Edge rotation as governed by momentum transport due to neutrals
NASA Astrophysics Data System (ADS)
Pusztai, Istvan; Omotani, John; Fülöp, Tünde
2016-10-01
Neutrals can strongly affect momentum transport even in relatively small concentrations due to their high cross-field mobility. We present a framework to calculate numerically the momentum transport due to charge-exchanging neutrals, in the closed field-line region. We couple a short mean-free-path solution of the neutral kinetic equation to neoclassical ions. We can then determine self-consistently the radial electric field and plasma rotation velocity, assuming that the neutrals dominate the momentum transport. We use the neoclassical solver PERFECT [Landreman et al. 2014 PPCF 56 045005] to compute the ion distributions. Numerical solutions allow us to consider the full range of collisionalities; typical experimental parameters fall in the intermediate region that is not well described by analytical limits. We also compute the rotation velocities of minority impurity species, to facilitate experimental comparison of the results. We find that at a fixed collisionality, the important parameter determining the radial electric field and rotation is the major radius where the neutrals are localized. Therefore changes to the location of the peak neutral density, caused by altering the fuelling location or moving the X-point for example, should allow the rotation to be manipulated. Supported by the Framework Grant for Strategic Energy Research (Dnr. 2014-5392) and the International Career Grant (Dnr. 330-2014-6313) from Vetenskapsrådet.
Toroidal momentum transport in a tokamak due to profile shearing
Buchholz, R.; Grosshauser, S. R.; Hornsby, W. A.; Migliano, P.; Peeters, A. G.; Camenen, Y.; Casson, F. J.
2014-06-15
The effect of profile shearing on toroidal momentum transport is studied in linear and non-linear gyro-kinetic simulations. Retaining the radial dependence of both plasma and geometry parameters leads to a momentum flux that has contributions both linear in the logarithmic gradients of density and temperature, as well as contributions linear in the derivatives of the logarithmic gradients. The effect of the turbulence intensity gradient on momentum transport is found to be small for the studied parameters. Linear simulations at fixed normalized toroidal wave number predict a weak dependence of the momentum flux on the normalized Larmor radius ρ{sub *}=ρ/R. Non-linear simulations, however, at sufficiently small ρ{sub *} show a linear scaling of the momentum flux with ρ{sub *}. The obtained stationary rotation gradients are in the range of, although perhaps smaller than, current experiments. For a reactor plasma, however, a rather small rotation gradient should result from profile shearing.
NASA Astrophysics Data System (ADS)
Ball, Justin; Parra, Felix I.
2017-02-01
Introducing up-down asymmetry into the tokamak magnetic equilibria appears to be a feasible method to drive fast intrinsic toroidal rotation in future large devices. In this paper we investigate how the intrinsic momentum transport generated by up-down asymmetric shaping scales with the mode number of the shaping effects. Making use the gyrokinetic tilting symmetry (Ball et al 2016 Plasma Phys. Control. Fusion 58 045023), we study the effect of envelopes created by the beating of different high-order shaping effects. This reveals that the presence of an envelope can change the scaling of the momentum flux from exponentially small in the limit of large shaping mode number to just polynomially small. This enhancement of the momentum transport requires the envelope to be both up-down asymmetric and have a spatial scale on the order of the minor radius.
Singh, Rameswar; Singh, R; Jhang, Hogun; Diamond, P. H.
2014-01-15
We present an analytic study of momentum transport of tokamak plasmas in the vicinity of minimum safety factor (q) position in reversed magnetic shear configuration. Slab ion temperature gradient modes with an equilibrium flow profile are considered in this study. Quasi-linear calculations of momentum flux clearly show the novel effects of q-curvature on the generation of intrinsic rotation and mean poloidal flow without invoking reflectional symmetry breaking of parallel wavenumber (k{sub ∥}). This q-curvature effect originates from the inherent asymmetry in k{sub ∥} populations with respect to a rational surface due to the quadratic proportionality of k{sub ∥} when q-curvature is taken into account. Discussions are made of possible implications of q-curvature induced plasma flows on internal transport barrier formation in reversed shear tokamaks.
Interspecies Momentum transport in Collisionless Plasmas due to the two stream instability
NASA Astrophysics Data System (ADS)
Trejo, D. M.; Reyes-Ruiz, M.
2011-10-01
We study the linear development of the two-stream plasma instability in a system taken to represent the interaction of the solar wind and the ionosphere of non-magnetic solar system bodies. We consider the role of the instability in the interspecies momentum transfer in such systems.
NASA Astrophysics Data System (ADS)
Peeters, A. G.; Angioni, C.
2005-07-01
It is shown from a symmetry in the gyrokinetic equation that for up-down symmetric tokamak equilibria and for uϕ≫ρυthi/r (where uϕ is the toroidal velocity, υthi is the thermal ion velocity, ρ is the Larmor radius, and r is the radius of the flux surface), the transport of parallel momentum can be written as the sum of a diffusive and a pinch contribution with no off-diagonal terms due to temperature and pressure gradients. The measured parallel velocity gradient in ASDEX Upgrade [O. Gruber, H.-S. Bosch, S. Günter et al., Nucl. Fusion 39, 1321 (1999)] is insufficient to drive the parallel velocity shear instability. The parallel velocity is then transported by the ion temperature gradient mode. The diffusive contribution to the transport flux is investigated using a linear gyrokinetic approach, and it is found that the diffusion coefficient for parallel velocity transport divided by the ion heat conductivity coefficient is close to 1, and only weakly dependent on plasma parameters.
Electromagnetic angular momentum transport in Saturn's rings
NASA Technical Reports Server (NTRS)
Goertz, C. K.; Morfill, G. E.; Ip, W.; Gruen, E.; Havnes, O.
1986-01-01
It is shown here that submicrometer dust particles sporadically elevated above Saturn's ring are subject to electromagnetic forces which will reduce their angular momentum inside synchronous orbit and increase it outside. When the dust is reabsorbed by the ring the angular momentum of the ring is decreased (increased) inside (outside) of synchronous orbit. For the case of the spokes in Saturn's B-ring it is estimated that the timescale for transporting ring material due to this angular momentum coupling effect is comparable to the viscous transport time or even smaller. It is suggested that the minimum in the optical depth of the B-ring at synchronous orbit is due to this effect.
NASA Astrophysics Data System (ADS)
Tobias, B.; Ferraro, N.; Jardin, S.; Kramer, G.; Evans, T.; Domier, C. W.; Luhmann, N. C., Jr.
2016-10-01
The onset of energetic particle stochasticity has been correlated with the transition to a hollow rotation profile by scaling linear tearing modes from M3D-C1 to ECEI data and following energetic particles in the SPIRAL code. The superposition of two tearing modes of different n-number increases magnetic field line stochasticity by generating tertiary magnetic islands, even when the flux perturbation is composed of only two linearly independent solutions. Furthermore, particle orbit stochasticity increases with particle energy--a mechanism for non-ambipolar transport that modifies fluid rotation in a regime relevant to the saturated island widths, neutral beam injection energies, and physical dimensions of DIII-D. This demonstrates that energy-dependent stochastic effects operate alongside nonlinear MHD coupling and neoclassical toroidal viscosity to determine the dynamics of non-axisymmetric and tearing-unstable systems, including disruptive tokamak discharges. Supported by the U.S. DOE DE-AC02-09CH11466, DE-FC02-04ER54698, DE-FG02-99ER54531.
Analysis techniques for momentum transport
Scott, S.D.
1991-08-01
This report discusses the following topics on momentum analysis in tokamaks and stellarators: the momentum balance equation; deposition of torque by neutral beams; effects of toroidal rotation; and experimental observations. (LSP)
Edge rotation from momentum transport by neutrals
NASA Astrophysics Data System (ADS)
Omotani, JT; Newton, SL; Pusztai, I.; Fülöp, T.
2016-11-01
Due to their high cross field mobility, neutral atoms can have a strong effect on transport even at the low relative densities found inside the separatrix. We use a charge-exchange dominated model for the neutrals, coupled to neoclassical ions, to calculate momentum transport when it is dominated by the neutrals. We can then calculate self-consistently the radial electric field and predict the intrinsic rotation in an otherwise torque-free plasma. Using a numerical solver for the ion distribution to allow arbitrary collisionality, we investigate the effects of inverse aspect ratio and elongation on plasma rotation. We also calculate the rotation of a trace carbon impurity, to facilitate future comparison to experiments using charge exchange recombination spectroscopy diagnostics.
Role of convective scale momentum transport in climate simulation
Zhang, G.J.; McFarlane, N.A.
1995-01-20
This paper studies the effect of convective-scale momentum transport in climate simulation using a comprehensive parameterization scheme. A unique feature of the scheme is the inclusion of the perturbation pressure field induced by convection and its effect on the cloud momentum transport. Through two experiments of seasonal simulations, it is shown that the perturbation pressure forcing on the cloud momentum transport accounts for a significant part of the total convective momentum source/sink, indicating that the cloud momentum field is substantially modulated by the convection-induced pressure field. The overall effect of convective momentum transport is to reduce the vertical wind shear in both the zonal and the meridional directions. The responses of the large-scale circulation to convective momentum transport is very significant. The zonally averaged zonal wind decreases by as much as 5 ms{sup {minus}1} in a broad area in the upper tropical troposphere and the midlatitudes of the winter hemisphere. The Hadley circulation becomes stronger as a result of the zonal momentum transport. In general, inclusion of convective momentum transport leads to a much better simulation of the wind fields in both the upper and the lower troposphere. The temperature and moisture changes as a result of the inclusion of convective momentum transport are also examined in this study. The tropical troposphere is warmer and more moist due to the enhanced Hadley circulation. However, considering the uncertainties of the climatological analyses, most of these thermodynamic changes only make marginal improvement to the simulation. 20 refs., 10 figs.
Neoclassical momentum transport in an impure rotating tokamak plasma
Newton, S.; Helander, P.
2006-01-15
It is widely believed that transport barriers in tokamak plasmas are caused by radial electric-field shear, which is governed by angular momentum transport. Turbulence is suppressed in the barrier, and ion thermal transport is comparable to the neoclassical prediction, but experimentally angular momentum transport has remained anomalous. With this motivation, the collisional transport matrix is calculated for a low collisionality plasma with collisional impurity ions. The bulk plasma toroidal rotation velocity is taken to be subsonic, but heavy impurities undergo poloidal redistribution due to the centrifugal force. The impurities give rise to off-diagonal terms in the transport matrix, which cause the plasma to rotate spontaneously. At conventional aspect ratio, poloidal impurity redistribution increases the angular momentum flux by a factor up to {epsilon}{sup -3/2} over previous predictions, making it comparable to the 'banana' regime heat flux. The flux is primarily driven by radial pressure and temperature gradients.
Quantized adiabatic transport in momentum space.
Ho, Derek Y H; Gong, Jiangbin
2012-07-06
Though topological aspects of energy bands are known to play a key role in quantum transport in solid-state systems, the implications of Floquet band topology for transport in momentum space (i.e., acceleration) have not been explored so far. Using a ratchet accelerator model inspired by existing cold-atom experiments, here we characterize a class of extended Floquet bands of one-dimensional driven quantum systems by Chern numbers, reveal topological phase transitions therein, and theoretically predict the quantization of adiabatic transport in momentum space. Numerical results confirm our theory and indicate the feasibility of experimental studies.
Edge momentum transport by neutrals: an interpretive numerical framework
NASA Astrophysics Data System (ADS)
Omotani, J. T.; Newton, S. L.; Pusztai, I.; Viezzer, E.; Fülöp, T.; The ASDEX Upgrade Team
2017-06-01
Due to their high cross-field mobility, neutrals can contribute to momentum transport even at the low relative densities found inside the separatrix and they can generate intrinsic rotation. We use a charge-exchange dominated solution to the neutral kinetic equation, coupled to neoclassical ions, to evaluate the momentum transport due to neutrals. Numerical solutions to the drift-kinetic equation allow us to cover the full range of collisionality, including the intermediate levels typical of the tokamak edge. In the edge there are several processes likely to contribute to momentum transport in addition to neutrals. Therefore, we present here an interpretive framework that can evaluate the momentum transport through neutrals based on radial plasma profiles. We demonstrate its application by analysing the neutral angular momentum flux for an L-mode discharge in the ASDEX Upgrade tokamak. The magnitudes of the angular momentum fluxes we find here due to neutrals of 0.6-2 \\text{N} \\text{m} are comparable to the net torque on the plasma from neutral beam injection, indicating the importance of neutrals for rotation in the edge.
Stochastic models for convective momentum transport.
Majda, Andrew J; Stechmann, Samuel N
2008-11-18
The improved parameterization of unresolved features of tropical convection is a central challenge in current computer models for long-range ensemble forecasting of weather and short-term climate change. Observations, theory, and detailed smaller-scale numerical simulations suggest that convective momentum transport (CMT) from the unresolved scales to the resolved scales is one of the major deficiencies in contemporary computer models. Here, a combination of mathematical and physical reasoning is utilized to build simple stochastic models that capture the significant intermittent upscale transports of CMT on the large scales due to organized unresolved convection from squall lines. Properties of the stochastic model for CMT are developed below in a test column model environment for the large-scale variables. The effects of CMT from the stochastic model on a large-scale convectively coupled wave in an idealized setting are presented below as a nontrivial test problem. Here, the upscale transports from stochastic effects are significant and even generate a large-scale mean flow which can interact with the convectively coupled wave.
Mass and Momentum Turbulent Transport Experiments
NASA Technical Reports Server (NTRS)
Johnson, B. V.; Roback, R.
1984-01-01
An experimental study of mixing downstream of axial and swirling coaxial jets is being conducted to obtain data for the evaluation and improvement of turbulent transport models currently employed in a variety of computational procedures used throughout the propulsion community. Effort was directed toward the acquisition of length scale and dissipation rate data that will provide more accurate inlet boundary conditions for the computational procedures and a data base to evaluate the turbulent transport models in the near jet region where recirculation does not occur. Mass and momentum turbulent transport data with a blunt inner-jet inlet configuration will also be acquired.
Discoveries from the exploration of gyrokinetic momentum transport
Staebler, G.M.; Waltz, R. E.; Kinsey, J. E.
2011-05-15
The momentum transport due to gyroradius scale turbulence in tokamak plasmas is very complex. In general, some type of breaking of the parity of the gyrokinetic equation under simultaneous reflection of the poloidal angle and the sign of the parallel velocity phase space coordinate (poloidal parity) is always involved. There are three distinct types of poloidal parity breaking effects. In this paper, all three types of poloidal parity breaking are explored using the quasi-linear trapped gyro-Landau fluid [G. M. Staebler et al., Phys. Plasmas 12, 102508 (2005)] transport code. Selected results are verified with full nonlinear turbulence simulations using the gyro [J. Candy et al., J. Comput. Phys. 186, 545 (2003)] gyrokinetic code. The observable properties like an energy pinch driven by a parallel velocity shear and a dependence of momentum transport on the direction of the ion grad-B drift relative to the X-point location in single null divertor geometry have been discovered.
Turbulence induced radial transport of toroidal momentum in boundary plasma of EAST tokamak
Zhao, N.; Yan, N. Xu, G. S.; Wang, H. Q.; Wang, L.; Ding, S. Y.; Chen, R.; Chen, L.; Zhang, W.; Hu, G. H.; Shao, L. M.; Wang, Z. X.
2016-06-15
Turbulence induced toroidal momentum transport in boundary plasma is investigated in H-mode discharge using Langmuir-Mach probes on EAST. The Reynolds stress is found to drive an inward toroidal momentum transport, while the outflow of particles convects the toroidal momentum outwards in the edge plasma. The Reynolds stress driven momentum transport dominates over the passive momentum transport carried by particle flux, which potentially provides a momentum source for the edge plasma. The outflow of particles delivers a momentum flux into the scrape-off layer (SOL) region, contributing as a momentum source for the SOL flows. At the L-H transitions, the outward momentum transport suddenly decreases due to the suppression of edge turbulence and associated particle transport. The SOL flows start to decelerate as plasma entering into H-mode. The contributions from turbulent Reynolds stress and particle transport for the toroidal momentum transport are identified. These results shed lights on the understanding of edge plasma accelerating at L-H transitions.
Transport of parallel momentum by collisionless drift wave turbulence
Diamond, P. H.; McDevitt, C. J.; Guercan, Oe. D.; Hahm, T. S.; Naulin, V.
2008-01-15
This paper presents a novel, unified approach to the theory of turbulent transport of parallel momentum by collisionless drift waves. The physics of resonant and nonresonant off-diagonal contributions to the momentum flux is emphasized, and collisionless momentum exchange between waves and particles is accounted for. Two related momentum conservation theorems are derived. These relate the resonant particle momentum flux, the wave momentum flux, and the refractive force. A perturbative calculation, in the spirit of Chapman-Enskog theory, is used to obtain the wave momentum flux, which contributes significantly to the residual stress. A general equation for mean k{sub parallel} (
Momentum injection in tokamak plasmas and transitions to reduced transport.
Parra, F I; Barnes, M; Highcock, E G; Schekochihin, A A; Cowley, S C
2011-03-18
The effect of momentum injection on the temperature gradient in tokamak plasmas is studied. A plausible scenario for transitions to reduced transport regimes is proposed. The transition happens when there is sufficient momentum input so that the velocity shear can suppress or reduce the turbulence. However, it is possible to drive too much velocity shear and rekindle the turbulent transport. The optimal level of momentum injection is determined. The reduction in transport is maximized in the regions of low or zero magnetic shear.
Momentum Injection in Tokamak Plasmas and Transitions to Reduced Transport
Parra, F. I.; Highcock, E. G.; Schekochihin, A. A.; Barnes, M.
2011-03-18
The effect of momentum injection on the temperature gradient in tokamak plasmas is studied. A plausible scenario for transitions to reduced transport regimes is proposed. The transition happens when there is sufficient momentum input so that the velocity shear can suppress or reduce the turbulence. However, it is possible to drive too much velocity shear and rekindle the turbulent transport. The optimal level of momentum injection is determined. The reduction in transport is maximized in the regions of low or zero magnetic shear.
Perturbative momentum transport in MAST L-mode plasmas
NASA Astrophysics Data System (ADS)
Guttenfelder, W.; Field, A. R.; Lupelli, I.; Tala, T.; Kaye, S. M.; Ren, Y.; Solomon, W. M.
2017-05-01
Non-axisymmetric magnetic fields are used to perturbatively probe momentum transport physics in MAST L-mode plasmas. The low beta L-mode target was chosen to complement previous experiments conducted in high beta NSTX H-mode plasmas (β N = 3.5-4.6) where an inward momentum pinch was measured. In those cases quasi-linear gyrokinetic simulations of unstable ballooning micro-instabilities predict weak or outward momentum convection, in contrast to the measurements. The weak pinch was predicted to be due to both electromagnetic effects at high beta and low aspect ratio minimizing the symmetry-breaking of the instabilities responsible for momentum transport. In an attempt to lessen these electromagnetic effects at low aspect ratio, perturbative experiments were run in MAST L-mode discharges at lower beta (β N = 2). The perturbative transport analysis used the time-dependent response following the termination of applied 3D fields that briefly brake the plasma rotation (similar to the NSTX H-mode experiments). Assuming time-invariant diffusive (χ φ ) and convective (V φ ) transport coefficients, an inward pinch is inferred with magnitudes, (RV φ /χ φ ) = (-1)-(-9), similar to those found in NSTX H-modes and in conventional tokamaks. However, if experimental uncertainties due to non-stationary conditions during and after the applied 3D field are considered, a weak pinch or even outward convection is inferred, (RV φ /χ φ ) = (-1)-(+5). Linear gyrokinetic simulations indicate that for these lower beta L-modes, the predicted momentum pinch is predicted to be relatively small, (RV φ /χ φ )sim ≈ -1. While this falls within the experimentally inferred range, the uncertainties are practically too large to quantitatively validate the predictions. Challenges and implications for this particular experimental technique are discussed, as well as additional possible physical mechanisms that may be important in
Perturbative momentum transport in MAST L-mode plasmas
Guttenfelder, W.; Field, A. R.; Lupelli, I.; ...
2017-03-28
Non-axisymmetric magnetic fields are used to perturbatively probe momentum transport physics in MAST L-mode plasmas. The low beta L-mode target was chosen to complement previous experiments conducted in high beta NSTX H-mode plasmas (beta N = 3.5-4.6) where an inward momentum pinch was measured. In those cases quasi-linear gyrokinetic simulations of unstable ballooning micro-instabilities predict weak or outward momentum convection, in contrast to the measurements. The weak pinch was predicted to be due to both electromagnetic effects at high beta and low aspect ratio minimizing the symmetry-breaking of the instabilities responsible for momentum transport. In an attempt to lessen thesemore » electromagnetic effects at low aspect ratio, perturbative experiments were run in MAST L-mode discharges at lower beta (beta N = 2). The perturbative transport analysis used the time-dependent response following the termination of applied 3D fields that briefly brake the plasma rotation ( similar to the NSTX H-mode experiments). Assuming time-invariant diffusive (chi(phi))and convective (V-phi) transport coefficients, an inward pinch is inferred with magnitudes, (RV phi/chi(phi)) = (-1)-(-9), similar to those found in NSTX H-modes and in conventional tokamaks. However, if experimental uncertainties due to non-stationary conditions during and after the applied 3D field are considered, a weak pinch or even outward convection is inferred, ( RV phi/chi(phi)) = (-1)-(+5). Linear gyrokinetic simulations indicate that for these lower beta L-modes, the predicted momentum pinch is predicted to be relatively small, ( RV phi/chi(phi))(sim) approximate to -1. While this falls within the experimentally inferred range, the uncertainties are practically too large to quantitatively validate the predictions. Challenges and implications for this particular experimental technique are discussed, as well as additional possible physical mechanisms that may be important in understanding momentum
MOMENTUM TRANSPORT FROM CURRENT-DRIVEN RECONNECTION IN ASTROPHYSICAL DISKS
Ebrahimi, F.; Prager, S. C.
2011-12-20
Current-driven reconnection is investigated as a possible mechanism for angular momentum transport in astrophysical disks. A theoretical and computational study of angular momentum transport from current-driven magnetohydrodynamic instabilities is performed. It is found that both a single resistive tearing instability and an ideal instability can transport momentum in the presence of azimuthal Keplerian flow. The structure of the Maxwell stress is examined for a single mode through analytic quasilinear theory and computation. Full nonlinear multiple-mode computation shows that a global Maxwell stress causes significant momentum transport.
Energy and Momentum Transport in String Waves
ERIC Educational Resources Information Center
Juenker, D. W.
1976-01-01
Formulas are derived for the energy, momentum, and angular momentum transmitted by waves of arbitrary shape in an inextensible string by pure transverse waves in a string using Tait's procedure. (Author/CP)
Energy and Momentum Transport in String Waves
ERIC Educational Resources Information Center
Juenker, D. W.
1976-01-01
Formulas are derived for the energy, momentum, and angular momentum transmitted by waves of arbitrary shape in an inextensible string by pure transverse waves in a string using Tait's procedure. (Author/CP)
Design of Large Momentum Acceptance Transport Systems
D.R. Douglas
2005-05-01
The use of energy recovery to enable high power linac operation often gives rise to an attendant challenge--the transport of high power beams subtending large phase space volumes. In particular applications--such as FEL driver accelerators--this manifests itself as a requirement for beam transport systems with large momentum acceptance. We will discuss the design, implementation, and operation of such systems. Though at times counterintuitive in behavior (perturbative descriptions may, for example, be misleading), large acceptance systems have been successfully utilized for generations as spectrometers and accelerator recirculators [1]. Such systems are in fact often readily designed using appropriate geometric descriptions of beam behavior; insight provided using such a perspective may in addition reveal inherent symmetries that simplify construction and improve operability. Our discussion will focus on two examples: the Bates-clone recirculator used in the Jefferson Lab 10 kW IR U pgrade FEL (which has an observed acceptance of 10% or more) and a compaction-managed mirror-bend achromat concept with an acceptance ranging from 50 to 150 MeV.
Anomalous transport and holographic momentum relaxation
NASA Astrophysics Data System (ADS)
Copetti, Christian; Fernández-Pendás, Jorge; Landsteiner, Karl; Megías, Eugenio
2017-09-01
The chiral magnetic and vortical effects denote the generation of dissipationless currents due to magnetic fields or rotation. They can be studied in holographic models with Chern-Simons couplings dual to anomalies in field theory. We study a holographic model with translation symmetry breaking based on linear massless scalar field backgrounds. We compute the electric DC conductivity and find that it can vanish for certain values of the translation symmetry breaking couplings. Then we compute the chiral magnetic and chiral vortical conductivities. They are completely independent of the holographic disorder couplings and take the usual values in terms of chemical potential and temperature. To arrive at this result we suggest a new definition of energy-momentum tensor in presence of the gravitational Chern-Simons coupling.
Reynolds stress and the physics of turbulent momentum transport
NASA Astrophysics Data System (ADS)
Bernard, Peter S.; Handler, Robert A.
1990-11-01
The nature of the momentum transport processes responsible for the Reynolds shear stress is investigated using several ensembles of fluid particle paths obtained from a direct numerical simulation of turbulent channel flow. It is found that the Reynolds stress can be viewed as arising from two fundamentally different mechanisms. The more significant entails transport in the manner described by Prandtl in which momentum is carried unchanged from one point to another by the random displacement of fluid particles. One-point models, such as the gradient law are found to be inherently unsuitable for representing this process. However, a potentially useful non-local approximation to displacement transport, depending on the global distribution of the mean velocity gradient, may be developed as a natural consequence of its definition. A second important transport mechanism involves fluid particles experiencing systematic accelerations and decelerations. Close to the wall this results in a reduction in Reynolds stress due to the solving of sweep-type motions. Further away Reynolds stress is produced in spiralling motions, where particles accelerate or decelerate while changing direction. Both transport mechanisms appear to be closely associated with the dynamics of vortical structures in the wall region.
Spontaneous toroidal flow generation due to negative effective momentum diffusivity
McMillan, Ben F.
2015-02-15
Spontaneous structure formation, and in particular, zonal flows, is observed in a broad range of natural and engineered systems, often arising dynamically as the saturated state of a linear instability. Flows in tokamaks are known to self-organise on small scales, but large scale toroidal flows also arise even when externally applied torques are zero. This has previously been interpreted as the result of small externally imposed breaking of a symmetry. However, we show that for large enough field line pitch, a robust spontaneous symmetry breaking occurs, leading to the generation of strong toroidal flow structures; parameters are typical of Spherical Tokamak discharges with reversed shear profiles. The short wavelength dynamics are qualitatively similar to the growth of poloidal flow structures, and toroidal flow gradients nonlinearly saturate at levels where the shearing rate is comparable to linear growth rate. On long wavelengths, we measure Prandtl numbers of around zero for these systems, in conjunction with the formation of structured toroidal flows, and we show that this is consistent with a model of momentum transport where fluxes act to reinforce small flow gradients: the effective momentum diffusivity is negative. Toroidal flow structures are largely unaffected by collisional damping, so this may allow toroidal bulk flows of order the ion thermal velocity to be maintained with zero momentum input. This phenomenon also provides a mechanism for the generation of localised meso-scale structures like transport barriers.
Spontaneous toroidal flow generation due to negative effective momentum diffusivity
NASA Astrophysics Data System (ADS)
McMillan, Ben F.
2015-02-01
Spontaneous structure formation, and in particular, zonal flows, is observed in a broad range of natural and engineered systems, often arising dynamically as the saturated state of a linear instability. Flows in tokamaks are known to self-organise on small scales, but large scale toroidal flows also arise even when externally applied torques are zero. This has previously been interpreted as the result of small externally imposed breaking of a symmetry. However, we show that for large enough field line pitch, a robust spontaneous symmetry breaking occurs, leading to the generation of strong toroidal flow structures; parameters are typical of Spherical Tokamak discharges with reversed shear profiles. The short wavelength dynamics are qualitatively similar to the growth of poloidal flow structures, and toroidal flow gradients nonlinearly saturate at levels where the shearing rate is comparable to linear growth rate. On long wavelengths, we measure Prandtl numbers of around zero for these systems, in conjunction with the formation of structured toroidal flows, and we show that this is consistent with a model of momentum transport where fluxes act to reinforce small flow gradients: the effective momentum diffusivity is negative. Toroidal flow structures are largely unaffected by collisional damping, so this may allow toroidal bulk flows of order the ion thermal velocity to be maintained with zero momentum input. This phenomenon also provides a mechanism for the generation of localised meso-scale structures like transport barriers.
Angular momentum transport within evolved low-mass stars
Cantiello, Matteo; Bildsten, Lars; Paxton, Bill; Mankovich, Christopher; Christensen-Dalsgaard, Jørgen
2014-06-10
Asteroseismology of 1.0-2.0 M {sub ☉} red giants by the Kepler satellite has enabled the first definitive measurements of interior rotation in both first ascent red giant branch (RGB) stars and those on the helium burning clump. The inferred rotation rates are 10-30 days for the ≈0.2 M {sub ☉} He degenerate cores on the RGB and 30-100 days for the He burning core in a clump star. Using the Modules for Experiments in Stellar Evolution code, we calculate state-of-the-art stellar evolution models of low mass rotating stars from the zero-age main sequence to the cooling white dwarf (WD) stage. We include transport of angular momentum due to rotationally induced instabilities and circulations, as well as magnetic fields in radiative zones (generated by the Tayler-Spruit dynamo). We find that all models fail to predict core rotation as slow as observed on the RGB and during core He burning, implying that an unmodeled angular momentum transport process must be operating on the early RGB of low mass stars. Later evolution of the star from the He burning clump to the cooling WD phase appears to be at nearly constant core angular momentum. We also incorporate the adiabatic pulsation code, ADIPLS, to explicitly highlight this shortfall when applied to a specific Kepler asteroseismic target, KIC8366239.
Observation of anomalous momentum transport in tokamak plasmas with no momentum input.
Lee, W D; Rice, J E; Marmar, E S; Greenwald, M J; Hutchinson, I H; Snipes, J A
2003-11-14
Anomalous momentum transport has been observed in Alcator C-Mod tokamak plasmas through analysis of the time evolution of core impurity toroidal rotation velocity profiles. Following the L-mode to EDA (enhanced D(alpha)) H-mode transition, the ensuing cocurrent toroidal rotation velocity, which is generated in the absence of any external momentum source, is observed to propagate in from the edge plasma to the core. The steady state toroidal rotation velocity profiles are relatively flat and the momentum transport can be simulated with a simple diffusion model. Velocity profiles during edge localized mode free (ELM-free) H-modes are centrally peaked, which suggests the addition of inward momentum convection. In all operating regimes the observed momentum diffusivities are much larger than the neoclassical values.
Momentum transport from nonlinear mode coupling of magnetic fluctuations
Hansen; Almagri; Craig; Den Hartog DJ; Hegna; Prager; Sarff
2000-10-16
A cause of observed anomalous plasma momentum transport in a reversed-field pinch is determined experimentally. Magnetohydrodynamic theory predicts that nonlinear interactions involving triplets of tearing modes produce internal torques that redistribute momentum. Evidence for the nonlinear torque is acquired by detecting the correlation of momentum redistribution with the mode triplets, with the elimination of one of the modes in the triplet, and with the external driving of one of the modes.
Influence of Convective Momentum Transport on Tropical Waves
NASA Astrophysics Data System (ADS)
Zhou, L.
2012-12-01
Convective momentum transport (CMT) has been found to play an important role during the Madden-Julian Oscillation (MJO). Influences of CMT on tropical waves are analytically studied in a two-layer model, which captures the first-order baroclinic structure in the vertical. Since CMT is the momentum exchange between the lower and the upper troposphere during convection, the easterly and westerly vertical shears of background zonal winds lead to different CMT influences. Generally, CMT plays more important roles than a damping term to tropical waves. CMT is a critical factor for determining the meridional scale of tropical waves and leads to kinetic energy transfer against the direction of background wind shear in the vertical. CMT can also be favorable for internal instability and induce upscale momentum transfer. Specifically, due to CMT, the meridional scale in the two-layer model is wider than the Rossby radius of deformation (RL, the meridional scale of tropical waves in the classical theory) over the Indo-Pacific warm pool, but narrower than RL from the central to the eastern Pacific Ocean and over the Atlantic Ocean. Such variation is consistent with observations. CMT results in minor modifications to the speeds of Rossby waves, inertial gravity waves, and Kelvin waves. Nevertheless, CMT has significant influences on the mixed Rossby-gravity (MRG) waves, especially over the Indo-Pacific warm pool where the vertical wind shear in easterly. Westward propagating MRG waves with small wavenumber become unstable under the influence of CMT. The phase relation between the convergence and geopotential is no longer in quadrature, which is different from classical MRG waves. As a result, there is a net source of mechanical energy within one period and there is an upscale momentum transfer from the perturbed field to large scale velocities. This theoretical study sheds lights on the relation between CMT and slow variations in the atmosphere, including MJO.
ANGULAR MOMENTUM TRANSPORT IN CONVECTIVELY UNSTABLE SHEAR FLOWS
Kaepylae, Petri J.; Korpi, Maarit J.; Snellman, Jan E.; Brandenburg, Axel; Narayan, Ramesh
2010-08-10
Angular momentum transport due to hydrodynamic turbulent convection is studied using local three-dimensional numerical simulations employing the shearing box approximation. We determine the turbulent viscosity from non-rotating runs over a range of values of the shear parameter and use a simple analytical model in order to extract the non-diffusive contribution ({Lambda}-effect) to the stress in runs where rotation is included. Our results suggest that the turbulent viscosity is on the order of the mixing length estimate and weakly affected by rotation. The {Lambda}-effect is non-zero and a factor of 2-4 smaller than the turbulent viscosity in the slow rotation regime. We demonstrate that for Keplerian shear, the angular momentum transport can change sign and be outward when the rotation period is greater than the turnover time, i.e., when the Coriolis number is below unity. This result seems to be relatively independent of the value of the Rayleigh number.
INTERNAL GRAVITY WAVES IN MASSIVE STARS: ANGULAR MOMENTUM TRANSPORT
Rogers, T. M.; Lin, D. N. C.; McElwaine, J. N.; Lau, H. H. B. E-mail: lin@ucolick.org E-mail: hblau@astro.uni-bonn.de
2013-07-20
We present numerical simulations of internal gravity waves (IGW) in a star with a convective core and extended radiative envelope. We report on amplitudes, spectra, dissipation, and consequent angular momentum transport by such waves. We find that these waves are generated efficiently and transport angular momentum on short timescales over large distances. We show that, as in Earth's atmosphere, IGW drive equatorial flows which change magnitude and direction on short timescales. These results have profound consequences for the observational inferences of massive stars, as well as their long term angular momentum evolution. We suggest IGW angular momentum transport may explain many observational mysteries, such as: the misalignment of hot Jupiters around hot stars, the Be class of stars, Ni enrichment anomalies in massive stars, and the non-synchronous orbits of interacting binaries.
Momentum correction techniques for neoclassical transport in stellarators
Maassberg, H.; Beidler, C. D.; Turkin, Y.
2009-07-15
In the traditional neoclassical ordering for stellarators, monoenergetic transport coefficients are evaluated using the simplified Lorentz form of the pitch-angle collision operator which violates momentum conservation. In this paper, the parallel momentum balance with radial parallel momentum transport and viscosity terms is analyzed, in particular, with respect to the radial electric field. Next, the impact of momentum conservation in the stellarator long-mean-free-path regime is estimated for the radial transport and the parallel electric conductivity. Two different momentum correction techniques are described based on monoenergetic transport coefficients calculated by the DKES code [W. I. van Rij and S. P. Hirshman, Phys. Fluids B 1, 563 (1989)]. The benchmarking of the parallel electric conductivity and of the bootstrap current is presented for a tokamak as well as for two W7-X stellarator configurations [G. Grieger et al., Phys. Fluids B 4, 2081 (1992)]. Finally, the impact of the momentum correction on the expected total bootstrap current is briefly analyzed for two W7-X scenarios.
Laboratory Study of Angular Momentum Transport in Astrophysical Accretion Disks
NASA Astrophysics Data System (ADS)
Ji, Hantao
2014-10-01
Studying astrophysical processes in the lab becomes increasingly possible and exciting, as one of Stirling's favorite subjects throughout his scientific career. In this talk, I will describe experimental efforts to study mechanisms of rapid angular momentum transport required to occur in accretion disks to explain a wide range of phenomena from star formation, energetic activity of cataclysmic variables, to powering quasars, the most luminous steady sources in the Universe. By carefully isolating effects due to artificial boundaries, which are inherent to terrestrial experiments, certain astrophysical questions regarding hydrodynamic and magnetohydrodynamic stabilities are being addressed in the laboratory. Inspirations from Stirling as well as scientific exchanges with him will be mentioned during this talk as part of my scientific journey on this subject.
Belyaev, Mikhail A.; Rafikov, Roman R.; Stone, James M.
2013-06-10
We perform global unstratified three-dimensional magnetohydrodynamic simulations of an astrophysical boundary layer (BL)-an interface region between an accretion disk and a weakly magnetized accreting object such as a white dwarf-with the goal of understanding the effects of magnetic field on the BL. We use cylindrical coordinates with an isothermal equation of state and investigate a number of initial field geometries including toroidal, vertical, and vertical with zero net flux. Our initial setup consists of a Keplerian disk attached to a non-rotating star. In a previous work, we found that in hydrodynamical simulations, sound waves excited by shear in the BL were able to efficiently transport angular momentum and drive mass accretion onto the star. Here we confirm that in MHD simulations, waves serve as an efficient means of angular momentum transport in the vicinity of the BL, despite the magnetorotational instability (MRI) operating in the disk. In particular, the angular momentum current due to waves is at times larger than the angular momentum current due to MRI. Our results suggest that angular momentum transport in the BL and its vicinity is a global phenomenon occurring through dissipation of waves and shocks. This point of view is quite different from the standard picture of transport by a local anomalous turbulent viscosity. In addition to angular momentum transport, we also study magnetic field amplification within the BL. We find that the field is indeed amplified in the BL, but only by a factor of a few, and remains subthermal.
Rectified momentum transport for a kicked Bose-Einstein condensate.
Sadgrove, Mark; Horikoshi, Munekazu; Sekimura, Tetsuo; Nakagawa, Ken'ichi
2007-07-27
We report the experimental observation of rectified momentum transport for a Bose-Einstein condensate kicked at the Talbot time (quantum resonance) by an optical standing wave. Atoms are initially prepared in a superposition of the 0 and -2hkl momentum states using an optical pi/2 pulse. By changing the relative phase of the superposed states, a momentum current in either direction along the standing wave may be produced. We offer an interpretation based on matter-wave interference, showing that the observed effect is uniquely quantum.
Mass and momentum turbulent transport experiments with confined coaxial jets
NASA Technical Reports Server (NTRS)
Johnson, B. V.; Bennett, J. C.
1984-01-01
An experimental study of mixing downstream of coaxial jets discharging into an expanded circular duct was conducted to obtain data for the evaluation and improvement of turbulent transport models. A combination of turbulent momentum transport rate and two components of velocity data were obtained from simultaneous measurements with a two-color LV system. A combination of turbulent mass transport rate, concentration and velocity data were obtained from simultaneous measurements with laser velocimeter (LV) and laser induced fluorescence (LIF) systems.
Momentum Transport in Electron-Dominated Spherical Torus Plasmas
Kaye, S. M.; Solomon, W.; Bell, R. E.; LeBlanc, B. P.; Levinton, F.; Menard, J.; Rewoldt, G.; Sabbagh, S.; Wang, W.; Yuh, H.
2009-02-24
The National Spherical Torus Experiment (NSTX) operates between 0.35 and 0.55 T, which, when coupled to up to 7 MW of neutral beam injection, leads to central rotation velocities in excess of 300 km/s and ExB shearing rates up to 1 MHz. This level of ExB shear can be up to a factor of five greater than typical linear growth rates of long-wavelength ion (e.g., ITG) modes, at least partially suppressing these instabilities. Evidence for this turbulence suppression is that the inferred diffusive ion thermal flux in NSTX H-modes is often at the neoclassical level, and thus these plasmas operate in an electron-dominated transport regime. Analysis of experiments using n=3 magnetic fields to change plasma rotation indicate that local rotation shear influences local transport coefficients, most notably the ion thermal diffusivity, in a manner consistent with suppression of the low-k turbulence by this rotation shear. The value of the effective momentum diffusivity, as inferred from steady-state momentum balance, is found to be larger than the neoclassical value. Results of perturbative experiments indicate inward pinch velocities up to 40 m/s and perturbative momentum diffusivities of up to 4 m2/s, which are larger by a factor of several than those values inferred from steady-state analysis. The inferred pinch velocity values are consistent with values based on theories in which low-k turbulence drives the inward momentum pinch. Thus, in Spherical Tori (STs), while the neoclassical ion energy transport effects can be relatively high and dominate the ion energy transport, the neoclassical momentum transport effects are near zero, meaning that transport of momentum is dominated by any low-k turbulence that exists.
Turbulent Transport of Momentum and Scalars Above an Urban Canopy
NASA Astrophysics Data System (ADS)
Wang, Linlin; Li, Dan; Gao, Zhiqiu; Sun, Ting; Guo, Xiaofeng; Bou-Zeid, Elie
2014-03-01
Turbulent transport of momentum and scalars over an urban canopy is investigated using the quadrant analysis technique. High-frequency measurements are available at three levels above the urban canopy (47, 140 and 280 m). The characteristics of coherent ejection-sweep motions (flux contributions and time fractions) at the three levels are analyzed, particularly focusing on the difference between ejections and sweeps, the dissimilarity between momentum and scalars, and the dissimilarity between the different scalars (i.e., temperature, water vapour and . It is found that ejections dominate momentum and scalar transfer at all three levels under unstable conditions, while sweeps are the dominant eddy motions for transporting momentum and scalars in the urban roughness sublayer under neutral and stable conditions. The flux contributions and time fractions of ejections and sweeps can be adequately captured by assuming a Gaussian joint probability density function for flow variables. However, the inequality of flux contributions from ejections and sweeps is more accurately reproduced by the third-order cumulant expansion method (CEM). The incomplete cumulant expansion method (ICEM) also works well except for at 47 m where the skewness of fluctuations is significantly larger than that for vertical velocity. The dissimilarity between momentum and scalar transfers is linked to the dissimilarity in the characteristics of ejection-sweep motions and is further quantified by measures of transport efficiencies. Atmospheric stability is the controlling factor for the transport efficiencies of momentum and heat, and fitted functions from the literature describe their behaviour fairly accurately. However, transport efficiencies of water vapour and are less affected by the atmospheric stability. The dissimilarity among the three scalars examined in this study is linked to the active role of temperature and to the surface heterogeneity effect.
Mass and Momentum Turbulent Transport Experiments
NASA Technical Reports Server (NTRS)
Johnson, B. V.
1983-01-01
The downstream mixing of coaxial jets discharging in an expanded duct was studied to improve turbulent transport models which are used in computational procedures throughout the propulsion community for combustor flow modeling. Laser velocimeter (LV) and laser induced fluorescence (LIF) techniques were used to measure velocities and concentration and flow visualization techniques to determine the time dependent characteristics of the flow and the scale of the turbulent structure.
Momentum transport near a magnetic X line in collisionless reconnection
NASA Technical Reports Server (NTRS)
Cai, H. J.; Ding, D. Q.; Lee, L. C.
1994-01-01
Plasma dynamics and momentum transport near an X line during time-dependent magnetic reconnection in a collisionless plasma are investigated based on two-dimensional particle simulations. We find that a weakly skewed velocity distribution is formed near the magnetic X line, leading to the presence of off-diagonal elements of the plasma pressure tensor. Let the reconnection electric field be in the y direction. The gradients of the off-diagonal elements of the pressure tensor can provide a transport of the y momentum. During the normal magnetic reconnection, the momentum transport associated with the off-diagonal terms of the pressure tensor mediates a transfer of the y momentum from the region near the X line to regions outside the X line. A period of 'reverse magnetic reconnection,' during which the plasma kinetic energy is converted into magnetic energy, is also observed in the simulation. When reverse reconnection occurs, the gradients of the off-diagonal pressure tensor elements can mediate a transfer of y momentum into the X line. It is found that the inertial term also plays a significant role in the force balance near the magnetic X line. An explanation for the origin of the off-diagonal pressure terms is also given in this paper.
Intrinsic momentum transport in up-down asymmetric tokamaks
NASA Astrophysics Data System (ADS)
Ball, Justin; Parra, Felix I.; Barnes, Michael; Dorland, William; Hammett, Gregory W.; Rodrigues, Paulo; Loureiro, Nuno F.
2014-09-01
Recent work has demonstrated that breaking the up-down symmetry of tokamak flux surfaces removes a constraint that limits intrinsic momentum transport, and hence toroidal rotation, to be small. We show, through MHD analysis, that ellipticity is most effective at introducing up-down asymmetry throughout the plasma. We detail an extension to GS2, a local δf gyrokinetic code that self-consistently calculates momentum transport, to permit up-down asymmetric configurations. Tokamaks with tilted elliptical poloidal cross-sections were simulated to determine nonlinear momentum transport. The results, which are consistent with the experiment in magnitude, suggest that a toroidal velocity gradient, (∂uζi/∂ρ)/vthi, of 5% of the temperature gradient, (∂Ti/∂ρ)/Ti, is sustainable. Here vthi is the ion thermal speed, uζi is the ion toroidal mean flow, ρ is the minor radial coordinate normalized to the tokamak minor radius, and Ti is the ion temperature. Though other known core intrinsic momentum transport mechanisms scale poorly to larger machines, these results indicate that up-down asymmetry may be a feasible method to generate the current experimentally measured rotation levels in reactor-sized devices.
Xu Zhe; Greiner, Carsten
2007-08-15
To describe momentum isotropization of gluon matter produced in ultrarelativistic heavy-ion collisions, the transport rate of gluon drift and the transport collision rates of elastic (gg{r_reversible}gg) as well as inelastic (gg{r_reversible}ggg) perturbative quantum chromodynamics- (pQCD) scattering processes are introduced and calculated within the kinetic parton cascade Boltzmann approach of multiparton scatterings (BAMPS), which simulates the space-time evolution of partons. We define isotropization as the development of an anisotropic system as it reaches isotropy. The inverse of the introduced total transport rate gives the correct time scale of the momentum isotropization. The contributions of the various scattering processes to the momentum isotropization can be separated into the transport collision rates. In contrast to the transport cross section, the transport collision rate has an indirect but correctly implemented relationship with the collision-angle distribution. Based on the calculated transport collision rates from BAMPS for central Au+Au collisions at Relativistic Heavy Ion Collider energies, we show that pQCD gg{r_reversible}ggg bremsstrahlung processes isotropize the momentum five times more efficiently than elastic scatterings. The large efficiency of the bremsstrahlung stems mainly from its large momentum deflection. Due to kinematics, 2{yields}N (N>2) production processes allow more particles to become isotropic in momentum space and thus kinetically equilibrate more quickly than their back reactions or elastic scatterings. We also show that the relaxation time in the relaxation time approximation, which is often used, is strongly momentum dependent and thus cannot serve as a global quantity that describes kinetic equilibration.
Radial transport and momentum exchange in an axial compressor
Dring, R.P. )
1993-07-01
The objective of this work was to examine radial transport in axial compressors from two perspectives. The first was to compare the mixing coefficient based on a secondary flow model (using measured radial velocities) with that based on a turbulent diffusion model. The second was to use measured airfoil pressure forces and momentum changes to assess the validity of the assumption of diffusive radial transport, which is common to both models. These examinations were carried out at both design and off-design conditions as well as for two rotor tip clearances. In general it was seen that radial mixing was strongest near the hub and that it increased dramatically at near-stall conditions. It was also seen that radial transport could cause large differences ([approx] 100 percent) between the force on an airfoil and the change in momentum across the airfoil at the same spanwise location.
Gyrokinetic theory and simulation of angular momentum transport
Waltz, R. E.; Staebler, G. M.; Candy, J.; Hinton, F. L.
2007-12-15
A gyrokinetic theory of turbulent toroidal angular momentum transport as well as modifications to neoclassical poloidal rotation from turbulence is formulated starting from the fundamental six-dimensional kinetic equation. The gyro-Bohm scaled transport is evaluated from toroidal delta-f gyrokinetic simulations using the GYRO code [Candy and Waltz, J. Comput. Phys. 186, 545 (2003)]. The simulations recover two pinch mechanisms in the radial transport of toroidal angular momentum: The slab geometry ExB shear pinch [Dominguez and Staebler, Phys. Fluids B 5, 387 (1993)] and the toroidal geometry 'Coriolis' pinch [Peeters, Angioni, and Strintzi, Phys. Rev. Lett. 98, 265003 (2007)]. The pinches allow the steady state null stress (or angular momentum transport flow) condition required to understand intrinsic (or spontaneous) toroidal rotation in heated tokamak without an internal source of torque [Staebler, Kinsey, and Waltz, Bull. Am. Phys. Soc. 46, 221 (2001)]. A predicted turbulent shift in the neoclassical poloidal rotation [Staebler, Phys. Plasmas 11, 1064 (2004)] appears to be small at the finite relative gyroradius (rho-star) of current experiments.
Momentum transport and non-local transport in heat-flux-driven magnetic reconnection in HEDP
NASA Astrophysics Data System (ADS)
Liu, Chang; Fox, Will; Bhattacharjee, Amitava
2016-10-01
Strong magnetic fields are readily generated in high-energy-density plasmas and can affect the heat confinement properties of the plasma. Magnetic reconnection can in turn be important as an inverse process, which destroys or reconfigures the magnetic field. Recent theory has demonstrated a novel physics regime for reconnection in high-energy-density plasmas where the magnetic field is advected into the reconnection layer by plasma heat flux via the Nernst effect. In this work we elucidate the physics of the electron dissipation layer in this heat-flux-driven regime. Through fully kinetic simulation and a new generalized Ohm's law, we show that momentum transport due to the heat-flux-viscosity effect provides the dissipation mechanism to allow magnetic field line reconnection. Scaling analysis and simulations show that the characteristic width of the current sheet in this regime is several electron mean-free-paths. These results additionally show a coupling between non-local transport and momentum transport, which in turn affects the dynamics of the magnetic field. This work was supported by the U.S. Department of Energy under Contract No. DE-SC0008655.
Zombie Vortices: Angular Momentum Transport and Planetesimal Formation
NASA Astrophysics Data System (ADS)
Barranco, Joseph; Marcus, Philip; Pei, Suyang; Jiang, Chung-Hsiang; Hassanzadeh, Pedram; Lecoanet, Daniel
2014-11-01
Zombie vortices may fill the dead zones of protoplanetary disks, where they may play important roles in star and planet formation. We will investigate this new, purely hydrodynamic instability and explore the conditions necessary to resurrect the dead zone and fill it with large amplitude vortices that may transport angular momentum and allow mass to accrete onto the protostar. One unresolved issue is whether angular momentum transport is mediated via asymmetries in the vortices, vortex-vortex interactions, or acoustic waves launched by the vortices. Vortices may also play a crucial role in the formation of planetesimals, the building blocks of planets. It is still an open question how grains grow to kilometer-size. We will investigate the interactions of dust with vortices generated via our new hydrodynamic instability, and bridge the gap between micron-sized grains and kilometer-sized planetesimals. Supported by NSF AST-1010052.
Topological angular momentum and radiative heat transport in closed orbits
NASA Astrophysics Data System (ADS)
Silveirinha, Mário G.
2017-03-01
We study the role of topological edge states of light in the transport of thermally generated radiation in a closed cavity at a thermodynamic equilibrium. It is shown that even in the zero temperature limit—when the field fluctuations are purely quantum mechanical—there is a persistent flow of electromagnetic momentum in the cavity in closed orbits, deeply rooted in the emergence of spatially separated unidirectional edge state channels. It is highlighted that the electromagnetic orbital angular momentum of the system is nontrivial, and that the energy circulation is towards the same direction as that determined by incomplete cyclotron orbits near the cavity walls. Our findings open inroads in topological photonics and suggest that topological states of light can determine novel paradigms in the context of radiative heat transport.
Mass and Momentum Turbulent Transport Experiments with Confined Coaxial Jets
NASA Technical Reports Server (NTRS)
Johnson, B. V.; Bennett, J. C.
1981-01-01
Downstream mixing of coaxial jets discharging in an expanded duct was studied to obtain data for the evaluation and improvement of turbulent transport models currently used in a variety of computational procedures throughout the propulsion community for combustor flow modeling. Flow visualization studies showed four major shear regions occurring; a wake region immediately downstream of the inlet jet inlet duct; a shear region further downstream between the inner and annular jets; a recirculation zone; and a reattachment zone. A combination of turbulent momentum transport rate and two velocity component data were obtained from simultaneous measurements with a two color laser velocimeter (LV) system. Axial, radial and azimuthal velocities and turbulent momentum transport rate measurements in the r-z and r-theta planes were used to determine the mean value, second central moment (or rms fluctuation from mean), skewness and kurtosis for each data set probability density function (p.d.f.). A combination of turbulent mass transport rate, concentration and velocity data were obtained system. Velocity and mass transport in all three directions as well as concentration distributions were used to obtain the mean, second central moments, skewness and kurtosis for each p.d.f. These LV/LIF measurements also exposed the existence of a large region of countergradient turbulent axial mass transport in the region where the annular jet fluid was accelerating the inner jet fluid.
Intercomponent momentum transport and electrical conductivity of collisionless plasma
NASA Technical Reports Server (NTRS)
Wilhelm, H. E.
1973-01-01
Based on the Lenard-Balescu equation, the interaction integral for the intercomponent momentum transfer in a two-component, collisionless plasma is evaluated in closed form. The distribution functions of the electrons and ions are represented in the form of nonisothermal, displaced Maxwellians corresponding to the 5-moment approximation. As an application, the transport of electrical current in an electric field is discussed for infrasonic up to sonic electron-ion drift velocities.
Intercomponent momentum transport and electrical conductivity of collisionless plasma
NASA Technical Reports Server (NTRS)
Wilhelm, H. E.
1973-01-01
Based on the Lenard-Balescu equation, the interaction integral for the intercomponent momentum transfer in a two-component, collisionless plasma is evaluated in closed form. The distribution functions of the electrons and ions are represented in the form of nonisothermal, displaced Maxwellians corresponding to the 5-moment approximation. As an application, the transport of electrical current in an electric field is discussed for infrasonic up to sonic electron-ion drift velocities.
Angular momentum transport in thin accretion disks and intermittent accretion.
Coppi, B; Coppi, P S
2001-07-30
The plasma modes, transporting angular momentum in accretion disks, under minimally restrictive conditions when the magnetic energy density is significant relative to the thermal energy density, are shown to be singular if the ideal MHD approximation is adopted. A similarity with the modes producing magnetic reconnection in current carrying plasmas is established. The combined effects of finite plasma temperature, of plasma compressibility, of the gradient of the rotation frequency, and of appropriate transport processes (outside ideal MHD) are involved in the onset of these nonaxisymmetric and locally corotating modes.
Momentum transport experiments using NBI in an RFP
NASA Astrophysics Data System (ADS)
Nornberg, M. D.; Sarff, J. S.; den Hartog, D. J.; Kumar, S.; Anderson, J. K.; Waksman, J.; Dobbins, T.; Craig, D.; Ding, W. X.; Lin, L.; Brower, D. L.
2012-10-01
The self-organization process that shapes the current density profile in an RFP discharge gives rise to large turbulent stresses that also shape the parallel flow profile. These stresses drive rapid transport during relaxation events flattening both the plasma current and parallel flow profiles. Experiments using tangential neutral beam injection to create a core-localized torque are presented for a range of equilibrium conditions in MST plasmas: from standard RFP discharges where tearing modes give rise to stochastic transport to discharges with inductive profile control (PPCD) which greatly suppress the tearing modes. Measurements of plasma spin-down after NBI turn-off are used to gauge momentum transport in plasmas with varying levels of tearing mode activity. Plasmas tending toward the quasi-single-helicity state have a dominant core mode that induces a braking torque on the plasma. This core mode is suppressed by NBI thereby reducing the braking torque on the plasma. Variation of the magnetic fluctuation level through inductive profile control shows a reduction in momentum transport consistent with stochastic transport theory.
Nonlinear parallel momentum transport in strong electrostatic turbulence
Wang, Lu Wen, Tiliang; Diamond, P. H.
2015-05-15
Most existing theoretical studies of momentum transport focus on calculating the Reynolds stress based on quasilinear theory, without considering the nonlinear momentum flux-〈v{sup ~}{sub r}n{sup ~}u{sup ~}{sub ∥}〉. However, a recent experiment on TORPEX found that the nonlinear toroidal momentum flux induced by blobs makes a significant contribution as compared to the Reynolds stress [Labit et al., Phys. Plasmas 18, 032308 (2011)]. In this work, the nonlinear parallel momentum flux in strong electrostatic turbulence is calculated by using a three dimensional Hasegawa-Mima equation, which is relevant for tokamak edge turbulence. It is shown that the nonlinear diffusivity is smaller than the quasilinear diffusivity from Reynolds stress. However, the leading order nonlinear residual stress can be comparable to the quasilinear residual stress, and so may be important to intrinsic rotation in tokamak edge plasmas. A key difference from the quasilinear residual stress is that parallel fluctuation spectrum asymmetry is not required for nonlinear residual stress.
Particle, momentum and thermal transport in the PTRANSP code
NASA Astrophysics Data System (ADS)
Bateman, G.; Halpern, F. D.; Kritz, A. H.; Pankin, A. Y.; Rafiq, T.; McCune, D. C.; Budny, R. V.; Indireshkumar, K.
2008-11-01
The combined effects of particle, momentum and thermal transport are investigated in tokamak discharges using a coupled system of transport equations implemented in the PTRANSP integrated modeling code. The magnetic diffusion equation is advanced separately, along with the evolution of the equilibrium. Simulations are carried out using theory-based models to compute transport, sources and sinks. Boundary conditions are either read from data or computed using a pedestal model for H-mode discharges. Different techniques are explored for controlling numerical problems [1] in time-dependent simulations that include sawtooth oscillations and other rapid changes in the profiles. Results for the density, temperature and toroidal angular velocity profiles are compared with experimental data. [1] S.C. Jardin et al, ``On 1D diffusion problems with a gradient-dependent diffusion coefficient''; G.V. Pereverzev and G. Corrigan, ``Stable numeric scheme for diffusion equation with a stiff transport''; both papers to appear in Comp. Phys. Comm. (2008).
Hydrodynamic turbulence cannot transport angular momentum effectively in astrophysical disks.
Ji, Hantao; Burin, Michael; Schartman, Ethan; Goodman, Jeremy
2006-11-16
The most efficient energy sources known in the Universe are accretion disks. Those around black holes convert 5-40 per cent of rest-mass energy to radiation. Like water circling a drain, inflowing mass must lose angular momentum, presumably by vigorous turbulence in disks, which are essentially inviscid. The origin of the turbulence is unclear. Hot disks of electrically conducting plasma can become turbulent by way of the linear magnetorotational instability. Cool disks, such as the planet-forming disks of protostars, may be too poorly ionized for the magnetorotational instability to occur, and therefore essentially unmagnetized and linearly stable. Nonlinear hydrodynamic instability often occurs in linearly stable flows (for example, pipe flows) at sufficiently large Reynolds numbers. Although planet-forming disks have extreme Reynolds numbers, keplerian rotation enhances their linear hydrodynamic stability, so the question of whether they can be turbulent and thereby transport angular momentum effectively is controversial. Here we report a laboratory experiment, demonstrating that non-magnetic quasi-keplerian flows at Reynolds numbers up to millions are essentially steady. Scaled to accretion disks, rates of angular momentum transport lie far below astrophysical requirements. By ruling out purely hydrodynamic turbulence, our results indirectly support the magnetorotational instability as the likely cause of turbulence, even in cool disks.
Angular momentum transport via internal gravity waves in evolving stars
Fuller, Jim; Lecoanet, Daniel; Cantiello, Matteo; Brown, Ben
2014-11-20
Recent asteroseismic advances have allowed for direct measurements of the internal rotation rates of many subgiant and red giant stars. Unlike the nearly rigidly rotating Sun, these evolved stars contain radiative cores that spin faster than their overlying convective envelopes, but slower than they would in the absence of internal angular momentum transport. We investigate the role of internal gravity waves in angular momentum transport in evolving low-mass stars. In agreement with previous results, we find that convectively excited gravity waves can prevent the development of strong differential rotation in the radiative cores of Sun-like stars. As stars evolve into subgiants, however, low-frequency gravity waves become strongly attenuated and cannot propagate below the hydrogen-burning shell, allowing the spin of the core to decouple from the convective envelope. This decoupling occurs at the base of the subgiant branch when stars have surface temperatures of T ≈ 5500 K. However, gravity waves can still spin down the upper radiative region, implying that the observed differential rotation is likely confined to the deep core near the hydrogen-burning shell. The torque on the upper radiative region may also prevent the core from accreting high angular momentum material and slow the rate of core spin-up. The observed spin-down of cores on the red giant branch cannot be totally attributed to gravity waves, but the waves may enhance shear within the radiative region and thus increase the efficacy of viscous/magnetic torques.
Temperature dependence of angular momentum transport across interfaces
NASA Astrophysics Data System (ADS)
Chen, Kai; Lin, Weiwei; Chien, C. L.; Zhang, Shufeng
2016-08-01
Angular momentum transport in magnetic multilayered structures plays a central role in spintronic physics and devices. The angular momentum currents or spin currents are carried by either quasiparticles such as electrons and magnons, or by macroscopic order parameters such as local magnetization of ferromagnets. Based on the generic interface exchange interaction, we develop a microscopic theory that describes interfacial spin conductance for various interfaces among nonmagnetic metals, ferromagnetic insulators, and antiferromagnetic insulators. Spin conductance and its temperature dependence are obtained for different spin batteries including spin pumping, temperature gradient, and spin Hall effect. As an application of our theory, we calculate the spin current in a trilayer made of a ferromagnetic insulator, an antiferromagnetic insulator, and a nonmagnetic heavy metal. The calculated results on the temperature dependence of spin conductance quantitatively agree with the existing experiments.
Inhomogeneous helicity effect in the solar angular-momentum transport
NASA Astrophysics Data System (ADS)
Yokoi, Nobumitsu
2017-04-01
Coupled with mean absolute vorticity Ω∗ (rotation and mean relative vorticity), inhomogeneous turbulent helicity is expected to contribute to the generation of global flow structure against the linear and angular momentum mixing due to turbulent or eddy viscosity. This inhomogeneous helicity effect was originally derived in Yokoi & Yoshizawa (1993) [1], and recently has been validated by direct numerical simulations (DNSs) of rotating helical turbulence [2]. Turbulence effect enters the mean-vorticity equation through the turbulent vortexmotive force ⟨u'×ω'⟩ [u': velocity fluctuation, ω'(= ∇× u'): vorticity fluctuation], which is the vorticity counterpart of the electromotive force ⟨u'× b'⟩ (b': magnetic fluctuation) in the mean magnetic-field induction. The mean velocity induction δU is proportional to the vortexmotive force. According to the theoretical result [1,2], it is expressed as δU = -νT∇×Ω∗-ηT(∇2H)Ω∗, where ηT is the transport coefficient, H = ⟨u'ṡω'⟩ the turbulent helicity, and Ω∗ the mean absolute vorticity. The first term corresponds to the enhanced diffusion due to turbulent viscosity νT. The second term expresses the large-scale flow generation due to inhomogeneous helicity. Since helicity is self-generated in rotating stratified turbulence [3], an inhomogeneous helicity distribution is expected to exist in the solar convection zone. A rising flow with expansion near the surface of the Sun generates a strongly negative helicity there [4]. This spatial distribution of helicity would lead to a positive Laplacian of turbulent helicity (∇2H > 0) in the subsurface layer of the Sun. In the combination with the large-scale vorticity associated with the meridional circulation, the inhomogeneous helicity effect works for accelerating the mean velocity in the azimuthal direction. The relevance of this inhomogeneous helicity effect in the solar convection zone is discussed further. References [1] Yokoi, N. and
Hoshino, Masahiro
2015-02-13
Angular momentum transport and particle acceleration during the magnetorotational instability (MRI) in a collisionless accretion disk are investigated using three-dimensional particle-in-cell simulation. We show that the kinetic MRI can provide not only high-energy particle acceleration but also enhancement of angular momentum transport. We find that the plasma pressure anisotropy inside the channel flow with p(∥)>p(⊥) induced by active magnetic reconnection suppresses the onset of subsequent reconnection, which, in turn, leads to high-magnetic-field saturation and enhancement of the Maxwell stress tensor of angular momentum transport. Meanwhile, during the quiescent stage of reconnection, the plasma isotropization progresses in the channel flow and the anisotropic plasma with p(⊥)>p(∥) due to the dynamo action of MRI outside the channel flow contribute to rapid reconnection and strong particle acceleration. This efficient particle acceleration and enhanced angular momentum transport in a collisionless accretion disk may explain the origin of high-energy particles observed around massive black holes.
NASA Astrophysics Data System (ADS)
Hoshino, Masahiro
2015-02-01
Angular momentum transport and particle acceleration during the magnetorotational instability (MRI) in a collisionless accretion disk are investigated using three-dimensional particle-in-cell simulation. We show that the kinetic MRI can provide not only high-energy particle acceleration but also enhancement of angular momentum transport. We find that the plasma pressure anisotropy inside the channel flow with p∥>p⊥ induced by active magnetic reconnection suppresses the onset of subsequent reconnection, which, in turn, leads to high-magnetic-field saturation and enhancement of the Maxwell stress tensor of angular momentum transport. Meanwhile, during the quiescent stage of reconnection, the plasma isotropization progresses in the channel flow and the anisotropic plasma with p⊥>p∥ due to the dynamo action of MRI outside the channel flow contribute to rapid reconnection and strong particle acceleration. This efficient particle acceleration and enhanced angular momentum transport in a collisionless accretion disk may explain the origin of high-energy particles observed around massive black holes.
Theory for plasma confinement and momentum transport in snakes
Shaing, K.C.
2005-07-15
A theory for plasma confinement in snakes is developed based on the consequences of the momentum transport resulting from the symmetry-breaking-induced plasma viscosity in the vicinity of an m=1 magnetic island. Here, m is the poloidal mode number of the island. The symmetry-breaking mechanism is the distortion of the magnetic surface associated with the magnetic island embedded in the equilibrium magnetic field. It is demonstrated that a combination of the turbulence suppression and the effects of the orbit squeezing could be responsible for the observed improved plasma confinement in snakes.
Plasma rotation from momentum transport by neutrals in tokamaks
NASA Astrophysics Data System (ADS)
Omotani, J.; Pusztai, I.; Newton, S.; Fülöp, T.
2016-12-01
Neutral atoms can strongly influence the intrinsic rotation and radial electric field at the tokamak edge. Here, we present a framework to investigate these effects when the neutrals dominate the momentum transport. We explore the parameter space numerically, using highly flexible model geometries and a state of the art kinetic solver. We find that the most important parameters controlling the toroidal rotation and electric field are the major radius where the neutrals are localized and the plasma collisionality. This offers a means to influence the rotation and electric field by, for example, varying the radial position of the X-point to change the major radius of the neutral peak.
Momentum and particle transport in a nonhomogenous canopy
NASA Astrophysics Data System (ADS)
Gould, Andrew W.
