gate. The dot is embedded in a finite wire with length Lx assumed to lie along the x-direction with a parabolic confinement in the y-direction. The quantum wire, originally with hard-wall confinement at its ends, ±Lx/2, is weakly coupled at t = 0 to left and right leads acting as external electron reservoirs. The central system, the dot and the finite wire, is strongly coupled to a single cavity photon mode. A non-Markovian density-matrix formalism is employed to take into account the full electron-photon interaction in the transient regime. In the absence of a photon cavity, a resonant current peak can be found by tuning the plunger-gate voltage to lift a many-body state of the system into the source-drain bias window. In the presence of an x-polarized photon field, additional side peaks can be found due to photon-assisted transport. By appropriately tuning the plunger-gate voltage, the electrons in the left lead are allowed to undergo coherent inelastic scattering to a two-photon state above the bias window if initially one photon was present in the cavity. However, this photon-assisted feature is suppressed in the case of a y-polarized photon field due to the anisotropy of our system caused by its geometry. PMID:24132041

  19. Control of electronic transport in graphene by electromagnetic dressing.

    PubMed

    Kristinsson, K; Kibis, O V; Morina, S; Shelykh, I A

    2016-01-01

    We demonstrated theoretically that the renormalization of the electron energy spectrum near the Dirac point of graphene by a strong high-frequency electromagnetic field (dressing field) drastically depends on polarization of the field. Namely, linear polarization results in an anisotropic gapless energy spectrum, whereas circular polarization leads to an isotropic gapped one. As a consequence, the stationary (dc) electronic transport in graphene strongly depends on parameters of the dressing field: A circularly polarized field monotonically decreases the isotropic conductivity of graphene, whereas a linearly polarized one results in both giant anisotropy of conductivity (which can reach thousands of percents) and the oscillating behavior of the conductivity as a function of the field intensity. Since the predicted phenomena can be observed in a graphene layer irradiated by a monochromatic electromagnetic wave, the elaborated theory opens a substantially new way to control electronic properties of graphene with light. PMID:26838371

  20. Fast-electron transport in cylindrically laser-compressed matter

    NASA Astrophysics Data System (ADS)

    Perez, F.; Koenig, M.; Batani, D.; Baton, S. D.; Beg, F. N.; Benedetti, C.; Brambrink, E.; Chawla, S.; Dorchies, F.; Fourment, C.; Galimberti, M.; Gizzi, L. A.; Heathcote, R.; Higginson, D. P.; Hulin, S.; Jafer, R.; Koester, P.; Labate, L.; Lancaster, K.; Mac Kinnon, A. J.; McPhee, A. G.; Nazarov, W.; Nicolai, P.; Pasley, J.; Ravasio, A.; Richetta, M.; Santos, J. J.; Sgattoni, A.; Spindloe, C.; Vauzour, B.; Volpe, L.

    2009-12-01

    Experimental and theoretical results of relativistic electron transport in cylindrically compressed matter are presented. This experiment, which is a part of the HiPER roadmap, was achieved on the VULCAN laser facility (UK) using four long pulses beams (~4 × 50 J, 1 ns, at 0.53 µm) to compress a hollow plastic cylinder filled with plastic foam of three different densities (0.1, 0.3 and 1 g cm-3). 2D simulations predict a density of 2-5 g cm-3 and a plasma temperature up to 100 eV at maximum compression. A short pulse (10 ps, 160 J) beam generated fast electrons that propagate through the compressed matter by irradiating a nickel foil at an intensity of 5 × 1018 W cm-2. X-ray spectrometer and imagers were implemented in order to estimate the compressed plasma conditions and to infer the hot electron characteristics. Results are discussed and compared with simulations.

  1. Control of electronic transport in graphene by electromagnetic dressing

    PubMed Central

    Kristinsson, K.; Kibis, O. V.; Morina, S.; Shelykh, I. A.

    2016-01-01

    We demonstrated theoretically that the renormalization of the electron energy spectrum near the Dirac point of graphene by a strong high-frequency electromagnetic field (dressing field) drastically depends on polarization of the field. Namely, linear polarization results in an anisotropic gapless energy spectrum, whereas circular polarization leads to an isotropic gapped one. As a consequence, the stationary (dc) electronic transport in graphene strongly depends on parameters of the dressing field: A circularly polarized field monotonically decreases the isotropic conductivity of graphene, whereas a linearly polarized one results in both giant anisotropy of conductivity (which can reach thousands of percents) and the oscillating behavior of the conductivity as a function of the field intensity. Since the predicted phenomena can be observed in a graphene layer irradiated by a monochromatic electromagnetic wave, the elaborated theory opens a substantially new way to control electronic properties of graphene with light. PMID:26838371

  2. Unified electronic charge transport model for organic solar cells

    NASA Astrophysics Data System (ADS)

    Mottaghian, Seyyed Sadegh; Biesecker, Matt; Bayat, Khadijeh; Farrokh Baroughi, Mahdi

    2013-07-01

    This paper provides a comprehensive modeling approach for simulation of electronic charge transport in excitonic solar cells with organic and organic/inorganic structures. Interaction of energy carrying particles (electrons, holes, singlet excitons, and triplet excitons) with each other and their transformation in the bulk of the donor and acceptor media as well as the donor/acceptor interfaces are incorporated in form of coupling matrices into the continuity equations and interface boundary conditions. As a case study, the model is applied to simulate an organic bilayer photovoltaic (PV) device to quantify the effects of photo generation, recombination coefficient, carrier mobility, and electrode work function on its PV characteristics. The study proves that electron-hole recombination at the donor/acceptor interface is the dominant mechanism that limits open circuit voltage of the device.

  3. Predicting X-ray absorption spectra of semiconducting polymers for electronic structure and morphology characterization

    NASA Astrophysics Data System (ADS)

    Su, Gregory; Patel, Shrayesh; Pemmaraju, C. Das; Kramer, Edward; Prendergast, David; Chabinyc, Michael

    2015-03-01

    Core-level X-ray absorption spectroscopy (XAS) reveals important information on the electronic structure of materials and plays a key role in morphology characterization. Semiconducting polymers are the active component in many organic electronics. Their electronic properties are critically linked to device performance, and a proper understanding of semiconducting polymer XAS is crucial. Techniques such as resonant X-ray scattering rely on core-level transitions to gain materials contrast and probe orientational order. However, it is difficult to identify these transitions based on experiments alone, and complementary simulations are required. We show that first-principles calculations can capture the essential features of experimental XAS of semiconducting polymers, and provide insight into which molecular model, such as oligomers or periodic boundary conditions, are best suited for XAS calculations. Simulated XAS can reveal contributions from individual atoms and be used to visualize molecular orbitals. This allows for improved characterization of molecular orientation and scattering analysis. These predictions lay the groundwork for understanding how chemical makeup is linked to electronic structure, and to properly utilize experiments to characterize semiconducting polymers.

  4. Electronic transitions and fermi edge singularity in polar heterostructures studied by absorption and emission spectroscopy

    NASA Astrophysics Data System (ADS)

    Pandey, S.; Cavalcoli, D.; Minj, A.; Fraboni, B.; Cavallini, A.; Gamarra, P.; Poisson, M. A.

    2012-12-01

    Optically induced electronic transitions in nitride based polar heterostructures have been investigated by absorption and emission spectroscopy. Surface photovoltage (SPV), photocurrent (PC), and photo luminescence spectroscopy have been applied to high quality InAlN/AlN/GaN structures to study the optical properties of two dimensional electron gas. Energy levels within the two dimensional electron gas (2DEG) well at the interface between the GaN and AlN have been directly observed by SPV and PC. Moreover, a strong enhancement of the photoluminescence intensity due to holes recombining with electrons at the Fermi Energy, known as fermi energy singularity, has been observed. These analyses have been carried out on InAlN/AlN/GaN heterojunctions with the InAlN barrier layer having different In content, a parameter which affects the energy levels within the 2DEG well as well as the optical signal intensity. The measured energy values are in a very good agreement with the ones obtained by Schrödinger-Poisson simulations.

  5. Hot-Electron Temperature and Laser-Light Absorption in Fast Ignition

    SciTech Connect

    Haines, M. G.; Wei, M. S.; Beg, F. N.; Stephens, R. B.

    2009-01-30

    Experimental data [F. N. Beg et al., Phys. Plasmas 4, 447 (1997)] indicate that for intense short-pulse laser-solid interactions at intensities up to 5x10{sup 18} W cm{sup -2} the hot-electron temperature {proportional_to}(I{lambda}{sup 2}){sup 1/3}. A fully relativistic analytic model based on energy and momentum conservation laws for the laser interaction with an overdense plasma is presented here. A general formula for the hot-electron temperature is found that closely agrees with the experimental scaling over the relevant intensity range. This scaling is much lower than ponderomotive scaling. Examination of the electron forward displacement compared to the collisionless skin depth shows that electrons experience only a fraction of a laser-light period before being accelerated forward beyond the laser light's penetration region. Inclusion of backscattered light in a modified model indicates that light absorption approaches 80%-90% for intensity >10{sup 19} W cm{sup -2}.

  6. Modelling electron transport in magnetized low-temperature discharge plasmas

    NASA Astrophysics Data System (ADS)

    Hagelaar, G. J. M.

    2007-02-01

    Magnetic fields are sometimes used to confine the plasma in low-pressure low-temperature gas discharges, for example in magnetron discharges, Hall-effect-thruster discharges, electron-cyclotron-resonance discharges and helicon discharges. We discuss how these magnetized discharges can be modelled by two-dimensional self-consistent models based on electron fluid equations. The magnetized electron flux is described by an anisotropic drift diffusion equation, where the electron mobility is much smaller perpendicular to the magnetic field than parallel to it. The electric potential is calculated either from Poisson's equation or from the electron equations, assuming quasineutrality. Although these models involve many assumptions, they are appropriate to study the main effects of the magnetic field on the charged particle transport and space charge electric fields in realistic two-dimensional discharge configurations. We demonstrate by new results that these models reproduce known phenomena such as the establishment of the Boltzmann relation along magnetic field lines, the penetration of perpendicular applied electric fields into the plasma bulk and the decrease in magnetic confinement by short-circuit wall currents. We also present an original method to prevent numerical errors arising from the extreme anisotropy of the electron mobility, which tend to invalidate model results from standard numerical methods.

  7. Electron transport and dephasing in semiconductor quantum dots

    NASA Astrophysics Data System (ADS)

    Huibers, Andrew Gerrit A.

    At low temperatures, electrons in semiconductors can be phase coherent over distances exceeding tens of microns and are sufficiently monochromatic that a variety of interesting quantum interference phenomena can be observed and manipulated. This work discusses electron transport measurements through cavities (quantum dots) formed by laterally confining electrons in the two-dimensional sub-band of a GaAs/AlGaAs heterojunction. Metal gates fabricated using e-beam lithography enable fine control of the cavity shape as well as the leads which connect the dot cavity to source and drain reservoirs. Quantum dots can be modeled by treating the devices as chaotic scatterers. Predictions of this theoretical description are found to be in good quantitative agreement with experimental measurements of full conductance distributions at different temperatures. Weak localization, the suppression of conductance due to phase-coherent backscattering at zero magnetic field, is used to measure dephasing times in the system. Mechanisms responsible for dephasing, including electron-electron scattering and Nyquist phase relaxation, are investigated by studying the loss of phase coherence as a function of temperature. Coupling of external microwave fields to the device is also studied to shed light on the unexpected saturation of dephasing that is observed below an electron temperature of 100 mK. The effect of external fields in the present experiment is explained in terms of Joule heating from an ac bias.

  8. The macro response Monte Carlo method for electron transport

    NASA Astrophysics Data System (ADS)

    Svatos, Michelle Marie

    1998-10-01

    This thesis proves the feasibility of basing depth dose calculations for electron radiotherapy on first- principles single scatter physics, in an amount of time that is comparable to or better than current electron Monte Carlo methods. The Macro Response Monte Carlo (MRMC) method achieves run times that have potential to be much faster than conventional electron transport methods such as condensed history. This is possible because MRMC is a Local-to- Global method, meaning the problem is broken down into two separate transport calculations. The first stage is a local, single scatter calculation, which generates probability distribution functions (PDFs) to describe the electron's energy, position and trajectory after leaving the local geometry, a small sphere or 'kugel'. A number of local kugel calculations were run for calcium and carbon, creating a library of kugel data sets over a range of incident energies (0.25 MeV-8 MeV) and sizes (0.025 cm to 0.1 cm in radius). The second transport stage is a global calculation, where steps that conform to the size of the kugels in the library are taken through the global geometry, which in this case is a CT (computed tomography) scan of a patient or phantom. For each step, the appropriate PDFs from the MRMC library are sampled to determine the electron's new energy, position and trajectory. The electron is immediately advanced to the end of the step and then chooses another kugel to sample, which continues until transport is completed. The MRMC global stepping code was benchmarked as a series of subroutines inside of the Peregrine Monte Carlo code against EGS4 and MCNP for depth dose in simple phantoms having density inhomogeneities. The energy deposition algorithms for spreading dose across 5-10 zones per kugel were tested. Most resulting depth dose calculations were within 2-3% of well-benchmarked codes, with one excursion to 4%. This thesis shows that the concept of using single scatter-based physics in clinical radiation

  9. Physicochemical processes and the formulation of dosimetry models. [Transport and absorption of ozone and nitrogen dioxide in the respiratory tract

    SciTech Connect

    Overton, J.H. Jr.

    1984-01-01

    The major physical and chemical processes involved in the transport and absorption of O/sub 3/ or NO/sub 2/ in the lower respiratory tract are discussed. This included the development of respiratory tract models, flow patterns, and transport in tube networks, the mucous, surfactant, and tissue layers, and chemical reactions and transport of O/sub 3/ or NO/sub 2/ within these layers. Descriptions of the individual processes are simplified and integrated to illustrate the formulation of dosimetry models. Data from a dosimetry model, formulated from the concepts discussed, are used to illustrate the types of information obtained by modeling. 31 references.

  10. Low-lying singlet states of carotenoids having 8-13 conjugated double bonds as determined by electronic absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Wang, Peng; Nakamura, Ryosuke; Kanematsu, Yasuo; Koyama, Yasushi; Nagae, Hiroyoshi; Nishio, Tomohiro; Hashimoto, Hideki; Zhang, Jian-Ping

    2005-07-01

    Electronic absorption spectra were recorded at room temperature in solutions of carotenoids having different numbers of conjugated double bonds, n = 8-13, including a spheroidene derivatives, neurosporene, spheroidene, lycopene, anhydrorhodovibrin and spirilloxanthin. The vibronic states of 1Bu+(v=0-4), 2Ag-(v=0-3), 3Ag- (0) and 1Bu- (0) were clearly identified. The arrangement of the four electronic states determined by electronic absorption spectroscopy was identical to that determined by measurement of resonance Raman excitation profiles [K. Furuichi et al., Chem. Phys. Lett. 356 (2002) 547] for carotenoids in crystals.

  11. Helium, Iron and Electron Particle Transport and Energy Transport Studies on the TFTR Tokamak

    DOE R&D Accomplishments Database

    Synakowski, E. J.; Efthimion, P. C.; Rewoldt, G.; Stratton, B. C.; Tang, W. M.; Grek, B.; Hill, K. W.; Hulse, R. A.; Johnson, D .W.; Mansfield, D. K.; McCune, D.; Mikkelsen, D. R.; Park, H. K.; Ramsey, A. T.; Redi, M. H.; Scott, S. D.; Taylor, G.; Timberlake, J.; Zarnstorff, M. C. (Princeton Univ., NJ (United States). Plasma Physics Lab.); Kissick, M. W. (Wisconsin Univ., Madison, WI (United States))

    1993-03-01

    Results from helium, iron, and electron transport on TFTR in L-mode and Supershot deuterium plasmas with the same toroidal field, plasma current, and neutral beam heating power are presented. They are compared to results from thermal transport analysis based on power balance. Particle diffusivities and thermal conductivities are radially hollow and larger than neoclassical values, except possibly near the magnetic axis. The ion channel dominates over the electron channel in both particle and thermal diffusion. A peaked helium profile, supported by inward convection that is stronger than predicted by neoclassical theory, is measured in the Supershot The helium profile shape is consistent with predictions from quasilinear electrostatic drift-wave theory. While the perturbative particle diffusion coefficients of all three species are similar in the Supershot, differences are found in the L-Mode. Quasilinear theory calculations of the ratios of impurity diffusivities are in good accord with measurements. Theory estimates indicate that the ion heat flux should be larger than the electron heat flux, consistent with power balance analysis. However, theoretical values of the ratio of the ion to electron heat flux can be more than a factor of three larger than experimental values. A correlation between helium diffusion and ion thermal transport is observed and has favorable implications for sustained ignition of a tokamak fusion reactor.

  12. Helium, iron and electron particle transport and energy transport studies on the TFTR tokamak

    SciTech Connect

    Synakowski, E.J.; Efthimion, P.C.; Rewoldt, G.; Stratton, B.C.; Tang, W.M.; Grek, B.; Hill, K.W.; Hulse, R.A.; Johnson, D.W.; Mansfield, D.K.; McCune, D.; Mikkelsen, D.R.; Park, H.K.; Ramsey, A.T.; Redi, M.H.; Scott, S.D.; Taylor, G.; Timberlake, J.; Zarnstorff, M.C.; Kissick, M.W.

    1993-03-01

    Results from helium, iron, and electron transport on TFTR in L-mode and Supershot deuterium plasmas with the same toroidal field, plasma current, and neutral beam heating power are presented. They are compared to results from thermal transport analysis based on power balance. Particle diffusivities and thermal conductivities are radially hollow and larger than neoclassical values, except possibly near the magnetic axis. The ion channel dominates over the electron channel in both particle and thermal diffusion. A peaked helium profile, supported by inward convection that is stronger than predicted by neoclassical theory, is measured in the Supershot The helium profile shape is consistent with predictions from quasilinear electrostatic drift-wave theory. While the perturbative particle diffusion coefficients of all three species are similar in the Supershot, differences are found in the L-Mode. Quasilinear theory calculations of the ratios of impurity diffusivities are in good accord with measurements. Theory estimates indicate that the ion heat flux should be larger than the electron heat flux, consistent with power balance analysis. However, theoretical values of the ratio of the ion to electron heat flux can be more than a factor of three larger than experimental values. A correlation between helium diffusion and ion thermal transport is observed and has favorable implications for sustained ignition of a tokamak fusion reactor.

  13. Probing electronic transport of individual nanostructures with atomic precision

    SciTech Connect

    Qin, Shengyong; Li, An-Ping

    2012-01-01

    Accessing individual nanostructures with atomic precision is an important process in the bottom-up fabrication and characterization of electronic nanodevices. Local electrical contacts, namely nanoelectrodes, are often fabricated by using top-down lithography and chemical etching techniques. These processes however lack atomic precision and introduce the possibility of contamination. Here, we review recent reports on the application of a field-induced emission process in the fabrication of local contacts onto individual nanowires and nanotubes with atomic spatial precision. In this method, gold nanoislands are deposited onto nanostructures precisely by using a scanning tunneling microscope tip, which provides a clean and controllable process to ensure both electrically conductive and mechanically reliable contacts. The applicability of the technique has been demonstrated in a wide variety of nanostructures, including silicide atomic wires, carbon nanotubes, and copper nanowires. These local contacts bridge the nanostructures and the transport probes, allowing for the measurements of both electrical transport and scanning tunneling microscopy on the same nanostructures in situ. The direct correlation between electronic and transport properties and atomic structures can be explored on individual nanostructures at the unprecedented atomic level.

  14. Understanding electronic structure and transport properties in nanoscale junctions

    NASA Astrophysics Data System (ADS)

    Dhungana, Kamal B.

    Understanding the electronic structure and the transport properties of nanoscale materials are pivotal for designing future nano-scale electronic devices. Nanoscale materials could be individual or groups of molecules, nanotubes, semiconducting quantum dots, and biomolecules. Among these several alternatives, organic molecules are very promising and the field of molecular electronics has progressed significantly over the past few decades. Despite these progresses, it has not yet been possible to achieve atomic level control at the metal-molecule interface during a conductance measurement, which hinders the progress in this field. The lack of atomic level information of the interface also makes it much harder for theorist to interpret the experimental results. To identify the junction configuration that possibly exists during the experimental measurement of conductance in molecular junction, we created an ensemble of Ruthanium-bis(terpyridine) molecular devices, and studied the transport behavior in these molecular junctions. This helps us identifying the junction geometry that yields the experimentally measured current-voltage characteristics. Today's electronic devices mostly ignore the spin effect of an electron. The inclusion of spin effect of an electron on solid-state transistor allows us to build more efficient electronic devices; this also alleviates the problem of huge heat dissipation in the nanoscale electronic devices. Different materials have been utilized to build three terminals spin transistor since its inception in 1950. In search of suitable candidates for the molecular spin transistor, we have recently designed a spin-valve transistor based on an organometallic molecule; a large amplification (320 %) in tunnel magneto-resistance (TMR) is found to occur at an experimentally accessible gate field. This suggests that the organic molecules can be utilized for making the next generation three terminal spintronic devices. Similarly, we have designed a

  15. Momentum Transport in Electron-Dominated Spherical Torus Plasmas

    SciTech Connect

    Kaye, S. M.; Solomon, W.; Bell, R. E.; LeBlanc, B. P.; Levinton, F.; Menard, J.; Rewoldt, G.; Sabbagh, S.; Wang, W.; Yuh, H.

