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Sample records for ambipolar diffusion calcuations

  1. The Heavy-Ion Approximation for Ambipolar Diffusion Calcuations for Weakly Ionized Plasmas

    SciTech Connect

    Li, P; McKee, C; Klein, R

    2006-07-27

    Ambipolar diffusion redistributes magnetic flux in weakly ionized plasmas and plays a critical role in star formation. Simulations of ambipolar diffusion using explicit MHD codes are prohibitively expensive for the level of ionization observed in molecular clouds ({approx}< 10{sup -6}) since an enormous number of time steps is required to represent the dynamics of the dominant neutral component with a time step determined by the trace ion component. Here we show that ambipolar diffusion calculations can be significantly accelerated by the 'heavy-ion approximation', in which the mass density of the ions is increased and the collisional coupling constant with the neutrals decreased such that the product remains constant. In this approximation, the ambipolar diffusion time and the ambipolar magnetic Reynolds number remain unchanged. We present three tests of the heavy-ion approximation: C-type shocks, the Wardle instability, and the 1D collapse of a magnetized slab. We show that this approximation is quite accurate provided that (1) the square of the Alfven Mach number is small compared to the ambipolar diffusion Reynolds number for dynamical problems, and that (2) the ion mass density is negligible for quasi-static problems; a specific criterion is given for the magnetized slab problem. The first condition can be very stringent for turbulent flows with large density fluctuations.

  2. Ambipolar diffusion in strongly electronegative plasma

    NASA Astrophysics Data System (ADS)

    Lisovskiy, Valeriy; Yegorenkov, Vladimir

    2012-10-01

    This paper presents the treatment of the analytical model of ambipolar diffusion in quasi-neutral electronegative plasma consisting of electrons, a single species of negative ions and a single species of positive ions, which was proposed by Thompson J.B. [Proc. Phys. Soc., 73 (1959) 818]. We demonstrate that in plasma with the concentration of negative ions more than 10 times exceeding that of electrons one has to take into account the mobility of negative and positive ions. We established that in strongly electronegative plasma when both conditions α >> 1 (α = n-/ne) and μe << α.μ- hold, the ambipolar diffusion coefficients for positive and negative ions as well as electrons are close to the coefficients of their free diffusion. Consequently in strongly electronegative plasma the diffusion ceases to be ambipolar (even for large plasma concentration) and becomes to be free, i.e. charged particles of different species and sign cease to affect the diffusion motion of each other.

  3. MAGNETIC TRANSPORT ON THE SOLAR ATMOSPHERE BY LAMINAR AND TURBULENT AMBIPOLAR DIFFUSION

    SciTech Connect

    Hiraki, Y.; Krishan, V.; Masuda, S.

    2010-09-10

    The lower solar atmosphere consists of partially ionized turbulent plasmas harboring velocity field, magnetic field, and current density fluctuations. The correlations among these small-scale fluctuations give rise to large-scale flows and magnetic fields which decisively affect all transport processes. The three-fluid system consisting of electrons, ions, and neutral particles supports nonideal effects such as the Hall effect and ambipolar diffusion. Here, we study magnetic transport by the laminar- and turbulent-scale ambipolar diffusion processes using a simple model of the magnetic induction equation. Based on a linear analysis of the induction equation, we perform a one-dimensional numerical simulation to study the laminar ambipolar effect on medium-scale magnetic field structures. The nonlinearity of the laminar ambipolar diffusion creates magnetic structures with sharp gradients in the scale of hundreds of kilometers. We expect that these can be amenable to processes such as magnetic reconnection and energy release therefrom for heating and flaring of the solar plasma. Analyzing the characteristic timescales of these processes, we find that the turbulent diffusion timescale is smaller by several orders of magnitude than the laminar diffusion timescale. The effect of the modeled turbulent ambipolar diffusion on the obtained field structures is briefly discussed.

  4. The effect of ambipolar diffusion on low-density molecular ISM filaments

    NASA Astrophysics Data System (ADS)

    Ntormousi, Evangelia; Hennebelle, Patrick; André, Philippe; Masson, Jacques

    2016-05-01

    Context. The filamentary structure of the molecular interstellar medium and the potential link of this morphology to star formation have been brought into focus recently by high resolution observational surveys. An especially puzzling matter is that local interstellar filaments appear to have the same thickness, independent of their column density. This requires a theoretical understanding of their formation process and the physics that governs their evolution. Aims: In this work we explore a scenario in which filaments are dissipative structures of the large-scale interstellar turbulence cascade and ion-neutral friction (also called ambipolar diffusion) is affecting their sizes by preventing small-scale compressions. Methods: We employ high-resolution (5123 and 10243), 3D magnetohydrodynamic (MHD) simulations, performed with the grid code RAMSES, to investigate non-ideal MHD turbulence as a filament formation mechanism. We focus the analysis on the mass and thickness distributions of the resulting filamentary structures. Results: Simulations of both driven and decaying MHD turbulence show that the morphologies of the density and the magnetic field are different when ambipolar diffusion is included in the models. In particular, the densest structures are broader and more massive as an effect of ion-neutral friction and the power spectra of both the velocity and the density steepen at a smaller wavenumber. Conclusions: The comparison between ideal and non-ideal MHD simulations shows that ambipolar diffusion causes a shift of the filament thickness distribution towards higher values. However, none of the distributions exhibit the pronounced peak found in the observed local filaments. Limitations in dynamical range and the absence of self-gravity in these numerical experiments do not allow us to conclude at this time whether this is due to the different filament selection or due to the physics inherent of the filament formation.

  5. Probing the turbulent ambipolar diffusion scale in molecular clouds with spectroscopy

    NASA Astrophysics Data System (ADS)

    Hezareh, T.; Csengeri, T.; Houde, M.; Herpin, F.; Bontemps, S.

    2014-02-01

    We estimate the turbulent ambipolar diffusion length-scale and magnetic field strength in the massive dense cores CygX-N03 and CygX-N53, located in the Cygnus-X star-forming region. The method we use requires comparing the velocity dispersions in the spectral line profiles of the coexistent ion and neutral pair H13CN and H13CO+ (J = 1 → 0) at different length-scales. We fit Kolmogorov-type power laws to the lower envelopes of the velocity dispersion spectra of the two species. This allows us to calculate the turbulent ambipolar diffusion scale, which in turn determines the plane-of-the-sky magnetic field strength. We find turbulent ambipolar diffusion length-scales of 3.8 ± 0.1 and 21.2 ± 0.4 mpc, and magnetic field strengths of 0.33 and 0.76 mG for CygX-N03 and CygX-N53, respectively. These magnetic field values have uncertainties of a factor of a few. Despite a lower signal-to-noise ratio of the data in CygX-N53 than in CygX-N03, and the caveat that its stronger field might stem in part from projection effects, the difference in field strengths suggests different fragmentation efficiencies of the two cores. Even though the quality of our data, obtained with the Institut de Radio Astronomie Millimetrique (IRAM) Plateau de Bure Interferometer, is somewhat inferior to previous single-dish data, we demonstrate that this method is suited also for observations at high spatial resolution.

  6. Ambipolar Diffusion and Star Formation: Formation and Contraction of Axisymmetric Cloud Cores. II. Results

    NASA Astrophysics Data System (ADS)

    Fiedler, Robert A.; Mouschovias, Telemachos Ch.

    1993-10-01

    The problem of the formation and contraction of fragments (or cores) in magnetically supported parent molecular clouds was formulated in a previous paper. Three dimensionless free parameters appear in the evolution equations: the initial ratio of the free-fall and neutral-ion collision times (in the uniform reference state), νff,0, the exponent κ in the relation between the ion and neutral densities ni ∝ nkn, and the initial ratio of the magnetic and thermal pressures, α0. The initial central mass-to-flux ratio in units of the critical value for gravitational collapse, μ0 enters through the initial conditions. We follow both the quasistatic and dynamic phases of contraction and demonstrate that ambipolar diffusion leads to self-initiated protostar formation ("quasistatic" meaning motion with negligible acceleration). A typical cloud core forms and contracts quasi- statically on the flux-loss time scale until the central mass-to-flux ratio (dM/dΦB)c exceeds the critical value. During quasistatic contraction, the magnetic field lines are essentially "held in place" as the neutrals contract through them, and the field strength increases by less than a factor of 2. Despite subsequent dynamic contraction perpendicular to magnetic field lines, thermal pressure continues to balance gravity along field lines, thereby enforcing quasistatic contraction in this direction. We follow the contraction until the central density nc increases by a factor of 106 (typically from 3 × 102 to 3 × 108 cm-3). The envelope remains magnetically supported. The results from our parameter study show that decreasing νff,0 speeds up ambipolar diffusion, shortens the quasistatic phase of contraction, and causes (dM/dΦB)c to increase by a greater amount above the critical value. The enhancement of the central magnetic field Bc, however, is not sensitive to the value of νff,0. A smaller κ leads to progressively more rapid ambipolar diffusion as nc increases. Reducing μ0 lengthens the

  7. Sub-Alfvenic Non-Ideal MHD Turbulence Simulations with Ambipolar Diffusion: I. Turbulence Statistics

    SciTech Connect

    Klein, R I; Li, P S; McKee, C F; Fisher, R

    2008-04-10

    Most numerical investigations on the role of magnetic fields in turbulent molecular clouds (MCs) are based on ideal magneto-hydrodynamics (MHD). However, MCs are weakly ionized, so that the time scale required for the magnetic field to diffuse through the neutral component of the plasma by ambipolar diffusion (AD) can be comparable to the dynamical time scale. We have performed a series of 256{sup 3} and 512{sup 3} simulations on supersonic but sub-Alfvenic turbulent systems with AD using the Heavy-Ion Approximation developed in Li et al. (2006). Our calculations are based on the assumption that the number of ions is conserved, but we show that these results approximately apply to the case of time-dependent ionization in molecular clouds as well. Convergence studies allow us to determine the optimal value of the ionization mass fraction when using the heavy-ion approximation for low Mach number, sub-Alfvenic turbulent systems. We find that ambipolar diffusion steepens the velocity and magnetic power spectra compared to the ideal MHD case. Changes in the density PDF, total magnetic energy, and ionization fraction are determined as a function of the AD Reynolds number. The power spectra for the neutral gas properties of a strongly magnetized medium with a low AD Reynolds number are similar to those for a weakly magnetized medium; in particular, the power spectrum of the neutral velocity is close to that for Burgers turbulence.

  8. Controlled ambipolar doping and gate voltage dependent carrier diffusion length in lead sulfide nanowires.

    PubMed

    Yang, Yiming; Li, Jiao; Wu, Hengkui; Oh, Eunsoon; Yu, Dong

    2012-11-14

    We report a simple, controlled doping method for achieving n-type, intrinsic, and p-type lead sulfide (PbS) nanowires (NWs) grown by chemical vapor deposition without introducing any impurities. A wide range of carrier concentrations is realized by adjusting the ratio between the Pb and S precursors. The field effect electron mobility of n-type PbS NWs is up to 660 cm(2)/(V s) at room temperature, in agreement with a long minority carrier diffusion length measured by scanning photocurrent microscopy (SPCM). Interestingly, we have observed a strong dependence of minority carrier diffusion length on gate voltage, which can be understood by considering a carrier concentration dependent recombination lifetime. The demonstrated ambipolar doping of high quality PbS NWs opens up exciting avenues for their applications in photodetectors and photovoltaics.

  9. Ambipolar diffusion in low-mass star formation. I. General comparison with the ideal magnetohydrodynamic case

    NASA Astrophysics Data System (ADS)

    Masson, J.; Chabrier, G.; Hennebelle, P.; Vaytet, N.; Commerçon, B.

    2016-03-01

    Angular momentum transport and the formation of rotationally supported structures are major issues in our understanding of protostellar core formation. Whereas purely hydrodynamical simulations lead to large Keplerian disks, ideal magnetohydrodynamics (MHD) models yield the opposite result, with essentially no disk formation. This stems from the flux-freezing condition in ideal MHD, which leads to strong magnetic braking. In this paper, we provide a more accurate description of the evolution of the magnetic flux redistribution by including resistive terms in the MHD equations. We focus more particularly on the effect of ambipolar diffusion on the properties of the first Larson core and its surrounding structure, exploring various initial magnetisations and magnetic field versus rotation axis orientations of a 1 M⊙ collapsing prestellar dense core. We used the non-ideal magnetohydrodynamics version of the adaptive mesh refinement code RAMSES to carry out these calculations. The resistivities required to calculate the ambipolar diffusion terms were computed using a reduced chemical network of charged, neutral, and grain species. Including ambipolar diffusion leads to the formation of a magnetic diffusion barrier (also known as the decoupling stage) in the vicinity of the core, which prevents accumulation of magnetic flux in and around the core and amplification of the field above 0.1 G. The mass and radius of the first Larson core, however, remain similar between ideal and non-ideal MHD models. This diffusion plateau, preventing further amplification of the field and reorganising the field topology, has crucial consequences for magnetic braking processes, allowing the formation of disk structures. Magnetically supported outflows launched in ideal MHD models are weakened or even disappear when using non-ideal MHD. In contrast to ideal MHD calculations, misalignment between the initial rotation axis and the magnetic field direction does not significantly affect the

  10. Magnetic braking, ambipolar diffusion, cloud cores, and star formation - Natural length scales and protostellar masses

    NASA Astrophysics Data System (ADS)

    Mouschovias, Telemachos Ch.

    1991-05-01

    Magnetic braking is essential for cloud contraction and star formation. Ambipolar diffusion is unavoidable in self-gravitating, magnetic clouds and leads to single-stage (as opposed to hierarchical) fragmentation (or core formation) and protostar formation. Magnetic forces dominate thermal-pressure and centrifugal forces over scales comparable to molecular cloud radii. Magnetic support of molecular clouds and the imperfect collisional coupling between charged and neutral particles introduce a critical magnetic length scale (λM,cr = 0.62υAτff) and an Alfvén length scale ((λA = πυAτni), respectively, in the problem which together with a critical thermal length scale (λT,cr = 1.09Caτff) explain naturally the formation of fragments (or cores) in otherwise quiescent clouds and determine the sizes and masses of these fragments during the subsequent stages of contraction. (The quantity υA is the Alfvén speed, τni the mean neutral-ion collision time, Ca the adiabatic speed of sound, and τff the free4all time scale.) Numerical calculations based on new adaptive-grid techniques follow the formation of fragments by ambipolar diffusion and their subsequent collapse up to an enhancement in central density above its initial equilibrium value by a factor ≃106 with excellent spatial resolution. The results confirm the existence and relevance of the three length scales and extend the analytical understanding of fragmentation and star formation derived from them. The ultimately bimodal opposition to gravity (by magnetic forces in the envelope and by thermal-pressure forces in the core) introduces a break in the slope of the log pn -log r profile. The relation Bc ∞ pkc between the magnetic field strength and the gas density in cloud cores holds with K = 0.4 - 0.5 even in the presence of ambipolar diffusion up to densities ˜109 cm-3 for a wide variety of clouds. The value K ≃ ½ is fairly typical. At the late stages of evolution, for example, at a central density

  11. Thanatology in protoplanetary discs. The combined influence of Ohmic, Hall, and ambipolar diffusion on dead zones

    NASA Astrophysics Data System (ADS)

    Lesur, Geoffroy; Kunz, Matthew W.; Fromang, Sébastien

    2014-06-01

    Protoplanetary discs are poorly ionised due to their low temperatures and high column densities and are therefore subject to three "non-ideal" magnetohydrodynamic (MHD) effects: Ohmic dissipation, ambipolar diffusion, and the Hall effect. The existence of magnetically driven turbulence in these discs has been a central question since the discovery of the magnetorotational instability (MRI). Early models considered Ohmic diffusion only and led to a scenario of layered accretion, in which a magnetically "dead" zone in the disc midplane is embedded within magnetically "active" surface layers at distances of about 1-10 au from the central protostellar object. Recent work has suggested that a combination of Ohmic dissipation and ambipolar diffusion can render both the midplane and surface layers of the disc inactive and that torques due to magnetically driven outflows are required to explain the observed accretion rates. We reassess this picture by performing three-dimensional numerical simulations that include all three non-ideal MHD effects for the first time. We find that the Hall effect can generically "revive" dead zones by producing a dominant azimuthal magnetic field and a large-scale Maxwell stress throughout the midplane, provided that the angular velocity and magnetic field satisfy Ω·B > 0. The attendant large magnetic pressure modifies the vertical density profile and substantially increases the disc scale height beyond its hydrostatic value. Outflows are produced but are not necessary to explain accretion rates ≲ 10-7 M⊙ yr-1. The flow in the disc midplane is essentially laminar, suggesting that dust sedimentation may be efficient. These results demonstrate that if the MRI is relevant for driving mass accretion in protoplanetary discs, one must include the Hall effect to obtain even qualitatively correct results. Appendices are available in electronic form at http://www.aanda.org

  12. A universal filament width? The effect of ambipolar diffusion on the size distribution of dense filaments.

    NASA Astrophysics Data System (ADS)

    Ntormousi, Evangelia; Hennebelle, Patrick; André, Philippe

    2015-08-01

    The filamentary structure of molecular clouds and its potential link to star formation have been brought into focus by Herschel's high resolution observations of the local Interstellar Medium. An especially puzzling result from the same surveys is that local interstellar filaments have a preferred thickness of 0.1 pc, independent of their column density. What can be the origin of this apparently universal property?Filamentary structure is characteristic of MHD turbulence, appearing as a result of shear, magnetic tension and shocks. If the observed filaments are indeed the dissipative structures of interstellar turbulence, then ambipolar diffusion is the best candidate for setting a characteristic thickness by damping MHD waves. We test this hyporthesis with high-resolution, 3D MHD simulations performed with the AMR code RAMSES. To avoid confusion with grid effects, our simulations reach a physical resolution of 200 AU, resolving the observed 0.1 pc with about 100 cells.These simulations of both driven and decaying MHD turbulence show that the fluid assumes a different morphology when ambipolar diffusion is included in the models: ion-neutral friction acts on a characteristic scale to cut off the cascade, broadening the dense structures and flattening their mass spectra with respect to the corresponding ideal MHD situation. Altough the peak in the thickness distribution of filaments is not as dramatic in this series of simulations as in the observations, the comparison between ideal and non-ideal MHD points to ion-neutral friction as a very good candidate for setting a characteristic scale for interstellar filaments.

  13. INCORPORATING AMBIPOLAR AND OHMIC DIFFUSION IN THE AMR MHD CODE RAMSES

    SciTech Connect

    Masson, J.; Mulet-Marquis, C.; Chabrier, G.; Teyssier, R.

    2012-08-01

    We have implemented non-ideal magnetohydrodynamics (MHD) effects in the adaptive mesh refinement code RAMSES, namely, ambipolar diffusion and Ohmic dissipation, as additional source terms in the ideal MHD equations. We describe in details how we have discretized these terms using the adaptive Cartesian mesh, and how the time step is diminished with respect to the ideal case, in order to perform a stable time integration. We have performed a large suite of test runs, featuring the Barenblatt diffusion test, the Ohmic diffusion test, the C-shock test, and the Alfven wave test. For the latter, we have performed a careful truncation error analysis to estimate the magnitude of the numerical diffusion induced by our Godunov scheme, allowing us to estimate the spatial resolution that is required to address non-ideal MHD effects reliably. We show that our scheme is second-order accurate, and is therefore ideally suited to study non-ideal MHD effects in the context of star formation and molecular cloud dynamics.

  14. A numerical study of the effects of ambipolar diffusion on the collapse of magnetic gas clouds

    NASA Technical Reports Server (NTRS)

    Black, D. C.; Scott, E. H.

    1982-01-01

    The gravitational collapse of isothermal, nonrotating magnetic gas clouds have been calculated numerically, including the effects of ambipolar diffusion. The fractional ionization in the clouds is approximated by a power-law function of the gas density, f = K/n to the q-power, where K and q are adjustable parameters. Eleven numerical experiments were run, and the results indicate that the asymptotic character of collapse is determined mainly by the value of q and is largely independent of the other parameters characterizing a cloud (e.g., K, cloud mass). In particular, there is nearly a one-to-one correspondence between q and the slope, x, of the central magnetic field strength-gas density relationship. If q is no more than 0.8, a cloud collapses asymptotically, as though the magnetic field were 'frozen' to the neutral matter. The magnetic field strength at the center of a collapsing cloud is strongly amplified during collapse even for values of q of about 1, despite extremely low values of fractional ionization. A discussion of the theoretical basis for this unexpected behavior is given. Possible implications of our results for the problems of magnetic braking of rotating protostars and star formation in general are also presented.

  15. Energy balance in the solar transition region. I - Hydrostatic thermal models with ambipolar diffusion

    NASA Technical Reports Server (NTRS)

    Fontenla, J. M.; Avrett, E. H.; Loeser, R.

    1990-01-01

    The energy balance in the lower transition region is analyzed by constructing theoretical models which satisfy the energy balance constraint. The energy balance is achieved by balancing the radiative losses and the energy flowing downward from the corona. This energy flow is mainly in two forms: conductive heat flow and hydrogen ionization energy flow due to ambipolar diffusion. Hydrostatic equilibrium is assumed, and, in a first calculation, local mechanical heating and Joule heating are ignored. In a second model, some mechanical heating compatible with chromospheric energy-balance calculations is introduced. The models are computed for a partial non-LTE approach in which radiation departs strongly from LTE but particles depart from Maxwellian distributions only to first order. The results, which apply to cases where the magnetic field is either absent, or uniform and vertical, are compared with the observed Lyman lines and continuum from the average quiet sun. The approximate agreement suggests that this type of model can roughly explain the observed intensities in a physically meaningful way, assuming only a few free parameters specified as chromospheric boundary conditions.

  16. Global Simulations of Protoplanetary Disks With Ohmic Resistivity and Ambipolar Diffusion

    NASA Astrophysics Data System (ADS)

    Gressel, Oliver; Turner, Neal J.; Nelson, Richard P.; McNally, Colin P.

    2015-03-01

    Protoplanetary disks (PPDs) are believed to accrete onto their central T Tauri star because of magnetic stresses. Recently published shearing box simulations indicate that Ohmic resistivity, ambipolar diffusion (AD) and the Hall effect all play important roles in disk evolution. In the presence of a vertical magnetic field, the disk remains laminar between 1-5 AU, and a magnetocentrifugal disk wind forms that provides an important mechanism for removing angular momentum. Questions remain, however, about the establishment of a true physical wind solution in the shearing box simulations because of the symmetries inherent in the local approximation. We present global MHD simulations of PPDs that include Ohmic resistivity and AD, where the time-dependent gas-phase electron and ion fractions are computed under FUV and X-ray ionization with a simplified recombination chemistry. Our results show that the disk remains laminar, and that a physical wind solution arises naturally in global disk models. The wind is sufficiently efficient to explain the observed accretion rates. Furthermore, the ionization fraction at intermediate disk heights is large enough for magneto-rotational channel modes to grow and subsequently develop into belts of horizontal field. Depending on the ionization fraction, these can remain quasi-global, or break-up into discrete islands of coherent field polarity. The disk models we present here show a dramatic departure from our earlier models including Ohmic resistivity only. It will be important to examine how the Hall effect modifies the evolution, and to explore the influence this has on the observational appearance of such systems, and on planet formation and migration.

  17. Bridging the gap: disk formation in the Class 0 phase with ambipolar diffusion and Ohmic dissipation

    NASA Astrophysics Data System (ADS)

    Dapp, Wolf B.; Basu, Shantanu; Kunz, Matthew W.

    2012-05-01

    Context. Ideal magnetohydrodynamical (MHD) simulations have revealed catastrophic magnetic braking in the protostellar phase, which prevents the formation of a centrifugal disk around a nascent protostar. Aims: We determine if non-ideal MHD, including the effects of ambipolar diffusion and Ohmic dissipation determined from a detailed chemical network model, will allow for disk formation at the earliest stages of star formation. Methods: We employ the axisymmetric thin-disk approximation in order to resolve a dynamic range of 9 orders of magnitude in length and 16 orders of magnitude in density, while also calculating partial ionization using up to 19 species in a detailed chemical equilibrium model. Magnetic braking is applied to the rotation using a steady-state approximation, and a barotropic relation is used to capture the thermal evolution. Results: We resolve the formation of the first and second cores, with expansion waves at the periphery of each, a magnetic diffusion shock, and prestellar infall profiles at larger radii. Power-law profiles in each region can be understood analytically. After the formation of the second core, the centrifugal support rises rapidly and a low-mass disk of radius ≈ 10 R⊙ is formed at the earliest stage of star formation, when the second core has mass ~10-3 M⊙. The mass-to-flux ratio is ~104 times the critical value in the central region. Conclusions: A small centrifugal disk can form in the earliest stage of star formation, due to a shut-off of magnetic braking caused by magnetic field dissipation in the first core region. There is enough angular momentum loss to allow the second collapse to occur directly, and a low-mass stellar core to form with a surrounding disk. The disk mass and size will depend upon how the angular momentum transport mechanisms within the disk can keep up with mass infall onto the disk. Accounting only for direct infall, we estimate that the disk will remain ≲10 AU, undetectable even by ALMA, for

  18. Influence of the ambipolar-to-free diffusion transition on dust particle charge in a complex plasma afterglow

    SciTech Connect

    Coueedel, L.; Mikikian, M.; Boufendi, L.

    2008-06-15

    The influence of diffusive losses on residual dust charge in a complex plasma afterglow has been investigated. The residual charge distribution was measured and exhibits a mean value Q{sub dres}{approx}(-3e-5e) with a tail in the positive region. The experimental results have been compared with simulated charge distributions. The dust residual charges were simulated based on a model developed to describe complex plasma decay. The experimental and simulated data show that the transition from ambipolar to free diffusion in the decaying plasma plays a significant role in determining the residual dust particle charges. The presence of positively charged dust particles is explained by a broadening of the charge distribution function in the afterglow plasma.

  19. The Role of Magnetic Braking and Ambipolar Diffusion in the Formation of Interstellar Cloud Cores and Protostars

    NASA Astrophysics Data System (ADS)

    Basu, Shantanu

    The means by which parent molecular clouds give birth to stars constitutes a fundamental unsolved problem in astrophysics. Magnetic fields, which dominate thermal -pressure as a source of support against self-gravity in interstellar molecular clouds, are an important regulator of star-formation. We study the formation and contraction of fragments (or cores) in isothermal, rotating, magnetic molecular clouds. Initial states are exact equilibria with magnetic, centrifugal, and thermal-pressure forces balancing self-gravity. The full nonlinear two-fluid MHD equations for a flattened disk are solved numerically to obtain the cloud's evolution. The evolution of the model clouds is initiated entirely by the onset of magnetic braking (the transport of angular momentum by torsional Alfven waves) and ambipolar diffusion (the relative drift between neutral and charged particles). A core forms and ultimately evolves much more rapidly than the surrounding cloud. A core-envelope separation is demonstrated, and the final mass and angular momentum of the core is determined. Predictions are made for the spatial profiles of important physical quantities, e.g., angular velocity, density, magnetic field. A full parameter study is conducted.

  20. Kinetic Monte Carlo Study of Ambipolar Lithium Ion and Electron–Polaron Diffusion into Nanostructured TiO2

    SciTech Connect

    Yu, Jianguo; Sushko, Maria L.; Kerisit, Sebastien N.; Rosso, Kevin M.; Liu, Jun

    2012-08-02

    Nanostructured titania (TiO2) polymorphs have proved to be promising electrode materials for next generation lithium-ion batteries. However, there is still a lack of understanding of the fundamental microscopic processes that control charge transport in these materials. Here we present microscopic simulations of the collective dynamics of lithium-ion (Li+) and charge compensating electron polarons (e-) in rutile TiO2 nanoparticles in contact with idealized conductive matrix and electrolyte. Kinetic Monte Carlo simulations are used, parameterized by molecular dynamics-based predictions of activation energy barriers for Li+ and e- diffusion. Simulations reveal the central role of electrostatic coupling between Li+ and e- on their collective drift diffusion at the nanoscale. They also demonstrate that high contact area between conductive matrix and rutile nanoparticles leads to undesirable coupling-induced surface saturation effects during Li+ insertion, which limits the overall capacity and conductivity of the material. These results help provide guidelines for design of nanostructured electrode materials with improved electrochemical performance.

  1. Non-ambipolar transport in a magnetic divertor

    SciTech Connect

    Strawitch, C M; Emmert, G A

    1980-02-01

    Plasma transport is studied in a simulated magnetic divertor in the Wisconsin single ring DC machine. The transport perpendicular and parallel to the magnetic field is shown to be non-ambipolar by a variety of measurements, but can be forced to be ambipolar by an appropriately designed divertor target plate. The density profile in the scrape-off zone agrees with the predictions of a one-dimensional diffusion equation that assumes classical cross-field transport and plasma flow parallel to the field at the local ion acoustic velocity.

  2. Ambipolar potential formation in TMX

    SciTech Connect

    Correll, D.L.; Allen, S.L.; Casper, T.A.

    1981-05-05

    TMX experimental data on ambipolar potential control and on the accompanying electrostatic confinement are reported. New results on the radial dependence of the central-cell confining potential are given. Radial and axial particle losses as well as scaling of the central-cell axial confinement are discussed.

  3. Passivated ambipolar black phosphorus transistors.

    PubMed

    Yue, Dewu; Lee, Daeyeong; Jang, Young Dae; Choi, Min Sup; Nam, Hye Jin; Jung, Duk-Young; Yoo, Won Jong

    2016-07-01

    We report the first air-passivated ambipolar BP transistor formed by applying benzyl viologen, which serves as a surface charge transfer donor for BP flakes. The passivated BP devices exhibit excellent stability under both an ambient atmosphere and vacuum; their transistor performance is maintained semi-permanently. Unlike their intrinsic p-type properties, passivated BP devices present advantageous ambipolar properties with much higher electron mobility up to ∼83 cm(2) V(-1) s(-1) from 2-terminal measurement at 300 K, compared to other reported studies on n-type BP transistors. On the basis of the n-type doping effect that originated from benzyl viologen, we also systematically investigated the BP thickness dependence of our devices on electrical properties, in which we found the best electron transport performance to be attained when an ∼10 nm thick BP flake was used. PMID:27283027

  4. Ambipolar acoustic transport in silicon

    NASA Astrophysics Data System (ADS)

    Barros, A. D.; Batista, P. D.; Tahraoui, A.; Diniz, J. A.; Santos, P. V.

    2012-07-01

    We have investigated the ambipolar transport of electrons and holes by electrically generated surface acoustic waves (SAWs) on silicon wafers coated with a piezoelectric ZnO film. The transport experiments were carried out by using a focused laser beam to optically excite carriers. The carriers are then captured by the moving SAW piezoelectric field and then transported towards a lateral p-i-n junction, where they are electrically detected. The piezoelectric modulation modifies the current vs. voltage characteristics of the lateral p-i-n junction. This behavior is accounted for by a simple model for the change of the junction potential by the SAW fields. We demonstrate that electrons and holes can be acoustically transported over distances approaching 100 μm, the transport efficiency being limited by the low mobility of holes in the material. These results open the way for silicon-based acousto-electric devices using ambipolar transport such as photo-detectors and solar cells.

  5. Ambipolar phosphorene field effect transistor.

    PubMed

    Das, Saptarshi; Demarteau, Marcel; Roelofs, Andreas

    2014-11-25

    In this article, we demonstrate enhanced electron and hole transport in few-layer phosphorene field effect transistors (FETs) using titanium as the source/drain contact electrode and 20 nm SiO2 as the back gate dielectric. The field effect mobility values were extracted to be ∼38 cm(2)/Vs for electrons and ∼172 cm(2)/Vs for the holes. On the basis of our experimental data, we also comprehensively discuss how the contact resistances arising due to the Schottky barriers at the source and the drain end effect the different regime of the device characteristics and ultimately limit the ON state performance. We also propose and implement a novel technique for extracting the transport gap as well as the Schottky barrier height at the metal-phosphorene contact interface from the ambipolar transfer characteristics of the phosphorene FETs. This robust technique is applicable to any ultrathin body semiconductor which demonstrates symmetric ambipolar conduction. Finally, we demonstrate a high gain, high noise margin, chemical doping free, and fully complementary logic inverter based on ambipolar phosphorene FETs.

  6. Passivated ambipolar black phosphorus transistors

    NASA Astrophysics Data System (ADS)

    Yue, Dewu; Lee, Daeyeong; Jang, Young Dae; Choi, Min Sup; Nam, Hye Jin; Jung, Duk-Young; Yoo, Won Jong

    2016-06-01

    We report the first air-passivated ambipolar BP transistor formed by applying benzyl viologen, which serves as a surface charge transfer donor for BP flakes. The passivated BP devices exhibit excellent stability under both an ambient atmosphere and vacuum; their transistor performance is maintained semi-permanently. Unlike their intrinsic p-type properties, passivated BP devices present advantageous ambipolar properties with much higher electron mobility up to ~83 cm2 V-1 s-1 from 2-terminal measurement at 300 K, compared to other reported studies on n-type BP transistors. On the basis of the n-type doping effect that originated from benzyl viologen, we also systematically investigated the BP thickness dependence of our devices on electrical properties, in which we found the best electron transport performance to be attained when an ~10 nm thick BP flake was used.We report the first air-passivated ambipolar BP transistor formed by applying benzyl viologen, which serves as a surface charge transfer donor for BP flakes. The passivated BP devices exhibit excellent stability under both an ambient atmosphere and vacuum; their transistor performance is maintained semi-permanently. Unlike their intrinsic p-type properties, passivated BP devices present advantageous ambipolar properties with much higher electron mobility up to ~83 cm2 V-1 s-1 from 2-terminal measurement at 300 K, compared to other reported studies on n-type BP transistors. On the basis of the n-type doping effect that originated from benzyl viologen, we also systematically investigated the BP thickness dependence of our devices on electrical properties, in which we found the best electron transport performance to be attained when an ~10 nm thick BP flake was used. Electronic supplementary information (ESI) available: Transfer characteristics of BP field effect transistors (BV1-BV4) (Fig. S1 and S2 and Table S1); output characteristics of BP field effect transistors in different directions (Fig. S3

  7. Reconfigurable Complementary Logic Circuits with Ambipolar Organic Transistors

    PubMed Central

    Yoo, Hocheon; Ghittorelli, Matteo; Smits, Edsger C. P.; Gelinck, Gerwin H.; Lee, Han-Koo; Torricelli, Fabrizio; Kim, Jae-Joon

    2016-01-01

    Ambipolar organic electronics offer great potential for simple and low-cost fabrication of complementary logic circuits on large-area and mechanically flexible substrates. Ambipolar transistors are ideal candidates for the simple and low-cost development of complementary logic circuits since they can operate as n-type and p-type transistors. Nevertheless, the experimental demonstration of ambipolar organic complementary circuits is limited to inverters. The control of the transistor polarity is crucial for proper circuit operation. Novel gating techniques enable to control the transistor polarity but result in dramatically reduced performances. Here we show high-performance non-planar ambipolar organic transistors with electrical control of the polarity and orders of magnitude higher performances with respect to state-of-art split-gate ambipolar transistors. Electrically reconfigurable complementary logic gates based on ambipolar organic transistors are experimentally demonstrated, thus opening up new opportunities for ambipolar organic complementary electronics. PMID:27762321

  8. Edge ambipolar potential in toroidal fusion plasmas

    SciTech Connect

    Spizzo, G. Vianello, N.; Agostini, M.; Puiatti, M. E.; Scarin, P.; Spolaore, M.; Terranova, D.; White, R. B.; Abdullaev, S. S.; Schmitz, O.; Cavazzana, R.; Ciaccio, G.

    2014-05-15

    A series of issues with toroidally confined fusion plasmas are related to the generation of 3D flow patterns by means of edge magnetic islands, embedded in a chaotic field and interacting with the wall. These issues include the Greenwald limit in Tokamaks and reversed-field pinches, the collisionality window for ELM mitigation with the resonant magnetic perturbations (RMPs) in Tokamaks, and edge islands interacting with the bootstrap current in stellarators. Measurements of the 2D map of the edge electric field E{sup r}(r=a,θ,ϕ) in the RFX reversed-field pinch show that E{sup r} has the same helicity of the magnetic islands generated by a m/n perturbation: in fact, defining the helical angle u=mθ−nϕ+ωt, maps show a sinusoidal dependence as a function of u, E{sup r}=E{sup ~r}sin u. The associated E × B flow displays a huge convective cell with v(a)≠0 which, in RFX and near the Greenwald limit, determines a stagnation point for density and a reversal of the sign of E{sup r}. From a theoretical point of view, the question is how a perturbed toroidal flux of symmetry m/n gives rise to an ambipolar potential Φ=Φ{sup ~}sin u. On the basis of a model developed with the guiding center code ORBIT and applied to RFX and the TEXTOR tokamak, we will show that the presence of an m/n perturbation in any kind of device breaks the toroidal symmetry with a drift proportional to the gyroradius ρ, thus larger for ions (ρ{sub i} ≫ ρ{sub e}). Immediately, an ambipolar potential arises to balance the drifts, with the same symmetry as the original perturbation.

  9. Electrolyte-Gated Graphene Ambipolar Frequency Multipliers for Biochemical Sensing.

    PubMed

    Fu, Wangyang; Feng, Lingyan; Mayer, Dirk; Panaitov, Gregory; Kireev, Dmitry; Offenhäusser, Andreas; Krause, Hans-Joachim

    2016-04-13

    In this Letter, the ambipolar properties of an electrolyte-gated graphene field-effect transistor (GFET) have been explored to fabricate frequency-doubling biochemical sensor devices. By biasing the ambipolar GFETs in a common-source configuration, an input sinusoidal voltage at frequency f applied to the electrolyte gate can be rectified to a sinusoidal wave at frequency 2f at the drain electrode. The extraordinary high carrier mobility of graphene and the strong electrolyte gate coupling provide the graphene ambipolar frequency doubler an unprecedented unity gain, as well as a detection limit of ∼4 pM for 11-mer single strand DNA molecules in 1 mM PBS buffer solution. Combined with an improved drift characteristics and an enhanced low-frequency 1/f noise performance by sampling at doubled frequency, this good detection limit suggests the graphene ambipolar frequency doubler a highly promising biochemical sensing platform. PMID:26928906

  10. Electrolyte-Gated Graphene Ambipolar Frequency Multipliers for Biochemical Sensing.

    PubMed

    Fu, Wangyang; Feng, Lingyan; Mayer, Dirk; Panaitov, Gregory; Kireev, Dmitry; Offenhäusser, Andreas; Krause, Hans-Joachim

    2016-04-13

    In this Letter, the ambipolar properties of an electrolyte-gated graphene field-effect transistor (GFET) have been explored to fabricate frequency-doubling biochemical sensor devices. By biasing the ambipolar GFETs in a common-source configuration, an input sinusoidal voltage at frequency f applied to the electrolyte gate can be rectified to a sinusoidal wave at frequency 2f at the drain electrode. The extraordinary high carrier mobility of graphene and the strong electrolyte gate coupling provide the graphene ambipolar frequency doubler an unprecedented unity gain, as well as a detection limit of ∼4 pM for 11-mer single strand DNA molecules in 1 mM PBS buffer solution. Combined with an improved drift characteristics and an enhanced low-frequency 1/f noise performance by sampling at doubled frequency, this good detection limit suggests the graphene ambipolar frequency doubler a highly promising biochemical sensing platform.

  11. Ambipolar solution-processed hybrid perovskite phototransistors

    PubMed Central

    Li, Feng; Ma, Chun; Wang, Hong; Hu, Weijin; Yu, Weili; Sheikh, Arif D.; Wu, Tom

    2015-01-01

    Organolead halide perovskites have attracted substantial attention because of their excellent physical properties, which enable them to serve as the active material in emerging hybrid solid-state solar cells. Here we investigate the phototransistors based on hybrid perovskite films and provide direct evidence for their superior carrier transport property with ambipolar characteristics. The field-effect mobilities for triiodide perovskites at room temperature are measured as 0.18 (0.17) cm2 V−1 s−1 for holes (electrons), which increase to 1.24 (1.01) cm2 V−1 s−1 for mixed-halide perovskites. The photoresponsivity of our hybrid perovskite devices reaches 320 A W−1, which is among the largest values reported for phototransistors. Importantly, the phototransistors exhibit an ultrafast photoresponse speed of less than 10 μs. The solution-based process and excellent device performance strongly underscore hybrid perovskites as promising material candidates for photoelectronic applications. PMID:26345730

  12. Ambipolar Organic Tri-Gate Transistor for Low-Power Complementary Electronics.

    PubMed

    Torricelli, Fabrizio; Ghittorelli, Matteo; Smits, Edsger C P; Roelofs, Christian W S; Janssen, René A J; Gelinck, Gerwin H; Kovács-Vajna, Zsolt M; Cantatore, Eugenio

    2016-01-13

    Ambipolar transistors typically suffer from large off-current inherently due to ambipolar conduction. Using a tri-gate transistor it is shown that it is possible to electrostatically switch ambipolar polymer transistors from ambipolar to unipolar mode. In unipolar mode, symmetric characteristics with an on/off current ratio of larger than 10(5) are obtained. This enables easy integration into low-power complementary logic and volatile electronic memories. PMID:26573767

  13. Implementación numérica del efecto Hall, difusión ambipolar y difusión de Ohm en un código MHD

    NASA Astrophysics Data System (ADS)

    Krapp, L.; Benítez-Llambay, P.

    2016-08-01

    The goal of this work is to present an extension to the public magnetohydrodynamic code fargo3d via the implementation of a new physical module which includes the non-ideal magnetohydrodynamics terms, known as Hall effect and Ohmic and ambipolar diffusions. We present a set of simulations which allows to study the damping of Alfven waves by ambipolar diffusion, the Alfven wave splitting by Hall effect, and the behaviour of the magnetorotational instability under the Hall effect and Ohmic resistivity. The results of these simulations validate our implementation.

  14. Entropy production determination of the ambipolar solution nearest equilibrium

    SciTech Connect

    Catto, P.J.; Myra, J.R.

    1984-10-01

    A general derivation of the steady state entropy production equation is presented for a confined plasma which loses particles and energy via radial transport and, perhaps, end loss. The resulting equation is employed to determine which root or solution is closest to thermodynamic equilibrium when more than one self-consistent or ambipolar solution is possible.

  15. Electrically induced ambipolar spin vanishments in carbon nanotubes

    PubMed Central

    Matsumoto, D.; Yanagi, K.; Takenobu, T.; Okada, S.; Marumoto, K.

    2015-01-01

    Carbon nanotubes (CNTs) exhibit various excellent properties, such as ballistic transport. However, their electrically induced charge carriers and the relation between their spin states and the ballistic transport have not yet been microscopically investigated because of experimental difficulties. Here we show an electron spin resonance (ESR) study of semiconducting single-walled CNT thin films to investigate their spin states and electrically induced charge carriers using transistor structures under device operation. The field-induced ESR technique is suitable for microscopic investigation because it can directly observe spins in the CNTs. We observed a clear correlation between the ESR decrease and the current increase under high charge density conditions, which directly demonstrated electrically induced ambipolar spin vanishments in the CNTs. The result provides a first clear evidence of antimagnetic interactions between spins of electrically induced charge carriers and vacancies in the CNTs. The ambipolar spin vanishments would contribute the improvement of transport properties of CNTs because of greatly reduced carrier scatterings. PMID:26148487

  16. Ambipolar organic field-effect transistors on unconventional substrates

    NASA Astrophysics Data System (ADS)

    Cosseddu, P.; Mattana, G.; Orgiu, E.; Bonfiglio, A.

    2009-04-01

    In this paper we report on the realization of flexible all-organic ambipolar field-effect transistors (FETs) realized on unconventional substrates, such as plastic films and textile yarns. A double layer pentacene-C60 heterojunction was used as the semiconductor layer. The contacts were made with poly(ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) and patterned by means of soft lithography microcontact printing (μCP). Very interestingly growing C60 on a predeposited pentacene buffer layer leads to a clear improvement in the morphology and crystallinity of the film so it obtains n-type conduction despite the very high electron injection barrier at the interface between PEDOT:PSS and C60. As a result, it was possible to obtain all-organic ambipolar FETs and to optimize their electrical properties by tuning the thicknesses of the two employed active layers. Moreover, it will be shown that modifying the triple interface between dielectric/semiconductor/electrodes is a crucial point for optimizing and balancing injection and transport of both kinds of charge carriers. In particular, we demonstrate that using a middle contact configuration in which source and drain electrodes are sandwiched between pentacene and C60 layers allows significantly improving the electrical performance in planar ambipolar devices. These findings are very important because they pave the way for the realization of low-cost, fully flexible and stretchable organic complementary circuits for smart wearable and textile electronics applications.

  17. Graphene Ambipolar Nanoelectronics for High Noise Rejection Amplification.

    PubMed

    Liu, Che-Hung; Chen, Qi; Liu, Chang-Hua; Zhong, Zhaohui

    2016-02-10

    In a modern wireless communication system, signal amplification is critical for overcoming losses during multiple data transformations/processes and long-distance transmission. Common mode and differential mode are two fundamental amplification mechanisms, and they utilize totally different circuit configurations. In this paper, we report a new type of dual-gate graphene ambipolar device with capability of operating under both common and differential modes to realize signal amplification. The signal goes through two stages of modulation where the phase of signal can be individually modulated to be either in-phase or out-of-phase at two stages by exploiting the ambipolarity of graphene. As a result, both common and differential mode amplifications can be achieved within one single device, which is not possible in the conventional circuit configuration. In addition, a common-mode rejection ratio as high as 80 dB can be achieved, making it possible for low noise circuit application. These results open up new directions of graphene-based ambipolar electronics that greatly simplify the RF circuit complexity and the design of multifunction device operation. PMID:26808093

  18. Calculation of Non-ambipolar Transport in Tokamaks

    NASA Astrophysics Data System (ADS)

    Park, Jong-Kyu; Boozer, Allen; Menard, Jonathan

    2009-05-01

    Small non-axisymmetric perturbations of the magnetic field can greatly change the performance of tokamaks through non-ambipolar transport. The recently generalized analytic calculations of the non-ambipolar transport have shown that the consistency between theory and experiment can be significantly improved by two effects [J.-K. Park, et al., ``Non-ambipolar Transport by Trapped Particles in Tokamaks,'' Phys. Rev. Lett. (2009), To be published] : (1) The small fraction of trapped particles for which the bounce and precession rates of particles resonate. (2) The non-axisymmetric variation in the field strength along the perturbed magnetic field lines rather than along the unperturbed magnetic field lines. Most apparent effects can be found in toroidal momentum transport, and thus by a torodial rotational damping associated with Neoclassical Toroidal Viscosity (NTV). Various experiments for NTV rotation braking in NSTX and DIII-D will be compared with theoretical predictions, and the expected sensitivity of ITER to non-axisymmetries will be presented. Also, the effects of non-axisymmetic field on particle and heat transport will be discussed with regard to ELM suppressions. This work was supported by DOE contract DE-AC02-76CH03073 (PPPL), and DE-FG02-03ERS496 (CU).

  19. Orthogonal Ambipolar Semiconductor Nanostructures for Complementary Logic Gates.

    PubMed

    Huang, Weiguo; Markwart, Jens C; Briseno, Alejandro L; Hayward, Ryan C

    2016-09-27

    We report orthogonal ambipolar semiconductors that exhibit hole and electron transport in perpendicular directions based on aligned films of nanocrystalline "shish-kebabs" containing poly(3-hexylthiophene) (P3HT) and N,N'-di-n-octyl-3,4,9,10-perylenetetracarboxylic diimide (PDI) as p- and n-type components, respectively. Polarized optical microscopy, scanning electron microscopy, and X-ray diffraction measurements reveal a high degree of in-plane alignment. Relying on the orientation of interdigitated electrodes to enable efficient charge transport from either the respective p- or n-channel materials, we demonstrate semiconductor films with high anisotropy in the sign of charge carriers. Films of these aligned crystalline semiconductors were used to fabricate complementary inverter devices, which exhibited good switching behavior and a high noise margin of 80% of 1/2 Vdd. Moreover, complementary "NAND" and "NOR" logic gates were fabricated and found to exhibit excellent voltage transfer characteristics and low static power consumption. The ability to optimize the performance of these devices, simply by adjusting the solution concentrations of P3HT and PDI, makes this a simple and versatile method for preparing ambipolar organic semiconductor devices and high-performance logic gates. Further, we demonstrate that this method can also be applied to mixtures of PDI with another conjugated polymer, poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene]) (PBTTT), with better hole transport characteristics than P3HT, opening the door to orthogonal ambipolar semiconductors with higher performance.

  20. Observation and interpretation of energy efficient, diffuse direct current glow discharge at atmospheric pressure

    SciTech Connect

    Tang, Jie Jiang, Weiman; Wang, Yishan; Zhao, Wei; Li, Jing; Duan, Yixiang

    2015-08-24

    A diffuse direct-current glow discharge was realized with low energy consumption and high energy utilization efficiency at atmospheric pressure. The formation of diffuse discharge was demonstrated by examining and comparing the electrical properties and optical emissions of plasmas. In combination with theoretical derivation and calculation, we draw guidelines that appearance of nitrogen ions at low electron density is crucial to enhance the ambipolar diffusion for the expansion of discharge channel and the increasing ambipolar diffusion near the cathode plays a key role in the onset of diffuse discharge. An individual-discharge-channel expansion model is proposed to explain the diffuse discharge formation.

  1. Improving Ambipolar Charge Injection in Polymer FETs with Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Zaumseil, Jana

    2013-03-01

    Efficient charge injection is a key issue for organic field-effect transistors (FET). Various methods can be used to optimize injection of either holes or electrons, for example, by modifying the workfunction of metallic electrodes with self-assembled monolayers. For ambipolar FETs this is much more difficult because injection of both charge carriers has to be improved at the same time. Here we demonstrate a simple process to significantly improve ambipolar charge injection in bottom contact/top gate polymer field-effect transistors by adding single-walled carbon nanotubes (SWNT) to the semiconducting polymer at concentrations well below the percolation limit. Such polymer/carbon nanotube hybrid systems are easily produced by ultrasonication and dispersion of SWNT in a conjugated polymer solution. Even at very low nanotube concentrations the charge injection of both holes and electrons, for example, into poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) and poly(9,9-dioctylfluorene) (PFO) is significantly enhanced leading to lower contact resistances and threshold voltages than in FETs with pristine polymer films. This method can be extended to other semiconductors like n-type naphthalene-bis(dicarboximide)-based polymers (e.g. P(NDI2OD-T2)) for which hole injection was greatly enhanced. The proposed mechanism for this effect of carbon nanotubes on injection is independent of the polarity of the charge carriers. It can be maximized by patterning layers of pure carbon nanotubes onto the injecting electrodes before spincoating the pristine polymers leading to almost ohmic contacts for polymers, which usually show only strongly Schottky-barrier-limited injection. This improved injection of holes and electrons allows for a wider range of accessible polymers for ambipolar and thus also light-emitting transistors.

  2. A Highly Sensitive Diketopyrrolopyrrole-Based Ambipolar Transistor for Selective Detection and Discrimination of Xylene Isomers.

    PubMed

    Wang, Bin; Huynh, Tan-Phat; Wu, Weiwei; Hayek, Naseem; Do, Thu Trang; Cancilla, John C; Torrecilla, Jose S; Nahid, Masrur Morshed; Colwell, John M; Gazit, Oz M; Puniredd, Sreenivasa Reddy; McNeill, Christopher R; Sonar, Prashant; Haick, Hossam

    2016-06-01

    An ambipolar poly(diketopyrrolopyrrole-terthiophene)-based field-effect transistor (FET) sensitively detects xylene isomers at low ppm levels with multiple sensing features. Combined with pattern-recognition algorithms, a sole ambipolar FET sensor, rather than arrays of sensors, can discriminate highly similar xylene structural isomers from one another. PMID:26996398

  3. A Highly Sensitive Diketopyrrolopyrrole-Based Ambipolar Transistor for Selective Detection and Discrimination of Xylene Isomers.

    PubMed

    Wang, Bin; Huynh, Tan-Phat; Wu, Weiwei; Hayek, Naseem; Do, Thu Trang; Cancilla, John C; Torrecilla, Jose S; Nahid, Masrur Morshed; Colwell, John M; Gazit, Oz M; Puniredd, Sreenivasa Reddy; McNeill, Christopher R; Sonar, Prashant; Haick, Hossam

    2016-06-01

    An ambipolar poly(diketopyrrolopyrrole-terthiophene)-based field-effect transistor (FET) sensitively detects xylene isomers at low ppm levels with multiple sensing features. Combined with pattern-recognition algorithms, a sole ambipolar FET sensor, rather than arrays of sensors, can discriminate highly similar xylene structural isomers from one another.

  4. Fabrication and characterisation of gallium arsenide ambipolar quantum point contacts

    SciTech Connect

    Chen, J. C. H. Klochan, O.; Micolich, A. P.; Hamilton, A. R.; Das Gupta, K.; Sfigakis, F.; Ritchie, D. A.; Trunov, K.; Wieck, A. D.; Reuter, D.

    2015-05-04

    We show that ballistic one-dimensional channels can be formed in an ambipolar device fabricated on a high mobility Al{sub 0.34}Ga{sub 0.66}As/GaAs heterostructure. Both electron and hole quantised conductances can be measured in the same one-dimensional channel. We have used this device to compare directly the subband spacings of the two charge carriers in the same confining potential and used this to compare the electron and hole effective masses.

  5. Ambipolarity in a tokamak with magnetic field ripple

    NASA Astrophysics Data System (ADS)

    Hazeltine, R. D.

    2016-08-01

    In view of the recognized importance of electrostatic fields regarding turbulent transport, the radial electric field in a tokamak with magnetic field ripple is reconsidered. Terms in the ambipolarity condition involving the radial derivative of the field are derived from an extended drift-kinetic equation, including effects of second order in the gyroradius. Such terms are of interest in part because of their known importance in rotational relaxation equations for the axisymmetric case. The electric field is found to satisfy a nonlinear differential equation that is universal in a certain sense, and that implies spatial relaxation of the potential to its conventionally predicted value.

  6. Entropy production determination of the ambipolar solution nearest equilibrium. Revision

    SciTech Connect

    Catto, P.J.; Myra, J.R.

    1985-05-01

    A general derivation of the steady state entropy production equation is presented for a confined plasma which loses particles and energy via radial transport and, perhaps, end loss. The resulting equation is employed to determine which root or solution at each pressure surface is closest to local thermodynamic equilibrium when more than one self-consistent or ambipolar solution is possible. The solution closest to local thermodynamic equilibrium is presumed to be the one with the smallest total collisional entropy production rate. This solution makes the distribution functions as close to local Maxwellians as possible.

  7. Ambipolar Electric Double Layer Transistors Using Organic Single Crystals

    NASA Astrophysics Data System (ADS)

    Takenobu, Taishi; Wen, Di; Shimotani, Hidekazu; Ono, Shimpei; Iwasa, Yoshihiro

    2011-03-01

    Among organic devices, ambipolar transistors are very unique device, in which both electrons and holes are equally mobile and we are able to observe light emission through the recombination of them. Progress in the applications of such light-emitting transistors (LETs) based on organic single crystals has provided possibilities in developing organic laser. However, in these LETs, the current density is still low for lasing, and, therefore, a different device structure is necessary to overcome this issue. Here we show the first demonstration of organic ambipolar electric double layer transistors (EDLTs), in which the gate dielectric is not a conventional insulator but an electrolyte. The peculiar merit of EDLT is extremely high conductivity due to the huge capacitance of the EDL formed at the organic/electrolyte interfaces. Consequently, we can increase current density. In this study, we used rubrene single crystal and ion-gel as the active material and electrolyte, respectively. These present results will provide a prospect for further development in LET operation.

  8. Ambipolar MoTe2 transistors and their applications in logic circuits.

    PubMed

    Lin, Yen-Fu; Xu, Yong; Wang, Sheng-Tsung; Li, Song-Lin; Yamamoto, Mahito; Aparecido-Ferreira, Alex; Li, Wenwu; Sun, Huabin; Nakaharai, Shu; Jian, Wen-Bin; Ueno, Keiji; Tsukagoshi, Kazuhito

    2014-05-28

    We report ambipolar charge transport in α-molybdenum ditelluride (MoTe2 ) flakes, whereby the temperature dependence of the electrical characteristics was systematically analyzed. The ambipolarity of the charge transport originated from the formation of Schottky barriers at the metal/MoTe2 contacts. The Schottky barrier heights as well as the current on/off ratio could be modified by modulating the electrostatic fields of the back-gate voltage (Vbg) and drain-source voltage (Vds). Using these ambipolar MoTe2 transistors we fabricated complementary inverters and amplifiers, demonstrating their feasibility for future digital and analog circuit applications. PMID:24692079

  9. Absence of carrier separation in ambipolar charge and spin drift in p{sup +}-GaAs

    SciTech Connect

    Cadiz, F.; Paget, D.; Rowe, A. C. H.; Martinelli, L.; Arscott, S.

    2015-10-19

    The electric field-induced modifications of the spatial distribution of photoelectrons, photoholes, and electronic spins in optically pumped p{sup +} GaAs are investigated using a polarized luminescence imaging microscopy. At low pump intensity, application of an electric field reveals the tail of charge and spin density of drifting electrons. These tails disappear when the pump intensity is increased since a slight differential drift of photoelectrons and photoholes causes the buildup of a strong internal electric field. Spatial separation of photoholes and photoelectrons is very weak so that photoholes drift in the same direction as photoelectrons, thus exhibiting a negative effective mobility. In contrast, for a zero electric field, no significant ambipolar diffusive effects are found in the same sample.

  10. Evolution of views on the structure of the ambipolar electric field in toroidal magnetic confinement systems

    SciTech Connect

    Kovrizhnykh, L. M.

    2015-12-15

    Various methods of determining the ambipolar electric field in toroidal magnetic systems (predominantly, in stellarators) and the evolution of views on this problem are discussed. Paradoxes encountered in solving this problem are analyzed, and ways of resolving them are proposed.

  11. Ambipolar radial electric field generated by anomalous transport induced by magnetic perturbations

    NASA Astrophysics Data System (ADS)

    Chen, Dunqiang; Zhu, Siqiang; Zhang, Debing; Wang, Shaojie

    2016-05-01

    The anomalous particle transport induced by magnetic perturbations in a tokamak is investigated. The correlation between the radial position and the kinetic energy of electrons, Dr K=-e ErDr r , is predicted theoretically and is verified by simulations in the presence of a mean radial electric field. This correlation leads to a radial particle flux produced by the radial electric field. The ambipolar radial electric field can thus be predicted by using the ambipolarity condition Γri=Γre .

  12. Small molecules with ambipolar transporting properties for efficient OLEDs

    NASA Astrophysics Data System (ADS)

    Duan, Lian; Wei, Peng; Qiu, Yong

    2007-11-01

    For stable and efficienct organic light-emitting diodes, it is essential to find molecules with high photoluminescent efficiency, little self-quenching and balanced charge transporting properties. Recently, we've designed and synthesized some highly emissive naphtho[2,3-c][1,2,5]thiadiazole (NTD) derivatives and naphtho[2,3-c][1,2,5]selenadiazole (NSeD) derivatives with unusual ambipolar transporting properties. The ambipolar transporting properties of the NTDs were explained by Marcus theory with carrier reorganization energies and charge-transfer integrals. We obtained high quality single crystals of 4,9-di(biphenyl-4-yl)-naphtho[2,3-c][1,2,5]thiadiazole (NTD02) and 4,9-bis(4-(2,2-diphenylvinyl)phenyl)-naphtho[2,3-c][1,2,5]thiadiazole (NTD05). They have disordered NTD rings' orientation with the opposite directions in the center of the molecule because of NTD's planar configuration and the single-bond connection with the phenyl substituents. The packing structure of NTD02 shows the planar arrangement of NTD rings, forming a "charge transporting channel". Quantum calculation also confirms that the π-π stacking interaction in NTD derivatives benefits the charge transporting via intermolecular hopping on NTD rings. The hole and electron mobilities of NTD05 are 7.16×10 -4 cm2/VÂ.s and 6.19×10 -4 cm2/V•s at an electronic field E = 2.0×10 5 V/cm, respectively. The hole mobility of NTD05 is close to that of N,N'-diphenyl-N,N'-bis(1-naphthyl)(1,1'-biphenyl)-4,4'-diamine (NPB) and the electron mobility of NTD05 is two orders-of-magnitude higher than that of tris(8-hydroxyquinoline) aluminum (Alq 3). For the NTD derivatives, NTD05 also shows the best performance in non-doped OLEDs. CIE coordinates of (0.65, 0.35) and a peak efficiency of 2.4% are achieved for a double layer OLED with NPB as the hole transporting layer and NTD05 as the emitting layer. Moreover, we get ultimate red emission with CIE coordinates of (0.71, 0.29) for some of the NSeD based non

  13. Electron and hole transport in ambipolar, thin film pentacene transistors

    SciTech Connect

    Saudari, Sangameshwar R.; Kagan, Cherie R.

    2015-01-21

    Solution-processed, ambipolar, thin-film pentacene field-effect transistors were employed to study both electron and hole transport simultaneously in a single, organic solid-state device. Electron and hole mobilities were extracted from the respective unipolar saturation regimes and show thermally activated behavior and gate voltage dependence. We fit the gate voltage dependent saturation mobility to a power law to extract the characteristic Meyer-Neldel (MN) energy, a measure of the width of the exponential distribution of localized states extending into the energy gap of the organic semiconductor. The MN energy is ∼78 and ∼28 meV for electrons and holes, respectively, which reflects a greater density of localized tail states for electrons than holes. This is consistent with the lower measured electron than hole mobility. For holes, the well-behaved linear regime allows for four-point probe measurement of the contact resistance independent mobility and separate characterization of the width of the localized density of states, yielding a consistent MN energy of 28 meV.

  14. Ambipolar MoS2 thin flake transistors.

    PubMed

    Zhang, Yijin; Ye, Jianting; Matsuhashi, Yusuke; Iwasa, Yoshihiro

    2012-03-14

    Field effect transistors (FETs) made of thin flake single crystals isolated from layered materials have attracted growing interest since the success of graphene. Here, we report the fabrication of an electric double layer transistor (EDLT, a FET gated by ionic liquids) using a thin flake of MoS(2), a member of the transition metal dichalcogenides, an archetypal layered material. The EDLT of the thin flake MoS(2) unambiguously displayed ambipolar operation, in contrast to its commonly known bulk property as an n-type semiconductor. High-performance transistor operation characterized by a large "ON" state conductivity in the order of ~mS and a high on/off ratio >10(2) was realized for both hole and electron transport. Hall effect measurements revealed mobility of 44 and 86 cm(2) V(-1) s(-1) for electron and hole, respectively. The hole mobility is twice the value of the electron mobility, and the density of accumulated carrier reached 1 × 10(14) cm(-2), which is 1 order of magnitude larger than conventional FETs with solid dielectrics. The high-density carriers of both holes and electrons can create metallic transport in the MoS(2) channel. The present result is not only important for device applications with new functionalities, but the method itself would also act as a protocol to study this class of material for a broader scope of possibilities in accessing their unexplored properties.

  15. Thermoelectric properties of hole- and electron-doped ambipolar polymers

    NASA Astrophysics Data System (ADS)

    Glaudell, Anne; Perry, Erin; Schlitz, Ruth; Chabinyc, Michael

    2015-03-01

    The library of possible materials, both p- and n-type, for organic thermoelectric devices has been steadily growing with the continuous improvement in electrical properties and stability. Maximizing the thermoelectric power factor in these materials requires the simultaneous optimization of both electrical conductivity and thermopower. The challenge remains that charge transport is not well understood in organic materials due to energetic disorder from crystalline and non-crystalline domains. We have performed temperature-dependent measurements of both thermopower and electrical conductivity to uncover the relationship between microstructure and thermoelectric performance. These measurements were complemented by techniques such as electronic paramagnetic resonance (EPR) that help provide the carrier concentration to give a more complete picture of the competing charge transport mechanisms and structure-property relationships. We will present results on p- and n-type doping of ambipolar polymers that reveal the difference in thermopower for electrons and holes in the same material. An ideal thermoelectric device has n- and p-type legs with similar mechanical and thermoelectric properties, a balance more easily realized using the same polymer for each leg.

