Helium, Iron and Electron Particle Transport and Energy Transport Studies on the TFTR Tokamak
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.
Helium, iron and electron particle transport and energy transport studies on the TFTR tokamak
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.
Electron-tomographic analysis of intraflagellar transport particle trains in situ.
Pigino, Gaia; Geimer, Stefan; Lanzavecchia, Salvatore; Paccagnini, Eugenio; Cantele, Francesca; Diener, Dennis R; Rosenbaum, Joel L; Lupetti, Pietro
2009-10-05
Intraflagellar transport (IFT) is the bidirectional movement of multipolypeptide particles between the ciliary membrane and the axonemal microtubules, and is required for the assembly, maintenance, and sensory function of cilia and flagella. In this paper, we present the first high-resolution ultrastructural analysis of trains of flagellar IFT particles, using transmission electron microscopy and electron-tomographic analysis of sections from flat-embedded Chlamydomonas reinhardtii cells. Using wild-type and mutant cells with defects in IFT, we identified two different types of IFT trains: long, narrow trains responsible for anterograde transport; and short, compact trains underlying retrograde IFT. Both types of trains have characteristic repeats and patterns that vary as one sections longitudinally through the trains of particles. The individual IFT particles are highly complex, bridged to each other and to the outer doublet microtubules, and are closely apposed to the inner surface of the flagellar membrane.
Evaluation of atomic electron binding energies for Monte Carlo particle transport
Pia, Maria Grazia; Batic, Matej; Begalli, Marcia; Kim, Chan Hyeong; Quintieri, Lina; Saracco, Paolo
2011-01-01
A survey of atomic binding energies used by general purpose Monte Carlo systems is reported. Various compilations of these parameters have been evaluated; their accuracy is estimated with respect to experimental data. Their effects on physics quantities relevant to Monte Carlo particle transport are highlighted: X-ray fluorescence emission, electron and proton ionization cross sections, and Doppler broadening in Compton scattering. The effects due to different binding energies are quantified with respect to experimental data. The results of the analysis provide quantitative ground for the selection of binding energies to optimize the accuracy of Monte Carlo simulation in experimental use cases. Recommendations on software design dealing with these parameters and on the improvement of data libraries for Monte Carlo simulation are discussed.
Scoggins, James B.; Knisely, Carleton P.; Magin, Thierry E.
2016-11-01
We propose a unified fluid model for multicomponent plasmas in thermal nonequilibrium accounting for the influence of the electromagnetic field. In a previous work, this model was derived from kinetic theory based on a generalized Chapman-Enskog perturbative solution of the Boltzmann equation, scaled using the ratio of electron to heavy-particle masses. Anisotropic transport properties were derived in terms of bracket integrals. In this work, explicit expressions for asymptotic solutions of the transport properties are derived using a spectral Galerkin projection supplied with Laguerre-Sonine polynomial basis functions, and we analyze the crossed contributions to electron and heavy particle mass and energy fluxes, known as the Kolesnikov effect.
Measurement of electron particle transport coefficients in different operational modes of DIII-D
Baker, D. R.; Wade, M. R.; Jackson, G. L.; Maingi, R.; Stockdale, R. E.; de Grassie, J. S.; Groebner, R. J.; Forest, C. B.; Porter, G. D.; DIII-D Team
1998-04-01
Electron transport coefficients have been obtained for different operational modes on the DIII-D tokamak. The operational modes are: double null diverted (DND) low confinement (L mode), DND high confinement (H mode) without edge localized modes (ELM-free), single null diverted (SND) ELM-free H mode and pumped SND ELMing H mode. Various values of plasma current and safety factor (q) profiles were investigated. For the L mode and ELMing H mode, the coefficients were obtained by a modulated puff of deuterium gas at the edge. For the ELM-free modes, the coefficients were obtained by analysing the temporal evolution of the electron density profile immediately after the L-H transition. The results show clearly that the radial profile of the electron diffusion coefficient depends on the operational mode of DIII-D. The difference in the radial dependences of the transport coefficients between the different tokamak operational modes is significant. In the L mode and the ELMing H mode, the diffusion coefficient increases with radius. In ELMing H mode, the diffusion coefficient increases with the edge value of q. The value at the edge for L mode is about twice that for ELMing H mode. In ELM-free H mode, the diffusion coefficient decreases rapidly outside a normalized radius of about 0.8. Within the (relatively large) error bars for ELM-free H mode, there is no measurable difference in diffusion coefficient between the DND and SND plasmas.
Croes, Vivien; Lafleur, Trevor; Bonaventura, Zdeněk; Bourdon, Anne; Chabert, Pascal
2017-03-01
In this work we study the electron drift instability in Hall-effect thrusters (HETs) using a 2D electrostatic particle-in-cell (PIC) simulation. The simulation is configured with a Cartesian coordinate system modeling the radial-azimuthal (r{--}θ ) plane for large radius thrusters. A magnetic field, {{B}}0, is aligned along the Oy axis (r direction), a constant applied electric field, {{E}}0, along the Oz axis (perpendicular to the simulation plane), and the {{E}}0× {{B}}0 direction is along the Ox axis (θ direction). Although electron transport can be well described by electron–neutral collisions for low plasma densities, at high densities (similar to those in typical HETs), a strong instability is observed that enhances the electron cross-field mobility; even in the absence of electron–neutral collisions. The instability generates high frequency (of the order of MHz) and short wavelength (of the order of mm) fluctuations in both the azimuthal electric field and charged particle densities, and propagates in the {{E}}0× {{B}}0 direction with a velocity close to the ion sound speed. The correlation between the electric field and density fluctuations (which leads to an enhanced electron–ion friction force) is investigated and shown to be directly responsible for the increased electron transport. Results are compared with a recent kinetic theory, showing good agreement with the instability properties and electron transport.
Cobley, J G
1976-01-01
1. A novel component in the respiratory chain of Nitrobacter winogradskyi was identified. This component absorbs maximally at 552.5 nm when in its reduced form, has an Eo' (pH7.0) value of-110mV and undergoes reduction by a mechanism involving the transfer of a single electron. 2. Degrees of reduction of cytochromes c and a1 in electron-transport (ET) particles were monitored during the course of NO2- oxidation, and the effects of ADP together with Pi, oligomycin and of carbonyl cyanide phenylhydrazone were determined. 3. The influences of ionophorous antibiotics, NH4Cl and cyclohexylamine hydrochloride on the reductions of cytochromes c and a1 by NO2- indicate that the flow of reducing equivalents from cytochrome a1 (+350mV) to cytochrome c (+270mV) is facilitated by deltapsi, the electrical component of the protonmotive force. 4. Cytochromes c and a1 in ET particles are reduced by the non-physiological reductant KBH4 in a manner similar to that observed with the physiological reductant NO2-. 5. To account both for the observed cytochrome reductions and for the translocation of H+ ions which accompanies NO2- oxidation, a mechanism is proposed which involves the transfer of a hydride equivalent (H+ plus 2e) inward across the membrane of the ET particle in response to deltapsi. PMID:182153
Das, B. K., E-mail: bdyt.ds@rediffmail.com; Hazarika, P.; Chakraborty, M. [Centre of Plasma Physics-Institute for Plasma Research, Tepesia-782402, Kamrup, Assam (India); Bandyopadhyay, M., E-mail: mainak@iter-india.org [ITER-India, Institute for Plasma Research, Gandhinagar-382025, Gujarat (India)
2014-07-15
A study on the transport of charged particles across a magnetic filter field has been carried out in a double plasma device (DPD) and presented in this manuscript. The DPD is virtually divided into two parts viz. source and target regions by a transverse magnetic field (TMF) which is constructed by inserting strontium ferrite magnets into two stainless steel rectangular tubes. Plasma electrons are magnetized but ions are unmagnetized inside the TMF region. Negative voltages are applied to the TMF tubes in order to reduce the loss of electrons towards them. Plasma is produced in the source region by filament discharge method and allowed to flow towards the target region through this negatively biased TMF. It is observed that in the target region, plasma density can be increased and electron temperature decreased with the help of negatively biased TMF. This observation is beneficial for negative ion source development. Plasma diffusion across the negatively biased TMF follows Bohm or anomalous diffusion process when negative bias voltage is very less. At higher negative bias, diffusion coefficient starts deviating from the Bohm diffusion value, associated with enhanced plasma flow in the target region.
Fukuhara, M., E-mail: fukuhara@niche.tohoku.ac.jp [New Industry Creation Hatchery Center, Tohoku University, Sendai 980-8579 (Japan); Kawarada, H. [Research and Development Center, Waseda University, Tokyo 162-0041 (Japan)
2015-02-28
The realization of room-temperature macroscopic field effect transistors (FETs) will lead to new epoch-making possibilities for electronic applications. The I{sub d}-V{sub g} characteristics of the millimeter-sized aluminum-oxide amorphous alloy (Ni{sub 0.36}Nb{sub 0.24}Zr{sub 0.40}){sub 90}H{sub 10} FETs were measured at a gate-drain bias voltage of 0–60 μV in nonmagnetic conditions and under a magnetic fields at room temperature. Application of dc voltages to the gate electrode resulted in the transistor exhibiting one-electron Coulomb oscillation with a period of 0.28 mV, Fabry-Perot interference with a period of 2.35 μV under nonmagnetic conditions, and a Fano effect with a period of 0.26 mV for Vg and 0.2 T under a magnetic field. The realization of a low-energy controllable device made from millimeter-sized Ni-Nb-Zr-H amorphous alloy throws new light on cluster electronics.
Roger Chang
2016-01-01
Full Text Available Owing to its high electron mobility, zinc oxide represents a promising alternative to titanium dioxide as the working electrode material in dye-sensitized solar cells (DSCs. When zinc oxide is grown into 1-D nanowire arrays and incorporated into the working electrode of DSCs, enhanced electron dynamics and even a decoupling of electron transport (τd and electron lifetime (τn have been observed. In this work, DSCs with working electrodes composed of solution-grown, unarrayed ZnO nanorods are investigated. In order to determine whether such devices give rise to similar decoupling, intensity modulated photocurrent and photovoltage spectroscopies are used to measure τd and τn, while varying the illumination intensity. In addition, ZnO nanorod-based DSCs are compared with ZnO nanoparticle-based DSCs and nanomaterial shape is shown to affect electron dynamics. Nanorod-based DSCs exhibit shorter electron transport times, longer electron lifetimes, and a higher τn/τd ratio than nanoparticle-based DSCs.
Transport methods for energetic particles
WuHong－Lu; YangChui－Hsu
1997-01-01
In order to estimate radiation risk assessment for astronaut's radiation safety in space activities.transport codes for high energy particles have been created.Two of the transport methods,perturbation and Green function methods,for high energy particles are reviewed in this paper,and some of the calculated results with the perturbation method are presented.Finally,the low energy transport in the regard of the biological effects by low energy ions in also briefly discussed.
Quadrupole Induced Resonant Particle Transport
Gilson, Erik; Fajans, Joel
1999-11-01
We have performed experiments that explore the effects of a magnetic quadrupole field on a pure electron plasma confined in a Malmberg-Penning trap. A model that we have developed describes the shape of the plasma and shows that a certain class of resonant particles follows trajectories that take them out of the plasma. Even though the quadrupole field destroys the cylindrical symmetry of the system, our theory predicts that if the electrons are off resonance, then the lifetime of the plasma will not be greatly affected by the quadrupole field. Our preliminary experimental results show that the shape of the plasma and the plasma lifetime agree with our model. We are investigating the scaling of this behavior with various experimental parameters such as the plasma length, density, and strength of the quadrupole field. In addition to being an example of resonant particle transport, this effect may find practical applications in experiments that plan to use magnetic quadrupole neutral atom traps to confine anti-hydrogen created in double-well positron/anti-proton Malmberg-Penning traps. (ATHENA Collaboration.)
Croes, Vivien; Lafleur, Trevor; Bonaventura, Zdenek; Péchereau, François; Bourdon, Anne; Chabert, Pascal
2016-09-01
This work studies the electron-cyclotron instability in Hall-Effect Thrusters (HETs) using a 2D Particle-In-Cell (PIC) simulation. The simulation is configured with a Cartesian coordinate system where a magnetic field, B0, is aligned along the X-axis (radial direction, including absorbing walls), a constant electric field, E0, along the Z-axis (axial direction, perpendicular to simulation plane), and the E0xB0 direction along the Y-axis (O direction, with periodic boundaries). Although for low plasma densities classical electron-neutral collisions theory describes well electron transport, at sufficiently high densities (as measured in HETs) a strong instability can be observed that enhances the electron mobility, even in the absence of collisions. The instability generates high frequency ( MHz) and short wavelength ( mm) fluctuations in both the electric field and charged particle densities. We investigate the correlation between these fluctuations and their role with anomalous electron transport; complementing previous 1D simulations. Plasma is self-consistently heated by the instability, but since the latter does not reach saturation in an infinitely long 2D system, saturation is achieved through implementation of a finite axial length that models convection in E0 direction. With support of Safran Aircraft Engines.
Santos-Costa, D.; Hill, T. W.; Johnson, R. E.; Rymer, A.; Paty, P. S.; Coates, A. J.; Young, D. T.; Bolton, S. J.; Menietti, J. D.; Dougherty, M.
2007-12-01
Our first analysis of electron populations using a diffusion theory model allowed the discussion of plasma production and its distribution in Saturn's inner magnetosphere. Our results in modeling the interactions between low-energy electrons and different components of the Kronian system (satellites, dust, and neutral clouds) showed that 1) part of the cold plasma observed by the Cassini Plasma Spectrometer is produced during the impact-ionization of neutrals, and 2) during such a process, the hot component of the electron populations is redistributed along the field lines. Our primary result was then the theoretical demonstration that the impact- ionization process contributes to the `bimodal' energy distributions and `butterfly' pitch-angle distributions. We now present our recent investigation of the sources, sinks and transports of electron plasma populations obtained by combining CAPS-ELS data with our physical particle transport model. We will focus on presenting our results for the period where Cassini was orbiting near the equatorial plane (from late 2005 to early 2006). Plasma data will be used for constraining our modeling, and assisting with the validation of our new simulations. Interaction with neutrals will be studied in the purpose of analyzing the various Saturnian plasma domains. We will also reexamine the diffusive radial transport by discussing magnetospheric processes susceptible to drive inward transport and outward plasma flow.
Improved electron transport layer
2012-01-01
The present invention provides: a method of preparing a coating ink for forming a zinc oxide electron transport layer, comprising mixing zinc acetate and a wetting agent in water or methanol; a coating ink comprising zinc acetate and a wetting agent in aqueous solution or methanolic solution...
Single particle electron microscopy
Boekema, Egbert J.; Folea, Mihaela; Kouril, Roman; Kouřil, Roman
2009-01-01
Electron microscopy (EM) in combination with image analysis is a powerful technique to study protein structures at low, medium, and high resolution. Since electron micrographs of biological objects are very noisy, improvement of the signal-to-noise ratio by image processing is an integral part of EM
Yan, Qiang; Shao, Lin
2017-03-01
Current popular Monte Carlo simulation codes for simulating electron bombardment in solids focus primarily on electron trajectories, instead of electron-induced displacements. Here we report a Monte Carol simulation code, DEEPER (damage creation and particle transport in matter), developed for calculating 3-D distributions of displacements produced by electrons of incident energies up to 900 MeV. Electron elastic scattering is calculated by using full-Mott cross sections for high accuracy, and primary-knock-on-atoms (PKAs)-induced damage cascades are modeled using ZBL potential. We compare and show large differences in 3-D distributions of displacements and electrons in electron-irradiated Fe. The distributions of total displacements are similar to that of PKAs at low electron energies. But they are substantially different for higher energy electrons due to the shifting of PKA energy spectra towards higher energies. The study is important to evaluate electron-induced radiation damage, for the applications using high flux electron beams to intentionally introduce defects and using an electron analysis beam for microstructural characterization of nuclear materials.
Glutamine transport in submitochondrial particles
Sastrasinh, S.; Sastrasinh, M.
1989-12-01
Glutamine transport was studied in submitochondrial particles (SMP) to avoid interference from glutamine metabolism. Phosphate-dependent glutaminase activity in SMP was only 0.04% of that in intact mitochondria. The uptake of glutamine in SMP represented both the transport into vesicles and membrane binding (about one-third of total uptake). Sulfhydryl reagents inhibited glutamine uptake in SMP. The uptake of L-({sup 3}H)glutamine increased more than twofold in SMP preloaded with 1 mM L-glutamine, an effect that was not seen with 1 mM D-glutamine. The uptake of L-({sup 3}H)glutamine was inhibited in the presence of either L-glutamine or L-alanine in the incubation medium. Other amino acids did not inhibit glutamine uptake. Alanine was also shown to trans-stimulate glutamine transport in SMP and cis-inhibit glutamine transport in both SMP and intact mitochondria. Glutamine transport showed a positive cooperativity effect with a Hill coefficient of 1.45. Metabolic acidosis increased the affinity of the transporter for glutamine without any change in other kinetic parameters. These data indicated that mitochondrial glutamine transport occurs via a specific carrier with multiple binding sites and that the transport of glutamine into mitochondria has an important role in increased ammoniagenesis during metabolic acidosis.
Coupled electron-photon radiation transport
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.
Electron transport in molecular junctions
Jin, Chengjun
This thesis addresses the electron transport in molecular junctions, focusing on the energy level alignment and correlation effects. Various levels of theory have been applied to study the structural and electronic effects in different molecular junctions, starting from the single particle density...... charge position are in quantitative agreement with the experiments, while pure DFT is not. This is the consequence of the accurate energy level alignment, where the DFT+∑ method corrects the self-interaction error in the standard DFT functional and uses a static image charge model to include the image...... charge effect on the energy level renormalization. Additionally, the gating of the 4,4’-bipyridine (44BP) molecule contacted to either Ni or Au electrodes has been investigated. Here it is found that the gating mechanism is conceptually different between two cases. In the case of Ni contacts where...
Electron transporting semiconducting polymers in organic electronics.
Zhao, Xingang; Zhan, Xiaowei
2011-07-01
Significant progress has been achieved in the preparation of semiconducting polymers over the past two decades, and successful commercial devices based on them are slowly beginning to enter the market. However, most of the conjugated polymers are hole transporting, or p-type, semiconductors that have seen a dramatic rise in performance over the last decade. Much less attention has been devoted to electron transporting, or n-type, materials that have lagged behind their p-type counterparts. Organic electron transporting materials are essential for the fabrication of organic p-n junctions, organic photovoltaic cells (OPVs), n-channel organic field-effect transistors (OFETs), organic light-emitting diodes (OLEDs) and complementary logic circuits. In this critical review we focus upon recent developments in several classes of electron transporting semiconducting polymers used in OLEDs, OFETs and OPVs, and survey and analyze what is currently known concerning electron transporting semiconductor architecture, electronic structure, and device performance relationships (87 references).
Moscicka, Katarzyna B.; Krupnik, Tomasz; Boekema, Egbert J.; Lolkema, Juke S.; Mościcka, Katarzyna B.
2009-01-01
The structure of three secondary transporter proteins, GltT of Bacillus stearothermophilus, CitS of Klebsiella pneumoniae, and GltS of Escherichia coli, was studied. The proteins were purified to homogeneity ill detergent solution by Ni(2+)-NTA affinity chromatography, and the complexes were determi
Molecular electronic junction transport
Solomon, Gemma C.; Herrmann, Carmen; Ratner, Mark
2012-01-01
Whenasinglemolecule,oracollectionofmolecules,isplacedbetween two electrodes and voltage is applied, one has a molecular transport junction. We discuss such junctions, their properties, their description, and some of their applications. The discussion is qualitative rather than quantitative, and f...
C. Brühl
2008-12-01
Full Text Available The atmospheric chemistry general circulation model ECHAM5/MESSy1 has been extended by processes that parameterize particle precipitation. Several types of particle precipitation that directly affect NOy and HOx concentrations in the middle atmosphere are accounted for and discussed in a series of papers. In the companion paper, the ECHAM5/MESSy1 solar proton event parameterization is discussed, while in the current paper we focus on low energy electrons (LEE that produce NOx in the upper atmosphere. For the flux of LEE NOx into the top of the model domain a novel technique which can be applied to most atmospheric chemistry general circulation models has been developed and is presented here. The technique is particularly useful for models with an upper boundary between the stratopause and mesopause and therefore cannot directly incorporate upper atmospheric NOx production. The additional NOx source parametrization is based on a measure of geomagnetic activity, the Ap index, which has been shown to be a good proxy for LEE NOx interannual variations. HALOE measurements of LEE NOx that has been transported into the stratosphere are used to develop a scaling function which yields a flux of NOx that is applied to the model top. We describe the implementation of the parameterization as the submodel SPACENOX in ECHAM5/MESSy1 and discuss the results from test simulations. The NOx enhancements and associated effects on ozone are shown to be in good agreement with independent measurements. Ap index data is available for almost one century, thus the parameterization is suitable for simulations of the recent climate.
C. Brühl
2009-04-01
Full Text Available The atmospheric chemistry general circulation model ECHAM5/MESSy1 has been extended by processes that parameterise particle precipitation. Several types of particle precipitation that directly affect NOy and HOx concentrations in the middle atmosphere are accounted for and discussed in a series of papers. In the companion paper, the ECHAM5/MESSy1 solar proton event parametrisation is discussed, while in the current paper we focus on low energy electrons (LEE that produce NOx in the upper atmosphere. For the flux of LEE NOx into the top of the model domain a novel technique which can be applied to most atmospheric chemistry general circulation models has been developed and is presented here. The technique is particularly useful for models with an upper boundary between the stratopause and mesopause and therefore cannot directly incorporate upper atmospheric NOx production. The additional NOx source parametrisation is based on a measure of geomagnetic activity, the Ap index, which has been shown to be a good proxy for LEE NOx interannual variations. HALOE measurements of LEE NOx that has been transported into the stratosphere are used to develop a scaling function which yields a flux of NOx that is applied to the model top. We describe the implementation of the parametrisation as the submodel SPACENOX in ECHAM5/MESSy1 and discuss the results from test simulations. The NOx enhancements are shown to be in good agreement with independent measurements. Ap index data is available for almost one century, thus the parametrisation is suitable for simulations of the recent climate.
Electronic transport in nanosystems
Wulf, Ulrich; Racec, E.R.; Racec, P.N.; Aldea, A
2003-12-15
We demonstrate the application of the Landauer-Buettiker formalism (LBF) to MIS (metal-insulator-semiconductor)-type quantum nanostructures and analyze their static and dynamical response properties. For the time-dependent problem, we employ the random phase approximation (RPA) and calculate the irreducible polarization from the one-particle scattering wave functions in the Hartree approximation. For their calculation, we employ the R-matrix approach which we have developed over the past years. We find in the low frequency limit a reasonable agreement with the static Hartree calculations and experimental capacitance data.
Monte Carlo methods for particle transport
Haghighat, Alireza
2015-01-01
The Monte Carlo method has become the de facto standard in radiation transport. Although powerful, if not understood and used appropriately, the method can give misleading results. Monte Carlo Methods for Particle Transport teaches appropriate use of the Monte Carlo method, explaining the method's fundamental concepts as well as its limitations. Concise yet comprehensive, this well-organized text: * Introduces the particle importance equation and its use for variance reduction * Describes general and particle-transport-specific variance reduction techniques * Presents particle transport eigenvalue issues and methodologies to address these issues * Explores advanced formulations based on the author's research activities * Discusses parallel processing concepts and factors affecting parallel performance Featuring illustrative examples, mathematical derivations, computer algorithms, and homework problems, Monte Carlo Methods for Particle Transport provides nuclear engineers and scientists with a practical guide ...
One Dimensional Ballistic Electron Transport
Thomas K J
2009-10-01
Full Text Available Research in low-dimensional semiconductor systems over the last three decades has been largely responsible for the current progress in the areas of nanoscience and nanotechnology. The ability to control and manipulate the size, the carrier density, and the carrier type in two-, one-, and zero- dimensional structures has been widely exploited to study various quantum transport phenomena. In this article, a brief introduction is given to ballistic electron transport in one-dimensional quantum wires.
Transport of energetic particles in the heliosphere
Schreiner, Cedric
2014-07-01
With most of our simulations being numerically very expensive, we were able to run only a few different setups. The overall conclusion we have drawn so far is that our code - or PIC codes in general - is suitable for studies of particle transport characteristics on a microscopic scale. However, simulation runs and physical setups have to be chosen carefully, in order not to waste computing time. We are planning follow-up simulations, which will be run either within our current project pr85li or in a successional project. Especially the above mentioned scenario of electrons scattering off of Whistler modes will be a point of interest, since it is a relevant process in the solar wind. (orig.)
Electronic transport in partially ionized water plasmas
French, Martin; Redmer, Ronald
2017-09-01
We use ab initio simulations based on density functional theory to calculate the electrical and thermal conductivities of electrons in partially ionized water plasmas at densities above 0.1 g/cm3. The resulting conductivity data are then fitted to analytic expressions for convenient application. For low densities, we develop a simple and fully analytic model for electronic transport in low-density plasmas in the chemical picture using the relaxation-time approximation. In doing so, we derive a useful analytic expression for electronic transport cross sections with neutral particles, based on a model potential. In the regime of thermal ionization, electrical conductivities from the analytic model agree with the ab initio data within a factor of 2. Larger deviations are observed for the thermal conductivity, and their origin is discussed. Our results are relevant for modeling the interior and evolution of water-rich planets as well as for technical plasma applications.
Isotope effects on particle transport in the Compact Helical System
Tanaka, K.; Okamura, S.; Minami, T.; Ida, K.; Mikkelsen, D. R.; Osakabe, M.; Yoshimura, Y.; Isobe, M.; Morita, S.; Matsuoka, K.
2016-05-01
The hydrogen isotope effects of particle transport were studied in the hydrogen and deuterium dominant plasmas of the Compact Helical System (CHS). Longer decay time of electron density after the turning-off of the gas puffing was observed in the deuterium dominant plasma suggesting that the recycling was higher and/or the particle confinement was better in the deuterium dominant plasma. Density modulation experiments showed the quantitative difference of the particle transport coefficients. Density was scanned from 0.8 × 1019 m-3 to 4 × 1019 m-3 under the same magnetic field and almost the same heating power. In the low density regime (line averaged density 2.5 × 1019 m-3) no clear difference was observed. This result indicates that the isotope effects of particle transport exist only in the low density regime. Comparison with neoclassical transport coefficients showed that the difference of particle transport is likely to be due to the difference of turbulence driven anomalous transport. Linear character of the ion scale turbulence was studied. The smaller linear growth rate qualitatively agreed with the reduced particle transport in the deuterium dominant plasma of the low density regime.
Ballistic transport and electronic structure
Schep, Kees M.; Kelly, Paul J.; Bauer, Gerrit E.W.
1998-01-01
The role of the electronic structure in determining the transport properties of ballistic point contacts is studied. The conductance in the ballistic regime is related to simple geometrical projections of the Fermi surface. The essential physics is first clarified for simple models. For real
Particle Transport in Parallel-Plate Reactors
Rader, D.J.; Geller, A.S.
1999-08-01
A major cause of semiconductor yield degradation is contaminant particles that deposit on wafers while they reside in processing tools during integrated circuit manufacturing. This report presents numerical models for assessing particle transport and deposition in a parallel-plate geometry characteristic of a wide range of single-wafer processing tools: uniform downward flow exiting a perforated-plate showerhead separated by a gap from a circular wafer resting on a parallel susceptor. Particles are assumed to originate either upstream of the showerhead or from a specified position between the plates. The physical mechanisms controlling particle deposition and transport (inertia, diffusion, fluid drag, and external forces) are reviewed, with an emphasis on conditions encountered in semiconductor process tools (i.e., sub-atmospheric pressures and submicron particles). Isothermal flow is assumed, although small temperature differences are allowed to drive particle thermophoresis. Numerical solutions of the flow field are presented which agree with an analytic, creeping-flow expression for Re < 4. Deposition is quantified by use of a particle collection efficiency, which is defined as the fraction of particles in the reactor that deposit on the wafer. Analytic expressions for collection efficiency are presented for the limiting case where external forces control deposition (i.e., neglecting particle diffusion and inertia). Deposition from simultaneous particle diffusion and external forces is analyzed by an Eulerian formulation; for creeping flow and particles released from a planar trap, the analysis yields an analytic, integral expression for particle deposition based on process and particle properties. Deposition from simultaneous particle inertia and external forces is analyzed by a Lagrangian formulation, which can describe inertia-enhanced deposition resulting from particle acceleration in the showerhead. An approximate analytic expression is derived for particle
Particle transport in density gradient driven TE mode turbulence
Skyman, Andreas; Strand, P I
2011-01-01
The turbulent transport of main ion and trace impurities in a tokamak device in the presence of steep electron density gradients has been studied. The parameters are chosen for trapped electron (TE) mode turbulence, driven primarily by steep electron density gradients relevant to H-mode physics, but with a transition to temperature gradient driven turbulence as the density gradient flattens. Results obtained through non-linear (NL) and quasilinear (QL) gyrokinetic simulations using the GENE code are compared with results obtained from a fluid model. Main ion and impurity transport is studied by examining the balance of convective and diffusive transport, as quantified by the density gradient corresponding to zero particle flux (peaking factor). Scalings are obtained for the impurity peaking with the background electron density gradient and the impurity charge number. It is shown that the impurity peaking factor is weakly dependent on impurity charge and significantly smaller than the driving electron density ...
Zhdanov, V. M.; Stepanenko, A. A.
2016-11-01
The previously obtained in (Zhdanov and Stepanenko, 2016) general transport equations for partially ionized reactive plasma are employed for analysis of electron transport properties in molecular and atomic plasmas. We account for both elastic and inelastic interaction channels of electrons with atoms and molecules of plasma and also the processes of electron impact ionization of neutral particles and three-body ion-electron recombination. The system of scalar transport equations for electrons is discussed and the expressions for non-equilibrium corrections to electron ionization and recombination rates and the diagonal part of the electron pressure tensor are derived. Special attention is paid to analysis of electron energy relaxation during collisions with plasma particles having internal degrees of freedom and the expression for the electron coefficient of inelastic energy losses is deduced. We also derive the expressions for electron vector and tensorial transport fluxes and the corresponding transport coefficients for partially ionized reactive plasma, which represent a generalization of the well-known results obtained by Devoto (1967). The results of numerical evaluation of contribution from electron inelastic collisions with neutral particles to electron transport properties are presented for a series of molecular and atomic gases.
Transport velocities of coal and sand particles
Adanez, J. (Inst. de Carboquimica, Zaragoza (Spain)); Diego, L.F. de (Inst. de Carboquimica, Zaragoza (Spain)); Gayan, P. (Inst. de Carboquimica, Zaragoza (Spain))
1993-10-01
Transport velocities of narrow cut sizes of coarse particles of sand and coal were determined at room temperature and atmospheric pressure. These velocities were obtained by four different methods previously utilized by other authors with fine particles. The four methods tested gave good predictions of the transport velocities. The method based on the measurement of the time required for all the solids to leave the bed without feeding in any fresh solid is specially interesting because of its rapidity and simplicity. The determined transport velocities were strongly dependent on the solid particle size and density. The experimental values were fitted to an equation which fitted both the experimental results obtained in this work and other published results obtained with fine particles. (orig.)
Excess electron transport in cryoobjects
Eshchenko, D G; Brewer, J H; Cottrell, S P; Cox, S F J
2003-01-01
Experimental results on excess electron transport in solid and liquid phases of Ne, Ar, and solid N sub 2 -Ar mixture are presented and compared with those for He. Muon spin relaxation technique in frequently switching electric fields was used to study the phenomenon of delayed muonium formation: excess electrons liberated in the mu sup + ionization track converge upon the positive muons and form Mu (mu sup + e sup -) atoms. This process is shown to be crucially dependent upon the electron's interaction with its environment (i.e., whether it occupies the conduction band or becomes localized in a bubble of tens of angstroms in radius) and upon its mobility in these states. The characteristic lengths involved are 10 sup - sup 6 -10 sup - sup 4 cm, the characteristic times range from nanoseconds to tens microseconds. Such a microscopic length scale sometimes enables the electron spend its entire free lifetime in a state which may not be detected by conventional macroscopic techniques. The electron transport proc...
Particle transport and deposition: basic physics of particle kinetics.
Tsuda, Akira; Henry, Frank S; Butler, James P
2013-10-01
The human body interacts with the environment in many different ways. The lungs interact with the external environment through breathing. The enormously large surface area of the lung with its extremely thin air-blood barrier is exposed to particles suspended in the inhaled air. The particle-lung interaction may cause deleterious effects on health if the inhaled pollutant aerosols are toxic. Conversely, this interaction can be beneficial for disease treatment if the inhaled particles are therapeutic aerosolized drugs. In either case, an accurate estimation of dose and sites of deposition in the respiratory tract is fundamental to understanding subsequent biological response, and the basic physics of particle motion and engineering knowledge needed to understand these subjects is the topic of this article. A large portion of this article deals with three fundamental areas necessary to the understanding of particle transport and deposition in the respiratory tract. These are: (i) the physical characteristics of particles, (ii) particle behavior in gas flow, and (iii) gas-flow patterns in the respiratory tract. Other areas, such as particle transport in the developing lung and in the diseased lung are also considered. The article concludes with a summary and a brief discussion of areas of future research.
Mesoscopic electronics beyond DC transport
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
Electronic transport in unconventional superconductors
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.
Delgado-Aparicio, L F [Johns Hopkins University, Department of Physics and Astronomy, Baltimore, MD 21218 (United States); Stutman, D [Johns Hopkins University, Department of Physics and Astronomy, Baltimore, MD 21218 (United States); Tritz, K [Johns Hopkins University, Department of Physics and Astronomy, Baltimore, MD 21218 (United States); Finkenthal, M [Johns Hopkins University, Department of Physics and Astronomy, Baltimore, MD 21218 (United States); Bell, R [Princeton Plasma Physics Laboratory, Princeton, NJ 08543-0451 (United States); Gates, D [Princeton Plasma Physics Laboratory, Princeton, NJ 08543-0451 (United States); Kaita, R [Princeton Plasma Physics Laboratory, Princeton, NJ 08543-0451 (United States); LeBlanc, B [Princeton Plasma Physics Laboratory, Princeton, NJ 08543-0451 (United States); Maingi, R [Oak Ridge National Laboratory/UT-Battelle, Oak Ridge, TN 37831 (United States); Yuh, H [Nova Photonics, Inc., One Oak Place, Princeton, NJ 08540 (United States); Levinton, F [Nova Photonics, Inc., One Oak Place, Princeton, NJ 08540 (United States); Heidbrink, W [University of California-Irvine, Department of Physics and Astronomy, Irvine, CA 92697 (United States)
2007-08-01
A fast ({<=}0.1 ms) and compact 'multi-colour' soft x-ray array has been developed for time and space-resolved electron temperature (T{sub e}) measurements in magnetically confined fusion (MCF) plasmas. The electron temperature is obtained by modelling the slope of the continuum radiation from ratios of the available 1D-Abel inverted radial emissivity profiles over different energy ranges, with no a priori assumptions of plasma profiles, magnetic field reconstruction constraints or need of shot-to-shot reproducibility. This technique has been used to perform fast T{sub e} measurements in the National Spherical Torus Experiment (NSTX), avoiding the limitations imposed by the well-known multi-point Thompson scattering, electron cyclotron emission and electron Bernstein wave mode conversion diagnostics. The applicability of this 'multi-colour' technique for magnetohydrodynamic (MHD) mode recognition and a variety of perturbative electron and impurity transport studies in MCF plasmas is also discussed. Reconstructed 'multi-colour' emissivity profiles for a variety of NSTX scenarios are presented here for the first time.
Turbulence driven particle transport in Texas Helimak
Toufen, Dennis L; Caldas, Iberê L; Marcus, Francisco A; Gentle, Kenneth W
2011-01-01
We analyze the turbulence driven particle transport in Texas Helimak (K. W. Gentle and Huang He, Plasma Sci. and Technology, 10, 284 (2008)), a toroidal plasma device with one-dimensional equilibrium with magnetic curvature and shear. Alterations on the radial electric field, through an external voltage bias, change spectral plasma characteristics inducing a dominant frequency for negative bias values and a broad band frequency spectrum for positive bias values. For negative biased plasma discharges, the transport is high where the waves propagate with phase velocities near the plasma flow velocity, an indication that the transport is strongly affected by a wave particle resonant interaction. On the other hand, for positive bias the plasma has a reversed shear flow and we observe that the transport is almost zero in the shearless radial region, an evidence of a transport barrier in this region.
Kinetic transport simulation of energetic particles
Sheng, He; Waltz, R. E.
2016-05-01
A kinetic transport code (EPtran) is developed for the transport of the energetic particles (EPs). The EPtran code evolves the EP distribution function in radius, energy, and pitch angle phase space (r, E, λ) to steady state with classical slowing down, pitch angle scattering, as well as radial and energy transport of the injected EPs (neutral beam injection (NBI) or fusion alpha). The EPtran code is illustrated by treating the transport of NBI fast ions from high-n ITG/TEM micro-turbulence and EP driven unstable low-n Alfvén eigenmodes (AEs) in a well-studied DIII-D NBI heated discharge with significant AE central core loss. The kinetic transport code results for this discharge are compared with previous study using a simple EP density moment transport code ALPHA (R.E. Waltz and E.M. Bass 2014 Nucl. Fusion 54 104006). The dominant EP-AE transport is treated with a local stiff critical EP density (or equivalent pressure) gradient radial transport model modified to include energy-dependence and the nonlocal effects EP drift orbits. All previous EP transport models assume that the EP velocity space distribution function is not significantly distorted from the classical ‘no transport’ slowing down distribution. Important transport distortions away from the slowing down EP spectrum are illustrated by a focus on the coefficient of convection: EP energy flux divided by the product of EP average energy and EP particle flux.
Discrete particle simulation of mixed sand transport
Fengjun Xiao; Liejin Guo; Debiao Li; Yueshe Wang
2012-01-01
An Eulerian/Lagrangian numerical simulation is performed on mixed sand transport.Volume averaged Navier-Stokes equations are solved to calculate gas motion,and particle motion is calculated using Newton's equation,involving a hard sphere model to describe particle-to-particle and particle-to-wall collisions.The influence of wall characteristics,size distribution of sand particles and boundary layer depth on vertical distribution of sand mass flux and particle mean horizontal velocity is analyzed,suggesting that all these three factors affect sand transport at different levels.In all cases,for small size groups,sand mass flux first increases with height and then decreases while for large size groups,it decreases exponentially with height and for middle size groups the behavior is in-between.The mean horizontal velocity for all size groups well fits experimental data,that is,increasing logarithmically with height in the middle height region.Wall characteristics greatly affects particle to wall collision and makes the flat bed similar to a Gobi surface and the rough bed similar to a sandy surface.Particle size distribution largely affects the sand mass flux and the highest heights they can reach especially for larger particles.
Particle transport in inclined annuli
Kurtzhals, Erik
1993-12-31
A new model for the formation and behaviour of deposits in inclined wellbores is formulated. The annular space is divided into two layers, separated by a distinct plane boundary. While the lower layer is taken to consist of closely packed cuttings, the upper layer is presumed to behave as a pure fluid. A force balance for the lower layer decides whether it is stationary or slides in the upwards- or downwards direction. The position of the deposit surface is governed by the fluid shear stress at the deposit surface. The proposed model represents a major improvement compared to an earlier model. The predictions from the SCSB-model are in good qualitative agreement with experimental results obtained by the author, and results published by research groups in the U.S.A., United Kingdom and Germany. The quantitative agreement is variable, presumably because the SCSB-model is a somewhat simplified description of particle behaviour in inclined annuli. However, the model provides a clearer understanding of the physical background for previously published experimental results. In order to couple the theoretical work with experimental observations, an annular flow loop has been constructed. A characteristic feature in the flow loop design is the application of load cells, which permits determination of the annular particle content at steady state as well as under transient conditions. Due to delays in the constructional work, it has only been possible to perform a limited number of investigations in the loop. However, the results produced are in agreement with results published by other research groups. (au)
Turbulent transport of alpha particles in tokamak plasmas
Croitoru, A.; Palade, D. I.; Vlad, M.; Spineanu, F.
2017-03-01
We investigate the \\boldsymbol{E}× \\boldsymbol{B} diffusion of fusion born α particles in tokamak plasmas. We determine the transport regimes for a realistic model that has the characteristics of the ion temperature gradient (ITG) or of the trapped electron mode (TEM) driven turbulence. It includes a spectrum of potential fluctuations that is modeled using the results of the numerical simulations, the drift of the potential with the effective diamagnetic velocity and the parallel motion. Our semi-analytical statistical approach is based on the decorrelation trajectory method (DTM), which is adapted to the gyrokinetic approximation. We obtain the transport coefficients as a function of the parameters of the turbulence and of the energy of the α particles. According to our results, significant turbulent transport of the α particles can appear only at energies of the order of 100 KeV. We determine the corresponding conditions.
Electron transport in a methanofullerene
Mihailetchi, V.D.; Duren, J.K.J. van; Blom, P.W.M.; Hummelen, J.C.; Rispens, M.T. [Materials Science Centre, University of Groningen, Nijenborgh 4, NL-9747 AG Groningen (Netherlands); Janssen, R.A.J.; Wienk, M.M. [Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, PO Box 513, NL-5600 MB Eindhoven (Netherlands); Kroon, J.M.; Verhees, W.J.H. [Energy Research Centre of the Netherlands (ECN), Solar Energy, PO Box 1, NL-1755 ZG Petten (Netherlands)
2003-01-01
The current-voltage characteristics of methanofullerene [6,6]-phenyl C{sub 61}-butyric acid methyl ester (PCBM)-based devices are investigated as a function of temperature. The occurrence of space-charge limited current enables a direct determination of the electron mobility. At room temperature, an electron mobility of {mu}{sub e}=2 x 10{sup -7} m{sup 2}V{sup -1}s{sup -1} has been obtained. This electron mobility is more than three orders of magnitude larger than the hole mobility of donor-type conjugated polymer poly(2-methoxy-5-(3',7'-dimethyloctyloxy)-p-phenylene vinylene) (OC{sub 1}C{sub 10}-PPV). As a result, the dark current in PCBM/OC{sub 1}C{sub 10}-PPV based devices is completely dominated by electrons. The observed field and temperature-dependence of the electron mobility of PCBM can be described with a Gaussian disorder model. This provides information about the energetic disorder and average transport-site separation in PCBM. (Abstract Copyright [2003], Wiley Periodicals, Inc.)
Electron Transport in a Methanofullerene
Kroon, J.M.; Verhees, W.J.H. [ECN Solar Energy, Petten (Netherlands); Blom, P.W.M.; Hummelen, J.C.; Mihailetchi, V.D.; Rispens, T. [Materials Science Centre, University of Groningen, Groningen (Netherlands); Van Duren, J.K.J.; Janssen, R.A.J.; Wienk, M.M. [Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, Eindhoven (Netherlands)
2003-01-01
The current-voltage characteristics of methanofullerene [6,6]-phenyl C{sub 61}-butyric acid methyl ester (PCBM)-based devices are investigated as a function of temperature. The occurrence of space-charge limited current enables a direct determination of the electron mobility. At room temperature, an electron mobility of {mu}{sub e} = 2 x 10{sup -7} m{sup 2}V{sup -1}s{sup -1} has been obtained. This electron mobility is more than three orders of magnitude larger than the hole mobility of donor-type conjugated polymer poly(2-methoxy-5-(3',7'-dimethyloctyloxy)-p-phenylene vinylene) (OC{sub 1}C{sub 10}-PPV). As a result, the dark current in PCBM/OC{sub 1}C{sub 10}-PPV based devices is completely dominated by electrons. The observed field and temperature-dependence of the electron mobility of PCBM can be described with a Gaussian disorder model. This provides information about the energetic disorder and average transport-site separation in PCBM.
The energetic alpha particle transport method EATM
Kirkpatrick, R.C.
1998-02-01
The EATM method is an evolving attempt to find an efficient method of treating the transport of energetic charged particles in a dynamic magnetized (MHD) plasma for which the mean free path of the particles and the Larmor radius may be long compared to the gradient lengths in the plasma. The intent is to span the range of parameter space with the efficiency and accuracy thought necessary for experimental analysis and design of magnetized fusion targets.
Krommes, J.A.; Kleva, R.G.; Oberman, C.
1978-05-01
A systematic theory is developed for the computation of electron transport in stochastic magnetic fields. Small scale magnetic perturbations arising, for example, from finite-..beta.. micro-instabilities are assumed to destroy the flux surfaces of a standard tokamak equilibrium. Because the magnetic lines then wander in a volume, electron radial flux is enhanced due to the rapid particle transport along as well as across the lines. By treating the magnetic lines as random variables, it is possible to develop a kinetic equation for the electron distribution function. This is solved approximately to yield the diffusion coefficient.
FLUKA: A Multi-Particle Transport Code
Ferrari, A.; Sala, P.R.; /CERN /INFN, Milan; Fasso, A.; /SLAC; Ranft, J.; /Siegen U.
2005-12-14
This report describes the 2005 version of the Fluka particle transport code. The first part introduces the basic notions, describes the modular structure of the system, and contains an installation and beginner's guide. The second part complements this initial information with details about the various components of Fluka and how to use them. It concludes with a detailed history and bibliography.
Scalable Domain Decomposed Monte Carlo Particle Transport
O' Brien, Matthew Joseph [Univ. of California, Davis, CA (United States)
2013-12-05
In this dissertation, we present the parallel algorithms necessary to run domain decomposed Monte Carlo particle transport on large numbers of processors (millions of processors). Previous algorithms were not scalable, and the parallel overhead became more computationally costly than the numerical simulation.
Electron transport in quantum dots
2003-01-01
When I was contacted by Kluwer Academic Publishers in the Fall of 200 I, inviting me to edit a volume of papers on the issue of electron transport in quantum dots, I was excited by what I saw as an ideal opportunity to provide an overview of a field of research that has made significant contributions in recent years, both to our understanding of fundamental physics, and to the development of novel nanoelectronic technologies. The need for such a volume seemed to be made more pressing by the fact that few comprehensive reviews of this topic have appeared in the literature, in spite of the vast activity in this area over the course of the last decade or so. With this motivation, I set out to try to compile a volume that would fairly reflect the wide range of opinions that has emerged in the study of electron transport in quantum dots. Indeed, there has been no effort on my part to ensure any consistency between the different chapters, since I would prefer that this volume instead serve as a useful forum for the...
Spin dependent electron transport in nanostructures
Yanik, Ahmet Ali
2007-12-01
Spin-electronic devices, exploiting the spin degree of freedom of the current carrying particles, are currently a topic of great interest. In parallel with experimental developments, theoretical studies in this field have been mainly focused on the coherent transport regime characteristics of these devices. However, spin dephasing processes are still a fundamental concern [1-6]. The Landauer transmission formalism has been the widely used method in the coherent transport regime [7]. Recently this formalism has been adapted to incorporate spin scattering processes by introducing random disorder directly into the conducting medium and subsequently solving the disordered transport problem over a large ensemble of disorder distributions [8-10]. Although proposed to be a way of incorporating spin scattering processes, what this approach basically offers is an averaged way of adding random coherent scatterings (similar to the scatterings from boundaries) into the transport problem. Certainly such a treatment of spin-dephasing processes misses the incoherent and inelastic nature of the scattering processes. As a result, a rigorous way of treating the spin scattering processes is still needed [10-12]. The objective of this thesis is to present a quantum transport model based on non-equilibrium Green's function (NEGF) formalism providing a unified approach to incorporate spin scattering processes using generalized interaction Hamiltonians. Here, the NEGF formalism is presented for both coherent and incoherent transport regimes without going into derivational details. Subsequently, spin scattering operators are derived for the specific case of electron-impurity exchange interactions and the model is applied to clarify the experimental measurements [5]. Device characteristics of magnetic tunnel junctions (MTJs) with embedded magnetic impurity layers are studied as a function of tunnel junction thicknesses and barrier heights for varying impurity concentrations in comparison
PREDICTION OF PARTICLE TRANSPORT IN ENCLOSED ENVIRONMENT
Qingyan Chen; Zhao Zhang
2005-01-01
Prediction of particle transport in enclosed environment is crucial to the welfare of its occupants. The prediction requires not only a reliable particle model but also an accurate flow model. This paper introduces two categories of flow models - Reynolds Averaged Navier-Stokes equation modeling (RANS modeling) and Large Eddy Simulation (LES); as well as two popular particle models - Lagrangian and Eulerian methods. The computed distributions of air velocity, air temperature, and tracer-gas concentration in a ventilated room by the RANS modeling and LES agreed reasonably with the experimental data from the literature. The two flow models gave similar prediction accuracy. Both the Lagrangian and Eulerian methods were applied to predict particle transport in a room. Again, the computed results were in reasonable agreement with the experimental data obtained in an environmental chamber. The performance of the two methods was nearly identical. Finally the flow and particle models were applied to study particle dispersion in a Boeing 767 cabin and in a small building with six rooms. The computed results look plausible.
Paleoclassical transport explains electron transport barriers in RTP and TEXTOR
Hogeweij, G. M. D.; Callen, J.D.
2008-01-01
The recently developed paleoclassical transport model sets the minimum level of electron thermal transport in a tokamak. This transport level has proven to be in good agreement with experimental observations in many cases when fluctuation-induced anomalous transport is small, i.e. in (near-) ohmic
Paleoclassical transport explains electron transport barriers in RTP and TEXTOR
Hogeweij, G. M. D.; Callen, J.D.
2008-01-01
The recently developed paleoclassical transport model sets the minimum level of electron thermal transport in a tokamak. This transport level has proven to be in good agreement with experimental observations in many cases when fluctuation-induced anomalous transport is small, i.e. in (near-) ohmic p
Particle Swarm Transport in Fracture Networks
Pyrak-Nolte, L. J.; Mackin, T.; Boomsma, E.
2012-12-01
Colloidal particles of many types occur in fractures in the subsurface as a result of both natural and industrial processes (e.g., environmental influences, synthetic nano- & micro-particles from consumer products, chemical and mechanical erosion of geologic material, proppants used in gas and oil extraction, etc.). The degree of localization and speed of transport of such particles depends on the transport mechanisms, the chemical and physical properties of the particles and the surrounding rock, and the flow path geometry through the fracture. In this study, we investigated the transport of particle swarms through artificial fracture networks. A synthetic fracture network was created using an Objet Eden 350V 3D printer to build a network of fractures. Each fracture in the network had a rectangular cross-sectional area with a constant depth of 7 mm but with widths that ranged from 2 mm to 11 mm. The overall dimensions of the network were 132 mm by 166 mm. The fracture network had 7 ports that were used either as the inlet or outlet for fluid flow through the sample or for introducing a particle swarm. Water flow rates through the fracture were controlled with a syringe pump, and ranged from zero flow to 6 ml/min. Swarms were composed of a dilute suspension (2% by mass) of 3 μm fluorescent polystyrene beads in water. Swarms with volumes of 5, 10, 20, 30 and 60 μl were used and delivered into the network using a second syringe pump. The swarm behavior was imaged using an optical fluorescent imaging system illuminated by green (525 nm) LED arrays and captured by a CCD camera. For fracture networks with quiescent fluids, particle swarms fell under gravity and remained localized within the network. Large swarms (30-60 μl) were observed to bifurcate at shallower depths resulting in a broader dispersal of the particles than for smaller swarm volumes. For all swarm volumes studied, particle swarms tended to bifurcate at the intersection between fractures. These
Charged Particle Energization and Transport in the Magnetotail during Substorms
Pan, Qingjiang
This dissertation addresses the problem of energization of particles (both electrons and ions) to tens and hundreds of keV and the associated transport process in the magnetotail during substorms. Particles energized in the magnetotail are further accelerated to even higher energies (hundreds of keV to MeV) in the radiation belts, causing space weather hazards to human activities in space and on ground. We develop an analytical model to quantitatively estimate flux changes caused by betatron and Fermi acceleration when particles are transported along narrow high-speed flow channels from the magnetotail to the inner magnetosphere. The model shows that energetic particle flux can be significantly enhanced by a modest compression of the magnetic field and/or shrinking of the distance between the magnetic mirror points. We use coordinated spacecraft measurements, global magnetohydrodynamic (MHD) simulations driven by measured upstream solar wind conditions, and large-scale kinetic (LSK) simulations to quantify electron local acceleration in the near-Earth reconnection region and nonlocal acceleration during plasma earthward transport. Compared to the analytical model, application of the LSK simulations is much less restrictive because trajectories of millions of test particles are calculated in the realistically determined global MHD fields and the results are statistical. The simulation results validated by the observations show that electrons following a power law distribution at high energies are generated earthward of the reconnection site, and that the majority of the energetic electrons observed in the inner magnetosphere are caused by adiabatic acceleration in association with magnetic dipolarizations and fast flows during earthward transport. We extend the global MHD+LSK simulations to examine ion energization and compare it with electron energization. The simulations demonstrate that ions in the magnetotail are first nonadiabatically accelerated in the weak
Density Dependence of Particle Transport in ECH Plasmas of the TJ-II Stellarator
Vargas, V. I.; Lopez-Bruna, D.; Guasp, J.; Herranz, J.; Estrada, T.; Medina, F.; Ochando, M.A.; Velasco, J.L.; Reynolds, J.M.; Ferreira, J.A.; Tafalla, D.; Castejon, F.; Salas, A.
2009-05-21
We present the experimental dependence of particle transport on average density in electron cyclotron heated (ECH) hydrogen plasmas of the TJ-II stellarator. The results are based on: (I) electron density and temperature data from Thomson Scattering and reflectometry diagnostics; (II) a transport model that reproduces the particle density profiles in steady state; and (III) Eirene, a code for neutrals transport that calculates the particle source in the plasma from the particle confinement time and the appropriate geometry of the machine/plasma. After estimating an effective particle diffusivity and the particle confinement time, a threshold density separating qualitatively and quantitatively different plasma transport regimes is found. The poor confinement times found below the threshold are coincident with the presence of ECH-induced fast electron losses and a positive radial electric field all over the plasma. (Author) 40 refs.
Inelastic Electron Transport in Monoatomic Wires
ZHANG Jin; CHEN Jing-Zhe; CHEN Qing; REN Shang-Fen; HAN Ru-Shan
2007-01-01
@@ Based on non-equilibrium Green's function theory and density functional theory, we investigate the vibrational property and electron-phonon (el-ph) interaction induced inelastic scattering in electron transport through metallic monoatomic wires.
Particle Simulations of DARHT-II Transport System
Poole, B; Chen, Y J
2001-06-11
The DARHT-II beam line utilizes a fast stripline kicker to temporally chop a high current electron beam from a single induction LINAC and deliver multiple temporal electron beam pulses to an x-ray converter target. High beam quality needs to be maintained throughout the transport line from the end of the accelerator through the final focus lens to the x-ray converter target to produce a high quality radiographic image. Issues that will affect beam quality such as spot size and emittance at the converter target include dynamic effects associated with the stripline kicker as well as emittance growth due to the nonlinear forces associated with the kicker and various focusing elements in the transport line. In addition, dynamic effects associated with transverse resistive wall instability as well as gas focusing will affect the beam transport. A particle-in-cell code is utilized to evaluate beam transport in the downstream transport line in DARHT-II. External focusing forces are included utilizing either analytic expressions or field maps. Models for wakefields from the beam kicker, transverse resistive wall instability, and gas focusing are included in the simulation to provide a more complete picture of beam transport in DARHT-II. From these simulations, for various initial beam loads based on expected accelerator performance the temporally integrated target spot size and emittance can be estimated.