    2009-02-24

    The National Spherical Torus Experiment (NSTX) operates between 0.35 and 0.55 T, which, when coupled to up to 7 MW of neutral beam injection, leads to central rotation velocities in excess of 300 km/s and ExB shearing rates up to 1 MHz. This level of ExB shear can be up to a factor of five greater than typical linear growth rates of long-wavelength ion (e.g., ITG) modes, at least partially suppressing these instabilities. Evidence for this turbulence suppression is that the inferred diffusive ion thermal flux in NSTX H-modes is often at the neoclassical level, and thus these plasmas operate in an electron-dominated transport regime. Analysis of experiments using n=3 magnetic fields to change plasma rotation indicate that local rotation shear influences local transport coefficients, most notably the ion thermal diffusivity, in a manner consistent with suppression of the low-k turbulence by this rotation shear. The value of the effective momentum diffusivity, as inferred from steady-state momentum balance, is found to be larger than the neoclassical value. Results of perturbative experiments indicate inward pinch velocities up to 40 m/s and perturbative momentum diffusivities of up to 4 m2/s, which are larger by a factor of several than those values inferred from steady-state analysis. The inferred pinch velocity values are consistent with values based on theories in which low-k turbulence drives the inward momentum pinch. Thus, in Spherical Tori (STs), while the neoclassical ion energy transport effects can be relatively high and dominate the ion energy transport, the neoclassical momentum transport effects are near zero, meaning that transport of momentum is dominated by any low-k turbulence that exists.

  16. Ab initio electronic transport model with explicit solution to the linearized Boltzmann transport equation

    NASA Astrophysics Data System (ADS)

    Faghaninia, Alireza; Ager, Joel W.; Lo, Cynthia S.

    2015-06-01

    Accurate models of carrier transport are essential for describing the electronic properties of semiconductor materials. To the best of our knowledge, the current models following the framework of the Boltzmann transport equation (BTE) either rely heavily on experimental data (i.e., semiempirical), or utilize simplifying assumptions, such as the constant relaxation time approximation (BTE-cRTA). While these models offer valuable physical insights and accurate calculations of transport properties in some cases, they often lack sufficient accuracy—particularly in capturing the correct trends with temperature and carrier concentration. We present here a transport model for calculating low-field electrical drift mobility and Seebeck coefficient of n -type semiconductors, by explicitly considering relevant physical phenomena (i.e., elastic and inelastic scattering mechanisms). We first rewrite expressions for the rates of elastic scattering mechanisms, in terms of ab initio properties, such as the band structure, density of states, and polar optical phonon frequency. We then solve the linear BTE to obtain the perturbation to the electron distribution—resulting from the dominant scattering mechanisms—and use this to calculate the overall mobility and Seebeck coefficient. Therefore, we have developed an ab initio model for calculating mobility and Seebeck coefficient using the Boltzmann transport (aMoBT) equation. Using aMoBT, we accurately calculate electrical transport properties of the compound n -type semiconductors, GaAs and InN, over various ranges of temperature and carrier concentration. aMoBT is fully predictive and provides high accuracy when compared to experimental measurements on both GaAs and InN, and vastly outperforms both semiempirical models and the BTE-cRTA. Therefore, we assert that this approach represents a first step towards a fully ab initio carrier transport model that is valid in all compound semiconductors.

  17. Transport properties of overheated electrons trapped on a helium surface

    NASA Astrophysics Data System (ADS)

    Closa, Fabien; Raphäel, Elie; Chepelianskii, Alexei D.

    2014-08-01

    An ultra-strong photovoltaic effect has recently been reported for electrons trapped on a liquid helium surface under a microwave excitation tuned at intersubband resonance [D. Konstantinov, A.D. Chepelianskii, K. Kono, J. Phys. Soc. Jpn 81, 093601 (2012)]. In this article, we analyze theoretically the redistribution of the electron density induced by an overheating of the surface electrons under irradiation, and obtain quantitative predictions for the photocurrent dependence on the effective electron temperature and confinement voltages. We show that the photo-current can change sign as a function of the parameters of the electrostatic confinement potential on the surface, while the photocurrent measurements reported so far have been performed only at a fixed confinement potential. The experimental observation of this sign reversal could provide a reliable estimation of the electron effective temperature in this new out of equilibrium state. Finally, we have also considered the effect of the temperature on the outcome of capacitive transport measurement techniques. These investigations led us to develop, numerical and analytical methods for solving the Poisson-Boltzmann equation in the limit of very low temperatures which could be useful for other systems.

  18. Electron and hole transport in ambipolar, thin film pentacene transistors

    SciTech Connect

    Saudari, Sangameshwar R.; Kagan, Cherie R.

    2015-01-21

    Solution-processed, ambipolar, thin-film pentacene field-effect transistors were employed to study both electron and hole transport simultaneously in a single, organic solid-state device. Electron and hole mobilities were extracted from the respective unipolar saturation regimes and show thermally activated behavior and gate voltage dependence. We fit the gate voltage dependent saturation mobility to a power law to extract the characteristic Meyer-Neldel (MN) energy, a measure of the width of the exponential distribution of localized states extending into the energy gap of the organic semiconductor. The MN energy is ∼78 and ∼28 meV for electrons and holes, respectively, which reflects a greater density of localized tail states for electrons than holes. This is consistent with the lower measured electron than hole mobility. For holes, the well-behaved linear regime allows for four-point probe measurement of the contact resistance independent mobility and separate characterization of the width of the localized density of states, yielding a consistent MN energy of 28 meV.

  19. Electrokinesis is a microbial behavior that requires extracellular electron transport

    PubMed Central

    Harris, H. W.; El-Naggar, M. Y.; Bretschger, O.; Ward, M. J.; Romine, M. F.; Obraztsova, A. Y.; Nealson, K. H.

    2009-01-01

    We report a previously undescribed bacterial behavior termed electrokinesis. This behavior was initially observed as a dramatic increase in cell swimming speed during reduction of solid MnO2 particles by the dissimilatory metal-reducing bacterium Shewanella oneidensis MR-1. The same behavioral response was observed when cells were exposed to small positive applied potentials at the working electrode of a microelectrochemical cell and could be tuned by adjusting the potential on the working electrode. Electrokinesis was found to be different from both chemotaxis and galvanotaxis but was absent in mutants defective in electron transport to solid metal oxides. Using in situ video microscopy and cell tracking algorithms, we have quantified the response for different strains of Shewanella and shown that the response correlates with current-generating capacity in microbial fuel cells. The electrokinetic response was only exhibited by a subpopulation of cells closest to the MnO2 particles or electrodes. In contrast, the addition of 1 mM 9,10-anthraquinone-2,6-disulfonic acid, a soluble electron shuttle, led to increases in motility in the entire population. Electrokinesis is defined as a behavioral response that requires functional extracellular electron transport and that is observed as an increase in cell swimming speeds and lengthened paths of motion that occur in the proximity of a redox active mineral surface or the working electrode of an electrochemical cell. PMID:20018675

  20. Electrokinesis is a microbial behavior that requires extracellular electron transport.

    PubMed

    Harris, H W; El-Naggar, M Y; Bretschger, O; Ward, M J; Romine, M F; Obraztsova, A Y; Nealson, K H

    2010-01-01

    We report a previously undescribed bacterial behavior termed electrokinesis. This behavior was initially observed as a dramatic increase in cell swimming speed during reduction of solid MnO(2) particles by the dissimilatory metal-reducing bacterium Shewanella oneidensis MR-1. The same behavioral response was observed when cells were exposed to small positive applied potentials at the working electrode of a microelectrochemical cell and could be tuned by adjusting the potential on the working electrode. Electrokinesis was found to be different from both chemotaxis and galvanotaxis but was absent in mutants defective in electron transport to solid metal oxides. Using in situ video microscopy and cell tracking algorithms, we have quantified the response for different strains of Shewanella and shown that the response correlates with current-generating capacity in microbial fuel cells. The electrokinetic response was only exhibited by a subpopulation of cells closest to the MnO(2) particles or electrodes. In contrast, the addition of 1 mM 9,10-anthraquinone-2,6-disulfonic acid, a soluble electron shuttle, led to increases in motility in the entire population. Electrokinesis is defined as a behavioral response that requires functional extracellular electron transport and that is observed as an increase in cell swimming speeds and lengthened paths of motion that occur in the proximity of a redox active mineral surface or the working electrode of an electrochemical cell. PMID:20018675

  1. Electron Transport Dominated Regimes in Alcator C-Mod

    NASA Astrophysics Data System (ADS)

    Porkolab, M.; Dorris, J.; Bonoli, P. T.; Ennever, P.; Fiore, C.; Greenwald, M.; Hubbard, A.; Ma, Y.; Reinke, M. L.; Rice, J.; Rost, J.; Tsujii, N.; Lin, L.; Candy, J.; Waltz, R.; Diamond, P.; Lee, C. J.

    2010-11-01

    In ohmically heated low density plasmas where τE ne, the so-called neo-Alcator regime, TRANSP results indicate that χi<< χe, while nonlinear gyrokinetic analysis for the measured profiles predicts the opposite inequality [1]. This regime is of great interest for transport studies since Ti < Te, and the electron and ion transport channels can be separated and studied separately. At the same time, measurements of turbulent fluctuations with Phase Contrast Imaging diagnostic (PCI) indicated reasonable agreement with GYRO predictions at frequencies 80-250 kHz, corresponding to core ITG turbulence. The turbulent spectrum at lower frequencies could not be identified since the PCI technique does not allow separation of the core plasma fluctuations from those at the edge. Here we present measurements and analysis from a more extensive set of plasma regimes than previously. Of particular current interest is the role of electron drift wave turbulence driven by ohmic electron drift, U [2], since in these low density regimes U/Cs <= 6, and experimentally we find that the global confinement τE Cs/U where Cs = (Te/mi)^1/2. [1] L. Lin, Invited talk, APS-DPP, 11, 2009, Atlanta, GA. [2] C.J. Lee, P. Diamond, M. Porkolab, presented at TTF workshop, 2010.

  2. Artemisinin Inhibits Chloroplast Electron Transport Activity: Mode of Action

    PubMed Central

    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

  3. Metallic carbon nanotubes with metal contacts: electronic structure and transport

    NASA Astrophysics Data System (ADS)

    Zienert, A.; Schuster, J.; Gessner, T.

    2014-10-01

    We study quasi-ballistic electron transport in metallic (6,0) carbon nanotubes (CNTs) of variable length in contact with Al, Cu, Pd, Pt, Ag, and Au electrodes by using the non-equilibrium Green's function formalism in combination with either density functional theory or self-consistent extended Hückel theory. We find good agreement between both. Visualizing the local device density of states of the systems gives a descriptive link between electronic structure and transport properties. In comparison with bare finite and infinite tubes, we show that the electronic structure of short metallic CNTs is strongly modified by the presence of the metallic electrodes, which leads to pronounced size effects in the conductance. The mean conductances and linear response currents allow a ranking of the metals regarding their ability to form low-Ohmic contacts with the nanotube: Ag≲ Au\\lt Cu\\ll Pt≈ Pd\\ll Al. These findings are contrasted with similar trends in contact distance, binding energy, calculated work function of the metal surfaces, and various results from literature.

  4. Nanoscale Electron Transport Measurements of Immobilized Cytochrome P450 Proteins

    PubMed Central

    Bostick, Christopher D.; Flora, Darcy R.; Gannett, Peter M.; Tracy, Timothy S.; Lederman, David

    2015-01-01

    Gold nanopillars, functionalized with an organic self-assembled monolayer, can be used to measure the electrical conductance properties of immobilized proteins without aggregation. Measurements of the conductance of nanopillars with cytochrome P450 2C9 (CYP2C9) proteins using conducting probe atomic force microscopy demonstrate that a correlation exists between the energy barrier height between hopping sites and CYP2C9 metabolic activity. Measurements performed as a function of tip force indicate that, when subjected to a large force, the protein is more stable in the presence of a substrate. This agrees with the hypothesis that substrate entry into the active site helps to stabilize the enzyme. The relative distance between hopping sites also increases with increasing force, possibly because protein functional groups responsible for electron transport depend on the structure of the protein. The inhibitor sulfaphenazole, in addition to the previously studied aniline, increased the barrier height for electron transfer and thereby makes CYP2C9 reduction more difficult and inhibits metabolism. This suggests that P450 Type II binders may decrease the ease of electron transport processes in the enzyme, in addition to occupying the active site. PMID:25804257

  5. Hot Electron Transport Properties of Thin Copper Films Using Ballistic Electron Emission Microscopy

    NASA Astrophysics Data System (ADS)

    Garramone, J. J.; Abel, J. R.; Sitnitsky, I. L.; Zhao, L.; Appelbaum, I.; Labella, V. P.

    2009-03-01

    Copper is widely used material for electrical interconnects within integrated circuits and recently as a base layer for hot electron spin injection and readout into silicon. Integral to both their applications is the knowledge of the electron scattering length. To the best of our knowledge, little work exists that directly measures the scattering length of electrons in copper. In this study we used ballistic electron emission microscopy (BEEM) to measure the hot electron attenuation length of copper thin films deposited on Si(001). BEEM is a three terminal scanning tunneling microcopy (STM) based technique that can measure transport and Schottky heights of metal/semiconductor systems. We find a Schottky height of 0.67 eV and an attenuation length approaching 40 nm just above the Schottky height at 77 K. We also measure a decrease in the attenuation length with increasing tip bias to determine the relative roles of inelastic and elastic scattering.

  6. Epitaxial 1D electron transport layers for high-performance perovskite solar cells

    NASA Astrophysics Data System (ADS)

    Han, Gill Sang; Chung, Hyun Suk; Kim, Dong Hoe; Kim, Byeong Jo; Lee, Jin-Wook; Park, Nam-Gyu; Cho, In Sun; Lee, Jung-Kun; Lee, Sangwook; Jung, Hyun Suk

    2015-09-01

    We demonstrate high-performance perovskite solar cells with excellent electron transport properties using a one-dimensional (1D) electron transport layer (ETL). The 1D array-based ETL is comprised of 1D SnO2 nanowires (NWs) array grown on a F:SnO2 transparent conducting oxide substrate and rutile TiO2 nanoshells epitaxially grown on the surface of the 1D SnO2 NWs. The optimized devices show more than 95% internal quantum yield at 750 nm, and a power conversion efficiency (PCE) of 14.2%. The high quantum yield is attributed to dramatically enhanced electron transport in the epitaxial TiO2 layer, compared to that in conventional nanoparticle-based mesoporous TiO2 (mp-TiO2) layers. In addition, the open space in the 1D array-based ETL increases the prevalence of uniform TiO2/perovskite junctions, leading to reproducible device performance with a high fill factor. This work offers a method to achieve reproducible, high-efficiency perovskite solar cells with high-speed electron transport.We demonstrate high-performance perovskite solar cells with excellent electron transport properties using a one-dimensional (1D) electron transport layer (ETL). The 1D array-based ETL is comprised of 1D SnO2 nanowires (NWs) array grown on a F:SnO2 transparent conducting oxide substrate and rutile TiO2 nanoshells epitaxially grown on the surface of the 1D SnO2 NWs. The optimized devices show more than 95% internal quantum yield at 750 nm, and a power conversion efficiency (PCE) of 14.2%. The high quantum yield is attributed to dramatically enhanced electron transport in the epitaxial TiO2 layer, compared to that in conventional nanoparticle-based mesoporous TiO2 (mp-TiO2) layers. In addition, the open space in the 1D array-based ETL increases the prevalence of uniform TiO2/perovskite junctions, leading to reproducible device performance with a high fill factor. This work offers a method to achieve reproducible, high-efficiency perovskite solar cells with high-speed electron transport

  7. Conservative differencing of the electron Fokker-Planck transport equation

    SciTech Connect

    Langdon, A.B.

    1981-01-12

    We need to extend the applicability and improve the accuracy of kinetic electron transport codes. In this paper, special attention is given to modelling of e-e collisions, including the dominant contributions arising from anisotropy. The electric field and spatial gradient terms are also considered. I construct finite-difference analogues to the Fokker-Planck integral-differential collision operator, which conserve the particle number, momentum and energy integrals (sums) regardless of the coarseness of the velocity zoning. Such properties are usually desirable, but are especially useful, for example, when there are spatial regions and/or time intervals in which the plasma is cool, so that the collision operator acts rapidly and the velocity distribution is poorly resolved, yet it is crucial that gross conservation properties be respected in hydro-transport applications, such as in the LASNEX code. Some points are raised concerning spatial differencing and time integration.

  8. Contacting nanowires and nanotubes with atomic precision for electronic transport

    SciTech Connect

    Qin, Shengyong; Hellstrom, Sondra L; Bao, Zhenan; Boyanov, Boyan; Li, An-Ping

    2012-01-01

    Making contacts to nanostructures with atomic precision is an important process in the bottom-up fabrication and characterization of electronic nanodevices. Existing contacting techniques use top-down lithography and chemical etching, but lack atomic precision and introduce the possibility of contamination. Here, we report that a field-induced emission process can be used to make local contacts onto individual nanowires and nanotubes with atomic spatial precision. The gold nano-islands are deposited onto nanostructures precisely by using a scanning tunneling microscope tip, which provides a clean and controllable method to ensure both electrically conductive and mechanically reliable contacts. To demonstrate the wide applicability of the technique, nano-contacts are fabricated on silicide atomic wires, carbon nanotubes, and copper nanowires. The electrical transport measurements are performed in situ by utilizing the nanocontacts to bridge the nanostructures to the transport probes.

  9. Studies of local electron heat transport on TFTR

    SciTech Connect

    Fredrickson, E.D.; Chang, Z.Y.; Janos, A.; McGuire, K.M.; Scott, S.; Taylor, G.

    1993-08-16

    The anomalously fast relaxation of the perturbations to the electron temperature profile caused by a sawtooth crash has been studied extensively on TFTR. We will show that on a short timescale the heat pulse is not simply diffusive as has been generally assumed, but that modeling of the heat pulse requires a transient enhancement in {chi}{sub e} following the sawtooth crash. It will be shown that the time-dependent enhancement in {chi}{sub e} predicted by non-linear thermal transport models, i.e., incremental {chi} models or the Rebut-Lallia-Watkins transport model, is much smaller than that required to explain the anomalies in the heat pulse propagation.

  10. Electronic absorption spectroscopy probed side-chain movement in chromic transitions of polydiacetylene vesicles.

    PubMed

    Potisatityuenyong, Anupat; Rojanathanes, Rojrit; Tumcharern, Gamolwan; Sukwattanasinitt, Mongkol

    2008-05-01

    Thermochromism, solvatochromism, and alkalinochromism of a poly-10,12-pentacosadiynoic acid (poly(PCDA)) vesicle solution are studied by electronic absorption spectroscopy. The spectroscopic profiles reveal different sequences of side-chain movement during the chromic transitions. The gradual hypsochromic shift and reversibility of the purple solution at low temperature in the thermochromic transition indicates that the transition starts with reversible conformational alteration of methylene side chains leading to metastable purple vesicles. Further heating to 80 degrees C or higher eventually causes the hydrogen bonds at the carboxylic head groups to break and turns the vesicle solution to red. The irreversibility of the red vesicles indicates that it is the most thermodynamically stable form. In the ethanolochromism and alkalinochromism, the processes are however induced at the vesicle-media interface, directly bringing about the hydrogen bond breaking. The purple solutions observed in the ethanolochromism and alkalinochromism cannot reverse back to the blue one. The absorption spectra clearly demonstrate that they are mixtures of the blue and red vesicles. PMID:18366237

  11. Consequences of partitioning the photon into its electrical and magnetic vectors upon absorption by an electron

    NASA Astrophysics Data System (ADS)

    Szumski, Daniel S.

    2013-10-01

    This research uses classical arguments to develop a blackbody spectral equation that provides useful insights into heat processes. The theory unites in a single equation, the heat radiation theory of Planck and the heat of molecular motion theory of Maxwell and Boltzmann. Light absorption is considered a two-step process. The first is an adiabatic reversible step, wherein one-dimensional light energy is absorbed in a quantum amount, ! h" , by an electron. The absorbed quanta is still 1-dimensional(1-D), and remains within the domain of reversible thermodynamics. There is no recourse to the Second Law during this first step. The absorption process' second step is a dimensional restructuring wherein the electrical and magnetic vectors evolve separately. The 1-D electrical quanta transforms into its 3-D equivalent, electrical charge density. The resulting displacement of the generalized coordinates translates to 3-D motion, the evolution of Joule heat, and irreversible thermodynamics. The magnetic vector has no 3-D equivalent, and can only transform to 1-D paramagnetic spin. Accordingly, photon decoupling distorts time's fabric, giving rise to the characteristic blackbody spectral emittance. This study's spectral equation introduces a new quantity to physics, the radiation temperature. Where it is identical to the classical thermodynamic temperature, the blackbody spectral curves are consistent with Planck's. However, by separating these two temperatures in a stable far-from-equilibrium manner, new energy storage modes become possible at the atomic level, something that could have profound implications in understanding matter's living state.

  12. Broadband Transient Absorption and Two-Dimensional Electronic Spectroscopy of Methylene Blue.

    PubMed

    Dean, Jacob C; Rafiq, Shahnawaz; Oblinsky, Daniel G; Cassette, Elsa; Jumper, Chanelle C; Scholes, Gregory D

    2015-08-27

    Broadband transient absorption and two-dimensional electronic spectroscopy (2DES) studies of methylene blue in aqueous solution are reported. By isolating the coherent oscillations of the nonlinear signal amplitude and Fourier transforming with respect to the population time, we analyzed a significant number of coherences in the frequency domain and compared them with predictions of the vibronic spectrum from density function theory (DFT) calculations. We show here that such a comparison enables reliable assignments of vibrational coherences to particular vibrational modes, with their constituent combination bands and overtones also being identified via Franck–Condon analysis aided by DFT. Evaluation of the Fourier transform (FT) spectrum of transient absorption recorded to picosecond population times, in coincidence with 2D oscillation maps that disperse the FT spectrum into the additional excitation axis, is shown to be a complementary approach toward detailed coherence determination. Using the Franck–Condon overlap integrals determined from DFT calculations, we modeled 2D oscillation maps up to two vibrational quanta in the ground and excited state (six-level model), showing agreement with experiment. This semiquantitative analysis is used to interpret the geometry change upon photoexcitation as an expansion of the central sulfur/nitrogen containing ring due to the increased antibonding character in the excited state. PMID:26274093

  13. Attosecond transient absorption probing of electronic superpositions of bound states in neon. Detection of quantum beats

    SciTech Connect

    Beck, Annelise R; Bernhardt, Birgitta; Warrick, Erika R.; Wu, Mengxi; Chen, Shaohao; Gaarde, Mette B.; Schafer, Kenneth J.; Neumark, Daniel M.; Leone, Stephen R.