  16. Enhancement of ambipolar characteristics in single-walled carbon nanotubes using C{sub 60} and fabrication of logic gates

    SciTech Connect

    Park, Steve; Nam, Ji Hyun; Koo, Ja Hoon; Lei, Ting; Bao, Zhenan

    2015-03-09

    We demonstrate a technique to convert p-type single-walled carbon nanotube (SWNT) network transistor into ambipolar transistor by thermally evaporating C{sub 60} on top. The addition of C{sub 60} was observed to have two effects in enhancing ambipolar characteristics. First, C{sub 60} served as an encapsulating layer that enhanced the ambipolar characteristics of SWNTs. Second, C{sub 60} itself served as an electron transporting layer that contributed to the n-type conduction. Such a dual effect enables effective conversion of p-type into ambipolar characteristics. We have fabricated inverters using our SWNT/C{sub 60} ambipolar transistors with gain as high as 24, along with adaptive NAND and NOR logic gates.

  17. Ambipolar transport via trapped-electron whistler instability along open magnetic field lines.

    PubMed

    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.

  18. Ambipolar organic thin-film transistor-based nano-floating-gate nonvolatile memory

    SciTech Connect

    Han, Jinhua; Wang, Wei Ying, Jun; Xie, Wenfa

    2014-01-06

    An ambipolar organic thin-film transistor-based nano-floating-gate nonvolatile memory was demonstrated, with discrete distributed gold nanoparticles, tetratetracontane (TTC), pentacene as the floating-gate layer, tunneling layer, and active layer, respectively. The electron traps at the TTC/pentacene interface were significantly suppressed, which resulted in an ambipolar operation in present memory. As both electrons and holes were supplied in the channel and trapped in the floating-gate by programming/erasing operations, respectively, i.e., one type of charge carriers was used to overwrite the other, trapped, one, a large memory window, extending on both sides of the initial threshold voltage, was realized.

  19. Nonvolatile multilevel data storage memory device from controlled ambipolar charge trapping mechanism.

    PubMed

    Zhou, Ye; Han, Su-Ting; Sonar, Prashant; Roy, V A L

    2013-01-01

    The capability of storing multi-bit information is one of the most important challenges in memory technologies. An ambipolar polymer which intrinsically has the ability to transport electrons and holes as a semiconducting layer provides an opportunity for the charge trapping layer to trap both electrons and holes efficiently. Here, we achieved large memory window and distinct multilevel data storage by utilizing the phenomena of ambipolar charge trapping mechanism. As fabricated flexible memory devices display five well-defined data levels with good endurance and retention properties showing potential application in printed electronics.

  20. A furan-containing conjugated polymer for high mobility ambipolar organic thin film transistors.

    PubMed

    Sonar, Prashant; Foong, Thelese Ru Bao; Singh, Samarendra P; Li, Yuning; Dodabalapur, Ananth

    2012-08-28

    Furan substituted diketopyrrolopyrrole (DBF) combined with benzothiadiazole based polymer semiconductor PDPP-FBF has been synthesized and evaluated as an ambipolar semiconductor in organic thin-film transistors. Hole and electron mobilities as high as 0.20 cm(2) V(-1) s(-1) and 0.56 cm(2) V(-1) s(-1), respectively, are achieved for PDPP-FBF.

  1. Surface engineering of reduced graphene oxide for controllable ambipolar flash memories.

    PubMed

    Han, Su-Ting; Zhou, Ye; Sonar, Prashant; Wei, Huaixin; Zhou, Li; Yan, Yan; Lee, Chun-Sing; Roy, V A L

    2015-01-28

    Tunable charge-trapping behaviors including unipolar charge trapping of one type of charge carrier and ambipolar trapping of both electrons and holes in a complementary manner is highly desirable for low power consumption multibit flash memory design. Here, we adopt a strategy of tuning the Fermi level of reduced graphene oxide (rGO) through self-assembled monolayer (SAM) functionalization and form p-type and n-type doped rGO with a wide range of manipulation on work function. The functionalized rGO can act as charge-trapping layer in ambipolar flash memories, and a dramatic transition of charging behavior from unipolar trapping of electrons to ambipolar trapping and eventually to unipolar trapping of holes was achieved. Adjustable hole/electron injection barriers induce controllable Vth shift in the memory transistor after programming operation. Finally, we transfer the ambipolar memory on flexible substrates and study their charge-trapping properties at various bending cycles. The SAM-functionalized rGO can be a promising candidate for next-generation nonvolatile memories.

  2. Magnetic Braking, Ambipolar Diffusion, and the Formation of Cloud Cores and Protostars. II. A Parameter Study

    NASA Astrophysics Data System (ADS)

    Basu, Shantanu; Mouschovias, Telemachos Ch.

    1995-10-01

    The formulation of the problem of the formation of protostellar cores in self-gravitating, magnetically supported, rotating, isothermal model molecular clouds was presented in a previous paper, where detailed numerical simulations for two different model clouds were also discussed. In this paper, we study the effect of varying five dimensionless free parameters: the ratio ˜p of external density and central density in a reference state (which is related simply to an initial equilibrium state), the initial radial length scale l˜ref of the column density of the cloud, the central angular velocity of the reference state ˜Ωc,ref, the central neutral-ion collision time in the reference state ˜τni,ref (which is inversely proportional to the collapse retardation factor Vff ≡ τff/τni) and the exponent k in the relation between the ion and neutral densities ni ∝ nkn. In addition to the models previously presented, seven more models are investigated here. Different values (1/1000 to 1/100) of the initial magnetic-braking efficiency parameter ˜p(>0) do not significantly affect the evolution; magnetic braking remains effective during the quasistatic phase and ineffective during the (dynamic) collapse of the magnetically and thermally supercritical core. The initially very effective magnetic braking also means that the solution is insensitive to values of ˜Ωc,ref. Different values of l˜ref yield qualitatively similar evolution, with smaller cloud sizes leading to slightly smaller core sizes. Increasing the value of τni,ref leads to a more rapid evolution and larger, more rapidly rotating cores. A smaller k leads to relatively more rapid evolution in the core and a better core-envelope separation. We also give an analytical explanation of the previously presented result, that the gravitational field acting on an infalling mass shell in the central region of a nonhomologously contracting thin disk increases as 1/r3m, where rm is the Lagrangian radius of the shell.

  3. Inkjet printed ambipolar transistors and inverters based on carbon nanotube/zinc tin oxide heterostructures

    SciTech Connect

    Kim, Bongjun; Jang, Seonpil; Dodabalapur, Ananth; Geier, Michael L.; Prabhumirashi, Pradyumna L.; Hersam, Mark C.

    2014-02-10

    We report ambipolar field-effect transistors (FETs) consisting of inkjet printed semiconductor bilayer heterostructures utilizing semiconducting single-walled carbon nanotubes (SWCNTs) and amorphous zinc tin oxide (ZTO). The bilayer structure allows for electron transport to occur principally in the amorphous oxide layer and hole transport to occur exclusively in the SWCNT layer. This results in balanced electron and hole mobilities exceeding 2 cm{sup 2} V{sup −1} s{sup −1} at low operating voltages (<5 V) in air. We further show that the SWCNT-ZTO hybrid ambipolar FETs can be integrated into functional inverter circuits that display high peak gain (>10). This work provides a pathway for realizing solution processable, inkjet printable, large area electronic devices, and systems based on SWCNT-amorphous oxide heterostructures.

  4. High-mobility ambipolar ZnO-graphene hybrid thin film transistors

    PubMed Central

    Song, Wooseok; Kwon, Soon Yeol; Myung, Sung; Jung, Min Wook; Kim, Seong Jun; Min, Bok Ki; Kang, Min-A; Kim, Sung Ho; Lim, Jongsun; An, Ki-Seok

    2014-01-01

    In order to combine advantages of ZnO thin film transistors (TFTs) with a high on-off ratio and graphene TFTs with extremely high carrier mobility, we present a facile methodology for fabricating ZnO thin film/graphene hybrid two-dimensional TFTs. Hybrid TFTs exhibited ambipolar behavior, an outstanding electron mobility of 329.7 ± 16.9 cm2/V·s, and a high on-off ratio of 105. The ambipolar behavior of the ZnO/graphene hybrid TFT with high electron mobility could be due to the superimposed density of states involving the donor states in the bandgap of ZnO thin films and the linear dispersion of monolayer graphene. We further established an applicable circuit model for understanding the improvement in carrier mobility of ZnO/graphene hybrid TFTs. PMID:24513629

  5. Ambipolar insulator-to-metal transition in black phosphorus by ionic-liquid gating.

    PubMed

    Saito, Yu; Iwasa, Yoshihiro

    2015-03-24

    We report ambipolar transport properties in black phosphorus using an electric-double-layer transistor configuration. The transfer curve clearly exhibits ambipolar transistor behavior with an ON-OFF ratio of ∼5 × 10(3). The band gap was determined as ≅0.35 eV from the transfer curve, and Hall-effect measurements revealed that the hole mobility was ∼190 cm(2)/(V s) at 170 K, which is 1 order of magnitude larger than the electron mobility. By inducing an ultrahigh carrier density of ∼10(14) cm(-2), an electric-field-induced transition from the insulating state to the metallic state was realized, due to both electron and hole doping. Our results suggest that black phosphorus will be a good candidate for the fabrication of functional devices, such as lateral p-n junctions and tunnel diodes, due to the intrinsic narrow band gap.

  6. Light emission from an ambipolar semiconducting polymer field-effect transistor

    NASA Astrophysics Data System (ADS)

    Swensen, James S.; Soci, Cesare; Heeger, Alan J.

    2006-02-01

    Ambipolar light-emitting field-effect transistors are fabricated with two different metals for the top-contact source and drain electrodes; a low-work-function metal defining the channel for the source electrode and a high-work-function metal defining the channel for the drain electrode. A thin film of polypropylene-co-1-butene on SiN x is used as the gate dielectric on an n ++-Si wafer, which functioned as the substrate and the gate electrode. Transport data show ambipolar behavior. Recombination of electrons and holes results in a narrow zone of light emission within the channel. The location of the emission zone is controlled by the gate bias.

  7. Light emission from an ambipolar semiconducting polymer field-effect transistor

    NASA Astrophysics Data System (ADS)

    Swensen, James S.; Soci, Cesare; Heeger, Alan J.

    2005-12-01

    Ambipolar light-emitting field-effect transistors are fabricated with two different metals for the top-contact source and drain electrodes; a low-work-function metal defining the channel for the source electrode and a high-work-function metal defining the channel for the drain electrode. A thin film of polypropylene-co-1-butene on SiNx is used as the gate dielectric on an n++-Si wafer, which functioned as the substrate and the gate electrode. Transport data show ambipolar behavior. Recombination of electrons and holes results in a narrow zone of light emission within the channel. The location of the emission zone is controlled by the gate bias.

  8. BPTs: thiophene-flanked benzodipyrrolidone conjugated polymers for ambipolar organic transistors.

    PubMed

    Rumer, Joseph W; Levick, Matthew; Dai, Sheng-Yao; Rossbauer, Stephan; Huang, Zhenggang; Biniek, Laure; Anthopoulos, Thomas D; Durrant, James R; Procter, David J; McCulloch, Iain

    2013-05-18

    A series of novel thiophene-flanked benzodipyrrolidone (BPT)-based alternating copolymers are synthesised, their optical and electrical properties evaluated. The BPT unit promotes a conjugated, planar polymer backbone, with a low bandgap, primarily due to low lying LUMO energy levels. Copolymerisation with thiophene exhibits well balanced ambipolar organic field-effect transistor performance, with electron and hole mobilities 0.1 and 0.2 cm(2) V(-1) s(-1), respectively.

  9. Electrostatically Reversible Polarity of Ambipolar α-MoTe2 Transistors.

    PubMed

    Nakaharai, Shu; Yamamoto, Mahito; Ueno, Keiji; Lin, Yen-Fu; Li, Song-Lin; Tsukagoshi, Kazuhito

    2015-06-23

    A doping-free transistor made of ambipolar α-phase molybdenum ditelluride (α-MoTe2) is proposed in which the transistor polarity (p-type and n-type) is electrostatically controlled by dual top gates. The voltage signal in one of the gates determines the transistor polarity, while the other gate modulates the drain current. We demonstrate the transistor operation experimentally, with electrostatically controlled polarity of both p- and n-type in a single transistor. PMID:25988597

  10. Efficient and Hysteresis-Free Field Effect Modulation of Ambipolarly Doped Vanadium Dioxide Nanowires

    NASA Astrophysics Data System (ADS)

    Peng, Xingyue; Yang, Yiming; Hou, Yasen; Travaglini, Henry C.; Hellwig, Luke; Hihath, Sahar; van Benthem, Klaus; Lee, Kathleen; Liu, Weifeng; Yu, Dong

    2016-05-01

    The subpicosecond metal-insulator phase transition in vanadium dioxide (VO2 ) has attracted extensive attention with potential applications in ultrafast Mott transistors, which are based on electric-field-induced phase transition. However, the development of VO2 -based transistors lags behind, owing to inefficient and hysteretic gate modulation. Here we report ambipolar doping and strong field effects free of hysteresis in single-crystal VO2 nanowires synthesized via catalyst-free chemical vapor deposition. The ambipolarly doped VO2 nanowires are achieved by controlling the oxygen vacancy density during the synthesis and show strong gate effects because of their relatively low doping level. Both the doping type of the nanowires and the band-bending direction at the metal-insulator domain walls are reversibly switched by electrochemical gating, as revealed by scanning photocurrent microscopy. Furthermore, we eliminate the hysteresis in gate sweep via a hybrid gating method, which combines the merits of liquid-ionic and solid gating. The capability of efficient field effect modulation of ambipolar conduction and band alignment offers opportunities on understanding the phase transition mechanism and enables electronic applications based on VO2 .

  11. Ambipolar Transport and Gate-Induced Superconductivity in Layered Transition Metal Dichalcogenides

    NASA Astrophysics Data System (ADS)

    Shi, Wu; Ye, Jianting; Zhang, Yijing; Suzuki, Ryuji; Saito, Yu; Iwasa, Yoshihiro

    2014-03-01

    Transition metal dichalcogenides (TMDs) are well known van der Waals layered materials that are easy to be exfoliated into atomically flat nano scale flakes. Owing to high efficiency of electrical double layer (EDL) dielectrics, thin flakes of TMDs have achieved high performance ambipolar transistor operation and established metallic states with high mobility, which are ideal for inducing superconductivity. Here, we report a comprehensive study of ambipolar transport behaviors in the EDL transistors (EDLTs) of MoS2, MoSe2 and MoTe2 thin flakes down to 2 K. In comparison, MoSe2 EDLT displayed a well-balanced ambipolar transistor operation while the other two showed opposite predominance in electron and hole accumulation, respectively. By modulation of carrier densities, the metal insulator transition (MIT) was observed in both electron and hole transport measurements. Particularly, superconducting transitions were reached after the formation of metallic states in the electron side. The phase diagram of transition temperature-carrier density was established and a dome-shaped structure was confirmed, revealing a universal feature of gate-induce superconductivity in layered band insulators. Present address: University of Groningen.

  12. Measurement of current density fluctuations and ambipolar particle flux due to magnetic fluctuations in MST

    SciTech Connect

    Shen, Weimin.

    1992-08-01

    Studies of magnetic fluctuation induced particle transport on Reversed Field Pinch plasmas were done on the Madison Symmetric Torus. Plasma current density and current density fluctuations were measured using a multi-coil magnetic probes. The low frequency (f<50 kHz) current density fluctuations are consistent with the global resistive tearing instabilities predicted by 3-D MHD simulations. At frequencies above 50 kHz, the magnetic fluctuations were detected to be localized with a radial correlation length of about 1--2 cm. These modes are locally resonant modes since the measured dominant mode number spectra match the local safety factor q. The net charged particle flux induced by magnetic fluctuations was obtained by measuring the correlation term <{tilde j}{sub {parallel}} {tilde B}{sub r}>. The result of zero net charged particle loss was obtained, meaning the flux is ambipolar. The ambipolarity of low frequency global tearing modes is satisfied through the phase relations determined by tearing instabilities. The ambipolarity of high frequency localized modes could be partially explained by the simple model of Waltz based on the radial average of small scale turbulence.

  13. Hydrodynamic theory of diffusion in two-temperature multicomponent plasmas

    SciTech Connect

    Ramshaw, J.D.; Chang, C.H.

    1995-12-31

    Detailed numerical simulations of multicomponent plasmas require tractable expressions for species diffusion fluxes, which must be consistent with the given plasma current density J{sub q} to preserve local charge neutrality. The common situation in which J{sub q} = 0 is referred to as ambipolar diffusion. The use of formal kinetic theory in this context leads to results of formidable complexity. We derive simple tractable approximations for the diffusion fluxes in two-temperature multicomponent plasmas by means of a generalization of the hydrodynamical approach used by Maxwell, Stefan, Furry, and Williams. The resulting diffusion fluxes obey generalized Stefan-Maxwell equations that contain driving forces corresponding to ordinary, forced, pressure, and thermal diffusion. The ordinary diffusion fluxes are driven by gradients in pressure fractions rather than mole fractions. Simplifications due to the small electron mass are systematically exploited and lead to a general expression for the ambipolar electric field in the limit of infinite electrical conductivity. We present a self-consistent effective binary diffusion approximation for the diffusion fluxes. This approximation is well suited to numerical implementation and is currently in use in our LAVA computer code for simulating multicomponent thermal plasmas. Applications to date include a successful simulation of demixing effects in an argon-helium plasma jet, for which selected computational results are presented. Generalizations of the diffusion theory to finite electrical conductivity and nonzero magnetic field are currently in progress.

  14. Ambipolar and unipolar PbSe nanowire field-effect transistors.

    PubMed

    Kim, David K; Vemulkar, Tarun R; Oh, Soong Ju; Koh, Weon-Kyu; Murray, Christopher B; Kagan, Cherie R

    2011-04-26

    Wet-chemical methods, under rigorous air-free conditions, were used to synthesize single-crystalline 10 nm diameter PbSe nanowires (NWs), and electric-field, directed assembly was employed to align NW arrays to form the semiconducting channels of field-effect transistors (FETs). Electrical measurements revealed as-aligned NWs in bottom, gold, contact FETs are predominantly p-type ambipolar, consistent with the presentation of small barriers to electron and hole injection for this low band gap semiconductor. Exposing the NW FET to UV-ozone p-doped the NWs, illustrating the sensitivity of PbSe to oxygen, but controlled oxidation allowed the fabrication of unipolar p-type FETs. Selectively exposing the contact region of as-aligned NW FETs to low to moderate concentrations of hydrazine, commonly used to n-dope nanocrystal and NW devices, switched the predominantly p- to n-type ambipolar behavior as if the entire NW channel was exposed. At these hydrazine concentrations, charge transfer doping the metal-semiconductor interface dominates the FET characteristics. Only upon exposing the NW FETs to high hydrazine concentrations did charge transfer doping of the NW channel overcome the large intrinsic, thermally generated carrier concentration of this low band gap material, modulating the NW carrier concentration and forming unipolar n-type FETs. Pulling low vacuum removed surface hydrazine returning the predominantly p-type ambipolar FET behavior. Doping and dedoping with hydrazine were repeatedly reversible. By applying surface modification to n- and p-dope PbSe NW FETs, we fabricated the first PbSe NW inverters, demonstrating the promise of these nanostructured materials in integrated circuits. PMID:21405024

  15. Ambipolar organic field-effect transistors based on a low band gap semiconductor with balanced hole and electron mobilities

    NASA Astrophysics Data System (ADS)

    Chikamatsu, Masayuki; Mikami, Takefumi; Chisaka, Jiro; Yoshida, Yuji; Azumi, Reiko; Yase, Kiyoshi; Shimizu, Akihiro; Kubo, Takashi; Morita, Yasushi; Nakasuji, Kazuhiro

    2007-07-01

    The authors have demonstrated the thin-film properties and the ambipolar transport of a delocalized singlet biradical hydrocarbon with two phenalenyl radical moieties (Ph2-IDPL). The organic field-effect transistors (OFETs) based on Ph2-IDPL exhibit ambipolar transport with balanced hole and electron mobilities in the order of 10-3cm2/Vs. The Ph2-IDPL film is an organic semiconductor with a low band gap of 0.8eV and has small injection barriers from gold electrodes to both the highest occupied molecular orbital and the lowest unoccupied molecular orbital. A complementary metal-oxide-semiconductor-like inverter using two identical Ph2-IDPL based ambipolar OFETs shows a sharp inversion of the input voltage with high gain.

  16. Effect of Electronic Acceptor Segments on Photophysical Properties of Low-Band-Gap Ambipolar Polymers

    PubMed Central

    Li, Yuanzuo; Cui, Jingang; Zhao, Jianing; Liu, Jinglin; Song, Peng; Ma, Fengcai

    2013-01-01

    Stimulated by a recent experimental report, charge transfer and photophysical properties of donor-acceptor ambipolar polymer were studied with the quantum chemistry calculation and the developed 3D charge difference density method. The effects of electronic acceptor strength on the structure, energy levels, electron density distribution, ionization potentials, and electron affinities were also obtained to estimate the transporting ability of hole and electron. With the developed 3D charge difference density, one visualizes the charge transfer process, distinguishes the role of molecular units, and finds the relationship between the role of DPP and excitation energy for the three polymers during photo-excitation. PMID:23365549

  17. Synthesis, crystal packing, and ambipolar carrier transport property of twisted dibenzo[g,p]chrysenes.

    PubMed

    Ueda, Yasuyuki; Tsuji, Hayato; Tanaka, Hideyuki; Nakamura, Eiichi

    2014-06-01

    A versatile method for the synthesis of dibenzo[g,p]chrysene (DBC) derivatives based on regio- and stereoselective stannyllithiation to diarylacetylenes is described. This method affords a variety of DBCs possessing both electron-donating and electron-withdrawing functional groups. These twisted molecules take brickwork packing structures in single crystals. Thus, ambipolar carrier transport properties with mobility values of up to 10(-3)  cm(2)  V(-1)  s(-1) in the amorphous state were achieved. Functional groups on DBC frameworks are considered to increase carrier mobility through the enhancement of intermolecular interactions in the brickwork packing structures.

  18. High-Mobility Ambipolar Organic Thin-Film Transistor Processed From a Nonchlorinated Solvent.

    PubMed

    Sonar, Prashant; Chang, Jingjing; Kim, Jae H; Ong, Kok-Haw; Gann, Eliot; Manzhos, Sergei; Wu, Jishan; McNeill, Christopher R

    2016-09-21

    Polymer semiconductor PDPPF-DFT, which combines furan-substituted diketopyrrolopyrrole (DPP) and a 3,4-difluorothiophene base, has been designed and synthesized. PDPPF-DFT polymer semiconductor thin film processed from nonchlorinated hexane is used as an active layer in thin-film transistors. As a result, balanced hole and electron mobilities of 0.26 and 0.12 cm(2)/(V s) are achieved for PDPPF-DFT. This is the first report of using nonchlorinated hexane solvent for fabricating high-performance ambipolar thin-film transistor devices.

  19. Giant ambipolar Rashba effect in the semiconductor BiTeI.

    PubMed

    Crepaldi, A; Moreschini, L; Autès, G; Tournier-Colletta, C; Moser, S; Virk, N; Berger, H; Bugnon, Ph; Chang, Y J; Kern, K; Bostwick, A; Rotenberg, E; Yazyev, O V; Grioni, M

    2012-08-31

    We observe a giant spin-orbit splitting in the bulk and surface states of the noncentrosymmetric semiconductor BiTeI. We show that the Fermi level can be placed in the valence or in the conduction band by controlling the surface termination. In both cases, it intersects spin-polarized bands, in the corresponding surface depletion and accumulation layers. The momentum splitting of these bands is not affected by adsorbate-induced changes in the surface potential. These findings demonstrate that two properties crucial for enabling semiconductor-based spin electronics-a large, robust spin splitting and ambipolar conduction-are present in this material. PMID:23002871

  20. Giant Ambipolar Rashba Effect in the Semiconductor BiTeI

    NASA Astrophysics Data System (ADS)

    Crepaldi, A.; Moreschini, L.; Autès, G.; Tournier-Colletta, C.; Moser, S.; Virk, N.; Berger, H.; Bugnon, Ph.; Chang, Y. J.; Kern, K.; Bostwick, A.; Rotenberg, E.; Yazyev, O. V.; Grioni, M.

    2012-08-01

    We observe a giant spin-orbit splitting in the bulk and surface states of the noncentrosymmetric semiconductor BiTeI. We show that the Fermi level can be placed in the valence or in the conduction band by controlling the surface termination. In both cases, it intersects spin-polarized bands, in the corresponding surface depletion and accumulation layers. The momentum splitting of these bands is not affected by adsorbate-induced changes in the surface potential. These findings demonstrate that two properties crucial for enabling semiconductor-based spin electronics—a large, robust spin splitting and ambipolar conduction—are present in this material.

  1. Balanced Ambipolar Poly(diketopyrrolopyrrole-alt-tetrafluorobenzene) Semiconducting Polymers Synthesized via Direct Arylation Polymerization.

    PubMed

    Wang, Kai; Wang, Guojie; Wang, Mingfeng

    2015-12-01

    The synthesis of an ambipolar π-conjugated copolymer consisting of alternating diketopyrrolopyrrole and tetrafluorobenzene via direct arylation polymerization (DAP) is reported. Two different combinations of monomers are investigated under various catalytic conditions for DAP. The target polymer obtained under an optimized catalytic condition shows minimal structural defects, a number-average molecular weight of 33.2 kDa, and balanced electron and hole mobility of 1 × 10(-2) cm(2) V(-1) S(-1) in the organic field-effect transistors fabricated and tested under ambient conditions.

  2. High-Mobility Ambipolar Organic Thin-Film Transistor Processed From a Nonchlorinated Solvent.

    PubMed

    Sonar, Prashant; Chang, Jingjing; Kim, Jae H; Ong, Kok-Haw; Gann, Eliot; Manzhos, Sergei; Wu, Jishan; McNeill, Christopher R

    2016-09-21

    Polymer semiconductor PDPPF-DFT, which combines furan-substituted diketopyrrolopyrrole (DPP) and a 3,4-difluorothiophene base, has been designed and synthesized. PDPPF-DFT polymer semiconductor thin film processed from nonchlorinated hexane is used as an active layer in thin-film transistors. As a result, balanced hole and electron mobilities of 0.26 and 0.12 cm(2)/(V s) are achieved for PDPPF-DFT. This is the first report of using nonchlorinated hexane solvent for fabricating high-performance ambipolar thin-film transistor devices. PMID:27595165

  3. A planarized triphenylborane mesogen: discotic liquid crystals with ambipolar charge-carrier transport properties.

    PubMed

    Kushida, Tomokatsu; Shuto, Ayumi; Yoshio, Masafumi; Kato, Takashi; Yamaguchi, Shigehiro

    2015-06-01

    A discotic liquid-crystalline (LC) material, consisting of a planarized triphenylborane mesogen, was synthesized. X-ray diffraction analysis confirmed that this compound forms a hexagonal columnar LC phase with an interfacial distance of 3.57 Å between the discs. At ambient temperature, this boron-centered discotic liquid crystal exhibited ambipolar carrier transport properties with electron and hole mobility values of approximately 10(-3) and 3×10(-5)  cm(2)  V(-1)  s(-1), respectively.

  4. Influence of plasma diffusion losses on dust charge relaxation in discharge afterglow

    SciTech Connect

    Coueedel, L.; Mikikian, M.; Boufendi, L.

    2008-09-07

    The influence of diffusive losses on residual dust charge in a complex plasma afterglow has been investigated. The dust residual charges were simulated based on a model developed to describe complex plasma decay. The experimental and simulated data show that the transition from ambipolar to free diffusion in the decaying plasma plays a significant role in determining the residual dust particle charges. The presence of positively charged dust particles is explained by a broadening of the charge distribution function in the afterglow plasma.

  5. Ambipolar Electric Field, Photoelectrons, and Their Role in Atmospheric Escape From Hot Jupiters

    NASA Technical Reports Server (NTRS)

    Cohen, O.; Glocer, A.

    2012-01-01

    Atmospheric mass loss from Hot Jupiters can be large due to the close proximity of these planets to their host star and the strong radiation the planetary atmosphere receives. On Earth, a major contribution to the acceleration of atmospheric ions comes from the vertical separation of ions and electrons, and the generation of the ambipolar electric field. This process, known as the "polar wind," is responsible for the transport of ionospheric constituents to Earth's magnetosphere, where they are well observed. The polar wind can also be enhanced by a relatively small fraction of super-thermal electrons (photoelectrons) generated by photoionization.We formulate a simplified calculation of the effect of the ambipolar electric field and the photoelectrons on the ion scale height in a generalized manner. We find that the ion scale height can be increased by a factor of 2-15 due to the polar wind effects. We also estimate a lower limit of an order of magnitude increase of the ion density and the atmospheric mass-loss rate when polar wind effects are included.

  6. Surface transfer doping induced effective modulation on ambipolar characteristics of few-layer black phosphorus.

    PubMed

    Xiang, Du; Han, Cheng; Wu, Jing; Zhong, Shu; Liu, Yiyang; Lin, Jiadan; Zhang, Xue-Ao; Ping Hu, Wen; Özyilmaz, Barbaros; Neto, A H Castro; Wee, Andrew Thye Shen; Chen, Wei

    2015-03-12

    Black phosphorus, a fast emerging two-dimensional material, has been configured as field effect transistors, showing a hole-transport-dominated ambipolar characteristic. Here we report an effective modulation on ambipolar characteristics of few-layer black phosphorus transistors through in situ surface functionalization with caesium carbonate (Cs2CO3) and molybdenum trioxide (MoO3), respectively. Cs2CO3 is found to strongly electron dope black phosphorus. The electron mobility of black phosphorus is significantly enhanced to ~27 cm(2) V(-1) s(-1) after 10 nm Cs2CO3 modification, indicating a greatly improved electron-transport behaviour. In contrast, MoO3 decoration demonstrates a giant hole-doping effect. In situ photoelectron spectroscopy characterization reveals significant surface charge transfer occurring at the dopants/black phosphorus interfaces. Moreover, the surface-doped black phosphorus devices exhibit a largely enhanced photodetection behaviour. Our findings coupled with the tunable nature of the surface transfer doping scheme ensure black phosphorus as a promising candidate for further complementary logic electronics.

  7. Surface transfer doping induced effective modulation on ambipolar characteristics of few-layer black phosphorus

    NASA Astrophysics Data System (ADS)

    Xiang, Du; Han, Cheng; Wu, Jing; Zhong, Shu; Liu, Yiyang; Lin, Jiadan; Zhang, Xue-Ao; Ping Hu, Wen; Özyilmaz, Barbaros; Neto, A. H. Castro; Wee, Andrew Thye Shen; Chen, Wei

    2015-03-01

    Black phosphorus, a fast emerging two-dimensional material, has been configured as field effect transistors, showing a hole-transport-dominated ambipolar characteristic. Here we report an effective modulation on ambipolar characteristics of few-layer black phosphorus transistors through in situ surface functionalization with caesium carbonate (Cs2CO3) and molybdenum trioxide (MoO3), respectively. Cs2CO3 is found to strongly electron dope black phosphorus. The electron mobility of black phosphorus is significantly enhanced to ~27 cm2 V-1 s-1 after 10 nm Cs2CO3 modification, indicating a greatly improved electron-transport behaviour. In contrast, MoO3 decoration demonstrates a giant hole-doping effect. In situ photoelectron spectroscopy characterization reveals significant surface charge transfer occurring at the dopants/black phosphorus interfaces. Moreover, the surface-doped black phosphorus devices exhibit a largely enhanced photodetection behaviour. Our findings coupled with the tunable nature of the surface transfer doping scheme ensure black phosphorus as a promising candidate for further complementary logic electronics.

  8. Polymer-sorted semiconducting carbon nanotube networks for high-performance ambipolar field-effect transistors.

    PubMed

    Schiessl, Stefan P; Fröhlich, Nils; Held, Martin; Gannott, Florentina; Schweiger, Manuel; Forster, Michael; Scherf, Ullrich; Zaumseil, Jana

    2015-01-14

    Efficient selection of semiconducting single-walled carbon nanotubes (SWNTs) from as-grown nanotube samples is crucial for their application as printable and flexible semiconductors in field-effect transistors (FETs). In this study, we use atactic poly(9-dodecyl-9-methyl-fluorene) (a-PF-1-12), a polyfluorene derivative with asymmetric side-chains, for the selective dispersion of semiconducting SWNTs with large diameters (>1 nm) from plasma torch-grown SWNTs. Lowering the molecular weight of the dispersing polymer leads to a significant improvement of selectivity. Combining dense semiconducting SWNT networks deposited from an enriched SWNT dispersion with a polymer/metal-oxide hybrid dielectric enables transistors with balanced ambipolar, contact resistance-corrected mobilities of up to 50 cm(2)·V(-1)·s(-1), low ohmic contact resistance, steep subthreshold swings (0.12-0.14 V/dec) and high on/off ratios (10(6)) even for short channel lengths (<10 μm). These FETs operate at low voltages (<3 V) and show almost no current hysteresis. The resulting ambipolar complementary-like inverters exhibit gains up to 61. PMID:25493421

  9. AMBIPOLAR ELECTRIC FIELD, PHOTOELECTRONS, AND THEIR ROLE IN ATMOSPHERIC ESCAPE FROM HOT JUPITERS

    SciTech Connect

    Cohen, O.; Glocer, A.

    2012-07-01

    Atmospheric mass loss from Hot Jupiters can be large due to the close proximity of these planets to their host star and the strong radiation the planetary atmosphere receives. On Earth, a major contribution to the acceleration of atmospheric ions comes from the vertical separation of ions and electrons, and the generation of the ambipolar electric field. This process, known as the 'polar wind', is responsible for the transport of ionospheric constituents to Earth's magnetosphere, where they are well observed. The polar wind can also be enhanced by a relatively small fraction of super-thermal electrons (photoelectrons) generated by photoionization. We formulate a simplified calculation of the effect of the ambipolar electric field and the photoelectrons on the ion scale height in a generalized manner. We find that the ion scale height can be increased by a factor of 2-15 due to the polar wind effects. We also estimate a lower limit of an order of magnitude increase of the ion density and the atmospheric mass-loss rate when polar wind effects are included.

  10. Polymer-Sorted Semiconducting Carbon Nanotube Networks for High-Performance Ambipolar Field-Effect Transistors

    PubMed Central

    2014-01-01

    Efficient selection of semiconducting single-walled carbon nanotubes (SWNTs) from as-grown nanotube samples is crucial for their application as printable and flexible semiconductors in field-effect transistors (FETs). In this study, we use atactic poly(9-dodecyl-9-methyl-fluorene) (a-PF-1-12), a polyfluorene derivative with asymmetric side-chains, for the selective dispersion of semiconducting SWNTs with large diameters (>1 nm) from plasma torch-grown SWNTs. Lowering the molecular weight of the dispersing polymer leads to a significant improvement of selectivity. Combining dense semiconducting SWNT networks deposited from an enriched SWNT dispersion with a polymer/metal-oxide hybrid dielectric enables transistors with balanced ambipolar, contact resistance-corrected mobilities of up to 50 cm2·V–1·s–1, low ohmic contact resistance, steep subthreshold swings (0.12–0.14 V/dec) and high on/off ratios (106) even for short channel lengths (<10 μm). These FETs operate at low voltages (<3 V) and show almost no current hysteresis. The resulting ambipolar complementary-like inverters exhibit gains up to 61. PMID:25493421

  11. Leveraging the ambipolar transport in polymeric field-effect transistors via blending with liquid-phase exfoliated graphene.

    PubMed

    El Gemayel, Mirella; Haar, Sébastien; Liscio, Fabiola; Schlierf, Andrea; Melinte, Georgian; Milita, Silvia; Ersen, Ovidiu; Ciesielski, Artur; Palermo, Vincenzo; Samorì, Paolo

    2014-07-23

    Enhancement in the ambipolar behavior of field-effect transistors based on an n-type polymer, P(NDI2OD-T2), is obtained by co-deposition with liquid-phase exfoliated graphene. This approach provides a prospective pathway for the application of graphene-based nanocomposites for logic circuits.

  12. Electron and hole polaron accumulation in low-bandgap ambipolar donor-acceptor polymer transistors imaged by infrared microscopy

    NASA Astrophysics Data System (ADS)

    Khatib, O.; Mueller, A. S.; Stinson, H. T.; Yuen, J. D.; Heeger, A. J.; Basov, D. N.

    2014-12-01

    A resurgence in the use of the donor-acceptor approach in synthesizing conjugated polymers has resulted in a family of high-mobility ambipolar systems with exceptionally narrow energy bandgaps below 1 eV. The ability to transport both electrons and holes is critical for device applications such as organic light-emitting diodes and transistors. Infrared spectroscopy offers direct access to the low-energy excitations associated with injected charge carriers. Here we use a diffraction-limited IR microscope to probe the spectroscopic signatures of electron and hole injection in the conduction channel of an organic field-effect transistor based on an ambipolar DA polymer polydiketopyrrolopyrrole-benzobisthiadiazole. We observe distinct polaronic absorptions for both electrons and holes and spatially map the carrier distribution from the source to drain electrodes for both unipolar and ambipolar biasing regimes. For ambipolar device configurations, we observe the spatial evolution of hole-induced to electron-induced polaron absorptions throughout the transport path. Our work provides a platform for combined transport and infrared studies of organic semiconductors on micron length scales relevant to functional devices.

  13. Beyond modulation doping: Engineering a semiconductor to be ambipolar, or making an ON-OFF-ON transistor

    SciTech Connect

    Gupta, K. Das; Croxall, A. F.; Zheng, B.; Sfigakis, F.; Farrer, I.; Nicoll, C. A.; Beere, H. E.; Ritchie, D. A.

    2014-04-24

    Semiconductors are traditionaly either p-type or n-type, meaning that the mobile charge carriers in them are either 'holes' in the valence band or electrons in the conduction band. Ambipolar conduction implies that the experimenter should be able to populate the same channel with either electrons or holes in a controlled manner. This has been shown to be possible in newer materials like Graphene and some organic semiconductors. 'Ambipolarity' can open up new device possibilities as well as new ways to study fundamental scattering mechanisms in semiconductors. However, achieving this in a conventional high mobility structure like a GaAs-AlGaAs heterostructure/quantum well requires new thinking. It was realized, that to do this modulation doping must be given up and techniques to make an undoped heterostructure conduct, must be developed first. Such structures have been developed by only a few groups worldwide. They are of great interest to low temperature physicists working with Quantum Hall states and mesoscopic/nano structures in the ballistic regime. We discuss the reason behind this interest and the analysis of scattering mechanisms in such structures. Finally very recent experimental success in developing fully gate controlled ambipolar structures where both electron and hole mobilites exceed 1 million cm{sup 2}/Vs at low temperatures (T∼1Kelvin) are discussed. Such gated ambipolar structures can be used to analyse scattering mechanisms in ultra-high mobility 2dimensional electron and hole gases in a way that is not possible using other techniques.

  14. Light emission from an ambipolar semiconducting polymer field-effect transistor

    NASA Astrophysics Data System (ADS)

    Swensen, James Sherman

    The successful demonstration of light emitting field-effect transistors (LEFETs) has been worked towards for years within the organic electronics community. The belief was held that if an ambipolar FET could be developed with high enough density of both electrons and holes within the channel region of an FET simultaneously, then recombination of those carriers would result in electroluminescence. The challenge to demonstrating such a device centered on the issue of electron transport; why was electron transport not observed for nearly all SCPs in a field-effect transistor? Use of a low dielectric constant material to passivate inorganic dielectrics in order to observe electron transport for semiconducting conjugated polymers in a field-effect transistor was verified. A different material, polypropylene-co-1-butene, was shown to passivate various inorganic insulators to eliminate or reduce trap states such that electron transport can be observed for SCPs. Another challenge to demonstrating an LEFET involved developing a method to deposit a low work function metal as either the source or the drain electrode in the FET structure. In this research, a process was developed in which an SCP FET can be fabricated inside of a nitrogen glove box where one electrode is a high work function metal and the other electrode is a low work function metal with the precision of photolithography using a silicon shadow mask and an angled evaporation technique. As a result, the SCP LED electrodes architecture was successfully transferred to an FET platform as the source and drain electrodes, which we "call two-color electrodes." In summary, by combining the passivation layer technology which allows for electron transport and the silicon shadow mask/angled evaporation technique which gives two color electrodes, ambipolar SCP LEFETs were demonstrated. Transport data show ambipolar behavior. Recombination of electrons and holes result in a narrow zone of light emission within the channel

  15. Transparent ambipolar organic thin film transistors based on multilayer transparent source-drain electrodes

    NASA Astrophysics Data System (ADS)

    Zhang, Nan; Hu, Yongsheng; Lin, Jie; Li, Yantao; Liu, Xingyuan

    2016-08-01

    A fabrication method for transparent ambipolar organic thin film transistors with transparent Sb2O3/Ag/Sb2O3 (SAS) source and drain electrodes has been developed. A pentacene/N,N'-ditridecylperylene-3,4,9,10-tetracarboxylic di-imide (PTCDI-C13) bilayer heterojunction is used as the active semiconductor. The electrodes are deposited by room temperature electron beam evaporation. The devices are fabricated without damaging the active layers. The SAS electrodes have high transmittance (82.5%) and low sheet resistance (8 Ω/sq). High performance devices with hole and electron mobilities of 0.3 cm2/V s and 0.027 cm2/V s, respectively, and average visible range transmittance of 72% were obtained. These transistors have potential for transparent logic integrated circuit applications.

  16. Reversible conversion of dominant polarity in ambipolar polymer/graphene oxide hybrids

    SciTech Connect

    Zhou, Ye; Han, Su -Ting; Sonar, Prashant; Ma, Xinlei; Chen, Jihua; Zheng, Zijian; Roy, V. A. L.

    2015-03-24

    The possibility to selectively modulate the charge carrier transport in semiconducting materials is extremely challenging for the development of high performance and low-power consuming logic circuits. Systematical control over the polarity (electrons and holes) in transistor based on solution processed layer by layer polymer/graphene oxide hybrid system has been demonstrated. The conversion degree of the polarity is well controlled and reversible by trapping the opposite carriers. Basically, an electron device is switched to be a hole only device or vice versa. Finally, a hybrid layer ambipolar inverter is demonstrated in which almost no leakage of opposite carrier is found. We conclude that this hybrid material has wide range of applications in planar p-n junctions and logic circuits for high-throughput manufacturing of printed electronic circuits.

  17. Reversible conversion of dominant polarity in ambipolar polymer/graphene oxide hybrids

    DOE PAGES

    Zhou, Ye; Han, Su -Ting; Sonar, Prashant; Ma, Xinlei; Chen, Jihua; Zheng, Zijian; Roy, V. A. L.

    2015-03-24

    The possibility to selectively modulate the charge carrier transport in semiconducting materials is extremely challenging for the development of high performance and low-power consuming logic circuits. Systematical control over the polarity (electrons and holes) in transistor based on solution processed layer by layer polymer/graphene oxide hybrid system has been demonstrated. The conversion degree of the polarity is well controlled and reversible by trapping the opposite carriers. Basically, an electron device is switched to be a hole only device or vice versa. Finally, a hybrid layer ambipolar inverter is demonstrated in which almost no leakage of opposite carrier is found. Wemore » conclude that this hybrid material has wide range of applications in planar p-n junctions and logic circuits for high-throughput manufacturing of printed electronic circuits.« less

  18. In situ tuning and probing the ambipolar field effect on multiwall carbon nanotubes

    SciTech Connect

    Chen, Li-Ying; Chang, Chia-Seng

    2014-12-15

    We report a method of fabricating ultra-clean and hysteresis-free multiwall carbon nanotube field-effect transistors (CNFETs) inside the ultra-high vacuum transmission electron microscope equipped with a movable gold tip as a local gate. By tailoring the shell structure of the nanotube and varying the drain-source voltage (V{sub ds}), we can tune the electronic characteristic of a multiwall CNFET in situ. We have also found that the Schottky barriers of a multiwall CNFET are generated within the nanotube, but not at the nanotube/electrode contacts, and the barrier height has been derived. We have subsequently demonstrated the ambipolar characteristics of the CNFET with concurrent high-resolution imaging and local gating.

  19. Memory operation devices based on light-illumination ambipolar carbon-nanotube thin-film-transistors

    SciTech Connect

    Aïssa, B.; Nedil, M.; Kroeger, J.; Haddad, T.; Rosei, F.

    2015-09-28

    We report the memory operation behavior of a light illumination ambipolar single-walled carbon nanotube thin film field-effect transistors devices. In addition to the high electronic-performance, such an on/off transistor-switching ratio of 10{sup 4} and an on-conductance of 18 μS, these memory devices have shown a high retention time of both hole and electron-trapping modes, reaching 2.8 × 10{sup 4} s at room temperature. The memory characteristics confirm that light illumination and electrical field can act as an independent programming/erasing operation method. This could be a fundamental step toward achieving high performance and stable operating nanoelectronic memory devices.

  20. Ambipolar escape from Venus, Mars and Titan, and negative ions at Titan

    NASA Astrophysics Data System (ADS)

    Coates, Andrew

    2016-07-01

    Ionospheric photoelectrons are a natural product of the photo-ionisation of planetary atmospheres. Their energy spectrum is distinctive and depends on the solar spectrum in the EUV and X-ray region. On production, the energetic electrons move along the magnetic field (open or draped), setting up an ambipolar electric field which can extract ions. This provides an escape mechanism similar to Earth's 'polar wind'. As these objects are unmagnetised, this produces an extended escape mechanism over the whole sunlit ionosphere. Here, we review recent measurements of photoelectrons far from the parent objects at Venus, Mars and Titan, from Venus Express, Mars Express, Maven and Cassini, and discuss similarities and related escape rates. We also review the pioneering observations of the remarkably heavy negative ions discovered in Titan's ionosphere.

  1. Ambipolar nonvolatile memory based on a quantum-dot transistor with a nanoscale floating gate

    NASA Astrophysics Data System (ADS)

    Che, Yongli; Zhang, Yating; Cao, Xiaolong; Song, Xiaoxian; Cao, Mingxuan; Dai, Haitao; Yang, Junbo; Zhang, Guizhong; Yao, Jianquan

    2016-07-01

    Using only solution processing methods, we developed ambipolar quantum-dot (QD) transistor floating-gate memory (FGM) that uses Au nanoparticles as a floating gate. Because of the bipolarity of the active channel of PbSe QDs, the memory could easily trap holes or electrons in the floating gate by programming/erasing (P/E) operations, which could shift the threshold voltage both up and down. As a result, the memory exhibited good programmable memory characteristics: a large memory window (ΔVth ˜ 15 V) and a long retention time (>105 s). The magnitude of ΔVth depended on both P/E voltages and the bias voltage (VDS): ΔVth was a cubic function to VP/E and linearly depended on VDS. Therefore, this FGM based on a QD transistor is a promising alternative to its inorganic counterparts owing to its advantages of bipolarity, high mobility, low cost, and large-area production.

  2. Tetracene dicarboxylic imide and its disulfide: synthesis of ambipolar organic semiconductors for organic photovoltaic cells.

    PubMed

    Okamoto, Toshihiro; Suzuki, Tsuyoshi; Tanaka, Hideyuki; Hashizume, Daisuke; Matsuo, Yutaka

    2012-01-01

    We have designed and synthesized a new donor/acceptor-type tetracene derivative by the introduction of dicarboxylic imide and disulfide groups as electron-withdrawing and -donating units, respectively. The prepared compounds, tetracene dicarboxylic imide (TI) and its disulfide (TIDS) have high chemical and electrochemical stability as well as long-wavelength absorptions of up to 886 nm in the thin films. The crystal packing structure of TIDS molecules features face-to-face π-stacking, derived from dipole-dipole interactions. Notably, TIDS exhibited ambipolar properties of both electron-donating and -accepting natures in p-n and p-i-n heterojunction organic thin-film photovoltaic devices. Accordingly, TI and TIDS are expected to be promising compounds for designing new organic semiconductors.

  3. Coexistence of Midgap Antiferromagnetic and Mott States in Undoped, Hole- and Electron-Doped Ambipolar Cuprates.

    PubMed

    Yin, Xinmao; Zeng, Shengwei; Das, Tanmoy; Baskaran, G; Asmara, Teguh Citra; Santoso, Iman; Yu, Xiaojiang; Diao, Caozheng; Yang, Ping; Breese, Mark B H; Venkatesan, T; Lin, Hsin; Ariando; Rusydi, Andrivo

    2016-05-13

    We report the first observation of the coexistence of a distinct midgap state and a Mott state in undoped and their evolution in electron and hole-doped ambipolar Y_{0.38}La_{0.62}(Ba_{0.82}La_{0.18})_{2}Cu_{3}O_{y} films using spectroscopic ellipsometry and x-ray absorption spectroscopies at the O K and Cu L_{3,2} edges. Supported by theoretical calculations, the midgap state is shown to originate from antiferromagnetic correlation. Surprisingly, while the magnetic state collapses and its correlation strength weakens with dopings, the Mott state in contrast moves toward a higher energy and its correlation strength increases. Our result provides important clues to the mechanism of electronic correlation strengths and superconductivity in cuprates. PMID:27232036

  4. Reversible conversion of dominant polarity in ambipolar polymer/graphene oxide hybrids.

    PubMed

    Zhou, Ye; Han, Su-Ting; Sonar, Prashant; Ma, Xinlei; Chen, Jihua; Zheng, Zijian; Roy, V A L

    2015-01-01

    The possibility to selectively modulate the charge carrier transport in semiconducting materials is extremely challenging for the development of high performance and low-power consuming logic circuits. Systematical control over the polarity (electrons and holes) in transistor based on solution processed layer by layer polymer/graphene oxide hybrid system has been demonstrated. The conversion degree of the polarity is well controlled and reversible by trapping the opposite carriers. Basically, an electron device is switched to be a hole only device or vice versa. Finally, a hybrid layer ambipolar inverter is demonstrated in which almost no leakage of opposite carrier is found. This hybrid material has wide range of applications in planar p-n junctions and logic circuits for high-throughput manufacturing of printed electronic circuits.

  5. Reversible Conversion of Dominant Polarity in Ambipolar Polymer/Graphene Oxide Hybrids

    PubMed Central

    Zhou, Ye; Han, Su-Ting; Sonar, Prashant; Ma, Xinlei; Chen, Jihua; Zheng, Zijian; Roy, V. A. L.

    2015-01-01

    The possibility to selectively modulate the charge carrier transport in semiconducting materials is extremely challenging for the development of high performance and low-power consuming logic circuits. Systematical control over the polarity (electrons and holes) in transistor based on solution processed layer by layer polymer/graphene oxide hybrid system has been demonstrated. The conversion degree of the polarity is well controlled and reversible by trapping the opposite carriers. Basically, an electron device is switched to be a hole only device or vice versa. Finally, a hybrid layer ambipolar inverter is demonstrated in which almost no leakage of opposite carrier is found. This hybrid material has wide range of applications in planar p-n junctions and logic circuits for high-throughput manufacturing of printed electronic circuits. PMID:25801827

  6. Ambipolar-transporting coaxial nanotubes with a tailored molecular graphene–fullerene heterojunction

    PubMed Central

    Yamamoto, Yohei; Zhang, Guanxin; Jin, Wusong; Fukushima, Takanori; Ishii, Noriyuki; Saeki, Akinori; Seki, Shu; Tagawa, Seiichi; Minari, Takeo; Tsukagoshi, Kazuhito; Aida, Takuzo

    2009-01-01

    Despite a large steric bulk of C60, a molecular graphene with a covalently linked C60 pendant [hexabenzocoronene (HBC)–C60; 1] self-assembles into a coaxial nanotube whose wall consists of a graphite-like π-stacked HBC array, whereas the nanotube surface is fully covered by a molecular layer of clustering C60. Because of this explicit coaxial configuration, the nanotube exhibits an ambipolar character in the field-effect transistor output [hole mobility (μh) = 9.7 × 10−7 cm2 V−1 s−1; electron mobility (μe) = 1.1 × 10−5 cm2 V−1 s−1] and displays a photovoltaic response upon light illumination. Successful coassembly of 1 and an HBC derivative without C60 (2) allows for tailoring the p/n heterojunction in the nanotube, so that its ambipolar carrier transport property can be optimized for enhancing the open-circuit voltage in the photovoltaic output. As evaluated by an electrodeless method called flash-photolysis time-resolved microwave conductivity technique, the intratubular hole mobility (2.0 cm2 V−1 s−1) of a coassembled nanotube containing 10 mol % of HBC–C60 (1) is as large as the intersheet mobility in graphite. The homotropic nanotube of 2 blended with a soluble C60 derivative [(6,6)-phenyl C61 butyric acid methyl ester] displayed a photovoltaic response with a much different composition dependency, where the largest open-circuit voltage attained was obviously lower than that realized by the coassembly of 1 and 2. PMID:19940243

  7. Ambipolar, low-voltage and low-hysteresis PbSe nanowire field-effect transistors by electrolyte gating

    NASA Astrophysics Data System (ADS)

    Lokteva, Irina; Thiemann, Stefan; Gannott, Florentina; Zaumseil, Jana

    2013-05-01

    Semiconductor nanowire field-effect transistors (FETs) are interesting for fundamental studies of charge transport as well as possible applications in electronics. Here, we report low-voltage, low-hysteresis and ambipolar PbSe nanowire FETs using electrolyte-gating with ionic liquids and ion gels. We obtain balanced hole and electron mobilities at gate voltages below 1 V. Due to the large effective capacitance of the ionic liquids and thus high charge carrier densities electrolyte-gated nanowire FETs are much less affected by external doping and traps than nanowire FETs with traditional dielectrics such as SiO2. The observed current-voltage characteristics and on/off ratios indicate almost completely transparent Schottky barriers and efficient ambipolar charge injection into a low band gap one-dimensional semiconductor. Finally, we explore the possibility of applying these ambipolar nanowire FETs in complementary inverters for printed electronics.Semiconductor nanowire field-effect transistors (FETs) are interesting for fundamental studies of charge transport as well as possible applications in electronics. Here, we report low-voltage, low-hysteresis and ambipolar PbSe nanowire FETs using electrolyte-gating with ionic liquids and ion gels. We obtain balanced hole and electron mobilities at gate voltages below 1 V. Due to the large effective capacitance of the ionic liquids and thus high charge carrier densities electrolyte-gated nanowire FETs are much less affected by external doping and traps than nanowire FETs with traditional dielectrics such as SiO2. The observed current-voltage characteristics and on/off ratios indicate almost completely transparent Schottky barriers and efficient ambipolar charge injection into a low band gap one-dimensional semiconductor. Finally, we explore the possibility of applying these ambipolar nanowire FETs in complementary inverters for printed electronics. Electronic supplementary information (ESI) available: Diameter distribution

  8. Sensors: A Highly Sensitive Diketopyrrolopyrrole-Based Ambipolar Transistor for Selective Detection and Discrimination of Xylene Isomers (Adv. Mater. 21/2016).

    PubMed

    Wang, Bin; Huynh, Tan-Phat; Wu, Weiwei; Hayek, Naseem; Do, Thu Trang; Cancilla, John C; Torrecilla, Jose S; Nahid, Masrur Morshed; Colwell, John M; Gazit, Oz M; Puniredd, Sreenivasa Reddy; McNeill, Christopher R; Sonar, Prashant; Haick, Hossam

    2016-06-01

    An ambipolar organic field-effect transistor (OFET) based on poly(diketopyrrolopyrrole-terthiophene) (PDPPHD-T3) is shown by P. Sonar, H. Haick, and co-workers on page 4012 to sensitively detect xylene isomers at low to 40 ppm level in multiple sensing features. Combined with pattern-recognition algorithms, a sole ambipolar FET sensor, rather than arrays of sensors, is able to discriminate highly similar xylene structural isomers from each other. PMID:27246920

  9. Sensors: A Highly Sensitive Diketopyrrolopyrrole-Based Ambipolar Transistor for Selective Detection and Discrimination of Xylene Isomers (Adv. Mater. 21/2016).

    PubMed

    Wang, Bin; Huynh, Tan-Phat; Wu, Weiwei; Hayek, Naseem; Do, Thu Trang; Cancilla, John C; Torrecilla, Jose S; Nahid, Masrur Morshed; Colwell, John M; Gazit, Oz M; Puniredd, Sreenivasa Reddy; McNeill, Christopher R; Sonar, Prashant; Haick, Hossam

    2016-06-01

    An ambipolar organic field-effect transistor (OFET) based on poly(diketopyrrolopyrrole-terthiophene) (PDPPHD-T3) is shown by P. Sonar, H. Haick, and co-workers on page 4012 to sensitively detect xylene isomers at low to 40 ppm level in multiple sensing features. Combined with pattern-recognition algorithms, a sole ambipolar FET sensor, rather than arrays of sensors, is able to discriminate highly similar xylene structural isomers from each other.

  10. Control of Threshold Voltage for Top-Gated Ambipolar Field-Effect Transistor by Gate Buffer Layer.

    PubMed

    Khim, Dongyoon; Shin, Eul-Yong; Xu, Yong; Park, Won-Tae; Jin, Sung-Ho; Noh, Yong-Young

    2016-07-13

    The threshold voltage and onset voltage for p-channel and n-channel regimes of solution-processed ambipolar organic transistors with top-gate/bottom-contact (TG/BC) geometry were effectively tuned by gate buffer layers in between the gate electrode and the dielectric. The work function of a pristine Al gate electrode (-4.1 eV) was modified by cesium carbonate and vanadium oxide to -2.1 and -5.1 eV, respectively, which could control the flat-band voltage, leading to a remarkable shift of transfer curves in both negative and positive gate voltage directions without any side effects. One important feature is that the mobility of transistors is not very sensitive to the gate buffer layer. This method is simple but useful for electronic devices where the threshold voltage should be precisely controlled, such as ambipolar circuits, memory devices, and light-emitting device applications. PMID:27323003

  11. H-Bonded Donor-Acceptor Units Segregated in Coaxial Columnar Assemblies: Toward High Mobility Ambipolar Organic Semiconductors.

    PubMed

    Feringán, Beatriz; Romero, Pilar; Serrano, José Luis; Folcia, César L; Etxebarria, Jesús; Ortega, Josu; Termine, Roberto; Golemme, Attilio; Giménez, Raquel; Sierra, Teresa

    2016-09-28

    A novel approach to ambipolar semiconductors based on hydrogen-bonded complexes between a star-shaped tris(triazolyl)triazine and triphenylene-containing benzoic acids is described. The formation of 1:3 supramolecular complexes was evidenced by different techniques. Mesogenic driving forces played a decisive role in the formation of the hydrogen-bonded complexes in the bulk. All of the complexes formed by nonmesogenic components gave rise to hexagonal columnar (Colh) liquid crystal phases, which are stable at room temperature. In all cases, X-ray diffraction experiments supported by electron density distribution maps confirmed triphenylene/tris(triazolyl)triazine segregation into hexagonal sublattices and lattices, respectively, as well as remarkable intracolumnar order. These highly ordered nanostructures, obtained by the combined supramolecular H-bond/columnar liquid crystal approach, yielded donor/acceptor coaxial organization that is promising for the formation of ambipolar organic semiconductors with high mobilities, as indicated by charge transport measurements. PMID:27577722

  12. H-Bonded Donor-Acceptor Units Segregated in Coaxial Columnar Assemblies: Toward High Mobility Ambipolar Organic Semiconductors.

    PubMed

    Feringán, Beatriz; Romero, Pilar; Serrano, José Luis; Folcia, César L; Etxebarria, Jesús; Ortega, Josu; Termine, Roberto; Golemme, Attilio; Giménez, Raquel; Sierra, Teresa

    2016-09-28

    A novel approach to ambipolar semiconductors based on hydrogen-bonded complexes between a star-shaped tris(triazolyl)triazine and triphenylene-containing benzoic acids is described. The formation of 1:3 supramolecular complexes was evidenced by different techniques. Mesogenic driving forces played a decisive role in the formation of the hydrogen-bonded complexes in the bulk. All of the complexes formed by nonmesogenic components gave rise to hexagonal columnar (Colh) liquid crystal phases, which are stable at room temperature. In all cases, X-ray diffraction experiments supported by electron density distribution maps confirmed triphenylene/tris(triazolyl)triazine segregation into hexagonal sublattices and lattices, respectively, as well as remarkable intracolumnar order. These highly ordered nanostructures, obtained by the combined supramolecular H-bond/columnar liquid crystal approach, yielded donor/acceptor coaxial organization that is promising for the formation of ambipolar organic semiconductors with high mobilities, as indicated by charge transport measurements.

  13. Multiple Negative Differential Resistance Device by Using the Ambipolar Behavior of Tunneling Field Effect Transistor with Fast Switching Characteristics.

    PubMed

    Jeong, Jae Won; Jang, E-San; Shin, Sunhae; Kim, Kyung Rok

    2016-05-01

    We propose a novel double-peak negative differential resistance (NDR) characteristic at the conventional single-peak MOS-NDR circuit by employing ambipolar behavior of TFET. The fluctuated voltage transfer curve (VTC) from ambipolar inverter is analyzed with simple model and successfully demonstrated with TFET, as a practical example, on the device simulation. We also verified that the fluctuated VTC generates additional peak and valleys on NDR characteristics by using circuit simulations. Moreover, by adjusting the threshold voltage of conventional MOSFET, ultra-high 1st and 2nd peak-to-valley current ratio (PVCR) over 10(7) is obtained with fully suppressed valley currents. The proposed double-peak NDR circuit expected to apply on faster switching and low power multi-functional applications. PMID:27483818

  14. Multicomponent diffusion in two-temperature magnetohydrodynamics

    NASA Astrophysics Data System (ADS)

    Ramshaw, J. D.; Chang, C. H.

    1996-06-01

    A recent hydrodynamic theory of multicomponent diffusion in multitemperature gas mixtures [J. D. Ramshaw, J. Non-Equilib. Thermodyn. 18, 121 (1993)] is generalized to include the velocity-dependent Lorentz force on charged species in a magnetic field B. This generalization is used to extend a previous treatment of ambipolar diffusion in two-temperature multicomponent plasmas [J. D. Ramshaw and C. H. Chang, Plasma Chem. Plasma Process. 13, 489 (1993)] to situations in which B and the electrical current density are nonzero. General expressions are thereby derived for the species diffusion fluxes, including thermal diffusion, in both single- and two-temperature multicomponent magnetohydrodynamics (MHD). It is shown that the usual zero-field form of the Stefan-Maxwell equations can be preserved in the presence of B by introducing generalized binary diffusion tensors dependent on B. A self-consistent effective binary diffusion approximation is presented that provides explicit approximate expressions for the diffusion fluxes. Simplifications due to the small electron mass are exploited to obtain an ideal MHD description in which the electron diffusion coefficients drop out, resistive effects vanish, and the electric field reduces to a particularly simple form. This description should be well suited for numerical calculations.