Particle Simulations of DARHT-II Transport System
Poole, B; Chen, Y J
2001-06-11
The DARHT-II beam line utilizes a fast stripline kicker to temporally chop a high current electron beam from a single induction LINAC and deliver multiple temporal electron beam pulses to an x-ray converter target. High beam quality needs to be maintained throughout the transport line from the end of the accelerator through the final focus lens to the x-ray converter target to produce a high quality radiographic image. Issues that will affect beam quality such as spot size and emittance at the converter target include dynamic effects associated with the stripline kicker as well as emittance growth due to the nonlinear forces associated with the kicker and various focusing elements in the transport line. In addition, dynamic effects associated with transverse resistive wall instability as well as gas focusing will affect the beam transport. A particle-in-cell code is utilized to evaluate beam transport in the downstream transport line in DARHT-II. External focusing forces are included utilizing either analytic expressions or field maps. Models for wakefields from the beam kicker, transverse resistive wall instability, and gas focusing are included in the simulation to provide a more complete picture of beam transport in DARHT-II. From these simulations, for various initial beam loads based on expected accelerator performance the temporally integrated target spot size and emittance can be estimated.
Electronically shielded solid state charged particle detector
Balmer, D.K.; Haverty, T.W.; Nordin, C.W.; Tyree, W.H.
1996-08-20
An electronically shielded solid state charged particle detector system having enhanced radio frequency interference immunity includes a detector housing with a detector entrance opening for receiving the charged particles. A charged particle detector having an active surface is disposed within the housing. The active surface faces toward the detector entrance opening for providing electrical signals representative of the received charged particles when the received charged particles are applied to the active surface. A conductive layer is disposed upon the active surface. In a preferred embodiment, a nonconductive layer is disposed between the conductive layer and the active surface. The conductive layer is electrically coupled to the detector housing to provide a substantially continuous conductive electrical shield surrounding the active surface. The inner surface of the detector housing is supplemented with a radio frequency absorbing material such as ferrite. 1 fig.
Electronically shielded solid state charged particle detector
Balmer, David K. (155 Coral Way, Broomfield, CO 80020); Haverty, Thomas W. (1173 Logan, Northglenn, CO 80233); Nordin, Carl W. (7203 W. 32nd Ave., Wheatridge, CO 80033); Tyree, William H. (1977 Senda Rocosa, Boulder, CO 80303)
1996-08-20
An electronically shielded solid state charged particle detector system having enhanced radio frequency interference immunity includes a detector housing with a detector entrance opening for receiving the charged particles. A charged particle detector having an active surface is disposed within the housing. The active surface faces toward the detector entrance opening for providing electrical signals representative of the received charged particles when the received charged particles are applied to the active surface. A conductive layer is disposed upon the active surface. In a preferred embodiment, a nonconductive layer is disposed between the conductive layer and the active surface. The conductive layer is electrically coupled to the detector housing to provide a substantially continuous conductive electrical shield surrounding the active surface. The inner surface of the detector housing is supplemented with a radio frequency absorbing material such as ferrite.
Recent development of organic electron transport materials
无
2003-01-01
This article reviews the recent development of organic electron transport materials applied in the fields of organic photoconductors, light-emitting diodes, field-effect transistors and solar cells. Several technologies for charge carrier mobility measurement are summarized and compared, and a series of basic principles for designing high-performance organic electron transport materials are suggested as well.
Analysis of electron transport in the plasma of thermionic converters
Stoenescu, M.L.; Heinicke, P.H.
1980-03-01
Electron transport coefficients of a gaseous ensemble are expressed analytically as function of density, and are expressed analytically as function of temperature up to an unknown function which has to be evaluated for each specific electron-neutral atom cross section. In order to complete the analytical temperature dependence one may introduce a polynomial expansion of the function or one may derive the temperature dependence of a set of coefficients, numbering thirteen for a third approximation transport evaluation, which completely determine the transport coefficients. The latter approach is used for determining the electron transport coefficients of a cesium plasma for any ion neutral composition and any temperature between 500/sup 0/K and 3500/sup 0/K. The relation between the transport coefficients of a fully and partly ionized gas is readily available and shows that, in the classical formalism, electron-ion and electron-neutral resistivities are not additive. The present form of the transport coefficients makes possible an accurate numerical integration of transport equations eliminating lengthy computations which are frequently inaccessible. It thus provides a detailed knowledge of spatial distribution of particle and energy transport and makes possible the determination of one of the three internal voltage drops, surface barrier, sheath and plasma, which are linked together experimentally by current density versus voltage characteristics of thermionic converters.
Particle transport in microturbulence and acceleration performances of relativistic shocks
Plotnikov, Illya; Lemoine, Martin
2012-01-01
Collisionless relativistic shocks have been the focus of intense theoretical and numerical investigations and these interesting physics have a direct impact on the generation of energetic particles and the interpretation of gamma ray spectra. The Fermi acceleration process that takes place in these shocks is intimately linked with the excitation of micro-turbulence responsible for the shock formation, electron heating and supra-thermal tail generation that in turn excites micro-turbulence, developing thus a self-sustaining phenomenon. In this paper we discuss the development of the micro-turbulence and we investigate two important issues: firstly the transport of supra-thermal particles in the excited microturbulence upstream of the shock and its consequences for the efficiency of the Fermi process; secondly, the preheating process of the incoming background electrons as they cross the shock precursor and experience relativistic oscillations in the electric field of the micro-turbulence.We emphasize the impor...
Nonlinear saturation of trapped electron modes via perpendicular particle diffusion.
Merz, F; Jenko, F
2008-01-25
In magnetized fusion plasmas, trapped electron mode (TEM) turbulence constitutes, together with ion temperature gradient (ITG) turbulence, the dominant source of anomalous transport on ion scales. While ITG modes are known to saturate via nonlinear zonal flow generation, this mechanism is shown to be of little importance for TEM turbulence in the parameter regime explored here. Instead, a careful analysis of the statistical properties of the ExB nonlinearity in the context of gyrokinetic turbulence simulations reveals that perpendicular particle diffusion is the dominant saturation mechanism. These findings allow for the construction of a rather realistic quasilinear model of TEM induced transport.
Measurement of particle transport coefficients on Alcator C-Mod
Luke, T.C.T.
1994-10-01
The goal of this thesis was to study the behavior of the plasma transport during the divertor detachment in order to explain the central electron density rise. The measurement of particle transport coefficients requires sophisticated diagnostic tools. A two color interferometer system was developed and installed on Alcator C-Mod to measure the electron density with high spatial ({approx} 2 cm) and high temporal ({le} 1.0 ms) resolution. The system consists of 10 CO{sub 2} (10.6 {mu}m) and 4 HeNe (.6328 {mu}m) chords that are used to measure the line integrated density to within 0.08 CO{sub 2} degrees or 2.3 {times} 10{sup 16}m{sup {minus}2} theoretically. Using the two color interferometer, a series of gas puffing experiments were conducted. The density was varied above and below the threshold density for detachment at a constant magnetic field and plasma current. Using a gas modulation technique, the particle diffusion, D, and the convective velocity, V, were determined. Profiles were inverted using a SVD inversion and the transport coefficients were extracted with a time regression analysis and a transport simulation analysis. Results from each analysis were in good agreement. Measured profiles of the coefficients increased with the radius and the values were consistent with measurements from other experiments. The values exceeded neoclassical predictions by a factor of 10. The profiles also exhibited an inverse dependence with plasma density. The scaling of both attached and detached plasmas agreed well with this inverse scaling. This result and the lack of change in the energy and impurity transport indicate that there was no change in the underlying transport processes after detachment.
Transport of solar electrons in the turbulent interplanetary magnetic field
Ablaßmayer, J.; Tautz, R. C., E-mail: robert.c.tautz@gmail.com [Zentrum für Astronomie und Astrophysik, Technische Universität Berlin, Hardenbergstraße 36, D-10623 Berlin (Germany); Dresing, N., E-mail: dresing@physik.uni-kiel.de [Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, Leibnizstraße 11, D-24118 Kiel (Germany)
2016-01-15
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.
Study of Electron Transport and Amplification in Diamond
Ben-Zvi, Ilan [Stony Brook Univeristy; Muller, Erik [Stony Brook University
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
Electronic structure and thermoelectric transport of black phosphorus
Craco, L.; Pereira, T. A. da Silva; Leoni, S.
2017-08-01
We investigate anisotropic electronic structure and thermal transport properties of bulk black phosphorus (BP). Using density functional dynamical mean-field theory we first derive a correlation-induced electronic reconstruction, showing band-selective Kondoesque physics in this elemental p -band material. The resulting correlated picture is expected to shed light onto the temperature and doping dependent evolution of resistivity, Seebeck coefficient, and thermal conductivity, as seen in experiments on bulk single crystal BP. Therein, large anisotropic particle-hole excitations are key to consistently understand thermoelectric transport responses of pure and doped BP.
Electron Transport in Quantum Dots and Heat Transport in Molecules
Kirsanskas, Gediminas
Since the invention of the transistor in 1947 and the development of integrated circuits in the late 1950’s, there was a rapid progress in the development and miniaturization of the solid state devices and electronic circuit components. This miniaturization raises a question “How small do we have......, electrically confined electrons in semiconductor nanowires, two dimensional electron gases, carbon nanotubes, or just small metallic particles, nanoscale pieces of semiconductor....
Ion age transport: developing devices beyond electronics
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
Walsh, Jonathan A., E-mail: walshjon@mit.edu [Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, 24-107, Cambridge, MA 02139 (United States); Palmer, Todd S. [Department of Nuclear Engineering and Radiation Health Physics, Oregon State University, 116 Radiation Center, Corvallis, OR 97331 (United States); Urbatsch, Todd J. [XTD-IDA: Theoretical Design, Integrated Design and Assessment, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)
2015-12-15
Highlights: • Generation of discrete differential scattering angle and energy loss cross sections. • Gauss–Radau quadrature utilizing numerically computed cross section moments. • Development of a charged particle transport capability in the Milagro IMC code. • Integration of cross section generation and charged particle transport capabilities. - Abstract: We investigate a method for numerically generating discrete scattering cross sections for use in charged particle transport simulations. We describe the cross section generation procedure and compare it to existing methods used to obtain discrete cross sections. The numerical approach presented here is generalized to allow greater flexibility in choosing a cross section model from which to derive discrete values. Cross section data computed with this method compare favorably with discrete data generated with an existing method. Additionally, a charged particle transport capability is demonstrated in the time-dependent Implicit Monte Carlo radiative transfer code, Milagro. We verify the implementation of charged particle transport in Milagro with analytic test problems and we compare calculated electron depth–dose profiles with another particle transport code that has a validated electron transport capability. Finally, we investigate the integration of the new discrete cross section generation method with the charged particle transport capability in Milagro.
Speedup of Particle Transport Problems with a Beowulf Cluster
Zhongxiang Zhao
2006-01-01
Full Text Available The MCNP code is a general Monte Carlo N-Particle Transport program that is widely used in health physics, medical physics and nuclear engineering for problems involving neutron, photon and electron transport[1]. However, due to the stochastic nature of the algorithms employed to solve the Boltzmann transport equation, MCNP generally exhibits a slow rate of convergence. In fact, engineers and scientists can quickly identify intractable versions of their most challenging and CPU-intensive problems. For example, despite the latest advancements in personal computers (PCs and quantum leaps in their computational capabilities, an ordinary electron transport problem could require up to several CPU-days or even CPU-weeks on a typical desktop PC of today. One common contemporary approach to help address these performance limitations is by taking advantage of parallel processing. In fact, the very nature of the Monte Carlo approach embedded within MCNP is inherently parallel because, at least in principle, every particle history can potentially be tracked individually in an independent processor. In practice, however, there are many issues that must be confronted to achieve a reasonable level of parallelization. First, of course, a suitable parallel computing platform is required. Next, the computer program itself should exploit parallelism from within by combining such tools as Fortran-90 and PVM, for example. This article describes the installation and performance testing of the latest release of MCNP, Version 5 (MCNP5, compiled with PGI Fortran-90 and with PVM on a recently assembled 22-node Beowulf cluster that is now a dedicated platform for the faculty and students of the University of Cincinnatis Nuclear and Radiological Engineering (UCNRE Program. The performance of a neutron transport problem and that of a more challenging gamma-electron (coupled problem are both highlighted. The results show that the PVM-compiled MCNP5 version with 20 tasks
Transport of particles in an atmospheric turbulent boundary layer
Xiongping Luo; Shiyi Chen
2005-01-01
A program incorporating the parallel code of large eddy simulation (LES) and particle transportation model is developed to simulate the motion of particles in an atmospheric turbulent boundary layer (ATBL). A model of particles of 100-micrometer order coupling with large scale ATBL is proposed. Two typical cases are studied, one focuses on the evolution of particle profile in the ATBL and the landing displacement of particles, whereas the other on the motion of particle stream.
The Electron Transport Chain: An Interactive Simulation
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…
The Electron Transport Chain: An Interactive Simulation
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…
Parallelization of a Monte Carlo particle transport simulation code
Hadjidoukas, P.; Bousis, C.; Emfietzoglou, D.
2010-05-01
We have developed a high performance version of the Monte Carlo particle transport simulation code MC4. The original application code, developed in Visual Basic for Applications (VBA) for Microsoft Excel, was first rewritten in the C programming language for improving code portability. Several pseudo-random number generators have been also integrated and studied. The new MC4 version was then parallelized for shared and distributed-memory multiprocessor systems using the Message Passing Interface. Two parallel pseudo-random number generator libraries (SPRNG and DCMT) have been seamlessly integrated. The performance speedup of parallel MC4 has been studied on a variety of parallel computing architectures including an Intel Xeon server with 4 dual-core processors, a Sun cluster consisting of 16 nodes of 2 dual-core AMD Opteron processors and a 200 dual-processor HP cluster. For large problem size, which is limited only by the physical memory of the multiprocessor server, the speedup results are almost linear on all systems. We have validated the parallel implementation against the serial VBA and C implementations using the same random number generator. Our experimental results on the transport and energy loss of electrons in a water medium show that the serial and parallel codes are equivalent in accuracy. The present improvements allow for studying of higher particle energies with the use of more accurate physical models, and improve statistics as more particles tracks can be simulated in low response time.
Overview of Particle and Heavy Ion Transport Code System PHITS
Sato, Tatsuhiko; Niita, Koji; Matsuda, Norihiro; Hashimoto, Shintaro; Iwamoto, Yosuke; Furuta, Takuya; Noda, Shusaku; Ogawa, Tatsuhiko; Iwase, Hiroshi; Nakashima, Hiroshi; Fukahori, Tokio; Okumura, Keisuke; Kai, Tetsuya; Chiba, Satoshi; Sihver, Lembit
2014-06-01
A general purpose Monte Carlo Particle and Heavy Ion Transport code System, PHITS, is being developed through the collaboration of several institutes in Japan and Europe. The Japan Atomic Energy Agency is responsible for managing the entire project. PHITS can deal with the transport of nearly all particles, including neutrons, protons, heavy ions, photons, and electrons, over wide energy ranges using various nuclear reaction models and data libraries. It is written in Fortran language and can be executed on almost all computers. All components of PHITS such as its source, executable and data-library files are assembled in one package and then distributed to many countries via the Research organization for Information Science and Technology, the Data Bank of the Organization for Economic Co-operation and Development's Nuclear Energy Agency, and the Radiation Safety Information Computational Center. More than 1,000 researchers have been registered as PHITS users, and they apply the code to various research and development fields such as nuclear technology, accelerator design, medical physics, and cosmic-ray research. This paper briefly summarizes the physics models implemented in PHITS, and introduces some important functions useful for specific applications, such as an event generator mode and beam transport functions.
High performance stream computing for particle beam transport simulations
Appleby, R; Bailey, D; Higham, J; Salt, M [School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester, M13 9PL (United Kingdom)], E-mail: Robert.Appleby@manchester.ac.uk, E-mail: David.Bailey-2@manchester.ac.uk
2008-07-15
Understanding modern particle accelerators requires simulating charged particle transport through the machine elements. These simulations can be very time consuming due to the large number of particles and the need to consider many turns of a circular machine. Stream computing offers an attractive way to dramatically improve the performance of such simulations by calculating the simultaneous transport of many particles using dedicated hardware. Modern Graphics Processing Units (GPUs) are powerful and affordable stream computing devices. The results of simulations of particle transport through the booster-to-storage-ring transfer line of the DIAMOND synchrotron light source using an NVidia GeForce 7900 GPU are compared to the standard transport code MAD. It is found that particle transport calculations are suitable for stream processing and large performance increases are possible. The accuracy and potential speed gains are compared and the prospects for future work in the area are discussed.
High performance stream computing for particle beam transport simulations
Appleby, R.; Bailey, D.; Higham, J.; Salt, M.
2008-07-01
Understanding modern particle accelerators requires simulating charged particle transport through the machine elements. These simulations can be very time consuming due to the large number of particles and the need to consider many turns of a circular machine. Stream computing offers an attractive way to dramatically improve the performance of such simulations by calculating the simultaneous transport of many particles using dedicated hardware. Modern Graphics Processing Units (GPUs) are powerful and affordable stream computing devices. The results of simulations of particle transport through the booster-to-storage-ring transfer line of the DIAMOND synchrotron light source using an NVidia GeForce 7900 GPU are compared to the standard transport code MAD. It is found that particle transport calculations are suitable for stream processing and large performance increases are possible. The accuracy and potential speed gains are compared and the prospects for future work in the area are discussed.
Peristaltic particle transport using the Lattice Boltzmann method
Connington, Kevin William [Los Alamos National Laboratory; Kang, Qinjun [Los Alamos National Laboratory; Viswanathan, Hari S [Los Alamos National Laboratory; Abdel-fattah, Amr [Los Alamos National Laboratory; Chen, Shiyi [JOHNS HOPKINS UNIV.
2009-01-01
Peristaltic transport refers to a class of internal fluid flows where the periodic deformation of flexible containing walls elicits a non-negligible fluid motion. It is a mechanism used to transport fluid and immersed solid particles in a tube or channel when it is ineffective or impossible to impose a favorable pressure gradient or desirous to avoid contact between the transported mixture and mechanical moving parts. Peristaltic transport occurs in many physiological situations and has myriad industrial applications. We focus our study on the peristaltic transport of a macroscopic particle in a two-dimensional channel using the lattice Boltzmann method. We systematically investigate the effect of variation of the relevant dimensionless parameters of the system on the particle transport. We find, among other results, a case where an increase in Reynolds number can actually lead to a slight increase in particle transport, and a case where, as the wall deformation increases, the motion of the particle becomes non-negative only. We examine the particle behavior when the system exhibits the peculiar phenomenon of fluid trapping. Under these circumstances, the particle may itself become trapped where it is subsequently transported at the wave speed, which is the maximum possible transport in the absence of a favorable pressure gradient. Finally, we analyze how the particle presence affects stress, pressure, and dissipation in the fluid in hopes of determining preferred working conditions for peristaltic transport of shear-sensitive particles. We find that the levels of shear stress are most hazardous near the throat of the channel. We advise that shear-sensitive particles should be transported under conditions where trapping occurs as the particle is typically situated in a region of innocuous shear stress levels.
Wang, G. Q.; Ma, J. [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China); Centre for Magnetic Fusion Theory, Chinese Academy of Sciences, Hefei 230031 (China); Weiland, J.; Zang, Q. [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China)
2013-10-15
We have made the first drift wave study of particle transport in the Experimental Advanced Superconducting Tokamak (Wan et al., Nucl. Fusion 49, 104011 (2009)). The results reveal that collisions make the particle flux more inward in the high collisionality regime. This can be traced back to effects that are quadratic in the collision frequency. The particle pinch is due to electron trapping which is not very efficient in the high collisionality regime so the approach to equilibrium is slow. We have included also the electron temperature gradient (ETG) mode to give the right electron temperature gradient, since the Trapped Electron Mode (TE mode) is weak in this regime. However, at the ETG mode number ions are Boltzmann distributed so the ETG mode does not give particle transport.
Microfabricated high-throughput electronic particle detector
Wood, D. K.; Requa, M. V.; Cleland, A. N.
2007-10-01
We describe the design, fabrication, and use of a radio frequency reflectometer integrated with a microfluidic system, applied to the very high-throughput measurement of micron-scale particles, passing in a microfluidic channel through the sensor region. The device operates as a microfabricated Coulter counter [U.S. Patent No. 2656508 (1953)], similar to a design we have described previously, but here with significantly improved electrode geometry as well as including electronic tuning of the reflectometer; the two improvements yielding an improvement by more than a factor of 10 in the signal to noise and in the diametric discrimination of single particles. We demonstrate the high-throughput discrimination of polystyrene beads with diameters in the 4-10μm range, achieving diametric resolutions comparable to the intrinsic spread of diameters in the bead distribution, at rates in excess of 15×106beads/h.
Transport of active ellipsoidal particles in ratchet potentials
Ai, Bao-Quan, E-mail: aibq@scnu.edu.cn; Wu, Jian-Chun [Laboratory of Quantum Engineering and Quantum Materials, School of Physics and Telecommunication Engineering, South China Normal University, 510006 Guangzhou (China)
2014-03-07
Rectified transport of active ellipsoidal particles is numerically investigated in a two-dimensional asymmetric potential. The out-of-equilibrium condition for the active particle is an intrinsic property, which can break thermodynamical equilibrium and induce the directed transport. It is found that the perfect sphere particle can facilitate the rectification, while the needlelike particle destroys the directed transport. There exist optimized values of the parameters (the self-propelled velocity, the torque acting on the body) at which the average velocity takes its maximal value. For the ellipsoidal particle with not large asymmetric parameter, the average velocity decreases with increasing the rotational diffusion rate, while for the needlelike particle (very large asymmetric parameter), the average velocity is a peaked function of the rotational diffusion rate. By introducing a finite load, particles with different shapes (or different self-propelled velocities) will move to the opposite directions, which is able to separate particles of different shapes (or different self-propelled velocities)
Entropic Ratchet transport of interacting active Brownian particles
Ai, Bao-Quan, E-mail: aibq@hotmail.com [Laboratory of Quantum Engineering and Quantum Materials, School of Physics and Telecommunication Engineering, South China Normal University, 510006 Guangzhou (China); He, Ya-Feng [College of Physics Science and Technology, Hebei University, 071002 Baoding (China); Zhong, Wei-Rong, E-mail: wrzhong@jnu.edu.cn [Department of Physics and Siyuan Laboratory, College of Science and Engineering, Jinan University, 510632 Guangzhou (China)
2014-11-21
Directed transport of interacting active (self-propelled) Brownian particles is numerically investigated in confined geometries (entropic barriers). The self-propelled velocity can break thermodynamical equilibrium and induce the directed transport. It is found that the interaction between active particles can greatly affect the ratchet transport. For attractive particles, on increasing the interaction strength, the average velocity first decreases to its minima, then increases, and finally decreases to zero. For repulsive particles, when the interaction is very weak, there exists a critical interaction at which the average velocity is minimal, nearly tends to zero, however, for the strong interaction, the average velocity is independent of the interaction.
Electron transport through monovalent atomic wires
Lee, Y. J.; Brandbyge, Mads; Puska, M. J.
2004-01-01
Using a first-principles density-functional method we model electron transport through linear chains of monovalent atoms between two bulk electrodes. For noble-metal chains the transport resembles that for free electrons over a potential barrier whereas for alkali-metal chains resonance states...... at the chain determine the conductance. As a result, the conductance for noble-metal chains is close to one quantum of conductance, and it oscillates moderately so that an even number of chain atoms yields a higher value than an odd number. The conductance oscillations are large for alkali-metal chains...
Filamentous bacteria transport electrons over centimetre distances
Pfeffer, Christian; Larsen, Steffen; Song, Jie
2012-01-01
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......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......, electrical cables add a new dimension to the understanding of interactions in nature and may find use in technology development....
Mitochondrial Electron Transport and Plant Stress
Rasmusson, Allan G; Møller, Ian Max
2011-01-01
for metabolic pathways, which allow a wide range of adjustments of metabolic processes in response to environmental variations. Many of the metabolic pathways in plants involve the processing of redox compounds and the use of adenylates. They converge at the mitochondrial electron transport chain (ETC) where...... therefore give a great flexibility in the type and origin of the substrate, the electron transport route(s) used, and the energy yield. At the same time special reactions, such as ascorbate biosynthesis, can take place. In this way, the mitochondrial ETC can mediate major adjustments in cellular metabolism...
Semiconductor Nanostructures Quantum States and Electronic Transport
Ihn, Thomas
2009-01-01
This textbook describes the physics of semiconductor nanostructures with emphasis on their electronic transport properties. At its heart are five fundamental transport phenomena: quantized conductance, tunnelling transport, the Aharonov-Bohm effect, the quantum Hall effect, and the Coulomb blockade effect. The book starts out with the basics of solid state and semiconductor physics, such as crystal structure, band structure, and effective mass approximation, including spin-orbit interaction effects important for research in semiconductor spintronics. It contains material aspects such as band e
Dynamics and transport of laser-accelerated particle beams
Becker, Stefan
2010-04-19
The subject of this thesis is the investigation and optimization of beam transport elements in the context of the steadily growing field of laser-driven particle acceleration. The first topic is the examination of the free vacuum expansion of an electron beam at high current density. It could be shown that particle tracking codes which are commonly used for the calculation of space charge effects will generate substantial artifacts in the regime considered here. The artifacts occurring hitherto predominantly involve insufficient prerequisites for the Lorentz transformation, the application of inadequate initial conditions and non negligible retardation artifacts. A part of this thesis is dedicated to the development of a calculation approach which uses a more adequate ansatz calculating space charge effects for laser-accelerated electron beams. It can also be used to validate further approaches for the calculation of space charge effects. The next elements considered are miniature magnetic quadrupole devices for the focusing of charged particle beams. General problems involved with their miniaturization concern distorting higher order field components. If these distorting components cannot be controlled, the field of applications is very limited. In this thesis a new method for the characterization and compensation of the distorting components was developed, which might become a standard method when assembling these permanent magnet multipole devices. The newly developed characterization method has been validated at the Mainz Microtron (MAMI) electron accelerator. Now that we can ensure optimum performance, the first application of permanent magnet quadrupole devices in conjunction with laser-accelerated ion beams is presented. The experiment was carried out at the Z-Petawatt laser system at Sandia National Laboratories. A promising application for laser-accelerated electron beams is the FEL in a university-scale size. The first discussion of all relevant aspects
Epitaxial graphene electronic structure and transport
De Heer, Walt A; Berger, Claire; Wu Xiaosong; Sprinkle, Mike; Hu Yike; Ruan Ming; First, Phillip N [School of Physics, Georgia Institute of Technology, Atlanta, GA 30332 (United States); Stroscio, Joseph A [Center for Nanoscale Science and Technology, NIST, Gaithersburg, MD 20899 (United States); Haddon, Robert [Center for Nanoscale Science and Engineering, Departments of Chemistry and Chemical and Environmental Engineering, University of California, Riverside, CA 92521 (United States); Piot, Benjamin; Faugeras, Clement; Potemski, Marek [LNCMI -CNRS, Grenoble, 38042 Cedex 9 (France); Moon, Jeong-Sun, E-mail: walt.deheer@physics.gateh.ed [HRL Laboratories LLC, Malibu, CA 90265 (United States)
2010-09-22
Since its inception in 2001, the science and technology of epitaxial graphene on hexagonal silicon carbide has matured into a major international effort and is poised to become the first carbon electronics platform. A historical perspective is presented and the unique electronic properties of single and multilayered epitaxial graphenes on electronics grade silicon carbide are reviewed. Early results on transport and the field effect in Si-face grown graphene monolayers provided proof-of-principle demonstrations. Besides monolayer epitaxial graphene, attention is given to C-face grown multilayer graphene, which consists of electronically decoupled graphene sheets. Production, structure and electronic structure are reviewed. The electronic properties, interrogated using a wide variety of surface, electrical and optical probes, are discussed. An overview is given of recent developments of several device prototypes including resistance standards based on epitaxial graphene quantum Hall devices and new ultrahigh frequency analogue epitaxial graphene amplifiers.
Bostedt, C; van Buuren, T; Willey, T M; Terminello, L J
2004-09-27
The change in the electronic structure of germanium nanocrystals is investigated as their concentration is increased from non-interacting, individual particles to assembled arrays of particles. The electronic structure of the individual nanoclusters shows clear effects due to quantum confinement which are lost in the concentrated assemblies of bare particles. When the surface of the individual particles is passivated, they retain their quantum confinement properties also upon assembly. These effects are interpreted in terms of a particle - particle interaction model.
Electron transport studies of chemical nanostructures
Liang, Wenjie
2005-11-01
In this thesis, I present electron transport studies of chemical nanostructures: single-walled carbon nanotubes (SWNTs) and single molecules. In chemical nanostructures, coulomb blockade and electronic energy level quantization dominate electron transport properties. High order correlated transport processes also play an important role in those nanostructures that are strongly coupled to electrodes. The electron transport spectra of SWNTs are investigated as a function of coupling strength of nanotube-electrode contacts. Measurements of nanotube devices at different coupling regimes showed distinct transport phenomena, including coulomb charging and electron level quantization, the experimental determination of all Hartree-Fock parameters that govern the electronic structure of metallic nanotubes and the demonstration of Fabry-Perot resonators based on the interference of electron waves. The presence of defects is important in low dimensional materials, for instance 1D SWNTs. A scanned gate microscopy (SGM) is used to locate defect center on SWNTs and study electron resonant scattering by defects. The reflection coefficient at the peak of a scattering resonance is determined to be ˜0.5 at room temperature. An intra-tube quantum-dot device formed by two defects was demonstrated by low-temperature transport measurements. Transport investigation of semiconducting SWNTs transistors shows large hysteresis effect upon gate voltage sweeping, which came from local charge redistribution around semiconducting SWNTs. A nonvolatile charge storage memory operating at room temperature was realized. Single molecule transistors incorporating different molecule (divanadium molecule [(N,N',N ″-trimethyl-1,4,7-triazacyclononane)2V2(CN) 4(mu-C4N4)], ferrocene and nickelocene) molecule, were achieved utilizing electromigration-induced break junction technique. Transport spectrum of divanadium molecules showed strange Kondo resonance where individual divanadium molecule serves as
Synthesis of electrostatic fields for transportation of charged particle beams
Vladimir V. Pavlov
2016-06-01
Full Text Available In this paper, an approach to creating corpuscular-optical devices for transportation and transformation of charged particle beams has been elucidated. These devices are able to optimize and create the most convenient configuration of ionic or electron paths. The approach relies upon the inverse dynamics problem formulated on the basis of the Hamilton-Jacobi equation. The motion in the symmetry plane of a three-dimensional (3D field was considered. The problem was solved by analytical methods. An algorithm for constructing electric fields providing the particle motion on the desired trajectories was described. А key to this algorithm lies with a concept of conformal transformation from the theory of complex-valued function. This procedure was illustrated by examples. Quadratic potential was chosen as a basis. Three functions of conformal transformation were considered, providing the rotation of the focused charged particle beam at a fixed angle, the transformation of divergent flow to parallel one. The calculated two-dimensional potentials were extended into 3D-space by power series expansion on transverse coordinate. Device embodiments were suggested on the basis of the calculated field structures.
Electron transport chains of lactic acid bacteria
Brooijmans, R.J.W.
2008-01-01
Lactic acid bacteria are generally considered facultative anaerobic obligate fermentative bacteria. They are unable to synthesize heme. Some lactic acid bacteria are unable to form menaquinone as well. Both these components are cofactors of respiratory (electron transport) chains of prokaryotic bact
Filamentous bacteria transport electrons over centimetre distances
Pfeffer, Christian; Larsen, Steffen; Song, Jie
2012-01-01
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...
Particle and thermal transport due to drift resistive ballooning modes
Goldstein, T.; Rafiq, T.; Kritz, A. H.; Bateman, G.; Pankin, A. Y.
2009-11-01
The ion-temperature-gradient and trapped electron modes are primary candidates for producing the turbulence that drives anomalous transport in the core of magnetically confined plasmas. The situation at the edge is different. Since the edge plasma is influenced strongly by collisions, it is expected that resistive ballooning modes (RBMs) are an important driver of turbulence in the edge region. In this work, a new advanced RBM model [1] is tested as a function of plasma parameters. In this model, the eigenvalues and eigenvectors are used together with a quasi-linear mixing length estimate to determine fluxes and diffusivities. Particle and thermal transport coefficients are investigated in systematic scans over plasma density, density gradient, electron and ion temperature gradients, magnetic q, collisions, magnetic shear, finite Larmor radius effects, and pressure gradient. In the low temperature plasma region, it is found that RBM diffusivities increase with increasing density gradient, magnetic q, and collisionality.[4pt] [1] T. Rafiq, et al, poster at this APS meeting
Control And Transport Of Intense Electron Beams
Li, H
2004-01-01
The transport of intense beams for advanced accelerator applications with high-intensity beams such as heavy-ion inertial fusion, spallation neutron sources, and intense light sources requires tight control of beam characteristics over long distances. The University of Maryland Electron Ring (UMER), which uses low energy, high current electron beams to model the transport physics of intense space-charge-dominated beams, employs real-time beam characterization and control in order to optimize beam quality throughout the strong focusing lattice. We describe in this dissertation the main beam control techniques used in UMER, which include optimal beam steering by quadrupole scans, beam rotation correction using a skew corrector, rms envelope matching and optimization, empirical envelope matching, beam injection, and phase space reconstruction using a tomographic method. Using these control techniques, we achieved the design goals for UMER. The procedure is not only indispensable for optimum beam transport over l...
BITLLES: Electron Transport Simulation with Quantum Trajectories
Albareda, Guillermo; Benali, Abdelilah; Alarcón, Alfonso; Moises, Simeon; Oriols, Xavier
2016-01-01
After the seminal work of R. Landauer in 1957 relating the electrical resistance of a conductor to its scattering properties, much progress has been made in our ability to predict the performance of electron devices in the DC (stationary) regime. Computational tools to describe their dynamical behavior (including the AC, transient and noise performance), however, are far from being as trustworthy as would be desired by the electronic industry. While there is no fundamental limitation to correctly modeling the high-frequency quantum transport and its fluctuations, certainly more careful attention must be paid to delicate issues such as overall charge neutrality, total current conservation, or the back action of the measuring apparatus. In this review, we will show how the core ideas behind the Bohmian formulation of quantum mechanics can be exploited to design an efficient Monte Carlo algorithm that provides a quantitative description of electron transport in open quantum systems. By making the most of traject...
Electron and Phonon Transport in Molecular Junctions
Li, Qian
transmission at the Fermi energy. We propose and analyze a way of using π stacking to design molecular junctions to control heat transport. We develop a simple model system to identify optimal parameter regimes and then use density functional theory (DFT) to extract model parameters for a number of specific....... The system we are interested in here are π-stacked molecules connected with two semi-infinite leads. π-stacked aromatic rings, connected via π-π electronic coupling, provides a rather soft mechanical bridge while maintaining high electronic conductivity. We investigate electron transport...... and the thermoelectric response of five representative π-stacked systems. We find that the transmission and power factor are both enhanced by increasing the conjugation length or adding substituent groups. The local transmission shows that several extra paths are added by cyano groups, which increases the total...
Electronic and transport properties of kinked graphene
Rasmussen, Jesper Toft; Gunst, Tue; Bøggild, Peter
2013-01-01
Local curvature, or bending, of a graphene sheet is known to increase the chemical reactivity presenting an opportunity for templated chemical functionalisation. Using first-principles calculations based on density functional theory (DFT), we investigate the reaction barrier reduction...... for the adsorption of atomic hydrogen at linear bends in graphene. We find a significant barrier lowering (≈15%) for realistic radii of curvature (≈20 Å) and that adsorption along the linear bend leads to a stable linear kink. We compute the electronic transport properties of individual and multiple kink lines......, and demonstrate how these act as efficient barriers for electron transport. In particular, two parallel kink lines form a graphene pseudo-nanoribbon structure with a semimetallic/semiconducting electronic structure closely related to the corresponding isolated ribbons; the ribbon band gap translates...
High energy electromagnetic particle transportation on the GPU
Canal, P.; Elvira, D.; Jun, S. Y.; Kowalkowski, J.; Paterno, M.; Apostolakis, J.
2014-06-01
We present massively parallel high energy electromagnetic particle transportation through a finely segmented detector on a Graphics Processing Unit (GPU). Simulating events of energetic particle decay in a general-purpose high energy physics (HEP) detector requires intensive computing resources, due to the complexity of the geometry as well as physics processes applied to particles copiously produced by primary collisions and secondary interactions. The recent advent of hardware architectures of many-core or accelerated processors provides the variety of concurrent programming models applicable not only for the high performance parallel computing, but also for the conventional computing intensive application such as the HEP detector simulation. The components of our prototype are a transportation process under a non-uniform magnetic field, geometry navigation with a set of solid shapes and materials, electromagnetic physics processes for electrons and photons, and an interface to a framework that dispatches bundles of tracks in a highly vectorized manner optimizing for spatial locality and throughput. Core algorithms and methods are excerpted from the Geant4 toolkit, and are modified and optimized for the GPU application. Program kernels written in C/C++ are designed to be compatible with CUDA and OpenCL and with the aim to be generic enough for easy porting to future programming models and hardware architectures. To improve throughput by overlapping data transfers with kernel execution, multiple CUDA streams are used. Issues with floating point accuracy, random numbers generation, data structure, kernel divergences and register spills are also considered. Performance evaluation for the relative speedup compared to the corresponding sequential execution on CPU is presented as well.
High energy electromagnetic particle transportation on the GPU
Canal, P. [Fermilab; Elvira, D. [Fermilab; Jun, S. Y. [Fermilab; Kowalkowski, J. [Fermilab; Paterno, M. [Fermilab; Apostolakis, J. [CERN
2014-01-01
We present massively parallel high energy electromagnetic particle transportation through a finely segmented detector on a Graphics Processing Unit (GPU). Simulating events of energetic particle decay in a general-purpose high energy physics (HEP) detector requires intensive computing resources, due to the complexity of the geometry as well as physics processes applied to particles copiously produced by primary collisions and secondary interactions. The recent advent of hardware architectures of many-core or accelerated processors provides the variety of concurrent programming models applicable not only for the high performance parallel computing, but also for the conventional computing intensive application such as the HEP detector simulation. The components of our prototype are a transportation process under a non-uniform magnetic field, geometry navigation with a set of solid shapes and materials, electromagnetic physics processes for electrons and photons, and an interface to a framework that dispatches bundles of tracks in a highly vectorized manner optimizing for spatial locality and throughput. Core algorithms and methods are excerpted from the Geant4 toolkit, and are modified and optimized for the GPU application. Program kernels written in C/C++ are designed to be compatible with CUDA and OpenCL and with the aim to be generic enough for easy porting to future programming models and hardware architectures. To improve throughput by overlapping data transfers with kernel execution, multiple CUDA streams are used. Issues with floating point accuracy, random numbers generation, data structure, kernel divergences and register spills are also considered. Performance evaluation for the relative speedup compared to the corresponding sequential execution on CPU is presented as well.
The effects of realistic pancake solenoids on particle transport
Gu, X.; Okamura, M.; Pikin, A.; Fischer, W.; Luo, Y.
2011-02-01
Solenoids are widely used to transport or focus particle beams. Usually, they are assumed as being ideal solenoids with a high axial-symmetry magnetic field. Using the Vector Field Opera program, we modeled asymmetrical solenoids with realistic geometry defects, caused by finite conductor and current jumpers. Their multipole magnetic components were analyzed with the Fourier fit method; we present some possible optimized methods for them. We also discuss the effects of 'realistic' solenoids on low energy particle transport. The finding in this paper may be applicable to some lower energy particle transport system design.
Minimum ionizing particle detection by secondary electron emission
Faivre, J.C.; Fanet, H.; Garin, A.; Robert, J.P.; Rouger, M.; Saudinos, J.
1977-02-01
The use of secondary electron emission to detect high energy particles is investigated. Low density KCl layers have been tested to detect MeV electrons, 400-750 MeV protons and high energy deuterons. The efficiency and the secondary electron spectrum are presented. The results justify the use of low-density KCl layer to detect minimum ionizing particles.
Problems in single-particle dynamics specific to electrons
Renieri, A
1977-01-01
The author investigates the specific problems related to the electron motion in a circular high-energy accelerator. The main difference between electrons and protons (or other heavy particles) is the synchrotron radiation energy loss. This phenomenon is negligible for heavy particles, but not for electrons. (5 refs).
Electron transport in wurtzite InN
F M Abou El-Ela; B M El-Assy
2012-07-01
Using ensemble Monte Carlo simulation technique, we have calculated the transport properties of InN such as the drift velocity, the drift mobility, the average electron, energy relaxation times and momentum relaxation times at high electric ﬁeld. The scattering mechanisms included are polar optical phonon, ionized impurity, acoustic phonon and intervalley phonon. It is found that the maximum peak velocity only occurs when the electric ﬁeld is increased to a value above a certain critical ﬁeld. This critical ﬁeld is strongly dependent on InN parameters. The steady-state transport parameters are in fair agreement with other recent calculations.
Ambipolar transport via trapped-electron whistler instability along open magnetic field lines.
Guo, Zehua; Tang, Xian-Zhu
2012-09-28
An open field line plasma is bounded by a chamber wall which intercepts the magnetic field. Steady state requires an upstream plasma source balancing the particle loss to the boundary. In cases where the electrons have a long mean free path, ambipolarity in parallel transport critically depends on collisionless detrapping of the electrons via wave-particle interaction. The trapped-electron whistler instability, whose nonlinear saturation produces a spectrum of whistler waves that is responsible for the electron detrapping flux, is shown to be an unusually robust kinetic instability, which is essential to the universality of the ambipolar constraint in plasma transport.
Gyrokinetic δ particle simulation of trapped electron mode driven turbulence
Lang, Jianying
2007-11-01
Turbulent transport driven by collisionless trapped electron modes (CTEM) is systematically studied using gyrokinetic delta-f particle-in-cell simulation. Scaling with local plasma parameters, including density gradient, electron temperature gradient, magnetic shear, temperature ratio and aspect ratio, is investigated. Simulation results are compared with previous simulations and theoretical predictions. Nonlinearly the transport level increases with increasing magnetic shear. We explain the nonlinear magnetic shear scaling by differences in the radial correlation lengths caused by toroidal coupling. The turbulence is more radially elongated at higher magnetic shear compared with low magnetic shear. We show that the suppression effect of zonal flow on CTEM transport depends on both the electron temperature gradient and the electron to ion temperature ratio. This helps explain the previous contradictory conclusions on the importance of zonal flows in different parameter regimes.ootnotetextT. Dannert, F. Jenko, Phys. Plasmas 12, 072309 (2005); D. Ernst, et al., Phys. Plasmas 11, 2637 (2004). Zonal flow suppression is consistent with the rate of EXB shearing from the ambient turbulence as well as the radial broadening of the spectra. Strong geodesic acoustic modes (GAMs) are generated along with zonal flows and the frequency of the GAMs agrees well with kinetic theory.ootnotetextT. Watari, et al., Phys. Plasmas 13, 062504 (2006). We further explore the nonlinear saturation mechanism when the zonal flows are not important. We find that when only a single toroidal mode (and its conjugate) is kept, reasonable nonlinear saturation is obtained. Investigating a range of n, modes with larger mode number n saturate at a higher level relative to lower n modes, indicating a turbulent inverse cascade process.
Low energy electron transport in furfural
Lozano, Ana I.; Krupa, Kateryna; Ferreira da Silva, Filipe; Limão-Vieira, Paulo; Blanco, Francisco; Muñoz, Antonio; Jones, Darryl B.; Brunger, Michael J.; García, Gustavo
2017-09-01
We report on an initial investigation into the transport of electrons through a gas cell containing 1 mTorr of gaseous furfural. Results from our Monte Carlo simulation are implicitly checked against those from a corresponding electron transmission measurement. To enable this simulation a self-consistent cross section data base was constructed. This data base is benchmarked through new total cross section measurements which are also described here. In addition, again to facilitate the simulation, our preferred energy loss distribution function is presented and discussed.
Nonlinear electronic transport behavior in Indium Nitride
Rodrigues, Cloves G., E-mail: cloves@pucgoias.edu.br [Departamento de Fisica, Pontificia Universidade Catolica de Goias, CP 86, 74605-010 Goiania, Goias (Brazil)
2012-11-15
A theoretical study on the nonlinear transport of electrons and of the nonequilibrium temperature in n-doped Indium Nitride under influence of moderate to high electric fields (in this nonlinear domain) is presented. It is based on a nonlinear quantum kinetic theory which provides a description of the dissipative phenomena developing in the system. The electric current and the mobility in the steady state are obtained, and their dependence on the electric field strength and on the concentration (that is, a mobility dependent nonlinearly on field and concentration) is obtained and analyzed. -- Highlights: Black-Right-Pointing-Pointer We have reported on the topic of nonlinear transport (electron mobility) in n-doped InN. Black-Right-Pointing-Pointer The results evidence the presence of two distinctive regimes. Black-Right-Pointing-Pointer The dependence of the mobility on the electric field is manifested through of the relaxation times.
Mitochondrial Electron Transport and Plant Stress
Rasmusson, Allan G; Møller, Ian Max
2011-01-01
redox compounds from carbon degradation are used for powering ATP synthesis. The standard ETC contains three sites of energy conservation in complexes I, III, and IV, which are in common with most other eukaryotes. However, the complexity of the plant metabolic system is mirrored in the ETC. In addition...... conservation in the ETC. The alternative oxidase provides a non-energy-conserving alternative to electron transport through complexes III and IV. There also appears to be a special coupling between specific NAD(P)H dehydrogenases and specific members of the alternative oxidase family. These additional enzymes...... therefore give a great flexibility in the type and origin of the substrate, the electron transport route(s) used, and the energy yield. At the same time special reactions, such as ascorbate biosynthesis, can take place. In this way, the mitochondrial ETC can mediate major adjustments in cellular metabolism...
Transport in nanoscale systems: hydrodynamics, turbulence, and local electron heating
di Ventra, Massimiliano
2007-03-01
Transport in nanoscale systems is usually described as an open-boundary scattering problem. This picture, however, says nothing about the dynamical onset of steady states, their microscopic nature, or their dependence on initial conditions [1]. In order to address these issues, I will first describe the dynamical many-particle state via an effective quantum hydrodynamic theory [2]. This approach allows us to predict a series of novel phenomena like turbulence of the electron liquid [2], local electron heating in nanostructures [3], and the effect of electron viscosity on resistance [4]. I will provide both analytical results and numerical examples of first-principles electron dynamics in nanostructures using the above approach. I will also discuss possible experimental tests of our predictions. Work supported in part by NSF and DOE. [1] N. Bushong, N. Sai and M. Di Ventra, ``Approach to steady-state transport in nanoscale systems'' Nano Letters, 5 2569 (2005); M. Di Ventra and T.N. Todorov, ``Transport in nanoscale systems: the microcanonical versus grand-canonical picture,'' J. Phys. Cond. Matt. 16, 8025 (2004). [2] R. D'Agosta and M. Di Ventra, ``Hydrodynamic approach to transport and turbulence in nanoscale conductors,'' cond-mat/05123326; J. Phys. Cond. Matt., in press. [3] R. D'Agosta, N. Sai and M. Di Ventra, ``Local electron heating in nanoscale conductors,'' cond-mat/0605312; Nano Letters, in press. [4] N. Sai, M. Zwolak, G. Vignale and M. Di Ventra, ``Dynamical corrections to the DFT-LDA electron conductance in nanoscale systems,'' Phys. Rev. Lett. 94, 186810 (2005).
Electronic transport in methylated fragments of DNA
Almeida, M. L. de; Oliveira, J. I. N.; Lima Neto, J. X.; Gomes, C. E. M.; Fulco, U. L., E-mail: umbertofulco@gmail.com; Albuquerque, E. L. [Departamento de Biofísica e Farmacologia, Universidade Federal do Rio Grande do Norte, 59072-970 Natal-RN (Brazil); Freire, V. N. [Departamento de Física, Universidade Federal do Ceará, 60455-760 Fortaleza, CE (Brazil); Caetano, E. W. S. [Instituto Federal de Educação, Ciência e Tecnologia do Ceará, 60040-531 Fortaleza, CE (Brazil); Moura, F. A. B. F. de; Lyra, M. L. [Instituto de Física, Universidade Federal de Alagoas, 57072-900 Maceió-AL (Brazil)
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.
Controlled Electronic Transport through Branched Molecular Conductors
2008-01-01
Abstract The conductance through a branched conductor placed between two electrodes is analyzed using the Landauer transport formulation within the framework of the single electron, and the tight binding approximations. Terminal side chains are expressed as self energy terms which map the branched conductor onto an effective linear chain Hamiltonian. The effect of uniform side branches on resonant zero-bias conductance is shown to be analytically solvable and particularly simple, w...
Variables Affecting Two Electron Transport System Assays
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; methan...
Heavy Particle Transport in the Turbulent Boundary Layer
Richter, D. H.
2016-12-01
To describe the emission and transport of dust in the atmosphere, assumptions must typically be made in order to connect the micro-scale emission and saltation process with the larger-scale atmospheric uptake and turbulent flux. In the context of numerical models, this can be thought of as the transport process which occurs between the domain bottom and the first vertical grid point. For example, in the limit of small particles (both low inertia and low settling velocity), theory built upon Monin-Obukhov similarity has proven effective in relating mean dust concentration profiles to surface emission fluxes. For increasing particle mass, however, it becomes more difficult to represent dust transport as a simple extension of the transport of a passive scalar due to issues such as the crossing trajectories effect. This study focuses specifically on the problem of large particle transport and dispersion in the turbulent boundary layer by utilizing direct numerical simulations with Lagrangian point-particle tracking to determine under what, if any, conditions the large particles can be described in a simplified Eulerian framework such as Monin-Obukhov similarity theory. In particular, results will be presented detailing the independent contributions of both particle inertia and particle settling velocity relative to the strength of the surrounding turbulent flow.
Electronic transport properties in graphene oxide frameworks
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.
Spatiotemporal Structure of Aeolian Particle Transport on Flat Surface
Niiya, Hirofumi; Nishimura, Kouichi
2017-05-01
We conduct numerical simulations based on a model of blowing snow to reveal the long-term properties and equilibrium state of aeolian particle transport from 10-5 to 10 m above the flat surface. The numerical results are as follows. (i) Time-series data of particle transport are divided into development, relaxation, and equilibrium phases, which are formed by rapid wind response below 10 cm and gradual wind response above 10 cm. (ii) The particle transport rate at equilibrium is expressed as a power function of friction velocity, and the index of 2.35 implies that most particles are transported by saltation. (iii) The friction velocity below 100 µm remains roughly constant and lower than the fluid threshold at equilibrium. (iv) The mean particle speed above 300 µm is less than the wind speed, whereas that below 300 µm exceeds the wind speed because of descending particles. (v) The particle diameter increases with height in the saltation layer, and the relationship is expressed as a power function. Through comparisons with the previously reported random-flight model, we find a crucial problem that empirical splash functions cannot reproduce particle dynamics at a relatively high wind speed.
Microstripes for transport and separation of magnetic particles
Donolato, Marco; Dalslet, Bjarke Thomas; Hansen, Mikkel Fougt
2012-01-01
We present a simple technique for creating an on-chip magnetic particle conveyor based on exchange-biased permalloy microstripes. The particle transportation relies on an array of stripes with a spacing smaller than their width in conjunction with a periodic sequence of four different externally...
An Optimal Transport Formulation of the Linear Feedback Particle Filter
Taghvaei, Amirhossein; Mehta, Prashant G.
2015-01-01
Feedback particle filter (FPF) is an algorithm to numerically approximate the solution of the nonlinear filtering problem in continuous time. The algorithm implements a feedback control law for a system of particles such that the empirical distribution of particles approximates the posterior distribution. However, it has been noted in the literature that the feedback control law is not unique. To find a unique control law, the filtering task is formulated here as an optimal transportation pro...
Friedel, R. H. W.; Bourdarie, S.; Fennell, J.; Kanekal, S.; Cayton, T. E.
2004-01-01
The highly energetic electron environment in the inner magnetosphere (GEO inward) has received a lot of research attention in resent years, as the dynamics of relativistic electron acceleration and transport are not yet fully understood. These electrons can cause deep dielectric charging in any space hardware in the MEO to GEO region. We use a new and novel approach to obtain a global representation of the inner magnetospheric energetic electron environment, which can reproduce the absolute environment (flux) for any spacecraft orbit in that region to within a factor of 2 for the energy range of 100 KeV to 5 MeV electrons, for any levels of magnetospheric activity. We combine the extensive set of inner magnetospheric energetic electron observations available at Los Alamos with the physics based Salammbo transport code, using the data assimilation technique of "nudging". This in effect input in-situ data into the code and allows the diffusion mechanisms in the code to interpolate the data into regions and times of no data availability. We present here details of the methods used, both in the data assimilation process and in the necessary inter-calibration of the input data used. We will present sample runs of the model/data code and compare the results to test spacecraft data not used in the data assimilation process.
Baräo, Fernando; Nakagawa, Masayuki; Távora, Luis; Vaz, Pedro
2001-01-01
This book focusses on the state of the art of Monte Carlo methods in radiation physics and particle transport simulation and applications, the latter involving in particular, the use and development of electron--gamma, neutron--gamma and hadronic codes. Besides the basic theory and the methods employed, special attention is paid to algorithm development for modeling, and the analysis of experiments and measurements in a variety of fields ranging from particle to medical physics.
Efficiency of a statistical transport model for turbulent particle dispersion
Litchford, Ron J.; Jeng, San-Mou
1992-01-01
In developing its theory for turbulent dispersion transport, the Litchford and Jeng (1991) statistical transport model for turbulent particle dispersion took a generalized approach in which the perturbing influence of each turbulent eddy on consequent interactions was transported through all subsequent eddies. Nevertheless, examinations of this transport relation shows it to be able to decay rapidly: this implies that additional computational efficiency may be obtained via truncation of unneccessary transport terms. Attention is here given to the criterion for truncation, as well as to expected efficiency gains.
Directed Transport of Interacting Particle Systems: Recent Progress
ZHENG Zhi-Gang
2005-01-01
Recent developments in studies of directed transport processes in interacting particle systems are retrospected. Due to the interactions among elements, the directed transport process exhibits complicated and novel cooperative dynamics. We considered various possibilities in achieving ratchet motion by breaking different symmetries of many-body systems. It is shown that the directional transport can even be induced by breaking the coupling symmetry and the spatiotemporal symmetries.
Big Bang Day: 5 Particles - 1. The Electron
Simon Singh
2008-01-01
Simon Singh looks at the stories behind the discovery of 5 of the universe's most significant subatomic particles: the Electron, the Quark, the Anti-particle, the Neutrino and the "next particle". 1. The Electron Just over a century ago, British physicist J.J. Thompson experimenting with electric currents and charged particles inside empty glass tubes, showed that atoms are divisible into indivisible elementary particles. But how could atoms be built up of these so called "corpuscles"? An exciting 30 year race ensued, to grasp the planetary model of the atom with its orbiting electrons, and the view inside the atom was born. Whilst the number of electrons around the nucleus of an atom determines their the chemistry of all elements, the power of electrons themselves have been harnessed for everyday use: electron beams for welding,cathode ray tubes and radiation therapy.