    2014-11-07

    Electronic wavepackets composed of multiple bound excited states of atomic neon lying between 19.6 and 21.5 eV are launched using an isolated attosecond pulse. Individual quantum beats of the wavepacket are detected by perturbing the induced polarization of the medium with a time-delayed few-femtosecond near-infrared (NIR) pulse via coupling the individual states to multiple neighboring levels. All of the initially excited states are monitored simultaneously in the attosecond transient absorption spectrum, revealing Lorentzian to Fano lineshape spectral changes as well as quantum beats. The most prominent beating of the several that were observed was in the spin–orbit split 3d absorption features, which has a 40 femtosecond period that corresponds to the spin–orbit splitting of 0.1 eV. The few-level models and multilevel calculations confirm that the observed magnitude of oscillation depends strongly on the spectral bandwidth and tuning of the NIR pulse and on the location of possible coupling states.

  14. Change In The Electronic Structure And Optical Absorption Of Cuprate Delafossites Via B-site Alloying

    NASA Astrophysics Data System (ADS)

    Beesley, Ramon; Panapitiya, Gihan; Lewis, James; Lewis Group Team

    Delafossite oxides are a family of materials with the form ABO2 , where the A-site is a monovalent cation (Cu , Ag , Au) and the B-site is a trivalent cation (Ga , Al , In). Delafossites typically have a wide optical band gap, this band gap may be tuned by adding a second B-site element forming an AB(1- x) 1B(x)2O2 alloy. We investigate changes in the electronic structure of CuAlO2 , CuGaO2 , and CuInO2 when alloyed with CuFeO2 . Using the FIREBALL program to optimize the atomic structure, calculate the total and partial density of states, calculate the valence band edge for each alloy level, and investigate the clustering factor of the second B-site atom, it is found that alloying with Fe creates midgap states caused by Fe - O interactions. From the partial density of state, each type of atoms contribution to the change in the valence band edge can be seen. Observed changes to the materials include increased optical absorption in the visible range, and symmetry breaking because of the deformation in the crystal structure. The CuFeO2 alloying percentages range from 0-5%. We are synthesizing these alloys to experimentally verify the changes in the optical absorption spectra.

  15. Electron-cyclotron wave propagation, absorption and current drive in the presence of neoclassical tearing modes

    NASA Astrophysics Data System (ADS)

    Isliker, Heinz; Chatziantonaki, Ioanna; Tsironis, Christos; Vlahos, Loukas

    2012-09-01

    We analyze the propagation of electron-cyclotron waves, their absorption and current drive when neoclassical tearing modes (NTMs), in the form of magnetic islands, are present in a tokamak plasma. So far, the analysis of the wave propagation and power deposition in the presence of NTMs has been performed mainly in the frame of an axisymmetric magnetic field, ignoring any effects from the island topology. Our analysis starts from an axisymmetric magnetic equilibrium, which is perturbed such as to exhibit magnetic islands. In this geometry, we compute the wave evolution with a ray-tracing code, focusing on the effect of the island topology on the efficiency of the absorption and current drive. To increase the precision in the calculation of the power deposition, the standard analytical flux-surface labeling for the island region has been adjusted from the usual cylindrical to toroidal geometry. The propagation up to the O-point is found to be little affected by the island topology, whereas the power absorbed and the driven current are significantly enhanced, because the resonant particles are bound to the small volumes in between the flux surfaces of the island. The consequences of these effects on the NTM evolution are investigated in terms of the modified Rutherford equation.

  16. Electronic Structure and Absorption Properties of Strongly Coupled Porphyrin-Perylene Arrays.

    PubMed

    High, Judah S; Virgil, Kyle A; Jakubikova, Elena

    2015-09-24

    Porphyrin-perylene arrays are ideal candidates for light-harvesting systems capable of panchromatic absorption. In this work, we employ density functional theory (DFT) and time-dependent DFT to investigate the unique UV-vis absorption properties exhibited by a series of ethynyl-linked porphyrin-perylene arrays that were previously synthesized and characterized spectroscopically [Chem. Commun. 2014, 50, 14512-5]. We find that the ethynyl linker is responsible for strong electronic coupling of porphyrin and perylene subunits in these systems. Additionally, these arrays exhibit a low barrier to rotation around the ethynyl linker (<1.4 kcal/mol per one perylene substituent), which results in a wide range of molecular conformations characterized by different porphyrin-perylene dihedral angles being accessible at room temperature. The best match between the calculated and experimental UV-vis spectra is obtained by averaging the calculated UV-vis spectra over the range of conformations defined by the porphyrin-perylene dihedral angles. Finally, our calculations suggest that the transitions in the lower energy region (550-750 nm) can be assigned to the excitations originating from the porphyrin subunit; the mid-energy region transitions (450-550 nm) are assigned to the perylene-centered excitations, while the high-energy transitions (350-450 nm) involve contributions from both porphyrin and perylene subunits. PMID:26322743

  17. Electron cyclotron ray tracing and absorption predictions for Compact Toroidal Hybrid plasmas using TRAVIS

    NASA Astrophysics Data System (ADS)

    Knowlton, S. F.; Hartwell, G. J.; Maurer, D. A.; Marushchenko, N. B.; Turkin, Y.; Bigelow, T.

    2015-11-01

    Plasmas in the Compact Toroidal Hybrid (CTH), a five field period, l = 2 torsatron (B0 = 0 . 5 T R0 = 0 . 75 m, ap ~ 0 . 2 m) will be heated by second harmonic X-mode electron cyclotron heating with power provided by a 28 GHz gyrotron capable of producing up to 200 kW. Ray-tracing calculations that will guide the selection of the launching position, antenna focal length, and beam-steering characteristics are performed with the TRAVIS code. Non-axisymmetric vacuum and current-carrying CTH equilibria for the ray tracing are modeled with the V3FIT code. The calculated absorption is highest for vertically propagating rays that traverse the region where a saddle of resonant field strength exists. However, the absorption for top-launched waves is more sensitive to variations in the magnetic equilibria than for a radial side launch where the magnetic field profile is tokamak-like. This work is supported by U.S. Department of Energy Grant No. DE-FG02-00ER54610.

  18. Finite-element methods for spatially resolved mesoscopic electron transport

    NASA Astrophysics Data System (ADS)

    Kramer, Stephan

    2013-09-01

    A finite-element method is presented for calculating the quantum conductance of mesoscopic two-dimensional electron devices of complex geometry attached to semi-infinite leads. For computational purposes, the leads must be cut off at some finite length. To avoid spurious, unphysical reflections, this is modeled by transparent boundary conditions. We introduce the Hardy space infinite-element technique from acoustic scattering as a way of setting up transparent boundary conditions for transport computations spanning the range from the quantum mechanical to the quasiclassical regime. These boundary conditions are exact even for wave packets and thus are especially useful in the limit of high energies with many excited modes. Yet, they possess a memory-friendly sparse matrix representation. In addition to unbounded domains, Hardy space elements allow us to truncate those parts of the computational domain which are irrelevant for the calculation of the transport properties. Thus, the computation can be done only on the region that is essential for a physically meaningful simulation of the scattering states. The benefits of the method are demonstrated by three examples. The convergence properties are tested on the transport through a quasi-one-dimensional quantum wire. It is shown that higher-order finite elements considerably improve current conservation and establish the correct phase shift between the real and the imaginary parts of the electron wave function. The Aharonov-Bohm effect demonstrates that characteristic features of quantum interference can be assessed. A simulation of electron magnetic focusing exemplifies the capability of the computational framework to study the crossover from quantum to quasiclassical behavior.

  19. Electronic absorption spectroscopy of polycyclic aromatic hydrocarbons (PAHs) radical cations generated in oleum: A superacid medium

    NASA Astrophysics Data System (ADS)

    Cataldo, Franco; Iglesias-Groth, Susana; Manchado, Arturo

    2010-12-01

    Oleum (fuming sulphuric acid), a well known superacid, was used as medium for the generation of the radical cation of a series of selected PAHs. The resulting radical cation spectra were studied by electronic absorption spectroscopy. Not only common PAHs like naphthalene, anthracene, tetracene, pentacene, perylene, pyrene, benzo[ a]pyrene, phenanthrene and picene were studied but also the less common and very large PAHs relevant also for the astrochemical research, like coronene, hexabenzocoronene, quaterrylene, dicoronylene and a coronene oligomer. A correlation between the first ionization potential ( IP1) of the PAHs studied and the energy to the so-called A-type band of the radical cations observed in oleum has led to the equation IP1 = 1.30 EA + 4.39 (in eV) which permits to estimate the energy of the PAHs radical cation transition ( EA) in the VIS-NIR knowing the relative ionization potential or vice versa.

  20. The Electronic Absorption Spectrum of Molecular Iodine: A New Fitting Procedure for the Physical Chemistry Laboratory

    NASA Astrophysics Data System (ADS)

    Pursell, Christopher J.; Doezema, Lambert

    1999-06-01

    This paper presents a different approach to the data treatment for the electronic absorption spectrum of molecular iodine, a standard experiment in the undergraduate physical chemistry laboratory. Traditionally, students analyze the transitions originating from the u'' = 0 level using a Birge-Sponer plot and thereby determine the various molecular constants and energies. Our treatment involves simply fitting the transition frequencies to a second-order polynomial. This fit then yields a direct determination of the important molecular constants along with the various energy terms. With the availability of common graphing programs such as Excel, Kaleidagraph, and SigmaPlot, students can take advantage of more advanced fitting techniques and no longer have to rely on simple linear plots. Additionally, students find this new approach more satisfying and we believe it has pedagogical advantages over the Birge-Sponer treatment.

  1. Electronic absorption spectra of protonated pyrene and coronene in neon matrixes.

    PubMed

    Garkusha, Iryna; Fulara, Jan; Sarre, Peter J; Maier, John P

    2011-10-13

    Protonated pyrene and coronene have been isolated in 6 K neon matrixes. The cations were produced in the reaction of the parent aromatics with protonated ethanol in a hot-cathode discharge source, mass selected, and co-deposited with neon. Three electronic transitions of the most stable isomer of protonated pyrene and four of protonated coronene were recorded. The strongest, S(1) ← S(0) transitions, are in the visible region, with onset at 487.5 nm for protonated pyrene and 695.6 nm for protonated coronene. The corresponding neutrals were also observed. The absorptions were assigned on the basis of ab initio coupled-cluster and time-dependent density functional theory calculations. The astrophysical relevance of protonated polycyclic aromatic hydrocarbons is discussed. PMID:21861507

  2. Selective two-photon absorptive resonance femtosecond-laser electronic-excitation tagging velocimetry.

    PubMed

    Jiang, Naibo; Halls, Benjamin R; Stauffer, Hans U; Danehy, Paul M; Gord, James R; Roy, Sukesh

    2016-05-15

    Selective two-photon absorptive resonance femtosecond-laser electronic-excitation tagging (STARFLEET), a nonseeded ultrafast-laser-based velocimetry technique, is demonstrated in reactive and nonreactive flows. STARFLEET is pumped via a two-photon resonance in N2 using 202.25 nm 100 fs light. STARFLEET greatly reduces the per-pulse energy required (30 μJ/pulse) to generate the signature FLEET emission compared to the conventional FLEET technique (1.1 mJ/pulse). This reduction in laser energy results in less energy deposited in the flow, which allows for reduced flow perturbations (reactive and nonreactive), increased thermometric accuracy, and less severe damage to materials. Velocity measurements conducted in a free jet of N2 and in a premixed flame show good agreement with theoretical velocities, and further demonstrate the significantly less intrusive nature of STARFLEET. PMID:27176968

  3. Electronic Structure of Transition Metal-Cysteine Complexes From X-Ray Absorption Spectroscopy

    SciTech Connect

    Leung, B.O.; Jalilehvand, F.; Szilagyi, R.K.

    2009-05-19

    The electronic structures of Hg{sup II}, Ni{sup II}, Cr{sup III}, and Mo{sup V} complexes with cysteine were investigated by sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy and density functional theory. The covalency in the metal-sulfur bond was determined by analyzing the intensities of the electric-dipole allowed pre-edge features appearing in the XANES spectra below the ionization threshold. Because of the well-defined structures of the selected cysteine complexes, the current work provides a reference set for further sulfur K-edge XAS studies of bioinorganic active sites with transition metal-sulfur bonds from cysteine residues as well as more complex coordination compounds with thiolate ligands.

  4. Nanoscale transport of electrons and ions in water

    NASA Astrophysics Data System (ADS)

    Boynton, Paul Christopher

    The following dissertation discusses the theoretical study of water on the nanoscale, often involved with essential biological molecules such as DNA and proteins. First I introduce the study of water on the nanoscale and how experimentalists approach confinement with nanopores and nanogaps. Then I discuss the theoretical method we choose for understanding this important biological medium on the molecular level, namely classical molecular dynamics. This leads into transport mechanisms that utilize water on the nanoscale, in our case electronic and ionic transport. On the scale of mere nanometers or less electronic transport in water enters the tunneling regime, requiring the use of a quantum treatment. In addition, I discuss the importance of water in ionic transport and its known effects on biological phenomena such as ion selectivity. Water also has great influence over DNA and proteins, which are both introduced in the context of nanopore sequencing. Several techniques for nanopore sequencing are examined and the importance of protein sequencing is explained. In Chapter 2, we study the effect of volumetric constraints on the structure and electronic transport properties of distilled water in a nanopore with embedded electrodes. Combining classical molecular dynamics simulations with quantum scattering theory, we show that the structural motifs water assumes inside the pore can be probed directly by tunneling. In Chapter 3, we propose an improvement to the original sequencing by tunneling method, in which N pairs of electrodes are built in series along a synthetic nanochannel. Each current time series for each nucleobase is cross-correlated together, reducing noise in the signals. We show using random sampling of data from classical molecular dynamics, that indeed the sequencing error is significantly reduced as the number of pairs of electrodes, N, increases. In Chapter 4, we propose a new technique for de novo protein sequencing that involves translocating a

  5. Inverted organic photovoltaic device with a new electron transport layer

    PubMed Central

    2014-01-01

    We demonstrate that there is a new solution-processed electron transport layer, lithium-doped zinc oxide (LZO), with high-performance inverted organic photovoltaic device. The device exhibits a fill factor of 68.58%, an open circuit voltage of 0.86 V, a short-circuit current density of −9.35 cm/mA2 along with 5.49% power conversion efficiency. In addition, we studied the performance of blend ratio dependence on inverted organic photovoltaics. Our device also demonstrates a long stability shelf life over 4 weeks in air. PMID:24674457

  6. Thermal and Electronic Transport in Inorganic and Organic Thermoelectric Materials

    NASA Astrophysics Data System (ADS)

    Tian, Zhiting

    In this talk, we will first talk about first-principles calculations of phonon and electron transport in inorganic thermoelectric materials. We will start with rocksalt PbTe and PbSe, and move on to wurtzite ZnO. We will emphasize the strategies to reduce the lattice thermal conductivity. Then we apply first-principles calculations to organic thermoelectric materials. The thermoelectric properties of doped polypyrrole (PPy) will be discussed. In addition, we will cover the chain confinement effects observed in amorphous polymer thin films using molecular dynamics simulations, which highlights the fundamental difference in heat conduction between crystalline polymers and amorphous polymers

  7. Electron transport in argon in crossed electric and magnetic fields

    PubMed

    Ness; Makabe

    2000-09-01

    An investigation of electron transport in argon in the presence of crossed electric and magnetic fields is carried out over a wide range of values of electric and magnetic field strengths. Values of mean energy, ionization rate, drift velocity, and diffusion tensor are reported here. Two unexpected phenomena arise; for certain values of electric and magnetic field we find regions where the swarm mean energy decreases with increasing electric fields for a fixed magnetic field and regions where swarm mean energy increases with increasing magnetic field for a fixed electric field. PMID:11088933

  8. Nonlinear Electron Transport Effects in a Chiral Carbon Nanotube

    SciTech Connect

    Yevtushenko, O.M.; Slepyan, G.Y.; Maksimenko, S.A.; Lakhtakia, A.; Romanov, D.A.

    1997-08-01

    We present a novel, general, semiclassical theory of electron transport in a carbon nanotube exposed to an external electric field. The charge carriers are treated in the framework of the simplified tight-binding model. Simultaneous exposure to rapidly oscillating (ac) and constant (dc) electric fields is considered to exemplify our theory. Nonlinear and chiral effects are found, and their interaction is delineated. We predict the effect of an ac electric field on the magnitude and the direction of the total time-averaged current. {copyright} {ital 1997} {ital The American Physical Society}

  9. Study of electronic transport properties of doped 8AGNR

    SciTech Connect

    Sharma, Uma Shankar; Srivastava, Anurag; Verma, U. P.

    2014-04-24

    The electronic and transport properties of 8-armchair graphene nanoribbon (8AGNR) with defect at different sites are investigated by performing first-principles calculations based on density functional theory (DFT). The calculated results show that the 8AGNR are semiconductor. The introduction of 3d transition metals, creates the nondegenerate states in the conduction band, makes 8AGNR metallic. The computed transmission spectrum confirms that AGNR are semiconducting in nature and their band gap remain unchanged and localized states appear when there is vacancy in their structures, and the conductance decreases due to defects compared with the pristine nanoribbon.

  10. Electronic Transport of a Molecular Photoswitch with Graphene Nanoribbon Electrodes

    NASA Astrophysics Data System (ADS)

    Wu, Qiu-Hua; Zhao, Peng; Liu, De-Sheng

    2014-05-01

    Based on non-equilibrium Green's function formalism and density functional theory calculations, we investigate the electronic transport properties of 15,16-dinitrile dihydropyrene/cyclophanediene bridged between two zigzag graphene nanoribbon electrodes. Our results demonstrate that the system can exhibit good switching behavior with the maximum on-off ratio high up to 146 which is improved dramatically compared with the case of gold electrodes. Moreover, an obvious negative differential resistance behavior occurs at 0.3 V, making the system have more potential in near future molecular circuits.

  11. Studies of fullerene absorption and production using an infrared free-electron laser

    SciTech Connect

    Affatigato, M.; Haglund, R.F.; Ying, Z.C.; Compton, R.N.

    1995-12-31

    Tunable photon sources such as free-electron lasers are potentially valuable tools in spectroscopic studies of fullerenes, a new class of carbon materials with unique cage structures. We have used the infrared free-electron-laser facility at Vanderbilt University to study the infrared absorption of gas-phase fullerene molecules and also to investigate the effects of an infrared laser in the synthesis and crystallization of fullerene materials. In one experiment, fullerene vapor was created in a heat pipe through which the FEL beam was passed; the transmission of the FEL beam relative to a reference detector was measured as a function of wavelength. A large (>10%) absorption of the IR laser was observed when it passed through C{sub 60} vapor at {approximately}800{degrees}C. Due to the broad spectral width of the FEL as well as spectral congestion, no spectral peaks were seen when the laser wavelength was tuned across a T{sub 1u}C{sub 60} IR mode near 7.0 {mu}. However, it is expected that the vibrational features can be resolved experimentally by passing the transmitted beam through a monochromator. In a separate experiment, the FEL beam was focused onto a surface of graphite or graphite/metal mixture target. Various fullerene molecules, including endohedral types, were produced when the soot was recovered from the ablation chamber. The yield of the products was measured to be {approximately}0.4 g/J of the incident laser energy. However, both the yield and the product distribution are virtually, the same as those in experiments using a nanosecond Nd:YAG laser. This suggests that the laser wavelength is not a crucial parameter in making fullerenes by laser ablation. Even when the laser is at resonance with one of the vibrational modes of C{sub 60}, the fullerene production is neither substantially enhanced nor suppressed.

  12. Shallow electron traps in alkali halide crystals: Mollwo-Ivey relations of the optical absorption bands

    NASA Astrophysics Data System (ADS)

    Ziraps, Valters

    2001-03-01

    Evidences are given that two classes of the transient IR- absorption bands: (a) with max. at 0.27-0.36 eV in NaCl, KCl, KBr, KI and RbCl (due to shallow electron traps according G. Jacobs or due to bound polarons according E.V. Korovkin and T.A. Lebedkina) and (b) with max. at 0.15-0.36 eV in NaI, NaBr, NaCl:I, KCl:I, RbCl:I and RbBr:I (due to on-center STE localized at iodine dimer according M. Hirai and collaborators) are caused by the same defect- atomic alkali impurity center [M+]c0e- (electron e- trapped by a substitutional smaller size alkali cation impurity [M+]c0). The Mollwo-Ivey plots (for the transient IR-absorption bands) of the zero-phonon line energy E0 (for NaCl, KCl, KBr, RbCl and NaBr, KCl:I) and/or the low-energy edge valued E0 (for NaI, RbCl:I, RbBr:I) versus anion-cation distance (d) evidence that two types of the [M+]c0e- centers are predominant: (a) [Na+]c0e- in the KX and RbX host crystals with the relation E0approximately equals 6.15/d2.74, (b) [Li+]c03- in the NaX host crystals - E0approximately equals 29.4/d4.72. The Mollwo-Ivey relation E0approximately equals 18.36/d(superscript 2.70 is fulfilled as well for the F' band in NaCl, KCl, KBr, KI, RbCl, RbI if we use the F' center optical binding energy values E0.

  13. Active intestinal absorption of fluoroquinolone antibacterial agent ciprofloxacin by organic anion transporting polypeptide, Oatp1a5.