  15. Anti-Ambipolar Field-Effect Transistors Based On Few-Layer 2D Transition Metal Dichalcogenides.

    PubMed

    Li, Yongtao; Wang, Yan; Huang, Le; Wang, Xiaoting; Li, Xingyun; Deng, Hui-Xiong; Wei, Zhongming; Li, Jingbo

    2016-06-22

    Two-dimensional (2D) materials and their related van der Waals heterostructures have attracted considerable interest for their fascinating new properties. There are still many challenges in realizing the potential of 2D semiconductors in practical (opto)electronics such as signal transmission and logic circuit, etc. Herein, we report the gate-tunable anti-ambipolar devices on the basis of few-layer transition metal dichalcogenides (TMDs) heterostructures to gain higher information storage density. Our study shows that carrier concentration regulated by the gate voltage plays a major role in the "anti-ambipolar" behavior, where the drain-source current can only pass through in specific range of gate voltage (Vg) and it will be restrained if the Vg goes beyond the range. Several improved strategies were theoretically discussed and experimentally adopted to obtain higher current on/off ratio for the anti-ambipolar devices, such as choosing suitable p-/n-pair, increasing carrier concentration by using thicker-layer TMDs, and so on. The modified SnS2/WSe2 device with the current on/off ratio exceeding 200 and on-state Vg ranging from -20 to 0 V was successfully achieved. On the basis of the anti-ambipolar field-effect transistors (FETs), we also reveal the potential of three-channel device unit for signal processing and information storage. With the equal quantity N of device units, 3(N) digital signals can be obtained from such three-channel devices, which are much larger than 2(N) ones obtained from traditional two-channel complementary metal oxide semiconductors (CMOS). PMID:27258569

  16. Imaging ambipolar two-dimensional carriers induced by the spontaneous electric polarization of a polar semiconductor BiTeI

    NASA Astrophysics Data System (ADS)

    Kohsaka, Y.; Kanou, M.; Takagi, H.; Hanaguri, T.; Sasagawa, T.

    2015-06-01

    Two-dimensional (2D) mobile carriers are a wellspring of quantum phenomena. Among various 2D-carrier systems, such as field effect transistors and heterostructures, polar materials hold a unique potential; the spontaneous electric polarization in the bulk could generate positive and negative 2D carriers at the surface. Although several experiments have shown ambipolar carriers at the surface of a polar semiconductor BiTeI, their origin is yet to be specified. Here we provide compelling experimental evidences that the ambipolar 2D carriers at the surface of BiTeI are induced by the spontaneous electric polarization. By imaging electron standing waves with spectroscopic imaging scanning tunneling microscopy, we find that positive or negative carriers with Rashba-type spin splitting emerge at the surface corresponding to the polar directions in the bulk. The electron densities at the surface are constant independently of those in the bulk, corroborating that the 2D carriers are induced by the spontaneous electric polarization. We also successfully image that lateral p -n junctions are formed along the boundaries of submicron-scale domains with opposite polar directions. Our study presents a means to endow nonvolatile, spin-polarized, and ambipolar 2D carriers as well as, without elaborate fabrication, lateral p -n junctions of those carriers at atomically sharp interfaces.

  17. Ambipolar conduction in MoS2/WSe2 hetero-bilayers

    NASA Astrophysics Data System (ADS)

    Movva, Hema Chandra Prakash; Kang, Sangwoo; Rai, Amritesh; Banerjee, Sanjay

    2015-03-01

    Recent interest in layered semiconductors, and the ability to assemble them into artificial heterostructures with atomically sharp interfaces has opened up new avenues for the design of future electronic devices. In this work, we fabricated vertical heterostructures of exfoliated monolayer MoS2 and monolayer WSe2 using a facile flake pick-up-and-place technique, and studied their optical and electrical properties. Photoluminescence measurements showed evidence of indirect excitons at ~ 1.55 eV, indicating a clean interface between the two layers. We observed back-gate tunable, layer-selective ambipolar conduction in field effect transistors (FETs) made using these hetero-bilayers, with e-transport occurring through the MoS2, and h-transport through WSe2. The addition of a top-gate using a thin hBN dielectric further enabled selective operation of the hetero-bilayer FET as an n-FET/p-FET depending on the back-gate bias.

  18. Organic integrated circuits for information storage based on ambipolar polymers and charge injection engineering

    NASA Astrophysics Data System (ADS)

    Dell'Erba, Giorgio; Luzio, Alessandro; Natali, Dario; Kim, Juhwan; Khim, Dongyoon; Kim, Dong-Yu; Noh, Yong-Young; Caironi, Mario

    2014-04-01

    Ambipolar semiconducting polymers, characterized by both high electron (μe) and hole (μh) mobility, offer the advantage of realizing complex complementary electronic circuits with a single semiconducting layer, deposited by simple coating techniques. However, to achieve complementarity, one of the two conduction paths in transistors has to be suppressed, resulting in unipolar devices. Here, we adopt charge injection engineering through a specific interlayer in order to tune injection into frontier energy orbitals of a high mobility donor-acceptor co-polymer. Starting from field-effect transistors with Au contacts, showing a p-type unbalanced behaviour with μh = 0.29 cm2/V s and μe = 0.001 cm2/V s, through the insertion of a caesium salt interlayer with optimized thickness, we obtain an n-type unbalanced transistor with μe = 0.12 cm2/V s and μh = 8 × 10-4 cm2/V s. We applied this result to the development of the basic pass-transistor logic building blocks such as inverters, with high gain and good noise margin, and transmission-gates. In addition, we developed and characterized information storage circuits like D-Latches and D-Flip-Flops consisting of 16 transistors, demonstrating both their static and dynamic performances and thus the suitability of this technology for more complex circuits such as display addressing logic.

  19. Ringing After a High-Energy Collision: Ambipolar Oscillations During Impact Plasma Expansion

    NASA Technical Reports Server (NTRS)

    Zimmerman, M. I.; Farrell, W. M.; Stubbs, T. J.

    2012-01-01

    High-velocity impacts on the Moon and other airless bodies deliver energy and material to the lunar surface and exosphere. The target and i mpactor material may become vaporized and ionized to form a collision al plasma that expands outward and eventually becomes collisionless. In the present work, kinetic simulations of the later collision less stage of impact plasma expansion are performed. Attention is paid to characterizing "ambipolar oscillations" in which thermodynamic distur bances propagate outward to generate "ringing" within the expanding e lectron cloud, which could radiate an electromagnetic signature of lo cal plasma conditions. The process is not unlike a beam-plasma intera ction, with the perturbing electron population in the present case ac ting as a highly thermal "beam" that resonates along the expanding de nsity gradient. Understanding the electromagnetic aspects of impact p lasma expansion could provide insight into the lasting effects of nat ural, impact-generated currents on airless surfaces and charging haza rds to human exploration infrastructure and instrumentation.

  20. Device perspective for black phosphorus field-effect transistors: contact resistance, ambipolar behavior, and scaling.

    PubMed

    Du, Yuchen; Liu, Han; Deng, Yexin; Ye, Peide D

    2014-10-28

    Although monolayer black phosphorus (BP), or phosphorene, has been successfully exfoliated and its optical properties have been explored, most of the electrical performance of the devices is demonstrated on few-layer phosphorene and ultrathin BP films. In this paper, we study the channel length scaling of ultrathin BP field-effect transistors (FETs) and discuss a scheme for using various contact metals to change the transistor characteristics. Through studying transistor behaviors with various channel lengths, the contact resistance can be extracted with the transfer length method (TLM). With different contact metals, we find out that the metal/BP interface has different Schottky barrier heights, leading to a significant difference in contact resistance, which is quite different from previous studies of transition metal dichalcogenides (TMDs), such as MoS2, where the Fermi level is strongly pinned near the conduction band edge at the metal/MoS2 interface. The nature of BP transistors is Schottky barrier FETs, where the on and off states are controlled by tuning the Schottky barriers at the two contacts. We also observe the ambipolar characteristics of BP transistors with enhanced n-type drain current and demonstrate that the p-type carriers can be easily shifted to n-type or vice versa by controlling the gate bias and drain bias, showing the potential to realize BP CMOS logic circuits.

  1. Enhanced O2+ loss at Mars due to an ambipolar electric field from electron heating

    NASA Astrophysics Data System (ADS)

    Ergun, R. E.; Andersson, L. A.; Fowler, C. M.; Woodson, A. K.; Weber, T. D.; Delory, G. T.; Andrews, D. J.; Eriksson, A. I.; McEnulty, T.; Morooka, M. W.; Stewart, A. I. F.; Mahaffy, P. R.; Jakosky, B. M.

    2016-05-01

    Recent results from the MAVEN Langmuir Probe and Waves instrument suggest higher than predicted electron temperatures (Te) in Mars' dayside ionosphere above ~180 km in altitude. Correspondingly, measurements from Neutral Gas and Ion Mass Spectrometer indicate significant abundances of O2+ up to ~500 km in altitude, suggesting that O2+ may be a principal ion loss mechanism of oxygen. In this article, we investigate the effects of the higher Te (which results from electron heating) and ion heating on ion outflow and loss. Numerical solutions show that plasma processes including ion heating and higher Te may greatly increase O2+ loss at Mars. In particular, enhanced Te in Mars' ionosphere just above the exobase creates a substantial ambipolar electric field with a potential (eΦ) of several kBTe, which draws ions out of the region allowing for enhanced escape. With active solar wind, electron, and ion heating, direct O2+ loss could match or exceed loss via dissociative recombination of O2+. These results suggest that direct loss of O2+ may have played a significant role in the loss of oxygen at Mars over time.

  2. Ambipolar light-emitting organic single-crystal transistors with a grating resonator

    PubMed Central

    Maruyama, Kenichi; Sawabe, Kosuke; Sakanoue, Tomo; Li, Jinpeng; Takahashi, Wataru; Hotta, Shu; Iwasa, Yoshihiro; Takenobu, Taishi

    2015-01-01

    Electrically driven organic lasers are among the best lasing devices due to their rich variety of emission colors as well as other advantages, including printability, flexibility, and stretchability. However, electrically driven lasing in organic materials has not yet been demonstrated because of serious luminescent efficiency roll-off under high current density. Recently, we found that the organic ambipolar single-crystal transistor is an excellent candidate for lasing devices because it exhibits less efficient roll-off, high current density, and high luminescent efficiency. Although a single-mode resonator combined with light-emitting transistors (LETs) is necessary for electrically driven lasing devices, the fragility of organic crystals has strictly limited the fabrication of resonators, and LETs with optical cavities have never been fabricated until now. To achieve this goal, we improved the soft ultraviolet-nanoimprint lithography method and demonstrated electroluminescence from a single-crystal LET with a grating resonator, which is a crucial milestone for future organic lasers. PMID:25959455

  3. Sub-10 nm transparent all-around-gated ambipolar ionic field effect transistor

    NASA Astrophysics Data System (ADS)

    Lee, Seung-Hyun; Lee, Hyomin; Jin, Tianguang; Park, Sungmin; Yoon, Byung Jun; Sung, Gun Yong; Kim, Ki-Bum; Kim, Sung Jae

    2014-12-01

    In this paper, we developed a versatile ionic field effect transistor (IFET) which has an ambipolar function for manipulating molecules regardless of their polarity and can be operated at a wide range of electrolytic concentrations (10-5 M-1 M). The IFET has circular nanochannels radially covered by gate electrodes, called ``all-around-gate'', with an aluminum oxide (Al2O3) oxide layer of a near-zero surface charge. Experimental and numerical validations were conducted for characterizing the IFET. We found that the versatility originated from the zero-charge density of the oxide layer and all-around-gate structure which increased the efficiency of the gate effect 5 times higher than a previously developed planar-gate by capacitance calculations. Our numerical model adapted Poisson-Nernst-Planck-Stokes (PNPS) formulations with additional nonlinear constraints of a fringing field effect and a counter-ion condensation and the experimental and numerical results were well matched. The device can control the transportation of ions at concentrations up to 1 M electrolyte which resembles a backflow of a shale gas extraction process. Furthermore, while traditional IFETs can manipulate either positively or negatively charged species depending on the inherently large surface charge of oxide layer, the presenting device and mechanism provide effective means to control the motion of both negatively and positively charged molecules which is important in biomolecule transport through nanochannels, medical diagnosis system and point-of-care system, etc.In this paper, we developed a versatile ionic field effect transistor (IFET) which has an ambipolar function for manipulating molecules regardless of their polarity and can be operated at a wide range of electrolytic concentrations (10-5 M-1 M). The IFET has circular nanochannels radially covered by gate electrodes, called ``all-around-gate'', with an aluminum oxide (Al2O3) oxide layer of a near-zero surface charge. Experimental and

  4. Mechanisms of current fluctuation in ambipolar black phosphorus field-effect transistors.

    PubMed

    Li, Xuefei; Du, Yuchen; Si, Mengwei; Yang, Lingming; Li, Sichao; Li, Tiaoyang; Xiong, Xiong; Ye, Peide; Wu, Yanqing

    2016-02-14

    Multi-layer black phosphorus has emerged as a strong candidate owing to its high carrier mobility with most of the previous research work focused on its p-type properties. Very few studies have been performed on its n-type electronic characteristics which are important not only for the complementary operation for logic, but also crucial for understanding the carrier transport through the metal-black phosphorus junction. A thorough understanding and proper evaluation of the performance potential of both p- and n-types are highly desirable. In this paper, we investigate the temperature dependent ambipolar operation of both electron and hole transport from 300 K to 20 K. On-currents as high as 85 μA μm(-1) for a 0.2 μm channel length BP nFET at 300 K are observed. Moreover, we provide the first systematic study on the low frequency noise mechanisms for both n-channel and p-channel BP transistors. The dominated noise mechanisms of the multi-layer BP nFET and pFET are mobility fluctuation and carrier number fluctuations with correlated mobility fluctuations, respectively. We have also established a baseline of the low electrical noise of 8.1 × 10(-9)μm(2) Hz(-1) at 10 Hz at room temperature for BP pFETs, which is 3 times improvement over previous reports, and 7.0 × 10(-8)μm(2) Hz(-1) for BP nFETs for the first time. PMID:26806878

  5. Organic integrated circuits for information storage based on ambipolar polymers and charge injection engineering

    SciTech Connect

    Dell'Erba, Giorgio; Natali, Dario; Luzio, Alessandro; Caironi, Mario E-mail: yynoh@dongguk.edu; Noh, Yong-Young E-mail: yynoh@dongguk.edu

    2014-04-14

    Ambipolar semiconducting polymers, characterized by both high electron (μ{sub e}) and hole (μ{sub h}) mobility, offer the advantage of realizing complex complementary electronic circuits with a single semiconducting layer, deposited by simple coating techniques. However, to achieve complementarity, one of the two conduction paths in transistors has to be suppressed, resulting in unipolar devices. Here, we adopt charge injection engineering through a specific interlayer in order to tune injection into frontier energy orbitals of a high mobility donor-acceptor co-polymer. Starting from field-effect transistors with Au contacts, showing a p-type unbalanced behaviour with μ{sub h} = 0.29 cm{sup 2}/V s and μ{sub e} = 0.001 cm{sup 2}/V s, through the insertion of a caesium salt interlayer with optimized thickness, we obtain an n-type unbalanced transistor with μ{sub e} = 0.12 cm{sup 2}/V s and μ{sub h} = 8 × 10{sup −4} cm{sup 2}/V s. We applied this result to the development of the basic pass-transistor logic building blocks such as inverters, with high gain and good noise margin, and transmission-gates. In addition, we developed and characterized information storage circuits like D-Latches and D-Flip-Flops consisting of 16 transistors, demonstrating both their static and dynamic performances and thus the suitability of this technology for more complex circuits such as display addressing logic.

  6. MarsCAT: Mars Array of ionospheric Research Satellites using the CubeSat Ambipolar Thruster

    NASA Astrophysics Data System (ADS)

    Bering, E. A., III; Pinsky, L.; Li, L.; Jackson, D. R.; Chen, J.; Reed, H.; Moldwin, M.; Kasper, J. C.; Sheehan, J. P.; Forbes, J.; Heine, T.; Case, A. W.; Stevens, M. L.; Sibeck, D. G.

    2015-12-01

    The MarsCAT (Mars Array of ionospheric Research Satellites using the CubeSat Ambipolar Thruster) Mission is a two 6U CubeSat mission to study the ionosphere of Mars proposed for the NASA SIMPLeX opportunity. The mission will investigate the plasma and magnetic structure of the Martian ionosphere, including transient plasma structures, magnetic field structure and dynamics, and energetic particle activity. The transit plan calls for a piggy back ride with Mars 2020 using a CAT burn for MOI, the first demonstration of CubeSat propulsion for interplanetary travel. MarsCAT will make correlated multipoint studies of the ionosphere and magnetic field of Mars. Specifically, the two spacecraft will make in situ observations of the plasma density, temperature, and convection in the ionosphere of Mars. They will also make total electron content measurements along the line of sight between the two spacecraft and simultaneous 3-axis local magnetic field measurements in two locations. Additionally, MarsCAT will demonstrate the performance of new CubeSat telemetry antennas designed at the University of Houston that are designed to be low profile, rugged, and with a higher gain than conventional monopole (whip) antennas. The two MarsCAT CubeSats will have five science instruments: a 3-axis DC magnetometer, adouble-Langmuir probe, a Faraday cup, a solid state energetic particle detector (Science Enhancement Option), and interspacecraft total electron content radio occulation experiment. The MarsCAT spacecraft will be solar powered and equipped with a CAT thruster that can provide up to 4.8 km/s of delta-V, which is sufficient to achieve Mars orbit using the Mars 2020 piggyback. They have an active attitude control system, using a sun sensor and flight-proven star tracker for determination, and momentum wheels for 3-axis attitude control.

  7. MarsCAT: Mars Array of ionospheric Research Satellites using the CubeSat Ambipolar Thruster

    NASA Astrophysics Data System (ADS)

    Bering, Edgar Andrew; Pinsky, Lawrence S.; Li, Liming; Jackson, David; Chen, Ji; Reed, Helen; Moldwin, Mark; Kasper, Justin; Sheehan, J. P.; Forbes, James Richard; Heine, Thomas; Case, Anthony; Stevens, Michael; Sibeck, David G.

    2015-11-01

    The MarsCAT (Mars Array of ionospheric Research Satellites using the CubeSat Ambipolar Thruster) Mission is a two 6U CubeSat mission to study the ionosphere of Mars proposed for the NASA SIMPLeX opportunity. The mission will investigate the plasma and magnetic structure of the Martian ionosphere, including transient plasma structures, magnetic field structure and dynamics, and energetic particle activity. The transit plan calls for a piggy back ride with Mars 2020 using a CAT burn for MOI, the first demonstration of CubeSat propulsion for interplanetary travel. MarsCAT will make correlated multipoint studies of the ionosphere and magnetic field of Mars. Specifically, the two spacecraft will make in situ observations of the plasma density, temperature, and convection in the ionosphere of Mars. They will also make total electron content measurements along the line of sight between the two spacecraft and simultaneous 3-axis local magnetic field measurements in two locations. Additionally, MarsCAT will demonstrate the performance of new CubeSat telemetry antennas designed at the University of Houston that are designed to be low profile, rugged, and with a higher gain than conventional monopole (whip) antennas. The two MarsCAT CubeSats will have five science instruments: a 3-axis DC magnetometer, adouble-Langmuir probe, a Faraday cup, a solid state energetic particle detector (Science Enhancement Option), and interspacecraft total electron content radio occulation experiment. The MarsCAT spacecraft will be solar powered and equipped with a CAT thruster that can provide up to 4.8 km/s of delta-V, which is sufficient to achieve Mars orbit using the Mars 2020 piggyback. They have an active attitude control system, using a sun sensor and flight-proven star tracker for determination, and momentum wheels for 3-axis attitude control.

  8. Strong ambipolar-driven ion upflow within the cleft ion fountain during low geomagnetic activity

    NASA Astrophysics Data System (ADS)

    Shen, Yangyang; Knudsen, David J.; Burchill, Johnathan K.; Howarth, Andrew; Yau, Andrew; Redmon, Robert J.; Miles, David M.; Varney, Roger H.; Nicolls, Michael J.

    2016-07-01

    We investigate low-energy (<10 eV) ion upflows (mainly O+) within the cleft ion fountain (CIF) using conjunctions of the Enhanced Polar Outflow Probe (e-POP) satellite, the DMSP F16 satellite, the SuperDARN radar, and the Resolute Bay Incoherent Scatter Radar North (RISR-N). The SEI instrument on board e-POP enables us to derive ion upflow velocities from the 2-D images of ion distribution functions with a frame rate of 100 images per second, and with a velocity resolution of the order of 25 m/s. We identify three cleft ion fountain events with very intense (>1.6 km/s) ion upflow velocities near 1000 km altitude during quiet geomagnetic activity (Kp < 3). Such large ion upflow velocities have been reported previously at or below 1000 km, but only during active periods. Analysis of the core ion distribution images allows us to demonstrate that the ion temperature within the CIF does not rise by more than 0.3 eV relative to background values, which is consistent with RISR-N observations in the F region. The presence of soft electron precipitation seen by DMSP and lack of significant ion heating indicate that the ion upflows we observe near 1000 km altitude are primarily driven by ambipolar electric fields. DC field-aligned currents (FACs) and convection velocity gradients accompany these events. The strongest ion upflows are associated with downward current regions, which is consistent with some (although not all) previously published results. The moderate correlation coefficient (0.51) between upflow velocities and currents implies that FACs serve as indirect energy inputs to the ion upflow process.

  9. Mechanisms of current fluctuation in ambipolar black phosphorus field-effect transistors

    NASA Astrophysics Data System (ADS)

    Li, Xuefei; Du, Yuchen; Si, Mengwei; Yang, Lingming; Li, Sichao; Li, Tiaoyang; Xiong, Xiong; Ye, Peide; Wu, Yanqing

    2016-02-01

    Multi-layer black phosphorus has emerged as a strong candidate owing to its high carrier mobility with most of the previous research work focused on its p-type properties. Very few studies have been performed on its n-type electronic characteristics which are important not only for the complementary operation for logic, but also crucial for understanding the carrier transport through the metal-black phosphorus junction. A thorough understanding and proper evaluation of the performance potential of both p- and n-types are highly desirable. In this paper, we investigate the temperature dependent ambipolar operation of both electron and hole transport from 300 K to 20 K. On-currents as high as 85 μA μm-1 for a 0.2 μm channel length BP nFET at 300 K are observed. Moreover, we provide the first systematic study on the low frequency noise mechanisms for both n-channel and p-channel BP transistors. The dominated noise mechanisms of the multi-layer BP nFET and pFET are mobility fluctuation and carrier number fluctuations with correlated mobility fluctuations, respectively. We have also established a baseline of the low electrical noise of 8.1 × 10-9 μm2 Hz-1 at 10 Hz at room temperature for BP pFETs, which is 3 times improvement over previous reports, and 7.0 × 10-8 μm2 Hz-1 for BP nFETs for the first time.

  10. Mechanisms of current fluctuation in ambipolar black phosphorus field-effect transistors.

    PubMed

    Li, Xuefei; Du, Yuchen; Si, Mengwei; Yang, Lingming; Li, Sichao; Li, Tiaoyang; Xiong, Xiong; Ye, Peide; Wu, Yanqing

    2016-02-14

    Multi-layer black phosphorus has emerged as a strong candidate owing to its high carrier mobility with most of the previous research work focused on its p-type properties. Very few studies have been performed on its n-type electronic characteristics which are important not only for the complementary operation for logic, but also crucial for understanding the carrier transport through the metal-black phosphorus junction. A thorough understanding and proper evaluation of the performance potential of both p- and n-types are highly desirable. In this paper, we investigate the temperature dependent ambipolar operation of both electron and hole transport from 300 K to 20 K. On-currents as high as 85 μA μm(-1) for a 0.2 μm channel length BP nFET at 300 K are observed. Moreover, we provide the first systematic study on the low frequency noise mechanisms for both n-channel and p-channel BP transistors. The dominated noise mechanisms of the multi-layer BP nFET and pFET are mobility fluctuation and carrier number fluctuations with correlated mobility fluctuations, respectively. We have also established a baseline of the low electrical noise of 8.1 × 10(-9)μm(2) Hz(-1) at 10 Hz at room temperature for BP pFETs, which is 3 times improvement over previous reports, and 7.0 × 10(-8)μm(2) Hz(-1) for BP nFETs for the first time.

  11. Electrical transport and photoconduction in ambipolar tungsten diselenide and n-type indium selenide

    NASA Astrophysics Data System (ADS)

    Fralaide, Michael Orcino

    In today's "silicon age" in which we live, field-effect transistors (FET) are the workhorse of virtually all modern-day electronic gadgets. Although silicon currently dominates most of these electronics, layered 2D transition metal dichalcogenides (TMDCs) have great potential in low power optoelectronic applications due to their indirect-to-direct band gap transition from bulk to few-layer and high on/off switching ratios. TMDC WSe2 is studied here, mechanically exfoliated from CVT-grown bulk WSe2 crystals, to create a few-layered ambipolar FET, which transitions from dominant p-type behavior to n-type behavior dominating as temperature decreases. A high electron mobility mu>150 cm2V-1s-1 was found in the low temperature region near 50 K. Temperature-dependent photoconduction measurements were also taken, revealing that both the application of negative gate bias and decreasing the temperature resulted in an increase of the responsivity of the WSe2 sample. Besides TMDCs, Group III-VI van der Waals structures also show promising anisotropic optical, electronic, and mechanical properties. In particular, mechanically exfoliated few-layered InSe is studied here for its indirect band gap of 1.4 eV, which should offer a broad spectral response. It was found that the steady state photoconduction slightly decreased with the application of positive gate bias, likely due to the desorption of adsorbates on the surface of the sample. A room temperature responsivity near 5 AW -1 and external quantum efficiency of 207% was found for the InSe FET. Both TMDC's and group III-VI chalcogenides continue to be studied for their remarkably diverse properties that depend on their thickness and composition for their applications as transistors, sensors, and composite materials in photovoltaics and optoelectronics.

  12. Observation of ambipolar switching in a silver nanoparticle single-electron transistor with multiple molecular floating gates

    NASA Astrophysics Data System (ADS)

    Yamamoto, Makoto; Shinohara, Shuhei; Tamada, Kaoru; Ishii, Hisao; Noguchi, Yutaka

    2016-03-01

    Ambipolar switching behavior was observed in a silver nanoparticle (AgNP)-based single-electron transistor (SET) with tetra-tert-butyl copper phthalocyanine (ttbCuPc) as a molecular floating gate. Depending on the wavelength of the incident light, the stability diagram shifted to the negative and positive directions along the gate voltage axis. These results were explained by the photoinduced charging of ttbCuPc molecules in the vicinity of AgNPs. Moreover, multiple device states were induced by the light irradiation at a wavelength of 600 nm, suggesting that multiple ttbCuPc molecules individually worked as a floating gate.

  13. Utilizing carbon nanotube electrodes to improve charge injection and transport in bis(trifluoromethyl)-dimethyl-rubrene ambipolar single crystal transistors.

    PubMed

    Xie, Wei; Prabhumirashi, Pradyumna L; Nakayama, Yasuo; McGarry, Kathryn A; Geier, Michael L; Uragami, Yuki; Mase, Kazuhiko; Douglas, Christopher J; Ishii, Hisao; Hersam, Mark C; Frisbie, C Daniel

    2013-11-26

    We have examined the significant enhancement of ambipolar charge injection and transport properties of bottom-contact single crystal field-effect transistors (SC-FETs) based on a new rubrene derivative, bis(trifluoromethyl)-dimethyl-rubrene (fm-rubrene), by employing carbon nanotube (CNT) electrodes. The fundamental challenge associated with fm-rubrene crystals is their deep-lying HOMO and LUMO energy levels, resulting in inefficient hole injection and suboptimal electron injection from conventional Au electrodes due to large Schottky barriers. Applying thin layers of CNT network at the charge injection interface of fm-rubrene crystals substantially reduces the contact resistance for both holes and electrons; consequently, benchmark ambipolar mobilities have been achieved, reaching 4.8 cm(2) V(-1) s(-1) for hole transport and 4.2 cm(2) V(-1) s(-1) for electron transport. We find that such improved injection efficiency in fm-rubrene is beneficial for ultimately unveiling its intrinsic charge transport properties so as to exceed those of its parent molecule, rubrene, in the current device architecture. Our studies suggest that CNT electrodes may provide a universal approach to ameliorate the charge injection obstacles in organic electronic devices regardless of charge carrier type, likely due to the electric field enhancement along the nanotube located at the crystal/electrode interface.

  14. Modeling solar flare conduction fronts. I - Homogeneous plasmas and ion-acoustic turbulence. II - Inhomogeneous plasmas and ambipolar electric fields

    NASA Technical Reports Server (NTRS)

    Mckean, M. E.; Winglee, R. M.; Dulk, G. A.

    1990-01-01

    A one-dimensional, electrostatic, particle-in-cell simulation is used here to model the expansion of a heated electron population in a coronal loop during a solar flare and the characteristics of the associated X-ray emissions. The hot electrons expand outward from the localized region, creating an ambipolar electric field which accelerates a return current of cooler, ambient electrons. Ion-acoustic waves are generated by the return currents as proposed by Brown et al. (1979), but they play little or no role in containing energetic electrons and the conduction front proposed by Brown et al. does not form. The X-ray emission efficiency of the electrons is too low in the corona for them to be the source of hard X-ray bursts. The particle dynamics changes dramatically if the heated plasma is at low altitudes and expands upward into the more tenuous plasma at higher altitudes. Two important applications of this finding are the radio-frequency heating of the corona and the collisional heating of the chromosphere by precipitating energetic electrons. In both cases, the overlying plasma has a density that is too low to supply a balancing return current to the expanding hot electrons. As a result, an ambipolar electric field develops that tends to confine the energetic electrons behind a front that propagate outward at about the speed of sound.

  15. Importance of Solubilizing Group and Backbone Planarity in Low Band Gap Polymers for High Performance Ambipolar field-effect Transistors

    SciTech Connect

    Lee, Joong Suk; Son, Seon Kyoung; Song, Sanghoon; Kim, Hyunjung; Lee, Dong Ryoul; Kim, Kyungkon; Ko, Min Jae; Choi, Dong Hoon; Kim, BongSoo; Cho, Jeong Ho

    2012-06-13

    We investigated the performance of ambipolar field-effect transistors based on a series of alternating low band gap polymers of oligothiophene and diketopyrrolopyrrole (DPP). The polymers contain oligothiophene units of terthiophene [T3] and thiophene-thienothiophene-thiophene [T2TT] and DPP units carrying branched alkyl chains of 2-hexyldecyl [HD] or 2-octyldodecyl [OD]. The structural variation allows us to do a systematic study on the relationship between the interchain stacking/ordering of semiconducting polymers and their resulting device performance. On the basis of synchrotron X-ray diffraction and atomic force microscopy measurements on polymer films, we found that longer branched alkyl side chains, i.e., OD, and longer and more planar oligothiophene, i.e., T2TT, generate the more crystalline structures. Upon thermal annealing, the crystallinity of the polymers was largely improved, and polymers containing a longer branched alkyl chain responded faster because longer alkyl chains have larger cohesive forces than shorter chains. For all the polymers, excellent ambipolar behavior was observed with a maximum hole and electron mobility of 2.2 and 0.2 cm{sup 2} V{sup -1} s{sup -1}, respectively.

  16. Utilizing carbon nanotube electrodes to improve charge injection and transport in bis(trifluoromethyl)-dimethyl-rubrene ambipolar single crystal transistors.

    PubMed

    Xie, Wei; Prabhumirashi, Pradyumna L; Nakayama, Yasuo; McGarry, Kathryn A; Geier, Michael L; Uragami, Yuki; Mase, Kazuhiko; Douglas, Christopher J; Ishii, Hisao; Hersam, Mark C; Frisbie, C Daniel

    2013-11-26

    We have examined the significant enhancement of ambipolar charge injection and transport properties of bottom-contact single crystal field-effect transistors (SC-FETs) based on a new rubrene derivative, bis(trifluoromethyl)-dimethyl-rubrene (fm-rubrene), by employing carbon nanotube (CNT) electrodes. The fundamental challenge associated with fm-rubrene crystals is their deep-lying HOMO and LUMO energy levels, resulting in inefficient hole injection and suboptimal electron injection from conventional Au electrodes due to large Schottky barriers. Applying thin layers of CNT network at the charge injection interface of fm-rubrene crystals substantially reduces the contact resistance for both holes and electrons; consequently, benchmark ambipolar mobilities have been achieved, reaching 4.8 cm(2) V(-1) s(-1) for hole transport and 4.2 cm(2) V(-1) s(-1) for electron transport. We find that such improved injection efficiency in fm-rubrene is beneficial for ultimately unveiling its intrinsic charge transport properties so as to exceed those of its parent molecule, rubrene, in the current device architecture. Our studies suggest that CNT electrodes may provide a universal approach to ameliorate the charge injection obstacles in organic electronic devices regardless of charge carrier type, likely due to the electric field enhancement along the nanotube located at the crystal/electrode interface. PMID:24175573

  17. Highly tunable Berry phase and ambipolar field effect in topological crystalline insulator Pb(1-x)Sn(x)Se.

    PubMed

    Zhang, Cheng; Liu, Yanwen; Yuan, Xiang; Wang, Weiyi; Liang, Sihang; Xiu, Faxian

    2015-03-11

    Recently, rock-salt IV-VI semiconductors, such as Pb(1-x)Sn(x)Se(Te) and SnTe, have been observed to host topological crystalline insulator (TCI) states. The nontrivial states have long been believed to exhibit ambipolar field effects and possess massive Dirac Fermions in two-dimension (2D) limit due to the surface hybridization. However, these exciting attributes of TCI remain previously inaccessible owing to the complicated control over composition and thickness. Here, we systematically investigate doping and thickness-induced topological phase transitions by electrical transport. We demonstrate the first evidence of the ambipolar properties in Pb(1-x)Sn(x)Se thin films. Surface gap opening is observed in 10 nm TCI originated from the strong finite-size effect. Importantly, magnetoconductance hosts a competition between weak antilocalization and weak localization, suggesting a strikingly tunable Berry phase evolution and strong electron-electron interaction. Our findings serve as a new probe to study electron behavior and pave the way for further exploring and manipulating this novel 2D TCI phase.

  18. The effects of deionization processes on meteor radar diffusion coefficients below 90 km

    NASA Astrophysics Data System (ADS)

    Younger, J. P.; Lee, C. S.; Reid, I. M.; Vincent, R. A.; Kim, Y. H.; Murphy, D. J.

    2014-08-01

    The decay times of VHF radar echoes from underdense meteor trails are reduced in the lower portions of the meteor region. This is a result of plasma neutralization initiated by the attachment of positive trail ions to neutral atmospheric molecules. Decreased echo decay times cause meteor radars to produce erroneously high estimates of the ambipolar diffusion coefficient at heights below 90 km, which affects temperature estimation techniques. Comparisons between colocated radars and satellite observations show that meteor radar estimates of diffusion coefficients are not consistent with estimates from the Aura Microwave Limb Sounder satellite instrument and that colocated radars operating at different frequencies estimate different values of the ambipolar diffusion coefficient for simultaneous detections of the same meteors. Loss of free electrons from meteor trails due to attachment to aerosols and chemical processes were numerically simulated and compared with observations to determine the specific mechanism responsible for low-altitude meteor trail plasma neutralization. It is shown that three-body attachment of positive metal ions significantly reduces meteor radar echo decay times at low altitudes compared to the case of diffusion only that atmospheric ozone plays little part in the evolution of low-altitude underdense meteor trails and that the effect of three-body attachment begins to exceed diffusion in echo decay times at a constant density surface.

  19. Tuning charge balance in PHOLEDs with ambipolar host materials to achieve high efficiency

    SciTech Connect

    Padmaperuma, Asanga B.; Koech, Phillip K.; Cosimbescu, Lelia; Polikarpov, Evgueni; Swensen, James S.; Chopra, Neetu; So, Franky; Sapochak, Linda S.; Gaspar, Daniel J.

    2009-08-27

    operating voltages, particularly if this is to be achieved in a device that can be manufactured at low cost. To avoid the efficiency losses associated with phosphorescence quenching by back-energy transfer from the dopant onto the host, the triplet excited states of the host material must be higher in energy than the triplet excited state of the dopant.5 This must be accomplished without sacrificing the charge transporting properties of the composite.6 Similar problems limit the efficiency of OLED-based displays, where blue light emitters are the least efficient and least stable. We previously demonstrated the utility of organic phosphine oxide (PO) materials as electron transporting HMs for FIrpic in blue OLEDs.7 However, the high reluctance of PO materials to oxidation and thus, hole injection limits the ability to balance charge injection and transport in the EML without relying on charge transport by the phosphorescent dopant. PO host materials were engineered to transport both electrons and holes in the EML and still maintain high triplet exciton energy to ensure efficient energy transfer to the dopant (Figure 1). There are examples of combining hole transporting moieties (mainly aromatic amines) with electron transport moieties (e.g., oxadiazoles, triazines, boranes)8 to develop new emitter and host materials for small molecule and polymer9 OLEDs. The challenge is to combine the two moieties without lowering the triplet energy of the target molecule. For example, coupling of a dimesitylphenylboryl moiety with a tertiary aromatic amine (FIAMBOT) results in intramolecular electron transfer from the amine to the boron atom through the bridging phenyl. The mesomeric effect of the dimesitylphenylboryl unit acts to extend conjugation and lowers triplet exciton energies (< 2.8 eV) rendering such systems inadequate as ambipolar hosts for blue phosphors.

  20. Toward printed integrated circuits based on unipolar or ambipolar polymer semiconductors.

    PubMed

    Baeg, Kang-Jun; Caironi, Mario; Noh, Yong-Young

    2013-08-21

    transport properties. Among this class of materials, various polymers can show well balanced electrons and holes mobility, therefore being indicated as ambipolar semiconductors, good environmental stability, and a small band-gap, which simplifies the tuning of charge injection. This opened up the possibility of taking advantage of the superior performances offered by complementary "CMOS-like" logic for the design of digital ICs, easing the scaling down of critical geometrical features, and achieving higher complexity from robust single gates (e.g., inverters) and test circuits (e.g., ring oscillators) to more complete circuits. Here, we review the recent progress in the development of printed ICs based on polymeric semiconductors suitable for large-volume micro- and nano-electronics applications. Particular attention is paid to the strategies proposed in the literature to design and synthesize high mobility polymers and to develop suitable printing tools and techniques to allow for improved patterning capability required for the down-scaling of devices in order to achieve the operation frequencies needed for applications, such as flexible radio-frequency identification (RFID) tags, near-field communication (NFC) devices, ambient electronics, and portable flexible displays.

  1. Reconnection Diffusion in Turbulent Fluids and Its Implications for Star Formation

    NASA Astrophysics Data System (ADS)

    Lazarian, A.

    2014-05-01

    Astrophysical fluids are turbulent a fact which changes the dynamics of many key processes, including magnetic reconnection. Fast reconnection of magnetic field in turbulent fluids allows the field to change its topology and connections. As a result, the traditional concept of magnetic fields being frozen into the plasma is no longer applicable. Plasma associated with a given magnetic field line at one instant is distributed along a different set of magnetic field lines at the next instant. This diffusion of plasmas and magnetic field is enabled by reconnection and therefore is termed "reconnection diffusion". The astrophysical implications of this concept include heat transfer in plasmas, advection of heavy elements in interstellar medium, magnetic field generation etc. However, the most dramatic implications of the concept are related to the star formation process. The reason is that magnetic fields are dynamically important for most of the stages of star formation. The existing theory of star formation has been developed ignoring the possibility of reconnection diffusion. Instead, it appeals to the decoupling of mass and magnetic field arising from neutrals drifting in respect to ions entrained on magnetic field lines, i.e. through the process that is termed "ambipolar diffusion". The predictions of ambipolar diffusion and reconnection diffusion are very different. For instance, if the ionization of media is high, ambipolar diffusion predicts that the coupling of mass and magnetic field is nearly perfect. At the same time, reconnection diffusion is independent of the ionization but depends on the scale of the turbulent eddies and on the turbulent velocities. In the paper we explain the physics of reconnection diffusion both from macroscopic and microscopic points of view, i.e. appealing to the reconnection of flux tubes and to the diffusion of magnetic field lines. We make use of the Lazarian and Vishniac (Astrophys. J. 517:700, 1999) theory of magnetic

  2. Non-ambipolar radio-frequency plasma electron source and systems and methods for generating electron beams

    NASA Technical Reports Server (NTRS)

    Hershkowitz, Noah (Inventor); Longmier, Benjamin (Inventor); Baalrud, Scott (Inventor)

    2009-01-01

    An electron generating device extracts electrons, through an electron sheath, from plasma produced using RF fields. The electron sheath is located near a grounded ring at one end of a negatively biased conducting surface, which is normally a cylinder. Extracted electrons pass through the grounded ring in the presence of a steady state axial magnetic field. Sufficiently large magnetic fields and/or RF power into the plasma allow for helicon plasma generation. The ion loss area is sufficiently large compared to the electron loss area to allow for total non-ambipolar extraction of all electrons leaving the plasma. Voids in the negatively-biased conducting surface allow the time-varying magnetic fields provided by the antenna to inductively couple to the plasma within the conducting surface. The conducting surface acts as a Faraday shield, which reduces any time-varying electric fields from entering the conductive surface, i.e. blocks capacitive coupling between the antenna and the plasma.

  3. Non-ambipolar radio-frequency plasma electron source and systems and methods for generating electron beams

    NASA Technical Reports Server (NTRS)

    Hershkowitz, Noah (Inventor); Longmier, Benjamin (Inventor); Baalrud, Scott (Inventor)

    2011-01-01

    An electron generating device extracts electrons, through an electron sheath, from plasma produced using RF fields. The electron sheath is located near a grounded ring at one end of a negatively biased conducting surface, which is normally a cylinder. Extracted electrons pass through the grounded ring in the presence of a steady state axial magnetic field. Sufficiently large magnetic fields and/or RF power into the plasma allow for helicon plasma generation. The ion loss area is sufficiently large compared to the electron loss area to allow for total non-ambipolar extraction of all electrons leaving the plasma. Voids in the negatively-biased conducting surface allow the time-varying magnetic fields provided by the antenna to inductively couple to the plasma within the conducting surface. The conducting surface acts as a Faraday shield, which reduces any time-varying electric fields from entering the conductive surface, i.e. blocks capacitive coupling between the antenna and the plasma.

  4. Non-ambipolar radio-frequency plasma electron source and systems and methods for generating electron beams

    DOEpatents

    Hershkowitz, Noah; Longmier, Benjamin; Baalrud, Scott

    2009-03-03

    An electron generating device extracts electrons, through an electron sheath, from plasma produced using RF fields. The electron sheath is located near a grounded ring at one end of a negatively biased conducting surface, which is normally a cylinder. Extracted electrons pass through the grounded ring in the presence of a steady state axial magnetic field. Sufficiently large magnetic fields and/or RF power into the plasma allow for helicon plasma generation. The ion loss area is sufficiently large compared to the electron loss area to allow for total non-ambipolar extraction of all electrons leaving the plasma. Voids in the negatively-biased conducting surface allow the time-varying magnetic fields provided by the antenna to inductively couple to the plasma within the conducting surface. The conducting surface acts as a Faraday shield, which reduces any time-varying electric fields from entering the conductive surface, i.e. blocks capacitive coupling between the antenna and the plasma.

  5. Improvement of properties of an ambipolar organic field-effect transistor by using a singlet biradicaloid film

    NASA Astrophysics Data System (ADS)

    Yamane, Wataru; Koike, Harunobu; Chikamatsu, Masayuki; Kubo, Takashi; Nishiuchi, Tomohiko; Kanai, Kaname

    2016-01-01

    We have improved the properties of ambipolar organic field-effect transistors by chemically treating the source and drain electrodes with a vacuum-deposited biradicaloid film. Biradicaloid was a diphenyl derivative of s-indacenodiphenalene (Ph2-IDPL). An alkane thiol self-assembled monolayer (SAM) was used as an insulator buffer layer at the Ph2-IDPL/electrode interface to prevent off-current. We confirmed the transport level alignment at the Ph2-IDPL/SAM/electrode interface by ultraviolet photoemission spectroscopy and inverse photoemission spectroscopy. Although Ph2-IDPL transistors containing the SAM showed a higher on/off ratio or mobility than a previously reported device without the buffer layer, there was a trade-off between on/off ratio and mobility. Our results suggest that biradical molecules are promising candidates for use in low-power inverters.

  6. Diffuse spreading of inhomogeneities in the ionospheric dusty plasma

    SciTech Connect

    Shalimov, S. L.; Kozlovsky, A.

    2015-08-15

    According to results of sounding of the lower ionosphere at altitudes of about 100 km, the duration of radio reflections from sufficiently dense ionized meteor trails, which characterizes their lifetime, can reach a few tens of seconds to several tens of minutes. This is much longer than the characteristic spreading time (on the order of fractions of a second to several seconds) typical in meteor radar measurements. The presence of dust in the lower ionosphere is shown to affect the ambipolar diffusion coefficient, which determines the spreading of plasma inhomogeneities. It is found that the diffusion coefficient depends substantially on the charge and size of dust grains, which allows one to explain the results of ionospheric sounding.

  7. Diffusion Coefficient and Electric Field Studies for HSX using Monte Carlo Methods

    NASA Astrophysics Data System (ADS)

    Gerhardt, S. P.; Talmadge, J. N.

    1999-11-01

    The HSX experiment has a magnetic field spectrum which closely approximates helical symmetry. Never the less, symmetry breaking terms are present which lead to asymmetric diffusion. Models for the asymmetric component of the monoenergetic diffusion coefficient are unable to account for all the terms in the HSX magnetic spectrum and the functional dependence on the radial electric field (Er). To model the diffusion coefficient as a function of Er and collisionality, Monte Carlo simulations have been made for different values of Er and background density. These results are fit to analytic models for the diffusion coefficient. Enforcing ambipolarity on these fluxes can lead to a calculation of the stellarator Er. To measure Er, we will use a spectroscopic system to measure impurity flow. A 1-meter spectrometer with a CCD detector has been purchased for this purpose; a LabVIEW control system has been implemented and collection optics designed. Details of the spectroscopic system will be presented.

  8. Carrier diffusion in Cd1-xMnxTe

    NASA Astrophysics Data System (ADS)

    Moussu, C.; Zaquine, I.; Maruani, A.; Frey, R.

    1998-09-01

    Carrier diffusion and electron-hole recombination are shown to be considerably slowed down in Cd1-xMnxTe semimagnetic semiconductors due to the efficient trapping of electrons on manganese sites. The theoretical interpretation is based on population dynamics, charge continuity equations, and Poisson's law. A simple analytical solution of this complicated system of equations is in very good agreement with the numerical one for a large range of durations of the write pulses (from 100 ps to 1 μs). Both calculations predict a reduction of electron mobility by a factor of 6000. These theoretical predictions are confirmed by the results of an experimental study performed by using the simple grating technique: We observe the temporal evolution of the diffracted signal when a continuous read beam is used to read gratings of different wavelengths encoded in the material by interfering write laser pulses. An effective ambipolar mobility of 0.54 cm2/V s is measured, which provides a value of 3400 cm2/V s for the intrinsic mobility in Cd0.7Mn0.3Te. This low ambipolar mobility could make this efficient material potentially interesting for parallel optical processing in the microsecond range.

  9. F and CF3 substituted solution processable oligo para-phenylenevinylene for ambipolar and hole-transporting organic field effect transistors

    NASA Astrophysics Data System (ADS)

    Chini, Mrinmoy Kumar; Das, Chayanika; Chatterjee, Shyambo

    2016-07-01

    We have synthesized benzotrifluoromethyl group substituted para-phenylenevinylene oligomer (denoted as PI) and a cooligomer (denoted as PII) by Gilch polymerization route. The ambipolar field-effect transistor (FET) material PI shows hole and electron mobility 1 × 10-4 cm2 V-1 s-1 and 2 × 10-5 cm2 V-1 s-1 respectively. PII shows only hole mobility as high as 0.05 cm2 V-1 s-1 as p-type material. This work highlights the progress of hole-transporting as well as ambipolar material for para-phenylenevinylene derivatives. The results are enlightened on the basis of presence of electronegative substituents and structural modification of the oligomer backbone.

  10. Polyethylenimine (PEI) As an Effective Dopant To Conveniently Convert Ambipolar and p-Type Polymers into Unipolar n-Type Polymers.

    PubMed

    Sun, Bin; Hong, Wei; Thibau, Emmanuel S; Aziz, Hany; Lu, Zheng-Hong; Li, Yuning

    2015-08-26

    In this study, we added a small amount of polyethylenimine (PEI) into several ambipolar and p-type polymer semiconductors and used these blends as channel materials in organic thin film transistors (OTFTs). It is found that PEI can effectively suppress hole transport characteristics while maintaining or promoting the electron transport performance. Unipolar n-channel OTFTs with electron-only transport behavior is achieved for all the polymer semiconductors chosen with 2-10 wt % PEI. The electron-rich nitrogen atoms in PEI are thought to fill the electron traps, raise the Fermi level and function as trapping sites for holes, leading to promotion of electron transport and suppression of hole transport. This work demonstrates a convenient general approach to transforming ambipolar and p-type polymer semiconductors into unipolar n-type polymer semiconductors that are useful for printed logic circuits and many other applications.

  11. Discharge regime of non-ambipolarity with a self-induced steady-state magnetic field in plasma sources with localized radio-frequency power deposition

    SciTech Connect

    Shivarova, A. Lishev, St.; Todorov, D.; Paunska, Ts.

    2015-10-15

    Involving the idea for the Biermann effect known from space physics as well as recent discussions on non-ambipolarity of the electron and ion fluxes in low-pressure discharges, the study builds the discharge pattern in a source with localized RF power deposition outside the region of high electron density. A vortex dc current flowing in an RF discharge and a steady-state magnetic field induced by this current govern the discharge behavior. Owing to a shift in the positions of the electron-density and plasma-potential maxima, the dc current is driven with the purpose of keeping the conservativity of the dc field in the discharge. The results present the spatial structure of a discharge in a regime of non-ambipolarity of the electron and ion fluxes, including its modifications by the magnetic field.

  12. Novel red phosphorescent polymers bearing both ambipolar and functionalized Ir(III) phosphorescent moieties for highly efficient organic light-emitting diodes.

    PubMed

    Zhao, Jiang; Lian, Meng; Yu, Yue; Yan, Xiaogang; Xu, Xianbin; Yang, Xiaolong; Zhou, Guijiang; Wu, Zhaoxin

    2015-01-01

    A series of novel red phosphorescent polymers is successfully developed through Suzuki cross-coupling among ambipolar units, functionalized Ir(III) phosphorescent blocks, and fluorene-based silane moieties. The photophysical and electrochemical investigations indicate not only highly efficient energy-transfer from the organic segments to the phosphorescent units in the polymer backbone but also the ambipolar character of the copolymers. Benefiting from all these merits, the phosphorescent polymers can furnish organic light-emitting diodes (OLEDs) with exceptional high electroluminescent (EL) efficiencies with a current efficiency (η L ) of 8.31 cd A(-1) , external quantum efficiency (η ext ) of 16.07%, and power efficiency (η P ) of 2.95 lm W(-1) , representing the state-of-the-art electroluminescent performances ever achieved by red phosphorescent polymers. This work here might represent a new pathway to design and synthesize highly efficient phosphorescent polymers.

  13. Effect of asymmetrical double-pockets and gate-drain underlap on Schottky barrier tunneling FET: Ambipolar conduction vs. high frequency performance

    NASA Astrophysics Data System (ADS)

    Shaker, Ahmed; Ossaimee, Mahmoud; Zekry, A.

    2016-08-01

    In this paper, a proposed structure based on asymmetrical double pockets SB-TFET with gate-drain underlap is presented. 2D extensive modeling and simulation, using Silvaco TCAD, were carried out to study the effect of both underlap length and pockets' doping on the transistor performance. It was found that the underlap from the drain side suppresses the ambipolar conduction and doesn't enhance the high-frequency characteristics. The enhancement of the high-frequency characteristics could be realized by increasing the doping of the drain pocket over the doping of the source pocket. An optimum choice was found which gives the conditions of minimum ambipolar conduction, maximum ON current and maximum cut-off frequency. These enhancements render the device more competitive as a nanometer transistor.

  14. Two-stage bulk electron heating in the diffusion region of anti-parallel symmetric reconnection

    NASA Astrophysics Data System (ADS)

    Le, A.; Egedal, J.; Daughton, W.

    2016-10-01

    Electron bulk energization in the diffusion region during anti-parallel symmetric reconnection entails two stages. First, the inflowing electrons are adiabatically trapped and energized by an ambipolar parallel electric field. Next, the electrons gain energy from the reconnection electric field as they undergo meandering motion. These collisionless mechanisms have been described previously, and they lead to highly structured electron velocity distributions. Nevertheless, a simplified control-volume analysis gives estimates for how the net effective heating scales with the upstream plasma conditions in agreement with fully kinetic simulations and spacecraft observations.

  15. Diffusion MRI

    NASA Astrophysics Data System (ADS)

    Fukuyama, Hidenao

    Recent advances of magnetic resonance imaging have been described, especially stressed on the diffusion sequences. We have recently applied the diffusion sequence to functional brain imaging, and found the appropriate results. In addition to the neurosciences fields, diffusion weighted images have improved the accuracies of clinical diagnosis depending upon magnetic resonance images in stroke as well as inflammations.

  16. Scaling and Graphical Transport-Map Analysis of Ambipolar Schottky-Barrier Thin-Film Transistors Based on a Parallel Array of Si Nanowires.

    PubMed

    Jeon, Dae-Young; Pregl, Sebastian; Park, So Jeong; Baraban, Larysa; Cuniberti, Gianaurelio; Mikolajick, Thomas; Weber, Walter M

    2015-07-01

    Si nanowire (Si-NW) based thin-film transistors (TFTs) have been considered as a promising candidate for next-generation flexible and wearable electronics as well as sensor applications with high performance. Here, we have fabricated ambipolar Schottky-barrier (SB) TFTs consisting of a parallel array of Si-NWs and performed an in-depth study related to their electrical performance and operation mechanism through several electrical parameters extracted from the channel length scaling based method. Especially, the newly suggested current-voltage (I-V) contour map clearly elucidates the unique operation mechanism of the ambipolar SB-TFTs, governed by Schottky-junction between NiSi2 and Si-NW. Further, it reveals for the first-time in SB based FETs the important internal electrostatic coupling between the channel and externally applied voltages. This work provides helpful information for the realization of practical circuits with ambipolar SB-TFTs that can be transferred to different substrate technologies and applications.

  17. Nano-needle structured, ambipolar high electrical conductivity SnOx (x ≤ 1) thin films for infrared optoelectronics

    NASA Astrophysics Data System (ADS)

    Wong, Andrew; Wang, Xiaoxin; Liu, Jifeng

    2015-03-01

    SnO has become an important earth-abundant transparent conductive oxide (TCO) with applications not only in photovoltaics but also in electrodes for energy storage. For optoelectronic applications, low fabrication temperature, high electrical conductivity, and low optical losses are highly desirable. This study presents self-assembled, ambipolar (i.e., n and p-type) nano-needle structured SnOx (x ≤ 1) thin films with high electrical conductivity, low infrared (IR) optical losses, and potentials for effective light trapping. These nano-needle structured SnOx films are fabricated through non-reactive co-sputtering of Sn and SnO2 followed by crystallization annealing at low temperatures <250 °C. The crystallization of SnOx thin films occurred rapidly above 210 °C, resulting in SnO nano-needles with average dimensions of 1 μm long, 0.1 μm wide, and 0.15 μm thick that are interspersed with Sn nanocrystals. The optical scattering from these nanostructures can be utilized for light trapping in thin film absorbers. We also found that laser pre-patterning enabled control over nano-needle crystal size and growth directions. The electrical conductivity of 1500-2000 S/cm is comparable to state-of-the-art SnO2:F TCOs while the fabrication temperature is reduced by ˜200 °C, enabling a broader range of applications, such as optoelectronics on flexible substrates. Hall effect measurements show an intriguing ambipolar behavior depending on the annealing ambient. Especially, a strong p-type conductivity with a hole concentration of p ˜ 5 × 1021 cm-3 and mobility μp ˜ 2 cm2 V-1 s-1 is obtained in a weak oxidizing ambient. Such a high p-type conductivity is particularly rare in TCOs, and it offers potential applications in bipolar oxide semiconductor devices. Optical measurements showed a low absorption loss of <3% in a broad IR wavelength regime of λ = 1100-2500 nm for p-type SnOx, suggesting that these nano-needle structured SnOx TCOs can be engineered to enhance low

  18. Synthesis of diketopyrrolopyrrole based copolymers via the direct arylation method for p-channel and ambipolar OFETs.

    PubMed

    Sonar, Prashant; Foong, Thelese Ru Bao; Dodabalapur, Ananth

    2014-03-01

    In this paper, we have synthesized two novel diketopyrrolopyrrole (DPP) based donor–acceptor (D–A) copolymers poly{3,6-dithiophene-2-yl-2,5-di(2-octyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-alt-1,5-bis(dodecyloxy)naphthalene} (PDPPT-NAP) and poly{3,6-dithiophene-2-yl-2,5-di(2-butyldecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-alt-2-dodecyl-2H-benzo[d][1,2,3]triazole} (PDPPT-BTRZ) via direct arylation organometallic coupling. Both copolymers contain a common electron withdrawing DPP building block which is combined with electron donating alkoxy naphthalene and electron withdrawing alkyl-triazole comonomers. The number average molecular weight (M(n)) determined by gel permeation chromatography (GPC) for polymer PDPPT-NAP is around 23400 g mol(−1) whereas for polymer PDPPT-BTRZ it is 18600 g mol(−1). The solid state absorption spectra of these copolymers show a wide range of absorption from 400 nm to 1000 nm with optical band gaps calculated from absorption cut off values in the range of 1.45–1.30 eV. The HOMO values determined for PDPPT-NAP and PDPPT-BTRZ copolymers from photoelectron spectroscopy in air (PESA) data are 5.15 eV and 5.25 eV respectively. These polymers exhibit promising p-channel and ambipolar behaviour when used as an active layer in organic thin-film transistor (OTFT) devices. The highest hole mobility measured for polymer PDPPT-NAP is around 0.0046 cm(2) V(−1) s(−1) whereas the best ambipolar performance was calculated for PDPPT-BTRZ with a hole and electron mobility of 0.01 cm(2) V(−1) s(−1) and 0.006 cm(2) V(−1) s(−1) .

  19. Flexible ambipolar organic field-effect transistors with reverse-offset-printed silver electrodes for a complementary inverter.

    PubMed

    Park, Junsu; Kim, Minseok; Yeom, Seung-Won; Ha, Hyeon Jun; Song, Hyenggun; Min Jhon, Young; Kim, Yun-Hi; Ju, Byeong-Kwon

    2016-06-01

    We report ambipolar organic field-effect transistors and complementary inverter circuits with reverse-offset-printed (ROP) Ag electrodes fabricated on a flexible substrate. A diketopyrrolopyrrole-based co-polymer (PDPP-TAT) was used as the semiconductor and poly(methyl methacrylate) was used as the gate insulator. Considerable improvement is observed in the n-channel electrical characteristics by inserting a cesium carbonate (Cs2CO3) as the electron-injection/hole-blocking layer at the interface between the semiconductors and the electrodes. The saturation mobility values are 0.35 cm(2) V(-1) s(-1) for the p-channel and 0.027 cm(2) V(-1) s(-1) for the n-channel. A complementary inverter is demonstrated based on the ROP process, and it is selectively controlled by the insertion of Cs2CO3 onto the n-channel region via thermal evaporation. Moreover, the devices show stable operation during the mechanical bending test using tensile strains ranging from 0.05% to 0.5%. The results confirm that these devices have great potential for use in flexible and inexpensive integrated circuits over a large area. PMID:27114463

  20. High-performance ambipolar self-assembled Au/Ag nanowire based vertical quantum dot field effect transistor

    NASA Astrophysics Data System (ADS)

    Song, Xiaoxian; Zhang, Yating; Zhang, Haiting; Yu, Yu; Cao, Mingxuan; Che, Yongli; Wang, Jianlong; Dai, Haitao; Yang, Junbo; Ding, Xin; Yao, Jianquan

    2016-10-01

    Most lateral PbSe quantum dot field effect transistors (QD FETs) show a low on current/off current (I on/I off) ratio in charge transport measurements. A new strategy to provide generally better performance is to design PbSe QD FETs with vertical architecture, in which the structure parameters can be tuned flexibly. Here, we fabricated a novel room-temperature operated vertical quantum dot field effect transistor with a channel of 580 nm, where self-assembled Au/Ag nanowires served as source transparent electrodes and PbSe quantum dots as active channels. Through investigating the electrical characterization, the ambipolar device exhibited excellent characteristics with a high I on/I off current ratio of about 1 × 105 and a low sub-threshold slope (0.26 V/decade) in the p-type regime. The all-solution processing vertical architecture provides a convenient way for low cost, large-area integration of the device.

  1. Flexible ambipolar organic field-effect transistors with reverse-offset-printed silver electrodes for a complementary inverter

    NASA Astrophysics Data System (ADS)

    Park, Junsu; Kim, Minseok; Yeom, Seung-Won; Ha, Hyeon Jun; Song, Hyenggun; Jhon, Young Min; Kim, Yun-Hi; Ju, Byeong-Kwon

    2016-06-01

    We report ambipolar organic field-effect transistors and complementary inverter circuits with reverse-offset-printed (ROP) Ag electrodes fabricated on a flexible substrate. A diketopyrrolopyrrole-based co-polymer (PDPP-TAT) was used as the semiconductor and poly(methyl methacrylate) was used as the gate insulator. Considerable improvement is observed in the n-channel electrical characteristics by inserting a cesium carbonate (Cs2CO3) as the electron-injection/hole-blocking layer at the interface between the semiconductors and the electrodes. The saturation mobility values are 0.35 cm2 V‑1 s‑1 for the p-channel and 0.027 cm2 V‑1 s‑1 for the n-channel. A complementary inverter is demonstrated based on the ROP process, and it is selectively controlled by the insertion of Cs2CO3 onto the n-channel region via thermal evaporation. Moreover, the devices show stable operation during the mechanical bending test using tensile strains ranging from 0.05% to 0.5%. The results confirm that these devices have great potential for use in flexible and inexpensive integrated circuits over a large area.

  2. Flexible ambipolar organic field-effect transistors with reverse-offset-printed silver electrodes for a complementary inverter

    NASA Astrophysics Data System (ADS)

    Park, Junsu; Kim, Minseok; Yeom, Seung-Won; Ha, Hyeon Jun; Song, Hyenggun; Jhon, Young Min; Kim, Yun-Hi; Ju, Byeong-Kwon

    2016-06-01

    We report ambipolar organic field-effect transistors and complementary inverter circuits with reverse-offset-printed (ROP) Ag electrodes fabricated on a flexible substrate. A diketopyrrolopyrrole-based co-polymer (PDPP-TAT) was used as the semiconductor and poly(methyl methacrylate) was used as the gate insulator. Considerable improvement is observed in the n-channel electrical characteristics by inserting a cesium carbonate (Cs2CO3) as the electron-injection/hole-blocking layer at the interface between the semiconductors and the electrodes. The saturation mobility values are 0.35 cm2 V-1 s-1 for the p-channel and 0.027 cm2 V-1 s-1 for the n-channel. A complementary inverter is demonstrated based on the ROP process, and it is selectively controlled by the insertion of Cs2CO3 onto the n-channel region via thermal evaporation. Moreover, the devices show stable operation during the mechanical bending test using tensile strains ranging from 0.05% to 0.5%. The results confirm that these devices have great potential for use in flexible and inexpensive integrated circuits over a large area.