Dissipative particle dynamics model for colloid transport in porous media
Pan, W.; Tartakovsky, A. M.
2013-08-01
We present that the transport of colloidal particles in porous media can be effectively modeled with a new formulation of dissipative particle dynamics, which augments standard DPD with non-central dissipative shear forces between particles while preserving angular momentum. Our previous studies have demonstrated that the new formulation is able to capture accurately the drag forces as well as the drag torques on colloidal particles that result from the hydrodynamic retardation effect. In the present work, we use the new formulation to study the contact efficiency in colloid filtration in saturated porous media. Note that the present model include all transport mechanisms simultaneously, including gravitational sedimentation, interception and Brownian diffusion. Our results of contact efficiency show a good agreement with the predictions of the correlation equation proposed by Tufenkji and EliMelech, which also incorporate all transport mechanisms simultaneously without the additivity assumption.
Isobe, Mitsutaka; Shinohara, Kouji
Escaping energetic ion diagnostics in magnetically confined plasma experiments are described in this lecture note. Experimental results from escaping energetic ion diagnostics in TFTR, JFT-2M, CHS and W7-AS are shown. In addition to mechanism of energetic ion loss from a viewpoint of particle orbit, effect of MHD activity on energetic particle transport is reviewed.
Transport of Sputtered Particles in Capacitive Sputter Sources
Trieschmann, Jan
2015-01-01
The transport of sputtered aluminum inside a multi frequency capacitively coupled plasma chamber is simulated by means of a kinetic test multi-particle approach. A novel consistent set of scattering parameters obtained for a modified variable hard sphere collision model is presented for both argon and aluminum. An angular dependent Thompson energy distribution is fitted to results from Monte-Carlo simulations and used for the kinetic simulation of the transport of sputtered aluminum. For the proposed configuration the transport of sputtered particles is characterized under typical process conditions at a gas pressure of p = 0.5 Pa. It is found that - due to the peculiar geometric conditions - the transport can be understood in a one dimensional picture, governed by the interaction of the imposed and backscattered particle fluxes. It is shown that the precise geometric features play an important role only in proximity to the electrode edges, where the effect of backscattering from the outside chamber volume be...
Design of colored multilayered electrophoretic particles for electronic inks.
Badila, M; Hébraud, A; Brochon, C; Hadziioannou, G
2011-09-01
The preparation of multilayered latex particles with surface functional groups suitable for use as electrophoretic particles in electronic inks has been studied. The particles are formed by dispersion polymerization and have a polystyrene core, slightly cross-linked with divinylbenzene (DVB), and a poly(methyl methacrylate) (PMMA) or a poly(acrylic acid) (PAA) shell. After grafting alkyl chains on their surface, the particles are negatively or positively charged and sterically stabilized against aggregation in nonpolar solvent. The particles were dyed by incorporation of Nigrosin during polymerization or by swelling in supercritical CO(2) in the presence of a dye. Particle size, morphology, incorporated dye content and zeta potential were determined. A dual-particle electronic ink based on a mixture of the colored multilayered particles and white hybrid TiO(2)-polymer particles was prepared and electro-optically tested.
Transport of large particles released in a nuclear accident
Poellaenen, R.; Toivonen, H.; Lahtinen, J.; Ilander, T.
1995-10-01
Highly radioactive particulate material may be released in a nuclear accident or sometimes during normal operation of a nuclear power plant. However, consequence analyses related to radioactive releases are often performed neglecting the particle nature of the release. The properties of the particles have an important role in the radiological hazard. A particle deposited on the skin may cause a large and highly non-uniform skin beta dose. Skin dose limits may be exceeded although the overall activity concentration in air is below the level of countermeasures. For sheltering purposes it is crucial to find out the transport range, i.e. the travel distance of the particles. A method for estimating the transport range of large particles (aerodynamic diameter d{sub a} > 20 {mu}m) in simplified meteorological conditions is presented. A user-friendly computer code, known as TROP, is developed for fast range calculations in a nuclear emergency. (orig.) (23 refs., 13 figs.).
China, Swarup; Alpert, Peter A.; Zhang, Bo; Schum, Simeon; Dzepina, Katja; Wright, Kendra; Owen, R. Chris; Fialho, Paulo; Mazzoleni, Lynn R.; Mazzoleni, Claudio; Knopf, Daniel A.
2017-03-01
Long-range transported free tropospheric particles can play a significant role on heterogeneous ice nucleation. Using optical and electron microscopy we examine the physicochemical characteristics of ice nucleating particles (INPs). Particles were collected on substrates from the free troposphere at the remote Pico Mountain Observatory in the Azores Islands, after long-range transport and aging over the Atlantic Ocean. We investigate four specific events to study the ice formation potential by the collected particles with different ages and transport patterns. We use single-particle analysis, as well as bulk analysis to characterize particle populations. Both analyses show substantial differences in particle composition between samples from the four events; in addition, single-particle microscopy analysis indicates that most particles are coated by organic material. The identified INPs contained mixtures of dust, aged sea salt and soot, and organic material acquired either at the source or during transport. The temperature and relative humidity (RH) at which ice formed, varied only by 5% between samples, despite differences in particle composition, sources, and transport patterns. We hypothesize that this small variation in the onset RH may be due to the coating material on the particles. This study underscores and motivates the need to further investigate how long-range transported and atmospherically aged free tropospheric particles impact ice cloud formation.
Unconventional dc Transport in Rashba Electron Gases.
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.
Electron transport properties of cobalt doped polyaniline
Ghosh, P [Department of Physics, National Institute of Technology, Durgapur, Deemed University, Mahatma Gandhi Avenue, PIN-713 209, West Bengal (India); Sarkar, A [Department of Physics, National Institute of Technology, Durgapur, Deemed University, Mahatma Gandhi Avenue, PIN-713 209, West Bengal (India); Meikap, A K [Department of Physics, National Institute of Technology, Durgapur, Deemed University, Mahatma Gandhi Avenue, PIN-713 209, West Bengal (India); Chattopadhyay, S K [Department of Physics, National Institute of Technology, Durgapur, Deemed University, Mahatma Gandhi Avenue, PIN-713 209, West Bengal (India); Chatterjee, S K [Department of Physics, National Institute of Technology, Durgapur, Deemed University, Mahatma Gandhi Avenue, PIN-713 209, West Bengal (India); Ghosh, M [Department of Physics, Ramananda College, Bishnupur, Bankura-722 122, West Bengal (India)
2006-07-21
Electrical transport properties of cobalt doped polyaniline in an aqueous ethanol medium were investigated in the temperature range 77 {<=} T {<=} 300 K, applying magnetic fields up to 1 T in the frequency range 20 Hz-1 MHz. The room temperature dc resistivity increases with increase in Co content. The dc resistivity and magnetoresistivity of these samples have been interpreted in terms of the variable range hopping theory. The frequency dependence of conductivity has been described by a power law {sigma}({omega}) {approx} {omega}{sup S}. The value of s is found to be temperature dependent, which shows a decreasing trend with temperature. The correlated barrier hopping model is the most likely mechanism for the electron transport. The different physical parameters were calculated from the experimental data.
Replacing Electron Transport Cofactors with Hydrogenases
Laamarti, Rkia
2016-12-01
Enzymes have found applications in a broad range of industrial production processes. While high catalytic activity, selectivity and mild reaction conditions are attractive advantages of the biocatalysts, particularly costs arising from required cofactors pose a sever limitation. While cofactor-recycling systems are available, their use implies constraints for process set-up and conditions, which are a particular problem e.g. for solid-gas-phase reactions. Several oxidoreductases are able to directly exchange electrons with electrodes. Hence, the co-immobilization of both, an electron-utilizing and an electron-generating oxidoreductase on conductive nanoparticles should facilitate the direct electron flow from an enzymatic oxidation to a reduction reaction circumventing redox-cofactors requirements. In such a set-up, hydrogenases could generate and provide electrons directly form gaseous hydrogen. This thesis describes the co-immobilization of the oxygen tolerant hydrogenases from C. eutropha or C. metallidurans and cytochrome P450BM3 as test system. Conductive material in the form of carbon nanotubes (CNT) serves as a suitable support. A combination of the hydrogenase and the catalytic domain of P450BM3 immobilized on carbon nanotubes were tested for the oxidation of lauric acid in the presence of hydrogen instead of an electron-transport cofactor. The GC-MS analysis reveals the conversion of 4% of lauric acid (LA) into three products, which correspond to the hydroxylated lauric acid in three different positions with a total turnover (TON) of 34. The product distribution is similar to that obtained when using the wildtype P450BM3 with the nicotinamide adenine dinucleotide phosphate (NADPH) cofactor. Such electronic coupling couldn’t be achieved for the conversion of other substrates such as propane and cyclohexane, probably due to the high uncoupling rate within the heme-domain of cytochrome P450BM3 when unnatural substrates are introduced.
Modelling of electron transport and of sawtooth activity in tokamaks
Angioni, C
2001-10-01
Transport phenomena in tokamak plasmas strongly limit the particle and energy confinement and represent a crucial obstacle to controlled thermonuclear fusion. Within the vast framework of transport studies, three topics have been tackled in the present thesis: first, the computation of neoclassical transport coefficients for general axisymmetric equilibria and arbitrary collisionality regime; second, the analysis of the electron temperature behaviour and transport modelling of plasma discharges in the Tokamak a configuration Variable (TCV); third, the modelling and simulation of the sawtooth activity with different plasma heating conditions. The work dedicated to neoclassical theory has been undertaken in order to first analytically identify a set of equations suited for implementation in existing Fokker-Planck codes. Modifications of these codes enabled us to compute the neoclassical transport coefficients considering different realistic magnetic equilibrium configurations and covering a large range of variation of three key parameters: aspect ratio, collisionality, and effective charge number. A comparison of the numerical results with an analytical limit has permitted the identification of two expressions for the trapped particle fraction, capable of encapsulating the geometrical effects and thus enabling each transport coefficient to be fitted with a single analytical function. This has allowed us to provide simple analytical formulae for all the neoclassical transport coefficients valid for arbitrary aspect ratio and collisionality in general realistic geometry. This work is particularly useful for a correct evaluation of the neoclassical contribution in tokamak scenarios with large bootstrap cur- rent fraction, or improved confinement regimes with low anomalous transport and for the determination of the plasma current density profile, since the plasma conductivity is usually assumed neoclassical. These results have been included in the plasma transport code
Stochastic Simulation of Lagrangian Particle Transport in Turbulent Flows
Sun, Guangyuan
This dissertation presents the development and validation of the One Dimensional Turbulence (ODT) multiphase model in the Lagrangian reference frame. ODT is a stochastic model that captures the full range of length and time scales and provides statistical information on fine-scale turbulent-particle mixing and transport at low computational cost. The flow evolution is governed by a deterministic solution of the viscous processes and a stochastic representation of advection through stochastic domain mapping processes. The three algorithms for Lagrangian particle transport are presented within the context of the ODT approach. The Type-I and -C models consider the particle-eddy interaction as instantaneous and continuous change of the particle position and velocity, respectively. The Type-IC model combines the features of the Type-I and -C models. The models are applied to the multi-phase flows in the homogeneous decaying turbulence and turbulent round jet. Particle dispersion, dispersion coefficients, and velocity statistics are predicted and compared with experimental data. The models accurately reproduces the experimental data sets and capture particle inertial effects and trajectory crossing effect. A new adjustable particle parameter is introduced into the ODT model, and sensitivity analysis is performed to facilitate parameter estimation and selection. A novel algorithm of the two-way momentum coupling between the particle and carrier phases is developed in the ODT multiphase model. Momentum exchange between the phases is accounted for through particle source terms in the viscous diffusion. The source term is implemented in eddy events through a new kernel transformation and an iterative procedure is required for eddy selection. This model is applied to a particle-laden turbulent jet flow, and simulation results are compared with experimental measurements. The effect of particle addition on the velocities of the gas phase is investigated. The development of
Heat Transport of Electron-Doped Cobaltates
LIU Bin; LIANG Ying; FENG Shi-Ping; CHEN Wei-Yeu
2006-01-01
Within the t-J model, the heat transport of electron-doped cobaltates is studied based on the fermionspin theory. It is shown that the temperature-dependent thermal conductivity is characterized by the low-temperature peak located at a finite temperature. The thermal conductivity increases monotonously with increasing temperature at low-temperatures T ＜ 0.1 J, and then decreases with increasing temperature for higher temperatures T ＞ 0.1 J, in qualitative agreement with experimental result observed from NaxCoO2.
Electronic transport properties of (fluorinated) metal phthalocyanine
Fadlallah, M M
2015-12-21
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.
Electron transport in doped fullerene molecular junctions
Kaur, Milanpreet; Sawhney, Ravinder Singh; Engles, Derick
The effect of doping on the electron transport of molecular junctions is analyzed in this paper. The doped fullerene molecules are stringed to two semi-infinite gold electrodes and analyzed at equilibrium and nonequilibrium conditions of these device configurations. The contemplation is done using nonequilibrium Green’s function (NEGF)-density functional theory (DFT) to evaluate its density of states (DOS), transmission coefficient, molecular orbitals, electron density, charge transfer, current, and conductance. We conclude from the elucidated results that Au-C16Li4-Au and Au-C16Ne4-Au devices behave as an ordinary p-n junction diode and a Zener diode, respectively. Moreover, these doped fullerene molecules do not lose their metallic nature when sandwiched between the pair of gold electrodes.
Transport and Entrapment of Particles in Steel Continuous Casting
Thomas, Brian G.; Yuan, Quan; Mahmood, Sana; Liu, Rui; Chaudhary, Rajneesh
2013-08-01
A particle-capture model based on local force balances has been developed, implemented into computational models of turbulent fluid flow and particle transport, and applied to simulate the entrapment of slag inclusions and bubbles during the continuous casting of steel slabs. Turbulent flow of molten steel is computed in the nozzle and mold using transient computational fluid flow models, both with and without the effects of argon gas injection. Next, the transport and capture of many particles are simulated using a Lagrangian approach. Particles touching the dendritic interface may be pushed away, dragged away by the transverse flow, or captured into the solidifying shell according to the results of a local balance of ten different forces. This criterion was validated by reproducing experimental results in two different systems. The implications of this criterion are discussed quantitatively. Finally, the fluid flow/particle transport model results and capture criterion are applied together to predict the entrapment distributions of different sized particles in a typical slab caster. More large particles are safely removed than small ones, but the entrapment rate into the solidifying shell as defects is still very high.
A reduced model for relativistic electron beam transport in solids and dense plasmas
Touati, M.; Feugeas, J.-L.; Nicolaï, Ph; Santos, J. J.; Gremillet, L.; Tikhonchuk, V. T.
2014-07-01
A hybrid reduced model for relativistic electron beam transport based on the angular moments of the relativistic kinetic equation with a special closure is presented. It takes into account collective effects with the self-generated electromagnetic fields as well as collisional effects with the slowing down of the relativistic electrons by plasmons, bound and free electrons and their angular scattering on both ions and electrons. This model allows for fast computations of relativistic electron beam transport while describing their energy distribution evolution. Despite the loss of information concerning the angular distribution of the electron beam, the model reproduces analytical estimates in the academic case of a monodirectional and monoenergetic electron beam propagating through a warm and dense plasma and hybrid particle-in-cell simulation results in a realistic laser-generated electron beam transport case.
Drift Wave Test Particle Transport in Reversed Shear Profile
Horton, W.; Park, H.B.; Kwon, J.M.; Stronzzi, D.; Morrison, P.J.; Choi, D.I.
1998-06-01
Drift wave maps, area preserving maps that describe the motion of charged particles in drift waves, are derived. The maps allow the integration of particle orbits on the long time scale needed to describe transport. Calculations using the drift wave maps show that dramatic improvement in the particle confinement, in the presence of a given level and spectrum of E x B turbulence, can occur for q(r)-profiles with reversed shear. A similar reduction in the transport, i.e. one that is independent of the turbulence, is observed in the presence of an equilibrium radial electric field with shear. The transport reduction, caused by the combined effects of radial electric field shear and both monotonic and reversed shear magnetic q-profiles, is also investigated.
Directed transport of Brownian particles in a changing temperature field
Grillo, A [DMFCI, Facolta di Ingegneria, Universita di Catania. Viale Andrea Doria 6, 95125 Catania (Italy); Jinha, A [HPL-Faculty of Kinesiology, University of Calgary, 2500 University Drive NW, Calgary, Alberta, T2N 1N4 (Canada); Federico, S [HPL-Faculty of Kinesiology, University of Calgary, 2500 University Drive NW, Calgary, Alberta, T2N 1N4 (Canada); Ait-Haddou, R [HPL-Faculty of Kinesiology, University of Calgary, 2500 University Drive NW, Calgary, Alberta, T2N 1N4 (Canada); Herzog, W [HPL-Faculty of Kinesiology, University of Calgary, 2500 University Drive NW, Calgary, Alberta, T2N 1N4 (Canada); Giaquinta, G [DMFCI, Facolta di Ingegneria, Universita di Catania. Viale Andrea Doria 6, 95125 Catania (Italy)
2008-01-11
We study the interaction of Brownian particles with a changing temperature field in the presence of a one-dimensional periodic adiabatic potential. We show the existence of directed transport through the determination of the overall current of Brownian particles crossing the boundary of the system. With respect to the case of Brownian particles in a thermal bath, we determine a current which exhibits a contribution explicitly related to the presence of a thermal gradient. Beyond the self-consistent calculation of the temperature and probability density distribution of Brownian particles, we evaluate the energy consumption for directed transport to take place. Our description is based on Streater's model, and solutions are obtained by perturbing the system from its initial thermodynamic equilibrium state.
Electron thermal transport in tokamak plasmas
Konings, J.A.
1994-11-30
The process of fusion of small nuclei thereby releasing energy, as it occurs continuously in the sun, is essential for the existence of mankind. The same process applied in a controlled way on earth would provide a clean and an abundant energy source, and be the long term solution of the energy problem. Nuclear fusion requires an extremely hot (10{sup 8} K) ionized gas, a plasma, that can only be maintained if it is kept insulated from any material wall. In the so called `tokamak` this is achieved by using magnetic fields. The termal insulation, which is essential if one wants to keep the plasma at the high `fusion` temperature, can be predicted using basic plasma therory. A comparison with experiments in tokamaks, however, showed that the electron enery losses are ten to hundred times larger than this theory predicts. This `anomalous transport` of thermal energy implies that, to reach the condition for nuclear fusion, a fusion reactor must have very large dimensions. This may put the economic feasibility of fusion power in jeopardy. Therefore, in a worldwide collaboration, physicists study tokamak plasmas in an attempt to understand and control the energy losses. From a scientific point of view, the mechanisms driving anomalous transport are one of the challenges in fudamental plasma physics. In Nieuwegein, a tokamak experiment (the Rijnhuizen Tokamak Project, RTP) is dedicated to the study of anomalous transport, in an international collaboration with other laboratories. (orig./WL).
Computational methods for two-phase flow and particle transport
Lee, Wen Ho
2013-01-01
This book describes mathematical formulations and computational methods for solving two-phase flow problems with a computer code that calculates thermal hydraulic problems related to light water and fast breeder reactors. The physical model also handles the particle and gas flow problems that arise from coal gasification and fluidized beds. The second part of this book deals with the computational methods for particle transport.
Spatiotemporal Structure of Aeolian Particle Transport on Flat Surface
Niiya, Hirofumi
2016-01-01
We conduct numerical simulations based on a model of blowing snow to reveal the long-term properties and equilibrium state of aeolian particle transport from $10^{-5} \\hspace{0.5 ex} \\mathrm{m}$ to $10 \\hspace{0.5 ex} \\mathrm{m}$ above the flat surface. The numerical results are s follows. (i) Time-series data of particle transport are divided into development, relaxation, and equilibrium phases, which are formed by rapid wind response below $10 \\hspace{0.5 ex} \\mathrm{cm}$ and gradual wind response above $10 \\hspace{0.5 ex} \\mathrm{cm}$. (ii) The particle transport rate at equilibrium is expressed as a power function of friction velocity, and the index of 2.35 implies that most particles are transported by saltation. (iii) The friction velocity below $100 \\hspace{0.5 ex} \\mu\\mathrm{m}$ remains roughly constant and lower than the fluid threshold at equilibrium. (iv) The mean particle speed above $300 \\hspace{0.5 ex} \\mu\\mathrm{m}$ is less than the wind speed, whereas that below $300 \\hspace{0.5 ex} \\mu\\mathrm...
Particle swarm optimization - Genetic algorithm (PSOGA) on linear transportation problem
Rahmalia, Dinita
2017-08-01
Linear Transportation Problem (LTP) is the case of constrained optimization where we want to minimize cost subject to the balance of the number of supply and the number of demand. The exact method such as northwest corner, vogel, russel, minimal cost have been applied at approaching optimal solution. In this paper, we use heurisitic like Particle Swarm Optimization (PSO) for solving linear transportation problem at any size of decision variable. In addition, we combine mutation operator of Genetic Algorithm (GA) at PSO to improve optimal solution. This method is called Particle Swarm Optimization - Genetic Algorithm (PSOGA). The simulations show that PSOGA can improve optimal solution resulted by PSO.
Energetic particle transport across the mean magnetic field: before diffusion
Laitinen, T
2016-01-01
Current particle transport models describe the propagation of charged particles across the mean field direction in turbulent plasmas as diffusion. However, recent studies suggest that at short time-scales, such as soon after solar energetic particle (SEP) injection, particles remain on turbulently meandering field lines, which results in non-diffusive initial propagation across the mean magnetic field. In this work, we use a new technique to investigate how the particles are displaced from their original field lines, and quantify the parameters of the transition from field-aligned particle propagation along meandering field lines to particle diffusion across the mean magnetic field. We show that the initial decoupling of the particles from the field lines is slow, and particles remain within a Larmor radius from their initial meandering field lines for tens to hundreds of Larmor periods, for 0.1-10 MeV protons in turbulence conditions typical of the solar wind at 1~AU. Subsequently, particles decouple from th...
Particles and waves in electron optics and microscopy
Pozzi, Giulio
2016-01-01
Advances in Imaging and Electron Physics merges two long-running serials, Advances in Electronics and Electron Physics and Advances in Optical and Electron Microscopy. The series features extended articles on the physics of electron devices (especially semiconductor devices), particle optics at high and low energies, microlithography, image science, digital image processing, electromagnetic wave propagation, electron microscopy, and the computing methods used in all these domains. * Contains contributions from leading authorities on the subject matter* Informs and updates all the latest developments in the field of imaging and electron physics* Provides practitioners interested in microscopy, optics, image processing, mathematical morphology, electromagnetic fields, electron, and ion emission with a valuable resource* Features extended articles on the physics of electron devices (especially semiconductor devices), particle optics at high and low energies, microlithography, image science, and digital image pro...
Particle Tracking Model and Abstraction of Transport Processes
B. Robinson
2000-04-07
The purpose of the transport methodology and component analysis is to provide the numerical methods for simulating radionuclide transport and model setup for transport in the unsaturated zone (UZ) site-scale model. The particle-tracking method of simulating radionuclide transport is incorporated into the FEHM computer code and the resulting changes in the FEHM code are to be submitted to the software configuration management system. This Analysis and Model Report (AMR) outlines the assumptions, design, and testing of a model for calculating radionuclide transport in the unsaturated zone at Yucca Mountain. In addition, methods for determining colloid-facilitated transport parameters are outlined for use in the Total System Performance Assessment (TSPA) analyses. Concurrently, process-level flow model calculations are being carrier out in a PMR for the unsaturated zone. The computer code TOUGH2 is being used to generate three-dimensional, dual-permeability flow fields, that are supplied to the Performance Assessment group for subsequent transport simulations. These flow fields are converted to input files compatible with the FEHM code, which for this application simulates radionuclide transport using the particle-tracking algorithm outlined in this AMR. Therefore, this AMR establishes the numerical method and demonstrates the use of the model, but the specific breakthrough curves presented do not necessarily represent the behavior of the Yucca Mountain unsaturated zone.
Application of particle damper on electronic packages for spacecraft
Veeramuthuvel, P.; Shankar, K.; Sairajan, K. K.
2016-10-01
Particle damping is an effective method of passive vibration control, which is of recent research interest. This paper presents a novel application of particle damper on an electronic package of a spacecraft, tested at ISRO Satellite Centre. The effectiveness of particle damper on the random vibration response of electronic package for spacecraft application exposed to random vibration environments experienced during the launch is studied. The use of particle damper under shock environments are also demonstrated. Optimal particle damper parameters were used based on the design guidelines derived from previous publications of the authors. The comparison of particle damper effectiveness under random vibration loads with respect to the shape of the particle damper capsule and packing ratio are also examined.
Liu, Quansheng; Cui, Xianze; Zhang, Chengyuan; Huang, Shibing
2016-01-01
Particle and grain size may influence the transportation and deposition characteristics of particles within pollutant transport and within granular filters that are typically used in wastewater treatment. We conducted two-dimensional sandbox experiments using quartz powder as the particles and quartz sand as the porous medium to study the response of transportation and deposition formation to changes in particle diameter (ds, with median diameter 18, 41, and 82 μm) and grain diameter (dp, with median diameter 0.36, 1.25, and 2.82 mm) considering a wide range of diameter ratios (ds/dp) from 0.0064 to 0.228. Particles were suspended in deionized water, and quartz sand was used as the porous medium, which was meticulously cleaned to minimize any physicochemical and impurities effects that could result in indeterminate results. After the experiments, the particle concentration of the effluent and particle mass per gram of dry sands were measured to explore changes in transportation and deposition characteristics under different conditions. In addition, a micro-analysis was conducted to better analyse the results on a mesoscopic scale. The experimental observation analyses indicate that different diameter ratios (ds/dp) may lead to different deposit formations. As ds/dp increased, the deposit formation changed from 'Random Deposition Type' to 'Gradient Deposition Type', and eventually became 'Inlet Deposition Type'.
Electron Transport through Porphyrin Molecular Junctions
Zhou, Qi
The goal of this work is to study the properties that would affect the electron transport through a porphyrin molecular junction. This work contributes to the field of electron transport in molecular junctions in the following 3 aspects. First of all, by carrying out experiments comparing the conductance of the iron (III) porphyrin (protected) and the free base porphyrin (protected), it is confirmed that the molecular energy level broadening and shifting occurs for porphyrin molecules when coupled with the metal electrodes, and this level broadening and shifting plays an important role in the electron transport through molecular junctions. Secondly, by carrying out an in-situ deprotection of the acetyl-protected free base porphyrin molecules, it is found out that the presence of acetyl groups reduces the conductance. Thirdly, by incorporating the Matrix-assisted laser desorption/ionization (MALDI) spectrum and the in-situ deprotection prior to formation of molecular junctions, it allows a more precise understanding of the molecules involved in the formation of molecular junctions, and therefore allows an accurate analysis of the conductance histogram. The molecules are prepared by self-assembly and the junctions are formed using a Scanning Tunneling Microscopy (STM) molecular break junction technique. The porphyrin molecules are characterized by MALDI in solution before self-assembly to a gold/mica substrate. The self-assembled monolayers (SAMs) of porphyrins on gold are characterized by Ultraviolet-visible (UV-Vis) reflection spectroscopy to confirm that the molecules are attached to the substrate. The SAMs are then characterized by Angle-Resolved X-ray photoelectron spectroscopy (ARXPS) to determine the thickness and the average molecular orientation of the molecular layer. The electron transport is measured by conductance-displacement (G-S) experiments under a given bias (-0.4V). The conductance value of a single molecule is identified by a statistical analysis
Electron Lenses for particle collimation in LHC
Shiltsev, V
2008-01-01
Electron Lenses built and installed in Tevatron have proven themselves as safe and very reliable instruments which can be effectively used in hadron collider operation for a number of applications, including compensation of beam-beam effects , DC beam removal from abort gaps , as a diagnostic tool. In this presentation we – following original proposal – consider in more detail a possibility of using electron lenses with hollow electron beam for ion and proton collimation in LHC.
Electron Fluid Description of Wave-Particle Interactions in Strong Buneman Turbulence
Che, H
2014-01-01
To understand the nature of anomalous resistivity in magnetic reconnection, we investigate turbulence-induced momentum transport and energy dissipation during Buneman instability in force-free current sheets. Using 3D particle-in-cell simulations, we find that the macroscopic effects generated by wave-particle interactions in Buneman instability can be approximately described by a set of electron fluid equations. These equations show that the energy dissipation and momentum transports along current sheets are locally quasi-static but globally non-static and irreversible. Turbulence drag dissipates both the streaming energy of current sheets and the associated magnetic energy. The decrease of magnetic field maintains an inductive electric field that re-accelerates electrons. The net loss of streaming energy is converted into the heat of electrons moving along the magnetic field and increases the electron Boltzmann entropy. The growth of self-sustained Buneman waves satisfies a Bernoulli-like equation that rela...
Atmospheric fate and transport of fine volcanic ash: Does particle shape matter?
White, C. M.; Allard, M. P.; Klewicki, J.; Proussevitch, A. A.; Mulukutla, G.; Genareau, K.; Sahagian, D. L.
2013-12-01
velocimetry (PIV). Scanning Electron Microscopy (SEM) of ash particles collected in localized deposition areas is used to correlate the PIV results to particle shape. In addition, controlled wind tunnel experiments are used to determine particle fate and transport in a turbulent boundary layer for a mixed particle population. Collectively, these studies will provide an improved understanding of the effects of particle shape on sedimentation and dispersion, and foundational data for the predictive modeling of the fate and transport of fine ash particles suspended in the atmosphere.
Electronic transport properties of phenylacetylene molecular junctions
Liu Wen; Cheng Jie; Yah Cui-Xia; Li Hai-Hong; Wang Yong-Juan; Liu De-Sheng
2011-01-01
Electronic transport properties of a kind of phenylacetylene compound- (4-mercaptophenyl)-phenylacetylene are calculated by the first-principles method in the framework of density functional theory and the nonequilibrium Green's function formalism.The molecular junction shows an obvious rectifying behaviour at a bias voltage larger than 1.0 V.The rectification effect is attributed to the asymmetry of the interface contacts.Moreover,at a bias voltage larger than 2.0 V,which is not referred to in a relevant experiment [Fang L,Park J Y,Ma H,Jan A K Y and Salmeron M 2007 Langmuir 23 11522],we find a negative differential resistance phenomenon.The negative differential resistance effect may originate from the change of the delocalization degree of the molecular orbitais induced by the bias.
Electronic transport and dynamics in correlated heterostructures
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.
Modeling transport and aggregation of volcanic ash particles
Costa, Antonio; Folch, Arnau; Macedonio, Giovanni; Durant, Adam
2010-05-01
A complete description of ash aggregation processes in volcanic clouds is an very arduous task and the full coupling of ash transport and ash aggregation models is still computationally prohibitive. A large fraction of fine ash injected in the atmosphere during explosive eruptions aggregate because of complex interactions of surface liquid layers, electrostatic forces, and differences in settling velocities. The formation of aggregates of size and density different from those of the primary particles dramatically changes the sedimentation dynamics and results in lower atmospheric residence times of ash particles and in the formation of secondary maxima of tephra deposit. Volcanic ash transport models should include a full aggregation model accounting for all particle class interaction. However this approach would require prohibitive computational times. Here we present a simplified model for wet aggregation that accounts for both atmospheric and volcanic water transport. The aggregation model assumes a fractal relationship for the number of primary particles in aggregates, average efficiencies factors, and collision frequency functions accounting for Brownian motion, laminar and turbulent fluid shear, and differential settling velocity. We implemented the aggregation model in the WRF+FALL3D coupled modelling system and applied it to different eruptions where aggregation has been recognized to play an important role, such as the August and September 1992 Crater Peak eruptions and the 1980 Mt St Helens eruption. Moreover, understanding aggregation processes in volcanic clouds will contribute to mitigate the risks related with volcanic ash transport and sedimentation.
Linear kinetic theory and particle transport in stochastic mixtures
Pomraning, G.C. [Univ. of California, Los Angeles, CA (United States)
1995-12-31
We consider the formulation of linear transport and kinetic theory describing energy and particle flow in a random mixture of two or more immiscible materials. Following an introduction, we summarize early and fundamental work in this area, and we conclude with a brief discussion of recent results.
Particle Transport in ECRH Plasmas of the TJ-II; Transporte de Particulas en Plasmas ECRH del TJ-II
Vargas, V. I.; Lopez-Bruna, D.; Estrada, T.; Guasp, J.; Reynolds, J. M.; Velasco, J. L.; Herranz, J.
2007-07-01
We present a systematic study of particle transport in ECRH plasmas of TJ-II with different densities. The goal is to fi nd particle confinement time and electron diffusivity dependence with line-averaged density. The experimental information consists of electron temperature profiles, T{sub e} (Thomson Scattering TS) and electron density, n{sub e}, (TS and reflectometry) and measured puffing data in stationary discharges. The profile of the electron source, Se, was obtained by the 3D Monte-Carlo code EIRENE. The analysis of particle balance has been done by linking the results of the code EIRENE with the results of a model that reproduces ECRH plasmas in stationary conditions. In the range of densities studied (0.58 {<=}n{sub e}> (10{sup 1}9m{sup -}3) {<=}0.80) there are two regions of confinement separated by a threshold density,
A concurrent vector-based steering framework for particle transport
Apostolakis, John; Carminati, Federico; Gheata, Andrei; Wenzel, Sandro
2014-01-01
High Energy Physics has traditionally been a technology - limited science that has pushed the boundaries of both the detectors collecting the information about the particles and the computing infrastructure processing this information. However, since a few years the increase in computing power comes in the form of increased parallelism at all levels, and High Energy Physics has now to optimise its code to take advantage of the new architectures, including GPUs and hybrid systems. One of the primary targets for optimisation is the particle transport code used to simulate the detector response, as it is largely experiment independent and one of the most demanding applications in terms of CPU resources . The Geant Vector Prototype project aims to explore innovative designs in particle transport aimed at obtaining maximal performance on the new architectures. This paper describes the current status of the project and its future perspectives. In particular we describe how the present design tries to expose the par...
A generalized transport-velocity formulation for smoothed particle hydrodynamics
Zhang, Chi; Hu, Xiangyu Y., E-mail: xiangyu.hu@tum.de; Adams, Nikolaus A.
2017-05-15
The standard smoothed particle hydrodynamics (SPH) method suffers from tensile instability. In fluid-dynamics simulations this instability leads to particle clumping and void regions when negative pressure occurs. In solid-dynamics simulations, it results in unphysical structure fragmentation. In this work the transport-velocity formulation of Adami et al. (2013) is generalized for providing a solution of this long-standing problem. Other than imposing a global background pressure, a variable background pressure is used to modify the particle transport velocity and eliminate the tensile instability completely. Furthermore, such a modification is localized by defining a shortened smoothing length. The generalized formulation is suitable for fluid and solid materials with and without free surfaces. The results of extensive numerical tests on both fluid and solid dynamics problems indicate that the new method provides a unified approach for multi-physics SPH simulations.
Electronic spin susceptibility of metallic superconductive nano-particles
Li Feng; Chen Zhi-Qian; Li Qing
2006-01-01
We have observed the thermodynamic properties of metallic superconductive nano-particles in the grand canonical ensemble; and the level distribution and the level correlation between the discrete electronic energy levels are considered in the calculation of the electronic spin susceptibility of the ensemble numerically. The quantum effect, even-odd effect and other special effects existing in the metallic nano-particles are also studied in this article.
Applying dispersive changes to Lagrangian particles in groundwater transport models
Konikow, Leonard F.
2010-01-01
Method-of-characteristics groundwater transport models require that changes in concentrations computed within an Eulerian framework to account for dispersion be transferred to moving particles used to simulate advective transport. A new algorithm was developed to accomplish this transfer between nodal values and advecting particles more precisely and realistically compared to currently used methods. The new method scales the changes and adjustments of particle concentrations relative to limiting bounds of concentration values determined from the population of adjacent nodal values. The method precludes unrealistic undershoot or overshoot for concentrations of individual particles. In the new method, if dispersion causes cell concentrations to decrease during a time step, those particles in the cell having the highest concentration will decrease the most, and those with the lowest concentration will decrease the least. The converse is true if dispersion is causing concentrations to increase. Furthermore, if the initial concentration on a particle is outside the range of the adjacent nodal values, it will automatically be adjusted in the direction of the acceptable range of values. The new method is inherently mass conservative.
Automated data collection in single particle electron microscopy
Tan, Yong Zi; Cheng, Anchi; Potter, Clinton S.; Carragher, Bridget
2016-01-01
Automated data collection is an integral part of modern workflows in single particle electron microscopy (EM) research. This review surveys the software packages available for automated single particle EM data collection. The degree of automation at each stage of data collection is evaluated, and the capabilities of the software packages are described. Finally, future trends in automation are discussed. PMID:26671944
Modeling reactive transport with particle tracking and kernel estimators
Rahbaralam, Maryam; Fernandez-Garcia, Daniel; Sanchez-Vila, Xavier
2015-04-01
Groundwater reactive transport models are useful to assess and quantify the fate and transport of contaminants in subsurface media and are an essential tool for the analysis of coupled physical, chemical, and biological processes in Earth Systems. Particle Tracking Method (PTM) provides a computationally efficient and adaptable approach to solve the solute transport partial differential equation. On a molecular level, chemical reactions are the result of collisions, combinations, and/or decay of different species. For a well-mixed system, the chem- ical reactions are controlled by the classical thermodynamic rate coefficient. Each of these actions occurs with some probability that is a function of solute concentrations. PTM is based on considering that each particle actually represents a group of molecules. To properly simulate this system, an infinite number of particles is required, which is computationally unfeasible. On the other hand, a finite number of particles lead to a poor-mixed system which is limited by diffusion. Recent works have used this effect to actually model incomplete mix- ing in naturally occurring porous media. In this work, we demonstrate that this effect in most cases should be attributed to a defficient estimation of the concentrations and not to the occurrence of true incomplete mixing processes in porous media. To illustrate this, we show that a Kernel Density Estimation (KDE) of the concentrations can approach the well-mixed solution with a limited number of particles. KDEs provide weighting functions of each particle mass that expands its region of influence, hence providing a wider region for chemical reactions with time. Simulation results show that KDEs are powerful tools to improve state-of-the-art simulations of chemical reactions and indicates that incomplete mixing in diluted systems should be modeled based on alternative conceptual models and not on a limited number of particles.
Stochastic transport of interacting particles in periodically driven ratchets
Savel'Ev, Sergey; Marchesoni, Fabio; Nori, Franco
2004-12-01
An open system of overdamped, interacting Brownian particles diffusing on a periodic substrate potential U(x+l)=U(x) is studied in terms of an infinite set of coupled partial differential equations describing the time evolution of the relevant many-particle distribution functions. In the mean-field approximation, this hierarchy of equations can be replaced by a nonlinear integro-differential Fokker-Planck equation. This is applicable when the distance a between particles is much less than the interaction length λ , i.e., a particle interacts with many others, resulting in averaging out fluctuations. The equation obtained in the mean-field approximation is applied to an ensemble of locally (a≪λ≪l) interacting (either repelling or attracting) particles placed in an asymmetric one-dimensional substrate potential, either with an oscillating temperature (temperature rachet) or driven by an ac force (rocked ratchet). In both cases we focus on the high-frequency limit. For the temperature ratchet, we find that the net current is typically suppressed (or can even be inverted) with increasing density of the repelling particles. In contrast, the net current through a rocked ratchet can be enhanced by increasing the density of the repelling particles. In the case of attracting particles, our perturbation technique is valid up to a critical value of the particle density, above which a finite fraction of the particles starts condensing in a liquidlike state near the substrate minima. The dependence of the net transport current on the particle density and the interparticle potential is analyzed in detail for different values of the ratchet parameters.
Taasti, Vicki Trier; Knudsen, Helge; Holzscheiter, Michael
2015-01-01
The Monte Carlo particle transport code SHIELD-HIT12A is designed to simulate therapeutic beams for cancer radiotherapy with fast ions. SHIELD-HIT12A allows creation of antiproton beam kernels for the treatment planning system TRiP98, but first it must be benchmarked against experimental data...
Transmission electron microscopy study of aerosol particles from the brown hazes in northern China
Li, Weijun; Shao, Longyi
2009-05-01
Airborne aerosol collections were performed in urban areas of Beijing that were affected by regional brown haze episodes over northern China from 31 May to 12 June 2007. Morphologies, elemental compositions, and mixing states of 810 individual aerosol particles of different sizes were obtained by transmission electron microscopy coupled with energy-dispersive X-ray spectrometry. The phases of some particles were verified using selected-area electron diffraction. Aerosol particle types less than 10 μm in diameter include mineral, complex secondary (Ca-S, K-, and S-rich), organic, soot, fly ash, and metal (Fe-rich and Zn-bearing). Most soot, fly ash, and organic particles are less than 2 μm in diameter. Approximately 84% of the analyzed mineral particles have diameters between 2 and 10 μm, while 81% of the analyzed complex secondary and metal particles are much smaller, from 0.1 to 2 μm. Trajectory analysis with fire maps show that southerly air masses arriving at Beijing have been transported through many agricultural biomass burning sites and heavy industrial areas. Spherical fly ash and Fe-rich particles were from industrial emissions, and abundant K-rich and organic particles likely originated from field burning of crop residues. Abundant Zn-bearing particles are associated with industrial activities and local waste incinerators. On the basis of the detailed analysis of 443 analyzed aerosol particles, about 70% of these particles are internally mixed with two or more aerosol components from different sources. Most mineral particles are covered with visible coatings that contain N, O, Ca (or Mg), minor S, and Cl. K- and S-rich particles tend to be coagulated with fly ash, soot, metal, and fine-grained mineral particles. Organic materials internally mixed with K- and S-rich particles can be their inclusions and coatings.
Electron heat conduction and suprathermal particles
Bakunin, O.G.; Krasheninnikov, S.I. (I.V. Kurchatov Institute, Moscow (Russian Federation))
1991-01-01
As recognized at present, the applicability of Spitzer-Harm's theory on electron heat conduction along the magnetic field is limited by comparatively small values of the thermal electron mean free path ratio, [lambda] to the characteristic length of changes in plasma parameters, L: [gamma]=[lambda]/L[<=]10[sup -2]. The stationary kinetic equation for the electron distribution function inhomogeneous along the x-axis f[sub e](v,x) allows one to have solutions in the self-similar variables. The objective of a given study is to generalize the solutions for the case of arbitrary Z[sub eff], that will allow one to compare approximate solutions to the kinetic equation with the precise ones in a wide range of parameters. (author) 8 refs., 2 figs.
Electronic transport in graphene; Elektronischer Transport in Graphen
Lohmann, Timm
2010-06-08
In 2004 graphene, a monolayer of carbon atoms, has been isolated as the first real two-dimensional solid by the group of A. Geim at the University of Manchester. Graphene's properties have been theoretically investigated since the 1950s. Until the successful preparation by Geim et al., graphene was suspected to be unstable under ambient conditions above 0 K (Mermin-Wagner theorem). Its two dimensionality and hexagonal lattice symmetry cause interesting novel properties and effects. At experimentally relevant energies, graphene has a linear band structure and charge carrier dynamics must be treated using Dirac's equation. Therefore charge carriers in graphene are called ''Dirac fermions''. Beside exotic effects like ''Klein tunneling'' an unconventional quantum Hall effect (QHE) can be observed with a Hall conductance quantized in units of 2e{sup 2}/h, 6e{sup 2}/h, 10e{sup 2}/h, 14e{sup 2}/h. As a starting point for in-depth transport measurements the processing of graphene field effect transistors (GFETs) has been developed and optimized, based on the pioneering work by Novoselov et al. The optimized process provides samples with carrier mobilities up to 16000 cm{sup 2}/Vs and a well defined Hall geometry. These samples are used to investigate external influences on the electronic properties of graphene. Among those influences molecular adsorbates are responsible for various effects of freshly prepared graphene samples e.g. an intrinsic p-doping, a mobility asymmetry of electrons and holes, the so called ''minimal conductivity'' and a field effect hysteresis at room temperature. In collaboration with the group of A. Yacoby (Harvard) density fluctuations in the vicinity of the Dirac point (''electron-hole puddles'') could be observed using a scanning single electron transistor (SSET). These fluctuations might be one reason for the ''minimal conductivity'' at
Liu, Baoshun; Li, Ziqiang; Zhao, Xiujian
2015-02-21
In this research, Monte-Carlo Continuity Random Walking (MC-RW) model was used to study the relation between electron transport and photocatalysis of nano-crystalline (nc) clusters. The effects of defect energy disorder, spatial disorder of material structure, electron density, and interfacial transfer/recombination on the electron transport and the photocatalysis were studied. Photocatalytic activity is defined as 1/τ from a statistical viewpoint with τ being the electron average lifetime. Based on the MC-RW simulation, a clear physical and chemical "picture" was given for the photocatalytic kinetic analysis of nc-clusters. It is shown that the increase of defect energy disorder and material spatial structural disorder, such as the decrease of defect trap number, the increase of crystallinity, the increase of particle size, and the increase of inter-particle connection, can enhance photocatalytic activity through increasing electron transport ability. The increase of electron density increases the electron Fermi level, which decreases the activation energy for electron de-trapping from traps to extending states, and correspondingly increases electron transport ability and photocatalytic activity. Reducing recombination of electrons and holes can increase electron transport through the increase of electron density and then increases the photocatalytic activity. In addition to the electron transport, the increase of probability for electrons to undergo photocatalysis can increase photocatalytic activity through the increase of the electron interfacial transfer speed.
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.
Particle, momentum and thermal transport in the PTRANSP code
Bateman, G.; Halpern, F. D.; Kritz, A. H.; Pankin, A. Y.; Rafiq, T.; McCune, D. C.; Budny, R. V.; Indireshkumar, K.
2008-11-01
The combined effects of particle, momentum and thermal transport are investigated in tokamak discharges using a coupled system of transport equations implemented in the PTRANSP integrated modeling code. The magnetic diffusion equation is advanced separately, along with the evolution of the equilibrium. Simulations are carried out using theory-based models to compute transport, sources and sinks. Boundary conditions are either read from data or computed using a pedestal model for H-mode discharges. Different techniques are explored for controlling numerical problems [1] in time-dependent simulations that include sawtooth oscillations and other rapid changes in the profiles. Results for the density, temperature and toroidal angular velocity profiles are compared with experimental data. [1] S.C. Jardin et al, ``On 1D diffusion problems with a gradient-dependent diffusion coefficient''; G.V. Pereverzev and G. Corrigan, ``Stable numeric scheme for diffusion equation with a stiff transport''; both papers to appear in Comp. Phys. Comm. (2008).
Problems of linear electron (polaron) transport theory in semiconductors
Klinger, M I
1979-01-01
Problems of Linear Electron (Polaron) Transport Theory in Semiconductors summarizes and discusses the development of areas in electron transport theory in semiconductors, with emphasis on the fundamental aspects of the theory and the essential physical nature of the transport processes. The book is organized into three parts. Part I focuses on some general topics in the theory of transport phenomena: the general dynamical theory of linear transport in dissipative systems (Kubo formulae) and the phenomenological theory. Part II deals with the theory of polaron transport in a crystalline semicon
Three-Dimensional PIC-MC Modeling for Relativistic Electron Beam Transport Through Dense Plasma
CAO Lihua; CHANG Tieqiang; PEI Wenbing; LIU Zhanjun; LI Meng; ZHENG Chunyang
2008-01-01
We have developed a three dimensional (3D) PIC (particle-in-cell)-MC (Monte Carlo) code in order to simulate an electron beam transported into the dense matter based on our previous two dimensional code. The relativistic motion of fast electrons is treated by the particle-in-cell method under the influence of both a self-generated transverse magnetic field and an axial electric field, as well as collisions. The electric field generated by return current is ex-pressed by Ohm's law and the magnetic field is calculated from Faraday's law. The slowing down of monoenergy electrons in DT plasma is calculated and discussed.
A study on the particle penetration in RMS Right Single Quotation Marks particle transport system
Son, S. M.; Oh, S. H.; Choi, C. R. [ELSOLTEC Inc., Youngin (Korea, Republic of)
2014-10-15
In nuclear facilities, a radiation monitoring system (RMS) monitors the exhaust gas containing the radioactive material. Samples of exhaust gas are collected in the downstream region of air cleaning units (ACUs) in order to examine radioactive materials. It is possible to predict an amount of radioactive material by analyzing the corrected samples. Representation of the collected samples should be assured in order to accurately sense and measure of radioactive materials. The radius of curvature is mainly 5 times of tube diameter. Sometimes, a booster fan is additionally added to enhance particle penetration rate... In this study, particle penetrations are calculated to evaluate particle penetration rate with various design parameters (tube lengths, tube declined angles, radius of curvatures, etc). The particle penetration rates have been calculated for several elements in the particle transport system. In general, the horizontal length of tube and the number of bending tube have a big impact on the penetration rate in the particle transport system. If the sampling location is far from the radiation monitoring system, additional installation of booster fans could be considered in case of large diameter tubes, but is not recommended in case of small diameter tube. In order to enhance particle penetration rate, the following works are recommended by priority. 1) to reduce the interval between sampling location and radiation monitoring system 2) to reduce the number of the bending tube.
The Roles of Transport and Wave-Particle Interactions on Radiation Belt Dynamics
Fok, Mei-Ching; Glocer, Alex; Zheng, Qiuhua
2011-01-01
Particle fluxes in the radiation belts can vary dramatically during geomagnetic active periods. Transport and wave-particle interactions are believed to be the two main types of mechanisms that control the radiation belt dynamics. Major transport processes include substorm dipolarization and injection, radial diffusion, convection, adiabatic acceleration and deceleration, and magnetopause shadowing. Energetic electrons and ions are also subjected to pitch-angle and energy diffusion when interact with plasma waves in the radiation belts. Important wave modes include whistler mode chorus waves, plasmaspheric hiss, electromagnetic ion cyclotron waves, and magnetosonic waves. We investigate the relative roles of transport and wave associated processes in radiation belt variations. Energetic electron fluxes during several storms are simulated using our Radiation Belt Environment (RBE) model. The model includes important transport and wave processes such as substorm dipolarization in global MHD fields, chorus waves, and plasmaspheric hiss. We discuss the effects of these competing processes at different phases of the storms and validate the results by comparison with satellite and ground-based observations. Keywords: Radiation Belts, Space Weather, Wave-Particle Interaction, Storm and Substorm
Particle acceleration, transport and turbulence in cosmic and heliospheric physics
Matthaeus, W.
1992-01-01
In this progress report, the long term goals, recent scientific progress, and organizational activities are described. The scientific focus of this annual report is in three areas: first, the physics of particle acceleration and transport, including heliospheric modulation and transport, shock acceleration and galactic propagation and reacceleration of cosmic rays; second, the development of theories of the interaction of turbulence and large scale plasma and magnetic field structures, as in winds and shocks; third, the elucidation of the nature of magnetohydrodynamic turbulence processes and the role such turbulence processes might play in heliospheric, galactic, cosmic ray physics, and other space physics applications.
Electronic and Ionic Transport Dynamics in Organolead Halide Perovskites.
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.
Momentum and particle transport in a nonhomogenous canopy
Gould, Andrew W.
Turbulent particle transport through the air plays an important role in the life cycle of many plant pathogens. In this study, data from a field experiment was analyzed to explore momentum and particle transport within a grape vineyard. The overall goal of these experiments was to understand how the architecture of a sparse agricultural canopy interacts with turbulent flow and ultimately determines the dispersion of airborne fungal plant pathogens. Turbulence in the vineyard canopy was measured using an array of four sonic anemometers deployed at heights z/H 0.4, 0.9, 1.45, and 1.95 where z is the height of the each sonic and H is the canopy height. In addition to turbulence measurements from the sonic anemometers, particle dispersion was measured using inert particles with the approximate size and density of powdery mildew spores and a roto-rod impaction trap array. Measurements from the sonic anemometers demonstrate that first and second order statistics of the wind field are dependent on wind direction orientation with respect to vineyard row direction. This dependence is a result of wind channeling which transfers energy between the velocity components when the wind direction is not aligned with the rows. Although the winds have a strong directional dependence, spectra analysis indicates that the structure of the turbulent flow is not fundamentally altered by the interaction between wind direction and row direction. Examination of a limited number of particle release events indicates that the wind turning and channeling observed in the momentum field impacts particle dispersion. For row-aligned flow, particle dispersion in the direction normal to the flow is decreased relative to the plume spread predicted by a standard Gaussian plume model. For flow that is not aligned with the row direction, the plume is found to rotate in the same manner as the momentum field.
Walsh, J. A. [Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, NW12-312 Albany, St. Cambridge, MA 02139 (United States); Palmer, T. S. [Department of Nuclear Engineering and Radiation Health Physics, Oregon State University, 116 Radiation Center, Corvallis, OR 97331 (United States); Urbatsch, T. J. [XTD-5: Air Force Systems, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)
2013-07-01
A new method for generating discrete scattering cross sections to be used in charged particle transport calculations is investigated. The method of data generation is presented and compared to current methods for obtaining discrete cross sections. The new, more generalized approach allows greater flexibility in choosing a cross section model from which to derive discrete values. Cross section data generated with the new method is verified through a comparison with discrete data obtained with an existing method. Additionally, a charged particle transport capability is demonstrated in the time-dependent Implicit Monte Carlo radiative transfer code package, Milagro. The implementation of this capability is verified using test problems with analytic solutions as well as a comparison of electron dose-depth profiles calculated with Milagro and an already-established electron transport code. An initial investigation of a preliminary integration of the discrete cross section generation method with the new charged particle transport capability in Milagro is also presented. (authors)
Beam Dynamics in an Electron Lens with the Warp Particle-in-cell Code
Stancari, Giulio; Redaelli, Stefano
2014-01-01
Electron lenses are a mature technique for beam manipulation in colliders and storage rings. In an electron lens, a pulsed, magnetically confined electron beam with a given current-density profile interacts with the circulating beam to obtain the desired effect. Electron lenses were used in the Fermilab Tevatron collider for beam-beam compensation, for abort-gap clearing, and for halo scraping. They will be used in RHIC at BNL for head-on beam-beam compensation, and their application to the Large Hadron Collider for halo control is under development. At Fermilab, electron lenses will be implemented as lattice elements for nonlinear integrable optics. The design of electron lenses requires tools to calculate the kicks and wakefields experienced by the circulating beam. We use the Warp particle-in-cell code to study generation, transport, and evolution of the electron beam. For the first time, a fully 3-dimensional code is used for this purpose.
Gyrokinetics Simulation of Energetic Particle Turbulence and Transport
Diamond, Patrick H.
2011-09-21
Progress in research during this year elucidated the physics of precession resonance and its interaction with radial scattering to form phase space density granulations. Momentum theorems for drift wave-zonal flow systems involving precession resonance were derived. These are directly generalizable to energetic particle modes. A novel nonlinear, subcritical growth mechanism was identified, which has now been verified by simulation. These results strengthen the foundation of our understanding of transport in burning plasmas
Chemically generated convective transport of micron sized particles
Shklyaev, Oleg; Das, Sambeeta; Altemose, Alicia; Shum, Henry; Balazs, Anna; Sen, Ayusman
2015-11-01
A variety of chemical and biological applications require manipulation of micron sized objects like cells, viruses, and large molecules. Increasing the size of particles up to a micron reduces performance of techniques based on diffusive transport. Directional transport of cargo toward detecting elements reduces the delivery time and improves performance of sensing devices. We demonstrate how chemical reactions can be used to organize fluid flows carrying particles toward the assigned destinations. Convection is driven by density variations caused by a chemical reaction occurring at a catalyst or enzyme-covered target site. If the reaction causes a reduction in fluid density, as in the case of catalytic decomposition of hydrogen peroxide, then fluid and suspended cargo is drawn toward the target along the bottom surface. The intensity of the fluid flow and the time of cargo delivery are controlled by the amount of reagent in the system. After the reagent has been consumed, the fluid pump stops and particles are found aggregated on and around the enzyme-coated patch. The pumps are reusable, being reactivated upon injection of additional reagent. The developed technique can be implemented in lab-on-a-chip devices for transportation of micro-scale object immersed in solution.