Turbulent particle transport through the air plays an important role in the life cycle of many plant pathogens. In this study, data from a field experiment was analyzed to explore momentum and particle transport within a grape vineyard. The overall goal of these experiments was to understand how the architecture of a sparse agricultural canopy interacts with turbulent flow and ultimately determines the dispersion of airborne fungal plant pathogens. Turbulence in the vineyard canopy was measured using an array of four sonic anemometers deployed at heights z/H 0.4, 0.9, 1.45, and 1.95 where z is the height of the each sonic and H is the canopy height. In addition to turbulence measurements from the sonic anemometers, particle dispersion was measured using inert particles with the approximate size and density of powdery mildew spores and a roto-rod impaction trap array. Measurements from the sonic anemometers demonstrate that first and second order statistics of the wind field are dependent on wind direction orientation with respect to vineyard row direction. This dependence is a result of wind channeling which transfers energy between the velocity components when the wind direction is not aligned with the rows. Although the winds have a strong directional dependence, spectra analysis indicates that the structure of the turbulent flow is not fundamentally altered by the interaction between wind direction and row direction. Examination of a limited number of particle release events indicates that the wind turning and channeling observed in the momentum field impacts particle dispersion. For row-aligned flow, particle dispersion in the direction normal to the flow is decreased relative to the plume spread predicted by a standard Gaussian plume model. For flow that is not aligned with the row direction, the plume is found to rotate in the same manner as the momentum field.
Momentum and Current Transport in the MST Reversed Field Pinch
NASA Astrophysics Data System (ADS)
Ding, W. X.; Lin, Liang; Brower, D. L.; Almagri, A. F.; Chapman, B. E.; Hartog, D. J. Den; Duff, J.; Sarff, J. S.
2013-10-01
Self-generated flows and current (dynamo effects) are routinely observed in the MST RFP where both parallel flow and electric field reverse sign compared to the edge. In the absence of external torque and applied poloidal electric field, both the flow and electric field may arise from kinetic effects. Kinetic effects, defined as the correlated product of parallel pressure and radial magnetic field fluctuations, have been measured by using a high-speed polarimetry-interferometry diagnostic (for combined radial magnetic field and density fluctuation measurement). Between sawtooth crashes it is found that the measured kinetic effects associated with density fluctuations (a component of parallel pressure fluctuation) has a finite amplitude that may account for the observed flow in the core. In addition, the same fluctuations also influence electron dynamics via the kinetic dynamo. These results suggest kinetic effects may play an important role in coupling between momentum transport and current transport. Work supported by US DOE and NSF.
Cloud-top meridional momentum transports on Saturn and Jupiter
NASA Technical Reports Server (NTRS)
Stromovsky, L. A.; Revercomb, H. E.; Krauss, R. J.
1986-01-01
Cloud-tracked wind measurements reported by Sromovsky et al. were analyzed to determine meridional momentum transports in Saturn's northern middle latitudes. Results are expressed in terms of eastward and northward velocity components (u and v), and eddy components u and v. At most latitudes between 13 and 44 deg N (planetocentric), the transport by the mean flow (
Enhanced understanding of momentum transport barrier observed in KSTAR
NASA Astrophysics Data System (ADS)
Lee, H. H.; Seol, J.; Ko, W. H.; Terzolo, L.; Aydemir, A. Y.; in, Y.; Ghime, Y. C.; Lee, S. G.
2016-10-01
It is expected that H-mode plasmas exhibit transport barriers not only for plasma particles and energy but also for toroidal angular momentum. Although density and temperature pedestals at the edge have been seen since the first observations of H-mode in tokamaks three decades ago, a toroidal rotation pedestal is not commonly observed except in some special cases such as QH-mode or is much weaker than those in the density and temperature profiles. But, in the KSTAR tokamak, H-mode plasma is always accompanied by the noticeable toroidal rotation pedestal. We show that the inherent nonaxisymmetric error fields and toroidal ripple can generate significant neoclassical toroidal viscosity (NTV), which damps the toroidal rotation at the edge and to a large extent remove the pedestal in the rotation profile. On the other hand, we demonstrate that the NTV torque induced by the intrinsic error fields and toroidal field ripple in the level of the KSTAR tokamak, which are expected to be smaller than most tokamaks by at least one order of magnitude, is negligible in determining the toroidal rotation velocity profile. Thus we conclusively show that H-mode provides a transport barrier against all three transport channels when turbulent transport is suppressed at the edge.
Wave mediated angular momentum transport in astrophysical boundary layers
NASA Astrophysics Data System (ADS)
Hertfelder, Marius; Kley, Wilhelm
2015-07-01
Context. Disk accretion onto weakly magnetized stars leads to the formation of a boundary layer (BL) where the gas loses its excess kinetic energy and settles onto the star. There are still many open questions concerning the BL, for instance the transport of angular momentum (AM) or the vertical structure. Aims: It is the aim of this work to investigate the AM transport in the BL where the magneto-rotational instability (MRI) is not operating owing to the increasing angular velocity Ω(r) with radius. We will therefore search for an appropriate mechanism and examine its efficiency and implications. Methods: We perform 2D numerical hydrodynamical simulations in a cylindrical coordinate system (r,ϕ) for a thin, vertically integrated accretion disk around a young star. We employ a realistic equation of state and include both cooling from the disk surfaces and radiation transport in radial and azimuthal direction. The viscosity in the disk is treated by the α-model; in the BL there is no viscosity term included. Results: We find that our setup is unstable to the sonic instability which sets in shortly after the simulations have been started. Acoustic waves are generated and traverse the domain, developing weak shocks in the vicinity of the BL. Furthermore, the system undergoes recurrent outbursts where the activity in the disk increases strongly. The instability and the waves do not die out for over 2000 orbits. Conclusions: There is indeed a purely hydrodynamical mechanism that enables AM transport in the BL. It is efficient and wave mediated; however, this renders it a non-local transport method, which means that models of a effective local viscosity like the α-viscosity are probably not applicable in the BL. A variety of further implications of the non-local AM transport are discussed.
Gyrokinetic study of electromagnetic effects on toroidal momentum transport in tokamak plasmas
Hein, T.; Angioni, C.; Fable, E.; Candy, J.; Peeters, A. G.
2011-07-15
The effect of a finite {beta}{sub e} = 8{pi}n{sub e}T{sub e}/B{sup 2} on the turbulent transport of toroidal momentum in tokamak plasmas is discussed. From an analytical gyrokinetic model as well as local linear gyrokinetic simulations, it is shown that the modification of the parallel mode structure due to the nonadiabatic response of passing electrons, which changes the parallel wave vector k{sub ||} with increasing {beta}{sub e}, leads to a decrease in size of both the diagonal momentum transport as well as the Coriolis pinch under ion temperature gradient turbulence conditions, while for trapped electron modes, practically no modification is found. The decrease is particularly strong close to the onset of the kinetic ballooning modes. There, the Coriolis pinch even reverses its direction.
Be Star Outbursts: Transport of Angular Momentum by Waves
NASA Astrophysics Data System (ADS)
Neiner, C.; Mathis, S.; Saio, H.; Lee, U.
2013-12-01
The Be phenomenon, that is the ejection of matter from Be stars into a circumstellar disk, has been a long lasting mystery. In the last few years, the CoRoT (Convection Rotation and planetary Transits) satellite brought clear evidence that Be outbursts are directly correlated with pulsations. We found that it may be the transport of angular momentum by waves or pulsation modes that brings the already rapid stellar rotation to its critical value at the surface, and allows the star to eject material. The recent discovery of stochastically excited gravito-inertial modes by CoRoT in a hot Be star strengthens this scenario. We present the CoRoT observations and modeling of several Be stars and describe the new picture of the Be phenomenon which arose from these results.
NASA Astrophysics Data System (ADS)
Buchholz, R.; Grosshauser, S.; Guttenfelder, W.; Hornsby, W. A.; Migliano, P.; Peeters, A. G.; Strintzi, D.
2015-08-01
This paper studies the effect of rotation on microinstabilities under experimentally relevant conditions in the spherical tokamak National Spherical Torus Experiment (NSTX). The focus is specifically on the centrifugal force effects on the impurity and momentum transport in the core ( r /a =0.7 ) of an H-mode plasma. Due to relatively high beta, the linear simulations predict the presence of both microtearing mode (MTM) and hybrid ion temperature gradient-kinetic ballooning mode (ITG-KBM) electromagnetic instabilities. Rotation effects on both MTM and ITG-KBM growth rates and mode frequencies are found to be small for the experimental values. However, they do influence the quasi-linear particle and momentum fluxes predicted by ITG-KBM (MTM contributes only to electron heat flux). The gradient of the intrinsic carbon impurity in the source-free core region is predicted to be locally hollow, strengthened by centrifugal effects. This result is consistent with experimental measurements and contradicts neoclassical theory that typically provides a reasonable explanation of the impurity profiles in NSTX. The diffusive and Coriolis pinch contributions to momentum transport are found to be relatively weak. Surprisingly, the strongest contribution derives from a centrifugal effect proportional to the product of rotation and rotation shear, which predicts an inward momentum flux roughly three times bigger than the Coriolis pinch, suggesting it should be considered when interpreting previous experimental pinch measurements.
NASA Astrophysics Data System (ADS)
Wang, Weixing
2008-11-01
Global gyrokinetic simulations using the GTS code [1] have found that a large inward flux of toroidal momentum is driven robustly in the post saturation phase of ion temperature gradient (ITG) turbulence. As a consequence, core plasma rotation spins up resulting in δu a few percent of vth in the case with no momentum source at the edge. The underlying physics for the inward flux is identified to be the generation of residual stress due to the k symmetry breaking [2] induced by self-generated zonal flow shear which is quasi-stationary in global simulations. The elatively low level momentum flux in the long- time steady state appears to be approximately diffusive, with effective χφ/χi on the order of unity, in broad agreement with experimental observations and theory predictions for ITG turbulence [3]. Neoclassical simulations using the GTC- NEO code [4] also show that the ion temperature gradient can drive a significant inward nondiffusive momentum flux. However, the overall neoclassical contribution to the momentum transport is negligibly small compared to experimental levels for NSTX and DIII-D plasmas. It is also found that finite residual turbulence can survive strong mean ExB shear flow induced damping. This residual turbulence in the presence of strong ExB shear may drive an insignificant ion heat flux reasonably close to the neoclassical value, and a finite momentum flux significantly higher than the neoclassical level. Moreover, the equilibrium ExB flow shear is found to reduce the turbulence driven transport for energy more efficiently than for momentum. These findings may offer an explanation for rather peculiar observations of near neoclassical ion heat and anomalous momentum transport in experiments, which has been often observed in various machines, but with little theoretical understanding. [1] W.X. Wang et al., Phys. Plasmas 14, 072306 (2007). [2] O.D. Gurcan et al., Phys. Plasmas 14, 042306 (2007). [3] N. Mattor and P.H. Diamond, Phys. Fluids 31
Spin transport in the XXZ chain at finite temperature and momentum.
Steinigeweg, Robin; Brenig, Wolfram
2011-12-16
We investigate the role of momentum for the transport of magnetization in the spin-1/2 Heisenberg chain above the isotropic point at finite temperature and momentum. Using numerical and analytical approaches, we analyze the autocorrelations of density and current and observe a finite region of the Brillouin zone with diffusive dynamics below a cutoff momentum, and a diffusion constant independent of momentum and time, which scales inversely with anisotropy. Lowering the temperature over a wide range, starting from infinity, the diffusion constant is found to increase strongly while the cutoff momentum for diffusion decreases. Above the cutoff momentum diffusion breaks down completely.
The angular momentum transport by unstable toroidal magnetic fields
NASA Astrophysics Data System (ADS)
Rüdiger, G.; Gellert, M.; Spada, F.; Tereshin, I.
2015-01-01
We demonstrate with a nonlinear magnetohydrodynamic (MHD) code that angular momentum can be transported because of the magnetic instability of toroidal fields under the influence of differential rotation, and that the resulting effective viscosity may be high enough to explain the almost rigid-body rotation observed in radiative stellar cores. We only consider stationary, current-free fields, and only those combinations of rotation rates and magnetic field amplitudes which provide maximal numerical values of the viscosity. We find that the dimensionless ratio of the effective over molecular viscosity, νT/ν, linearly grows with the Reynolds number of the rotating fluid multiplied by the square-root of the magnetic Prandtl number, which is approximately unity for the considered red subgiant star KIC 7341231. For the interval of magnetic Reynolds numbers considered - which is restricted by numerical constraints of the nonlinear MHD code - the magnetic Prandtl number has a remarkable influence on the relative importance of the contributions of the Reynolds stress and the Maxwell stress to the total viscosity, which is magnetically dominated only for Pm ≳ 0.5. We also find that the magnetized plasma behaves as a non-Newtonian fluid, i.e., the resulting effective viscosity depends on the shear in the rotation law. The decay time of the differential rotation thus depends on its shear and becomes longer and longer during the spin-down of a stellar core.
Heat and momentum transport scalings in vertical convection
NASA Astrophysics Data System (ADS)
Shishkina, Olga
2016-11-01
For vertical convection, where a fluid is confined between two differently heated isothermal vertical walls, we investigate the heat and momentum transport, which are measured, respectively, by the Nusselt number Nu and the Reynolds number Re . For laminar vertical convection we derive analytically the dependence of Re and Nu on the Rayleigh number Ra and the Prandtl number Pr from our boundary layer equations and find two different scaling regimes: Nu Pr 1 / 4 Ra 1 / 4 , Re Pr - 1 / 2 Ra 1 / 2 for Pr << 1 and Nu Pr0 Ra 1 / 4 , Re Pr-1 Ra 1 / 2 for Pr >> 1 . Direct numerical simulations for Ra from 105 to 1010 and Pr from 0.01 to 30 are in excellent ageement with our theoretical findings and show that the transition between the regimes takes place for Pr around 0.1. We summarize the results from and present new theoretical and numerical results for transitional and turbulent vertical convection. The work is supported by the Deutsche Forschungsgemeinschaft (DFG) under the Grant Sh 405/4 - Heisenberg fellowship.
NASA Technical Reports Server (NTRS)
Hablani, Hari B.
1993-01-01
This paper has a two-fold objective: determination of yearly momentum accumulation due to solar radiation pressure, and optimum reaction wheel sizing. The first objective is confronted while determining propellant consumption by the attitude control system over a spacecraft's lifetime. This, however, cannot be obtained from the daily momentum accumulation and treating that constant throughout the year, because the orientation of the solar arrays relative to the spacecraft changes over a wide range in a year, particularly if the spacecraft has two arrays, one normal and the other off-normal to different extent at different times to the sun rays. The paper first develops commands for the arrays for tracking the sun, the arrays articulated to earth-pointing spacecraft with two rotational degrees of freedom, and spacecraft in an arbitrary circular orbit. After developing expressions for solar radiation torque due to one or both arrays, arranged symmetrically or asymmetrically relative to the spacecraft bus, momentum accumulation over an orbit and then over a year are determined. The remainder of the paper is concerned with designing reaction wheel configurations. Four-, six-, and three-wheel configurations are considered, and for given torque and momentum requirements, their cant angles with the roll/yaw plane are optimized for minimum power consumption. Finally, their momentum and torque capacities are determined for one-wheel failure scenario, and six configurations are compared and contrasted.
Towards a More Realistic Description of Swing Pumping Due to the Exchange of Angular Momentum
ERIC Educational Resources Information Center
Roura, P.; Gonzalez, J. A.
2010-01-01
The pumping mechanism of a swing in a playground is due to the exchange of angular momentum from the rocking movement of the swinger to the swing oscillation around the point from which the swing is suspended. We describe the rocking events as square pulses of short duration. This choice, together with a simplified mechanical model for the…
Towards a More Realistic Description of Swing Pumping Due to the Exchange of Angular Momentum
ERIC Educational Resources Information Center
Roura, P.; Gonzalez, J. A.
2010-01-01
The pumping mechanism of a swing in a playground is due to the exchange of angular momentum from the rocking movement of the swinger to the swing oscillation around the point from which the swing is suspended. We describe the rocking events as square pulses of short duration. This choice, together with a simplified mechanical model for the…
Momentum and spin transport properties of spin polarized Fermi systems
NASA Astrophysics Data System (ADS)
Wei, Lijuan
We carried out experiments on a spin polarized 3He- 4He mixture with 3He concentration x 3 = 6.26 x 10-4, and on pure 3He liquid. Spin polarization affects the transport properties of these Fermi systems. The effect on momentum transport was studied by using a vibrating-wire viscometer to measure viscosity of the 3He-4He mixture over the temperature range 6.09 mK--100 mK in 7.96 T and 1.00 T magnetic fields. A large viscosity increase was observed upon application of the 7.96 T magnetic field for temperature T < TF(TF = 19.5 mK is the Fermi temperature). The observed viscosity is in very good agreement with theoretical calculations for a dilute Fermi gas by Jeon and Mullin [1988, 1989] and Mullin and Jeon [1992]. The polarization effect on spin transport was investigated by measuring the transverse diffusion coefficient D ⊥ in pure 3He liquid at saturated vapor pressure and at 15.85 bar over the temperature range 4.5 mK--159 mK in a 7.96 T magnetic field. We used a pulsed NMR spin echo technique in a field gradient of 16.0 G/cm to do the measurements and fits to the Leggett equations [1970] to obtain D⊥. For T < 20 mK, we found D⊥ is less than measured in earlier experiments at lower magnetic fields. D⊥ does not increase with decreasing temperature as 1/T2, but appears to approach a constant as T → 0 while it is expected that the longitudinal spin diffusion coefficient D∥ ∝ 1/ T2. This is called spin diffusion anisotropy and it was observed for the first time in our 3He liquid experiments. The anisotropy temperature we determined for 3He liquid was Ta = 16.4 +/- 2.2 mK at saturated vapor pressure and in a 7.96 T magnetic field. The transverse spin diffusion in 3 He results agree qualitatively with theories proposed by Meyerovich and Musaeflan [1992, 1994]. They also agree qualitatively with theories proposed by Golosov and Ruckenstein [1995, 1998] by extrapolation of the dilute theory to a strongly interacting system.
Momentum relaxation due to polar optical phonons in AlGaN/GaN heterostructures
NASA Astrophysics Data System (ADS)
Zhang, J.-Z.; Dyson, A.; Ridley, B. K.
2011-10-01
Using the dielectric continuum (DC) model, momentum relaxation rates are calculated for electrons confined in quasi-two-dimensional (quasi-2D) channels of AlGaN/GaN heterostructures. Particular attention is paid to the effects of half-space and interface modes on the momentum relaxation. The total momentum relaxation rates are compared with those evaluated by the three-dimensional phonon (3DP) model, and also with the Callen results for bulk GaN. In heterostructures with a wide channel (effective channel width >100 Å), the DC and 3DP models yield very close momentum relaxation rates. Only for narrow-channel heterostructures do interface phonons become important in momentum relaxation processes, and an abrupt threshold occurs for emission of interface as well as half-space phonons. For a 30-Å GaN channel, for instance, the 3DP model is found to underestimate rates just below the bulk phonon energy by 70% and overestimate rates just above the bulk phonon energy by 40% compared to the DC model. Owing to the rapid decrease in the electron-phonon interaction with the phonon wave vector, negative momentum relaxation rates are predicted for interface phonon absorption in usual GaN channels. The total rates remain positive due to the dominant half-space phonon scattering. The quasi-2D rates can have substantially higher peak values than the three-dimensional rates near the phonon emission threshold. Analytical expressions for momentum relaxation rates are obtained in the extreme quantum limits (i.e., the threshold emission and the near subband-bottom absorption). All the results are well explained in terms of electron and phonon densities of states.
Quantifying Momentum Transfer Due to Blast Waves from Oxy-Acetylene Driven Shock Tubes
2012-05-30
Transfer Due to Blast Waves from Oxy - Acetylene Driven Shock Tubes 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d...and the response of materiel to blast loading. Recently, laboratory-scale shock tubes driven by oxy - acetylene were described. It was estimated that...later. In each case, most of the momentum transfer was due to the shock wave itself. The results support previous estimates that the oxy - acetylene
Gravity Shifting Due to Distribution of Momentum in Black Hole and its Relation with Time Flux
NASA Astrophysics Data System (ADS)
Gholibeigian, Hassan; Gholibeygian, Mohammad Hossein
2017-04-01
There are many local convection systems of heat and mass in black holes. These large scale coupled systems including planets and molten masses which generate momentum in black hole and consequently generate coupled gravitational and electromagnetic waves. Therefore black hole's gravity is shifting due to distribution of masses/momentum in its convection systems. Two massive black holes which merged at a distance of 1.3 billion light years far from the Earth, produced different momentum and energy before, during, and after the event in different locations of the black hole. This energy and momentum produced gravitational waves which radiated away and recorded on September 14, 2015 by two detectors of the Laser Interferometry Gravitational Observatories (LIGO) in USA. On the other hand, the nature of time is wavy-like motion of the matter and nature of space is jerky-like motion of the matter. These two natures of space-time can be matched on wave-particle duality in quantum mechanics. And also magnitude of the time for an atom is momentum of its involved fundamental particles [Gholibeigian, adsabs.harvard.edu/abs/2016APS.APR.D1032G]. ∑ ⃗R(mv, σ,τ ) = (pnucleons + pelectrons) In which ⃗Ris time flux, σ&τare space and time coordinates on the string world sheet and p is momentum. Therefore, gravitational waves which travel from black hole to us including different fluxes of time which accompaniment propagated gravitational waves of momentum. As an observable factor, we can look at the 7 milliseconds difference of recorded at the time of arrival of the signals on September 14, 2015 by detector in Livingston before detector in Hanford. This difference of recorded time of signal GW150914 by LIGO cannot be due to warped space-time, because 3002 kilometers distance between two detectors with respect to the 1.3 billion light years (distance of black hole to detectors) is like zero! So, this 7 milliseconds difference between two time's fluxes can be due to
Momentum transport from current-driven reconnection in the reversed field pinch.
Ebrahimi, F; Mirnov, V V; Prager, S C; Sovinec, C R
2007-08-17
We calculate momentum transport from tearing fluctuations in a reversed field pinch with sheared flow, considering both the effect of a single tearing mode (through quasilinear theory and MHD computation) and multiple tearing modes (through nonlinear MHD computation). A single tearing mode transports momentum, via Maxwell and Reynolds stresses, more rapidly than classical viscous forces. Moreover, the transport is enhanced by nonlinear coupling of multiple modes.
Reynolds number influences on turbulent boundary layer momentum transport
NASA Astrophysics Data System (ADS)
Priyadarshana, Paththage A.
There are many engineering applications at Reynolds numbers orders of magnitude higher than existing turbulent boundary layer studies. Currently, the mechanisms for turbulent transport and the Reynolds number dependence of these mechanisms are not well understood. This dissertation presents Reynolds number influences on velocity and vorticity statistics, Reynolds shear stress, and velocity-vorticity correlations for turbulent boundary layers. Well resolved hot-wire data for this study were acquired in the atmospheric surface layer at the SLTEST facility in western Utah. It is shown that during near neutral thermal stability, the flow behaves as a canonical zero pressure gradient turbulent boundary layer, in which the Reynolds number based on momentum thickness, Rtheta, is approximately 2 x 106. The present study also provides information regarding the effects of wall roughness over a limited range of roughness. It is observed that with increasing Rtheta, the inner normalized streamwise intensity increases. This statistic is less sensitive to wall roughness away from the roughness sublayer. In contrast, the inner normalized wall normal intensity is less sensitive to the variation of Rtheta, and it is significantly sensitive to wall roughness. Outside the viscous sublayer, the inner normalized vorticity intensity is less sensitive to both Rtheta and roughness. A primary observation of the Reynolds stress study is that the predominant motions underlying the Reynolds shear stress undergo a significant shift from large to intermediate scales as Rtheta becomes large, irrespective of surface roughness. Quadrant analysis shows that types of motions contributing to the Reynolds stress change significantly at comparable wall normal locations with increasing Rtheta. The mean wall normal gradients of the Reynolds shear stress and the turbulent kinetic energy have direct connections to the transport mechanisms of the turbulent boundary layer. These gradients can be expressed in
Anomalous transport due to magnetic turbulence
Cardozo, N.J.L.
1996-03-01
Transport in a toroidal system with broken flux surfaces is considered. Flux surfaces with rational field line winding number can degenerate and form magnetic islands. The experimental evidence for the existence of magnetic structures is reviewed. If neighboring chains of islands overlap, a region of stochastic field is formed. In a stochastic field, a field line fills up a region of space and thus makes significant radial excursions. Particles following a stochastic field line may experience rapid radial transport. The problem of computing transport in a stochastic field has two stages: what is the behavior of field lines in a stochastic region? and what is the implication for particle transport? The much used formula due to Rechester & Rosenbluth for collisionless transport in a fully ergodic field is treated. It is shown that the conditions for the validity of this formula are normally not met in a tokamak. 16 refs.
Belyaev, Mikhail A.; Rafikov, Roman R.; Stone, James M.
2013-06-10
The nature of angular momentum transport in the boundary layers of accretion disks has been one of the central and long-standing issues of accretion disk theory. In this work we demonstrate that acoustic waves excited by supersonic shear in the boundary layer serve as an efficient mechanism of mass, momentum, and energy transport at the interface between the disk and the accreting object. We develop the theory of angular momentum transport by acoustic modes in the boundary layer, and support our findings with three-dimensional hydrodynamical simulations, using an isothermal equation of state. Our first major result is the identification of three types of global modes in the boundary layer. We derive dispersion relations for each of these modes that accurately capture the pattern speeds observed in simulations to within a few percent. Second, we show that angular momentum transport in the boundary layer is intrinsically nonlocal, and is driven by radiation of angular momentum away from the boundary layer into both the star and the disk. The picture of angular momentum transport in the boundary layer by waves that can travel large distances before dissipating and redistributing angular momentum and energy to the disk and star is incompatible with the conventional notion of local transport by turbulent stresses. Our results have important implications for semianalytical models that describe the spectral emission from boundary layers.
Protostellar angular momentum transport by spiral density waves
NASA Technical Reports Server (NTRS)
Yuan, C.; Cassen, P.
1985-01-01
The application of rotational stability criteria to a specific model of star formation leads to the conclusion that the growth of stellar angular momentum is limited by its transfer to the disk. Excess accreted angular momentum can be transferred by torques connected with spiral density waves induced by even a slight protostellar triaxiality. In addition, viscous damping of the density waves is likely to cause the excess angular momentum to be deposited within a small region close to the protostar. Thus, it would be appropriate to treat that part of the growing protostellar disk beyond the outer Lindblad resonance as an accretion disk with a torque applied to its inner edge. It is noted that this situation is directly relevant to certain models of the evolution of the protosun and solar nebula.
NASA Astrophysics Data System (ADS)
Rousseau, F.; Coppi, B.
2006-10-01
The presence of angular momentum transport associated with an accretion process in an axisymmetric differentially rotating structure affects the equilibrium configuration that this can take and can introduce a toroidal Lorentz force with the associated poloidal current densities. All three components (vertical, radial and toroidal) of the total momentum conservation equation are considered. A sequence of ring solutions can be found by making use of the inequalities vNJ
Stability and angular-momentum transport of fluid flows between corotating cylinders.
Avila, M
2012-03-23
Turbulent transport of angular momentum is a necessary process to explain accretion in astrophysical disks. Although the hydrodynamic stability of disklike flows has been tested in experiments, results are contradictory and suggest either laminar or turbulent flow. Direct numerical simulations reported here show that currently investigated laboratory flows are hydrodynamically unstable and become turbulent at low Reynolds numbers. The underlying instabilities stem from the axial boundary conditions, affect the flow globally, and enhance angular-momentum transport.
Second order kinetic theory of parallel momentum transport in collisionless drift wave turbulence
Li, Yang; Gao, Zhe; Chen, Jiale
2016-08-15
A second order kinetic model for turbulent ion parallel momentum transport is presented. A new nonresonant second order parallel momentum flux term is calculated. The resonant component of the ion parallel electrostatic force is the momentum source, while the nonresonant component of the ion parallel electrostatic force compensates for that of the nonresonant second order parallel momentum flux. The resonant component of the kinetic momentum flux can be divided into three parts, including the pinch term, the diffusive term, and the residual stress. By reassembling the pinch term and the residual stress, the residual stress can be considered as a pinch term of parallel wave-particle resonant velocity, and, therefore, may be called as “resonant velocity pinch” term. Considering the resonant component of the ion parallel electrostatic force is the transfer rate between resonant ions and waves (or, equivalently, nonresonant ions), a conservation equation of the parallel momentum of resonant ions and waves is obtained.
NASA Technical Reports Server (NTRS)
Stepinski, T. F.; Levy, E. H.
1990-01-01
Magnetic torques can produce angular momentum redistribution in protostellar nebulas. Dynamo magnetic fields can be generated in differentially rotating and turbulent nebulas and can be the source of magnetic torques that transfer angular momentum from a protostar to a disk, as well as redistribute angular momentum within a disk. A magnetic field strength of 100-1000 G is needed to transport the major part of a protostar's angular momentum into a surrounding disk in a time characteristic of star formation, thus allowing formation of a solar-system size protoplanetary nebula in the usual 'minimum-mass' model of the protosolar nebula. This paper examines the possibility that a dynamo magnetic field could have induced the needed angular momentum transport from the proto-Sun to the protoplanetary nebula.
NASA Technical Reports Server (NTRS)
Stepinski, T. F.; Levy, E. H.
1990-01-01
Magnetic torques can produce angular momentum redistribution in protostellar nebulas. Dynamo magnetic fields can be generated in differentially rotating and turbulent nebulas and can be the source of magnetic torques that transfer angular momentum from a protostar to a disk, as well as redistribute angular momentum within a disk. A magnetic field strength of 100-1000 G is needed to transport the major part of a protostar's angular momentum into a surrounding disk in a time characteristic of star formation, thus allowing formation of a solar-system size protoplanetary nebula in the usual 'minimum-mass' model of the protosolar nebula. This paper examines the possibility that a dynamo magnetic field could have induced the needed angular momentum transport from the proto-Sun to the protoplanetary nebula.
NASA Astrophysics Data System (ADS)
Takehiro, S.; Sasaki, Y.; Hayashi, Y.-Y.; Yamada, M.
2013-12-01
We investigate generation mechanisms of differential rotation and angular momentum transport caused by Boussinesq thermal convection in a rotating spherical shell based on weakly nonlinear numerical calculations for various values of the Prandtl and Ekman numbers under a setup similar to the solar convection layer. When the Prandtl number is of order unity or less and the rotation rate of the system is small (the Ekman number is larger than O(10-2)), the structure of thermal convection is not governed by the Taylor-Proudman theorem; banana-type convection cells emerge which follow the spherical shell boundaries rather than the rotation axis. Due to the Coriolis effect, the velocity field associated with those types of convection cells accompanies the Reynolds stress which transports angular momentum from high-latitudes to the equatorial region horizontally, and equatorial prograde flows are produced. The surface and internal distributions of differential rotation realized in this regime are quite similar to those observed in the Sun with helioseismology. These results may suggest that we should apply larger values of the eddy diffusivities than those believed so far when we use a low resolution numerical model for thermal convection in the solar interior.
Latitudinal Transport of Angular Momentum by Cellular Flows Observed with MDI
NASA Technical Reports Server (NTRS)
Hathaway, David H.; Gilman, Peter A.; Beck, John G.; Rose, M. Franklin (Technical Monitor)
2001-01-01
We have analyzed Doppler velocity images from the MDI instrument on SOHO to determine the latitudinal transport of angular momentum by the cellular photospheric flows. Doppler velocity images from 60-days in May to July of 1996 were processed to remove the p-mode oscillations, the convective blue shift, the axisymmetric flows, and any instrumental artifacts. The remaining cellular flows were examined for evidence of latitudinal angular momentum transport. Small cells show no evidence of any such transport. Cells the size of supergranules (30,000 km in diameter) show strong evidence for a poleward transport of angular momentum. This would be expected if supergranules are influenced by the Coriolis force, and if the cells are elongated in an east-west direction. We find good evidence for just such an east-west elongation of the supergranules. This elongation may be the result of differential rotation shearing the cellular structures. Data simulations of this effect support the conclusion that elongated supergranules transport angular momentum from the equator toward the poles, Cells somewhat larger than supergranules do not show evidence for this poleward transport. Further analysis of the data is planned to determine if the direction of angular momentum transport reverses for even larger cellular structures. The Sun's rapidly rotating equator must be maintained by such transport somewhere within the convection zone.
Latitudinal Transport of Angular Momentum by Cellular Flows Observed with MDI
NASA Technical Reports Server (NTRS)
Hathaway, David H.; Gilman, Peter A.; Beck, John G.; Rose, M. Franklin (Technical Monitor)
2001-01-01
We have analyzed Doppler velocity images from the MDI instrument on SOHO to determine the latitudinal transport of angular momentum by the cellular photospheric flows. Doppler velocity images from 60-days in May to July of 1996 were processed to remove the p-mode oscillations, the convective blue shift, the axisymmetric flows, and any instrumental artifacts. The remaining cellular flows were examined for evidence of latitudinal angular momentum transport. Small cells show no evidence of any such transport. Cells the size of supergranules (30,000 km in diameter) show strong evidence for a poleward transport of angular momentum. This would be expected if supergranules are influenced by the Coriolis force, and if the cells are elongated in an east-west direction. We find good evidence for just such an east-west elongation of the supergranules. This elongation may be the result of differential rotation shearing the cellular structures. Data simulations of this effect support the conclusion that elongated supergranules transport angular momentum from the equator toward the poles, Cells somewhat larger than supergranules do not show evidence for this poleward transport. Further analysis of the data is planned to determine if the direction of angular momentum transport reverses for even larger cellular structures. The Sun's rapidly rotating equator must be maintained by such transport somewhere within the convection zone.
The momentum transfer of incompressible turbulent separated flow due to cavities with steps
NASA Technical Reports Server (NTRS)
White, R. E.; Norton, D. J.
1977-01-01
An experimental study was conducted using a plate test bed having a turbulent boundary layer to determine the momentum transfer to the faces of step/cavity combinations on the plate. Experimental data were obtained from configurations including an isolated configuration and an array of blocks in tile patterns. A momentum transfer correlation model of pressure forces on an isolated step/cavity was developed with experimental results to relate flow and geometry parameters. Results of the experiments reveal that isolated step/cavity excrecences do not have a unique and unifying parameter group due in part to cavity depth effects and in part to width parameter scale effects. Drag predictions for tile patterns by a kinetic pressure empirical method predict experimental results well. Trends were not, however, predicted by a method of variable roughness density phenomenology.
Angular momentum transport in turbulent flow between independently rotating cylinders.
Paoletti, M S; Lathrop, D P
2011-01-14
We present measurements of the angular momentum flux (torque) in Taylor-Couette flow of water between independently rotating cylinders for all regions of the (Ω1, Ω2) parameter space at high Reynolds numbers, where Ω1 (Ω2) is the inner (outer) cylinder angular velocity. We find that the Rossby number Ro = (Ω1 - Ω2)/Ω2 fully determines the state and torque G as compared to G(Ro = ∞) ≡ G∞. The ratio G/G∞ is a linear function of Ro(-1) in four sections of the parameter space. For flows with radially increasing angular momentum, our measured torques greatly exceed those of previous experiments [Ji et al., Nature (London), 444, 343 (2006)], but agree with the analysis of Richard and Zahn [Astron. Astrophys. 347, 734 (1999)].
Angular Momentum Transport in Turbulent Flow between Independently Rotating Cylinders
NASA Astrophysics Data System (ADS)
Paoletti, M. S.; Lathrop, D. P.
2011-01-01
We present measurements of the angular momentum flux (torque) in Taylor-Couette flow of water between independently rotating cylinders for all regions of the (Ω1, Ω2) parameter space at high Reynolds numbers, where Ω1 (Ω2) is the inner (outer) cylinder angular velocity. We find that the Rossby number Ro=(Ω1-Ω2)/Ω2 fully determines the state and torque G as compared to G(Ro=∞)≡G∞. The ratio G/G∞ is a linear function of Ro-1 in four sections of the parameter space. For flows with radially increasing angular momentum, our measured torques greatly exceed those of previous experiments [Ji et al., Nature (London)NATUAS0028-0836, 444, 343 (2006)10.1038/nature05323], but agree with the analysis of Richard and Zahn [Astron. Astrophys. 347, 734 (1999)AAEJAF0004-6361].
Angular Momentum Transport in Turbulent Flow between Independently Rotating Cylinders
Paoletti, M. S.; Lathrop, D. P.
2011-01-14
We present measurements of the angular momentum flux (torque) in Taylor-Couette flow of water between independently rotating cylinders for all regions of the ({Omega}{sub 1}, {Omega}{sub 2}) parameter space at high Reynolds numbers, where {Omega}{sub 1} ({Omega}{sub 2}) is the inner (outer) cylinder angular velocity. We find that the Rossby number Ro=({Omega}{sub 1}-{Omega}{sub 2})/{Omega}{sub 2} fully determines the state and torque G as compared to G(Ro={infinity}){identical_to}G{sub {infinity}.} The ratio G/G{sub {infinity}} is a linear function of Ro{sup -1} in four sections of the parameter space. For flows with radially increasing angular momentum, our measured torques greatly exceed those of previous experiments [Ji et al., Nature (London), 444, 343 (2006)], but agree with the analysis of Richard and Zahn [Astron. Astrophys. 347, 734 (1999)].
A numerical study of the vertical transport of momentum in a tropical rainband
NASA Technical Reports Server (NTRS)
Soong, S.-T.; Tao, W.-K.
1984-01-01
The vertical transport of horizontal momentum in a convective tropical rainband is studied using a two-dimensional cloud ensemble model. Twelve simulations are made under the same large-scale conditions. The vertical transports of v momentum (parallel to the rainband) are essentially the same in all of the simulations, even though the structure of the clouds is different in each of the runs. The magnitude of the v-momentum transport by clouds is fairly large. It takes only half of a day to smooth out the tropical low-level easterly jet parallel to the rainband if no other processes are operating. The vertical transports of u momentum (perpendicular to the rainband) are quite different in all of the simulations. This difference can be explained by the dissimilarities in the distributions of horizontal momentum associated with various cloud configurations. The simulated vertical transports of horizontal momentum are compared with those computed with the Schneider and Lindzen scheme. The results suggest that their scheme is basically correct and usable if some improvements are made.
An instability in planetary rings due to ballistic transport
NASA Technical Reports Server (NTRS)
Durisen, Richard H.
1995-01-01
Ballistic transport in planetary rings is the net radial transport of mass and angular momentum due to exchanges of meteoroid impact ejecta between neighboring ring regions. The detailed linear stability analysis in this paper demonstrates that ballistic transport causes wavelike disturbances to grow and propagate in an otherwise uniform ring. The growth is strongest for intermediate values of the normal ring optical depth tau = 0.1 to 1.0 and goes to zero as tau approaches 0 and tau approaches infinity. For nominal values of various physical parameters, the minimum e-folding time is approximately 10(exp 5) years for tau approximately 0.4. The direction of propagation is opposite to the sense of any asymmetry that may exist in the ejecta direction distribution (inward for prograde ejecta and outward for retrograde ejecta). The additional effect of viscous transport tends to damp wavelike perturbations strongly at short wavelengths and at high values of tau. The quantitative agreement between this analytic work and numerical simulations reported elsewhere is generally quite good. As applied to Saturn's rings, the results in this paper strengthen the earlier conclusion from numerical calculations that the 100-km structure in the inner B Ring is caused by ballistic transport. However, it is also clear that ballistic transport cannot produce the complex structure seen in the outer two-thirds of the B Ring where tau greater than or approximately 1.5. Wavelike structures in the C Ring might also be attributed to ballistic transport; but this requires further study.
Lysosomal solute carrier transporters gain momentum in research.
Bissa, B; Beedle, A M; Govindarajan, R
2016-11-01
Emerging evidence indicates that lysosome function extends beyond macromolecular degradation. Genetic and functional defects in components of the lysosomal transport machinery cause lysosomal storage disorders implicating the lysosomal solute carrier (SLC) transporters as essential to vital cell processes. The pathophysiology and therapeutic potential of lysosomal SLC transporters are highlighted here, focusing on recent discoveries in autophagic amino acid sensing (SLC38A9), phagocytic regulation in macrophages (SLC29A3, SLC15A3/A4), adenosine triphosphate (ATP) exocytosis in neurotransmission (SLC17A9), and lysosomal transport of maytansine catabolites into the cytoplasm (SLC46A3).
Lysosomal solute carrier transporters gain momentum in research
Beedle, AM; Govindarajan, R
2016-01-01
Emerging evidence indicates that lysosome function extends beyond macromolecular degradation. Genetic and functional defects in components of the lysosomal transport machinery cause lysosomal storage disorders implicating the lysosomal solute carrier (SLC) transporters as essential to vital cell processes. The pathophysiology and therapeutic potential of lysosomal SLC transporters are highlighted here, focusing on recent discoveries in autophagic amino acid sensing (SLC38A9), phagocytic regulation in macrophages (SLC29A3, SLC15A3/A4), adenosine triphosphate (ATP) exocytosis in neurotransmission (SLC17A9), and lysosomal transport of maytansine catabolites into the cytoplasm (SLC46A3). PMID:27530302
Transport of absolute angular momentum in quasi-axisymmetric equatorial jet streams
NASA Technical Reports Server (NTRS)
Read, P. L.
1986-01-01
It is well known that prograde equatorial jet stresses cannot occur in an axisymmetric inviscid fluid, owing to the constraints of local angular momentum conservation. For a viscous fluid, the constraints of mass conservation prevent the formation of any local maximum of absolute angular momentum (m) without a means of transferring m against its gradient (delta m) in the meridional plane. The circumstances under which m can be diffused up-gradient by normal molecular viscosity are derived, and illustrated with reference to numerical simulations of axisymmetric flows in a cylindrical annulus. Viscosity is shown to act so as to tend to expel m from the interior outwards from the rotation axis. Such an effect can produce local super-rotation even in a mechanically isolated fluid. The tendency of viscosity to result in the expulsion of m is shown to be analogous in certain respects to a vorticity-mixing hypothesis for the effects of non-axisymmetric eddies of the zonally-averaged flow. It is shown how the advective and diffusive transport of m by non-axisymmetric eddies can be represented by the Transformed Eulerian Mean meridional circulation and the Eliassen-Palm (EP) flux of Andrews and McIntyre respectively, in the zonal mean. Constraints on the form and direction of the EP flux in an advective/diffusive flow for such eddies are derived, by analogy with similar constraints on the diffusive flux of m due to viscosity.
Local momentum and heat fluxes in transient transport processes and inhomogeneous systems.
Chen, Youping; Diaz, Adrian
2016-11-01
This work examines existing formalisms for the derivation of microscopic momentum and heat fluxes. Both analytical and simulation results are provided to show that the widely used flux formulas are not applicable to transient transport processes or highly inhomogeneous systems, e.g., materials with atomically sharp interfaces. A method is formulated for formally deriving microscopic momentum and heat fluxes through the integral representation of conservation laws. The resulting flux formulas are mathematically rigorous, fully consistent with the physical concepts of momentum and heat fluxes, and applicable to nonequilibrium transient processes in atomically inhomogeneous systems with general many-body forces.
Local momentum and heat fluxes in transient transport processes and inhomogeneous systems
NASA Astrophysics Data System (ADS)
Chen, Youping; Diaz, Adrian
2016-11-01
This work examines existing formalisms for the derivation of microscopic momentum and heat fluxes. Both analytical and simulation results are provided to show that the widely used flux formulas are not applicable to transient transport processes or highly inhomogeneous systems, e.g., materials with atomically sharp interfaces. A method is formulated for formally deriving microscopic momentum and heat fluxes through the integral representation of conservation laws. The resulting flux formulas are mathematically rigorous, fully consistent with the physical concepts of momentum and heat fluxes, and applicable to nonequilibrium transient processes in atomically inhomogeneous systems with general many-body forces.
Poloidal rotation driven by nonlinear momentum transport in strong electrostatic turbulence
NASA Astrophysics Data System (ADS)
Wang, Lu; Wen, Tiliang; Diamond, P. H.
2016-10-01
Virtually, all existing theoretical works on turbulent poloidal momentum transport are based on quasilinear theory. Nonlinear poloidal momentum flux—< {{\\tilde{v}}r}\\tilde{n}{{\\tilde{v}}θ}> is universally neglected. However, in the strong turbulence regime where relative fluctuation amplitude is no longer small, quasilinear theory is invalid. This is true at the all-important plasma edge. In this work, nonlinear poloidal momentum flux < {{\\tilde{v}}r}\\tilde{n}{{\\tilde{v}}θ}> in strong electrostatic turbulence is calculated using the Hasegawa-Mima equation, and is compared with quasilinear poloidal Reynolds stress. A novel property is that symmetry breaking in fluctuation spectrum is not necessary for a nonlinear poloidal momentum flux. This is fundamentally different from the quasilinear Reynold stress. Furthermore, the comparison implies that the poloidal rotation drive from the radial gradient of nonlinear momentum flux is comparable to that from the quasilinear Reynolds force. Nonlinear poloidal momentum transport in strong electrostatic turbulence is thus not negligible for poloidal rotation drive, and so may be significant to transport barrier formation.
Uncertainties related to the representation of momentum transport in shallow convection
NASA Astrophysics Data System (ADS)
Schlemmer, Linda; Bechtold, Peter; Sandu, Irina; Ahlgrimm, Maike
2017-04-01
The vertical transport of horizontal momentum by convection has an important impact on the general circulation of the atmosphere as well as on the life cycle and track of cyclones. So far convective momentum transport (CMT) has mostly been studied for deep convection, whereas little is known about its characteristics and importance in shallow convection. In this study CMT by shallow convection is investigated by analyzing both data from large-eddy simulations (LES) and simulations performed with the Integrated Forecasting System (IFS) of the European Centre for Medium-Range Weather Forecasts (ECMWF). In addition, the central terms underlying the bulk mass-flux parametrization of CMT are evaluated offline. Further, the uncertainties related to the representation of CMT are explored by running the stochastically perturbed parametrizations (SPP) approach of the IFS. The analyzed cases exhibit shallow convective clouds developing within considerable low-level wind shear. Analysis of the momentum fluxes in the LES data reveals significant momentum transport by the convection in both cases, which is directed down-gradient despite substantial organization of the cloud field. A detailed inspection of the convection parametrization reveals a very good representation of the entrainment and detrainment rates and an appropriate representation of the convective mass and momentum fluxes. To determine the correct values of mass-flux and in-cloud momentum at the cloud base in the parametrization yet remains challenging. The spread in convection-related quantities generated by the SPP is reasonable and addresses many of the identified uncertainties.
Effect of nonlinear instability on gravity-wave momentum transport
NASA Technical Reports Server (NTRS)
Dunkerton, Timothy J.
1987-01-01
This paper investigates the nonlinear instability of internal gravity waves and the effects of their nonlinear interaction on momentum flux, using simple theoretical and numerical models. From the result of an analysis of parametric instability of a two-dimensional internal gravity wave as discussed by Yeh and Liu (1981) and Klostermeyer (1982), a group trajectory length scale for a gravity wave packet was determined, expressed in terms of the dominant vertical wavelenght and the degree of convective saturation. It is shown that this analysis justifies the Eikonal saturation method for relatively transient packets, that are well below the saturation amplitude, propagating in a slowly varying mean flow. Conversely, linear theory fails for persistent disturbances and trasient wave packets near convective saturation.
NASA Astrophysics Data System (ADS)
Tobias, B. J.
2015-11-01
The dynamic, nonlinear evolution of tearing instabilities on DIII-D reveals a coupling of rational surfaces that can lead to phase-locking amongst multiple rotating magnetic island chains. This loss of flow shear increases disruptivity, particularly at the low level of rotation expected in ITER. Bifurcation of differential mode frequency and fluid rotation in hybrid scenario discharges has been interpreted by comparison to a recently developed theory of nonlinear mode coupling. Magnetic islands of different toroidal mode number couple to flatten the toroidal rotation profile, and the resulting phase-locked state is similar to the so-called ``slinky'' mode observed in reversed field pinch devices. Reduction of the edge safety factor increases the momentum transport, easily overwhelming the local torque density available from neutral beam injection. In discharges with q95 ~ 4.5, however, the participating modes do not remain phase-locked. In these cases, ECE-Imaging data have been used to show that the poloidal rotation of the composite, multi-helicity structure exceeds that of the measured carbon (and estimated deuterium) fluid flow. The present model of nonlinear 3-wave mode coupling does not generate the forces required to drive this rotation. Therefore, flow shear inversion represents a transition from phase-locking to a new regime of convective momentum transport in which additional mechanisms become important. These results highlight the importance of controlling multi-mode interactions in order to maintain stabilizing flow shear. Supported by US DOE DE-AC02-09CH11466, DE-FC02-04ER54698, DE-FG02-07ER54917, DE-FG02-92-ER54141.
GYRO Simulations of Core Momentum Transport in DIII-D and JET Plasmas
R.V. Budny; J. Candy; R.E. Waltz; and contributors to the DIII-D and JET-EFDA work programs
2005-06-27
Momentum, energy, and particle transport in DIII-D and JET ELMy H-mode plasmas is simulated with GYRO and compared with measurements analyzed using TRANSP. The simulated transport depends sensitively on the nabla(T(sub)i) turbulence drive and the nabla(E(sub)r) turbulence suppression inputs. With their nominal values indicated by measurements, the simulations over-predict the momentum and energy transport in the DIII-D plasmas, and under-predict in the JET plasmas. Reducing |nabla(T(sub)i)| and increasing |nabla(E(sub)r)| by up to 15% leads to approximate agreement (within a factor of two) for the DIII-D cases. For the JET cases, increasing |nabla(T(sub)i)| or reducing |nabla(E(sub)r)| results in approximate agreement for the energy flow, but the ratio of the simulated energy and momentum flows remains higher than measurements by a factor of 2-4.
Up-down symmetry of the turbulent transport of toroidal angular momentum in tokamaks
Parra, Felix I.; Barnes, Michael
2011-06-15
Two symmetries of the local nonlinear {delta}f gyrokinetic system of equations in tokamaks in the high flow regime are presented. The turbulent transport of toroidal angular momentum changes sign under an up-down reflection of the tokamak and a sign change of both the rotation and the rotation shear. Thus, the turbulent transport of toroidal angular momentum must vanish for up-down symmetric tokamaks in the absence of both rotation and rotation shear. This has important implications for the modeling of spontaneous rotation.
Nanoscale hotspots due to nonequilibrium thermal transport.
Sinha, Sanjiv; Goodson, Kenneth E.
2004-01-01
Recent experimental and modeling efforts have been directed towards the issue of temperature localization and hotspot formation in the vicinity of nanoscale heat generating devices. The nonequilibrium transport conditions which develop around these nanoscale devices results in elevated temperatures near the heat source which can not be predicted by continuum diffusion theory. Efforts to determine the severity of this temperature localization phenomena in silicon devices near and above room temperature are of technological importance to the development of microelectronics and other nanotechnologies. In this work, we have developed a new modeling tool in order to explore the magnitude of the additional thermal resistance which forms around nanoscale hotspots from temperatures of 100-1000K. The models are based on a two fluid approximation in which thermal energy is transferred between ''stationary'' optical phonons and fast propagating acoustic phonon modes. The results of the model have shown excellent agreement with experimental results of localized hotspots in silicon at lower temperatures. The model predicts that the effect of added thermal resistance due to the nonequilibrium phonon distribution is greatest at lower temperatures, but is maintained out to temperatures of 1000K. The resistance predicted by the numerical code can be easily integrated with continuum models in order to predict the temperature distribution around nanoscale heat sources with improved accuracy. Additional research efforts also focused on the measurements of the thermal resistance of silicon thin films at higher temperatures, with a focus on polycrystalline silicon. This work was intended to provide much needed experimental data on the thermal transport properties for micro and nanoscale devices built with this material. Initial experiments have shown that the exposure of polycrystalline silicon to high temperatures may induce recrystallization and radically increase the thermal
Flow anisotropy due to momentum deposition in ultra-relativistic nuclear collisions
NASA Astrophysics Data System (ADS)
Tomášik, Boris; Schulc, Martin
2017-03-01
Minijets and jets are produced in large numbers in nuclear collisions at TeV energies, so that there are many of them in a single fireball. They deposit non-negligible amount of momentum and energy into the hydrodynamically expanding bulk and cause anisotropies of the expansion. Moreover, due to their multiple production in a single event the resulting anisotropies are correlated with the collision geometry and thus contribute positively also to event-averaged anisotropies in non-central collisions. Using simulations with three-dimensional ideal hydrodynamic model we demonstrate the importance of this effect. It must be taken into account if conclusions about the properties of the hot matter are to be drawn.
NASA Technical Reports Server (NTRS)
Johnson, B. V.; Bennett, J. C.
1983-01-01
An experimental study of mixing downstream of coaxial jets discharging into an expanded circular duct was conducted to obtain data for the evaluation and improvement of turbulent transport models currently used for combustor flow modeling. A combination of turbulent momentum transport rate and two velocity component data was obtained from simultaneous measurements with a two-color LV system. A combination of turbulent mass transport rate, concentration and velocity data was obtained from simultaneous measurements with laser velocimeter (LV) and laser induced fluorescence (LIF) systems. These measurements were used to obtain mean, second central moment, skewness and kurtosis values for three velocity components and the concentration. These measurements showed the existence of countergradient turbulent axial mass transport where the annular jet fluid was accelerating the inner jet fluid. Results from the study are related to the assumptions employed in the current mass and momentum turbulent transport models.
Momentum and eddy kinetic energy transports by a multiple microburst- producing storm
NASA Astrophysics Data System (ADS)
Lin, Yeong-Jer; Coover, John A.
1990-05-01
A comprehensive study of the structure and internal dynamics was made for a multiple microburst-producing storm for August 5, 1982, in Colorado during the Joint Airport Weather Studies (JAWS) Project at Denver's Stapleton International Airport. The analysis levels were contained between 0.25 and 2 km. The horizontal and vertical grid spacings were 0.5 and 0.25 km, respectively. These fields were subjected to internal consistency checks to determine the level of confidence before interpretation. Results show that the combined effects of misocyclone circulations, perturbation-pressure gradients, melting, buoyancy, and precipitation loading contribute to the maintenance of the microburst downdrafts in the atmospheric boundary layer (ABL). At low levels where the microbursts dominate, the presence of microburst gust fronts and diverging outflow enhances the vertical transport of horizontal momentum and eddy kinetic energy. The misocyclones located above the microbursts largely determine the transport of horizontal momentum and eddy kinetic energy there. In the microburst subdomain, a net transport of horizontal momentum and eddy kinetic energy is downward from the misocyclone to the surface. Its magnitude is directly proportional to the strength of a microburst at low levels and the misocyclone aloft. Budget studies of horizontal momentum flux and eddy kinetic energy within the storm domain and the microburst subdomain have added to a further understanding of the storm's structure and internal dynamics. The pressure and buoyancy effects are two main contributors to the generation/decay of horizontal momentum fluxes and eddy kinetic energy at the microburst levels.
Wang, W X; Hahm, T S; Ethier, S; Rewoldt, G; Lee, W W; Tang, W M; Kaye, S M; Diamond, P H
2009-01-23
A significant inward flux of toroidal momentum is found in global gyrokinetic simulations of ion temperature gradient turbulence, leading to core plasma rotation spin-up. The underlying mechanism is identified to be the generation of residual stress due to the k parallel symmetry breaking induced by global quasistationary zonal flow shear. Simulations also show a significant off-diagonal element associated with the ion temperature gradient in the neoclassical momentum flux, while the overall neoclassical flux is small. In addition, the residual turbulence found in the presence of strong E x B flow shear may account for neoclassical-level ion heat and anomalous momentum transport widely observed in experiments.
Molecular Momentum Transport at Fluid-Solid Interfaces in MEMS/NEMS: A Review
Cao, Bing-Yang; Sun, Jun; Chen, Min; Guo, Zeng-Yuan
2009-01-01
This review is focused on molecular momentum transport at fluid-solid interfaces mainly related to microfluidics and nanofluidics in micro-/nano-electro-mechanical systems (MEMS/NEMS). This broad subject covers molecular dynamics behaviors, boundary conditions, molecular momentum accommodations, theoretical and phenomenological models in terms of gas-solid and liquid-solid interfaces affected by various physical factors, such as fluid and solid species, surface roughness, surface patterns, wettability, temperature, pressure, fluid viscosity and polarity. This review offers an overview of the major achievements, including experiments, theories and molecular dynamics simulations, in the field with particular emphasis on the effects on microfluidics and nanofluidics in nanoscience and nanotechnology. In Section 1 we present a brief introduction on the backgrounds, history and concepts. Sections 2 and 3 are focused on molecular momentum transport at gas-solid and liquid-solid interfaces, respectively. Summary and conclusions are finally presented in Section 4. PMID:20087458
Molecular momentum transport at fluid-solid interfaces in MEMS/NEMS: a review.
Cao, Bing-Yang; Sun, Jun; Chen, Min; Guo, Zeng-Yuan
2009-10-29
This review is focused on molecular momentum transport at fluid-solid interfaces mainly related to microfluidics and nanofluidics in micro-/nano-electro-mechanical systems (MEMS/NEMS). This broad subject covers molecular dynamics behaviors, boundary conditions, molecular momentum accommodations, theoretical and phenomenological models in terms of gas-solid and liquid-solid interfaces affected by various physical factors, such as fluid and solid species, surface roughness, surface patterns, wettability, temperature, pressure, fluid viscosity and polarity. This review offers an overview of the major achievements, including experiments, theories and molecular dynamics simulations, in the field with particular emphasis on the effects on microfluidics and nanofluidics in nanoscience and nanotechnology. In Section 1 we present a brief introduction on the backgrounds, history and concepts. Sections 2 and 3 are focused on molecular momentum transport at gas-solid and liquid-solid interfaces, respectively. Summary and conclusions are finally presented in Section 4.
Mass and Momentum Transport Experiments with Swirling Flow
NASA Technical Reports Server (NTRS)
Johnson, B. V.; Roback, R.
1984-01-01
An experimental study of mixing downstream of axial and swirling coaxial jets is being conducted to obtain data for the evaluation and improvement of turbulent transport models currently employed in a variety of computational procedures used throughout the propulsion community. The axial coaxial jet study was completed under Phase 1. The swirling coaxial jet study, which is the subject of this paper, was conducted under Phase 2 of the contract. A TEACH code was acquired, checked out for several test cases, and is reported. A study to measure length scales and to obtain a limited number of measurements with a blunt trailing edge inlet is being conducted under Phase 3 of the contract.
NASA Astrophysics Data System (ADS)
Ball, Justin; Parra, Felix I.; Lee, Jungpyo; Cerfon, Antoine J.
2016-12-01
Tokamaks with up-down asymmetric poloidal cross-sections spontaneously rotate due to turbulent transport of momentum. In this work, we investigate the effect of the Shafranov shift on this intrinsic rotation, primarily by analyzing tokamaks with tilted elliptical flux surfaces. By expanding the Grad-Shafranov equation in the large aspect ratio limit we calculate the magnitude and direction of the Shafranov shift in tilted elliptical tokamaks. The results show that, while the Shafranov shift becomes up-down asymmetric and depends strongly on the tilt angle of the flux surfaces, it is insensitive to the shape of the current and pressure profiles (when the geometry, total plasma current, and average pressure gradient are kept fixed). Next, local nonlinear gyrokinetic simulations of these MHD equilibria are performed with GS2, which reveal that the Shafranov shift can significantly enhance the momentum transport. However, to be consistent, the effect of {β\\prime} (i.e. the radial gradient of β) on the magnetic equilibrium was also included, which was found to significantly reduce momentum transport. Including these two competing effects broadens the rotation profile, but leaves the on-axis value of the rotation roughly unchanged. Consequently, the shape of the β profile has a significant effect on the rotation profile of an up-down asymmetric tokamak.
Predicting rotation for ITER via studies of intrinsic torque and momentum transport in DIII-D
Chrystal, C.; Grierson, B. A.; Staebler, G. M.; ...
2017-03-30
Here, experiments at the DIII-D tokamak have used dimensionless parameter scans to investigate the dependencies of intrinsic torque and momentum transport in order to inform a prediction of the rotation profile in ITER. Measurements of intrinsic torque profiles and momentum confinement time in dimensionless parameter scans of normalized gyroradius and collisionality are used to predict the amount of intrinsic rotation in the pedestal of ITER. Additional scans of Te/Ti and safety factor are used to determine the accuracy of momentum flux predictions of the quasi-linear gyrokinetic code TGLF. In these scans, applications of modulated torque are used to measure themore » incremental momentum diffusivity, and results are consistent with the E x B shear suppression of turbulent transport. These incremental transport measurements are also compared with the TGLF results. In order to form a prediction of the rotation profile for ITER, the pedestal prediction is used as a boundary condition to a simulation that uses TGLF to determine the transport in the core of the plasma. The predicted rotation is ≈20 krad/s in the core, lower than in many current tokamak operating scenarios. TGLF predictions show that this rotation is still significant enough to have a strong effect on confinement via E x B shear.« less
Angular Momentum Transport in Accretion Disk Boundary Layers Around Weakly Magnetized Stars
NASA Astrophysics Data System (ADS)
Pessah, Martin E.; Chan, Chi-kwan
2013-04-01
The standard model for turbulent shear viscosity in accretion disks is based on the assumption that angular momentum transport is opposite to the radial angular frequency gradient of the disk. This implies that the turbulent stress must be negative and thus transport angular momentum inwards, in the boundary layer where the accretion disk meets the surface of a weakly magnetized star. However, this behavior is not supported by numerical simulations of turbulent magnetohydrodynamic (MHD) accretion disks, which show that angular momentum transport driven by the magnetorotational instability (MRI) is inefficient in disk regions where, as expected in boundary layers, the angular frequency increases with radius. Motivated by the need of a deeper understanding of the behavior of an MHD fluid in a differentially rotating background that deviates from a Keplerian profile, we study the dynamics of MHD waves in configurations that are stable to the standard MRI. Employing the shearing-sheet framework, we show that transient amplification of shearing MHD waves can generate magnetic energy without leading to a substantial generation of hydromagnetic stresses. While these results are in agreement with numerical simulations, they emphasize the need to better understand the mechanism for angular momentum transport in the inner disk regions on more solid grounds.
NASA Astrophysics Data System (ADS)
Gerchikov, L.; Guillemin, R.; Simon, M.; Sheinerman, S.
2017-06-01
A concrete mechanism of angular-momentum transfer in photoionization process is proposed for electron photoemission from deep inner atomic shells. It is demonstrated that the leading contribution to angular-momentum transfer is provided by postcollision interaction of the photoelectrons and Auger electrons. The standard theoretical approach to postcollision interaction has been considerably improved by taking into account angular-momentum transfer. The theory developed is applied to the photoionization of 1 s2 shell in Ar. Calculations show the noticeable influence of angular-momentum transfer on the photoelectron angular distribution.
Mass and momentum turbulent transport experiments with confined swirling coaxial jets
NASA Technical Reports Server (NTRS)
Roback, R.; Johnson, B. V.
1983-01-01
Swirling coaxial jets mixing downstream, discharging into an expanded duct was conducted to obtain data for the evaluation and improvement of turbulent transport models currently used in a variety of computational procedures throughout the combustion community. A combination of laser velocimeter (LV) and laser induced fluorescence (LIF) techniques was employed to obtain mean and fluctuating velocity and concentration distributions which were used to derive mass and momentum turbulent transport parameters currently incorporated into various combustor flow models. Flow visualization techniques were also employed to determine qualitatively the time dependent characteristics of the flow and the scale of turbulence. The results of these measurements indicated that the largest momentum turbulent transport was in the r-z plane. Peak momentum turbulent transport rates were approximately the same as those for the nonswirling flow condition. The mass turbulent transport process for swirling flow was complicated. Mixing occurred in several steps of axial and radial mass transport and was coupled with a large radial mean convective flux. Mixing for swirling flow was completed in one-third the length required for nonswirling flow.
Uncertainties related to the representation of momentum transport in shallow convection
NASA Astrophysics Data System (ADS)
Schlemmer, L.; Bechtold, P.; Sandu, I.; Ahlgrimm, M.
2017-06-01
Convective momentum transport (CMT) has mostly been studied for deep convection, whereas little is known about its characteristics and importance in shallow convection. In this study, CMT by shallow convection is investigated by analyzing both data from large-eddy simulations (LESs) and reforecasts performed with the Integrated Forecasting System (IFS) of the European Centre for Medium-Range Weather Forecasts (ECMWF). In addition, the central terms underlying the bulk mass-flux parametrization of CMT are evaluated offline. Further, the uncertainties related to the representation of CMT are explored by running the stochastically perturbed parametrizations (SPP) approach of the IFS. The analyzed cases exhibit shallow convective clouds developing within considerable low-level wind shear. Analysis of the momentum fluxes in the LES data reveals significant momentum transport by the convection in both cases, which is directed downgradient despite substantial organization of the cloud field. A detailed inspection of the convection parametrization reveals a very good representation of the entrainment and detrainment rates and an appropriate representation of the convective mass and momentum fluxes. To determine the correct values of mass-flux and in-cloud momentum at the cloud base in the parametrization yet remains challenging. The spread in convection-related quantities generated by the SPP is reasonable and addresses many of the identified uncertainties.
Momentum Transport: 2D and 3D Cloud Resolving Model Simulations
NASA Technical Reports Server (NTRS)
Tao, Wei-Kuo
2001-01-01
The major objective of this study is to investigate the momentum budgets associated with several convective systems that developed during the TOGA COARE IOP (west Pacific warm pool region) and GATE (east Atlantic region). The tool for this study is the improved Goddard Cumulas Ensemble (GCE) model which includes a 3-class ice-phase microphysical scheme, explicit cloud radiative interactive processes and air-sea interactive surface processes. The model domain contains 256 x 256 grid points (with 2 km resolution) in the horizontal and 38 grid points (to a depth of 22 km) in the vertical. The 2D domain has 1024 grid points. The simulations were performed over a 7-day time period (December 19-26, 1992, for TOGA COARE and September 1-7, 1994 for GATE). Cyclic literal boundary conditions are required for this type of long-term integration. Two well organized squall systems (TOGA, COARE February 22, 1993, and GATE September 12, 1994) were also simulated using the 3D GCE model. Only 9 h simulations were required to cover the life time of the squall systems. the lateral boundary conditions were open for these two squall systems simulations. the following will be examined: (1) the momentum budgets in the convective and stratiform regions, (2) the relationship between momentum transport and cloud organization (i.e., well organized squall lines versus less organized convective), (3) the differences and similarities in momentum transport between 2D and 3D simulated convective systems, and (4) the differences and similarities in momentum budgets between cloud systems simulated with open and cyclic lateral boundary conditions. Preliminary results indicate that there are only small differences between 2D and 3D simulated momentum budgets. Major differences occur, however, between momentum budgets associated with squall systems simulated using different lateral boundary conditions.