  3. Field-Effect Transistors Based on Few-Layered Ambipolar MoSe2 and α-MoTe2

    NASA Astrophysics Data System (ADS)

    Rhodes, Daniel; Pradhan, Nihar; Feng, Simin; Moon, Byoung-Hee; Xin, Yan; Memaran, Sharhriar; Siddiq, Muhandis; Bhaskaran, Lakshmi; Hill, Stephen; Terrones, Humberto; Terrones, Mauricio; Pulickel, Ajayan; Balicas, Luis

    2015-03-01

    We report a room temperature study on the electrical responses of field-effect transistors (FETs) based on few-layered MoSe2 and MoTe2, grown by chemical vapor transport, mechanically exfoliated onto SiO2. MoSe2 FETs electrically contacted with Ti display ambipolar behavior with current on/off ratios up to 106 for both hole and electron channels. For both channels the Hall effect indicates Hall mobilities μH ~= 250 cm2/(Vs), which are comparable to the corresponding field-effect mobilities, μFE ~ 175 cm2/(Vs), evaluated through two-terminal field-effect configuration. MoTe2 field-effect transistors are observed to be hole-doped, displaying on/off ratios of ~ 106 and subthreshold swings of ~140 mV per decade. Our results suggest that MoSe2 is a good candidate for single atomic layer p -n junctions and for low-power, complementary logic applications, with MoTe2 having similar properties. However, in MoTe2 we observe a field-effect mobility of only μFE ~ 20 cm2/(Vs) in a bilayer device and ~ 27 cm2/(Vs) in seven layers. This work was supported by the U.S. Army Research Office MURI Grant No. W911NF-11-1-0362. The NHMFL is supported by NSF through NSF-DMR-0084173 and the State of Florida.

  4. A two-dimensional π-d conjugated coordination polymer with extremely high electrical conductivity and ambipolar transport behaviour.

    PubMed

    Huang, Xing; Sheng, Peng; Tu, Zeyi; Zhang, Fengjiao; Wang, Junhua; Geng, Hua; Zou, Ye; Di, Chong-an; Yi, Yuanping; Sun, Yimeng; Xu, Wei; Zhu, Daoben

    2015-06-15

    Currently, studies on organic two-dimensional (2D) materials with special optic-electronic properties are attracting great research interest. However, 2D organic systems possessing promising electrical transport properties are still rare. Here a highly crystalline thin film of a copper coordination polymer, Cu-BHT (BHT=benzenehexathiol), is prepared via a liquid-liquid interface reaction between BHT/dichloromethane and copper(II) nitrate/H2O. The morphology and structure characterization reveal that this film is piled up by nanosheets of 2D lattice of [Cu3(C6S6)]n, which is further verified by quantum simulation. Four-probe measurements show that the room temperature conductivity of this material can reach up to 1,580 S cm(-1), which is the highest value ever reported for coordination polymers. Meanwhile, it displays ambipolar charge transport behaviour and extremely high electron and hole mobilities (99 cm(2 )V(-1 )s(-1) for holes and 116 cm(2 )V(-1 )s(-1) for electrons) under field-effect modulation.

  5. High-performance ambipolar self-assembled Au/Ag nanowire based vertical quantum dot field effect transistor.

    PubMed

    Song, Xiaoxian; Zhang, Yating; Zhang, Haiting; Yu, Yu; Cao, Mingxuan; Che, Yongli; Wang, Jianlong; Dai, Haitao; Yang, Junbo; Ding, Xin; Yao, Jianquan

    2016-10-01

    Most lateral PbSe quantum dot field effect transistors (QD FETs) show a low on current/off current (I on/I off) ratio in charge transport measurements. A new strategy to provide generally better performance is to design PbSe QD FETs with vertical architecture, in which the structure parameters can be tuned flexibly. Here, we fabricated a novel room-temperature operated vertical quantum dot field effect transistor with a channel of 580 nm, where self-assembled Au/Ag nanowires served as source transparent electrodes and PbSe quantum dots as active channels. Through investigating the electrical characterization, the ambipolar device exhibited excellent characteristics with a high I on/I off current ratio of about 1 × 10(5) and a low sub-threshold slope (0.26 V/decade) in the p-type regime. The all-solution processing vertical architecture provides a convenient way for low cost, large-area integration of the device.

  6. Flexible ambipolar organic field-effect transistors with reverse-offset-printed silver electrodes for a complementary inverter.

    PubMed

    Park, Junsu; Kim, Minseok; Yeom, Seung-Won; Ha, Hyeon Jun; Song, Hyenggun; Min Jhon, Young; Kim, Yun-Hi; Ju, Byeong-Kwon

    2016-06-01

    We report ambipolar organic field-effect transistors and complementary inverter circuits with reverse-offset-printed (ROP) Ag electrodes fabricated on a flexible substrate. A diketopyrrolopyrrole-based co-polymer (PDPP-TAT) was used as the semiconductor and poly(methyl methacrylate) was used as the gate insulator. Considerable improvement is observed in the n-channel electrical characteristics by inserting a cesium carbonate (Cs2CO3) as the electron-injection/hole-blocking layer at the interface between the semiconductors and the electrodes. The saturation mobility values are 0.35 cm(2) V(-1) s(-1) for the p-channel and 0.027 cm(2) V(-1) s(-1) for the n-channel. A complementary inverter is demonstrated based on the ROP process, and it is selectively controlled by the insertion of Cs2CO3 onto the n-channel region via thermal evaporation. Moreover, the devices show stable operation during the mechanical bending test using tensile strains ranging from 0.05% to 0.5%. The results confirm that these devices have great potential for use in flexible and inexpensive integrated circuits over a large area.

  7. A two-dimensional π–d conjugated coordination polymer with extremely high electrical conductivity and ambipolar transport behaviour

    PubMed Central

    Huang, Xing; Sheng, Peng; Tu, Zeyi; Zhang, Fengjiao; Wang, Junhua; Geng, Hua; Zou, Ye; Di, Chong-an; Yi, Yuanping; Sun, Yimeng; Xu, Wei; Zhu, Daoben

    2015-01-01

    Currently, studies on organic two-dimensional (2D) materials with special optic-electronic properties are attracting great research interest. However, 2D organic systems possessing promising electrical transport properties are still rare. Here a highly crystalline thin film of a copper coordination polymer, Cu-BHT (BHT=benzenehexathiol), is prepared via a liquid–liquid interface reaction between BHT/dichloromethane and copper(II) nitrate/H2O. The morphology and structure characterization reveal that this film is piled up by nanosheets of 2D lattice of [Cu3(C6S6)]n, which is further verified by quantum simulation. Four-probe measurements show that the room temperature conductivity of this material can reach up to 1,580 S cm−1, which is the highest value ever reported for coordination polymers. Meanwhile, it displays ambipolar charge transport behaviour and extremely high electron and hole mobilities (99 cm2 V−1 s−1 for holes and 116 cm2 V−1 s−1 for electrons) under field-effect modulation. PMID:26074272

  8. A two-dimensional π-d conjugated coordination polymer with extremely high electrical conductivity and ambipolar transport behaviour

    NASA Astrophysics Data System (ADS)

    Huang, Xing; Sheng, Peng; Tu, Zeyi; Zhang, Fengjiao; Wang, Junhua; Geng, Hua; Zou, Ye; di, Chong-An; Yi, Yuanping; Sun, Yimeng; Xu, Wei; Zhu, Daoben

    2015-06-01

    Currently, studies on organic two-dimensional (2D) materials with special optic-electronic properties are attracting great research interest. However, 2D organic systems possessing promising electrical transport properties are still rare. Here a highly crystalline thin film of a copper coordination polymer, Cu-BHT (BHT=benzenehexathiol), is prepared via a liquid-liquid interface reaction between BHT/dichloromethane and copper(II) nitrate/H2O. The morphology and structure characterization reveal that this film is piled up by nanosheets of 2D lattice of [Cu3(C6S6)]n, which is further verified by quantum simulation. Four-probe measurements show that the room temperature conductivity of this material can reach up to 1,580 S cm-1, which is the highest value ever reported for coordination polymers. Meanwhile, it displays ambipolar charge transport behaviour and extremely high electron and hole mobilities (99 cm2 V-1 s-1 for holes and 116 cm2 V-1 s-1 for electrons) under field-effect modulation.

  9. High-performance ambipolar self-assembled Au/Ag nanowire based vertical quantum dot field effect transistor.

    PubMed

    Song, Xiaoxian; Zhang, Yating; Zhang, Haiting; Yu, Yu; Cao, Mingxuan; Che, Yongli; Wang, Jianlong; Dai, Haitao; Yang, Junbo; Ding, Xin; Yao, Jianquan

    2016-10-01

    Most lateral PbSe quantum dot field effect transistors (QD FETs) show a low on current/off current (I on/I off) ratio in charge transport measurements. A new strategy to provide generally better performance is to design PbSe QD FETs with vertical architecture, in which the structure parameters can be tuned flexibly. Here, we fabricated a novel room-temperature operated vertical quantum dot field effect transistor with a channel of 580 nm, where self-assembled Au/Ag nanowires served as source transparent electrodes and PbSe quantum dots as active channels. Through investigating the electrical characterization, the ambipolar device exhibited excellent characteristics with a high I on/I off current ratio of about 1 × 10(5) and a low sub-threshold slope (0.26 V/decade) in the p-type regime. The all-solution processing vertical architecture provides a convenient way for low cost, large-area integration of the device. PMID:27578613

  10. Quantum and classical magnetoresistance in ambipolar topological insulator transistors with gate-tunable bulk and surface conduction.

    PubMed

    Tian, Jifa; Chang, Cuizu; Cao, Helin; He, Ke; Ma, Xucun; Xue, Qikun; Chen, Yong P

    2014-05-07

    Weak antilocalization (WAL) and linear magnetoresistance (LMR) are two most commonly observed magnetoresistance (MR) phenomena in topological insulators (TIs) and often attributed to the Dirac topological surface states (TSS). However, ambiguities exist because these phenomena could also come from bulk states (often carrying significant conduction in many TIs) and are observable even in non-TI materials. Here, we demonstrate back-gated ambipolar TI field-effect transistors in (Bi0.04Sb0.96)2Te3 thin films grown by molecular beam epitaxy on SrTiO3(111), exhibiting a large carrier density tunability (by nearly 2 orders of magnitude) and a metal-insulator transition in the bulk (allowing switching off the bulk conduction). Tuning the Fermi level from bulk band to TSS strongly enhances both the WAL (increasing the number of quantum coherent channels from one to peak around two) and LMR (increasing its slope by up to 10 times). The SS-enhanced LMR is accompanied by a strongly nonlinear Hall effect, suggesting important roles of charge inhomogeneity (and a related classical LMR), although existing models of LMR cannot capture all aspects of our data. Our systematic gate and temperature dependent magnetotransport studies provide deeper insights into the nature of both MR phenomena and reveal differences between bulk and TSS transport in TI related materials.

  11. Charge collected by diffusion from an ion track under mixed boundary conditions

    SciTech Connect

    Edmonds, L.D. )

    1991-04-01

    This paper analyzes charge-carrier diffusion from an ion track in a silicon substrate, at least a few hundred {mu}m thick. The substrate upper surface is treated as reflective except for a small section, intended to represent a reverse-biased junction, which is treated as a sink. Total charge collected by the sink is calculated by assuming transport to be governed by an ambipolar diffusion equation with temporally constant and spatially uniform carrier lifetime and diffusion coefficient. Present results apply to a normally incident track but could easily be generalized to arbitrary track direction. The collected charge is found to depend on track length and on the electrostatic capacitance, rather than the area, of the sink. Theoretical prediction are compared to the results of a numerical simulation called the Poisson and Continuity Equation Solver (PISCES) for three cases and are found to agree within a factor of two in the worst case.

  12. Driving voltage reduction in white organic light-emitting devices from selectively doping in ambipolar blue-emitting layer

    NASA Astrophysics Data System (ADS)

    Hsiao, Chih-Hung; Lin, Chi-Feng; Lee, Jiun-Haw

    2007-11-01

    White organic light-emitting devices (OLEDs) consisting of ambipolar 9,10-bis(2'-naphthyl) anthracene (ADN) as a host of blue-emitting layer (EML) were investigated. A thin codoped layer of yellow 5,6,11,12-Tetraphenylnaphthacene (rubrene) served as a probe for detecting the position of maximum recombination rate in the 4,4'-bis[2-(4-(N,N-diphenylamino)phenyl)vinyl]biphenyl (DPAVBi) doped-ADN EML. Due to the energy barrier and bipolar carrier transport, the maximum recombination rate was found to be close to but not exactly at the interface of the hole-transporting layer and the EML. With appropriate tuning in the thickness, position, and dopant concentrations of the codoped layer (rubrene:DPAVBi:ADN) in the EML, the device driving voltage decreased by 21.7%, nearly 2 V in reduction, due to the increased recombination current from the faster exciton relaxation induced by the yellow dopants. Among the advantages of introducing the codoped layer over conventional single-doped layers are the elimination of the trapping effect to avoid increasing the device driving voltage, the alleviation of the dependence of the recombination zone on the applied voltage for improving color stability, and the utilization of excitons in a more efficient way to enhance device efficiency. Without using any electrically conductive layers such as the p-i-n structure, we were able to successfully generate 112 cd/m2 at 4 V from our white OLED simply by engineering the structure of the EML.

  13. Vaneless diffusers

    NASA Astrophysics Data System (ADS)

    Senoo, Y.

    The influence of vaneless diffusers on flow in centrifugal compressors, particularly on surge, is discussed. A vaneless diffuser can demonstrate stable operation in a wide flow range only if it is installed with a backward leaning blade impeller. The circumferential distortion of flow in the impeller disappears quickly in the vaneless diffuser. The axial distortion of flow at the diffuser inlet does not decay easily. In large specific speed compressors, flow out of the impeller is distorted axially. Pressure recovery of diffusers at distorted inlet flow is considerably improved by half guide vanes. The best height of the vanes is a little 1/2 diffuser width. In small specific speed compressors, flow out of the impeller is not much distorted and pressure recovery can be predicted with one-dimensional flow analysis. Wall friction loss is significant in narrow diffusers. The large pressure drop at a small flow rate can cause the positive gradient of the pressure-flow rate characteristic curve, which may cause surging.

  14. Mobilities in ambipolar field effect transistors based on single-walled carbon nanotube network and formed on a gold nanoparticle template

    SciTech Connect

    Wongsaeng, Chalao; Singjai, Pisith

    2014-04-07

    Ambipolar field effect transistors based on a single-walled carbon nanotube (SWNT) network formed on a gold nanoparticle (AuNP) template with polyvinyl alcohol as a gate insulator were studied by measuring the current–gate voltage characteristics. It was found that the mobilities of holes and electrons increased with increasing AuNP number density. The disturbances in the flow pattern of the carbon feedstock in the chemical vapor deposition growth that were produced by the AuNP geometry, resulted in the differences in the crystallinity and the diameter, as well as the changes in the degree of the semiconductor behavior of the SWNTs.

  15. Diffuse radiation

    NASA Technical Reports Server (NTRS)

    1981-01-01

    A diffuse celestial radiation which is isotropic at least on a course scale were measured from the soft X-ray region to about 150 MeV, at which energy the intensity falls below that of the galactic emission for most galactic latitudes. The spectral shape, the intensity, and the established degree of isotropy of this diffuse radiation already place severe constraints on the possible explanations for this radiation. Among the extragalactic theories, the more promising explanations of the isotropic diffuse emission appear to be radiation from exceptional galaxies from matter antimatter annihilation at the boundaries of superclusters of galaxies of matter and antimatter in baryon symmetric big bang models. Other possible sources for extragalactic diffuse gamma radiation are discussed and include normal galaxies, clusters of galaxies, primordial cosmic rays interacting with intergalactic matter, primordial black holes, and cosmic ray leakage from galaxies.

  16. Diffusion barriers

    NASA Technical Reports Server (NTRS)

    Nicolet, M. A.

    1983-01-01

    The choice of the metallic film for the contact to a semiconductor device is discussed. One way to try to stabilize a contact is by interposing a thin film of a material that has low diffusivity for the atoms in question. This thin film application is known as a diffusion barrier. Three types of barriers can be distinguished. The stuffed barrier derives its low atomic diffusivity to impurities that concentrate along the extended defects of a polycrystalline layer. Sacrificial barriers exploit the fact that some (elemental) thin films react in a laterally uniform and reproducible fashion. Sacrificial barriers have the advantage that the point of their failure is predictable. Passive barriers are those most closely approximating an ideal barrier. The most-studied case is that of sputtered TiN films. Stuffed barriers may be viewed as passive barriers whose low diffusivity material extends along the defects of the polycrystalline host.

  17. Study on copper phthalocyanine and perylene-based ambipolar organic light-emitting field-effect transistors produced using neutral beam deposition method

    SciTech Connect

    Kim, Dae-Kyu; Oh, Jeong-Do; Shin, Eun-Sol; Seo, Hoon-Seok; Choi, Jong-Ho

    2014-04-28

    The neutral cluster beam deposition (NCBD) method has been applied to the production and characterization of ambipolar, heterojunction-based organic light-emitting field-effect transistors (OLEFETs) with a top-contact, multi-digitated, long-channel geometry. Organic thin films of n-type N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic diimide and p-type copper phthalocyanine were successively deposited on the hydroxyl-free polymethyl-methacrylate (PMMA)-coated SiO{sub 2} dielectrics using the NCBD method. Characterization of the morphological and structural properties of the organic active layers was performed using atomic force microscopy and X-ray diffraction. Various device parameters such as hole- and electron-carrier mobilities, threshold voltages, and electroluminescence (EL) were derived from the fits of the observed current-voltage and current-voltage-light emission characteristics of OLEFETs. The OLEFETs demonstrated good field-effect characteristics, well-balanced ambipolarity, and substantial EL under ambient conditions. The device performance, which is strongly correlated with the surface morphology and the structural properties of the organic active layers, is discussed along with the operating conduction mechanism.

  18. Self-consistent modeling for estimation of the reduced electric field in a DC excited diffusion controlled CW CO2 laser

    NASA Astrophysics Data System (ADS)

    Kumar, Manoj; Bhagat, M. S.; Biswas, A. K.; Rana, L. B.; Pakhare, Jagdish; Rawat, B. S.; Kukreja, L. M.

    2016-07-01

    The results of a numerical simulation method that estimate various discharge parameters in the positive column of a DC glow discharge controlled by ambipolar diffusion are presented. The parameters like reduced electric field (E/N), electron temperature, ionization rates, ambipolar diffusion losses and the average gas temperature were numerically evaluated for several mixtures of CO2, N2 and He in low pressure regime. The estimated E/N value which is a primary governing parameter of positive column was verified experimentally using a double probe in diffusion controlled CW CO2 laser for a variety of CO2, N2 and He mixtures. The role of auxiliary ionization source like pulser used for pre-ionization and its effect on the steady state E/N value was also studied. A reasonably good agreement was found between the theoretical and the experimental results. Based on the results of this simulation a zigzag folded, diffusion-cooled, 500 W CW CO2 laser has been designed and developed for research in gas phase nanoparticle synthesis.

  19. HTCAP-1: a program for calcuating operating temperatures in HFIR target irradiation experiments

    SciTech Connect

    Kania, M.J.; Howard A.M.

    1980-06-01

    The thermal modeling code, HTCAP-1, calculates in-reactor operating temperatures of fueled specimens contained in the High Flux Isotope Reactor (HFIR) target irradiation experiments (HT-series). Temperature calculations are made for loose particle and bonded fuel rod specimens. Maximum particle surface temperatures are calculated for the loose particles and centerline and surface temperatures for the fuel rods. Three computational models are employed to determine fission heat generation rates, capsule heat transfer analysis, and specimen temperatures. This report is also intended to be a users' manual, and the application of HTCAP-1 to the HT-34 irradiation capsule is presented.

  20. Demonstrating Diffusion

    ERIC Educational Resources Information Center

    Foy, Barry G.

    1977-01-01

    Two demonstrations are described. Materials and instructions for demonstrating movement of molecules into cytoplasm using agar blocks, phenolphthalein, and sodium hydroxide are given. A simple method for demonstrating that the rate of diffusion of a gas is inversely proportional to its molecular weight is also presented. (AJ)

  1. Relativistic diffusion

    NASA Astrophysics Data System (ADS)

    Haba, Z.

    2009-02-01

    We discuss relativistic diffusion in proper time in the approach of Schay (Ph.D. thesis, Princeton University, Princeton, NJ, 1961) and Dudley [Ark. Mat. 6, 241 (1965)]. We derive (Langevin) stochastic differential equations in various coordinates. We show that in some coordinates the stochastic differential equations become linear. We obtain momentum probability distribution in an explicit form. We discuss a relativistic particle diffusing in an external electromagnetic field. We solve the Langevin equations in the case of parallel electric and magnetic fields. We derive a kinetic equation for the evolution of the probability distribution. We discuss drag terms leading to an equilibrium distribution. The relativistic analog of the Ornstein-Uhlenbeck process is not unique. We show that if the drag comes from a diffusion approximation to the master equation then its form is strongly restricted. The drag leading to the Tsallis equilibrium distribution satisfies this restriction whereas the one of the Jüttner distribution does not. We show that any function of the relativistic energy can be the equilibrium distribution for a particle in a static electric field. A preliminary study of the time evolution with friction is presented. It is shown that the problem is equivalent to quantum mechanics of a particle moving on a hyperboloid with a potential determined by the drag. A relation to diffusions appearing in heavy ion collisions is briefly discussed.

  2. Defusing Diffusion

    ERIC Educational Resources Information Center

    Dou, Remy; Hogan, DaNel; Kossover, Mark; Spuck, Timothy; Young, Sarah

    2013-01-01

    Diffusion has often been taught in science courses as one of the primary ways by which molecules travel, particularly within organisms. For years, classroom teachers have used the same common demonstrations to illustrate this concept (e.g., placing drops of food coloring in a beaker of water). Most of the time, the main contributor to the motion…

  3. Relativistic diffusion.

    PubMed

    Haba, Z

    2009-02-01

    We discuss relativistic diffusion in proper time in the approach of Schay (Ph.D. thesis, Princeton University, Princeton, NJ, 1961) and Dudley [Ark. Mat. 6, 241 (1965)]. We derive (Langevin) stochastic differential equations in various coordinates. We show that in some coordinates the stochastic differential equations become linear. We obtain momentum probability distribution in an explicit form. We discuss a relativistic particle diffusing in an external electromagnetic field. We solve the Langevin equations in the case of parallel electric and magnetic fields. We derive a kinetic equation for the evolution of the probability distribution. We discuss drag terms leading to an equilibrium distribution. The relativistic analog of the Ornstein-Uhlenbeck process is not unique. We show that if the drag comes from a diffusion approximation to the master equation then its form is strongly restricted. The drag leading to the Tsallis equilibrium distribution satisfies this restriction whereas the one of the Jüttner distribution does not. We show that any function of the relativistic energy can be the equilibrium distribution for a particle in a static electric field. A preliminary study of the time evolution with friction is presented. It is shown that the problem is equivalent to quantum mechanics of a particle moving on a hyperboloid with a potential determined by the drag. A relation to diffusions appearing in heavy ion collisions is briefly discussed.

  4. Diffusion bonding

    DOEpatents

    Anderson, Robert C.

    1976-06-22

    1. A method for joining beryllium to beryllium by diffusion bonding, comprising the steps of coating at least one surface portion of at least two beryllium pieces with nickel, positioning a coated surface portion in a contiguous relationship with an other surface portion, subjecting the contiguously disposed surface portions to an environment having an atmosphere at a pressure lower than ambient pressure, applying a force upon the beryllium pieces for causing the contiguous surface portions to abut against each other, heating the contiguous surface portions to a maximum temperature less than the melting temperature of the beryllium, substantially uniformly decreasing the applied force while increasing the temperature after attaining a temperature substantially above room temperature, and maintaining a portion of the applied force at a temperature corresponding to about maximum temperature for a duration sufficient to effect the diffusion bond between the contiguous surface portions.

  5. The electric wind of Venus: A global and persistent "polar wind"-like ambipolar electric field sufficient for the direct escape of heavy ionospheric ions

    NASA Astrophysics Data System (ADS)

    Collinson, Glyn A.; Frahm, Rudy A.; Glocer, Alex; Coates, Andrew J.; Grebowsky, Joseph M.; Barabash, Stas; Domagal-Goldman, Shawn D.; Fedorov, Andrei; Futaana, Yoshifumi; Gilbert, Lin K.; Khazanov, George; Nordheim, Tom A.; Mitchell, David; Moore, Thomas E.; Peterson, William K.; Winningham, John D.; Zhang, Tielong L.

    2016-06-01

    Understanding what processes govern atmospheric escape and the loss of planetary water is of paramount importance for understanding how life in the universe can exist. One mechanism thought to be important at all planets is an "ambipolar" electric field that helps ions overcome gravity. We report the discovery and first quantitative extraterrestrial measurements of such a field at the planet Venus. Unexpectedly, despite comparable gravity, we show the field to be five times stronger than in Earth's similar ionosphere. Contrary to our understanding, Venus would still lose heavy ions (including oxygen and all water-group species) to space, even if there were no stripping by the solar wind. We therefore find that it is possible for planets to lose heavy ions to space entirely through electric forces in their ionospheres and such an "electric wind" must be considered when studying the evolution and potential habitability of any planet in any star system.

  6. Molecular host-guest energy-transfer system with an ultralow amplified spontaneous emission threshold employing an ambipolar semiconducting host matrix.

    PubMed

    Toffanin, Stefano; Capelli, Raffaella; Hwu, Tsyr-Yuan; Wong, Ken-Tsung; Plötzing, Tobias; Först, Michael; Muccini, Michele

    2010-01-14

    We report on the characteristics of a host-guest lasing system obtained by coevaporation of an oligo(9,9-diarylfluorene) derivative named T3 with the red-emitter 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran dye (DCM). We demonstrate that the ambipolar semiconductor T3 can be implemented as an active matrix in the realization of a host-guest system in which an efficient energy transfer takes place from the T3 matrix to the lasing DCM molecules. We performed a detailed spectroscopic study on the system by systematically varying the DCM concentration in the T3 matrix. Measurements of steady-state photoluminescence (PL), PL quantum yield (PLQY), time-resolved picosecond PL, and amplified spontaneous emission (ASE) threshold are used to optimize the acceptor concentration at which the ASE from DCM molecules takes place with the lowest threshold. The sample with a DCM relative deposition ratio of 2% shows an ASE threshold as low as 0.6 kW/cm(2) and a net optical gain measured by femtosecond time-resolved pump-and-probe spectroscopy as high as 77 cm(-1). The reference model system Alq(3):DCM sample measured in exactly the same experimental conditions presents an one-order-of-magnitude higher ASE threshold. The ASE threshold of T3:DCM is the lowest reported to date for a molecular host-guest energy-transfer system, which makes the investigated blend an appealing system for use as an active layer in lasing devices. In particular, the ambipolar charge transport properties of the T3 matrix and its field-effect characteristics make the host-guest system presented here an ideal candidate for the realization of electrically pumped organic lasers.

  7. DIFFUSION PUMP

    DOEpatents

    Levenson, L.

    1963-09-01

    A high-vacuum diffusion pump is described, featuring a novel housing geometry for enhancing pumping speed. An upright, cylindrical lower housing portion is surmounted by a concentric, upright, cylindrical upper housing portion of substantially larger diameter; an uppermost nozzle, disposed concentrically within the upper portion, is adapted to eject downwardly a conical sheet of liquid outwardly to impinge upon the uppermost extremity of the interior wall of the lower portion. Preferably this nozzle is mounted upon a pedestal rising coaxially from within the lower portion and projecting up into said upper portion. (AEC)

  8. Experimental Radar Studies of Anisotropic Diffusion of High Altitude Meteor Trails

    NASA Astrophysics Data System (ADS)

    Hocking, W. K.

    2004-12-01

    At altitudes above 93 km in the atmosphere, magnetic and electric fields can affect the modes and rates of non-turbulent diffusion of ionized meteor trails. Anisotropic diffusion is expected. Most theories of anisotropic diffusion, and indeed most experimental studies, have concentrated on the effects of the magnetic field in producing this anisotropy, and different rates of expansion are expected in directions parallel to and perpendicular to the magnetic field lines. In this study, we use interferometric meteor radars to investigate the dependence of the ambipolar diffusion coefficient on viewing direction relative to the magnetic field, and show that the dependence is at best weak when daily averages are used. We then demonstrate that the reason for this effect is that the positions of maximum and minimum diffusion rates varies as a function of time of day, and that daily averaging masks the anisotropy. One possibility to account for the observations is that this strong diurnal variation is a consequence of the electric fields in the upper atmosphere, which are often tidally driven. An alternative possibility is a diurnal cycle in mean meteor entrance speeds. We lean towards the first hypothesis, but both possibilities are discussed. We demonstrate our results with data from several sites, but particularly using the Clovar radar near London, Ontario, Canada.

  9. Self-similar and diffusive expansion of nonextensive plasmas

    SciTech Connect

    Akbari-Moghanjoughi, M.

    2015-03-15

    Exact analytical self-similar solution is presented for free collisionless expansion of a two-component plasma of inertial ions and nonextensive electrons into vacuum, using the generalized nonextensive velocity distribution for electrons. Furthermore, a hydrodynamic model of plasma expansion in the presence of the ambipolar diffusion caused by collisions among the plasma species, such as electrons and ions, is developed and a Fokker-Planck-like generalized diffusion equation for steady-state expansion of a nonextensive electron-ion plasma is derived. For the case of generalized statistics and in the absence of particle diffusion, the density, velocity, electric potential, and field of expansion profiles are exactly obtained and studied in terms of the self-similar parameter. It is found that superthermal electrons lead to an accelerated expansion of plasma compared to that of Maxwellian electrons. It is also revealed that the nonextensivity parameter plays a fundamental role on the density, velocity, electric potential, and field configuration of the expansion. Therefore, one is able to distinguish three different regimes q < 1, q = 1, and q > 1 for expansion corresponding to sub-nonextensive, extensive, and super-nonextensive statistical profiles for electrons, respectively. Current research can provide useful information and suggests techniques for investigation of the involved statistical mechanism on the role of the energetic electron fluid in the expansion of plasma in strong pulsed laser-matter interaction experiments. It is also shown that the particle diffusion expansion mechanism becomes more dominant for relatively large values of the nonextensivity parameter, q.

  10. NIST Diffusion Data Center

    National Institute of Standards and Technology Data Gateway

    NIST Diffusion Data Center (Web, free access)   The NIST Diffusion Data Center is a collection of over 14,100 international papers, theses, and government reports on diffusion published before 1980.

  11. Parallel flow diffusion battery

    DOEpatents

    Yeh, H.C.; Cheng, Y.S.

    1984-01-01

    A parallel flow diffusion battery for determining the mass distribution of an aerosol has a plurality of diffusion cells mounted in parallel to an aerosol stream, each diffusion cell including a stack of mesh wire screens of different density.

  12. Parallel flow diffusion battery

    DOEpatents

    Yeh, Hsu-Chi; Cheng, Yung-Sung

    1984-08-07

    A parallel flow diffusion battery for determining the mass distribution of an aerosol has a plurality of diffusion cells mounted in parallel to an aerosol stream, each diffusion cell including a stack of mesh wire screens of different density.

  13. Dependence of the Carrier Transport Characteristics on the Buried Layer Thickness in Ambipolar Double-Layer Organic Field-Effect Transistors Investigated by Electrical and Optical Measurements

    NASA Astrophysics Data System (ADS)

    Zhang, Le; Taguchi, Dai; Manaka, Takaaki; Iwamoto, Mitsumasa

    2013-05-01

    By using current-voltage (I-V) measurements and optical modulation spectroscopy, we investigated the dependence of the carrier behaviour on the film thickness of the buried pentacene layer in C60/pentacene ambipolar double-layer organic field-effect transistors (OFETs). It was found that the buried pentacene layer not only acted as a hole transport layer, but also accounted for the properties of the C60/pentacene interface. The hole and electron behaviour exhibited different thickness dependence on the buried pentacene layer, implying the presence of the spatially separated conduction paths. It was suggested that the injected holes transported along the pentacene/gate dielectric interface, which were little affected by the buried pentacene layer thickness or the upper C60 layer; while, the injected electrons accumulated at the C60/pentacene interface, which were sensitive to the interfacial conditions or the buried pentacene layer. Furthermore, it was suggested that the enhanced surface roughness of the buried pentacene layer was responsible for the observed electron behaviour, especially when dpent>10 nm.

  14. Self-Driven Photodetector and Ambipolar Transistor in Atomically Thin GaTe-MoS2 p-n vdW Heterostructure.

    PubMed

    Yang, Shengxue; Wang, Cong; Ataca, Can; Li, Yan; Chen, Hui; Cai, Hui; Suslu, Aslihan; Grossman, Jeffrey C; Jiang, Chengbao; Liu, Qian; Tongay, Sefaattin

    2016-02-01

    Heterostructure engineering of atomically thin two-dimensional materials offers an exciting opportunity to fabricate atomically sharp interfaces for highly tunable electronic and optoelectronic devices. Here, we demonstrate abrupt interface between two completely dissimilar material systems, i.e, GaTe-MoS2 p-n heterojunction transistors, where the resulting device possesses unique electronic properties and self-driven photoelectric characteristics. Fabricated heterostructure transistors exhibit forward biased rectifying behavior where the transport is ambipolar with both electron and hole carriers contributing to the overall transport. Under illumination, photoexcited electron-hole pairs are readily separated by large built-in potential formed at the GaTe-MoS2 interface efficiently generating self-driven photocurrent within <10 ms. Overall results suggest that abrupt interfaces between vastly different material systems with different crystal symmetries still allow efficient charge transfer mechanisms at the interface and are attractive for photoswitch, photodetector, and photovoltaic applications because of large built-in potential at the interface. PMID:26796869

  15. N-type ohmic contacts to undoped GaAs/AlGaAs quantum wells using only front-sided processing: application to ambipolar FETs

    NASA Astrophysics Data System (ADS)

    Taneja, D.; Sfigakis, F.; Croxall, A. F.; Das Gupta, K.; Narayan, V.; Waldie, J.; Farrer, I.; Ritchie, D. A.

    2016-06-01

    We report the development of a simple and reliable, front-sided-only fabrication technique for n-type ohmic contacts to two-dimensional electron gases (2DEGs) in undoped GaAs/AlGaAs quantum wells. We have adapted the well-established recessed ohmic contacts/insulated metal gate technique for inducing a 2DEG in an undoped triangular well to also work reliably for undoped square quantum wells. Our adaptation involves a change in the procedure for etching the ohmic contact pits to optimise the etch side-wall profile and depth. As an application of our technique, we present a front-side-gated ambipolar field effect transistor (FET), where both 2D electron and hole gases can be induced in the same quantum well. We present results of low-temperature (0.3 K - 4 K) transport measurements of this device, including assessment of the n-type ohmic contact quality. On the basis of our findings, we discuss why the fabrication of these contacts is difficult and how our technique circumvents the challenges.

  16. Ambipolar organic heterojunction transistors based on F16CuPc/CuPc with a MoO3 buffer layer

    NASA Astrophysics Data System (ADS)

    Mingdong, Yi; Ning, Zhang; Linghai, Xie; Wei, Huang

    2015-10-01

    We fabricated heterojunction organic field-effect transistors (OFETs) using copper phthalocyanine (CuPc) and hexadecafluorophtholocyaninatocopper (F16CuPc) as hole transport layer and electron transport layer, respectively. Compared with F16CuPc based OFETs, the electron field-effect mobility in the heterojunction OFETs increased from 3.1 × 10-3 to 8.7 × 10-3 cm2/(V·s), but the p-type behavior was not observed. To enhanced the hole injection, we modified the source-drain electrodes using the MoO3 buffer layer, and the hole injection can be effectively improved. Eventually, the ambipolar transport characteristics of the CuPc/F16CuPc based OFETs with a MoO3 buffer layer were achieved, and the field-effect mobilities of electron and hole were 2.5 × 10-3 and 3.1 × 10-3 cm2/(V·s), respectively. Project supported by the National Natural Science Foundation of China (Nos. 61475074, 61204095).

  17. Self-Driven Photodetector and Ambipolar Transistor in Atomically Thin GaTe-MoS2 p-n vdW Heterostructure.

    PubMed

    Yang, Shengxue; Wang, Cong; Ataca, Can; Li, Yan; Chen, Hui; Cai, Hui; Suslu, Aslihan; Grossman, Jeffrey C; Jiang, Chengbao; Liu, Qian; Tongay, Sefaattin

    2016-02-01

    Heterostructure engineering of atomically thin two-dimensional materials offers an exciting opportunity to fabricate atomically sharp interfaces for highly tunable electronic and optoelectronic devices. Here, we demonstrate abrupt interface between two completely dissimilar material systems, i.e, GaTe-MoS2 p-n heterojunction transistors, where the resulting device possesses unique electronic properties and self-driven photoelectric characteristics. Fabricated heterostructure transistors exhibit forward biased rectifying behavior where the transport is ambipolar with both electron and hole carriers contributing to the overall transport. Under illumination, photoexcited electron-hole pairs are readily separated by large built-in potential formed at the GaTe-MoS2 interface efficiently generating self-driven photocurrent within <10 ms. Overall results suggest that abrupt interfaces between vastly different material systems with different crystal symmetries still allow efficient charge transfer mechanisms at the interface and are attractive for photoswitch, photodetector, and photovoltaic applications because of large built-in potential at the interface.

  18. Theoretical study of stability and charge-transport properties of coronene molecule and some of its halogenated derivatives: A path to ambipolar organic-based materials?

    SciTech Connect

    Sancho-García, J. C. Pérez-Jiménez, A. J.

    2014-10-07

    We have carefully investigated the structural and electronic properties of coronene and some of its fluorinated and chlorinated derivatives, including full periphery substitution, as well as the preferred orientation of the non-covalent dimer structures subsequently formed. We have paid particular attention to a set of methodological details, to first obtain single-molecule magnitudes as accurately as possible, including next the use of modern dispersion-corrected methods to tackle the corresponding non-covalently bound dimers. Generally speaking, this class of compounds is expected to self-assembly in neighboring π-stacks with dimer stabilization energies ranging from –20 to –30 kcal mol{sup −1} at close distances around 3.0–3.3 Å. Then, in a further step, we have also calculated hole and electron transfer rates of some suitable candidates for ambipolar materials, and corresponding charge mobility values, which are known to critically depend on the supramolecular organization of the samples. For coronene and per-fluorinated coronene, we have found high values for their hopping rates, although slightly smaller for the latter due to an increase (decrease) of the reorganization energies (electronic couplings)

  19. Theoretical study of stability and charge-transport properties of coronene molecule and some of its halogenated derivatives: a path to ambipolar organic-based materials?

    PubMed

    Sancho-García, J C; Pérez-Jiménez, A J

    2014-10-01

    We have carefully investigated the structural and electronic properties of coronene and some of its fluorinated and chlorinated derivatives, including full periphery substitution, as well as the preferred orientation of the non-covalent dimer structures subsequently formed. We have paid particular attention to a set of methodological details, to first obtain single-molecule magnitudes as accurately as possible, including next the use of modern dispersion-corrected methods to tackle the corresponding non-covalently bound dimers. Generally speaking, this class of compounds is expected to self-assembly in neighboring π-stacks with dimer stabilization energies ranging from -20 to -30 kcal mol(-1) at close distances around 3.0-3.3 Å. Then, in a further step, we have also calculated hole and electron transfer rates of some suitable candidates for ambipolar materials, and corresponding charge mobility values, which are known to critically depend on the supramolecular organization of the samples. For coronene and per-fluorinated coronene, we have found high values for their hopping rates, although slightly smaller for the latter due to an increase (decrease) of the reorganization energies (electronic couplings). PMID:25296829

  20. Diffusing Diffusivity: A Model for Anomalous, yet Brownian, Diffusion

    NASA Astrophysics Data System (ADS)

    Chubynsky, Mykyta V.; Slater, Gary W.

    2014-08-01

    Wang et al. [Proc. Natl. Acad. Sci. U.S.A. 106, 15160 (2009)] have found that in several systems the linear time dependence of the mean-square displacement (MSD) of diffusing colloidal particles, typical of normal diffusion, is accompanied by a non-Gaussian displacement distribution G(x ,t), with roughly exponential tails at short times, a situation they termed "anomalous yet Brownian" diffusion. The diversity of systems in which this is observed calls for a generic model. We present such a model where there is diffusivity memory but no direction memory in the particle trajectory, and we show that it leads to both a linear MSD and a non-Gaussian G(x ,t) at short times. In our model, the diffusivity is undergoing a (perhaps biased) random walk, hence the expression "diffusing diffusivity". G(x ,t) is predicted to be exactly exponential at short times if the distribution of diffusivities is itself exponential, but an exponential remains a good fit for a variety of diffusivity distributions. Moreover, our generic model can be modified to produce subdiffusion.

  1. Temporal Evolution of the Electron Diffusion Coefficient in Electrolyte-Filled Mesoporous Nanocrystalline TiO2 Films

    SciTech Connect

    van de Lagemaat, J.; Zhu, K.; Benkstein, K. D.; Frank, A. J.

    2008-02-01

    Electron transport in electrolyte-filled mesoporous TiO{sub 2}-based solar cells is described quantitatively from the perspective of the continuous-time random walk model. An analytical expression is derived for the time-dependent diffusion coefficient of electrons, which transforms at a characteristic (Fermi) time from strongly time-dependent values (dispersive transport) at short times to relatively time-independent values (nondispersive transport) at long times. At short times, the diffusion coefficient displays a power-law behavior with time. The timescale for the diffusion coefficient to reach its steady-state value is substantially longer than the Fermi time. The Fermi time and the steepness of the distribution of waiting times associated with trap sites have a strong influence on both the steady-state diffusion coefficient of electrons and on the dispersiveness of electron transport. At short timescales, ionic drag, associated with the ambipolar effect, slows electron transport through the TiO{sub 2} matrix, whereas at steady state, transport is trap limited. Decreasing the electron density lowers the steady-state limit of the diffusion coefficient and increases the timescale over which transport is dispersive.

  2. Large-scale magnetic field in the accretion discs of young stars: the influence of magnetic diffusion, buoyancy and Hall effect

    NASA Astrophysics Data System (ADS)

    Khaibrakhmanov, S. A.; Dudorov, A. E.; Parfenov, S. Yu.; Sobolev, A. M.

    2016-09-01

    We investigate the fossil magnetic field in the accretion and protoplanetary discs using the Shakura and Sunyaev approach. The distinguishing feature of this study is the accurate solution of the ionization balance equations and the induction equation with Ohmic diffusion, magnetic ambipolar diffusion, buoyancy and the Hall effect. We consider the ionization by cosmic rays, X-rays and radionuclides, radiative recombinations, recombinations onto dust grains, and also thermal ionization. The buoyancy appears as the additional mechanism of magnetic flux escape in the steady-state solution of the induction equation. Calculations show that Ohmic diffusion and magnetic ambipolar diffusion constraint the generation of the magnetic field inside the `dead' zones. The magnetic field in these regions is quasi-vertical. The buoyancy constraints the toroidal magnetic field strength close to the disc inner edge. As a result, the toroidal and vertical magnetic fields become comparable. The Hall effect is important in the regions close to the borders of the `dead' zones because electrons are magnetized there. The magnetic field in these regions is quasi-radial. We calculate the magnetic field strength and geometry for the discs with accretion rates (10^{-8}-10^{-6}) {M}_{⊙} {yr}^{-1}. The fossil magnetic field geometry does not change significantly during the disc evolution while the accretion rate decreases. We construct the synthetic maps of dust emission polarized due to the dust grain alignment by the magnetic field. In the polarization maps, the `dead' zones appear as the regions with the reduced values of polarization degree in comparison to those in the adjacent regions.

  3. Focused ion beam and field-emission microscopy of metallic filaments in memory devices based on thin films of an ambipolar organic compound consisting of oxadiazole, carbazole, and fluorene units

    USGS Publications Warehouse

    Pearson, Christopher; Bowen, Leon; Lee, Myung Won; Fisher, Alison L.; Linton, Katherine E.; Bryce, Martin R.; Petty, Michael C.

    2013-01-01

    We report on the mechanism of operation of organic thin film resistive memory architectures based on an ambipolar compound consisting of oxadiazole, carbazole, and fluorene units. Cross-sections of the devices have been imaged by electron microscopy both before and after applying a voltage. The micrographs reveal the growth of filaments, with diameters of 50 nm–100 nm, on the metal cathode. We suggest that these are formed by the drift of aluminium ions from the anode and are responsible for the observed switching and negative differential resistance phenomena in the memory devices.

  4. Microfabricated diffusion source

    DOEpatents

    Oborny, Michael C.; Frye-Mason, Gregory C.; Manginell, Ronald P.

    2008-07-15

    A microfabricated diffusion source to provide for a controlled diffusion rate of a vapor comprises a porous reservoir formed in a substrate that can be filled with a liquid, a headspace cavity for evaporation of the vapor therein, a diffusion channel to provide a controlled diffusion of the vapor, and an outlet to release the vapor into a gas stream. The microfabricated diffusion source can provide a calibration standard for a microanalytical system. The microanalytical system with an integral diffusion source can be fabricated with microelectromechanical systems technologies.

  5. Microscopic Foundation and Simulation of Coupled Carrier-Temperature Diffusions in Semiconductor Lasers

    NASA Technical Reports Server (NTRS)

    Li, J.; Ning, Cun-Zheng; Biegel, Bryan A. (Technical Monitor)

    2002-01-01

    and energy relaxation rates. These rates expressed as functions of temperatures and densities lead to microscopic expressions for self- and mutual-diffusion coefficients in the coupled density-temperature diffusion equations. Approximations for reducing the general two-component description of the electron-hole plasma (EHP) to a single-component one are discussed. In particular, we show that a special single-component reduction is possible when e-h scattering dominates over c-LO phonon scattering. The ambipolar diffusion approximation is also discussed and we show that the ambipolar diffusion coefficients are independent of e-h scattering, even though the diffusion coefficients of individual components depend sensitively on the e-h scattering rates. Our discussions lead to new perspectives into the roles played in the single-component reduction by the electron-hole correlation in momentum space induced by scatterings and the electron-hole correlation in real space via internal static electrical field. Finally, the theory is completed by coupling the diffusion equations to the lattice temperature equation and to the effective optical polarization which in turn couples to the laser field. The equations derived above are implemented in various limiting cases to a typical diode laser to study the consequences of nonlinear diffusion and the cross diffusion terms on laser behavior, especially the dynamic behavior of a diode laser under modulation. Detailed results will be presented by comparing with the standard rate equation results.

  6. Hybrid Diffusion Imaging

    PubMed Central

    Wu, Yu-Chien; Alexander, Andrew L.

    2007-01-01

    Diffusion measurements in the human central nervous system are complex to characterize and a broad spectrum of methods have been proposed. In this study, a comprehensive diffusion encoding and analysis approach, Hybrid Diffusion Imaging (HYDI), is described. The HYDI encoding scheme is composed of multiple concentric “shells” of constant diffusion-weighting, which may be used to characterize the signal behavior with low, moderate and high diffusion-weighting. HYDI facilitates the application of multiple data-analyses strategies including diffusion tensor imaging (DTI), multi-exponential diffusion measurements, diffusion spectrum imaging (DSI) and q-ball imaging (QBI). These different analysis strategies may provide complementary information. DTI measures (mean diffusivity and fractional anisotropy) may be estimated from either data in the inner shells or the entire HYDI data. Fast and slow diffusivities were estimated using a nonlinear least-squares bi-exponential fit on geometric means of the HYDI shells. DSI measurements from the entire HYDI data yield empirical model-independent diffusion information and are well-suited for characterizing tissue regions with complex diffusion behavior. DSI measurements were characterized using the zero displacement probability and the mean squared displacement. The outermost HYDI shell was analyzed using QBI analysis to estimate the orientation distribution function (ODF), which is useful for characterizing the directions of multiple fiber groups within a voxel. In this study, a HYDI encoding scheme with 102 diffusion-weighted measurements was obtained over most of the human cerebrum in under 30 minutes. PMID:17481920

  7. Diffusion bonding aeroengine components

    NASA Astrophysics Data System (ADS)

    Fitzpatrick, G. A.; Broughton, T.

    1988-10-01

    The use of diffusion bonding processes at Rolls-Royce for the manufacture of titanium-alloy aircraft engine components and structures is described. A liquid-phase diffusion bonding process called activated diffusion bonding has been developed for the manufacture of the hollow titanium wide chord fan blade. In addition, solid-state diffusion bonding is being used in the manufacture of hollow vane/blade airfoil constructions mainly in conjunction with superplastic forming and hot forming techniques.

  8. Updating applied diffusion models

    SciTech Connect

    Weil, J.C.

    1985-11-01

    Most diffusion models currently used in air quality applications are substantially out of date with understanding of turbulence and diffusion in the planetary boundary layer. Under a Cooperative Agreement with the Environmental Protection Agency, the American Meteorological Society organized a workshop to help improve the basis of such models, their physics and hopefuly their performance. Reviews and recommendations were made on models in three areas: diffusion in the convective boundary layer (CBL), diffusion in the stabe boundary layer (SBL), and model uncertainty.

  9. Diffusion Strategy Guide.

    ERIC Educational Resources Information Center

    McCutcheon, James R.; Sanders, John R.

    A methodology is presented for planning and managing the spread of educational innovations. The first portion of the guide develops a theoretical framework for diffusion which summarizes and capitalizes on the latest marketing and on the latest marketing and diffusion research findings. Major stages in the diffusion paradigm discussed include…

  10. Reduce Confusion about Diffusion.

    ERIC Educational Resources Information Center

    Hebrank, Mary R.

    1997-01-01

    Presents activities that allow students to explore the fundamental but poorly understood concept of diffusion by appealing to their kinesthetic senses first, then challenging their analytical skills as they try to deduce the mathematical principle involved. Presents a computer simulation of diffusion and discusses diffusion's limitations and…

  11. Handbook on atmospheric diffusion

    SciTech Connect

    Hanna, S.R.; Briggs, G.A.; Hosker, R.P. Jr.

    1982-01-01

    Basic meteorological concepts are covered as well as plume rise, source effects, and diffusion models. Chapters are included on cooling tower plumes and urban diffusion. Suggestions are given for calculating diffusion in special situations, such as for instantaneous releases over complex terrain, over long distances, and during times when chemical reactions or dry or wet deposition are important. (PSB)

  12. Li diffusion in zircon

    NASA Astrophysics Data System (ADS)

    Cherniak, D. J.; Watson, E. B.

    2010-09-01

    Diffusion of Li under anhydrous conditions at 1 atm and under fluid-present elevated pressure (1.0-1.2 GPa) conditions has been measured in natural zircon. The source of diffusant for 1-atm experiments was ground natural spodumene, which was sealed under vacuum in silica glass capsules with polished slabs of zircon. An experiment using a Dy-bearing source was also conducted to evaluate possible rate-limiting effects on Li diffusion of slow-diffusing REE+3 that might provide charge balance. Diffusion experiments performed in the presence of H2O-CO2 fluid were run in a piston-cylinder apparatus, using a source consisting of a powdered mixture of spodumene, quartz and zircon with oxalic acid added to produce H2O-CO2 fluid. Nuclear reaction analysis (NRA) with the resonant nuclear reaction 7Li(p,γ)8Be was used to measure diffusion profiles for the experiments. The following Arrhenius parameters were obtained for Li diffusion normal to the c-axis over the temperature range 703-1.151°C at 1 atm for experiments run with the spodumene source: D_{text{Li}} = 7.17 × 10^{ - 7} { exp }( - 275 ± 11 {text{kJmol}}^{ - 1} /{text{RT}}){text{m}}2 {text{s}}^{ - 1}. Diffusivities are similar for transport parallel to the c-axis, indicating little anisotropy for Li diffusion in zircon. Similar Li diffusivities were also found for experiments run under fluid-present conditions and for the experiment run with the Dy-bearing source. Li diffusion is considerably faster than diffusion of other cations in zircon, with a smaller activation energy for diffusion. Although Li diffusion in zircon is comparatively rapid, zircons will be moderately retentive of Li signatures at mid-crustal metamorphic temperatures, but they are unlikely to retain this information for geologically significant times under high-grade metamorphism.

  13. Tunneling Characteristics Depending on Schottky Barriers and Diffusion Current in SiOC.

    PubMed

    Oh, Teresa; Kim, Chy Hyung

    2016-02-01

    To obtain a diffusion current in SiOC, the aluminum doped zinc oxide films were deposited on SiOC/Si wafer by a RF magnetron sputtering. All the X-ray patterns of the SiOC films showed amorphous phases. The level of binding energy of Si atoms will lead to an additional potential modulation by long range Coulombic and covalent interactions with oxygen ions. The growth of the AZO film was affected by the characteristics of SiOC, resulting in similar trends in XPS spectra and a shift to higher AZO lattice d values than the original AZO d values in XRD analyses. The charges trapped by the defects at the interlayer between AZO and SiOC films induced the decreased mobility of carriers. In the absence of trap charges, AZO grown on SiOC film such as the sample prepared at O2 = 25 or 30 sccm, which has low charge carrier concentration and high mobility, showed high mobility in an ambipolar characteristic of oxide semiconductor due to the tunneling effect and diffusion current. The structural matching of an interface between AZO and amorphous SiOC enhanced the height of Schottky Barrier (SB), and then the mobility was increased by the tunneling effect from band to band through the high SB. PMID:27433737

  14. Transport and trapping of dust particles in a potential well created by inductively coupled diffused plasmas.

    PubMed

    Choudhary, Mangilal; Mukherjee, S; Bandyopadhyay, P

    2016-05-01

    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 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 particle, and some of the preliminary experimental results are presented.

  15. Transport and trapping of dust particles in a potential well created by inductively coupled diffused plasmas

    NASA Astrophysics Data System (ADS)

    Choudhary, Mangilal; Mukherjee, S.; Bandyopadhyay, P.

    2016-05-01

    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 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 particle, and some of the preliminary experimental results are presented.

  16. Transport and trapping of dust particles in a potential well created by inductively coupled diffused plasmas.

    PubMed

    Choudhary, Mangilal; Mukherjee, S; Bandyopadhyay, P

    2016-05-01

    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 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 particle, and some of the preliminary experimental results are presented. PMID:27250421

  17. Updating applied diffusion models

    SciTech Connect

    Weil, J.C.

    1985-01-01

    Most diffusion models currently used in air-quality applications are substantially out of date with understanding of turbulence and diffusion in the planetary boundary layer. Under a Cooperative Agreement with the Environmental Protection Agency, the American Meteorological Society organized a workshop to help improve the basis of such models, their physics and hopefully their performance. Reviews and recommendations were made on models in three areas: diffusion in the convective boundary layer (CBL), diffusion in the stable boundary layer (SBL), and model uncertainty. Progress has been made in all areas, but it is most significant and ready for application to practical models in the case of the CBL. This has resulted from a clear understanding of the vertical structure and diffusion in the CBL, as demonstrated by laboratory experiments, numerical simulations, and field observations. Understanding of turbulence structure and diffusion in the SBL is less complete and not yet ready for general use in applications.

  18. Gaseous diffusion system

    DOEpatents

    Garrett, George A.; Shacter, John

    1978-01-01

    1. A gaseous diffusion system comprising a plurality of diffusers connected in cascade to form a series of stages, each of said diffusers having a porous partition dividing it into a high pressure chamber and a low pressure chamber, and means for combining a portion of the enriched gas from a succeeding stage with a portion of the enriched gas from the low pressure chamber of each stage and feeding it into one extremity of the high pressure chamber thereof.

  19. Inpainting using airy diffusion

    NASA Astrophysics Data System (ADS)

    Lorduy Hernandez, Sara

    2015-09-01

    One inpainting procedure based on Airy diffusion is proposed, implemented via Maple and applied to some digital images. Airy diffusion is a partial differential equation with spatial derivatives of third order in contrast with the usual diffusion with spatial derivatives of second order. Airy diffusion generates the Airy semigroup in terms of the Airy functions which can be rewritten in terms of Bessel functions. The Airy diffusion can be used to smooth an image with the corresponding noise elimination via convolution. Also the Airy diffusion can be used to erase objects from an image. We build an algorithm using the Maple package ImageTools and such algorithm is tested using some images. Our results using Airy diffusion are compared with the similar results using standard diffusion. We observe that Airy diffusion generates powerful filters for image processing which could be incorporated in the usual packages for image processing such as ImageJ and Photoshop. Also is interesting to consider the possibility to incorporate the Airy filters as applications for smartphones and smart-glasses.

  20. Multicomponent diffusion revisited

    NASA Astrophysics Data System (ADS)

    Lam, S. H.

    2006-07-01

    The derivation of the multicomponent diffusion law is revisited. Following Furry [Am. J. Phys. 16, 63 (1948)], Williams [Am. J. Phys. 26, 467 (1958); Combustion Theory, 2nd ed. (Benjamin/Cummings , Menlo Park, CA,1985)] heuristically rederived the classical kinetic theory results using macroscopic equations, and pointed out that the dynamics of the mixture fluid had been assumed inviscid. This paper generalizes the derivation, shows that the inviscid assumption can easily be relaxed to add a new term to the classical diffusion law, and the thermal diffusion term can also be easily recovered. The nonuniqueness of the multicomponent diffusion coefficient matrix is emphasized and discussed.

  1. Experimental study of vortex diffusers

    SciTech Connect

    Shakerin, S.; Miller, P.L.

    1995-11-01

    This report documents experimental research performed on vortex diffusers used in ventilation and air-conditioning systems. The main objectives of the research were (1) to study the flow characteristics of isothermal jets issuing from vortex diffusers, (2) to compare the vortex diffuser`s performance with that of a conventional diffuser, and (3) to prepare a report that disseminates the results to the designers of ventilation and air-conditioning systems. The researchers considered three diffusers: a conventional round ceiling diffuser and two different styles of vortex diffusers. Overall, the vortex diffusers create slightly more induction of ambient air in comparison to the conventional diffuser.

  2. Cosmology with matter diffusion

    SciTech Connect

    Calogero, Simone; Velten, Hermano E-mail: velten@cce.ufes.br

    2013-11-01

    We construct a viable cosmological model based on velocity diffusion of matter particles. In order to ensure the conservation of the total energy-momentum tensor in the presence of diffusion, we include a cosmological scalar field φ which we identify with the dark energy component of the universe. The model is characterized by only one new degree of freedom, the diffusion parameter σ. The standard ΛCDM model can be recovered by setting σ = 0. If diffusion takes place (σ > 0) the dynamics of the matter and of the dark energy fields are coupled. We argue that the existence of a diffusion mechanism in the universe may serve as a theoretical motivation for interacting models. We constrain the background dynamics of the diffusion model with Supernovae, H(z) and BAO data. We also perform a perturbative analysis of this model in order to understand structure formation in the universe. We calculate the impact of diffusion both on the CMB spectrum, with particular attention to the integrated Sachs-Wolfe signal, and on the matter power spectrum P(k). The latter analysis places strong constraints on the magnitude of the diffusion mechanism but does not rule out the model.

  3. Speckle reducing anisotropic diffusion.

    PubMed

    Yu, Yongjian; Acton, Scott T

    2002-01-01

    This paper provides the derivation of speckle reducing anisotropic diffusion (SRAD), a diffusion method tailored to ultrasonic and radar imaging applications. SRAD is the edge-sensitive diffusion for speckled images, in the same way that conventional anisotropic diffusion is the edge-sensitive diffusion for images corrupted with additive noise. We first show that the Lee and Frost filters can be cast as partial differential equations, and then we derive SRAD by allowing edge-sensitive anisotropic diffusion within this context. Just as the Lee and Frost filters utilize the coefficient of variation in adaptive filtering, SRAD exploits the instantaneous coefficient of variation, which is shown to be a function of the local gradient magnitude and Laplacian operators. We validate the new algorithm using both synthetic and real linear scan ultrasonic imagery of the carotid artery. We also demonstrate the algorithm performance with real SAR data. The performance measures obtained by means of computer simulation of carotid artery images are compared with three existing speckle reduction schemes. In the presence of speckle noise, speckle reducing anisotropic diffusion excels over the traditional speckle removal filters and over the conventional anisotropic diffusion method in terms of mean preservation, variance reduction, and edge localization.

  4. Galactic Diffuse Emissions

    SciTech Connect

    Digel, Seth W.; /SLAC

    2007-10-25

    Interactions of cosmic rays with interstellar nucleons and photons make the Milky Way a bright, diffuse source of high-energy {gamma}-rays. Observationally, the results from EGRET, COMPTEL, and OSSE have now been extended to higher energies by ground-based experiments, with detections of diffuse emission in the Galactic center reported by H.E.S.S. in the range above 100 GeV and of diffuse emission in Cygnus by MILAGRO in the TeV range. In the range above 100 keV, INTEGRAL SPI has found that diffuse emission remains after point sources are accounted for. I will summarize current knowledge of diffuse {gamma}-ray emission from the Milky Way and review some open issues related to the diffuse emission -- some old, like the distribution of cosmic-ray sources and the origin of the 'excess' of GeV emission observed by EGRET, and some recently recognized, like the amount and distribution of molecular hydrogen not traced by CO emission -- and anticipate some of the advances that will be possible with the Large Area Telescope on GLAST. We plan to develop an accurate physical model for the diffuse emission, which will be useful for detecting and accurately characterizing emission from Galactic point sources as well as any Galactic diffuse emission from exotic processes, and for studying the unresolved extragalactic emission.

  5. Investigating Diffusion with Technology

    ERIC Educational Resources Information Center

    Miller, Jon S.; Windelborn, Augden F.

    2013-01-01

    The activities described here allow students to explore the concept of diffusion with the use of common equipment such as computers, webcams and analysis software. The procedure includes taking a series of digital pictures of a container of water with a webcam as a dye slowly diffuses. At known time points, measurements of the pixel densities…

  6. Anatomy of Particle Diffusion

    ERIC Educational Resources Information Center

    Bringuier, E.

    2009-01-01

    The paper analyses particle diffusion from a thermodynamic standpoint. The main goal of the paper is to highlight the conceptual connection between particle diffusion, which belongs to non-equilibrium statistical physics, and mechanics, which deals with particle motion, at the level of third-year university courses. We start out from the fact…

  7. Combustor diffuser interaction program

    NASA Technical Reports Server (NTRS)

    Srinivasan, Ram; Thorp, Daniel

    1986-01-01

    Advances in gas turbine engine performance are achieved by using compressor systems with high stage loading and low part count, which result in high exit Mach numbers. The diffuser and combustor systems in such engines should be optimized to reduce system pressure loss and to maximize the engine thrust-to-weight ratio and minimize length. The state-of-the-art combustor-diffuser systems do not meet these requirements. Detailed understanding of the combustor-diffuser flow field interaction is required for designing advanced gas turbine engines. An experimental study of the combustor-diffuser interaction (CDI) is being conducted to obtain data for the evaluation and improvement of analytical models applicable to a wide variety of diffuser designs. The CDI program consists of four technical phases: Literature Search; Baseline Configuration; Parametric Configurations; and Performance Configurations. Phase 2 of the program is in progress.