Nonclassical Particle Transport in 1-D Random Periodic Media
Vasques, Richard; Slaybaugh, Rachel N
2016-01-01
We investigate the accuracy of the recently proposed nonclassical transport equation. This equation contains an extra independent variable compared to the classical transport equation (the path-length $s$), and models particle transport taking place in homogenized random media in which a particle's distance-to-collision is not exponentially distributed. To solve the nonclassical equation one needs to know the $s$-dependent ensemble-averaged total cross section, $\\Sigma_t(\\mu,s)$, or its corresponding path-length distribution function, $p(\\mu,s)$. We consider a 1-D spatially periodic system consisting of alternating solid and void layers, randomly placed in the $x$-axis. We obtain an analytical expression for $p(\\mu,s)$ and use this result to compute the corresponding $\\Sigma_t(\\mu,s)$. Then, we proceed to numerically solve the nonclassical equation for different test problems in rod geometry; that is, particles can move only in the directions $\\mu=\\pm 1$. To assess the accuracy of these solutions, we produce ...
Simulation of Cell Adhesion using a Particle Transport Model
Chesnutt, Jennifer
2005-11-01
An efficient computational method for simulation of cell adhesion through protein binding forces is discussed. In this method, the cells are represented by deformable elastic particles, and the protein binding is represented by a rate equation. The method is first developed for collision and adhesion of two similar cells impacting on each other from opposite directions. The computational method is then applied in a particle-transport model for a cloud of interacting and colliding cells, each of which are represented by particles of finite size. One application might include red blood cells adhering together to form rouleaux, which are chains of red blood cells that are found in different parts of the circulatory system. Other potential applications include adhesion of platelets to a blood vessel wall or mechanical heart valve, which is a precursor of thrombosis formation, or adhesion of cancer cells to organ walls in the lymphatic, circulatory, digestive or pulmonary systems.
Transient Characterization of Type B Particles in a Transport Riser
Shadle, L.J.; Monazam, E.R. (REM Engineering Services, Morgantown, WV); Mei, J.S.
2007-01-01
Simple and rapid dynamic tests were used to evaluate fluid dynamic behavior of granular materials in the transport regime. Particles with densities ranging from 189 to 2,500 kg/m3 and Sauter mean size from 61 to 812 μm were tested in a 0.305 m diameter, 15.5 m height circulating fluidized bed (CFB) riser. The transient tests involved the abrupt stoppage of solids flow for each granular material over a wide range gas flow rates. The riser emptying time was linearly related to the Froude number in each of three different operating regimes. The flow structure along the height of the riser followed a distinct pattern as tracked through incremental pressures. These results are discussed to better understand the transformations that take place when operating over various regimes. During the transients the particle size distribution was measured. The effects of pressure, particle size, and density on test performance are also presented.
Particle Tracking Model and Abstraction of Transport Processes
B. Robinson
2004-10-21
The purpose of this report is to document the abstraction model being used in total system performance assessment (TSPA) model calculations for radionuclide transport in the unsaturated zone (UZ). The UZ transport abstraction model uses the particle-tracking method that is incorporated into the finite element heat and mass model (FEHM) computer code (Zyvoloski et al. 1997 [DIRS 100615]) to simulate radionuclide transport in the UZ. This report outlines the assumptions, design, and testing of a model for calculating radionuclide transport in the UZ at Yucca Mountain. In addition, methods for determining and inputting transport parameters are outlined for use in the TSPA for license application (LA) analyses. Process-level transport model calculations are documented in another report for the UZ (BSC 2004 [DIRS 164500]). Three-dimensional, dual-permeability flow fields generated to characterize UZ flow (documented by BSC 2004 [DIRS 169861]; DTN: LB03023DSSCP9I.001 [DIRS 163044]) are converted to make them compatible with the FEHM code for use in this abstraction model. This report establishes the numerical method and demonstrates the use of the model that is intended to represent UZ transport in the TSPA-LA. Capability of the UZ barrier for retarding the transport is demonstrated in this report, and by the underlying process model (BSC 2004 [DIRS 164500]). The technical scope, content, and management of this report are described in the planning document ''Technical Work Plan for: Unsaturated Zone Transport Model Report Integration'' (BSC 2004 [DIRS 171282]). Deviations from the technical work plan (TWP) are noted within the text of this report, as appropriate. The latest version of this document is being prepared principally to correct parameter values found to be in error due to transcription errors, changes in source data that were not captured in the report, calculation errors, and errors in interpretation of source data.
Instability of nanoscale metallic particles under electron irradiation in TEM
Chen, X. Y.; Zhang, S. G.; Xia, M. X.; Li, J. G.
2016-03-01
The stability of nano metallic glass under electron beam in transmission electron microscope (TEM) was investigated. The most common voltage of TEM used in metallic materials characterization was either 200 kV or 300 kV. Both situations were investigated in this work. An amorphous metallic particle with a dimension of a few hundred nanometers was tested under 300 keV electron irradiation. New phase decomposed from the parent phase was observed. Moreover, a crystal particle with the same composition and dimension was tested under 200 keV irradiation. Decomposition process also occurred in this situation. Besides, crystal orientation modification was observed during irradiation. These results proved that the electron beam in TEM have an effect on the stability of nanoscale samples during long time irradiation. Atomic displacement was induced and diffusion was enhanced by electron irradiation. Thus, artifacts would be induced when a nanoscale metallic sample was characterized in TEM.
Nonlinear mechanisms for drift wave saturation and induced particle transport
Dimits, A.M. (Maryland Univ., College Park, MD (USA). Lab. for Plasma Research); Lee, W.W. (Princeton Univ., NJ (USA). Plasma Physics Lab.)
1989-12-01
A detailed theoretical study of the nonlinear dynamics of gyrokinetic particle simulations of electrostatic collisionless and weakly collisional drift waves is presented. In previous studies it was shown that, in the nonlinearly saturated phase of the evolution, the saturation levels and especially the particle fluxes have an unexpected dependence on collisionality. In this paper, the explanations for these collisionality dependences are found to be as follows: The saturation level is determined by a balance between the electron and ion fluxes. The ion flux is small for levels of the potential below an E {times} B-trapping threshold and increases sharply once this threshold is crossed. Due to the presence of resonant electrons, the electron flux has a much smoother dependence on the potential. In the 2-1/2-dimensional ( pseudo-3D'') geometry, the electrons are accelerated away from the resonance as they diffuse spatially, resulting in an inhibition of their diffusion. Collisions and three-dimensional effects can repopulate the resonance thereby increasing the value of the particle flux. 30 refs., 32 figs., 2 tabs.
Particle analysis of volcanic ash with Electron Microscopy
Lieke, K. I.; Kristensen, T. B.; Koch, C. B.; Korsholm, U. S.; Sørensen, J. H.; Bilde, M.
2012-04-01
Since the airspace closure over Europe due to the Eyjafjalla eruption in 2010, volcanic ash has come more in the focus of atmospheric science. The airspace closure accompanying the Grímsvötn eruption in 2011 clearly indicates that there is still a great need to increase the scientific understanding of the properties and impacts of volcanic ash particles. Determination of particle characteristics, preferably in near real time, serves as an important input to transport models in operational use for decision support and guidance of authorities. We collected particles before and after the Grímsvötn volcanic ash arrived at Copenhagen, Denmark, between 23 May and 31 May 2011, as well as at a number of other locations. The analysis of meteorological conditions shows that the particle collection performed before arrival of the volcanic ash may serve as a good reference sample. We have thus been able to identify significant differences in aerosol chemical composition during a volcanic ash event over Copenhagen. These results are compared to volcanic ash particles collected on Iceland. We provide unique data about single-particle structure, chemical composition, size and morphology of volcanic ash particles. Single-particle analysis by SEM, and mineralogical studies by XRD and TEM prove that the particles are composed of glass of a characteristic composition and small, nm sized minerals attached to the large (up to tens of µm) glass fragments. The derived information about volcanic ash particles can be used by transport models, resulting in improved information to the authorities in case of new volcanic ash events over Scandinavia or Europe.
Effective N-particle collisions in a hadronic transport approach
Oliinychenko, Dmytro
2016-01-01
Hadronic transport approaches based on an effective solution of the relativistic Boltzmann equation are widely applied for the dynamical description of heavy ion reactions at low beam energies. At high densities, the assumption of binary interactions often used in hadronic transport approaches may not be applicable anymore. Therefore, we introduce a way to include N-particle collisions effectively in a transport approach. This framework provides the opportunity to interpolate in a dynamical way between two different limits of kinetic theory: the dilute gas approximation and the ideal fluid case. This approach will be important for studies of the dynamical evolution of heavy ion collisions at low and intermediate energies as experimentally investigated at the beam energy scan program at RHIC, and in the future at FAIR and NICA. On the other hand, this new way of modelling hot and dense strongly-interacting matter might be relevant for small systems at high energies (LHC and RHIC) as well.
Simulated electron holography of PSD particles
Conbhuí, Pádraig Ó.; Williams, Wyn; Nagy, Les
2016-04-01
Electron holography is an experimental technique that is capable of observing magnetic microstructures on the same scale as can be determined using numerical modeling and thus bridge the gap between experimental measurements and theory. I will present a technique for simulating holographic images from the results of micromagnetic models and demonstrate an easily used tool for generating holograms on the fly in an interactive environment (ie in ParaView). Since holography flattens 3D information onto a 2D image, some useful information can be lost. By looking at some examples of holograms of interesting 3D magnetizations (ie PSD structures), particularly how they change as they're rotated, along with comparisons of different structures, I will examine what information can be retrieved and what might be lost. The existance of an external dipole can be indicative of an in-plane component of a seemingly out-of-plane vortex core. It is also seen, however, that two quite different structures (in this case a [111] vortex core and a [111] uniform magnetization) can sometimes be quite indistinguishable.
Taasti, Vicki Trier; Knudsen, Helge; Holzscheiter, Michael
2015-01-01
The Monte Carlo particle transport code SHIELD-HIT12A is designed to simulate therapeutic beams for cancer radiotherapy with fast ions. SHIELD-HIT12A allows creation of antiproton beam kernels for the treatment planning system TRiP98, but first it must be benchmarked against experimental data. An...... conclude that more experimental cross section data are needed in the lower energy range in order to resolve this contradiction, ideally combined with more rigorous models for annihilation on compounds....
Tsurutani, B. T.; Zhang, L. D.; Mason, G. L.; Lakhina, G. S.; Hada, T.; Arballo, J. K.; Zwickl, R. D.
2002-04-01
Energetic particles and MHD waves are studied using simultaneous ISEE-3 data to investigate particle propagation and scattering between the source near the Sun and 1 AU. 3 He-rich events are of particular interest because they are typically low intensity "scatter-free" events. The largest solar proton events are of interest because they have been postulated to generate their own waves through beam instabilities. For 3 He-rich events, simultaneous interplanetary magnetic spectra are measured. The intensity of the interplanetary "fossil" turbulence through which the particles have traversed is found to be at the "quiet" to "intermediate" level of IMF activity. Pitch angle scattering rates and the corresponding particle mean free paths l
A Generalized Boltzmann Fokker-Planck Method for Coupled Charged Particle Transport
Prinja, Anil K
2012-01-09
The goal of this project was to develop and investigate the performance of reduced-physics formulations of high energy charged particle (electrons, protons and heavier ions) transport that are computationally more efficient than not only analog Monte Carlo methods but also the established condensed history Monte Carlo technique. Charged particles interact with matter by Coulomb collisions with target nuclei and electrons, by bremsstrahlung radiation loss and by nuclear reactions such as spallation and fission. Of these, inelastic electronic collisions and elastic nuclear collisions are the dominant cause of energy-loss straggling and angular deflection or range straggling of a primary particle. These collisions are characterized by extremely short mean free paths (sub-microns) and highly peaked, near-singular differential cross sections about forward directions and zero energy loss, with the situation for protons and heavier ions more extreme than for electrons. For this reason, analog or truephysics single-event Monte Carlo simulation, while possible in principle, is computationally prohibitive for routine calculation of charged particle interaction phenomena.
Kubo, Yûki; Sato, Tatsuhiko
2015-01-01
Solar energetic particles (SEPs) are one of the extreme space weather phenomena. A huge SEP event increases the radiation dose received by aircrews, who should be warned of such events as early as possible. We developed a warning system for aviation exposure to SEPs. This article describes one component of the system, which calculates the temporal evolution of the SEP intensity and the spectrum immediately outside the terrestrial magnetosphere. To achieve this, we performed numerical simulations of SEP transport in interplanetary space, in which interplanetary SEP transport is described by the focused transport equation. We developed a new simulation code to solve the equation using a set of stochastic differential equations. In the code, the focused transport equation is expressed in a magnetic field line coordinate system, which is a non-orthogonal curvilinear coordinate system. An inverse Gaussian distribution is employed as the injection profile of SEPs at an inner boundary located near the Sun. We applie...
O' Brien, M. J.; Brantley, P. S.
2015-01-20
In order to run Monte Carlo particle transport calculations on new supercomputers with hundreds of thousands or millions of processors, care must be taken to implement scalable algorithms. This means that the algorithms must continue to perform well as the processor count increases. In this paper, we examine the scalability of:(1) globally resolving the particle locations on the correct processor, (2) deciding that particle streaming communication has finished, and (3) efficiently coupling neighbor domains together with different replication levels. We have run domain decomposed Monte Carlo particle transport on up to 2^{21} = 2,097,152 MPI processes on the IBM BG/Q Sequoia supercomputer and observed scalable results that agree with our theoretical predictions. These calculations were carefully constructed to have the same amount of work on every processor, i.e. the calculation is already load balanced. We also examine load imbalanced calculations where each domain’s replication level is proportional to its particle workload. In this case we show how to efficiently couple together adjacent domains to maintain within workgroup load balance and minimize memory usage.
High field electron and hole transport in wurtzite InN
Reklaitis, Antanas [Semiconductor Physics Institute, Centre for Physical Sciences and Technology, Vilnius (Lithuania)
2012-08-15
A Monte Carlo technique has been used to investigate the steady-state, transient, and small-signal transport of electrons and holes in InN in high electric fields. The drift velocities and diffusion coefficients of electrons and holes are calculated using single-particle Monte Carlo method. The transient drift velocities of electrons and holes are evaluated from ensemble Monte Carlo simulations. The electron small-signal mobility is estimated. The threshold frequency of 550 GHz for the negative differential mobility (NDM) in InN is obtained. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Ukhorskiy, A Y; Sitnov, M I; Millan, R M; Kress, B T; Smith, D C
2014-01-01
[1]Relativistic electron intensities in Earth's outer radiation belt can vary by multiple orders of magnitude on the time scales ranging from minutes to days. One fundamental process contributing to dynamic variability of radiation belt intensities is the radial transport of relativistic electrons across their drift shells. In this paper we analyze the properties of three-dimensional radial transport in a global magnetic field model driven by variations in the solar wind dynamic pressure. We use a test particle approach which captures anomalous effects such as drift orbit bifurcations. We show that the bifurcations lead to an order of magnitude increase in radial transport rates and enhance the energization at large equatorial pitch angles. Even at quiet time fluctuations in dynamic pressure, radial transport at large pitch angles exhibits strong deviations from the diffusion approximation. The radial transport rates are much lower at small pitch angle values which results in a better agreement with the diffusion approximation.
A concurrent vector-based steering framework for particle transport
Apostolakis, John; Brun, René; Carminati, Federico; Gheata, Andrei; Wenzel, Sandro
2014-06-01
High Energy Physics has traditionally been a technology-limited science that has pushed the boundaries of both the detectors collecting the information about the particles and the computing infrastructure processing this information. However, since a few years the increase in computing power comes in the form of increased parallelism at all levels, and High Energy Physics has now to optimise its code to take advantage of the new architectures, including GPUs and hybrid systems. One of the primary targets for optimisation is the particle transport code used to simulate the detector response, as it is largely experiment independent and one of the most demanding applications in terms of CPU resources. The Geant Vector Prototype project aims to explore innovative designs in particle transport aimed at obtaining maximal performance on the new architectures. This paper describes the current status of the project and its future perspectives. In particular we describe how the present design tries to expose the parallelism of the problem at all possible levels, in a design that is aimed at minimising contentions and maximising concurrency, both at the coarse granularity level (threads) and at the micro granularity one (vectorisation, instruction pipelining, multiple instructions per cycle). The future plans and perspectives will also be mentioned.
T. Hada
Full Text Available Energetic particles and MHD waves are studied using simultaneous ISEE-3 data to investigate particle propagation and scattering between the source near the Sun and 1 AU. 3 He-rich events are of particular interest because they are typically low intensity "scatter-free" events. The largest solar proton events are of interest because they have been postulated to generate their own waves through beam instabilities. For 3 He-rich events, simultaneous interplanetary magnetic spectra are measured. The intensity of the interplanetary "fossil" turbulence through which the particles have traversed is found to be at the "quiet" to "intermediate" level of IMF activity. Pitch angle scattering rates and the corresponding particle mean free paths lW - P are calculated using the measured wave intensities, polarizations, and k directions. The values of lW - P are found to be ~ 5 times less than the value of lHe , the latter derived from He intensity and anisotropy time profiles. It is demonstrated by computer simulation that scattering rates through a 90° pitch angle are lower than that of other pitch angles, and that this is a possible explanation for the discrepancy between the lW - P and lHe values. At this time the scattering mechanism(s is unknown. We suggest a means where a direct comparison between the two l values could be made. Computer simulations indicate that although scattering through 90° is lower, it still occurs. Possibilities are either large pitch angle scattering through resonant interactions, or particle mirroring off of field compression regions. The largest solar proton events are analyzed to investigate the possibilities of local wave generation at 1 AU. In accordance with the results of a previous calculation (Gary et al., 1985 of beam stability, proton beams at 1 AU are found to be marginally stable. No evidence for substantial wave amplitude was found. Locally generated waves, if present, were less than 10-3 nT 2 Hz-1 at the leading
High energy particle transport code NMTC/JAM
Niita, Koji [Research Organization for Information Science and Technology, Tokai, Ibaraki (Japan); Meigo, Shin-ichiro; Takada, Hiroshi; Ikeda, Yujiro [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment
2001-03-01
We have developed a high energy particle transport code NMTC/JAM, which is an upgraded version of NMTC/JAERI97. The applicable energy range of NMTC/JAM is extended in principle up to 200 GeV for nucleons and mesons by introducing the high energy nuclear reaction code JAM for the intra-nuclear cascade part. For the evaporation and fission process, we have also implemented a new model, GEM, by which the light nucleus production from the excited residual nucleus can be described. According to the extension of the applicable energy, we have upgraded the nucleon-nucleus non-elastic, elastic and differential elastic cross section data by employing new systematics. In addition, the particle transport in a magnetic field has been implemented for the beam transport calculations. In this upgrade, some new tally functions are added and the format of input of data has been improved very much in a user friendly manner. Due to the implementation of these new calculation functions and utilities, consequently, NMTC/JAM enables us to carry out reliable neutronics study of a large scale target system with complex geometry more accurately and easily than before. This report serves as a user manual of the code. (author)
Silver (Ag) Transport Mechanisms in TRISO coated particles: A Critical Review
I J van Rooyen; J H Neethling; J A A Engelbrecht; P M van Rooyen; G Strydom
2012-10-01
Transport of 110mAg in the intact SiC layer of TRISO coated particles has been studied for approximately 30 years without arriving at a satisfactory explanation of the transport mechanism. In this paper the possible mechanisms postulated in previous experimental studies, both in-reactor and out-of reactor research environment studies are critically reviewed and of particular interest are relevance to very high temperature gas reactor operating and accident conditions. Among the factors thought to influence Ag transport are grain boundary stoichiometry, SiC grain size and shape, the presence of free silicon, nano-cracks, thermal decomposition, palladium attack, transmutation products, layer thinning and coated particle shape. Additionally new insight to nature and location of fission products has been gained via recent post irradiation electron microscopy examination of TRISO coated particles from the DOE’s fuel development program. The combined effect of critical review and new analyses indicates a direction for investigating possible the Ag transport mechanism including the confidence level with which these mechanisms may be experimentally verified.
Numerical study of the auroral particle transport in the polar upper atmosphere
2008-01-01
Starting from the Boltzmann equation and with some reasonable assumptions, a one-dimensional transport equation of charged energetic particles is derived by taking account of major interactions with neutral species in the upper atmosphere, including the processes of elastic scattering, the excitation, the ionization and the secondary electron production. The transport equation is numerically solved, for a simplified atmosphere consisting only of nitrogen molecules (N2), to obtain the variations of incident electron fluxes as a function of altitude, energy and pitch angle. The model results can describe fairly the transport characteristics of pre-cipitating auroral electron spectra in the polar upper atmosphere; meanwhile the N2 ionization rates calculated from the modeled differential flux spectra also exhibit good agreements with existing empirical models in terms of several key parameters. Taking the energy flux spectra of precipitating electrons observed by FAST satellite flying over EISCAT site on May 15, 1997 as model inputs, the model-calculated ionization rate profile of neutral atmosphere consists reasonably with that recon-structed from electron density measurements by the radar.
Particle Acceleration in Relativistic Magnetized Collisionless Electron-Ion Shocks
Sironi, Lorenzo
2010-01-01
We investigate shock structure and particle acceleration in relativistic magnetized collisionless electron-ion shocks by means of 2.5D particle-in-cell simulations with ion-to-electron mass ratios (m_i/m_e) ranging from 16 to 1000. We explore a range of inclination angles between the pre-shock magnetic field and the shock normal. In "subluminal" shocks, where relativistic particles can escape ahead of the shock along the magnetic field lines, ions are efficiently accelerated via a Fermi-like mechanism. The downstream ion spectrum consists of a relativistic Maxwellian and a high-energy power-law tail, which contains ~5% of ions and ~30% of ion energy. Its slope is -2.1. Upstream electrons enter the shock with lower energy than ions, so they are more strongly tied to the field. As a result, only ~1% of the incoming electrons are Fermi-accelerated at the shock before being advected downstream, where they populate a steep power-law tail (with slope -3.5). For "superluminal" shocks, where relativistic particles ca...
Progress in Solving the Elusive Ag Transport Mechanism in TRISO Coated Particles: What is new?
Isabella Van Rooyen
2014-10-01
The TRISO particle for HTRs has been developed to an advanced state where the coating withstands internal gas pressures and retains fission products during irradiation and under postulated accidents. However, one exception is Ag that has been found to be released from high quality TRISO coated particles when irradiated and can also during high temperature accident heating tests. Although out- of- pile laboratory tests have never hither to been able to demonstrate a diffusion process of Ag in SiC, effective diffusion coefficients have been derived to successfully reproduce measured Ag-110m releases from irradiated HTR fuel elements, compacts and TRISO particles It was found that silver transport through SiC does not proceed via bulk volume diffusion. Presently grain boundary diffusion that may be irradiation enhanced either by neutron bombardment or by the presence of fission products such as Pd, are being investigated. Recent studies of irradiated AGR-1 TRISO fuel using scanning transmission electron microscopy (STEM), transmission kukuchi diffraction (TKD) patterns and high resolution transmission electron microscopy (HRTEM) have been used to further the understanding of Ag transport through TRISO particles. No silver was observed in SiC grains, but Ag was identified at triple-points and grain boundaries of the SiC layer in the TRISO particle. Cadmium was also found in some of the very same triple junctions, but this could be related to silver behavior as Ag-110m decays to Cd-110. Palladium was identified as the main constituent of micron-sized precipitates present at the SiC grain boundaries and in most SiC grain boundaries and the potential role of Pd in the transport of Ag will be discussed.
Electronic, transport, and magnetic properties of punctured carbon nanotubes
dos Santos, Jeová Calisto; de Vasconcelos, Fabrício Morais; de Aguiar, Acrísio Lins; Alves, Tayroni Francisco de Alencar; Meunier, Vincent; Girão, Eduardo Costa
2016-12-01
We use a spin-polarized tight-binding model Hamiltonian and the Landauer transport formalism to investigate the electronic transport properties of carbon nanotubes where different types of holes have been drilled through their sidewalls. We focus on zigzag edged defects with different atomic configurations since these systems enable the emergence of magnetic properties. We show that a number of hole geometries, magnetic states, and electronic spins yield attractive transport properties, such as ON/OFF switching for the electronic current, and nontrivial dependence of transmission with hole size.
Terahertz electromodulation spectroscopy of electron transport in GaN
Engelbrecht, S. G.; Arend, T. R.; Zhu, T.; Kappers, M. J.; Kersting, R.
2015-03-01
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.
Terahertz electromodulation spectroscopy of electron transport in GaN
Engelbrecht, S. G.; Arend, T. R.; Kersting, R., E-mail: roland.kersting@lmu.de [Photonics and Optoelectronics Group, Physics Department and Center for NanoScience (CeNS), Ludwig-Maximilians-Universität, Amalienstr. 54, 80799 München (Germany); Zhu, T.; Kappers, M. J. [Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB3 0FS (United Kingdom)
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.
Extracellular Electron Transport Coupling Biogeochemical Processes Centimeters
Risgaard-Petersen, Nils; Fossing, Henrik; Christensen, Peter Bondo
2010-01-01
confirmed the depth range of the electric communication and indicated donation of electrons directly from organotrophic bacteria. The separation of oxidation and reduction processes created steep pH gradients eventually causing carbonate precipitation at the surface. The results indicate that electron...... of the oxygen uptake in laboratory incubations of initially homogenized and stabilized sediment. Using microsensors and process rate measurements we further investigated the effect of the electric currents on sediment biogeochemistry. Dissolved sulfide readily donated electrons to the networks and could...
Extracellular Electron Transport Coupling Biogeochemical Processes Centimeters
Risgaard-Petersen, Nils; Fossing, Henrik; Christensen, Peter Bondo
2010-01-01
of the oxygen uptake in laboratory incubations of initially homogenized and stabilized sediment. Using microsensors and process rate measurements we further investigated the effect of the electric currents on sediment biogeochemistry. Dissolved sulfide readily donated electrons to the networks and could...... confirmed the depth range of the electric communication and indicated donation of electrons directly from organotrophic bacteria. The separation of oxidation and reduction processes created steep pH gradients eventually causing carbonate precipitation at the surface. The results indicate that electron...... exchanging organisms have major biogeochemical importance as they allow widely separated electron donors and acceptors to react with one another....
Computational transport phenomena of fluid-particle systems
Arastoopour, Hamid; Abbasi, Emad
2017-01-01
This book concerns the most up-to-date advances in computational transport phenomena (CTP), an emerging tool for the design of gas-solid processes such as fluidized bed systems. The authors examine recent work in kinetic theory and CTP and illustrate gas-solid processes’ many applications in the energy, chemical, pharmaceutical, and food industries. They also discuss the kinetic theory approach in developing constitutive equations for gas-solid flow systems and how it has advanced over the last decade as well as the possibility of obtaining innovative designs for multiphase reactors, such as those needed to capture CO2 from flue gases. Suitable as a concise reference and a textbook supplement for graduate courses, Computational Transport Phenomena of Gas-Solid Systems is ideal for practitioners in industries involved with the design and operation of processes based on fluid/particle mixtures, such as the energy, chemicals, pharmaceuticals, and food processing. Explains how to couple the population balance e...
Particle-in-cell Simulations with Kinetic Electrons
J.L.V. Lewandowski
2004-02-12
A new scheme, based on an exact separation between adiabatic and nonadiabatic electron responses, for particle-in-cell (PIC) simulations of drift-type modes is presented. The (linear and nonlinear) elliptic equations for the scalar fields are solved using a multi-grid solver. The new scheme yields linear growth rates in excellent agreement with theory and it is shown to conserve energy well into the nonlinear regime. It is also demonstrated that simulations with few electrons are reliable and accurate, suggesting that large-scale, PIC simulations with electron dynamics in toroidal geometry (e.g., tokamaks and stellarators plasmas) are within reach of present-day massively parallel supercomputers.
Tornow, S.; Tong, N.-H.; Bulla, R.
2006-03-01
We investigate electron transfer processes in donor-acceptor systems with a coupling of the electronic degrees of freedom to a common bosonic bath. The model allows to study many-particle effects and the influence of the local Coulomb interaction U between electrons on donor and acceptor sites. Using the non-perturbative numerical renormalization group approach we find distinct differences between the electron transfer characteristics in the single- and two-particle subspaces. We calculate the critical electron-boson coupling αc as a function of U and show results for density-density correlation functions in the whole parameter space. The possibility of many-particle (bipolaronic) and Coulomb-assisted transfer is discussed.
ULF Waves and Diffusive Radial Transport of Charged Particles
Ali, Ashar Fawad
The Van Allen radiation belts contain highly energetic particles which interact with a variety of plasma and magnetohydrodynamic (MHD) waves. Waves in the ultra low-frequency (ULF) range play an important role in the loss and acceleration of energetic particles. Considering the geometry of the geomagnetic field, charged particles trapped in the inner magnetosphere undergo three distinct types of periodic motions; an adiabatic invariant is associated with each type of motion. The evolution of the phase space density of charged particles in the magnetosphere in the coordinate space of the three adiabatic invariants is modeled by the Fokker-Planck equation. If we assume that the first two adiabatic invariants are conserved while the third invariant is violated, then the general Fokker-Planck equation reduces to a radial diffusion equation with the radial diffusion coefficient quantifying the rate of the radial diffusion of charged particles, including contributions from perturbations in both the magnetic and the electric fields. This thesis investigates two unanswered questions about ULF wave-driven radial transport of charged particles. First, how important are the ULF fluctuations in the magnetic field compared with the ULF fluctuations in the electric field in driving the radial diffusion of charged particles in the Earth's inner magnetosphere? It has generally been accepted that magnetic field perturbations dominate over electric field perturbations, but several recently published studies suggest otherwise. Second, what is the distribution of ULF wave power in azimuth, and how does ULF wave power depend upon radial distance and the level of geomagnetic activity? Analytic treatments of the diffusion coefficients generally assume uniform distribution of power in azimuth, but in situ measurements suggest that this may not be the case. We used the magnetic field data from the Combined Release and Radiation Effects Satellite (CRRES) and the electric and the magnetic
Study of Black Sand Particles from Sand Dunes in Badr, Saudi Arabia Using Electron Microscopy
Haider Abbas Khwaja
2015-08-01
Full Text Available Particulate air pollution is a health concern. This study determines the microscopic make-up of different varieties of sand particles collected at a sand dune site in Badr, Saudi Arabia in 2012. Three categories of sand were studied: black sand, white sand, and volcanic sand. The study used multiple high resolution electron microscopies to study the morphologies, emission source types, size, and elemental composition of the particles, and to evaluate the presence of surface “coatings or contaminants” deposited or transported by the black sand particles. White sand was comprised of natural coarse particles linked to wind-blown releases from crustal surfaces, weathering of igneous/metamorphic rock sources, and volcanic activities. Black sand particles exhibited different morphologies and microstructures (surface roughness compared with the white sand and volcanic sand. Morphological Scanning Electron Microscopy (SEM and Laser Scanning Microscopy (LSM analyses revealed that the black sand contained fine and ultrafine particles (50 to 500 nm ranges and was strongly magnetic, indicating the mineral magnetite or elemental iron. Aqueous extracts of black sands were acidic (pH = 5.0. Fe, C, O, Ti, Si, V, and S dominated the composition of black sand. Results suggest that carbon and other contaminant fine particles were produced by fossil-fuel combustion and industrial emissions in heavily industrialized areas of Haifa and Yanbu, and transported as cloud condensation nuclei to Douf Mountain. The suite of techniques used in this study has yielded an in-depth characterization of sand particles. Such information will be needed in future environmental, toxicological, epidemiological, and source apportionment studies.
Electron Transport in Quantum Dots and Heat Transport in Molecules
Kirsanskas, Gediminas
to as artificial atoms [2, 3]. Additionally, in order for the system to be truly quantum, the size of the dot has to be comparable to the de Broglie wavelength of the electrons in it. What we have mentioned so far is rather abstract conditions, which practically can be realized in various systems, such as...... in all three directions, which makes it effectively zero dimensional and corresponds to discrete electronic orbitals (levels) and excitation spectrum. This is analogous to the situation in atoms, where confinement potential replaces the potential of the nucleus, thus quantum dots are often referred...
An ab initio electronic transport database for inorganic materials
Ricci, Francesco; Chen, Wei; Aydemir, Umut; Snyder, G. Jeffrey; Rignanese, Gian-Marco; Jain, Anubhav; Hautier, Geoffroy
2017-07-01
Electronic transport in materials is governed by a series of tensorial properties such as conductivity, Seebeck coefficient, and effective mass. These quantities are paramount to the understanding of materials in many fields from thermoelectrics to electronics and photovoltaics. Transport properties can be calculated from a material's band structure using the Boltzmann transport theory framework. We present here the largest computational database of electronic transport properties based on a large set of 48,000 materials originating from the Materials Project database. Our results were obtained through the interpolation approach developed in the BoltzTraP software, assuming a constant relaxation time. We present the workflow to generate the data, the data validation procedure, and the database structure. Our aim is to target the large community of scientists developing materials selection strategies and performing studies involving transport properties.
Nonequilibrium electron transport through quantum dots in the Kondo regime
Wölfle, Peter; Paaske, Jens; Rosch, Achim
2005-01-01
Electron transport at large bias voltage through quantum dots in the Kondo regime is described within the perturbative renormalization group extended to nonequilibrium. The conductance, local magnetization, dynamical spin susceptibility and local spectral function are calculated. We show how the ...
Transport of electrons in lead oxide studied by CELIV technique
Semeniuk, O.; Juska, G.; Oelerich, J. O.; Jandieri, K.; Baranovskii, S. D.; Reznik, A.
2017-01-01
Although polycrystalline lead oxide (PbO) has a long history of application in optoelectronics and imaging, the transport mechanism for electrons in this material has not yet been clarified. Using the photo-generated charge extraction by linear increasing voltage (photo-CELIV) technique, we provide the temperature- and field-dependences of electron mobility in poly-PbO. It is found that electrons undergo dispersive transport, i.e. their mobility decreases in the course of time. Multiple trapping of electrons from the conduction band into the developed band tail is revealed as the dominant transport mechanism. This differs dramatically from the dispersive transport of holes in the same material, dominated by topological factors and not by energy disorder.
Channeling of particles and associated anomalous transport in a 2D complex plasma crystal
Du, Cheng-Ran; Zhdanov, Sergey; Thomas, Hubertus M; Morfill, Gregor E
2013-01-01
Implications of recently discovered effect of channeling of upstream extra particles for transport phenomena in a two-dimensional plasma crystal are discussed. Upstream particles levitated above the lattice layer and tended to move between the rows of lattice particles. An example of heat transport is considered, where upstream particles act as moving heat sources, which may lead to anomalous heat transport. The average channeling length observed was 15 - 20 interparticle distances. New features of the channeling process are also reported.
Particle Flow Characteristics and Transportation Optimization of Superfine Unclassified Backfilling
Ke-ping Zhou
2017-01-01
Full Text Available In order to investigate the high volume fraction problem of the solid phase in superfine unclassified backfilling pipeline transportation, characteristic parameters were obtained by fitting to test data with an R–R particle size distribution function; then, a Euler dense-phase DPM (Discrete phase model model was established by applying solid–liquid two-phase flow theory and the kinetic theory of granular flow (KTGF. The collision and friction of particles were imported by the UDF (User-define function function, and the pipeline fluidization system, dominated by interphase drag forces, was analyzed. The best concentration and flow rate were finally obtained by comparing the results of the stress conditions, flow field characteristics, and the discrete phase distributions. It is revealed that reducing the concentration and flow rate could control pressure loss and pipe damage to a certain degree, while lower parameters show negative effects on the transportation integrity and backfilling strength. Indoor tests and field industrial tests verify the reliability of the results of the numerical simulations. Research shows that the model optimization method is versatile and practical for other, similar, complex flow field working conditions.
Gradient B drift transport of high current electron beams
Lee, J.R.; Backstrom, R.C.; Halbleib, J.A.; Quintenz, J.P.; Wright, T.P.
1984-12-01
A 1-MeV, 200-kA electron beam was transported 89 cm in a low pressure background gas via gradient B drift in the 1/r azimuthal magnetic field of a current carrying wire. The electron drift velocity was measured and found to be in good agreement with theory. Measurements of x-ray production in the target indicated high transport efficiency.
Hot electron transport and current sensing
Abraham, Mathew Cheeran
The effect of hot electrons on momentum scattering rates in a two-dimensional electron gas is critically examined. It is shown that with hot electrons it is possible to explore the temperature dependence of individual scattering mechanisms not easily probed under equilibrium conditions; both the Bloch-Gruneisen (BG) phonon scattering phenomena and the reduction in impurity scattering are clearly observed. The theoretical calculations are consistent with the results obtained from hot electrons experiments. As a function of bias current, a resistance peak is formed in a 2DEG if the low temperature impurity limited mobilities muI( T = 0) is comparable to muph(TBG ) the phonon limited mobility at the critical BG temperature. In this case, as the bias current is increased, the electron temperature Te rises due to Joule heating and the rapid increase in phonon scattering can be detected before the effect of the reduction in impurity scattering sets in. If muI(T = 0) wire defined in a 2DEG. Concurrently, an appropriate current imaging technique to detect this transition is sought. A rigorous evaluation of magnetic force microscopy (MFM) as a possible candidate to detect Poiseuille electronic flow was conducted, and a method that exploits the mechanical resonance of the MFM cantilever was implemented to significantly improve its current sensitivity.
Time-Resolved Hot Electron Transport in Electronic Devices
1988-12-01
wavevector in the barrier). For the heavy holes tunneling from QWI to QW2 the k’s are k2 = (2mb(VI-E) A2" k3 = (2m 3E/ hZJ . For the electrons tunneling from...Laser-Exci, td bem~onductors,’ Prog. Quantum Electron. 9, 3 (1984). 9 G. D. Sanders and Yia-Chung Chang, "Theory of Photoabsorption in Modulation-Doped
Hot electrons in superlattices: quantum transport versus Boltzmann equation
Wacker, Andreas; Jauho, Antti-Pekka; Rott, S.;
1999-01-01
A self-consistent solution of the transport equation is presented for semiconductor superlattices within different approaches: (i) a full quantum transport model based on nonequilibrium Green functions, (ii) the semiclassical Boltzmann equation for electrons in a miniband, and (iii) Boltzmann...
Electron transport across complex oxide heterointerfaces
Rana, Kumari Gaurav
2013-01-01
Deze these is het eerste verschenen werk dat het gebruik van BEEM om heet elektron transport in complexe oxide heterostructuren te bestuderen, demonstreert. Belangrijke transportparameters van LSMO zoals de hete elektron attenuatie-lengte en de energieafhankelijkheid zijn succesvol verkregen. Dit we
Evidence for particle transport between alveolar macrophages in vivo
Benson, J.M.; Nikula, K.J.; Guilmette, R.A.
1995-12-01
Recent studies at this Institute have focused on determining the role of alveolar macrophages (AMs) in the transport of particles within and form the lung. For those studies, AMs previously labeled using the nuclear stain Hoechst 33342 and polychromatic Fluoresbrite microspheres (1 {mu}m diameter, Polysciences, Inc., Warrington, PA) were instilled into lungs of recipient F344 rats. The fate of the donor particles and the doubly labeled AMs within recipient lungs was followed for 32 d. Within 2-4 d after instillation, the polychromatic microspheres were found in both donor and resident AMs, suggesting that particle transfer occurred between the donor and resident AMs. However, this may also have been an artifact resulting from phagocytosis of the microspheres form dead donor cells or from the fading or degradation of Hoechst 33342 within the donor cells leading to their misidentification as resident AMs. The results support the earlier findings that microspheres in donor AMs can be transferred to resident AMs within 2 d after instillation.
Diffusive transport of energetic electrons in the solar corona: X-ray and radio diagnostics
Musset, Sophie; Kontar, Eduard; Vilmer, Nicole
2017-08-01
Solar flares are associated with efficient particle acceleration. In particular, energetic electrons are diagnosed through X-ray and radio emissions produced as they interact with the solar atmosphere. Particle transport from the acceleration region to the emission sites remains one of the challenging topics in the field of high energy solar physics and has a crucial impact on the interpretation of particles emissions in the context of acceleration models.In order to address the transport of flare associated energetic electrons in the low corona, we used the imaging spectroscopy capabilities of the RHESSI spacecraft to analyze the X-ray emission during the 2004 May 21 solar flare. We show that non-thermal X-ray emitting energetic electrons are trapped in the coronal part of the flaring loop. In the hypothesis of turbulent pitch-angle scattering of energetic electrons (Kontar et al. 2014), diffusive transport can lead to a confinement of energetic electrons in the coronal part of the loop. We show that this model can explain the X-ray observations with a scattering mean free path of the order of 10^8 cm, much smaller than the length of the loop itself.Such results are compared with the study by Kuznetsov and Kontar (2015) of the gyrosynchrotron emission of the same flare. The diffusive transport model can explain the radio observations with a scattering mean free path of the order of 10^7 cm. This combination of X-ray and radio observations during a flare leads to the first estimate of the energy dependence of the scattering mean free path of energetic electrons in the low corona. This result is comparable with studies of the energy dependence of the scattering mean free path of electrons in the interplanetary medium.
Applications to particle transport in the Earth`s aurora
Jasperse, J.R.
1994-12-31
The visual display of light called the aurora borealis occurs when energetic (1 to 100-keV) electrons, protons, and hydrogen atoms from the Earth`s magnetosphere enter the Earth`s upper atmosphere and collide with the ambient neutral particles. Two kinds of auroras occur in nature: those excited by incident electrons and those excited by incident protons and hydrogen atoms. In this paper, we consider only the latter. The proton-hydrogen aurora may be divided into two altitude regions: high altitudes ({approximately}250 to {approximately}600 km) where charge-changing collisions dominate and energy-loss collisions may be neglected and low altitudes ({approximately}100 to {approximately}250 km) where energy-loss collisions also become important and cause rapid energy degradation. The focus of this review is on the high-altitude region where the one-group approximation is valid.
Computer modeling of electron and proton transport in chloroplasts.
Tikhonov, Alexander N; Vershubskii, Alexey V
2014-07-01
Photosynthesis is one of the most important biological processes in biosphere, which provides production of organic substances from atmospheric CO2 and water at expense of solar energy. In this review, we contemplate computer models of oxygenic photosynthesis in the context of feedback regulation of photosynthetic electron transport in chloroplasts, the energy-transducing organelles of the plant cell. We start with a brief overview of electron and proton transport processes in chloroplasts coupled to ATP synthesis and consider basic regulatory mechanisms of oxygenic photosynthesis. General approaches to computer simulation of photosynthetic processes are considered, including the random walk models of plastoquinone diffusion in thylakoid membranes and deterministic approach to modeling electron transport in chloroplasts based on the mass action law. Then we focus on a kinetic model of oxygenic photosynthesis that includes key stages of the linear electron transport, alternative pathways of electron transfer around photosystem I (PSI), transmembrane proton transport and ATP synthesis in chloroplasts. This model includes different regulatory processes: pH-dependent control of the intersystem electron transport, down-regulation of photosystem II (PSII) activity (non-photochemical quenching), the light-induced activation of the Bassham-Benson-Calvin (BBC) cycle. The model correctly describes pH-dependent feedback control of electron transport in chloroplasts and adequately reproduces a variety of experimental data on induction events observed under different experimental conditions in intact chloroplasts (variations of CO2 and O2 concentrations in atmosphere), including a complex kinetics of P700 (primary electron donor in PSI) photooxidation, CO2 consumption in the BBC cycle, and photorespiration. Finally, we describe diffusion-controlled photosynthetic processes in chloroplasts within the framework of the model that takes into account complex architecture of
Furbish, D. J.
2009-04-01
Sediment particles transported by rainsplash, by bioturbation, and as bedload in turbulent flows, undergo motions that are quasi-random in magnitude and direction. Moreover, these motions characteristically are intermittent, in that particles are mostly at rest most of the time, and heterogeneous, in that the volumetric or areal concentration of particles in motion at any instant is spatially patchy. These particle motions can be formulated as a stochastic processes involving both advective and dispersive parts. By taking into account the intermittent activity of particles, and separating this activity from the physics of motion in the parametric description of transport, the formulation indicates that gradients in particle activity can have a key role in transport. The formulation illustrates, for example, how the growth of soil mounds beneath desert shrubs involves differential rainsplash that initially causes more grains to be splashed inward beneath protective shrub canopies than outward. This ‘harvesting' of nearby soil material, including nutrients, means that shrubs locally participate in regulating the rate sediment transport down a hillslope. With soil bioturbation, spatial variations in the disturbance frequency strongly influence the mixing of soil constituents, including distinct particle fractions (such as specific size or mineral fractions, seeds, or debitage), or elements and compounds adsorbed to particles. The formulation also provides a probabilistic version of the Exner equation. During bedload transport, gradients in particle activity, through both advective and dispersive effects, may contribute importantly to the local divergence of the particle flux, thereby influencing initial bedform growth.
Electrokinetic Particle Transport in Micro-Nanofluidics Direct Numerical Simulation Analysis
Qian, Shizhi
2012-01-01
Numerous applications of micro-/nanofluidics are related to particle transport in micro-/nanoscale channels, and electrokinetics has proved to be one of the most promising tools to manipulate particles in micro/nanofluidics. Therefore, a comprehensive understanding of electrokinetic particle transport in micro-/nanoscale channels is crucial to the development of micro/nano-fluidic devices. Electrokinetic Particle Transport in Micro-/Nanofluidics: Direct Numerical Simulation Analysis provides a fundamental understanding of electrokinetic particle transport in micro-/nanofluidics involving elect
Electron transport to nitrogenase in Klebsiella pneumoniae.
1980-01-01
Cell-free extracts of nifF and nifJ mutants of Klebsiella pneumoniae are unable to couple acetylene reduction (N2 fixation) by nitrogenase to the oxidation of organic metabolites. However, nifF and nifJ mutants can complement each other in vitro to establish the coupling. This indicates that the products of the nifF and nifJ genes constitute essential elements of the physiological electron pathway to nitrogenase. The electron-transfer-active product of the nifF gene, a flavoprotein, has been ...
A Deterministic Transport Code for Space Environment Electrons
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.
Electronic transport and scattering times in tungsten-decorated graphene
Elias, Jamie A.; Henriksen, Erik A.
2017-02-01
The electronic transport properties of a monolayer graphene device have been studied before and after the deposition of a dilute coating of tungsten adatoms on the surface. For coverages up to 2.5% of a monolayer, we find tungsten adatoms simultaneously donate electrons to graphene and reduce the carrier mobility, impacting the zero- and finite-field transport properties. Two independent transport analyses suggest the adatoms lie nearly 1 nm above the surface. The presence of adatoms is also seen to impact the low-field magnetoresistance, altering the signatures of weak localization.
Transport phenomena in disordered interacting electron systems
Michaeli, Karen
We develop a user friendly scheme based on the quantum kinetic equation for studying electric and thermal transport phenomena in the presence of interactions and disorder. We demonstrate that this scheme is suitable for both a systematic perturbative calculation as well as a general analysis. The work was motivated by the growing number of experiments of thermal and thermoelectric transport, and the absence of adequate theoretical tools for studying them. In particular, for thermal transport, the widely used Kubo formula is rather cumbersome. In this thesis, we present a systematic derivation of the quantum kinetic approach which we believe can be a good alternative to the Kubo formula. One main advantage of the kinetic approach is that it provides us with an intuitive picture for both electric and thermal transport. The strength of our scheme is in its generality that allow us to apply it for different kinds of interactions. We study the effect of the superconducting fluctuations on the Hall and Nernst effects. We show that the strong Nernst effect observed recently in amorphous superconducting films far above the critical temperature is caused by the fluctuations of the superconducting order parameter. We demonstrate that in the limit T → 0 the contribution of the magnetization ensures the vanishing of the Nernst signal in accordance with the third law of thermodynamics. We obtained a striking agreement between our theoretical calculations and the experimental data in a broad region of temperatures and magnetic fields. In addition, we present the calculation of the Hall conductivity in the vicinity of the superconducting transition driven by a magnetic field. We discuss the peculiar feature of both the Hall coefficient and Nernst signal anticipated near the quantum phase transition.
Kerschnitzki, Michael; Akiva, Anat; Ben Shoham, Adi; Koifman, Naama; Shimoni, Eyal; Rechav, Katya; Arraf, Alaa A; Schultheiss, Thomas M; Talmon, Yeshayahu; Zelzer, Elazar; Weiner, Stephen; Addadi, Lia
2016-02-01
During bone formation in embryos, large amounts of calcium and phosphate are taken up and transported to the site where solid mineral is first deposited. The initial mineral forms in vesicles inside osteoblasts and is deposited as a highly disordered calcium phosphate phase. The mineral is then translocated to the extracellular space where it penetrates the collagen matrix and crystallizes. To date little is known about the transport mechanisms of calcium and phosphate in the vascular system, especially when high transport rates are needed and the concentrations of these ions in the blood serum may exceed the solubility product of the mineral phase. Here we used a rapidly growing biological model, the chick embryo, to study the bone mineralization pathway taking advantage of the fact that large amounts of bone mineral constituents are transported. Cryo scanning electron microscopy together with cryo energy dispersive X-ray spectroscopy and focused-ion beam imaging in the serial surface view mode surprisingly reveal the presence of abundant vesicles containing small mineral particles in the lumen of the blood vessels. Morphologically similar vesicles are also found in the cells associated with bone formation. This observation directly implicates the vascular system in solid mineral distribution, as opposed to the transport of ions in solution. Mineral particle transport inside vesicles implies that far larger amounts of the bone mineral constituents can be transported through the vasculature, without the danger of ectopic precipitation. This introduces a new stage into the bone mineral formation pathway, with the first mineral being formed far from the bone itself.
Numerical Solution of the Equation of Electron Transport in Matter
Golovin, A I
2002-01-01
One introduces a numerical approach to solve equation of fast electron transport in a matter in plane and spherical geometry with regard to fluctuations of energy losses and generation of secondary electrons. Calculation results are shown to be in line with the experimental data. One compared the introduced approach with the method of moments
Electron thermal transport barriers in RTP: experiment and modelling
Schilham, A.M.R.; Hogeweij, G. M. D.; Cardozo, N. J. L.
2001-01-01
Experiments in which very localized electron cyclotron heating (ECH) is scanned through the RTP plasma show sharp transitions, in which the electron temperature profile abruptly changes shape. The phenomenology-the profiles shapes, the sharp transitions-can be reproduced with a transport model which
Considerations of beta and electron transport in internal dose calculations
Bolch, W.E.; Poston, J.W. Sr.
1990-12-01
Ionizing radiation has broad uses in modern science and medicine. These uses often require the calculation of energy deposition in the irradiated media and, usually, the medium of interest is the human body. Energy deposition from radioactive sources within the human body and the effects of such deposition are considered in the field of internal dosimetry. In July of 1988, a three-year research project was initiated by the Nuclear Engineering Department at Texas A M University under the sponsorship of the US Department of Energy. The main thrust of the research was to consider, for the first time, the detailed spatial transport of electron and beta particles in the estimation of average organ doses under the Medical Internal Radiation Dose (MIRD) schema. At the present time (December of 1990), research activities are continuing within five areas. Several are new initiatives begun within the second or third year of the current contract period. They include: (1) development of small-scale dosimetry; (2) development of a differential volume phantom; (3) development of a dosimetric bone model; (4) assessment of the new ICRP lung model; and (5) studies into the mechanisms of DNA damage. A progress report is given for each of these tasks within the Comprehensive Report. In each case, preliminary results are very encouraging and plans for further research are detailed within this document.
Kopp, Andreas; Wiengarten, Tobias; Fichtner, Horst; Effenberger, Frederic; Kühl, Patrick; Heber, Bernd; Raath, Jan-Louis; Potgieter, Marius S.
2017-03-01
The transport of cosmic rays (CRs) in the heliosphere is determined by the properties of the solar wind plasma. The heliospheric plasma environment has been probed by spacecraft for decades and provides a unique opportunity for testing transport theories. Of particular interest for the three-dimensional (3D) heliospheric CR transport are structures such as corotating interaction regions (CIRs), which, due to the enhancement of the magnetic field strength and magnetic fluctuations within and due to the associated shocks as well as stream interfaces, do influence the CR diffusion and drift. In a three-fold series of papers, we investigate these effects by modeling inner-heliospheric solar wind conditions with the numerical magnetohydrodynamic (MHD) framework Cronos (Wiengarten et al., referred as Paper I), and the results serve as input to a transport code employing a stochastic differential equation approach (this paper). While, in Paper I, we presented results from 3D simulations with Cronos, the MHD output is now taken as an input to the CR transport modeling. We discuss the diffusion and drift behavior of Galactic cosmic rays using the example of different theories, and study the effects of CIRs on these transport processes. In particular, we point out the wide range of possible particle fluxes at a given point in space resulting from these different theories. The restriction of this variety by fitting the numerical results to spacecraft data will be the subject of the third paper of this series.
Transport of secondary electrons and reactive species in ion tracks
Surdutovich, Eugene
2015-01-01
The transport of reactive species brought about by ions traversing tissue-like medium is analysed analytically. Secondary electrons ejected by ions are capable of ionizing other molecules; the transport of these generations of electrons is studied using the random walk approximation until these electrons remain ballistic. Then, the distribution of solvated electrons produced as a result of interaction of low-energy electrons with water molecules is obtained. The radial distribution of energy loss by ions and secondary electrons to the medium yields the initial radial dose distribution, which can be used as initial conditions for the predicted shock waves. The formation, diffusion, and chemical evolution of hydroxyl radicals in liquid water are studied as well.
Limburg, B; Bouwman, E; Bonnet, S
2015-12-14
Unidirectional photocatalytic electron transfer from a hydrophilic electron donor encapsulated in the interior of a liposome, to a hydrophilic electron acceptor on the other side of the membrane, has been achieved using the simple membrane-soluble electron relay 1-methoxy-N-methylphenazinium (MMP(+)). The total amount of photoproduct (>140 nmol) exceeds the number of moles of MMP(+) present (125 nmol), thus showing that the transport of electrons is catalytic.
Grad-B drift transport of high current electron beams
Lee, J.R.; Backstrom, R.C.; Halbleib, J.A.; Wright, T.P.
1983-01-01
Grad-B transport, bunching and focusing of relativistic electron beams has been proposed as a method of increasing the power delivered to an ICF target by an order of magnitude. Recent experiments have demonstrated the efficient transport of high current electron beams over 1.0 m distances in the 1/r azimuthal magnetic field of a current-carrying wire. The electron drift velocity was measured as a function of wire current and found to be in good agreement with theory. Measurements of x-ray production in a tantalum target were used as a diagnostic tool to study transport efficiency. A theoretical model of the experiment was developed to calculate bremsstrahlung production in the target, assuming 100 percent transport efficiency. This model predicted radial x-ray dose profiles in the experimental converter assembly which were in good agreement with the measurements.