    PubMed

    Arakawa, Hiroshi; Shirasaka, Yoshiyuki; Haga, Makoto; Nakanishi, Takeo; Tamai, Ikumi

    2012-09-01

    Fluoroquinolone antimicrobial drugs are absorbed efficiently after oral administration despite of their hydrophilic nature, implying an involvement of carrier-mediated transport in their membrane transport process. It has been that several fluoroquinolones are substrates of organic anion transporter polypeptides OATP1A2 expressed in human intestine derived Caco-2 cells. In the present study, to clarify the involvement of OATP in intestinal absorption of ciprofloxacin, the contribution of Oatp1a5, which is expressed at the apical membranes of rat enterocytes, to intestinal absorption of ciprofloxacin was investigated in rats. The intestinal membrane permeability of ciprofloxacin was measured by in situ and the vascular perfused closed loop methods. The disappeared and absorbed amount of ciprofloxacin from the intestinal lumen were increased markedly in the presence of 7,8-benzoflavone, a breast cancer resistance protein inhibitor, and ivermectin, a P-glycoprotein inhibitor, while it was decreased significantly in the presence of these inhibitors in combination with naringin, an Oatp1a5 inhibitor. Furthermore, the Oatp1a5-mediated uptake of ciprofloxacin was saturable with a K(m) value of 140 µm, and naringin inhibited the uptake with an IC(50) value of 18 µm by Xenopus oocytes expressing Oatp1a5. Naringin reduced the permeation of ciprofloxacin from the mucosal-to-serosal side, with an IC(50) value of 7.5 µm by the Ussing-type chamber method. The estimated IC(50) values were comparable to that of Oatp1a5. These data suggest that Oatp1a5 is partially responsible for the intestinal absorption of ciprofloxacin. In conclusion, the intestinal absorption of ciprofloxacin could be affected by influx transporters such as Oatp1a5 as well as the efflux transporters such as P-gp and Bcrp. PMID:22899169

  14. Electronic transport in B-N substituted bilayer graphene nanojunctions

    NASA Astrophysics Data System (ADS)

    Giofré, Daniele; Ceresoli, Davide; Fratesi, Guido; Trioni, Mario I.

    2016-05-01

    We investigated a suspended bilayer graphene where the bottom/top layer is doped by boron/nitrogen substitutional atoms. By using density functional theory calculations, we found that at high dopant concentration (one B-N pair every 32 C atoms), the electronic structure of the bilayer does not depend on the B-N distance but on the relative occupation of the bilayer graphene sublattices by B and N. The presence of the dopants and the consequent charge transfer establish a built-in electric field between the layers, giving rise to an energy gap. We further investigated the electronic transport properties and found that intralayer current is weakly influenced by the presence of these dopants while the interlayer one is enhanced for biases, allowing an easy tunneling between layers. This effect leads to current rectification in asymmetric junctions.

  15. Orthogonally modulated molecular transport junctions for resettable electronic logic gates

    PubMed Central

    Meng, Fanben; Hervault, Yves-Marie; Shao, Qi; Hu, Benhui; Norel, Lucie; Rigaut, Stéphane; Chen, Xiaodong

    2014-01-01

    Individual molecules have been demonstrated to exhibit promising applications as functional components in the fabrication of computing nanocircuits. Based on their advantage in chemical tailorability, many molecular devices with advanced electronic functions have been developed, which can be further modulated by the introduction of external stimuli. Here, orthogonally modulated molecular transport junctions are achieved via chemically fabricated nanogaps functionalized with dithienylethene units bearing organometallic ruthenium fragments. The addressable and stepwise control of molecular isomerization can be repeatedly and reversibly completed with a judicious use of the orthogonal optical and electrochemical stimuli to reach the controllable switching of conductivity between two distinct states. These photo-/electro-cooperative nanodevices can be applied as resettable electronic logic gates for Boolean computing, such as a two-input OR and a three-input AND-OR. The proof-of-concept of such logic gates demonstrates the possibility to develop multifunctional molecular devices by rational chemical design. PMID:24394717

  16. Time dependent electronic transport in chiral edge channels

    NASA Astrophysics Data System (ADS)

    Fève, G.; Berroir, J.-M.; Plaçais, B.

    2016-02-01

    We study time dependent electronic transport along the chiral edge channels of the quantum Hall regime, focusing on the role of Coulomb interaction. In the low frequency regime, the a.c. conductance can be derived from a lumped element description of the circuit. At higher frequencies, the propagation equations of the Coulomb coupled edge channels need to be solved. As a consequence of the interchannel coupling, a charge pulse emitted in a given channel fractionalized in several pulses. In particular, Coulomb interaction between channels leads to the fractionalization of a charge pulse emitted in a given channel in several pulses. We finally study how the Coulomb interaction, and in particular the fractionalization process, affects the propagation of a single electron in the circuit. All the above-mentioned topics are illustrated by experimental realizations.

  17. Scanning Tunneling Electron Transport into a Kondo Lattice

    NASA Astrophysics Data System (ADS)

    Yang, Fu-Bin; Wu, Hua

    2016-05-01

    We theoretically present the results for a scanning tunneling transport between a metallic tip and a Kondo lattice. We calculate the density of states (DOS) and the tunneling current and differential conductance (DC) under different conduction-fermion band hybridization and temperature in the Kondo lattice. It is found that the hybridization strength and temperature give asymmetric coherent peaks in the DOS separated by the Fermi energy. The corresponding current and DC intensity depend on the temperature and quantum interference effect among the c-electron and f-electron states in the Kondo lattice. Supported by the National Natural Science Foundation of China under Grant No. 11547203, and the Research Project of Education Department in Sichuan Province of China under Grant No. 15ZB0457

  18. Behaviour of fast electron transport in solid targets

    NASA Astrophysics Data System (ADS)

    Koenig, M.; Baton, S. D.; Benuzzi-Mounaix, A.; Fuchs, J.; Loupias, B.; Guillou, P.; Batani, D.; Morace, A.; Piazza, D.; Kodama, R.; Norimatsu, T.; Nakatsutsumi, M.; Aglitskiy, Y.; Rousseaux, C.

    2006-06-01

    One of the main issues of the fast ignitor scheme is the role of fast electron transport in the solid fuel heating. Recent experiments used a new target scheme based on the use of cone to guide the PW laser and enhance the electron production. In this context it is fundamental to understand the physics underlying this new target scheme. We report here recent and preliminary results of ultra-intense laser pulse interaction with three layer targets in presence of the cone or without. Experiments have been performed at LULI with the 100 TW laser facility, at intensities up to 3 1019 W/cm2. Several diagnostics have been implemented (2D Kα imaging, Kα spectroscopy and rear side imaging, protons emission) to quantify the cone effect.

  19. Reprint of : Time dependent electronic transport in chiral edge channels

    NASA Astrophysics Data System (ADS)

    Fève, G.; Berroir, J.-M.; Plaçais, B.

    2016-08-01

    We study time dependent electronic transport along the chiral edge channels of the quantum Hall regime, focusing on the role of Coulomb interaction. In the low frequency regime, the a.c. conductance can be derived from a lumped element description of the circuit. At higher frequencies, the propagation equations of the Coulomb coupled edge channels need to be solved. As a consequence of the interchannel coupling, a charge pulse emitted in a given channel fractionalized in several pulses. In particular, Coulomb interaction between channels leads to the fractionalization of a charge pulse emitted in a given channel in several pulses. We finally study how the Coulomb interaction, and in particular the fractionalization process, affects the propagation of a single electron in the circuit. All the above-mentioned topics are illustrated by experimental realizations.

  20. Orthogonally modulated molecular transport junctions for resettable electronic logic gates

    NASA Astrophysics Data System (ADS)

    Meng, Fanben; Hervault, Yves-Marie; Shao, Qi; Hu, Benhui; Norel, Lucie; Rigaut, Stéphane; Chen, Xiaodong

    2014-01-01

    Individual molecules have been demonstrated to exhibit promising applications as functional components in the fabrication of computing nanocircuits. Based on their advantage in chemical tailorability, many molecular devices with advanced electronic functions have been developed, which can be further modulated by the introduction of external stimuli. Here, orthogonally modulated molecular transport junctions are achieved via chemically fabricated nanogaps functionalized with dithienylethene units bearing organometallic ruthenium fragments. The addressable and stepwise control of molecular isomerization can be repeatedly and reversibly completed with a judicious use of the orthogonal optical and electrochemical stimuli to reach the controllable switching of conductivity between two distinct states. These photo-/electro-cooperative nanodevices can be applied as resettable electronic logic gates for Boolean computing, such as a two-input OR and a three-input AND-OR. The proof-of-concept of such logic gates demonstrates the possibility to develop multifunctional molecular devices by rational chemical design.

  1. Analytical band Monte Carlo analysis of electron transport in silicene

    NASA Astrophysics Data System (ADS)

    Yeoh, K. H.; Ong, D. S.; Ooi, C. H. Raymond; Yong, T. K.; Lim, S. K.

    2016-06-01

    An analytical band Monte Carlo (AMC) with linear energy band dispersion has been developed to study the electron transport in suspended silicene and silicene on aluminium oxide (Al2O3) substrate. We have calibrated our model against the full band Monte Carlo (FMC) results by matching the velocity-field curve. Using this model, we discover that the collective effects of charge impurity scattering and surface optical phonon scattering can degrade the electron mobility down to about 400 cm2 V‑1 s‑1 and thereafter it is less sensitive to the changes of charge impurity in the substrate and surface optical phonon. We also found that further reduction of mobility to ∼100 cm2 V‑1 s‑1 as experimentally demonstrated by Tao et al (2015 Nat. Nanotechnol. 10 227) can only be explained by the renormalization of Fermi velocity due to interaction with Al2O3 substrate.

  2. Microarray Determination of the Expression of Drug Transporters in Humans and Animal Species Used for the Investigation of Nasal Absorption

    PubMed Central

    Al-Ghabeish, Manar; Scheetz, Todd; Assem, Mahfoud; Donovan, Maureen D.

    2015-01-01

    Purpose Mice and rats are commonly used to investigate in vivo nasal drug absorption, yet their small nasal cavities limit their use for in vitro investigations. Bovine tissue explants have been used to investigate drug transport through the nasal respiratory and olfactory mucosae, yet limited information is available regarding the similarities and differences among these animal models compared to humans. The aim of this study was to compare the presence of a number of important drug transporters in the nasal mucosa of these species. Methods DNA microarray results for nasal samples from humans, rats and mice were obtained from GenBank, while DNA microarray and RT-PCR were performed on bovine nasal explants. The drug transporters of interest include multidrug resistance, cation, anion, peptide, and nucleoside transporters. Results Each of the species (mouse, rat, cow and human) shows similar patterns of expression for most of the important drug transporters. Several transporters were highly expressed in all the species, including MRP1, OCTN2, PEPT2 and y+LAT2. Conclusion While some differences in transporter mRNA and protein expression were observed, the transporter expression patterns were quite similar among the species. The differences suggest that it is important to be aware of any specific differences in transporter expression for a given compound being investigated, yet the similarities support the continued use of these animal models during preclinical investigation of intranasally administered therapeutics. PMID:26106909

  3. Microarray Determination of the Expression of Drug Transporters in Humans and Animal Species Used for the Investigation of Nasal Absorption.

    PubMed

    Al-Ghabeish, Manar; Scheetz, Todd; Assem, Mahfoud; Donovan, Maureen D

    2015-08-01

    Mice and rats are commonly used to investigate in vivo nasal drug absorption, yet their small nasal cavities limit their use for in vitro investigations. Bovine tissue explants have been used to investigate drug transport through the nasal respiratory and olfactory mucosae, yet limited information is available regarding the similarities and differences among these animal models compared to humans. The aim of this study was to compare the presence of a number of important drug transporters in the nasal mucosa of these species. DNA microarray results for nasal samples from humans, rats, and mice were obtained from GenBank, while DNA microarray and RT-PCR were performed on bovine nasal explants. The drug transporters of interest include multidrug resistance, cation, anion, peptide, and nucleoside transporters. Each of the species (mouse, rat, cattle, and human) shows similar patterns of expression for most of the important drug transporters. Several transporters were highly expressed in all the species, including MRP1, OCTN2, PEPT2, and y+LAT2. While some differences in transporter mRNA and protein expression were observed, the transporter expression patterns were quite similar among the species. The differences suggest that it is important to be aware of any specific differences in transporter expression for a given compound being investigated, yet the similarities support the continued use of these animal models during preclinical investigation of intranasally administered therapeutics. PMID:26106909

  4. Refractory metals in molten salts: Theory and simulation of geometry, electronic structure, and electron transport

    NASA Astrophysics Data System (ADS)

    Koslowski, Thorsten

    2000-12-01

    In this work, we present a theoretical and numerical study of the microscopic and electronic structure of solutions of refractory metal halides in alkali halide melts, [NbCl5]x[KCl]1-x and [TaCl5]x[KCl]1-x with 0⩽x⩽0.5. The geometry of the melts is described by ensembles of charged hard spheres, the electronic structure is modeled by a tight-binding Hamiltonian, which is extended by a reaction field to describe the diabatic energy profile of the electronic self-exchange in many-orbital mixed-valence systems. Despite its simplicity, the model leads to the formation of distorted octahedral [NbCl6]- and [TaCl6]- clusters, as evident both from the inspection of the simulation geometries and from the analysis of the partial pair distribution functions. Even in the presence of the strong potential energy fluctuations characteristic of ionic liquids, the octahedral structure is manifest in the density of states in a t2g-eg splitting of the conduction band. The Hamiltonian that describes mixed-valence systems is solved self-consistently. Using an attractive Hubbard parameter of 1.5 eV, we show that the numerical results can be interpreted by Marcus' theory of outer-sphere electron transfer reactions with a reorganization energy of 2.2 eV, an electronic coupling parameter of 0.12 eV, and an activation energy of 0.42 eV. Both anion-d metal cation and intervalence charge transfer excitations contribute to the optical absorption spectrum, the latter leads to a pronounced polaron absorption peak. These findings are compared to recent experimental results.

  5. Electron transport estimated from electron spectra using electron spectrometer in LFEX laser target experiments

    NASA Astrophysics Data System (ADS)

    Ozaki, T.; Hata, M.; Matsuo, K.; Kojima, S.; Arikawa, Y.; Fujioka, S.; Sakagami, H.; Sunahara, A.; Nagatomo, H.; Johzaki, T.; Yogo, A.; Morace, A.; Zhang, Z.; Shiraga, H.; Sakata, S.; Nagai, T.; Abe, Y.; Lee, S.; Nakai, M.; Nishimura, H.; Azechi, H.; FIREX group; GXII-LFEX group

    2016-05-01

    Hot electrons which are generated from targets irradiated by a high-intense laser are measured by two electron spectrometers (ESMs). However, total electron energy observed by the ESM is only less than 1%. Hot electrons are confined by self-fields due to the huge current. When an external magnetic field of several hundred Tesla is applied during the laser irradiation on targets, the ESM signals always increase. In the simulation, the same result can be obtained. The reason is that the Alfvén limit can be mitigated due to the external longitudinal magnetic field.

  6. Interfacial Charge Transport in Organic Electronic Materials: the Key to a New Electronics Technology

    SciTech Connect

    Smith, D.L.; Campbell, I.H.; Davids, P.S.; Heller, C.M.; Laurich, B.K.; Crone, B.K.; Saxena, A.; Bishop, A.R.; Ferraris, J.P.; Yu, Z.G.

    1999-06-04

    This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The primary aim of this project is to obtain a basic scientific understanding of electrical transport processes at interfaces that contain an organic electronic material. Because of their processing advantages and the tunability of their electronic properties, organic electronic materials are revolutionizing major technological areas such as information display. We completed an investigation of the fundamental electronic excitation energies in the prototype conjugated polymer MEH-PPV. We completed a combined theoretical/experimental study of the energy relation between charged excitations in a conjugated polymer and the metal at a polymer/metal interface. We developed a theoretical model that explains injection currents at polymer/metal interfaces. We have made electrical measurements on devices fabricated using the conjugated polymer MEH-PPV a nd a series of metals.

  7. Electron Temperature Measurements and Energy Transport in SSPX

    NASA Astrophysics Data System (ADS)

    Hudson, B. F.; Casper, T. A.; Hooper, E. B.; Jayakumar, R. J.; Lodestro, L. L.; McLean, H. S.; Moller, J. M.; Romero-Talamas, C. A.; Wood, R. D.

    2007-11-01

    Time-resolved measurements (<100 μs) have been made with a multi-pulse Thomson scattering diagnostic in the SSPX spheromak experiment, to obtain radial electron density and temperature profile during plasma formation and sustainment. In most discharges three regimes are observed with respect to Te and ne evolution. Initially there is a cold (<100 eV) formation phase, followed by a hollow Te profile with maximum temperatures 100-200 eV, and a final heat-up and cool-down phase where we obtain the highest plasma temperatures (350+ eV). The transition from hollow to peaked Te is quite sharp (˜50 μs) and the recent upgrade to double-pulse Thomson scattering (˜40 μs between pulses) facilitates capturing this transition. We also present simulations using the CORSICA code where the equilibrium is kept fixed and the discharge is evolved to observe the change in temperature profiles for different transport coefficients. In addition, electron transport and heating will be correlated with measured MHD mode activity. Temperature and density measurements during multi-pulse coaxial gun-current operation will also be presented. * Work performed under the auspices of the US DOE by University of California Lawrence Livermore National Laboratory under contract W--7405--ENG--48.

  8. Role of fluctuations on electron transport in soft materials

    NASA Astrophysics Data System (ADS)

    Gomez, Enrique

    2014-03-01

    Soft materials are characterized by weak intermolecular interactions and disorder. Although the extent of spatial fluctuations depends on the molecular structure, lattice fluctuations can be on the order of the unit cell dimensions in molecular crystals and soft materials. For example, our results from Quasi-elastic Neutron Scattering demonstrates that longer side chains in poly(3-alkylthiophene)s leads to an enhancement in motion of the thiophene rings. To ascertain the effect of dynamics on charge transport, we have developed a simple model to describe the roles of longitudinal and transverse modes of the intermolecular spacing between molecules on intrinsic electron mobilities. We demonstrate that the intrinsic mobility of soft materials appears thermally-activated by assuming fluctuations in a harmonic potential and an exponential decay in the charge transfer rate with intermolecular distance. For example, for poly(3-hexylthiophene), we can extract the characteristic decay as a function of separation distance from Density Functional Theory calculations and the extent of fluctuations from Molecular Dynamics simulations to predict the temperature dependence of the charge mobility. We find that the temperature dependence appears Arrhenius with activation energy of approximately 50 meV for a wide temperature range, in good agreement with experiments. This model suggests that fluctuations in the lattice spacing of soft materials lead to a significant intrinsic dependence of electron transport on temperature, regardless of the presence of band-tail states or traps.

  9. Electron transport in coupled double quantum wells and wires

    SciTech Connect

    Harff, N.E.; Simmons, J.A.; Lyo, S.K.

    1997-04-01

    Due to inter-quantum well tunneling, coupled double quantum wells (DQWs) contain an extra degree of electronic freedom in the growth direction, giving rise to new transport phenomena not found in single electron layers. This report describes work done on coupled DQWs subject to inplane magnetic fields B{sub {parallel}}, and is based on the lead author`s doctoral thesis, successfully defended at Oregon State University on March 4, 1997. First, the conductance of closely coupled DQWs in B{sub {parallel}} is studied. B{sub {parallel}}-induced distortions in the dispersion, the density of states, and the Fermi surface are described both theoretically and experimentally, with particular attention paid to the dispersion anticrossing and resulting partial energy gap. Measurements of giant distortions in the effective mass are found to agree with theoretical calculations. Second, the Landau level spectra of coupled DQWs in tilted magnetic fields is studied. The magnetoresistance oscillations show complex beating as Landau levels from the two Fermi surface components cross the Fermi level. A third set of oscillations resulting from magnetic breakdown is observed. A semiclassical calculation of the Landau level spectra is then performed, and shown to agree exceptionally well with the data. Finally, quantum wires and quantum point contacts formed in DQW structures are investigated. Anticrossings of the one-dimensional DQW dispersion curves are predicted to have interesting transport effects in these devices. Difficulties in sample fabrication have to date prevented experimental verification. However, recently developed techniques to overcome these difficulties are described.

  10. Simulations of Electron Transport in Laser Hot Spots

    SciTech Connect

    S. Brunner; E. Valeo

    2001-08-30

    Simulations of electron transport are carried out by solving the Fokker-Planck equation in the diffusive approximation. The system of a single laser hot spot, with open boundary conditions, is systematically studied by performing a scan over a wide range of the two relevant parameters: (1) Ratio of the stopping length over the width of the hot spot. (2) Relative importance of the heating through inverse Bremsstrahlung compared to the thermalization through self-collisions. As for uniform illumination [J.P. Matte et al., Plasma Phys. Controlled Fusion 30 (1988) 1665], the bulk of the velocity distribution functions (VDFs) present a super-Gaussian dependence. However, as a result of spatial transport, the tails are observed to be well represented by a Maxwellian. A similar dependence of the distributions is also found for multiple hot spot systems. For its relevance with respect to stimulated Raman scattering, the linear Landau damping of the electron plasma wave is estimated for such VD Fs. Finally, the nonlinear Fokker-Planck simulations of the single laser hot spot system are also compared to the results obtained with the linear non-local hydrodynamic approach [A.V. Brantov et al., Phys. Plasmas 5 (1998) 2742], thus providing a quantitative limit to the latter method: The hydrodynamic approach presents more than 10% inaccuracy in the presence of temperature variations of the order delta T/T greater than or equal to 1%, and similar levels of deformation of the Gaussian shape of the Maxwellian background.

  11. Electron Transport Materials: Synthesis, Properties and Device Performance

    SciTech Connect

    Cosimbescu, Lelia; Wang, Liang; Helm, Monte L.; Polikarpov, Evgueni; Swensen, James S.; Padmaperuma, Asanga B.

    2012-06-01

    We report the design, synthesis and characterization, thermal and photophysical properties of two silane based electron transport materials, dibenzo[b,d]thiophen-2-yltriphenylsilane (Si{phi}87) and (dibenzo[b,d]thiophen-2-yl)diphenylsilane (Si{phi}88) and their performance in blue organic light emitting devices (OLEDs). The utility of these materials in blue OLEDs with iridium (III) bis[(4,6-difluorophenyl)-pyridinato-N,C']picolinate (Firpic) as the phosphorescent emitter was demonstrated. Using the silane Si{phi}87 as the electron transport material (ETm) an EQE of 18.2% was obtained, with a power efficiency of 24.3 lm/W (5.8V at 1mA/cm{sup 2}), in a heterostructure. When Si{phi}88 is used, the EQE is 18.5% with a power efficiency of 26.0 lm/W (5.5V at 1mA/cm{sup 2}).