  8. Diffusion in Coulomb crystals.

    PubMed

    Hughto, J; Schneider, A S; Horowitz, C J; Berry, D K

    2011-07-01

    Diffusion in Coulomb crystals can be important for the structure of neutron star crusts. We determine diffusion constants D from molecular dynamics simulations. We find that D for Coulomb crystals with relatively soft-core 1/r interactions may be larger than D for Lennard-Jones or other solids with harder-core interactions. Diffusion, for simulations of nearly perfect body-centered-cubic lattices, involves the exchange of ions in ringlike configurations. Here ions "hop" in unison without the formation of long lived vacancies. Diffusion, for imperfect crystals, involves the motion of defects. Finally, we find that diffusion, for an amorphous system rapidly quenched from Coulomb parameter Γ=175 to Coulomb parameters up to Γ=1750, is fast enough that the system starts to crystalize during long simulation runs. These results strongly suggest that Coulomb solids in cold white dwarf stars, and the crust of neutron stars, will be crystalline and not amorphous. PMID:21867316

  9. Diffusion in Coulomb crystals.

    PubMed

    Hughto, J; Schneider, A S; Horowitz, C J; Berry, D K

    2011-07-01

    Diffusion in Coulomb crystals can be important for the structure of neutron star crusts. We determine diffusion constants D from molecular dynamics simulations. We find that D for Coulomb crystals with relatively soft-core 1/r interactions may be larger than D for Lennard-Jones or other solids with harder-core interactions. Diffusion, for simulations of nearly perfect body-centered-cubic lattices, involves the exchange of ions in ringlike configurations. Here ions "hop" in unison without the formation of long lived vacancies. Diffusion, for imperfect crystals, involves the motion of defects. Finally, we find that diffusion, for an amorphous system rapidly quenched from Coulomb parameter Γ=175 to Coulomb parameters up to Γ=1750, is fast enough that the system starts to crystalize during long simulation runs. These results strongly suggest that Coulomb solids in cold white dwarf stars, and the crust of neutron stars, will be crystalline and not amorphous.

  10. Helium Diffusion in Olivine

    NASA Astrophysics Data System (ADS)

    Cherniak, D. J.; Watson, E. B.

    2011-12-01

    Diffusion of helium has been characterized in natural Fe-bearing olivine (~Fo90) and synthetic forsterite. Polished, oriented slabs of olivine were implanted with 3He, at 100 keV at a dose of 5x1015/cm2 or at 3.0 MeV at a dose of 1x1016/cm2. A set of experiments on the implanted olivine were run in 1-atm furnaces. In addition to the one-atm experiments, experiments on implanted samples were also run at higher pressures (2.6 and 2.7 GPa) to assess the potential effects of pressure on He diffusion and the applicability of the measured diffusivities in describing He transport in the mantle. The high-pressure experiments were conducted in a piston-cylinder apparatus using an "ultra-soft" pressure cell, with the diffusion sample directly surrounded by AgCl. 3He distributions following experiments were measured with Nuclear Reaction Analysis using the reaction 3He(d,p)4He. This direct profiling method permits us to evaluate anisotropy of diffusion, which cannot be easily assessed using bulk-release methods. For diffusion in forsterite parallel to c we obtain the following Arrhenius relation over the temperatures 250-950°C: D = 3.91x10-6exp(-159 ± 4 kJ mol-1/RT) m2/sec. The data define a single Arrhenius line spanning more than 7 orders of magnitude in D and 700°C in temperature. Diffusion parallel to a appears slightly slower, yielding an activation energy for diffusion of 135 kJ/mol and a pre-exponential factor of 3.73x10-8 m2/sec. Diffusion parallel to b is slower than diffusion parallel to a (by about two-thirds of a log unit); for this orientation an activation energy of 138 kJ/mol and a pre-exponential factor of 1.34x10-8 m2/sec are obtained. This anisotropy is broadly consistent with observations for diffusion of Ni and Fe-Mg in olivine. Diffusion in Fe-bearing olivine (transport parallel to b) agrees within uncertainty with findings for He diffusion in forsterite. The higher-pressure experiments yield diffusivities in agreement with those from the 1-atm

  11. Tungsten diffusion in silicon

    SciTech Connect

    De Luca, A.; Texier, M.; Burle, N.; Oison, V.; Pichaud, B.; Portavoce, A.; Grosjean, C.

    2014-01-07

    Two doses (10{sup 13} and 10{sup 15} cm{sup −2}) of tungsten (W) atoms were implanted in different Si(001) wafers in order to study W diffusion in Si. The samples were annealed or oxidized at temperatures between 776 and 960 °C. The diffusion profiles were measured by secondary ion mass spectrometry, and defect formation was studied by transmission electron microscopy and atom probe tomography. W is shown to reduce Si recrystallization after implantation and to exhibit, in the temperature range investigated, a solubility limit close to 0.15%–0.2%, which is higher than the solubility limit of usual metallic impurities in Si. W diffusion exhibits unusual linear diffusion profiles with a maximum concentration always located at the Si surface, slower kinetics than other metals in Si, and promotes vacancy accumulation close to the Si surface, with the formation of hollow cavities in the case of the higher W dose. In addition, Si self-interstitial injection during oxidation is shown to promote W-Si clustering. Taking into account these observations, a diffusion model based on the simultaneous diffusion of interstitial W atoms and W-Si atomic pairs is proposed since usual models used to model diffusion of metallic impurities and dopants in Si cannot reproduce experimental observations.

  12. Tungsten diffusion in olivine

    NASA Astrophysics Data System (ADS)

    Cherniak, D. J.; Van Orman, J. A.

    2014-03-01

    Diffusion of tungsten has been characterized in synthetic forsterite and natural olivine (Fo90) under dry conditions. The source of diffusant was a mixture of magnesium tungstate and olivine powders. Experiments were prepared by sealing the source material and polished olivine under vacuum in silica glass ampoules with solid buffers to buffer at NNO or IW. Prepared capsules were annealed in 1 atm furnaces for times ranging from 45 min to several weeks, at temperatures from 1050 to 1450 °C. Tungsten distributions in the olivine were profiled by Rutherford Backscattering Spectrometry (RBS). The following Arrhenius relation is obtained for W diffusion in forsterite: D=1.0×10-8exp(-365±28 kJ mol/RT) m s Diffusivities for the synthetic forsterite and natural Fe-bearing olivine are similar, and tungsten diffusion in olivine shows little dependence on crystallographic orientation or oxygen fugacity. The slow diffusivities measured for W in olivine indicate that Hf-W ages in olivine-metal systems will close to diffusive exchange at higher temperatures than other chronometers commonly used in cosmochronology, and that tungsten isotopic signatures will be less likely to be reset by subsequent thermal events.

  13. Diffusion Flame Stabilization

    NASA Technical Reports Server (NTRS)

    Takahashi, Fumiaki; Katta, V. R.

    2006-01-01

    Diffusion flames are commonly used for industrial burners in furnaces and flares. Oxygen/fuel burners are usually diffusion burners, primarily for safety reasons, to prevent flashback and explosion in a potentially dangerous system. Furthermore, in most fires, condensed materials pyrolyze, vaporize, and burn in air as diffusion flames. As a result of the interaction of a diffusion flame with burner or condensed-fuel surfaces, a quenched space is formed, thus leaving a diffusion flame edge, which plays an important role in flame holding in combustion systems and fire spread through condensed fuels. Despite a long history of jet diffusion flame studies, lifting/blowoff mechanisms have not yet been fully understood, compared to those of premixed flames. In this study, the structure and stability of diffusion flames of gaseous hydrocarbon fuels in coflowing air at normal earth gravity have been investigated experimentally and computationally. Measurements of the critical mean jet velocity (U(sub jc)) of methane, ethane, or propane at lifting or blowoff were made as a function of the coflowing air velocity (U(sub a)) using a tube burner (i.d.: 2.87 mm). By using a computational fluid dynamics code with 33 species and 112 elementary reaction steps, the internal chemical-kinetic structures of the stabilizing region of methane and propane flames were investigated. A peak reactivity spot, i.e., reaction kernel, is formed in the flame stabilizing region due to back-diffusion of heat and radical species against an oxygen-rich incoming flow, thus holding the trailing diffusion flame. The simulated flame base moved downstream under flow conditions close to the measured stability limit.

  14. Diffusion Flame Stabilization

    NASA Technical Reports Server (NTRS)

    Takahashi, Fumiaki; Katta, Viswanath R.

    2007-01-01

    Diffusion flames are commonly used for industrial burners in furnaces and flares. Oxygen/fuel burners are usually diffusion burners, primarily for safety reasons, to prevent flashback and explosion in a potentially dangerous system. Furthermore, in most fires, condensed materials pyrolyze, vaporize, and burn in air as diffusion flames. As a result of the interaction of a diffusion flame with burner or condensed-fuel surfaces, a quenched space is formed, thus leaving a diffusion flame edge, which plays an important role in flame holding in combustion systems and fire spread through condensed fuels. Despite a long history of jet diffusion flame studies, lifting/blowoff mechanisms have not yet been fully understood, compared to those of premixed flames. In this study, the structure and stability of diffusion flames of gaseous hydrocarbon fuels in coflowing air at normal earth gravity have been investigated experimentally and computationally. Measurements of the critical mean jet velocity (U(sub jc)) of methane, ethane, or propane at lifting or blowoff were made as a function of the coflowing air velocity (U(sub a)) using a tube burner (i.d.: 2.87 mm) (Fig. 1, left). By using a computational fluid dynamics code with 33 species and 112 elementary reaction steps, the internal chemical-kinetic structures of the stabilizing region of methane and propane flames were investigated (Fig. 1, right). A peak reactivity spot, i.e., reaction kernel, is formed in the flame stabilizing region due to back-diffusion of heat and radical species against an oxygen-rich incoming flow, thus holding the trailing diffusion flame. The simulated flame base moved downstream under flow conditions close to the measured stability limit.

  15. Hereditary Diffuse Gastric Cancer

    MedlinePlus

    ... with the syndrome is recommended. What are the estimated cancer risks associated with HDGC? Not everyone who ... the lifetime risk for diffuse gastric cancer is estimated to be 70% to 80% for men and ...

  16. Multinomial Diffusion Equation

    SciTech Connect

    Balter, Ariel I.; Tartakovsky, Alexandre M.

    2011-06-01

    We have developed a novel stochastic, space/time discrete representation of particle diffusion (e.g. Brownian motion) based on discrete probability distributions. We show that in the limit of both very small time step and large concentration, our description is equivalent to the space/time continuous stochastic diffusion equation. Being discrete in both time and space, our model can be used as an extremely accurate, efficient, and stable stochastic finite-difference diffusion algorithm when concentrations are so small that computationally expensive particle-based methods are usually needed. Through numerical simulations, we show that our method can generate realizations that capture the statistical properties of particle simulations. While our method converges converges to both the correct ensemble mean and ensemble variance very quickly with decreasing time step, but for small concentration, the stochastic diffusion PDE does not, even for very small time steps.

  17. Lung diffusion testing

    MedlinePlus

    Lung diffusion testing measures how well the lungs exchange gases. This is an important part of lung testing , because ... gases do not move normally across the lung tissues into the blood vessels of the lung. This ...

  18. Investigating diffusion with technology

    NASA Astrophysics Data System (ADS)

    Miller, Jon S.; Windelborn, Augden F.

    2013-07-01

    The activities described here allow students to explore the concept of diffusion with the use of common equipment such as computers, webcams and analysis software. The procedure includes taking a series of digital pictures of a container of water with a webcam as a dye slowly diffuses. At known time points, measurements of the pixel densities (darkness) of the digital pictures are recorded and then plotted on a graph. The resulting graph of darkness versus time allows students to see the results of diffusion of the dye over time. Through modification of the basic lesson plan, students are able to investigate the influence of a variety of variables on diffusion. Furthermore, students are able to expand the boundaries of their thinking by formulating hypotheses and testing their hypotheses through experimentation. As a result, students acquire a relevant science experience through taking measurements, organizing data into tables, analysing data and drawing conclusions.

  19. Hydrogen Diffusion in Forsterite

    NASA Astrophysics Data System (ADS)

    Demouchy, S.; Mackwell, S.

    2002-12-01

    Physical and chemical properties of Earth's mantle are readily modified by interaction with volatiles, such as water. Thus, characterization of solubility and kinetics of incorporation for water in nominally anhydrous minerals is important in order to understand the behavior of Earth's interior under hydrous conditions. Experimental studies on the olivine-water system indicate that significant amounts of OH can dissolve within olivine as point defects (Bell and Rossman, 1992; Kohlstedt et al. 1996). Extending Kohlstedt and Mackwell's (1998) work, our study concerns the kinetics of hydrogen transport in the iron-free olivine-water system. This study is based on hydrogenation of forsterite samples during piston-cylinder and TZM cold-seal vessel experiments. We use infrared analyses in order to constrain the speciation of the mobile water-derived defects in forsterite single-crystal sample, and the rates of diffusion of such species under uppermost mantle conditions (0.2 to 1.5 GPa, 900 to 1100° C). Hydrogen defect transport in single crystals of forsterite is investigated for diffusion parallel to each crystallographic axis. Defect diffusivities are obtained by fitting a diffusion law to the OH content as a function of position in the sample. Our current results indicate that incorporation of hydroxyl species into iron-free olivine is a one-stage process with hydrogen diffusion linked to magnesium vacancy self-diffusion DV, such that DV = D~/3 = 10-12 m2/s at 1000° C parallel to [001], where D~ represents the chemical diffusivity. Those diffusion rates are slightly lower than in iron-bearing olivine for the same incorporation mechanism. The different concentration profiles show a clear anisotropy of diffusion, with fastest diffusion parallel to [001] as in iron-bearing olivine. Thus, while hydrogen solubilities are dependent on iron content, the rate of incorporation of water-derived species in olivine is not strongly coupled to the concentration of iron. This

  20. Nodal Diffusion & Transport Theory

    1992-02-19

    DIF3D solves multigroup diffusion theory eigenvalue, adjoint, fixed source, and criticality (concentration, buckling, and dimension search) problems in 1, 2, and 3-space dimensions for orthogonal (rectangular or cylindrical), triangular, and hexagonal geometries. Anisotropic diffusion theory coefficients are permitted. Flux and power density maps by mesh cell and regionwise balance integrals are provided. Although primarily designed for fast reactor problems, upscattering and internal black boundary conditions are also treated.

  1. Advanced manufacturing: Technology diffusion

    SciTech Connect

    Tesar, A.

    1995-12-01

    In this paper we examine how manufacturing technology diffuses rom the developers of technology across national borders to those who do not have the capability or resources to develop advanced technology on their own. None of the wide variety of technology diffusion mechanisms discussed in this paper are new, yet the opportunities to apply these mechanisms are growing. A dramatic increase in technology diffusion occurred over the last decade. The two major trends which probably drive this increase are a worldwide inclination towards ``freer`` markets and diminishing isolation. Technology is most rapidly diffusing from the US In fact, the US is supplying technology for the rest of the world. The value of the technology supplied by the US more than doubled from 1985 to 1992 (see the Introduction for details). History shows us that technology diffusion is inevitable. It is the rates at which technologies diffuse to other countries which can vary considerably. Manufacturers in these countries are increasingly able to absorb technology. Their manufacturing efficiency is expected to progress as technology becomes increasingly available and utilized.

  2. Multispecies diffusion models: A study of uranyl species diffusion

    SciTech Connect

    Liu, Chongxuan; Shang, Jianying; Zachara, John M.

    2011-12-14

    Rigorous numerical description of multi-species diffusion requires coupling of species, charge, and aqueous and surface complexation reactions that collectively affect diffusive fluxes. The applicability of a fully coupled diffusion model is, however, often constrained by the availability of species self-diffusion coefficients, as well as by computational complication for imposing charge conservation. In this study, several diffusion models with variable complexity in charge and species coupling were formulated and compared to describe reactive multi-species diffusion in groundwater. Diffusion of uranyl [U(VI)] species was used as an example in demonstrating the effectiveness of the models in describing multi-species diffusion. Numerical simulations found that a diffusion model with a single, common diffusion coefficient for all species was sufficient to describe multi-species U(VI) diffusion under steady-state condition of major chemical composition, but not under transient chemical conditions. Simulations revealed that a fully coupled diffusion model can be well approximated by a component-based diffusion model, which considers difference in diffusion coefficients between chemical components, but not between the species within each chemical component. This treatment significantly enhanced computational efficiency at the expense of minor charge conservation. The charge balance in the component-based diffusion model can be rigorously enforced, if necessary, by adding an artificial kinetic reaction term induced by the charge separation. The diffusion models were applied to describe U(VI) diffusive mass transfer in intragranular domains in two sediments collected from US Department of Energy's Hanford 300A where intragrain diffusion is a rate-limiting process controlling U(VI) adsorption and desorption. The grain-scale reactive diffusion model was able to describe U(VI) adsorption/desorption kinetics that has been described using a semi-empirical, multi-rate model

  3. Anomalous Diffusion Near Resonances

    SciTech Connect

    Sen, Tanaji; /Fermilab

    2010-05-01

    Synchro-betatron resonances can lead to emittance growth and the loss of luminosity. We consider the detailed dynamics of a bunch near such a low order resonance driven by crossing angles at the collision points. We characterize the nature of diffusion and find that it is anomalous and sub-diffusive. This affects both the shape of the beam distribution and the time scales for growth. Predictions of a simplified anomalous diffusion model are compared with direct simulations. Transport of particles near resonances is still not a well understood phenomenon. Often, without justification, phase space motion is assumed to be a normal diffusion process although at least one case of anomalous diffusion in beam dynamics has been reported [1]. Here we will focus on the motion near synchro-betatron resonances which can be excited by several means, including beams crossing at an angle at the collision points as in the LHC. We will consider low order resonances which couple the horizontal and longitudinal planes, both for simplicity and to observe large effects over short time scales. While the tunes we consider are not practical for a collider, nonetheless the transport mechanisms we uncover are also likely to operate at higher order resonances.

  4. Apparatus for diffusion separation

    DOEpatents

    Nierenberg, William A.; Pontius, Rex B.

    1976-08-10

    1. The method of testing the separation efficiency of porous permeable membranes which comprises causing a stream of a gaseous mixture to flow into contact with one face of a finely porous permeable membrane under such conditions that a major fraction of the mixture diffuses through the membrane, maintaining a rectangular cross section of the gaseous stream so flowing past said membrane, continuously recirculating the gas that diffuses through said membrane and continuously withdrawing the gas that does not diffuse through said membrane and maintaining the volume of said recirculating gas constant by continuously introducing into said continuously recirculating gas stream a mass of gas equivalent to that which is continuously withdrawn from said gas stream and comparing the concentrations of the light component in the entering gas, the withdrawn gas and the recirculated gas in order to determine the efficiency of said membrane.

  5. Cesium diffusion in graphite

    SciTech Connect

    Evans, R.B. III; Davis, W. Jr.; Sutton, A.L. Jr.

    1980-05-01

    Experiments on diffusion of /sup 137/Cs in five types of graphite were performed. The document provides a completion of the report that was started and includes a presentation of all of the diffusion data, previously unpublished. Except for data on mass transfer of /sup 137/Cs in the Hawker-Siddeley graphite, analyses of experimental results were initiated but not completed. The mass transfer process of cesium in HS-1-1 graphite at 600 to 1000/sup 0/C in a helium atmosphere is essentially pure diffusion wherein values of (E/epsilon) and ..delta..E of the equation D/epsilon = (D/epsilon)/sub 0/ exp (-..delta..E/RT) are about 4 x 10/sup -2/ cm/sup 2//s and 30 kcal/mole, respectively.

  6. Hydrogen diffusion in Zircon

    NASA Astrophysics Data System (ADS)

    Ingrin, Jannick; Zhang, Peipei

    2016-04-01

    Hydrogen mobility in gem quality zircon single crystals from Madagascar was investigated through H-D exchange experiments. Thin slices were annealed in a horizontal furnace flushed with a gas mixture of Ar/D2(10%) under ambient pressure between 900 ° C to 1150 ° C. FTIR analyses were performed on oriented slices before and after each annealing run. H diffusion along [100] and [010] follow the same diffusion law D = D0exp[-E /RT], with log D0 = 2.24 ± 1.57 (in m2/s) and E = 374 ± 39 kJ/mol. H diffusion along [001] follows a slightly more rapid diffusion law, with log D0 = 1.11 ± 0.22 (in m2/s) and E = 334 ± 49 kJ/mol. H diffusion in zircon has much higher activation energy and slower diffusivity than other NAMs below 1150 ° C even iron-poor garnets which are known to be among the slowest (Blanchard and Ingrin, 2004; Kurka et al. 2005). During H-D exchange zircon incorporates also deuterium. This hydration reaction involves uranium reduction as it is shown from the exchange of U5+ and U4+ characteristic bands in the near infrared region during annealing. It is the first time that a hydration reaction U5+ + OH‑ = U4+ + O2‑ + 1/2H2, is experimentally reported. The kinetics of deuterium incorporation is slightly slower than hydrogen diffusion, suggesting that the reaction is limited by hydrogen mobility. Hydrogen isotopic memory of zircon is higher than other NAMs. Zircons will be moderately retentive of H signatures at mid-crustal metamorphic temperatures. At 500 ° C, a zircon with a radius of 300 μm would retain its H isotopic signature over more than a million years. However, a zircon is unable to retain this information for geologically significant times under high-grade metamorphism unless the grain size is large enough. Refrences Blanchard, M. and Ingrin, J. (2004) Hydrogen diffusion in Dora Maira pyrope. Physics and Chemistry of Minerals, 31, 593-605. Kurka, A., Blanchard, M. and Ingrin, J. (2005) Kinetics of hydrogen extraction and deuteration in

  7. Hydrogen diffusion in Zircon

    NASA Astrophysics Data System (ADS)

    Ingrin, Jannick; Zhang, Peipei

    2016-04-01

    Hydrogen mobility in gem quality zircon single crystals from Madagascar was investigated through H-D exchange experiments. Thin slices were annealed in a horizontal furnace flushed with a gas mixture of Ar/D2(10%) under ambient pressure between 900 ° C to 1150 ° C. FTIR analyses were performed on oriented slices before and after each annealing run. H diffusion along [100] and [010] follow the same diffusion law D = D0exp[-E /RT], with log D0 = 2.24 ± 1.57 (in m2/s) and E = 374 ± 39 kJ/mol. H diffusion along [001] follows a slightly more rapid diffusion law, with log D0 = 1.11 ± 0.22 (in m2/s) and E = 334 ± 49 kJ/mol. H diffusion in zircon has much higher activation energy and slower diffusivity than other NAMs below 1150 ° C even iron-poor garnets which are known to be among the slowest (Blanchard and Ingrin, 2004; Kurka et al. 2005). During H-D exchange zircon incorporates also deuterium. This hydration reaction involves uranium reduction as it is shown from the exchange of U5+ and U4+ characteristic bands in the near infrared region during annealing. It is the first time that a hydration reaction U5+ + OH- = U4+ + O2- + 1/2H2, is experimentally reported. The kinetics of deuterium incorporation is slightly slower than hydrogen diffusion, suggesting that the reaction is limited by hydrogen mobility. Hydrogen isotopic memory of zircon is higher than other NAMs. Zircons will be moderately retentive of H signatures at mid-crustal metamorphic temperatures. At 500 ° C, a zircon with a radius of 300 μm would retain its H isotopic signature over more than a million years. However, a zircon is unable to retain this information for geologically significant times under high-grade metamorphism unless the grain size is large enough. Refrences Blanchard, M. and Ingrin, J. (2004) Hydrogen diffusion in Dora Maira pyrope. Physics and Chemistry of Minerals, 31, 593-605. Kurka, A., Blanchard, M. and Ingrin, J. (2005) Kinetics of hydrogen extraction and deuteration in

  8. Multispecies diffusion models: A study of uranyl species diffusion

    NASA Astrophysics Data System (ADS)

    Liu, Chongxuan; Shang, Jianying; Zachara, John M.

    2011-12-01

    Rigorous numerical description of multispecies diffusion requires coupling of species, charge, and aqueous and surface complexation reactions that collectively affect diffusive fluxes. The applicability of a fully coupled diffusion model is, however, often constrained by the availability of species self-diffusion coefficients, as well as by computational complication in imposing charge conservation. In this study, several diffusion models with variable complexity in charge and species coupling were formulated and compared to describe reactive multispecies diffusion in groundwater. Diffusion of uranyl [U(VI)] species was used as an example in demonstrating the effectiveness of the models in describing multispecies diffusion. Numerical simulations found that a diffusion model with a single, common diffusion coefficient for all species was sufficient to describe multispecies U(VI) diffusion under a steady state condition of major chemical composition, but not under transient chemical conditions. Simulations revealed that for multispecies U(VI) diffusion under transient chemical conditions, a fully coupled diffusion model could be well approximated by a component-based diffusion model when the diffusion coefficient for each chemical component was properly selected. The component-based diffusion model considers the difference in diffusion coefficients between chemical components, but not between the species within each chemical component. This treatment significantly enhanced computational efficiency at the expense of minor charge conservation. The charge balance in the component-based diffusion model can be enforced, if necessary, by adding a secondary migration term resulting from model simplification. The effect of ion activity coefficient gradients on multispecies diffusion is also discussed. The diffusion models were applied to describe U(VI) diffusive mass transfer in intragranular domains in two sediments collected from U.S. Department of Energy's Hanford 300A

  9. Osmosis and Diffusion

    ERIC Educational Resources Information Center

    Sack, Jeff

    2005-01-01

    OsmoBeaker is a CD-ROM designed to enhance the learning of diffusion and osmosis by presenting interactive experimentation to the student. The software provides several computer simulations that take the student through different scenarios with cells, having different concentrations of solutes in them.

  10. Thermodynamics of diffusion

    NASA Astrophysics Data System (ADS)

    Matuszak, Daniel

    Diffusion is the migration of molecules in the reference frame of a system's center of mass and it is a physical process that occurs in all chemical and biological systems. Diffusion generally involves intermolecular interactions that lead to clustering, adsorption, and phase transitions; as such, it is difficult to describe theoretically on a molecular level in systems containing both intermolecular repulsions and attractions. This work describes a simple thermodynamic approach that accounts for intermolecular attractions and repulsions (much like how the van der Waals equation does) to model and help provide an understanding of diffusion. The approach is an extension of the equilibrium Lattice Density Functional Theory of Aranovich and Donohue; it was developed with Mason and Lonsdale's guidelines on how to construct and test a transport theory. In the framework of lattice fluids, this new approach gives (a) correct equilibrium limits, (b) Fickian behavior for non-interacting systems, (c) correct departures from Fickian behavior in non-ideal systems, (d) the correct Maxwell-Stefan formulation, (e) symmetry behavior upon re-labeling species, (f) reasonable non-equilibrium phase behavior, (g) agreement with Molecular Dynamics simulations, (h) agreement with the theory of non-equilibrium thermodynamics, (i) a vanishing diffusive flux at the critical point, and (j) other qualitatively-correct behaviors when applied to problems in porous membranes and in packed beds.

  11. Water vapor diffusion membranes

    NASA Technical Reports Server (NTRS)

    Holland, F. F., Jr.; Smith, J. K.

    1974-01-01

    The program is reported, which was designed to define the membrane technology of the vapor diffusion water recovery process and to test this technology using commercially available or experimental membranes. One membrane was selected, on the basis of the defined technology, and was subjected to a 30-day demonstration trial.

  12. Ti Diffusion in Zircon

    NASA Astrophysics Data System (ADS)

    Cherniak, D. J.; Watson, E. B.

    2006-12-01

    Diffusion of Ti under anhydrous conditions at 1 atmosphere and under fluid-present conditions at 1.1-1.2 GPa has been measured in natural zircon. The source of diffusant for 1-atm experiments was a ZrO2- TiO2-ZrSiO4 mixture, with experiments run in Pt capsules. Diffusion experiments conducted in the presence of H2O-CO2 fluid were run in a piston-cylinder apparatus, using a source of ground TiO2, ZrSiO4 and SiO2, with oxalic acid added to produce H2O-CO2 vapor and partially melt the solid source material, yielding an assemblage of rutile + zircon + melt + vapor. Resonant nuclear reaction analysis (NRA) with the nuclear reaction ^{48}Ti(p,Γ)^{49}V was used to measure diffusion profiles for both sets of experiments. The following Arrhenius relation was obtained for Ti diffusion normal to c over the temperature range 1350-1550C at one atmosphere: DTi = 3.3x102 exp(-754 ± 56 kJ mol-1 /RT) m2sec-1 Ti diffusivities were found to be similar for experiments run under fluid-present conditions. A fit to all of the data yields the Arrhenius relation D = 1.3x103 exp(-741 ± 46 kJ mol-1 /RT) m2sec-1. These data suggest that zircon should be extremely retentive of Ti chemical signatures, indicating that the recently developed Ti-in-zircon crystallization geothermometer (Watson and Harrison, 2005; Watson et al., 2006) will be quite robust in preserving temperatures of zircon crystallization. Titanium diffuses somewhat faster in zircon than larger tetravalent cations U, Th, and Hf, but considerably more slowly than Pb, the REE, and oxygen; hence Ti crystallization temperatures may be retained under circumstances when radiometric ages or other types of geochemical information are lost. Watson EB, Harrison TM (2005) Science 308, 841-844. Watson EB, Wark DA, Thomas JB (2006) CMP(in press).

  13. Erbium diffusion in silicon dioxide

    SciTech Connect

    Lu Yingwei; Julsgaard, B.; Petersen, M. Christian; Jensen, R. V. Skougaard; Pedersen, T. Garm; Pedersen, K.; Larsen, A. Nylandsted

    2010-10-04

    Erbium diffusion in silicon dioxide layers prepared by magnetron sputtering, chemical vapor deposition, and thermal growth has been investigated by secondary ion mass spectrometry, and diffusion coefficients have been extracted from simulations based on Fick's second law of diffusion. Erbium diffusion in magnetron sputtered silicon dioxide from buried erbium distributions has in particular been studied, and in this case a simple Arrhenius law can describe the diffusivity with an activation energy of 5.3{+-}0.1 eV. Within a factor of two, the erbium diffusion coefficients at a given temperature are identical for all investigated matrices.

  14. Instrumentation in Diffuse Optical Imaging

    PubMed Central

    Zhang, Xiaofeng

    2014-01-01

    Diffuse optical imaging is highly versatile and has a very broad range of applications in biology and medicine. It covers diffuse optical tomography, fluorescence diffuse optical tomography, bioluminescence, and a number of other new imaging methods. These methods of diffuse optical imaging have diversified instrument configurations but share the same core physical principle – light propagation in highly diffusive media, i.e., the biological tissue. In this review, the author summarizes the latest development in instrumentation and methodology available to diffuse optical imaging in terms of system architecture, light source, photo-detection, spectral separation, signal modulation, and lastly imaging contrast. PMID:24860804

  15. Fractal model of anomalous diffusion.

    PubMed

    Gmachowski, Lech

    2015-12-01

    An equation of motion is derived from fractal analysis of the Brownian particle trajectory in which the asymptotic fractal dimension of the trajectory has a required value. The formula makes it possible to calculate the time dependence of the mean square displacement for both short and long periods when the molecule diffuses anomalously. The anomalous diffusion which occurs after long periods is characterized by two variables, the transport coefficient and the anomalous diffusion exponent. An explicit formula is derived for the transport coefficient, which is related to the diffusion constant, as dependent on the Brownian step time, and the anomalous diffusion exponent. The model makes it possible to deduce anomalous diffusion properties from experimental data obtained even for short time periods and to estimate the transport coefficient in systems for which the diffusion behavior has been investigated. The results were confirmed for both sub and super-diffusion.

  16. Turbo fluid machinery and diffusers

    NASA Technical Reports Server (NTRS)

    Sakurai, T.

    1984-01-01

    The general theory behind turbo devices and diffusers is explained. Problems and the state of research on basic equations of flow and experimental and measuring methods are discussed. Conventional centrifugation-type compressor and fan diffusers are considered in detail.

  17. Diffuse UV Background Radiation

    NASA Astrophysics Data System (ADS)

    Conn Henry, Richard; Murthy, J.

    2012-01-01

    The diffuse UV sky is expected to glow with significant amounts of starlight that is scattered from the interstellar dust. The albedo and scattering pattern of the dust in the ultraviolet are both well established, and are both fairly independent of wavelength from 912 Å to 3000 Å. We present 1943 Voyager spectra of the diffuse cosmic background radiation from 500 Å to 1200 Å, and we compare their brightnesses, and their distribution on the sky, to those observed (Murthy et al., ApJ 724, 1389, 2010) from the GALEX mission at longer wavelengths (1530 Å). Significant differences appear, suggesting that background radiation components in addition to dust-scattered starlight may be present in both spectral regions.

  18. Nonlocal electrical diffusion equation

    NASA Astrophysics Data System (ADS)

    Gómez-Aguilar, J. F.; Escobar-Jiménez, R. F.; Olivares-Peregrino, V. H.; Benavides-Cruz, M.; Calderón-Ramón, C.

    2016-07-01

    In this paper, we present an analysis and modeling of the electrical diffusion equation using the fractional calculus approach. This alternative representation for the current density is expressed in terms of the Caputo derivatives, the order for the space domain is 0<β≤1 and for the time domain is 0<γ≤2. We present solutions for the full fractional equation involving space and time fractional derivatives using numerical methods based on Fourier variable separation. The case with spatial fractional derivatives leads to Levy flight type phenomena, while the time fractional equation is related to sub- or super diffusion. We show that the mathematical concept of fractional derivatives can be useful to understand the behavior of semiconductors, the design of solar panels, electrochemical phenomena and the description of anomalous complex processes.

  19. Diffusion dans les liquides

    NASA Astrophysics Data System (ADS)

    Dianoux, A. J.

    2003-09-01

    Après une brève introduction qui rappelle les concepts détaillés dans le cours de M. Bée, nous présentons un aperçu de trois de nos travaux sur l'étude de la diffusion. Tout d'abord la dynamique de l'eau, dans son état normal ou surfondu, révèle la complexité apportée par le réseau de liaisons hydrogène. Ensuite l'effet du confinement sur la dynamique de l'eau sera étudié dans le cas de la membrane Nafion. Enfin la diffusion dans les phases nématique et smectique A d'un cristal liquide permet d'obtenir la valeur du potentiel qui maintient les couches dans la phase smectique.

  20. Orientability and Diffusion Maps

    PubMed Central

    Singer, Amit; Wu, Hau-tieng

    2010-01-01

    One of the main objectives in the analysis of a high dimensional large data set is to learn its geometric and topological structure. Even though the data itself is parameterized as a point cloud in a high dimensional ambient space ℝp, the correlation between parameters often suggests the “manifold assumption” that the data points are distributed on (or near) a low dimensional Riemannian manifold ℳd embedded in ℝp, with d ≪ p. We introduce an algorithm that determines the orientability of the intrinsic manifold given a sufficiently large number of sampled data points. If the manifold is orientable, then our algorithm also provides an alternative procedure for computing the eigenfunctions of the Laplacian that are important in the diffusion map framework for reducing the dimensionality of the data. If the manifold is non-orientable, then we provide a modified diffusion mapping of its orientable double covering. PMID:21765628

  1. Galactic Diffuse Polarized Emission

    NASA Astrophysics Data System (ADS)

    Carretti, Ettore

    2011-12-01

    Diffuse polarized emission by synchrotron is a key tool to investigate magnetic fields in the Milky Way, particularly the ordered component of the large scale structure. Key observables are the synchrotron emission itself and the RM is by Faraday rotation. In this paper the main properties of the radio polarized diffuse emission and its use to investigate magnetic fields will be reviewed along with our current understanding of the galactic magnetic field and the data sets available. We will then focus on the future perspective discussing RM-synthesis - the new powerful instrument devised to unlock the information encoded in such an emission - and the surveys currently in progress like S-PASS and GMIMS.

  2. Thermal diffusivity imaging

    NASA Astrophysics Data System (ADS)

    Gfroerer, Tim; Phillips, Ryan; Rossi, Peter

    2015-11-01

    The tip of a rod is heated with a torch and brought into contact with the center of a metal sheet. A thermal camera is then used to image the temperature profile of the surface as a function of time. The infrared camera is capable of recording radiometric data with 1 mK resolution in nearly 105 pixels, so thermal diffusion can be monitored with unprecedented precision. With a frame rate of approximately 10 Hz, the pace of the data acquisition minimizes the loss of accuracy due to inevitable cooling mechanisms. We report diffusivity constants equal to 1.23 ± 0.06 cm2/s in copper and 0.70 ± 0.05 cm2/s in aluminum. The behavior is modeled with a straightforward but oddly under-utilized one-dimensional finite difference method.

  3. Mass transport by diffusion

    NASA Technical Reports Server (NTRS)

    Baird, James K.

    1987-01-01

    For the purpose of determining diffusion coefficients as required for electrodeposition studies and other applications, a diaphragm cell and an isothermal water bath were constructed. the calibration of the system is discussed. On the basis of three calibration runs on the diaphram cell, researchers concluded that the cell constant beta equals 0.12 cm -2 . Other calibration runs in progress should permit the cell constant to be determined with an accuracy of one percent.

  4. Peridynamic thermal diffusion

    SciTech Connect

    Oterkus, Selda; Madenci, Erdogan; Agwai, Abigail

    2014-05-15

    This study presents the derivation of ordinary state-based peridynamic heat conduction equation based on the Lagrangian formalism. The peridynamic heat conduction parameters are related to those of the classical theory. An explicit time stepping scheme is adopted for numerical solution of various benchmark problems with known solutions. It paves the way for applying the peridynamic theory to other physical fields such as neutronic diffusion and electrical potential distribution.

  5. Random diffusion model.

    PubMed

    Mazenko, Gene F

    2008-09-01

    We study the random diffusion model. This is a continuum model for a conserved scalar density field varphi driven by diffusive dynamics. The interesting feature of the dynamics is that the bare diffusion coefficient D is density dependent. In the simplest case, D=D[over ]+D_{1}deltavarphi , where D[over ] is the constant average diffusion constant. In the case where the driving effective Hamiltonian is quadratic, the model can be treated using perturbation theory in terms of the single nonlinear coupling D1 . We develop perturbation theory to fourth order in D1 . The are two ways of analyzing this perturbation theory. In one approach, developed by Kawasaki, at one-loop order one finds mode-coupling theory with an ergodic-nonergodic transition. An alternative more direct interpretation at one-loop order leads to a slowing down as the nonlinear coupling increases. Eventually one hits a critical coupling where the time decay becomes algebraic. Near this critical coupling a weak peak develops at a wave number well above the peak at q=0 associated with the conservation law. The width of this peak in Fourier space decreases with time and can be identified with a characteristic kinetic length which grows with a power law in time. For stronger coupling the system becomes metastable and then unstable. At two-loop order it is shown that the ergodic-nonergodic transition is not supported. It is demonstrated that the critical properties of the direct approach survive, going to higher order in perturbation theory.

  6. Diffusive Shock Acceleration

    NASA Astrophysics Data System (ADS)

    Baring, Matthew

    2003-04-01

    The process of diffusive acceleration of charged particles in shocked plasmas is widely invoked in astrophysics to account for the ubiquitous presence of signatures of non-thermal relativistic electrons and ions in the universe. This statistical energization mechanism, manifested in turbulent media, was first posited by Enrico Fermi in 1949 to explain the observed cosmic ray population, which exhibits an almost power-law distribution in rigidity. The absence of a momentum scale is a key characteristic of diffusive shock acceleration, and astrophysical systems generally only impose scales at the injection (low energy) and loss (high energy) ends of the particle spectrum. The existence of structure in the cosmic ray spectrum (the "knee") at around 3000 TeV has promoted contentions that there are at least two origins for cosmic rays, a galactic one supplying those up to the knee, and perhaps an extragalactic one that can explain even the ultra-high energy cosmic rays (UHECRs) seen at 1-300 EeV. Accounting for the UHECRs with familiar astrophysical sites of acceleration has historically proven difficult due to the need to assume high magnetic fields in order to reduce the shortest diffusive acceleration timescale, the ion gyroperiod, to meaningful values. Yet active galaxies and gamma-ray bursts remain strong and interesting candidate sources for UHECRs, turning the theoretical focus to relativistic shocks. This review summarizes properties of diffusive shock acceleration that are salient to the issue of UHECR generation. These include spectral indices, anisotropies, acceleration efficencies and timescales, as functions of the shock speed and mean field orientation, and also the degree of field turbulence. Astrophysical sites for UHECR production are also critiqued.

  7. Solute diffusion in liquid metals

    NASA Technical Reports Server (NTRS)

    Bhat, B. N.

    1973-01-01

    A gas model of diffusion in liquid metals is presented. In this model, ions of liquid metals are assumed to behave like the molecules in a dense gas. Diffusion coefficient of solute is discussed with reference to its mass, ionic size, and pair potential. The model is applied to the case of solute diffusion in liquid silver. An attempt was made to predict diffusion coefficients of solutes with reasonable accuracy.

  8. Percolation of interaction diffusing particles

    NASA Technical Reports Server (NTRS)

    Selinger, Robin Blumberg; Stanley, H. Eugene

    1990-01-01

    The connectivity properties of systems of diffusing interacting particles with the blind and myopic diffusion rules are studied. It is found that the blind rule case is equivalent to the lattice gas with J = 0 in all dimensions. The connectivity properties of blind rule diffusion are described by random site percolation due to the fact that the density on neighboring sites is uncorrelated.

  9. Particle diffusion in a spheromak

    SciTech Connect

    Meyerhofer, D.D.; Levinton, F.M.; Yamada, M.

    1988-01-01

    The local carbon particle diffusion coefficient was measured in the Proto S-1/C spheromak using a test particle injection scheme. When the plasma was not in a force-free Taylor state, and when there were pressure gradients in the plasma, the particle diffusion was five times that predicted by Bohm and was consistent with collisional drift wave diffusion. The diffusion appears to be driven by correlations of the fluctuating electric field and density. During the decay phase of the discharge when the plasma was in the Taylor state, the diffusion coefficient of the carbon was classical. 23 refs., 4 figs.

  10. Diffuse, Warm Ionized Gas

    NASA Astrophysics Data System (ADS)

    Haffner, L. M.

    2002-05-01

    Over the past decade, new high-sensitivity observations have significantly advanced our knowledge of the diffuse, ionized gas in spiral galaxies. This component of the interstellar medium, often referred to as Warm Ionized Medium (WIM) or Diffuse Ionized Gas (DIG), plays an important role in the complex stellar-interstellar matter and energy cycle. In examining the distribution and physical properties of this gas, we learn not only about the conditions of the medium but also about processes providing heating and ionization in the halos of spiral galaxies. For the Milky Way, three new Hα surveys are available providing large sky coverage, arc-minute spatial resolution, and the ability to kinematically resolve this prominent optical emission line. These new, global views show that the Warm Ionized Medium of the Galaxy is ubiquitous as previously suspected, is rich with filamentary structure down to current resolution limits, and can be traced into the halo at large distances from the Galactic plane. Observations of additional optical emission lines are beginning to probe the physical conditions of the WIM. Early results suggest variations in the temperature and ionization state of the gas which are not adequately explained by Lyman continuum stellar photoionization alone. In parallel with this intensive work in the Milky Way have been numerous studies about the diffuse, ionized gas in other spiral galaxies. Here, deep, face-on spiral investigations provide some of the best maps of the global DIG distribution in a galaxy and begin to allow a probe of the local link between star formation and the powering of ionized gas. In addition, ionized gas has been traced out to impressive distances (z > 3 kpc) in edge-on spirals, revealing out large-scale changes in the physical conditions and kinematics of galactic halos.

  11. Diffusion in silicon isotope heterostructures

    SciTech Connect

    Silvestri, Hughes Howland

    2004-05-14

    The simultaneous diffusion of Si and the dopants B, P, and As has been studied by the use of a multilayer structure of isotopically enriched Si. This structure, consisting of 5 pairs of 120 nm thick natural Si and {sup 28}Si enriched layers, enables the observation of {sup 30}Si self-diffusion from the natural layers into the {sup 28}Si enriched layers, as well as dopant diffusion from an implanted source in an amorphous Si cap layer, via Secondary Ion Mass Spectrometry (SIMS). The dopant diffusion created regions of the multilayer structure that were extrinsic at the diffusion temperatures. In these regions, the Fermi level shift due to the extrinsic condition altered the concentration and charge state of the native defects involved in the diffusion process, which affected the dopant and self-diffusion. The simultaneously recorded diffusion profiles enabled the modeling of the coupled dopant and self-diffusion. From the modeling of the simultaneous diffusion, the dopant diffusion mechanisms, the native defect charge states, and the self- and dopant diffusion coefficients can be determined. This information is necessary to enhance the physical modeling of dopant diffusion in Si. It is of particular interest to the modeling of future electronic Si devices, where the nanometer-scale features have created the need for precise physical models of atomic diffusion in Si. The modeling of the experimental profiles of simultaneous diffusion of B and Si under p-type extrinsic conditions revealed that both species are mediated by neutral and singly, positively charged Si self-interstitials. The diffusion of As and Si under extrinsic n-type conditions yielded a model consisting of the interstitialcy and vacancy mechanisms of diffusion via singly negatively charged self-interstitials and neutral vacancies. The simultaneous diffusion of P and Si has been modeled on the basis of neutral and singly negatively charged self-interstitials and neutral and singly positively charged P

  12. Accelerated stochastic diffusion processes

    NASA Astrophysics Data System (ADS)

    Garbaczewski, Piotr

    1990-07-01

    We give a purely probabilistic demonstration that all effects of non-random (external, conservative) forces on the diffusion process can be encoded in the Nelson ansatz for the second Newton law. Each random path of the process together with a probabilistic weight carries a phase accumulation (complex valued) weight. Random path summation (integration) of these weights leads to the transition probability density and transition amplitude respectively between two spatial points in a given time interval. The Bohm-Vigier, Fenyes-Nelson-Guerra and Feynman descriptions of the quantum particle behaviours are in fact equivalent.

  13. Turbulent forced diffusion flames

    SciTech Connect

    Arpaci, V.S.; Li, C.Y.

    1995-07-01

    It is the purpose of this study to introduce a turbulent microscale appropriate for forced diffusion flames and to propose models for fuel consumption and skin friction in terms of this scale. The study consists of four sections. Following the introduction, Section 2 recapitulates the laminar theories of reacting boundary layers in terms of dimensional arguments and proposes models for fuel consumption and skin friction. Section 3 extends these arguments by introducing a microscale appropriate for turbulent flames and, in terms of this scale, develops models for fuel consumption and skin friction, correlates the experimental data on skin friction, and Section 4 concludes the study.

  14. Diffusion from solid cylinders

    SciTech Connect

    Nestor, C.W. Jr.

    1980-01-01

    The problem considered is the diffusion of material from a solid cylinder initially containng a uniform concentration and immersed in a well-stirred bath which maintains the external concentration at zero. The Fourier-Bessel series form of the fraction of the original material removed from the cylinder as a function of time converges very slowly for small time. An alternate form was obtained, which converges reasonably rapidly for small time. The convergence acceleration method of P. Wynn was also used to provide an efficient method for computation. Numerical examples and program listings are included.

  15. Vapor Diffusion Apparatus

    NASA Technical Reports Server (NTRS)

    2001-01-01

    Vapor Diffusion Apparatus (VDA and VDA-2) was developed by the University of Alabama in Birmingham for NASA's Marshall Space Flight Center. In the original VDA, a protein solution and a precipitant are extruded by two plungers onto the tip of a small syringe and allowed to evaporate, raising the concentration and prompting protein molecules to crystallize. In the VDA-2 version, a third plunger was added to mix the two solutions before returning the mix to the syringe tip. The principal investigator is Dr. Larry Delucas of the University of Alabama in Birmingham

  16. Vapor Diffusion Apparatus

    NASA Technical Reports Server (NTRS)

    2001-01-01

    Vapor Diffusion Apparatus (VDA-2) was developed by the University of Alabama in Birmingham for NASA's Marshall Space Flight Center. In the original VDA, a protein solution and a precipitant are extruded by two plungers onto the tip of a small syringe and allowed to evaporate, raising the concentration and prompting protein molecules to crystallize. In the VDA-2 version, a third plunger was added to mix the two solutions before returning the mix to the syringe tip. The principal investigator is Dr. Larry Delucas of the University of Alabama in Birmingham.

  17. Apparatus for diffusion separation

    DOEpatents

    Nierenberg, William A.

    1976-08-10

    1. A diffuser separator apparatus which comprises a plurality of flow channels in a single stage, each of said channels having an inlet port and an outlet port and a constant cross sectional area between said ports, at least a portion of the defining surface of each of said channels being a diffusion separation membrane, and each of said channels having a different cross sectional area, means for connecting said channels in series so that each successive channel of said series has a smaller cross sectional area than the previous channel of said series, a source of gaseous mixture, individual means for flowing said gaseous mixture to the inlet port of each of said channels, gas receiving and analyzing means, individual means for flowing gas passing from each of said outlet ports and means for flowing gas passing through said membranes to said receiving and analyzing means, and individual means for connecting the outlet port of each channel with the inlet port of the channel having the next smaller cross sectional area.

  18. Diffusing obesity myths.

    PubMed

    Ramos Salas, X; Forhan, M; Sharma, A M

    2014-06-01

    Misinformation or myths about obesity can lead to weight bias and obesity stigma. Counteracting myths with facts and evidence has been shown to be effective educational tools to increase an individuals' knowledge about a certain condition and to reduce stigma.The purpose of this study was to identify common obesity myths within the healthcare and public domains and to develop evidence-based counterarguments to diffuse them. An online search of grey literature, media and public health information sources was conducted to identify common obesity myths. A list of 10 obesity myths was developed and reviewed by obesity experts and key opinion leaders. Counterarguments were developed using current research evidence and validated by obesity experts. A survey of obesity experts and health professionals was conducted to determine the usability and potential effectiveness of the myth-fact messages to reduce weight bias. A total of 754 individuals responded to the request to complete the survey. Of those who responded, 464 (61.5%) completed the survey. All 10 obesity myths were identified to be deeply pervasive within Canadian healthcare and public domains. Although the myth-fact messages were endorsed, respondents also indicated that they would likely not be sufficient to reduce weight bias. Diffusing deeply pervasive obesity myths will require multilevel approaches. PMID:25826775

  19. Sampling diffusive transition paths

    SciTech Connect

    F. Miller III, Thomas; Predescu, Cristian

    2006-10-12

    We address the problem of sampling double-ended diffusive paths. The ensemble of paths is expressed using a symmetric version of the Onsager-Machlup formula, which only requires evaluation of the force field and which, upon direct time discretization, gives rise to a symmetric integrator that is accurate to second order. Efficiently sampling this ensemble requires avoiding the well-known stiffness problem associated with sampling infinitesimal Brownian increments of the path, as well as a different type of stiffness associated with sampling the coarse features of long paths. The fine-features sampling stiffness is eliminated with the use of the fast sampling algorithm (FSA), and the coarse-feature sampling stiffness is avoided by introducing the sliding and sampling (S&S) algorithm. A key feature of the S&S algorithm is that it enables massively parallel computers to sample diffusive trajectories that are long in time. We use the algorithm to sample the transition path ensemble for the structural interconversion of the 38-atom Lennard-Jones cluster at low temperature.

  20. Anisotropic Thermal Diffusion

    NASA Astrophysics Data System (ADS)

    Gardiner, Thomas

    2013-10-01

    Anisotropic thermal diffusion in magnetized plasmas is an important physical phenomena for a diverse set of physical conditions ranging from astrophysical plasmas to MFE and ICF. Yet numerically simulating this phenomenon accurately poses significant challenges when the computational mesh is misaligned with respect to the magnetic field. Particularly when the temperature gradients are unresolved, one frequently finds entropy violating solutions with heat flowing from cold to hot zones for χ∥ /χ⊥ >=102 which is substantially smaller than the range of interest which can reach 1010 or higher. In this talk we present a new implicit algorithm for solving the anisotropic thermal diffusion equations and demonstrate its characteristics on what has become a fairly standard set of test problems in the literature. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. SAND2013-5687A.

  1. Diffuse Alveolar Hemorrhage

    PubMed Central

    2013-01-01

    Diffuse alveolar hemorrhage (DAH) is a life-threatening and medical emergency that can be caused by numerous disorders and presents with hemoptysis, anemia, and diffuse alveolar infiltrates. Early bronchoscopy with bronchoalveolar lavage is usually required to confirm the diagnosis and rule out infection. Most cases of DAH are caused by capillaritis associated with systemic autoimmune diseases such as anti-neutrophil cytoplasmic antibody-associated vasculitis, anti-glomerular basement membrane disease, and systemic lupus erythematosus, but DAH may also result from coagulation disorders, drugs, inhaled toxins, or transplantation. The diagnosis of DAH relies on clinical suspicion combined with laboratory, radiologic, and pathologic findings. Early recognition is crucial, because prompt diagnosis and treatment is necessary for survival. Corticosteroids and immunosuppressive agents remain the gold standard. In patients with DAH, biopsy of involved sites can help to identify the cause and to direct therapy. This article aims to provide a general review of the causes and clinical presentation of DAH and to recommend a diagnostic approach and a management plan for the most common causes. PMID:23678356

  2. Diffuse alveolar hemorrhage.

    PubMed

    Park, Moo Suk

    2013-04-01

    Diffuse alveolar hemorrhage (DAH) is a life-threatening and medical emergency that can be caused by numerous disorders and presents with hemoptysis, anemia, and diffuse alveolar infiltrates. Early bronchoscopy with bronchoalveolar lavage is usually required to confirm the diagnosis and rule out infection. Most cases of DAH are caused by capillaritis associated with systemic autoimmune diseases such as anti-neutrophil cytoplasmic antibody-associated vasculitis, anti-glomerular basement membrane disease, and systemic lupus erythematosus, but DAH may also result from coagulation disorders, drugs, inhaled toxins, or transplantation. The diagnosis of DAH relies on clinical suspicion combined with laboratory, radiologic, and pathologic findings. Early recognition is crucial, because prompt diagnosis and treatment is necessary for survival. Corticosteroids and immunosuppressive agents remain the gold standard. In patients with DAH, biopsy of involved sites can help to identify the cause and to direct therapy. This article aims to provide a general review of the causes and clinical presentation of DAH and to recommend a diagnostic approach and a management plan for the most common causes.

  3. Configurational diffusion of coal macromolecules

    SciTech Connect

    Guin, J.A.; Curtis, C.W.; Tarrer, A.R.

    1991-01-01

    It has been reported that the most predominant constituents of coal extract are the polycyclic aromatic hydrocarbons. Yet the experimental values of diffusivity in ethyl acetate for the most of these materials were not available in the literature. Thus, the diffusion coefficients of some of these materials were measured to increase an understanding of the diffusional behavior of coal macromolecules. In an earlier quarterly report, the authors reported the diffusion coefficients of some model coal molecules determined using their diffusion cell with polycarbonate membranes. Subsequently, they have found that these polycarbonate membranes are semi-permeable to some of the model compounds, so that the measured diffusion flux was greater than that through the pores alone. This extra solute flux could result in over estimation of the diffusion coefficients, therefore, they have now re-measured these diffusivities using polyester, rather than polycarbonate, membranes. The polyester material is not permeable to the solute molecules, except through the open pore area. Thus the only diffusion flux is that through the pores, resulting in correct diffusion coefficients as reported herein. The detailed results are presented in the body of this report. Finally in the last section the authors discuss a slight departure in methodology of some of their earlier planned work. This change will have a positive beneficial impact on the results and speed-up the collection of configurational diffusion data in actual tortuous porous media. 12 refs., 3 figs., 4 tabs.

  4. Sucrose diffusion in aqueous solution.

    PubMed

    Price, Hannah C; Mattsson, Johan; Murray, Benjamin J

    2016-07-28

    The diffusion of sugar in aqueous solution is important both in nature and in technological applications, yet measurements of diffusion coefficients at low water content are scarce. We report directly measured sucrose diffusion coefficients in aqueous solution. Our technique utilises a Raman isotope tracer method to monitor the diffusion of non-deuterated and deuterated sucrose across a boundary between the two aqueous solutions. At a water activity of 0.4 (equivalent to 90 wt% sucrose) at room temperature, the diffusion coefficient of sucrose was determined to be approximately four orders of magnitude smaller than that of water in the same material. Using literature viscosity data, we show that, although inappropriate for the prediction of water diffusion, the Stokes-Einstein equation works well for predicting sucrose diffusion under the conditions studied. As well as providing information of importance to the fundamental understanding of diffusion in binary solutions, these data have technological, pharmaceutical and medical implications, for example in cryopreservation. Moreover, in the atmosphere, slow organic diffusion may have important implications for aerosol growth, chemistry and evaporation, where processes may be limited by the inability of a molecule to diffuse between the bulk and the surface of a particle. PMID:27364512

  5. Sucrose diffusion in aqueous solution

    PubMed Central

    Murray, Benjamin J.

    2016-01-01

    The diffusion of sugar in aqueous solution is important both in nature and in technological applications, yet measurements of diffusion coefficients at low water content are scarce. We report directly measured sucrose diffusion coefficients in aqueous solution. Our technique utilises a Raman isotope tracer method to monitor the diffusion of non-deuterated and deuterated sucrose across a boundary between the two aqueous solutions. At a water activity of 0.4 (equivalent to 90 wt% sucrose) at room temperature, the diffusion coefficient of sucrose was determined to be approximately four orders of magnitude smaller than that of water in the same material. Using literature viscosity data, we show that, although inappropriate for the prediction of water diffusion, the Stokes–Einstein equation works well for predicting sucrose diffusion under the conditions studied. As well as providing information of importance to the fundamental understanding of diffusion in binary solutions, these data have technological, pharmaceutical and medical implications, for example in cryopreservation. Moreover, in the atmosphere, slow organic diffusion may have important implications for aerosol growth, chemistry and evaporation, where processes may be limited by the inability of a molecule to diffuse between the bulk and the surface of a particle. PMID:27364512

  6. The Harrison Diffusion Kinetics Regimes in Solute Grain Boundary Diffusion

    SciTech Connect

    Belova, Irina; Fiedler, T; Kulkarni, Nagraj S; Murch, Prof. Graeme

    2012-01-01

    Knowledge of the limits of the principal Harrison kinetics regimes (Type-A, B and C) for grain boundary diffusion is very important for the correct analysis of the depth profiles in a tracer diffusion experiment. These regimes for self-diffusion have been extensively studied in the past by making use of the phenomenological Lattice Monte Carlo (LMC) method with the result that the limits are now well established. The relationship of those self-diffusion limits to the corresponding ones for solute diffusion in the presence of solute segregation to the grain boundaries remains unclear. In the present study, the influence of solute segregation on the limits is investigated with the LMC method for the well-known parallel grain boundary slab model by showing the equivalence of two diffusion models. It is shown which diffusion parameters are useful for identifying the limits of the Harrison kinetics regimes for solute grain boundary diffusion. It is also shown how the measured segregation factor from the diffusion experiment in the Harrison Type-B kinetics regime may differ from the global segregation factor.

  7. Diffusing Diffusivity: Survival in a Crowded Rearranging and Bounded Domain.

    PubMed

    Jain, Rohit; Sebastian, Kizhakeyil L

    2016-09-01

    We consider a particle diffusing in a bounded, crowded, rearranging medium. The rearrangement happens on a time scale longer than the typical time scale of diffusion of the particle; as a result, effectively, the diffusion coefficient of the particle varies as a stochastic function of time. What is the probability that the particle will survive within the bounded region, given that it is absorbed the first time it hits the boundary of the region in which it diffuses? This question is of great interest in a variety of chemical and biological problems. If the diffusion coefficient is a constant, then analytical solutions for a variety of cases are available in the literature. However, there is no solution available for the case in which the diffusion coefficient is a random function of time. We discuss a class of models for which it is possible to find analytical solutions to the problem. We illustrate the method for a circular, two-dimensional region, but our methods are easy to apply to diffusion in arbitrary dimensions and spherical/rectangular regions. Our solution shows that if the dimension of the region is large, then only the average value of the diffusion coefficient determines the survival probability. However, for smaller-sized regions, one would be able to see the effects of the stochasticity of the diffusion coefficient. We also give generalizations of the results to N dimensions. PMID:27478982

  8. Is anomalous transport diffusive

    SciTech Connect

    Rewoldt, G.

    1989-09-01

    It has often been assumed that the anomalous transport from saturated plasma instabilities is diffusive'' in the sense that the particle flux, {Gamma}, the electron energy flux, q{sub e}, and the ion energy flux, q{sub i}, can be written in forms that are linear in the density gradient, dn/dr, the electron temperature gradient, dT{sub e}/dr, and the ion temperature gradient dT{sub i}/dr. In the simplest form, {Gamma} = {minus} D{sub n}{sup n}(dn/dr), q{sub e} = {minus} D{sub e}{sup e}n(dT{sub e}/dr), and q{sub i} = {minus}D{sub i}{sup i}n(dT{sub i}/dr). A possible generalization of this is to include so-called off-diagonal'' terms, with {Gamma} = nV{sub n} {minus} D{sub n}{sup n}(dn/dr) {minus} D{sub n}{sup e}(n/T{sub e})(dT{sub e}/dr) {minus} D{sub n}{sup i}(n/T{sub i})(dT{sub i}/dr), with corresponding forms for the energy fluxes. Here, general results for the quasilinear particle and energy fluxes, resulting from tokamak linear microinstabilities, are evaluated to assess the relative importance of the diagonal and the off-diagonal terms. A further possible generatlization is to include also contributions to the fluxes from higher powers of the gradients, specifically quadratic'' contributions proportional to (dn/dr){sup 2}, (dn/dr)(dT{sub e}/dr), and so on. A procedure is described for evaluating the corresponding coefficients, and results are presented for illustrative realistic tokamak cases. Qualitatively, it is found that the off-diagonal diffusion coefficients can be as big as the diagonal ones, and that the quadratic terms can be larger than the linear ones. The results thus strongly suggest that the commonly used diffusive'' approximation with only diagonal terms, {Gamma} = {minus}D{sub n}{sup n}(dn/dr), and correspondingly for the energy fluxes, is not adequate in practice. 9 refs., 1 tabs.

  9. Apoplastic diffusion barriers in Arabidopsis.

    PubMed

    Nawrath, Christiane; Schreiber, Lukas; Franke, Rochus Benni; Geldner, Niko; Reina-Pinto, José J; Kunst, Ljerka

    2013-12-27

    During the development of Arabidopsis and other land plants, diffusion barriers are formed in the apoplast of specialized tissues within a variety of plant organs. While the cuticle of the epidermis is the primary diffusion barrier in the shoot, the Casparian strips and suberin lamellae of the endodermis and the periderm represent the diffusion barriers in the root. Different classes of molecules contribute to the formation of extracellular diffusion barriers in an organ- and tissue-specific manner. Cutin and wax are the major components of the cuticle, lignin forms the early Casparian strip, and suberin is deposited in the stage II endodermis and the periderm. The current status of our understanding of the relationships between the chemical structure, ultrastructure and physiological functions of plant diffusion barriers is discussed. Specific aspects of the synthesis of diffusion barrier components and protocols that can be used for the assessment of barrier function and important barrier properties are also presented.

  10. Apoplastic Diffusion Barriers in Arabidopsis

    PubMed Central

    Schreiber, Lukas; Franke, Rochus Benni; Geldner, Niko; Reina-Pinto, José J.; Kunst, Ljerka

    2013-01-01

    During the development of Arabidopsis and other land plants, diffusion barriers are formed in the apoplast of specialized tissues within a variety of plant organs. While the cuticle of the epidermis is the primary diffusion barrier in the shoot, the Casparian strips and suberin lamellae of the endodermis and the periderm represent the diffusion barriers in the root. Different classes of molecules contribute to the formation of extracellular diffusion barriers in an organ- and tissue-specific manner. Cutin and wax are the major components of the cuticle, lignin forms the early Casparian strip, and suberin is deposited in the stage II endodermis and the periderm. The current status of our understanding of the relationships between the chemical structure, ultrastructure and physiological functions of plant diffusion barriers is discussed. Specific aspects of the synthesis of diffusion barrier components and protocols that can be used for the assessment of barrier function and important barrier properties are also presented. PMID:24465172

  11. Osmosis and diffusion conceptual assessment.

    PubMed

    Fisher, Kathleen M; Williams, Kathy S; Lineback, Jennifer Evarts

    2011-01-01

    Biology student mastery regarding the mechanisms of diffusion and osmosis is difficult to achieve. To monitor comprehension of these processes among students at a large public university, we developed and validated an 18-item Osmosis and Diffusion Conceptual Assessment (ODCA). This assessment includes two-tiered items, some adopted or modified from the previously published Diffusion and Osmosis Diagnostic Test (DODT) and some newly developed items. The ODCA, a validated instrument containing fewer items than the DODT and emphasizing different content areas within the realm of osmosis and diffusion, better aligns with our curriculum. Creation of the ODCA involved removal of six DODT item pairs, modification of another six DODT item pairs, and development of three new item pairs addressing basic osmosis and diffusion concepts. Responses to ODCA items testing the same concepts as the DODT were remarkably similar to responses to the DODT collected from students 15 yr earlier, suggesting that student mastery regarding the mechanisms of diffusion and osmosis remains elusive.