Electron Trapping and Charge Transport by Large Amplitude Whistlers
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.
Single-particle cryo-electron microscopy of macromolecular assemblies
Cheng, Kimberley
2009-01-01
In this thesis, single-particle cryo-electron microscopy (cryo-EM) was used to study the structure of three macromolecular assemblies: the two hemocyanin isoforms from Rapana thomasiana, the Pyrococcus furiosus chaperonin, and the ribosome from Escherichia coli. Hemocyanins are large respiratory proteins in arthropods and molluscs. Most molluscan hemocyanins exist as two distinct isoforms composed of related polypeptides. In most species the two isoforms differ in terms of their oligomeric st...
Elimination of Ferromagnetic Particles Aggregation for Investigation by Electron Microscopy
О.S. Kuzema
2011-01-01
Full Text Available It has been described the device for sample preparation of highly dispersed ferromagnetic powders including micropowders for permanent magnets, magnetic carriers, machine and mechanism components’ wear products contained in lubricants for investigation of these materials by light and electron microscopy. The device eliminates the coalescence of ferromagnetic particles and improves reliability of the results of such objects investigation. The technique of such device application has been described and exemplified for various materials investigation.
Electronic transport in Si:P δ-doped wires
Smith, J. S.; Drumm, D. W.; Budi, Akin
2015-01-01
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...... 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....
Electron transport through nuclear pasta in magnetized neutron stars
Yakovlev, D G
2015-01-01
We present a simple model for electron transport in a possible layer of exotic nuclear clusters (in the so called nuclear pasta layer) between the crust and liquid core of a strongly magnetized neutron star. The electron transport there can be strongly anisotropic and gyrotropic. The anisotropy is produced by different electron effective collision frequencies along and across local symmetry axis in domains of exotic ordered nuclear clusters and by complicated effects of the magnetic field. We also calculate averaged kinetic coefficients in case local domains are freely oriented. Possible applications of the obtained results and open problems are outlined.
Chi, Yujie; Tian, Zhen; Jia, Xun
2016-08-01
Monte Carlo (MC) particle transport simulation on a graphics-processing unit (GPU) platform has been extensively studied recently due to the efficiency advantage achieved via massive parallelization. Almost all of the existing GPU-based MC packages were developed for voxelized geometry. This limited application scope of these packages. The purpose of this paper is to develop a module to model parametric geometry and integrate it in GPU-based MC simulations. In our module, each continuous region was defined by its bounding surfaces that were parameterized by quadratic functions. Particle navigation functions in this geometry were developed. The module was incorporated to two previously developed GPU-based MC packages and was tested in two example problems: (1) low energy photon transport simulation in a brachytherapy case with a shielded cylinder applicator and (2) MeV coupled photon/electron transport simulation in a phantom containing several inserts of different shapes. In both cases, the calculated dose distributions agreed well with those calculated in the corresponding voxelized geometry. The averaged dose differences were 1.03% and 0.29%, respectively. We also used the developed package to perform simulations of a Varian VS 2000 brachytherapy source and generated a phase-space file. The computation time under the parameterized geometry depended on the memory location storing the geometry data. When the data was stored in GPU's shared memory, the highest computational speed was achieved. Incorporation of parameterized geometry yielded a computation time that was ~3 times of that in the corresponding voxelized geometry. We also developed a strategy to use an auxiliary index array to reduce frequency of geometry calculations and hence improve efficiency. With this strategy, the computational time ranged in 1.75-2.03 times of the voxelized geometry for coupled photon/electron transport depending on the voxel dimension of the auxiliary index array, and in 0
Chi, Yujie; Tian, Zhen; Jia, Xun
2016-08-01
Monte Carlo (MC) particle transport simulation on a graphics-processing unit (GPU) platform has been extensively studied recently due to the efficiency advantage achieved via massive parallelization. Almost all of the existing GPU-based MC packages were developed for voxelized geometry. This limited application scope of these packages. The purpose of this paper is to develop a module to model parametric geometry and integrate it in GPU-based MC simulations. In our module, each continuous region was defined by its bounding surfaces that were parameterized by quadratic functions. Particle navigation functions in this geometry were developed. The module was incorporated to two previously developed GPU-based MC packages and was tested in two example problems: (1) low energy photon transport simulation in a brachytherapy case with a shielded cylinder applicator and (2) MeV coupled photon/electron transport simulation in a phantom containing several inserts of different shapes. In both cases, the calculated dose distributions agreed well with those calculated in the corresponding voxelized geometry. The averaged dose differences were 1.03% and 0.29%, respectively. We also used the developed package to perform simulations of a Varian VS 2000 brachytherapy source and generated a phase-space file. The computation time under the parameterized geometry depended on the memory location storing the geometry data. When the data was stored in GPU’s shared memory, the highest computational speed was achieved. Incorporation of parameterized geometry yielded a computation time that was ~3 times of that in the corresponding voxelized geometry. We also developed a strategy to use an auxiliary index array to reduce frequency of geometry calculations and hence improve efficiency. With this strategy, the computational time ranged in 1.75-2.03 times of the voxelized geometry for coupled photon/electron transport depending on the voxel dimension of the auxiliary index array, and in 0
Optical principles of beam transport for relativistic electron cooling
A. Burov
2000-09-01
Full Text Available In conventional low energy electron coolers, the electron beam is immersed in a continuous solenoid, which provides a calm and tightly focused beam in a cooling section. While suitable for low energies, the continuity of the accompanying magnetic field is hardly realizable at relativistic energies. We consider the possibility of using an extended solenoid in the gun and the cooling section only, applying lumped focusing for the rest of the electron transport line.
Electronic and Ionic Transport in Polymers
1988-07-12
containing electrolytes such as Bu4,NBF4 and LiBF4 to demonstrate the effect of ion size on charge transport. We show that, compared to polypyrrole, in the...activated molecular sieves prior to use. Tetrabutylammonium fluoroborate (TBABF4), lithium fluoroborate ( LiBF4 ), and tetraethyl- ammonium tosylate...0.1M ( LiBF4 ) is shown in S Figure 2 with the CV for polypyrrole (PP) in the same medium for comparison. The apparent , oscillations in the CV of the
Particle model for nonlocal heat transport in fusion plasmas.
Bufferand, H; Ciraolo, G; Ghendrih, Ph; Lepri, S; Livi, R
2013-02-01
We present a simple stochastic, one-dimensional model for heat transfer in weakly collisional media as fusion plasmas. Energies of plasma particles are treated as lattice random variables interacting with a rate inversely proportional to their energy schematizing a screened Coulomb interaction. We consider both the equilibrium (microcanonical) and nonequilibrium case in which the system is in contact with heat baths at different temperatures. The model exhibits a characteristic length of thermalization that can be associated with an interaction mean free path and one observes a transition from ballistic to diffusive regime depending on the average energy of the system. A mean-field expression for heat flux is deduced from system heat transport properties. Finally, it is shown that the nonequilibrium steady state is characterized by long-range correlations.
Vectorising the detector geometry to optimize particle transport
Apostolakis, John; Carminati, Federico; Gheata, Andrei; Wenzel, Sandro
2014-01-01
Among the components contributing to particle transport, geometry navigation is an important consumer of CPU cycles. The tasks performed to get answers to "basic" queries such as locating a point within a geometry hierarchy or computing accurately the distance to the next boundary can become very computing intensive for complex detector setups. So far, the existing geometry algorithms employ mainly scalar optimisation strategies (voxelization, caching) to reduce their CPU consumption. In this paper, we would like to take a different approach and investigate how geometry navigation can benefit from the vector instruction set extensions that are one of the primary source of performance enhancements on current and future hardware. While on paper, this form of microparallelism promises increasing performance opportunities, applying this technology to the highly hierarchical and multiply branched geometry code is a difficult challenge. We refer to the current work done to vectorise an important part of the critica...
Battaglia, D. J. [PPPL; Boedo, J. A. [University of California San Diego; Burrell, K. H. [General Atomics; Chang, C. S. [PPPL; Canik, J. M. [ORNL; deGrassie, J. S. [General Atomics; Gerhardt, S. P. [PPPL; Grierson, B. A. [General Atomics; Groebner, R. J. [General Atomics; Maingi, Rajesh [PPPL; Smith, S. P. [General Atomics
2014-09-01
Energy and particle transport rates are decoupled in the H-mode edge since the ion thermal transport rate is primarily set by the neoclassical transport of the deuterium ions in the tail of the thermal energy distribution, while the net particle transport rate is set by anomalous transport of the colder bulk ions. Ion orbit loss drives the energy distributions away from Maxwellian, and describes the anisotropy, poloidal asymmetry and local minimum near the separatrix observed in the Ti profile. Non-Maxwellian distributions also drive large intrinsic edge flows, and the interaction of turbulence at the top of the pedestal with the intrinsic edge flow can generate an intrinsic core torque. The primary driver of the radial electric field (Er) in the pedestal and scrapeoff layer (SOL) are kinetic neoclassical effects, such as ion orbit loss of tail ions and parallel electron loss to the divertor. This paper describes the first multi-species kinetic neoclassical transport calculations for ELM-free H-mode pedestal and scrape-off layer on DIII-D using XGC0, a 5D full-f particle-in-cell drift-kinetic solver with self-consistent neutral recycling and sheath potentials. Quantitative agreement between the flux-driven simulation and the experimental electron density, impurity density and orthogonal measurements of impurity temperature and flow profiles is achieved by adding random-walk particle diffusion to the guiding-center drift motion. This interpretative technique quantifies the role of neoclassical, anomalous and neutral transport to the overall pedestal structure, and consequently illustrates the importance of including kinetic effects self-consistently in transport calculations around transport barriers.
Iosune Ibiricu
2011-12-01
Full Text Available During herpes simplex virus 1 (HSV1 egress in neurons, viral particles travel from the neuronal cell body along the axon towards the synapse. Whether HSV1 particles are transported as enveloped virions as proposed by the 'married' model or as non-enveloped capsids suggested by the 'separate' model is controversial. Specific viral proteins may form a recruitment platform for microtubule motors that catalyze such transport. However, their subviral location has remained elusive. Here we established a system to analyze herpesvirus egress by cryo electron tomography. At 16 h post infection, we observed intra-axonal transport of progeny HSV1 viral particles in dissociated hippocampal neurons by live-cell fluorescence microscopy. Cryo electron tomography of frozen-hydrated neurons revealed that most egressing capsids were transported independently of the viral envelope. Unexpectedly, we found not only DNA-containing capsids (cytosolic C-capsids, but also capsids lacking DNA (cytosolic A-/B-capsids in mid-axon regions. Subvolume averaging revealed lower amounts of tegument on cytosolic A-/B-capsids than on C-capsids. Nevertheless, all capsid types underwent active axonal transport. Therefore, even few tegument proteins on the capsid vertices seemed to suffice for transport. Secondary envelopment of capsids was observed at axon terminals. On their luminal face, the enveloping vesicles were studded with typical glycoprotein-like spikes. Furthermore, we noted an accretion of tegument density at the concave cytosolic face of the vesicle membrane in close proximity to the capsids. Three-dimensional analysis revealed that these assembly sites lacked cytoskeletal elements, but that filamentous actin surrounded them and formed an assembly compartment. Our data support the 'separate model' for HSV1 egress, i.e. progeny herpes viruses being transported along axons as subassemblies and not as complete virions within transport vesicles.
Gyrokinetic Particle Simulation of Turbulent Transport in Burning Plasmas
Diamond, P.H.; Lin, Z.; Wang, W.; Horton, W.; Klasky, S.; Decyk, V.; Ma, K.-L.; Chames, J.; Adams, M.
2011-09-21
The three-year project GPS-TTBP resulted in over 152 publications and 135 presentations. This summary focuses on the scientific progress made by the project team. A major focus of the project was on the physics intrinsic rotation in tokamaks. Progress included the first ever flux driven study of net intrinsic spin-up, mediated by boundary effects (in collaboration with CPES), detailed studies of the microphysics origins of the Rice scaling, comparative studies of symmetry breaking mechanisms, a pioneering study of intrinsic torque driven by trapped electron modes, and studies of intrinsic rotation generation as a thermodynamic engine. Validation studies were performed with C-Mod, DIII-D and CSDX. This work resulted in very successful completion of the FY2010 Theory Milestone Activity for OFES, and several prominent papers of the 2008 and 2010 IAEA Conferences. A second major focus was on the relation between zonal flow formation and transport non-locality. This culminated in the discovery of the ExB staircase - a conceptually new phenomenon. This also makes useful interdisciplinary contact with the physics of the PV staircase, well-known in oceans and atmospheres. A third topic where progress was made was in the simulation and theory of turbulence spreading. This work, now well cited, is important for understanding the dynamics of non-locality in turbulent transport. Progress was made in studies of conjectured non-diffusive transport in trapped electron turbulence. Pioneering studies of ITB formation, coupling to intrinsic rotation and hysteresis were completed. These results may be especially significant for future ITER operation. All told, the physics per dollar performance of this project was quite good. The intense focus was beneficial and SciDAC resources were essential to its success.
Wang, Haobin; Thoss, Michael
2016-12-01
The accuracy of the noninteracting electron approximation is examined for a model of vibrationally coupled electron transport in single molecule junction. In the absence of electronic-vibrational coupling, steady state transport in this model is described exactly by Landauer theory. Including coupling, both electronic-vibrational and vibrationally induced electron-electron correlation effects may contribute to the real time quantum dynamics. Using the multilayer multiconfiguration time-dependent Hartree (ML-MCTDH) theory to describe nuclear dynamics exactly while maintaining the noninteracting electron approximation for the electronic dynamics, the correlation effects are analyzed in different physical regimes. It is shown that although the noninteracting electron approximation may be reasonable for describing short time dynamics, it does not give the correct long time limit for certain initial conditions.
Antici, P. [Istituto Nazionale di Fisica Nucleare (INFN), Laboratori Nazionali di Frascati, Via E. Fermi, 40, 00044 Frascati (Italy); SAPIENZA, University of Rome, Dip. SBAI, Via A. Scarpa 14, 00161 Rome (Italy); INFN - Sezione di Roma, c/o Dipartimento di Fisica - SAPIENZA, University of Rome, P.le Aldo Moro, 2 - 00185 Rome (Italy); Bacci, A.; Chiadroni, E.; Ferrario, M.; Rossi, A. R. [Istituto Nazionale di Fisica Nucleare (INFN), Laboratori Nazionali di Frascati, Via E. Fermi, 40, 00044 Frascati (Italy); Benedetti, C. [University of Bologna and INFN - Bologna (Italy); Lancia, L.; Migliorati, M.; Mostacci, A.; Palumbo, L. [SAPIENZA, University of Rome, Dip. SBAI, Via A. Scarpa 14, 00161 Rome (Italy); INFN - Sezione di Roma, c/o Dipartimento di Fisica - SAPIENZA, University of Rome, P.le Aldo Moro, 2 - 00185 Rome (Italy); Serafini, L. [INFN-Milan and Department of Physics, University of Milan, Via Celoria 16, 20133 Milan (Italy)
2012-08-15
Laser-driven electron beamlines are receiving increasing interest from the particle accelerator community. In particular, the high initial energy, low emittance, and high beam current of the plasma based electron source potentially allow generating much more compact and bright particle accelerators than what conventional accelerator technology can achieve. Using laser-generated particles as injectors for generating beamlines could significantly reduce the size and cost of accelerator facilities. Unfortunately, several features of laser-based particle beams need still to be improved before considering them for particle beamlines and thus enable the use of plasma-driven accelerators for the multiple applications of traditional accelerators. Besides working on the plasma source itself, a promising approach to shape the laser-generated beams is coupling them with conventional accelerator elements in order to benefit from both a versatile electron source and a controllable beam. In this paper, we perform start-to-end simulations to generate laser-driven beamlines using conventional accelerator codes and methodologies. Starting with laser-generated electrons that can be obtained with established multi-hundred TW laser systems, we compare different options to capture and transport the beams. This is performed with the aim of providing beamlines suitable for potential applications, such as free electron lasers. In our approach, we have analyzed which parameters are critical at the source and from there evaluated different ways to overcome these issues using conventional accelerator elements and methods. We show that electron driven beamlines are potentially feasible, but exploiting their full potential requires extensive improvement of the source parameters or innovative technological devices for their transport and capture.
Antici, P.; Bacci, A.; Benedetti, C.; Chiadroni, E.; Ferrario, M.; Rossi, A. R.; Lancia, L.; Migliorati, M.; Mostacci, A.; Palumbo, L.; Serafini, L.
2012-08-01
Laser-driven electron beamlines are receiving increasing interest from the particle accelerator community. In particular, the high initial energy, low emittance, and high beam current of the plasma based electron source potentially allow generating much more compact and bright particle accelerators than what conventional accelerator technology can achieve. Using laser-generated particles as injectors for generating beamlines could significantly reduce the size and cost of accelerator facilities. Unfortunately, several features of laser-based particle beams need still to be improved before considering them for particle beamlines and thus enable the use of plasma-driven accelerators for the multiple applications of traditional accelerators. Besides working on the plasma source itself, a promising approach to shape the laser-generated beams is coupling them with conventional accelerator elements in order to benefit from both a versatile electron source and a controllable beam. In this paper, we perform start-to-end simulations to generate laser-driven beamlines using conventional accelerator codes and methodologies. Starting with laser-generated electrons that can be obtained with established multi-hundred TW laser systems, we compare different options to capture and transport the beams. This is performed with the aim of providing beamlines suitable for potential applications, such as free electron lasers. In our approach, we have analyzed which parameters are critical at the source and from there evaluated different ways to overcome these issues using conventional accelerator elements and methods. We show that electron driven beamlines are potentially feasible, but exploiting their full potential requires extensive improvement of the source parameters or innovative technological devices for their transport and capture.
Study of transport of laser-driven relativistic electrons in solid materials
Leblanc, Philippe
With the ultra intense lasers available today, it is possible to generate very hot electron beams in solid density materials. These intense laser-matter interactions result in many applications which include the generation of ultrashort secondary sources of particles and radiation such as ions, neutrons, positrons, x-rays, or even laser-driven hadron therapy. For these applications to become reality, a comprehensive understanding of laser-driven energy transport including hot electron generation through the various mechanisms of ionization, and their subsequent transport in solid density media is required. This study will focus on the characterization of electron transport effects in solid density targets using the state-of- the-art particle-in-cell code PICLS. A number of simulation results will be presented on the topics of ionization propagation in insulator glass targets, non-equilibrium ionization modeling featuring electron impact ionization, and electron beam guiding by the self-generated resistive magnetic field. An empirically derived scaling relation for the resistive magnetic in terms of the laser parameters and material properties is presented and used to derive a guiding condition. This condition may prove useful for the design of future laser-matter interaction experiments.
Vibrationally coupled electron transport through single-molecule junctions
Haertle, Rainer
2012-04-26
Single-molecule junctions are among the smallest electric circuits. They consist of a molecule that is bound to a left and a right electrode. With such a molecular nanocontact, the flow of electrical currents through a single molecule can be studied and controlled. Experiments on single-molecule junctions show that a single molecule carries electrical currents that can even be in the microampere regime. Thereby, a number of transport phenomena have been observed, such as, for example, diode- or transistor-like behavior, negative differential resistance and conductance switching. An objective of this field, which is commonly referred to as molecular electronics, is to relate these transport phenomena to the properties of the molecule in the contact. To this end, theoretical model calculations are employed, which facilitate an understanding of the underlying transport processes and mechanisms. Thereby, one has to take into account that molecules are flexible structures, which respond to a change of their charge state by a profound reorganization of their geometrical structure or may even dissociate. It is thus important to understand the interrelation between the vibrational degrees of freedom of a singlemolecule junction and the electrical current flowing through the contact. In this thesis, we investigate vibrational effects in electron transport through singlemolecule junctions. For these studies, we calculate and analyze transport characteristics of both generic and first-principles based model systems of a molecular contact. To this end, we employ a master equation and a nonequilibrium Green's function approach. Both methods are suitable to describe this nonequilibrium transport problem and treat the interactions of the tunneling electrons on the molecular bridge non-perturbatively. This is particularly important with respect to the vibrational degrees of freedom, which may strongly interact with the tunneling electrons. We show in detail that the resulting
EMC/FDTD/MD simulation of carrier transport and electrodynamics in two-dimensional electron systems
Sule, N.; Willis, K. J.; Hagness, S. C.; Knezevic, I.
2014-01-01
We present the implementation and application of a multiphysics simulation technique to carrier dynamics under electromagnetic excitation in supported two-dimensional electronic systems. The technique combines ensemble Monte Carlo (EMC) for carrier transport with finite-difference time-domain (FDTD) for electrodynamics and molecular dynamics (MD) for short-range Coulomb interactions among particles. We demonstrate the use of this EMC/FDTD/MD technique by calculating the room-temperature dc an...
Fokker-Planck description of electron and photon transport in homogeneous media
Akcasu, A. Ziya; Holloway, James Paul
1997-06-01
Starting from a Fokker-Planck description of particle transport, which is valid when the scattering is forwardly peaked and the energy change in scattering is small, we systematically obtain an approximate diffusionlike equation for the particle density by eliminating the direction variable Ω-hat with an elimination scheme based on Zwanzig's projection operator formalism in the interaction representation. The elimination procedure closely follows one described by Grigolini and Marchesoni [in Memory Function Approaches to Stochastic Problems in Condensed Matter, edited by Myron W. Evans, Paolo Grigolini, and Guiseppe P. Parravicini, Advances in Physical Chemistry, Vol. 62 (Wiley-Interscience, New York, 1985), Chap. II, p. 29], but with a different projection operator. The resulting diffusion equation is correct up to the second order in the coupling operator between the particle direction and position variable. The diffusion coefficients and mobility in the resulting diffusion equation depend on the initial distribution of the particles in direction and on the path length traveled by the particles. The full solution is obtained for a monoenergetic and monodirectional pulsed point source of particles in an infinite homogeneous medium. This solution is used to study the penetration and the transverse and longitudinal spread of the particles as they are transported through the medium. Application to diffusive wave spectroscopy in calculating the path-length distribution of photons, as well as application to dose calculations in tissue due to an electron beam are mentioned.
Low voltage scanning electron microscopy of interplanetary dust particles
Blake, D. F.; Bunch, T. E.; Reilly, T. W.; Brownlee, D. E.
1987-01-01
The resolution of available low-voltage SEM (LVSEM) models used in the characterization of interplanetary dust particles (IDPs) is limited by a number of factors including energy spread in the electron source, beam brightness, scanning electron detector geometry, and various lens aberrations. This paper describes an improved model of LVSEM which offers an increased resolution at low voltage. The improvements include a cold cathode FE source which has an extremely low inherent energy spread and high brightness, a second condenser lens to converge the beam and maintain an optimum aperture half-angle, and a detector optimized for low-voltage scanning-electron collection. To reduce lens aberrations, the specimen is immersed in the objective lens field. The features of several IDP samples observed using the images obtained with this LVSEM model are described.
Fast Frontend Electronics for high luminosity particle detectors
Cardinali, M; Bondy, M I Ferretti; Hoek, M; Lauth, W; Rosner, C; Sfienti, C; Thiel, M
2015-01-01
Future experiments of nuclear and particle physics are moving towards the high luminosity regime, in order to access suppressed processes like rare B decays or exotic charmonium resonances. In this scenario, high rate capability is a key requirement for electronics instrumentation, together with excellent timing resolution for precise event reconstruction. The development of dedicated FrontEnd Electronics (FEE) for detectors has become increasingly challenging. A current trend in R&D is towards multipurpose FEE which can be easily adapted to a great variety of detectors, without impairing the required high performance. We report on high-precision timing solutions which utilise high-bandwidth preamplifiers and fast discriminators providing Time-over-Threshold information, which can be used for charge measurements or walk corrections thus improving the obtainable timing resolution. The output signal are LVDS and can be directly fed into a multi-hit TDC readout. The performance of the electronics was investi...
Low voltage scanning electron microscopy of interplanetary dust particles
Blake, D. F.; Bunch, T. E.; Reilly, T. W.; Brownlee, D. E.
1987-01-01
The resolution of available low-voltage SEM (LVSEM) models used in the characterization of interplanetary dust particles (IDPs) is limited by a number of factors including energy spread in the electron source, beam brightness, scanning electron detector geometry, and various lens aberrations. This paper describes an improved model of LVSEM which offers an increased resolution at low voltage. The improvements include a cold cathode FE source which has an extremely low inherent energy spread and high brightness, a second condenser lens to converge the beam and maintain an optimum aperture half-angle, and a detector optimized for low-voltage scanning-electron collection. To reduce lens aberrations, the specimen is immersed in the objective lens field. The features of several IDP samples observed using the images obtained with this LVSEM model are described.
Hybrid Simulation of Laser-Plasma Interactions and Fast Electron Transport in Inhomogeneous Plasma
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.
Verification of Gyrokinetic Particle of Turbulent Simulation of Device Size Scaling Transport
LIN Zhihong; S. ETHIER; T. S. HAHM; W. M. TANG
2012-01-01
Verification and historical perspective are presented on the gyrokinetic particle simulations that discovered the device size scaling of turbulent transport and indentified the geometry model as the source of the long-standing disagreement between gyrokinetic particle and continuum simulations.
Graphical User Interface for High Energy Multi-Particle Transport Project
National Aeronautics and Space Administration — Computer codes such as MCNPX now have the capability to transport most high energy particle types (34 particle types now supported in MCNPX) with energies extending...
Study of electron transport in hydrocarbon gases
Hasegawa, H. [Tomakomai National College of Technology, Tomakomai 059-1275 (Japan); Date, H. [Faculty of Health Sciences, Hokkaido University, Sapporo 060-0812 (Japan)
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.
In Situ Electron Microscopy of Lactomicroselenium Particles in Probiotic Bacteria
Gabor Nagy
2016-06-01
Full Text Available Electron microscopy was used to test whether or not (a in statu nascendi synthesized, and in situ measured, nanoparticle size does not differ significantly from the size of nanoparticles after their purification; and (b the generation of selenium is detrimental to the bacterial strains that produce them. Elemental nano-sized selenium produced by probiotic latic acid bacteria was used as a lactomicroselenium (lactomicroSel inhibitor of cell growth in the presence of lactomicroSel, and was followed by time-lapse microscopy. The size of lactomicroSel produced by probiotic bacteria was measured in situ and after isolation and purification. For these measurements the TESLA BS 540 transmission electron microscope was converted from analog (aTEM to digital processing (dTEM, and further to remote-access internet electron microscopy (iTEM. Lactobacillus acidophilus produced fewer, but larger, lactomicroSel nanoparticles (200–350 nm than Lactobacillus casei (L. casei, which generated many, smaller lactomicroSel particles (85–200 nm and grains as a cloudy, less electrodense material. Streptococcus thermophilus cells generated selenoparticles (60–280 nm in a suicidic manner. The size determined in situ in lactic acid bacteria was significantly lower than those measured by scanning electron microscopy after the isolation of lactomicroSel particles obtained from lactobacilli (100–500 nm, but higher relative to those isolated from Streptococcus thermopilus (50–100 nm. These differences indicate that smaller lactomicroSel particles could be more toxic to the producing bacteria themselves and discrepancies in size could have implications with respect to the applications of selenium nanoparticles as prebiotics.
Relativistic particle transport in extragalactic jets: I. Coupling MHD and kinetic theory
Casse, F
2003-01-01
Multidimensional magneto-hydrodynamical (MHD) simulations coupled with stochastic differential equations (SDEs) adapted to test particle acceleration and transport in complex astrophysical flows are presented. The numerical scheme allows the investigation of shock acceleration, adiabatic and radiative losses as well as diffusive spatial transport in various diffusion regimes. The applicability of SDEs to astrophysics is first discussed in regards to the different regimes and the MHD code spatial resolution. The procedure is then applied to 2.5D MHD-SDE simulations of kilo-parsec scale extragalactic jets. The ability of SDE to reproduce analytical solutions of the diffusion-convection equation for electrons is tested through the incorporation of an increasing number of effects: shock acceleration, spatially dependent diffusion coefficients and synchrotron losses. The SDEs prove to be efficient in various shock configuration occurring in the inner jet during the development of the Kelvin-Helmholtz instability. ...
Behaviors of Electron Heat Transportation in HT-7 Sawtoothing Plasma
Hu Liqun; Xu Yi; Wan Baonian; Shi Yuejiang; Zhen Xiangjun; Chen Zhongyong; Lin Shiyao; HT-7 Team
2005-01-01
It is found that in HT-7 ohmic plasma, main energy loss comes from electron heat conduction, hence quantitative data of electron heat diffusivity is a very important issue for investigation of electron heat transportation behavior in different target plasmas so as to get high performance plasma. A time-to-peak method of the heat pulse propagation originating from the sawtooth activity on the soft x-ray intensity signal has been adopted to experimentally determine electron heat diffusivity XHPe on the HT-7 tokamak. Aiming to improve the signal-to-noise (S/N)ratio of the original signal to get a stable and reasonable electron heat diffusivity XHDe value, some data processing methods, including average of tens of sawteeth, is discussed. The electron heat diffusivity XHPe is larger than XPBe which is determined from the balance of background plasma power. Based on variation of the measured electron heat diffusivity XHPe, performances of different high confinement plasmas are analyzed.
ELECTRON TRANSPORT BEHAVIOURS IN THE NITROGEN DIRECT CURRENT GLOW DISCHARGE
ZHANG LIAN-ZHU; YU WEI; WANG JIU-LI; HAN LI; FU GUANG-SHENG
2001-01-01
A Monte Carlo simulation is presented to describe the electron transport behaviours in the nitrogen direct current glow discharge. The energy and angular distributions of the electrons at different positions of the cathode dark space are calculated; their energy and density distribution features throughout the entire discharge are discussed. The influence of molecular vibrational excitation, typical for electron-molecule collisions, has been studied and the elementary process of active species generation has been illustrated. The simulated results reveal that, in the cathode dark space, the high-energy electrons are mainly forward scattering and behave as a high-energy ‘electron beam'. The sharp increase of the number of secondary electrons plays an important role in producing active species at the interface between the cathode dark space and the negative glow region. The vibrational excitation enhances the energy loss of electrons in the negative glow region.
SciDAC Center for Gyrokinetic Particle Simulation of Turbulent Transport in Burning Plasmas
Lin, Zhihong [Univ. of California, Irvine, CA (United States)
2013-12-18
During the first year of the SciDAC gyrokinetic particle simulation (GPS) project, the GPS team (Zhihong Lin, Liu Chen, Yasutaro Nishimura, and Igor Holod) at the University of California, Irvine (UCI) studied the tokamak electron transport driven by electron temperature gradient (ETG) turbulence, and by trapped electron mode (TEM) turbulence and ion temperature gradient (ITG) turbulence with kinetic electron effects, extended our studies of ITG turbulence spreading to core-edge coupling. We have developed and optimized an elliptic solver using finite element method (FEM), which enables the implementation of advanced kinetic electron models (split-weight scheme and hybrid model) in the SciDAC GPS production code GTC. The GTC code has been ported and optimized on both scalar and vector parallel computer architectures, and is being transformed into objected-oriented style to facilitate collaborative code development. During this period, the UCI team members presented 11 invited talks at major national and international conferences, published 22 papers in peer-reviewed journals and 10 papers in conference proceedings. The UCI hosted the annual SciDAC Workshop on Plasma Turbulence sponsored by the GPS Center, 2005-2007. The workshop was attended by about fifties US and foreign researchers and financially sponsored several gradual students from MIT, Princeton University, Germany, Switzerland, and Finland. A new SciDAC postdoc, Igor Holod, has arrived at UCI to initiate global particle simulation of magnetohydrodynamics turbulence driven by energetic particle modes. The PI, Z. Lin, has been promoted to the Associate Professor with tenure at UCI.
Effect of dephasing on DNA sequencing via transverse electronic transport
Zwolak, Michael [Los Alamos National Laboratory; Krems, Matt [NON LANL; Pershin, Yuriy V [NON LANL; Di Ventra, Massimiliano [NON LANL
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.
Vadim V. Korablev
2016-06-01
Full Text Available Features of the formation of angular dependences of electrons emitted from a disordered solid and experiencing inelastic scattering have been considered. Such fine details of the dependences are formed by the processes of quantum transport of emitted particles. We took the cases of two-particle and multi-particle inelastic processes. Qualitative and quantitative assessments of the relative contributions of different groups of particles were carried out. The effects related to quantum electron transport were shown to be generally more pronounced in the case of registration of electrons generated inside the solid in the inelastic scattering of particles of the primary beam. This is true both for the electrons generated by ionization processes and Auger electrons. The obtained results point to the possibility of using this effect in applied electron spectroscopy.
Mitochondrial ROS Produced via Reverse Electron Transport Extend Animal Lifespan.
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
2016-04-12
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.
Application of Generalized Fokker-Planck Theory To Electron And Photon Transport In Tissue
Olbrant, Edgar
2009-01-01
We study a deterministic method for particle transport in tissue in selected medical applications. Generalized Fokker-Planck (GFP) theory has been developed to improve the Fokker-Planck (FP) equation in cases where scattering is forward-peaked and where there is a sufficient amount of large-angle scattering. We compare grid-based numerical solutions to Fokker-Planck and Generalized Fokker-Planck (GFP) in realistic applications. Electron dose calculations in heterogeneous parts of the human body are performed. Accurate electron scattering cross sections are therefore included and their incorporation in our model is extensively described. Moreover, we solve GFP approximations of the radiative transport equation to investigate reflectance and transmittance of light in tissue. All results are compared with either Monte Carlo or discrete-ordinates transport solutions.
Load balancing in highly parallel processing of Monte Carlo code for particle transport
Higuchi, Kenji; Takemiya, Hiroshi [Japan Atomic Energy Research Inst., Tokyo (Japan); Kawasaki, Takuji [Fuji Research Institute Corporation, Tokyo (Japan)
2001-01-01
In parallel processing of Monte Carlo(MC) codes for neutron, photon and electron transport problems, particle histories are assigned to processors making use of independency of the calculation for each particle. Although we can easily parallelize main part of a MC code by this method, it is necessary and practically difficult to optimize the code concerning load balancing in order to attain high speedup ratio in highly parallel processing. In fact, the speedup ratio in the case of 128 processors remains in nearly one hundred times when using the test bed for the performance evaluation. Through the parallel processing of the MCNP code, which is widely used in the nuclear field, it is shown that it is difficult to attain high performance by static load balancing in especially neutron transport problems, and a load balancing method, which dynamically changes the number of assigned particles minimizing the sum of the computational and communication costs, overcomes the difficulty, resulting in nearly fifteen percentage of reduction for execution time. (author)
Miyashita, Shin-Ichi; Mitsuhashi, Hiroaki; Fujii, Shin-Ichiro; Takatsu, Akiko; Inagaki, Kazumi; Fujimoto, Toshiyuki
2017-02-01
In order to facilitate reliable and efficient determination of both the particle number concentration (PNC) and the size of nanoparticles (NPs) by single-particle ICP-MS (spICP-MS) without the need to correct for the particle transport efficiency (TE, a possible source of bias in the results), a total-consumption sample introduction system consisting of a large-bore, high-performance concentric nebulizer and a small-volume on-axis cylinder chamber was utilized. Such a system potentially permits a particle TE of 100 %, meaning that there is no need to include a particle TE correction when calculating the PNC and the NP size. When the particle TE through the sample introduction system was evaluated by comparing the frequency of sharp transient signals from the NPs in a measured NP standard of precisely known PNC to the particle frequency for a measured NP suspension, the TE for platinum NPs with a nominal diameter of 70 nm was found to be very high (i.e., 93 %), and showed satisfactory repeatability (relative standard deviation of 1.0 % for four consecutive measurements). These results indicated that employing this total consumption system allows the particle TE correction to be ignored when calculating the PNC. When the particle size was determined using a solution-standard-based calibration approach without an NP standard, the particle diameters of platinum and silver NPs with nominal diameters of 30-100 nm were found to agree well with the particle diameters determined by transmission electron microscopy, regardless of whether a correction was performed for the particle TE. Thus, applying the proposed system enables NP size to be accurately evaluated using a solution-standard-based calibration approach without the need to correct for the particle TE.
Electron cross-sections and transport in liquids and biomolecules
White, Ronald; Casey, M.; Cocks, D.; Konvalov, D.; Brunger, M. J.; Garcia, G.; Petrovic, Z.; McEachran, R.; Buckman, S. J.; de Urquijo, J.
2016-09-01
Modelling of electron induced processes in plasma medicine and radiation damage is reliant on accurate self-consistent sets of cross-sections for electrons in tissue. These cross-sections (and associated transport theory) must accurately account not only the electron-biomolecule interactions but also for the soft-condensed nature of tissue. In this presentation, we report on recent swarm experiments for electrons in gaseous water and tetrahydrofuran using the pulsed-Townsend experiment, and the associated development of self-consistent cross-section sets that arise from them. We also report on the necessary modifications to gas-phase cross-sections required to accurately treat electron transport in liquids. These modifications involve the treatment of coherent scattering and screening of the electron interaction potential as well as the development of a new transport theory to accommodate these cross-sections. The accuracy of the ab-initio cross-sections is highlighted through comparison of theory and experiment for electrons in liquid argon and xenon.
Transport Properties of III-N Hot Electron Transistors
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.
Jeans Collapse of a System of Electron Emitting Dust Particles
Delzanno, G. L.; Lapenta, G.
2004-05-01
The collapse of a molecular cloud to form a planetary system is a classic process in astrophysics. The length scale of the collapsed system and the rate of its formation is described in the simplest model by the Jeans instability. When the model is complicated by additional processes, the rate and scale of the Jeans instability is modified [1]. We focus on the processes involved with the charging of the dust in the initial cloud. The presence of charge of the same sign on the dust particles inhibits the process of collapse. Yet, the process of charging is expected to be operational. We propose a mechanism that can explain this apparent contradiction. In a recent work [2], we have shown that in presence of electron emission from the dust the interaction potential of a dust particle becomes similar to the Lennard-Jones (LJ) potential. The important consequence of this discovery is that emitting dust particles with LJ like potential can actually attract each other even though they all share the same sign of charge. Here, we present a series of simulations conducted with a new code designed to study a large system of weakly coupled dust particles, interacting with a LJ like potential. [1] P. K. Shukla, Dust plasma interaction in space, Nova Science Publ., 2002. [2] G.L. Delzanno, G. Lapenta, M. Rosenberg, Phys. Rev. Lett., to appear.
Resolving Rapid Variation in Energy for Particle Transport
Haut, Terry Scot [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Computer, Computational, and Statistical Sciences Division; Ahrens, Cory Douglas [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Computer, Computational, and Statistical Sciences Division; Jonko, Alexandra [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Computer, Computational, and Statistical Sciences Division; Till, Andrew Thomas [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Computer, Computational, and Statistical Sciences Division; Lowrie, Robert Byron [Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Computer, Computational, and Statistical Sciences Division
2016-08-23
Resolving the rapid variation in energy in neutron and thermal radiation transport is needed for the predictive simulation capability in high-energy density physics applications. Energy variation is difficult to resolve due to rapid variations in cross sections and opacities caused by quantized energy levels in the nuclei and electron clouds. In recent work, we have developed a new technique to simultaneously capture slow and rapid variations in the opacities and the solution using homogenization theory, which is similar to multiband (MB) and to the finite-element with discontiguous support (FEDS) method, but does not require closure information. We demonstrated the accuracy and efficiency of the method for a variety of problems. We are researching how to extend the method to problems with multiple materials and the same material but with different temperatures and densities. In this highlight, we briefly describe homogenization theory and some results.
Quantum Transport in Solids: Two-Electron Processes.
1995-06-01
The central objective of this research program has been to study theoretically the underlying principles of quantum transport in solids. The area of...research investigated has emphasized the understanding of two electron processes in quantum transport . The problems have been treated analytically to...the extent possible through the use of dynamical localized Wannier functions. These results have been and are being incorporated in a full quantum
Terahertz electromodulation spectroscopy of electron transport in GaN
Engelbrecht, S. G.; Arend, T. R.; Zhu, T.; M. J. Kappers; Kersting, R.
2015-01-01
This is the accepted manuscript. The final version is available at http://scitation.aip.org/content/aip/journal/apl/106/9/10.1063/1.4914326. 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 fundamenta...
Barchyn, Thomas E.; Hugenholtz, Chris H.; Li, Bailiang; Neuman, Cheryl McKenna; Steven Sanderson, R.
2014-12-01
Despite almost a century of study, aeolian sediment transport remains difficult to measure. Low temporal resolution sediment traps filter sub-second scale variability hypothesized to be important, and high resolution electronic sensors are poorly tested, inconsistent, and often produce incomparable particle count outputs. No sediment transport prediction model can be validated or applied without quality empirical transport measurements. Here, we test a popular electronic laser gate sensor (Wenglor YH03PCT8, 'the Wenglor') in a wind tunnel. We have 3 goals: (i) assess the reproducibility of Wenglor measurements, (ii) examine saturation potential, and (iii) relate trap-measured sediment flux to particle counts. To assess reproducibility we measured particle counts with two co-located Wenglors. Temporally-autocorrelated sections of the time series occurred where one Wenglor deviated; this is likely the result of lens contamination. To examine saturation potential, we measured saltator velocity to calculate particle concentration within the airstream. Particle concentrations suggest the mean number of particles within the laser sampling volume is consistently less than one. To relate trap-measured sediment flux to particle counts, we used particle size samples to calculate an average mass per counted particle. We relate count predicted mass fluxes to trap-measured mass fluxes with linear regression and obtain the relation: trap flux = 2.1 * Wenglor predicted flux (r2 = 0.99). The constant represents aspects of the Wenglor operation that cannot be directly evaluated. Together, these investigations suggest the Wenglor provides a consistent and low-cost method to measure aeolian saltation flux at a high resolution in non-dusty settings.
Plasma membrane electron transport in frog blood vessels
Rashmi P Rao; K Nalini; J Prakasa Rao
2009-12-01
In an attempt to see if frog blood vessels possess a plasma membrane electron transport system, the postcaval vein and aorta isolated from Rana tigrina were tested for their ability to reduce ferricyanide, methylene blue, and 2,6-dichloroindophenol. While the dyes remained unchanged, ferricyanide was reduced to ferrocyanide. This reduction was resistant to inhibition by cyanide and azide. Heptane extraction or formalin fixation of the tissues markedly reduced the capability to reduce ferricyanide. Denuded aortas retained only 30% of the activity of intact tissue. Our results indicate that the amphibian postcaval vein and aorta exhibit plasma membrane electron transport
The influence of small intestinal mucus structure on particle transport ex vivo.
Bajka, Balázs H; Rigby, Neil M; Cross, Kathryn L; Macierzanka, Adam; Mackie, Alan R
2015-11-01
Mucus provides a barrier to bacteria and toxins while allowing nutrient absorption and waste transport. Unlike colonic mucus, small intestinal mucus structure is poorly understood. This study aimed to provide evidence for a continuous, structured mucus layer and assess the diffusion of different sized particles through it. Mucus structure was assessed by histology and immunohistochemistry. Ultra-structure was assessed by scanning electron microscopy. Tracking of 100 nm and 500 nm latex beads was conducted using ex vivo porcine mucus. The porcine jejunum and ileum were filled with mucus. Layered MUC2 staining was visible throughout the small intestine, covering villus tips. Scanning electron microscopy showed net-like mucin sheets covering villi (211 ± 7 nm pore diameter). Particle tracking of 100 nm latex beads, showed no inhibition of diffusion through mucus while 500 nm beads displayed limited diffusion. These results suggest a continuous mucus layer exists throughout the small intestine, which is highly stratified adjacent to the epithelium. The network observed is consistent with previous observations and correlates with stratified MUC2 staining. Mucin pore size is consistent with free diffusion of 100 nm and limited diffusion of 500 nm particles. Small Intestinal mucus structure has important implications for drug delivery systems and prevention and treatment of conditions like mucositis and inflammatory bowel disease.
A unified transport equation for both cosmic rays and thermal particles
Williams, L. L.; Schwadron, N.; Jokipii, J. R.; Gombosi, T. I.
1993-01-01
We present a unified transport equation that is valid for particles of all energies if the particle mean free paths are much smaller than macroscopic fluid length scales. If restricted to particles with random speeds much greater than fluid flow speeds, this equation reduces to the previously discussed extended cosmic-ray transport equation. It is significant that this allows one to describe the acceleration of particles from thermal energies to cosmic-ray energies using one transport equation. This is in contrast to previous transport equations (the Parker equation and the extended cosmic-ray transport equation), which were restricted to fast particles. The close connection to the extended cosmic-ray transport equation is demonstrated.
Electronic transport in benzodifuran single-molecule transistors.
Xiang, An; Li, Hui; Chen, Songjie; Liu, Shi-Xia; Decurtins, Silvio; Bai, Meilin; Hou, Shimin; Liao, Jianhui
2015-05-07
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.
Liu, Dingxin; Yang, Aijun; Wang, Xiaohua; Chen, Chen; Rong, Mingzhe; Kong, Michael G.
2016-12-01
In this letter, a 1D fluid model has been used to study the electron heating and particle transport in dual frequency atmospheric-pressure helium capacitive discharge with a high-frequency (HF) voltage of 10 MHz and a low-frequency (LF) voltage of 1 MHz. The electric field is decoupled to three components: the HF, the LF and the direct current (DC) ones, and they have much different effects on the plasmas. The eletrons in plasma bulk are mainly heated by the HF electric field, while in plasma sheath they are heated and cooled by the LF and DC electric fields, respectively. With a fixed total input power, the increase of LF power leads to great enhancement of the electrode fluxes of electrons and ions, especially for the energetic electrons of T e > 2 eV, because more power is dissipated in the vicinity of electrodes and the inelastic collision is more pronounced. Therefore, the particle transport on the treated sample can be greatly enhanced without additional gas heating in dual frequency plasmas, which meets the application requirements more compared to the single frequency plasmas.
Power electronics applied to industrial systems and transports
Patin, Nicolas
2015-01-01
If the operation of electronic components switching scheme to reduce congestion and losses (in power converters in general and switching power supplies in particular), it also generates electromagnetic type of pollution in its immediate environment. Power Electronics for Industry and Transport, Volume 4 is devoted to electromagnetic compatibility. It presents the sources of disturbance and the square wave signal, spectral modeling generic perturbation. Disturbances propagation mechanisms called ""lumped"" by couplings such as a common impedance, a parasitic capacitance or a mutual and ""dis
Transport of fast electrons in a nanowire array with collisional effects included
Li, Boyuan; Zhang, Zhimeng; Wang, Jian; Zhang, Bo; Zhao, Zongqing; Shan, Lianqiang; Zhou, Weimin; Zhang, Baohan [Science and Technology on Plasma Physics Laboratory, Laser Fusion Research Center, China Academy of Engineering Physics, 621900 Mianyang (China); Cao, Lihua [Center for Applied physics and Technology, HEDPs, Peking University, Beijing 100871 (China); Gu, Yuqiu, E-mail: yqgu@caep.ac.cn [Science and Technology on Plasma Physics Laboratory, Laser Fusion Research Center, China Academy of Engineering Physics, 621900 Mianyang (China); Center for Applied physics and Technology, HEDPs, Peking University, Beijing 100871 (China)
2015-12-15
The transport of picosecond laser generated fast electrons in a nanowire array is studied with two-dimensional particle-in-cell simulations. Our simulations show that a fast electron beam is initially guided and collimated by strong magnetic filaments in the array. Subsequently, after the decomposition of the structure of nanowire array due to plasma expansion, the beam is still collimated by the resistive magnetic field. An analytical model is established to give a criterion for long-term beam collimation in a nanowire array; it indicates that the nanowire cell should be wide enough to keep the beam collimated in picosecond scale.
Single electron charging and transport in silicon rich oxide
Yu Zhenrui; Aceves-Mijares, Mariano; Cabrera, Marco Antonio Ipina [Department of Electronics, INAOE, Apartado 51, Puebla, Puebla 72000 (Mexico)
2006-08-14
Single electron charging and single electron tunnelling effects were observed in silicon rich oxide (SRO). The devices used in this study have an Al/SRO/Si metal-oxide-semiconductor-like structure, where the SRO layer was deposited using low pressure chemical vapour deposition. Two types of Si nanodots (NDs), interface NDs and bulk NDs, were identified by transmission electron microscopy measurements. Under electric field, charges from the Si substrate are transferred into the interface NDs that locate at the interface, and each interface ND traps only one carrier. As the voltage increases, conduction paths between the Al electrode and the silicon substrate are formed, and the conduction of electrons is via sequential tunnelling through the bulk NDs. Due to the Coulomb blockade effect, only one electron tunnels on each nanodot at a specific electric field. The transport of the electrons through the Si nanodots is due to the Poole-Frenkel mechanism in the voltage regime studied.
Trieschmann, Jan; Schmidt, Frederik; Mussenbrock, Thomas
2016-01-01
The paper provides a tutorial to the conceptual layout of a self-consistently coupled Particle-In-Cell/Test-Particle model for the kinetic simulation of sputtering transport in capacitively coupled plasmas at low gas pressures. It explains when a kinetic approach is actually needed and which numerical concepts allow for the inherent nonequilibrium behavior of the charged and neutral particles. At the example of a generic sputtering discharge both the fundamentals of the applied Monte Carlo me...
Krauland, C. M.; Wei, M.; Zhang, S.; Santos, J.; Nicolai, P.; Theobald, W.; Kim, J.; Forestier-Colleoni, P.; Beg, F.
2016-10-01
Understanding the transport physics of a relativistic electron beam in various plasma regimes is crucial for many high-energy-density applications, such as fast heating for advanced ICF schemes and ion sources. Most short pulse laser-matter interaction experiments for transport studies have been performed with initially cold targets where the resistivity is far from that in warm dense plasmas. We present three experiments that have been performed on OMEGA EP in order to extend fast electron transport and energy coupling studies in pre-assembled plasmas from different carbon samples. Each experiment has used one 4 ns long pulse UV beam (1014 W/cm2) to drive a shockwave through the target and a 10 ps IR beam (1019 W/cm2) to create an electron beam moving opposite the shock propagation direction. These shots were compared with initially cold target shots without the UV beam. We fielded three different samples including 340 mg/cc CRF foam, vitreous carbon at 1.4 g/cc, and high density carbon at 3.4 g/cc. Electrons were diagnosed via x-ray fluorescence measurements from a buried Cu tracer in the target, as well as bremsstrahlung emission and escaped electrons reaching an electron spectrometer. Proton radiograph was also performed in the foam shots. Details of each experiment, available data and particle-in-cell simulations will be presented. This work is supported by US DOE NLUF Program, Grant Number DE-NA0002728.
Moroni, Beatrice; Cappelletti, David; Crocchianti, Stefano; Becagli, Silvia; Caiazzo, Laura; Traversi, Rita; Udisti, Roberto; Mazzola, Mauro; Markowicz, Krzysztof; Ritter, Christoph; Zielinski, Tymon
2017-05-01
A prolonged and exceptionally intense air mass advection event transporting biomass burning aerosols generated in Alaska affected Ny-Ålesund in the mid of July 2015. This paper reports the morphochemical characteristics and mixing state of individual aerosol particles collected during the event. To this aim aerosol samples were collected on nucleopore polycarbonate membrane filters using a DEKATI 12-stage low volume impactor and analyzed by scanning electron microscopy (SEM) techniques. Results of SEM investigations depict a complex aerosol characterized by an external mixing between a main part of carbonaceous organic particles (tar balls and organic particles), lower ammonium sulfate and minor potassium chloride and mineral dust amounts. The carbonaceous particles are spherical to slightly elongated and the organic particles show an internal mixing of low density organics and/or ammonium sulfate upon denser nuclei. Most particles are in the accumulation mode size range although the size and the morphology of the chloride and the sulfate salts evidence the growth of these species both in the air and upon the sampling membranes. Individual particle analyses were complemented by aerosol size distribution (Aerodynamic Particle Sizer, Scanning Mobility Particle Sizer) and optical (Particle Soot Absorption Photometer, nephelometer) measurements at ground level in order to retrieve the optical and radiative properties of the aerosol in the atmosphere and to predict the fate and behaviour of particles upon deposition at ground level. Individual particle analyses were also compared with bulk chemical analyses on daily sampling filters and back-trajectory analyses of the air mass movement in order to enucleate distinct sources of the aerosol during the long range transport.
Kinetic simulation of neutral particle transport in sputtering processes
Trieschmann, Jan; Gallian, Sara; Brinkmann, Ralf Peter; Mussenbrock, Thomas; Ries, Stefan; Bibinov, Nikita; Awakowicz, Peter
2013-09-01
For many physical vapor deposition applications using sputtering processes, knowledge about the detailed spatial and temporal evolution of the involved gas species is of great importance. Modeling of the involved gas dynamic and plasma processes is however challenging, because the operating pressure is typically below 1 Pa. In consequence, only kinetic descriptions are appropriate. In order to approach this problem, the dynamics of sputtered particle transport through a neutral gas background is simulated. For this study, a modified version of the three-dimensional Direct Simulation Monte Carlo (DSMC) code dsmcFoam is utilized. The impact of a transient sputtering wind is investigated in a generic reactor geometry, which may be used for dc Magnetron Sputtering (dcMS), High Power Impulse Magnetron Sputtering (HiPIMS), as well as sputtering in capacitively coupled discharges. In the present work a rarefaction of the background gas is observed. Moreover in pulsed mode the temporal dynamics of the rarefaction and subsequent recovery of the background gas is investigated. This work is supported by the German Research Foundation in the frame of TRR 87.
Drug transport in HEMA conjunctival inserts containing precipitated drug particles.
Gupta, Chhavi; Chauhan, Anuj
2010-07-01
This paper focuses on exploring the mechanism of cyclosporine A transport in hydroxyethyl methacrylate (HEMA) rods to develop conjunctival inserts for extended ocular delivery. Cylindrical conjunctival HEMA inserts were prepared by thermal polymerization in presence of drug at high loadings to create rods containing particles of drug dispersed in the matrix. The drug release rates were measured to explore the effect of length, drug loading, crosslinking, and mixing in the release medium. Also microstructure of the inserts was characterized by SEM imaging. The inserts release the drug for a period of about a month at therapeutic rates. The rates of drug release are zero order and independent of drug loading and crosslinking for certain period of time. These effects were shown to arise due to a mass-transfer boundary layer in the fluid and a mathematical model was developed by coupling mass transfer in the insert with that in the boundary layer in the surrounding fluid. The model with diffusivity in the insert and boundary layer thickness as parameters fits the experimental data and explains all trends in release kinetics. The fitted diffusivity is about twice that obtained by direct measurements, which agreed well with the value obtained by using the Brinkman's equation but only after accounting for drug binding to the polymer.
Transient Particle Transport Analysis on TJ-II Stellarator
Eguilior, S.; Castejon, F.; Guasp, J.; Estrada, T.; Medina, F.; Tabares, F.L.; Branas, B.
2006-12-18
Particle diffusivity and convective velocity have been determined in ECRH plasmas confined in the stellarator TJ-II by analysing the evolving density profile. This is obtained from an amplitude modulation reflectometry system in addition to an X-ray tomographic reconstruction. The source term, which is needed as an input for transport equations, is obtained using EIRENE code. In order to discriminate between the diffusive and convective contributions, the dynamics of the density evolution has been analysed in several perturbative experiments. This evolution has been considered in discharges with injection of a single pulse of H2 as well as in those that present a spontaneous transition to an enhanced confinement mode and whose confinement properties are modified by inducing an ohmic current. The pinch velocity and diffusivity are parameterized by different expressions in order to fit the experimental time evolution of density profile. The profile evolution is very different from one case to another due to the different values of convective velocities and diffusivities, besides the different source terms. (Author) 19 refs.