  12. Effect of Noise on DNA Sequencing via Transverse Electronic Transport

    PubMed Central

    Krems, Matt; Zwolak, Michael; Pershin, Yuriy V.; Di Ventra, Massimiliano

    2009-01-01

    Abstract Previous theoretical studies have shown that measuring the transverse current across DNA strands while they translocate through a nanopore or channel may provide a statistically distinguishable signature of the DNA bases, and may thus allow for rapid DNA sequencing. However, fluctuations of the environment, such as ionic and DNA motion, introduce important scattering processes that may affect the viability of this approach to sequencing. To understand this issue, we have analyzed a simple model that captures the role of this complex environment in electronic dephasing and its ability to remove charge carriers from current-carrying states. We find that these effects do not strongly influence the current distributions due to the off-resonant nature of tunneling through the nucleotides—a result we expect to be a common feature of transport in molecular junctions. In particular, only large scattering strengths, as compared to the energetic gap between the molecular states and the Fermi level, significantly alter the form of the current distributions. Since this gap itself is quite large, the current distributions remain protected from this type of noise, further supporting the possibility of using transverse electronic transport measurements for DNA sequencing. PMID:19804730

  13. Computing Rydberg Electron Transport Rates via Classical Periodic Orbits

    NASA Astrophysics Data System (ADS)

    Sattari, Sulimon; Mitchell, Kevin

    2016-05-01

    Electron transport properties of chaotic atomic systems may be computable from classical periodic orbits. This technique allows for replacing a Monte Carlo simulation launching millions of orbits with a sum over tens or hundreds of properly chosen periodic orbits. A firm grasp of the structure of the periodic orbits is required to obtain accurate transport rates. We apply a technique called homotopic lobe dynamics (HLD) to understand the structure of periodic orbits to compute the ionization rate of a hydrogen atom in strong parallel electric and magnetic fields. HLD uses information encoded in the intersections of stable and unstable manifolds of a few orbits to compute all relevant periodic orbits in the system. The ionization rate computed from periodic orbits using HLD converges exponentially to the true value as a function of the highest period used. We then use periodic orbit continuation to accurately compute the ionization rate when the field strengths are varied. The ability to use periodic orbits in a mixed phase space could allow for studying transport in even more complex few body systems.

  14. Real-space method for highly parallelizable electronic transport calculations

    NASA Astrophysics Data System (ADS)

    Feldman, Baruch; Seideman, Tamar; Hod, Oded; Kronik, Leeor

    2014-07-01

    We present a real-space method for first-principles nanoscale electronic transport calculations. We use the nonequilibrium Green's function method with density functional theory and implement absorbing boundary conditions (ABCs, also known as complex absorbing potentials, or CAPs) to represent the effects of the semi-infinite leads. In real space, the Kohn-Sham Hamiltonian matrix is highly sparse. As a result, the transport problem parallelizes naturally and can scale favorably with system size, enabling the computation of conductance in relatively large molecular junction models. Our use of ABCs circumvents the demanding task of explicitly calculating the leads' self-energies from surface Green's functions, and is expected to be more accurate than the use of the jellium approximation. In addition, we take advantage of the sparsity in real space to solve efficiently for the Green's function over the entire energy range relevant to low-bias transport. We illustrate the advantages of our method with calculations on several challenging test systems and find good agreement with reference calculation results.

  15. Stoichiometry-Control of Electronic Transport at Complex Oxide Interface

    NASA Astrophysics Data System (ADS)

    Xu, Peng; Jalan, Bharat

    2014-03-01

    Employing the hybrid molecular beam epitaxy approach to grow NdTiO3/SrTiO3 heterostructures - a polar/nonpolar system sharing many similarities with LaAlO3/SrTiO3 with an added functionality of NdTiO3 being an antiferromagnetic Mott insulator- we will present a detailed film growth and transport study as a function of cation stoichiometry in NdTiO3. Irrespective of the cation stoichiometry (measured by high resolution x-ray diffraction and x-ray photoelectron spectroscopy), films grew in an atomic layer-by-layer fashion as evidenced by the reflection high-energy electron diffraction intensity oscillations, and films showed a temperature dependent metal-to-insulator (M-I) type behavior. Remarkably, TMI was found to increase irrespective of whether films were Nd- or Ti-rich. Furthermore, hall measurement of a 3.5 nm NdTiO3 film grown on 3 nm SrTiO3 layer on LSAT substrate revealed n type carrier density, 3 x 1014 cm-2 for stoichiometric samples, which would be consistent with the interface conduction due to an interfacial polar discontinuity effect. Using detailed temperature dependent magneto-transport measurements, we will present a comprehensive study of correlation between film stoichiometry, interface conduction, and transport mechanisms.

  16. Impact of Absorption and Transport on Intelligent Therapeutics and Nano-scale Delivery of Protein Therapeutic Agents

    PubMed Central

    Peppas, Nicholas A.; Carr, Daniel A

    2009-01-01

    The combination of materials design and advances in nanotechnology has led to the development of new therapeutic protein delivery systems. The pulmonary, nasal, buccal and other routes have been investigated as delivery options for protein therapy, but none result in improved patient compliances and patient quality of life as the oral route. For the oral administration of these new systems, an understanding of protein transport is essential because of the dynamic nature of the gastrointestinal tract and the barriers to transport that exist. Models have been developed to describe the transport between the gastrointestinal lumen and the bloodstream, and laboratory techniques like cell culture provide a means to investigate the absorption and transport of many therapeutic agents. Biomaterials, including stimuli-sensitive complexation hydrogels, have been investigated as promising carriers for oral delivery. However, the need to develop models that accurately predict protein blood concentration as a function of the material structure and properties still exists. PMID:20161384

  17. Ultra reliable infrared absorption water vapor detection through the all-electronic feedback stabilization

    NASA Astrophysics Data System (ADS)

    Zhu, C. G.; Chang, J.; Wang, P. P.; Wang, Q.; Wei, W.; Tian, J. Q.; Chang, H. T.; Liu, X. Z.; Zhang, S. S.

    2014-03-01

    Single-beam balanced radiometric detection (BRD) system with all-electronic feedback stabilization has been proposed for high reliability water vapor detection under rough environmental conditions, which is insensitive to the fluctuation of transmission loss of light. The majority of photocurrent attenuation caused by the optical loss can be effectively compensated by automatically adjusting the splitting ratio of probe photocurrent. Based on the Ebers-Moll model, we present a theoretical analysis which can be suppressed the photocurrent attenuation caused by optical loss from 0.5552 dB to 0.0004 dB by using the all-electronic feedback stabilization. The deviation of the single-beam BRD system is below 0.29% with the bending loss of 0.31 dB in fiber, which is obviously lower than the dual-beam BRD system (5.96%) and subtraction system (11.3%). After averaging and filtering, the absorption sensitivity of water vapor at 1368.597 nm has been demonstrated, which is 7.368×10-6.

  18. Physiological Functions of Cyclic Electron Transport Around Photosystem I in Sustaining Photosynthesis and Plant Growth.

    PubMed

    Yamori, Wataru; Shikanai, Toshiharu

    2016-04-29

    The light reactions in photosynthesis drive both linear and cyclic electron transport around photosystem I (PSI). Linear electron transport generates both ATP and NADPH, whereas PSI cyclic electron transport produces ATP without producing NADPH. PSI cyclic electron transport is thought to be essential for balancing the ATP/NADPH production ratio and for protecting both photosystems from damage caused by stromal overreduction. Two distinct pathways of cyclic electron transport have been proposed in angiosperms: a major pathway that depends on the PROTON GRADIENT REGULATION 5 (PGR5) and PGR5-LIKE PHOTOSYNTHETIC PHENOTYPE 1 (PGRL1) proteins, which are the target site of antimycin A, and a minor pathway mediated by the chloroplast NADH dehydrogenase-like (NDH) complex. Recently, the regulation of PSI cyclic electron transport has been recognized as essential for photosynthesis and plant growth. In this review, we summarize the possible functions and importance of the two pathways of PSI cyclic electron transport. PMID:26927905

  19. Electron transport in the solar wind -results from numerical simulations

    NASA Astrophysics Data System (ADS)

    Smith, Håkan; Marsch, Eckart; Helander, Per

    A conventional fluid approach is in general insufficient for a correct description of electron trans-port in weakly collisional plasmas such as the solar wind. The classical Spitzer-Hürm theory is a not valid when the Knudsen number (the mean free path divided by the length scale of tem-perature variation) is greater than ˜ 10-2 . Despite this, the heat transport from Spitzer-Hürm a theory is widely used in situations with relatively long mean free paths. For realistic Knud-sen numbers in the solar wind, the electron distribution function develops suprathermal tails, and the departure from a local Maxwellian can be significant at the energies which contribute the most to the heat flux moment. To accurately model heat transport a kinetic approach is therefore more adequate. Different techniques have been used previously, e.g. particle sim-ulations [Landi, 2003], spectral methods [Pierrard, 2001], the so-called 16 moment method [Lie-Svendsen, 2001], and approximation by kappa functions [Dorelli, 2003]. In the present study we solve the Fokker-Planck equation for electrons in one spatial dimension and two velocity dimensions. The distribution function is expanded in Laguerre polynomials in energy, and a finite difference scheme is used to solve the equation in the spatial dimension and the velocity pitch angle. The ion temperature and density profiles are assumed to be known, but the electric field is calculated self-consistently to guarantee quasi-neutrality. The kinetic equation is of a two-way diffusion type, for which the distribution of particles entering the computational domain in both ends of the spatial dimension must be specified, leaving the outgoing distributions to be calculated. The long mean free path of the suprathermal electrons has the effect that the details of the boundary conditions play an important role in determining the particle and heat fluxes as well as the electric potential drop across the domain. Dorelli, J. C., and J. D. Scudder, J. D

  20. Intestinal absorption mechanism of tebipenem pivoxil, a novel oral carbapenem: involvement of human OATP family in apical membrane transport.

    PubMed

    Kato, Kazuhiko; Shirasaka, Yoshiyuki; Kuraoka, Erika; Kikuchi, Akihiro; Iguchi, Maki; Suzuki, Hisashi; Shibasaki, Shigeki; Kurosawa, Tohru; Tamai, Ikumi

    2010-10-01

    Tebipenem pivoxil (TBPM-PI) is an oral carbapenem antibiotic for treating otolaryngologic and respiratory infections in pediatric patients. This agent is a prodrug to improve intestinal absorption of TBPM, an active form, and an absorption rate of TBPM-PI is higher than those of other prodrug-type β-lactam antibiotics. In the present study, we hypothesized that a certain mechanism other than simple diffusion is involved in the process of improved intestinal absorption of TBPM-PI and examined the mechanism. TBPM-PI uptake by Caco-2 cells was decreased by ATP-depletion and lowering the temperature to 4 °C, suggesting the contribution of carrier-mediated transport mechanisms. This uptake was partially decreased by ACE inhibitors, and the reduction of the absorption by captopril was observed by in vivo study and in situ single-pass intestinal perfusion study in rat, supporting the contribution of influx transporters. Since some ACE inhibitors and β-lactam antibiotics are reported to be substrates of PEPT and OATP families, we measured transporting activity of TBPM-PI by intestinally expressed transporters, PEPT1, OATP1A2, and OATP2B1. As a result, significant transport activities were observed by both OATP1A2 and OATP2B1 but not by PEPT1. Interestingly, pH dependence of TBPM-PI transports was different between OATP1A2 and OATP2B1, showing highest activity by OATP1A2 at pH 6.5, while OATP2B1-mediated uptake was higher at neutral and weak alkaline pH. OATP1A2 exhibited higher affinity for TBPM-PI (K(m) = 41.1 μM) than OATP2B1 (K(m) > 1 mM) for this agent. These results suggested that TBPM-PI has high intestinal apical membrane permeability due to plural intestinal transport routes, including the uptake transporters such as OATP1A2 and OATP2B1 as well as simple diffusion. PMID:20735088

  1. Composition dependence of electronic, magnetic, transport and morphological properties of mixed valence manganite thin films

    DOE PAGESBeta

    Singh, Surendra; Freeland, J. W.; Fitzsimmons, Michael R.; Jeen, H.; Biswas, A.

    2016-07-27

    Mixed-valence manganese oxides present striking properties like the colossal magnetoresistance, metal-insulator transition (MIT) that may result from coexistence of ferromagnetic, metallic and insulating phases. Percolation of such phase coexistence in the vicinity of MIT leads to first-order transition in these manganites. However the length scales over which the electronic and magnetic phases are separated across MIT which appears compelling for bulk systems has been elusive in (La1-yPry)1-xCaxMnO3 films. Here we show the in-plane length scale over which charge and magnetism are correlated in (La0.4Pr0.6)1-xCaxMnO3 films with x = 0.33 and 0.375, across the MIT temperature. We combine electrical transport (resistance)more » measurements, x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD), and specular/off-specular x-ray resonant magnetic scattering (XRMS) measurements as a function of temperature to elucidate relationships between electronic, magnetic and morphological structure of the thin films. Using off-specular XRMS we obtained the charge-charge and charge-magnetic correlation length of these LPCMO films across the MIT. We observed different charge-magnetic correlation length for two films which increases below the MIT. The different correlation length shown by two films may be responsible for different macroscopic (transport and magnetic) properties.« less

  2. Involvement of Concentrative Nucleoside Transporter 1 in Intestinal Absorption of Trifluridine Using Human Small Intestinal Epithelial Cells.

    PubMed

    Takahashi, Koichi; Yoshisue, Kunihiro; Chiba, Masato; Nakanishi, Takeo; Tamai, Ikumi

    2015-09-01

    TAS-102, which is effective for refractory metastatic colorectal cancer, is a combination drug of anticancer trifluridine (FTD; which is derived from pyrimidine nucleoside) and FTD-metabolizing enzyme inhibitor tipiracil hydrochloride (TPI) at a molecular ratio of 1:0.5. To evaluate the intestinal absorption mechanism of FTD, the uptake and transcellular transport of FTD by human small intestinal epithelial cell (HIEC) monolayer as a model of human intestinal epithelial cells was investigated. The uptake and membrane permeability of FTD by HIEC monolayers were saturable, Na(+) -dependent, and inhibited by nucleosides. These transport characteristics are mostly comparable with those of concentrative nucleoside transporters (CNTs). Moreover, the uptake of FTD by CNT1-expressing Xenopus oocytes was the highest among human CNT transporters. The obtained Km and Vmax values of FTD by CNT1 were 69.0 μM and 516 pmol/oocyte/30 min, respectively. The transcellular transport of FTD by Caco-2 cells, where CNT1 is heterologously expressed, from apical to basolateral side was greater than that by Mock cells. In conclusion, these results demonstrated that FTD exhibits high oral absorption by the contribution of human CNT1. PMID:25900515

  3. Electron beam transport for the LBL IR-FEL. [Infrared free-electron laser

    SciTech Connect

    Staples, J.; Edighoffer, J.; Kim, Kwang-Je.

    1992-07-01

    The infrared flee-electron laser (IR-FEL) proposed by LBL as part of the Combustion Dynamics Research Laboratory (CDRL) consists of a multiple-pass accelerator with superconducting cavities supplying a 55 MeV 12 mA beam to an undulator within a 24-meter optical cavity. Future options include deceleration through the same cavities for energy recovery and reducing the power in the beam dump. The electron transport system from the injector through the cavities and undulator must satisfy conditions of high order achromaticity, isochronicity, unity first-order transport matrix around the recirculation loop, variable betatron match into the undulator, ease of operation and economical implementation. This paper presents a workable solution that satisfies these requirements.

  4. Spin-dependent electron transport in nanoscale samples

    NASA Astrophysics Data System (ADS)

    Wei, Yaguang

    In this thesis, we describe the research in which we use metallic nanoparticles to explore spin-dependent electron transport at nanometer scale. Nanoscale samples were fabricated by using a state of the art electron beam lithography and shadow evaporation technique. We have investigated spin relaxation and decoherence in metallic grains as a function of bias voltage and magnetic field at low temperatures (down to ˜30mK). At low temperatures, the discrete energy levels within a metallic nanoparticle provides a new means to study the physics of the spin-polarized electron tunneling. We describe measurements of spin-polarized tunneling via discrete energy levels of single Aluminum grain. Spin polarized current saturates quickly as a function of bias voltage, which demonstrates that the ground state and the lowest excited states carry spin polarized current. The ratio of electron-spin relaxation time (T1) to the electron-phonon relaxation rate is in quantitative agreement with the Elliot-Yafet scaling, an evidence that spin-relaxation in Al grains is driven by the spin-orbit interaction. The spin-relaxation time of the low-lying excited states is T1 ≈ 0.7 mus and 0.1 mus in two samples, showing that electron spin in a metallic grain could be a potential candidate for quantum information research. We also present measurements of mesoscopic resistance fluctuations in cobalt nanoparticles at low temperature and study how the fluctuations with bias voltage, bias fingerprints, respond to magnetization-reversal processes. Bias fingerprints rearrange when domains are nucleated or annihilated. The domain wall causes an electron wave function-phase shift of ˜5 pi. The phase shift is not caused by the Aharonov-Bohm effect; we explain how it arises from the mistracking effect, where electron spins lag in orientation with respect to the moments inside the domain wall. The dephasing length at low temperatures is only 30 nm, which is attributed to the large magnetocrystalline

  5. Role of defects in BiFeO₃ multiferroic films and their local electronic structure by x-ray absorption spectroscopy

    SciTech Connect

    Ravalia, Ashish; Vagadia, Megha; Solanki, P. S.; Shah, N. A.; Kuberkar, D. G.; Gautam, S.; Chae, K. H.; Asokan, K.

    2014-10-21

    Present study reports the role of defects in the electrical transport in BiFeO₃ (BFO) multiferroic films and its local electronic structure investigated by near-edge X-ray absorption fine structure. Defects created by high energy 200 MeV Ag⁺¹⁵ ion irradiation with a fluence of ∼5 × 10¹¹ ions/cm² results in the increase in structural strain and reduction in the mobility of charge carriers and enhancement in resistive (I-V) and polarization (P-E) switching behaviour. At higher fluence of ∼5 × 10¹² ions/cm², there is a release in the structural strain due to local annealing effect, resulting in an increase in the mobility of charge carriers, which are released from oxygen vacancies and hence suppression in resistive and polarization switching. Near-edge X-ray absorption fine structure studies at Fe L₃,₂- and O K-edges show a significant change in the spectral features suggesting the modifications in the local electronic structure responsible for changes in the intrinsic magnetic moment and electrical transport properties of BFO.

  6. Nanogap structures: combining enhanced Raman spectroscopy and electronic transport.

    PubMed

    Natelson, Douglas; Li, Yajing; Herzog, Joseph B

    2013-04-21

    Surface-enhanced Raman spectroscopy (SERS) is an experimental tool for accessing vibrational and chemical information, down to the single molecule level. SERS typically relies on plasmon excitations in metal nanostructures to concentrate the incident radiation and to provide an enhanced photon density of states to couple emitted radiation to the far field. Many common SERS platforms involve metal nanoparticles to generate the required electromagnetic enhancements. Here we concentrate on an alternative approach, in which the relevant plasmon excitations are supported at a truly nanoscale gap between extended electrodes, rather than discrete subwavelength nanoparticles. The ability to fabricate precise gaps on demand, and in some cases to tune the gap size in situ, combined with the additional capability of simultaneous electronic transport measurements of the nanogap, provides access to information not previously available in standard SERS. We summarize the rich plasmonic physics at work in these extended systems and highlight the recent state of the art including tip-enhanced Raman spectroscopy (TERS) and the application of mechanical break junctions and electromigrated junctions. We describe in detail how we have performed in situ gap-enhanced Raman measurements of molecular-scale junctions while simultaneously subjecting these structures to electronic transport. These extended electrode structures allow us to study the pumping of vibrational modes by the flow of tunneling electrons, as well as the shifting of vibrational energies due to the applied bias. These experiments extend SERS into a tool for examining fundamental processes of dissipation, and provide insight into the mechanisms behind SERS spectral diffusion. We conclude with a brief discussion of future directions. PMID:23385304

  7. Effect of runaway electrons on transport in Fast Ignition targets

    NASA Astrophysics Data System (ADS)

    Tabak, Max; Kruer, William; Langdon, A. Bruce; Lasinski, Barbara; Town, Richard; Welch, Dale

    2002-11-01

    A crucial issue for the viability of the fast ignition approach [1] to inertial fusion energy is the transport of the ignitor pulse energy from the critical surface to the high-density compressed fuel. For example, the required ignitor beam energy depends on the cross section area of the electron beam. Experiments of the interaction of short-pulse high intensity lasers with surrogate solid-density thin targets have shown, a fairly well collimated beam [2]. We report on LSP calculations of these experiments. The LSP code [3] uses a direct implicit particle-in-cell algorithm in 3 dimensions to solve for the beam particles. The background particles are treated as fluid particles. The behavior of the return current is essential in controlling the background plasma heating as well as the beam propagation. Previous calculations have used the collisional resistivity of a fluid bath for the return current. We estimate the effects of runaway electrons on the electron transport. In addition we make estimates of the effects of various microinstabilities on the effective collisionality. Analytic estimates and preliminary LSP calculations will be shown. The implications for fast ignition will be discussed. [1] M. Tabak, et al, Phys. Plasmas 1, 1626 (1994). [2] J. A. Koch, et al, Phys. Rev. E 65, 016410-1 (2001). [3] D. R. Welch, D. V. Rose, B. V. Oliver, and R. E. Clark, Nucl. Inst. Meth. Phys. Res. A 242, 134 (2001). *This work was performed under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.

  8. Constraint on a Cosmological Variation in the Proton-to-electron Mass Ratio from Electronic CO Absorption

    NASA Astrophysics Data System (ADS)

    Daprà, M.; Niu, M. L.; Salumbides, E. J.; Murphy, M. T.; Ubachs, W.

