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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 the middle atmosphere

    NASA Technical Reports Server (NTRS)

    Tzur, I.; Roble, R. G.

    1984-01-01

    In the middle atmosphere above 60 km, the electron concentration increases with altitude, reaching values of 10 to the 10th per cu m in the daytime ionospheric E region near 100 km. The electrons are more mobile than the ions and diffuse more rapidly through the neutral atmosphere. The electron diffusion polarizes the medium, causing an electric field to develop that acts to retard the electron diffusion and enhance the conduction current of ions. A global zonally averaged numerical model of atmosheric electricity from the ground to 100 km is used to examine the effect of ambipolar diffusion and the earth's geomagnetic field on the currents and fields in the middle atmosphere. The results show that above about 65 km, ambipolar diffusion generates local electric fields and conduction currents that balance electron diffusion currents. The electric fields and conduction currents are a few orders of magnitude larger than the vertical fields and currents calculated from the downward mapping of the ionospheric potential without taking electron diffusion into account. Ambipolar diffusion does not alter the total current flowing in the global circuit. It is a local effect where enhanced conduction currens flow to balance the electron diffusion current.

  3. TRACING TURBULENT AMBIPOLAR DIFFUSION IN MOLECULAR CLOUDS

    SciTech Connect

    Li Huabai; Houde, Martin; Lai Shihping; Sridharan, T. K.

    2010-08-01

    Though flux freezing is a good approximation frequently assumed for molecular clouds, ambipolar diffusion (AD) is inevitable at certain scales. The scale at which AD sets in can be a crucial parameter for turbulence and the star formation process. However, both observation and simulation of AD are very challenging and our knowledge of it is very limited. We recently proposed that the difference between ion and neutral velocity spectra is a signature of turbulent AD and can be used to estimate the AD scales and magnetic field strengths. Here, we present observational evidence showing that this difference between the velocity dispersions from coexistent ions and neutrals is indeed correlated with magnetic field strength.

  4. AMBIPOLAR DIFFUSION HEATING IN TURBULENT SYSTEMS

    SciTech Connect

    Li, Pak Shing; Myers, Andrew; McKee, Christopher F. E-mail: atmyers@berkeley.edu

    2012-11-20

    The temperature of the gas in molecular clouds is a key determinant of the characteristic mass of star formation. Ambipolar diffusion (AD) is considered one of the most important heating mechanisms in weakly ionized molecular clouds. In this work, we study the AD heating rate using two-fluid turbulence simulations and compare it with the overall heating rate due to turbulent dissipation. We find that for observed molecular clouds, which typically have Alfven Mach numbers of {approx}1 and AD Reynolds numbers of {approx}20, about 70% of the total turbulent dissipation is in the form of AD heating. AD has an important effect on the length scale where energy is dissipated: when AD heating is strong, most of the energy in the cascade is removed by ion-neutral drift, with a comparatively small amount of energy making it down to small scales. We derive a relation for the AD heating rate that describes the results of our simulations to within a factor of two. Turbulent dissipation, including AD heating, is generally less important than cosmic-ray heating in molecular clouds, although there is substantial scatter in both.

  5. Turbulent energy dissipation and intermittency in ambipolar diffusion magnetohydrodynamics

    NASA Astrophysics Data System (ADS)

    Momferratos, G.; Lesaffre, P.; Falgarone, E.; Pineau des Forêts, G.

    2014-09-01

    The dissipation of kinetic and magnetic energy in the interstellar medium (ISM) can proceed through viscous, Ohmic or ambipolar diffusion (AD). It occurs at very small scales compared to the scales at which energy is presumed to be injected. This localized heating may impact the ISM evolution but also its chemistry, thus providing observable features. Here, we perform 3D spectral simulations of decaying magnetohydrodynamic turbulence including the effects of AD. We find that the AD heating power spectrum peaks at scales in the inertial range, due to a strong alignment of the magnetic and current vectors in the dissipative range. AD affects much greater scales than the AD scale predicted by dimensional analysis. We find that energy dissipation is highly concentrated on thin sheets. Its probability density function follows a lognormal law with a power-law tail which hints at intermittency, a property which we quantify by use of structure function exponents. Finally, we extract structures of high dissipation, defined as connected sets of points where the total dissipation is most intense and we measure the scaling exponents of their geometric and dynamical characteristics: the inclusion of AD favours small sizes in the dissipative range.

  6. A discussion on the assumption of ambipolar diffusion of meteor trails in the Earth's upper atmosphere

    NASA Astrophysics Data System (ADS)

    Kumar, Karanam Kishore; Subrahmanyam, Kandula Venkata

    2012-09-01

    For the first time, height profiles of meteor trail decay time due to the ambipolar diffusion process are estimated using temperature and pressure measurements by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on-board Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite. The comparison of the meteor trail decay time measured by a meteor radar over Thumba (8?5 N, 77°E) and SABER offered very valuable insights into the meteor trail decay processes and also provided much needed validation for assumption of ambipolar diffusion of meteor trails. It is observed that the assumption of ambipolar diffusion is valid in the height region of 90-96 km only where both SABER and radar measurements show excellent agreement in meteor trail decay time. The present analysis also shows that there are other processes which govern the meteor trail decay in the 80-90 km region, where large deviations are found between radar and SABER measurements. The differences between the SABER- and radar-observed decay times are quantified, and the processes responsible for the observed differences are also discussed extensively in the light of present understanding. The important outcome of the present study is the validation of assumption on ambipolar diffusivity of the meteor trails, which has significant implications in estimating the temperature using meteor trail decay time.

  7. Ambipolar Diffusion and Far-Infrared Polarization from the Galactic Circumnuclear Disk

    NASA Astrophysics Data System (ADS)

    Desch, S. J.; Roberge, W. G.

    1997-02-01

    We describe an implicit prediction of the accretion disk models constructed by Wardle & Königl for the circumnuclear disk (CND) of gas and dust near the Galactic center: supersonic ambipolar diffusion, an essential dynamical ingredient of the Wardle-Königl disks, will cause the alignment of dust grains because of a process described by Roberge, Hanany, & Messinger. We calculate synthetic maps of the polarized thermal emission which would be caused by ambipolar alignment in the preferred Wardle-Königl model. Our maps are in reasonable agreement with 100 μm polarimetry of the CND if we assume that the grains have shapes similar to those of grains in nearby molecular clouds and that the CND contains a disordered magnetic field in energy equipartition with its ordered field.

  8. 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.

  9. Effect of boundary conditions on the character of ambipolar diffusion in electrolytes.

    PubMed

    Chikina, I; Shikin, V B; Varlamov, A A

    2015-07-01

    We discuss the details of ambipolar relaxation of the electric field in liquid asymmetric electrolytes to its stationary value. It is demonstrated that the account for finite boundary conditions modifies the existing concepts of this diffusion process. In particular, we succeeded to suggest a qualitatively correct explanation of the observed distribution of the electric fields over the bulk of the cuvette and its nonmonotonic behavior in measurements on the finite-size cuvette. We analyze the conditions of such an anomaly at the intermediate stages of the relaxation process. PMID:26274165

  10. Effect of boundary conditions on the character of ambipolar diffusion in electrolytes

    NASA Astrophysics Data System (ADS)

    Chikina, I.; Shikin, V. B.; Varlamov, A. A.

    2015-07-01

    We discuss the details of ambipolar relaxation of the electric field in liquid asymmetric electrolytes to its stationary value. It is demonstrated that the account for finite boundary conditions modifies the existing concepts of this diffusion process. In particular, we succeeded to suggest a qualitatively correct explanation of the observed distribution of the electric fields over the bulk of the cuvette and its nonmonotonic behavior in measurements on the finite-size cuvette. We analyze the conditions of such an anomaly at the intermediate stages of the relaxation process.

  11. 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.

  12. 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

  13. 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

  14. THE EFFECT OF MAGNETIC FIELDS AND AMBIPOLAR DIFFUSION ON CORE MASS FUNCTIONS

    SciTech Connect

    Bailey, Nicole D.; Basu, Shantanu E-mail: basu@uwo.ca

    2013-03-20

    Linear analysis of the formation of protostellar cores in planar magnetic interstellar clouds yields information about length scales involved in star formation. Combining these length scales with various distributions of other environmental variables (i.e., column density and mass-to-flux ratio) and applying Monte Carlo methods allow us to produce synthetic core mass functions (CMFs) for different environmental conditions. Our analysis shows that the shape of the CMF is directly dependent on the physical conditions of the cloud. Specifically, magnetic fields act to broaden the mass function and develop a high-mass tail while ambipolar diffusion will truncate this high-mass tail. In addition, we analyze the effect of small number statistics on the shape and high-mass slope of the synthetic CMFs. We find that observed CMFs are severely statistically limited, which has a profound effect on the derived slope for the high-mass tail.

  15. 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.

  16. Midnight ionosphere collapse at Arecibo and its relationship to the neutral wind, electric field, and ambipolar diffusion

    NASA Astrophysics Data System (ADS)

    Gong, Yun; Zhou, Qihou; Zhang, Shaodong; Aponte, Nestor; Sulzer, Michael; Gonzalez, Sixto

    2012-08-01

    We report the analysis of "midnight collapse," a large drop in the F-layer peak height (HmF2) around midnight, observed at Arecibo during Jan. 14-22, 2010. During the nine nights of observations, the first four nights (Jan. 14-17) exhibited modest drops in HmF2 while the last five nights (Jan. 18-22) showed more severe drops. We examine the roles played by the meridional wind, electric field, and ambipolar diffusion in driving the vertical ion motion. The collapse process can be classified into three stages: preconditioning, initial descent, and sustained descent. Severe collapses occur when HmF2 is preconditioned high prior to the collapse. Ambipolar diffusion is most important during the initial descent. Neutral wind and electric field are responsible for sustaining the collapse. During Jan. 18-22, HmF2 was pushed high by the neutral wind before the collapse started. Neutral wind and electric field were in phase during the sustained severe collapses. The diurnal tide of the meridional wind provided the general condition for the collapses. The terdiurnal tide was most important to cause the difference between the two periods in our observation. Previous studies largely emphasized meridional wind being the dominant mechanism causing midnight collapse. Our study suggests that electric field and ambipolar diffusion also play an important role and the former can be the most dominant factor in some cases.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. Direct measurement of ambipolar diffusion in bulk silicon by ultrafast infrared imaging of laser-induced microplasmas

    NASA Astrophysics Data System (ADS)

    Mouskeftaras, Alexandros; Chanal, Margaux; Chambonneau, Maxime; Clady, Raphaël; Utéza, Olivier; Grojo, David

    2016-01-01

    Carrier kinetics in the density range of N = 10 17 - 10 20 cm - 3 is investigated inside the bulk of crystalline silicon. Most conventional experimental techniques used to study carrier mobility are indirect and lack sensitivity because of charging effects and recombination on the surface. An all optical technique is used to overcome these obstacles. By focusing 1.3-μm femtosecond laser pulses in the volume, we inject an initial free-carrier population by two-photon absorption. Then, we use pump-and-probe infrared microscopy as a tool to obtain simultaneous measurements of the carrier diffusion and recombination dynamics in a microscale region deep inside the material. The rate equation model is used to simulate our experimental results. We report a constant ambipolar diffusion coefficient D a of 2.5 cm 2 s - 1 and an effective carrier lifetime τ eff of 2.5 ns at room temperature. A discussion on our findings at these high-injection levels is presented.

  2. Influence of nonideality of semiconductor plasma on the ambipolar diffusion of ionized impurity

    SciTech Connect

    Vasilevskii, M.I.; Murav'ev, V.A.; Panteleev, V.A. )

    1988-07-01

    Numerous works have been devoted to taking account of the internal electric field in Fick's law, describing the diffusion of ionizational impurity. Doubts have also been considered on the basis that the current-carrier gas screens the ions, which reduces the force acting on them. In this present work, systematic consideration of this problem is attempted, on the basis of the principles of nonequilibrium thermodynamics.

  3. 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.

  4. 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.

  5. Achieving an intense enough maintenance electric field in a low-pressure discharge sustained by a microwave field under ambipolar diffusion regime such that periodic parametric instabilities are generated

    NASA Astrophysics Data System (ADS)

    Moisan, M.; Nowakowska, H.

    2015-11-01

    The intensity of the maintenance electric field of a given discharge is one of its internal parameters. Under ambipolar diffusion conditions, it is almost exclusively set by particle losses, which are related to the dimensions of the discharge vessel and to the gas pressure, and ultimately are determined by the electron energy distribution function. For instance, raising the density of microwave power absorbed in a discharge tube essentially increases the electron density without much increasing the amplitude of the maintenance E-field. To raise the intensity of this E-field in such a case, one needs to reduce the volume into which electromagnetic power is absorbed relative to the diffusion volume, i.e. the volume within which electrons transfer their power through collisions with heavy particles. To show this point, we consider a power balance based on the power lost per electron through collisions with heavy particles, θ L, to the power absorbed (over a period of the microwave field) per electron in the discharge, θ A. The power θ A, which depends on E02 , the square of the amplitude (intensity) of the maintenance electric field, adjusts to compensate for the power lost θ L. The analysis presented is achieved for a particular microwave discharge configuration that is known to provide an intense E 0-field, which means x  ⩾  λ De, where x is the oscillation amplitude of electrons in the E 0-field and λ De the electron Debye length. Such a condition allows one to observe periodic parametric instabilities at, or close to, the electron-plasma frequency f pe and at their corresponding ion-plasma frequency f pi, these oscillations being caused by the simultaneous propagation of an electron-plasma wave and an ion-plasma wave in the discharge as a result of an applied ‘pump’ power, which also sustains the discharge. A 2D hydrodynamic calculation of the specific plasma discharge system is performed, which yields the value of the x/λ De ratio in

  6. 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.

  7. 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

  8. 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. PMID:25329532

  9. 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

  10. Ambipolar magnetic fluctuation-induced heat transport in toroidal devices

    SciTech Connect

    Terry, P.W.; Fiksel, G.; Ji, H.; Almagri, A.F.; Cekic, M.; Den Hartog, D.J.; Diamond, P.H.; Prager, S.C.; Sarff, J.S.; Shen, W.; Stoneking, M.; Ware, A.S.

    1996-05-01

    The total magnetic fluctuation-induced electron thermal flux has been determined in the Madison Symmetric Torus (MST) reversed-field pinch [Fusion Technol. {bold 19}, 131 (1991)] from the measured correlation of the heat flux along perturbed fields with the radial component of the perturbed field. In the edge region the total flux is convective and intrinsically ambipolar constrained, as evidenced by the magnitude of the thermal diffusivity, which is well approximated by the product of ion thermal velocity and the magnetic diffusivity. A self-consistent theory is formulated and shown to reproduce the experimental results, provided nonlinear charge aggregation in streaming electrons is accounted for in the theory. For general toroidal configurations, it is shown that ambipolar constrained transport applies when remote magnetic fluctuations (i.e., global modes resonant at distant rational surfaces) dominate the flux. Near locations where the dominant modes are resonant, the transport is nonambipolar. This agrees with the radial variation of diffusivity in MST. Expectations for the tokamak are also discussed. {copyright} {ital 1996 American Institute of Physics.}

  11. Direct current-self-sustained non-ambipolar plasma at low pressure

    SciTech Connect

    Chen, Zhiying; Chen, Lee; Funk, Merritt

    2013-12-16

    For decades, non-ambipolar diffusion has been observed and studied in laboratory plasmas that contain a double layer. However, self-sustained non-ambipolar plasma has yet to be demonstrated. This article reports the method and results for achieving such a condition at low pressure, with a wide power range (as low as 6 W). The findings reveal that to achieve self-sustained non-ambipolar plasma, both the balance between electron and ion heating and the space-potential gradient are critical. The plasma reactor developed in this work has potential applications that include microelectronic surface processing and space propulsion, via space-charge-neutral plasma-beam thruster, when operated in the high power regime.

  12. Current density fluctuations and ambipolarity of transport

    SciTech Connect

    Shen, W.; Dexter, R.N.; Prager, S.C.

    1991-10-01

    The fluctuation in the plasma current density is measured in the MIST reversed field pinch experiment. Such fluctuations, and the measured radial profile of the k spectrum of magnetic fluctuations, supports the view and that low frequency fluctuations (f < 30 kHz) are tearing modes and high frequency fluctuations (30 kHz < f < 250 kHz) are localized turbulence in resonance with the local equilibrium magnetic field (i.e., k {center_dot} B = 0). Correlation of current density and magnetic fluctuations (< {tilde j}{parallel}{tilde B}{sub r} >) demonstrates that radial particle transport from particle motion parallel to a fluctuating magnetic field is ambipolar over the full frequency range.

  13. Current density fluctuations and ambipolarity of transport

    SciTech Connect

    Shen, W.; Dexter, R.N.; Prager, S.C.

    1991-10-01

    The fluctuation in the plasma current density is measured in the MIST reversed field pinch experiment. Such fluctuations, and the measured radial profile of the k spectrum of magnetic fluctuations, supports the view and that low frequency fluctuations (f < 30 kHz) are tearing modes and high frequency fluctuations (30 kHz < f < 250 kHz) are localized turbulence in resonance with the local equilibrium magnetic field (i.e., k {center dot} B = 0). Correlation of current density and magnetic fluctuations (< {tilde j}{parallel}{tilde B}{sub r} >) demonstrates that radial particle transport from particle motion parallel to a fluctuating magnetic field is ambipolar over the full frequency range.

  14. Edge ambipolar potential in toroidal fusion plasmasa)

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    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 Er(r =a,θ,ϕ) in the RFX reversed-field pinch show that Er 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, Er=E ˜rsin 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 Er. 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˜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 (ρi ≫ ρe). Immediately, an ambipolar potential arises to balance the drifts, with the same symmetry as the original perturbation.

  15. 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.

  16. 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

  17. 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

  18. 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

  19. Ambipolar acceleration of ions in a magnetic nozzle

    SciTech Connect

    Arefiev, Alexey V.; Breizman, Boris N.

    2008-04-15

    This paper describes a magnetic nozzle with a magnetic mirror configuration that transforms a collisionless subsonic plasma flow into a supersonic jet expanding into the vacuum. The nozzle converts electron thermal energy into the ion kinetic energy via an ambipolar electric field. The ambipolar potential in the expanding plume involves a time-dependent rarefaction wave. Travelling through the rarefaction wave, electrons lose some kinetic energy and can become trapped downstream from the mirror throat. This work presents a rigorous adiabatic description of the trapped electron population. It examines the impact of the adiabatic cooling of the trapped electrons on the ambipolar potential and the ensuing ion acceleration. The problem is formulated for an arbitrary incoming electron distribution and then a ''water-bag'' electron distribution is used to obtain a closed-form analytical solution.

  20. Ambipolar/unipolar conversion in graphene transistors by surface doping

    NASA Astrophysics Data System (ADS)

    Feng, Tingting; Xie, Dan; Zhao, Haiming; Li, Gang; Xu, Jianlong; Ren, Tianling; Zhu, Hongwei

    2013-11-01

    An ambipolar/unipolar conversion of conduction polarity in bottom-gate graphene field-effect transistor (FET) was realized by intended/unintended surface doping. Exposing the graphene FET in air made it fully p-type while covering graphene with Al nanofilm or poly(ethylene imine) (PEI) layer yielded a recovery of ambipolar conduction. The alteration of the conduction polarity in graphene FET was due to hole or electron-doping effect on graphene. Distinct changes in carrier mobility and current-voltage relationship were discussed between graphene with Al and PEI doping, and the dielectric screening by PEI was proposed as the possible mechanism.

  1. 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.

  2. Flexible black phosphorus ambipolar transistors, circuits and AM demodulator.

    PubMed

    Zhu, Weinan; Yogeesh, Maruthi N; Yang, Shixuan; Aldave, Sandra H; Kim, Joon-Seok; Sonde, Sushant; Tao, Li; Lu, Nanshu; Akinwande, Deji

    2015-03-11

    High-mobility two-dimensional (2D) semiconductors are desirable for high-performance mechanically flexible nanoelectronics. In this work, we report the first flexible black phosphorus (BP) field-effect transistors (FETs) with electron and hole mobilities superior to what has been previously achieved with other more studied flexible layered semiconducting transistors such as MoS2 and WSe2. Encapsulated bottom-gated BP ambipolar FETs on flexible polyimide afforded maximum carrier mobility of about 310 cm(2)/V·s with field-effect current modulation exceeding 3 orders of magnitude. The device ambipolar functionality and high-mobility were employed to realize essential circuits of electronic systems for flexible technology including ambipolar digital inverter, frequency doubler, and analog amplifiers featuring voltage gain higher than other reported layered semiconductor flexible amplifiers. In addition, we demonstrate the first flexible BP amplitude-modulated (AM) demodulator, an active stage useful for radio receivers, based on a single ambipolar BP transistor, which results in audible signals when connected to a loudspeaker or earphone. Moreover, the BP transistors feature mechanical robustness up to 2% uniaxial tensile strain and up to 5000 bending cycles. PMID:25715122

  3. Ambipolar charge transport in microcrystalline silicon thin-film transistors

    SciTech Connect

    Knipp, Dietmar; Marinkovic, M.; Chan, Kah-Yoong; Gordijn, Aad; Stiebig, Helmut

    2011-01-15

    Hydrogenated microcrystalline silicon ({mu}c-Si:H) is a promising candidate for thin-film transistors (TFTs) in large-area electronics due to high electron and hole charge carrier mobilities. We report on ambipolar TFTs based on {mu}c-Si:H prepared by plasma-enhanced chemical vapor deposition at temperatures compatible with flexible substrates. Electrons and holes are directly injected into the {mu}c-Si:H channel via chromium drain and source contacts. The TFTs exhibit electron and hole charge carrier mobilities of 30-50 cm{sup 2}/V s and 10-15 cm{sup 2}/V s, respectively. In this work, the electrical characteristics of the ambipolar {mu}c-Si:H TFTs are described by a simple analytical model that takes the ambipolar charge transport into account. The analytical expressions are used to model the transfer curves, the potential and the net surface charge along the channel of the TFTs. The electrical model provides insights into the electronic transport of ambipolar {mu}c-Si:H TFTs.

  4. Ambipolar Black Phosphorus MOSFETs With Record n-Channel Transconductance

    NASA Astrophysics Data System (ADS)

    Haratipour, Nazila; Koester, Steven J.

    2016-01-01

    Ambipolar black phosphorus MOSFETs with record n-channel extrinsic transconductance are reported. The devices consist of multi-layer black phosphorus aligned to a local back-gate electrode with 10-nm-thick HfO2 gate dielectric. Before passivation, devices with 0.3-um gate length behaved as p-MOSFETs with peak extrinsic transconductance, gm, of 282 uS/um at VDS = -2 V. After passivation, the same devices displayed ambipolar behavior, and when tested as n-MOSFETs, had peak gm = 66 uS/um at VDS = +2 V, and similar devices on the same wafer had gm as high as 80 uS/um. These results are an important step toward realization of high-performance black phosphorus complementary logic circuits.

  5. Investigation of charge injection characteristics in diketopyrrolopyrrole ambipolar semiconducting polymers

    NASA Astrophysics Data System (ADS)

    Lee, Seon Jeng; Jung, Seok Heon; Lee, Jin-Kyun; Kim, Cheawon; Lee, Mi Jung

    2014-10-01

    A semiconducting polymers with conjugated diketopyrrolopyrrole (DPP) unit was developed for high performance ambipolar organic field-effect transistors (OFETs). We report electrical characteristics of DPP OFETs in various ways which measured transistor and inverter performance with various bias conditions and self-assembled monolayers (SAMs) treatment. Ambipolar DPP conjugated polymer OFETs showed high hole and electron mobility of μh=0.57 cm2V-1s-1 and μe=0.51 cm2V-1s-1 with O2 plasma treatment and 1-decanethiol SAMs treatment, respectively with annealing at 100°C. Contact resistance effect on mobilities was investigated by measuring contact resistance during device operation through gated four-point probe (gFPP) and simultaneous contact resistance extraction model directly from current voltage characteristics.

  6. Evanescent ergosurfaces and ambipolar hyperkähler metrics

    NASA Astrophysics Data System (ADS)

    Niehoff, Benjamin E.; Reall, Harvey S.

    2016-04-01

    A supersymmetric solution of 5d supergravity may admit an `evanescent ergosurface': a timelike hypersurface such that the canonical Killing vector field is timelike everywhere except on this hypersurface. The hyperkähler `base space' of such a solution is `ambipolar', changing signature from (+ + ++) to (- - --) across a hypersurface. In this paper, we determine how the hyperkähler structure must degenerate at the hyper-surface in order for the 5d solution to remain smooth. This leads us to a definition of an ambipolar hyperkähler manifold which generalizes the recently-defined notion of a `folded' hyperkähler manifold. We prove that such manifolds can be constructed from `initial' data prescribed on the hypersurface. We present an `initial value' construction of supersymmetric solutions of 5d supergravity, in which such solutions are determined by data prescribed on a timelike hypersurface, both for the generic case and for the case of an evanescent ergosurface.

  7. 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

  8. 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

  9. 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.