Particle Acceleration in Relativistic Electron-Ion Outlfows
Lloyd-Ronning, Nicole M
2016-01-01
We use the Los Alamos VPIC code to investigate particle acceleration in relativistic, unmagnetized, collisionless electron-ion plasmas. We run our simulations both with a realistic proton-to-electron mass ratio m_p/m_e = 1836, as well as commonly employed mass ratios of m_p/m_e =100 and 25, and show that results differ among the different cases. In particular, for the physically accurate mass ratio, electron acceleration occurs efficiently in a narrow region of a few hundred inertial lengths near the flow front, producing a power law dN/dgamma ~ gamma^(-p) with p ~ -2 developing over a few decades in energy, while acceleration is weak in the region far downstream. We find 20%, 10%, and 0.2% of the total energy given to the electrons for mass ratios of 25, 100, and 1836 respectively at a time of 2500 (w_p)^-1. Our simulations also show significant magnetic field generation just ahead of and behind the the flow front, with about 1% of the total energy going into the magnetic field for a mass ratio of 25 and 100...
Role of hot electron transport in scintillators: A theoretical study
Huang, Huihui [SZU-NUS Collaborative Innovation Center for Optoelectronic Science and Technology, Key Lab. of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen Univ. (China); Li, Qi [Physical Sciences Division, IBM TJ Watson Research Center, Yorktown Heights, NY (United States); Department of Computer Science, University of Illinois at Urbana-Champaign, Urbana, IL (United States); Lu, Xinfu; Williams, R.T. [Department of Physics, Wake Forest University, Winston Salem, NC (United States); Qian, Yiyang [College of Engineering and Applied Science, Nanjing University (China); Wu, Yuntao [Scintillation Materials Research Center, University of Tennessee, Knoxville, TN (United States)
2016-10-15
Despite recent intensive study on scintillators, several fundamental questions on scintillator properties are still unknown. In this work, we use ab-initio calculations to determine the energy dependent group velocity of the hot electrons from the electronic structures of several typical scintillators. Based on the calculated group velocities and optical phonon frequencies, a Monte-Carlo simulation of hot electron transport in scintillators is carried out to calculate the thermalization time and diffusion range in selected scintillators. Our simulations provide physical insights on a recent trend of improved proportionality and light yield from mixed halide scintillators. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Nonequilibrium Electron Transport Through a Quantum Dot from Kubo Formula
L(U) Rong; ZHANG Guang-Ming
2005-01-01
Based on the Kubo formula for an electron tunneling junction, we revisit the nonequilibrium transport properties through a quantum dot. Since the Fermi level of the quantum dot is set by the conduction electrons of the leads, we calculate the electron current from the left side by assuming the quantum dot coupled to the right lead as another side of the tunneling junction, and the other way round is used to calculate the current from the right side. By symmetrizing these two currents, an effective local density states on the dot can be obtained, and is discussed at high and low temperatures, respectively.
Nonlinear electron transport in normally pinched-off quantum wire
Novoselov, K.S.; Dubrovskii, Yu. V.; Sablikov, V. A.; Ivanov, D. Yu.; Vdovin, E. E.; Khanin, Yu N.; Tulin, V. A.; Esteve, D.; Beaumont, S.
2000-01-01
Nonlinear electron transport in normally pinched-off quantum wires was studied. The wires were fabricated from AlGaAs/GaAs heterostructures with high-mobility two-dimensional electron gas by electron beam lithography and following wet etching. At certain critical source-drain voltage the samples exhibited a step rise of the conductance. The differential conductance of the open wires was noticeably lower than e^2/h as far as only part of the source-drain voltage dropped between source contact ...
Transport Experiments on 2D Correlated Electron Physics in Semiconductors
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.
Molecular modeling of inelastic electron transport in molecular junctions
Jiang, Jun; Kula, Mathias; Luo, Yi
2008-09-01
A quantum chemical approach for the modeling of inelastic electron tunneling spectroscopy of molecular junctions based on scattering theory is presented. Within a harmonic approximation, the proposed method allows us to calculate the electron-vibration coupling strength analytically, which makes it applicable to many different systems. The calculated inelastic electron transport spectra are often in very good agreement with their experimental counterparts, allowing the revelation of detailed information about molecular conformations inside the junction, molecule-metal contact structures, and intermolecular interaction that is largely inaccessible experimentally.
Molecular modeling of inelastic electron transport in molecular junctions
Jiang Jun; Kula, Mathias; Luo Yi [Department of Theoretical Chemistry, School of Biotechnology, Royal Institute of Technology, S-106 91 Stockholm (Sweden)], E-mail: luo@kth.se
2008-09-17
A quantum chemical approach for the modeling of inelastic electron tunneling spectroscopy of molecular junctions based on scattering theory is presented. Within a harmonic approximation, the proposed method allows us to calculate the electron-vibration coupling strength analytically, which makes it applicable to many different systems. The calculated inelastic electron transport spectra are often in very good agreement with their experimental counterparts, allowing the revelation of detailed information about molecular conformations inside the junction, molecule-metal contact structures, and intermolecular interaction that is largely inaccessible experimentally.
Electron transport and coherence in semiconductor quantum dots and rings
Van der Wiel, W.G.
2002-01-01
A number of experiments on electron transport and coherence in semiconductor vertical and lateral quantum dots and semiconductor rings is described. Quantum dots are often referred to as "artificial atoms", because of their similarities with real atoms. Examples of such atom-like properties that
Electronic transport in gadolinium atomic-size contacts
Olivera, B.; Salgado, C.; Lado, J. L.; Karimi, A.; Henkel, V.; Scheer, E.; Fernández-Rossier, J.; Palacios, J. J.; Untiedt, C.
2017-02-01
We report on the fabrication, transport measurements, and density functional theory (DFT) calculations of atomic-size contacts made of gadolinium (Gd). Gd is known to have local moments mainly associated with f electrons. These coexist with itinerant s and d bands that account for its metallic character. Here we explore whether and how the local moments influence electronic transport properties at the atomic scale. Using both scanning tunneling microscope and lithographic mechanically controllable break junction techniques under cryogenic conditions, we study the conductance of Gd when only few atoms form the junction between bulk electrodes made of the very same material. Thousands of measurements show that Gd has an average lowest conductance, attributed to single-atom contact, below 2/e2 h . Our DFT calculations for monostrand chains anticipate that the f bands are fully spin polarized and insulating and that the conduction may be dominated by s , p , and d bands. We also analyze the electronic transport for model nanocontacts using the nonequilibrium Green's function formalism in combination with DFT. We obtain an overall good agreement with the experimental results for zero bias and show that the contribution to the electronic transport from the f channels is negligible and that from the d channels is marginal.
Kosov, Daniel S.
2017-02-01
On the elementary level, electronic current consists of individual electron tunnelling events that are separated by random time intervals. The waiting time distribution is a probability to observe the electron transfer in the detector electrode at time t +τ given that an electron was detected in the same electrode at an earlier time t. We study waiting time distribution for quantum transport in a vibrating molecular junction. By treating the electron-vibration interaction exactly and molecule-electrode coupling perturbatively, we obtain the master equation and compute the distribution of waiting times for electron transport. The details of waiting time distributions are used to elucidate microscopic mechanism of electron transport and the role of electron-vibration interactions. We find that as nonequilibrium develops in the molecular junction, the skewness and dispersion of the waiting time distribution experience stepwise drops with the increase of the electric current. These steps are associated with the excitations of vibrational states by tunnelling electrons. In the strong electron-vibration coupling regime, the dispersion decrease dominates over all other changes in the waiting time distribution as the molecular junction departs far away from the equilibrium.
Electron beam induced electronic transport in alkyl amine-intercalated VOx nanotubes
O'Dwyer, C.; Lavayen, V.; Clavijo-Cedeno, C.; Sotomayor Torres, C.M.
2008-01-01
The electron beam induced electronic transport in primary alkyl amine-intercalated V2O5 nanotubes is investigated where the organic amine molecules are employed as molecular conductive wires to an aminosilanized substrate surface and contacted to Au interdigitated electrode contacts. The results dem
Transport at low electron density in the two-dimensional electron gas of silicon MOSFETs
Heemskerk, Richard
1998-01-01
his thesis contains the result of an experimental study on the transport properties of high quality Si MOSFETs at low temperatures. A metalinsulator transition is found at a critical electron density. The electrons in the inversion layer of a silicon MOSFET are trapped in a potential well at the Si-
Geometrical effects on the electron residence time in semiconductor nano-particles
Koochi, Hakimeh [Physics Department, University of Birjand, Birjand 97175-615 (Iran, Islamic Republic of); Ebrahimi, Fatemeh, E-mail: f-ebrahimi@birjand.ac.ir [Physics Department, University of Birjand, Birjand 97175-615 (Iran, Islamic Republic of); Solar Energy Research Group, University of Birjand, Birjand (Iran, Islamic Republic of)
2014-09-07
We have used random walk (RW) numerical simulations to investigate the influence of the geometry on the statistics of the electron residence time τ{sub r} in a trap-limited diffusion process through semiconductor nano-particles. This is an important parameter in coarse-grained modeling of charge carrier transport in nano-structured semiconductor films. The traps have been distributed randomly on the surface (r{sup 2} model) or through the whole particle (r{sup 3} model) with a specified density. The trap energies have been taken from an exponential distribution and the traps release time is assumed to be a stochastic variable. We have carried out (RW) simulations to study the effect of coordination number, the spatial arrangement of the neighbors and the size of nano-particles on the statistics of τ{sub r}. It has been observed that by increasing the coordination number n, the average value of electron residence time, τ{sup ¯}{sub r} rapidly decreases to an asymptotic value. For a fixed coordination number n, the electron's mean residence time does not depend on the neighbors' spatial arrangement. In other words, τ{sup ¯}{sub r} is a porosity-dependence, local parameter which generally varies remarkably from site to site, unless we are dealing with highly ordered structures. We have also examined the effect of nano-particle size d on the statistical behavior of τ{sup ¯}{sub r}. Our simulations indicate that for volume distribution of traps, τ{sup ¯}{sub r} scales as d{sup 2}. For a surface distribution of traps τ{sup ¯}{sub r} increases almost linearly with d. This leads to the prediction of a linear dependence of the diffusion coefficient D on the particle size d in ordered structures or random structures above the critical concentration which is in accordance with experimental observations.
Energy-filtered Electron Transport Structures for Low-power Low-noise 2-D Electronics.
Pan, Xuan; Qiu, Wanzhi; Skafidas, Efstratios
2016-10-31
In addition to cryogenic techniques, energy filtering has the potential to achieve high-performance low-noise 2-D electronic systems. Assemblies based on graphene quantum dots (GQDs) have been demonstrated to exhibit interesting transport properties, including resonant tunnelling. In this paper, we investigate GQDs based structures with the goal of producing energy filters for next generation lower-power lower-noise 2-D electronic systems. We evaluate the electron transport properties of the proposed GQD device structures to demonstrate electron energy filtering and the ability to control the position and magnitude of the energy passband by appropriate device dimensioning. We also show that the signal-to-thermal noise ratio performance of the proposed nanoscale device can be modified according to device geometry. The tunability of two-dimensional GQD structures indicates a promising route for the design of electron energy filters to produce low-power and low-noise electronics.
Airborne bacteria transported with Sahara dust particles from Northern Africa to the European Alps
Lazzaro, A.; Meola, M.
2015-12-01
The Sahara Desert is the most important source of aerosols transported across the Mediterranean towards Europe. Airborne microorganisms associated with aerosols may be transported over long distances and act as colonizers of distant habitats. However, little is known on the composition and viability of such microorganisms, due to difficulties related to their detection, collection and isolation. Here we describe an in-depth assessment of the bacterial communities associated with Sahara dust (SD) particles deposited on snow. Two distinct SD events reaching the European Alps in February and May 2014 were preserved as distinct ochre-coloured layers within the snowpack. In June 2014, we collected samples from a snow profile at 3621 m a.s.l. close to the Jungfraujoch (Swiss Alps). SD particles were analyzed by Scanning Electron Microscopy and Energy-Dispersive X-Ray Spectroscopy (SEM-EDX). Backward trajectories were calculated using the NOAA HYSPLIT model. Bacterial communities were charac-terized by MiSeq Illumina sequencing of the 16S rRNA gene. Microbial physiological profiles were assessed by incubation of samples on BIOLOG plates. The SD-layers were generally enriched in illite and kaolinite particles as compared to the adjacent snow layers. The source of SD could be traced back to Algeria. We observed distinct bacterial community structures in the SD-layers as compared to the clean snow layers. While sporulating bacteria were not enriched in the SD-layers, low abundant (<1%) phyla such as Gemmatimonadetes and Deinococcus-Thermus appeared to be specific bioindicators for SD. Both phyla are adapted to arid oligotrophic environments and UV radiation and thus are well suited to survive the harsh conditions of long-distance airborne transport. Our results show that bacteria are viable and metabolically active after the trek to the European Alps.
Electronic transport through thiophene-1,4-dithiol molecule
Santos, Sergio Selma dos; Hobbi Junior, Edwin; Correia, Nestor Santos, E-mail: sergioss2001@yahoo.com.br [Universidade Estadual de Santa Cruz (UESC), Ilheus, BA (Brazil). Campus Soane Nazare de Andrade
2015-08-15
In this paper, we study electronic transport through thiophene-1,4-dithiol molecules attached to gold electrodes Au (111) and subjected to bias voltage. The choice of this molecule is justified by its promising applications in the construction of molecular devices. The electronic structure of thiophene-1,4-dithiol was investigated by using Density Functional Theory (DFT) combined with non-equilibrium Green's functions (NEGF), as implemented in TRANSIESTA program. We found that both an increased separation between the electrodes and the presence of anchor group S, cause an increase in transmittance through the molecule. Also, we obtain a structure in the transmittance curve, a Fano resonance feature, present in electronic transport phenomena in nanostructured devices. The results are reported in terms of transmittance versus energy around Fermi Level and voltage versus current plots. (author)
Interaction between SWCNTS and the mitochondriai electron transport chain
YanleiLiu; Yingge Zhang
2012-01-01
Objective： To investigate the effect of single-wall carbon nanotubes on the mitochondrial electron transport chain （METC） of tumor cells. Methods： Human hepatocarcinoma cell line HepG2 were cultured in DMEM medium （Hyclone） supplemented with 10% fetal calf serum （Gibco） in a atmosphere of 95% oxygen and 5% carbon dioxide under 37C. Cells were exposed by adding SWCNTs in the medium in concentrations of 1.5 - 12btg/ml. HepG2 cells exposed to narmal saline were used as control. The cells were collected after at 24h. The mitochondrial of HepG2 cells were obtained by density gradient centrifugation and were examined under transmis- sion electron microscope （TEM） . Four enzyme activity of the mitochondrial electron transport chain （METC） were determined by enzyme mark instrument. Results：
Electronic transport experiments on osmium-adatom-decorated graphene
Elias, Jamie; Henriksen, Erik
Monolayer graphene is theoretically predicted to inherit a spin-orbit coupling from a dilute coating of certain transition metal adatoms. To explore these predictions we have constructed a cryogenic probe capable of in situ thermal annealing of graphene followed immediately by electronic transport measurements and controlled deposition of sub-monolayer coatings of most any metal. Previously a light coating of indium on graphene was investigated, and found to transfer electrons to graphene and reduce the mobility although no evidence of an induced spin-orbit coupling was seen. We are now depositing osmium and tungsten on graphene devices. Our initial results show an unexpected hole-doping and a sizable increase in resistance of the sample. We will report our progress on characterizing these samples by electronic transport measurements.
Power electronics for renewable energy systems, transportation and industrial applications
Malinowski, Mariusz; Al-Haddad, Kamal
2014-01-01
Power Electronics for Renewable Energy, Transportation, and Industrial Applications combines state-of-the-art global expertise to present the latest research on power electronics and its application in transportation, renewable energy, and different industrial applications. This timely book aims to facilitate the implementation of cutting-edge techniques to design problems offering innovative solutions to the growing power demands in small- and large-size industries. Application areas in the book range from smart homes and electric and plug-in hybrid electrical vehicles (PHEVs), to smart distribution and intelligence operation centers where significant energy efficiency improvements can be achieved through the appropriate use and design of power electronics and energy storage devices.
Models and numerical methods for time- and energy-dependent particle transport
Olbrant, Edgar
2012-04-13
Particles passing through a medium can be described by the Boltzmann transport equation. Therein, all physical interactions of particles with matter are given by cross sections. We compare different analytical models of cross sections for photons, electrons and protons to state-of-the-art databases. The large dimensionality of the transport equation and its integro-differential form make it analytically difficult and computationally costly to solve. In this work, we focus on the following approximative models to the linear Boltzmann equation: (i) the time-dependent simplified P{sub N} (SP{sub N}) equations, (ii) the M{sub 1} model derived from entropy-based closures and (iii) a new perturbed M{sub 1} model derived from a perturbative entropy closure. In particular, an asymptotic analysis for SP{sub N} equations is presented and confirmed by numerical computations in 2D. Moreover, we design an explicit Runge-Kutta discontinuous Galerkin (RKDG) method to the M{sub 1} model of radiative transfer in slab geometry and construct a scheme ensuring the realizability of the moment variables. Among other things, M{sub 1} numerical results are compared with an analytical solution in a Riemann problem and the Marshak wave problem is considered. Additionally, we rigorously derive a new hierarchy of kinetic moment models in the context of grey photon transport in one spatial dimension. For the perturbed M{sub 1} model, we present numerical results known as the two beam instability or the analytical benchmark due to Su and Olson and compare them to the standard M{sub 1} as well as transport solutions.
ABCD-Type Law for Charged-Particle Beam Transport in Paraxial Approximation
陈宝信; 孙别和
2003-01-01
Based on the similarity between charged-particle beam transversal transport and transmission of ellipse Gaussian light beam in paraxial approximation, it is shown that charged-particle beam transversal transport in real space is governed by the ABCD-type law for a complex curvature radius of the charged-particle beam in which the beam transverse emittance plays the role of wavelength; from this, a novel technique for characterizing charged-particle beam is proposed. Finally, this analogy provides an insight observation that it is hopeful to attain possible coherent charged-particle beam in favourable accelerator environment.
Theory for the anomalous electron transport in Hall effect thrusters. II. Kinetic model
Lafleur, T.; Baalrud, S. D.; Chabert, P.
2016-05-01
In Paper I [T. Lafleur et al., Phys. Plasmas 23, 053502 (2016)], we demonstrated (using particle-in-cell simulations) the definite correlation between an anomalously high cross-field electron transport in Hall effect thrusters (HETs), and the presence of azimuthal electrostatic instabilities leading to enhanced electron scattering. Here, we present a kinetic theory that predicts the enhanced scattering rate and provides an electron cross-field mobility that is in good agreement with experiment. The large azimuthal electron drift velocity in HETs drives a strong instability that quickly saturates due to a combination of ion-wave trapping and wave-convection, leading to an enhanced mobility many orders of magnitude larger than that expected from classical diffusion theory. In addition to the magnetic field strength, B0, this enhanced mobility is a strong function of the plasma properties (such as the plasma density) and therefore does not, in general, follow simple 1 /B02 or 1 /B0 scaling laws.
Ultrafast electron transport in graphene and magnetic nanostructures
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.
Shaoping, Hu; Xincai, Chen; Jiyan, Shi; Yingxu, Chen; Qi, Lin
2008-05-01
The role of acid rain in affecting Pb and As transport from mine tailings was investigated by pumping simulated acid rain at a infiltration rate of 10.2 cm/h through soil columns. Simulated acid rain with pH of 3.0, 4.5 and 5.6 were used as leaching solutions. Results showed that 86.9-95.9% of Pb and 90-91.8% of As eluted from the columns were adsorbed by particles in the leachates. Scanning electron microscopy (SEM) analysis showed that particles released from the columns were mainly composed of flocculated aggregates and plate or rod shaped discrete grains. Transmission electron microscopy (TEM) coupled with energy dispersive X-ray analysis (EDX) showed that these particles were predominantly silicate minerals. Results from our experiments demonstrated that when rapid infiltration conditions or a rainstorm exist, particle-facilitated transport of contaminants is likely to the dominant metal transport pathway influenced by acid rain.
Carroll, Natalie R.
There are vast numbers of organic compounds that could be considered for use in molecular electronics. Hence there is a need for efficient and economical screening tools. Here we develop theoretical methods to describe electron transport through individual molecules, the ultimate goal of which is to establish design tools for molecular electronic devices. To successfully screen a compound for its use as a device component requires a proper representation of the quantum mechanics of electron transmission. In this work we report the development of tools for the description of electron transmission that are: Charge self-consistent, valid in the presence of a finite applied potential field and (in some cases) explicitly time-dependent. In addition, the tools can be extended to any molecular system, including biosystems, because they are free of restrictive parameterizations. Two approaches are explored: (1) correlation of substituent parameter values (sigma), (commonly found in organic chemistry textbooks) to properties associated with electron transport, (2) explicit tracking of the time evolution of the wave function of a nonstationary electron. In (1) we demonstrate that the a correlate strongly with features of the charge migration process, establishing them as useful indicators of electronic properties. In (2) we employ a time-dependent description of electron transport through molecular junctions. To date, the great majority of theoretical treatments of electron transport in molecular junctions have been of the time-independent variety. Time dependence, however, is critical to such properties as switching speeds in binary computer components and alternating current conductance, so we explored methods based on time-dependent quantum mechanics. A molecular junction is modeled as a single molecule sandwiched between two clusters of close-packed metal atoms or other donor and acceptor groups. The time dependence of electron transport is investigated by initially
Electronic transport in benzodifuran single-molecule transistors
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
Electronic Transport Properties of (7,0) Semiconducting Carbon Nanotube
SONG Jiu-Xu; YANG Yin-Wang; CHAI Chang-Chun; LIU Hong-Xia; DING Rui-Xue
2008-01-01
Electronic transport properties of a finite (7,0) carbon nanotube (CNT) coupled to Au (111) surfaces are investigated with a fully nonequilibrium Green's functions method combined with the density functional theory. The results show that the coupling effect between the CNT and Au electrode plays an important role in the transport properties, which leads to the formation of a high plateau in the transmission spectrum around Fermi energy. In addition, the current-voltage characteristic of the (7,0) CNT coupled to Au electrodes is different from an isolated (7,0) CNT.
LDRD project 151362 : low energy electron-photon transport.
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.
Semiclassical electronic transport in MnAs thin films
Helman, C. [Dpto de Fisica, ' Juan Jose Giambiagi' , Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires (Argentina); Unidad de Actividad Fisica, Centro Atomico Constituyentes, Comision Nacional de Energia Atomica, Buenos Aires (Argentina)], E-mail: helman@tandar.cnea.gov.ar; Milano, J.; Steren, L. [Departamento de Fisica, Centro Atomico Bariloche, Comision Nacional de Energia Atomica, S.C. Bariloche (Argentina); Llois, A.M. [Dpto de Fisica, ' Juan Jose Giambiagi' , Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires (Argentina); Unidad de Actividad Fisica, Centro Atomico Constituyentes, Comision Nacional de Energia Atomica, Buenos Aires (Argentina)
2008-07-15
Magneto-transport experiments have been recently performed on MnAs thin films. Hall effect and transverse magnetoresistance measurements have shown interesting and, until now, unknown results. For instance, the transverse magnetoresistance shows no saturation in the presence of very high magnetic fields. In order to understand the contribution of the electronic band structure to the non-saturating magnetoresistance, we perform ab initio calculations, using the Wien2K code and analyze the magneto-transport properties within the semiclassical approximation. We show that non-saturation may be due to the presence of open orbits on the majority Fermi surface.
G. Y. Jeong
2013-08-01
Full Text Available Giant particles transported over long distances are generally of limited concern in atmospheric studies due to their low number concentrations in mineral dust and possible local origin. However, they can play an important role in regional circulation of earth materials due to their enormous volume concentration. Asian dust laden with giant particles was observed in Korea on 31 March 2012, after a migration of about 2000 km across the Yellow Sea from the Gobi Desert. Scanning electron microscopy (SEM revealed that 20% of the particles exceeded 10 μm in equivalent sphere diameter, with a maximum of 60 μm. The median diameter from the number distribution was 5.7 μm, which was larger than the diameters recorded of 2.5 and 2.9 μm in Asian dust storms in 2010 and 2011, respectively, and was consistent with independent optical particle counter data. Giant particles (> 10 μm contributed about 89% of the volume of the dust in the 2012 storm. Illite-smectite series clay minerals were the major mineral group followed by quartz, plagioclase, K-feldspar, and calcite. The total phyllosilicate content was ~ 52%. The direct long-range transport of giant particles was confirmed by calcite nanofibers closely associated with clays in a submicron scale identified by high-resolution SEM and transmission electron microscopy. Since giant particles consisted of clay agglomerates and clay-coated quartz, feldspars, and micas, the mineral composition varied little throughout the fine ( 20 μm size bins. Analysis of the synoptic conditions of the 2012 dust event and its migration indicated that the mid-tropospheric strong wind belt directly stretching to Korea induced rapid transport of the dust, delivering giant particles. Giant dust particles with high settling velocity would be the major input into the terrestrial and marine sedimentary and ecological systems of East Asia and the western Pacific. Analysis of ancient aeolian deposits in Korea suggested the common
Impurity transport in trapped electron mode driven turbulence
Mollén, A; Moradi, S; Fülöp, T
2013-01-01
Collisionless trapped electron mode turbulence is studied by gyrokinetic simulations with the GYRO code. Its impact on radial transport of high-Z trace impurities close to the core is thoroughly investigated, including the situation when a poloidally varying equilibrium electrostatic potential is present, 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.
The macro response Monte Carlo method for electron transport
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
Largest Particle Simulations Downgrade the Runaway Electron Risk for ITER
Liu, Jian; Wang, Yulei; Yang, Guangwen; Zheng, Jiangshan; Yao, Yicun; Zheng, Yifeng; Liu, Zhao; Liu, Xin
2016-01-01
Fusion energy will be the ultimate clean energy source for mankind. One of the most visible concerns of the future fusion device is the threat of deleterious runaway electrons (REs) produced during unexpected disruptions of the fusion plasma. Both efficient long-term algorithms and super-large scale computing power are necessary to reveal the complex dynamics of REs in a realistic fusion reactor. In the present study, we deploy the world's fastest supercomputer, Sunway TaihuLight, and the newly developed relativistic volume-preserving algorithm to carry out long-term particle simulations of 10^7 sampled REs in 6D phase space, which involves simulation scale of 10^18 particle-steps, the largest ever achieved in fusion research. Our simulations show that in a realistic fusion reactor, the concern of REs is not as serious as previously thought. Specifically, REs are confined much better than previously predicted and the maximum average energy is in the range of 150MeV, less than half of previous estimate.
Fabrication and electronic transport studies of single nanocrystal systems
Klein, David Louis [Univ. of California, Berkeley, CA (United States). Dept. of Physics
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.
Ogawa, Shun; Leoncini, Xavier; Dif-Pradalier, Guilhem; Garbet, Xavier
2016-01-01
Charged particles with low kinetic energy move along magnetic field lines, but so do not energetic particles. We investigate the topological structure changes in the phase space of energetic particles with respect to the magnetic one. For this study cylindrical magnetic fields with non-monotonic safety factors that induce the magnetic internal transport barrier are considered. We show that the topological structure of the magnetic field line and of the particle trajectories can be quite diffe...
Electronic transport properties of graphene doped by gallium
Mach, J.; Procházka, P.; Bartošík, M.; Nezval, D.; Piastek, J.; Hulva, J.; Švarc, V.; Konečný, M.; Kormoš, L.; Šikola, T.
2017-10-01
In this work we present the effect of low dose gallium (Ga) deposition (graphene grown by chemical vapor deposition. In situ graphene transport measurements performed with a graphene field-effect transistor structure show that at low Ga coverages a graphene layer tends to be strongly n-doped with an efficiency of 0.64 electrons per one Ga atom, while the further deposition and Ga cluster formation results in removing electrons from graphene (less n-doping). The experimental results are supported by the density functional theory calculations and explained as a consequence of distinct interaction between graphene and Ga atoms in case of individual atoms, layers, or clusters.
Power electronics applied to industrial systems and transports
Patin, Nicolas
2015-01-01
This book provides a comprehensive overview of power electronic converters (DC / DC, DC / AC, AC / DC and AC / AC) conventionally used in industrial and transportation applications, specifically for the supply of electric machines with variable speed drop off window. From the perspective of design and sizing, this book presents the different functions encountered in a modular way for power electronics.Power Converters and Their Control details less traditional topics such as matrix converters and multilevel converters. This book also features a case study design of an industrial controller, wh
Power electronics applied to industrial systems and transports
Patin, Nicolas
2015-01-01
Some power electronic converters are specifically designed to power equipment under a smoothed DC voltage. Therefore, the filtering part necessarily involves the use of auxiliary passive components (inductors and capacitors). This book deals with technical aspects such as classical separation between isolated and non-isolated power supplies, and soft switching through a special converter. It addresses the problem of regulating the output voltage of the switching power supplies in terms of modeling and obtaining transfer of SMPS functions.Power Electronics for Industry and Transport, Volume 3,
Heyman, J.; Bohorquez, P.; Ancey, C.
2016-10-01
In gravel bed rivers, bed load transport exhibits considerable variability in time and space. Recently, stochastic bed load transport theories have been developed to address the mechanisms and effects of bed load transport fluctuations. Stochastic models involve parameters such as particle diffusivity, entrainment, and deposition rates. The lack of hard information on how these parameters vary with flow conditions is a clear impediment to their application to real-world scenarios. In this paper, we determined the closure equations for the above parameters from laboratory experiments. We focused on shallow supercritical flow on a sloping mobile bed in straight channels, a setting that was representative of flow conditions in mountain rivers. Experiments were run at low sediment transport rates under steady nonuniform flow conditions (i.e., the water discharge was kept constant, but bed forms developed and migrated upstream, making flow nonuniform). Using image processing, we reconstructed particle paths to deduce the particle velocity and its probability distribution, particle diffusivity, and rates of deposition and entrainment. We found that on average, particle acceleration, velocity, and deposition rate were responsive to local flow conditions, whereas entrainment rate depended strongly on local bed activity. Particle diffusivity varied linearly with the depth-averaged flow velocity. The empirical probability distribution of particle velocity was well approximated by a Gaussian distribution when all particle positions were considered together. In contrast, the particles located in close vicinity to the bed had exponentially distributed velocities. Our experimental results provide closure equations for stochastic or deterministic bed load transport models.
Trieschmann, Jan; Mussenbrock, Thomas
2016-01-01
The paper provides a tutorial to the conceptual layout of a self-consistently coupled Particle-In-Cell/Test-Particle model for the kinetic simulation of sputtering transport in capacitively coupled plasmas at low gas pressures. It explains when a kinetic approach is actually needed and which numerical concepts allow for the inherent nonequilibrium behavior of the charged and neutral particles. At the example of a generic sputtering discharge both the fundamentals of the applied Monte Carlo methods as well as the conceptual details in the context of the sputtering scenario are elaborated on. Finally, two in the context of sputtering transport simulations often exploited assumptions, namely on the energy distribution of impinging ions as well as on the test particle approach, are validated for the proposed example discharge.
Drummond, Jen; Davies-Colley, Rob; Stott, Rebecca; Sukias, James; Nagels, John; Sharp, Alice; Packman, Aaron
2014-05-01
Transport dynamics of microbial cells and organic fine particles are important to stream ecology and biogeochemistry. Cells and particles continuously deposit and resuspend during downstream transport owing to a variety of processes including gravitational settling, interactions with in-stream structures or biofilms at the sediment-water interface, and hyporheic exchange and filtration within underlying sediments. Deposited cells and particles are also resuspended following increases in streamflow. Fine particle retention influences biogeochemical processing of substrates and nutrients (C, N, P), while remobilization of pathogenic microbes during flood events presents a hazard to downstream uses such as water supplies and recreation. We are conducting studies to gain insights into the dynamics of fine particles and microbes in streams, with a campaign of experiments and modeling. The results improve understanding of fine sediment transport, carbon cycling, nutrient spiraling, and microbial hazards in streams. We developed a stochastic model to describe the transport and retention of fine particles and microbes in rivers that accounts for hyporheic exchange and transport through porewaters, reversible filtration within the streambed, and microbial inactivation in the water column and subsurface. This model framework is an advance over previous work in that it incorporates detailed transport and retention processes that are amenable to measurement. Solute, particle, and microbial transport were observed both locally within sediment and at the whole-stream scale. A multi-tracer whole-stream injection experiment compared the transport and retention of a conservative solute, fluorescent fine particles, and the fecal indicator bacterium Escherichia coli. Retention occurred within both the underlying sediment bed and stands of submerged macrophytes. The results demonstrate that the combination of local measurements, whole-stream tracer experiments, and advanced modeling
Nanoscale electron transport at the surface of a topological insulator
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
Nanoscale electron transport at the surface of a topological insulator
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.
Restoration of electron transport without proton pumping in mammalian mitochondria
Perales-Clemente, Ester; Bayona-Bafaluy, Maria Pilar; Pérez-Martos, Acisclo; Barrientos, Antoni; Fernández-Silva, Patricio; Enriquez, Jose Antonio
2008-01-01
We have restored the CoQ oxidative capacity of mouse mtDNA-less cells (ρ° cells) by transforming them with the alternative oxidase Aox of Emericella nidulans. Cotransforming ρ° cells with the NADH dehydrogenase of Saccharomyces cerevisiae, Ndi1 and Aox recovered the NADH DH/CoQ reductase and the CoQ oxidase activities. CoQ oxidation by AOX reduces the dependence of ρ° cells on pyruvate and uridine. Coexpression of AOX and NDI1 further improves the recycling of NAD+. Therefore, 2 single-protein enzymes restore the electron transport in mammalian mitochondria substituting >80 nuclear DNA-encoded and 11 mtDNA-encoded proteins. Because those enzymes do not pump protons, we were able to split electron transport and proton pumping (ATP synthesis) and inquire which of the metabolic deficiencies associated with the loss of oxidative phosphorylation should be attributed to each of the 2 processes. PMID:19020091
The Role of Diffusion in the Transport of Energetic Electrons during Solar Flares
Bian, Nicolas H.; Emslie, A. Gordon; Kontar, Eduard P.
2017-02-01
The transport of the energy contained in suprathermal electrons in solar flares plays a key role in our understanding of many aspects of flare physics, from the spatial distributions of hard X-ray emission and energy deposition in the ambient atmosphere to global energetics. Historically the transport of these particles has been largely treated through a deterministic approach, in which first-order secular energy loss to electrons in the ambient target is treated as the dominant effect, with second-order diffusive terms (in both energy and angle) generally being either treated as a small correction or even neglected. Here, we critically analyze this approach, and we show that spatial diffusion through pitch-angle scattering necessarily plays a very significant role in the transport of electrons. We further show that a satisfactory treatment of the diffusion process requires consideration of non-local effects, so that the electron flux depends not just on the local gradient of the electron distribution function but on the value of this gradient within an extended region encompassing a significant fraction of a mean free path. Our analysis applies generally to pitch-angle scattering by a variety of mechanisms, from Coulomb collisions to turbulent scattering. We further show that the spatial transport of electrons along the magnetic field of a flaring loop can be modeled rather effectively as a Continuous Time Random Walk with velocity-dependent probability distribution functions of jump sizes and occurrences, both of which can be expressed in terms of the scattering mean free path.
Modeling particle-induced electron emission in a simplified plasma Test Cell
Giuliano, Paul N.; Boyd, Iain D. [Department of Aerospace Engineering, University of Michigan, Ann Arbor, Michigan 48109 (United States)
2013-03-21
Particle-induced electron emission (PIE) is modeled in a simplified, well-characterized plasma Test Cell operated at UCLA. In order for PIE to be a useful model in this environment, its governing equations are first reduced to lower-order models which can be implemented in a direct simulation Monte Carlo and Particle-in-Cell framework. These reduced-order models are described in full and presented as semi-empirical models. The models are implemented to analyze the interaction of low- and high-energy ({approx}1-2 keV) xenon ions and atoms with the stainless steel electrodes of the Test Cell in order to gain insight into the emission and transport of secondary electrons. Furthermore, there is a lack of data for xenon-stainless steel atom- and ion-surface interactions for similar environments. Using experimental data as a reference, both total yields and emitted electron energy distribution functions can be deduced by observing sensitivities of current collection results to these numerical models and their parameters.
Quantum effective potential, electron transport and conformons in biopolymers
Dandoloff, Rossen [Laboratoire de Physique Theorique et Modelisation, Universite de Cergy-Pontoise, F-95302 Cergy-Pontoise (France); Balakrishnan, Radha [The Institute of Mathematical Sciences, Chennai 600113 (India)
2005-07-08
In the Kirchhoff model of a biopolymer, conformation dynamics can be described in terms of solitary waves, for certain special cross-section asymmetries. Applying this to the problem of electron transport, we show that the quantum effective potential arising due to the bends and twists of the polymer enables us to formalize and quantify the concept of a conformon that has been hypothesized in biology. Its connection to the soliton solution of the cubic nonlinear Schroedinger equation emerges in a natural fashion.
Electronic transport properties of metallic single-walled carbon nanotubes
曹觉先; 颜晓红; 肖杨; 丁建文
2003-01-01
We have calculated the differential conductance of metallic carbon nanotubes by the scatter matrix method. It is found that the differential conductance of metallic nanotube-based devices oscillates as a function of the bias voltage between the two leads and the gate voltage. Oscillation period T is directly proportional to the reciprocal of nanotube length. In addition, we found that electronic transport properties are sensitive to variation of the length of the nanotube.
Unified fluid model analysis and benchmark study for electron transport in gas and liquid analogs
Garland, N. A.; Cocks, D. G.; Boyle, G. J.; Dujko, S.; White, R. D.
2017-07-01
The interaction of plasmas with liquids requires an understanding of charged particle transport in both the gaseous and liquid phases. In this study we present a generalized fluid-equation framework to describe bulk electron transport in both gaseous and non-polar liquid environments under non-hydrodynamic non-equilibrium conditions. The framework includes liquid structural effects through appropriate inclusion of coherent scattering effects and adaption of swarm data to account for the modification to the scattering environment present in such systems. In the limit of low-densities it reduces to the traditional gas-phase fluid-equation model. Using a higher-order fluid model (four moments), it is shown that by applying steady state electron swarm data in both the gaseous and liquid phases, to close the system of equations and evaluate collisional rates, an improvement in macroscopic electron transport results over popular existing assumptions used. The failure of the local mean energy approximation in fluid models to accurately describe complex spatial oscillatory structures in both the gaseous and liquid phases is discussed in terms of the spatial variation of the electron distribution function itself.
Kontar, E P; Bian, N H
2011-01-01
Plasma turbulence is thought to be associated with various physical processes involved in solar flares, including magnetic reconnection, particle acceleration and transport. Using Ramaty High Energy Solar Spectroscopic Imager ({\\it RHESSI}) observations and the X-ray visibility analysis, we determine the spatial and spectral distributions of energetic electrons for a flare (GOES M3.7 class, April 14, 2002 23$:$55 UT), which was previously found to be consistent with a reconnection scenario. It is demonstrated that because of the high density plasma in the loop, electrons have to be continuously accelerated about the loop apex of length $\\sim 2\\times 10^9$cm and width $\\sim 7\\times 10^8$cm. Energy dependent transport of tens of keV electrons is observed to occur both along and across the guiding magnetic field of the loop. We show that the cross-field transport is consistent with the presence of magnetic turbulence in the loop, where electrons are accelerated, and estimate the magnitude of the field line diffu...
Electron correlations in single-electron capture from helium by fast protons and α particles
Mančev, Ivan; Milojević, Nenad
2010-02-01
Single-electron capture from heliumlike atomic systems by bare projectiles is investigated by means of the four-body boundary-corrected first Born approximation (CB1-4B). The effect of the dynamic electron correlation is explicitly taken into account through the complete perturbation potential. The quantum-mechanical post and prior transition amplitudes for single charge exchange encompassing symmetric and/or asymmetric collisions are derived in terms of two-dimensional real integrals in the case of the prior form and five-dimensional quadratures for the post form. An illustrative computation is performed for single-electron capture from helium by protons and α particles at intermediate and high impact energies. The role of dynamic correlations is examined as a function of increased projectile energy. The validity and utility of the proposed CB1-4B method is critically assessed in comparison with the existing experimental data for total cross sections, and excellent agreement is obtained.
Modeling of electron-electron collisions for particle-in-cell simulations
Andrea, D. d'
2006-09-15
The modeling of the physics of pulsed plasma thrusters requires the numerical solution of the Boltzmann equation for rarefied plasma flows where continuum assumptions fail. To tackle this challenging task, a cooperation between several institutes has been formed with the goal to develop a hybrid code based on Particle-In-Cell and Direct Simulation Monte Carlo techniques. These development activities are bundled in the project ''Numerische Simulation und Auslegung eines instationaeren gepulsten magnetoplasmadynamischen Triebwerks fuer eine Mondsonde'' which is funded by the Landesstiftung Baden-Wuerttemberg within the subject area ''Modellierung und Simulation auf Hochleistungscomputern''. In the frame of this project, the IHM is in charge to develop suitable physical-mathematical and numerical models to include charged particle collisions into the simulation. which can significantly affect the Parameters of such plasma devices. The intention of the present report is to introduce the Fokker-Planck approach for electron-electron interaction in Standard charged particle simulations. where the impact Parameter is usually large resulting in a small deflection angle. The theoretical and applicative framework is discussed in detail paying particular attention to the Particle-In-Cell approach in velocity space. a new technique which allows the self-consistent computation of the friction and diffusion coefficients arising from the Fokker-Planck treatment of collisions. These velocity-dependent coefficients thernselves are responsible for the change in velocity of the simulation particles, which is determined by the numerical solution of a Langevin-type equation. Simulation results for typical numerical experiments computed with the new developed Fokker-Planck solver are presented. demonstrating the quality. property and reliability of the applied numerical methods. (orig.)
Isolation systems for electronic black-box transportation to orbit
Jedrich, Nicholas M.; Pendleton, Scott C.
1998-06-01
Servicing the Hubble Space Telescope (HST) requires the safe transportation of electronic Orbital Replacement Units (ORUs) on the Space Transportation System (STS) to replace or enhance the capability of existing units. The delicate design of these electronic ORUs makes it imperative to provide isolation from the STS launch random vibration, while maintaining fundamental modes above the transient load environment. Two methods were developed and used exclusively, on Servicing Mission 2 (SM2), to isolate the ORUs from the environmental launch loads imposed by the STS. The first load isolation system utilizes a refined open/closed cell foam design to provide the required damping and corner frequency, while the second method uses an innovative Viscoelastic Material (VEM) design. This paper addresses both systems as initially designed including finite element (FE) model analysis of the VEM system. Vibration testing of prototype systems and modifications to the design resulting from test will be discussed. The final design as flown on HST SM2 with recommendations for future applications of these technologies in transporting electronic black boxes to orbit will conclude the paper.
Electron Production and Collective Field Generation in Intense Particle Beams
Molvik, A W; Vay, J; Cohen, R; Friedman, A; Lee, E; Verboncoeur, J; Covo, M K
2006-02-09
Electron cloud effects (ECEs) are increasingly recognized as important, but incompletely understood, dynamical phenomena, which can severely limit the performance of present electron colliders, the next generation of high-intensity rings, such as PEP-II upgrade, LHC, and the SNS, the SIS 100/200, or future high-intensity heavy ion accelerators such as envisioned in Heavy Ion Inertial Fusion (HIF). Deleterious effects include ion-electron instabilities, emittance growth, particle loss, increase in vacuum pressure, added heat load at the vacuum chamber walls, and interference with certain beam diagnostics. Extrapolation of present experience to significantly higher beam intensities is uncertain given the present level of understanding. With coordinated LDRD projects at LLNL and LBNL, we undertook a comprehensive R&D program including experiments, theory and simulations to better understand the phenomena, establish the essential parameters, and develop mitigating mechanisms. This LDRD project laid the essential groundwork for such a program. We developed insights into the essential processes, modeled the relevant physics, and implemented these models in computational production tools that can be used for self-consistent study of the effect on ion beams. We validated the models and tools through comparison with experimental data, including data from new diagnostics that we developed as part of this work and validated on the High-Current Experiment (HCX) at LBNL. We applied these models to High-Energy Physics (HEP) and other advanced accelerators. This project was highly successful, as evidenced by the two paragraphs above, and six paragraphs following that are taken from our 2003 proposal with minor editing that mostly consisted of changing the tense. Further benchmarks of outstanding performance are: we had 13 publications with 8 of them in refereed journals, our work was recognized by the accelerator and plasma physics communities by 8 invited papers and we have 5
Theory for the anomalous electron transport in Hall-effect thrusters
Lafleur, Trevor; Baalrud, Scott; Chabert, Pascal
2016-09-01
Using insights from particle-in-cell (PIC) simulations, we develop a kinetic theory to explain the anomalous cross-field electron transport in Hall-effect thrusters (HETs). The large axial electric field in the acceleration region of HETs, together with the radially applied magnetic field, causes electrons to drift in the azimuthal direction with a very high velocity. This drives an electron cyclotron instability that produces large amplitude oscillations in the plasma density and azimuthal electric field, and which is convected downstream due to the large axial ion drift velocity. The frequency and wavelength of the instability are of the order of 5 MHz and 1 mm respectively, while the electric field amplitude can be of a similar magnitude to axial electric field itself. The instability leads to enhanced electron scattering many orders of magnitude higher than that from standard electron-neutral or electron-ion Coulomb collisions, and gives electron mobilities in good agreement with experiment. Since the instability is a strong function of almost all plasma properties, the mobility cannot in general be fitted with simple 1/B or 1/B2 scaling laws, and changes to the secondary electron emission coefficient of the HET channel walls are expected to play a role in the evolution of the instability. This work received financial support from a CNES postdoctoral research award.
Duque, H. V. [School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide, South Australia 5001 (Australia); Departamento de Física, Universidade Federal de Juiz de Fora, 36036-330 Juiz de Fora, Minas Gerais (Brazil); Do, T. P. T. [School of Education, Can Tho University, Campus II, 3/2 Street, Xuan Khanh, Ninh Kieu, Can Tho City (Viet Nam); Lopes, M. C. A. [Departamento de Física, Universidade Federal de Juiz de Fora, 36036-330 Juiz de Fora, Minas Gerais (Brazil); Konovalov, D. A.; White, R. D. [College of Science, Technology and Engineering, James Cook University, Townsville (Australia); Brunger, M. J., E-mail: michael.brunger@flinders.edu.au, E-mail: darryl.jones@flinders.edu.au [School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide, South Australia 5001 (Australia); Institute of Mathematical Sciences, University of Malaya, 50603 Kuala Lumpur (Malaysia); Jones, D. B., E-mail: michael.brunger@flinders.edu.au, E-mail: darryl.jones@flinders.edu.au [School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide, South Australia 5001 (Australia)
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.
Electronic transport in VO{sub 2}—Experimentally calibrated Boltzmann transport modeling
Kinaci, Alper; Rosenmann, Daniel; Chan, Maria K. Y., E-mail: debasish.banerjee@toyota.com, E-mail: mchan@anl.gov [Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Kado, Motohisa [Higashifuji Technical Center, Toyota Motor Corporation, Susono, Shizuoka 410-1193 (Japan); Ling, Chen; Zhu, Gaohua; Banerjee, Debasish, E-mail: debasish.banerjee@toyota.com, E-mail: mchan@anl.gov [Materials Research Department, Toyota Motor Engineering and Manufacturing North America, Inc., Ann Arbor, Michigan 48105 (United States)
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.
Neutral Particle Transport in Cylindrical Plasma Simulated by a Monte Carlo Code
YU Deliang; YAN Longwen; ZHONG Guangwu; LU Jie; YI Ping
2007-01-01
A Monte Carlo code (MCHGAS) has been developed to investigate the neutral particle transport.The code can calculate the radial profile and energy spectrum of neutral particles in cylindrical plasmas.The calculation time of the code is dramatically reduced when the Splitting and Roulette schemes are applied. The plasma model of an infinite cylinder is assumed in the code,which is very convenient in simulating neutral particle transports in small and middle-sized tokamaks.The design of the multi-channel neutral particle analyser (NPA) on HL-2A can be optimized by using this code.
Particle-based simulations of steady-state mass transport at high P\\'eclet numbers
Müller, Thomas; Rajah, Luke; Cohen, Samuel I A; Yates, Emma V; Vendruscolo, Michele; Dobson, Chrisopher M; Knowles, Tuomas P J
2015-01-01
Conventional approaches for simulating steady-state distributions of particles under diffusive and advective transport at high P\\'eclet numbers involve solving the diffusion and advection equations in at least two dimensions. Here, we present an alternative computational strategy by combining a particle-based rather than a field-based approach with the initialisation of particles in proportion to their flux. This method allows accurate prediction of the steady state and is applicable even at high P\\'eclet numbers where traditional particle-based Monte-Carlo methods starting from randomly initialised particle distributions fail. We demonstrate that generating a flux of particles according to a predetermined density and velocity distribution at a single fixed time and initial location allows for accurate simulation of mass transport under flow. Specifically, upon initialisation in proportion to their flux, these particles are propagated individually and detected by summing up their Monte-Carlo trajectories in p...
Yu, Choongho; Ryu, Yeontack; Yin, Liang; Yang, Hongjoo
2011-02-22
Nanoparticle decoration on carbon nanotubes was employed to modulate their electrical conductance and thermopower and thereby improved the thermoelectric power factor. Nanotubes were made into films by spraying nanotube solutions on glass substrates, and then the films were immersed in different concentrations of CuSO(4) or HAuCl(4) solutions for various time periods. Copper ions in the solutions were reduced on nanotubes by obtaining electrons from zinc electrodes, whose reduction potential is lower than that of copper (galvanic displacement). Gold ions were reduced on nanotubes by both silver counter electrodes and spontaneous reaction due to larger reduction potentials than those of nanotubes. These reactions made electrons donated to (copper incorporation) or withdrawn from (gold incorporation) nanotubes depending on the difference in their work functions and reduction potentials, resulting in considerable changes in electron transport. In this paper, a series of experiments at different ion concentrations and reaction time periods were systematically performed in order to find optimum nanoparticle formation conditions and corresponding electronic transport changes for better thermoelectric power factor. Transport measurement results show that electronic properties can be considerably altered and modulated, resulting in 2-fold improvement in the thermoelectric power factor with 1 mM/30 min reaction. Reactions with solutions of a low metal ion concentration, such as 1 mM, yielded well-distributed small particles over large surface areas, which strongly affected electron transfer between nanoparticles and nanotubes. Successive copper and gold decorations on nanotubes made electrical conductance (or thermopower) serially decreased and increased (or increased and decreased) upon precipitating different metal particles. This transport behavior is believed to be from the changes in the Fermi level as a result of electron exchanges between reduced metals and nanotubes
Tabony, James; Rigotti, Nathalie; Glade, Nicolas; Cortès, Sandra
2007-05-01
Weightlessness is known to effect cellular functions by as yet undetermined processes. Many experiments indicate a role of the cytoskeleton and microtubules. Under appropriate conditions in vitro microtubule preparations behave as a complex system that self-organises by a combination of reaction and diffusion. This process also results in the collective transport and organisation of any colloidal particles present. In large centimetre-sized samples, self-organisation does not occur when samples are exposed to a brief early period of weightlessness. Here, we report both space-flight and ground-based (clinorotation) experiments on the effect of weightlessness on the transport and segregation of colloidal particles and chromosomes. In centimetre-sized containers, both methods show that a brief initial period of weightlessness strongly inhibits particle transport. In miniature cell-sized containers under normal gravity conditions, the particle transport that self-organisation causes results in their accumulation into segregated regions of high and low particle density. The gravity dependence of this behaviour is strongly shape dependent. In square wells, neither self-organisation nor particle transport and segregation occur under conditions of weightlessness. On the contrary, in rectangular canals, both phenomena are largely unaffected by weightlessness. These observations suggest, depending on factors such as cell and embryo shape, that major biological functions associated with microtubule driven particle transport and organisation might be strongly perturbed by weightlessness.
Simulations of electron transport in GaN devices
Arabshahi, H
2002-01-01
model of a device with traps to investigate this suggestion. The model includes the simulation of the capture and release of electrons by traps whose charge has a direct effect on the current flowing through the transistor terminals. The influence of temperature and light on the occupancy of the traps and the I-V characteristics are considered. It is concluded that traps are likely to play a substantial role in the behaviour of GaN field effect transistors. Further simulations were performed to model electron transport in AIGaN/GaN heterojunction FETs. So called HFET structures with a 78 nm Al sub 0 sub . sub 2 Ga sub 0 sub . sub 8 N pseudomorphically strained layer have been simulated, with the inclusion of spontaneous and piezoelectric polarization effects in the strained layer. The polarization effects are shown to not only increase the current density, but also improve the electron transport by inducing a higher electron density close to the positive charge sheet that occurs in the channel. This thesis de...
Jiang, Wei; Wang, Langping; Zhou, Guangxue; Wang, Xiaofeng
2017-02-01
In order to study electron trajectories in an annular cathode high current pulsed electron beam (HCPEB) source based on carbon fiber bunches, the transmission process of electrons emitted from the annular cathode was simulated using a particle-in-cell model with Monte Carlo collisions (PIC-MCC). The simulation results show that the intense flow of the electrons emitted from the annular cathode are expanded during the transmission process, and the uniformity of the electron distribution is improved in the transportation process. The irradiation current decreases with the irradiation distance and the pressure, and increases with the negative voltage. In addition, when the irradiation distance and the cathode voltage are larger than 40 mm and -15 kV, respectively, a uniform irradiation current distribution along the circumference of the anode can be obtained. The simulation results show that good irradiation uniformity of circular components can be achieved by this annular cathode HCPEB source.
Measurement of hot electron transport in overdense plasma VIA self induced giant magnetic pulses
Mondal, S.; Narayanan, V.; Lad, Amit D.; Ahmed, Saima; Sengupta, S.; Das, A.; Sheng, Z. M.; Kaw, P. K.; Kumar, G. Ravindra
2010-08-01
Spatial and temporal resolved ultrashort(8ps) multimegagauss(65 MG) magnetic field has been measured in plasma produced on Al-coated BK-7 glass by the interaction of a relativististic intensity laser(4x1018W/cm2, 30 fs) using pump-probe polarimetry. The 2D profile of magnetic field is captured using a CCD camera. Mapping of this magnetic field maps the transport of relativistic electrons in the plasma. The magnetic field profiles indicate filamentary behavior (Weibel-like instability). Particle in cell simulation are used to explain the result obtained.
Izawa, Seikichi; Good, Norman E.