    2016-08-01

    Carbon monoxide (CO) absorption in the sub-damped Lyα absorber at redshift {z}{abs}≃ 2.69 toward the background quasar SDSS J123714.60+064759.5 (J1237+0647) was investigated for the first time in order to search for a possible variation of the proton-to-electron mass ratio, μ, over a cosmological timescale. The observations were performed with the Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph with a signal-to-noise ratio of 40 per 2.5 km s‑1 per pixel at ˜5000 Å. Thirteen CO vibrational bands in this absorber are detected: the {{{A}}}1{{\\Pi }} ‑ {{{X}}}1{{{Σ }}}+ (ν \\prime , 0) for ν \\prime =0{--}8, {{{B}}}1{{{Σ }}}+ ‑ {{{X}}}1{{{Σ }}}+ (0, 0), {{{C}}}1{{{Σ }}}+ ‑ {{{X}}}1{{{Σ }}}+ (0, 0), and {{{E}}}1{{\\Pi }} ‑ {{{X}}}1{{{Σ }}}+ (0, 0) singlet–singlet bands and the {d}3{{Δ }} ‑ {{{X}}}1{{{Σ }}}+ (5, 0) singlet–triplet band. An updated database including the most precise molecular inputs needed for a μ-variation analysis is presented for rotational levels J = 0–5, consisting of transition wavelengths, oscillator strengths, natural lifetime damping parameters, and sensitivity coefficients to a variation of the proton-to-electron mass ratio. A comprehensive fitting method was used to fit all the CO bands at once and an independent constraint of {{Δ }}μ /μ =(0.7+/- {1.6}{stat}+/- {0.5}{syst})× {10}-5 was derived from CO only. A combined analysis using both molecular hydrogen and CO in the same J1237+0647 absorber returned a final constraint on the relative variation of {{Δ }}μ /μ =(-5.6+/- {5.6}{stat}+/- {3.1}{syst})× {10}-6, which is consistent with no variation over a look-back time of ˜11.4 Gyr.

  9. Constraint on a Cosmological Variation in the Proton-to-electron Mass Ratio from Electronic CO Absorption

    NASA Astrophysics Data System (ADS)

    Daprà, M.; Niu, M. L.; Salumbides, E. J.; Murphy, M. T.; Ubachs, W.

    2016-08-01

    Carbon monoxide (CO) absorption in the sub-damped Lyα absorber at redshift {z}{abs}≃ 2.69 toward the background quasar SDSS J123714.60+064759.5 (J1237+0647) was investigated for the first time in order to search for a possible variation of the proton-to-electron mass ratio, μ, over a cosmological timescale. The observations were performed with the Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph with a signal-to-noise ratio of 40 per 2.5 km s‑1 per pixel at ∼5000 Å. Thirteen CO vibrational bands in this absorber are detected: the {{{A}}}1{{\\Pi }} ‑ {{{X}}}1{{{Σ }}}+ (ν \\prime , 0) for ν \\prime =0{--}8, {{{B}}}1{{{Σ }}}+ ‑ {{{X}}}1{{{Σ }}}+ (0, 0), {{{C}}}1{{{Σ }}}+ ‑ {{{X}}}1{{{Σ }}}+ (0, 0), and {{{E}}}1{{\\Pi }} ‑ {{{X}}}1{{{Σ }}}+ (0, 0) singlet–singlet bands and the {d}3{{Δ }} ‑ {{{X}}}1{{{Σ }}}+ (5, 0) singlet–triplet band. An updated database including the most precise molecular inputs needed for a μ-variation analysis is presented for rotational levels J = 0–5, consisting of transition wavelengths, oscillator strengths, natural lifetime damping parameters, and sensitivity coefficients to a variation of the proton-to-electron mass ratio. A comprehensive fitting method was used to fit all the CO bands at once and an independent constraint of {{Δ }}μ /μ =(0.7+/- {1.6}{stat}+/- {0.5}{syst})× {10}-5 was derived from CO only. A combined analysis using both molecular hydrogen and CO in the same J1237+0647 absorber returned a final constraint on the relative variation of {{Δ }}μ /μ =(-5.6+/- {5.6}{stat}+/- {3.1}{syst})× {10}-6, which is consistent with no variation over a look-back time of ∼11.4 Gyr.

  10. Polarized electronic absorption spectra of Cr2SiO4 single crystals

    NASA Astrophysics Data System (ADS)

    Furche, A.; Langer, K.

    Polarized electronic absorption spectra, E∥a(∥X), E∥b(∥Y) and E∥c(∥Z), in the energy range 3000-5000 cm-1 were obtained for the orthorhombic thenardite-type phase Cr2SiO4, unique in its Cr2+-allocation suggesting some metal-metal bonding in Cr2+Cr2+ pairs with Cr-Cr distance 2.75 Å along [001]. The spectra were scanned at 273 and 120 K on single crystal platelets ∥(100), containing optical Y and Z, and ∥(010), containing optical X and Z, with thicknesses 12.3 and 15.6 μm, respectively. Microscope-spectrometric techniques with a spatial resolution of 20 μm and 1 nm spectral resolution were used. The orientations were obtained by means of X-ray precession photographs. The xenomorphic, strongly pleochroic crystal fragments (X deeply greenish-blue, Y faint blue almost colourless, Z deeply purple almost opaque) were extracted from polycrystalline Cr2SiO4, synthesized at 35 kbar, above 1440 °C from high purity Cr2O3, Cr (10% excess) and SiO2 in chromium capsules. The Cr2SiO4-phase was identified by X-ray diffraction (XRD). Four strongly polarized bands, at about 13500 (I), 15700 (II), 18700 (III) and 19700 (IV) cm-1, in the absorption spectra of Cr2SiO4 single crystals show properties (temperature behaviour of linear and integral absorption coefficients, polarization behaviour, molar absorptivities) which are compatible with an assignment to localized spin-allowed transitions of Cr2+ in a distorted square planar coordination of point symmetry C2. The crystal field parameter of Cr2+ is estimated to be 10 Dq =10700 cm-1. A relatively intense, sharp band at 18400 cm-1 and three other minor features can, from their small half widths, be assigned to spin-forbidden dd-transitions of Cr2+. The intensity of such bands strongly decreases on decreasing temperature. The large half widths, near 5000 cm-1 of band III are indicative of some Cr-Cr interactions, i.e. δ-δ* transitions of Cr24+, whereas the latter alone would be in conflict with the strong

  11. When electron transfer meets electron transport in redox-active molecular nanojunctions.

    PubMed

    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

  12. Tuning The Optical, Charge Injection, and Charge Transport Properties of Organic Electronic Devices

    NASA Astrophysics Data System (ADS)

    Zalar, Peter

    Since the early 1900's, synthetic insulating polymers (plastics) have slowly taken over the role that traditional materials like wood or metal have had as basic components for construction, manufactured goods, and parts. Plastics allow for high throughput, low temperature processing, and control of bulk properties through molecular modifications. In the same way, pi-conjugated organic molecules are emerging as a possible substitute for inorganic materials due to their electronic properties. The semiconductive nature of pi-conjugated materials make them an attractive candidate to replace inorganic materials, primarily due to their promise for low cost and large-scale production of basic semiconducting devices such as light-emitting diodes, solar cells, and field-effect transistors. Before organic semiconductors can be realized as a commercial product, several hurdles must be cleared. The purpose of this dissertation is to address three distinct properties that dominate the functionality of devices harnessing these materials: (1) optical properties, (2) charge injection, and (3) charge transport. First, it is shown that the electron injection barrier in the emissive layer of polymer light-emitting diodes can be significantly reduced by processing of novel conjugated oligoelectrolytes or deoxyribonucleic acid atop the emissive layer. Next, the charge transport properties of several polymers could be modified by processing them from solvents containing small amounts of additives or by using regioregular and enantiopure chemical structures. It is then demonstrated that the optical and electronic properties of Lewis basic polymer structures can be readily modified by interactions with strongly electron-withdrawing Lewis acids. Through red-shifted absorption, photoluminescence, and electroluminescence, a single pi-conjugated backbone can be polychromatic. In addition, interaction with Lewis acids can remarkably p-dope the hole transport of the parent polymer, leading to a

  13. Transport of electrons in Ar/H2 mixtures

    NASA Astrophysics Data System (ADS)

    Nikitović, Ž.; Stojanović, V.; Petrović, Z. Lj.

    2012-08-01

    In this work we present transport coefficients for electrons in Ar/H2 mixtures for the conditions used in plasma-assisted technologies for semiconductor production, i.e., in moderate and very high E/N. We used a two-term numerical solution of the Boltzmann equation at the lowest E/N (E is the electric field; N is the gas density) and correspondingly at the lowest mean energies. We also use the Monte Carlo simulation technique at moderate and high E/N. We show that a good agreement with experimental data exists for low and moderate E/N and that based on the tests for pure H2 and Ar we can model properly the swarm properties at high E/N. For the conditions of very high electric fields runaway peaks develop in the electron energy distribution function and appreciable contribution of backscattered high-energy electrons produces additional emission of Hα emission close to the anode (made of stainless steel). Results are obtained for abundances of H2 from 1% to 30%, which are necessary in kinetic models for this mixture in a number of applications.

  14. Hot electron spin transport in C60 fullerene

    NASA Astrophysics Data System (ADS)

    Hueso, Luis Eduardo; Gobbi, Marco; Bedoya-Pinto, Amilcar; Golmar, Federico; Llopis, Roger; Casanova, Felix

    2012-02-01

    Carbon-based molecular materials are interesting for spin transport application mainly due to their small sources of spin relaxation [1]. However, spin coherence lengths reported in many molecular films do not exceed a few tens of nanometers [2]. In this work we will present results showing how hot spin-polarized electrons injected well above the Fermi level in C60 fullerene films travel coherently for hundreds of nanometers. We fabricated hot-electron vertical transistors, in which the current created across an Al/Al2O3 junction is polarized by a metallic Co/Cu/Py spin valve trilayer and subsequently injected in the molecular thin film. This geometry allows us to determine the energy level alignment at each interface between different materials. Moreover, the collector magnetocurrent excess 85%, even for C60 films thicknesses of 300 nm. We believe these results show the importance of hot spin-polarized electron injection and propagation in molecular materials. [1] V. Dediu, L.E. Hueso, I. Bergenti, C. Taliani, Nature Mater. 8, 707 (2009) [2] M. Gobbi, F. Golmar, R. Llopis, F. Casanova, L.E. Hueso, Adv. Mater. 23, 1609 (2011)

  15. Kinetic Modelling of Parallel Electron Transport in TdeV.

    NASA Astrophysics Data System (ADS)

    Shoucri, M.; Shkarofsky, I.; Stansfield, B.; Batishchev, O.; Batishcheva, A.; Krasheninnikov, S.; Sigmar

    1996-11-01

    The 1D2V Fokker-Planck code ALLA [1] is used to model parallel electron transport in the SOL of TdeV. Our model uses detached and attached experimental data [2] given by Langmuir probes, Li ablation and He spectroscopy. We obtain the electron distribution function on a precise 257x65x60 non-uniform grid. Strong deviations of hydrogen and carbon excitation rates, and heat conduction coefficient from their Maxwellian values are shown. We compare the calculated variation of the effective temperature at the reciprocating probe position with experimental measurements. We also explain by non-local effects why different experimental techniques show differences in the electron temperature. altaffiltext [1] A.A.Batishcheva et al., Physics of Plasmas 3 (1996) 1634 altaffiltext [2] B.L.Stansfield et al., Proc. 22 Eur.Conf., Bornemouth, 19C pIII-101. *Supported by Government of Canada, Hydro-Québec and INRS. Work performed under USDoE contracts DE-FG02-91-ER-54109 at MIT and DE-FG02-88-ER-53263 at Lodestar.

  16. Low temperature transport in undoped electron-hole bilayers

    NASA Astrophysics Data System (ADS)

    Seamons, John Andrew

    2007-05-01

    There is intense interest in the possibility of exciton condensation occurring in electron-hole bilayer systems. Exciton condensation effects have been studied in nuTOT = 1 unipolar bilayer systems and optically-generated electron-hole bilayer systems; however, performing transport experiments in electron-hole bilayer systems in the low density, low temperature regime where exciton condensation is expected has proven to be extremely difficult. This is a report on the fabrication details and electrical transport studies of a new type of completely undoped electron-hole bilayer (uEHBL) device that operates in this regime. The devices are formed using GaAs/AlGaAs double quantum well semiconductor heterostructures; a two-dimensional electron gas (2DEG) and a two-dimensional hole gas (2DHG) are induced in the upper quantum well and in the lower quantum well, respectively using gates for a field effect. The quantum wells are 18 nm wide and are separated by a 20 nm or 30 nm Al0.9Ga0.1As barrier. The uEHBL device design incorporates independent ohmic contact to each quantum well allowing four terminal conductance measurements of the 2DEG and 2DHG to be taken. Furthermore, the density of the 2DEG and 2DHG in the uEHBL devices are independently tunable which enables them to be matched. Transport properties are measured in the uEHBL as a function of the density in each layer; barrier width, magnetic field, and temperature. The matched densities range from 4 x 1010 cm-2 to 1.2 x 1011 cm -2 at T = 0.3 K. The 2DEG and 2DHG mobilities are measured directly and depend upon the carrier density in each well; mobilities exceed 10 x 105 cm2V-1s -1 (4 x 105 cm2 V-1s-1) for the 2DEG (2DHG). The uEHBL devices also permit bipolar Coulomb drag measurements to be taken, thereby allowing the nature of electron-hole scattering to be explored. Above 1 K the measured Coulomb drag resistivity (rhoD) is approximately proportional to T2. In the 20 nm wide barrier samples below 1 K and at zero

  17. Near Edge X-Ray Absorption Fine Structure Spectroscopy with X-Ray Free-Electron Lasers

    SciTech Connect

    Bernstein, D.P.; Acremann, Y.; Scherz, A.; Burkhardt, M.; Stohr, J.; Beye, M.; Schlotter, W.F.; Beeck, T.; Sorgenfrei, F.; Pietzsch, A.; Wurth, W.; Fohlisch, A.; /Hamburg U.

    2009-12-11

    We demonstrate the feasibility of Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy on solids by means of femtosecond soft x-ray pulses from a free-electron laser (FEL). Our experiments, carried out at the Free-Electron Laser at Hamburg (FLASH), used a special sample geometry, spectrographic energy dispersion, single shot position-sensitive detection and a data normalization procedure that eliminates the severe fluctuations of the incident intensity in space and photon energy. As an example we recorded the {sup 3}D{sub 1} N{sub 4,5}-edge absorption resonance of La{sup 3+}-ions in LaMnO{sub 3}. Our study opens the door for x-ray absorption measurements on future x-ray FEL facilities.

  18. On the application of quantum transport theory to electron sources.

    PubMed

    Jensen, Kevin L

    2003-01-01

    Electron sources (e.g., field emitter arrays, wide band-gap (WBG) semiconductor materials and coatings, carbon nanotubes, etc.) seek to exploit ballistic transport within the vacuum after emission from microfabricated structures. Regardless of kind, all sources strive to minimize the barrier to electron emission by engineering material properties (work function/electron affinity) or physical geometry (field enhancement) of the cathode. The unique capabilities of cold cathodes, such as instant ON/OFF performance, high brightness, high current density, large transconductance to capacitance ratio, cold emission, small size and/or low voltage operation characteristics, commend their use in several advanced devices when physical size, weight, power consumption, beam current, and pulse repletion frequency are important, e.g., RF power amplifier such as traveling wave tubes (TWTs) for radar and communications, electrodynamic tethers for satellite deboost/reboost, and electric propulsion systems such as Hall thrusters for small satellites. The theoretical program described herein is directed towards models to evaluate emission current from electron sources (in particular, emission from WBG and Spindt-type field emitter) in order to assess their utility, capabilities and performance characteristics. Modeling efforts particularly include: band bending, non-linear and resonant (Poole-Frenkel) potentials, the extension of one-dimensional theory to multi-dimensional structures, and emission site statistics due to variations in geometry and the presence of adsorbates. Two particular methodologies, namely, the modified Airy approach and metal-semiconductor statistical hyperbolic/ellipsoidal model, are described in detail in their present stage of development. PMID:12535543

  19. Electron-electron interaction, weak localization and spin valve effect in vertical-transport graphene devices

    SciTech Connect

    Long, Mingsheng; Gong, Youpin; Wei, Xiangfei; Zhu, Chao; Xu, Jianbao; Liu, Ping; Guo, Yufen; Li, Weiwei; Liu, Liwei; Liu, Guangtong

    2014-04-14

    We fabricated a vertical structure device, in which graphene is sandwiched between two asymmetric ferromagnetic electrodes. The measurements of electron and spin transport were performed across the combined channels containing the vertical and horizontal components. The presence of electron-electron interaction (EEI) was found not only at low temperatures but also at moderate temperatures up to ∼120 K, and EEI dominates over weak localization (WL) with and without applying magnetic fields perpendicular to the sample plane. Moreover, spin valve effect was observed when magnetic filed is swept at the direction parallel to the sample surface. We attribute the EEI and WL surviving at a relatively high temperature to the effective suppress of phonon scattering in the vertical device structure. The findings open a way for studying quantum correlation at relatively high temperature.

  20. Density-dependent electron transport and precise modeling of GaN high electron mobility transistors

    SciTech Connect

    Bajaj, Sanyam Shoron, Omor F.; Park, Pil Sung; Krishnamoorthy, Sriram; Akyol, Fatih; Hung, Ting-Hsiang; Reza, Shahed; Chumbes, Eduardo M.; Khurgin, Jacob; Rajan, Siddharth

    2015-10-12

    We report on the direct measurement of two-dimensional sheet charge density dependence of electron transport in AlGaN/GaN high electron mobility transistors (HEMTs). Pulsed IV measurements established increasing electron velocities with decreasing sheet charge densities, resulting in saturation velocity of 1.9 × 10{sup 7 }cm/s at a low sheet charge density of 7.8 × 10{sup 11 }cm{sup −2}. An optical phonon emission-based electron velocity model for GaN is also presented. It accommodates stimulated longitudinal optical (LO) phonon emission which clamps the electron velocity with strong electron-phonon interaction and long LO phonon lifetime in GaN. A comparison with the measured density-dependent saturation velocity shows that it captures the dependence rather well. Finally, the experimental result is applied in TCAD-based device simulator to predict DC and small signal characteristics of a reported GaN HEMT. Good agreement between the simulated and reported experimental results validated the measurement presented in this report and established accurate modeling of GaN HEMTs.

  1. Modulation in concentrative nucleoside transporters-mediated intestinal absorption of mizoribine, an immunosuppressive agent, in lipopolysaccharide-treated rats.

    PubMed

    Mori, N; Shimomukai, Y; Yokooji, T; Ishiguro, M; Kamio, Y; Murakami, T

    2011-03-01

    The characteristics of intestinal absorption of mizoribine and cephalexin, that are mediated by concentrative nucleoside transporters (CNTs) and PEPT1, respectively, was examined in lipopolysaccharide (LPS)-treated rats. LPS treatment is known to modify the expression of some transporters and induce cholestasis. At 24 h after the LPS treatment, averaged concentrations of IL-6 and total bile acids in plasma were 15-fold and 2-fold that in untreated control rats, respectively, and bile flow rate decreased by 40% of control, indicating the induction of inflammatory and cholestatic states. The oral bioavailability, estimated by urinary excretion percentage of unchanged form, of mizoribine in LPS-treated rats was 1.5-fold higher than that in control rats, whereas the bioavailability of cephalexin remained unchanged. When mizoribine and cephalexin were administered into in-situ jejunum loops, there were no differences in the absorption rates between control and LPS-treated rats. These results indicated that the functional expression of CNT1, CNT2, and PEPT1 were not modulated by LPS treatment. When mizoribine (a CNT1/CNT2 substrate) and gemcitabin (a CNT1 substrate) were administered as a solution dissolved in bile into the intestinal loop, their absorption rates decreased significantly. In contrast, the absorption rate of ribavirin (a CNT2 substrate) remained unchanged. In conclusion, LPS treatment exerted no significant effect on the expression of CNT1 and CNT2 in the intestine. Bile was found to suppress the CNT1-mediated intestinal absorption of mizoribine and gemcitabin. The increased oral bioavailability of mizoribine in LPS-treated rats could be ascribed to the less amount of bile or bile acids in the intestine under cholestatic state of rats. PMID:21553652

  2. Perpendicular hot electron transport in the spin-valve photodiode

    NASA Astrophysics Data System (ADS)

    Huang, Biqin; Appelbaum, Ian

    2006-08-01

    The spin-valve photodiode is a ferromagnetic metal multilayer/n-type semiconductor Schottky device operated by photoexciting hot electrons in the metal and causing internal photoemission (IPE) into the semiconductor. Simple IPE theory predicts that the magnitude of the spin-valve effect (modulation of the photocurrent) should monotonically increase as a metallic capping layer thickness increases. Experimentally, however, we observe a nonmonotonic behavior with cap layer thickness, where the magnetocurrent reaches an optimum value and then decreases. The disagreement between this experimental result and the previous theoretical model is discussed, leading to an alternative interpretation of transport including reflection from the air-metal interface. Calculations with this model are consistent with the observed phenomena.

  3. Electronic and transport properties of LiCoO2.

    PubMed

    Andriyevsky, Bohdan; Doll, Klaus; Jacob, Timo

    2014-11-14

    Using first principles density functional theory (DFT), the electronic and magnetic properties as well as the Li-ion migration in LiCoO2 have been studied with a gradient corrected functional. The magnetic properties were also investigated in addition using a gradient corrected functional in combination with an on-site repulsion U and a hybrid functional. We find LiCoO2 to be non-magnetic under ambient conditions. A magnetic ground state can be obtained by a volume expansion corresponding to a negative pressure of -8 GPa due to a competition between Hund's rules favoring magnetism on the Co(3+) ions and the crystal field splitting, which suppresses magnetism at zero pressure. The barrier for lithium transport is determined to be 0.44 eV from nudged elastic band (NEB) calculations on the Li0.917CoO2 system. PMID:25264622

  4. Velocity modulation of electron transport through a ferromagnetic silicene junction

    NASA Astrophysics Data System (ADS)

    Huai-Hua, Shao; Dan, Guo; Ben-Liang, Zhou; Guang-Hui, Zhou

    2016-03-01

    We address velocity-modulation control of electron wave propagation in a normal/ferromagnetic/normal silicene junction with local variation of Fermi velocity, where the properties of charge, valley, and spin transport through the junction are investigated. By matching the wavefunctions at the normal-ferromagnetic interfaces, it is demonstrated that the variation of Fermi velocity in a small range can largely enhance the total conductance while keeping the current nearly fully valley- and spin-polarized. Further, the variation of Fermi velocity in ferromagnetic silicene has significant influence on the valley and spin polarization, especially in the low-energy regime. It may drastically reduce the high polarizations, which can be realized by adjusting the local application of a gate voltage and exchange field on the junction. Project supported by the National Natural Science Foundation of China (Grant No. 11274108).