  10. Ambipolar transistors based on random networks of WS2 nanotubes

    NASA Astrophysics Data System (ADS)

    Sugahara, Mitsunari; Kawai, Hideki; Yomogida, Yohei; Maniwa, Yutaka; Okada, Susumu; Yanagi, Kazuhiro

    2016-07-01

    WS2 nanotubes are rolled multiwalled nanotubes made of a layered material, tungsten disulfide. Their fibril structures enable the fabrication of random network films; however, these films are nonconducting, and thus have not been used for electronic applications. Here, we demonstrate that carrier injection into WS2 networks using an electrolyte gating approach could cause these networks to act as semiconducting channels. We clarify the Raman characteristics of WS2 nanotubes under electrolyte gating and confirm the feasibility of the injection of electrons and holes. We reveal ambipolar behaviors of the WS2 nanotube networks in field-effect transistor setups with electrolyte gating.

  11. 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.

  12. 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.

  13. 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.

  14. 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

  15. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

    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.

  17. Current-density fluctuations and ambipolarity of transport

    SciTech Connect

    Shen, W.; Dexter, R.N.; Prager, S.C. )

    1992-03-02

    The fluctuation in the plasma current density is measured in the MST reversed-field-pinch experiment. Such fluctuations, ad the measured radial profile of the {ital k} spectrum of magnetic fluctuations, support the view that low-frequency fluctuations ({ital f}{lt}30 kHz) are tearing modes and high-frequency fluctuations (30 kHz{lt}{ital f}{lt}250 kHz) are localized turbulence in resonance with the local equilibrium magnetic field (i.e., {bold k}{center dot}{bold B}=0). Correlation of current-density and magnetic fluctuations ({l angle}{ital {tilde j}}{sub {parallel}}{ital {tilde B}{ital r}}{r angle}) demonstrates that radial particle transport from particle motion parallel to a fluctuating magnetic field is ambipolar over the full frequency range.

  18. Internal electron transport barrier due to neoclassical ambipolarity in the Helically Symmetric Experiment

    SciTech Connect

    Lore, J.; Guttenfelder, Walter; Briesemeister, Alexis; Anderson, David; Anderson, F. S.B.; Deng, C. B.; Likin, K.; Spong, Donald A; Talmadge, Joseph; Zhai, Kan

    2010-01-01

    Electron cyclotron heated plasmas in the Helically Symmetric Experiment (HSX) feature strongly peaked electron temperature profiles; central temperatures are 2.5 keV with 100 kW injected power. These measurements, coupled with neoclassical predictions of large 'electron root' radial electric fields with strong radial shear, are evidence of a neoclassically driven thermal transport barrier. Neoclassical transport quantities are calculated using the PENTA code [D. A. Spong, Phys. Plasmas 12, 056114 (2005)], in which momentum is conserved and parallel flow is included. Unlike a conventional stellarator, which exhibits strong flow damping in all directions on a flux surface, quasisymmetric stellarators are free to rotate in the direction of symmetry, and the effect of momentum conservation in neoclassical calculations may therefore be significant. Momentum conservation is shown to modify the neoclassical ion flux and ambipolar ion root radial electric fields in the quasisymmetric configuration. The effect is much smaller in a HSX configuration where the symmetry is spoiled. In addition to neoclassical transport, a model of trapped electron mode turbulence is used to calculate the turbulent-driven electron thermal diffusivity. Turbulent transport quenching due to the neoclassically predicted radial electric field profile is needed in predictive transport simulations to reproduce the peaking of the measured electron temperature profile [Guttenfelder et al., Phys. Rev. Lett. 101, 215002 (2008)].

  19. 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.

  20. 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.

  1. Observation of electron behavior in ambipolar polymer-based light-emitting transistor by optical second harmonic generation

    NASA Astrophysics Data System (ADS)

    Ohshima, Yuki; Lim, Eunju; Manaka, Takaaki; Iwamoto, Mitsumasa; Sirringhaus, Henning

    2011-07-01

    By using the optical second harmonic generation (SHG) measurement, we directly visualized the carrier behavior leading to carrier recombination and electroluminescence (EL) in ambipolar polymer-based organic light-emitting transistor (OLET) with an active layer of poly 9,9-di-n-octylfluorene-alt-benzothiadiszole (F8BT). Eliminating photoluminescence generated at 560 nm by a two-photon absorption process, the dynamical carrier motion in the F8BT-OLET was visualized by the electric field induced SHG induced at 420 nm. Diffusion-like electron transport that starts from the drain electrode was directly caught as the transits of the SHG images. Accordingly, EL was obtained at the edge of the source electrode. The electron mobility was estimated from the visualized carrier motion as 9.2×10-4cm2/Vs, which was larger than that obtained from the transfer curve of the OLET.

  2. Single-charge transport in ambipolar silicon nanoscale field-effect transistors

    SciTech Connect

    Mueller, Filipp; Konstantaras, Georgios; Wiel, Wilfred G. van der; Zwanenburg, Floris A.

    2015-04-27

    We report single-charge transport in ambipolar nanoscale MOSFETs, electrostatically defined in near-intrinsic silicon. We use the ambipolarity to demonstrate the confinement of either a few electrons or a few holes in exactly the same crystalline environment underneath a gate electrode. We find similar electron and hole quantum dot properties while the mobilities differ quantitatively like in microscale devices. The understanding and control of individual electrons and holes are essential for spin-based quantum information processing.

  3. 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 .

  4. 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.

  5. Regulating charge injection in ambipolar organic field-effect transistors by mixed self-assembled monolayers.

    PubMed

    Xu, Yong; Baeg, Kang-Jun; Park, Won-Tae; Cho, Ara; Choi, Eun-Young; Noh, Yong-Young

    2014-08-27

    We report on a technique using mixed self-assembled monolayers (SAMs) to finely regulate ambipolar charge injection in polymer organic field-effect transistors. Differing from the other works that employ single SAM specifically for efficient charge injection in p-type and n-type transistors, we blend two different SAMs of alkyl- and perfluoroalkyl thiols at different ratios and apply them to ambipolar OFETs and inverter. Thanks to the utilization of ambipolar semiconductor and one SAM mixture, the device and circuit fabrications are facile with only one step for semiconductor deposition and another for SAM treatment. This is much simpler with respect to the conventional scheme for the unipolar-device-based complementary circuitry that demands separate deposition and processing for individual p-channel and n-channel transistors. Our results show that the mixed-SAM treatments not only improve ambipolar charge injection manifesting as higher hole- and electron-mobility and smaller threshold voltage but also gradually tune the device characteristics to reach a desired condition for circuit application. Therefore, this simple but useful approach is promising for ambipolar electronics. PMID:25093699

  6. Enhancement of minority carrier injection in ambipolar carbon nanotube transistors using double-gate structures

    NASA Astrophysics Data System (ADS)

    Kim, Bongjun; Liang, Kelly; Geier, Michael L.; Hersam, Mark C.; Dodabalapur, Ananth

    2016-07-01

    We show that double-gate ambipolar thin-film transistors can be operated to enhance minority carrier injection. The two gate potentials need to be significantly different for enhanced injection to be observed. This enhancement is highly beneficial in devices such as light-emitting transistors where balanced electron and hole injections lead to optimal performance. With ambipolar single-walled carbon nanotube semiconductors, we demonstrate that higher ambipolar currents are attained at lower source-drain voltages, which is desired for portable electronic applications, by employing double-gate structures. In addition, when the two gates are held at the same potential, the expected advantages of the double-gate transistors such as enhanced on-current are also observed.

  7. 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.

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

    PubMed Central

    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. PMID:23900459

  9. 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. PMID:23900459

  10. 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.

  11. Low threshold amplified spontaneous emission and ambipolar charge transport in non-volatile liquid fluorene derivatives.

    PubMed

    Ribierre, Jean-Charles; Zhao, Li; Inoue, Munetomo; Schwartz, Pierre-Olivier; Kim, Ju-Hyung; Yoshida, Kou; Sandanayaka, Atula S D; Nakanotani, Hajime; Mager, Loic; Méry, Stéphane; Adachi, Chihaya

    2016-02-21

    Highly fluorescent non-volatile fluidic fluorene derivatives functionalized with siloxane chains were synthesized and used in monolithic solvent-free liquid organic semiconductor distributed feedback lasers. The photoluminescence quantum yield values, the amplified spontaneous emission thresholds and the ambipolar charge carrier mobilities demonstrate that this class of materials is extremely promising for organic fluidic light-emitting and lasing devices. PMID:26734693

  12. Anomalous ion heating from ambipolar-constrained magnetic fluctuation-induced transport

    SciTech Connect

    Gatto, R.; Terry, P. W.

    2001-01-01

    A kinetic theory for the anomalous heating of ions from energy stored in magnetic turbulence is presented. Imposing self consistency through the constitutive relations between particle distributions and fields, a turbulent Kirchhoff's law is derived that expresses a direct connection between rates of ion heating and electron thermal transport. This connection arises from the kinematics of electron motion along turbulent fields, which results in granular structures in the electron distribution. The drag exerted on these structures through emission into collective modes mediates ambipolar-constrained transport. Resonant damping of the collective modes by ions produces the heating. In collisionless plasmas the rate of ion damping controls the rate of emission, and hence the ambipolar-constrained electron heat flux. The heating rate is calculated for both a resonant and non-resonant magnetic fluctuation spectrum and compared with observations. The theoretical heating rate is sufficient to account for the observed two-fold rise in ion temperature during sawtooth events in experimental discharges.

  13. 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

  14. 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.

  15. Study on contact and channel resistance of pentacene-based ambipolar organic thin-film transistors

    NASA Astrophysics Data System (ADS)

    Ho, Tsung-Jun; Yan, Guo-En; Cheng, Horng-Long

    2015-08-01

    In this work, we investigated the electrical characteristics of pentacene-based ambipolar organic thin-film transistors (OTFTs) by modifying the channel length. We fabricated a top contact device structure with sliver as the source and drain electrodes and heavy doped p-type silicon wafer as the gate electrode. The channel length of the pentacene-based ambipolar OTFTs are 50, 100, 250, and 400 μm; the channel width is fixed. The output current of the n-channel and p-channel decreases with increasing channel length. The saturated mobility and threshold voltage of both channels increase with the increase in channel length. The increase rate of saturated mobility and threshold voltage of the n-channel is larger than that of the p-channel. The influence of channel length on the electrical properties of the p-channel and n-channel is different. We utilized the gated-transfer length method to study the contact resistance between sliver and pentacene and the channel resistance of pentacene. Contact and channel resistance decrease with the increase in gate voltage in the saturation region. The total resistance of pentacene-based ambipolar OTFTs increases with channel length at a fixed gate voltage. However, n-channel total resistance has stronger gate voltage and channel length dependence than p-channel total resistance. This result reveals that electron transport in the device channel requires a larger driving voltage than in the hole. Selecting a suitable channel length is critical to obtain a well-balanced performance of the dual carriers that transport ambipolar OTFTs and to avoid a large loss in injection barrier.

  16. Indigo--a natural pigment for high performance ambipolar organic field effect transistors and circuits.

    PubMed

    Irimia-Vladu, Mihai; Głowacki, Eric D; Troshin, Pavel A; Schwabegger, Günther; Leonat, Lucia; Susarova, Diana K; Krystal, Olga; Ullah, Mujeeb; Kanbur, Yasin; Bodea, Marius A; Razumov, Vladimir F; Sitter, Helmut; Bauer, Siegfried; Sariciftci, Niyazi Serdar

    2012-01-17

    Millenniums-old natural dye indigo--a "new" ambipolar organic semiconductor. Indigo shows balanced electron and hole mobilities of 1 × 10(-2) cm(2) V(-1) s(-1) and good stability against degradation in air. Inverters with gains of 105 in the first and 110 in the third quadrant are demonstrated. Fabricated entirely from natural and biodegradable compounds, these devices show the large potential of such materials for green organic electronics. PMID:22109816

  17. Spatial control of the recombination zone in ambipolar light-emitting polymer transistors

    NASA Astrophysics Data System (ADS)

    Zaumseil, Jana; Donley, Carrie L.; Kim, Ji-Seon; Friend, Richard H.; Sirringhaus, Henning

    2006-04-01

    Ambipolar organic field-effect transistors (FET) are interesting as building blocks for low power complementary circuits in organic electronics. Another intriguing feature of ambipolar FETs is the recombination of holes and electrons within the channel, which leads to the formation of excitons that can relax radiatively and thus emit light. We have recently demonstrated that ambipolar charge transport is a generic feature in a wide range of polymer semiconductors when appropriate injection electrodes and trapfree dielectrics are used. Among these materials are those that are generally used in light-emitting diodes and thus show high photoluminescence efficiencies. Here we demonstrate ambipolar light-emitting field-effect transistors based on the conjugated polymer OC IC 10-PPV (poly(2-methoxy-5-(3,7-dimethyloctoxy)-p-phenylenevinylene)) as the semiconducting and emissive layer. OC IC 10- PPV shows efficient electron and hole transport with field-effect mobilities of 3.10 -3 cm2/Vs and 6.10 -4 cm2/Vs, respectively. Electrons and holes are injected from calcium and gold source and drain electrodes, respectively, and recombine radiatively within the transistor channel leading to visible light emission. We can actively control the position of the recombination zone through the applied gate and source-drain bias in both constant and variable current mode and thus move the emission zone from the source through the channel to the drain electrode and vice versa. The intensity of light emitted from the channel is proportional to the drain current with efficiencies comparable to those of LEDs based on OC IC 10-PPV.

  18. Laterally-stacked, solution-processed organic microcrystal with ambipolar charge transport behavior.

    PubMed

    Shim, Hyunseok; Kumar, Amit; Cho, Hyejin; Yang, Dongmyung; Palai, Akshaya K; Pyo, Seungmoon

    2014-10-22

    We report the formation of laterally stacked ambipolar crystal wire for high-mobility organic field-effect transistors (OFETs), along with a simple logic circuit through a solution process. A soluble pentacene derivative, 6,13-bis(triisopropylsilylethynyl)pentacene (Tips-pentacene), and N,N'-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8) were used as p-type and n-type organic semiconductors, respectively. The laterally stacked ambipolar crystal wire is made up of Tips-pentacene and PTCDI-C8 crystals in a structure of Tips-pentacene/PTCDI-C8/Tips-pentacene (TPT). The inner part of the crystal is made up of PTCDI-C8, and Tips-pentacene is present on both sides. These TPT crystals exhibit typical ambipolar charge transport behavior in organic electronic devices, which show very balanced hole and electron mobility as high as 0.23 cm(2)/V·s and 0.13 cm(2)/V·s, respectively. Static and dynamic operational stability of the device is investigated by measuring the device performance as a function of storage time and applying voltage pulse, respectively, and it shows good air stability. In addition, a simple logic circuit based on the TPT crystal wire has been fabricated, and the static and dynamic performance has been evaluated. The results indicate that the TPT crystals are potentially useful for miniaturized organic electronic devices. PMID:25244525

  19. Solution-Processed Ambipolar Field-Effect Transistor Based on Diketopyrrolopyrrole Functionalized with Benzothiadiazole

    SciTech Connect

    Zhang, Yuan; Kim, Chunki; Lin, Jason; Nguyen, Thuc-Quyen

    2012-01-01

    Ambipolar charge transport in a solution-processed small molecule 4,7-bis{2-[2,5-bis(2-ethylhexyl)-3-(5-hexyl-2,2':5',2"-terthiophene-5"-yl)-pyrrolo[3,4-c]pyrrolo-1,4-dione-6-yl]-thiophene-5-yl}-2,1,3-benzothiadiazole (BTDPP2) transistor has been investigated and shows a balanced field-effect mobility of electrons and holes of up to ~10-2 cm² V-1 s-1. Using low-work-function top electrodes such as Ba, the electron injection barrier is largely reduced. The observed ambipolar transport can be enhanced over one order of magnitude compared to devices using Al or Au electrodes. The field-effect mobility increases upon thermal annealing at 150 °C due to the formation of large crystalline domains, as shown by atomic force microscopy and X-ray diffraction. Organic inverter circuits based on BTDPP2 ambipolar transistors display a gain of over 25.

  20. 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 .

  1. Fingerprints of collisionless reconnection at the separator, I, Ambipolar-Hall signatures

    NASA Astrophysics Data System (ADS)

    Scudder, J. D.; Mozer, F. S.; Maynard, N. C.; Russell, C. T.

    2002-10-01

    Plasma, electric, and magnetic field data on the Polar spacecraft have been analyzed for the 29 May 1996 magnetopause traversal searching for evidence of in situ reconnection and traversal of the separator. In this paper we confine our analysis to model-free observations and intrasensor coherence of detection of the environs of the separator. (1) We illustrate the first documented penetration of the separator of collisionless magnetic reconnection in temporal proximity to successful Walén tests with opposite slopes. (2) We present the first direct measurements of E∥ at the magnetopause. (3) We make the first empirical argument that E∥ derives from the electron pressure gradient force. (4) We document the first detection of the electron pressure ridge astride the magnetic depression that extends from the separator. (5) We provide the first empirical detection of the reconnection rate at the magnetopause with the locally sub-Alfvénic ion inflow, MAi ≃ 0.1, and trans-Alfvénic exhaust at high electron pressure of MiA ≃ 1.1-5. (6) We exhibit the first empirical detection of supra-Alfvénic electron flows parallel to B in excess of 5 in narrow sheets. (7) We illustrate the detection of heat flux sheets indicative of separatrices near, but not always in superposition, with the supra-Alfvénic parallel electron bulk flows. (8) We present the first evidence that pressure gradient scales are short enough to explain the electron fluid's measured cross-field drifts not explained by E × B drift but predicted by the measured size of E∥. (9) We illustrate that the size of the observed E∥ is well organized with the limit implied by Vasyliunas's analysis of the generalized Ohm's law of scale length ?, indicative of the intermediate scale of the diffusion region. (10) We document the first detection of departure from electron gyrotropy not only at the separator crossing but also in its vicinity, an effect presaged by [1975]. (11) We make the first reports of very

  2. 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

  3. 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. PMID:26421942

  4. o-Carborane functionalized pentacenes: synthesis, molecular packing and ambipolar organic thin-film transistors.

    PubMed

    Guo, Jixi; Liu, Danqing; Zhang, Jiahui; Zhang, Jiji; Miao, Qian; Xie, Zuowei

    2015-08-01

    New 6,13-bis[1'-(C≡C)-2'-R-1',2'-C2B10H10]pentacenes (R = H, Me, Et, n-Bu) are synthesized and fully characterized. The results show that the alkyl substituents on the second cage carbon have a significant impact on the molecular packing, and the incorporation of the o-carboranyl moiety into a π conjugated system can lower both LUMO and HOMO energy levels, converting a typical p-type semiconductor into an ambipolar one. PMID:26121634

  5. High mobility flexible graphene field-effect transistors and ambipolar radio-frequency circuits

    NASA Astrophysics Data System (ADS)

    Liang, Yiran; Liang, Xuelei; Zhang, Zhiyong; Li, Wei; Huo, Xiaoye; Peng, Lianmao

    2015-06-01

    Field-effect transistors (GFETs) were fabricated on mechanically flexible substrates using chemical vapor deposition grown graphene. High current density (nearly 200 μA μm-1) with saturation, almost perfect ambipolar electron-hole behavior, high transconductance (120 μS μm-1) and good stability over 381 days were obtained. The average carrier mobility for holes (electrons) is 13 540 cm2 V-1 s-1 (12 300 cm2 V-1 s-1) with the highest value over 24 000 cm2 V-1 s-1 (20 000 cm2 V-1 s-1) obtained in flexible GFETs. Ambipolar radio-frequency circuits, frequency doubler, were constructed based on the high performed flexible GFET, which show record high output power spectra purity (~97%) and high conversion gain of -13.6 dB. Bending measurements show the flexible GFETs are able to work under modest strain. These results show that flexible GFETs are a very promising option for future flexible radio-frequency electronics.Field-effect transistors (GFETs) were fabricated on mechanically flexible substrates using chemical vapor deposition grown graphene. High current density (nearly 200 μA μm-1) with saturation, almost perfect ambipolar electron-hole behavior, high transconductance (120 μS μm-1) and good stability over 381 days were obtained. The average carrier mobility for holes (electrons) is 13 540 cm2 V-1 s-1 (12 300 cm2 V-1 s-1) with the highest value over 24 000 cm2 V-1 s-1 (20 000 cm2 V-1 s-1) obtained in flexible GFETs. Ambipolar radio-frequency circuits, frequency doubler, were constructed based on the high performed flexible GFET, which show record high output power spectra purity (~97%) and high conversion gain of -13.6 dB. Bending measurements show the flexible GFETs are able to work under modest strain. These results show that flexible GFETs are a very promising option for future flexible radio-frequency electronics. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr02292d

  6. Improved Tunnel-FET inverter performance with SiGe/Si heterostructure nanowire TFETs by reduction of ambipolarity

    NASA Astrophysics Data System (ADS)

    Richter, S.; Trellenkamp, S.; Schäfer, A.; Hartmann, J. M.; Bourdelle, K. K.; Zhao, Q. T.; Mantl, S.

    2015-06-01

    Complementary MOSFET and Tunnel-FET inverters based on tri-gated strained Si nanowire arrays are demonstrated. The voltage transfer characteristics as well as the inverter supply currents of both inverter types are analyzed and compared. A degradation of the inverter output voltage is observed due to the ambipolar transfer characteristics of the symmetric homostructure TFET devices. Emulated TFET inverters based on the measured transfer characteristics of SiGe/Si heterostructure nanowire array n-channel TFETs with reduced ambipolarity demonstrate improved inverter switching for supply voltages down to VDD = 0.2 V.

  7. Effect of Ambipolar Plasma Flow on the Penetration of Resonant Magnetic Perturbations in a Quasi-axisymmetric Stellarator

    SciTech Connect

    A. Reiman; M. Zarnstorff; D. Mikkelsen; L. Owen; H. Mynick; S. Hudson; D. Monticello

    2005-04-19

    A reference equilibrium for the U.S. National Compact Stellarator Experiment is predicted to be sufficiently close to quasi-symmetry to allow the plasma to flow in the toroidal direction with little viscous damping, yet to have sufficiently large deviations from quasi-symmetry that nonambipolarity significantly affects the physics of the shielding of resonant magnetic perturbations by plasma flow. The unperturbed velocity profile is modified by the presence of an ambipolar potential, which produces a broad velocity profile. In the presence of a resonant magnetic field perturbation, nonambipolar transport produces a radial current, and the resulting j x B force resists departures from the ambipolar velocity and enhances the shielding.

  8. 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.

  9. 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

  10. Efficient ambipolar transport properties in alternate stacking donor-acceptor complexes: from experiment to theory.

    PubMed

    Qin, Yunke; Cheng, Changli; Geng, Hua; Wang, Chao; Hu, Wenping; Xu, Wei; Shuai, Zhigang; Zhu, Daoben

    2016-05-18

    Comprehensive investigations of crystal structures, electrical transport properties and theoretical simulations have been performed over a series of sulfur-bridged annulene-based donor-acceptor complexes with an alternate stacking motif. A remarkably high mobility, up to 1.57 cm(2) V(-1) s(-1) for holes and 0.47 cm(2) V(-1) s(-1) for electrons, was obtained using organic single crystal field-effect transistor devices, demonstrating the efficient ambipolar transport properties. These ambipolar properties arise from the fact that the electronic couplings for both holes and electrons have the same super-exchange nature along the alternate stacking direction. The magnitude of super-exchange coupling depends not only on the intermolecular stacking distance and pattern, but also the energy level alignments between the adjacent donor-acceptor moieties. The concluded transport mechanism and structure-property relationship from this research will provide an important guideline for the future design of organic semiconductors based on donor-acceptor complexes. PMID:27157854

  11. 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.

  12. High mobility flexible graphene field-effect transistors and ambipolar radio-frequency circuits.

    PubMed

    Liang, Yiran; Liang, Xuelei; Zhang, Zhiyong; Li, Wei; Huo, Xiaoye; Peng, Lianmao

    2015-07-01

    Field-effect transistors (GFETs) were fabricated on mechanically flexible substrates using chemical vapor deposition grown graphene. High current density (nearly 200 μA μm(-1)) with saturation, almost perfect ambipolar electron-hole behavior, high transconductance (120 μS μm(-1)) and good stability over 381 days were obtained. The average carrier mobility for holes (electrons) is 13,540 cm(2) V(-1) s(-1) (12,300 cm(2) V(-1) s(-1)) with the highest value over 24,000 cm(2) V(-1) s(-1) (20,000 cm(2) V(-1) s(-1)) obtained in flexible GFETs. Ambipolar radio-frequency circuits, frequency doubler, were constructed based on the high performed flexible GFET, which show record high output power spectra purity (∼97%) and high conversion gain of -13.6 dB. Bending measurements show the flexible GFETs are able to work under modest strain. These results show that flexible GFETs are a very promising option for future flexible radio-frequency electronics. PMID:26061485

  13. 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.

  14. Infrared spectroscopy of narrow gap donor-acceptor polymer-based ambipolar transistors

    NASA Astrophysics Data System (ADS)

    Khatib, Omar; Yuen, Jonathan; Wilson, Jim; Kumar, Rajeev; di Ventra, Massimiliano; Heeger, Alan; Basov, Dimitri

    2013-03-01

    Donor-acceptor (D-A) copolymers have recently emerged as versatile materials for use in a large variety of device applications. Specifically, these systems possess extremely narrow band gaps, enabling ambipolar charge transport when integrated in solution-processed organic field-effect transistors (OFETs). However, the fundamentals of electronic transport in this class of materials remain unexplored. We present a systematic investigation of ambipolar charge injection in a family of narrow-gap D-A conjugated polymers based on benzobisthiadiazole (BBT) using infrared (IR) spectroscopy. We observe a significant modification of the absorption edge in polymer-based OFETs under the applied electric field. The absorption edge reveals hardening under electron injection and softening under hole injection. Additionally, we register localized vibrational resonances associated with injected charges. Our findings indicate a significant self-doping of holes that is modified by charge injection. Observations of both electron and hole transport with relatively high carrier mobility strongly suggest an inhomogeneous, phase-separated conducting polymer.