Effect of Ocean Spray on Vertical Momentum Transport Under High-Wind Conditions
NASA Astrophysics Data System (ADS)
Rastigejev, Yevgenii; Suslov, Sergey A.; Lin, Yuh-Lang
2011-10-01
Two mathematical models are proposed detailing the influence of ocean spray on vertical momentum transport under high-wind conditions associated with a hurricane or severe storm. The first model is based on a turbulent kinetic energy (TKE) equation and accounts for the so-called lubrication effect due to the reduction of turbulence intensity. The second model is based on Monin-Obukhov similarity (MOS) and uses available experimental data. It is demonstrated that the flow acceleration is negligible for wind speeds below a certain critical value due to the fact that the spray volume concentration is low for such speeds. For wind speeds higher than the critical value, the spray concentration rapidly increases, which results in significant flow acceleration. Both models produce qualitatively similar results for all turbulent flow parameters considered. It was found that the MOS-based model tends to predict a noticeably stronger lubrication effect than the TKE-based model, especially for lower wind speeds. The results of model calculations are in very good agreement with available experimental data for the spray production values near the upper bound. It is also shown that neither the value of the turbulent Schmidt number in the TKE-based model nor the choice of a stability profile function affects the spray-laden flow dynamics significantly.
Protostellar disk formation and transport of angular momentum during magnetized core collapse
NASA Astrophysics Data System (ADS)
Joos, M.; Hennebelle, P.; Ciardi, A.
2012-07-01
Context. Theoretical studies of collapsing clouds have found that even a relatively weak magnetic field may prevent the formation of disks and their fragmentation. However, most previous studies have been limited to cases where the magnetic field and the rotation axis of the cloud are aligned. Aims: We study the transport of angular momentum, and its effects on disk formation, for non-aligned initial configurations and a range of magnetic intensities. Methods: We perform three-dimensional, adaptive mesh, numerical simulations of magnetically supercritical collapsing dense cores using the magneto-hydrodynamic code Ramses. We compute the contributions of all the relevant processes transporting angular momentum, in both the envelope and the region of the disk. We clearly define centrifugally supported disks and thoroughly study their properties. Results: At variance with earlier analyses, we show that the transport of angular momentum acts less efficiently in collapsing cores with non-aligned rotation and magnetic field. Analytically, this result can be understood by taking into account the bending of field lines occurring during the gravitational collapse. For the transport of angular momentum, we conclude that magnetic braking in the mean direction of the magnetic field tends to dominate over both the gravitational and outflow transport of angular momentum. We find that massive disks, containing at least 10% of the initial core mass, can form during the earliest stages of star formation even for mass-to-flux ratios as small as three to five times the critical value. At higher field intensities, the early formation of massive disks is prevented. Conclusions: Given the ubiquity of Class I disks, and because the early formation of massive disks can take place at moderate magnetic intensities, we speculate that for stronger fields, disks will form later, when most of the envelope will have been accreted. In addition, we speculate that some observed early massive disks
Momentum and energy transport by waves in the solar atmosphere and solar wind
NASA Technical Reports Server (NTRS)
Jacques, S. A.
1977-01-01
The fluid equations for the solar wind are presented in a form which includes the momentum and energy flux of waves in a general and consistent way. The concept of conservation of wave action is introduced and is used to derive expressions for the wave energy density as a function of heliocentric distance. The explicit form of the terms due to waves in both the momentum and energy equations are given for radially propagating acoustic, Alfven, and fast mode waves. The effect of waves as a source of momentum is explored by examining the critical points of the momentum equation for isothermal spherically symmetric flow. We find that the principal effect of waves on the solutions is to bring the critical point closer to the sun's surface and to increase the Mach number at the critical point. When a simple model of dissipation is included for acoustic waves, in some cases there are multiple critical points.
Anomalous Transport due to Magnetic Turbulence
Lopes Cardozo, Niek
2004-03-15
In this paper we consider transport in a toroidal system with broken flux surfaces. Flux surfaces with rational field line winding number can degenerate and form magnetic islands. Where neighbouring chains of islands overlap, a region of chaotic field forms. Thus, the generic topology of the magnetic field in a toroidal device consists of an alternation of shells with 'good' surfaces and shells with islands or chaotic field.In a chaotic field, a field line fills up a region of space and thus makes significant radial excursions. Particles following a chaotic field line may experience rapid radial transport. Recent experimental evidence for the existence of alternating layers with high and low thermal transport is presented. The implication for the determination of transport coefficients is discussed. It is shown that a transport analysis that does not resolve the fine structure of the transport coefficient yields results that are almost meaningless.
Rotation drive and momentum transport with electron cyclotron heating in tokamak plasmas.
Yoshida, M; Sakamoto, Y; Takenaga, H; Ide, S; Oyama, N; Kobayashi, T; Kamada, Y
2009-08-07
The role of electron cyclotron resonance heating (ECRH) on the toroidal rotation velocity profile has been investigated in the JT-60U tokamak device by separating the effects of the change in momentum transport, the intrinsic rotation by pressure gradient, and the intrinsic rotation by ECRH. It is found that ECRH increases the toroidal momentum diffusivity and the convection velocity. It is also found that ECRH drives the codirection (co) intrinsic rotation inside the EC deposition radius and the counterdirection (ctr) intrinsic rotation outside the EC deposition radius. This ctr rotation starts from the EC deposition radius and propagates to the edge region.
Turbulent momentum transport in core tokamak plasmas and penetration of scrape-off layer flows
NASA Astrophysics Data System (ADS)
Abiteboul, J.; Ghendrih, Ph; Grandgirard, V.; Cartier-Michaud, T.; Dif-Pradalier, G.; Garbet, X.; Latu, G.; Passeron, C.; Sarazin, Y.; Strugarek, A.; Thomine, O.; Zarzoso, D.
2013-07-01
The turbulent transport of toroidal angular momentum in the core of a tokamak plasma is investigated in global, full-f gyrokinetic simulations, performed with the GYSELA code in the flux-driven regime. During the initial turbulent phase, a front of positive Reynolds stress propagates radially, generating intrinsic toroidal rotation from a vanishing initial profile. This is also accompanied by a propagating front of turbulent heat flux. In the statistical steady-state regime, turbulent transport exhibits large-scale avalanche-like events which are found to transport both heat and momentum, and similar statistical properties are obtained for both fluxes. The impact of scrape-off layer flows is also investigated by modifying the boundary conditions in the simulations. The observed impact is radially localized for L-mode like poloidal profiles of parallel velocity at the edge, while a constant velocity at the edge can modify the core toroidal rotation profile in a large fraction of the radial domain.
Wilsonian RG-flow approach to holographic transport with momentum dissipation
NASA Astrophysics Data System (ADS)
Tian, Yu; Ge, Xian-Hui; Wu, Shao-Feng
2017-08-01
We systematically present a new approach for studying the coupled linear transport of holographic systems. In this approach, the set of equations for the linear perturbations can be reduced to a first-order nonlinear ordinary differential equation expressed as the radial (renormalization group) flow equation of the transport matrices. As an important application, we use this approach to compute the dc and ac conductivities of a holographic model with momentum dissipation, which can be easily read off from the nonlinear flow equations. This method also works for transport in the presence of an external magnetic field.
NASA Astrophysics Data System (ADS)
Oh, J. H.; Jiang, X.; Waliser, D. E.; Moncrieff, M. W.; Johnson, R. H.
2014-12-01
As one of the most prominent tropical atmospheric variability modes, the Madden-Julian Oscillation (MJO) exerts profound influences on global weather and climate, and serves as a critical predictability source for extend-range forecast. In spite of the recent effort toward improving the ability of general circulation models (GCMs) to simulate the MJO, significant challenges still remain for current GCMs to produce more realistic MJO simulations. Previous studies have highlighted the important role of multi-scale interactions within the MJO including the momentum exchanges in order to improve MJO prediction skill. In this study, convective momentum transport (CMT) associated with the MJO is analyzed based on the recent NOAA Climate Forecast System Reanalysis (CFSR), in particular, by capitalizing on its archive of the parameterized subgrid CMT. Consistent with previous cloud-resolving model study, a three-layer vertical structure associated with the MJO is clear in the subgrid CMT from the CFSR. In association with enhanced MJO convection over both the Indian Ocean (IO) and western Pacific (WP), within and to the west (east) of the MJO convection, positive (negative), negative (positive), positive (negative) subgrid CMT momentum tendency anomalies are evident in the upper, middle, and lower troposphere, respectively. This subgrid CMT vertical structure tends to damp the large-scale MJO circulation in the middle and upper troposphere, but enhances MJO winds in a shallow near-surface layer. Further analyses illustrate that this three-layer vertical structure in subgrid momentum tendency of the MJO is largely balanced by grid-scale u-momentum transport. The momentum tendency structure associated with the MJO based on the CFSR is also confirmed with the European Centre for Medium-Range Forecasts (ECMWF) analysis for the two-year period of the Year of the Tropical Convection (YOTC), which further lends confidence to our results.
NASA Astrophysics Data System (ADS)
Egito, F.; Andrioli, V. F.; Batista, P. P.
2016-11-01
In the equatorial region planetary scale waves play an important role transporting significant amount of energy and momentum through atmosphere. Quantifying the momentum transported by these waves and its effects on the mean flow is rather important. Direct estimates of the momentum flux transported by waves require horizontal and vertical wind measurements. Ground-based meteor radars have provided continuous and reliable measurements of the horizontal wind components in the Mesosphere and Lower Thermosphere (MLT) region and have contributed to improve our knowledge of the dynamics of this region. However, instrumental limitations hinder its use for measuring vertical winds and momentum fluxes. On the other hand, according to Babu et al (2012), all- sky meteor radars are able to infer tridimensional winds when using a large number of meteor echoes centered at the meteor ablation peak. Following this approach, we have used measurements performed by a Meteor Radar installed at São João do Cariri, Brazil (7.4°S; 36.5°W) in order to measure vertical winds and calculate the momentum flux transported by equatorial planetary scale waves. In order to evaluate the accuracy of vertical wind values we have performed several tests based on a simple model considering real meteor distributions and theoretical equations for the MLT winds motion. From our tests, we inferred that Brazilian meteor radar data can be used for this purpose with an accuracy of 1.8 m/s. The results show that the vertical wind presents magnitudes of a few meters per second and occasionally reaches magnitudes around 10 m/s. Below 92 km the vertical wind is predominantly upward during the whole year and above exhibits a semi-annual oscillation with downward phase during the equinoxes. Variations associated to planetary scale waves in the vertical wind are also observed and some of them appear simultaneously in the zonal and meridional wind as well. Largest wave induced amplitudes in the vertical wind
NASA Astrophysics Data System (ADS)
Meheut, Heloise; Fromang, Sébastien; Lesur, Geoffroy; Joos, Marc; Longaretti, Pierre-Yves
2015-07-01
Context. Angular momentum transport in accretion discs is often believed to be due to magnetohydrodynamic turbulence mediated by the magnetorotational instability (MRI). Despite an abundant literature on the MRI, the parameters governing the saturation amplitude of the turbulence are poorly understood and the existence of an asymptotic behaviour in the Ohmic diffusion regime has not been clearly established. Aims: We investigate the properties of the turbulent state in the small magnetic Prandtl number limit. Since this is extremely computationally expensive, we also study the relevance and range of applicability of the most common subgrid scale models for this problem. Methods: Unstratified shearing box simulations are performed both in the compressible and incompressible limits, with a resolution up to 800 cells per disc scale height. This is the highest resolution ever attained for a simulation of MRI turbulence. Different magnetic field geometry and a wide range of dimensionless dissipative coefficients are considered. We also systematically investigate the relevance of using large eddy simulations (LES) in place of direct numerical simulations. Results: In the presence of a mean magnetic field threading the domain, angular momentum transport converges to a finite value in the small Pm limit. When the mean vertical field amplitude is such that β (the ratio between the thermal and magnetic pressure) equals 103, we find α ~ 3.2 × 10-2 when Pm approaches zero. In the case of a mean toroidal field for which β = 100, we find α ~ 1.8 × 10-2 in the same limit. Implicit LES and the Chollet-Lesieur closure model both reproduce these results for the α parameter and the power spectra. A reduction in computational cost by a factor of at least 16 (and up to 256) is achieved when using such methods. Conclusions: MRI turbulence operates efficiently in the small Pm limit provided there is a mean magnetic field. Implicit LES offers a practical and efficient means of
Toroidal momentum transport in a tokamak caused by symmetry breaking parallel derivatives
Sung, T.; Buchholz, R.; Grosshauser, S. R.; Hornsby, W. A.; Migliano, P.; Peeters, A. G.; Casson, F. J.; Fable, E.
2013-04-15
A new mechanism for toroidal momentum transport in a tokamak is investigated using the gyro-kinetic model. First, an analytic model is developed through the use of the ballooning transform. The terms that generate the momentum transport are then connected with the poloidal derivative of the ballooning envelope, which are one order smaller in the normalised Larmor radius, compared with the derivative of the eikonal. The mechanism, therefore, does not introduce an inhomogeneity in the radial direction, in contrast with the effect of profile shearing. Numerical simulations of the linear ion temperature gradient mode with adiabatic electrons, retaining the finite {rho}{sub *} effects in the E Multiplication-Sign B velocity, the drift, and the gyro-average, are presented. The momentum flux is found to be linear in the normalised Larmor radius ({rho}{sub *}) but is, nevertheless, generating a sizeable counter-current rotation. The total momentum flux scales linear with the aspect ratio of the considered magnetic surface, and increases with increasing magnetic shear, safety factor, and density and temperature gradients.
Solitonic transport of energy-momentum in a deformed magnetic medium
NASA Astrophysics Data System (ADS)
Kavitha, L.; Saravanan, M.; Akila, N.; Bhuvaneswari, S.; Gopi, D.
2012-03-01
The energy-momentum transport phenomenon between interacting spins in a deformed ferromagnetic medium is investigated theoretically. The spin dynamics of a one-dimensional (1D) classical continuum Heisenberg ferromagnetic spin system in the presence of varying exchange interactions is considered. The state of the 1D continuum spin system with varying exchange interactions is mapped onto a moving helical space curve in E3. The results are recast in conjunction with the evolution of energy and current densities of the deformed ferromagnetic medium, through a knowledge of the underlying geometry of this system. A set of soliton solutions for energy and current densities is constructed by employing the sine-cosine method coupled with symbolic computation. The evolution and propagation of solitonic energy-momentum transport under the influence of competing linear and nonlinear inhomogeneities have been analyzed briefly.
Modeling of momentum transport of axially parallel turbulent flows in rod cascades
NASA Astrophysics Data System (ADS)
Neelen, Neele
Problems and boundary conditions of the turbulent flow in heat exchangers, especially for nuclear fuel elements, are treated using mathematical models. Rod cascade flow and the physical fundamentals of turbulent flows are introduced. It is shown that the momentum transport phenomena can be separated into the radial and azimuthal directions. The geometrical characteristics of rod bundle geometries and a regression analysis are considered. The correlation coefficients for the wall parallel vortex viscosity are determined using a numerical optimization method. The order of magnitude of the secondary flow occurring perpendicularly to the main flow direction are determined to be 1 pct to 2 pct of the average axial velocity. The results obtained with the code VELASCO-BS are superior to those of previous codes. The azimuthal vortex viscosity is the decisive parameter, and secondary flow is not important for wall parallel momentum transport.
Transport driven by eddy momentum fluxes in the Gulf Stream Extension region
NASA Astrophysics Data System (ADS)
Greatbatch, R. J.; Zhai, X.; Claus, M.; Czeschel, L.; Rath, W.
2010-12-01
The importance of the Gulf Stream Extension region in climate and seasonal prediction research is being increasingly recognised. Here we use satellite-derived eddy momentum fluxes to drive a shallow water model for the North Atlantic Ocean that includes the realistic ocean bottom topography. The results show that the eddy momentum fluxes can drive significant transport, sufficient to explain the observed increase in transport of the Gulf Stream following its separation from the coast at Cape Hatteras, as well as the observed recirculation gyres. The model also captures recirculating gyres seen in the mean sea surface height field within the North Atlantic Current system east of the Grand Banks of Newfoundland, including a representation of the Mann Eddy.
Simulations of Turbulent Momentum and Scalar Transport in Confined Swirling Coaxial Jets
NASA Technical Reports Server (NTRS)
Shih, Tsan-Hsing; Liu, Nan-Suey; Moder, Jeffrey P.
2015-01-01
This paper presents the numerical simulations of confined three-dimensional coaxial water jets. The objectives are to validate the newly proposed nonlinear turbulence models of momentum and scalar transport, and to evaluate the newly introduced scalar APDF and DWFDF equation along with its Eulerian implementation in the National Combustion Code(NCC). Simulations conducted include the steady RANS, the unsteady RANS (URANS), and the time-filtered Navier-Stokes (TFNS); both without and with invoking the APDF or DWFDF equation.
An overview of intrinsic torque and momentum transport bifurcations in toroidal plasmas
NASA Astrophysics Data System (ADS)
Diamond, P. H.; Kosuga, Y.; Gürcan, Ö. D.; McDevitt, C. J.; Hahm, T. S.; Fedorczak, N.; Rice, J. E.; Wang, W. X.; Ku, S.; Kwon, J. M.; Dif-Pradalier, G.; Abiteboul, J.; Wang, L.; Ko, W. H.; Shi, Y. J.; Ida, K.; Solomon, W.; Jhang, H.; Kim, S. S.; Yi, S.; Ko, S. H.; Sarazin, Y.; Singh, R.; Chang, C. S.
2013-10-01
An overview of the physics of intrinsic torque is presented, with special emphasis on the phenomenology of intrinsic toroidal rotation in tokamaks, its theoretical understanding, and the variety of momentum transport bifurcation dynamics. Ohmic reversals and electron cyclotron heating-driven counter torque are discussed in some detail. Symmetry breaking by lower single null versus upper single null asymmetry is related to the origin of intrinsic torque at the separatrix.
NASA Astrophysics Data System (ADS)
Lore, J.; Guttenfelder, W.; Briesemeister, A.; Anderson, D. T.; Anderson, F. S. B.; Deng, C. B.; Likin, K. M.; Spong, D. A.; Talmadge, J. N.; Zhai, K.
2010-05-01
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)].
Reverse Fluid Transport Due to Boundary Pulsations
NASA Astrophysics Data System (ADS)
Coloma, Mikhail; Schaffer, David; Chiarot, Paul; Huang, Peter
2016-11-01
We investigate a reverse fluid transport mechanism consisting of peristaltic flow and boundary wave reflections. The reverse flow occurs in a rectangular conduit aligned in parallel between two cylindrical channels embedded in an elastic PDMS medium. The pulsating flow in the cylindrical channels, driven by a peristaltic pump, deform the PDMS medium and induce a pulsating flow in the rectangular conduit. Waveforms along the conduit boundaries, and their transmission and reflections, can be controlled by changing the PDMS rigidity. Our results show that while the overall wave propagation direction is in the forward direction, a reverse flow in the rectangular conduit can be preferentially induced by varying the elastic rigidity in one of the cylindrical channels. We study the overall flow velocity and direction under various PDMS rigidities. The identified set of experimental parameters that leads to a reverse flow will provide insights in understanding metabolic waste transport within the arterial walls in the brain.
Brauckmann, Hannes J; Eckhardt, Bruno; Schumacher, Jörg
2017-03-13
Rayleigh-Bénard convection and Taylor-Couette flow are two canonical flows that have many properties in common. We here compare the two flows in detail for parameter values where the Nusselt numbers, i.e. the thermal transport and the angular momentum transport normalized by the corresponding laminar values, coincide. We study turbulent Rayleigh-Bénard convection in air at Rayleigh number Ra=10(7) and Taylor-Couette flow at shear Reynolds number ReS=2×10(4) for two different mean rotation rates but the same Nusselt numbers. For individual pairwise related fields and convective currents, we compare the probability density functions normalized by the corresponding root mean square values and taken at different distances from the wall. We find one rotation number for which there is very good agreement between the mean profiles of the two corresponding quantities temperature and angular momentum. Similarly, there is good agreement between the fluctuations in temperature and velocity components. For the heat and angular momentum currents, there are differences in the fluctuations outside the boundary layers that increase with overall rotation and can be related to differences in the flow structures in the boundary layer and in the bulk. The study extends the similarities between the two flows from global quantities to local quantities and reveals the effects of rotation on the transport.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.
NASA Astrophysics Data System (ADS)
Brauckmann, Hannes J.; Eckhardt, Bruno; Schumacher, Jörg
2017-03-01
Rayleigh-Bénard convection and Taylor-Couette flow are two canonical flows that have many properties in common. We here compare the two flows in detail for parameter values where the Nusselt numbers, i.e. the thermal transport and the angular momentum transport normalized by the corresponding laminar values, coincide. We study turbulent Rayleigh-Bénard convection in air at Rayleigh number Ra=107 and Taylor-Couette flow at shear Reynolds number ReS=2×104 for two different mean rotation rates but the same Nusselt numbers. For individual pairwise related fields and convective currents, we compare the probability density functions normalized by the corresponding root mean square values and taken at different distances from the wall. We find one rotation number for which there is very good agreement between the mean profiles of the two corresponding quantities temperature and angular momentum. Similarly, there is good agreement between the fluctuations in temperature and velocity components. For the heat and angular momentum currents, there are differences in the fluctuations outside the boundary layers that increase with overall rotation and can be related to differences in the flow structures in the boundary layer and in the bulk. The study extends the similarities between the two flows from global quantities to local quantities and reveals the effects of rotation on the transport.
Gyrokinetic simulations of momentum transport and fluctuation spectra for ICRF-heated L-Mode plasmas
NASA Astrophysics Data System (ADS)
Sierchio, J. M.; White, A. E.; Howard, N. T.; Sung, C.; Ennever, P.; Porkolab, M.; Candy, J.
2014-10-01
We examine ICRF-heated L-mode plasmas in Alcator C-Mod, with differing momentum transport (hollow vs. peaked radial profiles of intrinsic toroidal rotation) but similar heat and particle transport. Nonlinear gyrokinetic simulations of heat and particle transport with GYRO [Candy and Waltz, J. Comp. Phys. 186, 545 (2003)] have previously been compared with these experiments [White et al., Phys. Plasmas 20, 056106 (2013); Howard et al. PPCF submitted (2014)] as part of an effort to validate the gyrokinetic model for core turbulent transport in C-Mod plasmas. To further test the model for these plasmas, predicted core turbulence characteristics such as fluctuation spectra will be compared with experiment. Using synthetic diagnostics for the CECE, reflectometry, and PCI systems at C-Mod, synthetic spectra and, when applicable, fluctuation amplitudes, are generated. We compare these generated results with fluctuation measurements from the experiment. We also report the momentum transport results from simulations of these plasmas and compare them to experiment. Supported by USDoE award DE-FC02-99ER54512.
Accuracy of momentum and gyrodensity transport in global gyrokinetic particle-in-cell simulations
McMillan, B. F.; Villard, L.
2014-05-15
Gyrokinetic Particle-In-Cell (PIC) simulations based on conservative Lagrangian formalisms admit transport equations for conserved quantities such as gyrodensity and toroidal momentum, and these can be derived for arbitrary wavelength, even though previous applications have used the long-wavelength approximation. In control-variate PIC simulations, a consequence of the different treatment of the background (f{sub 0}) and perturbed parts (δf), when a splitting f = f{sub 0} + δf is performed, is that analytical transport relations for the relevant fluxes and moments are only reproduced in the large marker number limit. The transport equations for f can be used to write the inconsistency in the perturbed quantities explicitly in terms of the sampling of the background distribution f{sub 0}. This immediately allows estimates of the error in consistency of momentum transport in control-variate PIC simulations. This inconsistency tends to accumulate secularly and is not directly affected by the sources and noise control in the system. Although physical tokamaks often rotate quite strongly, the standard gyrokinetic formalism assumes weak perpendicular flows, comparable to the drift speed. For systems with such weak flows, maintaining acceptably small relative errors requires that a number of markers scale with the fourth power of the linear system size to consistently resolve long-wavelength evolution. To avoid this unfavourable scaling, an algorithm for exact gyrodensity transport has been developed, and this is shown to allow accurate simulations with an order of magnitude fewer markers.
IMPLICATIONS OF RAPID CORE ROTATION IN RED GIANTS FOR INTERNAL ANGULAR MOMENTUM TRANSPORT IN STARS
Tayar, Jamie; Pinsonneault, Marc H.
2013-09-20
Core rotation rates have been measured for red giant stars using asteroseismology. These data, along with helioseismic measurements and open cluster spin-down studies, provide powerful clues about the nature and timescale for internal angular momentum transport in stars. We focus on two cases: the metal-poor red giant KIC 7341231 ({sup O}tto{sup )} and intermediate-mass core helium burning stars. For both, we examine limiting case studies for angular momentum coupling between cores and envelopes under the assumption of rigid rotation on the main sequence. We discuss the expected pattern of core rotation as a function of mass and radius. In the case of Otto, strong post-main-sequence coupling is ruled out and the measured core rotation rate is in the range of 23-33 times the surface value expected from standard spin-down models. The minimum coupling timescale (0.17-0.45 Gyr) is significantly longer than that inferred for young open cluster stars. This implies ineffective internal angular momentum transport in early first ascent giants. By contrast, the core rotation rates of evolved secondary clump stars are found to be consistent with strong coupling given their rapid main-sequence rotation. An extrapolation to the white dwarf regime predicts rotation periods between 330 and 0.0052 days, depending on mass and decoupling time. We identify two key ingredients that explain these features: the presence of a convective core and inefficient angular momentum transport in the presence of larger mean molecular weight gradients. Observational tests that can disentangle these effects are discussed.
Implications of Rapid Core Rotation in Red Giants for Internal Angular Momentum Transport in Stars
NASA Astrophysics Data System (ADS)
Tayar, Jamie; Pinsonneault, Marc H.
2013-09-01
Core rotation rates have been measured for red giant stars using asteroseismology. These data, along with helioseismic measurements and open cluster spin-down studies, provide powerful clues about the nature and timescale for internal angular momentum transport in stars. We focus on two cases: the metal-poor red giant KIC 7341231 ("Otto") and intermediate-mass core helium burning stars. For both, we examine limiting case studies for angular momentum coupling between cores and envelopes under the assumption of rigid rotation on the main sequence. We discuss the expected pattern of core rotation as a function of mass and radius. In the case of Otto, strong post-main-sequence coupling is ruled out and the measured core rotation rate is in the range of 23-33 times the surface value expected from standard spin-down models. The minimum coupling timescale (0.17-0.45 Gyr) is significantly longer than that inferred for young open cluster stars. This implies ineffective internal angular momentum transport in early first ascent giants. By contrast, the core rotation rates of evolved secondary clump stars are found to be consistent with strong coupling given their rapid main-sequence rotation. An extrapolation to the white dwarf regime predicts rotation periods between 330 and 0.0052 days, depending on mass and decoupling time. We identify two key ingredients that explain these features: the presence of a convective core and inefficient angular momentum transport in the presence of larger mean molecular weight gradients. Observational tests that can disentangle these effects are discussed.
Angular Momentum Transport in Solar-type Stars: Testing the Timescale for Core-Envelope Coupling
NASA Astrophysics Data System (ADS)
Denissenkov, Pavel A.; Pinsonneault, Marc; Terndrup, Donald M.; Newsham, Grant
2010-06-01
We critically examine the constraints on internal angular momentum transport which can be inferred from the spin-down of open cluster stars. The rotation distribution inferred from rotation velocities and periods is consistent for larger and more recent samples, but smaller samples of rotation periods appear biased toward shorter periods relative to vsin i studies. We therefore focus on whether the rotation period distributions observed in star forming regions can be evolved into the observed ones in the Pleiades, NGC 2516, M 34, M 35, M 37, and M 50 with plausible assumptions about star-disk coupling and angular momentum loss from magnetized solar-like winds. Solid-body (SB) models are consistent with the data for low-mass fully convective stars but highly inconsistent for higher mass stars where the surface convection zone can decouple for angular momentum purposes from the radiative interior. The Tayler-Spruit magnetic angular momentum transport mechanism, commonly employed in models of high-mass stars, predicts SB rotation on extremely short timescales of less than 1 Myr and is therefore unlikely to operate in solar-type pre-main-sequence (pre-MS) and MS stars at the predicted rate. Models with core-envelope decoupling can explain the spin-down of 1.0 and 0.8 solar mass slow rotators with characteristic coupling timescales of 55 ± 25 Myr and 175 ± 25 Myr, respectively. The upper envelope of the rotation distribution is more strongly coupled than the lower envelope of the rotation distribution, in accord with theoretical predictions that the angular momentum transport timescale should be shorter for more rapidly rotating stars. Constraints imposed by the solar rotation curve are also discussed. We argue that neither hydrodynamic mechanisms nor our revised and less efficient prescription for the Tayler-Spruit dynamo can reproduce both spin-down and the internal solar rotation profile by themselves. It is likely that a successful model of angular momentum
Momentum-transport studies in high E x B shear plasmas in the National Spherical Torus Experiment.
Solomon, W M; Kaye, S M; Bell, R E; Leblanc, B P; Menard, J E; Rewoldt, G; Wang, W; Levinton, F M; Yuh, H; Sabbagh, S A
2008-08-08
Experiments have been conducted at the National Sperical Torus Experiment (NSTX) to study both steady state and perturbative momentum transport. These studies are unique in their parameter space under investigation, where the low aspect ratio of NSTX results in rapid plasma rotation with ExB shearing rates high enough to suppress low-k turbulence. In some cases, the ratio of momentum to energy confinement time is found to exceed five. Momentum pinch velocities of order 10-40 m/s are inferred from the measured angular momentum flux evolution after nonresonant magnetic perturbations are applied to brake the plasma.
Computational Study of Poloidal Angular Momentum Transport in DIII-D
NASA Astrophysics Data System (ADS)
Pankin, Alexei; Kruger, Scott; Kritz, Arnold; Rafiq, Tariq; Weiland, Jan
2013-10-01
The new Multi-Mode Model, MMM8.1, includes the capability to predict the anomalous poloidal momentum diffusivity [T. Rafiq et al., Phys. Plasmas 20, 032506 (2013)]. It is important to consider the effect of this diffusivity on the poloidal rotation of tokamak plasmas since some experimental observations suggest that neoclassical effects are not always sufficient to explain the observed poloidal rotation [B.A. Grierson et al., Phys. Plasmas 19, 056107 (2012)]. One of the objectives of this research is to determine if the anomalous contribution to the poloidal rotation can be significant in the regions of internal transport barriers (ITBs). In this study, the MMM8.1 model is used to compute the poloidal momentum diffusivity for a range of plasma parameters that correspond to the parameters that occur in DIII-D discharges. The parameters that are considered include the temperature and density gradients, and magnetic shear. The role of anomalous poloidal transport in the possible poloidal spin up in the ITB regions is discussed. Progress in the implementation of poloidal transport equations in the ASTRA transport code is reported and initial predictive simulation results for the poloidal rotation profiles are presented. This research is partially support by the DOE Grants DE-SC0006629 and DE-FG02-92ER54141.
Momentum and charge transport in non-relativistic holographic fluids from Hořava gravity
NASA Astrophysics Data System (ADS)
Davison, Richard A.; Grozdanov, Sašo; Janiszewski, Stefan; Kaminski, Matthias
2016-11-01
We study the linearized transport of transverse momentum and charge in a conjectured field theory dual to a black brane solution of Hořava gravity with Lifshitz exponent z = 1. As expected from general hydrodynamic reasoning, we find that both of these quantities are diffusive over distance and time scales larger than the inverse temperature. We compute the diffusion constants and conductivities of transverse momentum and charge, as well the ratio of shear viscosity to entropy density, and find that they differ from their relativistic counterparts. To derive these results, we propose how the holographic dictionary should be modified to deal with the multiple horizons and differing propagation speeds of bulk excitations in Hořava gravity. When possible, as a check on our methods and results, we use the covariant Einstein-Aether formulation of Hořava gravity, along with field redefinitions, to re-derive our results from a relativistic bulk theory.
Predicting Rotation via Studies of Intrinsic Torque and Momentum Transport in DIII-D
NASA Astrophysics Data System (ADS)
Chrystal, C.
2016-10-01
Experiments at DIII-D using dimensionless parameter scans to study momentum transport and intrinsic (self-generated) torque have yielded a predicted average toroidal rotation in ITER of 10 krad/s and shown that intrinsic torque is relevant for large tokamaks. Intrinsic torque can generate toroidal rotation via various mechanisms (residual stress, orbit loss, field ripple, etc.), and rotation is important for determining turbulence suppression, MHD stability, and high-Z impurity transport. The 10 krad/s prediction is 2x higher than when only neutral beam torque is accounted for, an increase that is predicted to benefit ITER's performance. This work employs scans of normalized gyroradius (ρ*), normalized collision frequency (ν*), Te /Ti , and q. Intrinsic torque normalized by Ti has been found to scale as ρ*- 1.5 , yielding significant intrinsic torque in ITER. The measurements disagree with theoretical predictions and suggest that residual stress is not the primary source of intrinsic torque. These results are consistent with a companion scan in JET. The ν* scaling of normalized intrinsic torque is smaller (ν*0.3). Momentum confinement time was measured to have gyro-Bohm like scaling (ρ*- 0.7 , similar to ITB98(y,2) energy confinement time scaling), and weaker ν* scaling (ν*0.4). Intrinsic torque and momentum confinement time results are found by analyzing the time history of the angular momentum. The time variation of main-ion and impurity rotation were found to be the same, verifying a key assumption in the analysis. The same intrinsic torque was measured when canceling the intrinsic torque with neutral beam torque, suggesting that the Mach number is not an important parameter. The beneficial level of rotation in ITER implied by these results is encouraging. Work supported by US DOE under DE-FC02-04ER54698.
Scalar and momentum turbulent transport experiments with swirling and nonswirling flows
NASA Technical Reports Server (NTRS)
Johnson, B. V.; Roback, R.; Bennett, J. C.
1984-01-01
Combustor models for the aircraft gas turbine industry have been obtained because of the need to reduce the costs of developing improved performance and more durable engines. A few years ago, it became apparent that the mass concentration and velocity predictions provided by the computer codes were not representing the data measured in some confined recirculating flows. It is pointed out that errors in the mass concentration distribution are an especially serious problem because of their influence on the heat release, temperature, and reactant distributions. Combined mass and momentum turbulent transport experiments with swirling and nonswirling flow have been conducted with the objective to obtain an experimental data base which can be used to evaluate and improve the turbulent transport submodes employed in the aerothermal models. The present paper is mainly concerned with the overall characteristics of the mass turbulent transport processes in complex flows with recirculation and the deficiencies of the conventional models.
Enhanced momentum delivery by electric force to ions due to collisions of ions with neutrals
Makrinich, G.; Fruchtman, A.
2013-04-15
Ions in partially ionized argon, nitrogen, and helium gas discharges are accelerated across a magnetic field by an applied electric field, colliding with neutrals during the acceleration. The momentum delivered by the electric force to the ions, which is equal to the momentum carried by the mixed ion-neutral flow, is found by measuring the force exerted on a balance force meter by that flow exiting the discharge. The power deposited in the ions is calculated by measuring the ion flux and the accelerating voltage. The ratio of force over power is found for the three gases, while the gas flow rates and magnetic field intensities are varied over a wide range of values, resulting in a wide range of gas pressures and applied voltages. The measurements for the three different gases confirm our previous suggestion [G. Makrinich and A. Fruchtman, Appl. Phys. Lett. 95, 181504 (2009)] that the momentum delivered to the ions for a given power is enhanced by ion-neutral collisions during the acceleration and that this enhancement is proportional to the square root of the number of ion-neutral collisions.
Mass and momentum turbulent transport experiments with swirling confined coaxial jets. II
NASA Technical Reports Server (NTRS)
Roback, R.; Johnson, B. V.
1986-01-01
An experimental study of mixing downstream of swirling coaxial jets discharging into an expanded duct was conducted to obtain data for the evaluation and improvement of turbulent transport models currently used in a variety of computational procedures throughout the combustion community. A combination of laser velocimeter and laser induced fluorescence techniques was employed to obtain mean and fluctuating velocity and concentration distributions at selected axial and radial locations throughout the flow field. Flow visualization techniques were also employed to determine qualitatively the time dependent characteristics of the flow and the scale of turbulence. Simultaneous two component velocity and concentration/velocity measurements provided data which were used to determine the average momentum and mass transport rates for each of three measurement planes. Mixing for swirling flows occurred in several steps of axial and radial mean convective flow and was completed in one-third the length required for nonswirling flow. Comparison of the mass and momentum transport processes for swirling and nonswirling flows indicated that large differences existed in these processes between the two flows.
NASA Astrophysics Data System (ADS)
Fiete, Gregory
2006-03-01
In a one dimensional electron gas at low enough density the magnetic exchange energy J between neighboring electrons is exponentially suppressed relative to the Fermi energy, EF. At finite temperature T, the energy hierarchy J << T << EF can be reached, and we refer to this as the spin incoherent (SI) Luttinger liquid state. By using a model of a fluctuating Wigner solid, we theoretically explore the signatures of spin incoherence in the single particle Green’s function[1], momentum resolved tunneling[2], transport[3], and Coulomb drag[4]. In the SI Green’s function the spin modes of a Luttinger liquid (LL) are thermally washed out leaving only singular behavior from the charge modes. The charge modes are broadened in momentum space by an amount of order kF and the energy dependence of the tunneling density of states qualitatively changes from the low energy suppression of the LL regime to a possible low energy divergence in the SI regime. Such a state may be probed directly in momentum resolved tunneling between parallel quantum wires. Deep in the SI regime, the physics of transport and Coulomb drag can be mapped onto spinless electrons. Various crossovers in temperature and for finite systems connected to Fermi liquid leads are discussed. Both transport and Coulomb drag may exhibit interesting non-monotonic temperature dependence. [1] G. A. Fiete and L. Balents, Phys. Rev. Lett. 93, 226401 (2004). [2] G. A. Fiete, J. Qian, Y. Tserkovnyak, and B. I. Halperin, Phys. Rev. B 72, 045315 (2005). [3] G. A. Fiete, K. Le Hur, and L. Balents, Phys. Rev. B 72, 125416 (2005). [4] G. A. Fiete, K. Le Hur, and L. Balents, Submitted, cond-mat/0511715.
Center for Momentum Transport and Flow Organization in Plasmas and Magnetofluids (CMTFO)
Lin, Zhihong
2014-02-28
The CMTFO funding partially supports a junior researcher and a graduate student at UCI. During this project, we have further developed the global gyrokinetic particle code GTC to study the momentum transport in tokamak driven by electrostatic ion temperature gradient (ITG) turbulence [1] with kinetic electrons and by collisionless trapped electron mode (CTEM) turbulence [2]. We have also upgraded GTC for fully electromagnetic simulation and for linear plasma configuration with verification and validation of the electron temperature gradient (ETG) turbulence in Columbia Linear Machine. The followings are the highlights on the physics results reported in the key publications of this project.
NASA Astrophysics Data System (ADS)
Liu, Caixi; Tang, Shuai; Shen, Lian; Dong, Yuhong
2017-03-01
The dynamic and thermal performance of particle-laden turbulent flow is investigated via direction numerical simulation combined with the Lagrangian point-particle tracking under the condition of two-way coupling, with a focus on the contributions of particle feedback effect to momentum and heat transfer of turbulence. We take into account the effects of particles on flow drag and Nusselt number and explore the possibility of drag reduction in conjunction with heat transfer enhancement in particle-laden turbulent flows. The effects of particles on momentum and heat transfer are analyzed, and the possibility of drag reduction in conjunction with heat transfer enhancement for the prototypical case of particle-laden turbulent channel flows is addressed. We present results of turbulence modification and heat transfer in turbulent particle-laden channel flow, which shows the heat transfer reduction when large inertial particles with low specific heat capacity are added to the flow. However, we also found an enhancement of the heat transfer and a small reduction of the flow drag when particles with high specific heat capacity are involved. The present results show that particles, which are active agents, interact not only with the velocity field, but also the temperature field and can cause a dissimilarity in momentum and heat transport. This demonstrates that the possibility to increase heat transfer and suppress friction drag can be achieved with addition of particles with different thermal properties.
Tropical Pacific impacts of convective momentum transport in the SNU coupled GCM
NASA Astrophysics Data System (ADS)
Kim, Daehyun; Kug, Jong-Seong; Kang, In-Sik; Jin, Fei-Fei; Wittenberg, Andrew T.
2008-08-01
Impacts of convective momentum transport (CMT) on tropical Pacific climate are examined, using an atmospheric (AGCM) and coupled GCM (CGCM) from Seoul National University. The CMT scheme affects the surface mainly via a convection-compensating atmospheric subsidence which conveys momentum downward through most of the troposphere. AGCM simulations—with SSTs prescribed from climatological and El Nino Southern Oscillation (ENSO) conditions—show substantial changes in circulation when CMT is added, such as an eastward shift of the climatological trade winds and west Pacific convection. The CMT also alters the ENSO wind anomalies by shifting them eastward and widening them meridionally, despite only subtle changes in the precipitation anomaly patterns. During ENSO, CMT affects the low-level winds mainly via the anomalous convection acting on the climatological westerly wind shear over the central Pacific—so that an eastward shift of convection transfers more westerly momentum toward the surface than would occur without CMT. By altering the low-level circulation, the CMT further alters the precipitation, which in turn feeds back on the CMT. In the CGCM, CMT affects the simulated climatology by shifting the mean convection and trade winds eastward and warming the equatorial SST; the ENSO period and amplitude also increase. In contrast to the AGCM simulations, CMT substantially alters the El Nino precipitation anomaly patterns in the CGCM. Also discussed are possible impacts of the CMT-induced changes in climatology on the simulated ENSO.
Characterization of fluid transport due to multiciliary beating
NASA Astrophysics Data System (ADS)
Lukens, Sarah; Yang, Xingzhou; Fauci, Lisa
2008-11-01
Understanding fluid transport caused by beating cilia can give insight on biological systems such as transport of respiratory mucus, ovum transport in the oviduct, and feeding currents around unicellular organisms. Here we investigate fluid transport due to coordinated beating of motile cilia based upon a computational model that couples their internal force generating mechanisms with external fluid dynamics. Velocity field data is used to identify Lagrangian Coherent Structures (LCS) within the domain. These coherent structures give spatial information on fluid mixing and nutrient transport within this dynamic environment.
NASA Technical Reports Server (NTRS)
Shih, Tsan-Hsing; Liu, Nan-Suey; Moder, Jeffrey P.
2015-01-01
This paper presents the numerical simulations of confined three-dimensional coaxial water jets. The objectives are to validate the newly proposed nonlinear turbulence models of momentum and scalar transport, and to evaluate the newly introduced scalar APDF and DWFDF equation along with its Eulerian implementation in the National Combustion Code (NCC). Simulations conducted include the steady RANS, the unsteady RANS (URANS), and the time-filtered Navier-Stokes (TFNS); both without and with invoking the APDF or DWFDF equation. When the APDF (ensemble averaged probability density function) or DWFDF (density weighted filtered density function) equation is invoked, the simulations are of a hybrid nature, i.e., the transport equations of energy and species are replaced by the APDF or DWFDF equation. Results of simulations are compared with the available experimental data. Some positive impacts of the nonlinear turbulence models and the Eulerian scalar APDF and DWFDF approach are observed.
Simulations of Turbulent Momentum and Scalar Transport in Confined Swirling Coaxial Jets
NASA Technical Reports Server (NTRS)
Shih, Tsan-Hsing; Liu, Nan-Suey
2014-01-01
This paper presents the numerical simulations of confined three dimensional coaxial water jets. The objectives are to validate the newly proposed nonlinear turbulence models of momentum and scalar transport, and to evaluate the newly introduced scalar APDF and DWFDF equation along with its Eulerian implementation in the National Combustion Code (NCC). Simulations conducted include the steady RANS, the unsteady RANS (URANS), and the time-filtered Navier-Stokes (TFNS) with and without invoking the APDF or DWFDF equation. When the APDF or DWFDF equation is invoked, the simulations are of a hybrid nature, i.e., the transport equations of energy and species are replaced by the APDF or DWFDF equation. Results of simulations are compared with the available experimental data. Some positive impacts of the nonlinear turbulence models and the Eulerian scalar APDF and DWFDF approach are observed.
Momentum transport in strongly coupled anisotropic plasmas in the presence of strong magnetic fields
NASA Astrophysics Data System (ADS)
Finazzo, Stefano Ivo; Critelli, Renato; Rougemont, Romulo; Noronha, Jorge
2016-09-01
We present a holographic perspective on momentum transport in strongly coupled, anisotropic non-Abelian plasmas in the presence of strong magnetic fields. We compute the anisotropic heavy quark drag forces and Langevin diffusion coefficients and also the anisotropic shear viscosities for two different holographic models, namely, a top-down deformation of strongly coupled N =4 super-Yang-Mills theory triggered by an external Abelian magnetic field, and a bottom-up Einstein-Maxwell-dilaton (EMD) model which is able to provide a quantitative description of lattice QCD thermodynamics with (2 +1 ) flavors at both zero and nonzero magnetic fields. We find that, in general, energy loss and momentum diffusion through strongly coupled anisotropic plasmas are enhanced by a magnetic field being larger in transverse directions than in the direction parallel to the magnetic field. Moreover, the anisotropic shear viscosity coefficient is smaller in the direction of the magnetic field than in the plane perpendicular to the field, which indicates that strongly coupled anisotropic plasmas become closer to the perfect fluid limit along the magnetic field. We also present, in the context of the EMD model, holographic predictions for the entropy density and the crossover critical temperature in a wider region of the (T , B ) phase diagram that has not yet been covered by lattice simulations. Our results for the transport coefficients in the phenomenologically realistic magnetic EMD model could be readily used as inputs in numerical codes for magnetohydrodynamics.
NASA Astrophysics Data System (ADS)
Merino, Enrique; Berrios, William; Greess, Samuel; Ji, Hantao
2013-10-01
Fast angular momentum transport in accretion disks is a lasting problem in astrophysics. Classically estimated viscosity of neutral fluid is too small to account for the fast accretion rate accompanied by angular momentum transport. Magnetorotational instability (MRI) and nonlinear hydrodynamic instabilities are proposed to be responsible mechanisms to generate the required turbulence. In addition to ongoing experiments using water, liquid metals and plasmas, a new experimental scheme is being developed at Princeton. High-speed gas is injected tangentially to the large radius in a cylindrical container. The gas gradually spirals-in and is pumped out from the container's center. This principle was successfully tested on a small scale prototype. To overcome large viscous forces, a 2nd generation prototype has been built. To provide information on the rotation profile of this swirling gas, a fog cloud is introduced. Motion is recorded by a hi-speed camera and using Particle Imaging Velocimetry, radial profiles of rotation speeds can be measured. Other improvements in this new device include addition of a three-axis translation mechanism, high-power heater and high-flow gas system. Technical designs and preliminary results will be presented and discussed, including near-future plans.
Coherent structures and momentum transport at various scales above an array of multiscale structures
NASA Astrophysics Data System (ADS)
Bai, Kunlun; Katz, Joseph; Meneveau, Charles
2013-11-01
Detailed PIV measurements are carried out to study the turbulence and coherent structures at various scales above a canopy composed of multiscale fractal tree-like objects. The fractal tree has five generations, each consisting of three branches. To study the turbulent structures and momentum transport at large scales, quadrant analysis of fluctuation velocity is carried out. It shows that close to the canopy, sweeping events have larger contribution to the Reynolds shear stress than ejections. Away from the canopy, on the other hand, sweeping contributes less to shear stress than ejection. When the ejection is at present, the flow is disturbed greatly, and the inclined angle of vortices packets can be more than 30 degree. Close to the canopy, the correlation spectrum, i.e. -Euw /(EuuEww) 0 . 5 (where Euw is the co-spectrum and Euu and Eww are spectra of streamwise and vertical velocities, respectively), first decreases and then lifts up as wavenumber increases or scale decreases. It indicates the presence of small-scale coherent structures close to the canopy that contribute, at small scales, to momentum transport. A physical space filtering technique is applied to the velocity field to study such structures and the associated large-scale flow patterns. Acknowledgement: This research is supported by NSF-AGS-1047550 and the Sardella Chair at Johns Hopkins University.
NASA Technical Reports Server (NTRS)
Rigby, D. L.; Vanfossen, G. J.
1992-01-01
A study of the effect of spanwise variation in momentum on leading edge heat transfer is discussed. Numerical and experimental results are presented for both a circular leading edge and a 3:1 elliptical leading edge. Reynolds numbers in the range of 10,000 to 240,000 based on leading edge diameter are investigated. The surface of the body is held at a constant uniform temperature. Numerical and experimental results with and without spanwise variations are presented. Direct comparison of the two-dimensional results, that is, with no spanwise variations, to the analytical results of Frossling is very good. The numerical calculation, which uses the PARC3D code, solves the three-dimensional Navier-Stokes equations, assuming steady laminar flow on the leading edge region. Experimentally, increases in the spanwise-averaged heat transfer coefficient as high as 50 percent above the two-dimensional value were observed. Numerically, the heat transfer coefficient was seen to increase by as much as 25 percent. In general, under the same flow conditions, the circular leading edge produced a higher heat transfer rate than the elliptical leading edge. As a percentage of the respective two-dimensional values, the circular and elliptical leading edges showed similar sensitivity to span wise variations in momentum. By equating the root mean square of the amplitude of the spanwise variation in momentum to the turbulence intensity, a qualitative comparison between the present work and turbulent results was possible. It is shown that increases in leading edge heat transfer due to spanwise variations in freestream momentum are comparable to those due to freestream turbulence.
Stacey, Weston M.; Grierson, Brian A.
2014-05-08
Here, a low-confinement mode discharge which optimizes the capability of the new main-ion chargeexchange-recombination spectroscopy system on DIII-D to measure deuterium toroidal velocity is interpretted in comparison with the predictions of neoclassical theory, with an emphasis on the plasma edge region. The observed peaking in the deuterium toroidal velocity near the separatrix is shown to be consistent with intrinsic co-rotation due to ion orbit loss. In general, the standard neoclassical toroidal and poloidal momentum transport rates are found to be smaller than those inferred from experiment, but a comparison has not yet been made with the more recent extended neoclassicalmore » theory that calculates the effects of poloidal asymmetries using an elongated flux surface representation.« less
Stacey, Weston M.; Grierson, Brian A.
2014-05-08
Here, a low-confinement mode discharge which optimizes the capability of the new main-ion chargeexchange-recombination spectroscopy system on DIII-D to measure deuterium toroidal velocity is interpretted in comparison with the predictions of neoclassical theory, with an emphasis on the plasma edge region. The observed peaking in the deuterium toroidal velocity near the separatrix is shown to be consistent with intrinsic co-rotation due to ion orbit loss. In general, the standard neoclassical toroidal and poloidal momentum transport rates are found to be smaller than those inferred from experiment, but a comparison has not yet been made with the more recent extended neoclassical theory that calculates the effects of poloidal asymmetries using an elongated flux surface representation.
NASA Astrophysics Data System (ADS)
Takahashi, Kazunori; Takao, Yoshinori; Chiba, Aiki; Ando, Akira
2016-09-01
Axial momentum lost to a lateral wall of a helicon source is directly measured by using a pendulum force balance, where only the lateral wall is attached to the balance immersed in 60-cm-diam and 1.4-m-long vacuum tank (pumping speed of 300-400 L/s). When operating the source with highly ionized krypton and xenon, the strong density decay along the axis is observed inside the source tube, which seems to be due to the neutral depletion. Under such a condition, a non-negligible loss of the axial momentum to the lateral wall is detected. The presently detected loss of the axial momentum indicates the presence of the ions which are axially accelerated by the electric field in the plasma core and then lost to the lateral wall. Furthermore, the helicon thruster immersed in 1-m-diam and 2-m-long vacuum tank (pumping speed of 4000-5000 L/s) is operated at high rf power up to 5 kW in argon, to demonstrate the neutral-depletion-induced axially asymmetric density profile. Combination between the Langmuir probe and the optical diagnosis indicates that the neutral density at the axial center of the source is reduced to 20% of the initial neutral density. This work is partially supported by grant-in-aid for scientific research (16H04084 and 26247096) from the Japan Society for the Promotion of Science.
NASA Astrophysics Data System (ADS)
Zanino, R.
1992-02-01
We have developed a 1 + 1 D time dependent code for the description of ion-impurity transport in a rotating tokamak plasma, using a pseudo-spectral discretization in the poloidal angle θ and a staggered finite difference mesh in the minor radius r. The plasma is assumed to have a constant uniform temperature T, to be in the high collisionality (Pfirsch-Schlüter) regime, and to contain electrons " e," fuel ions " i," and a single impurity species " Z" of charge eZ, where e is the proton charge. We are particularly interested in the case when: (1) flow velocities in the toroidal (symmetry) direction φ are in the range typical of neutral beam injection experiments, i.e., vthZ < Vφi, Z ⪅ vthi, ( vthj √2 T/ mj is the thermal speed, mj is the mass); (2) the relative concentration of impurities in the plasma, {ṅz}/{ṅi}, is significant and comparable to that observed in present tokamaks, i.e., √m e/m i ≪ ṅzZ 2/ ṅi ≈ 1 in order of magnitude. The model fluid equations are obtained via a moment approach, and an expansion in powers of the small ordering parameter δpi = ( mivthi/ eBθ) ((1/ ṅ | ∂ ṅi/∂r| ≪ 1 ( B is the magnetic field) is then employed. The equations at each order in δpi up to the second are solved, and the characteristic features of the results presented: to lowest order, outboard impurity peaking on each magnetic surface appears due to centrifugal forces; to first order, radial gradients driven ion-impurity friction gives rise to up-down asymmetries in the poloidal profiles; to second order, the radial profiles of density and rotation frequency evolve to steady state under the action of particle and angular momentum sources. The evolution of the poloidal profiles is decoupled from the evolution of the radial ones, thanks to the fact that the corresponding time scales belong to different orders in δpi: an algorithm is proposed to treat the 2D problem, alternating the solution of 1D problems.
NASA Technical Reports Server (NTRS)
Durisen, Richard H.; Murphy, Brian W.; Cramer, Nichael Lynn; Cuzzi, Jeffrey N.; Mullikin, Thomas L.
1989-01-01
Ballistic transport, defined as the net radial transport of mass and angular momentum due to exchanges of meteoroid hypersonic-impact ejecta by neighboring planetary ring regions on time-scales orders-of-magnitude shorter than the age of the solar system, is presently considered as a problem in mathematical physics. The preliminary results of a numerical scheme for following the combined effects of ballistic transport and viscous diffusion demonstrate that ballistic transport generates structure near sharp edges already present in the ring-mass distribution; the entire ring system ultimately develops an undulatory structure whose length scale is typically of the order of the radial excursion of the impact ejecta.
NASA Technical Reports Server (NTRS)
Durisen, Richard H.; Murphy, Brian W.; Cramer, Nichael Lynn; Cuzzi, Jeffrey N.; Mullikin, Thomas L.
1989-01-01
Ballistic transport, defined as the net radial transport of mass and angular momentum due to exchanges of meteoroid hypersonic-impact ejecta by neighboring planetary ring regions on time-scales orders-of-magnitude shorter than the age of the solar system, is presently considered as a problem in mathematical physics. The preliminary results of a numerical scheme for following the combined effects of ballistic transport and viscous diffusion demonstrate that ballistic transport generates structure near sharp edges already present in the ring-mass distribution; the entire ring system ultimately develops an undulatory structure whose length scale is typically of the order of the radial excursion of the impact ejecta.
NASA Astrophysics Data System (ADS)
Durisen, R. H.; Cramer, N. L.; Murphy, B. W.; Cuzzi, J. N.; Mullikin, T. L.; Cederbloom, S. E.
1989-07-01
Ballistic transport, defined as the net radial transport of mass and angular momentum due to exchanges of meteoroid hypersonic-impact ejecta by neighboring planetary ring regions on time-scales orders-of-magnitude shorter than the age of the solar system, is presently considered as a problem in mathematical physics. The preliminary results of a numerical scheme for following the combined effects of ballistic transport and viscous diffusion demonstrate that ballistic transport generates structure near sharp edges already present in the ring-mass distribution; the entire ring system ultimately develops an undulatory structure whose length scale is typically of the order of the radial excursion of the impact ejecta.
Angular Momentum Ejection and Transport Equation for the ``Spontaneous Rotation'' Process*
NASA Astrophysics Data System (ADS)
Nataf, P.; Coppi, B.
2006-10-01
a process of ejection of angular momentum, from the edge of the plasma column [1,2]. This is attributed to modes driven by the local (edge) plasma pressure gradient. The unstable mode associated with the effect of finite resistivity, is characterized by a phase velocity direction that changes from that of the electron diamagnetic velocity [3] to the opposite as the temperature and the electron pressure gradient decrease. The recoil angular momentum is transported towards the center of the plasma plasma column by collectives modes (V.T.G.modes [4]) that the gradient of both the ion temperature and the longitudinal (toroidal) velocity. A smplified angular momentum equation that includes an inflow term associated with the ion temperatue gradient has been employed to reproduce velocity profiles available from current experiments as well as past experiments [5] on rotation induced by neutral beam injection. [1]B. Coppi, Nucl. Fusion 42, 1 (2002) and B. Coppi, Paper IAEA-CN-TH/P1-02, (Lyon, 2002) and MIT-RLE Report PTP02/05 (2002).[2]B. Coppi, et al., Paper IAEA-F1- CN-TH3/7 (Yokohama, 1998). [3]B. Coppi and M.N. Rosenbluth, Plasma Phys. Control Fus. Res. 1, 617 (1966). [4]B. Coppi, et al., Paper 04.017, Proceeding of the 2006- E.P.S. Meeting on Plasma Physics. [5]K. Nagashima, Y. Koide, H. Shirai, Nucl. Fusion 34, 3 (2002). *Supported in part by the U.S. D.O.E.
Enhanced spin Seebeck effect signal due to spin-momentum locked topological surface states
Jiang, Zilong; Chang, Cui -Zu; Masir, Massoud Ramezani; ...
2016-05-04
Spin-momentum locking in protected surface states enables efficient electrical detection of magnon decay at a magnetic-insulator/topological-insulator heterojunction. Here we demonstrate this property using the spin Seebeck effect (SSE), that is, measuring the transverse thermoelectric response to a temperature gradient across a thin film of yttrium iron garnet, an insulating ferrimagnet, and forming a heterojunction with (BixSb1–x)2Te3, a topological insulator. The non-equilibrium magnon population established at the interface can decay in part by interactions of magnons with electrons near the Fermi energy of the topological insulator. When this decay channel is made active by tuning (BixSb1–x)2Te3 into a bulk insulator, amore » large electromotive force emerges in the direction perpendicular to the in-plane magnetization of yttrium iron garnet. Lastly, the enhanced, tunable SSE which occurs when the Fermi level lies in the bulk gap offers unique advantages over the usual SSE in metals and therefore opens up exciting possibilities in spintronics.« less
Enhanced spin Seebeck effect signal due to spin-momentum locked topological surface states
NASA Astrophysics Data System (ADS)
Jiang, Zilong; Chang, Cui-Zu; Masir, Massoud Ramezani; Tang, Chi; Xu, Yadong; Moodera, Jagadeesh S.; MacDonald, Allan H.; Shi, Jing
2016-05-01
Spin-momentum locking in protected surface states enables efficient electrical detection of magnon decay at a magnetic-insulator/topological-insulator heterojunction. Here we demonstrate this property using the spin Seebeck effect (SSE), that is, measuring the transverse thermoelectric response to a temperature gradient across a thin film of yttrium iron garnet, an insulating ferrimagnet, and forming a heterojunction with (BixSb1-x)2Te3, a topological insulator. The non-equilibrium magnon population established at the interface can decay in part by interactions of magnons with electrons near the Fermi energy of the topological insulator. When this decay channel is made active by tuning (BixSb1-x)2Te3 into a bulk insulator, a large electromotive force emerges in the direction perpendicular to the in-plane magnetization of yttrium iron garnet. The enhanced, tunable SSE which occurs when the Fermi level lies in the bulk gap offers unique advantages over the usual SSE in metals and therefore opens up exciting possibilities in spintronics.
Enhanced spin Seebeck effect signal due to spin-momentum locked topological surface states
Jiang, Zilong; Chang, Cui-Zu; Masir, Massoud Ramezani; Tang, Chi; Xu, Yadong; Moodera, Jagadeesh S.; MacDonald, Allan H.; Shi, Jing
2016-01-01
Spin-momentum locking in protected surface states enables efficient electrical detection of magnon decay at a magnetic-insulator/topological-insulator heterojunction. Here we demonstrate this property using the spin Seebeck effect (SSE), that is, measuring the transverse thermoelectric response to a temperature gradient across a thin film of yttrium iron garnet, an insulating ferrimagnet, and forming a heterojunction with (BixSb1−x)2Te3, a topological insulator. The non-equilibrium magnon population established at the interface can decay in part by interactions of magnons with electrons near the Fermi energy of the topological insulator. When this decay channel is made active by tuning (BixSb1−x)2Te3 into a bulk insulator, a large electromotive force emerges in the direction perpendicular to the in-plane magnetization of yttrium iron garnet. The enhanced, tunable SSE which occurs when the Fermi level lies in the bulk gap offers unique advantages over the usual SSE in metals and therefore opens up exciting possibilities in spintronics. PMID:27142594
Enhanced spin Seebeck effect signal due to spin-momentum locked topological surface states.
Jiang, Zilong; Chang, Cui-Zu; Masir, Massoud Ramezani; Tang, Chi; Xu, Yadong; Moodera, Jagadeesh S; MacDonald, Allan H; Shi, Jing
2016-05-04
Spin-momentum locking in protected surface states enables efficient electrical detection of magnon decay at a magnetic-insulator/topological-insulator heterojunction. Here we demonstrate this property using the spin Seebeck effect (SSE), that is, measuring the transverse thermoelectric response to a temperature gradient across a thin film of yttrium iron garnet, an insulating ferrimagnet, and forming a heterojunction with (BixSb1-x)2Te3, a topological insulator. The non-equilibrium magnon population established at the interface can decay in part by interactions of magnons with electrons near the Fermi energy of the topological insulator. When this decay channel is made active by tuning (BixSb1-x)2Te3 into a bulk insulator, a large electromotive force emerges in the direction perpendicular to the in-plane magnetization of yttrium iron garnet. The enhanced, tunable SSE which occurs when the Fermi level lies in the bulk gap offers unique advantages over the usual SSE in metals and therefore opens up exciting possibilities in spintronics.
Enhanced spin Seebeck effect signal due to spin-momentum locked topological surface states
Jiang, Zilong; Chang, Cui -Zu; Masir, Massoud Ramezani; Tang, Chi; Xu, Yadong; Moodera, Jagadeesh S.; MacDonald, Allan H.; Shi, Jing
2016-05-04
Spin-momentum locking in protected surface states enables efficient electrical detection of magnon decay at a magnetic-insulator/topological-insulator heterojunction. Here we demonstrate this property using the spin Seebeck effect (SSE), that is, measuring the transverse thermoelectric response to a temperature gradient across a thin film of yttrium iron garnet, an insulating ferrimagnet, and forming a heterojunction with (Bi_{x}Sb_{1–x})_{2}Te_{3}, a topological insulator. The non-equilibrium magnon population established at the interface can decay in part by interactions of magnons with electrons near the Fermi energy of the topological insulator. When this decay channel is made active by tuning (Bi_{x}Sb_{1–x})_{2}Te_{3} into a bulk insulator, a large electromotive force emerges in the direction perpendicular to the in-plane magnetization of yttrium iron garnet. Lastly, the enhanced, tunable SSE which occurs when the Fermi level lies in the bulk gap offers unique advantages over the usual SSE in metals and therefore opens up exciting possibilities in spintronics.
Mini-conference on Angular Momentum Transport in Laboratory and Nature
Ji, Hantao; Kronberg, Philipp; Prager, Stewart C.; Uzdensky, Dmitri A.
2008-05-06
This paper provides a concise summary of the current status of the research and future perspectives discussed in the Mini-Conference on Angular Momentum Transport in Laboratory and Nature. This Mini-conference, sponsored by the Topical Group on Plasma Astrophysics, was held as part of the American Physical Society's Division of Plasma Physics 2007 Annual Meeting (November 12{16, 2007). This Mini-conference covers a wide range of phenomena happening in fluids and plasmas, either in laboratory or in nature. The purpose of this paper is not to comprehensively review these phenomena, but to provide a starting point for interested readers to refer to related research in areas other than their own.
NASA Astrophysics Data System (ADS)
Obabko, Aleksandr V.; Cattaneo, Fausto; F Fischer, Paul
2008-12-01
We present numerical simulations of circular Couette flow in axisymmetric and fully three-dimensional geometry of a cylindrical annulus inspired by Princeton magnetorotational instability (MRI) liquid gallium experiment. The incompressible Navier-Stokes equations are solved with the spectral element code Nek5000 incorporating realistic horizontal boundary conditions of differentially rotating rings. We investigate the effect of changing rotation rates (Reynolds number) and of the horizontal boundary conditions on flow structure, Ekman circulation and associated transport of angular momentum through the onset of unsteadiness and three-dimensionality. A mechanism for the explanation of the dependence of the Ekman flows and circulation on horizontal boundary conditions is proposed. First International Conference 'Turbulent Mixing and Beyond' held on 18-26 August 2007 at the Abdus Salam International Centre for Theoretical Physics, Trieste, Italy.
Transport effects due to particle erosion mechanisms. [in planetary rings
NASA Technical Reports Server (NTRS)
Durisen, R. H.
1984-01-01
Various processes can erode the surfaces of planetary ring particles. Recent estimates for Saturn's rings suggest that a centimeter-thick surface layer could be eroded from an isolated ring particle in less than 1000 yr by meteoroid impacts alone. The atoms, molecules, and chips ejected from ring particles by erosion will arc across the rings along elliptical orbits. For moderate ring optical depths, ejecta will be absorbed or inelastically scattered upon reintersecting the ring plane. Continuous exchange of ejecta between different ring regions can lead to net radial transport of mass and angular momentum, to changes in particle sizes, and to the buildup of chip regoliths several centimeters deep on the surfaces of ring particles. Because most of the erosional ejecta are not lost but merely exchanged over short distances, the net erosion rate of the surfaces of these ring particles will be much less than that estimated for an isolated particle. Numerical solutions for time-dependent ballistic transport under various assumptions suggest pile-up and spillover effects especially near regions of preexisting high optical depth contrast, such as the inner edges of A and B rings. Global redistribution could be significant over billions of years. Other features in planetary ring systems may be influenced by ballistic transport.
Mass and momentum turbulent transport experiments with confined swirling coaxial jets. I
NASA Technical Reports Server (NTRS)
Johnson, B. V.; Roback, R.
1984-01-01
An experimental study of mixing downstream of swirling coaxial jets discharging into an expanded duct was conducted to obtain data for the evaluation and improvement of turbulent transport models currently used in a variety of computational procedures throughout the combustion community. A combination of laser velocimeter and laser induced fluorescence techniques was employed to obtain mean and fluctuating velocity and concentration distributions which were used to derive mass and momentum turbulent transport parameters currently incorporated into various combustor flow models. Flow visualization techniques were also employed to determine qualitatively the time dependent characteristics of the flow and the scale of turbulence. Mean and fluctuating velocity profiles and probability density functions were obtained at selected axial and radial locations throughout the flow field. Mixing occurred in several steps of axial and radial mass transport and was coupled with a large radial mean convective flux. Major mixing regions were observed to occur (1) at the interface between the inner stream and the centerline recirculation zone, and (2) at the interface between the inner jet and the annular jet streams. Mixing for swirling flow was completed in one-third the length required for nonswirling flow.