  5. Electronic measurement of strain effects on spin transport in silicon

    NASA Astrophysics Data System (ADS)

    Qing, Lan; Tinkey, Holly; Appelbaum, Ian

    Spin transport in silicon is limited by the Elliott-Yafet spin relaxation mechanism, which is driven by scattering between degenerate conduction band valleys. Mechanical strain along a valley axis partially breaks this degeneracy, and will ultimately quench intervalley spin relaxation for transitions between states on orthogonal axes. Using a custom-designed and constructed strain probe, we study the effects of uniaxial compressive strain along the < 100 > direction on ballistic tunnel junction devices used to inject spin-polarized electrons into silicon. The effects of strain-induced valley splitting will be presented and compared to our theoretical model. This work is supported by the Office of Naval Research under Contract No. N000141410317, the National Science Foundation under Contract No. ECCS-1231855, the Defense Threat Reduction Agency under Contract No. HDTRA1-13-1-0013, and the Maryland NanoCenter.

  6. Electron Transport Simulations of 4-Terminal Crossed Graphene Nanoribbons Devices

    NASA Astrophysics Data System (ADS)

    Brandimarte, Pedro; Papior, Nick R.; Engelund, Mads; Garcia-Lekue, Aran; Frederiksen, Thomas; Sánchez-Portal, Daniel

    Recently, it has been reported theoretically a current switching mechanism by voltage control in a system made by two perpendicular 14-armchair graphene nanoribbons (GNRs). In order to investigate the possibilities of using crossed GNRs as ON/OFF devices, we have studied their electronic and transport properties as function structural parameters determining the crossing. Our calculations were performed with TranSIESTA code, which has been recently generalized to consider N >= 1 arbitrarily distributed electrodes at finite bias. We find that the transmission along each individual GNR and among them strongly depends on the stacking. For a 60° rotation angle, the lattice matching in the crossing region provokes a strong scattering effect that translates into an increased interlayer transmission. FP7 FET-ICT PAMS-project (European Commission, contract 610446), MINECO (Grant MAT2013-46593-C6-2-P) and Basque Dep. de Educación, UPV/EHU (Grant IT-756-13).

  7. Hot Electron Generation and Transport Using K(alpha) Emission

    SciTech Connect

    Akli, K U; Stephens, R B; Key, M H; Bartal, T; Beg, F N; Chawla, S; Chen, C D; Fedosejevs, R; Freeman, R R; Friesen, H; Giraldez, E; Green, J S; Hey, D S; Higginson, D P; Hund, J; Jarrott, L C; Kemp, G E; King, J A; Kryger, A; Lancaster, K; LePape, S; Link, A; Ma, T; Mackinnon, A J; MacPhee, A G; McLean, H S; Murphy, C; Norreys, P A; Ovchinnikov, V; Patel, P K; Ping, Y; Sawada, H; Schumacher, D; Theobald, W; Tsui, Y Y; Van Woerkom, L D; Wei, M S; Westover, B; Yabuuchi, T

    2009-10-15

    We have conducted experiments on both the Vulcan and Titan laser facilities to study hot electron generation and transport in the context of fast ignition. Cu wires attached to Al cones were used to investigate the effect on coupling efficiency of plasma surround and the pre-formed plasma inside the cone. We found that with thin cones 15% of laser energy is coupled to the 40{micro}m diameter wire emulating a 40{micro}m fast ignition spot. Thick cone walls, simulating plasma in fast ignition, reduce coupling by x4. An increase of prepulse level inside the cone by a factor of 50 reduces coupling by a factor of 3.

  8. Graphene on graphene antidot lattices: Electronic and transport properties

    NASA Astrophysics Data System (ADS)

    Gregersen, Søren Schou; Pedersen, Jesper Goor; Power, Stephen R.; Jauho, Antti-Pekka

    2015-03-01

    Graphene bilayer systems are known to exhibit a band gap when the layer symmetry is broken by applying a perpendicular electric field. The resulting band structure resembles that of a conventional semiconductor with a parabolic dispersion. Here, we introduce a bilayer graphene heterostructure, where single-layer graphene is placed on top of another layer of graphene with a regular lattice of antidots. We dub this class of graphene systems GOAL: graphene on graphene antidot lattice. By varying the structure geometry, band-structure engineering can be performed to obtain linearly dispersing bands (with a high concomitant mobility), which nevertheless can be made gapped with a perpendicular field. We analyze the electronic structure and transport properties of various types of GOALs, and draw general conclusions about their properties to aid their design in experiments.

  9. Conformation dependent electronic transport in a DNA double-helix

    SciTech Connect

    Kundu, Sourav Karmakar, S. N.

    2015-10-15

    We present a tight-binding study of conformation dependent electronic transport properties of DNA double-helix including its helical symmetry. We have studied the changes in the localization properties of DNA as we alter the number of stacked bases within every pitch of the double-helix keeping fixed the total number of nitrogen bases within the DNA molecule. We take three DNA sequences, two of them are periodic and one is random and observe that in all the cases localization length increases as we increase the radius of DNA double-helix i.e., number of nucleobases within a pitch. We have also investigated the effect of backbone energetic on the I-V response of the system and found that in presence of helical symmetry, depending on the interplay of conformal variation and disorder, DNA can be found in either metallic, semiconducting and insulating phases, as observed experimentally.

  10. Revealing electronic structure changes in Chevrel phase cathodes upon Mg insertion using X-ray absorption spectroscopy.

    PubMed

    Wan, Liwen F; Wright, Joshua; Perdue, Brian R; Fister, Timothy T; Kim, Soojeong; Apblett, Christopher A; Prendergast, David

    2016-06-29

    Following previous work predicting the electronic response of the Chevrel phase Mo6S8 upon Mg insertion (Thöle et al., Phys. Chem. Chem. Phys., 2015, 17, 22548), we provide the experimental proof, evident in X-ray absorption spectroscopy, to illustrate the charge compensation mechanism of the Chevrel phase compound during Mg insertion and de-insertion processes. PMID:27314253

  11. Anomalous Electron Transport Due to Multiple High Frequency Beam Ion Driven Alfven Eigenmode

    SciTech Connect

    Gorelenkov, N. N.; Stutman, D.; Tritz, K.; Boozer, A.; Delgardo-Aparicio, L.; Fredrickson, E.; Kaye, S.; White, R.

    2010-07-13

    We report on the simulations of recently observed correlations of the core electron transport with the sub-thermal ion cyclotron frequency instabilities in low aspect ratio plasmas of the National Spherical Torus Experiment (NSTX). In order to model the electron transport of the guiding center code ORBIT is employed. A spectrum of test functions of multiple core localized Global shear Alfven Eigenmode (GAE) instabilities based on a previously developed theory and experimental observations is used to examine the electron transport properties. The simulations exhibit thermal electron transport induced by electron drift orbit stochasticity in the presence of multiple core localized GAE.

  12. Electron transport in molecular junctions with graphene as protecting layer

    SciTech Connect

    Hüser, Falco; Solomon, Gemma C.

    2015-12-07

    We present ab initio transport calculations for molecular junctions that include graphene as a protecting layer between a single molecule and gold electrodes. This vertical setup has recently gained significant interest in experiment for the design of particularly stable and reproducible devices. We observe that the signals from the molecule in the electronic transmission are overlayed by the signatures of the graphene sheet, thus raising the need for a reinterpretation of the transmission. On the other hand, we see that our results are stable with respect to various defects in the graphene. For weakly physiosorbed molecules, no signs of interaction with the graphene are evident, so the transport properties are determined by offresonant tunnelling between the gold leads across an extended structure that includes the molecule itself and the additional graphene layer. Compared with pure gold electrodes, calculated conductances are about one order of magnitude lower due to the increased tunnelling distance. Relative differences upon changing the end group and the length of the molecule on the other hand, are similar.

  13. Computing Rydberg Electron Transport Rates via Classical Periodic Orbits

    NASA Astrophysics Data System (ADS)

    Sattari, Sulimon; Mitchell, Kevin

    2015-05-01

    Electron transport properties of chaotic atomic systems are computable from classical periodic orbits. This technique allows for replacing a Monte Carlo simulation launching millions of orbits with a sum over tens or hundreds of properly chosen periodic orbits. Such computations are easiest to realize in sufficiently unstable systems dominated by a few short orbits. However, phase spaces exhibiting a mixture of chaos and regularity present a greater challenge, due to the rich dynamics in the vicinity of stable islands. Homotopic Lobe Dynamics (HLD) uses information encoded in the intersections of stable and unstable manifolds of a few orbits to compute almost all hyperbolic periodic orbits in a system. We compute the ionization rate for a Rydberg atom in parallel electric and magnetic fields. We apply HLD to compute orbits for parameters exhibiting both mixed and fully hyperbolic phase spaces. The ionization rate computed from periodic orbits converges exponentially to the true value as a function of highest period used. We then use periodic orbit continuation to accurately compute the ionization rate when the field strengths are perturbed. The ability to use periodic orbits in a mixed phase space could allow for studying transport in arbitrarily complex physical systems.

  14. Simple predictive electron transport models applied to sawtoothing plasmas

    NASA Astrophysics Data System (ADS)

    Kim, D.; Merle, A.; Sauter, O.; Goodman, T. P.

    2016-05-01

    In this work, we introduce two simple transport models to evaluate the time evolution of electron temperature and density profiles during sawtooth cycles (i.e. over a sawtooth period time-scale). Since the aim of these simulations is to estimate reliable profiles within a short calculation time, two simplified ad-hoc models have been developed. The goal for these models is to rely on a few easy-to-check free parameters, such as the confinement time scaling factor and the profiles’ averaged scale-lengths. Due to the simplicity and short calculation time of the models, it is expected that these models can also be applied to real-time transport simulations. We show that it works well for Ohmic and EC heated L- and H-mode plasmas. The differences between these models are discussed and we show that their predictive capabilities are similar. Thus only one model is used to reproduce with simulations the results of sawtooth control experiments on the TCV tokamak. For the sawtooth pacing, the calculated time delays between the EC power off and sawtooth crash time agree well with the experimental results. The map of possible locking range is also well reproduced by the simulation.

  15. Electron transport in molecular junctions with graphene as protecting layer

    NASA Astrophysics Data System (ADS)

    Hüser, Falco; Solomon, Gemma C.

    2015-12-01

    We present ab initio transport calculations for molecular junctions that include graphene as a protecting layer between a single molecule and gold electrodes. This vertical setup has recently gained significant interest in experiment for the design of particularly stable and reproducible devices. We observe that the signals from the molecule in the electronic transmission are overlayed by the signatures of the graphene sheet, thus raising the need for a reinterpretation of the transmission. On the other hand, we see that our results are stable with respect to various defects in the graphene. For weakly physiosorbed molecules, no signs of interaction with the graphene are evident, so the transport properties are determined by offresonant tunnelling between the gold leads across an extended structure that includes the molecule itself and the additional graphene layer. Compared with pure gold electrodes, calculated conductances are about one order of magnitude lower due to the increased tunnelling distance. Relative differences upon changing the end group and the length of the molecule on the other hand, are similar.

  16. Electron transport in molecular junctions with graphene as protecting layer.

    PubMed

    Hüser, Falco; Solomon, Gemma C

    2015-12-01

    We present ab initio transport calculations for molecular junctions that include graphene as a protecting layer between a single molecule and gold electrodes. This vertical setup has recently gained significant interest in experiment for the design of particularly stable and reproducible devices. We observe that the signals from the molecule in the electronic transmission are overlayed by the signatures of the graphene sheet, thus raising the need for a reinterpretation of the transmission. On the other hand, we see that our results are stable with respect to various defects in the graphene. For weakly physiosorbed molecules, no signs of interaction with the graphene are evident, so the transport properties are determined by offresonant tunnelling between the gold leads across an extended structure that includes the molecule itself and the additional graphene layer. Compared with pure gold electrodes, calculated conductances are about one order of magnitude lower due to the increased tunnelling distance. Relative differences upon changing the end group and the length of the molecule on the other hand, are similar. PMID:26646877

  17. Probing Warm Dense Matter electronic structure using X-ray absorption Near Edge Spectroscopy (XANES)

    NASA Astrophysics Data System (ADS)

    Benuzzi Mounaix, Alessandra

    2011-06-01

    The behavior and physical properties of warm dense matter, fundamental for various branches of physics including planetology and Inertial Confinement Fusion, are non trivial to simulate either theoretically, numerically or experimentally. Despite important progress obtained in the last decade on macroscopic characterization (e.g. equations of state), microscopic studies are today necessary to investigate finely the WDM structure changes, the phase transitions and to test physical hypothesis and approximations commonly used in calculations. In this work, highly compressed aluminum has been investigated with the aim of bringing information on the evolution of its electronic structure by using K-edge shift and XANES. The experiment was performed at LULI laboratory where we used one long pulse (500 ps, IL ~ 8 1013 W/cm2) to create a uniform shock and a second ps beam (IL ~ 1017 W/cm2) to generate an ultra-short broadband X-ray source near the Al K-edge. The spectra were registered by using two conical KAP Bragg crystals. The main target was designed to probe the Aluminum in reshocked conditions allowing us to probe and to test theories in an extreme regime up to now unexplored (ρ ~ 3 ρ0 and T ~ 8 eV). The hydrodynamical Al conditions were measured by using VISARs interferometers and self-emission diagnostics. By increasing the delay between the two beams, we have been able to observe the modification of absorption spectra for unloading Al conditions (ρ >= 0.5 g/cc), and to put in evidence the relocalization of the 3p valence electrons occurring in the metal-non metal transition. All data have been compared to ab initio and dense plasma calculations.

  18. Theory of the electronic states and absorption spectrum of the LiCl:Ag+ impurity system

    NASA Astrophysics Data System (ADS)

    Jackson, Koblar A.; Lin, Chun C.

    1990-01-01

    The impurity absorption spectra of Ag+ and Cu+ impurities in alkali halide hosts show characteristically different features, despite the similar nature of the corresponding free ions. We use the self-interaction-corrected local-spin-density (SIC-LSD) theory to calculate the electronic structure of the ground state (4d) and the 5s and 5p excited states of the LiCl:Ag+ impurity ion. The method of linear combinations of atomic orbitals is used to determine the wave functions and energy levels. By comparing with previous calculations for LiCl:Cu+, we are able to attribute the differences in the d-->s and d-->p transitions in the ultraviolet spectra of these systems to the increased bonding between host crystal and impurity orbitals in LiCl:Ag+, due to the more extensive nature of the Ag+ 4d orbitals. A modification of the earlier SIC-LSD impurity-crystal procedure is introduced to treat the strongly mixed impurity states.

  19. Electronic structures of silicon monoxide film probed by X-ray absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Baba, Yuji; Sekiguchi, Tetsuhiro; Shimoyama, Iwao; Hirao, Norie

    2013-06-01

    Electronic structures of thin films of silicon monoxides (SiO) deposited on a solid surface have been in-situ investigated by X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS). As a substrate, a highly oriented pyrolytic graphite (HOPG) was used because the hybridization between molecules and substrate can be excluded due to the inertness of the surface. For thin films with less than monolayer, XPS spectrum showed that the binding energy of the Si 1s is located just between those of the elemental silicon (Si0) and SiO2 (Si4 +). The result indicates that the stable divalent silicon surely exists in the deposited SiO layer. For the Si K-edge XAFS spectrum of the SiO thin film, the energy of the core-to-valence resonance peak is also located between those of the elemental silicon (Si0) and SiO2 (Si4 +). The polarization dependence of the Si K-edge XAFS spectra for the SiO film revealed that the SiO molecules are well-ordered and almost perpendicularly oriented on HOPG surface. The XAFS results also support the existence of the silicon divalent states in the deposited SiO films. The obtained well-ordered SiO films with divalent silicon will become an excellent starting material for the synthesis of low-dimensional SiOx films.

  20. Attosecond transient absorption probing of electronic superpositions of bound states in neon. Detection of quantum beats

    DOE PAGESBeta

    Beck, Annelise R; Bernhardt, Birgitta; Warrick, Erika R.; Wu, Mengxi; Chen, Shaohao; Gaarde, Mette B.; Schafer, Kenneth J.; Neumark, Daniel M.; Leone, Stephen R.

    2014-11-07

    Electronic wavepackets composed of multiple bound excited states of atomic neon lying between 19.6 and 21.5 eV are launched using an isolated attosecond pulse. Individual quantum beats of the wavepacket are detected by perturbing the induced polarization of the medium with a time-delayed few-femtosecond near-infrared (NIR) pulse via coupling the individual states to multiple neighboring levels. All of the initially excited states are monitored simultaneously in the attosecond transient absorption spectrum, revealing Lorentzian to Fano lineshape spectral changes as well as quantum beats. The most prominent beating of the several that were observed was in the spin–orbit split 3d absorptionmore » features, which has a 40 femtosecond period that corresponds to the spin–orbit splitting of 0.1 eV. The few-level models and multilevel calculations confirm that the observed magnitude of oscillation depends strongly on the spectral bandwidth and tuning of the NIR pulse and on the location of possible coupling states.« less

  1. Calculations of Electron Transport in Fast Ignition Targets.

    NASA Astrophysics Data System (ADS)

    Town, R. P. J.; Kruer, W. L.; Langdon, A. B.; Lasinski, B. F.; Tabak, M.; Welch, D. R.

    2002-11-01

    A crucial issue for the viability of the fast ignition approach [1] to inertial fusion energy is the transport of the ignition pulse energy from the critical surface to the high-density compressed fuel. For example, the ignition beam energy depends on the cross section area of the electron beam. Experiments of the interaction of short-pulse high intensity lasers with surrogate solid-density thin targets with buried K-α diagnostic layers have shown a fairly well collimated beam although with a larger radius than the laser beam spot [2]. We report on LSP calculations of these experiments. These calculations include the effects of non-normal electron beam injection, an effect previously not included in simulations. The LSP code [3] uses a direct implicit particle-in-cell algorithm in 3 dimensions to solve for the beam particles. The background particles are treated as a fluid. The implications for fast ignition will be discussed. This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract W-7405-ENG-48. [1] M. Tabak, et al, Phys. Plasmas 1, 1626 (1994). [2] J. A. Koch, et al, Phys. Rev. E 65, 016410-1 (2001). [3] D. R. Welch, D. V. Rose, B. V. Oliver, and R. E. Clark, Nucl. Inst. Meth. Phys. Res. A 242, 134 (2001).

  2. Nanoscale electron transport measurements of immobilized cytochrome P450 proteins

    NASA Astrophysics Data System (ADS)

    Bostick, Christopher D.; Flora, Darcy R.; Gannett, Peter M.; Tracy, Timothy S.; Lederman, David

    2015-04-01

    Gold nanopillars, functionalized with an organic self-assembled monolayer, can be used to measure the electrical conductance properties of immobilized proteins without aggregation. Measurements of the conductance of nanopillars with cytochrome P450 2C9 (CYP2C9) proteins using conducting probe atomic force microscopy demonstrate that a correlation exists between the energy barrier height between hopping sites and CYP2C9 metabolic activity. Measurements performed as a function of tip force indicate that, when subjected to a large force, the protein is more stable in the presence of a substrate. This agrees with the hypothesis that substrate entry into the active site helps to stabilize the enzyme. The relative distance between hopping sites also increases with increasing force, possibly because protein functional groups responsible for electron transport (ETp) depend on the structure of the protein. The inhibitor sulfaphenazole, in addition to the previously studied aniline, increased the barrier height for electron transfer and thereby makes CYP2C9 reduction more difficult and inhibits metabolism. This suggests that P450 Type II binders may decrease the ease of ETp processes in the enzyme, in addition to occupying the active site.

  3. Fast electron transport in lower-hybrid current drive

    SciTech Connect

    Kupfer, K.; Bers, A.

    1991-01-01

    We generalize the quasilinear-Fokker-Planck formulation for lower-hybrid current drive to include the wave induced radial transport of fast electrons. Toroidal ray tracing shows that the wave fields in the plasma develop a large poloidal component associated with the upshift in k1l and the filling of the "spectral gap". These fields lead to an enhanced radial E x B drift of resonant electrons. Two types of radial flows are obtained: an outward convective flow driven by the asymmetry in the poloidal wave spectrum, and a diffusive flow proportional to the width of the poloidal spectrum. Simulations of Alcator C and JT60, show that the radial convection velocity has a broad maximum of nearly 1 m/sec and is independent of the amplitude of fields. In both cases, the radial diffusion is found to be highly localized near the magnetic axis. For JT60, the peak of the diffusion profile can be quite large, nearly 1 m2/sec.

  4. Injection, transport, absorption and phosphorescence properties of a series of blue-emitting Ir(III) emitters in OLEDs: a DFT and time-dependent DFT study.