  15. Ambipolar Light-Emitting Transistors on Chemical Vapor Deposited Monolayer MoS₂.

    PubMed

    Ponomarev, Evgeniy; Gutiérrez-Lezama, Ignacio; Ubrig, Nicolas; Morpurgo, Alberto F

    2015-12-01

    We realize and investigate ionic liquid gated field-effect transistors (FETs) on large-area MoS2 monolayers grown by chemical vapor deposition (CVD). Under electron accumulation, the performance of these devices is comparable to that of FETs based on exfoliated flakes. FETs on CVD-grown material, however, exhibit clear ambipolar transport, which for MoS2 monolayers had not been reported previously. We exploit this property to estimate the bandgap Δ of monolayer MoS2 directly from the device transfer curves and find Δ ≈ 2.4-2.7 eV. In the ambipolar injection regime, we observe electroluminescence due to exciton recombination in MoS2, originating from the region close to the hole-injecting contact. Both the observed transport properties and the behavior of the electroluminescence can be consistently understood as due to the presence of defect states at an energy of 250-300 meV above the top of the valence band, acting as deep traps for holes. Our results are of technological relevance, as they show that devices with useful optoelectronic functionality can be realized on large-area MoS2 monolayers produced by controllable and scalable techniques. PMID:26594892

  16. 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

  17. Amphiphilic (Phthalocyaninato) (Porphyrinato) Europium Triple-Decker Nanoribbons with Air-Stable Ambipolar OFET Performance.

    PubMed

    Lu, Guang; Kong, Xia; Ma, Pan; Wang, Kang; Chen, Yanli; Jiang, Jianzhuang

    2016-03-01

    An amphiphilic mixed (phthalocyaninato) (porphyrinato) europium(III) triple-decker complex [Pc(OPh)8]Eu[Pc(OPh)8]Eu[TP(C≡CCOOH)PP] (1) with potential ambipolar semiconducting HOMO and LUMO energy levels has been designed, synthesized, and characterized. The OFET devices fabricated by quasi-Langmuir-Shäfer (QLS) technique at the air/water interface with nanoparticle morphology display hole mobility of 7.0 × 10(-7) cm(2) V(-1) s(-1) and electron mobility of 7.5 × 10(-7) cm(2) V(-1) s(-1), which reflects its ambipolar semiconducting nature. However, the performance of the devices fabricated via a "phase-transfer" method from n-hexane with one-dimensional nanoribbon morphology was significantly improved by 3-6 orders of magnitude in terms of hole and electron mobilities, 0.11 and 4 × 10(-4) cm(2) V(-1) s(-1), due to the enhanced π-π interaction in the direction perpendicular to the tetrapyrrole rings associated with the formation of a dimeric supramolecular structure building block depending on the intermolecular hydrogen bonding between the neighboring triple-decker molecules in the one-dimensional nanoribbons. PMID:26894989

  18. 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.

  19. 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.

  20. 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. PMID:25801827

  1. Investigation of ambipolar signature in SiGeOI homojunction tunnel FETs

    NASA Astrophysics Data System (ADS)

    Hutin, L.; Oeflein, R. P.; Borrel, J.; Martinie, S.; Tabone, C.; Le Royer, C.; Vinet, M.

    2016-01-01

    In this paper, we study the ambipolar tunneling signature from the output characteristics of TFETs featuring Si0.8Ge0.2 homojunctions, which we compare to those measured on conventional MOSFETs and Schottky Barrier FETs. The difference with the former is immediate since a single TFET can display a transistor effect under both pull-up (nTFET) and pull-down (pTFET) biasing conditions. This is however a property shared with SBFETs, in which injection occurs via tunneling through a single carrier Schottky Barrier instead of band-to-band tunneling. Without requiring quantitative considerations on the current levels or transfer characteristics, we find that simply performing the same dual ID-VDS electrical tests while voluntarily "swapping" the S/D terminals unequivocally characterizes TFET operation, even compared to asymmetrically doped SBFETs.

  2. 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

  3. 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

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

    NASA Astrophysics Data System (ADS)

    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

    2016-05-01

    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 Y0.38 La0.62 (Ba0.82 La0.18 )2Cu3 Oy films using spectroscopic ellipsometry and x-ray absorption spectroscopies at the O K and Cu L3 ,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.

  5. 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.

  6. 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.

  7. 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.

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

    DOE PAGESBeta

    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

  9. 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.

  10. 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.

  11. Ambipolar ballistic electron emission microscopy studies of gate-field modified Schottky barriers

    NASA Astrophysics Data System (ADS)

    Che, Y. L.; Pelz, J. P.

    2010-06-01

    Four-terminal ambipolar ballistic electron emission microscopy studies are conducted on Au/Si and Cu/Si Schottky contacts fabricated on back-gated silicon-on-insulator wafers, allowing the electric field to be varied so that both electron (n)- and hole (p)-Schottky barrier heights can be measured at the same sample location. While the individual n- and p-Schottky barrier heights varied by more than 200 meV between the Au/Si and Cu/Si contacts, for a given sample they sum to within 15 meV of the same value, indicating that the individual variations are due to variations in a local surface dipole as compared with tip effects or variations in local composition.

  12. 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.

  13. 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

  14. 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

  15. 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

  16. 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

  17. An ambipolar phosphine oxide-based host for high power efficiency blue phosphorescent organic light emitting devices

    SciTech Connect

    Polikarpov, Evgueni; Swensen, James S.; Chopra, Neetu; So, Franky; Padmaperuma, Asanga B.

    2009-06-01

    We report blue electrophosphorescent organic light emitting devices (OLEDs) with a new ambipolar host material, 4-(diphenylphosphoryl)-N,N-diphenylaniline (HM-A1), doped with the blue phosphor iridium (III) bis[(4,6-difluorophenyl)-pyridinato-N,C2’]picolinate (FIrpic). The ambipolar nature of the host was verified using single carrier devices. The power efficiency of devices that employed 2,8-bis(diphenylphosphoryl)dibenzothiophene (PO15) as the electron transport layer showed optimized device performance when the electron transport layer thickness was 500 Å, giving a peak power efficiency of 46 lm/W (corresponding external quantum efficiency of 17.1%). The external quantum efficiency and power efficiency at the brightness of 800 Cd/m2 were measured with no light outcoupling enhancement and found to be 15.4% and 26 lm/W, respectively.

  18. 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

  19. Enhanced ambipolar charge injection with semiconducting polymer/carbon nanotube thin films for light-emitting transistors.

    PubMed

    Gwinner, Michael C; Jakubka, Florian; Gannott, Florentina; Sirringhaus, Henning; Zaumseil, Jana

    2012-01-24

    We investigate the influence of small amounts of semiconducting single-walled carbon nanotubes (SWNTs) dispersed in polyfluorenes such as poly(9,9-di-n-octylfluorene-alt-benzothiadiazole (F8BT) and poly(9,9-dioctylfluorene) (F8) on device characteristics of bottom contact/top gate ambipolar light-emitting field-effect transistors (LEFETs) based on these conjugated polymers. We find that the presence of SWNTs within the semiconducting layer at concentrations below the percolation limit significantly increases both hole and electron injection, even for a large band gap semiconductor like F8, without leading to significant luminescence quenching of the conjugated polymer. As a result of the reduced contact resistance and lower threshold voltages, larger ambipolar currents and thus brighter light emission are observed. We examine possible mechanisms of this effect such as energy level alignment, reduced bulk resistance above the contacts, and field-enhanced injection at the nanotube tips. The observed ambipolar injection improvement is applicable to most conjugated polymers in staggered transistor configurations or similar organic electronic devices where injection barriers are an issue. PMID:22142143

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

    PubMed

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

    2015-01-21

    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. PMID:25363392

  1. 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.

  2. 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.

  3. 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.

  4. Numerical modeling of a fast-axial-flow CO2 laser with considering viscosity and ambipolar diffusion

    NASA Astrophysics Data System (ADS)

    Galeev, Ravil S.; Fedosov, A. A.

    1996-03-01

    A numerical method for analysis of a fast axial flow glow discharge carbon dioxide laser is developed. The method is based on the self-consistent solution to the two-dimensional steady- state Navier-Stokes equations in thin-shear-layer approximation (slender channel equations), the parabolized glow discharge equations, and the vibrational relaxation equations. The discharge equations include the continuity equations for the electrons, the positive and negative ions. The one-mode relaxation model for the vibrational kinetics and the plane-parallel optical resonator model are used. The present model is based on the assumption of the charge neutrality and limited by consideration of the positive column of discharge without taking into account the cathode-fall and anode-fall regions.

  5. 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

  6. 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

  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. 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.

  9. 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.

  10. 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.

  11. 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.

  12. Thiocyanate-capped PbS nanocubes: ambipolar transport enables quantum dot based circuits on a flexible substrate.

    PubMed

    Koh, Weon-Kyu; Saudari, Sangameshwar R; Fafarman, Aaron T; Kagan, Cherie R; Murray, Christopher B

    2011-11-01

    We report the use of thiocyanate as a ligand for lead sulfide (PbS) nanocubes for high-performance, thin-film electronics. PbS nanocubes, self-assembled into thin films and capped with the thiocyanate, exhibit ambipolar characteristics in field-effect transistors. The nearly balanced, high mobilities for electrons and holes enable the fabrication of CMOS-like inverters with promising gains of ∼22 from a single semiconductor material. The mild chemical treatment and low-temperature processing conditions are compatible with plastic substrates, allowing the realization of flexible, nonsintered quantum dot circuits. PMID:22011060

  13. 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.

  14. EED f and IED f of the non-ambipolar e--beam plasma and their effects on etch

    NASA Astrophysics Data System (ADS)

    Chen, Lee

    2014-10-01

    The control of electron shading is crucial in achieving the super-high aspect ratio contact (HARC); precise ion-energy control is essential in the selective etching of lamella diblock copolymers to develop the nano-lines for Direct Self Assembly (DSA). The plasma EED f not only determines the chemistry but also dictates the shading level of the features. The above processes are presented as examples to illustrate the effects of EED f and the surgical surface-excitation by a controlled IED f. In addition to demonstrating the methods of achieving a prescribed IED f through external bias, the properties of the non-ambipolar electron plasma (NEP) will be presented. NEP is heated by the non-ambipolar beam-current density in the range of 10s Acm-2 through beam-plasma instabilities. Its EED f has a Maxwellian bulk followed by a broad energy-continuum connecting to the most energetic group with energies above the beam-energy and such EED f seems consistent with that required for deep-contact etching. The remnant of the injected electron-beam power terminates at the NEP end-boundary (i.e., wafer) could set up a controllable DC sheath potential resulting in mono-energetic surface excitation by the charge-neutral plasma beam without the application of external bias. In collaboration with Zhiying Chen, Tokyo Electron America, Inc., Austin, TX 78741.

  15. 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.

  16. 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. PMID:23761043

  17. 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.

  18. Strongly Metallic Electron and Hole 2D Transport in an Ambipolar Si-Vacuum Field Effect Transistor

    NASA Astrophysics Data System (ADS)

    Hu, Binhui; Yazdanpanah, M. M.; Kane, B. E.; Hwang, E. H.; Das Sarma, S.

    2015-07-01

    We report experiment and theory on an ambipolar gate-controlled Si(111)-vacuum field effect transistor where we study electron and hole (low-temperature 2D) transport in the same device simply by changing the external gate voltage to tune the system from being a 2D electron system at positive gate voltage to a 2D hole system at negative gate voltage. The electron (hole) conductivity manifests strong (moderate) metallic temperature dependence with the conductivity decreasing by a factor of 8 (2) between 0.3 K and 4.2 K with the peak electron mobility (˜18 m2/V s ) being roughly 20 times larger than the peak hole mobility (in the same sample). Our theory explains the data well using random phase approximation screening of background Coulomb disorder, establishing that the observed metallicity is a direct consequence of the strong temperature dependence of the effective screened disorder.

  19. 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.

  20. Dielectric interface-dependent spatial charge distribution in ambipolar polymer semiconductors embedded in dual-gate field-effect transistors

    NASA Astrophysics Data System (ADS)

    Lee, Jiyoul; Roelofs, W. S. Christian; Janssen, Rene A. J.; Gelinck, Gerwin H.

    2016-07-01

    The spatial charge distribution in diketopyrrolopyrrole-containing ambipolar polymeric semiconductors embedded in dual-gate field-effect transistors (DGFETs) was investigated. The DGFETs have identical active channel layers but two different channel/gate interfaces, with a CYTOP™ organic dielectric layer for the top-gate and an octadecyltrichlorosilane (ODTS) self-assembled monolayer-treated inorganic SiO2 dielectric for the bottom-gate, respectively. Temperature-dependent transfer measurements of the DGFETs were conducted to examine the charge transport at each interface. By fitting the temperature-dependent measurement results to the modified Vissenberg-Matters model, it can be inferred that the top-channel interfacing with the fluorinated organic dielectric layers has confined charge transport to two-dimensions, whereas the bottom-channel interfacing with the ODTS-treated SiO2 dielectric layers has three-dimensional charge transport.

  1. 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.

  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. 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.

  4. Diffusion of magnetic field via turbulent reconnection

    NASA Astrophysics Data System (ADS)

    Santos de Lima, Reinaldo; Lazarian, Alexander; de Gouveia Dal Pino, Elisabete M.; Cho, Jungyeon

    2010-05-01

    The diffusion of astrophysical magnetic fields in conducting fluids in the presence of turbulence depends on whether magnetic fields can change their topology via reconnection in highly conducting media. Recent progress in understanding fast magnetic reconnection in the presence of turbulence is reassuring that the magnetic field behavior in computer simulations and turbulent astrophysical environments is similar, as far as magnetic reconnection is concerned. This makes it meaningful to perform MHD simulations of turbulent flows in order to understand the diffusion of magnetic field in astrophysical environments. Our studies of magnetic field diffusion in turbulent medium reveal interesting new phenomena. First of all, our 3D MHD simulations initiated with anti-correlating magnetic field and gaseous density exhibit at later times a de-correlation of the magnetic field and density, which corresponds well to the observations of the interstellar media. While earlier studies stressed the role of either ambipolar diffusion or time-dependent turbulent fluctuations for de-correlating magnetic field and density, we get the effect of permanent de-correlation with one fluid code, i.e. without invoking ambipolar diffusion. In addition, in the presence of gravity and turbulence, our 3D simulations show the decrease of the magnetic flux-to-mass ratio as the gaseous density at the center of the gravitational potential increases. We observe this effect both in the situations when we start with equilibrium distributions of gas and magnetic field and when we follow the evolution of collapsing dynamically unstable configurations. Thus the process of turbulent magnetic field removal should be applicable both to quasi-static subcritical molecular clouds and cores and violently collapsing supercritical entities. The increase of the gravitational potential as well as the magnetization of the gas increases the segregation of the mass and magnetic flux in the saturated final state of the

  5. 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.

  6. Graphene/Pentacene Barristor with Ion-Gel Gate Dielectric: Flexible Ambipolar Transistor with High Mobility and On/Off Ratio.

    PubMed

    Oh, Gwangtaek; Kim, Jin-Soo; Jeon, Ji Hoon; Won, EunA; Son, Jong Wan; Lee, Duk Hyun; Kim, Cheol Kyeom; Jang, Jingon; Lee, Takhee; Park, Bae Ho

    2015-07-28

    High-quality channel layer is required for next-generation flexible electronic devices. Graphene is a good candidate due to its high carrier mobility and unique ambipolar transport characteristics but typically shows a low on/off ratio caused by gapless band structure. Popularly investigated organic semiconductors, such as pentacene, suffer from poor carrier mobility. Here, we propose a graphene/pentacene channel layer with high-k ion-gel gate dielectric. The graphene/pentacene device shows both high on/off ratio and carrier mobility as well as excellent mechanical flexibility. Most importantly, it reveals ambipolar behaviors and related negative differential resistance, which are controlled by external bias. Therefore, our graphene/pentacene barristor with ion-gel gate dielectric can offer various flexible device applications with high performances. PMID:26083550

  7. 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.

  8. 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.

  9. 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.

  10. Drift and diffusion of spin and charge density waves in a two-dimensional electron gas

    NASA Astrophysics Data System (ADS)

    Yang, Luyi; Koralek, J. D.; Orenstein, J.; Tibbetts, D. R.; Reno, J. L.; Lilly, M. P.

    2011-03-01

    We use transient grating spectroscopy (TGS) to study the persistent spin helix (PSH) state and electron-hole density wave (EHDW) in a 2D electron gas in the presence of an in-plane electric field parallel to the wavevector of the PSH or EHDW. By directly measuring the phase, we can measure the PSH and EHDW displacement with 10 nm spatial and sub-picosecond time resolution. We obtain both the spin diffusion and mobility and ambipolar diffusion and mobility from the TGS measurements of PSH and EHDW, respectively. The spin transresistivity extracted from the spin diffusion is in excellent agreement with the RPA theory of spin Coulomb drag (SCD). The spin mobility data indicate that SCD may also play a role in the spin wave drifting process. From the ambipolar diffusion and mobility, we obtain the transresistivity of electrons and holes in the same layer, which is much stronger than is typically seen in the conventional Coulomb drag experiments on coupled quantum wells.

  11. Solution-Processed Ambipolar Organic Thin-Film Transistors by Blending p- and n-Type Semiconductors: Solid Solution versus Microphase Separation.

    PubMed

    Xu, Xiaomin; Xiao, Ting; Gu, Xiao; Yang, Xuejin; Kershaw, Stephen V; Zhao, Ni; Xu, Jianbin; Miao, Qian

    2015-12-30

    Here, we report solid solution of p- and n-type organic semiconductors as a new type of p-n blend for solution-processed ambipolar organic thin film transistors (OTFTs). This study compares the solid-solution films of silylethynylated tetraazapentacene 1 (acceptor) and silylethynylated pentacene 2 (donor) with the microphase-separated films of 1 and 3, a heptagon-embedded analogue of 2. It is found that the solid solutions of (1)x(2)1-x function as ambipolar semiconductors, whose hole and electron mobilities are tunable by varying the ratio of 1 and 2 in the solid solution. The OTFTs of (1)0.5(2)0.5 exhibit relatively balanced hole and electron mobilities comparable to the highest values as reported for ambipolar OTFTs of stoichiometric donor-acceptor cocrystals and microphase-separated p-n bulk heterojunctions. The solid solution of (1)0.5(2)0.5 and the microphase-separated blend of 1:3 (0.5:0.5) in OTFTs exhibit different responses to light in terms of absorption and photoeffect of OTFTs because the donor and acceptor are mixed at molecular level with π-π stacking in the solid solution. PMID:25886029

  12. 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

  13. Microcrystallization of a Solution-Processable Organic Semiconductor in Capillaries for High-Performance Ambipolar Field-Effect Transistors.

    PubMed

    Watanabe, Satoshi; Fujita, Takuma; Ribierre, Jean-Charles; Takaishi, Kazuto; Muto, Tsuyoshi; Adachi, Chihaya; Uchiyama, Masanobu; Aoyama, Tetsuya; Matsumoto, Mutsuyoshi

    2016-07-13

    We report on the use of microcrystallization in capillaries to fabricate patterned crystalline microstructures of the low-bandgap ambipolar quinoidal quaterthiophene derivative (QQT(CN)4) from a chloroform solution. Aligned needle-shaped QQT(CN)4 crystals were formed in thin film microstructures using either open- or closed- capillaries made of polydimethylsiloxane (PDMS). Their charge transport properties were evaluated in a bottom-gate top-contact transistor configuration. Hole and electron mobilities were found to be as high as 0.17 and 0.083 cm(2) V(-1) s(-1), respectively, approaching the values previously obtained in individual QQT(CN)4 single crystal microneedles. It was possible to control the size of the needle crystals and the microline arrays by adjusting the structure of the PDMS mold and the concentration of QQT(CN)4 solution. These results demonstrate that the microcrystallization in capillaries technique can be used to simultaneously pattern organic needle single crystals and control the microcrystallization processes. Such a simple and versatile method should be promising for the future development of high-performance organic electronic devices. PMID:27150559

  14. 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

  15. Field-Effect Modulation of Ambipolar Doping and Domain Wall Band Alignment in P-type Vanadium Dioxide Nanowires

    NASA Astrophysics Data System (ADS)

    Hou, Yasen; Peng, Xingyue; Yang, Yiming; Yu, Dong

    The sub-picosecond metal-insulator phase transition in vanadium dioxide (VO2) has attracted extensive attention with potential applications in ultrafast Mott transistors. However, the development of VO2-based transistors lags behind, owing to the lack of an efficient and hysteresis-free electrostatic doping control. Here we report the first synthesis of p-type single crystalline VO2nanowires via catalyst-free chemical vapor deposition. The p-type doping was unambiguously confirmed by both solid and electrochemical gating methods, and further evidenced by the scanning photocurrent microscopic measurements. Interestingly, we observed that the photocurrent spot polarity at the metal-insulator domain walls was reversibly switched by electrochemical gating, which indicates a band bending flipping. Furthermore, we eliminated the common hysteresis in gate sweep and greatly shortened the transistor response time 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 new opportunities on understanding the phase transition mechanism and enables novel electronic applications based on VO2.

  16. Quantum and Classical Magnetoresistance in Ambipolar Topological Insulator Transistors with Gate-tunable Bulk and Surface Conduction

    PubMed Central

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

    2014-01-01

    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. PMID:24810663

  17. Optically Induced PN Junction Diode and Photovoltaic Response on Ambipolar MoSe2 Field-effect Transistor

    NASA Astrophysics Data System (ADS)

    Pradhan, Nihar; Lu, Zhengguang; Rhodes, Daniel; Terrones, Mauricio; Smirnov, Dmitry; Balicas, Luis

    2015-03-01

    Transition metal dichalcogenides (TMDs) have emerged as an attractive material for electronic and optoelectronic devices due to their sizable band gap, flexibility and reduced dimensionality, which makes them promising candidates for applications in translucent optoelectronics components, such as solar cells and light emitting diodes. Here, we present an optically induced diode like response and concomitant photovoltaic effect in few-atomic layers molybdenum diselenide (MoSe2) field-effect transistors. Compared to recently reported PN junctions based on TMDs, ambipolar MoSe2 shows nearly ideal diode rectification under illumination, with a sizable photovoltaic efficiency. The observed light induced diode response under fixed gate voltage, yields a maximum open circuit voltage 0.28V and short circuit current 230nA at 30uW incident laser power. The sense of current rectification can be altered by changing the polarity of the applied gate voltage (Vbg) . At Vbg = 0V the highest electrical power obtained is 175pW corresponding to a maximum photovoltaic efficiency of 0.01%. These values increased to 11nW and 0.05% under a Vbg = -7.5V. At an excitation voltage 1V we observed maximum photocurrent responsivity surpassing 100mA/W with corresponding external quantum efficiency ~ 30%.

  18. 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

  19. 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.

  20. 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.

  1. 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

  2. On the diffusion of free carriers in {beta}-rhombohedral boron

    SciTech Connect

    Werheit, H. . E-mail: helmut.werheit@koeln.de; Moldenhauer, A.

    2006-09-15

    To determine the diffusion of untrapped carriers in {beta}-rhombohedral boron, we constructed a feedback pico-ammeter based on pulse integration technique. This enabled measuring deviations from the bias in a 10{sup 9}{omega} sample in the order of 1nA with 0.7ms time resolution. For the first time, we obtained the drift velocity of optically generated untrapped electron-hole pairs 106(20)cms{sup -1} yielding for the band-determined diffusion coefficient D=12(4)cm{sup 2}s{sup -1} and for the carrier mobility {mu}{sub ambipolar}=565(120)cm{sup 2}V{sup -1}s{sup -1}. Fitting Fick's second law to the measured trap-determined dispersion of carriers yields the ambipolar diffusion coefficient D*=0.043(14) and 0.28(10)cm{sup 2}s{sup -1} at 260 and 340K, respectively. The thermal activation energy of 0.18eV agrees with the well-known trapping levels in {beta}-rhombohedral boron.

  3. Holographic diffusers

    NASA Astrophysics Data System (ADS)

    Wadle, Stephen; Wuest, Daniel; Cantalupo, John; Lakes, Roderic S.

    1994-01-01

    Holographic diffusers are prepared using silver halide (Agfa 8E75 and Kodak 649F) and photopolymer (Polaroid DMP 128 and DuPont 600, 705, and 150 series) media. It is possible to control the diffusion angle in three ways: by selection of the properties of the source diffuser, by control of its subtended angle, and by selection of the holographic medium. Several conventional diffusers based on refraction or scattering of light are examined for comparison.

  4. 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.

  5. 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.