NASA Astrophysics Data System (ADS)
Mulders, Gijs D.; Pascucci, Ilaria; Manara, Carlo F.; Testi, Leonardo; Herczeg, Gregory J.; Henning, Thomas; Mohanty, Subhanjoy; Lodato, Giuseppe
2017-09-01
In this paper, we investigate the relation between disk mass and mass accretion rate to constrain the mechanism of angular momentum transport in protoplanetary disks. We find a correlation between dust disk mass and mass accretion rate in Chamaeleon I with a slope that is close to linear, similar to the one recently identified in Lupus. We investigate the effect of stellar mass and find that the intrinsic scatter around the best-fit {M}{dust}–{M}\\star and {\\dot{M}}{acc}–{M}\\star relations is uncorrelated. We simulate synthetic observations of an ensemble of evolving disks using a Monte Carlo approach and find that disks with a constant α viscosity can fit the observed relations between dust mass, mass accretion rate, and stellar mass but overpredict the strength of the correlation between disk mass and mass accretion rate when using standard initial conditions. We find two possible solutions. In the first one, the observed scatter in {M}{dust} and {\\dot{M}}{acc} is not primordial, but arises from additional physical processes or uncertainties in estimating the disk gas mass. Most likely grain growth and radial drift affect the observable dust mass, while variability on large timescales affects the mass accretion rates. In the second scenario, the observed scatter is primordial, but disks have not evolved substantially at the age of Lupus and Chamaeleon I owing to a low viscosity or a large initial disk radius. More accurate estimates of the disk mass and gas disk sizes in a large sample of protoplanetary disks, through either direct observations of the gas or spatially resolved multiwavelength observations of the dust with ALMA, are needed to discriminate between both scenarios or to constrain alternative angular momentum transport mechanisms such as MHD disk winds.
The Hilsch Tube, Rossby Vortices, and a Carnot Engine: Angular Momentum Transport in Astrophysics
NASA Astrophysics Data System (ADS)
Beckley, Howard F.; Klein, B.; Milburn, M.; Schindel, P.; Westpfahl, D. J.; Teare, S.; Li, H.; Colgate, S. A.
2008-05-01
We are attempting to demonstrate that the common laboratory vortex or Hilsch tube is a paradigm for the angular momentum transport by Rossby vortices in Keplerian accretion disks, either in super massive black hole formation or in star formation. Near supersonic rotating flow is induced in a cylinder by gas pressure injected through a tangential nozzle in a typical Ranque vortex or Hilsch tube. The gas exits through both an on-axis hole and a peripheral radially-aligned hole. The surprising result, demonstrated in hundreds of class rooms, is that one of the exit gas streams is hot and the other is cold. Depressing is that the typical explanation is given in terms of a "Maxwell daemon” that separates hot molecules from cold molecules, just as is the basis of any perpetual motion machine that violates the second law of thermodynamics. Instead we believe that the rotational flow is unstable to the formation of Rossby vortices that co-rotate with the azimuthal flow and act like semi-ridged turbine vanes. These quasi-vanes act like a Carnot turbine engine to the flow that escapes on axis and is therefore cooled by doing work. With the resulting free-energy, the vortices accelerate the peripheral flow which in turn becomes hot by friction with the cylinder wall. As a first step we expect to demonstrate that a free-running turbine, where metal vanes form the Carnot engine, will demonstrate the temperature effect. Such a suggestive result may lead to funding of time-dependent Schlerian photography of a vortex tube that can demonstrate the formation and pressure distribution of the Rossby vortices and coherent transport of angular momentum. This work is supported by a cooperative agreement between the New Mexico Institute of Mining and Technology, the University of California, Los Alamos National Laboratory, and the U.S. Dept. of Energy.
Transport in Nonneutral Plasmas due to Long-Range Collisions
NASA Astrophysics Data System (ADS)
Anderegg, F.; Driscoll, C. F.; Hollmann, E. M.; Kriesel, J. M.; Huang, X.-P.; Dubin, D. H. E.; O'Neil, T. M.
1997-11-01
Recent experiments on nonneutral plasmas have measured test particle transport, bulk viscous transport, and heat transport; all three measurements show enhanced transport due to long-range interactions. Classical Boltzmann theory describes transport in terms of short-range velocity-scattering collisions with impact parameters less than the cyclotron radius, i.e. ρ < r_c. Here we observe the effects of long-range collisions with rc < ρ applteq λ_D. Experiments show that: a) The measured test particle diffusion across B is about ten times faster than predicted by classical collisional theory, in precise agreement with long-range collisional theory over a wide range of parameters. b) Viscous transport measurements obtained from plasma density profiles relaxing to thermal equilibrium indicate that bulk particle transport across the magnetic field may be enhanced by up to 10^4. c) Preliminary measurements of heat transport created by localized laser cooling or heating indicate that the thermal conductivity can be much larger than predicted by classical theory, consistent with long-range theory. Supported by ONR N00014-96-1-0239 and NSF PHY94-21318. ^**Present address: NIST, 325 Broadway Ave., Boulder CO 80303.
ERIC Educational Resources Information Center
Natrajan, Vinay Kumar
2009-01-01
The impact of surface roughness on momentum and thermal transport in microscale flow passages of hydraulic diameter D[subscript h] = 600 micrometer is investigated in the laminar, transitional and turbulent flow regimes using microscopic PIV, two-color LIF thermometry and pressure-drop measurements. In addition to smooth-wall flow, two different…
ERIC Educational Resources Information Center
Natrajan, Vinay Kumar
2009-01-01
The impact of surface roughness on momentum and thermal transport in microscale flow passages of hydraulic diameter D[subscript h] = 600 micrometer is investigated in the laminar, transitional and turbulent flow regimes using microscopic PIV, two-color LIF thermometry and pressure-drop measurements. In addition to smooth-wall flow, two different…
NASA Astrophysics Data System (ADS)
Eggenberger, P.; Lagarde, N.; Miglio, A.; Montalbán, J.; Ekström, S.; Georgy, C.; Meynet, G.; Salmon, S.; Ceillier, T.; García, R. A.; Mathis, S.; Deheuvels, S.; Maeder, A.; den Hartogh, J. W.; Hirschi, R.
2017-02-01
Context. Constraints on the internal rotation of red giants are now available thanks to asteroseismic observations. Preliminary comparisons with rotating stellar models indicate that an undetermined additional process for the internal transport of angular momentum is required in addition to purely hydrodynamic processes. Aims: We investigate how asteroseismic measurements of red giants can help us characterize the additional transport mechanism. Methods: We first determine the efficiency of the missing transport mechanism for the low-mass red giant KIC 7341231 by computing rotating models that include an additional viscosity corresponding to this process. We then discuss the change in the efficiency of this transport of angular momentum with the mass, metallicity, and evolutionary stage in the light of the corresponding viscosity determined for the more massive red giant KIC 8366239. Results: In the case of the low-mass red giant KIC 7341231, we find that the viscosity corresponding to the additional mechanism is constrained to the range νadd = 1 × 103-1.3 × 104 cm2 s-1. This constraint on the efficiency of the unknown additional transport mechanism during the post-main sequence is obtained independently of any specific assumption about the modeling of rotational effects during the pre-main sequence and the main sequence (in particular, the braking of the surface by magnetized winds and the efficiency of the internal transport of angular momentum before the post-main-sequence phase). When we assume that the additional transport mechanism is at work during the whole evolution of the star together with a solar-calibrated braking of the surface by magnetized winds, the range of νadd is reduced to 1-4 × 103 cm2 s-1. In addition to being sensitive to the evolutionary stage of the star, the efficiency of the unknown process for internal transport of angular momentum increases with the stellar mass.
Waltz, R. E.; Staebler, G. M.; Solomon, W. M.
2011-04-15
Residual stress refers to the remaining toroidal angular momentum (TAM) flux (divided by major radius) when the shear in the equilibrium fluid toroidal velocity (and the velocity itself) vanishes. Previously [Waltz et al., Phys. Plasmas 14, 122507 (2007); errata 16, 079902 (2009)], we demonstrated with GYRO [Candy and Waltz, J. Comp. Phys. 186, 545 (2003)] gyrokinetic simulations that TAM pinching from (ion pressure gradient supported or diamagnetic level) equilibrium ExB velocity shear could provide some of the residual stress needed to support spontaneous toroidal rotation against normal diffusive loss. Here we show that diamagnetic level shear in the intrinsic drift wave velocities (or ''profile shear'' in the ion and electron density and temperature gradients) provides a comparable residual stress. The individual signed contributions of these small (rho-star level) ExB and profile velocity shear rates to the turbulence level and (rho-star squared) ion energy transport stabilization are additive if the rates are of the same sign. However because of the additive stabilization effect, the contributions to the small (rho-star cubed) residual stress is not always simply additive. If the rates differ in sign, the residual stress from one can buck out that from the other (and in some cases reduce the stabilization.) The residual stress from these diamagnetic velocity shear rates is quantified by the ratio of TAM flow to ion energy (power) flow (M/P) in a global GYRO core simulation of a ''null'' toroidal rotation DIII-D [Mahdavi and Luxon, Fusion Sci. Technol. 48, 2 (2005)] discharge by matching M/P profiles within experimental uncertainty. Comparison of global GYRO (ion and electron energy as well as particle) transport flow balance simulations of TAM transport flow in a high-rotation DIII-D L-mode quantifies and isolates the ExB shear and parallel velocity (Coriolis force) pinching components from the larger ''diffusive'' parallel velocity shear driven component and
Philippov, Alexander A.; Rafikov, Roman R.; Stone, James M.
2016-01-20
Disk accretion at a high rate onto a white dwarf (WD) or a neutron star has been suggested to result in the formation of a spreading layer (SL)—a belt-like structure on the object's surface, in which the accreted matter steadily spreads in the poleward (meridional) direction while spinning down. To assess its basic characteristics, we perform two-dimensional hydrodynamic simulations of supersonic SLs in the relevant morphology with a simple prescription for cooling. We demonstrate that supersonic shear naturally present at the base of the SL inevitably drives sonic instability that gives rise to large-scale acoustic modes governing the evolution of the SL. These modes dominate the transport of momentum and energy, which is intrinsically global and cannot be characterized via some form of local effective viscosity (e.g., α-viscosity). The global nature of the wave-driven transport should have important implications for triggering Type I X-ray bursts in low-mass X-ray binaries. The nonlinear evolution of waves into a system of shocks drives effective rearrangement (sensitively depending on thermodynamical properties of the flow) and deceleration of the SL, which ultimately becomes transonic and susceptible to regular Kelvin–Helmholtz instability. We interpret this evolution in terms of the global structure of the SL and suggest that mixing of the SL material with the underlying stellar fluid should become effective only at intermediate latitudes on the accreting object's surface, where the flow has decelerated appreciably. In the near-equatorial regions the transport is dominated by acoustic waves and mixing is less efficient. We speculate that this latitudinal nonuniformity of mixing in accreting WDs may be linked to the observed bipolar morphology of classical nova ejecta.
Final Technical Report for the Center for Momentum Transport and Flow Organization (CMTFO)
Forest, Cary B.; Tynan, George R.
2013-07-29
The Center for Momentum Transport and Flow Organization (CMTFO) is a DOE Plasma Science Center formed in late 2009 to focus on the general principles underlying momentum transport in magnetic fusion and astrophysical systems. It is composed of funded researchers from UCSD, UW Madison, U. Colorado, PPPL. As of 2011, UCSD supported postdocs are collaborating at MIT/Columbia and UC Santa Cruz and beginning in 2012, will also be based at PPPL. In the initial startup period, the Center supported the construction of two basic experiments at PPPL and UW Madison to focus on accretion disk hydrodynamic instabilities and solar physics issues. We now have computational efforts underway focused on understanding recent experimental tests of dynamos, solar tacholine physics, intrinsic rotation in tokamak plasmas and L-H transition physics in tokamak devices. In addition, we have the basic experiments discussed above complemented by work on a basic linear plasma device at UCSD and a collaboration at the LAPD located at UCLA. We are also performing experiments on intrinsic rotation and L-H transition physics in the DIII-D, NSTX, C-Mod, HBT EP, HL-2A, and EAST tokamaks in the US and China, and expect to begin collaborations on K-STAR in the coming year. Center funds provide support to over 10 postdocs and graduate students each year, who work with 8 senior faculty and researchers at their respective institutions. The Center has sponsored a mini-conference at the APS DPP 2010 meeting, and co-sponsored the recent Festival de Theorie (2011) with the CEA in Cadarache, and will co-sponsor a Winter School in January 2012 in collaboration with the CMSO-UW Madison. Center researchers have published over 50 papers in the peer reviewed literature, and given over 10 talks at major international meetings. In addition, the Center co-PI, Professor Patrick Diamond, shared the 2011 Alfven Prize at the EPS meeting. Key scientific results from this startup period include initial simulations of the
Center for Momentum Transport and Flow Organization (CMTFO). Final technical report
Tynan, George R.; Diamond, P. H.; Ji, H.; Forest, C. B.; Terry, P. W.; Munsat, T.; Brummell, N.
2013-07-29
The Center for Momentum Transport and Flow Organization (CMTFO) is a DOE Plasma Science Center formed in late 2009 to focus on the general principles underlying momentum transport in magnetic fusion and astrophysical systems. It is composed of funded researchers from UCSD, UW Madison, U. Colorado, PPPL. As of 2011, UCSD supported postdocs are collaborating at MIT/Columbia and UC Santa Cruz and beginning in 2012, will also be based at PPPL. In the initial startup period, the Center supported the construction of two basic experiments at PPPL and UW Madison to focus on accretion disk hydrodynamic instabilities and solar physics issues. We now have computational efforts underway focused on understanding recent experimental tests of dynamos, solar tachocline physics, intrinsic rotation in tokamak plasmas and L-H transition physics in tokamak devices. In addition, we have the basic experiments discussed above complemented by work on a basic linear plasma device at UCSD and a collaboration at the LAPD located at UCLA. We are also performing experiments on intrinsic rotation and L-H transition physics in the DIII-D, NSTX, C-Mod, HBT EP, HL-2A, and EAST tokamaks in the US and China, and expect to begin collaborations on K-STAR in the coming year. Center funds provide support to over 10 postdocs and graduate students each year, who work with 8 senior faculty and researchers at their respective institutions. The Center has sponsored a mini-conference at the APS DPP 2010 meeting, and co-sponsored the recent Festival de Theorie (2011) with the CEA in Cadarache, and will co-sponsor a Winter School in January 2012 in collaboration with the CMSO-UW Madison. Center researchers have published over 50 papers in the peer reviewed literature, and given over 10 talks at major international meetings. In addition, the Center co-PI, Professor Patrick Diamond, shared the 2011 Alfven Prize at the EPS meeting. Key scientific results from this startup period include initial simulations of the
NASA Astrophysics Data System (ADS)
Kuritsyn, A.; Fiksel, G.; Almagri, A. F.; Brower, D. L.; Ding, W. X.; Miller, M. C.; Mirnov, V. V.; Prager, S. C.; Sarff, J. S.
2009-05-01
In this paper measurements of momentum and current transport caused by current driven tearing instability are reported. The measurements are done in the Madison Symmetric Torus reversed-field pinch [R. N. Dexter, D. W. Kerst, T. W. Lovell, S. C. Prager, and J. C. Sprott, Fusion Technol. 19, 131 (1991)] in a regime with repetitive bursts of tearing instability causing magnetic field reconnection. It is established that the plasma parallel momentum profile flattens during these reconnection events: The flow decreases in the core and increases at the edge. The momentum relaxation phenomenon is similar in nature to the well established relaxation of the parallel electrical current and could be a general feature of self-organized systems. The measured fluctuation-induced Maxwell and Reynolds stresses, which govern the dynamics of plasma flow, are large and almost balance each other such that their difference is approximately equal to the rate of change of plasma momentum. The Hall dynamo, which is directly related to the Maxwell stress, drives the parallel current profile relaxation at resonant surfaces at the reconnection events. These results qualitatively agree with analytical calculations and numerical simulations. It is plausible that current-driven instabilities can be responsible for momentum transport in other laboratory and astrophysical plasmas.
1. Transport of Mass, Momentum and Energy in Planetary Magnetodisc Regions
NASA Astrophysics Data System (ADS)
Achilleos, Nicholas; André, Nicolas; Blanco-Cano, Xochitl; Brandt, Pontus C.; Delamere, Peter A.; Winglee, Robert
2015-04-01
the rate at which plasma mass and momentum are added to the magnetodisc. Following this, we describe the observational properties of plasma injections, and the consequent implications for the nature of global plasma transport and magnetodisc stability. The theory of the flux tube interchange instability is reviewed, and the influences of gravity and magnetic curvature on the instability are described. The interaction between simulated interchange plasma structures and Saturn's moon Titan is discussed, and its relationship to observed periodic phenomena at Saturn is described. Finally, the observation, generation and evolution of plasma waves associated with mass loading in the magnetodisc regions is reviewed.
NASA Astrophysics Data System (ADS)
Horing, N. J. M.; Lei, X. L.; Cui, H. L.
1986-05-01
A dielectric interpretation of the nonlinear Lei-Ting force-momentum-balance transport equation for steady-state dc current flow is developed here in correspondence with standard techniques for calculating fast-particle energy loss to a plasmalike medium. In conjunction with this we interpret the result to be an isothermal resistivity calculated to lowest order in the impurity scattering potentials, isothermal in the sense that all energy dissipated is removed from the system, essentially instantaneously as it is generated, by a heat bath in contact with the system which maintains it at constant temperature throughout the nonlinear dc conduction process. On the basis of its isothermal character, we argue that the Lei-Ting dc resistivity calculated to lowest order in the impurity scattering potentials-whose linear limit is significantly different from the corresponding linear resistivity of an adiabatic character (for a system admitting no drainoff of dissipated energy, developing under a purely mechanical Hamiltonian)-is immune to serious critical objections of the type brought by Argyres and Sigel against similar lowest-order adiabatic linear resistivity calculations some time ago. Moreover, we also show that a dielectric Lei-Ting type formulation of linearized ac resistivity leads to the standard high-frequency linear resistivity formula, and that its zero-frequency limit naturally yields the isothermal dc linear Lei-Ting resistivity.
NASA Astrophysics Data System (ADS)
Belyaev, Mikhail A.; Rafikov, Roman R.; Stone, James M.
2012-11-01
Disk accretion onto a weakly magnetized central object, e.g., a star, is inevitably accompanied by the formation of a boundary layer near the surface, in which matter slows down from the highly supersonic orbital velocity of the disk to the rotational velocity of the star. We perform high-resolution two-dimensional hydrodynamical simulations in the equatorial plane of an astrophysical boundary layer with the goal of exploring the dynamics of non-axisymmetric structures that form there. We generically find that the supersonic shear in the boundary layer excites non-axisymmetric quasi-stationary acoustic modes that are trapped between the surface of the star and a Lindblad resonance in the disk. These modes rotate in a prograde fashion, are stable for hundreds of orbital periods, and have a pattern speed that is less than and of the order of the rotational velocity at the inner edge of the disk. The origin of these intrinsically global modes is intimately related to the operation of a corotation amplifier in the system. Dissipation of acoustic modes in weak shocks provides a universal mechanism for angular momentum and mass transport even in purely hydrodynamic (i.e., non-magnetized) boundary layers. We discuss the possible implications of these trapped modes for explaining the variability seen in accreting compact objects.
Belyaev, Mikhail A.; Stone, James M.; Rafikov, Roman R.
2012-11-20
Disk accretion onto a weakly magnetized central object, e.g., a star, is inevitably accompanied by the formation of a boundary layer near the surface, in which matter slows down from the highly supersonic orbital velocity of the disk to the rotational velocity of the star. We perform high-resolution two-dimensional hydrodynamical simulations in the equatorial plane of an astrophysical boundary layer with the goal of exploring the dynamics of non-axisymmetric structures that form there. We generically find that the supersonic shear in the boundary layer excites non-axisymmetric quasi-stationary acoustic modes that are trapped between the surface of the star and a Lindblad resonance in the disk. These modes rotate in a prograde fashion, are stable for hundreds of orbital periods, and have a pattern speed that is less than and of the order of the rotational velocity at the inner edge of the disk. The origin of these intrinsically global modes is intimately related to the operation of a corotation amplifier in the system. Dissipation of acoustic modes in weak shocks provides a universal mechanism for angular momentum and mass transport even in purely hydrodynamic (i.e., non-magnetized) boundary layers. We discuss the possible implications of these trapped modes for explaining the variability seen in accreting compact objects.
Secondary Flows and Sediment Transport due to Wave - Current Interaction
NASA Astrophysics Data System (ADS)
Ismail, Nabil; Wiegel, Robert
2015-04-01
Objectives: The main purpose of this study is to determine the modifications of coastal processes driven by wave-current interaction and thus to confirm hydrodynamic mechanisms associated with the interaction at river mouths and tidal inlets where anthropogenic impacts were introduced. Further, the aim of the work has been to characterize the effect of the relative strength of momentum action of waves to the opposing current on the nearshore circulation where river flow was previously effective to entrain sediments along the shoreline. Such analytical information are useful to provide guidelines for sustainable design of coastal defense structures. Methodology and Analysis: Use is made of an earlier study reported by the authors (1983) on the interaction of horizontal momentum jets and opposing shallow water waves at shorelines, and of an unpublished laboratory study (1980). The turbulent horizontal discharge was shore-normal, directed offshore, and the incident wave direction was shore-normal, travelling toward shore. Flow visualization at the smooth bottom and the water surface, velocity and water surface elevation measurements were made. Results were obtained for wave , current modifications as well as the flow pattern in the jet and the induced circulation on both sides of the jet, for a range of wave and jet characteristics. The experimental data, obtained from measurement in the 3-D laboratory basin, showed several distinct flow pattern regimes on the bottom and the water surface. The observed flow circulation regimes were found to depend on the ratio of the wave momentum action on the jet to the jet initial momentum. Based on the time and length scales of wave and current parameters and using the time average of the depth integrated conservation equations, it is found that the relative strength of the wave action on the jet could be represented by a dimensionless expression; Rsm ( ) 12ρSa20g-L0h-Cg- 2 Rsm ≈ (C0 - U) /ρ0U w (1) In the above dimensionless
NASA Astrophysics Data System (ADS)
Waltz, R. E.; Staebler, G. M.; Solomon, W. M.
2011-04-01
Residual stress refers to the remaining toroidal angular momentum (TAM) flux (divided by major radius) when the shear in the equilibrium fluid toroidal velocity (and the velocity itself) vanishes. Previously [Waltz et al., Phys. Plasmas 14, 122507 (2007); errata 16, 079902 (2009)], we demonstrated with GYRO [Candy and Waltz, J. Comp. Phys. 186, 545 (2003)] gyrokinetic simulations that TAM pinching from (ion pressure gradient supported or diamagnetic level) equilibrium E ×B velocity shear could provide some of the residual stress needed to support spontaneous toroidal rotation against normal diffusive loss. Here we show that diamagnetic level shear in the intrinsic drift wave velocities (or "profile shear" in the ion and electron density and temperature gradients) provides a comparable residual stress. The individual signed contributions of these small (rho-star level) E ×B and profile velocity shear rates to the turbulence level and (rho-star squared) ion energy transport stabilization are additive if the rates are of the same sign. However because of the additive stabilization effect, the contributions to the small (rho-star cubed) residual stress is not always simply additive. If the rates differ in sign, the residual stress from one can buck out that from the other (and in some cases reduce the stabilization.) The residual stress from these diamagnetic velocity shear rates is quantified by the ratio of TAM flow to ion energy (power) flow (M/P) in a global GYRO core simulation of a "null" toroidal rotation DIII-D [Mahdavi and Luxon, Fusion Sci. Technol. 48, 2 (2005)] discharge by matching M/P profiles within experimental uncertainty. Comparison of global GYRO (ion and electron energy as well as particle) transport flow balance simulations of TAM transport flow in a high-rotation DIII-D L-mode quantifies and isolates the E ×B shear and parallel velocity (Coriolis force) pinching components from the larger "diffusive" parallel velocity shear driven component and
Burrell, K.H.; Groebner, R.J.; Carlstrom, T.N.; Lohr, J.; Sager, G.; St. John, H.; Seraydarian, R.P.; Schissel, D.P. ); Kurki-Suonio, T. ); Matsumoto, M. ); Wolfe, S.M. )
1990-06-01
We have carried out experiments using the hot-ion mode of operation to compare the bulk transport in L-mode and H-mode discharges. These experiments have demonstrated that the confinement improvement in the bulk of the plasma in DIII-D is due to a simultaneous improvement in electron and ion energy transport. In addition, the magnitude of electron and ion thermal diffusivities and angular momentum diffusivity as well as the change in these quantities between L- and H-mode have allowed us to place significant constraints on theories of tokamak transport. Although the most obvious improvement in confinement at the L to H transition occurs at the plasma edge, there is also a significant improvement in local energy transport throughout the plasma. Most of the previous experiments in this area made their comparison between L-mode and H-mode plasmas at significantly different densities. This could have affected the results if the local transport depends on density. The work by Jahns, et al. was done at the same line-averaged density; they still found a significant improvement in local transport, although they were not able to determine whether the improvement occurred in the electron or ion channel. We have extended the work of Jahns, et al. to hot-ion conditions where we can separately study the power flow in the electron and ion channels. We have made detailed comparisons of energy and angular momentum transport between deuterium L- and H-mode plasmas with the same density (3.5 {times} 10{sup 19} m{sup {minus}3}), the same current (1 MA), the same toroidal field (2.1 T), the same deuterium neutral beam input power (8.7 MW), and very similar internal flux surface shapes. 6 figs.
Camenen, Y; Bortolon, A; Duval, B P; Federspiel, L; Peeters, A G; Casson, F J; Hornsby, W A; Karpushov, A N; Piras, F; Sauter, O; Snodin, A P; Szepesi, G
2010-09-24
The first experimental evidence of parallel momentum transport generated by the up-down asymmetry of a toroidal plasma is reported. The experiments, conducted in the Tokamak à Configuration Variable, were motivated by the recent theoretical discovery of ion-scale turbulent momentum transport induced by an up-down asymmetry in the magnetic equilibrium. The toroidal rotation gradient is observed to depend on the asymmetry in the outer part of the plasma leading to a variation of the central rotation by a factor of 1.5-2. The direction of the effect and its magnitude are in agreement with theoretical predictions for the eight possible combinations of plasma asymmetry, current, and magnetic field.
Charge accumulation due to spin transport in magnetic multilayers
NASA Astrophysics Data System (ADS)
Zhu, Yao-Hui; Xu, Deng-Hui; Geng, Ai-Cong
2014-08-01
Starting with the Valet-Fert theory of the current-perpendicular-to-plane giant magnetoresistance, we studied the charge accumulation due to spin transport in magnetic multilayers by solving Poisson's equation analytically. Our results show that, in ferromagnetic layers, the charge accumulation has two exponential terms with opposite signs and different decaying lengths: the Thomas-Fermi screening length (on the order of angstrom) and the spin diffusion length (tens of nm in 3d ferromagnetic metals). The charge accumulation on the scale of the screening length is spin-unpolarized and also present in spin-independent transport in nonmagnetic multilayers. However, the charge accumulation on the scale of the spin diffusion length is spin-polarized and shows up only in ferromagnetic layers. Our analysis also provides new insights into the widely used quasi-neutrality approximation, which neglects the charge accumulation.
Impurity transport due to electromagnetic drift wave turbulence
NASA Astrophysics Data System (ADS)
Moradi, Sara; Pusztai, Istvan; Mollén, Albert; Fülöp, Tünde
2012-10-01
In the view of an increasing interest in high β operation scenarios, such as hybrid scenarios for ITER the question of finite β effects on the impurity transport is a critical issue due to possible fuel dilution and radiative cooling in the core. Here, electromagnetic effects at finite β on impurity transport are studied through local linear gyro-kinetic simulations with gyro [J. Candy and E. Belli, General Atomics Report GA-A26818 (2011)]; in particular we investigate the parametric dependences of the impurity peaking factor (zero-flux density gradient) and the onset of the kinetic ballooning modes (KBM) and micro-tearing modes (MTM) in spherical (NSTX) and standard tokamaks (AUG and JET).
NASA Astrophysics Data System (ADS)
Fisch, N. J.; Gladush, M. G.; Petrushevich, Y. V.; Quarati, P.; Starostin, A. N.
2012-06-01
This study concerns a situation when measurements of the nonresonant cross-section of nuclear reactions appear highly dependent on the environment in which the particles interact. An appealing example discussed in the paper is the interaction of a deuteron beam with a target of deuterated metal Ta. In these experiments, the reaction cross section for d(d, p)t was shown to be orders of magnitude greater than what the conventional model predicts for the low-energy particles. In this paper we take into account the influence of quantum effects due to the Heisenberg uncertainty principle for particles in a non-ideal plasma medium elastically interacting with the medium particles. In order to calculate the nuclear reaction rate in the non-ideal environment we apply both the Monte Carlo technique and approximate analytical calculation of the Feynman diagram using nonrelativistic kinetic Green's functions in the medium which correspond to the generalized energy and momentum distribution functions of interacting particles. We show a possibility to reduce the 12-fold integral corresponding to this diagram to a fivefold integral. This can significantly speed up the computation and control accuracy. Our calculations show that quantum effects significantly influence reaction rates such as p +7Be, 3He +4He, p +7Li, and 12C +12C. The new reaction rates may be much higher than the classical ones for the interior of the Sun and supernova stars. The possibility to observe the theoretical predictions under laboratory conditions is discussed.
Transport of runaway and thermal electrons due to magnetic microturbulence
Mynick, H.E.; Strachan, J.D.
1981-04-01
The ratio of the runaway electron confinement to thermal electron energy confinement is derived for tokamaks where both processes are determined by free streaming along stochastic magnetic field lines. The runaway electron confinement is enhanced at high runaway electron energies due to phase averaging over the magnetic perturbations when the runaway electron drift surfaces are displaced from the magnetic surfaces. Comparison with experimental data from LT-3, Ormak, PLT, ST, and TM-3 indicates that magnetic stochasticity may explain the relative transport rates of runaways and thermal electron energy.
Cross-shelf transport and dispersion due to baroclinic instabilities
NASA Astrophysics Data System (ADS)
Thyng, Kristen; Hetland, Robert
2014-05-01
The dominant forcing mechanisms for the circulation in the northwestern Gulf of Mexico are largely determined by location relative to the shelf break. On the inner shelf, the flow is mostly controlled by the wind and on the outer shelf is affected by the mesoscale loop-current eddies. However, in the summer, baroclinic instabilities can develop along the boundary of the mid-shelf river plume front, leading to large eddies (~50 km length scale) that can reach across the entire shelf and strongly affect the local flow field. These instabilities advect fresher water toward the shelf edge and pull denser water back toward the coast. The details of how the flow crosses between these two regimes is of interest because it controls the flux of river-borne biogeochemical properties to the deep ocean, as well as for the potential onshore transport of oil from offshore spills. We approach this problem using a high resolution numerical model of the Texas-Louisiana shelf run using the Regional Ocean Modeling System (ROMS) and a Lagrangian particle tracking model (TRACMASS). By initializing drifters at the sources of fresh water (the Atchafalaya and Mississippi rivers) in the numerical model, we are able to explicitly track its trajectory through the numerical domain in time. These trajectories can then be used to characterize the cross-shelf transport and lateral dispersion due to the instabilities caused by the presence of the fresher water. We expect the transport and dispersion to be enhanced when compared with these quantities at other times of the year when the instabilities are not present, as well as with other regions of the shelf break that are farther from the plume edge area. Additionally, an idealized numerical model of a shelf break with both horizontal and vertical density gradients has been run through relevant parameter spaces to examine the range of baroclinic instabilities. Drifters are run in these simulations for comparison of transport and dispersion with
NASA Astrophysics Data System (ADS)
Coppi, B.
2007-11-01
Differentially rotating structures in the prevalent field of a central object have been shown to develop a ``crystal'' magnetic structure resulting from toroidal internal currents and leading to the formation of density ring sequencesootnotetextB. Coppi and F. Rousseau, Ap. J. 641, 458 (2006) rather than disks. Poloidal current densities with appropriate symmetries are found to be connected with angular momentum transport processes represented by an effective viscosity. Jets are suggested to consist of a series of stable ``smoke- rings'' ejected vertically in opposite directions from the central region of the considered ring sequence. A small inward flow velocity is shown to induce a spiral pattern in the magnetic field lines on a selected family of magnetic surfaces. The accretion theoryootnotetextB. Coppi, Nuc. Fus. 42, 1 (2002) of the spontaneous rotation phenomenon in toroidal laboratory plasmas relies on the ejection of angular momentum toward the surrounding material wall, by collisional ballooning modes excited at the edge, whose phase velocity depends on collisionality. The resulting recoil gives rise to the rotation of the main body of the plasma column as other plasma modes (called VTG) provide the needed inward transport of angular momentum. *Sponsored in part by the US D.O.E.
Lee, J. P.; Wright, J. C.; Bonoli, P. T.; Parker, R. R.; Catto, P. J.; Podpaly, Y. A.; Rice, J. E.; Reinke, M. L.
2011-12-23
Significant ion toroidal rotation (50km/s) has been measured by X-Ray spectroscopy for impurities in Alcator C-Mod during lower hybrid (LH) RF power injection. We investigate the relation between the computed toroidal momentum input from LH waves and the measured INITIAL change of ion toroidal rotation when the LH power is turned on. The relation may depend on the plasma current and magnetic configuration. Because of the fast build up time of the electron quasilinear plateau (<1 millisecond), the electron distribution function rapidly reaches steady state in which the electrons transfer momentum to the ions. The LH wave momentum input is computed from the self consistent steady state electron distribution function and a bounce-averaged quasilinear diffusion coefficient that are obtained by iterating a full wave code (TORLH) with a Fokker Plank code (CQL3D)
Momentum transport in the solar wind erosion of the Mars ionosphere
NASA Astrophysics Data System (ADS)
Pérez-de-Tejada, H.
1998-12-01
Measurements in the Mars plasma environment indicate that a friction layer develops between the solar wind and that planet's ionosphere. The observed features include a velocity boundary layer in the solar wind that streams around the flanks of the Mars ionosphere and enhanced planetary particle fluxes detected when the solar wind speed decreases to low values within the boundary layer. It is suggested that a cold plasma flow is present in the tenuous Mars upper ionosphere and that its momentum is provided by the solar wind within the adjacent velocity boundary layer. Calculations are presented to estimate the momentum flux that is delivered to the Mars upper ionosphere. It is argued that an ionospheric flow can be driven by solar wind momentum transferred from a velocity boundary layer whose thickness is 100-200 km around the terminator. By comparison a dense early Mars ionosphere could have been eroded by the momentum flux delivered from a ~1000 km thick boundary layer which would be comparable to that present around the Venus ionosphere. The total mass loss eroded by this process through Martian history should have not been larger than that of a few meters-deep global layer of water. It is further suggested that the erosion of the Mars ionosphere is not axially symmetric around the terminator but should preferably occur over the magnetic polar regions of the ionosphere.
NASA Astrophysics Data System (ADS)
Mishra, S.; Chakraborty, S.; DebRoy, T.
2005-05-01
A transport phenomena-based mathematical model is developed to understand liquation cracking in weldments during fusion welding. Equations of conservation of mass, momentum, heat, and solute transport are numerically solved considering nonequilibrium solidification and filler metal addition to determine the solid and liquid phase fractions in the solidifying region and the solute distribution in the weld pool. An effective partition coefficient that considers the local interface velocity and the undercooling is used to simulate solidification during welding. The calculations show that convection plays a dominant role in the solute transport inside the weld pool. The predicted weld-metal solute content agreed well with the independent experimental observations. The liquation cracking susceptibility in Al-Cu alloy weldments could be reliably predicted by the model based on the computed solidifying weld-metal composition and solid fraction considering nonequilibrium solidification.
Li, C H; van 't Erve, O M J; Robinson, J T; Liu, Y; Li, L; Jonker, B T
2014-03-01
Topological insulators exhibit metallic surface states populated by massless Dirac fermions with spin-momentum locking, where the carrier spin lies in-plane, locked at right angles to the carrier momentum. Here, we show that a charge current produces a net spin polarization via spin-momentum locking in Bi2Se3 films, and this polarization is directly manifested as a voltage on a ferromagnetic contact. This voltage is proportional to the projection of the spin polarization onto the contact magnetization, is determined by the direction and magnitude of the charge current, scales inversely with Bi2Se3 film thickness, and its sign is that expected from spin-momentum locking rather than Rashba effects. Similar data are obtained for two different ferromagnetic contacts, demonstrating that these behaviours are independent of the details of the ferromagnetic contact. These results demonstrate direct electrical access to the topological insulators' surface-state spin system and enable utilization of its remarkable properties for future technological applications.
Transport of parallel momentum induced by current-symmetry breaking in toroidal plasmas.
Camenen, Y; Peeters, A G; Angioni, C; Casson, F J; Hornsby, W A; Snodin, A P; Strintzi, D
2009-03-27
The symmetry of a physical system strongly impacts on its properties. In toroidal plasmas, the symmetry along a magnetic field line usually constrains the radial flux of parallel momentum to zero in the absence of background flows. By breaking the up-down symmetry of the toroidal currents, this constraint can be relaxed. The parallel asymmetry in the magnetic configuration then leads to an incomplete cancellation of the turbulent momentum flux across a flux surface. The magnitude of the subsequent toroidal rotation increases with the up-down asymmetry and its sign depends on the direction of the toroidal magnetic field and plasma current. Such a mechanism offers new insights in the interpretation and control of the intrinsic toroidal rotation in present day experiments.
The Center for Momentum Transport and Flow Organization in Plasmas - Final Scientific Report
Munsat, Tobin
2015-12-14
Overview of University of Colorado Efforts: The University of Colorado group has focused on two primary fronts during the grant period: development of a variety of multi-point diagnostic and/or imaging analysis techniques, and momentum-transport related experiments on a variety of devices (NSTX at PPPL, CSDX at UCSD, LAPD at UCLA, DIII-D at GA). Experimental work has taken advantage of several diagnostic instruments, including fast-framing cameras for imaging of electron density fluctuations (either directly or using injected gas puffs), ECEI for imaging of electron temperature fluctuations, and multi-tipped Langmuir and magnetic probes for corroborating measurements of Reynolds and Maxwell stresses. Mode Characterization in CSDX: We have performed a series of experiments at the CSDX linear device at UCSD, in collaboration with Center PI G. Tynan's group. The experiments included a detailed study of velocity estimation techniques, including direct comparisons between Langmuir probes and image-based velocimetry from fast-framing camera data. We used the camera data in a second set of studies to identify the spatial and spectral structure of coherent modes, which illuminates wave behavior to a level of detail previously unavailable, and enables direct comparison of dispersion curves to theoretical estimates. In another CSDX study, similar techniques were used to demonstrate a controlled transition from nonlinearly coupled discrete eigenmodes to fully developed broadband turbulence. The axial magnetic field was varied from 40-240 mT, which drove the transition. At low magnetic fields, the plasma is dominated by drift waves. As the magnetic field is increased, a strong potential gradient at the edge introduces an ExB shear-driven instability. At the transition, another mode with signatures of a rotation-induced Rayleigh–Taylor instability appears at the central plasma region. Concurrently, large axial velocities were found in the plasma core. For larger magnetic
NASA Astrophysics Data System (ADS)
Aceves, H.; Reyes-Ruiz, M.; Trejo, D. M.; Perez De Tejada, H. A.
2011-12-01
We study the development of the two-stream plasma instability, and the ensuing momentum transfer between species, in a four component plasma. The system is taken to represent the interaction of heavy ions and electrons of planetary origin, assumed to be initially at rest, and a stream of protons and electrons representing the solar wind. A stability criterion in terms of solar wind and ionospheric plasma parameters, namely density and temperature as well as the solar wind streaming velocity, is derived from a linear analysis of the coupled fluid equations of motion for all species. The nonlinear development of the instability is studied using a particle plasma code developed by our group. A heuristic estimation of momentum transfer between species is compared with the value derived from the acceleration of the planetary ions resulting in our numerical simulations.
NASA Astrophysics Data System (ADS)
Muñoz, Joseph A.; Furlanetto, Steven
2012-11-01
We develop a radiation pressure-balanced model for the interstellar medium of high-redshift galaxies that describes many facets of galaxy formation at z ≳ 6, including star formation rates and distributions and gas accretion on to central black holes. We first show that the vertical gravitational force in the disc of such a model is dominated by the disc self-gravity supported by the radiation pressure of ionizing starlight on gas. Constraining our model to reproduce the UV luminosity function of Lyman-break galaxies (LBGs), we limit the available parameter space to wind mass-loading factors one to four times the canonical value for momentum-driven winds. We then focus our study by exploring the effects of different angular momentum transport mechanisms in the galactic disc and find that accretion driven by gravitational torques, such as from linear spiral waves or non-linear orbit crossings, can build up black hole masses by z = 6 consistent with the canonical M-σ relation with a duty cycle of unity, while accretion mediated by a local viscosity such as in an α-disc results in negligible black hole (BH) accretion. Both gravitational torque models produce X-ray emission from active galactic nuclei (AGN) in high-redshift LBGs in excess of the estimated contribution from high-mass X-ray binaries. Using a recent analysis of deep Chandra observations by Cowie et al., we can already begin to rule out the most extreme regions of our parameter space: the inflow velocity of gas through the disc must either be less than one per cent of the disc circular velocity or the X-ray luminosity of the AGN must be substantially obscured. Moderately deeper future observations or larger sample sizes will be able to probe the more reasonable range of angular momentum transport models and obscuring geometries.
NASA Astrophysics Data System (ADS)
Jovanović, J. V.; Vrhovac, S. B.
2004-12-01
In this paper we have presented two applications of Momentum Transfer Theory (MTT), which were both aimed at obtaining reliable data for modeling of non-equilibrium plasma. Transport properties of ion swarms in presence of Resonant Charge Transfer (RCT) collisions are studied using Momentum Transfer Theory (MTT). Using the developed MTT we tested a previously available anisotropic set of cross-sections for Ar++Ar collisions bay making the comparisons with the available data for the transverse diffusion coefficient. We also developed an anisotropic set of Ne++Ne integral cross-sections based on the available data for mobility, longitudinal and transverse diffusion. Anisotropic sets of cross-sections are needed for Monte Carlo simulations of ion transport and plasma models. Application of Blanc's Law for drift velocities of electrons and ions in gas mixtures at arbitrary reduced electric field strenghts E/n0 was studied theoretically and by numerical examples. Corrections for Blanc's Law that include effects of inelastic collisions were derived. In addition we have derived the common mean energy procedure that was proposed by Chiflikian in a general case both for ions and electrons. Both corrected common E/n0 and common mean energy procedures provide excellent results even for electrons at moderate E/n0 where application of Blanc's Law was regarded as impossible. In mixtures of two gases that have negative differential conductivity (NDC) even when neither of the two pure gases show NDC the Blanc's Law procedure was able to give excellent predictions.
Jovanovic, J.V.; Vrhovac, S. B.
2004-12-01
In this paper we have presented two applications of Momentum Transfer Theory (MTT), which were both aimed at obtaining reliable data for modeling of non-equilibrium plasma. Transport properties of ion swarms in presence of Resonant Charge Transfer (RCT) collisions are studied using Momentum Transfer Theory (MTT). Using the developed MTT we tested a previously available anisotropic set of cross-sections for Ar++Ar collisions bay making the comparisons with the available data for the transverse diffusion coefficient. We also developed an anisotropic set of Ne++Ne integral cross-sections based on the available data for mobility, longitudinal and transverse diffusion. Anisotropic sets of cross-sections are needed for Monte Carlo simulations of ion transport and plasma models. Application of Blanc's Law for drift velocities of electrons and ions in gas mixtures at arbitrary reduced electric field strengths E/n0 was studied theoretically and by numerical examples. Corrections for Blanc's Law that include effects of inelastic collisions were derived. In addition we have derived the common mean energy procedure that was proposed by Chiflikian in a general case both for ions and electrons. Both corrected common E/n0 and common mean energy procedures provide excellent results even for electrons at moderate E/n0 where application of Blanc's Law was regarded as impossible. In mixtures of two gases that have negative differential conductivity (NDC) even when neither of the two pure gases show NDC the Blanc's Law procedure was able to give excellent predictions.
Transport of orbital-angular-momentum entanglement through a turbulent atmosphere.
Pors, Bart-Jan; Monken, C H; Eliel, Eric R; Woerdman, J P
2011-03-28
We demonstrate experimentally how orbital-angular-momentum entanglement of two photons evolves under the influence of atmospheric turbulence. Experimental results are in excellent agreement with our theoretical model, which combines the formalism of two-photon coincidence detection with a Kolmogorov description of atmospheric turbulence. We express the robustness to turbulence in terms of the dimensionality of the measured correlations. This dimensionality is surprisingly robust: scaling up our system to real-life dimensions, a horizontal propagation distance of 2 km seems viable.
Thermo-electric transport in gauge/gravity models with momentum dissipation
NASA Astrophysics Data System (ADS)
Amoretti, Andrea; Braggio, Alessandro; Maggiore, Nicola; Magnoli, Nicodemo; Musso, Daniele
2014-09-01
We present a systematic definition and analysis of the thermo-electric linear response in gauge/gravity systems focusing especially on models with massive gravity in the bulk and therefore momentum dissipation in the dual field theory. A precise treatment of finite counter-terms proves to be essential to yield a consistent physical picture whose hydrodynamic and beyond-hydrodynamics behaviors noticeably match with field theoretical expectations. The model furnishes a possible gauge/gravity description of the crossover from the quantum-critical to the disorder-dominated Fermi-liquid behaviors, as expected in graphene.
NASA Astrophysics Data System (ADS)
Yamamoto, Masaru; Takahashi, Masaaki
2016-04-01
A high significance of planetary rotation and poleward eddy heat fluxes is determined for general circulation driven by baroclinic forcing due to cloud layer heating. In a high-resolution simplified Venus general circulation model, a planetary-scale mixed Rossby-gravity wave with meridional winds across the poles produces strong poleward heat flux and indirect circulation. This strong poleward heat transport induces downward momentum transport of indirect cells in the regions of weak high-latitude jets. It also reduces the meridional temperature gradient and vertical shear of the high-latitude jets in accordance with the thermal wind relation below the cloud layer. In contrast, strong equatorial superrotation and midlatitude jets form in the cloud layer in the absence of polar indirect cells in an experiment involving Titan's rotation. Both the strong midlatitude jet and meridional temperature gradient are maintained in the situation that eddy horizontal heat fluxes are weak. The presence or absence of strong poleward eddy heat flux is one of the important factors determining the slow or fast superrotation state in the cloud layer through the downward angular momentum transport and the thermal wind relation. For fast Earth rotation, a weak global-scale Hadley circulation of the low-density upper atmosphere maintains equatorial superrotation and midlatitude jets above the cloud layer, whereas multiple meridional circulations suppress the zonal wind speed below the cloud layer.
NASA Technical Reports Server (NTRS)
Durisen, Richard H.; Bode, Paul W.; Cuzzi, Jeffrey N.; Cederbloom, Steven E.; Murphy, Brian W.
1992-01-01
The present numerical simulations and analytic arguments show that many of the common morphological features of the Saturn A- and B-ring inner-edge regions are due to 'ballistic transport', or the net radial transport of mass and angular momentum generated by exchanges of meteoroid impact ejecta. It is suggested that the observed 100-km undulatory structure of the inner B-ring arises from ballistic transport echoing of the inner edge. A strongly prograde ejecta-distribution function is used to fit the edge-region features.
NASA Technical Reports Server (NTRS)
Durisen, Richard H.; Bode, Paul W.; Cuzzi, Jeffrey N.; Cederbloom, Steven E.; Murphy, Brian W.
1992-01-01
The present numerical simulations and analytic arguments show that many of the common morphological features of the Saturn A- and B-ring inner-edge regions are due to 'ballistic transport', or the net radial transport of mass and angular momentum generated by exchanges of meteoroid impact ejecta. It is suggested that the observed 100-km undulatory structure of the inner B-ring arises from ballistic transport echoing of the inner edge. A strongly prograde ejecta-distribution function is used to fit the edge-region features.
Anomalous transport due to shear-Alfven waves
Lee, W.W.; Chance, M.S.; Okuda, H.
1980-10-01
The behavior of shear-Alfven eigenmodes and the accompanied anomalous transport have been investigated. In the particle simulation, equilibrium thermal fluctuations associated with the eigenmodes have been observed to nullify the zeroth-order shear near the rational surface through the induced second-order eddy current, and, in turn, give rise to the formation of magnetic islands which cause rapid electron energy transport in the region. The theoretical verification of the observed behavior is discussed.
Investigation of heat and momentum transport in turbulent flows via numerical simulations
NASA Technical Reports Server (NTRS)
Kim, John
1988-01-01
Turbulent transport of heat is studied by examining the flow fields obtained from a direct simulation of a turbulent channel flow. The turbulence structures associated with the velocity and scalar fields are presented using air (Pr = 0.71) as the medium. A comparison is made between the wall-layer structures identified by the temperature field and the structures found in the velocity field. Consideration is also given to the role of the organized turbulence structures in scalar transport.
NASA Astrophysics Data System (ADS)
Tuegel, Thomas I.; Hughes, Taylor L.
2015-10-01
The Hall viscosity describes a nondissipative response to strain in systems with broken time-reversal symmetry. We develop a method for computing the Hall viscosity of lattice systems in strong magnetic fields based on momentum transport, which we compare to the method of momentum polarization used by Tu et al. [Phys. Rev. B 88, 195412 (2013), 10.1103/PhysRevB.88.195412] and Zaletel et al. [Phys. Rev. Lett. 110, 236801 (2013), 10.1103/PhysRevLett.110.236801] for noninteracting systems. We compare the Hall viscosity of square-lattice tight-binding models in magnetic field to the continuum integer quantum Hall effect (IQHE) showing agreement when the magnetic length is much larger than the lattice constant, but deviation as the magnetic field strength increases. We also relate the Hall viscosity of relativistic electrons in magnetic field (the Dirac IQHE) to the conventional IQHE. The Hall viscosity of the lattice Dirac model in magnetic field agrees with the continuum Dirac Hall viscosity when the magnetic length is much larger than the lattice constant. We also show that the Hall viscosity of the lattice model deviates further from the continuum model if the C4 symmetry of the square lattice is broken to C2, but the deviation is again minimized as the magnetic length increases.
Peeters, A G; Angioni, C; Strintzi, D
2007-06-29
In this Letter, the influence of the "Coriolis drift" on small scale instabilities in toroidal plasmas is shown to generate a toroidal momentum pinch velocity. Such a pinch results because the Coriolis drift generates a coupling between the density and temperature perturbations on the one hand and the perturbed parallel flow velocity on the other. A simple fluid model is used to highlight the physics mechanism and gyro-kinetic calculations are performed to accurately assess the magnitude of the pinch. The derived pinch velocity leads to a radial gradient of the toroidal velocity profile even in the absence of a torque on the plasma and is predicted to generate a peaking of the toroidal velocity profile similar to the peaking of the density profile. Finally, the pinch also affects the interpretation of current experiments.
Williams, Kenneth A; Saini, Sunil; Wick, Timothy M
2002-01-01
Computational fluid dynamics (CFD) models to quantify momentum and mass transport under conditions of tissue growth will aid bioreactor design for development of tissue-engineered cartilage constructs. Fluent CFD models are used to calculate flow fields, shear stresses, and oxygen profiles around nonporous constructs simulating cartilage development in our concentric cylinder bioreactor. The shear stress distribution ranges from 1.5 to 12 dyn/cm(2) across the construct surfaces exposed to fluid flow and varies little with the relative number or placement of constructs in the bioreactor. Approximately 80% of the construct surface exposed to flow experiences shear stresses between 1.5 and 4 dyn/cm(2), validating the assumption that the concentric cylinder bioreactor provides a relatively homogeneous hydrodynamic environment for construct growth. Species mass transport modeling for oxygen demonstrates that fluid-phase oxygen transport to constructs is uniform. Some O(2) depletion near the down stream edge of constructs is noted with minimum pO(2) values near the constructs of 35 mmHg (23% O(2) saturation). These values are above oxygen concentrations in cartilage in vivo, suggesting that bioreactor oxygen concentrations likely do not affect chondrocyte growth. Scale-up studies demonstrate the utility and flexibility of CFD models to design and characterize bioreactors for growth of tissue-engineered cartilage.
NASA Astrophysics Data System (ADS)
Morrill-Winter, Caleb; Philip, Jimmy; Klewicki, Joseph
2017-03-01
The turbulence contribution to the mean flow is reflected by the motions producing the Reynolds shear stress (<-uv>) and its gradient. Recent analyses of the mean dynamical equation, along with data, evidence that these motions asymptotically exhibit self-similar geometric properties. This study discerns additional properties associated with the uv signal, with an emphasis on the magnitudes and length scales of its negative contributions. The signals analysed derive from high-resolution multi-wire hot-wire sensor data acquired in flat-plate turbulent boundary layers. Space-filling properties of the present signals are shown to reinforce previous observations, while the skewness of uv suggests a connection between the size and magnitude of the negative excursions on the inertial domain. Here, the size and length scales of the negative uv motions are shown to increase with distance from the wall, whereas their occurrences decrease. A joint analysis of the signal magnitudes and their corresponding lengths reveals that the length scales that contribute most to <-uv> are distinctly larger than the average geometric size of the negative uv motions. Co-spectra of the streamwise and wall-normal velocities, however, are shown to exhibit invariance across the inertial region when their wavelengths are normalized by the width distribution, W(y), of the scaling layer hierarchy, which renders the mean momentum equation invariant on the inertial domain.
Turbulent transport of fast ions due to magnetic flux ropes
NASA Astrophysics Data System (ADS)
Preiwisch, Adam
The transport of fast ions in magnetic flux ropes in a laboratory plasma is studied. Strong perturbing flux ropes (deltaE ~175 V/m, deltaB ~7 G) are generated by secondary cathode-anode pair at the upgraded LArge Plasma Device (LAPD). A 500-1000 eV lithium ion test beam is passed through the turbulent region and recollected by a gridded collimated analyzer, revealing enhanced fast ion broadening attributable to flux rope perturbations. The broadening is observed to be well in excess of Coulomb scattering levels. Monte Carlo simulation is performed with model electrostatic and magnetic fields, revealing negligible spreading as a result of the magnetic perturbations. Modeled electrostatic perturbations are observed to broaden the beam by 3.0 mm2 at the closest recollection plane, increasing as the transit time squared further downstream. Transport attributed to electrostatic fluctuations has been shown to decrease with energy while magnetic transport does not. Enhanced fast ion transport observed during the flux rope off phase is presently unexplained.
Momentum Confinement at Low Torque
Solomon, W M; Burrell, K H; deGrassie, J S; Budny, R; Groebner, R J; Heidbrink, W W; Kinsey, J E; Kramer, G J; Makowski, M A; Mikkelsen, D; Nazikian, R; Petty, C C; Politzer, P A; Scott, S D; Van Zeeland, M A; Zarnstorff, M C
2007-06-26
Momentum confinement was investigated on DIII-D as a function of applied neutral beam torque at constant normalized {beta}{sub N}, by varying the mix of co (parallel to the plasma current) and counter neutral beams. Under balanced neutral beam injection (i.e. zero total torque to the plasma), the plasma maintains a significant rotation in the co-direction. This 'intrinsic' rotation can be modeled as being due to an offset in the applied torque (i.e. an 'anomalous torque'). This anomalous torque appears to have a magnitude comparable to one co-neutral beam source. The presence of such an anomalous torque source must be taken into account to obtain meaningful quantities describing momentum transport, such as the global momentum confinement time and local diffusivities. Studies of the mechanical angular momentum in ELMing H-mode plasmas with elevated q{sub min} show that the momentum confinement time improves as the torque is reduced. In hybrid plasmas, the opposite effect is observed, namely that momentum confinement improves at high torque/rotation. The relative importance of E x B shearing between the two is modeled using GLF23 and may suggest a possible explanation.
NASA Astrophysics Data System (ADS)
Jonker, Berend
2015-03-01
Topological insulators (TIs) exhibit topologically protected metallic surface states populated by massless Dirac fermions with spin-momentum locking - the carrier spin lies in-plane, locked at right angle to the carrier momentum. An unpolarized charge current should thus create a net spin polarization whose amplitude and orientation are controlled by the charge current. Here we show direct electrical detection of this bias current induced spin polarization as a voltage measured on a ferromagnetic (FM) metal tunnel barrier surface contact. The magnetization of the contact determines the spin detection axis, and the voltage measured at this contact is proportional to the projection of the TI spin polarization onto this axis. When the charge current is orthogonal to the magnetization of the FM detector contact, the TI spin is parallel (or antiparallel) to the magnetization, and a spin-related signal is detected at the FM contact proportional to the magnitude of the charge current. The voltage measured scales inversely with Bi2Se3 film thickness, and its sign is that expected from spin-momentum locking and opposite that of a Rashba effect. Similar data are obtained for two different FM contact structures, Fe/Al2O3 and Co/MgO/graphene, underscoring the fact that these behaviors are due to bias current induced spin polarization in the TI surface states rather than the bulk, and are independent of the details of the contact. These results demonstrate simple and direct electrical access to the TI Dirac surface state spin system, provide clear evidence for the spin-momentum locking and bias current-induced spin polarization, and enable utilization of these remarkable properties for future technological applications. This work was supported by core programs at NRL and the Office of Naval Research.
NASA Astrophysics Data System (ADS)
DeSouza, Alexander L.; Basu, Shantanu
2017-02-01
We model the mass accretion rate M˙ to stellar mass M* correlation that has been inferred from observations of intermediate to upper mass T Tauri stars-that is M˙ ∝ M*1.3±0.3. We explain this correlation within the framework of quiescent disk evolution, in which accretion is driven largely by gravitational torques acting in the bulk of the mass and volume of the disk. Stresses within the disk arise from the action of gravitationally driven torques parameterized in our 1D model in terms of Toomre's Q criterion. We do not model the hot inner sub-AU scale region of the disk that is likely stable according to this criterion, and appeal to other mechanisms to remove or redistribute angular momentum and allow accretion onto the star. Our model has the advantage of agreeing with large-scale angle-averaged values from more complex nonaxisymmetric calculations. The model disk transitions from an early phase (dominated by initial conditions inherited from the burst mode of accretion) into a later self-similar mode characterized by a steeper temporal decline in M˙. The models effectively reproduce the spread in mass accretion rates that have been observed for protostellar objects of 0.2 M⊙ ≤ M* ≤ 3.0 M⊙, such as those found in the ρ Ophiuchus and Taurus star forming regions. We then compare realistically sampled populations of young stellar objects produced by our model to their observational counterparts. We find these populations to be statistically coincident, which we argue is evidence for the role of gravitational torques in the late time evolution of quiescent protostellar disks.
Morrill-Winter, Caleb; Philip, Jimmy; Klewicki, Joseph
2017-03-13
The turbulence contribution to the mean flow is reflected by the motions producing the Reynolds shear stress (〈-uv〉) and its gradient. Recent analyses of the mean dynamical equation, along with data, evidence that these motions asymptotically exhibit self-similar geometric properties. This study discerns additional properties associated with the uv signal, with an emphasis on the magnitudes and length scales of its negative contributions. The signals analysed derive from high-resolution multi-wire hot-wire sensor data acquired in flat-plate turbulent boundary layers. Space-filling properties of the present signals are shown to reinforce previous observations, while the skewness of uv suggests a connection between the size and magnitude of the negative excursions on the inertial domain. Here, the size and length scales of the negative uv motions are shown to increase with distance from the wall, whereas their occurrences decrease. A joint analysis of the signal magnitudes and their corresponding lengths reveals that the length scales that contribute most to 〈-uv〉 are distinctly larger than the average geometric size of the negative uv motions. Co-spectra of the streamwise and wall-normal velocities, however, are shown to exhibit invariance across the inertial region when their wavelengths are normalized by the width distribution, W(y), of the scaling layer hierarchy, which renders the mean momentum equation invariant on the inertial domain.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.
Impurity transport due to electromagnetic drift wave turbulence
NASA Astrophysics Data System (ADS)
Moradi, S.; Pusztai, I.; Mollén, A.; Fülöp, T.
2012-03-01
Finite β effects on impurity transport are studied through local linear gyrokinetic simulations with GYRO [J. Candy and E. Belli, General Atomics Report No. GA-A26818, 2011]; in particular, we investigate the parametric dependences of the impurity peaking factor (zero-flux density gradient) and the onset of the kinetic ballooning modes (KBMs). We find that electromagnetic effects even at low β can have significant impact on the impurity transport. The KBM instability threshold depends on the plasma parameters, particularly strongly on plasma shape. We have shown that magnetic geometry significantly influences the results, and the commonly used s-α model overestimates the KBM growth rates and ITG stabilization at high β. In the β range, where the KBM is the dominant instability the impurity peaking factor is strongly reduced, with very little dependence on β and the impurity charge.
Mass and Momentum Transport in Microcavities for Diffusion-Dominant Cell Culture Applications
NASA Technical Reports Server (NTRS)
Yew, Alvin G.; Pinero, Daniel; Hsieh, Adam H.; Atencia, Javier
2012-01-01
For the informed design of microfluidic devices, it is important to understand transport phenomena at the microscale. This letter outlines an analytically-driven approach to the design of rectangular microcavities extending perpendicular to a perfusion microchannel for microfluidic cell culture devices. We present equations to estimate the spatial transition from advection- to diffusion-dominant transport inside cavities as a function of the geometry and flow conditions. We also estimate the time required for molecules, such as nutrients or drugs to travel from the microchannel to a given depth into the cavity. These analytical predictions can facilitate the rational design of microfluidic devices to optimize and maintain long-term, physiologically-based culture conditions with low fluid shear stress.
NASA Astrophysics Data System (ADS)
Escauriaza, Cristian; Sandoval, Jorge; Mignot, Emmanuel; Mao, Luca
2016-11-01
Turbulent flows developed in surface storage zones (SSZ) in rivers control many physical and biogeochemical processes of contaminants in the water. These regions are characterized by low velocities and long residence times, which favor particle deposition, nutrient uptake, and flow interactions with reactive sediments. The dynamics of the flow in SSZ is driven by a shear layer that induces multiple vortical structures with a wide range of temporal and spatial scales. In this work we study the flow in a lateral SSZ of the Lluta River, a high-altitude Andean stream (4,000 masl), with a Re=45,800. We describe the large-scale turbulent coherent structures using field measurements and 3D numerical simulations. We measure the bed topography, instantaneous 3D velocities at selected points, the mean 2D free-surface velocity field, and arsenic concentration in the sediment. Numerical simulations of the flow are also performed using a DES turbulence model. We focus on the mass and momentum transport processes, analyzing the statistics of mass exchange and residence times in the SSZ. With this information we provide new insights on the flow and transport processes between the main channel and the recirculating region in natural conditions. Supported by Fondecyt 1130940.
2014-01-01
spin polarized . Topological insulators are expected to produce new functionalities5 and enable insights into complex phenomena in many scientific... Topological insulators in three dimensions. Phys. Rev. Lett. 98, 106803 (2007). 4. Hsieh, D. et al. A topological Dirac insulator in a quantum spin Hall phase...in topological insulators. Phys. Rev. B 82, 155457 (2010). 18. Yazyev, V., Moore, J. E. & Louie, S. G. Spin polarization and transport of surface
Familial orthostatic tachycardia due to norepinephrine transporter deficiency
NASA Technical Reports Server (NTRS)
Robertson, D.; Flattem, N.; Tellioglu, T.; Carson, R.; Garland, E.; Shannon, J. R.; Jordan, J.; Jacob, G.; Blakely, R. D.; Biaggioni, I.
2001-01-01
Orthostatic intolerance (OI) or postural tachycardia syndrome (POTS) is a syndrome primarily affecting young females, and is characterized by lightheadedness, palpitations, fatigue, altered mentation, and syncope primarily occurring with upright posture and being relieved by lying down. There is typically tachycardia and raised plasma norepinephrine levels on upright posture, but little or no orthostatic hypotension. The pathophysiology of OI is believed to be very heterogeneous. Most studies of the syndrome have focused on abnormalities in norepinephrine release. Here the hypothesis that abnormal norepinephrine transporter (NET) function might contribute to the pathophysiology in some patients with OI was tested. In a proband with significant orthostatic symptoms and tachycardia, disproportionately elevated plasma norepinephrine with standing, impaired systemic, and local clearance of infused tritiated norepinephrine, impaired tyramine responsiveness, and a dissociation between stimulated plasma norepinephrine and DHPG elevation were found. Studies of NET gene structure in the proband revealed a coding mutation that converts a highly conserved transmembrane domain Ala residue to Pro. Analysis of the protein produced by the mutant cDNA in transfected cells demonstrated greater than 98% reduction in activity relative to normal. NE, DHPG/NE, and heart rate correlated with the mutant allele in this family. CONCLUSION: These results represent the first identification of a specific genetic defect in OI and the first disease linked to a coding alteration in a Na+/Cl(-)-dependent neurotransmitter transporter. Identification of this mechanism may facilitate our understanding of genetic causes of OI and lead to the development of more effective therapeutic modalities.
Familial orthostatic tachycardia due to norepinephrine transporter deficiency
NASA Technical Reports Server (NTRS)
Robertson, D.; Flattem, N.; Tellioglu, T.; Carson, R.; Garland, E.; Shannon, J. R.; Jordan, J.; Jacob, G.; Blakely, R. D.; Biaggioni, I.
2001-01-01
Orthostatic intolerance (OI) or postural tachycardia syndrome (POTS) is a syndrome primarily affecting young females, and is characterized by lightheadedness, palpitations, fatigue, altered mentation, and syncope primarily occurring with upright posture and being relieved by lying down. There is typically tachycardia and raised plasma norepinephrine levels on upright posture, but little or no orthostatic hypotension. The pathophysiology of OI is believed to be very heterogeneous. Most studies of the syndrome have focused on abnormalities in norepinephrine release. Here the hypothesis that abnormal norepinephrine transporter (NET) function might contribute to the pathophysiology in some patients with OI was tested. In a proband with significant orthostatic symptoms and tachycardia, disproportionately elevated plasma norepinephrine with standing, impaired systemic, and local clearance of infused tritiated norepinephrine, impaired tyramine responsiveness, and a dissociation between stimulated plasma norepinephrine and DHPG elevation were found. Studies of NET gene structure in the proband revealed a coding mutation that converts a highly conserved transmembrane domain Ala residue to Pro. Analysis of the protein produced by the mutant cDNA in transfected cells demonstrated greater than 98% reduction in activity relative to normal. NE, DHPG/NE, and heart rate correlated with the mutant allele in this family. CONCLUSION: These results represent the first identification of a specific genetic defect in OI and the first disease linked to a coding alteration in a Na+/Cl(-)-dependent neurotransmitter transporter. Identification of this mechanism may facilitate our understanding of genetic causes of OI and lead to the development of more effective therapeutic modalities.
Heat Transport due to Long-Range Collisions.
NASA Astrophysics Data System (ADS)
Hollmann, Eric M.