    PubMed

    Li, Xiao-Na; Wu, Zhi-Jian; Si, Zhen-Jun; Zhang, Hong-Jie; Zhou, Liang; Liu, Xiao-Juan

    2009-08-17

    Quantum-chemistry methods were explored to investigate the electronic structures, injection and transport properties, absorption and phosphorescence mechanism of a series of blue-emitting Ir(III) complexes {[(F(2)-ppy)(2)Ir(pta -X/pyN4)], where F(2)-ppy = (2,4-difluoro)phenylpyridine; pta = pyridine-1,2,4-triazole; X = phenyl(1); p-tolyl (2); 2,6-difluororophenyl (3); -CF(3) (4), and pyN4 = pyridine-1,2,4-tetrazolate (5)}, which are used as emitters in organic light-emitting diodes (OLEDs). The mobility of hole and electron were studied computationally based on the Marcus theory. Calculations of Ionization potentials (IPs) and electron affinities (EAs) were used to evaluate the injection abilities of holes and electrons into these complexes. The reasons for the lower EL efficiency and phosphorescence quantum yields in 3-5 than in 1and 2 have been investigated. These new structure-property relationships can guide an improved design and optimization of OLED devices based on blue-emitting phosphorescent Ir(III) complexes. PMID:19591441

  5. Atomistic modeling of electronic structure and transport in disordered nanostructures

    NASA Astrophysics Data System (ADS)

    Kharche, Neerav

    As the Si-CMOS technology approaches the end of the International Technology Roadmap for Semiconductors (ITRS), the semiconductor industry faces a formidable challenge to continue the transistor scaling according to Moore's law. To continue the scaling of classical devices, alternative channel materials such as SiGe, carbon nanotubes, nanowires, and III-V based materials are being investigated along with novel 3D device geometries. Researchers are also investigating radically new quantum computing devices, which are expected to perform calculations faster than the existing classical Si-CMOS based structures. Atomic scale disorders such as interface roughness, alloy randomness, non-uniform strain, and dopant fluctuations are routinely present in the experimental realization of such devices. These disorders now play an increasingly important role in determining the electronic structure and transport properties as device sizes enter the nanometer regime. This work employs the atomistic tight-binding technique, which is ideally suited for modeling systems with local disorders on an atomic scale. High-precision multi-million atom electronic structure calculations of (111) Si surface quantum wells and (100) SiGe/Si/SiGe heterostructure quantum wells are performed to investigate the modulation of valley splitting induced by atomic scale disorders. The calculations presented here resolve the existing discrepancies between theoretically predicted and experimentally measured valley splitting, which is an important design parameter in quantum computing devices. Supercell calculations and the zone-unfolding method are used to compute the bandstructures of inhomogeneous nanowires made of AlGaAs and SiGe and their connection with the transmission coefficients computed using non-equilibrium Green's function method is established. A unified picture of alloy nanowires emerges, in which the nanodevice (transmission) and nanomaterials (bandstructure) viewpoints complement each other

  6. Single and Few Layer Silicene: Structural, Electronic and Transport Properties

    NASA Astrophysics Data System (ADS)

    Carey, J. David; Roome, Nathanael

    Single layer silicene has weaker π bonding that graphene resulting in buckling of the Si atoms in different sub-lattices. Despite the loss of planarity, a linear bandstructure emerges where we find a Fermi velocity of about 5.3 x 105 m/s. Determination of the phonon dispersion characteristics reveals a Γ point optical phonon with an energy of 69 meV and a K point optical phonon with an energy of 62 meV. In graphene these phonons play important role in scattering electrons, and in Raman spectroscopy, but have larger energies of 194 and 166 meV, respectively. The lower phonon energies in silicene, arising from the higher atomic masses, would be expected to scatter carriers efficiently and limit carrier mobility. We have calculated, however, that the electron-optical phonon coupling matrix elements are about a factor of 25 times smaller than in graphene and this important result will help with the further development of silicene based devices due to reduced phonon scattering. The two stable stacking configurations of bilayer silicene, AA and AB, now have to account of the position of the atomic buckling in the two layers, leading to four possible atomic configurations with the buckling between the layers being in- or out-of-phase with each other. We find that in contrast to graphene, the two stable configurations are based on AA type stacking being about 70 meV per atom more stable than AB stacking. The potential for elemental layered materials beyond graphene for device applications will also be discussed. Single and Few Layer Silicene: Structural, Electronic and Transport Properties.

  7. Eicosapentaenoic acid inhibits intestinal β-carotene absorption by downregulation of lipid transporter expression via PPAR-α dependent mechanism.

    PubMed

    Mashurabad, Purna Chandra; Kondaiah, Palsa; Palika, Ravindranadh; Ghosh, Sudip; Nair, Madhavan K; Raghu, Pullakhandam

    2016-01-15

    The involvement of lipid transporters, the scavenger receptor class B, type I (SR-BI) and Niemann-Pick type C1 Like 1 protein (NPC1L1) in carotenoid absorption is demonstrated in intestinal cells and animal models. Dietary ω-3 fatty acids are known to possess antilipidemic properties, which could be mediated by activation of PPAR family transcription factors. The present study was conducted to determine the effect of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), on intestinal β-carotene absorption. β-carotene uptake in Caco-2/TC7 cells was inhibited by EPA (p < 0.01) and PPARα agonist (P < 0.01), but not by DHA, PPARγ or PPARδ agonists. Despite unaltered β-carotene uptake, both DHA and PPARδ agonists inhibited the NPC1L1 expression. Further, EPA also induced the expression of carnitine palmitoyl transferase 1A (CPT1A) expression, a PPARα target gene. Interestingly, EPA induced inhibition of β-carotene uptake and SR B1 expression were abrogated by specific PPARα antagonist, but not by PPARδ antagonist. EPA and PPARα agonist also inhibited the basolateral secretion of β-carotene from Caco-2 cells grown on permeable supports. These results suggest that EPA inhibits intestinal β-carotene absorption by down regulation of SR B1 expression via PPARα dependent mechanism and provide an evidence for dietary modulation of intestinal β-carotene absorption. PMID:26577021

  8. Electronic absorption spectra of U3+ and U4+ in molten LiCl-RbCl eutectic

    NASA Astrophysics Data System (ADS)

    Nagai, T.; Uehara, A.; Fujii, T.; Sato, N.; Yamana, H.

    2010-03-01

    In the non-aqueous reprocessing process of spent nuclear fuels by the pyro-electrochemical method, a spent fuel is dissolved into molten LiCl-KCl and NaCl-CsCl eutectics and dissolved uranium and plutonium are collected as either metal or oxide. However, the binary alkali chloride mixture with the lowest melting point is the LiCl-RbCl eutectic. In this study, electronic absorption spectra of U3+ and U4+ in molten LiCl-RbCl eutectic at various temperatures between 673 and 973 K were measured by the UV/Vis/NIR spectrophotometry. We confirmed that these spectra were similar to those in molten LiCl-KCl and NaCl-CsCl eutectics. The sensitive absorption bands of U4+ in LiCl-RbCl eutectic were found at 22000, 16500, 14900, 8600, and 4950 cm-1. The large absorption bands of U4+ over 25000 cm-1 increased with increasing melt temperature, while absorption peaks at 15500-4000 cm-1 decreased. The large absorption bands of U3+ in LiCl-RbCl eutectic were observed over 14000 cm-1. The sensitive absorption bands of U3+ at Vis/NIR region were found at 13300, 11500-11200, 9800-9400, and 8250 cm-1, and these peaks decreased with increasing temperature.

  9. Tunable Microwave Absorption Frequency by Aspect Ratio of Hollow Polydopamine@α-MnO2 Microspindles Studied by Electron Holography.

    PubMed

    She, Wen; Bi, Han; Wen, Zhiwei; Liu, Qinghe; Zhao, Xuebing; Zhang, Jie; Che, Renchao

    2016-04-20

    A tunable response frequency is highly desirable for practical applications of microwave absorption materials but remains a great challenge. Here, hollow lightweight polydopamine@α-MnO2 microspindles were facilely synthesized with the tunable absorption frequency governed by the aspect ratio. The size of the hard template is a key factor to achieve the unique shape; the polymer layer with uniform thickness plays an important role in obtaining spindles with homogeneous size. With the aspect ratio increasing, the maximum reflection loss, as well as the absorption bandwidth (<-10 dB), increases and then decreases; meanwhile, the microwave absorption band shifts to the low frequency. The optimized aspect ratio of the cavity about the hollow polydopamine@α-MnO2 microspindles is ∼2.8. With 3 mm thickness at 9.7 GHz, the strongest reflection reaches -21.8 dB, and the width of the absorbing band (<-10 dB) is as wide as 3.3 GHz. Via electron holography, it is confirmed that strong charge accumulates around the interface between the polydopamine and α-MnO2 layers, which mainly contributes to the dielectric polarization absorption. This study proposes a reliable strategy to tune the absorption frequency via different aspect ratio polymer@α-MnO2 microspindles. PMID:27027922

  10. Evidence for strong electron correlations in graphene molecular fragments: Theory and experiments on two-photon absorptions

    NASA Astrophysics Data System (ADS)

    Aryanpour, Karan; Roberts, Adam; Sandhu, Arvinder; Shukla, Alok; Mazumdar, Sumit

    2013-03-01

    Historically, the occurrence of the lowest two-photon state below the optical one-photon state in linear polyenes, polyacetylenes and polydiacetylenes provided the strongest evidence for strong electron correlations in these linear π-conjugated systems. We demonstrate similar behavior in several molecular fragments of graphene with D6 h symmetry, theoretically and experimentally. Theoretically, we have calculated one versus two-photon absorptions in coronene, two different hexabenzocoronenes and circumcoronene, within the Pariser-Parr-Pople π-electron Hamiltonian using high order configuration interaction. Experimentally, we have performed z-scan measurements using a white light super-continuum source on coronene and hexa-peri-hexabenzocoronene to determine frequency-dependent two-photon absorption coefficients, for comparison to the ground state absorptions. Excellent agreement between experiment and theory in our work gives strong evidence for significant electron correlations between the π-electrons in the graphene molecular fragments. We particularly benchmark high order electron-hole excitations in graphene fragments as a key element behind the agreement between theory and experiment in this work. We acknowledge NSF-CHE-1151475 grant as our funding source.

  11. Basic concepts of quantum interference and electron transport in single-molecule electronics.

    PubMed

    Lambert, C J

    2015-02-21

    This tutorial outlines the basic theoretical concepts and tools which underpin the fundamentals of phase-coherent electron transport through single molecules. The key quantity of interest is the transmission coefficient T(E), which yields the electrical conductance, current-voltage relations, the thermopower S and the thermoelectric figure of merit ZT of single-molecule devices. Since T(E) is strongly affected by quantum interference (QI), three manifestations of QI in single-molecules are discussed, namely Mach-Zehnder interferometry, Breit-Wigner resonances and Fano resonances. A simple MATLAB code is provided, which allows the novice reader to explore QI in multi-branched structures described by a tight-binding (Hückel) Hamiltonian. More generally, the strengths and limitations of materials-specific transport modelling based on density functional theory are discussed. PMID:25255961

  12. Simulation of electron beam formation and transport in a gas-filled electron-optical system with a plasma emitter

    NASA Astrophysics Data System (ADS)

    Grishkov, A. A.; Kornilov, S. Yu.; Rempe, N. G.; Shidlovskiy, S. V.; Shklyaev, V. A.

    2016-07-01

    The results of computer simulations of the electron-optical system of an electron gun with a plasma emitter are presented. The simulations are performed using the KOBRA3-INP, XOOPIC, and ANSYS codes. The results describe the electron beam formation and transport. The electron trajectories are analyzed. The mechanisms of gas influence on the energy inhomogeneity of the beam and its current in the regions of beam primary formation, acceleration, and transport are described. Recommendations for optimizing the electron-optical system with a plasma emitter are presented.

  13. Optical absorption and radiative heat transport in olivine at high temperature

    NASA Technical Reports Server (NTRS)

    Shankland, T. J.; Nitsan, U.; Duba, A. G.

    1979-01-01

    Results are presented of measurements of the optical absorption spectra (300-8000 nm) of olivine as a function of temperature (300-1700 K) under conditions of controlled and known oxygen fugacity within the stability field of the samples. The absorption spectra are used to calculate the temperature-dependent radiative transfer coefficient of olivine and to numerically study the accuracy of the method. The present absorption measurements in olivine under oxidizing conditions known to be within the olivine stability field indicate that the effective radiative conductivity K(R) is lower than that obtained in previous studies under different experimental conditions. The lower value of K(R) makes it more likely that some of the earth's internal heat is removed by convection and less likely that thermal models involving conduction and radiation alone will satisfactorily explain thermal conditions in the earth's mantle.

  14. Soft x-ray absorption spectroscopy on Co doped ZnO: structural distortions and electronic structure

    NASA Astrophysics Data System (ADS)

    Kowalik, I. A.; Guziewicz, E.; Godlewski, M.; Arvanitis, D.

    2016-05-01

    We present soft x-ray absorption spectra from a series of Co doped ZnO films. We discuss systematic variations of the Co L-edge white line intensity and multiplet features for this series of samples. We document sizeable differences in the electronic state of the Co ionic cores, as well as in the local environment of the host lattice atoms, characterised by means of x-ray absorption spectra at the O K-edge and Zn L-edges. Model calculations allow to correlate the observed effects to small structural distortions of the ZnO lattice.

  15. Electrical transport properties of individual WS2 nanotubes and their dependence on water and oxygen absorption

    NASA Astrophysics Data System (ADS)

    Zhang, Chaoying; Ning, Zhiyuan; Liu, Yang; Xu, Tingting; Guo, Yao; Zak, Alla; Zhang, Zhiyong; Wang, Sheng; Tenne, Reshef; Chen, Qing

    2012-09-01

    The electrical properties of WS2 nanotubes (NTs) were studied through measuring 59 devices. Important electrical parameters, such as the carrier concentration, mobility, and effective barrier height at the contacts, were obtained through fitting experimental non-linear I-V curves using a metal-semiconductor-metal model. The carrier mobility was found to be several orders of magnitude higher than that have been reported previously for WS2 NTs. Water absorption was found to decrease the conductivity and carrier mobility of the NTs, and could be removed when the sample was dried. Oxygen absorption also slightly decreased the conductivity of WS2 NTs.

  16. Electronic defect states at the LaAlO3/SrTiO3 heterointerface revealed by O K-edge X-ray absorption spectroscopy.

    PubMed

    Palina, Natalia; Annadi, Anil; Asmara, Teguh Citra; Diao, Caozheng; Yu, Xiaojiang; Breese, Mark B H; Venkatesan, T; Ariando; Rusydi, Andrivo

    2016-05-18

    Interfaces of two dissimilar complex oxides exhibit exotic physical properties that are absent in their parent compounds. Of particular interest is insulating LaAlO3 films on an insulating SrTiO3 substrate, where transport measurements have shown a metal-insulator transition as a function of LaAlO3 thickness. Their origin has become the subject of intense research, yet a unifying consensus remains elusive. Here, we report evidence for the electronic reconstruction in both insulating and conducting LaAlO3/SrTiO3 heterointerfaces revealed by O K-edge X-ray absorption spectroscopy. For the insulating samples, the O K-edge XAS spectrum exhibits features characteristic of electronically active point defects identified as noninteger valence states of Ti. For conducting samples, a new shape-resonance at ∼540.5 eV, characteristic of molecular-like oxygen (empty O-2p band), is observed. This implies that the concentration of electronic defects has increased in proportion with LaAlO3 thickness. For larger defect concentrations, the electronic defect states are no longer localized at the Ti orbitals and exhibit pronounced O 2p-O 2p character. Our results demonstrate that, above a critical thickness, the delocalization of O 2p electronic states can be linked to the presence of oxygen vacancies and is responsible for the enhancement of conductivity at the oxide heterointerfaces. PMID:27146607

  17. Interplay of metabolism and transport in determining oral drug absorption and gut wall metabolism: a simulation assessment using the "Advanced Dissolution, Absorption, Metabolism (ADAM)" model.

    PubMed

    Darwich, A S; Neuhoff, S; Jamei, M; Rostami-Hodjegan, A

    2010-11-01

    Bioavailability of orally administered drugs can be influenced by a number of factors including release from the formulation, dissolution, stability in the gastrointestinal (GI) environment, permeability through the gut wall and first-pass gut wall and hepatic metabolism. Although there are various enzymes in the gut wall which may contribute to gut first pass metabolism, Cytochrome P450 (CYP) 3A has been shown to play a major role. The efflux transporter P-glycoprotein (P-gp; MDR1/ABCB1) is the most extensively studied drug efflux transporter in the gut and might have a significant role in the regulation of GI absorption. Although not every CYP3A substrate will have a high extent of gut wall first-pass extraction, being a substrate for the enzyme increases the likelihood of a higher first-pass extraction. Similarly, being a P-gp substrate does not necessarily pose a problem with the gut wall absorption however it may reduce bioavailability in some cases (e.g. when drug has low passive permeability). An on-going debate has focused on the issue of the interplay between CYP3A and P-gp such that high affinity to P-gp increases the exposure of drug to CYP3A through repeated cycling via passive diffusion and active efflux, decreasing the fraction of drug that escapes first pass gut metabolism (F(G)). The presence of P-gp in the gut wall and the high affinity of some CYP3A substrates to this transporter are postulated to reduce the potential for saturating the enzymes, thus increasing gut wall first-pass metabolism for compounds which otherwise would have saturated CYP3A. Such inferences are based on assumptions in the modelling of oral drug absorption. These models should be as mechanistic as possible and tractable using available in vitro and in vivo information. We review, through simulation, this subject and examine the interplay between gut wall metabolism and efflux transporters by studying the fraction of dose absorbed into enterocytes (F(a)) and F(G) via

  18. Preparation of andrographolide-loaded solid lipid nanoparticles and their in vitro and in vivo evaluations: characteristics, release, absorption, transports, pharmacokinetics, and antihyperlipidemic activity.

    PubMed

    Yang, Tao; Sheng, Huan-Huan; Feng, Nian-Ping; Wei, Hai; Wang, Zheng-Tao; Wang, Chang-Hong

    2013-12-01

    Andrographolide (AND) is one of diterpenoids separated from Andrographis paniculata with a wide spectrum of biological activities of being anti-inflammatory, anticancer, hepatoprotective, and antihyperlipidemic. But its poor water solubility and instability resulted in lower bioavailability and seriously limited its pharmacological function. In this study, AND-loaded solid lipid nanoparticles (AND-SLNs) were prepared by a high-pressure homogenization method and presented as spherically shaped under transmission electron microscopy with an average diameter of 286.1 nm and zeta potential of -20.8 mV. The average drug-entrapment efficiency and drug loading were 91.00% and 3.49%, respectively. The results indicated that the lower bioavailability of AND is not only because of the poor solubility but also owing to its metabolic instability in intestinal segments. Furthermore, the transport mechanism of AND in Caco-2 cell model is complex in which an active transport carrier (P-glycoprotein) is involved in. The bioavailability and antihyperlipidemic activity of AND were improved by AND-SLNs by increasing the solubility and stability of AND in the intestine and by changing its transport mode in Caco-2 cell. The bioavailability of AND was increased to 241% by AND-SLNs as compared with AND suspension. AND-SLNs would be a promising drug-delivery system to enhance the oral absorption and bioavailability of AND. PMID:24166599

  19. Configuration of the electron transport algorithm of PENELOPE to simulate ion chambers

    NASA Astrophysics Data System (ADS)

    Sempau, J.; Andreo, P.

    2006-07-01

    The stability of the electron transport algorithm implemented in the Monte Carlo code PENELOPE with respect to variations of its step length is analysed in the context of the simulation of ion chambers used in photon and electron dosimetry. More precisely, the degree of violation of the Fano theorem is quantified (to the 0.1% level) as a function of the simulation parameters that determine the step size. To meet the premises of the theorem, we define an infinite graphite phantom with a cavity delimited by two parallel planes (i.e., a slab) and filled with a 'gas' that has the same composition as graphite but a mass density a thousand-fold smaller. The cavity walls and the gas have identical cross sections, including the density effect associated with inelastic collisions. Electrons with initial kinetic energies equal to 0.01, 0.1, 1, 10 or 20 MeV are generated in the wall and in the gas with a uniform intensity per unit mass. Two configurations, motivated by the design of pancake- and thimble-type chambers, are considered, namely, with the initial direction of emission perpendicular or parallel to the gas-wall interface. This version of the Fano test avoids the need of photon regeneration and the calculation of photon energy absorption coefficients, two ingredients that are common to some alternative definitions of equivalent tests. In order to reduce the number of variables in the analysis, a global new simulation parameter, called the speedup parameter (a), is introduced. It is shown that setting a = 0.2, corresponding to values of the usual PENELOPE parameters of C1 = C2 = 0.02 and values of WCC and WCR that depend on the initial and absorption energies, is appropriate for maximum tolerances of the order of 0.2% with respect to an analogue, i.e., interaction-by-interaction, simulation of the same problem. The precise values of WCC and WCR do not seem to be critical to achieve this level of accuracy. The step-size dependence of the absorbed dose is explained in

  20. Comparison between POES energetic electron precipitation observations and riometer absorptions: Implications for determining true precipitation fluxes

    NASA Astrophysics Data System (ADS)

    Rodger, Craig J.; Kavanagh, Andrew J.; Clilverd, Mark A.; Marple, Steve R.

    2013-12-01

    electron precipitation (EEP) impacts the chemistry of the middle atmosphere with growing evidence of coupling to surface temperatures at high latitudes. To better understand this link, it is essential to have realistic observations to properly characterize precipitation and which can be incorporated into chemistry-climate models. The Polar-orbiting Operational Environmental Satellite (POES) detectors measure precipitating particles but only integral fluxes and only in a fraction of the bounce loss cone. Ground-based riometers respond to precipitation from the whole bounce loss cone; they measure the cosmic radio noise absorption (CNA), a qualitative proxy with scant direct information on the energy flux of EEP. POES observations should have a direct relationship with ΔCNA and comparing the two will clarify their utility in studies of atmospheric change. We determined ionospheric changes produced by the EEP measured by the POES spacecraft in ~250 overpasses of an imaging riometer in northern Finland. The ΔCNA modeled from the POES data is 10-15 times less than the observed ΔCNA when the >30 keV flux is reported as <106 cm-2 s-1 sr-1. Above this level, there is relatively good agreement between the space-based and ground-based measurements. The discrepancy occurs mostly during periods of low geomagnetic activity, and we contend that weak diffusion is dominating the pitch angle scattering into the bounce loss cone at these times. A correction to the calculation using measurements of the trapped flux considerably reduces the discrepancy and provides further support to our hypothesis that weak diffusion leads to underestimates of the EEP.