  6. End-boundary sheath potential, electron and ion energy distribution in the low-pressure non-ambipolar electron plasma

    NASA Astrophysics Data System (ADS)

    Chen, Lee; Chen, Zhiying; Funk, Merritt

    2013-12-01

    The end-boundary floating-surface sheath potential, electron and ion energy distribution functions (EEDf, IEDf) in the low-pressure non-ambipolar electron plasma (NEP) are investigated. The NEP is heated by an electron beam extracted from an inductively coupled electron-source plasma (ICP) through a dielectric injector by an accelerator located inside the NEP. This plasma's EEDf has a Maxwellian bulk followed by a broad energy continuum connecting to the most energetic group with energies around the beam energy. The NEP pressure is 1-3 mTorr of N2 and the ICP pressure is 5-15 mTorr of Ar. The accelerator is biased positively from 80 to 600 V and the ICP power range is 200-300 W. The NEP EEDf and IEDf are determined using a retarding field energy analyser. The EEDf and IEDf are measured at various NEP pressures, ICP pressures and powers as a function of accelerator voltage. The accelerator current and sheath potential are also measured. The IEDf reveals mono-energetic ions with adjustable energy and it is proportionally controlled by the sheath potential. The NEP end-boundary floating surface is bombarded by a mono-energetic, space-charge-neutral plasma beam. When the injected energetic electron beam is adequately damped by the NEP, the sheath potential is linearly controlled at almost a 1 : 1 ratio by the accelerator voltage. If the NEP parameters cannot damp the electron beam sufficiently, leaving an excess amount of electron-beam power deposited on the floating surface, the sheath potential will collapse and become unresponsive to the accelerator voltage.

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

    NASA Technical Reports Server (NTRS)

    Edmonds, Larry D.

    1991-01-01

    Charge-carrier diffusion from an ion track in a silicon substrate at least a few hundred microns thick is analyzed. 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 predictions 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.

  8. Control of Ambipolar Transport in SnO Thin-Film Transistors by Back-Channel Surface Passivation for High Performance Complementary-like Inverters.

    PubMed

    Luo, Hao; Liang, Lingyan; Cao, Hongtao; Dai, Mingzhi; Lu, Yicheng; Wang, Mei

    2015-08-12

    For ultrathin semiconductor channels, the surface and interface nature are vital and often dominate the bulk properties to govern the field-effect behaviors. High-performance thin-film transistors (TFTs) rely on the well-defined interface between the channel and gate dielectric, featuring negligible charge trap states and high-speed carrier transport with minimum carrier scattering characters. The passivation process on the back-channel surface of the bottom-gate TFTs is indispensable for suppressing the surface states and blocking the interactions between the semiconductor channel and the surrounding atmosphere. We report a dielectric layer for passivation of the back-channel surface of 20 nm thick tin monoxide (SnO) TFTs to achieve ambipolar operation and complementary metal oxide semiconductor (CMOS) like logic devices. This chemical passivation reduces the subgap states of the ultrathin channel, which offers an opportunity to facilitate the Fermi level shifting upward upon changing the polarity of the gate voltage. With the advent of n-type inversion along with the pristine p-type conduction, it is now possible to realize ambipolar operation using only one channel layer. The CMOS-like logic inverters based on ambipolar SnO TFTs were also demonstrated. Large inverter voltage gains (>100) in combination with wide noise margins are achieved due to high and balanced electron and hole mobilities. The passivation also improves the long-term stability of the devices. The ability to simultaneously achieve field-effect inversion, electrical stability, and logic function in those devices can open up possibilities for the conventional back-channel surface passivation in the CMOS-like electronics. PMID:26189702

  9. 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.

  10. 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.

  11. Knudsen Reactivity Reduction: Kinetic Theory of Diffusion Process

    NASA Astrophysics Data System (ADS)

    Nelson, Eric; Dodd, Evan; Molvig, Kim; Albright, Brian; Hoffman, Nelson; Zimmerman, George; Williams, Ed

    2012-10-01

    Previous work that found significant fusion reactivity reduction due to Knudsen layer losses [1], utilized a twice simplified treatment of the loss process that first went to the diffusion limit of the transport and then replaced the spatial kinetic diffusion operator by a local loss process. The derivation of kinetic diffusion utilized a stochastic differential equation technique to show that convection in combination with pitch-angle scattering yields spatial diffusion asymptotically over long time and spatial intervals. The same technique can be extended to include the independent energy scattering stochastic process. For the linear Fokker-Planck equation that governs the tail ions this gives a very efficient (particle like) numerical technique that can solve the complete ion tail problem in the three phase space dimensions of pitch-angle, energy, and spatial coordinate. The method allows inclusion of a temperature gradient and specified ambipolar electric fields. We present simulation results of the depleted tail distributions and fusion reactivities, and compare with the predictions of the simple local loss method.[4pt] [1] Kim Molvig, Nelson N. Hoffman, Brian J. Albright, Eric M. Nelson, and, Robert J. Webster (submitted to Physical Review Letters, 2012)

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. High performance weak donor-acceptor polymers in thin film transistors: effect of the acceptor on electronic properties, ambipolar conductivity, mobility, and thermal stability.

    PubMed

    Yuen, Jonathan D; Fan, Jian; Seifter, Jason; Lim, Bogyu; Hufschmid, Ryan; Heeger, Alan J; Wudl, Fred

    2011-12-28

    We have studied the electronic, physical, and transistor properties of a family of donor-acceptor polymers consisting of diketopyrrolopyrrole (DPP) coupled with different accepting companion units in order to determine the effects of donor-acceptor interaction. Using the electronically neutral benzene (B), the weakly accepting benzothiadiazole (BT), and the strongly accepting benzobisthiadiazole (BBT), the accepting strength of the companion unit was systematically modulated. All polymers exhibited excellent transistor performance, with mobilities above 0.1 cm(2)V(-1)s(-1), even exceeding 1 cm(2)V(-1)s(-1) for one of the BBT-containing polymers. We find that the BBT is the strongest acceptor, enabling the BBT-containing polymers to be strongly ambipolar. The BBT moiety also strengthens interchain interactions, which provides higher thermal stability and performance for transistors with BBT-containing polymers as the active layer. PMID:22043809

  18. End-boundary sheath potential, Langmuir waves, electron and ion energy distribution in the low pressure DC powered Non-ambipolar Electron Plasma

    NASA Astrophysics Data System (ADS)

    Chen, Lee; Chen, Zhiying; Funk, Merritt

    2013-09-01

    The non-ambipolar electron plasma (NEP) is heated by electron beam extracted from the electron-source Ar plasma through a dielectric injector by an accelerator located inside NEP. NEP pressure is in the 1-3mTorr range of N2 and its accelerator voltage varied from VA = + 80 to VA = + 600V. The non-ambipolar beam-current injected into NEP is in the range of 10s Acm-2 and it heats NEP through beam-plasma instabilities. Its EED f has a Maxwellian bulk followed by a broad energy-continuum connecting to the most energetic group with energies above the beam-energy. The remnant of the injected electron-beam power terminates at the NEP end-boundary floating-surface setting up sheath potentials from VS = 80 to VS = 580V in response to the applied values of VA. The floating-surface is bombarded by a space-charge neutral plasma-beam whose IED f is near mono-energetic. When the injected electron-beam power is adequately damped by NEP, its end-boundary floating-surface VS can be linearly controlled at almost 1:1 ratio by VA. NEP does not have an electron-free sheath; its ``sheath'' is a widen presheath that consists of a thermal presheath followed by an ``anisotropic'' presheath, leading up to the end-boundary floating-surface. Its ion-current of the plasma-beam is much higher than what a conventional thermal presheath can supply. If the NEP parameters cannot damp the electron beam power sufficiently, VS will collapse and becomes irresponsive to VA.

  19. 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…

  20. 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.

  1. 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)

  2. 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. PMID:19391727

  3. 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.

  4. Quantum diffusion

    SciTech Connect

    Habib, S.

    1994-10-01

    We consider a simple quantum system subjected to a classical random force. Under certain conditions it is shown that the noise-averaged Wigner function of the system follows an integro-differential stochastic Liouville equation. In the simple case of polynomial noise-couplings this equation reduces to a generalized Fokker-Planck form. With nonlinear noise injection new ``quantum diffusion`` terms rise that have no counterpart in the classical case. Two special examples that are not of a Fokker-Planck form are discussed: the first with a localized noise source and the other with a spatially modulated noise source.

  5. 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)

  6. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Air-stable ambipolar organic field effect transistors with heterojunction of pentacene and N,N' -bis(4-trifluoromethylben-zyl) perylene-3,4,9,10-tetracarboxylic diimide

    NASA Astrophysics Data System (ADS)

    Li, Jian-Feng; Chang, Wen-Li; Ou, Gu-Ping; Zhang, Fu-Jia

    2009-07-01

    Fabrication of ambipolar organic field-effect transistors (OFETs) is essential for the achievement of an organic complementary logic circuit. Ambipolar transports in OFETs with heterojunction structures are realized. We select pentacene as a P-type material and N,N'-bis(4-trifluoromethylben-zyl)perylene-3,4,9,10-tetracarboxylic diimide (PTCDI-TFB) as a n-type material in the active layer of the OFETs. The field-effect transistor shows highly air-stable ambipolar characteristics with a field-effect hole mobility of 0.18 cm2/(V.s) and field-effect electron mobility of 0.031 cm2/(V.s). Furthermore the mobility only slightly decreases after being exposed to air and remains stable even for exposure to air for more than 60 days. The high electron affinity of PTCDI-TFB and the octadecyltrichlorosilane (OTS) self-assembly monolayer between the SiO2 gate dielectric and the organic active layer result in the observed air-stable characteristics of OFETs with high mobility. The results demonstrate that using the OTS as a modified gate insulator layer and using high electron affinity semiconductor materials are two effective methods to fabricate OFETs with air-stable characteristics and high mobility.

  7. 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.

  8. 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).

  9. Cyano-substituted oligo(p-phenylene vinylene) single-crystal with balanced hole and electron injection and transport for ambipolar field-effect transistors.

    PubMed

    Deng, Jian; Tang, Jia; Xu, Yuanxiang; Liu, Liqun; Wang, Yan; Xie, Zengqi; Ma, Yuguang

    2015-02-01

    High and balanced hole and electron mobilities were achieved in OFETs based on the high photoluminescence of a 1,4-bis(2-cyano-2-phenylethenyl)benzene single-crystal with symmetric electrodes. For electron and hole, the operation voltage in the OFETs based on symmetric gold electrodes was 30 and -20 V, respectively. The accumulation threshold voltage is low enough for the OFETs to operate in an ambipolar model with the source/drain voltage (Vds) around 50 V despite the high injection barrier. The highest electron and hole mobility was 0.745 cm(2) V(-1) s(-1) and 0.239 cm(2) V(-1) s(-1), and the current density reached 90.7 and 27.4 A cm(-2), respectively with an assumed 10 nm accumulation layer. The high mobility comes from the strong π-π interactions. In addition, the highly ordered hydrogen bonding matrix may create an efficient route to pump the charge to the inner layer which can improve the injection ability. PMID:25530541

  10. 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)

  11. 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

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

    NASA Astrophysics Data System (ADS)

    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).

  13. 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.

  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. Diffusion of Magnetic Field and Removal of Magnetic Flux from Clouds Via Turbulent Reconnection

    NASA Astrophysics Data System (ADS)

    Santos-Lima, R.; Lazarian, A.; de Gouveia Dal Pino, E. M.; Cho, J.

    2010-05-01

    The diffusion of astrophysical magnetic fields in conducting fluids in the presence of turbulence depends on whether magnetic fields can change their topology via reconnection in highly conducting media. Recent progress in understanding fast magnetic reconnection in the presence of turbulence reassures that the magnetic field behavior in computer simulations and turbulent astrophysical environments is similar, as far as magnetic reconnection is concerned. This makes it meaningful to perform MHD simulations of turbulent flows in order to understand the diffusion of magnetic field in astrophysical environments. Our studies of magnetic field diffusion in turbulent medium reveal interesting new phenomena. First of all, our three-dimensional MHD simulations initiated with anti-correlating magnetic field and gaseous density exhibit at later times a de-correlation of the magnetic field and density, which corresponds well to the observations of the interstellar media. While earlier studies stressed the role of either ambipolar diffusion or time-dependent turbulent fluctuations for de-correlating magnetic field and density, we get the effect of permanent de-correlation with one fluid code, i.e., without invoking ambipolar diffusion. In addition, in the presence of gravity and turbulence, our three-dimensional simulations show the decrease of the magnetic flux-to-mass ratio as the gaseous density at the center of the gravitational potential increases. We observe this effect both in the situations when we start with equilibrium distributions of gas and magnetic field and when we follow the evolution of collapsing dynamically unstable configurations. Thus, the process of turbulent magnetic field removal should be applicable both to quasi-static subcritical molecular clouds and cores and violently collapsing supercritical entities. The increase of the gravitational potential as well as the magnetization of the gas increases the segregation of the mass and magnetic flux in the

  16. 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.

  17. 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.

  18. 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.

  19. FRACTIONAL PEARSON DIFFUSIONS

    PubMed Central

    Leonenko, Nikolai N.; Meerschaert, Mark M.

    2013-01-01

    Pearson diffusions are governed by diffusion equations with polynomial coefficients. Fractional Pearson diffusions are governed by the corresponding time-fractional diffusion equation. They are useful for modeling sub-diffusive phenomena, caused by particle sticking and trapping. This paper provides explicit strong solutions for fractional Pearson diffusions, using spectral methods. It also presents stochastic solutions, using a non-Markovian inverse stable time change. PMID:23626377

  20. 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.

  1. 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.

  2. 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.

  3. Diffusion on spatial network

    NASA Astrophysics Data System (ADS)

    Hui, Zi; Tang, Xiaoyue; Li, Wei; Greneche, Jean-Marc; Wang, Qiuping A.

    2015-04-01

    In this work, we study the problem of diffusing a product (idea, opinion, disease etc.) among agents on spatial network. The network is constructed by random addition of nodes on the planar. The probability for a previous node to be connected to the new one is inversely proportional to their spatial distance to the power of α. The diffusion rate between two connected nodes is inversely proportional to their spatial distance to the power of β as well. Inspired from the Fick's first law, we introduce the diffusion coefficient to measure the diffusion ability of the spatial network. Using both theoretical analysis and Monte Carlo simulation, we get the fact that the diffusion coefficient always decreases with the increasing of parameter α and β, and the diffusion sub-coefficient follows the power-law of the spatial distance with exponent equals to -α-β+2. Since both short-range diffusion and long-range diffusion exist, we use anomalous diffusion method in diffusion process. We get the fact that the slope index δ in anomalous diffusion is always smaller that 1. The diffusion process in our model is sub-diffusion.

  4. UPDATING APPLIED DIFFUSION MODELS

    EPA Science Inventory

    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 Socie...

  5. 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.

  6. 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)

  7. 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…

  8. Diffusion of uranium hexafluoride

    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 uranium hexafluoride

  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. 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

  11. 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

  12. 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.

  13. Diffusion in disordered media

    NASA Astrophysics Data System (ADS)

    Havlin, Shlomo; Ben-Avraham, Daniel

    2002-01-01

    Diffusion in disordered systems does not follow the classical laws which describe transport in ordered crystalline media, and this leads to many anomalous physical properties. Since the application of percolation theory, the main advances in the understanding of these processes have come from fractal theory. Scaling theories and numerical simulations are important tools to describe diffusion processes (random walks: the 'ant in the labyrinth') on percolation systems and fractals. Different types of disordered systems exhibiting anomalous diffusion are presented (the incipient infinite percolation cluster, diffusion-limited aggregation clusters, lattice animals, and random combs), and scaling theories as well as numerical simulations of greater sophistication are described. Also, diffusion in the presence of singular distributions of transition rates is discussed and related to anomalous diffusion on disordered structures.

  14. Hereditary Diffuse Infiltrating Retinoblastoma.

    PubMed

    Schedler, Katharina J E; Traine, Peter G; Lohmann, Dietmar R; Haritoglou, Christos; Metz, Klaus A; Rodrigues, Eduardo B

    2016-03-01

    Retinoblastoma is one of the most common childhood cancers. The diffuse infiltrating retinoblastoma is a rare subtype of this neoplasm. The majority of cases of diffuse infiltrating retinoblastoma are unilateral and occur sporadically. Herein we report on a family with three children affected by retinoblastoma, among them one girl with diffuse infiltrating retinoblastoma. This girl was diagnosed at the age of 8 years with a unilateral diffuse infiltrating retinoblastoma. By contrast, the two brothers became clinically apparent in the first 2 years of life with bilateral retinoblastoma. The parents were clinically unremarkable. Genetic analysis of RB1 gene was performed. The girl with diffuse infiltrating RB was found to be heterozygous for an oncogenic mutation in the RB1 gene that was also carried by both brothers and the father of the family. These results show that diffuse infiltrating retinoblastoma can develop on the background of a hereditary predisposition to retinoblastoma. PMID:24892564

  15. Multinomial diffusion equation

    NASA Astrophysics Data System (ADS)

    Balter, Ariel; Tartakovsky, Alexandre M.

    2011-06-01

    We describe a new, microscopic model for diffusion that captures diffusion induced fluctuations at scales where the concept of concentration gives way to discrete particles. We show that in the limit as the number of particles N→∞, our model is equivalent to the classical stochastic diffusion equation (SDE). We test our new model and the SDE against Langevin dynamics in numerical simulations, and show that our model successfully reproduces the correct ensemble statistics, while the classical model fails.

  16. Multinomial diffusion equation

    SciTech Connect

    Balter, Ariel I.; Tartakovsky, Alexandre M.

    2011-06-24

    We describe a new, microscopic model for diffusion that captures diffusion induced uctuations at scales where the concept of concentration gives way to discrete par- ticles. We show that in the limit as the number of particles N ! 1, our model is equivalent to the classical stochastic diffusion equation (SDE). We test our new model and the SDE against Langevin dynamics in numerical simulations, and show that our model successfully reproduces the correct ensemble statistics, while the classical model fails.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. The Diffusion of Innovation

    NASA Technical Reports Server (NTRS)

    Earabino, Gerard J.; Heyl, G. Christopher; Percorini, Thomas J.

    1987-01-01

    New ideas encounter obstacles on way to becoming products. Report examines process by which new ideas become products, processes, or accepted standards. Sequence of events called "the diffusion of innovation." Focuses on development of material processing in low gravity as case study in diffusion of innovation.

  2. 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…

  3. 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…

  4. 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.

  5. 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

  6. 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.

  7. Diffusion on strained surfaces

    NASA Astrophysics Data System (ADS)

    Schroeder, M.; Wolf, D. E.

    1997-03-01

    The change of diffusion kinetics when elastic fields are present is discussed for diffusion on (001) surfaces of simple cubic, fcc and bcc lattices. All particles interact pairwise with a Lennard-Jones potential. The simple cubic lattice was stabilized by an anisotropic prefactor. It is found that generically compressive strain enhances diffusion whereas tensile strain increases the activation barrier. An approximately linear dependence of the barrier in a wide range of misfits is found. In heteroepitaxy, diffusion on top of large clusters is inhomogeneous and anisotropic. The kinetics close to edges and centers of islands are remarkably different. In many cases changes of binding energies are small compared to those of saddle point energies. Thermodynamic arguments (minimization of free energy) are not appropriate to describe diffusion on strained surfaces in these cases.

  8. Thorium Diffusion in Monazite

    NASA Astrophysics Data System (ADS)

    Cherniak, D. J.

    2006-05-01

    Diffusion of thorium has been characterized in synthetic monazite under dry conditions. The synthetic monazites (either pure CePO4, NdPO4, or a mixed LREE phosphate containing Ce, Nd, and Sm) were grown via a Na2CO3-MoO3 flux method. The source of diffusant for the experiments were either synthesized ThSiO4 or CaTh(PO4)2 powders. Experiments were performed by placing source and monazite in Pt capsules and annealing capsules in 1 atm furnaces for times ranging from 10 days to a few hours, at temperatures from 1400 to 1550C. The Th distributions in the monazite were profiled by Rutherford Backscattering Spectrometry (RBS). The following Arrhenius relation was obtained for diffusion in monazite: DSm = 7.2x103 exp(-814 kJ mol-1/RT) m2sec-1 The diffusivity of Th was similar for monazites containing a single REE and the mixed LREE phosphates. Th diffusion was also similar for experiments run using the Th silicate and Ca-Th phosphate sources, suggesting that the substitutional mechanism for Th in monazite, i.e, Th+4 + Si+4 for REE+3 + P+5 with the ThSiO4 source, and Th+4 + Ca+2 for 2REE+3 with the CaTh(PO4)2 source, does not significantly affect Th diffusivities, and that Th is likely the rate-limiting species. Th diffusion in monazite is about 4 orders of magnitude slower than Pb diffusion (Cherniak et al., 2004). This contrasts with findings of Gardes et al. (2005) who determined that Pb, Th and REE diffusivities in monazite are similar. Th diffusion in zircon (Cherniak et al., 1997) is about an order of magnitude slower than in monazite, but with similar activation energy for diffusion. The smaller diffusivities in zircon may be a consequence of the larger disparity in size between Th and the Zr site in zircon as compared with Th and the REE site in monazite. Nonetheless, Th is essentially immobile in monazite with respect to exchange by volume diffusion under most geologic conditions; these findings may have implications for containment of high- level actinide

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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 ...

  14. 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.

  15. 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.

  16. Mastocytosis, diffuse cutaneous (image)

    MedlinePlus

    This is a picture of diffuse, cutaneous mastocytosis. Abnormal collections of cells in the skin (mast cells) produce this rash. Unlike bullous mastocytosis, rubbing will not lead to formation of blisters ( ...

  17. Lung diffusion testing

    MedlinePlus

    Lung diffusion testing measures how well the lungs exchange gases. This is an important part of lung testing , because ... Gender Height Hemoglobin (the protein in red blood cells that carries oxygen) level

  18. 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

  19. Nodal Diffusion & Transport Theory

    Energy Science and Technology Software Center (ESTSC)

    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.

  20. 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.

  1. Cation Diffusion in Xenotime

    NASA Astrophysics Data System (ADS)

    Cherniak, D. J.

    2004-05-01

    Xenotime is an important mineral in metamorphic paragenesis, and useful in isotopic dating, garnet-xenotime thermometry, and monazite-xenotime thermometry, so diffusion data for xenotime of cations of geochronological and geochemical importance are of some interest. We report here on diffusion of the rare earth elements Sm, Dy and Yb in synthetic xenotime under dry conditions. The synthetic xenotime was grown via a Na2}CO{3}-MoO_{3 flux method. The source of diffusant for the experiments were REE phosphate powders, with experiments run with sources containing a single REE. Experiments were performed by placing source and xenotime in Pt capsules, and annealing capsules in 1 atm furnaces for times ranging from thirty minutes to a month, at temperatures from 1000 to 1400C. The REE distributions in the xenotime were profiled by Rutherford Backscattering Spectrometry (RBS). The following Arrhenius relations are obtained for diffusion in xenotime, normal to (101): DSm = 1.7x10-4 exp(-442 kJ mol-1/RT) m2}sec{-1 DDy = 3.5x10-7 exp(-365 kJ mol-1/RT) m2}sec{-1 DYb = 7.4x10-7 exp(-371 kJ mol-1/RT) m2}sec{-1. Diffusivities of these REE do not differ greatly in xenotime, in contrast to the findings noted for the REE in zircon (Cherniak et al., 1997), where the LREE diffuse more slowly, and with higher activation energies for diffusion, than the heavier rare earths. In zircon, these differences among diffusion of the rare earths are attributed to the relatively large size of the REE with respect to Zr, for which they substitute in the zircon lattice. With the systematic increase in ionic radius from the heavy to lighter REE, this size mismatch becomes more pronounced and diffusivities of the LREE are as consequence slower. Although xenotime is isostructural with zircon, the REE are more closely matched in size to Y, so in xenotime this effect appears much smaller and the REE diffuse at similar rates. In addition, the process of diffusion in xenotime likely involves simple REE+3

  2. Ti Diffusion in Pyroxene

    NASA Astrophysics Data System (ADS)

    Cherniak, D.; Liang, Y.