1999-11-01
Cross-magnetic-field heat transport in a quiescent pure ion plasma is found to be diffusive, with measured thermal diffusivity \\chi which is independent of magnetic field strength B and plasma density n. The measured values of \\chi are up to 100 times larger than the ``classical'' thermal diffusivity \\chic = (16 √π / 15) (n barv b^2 ) r_c^2 ln (rc / b) ∝ n^1 B-2 T-1/2 expected from velocity-scattering collisions;(M.N. Rosenbluth et al., Phys. Rev. 109), 1 (1958). but are in quantitative agreement with the thermal diffusivity \\chiL = 0.49 ( n barv b^2 ) λ_D^2 ∝ n^0 B^0 T-1/2 recently predicted to result from long-range ``guiding center'' collisions.(D.H.E. Dubin et al., Phys. Rev. Lett. 78), 3868 (1997). In these long-range collisions, which occur in plasmas with λD > r_c, particles on well-separated field lines exchange parallel kinetic energy only. In the present experiments, the maximal impact parameters are ρ <= λ_D but in larger plasmas (with cross-field dimension L > 100 λ_D) the emission and absorption of plasma waves over impact parameters ρ <= L is predicted to give a further enhancement of the heat transport. The experiments are performed by heating (or cooling) the ions locally with a laser beam to create a thermal gradient. A second laser is then used to monitor the resulting radial heat flow. Remarkably, the ions are held in steady-state for periods of weeks by an applied ``rotating wall'' drive;(X.-P. Huang et al., Phys. Rev. Lett. 78), 875 (1997). this allows for accurate, repeatable heat transport measurements over a wide range of plasma parameters. To date, the thermal diffusivity has been measured over a range of 100 in density, 4 in magnetic field, and 10^4 in temperature; and it is found that long-range collisions dominate the heat transport over this entire range.(E.M. Hollmann et al., Phys. Rev. Lett. 82). 4930 (1999). Separate measurements of the perp-to-parallel thermal isotropization rates show that short-range velocity
NASA Astrophysics Data System (ADS)
Kawata, Takuya; Alfredsson, P. Henrik
2016-07-01
Plane Couette flow under spanwise, anticyclonic system rotation [rotating plane Couette flow (RPCF)] is studied experimentally using stereoscopic particle image velocimetry for different Reynolds and rotation numbers in the fully turbulent regime. Similar to the laminar regime, the turbulent flow in RPCF is characterized by roll cells, however both instantaneous snapshots of the velocity field and space correlations show that the roll cell structure varies with the rotation number. All three velocity components are measured and both the mean flow and all four nonzero Reynolds stresses are obtained across the central parts of the channel. This also allows us to determine the wall shear stress from the viscous stress and the Reynolds stress in the center of the channel, and for low rotation rates the wall shear stress increases with increasing rotation rate as expected. The results show that zero absolute vorticity is established in the central parts of the channel of turbulent RPCF for high enough rotation rates, but also that the mean velocity profile for certain parameter ranges shows an S shape giving rise to a negative velocity gradient in the center of the channel. We find that from an analysis of the Reynolds stress transport equation using the present data there is a transport of the Reynolds shear stress towards the center of the channel, which may then result in a negative mean velocity gradient there.
Polarization momentum transfer collision: Faxen-Holtzmark theory and quantum dynamic shielding.
Ki, Dae-Han; Jung, Young-Dae
2013-04-21
The influence of the quantum dynamic shielding on the polarization momentum transport collision is investigated by using the Faxen-Holtzmark theory in strongly coupled Coulomb systems. The electron-atom polarization momentum transport cross section is derived as a function of the collision energy, de Broglie wavelength, Debye length, thermal energy, and atomic quantum states. It is found that the dynamic shielding enhances the scattering phase shift as well as the polarization momentum transport cross section. The variation of quantum effect on the momentum transport collision due to the change of thermal energy and de Broglie wavelength is also discussed.
Ion transport through macrocapillaries - Oscillations due to charge patch formation
NASA Astrophysics Data System (ADS)
Kulkarni, D. D.; Lyle, L. A. M.; Sosolik, C. E.
2016-09-01
We present results on ion transport through large bore capillaries (macrocapillaries) that probe both the geometric and ion-guided aspects of this ion delivery mechanism. We have demonstrated that guiding in macrocapillaries exhibits position- and angle-dependent transmission properties which are directly related to the capillary material (either metal or insulator) and geometry. Specifically, we have passed 1 keV Rb+ ions through glass and metal macrocapillaries, and have observed oscillations for the transmitted ion current passing through the insulating capillaries. Straightforward calculations show that these oscillations can be attributed to beam deflections from charge patches that form on the interior walls of the capillary. The absence of these oscillations in the metal capillary data serve as further confirmation of the role of charge patch formation.
Pierre, J; Oddou, C
2007-12-01
Successful bone cell culture in large implants still is a challenge to biologists and requires a strict control of the physicochemical and mechanical environments. This study analyses from the transport phenomena viewpoint the limiting factors of a perfusion bioreactor for bone cell culture within fibrous and porous large implants (2.5 cm in length, a few cubic centimetres in volume, 250 microm in fibre diameter with approximately 60% porosity). A two-dimensional mathematical model, based upon stationary mass and momentum transport in these implants is proposed and numerically solved. Cell oxygen consumption, in accordance theoretically with the Michaelis-Menten law, generates non linearity in the boundary conditions of the convection diffusion equation. Numerical solutions are obtained with a commercial code (Femlab 3.1; Comsol AB, Stockholm, Sweden). Moreover, based on the simplification of transport equations, a simple formula is given for estimating the length of the oxygen penetration within the implant. Results show that within a few hours of culture process and for a perfusion velocity of the order of 10(-4) m s(-1), the local oxygen concentration is everywhere sufficiently high to ensure a suitable cell metabolism. But shear stresses induced by the fluid flow with such a perfusion velocity are found to be locally too large (higher than 10(-3) Pa). Suitable shear stresses are obtained by decreasing the velocity at the inlet to around 2 x 10(-5) m s(-1). But consequently hypoxic regions (low oxygen concentrations) appear at the downstream part of the implant. Thus, it is suggested here that in the determination of the perfusion flow rate within a large implant, a compromise between oxygen supply and shear stress effects must be found in order to obtain a successful cell culture.
Biotin dependency due to a defect in biotin transport
Mardach, Rebecca; Zempleni, Janos; Wolf, Barry; Cannon, Martin J.; Jennings, Michael L.; Cress, Sally; Boylan, Jane; Roth, Susan; Cederbaum, Stephen; Mock, Donald M.
2002-01-01
We describe a 3-year-old boy with biotin dependency not caused by biotinidase, holocarboxylase synthetase, or nutritional biotin deficiency. We sought to define the mechanism of his biotin dependency. The child became acutely encephalopathic at age 18 months. Urinary organic acids indicated deficiency of several biotin-dependent carboxylases. Symptoms improved rapidly following biotin supplementation. Serum biotinidase activity and Biotinidase gene sequence were normal. Activities of biotin-dependent carboxylases in PBMCs and cultured skin fibroblasts were normal, excluding biotin holocarboxylase synthetase deficiency. Despite extracellular biotin sufficiency, biotin withdrawal caused recurrent abnormal organic aciduria, indicating intracellular biotin deficiency. Biotin uptake rates into fresh PBMCs from the child and into his PBMCs transformed with Epstein Barr virus were about 10% of normal fresh and transformed control cells, respectively. For fresh and transformed PBMCs from his parents, biotin uptake rates were consistent with heterozygosity for an autosomal recessive genetic defect. Increased biotin breakdown was ruled out, as were artifacts of biotin supplementation and generalized defects in membrane permeability for biotin. These results provide evidence for a novel genetic defect in biotin transport. This child is the first known with this defect, which should now be included in the identified causes of biotin dependency. PMID:12070309
Mantica, P.; Ferreira, J. S.; Salmi, A.; Strintzi, D.; Weiland, J.; Brix, M.; Giroud, C.; Corrigan, G.; Zastrow, K.-D.; Tardini, G.
2010-09-15
Perturbative experiments have been carried out in the Joint European Torus [Fusion Sci. Technol. 53(4) (2008)] in order to identify the diffusive and convective components of toroidal momentum transport. The torque source was modulated either by modulating tangential neutral beam power or by modulating in antiphase tangential and normal beams to produce a torque perturbation in the absence of a power perturbation. The resulting periodic perturbation in the toroidal rotation velocity was modeled using time-dependent transport simulations in order to extract empirical profiles of momentum diffusivity and pinch. Details of the experimental technique, data analysis, and modeling are provided. The momentum diffusivity in the core region (0.2<{rho}<0.8) was found to be close to the ion heat diffusivity ({chi}{sub {phi}/{chi}i{approx}}0.7-1.7) and a significant inward momentum convection term, up to 20 m/s, was found, leading to an effective momentum diffusivity significantly lower than the ion heat diffusivity ({chi}{sub {phi}}{sup eff}/{chi}{sub i}{sup eff{approx}}0.4). These results have significant implications on the prediction of toroidal rotation velocities in future tokamaks and are qualitatively consistent with recent developments in momentum transport theory. Detailed quantitative comparisons with the theoretical predictions of the linear gyrokinetic code GKW [A. G. Peeters et al., Comput. Phys. Commun. 180, 2650 (2009)] and of the quasilinear fluid Weiland model [J. Weiland, Collective Modes in Inhomogeneous Plasmas (IOP, Bristol, 2000)] are presented for two analyzed discharges.
NASA Technical Reports Server (NTRS)
Stepinski, Tomasz F.; Reyes-Ruiz, Mauricio; Vanhala, Harri A. T.
1993-01-01
A hydromagnetic dynamo provides the best mechanism for contemporaneously producing magnetic fields in a turbulent solar nebula. We investigate the solar nebula in the framework of a steady-state accretion disk model and establish the criteria for a viable nebular dynamo. We have found that typically a magnetic gap exists in the nebula, the region where the degree of ionization is too small for the magnetic field to couple to the gas. The location and width of this gap depend on the particular model; the supposition is that gaps cover different parts of the nebula at different evolutionary stages. We have found, from several dynamical constraints, that the generated magnetic field is likely to saturate at a strength equal to equipartition with the kinetic energy of turbulence. Maxwell stress arising from a large-scale magnetic field may significantly influence nebular structure, and Maxwell stress due to small-scale fields can actually dominate other stresses in the inner parts of the nebula. We also argue that the bulk of nebular gas, within the scale height from the midplane, is stable against Balbus-Hawley instability.
NASA Technical Reports Server (NTRS)
Stepinski, Tomasz F.; Reyes-Ruiz, Mauricio; Vanhala, Harri A. T.
1993-01-01
A hydromagnetic dynamo provides the best mechanism for contemporaneously producing magnetic fields in a turbulent solar nebula. We investigate the solar nebula in the framework of a steady-state accretion disk model and establish the criteria for a viable nebular dynamo. We have found that typically a magnetic gap exists in the nebula, the region where the degree of ionization is too small for the magnetic field to couple to the gas. The location and width of this gap depend on the particular model; the supposition is that gaps cover different parts of the nebula at different evolutionary stages. We have found, from several dynamical constraints, that the generated magnetic field is likely to saturate at a strength equal to equipartition with the kinetic energy of turbulence. Maxwell stress arising from a large-scale magnetic field may significantly influence nebular structure, and Maxwell stress due to small-scale fields can actually dominate other stresses in the inner parts of the nebula. We also argue that the bulk of nebular gas, within the scale height from the midplane, is stable against Balbus-Hawley instability.
NASA Astrophysics Data System (ADS)
Rousseau, F.; Coppi, B.
2007-04-01
Differentially rotating plasma structures in the prevalent gravity of a central object (e.g. black hole) can acquire a configuration characterized by a radial sequence of ringsootnotetextB. Coppi and F. Rousseau, Ap. J. 641 (1), 458 (2006) in the presence of a ``seed'' vertical magnetic field, rather than one typical of a gaseous disk. A sequence of pairs of counter-streaming toroidal current channels is associated with these rings and no poloidal currents are produced if a torque is absent. When a local transport process of angular momentum is present, loops of poloidal currents associated with the resulting torque are formed.ootnotetextB. Coppi, MIT-LNS Report 06/05 (Cambridge, MA, 2006) In particular, the vertical current densities are up- down antisymmetric. A jet that could emerge from the innermost ring would, in fact, have antisymmetric vertical current densities relative to the equatorial plane. When a small radial velocity, resulting for instance from accretion, is present we argue that matter will flow along the X-lines and the O-lines of a weakly spiraling ring configuration that is envisioned instead of the strictly axisymmetric^1 configuration found when only a toroidal velocity is present. *Sponsored in part by the U.S. Department of Energy.
NASA Technical Reports Server (NTRS)
Orlando, A. F.; Moffat, R. J.; Kays, W. M.
1974-01-01
The relationship between the turbulent transport of heat and momentum in an adverse pressure gradient boundary layer was studied. An experimental study was conducted of turbulent boundary layers subject to strong adverse pressure gradients with suction. Near-equilibrium flows were attained, evidenced by outer-region similarity in terms of defect temperature and defect velocity profiles. The relationship between Stanton number and enthalpy thickness was shown to be the same as for a flat plate flow both for constant wall temperature boundary conditions and for steps in wall temperature. The superposition principle used with the step-wall-temperature experimental result was shown to accurately predict the Stanton number variation for two cases of arbitrarily varying wall temperature. The Reynolds stress tensor components were measured for strong adverse pressure gradient conditions and different suction rates. Two peaks of turbulence intensity were found: one in the inner and one in the outer regions. The outer peak is shown to be displaced outward by an adverse pressure gradient and suppressed by suction.
Rigorous upper bounds for fluid and plasma transport due to passive advection
Krommes, J.A.; Smith, R.A.; Kim, C.B.
1987-07-01
The formulation of variational principles for transport due to passive advection is described. A detailed account of the work has been published elsewhere. In the present paper, the motivations, philosophy, and implications of the method are briefly discussed. 15 refs.
Anomalous perturbative transport in tokamaks due to drift-Alfven-wave turbulence
Thoul, A.A. ); Similon, P.L. ); Sudan, R.N. )
1994-03-01
The method developed in Thoul, Similon, and Sudan [Phys. Plasmas [bold 1], 579 (1994)] is used to calculate the transport due to drift-Alfven-wave turbulence, in which electromagnetic effects such as the fluttering of the magnetic field lines are important. Explicit expressions are obtained for all coefficients of the anomalous transport matrix relating particle and heat fluxes to density and temperature gradients in the plasma. Although the magnetic terms leave the transport by trapped electrons unaffected, they are important for the transport by circulating electrons.
Anomalous perturbative transport in tokamaks due to drift-Alfvén-wave turbulence
NASA Astrophysics Data System (ADS)
Thoul, Anne A.; Similon, P. L.; Sudan, R. N.
1994-03-01
The method developed in Thoul, Similon, and Sudan [Phys. Plasmas 1, 579 (1994)] is used to calculate the transport due to drift-Alfvén-wave turbulence, in which electromagnetic effects such as the fluttering of the magnetic field lines are important. Explicit expressions are obtained for all coefficients of the anomalous transport matrix relating particle and heat fluxes to density and temperature gradients in the plasma. Although the magnetic terms leave the transport by trapped electrons unaffected, they are important for the transport by circulating electrons.
Oishi, Jeffrey S.
2011-10-10
The magnetorotational instability (MRI) may dominate outward transport of angular momentum in accretion disks, allowing material to fall onto the central object. Previous work has established that the MRI can drive a mean-field dynamo, possibly leading to a self-sustaining accretion system. Recently, however, simulations of the scaling of the angular momentum transport parameter {alpha}{sub SS} with the magnetic Prandtl number Pm have cast doubt on the ability of the MRI to transport astrophysically relevant amounts of angular momentum in real disk systems. Here, we use simulations including explicit physical viscosity and resistivity to show that when vertical stratification is included, mean-field dynamo action operates, driving the system to a configuration in which the magnetic field is not fully helical. This relaxes the constraints on the generated field provided by magnetic helicity conservation, allowing the generation of a mean field on timescales independent of the resistivity. Our models demonstrate the existence of a critical magnetic Reynolds number Rm{sub crit}, below which transport becomes strongly Pm-dependent and chaotic, but above which the transport is steady and Pm-independent. Prior simulations showing Pm dependence had Rm < Rm{sub crit}. We conjecture that this steady regime is possible because the mean-field dynamo is not helicity-limited and thus does not depend on the details of the helicity ejection process. Scaling to realistic astrophysical parameters suggests that disks around both protostars and stellar mass black holes have Rm >> Rm{sub crit}. Thus, we suggest that the strong Pm dependence seen in recent simulations does not occur in real systems.
Oishi, Jeffrey S.; Low, Mordecai-Mark Mac; /Amer. Museum Natural Hist.
2012-02-14
The magnetorotational instability (MRI) may dominate outward transport of angular momentum in accretion disks, allowing material to fall onto the central object. Previous work has established that the MRI can drive a mean-field dynamo, possibly leading to a self-sustaining accretion system. Recently, however, simulations of the scaling of the angular momentum transport parameter {alpha}{sub SS} with the magnetic Prandtl number Pm have cast doubt on the ability of the MRI to transport astrophysically relevant amounts of angular momentum in real disk systems. Here, we use simulations including explicit physical viscosity and resistivity to show that when vertical stratification is included, mean field dynamo action operates, driving the system to a configuration in which the magnetic field is not fully helical. This relaxes the constraints on the generated field provided by magnetic helicity conservation, allowing the generation of a mean field on timescales independent of the resistivity. Our models demonstrate the existence of a critical magnetic Reynolds number Rm{sub crit}, below which transport becomes strongly Pm-dependent and chaotic, but above which the transport is steady and Pm-independent. Prior simulations showing Pm-dependence had Rm < Rm{sub crit}. We conjecture that this steady regime is possible because the mean field dynamo is not helicity-limited and thus does not depend on the details of the helicity ejection process. Scaling to realistic astrophysical parameters suggests that disks around both protostars and stellar mass black holes have Rm >> Rm{sub crit}. Thus, we suggest that the strong Pm dependence seen in recent simulations does not occur in real systems.
Anomalous perturbative transport in tokamaks due to drift-wave turbulence
Thoul, A.A. ); Similon, P.L. ); Sudan, R.N. )
1994-03-01
A new method for calculating the anomalous transport in tokamak plasmas is presented. The renormalized nonlinear plasma response function is derived using the direct-interaction approximation (DIA). A complete calculation for the case of electrostatic drift-wave turbulence is presented. Explicit expressions for all coefficients of the anomalous transport matrix relating particle and heat fluxes to density and temperature gradients in the plasma are obtained. The anomalous transport matrix calculated using the DIA does not have the Onsager symmetry. As an example of application, the parameters of the Texas Experimental Tokamak (TEXT) [Nucl. Technol. Fusion [bold 1], 479 (1981)] are used to evaluate all transport coefficients numerically, as well as the spectrum modulation. The relation between the theoretical results and the experimental data is discussed. Although this paper focuses on electron transport for simplicity, the method can also be used to calculate anomalous transport due to ion instabilities, such as the ion-temperature-gradient instability.
NASA Astrophysics Data System (ADS)
Li, F.-C.; Kawaguchi, Y.; Hishida, K.
2004-09-01
Simultaneous measurements of the velocity (u and ν in the streamwise and wall-normal directions, respectively) and temperature fluctuations (θ) in the thermal boundary layer were carried out for a heated drag-reducing surfactant solution flow in a two-dimensional channel by means of a two-component laser Doppler velocimetry and a fine-wire thermocouple probe. The drag-reducing fluid tested was a dilute aqueous solution of a cationic surfactant, cetyltrimethylammonium chloride (CTAC), with 30 ppm concentration. Measurements were performed for CTAC solution flows at an inlet temperature of 31 °C and at three Reynolds numbers of 3.5×104, 2.5×104, and 1.5×104, respectively, and for water flow at the Reynolds number of 2.5×104. Drag reduction (DR) and heat transfer reduction (HTR) for the three CTAC solution flows were DR(HTR)=33.0(20.2), 70.0(77.3), and 65.1(77.0) percentage, respectively. At a high HTR level, a large temperature gradient appeared when y+<50 in the measured range (the superscript "+" denotes normalization with inner variables). Temperature fluctuation intensity, θ'+, and the streamwise turbulent heat flux, u+θ+¯, were enhanced in the layer with large temperature gradient for the drag-reducing flow, whereas the wall-normal turbulent heat flux, -ν+θ+¯, was depressed throughout the measured range. The depression of -ν+θ+¯ was due to a cause similar to that of the depression of the Reynolds shear stress -u+ν+¯, i.e., in addition to the decrease of ν'+, decorrelation between the two variables occurred. The decrease of -ν+θ+¯ resulted in HTR, which was similar to that of the decrease of -u+ν+¯ resulted in DR for the drag-reducing flow by additives. The turbulence production terms, -u+ν+¯(∂U+/∂y+) and -ν+θ+¯(∂Θ+/∂y+) where U and Θ are mean velocity and temperature, were reduced in the drag-reducing CTAC solution flows. The estimated power spectra of temperature fluctuations implied that the drag-reducing surfactant
NASA Astrophysics Data System (ADS)
Das, Salil; Jhang, Hogun; Singh, R.; Nordman, H.
2016-10-01
The significant effect of impurities in radiation losses and plasma dilution, which result in lower fusion power, and the evaluation of the important effects of intrinsic rotation on transport barrier formation, determination of momentum pinch velocity and its theoretical basis, in tokamak performance is studied using the four-wave parametric process using an electrostatic, collisionless fluid model for ion-temperature-gradient and trapped-electron mode driven turbulence in the presence of radio frequency fields in the lower hybrid (LH) range of frequencies. The beating of the pump and the sidebands exert a ponderomotive force on electrons, modifying the eigenfrequency of the drift waves and influencing the growth rates and the turbulent transport properties. Explicit expressions for the non-linear growth rate and the associated ion thermal conductivity and effective impurity diffusivity are derived. The effects of the rf fields on the momentum and impurity transport coefficients are evaluated for key parameters like rf power, temperature gradients, and magnetic shear. Prince Georges Community College, Largo, Maryland 20774, USA.
Myers, William K; Scholes, Charles P; Tierney, David L
2009-08-05
We report Q-band ENDOR of (1)H, (14)N, and (11)B at the g( parallel) extreme of the EPR spectrum of bis(trispyrazolylborate) cobalt(II) [Co(Tp)(2)] and two structural analogs. This trigonally symmetric, high-spin (hs) S = 3/2 Co(II) complex shows large unquenched ground-state orbital angular momentum, which leads to highly anisotropic electronic g-values (g( parallel) = 8.48, g( perpendicular) = 1.02). The large g-anisotropy is shown to result in large dipolar couplings near g( parallel) and uniquely anisotropic (14)N Fermi couplings, which arise from spin transferred to the nitrogen 2s orbital (2.2%) via antibonding interactions with singly occupied metal d(x(2)-y(2)) and d(z(2)) orbitals. Large, well-resolved (1)H and (11)B dipolar couplings were also observed. Taken in concert with our previous X-band ENDOR measurements at g( perpendicular) ( Myers, W. K.; et al. Inorg. Chem. 2008, 47, 6701-6710 ), the present data allow a detailed analysis of the dipolar hyperfine tensors of two of the four symmetry distinct protons in the parent molecule. In the substituted analogs, changes in hyperfine coupling due to altered metal-proton distances give further evidence of an anisotropic Fermi contact interaction. For the pyrazolyl 3H proton, the data indicate a 0.2 MHz anisotropic contact interaction and approximately 4% transfer of spin away from Co(II). Dipolar coupling also dominates for the axial boron atoms, consistent with their distance from the Co(II) ion, and resolved (11)B quadrupolar coupling showed approximately 30% electronic inequivalence between the B-H and B-C sp(3) bonds. This is the first comprehensive ENDOR study of any hs Co(II) species and lays the foundation for future development.
NASA Astrophysics Data System (ADS)
Zaghloul, Mofreh R.; Bourham, Mohamed A.; Doster, J. Michael
2000-04-01
An exact analytical expression for the energy-averaged electron-ion momentum transport cross section in the Born approximation and Debye-Hückel exponentially screened potential has been derived and compared with the formulae given by other authors. A quantitative comparison between cut-off theory and quantum mechanical perturbation theory has been presented. Based on results from the Born approximation and Spitzer's formula, a new approximate formula for the quantum Coulomb logarithm has been derived and shown to be more accurate than previous expressions.
NASA Astrophysics Data System (ADS)
Zaghloul, Mofreh R.; Bourham, Mohamed A.; Doster, J. Michael
2000-02-01
An exact analytical expression for the energy-averaged electron-ion momentum transport cross section in the Born approximation and Debye-Hückel exponentially screened potential has been derived and compared with the formulae given by other authors. A quantitative comparison between cut-off theory and quantum mechanical perturbation theory has been presented. Based on results from the Born approximation and Spitzer's formula, a new approximate formula for the quantum Coulomb logarithm has been derived and shown to be more accurate than previous expressions.
NASA Technical Reports Server (NTRS)
Kim, J.; Simon, T. W.
1987-01-01
The effects of streamwise convex curvature, recovery, and freestream turbulence intensity on the turbulent transport of heat and momentum in a mature boundary layer are studied using a specially designed three-wire hot-wire probe. Increased freestream turbulence is found to increase the profiles throughout the boundary layer on the flat developing wall. Curvature effects were found to dominate turbulence intensity effects for the present cases considered. For the higher TI (turbulence intensity) case, negative values of the turbulent Prandtl number are found in the outer half of the boundary layer, indicating a breakdown in Reynolds analogy.
Adare, A; Afanasiev, S; Aidala, C; Ajitanand, N N; Akiba, Y; Al-Bataineh, H; Alexander, J; Al-Jamel, A; Aoki, K; Aphecetche, L; Armendariz, R; Aronson, S H; Asai, J; Atomssa, E T; Averbeck, R; Awes, T C; Azmoun, B; Babintsev, V; Baksay, G; Baksay, L; Baldisseri, A; Barish, K N; Barnes, P D; Bassalleck, B; Bathe, S; Batsouli, S; Baublis, V; Bauer, F; Bazilevsky, A; Belikov, S; Bennett, R; Berdnikov, Y; Bickley, A A; Bjorndal, M T; Boissevain, J G; Borel, H; Boyle, K; Brooks, M L; Brown, D S; Bucher, D; Buesching, H; Bumazhnov, V; Bunce, G; Burward-Hoy, J M; Butsyk, S; Campbell, S; Chai, J-S; Chang, B S; Charvet, J-L; Chernichenko, S; Chiba, J; Chi, C Y; Chiu, M; Choi, I J; Chujo, T; Chung, P; Churyn, A; Cianciolo, V; Cleven, C R; Cobigo, Y; Cole, B A; Comets, M P; Constantin, P; Csanád, M; Csörgo, T; Dahms, T; Das, K; David, G; Deaton, M B; Dehmelt, K; Delagrange, H; Denisov, A; d'Enterria, D; Deshpande, A; Desmond, E J; Dietzsch, O; Dion, A; Donadelli, M; Drachenberg, J L; Drapier, O; Drees, A; Dubey, A K; Durum, A; Dzhordzhadze, V; Efremenko, Y V; Egdemir, J; Ellinghaus, F; Emam, W S; Enokizono, A; En'yo, H; Espagnon, B; Esumi, S; Eyser, K O; Fields, D E; Finger, M; Finger, M; Fleuret, F; Fokin, S L; Forestier, B; Fraenkel, Z; Frantz, J E; Franz, A; Frawley, A D; Fujiwara, K; Fukao, Y; Fung, S-Y; Fusayasu, T; Gadrat, S; Garishvili, I; Gastineau, F; Germain, M; Glenn, A; Gong, H; Gonin, M; Gosset, J; Goto, Y; de Cassagnac, R Granier; Grau, N; Greene, S V; Perdekamp, M Grosse; Gunji, T; Gustafsson, H-A; Hachiya, T; Henni, A Hadj; Haegemann, C; Haggerty, J S; Hagiwara, M N; Hamagaki, H; Han, R; Harada, H; Hartouni, E P; Haruna, K; Harvey, M; Haslum, E; Hasuko, K; Hayano, R; Heffner, M; Hemmick, T K; Hester, T; Heuser, J M; He, X; Hiejima, H; Hill, J C; Hobbs, R; Hohlmann, M; Holmes, M; Holzmann, W; Homma, K; Hong, B; Horaguchi, T; Hornback, D; Hur, M G; Ichihara, T; Imai, K; Imrek, J; Inaba, M; Inoue, Y; Isenhower, D; Isenhower, L; Ishihara, M; Isobe, T; Issah, M; Isupov, A; Jacak, B V; Jia, J; Jin, J; Jinnouchi, O; Johnson, B M; Joo, K S; Jouan, D; Kajihara, F; Kametani, S; Kamihara, N; Kamin, J; Kaneta, M; Kang, J H; Kanou, H; Kawagishi, T; Kawall, D; Kazantsev, A V; Kelly, S; Khanzadeev, A; Kikuchi, J; Kim, D H; Kim, D J; Kim, E; Kim, Y-S; Kinney, E; Kiss, A; Kistenev, E; Kiyomichi, A; Klay, J; Klein-Boesing, C; Kochenda, L; Kochetkov, V; Komkov, B; Konno, M; Kotchetkov, D; Kozlov, A; Král, A; Kravitz, A; Kroon, P J; Kubart, J; Kunde, G J; Kurihara, N; Kurita, K; Kweon, M J; Kwon, Y; Kyle, G S; Lacey, R; Lai, Y-S; Lajoie, J G; Lebedev, A; Le Bornec, Y; Leckey, S; Lee, D M; Lee, M K; Lee, T; Leitch, M J; Leite, M A L; Lenzi, B; Lim, H; Liska, T; Litvinenko, A; Liu, M X; Li, X; Li, X H; Love, B; Lynch, D; Maguire, C F; Makdisi, Y I; Malakhov, A; Malik, M D; Manko, V I; Mao, Y; Masek, L; Masui, H; Matathias, F; McCain, M C; McCumber, M; McGaughey, P L; Miake, Y; Mikes, P; Miki, K; Miller, T E; Milov, A; Mioduszewski, S; Mishra, G C; Mishra, M; Mitchell, J T; Mitrovski, M; Morreale, A; Morrison, D P; Moss, J M; Moukhanova, T V; Mukhopadhyay, D; Murata, J; Nagamiya, S; Nagata, Y; Nagle, J L; Naglis, M; Nakagawa, I; Nakamiya, Y; Nakamura, T; Nakano, K; Newby, J; Nguyen, M; Norman, B E; Nyanin, A S; Nystrand, J; O'Brien, E; Oda, S X; Ogilvie, C A; Ohnishi, H; Ojha, I D; Okada, H; Okada, K; Oka, M; Omiwade, O O; Oskarsson, A; Otterlund, I; Ouchida, M; Ozawa, K; Pak, R; Pal, D; Palounek, A P T; Pantuev, V; Papavassiliou, V; Park, J; Park, W J; Pate, S F; Pei, H; Peng, J-C; Pereira, H; Peresedov, V; Peressounko, D Yu; Pinkenburg, C; Pisani, R P; Purschke, M L; Purwar, A K; Qu, H; Rak, J; Rakotozafindrabe, A; Ravinovich, I; Read, K F; Rembeczki, S; Reuter, M; Reygers, K; Riabov, V; Riabov, Y; Roche, G; Romana, A; Rosati, M; Rosendahl, S S E; Rosnet, P; Rukoyatkin, P; Rykov, V L; Ryu, S S; Sahlmueller, B; Saito, N; Sakaguchi, T; Sakai, S; Sakata, H; Samsonov, V; Sato, H D; Sato, S; Sawada, S; Seele, J; Seidl, R; Semenov, V; Seto, R; Sharma, D; Shea, T K; Shein, I; Shevel, A; Shibata, T-A; Shigaki, K; Shimomura, M; Shohjoh, T; Shoji, K; Sickles, A; Silva, C L; Silvermyr, D; Silvestre, C; Sim, K S; Singh, C P; Singh, V; Skutnik, S; Slunecka, M; Smith, W C; Soldatov, A; Soltz, R A; Sondheim, W E; Sorensen, S P; Sourikova, I V; Staley, F; Stankus, P W; Stenlund, E; Stepanov, M; Ster, A; Stoll, S P; Sugitate, T; Suire, C; Sullivan, J P; Sziklai, J; Tabaru, T; Takagi, S; Takagui, E M; Taketani, A; Tanaka, K H; Tanaka, Y; Tanida, K; Tannenbaum, M J; Taranenko, A; Tarján, P; Thomas, T L; Togawa, M; Toia, A; Tojo, J; Tomásek, L; Torii, H; Towell, R S; Tram, V-N; Tserruya, I; Tsuchimoto, Y; Tuli, S K; Tydesjö, H; Tyurin, N; Vale, C; Valle, H; van Hecke, H W; Velkovska, J; Vertesi, R; Vinogradov, A A; Virius, M; Vrba, V; Vznuzdaev, E; Wagner, M; Walker, D; Wang, X R; Watanabe, Y; Wessels, J; White, S N; Willis, N; Winter, D; Woody, C L; Wysocki, M; Xie, W; Yamaguchi, Y L; Yanovich, A; Yasin, Z; Ying, J; Yokkaichi, S; Young, G R; Younus, I; Yushmanov, I E; Zajc, W A; Zaudtke, O; Zhang, C; Zhou, S; Zimányi, J; Zolin, L
2008-12-05
For Au + Au collisions at 200 GeV, we measure neutral pion production with good statistics for transverse momentum, pT, up to 20 GeV/c. A fivefold suppression is found, which is essentially constant for 5 < pT < 20 GeV/c. Experimental uncertainties are small enough to constrain any model-dependent parametrization for the transport coefficient of the medium, e.g., q in the parton quenching model. The spectral shape is similar for all collision classes, and the suppression does not saturate in Au + Au collisions.
NASA Astrophysics Data System (ADS)
Sun, Yue; Chen, Z. P.; Zhuang, G.; Wang, L.; Liu, H.; Wang, Z. J.
2016-04-01
The influences of electrode biasing (EB) on toroidal rotation and turbulent (toroidal) momentum transport at the plasma edge have been experimentally studied in the J-TEXT tokamak. In the absence of bias (i.e. the bias current I b = 0 A), plasma toroidal rotation at the edge of the confined region is intrinsically towards the co-I p direction (parallel to plasma current); in the presence of bias, edge rotation can be greatly modified, and shows positive correlation with the bias current. As the dominant term in the turbulent momentum flux, the toroidal-radial Reynolds stress term is found to give rise to an intrinsic torque in the experiments. The local momentum balance is provided by a viscous damping-like term on the velocity. Moreover, the existence of intrinsic torque at the edge is directly verified by cancelling out the local rotation under negative bias (I b ≈ -60 A). The corresponding intrinsic torque density at the plasma edge is about 0.65 N m-2, in the co-I p direction. Further comparison shows that this intrinsic torque can be reasonably explained by the measured residual stress, providing direct evidence for the hypothesis that the residual stress is the origin of the intrinsic rotation.
Absorption of intense microwaves and ion acoustic turbulence due to heat transport
De Groot, J.S.; Liu, J.M.; Matte, J.P.
1994-02-04
Measurements and calculations of the inverse bremsstrahlung absorption of intense microwaves are presented. The isotropic component of the electron distribution becomes flat-topped in agreement with detailed Fokker-Planck calculations. The plasma heating is reduced due to the flat-topped distributions in agreement with calculations. The calculations show that the heat flux at high microwave powers is very large, q{sub max} {approx} 0.3 n{sub e}v{sub e}T{sub e}. A new particle model to, calculate the heat transport inhibition due to ion acoustic turbulence in ICF plasmas is also presented. One-dimensional PIC calculations of ion acoustic turbulence excited due to heat transport are presented. The 2-D PIC code is presently being used to perform calculations of heat flux inhibition due to ion acoustic turbulence.
Deterministic transport calculations of dose profiles due to proton beam irradiation
Filippone, W.L.; Smith, M.S.; Santoro, R.T.; Gabriel, T.A.; Alsmiller, R.G. Jr.
1988-01-01
Charged-particle transport calculations are most often carried out using the Monte Carlo technique. For example, the TIGER and EGS codes are used for electron transport calculations, while HETC models the transport of protons and heavy ions. In recent years there has been considerable progress in deterministic models of electron transport. Many of these models are also applicable to protons. In this paper we present discrete ordinates solutions to the Spencer-Lewis equation for protons. In its present form, our code calculates the energy deposition profile and primary proton flux in x-y geometry due to proton beam irradiation. Proton energies up to 0.4 GeV are permissible.
NASA Astrophysics Data System (ADS)
Jovanović, J. V.; Vrhovac, S. B.; Petrović, Z. Lj.
2002-12-01
Transport properties of ion swarms in presence of Resonant Charge Transfer (RCT) collisions are studied using Momentum Transfer Theory (MTT). It was shown that, not surprisingly, RCT collisions may be represented as a special case of elastic scattering. Using the developed MTT we tested a previously available anisotropic set of cross-sections for Ar+Ar^+ collisions by making the comparisons with the available data for the transverse diffusion coefficient. We also developed an anisotropic set of Ne+Ne^+ integral cross-sections based on the available data for mobility, longitudinal and transverse diffusion. Anisotropic sets of cross-sections are needed for Monte Carlo simulations of ion transport and plasma models.
NASA Astrophysics Data System (ADS)
Estrada, Paul R.; Durisen, Richard H.; Cuzzi, Jeffrey N.; Morgan, Demitri A.
2015-05-01
We introduce improved numerical techniques for simulating the structural and compositional evolution of planetary rings due to micrometeoroid bombardment and subsequent ballistic transport of impact ejecta. Our current, robust code is capable of modeling structural changes and pollution transport simultaneously over long times on both local and global scales. In this paper, we describe the methodology based on the original structural code of Durisen et al. (Durisen, R.H. et al. [1989]. Icarus 80, 136-166) and on the pollution transport code of Cuzzi and Estrada (Cuzzi, J.N., Estrada, P.R. [1998]. Icarus 132, 1-35). We provide demonstrative simulations to compare with, and extend upon previous work, as well as examples of how ballistic transport can maintain the observed structure in Saturn's rings using available Cassini occultation optical depth data. In particular, we explicitly verify the claim that the inner B (and presumably A) ring edge can be maintained over long periods of time due to an ejecta distribution that is heavily biased in the prograde direction through a balance between the sharpening effects of ballistic transport and the broadening effects of viscosity. We also see that a "ramp"-like feature forms over time just inside that edge. However, it does not remain linear for the duration of the runs presented here unless a less steep ejecta velocity distribution is adopted. We also model the C ring plateaus and find that their outer edges can be maintained at their observed sharpness for long periods due to ballistic transport. We hypothesize that the addition of a significant component of a retrograde-biased ejecta distribution may help explain the linearity of the ramp and could provide a mechanism for maintaining the sharpness of C ring plateau inner edges. This component would arise for the subset of micrometeoroid impacts which are destructive rather than merely cratering. Such a distribution will be introduced in future work.
NASA Technical Reports Server (NTRS)
Estrada, Paul R.; Durisen, Richard H.; Cuzzi, Jeffrey N.; Morgan, Demitri A.
2015-01-01
We introduce improved numerical techniques for simulating the structural and compositional evolution of planetary rings due to micrometeoroid bombardment and subsequent ballistic transport of impact ejecta. Our current, robust code is capable of modeling structural changes and pollution transport simultaneously over long times on both local and global scales. In this paper, we describe the methodology based on the original structural code of Durisen et al. (1989, Icarus 80, 136-166) and on the pollution transport code of Cuzzi and Estrada (1998, Icarus 132, 1-35). We provide demonstrative simulations to compare with, and extend upon previous work, as well as examples of how ballistic transport can maintain the observed structure in Saturn's rings using available Cassini occultation optical depth data. In particular, we explicitly verify the claim that the inner B (and presumably A) ring edge can be maintained over long periods of time due to an ejecta distribution that is heavily biased in the prograde direction through a balance between the sharpening effects of ballistic transport and the broadening effects of viscosity. We also see that a "ramp"-like feature forms over time just inside that edge. However, it does not remain linear for the duration of the runs presented here unless a less steep ejecta velocity distribution is adopted. We also model the C ring plateaus and find that their outer edges can be maintained at their observed sharpness for long periods due to ballistic transport. We hypothesize that the addition of a significant component of a retrograde-biased ejecta distribution may help explain the linearity of the ramp and is probably essential for maintaining the sharpness of C ring plateau inner edges. This component would arise for the subset of micrometeoroid impacts which are destructive rather than merely cratering. Such a distribution will be introduced in future work.
NASA Astrophysics Data System (ADS)
Padurariu, C.; Jonckheere, T.; Rech, J.; Martin, T.; Feinberg, D.
2017-05-01
We investigate the proximity effect in junctions between N =3 superconductors under commensurate voltage bias. The bias is chosen to highlight the role of transport processes that exchange multiple Cooper pairs coherently between more than two superconductors. Such nonlocal processes can be studied in the dc response, where local transport processes do not contribute. We focus on the proximity-induced normal density of states that we investigate in a wide parameter space. We reveal the presence of deep and highly tunable pseudogaps and other rich structures. These are due to a static proximity effect that is absent for N =2 and is sensitive to an emergent superconducting phase associated to nonlocal coherent transport. In comparison with results for N =2 , we find similarities in the signature peaks of multiple Andreev reflections. We discuss the effect of electron-hole decoherence and of various types of junction asymmetries. Our predictions can be investigated experimentally using tunneling spectroscopy.
Battaglia, D. J.; Boedo, J. A.; Burrell, K. H.; Chang, C. S.; Canik, J. M.; deGrassie, J. S.; Gerhardt, S. P.; Grierson, B. A.; Groebner, R. J.; Maingi, Rajesh; Smith, S. P.
2014-09-01
Energy and particle transport rates are decoupled in the H-mode edge since the ion thermal transport rate is primarily set by the neoclassical transport of the deuterium ions in the tail of the thermal energy distribution, while the net particle transport rate is set by anomalous transport of the colder bulk ions. Ion orbit loss drives the energy distributions away from Maxwellian, and describes the anisotropy, poloidal asymmetry and local minimum near the separatrix observed in the Ti profile. Non-Maxwellian distributions also drive large intrinsic edge flows, and the interaction of turbulence at the top of the pedestal with the intrinsic edge flow can generate an intrinsic core torque. The primary driver of the radial electric field (Er) in the pedestal and scrapeoff layer (SOL) are kinetic neoclassical effects, such as ion orbit loss of tail ions and parallel electron loss to the divertor. This paper describes the first multi-species kinetic neoclassical transport calculations for ELM-free H-mode pedestal and scrape-off layer on DIII-D using XGC0, a 5D full-f particle-in-cell drift-kinetic solver with self-consistent neutral recycling and sheath potentials. Quantitative agreement between the flux-driven simulation and the experimental electron density, impurity density and orthogonal measurements of impurity temperature and flow profiles is achieved by adding random-walk particle diffusion to the guiding-center drift motion. This interpretative technique quantifies the role of neoclassical, anomalous and neutral transport to the overall pedestal structure, and consequently illustrates the importance of including kinetic effects self-consistently in transport calculations around transport barriers.
NASA Astrophysics Data System (ADS)
Coppi, B.; Basu, B.; Fletcher, A.
2016-10-01
The two-fluid theory of magnetic reconnection, when the longitudinal electron thermal conductivity is relatively large, shows that the perturbed electron temperature tends to become singular in the presence of a reconnected field component and an electron temperature gradient. A transverse thermal diffusivity can remove this singularity while a finite ``inductivity'' can remove the singularity of the corresponding plasma displacement. Then i) a new ``magneto-thermal reconnection'' producing mode, driven by the electron temperature gradient, is found; ii) the characteristic widths of the layers where reconnection takes place remain significant even when the relevant macroscopic distances are very large; iii) modes with phase velocities both in the electron diamagnetic velocity direction and in the opposite one are found. Their growth rates depend on small dissipative factors. The found modes can extract angular momentum from the plasma and thereby sustain a ``spontaneous rotation'' process. Sponsored by the U.S. D.O.E.
NASA Astrophysics Data System (ADS)
Ramalho, Inês; Omira, Rachid; Baptista, Maria Ana; El Moussaoui, Said; Najib Zaghloul, Mohamed
2016-04-01
Coastal areas in the North of Morocco are at risk of tsunami inundation. Overland tsunami propagation leads to widespread and dramatic changes in coastal morphology due to sediments erosion, transport and deposition processes. Tsunami sediments transport and morphological changes must take into consideration bed-load and suspended load transport of non-cohesive sediments and suspended load of cohesive sediments. Numerical calculation of suspended sediment transport/deposition is performed by solving the advection-diffusion equations for the suspended sediment, where the velocities are obtained from the hydrodynamic modelling. In this study, we assess the morphological changes under tsunami impact at the Bay of Tangier-Morocco. We use a coupled hydrodynamic and morpho-dynamic numerical code, based on two open sources codes: COMCOT and Xbeach, to simulate the tsunami impact and the associated sediments transport and deposition. COMCOT solves the shallow water equations to calculate the inundation characteristics (flow depth and velocity), while Xbeach allows solving the advection-diffusion equations to determine the amount of sediments eroded, transported and deposed. The results of this study are presented in terms of maps displaying the amount of sediments eroded, transported and deposed at the bay of Tangier following a tsunami similar to the 1755 Lisbon event. We find that the bay of Tangier is vulnerable to morphological changes under tsunami threat coming from SW Iberia margin. This work is supported by the EU project ASTARTE - Assessment, Strategy And Risk Reduction for Tsunamis in Europe, Grant 603839, 7th FP (ENV.2013,6.4-3).
ERIC Educational Resources Information Center
Shakur, Asif; Sinatra, Taylor
2013-01-01
The gyroscope in a smartphone was employed in a physics laboratory setting to verify the conservation of angular momentum and the nonconservation of rotational kinetic energy. As is well-known, smartphones are ubiquitous on college campuses. These devices have a panoply of built-in sensors. This creates a unique opportunity for a new paradigm in…
ERIC Educational Resources Information Center
Shakur, Asif; Sinatra, Taylor
2013-01-01
The gyroscope in a smartphone was employed in a physics laboratory setting to verify the conservation of angular momentum and the nonconservation of rotational kinetic energy. As is well-known, smartphones are ubiquitous on college campuses. These devices have a panoply of built-in sensors. This creates a unique opportunity for a new paradigm in…
Gravity wave motions and momentum fluxes in the middle atmosphere at Adelaide, Australia
NASA Technical Reports Server (NTRS)
Vincent, R. A.; Fritts, D. C.
1985-01-01
A study was made of gravity wave momentum fluxes in the middle atmosphere using data collected during June 1984 at Adelaide, Australia (35 deg S). The primary objectives were to identify that portion of the gravity wave spectrum that contributes most of the momentum transport and flux divergence and to examine the temporal variability of wave energies and momentum fluxes. The data were obtained with an HF (2 MHz) radar operated in a Doppler configuration with two coplanar off-vertical beams. This technique provides a direct measure of the vertical flux of horizontal momentum due to an arbitrary spectrum of gravity wave and other motions in the plane of the radar beams.
NASA Astrophysics Data System (ADS)
Moradi, Gelare; Cardot, Romain; Lane, Stuart; Rennie, Colin
2017-04-01
River confluences are zones where two or more rivers join and form a single channel downstream of their junction. Because of their essential role in the dynamic of fluvial networks, there has been an increase in the attention given to their hydrodynamics and morphodynamics during last three decades. Despite this increased understanding of the complex flow behavior and morphological aspects, few studies has been focused on low momentum ratio river confluences and mixing processes. As among these few studies, most of them have been driven by the mean of laboratory experiments and numerical models, a combination of field data collection and data processing is required to study the effect of low momentum ratio on flow dynamic, rive morphology and rate of mixing in river confluences. In the present poster, the flow discharge and velocity data of two upper Rhône river confluences in Switzerland, which are characterized by low momentum ratio and a varied rate of poorly sorted sediment transport is shown. The data set is mostly collected, using spatial distributed acoustic Doppler current profiling (aDcp) measurements. The morphological changes are studied using a combination of high-resolution aerial imagery data obtained by a phantom drone and acoustic bathymetric surveys. The mixing processes are investigated by measuring the surface water temperature with a thermic camera mounted on an E-bee drone [, whereas sediment pathways can be explored through the use of the 'bottom-tracking' feature of the aDcp device (not sure there will be such results at the conference time)]. These collected data is processed using a matlab code, Pix4D and visualization software. These processed data then can be used to describe the flow behavior, morphological aspects and mixing processes at river confluences characterized by low momentum ratio and to test laboratory derived conceptual models of flow processes at such junctions. The obtained results can be used under a wider range of
Slope Evolution by Stochastic Soil Production and Transport due to Biota
NASA Astrophysics Data System (ADS)
Dietrich, W. E.; Bellugi, D.
2006-05-01
To explore the role of variability in prediction of landscape form and evolution we need transport expressions that explicitly account for mechanisms linking a process to a stochastic driver or variable state. Recent work has begun the important task of exploring how stochastic rainfall events (rather than steady runoff) may affect landscape development. Another source of variability, bedrock characteristics, has long been discussed and noted, but predictions, using testable mechanistic expressions of processes, of how, say, bedrock fractures direct streams, or lithology determines hillslope gradients are lacking. A third source of stochasticity is the action of biota, and, here, even less is known. For hillslope processes, the role of biota is swept into parameters that set rates or controls strength or resistance in physical transport laws. While these parameters can be determined from field studies, they are usually evaluated for geomorphically significant periods in which the stochastic nature of biotic activity is ignored. Some aspects of stochasticity due to periodic fires have been explored. On hillslopes, rates of soil production from bedrock is often treated as an inverse function of soil depth, with the explanation being that biotic disruption of underlying weathered bedrock is less likely the thicker the soil. Transport downslope is modeled with linear and non-linear slope dependent expressions, with the rate constant parameters often assumed to be driven by dilational activity of biota in the soil. Here we explore the evolution of soil thickness and hillslope form caused by stochastic soil production and transport due to tree throw. For soil production the average recurrence interval of production is specified, and production occurrence at any cell is an independent random event at each time step. The amount of bedrock converted to soil at a production event is specified by the empirical soil production function. All disrupted bedrock and overlying soil
Cen, Renyue
2015-05-20
We reason that without physical fine-tuning, neither the supermassive black holes (SMBHs) nor the stellar bulges can self-regulate or inter-regulate by driving away already fallen cold gas to produce the observed correlation between them. We suggest an alternative scenario where the observed mass ratios of the SMBHs to bulges reflect the angular momentum distribution of infallen gas such that the mass reaching the stable accretion disk is a small fraction of that reaching the bulge region, averaged over the cosmological timescales. We test this scenario using high-resolution, large-scale cosmological hydrodynamic simulations, without active galactic nucleus (AGN) feedback, assuming the angular momentum distribution of gas landing in the bulge region yields a Mestel disk that is supported by independent simulations resolving the Bondi radii of SMBHs. A mass ratio of 0.1%–0.3% between the very low angular momentum gas that free falls to the subparsec region to accrete to the SMBH and the overall star formation rate is found. This ratio is found to increase with increasing redshift to within a factor of ∼2, suggesting that the SMBH-to-bulge ratio is nearly redshift independent, with a modest increase with redshift, which is a testable prediction. Furthermore, the duty cycle of AGNs with high Eddington ratios is expected to increase significantly with redshift. Finally, while SMBHs and bulges are found to coevolve on ∼30–150 Myr timescales or longer, there is indication that on still smaller timescales, the SMBH accretion and star formation may be less correlated.
Investigation of VOC Transport in Soil Vapors due to Wind Effects using Models and Measurement
NASA Astrophysics Data System (ADS)
Pennell, K. G.; Roghani, M.; Shirazi, E.; Willett, E.
2014-12-01
For the past several years, vapor intrusion of volatile organic compounds (VOCs) that emanate from hazardous waste sites has been gaining attention due to adverse health effects and regulatory action. Most studies of VOC vapor intrusion suggest that diffusion is the dominant contaminant transport mechanism, while advection is only considered important near contaminant entry points (i.e. building cracks). This conceptual framework is accurate when above-ground surface features do not promote air flow into (or out of) the ground surface. Recent research related to air flow in the atmospheric boundary layer (ABL) due to wind effects around buildings suggests a need for better understanding how advective transport processes can impact contaminant profiles and vapor intrusion exposure risks. In this study, a numerical model using COMSOL Multiphysics was developed to account for parameters affecting the transport of VOCs from the subsurface into buildings by considering wind effects in the ABL. Model simulations are compared to preliminary laboratory and field data to evaluate the relative importance of wind induced pressure gradients, soil permeability, soil porosity, and soil effective diffusivity on vapor intrusion entry rates. The major goal of this research is to develop an improved conceptual understanding of the vapor intrusion process so that remediation efforts can be better designed and implemented.
Menezes, Manoj P; O'Brien, Katherine; Hill, Mandy; Webster, Richard; Antony, Jayne; Ouvrier, Robert; Birman, Catherine; Gardner-Berry, Kirsty
2016-08-01
Mutations in the genes encoding the riboflavin transporters RFVT2 and RFVT3 have been identified in Brown-Vialetto-Van Laere syndrome, a neurodegenerative disorder characterized by hearing loss and pontobulbar palsy. Treatment with riboflavin has been shown to benefit individuals with the phenotype of RFVT2 deficiency. Understanding the characteristics of hearing loss in riboflavin transporter deficiency would enable early diagnosis and therapy. We performed hearing assessments in seven children (from four families) with RFVT2 deficiency and reviewed results from previous assessments. Assessments were repeated after 12 months and 24 months of riboflavin therapy and after cochlear implantation in one individual. Hearing loss in these individuals was due to auditory neuropathy spectrum disorder (ANSD). Hearing loss was identified between 3 years and 8 years of age and progressed rapidly. Hearing aids were not beneficial. Riboflavin therapy resulted in improvement of hearing thresholds during the first year of treatment in those with recent-onset hearing loss. Cochlear implantation resulted in a significant improvement in speech perception in one individual. Riboflavin transporter deficiency should be considered in all children presenting with an auditory neuropathy. Speech perception in children with ANSD due to RFVT2 deficiency may be significantly improved by cochlear implantation. © 2016 Mac Keith Press.
Holzinger, Dennis; Koch, Iris; Burgard, Stefan; Ehresmann, Arno
2015-07-28
An approach for a remotely controllable transport of magnetic micro- and/or nanoparticles above a topographically flat exchange-bias (EB) thin film system, magnetically patterned into parallel stripe domains, is presented where the particle manipulation is achieved by sub-mT external magnetic field pulses. Superparamagnetic core-shell particles are moved stepwise by the dynamic transformation of the particles' magnetic potential energy landscape due to the external magnetic field pulses without affecting the magnetic state of the thin film system. The magnetic particle velocity is adjustable in the range of 1-100 μm/s by the design of the substrate's magnetic field landscape (MFL), the particle-substrate distance, and the magnitude of the applied external magnetic field pulses. The agglomeration of magnetic particles is avoided by the intrinsic magnetostatic repulsion of particles due to the parallel alignment of the particles' magnetic moments perpendicular to the transport direction and parallel to the surface normal of the substrate during the particle motion. The transport mechanism is modeled by a quantitative theory based on the precise knowledge of the sample's MFL and the particle-substrate distance.
Incorporating Super-Diffusion due to Sub-Grid Heterogeneity to Capture Non-Fickian Transport.
Baeumer, Boris; Zhang, Yong; Schumer, Rina
2015-01-01
Numerical transport models based on the advection-dispersion equation (ADE) are built on the assumption that sub-grid cell transport is Fickian such that dispersive spreading around the average velocity is symmetric and without significant tailing on the front edge of a solute plume. However, anomalous diffusion in the form of super-diffusion due to preferential pathways in an aquifer has been observed in field data, challenging the assumption of Fickian dispersion at the local scale. This study develops a fully Lagrangian method to simulate sub-grid super-diffusion in a multidimensional regional-scale transport model by using a recent mathematical model allowing super-diffusion along the flow direction given by the regional model. Here, the time randomizing procedure known as subordination is applied to flow field output from MODFLOW simulations. Numerical tests check the applicability of the novel method in mapping regional-scale super-diffusive transport conditioned on local properties of multidimensional heterogeneous media.
NASA Astrophysics Data System (ADS)
Simakov, Andrei N.; Catto, Peter J.
2005-10-01
Expressions for ion perpendicular viscosity, electron and ion parallel viscosities, gyroviscosities, and heat fluxes, as well as electron-ion energy and momentum exchange terms are derived for arbitrary mean-free path plasmas, in which the lowest order distribution function is a Maxwellian. The latter assumption often holds for plasmas confined by magnetic fields with closed flux surfaces in the absence of strong external driving forces [1], such as neutral beams or radio-frequency waves. In particular, it is always employed in the neoclassical theory. The results are given in terms of a few velocity space integrals of the gyrophase averaged correction to the Maxwellian by assuming the gyroradius is small compared to the shortest perpendicular scale length. The general expressions make possible a hybrid fluid-kinetic description, and correctly reproduce known results in the collisional limit [2].[1] R. D. Hazeltine and J. D. Meiss, Plasma Confinement (Addison-Wesley, Redwood City, CA, 1991).[2] P. J. Catto and A. N. Simakov, Phys. Plasmas 11, 90 (2004).
NASA Astrophysics Data System (ADS)
Frosini, Mikael; Bernard, Denis
2017-09-01
We revisit the precision of the measurement of track parameters (position, angle) with optimal methods in the presence of detector resolution, multiple scattering and zero magnetic field. We then obtain an optimal estimator of the track momentum by a Bayesian analysis of the filtering innovations of a series of Kalman filters applied to the track. This work could pave the way to the development of autonomous high-performance gas time-projection chambers (TPC) or silicon wafer γ-ray space telescopes and be a powerful guide in the optimization of the design of the multi-kilo-ton liquid argon TPCs that are under development for neutrino studies.
Nonlinear thermoelectric response due to energy-dependent transport properties of a quantum dot
NASA Astrophysics Data System (ADS)
Svilans, Artis; Burke, Adam M.; Svensson, Sofia Fahlvik; Leijnse, Martin; Linke, Heiner
2016-08-01
Quantum dots are useful model systems for studying quantum thermoelectric behavior because of their highly energy-dependent electron transport properties, which are tunable by electrostatic gating. As a result of this strong energy dependence, the thermoelectric response of quantum dots is expected to be nonlinear with respect to an applied thermal bias. However, until now this effect has been challenging to observe because, first, it is experimentally difficult to apply a sufficiently large thermal bias at the nanoscale and, second, it is difficult to distinguish thermal bias effects from purely temperature-dependent effects due to overall heating of a device. Here we take advantage of a novel thermal biasing technique and demonstrate a nonlinear thermoelectric response in a quantum dot which is defined in a heterostructured semiconductor nanowire. We also show that a theoretical model based on the Master equations fully explains the observed nonlinear thermoelectric response given the energy-dependent transport properties of the quantum dot.
NASA Astrophysics Data System (ADS)
Lindsay, Alexander; Anderson, Carly; Slikboer, Elmar; Shannon, Steven; Graves, David
2015-10-01
There is a growing interest in the study of plasma-liquid interactions with application to biomedicine, chemical disinfection, agriculture, and other fields. This work models the momentum, heat, and neutral species mass transfer between gas and aqueous phases in the context of a streamer discharge; the qualitative conclusions are generally applicable to plasma-liquid systems. The problem domain is discretized using the finite element method. The most interesting and relevant model result for application purposes is the steep gradients in reactive species at the interface. At the center of where the reactive gas stream impinges on the water surface, the aqueous concentrations of OH and ONOOH decrease by roughly 9 and 4 orders of magnitude respectively within 50 μ m of the interface. Recognizing the limited penetration of reactive plasma species into the aqueous phase is critical to discussions about the therapeutic mechanisms for direct plasma treatment of biological solutions. Other interesting results from this study include the presence of a 10 K temperature drop in the gas boundary layer adjacent to the interface that arises from convective cooling. Though the temperature magnitudes may vary among atmospheric discharge types (different amounts of plasma-gas heating), this relative difference between gas and liquid bulk temperatures is expected to be present for any system in which convection is significant. Accounting for the resulting difference between gas and liquid bulk temperatures has a significant impact on reaction kinetics; factor of two changes in terminal aqueous species concentrations like H2O2, NO2- , and NO3- are observed in this study if the effect of evaporative cooling is not included.
NASA Astrophysics Data System (ADS)
Li, Qi; Bou-Zeid, Elie; Anderson, William
2016-04-01
Spectral discretization of quantities exhibiting abrupt shifts results in oscillations, or ;ringing;, known as the Gibbs phenomenon. When spectral discretization is used to evaluate spatial gradients during numerical integration of the transport equations governing turbulent fluid flows, these oscillations can contaminate various flow quantities. A particularly relevant application where the emergence of Gibbs phenomenon is a well-recognized weakness is in the context of simulations using the immersed boundary method. In this paper, we examine the effect of the Gibbs phenomenon in such simulations in detail, and we propose a computationally efficient smoothing treatment to reduce the associated oscillations. The effectiveness of this treatment is demonstrated in a priori tests on functions with abrupt shifts, and in a posteriori tests in wall-modeled large-eddy simulations of incompressible flow and passive scalar transport over solid bluff bodies. Furthermore, the large eddy simulation results indicate that the Gibbs phenomenon's impacts are significantly more detrimental to the computations of the subgrid-scale quantities and of scalar transport close to the solid interface, as compared to their impact on computations involving the resolved velocity field.
Inhibition of quantum transport due to 'scars' of unstable periodic orbits
NASA Technical Reports Server (NTRS)
Jensen, R. V.; Sanders, M. M.; Saraceno, M.; Sundaram, B.
1989-01-01
A new quantum mechanism for the suppression of chaotic ionization of highly excited hydrogen atoms explains the appearance of anomalously stable states in the microwave ionization experiments of Koch et al. A novel phase-space representation of the perturbed wave functions reveals that the inhibition of quantum transport is due to the selective excitation of wave functions that are highly localized near unstable periodic orbits in the chaotic classical phase space. The 'scarred' wave functions provide a new basis for the quantum description of a variety of classically chaotic systems.
Rawl, Richard R; Scofield, Patricia A; Leggett, Richard Wayne; Eckerman, Keith F
2010-04-01
The International Atomic Energy Agency (IAEA) initiated an international Coordinated Research Project (CRP) to evaluate the safety of transport of naturally occurring radioactive material (NORM). This report presents the United States contribution to that IAEA research program. The focus of this report is on the analysis of the potential doses resulting from the transport of low level radioactive material. Specific areas of research included: (1) an examination of the technical approach used in the derivation of exempt activity concentration values and a comparison of the doses associated with the transport of materials included or not included in the provisions of Paragraph 107(e) of the IAEA Safety Standards, Regulations for the Safe Transport of Radioactive Material, Safety Requirements No. TS-R-1; (2) determination of the doses resulting from different treatment of progeny for exempt values versus the A{sub 1}/A{sub 2} values; and (3) evaluation of the dose justifications for the provisions applicable to exempt materials and low specific activity materials (LSA-I). It was found that the 'previous or intended use' (PIU) provision in Paragraph 107(e) is not risk informed since doses to the most highly exposed persons (e.g., truck drivers) are comparable regardless of intended use of the transported material. The PIU clause can also have important economic implications for co-mined ores and products that are not intended for the fuel cycle but that have uranium extracted as part of their industrial processing. In examination of the footnotes in Table 2 of TS-R-1, which identifies the progeny included in the exempt or A1/A2 values, there is no explanation of how the progeny were selected. It is recommended that the progeny for both the exemption and A{sub 1}/A{sub 2} values should be similar regardless of application, and that the same physical information should be used in deriving the limits. Based on the evaluation of doses due to the transport of low-level NORM
CFD Assessment of Aerodynamic Degradation of a Subsonic Transport Due to Airframe Damage
NASA Technical Reports Server (NTRS)
Frink, Neal T.; Pirzadeh, Shahyar Z.; Atkins, Harold L.; Viken, Sally A.; Morrison, Joseph H.
2010-01-01
A computational study is presented to assess the utility of two NASA unstructured Navier-Stokes flow solvers for capturing the degradation in static stability and aerodynamic performance of a NASA General Transport Model (GTM) due to airframe damage. The approach is to correlate computational results with a substantial subset of experimental data for the GTM undergoing progressive losses to the wing, vertical tail, and horizontal tail components. The ultimate goal is to advance the probability of inserting computational data into the creation of advanced flight simulation models of damaged subsonic aircraft in order to improve pilot training. Results presented in this paper demonstrate good correlations with slope-derived quantities, such as pitch static margin and static directional stability, and incremental rolling moment due to wing damage. This study further demonstrates that high fidelity Navier-Stokes flow solvers could augment flight simulation models with additional aerodynamic data for various airframe damage scenarios.
Time-dependent Radial Transport of Electron Distributions Due to ECCD in DIII-D
NASA Astrophysics Data System (ADS)
Harvey, R. W.; Smirnov, A. P.; Prater, R.; Petty, C. C.
2007-11-01
The radial transport modeling capability in the CQL3D bounce-averaged Fokker-Planck collisional-rf quasilinear code[1] has been greatly improved and the self-consistent time-dependent toroidal electric field added, making the code truly a ``Fokker-Planck-Transport'' code. The time-dependent, coupled 3D Fokker-Planck equation and the Ampere-Faraday Law equation are solved for the electron distribution, f( u,θu,ρ,t ), and the toroidal loop voltage, Vloop( ρ,t ). A fully 3D, time-implicit solution of the FP equation using sparse-matrix methods[2] is coupled to a new iterative toroidal electric field solve. The DIII-D ECH experiment is in an intermediate driven regime with τtransport τslowing[3] for the EC driven electrons. Results will be reported for time-evolution of radial profiles of current density, fast electrons, and toroidal loop voltage due to EC heating and current drive in DIII-D. [1] R.W. Harvey and M.G. McCoy, IAEA TCM on Advances in Simulation and Modeling of Thermonuclear Plasmas, Montreal, 1992; USDOC NTIS No. 93002962. [2] Y. Peysson et al., Radio Frequency Power in Plasmas, 15th Topical Conference, Moran, Wyoming (2003). [3] R.W. Harvey et al., Phys. Rev. Lett. 88, 205001 (2002).
Modeling Longshore Transport and Coastal Erosion Due to Storms at Barrow, Alaska
NASA Astrophysics Data System (ADS)
Peckham, S. D.