1966-01-01
Spinach chloroplasts isolated in media containing salts and the rare chloroplasts which are still within their envelopes alike retain grana similar to those seen in chloroplasts in situ. Chloroplasts isolated in low-salt media lose their grana without losing any chlorophyll. These grana-free chloroplasts are considerably swollen and consist almost entirely of continuous sheets of paired-membrane structures. These double structures, the lamellae, are only loosely held together, primarily at the edges, by tenuous material which does not react with permanganate. Addition of salts (methylamine hydrochloride, NaCl, MgCl2) to the grana-free low-salt chloroplasts provide strong interlamellar attractions. These attractions result in a stacking of the lamellae which is sometimes almost random but sometimes results in regular structures indistinguishable from the original grana. The phosphorylation-uncoupler atebrin causes further swelling of the chloroplasts in the absence of electron transport by increasing the space between the paired membranes of the lamellae. The rapid electron transport (Hill reaction) made possible by atebrin-uncoupling is associated with a great decrease in chloroplast volume. This decrease results from a collapsing together of the widely separated lamellar membrane pairs. The pairs approach each other so closely that they usually appear as a single membrane when viewed with the electron microscope. The much slower electron transport which occurs in the absence of uncouplers is associated with a similar but smaller decrease in the space between the lamellar membrane pairs. Chloroplasts swell during the rapid electron transport made possible by the phosphorylation-uncoupler methylamine. This swelling is accompanied by a degree of membrane distortion which precludes an interpretation of the mechanism. As with atebrin-faciliated electron transport, obviously paired membranes disappear but it is not yet clear whether this is by association or
Strozzi, D J; Larson, D J; Divol, L; Kemp, A J; Bellei, C; Marinak, M M; Key, M H
2012-01-01
Transport modeling of idealized, cone-guided fast ignition targets indicates the severe challenge posed by fast-electron source divergence. The hybrid particle-in-cell [PIC] code Zuma is run in tandem with the radiation-hydrodynamics code Hydra to model fast-electron propagation, fuel heating, and thermonuclear burn. The fast electron source is based on a 3D explicit-PIC laser-plasma simulation with the PSC code. This shows a quasi two-temperature energy spectrum, and a divergent angle spectrum (average velocity-space polar angle of 52 degrees). Transport simulations with the PIC-based divergence do not ignite for > 1 MJ of fast-electron energy, for a modest 70 micron standoff distance from fast-electron injection to the dense fuel. However, artificially collimating the source gives an ignition energy of 132 kJ. To mitigate the divergence, we consider imposed axial magnetic fields. Uniform fields ~50 MG are sufficient to recover the artificially collimated ignition energy. Experiments at the Omega laser facil...
Quantum transport equations for low-dimensional multiband electronic systems: I.
Kupčić, I; Rukelj, Z; Barišić, S
2013-04-10
A systematic method of calculating the dynamical conductivity tensor in a general multiband electronic model with strong boson-mediated electron-electron interactions is described. The theory is based on the exact semiclassical expression for the coupling between valence electrons and electromagnetic fields and on the self-consistent Bethe-Salpeter equations for the electron-hole propagators. The general diagrammatic perturbation expressions for the intraband and interband single-particle conductivity are determined. The relations between the intraband Bethe-Salpeter equation, the quantum transport equation and the ordinary transport equation are briefly discussed within the memory-function approximation. The effects of the Lorentz dipole-dipole interactions on the dynamical conductivity of low-dimensional spα models are described in the same approximation. Such formalism proves useful in studies of different (pseudo)gapped states of quasi-one-dimensional systems with the metal-to-insulator phase transitions and can be easily extended to underdoped two-dimensional high-Tc superconductors.
Particle simulation of neoclassical transport in the plasma Edge
Chang, C.S. [Department of Physics, Korea Advanced Institute of Science and Technology (Korea); Ku, S. [Courant Institute of Mathematical Sciences, New York University, 251 Mercer Street, New York, NY (United States); Department of Physics, Korea Advanced Institute of Science and Technology (Korea)
2006-09-15
Particle-in-cell is a popular technique for a global five dimensional numerical simulation of the neoclassical plasma phenomena in a toroidal plasma. In this paper, we briefly review the physical and mathematical aspects of the modern neoclassical particle simulation methodology for a plasma edge simulation and present representative results recently obtained from XGC (X-point included Guiding Center) code. The strength and weakness in the modern neoclassical particle simulation techniques will also be discussed. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Ness, H., E-mail: herve.ness@kcl.ac.uk [Department of Physics, School of Natural and Mathematical Sciences, King' s College London, Strand, London WC2R 2LS (United Kingdom); Department of Physics, University of York, Heslington, York YO10 5DD (United Kingdom); European Theoretical Spectroscopy Facility (ETSF), Liege (Belgium); Dash, L. K. [European Theoretical Spectroscopy Facility (ETSF), Liege (Belgium); Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom)
2014-04-14
We study the non-equilibrium (NE) fluctuation-dissipation (FD) relations in the context of quantum thermoelectric transport through a two-terminal nanodevice in the steady-state. The FD relations for the one- and two-particle correlation functions are derived for a model of the central region consisting of a single electron level. Explicit expressions for the FD relations of the Green's functions (one-particle correlations) are provided. The FD relations for the current-current and charge-charge (two-particle) correlations are calculated numerically. We use self-consistent NE Green's functions calculations to treat the system in the absence and in the presence of interaction (electron-phonon) in the central region. We show that, for this model, there is no single universal FD theorem for the NE steady state. There are different FD relations for each different class of problems. We find that the FD relations for the one-particle correlation function are strongly dependent on both the NE conditions and the interactions, while the FD relations of the current-current correlation function are much less dependent on the interaction. The latter property suggests interesting applications for single-molecule and other nanoscale transport experiments.
Ness, H; Dash, L K
2014-04-14
We study the non-equilibrium (NE) fluctuation-dissipation (FD) relations in the context of quantum thermoelectric transport through a two-terminal nanodevice in the steady-state. The FD relations for the one- and two-particle correlation functions are derived for a model of the central region consisting of a single electron level. Explicit expressions for the FD relations of the Green's functions (one-particle correlations) are provided. The FD relations for the current-current and charge-charge (two-particle) correlations are calculated numerically. We use self-consistent NE Green's functions calculations to treat the system in the absence and in the presence of interaction (electron-phonon) in the central region. We show that, for this model, there is no single universal FD theorem for the NE steady state. There are different FD relations for each different class of problems. We find that the FD relations for the one-particle correlation function are strongly dependent on both the NE conditions and the interactions, while the FD relations of the current-current correlation function are much less dependent on the interaction. The latter property suggests interesting applications for single-molecule and other nanoscale transport experiments.
Sun, Lingpeng; Klecker, Berndt; Krucker, Saem; Droege, Wolfgang
2010-01-01
We report for several solar energetic particle events intensity and anisotropy measurements of energetic electrons in the energy range ~ 27 to ~ 500 keV as observed with the Wind and ACE spacecraft in June 2000. The observations onboard Wind show bimodal pitch angle distributions (PAD), whereas ACE shows PADs with one peak, as usually observed for impulsive injection of electrons at the Sun. During the time of observation Wind was located upstream of the Earth's bow shock, in the dawn - noon sector, at distances of ~ 40 to ~ 70 Earth radii away from the Earth, and magnetically well connected to the quasi-parallel bow shock, whereas ACE, located at the libration point L1, was not connected to the bow shock. The electron intensity-time profiles and energy spectra show that the backstreaming electrons observed at Wind are not of magnetospheric origin. The observations rather suggest that the bi-modal electron PADs are due to reflection or scattering at an obstacle located at a distance of less than ~ 150 Earth r...
Particle transport in evolving protoplanetary disks: Implications for results from Stardust
Hughes, Anna L H
2010-01-01
Samples returned from comet 81P/Wild 2 by Stardust confirm that substantial quantities of crystalline silicates were incorporated into the comet at formation. We investigate the constraints that this observation places upon protoplanetary disk physics, assuming that outward transport of particles processed at high temperatures occurs via advection and turbulent diffusion in an evolving disk. We also look for constraints on particle formation locations. Our results are based upon 1D disk models that evolve with time under the action of viscosity and photoevaporation, and track solid transport using an ensemble of individual particle trajectories. We find that two classes of disk model are consistent with the Stardust findings. One class features a high particle diffusivity (a Schmidt number Sc 1, such models are unlikely to be viable, and significant outward transport requires that the particles of interest settle into a midplane layer that experiences an outward gas flow. In either class of models, the mass ...
Smoothed Particle Hydrodynamics Model for Reactive Transport and Mineral Precipitation
Tartakovsky, Alexandre M.; Scheibe, Timothy D.; Redden, George; Meakin, Paul; Fang, Yilin
2006-06-30
A new Lagrangian particle model based on smoothed particle hydrodynamics was used to simulate pore scale precipitation reactions. The side-by-side injection of reacting solutions into two halves of a two-dimensional granular porous medium was simulated. Precipitation on grain surfaces occurred along a narrow zone in the middle of the domain, where the reacting solutes mixed to generate a supersaturated reaction product. The numerical simulations qualitatively reproduced the behavior observed in related laboratory experiments.
Transport dissipative particle dynamics model for mesoscopic advection-diffusion-reaction problems
Li, Zhen; Yazdani, Alireza; Tartakovsky, Alexandre; Karniadakis, George Em
2015-01-01
We present a transport dissipative particle dynamics (tDPD) model for simulating mesoscopic problems involving advection-diffusion-reaction (ADR) processes, along with a methodology for implementation of the correct Dirichlet and Neumann boundary conditions in tDPD simulations. tDPD is an extension of the classic dissipative particle dynamics (DPD) framework with extra variables for describing the evolution of concentration fields. The transport of concentration is modeled by a Fickian flux a...
Electronic transport in narrow-gap semiconductor nanowires
Bloemers, Christian
2012-10-19
Throughout this work the electronic transport properties of InAs, InN, and GaAs/InAs core/shell nanowires have been analyzed. This includes the analysis of specific resistivity at room temperature and low temperatures as well as the breakdown of resistivity by a contribution of mobility and carrier concentration using gate measurements. While the InN nanowires showed homogeneous transport properties, there was a large statistical spread in the properties of InAs nanowires. Differing crystal structures and the surface conditions are identified to be the main reasons for the statistical spread. Both quantities of influence have been pointed out by comparing the transport parameters before and after a surface treatment (electron irradiation and long time ambient air exposure), and by comparing the transport parameters of wires grown by different growth methods which exhibit different kinds of crystal structure. In particular, the temperature dependence of the conductivity revealed different activation energies in nanowires with differing crystal structures. An explanation has been suggested in terms of stacking fault induced potential barriers. A field-effect measurement setup has been utilized to determine the nanowire mobility and carrier concentration. Even though this method is widely used for nanowires, it is subject to a serious disadvantage concerning the influence of surface and interface states on the measurements. As an alternative method which does not suffer from this drawback, Hall measurements have been successfully performed on InAs nanowires for the first time. These measurements became possible because of the utilization of a new electron beam lithographic procedure with an alignment accuracy in the 5 nm range. Carrier concentration values could be determined and compared to the ones obtained from conventional field-effect measurements. The results of the Hall measurements revealed a methodical overestimation of the carrier concentrations obtained
DANTSYS: A diffusion accelerated neutral particle transport code system
Alcouffe, R.E.; Baker, R.S.; Brinkley, F.W.; Marr, D.R.; O`Dell, R.D.; Walters, W.F.
1995-06-01
The DANTSYS code package includes the following transport codes: ONEDANT, TWODANT, TWODANT/GQ, TWOHEX, and THREEDANT. The DANTSYS code package is a modular computer program package designed to solve the time-independent, multigroup discrete ordinates form of the boltzmann transport equation in several different geometries. The modular construction of the package separates the input processing, the transport equation solving, and the post processing (or edit) functions into distinct code modules: the Input Module, one or more Solver Modules, and the Edit Module, respectively. The Input and Edit Modules are very general in nature and are common to all the Solver Modules. The ONEDANT Solver Module contains a one-dimensional (slab, cylinder, and sphere), time-independent transport equation solver using the standard diamond-differencing method for space/angle discretization. Also included in the package are solver Modules named TWODANT, TWODANT/GQ, THREEDANT, and TWOHEX. The TWODANT Solver Module solves the time-independent two-dimensional transport equation using the diamond-differencing method for space/angle discretization. The authors have also introduced an adaptive weighted diamond differencing (AWDD) method for the spatial and angular discretization into TWODANT as an option. The TWOHEX Solver Module solves the time-independent two-dimensional transport equation on an equilateral triangle spatial mesh. The THREEDANT Solver Module solves the time independent, three-dimensional transport equation for XYZ and RZ{Theta} symmetries using both diamond differencing with set-to-zero fixup and the AWDD method. The TWODANT/GQ Solver Module solves the 2-D transport equation in XY and RZ symmetries using a spatial mesh of arbitrary quadrilaterals. The spatial differencing method is based upon the diamond differencing method with set-to-zero fixup with changes to accommodate the generalized spatial meshing.
Phenomena of charged particles transport in variable magnetic fields
Savane, S Y; Faza-Barry, M; Vladmir, L
2002-01-01
This present work is dedicated to the study of the dynamical phenomena for the transport of ions in the presence of variable magnetic fields in front of the Jupiter wave shock. We obtain the spectrum of the accelerated ions and we study the conditions of acceleration by solving the transport equation in the planetocentric system. We discuss the theoretical results obtained and make a comparison with the experimental parameters in the region of acceleration behind the Jupiter wave shock.
Study of fast electron transport and ionization in isochorically heated solid foil
Sawada, Hiroshi; Sentoku, Yasuhiko; Pandit, Rishi; Yabuuchi, Toshinori; Zastrau, Ulf; Foerster, Eckhart; Beg, Farhat; McLean, Harry; Chen, Hui; Park, J.-B.; Patel, Prav; Link, Anthony; Ping, Yuan
2016-10-01
Interaction of a high-power, short-pulse laser with a solid target generates a significant number of relativistic MeV electrons, subsequently heating the target isochorically in the transport process. Fast electron driven ionization of a solid titanium foil was studied by measuring Ti K-alpha x-rays and performing 2-D particle-in-cell simulations. The experiment was performed using the 50 TW Leopard short-pulse laser at UNR's Nevada Terawatt Facility. The 15 J, 0.35 ps laser was tightly focused on to a various sized, 2- μm thick Ti foil within a 8 μm spot to achieve the peak intensity of 2×1019 W/cm2. The transport of the fast electrons produced 4.51 keV Ti K-alpha x-rays. The yields and 2-D monochromatic images were recorded with a Bragg crystal spectrometer and a spherically bent crystal imager. The ionization degree of the heated foil was determined to be 15 from the ionized K-alpha lines and the missing emission in the images. 2-D PIC simulations using a PICLS code with a radiation transport module were performed to calculate the K-alpha profiles and spectra. Details of the experiment and comparison will be presented.
Theory of Fast Electron Transport for Fast Ignition
Robinson, A P L; Davies, J R; Gremillet, L; Honrubia, J J; Johzaki, T; Kingham, R J; Sherlock, M; Solodov, A A
2013-01-01
Fast Ignition Inertial Confinement Fusion is a variant of inertial fusion in which DT fuel is first compressed to high density and then ignited by a relativistic electron beam generated by a fast (< 20 ps) ultra-intense laser pulse, which is usually brought in to the dense plasma via the inclusion of a re-entrant cone. The transport of this beam from the cone apex into the dense fuel is a critical part of this scheme, as it can strongly influence the overall energetics. Here we review progress in the theory and numerical simulation of fast electron transport in the context of Fast Ignition. Important aspects of the basic plasma physics, descriptions of the numerical methods used, a review of ignition-scale simulations, and a survey of schemes for controlling the propagation of fast electrons are included. Considerable progress has taken place in this area, but the development of a robust, high-gain FI `point design' is still an ongoing challenge.
Molecular orbital theory of ballistic electron transport through molecules
Ernzerhof, Matthias; Rocheleau, Philippe; Goyer, Francois
2009-03-01
Electron transport through molecules occurs, for instance, in STM imaging and in conductance measurements on molecular electronic devices (MEDs). To model these phenomena, we use a non-Hermitian model Hamiltonian [1] for the description of open systems that exchange current density with their environment. We derive qualitative, molecular-orbital-based rules relating molecular structure and conductance. We show how side groups attached to molecular conductors [2] can completely suppress the conductance. We discuss interference effects in aromatic molecules [3] that can also inhibit electron transport. Rules are developed [1] for the prediction of Fano resonances. All these phenomena are explained with a molecular orbital theory [1,4] for molecules attached to macroscopic reservoirs. [1] F. Goyer, M. Ernzerhof, and M. Zhuang, JCP 126, 144104 (2007); M. Ernzerhof, JCP 127, 204709 (2007). [2] M. Ernzerhof, M. Zhuang, and P. Rocheleau, JCP 123, 134704 (2005); G. C. Solomon, D Q. Andrews, R P. Van Duyne, and M A. Ratner, JACS 130, 7788 (2008). [3] M. Ernzerhof, H. Bahmann, F. Goyer, M. Zhuang, and P. Rocheleau, JCTC 2, 1291 (2006); G. C. Solomon, D. Q. Andrews, R. P. Van Duyne, and M. A. Ratner, JCP 129, 054701 (2008). [4] B.T. Pickup, P.W. Fowler, CPL 459, 198 (2008); P. Rocheleau and M. Ernzerhof, JCP, submitted.
Artemisinin inhibits chloroplast electron transport activity: mode of action.
Adyasha Bharati
Full Text Available 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 Q(B; 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.
Light Particle Tracking Model for Simulating Bed Sediment Transport Load in River Areas
Israel E. Herrera-Díaz
2017-01-01
Full Text Available In this work a fast computational particles tracer model is developed based on Particle-In-Cell method to estimate the sediment transport in the access zone of a river port area. To apply the particles tracer method, first it is necessary to calculate the hydrodynamic fields of the study zone to determine the velocity fields in the three directions. The particle transport is governed mainly by the velocity fields and the turbulent dispersion. The mechanisms of dispersion and resuspension of particles are based in stochastic models, which describes the movement through a probability function. The developed code was validated using two well known cases with a discrete transformation obtaining a max relative error around 4.8% in both cases. The simulations were carried out with 350,000 particles allowing us to determine under certain circumstances different hydrodynamic scenarios where the zones are susceptible to present erosion and siltation at the entrance of the port.
Pähtz, Thomas
2016-01-01
To sustain steady sediment transport, the loss of transported particles that become trapped in the soil bed must be balanced by the entrainment of bed particles through fluid forces or energetic impacts of transported particles. Here we show that the transition to fully impact-sustained transport occurs at a critical impact number $\\mathrm{Im}=\\Theta\\mathrm{Re}\\sqrt{s}\\approx3$, where $\\Theta$ is the Shields number, $\\mathrm{Re}$ the particle Reynolds number, and $s$ the particle-fluid-density ratio. Hence, fluid entrainment is negligible for most regimes, including turbulent bedload transport.
S, Savithiri; Dhar,Purbarun; Pattamatta, Arvind; Das, Sarit K
2015-01-01
Severe contradictions exist between experimental observations and computational predictions regarding natural convective thermal transport in nanosuspensions. The approach treating nanosuspensions as homogeneous fluids in computations has been pin pointed as the major contributor to such contradictions. To fill the void, inter particle and particle fluid interactivities (slip mechanisms), in addition to effective thermophysical properties, have been incorporated within the present formulation...
Van Ommen, J.R.
2010-01-01
The invention provides a process for depositing a coating onto particles being pneumatically transported in a tube. The process comprising the steps of providing a tube having an inlet opening and an outlet opening; feeding a carrier gas entraining particles into the tube at or near the inlet openin
Simulation of Neutral Particle Transport During HiPIMS
Trieschmann, Jan; Gallian, Sara; Brinkmann, Ralf Peter; Mussenbrock, Thomas
2014-10-01
In this work the importance of the knowledge of the spatial distribution, its temporal evolution as well as their energy distribution of heavy particles within sputtering processes is discussed. To describe these discharges - typically operated at very low pressures below 1 Pa - specific modeling approaches are required. Our approach comprises a three-dimensional kinetic Lagrangian description of neutral particles. A modified version of the direct simulation Monte Carlo (DSMC) code dsmcFoam is used, with the aim to describe the evolution of background and sputtered particles of a High Power Impulse Magnetron Sputtering (HiPIMS) process in a research reactor. Emphasize is put on the influence of the initial angular distribution of sputtered particles, as well as their energy distribution and its angular dependence. Based on the work of Stepanova and Dew a modified Thompson energy distribution is used. Differently distributed sputtered particles provide densities and fluxes concerning the corresponding film formation. This work is supported by the German Research Foundation in the frame of the Collaborative Research Centre TRR 87.
Multiscale modelling of charge transport in organic electronic materials
Nelson, Jenny
2010-03-01
Charge transport in disordered organic semiconductors is controlled by a complex combination of phenomena that span a range of length and time scales. As a result, it is difficult to rationalize charge transport properties in terms of material parameters. Until now, efforts to improve charge mobilities in molecular semiconductors have proceeded largely by trial and error rather than through systematic design. However, recent developments have enabled the first predictive simulation studies of charge transport in disordered organic semiconductors. In this presentation we will show how a set of computational methods, namely molecular modelling methods to simulate molecular packing, quantum chemical calculations of charge transfer rates, and Monte Carlo simulations of charge transport can be used to reproduce experimental charge mobilities with few or no fitting parameters. Using case studies, we will show how such simulations can explain the relative values of electron and hole mobility and the effects of grain size, side chains and polymer molecular weight on charge mobility. Although currently applied to material systems of relatively high symmetry or well defined structure, this approach can be developed to address more complex systems such as multicomponent solids and conjugated polymers.
Elastic properties and electron transport in InAs nanowires
Migunov, Vadim
2013-02-22
The electron transport and elastic properties of InAs nanowires grown by chemical vapor deposition on InAs (001) substrate were studied experimentally, in-situ in a transmission electron microscope (TEM). A TEM holder allowing the measurement of a nanoforce while simultaneous imaging nanowire bending was used. Diffraction images from local areas of the wire were recorded to correlate elastic properties with the atomic structure of the nanowires. Another TEM holder allowing the application of electrical bias between the nanowire and an apex of a metallic needle while simultaneous imaging the nanowire in TEM or performing electron holography was used to detect mechanical vibrations in mechanical study or holographical observation of the nanowire inner potential in the electron transport studies. The combination of the scanning probe methods with TEM allows to correlate the measured electric and elastic properties of the nanowires with direct identification of their atomic structure. It was found that the nanowires have different atomic structures and different stacking fault defect densities that impacts critically on the elastic properties and electric transport. The unique methods, that were applied in this work, allowed to obtain dependencies of resistivity and Young's modulus of left angle 111 right angle -oriented InAs nanowires on defect density and diameter. It was found that the higher is the defect density the higher are the resistivity and the Young's modulus. Regarding the resistivity, it was deduced that the stacking faults increase the scattering of the electrons in the nanowire. These findings are consistent with the literature, however, the effect described by the other groups is not so pronounced. This difference can be attributed to the significant incompleteness of the physical models used for the data analysis. Regarding the elastic modulus, there are several mechanisms affecting the elasticity of the nanowires discussed in the thesis. It
Electronic transport through InGaN heterojunctions
César, Mathieu; Liu, Donping; Guo, Hong
2012-02-01
InGaN nanowires have recently sparked great interest for their high tunability and potential in applications like solid-state lighting (LEDs) and concentrated photovoltaics. Determination of device characteristics from first principles modeling is of great importance. In order to treat quantum transport properties of nanoelectronic devices with atomistic disorder, a non-equilibrium vertex correction (NVC) theory was recently developed and implemented into the Keldysh non-equilibrium Green's function (NEGF) -based density functional theory (DFT). NEGF-DFT-NVC enables the representation of disordered structures such as the InGaN heterojunction under non-equilibrium conditions. Electronic and transport properties of a InGaN heterojunction are investigated using this accurate ab initio method.
Finite-frequency counting statistics of electron transport: Markovian theory
Marcos, D; Aguado, R [Departamento de Teoria y Simulacion de Materiales, Instituto de Ciencia de Materiales de Madrid, CSIC, Cantoblanco 28049, Madrid (Spain); Emary, C; Brandes, T, E-mail: david.marcos@icmm.csic.es [Institut fuer Theoretische Physik, Hardenbergstrasse 36, TU Berlin, D-10623 Berlin (Germany)
2010-12-15
We present a theory of frequency-dependent counting statistics of electron transport through nanostructures within the framework of Markovian quantum master equations. Our method allows the calculation of finite-frequency current cumulants of arbitrary order, as we explicitly show for the second- and third-order cumulants. Our formulae generalize previous zero-frequency expressions in the literature and can be viewed as an extension of MacDonald's formula beyond shot noise. When combined with an appropriate treatment of tunneling using, e.g., the Liouvillian perturbation theory in Laplace space, our method can deal with arbitrary bias voltages and frequencies, as we illustrate with the paradigmatic example of transport through a single resonant level model. We discuss various interesting limits, including the recovery of the fluctuation-dissipation theorem near linear response, as well as some drawbacks inherent to the Markovian description arising from the neglect of quantum fluctuations.
Electron transport in a mesoscopic superconducting ferromagnetic hybrid conductor
Giroud, M.; Hasselbach, K.; Courtois, H.; Pannetier, B. [Centre de Recherche sur les Tres Basses Temperatures, CNRS, 38 - Grenoble (France); Mailly, D. [Laboratoire de Photonique et de Nanostructures, 91 - Marcoussis (France)
2003-01-01
We present electrical transport experiments performed on submicron hybrid devices made of a ferromagnetic conductor (Co) and a superconducting (Al) electrode. The sample was patterned in order to separate the contributions of the Co conductor and of the Co-Al interface. We observed a strong influence of the Al electrode superconductivity on the resistance of the Co conductor. This effect is large only when the interface is highly transparent. We characterized the dependence of the observed resistance decrease on temperature, bias current and magnetic field. As the differential resistance of the ferromagnet exhibits a non-trivial asymmetry, we claim that the magnetic domain structure plays an important role in the electron transport properties of superconducting / ferromagnetic conductors. (authors)
Electronic transport through EuO spin filter tunnel junctions
Jutong, Nuttachai; Eckern, Ulrich [Institut fuer Physik, Universitaet Augsburg, 86135 Augsburg (Germany); Rungger, Ivan; Sanvito, Stefano [School of Physics and CRANN, Trinity College Dublin, Dublin (Ireland); Schwingenschloegl, Udo [KAUST, PSE Division, Thuwal 23955-6900, Kingdom of Saudi Arabia (Saudi Arabia)
2012-07-01
Spin filter tunnel junctions based on europium monoxide (EuO), a ferromagnetic semiconductor, are investigated by means of density functional theory. In particular, the spin transport of Cu/EuO/Cu junctions is investigated by using the self-consistent ab-initio electron transport code SMEAGOL. The dependence of the transmission coefficient on the interface spacing and on the EuO thickness is studied, and explained in terms of the density of states and the complex band structure of EuO. Our calculation indicates that EuO epitaxially grown on Cu can act as a perfect spin filter, with polarization close to 100%, which is related mainly to the Eu-4f states. The transmission coefficient is sensitive to the interface spacing, since this spacing determines the charge transfer between EuO and the Cu leads.
Contacting nanowires and nanotubes with atomic precision for electronic transport
Qin, Shengyong
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. © 2012 American Institute of Physics.
Third-order TRANSPORT: A computer program for designing charged particle beam transport systems
Carey, D.C. [Fermi National Accelerator Lab., Batavia, IL (United States); Brown, K.L.; Rothacker, F. [Stanford Linear Accelerator Center, Menlo Park, CA (United States)
1995-05-01
TRANSPORT has been in existence in various evolutionary versions since 1963. The present version of TRANSPORT is a first-, second-, and third-order matrix multiplication computer program intended for the design of static-magnetic beam transport systems. This report discusses the following topics on TRANSPORT: Mathematical formulation of TRANSPORT; input format for TRANSPORT; summaries of TRANSPORT elements; preliminary specifications; description of the beam; physical elements; other transformations; assembling beam lines; operations; variation of parameters for fitting; and available constraints -- the FIT command.
Influence of tube and particle diameter on heat transport in packed beds
Borkink, J.G.H.; Borkink, J.G.H.; Westerterp, K.R.
1992-01-01
Influence of the tube and particle diameter and shape, as well as their ratio, on the radial heat transport in packed beds has been studied. Heat transport experiments were performed with four different packings in three wall-cooled tubes, which differed in inner diameter only. Experimental values f
Influence of tube and particle diameter on heat transport in packed beds
Borkink, J.G.H.; Borkink, J.G.H.; Westerterp, K.R.
1992-01-01
Influence of the tube and particle diameter and shape, as well as their ratio, on the radial heat transport in packed beds has been studied. Heat transport experiments were performed with four different packings in three wall-cooled tubes, which differed in inner diameter only. Experimental values
Cai, Li; Tong, Meiping; Wang, Xueting; Kim, Hyunjung
2014-07-01
This study investigated the influence of two representative suspended clay particles, bentonite and kaolinite, on the transport of titanium dioxide nanoparticles (nTiO2) in saturated quartz sand in both NaCl (1 and 10 mM ionic strength) and CaCl2 solutions (0.1 and 1 mM ionic strength) at pH 7. The breakthrough curves of nTiO2 with bentonite or kaolinite were higher than those without the presence of clay particles in NaCl solutions, indicating that both types of clay particles increased nTiO2 transport in NaCl solutions. Moreover, the enhancement of nTiO2 transport was more significant when bentonite was present in nTiO2 suspensions relative to kaolinite. Similar to NaCl solutions, in CaCl2 solutions, the breakthrough curves of nTiO2 with bentonite were also higher than those without clay particles, while the breakthrough curves of nTiO2 with kaolinite were lower than those without clay particles. Clearly, in CaCl2 solutions, the presence of bentonite in suspensions increased nTiO2 transport, whereas, kaolinite decreased nTiO2 transport in quartz sand. The attachment of nTiO2 onto clay particles (both bentonite and kaolinite) were observed under all experimental conditions. The increased transport of nTiO2 in most experimental conditions (except for kaolinite in CaCl2 solutions) was attributed mainly to the clay-facilitated nTiO2 transport. The straining of larger nTiO2-kaolinite clusters yet contributed to the decreased transport (enhanced retention) of nTiO2 in divalent CaCl2 solutions when kaolinite particles were copresent in suspensions.
Electronic Transport Properties of Doped C28 Fullerene
Akshu Pahuja
2014-01-01
Full Text Available Endohedral doping of small fullerenes like C28 affects their electronic structure and increases their stability. The transport properties of Li@C28 sandwiched between two gold surfaces have been calculated using first-principles density functional theory and nonequilibrium Green’s function formalism. The transmission curves, IV characteristics, and molecular projected self-consistent Hamiltonian eigenstates of both pristine and doped molecule are computed. The current across the junction is found to decrease upon Li encapsulation, which can be attributed to change in alignment of molecular energy levels with bias voltage.
Electron transport in silicon nanowires having different cross-sections
Muscato Orazio
2016-06-01
Full Text Available Transport phenomena in silicon nanowires with different cross-section are investigated using an Extended Hydrodynamic model, coupled to the Schrödinger-Poisson system. The model has been formulated by closing the moment system derived from the Boltzmann equation on the basis of the maximum entropy principle of Extended Thermodynamics, obtaining explicit closure relations for the high-order fluxes and the production terms. Scattering of electrons with acoustic and non polar optical phonons have been taken into account. The bulk mobility is evaluated for square and equilateral triangle cross-sections of the wire.
Computation of electron quantum transport in graphene nanoribbons using GPU
Ihnatsenka, S
2011-01-01
The performance potential for simulating quantum electron transport on graphical processing units (GPUs) is studied. Using graphene ribbons of realistic sizes as an example it is shown that GPUs provide significant speed-ups in comparison to central processing units as the transverse dimension of the ribbon grows. The recursive Green's function algorithm is employed and implementation details on GPUs are discussed. Calculated conductances were found to accumulate significant numerical error due to single-precision floating-point arithmetic at energies close to the charge neutrality point of the graphene.
Interface Roughness Scattering on Electronic Transport in a Quantum Well
郑以松; 吕天全; 张程祥; 苏文辉
2003-01-01
Several theoretical models are established to simulate the interface roughness in a quantum well. The numerical result shows that the roughness correlation function always deviates from the extensively used Gaussian form to some extent, which depends on what a model is used. The influence of such a deviation on the electronic transport property is investigated by assuming several different analytical forms of the correlation function. It is found that the Fermi wavevector is crucial to determine whether the conductivity depends sensitively on the details of the correlation function.
Nuclear fuel particles in the environment - characteristics, atmospheric transport and skin doses
Poellaenen, R
2002-05-01
In the present thesis, nuclear fuel particles are studied from the perspective of their characteristics, atmospheric transport and possible skin doses. These particles, often referred to as 'hot' particles, can be released into the environment, as has happened in past years, through human activities, incidents and accidents, such as the Chernobyl nuclear power plant accident in 1986. Nuclear fuel particles with a diameter of tens of micrometers, referred to here as large particles, may be hundreds of kilobecquerels in activity and even an individual particle may present a quantifiable health hazard. The detection of individual nuclear fuel particles in the environment, their isolation for subsequent analysis and their characterisation are complicated and require well-designed sampling and tailored analytical methods. In the present study, the need to develop particle analysis methods is highlighted. It is shown that complementary analytical techniques are necessary for proper characterisation of the particles. Methods routinely used for homogeneous samples may produce erroneous results if they are carelessly applied to radioactive particles. Large nuclear fuel particles are transported differently in the atmosphere compared with small particles or gaseous species. Thus, the trajectories of gaseous species are not necessarily appropriate for calculating the areas that may receive large particle fallout. A simplified model and a more advanced model based on the data on real weather conditions were applied in the case of the Chernobyl accident to calculate the transport of the particles of different sizes. The models were appropriate in characterising general transport properties but were not able to properly predict the transport of the particles with an aerodynamic diameter of tens of micrometers, detected at distances of hundreds of kilometres from the source, using only the current knowledge of the source term. Either the effective release height has
Structure dependent spin selectivity in electron transport through oligopeptides
Kiran, Vankayala; Cohen, Sidney R.; Naaman, Ron
2017-03-01
The chiral-induced spin selectivity (CISS) effect entails spin-selective electron transmission through chiral molecules. In the present study, the spin filtering ability of chiral, helical oligopeptide monolayers of two different lengths is demonstrated using magnetic conductive probe atomic force microscopy. Spin-specific nanoscale electron transport studies elucidate that the spin polarization is higher for 14-mer oligopeptides than that of the 10-mer. We also show that the spin filtering ability can be tuned by changing the tip-loading force applied on the molecules. The spin selectivity decreases with increasing applied force, an effect attributed to the increased ratio of radius to pitch of the helix upon compression and increased tilt angles between the molecular axis and the surface normal. The method applied here provides new insights into the parameters controlling the CISS effect.
Orthogonally modulated molecular transport junctions for resettable electronic logic gates
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.
Kondo effect for electron transport through an artificial quantum dot
Sun Ke-Wei; Xiong Shi-Jie
2006-01-01
We have calculated the transport properties of electron through an artificial quantum dot by using the numerical renormalization group technique in this paper.We obtain the conductance for the system of a quantum dot which is embedded in a one-dimensional chain in zero and finite temperature cases.The external magnetic field gives rise to a negative magnetoconductance in the zero temperature case.It increases as the external magnetic field increases.We obtain the relation between the coupling coefficient and conductance.If the interaction is big enough to prevent conduction electrons from tunnelling through the dot,the dispersion effect is dominant in this case.In the Kondo temperature regime,we obtain the conductivity of a quantum dot system with Kondo correlation.
Electronic transport in disordered graphene antidot lattice devices
Power, Stephen; Jauho, Antti-Pekka
2014-01-01
Nanostructuring of graphene is in part motivated by the requirement to open a gap in the electronic band structure. In particular, a periodically perforated graphene sheet in the form of an antidot lattice may have such a gap. Such systems have been investigated with a view towards application...... in transistor or waveguiding devices. The desired properties have been predicted for atomically precise systems, but fabrication methods will introduce significant levels of disorder in the shape, position and edge configurations of individual antidots. We calculate the electronic transport properties of a wide...... range of finite graphene antidot devices to determine the effect of such disorders on their performance. Modest geometric disorder is seen to have a detrimental effect on devices containing small, tightly packed antidots, which have optimal performance in pristine lattices. Larger antidots display...
Electronic transport properties of carbon nanotube metal-semiconductor-metal
F Khoeini
2008-07-01
Full Text Available In this work, we study electronic transport properties of a quasi-one dimensional pure semi-conducting Zigzag Carbon Nanotube (CNT attached to semi-infinite clean metallic Zigzag CNT leads, taking into account the influence of topological defect in junctions. This structure may behave like a field effect transistor. The calculations are based on the tight-binding model and Green’s function method, in which the local density of states(LDOS in the metallic section to semi-conducting section, and muli-channel conductance of the system are calculated in the coherent and linear response regime, numerically. Also we have introduced a circuit model for the system and investigated its current. The theoretical results obtained, can be a base, for developments in designing nano-electronic devices.
Electronic transport properties of the armchair silicon carbide nanotube
Song Jiuxu; Yang Yintang; Liu Hongxia [Key Laboratory of Ministry of Education for Wide Band Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi' an 710071 (China); Guo Lixin [School of Science, Xidian University, Xi' an 710071 (China); Zhang Zhiyong, E-mail: songjiuxu@126.com [Information Science and Technology Institution, Northwest University, Xi' an 710069 (China)
2010-11-15
The electronic transport properties of the armchair silicon carbide nanotube (SiCNT) are investigated by using the combined nonequilibrium Green's function method with density functional theory. In the equilibrium transmission spectrum of the nanotube, a transmission valley of about 2.12 eV is discovered around Fermi energy, which means that the nanotube is a wide band gap semiconductor and consistent with results of first principle calculations. More important, negative differential resistance is found in its current voltage characteristic. This phenomenon originates from the variation of density of states caused by applied bias voltage. These investigations are meaningful to modeling and simulation in silicon carbide nanotube electronic devices.
The Random Ray Method for neutral particle transport
Tramm, John R., E-mail: jtramm@mit.edu [Massachusetts Institute of Technology, Department of Nuclear Science Engineering, 77 Massachusetts Avenue, 24-107, Cambridge, MA 02139 (United States); Argonne National Laboratory, Mathematics and Computer Science Department 9700 S Cass Ave, Argonne, IL 60439 (United States); Smith, Kord S., E-mail: kord@mit.edu [Massachusetts Institute of Technology, Department of Nuclear Science Engineering, 77 Massachusetts Avenue, 24-107, Cambridge, MA 02139 (United States); Forget, Benoit, E-mail: bforget@mit.edu [Massachusetts Institute of Technology, Department of Nuclear Science Engineering, 77 Massachusetts Avenue, 24-107, Cambridge, MA 02139 (United States); Siegel, Andrew R., E-mail: siegela@mcs.anl.gov [Argonne National Laboratory, Mathematics and Computer Science Department 9700 S Cass Ave, Argonne, IL 60439 (United States)
2017-08-01
A new approach to solving partial differential equations (PDEs) based on the method of characteristics (MOC) is presented. The Random Ray Method (TRRM) uses a stochastic rather than deterministic discretization of characteristic tracks to integrate the phase space of a problem. TRRM is potentially applicable in a number of transport simulation fields where long characteristic methods are used, such as neutron transport and gamma ray transport in reactor physics as well as radiative transfer in astrophysics. In this study, TRRM is developed and then tested on a series of exemplar reactor physics benchmark problems. The results show extreme improvements in memory efficiency compared to deterministic MOC methods, while also reducing algorithmic complexity, allowing for a sparser computational grid to be used while maintaining accuracy.
Particle Transport in a 3D duct by adding and doubling
Ganapol, Barry D
2016-01-01
Particle transport through a duct by Lambertian reflection from duct walls is again considered. This popular transport example has been solved by most numerical transport methods except notably one- the method of doubling. We shall show that the method of doubling provides every bit as, or more, accurate reflectances and transmittances as the numerical discrete ordinates (NDO) and analytical discrete ordinates (ADO) methods with less mathematical and numerical effort.
Mechanism for Particle Transport and Size Sorting via Low-Frequency Vibrations
Sherrit, Stewart; Scott, James S.; Bar-Cohen, Yoseph; Badescu, Mircea; Bao, Xiaoqi
2010-01-01
There is a need for effective sample handling tools to deliver and sort particles for analytical instruments that are planned for use in future NASA missions. Specifically, a need exists for a compact mechanism that allows transporting and sieving particle sizes of powdered cuttings and soil grains that may be acquired by sampling tools such as a robotic scoop or drill. The required tool needs to be low mass and compact to operate from such platforms as a lander or rover. This technology also would be applicable to sample handling when transporting samples to analyzers and sorting particles by size.
Perpendicular Diffusion of Solar Energetic Particles: Model Results and Implications for Electrons
Strauss, R. Du Toit; Dresing, Nina; Engelbrecht, N. Eugene
2017-03-01
The processes responsible for the effective longitudinal transport of solar energetic particles (SEPs) are still not completely understood. We address this issue by simulating SEP electron propagation using a spatially 2D transport model that includes perpendicular diffusion. By implementing, as far as possible, the most reasonable estimates of the transport (diffusion) coefficients, we compare our results, in a qualitative manner, to recent observations at energies of 55–105 keV, focusing on the longitudinal distribution of the peak intensity, the maximum anisotropy, and the onset time. By using transport coefficients that are derived from first principles, we limit the number of free parameters in the model to (i) the probability of SEPs following diffusing magnetic field lines, quantified by a\\in [0,1], and (ii) the broadness of the Gaussian injection function. It is found that the model solutions are extremely sensitive to the magnitude of the perpendicular diffusion coefficient and relatively insensitive to the form of the injection function as long as a reasonable value of a = 0.2 is used. We illustrate the effects of perpendicular diffusion on the model solutions and discuss the viability of this process as a dominant mechanism by which SEPs are transported in longitude. Lastly, we try to quantity the effectiveness of perpendicular diffusion as an interplay between the magnitude of the relevant diffusion coefficient and the SEP intensity gradient driving the diffusion process. It follows that perpendicular diffusion is extremely effective early in an SEP event when large intensity gradients are present, while the effectiveness quickly decreases with time thereafter.
Transport of Optically Active Particles from the Surface Mixed Layer
2005-09-30
aragonite in the form of abundant coccoliths and coccospheres, and occasional forams, pteropods and larval gastropods . The δ18O signature of the 2003... APPLICATIONS These experiments were designed to identify the major loss terms of optically-active particles. This indeed was accomplished. Such
Particle acceleration and transport in the solar atmosphere
Kontar, Eduard
2016-07-01
During periods of sporadic flare activity, the Sun releases energy stored in the magnetic field into the plasma of the solar atmosphere. This is an extremely efficient process, with a large fraction of the magnetic energy going into plasma particles. The solar flares are accompanied by prompt electromagnetic emission virtually over the entire electromagnetic spectrum from gamma-rays down to radio frequencies. The Sun, through its activity, also plays a driving role in the Sun-Earth system that substantially influences geophysical space. Solar flare energetic particles from the Sun are detected in interplanetary space by in-situ measurements making them a vital component of the single Sun-Earth system. Although a qualitative picture is generally agreed upon, many processes solar flare processes are poorly understood. Specifically, the processes of acceleration and propagation of energetic particles interacting on various physical scales remain major challenges in solar physics and basic plasma physics. In the talk, I will review the current understanding of solar flare energetic particles focusing on recent observational progress, which became possible due to the numerous spacecraft and ground-based observations.
Particle transport in fluidized beds : experiments and stochastic models
Dechsiri, Chutima
2004-01-01
Fluidization is a process in which solids are caused to behave like fluid by blowing gas or liquid upwards through the solid-filled reactor. The behavior of a bed of particles within the reactor during the process is very complex and difficult to predict. To make sure that a fluidized bed reactor is
Vertical Transport of Aerosol Particles across Mountain Topography near the Los Angeles Basin
Murray, J. J.; Schill, S.; Freeman, S.; Bertram, T. H.; Lefer, B. L.
2015-12-01
Transport of aerosol particles is known to affect air quality and is largely dependent on the characteristic topography of the surrounding region. To characterize this transport, aerosol number distributions were collected with an Ultra-High Sensitivity Aerosol Spectrometer (UHSAS, DMT) during the 2015 NASA Student Airborne Research Program (SARP) in and around the Los Angeles Basin in Southern California. Increases in particle number concentration and size were observed over mountainous terrain north of Los Angeles County. Chemical analysis and meteorological lagrangian trajectories suggest orographic lifting processes, known as the "chimney effect". Implications for spatial transport and distribution will be discussed.
Porth, O.; Vorster, M. J.; Lyutikov, M.; Engelbrecht, N. E.
2016-08-01
We study the transport of high-energy particles in pulsar wind nebulae (PWN) using three-dimensional magnetohydrodynamic (MHD) and test-particle simulations, as well as a Fokker-Planck particle transport model. The latter includes radiative and adiabatic losses, diffusion, and advection on the background flow of the simulated MHD nebula. By combining the models, the spatial evolution of flux and photon index of the X-ray synchrotron emission is modelled for the three nebulae G21.5-0.9, the inner regions of Vela, and 3C 58, thereby allowing us to derive governing parameters: the magnetic field strength, average flow velocity, and spatial diffusion coefficient. For comparison, the nebulae are also modelled with the semi-analytic Kennel & Coroniti model but the Porth et al. model generally yields better fits to the observational data. We find that high velocity fluctuations in the turbulent nebula (downstream of the termination shock) give rise to efficient diffusive transport of particles, with average Péclet number close to unity, indicating that both advection and diffusion play an important role in particle transport. We find that the diffusive transport coefficient of the order of ˜ 2 × 1027(Ls/0.42 Ly) cm2 s- 1 (Ls is the size of the termination shock) is independent of energy up to extreme particle Lorentz factors of γp ˜ 1010.
Choudhary, Mangilal; Bandyopadhyay, P
2016-01-01
A versatile linear dusty (complex) plasma device is designed to study the transport and dynamical behavior of dust particles in a large volume. Diffused inductively coupled plasma is generated in the background of argon gas. A novel technique is used to introduce the dust particles in the main plasma by striking a secondary direct current (DC) glow discharge. These dust particles are found to get trapped in an electrostatic potential well which is formed due to the combination of the ambipolar electric field caused by diffusive plasma and the field produced by the charged glass wall of the vacuum chamber. According to the requirements, the volume of the dust cloud can be controlled very precisely by tuning the plasma and discharge parameters. The present device can be used to address the underlying physics behind the transport of dust particles, self excited dust acoustic waves and instabilities. The detailed design of this device, plasma production and characterization, trapping and transport of the dust par...
Nonclassical Particle Transport in the 1-D Diffusive Limit
Vasques, Richard; Krycki, Kai
2016-01-01
This paper provides numerical results that demonstrate the validity of the nonclassical diffusion approximation to the nonclassical transport equation in certain 1-D diffusive systems. This result provides a more solid foundation in which to improve this theory for relevant nuclear applications.
Gonzalez, Arnulfo
2016-01-01
The problem of monoenergetic neutral particle transport in a duct, where particles travel inside the duct walls, is treated using an approximate one-dimensional model. The one-dimensional model uses three-basis functions, as part of a previously derived weighted-residual procedure, to account for the geometry of particle transport in a duct system (where particle migration into the walls is not considered). Our model introduces two stochastic parameters to account for particle-wall interactions: an albedo approximation yielding the fraction of particles that return to the duct after striking the walls, and a mean-distance travelled in the walls transverse to the duct by particles that re-enter the duct. Our model produces a set of three transport equations with a non-local scattering kernel. We solve these equations using discrete ordinates with source iteration. Numerical results for the reflection and transmission probabilities of neutron transport in ducts of circular cross section are compared to Monte Ca...
Cai, Zhengqing; Fu, Jie; Liu, Wen; Fu, Kunming; O'Reilly, S E; Zhao, Dongye
2017-01-15
This work investigated effects of three model oil dispersants (Corexit EC9527A, Corexit EC9500A and SPC1000) on settling of fine sediment particles and particle-facilitated distribution and transport of oil components in sediment-seawater systems. All three dispersants enhanced settling of sediment particles. The nonionic surfactants (Tween 80 and Tween 85) play key roles in promoting particle aggregation. Yet, the effects varied with environmental factors (pH, salinity, DOM, and temperature). Strongest dispersant effect was observed at neutral or alkaline pH and in salinity range of 0-3.5wt%. The presence of water accommodated oil and dispersed oil accelerated settling of the particles. Total petroleum hydrocarbons in the sediment phase were increased from 6.9% to 90.1% in the presence of Corexit EC9527A, and from 11.4% to 86.7% for PAHs. The information is useful for understanding roles of oil dispersants in formation of oil-sediment aggregates and in sediment-facilitated transport of oil and PAHs in marine eco-systems.
Ogawa, Shun; Dif-Pradalier, Guilhem; Garbet, Xavier
2016-01-01
Charged particles with low kinetic energy move along magnetic field lines, but so do not energetic particles. We investigate the topological structure changes in the phase space of energetic particles with respect to the magnetic one. For this study cylindrical magnetic fields with non-monotonic safety factors that induce the magnetic internal transport barrier are considered. We show that the topological structure of the magnetic field line and of the particle trajectories can be quite different. We explain this difference using the concept of effective particle $q$-profile. Using this notion we can investigate the location and existence of resonances for particle orbits that are different from the magnetic ones. These are examined both numerically by integrating an equation of motion and theoretically by use of Alfv\\'en's guiding center theory and by use of the effective reduced Hamiltonian for the integrable unperturbed system. It is clarified that, for the energetic particles, the grad $B$ drift effect sh...
Coupled Particle Transport and Pattern Formation in a Nonlinear Leaky-Box Model
Barghouty, A. F.; El-Nemr, K. W.; Baird, J. K.
2009-01-01
Effects of particle-particle coupling on particle characteristics in nonlinear leaky-box type descriptions of the acceleration and transport of energetic particles in space plasmas are examined in the framework of a simple two-particle model based on the Fokker-Planck equation in momentum space. In this model, the two particles are assumed coupled via a common nonlinear source term. In analogy with a prototypical mathematical system of diffusion-driven instability, this work demonstrates that steady-state patterns with strong dependence on the magnetic turbulence but a rather weak one on the coupled particles attributes can emerge in solutions of a nonlinearly coupled leaky-box model. The insight gained from this simple model may be of wider use and significance to nonlinearly coupled leaky-box type descriptions in general.
Attosecond photoelectron spectroscopy of electron transport in solids
Magerl, Elisabeth
2011-03-31
Time-resolved photoelectron spectroscopy of condensed matter systems in the attosecond regime promises new insights into excitation mechanisms and transient dynamics of electrons in solids. This timescale became accessible directly only recently with the development of the attosecond streak camera and of laser systems providing few-cycle, phase-controlled laser pulses in the near-infrared, which are used to generate isolated, sub-femtosecond extreme-ultraviolet pulses with a well-defined timing with respect to the near-infrared pulse. Employing these pulses, the attosecond streak camera offers time resolutions as short as a few 10 attoseconds. In the framework of this thesis, a new, versatile experimental apparatus combining attosecond pulse generation in gases with state of the art surface science techniques is designed, constructed, and commissioned. Employing this novel infrastructure and the technique of the attosecond transient recorder, we investigate transport phenomena occurring after photoexcitation of electrons in tungsten and rhenium single crystals and show that attosecond streaking is a unique method for resolving extremely fast electronic phenomena in solids. It is demonstrated that electrons originating from different energy levels, i.e. from the conduction band and the 4f core level, are emitted from the crystal surface at different times. The origin of this time delay, which is below 150 attoseconds for all studied systems, is investigated by a systematic variation of several experimental parameters, in particular the photon energy of the employed attosecond pulses. These experimental studies are complemented by theoretical studies of the group velocity of highly-excited electrons based on ab initio calculations. While the streaking technique applied on single crystals can provide only information about the relative time delay between two types of photoelectrons, the absolute transport time remains inaccessible. We introduce a scheme of a reference
Electron Transport Materials: Synthesis, Properties and Device Performance
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}).
Electron transport in stepped Bi2Se3 thin films
Bauer, S.; Bobisch, C. A.
2017-08-01
We analyse the electron transport in a 16 quintuple layer thick stepped Bi2Se3 film grown on Si(1 1 1) by means of scanning tunnelling potentiometry (STP) and multi-point probe measurements. Scanning tunnelling microscopy images reveal that the local structure of the Bi2Se3 film is dominated by terrace steps and domain boundaries. From a microscopic study on the nm scale by STP, we find a mostly linear gradient of the voltage on the Bi2Se3 terraces which is interrupted by voltage drops at the position of the domain boundaries. The voltage drops indicate that the domain boundaries are scatterers for the electron transport. Macroscopic resistance measurements (2PP and in-line 4PP measurement) on the µm scale support the microscopic results. An additional rotational square 4PP measurement shows an electrical anisotropy of the sheet conductance parallel and perpendicular to the Bi2Se3 steps of about 10%. This is a result of the anisotropic step distribution at the stepped Bi2Se3 surface while domain boundaries are distributed isotropically. The determined value of the conductivity of the Bi2Se3 steps of about 1000 S cm-1 verifies the value of an earlier STP study.
Electronic transport properties of copper and gold at atomic scale
Mohammadzadeh, Saeideh
2010-11-23
The factors governing electronic transport properties of copper and gold atomic-size contacts are theoretically examined in the present work. A two-terminal conductor using crystalline electrodes is adopted. The non-equilibrium Green's function combined with the density functional tight-binding method is employed via gDFTB simulation tool to calculate the transport at both equilibrium and non-equilibrium conditions. The crystalline orientation, length, and arrangement of electrodes have very weak influence on the electronic characteristics of the considered atomic wires. The wire width is found to be the most effective geometric aspect determining the number of conduction channels. The obtained conductance oscillation and linear current-voltage curves are interpreted. To analyze the conduction mechanism in detail, the transmission channels and their decomposition to the atomic orbitals are calculated in copper and gold single point contacts. The presented results offer a possible explanation for the relation between conduction and geometric structure. Furthermore, the results are in good agreement with available experimental and theoretical studies. (orig.)
One-Dimensional Electron Transport Layers for Perovskite Solar Cells
Ujwal K. Thakur
2017-04-01
Full Text Available The electron diffusion length (Ln is smaller than the hole diffusion length (Lp in many halide perovskite semiconductors meaning that the use of ordered one-dimensional (1D structures such as nanowires (NWs and nanotubes (NTs as electron transport layers (ETLs is a promising method of achieving high performance halide perovskite solar cells (HPSCs. ETLs consisting of oriented and aligned NWs and NTs offer the potential not merely for improved directional charge transport but also for the enhanced absorption of incoming light and thermodynamically efficient management of photogenerated carrier populations. The ordered architecture of NW/NT arrays affords superior infiltration of a deposited material making them ideal for use in HPSCs. Photoconversion efficiencies (PCEs as high as 18% have been demonstrated for HPSCs using 1D ETLs. Despite the advantages of 1D ETLs, there are still challenges that need to be overcome to achieve even higher PCEs, such as better methods to eliminate or passivate surface traps, improved understanding of the hetero-interface and optimization of the morphology (i.e., length, diameter, and spacing of NWs/NTs. This review introduces the general considerations of ETLs for HPSCs, deposition techniques used, and the current research and challenges in the field of 1D ETLs for perovskite solar cells.