  12. Light diffusing fiber optic chamber

    DOEpatents

    Maitland, Duncan J.

    2002-01-01

    A light diffusion system for transmitting light to a target area. The light is transmitted in a direction from a proximal end to a distal end by an optical fiber. A diffusing chamber is operatively connected to the optical fiber for transmitting the light from the proximal end to the distal end and transmitting said light to said target area. A plug is operatively connected to the diffusing chamber for increasing the light that is transmitted to the target area.

  13. Diffusion Coefficients in White Dwarfs

    NASA Astrophysics Data System (ADS)

    Saumon, D.; Starrett, C. E.; Daligault, J.

    2015-06-01

    Models of diffusion in white dwarfs universally rely on the coefficients calculated by Paquette et al. (1986). We present new calculations of diffusion coefficients based on an advanced microscopic theory of dense plasmas and a numerical simulation approach that intrinsically accounts for multiple collisions. Our method is validated against a state-of-the-art method and we present results for the diffusion of carbon ions in a helium plasma.

  14. Diffusion in Jammed Particle Packs.

    PubMed

    Bolintineanu, Dan S; Grest, Gary S; Lechman, Jeremy B; Silbert, Leonardo E

    2015-08-21

    Using random walk simulations we explore diffusive transport through monodisperse sphere packings over a range of packing fractions ϕ in the vicinity of the jamming transition at ϕ(c). Various diffusion properties are computed over several orders of magnitude in both time and packing pressure. Two well-separated regimes of normal "Fickian" diffusion, where the mean squared displacement is linear in time, are observed. The first corresponds to diffusion inside individual spheres, while the latter is the long-time bulk diffusion. The intermediate anomalous diffusion regime and the long-time value of the diffusion coefficient are both shown to be controlled by particle contacts, which in turn depend on proximity to ϕ(c). The time required to recover normal diffusion t* scales as (ϕ-ϕ(c))(-0.5) and the long-time diffusivity D(∞)∼(ϕ-ϕ(c))0.5, or D(∞)∼1/t*. It is shown that the distribution of mean first passage times associated with the escape of random walkers between neighboring particles controls both t* and D(∞) in the limit ϕ→ϕ(c).

  15. Enthalpy Diffusion in Multicomponent Flows

    SciTech Connect

    Cook, A W

    2009-01-20

    The conclusions of this paper are: (1) Enthalpy diffusion preserves the second law. (2) Euler solvers will not produce correct temperatures in mixing regions. (3) Navier-Stokes solvers will only produce correct temperatures if q{sub d} is included. (4) Errors from neglecting enthalpy diffusion are most severe when differences in molecular weights are large. (5) In addition to temperature, enthalpy diffusion affects density, dilatation and other fields in subtle ways. (6) Reacting flow simulations that neglect the term are a dubious proposition. (7) Turbulence models for RANS and LES closures should preserve consistency between energy and species diffusion.

  16. Diffusion rates for elevated releases

    SciTech Connect

    Ramsdell, J.V.

    1983-11-01

    A search of the literature related to diffusion from elevated sources has determined that an adequate data base exists for use in developing parameterizations for estimating diffusion rates for material released from free standing stacks at nuclear power plants. A review of published data analyses indicates that a new parameterization of horizontal diffusion rates specifically for elevated releases is not likely to significantly change the magnitudes of horizontal diffusion coefficients on the average. However, the uncertainties associated with horizontal diffusion coefficient estimates under any given set of atmospheric conditions could be reduced by a new parameterization. Similarly, a new parameterization of vertical diffusion rates would be unlikely to significantly alter the magnitudes of diffusion coefficients for unstable atmospheric conditons. However, for neutral and stable atmospheric conditions, a new parameterization of vertical diffusion rates might increase vertical diffusion coefficients significantly. The increase would move ground-level time-integrated concentration maxima closer to the plant and would increase the maxima. 55 references, 2 figures, 4 tables.

  17. Diffusion in Jammed Particle Packs.

    PubMed

    Bolintineanu, Dan S; Grest, Gary S; Lechman, Jeremy B; Silbert, Leonardo E

    2015-08-21

    Using random walk simulations we explore diffusive transport through monodisperse sphere packings over a range of packing fractions ϕ in the vicinity of the jamming transition at ϕ(c). Various diffusion properties are computed over several orders of magnitude in both time and packing pressure. Two well-separated regimes of normal "Fickian" diffusion, where the mean squared displacement is linear in time, are observed. The first corresponds to diffusion inside individual spheres, while the latter is the long-time bulk diffusion. The intermediate anomalous diffusion regime and the long-time value of the diffusion coefficient are both shown to be controlled by particle contacts, which in turn depend on proximity to ϕ(c). The time required to recover normal diffusion t* scales as (ϕ-ϕ(c))(-0.5) and the long-time diffusivity D(∞)∼(ϕ-ϕ(c))0.5, or D(∞)∼1/t*. It is shown that the distribution of mean first passage times associated with the escape of random walkers between neighboring particles controls both t* and D(∞) in the limit ϕ→ϕ(c). PMID:26340211

  18. Turing instability in reaction-diffusion systems with nonlinear diffusion

    NASA Astrophysics Data System (ADS)

    Zemskov, E. P.

    2013-10-01

    The Turing instability is studied in two-component reaction-diffusion systems with nonlinear diffusion terms, and the regions in parametric space where Turing patterns can form are determined. The boundaries between super- and subcritical bifurcations are found. Calculations are performed for one-dimensional brusselator and oregonator models.

  19. Turing instability in reaction-diffusion systems with nonlinear diffusion

    SciTech Connect

    Zemskov, E. P.

    2013-10-15

    The Turing instability is studied in two-component reaction-diffusion systems with nonlinear diffusion terms, and the regions in parametric space where Turing patterns can form are determined. The boundaries between super- and subcritical bifurcations are found. Calculations are performed for one-dimensional brusselator and oregonator models.

  20. Speckle in a thick diffuser

    NASA Astrophysics Data System (ADS)

    Chang, Nien-An

    Theory and experiments on speckle generated from a thick diffuser are presented in this thesis. An overview of speckle from a diffuser in a 4F optical processor gives a basic understanding of the speckle formation and properties. The speckle size depends on the F number of the system, while the interior properties of a diffuser are evident in the wavelength dependence of speckle. We then move on to analyzing speckle from a thick diffuser, which is composed of particles embedded in a host medium. Emphasis on the theory is placed on solving for the wavelength decorrelation of speckle in a thick diffuser. A brief overview of the scattering theory for a particle using the Lorenz-Mie theory is included. Then we present a careful analysis of the speckle created by propagation through a thick diffuser. In the analysis we use an angular spectrum approach that is valid in the non-paraxial case together with a decomposition of the thick diffuser into a cascade of many screens. This calculation is well-suited to numerical analysis and an original computer software program has been provided as an Appendix in this thesis. By adding the scattered field from the randomly-located particles on any screen and propagating through a free space between each screen, one can generate a speckled field after going through the whole cascade. The theoretical predictions are summarized and later compared with experimental results on a series of opal milk glass diffusers. In many practical applications it is particularly advantageous to have mild thick diffusers of controllable diffusivity. We have extensively studied a new diffuser series fabricated using polystyrene spheres of various diameters embedded in gelatin. Theory and experiments are in good agreement.

  1. Diffusion in jammed particle packs

    NASA Astrophysics Data System (ADS)

    Bolintineanu, Dan S.; Silbert, Leonardo E.; Grest, Gary S.; Lechman, Jeremy B.

    2015-03-01

    Diffusive transport in jammed particle packs is of interest for a number of applications, as well as being a potential indicator of structural properties near the jamming point. To this end, we report stochastic simulations of equilibrium diffusion through monodisperse sphere packs near the jamming point in the limit of a perfectly insulating surrounding medium. The time dependence of various diffusion properties is resolved over several orders of magnitude. Two time regimes of expected Fickian diffusion are observed, separated by an intermediate regime of anomalous diffusion. This intermediate regime grows as the particle volume fraction approaches the critical jamming transition. The diffusion behavior is fully controlled by the extent of the contacts between neighboring particles, which in turn depend on proximity to the jamming point. In particular, the mean first passage time associated with the escape of random walkers between neighboring particles is shown to control both the time to recover Fickian diffusion and the long time diffusivity. Scaling laws are established that relate these quantities to the difference between the actual and critical jamming volume fractions. Sandia National Laboratories is a multiprogram laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's NNSA under Contract DE- AC04-94AL85000.

  2. Fractional diffusion on bounded domains

    SciTech Connect

    Defterli, Ozlem; D'Elia, Marta; Du, Qiang; Gunzburger, Max Donald; Lehoucq, Richard B.; Meerschaert, Mark M.

    2015-03-13

    We found that the mathematically correct specification of a fractional differential equation on a bounded domain requires specification of appropriate boundary conditions, or their fractional analogue. In this paper we discuss the application of nonlocal diffusion theory to specify well-posed fractional diffusion equations on bounded domains.

  3. Osmosis and Diffusion Conceptual Assessment

    ERIC Educational Resources Information Center

    Fisher, Kathleen M.; Williams, Kathy S.; Lineback, Jennifer Evarts

    2011-01-01

    Biology student mastery regarding the mechanisms of diffusion and osmosis is difficult to achieve. To monitor comprehension of these processes among students at a large public university, we developed and validated an 18-item Osmosis and Diffusion Conceptual Assessment (ODCA). This assessment includes two-tiered items, some adopted or modified…

  4. Teaching Diffusion with a Coin

    ERIC Educational Resources Information Center

    Haddad, Hamilton; Baldo, Marcus Vinicius Chrysostomo

    2010-01-01

    In this article, the authors describe an inexpensive and simple way to make students intuitively experience the probabilistic nature and nonorientated motion of diffusing particles. This understanding allows students to realize why diffusion works so well over short distances and becomes increasingly and rapidly less effective as the distances…

  5. Demonstrating Diffusion: Why the Confusion?

    ERIC Educational Resources Information Center

    Panizzon, Debra Lee

    1998-01-01

    Examines the principles of diffusion and how it may be confused with convection. Suggests that educators may be misleading students and clouding their understanding of the process. Provides two contemporary examples to explain the process of diffusion and how it differs from convection. (Author/CCM)

  6. The Diffusion of New Math.

    ERIC Educational Resources Information Center

    Ready, Patricia M.

    The life cycle of "new math" is fertile ground for the study of the diffusion of an innovation. New math arrived in 1958 to save the day for America after the Soviet Union launched Sputnik, the first successful space flight in 1957. In a period of 16 years an entire diffusion cycle was completed throughout the entire educational system of the…

  7. Thermal diffusivity of diamond films

    NASA Technical Reports Server (NTRS)

    Albin, Sacharia; Winfree, William P.; Crews, B. Scott

    1990-01-01

    A laser pulse technique to measure the thermal diffusivity of diamond films deposited on a silicon substrate is developed. The effective thermal diffusivity of diamond film on silicon was measured by observing the phase and amplitude of the cyclic thermal waves generated by the laser pulses. An analytical model is developed to calculate the effective in-plane (face-parallel) diffusivity of a two layer system. The model is used to reduce the effective thermal diffusivity of the diamond/silicon sample to a value for the thermal diffusivity and conductivity of the diamond film. Phase and amplitude measurements give similar results. The thermal conductivity of the films is found to be better than that of type 1a natural diamond.

  8. Enthalpy Diffusion in Multicomponent Flows

    SciTech Connect

    Cook, A W

    2008-11-12

    The enthalpy diffusion flux in the multicomponent energy equation is a well known yet frequently neglected term. It accounts for energy changes, associated with compositional changes, resulting from species diffusion. Enthalpy diffusion is important in flows where significant mixing occurs between species of dissimilar molecular weight. The term plays a critical role in preventing local violations of the entropy condition. In simulations of nonpremixed combustion, omission of the enthalpy flux can lead to anomalous temperature gradients, which may cause mixing regions to exceed ignition conditions. The term can also play a role in generating acoustic noise in turbulent mixing layers. Euler solvers that rely on numerical diffusion to mix fluids cannot accurately predict the temperature in mixed regions. On the other hand, Navier-Stokes solvers that incorporate enthalpy diffusion can provide much more accurate results.

  9. Heat transfer, diffusion, and evaporation

    NASA Technical Reports Server (NTRS)

    Nusselt, Wilhelm

    1954-01-01

    Although it has long been known that the differential equations of the heat-transfer and diffusion processes are identical, application to technical problems has only recently been made. In 1916 it was shown that the speed of oxidation of the carbon in iron ore depends upon the speed with which the oxygen of the combustion air diffuses through the core of gas surrounding the carbon surface. The identity previously referred to was then used to calculate the amount of oxygen diffusing to the carbon surface on the basis of the heat transfer between the gas stream and the carbon surface. Then in 1921, H. Thoma reversed that procedure; he used diffusion experiments to determine heat-transfer coefficients. Recently Lohrisch has extended this work by experiment. A technically very important application of the identity of heat transfer and diffusion is that of the cooling tower, since in this case both processes occur simultaneously.

  10. Portable vapor diffusion coefficient meter

    DOEpatents

    Ho, Clifford K.

    2007-06-12

    An apparatus for measuring the effective vapor diffusion coefficient of a test vapor diffusing through a sample of porous media contained within a test chamber. A chemical sensor measures the time-varying concentration of vapor that has diffused a known distance through the porous media. A data processor contained within the apparatus compares the measured sensor data with analytical predictions of the response curve based on the transient diffusion equation using Fick's Law, iterating on the choice of an effective vapor diffusion coefficient until the difference between the predicted and measured curves is minimized. Optionally, a purge fluid can forced through the porous media, permitting the apparatus to also measure a gas-phase permeability. The apparatus can be made lightweight, self-powered, and portable for use in the field.

  11. Ammonia diffusion through Nalophan™ bags.

    PubMed

    Sironi, Selena; Eusebio, Lidia; Dentoni, Licinia; Capelli, Laura; Del Rosso, Renato

    2014-01-01

    The aim of the work is to verify the diffusion rate of ammonia through the Nalophan™ film that constitutes the sampling bag, considering storage times ranging from 1 to 26 h. The ammonia decay over time was evaluated using gas-chromatography for the quantification of ammonia concentration inside the bag. The research assesses the roles of both of ammonia and water concentration gradients at the polymeric film interface on the diffusion process. The results show that both the ammonia concentration gradient and, in a less pronounced way, the water concentration gradient are the main 'engines' of ammonia diffusion. Double bags seem to represent a simple solution for preventing ammonia losses during storage. Another interesting result concerns the role of the bag surface on the ammonia diffusion rate: the higher the surface/volume (S/V) ratio, the higher the ammonia diffusion rate through the polymeric film.

  12. Diffusion of childbearing within cohabitation.

    PubMed

    Vitali, Agnese; Aassve, Arnstein; Lappegård, Trude

    2015-04-01

    The article analyzes the diffusion of childbearing within cohabitation in Norway, using municipality data over a 24-year period (1988-2011). Research has found substantial spatial heterogeneity in this phenomenon but also substantial spatial correlation, and the prevalence of childbearing within cohabitation has increased significantly over time. We consider several theoretical perspectives and implement a spatial panel model that allows accounting for autocorrelation not only on the dependent variable but also on key explanatory variables, and hence identifies the key determinants of diffusion of childbearing within cohabitation across space and over time. We find only partial support for the second demographic transition as a theory able to explain the diffusion of childbearing within cohabitation. Our results show that at least in the first phase of the diffusion (1988-1997), economic difficulties as measured by increased unemployment among men contributed to the diffusion of childbearing within cohabitation. However, the most important driver for childbearing within cohabitation is expansion in education for women.

  13. Diffusion in membranes: Toward a two-dimensional diffusion map

    NASA Astrophysics Data System (ADS)

    Toppozini, Laura; Garcia-Sakai, Victoria; Bewley, Robert; Dalgliesh, Robert; Perring, Toby; Rheinstädter, Maikel C.

    2015-01-01

    For decades, quasi-elastic neutron scattering has been the prime tool for studying molecular diffusion in membranes over relevant nanometer distances. These experiments are essential to our current understanding of molecular dynamics of lipids, proteins and membrane-active molecules. Recently, we presented experimental evidence from X-ray diffraction and quasi-elastic neutron scattering demonstrating that ethanol enhances the permeability of membranes. At the QENS 2014/WINS 2014 conference we presented a novel technique to measure diffusion across membranes employing 2-dimensional quasi-elastic neutron scattering. We present results from our preliminary analysis of an experiment on the cold neutron multi-chopper spectrometer LET at ISIS, where we studied the self-diffusion of water molecules along lipid membranes and have the possibility of studying the diffusion in membranes. By preparing highly oriented membrane stacks and aligning them horizontally in the spectrometer, our aim is to distinguish between lateral and transmembrane diffusion. Diffusion may also be measured at different locations in the membranes, such as the water layer and the hydrocarbon membrane core. With a complete analysis of the data, 2-dimensional mapping will enable us to determine diffusion channels of water and ethanol molecules to quantitatively determine nanoscale membrane permeability.

  14. Diffusion with optimal resetting

    NASA Astrophysics Data System (ADS)

    Evans, Martin R.; Majumdar, Satya N.

    2011-10-01

    We consider the mean time to absorption by an absorbing target of a diffusive particle with the addition of a process whereby the particle is reset to its initial position with rate r. We consider several generalizations of the model of Evans and Majumdar (2011 Phys. Rev. Lett.106 160601): (i) a space-dependent resetting rate r(x); (ii) resetting to a random position z drawn from a resetting distribution { P}(z); and (iii) a spatial distribution for the absorbing target PT(x). As an example of (i) we show that the introduction of a non-resetting window around the initial position can reduce the mean time to absorption provided that the initial position is sufficiently far from the target. We address the problem of optimal resetting, that is, minimizing the mean time to absorption for a given target distribution. For an exponentially decaying target distribution centred at the origin we show that a transition in the optimal resetting distribution occurs as the target distribution narrows.

  15. Photoacoustic thermal diffusion flowmetry

    PubMed Central

    Sheinfeld, Adi; Eyal, Avishay

    2012-01-01

    Thermal Diffusion Flowmetry (TDF) (also called Heat Clearance Method or Thermal Clearance Method) is a longstanding technique for measuring blood flow or blood perfusion in living tissues. Typically, temperature transients and/or gradients are induced in a volume of interest and the temporal and/or spatial temperature variations which follow are measured and used for calculation of the flow. In this work a new method for implementing TDF is studied theoretically and experimentally. The heat deposition which is required for TDF is implemented photothermally (PT) and the measurement of the induced temperature variations is done by photoacoustic (PA) thermometry. Both excitation light beams (the PT and the PA) are produced by directly modulated 830 nm laser diodes and are conveniently delivered to the volume under test by the same optical fiber. The method was tested experimentally using a blood-filled phantom vessel and the results were compared with a theoretical prediction based on the heat and the photoacoustic equations. The fitting of a simplified lumped thermal model to the experimental data yielded estimated values of the blood velocity at different flow rates. By combining additional optical sources at different wavelengths it will be possible to utilize the method for non-invasive simultaneous measurement of blood flow and oxygen saturation using a single fiber probe. PMID:22574267

  16. Diffuse gamma radiation

    NASA Technical Reports Server (NTRS)

    Fichtel, C. E.; Simpson, G. A.; Thompson, D. J.

    1977-01-01

    An examination of the intensity, energy spectrum, and spatial distribution of the diffuse gamma-radiation observed by SAS-2 satellite away from the galactic plane in the energy range above 35 MeV has shown that it consists of two components. One component is generally correlated with galactic latitudes, the atomic hydrogen column density was deduced from 21 cm measurements, and the continuum radio emission, believed to be synchrotron emission. It has an energy spectrum similar to that in the plane and joins smoothly to the intense radiation from the plane. It is therefore presumed to be of galactic origin. The other component is apparently isotropic, at least on a coarse scale, and has a steep energy spectrum. No evidence is found for a cosmic ray halo surrounding the galaxy in the shape of a sphere or oblate spheroid with galactic dimensions. Constraints for a halo model with significantly larger dimensions are set on the basis of an upper limit to the gamma-ray anisotropy.

  17. Diffuse Microwave Emission Survey

    NASA Astrophysics Data System (ADS)

    Shafer, R. A.; Mather, J.; Kogut, A.; Fixsen, D. J.; Seiffert, M.; Lubin, P. M.; Levin, S. M.

    1996-12-01

    The Diffuse Microwave Emission Survey (DIMES) is a mission concept selected by NASA in 1995 to answer fundamental questions about the content and history of the universe. DIMES will use a set of absolutely calibrated cryogenic radiometers from a space platform to measure the frequency spectrum of the cosmic microwave background (CMB) at wavelengths 15--0.3 cm (frequency 2--100 GHz) to precision 0.1 mK or better. Measurements at centimeter wavelengths probe different physical processes than the COBE-FIRAS spectra at shorter wavelengths, and complement the anisotropy measurements from DMR, balloon and ground-based instruments, and the planned MAP and COBRAS/SAMBA satellites. DIMES will observe the free-free signal from early photoionization to establish the precise epoch of structure formation, and will measure or limit energy release at redshift 10(4) < z < 10(7) by measuring the chemical potential distortion of the CMB spectrum. Both are likely under current cosmological theory and allowed by current measurement limits; even an upper limit at the expected sensitivity 10(-5) MJy/sr will place important constraints on the matter content, structure, and evolution of the universe. Detecting these distortions or showing that they do not exist constitutes the last frontier of CMB observations.

  18. Handheld Diffusion Test Cells

    NASA Technical Reports Server (NTRS)

    2001-01-01

    This photo shows the Handheld Diffusion Test Cell (HH-DTC) apparatus flown on the Space Shuttle. Similar cells (inside the plastic box) will be used in the Observable Protein Crystal Growth Apparatus (OPCGA) to be operated aboard the International Space Station (ISS). The principal investigator is Dr. Alex McPherson of the University of California, Irvine. Each individual cell comprises two sample chambers with a rotating center section that isolates the two from each other until the start of the experiment and after it is completed. The cells are made from optical-quality quartz glass to allow photography and interferometric observations. Each cell has a small light-emitting diode and lens to back-light the solution. In protein crystal growth experiments, a precipitating agent such as a salt solution is used to absorb and hold water but repel the protein molecules. This increases the concentration of protein until the molecules nucleate to form crystals. This cell is one of 96 that make up the experiment module portion of the OPCGA.

  19. Handheld Diffusion Test Cells

    NASA Technical Reports Server (NTRS)

    2001-01-01

    This photo shows an individual cell from the Handheld Diffusion Test Cell (HH-DTC) apparatus flown on the Space Shuttle. Similar cells will be used in the Observable Protein Crystal Growth Apparatus (OPCGA) to be operated aboard the International Space Station (ISS). The principal investigator is Dr. Alex McPherson of the University of California, Irvine. Each individual cell comprises two sample chambers with a rotating center section that isolates the two from each other until the start of the experiment and after it is completed. The cells are made from optical-quality quartz glass to allow photography and interferometric observations. Each cell has a small light-emitting diode and lens to back-light the solution. In protein crystal growth experiments, a precipitating agent such as a salt solution is used to absorb and hold water but repel the protein molecules. This increases the concentration of protein until the molecules nucleate to form crystals. This cell is one of 96 that make up the experiment module portion of the OPCGA.

  20. Transdermal diffusion of xenon in vitro using diffusion cells

    NASA Astrophysics Data System (ADS)

    Verkhovsky, A.; Petrov, E.

    2015-11-01

    The aim of this research was to study the diffusion rate of xenon through guinea pig skin and how viscosity of cosmetic component capryl/capric triglyceride (CCT) facilitates to deliver xenon to surface of skin patches. They were placed in Franz cell for 24 hours and diffusion rate and permeability of xenon were calculated. Thus diffusion rate was 0.031 mg/hour*cm2 and permeability was 0.003 cm/hour. Using Brookfield viscometer it was shown that viscosity of CCT decreased upon increasing xenon concentration. Obtained results can be utilized in developing of new xenon containing drugs for topical administration.

  1. Single file diffusion in microtubules

    NASA Astrophysics Data System (ADS)

    Rutenberg, Andrew; Farrell, Spencer; Brown, Aidan

    2015-03-01

    We investigate the single file diffusion (SFD) of large particles entering a confined tubular geometry, such as luminal diffusion of proteins inside microtubules or flagella. While single-file effects have no effect on particle density, we report significant single-file effects for individually-tracked tracer particle motion. Both exact and approximate ordering statistics of particles entering semi-infinite tubes agree well with our stochastic simulations. Considering initially empty semi-infinite tubes, with particles entering at one end starting from an initial time t = 0 , tracked particles display super-diffusive effective exponents just after they enter the system and trends towards diffusive exponents at later times. Equivalently, if diffusive exponents are assumed the effective diffusivity is reduced at early times and enhanced at later times through a logarithmic factor logN , where N is the number of particles in the tube. When we number each particle from the first (n = 1) to the most recent (n = N), we find good scaling collapse of the effective diffusivity for all n. Techniques that track individual particles, or local groups of particles, such as photo-activation or photobleaching, will exhibit single-file effects.

  2. Cytoplasmic hydrogen ion diffusion coefficient.

    PubMed Central

    al-Baldawi, N F; Abercrombie, R F

    1992-01-01

    The apparent cytoplasmic proton diffusion coefficient was measured using pH electrodes and samples of cytoplasm extracted from the giant neuron of a marine invertebrate. By suddenly changing the pH at one surface of the sample and recording the relaxation of pH within the sample, an apparent diffusion coefficient of 1.4 +/- 0.5 x 10(-6) cm2/s (N = 7) was measured in the acidic or neutral range of pH (6.0-7.2). This value is approximately 5x lower than the diffusion coefficient of the mobile pH buffers (approximately 8 x 10(-6) cm2/s) and approximately 68x lower than the diffusion coefficient of the hydronium ion (93 x 10(-6) cm2/s). A mobile pH buffer (approximately 15% of the buffering power) and an immobile buffer (approximately 85% of the buffering power) could quantitatively account for the results at acidic or neutral pH. At alkaline pH (8.2-8.6), the apparent proton diffusion coefficient increased to 4.1 +/- 0.8 x 10(-6) cm2/s (N = 7). This larger diffusion coefficient at alkaline pH could be explained quantitatively by the enhanced buffering power of the mobile amino acids. Under the conditions of these experiments, it is unlikely that hydroxide movement influences the apparent hydrogen ion diffusion coefficient. PMID:1617134

  3. Amplitude equations for reaction-diffusion systems with cross diffusion

    NASA Astrophysics Data System (ADS)

    Zemskov, Evgeny P.; Vanag, Vladimir K.; Epstein, Irving R.

    2011-09-01

    Using Taylor series expansion, multiscaling, and further expansion in powers of a small parameter, we develop general amplitude equations for two-variable reaction-diffusion systems with cross-diffusion terms in the cases of Hopf and Turing instabilities. We apply this analysis to the Oregonator and Brusselator models and find that inhibitor cross diffusion induced by the activator and activator cross diffusion induced by the inhibitor have opposite effects in the two models as a result of the different structure of their community matrices. Our analysis facilitates finding regions of supercritical and subcritical bifurcations, as well as wave and antiwave domains and domains of turbulent waves in the case of Hopf instability.

  4. Amplitude equations for reaction-diffusion systems with cross diffusion.

    PubMed

    Zemskov, Evgeny P; Vanag, Vladimir K; Epstein, Irving R

    2011-09-01

    Using Taylor series expansion, multiscaling, and further expansion in powers of a small parameter, we develop general amplitude equations for two-variable reaction-diffusion systems with cross-diffusion terms in the cases of Hopf and Turing instabilities. We apply this analysis to the Oregonator and Brusselator models and find that inhibitor cross diffusion induced by the activator and activator cross diffusion induced by the inhibitor have opposite effects in the two models as a result of the different structure of their community matrices. Our analysis facilitates finding regions of supercritical and subcritical bifurcations, as well as wave and antiwave domains and domains of turbulent waves in the case of Hopf instability. PMID:22060484

  5. Turing instabilities in reaction-diffusion systems with cross diffusion

    NASA Astrophysics Data System (ADS)

    Fanelli, Duccio; Cianci, Claudia; Di Patti, Francesca

    2013-04-01

    The Turing instability paradigm is revisited in the context of a multispecies diffusion scheme derived from a self-consistent microscopic formulation. The analysis is developed with reference to the case of two species. These latter share the same spatial reservoir and experience a degree of mutual interference due to the competition for the available resources. Turing instability can set in for all ratios of the main diffusivities, also when the (isolated) activator diffuses faster then the (isolated) inhibitor. This conclusion, at odd with the conventional vision, is here exemplified for the Brusselator model and ultimately stems from having assumed a generalized model of multispecies diffusion, fully anchored to first principles, which also holds under crowded conditions.

  6. Fick's Insights on Liquid Diffusion

    SciTech Connect

    Narasimhan, T.N.

    2004-10-07

    In 1855, Adolph Fick published ''On Liquid Diffusion'', mathematically treating salt movements in liquids as a diffusion process, analogous to heat diffusion. Less recognized is the fact that Fick also provided a detailed account of the implications of salt diffusion to transport through membranes. A careful look at Fick (1855) shows that his conceptualization of molecular diffusion was more comprehensive than could be captured with the mathematical methods available to him, and therefore his expression, referred to as Fick's Law, dealt only with salt flux. He viewed salt diffusion in liquids as a binary process, with salt moving in one way and water moving in the other. Fick's analysis of the consequences of such a binary process operating in a hydrophilic pore in a membrane offers insights that are relevant to earth systems. This paper draws attention to Fick's rationale, and its implications to hydrogeological systems. Fick (1829-1901; Figure 1), a gifted scientist, published the first book on medical physics (Fick, 1858), discussing the application of optics, solid mechanics, gas diffusion, and heat budget to biological systems. Fick's paper is divisible into two parts. The first describes his experimental verification of the applicability of Fourier's equation to liquid diffusion. The second is a detailed discussion of diffusion through a membrane. Although Fick's Law specifically quantifies solute flux, Fick visualized a simultaneous movement of water and stated, ''It is evident that a volume of water equal to that of the salt passes simultaneously out of the upper stratum into the lower.'' (Fick, 1855, p.30). Fick drew upon Fourier's model purely by analogy. He assumed that concentration gradient impelled salt movement, without inquiring why concentration gradient should constitute a driving force. As for water movement, he stated intuitively, ''a force of suction comes into play on each side of the membrane, proportional to the difference of concentration

  7. ALUMINUM IMPURITY DIFFUSION IN MAGNESIUM

    SciTech Connect

    Brennan, Sarah; Warren, Andrew; Coffey, Kevin; Kulkarni, Nagraj S; Todd, Peter J; Sohn, Yong Ho; Klimov, Mikhail

    2012-01-01

    The Al impurity diffusion in polycrystalline Mg (99.9%) via depth profiling with secondary ion mass spectrometry was studied in the temperature range of 673-573K, utilizing the thin film method and thin film solution to the diffusion equation. Multiple samples were utilized and multiple profiles were obtained to determine statistically confident coefficient with maximum standard deviation of 16%. Activation energy and pre-exponential factor of Al impurity diffusion in Mg was determined as 155 kJ/mole and 3.9 x 10-3 m2/sec.

  8. BEAM DIFFUSION MEASUREMENTS AT RHIC.

    SciTech Connect

    FLILLER,R.P.,IIIDREES,A.GASSNER,D.MCINTYRE,G.PEGGS,S.TRBOJEVIC,D.

    2003-05-12

    During a store, particles from the beam core continually diffuse outwards into the halo through a variety of mechanisms. Understanding the diffusion rate as a function of particle amplitude can help discover which processes are important to halo growth. A collimator can be used to measure the amplitude growth rate as a function of the particle amplitude. In this paper we present results of diffusion measurements performed at the Relativistic Heavy Ion Collider (RHIC) with fully stripped gold ions, deuterons, and protons. We compare these results with measurements from previous years, and simulations, and discuss any factors that relate to beam growth in RHIC.

  9. Interference of diffusive light waves.

    PubMed

    Schmitt, J M; Knüttel, A; Knutson, J R

    1992-10-01

    We examine interference effects resulting from the superposition of photon-density waves produced by coherently modulated light incident upon a turbid medium. Photon-diffusion theory is used to derive expressions for the ac magnitude and phase of the aggregate diffusive wave produced in full- and half-space volumes by two sources. Using a frequency-domain spectrometer operating at 410 MHz, we verify interference patterns predicted by the model in scattering samples having optical properties similar to those of skin tissue. Potential imaging applications of interfering diffusive waves are discussed in the context of the theoretical and experimental results.

  10. Diffuser for augmenting a wind turbine

    DOEpatents

    Foreman, Kenneth M.; Gilbert, Barry L.

    1984-01-01

    A diffuser for augmenting a wind turbine having means for energizing the boundary layer at several locations along the diffuser walls is improved by the addition of a short collar extending radially outward from the outlet of the diffuser.

  11. Improved diffuser for augmenting a wind turbine

    DOEpatents

    Foreman, K.M.; Gilbert, B.L.

    A diffuser for augmenting a wind turbine having means for energizing the boundary layer at several locations along the diffuser walls is improved by the addition of a short collar extending radially outward from the outlet of the diffuser.

  12. Floating-diffusion electrometer with adjustable sensitivity

    NASA Technical Reports Server (NTRS)

    Tower, John R. (Inventor)

    1989-01-01

    The effective capacitance of the floating diffusion in a floating-diffusion electrometer is modified to adjust electrometer sensitivity. This is done by changing the direct potential applied to a gate electrode proximate to the floating diffusion.

  13. Flow development through interturbine diffusers

    SciTech Connect

    Dominy, R.G.; Kirkham, D.A.; Smith, A.D.

    1998-04-01

    Interturbine diffusers offer the potential advantage of reducing the flow coefficient in the following stages, leading to increased efficiency. The flows associated with these ducts differ from those in simple annular diffusers both as a consequence of their high-curvature S-shaped geometry and of the presence of wakes created by the upstream turbine. Experimental data and numerical simulations clearly reveal the generation of significant secondary flows as the flow develops through the diffuser in the presence of cross-passage pressure gradients. The further influence of inlet swirl is also demonstrated. Data from experimental measurements with and without an upstream turbine are discussed and computational simulations are shown not only to give a good prediction of the flow development within the diffuser but also to demonstrate the importance of modeling the fully three-dimensional nature of the flow.

  14. Diffusion technique stabilizes resistor values

    NASA Technical Reports Server (NTRS)

    Gallagher, R. C.; Giuliano, M. N.

    1966-01-01

    Reduction of the contact resistance stabilizes the values, over a broad temperature range, of resistors used in linear integrated circuits. This reduction is accomplished by p-plus diffusion under the alloyed aluminum contacts.

  15. Geometric diffusion of quantum trajectories.

    PubMed

    Yang, Fan; Liu, Ren-Bao

    2015-07-16

    A quantum object can acquire a geometric phase (such as Berry phases and Aharonov-Bohm phases) when evolving along a path in a parameter space with non-trivial gauge structures. Inherent to quantum evolutions of wavepackets, quantum diffusion occurs along quantum trajectories. Here we show that quantum diffusion can also be geometric as characterized by the imaginary part of a geometric phase. The geometric quantum diffusion results from interference between different instantaneous eigenstate pathways which have different geometric phases during the adiabatic evolution. As a specific example, we study the quantum trajectories of optically excited electron-hole pairs in time-reversal symmetric insulators, driven by an elliptically polarized terahertz field. The imaginary geometric phase manifests itself as elliptical polarization in the terahertz sideband generation. The geometric quantum diffusion adds a new dimension to geometric phases and may have applications in many fields of physics, e.g., transport in topological insulators and novel electro-optical effects.

  16. Fractional-calculus diffusion equation

    PubMed Central

    2010-01-01

    Background Sequel to the work on the quantization of nonconservative systems using fractional calculus and quantization of a system with Brownian motion, which aims to consider the dissipation effects in quantum-mechanical description of microscale systems. Results The canonical quantization of a system represented classically by one-dimensional Fick's law, and the diffusion equation is carried out according to the Dirac method. A suitable Lagrangian, and Hamiltonian, describing the diffusive system, are constructed and the Hamiltonian is transformed to Schrodinger's equation which is solved. An application regarding implementation of the developed mathematical method to the analysis of diffusion, osmosis, which is a biological application of the diffusion process, is carried out. Schrödinger's equation is solved. Conclusions The plot of the probability function represents clearly the dissipative and drift forces and hence the osmosis, which agrees totally with the macro-scale view, or the classical-version osmosis. PMID:20492677

  17. Uphill diffusion in multicomponent mixtures.

    PubMed

    Krishna, Rajamani

    2015-05-21

    Molecular diffusion is an omnipresent phenomena that is important in a wide variety of contexts in chemical, physical, and biological processes. In the majority of cases, the diffusion process can be adequately described by Fick's law that postulates a linear relationship between the flux of any species and its own concentration gradient. Most commonly, a component diffuses down the concentration gradient. The major objective of this review is to highlight a very wide variety of situations that cause the uphill transport of one constituent in the mixture. Uphill diffusion may occur in multicomponent mixtures in which the diffusion flux of any species is strongly coupled to that of its partner species. Such coupling effects often arise from strong thermodynamic non-idealities. For a quantitative description we need to use chemical potential gradients as driving forces. The transport of ionic species in aqueous solutions is coupled with its partner ions because of the electro-neutrality constraints; such constraints may accelerate or decelerate a specific ion. When uphill diffusion occurs, we observe transient overshoots during equilibration; the equilibration process follows serpentine trajectories in composition space. For mixtures of liquids, alloys, ceramics and glasses the serpentine trajectories could cause entry into meta-stable composition zones; such entry could result in phenomena such as spinodal decomposition, spontaneous emulsification, and the Ouzo effect. For distillation of multicomponent mixtures that form azeotropes, uphill diffusion may allow crossing of distillation boundaries that are normally forbidden. For mixture separations with microporous adsorbents, uphill diffusion can cause supra-equilibrium loadings to be achieved during transient uptake within crystals; this allows the possibility of over-riding adsorption equilibrium for achieving difficult separations.

  18. Boron diffusion in silicon devices

    DOEpatents

    Rohatgi, Ajeet; Kim, Dong Seop; Nakayashiki, Kenta; Rounsaville, Brian

    2010-09-07

    Disclosed are various embodiments that include a process, an arrangement, and an apparatus for boron diffusion in a wafer. In one representative embodiment, a process is provided in which a boric oxide solution is applied to a surface of the wafer. Thereafter, the wafer is subjected to a fast heat ramp-up associated with a first heating cycle that results in a release of an amount of boron for diffusion into the wafer.

  19. Visualization of Diffusion within Nanoarrays.

    PubMed

    Liu, Yang; Holzinger, Angelika; Knittel, Peter; Poltorak, Lukasz; Gamero-Quijano, Alonso; Rickard, William D A; Walcarius, Alain; Herzog, Grégoire; Kranz, Christine; Arrigan, Damien W M

    2016-07-01

    The direct experimental characterization of diffusion processes at nanoscale remains a challenge that could help elucidate processes in biology, medicine and technology. In this report, two experimental approaches were employed to visualize ion diffusion profiles at the orifices of nanopores (radius (ra) of 86 ± 6 nm) in array format: (1) electrochemically assisted formation of silica deposits based on surfactant ion transfer across nanointerfaces between two immiscible electrolyte solutions (nanoITIES); (2) combined atomic force - scanning electrochemical microscopy (AFM-SECM) imaging of topography and redox species diffusion through the nanopores. The nature of the diffusion zones formed around the pores is directly related to the interpore distance within the array. Nanopore arrays with different ratios of pore center-to-center separation (rc) to pore radius (ra) were fabricated by focused ion beam (FIB) milling of silicon nitride (SiN) membranes, with 100 pores in a hexagonal arrangement. The ion diffusion profiles determined by the two visualization methods indicated the formation of overlapped or independent diffusion profiles at nanopore arrays with rc/ra ratios of 21 ± 2 and 91 ± 7, respectively. In particular, the silica deposition method resulted in formation of a single deposit encompassing the complete array with closer nanopore arrangement, whereas individual silica deposits were formed around each nanopore within the more widely spaced array. The methods reveal direct experimental evidence of diffusion zones at nanopore arrays and provide practical illustration that the pore-pore separation within such arrays has a significant impact on diffusional transport as the pore size is reduced to the nanoscale. These approaches to nanoscale diffusion zone visualization open up possibilities for better understanding of molecular transport processes within miniaturized systems. PMID:27264360

  20. Uphill diffusion in multicomponent mixtures.

    PubMed

    Krishna, Rajamani

    2015-05-21

    Molecular diffusion is an omnipresent phenomena that is important in a wide variety of contexts in chemical, physical, and biological processes. In the majority of cases, the diffusion process can be adequately described by Fick's law that postulates a linear relationship between the flux of any species and its own concentration gradient. Most commonly, a component diffuses down the concentration gradient. The major objective of this review is to highlight a very wide variety of situations that cause the uphill transport of one constituent in the mixture. Uphill diffusion may occur in multicomponent mixtures in which the diffusion flux of any species is strongly coupled to that of its partner species. Such coupling effects often arise from strong thermodynamic non-idealities. For a quantitative description we need to use chemical potential gradients as driving forces. The transport of ionic species in aqueous solutions is coupled with its partner ions because of the electro-neutrality constraints; such constraints may accelerate or decelerate a specific ion. When uphill diffusion occurs, we observe transient overshoots during equilibration; the equilibration process follows serpentine trajectories in composition space. For mixtures of liquids, alloys, ceramics and glasses the serpentine trajectories could cause entry into meta-stable composition zones; such entry could result in phenomena such as spinodal decomposition, spontaneous emulsification, and the Ouzo effect. For distillation of multicomponent mixtures that form azeotropes, uphill diffusion may allow crossing of distillation boundaries that are normally forbidden. For mixture separations with microporous adsorbents, uphill diffusion can cause supra-equilibrium loadings to be achieved during transient uptake within crystals; this allows the possibility of over-riding adsorption equilibrium for achieving difficult separations. PMID:25761383

  1. Diffusion in silicate melts: III. Empirical models for multicomponent diffusion

    NASA Astrophysics Data System (ADS)

    Yan, Liang; Richter, Frank M.; Chamberlin, Laurinda

    1997-12-01

    Empirical models for multicomponent diffusion in an isotropic fluid were derived by splitting the component's dispersion velocity into two parts: (a) an intrinsic velocity which is proportional to each component's electrochemical potential gradient and independent of reference frame and (b) a net interaction velocity which is both model and reference frame dependent. Simple molecules (e.g., M pO q) were chosen as endmember components. The interaction velocity is assumed to be either the same for each component (leading to a common relaxation velocity U) or proportional to a common interaction force ( F). U or F is constrained by requiring no local buildup in either volume or charge. The most general form of the model-derived diffusion matrix [ D] can be written as a product of a model-dependent kinetic matrix [ L] and a model independent thermodynamic matrix [ G], [ D] = [ L] · [ G]. The elements of [ G] are functions of derivatives of chemical potential with respect to concentration. The elements of [ L] are functions of concentration and partial molar volume of the endmember components, Cio and Vio, and self diffusivity Di, and charge number zi of individual diffusing species. When component n is taken as the dependent variable they can be written in a common form L ij = D jδ ij + C io[V noD n - V joD j)A i + (p nz nD n - p jz jD j)B i] where the functional forms of the scaling factors Ai and Bi depend on the model considered. The off-diagonal element Lij ( i ≠ j) is directly proportional to the concentration of component i, and thus negligible when i is a dilute component. The salient feature of kinetic interaction or relaxation is to slow down larger (volume or charge) and faster diffusing components and to speed up smaller (volume or charge) and slower moving species, in order to prevent local volume or charge buildup. Empirical models for multicomponent diffusion were tested in the ternary system CaOAl 2O 3SiO 2 at 1500°C and 1 GPa over a large

  2. Lipid diffusion in alcoholic environment.

    PubMed

    Rifici, Simona; Corsaro, Carmelo; Crupi, Cristina; Nibali, Valeria Conti; Branca, Caterina; D'Angelo, Giovanna; Wanderlingh, Ulderico

    2014-08-01

    We have studied the effects of a high concentration of butanol and octanol on the phase behavior and on the lateral mobility of 1,2-palmitoyl-sn-glycero-3-phosphocholine (DPPC) by means of differential scanning calorimetry and pulsed-gradient stimulated-echo (PGSTE) NMR spectroscopy. A lowering of the lipid transition from the gel to the liquid-crystalline state for the membrane-alcohol systems has been observed. NMR measurements reveal three distinct diffusions in the DPPC-alcohol systems, characterized by a high, intermediate, and slow diffusivity, ascribed to the water, the alcohol, and the lipid, respectively. The lipid diffusion process is promoted in the liquid phase while it is hindered in the interdigitated phase due to the presence of alcohols. Furthermore, in the interdigitated phase, lipid lateral diffusion coefficients show a slight temperature dependence. To the best of our knowledge, this is the first time that lateral diffusion coefficients on alcohol with so a long chain, and at low temperatures, are reported. By the Arrhenius plots of the temperature dependence of the diffusion coefficients, we have evaluated the apparent activation energy in both the liquid and in the interdigitated phase. The presence of alcohol increases this value in both phases. An explanation in terms of a free volume model that takes into account also for energy factors is proposed.

  3. Gibbs Ringing in Diffusion MRI

    PubMed Central

    Veraart, Jelle; Fieremans, Els; Jelescu, Ileana O.; Knoll, Florian; Novikov, Dmitry S.

    2016-01-01

    Purpose To study and reduce the effect of Gibbs ringing artifact on computed diffusion parameters. Methods We reduce the ringing by extrapolating the k-space of each diffusion weighted image beyond the measured part by selecting an adequate regularization term. We evaluate several regularization terms and tune the regularization parameter to find the best compromise between anatomical accuracy of the reconstructed image and suppression of the Gibbs artifact. Results We demonstrate empirically and analytically that the Gibbs artifact, which is typically observed near sharp edges in magnetic resonance images, has a significant impact on the quantification of diffusion model parameters, even for infinitesimal diffusion weighting. We find the second order total generalized variation to be a good choice for the penalty term to regularize the extrapolation of the k-space, as it provides a parsimonious representation of images, a practically full suppression of Gibbs ringing, and the absence of staircasing artifacts typical for total variation methods. Conclusions Regularized extrapolation of the k-space data significantly reduces truncation artifacts without compromising spatial resolution in comparison to the default option of window filtering. In particular, accuracy of estimating diffusion tensor imaging and diffusion kurtosis imaging parameters improves so much that unconstrained fits become possible. PMID:26257388

  4. Osmosis and Diffusion Conceptual Assessment

    PubMed Central

    Fisher, Kathleen M.; Williams, Kathy S.; Lineback, Jennifer Evarts

    2011-01-01

    Biology student mastery regarding the mechanisms of diffusion and osmosis is difficult to achieve. To monitor comprehension of these processes among students at a large public university, we developed and validated an 18-item Osmosis and Diffusion Conceptual Assessment (ODCA). This assessment includes two-tiered items, some adopted or modified from the previously published Diffusion and Osmosis Diagnostic Test (DODT) and some newly developed items. The ODCA, a validated instrument containing fewer items than the DODT and emphasizing different content areas within the realm of osmosis and diffusion, better aligns with our curriculum. Creation of the ODCA involved removal of six DODT item pairs, modification of another six DODT item pairs, and development of three new item pairs addressing basic osmosis and diffusion concepts. Responses to ODCA items testing the same concepts as the DODT were remarkably similar to responses to the DODT collected from students 15 yr earlier, suggesting that student mastery regarding the mechanisms of diffusion and osmosis remains elusive. PMID:22135375

  5. Diffusion path representation for two-phase ternary diffusion couples

    SciTech Connect

    Dayananda, M A; Venkatasubramanian, R

    1986-01-01

    Several two-phase, solid-solid diffusion couples from diffusion studies in the ternary Cu-Ni-Zn, Fe-Ni-Al and Cu-Ag-Au systems were investigated for their analytical representation on the basis of characteristic path parameters. The concentration profiles were examined in terms of relative concentration variables for cross-over compositions and internal consistency. The diffusion paths delineated single or double S-shaped curves crossing the straight line joining the terminal alloy compositions once or thrice. Cross-over compositions were identified in the individual phase regions or at an interface. Based on the symmetry between the path segments on either side of cross-over compositions, the paths were analytically represented with the aid of cross-over compositions and path slopes at these compositions, considered as path parameters. Exprestion for the ratios of diffusion depth on the two sides of the Matano plane were derived in terms of cross-over compositions and the estimated ratios of diffusion depths were found to be consistent with those observed from the concentration profiles.

  6. Ambipolar quantum dots in intrinsic silicon

    SciTech Connect

    Betz, A. C. Gonzalez-Zalba, M. F.; Podd, G.; Ferguson, A. J.

    2014-10-13

    We electrically measure intrinsic silicon quantum dots with electrostatically defined tunnel barriers. The presence of both p- and n-type ohmic contacts enables the accumulation of either electrons or holes. Thus, we are able to study both transport regimes within the same device. We investigate the effect of the tunnel barriers and the electrostatically defined quantum dots. There is greater localisation of charge states under the tunnel barriers in the case of hole conduction, leading to higher charge noise in the p-type regime.

  7. Diffuse Gamma Rays Galactic and Extragalactic Diffuse Emission

    NASA Technical Reports Server (NTRS)

    Moskalenko, Igor V.; Strong, Andrew W.; Reimer, Olaf

    2004-01-01

    Diffuse gamma rays consist of several components: truly diffuse emission from the interstellar medium, the extragalactic background, whose origin is not firmly established yet, and the contribution from unresolved and faint Galactic point sources. One approach to unravel these components is to study the diffuse emission from the interstellar medium, which traces the interactions of high energy particles with interstellar gas and radiation fields. Because of its origin such emission is potentially able to reveal much about the sources and propagation of cosmic rays. The extragalactic background, if reliably determined, can be used in cosmological and blazar studies. Studying the derived average spectrum of faint Galactic sources may be able to give a clue to the nature of the emitting objects.

  8. Kramers turnover: From energy diffusion to spatial diffusion using metadynamics

    NASA Astrophysics Data System (ADS)

    Tiwary, Pratyush; Berne, B. J.

    2016-04-01

    We consider the rate of transition for a particle between two metastable states coupled to a thermal environment for various magnitudes of the coupling strength using the recently proposed infrequent metadynamics approach [P. Tiwary and M. Parrinello, Phys. Rev. Lett. 111, 230602 (2013)]. We are interested in understanding how this approach for obtaining rate constants performs as the dynamics regime changes from energy diffusion to spatial diffusion. Reassuringly, we find that the approach works remarkably well for various coupling strengths in the strong coupling regime, and to some extent even in the weak coupling regime.

  9. A Diffusion Approach to Study Leadership Reform

    ERIC Educational Resources Information Center

    Adams, Curt M.; Jean-Marie, Gaetane

    2011-01-01

    Purpose: This study aims to draw on elements of diffusion theory to understand leadership reform. Many diffusion studies examine the spread of an innovation across social units but the objective is to examine diffusion of a collective leadership model within school units. Specifically, the strength of reform diffusion is tested to account for…

  10. Devitrite-based optical diffusers.

    PubMed

    Butt, Haider; Knowles, Kevin M; Montelongo, Yunuen; Amaratunga, Gehan A J; Wilkinson, Timothy D

    2014-03-25

    Devitrite is a novel material produced by heat treatment of commercial soda-lime-silica glass. It consists of fans of needle-like crystals which can extend up to several millimeters and have interspacings of up to a few hundred nanometers. To date, only the material properties of devitrite have been reported, and there has been a distinct lack of research on using it for optical applications. In this study, we demonstrate that randomly oriented fans of devitrite crystals can act as highly efficient diffusers for visible light. Devitrite crystals produce phase modulation of light because of their relatively high anisotropy. The nanoscale spacings between these needles enable light to be diffused to large scattering angles. Experimentally measured results suggest that light diffusion patterns with beam widths of up to 120° are produced. Since devitrite is an inexpensive material to produce, it has the potential to be used in a variety of commercial applications.

  11. Anomalous diffusion in silo drainage.

    PubMed

    Arévalo, R; Garcimartín, A; Maza, D

    2007-06-01

    The silo discharge process is studied by molecular dynamics simulations. The development of the velocity profile and the probability density function for the displacements in the horizontal and vertical axis are obtained. The PDFs obtained at the beginning of the discharge reveal non-Gaussian statistics and superdiffusive behaviors. When the stationary flow is developed, the PDFs at shorter temporal scales are non-Gaussian too. For big orifices a well-defined transition between ballistic and diffusive regime is observed. In the case of a small outlet orifice, no well-defined transition is observed. We use a nonlinear diffusion equation introduced in the framework of non-extensive thermodynamics in order to describe the movements of the grains. The solution of this equation gives a well-defined relationship (gamma = 2/(3 - q)) between the anomalous diffusion exponent gamma and the entropic parameter q introduced by the non-extensive formalism to fit the PDF of the fluctuations.

  12. Load Diffusion in Composite Structures

    NASA Technical Reports Server (NTRS)

    Horgan, Cornelius O.; Simmonds, J. G.

    2000-01-01

    This research has been concerned with load diffusion in composite structures. Fundamental solid mechanics studies were carried out to provide a basis for assessing the complicated modeling necessary for large scale structures used by NASA. An understanding of the fundamental mechanisms of load diffusion in composite subcomponents is essential in developing primary composite structures. Analytical models of load diffusion behavior are extremely valuable in building an intuitive base for developing refined modeling strategies and assessing results from finite element analyses. The decay behavior of stresses and other field quantities provides a significant aid towards this process. The results are also amendable to parameter study with a large parameter space and should be useful in structural tailoring studies.

  13. Nonlinear Diffusion and Transient Osmosis

    NASA Astrophysics Data System (ADS)

    Akira, Igarashi; Lamberto, Rondoni; Antonio, Botrugno; Marco, Pizzi

    2011-08-01

    We investigate both analytically and numerically the concentration dynamics of a solution in two containers connected by a narrow and short channel, in which diffusion obeys a porous medium equation. We also consider the variation of the pressure in the containers due to the flow of matter in the channel. In particular, we identify a phenomenon, which depends on the transport of matter across nano-porous membranes, which we call “transient osmosis". We find that nonlinear diffusion of the porous medium equation type allows numerous different osmotic-like phenomena, which are not present in the case of ordinary Fickian diffusion. Experimental results suggest one possible candidate for transiently osmotic processes.

  14. Water vapor diffusion membranes, 2

    NASA Technical Reports Server (NTRS)

    Holland, F. F.; Klein, E.; Smith, J. K.; Eyer, C.

    1976-01-01

    Transport mechanisms were investigated for the three different types of water vapor diffusion membranes. Membranes representing porous wetting and porous nonwetting structures as well as dense diffusive membrane structures were investigated for water permeation rate as a function of: (1) temperature, (2) solids composition in solution, and (3) such hydrodynamic parameters as sweep gas flow rate, solution flow rate and cell geometry. These properties were measured using nitrogen sweep gas to collect the effluent. In addition, the chemical stability to chromic acid-stabilized urine was measured for several of each type of membrane. A technology based on the mechanism of vapor transport was developed, whereby the vapor diffusion rates and relative susceptibility of membranes to fouling and failure could be projected for long-term vapor recovery trials using natural chromic acid-stabilized urine.

  15. The diffusion of ions in unconsolidated sediments

    USGS Publications Warehouse

    Manheim, F. T.

    1970-01-01

    Diffusion in unconsolidated sediments generally proceeds at rates ranging from half to one twentieth of those applying to diffusion of ions and molecules in free solution. Diffusion rates are predictable with respect to porosity and path tortuosity in host sediments, and can be conveniently measured by determinations of electrical resistivity on bulk sediment samples. Net ion flux is further influenced by reactions of diffusing species with enclosing sediments, but such influences should not be confused with or lumped with diffusion processes. ?? 1970.

  16. Diffusion of polyelectrolytes in polyelectrolyte gels

    NASA Astrophysics Data System (ADS)

    Rahalkar, Anand; Muthukumar, Murugappan

    2015-03-01

    Using dynamic light scattering, we have investigated the diffusion coefficient of sodium poly(styrene sulfonate) in a matrix of poly(acrylamide-co-acrylate) gels. The diffusion coefficient of the probe polyelectrolyte exhibits a crossover behavior from a particle-diffusion to entropic-barrier dominated diffusion, as the molecular weight is increased. The effect of electrostatics, by varying the charge density of the matrix, on probe diffusion constant will be presented.

  17. Diffusion in Brain Extracellular Space

    PubMed Central

    Syková, Eva; Nicholson, Charles

    2009-01-01

    Diffusion in the extracellular space (ECS) of the brain is constrained by the volume fraction and the tortuosity and a modified diffusion equation represents the transport behavior of many molecules in the brain. Deviations from the equation reveal loss of molecules across the blood-brain barrier, through cellular uptake, binding or other mechanisms. Early diffusion measurements used radiolabeled sucrose and other tracers. Presently, the real-time iontophoresis (RTI) method is employed for small ions and the integrative optical imaging (IOI) method for fluorescent macromolecules, including dextrans or proteins. Theoretical models and simulations of the ECS have explored the influence of ECS geometry, effects of dead-space microdomains, extracellular matrix and interaction of macromolecules with ECS channels. Extensive experimental studies with the RTI method employing the cation tetramethylammonium (TMA) in normal brain tissue show that the volume fraction of the ECS typically is about 20% and the tortuosity about 1.6 (i.e. free diffusion coefficient of TMA is reduced by 2.6), although there are regional variations. These parameters change during development and aging. Diffusion properties have been characterized in several interventions, including brain stimulation, osmotic challenge and knockout of extracellular matrix components. Measurements have also been made during ischemia, in models of Alzheimer's and Parkinson's diseases and in human gliomas. Overall, these studies improve our conception of ECS structure and the roles of glia and extracellular matrix in modulating the ECS microenvironment. Knowledge of ECS diffusion properties are valuable in contexts ranging from understanding extrasynaptic volume transmission to the development of paradigms for drug delivery to the brain. PMID:18923183

  18. Interface analysis of diffusion barriers

    NASA Astrophysics Data System (ADS)

    Delarosa, Mark J.

    2000-10-01

    The utilization of thin films has enabled the success for much of modern technology. One goal of the research encompassed by this thesis was to monitor the interface of thin films and investigate ways to ensure their integrity, in spite of their propensity to react or diffuse. The materials selected for investigation were fluorinated dielectrics and copper. Fluorinated films have been integrated into an extensive range of applications, due to the relative inertness of many fluorinated polymers at low temperatures. Copper has long been the material of choice for electrical conduction due to its low resistivity and high thermal conductivity. Cobalt, cobalt-silicon, tantalum and tantalum-silicon were investigated as diffusion barrier materials to stabilize the interfaces. Co-Si and Ta-Si were found to be effective diffusion barriers on the fluorinated polymers PFCB and Pa-F up to the thermal degradation temperature of these materials. Incorporated in the current thesis research was the use of atomic layer deposition (ALD) to provide extremely thin, conformal, and pinhole-free diffusion barrier films. We were able to deposit cobalt films using ALD, including a dramatic breakthrough allowing the ALD of metals onto oxidized substrates at low temperatures (300°C). The ALD of Co on Ta and Cu on Co on SiO:F were performed to demonstrate this technique. To compliment the use of ALD for fabricating thin, dense diffusion barrier films, surface science analytical techniques were incorporated in this study, including x-ray photoelectron spectroscopy (XPS) and grazing angle x-ray diffraction. The ion beam techniques of nuclear reaction analysis (NRA) and Rutherford backscattering spectrometry (RBS) were also used to analyze the diffusion barrier interfaces.

  19. Innovation Diffusion: Assessment of Strategies within the Diffusion Simulation Game

    ERIC Educational Resources Information Center

    Enfield, Jacob; Myers, Rodney D.; Lara, Miguel; Frick, Theodore W.

    2012-01-01

    Educators increasingly view the high level of engagement and experiential learning offered by games as a means to promote learning. However, as with any designed learning experience, player experiences should provide an accurate representation of content to be learned. In this study, the authors investigated the DIFFUSION SIMULATION GAME (DSG) to…

  20. Diffusive mixing and Tsallis entropy

    SciTech Connect

    O'Malley, Daniel; Vesselinov, Velimir V.; Cushman, John H.

    2015-04-29

    Brownian motion, the classical diffusive process, maximizes the Boltzmann-Gibbs entropy. The Tsallis q-entropy, which is non-additive, was developed as an alternative to the classical entropy for systems which are non-ergodic. A generalization of Brownian motion is provided that maximizes the Tsallis entropy rather than the Boltzmann-Gibbs entropy. This process is driven by a Brownian measure with a random diffusion coefficient. In addition, the distribution of this coefficient is derived as a function of q for 1 < q < 3. Applications to transport in porous media are considered.

  1. Hindered diffusion of coal liquids

    SciTech Connect

    Tsotsis, T.T.; Sahimi, M. . Dept. of Chemical Engineering); Webster, I.A. )

    1992-01-01

    The molecules comprising coal liquids can range from less than 10 to several hundred [angstrom] in diameter. Their size is, therefore, comparable to the average pore size of most hydroprocessing catalysts. Thus, during processing, transport of these molecules into the catalyst occurs mainly by configurational'' or hindered diffusion,'' which is the result of two phenomena occurring in the pores; the distribution of solute molecules in the pores is affected by the pores and the solute molecules experience an increased hydrodynamic drag. The field of hindered diffusion has been reviewed by Deen [16]. The earliest studies in the filed were by Renkin et al. [17].

  2. Optimization of hydraulic turbine diffuser

    NASA Astrophysics Data System (ADS)

    Moravec, Prokop; Hliník, Juraj; Rudolf, Pavel

    2016-03-01

    Hydraulic turbine diffuser recovers pressure energy from residual kinetic energy on turbine runner outlet. Efficiency of this process is especially important for high specific speed turbines, where almost 50% of available head is utilized within diffuser. Magnitude of the coefficient of pressure recovery can be significantly influenced by designing its proper shape. Present paper focuses on mathematical shape optimization method coupled with CFD. First method is based on direct search Nelder-Mead algorithm, while the second method employs adjoint solver and morphing. Results obtained with both methods are discussed and their advantages/disadvantages summarized.