2006-12-01
Rapid erosion of Arctic coastlines is well-documented and is a major concern for the residents of Arctic coastal communities. This problem appears to be exacerbated by longer periods of ice-free conditions as the result of climate change. Despite substantial prior work and several engineering reports by agencies and firms charged with the investigation of mitigation options, there have been very few scientific studies aimed at modeling the dominant physical processes and making quantitative predictions of coastal erosion rates along Arctic coastlines in response to various forcing parameters/scenarios and storm return frequencies. Moreover, there has been virtually no work aimed at trying to quantify the relative contributions of various coastal erosion processes, including longshore sediment transport, cross-shore sediment transport due to storm surges and sediment inputs from coastal watersheds. In an effort to quantify erosion rates for the coastline near Barrow, Alaska, a numerical coastal erosion model has been developed that conserves sediment as longshore currents set up by oblique storm waves remove sediment from some locations and deposit it at others. This model uses the well-known CERC formula (or similar formulas), which expresses the longshore sediment transport rate as a nonlinear function of the angle that the coastline makes with the incoming wave crests. The rate of accretion or erosion is then computed from the spatial derivative of this sediment transport rate, with accretion where the derivative is negative and erosion where it is positive. Incoming wave angles are computed from hourly wind data by invoking the simple assumption that a fully-developed sea state is achieved in each time step. While this assumption is not valid in general, it is reasonable for the large, sustained storm events that are responsible for the bulk of the sediment transport. The 1955 coastline near Barrow, as digitized from aerial photos, was used to initialize the
NASA Astrophysics Data System (ADS)
Radl, Stefan; Municchi, Federico; Goniva, Christoph
2016-11-01
Understanding transport phenomena in fluid-particle systems is of primary importance for the design of large-scale equipment, e.g., in the chemical industry. Typically, the analysis of such systems is performed by numerically solving a set of partial differential equations modeling the particle phase and the fluid phase as interpenetrating continua. Such models require a number of closure models that are often constructed via spatial filtering of data obtained from particle-resolved direct numerical simulations (PR-DNS). In the present work we make use of PR-DNS to evaluate corrections to existing closure models. Specifically, we aim on accounting for wall effects on the fluid-particle drag force and the particle-individual Nusselt number. We then propose an improved closure model to be used in particle-unresolved Euler-Lagrange (PU-EL) simulations. We demonstrate that such an advanced closure should account for a dimensionless filter size, as well as a normalized distance from the wall. In addition, we make an attempt to model the filtered fluid velocity profile in wall-bounded suspension flows. The authors acknowledge funding from the European Commission through FP7 Grant Agreement No. 604656, as well as VSC-3 and dcluster.tugraz.at.
NASA Astrophysics Data System (ADS)
Watanabe, N.; Sun, Y.; Taron, J.; Shao, H.; Kolditz, O.
2013-12-01
Modeling fracture permeability evolution is of great interest in various geotechnical applications including underground waste repositories, carbon capture and storage, and engineered geothermal systems where fractures dominate transport behaviors. In this study, a numerical model is presented to simulate fracture permeability evolution due to reactive transport and pressure solution processes in single fractures. The model was developed within the international benchmarking project for radioactive waste disposals, DECOVALEX 2015 (Task C1). The model combines bulk behavior in pore spaces with intergranular process at asperity contacts. Hydraulic flow and reactive transport including mineral dissolution and precipitation in fracture pore space are simulated using the Galerkin finite element method. A pressure solution model developed by Taron and Elsworth (2010 JGR) is applied to simulating stress-enhanced dissolution, solute exchange with pore space, and volume removal at grain contacts. Fracture aperture and contact area ratio are updated as a result of the pore-space reaction and intergranular dissolution. In order to increase robustness and time step size, relevant processes are monolithically coupled with the simulations. The model is implemented in a scientific open-source project OpenGeoSys (www.opengeosys.org) for numerical simulation of thermo-hydro-mechanical/chemical processes in porous and fractured media. Numerical results are compared to previous experiment performed by Yasuhara et al. (2006) on flow through fractures in the Arkansas novaculite sample. The novaculite is approximated as pure quartz aggregates. Only with fitted quartz dissolution rate constants and solubility is the current model capable of reproducing observed hydraulic aperture reduction and aqueous silicate concentrations. Future work will examine reaction parameters and further validate the model against experimental results.
Oil droplets transport due to irregular waves: Development of large-scale spreading coefficients.
Geng, Xiaolong; Boufadel, Michel C; Ozgokmen, Tamay; King, Thomas; Lee, Kenneth; Lu, Youyu; Zhao, Lin
2016-03-15
The movement of oil droplets due to waves and buoyancy was investigated by assuming an irregular sea state following a JONSWAP spectrum and four buoyancy values. A technique known as Wheeler stretching was used to model the movement of particles under the moving water surface. In each simulation, 500 particles were released and were tracked for a real time of 4.0 h. A Monte Carlo approach was used to obtain ensemble properties. It was found that small eddy diffusivities that decrease rapidly with depth generated the largest horizontal spreading of the plume. It was also found that large eddy diffusivities that decrease slowly with depth generated the smallest horizontal spreading coefficient of the plume. The increase in buoyancy resulted in a decrease in the horizontal spreading coefficient, which suggests that two-dimensional (horizontal) models that predict the transport of surface oil could be overestimating the spreading of oil.
Significant change of spin transport property in Cu/Nb bilayer due to superconducting transition
Ohnishi, Kohei; Ono, Yuma; Nomura, Tatsuya; Kimura, Takashi
2014-01-01
The combination between the spin-dependent and super-conducting (SC) transports is expected to provide intriguing properties such as crossed Andreev reflection and spin-triplet superconductivity. This may be able to open a new avenue in the field of spintronics, namely superconducting spintronics because a superconductor itself has great potential for future nanoelectronic applications. To observe such SC spin transports, the suppression of the extrinsic effects originating from the heating and Oersted field due to the electric current is a crucial role. Pure spin current without accompanying the charge current is known as a powerful mean for preventing such extrinsic effects. However, non-negligible heat flow is found to exist even in a conventional pure spin current device based on laterally-configured spin valve because of the heating around the spin injector. Here, we develop a nanopillar-based lateral spin valve, which significantly reduces the heat generation, on a superconducting Nb film. By using this ideal platform, we found that the spin absorption is strongly suppressed by the SC transition of Nb. This demonstration is the clear evidence that the super-conducting Nb is an insulator for the pure spin current. PMID:25179118
Significant change of spin transport property in Cu/Nb bilayer due to superconducting transition
NASA Astrophysics Data System (ADS)
Ohnishi, Kohei; Ono, Yuma; Nomura, Tatsuya; Kimura, Takashi
2014-09-01
The combination between the spin-dependent and super-conducting (SC) transports is expected to provide intriguing properties such as crossed Andreev reflection and spin-triplet superconductivity. This may be able to open a new avenue in the field of spintronics, namely superconducting spintronics because a superconductor itself has great potential for future nanoelectronic applications. To observe such SC spin transports, the suppression of the extrinsic effects originating from the heating and Oersted field due to the electric current is a crucial role. Pure spin current without accompanying the charge current is known as a powerful mean for preventing such extrinsic effects. However, non-negligible heat flow is found to exist even in a conventional pure spin current device based on laterally-configured spin valve because of the heating around the spin injector. Here, we develop a nanopillar-based lateral spin valve, which significantly reduces the heat generation, on a superconducting Nb film. By using this ideal platform, we found that the spin absorption is strongly suppressed by the SC transition of Nb. This demonstration is the clear evidence that the super-conducting Nb is an insulator for the pure spin current.
Significant change of spin transport property in Cu/Nb bilayer due to superconducting transition.
Ohnishi, Kohei; Ono, Yuma; Nomura, Tatsuya; Kimura, Takashi
2014-09-02
The combination between the spin-dependent and super-conducting (SC) transports is expected to provide intriguing properties such as crossed Andreev reflection and spin-triplet superconductivity. This may be able to open a new avenue in the field of spintronics, namely superconducting spintronics because a superconductor itself has great potential for future nanoelectronic applications. To observe such SC spin transports, the suppression of the extrinsic effects originating from the heating and Oersted field due to the electric current is a crucial role. Pure spin current without accompanying the charge current is known as a powerful mean for preventing such extrinsic effects. However, non-negligible heat flow is found to exist even in a conventional pure spin current device based on laterally-configured spin valve because of the heating around the spin injector. Here, we develop a nanopillar-based lateral spin valve, which significantly reduces the heat generation, on a superconducting Nb film. By using this ideal platform, we found that the spin absorption is strongly suppressed by the SC transition of Nb. This demonstration is the clear evidence that the super-conducting Nb is an insulator for the pure spin current.
NASA Astrophysics Data System (ADS)
Ruiz, Maritza
Thermal management of systems under high heat fluxes on the order of hundreds of W/cm2 is important for the safety, performance and lifetime of devices, with innovative cooling technologies leading to improved performance of electronics or concentrating solar photovoltaics. A novel, spiraling radial inflow microchannel heat sink for high flux cooling applications, using a single phase or vaporizing coolant, has demonstrated enhanced heat transfer capabilities. The design of the heat sink provides an inward swirl flow between parallel, coaxial disks that form a microchannel of 1 cm radius and 300 micron channel height with a single inlet and a single outlet. The channel is heated on one side through a conducting copper surface, and is essentially adiabatic on the opposite side to simulate a heat sink scenario for electronics or concentrated photovoltaics cooling. Experimental results on the heat transfer and pressure drop characteristics in the heat sink, using single phase water as a working fluid, revealed heat transfer enhancements due to flow acceleration and induced secondary flows when compared to unidirectional laminar fully developed flow between parallel plates. Additionally, thermal gradients on the surface are small relative to the bulk fluid temperature gain, a beneficial feature for high heat flux cooling applications. Heat flux levels of 113 W/cm2 at a surface temperature of 77 deg C were reached with a ratio of pumping power to heat rate of 0.03%. Analytical models on single phase flow are used to explore the parametric trends of the flow rate and passage geometry on the streamlines and pressure drop through the device. Flow boiling heat transfer and pressure drop characteristics were obtained for this heat sink using water at near atmospheric pressure as the working fluid for inlet subcooling levels ranging from 20 to 80 deg C and mean mass flux levels ranging from 184-716 kg/m. 2s. Flow enhancements similar to singlephase flow were expected, as well
Douberly, Gary E. Liang, Tao; Raston, Paul L.; Marshall, Mark D.
2015-04-07
The T-shaped OH–C{sub 2}H{sub 2} complex is formed in helium droplets via the sequential pick-up and solvation of the monomer fragments. Rovibrational spectra of the a-type OH stretch and b-type antisymmetric CH stretch vibrations contain resolved parity splitting that reveals the extent to which electronic angular momentum of the OH moiety is quenched upon complex formation. The energy difference between the spin-orbit coupled {sup 2}B{sub 1} (A″) and {sup 2}B{sub 2} (A′) electronic states is determined spectroscopically to be 216 cm{sup −1} in helium droplets, which is 13 cm{sup −1} larger than in the gas phase [Marshall et al., J. Chem. Phys. 121, 5845 (2004)]. The effect of the helium is rationalized as a difference in the solvation free energies of the two electronic states. This interpretation is motivated by the separation between the Q(3/2) and R(3/2) transitions in the infrared spectrum of the helium-solvated {sup 2}Π{sub 3/2} OH radical. Despite the expectation of a reduced rotational constant, the observed Q(3/2) to R(3/2) splitting is larger than in the gas phase by ≈0.3 cm{sup −1}. This observation can be accounted for quantitatively by assuming the energetic separation between {sup 2}Π{sub 3/2} and {sup 2}Π{sub 1/2} manifolds is increased by ≈40 cm{sup −1} upon helium solvation.
Murakami, Shoko; Miyatake, Nobuyuki; Sakano, Noriko
2012-09-01
Changes in air temperature and its relation to ambulance transports due to heat stroke in all 47 prefectures, in Japan were evaluated. Data on air temperature were obtained from the Japanese Meteorological Agency. Data on ambulance transports due to heat stroke was directly obtained from the Fire and Disaster Management Agency, Japan. We also used the number of deaths due to heat stroke from the Ministry of Health, Labour and Welfare, Japan, and population data from the Ministry of Internal Affairs and Communications. Chronological changes in parameters of air temperature were analyzed. In addition, the relation between air temperature and ambulance transports due to heat stroke in August 2010 was also evaluated by using an ecological study. Positive and significant changes in the parameters of air temperature that is, the mean air temperature, mean of the highest air temperature, and mean of the lowest air temperature were noted in all 47 prefectures. In addition, changes in air temperature were accelerated when adjusted for observation years. Ambulance transports due to heat stroke was significantly correlated with air temperature in the ecological study. The highest air temperature was significantly linked to ambulance transports due to heat stroke, especially in elderly subjects. Global warming was demonstrated in all 47 prefectures in Japan. In addition, the higher air temperature was closely associated with higher ambulance transports due to heat stroke in Japan.
EPA's Ecological Risk Assessment Support Center (ERASC) announced the release of the final report, Evaluating Potential Exposures to Ecological Receptors Due to Transport of Hydrophobic Organic Contaminants in Subsurface Systems. This technical paper recommends several ty...
EPA's Ecological Risk Assessment Support Center (ERASC) announced the release of the final report, Evaluating Potential Exposures to Ecological Receptors Due to Transport of Hydrophobic Organic Contaminants in Subsurface Systems. This technical paper recommends several ty...
Fast transport in phase space due to nonlinear wave-particle interaction in the radiation belts.
NASA Astrophysics Data System (ADS)
Artemyev, Anton; Vasiliev, Alexii; Mourenas, Didier; Agapitov, Oleksiy; Krasnoselskikh, Vladimir; Boscher, Daniel; Rolland, Guy
2014-05-01
We present an analytical, simplified formulation accounting for the fast transport of particles in phase space, in the presence of nonlinear wave-particle resonant interactions in an inhomogeneous magnetic field representative of the radiation belts. We show that the general approach for the description of the evolution of the particle velocity distribution based on the Fokker-Plank equation can be modified to consider the process of nonlinear wave-particle interaction, including particle trapping. Such a modification consists in one additional operator describing fast particle jumps in phase space. The proposed approach is illustrated by considering the acceleration of relativistic electrons by strongly oblique whistler waves. We determine the typical variation of electron phase-density due to nonlinear wave-particle interaction and compare this variation with pitch-angle/energy diffusion due to quasi-linear electron scattering. We show that relation between nonlinear and quasi-linear effects is controlled by the distribution of wave-amplitudes. When this distribution has a heavy tail, nonlinear effects can become dominant in the formation of the electron energy distribution.
The metabolic basis for developmental disorders due to defective folate transport.
Desai, Ankuri; Sequeira, Jeffrey M; Quadros, Edward V
2016-07-01
Folates are essential in the intermediary metabolism of amino acids, synthesis of nucleotides and for maintaining methylation reactions. They are also linked to the production of neurotransmitters through GTP needed for the synthesis of tetrahydrobiopterin. During pregnancy, folate is needed for fetal development. Folate deficiency during this period has been linked to increased risk of neural tube defects. Disturbances of folate metabolism due to genetic abnormalities or the presence of autoantibodies to folate receptor alpha (FRα) can impair physiologic processes dependent on folate, resulting in a variety of developmental disorders including cerebral folate deficiency syndrome and autism spectrum disorders. Overall, adequate folate status has proven to be important during pregnancy as well as neurological development and functioning in neonates and children. Treatment with pharmacologic doses of folinic acid has led to reversal of some symptoms in many children diagnosed with cerebral folate deficiency syndrome and autism, especially in those positive for autoantibodies to FRα. Thus, as the brain continues to develop throughout fetal and infant life, it can be affected and become dysfunctional due to a defective folate transport contributing to folate deficiency. Treatment and prevention of these disorders can be achieved by identification of those at risk and supplementation with folinic acid.
Sanchez, J M; Cacace, V; Kusnier, C F; Nelson, R; Rubashkin, A A; Iserovich, P; Fischbarg, J
2016-08-01
We have presented prior evidence suggesting that fluid transport results from electro-osmosis at the intercellular junctions of the corneal endothelium. Such phenomenon ought to drag other extracellular solutes. We have investigated this using fluorescein-Na2 as an extracellular marker. We measured unidirectional fluxes across layers of cultured human corneal endothelial (HCE) cells. SV-40-transformed HCE layers were grown to confluence on permeable membrane inserts. The medium was DMEM with high glucose and no phenol red. Fluorescein-labeled medium was placed either on the basolateral or the apical side of the inserts; the other side carried unlabeled medium. The inserts were held in a CO2 incubator for 1 h (at 37 °C), after which the entire volume of the unlabeled side was collected. After that, label was placed on the opposite side, and the corresponding paired sample was collected after another hour. Fluorescein counts were determined with a (Photon Technology) DeltaScan fluorometer (excitation 380 nm; emission 550 nm; 2 nm bwth). Samples were read for 60 s. The cells utilized are known to transport fluid from the basolateral to the apical side, just as they do in vivo in several species. We used 4 inserts for influx and efflux (total: 20 1-h periods). We found a net flux of fluorescein from the basolateral to the apical side. The flux ratio was 1.104 ± 0.056. That difference was statistically significant (p = 0.00006, t test, paired samples). The endothelium has a definite restriction at the junctions. Hence, an asymmetry in unidirectional fluxes cannot arise from osmosis, and can only point instead to paracellular solvent drag. We suggest, once more, that such drag is due to electro-osmotic coupling at the paracellular junctions.
Reduced sediment transport in the Yellow River due to anthropogenic changes
NASA Astrophysics Data System (ADS)
Wang, Shuai; Fu, Bojie; Piao, Shilong; Lü, Yihe; Ciais, Philippe; Feng, Xiaoming; Wang, Yafeng
2016-01-01
The erosion, transport and redeposition of sediments shape the Earth’s surface, and affect the structure and function of ecosystems and society. The Yellow River was once the world’s largest carrier of fluvial sediment, but its sediment load has decreased by approximately 90% over the past 60 years. The decline in sediment load is due to changes in water discharge and sediment concentration, which are both influenced by regional climate change and human activities. Here we use an attribution approach to analyse 60 years of runoff and sediment load observations from the traverse of the Yellow River over China’s Loess Plateau -- the source of nearly 90% of its sediment load. We find that landscape engineering, terracing and the construction of check dams and reservoirs were the primary factors driving reduction in sediment load from the 1970s to 1990s, but large-scale vegetation restoration projects have also reduced soil erosion from the 1990s onwards. We suggest that, as the ability of existing dams and reservoirs to trap sediments declines in the future, erosion rates on the Loess Plateau will increasingly control the Yellow River’s sediment load.
NASA Astrophysics Data System (ADS)
Tulich, S. N.
2015-06-01
This paper describes a general method for the treatment of convective momentum transport (CMT) in large-scale dynamical solvers that use a cyclic, two-dimensional (2-D) cloud-resolving model (CRM) as a "superparameterization" of convective-system-scale processes. The approach is similar in concept to traditional parameterizations of CMT, but with the distinction that both the scalar transport and diagnostic pressure gradient force are calculated using information provided by the 2-D CRM. No assumptions are therefore made concerning the role of convection-induced pressure gradient forces in producing up or down-gradient CMT. The proposed method is evaluated using a new superparameterized version of the Weather Research and Forecast model (SP-WRF) that is described herein for the first time. Results show that the net effect of the formulation is to modestly reduce the overall strength of the large-scale circulation, via "cumulus friction." This statement holds true for idealized simulations of two types of mesoscale convective systems, a squall line, and a tropical cyclone, in addition to real-world global simulations of seasonal (1 June to 31 August) climate. In the case of the latter, inclusion of the formulation is found to improve the depiction of key synoptic modes of tropical wave variability, in addition to some aspects of the simulated time-mean climate. The choice of CRM orientation is also found to importantly affect the simulated time-mean climate, apparently due to changes in the explicit representation of wide-spread shallow convective regions.
Forest, Cary B.
2016-11-10
This report covers the UW-Madison activities that took place within a larger DoE Center Administered and directed by Professor George Tynan at the University of California, San Diego. The work at Wisconsin will also be covered in the final reporting for the entire center, which will be submitted by UCSD. There were two main activities, one experimental and one that was theoretical in nature, as part of the Center activities at the University of Wisconsin, Madison. First, the Center supported an experimentally focused postdoc (Chris Cooper) to carry out fundamental studies of momentum transport in rotating and weakly magnetized plasma. His experimental work was done on the Plasma Couette Experiment, a cylindrical plasma confinement device, with a plasma flow created through electromagnetically stirring plasma at the plasma edge facilitated by arrays of permanent magnets. Cooper's work involved developing optical techniques to measure the ion temperature and plasma flow through Doppler-shifted line radiation from the plasma argon ions. This included passive emission measurements and development of a novel ring summing Fabry-Perot spectroscopy system, and the active system involved using a diode laser to induce fluorescence. On the theoretical side, CMTFO supported a postdoc (Johannes Pueschel) to carry out a gyrokinetic extension of residual zonal flow theory to the case with magnetic fluctuations, showing that magnetic stochasticity disrupts zonal flows. The work included a successful comparison with gyrokinetic simulations. This work and its connection to the broader CMTFO will be covered more thoroughly in the final CMTFO report from Professor Tynan.
Discoveries from the exploration of gyrokinetic momentum transporta)
NASA Astrophysics Data System (ADS)
Staebler, G. M.; Waltz, R. E.; Kinsey, J. E.
2011-05-01
The momentum transport due to gyroradius scale turbulence in tokamak plasmas is very complex. In general, some type of breaking of the parity of the gyrokinetic equation under simultaneous reflection of the poloidal angle and the sign of the parallel velocity phase space coordinate (poloidal parity) is always involved. There are three distinct types of poloidal parity breaking effects. In this paper, all three types of poloidal parity breaking are explored using the quasi-linear trapped gyro-Landau fluid [G. M. Staebler et al., Phys. Plasmas 12, 102508 (2005)] transport code. Selected results are verified with full nonlinear turbulence simulations using the gyro [J. Candy et al., J. Comput. Phys. 186, 545 (2003)] gyrokinetic code. The observable properties like an energy pinch driven by a parallel velocity shear and a dependence of momentum transport on the direction of the ion grad-B drift relative to the X-point location in single null divertor geometry have been discovered.
NASA Astrophysics Data System (ADS)
Ristic, R.; Radic, B.; Vasiljevic, N.; Nikic, Z.; Malusevic, I.
2012-04-01
The construction or improvement of Serbian ski resorts provoked intensive erosion processes, sediment transport and hydrological responses due to land use changes, affecting the surrounding environment and even endangering the functionality of the built objects. The dominant disturbing activities (clear cuttings, trunk transport, machine grading of slopes, huge excavations, and access road construction) were followed by the activities during skiing and non skiing periods (skiing, usage of snow groomers, moving of vehicles and tourists, forestry activities and overgrazing). These activities put a lot of pressure on the environment, including the removal or compaction of the surface soil layer, the reduction of the infiltration capacity, the destruction or degradation of the vegetation cover, the intensifying of the surface runoff and the development of erosion processes. The most affected ski runs were surveyed (scale 1:1000) and all damages were mapped and classified during the summers of 2007-2010. The development of rills and gullies was measured at experimental plots (100x60 m), and the survey data were entered into a GIS application. The area sediment yield and the intensity of erosion processes were estimated on the basis of the "Erosion Potential Method"(EPM). The changes in hydrological conditions were estimated by comparing the computed values of maximal discharges in the conditions before and after massive activities in the ski resorts, as well as by using the local hydrological records. The determination of maximal discharges was achieved using a combined method: the synthetic unit hydrograph (maximum ordinate of unit runoff, qmax) and the Soil Conservation Service (SCS, 1979) methodology (deriving effective rainfall, Pe, from total precipitation, Pb). The determination was performed for AMC III (Antecedent Moisture Conditions III: high water content in the soil and significantly reduced infiltration capacity). The computations of maximal discharges were
Renormalization of the momentum density on the lattice using shifted boundary conditions
NASA Astrophysics Data System (ADS)
Robaina, D.
In order to extract transport quantities from energy-momentum-tensor (EMT) correlators in Lattice QCD there is a strong need for a non-perturbative renormalization of these operators. This is due to the fact that the lattice regularization explicitly breaks translational invariance, invalidating the non-renormalization-theorem. Here we present a non-perturbative calculation of the renormalization constant of the off-diagonal components of the EMT in SU(3) pure gauge theory using lattices with shifted boundary conditions. This allows us to induce a non-zero momentum in the system controlled by the shift parameter and to determine the normalization of the momentum density operator.
Titan's asymmetric lake distribution mediated by methane transport due to atmospheric eddies
NASA Astrophysics Data System (ADS)
Lora, Juan M.; Mitchell, Jonathan L.
2015-08-01
The hemispheric asymmetry of Titan's surface methane has been proposed to be a consequence of orbital forcing affecting Titan's hydrologic cycle, but the mechanism behind asymmetrical transport of moisture remains to be examined. Using general circulation model simulations of Titan's atmosphere, we show that atmospheric moisture transport by three-dimensional tropospheric eddies is critical in generating Titan's surface liquid asymmetry. Comparison of axisymmetric and three-dimensional simulations demonstrates that a significant asymmetry only develops in the latter case. Analysis of the components of the three-dimensional moisture transport reveals that nonaxisymmetric eddies transport methane away from the poles and into the midlatitudes, where they transfer moisture into the cross-equatorial transport by the mean meridional circulation, producing an atmospheric "bucket brigade." Because these high-latitude, baroclinic eddies are more intense in the south than in the north, the net transport is preferentially northward, with the northern hemisphere gaining surface liquid at the expense of the southern hemisphere.
Anomalous Electron Transport Due to Multiple High Frequency Beam Ion Driven Alfven Eigenmode
Gorelenkov, N. N.; Stutman, D.; Tritz, K.; Boozer, A.; Delgardo-Aparicio, L.; Fredrickson, E.; Kaye, S.; White, R.
2010-07-13
We report on the simulations of recently observed correlations of the core electron transport with the sub-thermal ion cyclotron frequency instabilities in low aspect ratio plasmas of the National Spherical Torus Experiment (NSTX). In order to model the electron transport of the guiding center code ORBIT is employed. A spectrum of test functions of multiple core localized Global shear Alfven Eigenmode (GAE) instabilities based on a previously developed theory and experimental observations is used to examine the electron transport properties. The simulations exhibit thermal electron transport induced by electron drift orbit stochasticity in the presence of multiple core localized GAE.
Mugglin, D.T.
1993-12-31
This dissertation is concerned with two light-induced kinetic effects, light-induced diffusive pulling and light-induced drift. We use a light-induced diffusive pulling experiment to measure the ground state velocity-changing collision cross section (related to the momentum transport cross section and the diffusion coefficient) and the relative difference ({Delta}{sigma}/{sigma}) of the excited and ground state cross sections with respect to that of the ground state for potassium mixed with inert buffer gases. The measured excited state cross section is a weighted average of the potassium 4{sup 2}P{sub 1/2} and 4{sup 2}P{sub 3/2} fine structure levels, which are mixed by collisions with inert gas atoms. For the ground state cross sections, we obtain the following experimental results for potassium mixed with He, Ne, Ar, Kr, and Xe, respectively: 52 {+-} 4, 57 {+-} 8, 61 {+-} 5, 43 {+-} 5, and 60 {+-}5 {angstrom}{sup 2}. For {Delta}{sigma}/{sigma}, we obtain the following (in the same order): 0.085 {+-} 0.010, 0.058 {+-} 0.006, 0.41 {+-} 0.03, 0.43 {+-} 0.03, and 0.61 {+-} 0.05. For potassium-Ne and potassium-Ar, we combine these measurements with light-induced drift measurements of the ratio {Delta}{sigma}(J = 3/2) : {Delta}{sigma}(J = 1/2) to obtain absolute transport cross sections for the individual 4{sup 2}S{sub 1/2}, 4{sup 2}P{sub 1/2}, and 4{sup 2}P{sub 3/2} levels. We also use the light-induced diffusive pulling experimental method to measure {Delta}{sigma}/{sigma} for Rb-inert gas mixtures. We obtain values for the ground state diffusion cross section for Rb in several of the inert gases as well. We report the first experimental observation of the separation of two isotopes using broadband light by the process of white light-induced drift. For a light source, we use a broadband laser with an acousto-optic modulator as an output coupler. We verify the separation of the {sup 85}Rb and {sup 87}Rb isotopes.
Jiang, Fangming; Peng, Peng
2016-01-01
Underutilization due to performance limitations imposed by species and charge transports is one of the key issues that persist with various lithium-ion batteries. To elucidate the relevant mechanisms, two groups of characteristic parameters were proposed. The first group contains three characteristic time parameters, namely: (1) te, which characterizes the Li-ion transport rate in the electrolyte phase, (2) ts, characterizing the lithium diffusion rate in the solid active materials, and (3) tc, describing the local Li-ion depletion rate in electrolyte phase at the electrolyte/electrode interface due to electrochemical reactions. The second group contains two electric resistance parameters: Re and Rs, which represent respectively, the equivalent ionic transport resistance and the effective electronic transport resistance in the electrode. Electrochemical modeling and simulations to the discharge process of LiCoO2 cells reveal that: (1) if te, ts and tc are on the same order of magnitude, the species transports may not cause any performance limitations to the battery; (2) the underlying mechanisms of performance limitations due to thick electrode, high-rate operation, and large-sized active material particles as well as effects of charge transports are revealed. The findings may be used as quantitative guidelines in the development and design of more advanced Li-ion batteries. PMID:27599870
Magnetic stochasticity and transport due to nonlinearly excited subdominant microtearing modes
Hatch, D. R.; Jenko, F.; Doerk, H.; Pueschel, M. J.; Terry, P. W.; Nevins, W. M.
2013-01-15
Subdominant, linearly stable microtearing modes are identified as the main mechanism for the development of magnetic stochasticity and transport in gyrokinetic simulations of electromagnetic ion temperature gradient driven plasma microturbulence. The linear eigenmode spectrum is examined in order to identify and characterize modes with tearing parity. Connections are demonstrated between microtearing modes and the nonlinear fluctuations that are responsible for the magnetic stochasticity and electromagnetic transport, and nonlinear coupling with zonal modes is identified as the salient nonlinear excitation mechanism. A simple model is presented, which relates the electromagnetic transport to the electrostatic transport. These results may provide a paradigm for the mechanisms responsible for electromagnetic stochasticity and transport, which can be examined in a broader range of scenarios and parameter regimes.
Ukhorskiy, A Y; Sitnov, M I; Millan, R M; Kress, B T; Smith, D C
2014-01-01
[1]Relativistic electron intensities in Earth's outer radiation belt can vary by multiple orders of magnitude on the time scales ranging from minutes to days. One fundamental process contributing to dynamic variability of radiation belt intensities is the radial transport of relativistic electrons across their drift shells. In this paper we analyze the properties of three-dimensional radial transport in a global magnetic field model driven by variations in the solar wind dynamic pressure. We use a test particle approach which captures anomalous effects such as drift orbit bifurcations. We show that the bifurcations lead to an order of magnitude increase in radial transport rates and enhance the energization at large equatorial pitch angles. Even at quiet time fluctuations in dynamic pressure, radial transport at large pitch angles exhibits strong deviations from the diffusion approximation. The radial transport rates are much lower at small pitch angle values which results in a better agreement with the diffusion approximation.
Anomalous Dirac point transport due to extended defects in bilayer graphene.
Shallcross, Sam; Sharma, Sangeeta; Weber, Heiko B
2017-08-24
Charge transport at the Dirac point in bilayer graphene exhibits two dramatically different transport states, insulating and metallic, that occur in apparently otherwise indistinguishable experimental samples. We demonstrate that the existence of these two transport states has its origin in an interplay between evanescent modes, that dominate charge transport near the Dirac point, and disordered configurations of extended defects in the form of partial dislocations. In a large ensemble of bilayer systems with randomly positioned partial dislocations, the distribution of conductivities is found to be strongly peaked at both the insulating and metallic limits. We argue that this distribution form, that occurs only at the Dirac point, lies at the heart of the observation of both metallic and insulating states in bilayer graphene.In seemingly indistinguishable bilayer graphene samples, two distinct transport regimes, insulating and metallic, have been identified experimentally. Here, the authors demonstrate that these two states originate from the interplay between extended defects and evanescent modes at the Dirac point.
Assessing the transfer of risk due to transportation of agricultural products.
Li, Pei-Chiun; Shih, Hsiu-Ching; Ma, Hwong-Wen
2015-02-01
Health risk assessment (HRA) is the process used to estimate adverse health effects on humans. The importance and sensitivity of food chains to HRA have been observed, but the impact of the transportation of food has generally been ignored. This study developed an exposure assessment to demonstrate the significance of the transportation of agricultural products in HRA. The associated case study estimated the health risks derived from various sources of arsenic emissions in Taiwan. Two assessment scenarios, self-sufficiency and transportation of agricultural products, were compared to calculate risk transfer ratios that show the impact of agriculture transportation. The risk transfer ratios found by the study range from 0.22 to 42.10, indicating that the quantity of transportation of agricultural products is the critical factor. High air deposition and high agricultural production are the two main contributors to the effect of the transportation of agricultural products on HRA. Risk reduction measures could be applied to high-pollution areas as well as to areas with high agricultural productivity to reduce ingestion risks to residents. Certain areas that are sensitive to the transportation of agricultural products may incur more risks if emissions increase in agriculturally productive counties. Copyright © 2014 Elsevier Ltd. All rights reserved.
Prausnitz, M R; Milano, C D; Gimm, J A; Langer, R; Weaver, J C
1994-01-01
Electroporation is believed to involve the creation of aqueous pathways in lipid bilayer membranes by transient elevation of the transmembrane voltage to approximately 1 V. Here, results are presented for a quantitative study of the number of bovine serum albumin (BSA) molecules transported into erythrocyte ghosts caused by electroportion. 1) Uptake of BSA was found to plateau at high field strength. However, this was not necessarily an absolute maximum in transport. Instead, it represented the maximum effect of increasing field strength for a particular pulse protocol. 2) Maximum uptake under any conditions used in this study corresponded to approximately one-fourth of apparent equilibrium with the external solution. 3) Multiple and longer pulses each increased uptake of BSA, where the total time integral of field strength correlated with uptake, independent of inter-pulse spacing. 4) Pre-pulse adsorption of BSA to ghost membranes appears to have increased transport. 5) Most transport of BSA probably occurred by electrically driven transport during pulses; post-pulse uptake occurred, but to a much lesser extent. Finally, approaches to increasing transport are discussed. Images FIGURE 1 FIGURE 2 PMID:8061201
Asymmetric lake distribution on Titan mediated by methane transport due to atmospheric eddies
NASA Astrophysics Data System (ADS)
Lora, Juan M.; Mitchell, Jonathan L.
2015-11-01
The observed north-south asymmetry in the distribution of Titan's seas and lakes has been proposed to be a consequence of orbital forcing affecting Titan's hydrologic cycle, as in the present the northern summer is longer but milder than its southern counterpart. Though recent general circulation models have simulated asymmetrical surface liquid distributions, the mechanism that generates this asymmetry has not been explained. In this work, we compare axisymmetric and three-dimensional simulations of Titan's atmospheric circulation with the Titan Atmospheric Model (TAM) [Lora et al. 2015, Icarus 250] to investigate the transport of moisture by the atmosphere. A significant hemispheric asymmetry only develops in the latter case, and we demonstrate that equatorward transport by high-latitude, baroclinic eddies is responsible. Eddies transport moisture from the high latitudes into the low and midlatitude cross-equatorial mean meridional circulation, producing an atmospheric "bucket brigade." The moisture transport by eddies is more intense in the south than in the north as a consequence of the orbital forcing, and therefore the result is net northward transport of methane, explaining the surface buildup in the north.
NASA Technical Reports Server (NTRS)
Vontiesenhausen, G.
1986-01-01
A summary of tether transportation is given. Four steps were used over a period of time. First, theoretical engineering feasibility and technology requirements were determined. Then the survivors of that effort went into step two in the analysis of promising candidates. Those survivors went into the third phase which is engineering design and cost benefits. Survivors entered into the demonstration mission definition phase. Transportation studies have covered two kinds of deployments. First, steady state deployment was studied. Like the TSS, it's nearly vertical. It takes a long time to deploy and involves relatively high tether tension. Secondly, dynamic deployment was studied. Deployment started in an almost horizontal direction under a very shallow angle which allows a high deployment rate under very low tension. Momentum transfer here occurs by libration. Specific payloads were used to study tethered transportation benefits. Four transportation concepts were studied with regard to cost benefits. A tethered orbiter deboost from the space station, an OTV boost up from the Space Station, a science platform on a tether with a possible micro-g lab moving in between platform and station, and a tethered boost of payloads fromthe orbiter are the four concepts. These benefits are examined in detail.
Peterson, J. L.; Hammet, G. W.; Mikkelsen, D. R.; Yuh, H. Y.; Candy, J.; Guttenfelder, W.; Kaye, S. M.; LeBlanc, B.
2011-05-11
The first nonlinear gyrokinetic simulations of electron internal transport barriers (e-ITBs) in the National Spherical Torus Experiment show that reversed magnetic shear can suppress thermal transport by increasing the nonlinear critical gradient for electron-temperature-gradient-driven turbulence to three times its linear critical value. An interesting feature of this turbulence is non- linearly driven off-midplane radial streamers. This work reinforces the experimental observation that magnetic shear is likely an effective way of triggering and sustaining e-ITBs in magnetic fusion devices.
Switching and transport mechanism in the branching tube network due to attached eddies
NASA Astrophysics Data System (ADS)
Nozaki, Yurika; Ohhashi, Kenta; Sano, Osamu
2017-04-01
An experimental study was performed on the quasi-two-dimensional symmetric branching tube under oscillatory flow. The velocity field and transport of materials in the Reynolds number Re = 1500 ∼ 3000 and the Womersley number α = 17 ∼ 23 were visualized by means of a dye or small spheres as well as measured by using Particle Image Velocimetry. The repeated growth and disappearance of the attached eddies near the junction of the branched channel are recognized, which play a role of the throttle valves to control the transport of newly taken gasses or suspended particles into, and older ones out of, the human lung in spite of zero net volume flux.
Nonlinearity effects on the directed momentum current.
Zhao, Wen-Lei; Fu, Li-Bin; Liu, Jie
2014-08-01
We investigate the quantum transport dynamics governed by the nonlinear Schrödinger equation with a periodically-δ-kicking potential and discover the emergence of a directed current in momentum space. With the increase of nonlinearity, we find strikingly that the momentum current decreases, reverses, and finally vanishes, indicating that the quantum transport can be effectively manipulated through adjusting the nonlinearity. The underlying dynamic mechanism is uncovered and some important implications are addressed.
Smoothed dissipative particle dynamics with angular momentum conservation
Müller, Kathrin Fedosov, Dmitry A. Gompper, Gerhard
2015-01-15
Smoothed dissipative particle dynamics (SDPD) combines two popular mesoscopic techniques, the smoothed particle hydrodynamics and dissipative particle dynamics (DPD) methods, and can be considered as an improved dissipative particle dynamics approach. Despite several advantages of the SDPD method over the conventional DPD model, the original formulation of SDPD by Español and Revenga (2003) [9], lacks angular momentum conservation, leading to unphysical results for problems where the conservation of angular momentum is essential. To overcome this limitation, we extend the SDPD method by introducing a particle spin variable such that local and global angular momentum conservation is restored. The new SDPD formulation (SDPD+a) is directly derived from the Navier–Stokes equation for fluids with spin, while thermal fluctuations are incorporated similarly to the DPD method. We test the new SDPD method and demonstrate that it properly reproduces fluid transport coefficients. Also, SDPD with angular momentum conservation is validated using two problems: (i) the Taylor–Couette flow with two immiscible fluids and (ii) a tank-treading vesicle in shear flow with a viscosity contrast between inner and outer fluids. For both problems, the new SDPD method leads to simulation predictions in agreement with the corresponding analytical theories, while the original SDPD method fails to capture properly physical characteristics of the systems due to violation of angular momentum conservation. In conclusion, the extended SDPD method with angular momentum conservation provides a new approach to tackle fluid problems such as multiphase flows and vesicle/cell suspensions, where the conservation of angular momentum is essential.
Smoothed dissipative particle dynamics with angular momentum conservation
NASA Astrophysics Data System (ADS)
Müller, Kathrin; Fedosov, Dmitry A.; Gompper, Gerhard
2015-01-01
Smoothed dissipative particle dynamics (SDPD) combines two popular mesoscopic techniques, the smoothed particle hydrodynamics and dissipative particle dynamics (DPD) methods, and can be considered as an improved dissipative particle dynamics approach. Despite several advantages of the SDPD method over the conventional DPD model, the original formulation of SDPD by Español and Revenga (2003) [9], lacks angular momentum conservation, leading to unphysical results for problems where the conservation of angular momentum is essential. To overcome this limitation, we extend the SDPD method by introducing a particle spin variable such that local and global angular momentum conservation is restored. The new SDPD formulation (SDPD+a) is directly derived from the Navier-Stokes equation for fluids with spin, while thermal fluctuations are incorporated similarly to the DPD method. We test the new SDPD method and demonstrate that it properly reproduces fluid transport coefficients. Also, SDPD with angular momentum conservation is validated using two problems: (i) the Taylor-Couette flow with two immiscible fluids and (ii) a tank-treading vesicle in shear flow with a viscosity contrast between inner and outer fluids. For both problems, the new SDPD method leads to simulation predictions in agreement with the corresponding analytical theories, while the original SDPD method fails to capture properly physical characteristics of the systems due to violation of angular momentum conservation. In conclusion, the extended SDPD method with angular momentum conservation provides a new approach to tackle fluid problems such as multiphase flows and vesicle/cell suspensions, where the conservation of angular momentum is essential.
Kobayashi, Takashi; Hitachi, Kenichi; Sasaki, Satoshi; Muraki, Koji
2011-11-18
We report a new transport feature in a GaAs lateral double quantum dot that emerges for magnetic-field sweeps and shows hysteresis due to dynamic nuclear spin polarization (DNP). This DNP signal appears in the Coulomb blockade regime by virtue of the finite interdot tunnel coupling and originates from the crossing between ground levels of the spin triplet and singlet extensively used for nuclear spin manipulations in pulsed-gate experiments. The magnetic-field dependence of the current level is suggestive of unbalanced DNP between the two dots, which opens up the possibility of controlling electron and nuclear spin states via dc transport.
Health risks in international container and bulk cargo transport due to volatile toxic compounds.
Baur, Xaver; Budnik, Lygia Therese; Zhao, Zhiwei; Bratveit, Magne; Djurhuus, Rune; Verschoor, Louis; Rubino, Federico Maria; Colosio, Claudio; Jepsen, Jorgen R
2015-01-01
To ensure the preservation and quality of the goods, physical (i.e. radiation) or chemical pest control is needed. The dark side of such consents may bear health risks in international transport and production sharing. In fact, between 10% and 20% of all containers arriving European harbors were shown to contain volatile toxic substances above the exposure limit values. Possible exposure to these toxic chemicals may occur not only for the applicators but also the receiver by off gassing from products, packing materials or transport units like containers. A number of intoxications, some with lethal outcome, occur not only during the fumigation, but also during freight transport (on bulk carriers and other transport vessels), as well as in the logistic lines during loading and unloading. Risk occupations include dock-workers, seafarers, inspectors, as well as the usually uninformed workers of importing enterprises that unload the products. Bystanders as well as vulnerable consumers may also be at risk. Ongoing studies focus on the release of these toxic volatile substances from various goods. It was shown that the half-lives of the off-gassing process range between minutes and months, depending on the toxic substance, its chemical reactivity, concentration, the temperature, the contaminated matrix (goods and packing materials), and the packing density in the transport units. Regulations on declaration and handling dangerous goods are mostly not followed. It is obvious that this hazardous situation in freight transport urgently requires preventive steps. In order to improve awareness and relevant knowledge there is a need for more comprehensive information on chemical hazards and a broader implementation of the already existing regulations and guidelines, such as those from ILO, IMO, and national authorities. It is also necessary to have regular controls by the authorities on a worldwide scale, which should be followed by sanctions in case of disregarding regulations
Cloaking of the momentum in acoustic waves.
Sklan, Sophia
2010-01-01
Through an appropriate change in variables, we find that the three-dimensional acoustic wave equation is subject to the transformation media interpretation. In particular, we determine that this interpretation can be extended beyond the pressure difference to also account for the momentum transported by the wave. The suitability of momentum transport is especially interesting as it is an example where the field of interest is not governed by a wave equation. We examine how both fields behave in the case of cloaking. Explicit consideration of the boundary conditions shows that perfect cloaking is preserved, even when the incoming momentum is nonzero at the surface of the cloak.
Otani, K.; Shigemori, K.; Kadono, T.; Hironaka, Y.; Nakai, M.; Shiraga, H.; Azechi, H.; Mima, K.; Ozaki, N.; Kimura, T.; Miyanishi, K.; Kodama, R.; Sakaiya, T.; Sunahara, A.
2010-03-15
This paper reports an experimental study on preheating of laser-irradiated targets. We performed temperature measurements at the rear surface of laser-irradiated targets under conditions of two different laser wavelengths (0.35 or 0.53 mum) and several intensities (2x10{sup 13}-1x10{sup 14} W/cm{sup 2}) in order to verify an effect of radiation and nonlocal electron heat transport. The preheating temperature was evaluated by observing self-emission, reflectivity, and expansion velocity at the rear surface of planar polyimide foils. The experimental results show that the x-ray radiation is dominant for preheating for 0.35-mum laser irradiation, but contribution of nonlocal electron heat transport is not negligible for 0.53-mum laser irradiation conditions.
Transport of energetic ions due to sawteeth, Alfven eigenmodes and microturbulence
Pace, D C; Fisher, R K; Garcia-Munoz, M; Murakami, Masanori; Park, J. M.
2011-01-01
Utilizing an array of new diagnostics and simulation/modelling techniques, recent DIII-D experiments have elucidated a variety of energetic ion transport behaviour in the presence of instabilities ranging from large-scale sawteeth to fine spatial scale microturbulence. Important new insights include sawteeth, such as those of the ITER baseline scenario, causing major redistribution of the energetic ion population; high levels of transport induced by low-amplitude Alfven eigenmodes can be caused by the integrated effect of a large number of simultaneous modes; and microturbulence can contribute to the removal of alpha ash while having little effect on fusion alphas. This paper provides an overview of recent and upcoming results from the DIII-D Energetic Particles research programme.
Gaboriau, F. Baude, R.; Hagelaar, G. J. M.
2014-05-26
This paper presents experimental results on plasma transport across the magnetic field (B) in magnetized low-temperature plasma sources. Due to the presence of chamber walls, this transport can be complex even in a non-turbulent regime. In particular, in configurations without cylindrical symmetry, the magnetic drifts tend to be bounded by the chamber walls, thereby inducing plasma asymmetry and reducing magnetic confinement. In this work, we measure electron and ion current densities at metal chamber walls bounding a rectangular magnetic filter and demonstrate that these current densities are asymmetrically nonuniform. We also provide an experimental confirmation of model predictions of increased cross-field electron transport in such filter configuration, scaling as 1/B rather than the classical 1/B{sup 2} scaling.
Observation of Photovoltaic Action from Photoacid-Modified Nafion Due to Light-Driven Ion Transport.
White, William; Sanborn, Christopher D; Reiter, Ronald S; Fabian, David M; Ardo, Shane
2017-08-30
Replacing passive ion-exchange membranes, like Nafion, with membranes that use light to drive ion transport would allow membranes in photoelectrochemical technologies to serve in an active role. Toward this, we modified perfluorosulfonic acid ionomer membranes with organic pyrenol-based photoacid dyes to sensitize the membranes to visible light and initiate proton transport. Covalent modification of the membranes was achieved by reacting Nafion sulfonyl fluoride poly(perfluorosulfonyl fluoride) membranes with the photoacid 8-hydroxypyrene-1,3,6-tris(2-aminoethylsulfonamide). The modified membranes were strongly colored and maintained a high selectivity for cations over anions. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and ion-exchange measurements together provided strong evidence of covalent bond formation between the photoacids and the polymer membranes. Visible-light illumination of the photoacid-modified membranes resulted in a maximum power-producing ionic photoresponse of ∼100 μA/cm(2) and ∼1 mV under 40 Suns equivalent excitation with 405 nm light. In comparison, membranes that did not contain photoacids and instead contained ionically associated Ru(II)-polypyridyl coordination compound dyes, which are not photoacids, exhibited little-to-no photoeffects (∼1 μA/cm(2)). These disparate photocurrents, yet similar yields for nonradiative excited-state decay from the photoacids and the Ru(II) dyes, suggest temperature gradients were not likely the cause of the observed photovoltaic action from photoacid-modified membranes. Moreover, spectral response measurements supported that light absorption by the covalently bound photoacids was required in order to observe photoeffects. These results represent the first demonstration of photovoltaic action from an ion-exchange membrane and offer promise for supplementing the power demands of electrochemical processes with renewable sunlight-driven ion transport.
NASA Astrophysics Data System (ADS)
Xu, T.; Haas, K. A.; List, J. H.; Safak, I.
2016-02-01
The inner continental shelf off the western half of the barrier island Fire Island, NY, is characterized by a series of obliquely oriented shoreface-connected ridges. The long-term historic shoreline record shows persistent undulations in shoreline shape at an alongshore scale similar to the alongshore scale of the ridges. This suggests that the ridges affect the wave transformation, alongshore sediment transport and corresponding shoreline change. These processes are investigated by utilizing the SWAN (Simulating WAves Nearshore) model, forced with realistic wave parameters, on a simplified, synthetic bathymetry replicating the scales of the shoreface-connected ridges. Results indicate that the relative magnitude of alongshore variations of modeled waves, alongshore transport, and the corresponding shoreline change are highly correlated with the relative orientation of the incoming waves to the ridges. Alongshore variations in both wave height and direction along the breaker line are much stronger when the predominant wave direction is along the main axis of the ridges rather than perpendicular to the ridge crests. This pattern of wave height variation is further explained by evaluating the directional energy spectrum and using a reverse ray-tracing technique. The gradients of the alongshore sediment transport, which lead to shoreline change, also appear to be stronger for waves with an angle of incidence similar to the ridge orientation. These results help explain the relationship between the oblique shoreface-connected ridges and the corresponding shoreline changes and shed light on the connection between the inner-shelf ridges and persistent shoreline undulations for the Western portion of Fire Island.
NASA Astrophysics Data System (ADS)
Yoo, K.; Amundson, R.; Heimsath, A. M.; Dietrich, W. E.
2003-12-01
Most soil C models assume that plant C inputs are matched by C loss through heterotrophic respiration. While these models are applicable for level terrain, on soil mantled uplands in hilly to mountainous regions, persistent soil mass transport represents a potentially large, but unstudied, flux of soil C. In this research we quantify the soil C erosional fluxes and non-steady state soil C storage within two undisturbed grass-covered hillslopes in Coastal California: Tennessee Valley (TV) (coastal Marin County) and Black Diamond (BD) (interior Contra Costa County). At both sites, previous geomorphic studies have quantified both the sediment transport processes (TV= gopher driven sediment transport; BD= abiotic soil shrink/swell) and their rates. Hillslope patterns of soil C storage were examined in relation to slope position with a hillslope sediment transport model. The average C erosion rates from convex slopes are between 1.4 and 2.7 g C m -2 yr-1 at TV and approximately 8 g C m-2 yr-1 at BD. The C erosional flux is locally as high as 14% of above ground net primary productivity (NPP) at TV and 8% at BD. The convex slopes are net C sinks because NPP likely exceeds respiration by a value equaling the size of C erosion. Eroded soils ultimately accumulate in depositional settings which have residence times on the order of 13kyrs at TV and 5.3kyrs at BD. At TV hollow, 15-24 kg C m-2 of soil C has accumulated at a long-term rate of 1.6-1.9 g C m-2 yr-1 . The present rates of C accumulation were calculated to be 0.3 g C m-2 yr-1 at TV and 0.6 g C m-2 yr-1 at BD. During the hollow infilling, the depositional C inputs have been greater than C accumulation rates, meaning that much of the incoming eroded C is ultimately oxidized to CO2. At both sites, a fraction of the eroded C is exported from the watershed (C of 0.1-0.5 g C m-2 yr-1 at TV and 2 g C m-2 yr-1 at BD). When all hillslope components are integrated, these watersheds are continuous atmospheric C sinks at rates
Multimodel estimates of premature human mortality due to intercontinental transport of air pollution
NASA Astrophysics Data System (ADS)
Liang, C.; Silva, R.; West, J. J.; Sudo, K.; Lund, M. T.; Emmons, L. K.; Takemura, T.; Bian, H.
2015-12-01
Numerous modeling studies indicate that emissions from one continent influence air quality over others. Reducing air pollutant emissions from one continent can therefore benefit air quality and health on multiple continents. Here, we estimate the impacts of the intercontinental transport of ozone (O3) and fine particulate matter (PM2.5) on premature human mortality by using an ensemble of global chemical transport models coordinated by the Task Force on Hemispheric Transport of Air Pollution (TF HTAP). We use simulations of 20% reductions of all anthropogenic emissions from 13 regions (North America, Central America, South America, Europe, Northern Africa, Sub-Saharan Africa, Former Soviet Union, Middle East, East Asia, South Asia, South East Asia, Central Asia, and Australia) to calculate their impact on premature mortality within each region and elsewhere in the world. To better understand the impact of potential control strategies, we also analyze premature mortality for global 20% perturbations from five sectors individually: power and industry, ground transport, forest and savannah fires, residential, and others (shipping, aviation, and agriculture). Following previous studies, premature human mortality resulting from each perturbation scenario is calculated using a health impact function based on a log-linear model for O3 and an integrated exposure response model for PM2.5 to estimate relative risk. The spatial distribution of the exposed population (adults aged 25 and over) is obtained from the LandScan 2011 Global Population Dataset. Baseline mortality rates for chronic respiratory disease, ischemic heart disease, cerebrovascular disease, chronic obstructive pulmonary disease, and lung cancer are estimated from the GBD 2010 country-level mortality dataset for the exposed population. Model results are regridded from each model's original grid to a common 0.5°x0.5° grid used to estimate mortality. We perform uncertainty analysis and evaluate the sensitivity
NASA Astrophysics Data System (ADS)
Tripathy, Sushanta; Khuntia, Arvind; Tiwari, Swatantra Kumar; Sahoo, Raghunath
2017-05-01
In the continuation of our previous work, the transverse-momentum (pT) spectra and nuclear modification factor (R_{AA}) are derived using the relaxation time approximation of Boltzmann Transport Equation (BTE). The initial pT-distribution used to describe p + p collisions has been studied with the perturbative-Quantum Chromodynamics (pQCD) inspired power-law distribution, Hagedorn's empirical formula and with the Tsallis non-extensive statistical distribution. The non-extensive Tsallis distribution is observed to describe the complete range of the transverse-momentum spectra. The Boltzmann-Gibbs Blast Wave (BGBW) distribution is used as the equilibrium distribution in the present formalism, to describe the pT-distribution and nuclear modification factor in nucleus-nucleus collisions. The experimental data for Pb+Pb collisions at √{s_{NN}} = 2.76 TeV at the Large Hadron Collider at CERN have been analyzed for pions, kaons, protons, K^{\\ast0} and φ. It is observed that the present formalism while explaining the transverse-momentum spectra up to 5 GeV/ c, explains the nuclear modification factor very well up to 8 GeV/ c in pT for all these particles except for protons. R_{AA} is found to be independent of the degree of non-extensivity, q_{pp} after pT ˜ 8 GeV/ c.
Electronic transport in the quantum spin Hall state due to the presence of adatoms in graphene
NASA Astrophysics Data System (ADS)
Lima, Leandro; Lewenkopf, Caio
Heavy adatoms, even at low concentrations, are predicted to turn a graphene sheet into a topological insulator with substantial gap. The adatoms mediate the spin-orbit coupling that is fundamental to the quantum spin Hall effect. The adatoms act as local spin-orbit scatterer inducing hopping processes between distant carbon atoms giving origin to transverse spin currents. Although there are effective models that describe spectral properties of such systems with great detail, quantitative theoretical work for the transport counterpart is still lacking. We developed a multiprobe recursive Green's function technique with spin resolution to analyze the transport properties for large geometries. We use an effective tight-binding Hamiltonian to describe the problem of adatoms randomly placed at the center of the honeycomb hexagons, which is the case for most transition metals. Our choice of current and voltage probes is favorable to experiments since it filters the contribution of only one spin orientation, leading to a quantized spin Hall conductance of e2 / h . We also discuss the electronic propagation in the system by imaging the local density of states and the electronic current densities. The authors acknowledge the Brazilian agencies CNPq, CAPES, FAPERJ and INCT de Nanoestruturas de Carbono for financial support.
Introducing Electromagnetic Field Momentum
ERIC Educational Resources Information Center
Hu, Ben Yu-Kuang
2012-01-01
I describe an elementary way of introducing electromagnetic field momentum. By considering a system of a long solenoid and line charge, the dependence of the field momentum on the electric and magnetic fields can be deduced. I obtain the electromagnetic angular momentum for a point charge and magnetic monopole pair partially through dimensional…
Introducing Electromagnetic Field Momentum
ERIC Educational Resources Information Center
Hu, Ben Yu-Kuang
2012-01-01
I describe an elementary way of introducing electromagnetic field momentum. By considering a system of a long solenoid and line charge, the dependence of the field momentum on the electric and magnetic fields can be deduced. I obtain the electromagnetic angular momentum for a point charge and magnetic monopole pair partially through dimensional…
NASA Astrophysics Data System (ADS)
Wang, Guihua; Ogden, Joan M.; Chang, Daniel P. Y.
Hydrogen has been proposed as a low polluting alternative transportation fuel that could help improve urban air quality. This paper examines the potential impact of introducing a hydrogen-based transportation system on urban ambient ozone concentrations. This paper considers two scenarios, where significant numbers of new hydrogen vehicles are added to a constant number of gasoline vehicles. In our scenarios hydrogen fuel cell vehicles (HFCVs) are introduced in Sacramento, California at market penetrations of 9% and 20%. From a life cycle analysis (LCA) perspective, considering all the emissions involved in producing, transporting, and using hydrogen, this research compares three hypothetical natural gas to hydrogen pathways: (1) on-site hydrogen production; (2) central hydrogen production with pipeline delivery; and (3) central hydrogen production with liquid hydrogen truck delivery. Using a regression model, this research shows that the daily maximum temperature correlates well with atmospheric ozone formation. However, increases in initial VOC and NO x concentrations do not necessarily increase the peak ozone concentration, and may even cause it to decrease. It is found that ozone formation is generally limited by NO x in the summer and is mostly limited by VOC in the fall in Sacramento. Of the three hydrogen pathways, the truck delivery pathway contributes the most to ozone precursor emissions. Ozone precursor emissions from the truck pathway at 9% market penetration can cause additional 3-h average VOC (or NO x) concentrations up to approximately 0.05% (or 1%) of current pollution levels, and at 20% market penetration up to approximately 0.1% (or 2%) of current pollution levels. However, all of the hydrogen pathways would result in very small (either negative or positive) changes in ozone air quality. In some cases they will result in worse ozone air quality (mostly in July, August, and September), and in some cases they will result in better ozone air quality
On the potential for transport due to internal tides in the coastal ocean
NASA Astrophysics Data System (ADS)
Trigo Cabrita Gil, Goncalo; Fringer, Oliver
2010-11-01
Non-linear effects associated with internal waves lead to advection of fluid particles along with suspended mass such as sediment, nutrients, larvae, as well as contaminants. These factors contribute to the development of benthic communities, the geological shaping of the continental slope and, in some situations, play a role in the transport and fate of contaminants. We compute particle trajectories and resulting Stokes velocity profiles using a Navier-Stokes code with a Lagrangian particle tracking model, both are second-order accurate in time and in space. Results are compared to linear theory and a semi-nonlinear formulation using a uniform stratification and stratification typically found at Huntington Beach, CA where there is recurring bacteriological contamination.
HLA class I deficiencies due to mutations in subunit 1 of the peptide transporter TAP1
de la Salle, Henri; Zimmer, Jacques; Fricker, Dominique; Angenieux, Catherine; Cazenave, Jean-Pierre; Okubo, Mitsuo; Maeda, Hiroo; Plebani, Alessandro; Tongio, Marie-Marthe; Dormoy, Anne; Hanau, Daniel
1999-01-01
The transporter associated with antigen processing (TAP), which is composed of two subunits (TAP1 and TAP2) that have different biochemical and functional properties, plays a key role in peptide loading and the cell surface expression of HLA class I molecules. Three cases of HLA class I deficiency have previously been shown to result from the absence of a functional TAP2 subunit. In the present study, we analyzed two cases displaying not only the typical lung syndrome of HLA class I deficiency but also skin lesions, and found these patients to be TAP1-deficient. This defect leads to unstable HLA class I molecules and their retention in the endoplasmic reticulum. However, the absence of TAP1 is compatible with life and does not seem to result in higher susceptibility to viral infections than TAP2 deficiency. This work also reveals that vasculitis is often observed in HLA class I–deficient patients. PMID:10074495
NASA Astrophysics Data System (ADS)
Nogues, Juan P.; Fitts, Jeffrey P.; Celia, Michael A.; Peters, Catherine A.
2013-09-01
A reactive transport model was developed to simulate reaction of carbonates within a pore network for the high-pressure CO2-acidified conditions relevant to geological carbon sequestration. The pore network was based on a synthetic oolithic dolostone. Simulation results produced insights that can inform continuum-scale models regarding reaction-induced changes in permeability and porosity. As expected, permeability increased extensively with dissolution caused by high concentrations of carbonic acid, but neither pH nor calcite saturation state alone was a good predictor of the effects, as may sometimes be the case. Complex temporal evolutions of interstitial brine chemistry and network structure led to the counterintuitive finding that a far-from-equilibrium solution produced less permeability change than a nearer-to-equilibrium solution at the same pH. This was explained by the pH buffering that increased carbonate ion concentration and inhibited further reaction. Simulations of different flow conditions produced a nonunique set of permeability-porosity relationships. Diffusive-dominated systems caused dissolution to be localized near the inlet, leading to substantial porosity change but relatively small permeability change. For the same extent of porosity change caused from advective transport, the domain changed uniformly, leading to a large permeability change. Regarding precipitation, permeability changes happen much slower compared to dissolution-induced changes and small amounts of precipitation, even if located only near the inlet, can lead to large changes in permeability. Exponent values for a power law that relates changes in permeability and porosity ranged from 2 to 10, but a value of 6 held constant when conditions led to uniform changes throughout the domain.
Preliminary experimental observation of nonlocal transport due to SMBI on the J-TEXT tokamak
NASA Astrophysics Data System (ADS)
Xiao, Jinshui; Yang, Zhoujun; Zhuang, Ge; Zhang, Chi; Liu, Minghai; State Key Laboratory of Advanced Electromagnetic Engineering; Technology Team
2014-10-01
Experimental studies of nonlocal electron heat transport have been carried out in J-TEXT ohmic plasmas exploiting Supersonic Molecular Beam Injection (SMBI) system. By cooling the very edge plasma, a prompt (~1 ms) temperature rise of the plasma core can be induced. For a low density discharge with ne = 1 . 1 ×1019 m-3, the amplitude of ΔTe/Te exceeds 30% at r/a = 0.17 (a is the minor radius). The duration of NLT phenomena is about 10ms, which is comparable with the energy confinement time of J-TEXT. The Te inverse radius in this discharge locates at r/a = 0.33 ~ 0.4 and is outside the q = 1 surface (r/a ~ 0.3), which the latter is estimated from the sawtooth inverse position. As plasma density increases, the nonlocal phenomena decay. Repetitive nonlocal phenomena can be induced by modulated SMBI, which distinctly exhibits the strong dependence on electron density. The critical density is about 1.6 × 1019 m-3.
Tang-Schomer, Min D; Johnson, Victoria E; Baas, Peter W; Stewart, William; Smith, Douglas H
2012-01-01
Due to their viscoelastic nature, white matter axons are susceptible to damage by high strain rates produced during traumatic brain injury (TBI). Indeed, diffuse axonal injury (DAI) is one of the most common features of TBI, characterized by the hallmark pathological profiles of axonal bulbs at disconnected terminal ends of axons and periodic swellings along axons, known as "varicosities." Although transport interruption underlies axonal bulb formation, it is unclear how varicosities arise, with multiple sites accumulating transported materials along one axon. Recently, axonal microtubules have been found to physically break during dynamic stretch injury of cortical axons in vitro. Here, the same in vitro model was used in parallel with histopathological analyses of human brains acquired acutely following TBI to examine the potential role of mechanical microtubule damage in varicosity formation post-trauma. Transmission electron microscopy (TEM) following in vitro stretch injury revealed periodic breaks of individual microtubules along axons that regionally corresponded with undulations in axon morphology. However, typically less than a third of microtubules were broken in any region of an axon. Within hours, these sites of microtubule breaks evolved into periodic swellings. This suggests axonal transport may be halted along one broken microtubule, yet can proceed through the same region via other intact microtubules. Similar axonal undulations and varicosities were observed following TBI in humans, suggesting primary microtubule failure may also be a feature of DAI. These data indicate a novel mechanism of mechanical microtubule damage leading to partial transport interruption and varicosity formation in traumatic axonal injury.
Stacey, W. M.
2016-06-15
A fluid model for the tokamak edge pressure profile required by the conservation of particles, momentum and energy in the presence of specified heating and fueling sources and electromagnetic and geometric parameters has been developed. Kinetics effects of ion orbit loss are incorporated into the model. The use of this model as a “transport” constraint together with a “Peeling-Ballooning (P-B)” instability constraint to achieve a prediction of edge pressure pedestal heights and widths in future tokamaks is discussed.
Sediment transport due to windthrow event in the Tatra Mountains, Poland
NASA Astrophysics Data System (ADS)
Strzyżowski, Dariusz; Fidelus-Orzechowska, Joanna
2017-04-01
Mountain areas are frequently affected by strong wind events which cause damage in forest stands by snapping or uprooting of trees. Uprooting contributes to sediment transport by displacement of soil material attached to a root system of a tree. The aim of the study was to investigate geomorphic effects of tree uprooting and to calculate sediment flux by windthrow for the area of Tatra National Park. Research was conducted within the Tatra Mountains, in the Tatra National Park. Windthrow event occurred on 25 December 2013. The field work was conducted from September to November 2015 within 7 research polygons with the total area of 0.97 ha. Type of the damage (uprooted, partly uprooted, snapped), dimensions of a root plate, slope inclination, aspect, angle of tree fall, and tree diameter were determined for every damaged tree. Also, basing on GIS analysis, area of the windthrow and directions of fallen trunks for the whole area of Tatra National Park were determined. In total 252 damaged trees were investigated. 66% of them were uprooted, 25% were snapped, and 9% were partly uprooted. Slope inclination, aspect, and tree diameter did not influence type of the damage significantly. Mean volume of a root plate is 2.7 m3, and the amount of uplifted material is 378.4 m3 ha-1. Totally within the Tatra National Park area 297.9 ha of the forest were affected. 77% of the tree trunks were fallen in downslope direction. Sediment flux by windthrow event in 2013, for the forested part of the Tatra National Park is at the order of magnitude of 10-4 m3 m-1.
Transition from pulled to pushed premixed turbulent flames due to countergradient transport
NASA Astrophysics Data System (ADS)
Sabelnikov, V. A.; Lipatnikov, A. N.
2013-12-01
The influence of countergradient transport on the speed of a statistically stationary, planar, 1D premixed flame that propagates in frozen turbulence is studied theoretically and numerically by considering the normalised magnitude NB of the countergradient flux to be an input parameter. Spectra of admissible flame speeds are analytically determined and explicit travelling wave solutions are found for two algebraic relations widely used to close the mean rate of product creation. A problem of selecting the physically relevant solution that is approached for sufficiently steep initial conditions is addressed. It is argued that, if NB is larger than an analytically determined critical number NcrB, then the type of the physically relevant solution is drastically changed. If NB < NcrB, the physically relevant solution is of pulled wave type, i.e. its speed is controlled by processes localised to the leading edge of the flame brush and can be determined within the framework of a linear analysis at the leading edge. If NB > NcrB, the physically relevant solution is of pushed wave type, i.e. its speed is controlled by processes in the entire flame brush. Analytical expressions for the speed of the physically relevant solution as a function of NB and the density ratio are obtained. For NB > NcrB, the mean flame brush thickness and the spatial profile of the Favre-averaged combustion progress variable are also determined analytically. These results are validated by numerical simulations. Both analytical expressions and numerical data indicate that (i) both turbulent flame speed and thickness are decreased when NB is increased and (ii) the direction of total scalar flux (i.e. the sum of countergradient and gradient contributions) is strongly affected not only by NB, but also by the shape of the dependence of the mean rate of product creation on the mean combustion progress variable.