    2008-12-01

    Diffusion of titanium has been characterized in natural enstatite and diopside under buffered conditions and in air. The sources of diffusant for the enstatite experiments were mixtures of Mg, Si and Ti oxide powders, which were combined and heated at 1300°C overnight, and then thoroughly mixed with synthesized enstatite powder and heated for an additional day at 1300°C. Sources for diopside experiments were prepared similarly, using Ca, Mg, Si, and Ti oxide powders combined with synthesized diopside powder, with heating of source materials at 1200°C. Buffered experiments were prepared by enclosing source material and pyroxene (polished and pre-annealed under conditions comparable to those to be experienced in the experiment) in AgPd or platinum capsules, placing the metal capsule in a silica glass capsule with a solid buffer (to buffer at NNO or IW) and sealing the assembly under vacuum. Some experiments on enstatite were run in air; sample and source were placed in Pt capsules and crimped shut. Prepared capsules were then annealed in 1 atm furnaces for times ranging from 8 hours to a few months, at temperatures from 950 to 1200°C. The Ti distributions in the pyroxene were profiled with Rutherford Backscattering Spectrometry (RBS). The following Arrhenius relation is obtained for Ti diffusion in a natural enstatite, for diffusion normal to the (210) cleavage face (950 - 1150°C, experiments run in air): DTi = 1.9×10-10 exp(-300 ± 44 kJ mol-1/RT) m2 sec-1. Diffusion under NNO and IW-buffered conditions is similar to that for experiments run in air, suggesting little dependence of Ti diffusion on oxygen fugacity. There is also little evidence of anisotropy, as diffusion normal to (001) does not differ significantly from diffusion for the other orientation. Preliminary findings for Ti diffusion in diopside suggest diffusivities similar to those for enstatite. Ti diffusivities in enstatite are similar to those of the trivalent REEs (Cherniak and Liang, 2007

  3. Counterion Diffusion in Ionomers

    NASA Astrophysics Data System (ADS)

    Walter, Russell; Winey, Karen; Kim, Joon-Seop; Composto, Russell

    2004-03-01

    Diffusion of Cs counterions to the air/ionomer film interface is followed using Rutherford backscattering spectrometry and results compared with the "sticky reptation" model[1]. The ionomer system is poly(styrene-ran-methacrylic acid) (Cs-SMAA) neutralized at 100% by Cs. The concentration profiles exhibit a surface excess, z*, of Cs followed by a depletion of Cs. The z* and depletion layer thickness grow as t1/2, consistent with diffusion limited growth. Annealing studies at 130 °C, 145 °C and 208 °C were used to extract the diffusion coefficient, D. In all cases, D is greater than that of the matrix chains. These results suggest that the diffusion rate is controlled by the fraction of counterions that disassociate from the acid groups and migrate through the matrix. Moreover, the "sticky reptation" model doesn't appear to predict the diffusion behavior in the Cs-SMAA system. [1] Leibler, L, Ludwick, L., Rubinstein, M., Colby, R.H., Macromolecules 24 (1991) 4701.

  4. 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.

  5. 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.

  6. Diffusion imaging concepts for clinicians.

    PubMed

    Neil, Jeffrey J

    2008-01-01

    This review covers the fundamentals of diffusion tensor imaging. It is written with the clinician in mind and assumes the reader has a passing familiarity with magnetic resonance imaging (MRI). Topics covered include comparison of diffusion MRI with conventional MRI, water apparent diffusion coefficient (ADC), diffusion anisotropy, tract tracing, and changes of water apparent diffusion in response to injury. The discussion centers primarily on applications to the central nervous system, but examples from other tissues are included. PMID:18050325

  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. Radon diffusion modelling.

    PubMed

    Wilkinson, P; Dimbylow, P J

    1985-10-01

    A mathematical model has been developed that examines the ingress of radon into houses, through a vertical crack in an otherwise impervious concrete floor. Initially, the model considered the diffusive flow of radon from its soil source and this simulation has highlighted the dependency of the flux of radon into the house on the magnitude of various parameters, such as the diffusion coefficient of radon in soil. A preliminary investigation of the modelling of pressure-driven flow into a building is presented, and the potential of this type of analysis is discussed. PMID:4081719

  9. Evolution of error diffusion

    NASA Astrophysics Data System (ADS)

    Knox, Keith T.

    1999-10-01

    As we approach the new millennium, error diffusion is approaching the 25th anniversary of its invention. Because of its exceptionally high image quality, it continues to be a popular choice among digital halftoning algorithms. Over the last 24 years, many attempts have been made to modify and improve the algorithm--to eliminate unwanted textures and to extend it to printing media and color. Some of these modifications have been very successful and are in use today. This paper will review the history of the algorithm and its modifications. Three watershed events in the development of error diffusion will be described, together with the lessons learned along the way.

  10. Evolution of error diffusion

    NASA Astrophysics Data System (ADS)

    Knox, Keith T.

    1998-12-01

    As we approach the new millennium, error diffusion is approaching the 25th anniversary of its invention. Because of its exceptionally high image quality, it continues to be a popular choice among digital halftoning algorithms. Over the last 24 years, many attempts have been made to modify and improve the algorithm - to eliminate unwanted textures and to extend it to printing media and color. Some of these modifications have been very successful and are in use today. This paper will review the history of the algorithm and its modifications. Three watershed events in the development of error diffusion will be described, together with the lesions learned along the way.

  11. Mass diffusion in liquids

    NASA Astrophysics Data System (ADS)

    Walter, H. U.

    Dimensionless number analysis indicates that diffusion-controlled conditions with liquid samples having characteristic dimensions larger than one millimetre can only be established under microgravity conditions.Consequently, heat and mass transport properties of fluids can only be quantitatively investigated in space.Results obtained from experiments on selfdiffusion, interdiffusion and thermodiffusion carried out during the SL-1 and D-1 Spacelab missions clearly demonstrate the potential of space platforms to determine such properties with a precision unattainable on earth. These results imply also that crystal growth from solutions, vapours and melts in the diffusive regime can be realised in space only.

  12. 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

  13. Irradiance calibration with solar diffuser

    NASA Technical Reports Server (NTRS)

    Haring, Robert E. (Inventor); Roeder, Herbert A. (Inventor); Hartmann, Ulli G. (Inventor)

    1993-01-01

    The sun's energy is used in combination of movable and fixed diffuser plates, windows and apertures which are positioned in a series of test sequences (modes) for reflectance monitoring and calibration without the use of man-made sources. There are three embodiments, or implementations, of the invention--one embodiment uses two diffusers--a working diffuser and a secondary diffuser--the second embodiment uses three diffusers, a working diffuser, a secondary diffuser and a reference diffuser--and the third embodiment uses two diffusers--a working diffuser and a secondary diffuser, the latter also functioning as a cover for the working diffuser. The movable diffusers are mounted on rotatable cones and, in all embodiments, the sun is blocked from reaching the diffusers when not in use. Thus, the sun is used as a stable source for calibration and monitoring and the sun/diffuser combination is used in such a way that the response of all elements of the optical subsystem of the TOMS can be unambiguously and efficiently characterized with high accuracy and precision.

  14. Diffusion in random networks

    NASA Astrophysics Data System (ADS)

    Padrino, Juan C.; Zhang, Duan Z.

    2015-11-01

    The ensemble phase averaging technique is applied to model mass transport in a porous medium. The porous material is idealized as an ensemble of random networks, where each network consists of a set of junction points representing the pores and tortuous channels connecting them. Inside a channel, fluid transport is assumed to be governed by the one-dimensional diffusion equation. Mass balance leads to an integro-differential equation for the pores mass density. Instead of attempting to solve this equation, and equivalent set of partial differential equations is derived whose solution is sought numerically. As a test problem, we consider the one-dimensional diffusion of a substance from one end to the other in a bounded domain. For a statistically homogeneous and isotropic material, results show that for relatively large times the pore mass density evolution from the new theory is significantly delayed in comparison with the solution from the classical diffusion equation. In the short-time case, when the solution evolves with time as if the domain were semi-infinite, numerical results indicate that the pore mass density becomes a function of the similarity variable xt- 1 / 4 rather than xt- 1 / 2 characteristic of classical diffusion. This result was verified analytically. Possible applications of this framework include flow in gas shales. Work supported by LDRD project of LANL.

  15. 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.

  16. 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.

  17. Diffuse sorption modeling.

    PubMed

    Pivovarov, Sergey

    2009-04-01

    This work presents a simple solution for the diffuse double layer model, applicable to calculation of surface speciation as well as to simulation of ionic adsorption within the diffuse layer of solution in arbitrary salt media. Based on Poisson-Boltzmann equation, the Gaines-Thomas selectivity coefficient for uni-bivalent exchange on clay, K(GT)(Me(2+)/M(+))=(Q(Me)(0.5)/Q(M)){M(+)}/{Me(2+)}(0.5), (Q is the equivalent fraction of cation in the exchange capacity, and {M(+)} and {Me(2+)} are the ionic activities in solution) may be calculated as [surface charge, mueq/m(2)]/0.61. The obtained solution of the Poisson-Boltzmann equation was applied to calculation of ionic exchange on clays and to simulation of the surface charge of ferrihydrite in 0.01-6 M NaCl solutions. In addition, a new model of acid-base properties was developed. This model is based on assumption that the net proton charge is not located on the mathematical surface plane but diffusely distributed within the subsurface layer of the lattice. It is shown that the obtained solution of the Poisson-Boltzmann equation makes such calculations possible, and that this approach is more efficient than the original diffuse double layer model. PMID:19159896

  18. Diffusion welding tool

    NASA Technical Reports Server (NTRS)

    Milam, T. B.

    1973-01-01

    Tool allows flat plate diffusion welding to be done in standard brazing furnace. Weld is achieved using high water pressure applied by hand-operated positive-displacement pump. Good welds have been obtained between nickel and nickel-base alloy plates at temperature of 1200 K and water pressure of 13.8 million N/sq m.

  19. 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.

  20. 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).

  1. Diffusion on Cu surfaces

    NASA Technical Reports Server (NTRS)

    Karimi, Majid

    1993-01-01

    Understanding surface diffusion is essential in understanding surface phenomena, such as crystal growth, thin film growth, corrosion, physisorption, and chemisorption. Because of its importance, various experimental and theoretical efforts have been directed to understand this phenomena. The Field Ion Microscope (FIM) has been the major experimental tool for studying surface diffusion. FIM have been employed by various research groups to study surface diffusion of adatoms. Because of limitations of the FIM, such studies are only limited to a few surfaces: nickel, platinum, aluminum, iridium, tungsten, and rhodium. From the theoretical standpoint, various atomistic simulations are performed to study surface diffusion. In most of these calculations the Embedded Atom Method (EAM) along with the molecular static (MS) simulation are utilized. The EAM is a semi-empirical approach for modeling the interatomic interactions. The MS simulation is a technique for minimizing the total energy of a system of particles with respect to the positions of its particles. One of the objectives of this work is to develop the EAM functions for Cu and use them in conjunction with the molecular static (MS) simulation to study diffusion of a Cu atom on a perfect as well as stepped Cu(100) surfaces. This will provide a test of the validity of the EAM functions on Cu(100) surface and near the stepped environments. In particular, we construct a terrace-ledge-kink (TLK) model and calculate the migration energies of an atom on a terrace, near a ledge site, near a kink site, and going over a descending step. We have also calculated formation energies of an atom on the bare surface, a vacancy in the surface, a stepped surface, and a stepped-kink surface. Our results are compared with the available experimental and theoretical results.

  2. 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

  3. 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.

  4. [Diffuse Pulmonary Ossification].

    PubMed

    Avsar, K; Behr, J; Morresi-Hauf, A

    2016-04-01

    Diffuse pulmonary ossification (DPO) represents an uncommon condition usually associated with different underlying pulmonary and extrapulmonary diseases. In this work, we discuss eleven patients of our clinic with the diagnosis of a diffuse pulmonary ossification. We focus on histological changes in the surrounding lung tissue. Clinical and radiological findings were analysed. The aim of the study is to collect data for a better understanding of this condition, especially in association with interstitial lung disease.Three patients with interstitial lung disease had histological findings of UIP. The follow-up data of these patients showed a benign course of the disease.The analysis of the clinical data yielded a very heterogenous group. Regarding these fact we assume, that DPO is not an own entity, but a pathological epiphenomenon in the context of different conditions, possibly with pathogenetic overlap. PMID:26829606

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. Peridynamic thermal diffusion

    NASA Astrophysics Data System (ADS)

    Oterkus, Selda; Madenci, Erdogan; Agwai, Abigail

    2014-05-01

    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.

  12. 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.

  13. 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.

  14. [Diffuse Lewy body disease].

    PubMed

    Kosaka, K

    1995-12-01

    Diffuse Lewy body disease (DLBD), which we have proposed since 1976, has received great attention among both researchers and clinicians. Recently, it was reported by some English and American research groups that DLBD is the second most frequent dementing illness in the elderly, following Alzheimer-type dementia (ATD). Our recent research of 79 autopsied dementia cases in a hospital disclosed that DLBD (15.4%) was the second most common degenerative dementia, following ATD (43.6%). In 1980 we proposed Lewy body disease, and classified it into three types: brain stem type, transitional type, and diffuse type. Diffuse type of LBD is now called DLBD. In 1990 we divided DLBD into two forms: common form and pure form. The common form of DLBD has more or less Alzheimer pathology, and pure form has none. Very recently, we proposed the cerebral type of LBD, in which numerous Lewy bodies are found in the cerebral cortex and amygdala, but no PD pathology is present in the brain stem. Therefore, LBD is now classified as follows: [table: see text] PMID:8752428

  15. 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.

  16. 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.

  17. Diffusion of Zonal Variables Using Node-Centered Diffusion Solver

    SciTech Connect

    Yang, T B

    2007-08-06

    Tom Kaiser [1] has done some preliminary work to use the node-centered diffusion solver (originally developed by T. Palmer [2]) in Kull for diffusion of zonal variables such as electron temperature. To avoid numerical diffusion, Tom used a scheme developed by Shestakov et al. [3] and found their scheme could, in the vicinity of steep gradients, decouple nearest-neighbor zonal sub-meshes leading to 'alternating-zone' (red-black mode) errors. Tom extended their scheme to couple the sub-meshes with appropriate chosen artificial diffusion and thereby solved the 'alternating-zone' problem. Because the choice of the artificial diffusion coefficient could be very delicate, it is desirable to use a scheme that does not require the artificial diffusion but still able to avoid both numerical diffusion and the 'alternating-zone' problem. In this document we present such a scheme.

  18. Carrier diffusion length measured by optical method in GaN epilayers grown by MOCVD on sapphire substrates

    NASA Astrophysics Data System (ADS)

    Yablonskii, G. P.; Gurskii, A. L.; Pavlovskii, V. N.; Lutsenko, E. V.; Zubialevich, V. Z.; Shulga, T. S.; Stognij, A. I.; Kalisch, H.; Szymakowski, A.; Jansen, R. H.; Alam, A.; Schineller, B.; Heuken, M.

    2005-02-01

    The carrier ambipolar diffusion length L of optically excited carriers in GaN epitaxial layers grown on sapphire substrate was estimated by an optical method using fitting of the experimental photoluminescence spectra recorded from the front and back sides of the samples by the theoretical equation describing light reflection, light absorption and carrier profile in the medium. The estimations were carried out in the range of excitation intensities from 5 W/cm 2 CW up to 1 MW/cm 2 (pulsed), using excitation at the wavelengths of 325, and 337.1 nm in order to vary the excited layer depth. It has been found that in the samples under study the value of L is about 120-130 nm and does not depend significantly on the excitation intensity up to 200 kW/cm 2. Further increase of excitation level leads to higher values of L about 150-170 nm, probably because of the electron-hole plasma expansion.

  19. Anisotropic fractional diffusion tensor imaging

    PubMed Central

    Meerschaert, Mark M; Magin, Richard L; Ye, Allen Q

    2015-01-01

    Traditional diffusion tensor imaging (DTI) maps brain structure by fitting a diffusion model to the magnitude of the electrical signal acquired in magnetic resonance imaging (MRI). Fractional DTI employs anomalous diffusion models to obtain a better fit to real MRI data, which can exhibit anomalous diffusion in both time and space. In this paper, we describe the challenge of developing and employing anisotropic fractional diffusion models for DTI. Since anisotropy is clearly present in the three-dimensional MRI signal response, such models hold great promise for improving brain imaging. We then propose some candidate models, based on stochastic theory.

  20. 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.

  1. 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

  2. A simple flow analysis of diffuser-getter-diffuser systems

    SciTech Connect

    Klein, J. E.; Howard, D. W.

    2008-07-15

    Tritium clean-up systems typically deploy gas processing technologies between stages of palladium-silver (Pd/Ag) diffusers/permeators. The number of diffusers positioned before and after a gas clean-up process to obtain optimal system performance will vary with feed gas inert composition. A simple method to analyze optimal diffuser configuration is presented. The method assumes equilibrium across the Pd/Ag tubes and system flows are limited by diffuser vacuum pump speeds preceding or following the clean-up process. A plot of system feed as a function of inert feed gas composition for various diffuser configuration allows selection of a diffuser configuration for maximum throughput based on feed gas composition. (authors)

  3. FLOW ANALYSIS OF DIFFUSER-GETTER-DIFFUSER SYSTEMS

    SciTech Connect

    Klein, J; Dave W. Howard, D

    2007-07-24

    Tritium clean-up systems typically deploy gas processing technologies between stages of palladium-silver (Pd/Ag) diffusers/permeators. The number of diffusers positioned before and after a gas clean-up process to obtain optimal system performance will vary with feed gas inert composition. A simple method to analyze optimal diffuser configuration is presented. The method assumes equilibrium across the Pd/Ag tubes and system flows are limited by diffuser vacuum pump speeds preceding or following the clean-up process. A plot of system feed as a function of inert feed gas composition for various diffuser configuration allows selection of a diffuser configuration for maximum throughput based on feed gas composition.

  4. 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.

  5. Sampling diffusive transition paths.

    PubMed

    Miller, Thomas F; Predescu, Cristian

    2007-04-14

    The authors 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 the sampling of infinitesimal Brownian increments of the path, as well as a different type of stiffness associated with the sampling of the coarse features of long paths. The fine-feature sampling stiffness is eliminated with the use of the fast sampling algorithm, 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. The authors use the algorithm to sample the transition path ensemble for the structural interconversion of the 38-atom Lennard-Jones cluster at low temperature. PMID:17444696

  6. 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.

  7. The diffusion of microfinance.

    PubMed

    Banerjee, Abhijit; Chandrasekhar, Arun G; Duflo, Esther; Jackson, Matthew O

    2013-07-26

    To study the impact of the choice of injection points in the diffusion of a new product in a society, we developed a model of word-of-mouth diffusion and then applied it to data on social networks and participation in a newly available microfinance loan program in 43 Indian villages. Our model allows us to distinguish information passing among neighbors from direct influence of neighbors' participation decisions, as well as information passing by participants versus nonparticipants. The model estimates suggest that participants are seven times as likely to pass information compared to informed nonparticipants, but information passed by nonparticipants still accounts for roughly one-third of eventual participation. An informed household is not more likely to participate if its informed friends participate. We then propose two new measures of how effective a given household would be as an injection point. We show that the centrality of the injection points according to these measures constitutes a strong and significant predictor of eventual village-level participation. PMID:23888042

  8. 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.

  9. 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

  10. Diffusion limited aggregation. The role of surface diffusion

    NASA Astrophysics Data System (ADS)

    García-Ruiz, Juan M.; Otálora, Fermín

    1991-11-01

    We present a growth model in which the hitting particles are able to diffuse to more stable growth sites in the perimeter of a cluster growing by diffusion limited aggregation. By tuning the diffusion path Ls, the morphological output - from disordered fractal to perfect single crystals - can be controlled. Instabilities appear when the mean length of the crystal faces Lf are greater than 2 Ls.

  11. 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.

  12. 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

  13. 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.

  14. Multilane driven diffusive systems

    NASA Astrophysics Data System (ADS)

    Curatolo, A. I.; Evans, M. R.; Kafri, Y.; Tailleur, J.

    2016-03-01

    We consider networks made of parallel lanes along which particles hop according to driven diffusive dynamics. The particles also hop transversely from lane to lane, hence indirectly coupling their longitudinal dynamics. We present a general method for constructing the phase diagram of these systems which reveals that in many cases their physics reduce to that of single-lane systems. The reduction to an effective single-lane description legitimizes, for instance, the use of a single TASEP to model the hopping of molecular motors along the many tracks of a single microtubule. Then, we show how, in quasi-2D settings, new phenomena emerge due to the presence of non-zero transverse currents, leading, for instance, to strong ‘shear localization’ along the network.

  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. Lateral Diffusion in an Archipelago

    PubMed Central

    Saxton, Michael J.

    1982-01-01

    Lateral diffusion of molecules in lipid bilayer membranes can be hindered by the presence of impermeable domains of gel-phase lipid or of proteins. Effective-medium theory and percolation theory are used to evaluate the effective lateral diffusion constant as a function of the area fraction of fluid-phase lipid and the permeability of the obstructions to the diffusing species. Applications include the estimation of the minimum fraction of fluid lipid needed for bacterial growth, and the enhancement of diffusion-controlled reactions by the channeling effect of solid patches of lipid. PMID:7052153

  17. Solvent diffusion into fluoropolymer membranes

    SciTech Connect

    Aminabhavi, T.M.; Munnolli, R.S.

    1993-12-31

    Solvent diffusion in polymers is important to the physical properties of the material from processing to end-use and shelf-life. Many aspects of diffusion in polymers have been studied using indirect and direct methods. Du Pont`s fluoropolymers are known for their excellent resistance to a variety of organic solvents. This paper describes the measurement of diffusion coefficients and the derived thermodynamic quantities on four different fluoropolymer membranes with several esters. This information is interpreted in terms of the molecular organization and phase structure. Diffusion coefficients are sensitive to structural changes as well as binding and association phenomena.

  18. Fractional diffusion on bounded domains

    DOE PAGESBeta

    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.

  19. 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…

  20. 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)

  1. 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…

  2. 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…

  3. 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.

  4. 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.

  5. 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. PMID:24552718

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Acid diffusion through polymer films

    NASA Astrophysics Data System (ADS)

    Zhang, P. Linda; Eckert, Andrew R.; Willson, C. Grant; Webber, Stephen E.; Byers, Jeffrey D.

    1997-07-01

    In order to perform 0.2 micrometer processes, one needs to study the diffusion of photoacid generators within the photoresist system, since diffusion during post exposure bake time has an influence on the critical dimension (CD). We have developed a new method to study the diffusion of photoacid generators within a polymer film. This new method is based on monitoring the change of the fluorescence intensity of a pH- sensitive fluorescent dye caused by the reaction with photoacid. A simplified version of this experiment has been conducted by introducing acid vapor to quench the fluorescence intensity of this pH sensor. A thin polymer film is spin cast onto the sensor to create a barrier to the acid diffusion process. During the acid diffusion process, the fluorescence intensity of this pH sensor is measured in situ, using excitation and emission wavelengths at 466 nm and 516 nm, respectively. Fluoresceinamine, the pH sensitive fluorescent dye, is covalently bonded onto the treated quartz substrate to form a single dye layer. Poly(hydroxystyrene) (Mn equals 13k, Tg equals 180 degrees Celsius) in PGMEA (5% - 18% by weight) is spin cast onto this quartz substrate to form films with varying thickness. The soft bake time is 60 seconds at 90 degrees Celsius and a typical film has a thickness of 1.4 micrometers. Trifluoroacetic acid is introduced into a small chamber while the fluorescence from this quartz window is observed. Our study focuses on finding the diffusion constant of the vaporized acid (trifluoroacetic acid) in the poly(hydroxystyrene) polymer film. By applying the Fick's second law, (It - Io)/(I(infinity ) - Io) equals erfc [L/(Dt)1/2] is obtained. The change of fluorescence intensity with respect to the diffusion time is monitored. The above equation is used for the data analysis, where L represents the film thickness and t represents the average time for the acid to diffuse through the film. The diffusion constant is calculated to be at the order of 10

  17. 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

  18. DiffuseModel: Modeling the diffuse ultraviolet background

    NASA Astrophysics Data System (ADS)

    Murthy, Jayant

    2015-12-01

    DiffuseModel calculates the scattered radiation from dust scattering in the Milky Way based on stars from the Hipparcos catalog. It uses Monte Carlo to implement multiple scattering and assumes a user-supplied grid for the dust distribution. The output is a FITS file with the diffuse light over the Galaxy. It is intended for use in the UV (900 - 3000 A) but may be modified for use in other wavelengths and galaxies.

  19. 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.

  20. Phosphorus diffusion in polycrystalline silicon

    NASA Astrophysics Data System (ADS)

    Losee, D. L.; Lavine, J. P.; Trabka, E. A.; Lee, S.-T.; Jarman, C. M.

    1984-02-01

    The diffusion of phosphorus in crystallized amorphous Si layers was studied with secondary-ion mass spectroscopy. A two-dimensional diffusion model is used to find effective grain (Dg) and grain-boundary (Dgb) diffusion coefficients. This simplified model leads to Dgb ≤ 10Dg, which is significantly lower than what has been deduced from conventional, larger grained polysilicon. Our result is consistent with specific-gravity measurements, which found a significantly lower ``mass defect'' for layers deposited amorphous and subsequently crystallized as compared to initially polycrystalline layers.

  1. Configurational diffusion of coal macromolecules

    SciTech Connect

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

    1990-01-01

    As shown in last quarter's report on the configurational diffusion of coal macromolecules, the hindered diffusion data for both TPP and coal macromolecules were significantly different from the theoretical correlations. In order to evaluate the factors which could lead to this difference an error analysis was conducted, and the detailed results reported herein. Generally, we did not find any errors which could account for the deviation from the theory, and thus we conclude that this deviation is real and can be ascribed to some factor not considered by the hindered diffusion theory, i.e., attractive or repulsive forces. 2 refs., 4 figs., 4 tabs.

  2. 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.

  3. 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.

  4. 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.

  5. Fluid diffusion in porous silica

    NASA Astrophysics Data System (ADS)

    McCann, Lowell I.