  3. A framework to analyze cerebral mean diffusivity using surface guided diffusion mapping in diffusion tensor imaging

    PubMed Central

    Kwon, Oh-Hun; Park, Hyunjin; Seo, Sang-Won; Na, Duk L.; Lee, Jong-Min

    2015-01-01

    The mean diffusivity (MD) value has been used to describe microstructural properties in Diffusion Tensor Imaging (DTI) in cortical gray matter (GM). Recently, researchers have applied a cortical surface generated from the T1-weighted volume. When the DTI data are analyzed using the cortical surface, it is important to assign an accurate MD value from the volume space to the vertex of the cortical surface, considering the anatomical correspondence between the DTI and the T1-weighted image. Previous studies usually sampled the MD value using the nearest-neighbor (NN) method or Linear method, even though there are geometric distortions in diffusion-weighted volumes. Here we introduce a Surface Guided Diffusion Mapping (SGDM) method to compensate for such geometric distortions. We compared our SGDM method with results using NN and Linear methods by investigating differences in the sampled MD value. We also projected the tissue classification results of non-diffusion-weighted volumes to the cortical midsurface. The CSF probability values provided by the SGDM method were lower than those produced by the NN and Linear methods. The MD values provided by the NN and Linear methods were significantly greater than those of the SGDM method in regions suffering from geometric distortion. These results indicate that the NN and Linear methods assigned the MD value in the CSF region to the cortical midsurface (GM region). Our results suggest that the SGDM method is an effective way to correct such mapping errors. PMID:26236180

  4. Spatial Mapping of Translational Diffusion Coefficients Using Diffusion Tensor Imaging: A Mathematical Description

    PubMed Central

    SHETTY, ANIL N.; CHIANG, SHARON; MALETIC-SAVATIC, MIRJANA; KASPRIAN, GREGOR; VANNUCCI, MARINA; LEE, WESLEY

    2016-01-01

    In this article, we discuss the theoretical background for diffusion weighted imaging and diffusion tensor imaging. Molecular diffusion is a random process involving thermal Brownian motion. In biological tissues, the underlying microstructures restrict the diffusion of water molecules, making diffusion directionally dependent. Water diffusion in tissue is mathematically characterized by the diffusion tensor, the elements of which contain information about the magnitude and direction of diffusion and is a function of the coordinate system. Thus, it is possible to generate contrast in tissue based primarily on diffusion effects. Expressing diffusion in terms of the measured diffusion coefficient (eigenvalue) in any one direction can lead to errors. Nowhere is this more evident than in white matter, due to the preferential orientation of myelin fibers. The directional dependency is removed by diagonalization of the diffusion tensor, which then yields a set of three eigenvalues and eigenvectors, representing the magnitude and direction of the three orthogonal axes of the diffusion ellipsoid, respectively. For example, the eigenvalue corresponding to the eigenvector along the long axis of the fiber corresponds qualitatively to diffusion with least restriction. Determination of the principal values of the diffusion tensor and various anisotropic indices provides structural information. We review the use of diffusion measurements using the modified Stejskal–Tanner diffusion equation. The anisotropy is analyzed by decomposing the diffusion tensor based on symmetrical properties describing the geometry of diffusion tensor. We further describe diffusion tensor properties in visualizing fiber tract organization of the human brain. PMID:27441031

  5. Nonlinear diffusion and superconducting hysteresis

    SciTech Connect

    Mayergoyz, I.D.

    1996-12-31

    Nonlinear diffusion of electromagnetic fields in superconductors with ideal and gradual resistive transitions is studied. Analytical results obtained for linear and nonlinear polarizations of electromagnetic fields are reported. These results lead to various extensions of the critical state model for superconducting hysteresis.

  6. Technology Diffusion. [SITE 2002 Section].

    ERIC Educational Resources Information Center

    Niederhauser, Dale S., Ed.; Strudler, Neal, Ed.

    This document contains the following papers on technology diffusion from the SITE (Society for Information Technology & Teacher Education) 2002 conference: (1) "Faculty Technology Integration Project" (Comfort Akwaji); (2) "If It Is Broke, Then What?" (D. Lynnwood Belvin and Jennifer Leaderer); (3) "Developing Video-Based E-Learning Applications"…

  7. Diffusion LMS Over Multitask Networks

    NASA Astrophysics Data System (ADS)

    Chen, Jie; Richard, Cedric; Sayed, Ali H.

    2015-06-01

    The diffusion LMS algorithm has been extensively studied in recent years. This efficient strategy allows to address distributed optimization problems over networks in the case where nodes have to collaboratively estimate a single parameter vector. Problems of this type are referred to as single-task problems. Nevertheless, there are several problems in practice that are multitask-oriented in the sense that the optimum parameter vector may not be the same for every node. This brings up the issue of studying the performance of the diffusion LMS algorithm when it is run, either intentionally or unintentionally, in a multitask environment. In this paper, we conduct a theoretical analysis on the stochastic behavior of diffusion LMS in the case where the so-called single-task hypothesis is violated. We explain under what conditions diffusion LMS continues to deliver performance superior to non-cooperative strategies in the multitask environment. When the conditions are violated, we explain how to endow the nodes with the ability to cluster with other similar nodes to remove bias. We propose an unsupervised clustering strategy that allows each node to select, via adaptive adjustments of combination weights, the neighboring nodes with which it can collaborate to estimate a common parameter vector. Simulations are presented to illustrate the theoretical results, and to demonstrate the efficiency of the proposed clustering strategy. The framework is applied to a useful problem involving a multi-target tracking task.

  8. Tiny Molybdenites Tell Diffusion Tales

    NASA Astrophysics Data System (ADS)

    Stein, H. J.; Hannah, J. L.

    2014-12-01

    Diffusion invokes micron-scale exchange during crystal growth and dissolution in magma chambers on short time-scales. Fundamental to interpreting such data are assumptions on magma-fluid dynamics at all scales. Nevertheless, elemental diffusion profiles are used to estimate time scales for magma storage, eruption, and recharge. An underutilized timepiece to evaluate diffusion and 3D mobility of magmatic fluids is high-precision Re-Os dating of molybdenite. With spatially unique molybdenite samples from a young ore system (e.g., 1 Ma) and a double Os spike, analytical errors of 1-3 ka unambiguously separate events in time. Re-Os ages show that hydrous shallow magma chambers locally recharge and expel Cu-Mo-Au-silica as superimposed stockwork vein networks at time scales less than a few thousand years [1]. Re-Os ages provide diffusion rates controlled by a dynamic crystal mush, accumulation and expulsion of metalliferous fluid, and magma reorganization after explosive crystallization events. Importantly, this approach has broad application far from ore deposits. Here, we use Re-Os dating of molybdenite to assess time scales for generating and diffusing metals through the deep crust. To maximize opportunity for chemical diffusion, we use a continental-scale Sveconorwegian mylonite zone for the study area. A geologically constrained suite of molybdenite samples was acquired from quarry exposures. Molybdenite, previously unreported, is extremely scarce. Tiny but telling molybdenites include samples from like occurrences to assure geologic accuracy in Re-Os ages. Ages range from mid-Mesoproterozoic to mid-Neoproterozoic, and correspond to early metamorphic dehydration of a regionally widespread biotite-rich gneiss, localized melting of gneiss to form cm-m-scale K-feldspar ± quartz pods, development of vapor-rich, vuggy mm stringers that serve as volatile collection surfaces in felsic leucosomes, and low-angle (relative to foliation) cross-cutting cm-scale quartz veins

  9. Analysis of Finite Difference Discretization Schemes for Diffusion in Spheres with Variable Diffusivity

    PubMed Central

    Versypt, Ashlee N. Ford; Braatz, Richard D.

    2014-01-01

    Two finite difference discretization schemes for approximating the spatial derivatives in the diffusion equation in spherical coordinates with variable diffusivity are presented and analyzed. The numerical solutions obtained by the discretization schemes are compared for five cases of the functional form for the variable diffusivity: (I) constant diffusivity, (II) temporally-dependent diffusivity, (III) spatially-dependent diffusivity, (IV) concentration-dependent diffusivity, and (V) implicitly-defined, temporally- and spatially-dependent diffusivity. Although the schemes have similar agreement to known analytical or semi-analytical solutions in the first four cases, in the fifth case for the variable diffusivity, one scheme produces a stable, physically reasonable solution, while the other diverges. We recommend the adoption of the more accurate and stable of these finite difference discretization schemes to numerically approximate the spatial derivatives of the diffusion equation in spherical coordinates for any functional form of variable diffusivity, especially cases where the diffusivity is a function of position. PMID:25642003

  10. Diffusion of oxygen in cork.

    PubMed

    Lequin, Sonia; Chassagne, David; Karbowiak, Thomas; Simon, Jean-Marc; Paulin, Christian; Bellat, Jean-Pierre

    2012-04-01

    This work reports measurements of effective oxygen diffusion coefficient in raw cork. Kinetics of oxygen transfer through cork is studied at 298 K thanks to a homemade manometric device composed of two gas compartments separated by a cork wafer sample. The first compartment contains oxygen, whereas the second one is kept under dynamic vacuum. The pressure decrease in the first compartment is recorded as a function of time. The effective diffusion coefficient D(eff) is obtained by applying Fick's law to transient state using a numerical method based on finite differences. An analytical model derived from Fick's law applied to steady state is also proposed. Results given by these two methods are in close agreement with each other. The harmonic average of the effective diffusion coefficients obtained from the distribution of 15 cork wafers of 3 mm thickness is 1.1 × 10(-9) m(2) s(-1) with a large distribution over four decades. The statistical analysis of the Gaussian distribution obtained on a 3 mm cork wafer is extrapolated to a 48 mm cork wafer, which length corresponds to a full cork stopper. In this case, the probability density distribution gives a mean value of D(eff) equal to 1.6 × 10(-9) m(2) s(-1). This result shows that it is possible to obtain the effective diffusion coefficient of oxygen through cork from short time (few days) measurements performed on a thin cork wafer, whereas months are required to obtain the diffusion coefficient for a full cork stopper. Permeability and oxygen transfer rate are also calculated for comparison with data from other studies.

  11. Diffusion and ion mixing in amorphous alloys

    SciTech Connect

    Hahn, H.; Averback, R.S.; Ding, F.; Loxton, C.; Baker, J.

    1986-10-01

    Tracer impurity diffusion and ion beam mixing in amorphous (a-)Ni/sub 50/Zr/sub 50/ were measured. A correlation between the metallic radius of an impurity and its tracer diffusivity was observed; it is similar to that found in crystalline ..cap alpha..-Zr and ..cap alpha..-Ti. In addition, the temperature dependence of diffusion in a-NiZr exhibits Arrhenius behavior. Ion beam mixing of different impurities in a-NiZr correlates with tracer diffusivity at both high and low temperatures. At higher temperatures radiation enhanced diffusion (RED) was observed. The activation enthalpy of the RED diffusion coefficient is 0.3 eV/atom.

  12. Diffusion of Ca and Mg in Calcite

    SciTech Connect

    Cygan, R.T.; Fisler, D.K.

    1999-02-10

    The self-diffusion of Ca and the tracer diffusion of Mg in calcite have been experimentally measured using isotopic tracers of {sup 25}Mg and {sup 44}Ca. Natural single crystals of calcite were coated with a thermally-sputtered oxide thin film and then annealed in a CO{sub 2} gas at one atmosphere total pressure and temperatures from 550 to 800 C. Diffusion coefficient values were derived from the depth profiles obtained by ion microprobe analysis. The resultant activation energies for Mg tracer diffusion and Ca self-diffusion are respectively: E{sub a}(Mg) = 284 {+-} 74 kJ/mol and E{sub a}(Ca) = 271 {+-} 80 kJ/mol. For the temperature ranges in these experiments, the diffusion of Mg is faster than Ca. The results are generally consistent in magnitude with divalent cation diffusion rates obtained in previous studies and provide a means of interpreting the thermal histories of carbonate minerals, the mechanism of dolomitization, and other diffusion-controlled processes. The results indicate that cation diffusion in calcite is relatively slow and cations are the rate-limiting diffusing species for the deformation of calcite and carbonate rocks. Application of the calcite-dolomite geothermometer to metamorphic assemblages will be constrained by cation diffusion and cooling rates. The direct measurement of Mg tracer diffusion in calcite indicates that dolomitization is unlikely to be accomplished by Mg diffusion in the solid state but by a recrystallization process.

  13. DIFFUSION IN CRYSTALLINE COMPOSITION-MODULATED FILMS

    SciTech Connect

    Jankowski, A; Saw, C; Harper, J

    2004-12-16

    The diffusivity in alloys at low temperatures is modeled for composition-modulated structures using Khachaturyan's microscopic theory of diffusion. The theory is now applied to assess a two-phase multilayer system.

  14. Surface self-diffusion of organic glasses.

    PubMed

    Brian, Caleb W; Yu, Lian

    2013-12-19

    Surface self-diffusion coefficients have been determined for the organic glass Nifedipine using the method of surface grating decay. The flattening of 1000 nm surface gratings occurs by viscous flow at 12 K or more above the glass transition temperature and by surface diffusion at lower temperatures. Surface diffusion is at least 10(7) times faster than bulk diffusion, indicating a highly mobile surface. Nifedipine glasses have faster surface diffusion than the previously studied Indomethacin glasses, despite their similar bulk relaxation times. Both glasses exhibit fast surface crystal growth, and its rate scales with surface diffusivity. The observed rate of surface diffusion implies substantial surface rearrangement during the preparation of low-energy glasses by vapor deposition. The Random First Order Transition Theory and the Coupling Model successfully predict the large surface-enhancement of mobility and its increase on cooling, but disagree with the experimental observation of the faster surface diffusion of Nifedipine.

  15. Tracer diffusion in silica inverse opals.

    PubMed

    Cherdhirankorn, Thipphaya; Retsch, Markus; Jonas, Ulrich; Butt, Hans-Juergen; Koynov, Kaloian

    2010-06-15

    We employed fluorescence correlation spectroscopy (FCS) to study the diffusion of small fluorescence tracers in liquid filled silica inverse opals. The inverse opals consisted of a nanoporous silica scaffold spanning a hexagonal crystal of spherical voids of 360 nm diameter connected by circular pores of 70 nm diameter. The diffusion of Alexa Fluor 488 in water and of perylene-3,4,9,10-tetracarboxylic diimide (PDI) in toluene was studied. Three diffusion modes could be distinguished: (1) Free diffusion limited by the geometric constraints given by the inverse opal, where, as compared to the free solution, this diffusion is slowed down by a factor of 3-4, (2) slow diffusion inside the nanoporous matrix of the silica scaffold, and (3) diffusion limited by adsorption. On the length scale of the focus of a confocal microscope of roughly 400 nm diffusion was non-Fickian in all cases.

  16. Osmotical liquid diffusion within sclera

    NASA Astrophysics Data System (ADS)

    Bashkatov, Alexey N.; Genina, Elina A.; Kochubey, Vyacheslav I.; Lakodina, Nina A.; Tuchin, Valery V.

    2000-06-01

    We present experimental results of investigation of the optical properties of the human eye sclera controlled by administration of osmotically active chemical, such as glucose solution with various concentrations. Administration of chemical agent induces diffusion of matter and as a result equalization of the refractive indices of collagen and ground material. Results of experimental study of influence of osmotical liquid (glucose solution) on reflectance and transmittance spectra of human sclera are presented. In vitro reflectance and transmittance spectra of the human sclera samples were investigated by commercially available spectrophotometer CARY-2415. The significant increasing of the transmittance and decreasing of the reflectance of human sclera samples under action of osmotical solutions were demonstrated. Results of our study show that the degree of the sclera samples clearing is increased with increasing of the chemical agent concentration in solution. The diffusion coefficients of glucose solution with various concentrations within scleral tissue was estimated.

  17. Oxygen diffusion in cuprate superconductors

    SciTech Connect

    Routbort, J.L.; Rothman, S.J.

    1995-01-01

    Superconducting properties of the cuprate superconductors depend on the oxygen content of the material; the diffusion of oxygen is thus an important process in the fabrication and application of these materials. This article reviews studies of the diffusion of oxygen in La{sub 2}{sub {minus}}{sub {times}}Sr{sub {times}}CuO{sub 4}, YBa{sub 2}Cu{sub 3}O{sub 7}{sub {minus}}{delta}, YBa{sub 2}Cu{sub 4}O{sub 8}, and the Bi{sub 2}Sr{sub 2}Ca{sub n}{sub {minus}}{sub 1}Cu{sub n}O{sub 2}{sub +}{sub 4} (n = 1, and 2) superconductors, and attempt to elucidate the atomic mechanisms responsible.

  18. Ultrasonic enhancement of battery diffusion.

    PubMed

    Hilton, R; Dornbusch, D; Branson, K; Tekeei, A; Suppes, G J

    2014-03-01

    It has been demonstrated that sonic energy can be harnessed to enhance convection in Galvanic cells during cyclic voltammetry; however, the practical value of this approach is limited due to the lack of open volumes for convection patterns to develop in most batteries. This study evaluates the ability of ultrasonic waves to enhance diffusion in membrane separators commonly used in sandwich-architecture batteries. Studies include the measuring of open-circuit performance curves to interpret performances in terms of reductions in concentration overpotentials. The use of a 40 kHz sonicator bath can consistently increase the voltage of the battery and reduce overpotential losses up to 30%. This work demonstrates and quantifies battery enhancement due to enhanced diffusion made possible with ultrasonic energy.

  19. HOT HYDROGEN IN DIFFUSE CLOUDS

    SciTech Connect

    Cecchi-Pestellini, Cesare; Duley, Walt W.; Williams, David A. E-mail: wwduley@uwaterloo.ca

    2012-08-20

    Laboratory evidence suggests that recombination of adsorbed radicals may cause an abrupt temperature excursion of a dust grain to about 1000 K. One consequence of this is the rapid desorption of adsorbed H{sub 2} molecules with excitation temperatures of this magnitude. We compute the consequences of injection of hot H{sub 2} into cold diffuse interstellar gas at a rate of 1% of the canonical H{sub 2} formation rate. We find that the level populations of H{sub 2} in J = 3, 4, and 5 are close to observed values, and that the abundances of CH{sup +} and OH formed in reactions with hot hydrogen are close to the values obtained from observations of diffuse clouds.

  20. Information filtering via preferential diffusion.

    PubMed

    Lü, Linyuan; Liu, Weiping

    2011-06-01

    Recommender systems have shown great potential in addressing the information overload problem, namely helping users in finding interesting and relevant objects within a huge information space. Some physical dynamics, including the heat conduction process and mass or energy diffusion on networks, have recently found applications in personalized recommendation. Most of the previous studies focus overwhelmingly on recommendation accuracy as the only important factor, while overlooking the significance of diversity and novelty that indeed provide the vitality of the system. In this paper, we propose a recommendation algorithm based on the preferential diffusion process on a user-object bipartite network. Numerical analyses on two benchmark data sets, MovieLens and Netflix, indicate that our method outperforms the state-of-the-art methods. Specifically, it can not only provide more accurate recommendations, but also generate more diverse and novel recommendations by accurately recommending unpopular objects.

  1. Information filtering via preferential diffusion

    NASA Astrophysics Data System (ADS)

    Lü, Linyuan; Liu, Weiping

    2011-06-01

    Recommender systems have shown great potential in addressing the information overload problem, namely helping users in finding interesting and relevant objects within a huge information space. Some physical dynamics, including the heat conduction process and mass or energy diffusion on networks, have recently found applications in personalized recommendation. Most of the previous studies focus overwhelmingly on recommendation accuracy as the only important factor, while overlooking the significance of diversity and novelty that indeed provide the vitality of the system. In this paper, we propose a recommendation algorithm based on the preferential diffusion process on a user-object bipartite network. Numerical analyses on two benchmark data sets, MovieLens and Netflix, indicate that our method outperforms the state-of-the-art methods. Specifically, it can not only provide more accurate recommendations, but also generate more diverse and novel recommendations by accurately recommending unpopular objects.

  2. Tracer diffusion inside fibrinogen layers.

    PubMed

    Cieśla, Michał; Gudowska-Nowak, Ewa; Sagués, Francesc; Sokolov, Igor M

    2014-01-28

    We investigate the obstructed motion of tracer (test) particles in crowded environments by carrying simulations of two-dimensional Gaussian random walk in model fibrinogen monolayers of different orientational ordering. The fibrinogen molecules are significantly anisotropic and therefore they can form structures where orientational ordering, similar to the one observed in nematic liquid crystals, appears. The work focuses on the dependence between level of the orientational order (degree of environmental crowding) of fibrinogen molecules inside a layer and non-Fickian character of the diffusion process of spherical tracer particles moving within the domain. It is shown that in general particles motion is subdiffusive and strongly anisotropic, and its characteristic features significantly change with the orientational order parameter, concentration of fibrinogens, and radius of a diffusing probe. PMID:25669566

  3. Extragalactic diffuse (C II) emission

    NASA Technical Reports Server (NTRS)

    Madden, Suzanne C.; Geis, Norbert; Townes, Charles H.; Genzel, R.; Herrmann, F.; Poglitsch, Albrecht; Stacey, G. J.

    1995-01-01

    The 158 micro m (CII) line has been mapped in the galaxies Centaurus A, M83, NGC 6946, and NGC 891. The emission exists over very large scales, peaking in the nuclei and extending beyond the spiral arms and molecular disks. While most of the (CII) emission from the nuclei and spiral arms originates in photodissociated gas, the diffuse atomic gas can account for much of the (CII) emission in the extended regions.

  4. Diffuse Cosmic Infrared Background Radiation

    NASA Technical Reports Server (NTRS)

    Dwek, Eli

    2002-01-01

    The diffuse cosmic infrared background (CIB) consists of the cumulative radiant energy released in the processes of structure formation that have occurred since the decoupling of matter and radiation following the Big Bang. In this lecture I will review the observational data that provided the first detections and limits on the CIB, and the theoretical studies explaining the origin of this background. Finally, I will also discuss the relevance of this background to the universe as seen in high energy gamma-rays.

  5. Spectralon diffuser calibration for MERIS

    NASA Astrophysics Data System (ADS)

    Olij, Carina; Schaarsberg, Jos G.; Werij, Henri G.; Zoutman, Erik; Baudin, Gilles; Chommeloux, Beatrice; Bezy, Jean-Loup; Gourmelon, Georges

    1997-12-01

    One of the key payload instruments of ESA's ENVISAT polar platform is the medium resolution imaging spectrometer (MERIS), aiming at improved knowledge of our planet in the fields of bio-optical oceanography, and atmospheric and land surface processes. MERIS, which is built under responsibility of Aerospatiale, will monitor the solar irradiation scattered by the Earth by employing five cameras which simultaneously record data in 15 visible and near-infrared programmable spectral bands with very low degree of polarization sensitivity. The combined field-of-view of the five cameras spans a range of 68.5 degrees. Crucial for obtaining the desired high accuracy during a four-years lifetime, is the on- board calibration unit. This calibration unit contains a set of Spectralon diffusers, which were manufactured having in mind excellent in-flight stability as well as spectral and spatial uniformity. Preflight calibration of the Spectralon diffusers was carried out at TNO-TPD. This calibration includes the measurement of the bidirectional reflectance distribution function (BRDF) for applicable angles and wavelengths, i.e., while varying angle of incidence, angle of observation, observation area on the elongated diffusers, wavelength and polarization. The diffuser calibration was performed in a class 100 cleanroom. For these measurements the TPD calibration facility, which is described in detail, has been adapted, so that it now has five geometrical degrees of freedom. Detectors have been optimized to minimize stray light. Due to extensive commissioning of the calibration setup the absolute error (1 sigma) of these measurements amounts to less than 0.5%; relative errors are in the 0.3 - 0.4% range.

  6. Diffusion from a line source

    NASA Technical Reports Server (NTRS)

    Burns, R. E.

    1973-01-01

    The problem with predicting pollutant diffusion from a line source of arbitrary geometry is treated. The concentration at the line source may be arbitrarily varied with time. Special attention is given to the meteorological inputs which act as boundary conditions for the problem, and a mixing layer of arbitrary depth is assumed. Numerical application of the derived theory indicates the combinations of meteorological parameters that may be expected to result in high pollution concentrations.

  7. Diffusion in the Lorentz Gas

    NASA Astrophysics Data System (ADS)

    Carl, P. Dettmann

    2014-10-01

    The Lorentz gas, a point particle making mirror-like reflections from an extended collection of scatterers, has been a useful model of deterministic diffusion and related statistical properties for over a century. This survey summarises recent results, including periodic and aperiodic models, finite and infinite horizon, external fields, smooth or polygonal obstacles, and in the Boltzmann—Grad limit. New results are given for several moving particles and for obstacles with flat points. Finally, a variety of applications are presented.

  8. Extended source model for diffusive coupling.

    PubMed

    González-Ochoa, Héctor O; Flores-Moreno, Roberto; Reyes, Luz M; Femat, Ricardo

    2016-01-01

    Motivated by the prevailing approach to diffusion coupling phenomena which considers point-like diffusing sources, we derived an analogous expression for the concentration rate of change of diffusively coupled extended containers. The proposed equation, together with expressions based on solutions to the diffusion equation, is intended to be applied to the numerical solution of systems exclusively composed of ordinary differential equations, however is able to account for effects due the finite size of the coupled sources.

  9. Optimal Network Modularity for Information Diffusion

    NASA Astrophysics Data System (ADS)

    Nematzadeh, Azadeh; Ferrara, Emilio; Flammini, Alessandro; Ahn, Yong-Yeol

    2014-08-01

    We investigate the impact of community structure on information diffusion with the linear threshold model. Our results demonstrate that modular structure may have counterintuitive effects on information diffusion when social reinforcement is present. We show that strong communities can facilitate global diffusion by enhancing local, intracommunity spreading. Using both analytic approaches and numerical simulations, we demonstrate the existence of an optimal network modularity, where global diffusion requires the minimal number of early adopters.

  10. Relativistic diffusive motion in random electromagnetic fields

    NASA Astrophysics Data System (ADS)

    Haba, Z.

    2011-08-01

    We show that the relativistic dynamics in a Gaussian random electromagnetic field can be approximated by the relativistic diffusion of Schay and Dudley. Lorentz invariant dynamics in the proper time leads to the diffusion in the proper time. The dynamics in the laboratory time gives the diffusive transport equation corresponding to the Jüttner equilibrium at the inverse temperature β-1 = mc2. The diffusion constant is expressed by the field strength correlation function (Kubo's formula).

  11. Extended source model for diffusive coupling.

    PubMed

    González-Ochoa, Héctor O; Flores-Moreno, Roberto; Reyes, Luz M; Femat, Ricardo

    2016-01-01

    Motivated by the prevailing approach to diffusion coupling phenomena which considers point-like diffusing sources, we derived an analogous expression for the concentration rate of change of diffusively coupled extended containers. The proposed equation, together with expressions based on solutions to the diffusion equation, is intended to be applied to the numerical solution of systems exclusively composed of ordinary differential equations, however is able to account for effects due the finite size of the coupled sources. PMID:26802012

  12. Approximate Solutions Of Equations Of Steady Diffusion

    NASA Technical Reports Server (NTRS)

    Edmonds, Larry D.

    1992-01-01

    Rigorous analysis yields reliable criteria for "best-fit" functions. Improved "curve-fitting" method yields approximate solutions to differential equations of steady-state diffusion. Method applies to problems in which rates of diffusion depend linearly or nonlinearly on concentrations of diffusants, approximate solutions analytic or numerical, and boundary conditions of Dirichlet type, of Neumann type, or mixture of both types. Applied to equations for diffusion of charge carriers in semiconductors in which mobilities and lifetimes of charge carriers depend on concentrations.

  13. Configurational diffusion of coal macromolecules

    SciTech Connect

    Guin, J.A.; Curtis, C.W.; Tarrer, A.R.; Kim, S.; Hwang, D.; Chen, C.C.; Chiou, Z.

    1991-01-01

    The objective of our research was to obtain fundamental information regarding the functional dependence of the diffusion coefficient of coal molecules on the ratio of molecule to pore diameter. That is, the objective of our study was to examine the effect of molecule size and configuration on hindered diffusion of coal macromolecules through as porous medium. To best accomplish this task, we circumvented the complexities of an actual porous catalyst by using a well defined porous matrix with uniform capillaric pores, i.e., a track-etched membrane. In this way, useful information was obtained regarding the relationship of molecular size and configuration on the diffusion rate of coal derived macromolecules through a pore structure with known geometry. Similar studies were performed using a pellet formed of porous alumina, to provide a link between the idealized membranes and the actual complex pore structure of real catalyst extrudates. The fundamental information from our study will be useful toward the tailoring of catalysts to minimize diffusional influences and thereby increase coal conversion and selectivity for desirable products. (VC)

  14. Electrophoresis of diffuse soft particles.

    PubMed

    Duval, Jérôme F L; Ohshima, Hiroyuki

    2006-04-11

    A theory is presented for the electrophoresis of diffuse soft particles in a steady dc electric field. The particles investigated consist of an uncharged impenetrable core and a charged diffuse polyelectrolytic shell, which is to some extent permeable to ions and solvent molecules. The diffuse character of the shell is defined by a gradual distribution of the density of polymer segments in the interspatial region separating the core from the bulk electrolyte solution. The hydrodynamic impact of the polymer chains on the electrophoretic motion of the particle is accounted for by a distribution of Stokes resistance centers. The numerical treatment of the electrostatics includes the possibility of partial dissociation of the hydrodynamically immobile ionogenic groups distributed throughout the shell as well as specific interaction between those sites with ions from the background electrolyte other than charge-determining ions. Electrophoretic mobilities are computed on the basis of an original numerical scheme allowing rigorous evaluation of the governing transport and electrostatic equations derived following the strategy reported by Ohshima, albeit within the restricted context of a discontinuous chain distribution. Attention is particularly paid to the influence of the type of distribution adopted on the electrophoretic mobility of the particle as a function of its size, charge, degree of permeability, and solution composition. The results are systematically compared with those obtained with a discontinuous representation of the interface. The theory constitutes a basis for interpreting electrophoretic mobilities of heterogeneous systems such as environmental or biological colloids or swollen/deswollen microgel particles.

  15. Helium diffusion in the sun

    NASA Technical Reports Server (NTRS)

    Bahcall, J. N.; Pinsonneault, M. H.

    1992-01-01

    We calculate improved standard solar models using the new Livermore (OPAL) opacity tables, an accurate (exportable) nuclear energy generation routine which takes account of recent measurements and analyses, and the recent Anders-Grevesse determination of heavy element abundances. We also evaluate directly the effect of the diffusion of helium with respect to hydrogen on the calculated neutrino fluxes, on the primordial solar helium abundance, and on the depth of the convective zone. Helium diffusion increases the predicted event rates by about 0.8 SNU, or 11 percent of the total rate, in the chlorine solar neutrino experiment, by about 3.5 SNU, or 3 percent, in the gallium solar neutrino experiments, and by about 12 percent in the Kamiokande and SNO solar neutrino experiments. The best standard solar model including helium diffusion and the most accurate nuclear parameters, element abundances, and radiative opacity predicts a value of 8.0 SNU +/- 3.0 SNU for the C1-37 experiment and 132 +21/-17 SNU for the Ga - 71 experiment, where the uncertainties include 3 sigma errors for all measured input parameters.

  16. Diffusion of cyclooctane (1); argon (2)

    NASA Astrophysics Data System (ADS)

    Winkelmann, J.

    This document is part of Subvolume A `Gases in Gases, Liquids and their Mixtures' of Volume 15 `Diffusion in Gases, Liquids and Electrolytes' of Landolt-Börnstein Group IV `Physical Chemistry'. It is part of the chapter of the chapter `Diffusion in Pure Gases' and contains data on diffusion of (1) cyclooctane; (2) argon

  17. Diffusion of cyclooctane (1); sulfur hexafluoride (2)

    NASA Astrophysics Data System (ADS)

    Winkelmann, J.

    This document is part of Subvolume A `Gases in Gases, Liquids and their Mixtures' of Volume 15 `Diffusion in Gases, Liquids and Electrolytes' of Landolt-Börnstein Group IV `Physical Chemistry'. It is part of the chapter of the chapter `Diffusion in Pure Gases' and contains data on diffusion of (1) cyclooctane; (2) sulfur hexafluoride

  18. Diffusion of cyclooctane (1); helium (2)

    NASA Astrophysics Data System (ADS)

    Winkelmann, J.

    This document is part of Subvolume A `Gases in Gases, Liquids and their Mixtures' of Volume 15 `Diffusion in Gases, Liquids and Electrolytes' of Landolt-Börnstein Group IV `Physical Chemistry'. It is part of the chapter of the chapter `Diffusion in Pure Gases' and contains data on diffusion of (1) cyclooctane; (2) helium

  19. Diffusion of cyclooctane (1); methane (2)

    NASA Astrophysics Data System (ADS)

    Winkelmann, J.

    This document is part of Subvolume A `Gases in Gases, Liquids and their Mixtures' of Volume 15 `Diffusion in Gases, Liquids and Electrolytes' of Landolt-Börnstein Group IV `Physical Chemistry'. It is part of the chapter of the chapter `Diffusion in Pure Gases' and contains data on diffusion of (1) cyclooctane; (2) methane

  20. Diffusion of air (1); furfural (2)

    NASA Astrophysics Data System (ADS)

    Winkelmann, J.

    This document is part of Subvolume A `Gases in Gases, Liquids and their Mixtures' of Volume 15 `Diffusion in Gases, Liquids and Electrolytes' of Landolt-Börnstein Group IV `Physical Chemistry'. It is part of the chapter of the chapter `Diffusion in Pure Gases' and contains data on diffusion of (1) air; (2) furfural

  1. Cosmic ray diffusion: Report of the Workshop in Cosmic Ray Diffusion Theory

    NASA Technical Reports Server (NTRS)

    Birmingham, T. J.; Jones, F. C.

    1975-01-01

    A workshop in cosmic ray diffusion theory was held at Goddard Space Flight Center on May 16-17, 1974. Topics discussed and summarized are: (1) cosmic ray measurements as related to diffusion theory; (2) quasi-linear theory, nonlinear theory, and computer simulation of cosmic ray pitch-angle diffusion; and (3) magnetic field fluctuation measurements as related to diffusion theory.

  2. Ultrafast demagnetization by hot electrons: Diffusion or super-diffusion?

    PubMed Central

    Salvatella, G.; Gort, R.; Bühlmann, K.; Däster, S.; Vaterlaus, A.; Acremann, Y.

    2016-01-01

    Ultrafast demagnetization of ferromagnetic metals can be achieved by a heat pulse propagating in the electron gas of a non-magnetic metal layer, which absorbs a pump laser pulse. Demagnetization by electronic heating is investigated on samples with different thicknesses of the absorber layer on nickel. This allows us to separate the contribution of thermalized hot electrons compared to non-thermal electrons. An analytical model describes the demagnetization amplitude as a function of the absorber thickness. The observed change of demagnetization time can be reproduced by diffusive heat transport through the absorber layer.

  3. Configurational diffusion of asphaltenes in fresh and aged catalysts extrudates. [Mathematical configurational diffusion model

    SciTech Connect

    Guin, J.A.; Tarrer, A.R.

    1992-01-01

    The objective of this research is to determine the relationship between the size and shape of coal and petroleum macromolecules and their diffusion rates i.e., effective diffusivities, in catalyst pore structures. That is, how do the effective intrapore diffusivities depend on molecule configuration and pore geometry. This quarter we made a more comprehensive literature survey concerning configurational diffusion in porous catalysts or catalyst supports. A detailed literature review is reported. Also, a mathematical configurational diffusion model was developed. By using this model, the effective diffusivity for model compounds diffusing in porous media and a linear adsorption constant can be determined by fitting experimental data.

  4. Replicator dynamics with diffusion on multiplex networks

    NASA Astrophysics Data System (ADS)

    Requejo, R. J.; Díaz-Guilera, A.

    2016-08-01

    In this study we present an extension of the dynamics of diffusion in multiplex graphs, which makes the equations compatible with the replicator equation with mutations. We derive an exact formula for the diffusion term, which shows that, while diffusion is linear for numbers of agents, it is necessary to account for nonlinear terms when working with fractions of individuals. We also derive the transition probabilities that give rise to such macroscopic behavior, completing the bottom-up description. Finally, it is shown that the usual assumption of constant population sizes induces a hidden selective pressure due to the diffusive dynamics, which favors the increase of fast diffusing strategies.

  5. Determination of aluminum diffusion parameters in silicon

    NASA Astrophysics Data System (ADS)

    Krause, O.; Ryssel, H.; Pichler, P.

    2002-05-01

    Aluminum as the fastest diffusing acceptor dopant in silicon is commonly used for the fabrication of power semiconductors with p-n junction depths ranging from some microns to more than a hundred microns. Although long used, its diffusion behavior was not sufficiently characterized to support computer-aided design of devices. In this work, the intrinsic diffusion of aluminum was investigated in the temperature range from 850 to 1290 °C. Combining nitridation and oxidation experiments, the fractional diffusivity via self-interstitials was determined. By diffusion in high-concentration boron- and phosphorus-doped silicon the behavior of aluminum under extrinsic conditions was investigated.

  6. Replicator dynamics with diffusion on multiplex networks.

    PubMed

    Requejo, R J; Díaz-Guilera, A

    2016-08-01

    In this study we present an extension of the dynamics of diffusion in multiplex graphs, which makes the equations compatible with the replicator equation with mutations. We derive an exact formula for the diffusion term, which shows that, while diffusion is linear for numbers of agents, it is necessary to account for nonlinear terms when working with fractions of individuals. We also derive the transition probabilities that give rise to such macroscopic behavior, completing the bottom-up description. Finally, it is shown that the usual assumption of constant population sizes induces a hidden selective pressure due to the diffusive dynamics, which favors the increase of fast diffusing strategies. PMID:27627311

  7. REGULAR VERSUS DIFFUSIVE PHOTOSPHERIC FLUX CANCELLATION

    SciTech Connect

    Litvinenko, Yuri E.

    2011-04-20

    Observations of photospheric flux cancellation on the Sun imply that cancellation can be a diffusive rather than regular process. A criterion is derived, which quantifies the parameter range in which diffusive photospheric cancellation should occur. Numerical estimates show that regular cancellation models should be expected to give a quantitatively accurate description of photospheric cancellation. The estimates rely on a recently suggested scaling for a turbulent magnetic diffusivity, which is consistent with the diffusivity measurements on spatial scales varying by almost two orders of magnitude. Application of the turbulent diffusivity to large-scale dispersal of the photospheric magnetic flux is discussed.

  8. TUNED FINITE-DIFFERENCE DIFFUSION OPERATORS

    SciTech Connect

    Maron, Jason; Low, Mordecai-Mark Mac E-mail: mordecai@amnh.org

    2009-05-15

    Finite-difference simulations of fluid dynamics and magnetohydrodynamics generally require an explicit diffusion operator, either to maintain stability by attenuating grid-scale structure, or to implement physical diffusivities such as viscosity or resistivity. If the goal is stability only, the diffusion must act at the grid scale, but should affect structure at larger scales as little as possible. For physical diffusivities the diffusion scale depends on the problem, and diffusion may act at larger scales as well. Diffusivity can undesirably limit the computational time step in both cases. We construct tuned finite-difference diffusion operators that minimally limit the time step while acting as desired near the diffusion scale. Such operators reach peak values at the diffusion scale rather than at the grid scale, but behave as standard operators at larger scales. These operators will be useful for simulations with high magnetic diffusivity or kinematic viscosity such as in the simulation of astrophysical dynamos with magnetic Prandtl number far from unity, or for numerical stabilization using hyperdiffusivity.

  9. Geometric considerations for diffusion in polycrystalline solids

    NASA Astrophysics Data System (ADS)

    Chen, Ying; Schuh, Christopher A.

    2007-03-01

    Mass transport in polycrystals is usually enhanced by short-circuit diffusion along various defect paths, e.g., grain boundaries, dislocation cores, and triple junctions. In the "kinetic-A" regime, diffusion fields associated with the various diffusion paths overlap each other, forming a macroscopically homogeneous diffusion profile that can be described by an effective diffusion coefficient. Here, we develop a composite diffusion model for polycrystals based on realistic arrangements between various microstructural elements, which usually exhibit complex network morphologies. Asymmetric effective medium equations and power-law scaling relationships are used to evaluate the effective diffusivity of a general isotropic polycrystal, and are compared to predictions of the simple arithmetic rule of mixtures used frequently in the literature. We also examine the grain size and temperature dependence of polycrystalline diffusion in terms of the apparent grain size exponent and activation energy, which in turn provide the basis by which we assess dominant diffusion processes and construct generalized diffusion mechanism maps. Implications of geometry on experimental diffusivity measurements are also discussed.

  10. Revealing mesoscopic structural universality with diffusion.

    PubMed

    Novikov, Dmitry S; Jensen, Jens H; Helpern, Joseph A; Fieremans, Els

    2014-04-01

    Measuring molecular diffusion is widely used for characterizing materials and living organisms noninvasively. This characterization relies on relations between macroscopic diffusion metrics and structure at the mesoscopic scale commensurate with the diffusion length. Establishing such relations remains a fundamental challenge, hindering progress in materials science, porous media, and biomedical imaging. Here we show that the dynamical exponent in the time dependence of the diffusion coefficient distinguishes between the universality classes of the mesoscopic structural complexity. Our approach enables the interpretation of diffusion measurements by objectively selecting and modeling the most relevant structural features. As an example, the specific values of the dynamical exponent allow us to identify the relevant mesoscopic structure affecting MRI-measured water diffusion in muscles and in brain, and to elucidate the structural changes behind the decrease of diffusion coefficient in ischemic stroke.

  11. Diffuse Optics for Tissue Monitoring and Tomography

    PubMed Central

    Durduran, T; Choe, R; Baker, W B; Yodh, A G

    2015-01-01

    This review describes the diffusion model for light transport in tissues and the medical applications of diffuse light. Diffuse optics is particularly useful for measurement of tissue hemodynamics, wherein quantitative assessment of oxy- and deoxy-hemoglobin concentrations and blood flow are desired. The theoretical basis for near-infrared or diffuse optical spectroscopy (NIRS or DOS, respectively) is developed, and the basic elements of diffuse optical tomography (DOT) are outlined. We also discuss diffuse correlation spectroscopy (DCS), a technique whereby temporal correlation functions of diffusing light are transported through tissue and are used to measure blood flow. Essential instrumentation is described, and representative brain and breast functional imaging and monitoring results illustrate the workings of these new tissue diagnostics. PMID:26120204

  12. Using light transmission to watch hydrogen diffuse

    PubMed Central

    Pálsson, Gunnar K.; Bliersbach, Andreas; Wolff, Max; Zamani, Atieh; Hjörvarsson, Björgvin

    2012-01-01

    Because of its light weight and small size, hydrogen exhibits one of the fastest diffusion rates in solid materials, comparable to the diffusion rate of liquid water molecules at room temperature. The diffusion rate is determined by an intricate combination of quantum effects and dynamic interplay with the displacement of host atoms that is still only partially understood. Here we present direct observations of the spatial and temporal changes in the diffusion-induced concentration profiles in a vanadium single crystal and we show that the results represent the experimental counterpart of the full time and spatial solution of Fick's diffusion equation. We validate the approach by determining the diffusion rate of hydrogen in a single crystal vanadium (001) film, with net diffusion in the [110] direction. PMID:22692535

  13. Diffusion of Ellipsoids in Bacterial Suspensions.

    PubMed

    Peng, Yi; Lai, Lipeng; Tai, Yi-Shu; Zhang, Kechun; Xu, Xinliang; Cheng, Xiang

    2016-02-12

    Active fluids such as swarming bacteria and motile colloids exhibit exotic properties different from conventional equilibrium materials. As a peculiar example, a spherical tracer immersed inside active fluids shows an enhanced translational diffusion, orders of magnitude stronger than its intrinsic Brownian motion. Here, rather than spherical tracers, we investigate the diffusion of isolated ellipsoids in a quasi-two-dimensional bacterial bath. Our study shows a nonlinear enhancement of both translational and rotational diffusions of ellipsoids. More importantly, we uncover an anomalous coupling between particles' translation and rotation that is strictly prohibited in Brownian diffusion. The coupling reveals a counterintuitive anisotropic particle diffusion, where an ellipsoid diffuses fastest along its minor axis in its body frame. Combining experiments with theoretical modeling, we show that such an anomalous diffusive behavior arises from the generic straining flow of swimming bacteria. Our work illustrates an unexpected feature of active fluids and deepens our understanding of transport processes in microbiological systems.

  14. Computational modeling of diffusion in the cerebellum.

    PubMed

    Marinov, Toma M; Santamaria, Fidel

    2014-01-01

    Diffusion is a major transport mechanism in living organisms. In the cerebellum, diffusion is responsible for the propagation of molecular signaling involved in synaptic plasticity and metabolism, both intracellularly and extracellularly. In this chapter, we present an overview of the cerebellar structure and function. We then discuss the types of diffusion processes present in the cerebellum and their biological importance. We particularly emphasize the differences between extracellular and intracellular diffusion and the presence of tortuosity and anomalous diffusion in different parts of the cerebellar cortex. We provide a mathematical introduction to diffusion and a conceptual overview of various computational modeling techniques. We discuss their scope and their limit of application. Although our focus is the cerebellum, we have aimed at presenting the biological and mathematical foundations as general as possible to be applicable to any other area in biology in which diffusion is of importance.

  15. Quantifying protein diffusion and capture on filaments.

    PubMed

    Reithmann, Emanuel; Reese, Louis; Frey, Erwin

    2015-02-17

    The functional relevance of regulating proteins is often limited to specific binding sites such as the ends of microtubules or actin-filaments. A localization of proteins on these functional sites is of great importance. We present a quantitative theory for a diffusion and capture process, where proteins diffuse on a filament and stop diffusing when reaching the filament's end. It is found that end-association after one-dimensional diffusion is the main source for tip-localization of such proteins. As a consequence, diffusion and capture is highly efficient in enhancing the reaction velocity of enzymatic reactions, where proteins and filament ends are to each other as enzyme and substrate. We show that the reaction velocity can effectively be described within a Michaelis-Menten framework. Together, one-dimensional diffusion and capture beats the (three-dimensional) Smoluchowski diffusion limit for the rate of protein association to filament ends.

  16. Optical diffusers based on silicone emulsions

    NASA Astrophysics Data System (ADS)

    Wang, Jui-Hao; Lien, Shui-Yang; Ho, Jeng-Rong; Shih, Teng-Kai; Chen, Chia-Fu; Chen, Chien-Chung; Whang, Wha-Tzong

    2009-12-01

    The present study provides an experimental approach for fabricating optical diffuser films based on silicone emulsions. The silicone emulsion consisting of silicone polymer (Sylgard 184) and NaCl aq. solution was used as the optical material of diffusers, wherein NaCl aq. solution was severed as surfactant to stabilize the emulsions. After stirring mechanically, microscaled water drop with various sizes distributed randomly in silicone polymer, wherein water drop was used as scattering diffusion particles. To modulate the volume of NaCl aq. solution, the diffusing performance of diffusers could be change by different amount drop particles. Thereafter, an optical examination was carried out to characterize optical properties, transmittance, and light diffusivity of volumetric diffuser films.

  17. Diffusion of Ellipsoids in Bacterial Suspensions

    NASA Astrophysics Data System (ADS)

    Peng, Yi; Lai, Lipeng; Tai, Yi-Shu; Zhang, Kechun; Xu, Xinliang; Cheng, Xiang

    2016-02-01

    Active fluids such as swarming bacteria and motile colloids exhibit exotic properties different from conventional equilibrium materials. As a peculiar example, a spherical tracer immersed inside active fluids shows an enhanced translational diffusion, orders of magnitude stronger than its intrinsic Brownian motion. Here, rather than spherical tracers, we investigate the diffusion of isolated ellipsoids in a quasi-two-dimensional bacterial bath. Our study shows a nonlinear enhancement of both translational and rotational diffusions of ellipsoids. More importantly, we uncover an anomalous coupling between particles' translation and rotation that is strictly prohibited in Brownian diffusion. The coupling reveals a counterintuitive anisotropic particle diffusion, where an ellipsoid diffuses fastest along its minor axis in its body frame. Combining experiments with theoretical modeling, we show that such an anomalous diffusive behavior arises from the generic straining flow of swimming bacteria. Our work illustrates an unexpected feature of active fluids and deepens our understanding of transport processes in microbiological systems.

  18. New methods in Diffusion Weighted and Diffusion Tensor Imaging

    PubMed Central

    Bammer, Roland; Holdsworth, Samantha J.; Veldhuis, Wouter B.; Skare, Stefan T.

    2009-01-01

    Synopsis Considerable strides have been made by countless individual researchers in diffusion-weighted imaging (DWI) to push DWI from an experimental tool – limited to a few institutions with specialized instrumentation – to a powerful tool used routinely for diagnostic imaging. Despite its current success, the field of DWI constantly evolves and progress has been made on several fronts, awaiting adoption by vendors and clinical users to bring in the next generation of DWI. These developments are primarily comprised of improved robustness against patient and physiologic motion, increased spatial resolution, new biophysical and tissue models, and new clinical applications for DWI. This article aims to provide a succinct overview of some of these new developments and a description of some of the major challenges associated with DWI. Trying to understand some of these challenges is helpful not only to the technically savvy MRI user, but also to radiologists who are interested in the potential strengths and weaknesses of these techniques, what is in the “diffusion pipeline”, and in how to interpret artifacts on DWI scans. PMID:19406353

  19. Probing the diffuse interstellar medium with diffuse interstellar bands

    NASA Astrophysics Data System (ADS)

    Theodorus van Loon, Jacco; Bailey, Mandy; Farhang, Amin; Javadi, Atefeh; Khosroshahi, Habib

    2015-08-01

    For a century already, a large number of absorption bands have been known at optical wavelengths, called the diffuse interstellar bands (DIBs). While their carriers remain unidentified, the relative strengths of these bands in various environments make them interesting new probes of the diffuse interstellar medium (ISM). We present the results from two large, dedicated campaigns to map the ISM using DIBs measured in the high signal-to-noise spectra of hundreds of early-type stars: [1] in and around the Local Bubble using ESO's New Technology Telescope and the Isaac Newton Telescope, and [2] across both Magellanic Clouds using the Very Large Telescope and the Anglo-Australian Telescope. We discuss the implications for the structure and dynamics of the ISM, as well as the constraints these maps place on the nature of the carriers of the DIBs. Partial results have appeared in the recent literature (van Loon et al. 2013; Farhang et al. 2015a,b; Bailey, PhD thesis 2014) with the remainder being prepared for publication now.

  20. Calculating effective diffusivities in the limit of vanishing molecular diffusion

    SciTech Connect

    Pavliotis, G.A. Stuart, A.M. Zygalakis, K.C.

    2009-03-01

    In this paper we study the problem of the numerical calculation (by Monte Carlo methods) of the effective diffusivity for a particle moving in a periodic divergent-free velocity field, in the limit of vanishing molecular diffusion. In this limit traditional numerical methods typically fail, since they do not represent accurately the geometry of the underlying deterministic dynamics. We propose a stochastic splitting method that takes into account the volume-preserving property of the equations of motion in the absence of noise, and when inertial effects can be neglected. An extension of the method is then proposed for the cases where the noise has a non-trivial time-correlation structure and when inertial effects cannot be neglected. The method of modified equations is used to explain failings of Euler-based methods. The new stochastic geometric integrators are shown to outperform standard Euler-based integrators. Various asymptotic limits of physical interest are investigated by means of numerical experiments, using the new integrators.

  1. DNest3: Diffusive Nested Sampling

    NASA Astrophysics Data System (ADS)

    Brewer, Brendon

    2016-04-01

    DNest3 is a C++ implementation of Diffusive Nested Sampling (ascl:1010.029), a Markov Chain Monte Carlo (MCMC) algorithm for Bayesian Inference and Statistical Mechanics. Relative to older DNest versions, DNest3 has improved performance (in terms of the sampling overhead, likelihood evaluations still dominate in general) and is cleaner code: implementing new models should be easier than it was before. In addition, DNest3 is multi-threaded, so one can run multiple MCMC walkers at the same time, and the results will be combined together.

  2. Inhomogeneous diffusion-limited aggregation

    NASA Technical Reports Server (NTRS)

    Selinger, Robin Blumberg; Nittmann, Johann; Stanley, H. E.

    1989-01-01

    It is demonstrated here that inhomogeneous diffusion-limited aggregation (DLA) model can be used to simulate viscous fingering in a medium with inhomogeneous permeability and homogeneous porosity. The medium consists of a pipe-pore square-lattice network in which all pores have equal volume and the pipes have negligible volume. It is shown that fluctuations in a DLA-based growth process may be tuned by noise reduction, and that fluctuations in the velocity of the moving interface are multiplicative in form.

  3. Laser activated diffuse discharge switch

    DOEpatents

    Christophorou, Loucas G.; Hunter, Scott R.

    1988-01-01

    The invention is a gas mixture for a diffuse discharge switch which is capable of changing from a conducting state to an insulating state in the presence of electrons upon the introduction of laser light. The mixture is composed of a buffer gas such as nitrogen or argon and an electron attaching gas such as C.sub.6 H.sub.5 SH, C.sub.6 H.sub.5 SCH.sub.3, CH.sub.3 CHO and CF.sub.3 CHO wherein the electron attachment is brought on by indirect excitation of molecules to long-lived states by exposure to laser light.

  4. Multicomponent diffusion in polymeric liquids.

    PubMed Central

    Curtiss, C F; Bird, R B

    1996-01-01

    It is shown how the phase-space kinetic theory of polymeric liquid mixtures leads to a set of extended Maxwell-Stefan equations describing multicomponent diffusion. This expression reduces to standard results for dilute solutions and for undiluted polymers. The polymer molecules are modeled as flexible bead-spring structures. To obtain the Maxwell-Stefan equations, the usual expression for the hydrodynamic drag force on a bead, used in previous kinetic theories, must be replaced by a new expression that accounts explicitly for bead-bead interactions between different molecules. PMID:11607693

  5. Water vapor diffusion membrane development

    NASA Technical Reports Server (NTRS)

    Tan, M. K.

    1976-01-01

    A total of 18 different membranes were procured, characterized, and tested in a modified bench-scale vapor diffusion water reclamation unit. Four membranes were selected for further studies involving membrane fouling. Emphasis was placed on the problem of flux decline due to membrane fouling. This is discussed in greater details under "Summary and Discussion on Membrane Fouling Studies" presented in pages 47-51. The system was also investigated for low temperature application on wash-water where the permeated water is not recovered but vented into space vacuum.

  6. Acid diffusion through polyaniline membranes

    SciTech Connect

    Su, T.M.; Huang, S.C.; Conklin, J.A.

    1995-12-01

    Polyaniline membranes in the undoped (base) and doped (acid) forms are studied for their utility as pervaporation membranes. The separation of water from mixtures of propionic acid, acetic acid and formic acid have been demonstrated from various feed compositions. Doped polyaniline displays an enhanced selectivity of water over these organic acids as compared with undoped polyaniline. For as-cast polyaniline membranes a diffusion coefficient (D) on the order of 10{sup -9} cm{sup 2}/sec has been determined for the flux of protons through the membranes using hydrochloric acid.

  7. Diffusion in Altered Tonalite Sample Using Time Domain Diffusion Simulations in Tomographic Images Combined with Lab-scale Diffusion Experiments

    NASA Astrophysics Data System (ADS)

    Voutilainen, M.; Sardini, P.; Togneri, L.; Siitari-Kauppi, M.; Timonen, J.

    2010-12-01

    In this work an effect of rock heterogeneity on diffusion was investigated. Time domain diffusion simulations were used to compare behavior of diffusion in homogeneous and heterogeneous 3D media. Tomographic images were used as heterogeneous rock media. One altered tonalite sample from Sievi, Finland, was chosen as test case for introduced analysis procedure. Effective diffusion coefficient of tonalite sample was determined with lab-scale experiments and the same coefficient was used also for homogeneous media. Somewhat technically complicated mathematical solution for analysis of through diffusion experiment is shortly described. Computed tomography (CT) is already quite widely used in many geological, petrological, and paleontological applications when the three-dimensional (3D) structure of the material is of interest, and is an excellent method for gaining information especially about its heterogeneity, grain size, or porosity. In addition to offering means for quantitative characterization, CT provides a lot of qualitative information [1]. A through -diffusion laboratory experiment using radioactive tracer was fitted using the Time Domain Diffusion (TDD) method. This rapid particle tracking method allows simulation of the heterogeneous diffusion based on pore-scale images and local values of diffusivities [2]. As a result we found out that heterogeneity has only a small effect to diffusion coefficient and in-diffusion profile for used geometry. Also direction dependency was tested and was found to be negligible. Whereas significant difference between generally accepted value and value obtained from simulations for constant m in Archie’s law was found. [1] Voutilainen, M., Siitari-Kauppi, M., Sardini, P., and Timonen, J., (2010). On pore-space characterization of an altered tonalite by X-ray µCT and the 14C-PMMA method (in progress). [2] Sardini, P., Robinet, J., Siitari-Kauppi, M., Delay, F., and Hellmuth, K-H, (2007). On direct simulation of heterogeneous

  8. Research on zinc diffusion in undoped InP

    NASA Astrophysics Data System (ADS)

    Zhuang, ChunQuan; Lv, YanQiu; Gong, HaiMei

    2005-10-01

    When Zinc diffuses into undoped InP, the diffusion profiles are severely influenced by the process parameters, such as the diffusion temperature, the diffusion time, etc. In order to reduce the surface damage and enhance reproducibility, the diffusion temperature and the diffusion time are optimized. Under optimized. diffusion temperature, curve of diffusion depth versus the square root of the diffusion time is achieved. From this curve, the diffusion coefficient for zinc under the optimized temperature is calculated. The zinc profile was determined by electrochemical capacitance-voltage profiling (ECV), according to which zinc diffusion mechanism was explained.

  9. An asixymmetric diffusion experiment for the determination of diffusion and sorption coefficients of rock samples

    SciTech Connect

    Takeda, M.; Hiratsuka, T.; Ito, K.; Finsterle, S.

    2011-02-01

    Diffusion anisotropy is a critical property in predicting migration of substances in sedimentary formations with very low permeability. The diffusion anisotropy of sedimentary rocks has been evaluated mainly from laboratory diffusion experiments, in which the directional diffusivities are separately estimated by through-diffusion experiments using different rock samples, or concurrently by in-diffusion experiments in which only the tracer profile in a rock block is measured. To estimate the diffusion anisotropy from a single rock sample, this study proposes an axisymmetric diffusion test, in which tracer diffuses between a cylindrical rock sample and a surrounding solution reservoir. The tracer diffusion between the sample and reservoir can be monitored from the reservoir tracer concentrations, and the tracer profile could also be obtained after dismantling the sample. Semi-analytical solutions are derived for tracer concentrations in both the reservoir and sample, accounting for an anisotropic diffusion tensor of rank two as well as the dilution effects from sampling and replacement of reservoir solution. The transient and steady-state analyses were examined experimentally and numerically for different experimental configurations, but without the need for tracer profiling. These experimental configurations are tested for in- and out-diffusion experiments using Koetoi and Wakkanai mudstones and Shirahama sandstone, and are scrutinized by a numerical approach to identify favorable conditions for parameter estimation. The analysis reveals the difficulty in estimating diffusion anisotropy; test configurations are proposed for enhanced identifiability of diffusion anisotropy. Moreover, it is demonstrated that the axisymmetric diffusion test is efficient in obtaining the sorption parameter from both steady-state and transient data, and in determining the effective diffusion coefficient if isotropic diffusion is assumed. Moreover, measuring reservoir concentrations in an

  10. An axisymmetric diffusion experiment for the determination of diffusion and sorption coefficients of rock samples.

    PubMed

    Takeda, M; Hiratsuka, T; Ito, K; Finsterle, S

    2011-04-25

    Diffusion anisotropy is a critical property in predicting migration of substances in sedimentary formations with very low permeability. The diffusion anisotropy of sedimentary rocks has been evaluated mainly from laboratory diffusion experiments, in which the directional diffusivities are separately estimated by through-diffusion experiments using different rock samples, or concurrently by in-diffusion experiments in which only the tracer profile in a rock block is measured. To estimate the diffusion anisotropy from a single rock sample, this study proposes an axisymmetric diffusion test, in which tracer diffuses between a cylindrical rock sample and a surrounding solution reservoir. The tracer diffusion between the sample and reservoir can be monitored from the reservoir tracer concentrations, and the tracer profile could also be obtained after dismantling the sample. Semi-analytical solutions are derived for tracer concentrations in both the reservoir and sample, accounting for an anisotropic diffusion tensor of rank two as well as the dilution effects from sampling and replacement of reservoir solution. The transient and steady-state analyses were examined experimentally and numerically for different experimental configurations, but without the need for tracer profiling. These experimental configurations are tested for in- and out-diffusion experiments using Koetoi and Wakkanai mudstones and Shirahama sandstone, and are scrutinized by a numerical approach to identify favorable conditions for parameter estimation. The analysis reveals the difficulty in estimating diffusion anisotropy; test configurations are proposed for enhanced identifiability of diffusion anisotropy. Moreover, it is demonstrated that the axisymmetric diffusion test is efficient in obtaining the sorption parameter from both steady-state and transient data, and in determining the effective diffusion coefficient if isotropic diffusion is assumed. Moreover, measuring reservoir concentrations in an

  11. An axisymmetric diffusion experiment for the determination of diffusion and sorption coefficients of rock samples.

    PubMed

    Takeda, M; Hiratsuka, T; Ito, K; Finsterle, S

    2011-04-25

    Diffusion anisotropy is a critical property in predicting migration of substances in sedimentary formations with very low permeability. The diffusion anisotropy of sedimentary rocks has been evaluated mainly from laboratory diffusion experiments, in which the directional diffusivities are separately estimated by through-diffusion experiments using different rock samples, or concurrently by in-diffusion experiments in which only the tracer profile in a rock block is measured. To estimate the diffusion anisotropy from a single rock sample, this study proposes an axisymmetric diffusion test, in which tracer diffuses between a cylindrical rock sample and a surrounding solution reservoir. The tracer diffusion between the sample and reservoir can be monitored from the reservoir tracer concentrations, and the tracer profile could also be obtained after dismantling the sample. Semi-analytical solutions are derived for tracer concentrations in both the reservoir and sample, accounting for an anisotropic diffusion tensor of rank two as well as the dilution effects from sampling and replacement of reservoir solution. The transient and steady-state analyses were examined experimentally and numerically for different experimental configurations, but without the need for tracer profiling. These experimental configurations are tested for in- and out-diffusion experiments using Koetoi and Wakkanai mudstones and Shirahama sandstone, and are scrutinized by a numerical approach to identify favorable conditions for parameter estimation. The analysis reveals the difficulty in estimating diffusion anisotropy; test configurations are proposed for enhanced identifiability of diffusion anisotropy. Moreover, it is demonstrated that the axisymmetric diffusion test is efficient in obtaining the sorption parameter from both steady-state and transient data, and in determining the effective diffusion coefficient if isotropic diffusion is assumed. Moreover, measuring reservoir concentrations in an

  12. Separation of gases by diffusion

    DOEpatents

    Peieris, R. E.; Simon, F. E.; Arms, H. S.

    1960-12-13

    An apparatus is described for the separation of mixtures of gaseous or vaporous media by diffusion through a permeable membrane. The apparatus consists principally of a housing member having an elongated internal chamber dissected longitudinally by a permeable membrane. Means are provided for producing a pressure difference between opposite sides of the membrane to cause a flow of the media in the chamber therethrough. This pressure difference is alternated between opposite sides of the membrane to produce an oscillating flow through the membrane. Additional means is provided for producing flow parallel to the membrane in opposite directions on the two sides thereof and of the same frequency and in phase wlth the alternating pressure difference. The lighter molecules diffuse through the membrane more readily than the heavier molecules and the parallel flow effects a net transport of the lighter molecules in one direction and the heavier molecules in the opposite direction wlthin the chamber. By these means a concentration gradient along the chamber is established. (auth)

  13. Water vapor diffusion membrane development

    NASA Technical Reports Server (NTRS)

    Tan, M. K.

    1977-01-01

    An application of the water vapor diffusion technique is examined whereby the permeated water vapor is vented to space vacuum to alleviate on-board waste storage and provide supplemental cooling. The work reported herein deals primarily with the vapor diffusion-heat rejection (VD-HR) as it applies to the Space Shuttle. A stack configuration was selected, designed and fabricated. An asymmetric cellulose acetate membrane, used in reverse osmosis application was selected and a special spacer was designed to enhance mixing and promote mass transfer. A skid-mount unit was assembled from components used in the bench unit although no attempt was made to render it flight-suitable. The operating conditions of the VD-HR were examined and defined and a 60-day continuous test was carried out. The membranes performed very well throughout the test; no membrane rupture and no unusual flux decay was observed. In addition, a tentative design for a flight-suitable VD-HR unit was made.