Studies on gravity waves momentum flux variations in different seasons using MST radar
NASA Astrophysics Data System (ADS)
I, V.; Y-H, C.; v, S.; D, N.; S, V.
2006-12-01
MST radars are the best tools to study the high frequency gravity waves and its associated momentum fluxes because of excellent temporal and spatial resolutions. The upward propagating gravity waves transport energy and momentum in different regions of the atmosphere along with their propagation to produce effects at upper heights. The estimation of the vertical flux of horizontal momentum in the troposphere and lower stratosphere involves two methods, using three beams V one vertical and two oblique, and using four beams V two pairs of oblique beams systematically offset from the vertical. The rapid steerability of the Indian MST radar allows to make three and four beam measurements simultaneously. The objective of this study is to examine the variations of zonal and meridional momentum fluxes with height, variation of momentum fluxes with wave periods and body forces. We choose frequency bands corresponding to periods of 30 min-2h, 2-8 h, and 2-16h. Vertical profiles of the zonal and meridional flux in each frequency band were found to be consistent, in general, with the total flux. The study also compares momentum fluxes computed with three and four beam methods. Zonal fluxes were small at lower levels and increasingly negative (westward) at higher heights. The dominant contributions to the meridional flux occur in the lower-frequency band. The large vertical momentum flux values observed around the 16 km altitude on most of the observations are due to the presence of large zonal wind shears at that altitude. Due to their persistent southward direction of propagation the meridional momentum flux during winter and summer shows southward direction of propagation and long period waves make contributions to the momentum flux in the lower stratosphere which is comparable to that of short period waves. The detailed discussion will be presented in the meeting.
Ralston, David K.; Warner, John C.; Geyer, W. Rockwell; Wall, Gary R.
2013-01-01
Tropical Storms Irene and Lee in 2011 produced intense precipitation and flooding in the U.S. Northeast, including the Hudson River watershed. Sediment input to the Hudson River was approximately 2.7 megaton, about 5 times the long-term annual average. Rather than the common assumption that sediment is predominantly trapped in the estuary, observations and model results indicate that approximately two thirds of the new sediment remained trapped in the tidal freshwater river more than 1 month after the storms and only about one fifth of the new sediment reached the saline estuary. High sediment concentrations were observed in the estuary, but the model results suggest that this was predominantly due to remobilization of bed sediment. Spatially localized deposits of new and remobilized sediment were consistent with longer term depositional records. The results indicate that tidal rivers can intercept (at least temporarily) delivery of terrigenous sediment to the marine environment during major flow events.
NASA Astrophysics Data System (ADS)
Lim, C.; Kim, D. H.; Woo, S. B.
2016-02-01
For direct consideration of seawater volume change by steric effect due to global warming, this study uses a MOM (Modular Ocean Model) version4 oceanic general circulation model, which does not use Boussinesq approximation. The model was improved to regional scale by increasing the grid resolution. Global simulation model results of CM2.1, HADCM3, MIROC3.2 provided by the IPCC AR4 (Intergovernmental Panel on Climate Change) were used as initial and boundary conditions, and SRES (Special Report on Emissions Scenarios) A1B was selected as a global warming scenario. The Northwestern Pacific region, which includes the Korean Peninsula, was selected as the study area, and the Yellow Sea which has a complex coastline, was expressed in detail by increasing grid resolution. By averaging the results of the three numerical experiments, we found that temperature & mean sea level(MSL) are increased by approximately 3℃/35cm from 2000 to 2100, respectively. Interestingly, The East Sea (Japan sea) appeared to show the largest change of MSL due to steric effect compared with Yellow and East China Sea. Numerical results showed that larger influence on East/Japan Sea is caused by the temperature and volume transport change in Tsushima Warm Current, which passes through the Korea Strait. A direct simulation of steric effect results in higher sea level rise compared with in-direct simulation of steric effect. Also, the Kuroshio Current, which is one of the major currents in the Northwestern Pacific, showed a decrease in transport as global warming progressed. Although there were differences between models, approximately 4 5SV of transport was reduced in 2100. However, there was no huge change in the transport of the Tsushima Warm Current.
NASA Astrophysics Data System (ADS)
Evangeliou, Nikolaos; Zibtsev, Sergey; Myroniuk, Viktor; Zhurba, Marina; Hamburger, Thomas; Stohl, Andreas; Balkanski, Yves; Paugam, Ronan; Mousseau, Timothy A.; Møller, Anders P.; Kireev, Sergey I.
2016-04-01
In 2015, two major fires in the Chernobyl Exclusion Zone (CEZ) have caused concerns about the secondary radioactive contamination that might have spread over Europe. The total active burned area was estimated to be about 15,000 hectares, of which 9000 hectares burned in April and 6000 hectares in August. The present paper aims to assess, for the first time, the transport and impact of these fires over Europe. For this reason, direct observations of the prevailing deposition levels of 137Cs and 90Sr, 238Pu, 239Pu, 240Pu and 241Am in the CEZ were processed together with burned area estimates. Based on literature reports, we made the conservative assumption that 20% of the deposited labile radionuclides 137Cs and 90Sr, and 10% of the more refractory 238Pu, 239Pu, 240Pu and 241Am, were resuspended by the fires. We estimate that about 10.9 TBq of 137Cs, 1.5 TBq of 90Sr, 7.8 GBq of 238Pu, 6.3 GBq of 239Pu, 9.4 GBq of 240Pu and 29.7 GBq of 241Am were released from both fire events. These releases could be classified as of "Level 3" on the relative INES (International Nuclear Events Scale) scale, which corresponds to a serious incident, in which non-lethal deterministic effects are expected from radiation. To simulate the dispersion of the resuspended radionuclides in the atmosphere and their deposition onto the terrestrial environment, we used a Lagrangian dispersion model. Spring fires redistributed radionuclides over the northern and eastern parts of Europe, while the summer fires also affected Central and Southern Europe. The more labile elements escaped more easily from the CEZ and then reached and deposited in areas far from the source, whereas the larger refractory particles were removed more efficiently from the atmosphere and thus did mainly affect the CEZ and its vicinity. For the spring 2015 fires, we estimate that about 80% of 137Cs and 90Sr and about 69% of 238Pu, 239Pu, 240Pu and 241Am were deposited over areas outside the CEZ. 93% of the labile and 97% of
NASA Astrophysics Data System (ADS)
Zhang, Debing; Xu, Yingfeng; Wang, Shaojie
2017-08-01
The quasilinear transport fluxes due to the ion temperature gradient instability are calculated in a toroidal plasma, in which the magnetic drift resonance is treated rigorously. The effects of the equilibrium parallel flow and flow shear on the radial particle and heat fluxes are studied numerically in detail. In the radial component of parallel viscosity, there exist the pinches driven by the density gradient, the temperature gradient, and the curvature of the background magnetic field. The direction of these pinches is discussed. It is found that each pinch can be inward or outward, which depends crucially on the resonance condition.
Constraining nucleon high momentum in nuclei
NASA Astrophysics Data System (ADS)
Yong, Gao-Chan
2017-02-01
Recent studies at Jefferson Lab show that there are a certain proportion of nucleons in nuclei have momenta greater than the so-called nuclear Fermi momentum pF. Based on the transport model of nucleus-nucleus collisions at intermediate energies, nucleon high momentum caused by the neutron-proton short-range correlations in nuclei is constrained by comparing with π and photon experimental data and considering some uncertainties. The high momentum cutoff value pmax ≤ 2pF is obtained.
Resolving the mystery of transport within internal transport barriers
Staebler, G. M.; Belli, E. A.; Candy, J.; Waltz, R. E.; Greenfield, C. M.; Lao, L. L.; Smith, S. P.; Kinsey, J. E.; Grierson, B. A.; Chrystal, C.
2014-05-15
The Trapped Gyro-Landau Fluid (TGLF) quasi-linear model [G. M. Staebler, et al., Phys. Plasmas 12, 102508 (2005)], which is calibrated to nonlinear gyrokinetic turbulence simulations, is now able to predict the electron density, electron and ion temperatures, and ion toroidal rotation simultaneously for internal transport barrier (ITB) discharges. This is a strong validation of gyrokinetic theory of ITBs, requiring multiple instabilities responsible for transport in different channels at different scales. The mystery of transport inside the ITB is that momentum and particle transport is far above the predicted neoclassical levels in apparent contradiction with the expectation from the theory of suppression of turbulence by E×B velocity shear. The success of TGLF in predicting ITB transport is due to the inclusion of ion gyro-radius scale modes that become dominant at high E×B velocity shear and to improvements to TGLF that allow momentum transport from gyrokinetic turbulence to be faithfully modeled.
Resolving the mystery of transport within internal transport barriers
Staebler, Gary M.; Kinsey, Jon E.; Belli, Emily A.; Candy, Jefferey; Waltz, Ronald E.; Greenfield, Charles M.; Lao, Lang L.; Smith, Sterling P.; Grierson, Brain A.; Chrystal, Colin
2014-05-02
Here, the Trapped Gyro-Landau Fluid (TGLF) quasi-linear model, which is calibrated to nonlinear gyrokinetic turbulence simulations, is now able to predict the electron density, electron and ion temperatures and ion toroidal rotation simultaneously for internal transport barrier (ITB) discharges. This is a strong validation of gyrokinetic theory of ITBs, requiring multiple instabilities responsible for transport in different channels at different scales. The mystery of transport inside the ITB is that momentum and particle transport is far above the predicted neoclassical levels in apparent contradiction with the expectation from the theory of suppression of turbulence by E × B velocity shear. The success of TGLF in predicting ITB transport is due to the inclusion of ion gyro-radius scale modes that become dominant at high E × B velocity shear and to improvements to TGLF that allow momentum transport from gyrokinetic turbulence to be faithfully modeled.
Resolving the mystery of transport within internal transport barriers
Staebler, Gary M.; Kinsey, Jon E.; Belli, Emily A.; ...
2014-05-02
Here, the Trapped Gyro-Landau Fluid (TGLF) quasi-linear model, which is calibrated to nonlinear gyrokinetic turbulence simulations, is now able to predict the electron density, electron and ion temperatures and ion toroidal rotation simultaneously for internal transport barrier (ITB) discharges. This is a strong validation of gyrokinetic theory of ITBs, requiring multiple instabilities responsible for transport in different channels at different scales. The mystery of transport inside the ITB is that momentum and particle transport is far above the predicted neoclassical levels in apparent contradiction with the expectation from the theory of suppression of turbulence by E × B velocity shear.more » The success of TGLF in predicting ITB transport is due to the inclusion of ion gyro-radius scale modes that become dominant at high E × B velocity shear and to improvements to TGLF that allow momentum transport from gyrokinetic turbulence to be faithfully modeled.« less
Nonsurvivable momentum exchange system
NASA Technical Reports Server (NTRS)
Roder, Russell (Inventor); Ahronovich, Eliezer (Inventor); Davis, III, Milton C. (Inventor)
2007-01-01
A demiseable momentum exchange system includes a base and a flywheel rotatably supported on the base. The flywheel includes a web portion defining a plurality of web openings and a rim portion. The momentum exchange system further includes a motor for driving the flywheel and a cover for engaging the base to substantially enclose the flywheel. The system may also include components having a melting temperature below 1500 degrees Celsius. The momentum exchange system is configured to demise on reentry.
TDRSS momentum unload planning
NASA Technical Reports Server (NTRS)
Cross, George R.; Potter, Mitchell A.; Whitehead, J. Douglass; Smith, James T.
1991-01-01
A knowledge-based system is described which monitors TDRSS telemetry for problems in the momentum unload procedure. The system displays TDRSS telemetry and commands in real time via X-windows. The system constructs a momentum unload plan which agrees with the preferences of the attitude control specialists and the momentum growth characteristics of the individual spacecraft. During the execution of the plan, the system monitors the progress of the procedure and watches for unexpected problems.
Giannopoulos, G; Larcher, M; Casadei, F; Solomos, G
2010-01-15
Terrorist attacks in New York have shocked the world community showing clearly the vulnerability of air transport in such events. However, the terrorist attacks in Madrid and London showed that land mass transport infrastructure is equally vulnerable in case of similar attacks. The fact that there has not been substantial investment in the domain of risk analysis and evaluation of the possible effects due to such events in land mass transportation infrastructure leaves large room for new developments that could eventually fill this gap. In the present work using the finite element code EUROPLEXUS there has been a large effort to perform a complete study of the land mass infrastructure in case of explosion events. This study includes a train station, a metro station and a metro carriage providing thus valuable simulation data for a variety of different situations. For the analysis of these structures it has been necessary to apply a laser scanning method for the acquisition of geometrical data, to improve the simulation capabilities of EUROPLEXUS by adding failure capabilities for specific finite elements, to implement new material models (e.g. glass), and to add new modules that achieve data post-processing for the calculation of fatal and non-fatal injuries risk. The aforementioned improvements are explained in the present work with emphasis in the newly developed risk analysis features of EUROPLEXUS.
Do waves carrying orbital angular momentum possess azimuthal linear momentum?
Speirits, Fiona C; Barnett, Stephen M
2013-09-06
All beams are a superposition of plane waves, which carry linear momentum in the direction of propagation with no net azimuthal component. However, plane waves incident on a hologram can produce a vortex beam carrying orbital angular momentum that seems to require an azimuthal linear momentum, which presents a paradox. We resolve this by showing that the azimuthal momentum is not a true linear momentum but the azimuthal momentum density is a true component of the linear momentum density.
Tang-Schomer, Min D.; Johnson, Victoria E.; Baas, Peter W.; Stewart, William; Smith, Douglas H.
2012-01-01
Due to their viscoelastic nature, white matter axons are susceptible to damage by high strain rates produced during traumatic brain injury (TBI). Indeed, diffuse axonal injury (DAI) is one of the most common features of TBI, characterized by the hallmark pathological profiles of axonal bulbs at disconnected terminal ends of axons and periodic swellings along axons, known as “varicosities.” Although transport interruption underlies axonal bulb formation, it is unclear how varicosities arise, with multiple sites accumulating transported materials along one axon. Recently, axonal microtubules have been found to physically break during dynamic stretch-injury of cortical axons in vitro. Here, the same in vitro model was used in parallel with histopathological analyses of human brains acquired acutely following TBI to examine the potential role of mechanical microtubule damage in varicosity formation post-trauma. Transmission electron microscopy (TEM) following in vitro stretch-injury revealed periodic breaks of individual microtubules along axons that regionally corresponded with undulations in axon morphology. However, typically less than a third of microtubules were broken in any region of an axon. Within hours, these sites of microtubule breaks evolved into periodic swellings. This suggests axonal transport may be halted along one broken microtubule, yet can proceed through the same region via other intact microtubules. Similar axonal undulations and varicosities were observed following TBI in humans, suggesting primary microtubule failure may also be a feature of DAI. These data indicate a novel mechanism of mechanical microtubule damage leading to partial transport interruption and varicosity formation in traumatic axonal injury. PMID:22079153
NASA Astrophysics Data System (ADS)
Thidé, B.; Tamburini, F.; Then, H.; Someda, C. G.; Mari, Elletra; Parisi, G.; Spinello, F.; Romanato, Fra
2014-02-01
Wireless communication amounts to encoding information onto physical observables carried by electromagnetic (EM) fields, radiating them into surrounding space, and detecting them remotely by an appropriate sensor connected to an informationdecoding receiver. Each observable is second order in the fields and fulfills a conservation law. In present-day radio only the EM linear momentum observable is fully exploited. A fundamental physical limitation of this observable, which represents the translational degrees of freedom of the charges (typically an oscillating current along a linear antenna) and the fields, is that it is single-mode. This means that a linear-momentum radio communication link comprising one transmitting and one receiving antenna, known as a single-input-single-output (SISO) link, can provide only one transmission channel per frequency (and polarization). In contrast, angular momentum, which represents the rotational degrees of freedom, is multi-mode, allowing an angular-momentum SISO link to accommodate an arbitrary number of independent transmission channels on one and the same frequency (and polarization). We describe the physical properties of EM angular momentum and how they can be exploited, discuss real-world experiments, and outline how the capacity of angular momentum links may be further enhanced by employing multi-port techniques, i.e., the angular momentum counterpart of linear-momentum multiple-input-multiple-output (MIMO).
Introducing Conservation of Momentum
ERIC Educational Resources Information Center
Brunt, Marjorie; Brunt, Geoff
2013-01-01
The teaching of the principle of conservation of linear momentum is considered (ages 15 + ). From the principle, the momenta of two masses in an isolated system are considered. Sketch graphs of the momenta make Newton's laws appear obvious. Examples using different collision conditions are considered. Conservation of momentum is considered…
Introducing Conservation of Momentum
ERIC Educational Resources Information Center
Brunt, Marjorie; Brunt, Geoff
2013-01-01
The teaching of the principle of conservation of linear momentum is considered (ages 15 + ). From the principle, the momenta of two masses in an isolated system are considered. Sketch graphs of the momenta make Newton's laws appear obvious. Examples using different collision conditions are considered. Conservation of momentum is considered…
2007-01-01
International (cont.) European Commission – Directorate General for Energy and Transport, Brussels, Belgium Headquarters Netherlands Customs ...100,000 by 2014. As a result of these challenges and due to the increase in intermodal freight traffic, a customer /client relationship has...increase by 50% domestically and 110% internationally by 2016 (CRS, 2007). United Parcel Service (UPS), FedEx, and DHL currently control the package
Phase-space dependent critical gradient behavior of fast-ion transport due to Alfvén eigenmodes
NASA Astrophysics Data System (ADS)
Collins, C. S.; Heidbrink, W. W.; Podestà, M.; White, R. B.; Kramer, G. J.; Pace, D. C.; Petty, C. C.; Stagner, L.; Van Zeeland, M. A.; Zhu, Y. B.; The DIII-D Team
2017-08-01
Experiments in the DIII-D tokamak show that many overlapping small-amplitude Alfvén eigenmodes (AEs) cause fast-ion transport to sharply increase above a critical threshold in beam power, leading to fast-ion density profile resilience and reduced fusion performance. The threshold is above the AE linear stability limit and varies between diagnostics that are sensitive to different parts of fast-ion phase-space. Comparison with theoretical analysis using the nova and orbit codes shows that, for the neutral particle diagnostic, the threshold corresponds to the onset of stochastic particle orbits due to wave-particle resonances with AEs in the measured region of phase space. The bulk fast-ion distribution and instability behavior was manipulated through variations in beam deposition geometry, and no significant differences in the onset threshold outside of measurement uncertainties were found, in agreement with the theoretical stochastic threshold analysis. Simulations using the ‘kick model’ produce beam ion density gradients consistent with the empirically measured radial critical gradient and highlight the importance of including the energy and pitch dependence of the fast-ion distribution function in critical gradient models. The addition of electron cyclotron heating changes the types of AEs present in the experiment, comparatively increasing the measured fast-ion density and radial gradient. These studies provide the basis for understanding how to avoid AE transport that can undesirably redistribute current and cause fast-ion losses, and the measurements are being used to validate AE-induced transport models that use the critical gradient paradigm, giving greater confidence when applied to ITER.
Phase-space dependent critical gradient behavior of fast-ion transport due to Alfvén eigenmodes
Collins, C. S.; Heidbrink, W. W.; Podestà, M.; ...
2017-06-09
Experiments in the DIII-D tokamak show that many overlapping small-amplitude Alfv en eigenmodes (AEs) cause fast-ion transport to sharply increase above a critical threshold, leading to fast-ion density profile resilience and reduced fusion performance. The threshold is above the AE linear stability limit and varies between diagnostics that are sensitive to different parts of fast-ion phase-space. A comparison with theoretical analysis using the nova and orbit codes shows that, for the neutral particle diagnostic, the threshold corresponds to the onset of stochastic particle orbits due to wave-particle resonances with AEs in the measured region of phase space. We manipulated themore » bulk fast-ion distribution and instability behavior through variations in beam deposition geometry, and no significant differences in the onset threshold outside of measurement uncertainties were found, in agreement with the theoretical stochastic threshold analysis. Simulations using the `kick model' produce beam ion density gradients consistent with the empirically measured radial critical gradient and highlight the importance of including the energy and pitch dependence of the fast-ion distribution function in critical gradient models. The addition of electron cyclotron heating changes the types of AEs present in the experiment, comparatively increasing the measured fast-ion density and radial gradient. Our studies provide the basis for understanding how to avoid AE transport that can undesirably redistribute current and cause fast-ion losses, and the measurements are being used to validate AE-induced transport models that use the critical gradient paradigm, giving greater confidence when applied to ITER.« less
NASA Astrophysics Data System (ADS)
Jamali Mahabadi, S. E.; Hu, Yue; Talukder, Muhammad Anisuzzaman; Carruthers, Thomas F.; Menyuk, Curtis R.
2016-10-01
We have developed a comprehensive model of gain recovery due to unipolar electron transport after a short optical pulse in quantum cascade lasers (QCLs) that takes into account all the participating energy levels, including the continuum, in a device. This work takes into account the incoherent scattering of electrons from one energy level to another and quantum coherent tunneling from an injector level to an active region level or vice versa. In contrast to the prior work that only considered transitions to and from a limited number of bound levels, this work include transitions between all bound levels and between the bound energy levels and the continuum. We simulated an experiment of S. Liu et al., in which 438-pJ femtosecond optical pulses at the device's lasing wavelength were injected into an I n0.653 Ga0.348 As/In0.310 Al0.690 As QCL structure; we found that approximately 1% of the electrons in the bound energy levels will be excited into the continuum by a pulse and that the probability that these electrons will be scattered back into bound energy levels is negligible, ˜10-4 . The gain recovery that is predicted is not consistent with the experiments, indicating that one or more phenomena besides unipolar electron transport in response to a short optical pulse play an important role in the observed gain recovery.
NASA Astrophysics Data System (ADS)
Wu, Phillip M.; Hart, Chris; Luna, Katherine; Munakata, Ko; Tsukada, Akio; Risbud, Subhash H.; Geballe, T. H.; Beasley, M. R.
2014-05-01
Via a two-step deposition and post-annealing procedure, K-doped WO3 thin films with reproducible transport properties are obtained. We observe a larger critical field Hc2 along the c axis, consistent with the picture of the Fermi surface containing one-dimensional bands along this direction. Reducing the film thickness results in a superconductor to insulator transition. Scanning electron microscopy (SEM) images show that KWO3 crystallites become less connected as the deposition time is reduced, providing a microscopic explanation for the transport behavior. In the superconducting films, a resistive anomaly is observed similar to bulk crystals, with a characteristic temperature that shifts lower with decreasing film thickness. The competing electronic effects manifest as a suppression of the density of states at the Fermi level, observed using point contact tunneling spectroscopy, demonstrating that disorder-induced increased Coulomb interactions are present. Using the theory of Belitz for the reduction of Tc due to disorder, we can infer that the film with the highest observed Tc has a relatively large disorder dependent electron-phonon interaction parameter ˜1.2. Understanding microscopically why certain films display higher Tc will aid in the search for the trace high-Tc superconducting anomalies observed in lightly surface doped bronzes.
NASA Technical Reports Server (NTRS)
Weaver, Clark J.; Ginoux, Paul; Hsu, Christina; Joiner, Joanna; Chou, Ming-Dah
1999-01-01
This study uses information on mineral aerosol from a transport model to calculate global radiative forcing values. The transport model is driven by assimilated meteorology and outputs three-dimensional dust spatial information for various size ranges. The dust fields are input to an off-line radiative transfer calculation to obtain the direct radiative forcing due to the dust fields. During June, July and August of 1988 presence of dust 1) reduces the global net incoming radiation at the top of atmosphere (TOA) by 0.3 to 0.7 W/sq m and 2) reduces net incoming radiation at the earth's surface by 1.3 to 2.0 W/sq m. Over Africa our estimates of the reduction of radiation at the top of atmosphere compare well with TOA reductions derived from ERBE and TOMS satellite data. However, our heating rates are not consistent with analysis temperature increments produced by the assimilation system over regions of high aerosol loading. These increments are based on differences between temperature observations and temperatures from the assimilation general circulation model. One explanation is that the lower tropospheric temperatures retrieved by TOVS are being contaminated by mineral aerosol.
Momentum fractionation on superstrata
Bena, Iosif; Martinec, Emil; Turton, David; Warner, Nicholas P.
2016-05-11
Superstrata are bound states in string theory that carry D1, D5, and momentum charges, and whose supergravity descriptions are parameterized by arbitrary functions of (at least) two variables. In the D1-D5 CFT, typical three-charge states reside in highdegree twisted sectors, and their momentum charge is carried by modes that individually have fractional momentum. Understanding this momentum fractionation holographically is crucial for understanding typical black-hole microstates in this system. We use solution-generating techniques to add momentum to a multi-wound supertube and thereby construct the first examples of asymptotically-flat superstrata. The resulting supergravity solutions are horizonless and smooth up to well-understood orbifold singularities. Upon taking the AdS3 decoupling limit, our solutions are dual to CFT states with momentum fractionation. We give a precise proposal for these dual CFT states. Lastly, our construction establishes the very nontrivial fact that large classes of CFT states with momentum fractionation can be realized in the bulk as smooth horizonless supergravity solutions.
Momentum fractionation on superstrata
Bena, Iosif; Martinec, Emil; Turton, David; ...
2016-05-11
Superstrata are bound states in string theory that carry D1, D5, and momentum charges, and whose supergravity descriptions are parameterized by arbitrary functions of (at least) two variables. In the D1-D5 CFT, typical three-charge states reside in highdegree twisted sectors, and their momentum charge is carried by modes that individually have fractional momentum. Understanding this momentum fractionation holographically is crucial for understanding typical black-hole microstates in this system. We use solution-generating techniques to add momentum to a multi-wound supertube and thereby construct the first examples of asymptotically-flat superstrata. The resulting supergravity solutions are horizonless and smooth up to well-understood orbifoldmore » singularities. Upon taking the AdS3 decoupling limit, our solutions are dual to CFT states with momentum fractionation. We give a precise proposal for these dual CFT states. Lastly, our construction establishes the very nontrivial fact that large classes of CFT states with momentum fractionation can be realized in the bulk as smooth horizonless supergravity solutions.« less
DOE R&D Accomplishments Database
Schwinger, J.
1952-01-26
The commutation relations of an arbitrary angular momentum vector can be reduced to those of the harmonic oscillator. This provides a powerful method for constructing and developing the properties of angular momentum eigenvectors. In this paper many known theorems are derived in this way, and some new results obtained. Among the topics treated are the properties of the rotation matrices; the addition of two, three, and four angular momenta; and the theory of tensor operators.
Interface area transport of monodispersed spherical particulates
Chang, Chong H.
2016-08-05
We present an interface area transport model required in tracking of mass, momentum, and energy exchange between dispersed and background materials. The basic transport equation has been rigorously derived from the volume fraction evolution equation. Interface area changes due to mass transport and local compression/expansion are included. The model is then simplified for the case in which the dispersed phase is composed of spheres of locally uniform size. A procedure for calculating advective flux with interface reconstruction has been suggested.
NASA Astrophysics Data System (ADS)
Kamidaira, Y.; Uchiyama, Y.; Mitarai, S.; Miyazawa, Y.
2014-12-01
A synoptic, regional downscaling experiment of Kuroshio off Ryukyu Islands, Japan, exhibits the evident predominance of submesoscale anticyclonic eddies over cyclones in the narrow strip between Kuroshio and the islands (Uchiyama et al., 2013). In the present study, the mechanism and impacts of the anticyclone dominance are examined with a detailed oceanic downscaling model in a double nested ROMS configuration at the horizontal resolution of 3km (ROMS-L1) and 1km (ROMS-L2), forced by the assimilative JCOPE2 oceanic reanalysis and the JMA GPV-MSM atmospheric hindcast. The model results are extensively validated against a variety of data including shipboard hydrography and satellite altimetry and temperature data to show a good agreement. An alternative ROMS-L2 experiment is also conducted to examine topographic effects on the anticyclones around the Ryukyu Islands by eliminating all the island topography above z > -1000 m, while the other configurations are held unchanged. If the islands are removed, the submesoscale negative vortices on the eastern side of the Kuroshio become much weaker than those of the original case with the islands. The experiment clearly demonstrates that dominance of the negative vorticity between Kuroshio and the Ryukyu Islands is caused by enhanced lateral shear due to the concentrated Kuroshio mean current associated with appropriate formation of the eastern branch, the northward-drifting Ryuku Current, and resultant eddy shedding in the narrow channel between the continental shelf of the East China Sea and the Okinawan ridge. A diagnostic eddy heat flux analysis illustrates that the submesoscale anticyclonic eddies play a crucial role in enhancing the eddy heat transport and thus the lateral mixing between Kuroshio and the islands as compared to those in the coarser resolution models (L1 and JCOPE2), resulting in promoting regional larval and material transport from Kuroshio to the islands.
Evidence of inward toroidal momentum convection in the JET tokamak.
Tala, T; Zastrow, K-D; Ferreira, J; Mantica, P; Naulin, V; Peeters, A G; Tardini, G; Brix, M; Corrigan, G; Giroud, C; Strintzi, D
2009-02-20
Experiments have been carried out on the Joint European Torus tokamak to determine the diffusive and convective momentum transport. Torque, injected by neutral beams, was modulated to create a periodic perturbation in the toroidal rotation velocity. Novel transport analysis shows the magnitude and profile shape of the momentum diffusivity are similar to those of the ion heat diffusivity. A significant inward momentum pinch, up to 20 m/s, has been found. Both results are consistent with gyrokinetic simulations. This evidence is complemented in plasmas with internal transport barriers.
Evidence of Inward Toroidal Momentum Convection in the JET Tokamak
Tala, T.; Zastrow, K.-D.; Brix, M.; Corrigan, G.; Giroud, C.; Naulin, V.; Peeters, A. G.; Tardini, G.; Strintzi, D.
2009-02-20
Experiments have been carried out on the Joint European Torus tokamak to determine the diffusive and convective momentum transport. Torque, injected by neutral beams, was modulated to create a periodic perturbation in the toroidal rotation velocity. Novel transport analysis shows the magnitude and profile shape of the momentum diffusivity are similar to those of the ion heat diffusivity. A significant inward momentum pinch, up to 20 m/s, has been found. Both results are consistent with gyrokinetic simulations. This evidence is complemented in plasmas with internal transport barriers.
Ballistic transport in Saturn's rings - An analytic theory
NASA Technical Reports Server (NTRS)
Lissauer, J. J.
1984-01-01
Ejecta from impacts of micrometeoroids on Saturn's ring particles will, in most cases, remain in orbit about Saturn and eventually be reaccreted by the rings, possibly at a different radial location. The resulting mass transport has been suggested as the cause of some of the features observed in Saturn's rings. Previous attempts to model this transport have used numerical simulations which have not included the effects of the angular momentum transport coincident with mass transport. An analytical model for ballistic mass transport in Saturn's rings is developed. The model includes the effects of angular momentum advection and shows that the net material movement due to angular momentum advection is comparable to that caused by direct ballistic mass transport.
Plasma momentum meter for momentum flux measurements
Zonca, Fulvio; Cohen, Samuel A.; Bennett, Timothy; Timberlake, John R.
1993-01-01
Invention comprises an instrument in which momentum flux onto a biasable target plate is transferred via a suspended quartz tube onto a sensitive force transducer--a capacitance-type pressure gauge. The transducer is protected from thermal damage, arcing and sputtering, and materials used in the target and pendulum are electrically insulating, rigid even at elevated temperatures, and have low thermal conductivity. The instrument enables measurement of small forces (10.sup.-5 to 10.sup.3 N) accompanied by high heat fluxes which are transmitted by energetic particles with 10's of eV of kinetic energy in a intense magnetic field and pulsed plasma environment.
Achromatic orbital angular momentum generator
NASA Astrophysics Data System (ADS)
Bouchard, Frédéric; Mand, Harjaspreet; Mirhosseini, Mohammad; Karimi, Ebrahim; Boyd, Robert W.
2014-12-01
We describe a novel approach for generating light beams that carry orbital angular momentum (OAM) by means of total internal reflection in an isotropic medium. A continuous space-varying cylindrically symmetric reflector, in the form of two glued hollow axicons, is used to introduce a nonuniform rotation of polarization into a linearly polarized input beam. This device acts as a full spin-to-orbital angular momentum convertor. It functions by switching the helicity of the incoming beam's polarization, and by conservation of total angular momentum thereby generates a well-defined value of OAM. Our device is broadband, since the phase shift due to total internal reflection is nearly independent of wavelength. We verify the broad-band behaviour by measuring the conversion efficiency of the device for three different wavelengths corresponding to the RGB colours, red, green and blue. An average conversion efficiency of 95% for these three different wavelengths is observed. This device may find applications in imaging from micro- to astronomical systems where a white vortex beam is needed.
NASA Astrophysics Data System (ADS)
Searle, Matthew; Maynes, Daniel; Crockett, Julie
2016-11-01
An analytical investigation of thermal transport due to a steady, laminar, buoyancy-driven flow past a vertical superhydrophobic (SHPo) surface was performed. The surface temperature was constant and uniform and exceeded the temperature of the surrounding liquid. Uniform stream-wise hydrodynamic slip and temperature jump are imposed at the wall to model the SHPo surface. Applying an integral analysis within the boundary layer results in a system of differential equations which are solved numerically to obtain boundary layer thickness, maximum velocity in the profile, and local and average values of both the friction coefficient and the Nusselt number. The classical smooth hydrophobic scenario with no-slip and no temperature jump showed excellent agreement with previous analysis of the same problem. The influence of varying temperature jump length on the local and average values of the friction coefficient and the Nusselt number was obtained for Rayleigh number ranging from 104 to 109 and Prandtl number ranging from 2 to 11. Local and average Nusselt numbers decrease dramatically, concomitant with a decrease in the maximum fluid velocity, as the temperature jump length increases. National Science Foundation(NSF) Grant No. CBET-1235881.
NASA Astrophysics Data System (ADS)
Shen, Ka; Raimondi, R.; Vignale, G.
2014-12-01
Spin-orbit interactions in two-dimensional electron liquids are responsible for many interesting transport phenomena in which particle currents are converted to spin polarizations and spin currents and vice versa. Prime examples are the spin Hall effect, the Edelstein effect, and their inverses. By similar mechanisms, it is also possible to partially convert an optically induced electron-hole density wave to a spin density wave and vice versa. In this paper, we present a unified theoretical treatment of these effects based on quantum kinetic equations that include not only the intrinsic spin-orbit coupling from the band structure of the host material, but also the spin-orbit coupling due to an external electric field and a random impurity potential. The drift-diffusion equations we derive in the diffusive regime are applicable to a broad variety of experimental situations, both homogeneous and nonhomogeneous, and include on equal footing "skew scattering" and "side jump" from electron-impurity collisions. As a demonstration of the strength and usefulness of the theory we apply it to the study of several effects of current experimental interest: the inverse Edelstein effect, the spin-current swapping effect, and the partial conversion of an electron-hole density wave to a spin density wave in a two-dimensional electron gas with Rashba and Dresselhaus spin-orbit couplings, subject to an electric field.
Ion momentum and energy transfer rates for charge exchange collisions
NASA Technical Reports Server (NTRS)
Horwitz, J.; Banks, P. M.
1973-01-01
The rates of momentum and energy transfer have been obtained for charge exchange collisions between ion and neutral gases having arbitrary Maxwellian temperatures and bulk transport velocities. The results are directly applicable to the F-region of the ionosphere where 0+ - 0 charge is the dominant mechanism affecting ion momentum and energy transfer.
Non-physical momentum sources in slab geometry gyrokinetics
NASA Astrophysics Data System (ADS)
Parra, Felix I.; Catto, Peter J.
2010-08-01
We investigate momentum transport in the Hamiltonian electrostatic gyrokinetic formulation of Dubin et al (1983 Phys. Fluids 26 3524). We prove that the long wavelength electric field obtained from the gyrokinetic quasineutrality introduces a non-physical momentum source in the low flow ordering.
Dorda, Antonius Schürrer, Ferdinand
2015-03-01
We present a novel numerical scheme for the deterministic solution of the Wigner transport equation, especially suited to deal with situations in which strong quantum effects are present. The unique feature of the algorithm is the expansion of the Wigner function in local basis functions, similar to finite element or finite volume methods. This procedure yields a discretization of the pseudo-differential operator that conserves the particle density on arbitrarily chosen grids. The high flexibility in refining the grid spacing together with the weighted essentially non-oscillatory (WENO) scheme for the advection term allows for an accurate and well-resolved simulation of the phase space dynamics. A resonant tunneling diode is considered as test case and a detailed convergence study is given by comparing the results to a non-equilibrium Green's functions calculation. The impact of the considered domain size and of the grid spacing is analyzed. The obtained convergence of the results towards a quasi-exact agreement of the steady state Wigner and Green's functions computations demonstrates the accuracy of the scheme, as well as the high flexibility to adjust to different physical situations.
Dorda, Antonius; Schürrer, Ferdinand
2015-03-01
We present a novel numerical scheme for the deterministic solution of the Wigner transport equation, especially suited to deal with situations in which strong quantum effects are present. The unique feature of the algorithm is the expansion of the Wigner function in local basis functions, similar to finite element or finite volume methods. This procedure yields a discretization of the pseudo-differential operator that conserves the particle density on arbitrarily chosen grids. The high flexibility in refining the grid spacing together with the weighted essentially non-oscillatory (WENO) scheme for the advection term allows for an accurate and well-resolved simulation of the phase space dynamics. A resonant tunneling diode is considered as test case and a detailed convergence study is given by comparing the results to a non-equilibrium Green's functions calculation. The impact of the considered domain size and of the grid spacing is analyzed. The obtained convergence of the results towards a quasi-exact agreement of the steady state Wigner and Green's functions computations demonstrates the accuracy of the scheme, as well as the high flexibility to adjust to different physical situations.
Dorda, Antonius; Schürrer, Ferdinand
2015-01-01
We present a novel numerical scheme for the deterministic solution of the Wigner transport equation, especially suited to deal with situations in which strong quantum effects are present. The unique feature of the algorithm is the expansion of the Wigner function in local basis functions, similar to finite element or finite volume methods. This procedure yields a discretization of the pseudo-differential operator that conserves the particle density on arbitrarily chosen grids. The high flexibility in refining the grid spacing together with the weighted essentially non-oscillatory (WENO) scheme for the advection term allows for an accurate and well-resolved simulation of the phase space dynamics. A resonant tunneling diode is considered as test case and a detailed convergence study is given by comparing the results to a non-equilibrium Green's functions calculation. The impact of the considered domain size and of the grid spacing is analyzed. The obtained convergence of the results towards a quasi-exact agreement of the steady state Wigner and Green's functions computations demonstrates the accuracy of the scheme, as well as the high flexibility to adjust to different physical situations. PMID:25892748
The Angular Momentum Dichotomy
NASA Astrophysics Data System (ADS)
Teklu, Adelheid; Remus, Rhea-Silvia; Dolag, Klaus; Burkert, Andreas
2015-02-01
In the context of the formation of spiral galaxies the evolution and distribution of the angular momentum of dark matter halos have been discussed for more than 20 years, especially the idea that the specific angular momentum of the halo can be estimated from the specific angular momentum of its disk (e.g. Fall & Efstathiou (1980), Fall (1983) and Mo et al. (1998)). We use a new set of hydrodynamic cosmological simulations called Magneticum Pathfinder which allow us to split the galaxies into spheroidal and disk galaxies via the circularity parameter ɛ, as commonly used (e.g. Scannapieco et al. (2008)). Here, we focus on the dimensionless spin parameter λ = J |E|1/2 / (G M5/2) (Peebles 1969, 1971), which is a measure of the rotation of the total halo and can be fitted by a lognormal distribution, e.g. Mo et al. (1998). The spin parameter allows one to compare the relative angular momentum of halos across different masses and different times. Fig. 1 reveals a dichotomy in the distribution of λ at all redshifts when the galaxies are split into spheroids (dashed) and disk galaxies (dash-dotted). The disk galaxies preferentially live in halos with slightly larger spin parameter compared to spheroidal galaxies. Thus, we see that the λ of the whole halo reflects the morphology of its central galaxy. For more details and a larger study of the angular momentum properties of disk and spheroidal galaxies, see Teklu et al. (in prep.).
NASA Technical Reports Server (NTRS)
Guo, Liwen; Cardullo, Frank M.; Kelly, Lon C.
2007-01-01
The desire to create more complex visual scenes in modern flight simulators outpaces recent increases in processor speed. As a result, simulation transport delay remains a problem. New approaches for compensating the transport delay in a flight simulator have been developed and are presented in this report. The lead/lag filter, the McFarland compensator and the Sobiski/Cardullo state space filter are three prominent compensators. The lead/lag filter provides some phase lead, while introducing significant gain distortion in the same frequency interval. The McFarland predictor can compensate for much longer delay and cause smaller gain error in low frequencies than the lead/lag filter, but the gain distortion beyond the design frequency interval is still significant, and it also causes large spikes in prediction. Though, theoretically, the Sobiski/Cardullo predictor, a state space filter, can compensate the longest delay with the least gain distortion among the three, it has remained in laboratory use due to several limitations. The first novel compensator is an adaptive predictor that makes use of the Kalman filter algorithm in a unique manner. In this manner the predictor can accurately provide the desired amount of prediction, while significantly reducing the large spikes caused by the McFarland predictor. Among several simplified online adaptive predictors, this report illustrates mathematically why the stochastic approximation algorithm achieves the best compensation results. A second novel approach employed a reference aircraft dynamics model to implement a state space predictor on a flight simulator. The practical implementation formed the filter state vector from the operator s control input and the aircraft states. The relationship between the reference model and the compensator performance was investigated in great detail, and the best performing reference model was selected for implementation in the final tests. Theoretical analyses of data from offline
Losing forward momentum holographically
NASA Astrophysics Data System (ADS)
Balasubramanian, Koushik; Herzog, Christopher P.
2014-06-01
We present a numerical scheme for solving Einstein’s Equations in the presence of a negative cosmological constant and an event horizon with planar topology. Our scheme allows for the introduction of a particular metric source at the conformal boundary. Such a spacetime has a dual holographic description in terms of a strongly interacting quantum field theory at nonzero temperature. By introducing a sinusoidal static metric source that breaks translation invariance, we study momentum relaxation in the field theory. In the long wavelength limit, our results are consistent with the fluid-gravity correspondence and relativistic hydrodynamics. In the small amplitude limit, our results are consistent with the memory function prediction for the momentum relaxation rate. Our numerical scheme allows us to study momentum relaxation outside these two limits as well.
NASA Technical Reports Server (NTRS)
1997-01-01
CTA Space Systems, Inc. has been licensed to sell commercially a reaction/momentum wheel originally developed for NASA's scientific satellites. NASA originally identified a need for the wheel in its Small Explorer program. The Submillimeter Wave Astronomy Satellite required extremely low jitter and a reaction/momentum wheel with a torque greater than any comparably sized commercially available wheel to keep the instrument pointed at celestial objects to a high degree of precision. After development, a market assessment by Research Triangle Institute was completed, showing commercial potential for the flywheel technology. A license was granted to CTA in the fall of 1996. The company currently uses the technology in its complete spacecraft fabrication services and has built over 10 reaction/momentum wheels for commercial, scientific, and military customers.
Optical orbital angular momentum.
Barnett, Stephen M; Babiker, Mohamed; Padgett, Miles J
2017-02-28
We present a brief introduction to the orbital angular momentum of light, the subject of our theme issue and, in particular, to the developments in the 13 years following the founding paper by Allen et al. (Allen et al. 1992 Phys. Rev. A 45, 8185 (doi:10.1103/PhysRevA.45.8185)). The papers by our invited authors serve to bring the field up to date and suggest where developments may take us next.This article is part of the themed issue 'Optical orbital angular momentum'.
NASA Astrophysics Data System (ADS)
Robinson, Stephen
2015-03-01
Angular momentum is a notoriously difficult concept to grasp. Visualization often requires three-dimensional pictures of vectors pointing in seemingly arbitrary directions. A simple student-run laboratory experiment coupled with intuitive explanations by an instructor can clear up some of the inherent ambiguity of rotational motion. Specifically, the precessional period of a suspended spinning bicycle wheel can be related to the spinning frequency through a simple algebraic expression. An explanation of this precession apart from the concept of angular momentum will be given.
Optical orbital angular momentum
NASA Astrophysics Data System (ADS)
Barnett, Stephen M.; Babiker, Mohamed; Padgett, Miles J.
2017-02-01
We present a brief introduction to the orbital angular momentum of light, the subject of our theme issue and, in particular, to the developments in the 13 years following the founding paper by Allen et al. (Allen et al. 1992 Phys. Rev. A 45, 8185 (doi:10.1103/PhysRevA.45.8185)). The papers by our invited authors serve to bring the field up to date and suggest where developments may take us next. This article is part of the themed issue 'Optical orbital angular momentum'.
Neoclassical Calculations with Momentum Conservation Using the PENTA Code
NASA Astrophysics Data System (ADS)
Lore, Jeremy; Spong, D. A.; Briesemeister, A.
2010-11-01
The PENTA code calculates neoclassical radial and parallel flows of heat and particles, including the effects of collisional momentum conservation, for arbitrary toroidal geometries. As an input, PENTA uses transport coefficients calculated using a pitch angle scattering (PAS) collision operator, for example from the DKES code. In this sense PENTA acts as a momentum correction technique to transport quantities calculated from the PAS transport coefficients, which are often used in stellarator transport analyses. PENTA has recently been upgraded to account for arbitrary ion impurity species, and to include multiple methods of momentum correction for comparison and benchmarking. For non-(quasi)symmetric configurations, the radial electric field is calculated from the nonambipolar particle fluxes. For (quasi)symmetric devices PENTA recaptures intrinsic ambipolarity, demonstrating its applicability to both 2D and 3D geometries. Momentum correction has been shown to have a significant effect on the calculated parallel flows in the HSX stellarator.
Angular Momentum Evolution of Young Solar-type Stars
NASA Astrophysics Data System (ADS)
Amard, Louis; Palacios, Ana; Charbonnel, Corinne
2016-01-01
We present stellar evolution models of young solar-type stars including self consistent treatment of rotational mixing and extraction of angular momentum (AM) by magnetized wind including the most up-to-date physic of AM transport.
Probing Electron Dynamics with the Laplacian of the Momentum Density
Sukumar, N.; MacDougall, Preston J.; Levit, M. Creon
2012-09-24
This chapter in the above-titled monograph presents topological analysis of the Laplacian of the electron momentum density in organic molecules. It relates topological features in this distribution to chemical and physical properties, particularly aromaticity and electron transport.
Plasma momentum meter for momentum flux measurements
Zonca, F.; Cohen, S.A.; Bennett, T.; Timberlake, J.R.
1993-08-24
An apparatus is described for measuring momentum flux from an intense plasma stream, comprising: refractory target means oriented normal to the flow of said plasma stream for bombardment by said plasma stream where said bombardment by said plasma stream applies a pressure to said target means, pendulum means for communicating a translational displacement of said target to a force transducer where said translational displacement of said target is transferred to said force transducer by an elongated member coupled to said target, where said member is suspended by a pendulum configuration means and where said force transducer is responsive to said translational displacement of said member, and force transducer means for outputting a signal representing pressure data corresponding to said displacement.
Schunk, P.R.; Sackinger, P.A.; Rao, R.R.
1996-01-01
GOMA is a two- and three-dimensional finite element program which excels in analyses of manufacturing processes, particularly those involving free or moving interfaces. Specifically, the full-Newton-coupled heat, mass, momentum, and pseudo-solid mesh motion algorithm makes GOMA ideally suited for simulating processes in which the bulk fluid transport is closely coupled to the interfacial physics. Examples include, but are not limited to, coating and polymer processing flows, soldering, crystal growth, and solid-network or solution film drying. The code is based on the premise that any boundary can be (1) moving or free, with an apriori unknown position dictated by the distinguishing physics, (2) fixed, according to a global analytical representation, or (3) moving in time and space under user-prescribed kinematics. The goal is to enable the user to predict boundary position or motion simultaneously with the physics of the problem being analyzed and to pursue geometrical design studies and fluid-structure interaction problems. The moving mesh algorithm treats the entire domain as a computational Lagrangian solid that deforms subject to the physical principles which dictate boundary position. As an added benefit, the same Lagrangian solid mechanics can be exploited to solve multi-field problems for which the solid motion and stresses interact with other transport phenomena, either within the same material phase (e.g. shrinking coating) or in neighboring material phases (e.g. flexible blade coating). Thus, analyses of many fluid-structure interaction problems and deformable porous media problems are accessible. This document serves as a user`s guide and reference for GOMA and provides a brief overview of GOMA`s capabilities, theoretical background, and classes of problems for which it is targeted.
Angular momentum flux of nonparaxial acoustic vortex beams and torques on axisymmetric objects.
Zhang, Likun; Marston, Philip L
2011-12-01
An acoustic vortex in an inviscid fluid and its radiation torque on an axisymmetric absorbing object are analyzed beyond the paraxial approximation to clarify an analogy with an optical vortex. The angular momentum flux density tensor from the conservation of angular momentum is used as an efficient description of the transport of angular momentum. Analysis of a monochromatic nonparaxial acoustic vortex beam indicates that the local ratio of the axial (or radial) flux density of axial angular momentum to the axial (or radial) flux density of energy is exactly equal to the ratio of the beam's topological charge l to the acoustic frequency ω. The axial radiation torque exerted by the beam on an axisymmetric object centered on the beam's axis due to the transfer of angular momentum is proportional to the power absorbed by the object with a factor l/ω, which can be understood as a result of phonon absorption from the beam. Depending on the vortex's helicity, the torque is parallel or antiparallel to the beam's axis.
ERIC Educational Resources Information Center
Parker, G. W.
1978-01-01
Discusses, classically and quantum mechanically, the angular momentum induced in the bound motion of an electron by an external magnetic field. Calculates the current density and its magnetic moment, and then uses two methods to solve the first-order perturbation theory equation for the required eigenfunction. (Author/GA)
ERIC Educational Resources Information Center
Parker, G. W.
1978-01-01
Discusses, classically and quantum mechanically, the angular momentum induced in the bound motion of an electron by an external magnetic field. Calculates the current density and its magnetic moment, and then uses two methods to solve the first-order perturbation theory equation for the required eigenfunction. (Author/GA)
Jet momentum balance independent of shear viscosity
NASA Astrophysics Data System (ADS)
Neufeld, R. B.
2012-03-01
Jet momentum balance measurements, such as those recently performed by the CMS collaboration, provide an opportunity to quantify the energy transferred from a parton shower to the underlying medium in heavy-ion collisions. Specifically, I argue that the Cooper-Frye freeze-out distribution associated with the energy and momentum deposited by the parton shower is controlled to a significant extent by the distribution of the underlying bulk matter and independent of the details of how deposited energy is redistributed in the medium, which is largely determined by transport coefficients such as shear viscosity. Thus, by matching the distribution of momentum associated with the secondary jet in such measurements to the thermal distribution of the underlying medium, one can obtain a model-independent estimate on the amount of parton shower energy deposited.
NASA Astrophysics Data System (ADS)
Rodríguez-Abudo, S.; Foster, D. L.
2014-12-01
Observations of the nearbed velocity field over a rippled sediment bed under asymmetric wave forcing conditions were collected using a submersible particle image velocimetry (PIV) system. To examine the role of bed form-induced dynamics in the total momentum transfer, a double-averaging technique was implemented on the two-dimensional time-dependent velocity field by means of the full momentum equation. This approach allows for direct determination of the bed form-induced stresses, i.e., stresses that arise due to the presence of bed forms, which are zero in flat bed conditions. This analysis suggests that bed form-induced stresses are closely related to the presence of coherent motions and may be partitioned from the turbulent stresses. Inferences of stress provided by a bed load transport model suggest that total momentum transfer obtained from the double-averaging technique is capable of reproducing bed form mobilization. Comparisons between the total momentum transfer and stress estimates obtained from local velocity profiles show significant variability across the ripple and suggest that an array of sensors is necessary to reproduce bed form evolution. The imbalance of momentum obtained by resolving the different terms constituting the near-bed momentum balance (i.e., acceleration deficit, stress gradient, and bed form-induced skin friction) provides an estimate of the bed form-induced pressure that is consistent with flow separation. This analysis reveals three regions in the flow: the free-stream, where all terms are relatively balanced; the near-bed, where momentum imbalance is significant during flow weakening; and below ripple crests, where bed form-induced pressure is the leading order mechanism.
Contrasts Between Momentum and Scalar Exchanges Over Very Rough Surfaces
NASA Astrophysics Data System (ADS)
Bou-Zeid, Elie; Li, Qi
2016-11-01
Understanding of the physical processes modulating transport of momentum and scalars over very rough walls is essential in a large range of engineering and environmental applications. Since passive scalars are advected with the flow, broad similarity is expected between momentum and scalar transport. However, unlike momentum, which is dominated by form drag over very rough walls, scalar transport must occur through the viscous exchanges at the solid-fluid interface, which might result in transport dissimilarity. To examine these similarities and differences of momentum and passive scalar exchanges over large three-dimensional roughness elements, a suite of large-eddy simulations is conducted. The turbulent components of the transport of momentum and scalars within the canopy and roughness sublayers are found to be similar. However, strong dissimilarity is noted between the dispersive fluxes. The dispersive components are also found to be a significant fraction of the total fluxes within and below the roughness sublayer. Increasing frontal density induces a general transition in the flow from a rough boundary layer type to a mixed-layer-like type, which is found to have contrasting effects on momentum and scalar transport. This study was funded by the US National Science Foundation's Sustainability Research Network Cooperative Agreement number 1444758 and Water Sustainability and Climate program Grant Number CBET-1058027.
Fried, Eliot; Shen, Amy Q; Gurtin, Morton E
2006-06-01
We develop a complete set of equations governing the evolution of a sharp interface separating a volatile-solvent/nonvolatile-surfactant solution from a vapor atmosphere. In addition to a sorption isotherm equation and the conventional balances for mass, linear momentum, and energy, these equations include an alternative to the Hertz-Knudsen-Langmuir equation familiar from conventional theories of evaporation and condensation. This additional equation arises from a consideration of configurational forces within a thermodynamical framework. While the notion of configurational forces is well developed and understood for the description of materials that, like crystalline solids, possess natural reference configurations, very little has been done regarding their role in materials, such as viscous fluids, that do not possess preferred reference states. We therefore provide comprehensive developments of configurational forces, the balance of configurational momentum, and configurational thermodynamics. Our treatment does not require a choice of reference configuration. The general evolution equations arising from our theory account for the thermodynamic structure of the solution and the interface and for sources of dissipation related to the transport of surfactant, momentum, and heat in the solution and within the interface along with the transport of solute, momentum, kinetic energy, and heat across the interface. Moreover, the equations account for the Soret and Dufour effects in the solution and on the interface and for observed discontinuities of the temperature and chemical potential across the interface. Due to the complexity of these equations, we provide approximate equations which we compare to equations preexistent in the literature.
NASA Astrophysics Data System (ADS)
Hua, Lijuan; Zhong, Linhao; Luo, Dehai
2017-04-01
This work examines the main sources of moisture and the poleward transport water vapor over Barents/Kara Sea (BKS) during boreal winter of 1979 2015 in the ERA-Interim reanalysis product through a revised dynamic recycling model during boreal winter. The methodology computes the water vapor contributions from sources along 15-day time-reverse trajectories. The large-scale circulation patterns associated with the moisture transport process. The results suggested that water vapor from Northern Atlantic play crucial role in regulating the sea ice loss in Barents Sea and Kara Sea. It seems that positive NAO events tend to transport the Atlantic moisture to the Eastern Europe, and then Ural blocking flow further transports the moisture northward to BKS. The Atlantic moisture approximately takes 3-6 days to BKS through the moisture pathway regulated by NAO and Ural blocking.
Cross-shelf transport into nearshore waters due to shoaling internal tides in San Pedro Bay, CA
Noble, M.; Jones, B.; Hamilton, P.; Xu, Jie; Robertson, G.; Rosenfeld, L.; Largier, J.
2009-01-01
In the summer of 2001, a coastal ocean measurement program in the southeastern portion of San Pedro Bay, CA, was designed and carried out. One aim of the program was to determine the strength and effectiveness of local cross-shelf transport processes. A particular objective was to assess the ability of semidiurnal internal tidal currents to move suspended material a net distance across the shelf. Hence, a dense array of moorings was deployed across the shelf to monitor the transport patterns associated with fluctuations in currents, temperature and salinity. An associated hydrographic program periodically monitored synoptic changes in the spatial patterns of temperature, salinity, nutrients and bacteria. This set of measurements show that a series of energetic internal tides can, but do not always, transport subthermocline water, dissolved and suspended material from the middle of the shelf into the surfzone. Effective cross-shelf transport occurs only when (1) internal tides at the shelf break are strong and (2) subtidal currents flow strongly downcoast. The subtidal downcoast flow causes isotherms to tilt upward toward the coast, which allows energetic, nonlinear internal tidal currents to carry subthermocline waters into the surfzone. During these events, which may last for several days, the transported water remains in the surfzone until the internal tidal current pulses and/or the downcoast subtidal currents disappear. This nonlinear internal tide cross-shelf transport process was capable of carrying water and the associated suspended or dissolved material from the mid-shelf into the surfzone, but there were no observation of transport from the shelf break into the surfzone. Dissolved nutrients and suspended particulates (such as phytoplankton) transported from the mid-shelf into the nearshore region by nonlinear internal tides may contribute to nearshore algal blooms, including harmful algal blooms that occur off local beaches.
Boubakri, Meriam; Chaya, Taro; Hirata, Hiromi; Kajimura, Naoko; Kuwahara, Ryusuke; Ueno, Akiko; Malicki, Jarema; Furukawa, Takahisa; Omori, Yoshihiro
2016-11-18
In the retina, aberrant opsin transport from cell bodies to outer segments leads to retinal degenerative diseases such as retinitis pigmentosa. Opsin transport is facilitated by the intraflagellar transport (IFT) system that mediates the bidirectional movement of proteins within cilia. In contrast to functions of the anterograde transport executed by IFT complex B (IFT-B), the precise functions of the retrograde transport mediated by IFT complex A (IFT-A) have not been well studied in photoreceptor cilia. Here, we analyzed developing zebrafish larvae carrying a null mutation in ift122 encoding a component of IFT-A. ift122 mutant larvae show unexpectedly mild phenotypes, compared with those of mutants defective in IFT-B. ift122 mutants exhibit a slow onset of progressive photoreceptor degeneration mainly after 7 days post-fertilization. ift122 mutant larvae also develop cystic kidney but not curly body, both of which are typically observed in various ciliary mutants. ift122 mutants display a loss of cilia in the inner ear hair cells and nasal pit epithelia. Loss of ift122 causes disorganization of outer segment discs. Ectopic accumulation of an IFT-B component, ift88, is observed in the ift122 mutant photoreceptor cilia. In addition, pulse-chase experiments using GFP-opsin fusion proteins revealed that ift122 is required for the efficient transport of opsin and the distal elongation of outer segments. These results show that IFT-A is essential for the efficient transport of outer segment proteins, including opsin, and for the survival of retinal photoreceptor cells, rendering the ift122 mutant a unique model for human retinal degenerative diseases. © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.
NASA Astrophysics Data System (ADS)
Snyder, Douglas
2015-04-01
If a photon impacts a much larger fixed object, the momentum transfer from the photon to the fixed object is essentially undetectable. This principle is the basis for a Mach Zehnder interferometer where fixed full-silvered and half-silvered mirrors do not provide which way information when impacted by an incoming photon. Kim relied on fixed mirrors impacted by photons to demonstrate quantum erasure. If the principle did not work, Kim would not have obtained symmetric and anti-symmetric interference. The present experiment relies on delayed choices for idler photons which initially possess ww information that immediately affect the distribution of signal photons initially entangled with the idler photons and for which the idler photons provide ww information. It relies on the principle noted. In the case of the present experiment, one of those fixed objects is an optical microcavity that is situated at the crossroads of two possible paths for the idler photon. The delayed choice concerns whether to maintain or eliminate the entanglement before any measurements are made. If the idler photon enters the microcavity filled with photons in the same mode as the idler photon, the entanglement is eliminated. The resulting distribution of the paired signal photons with this choice shows interference. If the choice is not to send the idler photon toward the microcavity and preserve the which-way information of the idler photons, the resulting distribution of the paired signal photons shows ww information.
Effects of momentum conservation on the analysis of anisotropic flow
Borghini, N.; Dinh, P.M.; Ollitrault, J.-Y.; Poskanzer, A.M.; Voloshin, S.A.
2002-02-05
We present a general method for taking into account correlations due to momentum conservation in the analysis of anisotropic flow. Momentum conservation mostly affects the first harmonic in azimuthal distributions, i.e., directed flow. It also modifies higher harmonics, for instance elliptic flow, when they are measured with respect to a first harmonic event plane such as one determined with the standard transverse momentum method. Our method is illustrated by application to NA49 data on pion directed flow.
NASA Astrophysics Data System (ADS)
Miller, S. M.; Fung, I.; Liu, J.; Hayek, M. N.; Andrews, A. E.
2014-09-01
Estimates of CO2 fluxes that are based on atmospheric data rely upon a meteorological model to simulate atmospheric CO2 transport. These models provide a quantitative link between surface fluxes of CO2 and atmospheric measurements taken downwind. Therefore, any errors in the meteorological model can propagate into atmospheric CO2 transport and ultimately bias the estimated CO2 fluxes. These errors, however, have traditionally been difficult to characterize. To examine the effects of CO2 transport errors on estimated CO2 fluxes, we use a global meteorological model-data assimilation system known as "CAM-LETKF" to quantify two aspects of the transport errors: error variances (standard deviations) and temporal error correlations. Furthermore, we develop two case studies. In the first case study, we examine the extent to which CO2 transport uncertainties can bias CO2 flux estimates. In particular, we use a common flux estimate known as CarbonTracker to discover the minimum hypothetical bias that can be detected above the CO2 transport uncertainties. In the second case study, we then investigate which meteorological conditions may contribute to month-long biases in modeled atmospheric transport. We estimate 6 hourly CO2 transport uncertainties in the model surface layer that range from 0.15 to 9.6 ppm (standard deviation), depending on location, and we estimate an average error decorrelation time of ∼2.3 days at existing CO2 observation sites. As a consequence of these uncertainties, we find that CarbonTracker CO2 fluxes would need to be biased by at least 29%, on average, before that bias were detectable at existing non-marine atmospheric CO2 observation sites. Furthermore, we find that persistent, bias-type errors in atmospheric transport are associated with consistent low net radiation, low energy boundary layer conditions. The meteorological model is not necessarily more uncertain in these conditions. Rather, the extent to which meteorological uncertainties
NASA Astrophysics Data System (ADS)
McCray, J. E.; Downs, W.; Falta, R. W.; Housley, T.
2005-12-01
DNAPL sources of carbon tetrachloride (CT) vapors are of interest at the Radioactive Waste Management Complex (RWMC) at the Idaho National Engineering and Environmental Laboratory (INEEL). The site is underlain by thick fractured basalt that includes sedimentary interbeds, each are a few meters thick. Daily atmospheric pressure fluctuations serve as driving forces for CT vapor transport in the subsurface. Other important transport processes for vapor movement include gas-phase diffusion and density-driven transport. The objective of this research is to investigate the influence and relative importance of these processes on gaseous transport of CT. Gas pressure and vapor concentration measurements were conducted at various depths in two wells. A numerical multiphase flow model (TOUGH2), calibrated to field pressure data, is used to conduct sensitivity analyses to elucidate the importance of the different transport mechanisms. Results show that the basalt is highly permeable to vertical air flow. The pressure dampening occurs mainly in the sedimentary interbeds. Model-calibrated permeability values for the interbeds are similar to those obtained in a study by the U.S. Geological Survey for shallow sediments, and an order of magnitude higher than column-scale values obtained by previous studies conducted by INEEL scientists. The transport simulations indicate that considering the effect of barometric pressure changes is critical to simulating transport of pollutants in the vadose zone above the DNAPL source. Predicted concentrations can be orders of magnitude smaller than actual concentrations if the effect is not considered. Below the DNAPL vapor source, accounting for density and diffusion alone would yield acceptable results provided that a 20% error in concentrations are acceptable, and that simulating concentrations trends (and not actual concentrations) is the primary goal.
NASA Astrophysics Data System (ADS)
Chowdhury, P.; Behera, M. R.
2016-12-01
Abstract Changing climate and the rapid socio-economic development in the west coast region of India is responsible for the increasing vulnerability of the sandy beaches located in this zone. Short, medium and long-term evolution of such sandy beaches remains a major area of investigation in order to achieve sustainable development and protection against coastal erosion. Longshore sediment transport (LST) plays a major role in the long-term shoreline evolution of coastlines. However, there exists a huge gap in available measured sediment transport data in this region. Therefore, this study was undertaken to find the suitability of applying a bulk sediment transport formula to estimate the long-term LST of regions with minimum available observed data. Wave climate plays a major role in determining the long-term shoreline changes and hence the past wave climate was studied to understand the variability in nearshore wave climate. Towards this, ERA-Interim hindcast data for a period of 37 years (1979-2015) is used to understand the temporal changes in regional wave climate. A suitable bulk formula was forced with the nearshore wave climate to compute annual LST in this region. West coast of India experiences oblique waves from which results in huge sediment transport in the north direction. To identify the major driver of transport, the total sediment transport was separated into swell and wind-wave driven transports. The swell-wave driven LST was found to be larger by an order of magnitude than the wind-wave driven transport. The seasonal variation in LST was also studied with respect to pre-monsoon, monsoon and post-monsoon seasons. The estimates derived from the bulk formula were compared with the shoreline evolution trend obtained from satellite imagery. The comparison shows acceptable results and proves that the formula could be used to estimate LST of regions with minimum observation data with considerable accuracy. Key words: Longshore sediment transport
NASA Astrophysics Data System (ADS)
Nagano, Akira; Kizu, Shoichi; Hanawa, Kimio; Roemmich, Dean
2016-12-01
Applying segment-wise altimetry-based gravest empirical mode method to expendable bathythermograph temperature, Argo salinity, and altimetric sea surface height data in March, June, and November from San Francisco to near Japan (30∘ N, 145∘ E) via Honolulu, we estimated the component of the heat transport variation caused by change in the southward interior geostrophic flow of the North Pacific subtropical gyre in the top 700 m layer during 1993-2012. The volume transport-weighted temperature ( T I) is strongly dependent on the season. The anomaly of T I from the mean seasonal variation, whose standard deviation is 0.14∘C, was revealed to be caused mainly by change in the volume transport in a potential density layer of 25.0-25.5 σ 𝜃 . The anomaly of T I was observed to vary on a decadal or shorter, i.e., quasi-decadal (QD), timescale. The QD-scale variation of T I had peaks in 1998 and 2007, equivalent to the reduction in the net heat transport by 6 and 10 TW, respectively, approximately 1 year before those of sea surface temperature (SST) in the warm pool region, east of the Philippines. This suggests that variation in T I affects the warm pool SST through modification of the heat balance owing to the entrainment of southward transported water into the mixed layer.