    Fluid motion in porous media has received a great deal of theoretical and experimental attention due to its importance in systems as diverse as ground water aquifers, catalytic processes, and size separation schemes. Often, the motion of interest is the random thermal motion of molecules in a fluid undergoing no net flow. This diffusive motion is particularly important when the size of the pores is nearly the same as the size of the molecules. In this study, fluid diffusion is measured in several varieties of porous silica whose pore structure is determined by the process by which it is made. The samples in this study have porosities (φ, the ratio of the pore volume to the total sample volume) that vary from 0.3 to 0.75 and average pore radii that range from approximately 15 to 120 A. Determining the effect of the pore structure on the diffusion of a liquid in a porous material is complicated by the chemical interactions between the diffusing molecules and the pore surface. In this study, ions in a hydrophilic fluid are used to block the adsorption of the diffusing dye molecules to the hydroxyl groups covering the silica surface. This technique is unlike typical surface treatments of silica in that it does not permanently alter the pore geometry. In this work, fluid diffusion is measured with a transient holographic grating technique where interfering laser beams create a periodic refractive index modulation in the fluid. The diffraction of a third laser off this grating is monitored to determine how quickly the grating relaxes, thereby determining the diffusion coefficient of the molecules in the fluid. Varying the grating periodicity controls the length scale of the diffusion measurement from 1.2 to 100 μm which is much larger than the average pore sizes of the samples. Therefore, over these large scales, we measure 'normal' diffusion, where the mean squared displacement of a diffusing particle varies linearly with time. In one particular type of porous silica

  6. Geometric diffusion of quantum trajectories

    PubMed Central

    Yang, Fan; Liu, Ren-Bao

    2015-01-01

    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. PMID:26178745

  7. Geometric diffusion of quantum trajectories.

    PubMed

    Yang, Fan; Liu, Ren-Bao

    2015-01-01

    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. PMID:26178745

  8. 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.

  9. ANALYSIS OF DIFFUSION FIELD EXPERIMENTS

    EPA Science Inventory

    The report describes general theoretical frameworks for the ordering of diffusion field data in terms of meteorological measurements. The three methods described are surface-layer (Monin-Obukhov) similarity, convective scaling, and statistical theory using wind fluctuations. Earl...

  10. Diffusion of monochromatic classical waves.

    PubMed

    Gerritsen, Sijmen; Bauer, Gerrit E W

    2006-01-01

    We study the diffusion of monochromatic classical waves in a disordered acoustic medium by scattering theory. In order to avoid artifacts associated with mathematical point scatterers, we model the randomness by small but finite insertions. We derive expressions for the configuration-averaged energy flux, energy density, and intensity for one-, two-, and three-dimensional (3D) systems with an embedded monochromatic source using the ladder approximation to the Bethe-Salpeter equation. We study the transition from ballistic to diffusive wave propagation and obtain results for the frequency dependence of the medium properties such as mean free path and diffusion coefficient as a function of the scattering parameters. We discover characteristic differences of the diffusion in 2D as compared to the conventional 3D case, such as an explicit dependence of the energy flux on the mean free path and quite different expressions for the effective transport velocity. PMID:16486306

  11. 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

  12. Energy Transfer and Joint Diffusion

    NASA Astrophysics Data System (ADS)

    Pajor-Gyulai, Zs.; Szász, D.

    2012-03-01

    A paradigm model is suggested for describing the diffusive limit of trajectories of two Lorentz disks moving in a finite horizon periodic configuration of smooth, strictly convex scatterers and interacting with each other via elastic collisions. For this model the diffusive limit of the two trajectories is a mixture of joint Gaussian laws (analogous behavior is expected for the mechanical model of two Lorentz disks).

  13. 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

  14. 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

  15. 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.

  16. 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

  17. 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

  18. An Introduction to Fractional Diffusion

    NASA Astrophysics Data System (ADS)

    Henry, B. I.; Langlands, T. A. M.; Straka, P.

    The mathematical description of diffusion has a long history with many different formulations including phenomenological models based on conservation of mass and constitutive laws; probabilistic models based on random walks and central limit theorems; microscopic stochastic models based on Brownian motion and Langevin equations; and mesoscopic stochastic models based on master equations and Fokker-Planck equations. A fundamental result common to the different approaches is that the mean square displacement of a diffusing particle scales linearly with time. However there have been numerous experimental measurements in which the mean square displacement of diffusing particles scales as a fractional order power law in time. In recent years a great deal of progress has been made in extending the different models for diffusion to incorporate this fractional diffusion. The tools of fractional calculus have proven very useful in these developments, linking together fractional constitutive laws, continuous time random walks, fractional Langevin equations and fractional Brownian motions. These notes provide a tutorial style overview of standard and fractional diffusion processes.

  19. Water diffusion in phonolite melts

    NASA Astrophysics Data System (ADS)

    Schmidt, Burkhard C.; Blum-Oeste, Nils; Flagmeier, Jens

    2013-04-01

    We report an experimental study of total water diffusion (irrespective of water speciation) in two different phonolite melts, which are representative of Montaña Blanca, Tenerife, Spain (MBP) and Laacher See, East Eifel, Germany (LSP-II). Both phonolites have Na-rich compositions, but differ in their alumina saturation index, with MBP being peralkaline and LSP-II being slightly peraluminous. Diffusion couple experiments for MBP were performed at 200-250 MPa in the temperature range of 800-1050 °C and water contents between 1 and 6.5 wt.%. Due to higher liquidus temperatures of LSP-II, the accessible temperature and water concentration range was reduced to 875-1050 °C and 3-6.5 wt.% water. All experiments were performed in rapid quench cold-seal pressure vessels, which enabled rapid heating and quenching of the samples within seconds. Compared to the run durations of 30-90 min, these short heating and cooling periods can be neglected and no corrections needed to be applied for the calculation of the diffusion coefficients. Water diffusion profiles were determined by FT-IR micro-spectroscopy on doubly polished glass sections and the diffusion coefficients were determined by Boltzmann-Matano analysis. Water diffusion increases with increasing water content and temperature and follows the empirical relations:

  20. 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.

  1. Drug diffusion across skin with diffusivity spatially modulated

    NASA Astrophysics Data System (ADS)

    Montoya Arroyave, Isabel

    2014-05-01

    A diffusion and delivery model of a drug across the skin with diffusivity spatially modulated is formulated and solved analytically using computer algebra. The model is developed using one-dimensional diffusion equation with a diffusivity which is a function of position in the skin; with an initial condition which is describing that the drug is initially contained inside a therapeutic patch; with a boundary condition according to which the change in concentration in the patch is minimal, such that assumption of zero flux at the patch-skin interface is valid; and with other boundary condition according to which the microcirculation in the capillaries just below the dermis carries the drug molecules away from the site at a very fast rate, maintaining the inner concentration at 0. The model is solved analytically by the method of the Laplace transform, with Bromwich integral and residue theorem. The concentration profile of the drug in the skin is expressed as an infinite series of Bessel functions. The corresponding total amount of delivered drug is expressed as an infinite series of decreasing exponentials. Also, the corresponding effective time for the therapeutic patch is determined. All computations were performed using computer algebra software, specifically Maple. The analytical results obtained are important for understanding and improving currentapplications of therapeutic patches. For future research it is interesting to consider more general models of spatial modulation of the diffusivity and the possible application of other computer algebra software such as Mathematica and Maxima.

  2. Restricted Diffusion in Biophysical Systems

    PubMed Central

    Cooper, Robert L.; Chang, David B.; Young, Allan C.; Martin, Carroll J.; Ancker-Johnson, Betsy

    1974-01-01

    The pulsed-gradient spin echo nuclear magnetic resonance (PGSENMR) technique was used to measure restricted diffusion of water in three types of animal tissue: human blood plasma and red cells; rat and rabbit heart; rat and rabbit liver. Characteristic lengths (L) for restriction of diffusion are estimated from dependence on the measuring time. Limitations on the range of observable restrictive lengths (1.5-15 μm) are discussed. The decrease in diffusivity due to 1 μm alumina powder (volume fraction = 0.18) in glycerin/water mixtures agrees with the Wang theory assuming spherical particles and no hydration. The characteristic length (L ≃ 4 μm) is larger than the particle size (1 μm) or separation (1.8 μm). Comparison of the diffusivities in tissues at short diffusion times with the Wang theory indicates some bound or trapped water. For packed red blood cells, a restriction (L ≃ 2.3 μm) was attributed tothe red cell membrane. A permeability p ≃ 0.014 cm/s may be estimated from the decrease in diffusivity. Average values of diffusivity ratio in heart were: 0.36 ± 0.02 for rat; and 0.26 ± 0.03 for rabbit; and in liver: 0.25 ± 0.01 for rat; 0.25 ± .04 for 10-day old rabbit; and 0.195 ± 0.03 for 2-yr old rabbit. A restriction (L ≃ 2.7 μm) in rat liver probably results from the mitochondria. PMID:4823458

  3. 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.

  4. 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.

  5. 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. PMID:25808022

  6. Fast Measurements Of Thermal Diffusivities Of Ceramics

    NASA Technical Reports Server (NTRS)

    Smith, Marnell; Goldstein, Howard E.

    1988-01-01

    Temperature rises of samples compared with reference sample. Apparatus quickly measures thermal diffusivities of ceramics at high temperatures. Produces data on relative thermal diffusivities of as many as six ceramic specimens per hour. Thermal-diffusivity tester makes it easy to determine thermal diffusivities of ceramics. Pronounced effects of processing parameters on thermal properties of ceramics evaluated quickly.

  7. A Short-Duration Gel Diffusion Experiment.

    ERIC Educational Resources Information Center

    Mulcahy, D. E.

    1980-01-01

    Described is a gel diffusion experiment that permits the completion of duplicate diffusion runs within a three-hour laboratory session. Information included for the short-duration gel diffusion experiment is the diffusion cell, the experiment, data treatment, and the expected results of the experiment. (Author/DS)

  8. 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…

  9. Upscaling diffusion waves in porous media

    NASA Astrophysics Data System (ADS)

    Valdés-Parada, Francisco J.; Álvarez Ramírez, José; Ochoa-Tapia, J. Alberto

    2016-04-01

    The aim of this work is to derive the effective-medium equations and to estimate the related effective diffusivities for diffusion waves in porous media. Effective diffusivities are estimated within the framework of the volume averaging method, where they are obtained from the solution of the associated closure problems in 2D and 3D periodic unit cells. The results showed that the transport of diffusion waves are governed by the diffusion and co-diffusion mechanisms of harmonic waves. In addition, numerical results showed that the effective diffusivities increase with frequency, while the effective co-diffusivities display a resonance-like behavior. Our results also indicate that geometry plays a more significant effect over the predictions of the co-diffusion coefficient at moderate frequencies and it mainly influences the predictions of the direct diffusivity at low frequencies (i . e .,ω∗ ≪ 1).

  10. Transverse Diffusion in Bedload Transport

    NASA Astrophysics Data System (ADS)

    Devauchelle, Olivier; Abramian, Anais; Seizilles, Gregoire; Lajeunesse, Eric

    2015-11-01

    When a fluid flows over a granular bed, it entrains the grains as bedload. This interaction produces a beautiful variety of shapes and landscapes, such as dunes, ripples and meanders. In this context, Coulomb's law of friction translates into a threshold shear stress, above which the grains are entrained. When the flow-induced stress is barely above this threshold, only a small proportion of the superficial grains move. Their trajectory is then strongly influenced by the layer of static grains below them. They mostly move in the flow direction, but the roughness of the underlying bed causes their velocity to fluctuate, and turns their trajectory into a random walk. As a consequence, bedload diffuses in the direction orthogonal to the flow. Laboratory experiments suggest that this diffusion opposes gravity to maintain the banks of a river. However, quantifying the terms of this balance remains an experimental challenge. We propose to use an instability generated by bedload diffusion to do so.

  11. 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. PMID:24559189

  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. 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.

  14. 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

  15. 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.

  16. Measurement of Diffusion in Flowing Complex Fluids

    PubMed Central

    Leonard, Edward F.; Aucoin, Christian P.; Nanne, Edgar E.

    2006-01-01

    A microfluidic device for the measurement of solute diffusion as well as particle diffusion and migration in flowing complex fluids is described. The device is particularly suited to obtaining diffusivities in such fluids, which require a desired flow state to be maintained during measurement. A method based on the Loschmidt diffusion theory and short times of exposure is presented to allow calculation of diffusivities from concentration differences in the flow streams leaving the cell. PMID:18560469

  17. 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.

  18. 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…

  19. 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].

  20. 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.

  1. Configurational diffusion of coal macromolecules

    SciTech Connect

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

    1989-01-01

    During this quarter, progress has been made in two areas: (1) preparation of the calibration curve for gel permeation chromatography analysis of coal asphaltene; (2) preliminary measurements of the effective diffusion coefficients of coal asphaltene fractions. A calibration curve was prepared with standard compounds including polystyrenes, polynuclear aromatic hydrocarbons and tetraphenylporphine in GPC analysis. A correlation equation was obtained from the calibration curve to estimate the molecular weights of coal asphaltene fractions. Based on this GPC analysis, effective diffusion coefficients of coal asphaltene fractions were measured.

  2. Eddy diffusion at Saturn's homopause

    NASA Technical Reports Server (NTRS)

    Sandel, B. R.; Mcconnell, J. C.; Strobel, D. F.

    1982-01-01

    Measurements of Saturn's He 584 A dayglow and the CH4 density profile deduced from stellar occultation data near the homopause have been combined to infer an eddy diffusion coefficient of 8 + or - 4 x 10 to the 7th sq cm/s and a temperature of 125 + 40 or - 25 K near the homopause at Voyager 2 encounter. It appears that the eddy diffusion coefficient may have increased between the Voyager encounters. Saturn's H Ly-alpha dayglow is qualitatively compatible with this increase and the interpretation of the He 584 A dayglow and CH4 absorption measurement.

  3. Diffusive mixing and Tsallis entropy

    DOE PAGESBeta

    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.

  4. 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

  5. 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.

  6. Living with Technology Diffusion Confusion.

    ERIC Educational Resources Information Center

    Isaak, Troy; Ward, John

    This paper is a report on the implementation of a project to diffuse technology throughout a teacher education program in elementary education at Millersville University (Pennsylvania). Rather than relying on a single technology course in a preservice program, students develop technology skills in a variety of courses in the education sequence and…

  7. Technology Diffusion. [SITE 2001 Section].

    ERIC Educational Resources Information Center

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

    This document contains the following papers on technology diffusion from the SITE (Society for Information Technology & Teacher Education) 2001 conference: (1) "A Response to Technology Integration in Teacher Education for Merit, Tenure, and Promotion" (Cindy L. Anderson and David Starrett); (2) "Online Technical Support Database for Educators"…

  8. In Vivo Facilitated Diffusion Model

    PubMed Central

    Bauer, Maximilian; Metzler, Ralf

    2013-01-01

    Under dilute in vitro conditions transcription factors rapidly locate their target sequence on DNA by using the facilitated diffusion mechanism. However, whether this strategy of alternating between three-dimensional bulk diffusion and one-dimensional sliding along the DNA contour is still beneficial in the crowded interior of cells is highly disputed. Here we use a simple model for the bacterial genome inside the cell and present a semi-analytical model for the in vivo target search of transcription factors within the facilitated diffusion framework. Without having to resort to extensive simulations we determine the mean search time of a lac repressor in a living E. coli cell by including parameters deduced from experimental measurements. The results agree very well with experimental findings, and thus the facilitated diffusion picture emerges as a quantitative approach to gene regulation in living bacteria cells. Furthermore we see that the search time is not very sensitive to the parameters characterizing the DNA configuration and that the cell seems to operate very close to optimal conditions for target localization. Local searches as implied by the colocalization mechanism are only found to mildly accelerate the mean search time within our model. PMID:23349772

  9. 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"…

  10. Diffusion of boron in alloys

    SciTech Connect

    Wang, W.; Zhang, S; He, X.

    1995-04-01

    By means of particle tracking autoradiography (PTA), the diffusion coefficients of boron between 900 and 1,200 C were measured in 04MnNbB steel, 25MnTiB steel, Ni-B, Fe-30%Ni-B and Fe-3%Si-B alloys, and the frequency factor D{sub 0} and activation energy Q were obtained respectively. The experiment results indicated that there was an obvious difference between the present result and the result obtained by Busby (in 1953). It was found that the boron diffusivity in {gamma}-Fe increased as Ni was added. The diffusivity of boron in Fe-3%Si-B alloy with b.c.c. structure was much slower than one obtained by Busby in {alpha}-Fe (1954), which, however, was much faster than the results obtained in {gamma}-Fe (with f.c.c. structure). Based on the present data of boron diffusion coefficients, the mechanism of segregation of boron to grain boundaries is discussed.

  11. Geometry-induced asymmetric diffusion

    PubMed Central

    Shaw, Robert S.; Packard, Norman; Schröter, Matthias; Swinney, Harry L.

    2007-01-01

    Past work has shown that ions can pass through a membrane more readily in one direction than the other. We demonstrate here in a model and an experiment that for a mixture of small and large particles such asymmetric diffusion can arise solely from an asymmetry in the geometry of the pores of the membrane. Our deterministic simulation considers a two-dimensional gas of elastic disks of two sizes diffusing through a membrane, and our laboratory experiment examines the diffusion of glass beads of two sizes through a metal membrane. In both experiment and simulation, the membrane is permeable only to the smaller particles, and the asymmetric pores lead to an asymmetry in the diffusion rates of these particles. The presence of even a small percentage of large particles can clog a membrane, preventing passage of the small particles in one direction while permitting free flow of the small particles in the other direction. The purely geometric kinetic constraints may play a role in common biological contexts such as membrane ion channels. PMID:17522257

  12. Double-diffusive layer formation

    NASA Astrophysics Data System (ADS)

    Zaussinger, Florian; Kupka, Friedrich; Hücker, Sebastian; Egbers, Christoph

    2015-04-01

    Double-diffusive convection plays an important role in geo- and astrophysical applications. The special case, where a destabilising temperature gradient counteracts a stabilising solute gradient leads to layering phenomena under certain conditions. Convectively mixed layers sandwiched in diffusive interfaces form a so-called stack. Well-known double-diffusive systems are observed in rift lakes in Africa and even from the coffee drink Latte Macciatto. Stacks of layers are also predicted to occur inside massive stars and inside giant planets. Their dynamics depend on the thermal, the solute and the momentum diffusivities, as well on the ratio of the gradients of the opposing stratifications. Since the layering process cannot be derived from linear stability analysis, the full nonlinear set of equations has to be investigated. Numerical simulations have become feasible for this task, despite the physical processes operate on a vast range of length and time scales, which is challenging for numerical hydrodynamical modelling. The oceanographically relevant case of fresh and salty water is investigated here in further details. The heat and mass transfer is compared with theoretical results and experimental measurements. Additionally, the initial dynamic of layering, the transient behaviour of a stack and the long time evolution are presented using the example of Lake Kivu and the interior of a giant planet.

  13. 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.

  14. Innovation Diffusion: Implications for Evaluation

    ERIC Educational Resources Information Center

    Ashley, Shena R.

    2009-01-01

    Whether looking at the spread and adoption of an intervention across a community, across multiple units, or within a single unit, an understanding of diffusion theory can help evaluators uncover patterns and impacts that might otherwise be overlooked. The theory alerts evaluators to examine why uptake of an intervention appeared different in…

  15. 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

  16. Diffusion of highly charged cations in olivine

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    Diffusion of tungsten, titanium and phosphorus have been measured in natural iron-bearing olivine (~Fo90) and synthetic forsterite. Experiments were run under buffered conditions (with iron-wustite or Ni-NiO buffers) in 1-atm furnaces. The sources of diffusant for experiments were MgWO4 for tungsten diffusion, Mg2TiO4 for Ti diffusion, and AlPO4 for P diffusion; in all cases these compounds were pre-reacted at high temperature with Mg2SiO4 or Fe-bearing olivine prior to diffusion anneals. Samples were placed with the source materials in noble metal or silica capsules, which were sealed under vacuum in silica glass ampoules with solid buffers. Rutherford backscattering spectrometry (RBS) was used to measure depth profiles for all sets of experiments; measurements of P were also made with Nuclear Reaction Analysis using the 31P(α,p)34S reaction. These new data suggest marked differences among diffusivities of these cations, with titanium diffusion faster than diffusion of tungsten, but slower than diffusion of phosphorus over the conditions investigated. Diffusivities of all of these elements appear significantly slower than those of divalent cations in olivine. These results will be discussed in context with extant diffusion data for major, trace and minor elements in olivine. The effects of oxygen fugacity and olivine composition on diffusion, and potential implications for diffusion mechanisms will also be considered.

  17. A diffuse-interface approximation for surface diffusion including adatoms

    NASA Astrophysics Data System (ADS)

    Rätz, Andreas; Voigt, A.

    2007-01-01

    We introduce a diffuse-interface approximation for solving partial differential equations on evolving surfaces. The model of interest is a fourth-order geometric evolution equation for a growing surface with an additional diffusive adatom density on the surface. Such models arise in the description of epitaxial growth, where the surface of interest is the solid-vapour interface. The model allows us to handle complex geometries in an implicit manner, by considering an evolution equation for a phase-field variable describing the surface and an evolution equation for an extended adatom concentration on a time-independent domain. Matched asymptotic analysis shows the formal convergence towards the sharp interface model and numerical results based on adaptive finite elements demonstrate the applicability of the approach.

  18. A diffusion-diffusion model for percutaneous drug absorption.

    PubMed

    Kubota, K; Ishizaki, T

    1986-08-01

    Several theories describing percutaneous drug absorption have been proposed, incorporating the mathematical solutions of differential equations describing percutaneous drug absorption processes where the vehicle and skin are regarded as simple diffusion membranes. By a solution derived from Laplace transforms, the mean residence time MRT and the variance of the residence time VRT in the vehicle are expressed as simple elementary functions of the following five pharmacokinetic parameters characterizing the percutaneous drug absorption: kd, which is defined as the normalized diffusion coefficient of the skin, kc, which is defined as the normalized skin-capillary boundary clearance, the apparent length of diffusion of the skin 1d, the effective length of the vehicle lv, and the diffusion coefficient of the vehicle Dv. All five parameters can be obtained by the methods proposed here. Results of numerical computation indicate that: concentration-distance curves in the vehicle and skin approximate two curves which are simply expressed using trigonometric functions when sufficient time elapses after an ointment application; the most suitable condition for the assumption that the concentration of a drug in the uppermost epidermis can be considered unchanged is the case where the partition coefficient between vehicle and skin is small, and the constancy of drug concentration is even more valid when the effective length of the vehicle is large; and the amount of a drug in the vehicle or skin and the flow rate of the drug from vehicle into skin or from skin into blood becomes linear on a semilogarithmic scale, and the slopes of those lines are small when Dv is small, when the partition coefficient between vehicle and skin is small, when lv is large, or when kc is small. A simple simulation method is also proposed using a biexponential for the concentration-time curve for the skin near the skin-capillary boundary, that is, the flow rate-time curve for drug passing from skin

  19. Diffuse volume transport in fluids

    NASA Astrophysics Data System (ADS)

    Brenner, Howard

    2010-10-01

    The diffuse flux of volume j in a single-component liquid or gas, the subject of this paper, is a purely molecular quantity defined as the difference between the flux of volume n and the convective flux of volume nvˆ carried by the flowing mass, with n the mass flux, vˆ=1/ρ the specific volume, and ρ the mass density. Elementary statistical-mechanical arguments are used to derive the linear constitutive equation j=DS∇lnρ, valid in near-equilibrium fluids from which body forces are absent. Here, DS is the fluid’s self-diffusion coefficient. The present derivation is based on Einstein’s mesoscopic Brownian motion arguments, albeit applied here to volume- rather than particle-transport phenomena. In contrast to these mesoscale arguments, all prior derivations were based upon macroscale linear irreversible thermodynamic (LIT) arguments. DS replaces the thermometric diffusivity α as the phenomenological coefficient appearing in earlier, ad hoc, derivations. The prior scheme based on α, which had been shown to accord with Burnett’s well-known gas-kinetic constitutive data for the heat flux and viscous stress, carries over intact to now show comparable accord of DS with these same data, since for gases the dimensionless Lewis number Le=α/DS is essentially unity. On the other hand for most liquids, where Le≫1, use of DS in place of α is shown to agree much better with existing experimental data for liquids. For the case of binary mixtures it is shown for the special case of isothermal, isobaric, force-free, Fick’s law-type molecular diffusion processes that j=D∇lnρ, where D is the binary diffusion coefficient. In contrast with the preceding use in the single-component case of both mesoscopic and LIT models to obtain a constitutive equation for j, the corresponding mixture result is derived here without use of any physical model whatsoever. Rather, the derivation effectively requires little more than the respective definitions of the diffuse volume

  20. 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.

  1. Analytical boron diffusivity model in silicon for thermal diffusion from boron silicate glass film

    NASA Astrophysics Data System (ADS)

    Kurachi, Ikuo; Yoshioka, Kentaro

    2015-09-01

    An analytical boron diffusivity model in silicon for thermal diffusion from a boron silicate glass (BSG) film has been proposed in terms of enhanced diffusion due to boron-silicon interstitial pair formation. The silicon interstitial generation is considered to be a result of the silicon kick-out mechanism by the diffused boron at the surface. The additional silicon interstitial generation in the bulk silicon is considered to be the dissociation of the diffused pairs. The former one causes the surface boron concentration dependent diffusion. The latter one causes the local boron concentration dependent diffusion. The calculated boron profiles based on the diffusivity model are confirmed to agree with the actual diffusion profiles measured by secondary ion mass spectroscopy (SIMS) for a wide range of the BSG boron concentration. This analytical diffusivity model is a helpful tool for p+ boron diffusion process optimization of n-type solar cell manufacturing.

  2. 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.

  3. 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.