One-Dimensional Electron Transport Layers for Perovskite Solar Cells
Thakur, Ujwal K.; Kisslinger, Ryan; Shankar, Karthik
2017-01-01
The electron diffusion length (Ln) is smaller than the hole diffusion length (Lp) in many halide perovskite semiconductors meaning that the use of ordered one-dimensional (1D) structures such as nanowires (NWs) and nanotubes (NTs) as electron transport layers (ETLs) is a promising method of achieving high performance halide perovskite solar cells (HPSCs). ETLs consisting of oriented and aligned NWs and NTs offer the potential not merely for improved directional charge transport but also for the enhanced absorption of incoming light and thermodynamically efficient management of photogenerated carrier populations. The ordered architecture of NW/NT arrays affords superior infiltration of a deposited material making them ideal for use in HPSCs. Photoconversion efficiencies (PCEs) as high as 18% have been demonstrated for HPSCs using 1D ETLs. Despite the advantages of 1D ETLs, there are still challenges that need to be overcome to achieve even higher PCEs, such as better methods to eliminate or passivate surface traps, improved understanding of the hetero-interface and optimization of the morphology (i.e., length, diameter, and spacing of NWs/NTs). This review introduces the general considerations of ETLs for HPSCs, deposition techniques used, and the current research and challenges in the field of 1D ETLs for perovskite solar cells. PMID:28468280
Electron transport in coupled double quantum wells and wires
Harff, N.E.; Simmons, J.A.; Lyo, S.K. [and others
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.
Energy losses of positive and negative charged particles in electron gas
Diachenko, M. M.; Kholodov, R. I.
2017-02-01
A heavy charged particle propagation through electron gas has been studied using combination of non-relativistic quantum mechanics and the Green’s functions method. The energy loss of a charged particle has been found in the case of large transferred momentum taking into account the interference term in the expression for the rate. The dependence of the energy loss of a charged particles in electron gas with nonzero temperature on the sign of the charge has been obtained.
沈辉; 徐雪青; 王伟
2003-01-01
The surface morphology of quasi-periodic stripe-shaped patterns of magnetite fluids was observed in applied perpendicular magnetic fields by means of scanning electron microscopy. The nanoparticles of the magnetite fluids are arranged in oriental quasilinear chains in applied perpendicular magnetic fields as observed using transmission electron microscopy. This arrangement results from particle-particle interactions and particle-carrier liquids interactions, which are eventually controlled by the magnetic fields distribution.
Borowik, Piotr; Thobel, Jean-Luc; Adamowicz, Leszek
2017-07-01
Standard computational methods used to take account of the Pauli Exclusion Principle into Monte Carlo (MC) simulations of electron transport in semiconductors may give unphysical results in low field regime, where obtained electron distribution function takes values exceeding unity. Modified algorithms were already proposed and allow to correctly account for electron scattering on phonons or impurities. Present paper extends this approach and proposes improved simulation scheme allowing including Pauli exclusion principle for electron-electron (e-e) scattering into MC simulations. Simulations with significantly reduced computational cost recreate correct values of the electron distribution function. Proposed algorithm is applied to study transport properties of degenerate electrons in graphene with e-e interactions. This required adapting the treatment of e-e scattering in the case of linear band dispersion relation. Hence, this part of the simulation algorithm is described in details.
Consolidant particle transport in limestone, concrete and bone
Campbell, Alanna Stacey
2013-01-01
The use of chemically compatible nano and fine particle colloidal consolidants is a new development within the field of cultural heritage conservation and applied most widely so far to the historic built environment. The ability to introduce a significantly higher quantity of chemically compatible consolidant to a substrate in fewer treatments with the possibility for greater penetration and fewer possible side-effects compared to more established consolidants is a significant ...
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.
Surface transport and stable trapping of particles and cells by an optical waveguide loop.
Hellesø, Olav Gaute; Løvhaugen, Pål; Subramanian, Ananth Z; Wilkinson, James S; Ahluwalia, Balpreet Singh
2012-09-21
Waveguide trapping has emerged as a useful technique for parallel and planar transport of particles and biological cells and can be integrated with lab-on-a-chip applications. However, particles trapped on waveguides are continuously propelled forward along the surface of the waveguide. This limits the practical usability of the waveguide trapping technique with other functions (e.g. analysis, imaging) that require particles to be stationary during diagnosis. In this paper, an optical waveguide loop with an intentional gap at the centre is proposed to hold propelled particles and cells. The waveguide acts as a conveyor belt to transport and deliver the particles/cells towards the gap. At the gap, the diverging light fields hold the particles at a fixed position. The proposed waveguide design is numerically studied and experimentally implemented. The optical forces on the particle at the gap are calculated using the finite element method. Experimentally, the method is used to transport and trap micro-particles and red blood cells at the gap with varying separations. The waveguides are only 180 nm thick and thus could be integrated with other functions on the chip, e.g. microfluidics or optical detection, to make an on-chip system for single cell analysis and to study the interaction between cells.
Liu, Zhongqiu; Li, Linmin; Li, Baokuan; Jiang, Maofa
2014-07-01
The current study developed a coupled computational model to simulate the transient fluid flow, solidification, and particle transport processes in a slab continuous-casting mold. Transient flow of molten steel in the mold is calculated using the large eddy simulation. An enthalpy-porosity approach is used for the analysis of solidification processes. The transport of bubble and non-metallic inclusion inside the liquid pool is calculated using the Lagrangian approach based on the transient flow field. A criterion of particle entrapment in the solidified shell is developed using the user-defined functions of FLUENT software (ANSYS, Inc., Canonsburg, PA). The predicted results of this model are compared with the measurements of the ultrasonic testing of the rolled steel plates and the water model experiments. The transient asymmetrical flow pattern inside the liquid pool exhibits quite satisfactory agreement with the corresponding measurements. The predicted complex instantaneous velocity field is composed of various small recirculation zones and multiple vortices. The transport of particles inside the liquid pool and the entrapment of particles in the solidified shell are not symmetric. The Magnus force can reduce the entrapment ratio of particles in the solidified shell, especially for smaller particles, but the effect is not obvious. The Marangoni force can play an important role in controlling the motion of particles, which increases the entrapment ratio of particles in the solidified shell obviously.
MCNPX Monte Carlo simulations of particle transport in SiC semiconductor detectors of fast neutrons
Sedlačková, K.; Zat'ko, B.; Šagátová, A.; Pavlovič, M.; Nečas, V.; Stacho, M.
2014-05-01
The aim of this paper was to investigate particle transport properties of a fast neutron detector based on silicon carbide. MCNPX (Monte Carlo N-Particle eXtended) code was used in our study because it allows seamless particle transport, thus not only interacting neutrons can be inspected but also secondary particles can be banked for subsequent transport. Modelling of the fast-neutron response of a SiC detector was carried out for fast neutrons produced by 239Pu-Be source with the mean energy of about 4.3 MeV. Using the MCNPX code, the following quantities have been calculated: secondary particle flux densities, reaction rates of elastic/inelastic scattering and other nuclear reactions, distribution of residual ions, deposited energy and energy distribution of pulses. The values of reaction rates calculated for different types of reactions and resulting energy deposition values showed that the incident neutrons transfer part of the carried energy predominantly via elastic scattering on silicon and carbon atoms. Other fast-neutron induced reactions include inelastic scattering and nuclear reactions followed by production of α-particles and protons. Silicon and carbon recoil atoms, α-particles and protons are charged particles which contribute to the detector response. It was demonstrated that although the bare SiC material can register fast neutrons directly, its detection efficiency can be enlarged if it is covered by an appropriate conversion layer. Comparison of the simulation results with experimental data was successfully accomplished.
Suspended particle transport through constriction channel with Brownian motion
Hanasaki, Itsuo; Walther, Jens H.
2017-08-01
It is well known that translocation events of a polymer or rod through pores or narrower parts of micro- and nanochannels have a stochastic nature due to the Brownian motion. However, it is not clear whether the objects of interest need to have a larger size than the entrance to exhibit the deviation from the dynamics of the surrounding fluid. We show by numerical analysis that the particle injection into the narrower part of the channel is affected by thermal fluctuation, where the particles have spherical symmetry and are smaller than the height of the constriction. The Péclet number (Pe) is the order parameter that governs the phenomena, which clarifies the spatio-temporal significance of Brownian motion compared to hydrodynamics. Furthermore, we find that there exists an optimal condition of Pe to attain the highest flow rate of particles relative to the dispersant fluid flow. Our finding is important in science and technology from nanopore DNA sequencers and lab-on-a-chip devices to filtration by porous materials and chromatography.
Stokes drift for inertial particles transported by water waves
Boffetta, G; Mazzino, A; Onorato, M; Santamaria, F
2012-01-01
We study the effect of surface gravity waves on the motion of inertial particles in an incompressible fluid. Using the multiple-scale technique, we perform an analytical calculation which allows us to predict the dynamics of such particles; results are shown for both the infinite- and finite-depth regimes. Numerical simulations based on the velocity field resulting from the second-order Stokes theory for the surface elevation have been performed, and an excellent agreement with the analytical predictions is observed. Such an agreement seems to hold even beyond the formal applicability of the theory. We find that the presence of inertia leads to a non-negligible correction to the well-known horizontal Stokes drift; moreover, we find that the vertical velocity is also affected by a drift. The latter result may have some relevant consequences on the rate of sedimentation of particles of finite size. We underline that such a drift would also be observed in the (hypothetical) absence of the gravitational force.
Electron transport properties of carbon-based nanostructures
Diaz Pinto, Carlos A.
Grapheme and graphene-related systems have been the focus of intensive research due to their exceptional electronic behavior. Their properties have been studied for decades, from the unique band structure predicted for a single layer of graphite, to the unexpected linear magnetoresistance observed in its bulk form. Since its experimental isolation in 2004, studies on graphene monolayer, bilayer, and few-layer systems garnered an overwhelming amount of attention from the scientific community, with studies focusing on multilayers with nanometer thicknesses paling in comparison. The main motivation of this study is to further the understanding of systems consisting of multilayer graphene and ultrathin graphite (graphitic multilayers) through electron transport experiments. Uniquely designed and fabricated devices based on carbon nanostructures were used to study the transport of charge carriers under high electric and magnetic fields. For short-channel suspended graphitic multilayer devices, the two-terminal differential conductance dI/dV as a function of drain-source bias Vd displays a pronounced dip pinned at Vd=0, explained by the hot electron effect. The dip is attenuated under high magnetic fields, likely due to intra-Landau level cyclotron phonon scattering. Also, distinct high-energy dI/dV anomalies have been observed and shown to be related to intrinsic phonon-emission processes in graphite. The evolution of such dI/dV anomalies under magnetic fields is understood as a consequence of the inter-Landau level cyclotron-phonon resonance scattering. The magnetoresistance (MR) of this system shows Shubnikov-de Haas oscillations on top of a strong positive nearly-linear background. Upon the introduction of a significant amount of short-range disorders through ion implantation, the positive MR transforms into a negative MR. The results for the MR of pure and implanted graphitic multilayers can be understood by considering a recent magneto-transport theory for two
Electron thermal transport analysis in Tokamak à Configuration Variable
Asp, E.; Kim, J.-H.; Horton, W.; Porte, L.; Alberti, S.; Karpushov, A.; Martin, Y.; Sauter, O.; Turri, G.; Tcv Team
2008-08-01
A Tokamak à Configuration Variable (TCV) [G. Tonetti, A. Heym, F. Hofmann et al., in Proceedings of the 16th Symposium on Fusion Technology, London, U.K., edited by R. Hemsworth (North-Holland, Amsterdam, 1991), p. 587] plasma with high power density (up to 8MW/m3) core deposited electron cyclotron resonance heating at significant plasma densities (⩽7×1019m-3) is analyzed for the electron thermal transport. The discharge distinguishes itself as it has four distinct high confinement mode (H-mode) phases. An Ohmic H-mode with type III edge localized modes (ELMs), which turns into a type I ELMy H-mode when the ECRH is switched on. The ELMs then vanish, which gives rise to a quasistationary ELM-free H-mode. This ELM-free phase can be divided into two, one without magnetohydrodynamics (MHD) and one with. The MHD mode in the latter case causes the confinement to drop by ˜15%. For all four phases both large-scale trapped electron (TEM) and ion temperature gradient (ITG) modes and small-scale electron temperature gradient (ETG) modes are analyzed. The analytical TEM formulas have difficulty in explaining both the magnitude and the radial profile of the electron thermal flux. Collisionality governs the drive of the TEM, which for the discharge in question implies it can be driven by either the temperature or density gradient. The TEM response function is derived and it is shown to be relatively small and to have sharp resonances in its energy dependence. The ETG turbulence, predicted by the Institute for Fusion Studies electron gyrofluid code, is on the other hand driven solely by the electron temperature gradient. Both trapped and passing electrons add to the ETG instability and turbulent thermal flux. For easy comparison of the results of the above approaches and also with the Weiland model, a dimensionless error measure, the so-called average relative variance is introduced. According to this method the ETG model explains 70% of the variation in the electron heat
Charged Particle Transport in High-Energy-Density Matter
Stanton, Liam; Murillo, Michael
2016-10-01
Transport coefficients for dense plasmas have been numerically computed using an effective Boltzmann approach. We have developed a simplified effective potential approach that yields accurate fits for all of the relevant cross sections and collision integrals. Our results have been validated with molecular dynamics simulations for self-diffusion, interdiffusion, viscosity, thermal conductivity and stopping power. Molecular dynamics has also been used to examine the underlying assumptions of the Boltzmann approach through a categorization of behaviors of the velocity autocorrelation function in the Yukawa phase diagram. Using a velocity-dependent screening model, we examine the role of dynamical screening in transport as well. Implications of these results for Coulomb logarithm approaches are discussed. This work is performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
White, M C
2000-01-01
The fundamental motivation for the research presented in this dissertation was the need to development a more accurate prediction method for characterization of mixed radiation fields around medical electron accelerators (MEAs). Specifically, a model is developed for simulation of neutron and other particle production from photonuclear reactions and incorporated in the Monte Carlo N-Particle (MCNP) radiation transport code. This extension of the capability within the MCNP code provides for the more accurate assessment of the mixed radiation fields. The Nuclear Theory and Applications group of the Los Alamos National Laboratory has recently provided first-of-a-kind evaluated photonuclear data for a select group of isotopes. These data provide the reaction probabilities as functions of incident photon energy with angular and energy distribution information for all reaction products. The availability of these data is the cornerstone of the new methodology for state-of-the-art mutually coupled photon-neutron tran...
Considerations of beta and electron transport in internal dose calculations. Progress report
Bolch, W.E.
1994-11-01
The goal of this particular task is to consider, for the first time, the explicit transport of beta particles and photon-generated electrons in the series of six phantoms developed by Cristy and Eckerman (1987) at the Oak Ridge National Laboratory. In their report, ORNL/TM-8381, specific absorbed fractions of energy are reported for phantoms representing the newborn (3.4 kg), the one-year-old (9.8 kg), the five-year-old (19 kg), the ten-year-old (32 kg), the fifteen-year-old/adult female (55-58 kg), and the adult male (70 kg). Radiation transport calculations were performed with the Monte Carlo code ALGAMP which allows photon transport only. In subsequent calculations of radionuclide S values as is done in the MIRDOSE2 computer program, electron absorbed fractions are thus considered to be either unity or zero depending upon whether the source region does or does not equal the target region, respectively.
Turbulent cross-field transport of non-thermal electrons in coronal loops: theory and observations
Bian, N; McKinnon, A
2011-01-01
A fundamental problem in astrophysics is the interaction between magnetic turbulence and charged particles. It is now possible to use \\emph{Ramaty High Energy Solar Spectroscopic Imager (RHESSI)} observations of hard X-rays (HXR) emitted by electrons to identify the presence of turbulence and to estimate the magnitude of the magnetic field line diffusion coefficient at least in dense coronal flaring loops.} {We discuss the various possible regimes of cross-field transport of non-thermal electrons resulting from broadband magnetic turbulence in coronal loops. The importance of the Kubo number $K$ as a governing parameter is emphasized and results applicable in both the large and small Kubo number limits are collected.} {Generic models, based on concepts and insights developed in the statistical theory of transport, are applied to the coronal loops and to the interpretation of hard X-ray imaging data in solar flares. The role of trapping effects, which become important in the non-linear regime of transport, is ...
Turner, Drew; Gkioulidou, Matina; Ukhorskiy, Aleksandr; Gabrielse, Christine; Runov, Andrei; Angelopoulos, Vassilis
2014-05-01
Earth's radiation belts provide a natural laboratory to study a variety of physical mechanisms important for understanding the nature of energetic particles throughout the Universe. The outer electron belt is a particularly variable population, with drastic changes in relativistic electron intensities occurring on a variety of timescales ranging from seconds to decades. Outer belt variability ultimately results from the complex interplay between different source, loss, and transport processes, and all of these processes are related to the dynamics of the inner magnetosphere. Currently, an unprecedented number of spacecraft are providing in situ observations of the inner magnetospheric environment, including missions such as NASA's THEMIS and Van Allen Probes and ESA's Cluster and operational monitors such as NOAA's GOES and POES constellations. From a sampling of case studies using multi-point observations, we present examples showcasing the significant importance of two processes to outer belt dynamics: energetic particle injections and wave-particle interactions. Energetic particle injections are transient events that tie the inner magnetosphere to the near-Earth magnetotail; they involve the rapid inward transport of plasmasheet particles into the trapping zone in the inner magnetosphere. We briefly review key concepts and present new evidence from Van Allen Probes, GOES, and THEMIS of how these injections provide: 1. the seed population of electrons that are subsequently accelerated locally to relativistic energies in the outer belt and 2. the source populations of ions and electrons that produce a variety of ULF and VLF waves, which are also important for driving outer belt dynamics via wave-particle interactions. Cases of electron acceleration by chorus waves, losses by plasmaspheric hiss and EMIC waves, and radial transport driven by ULF waves will also be presented. Finally, we discuss the implications of this developing picture of the system, namely how
Electron transport through nano-MOSFET in presence of electron-electron interaction
Hamidreza Simchi
2013-03-01
Full Text Available We investigate the effect of electron-electron interaction on voltage distribution, charge distribution and current-voltage curve of two dimensional nano-MOSFETs with dimension equal to 1 × 1 nm2, 3 × 3 nm2, and 6 × 6 nm2 by using non-equilibrium Green function method. It is shown that the turn on voltage increases by decreasing the size of sample because of size quantization. Also we show that for a critical drain-source voltage a negative resistance is seen at current-voltage curve of 1 × 1 nm2 sample because of electron-electron interaction, and in consequence it can tolerate lower gate voltage in real practical applications.
Simulations of electron capture supernovae with approximate neutrino transport
Moeller, Heiko [TU Darmstadt (Germany); Fischer, Tobias [University of Wroclaw (Poland); Jones, Sam [Keele University (United Kingdom); Martinez-Pinedo, Gabriel [TU Darmstadt (Germany); GSI Helmholtzzentrum fuer Schwerionenforschung, Darmstadt (Germany)
2014-07-01
We have performed simulations of electron capture supernovae in a spherically symmetric general relativistic radiation hydrodynamics model with approximate neutrino treatment. We base our study on an 8.8 M {sub CircleDot} O-Ne-Mg core progenitor (Nomoto, 1984, 1987). We successfully obtain an explosion and compare our results with a reference run performed with an state-of-the-art three-flavor Boltzmann neutrino transport scheme implemented into the same hydrodynamic code. In general, we find good agreement in the the electron-flavor neutrino spectra. However, we find shorter explosion timescales and also significantly lower explosion energies of only 1.4 . 10{sup 48} erg. This result is in agreement with the explosion energy of SN 2008S as derived by Tominaga et al. (2013) based on light curve studies. Currently we are extending our simulations to the recently published super-AGB star progenitor models by Jones et al. (2013) with regard to their evolution towards an electron capture supernova. Our study also explores the role of weak interaction rates in determining the evolution and shaping the spectra of the emitted neutrinos.
Hoshino, Masahiro
2015-02-13
Angular momentum transport and particle acceleration during the magnetorotational instability (MRI) in a collisionless accretion disk are investigated using three-dimensional particle-in-cell simulation. We show that the kinetic MRI can provide not only high-energy particle acceleration but also enhancement of angular momentum transport. We find that the plasma pressure anisotropy inside the channel flow with p(∥)>p(⊥) induced by active magnetic reconnection suppresses the onset of subsequent reconnection, which, in turn, leads to high-magnetic-field saturation and enhancement of the Maxwell stress tensor of angular momentum transport. Meanwhile, during the quiescent stage of reconnection, the plasma isotropization progresses in the channel flow and the anisotropic plasma with p(⊥)>p(∥) due to the dynamo action of MRI outside the channel flow contribute to rapid reconnection and strong particle acceleration. This efficient particle acceleration and enhanced angular momentum transport in a collisionless accretion disk may explain the origin of high-energy particles observed around massive black holes.
The role of unsteady forces for sediment particles in bedload transport
Liu, Detian; Liu, Xiaofeng; Fu, Xudong
2016-04-01
In engineering, bedload transport is usually predicted by a variety of formulas, and huge uncertainty is found from case to case. One of the fundamental reasons is the lack of fully understanding the dynamic behavior of bedload particles. We explore the dynamic characteristics of sediment particles transported in turbulent open-channel flows. A numerical model of sediment transport is built by combining the large eddy simulation (LES) with discrete element model (DEM) using a fully four-way coupling method. Particular attention is paid to the hydrodynamic forces acting on bedload particles. The result shows that, in addition to drag force, the unsteady forces (i.e. Basset history force and added mass force) are important (40%~60% in the summation of all the time-averaged magnitude of forces) for fine sediment particles (with a diameter of 0.5 mm), which are usually ignored for computational complexity. While the lift force has been found to be significant for gravel particles (with a diameter of 31 mm)[1], it is not relatively dominant for such fine particles (less than 3% in the summation). This helps explaining why the prediction of the same formula change greatly from case to case. The comparison with experimental data also shows great potential of the current LES-DEM model for fundamental research in bedload transport. Reference: [1] Nino, Y., & Garcia, M. (1994). Gravel saltation 2. Modeling. Water Resources Research, 30(6), 1915-1924.
Transport coefficients for relativistic gas mixtures of hard-sphere particles
Kremer, Gilberto M.; Moratto, Valdemar
2017-04-01
In the present work, we calculate the transport coefficients for a relativistic binary mixture of diluted gases of hard-sphere particles. The gas mixture under consideration is studied within the relativistic Boltzmann equation in the presence of a gravitational field described by the isotropic Schwarzschild metric. We obtain the linear constitutive equations for the thermodynamic fluxes. The driving forces for the fluxes of particles and heat will appear with terms proportional to the gradient of gravitational potential. We discuss the consequences of the gravitational dependence on the driving forces. We obtain general integral expressions for the transport coefficients and evaluate them by assuming a hard-sphere interaction amongst the particles when they collide and not very disparate masses and diameters of the particles of each species. The obtained results are expressed in terms of their temperature dependence through the relativistic parameter which gives the ratio of the rest energy of the particles and the thermal energy of the gas mixture. Plots are given to analyze the behavior of the transport coefficients with respect to the temperature when small variations in masses and diameters of the particles of the species are present. We also analyze for each coefficient the corresponding limits to a single gas so the non-relativistic and ultra-relativistic limiting cases are recovered as well. Furthermore, we show that the transport coefficients have a dependence on the gravitational field.
Modeling nitrogen transport and transformation in aquifers using a particle-tracking approach
Cui, Zhengtao; Welty, Claire; Maxwell, Reed M.
2014-09-01
We have integrated multispecies biodegradation and geochemical reactions into an existing particle-tracking code to simulate reactive transport in three-dimensional variably saturated media, with a focus on nitrification and denitrification processes. This new numerical model includes reactive air-phase transport so that gases such as N2 and CO2 can be tracked. Although nitrogen biodegradation is the primary problem addressed here, the method presented is also applicable to other reactive multispecies transport problems. We verified the model by comparison with (1) analytical solutions for saturated one- and two-dimensional cases; (2) a finite element model for a one-dimensional unsaturated case; and (3) laboratory observations for a one-dimensional saturated case. Good agreement between the new code and the verification problems is demonstrated. The new model can simulate nitrogen transport and transformation in a heterogeneous permeability field where sharp concentration gradients are present. An example application to nitrogen species biodegradation and transport of a plume emanating from a leaking sewer in a heterogeneous, variably saturated aquifer is presented to illustrate this capability. This example is a novel application of coupling unsaturated/saturated zone transport with nitrogen species biodegradation. The code has the computational advantages of particle-tracking algorithms, including local and global mass conservation and minimal numerical dispersion. We also present new methods for improving particle code efficiency by implementing the concept of tracking surplus/deficit particles and particle recycling in order to control the growth of particle numbers. The new model retains the advantages of the particle tracking approach such as allowing relatively low spatial and temporal resolutions to be used, while incorporating the robustness of grid-based Monod kinetics to simulate biogeochemical reactions.
De Geronimo, G. [Brookhaven National Laboratory, Instrumentation Division, Upton, NY 11973-5000 (United States); Deptuch, G. [Brookhaven National Laboratory, Instrumentation Division, Upton, NY 11973-5000 (United States); Dragone, A. [Brookhaven National Laboratory, Instrumentation Division, Upton, NY 11973-5000 (United States); Radeka, V. [Brookhaven National Laboratory, Instrumentation Division, Upton, NY 11973-5000 (United States); Rehak, P. [Brookhaven National Laboratory, Instrumentation Division, Upton, NY 11973-5000 (United States)]. E-mail: rehak@bnl.gov; Castoldi, A. [Politecnico di Milano, Dip. Ingegneria Nucleare, 20133 Milan (Italy); INFN Sez. Milano, 20133 Milan (Italy); Fazzi, A. [Politecnico di Milano, Dip. Ingegneria Nucleare, 20133 Milan (Italy); INFN Sez. Milano, 20133 Milan (Italy); Gatti, E. [Politecnico di Milano, Dip. Elettronica e Informazione, 20133 Milan (Italy); INFN Sez. Milano, 20133 Milan (Italy); Guazzoni, C. [Politecnico di Milano, Dip. Elettronica e Informazione, 20133 Milan (Italy); INFN Sez. Milano, 20133 Milan (Italy); Rijssenbeek, M. [Physics Department of State University of New York at Stony Brook, NY 11790 (United States); Dulinski, W. [Institut de Recherches Subatomiques, 23 rue du Loess BP 28, 67037 Strasbourg cedex (France); Besson, A. [Institut de Recherches Subatomiques, 23 rue du Loess BP 28, 67037 Strasbourg cedex (France); Deveaux, M. [Institut de Recherches Subatomiques, 23 rue du Loess BP 28, 67037 Strasbourg cedex (France); Winter, M. [Institut de Recherches Subatomiques, 23 rue du Loess BP 28, 67037 Strasbourg cedex (France)
2006-11-30
A new type of active pixel sensors (APSs) to track charged particles for particle physics experiments or to count number of electrons that cross any pixel at the focal plane of electron microscopes is described. The electric field of desirable shape is created inside the active volume of the pixel introducing the drift component in the movement of the signal electrons towards charge collecting electrodes. The electric field results from the flow of {approx}100 mA/cm{sup 2} hole currents within individual pixels of the sensor. The proposed sensor is produced using a standard industrially available complementary metal oxide silicon (CMOS) process. There are two main advantages of the proposed detectors when compared to the present (February 2005) state-of-the-art, i.e. field-free APS sensors. The first advantage of a field-assisted transport mechanism is the reduction of the charge collection time and of the sharing of the signal electrons between adjacent pixels by diffusion. The second advantage is the freedom to use both kinds of MOS transistors within each pixel of the sensor. Thus, the full functional power of CMOS circuits can be embedded in situ. As an example, 16-bit scalers will be implemented in each pixel of the sensor for electron microscopy. The reduced collection time combined with the state-of-the-art electronics within each pixel provides the most complete information about the position and the timing of incident charged particles for particle physics experiments. Position resolution of new sensors was computationally simulated to be a few microns, that is, the same as the resolution of standard APSs. Moreover, the active depth of the sensor and the associate electronics is less than about 20 {mu}m and a thinned down sensor together with its beryllium backing can have a total thickness of less than 0.1% of one radiation length. The reduction of the thickness of the detector reduces the amount of multiple scattering within the detector. The
Solar Energetic Particle Transport Near a Heliospheric Current Sheet
Battarbee, Markus; Dalla, Silvia; Marsh, Mike S.
2017-02-01
Solar energetic particles (SEPs), a major component of space weather, propagate through the interplanetary medium strongly guided by the interplanetary magnetic field (IMF). In this work, we analyze the implications that a flat Heliospheric Current Sheet (HCS) has on proton propagation from SEP release sites to the Earth. We simulate proton propagation by integrating fully 3D trajectories near an analytically defined flat current sheet, collecting comprehensive statistics into histograms, fluence maps, and virtual observer time profiles within an energy range of 1-800 MeV. We show that protons experience significant current sheet drift to distant longitudes, causing time profiles to exhibit multiple components, which are a potential source of confusing interpretations of observations. We find that variation of the current sheet thickness within a realistic parameter range has little effect on particle propagation. We show that the IMF configuration strongly affects the deceleration of protons. We show that in our model, the presence of a flat equatorial HCS in the inner heliosphere limits the crossing of protons into the opposite hemisphere.
He, H -Q
2015-01-01
In some solar energetic particle (SEP) events, a counter-streaming particle beam with a deep depression of flux near 90 degrees pitch angle during the beginning phase is observed. Two different interpretations exist in the community to explain this interesting phenomenon. One explanation invokes the hypothesis of an outer reflecting boundary or a magnetic mirror beyond the observer. The other one considers the effect of the perpendicular diffusion on the transport process of SEPs in the interplanetary space. In this work, we revisit the problem of the counter-streaming particle beams observed in SEP events and discuss the possible mechanisms responsible for the formation of this phenomenon. We clarify some results in previous works.
Ahfir, Nasre-Dine; Hammadi, Ahmed; Alem, Abdellah; Wang, HuaQing; Le Bras, Gilbert; Ouahbi, Tariq
2017-03-01
The effects of porous media grain size distribution on the transport and deposition of polydisperse suspended particles under different flow velocities were investigated. Selected Kaolinite particles (2-30μm) and Fluorescein (dissolved tracer) were injected in the porous media by step input injection technique. Three sands filled columns were used: Fine sand, Coarse sand, and a third sand (Mixture) obtained by mixing the two last sands in equal weight proportion. The porous media performance on the particle removal was evaluated by analysing particles breakthrough curves, hydro-dispersive parameters determined using the analytical solution of convection-dispersion equation with a first order deposition kinetics, particles deposition profiles, and particle-size distribution of the recovered and the deposited particles. The deposition kinetics and the longitudinal hydrodynamic dispersion coefficients are controlled by the porous media grain size distribution. Mixture sand is more dispersive than Fine and Coarse sands. More the uniformity coefficient of the porous medium is large, higher is the filtration efficiency. At low velocities, porous media capture all sizes of suspended particles injected with larger ones mainly captured at the entrance. A high flow velocity carries the particles deeper into the porous media, producing more gradual changes in the deposition profile. The median diameter of the deposited particles at different depth increases with flow velocity. The large grain size distribution leads to build narrow pores enhancing the deposition of the particles by straining. Copyright © 2016. Published by Elsevier B.V.
Jiang, Jun; Kula, Mathias; Luo, Yi
2006-01-01
A generalized quantum chemical approach for electron transport in molecular devices is developed. It allows one to treat devices where the metal electrodes and the molecule are either chemically or physically bonded on equal footing. An extension to include the vibration motions of the molecule has also been implemented which has produced the inelastic electron-tunneling spectroscopy of molecular electronics devices with unprecedented accuracy. Important information about the structure of the molecule and of metal-molecule contacts that are not accessible in the experiment are revealed. The calculated current-voltage (I-V) characteristics of different molecular devices, including benzene-1,4-dithiolate, octanemonothiolate [H(CH2)8S], and octanedithiolate [S(CH2)8S] bonded to gold electrodes, are in very good agreement with experimental measurements.
On the application of quantum transport theory to electron sources
Jensen, K.L
2003-05-15
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.
On the application of quantum transport theory to electron sources.
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.
Enzymology of Electron Transport: Energy Generation with Geochemical Consequences
Dichristina, Thomas J.; Fredrickson, Jim K.; Zachara, John M.
2005-12-20
Dissimilatory metal-reducing bacteria (DMRB) are important components of the microbial community residing in redox-stratified freshwater and marine environments. DMRB occupy a central position in the biogeochemical cycles of metals, metalloids and radionuclides, and serve as catalysts for a variety of other environmentally important processes including biomineralization, biocorrosion, bioremediation and mediators of ground water quality. DMRB are presented, however, with a unique physiological challenge: they are required to respire anaerobically on terminal electron acceptors which are either highly insoluble (e.g., Fe(III)- and Mn(IV)-oxides) and reduced to soluble end-products or highly soluble (e.g., U(VI) and Tc(VII)) and reduced to insoluble end-products. To overcome physiological problems associated with metal and radionuclide solubility, DMRB are postulated to employ a variety of novel respiratory strategies not found in other gram-negative bacteria which respire on soluble electron acceptors such as O2, NO3- and SO42-. The novel respiratory strategies include (1) direct enzymatic reduction at the outer membrane, (2) electron shuttling pathways and (3) metal solubilization by exogenous or bacterially-produced organic ligands followed by reduction of soluble organic-metal compounds. The first section of this chapter highlights the latest findings on the enzymatic mechanisms of metal and radionuclide reduction by two of the most extensively studied DMRB (Geobacter and Shewanella), with particular emphasis on electron transport chain enzymology. The second section emphasizes the geochemical consequences of DMRB activity, including the direct and indirect effects on metal solubility, the reductive transformation of Fe- and Mn-containing minerals, and the biogeochemical cycling of metals at redox interfaces in chemically stratified environments.
Density-dependent electron transport and precise modeling of GaN high electron mobility transistors
Bajaj, Sanyam, E-mail: bajaj.10@osu.edu; Shoron, Omor F.; Park, Pil Sung; Krishnamoorthy, Sriram; Akyol, Fatih; Hung, Ting-Hsiang [Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210 (United States); Reza, Shahed; Chumbes, Eduardo M. [Raytheon Integrated Defense Systems, Andover, Massachusetts 01810 (United States); Khurgin, Jacob [Department of Electrical and Computer Engineering, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Rajan, Siddharth [Department of Electrical and Computer Engineering, The Ohio State University, Columbus, Ohio 43210 (United States); Department of Material Science and Engineering, The Ohio State University, Columbus, Ohio 43210 (United States)
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.
Temple, R. C.; McLaren, M.; Brydson, R. M. D.; Hickey, B. J.; Marrows, C. H.
2016-01-01
We have investigated single electron spin transport in individual single crystal bcc Co30Fe70 nanoparticles using scanning tunnelling microscopy with a standard tungsten tip. Particles were deposited using a gas-aggregation nanoparticle source and individually addressed as asymmetric double tunnel junctions with both a vacuum and a MgO tunnel barrier. Spectroscopy measurements on the particles show a Coulomb staircase that is correlated with the measured particle size. Field emission tunnelling effects are incorporated into standard single electron theory to model the data. This formalism allows spin-dependent parameters to be determined even though the tip is not spin-polarised. The barrier spin polarisation is very high, in excess of 84%. By variation of the resistance, several orders of magnitude of the system timescale are probed, enabling us to determine the spin relaxation time on the island. It is found to be close to 10 μs, a value much longer than previously reported. PMID:27329575
Yin Vallgren, Christina; Calatroni, Sergio; Chiggiato, Paolo; Costa Pinto, Pedro; Marques, Hugo; Neupert, Holger; Taborelli, Mauro; Vollenberg, Wilhelmus; Wevers, Ivo; Yaqub, Kashif
2010-01-01
Electron-cloud is one of the main limitations for particle accelerators with positively charged beams of high intensity and short bunch spacing, as the SPS at CERN. The Secondary Electron Yield (SEY) of the inner surface of the vacuum chamber is the main parameter governing the phenomenon. The effect could be eliminated by coating the vacuum chambers with a material of low SEY, which does not require bake-out and is robust against air exposure. For such a purpose amorphous carbon (a-C) coatings were produced by magnetron sputtering of graphite targets. They exhibit maximum SEY between 0.95 and 1.05 after air transfer to the measuring instrument. After 1 month of air exposure the SEY rises by 10 - 20 % of the initial values. Storage in desiccator or by packaging in Al foil makes this increase negligible. The coatings have a similar X-ray photoelectron spectroscopy (XPS) C1s spectrum for a large set of deposition parameters and exhibit an enlarged linewidth compared to HOPG graphite. The static outgassing witho...
Particle dynamics in the electron current layer in collisionless magnetic reconnection
Zenitani, Seiji
2016-01-01
Particle dynamics in the electron current layer in collisionless magnetic reconnection is investigated by using a particle-in-cell simulation. Electron motion and velocity distribution functions are studied by tracking self-consistent trajectories. New classes of electron orbits are discovered: figure-eight-shaped regular orbits inside the electron jet, noncrossing regular orbits on the jet flanks, noncrossing Speiser orbits, and nongyrotropic electrons in the downstream of the jet termination region. Properties of a super-Alfv\\'{e}nic outflow jet are attributed to an ensemble of electrons traveling through Speiser orbits. Noncrossing orbits are mediated by the polarization electric field near the electron current layer, and it turns out that they are non-negligible in number density. The impact of these new orbits to electron mixing, spatial distribution of energetic electrons, and observational signatures, is presented.
Non-Markovian Model for Transport and Reactions of Particles in Spiny Dendrites
Fedotov, Sergei; Méndez, Vicenç
2008-11-01
Motivated by the experiments [Santamaria , Neuron 52, 635 (2006)NERNET0896-627310.1016/j.neuron.2006.10.025] that indicated the possibility of subdiffusive transport of molecules along dendrites of cerebellar Purkinje cells, we develop a mesoscopic model for transport and chemical reactions of particles in spiny dendrites. The communication between spines and a parent dendrite is described by a non-Markovian random process and, as a result, the overall movement of particles can be subdiffusive. A system of integrodifferential equations is derived for the particles densities in dendrites and spines. This system involves the spine-dendrite interaction term which describes the memory effects and nonlocality in space. We consider the impact of power-law waiting time distributions on the transport of biochemical signals and mechanism of the accumulation of plasticity-inducing signals inside spines.
Electronic transport properties of a quinone-based molecular switch
Zheng, Ya-Peng; Bian, Bao-An; Yuan, Pei-Pei
2016-09-01
In this paper, we carried out first-principles calculations based on density functional theory and non-equilibrium Green's function to investigate the electronic transport properties of a quinone-based molecule sandwiched between two Au electrodes. The molecular switch can be reversibly switched between the reduced hydroquinone (HQ) and oxidized quinone (Q) states via redox reactions. The switching behavior of two forms is analyzed through their I- V curves, transmission spectra and molecular projected self-consistent Hamiltonian at zero bias. Then we discuss the transmission spectra of the HQ and Q forms at different bias, and explain the oscillation of current according to the transmission eigenstates of LUMO energy level for Q form. The results suggest that this kind of a quinone-based molecule is usable as one of the good candidates for redox-controlled molecular switches.
Hot electron generation and transport using Kα emission
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.
2010-08-01
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 40μm diameter wire emulating a 40μm fast ignition spot. Thick cone walls, simulating plasma in fast ignition, reduce coupling by x4. An increase of pre-pulse level inside the cone by a factor of 50 reduces coupling by a factor of 3.
Pauli-Heisenberg Oscillations in Electron Quantum Transport.
Thibault, Karl; Gabelli, Julien; Lupien, Christian; Reulet, Bertrand
2015-06-12
We measure the current fluctuations emitted by a normal-metal-insulator-normal-metal tunnel junction with a very wide bandwidth, from 0.3 to 13 GHz, down to very low temperature T=35 mK. This allows us to perform the spectroscopy (i.e., measure the frequency dependence) of thermal noise (no dc bias, variable temperature) and shot noise (low temperature, variable dc voltage bias). Because of the very wide bandwidth of our measurement, we deduce the current-current correlator in the time domain. We observe the thermal decay of this correlator as well as its oscillations with a period h/eV, a direct consequence of the effect of the Pauli and Heisenberg principles in quantum electron transport.
Bias-dependent oscillatory electron transport of monatomic sulfur chains
Yu, Jing-Xin
2012-01-01
The bias-dependent oscillatory electron transport of monatomic sulfur chains sandwiched between gold electrodes is investigated with density functional theory and non-equilibrium Green\\'s function method. At zero bias, in contrast to the typical odd-even oscillations observed in most metallic chains, we find that the conductance oscillates with a period of four atoms. However, as the bias voltage is increased the current displays a two-atom periodicity. This emerges gradually, first for the longer chains and then, at voltages larger than 0.7 V, for lengths. The oscillatory behaviors are analyzed by the density of states and the energy-dependent and bias-dependent transmission coefficients. © 2012 American Institute of Physics.
Transport of electron-hole plasma in germanium
Kirch, S. J.; Wolfe, J. P.
1986-08-01
Time-resolved luminescence imaging techniques are used to observe the spectral and spatial evolution of laser-generated electron-hole plasma in Ge. Both pulsed and cw excitation conditions are examined above and below the critical temperature for electron-hole liquid formation, Tc(LG). For Q-switched Nd-doped yttrium aluminum garnet laser excitation, the transport behavior is qualitatively similar above and below Tc(LG), although the luminescence spectrum undergoes significant changes in this temperature range. A rapid initial expansion (v~105 cm/s) is followed by a period of slower growth which gradually reduces as the carriers recombine. The initial velocity for pulsed excitation increases monotonically as the crystal temperature is lowered and saturates near the phonon sound velocity for high-energy excitation. These observations are consistent with phonon-wind driven transport. For intense Q-switched excitation, the motion is characterized by three regimes: (1) During the laser pulse the plasma expands as a large drop with near-unity filling fraction. (2) Expansion at near-sonic velocity continues after the peak of the laser pulse due to a ``prompt'' pulse of ballistic phonons produced by the carrier thermalization process. (3) After this intense phonon wind passes the carrier distribution, the expansion velocity abruptly decreases, but the plasma continues to expand more slowly under the influence of a ``hot spot'' produced at the excitation point. The sound barrier observed on these time scales (>=30 ns) can be explained in terms of nonlinear damping of the plasma motion near the sound velocity. For cw excitation, the expansion is observed to occur at much lower velocities (v~104 cm/s). These expansion rates are much too low to require the inclusion of a drifted Fermi distribution in the spectral analysis as has been previously suggested. Instead, based upon a careful study of corresponding spectral data, an alternative explanation for these spectra is
Physical considerations relevant to HZE-particle transport in matter
Schimmerling, W.
1988-01-01
High-energy, highly charged (HZE) heavy nuclei may seem at first sight to be an exotic type of radiation, only remotely connected with nuclear power generation. On closer examination it becomes evident that heavy-ion accelerators are being seriously considered for driving inertial confinement fusion reactors, and high-energy heavy nuclei in the cosmic radiation are likely to place significant constraints on satellite power system deployment and space-based power generation. The use of beams of heavy nuclei in an increasing number of current applications, as well as their importance for the development of the state of the art of the future, makes it necessary to develop at the same time a good understanding of their transport through matter.
Physical considerations relevant to HZE-particle transport in matter.
Schimmerling, W
1988-06-01
High-energy, highly charged (HZE) heavy nuclei may seem at first sight to be an exotic type of radiation, only remotely connected with nuclear power generation. On closer examination it becomes evident that heavy-ion accelerators are being seriously considered for driving inertial confinement fusion reactors, and high-energy heavy nuclei in the cosmic radiation are likely to place significant constraints on satellite power system deployment and space-based power generation. The use of beams of heavy nuclei in an increasing number of current applications, as well as their importance for the development of the state of the art of the future, makes it necessary to develop at the same time a good understanding of their transport through matter.
Naqshband, Suleyman; McElroy, Brandon; Mahon, Robert C.
2017-05-01
The mechanics of sediment transport are of fundamental importance for fluvio-deltaic morphodynamics. The present study focuses on quantifying particle motions and trajectories across a wide range of flow conditions. In particular, a continuous model is presented that predicts particle travel distances for saltation and suspension based on Rouse number and relative grain roughness. By utilizing a series of eight video cameras in a plexiglass flume direct measurements of the distributions of particle travel distances (excursion lengths) were obtained. To this end, experiments were carried out in dark under black lights with fluorescent painted plastic and quartz sand particles. For relatively high Rouse numbers indicating bed load dominant transport regime (P≥2.5), particle motion is governed by the effect of gravitational forces (settling velocities) and measured excursion lengths closely follow a Gaussian distribution. For P=2.5, particle motion is equally subjected to both gravitational and turbulent forces. Consequently, measured excursion lengths exhibit a bimodal distribution with two distinct peaks. As turbulent fluctuations increase and dominate particle motion over gravity (P(P=1.8-8.9). Furthermore, measured excursion lengths are observed to fit within the predicted range of excursion lengths with no significant difference between measured excursion lengths of plastic and quartz sand particles.
Simple predictive electron transport models applied to sawtoothing plasmas
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.
Electron transport across metal/discotic liquid crystal interfaces
Boden, N.; Bushby, R. J.; Clements, J.; Movaghar, B.
1998-03-01
Electron transport across micron thick films of columnar hexagonal discotic liquid crystal phases homeotropically aligned between metal electrode surfaces has been studied both experimentally and theoretically. These molecules are unique in their combination of charge transport along individual molecular columns with liquidlike self-organization. Typical of organic insulators, a high resistance Ohmic regime is evident at fields of less than 0.05 MV cm-1, due to a low concentration of chemical impurities (nroom temperature. Our results show that triphenylene-based discotics form an excellent class of highly ordered optically transparent insulators. At high temperatures and high fields the current is injection controlled and exhibits typical tunneling and space charge limited, nonlinear I-V characteristics. Dramatic jumps in injection currents are observed at phase transitions. The change at the crystalline to liquid crystalline phase transition is mainly due to more efficient "wetting" of the electrode surface in the liquid crystalline phase, whilst at the liquid crystalline to isotropic phase transition it arises from the enhancement in the molecular mobility. The concepts of semiconducting gaps, band mobilities, and carrier injection rates are extended to these new materials. The experimental observations are interpreted in a framework which takes into account the important role played by liquidlike dynamics in establishing the microscopic structural order in, what is, otherwise a highly anisotropic and weakly bonded "molecular crystal."
Electron Transport through Models for Small-World Nanomaterials
Solomon, Lazarus; Novotny, Mark
2008-03-01
We investigate the quantum transport of (spinless) electrons through simplified models related to small-world nanomaterials. We employ a tight-binding Hamiltonian, and obtain the transmission coefficient from a matrix solution of the associated time-independent Schrödinger Equation. The system studied corresponds to d=1 semi-infinite input and output leads, connected to a `blob' of N atoms. We first present exact results for N inter-connected atoms, a fully-connected graph. The exact solution, for any N, is given both for symmetric and non-symmetric connections between the `blob' and the input/output. We then present numerical results obtained by removing some of the connections within the N-site `blob', thereby approaching transport through a small-world nanomaterial [1-4]. [1] S. Caliskan, M.A. Novotny, and J.I. Cerd'a, J. Appl. Phys., 102, 013707 (2007). [2] M.A. Novotny et al., J. Appl. Phys., 97, 10B309 (2005). [3] M.A. Novotny and S.M. Wheeler, Braz. J. Physics 34, 395 (2004). [4] J. Yancey, M.A. Novotny, and S.R. Gwaltney, 2008 March Meeting presentation.
Electron transport in molecular junctions with graphene as protecting layer
Hüser, Falco; Solomon, Gemma C., E-mail: gsolomon@nano.ku.dk [Nano-Science Center and Department of Chemistry, University of Copenhagen, 2100 København Ø (Denmark)
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.
Transport in an Electron Interferometer and an Artificial One-Dimensional Crystal
Wees, B.J. van; Kouwenhoven, L.P.; Kraayeveld, J.R.; Hekking, F.W.J.; Harmans, C.J.P.M.; Williamson, J.G.
1990-01-01
We have studied the electron transport in a one-dimensional electron interferometer. It consists of a quantum dot, defined in a two-dimensional electron gas, to which quantum point contacts are attached. Discrete electronic states are formed due to the constructive interference of electron waves whi
Measuring the Cosmic Particle Radiation from electrons to actinides - CALET
Mitchell, John; Calet Collaboration; Hnx/Tigeriss Collaboration
2017-01-01
CALET (Calorimetric Electron Telescope) was installed on the Exposed Facility of the Japanese Experiment Module (Kibo) on for 24 August 2015. CALET measures the high-energy spectra of electrons, nuclei, and gamma-rays. CALET will extend direct measurements of the total electron spectrum into the trans-TeV energy range for the first time. In this paper, we well present the science and current status of CALET and initial observations from its first 1.5 years in orbit.
Electronic transport through nanowires: a real-space finite-difference approach
Khomyakov, Petr
2006-01-01
Nanoelectronics is a fast developing ¯eld. Therefore understanding of the electronic transport at the nanoscale is currently of great interest. This thesis "Electronic transport through nanowires: a real-space ¯nite-difference approach" aims at a general theoretical treatment of coherent electronic
Agueda, N.; Lario, D.
2016-10-01
We study four consecutive 300-800 keV electron events observed on 1980 May 28 by Helios-1, when the spacecraft was located at 0.31 au from the Sun. We use two different techniques to extract the release time history of electrons at the Sun: (1) a data-driven method based on the assumption that particles conserve their magnetic moment as they propagate between the Sun and the spacecraft and (2) an inversion method that utilizes particle transport simulation results. Both methods make use of the particle angular distributions measured relative to the local direction of the magnetic field. The general characteristics of the release time profiles obtained by these two techniques are similar, especially during their rising phases. We find indications that the strength of the interplanetary scattering varies with the size of the solar parent event, suggesting that scattering processes are not necessarily an inherent property of the medium but are related to the amount of released particles at the Sun. We use the inferred release profiles to compute the expected intensities at 1 au. In contrast to simultaneous near-Earth observations by the Interplanetary Monitoring Platform (IMP-8), our simulations predict the observation of four separate events at 1 au. Processes that could contribute to the observation of one single time-extended event at 1 au include (1) distinct magnetic connections of the spacecraft to the particle sources, (2) the spatio-temporal evolution of the particle sources, and (3) different particle transport conditions, including a variation of {λ }r with radial distance and/or heliolongitude, as well as the possibility that electrons reached IMP-8 by diffusion perpendicular to the interplanetary magnetic field.
Barbosa, D. D.
1986-01-01
A theory of medium-energy (about keV) electrons and heavy ions in Jupiter's magnetosphere is presented. Lower hybrid waves are generated by the combined effects of a ring instability of neutral wind pickup ions and the modified two-stream instability associated with transport of cool Iogenic plasma. The quasi-linear energy diffusion coefficient for lower hybrid wave-particle interactions is evaluated, and several solutions to the diffusion equation are given. Calculations based on measured wave properties show that the noise substantially modifies the particle distribution functions. The effects are to accelerate superthermal ions and electrons to keV energies and to thermalize the pickup ions on time scales comparable to the particle residence time. The S(2+)/S(+) ratio at medium energies is a measure of the relative contribution from Iogenic thermal plasma and neutral wind ions, and this important quantity should be determined from future measurements. The theory also predicts a preferential acceleration of heavy ions with an accleration time that scales inversely with the root of the ion mass. Electrons accelerated by the process contribute to further reionization of the neutral wind by electron impact, thus providing a possible confirmation of Alfven's critical velocity effect in the Jovian magnetosphere.
The impact of advances in computer technology on particle transport Monte Carlo
Martin, W.R. [Michigan Univ., Ann Arbor, MI (United States). Dept. of Nuclear Engineering; Rathkopf, J.A. [Lawrence Livermore National Lab., CA (United States); Brown, F.B. [Knolls Atomic Power Lab., Schenectady, NY (United States)
1992-01-21
Advances in computer technology, including hardware, architectural, and software advances, have led to dramatic gains in computer performance over the past decade. We summarize these performance trends and discuss the extent to which particle transport Monte Carlo codes have been able to take advantage of these performance gains. We consider MIMD, SIMD, and parallel distributed computer configurations for particle transport Monte Carlo applications. Some specific experience with vectorization and parallelization of production Monte Carlo codes is included. The topic of parallel random number generation is discussed in some detail. Finally, some software issues that hinder the implementation of Monte Carlo methods on parallel processors are addressed.
Valyrakis, Manousos; Farhadi, Hamed
2017-04-01
This study, reports on the analysis of appropriately designed fluvial experiments investigating the transport of coarse bed material using two approaches: particle tracking velocimetry (PTV) to extract bulk transport parameters and inertia sensor data (via the use of "smart-pebbles") to obtain refined statistics for the transport of the particle. The purpose of this study is to provide further insight on the use of technologies (optical techniques and inertial sensors) that are complementary one to another, towards producing improved estimates of bedload transport in natural rivers. The experiments are conducted in the Water Engineering Lab at the University of Glasgow on a tilting recirculating flume with 90 cm width. Ten different discharges have been implemented in this study. A couple of fake beds, made of well-packed beads of three different sizes have been set up in the flume. The particle motion is captured by two high-speed commercial cameras, responsible for recording the top view covering the full length of the fake beds over which the "smart-pebble" is allowed to be transported. "Smart-pebbles" of four different densities are initially located at the upstream end of the configuration, fully exposed to the instream flow. These are instrumented with appropriate inertial sensors that allow recording the particle's motion, in the Langrangian frame, in high resolution. Specifically, the "smart-pebble" employ a tri-axial gyroscope, magnetometer and accelerometer, which are utilized to obtain minute linear and angular displacements in high frequency (up to 200Hz). However, these are not enough to accurately reconstruct the full trajectory of the particles rolling downstream. To that goal optical methods are used. In particular, by using particle tracking velocimetry data and image processing techniques, the location, orientation and velocities of the "smart-pebble" are derived. Specific consideration is given to appropriately preprocess the obtained video, as
Opto-electronic and quantum transport properties of semiconductor nanostructures
Sabathil, M.
2005-01-01
In this work a novel and efficient method for the calculation of the ballistic transport properties of open semiconductor nanostructures connected to external reservoirs is presented. It is based on the Green's function formalism and reduces the effort to obtain the transmission and the carrier density to a single solution of a hermitian eigenvalue problem with dimensions proportional to the size of the decoupled device and the multiple inversion of a small matrix with dimensions proportional to the size of the contacts to the leads. Using this method, the 4-band GaAs hole transport through a 2-dimensional three-terminal T-junction device, and the resonant tunneling current through a 3-dimensional InAs quantum dot molecule embedded into an InP heterostructure have been calculated. The further extension of the method into a charge self-consistent scheme enables the efficient prediction of the IV-characteristics of highly doped nanoscale field effect transistors in the ballistic regime, including the influence of quasi bound states and the exchange-correlation interaction. Buettiker probes are used to emulate the effect of inelastic scattering on the current for simple 1D devices, systematically analyzing the dependence of the density of states and the resulting self-consistent potential on the scattering strength. The second major topic of this work is the modeling of the optical response of quantum confined neutral and charged excitons in single and coupled self-assembled InGaAs quantum dots. For this purpose the existing device simulator nextnano{sup 3} has been extended to incorporate particle-particle interactions within the means of density functional theory in local density approximation. In this way the exciton transition energies for neutral and charged excitons as a function of an externally applied electric field have been calculated, revealing a systematic reduction of the intrinsic dipole with the addition of extra holes to the exciton, a finding