Optical angular momentum and atoms.
Franke-Arnold, Sonja
2017-02-28
Any coherent interaction of light and atoms needs to conserve energy, linear momentum and angular momentum. What happens to an atom's angular momentum if it encounters light that carries orbital angular momentum (OAM)? This is a particularly intriguing question as the angular momentum of atoms is quantized, incorporating the intrinsic spin angular momentum of the individual electrons as well as the OAM associated with their spatial distribution. In addition, a mechanical angular momentum can arise from the rotation of the entire atom, which for very cold atoms is also quantized. Atoms therefore allow us to probe and access the quantum properties of light's OAM, aiding our fundamental understanding of light-matter interactions, and moreover, allowing us to construct OAM-based applications, including quantum memories, frequency converters for shaped light and OAM-based sensors.This article is part of the themed issue 'Optical orbital angular momentum'.
Optical angular momentum and atoms
NASA Astrophysics Data System (ADS)
Franke-Arnold, Sonja
2017-02-01
Any coherent interaction of light and atoms needs to conserve energy, linear momentum and angular momentum. What happens to an atom's angular momentum if it encounters light that carries orbital angular momentum (OAM)? This is a particularly intriguing question as the angular momentum of atoms is quantized, incorporating the intrinsic spin angular momentum of the individual electrons as well as the OAM associated with their spatial distribution. In addition, a mechanical angular momentum can arise from the rotation of the entire atom, which for very cold atoms is also quantized. Atoms therefore allow us to probe and access the quantum properties of light's OAM, aiding our fundamental understanding of light-matter interactions, and moreover, allowing us to construct OAM-based applications, including quantum memories, frequency converters for shaped light and OAM-based sensors. This article is part of the themed issue 'Optical orbital angular momentum'.
Quantum Heuristics of Angular Momentum
ERIC Educational Resources Information Center
Levy-Leblond, Jean-Marc
1976-01-01
Discusses the quantization of angular momentum components, Heisenberg-type inequalities for their spectral dispersions, and the quantization of the angular momentum modulus, without using operators or commutation relations. (MLH)
Angular Momentum Transport in Turbulent Compressible Convection
NASA Astrophysics Data System (ADS)
Hurlburt, N. E.; Brummell, N. H.; Toomre, J.
1996-05-01
We consider the dynamics of compressible convection within a curved local segment of a rotating spherical shell, aiming to resolve the disparity between the differential rotation profiles predicted by previous laminar simulations (angular velocity constant on cylinders) and those deduced from helioseismic inversion of the observed frequency splitting of p modes. By limiting the horizontal extent of the domain under study, we can utilize the available spatial degrees of freedom on current supercomputers to attain more turbulent flows than in the full shell. Our previous study of three-dimensional convection within a slab geometry of an f-plane neglected the effects of curvature, and thus did not admit the generation of Rossby waves. These waves propagate in the longitudinal direction and thus produce rather different spectral characteristics and mean flows in the north-south and east-west directions. By considering motions in a curvilinear geometry in which the Coriolis parameter varies with latitude, we admit the possibility of Rossby waves which couple to the turbulent convection. Here we present simulations with Rayleigh numbers in excess of 10(6) , and Prandtl numbers less than 0.1 in such a curved local segment of a spherical shell using a newly developed code based on compact finite differences. This computational domain takes the form of a curved, periodic channel in longitude with stress-free sidewalls in latitude and radius. Despite the differences in geometry and boundary conditions, the flows maintain similarities with those of our previous f-plane simulations. The surface flows form broad, laminar networks which mask the much more turbulent flows of the interior. The dynamics within this turbulent region is controlled by the interactions of a tangled web of strong vortex tubes. These interactions are further complicated by the effects of curvature. The differential rotation generated by the turbulent convection typically increases with depth and attains a maximum at the base of the layer of about 10 % over the imposed rotation rate.
Plate tectonics conserves angular momentum
NASA Astrophysics Data System (ADS)
Bowin, C.
2009-03-01
A new combined understanding of plate tectonics, Earth internal structure, and the role of impulse in deformation of the Earth's crust is presented. Plate accelerations and decelerations have been revealed by iterative filtering of the quaternion history for the Euler poles that define absolute plate motion history for the past 68 million years, and provide an unprecedented precision for plate angular rotation variations with time at 2-million year intervals. Stage poles represent the angular rotation of a plate's motion between adjacent Euler poles, and from which the maximum velocity vector for a plate can be determined. The consistent maximum velocity variations, in turn, yield consistent estimates of plate accelerations and decelerations. The fact that the Pacific plate was shown to accelerate and decelerate, implied that conservation of plate tectonic angular momentum must be globally conserved, and that is confirmed by the results shown here (total angular momentum ~1.4 E+27 kgm2s-1). Accordingly, if a plate decelerates, other plates must increase their angular momentums to compensate. In addition, the azimuth of the maximum velocity vectors yields clues as to why the "bend" in the Emperor-Hawaiian seamount trend occurred near 46 Myr. This report summarizes processing results for 12 of the 14 major tectonic plates of the Earth (except for the Juan de Fuca and Philippine plates). Plate accelerations support the contention that plate tectonics is a product of torques that most likely are sustained by the sinking of positive density anomalies due to phase changes in subducted gabbroic lithosphere at depth in the upper lower mantle (above 1200 km depth). The tectonic plates are pulled along by the sinking of these positive mass anomalies, rather than moving at near constant velocity on the crests of convection cells driven by rising heat. These results imply that spreading centers are primarily passive reactive features, and fracture zones (and wedge-shaped sites
Electromagnetic momentum conservation in media
NASA Astrophysics Data System (ADS)
Brevik, Iver; Ellingsen, Simen Å.
2011-03-01
That static electric and magnetic fields can store momentum may be perplexing, but is necessary to ensure total conservation of momentum. Simple situations in which such field momentum is transferred to nearby bodies and point charges have often been considered for pedagogical purposes, normally assuming vacuum surroundings. If dielectric media are involved, however, the analysis becomes more delicate, not least since one encounters the electromagnetic energy-momentum problem in matter, the 'Abraham-Minkowski enigma', of what the momentum is of a photon in matter. We analyze the momentum balance in three nontrivial examples obeying azimuthal symmetry, showing how the momentum conservation is satisfied as the magnetic field decays and momentum is transferred to bodies present. In the last of the examples, that of point charge outside a dielectric sphere in an infinite magnetic field, we find that not all of the field momentum is transferred to the nearby bodies; a part of the momentum appears to vanish as momentum flux towards infinity. We discuss this and other surprising observations which can be attributed to the assumption of magnetic fields of infinite extent. We emphasize how formal arguments of conserved quantities cannot determine which energy-momentum tensor is more "correct", and each of our conservation checks may be performed equally well in the Minkowski or Abraham framework.
Electromagnetic momentum conservation in media
Brevik, Iver; Ellingsen, Simen A.
2011-03-15
That static electric and magnetic fields can store momentum may be perplexing, but is necessary to ensure total conservation of momentum. Simple situations in which such field momentum is transferred to nearby bodies and point charges have often been considered for pedagogical purposes, normally assuming vacuum surroundings. If dielectric media are involved, however, the analysis becomes more delicate, not least since one encounters the electromagnetic energy-momentum problem in matter, the 'Abraham-Minkowski enigma', of what the momentum is of a photon in matter. We analyze the momentum balance in three nontrivial examples obeying azimuthal symmetry, showing how the momentum conservation is satisfied as the magnetic field decays and momentum is transferred to bodies present. In the last of the examples, that of point charge outside a dielectric sphere in an infinite magnetic field, we find that not all of the field momentum is transferred to the nearby bodies; a part of the momentum appears to vanish as momentum flux towards infinity. We discuss this and other surprising observations which can be attributed to the assumption of magnetic fields of infinite extent. We emphasize how formal arguments of conserved quantities cannot determine which energy-momentum tensor is more 'correct', and each of our conservation checks may be performed equally well in the Minkowski or Abraham framework.
Presentation outline: transport principles, effective solubility; gasoline composition; and field examples (plume diving).
Presentation conclusions: MTBE transport follows from - phyiscal and chemical properties and hydrology. Field examples show: MTBE plumes > benzene plu...
Haack, Tobias B; Makowski, Christine; Yao, Yoshiaki; Graf, Elisabeth; Hempel, Maja; Wieland, Thomas; Tauer, Ulrike; Ahting, Uwe; Mayr, Johannes A; Freisinger, Peter; Yoshimatsu, Hiroki; Inui, Ken; Strom, Tim M; Meitinger, Thomas; Yonezawa, Atsushi; Prokisch, Holger
2012-11-01
Brown-Vialetto-Van Laere syndrome (BVVLS [MIM 211530]) is a rare neurological disorder characterized by infancy onset sensorineural deafness and ponto-bulbar palsy. Mutations in SLC52A3 (formerly C20orf54), coding for riboflavin transporter 2 (hRFT2), have been identified as the molecular genetic correlate in several individuals with BVVLS. Exome sequencing of just one single case revealed that compound heterozygosity for two pathogenic mutations in the SLC52A2 gene coding for riboflavin transporter 3 (hRFT3), another member of the riboflavin transporter family, is also associated with BVVLS. Overexpression studies confirmed that the gene products of both mutant alleles have reduced riboflavin transport activities. While mutations in SLC52A3 cause decreased plasma riboflavin levels, concordant with a role of SLC52A3 in riboflavin uptake from food, the SLC52A2-mutant individual had normal plasma riboflavin concentrations, a finding in line with a postulated function of SLC52A2 in riboflavin uptake from blood into target cells. Our results contribute to the understanding of human riboflavin metabolism and underscore its role in the pathogenesis of BVVLS, thereby providing a rational basis for a high-dose riboflavin treatment.
USDA-ARS?s Scientific Manuscript database
In this study, the flow fields and sediment transport in Lake Pontchartrain during a flood release from Bonnet Carré Spillway (BCS) was simulated using the computational model CCHE2D developed at the National Center for Computational Hydroscience and Engineering (NCCHE), the University of Mississipp...
This technical paper recommends several types of screening assessments to evaluate site conditions for the potential to enhance transport of HOCs, as well as site artifacts that result from inadequate well installation and sampling procedures within a ground-water monitoring netw...
Optical angular momentum in a rotating frame.
Speirits, Fiona C; Lavery, Martin P J; Padgett, Miles J; Barnett, Stephen M
2014-05-15
It is well established that light carrying orbital angular momentum (OAM) can be used to induce a mechanical torque causing an object to spin. We consider the complementary scenario: will an observer spinning relative to the beam axis measure a change in OAM as a result of their rotational velocity? Remarkably, although a linear Doppler shift changes the linear momentum of a photon, the angular Doppler shift induces no change in the angular momentum. Further, we examine the rotational Doppler shift in frequency imparted to the incident light due to the relative motion of the beam with respect to the observer and consider what must happen to the measured wavelength if the speed of light c is to remain constant. We show specifically that the OAM of the incident beam is not affected by the rotating observer and that the measured wavelength is shifted by a factor equal and opposite to that of the frequency shift induced by the rotational Doppler effect.
Ward, Andy
2005-06-01
At Hanford, the prediction of field-scale flow and transport in the vadose zone beneath tank farms and other waste-management facilities provide as good example of the limitations of current conceptualizations. Contaminant plumes in Hanford's vadose zone typically show extensive lateral spreading with splitting along flow paths and multiple zones of high-contaminant concentrations, even in sediments that appear homogeneous and isotropic at the regional scale. Because of the limited success in predicting current contaminant distributions using existing conceptual models and approaches to parameterization, there is some uncertainty about predictions of future transport behavior. This is mostly because current parameter upscaling procedures result in overly smoothed descriptions of the hydraulic functions that cause many of the important details (e.g. extreme water and solute flux, anisotropy), known to be caused by finescale heterogeneity, to be ignored.
García, Andrés; Evans, James W
2016-11-07
We show that steady-state catalytic conversion in nanoporous materials can occur in a quasi-counter-diffusion mode with the reactant (product) concentration strongly decaying (growing) into the pore, but also with oscillations in the total concentration. These oscillations reflect the response of the fluid to the transition from an extended to a confined environment near the pore opening. We focus on the regime of strongly inhibited transport in narrow pores corresponding to single-file diffusion. Here, limited penetration of the reactant into the pores and the associated low reaction yield is impacted by strong spatial correlations induced by both reaction (non-equilibrium correlations) and also by intermolecular interactions (thermodynamic correlations). We develop a generalized hydrodynamic formulation to effectively describe inhibited transport accounting for the effect of these correlations, and incorporate this description of transport into appropriate reaction-diffusion equations. These equations accurately describe both shorter-range concentration oscillations near the pore opening and the longer-range mesoscale variation of concentration profiles in the pore (and thus also describe reaction yield). Success of the analytic theory is validated by comparison with a precise kinetic Monte Carlo simulation of an appropriate molecular-level stochastic reaction-diffusion model. This work elucidates unconventional chemical kinetics in interacting confined systems.
NASA Astrophysics Data System (ADS)
García, Andrés; Evans, James W.
2016-11-01
We show that steady-state catalytic conversion in nanoporous materials can occur in a quasi-counter-diffusion mode with the reactant (product) concentration strongly decaying (growing) into the pore, but also with oscillations in the total concentration. These oscillations reflect the response of the fluid to the transition from an extended to a confined environment near the pore opening. We focus on the regime of strongly inhibited transport in narrow pores corresponding to single-file diffusion. Here, limited penetration of the reactant into the pores and the associated low reaction yield is impacted by strong spatial correlations induced by both reaction (non-equilibrium correlations) and also by intermolecular interactions (thermodynamic correlations). We develop a generalized hydrodynamic formulation to effectively describe inhibited transport accounting for the effect of these correlations, and incorporate this description of transport into appropriate reaction-diffusion equations. These equations accurately describe both shorter-range concentration oscillations near the pore opening and the longer-range mesoscale variation of concentration profiles in the pore (and thus also describe reaction yield). Success of the analytic theory is validated by comparison with a precise kinetic Monte Carlo simulation of an appropriate molecular-level stochastic reaction-diffusion model. This work elucidates unconventional chemical kinetics in interacting confined systems.
Garcia, Andres; Evans, James W.
2016-11-03
We show that steady-state catalytic conversion in nanoporous materials can occur in a quasi-counter-diffusion mode with the reactant (product) concentration strongly decaying (growing) into the pore, but also with oscillations in the total concentration. These oscillations reflect the response of the fluid to the transition from an extended to a confined environment near the pore opening. We focus on the regime of strongly inhibited transport in narrow pores corresponding to single-file diffusion. Here, limited penetration of the reactant into the pores and the associated low reaction yield is impacted by strong spatial correlations induced by both reaction (non-equilibrium correlations) and also by intermolecular interactions (thermodynamic correlations). We develop a generalized hydrodynamic formulation to effectively describe inhibited transport accounting for the effect of these correlations, and incorporate this description of transport into appropriate reaction-diffusion equations. These equations accurately describe both shorter-range concentration oscillations near the pore opening and the longer-range mesoscale variation of concentration profiles in the pore (and thus also describe reaction yield). Success of the analytic theory is validated by comparison with a precise kinetic Monte Carlo simulation of an appropriate molecular-level stochastic reaction-diffusion model. As a result, this work elucidates unconventional chemical kinetics in interacting confined systems.
Garcia, Andres; Evans, James W.
2016-11-03
We show that steady-state catalytic conversion in nanoporous materials can occur in a quasi-counter-diffusion mode with the reactant (product) concentration strongly decaying (growing) into the pore, but also with oscillations in the total concentration. These oscillations reflect the response of the fluid to the transition from an extended to a confined environment near the pore opening. We focus on the regime of strongly inhibited transport in narrow pores corresponding to single-file diffusion. Here, limited penetration of the reactant into the pores and the associated low reaction yield is impacted by strong spatial correlations induced by both reaction (non-equilibrium correlations) andmore » also by intermolecular interactions (thermodynamic correlations). We develop a generalized hydrodynamic formulation to effectively describe inhibited transport accounting for the effect of these correlations, and incorporate this description of transport into appropriate reaction-diffusion equations. These equations accurately describe both shorter-range concentration oscillations near the pore opening and the longer-range mesoscale variation of concentration profiles in the pore (and thus also describe reaction yield). Success of the analytic theory is validated by comparison with a precise kinetic Monte Carlo simulation of an appropriate molecular-level stochastic reaction-diffusion model. As a result, this work elucidates unconventional chemical kinetics in interacting confined systems.« less
NASA Astrophysics Data System (ADS)
Heinen, Dirk; Schroeder, Herbert; Schilling, Werner
1998-01-01
Electromigration (EM)-driven mass transport in "near-bamboo" Al-lines, which consist mostly of "blocking grains," is an important topic of research on ULSI-metallizations. Because the most easy diffusion path, i.e. grain boundaries parallel to the line, is suppressed in bamboo-like Al-lines other paths have to be considered. In this work two other possible paths of diffusion were examined by in-situ observations in a transmission electron microscope (TEM). For these experiments a special sample holder had to be constructed. One path is EM-driven intragranular diffusion in Al-lines. In this experiment, inert gas-filled voids with a mean diameter of about 10 nm, so-called bubbles, which were created after gas implantation and annealing of the Al-lines, serve as indicators of mass (or vacancy) transport. The in-situ EM-tests reveal no intragranular void motion over a period of more than 100 h at current densities of 1-1.75 MA/cm2 and temperatures of 150-225 °C. This leads to an estimation of the maximum void diffusion velocity which was compared with calculated values of surface and volume diffusion controlled void motion, respectively. The second point of interest was the behavior of dislocations in Al-lines under an applied EM-force. The importance of their observed motion for intragranular mass transport will be discussed.
Phonons with orbital angular momentum
Ayub, M. K.; Ali, S.; Mendonca, J. T.
2011-10-15
Ion accoustic waves or phonon modes are studied with orbital angular momentum (OAM) in an unmagnetized collissionless uniform plasma, whose constituents are the Boltzmann electrons and inertial ions. For this purpose, we have employed the fluid equations to obtain a paraxial equation in terms of ion density perturbations and discussed its Gaussian beam and Laguerre-Gauss (LG) beam solutions. Furthermore, an approximate solution for the electrostatic potential problem is presented, allowing to express the components of the electric field in terms of LG potential perturbations. The energy flux due to phonons is also calculated and the corresponding OAM is derived. Numerically, it is shown that the parameters such as azimuthal angle, radial and angular mode numbers, and beam waist, strongly modify the profiles of the phonon LG potential. The present results should be helpful in understanding the phonon mode excitations produced by Brillouin backscattering of laser beams in a uniform plasma.
Optical orbital angular momentum
Barnett, Stephen M.; Babiker, Mohamed; Padgett, Miles J.
2017-01-01
We present a brief introduction to the orbital angular momentum of light, the subject of our theme issue and, in particular, to the developments in the 13 years following the founding paper by Allen et al. (Allen et al. 1992 Phys. Rev. A 45, 8185 (doi:10.1103/PhysRevA.45.8185)). The papers by our invited authors serve to bring the field up to date and suggest where developments may take us next. This article is part of the themed issue ‘Optical orbital angular momentum’. PMID:28069775
NASA Astrophysics Data System (ADS)
Paul, Ganesh C.; Dutta, Paramita; Saha, Arijit
2017-05-01
We explore transport properties of a normal metal-superconductor-normal metal (NSN) junction, where the superconducting region supports mixed singlet and chiral triplet pairings. We show that in the subgapped regime when the chiral triplet pairing amplitude dominates over that of the singlet, a resonance phenomena emerges out where all the quantum mechanical scattering probabilities acquire a value of 0.25. At the resonance, crossed Andreev reflection mediating through such junction, acquires a zero energy peak. This reflects as a zero energy peak in the conductance as well in the topological phase when Δp > Δs.
NASA Technical Reports Server (NTRS)
Stone, Peter H.; Yao, Mao-Sung
1987-01-01
The role of eddy momentum fluxes in the general circulation was investigated using a two-dimensional zonally averaged statistical-dynamical model described by Yao and Stone (1987), which is almost two orders of magnitude faster than the three-dimensional climate model of Hansen et al. (1983). Results show that the vertical structure of the meridional eddy flux has relatively little impact on the general circulation, presumably because the vertical structure is strongly constrained by the thermal wind relation and surface friction. On the other hand, it was found that, in order to simulate accurately the general circulation and its response to climate changes, parameterization of the vertically integrated meridional eddy flux of angular momentum is necessary. A new parameterization of this eddy momentum transport was carried out, which is intended to represent the transport due to large-scale transient eddies arising from baroclinic instability.
Dandini, V.J.
1991-01-01
A version of the BRYNTRN baryon transport code written at the NASA Langley Research Center has been used to analyze the dose to a typical space reactor thermoelectric (TE) element due to a solar flare event. The code has been used in the past to calculate the dose/dose equivalent distributions to astronauts due to solar flares. It has been modified to accommodate multiple layers of spacecraft and component material. Differential and integrated doses to the TE element are presented and discussed. 5 refs.
Emittance compensation studies of photoinjector beams with angular momentum
Lidia, Steven
2003-05-19
Beam dynamics studies on the FNPL photo injector that seek to optimize the transport of intense electron beams with large values of canonical angular momentum have been performed. These studies investigate the effect of solenoid emittance compensation on beams that evolve under the combined influence of intense space charge forces and large angular momentum. We present details of experimental measurements and supporting simulations of beam envelope evolution.
Nishioka, K.; Nakamura, Y.; Nishimura, S.; Lee, H. Y.; Kobayashi, S.; Mizuuchi, T.; Nagasaki, K.; Okada, H.; Minami, T.; Kado, S.; Yamamoto, S.; Ohshima, S.; Konoshima, S.; Sano, F.
2016-03-15
A moment approach to calculate neoclassical transport in non-axisymmetric torus plasmas composed of multiple ion species is extended to include the external parallel momentum sources due to unbalanced tangential neutral beam injections (NBIs). The momentum sources that are included in the parallel momentum balance are calculated from the collision operators of background particles with fast ions. This method is applied for the clarification of the physical mechanism of the neoclassical parallel ion flows and the multi-ion species effect on them in Heliotron J NBI plasmas. It is found that parallel ion flow can be determined by the balance between the parallel viscosity and the external momentum source in the region where the external source is much larger than the thermodynamic force driven source in the collisional plasmas. This is because the friction between C{sup 6+} and D{sup +} prevents a large difference between C{sup 6+} and D{sup +} flow velocities in such plasmas. The C{sup 6+} flow velocities, which are measured by the charge exchange recombination spectroscopy system, are numerically evaluated with this method. It is shown that the experimentally measured C{sup 6+} impurity flow velocities do not contradict clearly with the neoclassical estimations, and the dependence of parallel flow velocities on the magnetic field ripples is consistent in both results.
Jacquet, Stéphanie; Huber, Karine; Pagès, Nonito; Talavera, Sandra; Burgin, Laura E; Carpenter, Simon; Sanders, Christopher; Dicko, Ahmadou H; Djerbal, Mouloud; Goffredo, Maria; Lhor, Youssef; Lucientes, Javier; Miranda-Chueca, Miguel A; Pereira Da Fonseca, Isabel; Ramilo, David W; Setier-Rio, Marie-Laure; Bouyer, Jérémy; Chevillon, Christine; Balenghien, Thomas; Guis, Hélène; Garros, Claire
2016-06-06
The role of the northward expansion of Culicoides imicola Kieffer in recent and unprecedented outbreaks of Culicoides-borne arboviruses in southern Europe has been a significant point of contention. We combined entomological surveys, movement simulations of air-borne particles, and population genetics to reconstruct the chain of events that led to a newly colonized French area nestled at the northern foot of the Pyrenees. Simulating the movement of air-borne particles evidenced frequent wind-transport events allowing, within at most 36 hours, the immigration of midges from north-eastern Spain and Balearic Islands, and, as rare events, their immigration from Corsica. Completing the puzzle, population genetic analyses discriminated Corsica as the origin of the new population and identified two successive colonization events within west-Mediterranean basin. Our findings are of considerable importance when trying to understand the invasion of new territories by expanding species.
Jacquet, Stéphanie; Huber, Karine; Pagès, Nonito; Talavera, Sandra; Burgin, Laura E.; Carpenter, Simon; Sanders, Christopher; Dicko, Ahmadou H.; Djerbal, Mouloud; Goffredo, Maria; Lhor, Youssef; Lucientes, Javier; Miranda-Chueca, Miguel A.; Pereira Da Fonseca, Isabel; Ramilo, David W.; Setier-Rio, Marie-Laure; Bouyer, Jérémy; Chevillon, Christine; Balenghien, Thomas; Guis, Hélène; Garros, Claire
2016-01-01
The role of the northward expansion of Culicoides imicola Kieffer in recent and unprecedented outbreaks of Culicoides-borne arboviruses in southern Europe has been a significant point of contention. We combined entomological surveys, movement simulations of air-borne particles, and population genetics to reconstruct the chain of events that led to a newly colonized French area nestled at the northern foot of the Pyrenees. Simulating the movement of air-borne particles evidenced frequent wind-transport events allowing, within at most 36 hours, the immigration of midges from north-eastern Spain and Balearic Islands, and, as rare events, their immigration from Corsica. Completing the puzzle, population genetic analyses discriminated Corsica as the origin of the new population and identified two successive colonization events within west-Mediterranean basin. Our findings are of considerable importance when trying to understand the invasion of new territories by expanding species. PMID:27263862
NASA Astrophysics Data System (ADS)
Chavare, Kushal; Bhatt, Nilesh; Prizomwala, Siddharth
2017-04-01
The boulder deposits on the coasts are interpreted and evaluated as high energy marine wave events like tsunami. Several numerical models are now available to estimate wave height and/or run up of the tsunami wave. The coast of Saurashtra, facing the Arabian Sea on its west hosts such deposits in younger ( 1 and 6 ka) and older ( 35 ka) coastal records. The dimensions, characteristics and morphology of these boulders were studied with different numeric models and were applied with reference to submerged, sub-aerial and joint bounded boulder scenarios which were combined with the local control variables like roughness coefficient, slope of platforms, fractures, shoaling effect, etc. The application of these models indicated a significant role of local control variables in boulder dislodgment, transport and final emplacement on shore platform. Examples from three different sites from the coast of Saurashtra, western India are reported and discussed in detail.
Merrill, Amy E.; Merriman, Barry; Farrington-Rock, Claire; Camacho, Natalia; Sebald, Eiman T.; Funari, Vincent A.; Schibler, Matthew J.; Firestein, Marc H.; Cohn, Zachary A.; Priore, Mary Ann; Thompson, Alicia K.; Rimoin, David L.; Nelson, Stanley F.; Cohn, Daniel H.; Krakow, Deborah
2009-01-01
The short-rib polydactyly (SRP) syndromes are a heterogenous group of perinatal lethal skeletal disorders with polydactyly and multisystem organ abnormalities. Homozygosity by descent mapping in a consanguineous SRP family identified a genomic region that contained DYNC2H1, a cytoplasmic dynein involved in retrograde transport in the cilium. Affected individuals in the family were homozygous for an exon 12 missense mutation that predicted the amino acid substitution R587C. Compound heterozygosity for one missense and one null mutation was identified in two additional nonconsanguineous SRP families. Cultured chondrocytes from affected individuals showed morphologically abnormal, shortened cilia. In addition, the chondrocytes showed abnormal cytoskeletal microtubule architecture, implicating an altered microtubule network as part of the disease process. These findings establish SRP as a cilia disorder and demonstrate that DYNC2H1 is essential for skeletogenesis and growth. PMID:19361615
Guo, Cen; Yang, Kyunghee; Brouwer, Kenneth R.; St. Claire, Robert L.
2016-01-01
Transporter-mediated alterations in bile acid disposition may have significant toxicological implications. Current methods to predict interactions are limited by the interplay of multiple transporters, absence of protein in the experimental system, and inaccurate estimates of inhibitor concentrations. An integrated approach was developed to predict altered bile acid disposition due to inhibition of multiple transporters using the model bile acid taurocholate (TCA). TCA pharmacokinetic parameters were estimated by mechanistic modeling using sandwich-cultured human hepatocyte data with protein in the medium. Uptake, basolateral efflux, and biliary clearance estimates were 0.63, 0.034, and 0.074 mL/min/g liver, respectively. Cellular total TCA concentrations (Ct,Cells) were selected as the model output based on sensitivity analysis. Monte Carlo simulations of TCA Ct,Cells in the presence of model inhibitors (telmisartan and bosentan) were performed using inhibition constants for TCA transporters and inhibitor concentrations, including cellular total inhibitor concentrations ([I]t,cell) or unbound concentrations, and cytosolic total or unbound concentrations. For telmisartan, the model prediction was accurate with an average fold error (AFE) of 0.99–1.0 when unbound inhibitor concentration ([I]u) was used; accuracy dropped when total inhibitor concentration ([I]t) was used. For bosentan, AFE was 1.2–1.3 using either [I]u or [I]t. This difference was evaluated by sensitivity analysis of the cellular unbound fraction of inhibitor (fu,cell,inhibitor), which revealed higher sensitivity of fu,cell,inhibitor for predicting TCA Ct,Cells when inhibitors exhibited larger ([I]t,cell/IC50) values. In conclusion, this study demonstrated the applicability of a framework to predict hepatocellular bile acid concentrations due to drug-mediated inhibition of transporters using mechanistic modeling and cytosolic or cellular unbound concentrations. PMID:27233294
Momentum Deposition in Curvilinear Coordinates
Cleveland, Mathew Allen; Lowrie, Robert Byron; Rockefeller, Gabriel M.; Thompson, Kelly Glen; Wollaber, Allan Benton
2015-08-03
The momentum imparted into a material by thermal radiation deposition is an important physical process in astrophysics and inertial confinement fusion (ICF) simulations. In recent work we presented a new method of evaluating momentum deposition that relies on the combination of a time-averaged approximation and a numerical integration scheme. This approach robustly and efficiently evaluates the momentum deposition in spherical geometry. Future work will look to extend this approach to 2D cylindrical geometries.
Partonic Transverse Momentum Distributions
Rossi, Patrizia
2010-08-04
In recent years parton distributions have been generalized to account also for transverse degrees of freedom and new sets of more general distributions, Transverse Momentum Dependent (TMD) parton distributions and fragmentation functions were introduced. Different experiments worldwide (HERMES, COMPASS, CLAS, JLab-Hall A) have measurements of TMDs in semi-inclusive DIS processes as one of their main focuses of research. TMD studies are also an important part of the present and future Drell-Yan experiments at RICH and JPARC and GSI, respectively, Studies of TMDs are also one of the main driving forces of the Jefferson Lab (JLab) 12 GeV upgrade project. Progress in phenomenology and theory is flourishing as well. In this talk an overview of the latest developments in studies of TMDs will be given and newly released results, ongoing activities, as well as planned near term and future measurements will be discussed.
Orbital angular momentum microlaser
NASA Astrophysics Data System (ADS)
Miao, Pei; Zhang, Zhifeng; Sun, Jingbo; Walasik, Wiktor; Longhi, Stefano; Litchinitser, Natalia M.; Feng, Liang
2016-07-01
Structured light provides an additional degree of freedom for modern optics and practical applications. The effective generation of orbital angular momentum (OAM) lasing, especially at a micro- and nanoscale, could address the growing demand for information capacity. By exploiting the emerging non-Hermitian photonics design at an exceptional point, we demonstrate a microring laser producing a single-mode OAM vortex lasing with the ability to precisely define the topological charge of the OAM mode. The polarization associated with OAM lasing can be further manipulated on demand, creating a radially polarized vortex emission. Our OAM microlaser could find applications in the next generation of integrated optoelectronic devices for optical communications in both quantum and classical regimes.
Orbital angular momentum microlaser.
Miao, Pei; Zhang, Zhifeng; Sun, Jingbo; Walasik, Wiktor; Longhi, Stefano; Litchinitser, Natalia M; Feng, Liang
2016-07-29
Structured light provides an additional degree of freedom for modern optics and practical applications. The effective generation of orbital angular momentum (OAM) lasing, especially at a micro- and nanoscale, could address the growing demand for information capacity. By exploiting the emerging non-Hermitian photonics design at an exceptional point, we demonstrate a microring laser producing a single-mode OAM vortex lasing with the ability to precisely define the topological charge of the OAM mode. The polarization associated with OAM lasing can be further manipulated on demand, creating a radially polarized vortex emission. Our OAM microlaser could find applications in the next generation of integrated optoelectronic devices for optical communications in both quantum and classical regimes. Copyright © 2016, American Association for the Advancement of Science.
Momentum Analysis for Metasurfaces
NASA Astrophysics Data System (ADS)
Liu, Wenwei; Li, Zhancheng; Cheng, Hua; Chen, Shuqi; Tian, Jianguo
2017-07-01
Utilizing discrete phase distribution to fit continuous phase distribution has been a primary routine for designing metasurfaces. In the existing method, the validation of the discrete designs is guaranteed only by using the subwavelength condition of unit cells, which is insufficient—especially for arbitrary phase distribution. Herein, we propose an analytical method to design metasurfaces by estimating the width of the source in a unit cell. Also, by calculating field patterns in both real and momentum space, we provide four guidelines for directing future applications of metasurfaces, such as an arbitrary multifocal lens with the same strength of each focus, a convex-concave double lens, and a lens with a large numerical aperture that can precisely prevent undesired diffraction orders. In addition to metalenses, this methodology can provide a wide platform for designing tailored and multifunctional metasurfaces in the future, especially large-area ones in practical applications.
Munera, Hector A.
2010-07-28
Advantages of a neo-Cartesian approach to classical mechanics are noted. If conservation of linear momentum is the fundamental principle, Newton's three laws become theorems. A minor paradox in static Newtonian mechanics is identified, and solved by reinterpreting force as a current of momentum. Contact force plays the role of a mere midwife in the exchange of momentum; however, force cannot be eliminated from physics because it provides the numerical value for momentum current. In this sense, in a neo-Cartesian formulation of mechanics the concept of force becomes strengthened rather than weakened.
NASA Astrophysics Data System (ADS)
Múnera, Héctor A.
2010-07-01
Advantages of a neo-Cartesian approach to classical mechanics are noted. If conservation of linear momentum is the fundamental principle, Newton's three laws become theorems. A minor paradox in static Newtonian mechanics is identified, and solved by reinterpreting force as a current of momentum. Contact force plays the role of a mere midwife in the exchange of momentum; however, force cannot be eliminated from physics because it provides the numerical value for momentum current. In this sense, in a neo-Cartesian formulation of mechanics the concept of force becomes strengthened rather than weakened.
Angular Momentum in Dwarf Galaxies
NASA Astrophysics Data System (ADS)
Del Popolo, A.
We study the ``angular momentum catastrophe" in the framework of interaction among baryons and dark matter through dynamical friction. By means of Del Popolo (2009) model we simulate 14 galaxies similar to those investigated by van den Bosch, Burkert and Swaters (2001), and calculate the distribution of their spin parameters and the angular momenta. Our model gives the angular momentum distribution which is in agreement with the van den Bosch et al. observations. Our result shows that the ``angular momentum catastrophe" can be naturally solved in a model that takes into account the baryonic physics and the exchange of energy and angular momentum between the baryonic clumps and dark matter through dynamical friction.
NASA Astrophysics Data System (ADS)
Eicken, H.; Gradinger, R.; Gaylord, A.; Mahoney, A.; Rigor, I.; Melling, H.
2005-12-01
Sediment-laden sea ice is widespread over the shallow, wide Siberian Arctic shelves, with off-shelf export from the Laptev and East Siberian Seas contributing substantially to the Arctic Ocean's sediment budget. By contrast, the North American shelves, owing to their narrow width and greater water depths, have not been deemed as important for basin-wide sediment transport by sea ice. Observations over the Chukchi and Beaufort shelves in 2001/02 revealed the widespread occurrence of sediment-laden ice over an area of more than 100,000 km 2 between 68 and 74°N and 155 and 170°W. Ice stratigraphic studies indicate that sediment inclusions were associated with entrainment of frazil ice into deformed, multiple layers of rafted nilas, indicative of a flaw-lead environment adjacent to the landfast ice of the Chukchi and Beaufort Seas. This is corroborated by buoy trajectories and satellite imagery indicating entrainment in a coastal polynya in the eastern Chukchi Sea in February of 2002 as well as formation of sediment-laden ice along the Beaufort Sea coast as far eastward as the Mackenzie shelf. Moored upward-looking sonar on the Mackenzie shelf provides further insight into the ice growth and deformation regime governing sediment entrainment. Analysis of Radarsat Synthetic Aperture (SAR) imagery in conjunction with bathymetric data help constrain the water depth of sediment resuspension and subsequent ice entrainment (>20 m for the Chukchi Sea). Sediment loads averaged at 128 t km -2, with sediment occurring in layers of roughly 0.5 m thickness, mostly in the lower ice layers. The total amount of sediment transported by sea ice (mostly out of the narrow zone between the landfast ice edge and waters too deep for resuspension and entrainment) is at minimum 4×10 6 t in the sampling area and is estimated at 5-8×10 6 t over the entire Chukchi and Beaufort shelves in 2001/02, representing a significant term in the sediment budget of the western Arctic Ocean. Recent
Construction of momentum theorem using cross moments
NASA Astrophysics Data System (ADS)
Hahm, T. S.; Wang, Lu; Diamond, P. H.
2009-11-01
Charney-Drazin theorem has been extended to Hasegawa Wakatani system for zonal flow problem in magnetic fusion [P.H. Diamond, et al., Plasma Phys. Control. Fusion 50, 124018 (2008)]. For this model, the guiding center density is the potential vorticity and zonal flow is influenced by the particle flux. In this work we construct momentum theorems in terms of a hierarchy of cross moments
2013-01-01
The need may arise to be able to simulate the migration of groundwater nanoparticles through the ground. Transportation velocities of nanoparticles are different from that of water and depend on many processes that occur during migration. Unstable nanoparticles, such as zero-valent iron nanoparticles, are especially slowed down by aggregation between them. The aggregation occurs when attracting forces outweigh repulsive forces between the particles. In the case of iron nanoparticles that are used for remediation, magnetic forces between particles contribute to attractive forces and nanoparticles aggregate rapidly. This paper describes the addition of attractive magnetic forces and repulsive electrostatic forces between particles (by ‘particle’, we mean both single nanoparticles and created aggregates) into a basic model of aggregation which is commonly used. This model is created on the basis of the flow of particles in the proximity of observed particles that gives the rate of aggregation of the observed particle. By using a limit distance that has been described in our previous work, the flow of particles around one particle is observed in larger spacing between the particles. Attractive magnetic forces between particles draw the particles into closer proximity and result in aggregation. This model fits more closely with rapid aggregation which occurs between magnetic nanoparticles. PMID:23302651
Rosická, Dana; Sembera, Jan
2013-01-10
: The need may arise to be able to simulate the migration of groundwater nanoparticles through the ground. Transportation velocities of nanoparticles are different from that of water and depend on many processes that occur during migration. Unstable nanoparticles, such as zero-valent iron nanoparticles, are especially slowed down by aggregation between them. The aggregation occurs when attracting forces outweigh repulsive forces between the particles. In the case of iron nanoparticles that are used for remediation, magnetic forces between particles contribute to attractive forces and nanoparticles aggregate rapidly. This paper describes the addition of attractive magnetic forces and repulsive electrostatic forces between particles (by 'particle', we mean both single nanoparticles and created aggregates) into a basic model of aggregation which is commonly used. This model is created on the basis of the flow of particles in the proximity of observed particles that gives the rate of aggregation of the observed particle. By using a limit distance that has been described in our previous work, the flow of particles around one particle is observed in larger spacing between the particles. Attractive magnetic forces between particles draw the particles into closer proximity and result in aggregation. This model fits more closely with rapid aggregation which occurs between magnetic nanoparticles.
Momentum-space electromagnetic induction in Weyl semimetals
NASA Astrophysics Data System (ADS)
Ishizuka, Hiroaki; Hayata, Tomoya; Ueda, Masahito; Nagaosa, Naoto
2017-06-01
We theoretically study the effect of the Berry curvature on the transport properties of Weyl semimetals using a semiclassical Boltzmann transport theory, which results in nonlinear optical responses. In the adiabatic process, the Berry curvature, which involves the time derivative of the Bloch states, contributes to the transport properties such as the adiabatic Thouless pump. Although this effect is very weak in usual solids, it is enhanced in Weyl semimetals, where the Berry curvature contributes to observable nonlinear optical responses due to its nodal structure. In this paper, using the semiclassical Boltzmann theory, we show that a dc photocurrent induced by the Berry curvature robustly persists even in the limit of short scattering time. We also show that the photocurrent is well explained as a consequence of the electromagnetic induction in momentum space. The results indicate that the electromagnetic induction gives rise to a nondissipative photocurrent that is robust against decoherence within a time scale shorter than the periodicity of the incident electromagnetic field. We also discuss the second harmonic response of an ac current when the electron distribution is displaced from the ground state by an external field.
Optical Momentum, Spin, and Angular Momentum in Dispersive Media
NASA Astrophysics Data System (ADS)
Bliokh, Konstantin Y.; Bekshaev, Aleksandr Y.; Nori, Franco
2017-08-01
We examine the momentum, spin, and orbital angular momentum of structured monochromatic optical fields in dispersive inhomogeneous isotropic media. There are two bifurcations in this general problem: the Abraham-Minkowski dilemma and the kinetic (Poynting-like) versus canonical (spin-orbital) pictures. We show that the kinetic Abraham momentum describes the energy flux and group velocity of the wave in the medium. At the same time, we introduce novel canonical Minkowski-type momentum, spin, and orbital angular momentum densities of the field. These quantities exhibit fairly natural forms, analogous to the Brillouin energy density, as well as multiple advantages as compared with previously considered formalisms. As an example, we apply this general theory to inhomogeneous surface plasmon-polariton (SPP) waves at a metal-vacuum interface and show that SPPs carry a "supermomentum," proportional to the wave vector kp>ω /c , and a transverse spin, which can change its sign depending on the frequency ω .
Optical Momentum, Spin, and Angular Momentum in Dispersive Media.
Bliokh, Konstantin Y; Bekshaev, Aleksandr Y; Nori, Franco
2017-08-18
We examine the momentum, spin, and orbital angular momentum of structured monochromatic optical fields in dispersive inhomogeneous isotropic media. There are two bifurcations in this general problem: the Abraham-Minkowski dilemma and the kinetic (Poynting-like) versus canonical (spin-orbital) pictures. We show that the kinetic Abraham momentum describes the energy flux and group velocity of the wave in the medium. At the same time, we introduce novel canonical Minkowski-type momentum, spin, and orbital angular momentum densities of the field. These quantities exhibit fairly natural forms, analogous to the Brillouin energy density, as well as multiple advantages as compared with previously considered formalisms. As an example, we apply this general theory to inhomogeneous surface plasmon-polariton (SPP) waves at a metal-vacuum interface and show that SPPs carry a "supermomentum," proportional to the wave vector k_{p}>ω/c, and a transverse spin, which can change its sign depending on the frequency ω.
Intrinsic spin and orbital angular momentum Hall effect.
Zhang, S; Yang, Z
2005-02-18
A generalized definition of intrinsic and extrinsic transport coefficients is introduced. We show that transport coefficients from the intrinsic origin are solely determined by local electronic structure, and thus the intrinsic spin Hall effect is not a transport phenomenon. The intrinsic spin Hall current is always accompanied by an equal but opposite intrinsic orbital angular momentum Hall current. We prove that the intrinsic spin Hall effect does not induce a spin accumulation at the edge of the sample or near the interface.
Kami, Chitose; Allenbach, Laure; Zourelidou, Melina; Ljung, Karin; Schütz, Frédéric; Isono, Erika; Watahiki, Masaaki K; Yamamoto, Kotaro T; Schwechheimer, Claus; Fankhauser, Christian
2014-02-01
Phototropism allows plants to orient their photosynthetic organs towards the light. In Arabidopsis, phototropins 1 and 2 sense directional blue light such that phot1 triggers phototropism in response to low fluence rates, while both phot1 and phot2 mediate this response under higher light conditions. Phototropism results from asymmetric growth in the hypocotyl elongation zone that depends on an auxin gradient across the embryonic stem. How phototropin activation leads to this growth response is still poorly understood. Members of the phytochrome kinase substrate (PKS) family may act early in this pathway, because PKS1, PKS2 and PKS4 are needed for a normal phototropic response and they associate with phot1 in vivo. Here we show that PKS proteins are needed both for phot1- and phot2-mediated phototropism. The phototropic response is conditioned by the developmental asymmetry of dicotyledonous seedlings, such that there is a faster growth reorientation when cotyledons face away from the light compared with seedlings whose cotyledons face the light. The molecular basis for this developmental effect on phototropism is unknown; here we show that PKS proteins play a role at the interface between development and phototropism. Moreover, we present evidence for a role of PKS genes in hypocotyl gravi-reorientation that is independent of photoreceptors. pks mutants have normal levels of auxin and normal polar auxin transport, however they show altered expression patterns of auxin marker genes. This situation suggests that PKS proteins are involved in auxin signaling and/or lateral auxin redistribution. © 2013 The Authors The Plant Journal © 2013 John Wiley & Sons Ltd.
Plate tectonics conserves angular momentum
NASA Astrophysics Data System (ADS)
Bowin, C.
2010-03-01
A new combined understanding of plate tectonics, Earth internal structure, and the role of impulse in deformation of the Earth's crust is presented. Plate accelerations and decelerations have been revealed by iterative filtering of the quaternion history for the Euler poles that define absolute plate motion history for the past 68 million years, and provide an unprecedented precision for plate angular rotation variations with time at 2-million year intervals. Stage poles represent the angular rotation of a plate's motion between adjacent Euler poles, and from which the maximum velocity vector for a plate can be determined. The consistent maximum velocity variations, in turn, yield consistent estimates of plate accelerations and decelerations. The fact that the Pacific plate was shown to accelerate and decelerate, implied that conservation of plate tectonic angular momentum must be globally conserved, and that is confirmed by the results shown here (total angular momentum ~1.4+27 kg m2 s-1). Accordingly, if a plate decelerates, other plates must increase their angular momentums to compensate. In addition, the azimuth of the maximum velocity vectors yields clues as to why the "bend" in the Emperor-Hawaiian seamount trend occurred near 46 Myr. This report summarizes processing results for 12 of the 14 major tectonic plates of the Earth (except for the Juan de Fuca and Philippine plates). Plate accelerations support the contention that plate tectonics is a product of torques that most likely are sustained by the sinking of positive density anomalies revealed by geoid anomalies of the degree 4-10 packet of the Earth's spherical harmonic coefficients. These linear positive geoid anomalies underlie plate subduction zones and are presumed due to phase changes in subducted gabbroic lithosphere at depth in the upper lower mantle (above 1200 km depth). The tectonic plates are pulled along by the sinking of these positive mass anomalies, rather than moving at near constant
A mass and momentum conserving unsplit semi-Lagrangian framework for simulating multiphase flows
NASA Astrophysics Data System (ADS)
Owkes, Mark; Desjardins, Olivier
2017-03-01
In this work, we present a computational methodology for convection and advection that handles discontinuities with second order accuracy and maintains conservation to machine precision. This method can transport a variety of discontinuous quantities and is used in the context of an incompressible gas-liquid flow to transport the phase interface, momentum, and scalars. The proposed method provides a modification to the three-dimensional, unsplit, second-order semi-Lagrangian flux method of Owkes & Desjardins (JCP, 2014). The modification adds a refined grid that provides consistent fluxes of mass and momentum defined on a staggered grid and discrete conservation of mass and momentum, even for flows with large density ratios. Additionally, the refined grid doubles the resolution of the interface without significantly increasing the computational cost over previous non-conservative schemes. This is possible due to a novel partitioning of the semi-Lagrangian fluxes into a small number of simplices. The proposed scheme is tested using canonical verification tests, rising bubbles, and an atomizing liquid jet.
Babu, C Anand; Agarwal, Sourabh; Sujish, D; Rajan, K K
2011-10-01
Fluoride removal using Reverse Osmosis has appreciable amount of fluorine in the reject stream. Disposal of reject water to surface water further contaminates the water body. It is required to dispose of this reject into the environment with minimal pollution. So a study on disposal of fluoride contaminated reject inside the ground water through bore well is done through theoretical modelling using COMSOL multiphysics software. It has been established that the rise in fluoride concentration in ground water due to injection of fluoride contaminated reject through bore well depends on the injection rate of reject inside the bore well and not on the initial background concentration of fluoride in the ground water. It has been found that for reject injection rate of 30 m3/day the rise in fluoride concentration in ground water with respect to initial background concentration of fluoride is less than 10% at a distance above 600m from the injection source after 100 years.
Mordijck, S.; Owen, L. W.; Moyer, R. A.
2010-02-23
In this paper we compare the pedestal density changes in resonant magnetic perturbations (RMP) H-modes at low collisionality with enhanced free streaming due to the creation of open field lines. First, we derive the effective radial transport coefficients by matching an ELMing (edge localized mode) H-mode using SOLPS5. Next, a vacuum field line tracing code, TRIP3D, is employed to calculate free streaming of particles along open field lines inside the traditional 2D axisymmetric separatrix. These coefficients are added to the effective radial transport coefficients from the ELMing H-mode and inserted in SOLPS5 to compute midplane profiles. Finally, we compare the SOLPS5 results with the experimental data from RMP H-modes and find good agreement. This good agreement was achieved not only for one single case, but also for two different experiments, with different triangularities, where the high triangularity case contains two RMP H-modes that give good agreement.
Imaging molecular geometry with electron momentum spectroscopy.
Wang, Enliang; Shan, Xu; Tian, Qiguo; Yang, Jing; Gong, Maomao; Tang, Yaguo; Niu, Shanshan; Chen, Xiangjun
2016-12-22
Electron momentum spectroscopy is a unique tool for imaging orbital-specific electron density of molecule in momentum space. However, the molecular geometry information is usually veiled due to the single-centered character of momentum space wavefunction of molecular orbital (MO). Here we demonstrate the retrieval of interatomic distances from the multicenter interference effect revealed in the ratios of electron momentum profiles between two MOs with symmetric and anti-symmetric characters. A very sensitive dependence of the oscillation period on interatomic distance is observed, which is used to determine F-F distance in CF4 and O-O distance in CO2 with sub-Ångström precision. Thus, using one spectrometer, and in one measurement, the electron density distributions of MOs and the molecular geometry information can be obtained simultaneously. Our approach provides a new robust tool for imaging molecules with high precision and has potential to apply to ultrafast imaging of molecular dynamics if combined with ultrashort electron pulses in the future.
Imaging molecular geometry with electron momentum spectroscopy
Wang, Enliang; Shan, Xu; Tian, Qiguo; Yang, Jing; Gong, Maomao; Tang, Yaguo; Niu, Shanshan; Chen, Xiangjun
2016-01-01
Electron momentum spectroscopy is a unique tool for imaging orbital-specific electron density of molecule in momentum space. However, the molecular geometry information is usually veiled due to the single-centered character of momentum space wavefunction of molecular orbital (MO). Here we demonstrate the retrieval of interatomic distances from the multicenter interference effect revealed in the ratios of electron momentum profiles between two MOs with symmetric and anti-symmetric characters. A very sensitive dependence of the oscillation period on interatomic distance is observed, which is used to determine F-F distance in CF4 and O-O distance in CO2 with sub-Ångström precision. Thus, using one spectrometer, and in one measurement, the electron density distributions of MOs and the molecular geometry information can be obtained simultaneously. Our approach provides a new robust tool for imaging molecules with high precision and has potential to apply to ultrafast imaging of molecular dynamics if combined with ultrashort electron pulses in the future. PMID:28004794
Turbulent Equipartition Theory of Toroidal Momentum Pinch
T.S. Hahm, P.H. Diamond, O.D. Gurcan, and G. Rewaldt
2008-01-31
The mode-independet part of magnetic curvature driven turbulent convective (TuroCo) pinch of the angular momentum density [Hahm et al., Phys. Plasmas 14,072302 (2007)] which was originally derived from the gyrokinetic equation, can be interpreted in terms of the turbulent equipartition (TEP) theory. It is shown that the previous results can be obtained from the local conservation of "magnetically weighted angular momentum density," nmi U|| R/B2, and its homogenization due to turbulent flows. It is also demonstrated that the magnetic curvature modification of the parallel acceleration in the nonlinear gyrokinetic equation in the laboratory frame, which was shown to be responsible for the TEP part of the TurCo pinch of angular momentum density in the previous work, is closely related to the Coriolis drift coupling to the perturbed electric field. In addition, the origin of the diffusive flux in the rotating frame is highlighted. Finally, it is illustratd that there should be a difference in scalings between the momentum pinch originated from inherently toroidal effects and that coming from other mechanisms which exist in a simpler geometry.
Turbulent equipartition theory of toroidal momentum pincha)
NASA Astrophysics Data System (ADS)
Hahm, T. S.; Diamond, P. H.; Gurcan, O. D.; Rewoldt, G.
2008-05-01
The mode-independent part of the magnetic curvature driven turbulent convective (TurCo) pinch of the angular momentum density [Hahm et al., Phys. Plasmas 14, 072302 (2007)], which was originally derived from the gyrokinetic equation, can be interpreted in terms of the turbulent equipartition (TEP) theory. It is shown that the previous results can be obtained from the local conservation of "magnetically weighted angular momentum density," nmiU∥R/B2, and its homogenization due to turbulent flows. It is also demonstrated that the magnetic curvature modification of the parallel acceleration in the nonlinear gyrokinetic equation in the laboratory frame, which was shown to be responsible for the TEP part of the TurCo pinch of angular momentum density in the previous work, is closely related to the Coriolis drift coupling to the perturbed electric field. In addition, the origin of the diffusive flux in the rotating frame is highlighted. Finally, it is illustrated that there should be a difference in scalings between the momentum pinch originated from inherently toroidal effects and that coming from other mechanisms that exist in a simpler geometry.
Imaging molecular geometry with electron momentum spectroscopy
NASA Astrophysics Data System (ADS)
Wang, Enliang; Shan, Xu; Tian, Qiguo; Yang, Jing; Gong, Maomao; Tang, Yaguo; Niu, Shanshan; Chen, Xiangjun
2016-12-01
Electron momentum spectroscopy is a unique tool for imaging orbital-specific electron density of molecule in momentum space. However, the molecular geometry information is usually veiled due to the single-centered character of momentum space wavefunction of molecular orbital (MO). Here we demonstrate the retrieval of interatomic distances from the multicenter interference effect revealed in the ratios of electron momentum profiles between two MOs with symmetric and anti-symmetric characters. A very sensitive dependence of the oscillation period on interatomic distance is observed, which is used to determine F-F distance in CF4 and O-O distance in CO2 with sub-Ångström precision. Thus, using one spectrometer, and in one measurement, the electron density distributions of MOs and the molecular geometry information can be obtained simultaneously. Our approach provides a new robust tool for imaging molecules with high precision and has potential to apply to ultrafast imaging of molecular dynamics if combined with ultrashort electron pulses in the future.
Exact momentum conservation laws for the gyrokinetic Vlasov-Poisson equations
Brizard, Alain J.; Tronko, Natalia
2011-08-15
The exact momentum conservation laws for the nonlinear gyrokinetic Vlasov-Poisson equations are derived by applying the Noether method on the gyrokinetic variational principle [A. J. Brizard, Phys. Plasmas 7, 4816 (2000)]. From the gyrokinetic Noether canonical-momentum equation derived by the Noether method, the gyrokinetic parallel momentum equation and other gyrokinetic Vlasov-moment equations are obtained. In addition, an exact gyrokinetic toroidal angular-momentum conservation law is derived in axisymmetric tokamak geometry, where the transport of parallel-toroidal momentum is related to the radial gyrocenter polarization, which includes contributions from the guiding-center and gyrocenter transformations.
Intrinsic Angular Momentum of Light.
ERIC Educational Resources Information Center
Santarelli, Vincent
1979-01-01
Derives a familiar torque-angular momentum theorem for the electromagnetic field, and includes the intrinsic torques exerted by the fields on the polarized medium. This inclusion leads to the expressions for the intrinsic angular momentum carried by the radiation traveling through a charge-free medium. (Author/MA)
Intrinsic Angular Momentum of Light.
ERIC Educational Resources Information Center
Santarelli, Vincent
1979-01-01
Derives a familiar torque-angular momentum theorem for the electromagnetic field, and includes the intrinsic torques exerted by the fields on the polarized medium. This inclusion leads to the expressions for the intrinsic angular momentum carried by the radiation traveling through a charge-free medium. (Author/MA)
Scattering and momentum space entanglement
NASA Astrophysics Data System (ADS)
Grignani, Gianluca; Semenoff, Gordon W.
2017-09-01
We derive a formula for the entanglement entropy of two regions in momentum space that is generated by the scattering of weakly interacting scalar particles. We discuss an example where weak interactions entangle momentum scales above and below an infrared cutoff.
Choudhury, S.R.; Jaluria, Y.
1995-04-01
The flow and heat transfer associated with the convective cooling of a heated cylinder moving in a channel with buoyancy and pressure-indicted flow has been numerically investigated. Three distinct transport mechanisms arise in this case due to material motion, forced flow, and buoyancy. Considered in this study are uniform flows at the inlet of the cooling channel in the same, as well as in the opposite, direction as the movement of the cylindrical rod. This problem is of interest in several manufacturing processes such as hot rolling, continuous casting, extrusion, wire drawing, and glass fiber drawing. The transport processes are time dependent at the initial stages, Following the onset of motion, and usually attain steady state conditions at large time. The temperature distribution in the solid is of particular interest in materials processing. A detailed numerical study is carried out, assuming an axisymmetric, transient circumstance with laminar flow. The governing full, elliptic equations are solved, employing the finite volume method. The conjugate problem, coupling the transport in the solid material with that in the fluid, is solved. The effect of thermal buoyancy on the heat transfer and on the flow for different orientations is studied in detail. Of particular interest is the numerical imposition of the boundary conditions. Not much work has been done in this regard with the combined effects of material motion, buoyancy, and forced flow present. When the flow opposes the movement of the rod, either due to pressure-induced flow or due to buoyancy, a recirculating region arises near the rod surface. This recirculation region plays a major role in the heat transfer and thus affects the resulting temperature decay in the moving rod. Validation of the numerical results is carried out by comparisons with earlier experimental results, indicating fairly good agreement.
Transverse angular momentum of photons
Aiello, Andrea
2010-05-15
We develop the quantum theory of transverse angular momentum of light beams. The theory applies to paraxial and quasiparaxial photon beams in vacuum and reproduces the known results for classical beams when applied to coherent states of the field. Both the Poynting vector, alias the linear momentum, and the angular-momentum quantum operators of a light beam are calculated including contributions from first-order transverse derivatives. This permits a correct description of the energy flow in the beam and the natural emergence of both the spin and the angular momentum of the photons. We show that for collimated beams of light, orbital angular-momentum operators do not satisfy the standard commutation rules. Finally, we discuss the application of our theory to some concrete cases.
NASA Astrophysics Data System (ADS)
Langer, Maria; Kühn, Michael
2016-04-01
Shallow groundwater resources could be possibly affected by intruding brines, which are displaced along hydraulically conductive faults as result of subsurface activities like CO2 injection. To avoid salinization of potable freshwater aquifers an early detection of intruding saline water is necessary, especially in regions where an initial geogenic salinization already exists. Our study is based on work of Tillner et al. [1] and Langer et al. [2] who investigated the influence of permeable fault systems on brine displacement for the prospective storage site Beeskow-Birkholz in the Northeast German Basin. With a 3D regional scale model considering the deep groundwater system, they demonstrated that the existence of hydraulically conductive faults is not necessarily an exclusion criterion for potential injection sites, because salinization of shallower aquifers strongly depends on the effective damage zone volume, the initial salinity distribution and overlying reservoirs [2], while permeability of fault zones does not influence salinization of shallower aquifers significantly [1]. Here we extracted a 2D cross section regarding the upper 220 m of the study area mainly represented by shallow freshwater aquifers, but also considering an initial geogenic salinization [3]. We took flow rates of the intruding brines from the previous studies [2] and implemented species transport simulations with the program code SHEMAT [4]. Results are investigated and interpreted with the hydrochemical genesis model GEBAH [5] which has been already applied as early warning of saltwater intrusions into freshwater aquifers and surface water [6]. GEBAH allows a categorization of groundwater by the ion ratios of the dissolved components and offers a first indicative determination for an existence and the intensity of saline water intrusion in shallow groundwater aquifer, independent of the concentration of the solution. With our model we investigated the migration of saline water through a
Orbital angular momentum entanglement
NASA Astrophysics Data System (ADS)
Romero, Mary Jacquiline Romero
Entanglement in higher dimensions is an attractive concept that is a challenge to realise experimentally. To this end, the entanglement of the orbital angular momentum (OAM) of photons holds promise. The OAM state-space is discrete and theoretically unbounded. In the work that follows, we investigate various aspects of OAM entanglement. We show how the correlations in OAM and its conjugate variable, angular position, are determined by phase- matching and the shape of the pump beam in spontaneous parametric down- conversion. We implement tests of quantum mechanics which have been previously done for other variables. We show the Einstein-Podolsky-Rosen paradox for OAM and angle, supporting the incompatibility of quantum mechanics with locality and realism. We demonstrate violations of Bell-type inequalities, thereby discounting local hidden variables for describing the correlations we observe. We show the Hardy paradox using OAM, again highlighting the nonlocal nature of quantum mechanics. We demonstrate violations of Leggett-type inequalities, thereby discounting nonlocal hidden variables for describing correlations. Lastly, we have looked into the entanglement of topological vortex structures formed from a special superposition of OAM modes and show violations of Bell-type inequalities confined to a finite, isolated volume.
Accelerating momentum for change!
Wenzel, S; Panetta, J
1995-05-01
As we develop strategies to compete globally, we are challenged with integrating our resources to execute these strategies effectively. Many companies are in the midst of dramatic shifts in corporate cultures, giving more responsibility to employees while raising expectations for their performance. The extent of these changes is far reaching and brings significant challenges to both employees and corporations. This article is a continuation of the evolution (over five years) of a corrective action/continuous improvement process implemented at Exide Electronics. It discusses organizational structures, including steering committees, corrective action teams, task teams, and work cells. Specific expectations, goals, and results of the teams are presented, along with ground rules for functioning within the organization. After structuring the organization and coordinating the resources effectively, the next challenge is accelerating momentum for change. The presentation also discusses the evolutionary process required to make a culture focused on change, including ongoing communication and feedback, constant evaluation and direction of the process, and measuring and paying for performance.
Photons with Momentum Along Curved Paths
NASA Astrophysics Data System (ADS)
Davis, Basil S.
Electromagnetic energy flow is expressed mathematically by the Poynting Vector. Quantum theory determines that the Poynting Vector provides the direction of movement of the photons which are the quanta of the electromagnetic field. In this dissertation important phenomena featuring the flow of electromagnetic energy—and hence transport of photons—along curved paths are investigated. A circuit is considered in the shape of a ring, with a battery of negligible size and a wire of uniform resistance. A linear charge distribution in the wire generates an electrostatic field and a steady current through the circuit which maintains a constant magnetic field. Earlier studies of the Poynting vector and the rate of flow of energy considered only idealized geometries in which the Poynting vector was confined to the space within the circuit. But in more realistic cases the Poynting vector is nonzero outside as well as inside the circuit. An expression is obtained for the Poynting vector in terms of products of integrals, which are evaluated numerically to show the energy flow. Limiting expressions are obtained analytically. It is shown that the total power generated by the battery equals the energy flowing into the wire per unit time. Whereas the Poynting Vector flows along the direction of propagation of a plane wave photon, it is a different matter with photons described by Laguerre-Gaussian transverse profiles. Such "twisted" photon beams have a spiraling Poynting Vector that generates an orbital angular momentum that is distinct from the photon's spin angular momentum. The transverse confinement of the twisted photon beam gives rise to a Gouy phase shift, and the transverse structure of this phase shift is characterized by the Gouy radius. A new expression is obtained for this radius in terms of the parameters
MSWAVEF: Momentum-Space Wavefunctions
NASA Astrophysics Data System (ADS)
Barklem, Paul S.
2017-01-01
MSWAVEF calculates hydrogenic and non-hydrogenic momentum-space electronic wavefunctions. Such wavefunctions are often required to calculate various collision processes, such as excitation and line broadening cross sections. The hydrogenic functions are calculated using the standard analytical expressions. The non-hydrogenic functions are calculated within quantum defect theory according to the method of Hoang Binh and van Regemorter (1997). Required Hankel transforms have been determined analytically for angular momentum quantum numbers ranging from zero to 13 using Mathematica. Calculations for higher angular momentum quantum numbers are possible, but slow (since calculated numerically). The code is written in IDL.
Integral momentum balance on a growing bubble
NASA Astrophysics Data System (ADS)
Siedel, S.; Cioulachtjian, S.; Robinson, A. J.; Bonjour, J.
2013-12-01
The integral momentum balance on a growing boiling bubble is investigated. All forces acting on the bubble are detailed, and the methods and assumptions used to calculate their integral resultants are discussed. The momentum balance computation is then performed using experimental data of bubbles growing on an artificial nucleation site in a controlled environment. The relative magnitude of each force component is compared, showing negligible dynamic forces, upwards forces composed mainly of the buoyancy and contact pressure components, and downwards forces being exclusively due to surface tension and adhesion. The difficulty encountered in measuring the apparent contact angle due to mirage effects has been highlighted; a new method, fitting numerically simulated bubble profile to the contour measurements has been proposed and used to correct the effects of refraction on the bubble profile determination. As all forces acting on the bubble were measured, it was possible to estimate the residuals of the momentum balance. Their small value validated both the expressions used for the forces and the methodology to evaluate their value.
2013-04-25
psi). (g) Maximum axle load (pneumatic tires) - 2,268 kg (5,000 lb). (h) Maximum wheel load (pneumatic tires) - 1,134 kg (2,500 lb). (i...survivability following the shock or vibration environment induced. Vehicles not typically transported with payload such as wreckers, truck tractors ...combination weight rating (GCWR) means the value specified by the manufacturer as the loaded weight of the combination vehicle. (d) Gross axle weight
Binary Solid Propellants for Constant Momentum Missions
Pakhomov, Andrew V.; Mahaffy, Kevin E.
2008-04-28
A constant momentum mission is achieved when the speed of the vehicle in the inertial frame of reference is equal to the speed of exhaust relative to the vehicle. Due to 100% propulsive efficiency such missions are superior to traditional constant specific impulse missions. A new class of solid binary propellants for constant momentum missions is under development. A typical propellant column is prepared as a solid solution of two components, with composition gradually changing from 100% of a propellant of high coupling coefficient (C{sub m}) to one which has high specific impulse (I{sub sp}). The high coupling component is ablated first, gradually giving way to the high I{sub sp} component, as the vehicle accelerates. This study opens new opportunities for further design of complex propellants for laser propulsion, providing variable C{sub m} and I{sub sp} during missions.