  4. Diffusion in a short base

    NASA Astrophysics Data System (ADS)

    Hansen, Ole

    1994-09-01

    Based on the solution of the Boltzmann transport equation for a homogeneous base transistor [A.A. Grinberg and S. Luryi, Solid-St. Electron, 35, 1299 (1992)] a very instructive model of carrier transport in a short base transistor is developed. Essential to the above is a replacement of the Schottky boundary conditions. Using modified boundary conditions to the diffusion equation, the transport current density in a homogeneous base is predicted, to an accuracy within ±3%, regardless of the base width, covering the whole range from the diffusion controlled regime to the thermionic regime. Based on the modified boundary conditions a corrected Moll-Ross-Kroemer relation valid for a very short non-homogeneous base is derived. Correspondingly, an expression for the base transit time is derived.

  5. 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.

  6. 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. PMID:21797453

  7. 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. PMID:24210813

  8. Riemann equation for prime number diffusion

    NASA Astrophysics Data System (ADS)

    Chen, Wen; Liang, Yingjie

    2015-05-01

    This study makes the first attempt to propose the Riemann diffusion equation to describe in a manner of partial differential equation and interpret in physics of diffusion the classical Riemann method for prime number distribution. The analytical solution of this equation is the well-known Riemann representation. The diffusion coefficient is dependent on natural number, a kind of position-dependent diffusivity diffusion. We find that the diffusion coefficient of the Riemann diffusion equation is nearly a straight line having a slope 0.99734 in the double-logarithmic axis. Consequently, an approximate solution of the Riemann diffusion equation is obtained, which agrees well with the Riemann representation in predicting the prime number distribution. Moreover, we interpret the scale-free property of prime number distribution via a power law function with 1.0169 the scale-free exponent in respect to logarithmic transform of the natural number, and then the fractal characteristic of prime number distribution is disclosed.

  9. Diffusion-Barrier Contacts For Solar Cells

    NASA Technical Reports Server (NTRS)

    Stella, Paul M.; Pool, Frederick S.; Nicolet, Marc; Iles, Peter A.

    1996-01-01

    Electrically conductive diffusion barriers of TaSiN prevent diffusion of metal from overlying metal contacts into underlying silicon during processing at high temperature, improving performance during subsequent use in low-intensity light at low temperature.

  10. Probability tree algorithm for general diffusion processes

    NASA Astrophysics Data System (ADS)

    Ingber, Lester; Chen, Colleen; Mondescu, Radu Paul; Muzzall, David; Renedo, Marco

    2001-11-01

    Motivated by path-integral numerical solutions of diffusion processes, PATHINT, we present a tree algorithm, PATHTREE, which permits extremely fast accurate computation of probability distributions of a large class of general nonlinear diffusion processes.

  11. Uncovering blue diffuse dwarf galaxies

    NASA Astrophysics Data System (ADS)

    James, Bethan L.; Koposov, Sergey; Stark, Daniel P.; Belokurov, Vasily; Pettini, Max; Olszewski, Edward W.

    2015-04-01

    Extremely metal poor (XMP) galaxies are known to be very rare, despite the large numbers of low-mass galaxies predicted by the local galaxy luminosity function. This paper presents a subsample of galaxies that were selected via a morphology-based search on Sloan Digital Sky Survey images with the aim of finding these elusive XMP galaxies. By using the recently discovered XMP galaxy, Leo P, as a guide, we obtained a collection of faint, blue systems, each with isolated H II regions embedded in a diffuse continuum, that have remained optically undetected until now. Here we show the first results from optical spectroscopic follow-up observations of 12 of ˜100 of these blue diffuse dwarf (BDD) galaxies yielded by our search algorithm. Oxygen abundances were obtained via the direct method for eight galaxies, and found to be in the range 7.45 < 12 + log (O/H) < 8.0, with two galaxies being classified as XMPs. All BDDs were found to currently have a young star-forming population (<10 Myr) and relatively high ionization parameters of their H II regions. Despite their low luminosities (-11 ≲ MB ≲ -18) and low surface brightnesses (˜23-25 mag arcsec-2), the galaxies were found to be actively star forming, with current star formation rates between 0.0003 and 0.078 M⊙ yr-1. From our current subsample, BDD galaxies appear to be a population of non-quiescent dwarf irregular galaxies, or the diffuse counterparts to blue compact galaxies and as such may bridge the gap between these two populations. Our search algorithm demonstrates that morphology-based searches are successful in uncovering more diffuse metal-poor star-forming galaxies, which traditional emission-line-based searches overlook.

  12. 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.

  13. Proton diffusion along biological membranes

    NASA Astrophysics Data System (ADS)

    Medvedev, E. S.; Stuchebrukhov, A. A.

    2011-06-01

    Biological surfaces are known to be capable of retaining protons and facilitating their lateral diffusion. Since the surface dynamically exchanges protons with the bulk, the proton movement from a source to a target at the surface acquires a complicated pattern of coupled surface and bulk (2D + 3D) diffusion of which the main feature is that the surface acts as a proton-collecting antenna enhancing the proton flux from the bulk. A phenomenological model of this process is reviewed and its applications to recent experiments on lipid bilayers and small unilaminar vesicles are discussed. The model (i) introduces the important notions of the fast and slow regimes of proton exchange between the surface and the bulk, (ii) permits evaluation of the antenna radius and amplification coefficient in both regimes, (iii) explains the observed macroscopically large distances (in the micrometer range; Antonenko and Pohl 1998 FEBS Lett. 429 197) that the proton can travel along lipid membranes embedded into pure aqueous solutions, and (iv) predicts the dependence of the steady-state proton flux and the kinetics of the non-stationary diffusion upon the buffer concentration in buffered solutions. The surface diffusion coefficient for small unilaminar vesicles is calculated from experimental data (Sandén et al 2010 Proc. Natl Acad. Sci. USA 107 4129) to be 1 × 10 - 5 cm2 s - 1. The dependence of the shape of the kinetic curves representing protonation/deprotonation of a lipid-bound pH-sensitive dye attached to a planar bilayer lipid membrane upon the buffer concentration (Serowy et al 2003 Biophys. J. 84 1031) and the effect of changing the membrane composition (Antonenko and Pohl 2008 Eur. Biophys. J. 37 865) are explained.

  14. Proton diffusion along biological membranes.

    PubMed

    Medvedev, E S; Stuchebrukhov, A A

    2011-06-15

    Biological surfaces are known to be capable of retaining protons and facilitating their lateral diffusion. Since the surface dynamically exchanges protons with the bulk, the proton movement from a source to a target at the surface acquires a complicated pattern of coupled surface and bulk (2D + 3D) diffusion of which the main feature is that the surface acts as a proton-collecting antenna enhancing the proton flux from the bulk. A phenomenological model of this process is reviewed and its applications to recent experiments on lipid bilayers and small unilaminar vesicles are discussed. The model (i) introduces the important notions of the fast and slow regimes of proton exchange between the surface and the bulk, (ii) permits evaluation of the antenna radius and amplification coefficient in both regimes, (iii) explains the observed macroscopically large distances (in the micrometer range; Antonenko and Pohl 1998 FEBS Lett. 429 197) that the proton can travel along lipid membranes embedded into pure aqueous solutions, and (iv) predicts the dependence of the steady-state proton flux and the kinetics of the non-stationary diffusion upon the buffer concentration in buffered solutions. The surface diffusion coefficient for small unilaminar vesicles is calculated from experimental data (Sandén et al 2010 Proc. Natl Acad. Sci. USA 107 4129) to be 1 × 10(-5) cm(2) s(-1). The dependence of the shape of the kinetic curves representing protonation/deprotonation of a lipid-bound pH-sensitive dye attached to a planar bilayer lipid membrane upon the buffer concentration (Serowy et al 2003 Biophys. J. 84 1031) and the effect of changing the membrane composition (Antonenko and Pohl 2008 Eur. Biophys. J. 37 865) are explained. PMID:21613715

  15. 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.

  16. 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.

  17. 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)

  18. 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).

  19. Finite-dimensional models of diffusion chaos

    NASA Astrophysics Data System (ADS)

    Glyzin, S. D.; Kolesov, A. Yu.; Rozov, N. Kh.

    2010-05-01

    Some parabolic systems of the reaction-diffusion type exhibit the phenomenon of diffusion chaos. Specifically, when the diffusivities decrease proportionally, while the other parameters of a system remain fixed, the system exhibits a chaotic attractor whose dimension increases indefinitely. Various finite-dimensional models of diffusion chaos are considered that represent chains of coupled ordinary differential equations and similar chains of discrete mappings. A numerical analysis suggests that these chains with suitably chosen parameters exhibit chaotic attractors of arbitrarily high dimensions.

  20. 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.

  1. 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.

  2. 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

  3. Thermal diffusivity measurements on composite porosity samples

    NASA Technical Reports Server (NTRS)

    Zalameda, Joseph N.; Winfree, William P.

    1990-01-01

    A phase lag technique is used to make quantitative measurements of diffusivity in composite porosity samples. Changes in through-ply diffusivity in a graphite composite due to varying porosity levels are examined. The relationship between the amount of porosity and the change in diffusivity is analyzed using an electrical analog for modeling heat flow in the composite.

  4. COMPUTER AIDED DESIGN OF DIFFUSED AERATION SYSTEMS

    EPA Science Inventory

    CADDAS (Computer Aided Design of Diffused Aeration Systems) is a microcomputer-based program that analyzes the cost and performance of diffused aeration used in activated sludge wastewater treatment systems. The program can analyze both coarse bubble and fine pore diffusers as we...

  5. Diffusion of oxygen (1); isoquinoline (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) oxygen; (2) isoquinoline

  6. Mathematical Methods for Diffusion MRI Processing

    PubMed Central

    Lenglet, C.; Campbell, J.S.W.; Descoteaux, M.; Haro, G.; Savadjiev, P.; Wassermann, D.; Anwander, A.; Deriche, R.; Pike, G.B.; Sapiro, G.; Siddiqi, K.; Thompson, P.

    2009-01-01

    In this article, we review recent mathematical models and computational methods for the processing of diffusion Magnetic Resonance Images, including state-of-the-art reconstruction of diffusion models, cerebral white matter connectivity analysis, and segmentation techniques. We focus on Diffusion Tensor Images (DTI) and Q-Ball Images (QBI). PMID:19063977

  7. Flux-limited diffusion with relativistic corrections

    SciTech Connect

    Pomraning, G.C.

    1983-03-15

    A recently reported flux-limited diffusion theory is extended to include relativistic terms, correct to first order in the fluid velocity. We show that this diffusion theory is fully flux limited, and yields the correct result for the radiative flux in the classical diffusion limit, namely a Fick's law component plus a v/c convective term.

  8. 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

  9. Diffusion of Distance Education in North Cyprus

    ERIC Educational Resources Information Center

    Isman, Aytekin; Dabaj, Fahme

    2005-01-01

    The purpose of the present paper is to explore how distance education has diffused in north Cyprus. In this paper, Rogers' diffusion theory (1995) was used to analyze the acceptance and implementation of distance education in institutions of higher learning in north Cyprus. The four main elements of the diffusion paradigm--the innovation,…

  10. 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.

  11. 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.

  12. In situ anion diffusion experiments using radiotracers

    NASA Astrophysics Data System (ADS)

    Jansson, Mats; Eriksen, Trygve E.

    2004-02-01

    Diffusion experiments in compacted bentonite have been carried out in situ using the borehole laboratory CHEMLAB. The "ordinary" anion iodide and the redox-sensitive pertechnetate ion have been investigated. In spite of strongly reducing groundwater conditions, technetium was found to diffuse mostly unreduced as TcO 4-, although in some spots in the compacted clay, the activity was significantly higher, which may be explained by reduction of some TcO 4- by iron-containing minerals in the bentonite. The measured concentration profiles in the clay cannot be accommodated by assuming one single diffusion process. The experimental data are modeled assuming two diffusion paths, intralamellar diffusion and diffusion in external water. The apparent diffusivity for the intralamellar diffusion was found to be 8.6×10 -11 m 2 s -1 for iodide with a capacity factor of 0.1, while the apparent diffusivity for the diffusion in external water was found to be 5×10 -14 m 2 s -1 with α=2.26. The corresponding values for Tc were found to be Da=6×10 -11 m 2 s -1, α=0.1 and Da=1×10 -13 m 2 s -1, α=0.46, respectively. The diffusion constants and capacity factors obtained in this study are in accordance with data from laboratory experiments.

  13. 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.

  14. 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.

  15. 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.

  16. Fractional diffusion-reaction stochastic simulations

    NASA Astrophysics Data System (ADS)

    Bayati, Basil S.

    2013-03-01

    A novel method is presented for the simulation of a discrete state space, continuous time Markov process subject to fractional diffusion. The method is based on Lie-Trotter operator splitting of the diffusion and reaction terms in the master equation. The diffusion term follows a multinomial distribution governed by a kernel that is the discretized solution of the fractional diffusion equation. The algorithm is validated and simulations are provided for the Fisher-KPP wavefront. It is shown that the wave speed is dictated by the order of the fractional derivative, where lower values result in a faster wave than in the case of classical diffusion. Since many physical processes deviate from classical diffusion, fractional diffusion methods are necessary for accurate simulations.

  17. 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. PMID:26919019

  18. 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

  19. Turbulent diffusion with memories and intrinsic shear

    NASA Technical Reports Server (NTRS)

    Tchen, C. M.

    1974-01-01

    The first part of the present theory is devoted to the derivation of a Fokker-Planck equation. The eddies smaller than the hydrodynamic scale of the diffusion cloud form a diffusivity, while the inhomogeneous, bigger eddies give rise to a nonuniform migratory drift. This introduces an eddy-induced shear which reflects on the large-scale diffusion. The eddy-induced shear does not require the presence of a permanent wind shear and is intrinsic to the diffusion. Secondly, a transport theory of diffusivity is developed by the method of repeated-cascade and is based upon a relaxation of a chain of memories with decreasing information. The full range of diffusion consists of inertia, composite, and shear subranges, for which variance and eddy diffusivities are predicted. The coefficients are evaluated. Comparison with experiments in the upper atmosphere and oceans is made.

  20. The Influence of Spatial Variations of Diffusion Length on Charge Collected by Diffusion from Ion Tracks

    NASA Technical Reports Server (NTRS)

    Edmonds, L. D.

    1996-01-01

    Charge collected by diffusion from ion tracks in a semiconductor substrate may be influenced by the substrate diffusion length, which is related to recombination losses. A theoretical analysis shows that, excluding some extreme cases, charge collection is insensitive to spatial variations in the diffusion length funciton, so it is possible to define an effective diffusion length having the property that collected charge can be approximated by assuming a uniform diffusion length equal to this effective value.

  1. Complex hydrogen diffusion in forsterite

    NASA Astrophysics Data System (ADS)

    Padron-Navarta, J.

    2013-12-01

    The singular geodynamic and chemical evolution of the Earth seems to be dictated by the influence of 'water' (more specifically hydrogen structurally bonded to oxygen forming hydroxyl groups, OH-) on the physical properties of the nominally minerals of the Earth's mantle. In the most abundant upper mantle phase, olivine, the presence of hydrogen has been shown to significantly modify the timescale of chemical diffusion, plastic deformation, electrical conductivity and the attenuation of seismic waves. In olivine there are four different hydrogen substitution mechanisms, associated with Mg vacancies, Si vacancies, trivalent cations and titanium substitution, hereafter referred to as H[Mg], H[Si], H[triv] and H[Ti] respectively. It seems possible that hydrogen diffusion rates vary with the type of defect. We addressed this hypothesis by an experimental investigation of the dehydroxylation of synthetic forsterite with two contrasting hydrous defect populations: (1) Ti4+-doped forsterite with H[Si], and H[Ti] dominant and H[Mg] and H[triv] subsidiary; and (2) MgO-buffered forsterite with only H[Si] hydrous defects. The experiments were conducted by annealing the hydroxylated forsterites at atmospheric pressure and 1073 to 1273 K, with OH- contents monitored at intervals by room-temperature FTIR spectroscopy. For the Ti4+-doped forsterite, four stages were observed during dehydoxylation. Firstly, the small amounts of H[Mg] and H[triv] disappear very quickly. Secondly, Ti is removed from the forsterite lattice by precipitation of a new phase; thirdly, the dehydroxylation of H[Ti] as monitored by the 3525 cm-1 peak proceeds at the same rate as H[Si] monitored by the 3613 cm-1 peak; and fourthly, once H[Ti] reaches zero, the dehydroxylation of H[Si] slows drastically, to rates that are unobservable in the duration of our experiments (1073-1273 K). Whereas the rates of loss of H[Mg] and H[triv] are in agreement with previous measurements of bulk hydrogen diffusion in

  2. 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.

  3. Diffusely Reflecting Paints Containing TFE

    NASA Technical Reports Server (NTRS)

    Shai, M. C.; Schutt, J. B.

    1985-01-01

    Highly reflective, diffused coatings developed by incorporating polytetrafluoroethylene (TFE) pigment with alcohol-soluble binders. Alcohol and binder mixed together in blender before adding TFE. TFE preferably outgassed in mechanical-pump vacuum for typical interval of 4 hours before adding to liquid. Like wetting agent, vacuum treatment helps to prevent clumping of TFE and eases dispersion throughout mixture. Mixture blended for 3 to 5 minutes before used. Coatings useful on reflectance-standard surfaces for calibrating radiometric instruments in both laboratory and field. Paints washable and usable as optical reference surfaces.

  4. Khinchin Theorem and Anomalous Diffusion

    NASA Astrophysics Data System (ADS)

    Lapas, Luciano C.; Morgado, Rafael; Vainstein, Mendeli H.; Rubí, J. Miguel; Oliveira, Fernando A.

    2008-12-01

    A recent Letter [M. H. Lee, Phys. Rev. Lett. 98, 190601 (2007)PRLTAO0031-900710.1103/PhysRevLett.98.190601] has called attention to the fact that irreversibility is a broader concept than ergodicity, and that therefore the Khinchin theorem [A. I. Khinchin, Mathematical Foundations of Statistical Mechanics (Dover, New York, 1949)] may fail in some systems. In this Letter we show that for all ranges of normal and anomalous diffusion described by a generalized Langevin equation the Khinchin theorem holds.

  5. 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.

  6. Diffusion on asymmetric fractal networks

    NASA Astrophysics Data System (ADS)

    Haynes, Christophe P.; Roberts, Anthony P.

    2010-12-01

    We derive a renormalization method to calculate the spectral dimension d¯ of deterministic self-similar networks with arbitrary base units and branching constants. The generality of the method allows the affect of a multitude of microstructural details to be quantitatively investigated. In addition to providing models for physical networks, the results allow precise tests of theories of diffusive transport. For example, the properties of a class of nonrecurrent trees (d¯>2) with asymmetric elements and branching violate the Alexander-Orbach scaling law.

  7. 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.

  8. Calculation of thermal diffuse scattering

    NASA Astrophysics Data System (ADS)

    Wakabayashi, N.; Nicklow, R. M.; Katano, S.; Ishii, Y.; Child, H. R.; Smith, H. G.; Fernandez-Baca, J. A.

    We have developed a computer program to calculate the thermal diffuse scattering (TDS) intensity distribution for single-crystal specimens in a diffractometer with no energy analysis. We assumed that the phonon frequencies are approximated by those of elastic waves and that the elastic constants, density and lattice parameters of the system under study are known. The results of the calculations were compared to experimental data obtain for single crystals of Si, diamond and NiAl at the wide-angle neutron diffractometer (WAND) at the HFIR at Oak Ridge National Laboratory. Excellent agreement was found between the calculations and the experimental observations.

  9. 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.

  10. 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

  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. Precision Measurement of Isospin Diffusion

    NASA Astrophysics Data System (ADS)

    Winkelbauer, Jack; Hodges, R.; Tsang, M. B.; Lynch, W. G.; Chajecki, Z.; Coupland, D.; Youngs, M.; Lu, F.; Sanetullaev, A.; Shane, R.; Tangwancharoen, S.; Famiano, M.; George, S.; Ghosh, T.; Dunn, J.; Dye, S.; Nielsen, S.; Ramos, A.; Charity, R.; Sobotka, L.; Elson, J.; Rana, T.; El Houssieny, M.

    2011-10-01

    In heavy-ion collisions, the tendency for isospin to drift from a neutron (proton) rich region to a neutron (proton) deficient region is sensitive to the density dependence of the symmetry energy. Until recently, most of the isospin diffusion results have been obtained with mid central to central collisions and different isospin observables have been used in experiment and in model simulations. To provide more accurate understanding of the dependence of isospin diffusion on impact parameters and different isospin observables, we have measured isotopic fragment and residue yields for 112 , 118 , 124Sn + 112 , 118 , 124Sn collisions at E/A = 70 MeV. The measurements were carried out at the Coupled Cyclotron Facility at Michigan State University. Fragment yields were measured using the Large Area Silicon Strip Array (LASSA) and heavy residue yields emitted at the forward angles were measured using the S800 Spectrograph. Impact parameter was selected using the MSU Miniball-WU Miniwall phoswich array. Preliminary results will be presented. Work supported by the National Science Foundation under Grant PHY-0606007.

  13. Virus diffusion in isolation rooms.

    PubMed

    Kao, P H; Yang, R J

    2006-03-01

    In hospitals, the ventilation of isolation rooms operating under closed-door conditions is vital if the spread of viruses and infection is to be contained. Engineering simulation, which employs computational fluid dynamics, provides a convenient means of investigating airflow behaviour in isolation rooms for various ventilation arrangements. A cough model was constructed to permit the numerical simulation of virus diffusion inside an isolation room for different ventilation system configurations. An analysis of the region of droplet fallout and the dilution time of virus diffusion of coughed gas in the isolation room was also performed for each ventilation arrangement. The numerical results presented in this paper indicate that the parallel-directional airflow pattern is the most effective means of controlling flows containing virus droplets. Additionally, staggering the positions of the supply vents at the door end of the room relative to the exhaust vents on the wall behind the bed head provides effective infection control and containment. These results suggest that this particular ventilation arrangement enhances the safety of staff when performing medical treatments within isolation rooms. PMID:16359753

  14. Diffuse alveolar hemorrhage following alemtuzumab.

    PubMed

    Sachdeva, Ashutosh; Matuschak, George M

    2008-06-01

    This study describes an unusual patient with X-linked Alport syndrome (XLAS) in whom diffuse alveolar hemorrhage (DAH) developed as a complication of alemtuzumab therapy following renal transplantation. A 26-year-old man with XLAS underwent retransplantation with a cadaveric renal allograft. He received alemtuzumab therapy as a part of an immunosuppressive induction protocol, and dyspnea and hemoptysis developed. A chest CT scan showed diffuse alveolar opacities. Bronchoscopy was performed to determine the cause of hemoptysis and hypoxia. BAL showed a characteristic increasingly bloody return in the sequential aliquots. There was no growth of pathogenic bacteria or evidence of opportunistic infection. Clinical improvement occurred with the initiation of steroids, and the patient required short-term mechanical ventilation for acute respiratory failure. To our knowledge, this is the first reported case of DAH associated with use of alemtuzumab therapy, although other pulmonary toxicities have been described. The prevalence of this form of pulmonary toxicity is unclear and requires further systematic study. PMID:18574290

  15. 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.

  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. Spectral clustering with epidemic diffusion.

    PubMed

    Smith, Laura M; Lerman, Kristina; Garcia-Cardona, Cristina; Percus, Allon G; Ghosh, Rumi

    2013-10-01

    Spectral clustering is widely used to partition graphs into distinct modules or communities. Existing methods for spectral clustering use the eigenvalues and eigenvectors of the graph Laplacian, an operator that is closely associated with random walks on graphs. We propose a spectral partitioning method that exploits the properties of epidemic diffusion. An epidemic is a dynamic process that, unlike the random walk, simultaneously transitions to all the neighbors of a given node. We show that the replicator, an operator describing epidemic diffusion, is equivalent to the symmetric normalized Laplacian of a reweighted graph with edges reweighted by the eigenvector centralities of their incident nodes. Thus, more weight is given to edges connecting more central nodes. We describe a method that partitions the nodes based on the componentwise ratio of the replicator's second eigenvector to the first and compare its performance to traditional spectral clustering techniques on synthetic graphs with known community structure. We demonstrate that the replicator gives preference to dense, clique-like structures, enabling it to more effectively discover communities that may be obscured by dense intercommunity linking. PMID:24229231

  18. Spectral clustering with epidemic diffusion

    NASA Astrophysics Data System (ADS)

    Smith, Laura M.; Lerman, Kristina; Garcia-Cardona, Cristina; Percus, Allon G.; Ghosh, Rumi

    2013-10-01

    Spectral clustering is widely used to partition graphs into distinct modules or communities. Existing methods for spectral clustering use the eigenvalues and eigenvectors of the graph Laplacian, an operator that is closely associated with random walks on graphs. We propose a spectral partitioning method that exploits the properties of epidemic diffusion. An epidemic is a dynamic process that, unlike the random walk, simultaneously transitions to all the neighbors of a given node. We show that the replicator, an operator describing epidemic diffusion, is equivalent to the symmetric normalized Laplacian of a reweighted graph with edges reweighted by the eigenvector centralities of their incident nodes. Thus, more weight is given to edges connecting more central nodes. We describe a method that partitions the nodes based on the componentwise ratio of the replicator's second eigenvector to the first and compare its performance to traditional spectral clustering techniques on synthetic graphs with known community structure. We demonstrate that the replicator gives preference to dense, clique-like structures, enabling it to more effectively discover communities that may be obscured by dense intercommunity linking.