  14. Cosmological baryon diffusion and nucleosynthesis

    NASA Astrophysics Data System (ADS)

    Applegate, James H.; Hogan, Craig J.; Scherrer, Robert J.

    1987-02-01

    The diffusion rate of baryons through the big-bang plasma is calculated. Fluctuations in baryon density in the early Universe lead to inhomogeneities in the neutron-proton ratio, due to the differential diffusion of these particles through the radiation plasma. For certain types of nonlinear fluctuations, some nucleosynthesis would occur in very neutron-rich regions. Nuclear products of homogeneous neutron-enriched regions are evaluated numerically using a standard reaction network and these results are used to estimate final abundances in an inhomogeneous universe. Net deuterium and lithium abundances tend to increase and the net helium abundance tends to decrease compared to an unperturbed standard model. It is suggested that pronounced nonlinear baryon-density fluctuations produced in QCD- or electroweak-epoch phase transitions could alter abundances sufficiently to make a closed baryonic universe consistent with current observations of these elements. In such a model the abundance of heavier elements (C,N,O, etc.) increases significantly and approaches observable levels. Abundances can be used to place constraints on extreme scenarios for phase transitions at these epochs.

  15. Uncovering Blue Diffuse Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    James, Bethan; Koposov, Sergey; Stark, Daniel; Belokurov, Vasily; Pettini, Max; Olszewski, Edward W.

    2015-01-01

    Extremely metal-poor galaxies (XMPs) and the star-formation within their chemically pristine environments are fundamental to our understanding of the galaxy formation process at early times. However, traditional emission-line surveys detect only the brightest metal-poor galaxies where star-formation occurs in compact, starbursting environments, and thereby give us only a partial view of the dwarf galaxy population. To avoid such biases, we have developed a new search algorithm based on the morphological, rather then spectral, properties of XMPs and have applied to the Sloan Digital Sky Survey database of images. Using this novel approach, we have discovered ~100 previously undetected, faint blue galaxies, each with isolated HII regions embedded in a diffuse continuum. In this talk I will present the first results from follow-up optical spectroscopy of this sample, which reveals these blue diffuse dwarfs (BDDs) to be young, very metal-poor and actively forming stars despite their intrinsically low luminosities. I will present evidence showing that BDDs appear to bridge the gap between quiescent dwarf irregular (dIrr) galaxies and blue compact galaxies (BCDs) and as such offer an ideal opportunity to assess how star-formation occurs in more `normal' metal-poor systems.

  16. The Foundations of Diffusion Revisited

    SciTech Connect

    van Milligen, B. Ph.; Carreras, Benjamin A; Sanchez, Raul

    2005-12-01

    Diffusion is essentially the macroscopic manifestation of random (Brownian) microscopic motion. This idea has been generalized in the continuous time random walk formalism, which under quite general conditions leads to a generalized master equation (GME) that provides a useful modelling framework for transport. Here we review some of the basic ideas underlying this formalism from the perspective of transport in (magnetic confinement) plasmas. Under some specific conditions, the fluid limit of the GME corresponds to the Fokker-Planck (FP) diffusion equation in inhomogeneous systems, which reduces to Fick's law when the system is homogeneous. It is suggested that the FP equation may be preferable in fusion plasmas due to the inhomogeneity of the system, which would imply that part of the observed inward convection ('pinch') can be ascribed to this inhomogeneity. The GME also permits a mathematically sound approach to more complex transport issues, such as the incorporation of critical gradients and non-local transport mechanisms. A toy model incorporating these ingredients was shown to possess behaviour that bears a striking similarity to certain unusual phenomena observed in fusion plasmas.

  17. Mechanisms of impurity diffusion in rutile

    SciTech Connect

    Peterson, N.L.; Sasaki, J.

    1984-01-01

    Tracer diffusion of /sup 46/Sc, /sup 51/Cr, /sup 54/Mn, /sup 59/Fe, /sup 60/Co, /sup 63/Ni, and /sup 95/Zr, was measured as functions of crystal orientation, temperature, and oxygen partial pressure in rutile single crystals using the radioactive tracer sectioning technique. Compared to cation self-diffusion, divalent impurities (e.g., Co and Ni) diffuse extremely rapidly in TiO/sub 2/ and exhibit a large anisotropy in the diffusion behavior; divalent-impurity diffusion parallel to the c-axis is much larger than it is perpendicular to the c-axis. The diffusion of trivalent impurity ions (Sc and Cr) and tetravalent impurity ions (Zr) is similar to cation self-diffusion, as a function of temperature and of oxygen partial pressure. The divalent impurity ions Co and Ni apparently diffuse as interstitial ions along open channels parallel to the c-axis. The results suggest that Sc, Cr, and Zr ions diffuse by an interstitialcy mechanism involving the simultaneous and cooperative migration of tetravalent interstitial titanium ions and the tracer-impurity ions. Iron ions diffused both as divalent and as trivalent ions. 8 figures.

  18. A Multimodal Theory of Affect Diffusion.

    PubMed

    Peters, Kim; Kashima, Yoshihisa

    2015-09-01

    There is broad consensus in the literature that affect diffuses through social networks (such that a person may "acquire" or "catch" an affective state from his or her social contacts). It is further assumed that affect diffusion primarily occurs as the result of people's tendencies to synchronize their affective actions (such as smiles and frowns). However, as we show, there is a lack of clarity in the literature about the substrate and scope of affect diffusion. One consequence of this is a difficulty in distinguishing between affect diffusion and several other affective influence phenomena that look similar but have very different consequences. There is also a growing body of evidence that action synchrony is unlikely to be the only, or indeed the most important, pathway for affect diffusion. This paper has 2 key aims: (a) to craft a formal definition of affect diffusion that does justice to the core of the phenomenon while distinguishing it from other phenomena with which it is frequently confounded and (b) to advance a theory of the mechanisms of affect diffusion. This theory, which we call the multimodal theory of affect diffusion, identifies 3 parallel multimodal mechanisms that may act as routes for affect diffusion. It also provides a basis for novel predictions about the conditions under which affect is most likely to diffuse. PMID:26011791

  19. Is Protein Folding Sub-Diffusive?

    PubMed Central

    Krivov, Sergei V.

    2010-01-01

    Protein folding dynamics is often described as diffusion on a free energy surface considered as a function of one or few reaction coordinates. However, a growing number of experiments and models show that, when projected onto a reaction coordinate, protein dynamics is sub-diffusive. This raises the question as to whether the conventionally used diffusive description of the dynamics is adequate. Here, we numerically construct the optimum reaction coordinate for a long equilibrium folding trajectory of a Go model of a -repressor protein. The trajectory projected onto this coordinate exhibits diffusive dynamics, while the dynamics of the same trajectory projected onto a sub-optimal reaction coordinate is sub-diffusive. We show that the higher the (cut-based) free energy profile for the putative reaction coordinate, the more diffusive the dynamics become when projected on this coordinate. The results suggest that whether the projected dynamics is diffusive or sub-diffusive depends on the chosen reaction coordinate. Protein folding can be described as diffusion on the free energy surface as function of the optimum reaction coordinate. And conversely, the conventional reaction coordinates, even though they might be based on physical intuition, are often sub-optimal and, hence, show sub-diffusive dynamics. PMID:20862361

  20. Anomalous extracellular diffusion in rat cerebellum.

    PubMed

    Xiao, Fanrong; Hrabe, Jan; Hrabetova, Sabina

    2015-05-01

    Extracellular space (ECS) is a major channel transporting biologically active molecules and drugs in the brain. Diffusion-mediated transport of these substances is hindered by the ECS structure but the microscopic basis of this hindrance is not fully understood. One hypothesis proposes that the hindrance originates in large part from the presence of dead-space (DS) microdomains that can transiently retain diffusing molecules. Because previous theoretical and modeling work reported an initial period of anomalous diffusion in similar environments, we expected that brain regions densely populated by DS microdomains would exhibit anomalous extracellular diffusion. Specifically, we targeted granular layers (GL) of rat and turtle cerebella that are populated with large and geometrically complex glomeruli. The integrative optical imaging (IOI) method was employed to evaluate diffusion of fluorophore-labeled dextran (MW 3000) in GL, and the IOI data analysis was adapted to quantify the anomalous diffusion exponent dw from the IOI records. Diffusion was significantly anomalous in rat GL, where dw reached 4.8. In the geometrically simpler turtle GL, dw was elevated but not robustly anomalous (dw = 2.6). The experimental work was complemented by numerical Monte Carlo simulations of anomalous ECS diffusion in several three-dimensional tissue models containing glomeruli-like structures. It demonstrated that both the duration of transiently anomalous diffusion and the anomalous exponent depend on the size of model glomeruli and the degree of their wrapping. In conclusion, we have found anomalous extracellular diffusion in the GL of rat cerebellum. This finding lends support to the DS microdomain hypothesis. Transiently anomalous diffusion also has a profound effect on the spatiotemporal distribution of molecules released into the ECS, especially at diffusion distances on the order of a few cell diameters, speeding up short-range diffusion-mediated signals in less permeable

  1. Anomalous Extracellular Diffusion in Rat Cerebellum

    PubMed Central

    Xiao, Fanrong; Hrabe, Jan; Hrabetova, Sabina

    2015-01-01

    Extracellular space (ECS) is a major channel transporting biologically active molecules and drugs in the brain. Diffusion-mediated transport of these substances is hindered by the ECS structure but the microscopic basis of this hindrance is not fully understood. One hypothesis proposes that the hindrance originates in large part from the presence of dead-space (DS) microdomains that can transiently retain diffusing molecules. Because previous theoretical and modeling work reported an initial period of anomalous diffusion in similar environments, we expected that brain regions densely populated by DS microdomains would exhibit anomalous extracellular diffusion. Specifically, we targeted granular layers (GL) of rat and turtle cerebella that are populated with large and geometrically complex glomeruli. The integrative optical imaging (IOI) method was employed to evaluate diffusion of fluorophore-labeled dextran (MW 3000) in GL, and the IOI data analysis was adapted to quantify the anomalous diffusion exponent dw from the IOI records. Diffusion was significantly anomalous in rat GL, where dw reached 4.8. In the geometrically simpler turtle GL, dw was elevated but not robustly anomalous (dw = 2.6). The experimental work was complemented by numerical Monte Carlo simulations of anomalous ECS diffusion in several three-dimensional tissue models containing glomeruli-like structures. It demonstrated that both the duration of transiently anomalous diffusion and the anomalous exponent depend on the size of model glomeruli and the degree of their wrapping. In conclusion, we have found anomalous extracellular diffusion in the GL of rat cerebellum. This finding lends support to the DS microdomain hypothesis. Transiently anomalous diffusion also has a profound effect on the spatiotemporal distribution of molecules released into the ECS, especially at diffusion distances on the order of a few cell diameters, speeding up short-range diffusion-mediated signals in less permeable

  2. Anomalous extracellular diffusion in rat cerebellum.

    PubMed

    Xiao, Fanrong; Hrabe, Jan; Hrabetova, Sabina

    2015-05-01

    Extracellular space (ECS) is a major channel transporting biologically active molecules and drugs in the brain. Diffusion-mediated transport of these substances is hindered by the ECS structure but the microscopic basis of this hindrance is not fully understood. One hypothesis proposes that the hindrance originates in large part from the presence of dead-space (DS) microdomains that can transiently retain diffusing molecules. Because previous theoretical and modeling work reported an initial period of anomalous diffusion in similar environments, we expected that brain regions densely populated by DS microdomains would exhibit anomalous extracellular diffusion. Specifically, we targeted granular layers (GL) of rat and turtle cerebella that are populated with large and geometrically complex glomeruli. The integrative optical imaging (IOI) method was employed to evaluate diffusion of fluorophore-labeled dextran (MW 3000) in GL, and the IOI data analysis was adapted to quantify the anomalous diffusion exponent dw from the IOI records. Diffusion was significantly anomalous in rat GL, where dw reached 4.8. In the geometrically simpler turtle GL, dw was elevated but not robustly anomalous (dw = 2.6). The experimental work was complemented by numerical Monte Carlo simulations of anomalous ECS diffusion in several three-dimensional tissue models containing glomeruli-like structures. It demonstrated that both the duration of transiently anomalous diffusion and the anomalous exponent depend on the size of model glomeruli and the degree of their wrapping. In conclusion, we have found anomalous extracellular diffusion in the GL of rat cerebellum. This finding lends support to the DS microdomain hypothesis. Transiently anomalous diffusion also has a profound effect on the spatiotemporal distribution of molecules released into the ECS, especially at diffusion distances on the order of a few cell diameters, speeding up short-range diffusion-mediated signals in less permeable

  3. Controllable uncertain opinion diffusion under confidence bound and unpredicted diffusion probability

    NASA Astrophysics Data System (ADS)

    Yan, Fuhan; Li, Zhaofeng; Jiang, Yichuan

    2016-05-01

    The issues of modeling and analyzing diffusion in social networks have been extensively studied in the last few decades. Recently, many studies focus on uncertain diffusion process. The uncertainty of diffusion process means that the diffusion probability is unpredicted because of some complex factors. For instance, the variety of individuals' opinions is an important factor that can cause uncertainty of diffusion probability. In detail, the difference between opinions can influence the diffusion probability, and then the evolution of opinions will cause the uncertainty of diffusion probability. It is known that controlling the diffusion process is important in the context of viral marketing and political propaganda. However, previous methods are hardly feasible to control the uncertain diffusion process of individual opinion. In this paper, we present suitable strategy to control this diffusion process based on the approximate estimation of the uncertain factors. We formulate a model in which the diffusion probability is influenced by the distance between opinions, and briefly discuss the properties of the diffusion model. Then, we present an optimization problem at the background of voting to show how to control this uncertain diffusion process. In detail, it is assumed that each individual can choose one of the two candidates or abstention based on his/her opinion. Then, we present strategy to set suitable initiators and their opinions so that the advantage of one candidate will be maximized at the end of diffusion. The results show that traditional influence maximization algorithms are not applicable to this problem, and our algorithm can achieve expected performance.

  4. Diffusion MR tractography of the heart

    PubMed Central

    2009-01-01

    Histological studies have shown that the myocardium consists of an array of crossing helical fiber tracts. Changes in myocardial fiber architecture occur in ischemic heart disease and heart failure, and can be imaged non-destructively with diffusion-encoded MR. Several diffusion-encoding schemes have been developed, ranging from scalar measurements of mean diffusivity to a 6-dimensional imaging technique known as diffusion spectrum imaging or DSI. The properties of DSI make it particularly suited to the generation of 3-dimensional tractograms of myofiber architecture. In this article we review the physical basis of diffusion-tractography in the myocardium and the attributes of the available techniques, placing particular emphasis on DSI. The application of DSI in ischemic heart disease is reviewed, and the requisites for widespread clinical translation of diffusion MR tractography in the heart are discussed. PMID:19912654

  5. Analysis of offshore atmospheric diffusion characteristics

    SciTech Connect

    Hiraga, Kunio; Omoto, Akira; Takahashi, Keiichi; Momoi, Kazuyoshi

    1994-12-31

    Although almost all of the thermal and nuclear power stations in Japan are located on the coastline to take advantage of seawater available to condense steam, offshore siting is one of the candidates for the future plant sitting. Figures developed by Pasquill-Gifford model has been conventionally utilized in analyzing atmospheric diffusion of gaseous effluent from power plants. However, there are limitations to apply this to offshore plants because these figures are based on inland diffusion experiments and this model does not specifically take into consideration the effects of thermal capacity of seawater, its surface roughness and so on. Even in the case of coastline sitting, atmospheric diffusion of gaseous effluent might be affected by atmospheric diffusion characteristics above seawater. With this background gaseous, diffusion experiments were conducted at one of TEPCo`s (Tokyo Electric Power Company) coastline power station and empirical formula to model atmospheric diffusion above seawater has been developed.

  6. Spin diffusion in disordered organic semiconductors

    NASA Astrophysics Data System (ADS)

    Li, Ling; Gao, Nan; Lu, Nianduan; Liu, Ming; Bässler, Heinz

    2015-12-01

    An analytical theory for spin diffusion in disordered organic semiconductors is derived. It is based on percolation theory and variable range hopping in a disordered energy landscape with a Gaussian density of states. It describes universally the dependence of the spin diffusion on temperature, carrier density, material disorder, magnetic field, and electric field at the arbitrary magnitude of the Hubbard energy of charge pairs. It is found that, compared to the spin transport carried by carriers hopping, the spin exchange will hinder the spin diffusion process at low carrier density, even under the condition of a weak electric field. Importantly, under the influence of a bias voltage, anomalous spreading of the spin packet will lead to an abnormal temperature dependence of the spin diffusion coefficient and diffusion length. This explains the recent experimental data for spin diffusion length observed in Alq3.

  7. Current diffusion in rail-gun conductors

    SciTech Connect

    Kerrisk, J.F.

    1982-06-01

    A method has been developed to analyze one- and two-dimensional, nonlinear current diffusion in rail-gun conductors. A nonlinear current-diffusion equation that accounts for the temperature dependence of electrical conductivity has been developed from Maxwell's equations. A finite-difference heat-transfer computer program was adapted to solve the current-diffusion and thermal-diffusion problems for rail-gun conductors in one and two dimensions. The nonlinear current-diffusion equation was also extended to account for the magnetic-field dependence of the magnetic permeability, thus allowing ferromagnetic materials to be considered. A one-dimensional finite-difference technique was developed for ferromagnetic materials. Two one-dimensional test problems that compare results with other analyses are discussed. A series of calculations of current density and rail temperature was done for various size rectangular rails. One analysis of current diffusion in a ferromagnetic material was also performed.

  8. Advanced diffusion studies with isotopically controlled materials

    SciTech Connect

    Bracht, Hartmut A.; Silvestri, Hughes H.; Haller, Eugene E.

    2004-11-14

    The use of enriched stable isotopes combined with modern epitaxial deposition and depth profiling techniques enables the preparation of material heterostructures, highly appropriate for self- and foreign-atom diffusion experiments. Over the past decade we have performed diffusion studies with isotopically enriched elemental and compound semiconductors. In the present paper we highlight our recent results and demonstrate that the use of isotopically enriched materials ushered in a new era in the study of diffusion in solids which yields greater insight into the properties of native defects and their roles in diffusion. Our approach of studying atomic diffusion is not limited to semiconductors and can be applied also to other material systems. Current areas of our research concern the diffusion in the silicon-germanium alloys and glassy materials such as silicon dioxide and ion conducting silicate glasses.

  9. Unstructured Polyhedral Mesh Thermal Radiation Diffusion

    SciTech Connect

    Palmer, T.S.; Zika, M.R.; Madsen, N.K.

    2000-07-27

    Unstructured mesh particle transport and diffusion methods are gaining wider acceptance as mesh generation, scientific visualization and linear solvers improve. This paper describes an algorithm that is currently being used in the KULL code at Lawrence Livermore National Laboratory to solve the radiative transfer equations. The algorithm employs a point-centered diffusion discretization on arbitrary polyhedral meshes in 3D. We present the results of a few test problems to illustrate the capabilities of the radiation diffusion module.

  10. Diffusion length and solar cell efficiency

    NASA Astrophysics Data System (ADS)

    Huber, D.; Wahlich, R.; Bachmaier, A.

    The diffusion length of the minority carriers of a solar cell defines the appropriate technology which should be applied for the solar cell fabrication. Back surface techniques only pay off if the diffusion length is long enough. Monocrystalline material with different lifetime killing defects was investigated and an experimental correlation between the diffusion length measured on the unprocessed wafer and the efficiency of the finished cell could be established.

  11. Relativistic diffusive motion in thermal electromagnetic fields

    NASA Astrophysics Data System (ADS)

    Haba, Z.

    2013-04-01

    We discuss relativistic dynamics in a random electromagnetic field which can be considered as a high temperature limit of the quantum electromagnetic field in a heat bath (cavity) moving with a uniform velocity w. We derive a diffusion approximation for the particle’s dynamics generalizing the diffusion of Schay and Dudley. It is shown that the Jüttner distribution is the equilibrium state of the diffusion.

  12. Modeling of hydrogen-air diffusion flame

    NASA Technical Reports Server (NTRS)

    Isaac, K. M.

    1988-01-01

    Work performed during the first six months of the project duration for NASA Grant (NAG-1-861) is reported. An analytical and computational study of opposed jet diffusion flame for the purpose of understanding the effects of contaminants in the reactants and thermal diffusion of light species on extinction and reignition of diffusion flames is in progress. The methodologies attempted so far are described.

  13. Diffusion processes in general relativistic radiating spheres

    SciTech Connect

    Barreto, W.; Herrera, L.; Santos, N.O.; Universidad Central de Venezuela, Caracas; Observatorio Nacional do Brasil, Rio de Janeiro )

    1989-09-01

    The influence of diffusion processes on the dynamics of general relativistic radiating spheres is systematically studied by means of two examples. Differences between the streaming-out limit and the diffusion limit are exhibited, for both models, through the evolution curves of dynamical variables. In particular it is shown the Bondi mass decreases, for both models, in the diffusion limit as compared with its value at the streaming-out regime. 15 refs.

  14. Diffusion in solid-Earth systems

    NASA Astrophysics Data System (ADS)

    Watson, E. Bruce; Baxter, Ethan F.

    2007-01-01

    Recent years have seen a rapid expansion in the acquisition and use of information on diffusive transport in phases relevant to the solid Earth (crystals, melts and fluids). Although far from complete, the data base on diffusion coefficients is now sufficiently large that broad constraints can be placed upon the length- and time scales of many natural transport phenomena in which diffusion plays a role. Conversely, observations of diffusion progress in specific natural samples can be used to extract time-temperature information for a variety of geologic and geochemical processes, ranging from sediment burial and crustal erosion to fluid-mediated reactions and biosignature retention. Despite this undeniable progress, several major challenges remain that largely define the frontiers of research in solid-Earth diffusion. Perhaps foremost among these is the need to address and understand the multi-scale, multi-path aspects of diffusion in many systems—a complication that is not limited to polyphase materials (individual mineral grains can exhibit clear indications of multi-path behavior even when visible evidence of such paths is lacking). Many other diffusion frontiers are linked in one way or another to this multi-scale issue; they include: diffusion of molecular H 2O and the effect of H species on diffusion in minerals and rocks; diffusive fractionation of multiple isotopes of a single element; diffusion at the extreme conditions of the deep Earth; reconciliation of observations from natural samples and laboratory studies; and development of theoretical approaches to 'predict' diffusion behavior in regions inaccessible to observation.

  15. String theory as a diffusing system

    NASA Astrophysics Data System (ADS)

    Calcagni, Gianluca; Nardelli, Giuseppe

    2010-02-01

    Recent results on the effective non-local dynamics of the tachyon mode of open string field theory (OSFT) show that approximate solutions can be constructed which obey the diffusion equation. We argue that this structure is inherited from the full theory, where it admits a universal formulation. In fact, all known exact OSFT solutions are superpositions of diffusing surface states. In particular, the diffusion equation is a spacetime manifestation of OSFT gauge symmetries.

  16. Reaction-diffusion waves in biology.

    PubMed

    Volpert, V; Petrovskii, S

    2009-12-01

    The theory of reaction-diffusion waves begins in the 1930s with the works in population dynamics, combustion theory and chemical kinetics. At the present time, it is a well developed area of research which includes qualitative properties of travelling waves for the scalar reaction-diffusion equation and for system of equations, complex nonlinear dynamics, numerous applications in physics, chemistry, biology, medicine. This paper reviews biological applications of reaction-diffusion waves. PMID:20416847

  17. Characterizing unsaturated diffusion in porous tuff gravel

    SciTech Connect

    Hu, Qinhong; Kneafsey, Timothy J.; Roberts, Jeffery J.; Tomutsa, Liviu; Wang, Joseph, S.Y.

    2003-11-12

    Evaluation of solute diffusion in unsaturated porous gravel is very important for investigations of contaminant transport and remediation, risk assessment, and waste disposal (for example, the potential high-level nuclear waste repository at Yucca Mountain, Nevada). For a porous aggregate medium such as granular tuff, the total water content is comprised of surface water and interior water. The surface water component (water film around grains and pendular water between the grain contacts) could serve as a predominant diffusion pathway. To investigate the extent to which surface water films and contact points affect solute diffusion in unsaturated gravel, we examined the configuration of water using x-ray computed tomography in partially saturated gravel, and made quantitative measurements of diffusion at multiple water contents using two different techniques. In the first, diffusion coefficients of potassium chloride in 2-4 mm granular tuff at multiple water contents were calculated from electrical conductivity measurements using the Nernst-Einstein equation. In the second, we used laser ablation with inductively coupled plasma-mass spectrometry to perform micro-scale mapping, allowing the measurement of diffusion coefficients for a mixture of chemical tracers for tuff cubes and tetrahedrons having two contact geometries (cube-cube and cube-tetrahedron). The x-ray computed tomography images show limited contact between grains, and this could hinder the pathways for diffusive transport. Experimental results show the critical role of surface water in controlling transport pathways and hence the magnitude of diffusion. Even with a bulk volumetric water content of 1.5%, the measured solute diffusion coefficient is as low as 1.5 x 10{sup -14} m{sup 2}/s for tuff gravel. Currently used diffusion models relating diffusion coefficients to total volumetric water content inadequately describe unsaturated diffusion behavior in porous gravel at very low water contents.

  18. Characterizing Unsaturated Diffusion in Porous Tuff Gravel

    SciTech Connect

    Hu, Q; Kneafsey, T J; Roberts, J J; Tomutsa, L; Wang, J S

    2003-11-12

    Evaluation of solute diffusion in unsaturated porous gravel is very important for investigations of contaminant transport and remediation, risk assessment, and waste disposal (e.g., the potential high-level nuclear waste repository at Yucca Mountain, Nevada). For a porous aggregate medium such as granular tuff, the total water content is comprised of surface water and interior water. The surface water component (water film around grains and pendular water between the grain contacts) could serve as a predominant diffusion pathway. To investigate the extent of surface water films and contact points affect solute diffusion in unsaturated gravel, we examined the configuration of water using x-ray computed tomography in partially saturated gravel, and made quantitative measurements of diffusion at multiple water contents using two different techniques. In the first, diffusion coefficients of potassium chloride in 2-4 mm granular tuff at multiple water contents are calculated from electrical conductivity measurements using the Nernst-Einstein equation. In the second, we used laser ablation with inductively coupled plasma-mass spectrometry to perform micro-scale mapping, allowing the measurement of diffusion coefficients for a mixture of chemical tracers for tuff cubes and tetrahedrons having two contact geometries (cube-cube and cube-tetrahedron). The x-ray computed tomography images show limited contact between grains, and this could significantly hinder the pathways for diffusive transport. Experimental results show the critical role of surface water in controlling transport pathways and hence the magnitude of diffusion. Even with a bulk volumetric water content of 1.5%, the measured solute diffusion coefficient is as low as 1.5 x 10{sup -14} m{sup 2}/s. Currently used diffusion models relating diffusion coefficients to total volumetric water content inadequately describe unsaturated diffusion behavior in porous gravel.

  19. Diffusions conditioned on occupation measures

    NASA Astrophysics Data System (ADS)

    Angeletti, Florian; Touchette, Hugo

    2016-02-01

    A Markov process fluctuating away from its typical behavior can be represented in the long-time limit by another Markov process, called the effective or driven process, having the same stationary states as the original process conditioned on the fluctuation observed. We construct here this driven process for diffusions spending an atypical fraction of their evolution in some region of state space, corresponding mathematically to stochastic differential equations conditioned on occupation measures. As an illustration, we consider the Langevin equation conditioned on staying for a fraction of time in different intervals of the real line, including the positive half-line which leads to a generalization of the Brownian meander problem. Other applications related to quasi-stationary distributions, metastable states, noisy chemical reactions, queues, and random walks are discussed.

  20. Diffuse Malignant Mesothelioma: A Review

    PubMed Central

    Rom, William N.; Lockey, James E.

    1982-01-01

    Diffuse malignant mesothelioma is a signal tumor of asbestos exposure. Mesothelioma incidence has been steadily rising during the past two decades, reflecting the increases in asbestos use during and following World War II. The onset of the disease follows exposure by 25 to 40 years. The dose-response relationship appears to be much lower than that for asbestosis or lung cancer—it is not known whether current levels of exposure will entail a risk for disease 30 years hence. There is no synergistic or additive interaction with smoking for this tumor. Current knowledge indicates that pleural plaques, per se, do not increase the risk for this tumor beyond that of the previous asbestos exposure alone. Durable fibers with high aspect ratios, especially amphiboles, are associated with experimental tumor induction. Treatment modalities including surgical procedures and chemotherapy with doxorubicin and 5-azacytidine offer prospects for palliation. ImagesFigure 1.Figure 2. PMID:6761970

  1. Coccidioidomycosis with diffuse miliary pneumonia.

    PubMed

    Sotello, David; Rivas, Marcella; Fuller, Audra; Mahmood, Tashfeen; Orellana-Barrios, Menfil; Nugent, Kenneth

    2016-01-01

    Coccidioidomycosis is a well-known infection in the southwestern United States, and its occurrence is becoming more frequent in endemic areas. This disease can have a significant economic and medical impact; therefore, accurate diagnosis is crucial. In conjunction with patient symptoms, residence in or travel to an endemic area is essential for diagnosis. Diagnosis is usually made with serology, culture, or biopsy and confirmed with DNA probe technology. Pulmonary disease is the most common presentation and is seen in almost 95% of all cases. One-half to two-thirds of all Coccidioides infections are asymptomatic or subclinical. Most pulmonary infections are self-limited and do not require treatment except in special populations. When treatment is warranted, itraconazole and fluconazole are frequently used. Diffuse miliary pneumonia is uncommon and is especially rare in immunocompetent patients. Herein we describe a rare presentation of miliary coccidioidomycosis in a nonimmunocompromised patient. PMID:26722164

  2. Word Diffusion and Climate Science

    PubMed Central

    Bentley, R. Alexander; Garnett, Philip; O'Brien, Michael J.; Brock, William A.

    2012-01-01

    As public and political debates often demonstrate, a substantial disjoint can exist between the findings of science and the impact it has on the public. Using climate-change science as a case example, we reconsider the role of scientists in the information-dissemination process, our hypothesis being that important keywords used in climate science follow “boom and bust” fashion cycles in public usage. Representing this public usage through extraordinary new data on word frequencies in books published up to the year 2008, we show that a classic two-parameter social-diffusion model closely fits the comings and goings of many keywords over generational or longer time scales. We suggest that the fashions of word usage contributes an empirical, possibly regular, correlate to the impact of climate science on society. PMID:23144839

  3. Multitask Diffusion Adaptation Over Networks

    NASA Astrophysics Data System (ADS)

    Chen, Jie; Richard, Cedric; Sayed, Ali H.

    2014-08-01

    Adaptive networks are suitable for decentralized inference tasks, e.g., to monitor complex natural phenomena. Recent research works have intensively studied distributed optimization problems in the case where the nodes have to estimate a single optimum parameter vector collaboratively. However, there are many important applications that are multitask-oriented in the sense that there are multiple optimum parameter vectors to be inferred simultaneously, in a collaborative manner, over the area covered by the network. In this paper, we employ diffusion strategies to develop distributed algorithms that address multitask problems by minimizing an appropriate mean-square error criterion with $\\ell_2$-regularization. The stability and convergence of the algorithm in the mean and in the mean-square sense is analyzed. Simulations are conducted to verify the theoretical findings, and to illustrate how the distributed strategy can be used in several useful applications related to spectral sensing, target localization, and hyperspectral data unmixing.

  4. [Tracheobronchoplasty for Severe Diffuse Tracheomalacia].

    PubMed

    Hoffmann, H; Gompelmann, D; Heußel, C P; Dienemann, H; Eberhardt, R

    2016-09-01

    Patients with diffuse airway instability due to tracheobronchomalacia or excessive dynamic airway collapse are typically highly symptomatic, with marked dyspnoea, recurrent bronchopulmonary infections and excruciating intractable cough. Silicone stents achieve immediate symptom control, but are - due to the typical complications associated with stent treatment - usually not an option for long-term treatment. The aim of surgical intervention is definitive stabilisation of the trachea and of both main bronchi by posterior splinting of the Paries membranaceus with a polypropylene mesh. This operation is an appropriate treatment option for patients with documented severe tracheobronchomalacia or excessive dynamic airway collapse and is ultimately the only therapy that can achieve permanent symptom control. The success of the operation, however, depends on many factors and requires close interdisciplinary collaboration. PMID:27607887

  5. Cooperation in Diffusive Spatial Games

    NASA Astrophysics Data System (ADS)

    Vainstein, Mendeli H.; Silva, Ana T. C.; Arenzon, Jeferson J.

    2007-05-01

    Random diffusion is shown to be an important mechanism on fostering cooperative behavior among simple agents (memoryless, unconditional cooperators or defectors) living on a spatially structured environment. In particular, under the Prisoner's Dilemma framework, when allowing the agents to move with the simple "always-move" rule, we find that cooperative behavior is not only possible but may even be enhanced. In addition, for a broad range of densities, mobile cooperators can more easily invade a population of mobile defectors, when compared with the fully viscous, immobile case. Thus, such simple mobility pattern may have played a fundamental role both in the onset and development of cooperative behavior, paving the way to more complex, individual and group, motility rules.

  6. Pb-Zn liquid metal diffusion

    NASA Technical Reports Server (NTRS)

    Pond, R. B., Sr.; Winter, J. M., Jr.

    1988-01-01

    The Lead-Zinc binary equilibrium system is currently being investigated. Ground based studies of this system were performed to examine the possibility of obtaining a couple which, after diffusion, could be examined continuously along the diffusion axis by quantitative metallography to determine the extent of diffusion. The specimens were analyzed by X-ray fluorescence in the scanning electron microscope to provide exact information on the chemical composition gradient. Two diffusion experiments were run simultaneously in the multipurpose furnace, each in its own isothermal cavity. Two flight samples, two flight backup samples, and two flight space samples were generated.

  7. Mechanism for hydrogen diffusion in amorphous silicon

    SciTech Connect

    Biswas, R.; Li, Q.; Pan, B.C.; Yoon, Y.

    1998-01-01

    Tight-binding molecular-dynamics calculations reveal a mechanism for hydrogen diffusion in hydrogenated amorphous silicon. Hydrogen diffuses through the network by successively bonding with nearby silicons and breaking their Si{endash}Si bonds. The diffusing hydrogen carries with it a newly created dangling bond. These intermediate transporting states are densely populated in the network, have lower energies than H at the center of stretched Si{endash}Si bonds, and can play a crucial role in hydrogen diffusion. {copyright} {ital 1998} {ital The American Physical Society}

  8. Modeling of hydrogen-air diffusion flame

    NASA Technical Reports Server (NTRS)

    Isaac, K. M.

    1989-01-01

    An analytical and computational study of opposed jet diffusion flame for the purpose of understanding the effects of contaminants in the reactants and thermal diffusion of light species on extinction and reignition of diffusion flames is in progress. The methodologies that have been attempted so far are described. Results using a simple, one-step reaction for the hydrogen-air counterflow diffusion flame are presented. These results show the correct trends in the profiles of chemical species and temperature. The extinction limit can be clearly seen in the plot of temperature vs. Damkohler number.

  9. Diffuse cloud chemistry. [in interstellar matter

    NASA Technical Reports Server (NTRS)

    Van Dishoeck, Ewine F.; Black, John H.

    1988-01-01

    The current status of models of diffuse interstellar clouds is reviewed. A detailed comparison of recent gas-phase steady-state models shows that both the physical conditions and the molecular abundances in diffuse clouds are still not fully understood. Alternative mechanisms are discussed and observational tests which may discriminate between the various models are suggested. Recent developments regarding the velocity structure of diffuse clouds are mentioned. Similarities and differences between the chemistries in diffuse clouds and those in translucent and high latitude clouds are pointed out.

  10. Biomimetic phantom for cardiac diffusion MRI

    PubMed Central

    Teh, Irvin; Zhou, Feng‐Lei; Hubbard Cristinacce, Penny L.; Parker, Geoffrey J.M.

    2015-01-01

    Purpose Diffusion magnetic resonance imaging (MRI) is increasingly used to characterize cardiac tissue microstructure, necessitating the use of physiologically relevant phantoms for methods development. Existing phantoms are generally simplistic and mostly simulate diffusion in the brain. Thus, there is a need for phantoms mimicking diffusion in cardiac tissue. Materials and Methods A biomimetic phantom composed of hollow microfibers generated using co‐electrospinning was developed to mimic myocardial diffusion properties and fiber and sheet orientations. Diffusion tensor imaging was carried out at monthly intervals over 4 months at 9.4T. 3D fiber tracking was performed using the phantom and compared with fiber tracking in an ex vivo rat heart. Results The mean apparent diffusion coefficient and fractional anisotropy of the phantom remained stable over the 4‐month period, with mean values of 7.53 ± 0.16 × 10‐4 mm2/s and 0.388 ± 0.007, respectively. Fiber tracking of the 1st and 3rd eigenvectors generated analogous results to the fiber and sheet‐normal direction respectively, found in the left ventricular myocardium. Conclusion A biomimetic phantom simulating diffusion in the heart was designed and built. This could aid development and validation of novel diffusion MRI methods for investigating cardiac microstructure, decrease the number of animals and patients needed for methods development, and improve quality control in longitudinal and multicenter cardiac diffusion MRI studies. J. MAGN. RESON. IMAGING 2016;43:594–600. PMID:26213152

  11. Fractional diffusion equations coupled by reaction terms

    NASA Astrophysics Data System (ADS)

    Lenzi, E. K.; Menechini Neto, R.; Tateishi, A. A.; Lenzi, M. K.; Ribeiro, H. V.

    2016-09-01

    We investigate the behavior for a set of fractional reaction-diffusion equations that extend the usual ones by the presence of spatial fractional derivatives of distributed order in the diffusive term. These equations are coupled via the reaction terms which may represent reversible or irreversible processes. For these equations, we find exact solutions and show that the spreading of the distributions is asymptotically governed by the same the long-tailed distribution. Furthermore, we observe that the coupling introduced by reaction terms creates an interplay between different diffusive regimes leading us to a rich class of behaviors related to anomalous diffusion.

  12. Wanted: Scalable Tracers for Diffusion Measurements

    PubMed Central

    2015-01-01

    Scalable tracers are potentially a useful tool to examine diffusion mechanisms and to predict diffusion coefficients, particularly for hindered diffusion in complex, heterogeneous, or crowded systems. Scalable tracers are defined as a series of tracers varying in size but with the same shape, structure, surface chemistry, deformability, and diffusion mechanism. Both chemical homology and constant dynamics are required. In particular, branching must not vary with size, and there must be no transition between ordinary diffusion and reptation. Measurements using scalable tracers yield the mean diffusion coefficient as a function of size alone; measurements using nonscalable tracers yield the variation due to differences in the other properties. Candidate scalable tracers are discussed for two-dimensional (2D) diffusion in membranes and three-dimensional diffusion in aqueous solutions. Correlations to predict the mean diffusion coefficient of globular biomolecules from molecular mass are reviewed briefly. Specific suggestions for the 3D case include the use of synthetic dendrimers or random hyperbranched polymers instead of dextran and the use of core–shell quantum dots. Another useful tool would be a series of scalable tracers varying in deformability alone, prepared by varying the density of crosslinking in a polymer to make say “reinforced Ficoll” or “reinforced hyperbranched polyglycerol.” PMID:25319586

  13. Point defects diffusion in $alpha;-Ti

    NASA Astrophysics Data System (ADS)

    Fernández, J. R.; Monti, A. M.; Pasianot, R. C.

    1996-04-01

    A research on the statics and dynamics of vacancies and self-interstitials in model α-Ti lattices is carried out by means of computer simulation techniques. A comprehensive study beginning with the development of an appropriate interatomic potential up to the final evaluation of the anisotropy of the self-diffusion by both vacancy and self-interstitial mechanisms is undertaken. Experimental results on self-diffusion in α-Ti single-crystals are analyzed within the framework of the calculated diffusion constants for a vacancy mechanism. A strongly dominating basal diffusion for self-interstitials is predicted.

  14. Silicon infrared diffuser for wireless communication

    NASA Astrophysics Data System (ADS)

    Massera, Ettore; Rea, Ilaria; Nasti, Ivana; Maddalena, Pasqualino; di Francia, Girolamo

    2006-09-01

    We show what we believe to be a novel way to use silicon in infrared radio communication as a suitable material for the realization of optical diffusers in the range of 850-1600 nm. A crystalline silicon wafer is made porous by means of electrochemical etching. The porous silicon produced is optically characterized, and measurements report a high reflectance in the band of interest. We also study the angular distribution of diffused radiation by the porous silicon surface at different angles of incident radiation. Measurements show that radiation diffuses in a quasi-Lambertian manner, confirming the good performance of this material as an incident radiation diffuser.

  15. Mechanism for diffusion induced grain boundary migration

    SciTech Connect

    Balluffi, R.W.; Cahn, J.W.

    1980-08-01

    Grain boundaries are found to migrate under certain conditions when solute atoms are diffused along them. This phenomenon, termed diffusion induced grain boundary migration (DIGM), has now been found in six systems. The observed phenomenon and empirical data are used to discard certain concepts for the driving force and the mechanism. A mechanism is proposed in which differences in the diffusion coefficients of the diffusing species along the grain boundary cause a self-sustaining climb of grain boundary dislocations and motion of their associated grain boundary steps.

  16. Modeling diffusion in foamed polymer nanocomposites.

    PubMed

    Ippalapalli, Sandeep; Ranaprathapan, A Dileep; Singh, Sachchida N; Harikrishnan, G

    2013-04-15

    Two-way multicomponent diffusion processes in polymeric nanocomposite foams, where the condensed phase is nanoscopically reinforced with impermeable fillers, are investigated. The diffusion process involves simultaneous outward permeation of the components of the dispersed gas phase and inward diffusion of atmospheric air. The transient variation in thermal conductivity of foam is used as the macroscopic property to track the compositional variations of the dispersed gases due to the diffusion process. In the continuum approach adopted, the unsteady-state diffusion process is combined with tortuosity theory. The simulations conducted at ambient temperature reveal distinct regimes of diffusion processes in the nanocomposite foams owing to the reduction in the gas-transport rate induced by nanofillers. Simulations at a higher temperature are also conducted and the predictions are compared with experimentally determined thermal conductivities under accelerated diffusion conditions for polyurethane foams reinforced with clay nanoplatelets of varying individual lamellar dimensions. Intermittent measurements of foam thermal conductivity are performed while the accelerated diffusion proceeded. The predictions under accelerated diffusion conditions show good agreement with experimentally measured thermal conductivities for nanocomposite foams reinforced with low and medium aspect-ratios fillers. The model shows higher deviations for foams with fillers that have a high aspect ratio.

  17. Phase diffusion in a chaotic pendulum

    SciTech Connect

    Blackburn, J.A.; Gro/nbech-Jensen, N.

    1996-04-01

    The rate of expansion of the phase coordinate for a harmonically driven pendulum is considered. The mean-squared displacement is found to grow as a linear function of time during chaotic motion, indicating deterministic diffusion. The diffusion coefficient can be significantly influenced by the proximity of a window containing a periodic solution. We find that diffusion associated with intermittent chaos can be described in terms of an interleaving of the diffusion properties of the separate modes taking part in the intermittency. {copyright} {ital 1996 The American Physical Society.}

  18. Self-Diffusion in Amorphous Silicon.

    PubMed

    Strauß, Florian; Dörrer, Lars; Geue, Thomas; Stahn, Jochen; Koutsioubas, Alexandros; Mattauch, Stefan; Schmidt, Harald

    2016-01-15

    The present Letter reports on self-diffusion in amorphous silicon. Experiments were done on ^{29}Si/^{nat}Si heterostructures using neutron reflectometry and secondary ion mass spectrometry. The diffusivities follow the Arrhenius law in the temperature range between 550 and 700 °C with an activation energy of (4.4±0.3)  eV. In comparison with single crystalline silicon the diffusivities are tremendously higher by 5 orders of magnitude at about 700 °C, which can be interpreted as the consequence of a high diffusion entropy. PMID:26824552

  19. Spectrum of fibrosing diffuse parenchymal lung disease.

    PubMed

    Morgenthau, Adam S; Padilla, Maria L

    2009-02-01

    The interstitial lung diseases are a heterogeneous group of disorders characterized by inflammation and/or fibrosis of the pulmonary interstitium. In 2002, the American Thoracic Society and the European Respiratory Society revised the classification of interstitial lung diseases and introduced the term diffuse parenchymal lung disease. The idiopathic interstitial pneumonias are a subtype of diffuse parenchymal lung disease. The idiopathic interstitial pneumonias are subdivided into usual interstitial pneumonia (with its clinical counterpart idiopathic interstitial pneumonia), nonspecific interstitial pneumonia, cryptogenic organizing pneumonia, acute interstitial pneumonia, desquamative interstitial pneumonia, respiratory bronchiolitis interstitial lung disease, and lymphocytic pneumonia. Sarcoidosis and hypersensitivity pneumonitis are the 2 most common granulomatous diffuse parenchymal lung diseases. Rheumatoid arthritis, systemic sclerosis, and dermatomyositis/polymyositis (causing antisynthetase syndrome) are diffuse parenchymal lung diseases of known association because these conditions are associated with connective tissue disease. Hermansky-Pudlak syndrome is a rare genetic diffuse parenchymal lung disease characterized by the clinical triad of pulmonary disease, oculocutaneous albinism, and bleeding diathesis. This review provides an overview of the chronic fibrosing diffuse parenchymal lung diseases. Its primary objective is to illuminate the clinical challenges encountered by clinicians who manage the diffuse parenchymal lung diseases regularly and to offer potential solutions to those challenges. Treatment for the diffuse parenchymal lung diseases is limited, and for many patients with end-stage disease, lung transplantation remains the best option. Although much has been learned about the diffuse parenchymal lung diseases during the past decade, research in these diseases is urgently needed. PMID:19170214

  20. Cloaking through cancellation of diffusive wave scattering

    NASA Astrophysics Data System (ADS)

    Farhat, M.; Chen, P. Y.; Guenneau, S.; Bağc, H.; Salama, K. N.; Alù, A.

    2016-08-01

    A new cloaking mechanism, which makes enclosed objects invisible to diffusive photon density waves, is proposed. First, diffusive scattering from a basic core-shell geometry, which represents the cloaked structure, is studied. The conditions of scattering cancellation in a quasi-static scattering regime are derived. These allow for tailoring the diffusivity constant of the shell enclosing the object so that the fields scattered from the shell and the object cancel each other. This means that the photon flow outside the cloak behaves as if the cloaked object were not present. Diffusive light invisibility may have potential applications in hiding hot spots in infrared thermography or tissue imaging.

  1. Diffuse hyperplastic oncocytosis of the parotid gland.

    PubMed

    Loreti, A; Sturla, M; Gentileschi, S; Bracaglia, R; Prat, Y; Fadda, G; Farallo, E

    2002-03-01

    Oncocytic tumours rarely affect the major salivary glands, accounting for less than 1% of all salivary-gland tumours. The World Health Organisation classification groups these tumours into three principal types: diffuse oncocytosis, focal adenomatous oncocytic hyperplasia and oncocytoma. Diffuse hyperplastic oncocytosis is the rarest lesion: only six cases have been previously reported in the literature. This condition of putative hyperplastic pathogenesis follows a benign course, whereas oncocytomas may recur after excision. No metastatic dissemination or recurrence of diffuse hyperplastic oncocytosis has been reported. We present and discuss a new case of diffuse hyperplastic oncocytosis of the parotid gland.

  2. Rare earth element diffusion in apatite

    NASA Astrophysics Data System (ADS)

    Cherniak, D. J.

    2000-11-01

    Diffusion of rare earth elements (REEs) in natural and synthetic fluorapatite has been characterized under anhydrous conditions. Three types of experiments were run. In the first set of experiments, Sm was introduced into the apatite by means of ion implantation, with diffusivities extracted through measurement of the "relaxation" of the implanted profile after diffusion anneals. The second group consisted of "in diffusion" experiments, in which apatite was immersed in reservoirs of synthetic REE apatite analogs of various compositions. The final set of experiments was "out-diffusion" experiments run on synthetic Nd-doped apatite immersed in a reservoir of synthetic (undoped) fluorapatite. REE depth profiles in all cases were measured with Rutherford Backscattering Spectrometry. Diffusion rates for the REE vary significantly among these sets of experiments. For the ion-implantation experiments, the following Arrhenius relation was obtained for Sm, over the temperature range 750°C to 1100°C: D imp=6.3×10-7exp(-298±17 kJ/mol/RT) m2/s Diffusion of a series of REE, from light to heavy, was investigated in the "in-diffusion" experiments. Over the temperature range 800°C to 1250°C, the following Arrhenius relations are obtained for La, Nd, Dy, and Yb, for in-diffusion experiments using REE silicate oxyapatite sources: D La=2.6×10-7exp(-324±9 kJ/mol/RT) m2/sD Nd=2.4×10-6exp(-348±13 kJ/mol/RT) m2/sD Dy=9.7×10-7exp(-340±11 kJ/mol/RT) m2/sD Yb=1.3×10-8exp(-292±23 kJ/mol/RT) m2/s Diffusivities of the REE in these "in-diffusion" experiments are all quite similar, suggesting little difference in diffusion rates in apatite with increasing ionic radii of the REEs. The "out-diffusion" experiments on the Nd-doped synthetic apatite, over the temperature range 950°C to 1400°C, yield the Arrhenius law: D out=9.3×10-6exp(-392±31 kJ/mol/RT) m2/s The differences in REE diffusion among these three sets of experiments (i.e., ion implantation, in-diffusion, and out-diffusion

  3. Diffusion tensor imaging suggests extrapontine extension of pediatric diffuse intrinsic pontine gliomas

    PubMed Central

    Wagner, Matthias W.; Bell, W. Robert; Kern, Jason; Bosemani, Thangamadhan; Mhlanga, Joyce; Carson, Kathryn A.; Cohen, Kenneth J.; Raabe, Eric H.; Rodriguez, Fausto; Huisman, Thierry A.G.M.; Poretti, Andrea

    2016-01-01

    Purpose To apply DTI to detect early extrapontine extension of pediatric diffuse intrinsic pontine glioma along the corticospinal tracts. Methods In children with diffuse intrinsic pontine glioma, low-grade brainstem glioma, and age-matched controls, DTI metrics were measured in the posterior limb of the internal capsule and posterior centrum semiovale. Histological examination was available in one patient. Results 6 diffuse intrinsic pontine glioma, 8 low-grade brainstem glioma, and two groups of 25 controls were included. In diffuse intrinsic pontine glioma compared to controls, fractional anisotropy was lower in the bilateral posterior limb of the internal capsule, axial diffusivity was lower in the bilateral posterior centrum semiovale and posterior limb of the internal capsule, while radial diffusivity was higher in the bilateral posterior limb of the internal capsule. No significant differences were found between low-grade brainstem glioma and controls. In diffuse intrinsic pontine glioma compared to low-grade brainstem glioma, axial diffusivity was lower in the bilateral posterior limb of the internal capsule. Histological examination in one child showed tumor cells in the posterior limb of the internal capsule. Conclusion Reduction in fractional anisotropy and axial diffusivity and increase in radial diffusivity in diffuse intrinsic pontine glioma may reflect tumor extension along the corticospinal tracts as shown by histology. DTI may detect early extrapontine tumor extension in diffuse intrinsic pontine glioma before it becomes apparent on conventional MRI sequences. PMID:26971411

  4. Molecular Diffusion Coefficients: Experimental Determination and Demonstration.

    ERIC Educational Resources Information Center

    Fate, Gwendolyn; Lynn, David G.

    1990-01-01

    Presented are laboratory methods which allow the demonstration and determination of the diffusion coefficients of compounds ranging in size from water to small proteins. Included are the procedures involving the use of a spectrometer, UV cell, triterated agar, and oxygen diffusion. Results including quantification are described. (CW)

  5. Particle Diffusion in an Inhomogeneous Medium

    ERIC Educational Resources Information Center

    Bringuier, E.

    2011-01-01

    This paper is an elementary introduction to particle diffusion in a medium where the coefficient of diffusion varies with position. The introduction is aimed at third-year university courses. We start from a simple model of particles hopping on a discrete lattice, in one or more dimensions, and then take the continuous-space limit so as to obtain…

  6. Finite-difference schemes for anisotropic diffusion

    SciTech Connect

    Es, Bram van; Koren, Barry; Blank, Hugo J. de

    2014-09-01

    In fusion plasmas diffusion tensors are extremely anisotropic due to the high temperature and large magnetic field strength. This causes diffusion, heat conduction, and viscous momentum loss, to effectively be aligned with the magnetic field lines. This alignment leads to different values for the respective diffusive coefficients in the magnetic field direction and in the perpendicular direction, to the extent that heat diffusion coefficients can be up to 10{sup 12} times larger in the parallel direction than in the perpendicular direction. This anisotropy puts stringent requirements on the numerical methods used to approximate the MHD-equations since any misalignment of the grid may cause the perpendicular diffusion to be polluted by the numerical error in approximating the parallel diffusion. Currently the common approach is to apply magnetic field-aligned coordinates, an approach that automatically takes care of the directionality of the diffusive coefficients. This approach runs into problems at x-points and at points where there is magnetic re-connection, since this causes local non-alignment. It is therefore useful to consider numerical schemes that are tolerant to the misalignment of the grid with the magnetic field lines, both to improve existing methods and to help open the possibility of applying regular non-aligned grids. To investigate this, in this paper several discretization schemes are developed and applied to the anisotropic heat diffusion equation on a non-aligned grid.

  7. NEEDED RESEARCH ON DIFFUSION WITHIN EDUCATIONAL ORGANIZATIONS.

    ERIC Educational Resources Information Center

    JAIN, NEMI C.; ROGERS, EVERETT M.

    IN SPITE OF THE VOLUME OF RESEARCH ATTENTION DEVOTED TO THE DIFFUSION OF INNOVATIONS, RELATIVELY LITTLE EMPHASIS HAS BEEN PLACED UPON DIFFUSION WITHIN ORGANIZATIONAL STRUCTURES. METHODOLOGICALLY, RELATIONAL ANALYSIS IN WHICH THE UNIT OF ANALYSIS IS A TWO-PERSON INTERACTING PAIR, A MULTIPLE PERSON COMMUNICATION CHAIN, OR CLIQUES OR SUBSYSTEMS IS…

  8. News Diffusion after the Reagan Shooting.

    ERIC Educational Resources Information Center

    Bantz, Charles R.; And Others

    1983-01-01

    Provides additional evidence on the role interpersonal communication plays in the diffusion of news about crisis events. Adds information about the rapidity of such diffusion, daily routine and first source, demographic differences and communicative behavior/personal reactions, and possible effects of research methods. (PD)

  9. [Study of multicomponent diffusion and transport phenomena

    SciTech Connect

    Not Available

    1993-01-01

    The major activities in this period are the percolation threshold in electronic conduction in [beta]-alumina type solid electrolytes, mixed alkali effects in ion conducting binary glasses, chemical diffusion problems, semiconductors, and relaxation process in diffusion. The last one constitutes the recent progress.

  10. Diffusion of silicon in crystalline germanium

    SciTech Connect

    Silvestri, H.H.; Bracht, H.; Hansen, J. Lundsgaard; Larsen, A.Nylandsted; Haller, E.E.

    2005-06-06

    We report the determination of the diffusion coefficient of Si in crystalline Ge over the temperature range of 550 to 900 C. A molecular beam epitaxy (MBE) grown buried Si layer in an epitaxial Ge layer on a crystalline Ge substrate was used as the source for the diffusion experiments. For samples annealed at temperatures above 700 C, a 50 nm thick SiO{sub 2} cap layer was deposited to prevent decomposition of the Ge surface. We found the temperature dependence of the diffusion coefficient to be described by a single activation energy (3.32 eV) and pre-factor (38 cm{sup 2}/s) over the entire temperature range studied. The diffusion of the isovalent Si in Ge is slower than Ge self-diffusion over the full temperature range and reveals an activation enthalpy which is higher than that of self-diffusion. This points to a reduced interaction potential between the Si atom and the native defect mediating the diffusion process. For Si, which is smaller in size than the Ge self-atom, a reduced interaction is expected for a Si-vacancy (Si-V{sub Ge}) pair. Therefore we conclude that Si diffuses in Ge via the vacancy mechanism.

  11. Diffusion mediated localization on membrane surfaces

    NASA Technical Reports Server (NTRS)

    Weaver, D. L.

    1982-01-01

    Using the model of a cell membrane of a spherical surface in which membrane components may diffuse, the rate of localization due to trapping under diffusion control has been estimated by computing an analytical expression for the mean trapping time including the possibilities of a trapping probability less than one and/or the establishment of an equilibrium at the trap boundary.

  12. Undergraduate Laboratory Module on Skin Diffusion

    ERIC Educational Resources Information Center

    Norman, James J.; Andrews, Samantha N.; Prausnitz, Mark R.

    2011-01-01

    To introduce students to an application of chemical engineering directly related to human health, we developed an experiment for the unit operations laboratory at Georgia Tech examining diffusion across cadaver skin in the context of transdermal drug delivery. In this laboratory module, students prepare mouse skin samples, set up diffusion cells…

  13. Models to assess perfume diffusion from skin.

    PubMed

    Schwarzenbach, R; Bertschi, L

    2001-04-01

    Temperature, fragrance concentration on the skin and power of ventilation have been determined as crucial parameters in fragrance diffusion from skin. A tool has been developed to simulate perfume diffusion from skin over time, allowing headspace analysis and fragrance profile assessments in a highly reproducible way.

  14. Diffusion and scattering in multifractal clouds

    SciTech Connect

    Lovejoy, S.; Schertzer, D.; Waston, B.

    1996-04-01

    This paper describes investigations of radiative properties of multifractal clouds using two different approaches. In the first, diffusion is considered by examining the scaling properties of one dimensional random walks on media with multifractal diffusivities. The second approach considers the scattering statistics associated with radiative transport.

  15. Diffusion of Salt in Tap Water

    ERIC Educational Resources Information Center

    Booth, C.; And Others

    1978-01-01

    A simple experiment is described to measure the diffusion coefficient of a solute in a fluid. Laboratory-made floats are used to monitor the density changes associated with diffusion behavior. The experiment is ideally suited for undergraduate project work. (BB)

  16. Primary diffuse leptomeningeal gliomatosis in 2 dogs

    PubMed Central

    Canal, Sara; Bernardini, Marco; Pavone, Silvia; Mandara, Maria T.

    2013-01-01

    Clinical, neuroimaging, and neuropathological findings of 2 cases of canine primary diffuse leptomeningeal gliomatosis are described. Magnetic resonance imaging and histopathological examination of the brain revealed diffuse leptomeningeal alterations with no parenchymal involvement. These cases share many similarities with the same disease in humans. PMID:24179244

  17. Fluid dynamics of double diffusive systems

    SciTech Connect

    Koseff, J.R.

    1989-04-07

    A study of mixing processes in doubly diffusive systems is being conducted. Continuous gradients of two diffusing components (heat and salinity in our case) are being used as initial conditions, and forcing is introduced by lateral heating and surface shear. The goals of the proposed work include: (1) quantification of the effects of finite amplitude disturbances on stable, double diffusive systems, particularly with respect to lateral heating, (2) development of an improved understanding of the physical phenomena present in wind-driven shear flows in double diffusive stratified environments, (3) increasing our knowledge-base on turbulent flow in stratified environments and how to represent it, and (4) formulation of a numerical code for such flows. The work is being carried out in an experimental facility which is located in the Stanford Environmental Fluid Mechanics Laboratory, and on laboratory minicomputers and CRAY computers. In particular we are focusing on the following key issues: (1) the formation and propagation of double diffusive intrusions away from a heated wall and the effects of lateral heating on the double diffusive system; (2) the interaction between the double diffusively influenced fluxes and the turbulence induced fluxes; (3) the measurement of heat and mass fluxes; and (4) the influence of double diffusive gradients on mixed layer deepening. 1 fig.

  18. DIFFUSE RADIO EMISSION IN ABELL 754

    SciTech Connect

    Kale, Ruta; Dwarakanath, K. S. E-mail: dwaraka@rri.res.in

    2009-07-10

    We present a low-frequency study of the diffuse radio emission in the galaxy cluster A754. We present a new 150 MHz image of the galaxy cluster A754 made with the Giant Metrewave Radio Telescope and discuss the detection of four diffuse features. We compare the 150 MHz image with the images at 74, 330, and 1363 MHz; one new diffuse feature is detected. The flux density upper limits at 330 and 1363 MHz imply a synchrotron spectral index, {alpha}>2 (S {proportional_to} {nu}{sup -{alpha}}), for the new feature. The 'west relic' detected at 74 MHz is not detected at 150 MHz and is thus consistent with its nondetection at 1363 MHz and 330 MHz. Integrated spectra of all the diffuse features are presented. The fourth diffuse feature is located along the proposed merger axis in A754 and 0.7 Mpc away from the peak of X-ray emission; we refer to it as a relic. We have made use of the framework of the adiabatic compression model to obtain spectra. We show that the spectrum of the fourth diffuse feature is consistent with that of a cocoon of a radio galaxy lurking for about 9 x 10{sup 7} yr; no shock compression is required. The other three diffuse emission have spectra steeper than 1.5 and could be cocoons lurking for longer time. We discuss other possibilities such as shocks and turbulent reacceleration being responsible for the diffuse emission in A754.

  19. Isotopic fractionation by diffusion in groundwater

    NASA Astrophysics Data System (ADS)

    Labolle, Eric M.; Fogg, Graham E.; Eweis, Juana B.; Gravner, Janko; Leaist, Derek G.

    2008-07-01

    During the last decade, isotopic fractionation has gained acceptance as an indicator of microbiological and chemical transformations of contaminants in groundwater. These transformation processes typically favor isotopically light, compared to isotopically heavy, contaminants, resulting in enrichment of the latter in the residual aqueous phase. In these isotope applications, it has been generally presumed that physical transport processes in groundwater have a negligible effect on isotopic enrichment. It is well known, however, that aqueous phase diffusion generally proceeds faster for isotopically light, compared to isotopically heavy, solute molecules, often resulting in isotopic fractionation in groundwater. This paper considers the potential for isotopic fractionation during transport in groundwater resulting from minute isotopic effects on aqueous diffusion coefficients. Analyses of transport in heterogeneous systems delimit the viable range of isotopic fractionation by diffusion in groundwater. Results show that diffusion can result in similar degrees of depletion and enrichment of isotopically heavy solutes during transport in heterogeneous systems with significant diffusion rate-limited mass transfer between fast- and slow-flow zones. Additional analyses and examples explore conditions that attenuate the development of significant fractionation. Examples are presented for 13C methyl tertiary butyl ether and deuterated and nondeuterated isopropanol and tertiary butyl alcohol using aqueous diffusion coefficients measured by the Taylor dispersion method with refractive index profiling as a part of this study. Examples elucidate the potential for diffusive fractionation as a confounder in isotope applications and emphasize the importance of hydrogeologic analysis for assessing the role of diffusive fractionation in isotope applications at contaminant field sites.

  20. Neoclassical diffusion in a turbulent plasma

    SciTech Connect

    Yushmanov, P. . Inst. Atomnoj Ehnergii Texas Univ., Austin, TX . Inst. for Fusion Studies)

    1991-11-01

    This work describes a new approach to plasma transport where the toroidal drift motion is considered as a perturbation to the fluctuating velocity. Percolation theory is used to determine the scaling of the diffusion coefficient. Several neoclassical phenomena should persist even when diffusion is enhanced from neoclassical predictions. Numerical simulation results support the theoretical scaling arguments.