  19. 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.

  20. 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.

  1. 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)

  2. 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.

  3. 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

  4. Modeling of hydrogen diffusion in metals

    SciTech Connect

    Yang, K.; Cao, M.Z.; Wan, X.J.; Shi, C.X.

    1989-02-01

    The study of the diffusion of hydrogen in metals is very important to further understand the hydrogen embrittlement of metals. To describe the diffusion of hydrogen in metals the diffusion equation deduced from Fick's law under an ideal condition has been generally used and the effect of hydrogen trapping in metals has been neglected. In the process of hydrogen diffusion through a metal, hydrogen fills the traps continuously and the fraction of the traps filled by hydrogen, which have only little effect on the diffusion of hydrogen, may be different at different places because the distribution of hydrogen concentration may be different at different places. Thus the hydrogen diffusion coefficient in the metal may also be different at different positions, i.e., the diffusion coefficient should be affected by time in a dynamic process of hydrogen diffusion through a metal. But in the previous analyses, the above fact is not considered and the hydrogen diffusion coefficient is generally taken as a constant. In the present paper a new model of hydrogen diffusion in metals in which the effect of time is taken into account is developed.

  5. 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

  6. 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

  7. 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.

  8. Role of diffusion in irreversible deposition

    SciTech Connect

    Luthi, P.O.; Ramsden, J.J.; Chopard, B.

    1997-03-01

    The adsorption of spheres onto solid surfaces is investigated using a cellular automaton model of diffusion deposition. Unlike previous models, the diffusive transport of the particles from the bulk to the surface as well as their interaction with adsorbed particles are explicitly considered at a microscopic level. We study the initial time regime, which determines the subsequent evolution and during which the particle flux at the surface is not constant. We observe that diffusion-driven adsorption differs significantly from random sequential adsorption (RSA) when particles diffuse in a two-dimensional bulk and are adsorbed on a one-dimensional substrate. We also find that the microscopic details of the diffusive motion influence both the kinetics of deposition and the jamming limit of the coverage. The RSA model appears to be a good approximation, especially for two-dimensional deposition, but cannot generally represent diffusion deposition. {copyright} {ital 1997} {ital The American Physical Society}

  9. 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.

  10. Short-time diffusivity of dicolloids.

    PubMed

    Panczyk, Mark M; Wagner, Norman J; Furst, Eric M

    2014-06-01

    The short-time diffusivity of dicolloid particles as a function of particle volume fraction ϕ from 0.01 ≤ ϕ ≤ 0.6 is measured using diffusing wave spectroscopy. The diffusivities of symmetric and asymmetric dicolloids are compared with similarly sized spheres. The short-time diffusivity is independent of salt concentration and decreases with increasing volume fraction for both spheres and asymmetric dicolloids. Symmetric dicolloids have a higher diffusivity than spheres at similar volume fractions. This difference is accounted for by rescaling the dicolloid volume fraction based on the ratio of the random close-packing volume fractions of spheres and dicolloids. Finally, a useful method is provided for calculating the diffusivity of symmetric dicolloid particles of arbitrary aspect ratio based on the calculated hydrodynamic resistance of Zabarankin [Proc. R. Soc. A 463, 2329 (2007)]. PMID:25019780

  11. Diffusion bonding of mismatch dental alloys.

    PubMed

    Liu, Honghua; Ni, Jiahua; Wu, Luhai; He, Guo

    2010-04-01

    The diffusion bonding of Ti-6Al-4V and Co-Cr-Mo dental alloys has been investigated in terms of the atoms diffusion, the microstructure evolution, and the bonding strength. The bonding performance reveals asymmetry diffusion profiles for both the Co and Cr in Ti-6Al-4V and the Ti in Co-Cr-Mo alloy. Their diffusion coefficients (Arrhenius relations) have been established based on the experiments. Co and Cr diffusion into Ti-6Al-4V leads to alpha --> beta transformation and the intermetallics-formation. Maximum bonding strength occurs at about 840 degrees C. The bonding joint fails under the shear stress in the Ti-6Al-4V side near the bonding interface in brittle manner. The intermetallics in the diffusion layer together with the unbonded areas and other flaws in the bonding interface are responsible for the shear brittle fracture, which also weaken the bonding strength. PMID:19957358

  12. 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.

  13. 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.

  14. 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.

  15. Diffusion bonding of Stratapax for drill bits

    SciTech Connect

    Middleton, J.N.; Finger, J.T.

    1983-01-01

    A process has been developed for the diffusion bonding of General Electric's Stratapax drill blanks to support studs for cutter assemblies in drill bits. The diffusion bonding process is described and bond strength test data are provided for a variety of materials. The extensive process details, provided in the Appendices, should be sufficient to enable others to successfully build diffusion-bonded drill bit cutter assemblies.

  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, 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.

  18. 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.

  19. 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.

  20. Public Good Diffusion Limits Microbial Mutualism

    NASA Astrophysics Data System (ADS)

    Menon, Rajita; Korolev, Kirill S.

    2015-04-01

    Standard game theory cannot describe microbial interactions mediated by diffusible molecules. Nevertheless, we show that one can still model microbial dynamics using game theory with parameters renormalized by diffusion. Contrary to expectations, greater sharing of metabolites reduces the strength of cooperation and leads to species extinction via a nonequilibrium phase transition. We report analytic results for the critical diffusivity and the length scale of species intermixing. Species producing slower public good is favored by selection when fitness saturates with nutrient concentration.

  1. 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.

  2. [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

  3. 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

  4. 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

  5. Hydrogen diffusion on Si(001)

    NASA Astrophysics Data System (ADS)

    Owen, J. H. G.; Bowler, D. R.; Goringe, C. M.; Miki, K.; Briggs, G. A. D.

    1996-11-01

    We have imaged hydrogen on Si(001) at low coverages in a variable-temperature STM from 300 K up to 700 K. Individual hydrogen atoms were imaged which became mobile at around 570 K. The observed rate of hopping along the dimer rows was consistent with an activation energy of 1.68 +/- 0.15 eV. Motion across dimer rows was rarely observed, even at the higher temperatures. The diffusion barrier for motion along the dimer rows has been calculated using tight-binding and density-functional theory in the generalized gradient approximation (GGA). The calculated barrier is 1.65 eV from tight binding and 1.51 eV from GGA.

  6. Diffuse cutaneous leishmaniasis in Mexico.

    PubMed

    Velasco, O; Savarino, S J; Walton, B C; Gam, A A; Neva, F A

    1989-09-01

    In Mexico, 6 cases of diffuse cutaneous leishmaniasis (DCL) were found in widely separated geographic regions. Information was also available on 2 other cases. In addition to the typical clinical features, half of the patients had evidence of nasopharyngeal mucosal involvement. All isolates from the DCL patients were identified as Leishmania mexicana mexicana by isoenzyme analysis and monoclonal antibody typing. In 1 region of Tabasco state where DCL was found, uncomplicated cutaneous leishmaniasis appeared to be highly endemic, and isolates from a few such patients were identified as L. mexicana mexicana. An incidental finding was the recovery of an isolate of L. braziliensis braziliensis from a patient with chiclero ulcer in Oaxaca state. The clinical and epidemiological significance of the reported cases are discussed. PMID:2802018

  7. Dopant diffusion in tungsten silicide

    SciTech Connect

    Pan, P.; Hsieh, N.; Geipel, H.J. Jr.; Slusser, G.J.

    1982-04-01

    The dopant (B, P, and As) redistribution in a silicide on polycrystalline silicon structure after annealing at 800 and 1000 /sup 0/C was studied. The distribution of boron was found to be quite different from these of phosphorus and arsenic. At 1000 /sup 0/C, the distribution coefficient for boron at the WSi/sub 2//polycrystalline silicon interface was found to be 2.7. The solubilities of phosphorus and arsenic in WSi/sub 2/ at 1000 /sup 0/C were estimated to be 6 x 10/sup 19/ and 1.6 x 10/sup 19/ atoms/cm/sup 3/, respectively. At 800 /sup 0/C, the diffusion coefficient for the dopants was found to be equal to, or greater than 3.3 x 10/sup -12/ cm/sup 2//s, which is at least three orders of magnitude larger than in silicon.

  8. 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.

  9. Facilitated diffusion buffers noise in gene expression

    PubMed Central

    Schoech, Armin P.; Zabet, Nicolae Radu

    2014-01-01

    Transcription factors perform facilitated diffusion (3D diffusion in the cytosol and 1D diffusion on the DNA) when binding to their target sites to regulate gene expression. Here, we investigated the influence of this binding mechanism on the noise in gene expression. Our results showed that, for biologically relevant parameters, the binding process can be represented by a two-state Markov model and that the accelerated target finding due to facilitated diffusion leads to a reduction in both the mRNA and the protein noise. PMID:25314467

  10. 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}

  11. 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.

  12. Silicon infrared diffuser for wireless communication.

    PubMed

    Massera, Ettore; Rea, Ilaria; Nasti, Ivana; Maddalena, Pasqualino; Di Francia, Girolamo

    2006-09-10

    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. PMID:16926908

  13. 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.

  14. Self-Diffusion in Amorphous Silicon

    NASA Astrophysics Data System (ADS)

    Strauß, Florian; Dörrer, Lars; Geue, Thomas; Stahn, Jochen; Koutsioubas, Alexandros; Mattauch, Stefan; Schmidt, Harald

    2016-01-01

    The present Letter reports on self-diffusion in amorphous silicon. Experiments were done on 29Si/natSi 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.

  15. 1-D EQUILIBRIUM DISCRETE DIFFUSION MONTE CARLO

    SciTech Connect

    T. EVANS; ET AL

    2000-08-01

    We present a new hybrid Monte Carlo method for 1-D equilibrium diffusion problems in which the radiation field coexists with matter in local thermodynamic equilibrium. This method, the Equilibrium Discrete Diffusion Monte Carlo (EqDDMC) method, combines Monte Carlo particles with spatially discrete diffusion solutions. We verify the EqDDMC method with computational results from three slab problems. The EqDDMC method represents an incremental step toward applying this hybrid methodology to non-equilibrium diffusion, where it could be simultaneously coupled to Monte Carlo transport.

  16. 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

  17. 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

  18. 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.}

  19. 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

  20. 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

  1. Grain boundary diffusion in olivine (Invited)

    NASA Astrophysics Data System (ADS)

    Marquardt, K.; Dohmen, R.

    2013-12-01

    Olivine is the main constituent of Earth's upper mantle. The individual mineral grains are separated by grain boundaries that have very distinct properties compared to those of single crystals and strongly affect large-scale physical and chemical properties of rocks, e.g. viscosity, electrical conductivity and diffusivity. Knowledge on the grain boundary physical and chemical properties, their population and distribution in polycrystalline materials [1] is a prerequisite to understand and model bulk (rock) properties, including their role as pathways for element transport [2] and the potential of grain boundaries as storage sites for incompatible elements [3]. Studies on selected and well characterized single grain boundaries are needed for a detailed understanding of the influence of varying grain boundaries. For instance, the dependence of diffusion on the grain boundary structure (defined by the lattice misfit) and width in silicates is unknown [2, 4], but limited experimental studies in material sciences indicate major effects of grain boundary orientation on diffusion rates. We characterized the effect of grain boundary orientation and temperature on element diffusion in forsterite grain boundaries by transmission electron microscopy (TEM).The site specific TEM-foils were cut using the focused ion beam technique (FIB). To study diffusion we prepared amorphous thin-films of Ni2SiO4 composition perpendicular to the grain boundary using pulsed laser deposition. Annealing (800-1450°C) leads to crystallization of the thin-film and Ni-Mg inter-diffuse into the crystal volume and along the grain boundary. The inter-diffusion profiles were measured using energy dispersive x-ray spectrometry in the TEM, standardized using the Cliff-Lorimer equation and EMPA measurements. We obtain volume diffusion coefficients that are comparable to Ni-Mg inter-diffusion rates in forsterite determined in previous studies at comparable temperatures, with similar activation energies

  2. Self diffusion of interacting membrane proteins.

    PubMed Central

    Abney, J R; Scalettar, B A; Owicki, J C

    1989-01-01

    A two-dimensional version of the generalized Smoluchowski equation is used to analyze the time (or distance) dependent self diffusion of interacting membrane proteins in concentrated membrane systems. This equation provides a well established starting point for descriptions of the diffusion of particles that interact through both direct and hydrodynamic forces; in this initial work only the effects of direct interactions are explicitly considered. Data describing diffusion in the presence of hard-core repulsions, soft repulsions, and soft repulsions with weak attractions are presented. The effect that interactions have on the self-diffusion coefficient of a real protein molecule from mouse liver gap junctions is also calculated. The results indicate that self diffusion is always inhibited by direct interactions; this observation is interpreted in terms of the caging that will exist at finite protein concentration. It is also noted that, over small distance scales, the diffusion coefficient is determined entirely by the very strong Brownian forces; therefore, as a function of displacement the self-diffusion coefficient decays (rapidly) from its value at infinite dilution to its steady-state interaction-averaged value. The steady-state self-diffusion coefficient describes motion over distance scales that range from approximately 10 nm to cellular dimensions and is the quantity measured in fluorescence recovery after photobleaching experiments. The short-ranged behavior of the diffusion coefficient is important on the interparticle-distance scale and may therefore influence the rate at which nearest-neighbor collisional processes take place. The hard-disk theoretical results presented here are in excellent agreement with lattice Monte-Carlo results obtained by other workers. The concentration dependence of experimentally measured diffusion coefficients of antibody-hapten complexes bound to the membrane surface is consistent with that predicted by the theory. The

  3. Electrolyte diffusion in compacted montmorillonite engineered barriers

    SciTech Connect

    Jahnke, F.M.; Radke, C.J.

    1985-09-01

    The bentonite-based engineered barrier or packing is a proposed component of several designs conceived to dispose of high-level nuclear waste in geologic repositories. Once radionuclides escape the waste package, they must first diffuse through the highly impermeable clay-rich barrier before they reach the host repository. To determine the effectiveness of the packing as a sorption barrier in the transient release period and as a mass-transfer barrier in the steady release period over the geologic time scales involved in nuclear waste disposal, a fundamental understanding of the diffusion of electrolytes in compacted clays is required. We present, and compare with laboratory data, a model quantifying the diffusion rates of cationic cesium and uncharged tritium in compacted montmorillonite clay. Neutral tritium characterizes the geometry (i.e., tortuosity) of the particulate gel. After accounting for cation exchange, we find that surface diffusion is the dominant mechanism of cation transport, with an approximate surface diffusion coefficient of 2 x 10 W cmS/s for cesium. This value increases slightly with increasing background ionic strength. The implications of this work for the packing as a migration barrier are twofold. During the transient release period, K/sub d/ values are of little importance in retarding ion migration. This is because sorption also gives rise to a surface diffusion path, and it is surface diffusion which controls the diffusion rate of highly sorbing cations in compacted montmorillonite. During the steady release period, the presence of surface diffusion leads to a flux through the packing which is greatly enhanced. In either case, if surface diffusion is neglected, the appropriate diffusion coefficient of ions in compacted packing will be in considerable error relative to current design recommendations. 11 refs., 4 figs., 1 tab.

  4. Atomistic Simulations of Ion Diffusion in Clay Barriers: Diffusive Path Energy Barriers

    NASA Astrophysics Data System (ADS)

    Newton, A. G.; Kozaki, T.

    2010-12-01

    Ion diffusion in clay-rich media is an important transport process relevant to models of contaminant fate and transport in groundwater and risk assessments for the geologic disposal of high-level radioactive waste (HLW). Smectite clay minerals are used as a buffer material in the geologic disposal of HLW due to their low permeability. Ion diffusion experiments with water-saturated, compacted clays have revealed a non-linear trend in which the diffusive energy barrier in clay media at dry densities near 1.0 Mg m-3 exhibited a smaller energy barrier to diffusion than in liquid water (Kozaki, et al. 2005). Although it is likely that the decreased energy barrier is related to preferential diffusion along smectite basal surfaces, experimental methods cannot unambiguously isolate this diffusion pathway. Atomistic simulations were designed to isolate this diffusive pathway and to test if the decreased energy barrier is related to preferential diffusion along the smectite basal surface. In addition, the simulations provide an atomic-scale perspective of this diffusion pathway as a function of temperature. In the present study, we report the energy barrier to diffusion for sodium ions (Na+) at the smectite basal surface. The energy barrier to diffusion at the Na-montmorillonite basal surface was determined by investigating the temperature dependence of ion diffusion through a series of long (9.0 ns) molecular dynamics (MD) simulations in the canonical ensemble (NVT). We show that the energy barrier to diffusion at the clay basal surface is less than the energy barrier to diffusion in free water and demonstrate that this methodology can provide results that are consistent with laboratory diffusion experiments and nanoscale insights into the interpretation of macroscale experimental investigations of ion diffusion in smectite-rich media. Kozaki, T., A. Fujishima, et al. (2005). Engineering Geology, 81(3): 246-254.

  5. Accounting for Diffusion in Agent Based Models of Reaction-Diffusion Systems with Application to Cytoskeletal Diffusion

    PubMed Central

    Azimi, Mohammad; Jamali, Yousef; Mofrad, Mohammad R. K.

    2011-01-01

    Diffusion plays a key role in many biochemical reaction systems seen in nature. Scenarios where diffusion behavior is critical can be seen in the cell and subcellular compartments where molecular crowding limits the interaction between particles. We investigate the application of a computational method for modeling the diffusion of molecules and macromolecules in three-dimensional solutions using agent based modeling. This method allows for realistic modeling of a system of particles with different properties such as size, diffusion coefficients, and affinity as well as the environment properties such as viscosity and geometry. Simulations using these movement probabilities yield behavior that mimics natural diffusion. Using this modeling framework, we simulate the effects of molecular crowding on effective diffusion and have validated the results of our model using Langevin dynamics simulations and note that they are in good agreement with previous experimental data. Furthermore, we investigate an extension of this framework where single discrete cells can contain multiple particles of varying size in an effort to highlight errors that can arise from discretization that lead to the unnatural behavior of particles undergoing diffusion. Subsequently, we explore various algorithms that differ in how they handle the movement of multiple particles per cell and suggest an algorithm that properly accommodates multiple particles of various sizes per cell that can replicate the natural behavior of these particles diffusing. Finally, we use the present modeling framework to investigate the effect of structural geometry on the directionality of diffusion in the cell cytoskeleton with the observation that parallel orientation in the structural geometry of actin filaments of filopodia and the branched structure of lamellipodia can give directionality to diffusion at the filopodia-lamellipodia interface. PMID:21966493

  6. 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

  7. Changes in "thermal lens" measure diffusivity

    NASA Technical Reports Server (NTRS)

    Gupta, A.; Hong, S. D.; Moacanin, J.

    1980-01-01

    In an extension of "thermal lens" effect to new applications and better resolution, two laser beams combine to rapidly measure thermal diffusivity and other molecular dynamic properties. New double-beam technique handles very small samples unlike classical techniques for measuring diffusivity. It can be used for measurements on samples undergoing stress, making it applicable to data collection for structural engineering.

  8. Measuring Thermal Diffusivity of Molten Semiconductors

    NASA Technical Reports Server (NTRS)

    Crouch, R.; Holland, L.; Taylor, R. E.

    1986-01-01

    Thermal diffusivity of molten and solid mercury cadmium telluride measured with aid of new apparatus. Knowledge gained from such measurements help efforts to grow high-quality single crystals of this semiconductor for use in infrared detectors: Without knowledge of thermal diffusivity, difficult to control growth rate of solid from molten material.

  9. Effective diffusion of confined active Brownian swimmers.

    PubMed

    Sandoval, Mario; Dagdug, Leornardo

    2014-12-01

    We theoretically find the effect of confinement and thermal fluctuations on the diffusivity of a spherical active swimmer moving inside a two-dimensional narrow cavity of general shape. The explicit formulas for the effective diffusion coefficient of a swimmer moving inside two particular cavities are presented. We also compare our analytical results with Brownian dynamics simulations and we obtain excellent agreement. PMID:25615133

  10. Diffuse knapweed (Centaurea diffusa) seed germination

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Diffuse knapweed is a deep tap rooted species that was introduced to North America about 1900 and by the mid 1990s occupied 1.2 million hectares in the western United States. Diffuse knapweed invasion has reduced biodiversity, forage for livestock and wildlife, and deteriorated watersheds character...

  11. Diffusion of triglycine sulfate in aqueous solution

    NASA Technical Reports Server (NTRS)

    Kroes, R. L.; Reiss, D.; Silberman, E.; Morgan, S.

    1985-01-01

    The diffusion coefficient of triglycine sulfate (TGS) in water was measured for several concentrations over a temperature range of 25 to 55 C. The activation energy for diffusion obtained from these measurements was 4180 cal/mol. No concentration dependence was seen. The maximum difference in D for the various ionic species present was determined by Raman spectroscopy to be about 5 percent.

  12. Riemann equation for prime number diffusion.

    PubMed

    Chen, Wen; Liang, Yingjie

    2015-05-01

    This study makes the first attempt to propose the Riemann diffusion equation to describe in a manner of partial differential equation and interpret in physics of diffusion the classical Riemann method for prime number distribution. The analytical solution of this equation is the well-known Riemann representation. The diffusion coefficient is dependent on natural number, a kind of position-dependent diffusivity diffusion. We find that the diffusion coefficient of the Riemann diffusion equation is nearly a straight line having a slope 0.99734 in the double-logarithmic axis. Consequently, an approximate solution of the Riemann diffusion equation is obtained, which agrees well with the Riemann representation in predicting the prime number distribution. Moreover, we interpret the scale-free property of prime number distribution via a power law function with 1.0169 the scale-free exponent in respect to logarithmic transform of the natural number, and then the fractal characteristic of prime number distribution is disclosed. PMID:26026319

  13. Diffusion coefficients of several aqueous alkanolamine solutions

    SciTech Connect

    Snijder, E.D.; Riele, M.J.M. te; Versteeg, G.F.; Swaaij, W.P.M. van . Dept. of Chemical Engineering)

    1993-07-01

    In absorption processes of acid gases (H[sub 2]S, CO[sub 2], COS) in alkanolamine solutions, diffusion coefficients are used for the calculation of the mass transfer rate. The Taylor dispersion technique was applied for the determination of diffusion coefficients of various systems. Experiments with the system KCl in water showed that the experimental setup provides accurate data. For the alkanolamines monoethanolamine (MEA), diethanolamine (DEA), methyldiethanolamine (MDEA), and di-2-propanolamine (DIPA), correlations for the diffusion coefficient as a function of temperature at different concentrations are given. A single relation for every amine has been derived which correlates the diffusion coefficients as a function of temperature and concentration. The temperature was varied between 298 and 348 K, and the concentration between 0 and 4000-5000 mol/m[sup 3]. Furthermore, a modified Stokes-Einstein relation is presented for the prediction of the diffusion coefficients in the alkanolamines in relation to the viscosity of the solvent and the diffusion coefficient at infinite dilution. The diffusion coefficients at low concentrations are compared with some available relations for the estimation of diffusion coefficients at infinite dilution, and it appears that the agreement is fairly good.

  14. Neoclassical diffusion in a turbulent plasma

    SciTech Connect

    Yushmanov, P. |

    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.

  15. 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.

  16. Pressure diffusion waves in porous media

    SciTech Connect

    Silin, Dmitry; Korneev, Valeri; Goloshubin, Gennady

    2003-04-08

    Pressure diffusion wave in porous rocks are under consideration. The pressure diffusion mechanism can provide an explanation of the high attenuation of low-frequency signals in fluid-saturated rocks. Both single and dual porosity models are considered. In either case, the attenuation coefficient is a function of the frequency.

  17. Attractive membrane domains control lateral diffusion.

    PubMed

    Forstner, Martin B; Martin, Douglas S; Rückerl, Florian; Käs, Josef A; Selle, Carsten

    2008-05-01

    Lipid membranes play a fundamental role in vital cellular functions such as signal transduction. Many of these processes rely on lateral diffusion within the membrane, generally a complex fluid containing ordered microdomains. However, little attention has been paid to the alterations in transport dynamics of a diffusing species caused by long-range interactions with membrane domains. In this paper, we address the effect of such interactions on diffusive transport by studying lateral diffusion in a phase-separated Langmuir phospholipid monolayer via single-particle tracking. We find that attractive dipole-dipole interactions between condensed phase domains and diffusing probe beads lead to transient confinement at the phase boundaries, causing a transition from two- to one-dimensional diffusion. Using Brownian dynamics simulations, the long-term diffusion constant for such a system is found to have a sensitive, Boltzmann-like, dependence on the interaction strength. In addition, this interaction strength is shown to be a strong function of the ratio of domain to particle size. As similar interactions are expected in biological membranes, the modulation of diffusive transport dynamics by varying interaction strength and/or domain size may offer cells selective spatial and temporal control over signaling processes. PMID:18643101

  18. The Classical Diffusion Paradigm in Crisis.

    ERIC Educational Resources Information Center

    Hooks, Gregory

    The erosion of the credibility of the classical diffusion paradigm by recent challenges to its fundamental assumptions has resulted in a "paradigmatic crisis" as related to research on the diffusion of agricultural innovations. Such basic assumptions as that of a harmonious and cooperative society and of agricultural research guided by endogenous…

  19. 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.

  20. 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…